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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
881

Variable selection and neural networks for high-dimensional data analysis: application in infrared spectroscopy and chemometrics

Benoudjit, Nabil 24 November 2003 (has links)
This thesis focuses particularly on the application of chemometrics in the field of analytical chemistry. Chemometrics (or multivariate analysis) consists in finding a relationship between two groups of variables, often called dependent and independent variables. In infrared spectroscopy for instance, chemometrics consists in the prediction of a quantitative variable (the obtention of which is delicate, requiring a chemical analysis and a qualified operator), such as the concentration of a component present in the studied product from spectral data measured on various wavelengths or wavenumbers (several hundreds, even several thousands). In this research we propose a methodology in the field of chemometrics to handle the chemical data (spectrophotometric data) which are often in high dimension. To handle these data, we first propose a new incremental method (step-by-step) for the selection of spectral data using linear and non-linear regression based on the combination of three principles: linear or non-linear regression, incremental procedure for the variable selection, and use of a validation set. This procedure allows on one hand to benefit from the advantages of non-linear methods to predict chemical data (there is often a non-linear relationship between dependent and independent variables), and on the other hand to avoid the overfitting phenomenon, one of the most crucial problems encountered with non-linear models. Secondly, we propose to improve the previous method by a judicious choice of the first selected variable, which has a very important influence on the final performances of the prediction. The idea is to use a measure of the mutual information between the independent and dependent variables to select the first one; then the previous incremental method (step-by-step) is used to select the next variables. The variable selected by mutual information can have a good interpretation from the spectrochemical point of view, and does not depend on the data distribution in the training and validation sets. On the contrary, the traditional chemometric linear methods such as PCR or PLSR produce new variables which do not have any interpretation from the spectrochemical point of view. Four real-life datasets (wine, orange juice, milk powder and apples) are presented in order to show the efficiency and advantages of both proposed procedures compared to the traditional chemometric linear methods often used, such as MLR, PCR and PLSR.
882

Judgements of cross-sex infidelity responses as a component of mating intelligence /

Johnson, John D. January 2007 (has links)
Thesis (M.A.)--State University of New York at New Paltz, 2007. / Also issued in electronic version. Includes bibliographical references (leaves 29-31). Online version available via the SUNY New Paltz Sojourner Truth Library : http://hdl.handle.net/1951/39633
883

Contribution théorique à l'étude des motivations multiples/Theoretical contribution to the study of multiple motivations

Anselme, Patrick 18 October 2007 (has links)
Behaviour is usually assumed to depend on the reach of a critical intensitytermed reactivity thresholdby its motivation. This view represents a simple, predictive theoretical framework in ethology and psychology. However, it is here argued that only the influence of an isolated motivation on behaviour can be explained that way; that such a view fails to account for behaviour when several motivations are jointly activated. Upon analysis, the 'classical' theory of behaviour proves to be under-specified and thus leads to three conceptual problems that make it logically inconsistent for the study of multiple motivations. A revision of the 'classical' théory, called Anticipatory Dynamics Model (ADM), is then developed in order to bring a theoretical solution to these conceptual problems. The ADM hypothesizes that an organisms motivational interactions are due to the limitation of the organisms attentional resources. Several experiments are designed to test major predictions of the ADM. Tout comportement est censé dépendre du fait que sa motivation atteint une valeur critique d'intensité appelée seuil de réactivité. Cette approche constitue un cadre théorique simple et prédictif aussi bien en éthologie qu'en psychologie. Cependant, je tente de montrer que seule l'influence d'une motivation isolée sur le comportement peut être expliquée de cette façon ; que cette approche cesse d'être applicable lorsque plusieurs motivations sont activées simultanément. Après analyse, cette théorie 'classique' s'avère sous-spécifiée et conduit à trois problèmes conceptuels qui la rendent logiquement inconsistante pour l'étude des motivations multiples. Une révision de cette théorie 'classique', appelée Modèle de Dynamique Anticipatoire (MDA), est ainsi développée en vue d'apporter une solution théorique à ces problèmes conceptuels. Le MDA fait l'hypothèse que les interactions motivationnelles d'un organisme sont causées par la limitation de ses ressources attentionnelles. Plusieurs expériences ont été imaginées pour tester des prédictions importantes du MDA.
884

Partnerval i joint ventures på den svenska 3G-marknaden En studie av de svenska nätoperatörerna

Danielsson, Teodor, Edgren, Erik January 2002 (has links)
Background: Traditionally defined boundaries and borders between organizations are at present being re-evaluated because of new and tougher demands. Today we can see a trend where these boundaries are being lowered or even eliminated when organizations choose to co-operate instead of compete. Purpose: In order to create an understanding for the partner selection process in the newly founded joint ventures between the companies which are building the Swedish 3G Network, the determining factors are being studied. Delimitation: The studies companies are co-operating as network operators but are at the same time competing as mobile operators. This relationship is in the literature described as co-opetition, which will not be investigated in this paper. Realization: Taking our starting point in Geringer’s task- and partner-related approach, a simple model has been created for the task. Empirical data have been collected through interviews, and have been analyzed with this model. Results: Essentially the same factors have been found determining for the companies which have committed themselves for co-operation. These factors do however tend to differ partly between the two joint ventures that have been founded. In the Europolitan Vodafone” Hi3G joint venture, compatibility between top management and culture&structure seem to be the motivating factors. From a Telia - Tele2-perspective, the mutual factors seem to be financing and compatibility between top management. An important criterion has in both joint venture constellations to the access to existing real capital and infrastructure as well as having existing customers.
885

Regressor and Structure Selection : Uses of ANOVA in System Identification

Lind, Ingela January 2006 (has links)
Identification of nonlinear dynamical models of a black box nature involves both structure decisions (i.e., which regressors to use and the selection of a regressor function), and the estimation of the parameters involved. The typical approach in system identification is often a mix of all these steps, which for example means that the selection of regressors is based on the fits that is achieved for different choices. Alternatively one could then interpret the regressor selection as based on hypothesis tests (F-tests) at a certain confidence level that depends on the data. It would in many cases be desirable to decide which regressors to use, independently of the other steps. A survey of regressor selection methods used for linear regression and nonlinear identification problems is given. In this thesis we investigate what the well known method of analysis of variance (ANOVA) can offer for this problem. System identification applications violate many of the ideal conditions for which ANOVA was designed and we study how the method performs under such non-ideal conditions. It turns out that ANOVA gives better and more homogeneous results compared to several other regressor selection methods. Some practical aspects are discussed, especially how to categorise the data set for the use of ANOVA, and whether to balance the data set used for structure identification or not. An ANOVA-based method, Test of Interactions using Layout for Intermixed ANOVA (TILIA), for regressor selection in typical system identification problems with many candidate regressors is developed and tested with good performance on a variety of simulated and measured data sets. Typical system identification applications of ANOVA, such as guiding the choice of linear terms in the regression vector and the choice of regime variables in local linear models, are investigated. It is also shown that the ANOVA problem can be recast as an optimisation problem. Two modified, convex versions of the ANOVA optimisation problem are then proposed, and it turns out that they are closely related to the nn-garrote and wavelet shrinkage methods, respectively. In the case of balanced data, it is also shown that the methods have a nice orthogonality property in the sense that different groups of parameters can be computed independently.
886

Postmating Sexual Selection and its Role in Population Divergence in Beetles

Fricke, Claudia January 2006 (has links)
Speciation is the process describing the formation of new species and is at the heart of evolutionary biology. According to the biological species concept only reproductively isolated forms are regarded good species. This thesis aims at identifying evolutionary processes that cause population divergence and, ultimately, speciation. Natural and sexual selection are two major candidates driving changes in traits that could render populations reproductively incompatible. In recent years, biologists have recognized that most animal species are polygamous. Therefore, sexual selection does not end at mating but continues to include interactions between individuals after mating has occurred but before zygote formation. Male-male sperm competition and cryptic female choice are two main forms of postmating sexual selection shaping reproductive traits like behaviour. The studies presented in this thesis focus on laboratory experiments attempting to identify the role of postmating sexual selection in causing reproductive divergence across populations in beetles. The majority of studies were performed using a Bruchid beetle, Callosobruchus maculatus, a common, worldwide pest on stored leguminose seeds. I used two major methodological approaches. One approach seeks to identify the traces left by past selection among extant conspecific populations, by assessing the pattern of female reproductive responses to mating with males of decreasing relatedness. Second, I used a selection experiment to disentangle the joint effect of natural and sexual selection acting simultaneously on diverging replicated selection lines. In general, these experiments revealed that postmating sexual selection can be a powerful engine of incipient divergence between allopatric populations. Changes in traits underlying variables such as female reproductive output, female mating rate or male success in sperm competition evolved rapidly and could in some cases effectively reduce gene flow between conspecific populations. While postmating sexual selection per se can drive divergence, I found that interactions with natural selection can limit divergence in reproductive characters. Sexual selection tended to reinforce natural selection under strong directional selection. In contrast, sexual selection inflicted a reproductive load on populations under weak natural selection. Thus, the joint effects of natural and sexual selection on allopatric populations are non-trivial and should be considered in greater detail in future studies of early divergence.
887

The Genetic Limits to Trait Evolution for a Suite of Sexually Selected Male Cuticular Hydrocarbons in Drosophila Serrata

Sztepanacz, Jacqueline L.P. 14 November 2011 (has links)
Directional selection is prevalent in nature yet phenotypes tend to remain relatively constant, suggesting a limit to trait evolution. The genetic basis of evolutionary limits in unmanipulated populations, however, is generally not known. Given widespread pleiotropy, opposing selection on a focal trait may arise from the effects of the underlying alleles on other fitness components, generating net stabilizing selection on trait genetic variance and thus limiting evolution. Here, I look for the signature of stabilizing selection for a suite of cuticular hydrocarbons (CHCs) in Drosophila serrata. Despite strong directional sexual selection on CHCs, genetic variance differed between high and low fitness individuals and was greater among the low fitness males for seven of eight CHCs. Univariate tests of a difference in genetic variance were non-significant but have low power. My results implicate stabilizing selection, arising through pleiotropy, in generating a genetic limit to the evolution of CHCs in this species.
888

The Genetic Limits to Trait Evolution for a Suite of Sexually Selected Male Cuticular Hydrocarbons in Drosophila Serrata

Sztepanacz, Jacqueline L.P. 14 November 2011 (has links)
Directional selection is prevalent in nature yet phenotypes tend to remain relatively constant, suggesting a limit to trait evolution. The genetic basis of evolutionary limits in unmanipulated populations, however, is generally not known. Given widespread pleiotropy, opposing selection on a focal trait may arise from the effects of the underlying alleles on other fitness components, generating net stabilizing selection on trait genetic variance and thus limiting evolution. Here, I look for the signature of stabilizing selection for a suite of cuticular hydrocarbons (CHCs) in Drosophila serrata. Despite strong directional sexual selection on CHCs, genetic variance differed between high and low fitness individuals and was greater among the low fitness males for seven of eight CHCs. Univariate tests of a difference in genetic variance were non-significant but have low power. My results implicate stabilizing selection, arising through pleiotropy, in generating a genetic limit to the evolution of CHCs in this species.
889

Internetbaserad rekrytering: mål, möjligheter och praktiker : En fallstudie av urvalet vid rekryteringen av sommarvikarier i Luleå kommun

Chertova, Evgeniya January 2012 (has links)
The purpose of this study is to examine web-based recruitment to short term summer jobs at the SocialServices Department in Luleå municipality in Sweden. Recruitment goals, selection options on therecruitment homepage Offentliga Jobb and recruitment practices were analysed in order to reach a deeperunderstanding of the interactions between these three levels in the selection process. Pre-selection throughOffentliga Jobb was a special concern of the study. Different consciousness levels in the selection process areemphasised according to Anthony Giddens' structuration theory. Ten recruiters from different parts of thedepartment were interviewed. Due to the qualitative nature of the study the conclusions concern only theactual respondents and can not be generalised to the whole population of recruiters. Selection options andselection practices at the Social Services Department were found to mostly correspond with the municipalityguidelines for recruitment as well as with policy documents such as shared values. There are however someconcerns about the Offentliga Jobb homepage not being user friendly. There is room for improvement insome rooted selection practices such as using age to measure social skills of the applicants and applying aslightly different skill-set profile to applicants with perceived international background. The importance ofmaking a universal skill-set profile for all applicants and of reflexions on the selection criteria at discursivelevel of consciousness is emphasised.
890

Strategy for Project Portfolio Selection in Private Corporations in Vietnam

Le, Cao Minh, Nguyen, Van Tau January 2008 (has links)
Selection of right sets of projects is considerably critical for organizations to successfully achieve their competitive advantages and corporate strategies. Due to limited resources and dynamic changes in business environment, this kind of selection is quite challenging for organizations. Beside one hundred selection tools and techniques, academics and practitioners have studied and recommended complex selection frameworks to facilitate the selection of right projects. However, these theoretical frameworks are not applied by private corporations in Vietnam. Therefore, this dissertation is intended to better understand the academic and practical literature about project portfolio selection; study current practices of project selection that private corporations in Vietnam are using; and propose a framework that is beneficially adaptable to these private corporations. A multiple-case study strategy accessing qualitative data through observations and semi-structure interviews is designed to investigate how private corporations select their project portfolio under the current contexts of booming economy in Vietnam to ensure successful realization of their growth and development strategy. The recommendations resulted from literature review and investigations do not only support the investigated corporations to improve the quantity and quality of their investment project portfolio(s) but also facilitate possible adaptation to project portfolio selection by other private corporations.

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