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The Impact of Ageing, Gamma(γ)-irradiation, and Varying Concentrations of Phosphate on the Stability and Solubility of Biogenic Iron Oxides (BIOS) in the Presence of Shewanella putrefaciens CN32Najem, Tarek January 2017 (has links)
The redox cycling of iron is intimately linked to the cycling of C, S, N, P as well as the speciation, mobility, and bioavailability of various toxic contaminants in soils and sediments. Within these environments, the cycling of iron is catalytically driven by iron-oxidizing (FeOB) and iron reducing bacteria (FeRB) which mediate the formation, transformation, and dissolution of various iron-bearing minerals. Under oxic conditions, FeOB promote the formation of iron oxides on or in close proximity of their cell walls and extracellular polymeric substances, and such composite, termed biogenic iron oxides (BIOS), offers highly reactive heterogenous sites that efficiently immobilize trace metals and contaminants alike. However, under reducing conditions, FeRB mediate the reductive dissolution of BIOS and in turn lead to the remobilization of associated contaminants. Conversely, contaminants may become immobilized by secondary iron minerals that form from the metabolic activity of FeRB. Therefore, determining the factors that influence the reactivity of BIOS, as well as the formation of secondary iron minerals is of critical importance to develop a better understanding of the geochemical cycling of iron and in turn the transport of contaminants in the environment. This thesis investigated (1) the impact of simulated diagenesis (ageing for ~5 years at 4ºC) on the mineral stability and reactivity of BIOS towards reduction by Shewanella putrefaciens CN32, (2) the effects of phosphate at an environmentally relevant (10µM) and excess (3.9mM) concentration on the rates and extent of microbial reduction of synthetic 2-line ferrihydrite and BIOS, as well as the formation of secondary iron minerals, and (3) the impact of sterilization by γ-irradiation on the mineral stability and reactivity of BIOS. It was found that simulated diagenesis did not affect the mineralogical composition of BIOS but significantly lowered the reactivity of BIOS towards microbial reduction. The concentration of phosphate was found to have contrasting effects on the rates of reduction of ferrihydrite and BIOS, but in general, excess concentration of phosphate enhanced the extent of Fe(III) reduction. The formation of a specific secondary iron mineral was also found to depend on the concentration of phosphate, as well as, in the case for BIOS, the presence of intermixed cell derived organic matter. γ-irradiation did not alter the mineralogy and reactivity of BIOS towards microbial reduction, and it was concluded to be a suitable technique to sterilize BIOS.
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Détermination des processus à l’échelle nanométrique responsables de l’agrégation des particules primaires de silice / Determination of nanoscale processes responsible for aggregation of silica primary particlesValente, Jules 15 December 2014 (has links)
L’incorporation de silice, obtenue par un procédé de précipitation en milieu aqueux, à la bande de roulement des pneumatiques a permis d’en réduire significativement la résistance au roulement et par conséquent, l’impact environnemental. L’efficacité de la silice précipitée en tant que charge de renfort est liée à la présence d’agrégats nanométriques au sein de ce matériau et à son interaction avec l’élastomère du pneumatique. La maîtrise de la morphologie des agrégats est donc un levier pour le développement de silices plus performantes. Dans ce contexte, la présente étude porte sur le développement d’un modèle prédictif de la formation de l’agrégat de silice au cours de la précipitation. Un suivi par turbidimétrie en ligne et par DLS a permis d’illustrer l’influence critique des paramètres de synthèse sur la cinétique d’agrégation. Un modèle optique basé sur les propriétés diffusantes des objets fractals a été développé pour extraire des informations morphologiques sur l’agrégat au cours de sa construction à partir des spectres de turbidité expérimentaux. Les résultats semblent indiquer une densification de la structure au fur et à mesure que se déroule l’agrégation. Les analyses de porosimétrie azote et mercure menées sur les produits finaux, obtenus après séchage, ont quant à elles mis en évidence des différences texturales qui ont pu être mises en lien avec la cinétique d’agrégation. L’ensemble de ces informations a été repris dans un bilan de population permettant de traiter à la fois la croissance et l’agrégation des particules de silice ainsi que de simuler les propriétés optiques de la suspension. / Tires manufactured with precipitated silica instead of carbon black present a significantly lower rolling resistance and are therefore more environmentally friendly. Existence of nanometric aggregates inside the precipitated silica is responsible for its efficiency as a reinforcing filler. This level of structure deeply affects the quality of the interactions between silica and the rubber of the tire tread. Gaining control over the morphology of the aggregates could thus be a way to produce silica even more suited to this application.The aim of the present study is to develop a theoretical model able to predict the formation of silica aggregates during the precipitation process. Critical influence of the synthesis parameters on the aggregation kinetics were evidenced by DLS and online turbidimetry measurements. Morphological parameters of the expanding aggregates could be extracted from the experimental turbidity spectra thanks to a fractal scattering optical model. The observed trend suggested a densification of the aggregates over time. Nitrogen and mercury porosimetry analyses were carried out on the dried powders obtained at the end of the precipitation. Differences between the characterized samples could be related to the variations in their aggregation kinetics. Finally, a population balance model was developed. A specific feature of our model is that it is able to take into account both growth and aggregation of silica particles as well as to simulate their optical properties.
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L'hyperthermie provoque l'agrégation de FLIP et restaure l'apoptose induite par TRAIL / Hyperthermia triggers FLIP aggregation and restore TRAIL induced apoptosisMorlé, Aymeric 17 December 2014 (has links)
TRAIL (TNF-related apoptosis inducing ligand) est une protéine du système immunitaire appartenant à la famille du TNF (Tumor necrosis factor). L'intérêt de TRAIL en thérapie anti-cancéreuse réside dans sa capacité à induire la mort par apoptose des cellules tumorales, sans exercer de toxicité envers les cellules saines. Le principal frein à l’utilisation de TRAIL est la survenue courante de résistances dans les tumeurs, limitant ainsi son efficacité. Mon travail de thèse a consisté à étudier l’intérêt de l’hyperthermie (ou choc thermique) en tant qu’adjuvant à TRAIL et a décrire ses capacités à contourner les mécanismes de résistance.Dans un premier temps, l’activité et la portée de cette combinaison a été évaluée dans de nombreuses et diverses lignées cellulaires cancéreuses sensibles ou résistantes à TRAIL. Un choc thermique (1h 42°C) permet de sensibiliser efficacement les lignées devenues résistantes à TRAIL et cette association s’est avérée efficace dans toutes les lignées testées.Dans un deuxième temps, mon travail s’est focalisé sur les mécanismes induits par l’hyperthermie, responsables de la sensibilisation et de l’apoptose des cellules. Les analyses des complexes initiateurs de la mort (DISC - Death-inducing signaling complex) ont révélé de nombreuses disparités suivant les conditions thermiques. Les différences majeures impliquent avant tout l’absence de FLIP dans le DISC, celui-ci étant l’inhibiteur principal de la voie, ainsi qu’un retard de la formation du complexe en condition d’hyperthermie. Ceci est associé à l’activation des caspases initiatrices d’une meilleure qualité, une fois la température revenue à la normale.L’absence de FLIP est expliquée par son inactivation due à l’agrégation de cette protéine suite à l’augmentation de la température. Ce phénomène est indépendant d’une quelconque modification post-traductionnelle connue, mais peut être inhibé par la présence de glycérol qui stabilise les protéines dénaturées.L’ensemble de ce travail met en lumière l’intérêt de la combinaison de TRAIL avec une hyperthermie et présente un point de vue nouveau sur les mécanismes expliquant son efficacité. / The TNF-family member TRAIL (TNF-related apoptosis inducing ligand) is a cytokine involved in the immune anti-tumour surveillance. TRAIL is a promising agent currently under investigation for its anti-cancer properties with limited side effects on healthy cells. However, the use of TRAIL in oncology has been limited due to its lack of efficiency, mainly associated with cell resistance to apoptosis. The aim of this project was to study the interest of hyperthermia (or heat shock - HS) as an adjuvant for TRAIL therapy and the mechanisms involved in this sensitization.We have first evaluated the significance of this combination in a large variety of cancer cell lines known to be sensitive or resistant to TRAIL. We could demonstrate that hyperthermia was able to efficiently sensitize resistant cancer cells to TRAIl-induced apoptosis in almost every cell lines tested.We next, focused our work on the molecular mechanisms responsible for the sensitization, during hyperthermia. Analyses of the DISC (Death-Inducing Signaling Complex) revealed a lack of recruitment of FLIP in the DISC, the main inhibitor of the extrinsic pathway, and a delay in the formation of the complex under hyperthermic conditions. Inhibition of FLIP recruitment was associated with enhanced initiator caspases activation when cells were reincubated at 37°C after the HS.The absence of FLIP within the TRAIL DISC was due to its aggregation during HS and was independent of post-translational modifications. Inhibition of FLIP aggregation by glycerol, which stabilizes denaturerated proteins, restored FLIP recruitment within the TRAIL DISC and consequently inhibited TRAIL-induced cell death. Taken together, these results highlight the interest of combining TRAIL with hyperthermia and highlight new mechanisms explaining its efficiency.
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Možnosti využití kompozitních indikátorů při hodnocení udržitelného rozvoje a kvality života / The applicability of methods that are based on the employment of composite indicators in assessing sustainable development and quality of lifePetkovová, Ludmila January 2011 (has links)
The main objective of this thesis is to assess the applicability of methods that are based on the employment of composite indicators when evaluating the 'sustainable development' and 'quality of live' indexes. The first issue observed in here is whether the composite indicators as such even represent a suitable tool for assessing the above mentioned area of analysis; if the answer is yes, then, secondly, under which conditions the composite indicators may be applied in the context of our analysis. After answering the questions above, it is crucial to find suitable methods for the particular steps of constructing the composite indicator for the sustainable development and quality of life categories, whereby it is also necessary to evaluate the advantages and disadvantages resulting from the application of the selected composite indicators for the purposes of the respective analysis. Within this thesis, the comparison of individual methods of constructing the indicators was performed by means of applying the individual indicators on the established set of data, as well as a subsequent comparison of results and the assessment of strengths and weaknesses of the individual methods has been done with respect to the factual side of the particular composite indicators (i.e. with respect to the sustainable development and quality of life in our case). Various composite indicators for the quality of life and sustainable development have already been established; the necessity of composing additional composite indicators for the above mentioned categories reflects the problematic nature of finding a suitable tool that would be generally accepted in this case. This thesis provides for relevant conclusions and recommendations that should contribute to establish a suitable approach towards the construction of composite indicators for the sustainable development and quality of life assessment. Furthermore, the thesis provides for the comparison of methods as employed in practical construction of composite indicators in our context with methods based on a professional theory. The professional theory/literature addresses and recommends certain methods for the construction of composite indicators in the relevant context, however, these methods are typically not applied in the practical construction of the most frequently/commonly used composite indicators for measuring the sustainable development and quality of life. The critical aspects that have been observed within comparison of the individual methods are transparency of calculation, interpretability of results, robustness of the composite indicator closely linked to the nature and character of the data, and the level of applicable compensation of the individual parameters within the respective indicator that is allowed by the particular aggregation mechanism employed. The thesis concludes on a rather questionable use of composite indicators in case of assessing the sustainable development, whereby deduces on recommending the application of composite indicators only in case of assessing the quality of life, which may also be understood as a part (sub-item) of the sustainable development and which is easier to be quantitatively expressed. In parallel, the circumstances of the quality of life are better to be compared across various items, e.g. regions. The results indicate that it is not possible to establish a uniform recommendation when selecting the most suitable method; in case of every construction of the particular composite indicator it is necessary to take into account the strengths and weaknesses of all the considered methods. At the same time, the results lead to consideration of relevancy of conclusions resulting from the evaluation of quality of life by means of composite indicators, especially by means of a single number.
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Essays on the measurement of povertyRoope, Laurence Stanley James January 2013 (has links)
This thesis is comprised of three distinct chapters, each of which is concerned in some way with the measurement of poverty. The first chapter provides social preference conditions which are both necessary and sufficient for a poverty line to arise endogenously. In so doing, it turns out that the apparently independent 'identification' and 'aggregation' problems in poverty measurement are subtly intertwined. Necessary and sufficient conditions are provided for the existence of both relative and absolute poverty lines. In each case, one of the conditions is a familiar weak monotonicity property. The other conditions are simple consistency requirements.In the second chapter, we propose classes of intertemporal poverty measures which take into account both the debilitating impact of prolonged spells in poverty and the mitigating effect of periods of affluence on subsequent poverty. The weight assigned to the level of poverty in each time period depends on the length of the preceding spell of poverty or of non-poverty. The proposed classes of intertemporal poverty measures are quite general and allow for a range of possible judgements as to the overall impact on a poor period of preceding spells of poverty or affluence. We discuss the properties of the proposed classes of measures and axiomatically characterize them.The third chapter is an empirical application of the intertemporal poverty measures proposed in the second chapter. The new measures, together with an existing intertemporal poverty measure from the literature, are used to analyse intertemporal poverty in Great Britain during the period 1991-2005, using data from the British Household Panel Survey. Previous studies on poverty using this data-set have employed static measures of poverty. We illustrate how the use of intertemporal poverty measures makes it possible to analyse aspects of poverty which cannot be captured by static, annual, measures of poverty. We then model the determinants of intertemporal poverty, conditional upon being poor, using a Heckman two-step selection model.
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Supporting VoIP in IEEE802.11 distributed WLANsLiu, Zuo January 2013 (has links)
Telecommunications is converging on the use of IP based networks. Due to the low cost of VoIP applications, they are being increasingly used instead of conventional telephony services. IEEE802.11 WLANs are already widely used both commercially and domestically. VoIP applications will also expand from usage over wired networks to voice communications over IEEE802.11 WLANs. This is known as VoWLAN. The use of VoWLAN may reach the maximum capacity of a wireless channel if there are many simultaneous VoIP calls operating close to each other. There is much published research based on a single IEEE802.11 infrastructure WLAN concluding that packet loss, transmission efficiency and latency issues are the major challenges limiting the VoWLAN capacity. The VoIP service quality will drop sharply when the demands exceed the WLAN’s capacity. This thesis demonstrates that these challenges also apply to distributed WLANs. To extend these findings from the existing research, the analysis in this thesis indicates that the capacity of a single IEEE802.11 WLAN channel is 12 VoIP calls. When the number of simultaneous VoIP calls is within the capacity, the WLAN can deliver more than 90% of the voice packets to the receiver within 150 ms (the lowest network performance for supporting acceptable VoIP service). However, as soon as the traffic loads are beyond the wireless channel capacity e.g. the number of simultaneous VoIP calls is greater than 13, the VoIP service quality catastrophically collapses. When the capacity is exceeded there are almost no voice packets that can be delivered to the receiver within 150 ms. Our research results indicate that the delay accumulation for voice packets in the transmitter’s outgoing buffer causes this problem. Our research also found that dropping ‘stale’ voice packets that are already late for delivery to the receiver can give more transmission opportunities to those voice packets that may still be delivered in time. This thesis presents a new strategy called Active Cleaning Queue (ACQ) which actively drops ‘stale’ voice packets from the outgoing buffer and prevents the accumulation of delay in congested conditions. When ACQ is applied in a saturated wireless channel the network performance for supporting VoIP traffic was found to gradually decrease proportional to the numbers of simultaneous VoIP calls rather than catastrophically collapse. There is also published research suggesting that the aggregation of packets can improve the efficiency of WLAN transmissions. An algorithm called Small Packet Aggregation for Wireless Networks (SPAWN) is also presented in this thesis to improve transmission efficiency of small voice packets in WLANs without introducing further delay to VoIP traffic. The evaluation result shows that after applying the SPAWN algorithm, the VoIP capacity of a single wireless channel can be extended up to 24 simultaneous calls.
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Kompozitní indikátory: konstrukce, využití, interpretace / Composite indicators: the construction, usage and interpretationHudrlíková, Lenka January 2014 (has links)
This thesis brings a comprehensive view on the construction, usage and interpretation of composite indicators. Methods and techniques, which can be used for constructing composite indicators, are introduced. The focus is on their contribution to the transparent solution of the problem of correlation and compensability among underlying indicators. Transparency in construction of composite indicators is a crucial requirement for obtaining reliable results and their correct interpretation. The thesis consists of two main parts. The first part is theoretically oriented. First, the problem of adequacy and subsequently a measurement of the phenomenon by means of statistical indicators are discussed. Different methods for data normalization, setting a weighting scheme and aggregation are introduced and compared. These three steps are considered to be crucial in a process of constructing a composite indicator and thus, they are the core of the thesis. The aim is to investigate an interaction of normalization methods, weight-setting and aggregation methods, since these steps are not separate. The second part of the thesis consists of two comprehensive cases. Theoretical findings are applied and empirically verified in these cases. I investigated a robustness of the composite indicator depending on a combination of selected methods of normalization, setting weights and aggregation on a set of Europe 2020 indicators. Whereas this first case dealt with the comparative analysis of methods, the second case is focused purely on one issue -- university ranking. The proposed method reacts to criticism of currently published university rankings and takes into account specifics of the particular university as well as the exogenous background characteristics. The main added value rests in a contribution to a discussion about the improvement of construction and overall quality of composite indicators including their interpretation. I pointed out the main concerns and difficulties of composite indicators that often remain unnoticed by users and even constructors. The conclusion brings several beneficial findings, which can be used for the construction of a composite indicator and an interpretation of final scores and ranking. This work can also serve as a scientific ground for further research and development of the methodology of constructing composite indicators.
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Caracterisation fonctionnelle des sortases de lactococcus lactis : de l’ancrage de protéines à la biogénèse de pili / Functional characterization of Lactococcus lactis sortases : from proteins anchoring to pili biogenesisOxaran David, Virginie 19 January 2012 (has links)
Les bactéries lactiques (BL), communément employées en industrie agroalimentaire, font à présent l’objet d’études visant à les utiliser pour de nouvelles applications telles que le développement de vaccins vivants ou la délivrance de molécules d’intérêt biothérapeutique chez l’hôte. Dans cette optique, différents systèmes de présentation de protéines à la surface des bactéries à Gram positif ont été développés. L’un d’entre eux est basé sur l’activité d’enzymes, les sortases, liant de façon covalente les protéines à la paroi bactérienne. Nous avons utilisé la BL modèle, Lactococcus lactis, afin d’étudier les sortases, jusqu’alors étudiées essentiellement chez les bactéries pathogènes. La sortase A (SrtA) est responsable de l’ancrage d’au moins cinq protéines à motif LPxTG à la surface. Une seconde sortase, de classe C (SrtC), a été identifiée et caractérisée. Nous avons mis en évidence la capacité de L. lactis à produire des pili à sa surface qui sont polymérisés par SrtC et ancrés à la paroi par SrtA. Ces pili résultent de la polymérisation de la piline majeure YhgE qui peut être surplombée par la piline mineure de coiffe YhgD. La production de pili chez L. lactis entraîne un changement de comportement des cellules résultant à des phénotypes particuliers. Nous avons pu l’associer à l’auto-agrégation des cellules en culture liquide, à la formation de biofilms hétérogènes et aériens, et à l’adhésion à la mucine gastrique de porc. Plus précisément, YhgE a été impliquée dans l’auto-agrégation et les biofilms atypiques, et une troisième piline, dont l’appartenance au pilus n’a pas été démontrée, semble aussi impliquée dans la production de biofilms atypiques. / Lactic acid bacteria (LAB), which are commonly used in food industry, are now being studied for their use in new applications such as biotherapeutic molecule delivery vehicules in human host or as live vaccines. Recently, surface protein delivery systems have been developed in Gram positive bacteria and one of them is based on enzymes, the sortases which covalently bind proteins to the cell wall. We used the LAB model, Lactococcus lactis, in order to study the sortases of these non-pathogenic bacteria. This work has functionally characterized the sortase A (SrtA) responsible for cell wall anchoring of at least five LPxTG proteins. A second sortase, from class C (SrtC), has been identified and characterized. We demonstrated the ability of L. lactis to produce pili on its surface that are polymerized by SrtC and cell wall anchored by SrtA. These pili result from polymerization of the YhgE major pilin and can be topped by the YhgD tip minor pilin. Pili production in L. lactis leads a change in cell behavior resulting in individual phenotypes. We were able to associate it with the self-aggregation of cells in liquid cultures, heterogeneous and aerial biofilm formation and bacterial adhesion onto pig gastric mucin. Specifically, YhgE was involved in both self-aggregation and atypical biofilm formation, while a third pilin, whose pilus membership has not been established, was also involved in the production of atypical biofilms.
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Antiagregantes plaquetários em perioperátorio de cirurgias não cardíacas e a tomada de decisão entre manter ou suspender / Antiplatelet agents in the perioperative period of non-cardiac surgeries and the decision making between maintaining or suspendingBorges, Juliana Maria Dantas Mendonça 15 June 2018 (has links)
Antiplatelet agents in the perioperative period of non-cardiac surgeries and the decision making between maintaining or suspending.Juliana Maria Dantas Mendonça Borges.2018
INTRODUCTION: In daily clinical practice there is the dilemma between maintaining or suspending antiplatelet agents in the perioperative period of non-cardiac surgeries. OBJECTIVES: To describe the prescribing pattern of antiplatelet agents in the perioperative period of noncardiac surgeries. METHODS: A cross-sectional study was carried out from October 2014 to October 2016 in a hospital. The study-dependent variable was the divergent therapy recommendations of the guidelines of the Brazilian Society of Cardiology (SBC). The independent variables included some characteristics, those responsible for the management and the causes of non adherence to the guidelines. Variables were included in the multivariate model. The analysis was based on the odds ratio (OR) and its respective 95% confidence interval (CI), estimated by logistic regression with a significance level of 5%. RESULTS: The sample consisted of adult patients undergoing non-cardiac surgeries using aspirin or clopidogrel (n = 161). The prescription of these drugs was in disagreement with that recommended by the guidelines in 80.75% of the sample. Surgeons performed the largest number (n = 63) of disagreeing guidelines. After the multivariate analysis, it was observed that patients with a higher level of education (OR = 0.24; 95% CI 0.07-0.78) and those with a previous episode of acute myocardial infarction (MI) (OR = 0,18; 95% CI 0.04-0.95), are more likely to use the therapy in agreement. CONCLUSION: Positive association between the educational level of the patients or previous history of AMI with the use of ASA and clopidogrel in the perioperative period of noncardiac surgeries. However, the divergences in the conduct reinforce the need to define internal protocols. / INTRODUÇÃO: Na prática clínica diária há o dilema entre manter ou suspender os antiagregantes plaquetários em perioperatório de cirurgias não cardíacas.
OBJETIVOS: Descrever o padrão de prescrição de antiagregantes plaquetários em periopetaratório de cirurgias não cardíacas.
MÉTODOS: Estudo transversal, realizado de outubro de 2014 a outubro de 2016 em hospital. A variável dependente do estudo foi a terapia divergente das recomendações das diretrizes da Sociedade Brasileira de Cardiologia (SBC). As variáveis independentes incluíram algumas características, os responsáveis pelo manejo e as causas de não adesão às diretrizes. As variáveis foram incluídas no modelo multivariado. A análise baseou-se no valor de oddsratio (OR) e seu respectivo intervalo de confiança (IC) de 95%, estimados por regressão logística com um nível de significância de 5%.
RESULTADOS: A amostra foi composta de pacientes adultos submetidos a cirurgias não cardíacas e que faziam uso de ácido acetilsalicílico (AAS) ou clopidogrel (n= 161). A prescrição destes medicamentos esteve em desacordo com o preconizado pelas diretrizes em 80,75% da amostra. Os cirurgiões realizaram o maior número (n=63) de orientações em desacordo. Após a análise multivariada, observou-se que os pacientes com nível de escolaridade superior (OR=0,24; IC95% 0,07-0,78) e aqueles com episódio prévio de infarto agudo do miocárdio (IAM) (OR=0,18; IC95% 0,04-0,95), possuem maior chance de utilizar a terapia em concordância.
CONCLUSÃO: Associação positiva entre o nível de escolaridade dos pacientes ou história prévia de IAM com o manejo do uso de AAS e clopidogrel em perioperatório de cirurgias não cardíacas. Porém, as divergências nas condutas reforçam a necessidade de definição de protocolos internos. / Aracaju
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Desenvolvimento de operadores de agrupamento por similaridade em SGBD relacionais / Development of similarity group operators in Relational DBMSNatan de Almeida Laverde 16 May 2018 (has links)
O operador de agrupamento e as funções de agregação são as principais ferramentas utilizadas para sumarizar dados em um Sistema de Gerenciamento de Base de Dados Relacionais (SGBDR). O operador de agrupamento funciona criando partições nos dados utilizando comparações por identidade, e permite que sejam aplicadas funções de agregação que retornam um único valor representando o grupo como um todo. Entretanto, para dados métricos, agrupamento utilizando identidade tem pouca utilidade. Neste caso, adotar o conceito de similaridade é frequentemente uma abordagem mais promissora. A literatura apresenta alguns operadores que podem agrupar os dados utilizando similaridade. Todos eles utilizam um limiar de valor de distância para atribuir os elementos aos grupos. No entanto, estes operadores não obtêm resultados satisfatórios quando a distribuição dos dados apresenta variações significativas na densidade de objetos em diferentes regiões do espaço. Para alcançar melhores resultados nestas situações, propusemos um novo operador que atribui os grupos utilizando uma eleição envolvendo grupos já atribuídos. Também propusemos generalizações, para os operadores existentes e propostos, para trabalhar com uma quantidade de vizinhos mais próximos e aproximação dos vizinhos mais próximos ao invés de um limiar de distância. Para possibilitar a inclusão destes operadores em SGBDR, propusemos uma extensão à Structured Query Language (SQL) e novas funções de agregação. Implementamos estes operadores em nosso framework em C++ usando a biblioteca Arboretum. Para avaliar os métodos propostos, analisamos tanto qualidade dos resultados quanto tempo de execução, utilizando conjuntos de dados reais e sintéticos. Os operadores propostos alcançaram melhores resultados quanto à qualidade de resultados, e mantiveram os tempos de execução similares. Os operadores que utilizam aproximação aos vizinhos mais próximos produziram resultados de qualidade similar quando comparados aos operadores que utilizando os vizinhos mais próximos, podendo ser executados em menor tempo que estes. / The grouping operator and aggregation functions are the primary tools used to summarize data inside a Relational Database Management Systems (RDBMS). The grouping operator works creating partitions in data using identity comparisons, and allow applying aggregation functions that return a single value that represent the entire group. However, for metric data, grouping by identity is seldom useful. In this case, adopting the concept of the similarity is often a better approach. The literature presents few operators that can group data using similarity. All of them use a distance threshold value to assign the elements in groups. However, these operators do not achieve satisfactory results when the data distribution present a significant variation in the density of objects in different regions of the space. To achieve better results in these situations, we have proposed a novel operator that assign groups using an election involving already assigned groups. We also proposed generalizations to existing and proposed operators to work with an amount of nearest neighbors and approximate neighbors instead of a distance threshold. To support these operators in RDBMS, we propose an extension to Structured Query Language (SQL) and new aggregation functions. Our proposed algorithms can run the proposed and existing operators. We implemented these operators in our framework in C++ using Arboretum library. To evaluate the proposed methods, we assess both results quality and the execution time, using both real and synthetic datasets. The proposed operators achieved better results comparing the quality and maintained similar executing time. The operators that use the approximate nearest neighbors produced similar quality results comparing with the operators that use the exact neighbors and can execute faster than that.
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