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81.
We consider the k most vital edges (nodes) and min edge (node) blocker versions of the p-median and p-center location problems. Given a weighted connected graph with distances on edges and weights on nodes, the k most vital edges (nodes) p-median (respectively p-center) problem consists of finding a subset of k edges (nodes) whose removal from the graph leads to an optimal solution for the p-median (respectively p-center) problem with the largest total weighted distance (respectively maximum weighted distance). The complementary problem, min edge (node) blocker p-median (respectively p-center), consists of removing a subset of edges (nodes) of minimum cardinality such that an optimal solution for the p-median (respectively p-center) problem has a total weighted distance (respectively a maximum weighted distance) at least as large as a specified threshold. We show that k most vital edges p-median and k most vital edges p-center are NP-hard to approximate within a factor $\frac{7}{5}-\epsilon$ and $\frac{4}{3}-\epsilon$ respectively, for any ?>0, while k most vital nodes p-median and k most vital nodes p-center are NP-hard to approximate within a factor $\frac{3}{2}-\epsilon$ , for any ?>0. We also show that the complementary versions of these four problems are NP-hard to approximate within a factor 1.36.  相似文献   
82.
We propose a Bayesian nonparametric procedure for density estimation, for data in a closed, bounded interval, say [0,1]. To this aim, we use a prior based on Bemstein polynomials. This corresponds to expressing the density of the data as a mixture of given beta densities, with random weights and a random number of components. The density estimate is then obtained as the corresponding predictive density function. Comparison with classical and Bayesian kernel estimates is provided. The proposed procedure is illustrated in an example; an MCMC algorithm for approximating the estimate is also discussed.  相似文献   
83.
Consistency of Bernstein polynomial posteriors   总被引:1,自引:0,他引:1  
A Bernstein prior is a probability measure on the space of all the distribution functions on [0, 1]. Under very general assumptions, it selects absolutely continuous distribution functions, whose densities are mixtures of known beta densities. The Bernstein prior is of interest in Bayesian nonparametric inference with continuous data. We study the consistency of the posterior from a Bernstein prior. We first show that, under mild assumptions, the posterior is weakly consistent for any distribution function P 0 on [0, 1] with continuous and bounded Lebesgue density. With slightly stronger assumptions on the prior, the posterior is also Hellinger consistent. This implies that the predictive density from a Bernstein prior, which is a Bayesian density estimate, converges in the Hellinger sense to the true density (assuming that it is continuous and bounded). We also study a sieve maximum likelihood version of the density estimator and show that it is also Hellinger consistent under weak assumptions. When the order of the Bernstein polynomial, i.e. the number of components in the beta distribution mixture, is truncated, we show that under mild restrictions the posterior concentrates on the set of pseudotrue densities. Finally, we study the behaviour of the predictive density numerically and we also study a hybrid Bayes–maximum likelihood density estimator.  相似文献   
84.
85.
The topic of immigration is attracting more and more attention also from the methodological point of view due to elusiveness and anonymity difficulties. Some results on a suitable sampling technique (Blangiardo 1996) and on the problem of estimating the mean of a quantitative characteristic of interest (Statistica LXIII 3:537–560, 2003) are almost consolidated nowadays. Yet the estimate of a parameter referring to a small sub-population is still open. In such a context the presence of rare domains calls for an eligible composite estimator. The present paper proposes some point and region composite estimates for the proportion and makes a comparison between them via a simulative study based on real data.  相似文献   
86.
Focusing on new women immigrants/migrants from Korea to Japan in recent years, this article explores the form of transmigratory practice of U‐turnees, who have past experiences of having lived in Japan or been born there prior to the end of Japan's colonial rule in 1945 and returned to Japan around the year 1989 when the South Korean government lifted the restriction of overseas travel for its citizens. I suggest through mini life histories of five women that their lives can best be understood in terms of ongoing engagement with more than one nation‐state as home. On this basis, I argue that what might look like a chaotic swirl of new immigrants/migrants is in fact not based on the discovery of a brave new world, but firmly based on family history and configurated by state‐to‐state relations.  相似文献   
87.
Statistical Methods & Applications - On 4th March 2018, elections took place in Italy for the two Chambers of the Parliament. Many newspapers emphasized the victory of the 5 Star Movement (5SM)...  相似文献   
88.
Objectives. This study explores the efficacy of visual appeals that may be used to communicate environmental risk.Methods. To better understand the social and cognitive barriers present in environmental risk communication associated with climate change, we conducted a series of six focus groups. Groups were asked to view images of environmental issues and select the best representation of their feelings out of a range of preselected emotions. While further research is required, preliminary investigation based on the focus groups suggests several themes. Results. First, an individual's familiarity with both an area and an event will decrease the individual's perception of urgency; conversely, the participants expressed greater concern for events that were local and new—in other words, familiarity diminishes urgency, while emergent problems create alacrity. Second, participants expressed a sentiment of tacit blame, in which the participant's own contribution to the issue received less emphasis when ascribing fault. Last, the participants reacted positively toward messages that emphasized a hopeful and solution-based narrative and were seemingly less motivated by images that relied on fear-based messaging. Conclusions. Preliminary findings suggest that hopeful, solution-based messaging may be more effective in facilitating pro-environmental behavior than either fear- or guilt-based appeals.  相似文献   
89.
The Metropolis–Hastings algorithm is one of the most basic and well-studied Markov chain Monte Carlo methods. It generates a Markov chain which has as limit distribution the target distribution by simulating observations from a different proposal distribution. A proposed value is accepted with some particular probability otherwise the previous value is repeated. As a consequence, the accepted values are repeated a positive number of times and thus any resulting ergodic mean is, in fact, a weighted average. It turns out that this weighted average is an importance sampling-type estimator with random weights. By the standard theory of importance sampling, replacement of these random weights by their (conditional) expectations leads to more efficient estimators. In this paper we study the estimator arising by replacing the random weights with certain estimators of their conditional expectations. We illustrate by simulations that it is often more efficient than the original estimator while in the case of the independence Metropolis–Hastings and for distributions with finite support we formally prove that it is even better than the “optimal” importance sampling estimator.  相似文献   
90.
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