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21.
This paper presents a conditional mixture, maximum likelihood methodology for performing clusterwise linear regression. This new methodology simultaneously estimates separate regression functions and membership inK clusters or groups. A review of related procedures is discussed with an associated critique. The conditional mixture, maximum likelihood methodology is introduced together with the E-M algorithm utilized for parameter estimation. A Monte Carlo analysis is performed via a fractional factorial design to examine the performance of the procedure. Next, a marketing application is presented concerning the evaluations of trade show performance by senior marketing executives. Finally, other potential applications and directions for future research are identified. 相似文献
22.
23.
The use of museum specimens to reconstruct the genetic variability and relationships of extinct populations 总被引:3,自引:0,他引:3
M. S. Roy D. J. Girman A. C. Taylor R. K. Wayne 《Cellular and molecular life sciences : CMLS》1994,50(6):551-557
In this review, we discuss the use of DNA from museum specimens to address conservation genetic questions. We provide four examples from our previous studies of the northern hairy-nosed wombat, African wild dog, Ethiopian wolf and red wolf. These species were genetically surveyed using two molecular approaches: first, analysis of short sequences in the mitochondrial genome using species-specific primers, and second, analysis of hypervariable microsatellite loci. The studies demonstrate that museum-derived DNA adds an important dimension to the genetic study of extant populations. Inaccessible populations can be studied, and both the loss of genetic variation and its distribution over space and time can be better understood. Finally, analysis of additional museum material provides definitive evidence for a hybrid origin of the red wolf. 相似文献
24.
Least squares algorithms for constructing constrained ultrametric and additive tree representations of symmetric proximity data 总被引:1,自引:1,他引:0
A mathematical programming algorithm is developed for fitting ultrametric or additive trees to proximity data where external constraints are imposed on the topology of the tree. The two procedures minimize a least squares loss function. The method is illustrated on both synthetic and real data. A constrained ultrametric tree analysis was performed on similarities between 32 subjects based on preferences for ten odors, while a constrained additive tree analysis was carried out on some proximity data between kinship terms. Finally, some extensions of the methodology to other tree fitting procedures are mentioned.The first author is supported as Bevoegdverklaard Navorser of the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek. 相似文献
25.
Wayne C. Myrvold 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2011,42(4):237-243
One finds, in Maxwell's writings on thermodynamics and statistical physics, a conception of the nature of these subjects that differs in interesting ways from the way they are usually conceived. In particular, though—in agreement with the currently accepted view—Maxwell maintains that the second law of thermodynamics, as originally conceived, cannot be strictly true, the replacement he proposes is different from the version accepted by most physicists today. The modification of the second law accepted by most physicists is a probabilistic one: although statistical fluctuations will result in occasional spontaneous differences in temperature or pressure, there is no way to predictably and reliably harness these to produce large violations of the original version of the second law. Maxwell advocates a version of the second law that is strictly weaker; the validity of even this probabilistic version is of limited scope, limited to situations in which we are dealing with large numbers of molecules en masse and have no ability to manipulate individual molecules. Connected with this is his conception of the thermodynamic concepts of heat, work, and entropy; on the Maxwellian view, these are concept that must be relativized to the means we have available for gathering information about and manipulating physical systems. The Maxwellian view is one that deserves serious consideration in discussions of the foundation of statistical mechanics. It has relevance for the project of recovering thermodynamics from statistical mechanics because, in such a project, it matters which version of the second law we are trying to recover. 相似文献
26.
Seven fish species were found in the Bitter Creek drainage of southwest Wyoming, but only speckled dace ( Rhinichthys osculus ), flannelmouth sucker ( Catostomus latipinnis ), and mountain sucker ( Catostomus platyrhynchus ) were indigenous. No relationships were found between fish standing stocks and habitat features, but species richness was related to elevation and stream width. No fish were found above an elevation of 2192 m. Only the most downstream study read had more than three species present. Two indigenous species, speckled dace and mountain sucker, and a nonnative species, fathead minnow ( Pimephales promelas ), were predominant fishes in the drainage. These three species withstand intermittent stream flows that are common in the drainage. 相似文献
27.
The charaeteristics of kokanee ( Oncorhynchus nerka ) spawning stocks in the Green River and Sheep Creek (tributaries to Flaming Gorge Reservoir) are described as observed in fall 1985 and spring 1986; the time of spawning; length, age, and sex structure of the stocks; fecundity and egg retention; density of eggs in redds; and the timing of downstream drift of emerging fry. The time of spawning, length-frequency distributions of spawning fish, and egg density in redds differed between the two stocks, but other differences were not observed. 相似文献
28.
Parthenogenesis, the production of offspring without fertilization by a male, is rare in vertebrate species, which usually reproduce after fusion of male and female gametes. Here we use genetic fingerprinting to identify parthenogenetic offspring produced by two female Komodo dragons (Varanus komodoensis) that had been kept at separate institutions and isolated from males; one of these females subsequently produced additional offspring sexually. This reproductive plasticity indicates that female Komodo dragons may switch between asexual and sexual reproduction, depending on the availability of a mate--a finding that has implications for the breeding of this threatened species in captivity. Most zoos keep only females, with males being moved between zoos for mating, but perhaps they should be kept together to avoid triggering parthenogenesis and thereby decreasing genetic diversity. 相似文献
29.
This paper develops a new procedure for simultaneously performing multidimensional scaling and cluster analysis on two-way
compositional data of proportions. The objective of the proposed procedure is to delineate patterns of variability in compositions
across subjects by simultaneously clustering subjects into latent classes or groups and estimating a joint space of stimulus
coordinates and class-specific vectors in a multidimensional space. We use a conditional mixture, maximum likelihood framework
with an E-M algorithm for parameter estimation. The proposed procedure is illustrated using a compositional data set reflecting
proportions of viewing time across television networks for an area sample of households. 相似文献
30.