Ore genesis of Pb-Zn deposits in the Nappe zone of Northern Tunisia: Constraints from Pb-S-C-O isotopic systems

The Jalta and Jebel Ghozlane ore deposits are located in the extreme North of Tunisia, within the Nappe zone. The mineralization of Jalta, hosted in Triassic dolostones and the overlying Mio-Pliocene conglomerates, consists of abundant galena, barite, and cerussite with accessory sphalerite, pyrite, and jordanite. At Jebel Ghozlane, large Pb-Zn concentrations occur in the Triassic dolostones and Eocene limestones. The mineral association consists of galena, sphalerite, barite, and celestite and their oxidation products (cerussite, smithsonite, and anglesite). Lead isotope ratios in galena from both districts are relatively homogeneous ((206)Pb/(204)Pb = 18.702-18.823, (207)Pb/(204)Pb = 15.665-15.677, (208)Pb/(204)Pb = 38.725-38.875). The delta(34)S values for sulfates from both areas (+12.2 to +16.2 parts per thousand at Jalta and + 14.3 to + 19.4 parts per thousand at Jebel Ghozlane) are compatible with a derivation of sulfur from marine sulfates, possibly sourced from the Triassic evaporites. The delta(34)S values of the sulfides have a range between -10 and +12.5 parts per thousand at Jalta, and between -9.1 and +22.1 parts per thousand at Jebel Ghozlane. The large range of values suggests reduction of the sulfate by bacterial and/or thermochemical reduction of sulfate to sulfur. The high delta(34)S values of sulfides require closed-system reduction processes. The isotopically light carbon in late calcites (-6.3 to -2.5 parts per thousand) and authigenic dolomite (-17.6 parts per thousand) suggests an organic source of at least some of the carbon in these samples, whereas the similarity of the delta(18)O values between calcite (+24.8 parts per thousand) and the authigenic dolomite (+24.7 parts per thousand) of Jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates. The secondary calcite isotope compositions of Jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200 degrees C, but temperatures as low as 50 degrees C may be indicated by the late calcite of Jebel Ghozlane (delta(18)O of +35.9 parts per thousand). Given the geological events related to the Alpine orogeny in the Nappe zone (nappe emplacement, bimodal volcanism, and reactivation of major faults, such as Ghardimaou-Cap Serrat) and the Neogene age of the host rocks in several localities, a Late-Miocene age is proposed for the Pb-Zn ore deposits considered in this study. Remobilization of deep-seated primary deposits in the Paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the Nappe zone as a whole. (C) 2011 Elsevier B.V. All rights reserved.

Binary classification of dyslipidemia from the waist-to-hip ratio and body mass index: a comparison of linear, logistic, and CART models.

BACKGROUND: We sought to improve upon previously published statistical modeling strategies for binary classification of dyslipidemia for general population screening purposes based on the waist-to-hip circumference ratio and body mass index anthropometric measurements. METHODS: Study subjects were participants in WHO-MONICA population-based surveys conducted in two Swiss regions. Outcome variables were based on the total serum cholesterol to high density lipoprotein cholesterol ratio. The other potential predictor variables were gender, age, current cigarette smoking, and hypertension. The models investigated were: (i) linear regression; (ii) logistic classification; (iii) regression trees; (iv) classification trees (iii and iv are collectively known as "CART"). Binary classification performance of the region-specific models was externally validated by classifying the subjects from the other region. RESULTS: Waist-to-hip circumference ratio and body mass index remained modest predictors of dyslipidemia. Correct classification rates for all models were 60-80%, with marked gender differences. Gender-specific models provided only small gains in classification. The external validations provided assurance about the stability of the models. CONCLUSIONS: There were no striking differences between either the algebraic (i, ii) vs. non-algebraic (iii, iv), or the regression (i, iii) vs. classification (ii, iv) modeling approaches. Anticipated advantages of the CART vs. simple additive linear and logistic models were less than expected in this particular application with a relatively small set of predictor variables. CART models may be more useful when considering main effects and interactions between larger sets of predictor variables.

Fate of linear and supercoiled multinucleosomic templates during transcription.

Electron microscopy was used to monitor the fate of reconstituted nucleosome cores during in vitro transcription of long linear and supercoiled multinucleosomic templates by the prokaryotic T7 RNA polymerase and the eukaryotic RNA polymerase II. Transcription by T7 RNA polymerase disrupted the nucleosomal configuration in the transcribed region, while nucleosomes were preserved upstream of the transcription initiation site and in front of the polymerase. Nucleosome disruption was independent of the topology of the template, linear or supercoiled, and of the presence or absence of nucleosome positioning sequences in the transcribed region. In contrast, the nucleosomal configuration was preserved during transcription from the vitellogenin B1 promoter with RNA polymerase II in a rat liver total nuclear extract. However, the persistence of nucleosomes on the template was not RNA polymerase II-specific, but was dependent on another activity present in the nuclear extract. This was demonstrated by addition of the extract to the T7 RNA polymerase transcription reaction, which resulted in retention of the nucleosomal configuration. This nuclear activity, also found in HeLa cell nuclei, is heat sensitive and could not be substituted by nucleoplasmin, chromatin assembly factor (CAF-I) or a combination thereof. Altogether, these results identify a novel nuclear activity, called herein transcription-dependent chromatin stabilizing activity I or TCSA-I, which may be involved in a nucleosome transfer mechanism during transcription.

Geographic patterns in the distribution of social systems in terrestrial arthropods.

The role of ecology in the evolution and maintenance of arthropod sociality has received increasing research attention in recent years. In some organisms, such as halictine bees, polistine wasps, and social spiders, researchers are investigating the environmental factors that may contribute to high levels of variation in the degree of sociality exhibited both among and within species. Within lineages that include only eusocial members, such as ants and termites, studies focus more on identifying extrinsic factors that may contribute to the dramatic variation in colony size, number of queens, and division of labour that is evident across these species. In this review, I propose a comparative approach that seeks to identify environmental factors that may have a common influence across such divergent social arthropod groups. I suggest that seeking common biogeographic patterns in the distribution of social systems or key social traits may help us to identify ecological factors that play a common role in shaping the evolution of sociality across different organisms. I first review previous studies of social gradients that form along latitudinal and altitudinal axes. Within families and within species, many organisms show an increasing degree of sociality at lower latitudes and altitudes. In a smaller number of cases, organisms form larger groups or found nests cooperatively at higher latitudes and altitudes. I then describe several environmental factors that vary consistently along such gradients, including climate variables and abundance of predators, and outline their proposed role in the social systems of terrestrial arthropods. Finally, I map distributions of a social trait against several climatic factors in five case studies to demonstrate how future comparative studies could inform empirical research.

Prediction of fat-free mass using bioelectrical impedance analysis in young adults from five populations of African origin.

Background/objectives:Bioelectrical impedance analysis (BIA) is used in population and clinical studies as a technique for estimating body composition. Because of significant under-representation in existing literature, we sought to develop and validate predictive equation(s) for BIA for studies in populations of African origin.Subjects/methods:Among five cohorts of the Modeling the Epidemiologic Transition Study, height, weight, waist circumference and body composition, using isotope dilution, were measured in 362 adults, ages 25-45 with mean body mass indexes ranging from 24 to 32. BIA measures of resistance and reactance were measured using tetrapolar placement of electrodes and the same model of analyzer across sites (BIA 101Q, RJL Systems). Multiple linear regression analysis was used to develop equations for predicting fat-free mass (FFM), as measured by isotope dilution; covariates included sex, age, waist, reactance and height(2)/resistance, along with dummy variables for each site. Developed equations were then tested in a validation sample; FFM predicted by previously published equations were tested in the total sample.Results:A site-combined equation and site-specific equations were developed. The mean differences between FFM (reference) and FFM predicted by the study-derived equations were between 0.4 and 0.6âeuro0/00kg (that is, 1% difference between the actual and predicted FFM), and the measured and predicted values were highly correlated. The site-combined equation performed slightly better than the site-specific equations and the previously published equations.Conclusions:Relatively small differences exist between BIA equations to estimate FFM, whether study-derived or published equations, although the site-combined equation performed slightly better than others. The study-derived equations provide an important tool for research in these understudied populations.

Interaction of alpha-melanotropin with central dopamine systems: role of hormonal state and molecular structure

The tubero-infundibular and nigrostriatal DA neurone systems of rats respond to systemic (i.p.) injection of alpha-MSH (2-100 microgram/kg). The response of the tubero-infundibular (arcuate) DA neurones, an increase in cellular fluorescence intensity which can be interpreted as a sign of increased neuronal activity, is essentially the same in males, estrogen-progesterone-pretreated ovariectomized females and hypophysectomized males, whereas the type of response elicited by alpha-MSH in the nigral DA neurones depends upon the hormonal state of the animal. Differences between the two DA neurone groups exist also with regard to the effects of peptide fragments containing the two active sites of the alpha-MSH molecule. Results of lesion experiments in the lower brainstem (area postrema) and of blockade of muscarinic mechanisms by atropine further point to differences in the mechanisms underlying the peptide effects on the two neurone systems. The reaction of the tubero-infundibular DA system (which controls the pars intermedia of the pituitary) can be considered to reflect the activation of a feedback mechanism on MSH secretion, while the functional counterpart of the changes observed in the nigral system remains unknown at the present time.

Evolution of uni- and bifactorial sexual compatibility systems in fungi.

Mating systems, that is, whether organisms give rise to progeny by selfing, inbreeding or outcrossing, strongly affect important ecological and evolutionary processes. Large variations in mating systems exist in fungi, allowing the study of their origin and consequences. In fungi, sexual incompatibility is determined by molecular recognition mechanisms, controlled by a single mating-type locus in most unifactorial fungi. In Basidiomycete fungi, however, which include rusts, smuts and mushrooms, a system has evolved in which incompatibility is controlled by two unlinked loci. This bifactorial system probably evolved from a unifactorial system. Multiple independent transitions back to a unifactorial system occurred. It is still unclear what force drove evolution and maintenance of these contrasting inheritance patterns that determine mating compatibility. Here, we give an overview of the evolutionary factors that might have driven the evolution of bifactoriality from a unifactorial system and the transitions back to unifactoriality. Bifactoriality most likely evolved for selfing avoidance. Subsequently, multiallelism at mating-type loci evolved through negative frequency-dependent selection by increasing the chance to find a compatible mate. Unifactoriality then evolved back in some species, possibly because either selfing was favoured or for increasing the chance to find a compatible mate in species with few alleles. Owing to the existence of closely related unifactorial and bifactorial species and the increasing knowledge of the genetic systems of the different mechanisms, Basidiomycetes provide an excellent model for studying the different forces that shape breeding systems.