Cofibrant complexes are free

We define a notion of cofibration among n-categories and show that the cofibrant objects are exactly the free ones, that is those generated by polygraphs.Comment: 16 page

Identification of yeasts present in artisanal yoghurt and traditionally fermented milks consumed in the northern part of Cameroon

Bacteria generally ferment milk but, sometimes, yeasts are found in fermented milks. The presence of these yeasts in the microbial community of some fermented milks could be intentional or accidental. The Diversity of yeasts in the products was investigated using a molecular technique employing variable regions of 26S rDNA profiles generated by PCR-DGGE (Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis). Two types of samples: artisanal or handcraft yoghurt and traditionally fermented milks were collected in three towns of the three regions of the northern part of Cameroon. Firstly, a comparison was made between the 16 traditionally fermented milks collected in Maroua, Garoua and Ngaoundre each of the 3 regions. Secondly, it was between 26 artisanal fermented milks of each region and finally, between the two types of products. The different PCR-DGGE 26S rDNA profiles obtained were analyzed and DNA sequencing was used to compare yeasts from each method of production. Twelve (12) species of Yeasts were identified as: Malassezia globosa, Hanseniaspora uvarum, Galactomyces candidum, Candida tropicalis, Aureobasidium pullulans, Torulaspora globosa, Saccharomyces cerevisiae/paradoxus, Pichia kluyveri, Candida parapsilosis, Torulaspora delbrueckii, Kluyveromyces marxianus, Candida orthopsilosis and Pseudozyma sp. Yeast diversity was higher for artisanal fermented milks (yoghurt) with at least 10 species, while for traditionally non packed fermented milks only 5 species were identified with a predominance strain of Galactomyces candidum, Candida parapsilosis, Torulaspora delbrueckii, Saccharomyces cerevisiae/paradoxus and Kluyveromyces marxianus. The different species of yeast might be introduced accidentally in artisanal yoghurt; however, for traditionally fermented milks their presence might be associated to the starter

Leptin receptor in the chicken ovary: potential involvement in ovarian dysfunction of ad libitum-fed broiler breeder hens

In hens, the ovarian follicles committed to ovulation are arranged in an ordered follicular hierarchy. In standard broiler breeders hens genetically selected for high growth rate the reproductive function is clearly dysfunctional. Feed restriction is needed during reproductive development to limit the formation of excessive numbers of ovarian yellow follicles arranged in multiple hierarchies. To determine whether leptin is involved in the nutritional and reproductive interactions controlling follicular hierarchy in hens, blood leptin levels and ovarian expression of the leptin receptor mRNA were determined during follicle maturation in three chicken lines; a slow growing broiler "Label" genotype without reproductive dysfunction, a fast growing "Standard" genotype fed ad libitum or restricted and a fast growing "Experimental" line with intermediate reproductive performance levels. Whereas expression of the leptin receptor mRNA did not change in the theca, it clearly decreased with follicular differentiation in the granulosa of slow growing hens. In fast growing standard hens fed ad libitum and presenting significant reproductive dysfunction, the decrease was disrupted and dramatic up-regulation of granulosa cell expression of the leptin receptor was observed. On the other hand, feed restriction decreased the overall level of expression of the leptin receptor mRNA and restored the decrease with follicular growth. The level of expression of the leptin receptor probably modulates the action of leptin on follicular differentiation. Since blood leptin and other metabolic factors were not affected by the genotype or by nutritional state, the factors involved in the regulation of leptin receptor gene expression remain to be determined. This study demonstrates the involvement of leptin in the nutritional control of reproduction in birds. Leptin action on the ovary probably controls follicular hierarchy through the regulation of steroidogenesis

Application of PCR-DGGE in determining food origin : cases studies of fish and fruits

The determination of geographical origin is a demand of the traceability system of import-export food products. For this purpose, molecular techniques employing 16S, 26S rDNA profiles generated by PCR-DGGE (polymerase chain reaction - denaturing gradient gel electrophoresis) were used to detect the variation in microbial community (bacteria, yeast) structures of Pangasius fish from Viet Nam harvested in different aquaculture farms and during different seasons and two fruits Physalis from Egypt and mandarins from Spain and Morocco. In Physalis case, ecology of yeasts was also studied for the same purpose. Bacterial band profiles of fish and mandarins, and yeast band profiles of Physalis were specific for each location and could be used as a bar code to certify the origin of fish and fruits. This method is a new traceability tool which provides food with a unique biological bar code and makes it possible to trace back the food to their original location. (Résumé d'auteur

Polycyclic aromatic hydrocarbons in residential dust: sources of variability.

BackgroundThere is interest in using residential dust to estimate human exposure to environmental contaminants.ObjectivesWe aimed to characterize the sources of variability for polycyclic aromatic hydrocarbons (PAHs) in residential dust and provide guidance for investigators who plan to use residential dust to assess exposure to PAHs.MethodsWe collected repeat dust samples from 293 households in the Northern California Childhood Leukemia Study during two sampling rounds (from 2001 through 2007 and during 2010) using household vacuum cleaners, and measured 12 PAHs using gas chromatography-mass spectrometry. We used a random- and a mixed-effects model for each PAH to apportion observed variance into four components and to identify sources of variability.ResultsMedian concentrations for individual PAHs ranged from 10 to 190 ng/g of dust. For each PAH, total variance was apportioned into regional variability (1-9%), intraregional between-household variability (24-48%), within-household variability over time (41-57%), and within-sample analytical variability (2-33%). Regional differences in PAH dust levels were associated with estimated ambient air concentrations of PAH. Intraregional differences between households were associated with the residential construction date and the smoking habits of residents. For some PAHs, a decreasing time trend explained a modest fraction of the within-household variability; however, most of the within-household variability was unaccounted for by our mixed-effects models. Within-household differences between sampling rounds were largest when the interval between dust sample collections was at least 6 years in duration.ConclusionsOur findings indicate that it may be feasible to use residential dust for retrospective assessment of PAH exposures in studies of health effects

Doping of Bi2Te3 using electron irradiation

Electron irradiation is investigated as a way to dope the topological insulator Bi2Te3. For this, p-type Bi2Te3 single crystals have been irradiated with 2.5 MeV electrons at room temperature and electrical measurements have been performed in-situ as well as ex-situ in magnetic fields up to 14 T. The defects created by irradiation act as electron donors allowing the compensation of the initial hole-type conductivity of the material as well as the conversion of the conductivity from p- to n-type. The changes in carrier concentration are investigated using Hall effect and Shubnikov-de Haas (SdH) oscillations, clearly observable in the p-type samples before irradiation, but also after the irradiation-induced conversion of the conductivity to n-type. The SdH patterns observed for the magnetic field along the trigonal axis can be entirely explained assuming the contribution of only one valence and conduction band, respectively, and Zeeman-splitting of the orbital levels.Comment: Final versio

Breastfeeding patterns and risk of childhood acute lymphoblastic leukaemia.

The risk of childhood acute lymphoblastic leukaemia (ALL) was investigated in relation to breastfeeding patterns in the Northern California Childhood Leukaemia Study. Data collected by self-administered and in-person questionnaires from biological mothers of leukaemia cases (age 0-14 years) in the period 1995-2002 were matched to birth certificate controls on date of birth, sex, Hispanic ethnic status, and maternal race. Ever compared to never breastfeeding was not associated with risk of ALL at ages 1-14 years (odds ratio=0.99; 95% CI=0.64-1.55) and ages 2-5 years (OR=1.49; 95% CI=0.83-2.65). Various measures of breastfeeding duration compared to absence of breastfeeding also had no significant effect on risk. Complimentary feeding characteristics such as type of milk/formula used and age started eating solid foods among breastfed children were not associated with ALL risk. This study provides no evidence that breastfeeding affects the occurrence of childhood ALL

Nouvelles stratégies de traçabilité pour déterminer l'origine géographique des fruits : création d'un code barre biologique par PCR-DGGE

La détermination de l'origine géographique est une demande du système de traçabilité des denrées alimentaires d'import-export. Une hypothèse de retrouver la source d'un produit est en analysant de façon globale les communautés microbiennes de la nourriture et des liens statistiquement cette analyse à l'origine géographique des produits alimentaires (Montet et al., 2004). La technique moléculaire employant rADN 26S profils générés par PCR-DGGE a été utilisée pour détecter la variation dans les structures communautaires de levure de fruits (El Sheikha et al., 2009). Nous avons appliqué cette nouvelle technique sur des fruits Physalis de trois pays (Égypte, Colombie, Ouganda) et sur le karité à partir de quatre pays (Cameroun, Mali, Sénégal, Ouganda). Les gels DGGE ont montré des différences significatives dans les schémas de migration. Toutefois, les doublons pour chaque point d'échantillonnage donne statistiquement les modèles DGGE similaires à travers l'étude. Nous avons démontré qu'il y avait un lien entre les populations de levures et l'aire géographique. Lorsque rADN 26S des profils ont été analysés par analyse multivariée, distinct des communautés microbiennes ont été détectés. Les profils de bande de différents pays étaient différentes et sont spécifiques pour chaque pays et pourrait être utilisé comme un code-barres de discriminer l'origine des fruits. Cette méthode est un outil de traçabilité qui offre de nouveaux produits fruitiers avec un code-barre unique et permet de retracer les fruits dans leur pays d'origine. Physalis est inclus dans la liste prioritaire de l'horticulture de nombreux gouvernements et d'exportation de fruits. Il est exporté dans plusieurs pays comme la Colombie, l'Egypte, le Zimbabwe et l'Afrique du Sud, mais la Colombie se distingue comme l'un des plus grands producteurs, consommateurs et exportateurs. Les exportations de la Colombie de Physalis en 2004 ont une valeur de 14 millions d'USD (El Sheikha et al., 2008a). En Egypte, l'importance économique de Physalis est en hausse, en raison, la réalisation d'un grand succès en arabe local, et les marchés européens (El Sheikha, 2004). Physalis que la plante a de nombreuses propriétés médicinales, y compris les antipyrétiques, dépuratif, diurétique, pectoral, et vermifuge. Une décoction est utilisée dans le traitement des abcès, toux, fièvre ou mal de gorge (Duke et Ayensu 1985). La pulpe est nutritif, contenant des niveaux particulièrement élevés de caroténoïdes, des minéraux, acides aminés essentiels et en vitamine C (El Sheikha et al., 2008b). En ce qui concerne les fruits des arbres de karité, seuls sept pays ont des statistiques. Nigeria compte plus de 60% de la production de beurre de karité en 2005. Il est suivi par le Mali, le Ghana et le Burkina Faso, qui représentent ensemble un peu moins du tiers de la production mondiale en 2005. En Europe, le beurre de karité est utilisé principalement (95%) par l'industrie du chocolat. Les quantités exportées vers le Japon, les États-Unis ou la Suisse serait principalement utilisé pour les cosmétiques ou pharmacologiques (FAOSTAT, 2007). (Texte intégral