ABSTRACT ROBUSTNESS OF TWO FORMULAS TO CORRECT PEARSON CORRELATION FOR RESTRICTION OF RANGE by Dung Minh Tran Many research studies involving Pearson correlations are conducted in settings where one of the two variables has a restricted range in the sample. For example, this situation occurs when tests are used for selecting candidates for employment or university admission. Often after selection, there is interest in correlating the selection variable, which has a restricted range, to a criterion variable. The focus of this research was to compare Alexander, Alliger, and Hanges’s (1984) formula to Thorndike’s (1947) formula and population values using Monte Carlo simulation when the assumption of normal distribution is violated in a particular way. In both Thorndike’s and Alexander et al.’s correction formulas, values for the variances in the restricted and the unrestricted situations are required. For both formulas, the variance in restricted situations was a sample estimate. In the Monte Carlo simulation, the difference between the two approaches was that in Thorndike’s formula, the variance in the unrestricted situation was the population variance from the exogenous variable, whereas in Alexander et al.’s approach, the population variance was estimated based on the sample variance in the restricted situation. In the simulation, robustness situations were created from non-normal distributions for predicted group membership in a classification problem. As expected, Thorndike’s corrected correlation values were more accurate than Alexander et al.’s corrected correlation values, and Thorndike’s formula had a smaller standard error of estimates. Absolute values of the mean differences between the estimated and population correlations for Alexander et al.’s approach compared to Thorndike’s approach in robustness situations ranged from 1.37 to 2.15 larger. Nevertheless, Alexander et al.’s approach, which is based only on estimated variances, appears to be a worthwhile correction in most of the simulated situations with a few notable exceptions for non-normal distributions.

Thesis (M.S.)--Miami University, Dept. of Physics, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], v, 296 p. : ill. Includes bibliographical references (p. 393-396).

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Made available in DSpace on 2014-10-09T12:33:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / O presente trabalho realiza a investigação dos parâmetros hiperfinos, incluindo a sua natureza dinâmica, em compostos ligantes em solução a temperatura ambiente (295 K) e resfriada (77K) através da espectroscopia de Correlação Angular γγ Perturbada (CAP). Para a realização das medidas experimentais, utilizou-se núcleos de prova radioativos de 111In111Cd, 181Hf181Ta e 111mCd111Cd, que decaem através de cascata gama. As amostras foram preparadas diluindo-se soluções com os núcleos radioativos em água, quando se investigou a interação do núcleo de prova com o ligante água; adicionando-se soluções com os núcleos radioativos em solução tampão, quando se investigou a interação do núcleo de prova com os íons ligantes provenientes do próprio tampão (CO32- e HCO31-) e com o OH1-; e adicionando-se soluções com os núcleos radioativos em soluções do ligante ácido etilenodiaminotetracético (EDTA), este em pH entre 4,0 e 5,0, (que corresponde ao pH da própria solução saturada do EDTA) e em solução tampão de pH entre 9 e 10. Assim foi possível investigar os efeitos gerados por cada um desses métodos de preparação de amostras nas medidas CAP. Finalmente foi feita uma análise comparativa para os vários métodos de inserção dos núcleos de prova na amostra, considerando-se aspectos químicos e nucleares. A inexistência de medidas para esse tipo de amostra, justifica a importância dos resultados obtidos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

This study dealt with shrinkage in multiple correlation coefficients computed for sample data when these coefficients are compared to the multiple correlation coefficients for populations and the effect of the ratio of utilized predictors to original predictors on the shrinkage in R square. The study sought to provide the rationale for selection of the shrinkage formula when the correlations between the predictors and the criterion are known and determine which of the three shrinkage formulas (Browne, Darlington, or Wherry) will yield the R square from sample data that is closest to the R square for the population data.

Dans les systèmes d'informations, les outils de détection produisent en continu un grand nombre d'alertes.Des outils de corrélation permettent de réduire le nombre d'alertes et de synthétiser au sein de méta-alertes les informations importantes pour les administrateurs.Cependant, la complexité des règles de corrélation rend difficile leur écriture et leur maintenance.Cette thèse propose par conséquent une méthode pour générer des règles de corrélation de manière semi-automatique à partir d’un scénario d’attaque exprimé dans un langage de niveau d'abstraction élevé.La méthode repose sur la construction et l'utilisation d’une base de connaissances contenant une modélisation des éléments essentiels du système d’information (par exemple les nœuds et le déploiement des outils de détection). Le procédé de génération des règles de corrélation est composé de différentes étapes qui permettent de transformer progressivement un arbre d'attaque en règles de corrélation.Nous avons évalué ce travail en deux temps. D'une part, nous avons déroulé la méthode dans le cadre d'un cas d'utilisation mettant en jeu un réseau représentatif d'un système d'une petite entreprise.D'autre part, nous avons mesuré l'influence de fautes touchant la base de connaissances sur les règles de corrélation générées et sur la qualité de la détection. / Information systems produce continuously a large amount of messages and alerts. In order to manage this amount of data, correlation system are introduced to reduce the alerts number and produce high-level meta-alerts with relevant information for the administrators. However, it is usually difficult to write complete and correct correlation rules and to maintain them. This thesis describes a method to create correlation rules from an attack scenario specified in a high-level language. This method relies on a specific knowledge base that includes relevant information on the system such as nodes or the deployment of sensor. This process is composed of different steps that iteratively transform an attack tree into a correlation rule. The assessment of this work is divided in two aspects. First, we apply the method int the context of a use-case involving a small business system. The second aspect covers the influence of a faulty knowledge base on the generated rules and on the detection.

The demand for smaller but more powerful electronic components is ever increasing. This demand puts a strain on engineers to produce optimal cooling designs for these electronic components. One method for cooling these electronic components is with heat sinks which effectively increase the surface area available for extracting the heat from the electronic components. Computational Fluid Dynamics (CFD) software is sometimes used to aid in the design process, but CFD simulations are computationally expensive and take long to complete. This causes the design engineer to test only a few proposed designs based on his/her experience and select the design that performs the best out of the tested designs, which might not be the optimum. The temperature distribution inside the heat sink can be solved relatively quickly with the diffusion equation, but the flow around the heat sink complicates the CFD simulation and increases the solving time significantly. Therefore, applications have been developed where the interaction between the heat sink and the flow around the heat sink is replaced by heat transfer coefficients. These coefficients are calculated from correlated equations which contain the flow properties. The flow properties are extracted from a flow network solver, which solves the flow around the heat sink. This procedure results in less expensive simulations, which can be used together with an optimisation procedure to develop an optimum cooling design. In this dissertation, a correlation for the contraction heat transfer coefficients of rectangular pin fin heat sinks was developed. A methodology was developed where consecutive regression lines were fitted to a large set of data extracted from numerous CFD simulations. The combination of these regression lines formed the basis of the correlation, which was divided into two correlations; one for laminar flow and another for turbulent flow. The correlations were tested against CFD simulations as well as experimental data. The results indicate that these correlations can be effectively used to calculate the contraction heat transfer coefficients on pin fin heat sinks. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Cognitive radio technology provides a solution for the spectrum scarcity issue by allowing the unlicensed users which are the cognitive radio devices to share the licensed band with the licensed (primary) users. The abilities of cognitive radio device help the secondary (unlicensed) nodes to observe the licensed band and to adjust their transmission parameters for maintaining the primary communication since in cognitive radio networks, it is essential that the existence of the unlicensed users must not harm the licensed network. Under these circumstances, we consider vertical cooperative transmission where primary transmission is not severely damaged by the secondary interference since each primary pair (transmitter and receiver) selects a neighbor secondary user as a cooperative relay to assist their transmission. Cooperation provides an increase in the signal-tointerference-ratio (SIR) of the primary network which can be harnessed by the secondary network as an additional bandwidth for their communication. We propose three relay selection rules so the influence of the relay’s position over the temporal and spatial correlations can be evaluated for different network conditions. Additionally, we implement primary exclusive region (PER) for each primary pair in the network which covers primary nodes, and all secondary users locate inside the zone become inactive. According to the outage model proposed in paper [2], temporal and spatial correlations are assumed to be 1 and 0 respectively; however it is estimated that regarding the environmental factors and the relay’s location, these correlation values may vary. This thesis work is based on the validation of the assumptions provided in paper [2] and our results demonstrate that the temporal and spatial correlation values changes under different circumstances and with different relay selection rules. The simulation results also show that PER significantly stimulates the cooperation performance thereby increases the transmission quality of the primary network.

Cette thèse propose une méthode théorique innovante pour l'étude des spectres d'excitation à un électron, mesurée par spectroscopie de photoémission directe et inverse.La plupart des calculs actuels au niveau de l’état de l’art reposent sur des fonctions de Green à plusieurs corps et des self-énergies complexes et non locales, évaluées spécifiquement pour chaque matériau. Même lorsque les spectres calculés sont en très bon accord avec les expériences, le coût de calcul est très important. La raison est que la méthode elle-même n'est pas efficace, car elle fournit beaucoup d'informations superflues qui ne sont pas nécessaires pour l'interprétation des données expérimentales.Dans cette thèse, nous proposons deux raccourcis par rapport à la méthode standard. Le premier est l'introduction d'un système auxiliaire qui cible, en principe, le spectre d'excitation du système réel. L'exemple type est la théorie de la fonctionnelle de la densité, pour lequel le système auxiliaire est le système de Kohn-Sham : elle reproduit exactement la densité du système réel par l'intermédiaire d'un potentiel réel et statique, le potentiel de Kohn-Sham. La théorie de la fonctionnelle de la densité est, cependant, une théorie de l'état fondamental, qui ne fournit que rarement des propriétés d'état excités : un exemple est le fameux problème de la sous-estimation de la bande interdite. Le potentiel que nous proposons (le potentiel spectral), local et dépendant de la fréquence, mais réelle, peut être considéré comme une généralisation dynamique du potentiel de Kohn-Sham qui donne en principe le spectre exact.Le deuxième raccourci est l'idée de calculer ce potentiel une fois pour toute dans un système modèle, le gaz d'électrons homogène, et de le tabuler. Pour étudier des matériaux réels, nous concevons un connecteur qui prescrit l'utilisation des résultats du gaz pour calculer les spectres électroniques.La première partie de la thèse traite de l'idée de systèmes auxiliaires, montrant le cadre général dans lequel ils peuvent être introduits et les équations qu'ils doivent satisfaire. Nous utilisons des modèles de Hubbard solubles exactement pour mieux comprendre le rôle du potentiel spectral ; en particulier, il est démontré que le potentiel peut être défini uniquement chaque fois que le spectre est non nul, et donne toujours les spectres attendus, même lorsque la partie imaginaire ou les contributions non locales de la self-énergie jouent un rôle de premier plan.Dans la deuxième partie de la thèse, nous nous concentrons sur les calculs pour les systèmes réels. Nous évaluons d'abord le potentiel spectral dans le gaz d'électrons homogène, puis l'importons dans le système auxiliaire pour évaluer le spectre d'excitation. Toute l’interdependence non triviale entre l'interaction électronique et l'inhomogénéité du système réel entre dans la forme du connecteur. Trouver une expression pour cela est le véritable défi de la procédure. Nous proposons une approximation raisonnable basée sur les propriétés locales du système, que nous appelons approximation du connecteur dynamique local.Nous mettons en œuvre cette procédure pour quatre prototypes de matériaux différents : le sodium, un métal presque homogène ; l'aluminium, encore un métal mais moins homogène ; le silicium, un semi-conducteur ; l'argon, un isolant inhomogène. Les spectres que nous obtenons avec cette approche concordent de manière impressionnante avec ceux qui sont évalués via la self-énergie, très coûteuse en temps de calcul, démontrant ainsi le potentiel de cette théorie. / This thesis proposes an innovative theoretical method for studying one-electron excitation spectra, as measured in photoemission and inverse photoemission spectroscopy.The current state-of-the-art realistic calculations rely usually on many-body Green’s functions and complex, non-local self energies, evaluated specifically for each material. Even when the calculated spectra are in very good agreement with experiments, the computational cost is very large. The reason is that the method itself is not efficient, as it yields much superfluous information that is not needed for the interpretation of experimental data.In this thesis we propose two shortcuts to the standard method. The first one is the introduction of an auxiliary system that exactly targets, in principle, the excitation spectrum of the real system. The prototypical example is density functional theory, in which the auxiliary system is the Kohn-Sham system: it exactly reproduces the density of the real system via a real and static potential, the Kohn-Sham potential. Density functional theory is, however, a ground state theory, which hardly yields excited state properties: an example is the famous band-gap problem. The potential we propose (the spectral potential), local and frequency-dependent, yet real, can be viewed as a dynamical generalisation of the Kohn-Sham potential which yields in principle the exact spectrum.The second shortcut is the idea of calculating this potential just once and forever in a model system, the homogeneous electron gas, and tabulating it. To study real materials, we design a connector which prescribes the use of the gas results for calculating electronic spectra.The first part of the thesis deals with the idea of auxiliary systems, showing the general framework in which they can be introduced and the equations they have to fulfill. We then use exactly-solvable Hubbard models to gain insight into the role of the spectral potential; in particular, it is shown that a meaningful potential can be defined wherever the spectrum is non-zero, and that it always yields the expected spectra, even when the imaginary or the non-local parts of the self energy play a prominent role.In the second part of the thesis, we focus on calculations for real systems. We first evaluate the spectral potential in the homogeneous electron gas, and then import it in the auxiliary system to evaluate the excitation spectrum. All the non-trivial interplay between electron interaction and inhomogeneity of the real system enters the form of the connector. Finding an expression for it is the real challenge of the procedure. We propose a reasonable approximation for it, based on local properties of the system, which we call dynamical local connector approximation.We implement this procedure for four different prototypical materials: sodium, an almost homogeneous metal; aluminum, still a metal but less homogeneous; silicon, a semiconductor; argon, an inhomogeneous insulator. The spectra we obtain with our approach agree to an impressive extent with the ones evaluated via the computationally expensive self energy, demonstrating the potential of this theory.

Indiana University-Purdue University Indianapolis (IUPUI) / Adaptive Optics Optical Coherence Tomography (AO-OCT) is a high-speed, high-resolution ophthalmic imaging technique offering detailed 3D analysis of retina structure in vivo. However, AO-OCT volume images are sensitive to involuntary eye movements that occur even during steady fixation and include tremor, drifts, and micro-saccades. To correct eye motion artifacts within a volume and to stabilize a sequence of volumes acquired of the same retina area, we propose a stripe-wise 3D image registration algorithm with phase correlation. In addition, using several ideas such as coarse-to-fine approach, spike noise filtering, pre-computation caching, and parallel processing on a GPU, our approach can register a volume of size 512 x 512 x 512 in less than 6 seconds, which is a 33x speedup as compared to an equivalent CPU version in MATLAB. Moreover, our 3D registration approach is reliable even in the presence of large motions (micro-saccades) that distort the volumes. Such motion was an obstacle for a previous en face approach based on 2D projected images. The thesis also investigates GPU implementations for 3D phase correlation and 2D normalized cross-correlation, which could be useful for other image processing algorithms.