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641.
Paul Fogel Douglas M. Hawkins Chris Beecher George Luta S. Stanley Young 《The American statistician》2013,67(4):207-218
In statistical practice, rectangular tables of numeric data are commonplace, and are often analyzed using dimension-reduction methods like the singular value decomposition and its close cousin, principal component analysis (PCA). This analysis produces score and loading matrices representing the rows and the columns of the original table and these matrices may be used for both prediction purposes and to gain structural understanding of the data. In some tables, the data entries are necessarily nonnegative (apart, perhaps, from some small random noise), and so the matrix factors meant to represent them should arguably also contain only nonnegative elements. This thinking, and the desire for parsimony, underlies such techniques as rotating factors in a search for “simple structure.” These attempts to transform score or loading matrices of mixed sign into nonnegative, parsimonious forms are, however, indirect and at best imperfect. The recent development of nonnegative matrix factorization, or NMF, is an attractive alternative. Rather than attempt to transform a loading or score matrix of mixed signs into one with only nonnegative elements, it directly seeks matrix factors containing only nonnegative elements. The resulting factorization often leads to substantial improvements in interpretability of the factors. We illustrate this potential by synthetic examples and a real dataset. The question of exactly when NMF is effective is not fully resolved, but some indicators of its domain of success are given. It is pointed out that the NMF factors can be used in much the same way as those coming from PCA for such tasks as ordination, clustering, and prediction. Supplementary materials for this article are available online. 相似文献
642.
This article proposes an adaptive sequential preventive maintenance (PM) policy for which an improvement factor is newly introduced to measure the PM effect at each PM. For this model, the PM actions are conducted at different time intervals so that an adaptive method needs to be utilized to determine the optimal PM times minimizing the expected cost rate per unit time. At each PM, the hazard rate is reduced by an amount affected by the improvement factor which depends on the number of PM's preceding the current one. We derive mathematical formulas to evaluate the expected cost rate per unit time by incorporating the PM cost, repair cost, and replacement cost. Assuming that the failure times follow a Weibull distribution, we propose an optimal sequential PM policy by minimizing the expected cost rate. Furthermore, we consider Bayesian aspects for the sequential PM policy to discuss its optimality. The effect of some parameters and the functional forms of improvement factor on the optimal PM policy is measured numerically by sensibility analysis and some numerical examples are presented for illustrative purposes. 相似文献
643.
Ji Young Kim 《统计学通讯:理论与方法》2013,42(7):1411-1425
Lasso has been widely used for variable selection because of its sparsity, and a number of its extensions have been developed. In this article, we propose a robust variant of Lasso for the time-course multivariate response, and develop an algorithm which transforms the optimization into a sequence of ridge regressions. The proposed method enables us to effectively handle multivariate responses and employs a basis representation of the regression parameters to reduce the dimensionality. We assess the proposed method through simulation and apply it to the microarray data. 相似文献
644.
This paper examines the robustness of the multivariate version of Grubs' (1950) procedure for detecting an outlier in a sample of n independent observations against equicorrelation of the observations. It is shown that the robustness of the univariate test to equicorrelation extends to the multivariate test in that the distribution of the maximum squared radii-test for a multivariate oulier in identical for both the independent and siaply equicorrelated data models. 相似文献
645.
Journal of Population Research - As this brief discussion suggests, census statistics are useful as an indicator of some socio-economic characteristics of the Aboriginal population, particularly... 相似文献
646.
Theory and Society - 相似文献
647.
Refractory ceramic fibre products are used extensively as high temperature furnace linings, because of their properties of a lower thermal conductivity, improved resistance to thermal shock, cheaper installation and maintenance costs, and reduced wall thickness when compared with traditional firebrick linings. Vacuum forming of the ceramic fibre enables modular linings for small laboratory furnaces to be produced efficiently and cost effectively. This process involves drawing a slurry of ceramic fibre, binder and water through a porous mould, and subsequently oven drying the finished product. The product mass, which is strongly related to its relevant thermal and structural properties, was identified as a suitable response variable. A resolution IV fractional 2n factorial design was employed to investigate the effects of 15 key process factors on the product mass in just 32 experimental runs. Analysis of the results revealed that only two of the 15 process factors investigated in the experiment significantly affected the mean product mass, while none of these factors significantly affected the variability of the product mass. The experimental design is described, and its results and their implications are presented and discussed. 相似文献
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650.
Internal migration from the Peruvian highlands and rural areas has burdened urban areas with rapid growth. Urban expansion
is threatening the desert habitat and unique vegetation communities surrounding Arequipa, one of Peru's largest cities. A
511 ha tract contiguous to the city of Arequipa has been informally designated an ecological park. Analysis of Landsat satellite
imagery over a 16-year interval indicates that urban expansion is occurring in the direction of the park. The land use/land
cover change analysis revealed other landscape patterns and processes, such as agricultural expansion, which are relevant
to the study area. These dynamics, plus principles of landscape ecology, suggest that the park's size and shape may not be
the most suitable. Conservation alternatives include the expansion of the park, the spatial connection to another nature reserve,
or the design of co-management strategies. Given local historical events and the paucity of regional conservation efforts,
social actors in Arequipa and in national governmental institutions will need to find practical ways to collaborate. 相似文献