Derivative-based global sensitivity measures: general links with Sobol' indices and numerical tests

The estimation of variance-based importance measures (called Sobol' indices) of the input variables of a numerical model can require a large number of model evaluations. It turns to be unacceptable for high-dimensional model involving a large number of input variables (typically more than ten). Recently, Sobol and Kucherenko have proposed the Derivative-based Global Sensitivity Measures (DGSM), defined as the integral of the squared derivatives of the model output, showing that it can help to solve the problem of dimensionality in some cases. We provide a general inequality link between DGSM and total Sobol' indices for input variables belonging to the class of Boltzmann probability measures, thus extending the previous results of Sobol and Kucherenko for uniform and normal measures. The special case of log-concave measures is also described. This link provides a DGSM-based maximal bound for the total Sobol indices. Numerical tests show the performance of the bound and its usefulness in practice

Kernel-based measures of association between inputs and outputs based on ANOVA

ANOVA decomposition of function with random input variables provides ANOVA functionals (AFs), which contain information about the contributions of the input variables on the output variable(s). By embedding AFs into an appropriate reproducing kernel Hilbert space regarding their distributions, we propose an efficient statistical test of independence between the input variables and output variable(s). The resulting test statistic leads to new dependent measures of association between inputs and outputs that allow for i) dealing with any distribution of AFs, including the Cauchy distribution, ii) accounting for the necessary or desirable moments of AFs and the interactions among the input variables. In uncertainty quantification for mathematical models, a number of existing measures are special cases of this framework. We then provide unified and general global sensitivity indices and their consistent estimators, including asymptotic distributions. For Gaussian-distributed AFs, we obtain Sobol' indices and dependent generalized sensitivity indices using quadratic kernels

Diversity in secondary metabolites including mycotoxins from strains of aspergillus section nigri isolated from raw cashew nuts from Benin, West Africa

Open access JournalIn a previous study, raw cashew kernels were assayed for the fungal contamination focusing on strains belonging to the genus Aspergillus and on aflatoxins producers. These samples showed high contamination with Aspergillus section Nigri species and absence of aflatoxins. To investigate the diversity of secondary metabolites, including mycotoxins, the species of A. section Nigri may produce and thus threaten to contaminate the raw cashew kernels, 150 strains were isolated from cashew samples and assayed for their production of secondary metabolites using liquid chromatography high resolution mass spectrometry (LC-HRMS). Seven species of black Aspergilli were isolated based on morphological and chemical identification: A. tubingensis (44%), A. niger (32%), A. brasiliensis (10%), A. carbonarius (8.7%), A. luchuensis (2.7%), A. aculeatus (2%) and A. aculeatinus (0.7%). From these, 45 metabolites and their isomers were identified. Aurasperone and pyranonigrin A, produced by all species excluding A. aculeatus and A. aculeatinus, were most prevalent and were encountered in 146 (97.3%) and 145 (95.7%) isolates, respectively. Three mycotoxins groups were detected: fumonisins (B2 and B4) (2.7%) ochratoxin A (13.3%), and secalonic acids (2%), indicating that these mycotoxins could occur in raw cashew nuts. Thirty strains of black Aspergilli were randomly sampled for verification of species identity based on sequences of β-tubulin and calmodulin genes. Among them, 27 isolates were positive to the primers used and 11 were identified as A. niger, 7 as A. tubingensis, 6 as A. carbonarius, 2 as A. luchuensis and 1 as A. welwitschiae confirming the species names as based on morphology and chemical features. These strains clustered in 5 clades in A. section Nigri. Chemical profile clustering also showed also 5 groups confirming the species specific metabolites production

Derivative based global sensitivity measures

The method of derivative based global sensitivity measures (DGSM) has recently become popular among practitioners. It has a strong link with the Morris screening method and Sobol' sensitivity indices and has several advantages over them. DGSM are very easy to implement and evaluate numerically. The computational time required for numerical evaluation of DGSM is generally much lower than that for estimation of Sobol' sensitivity indices. This paper presents a survey of recent advances in DGSM concerning lower and upper bounds on the values of Sobol' total sensitivity indices $S\_{i}^{tot}$. Using these bounds it is possible in most cases to get a good practical estimation of the values of $S\_{i}^{tot}$. Several examples are used to illustrate an application of DGSM

Derivative based global sensitivity measures

International audienceThe method of derivative based global sensitivity measures (DGSM) has recently become popular among practitioners. It has a strong link with the Morris screening method and Sobol' sensitivity indices and has several advantages over them. DGSM are very easy to implement and evaluate numerically. The computational time required for numerical evaluation of DGSM is generally much lower than that for estimation of Sobol' sensitivity indices. This paper presents a survey of recent advances in DGSM concerning lower and upper bounds on the values of Sobol' total sensitivity indices $S_{i}^{tot}$. Using these bounds it is possible in most cases to get a good practical estimation of the values of $S_{i}^{tot}$. Several examples are used to illustrate an application of DGSM

Déterminants des migrations de l’Afrique vers l’Europe : du court séjour à la migration durable et / ou irrégulière

International migration is often seen as a single, one-way movement from a country of origin to a host country. In contrast to this unidirectional view of migration, this thesis focuses on the articulation between temporary and long-term migration in the context of migration between Africa and Europe. More specifically, it focuses on the individual and contextual factors that explain why movements supposedly limited in time (called temporary) are transformed into long stays. In this research, temporary travel is approached from two perspectives: duration and law. In one case [1st empirical article], the aim is to study to what extent and for what reasons occasional stays (lasting less than one year) become the precursors of a sustainable settlement in Europe (for a period of at least one year). In the other case [2nd and 3rd empirical articles], the aim is to study how and why stays designed as temporary from a legal point of view (cases where migrants have a non-permanent right of residence) are transformed into irregular long-term stays. The thesis adopts a comparative approach that focuses on contextual effects in both three African countries of origin (Democratic Republic of Congo, Ghana and Senegal) and six European countries of destination (Belgium, United Kingdom, Netherlands, France, Italy and Spain), with a particular focus on migration policy changes. It draws on three international databases: on the one hand, the individual biographical data of the MAFE project (Migrations between Africa and Europe) and, on the other hand, two contextual databases containing a coded description of migration policy changes of the "Immigration Policy" and "Temporary vs permanent migration" projects, and the "Determinants of International Migration: A Theoretical and Empirical Assessment of Policy, Origin and Destination Effects" (DEMIG) project. The statistical methods used are, on the one hand, descriptive statistics, in particular Kaplan-Meier curves and bivariate analysis methods and, on the other hand, explanatory models, in particular discrete time risk and duration models and the logit model. In the first article, it appears that short-term stay has a positive effect on long-term migration for the three sub-Saharan flows considered, although this effect is much greater for Congolese than for Ghanaians and Senegalese. The effect of short stay migration also depends on the period for Congolese migrants, while this interaction is not significant for Senegalese migrants and Ghanaian migrants, which indicates not only the context of the country of origin modulates the effect of the short stay on sustainable migration, but also the variation of the context over time within the same country of origin can modify the relationship between short stay and long term migration. In addition, it is noted that the level of education, land and house ownership, unemployment in the country of origin, social networks and studies in Europe seem to favour the relationship between short and long stays, but economic activity and employment in the countries of origin seem to have the opposite effect. The second article revealed that the risk of being in an irregular situation was increased in periods when migration policies were becoming increasingly strict. The influence of the entry period is very clear for Ghanaian and Senegalese migrants, but the risk of being in an irregular situation decreased in the 1990s and 2000s among Congolese migrants, suggesting that migrants from a country in conflict benefit from some protection against irregularity. The risk of being in an irregular situation is higher in recent immigration countries (Italy and Spain) than in traditional immigration countries (France and the United Kingdom). The irregularity also depends on the individual characteristics and circumstances of departure for Europe. The third article unexpectedly revealed that only policies aimed at limiting entry appear to have a significant effect on the transition to irregularity of Senegalese migrants already legally entering France, Italy and Spain. This result suggests that when policies to control entry become more stringent, migrants no longer dare to leave for fear of not being able to return. Other contextual elements also influence the irregularity of migrants: a negative effect of Senegal's annual GDP growth on the transition to irregularity (immigrants would choose to return to the country to work, thus avoiding irregularity), but a positive effect of the host country's annual GDP growth on the transition to irregularity (they would remain there to benefit from growth despite irregularity).La migration internationale est souvent considérée comme un mouvement unique et unidirectionnel d’un pays d’origine vers un pays d’accueil. À l’encontre de cette vision unidirectionnelle des migrations, cette thèse s’intéresse à l’articulation entre les migrations temporaires et celles de longues durées, dans le contexte des migrations entre l’Afrique et l’Europe. Plus spécifiquement, elle s’intéresse aux facteurs, individuels et contextuels, qui expliquent que des déplacements supposés limités dans le temps (dits temporaires) se transforment en séjours de longues durées. Dans cette recherche, les déplacements temporaires sont abordés de deux points de vue : celui de la durée et celui du droit. Dans un cas [1er article empirique], il s’agit d’étudier dans quelle mesure et pour quelles raisons des séjours ponctuels (d’une durée inférieure à un an) deviennent les précurseurs d’une installation durable en Europe (pour une durée d’un an au moins). Dans l’autre cas [2ème et 3ème articles empiriques], il s’agit d’étudier comment et pourquoi des séjours conçus comme temporaires du point de vue légal (cas où les migrants ont un droit de séjour non permanent) se transforment en séjours durables irréguliers. La thèse adopte une approche comparative qui permet de s’intéresser aux effets de contexte à la fois dans trois pays africains d’origine (République Démocratique du Congo, Ghana et Sénégal) et dans six pays européens de destination (Belgique, Royaume-Uni, Pays-Bas, France, Italie et Espagne), avec une attention particulière pour les changements de politiques migratoires. Elle tire parti de trois bases de données internationales : d’une part, les données biographiques individuelles du projet MAFE (Migrations entre l’Afrique et l’Europe) et, d’autre part, de deux bases de données contextuelles qui contiennent une description codée des changements de politiques migratoires des projets « Immigration Policy » et « Temporary vs permanent migration », et du projet « Determinants of International Migration : A Theoretical and Empirical Assessment of Policy, Origin and Destination Effects » (DEMIG). Les méthodes statistiques utilisées sont, d’une part, les statistiques descriptives, notamment les courbes de Kaplan-Meier et les méthodes d’analyses bivariées et, d’autre part, les modèles explicatifs, en particulier les modèles de risque et de durée en temps discrets et le modèle logit. Dans le premier article, il ressort que le séjour de courte durée a un effet positif sur la migration de longue durée pour les trois flux subsahariens considérés, bien que cet effet soit beaucoup plus important pour les Congolais que les Ghanéens et les Sénégalais. L’effet d’une migration de court séjour dépend par ailleurs de la période pour les migrants congolais, alors que cette interaction n’est pas significative pour les migrants sénégalais et les migrants ghanéens, ce qui indique non seulement le contexte du pays d’origine module l’effet du court séjour sur la migration durable, mais aussi la variation du contexte dans le temps au sein d’un même pays d’origine peut modifier la relation entre le séjour de courte durée et la migration de longue durée. En outre, on note que le niveau d’éducation, la possession de terrain et de maison, le chômage dans le pays d’origine, les réseaux sociaux et les études en Europe semblent favoriser la relation entre les séjours court et long, mais l’activité économique et l’emploi dans les pays d’origine semblent avoir un effet contraire. Le deuxième article a révélé que le risque d’être en situation irrégulière était accru dans les périodes où les politiques migratoires devenaient de plus en plus strictes. L’influence de la période d’entrée est très claire pour les migrants ghanéens et sénégalais, mais le risque d’être en situation irrégulière a diminué dans les années 1990 et les années 2000 chez les migrants congolais, ce qui semble indiquer que les migrants issus d’un pays en conflit bénéficient d’une certaine protection face à l’irrégularité. Le risque d’être en situation irrégulière est plus élevé dans les pays d’immigration récents (l’Italie et l’Espagne) que dans les pays d’immigration traditionnels (France et Royaume-Uni). L’irrégularité dépend également des caractéristiques individuelles et des circonstances de départ pour l’Europe. Le troisième article a révélé, de manière inattendue, que seules les politiques destinées à limiter les entrées semblent avoir un effet significatif sur la transition vers l’irrégularité des migrants sénégalais déjà entrés légalement en France, en Italie et en Espagne. Ce résultat suggère que lorsque les politiques visant à contrôler les entrées se durcissent, les migrants n’osent plus sortir par peur de ne plus être capables de rentrer à nouveau. D’autres éléments contextuels influencent aussi l’irrégularité des migrants : un effet négatif de la croissance annuelle du PIB du Sénégal sur la transition vers l’irrégularité (les immigrants choisiraient de retourner au pays pour y travailler, évitant ainsi l’irrégularité), mais un effet positif de la croissance annuelle du PIB du pays d’accueil sur la transition vers l’irrégularité (ils y resteraient pour profiter de la croissance malgré l’irrégularité)

Diversity in Secondary Metabolites Including Mycotoxins from Strains of <i>Aspergillus </i>Section <i>Nigri </i>Isolated from Raw Cashew Nuts from Benin, West Africa

<p>In a previous study, raw cashew kernels were assayed for the fungal contamination focusin on strains belonging to the genus Aspergillus and on aflatoxins producers. These sample showed high contamination with Aspergillus section Nigri species and absence o aflatoxins. To investigate the diversity of secondary metabolites, including mycotoxins, th species of A. section Nigri may produce and thus threaten to contaminate the raw cashe kernels, 150 strains were isolated from cashew samples and assayed for their productio of secondary metabolites using liquid chromatography high resolution mass spectrometr (LC-HRMS). Seven species of black Aspergilli were isolated based on morphological an chemical identification: A.Tubingensis (44%), A. niger (32%), A. brasiliensis (10%), A. carbonariu (8.7%), A. luchuensis (2.7%), A. aculeatus (2%) and A. aculeatinus (0.7%). Fro these, 45 metabolites and their isomers were identified. Aurasperone and pyranonigrin A produced by all species excluding A. aculeatus and A. aculeatinus, were most prevalen and were encountered in 146 (97.3%) and 145 (95.7%) isolates, respectively. Three mycotoxin groups were detected: fumonisins (B2 and B4) (2.7%) ochratoxin A (13.3%), an secalonic acids (2%), indicating that these mycotoxins could occur in raw cashew nuts Thirty strains of black Aspergilli were randomly sampled for verification of species identit based on sequences of β-Tubulin and calmodulin genes. Among them, 27 isolates wer positive to the primers used and 11 were identified as A. niger, 7 as A.Tubingensis, 6 as A carbonarius, 2 as A. luchuensis and 1 as A. welwitschiae confirming the species names a based on morphology and chemical features. These strains clustered in 5 clades in A. sectio Nigri. Chemical profile clustering also showed also 5 groups confirming the speciespecific metabolites production.</p

Epidemiology of Use of a Traditional Spirit “Sodabi” in the General Population of Togo

The purpose of this paper is to evaluate the profile of sodabi consumption in the Togolese population. This transverse descriptive study was conducted over a nine month period from June 9, 2013 to March 9, 2014, throughout the five regions of Togo. Findings demonstrated a clear profile of 2388 sodabi drinkers. 1672 (70.02%) men and 716 (29.98%) women. Prevalence was 62.45% in the population studied. Mean age was 35.3 years. Almost all subjects interrogated (98.48%) were togolese nationals. The study included the following ethnic and regional groups, the Kabyè-Tem ethnic group (43.59%) and the Paragourma-Akan groups (23.50%) were the most represented among the subjects interrogated. More than a third (25.67%) of subjects interviewed was unemployed with a higher unemployment rate in the Maritime region and Lomé Commune (37.16%). Most of the people interrogated (49.66%) were living as couples (married or cohabiting). 4.06% of subjects drank sodabi only. 51.40% of drinkers abused sodabi (40.59% men against 10.81% women). The prevalence of noxious alcohol use was high (12.35%) among unemployed participants. 25.51% of drinkers visited drinking establishments once a week and 22.10% almost every day. The euphoric effect of alcohol (45.23%) and friendly atmosphere (19.39%) of the drinking establishment were the main reasons for attendance (64.62%). Of the damage caused by the abuse of sodabi, 39.26% of subjects showed somatic or neurological complications and 60.74% psychological and psychiatric complications. Updating these data seems necessary, because combating excessive drinking is one of the main objectives of current togolese public health policy

Effects of food flavour enhancer (Monosodium Glutamate and Maggi Poulet) supplementation on glucose tolerance in Sprague Dawley rat

This study was designed to evaluate the effects of purified monosodium glutamate and ‘Maggi Poulet’, on body weight gain, lipid profile, hepatic lipid peroxidation and glucose tolerance in rats. Thirty five young male Sprague Dawley rats were divided into five groups and fed by oral route as follow: group I (distilled water), group II (monosodium glutamate solution), group III (‘Maggi Poulet’solution), group IV (monosodium glutamate solution. and high fat solution) and group V (‘Maggi Poulet’ solution and high fat solution). During the experimental period, fasting glycemia was taken and an oral glucose tolerance test has been performed at the end . Blood samples were then collected in all groups and serum cholesterol and triglyceride were assayed. Animals were killed after and abdominal adipose tissue, liver and heart were excised and weighed. Liver samples were also used to estimate hepatic malondialdehyde level in rats. The results proved that the dietary feeding did not affect the body gain and lipid profile in experimental groups. The hepatic lipid peroxidation has also increased in all experimental groups and at the same time, rats in group II, group IV and group V present a two-hour plasma glucose level signifantly higher. However, purified monosodium glutamate and ‘Maggi Poulet’ at the dose of 1500 mg/kg. b. wt. have not impaired fasting glycemia in Sprague Dawley rat. All changes observed in the glycemia of rats in experimental groups do not allow to qualify them to be glucose intolerant, nevertheless monosodium glutamate consumption in association or not with high fat is hepatotoxic and may contribute to the emergence of prediabetes in human being. © 2013 International Formulae Group. All rights reserved.Keywords: Malondialdehyde, lipid profile, glucose homeostasis, prediabetes