Dans les études épidémiologiques, les erreurs de mesure de l’exposition étudiée peuvent biaiser l’estimation des risques liés à cette exposition. Un grand nombre de méthodes de correction de l’effet de ces erreurs a été développé mais en pratique elles ont été rarement appliquées, probablement à cause du fait que leur capacité de correction et leur mise en œuvre sont peu maîtrisées. Une autre raison non moins importante est que, en l’absence de données répétées ou de données de validation, ces méthodes de correction exigent la connaissance détaillée des caractéristiques (taille, nature, structure et distribution) des erreurs de mesure. L’objectif principal de cette thèse est d’étudier l’impact de la prise en compte des erreurs de mesure dans les analyses du risque de décès par cancer du poumon associé à l’exposition au radon à partir de la cohorte française des mineurs d’uranium (qui ne dispose ni de données répétées, ni de données de validation). Les objectifs spécifiques étaient (1) de caractériser les erreurs de mesure associées aux expositions radiologiques (radon et ses descendants, poussières d’uranium et rayonnements gamma), (2) d’étudier l’impact des erreurs de mesure de l’exposition au radon et à ses descendants sur l’estimation de l’excès de risque relatif (ERR) de décès par cancer du poumon et (3) d’étudier et comparer la performance des méthodes de correction de l’effet de ces erreurs. La cohorte française des mineurs d’uranium comprend plus de 5000 individus exposés de manière chronique au radon et à ses descendants qui ont été suivis en moyenne pendant 30 ans. Les erreurs de mesure ont été caractérisées en prenant en compte l’évolution des méthodes d’extraction et de la surveillance radiologique des mineurs au fil du temps. Une étude de simulation basée sur la cohorte française des mineurs d’uranium a été mise en place pour étudier l’impact de ces erreurs sur l’ERR ainsi que pour comparer la performance des méthodes de correction. Les résultats montrent que les erreurs de mesure de l’exposition au radon et à ses descendants ont diminué au fil des années. Pour les premières années, avant 1970, elles dépassaient 45 % et après 1980 elles étaient de l’ordre de 10 %. La nature de ces erreurs a aussi changé au cours du temps ; les erreurs essentiellement de nature Berkson ont fait place à des erreurs de nature classique après la mise en place des dosimètres individuels à partir de 1983. Les résultats de l’étude de simulation ont montré que les erreurs de mesure conduisent à une atténuation de l’ERR vers la valeur nulle, avec un biais important de l’ordre de 60 %. Les trois méthodes de correction d’erreurs considérées ont permis une réduction notable mais partielle du biais d’atténuation. Un avantage semble exister pour la méthode de simulation extrapolation (SIMEX) dans notre contexte, cependant, les performances des trois méthodes de correction sont fortement tributaires de la détermination précise des caractéristiques des erreurs de mesure.Ce travail illustre l’importance de l’effet des erreurs de mesure sur les estimations de la relation entre l’exposition au radon et le risque de décès par cancer du poumon. L’obtention d’estimation de risque pour laquelle l’effet des erreurs de mesure est corrigé devrait s’avérer d’un intérêt majeur en support des politiques de protection contre le radon en radioprotection et en santé publique. / In epidemiological studies, measurement errors in exposure can substantially bias the estimation of the risk associated to exposure. A broad variety of methods for measurement error correction has been developed, but they have been rarely applied in practice, probably because their ability to correct measurement error effects and their implementation are poorly understood. Another important reason is that many of the proposed correction methods require to know measurement errors characteristics (size, nature, structure and distribution).The aim of this thesis is to take into account measurement error in the analysis of risk of lung cancer death associated to radon exposure based on the French cohort of uranium miners. The mains stages were (1) to assess the characteristics (size, nature, structure and distribution) of measurement error in the French uranium miners cohort, (2) to investigate the impact of measurement error in radon exposure on the estimated excess relative risk (ERR) of lung cancer death associated to radon exposure, and (3) to compare the performance of methods for correction of these measurement error effects.The French cohort of uranium miners includes more than 5000 miners chronically exposed to radon with a follow-up duration of 30 years. Measurement errors have been characterized taking into account the evolution of uranium extraction methods and of radiation protection measures over time. A simulation study based on the French cohort of uranium miners has been carried out to investigate the effects of these measurement errors on the estimated ERR and to assess the performance of different methods for correcting these effects.Measurement error associated to radon exposure decreased over time, from more than 45% in the early 70’s to about 10% in the late 80’s. Its nature also changed over time from mostly Berkson to classical type from 1983. Simulation results showed that measurement error leads to an attenuation of the ERR towards the null, with substantial bias on ERR estimates in the order of 60%. All three error-correction methods allowed a noticeable but partial reduction of the attenuation bias. An advantage was observed for the simulation-extrapolation method (SIMEX) in our context, but the performance of the three correction methods highly depended on the accurate determination of the characteristics of measurement error.This work illustrates the importance of measurement error correction in order to obtain reliable estimates of the exposure-risk relationship between radon and lung cancer. Corrected risk estimates should prove of great interest in the elaboration of protection policies against radon in radioprotection and in public health.

<p>The development of the metabolic syndrome (MetS) and cardiovascular diseases have been suggested to be influenced more by the quality than the amount of dietary fat. The FA composition of serum lipids may be used as biomarkers of dietary fat quality. FAs can, however, also be endogenously synthesized by lipogenic enzymes such as elongases and desaturases. Three desaturases are important in humans: Stearoyl-CoA-desaturase (SCD), ∆6-desaturase (D6D) and ∆5-desaturase (D5D) and surrogate measures of desaturase activities can be estimated as product-to-precursor FA ratios.</p><p>In this thesis, we demonstrated that high SCD, D6D and low D5D estimated activities predicted MetS 20 years later, as well as cardiovascular and total mortality during a maximum of 33.7 years. The relation between D5D and MetS was independent of lifestyle and BMI, while the relation between SCD, D6D and MetS was confounded by BMI. Serum proportions of palmitic (16:0), palmitoleic (16:1) and dihomo-γ-linoleic acids were higher and the serum proportion of linoleic acid (LA) lower at baseline in those individuals who developed MetS. Further, LA was inversely related to mortality, while palmitic, palmitoleic and dihomo-γ-linoleic acids were directly associated with mortality. We also demonstrated that a diet rich in saturated fat “induced” a similar serum FA pattern (including estimated desaturase activities) that was associated with MetS, cardiovascular disease and mortality. We also propose that the SCD ratio [16:1/16:0] might be a novel and useful marker of dietary saturated fat, at least in Western high-fat diets. Finally, genetic variations in the human SCD1 gene were linked to obesity and insulin sensitivity, results that agree with data in SCD1 deficient mice.</p><p>This thesis suggests that dietary fat quality and endogenous desaturation may play a role in the development of metabolic and cardiovascular diseases and the results support current dietary guidelines.</p>

The development of the metabolic syndrome (MetS) and cardiovascular diseases have been suggested to be influenced more by the quality than the amount of dietary fat. The FA composition of serum lipids may be used as biomarkers of dietary fat quality. FAs can, however, also be endogenously synthesized by lipogenic enzymes such as elongases and desaturases. Three desaturases are important in humans: Stearoyl-CoA-desaturase (SCD), ∆6-desaturase (D6D) and ∆5-desaturase (D5D) and surrogate measures of desaturase activities can be estimated as product-to-precursor FA ratios. In this thesis, we demonstrated that high SCD, D6D and low D5D estimated activities predicted MetS 20 years later, as well as cardiovascular and total mortality during a maximum of 33.7 years. The relation between D5D and MetS was independent of lifestyle and BMI, while the relation between SCD, D6D and MetS was confounded by BMI. Serum proportions of palmitic (16:0), palmitoleic (16:1) and dihomo-γ-linoleic acids were higher and the serum proportion of linoleic acid (LA) lower at baseline in those individuals who developed MetS. Further, LA was inversely related to mortality, while palmitic, palmitoleic and dihomo-γ-linoleic acids were directly associated with mortality. We also demonstrated that a diet rich in saturated fat “induced” a similar serum FA pattern (including estimated desaturase activities) that was associated with MetS, cardiovascular disease and mortality. We also propose that the SCD ratio [16:1/16:0] might be a novel and useful marker of dietary saturated fat, at least in Western high-fat diets. Finally, genetic variations in the human SCD1 gene were linked to obesity and insulin sensitivity, results that agree with data in SCD1 deficient mice. This thesis suggests that dietary fat quality and endogenous desaturation may play a role in the development of metabolic and cardiovascular diseases and the results support current dietary guidelines.

Cinque varietà di sorgo (Sorghum bicolor (L.) Moench) provenienti da Nigeria, Senegal, Burkina Faso e due dall’Italia, sono state caratterizzate per il loro profilo nutrizionale, analizzando la modulazione di due marcatori cellulari (contenuto in proteine totali e attività della GPx), il contenuto di fattori chelanti (tannini e fitati), l’attività fitasica e il contenuto, la bioaccessibilità e la biodisponibilità di ferro e zinco e analizzando l’impatto di due importanti processi alimentari, quali fermentazione e cottura. I risultati mostrano che sia la varietà sia il processo influenzano la maggior parte dei parametri. Tannini e fitati, elementi in traccia, contenuto proteico totale e il processo (soprattutto la fermentazione) sono modulati dalla varietà. La fermentazione riduce il contenuto di fattori chelanti e aumenta l’attività fitasica, incrementando, così, la biodisponibilità degli elementi in traccia; mentre la cottura non ha un impatto significativo. D’altra parte, la fermentazione ha un impatto negativo su entrambi i marcatori cellulari, mentre la cottura solo sul contenuto proteico totale. Le varietà africane, soprattutto quella dal Senegal, hanno mostrato il migliore profilo nutrizionale, mentre, globalmente, le italiane il peggiore. I risultati indicano che la selezione di varietà e di adeguati processi alimentari può avere un impatto significativo sul valore nutrizionale del sorgo. / Five sorghum cultivars (Sorghum bicolor (L.) Moench) from Nigeria, Senegal, Burkina Faso and Italy (two), were characterized for their nutritional values by analysing the modulation of cellular functional markers (total protein content and GPx activity), chelating factors (iron-binding phenolic groups and phytates) content and phytase activity, as well as iron and zinc content, bioaccessibility and bioavailability, also considering the impact of food processing methods as fermentation and cooking. The results revealed that both variety and food processing affect most of the tested parameters. Chelating factors, trace elements, cellular total protein content, as well as the effect of processing (mainly fermentation) were modulated by variety. Fermentation decreased chelating factors content, as well as increased phytase activity, leading to enhancement of iron and zinc estimated bioavailability, whereas cooking had no substantial impact. On the other hand, fermentation process had a negative impact on both cellular functional markers while cooking only on the cellular total protein content. The African varieties, particularly the Senegal one, showed the most promising nutritional profile, whereas the two Italian varieties overall showed a poor one. The results indicate that selection of traditional varieties and processing methods can have a significant impact on parameters relevant to sorghum nutritional value.

Kostnaderna för den arbetsrelaterade ohälsan i form av sjukskrivningar och produktionsbortfall är stora. De arbetsorganisatoriska faktorer som har störst betydelse för ohälsan är arbetsmiljön och ledarskapet. Ledningen är den faktor som i sin tur har möjlighet till påverkan på arbetsmiljöns utformning. Detta betyder att ledaren är den faktor som har störst möjlighet att påverka medarbetarens hälsa. Enligt vissa teorier kan ledarskapsbeteendet direkt kopplas till medarbetarnas hälsa. Andra studier kopplar ledarskapsbeteendet till medarbetarnas arbetstillfredsställelse. Syftet med denna uppsats har varit att undersöka olika ledarbeteendens påverkan på medarbetarnas arbetstillfredsställelse och hälsa. Syftet har även varit att utreda om det finns något koppling mellan arbetstillfredsställelse och hälsa, det vill säga en mekanism mellan ledarskapsbeteende och medarbetarnas hälsa. För att undersöka detta har uppsatsen analyserat kvantitativa data från undersökningen ”Arbetsmiljömärkta arbetsplatser” eller  ”Attraktiva arbetsplatser i Jämtlands län”. Det teoretiska resonemang som låg till grund för framställningen omfattade olika ledarbeteenden, medarbetarens behov, hälsa och välbefinnande, arbetstillfredsställelse samt ledarens och medarbetarens interaktion via krav, kontroll och stöd. Resultatet i min studie visade att en ledare genom sitt beteende påverkar sina medarbetares hälsa direkt och/eller indirekt genom mekanismen arbetstillfredsställelse. / The costs of work-related illness, such as sick-leaves and drops in production, are considerable. The work organizational factors with the greatest influence over illness are workplace environment and leadership. Management, in turn, is the factor with the possibility of influencing the design of the workplace environment. This means that the leader is the one with the greatest opportunity to influence the health of co-workers. According to some theories, leader behavior may directly be connected to the health of co-workers. Other studies discern a link between leadership behavior and work satisfaction of co-workers. The purpose of this paper has been to investigate the influence of different types of leadership on the work satisfaction and health of co-workers. The essay also aimed at examining whether or not a link exists between work satisfaction and health, i.e. a mechanism between leadership behavior and health of co-workers. In order to carry out this study, quantitative data has been analyzed from the reports “Arbetsmiljömärkta arbetsplatser” or “Attraktiva arbetsplatser i Jämtlands län”. The theoretical reasoning that came to constitute a basis for the essay comprised different types of leadership, co-workers needs, health and well-being, work satisfaction and finally leader and co-worker interaction through demands, control and support. The results of my study indicated that leader behavior directly influenced the health of co-workers and/or indirectly through the mechanism work satisfaction.

Kostnaderna för den arbetsrelaterade ohälsan i form av sjukskrivningar och produktionsbortfall är stora. De arbetsorganisatoriska faktorer som har störst betydelse för ohälsan är arbetsmiljön och ledarskapet. Ledningen är den faktor som i sin tur har möjlighet till påverkan på arbetsmiljöns utformning. Detta betyder att ledaren är den faktor som har störst möjlighet att påverka medarbetarens hälsa. Enligt vissa teorier kan ledarskapsbeteendet direkt kopplas till medarbetarnas hälsa. Andra studier kopplar ledarskapsbeteendet till medarbetarnas arbetstillfredsställelse. Syftet med denna uppsats har varit att undersöka olika ledarbeteendens påverkan på medarbetarnas arbetstillfredsställelse och hälsa. Syftet har även varit att utreda om det finns något koppling mellan arbetstillfredsställelse och hälsa, det vill säga en mekanism mellan ledarskapsbeteende och medarbetarnas hälsa. För att undersöka detta har uppsatsen analyserat kvantitativa data från undersökningen ”Arbetsmiljömärkta arbetsplatser” eller  ”Attraktivaarbetsplatser i Jämtlands län”. Det teoretiska resonemang som låg tillgrund för framställningen omfattade olika ledarbeteenden, medarbetarens behov, hälsa och välbefinnande, arbetstillfredsställelse samt ledarens och medarbetarens interaktion via krav, kontroll och stöd. Resultatet i min studie visade att en ledare genom sitt beteende påverkar sina medarbetares hälsa direkt och/eller indirekt genom mekanismen arbetstillfredsställelse. / The costs of work-related illness, such as sick-leaves and drops in production, are considerable. The work organizational factors with the greatest influence over illness are workplace environment and leadership. Management, in turn, is the factor with the possibility of influencing the design of the workplace environment. This means that the leader is the one with the greatest opportunity to influence the health of co-workers. According to some theories, leader behavior may directly be connected to the health of co-workers. Other studies discern a link between leadership behavior and work satisfaction of co-workers. The purpose of this paper has been to investigate the influence of different types of leadership on the work satisfaction and health of co-workers. The essay also aimed at examining whether or not a link exists between work satisfaction and health, i.e. a mechanism between leadership behavior and health of co-workers. In order to carry out this study, quantitative data has been analyzed from the reports “Arbetsmiljömärkta arbetsplatser” or “Attraktiva arbetsplatser i Jämtlands län”. The theoretical reasoning that came to constitute a basis for the essay comprised different types of leadership, co-workers needs, health and well-being, work satisfaction and finally leader and co-worker interaction through demands, control and support. The results of my study indicated that leader behavior directly influenced the health of co-workers and/or indirectly through the mechanism work satisfaction.

在生態學、生物學、和比較文學的研究中，物種個數通常是評估生物多樣性的重要指標，單一群落物種數的估計已有非常豐富的相關研究。較為知名者包括Good (1953)提出未出現物種的機率，作為估計物種數的參考，往後Good的想法被大量延伸，推演出不少新的估計方法，像是Burnham and Overton (1978)的Jackknife估計法，Chao and Lee (1992)利用涵蓋機率的估計。相對而言，兩群落共有物種數的研究較少，現有研究中較為知名的有Chao et al. (2000)的估計式。 本研究延伸Good想法，探討Jackknife估計法在兩群落的應用，以出現一次的共有物種（一階Jackknife估計），推估未出現共有物種機率，並且仿造Burnham and Overton的想法，建立共有物種數的估計值及變異數。本文除了以電腦模擬，也使用實例（包括：金庸武俠小說、台灣野生水鳥、巴拿馬螃蟹和巴洛科羅拉多森林）檢驗本文的Jackknife估計法，利用涵蓋機率角度發現抽出某特定比例樣本時，估計值涵蓋母體共有物種數之機率值達到九成以上，且也與Chao提出的估計值比較。 / The number of species is frequently used to measure the biodiversity of a population in ecology, biology, and comparative literature. There are quite a lot of studies related to estimating the number of species. Among these studies, Good (1953) proposed a famous estimate (Turing’s estimate) for the probability of unseen species. Subsequently, many methods have been proposed for estimating the number of species based on Good’s idea. For example, the Jackknife estimator by Burnham and Overton (1978) and sample coverage probability by Chao and Lee (1992) are two famous estimates for the number of species. In contrast, there are not many studies for the number of shared species in two communities, and Chao et al. (2000) is probably the only one. This article extends Good’s idea and the Jackknife method to estimate the number of shared species in two communities. Similar to Burnham and Overton, we establish the estimate and its estimated variance, based on the number of species appearing exactly once. We also use computer simulation and real data sets (Jin-Yong martial arts novels, Taiwan wild birds, Panama crustacean, and Barro Colorado Island forest) to evaluate the proposed method. We found that the coverage probability for confidence interval covering the true number of shared species is more than 90%. In addition, we compare the proposed method with Chao’s method.

The multi-armed bandit (MAB) problem provides a convenient abstraction for many online decision problems arising in modern applications including Internet display advertising, crowdsourcing, online procurement, smart grids, etc. Several variants of the MAB problem have been proposed to extend the basic model to a variety of practical and general settings. The sleeping multi-armed bandit (SMAB) problem is one such variant where the set of available arms varies with time. This study is focused on analyzing the efficacy of the Thompson Sampling algorithm for solving the SMAB problem. Any algorithm for the classical MAB problem is expected to choose one of K available arms (actions) in each of T consecutive rounds. Each choice of an arm generates a stochastic reward from an unknown but fixed distribution. The goal of the algorithm is to maximize the expected sum of rewards over the T rounds (or equivalently minimize the expected total regret), relative to the best fixed action in hindsight. In many real-world settings, however, not all arms may be available in any given round. For example, in Internet display advertising, some advertisers might choose to stay away from the auction due to budget constraints; in crowdsourcing, some workers may not be available at a given time due to timezone difference, etc. Such situations give rise to the sleeping MAB abstraction. In the literature, several upper confidence bound (UCB)-based approaches have been proposed and investigated for the SMAB problem. Our contribution is to investigate the efficacy of a Thomp-son Sampling-based approach. Our key finding is to establish a logarithmic regret bound, which non-trivially generalizes a similar bound known for this approach in the classical MAB setting. Our bound also matches (up to constants) the best-known lower bound for the SMAB problem. Furthermore, we show via detailed simulations, that the Thompson Sampling approach in fact outperforms the known algorithms for the SMAB problem.

Annotation Erosion is a chronic problem in both agricultural and nonagricultural land. Its has an inconsiderable effect on overall stability of landscape. In the case of farming management on agricultural soils the risk of erosive processes increases severalfold. In foothill and mountain areas with dominance of slopes and hills the soil loss during higher maximum 24hrs N-rainfalls can reach up to several tons per hectare. This work deals with the evaluation of soil erosion vulnerability in selected catchment {--} Ostrice catchment {--} in the Lipno reservoir area. The CN method was used for calculations and following evaluation of soil loss.

Um dos métodos mais utilizados para proteção contra a corrosão de aços comuns consiste na proteção catódica com revestimentos metálicos eletroquimicamente mais ativos, que estes. Os revestimentos de zinco são os mais usados para este tipo de proteção. De forma a protegerem o substrato, estes revestimentos devem atuar como anodos de sacrifício, sofrendo corrosão e transformando o substrato de aço em catodo. Todavia, não é de interesse, que o revestimento de zinco apresente altas taxas de corrosão de forma que a proteção contra a corrosão conferida ao aço seja duradoura. Uma das formas mais empregadas para reduzir a velocidade de corrosão do revestimento de zinco é por meio de tratamentos da superfície, por exemplo, por tratamentos de conversão. Os tratamentos de conversão mais eficientes são os que utilizam e geram rejeitos, que contêm íons de cromo hexavalente. Todavia, estes íons são carcinogênicos e tóxicos e, dessa forma, os processos que os utilizam em alguma etapa do tratamento, vêm sofrendo crescentes restrições, já sendo proibidos em países com leis ambientais mais rígidas. Esta é a razão para o crescente interesse e grande investimento em pesquisa tratamentos, que possam resultar em revestimentos com potencialidade para substituir, de forma eficiente e efetiva o uso do cromo hexavalente. Este foi o objetivo do presente trabalho. Neste estudo, foi investigado o efeito de tratamentos, que resultam em camadas de conversão na presença de ácido oxálico e na proteção contra a corrosão da superfície do zinco. Camadas de conversão foram obtidas por imersão de amostras de zinco em soluções de ácido oxálico (ácido etanodióico) com diferentes concentrações. Todas as soluções de tratamento apresentaram elevada acidez e resultaram em ataque da superfície de zinco com formação de revestimento de conversão com diferentes características. Ensaios preliminares de névoa salina foram então realizados para investigar a proteção conferida pelo sistema revestimento de conversão-verniz contra a corrosão do substrato de zinco. Estes ensaios foram decisivos para a escolha da faixa de concentração do banho de conversão com maior potencial para formação de revestimentos de conversão protetores. Os resultados deste ensaio e os de espectroscopia de impedância eletroquímica mostraram que tratamentos em soluções com composição superiores a 10-1 M de ácido oxálico resultaram em camadas muito defeituosas, nas quais o ataque localizado do substrato metálico é favorecido, sendo obtidas impedâncias menores que a superfície do zinco sem qualquer tratamento. Os resultados de XPS mostraram, que os revestimentos de conversão formados em soluções de ácido oxálico na faixa de 10-3 M a 10-1 M são compostos de oxalato de zinco e produtos de corrosão do zinco, especificamente ZnO, Zn (OH)2, e ZnCO3. Já a concentração de 10-1 M de ácido oxálico foi a, que produziu os resultados mais promissores com a formação de um revestimento, que conferiu proteção mais duradoura à superfície do zinco entre os obtidos. As espessuras médias das camadas de conversão de oxalato de zinco formadas em soluções com 10-1 M e 1 M de ácido oxálico, estimadas por FIB, foram respectivamente 600 nm e 300 nm, o que mostra que a concentração de 1 M de ácido causou intenso ataque corrosivo da superfície, enquanto a camada formada em meio com 10-1 M permitiu a deposição de camada mais espessa e mais protetora contra a corrosão do substrato. Os resultados de XPS indicaram a degradação da camada de oxalato de zinco com o tempo de ensaio, porém o ataque desta ao longo do ensaio de corrosão, resulta na formação de simonkolleite, identificada por difração de raios X, para períodos mais longos do ensaio de corrosão, no caso do revestimento formado em solução com 10-1 M em comparação a 1M. A simonkolleite atua por efeito barreira bloqueando os defeitos/porosidade da camada. O crescente acúmulo destes produtos de corrosão com a continuidade do processo corrosivo e a aderência destes ao substrato metálico foi indicada para superfície tratada em solução com 10-1 M de ácido oxálico. Finalmente, foi proposto um modelo para interação entre o revestimento de conversão de oxalato de zinco e os produtos de corrosão em que a retenção dos produtos de corrosão na superfície faz com, que a camada na superfície se torne mais espessa e mais compacta com o tempo de exposição ao ensaio de corrosão. Estas observações explicam o aumento de impedância observado com o tempo de ensaio nesta condição. Os resultados obtidos permitiram concluir, que o revestimento de conversão de oxalato de zinco formado em solução com 10-1 M de ácido oxálico resulta em proteção efetiva do substrato metálico além de apresentar boa aderência com camada de verniz. Estes resultados indicam potencialidade deste tratamento como preparação de superfícies de zinco, que serão recobertas com revestimentos orgânicos (tintas, vernizes ou lacas). / One of the most used methods for protection of common steels is the cathodic protection by galvanic coupling with metallic coatings electrochemically more active than these. Zinc coatings are the most commonly used for this type of protection. In order to protect the metallic substrate, these coatings must act as sacrificial anodes, corroding themselves and converting the steel substrate into cathode. However, it is not appropriate that the zinc coating presents high corrosion rates, so that the corrosion protection conferred to the steel is long-lasting. One of the most commonly employed methods of reducing the corrosion rate of zinc coatings is by surface treatments, such as, conversion treatments. The most efficient conversion treatments to date are those that use hexavalent chromium ions or generate residues containing these ions. However, hexavalent chromium is carcinogenic and toxic and, therefore, the processes that involve their use at some stage of the treatment, are under increasing restrictions, and have already been prohibited in developed countries. This is the reason for the growing interest and great investment in research studies in search for treatments that may result in coatings with the potential to efficiently and effectively replace the use of hexavalent chromium. This was the objective of the present study. In this study, the effect of treatments in oxalic acid solutions that resulted in conversion layers on the corrosion protection of zinc surface has been investigated. Conversion layers were obtained by immersion of zinc samples in solutions of oxalic acid (ethanedioic acid) with different concentrations. All the treatment solutions presented high acidity and resulted in attack of zinc surface and formation of conversion coatings of different characteristics. A layer of varnish was applied and preliminary salt spray tests were then carried out to investigate the corrosion protection provided by the system conversion coating -varnish to the zinc substrate. These tests were decisive for the choice of the conversion bath composition range with greater potentialities for the formation of protective conversion coatings. The results of the salt spray test and of electrochemical impedance spectroscopy (EIS) showed that treatments in solutions with compositions greater than 10-1 M of oxalic acid resulted in very defective conversion layers in which the localized attack of the metallic substrate is favored, and lower impedances than the zinc surface without any treatment were obtained for surfaces treated in these solution. The XPS results showed that conversion coatings formed in oxalic acid solutions in the range of 10-3 M to 10-1 M are composed of zinc oxalate and zinc corrosion products, specifically ZnO, Zn (OH)2, and ZnCO3. The concentration related to the most promising results was 10-1 M and in this solution, the coating formed that promoted the longer lasting protection of the zinc surface among those obtained. The average thicknesses of the zinc oxalate conversion layers formed in solutions with 10-1 M and 1 M of oxalic acid, estimated by FIB, were respectively 600 nm and 300 nm. This result showed that in 1 M of oxalic acid an intense corrosive attack of the zinc surface occurred, while the layer formed in 10-1 M was thicker and more protective against substrate corrosion. The XPS results indicated degradation of the zinc oxalate layer formed in 10-1 M solution with time of exposure to the test solution, but for the protection of the coating lasted for longer periods, comparatively to that formed in 1M solution, once the attack of the first film resulted in formation of simonkolleite, which was identified by X-ray diffraction. Simonkolleite acts by barrier effect blocking defects / porosity in the conversion layer. The increasing accumulation of corrosion products with test time and their adhesion to the metallic substrate was indicated for surface treated in solution with 10-1 M of oxalic acid. Finally, a model has been proposed for the interaction between the zinc oxalate conversion coating and the corrosion products in which the retention of these products on the surface is promoted by the conversion coating and the surface layer becomes thicker and more compact with time of exposure. These observations explain the increased impedance observed with the test time associated to this coating. The obtained results allowed concluding that the conversion coating of zinc oxalate formed in solution with 10-1 M of oxalic acid results in effective protection of the metallic substrate besides promoting good adhesion with a layer of varnish. These results indicate the potential of this treatment as preparation of zinc surfaces that will be covered with organic coatings (paints, varnishes or lacquers).