The probability that a sum of random variables (RVs) exceeds (respectively falls below) a given threshold, is often encountered in the performance analysis of wireless communication systems. Generally, a closed-form expression of the sum distribution does not exist and a naive Monte Carlo (MC) simulation is computationally expensive when dealing with rare events. An alternative approach is represented by the use of variance reduction techniques, known for their efficiency in requiring less computations for achieving the same accuracy requirement. For the right-tail region, we develop a unified hazard rate twisting importance sampling (IS) technique that presents the advantage of being logarithmic efficient for arbitrary distributions under the independence assumption. A further improvement of this technique is then developed wherein the twisting is applied only to the components having more impacts on the probability of interest than others. Another challenging problem is when the components are correlated and distributed according to the Log-normal distribution. In this setting, we develop a generalized hybrid IS scheme based on a mean shifting and covariance matrix scaling techniques and we prove that the logarithmic efficiency holds again for two particular instances. We also propose two unified IS approaches to estimate the left-tail of sums of independent positive RVs. The first applies to arbitrary distributions and enjoys the logarithmic efficiency criterion, whereas the second satisfies the bounded relative error criterion under a mild assumption but is only applicable to the case of independent and identically distributed RVs. The left-tail of correlated Log-normal variates is also considered. In fact, we construct an estimator combining an existing mean shifting IS approach with a control variate technique and prove that it possess the asymptotically vanishing relative error property. A further interesting problem is the left-tail estimation of sums of ordered RVs. Two estimators are presented. The first is based on IS and achieves the bounded relative error under a mild assumption. The second is based on conditional MC approach and achieves the bounded relative error property for the Generalized Gamma case and the logarithmic efficiency for the Log-normal case.

El presente trabajo plantea una propuesta de mejora del proceso de planeamiento y control de la producción en una empresa metalúrgica fabricante de aleaciones del cobre, zinc y plomo, mediante la implementación del modelo de programación lineal, que permitirá reducir los niveles de stock de productos. Asimismo, formula la mejora en la exactitud del registro del inventario de los materiales, mediante la aplicación del inventario físico mensual y el conteo físico aleatorio permanente. Se detectó el problema de incoherencia entre stock físico y teórico de los materiales, cuyas causas principales son el software con limitaciones, desorden y la no buena señalización de la ubicación de los materiales en el almacén, la frecuencia del inventario físico y carencia de conteo físico aleatorio. Se detectó un nivel elevado de merma en el proceso productivo, por uso de chatarra contaminada y de utillajes desgastados. El elevado nivel de stock de productos, se debe al método de programación vigente. Se prevé un incremento del 93.6% al 97% en el nivel de exactitud del registro del inventario. El nivel del stock de los productos, se reducirá de un período de cobertura de 1.1 y 1.7 meses a 0.7 y 0.9 meses respectivamente para los dos productos. La inversión requerida para la implementación de las mejoras es de US$ 13,885, que permitirá un beneficio neto a valor presente de 4,369 US$/mes, posibilitando que la empresa recupere dicha inversión en 3 meses aproximadamente. / The present work proposes a proposal for improvement of the process of planning and production control in a metallurgical company that produces copper, zinc and lead alloys, through the implementation of the linear programming model, which will allow reducing the stock levels of products. Likewise, it formulates the improvement in the accuracy of the inventory register of the materials, through the application of the monthly physical inventory and the permanent random physical count. The problem of inconsistency between physical and theoretical stock of materials was detected, whose main causes are software with limitations, disorder and without good signage of the location of the materials in the warehouse, the frequency of the physical inventory and lack of random physical counting. A high level of depletion was detected in the productive process, due to the use of contaminated scrap metal and broken tools. The high level of stock of products is due to the current programming method. An increase of 93.6% to 97% is expected in the level of accuracy of the inventory record. The level of the stock of products, would be reduced from a coverage period of 1.1 and 1.7 months to 0.7 and 0.9 months respectively for the two products. The investment required for the implementation of the improvements is US $ 13,885, which will allow a net benefit at present value of 4,369 US $ / month, enabling the company to recover this investment in approximately 3 months. / Trabajo de investigación

O Huanglongbing (HLB) é a doença mais limitante para a produção de citros no mundo na atualidade. A alta capacidade de disseminação das bactérias associadas ao HLB pode estar associada com a movimentação do psilídeo vetor, Diaphorina citri, não apenas entre pomares vizinhos, mas também a longas distâncias. A análise de comportamento de dispersão em populações de D. citri e outras espécies de Psylloidea foi abordada mediante o monitoramento espaço-temporal de populações de psilídeos em diferentes alturas e em planta. O monitoramento foi realizado em dois contextos da disseminação primária do HLB, sendo áreas circunvizinhas de pomares comerciais de citros com manejo convencional no Estado de São Paulo. O monitoramento em alturas foi realizado por meio de armadilhas adesivas amarelas alocadas em duas alturas (2,5 e 7,5 m) e armadilha de sucção estacionária. Nos pontos monitorados foram selecionadas plantas hospedeiras de D. citri, amostradas quinzenalmente por meio de rede de varredura e armadilha de sucção portátil. Nos dois contextos foi encontrada correlação positiva entre abundância das espécies de psilídeos em relação às alturas e as épocas de monitoramento. No contexto de \"plantas de fundo de quintal\" coletaram-se 48.8% de psilídeos a 2,5 m e 51.2% a 7,5 m. No contexto de \"pomares com manejo deficiente\" foi encontrado 48.4% dos indivíduos a 2,5 m e 51.6% a 7,5 m. Foram coletados 148.802 espécimes de psilídeos por meio de armadilhas adesivas amarelas, pertencentes a 6 famílias e 24 gêneros, sendo que as espécies mais frequentes e constantes foram Heteropsylla sp., Isogonoceraia divergipennis, Mitrapsylla spp., Glycaspis brimblecombei e Trioza sp. No contexto de \"plantas de fundo de quintal\" a frequência de D. citri em alturas foi 1.5% e em planta foi 70.3%. No contexto de pomares com manejo deficiente, a frequência de D. citri em alturas foi 0.11% e em planta foi 81.8%. A maior densidade de psilídeos (incluindo D. citri) ocorreu do final do inverno até o começo do verão, sendo particularmente concentrada na primavera em ambos os contextos tanto nas áreas circunvizinhas como na borda dos pomares comerciais de citros. CLas foi detectada em 40% dos indivíduos de D. citri encontrados a 7,5 m e em 63.3% dos indivíduos coletados em plantas cítricas. A detecção de CLas foi negativa para as outras espécies de Psylloidea coletadas em altura e em plantas hospedeiras de D. citri. A correlação positiva entre psilídeos coletados a 2,5 m e 7,5 m evidencia possíveis movimentos de ascensão vertical nas camadas atmosféricas. A coleta de psilídeos a alturas superiores à da copa de plantas cítricas (como 7,5 m) evidencia possíveis movimentos de longa distância, sugerindo que os insetos estejam sendo transportados pelo vento. A análise da ocorrência espaço-temporal de Psylloidea em armadilhas adesivas pode auxiliar na previsão de movimentos a curta e longa distância de D. citri. / Huanglongbing (HLB) is the most limiting disease for the production of Citrus in the world today. The high dissemination capacity of the HLB-associated bacteria may be associated with the movement of the psyllid vector, Diaphorina citri, not only between neighboring groves, but also at long distances. The dispersion behavior analysis in populations of D. citri and other species of Psylloidea was approached through the spatio-temporal analysis of psyllid populations at different heights and plants. The monitoring was carried out in two contexts of the primary spread of HLB, in areas surrounding commercially managed groves in the State of São Paulo. Monitoring at heights was performed using yellow sticky traps allocated at two heights (2.5 and 7.5 m) and a stationery suction-trap. At the monitored points, host plants of D. citri were sampled biweekly by means of a sweep net and a portable suction device. In both contexts a positive correlation was found between the abundance of the species of psyllids in relation to the heights and the seasons of monitoring. In the context of backyard plants, 48.8% of the psyllids were collected at 2.5 m and 51.2% at 7.5m. In the context of poor management groves, 48.4% of the individuals were found at 2.5 m and 51.6% at 7.5 m. A total of 148,802 specimens of psyllids were collected using yellow sticky traps belonging to 6 families and 24 genera. The most frequent and constant species were Heteropsylla sp., Isogonoceraia divergipennis, Mitrapsylla spp., Glycaspis brimblecombei and Trioza sp. In the context of backyard plants the frequency of D. citri at the two sampling heights was 1.5% and on plants was 70.3%. In the context of poor management groves, the frequency of D. citri at the two heights was 0.11% and in plant was 81.8%. The highest density of psyllids occurred from late winter to early summer, but particularly concentrated in the spring in both contexts. Similarly, D. citri showed a population peak in the spring, both in the surrounding areas and on the edge of commercially managed Citrus groves. CLas was detected in 40% of the D. citri individuals found at 7.5 m and in 63.3% of the individuals collected on Citrus plants. The detection of CLas was negative for the other species of Psylloidea collected by yellow sticky traps and on host plants of D. citri. The positive correlation between psyllids collected at 2.5 m and 7.5 m shows possible vertical ascending movements in the atmospheric layers. The collection of psyllids at heights higher than the canopy of Citrus plants (e.g. 7.5 m) shows possible long distance movements, suggesting that the insects are being carried by the wind. The spatio-temporal analysis of Psylloidea in yellow sticky traps may aid in the prediction of short and long distance movements of D. citri.

Psychological research regarding mental imagery is heterogeneous in nature owing to its internal nature. Mental imagery involving music is most simply defined as hearing music in the mind’s ear. Musical imagery (MI) is an understudied phenomenon particularly by means of non-experimental methods. This study investigated four dimensions of everyday MI: namely it’s content, nature, constancy and associated corporeal manifestations (for instance, foot-tapping, humming and so forth), via experience-sampling methods. Stage one of data collection involved a cross-sectional survey (n = 87) whereby participants provided retrospective self-reports concerning MI, pertinent demographic information, and particulars concerning their musical history. Stage two – implemented subsequent to piloting – utilised iterative sampling to illuminate the dimensions and descriptive facets of MI during everyday activities. Each participant (n = 16; 8 musicians; 8 non-musicians) was selected based on specific inclusion criteria, following stage one participation, and were invited to complete 21 questionnaires over seven days, receiving three SMS prompts per day. In terms of prevalence, MI was consistently experienced by participants, regardless of their musical background although musicians reported higher rates of MI occurrences. There was a statistically significant association between MI and musical training/experience (χ² = 6.35; d.f. = 1; p = .012). Furthermore, odds ratios suggested that the musicians demonstrated an 85% likelihood of experiencing MI as compared to the non-musicians (OR 1.85; CI 1.14 – 2.99). Daily exposure to music appeared to be an equally significant factor relating to every day MI incidences, particularly given the finding that the majority of participant’s MI episodes were familiar and recently heard.

No description available.

Nous proposons un nouveau schéma d’échantillonnage non uniforme périodique appelé Système d’Échantillonnage Non Uniforme en Radio Intelligente (SENURI). Notre schéma détecte la localisation spectrale des bandes actives dans la bande totale échantillonnée afin de réduire la fréquence moyenne d’échantillonnage, le nombre d’échantillons prélevé et par conséquent la consommation d’énergie au niveau du traitement numérique. La fréquence moyenne d’échantillonnage du SENURI dépend uniquement du nombre de bandes contenues dans le signal d’entrée x(t). Il est nettement plus performant, en termes d’erreur quadratique, qu’une architecture classique d’échantillonnage non uniforme périodique constituée de p branches, lorsque le spectre de x(t) change dynamiquement. / In this work we consider the problem of designing an effective sampling scheme for sparse multi-band signals. Based on previous results on periodic non-uniform sampling (Multi-Coset) and using the well known Non-Uniform Fourier Transform through Bartlett’s method for Power Spectral Density estimation, we propose a new sampling scheme named the Dynamic Single Branch Non-uniform Sampler (DSB-NUS). The idea of the proposed scheme is to reduce the average sampling frequency, the number of samples collected, and consequently the power consumption of the Analog to Digital Converter (ADC). In addition to that our proposed method detects the location of the bands in order to adapt the sampling rate. In this thesis, we show through simulation results that compared to existing multi-coset based samplers, our proposed sampler provides superior performance, both in terms of sampling rate and energy consumption. It is notconstrained by the inflexibility of hardware circuitry and is easily reconfigurable. We also show the effect of the false detection of active bands on the average sampling rate of our new adaptive non-uniform sub-Nyquist sampler scheme.

Membrane assisted passive sampler (MAPS) is an informative, cost-effective and environmentally friendly approach for monitoring of ionisable organic compounds in water bodies. The sampler uses no organic solvent. By adjusting the pH of the acceptor phase, both acidic chlorophenols and basic triazine model compounds were extracted. The sampler was optimized under laboratory conditions followed by field applications on the same compounds. The optimised parameters were temperature of the water body, turbulence, protective cover, biofouling, matrix effects such as humic substances, degree of trapping in the acceptor phase and exposure time. It was found that the sampling kinetics of most of the tested analytes are dependent on temperature and on the hydrodynamic conditions. Also, a strong dependence of the sampling rates reduction on sample matrix and protective cover used was noted. The chemical uptake of both the acidic chlorophenols and basic triazine compounds into the passive sampler remained linear and integrative through out the exposure periods. The amounts quantified in the MAPS had relative standard deviations mostly between 10 % and 20 % (from repeat determinations) and did in no case exceed 30 %. The behaviour of the MAPS to monitor ionisable triazine compounds in dam water of the Hartebeespoort was compared to Chemcatcher and solid phase extraction technique with C18 sorbents of spot samples. Similarly, the behaviour of the MAPS to monitor ionisable chlorophenol compounds in wastewater of the Goudkoppies Wastewater Treatment Plant was compared to solid phase extraction technique. There were no triazine and chlorophenol compounds detected in any of the deployed passive samplers in the field applications. The same results were obtained in grab samples extracted with solid phase extraction under laboratory conditions. However, data from laboratory studies support the feasibility of MAPS to measure the freely dissolved fraction of ionisable organic chemicals in water. Using water from the Hartebeespoort dam spiked with 50 μg L-1 triazine, the detection limits of triazine compounds ranged from 11.38 to 61.86 μg L-1 for direct injection, 1.082 to 23.077 μg L-1 for MAPS, 0.892 to 5.769 μg L-1 for Chemcatcher and 1.482 to 7.410 μg L-1 for SPE. While using water from Goudkoppies Wastewater Treatment Plant spiked with 100 μg L-1 chlorophenols, the detection limits of the passive sampler were comparable with that of solid phase extraction and were around 1.5 μg L-1. Estimation and interpretation of enrichment factors in the passive samplers and SPE were generally comparable ranging from 46 to 295 for chlorophenol compounds. Also, for triazine compounds, the obtained enrichment factors in the passive samplers and SPE are generally comparable with the exception of enrichment factors of propazine, ametryn terbuthylazine, prometryn and terbutryn compounds which were higher for the MAPS ranging from 46 to 65.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. 21 October, 2014. / Three decades ago, the discovery of the Human Immunodeficiency Virus (HIV) was announced. The subsequent HIV pandemic has continued to devastate the global community, and many countries have set ambitious HIV reduction targets over the years. Reliable methods for measuring incidence, the rate of new infections, are essential for monitoring the virus, allocating resources, and assessing interventions. The estimation of incidence from single cross-sectional surveys using tests that distinguish between ‘recent’ and ‘non-recent’ infection has therefore attracted much interest. The approach provides a promising alternative to traditional estimation methods which often require more complex survey designs, rely on poorly known inputs, and are prone to bias. More specifically, the prevalence of HIV and ‘recent’ HIV infection, as measured in a survey, are used together with relevant test properties to infer incidence. However, there has been a lack of methodological consensus in the field, caused by limited applicability of proposed estimators, inconsistent test characterisation (or estimation of test properties) and uncertain test performance. This work aims to address these key obstacles. A general theoretical framework for incidence estimation is developed, relaxing unrealistic assumptions used in earlier estimators. Completely general definitions of the required test properties emerge from the analysis. The characterisation of tests is then explored: a new approach, that utilises specimens from subjects observed only once after infection, is demonstrated; and currently-used approaches, that require that subjects are followed-up over time after infection, are systematically benchmarked. The first independent and consistent characterisation of multiple candidate tests is presented, and was performed on behalf of the Consortium for the Evaluation and Performance of HIV Incidence Assays (CEPHIA), which was established to provide guidance and foster consensus in the field. Finally, the precision of the incidence estimator is presented as an appropriate metric for evaluating, optimising and comparing tests, and the framework serves to counter existing misconceptions about test performance. The contributions together provide sound theoretical and methodological foundations for the application, characterisation and optimisation of recent infection tests for HIV incidence surveillance, allowing the focus to now shift towards practical application.

Cette thèse introduit un cadre théorique pour l'étude de différents schémas d'échantillonnage dans un domaine sphérique, et de leurs effets sur le calcul d'intégrales pour l'illumination globale. Le calcul de l'illumination (du transport lumineux) est un composant majeur de la synthèse d'images réalistes, qui se traduit par l'évaluation d'intégrales multidimensionnelles. Les schémas d'intégration numériques de type Monte-Carlo sont utilisés intensivement pour le calcul de telles intégrales. L'un des aspects majeurs de tout schéma d'intégration numérique est l'échantillonnage. En effet, la façon dont les échantillons sont distribués dans le domaine d'intégration peut fortement affecter le résultat final. Par exemple, pour la synthèse d'images, les effets liés aux différents schémas d'échantillonnage apparaissent sous la forme d'artéfacts structurés ou, au contrire, de bruit non structuré. Dans de nombreuses situations, des résultats complètement faux (biaisés) peuvent être obtenus à cause du schéma d'échantillonnage utilisé pour réaliser l'intégration. La distribution d'un échantillonnage peut être caractérisée à l'aide de son spectre de Fourier. Des schémas d'échantillonnage peuvent être générés à partir d'un spectre de puissance dans le domaine de Fourier. Cette technique peut être utilisée pour améliorer l'erreur d'intégration, car un tel contrôle spectral permet d'adapter le schéma d'échantillonnage au spectre de Fourier de l'intégrande. Il n'existe cependant pas de relation directe entre l'erreur dans l'intégration par méthode de Monte-Carlo et le spectre de puissance de la distribution des échantillons. Dans ces travaux, nous proposons une formulation de la variance qui établit un lien direct entre la variance d'une méthode de Monte-Carlo, les spectres de puissance du schéma d'échantillonnage ainsi que de l'intégrande. Pour obtenir notre formulation de la variance, nous utilisons la notion d'homogénéité de la distribution des échantillons qui permet d'exprimer l'erreur de l'intégration par une méthode de Monte-Carlo uniquement sous forme de variance. À partir de cette formulation de la variance, nous développons un outil d'analyse pouvant être utilisé pour déterminer le taux de convergence théorique de la variance de différents schémas d'échantillonnage proposés dans la littérature. Notre analyse fournit un éclairage sur les bonnes pratiques à mettre en œuvre dans la définition de nouveaux schémas d'échantillonnage basés sur l'intégrande / This dissertation introduces a theoretical framework to study different sampling patterns in the spherical domain and their effects in the evaluation of global illumination integrals. Evaluating illumination (light transport) is one of the most essential aspect in image synthesis to achieve realism which involves solving multi-dimensional space integrals. Monte Carlo based numerical integration schemes are heavily employed to solve these high dimensional integrals. One of the most important aspect of any numerical integration method is sampling. The way samples are distributed on an integration domain can greatly affect the final result. For example, in images, the effects of various sampling patterns appear in the form of either structural artifacts or completely unstructured noise. In many cases, we may get completely false (biased) results due to the sampling pattern used in integration. The distribution of sampling patterns can be characterized using their Fourier power spectra. It is also possible to use the Fourier power spectrum as input, to generate the corresponding sample distribution. This further allows spectral control over the sample distributions. Since this spectral control allows tailoring new sampling patterns directly from the input Fourier power spectrum, it can be used to improve error in integration. However, a direct relation between the error in Monte Carlo integration and the sampling power spectrum is missing. In this work, we propose a variance formulation, that establishes a direct link between the variance in Monte Carlo integration and the power spectra of both the sampling pattern and the integrand involved. To derive our closed-form variance formulation, we use the notion of homogeneous sample distributions that allows expression of error in Monte Carlo integration, only in the form of variance. Based on our variance formulation, we develop an analysis tool that can be used to derive theoretical variance convergence rates of various state-of-the-art sampling patterns. Our analysis gives insights to design principles that can be used to tailor new sampling patterns based on the integrand

Orientador: Célia Regina Lopes Zimback / Coorientador: Alessandra Fagioli da Silva / Banca: Milton Barbosa Landim / Banca: Ana Paula Barbosa / Banca: Antonio Ribeiro da Cunha / Resumo: Os solos possuem alta variabilidade espacial devido aos diversos processos físicos, químicos e biológicos que atuam simultaneamente com diferentes intensidades na sua formação. O manejo uniforme dos solos não leva em conta tal variabilidade espacial, não sendo, portanto, a estratégia de manejo mais adequada. O uso do geoprocessamento, como ferramenta para o estudo da heterogeneidade dos solos, proporciona uma análise comportamental e uma visão espacial da realidade. Os fenômenos naturais são mais facilmente entendidos quando é possível a visualização da sua distribuição espacial e/ou temporal. Algumas das ferramentas que podem ser aplicadas para entender essas estruturas são os modelos geoestatísticos, em especial os modelos de simulação. Pela tentativa de reproduzir os mecanismos da realidade, esses modelos podem mostrar as características do solo em diferentes cenários ambientais. Pelos resultados das análises dos parâmetros físico hídricos da Sub-bacia da Cabeceira do Rio Pardo - SP, pode-se concluir: Os parâmetros que apresentaram maior variabilidade, correlação entre si e dependência espacial foram: teor de argila, umidade na capacidade de campo, umidade no ponto de murcha permanente e macroporosidade, que influenciam na condutividade hidráulica dos solos. A simulação sequencial direta de condutividade apresentou alto erro médio, o que indica o enviesamento dos dados e que o maior valor pode estar relacionado à pequena densidade amostral da área. A macroporosidade aprese... / Abstract: The soils have highly spatial variability due to various physical, chemical and biological processes that act simultaneously in their formation and with different intensities. Consequently, the uniform land management does not take into account such spatial variation, not being therefore more effective management strategy. The use of the GIS, as a tool for studying the dynamics of the soil, provides a behavioral analysis of spatial view and a soil reality. Natural phenomena are more easily understood when viewing the spatial distribution and/or time is possible. Some of the tools that can be applied to understand this dynamic are the geostatistical models, especially the simulation models. By trying to reproduce the mechanisms of fact, these models can show the soil behavior under different environmental scenarios. The results of the analysis of water physical parameters of the Sub-basin Headboard of Pardo River- SP, it can be concluded: The parameters that have greater variability, correlated and spatial dependence were clay content, humidity in the field capacity, moisture in point permanent wilting and macroporosity, that influence the hydraulic conductivity of the soil; direct sequential simulation of conductivity showed high mean error, indicating the bias of the data and that the greatest value may be related to the small sample density of the area; the macroporosity have had the best results anda was the co-factor chosen in the determination of management zones; it was... / Doutor