BPChAr—a Benzene Polycarboxylic Acid database to describe the molecular characteristics of laboratory-produced charcoal: Implications for soil science and archaeology

The benzene polycarboxylic acid (BPCA) method is a technique to characterise the aromaticity and aromatic condensation of pyrogenic carbon (PyC) in charred residues. As a molecular marker for polycondensed aromatic moieties, the analysis of BPCAs in archaeological contexts has great potential as a means of detecting and characterising charred residues where past fire traces are not evident. Despite the increased frequency of applications and significant developments since the method’s inception, no central database of BPCA results for modern charcoal pyrolysed under controlled laboratory conditions exists. Limited sample sizes in previous research have restricted the ability to precisely quantify the effects of combustion temperature, precursor feedstocks, pyrolysis parameters (e.g., oxygen availability), and methodological aspects (e.g., chromatography) on resultant BPCA profiles. To remedy this, we present the BPChAr database, which contains a total of 236 BPCA results on modern lab-produced charcoal. Through statistical analyses of the gathered data, we quantify the relationship between combustion temperature and resultant BPCA profiles, and construct random forest models to predict combustion temperature in unknown samples. Our findings show that additional variables hypothesised to play a role in shaping BPCA results — such as precursor feedstock type, oxygen availability during pyrolysis, and chromatographic separation method — have statistically significant implications for resultant BPCA profiles. Our analysis nuances these observations, highlighting at what charring temperatures and for what variables these concomitant parameters should be factored into the interpretation of BPCA results. Random forest models are also developed to predict precursor feedstock (hardwoods, softwoods, and grasses) in unknown samples, though further work is required to refine the accuracy of this model. The BPChAr database constitutes a fundamental tool for modern PyC research, and provides a baseline for future work aimed at employing the BPCA method in palaeoenvironmental and archaeological research

Organic geochemical investigations of an MIS 5 fire in the Palaeolithic deposits of Ormesson (Seine-et-Marne, France):Anthropic or natural?

Despite the central role of fire in Pleistocene and Palaeolithic lifeways, the relationship among hominins, fire, and their environment remains unclear. Ancient combustion residues hold a wealth of molecular data that may help to resolve some of these questions, yet standardised guidelines for reconstructing past fire traces are notably lacking. In this study, we examine extensive combustion residues overlying Middle Palaeolithic deposits from the open-air site of Ormesson (France). To determine whether the combustion residues are of natural or human origin, multiproxy approaches including anthracology, lipid biomarker, and benzene polycarboxylic acid (BPCA) analyses are applied. These techniques are used to characterise organic matter and pyrogenic carbon compositions in the deposits, providing insights into surrounding vegetation, palaeoenvironmental shifts, and the production parameters involved in the formation of the char assemblage. Lipid biomarker evidence suggests that the pre-fire local environment featured abundant coniferous vegetation (e.g., Pinaceae taxa), which is supported by anthracological evidence for a predominance of Pinus cf. sylvestris/nigra complemented by Betula sp. taxa. The post-fire environment saw a contraction of coniferous vegetation, concurrent with an expansion of deciduous taxa, grasses and herbaceous material. The combustion event, which resulted in 67 % of the charcoal assemblage exhibiting vitrification, produced PyC contents of up to 362 g/kg OC in soil samples and 443 g/kg OC in charcoal samples, with aromatic condensation values of up to 34 %. BPCA-derived predictions of heat treatment temperatures yielded values of approximately 300–400 °C for charcoal samples and 400–550 °C for soil samples in the burned layer, constituting the first instance in which quantitative temperature estimations are obtained from BPCA results. Based on the integrated evidence, we accept the null hypothesis that the studied combustion residues are natural in origin. However, the similarity of archaeometric and geochemical signatures from natural and human-controlled fires underscores the need for interdisciplinary, multiproxy efforts to improve the identification of past fire regimes

Non equilibrium ionization in magnetized two-temperature thermal plasma

A thermal plasma is studied accounting for both impact ionization, and an electromagnetic field. This plasma problem is modeled based on a system of Boltzmann type transport equations. Electron-neutral collisions are assumed to be much more frequently elastic than inelastic, to complete previous investigations of thermal plasma . A viscous hydrodynamic/diffusion limit is derived in two stagesdoing an Hilbert expansion and using the  Chapman-Enskog method. The resultant viscous fluid model is characterized by two temperatures, and non equilibrium ionization. Its diffusion coefficients depend on the magnetic field, and can be computed explicitely.</p

A hierarchy of diffusion models for partially ionized plasmas

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Taxonomic structure of lactic acid bacteria community in non-fermented beef meat ecosystems and natural population dynamic of the meat starter species Lactobacillus sakei assessed by genotype fingerprinting

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L’empreinte de population des bactéries lactiques dans le carpaccio de bœuf est sous l’influence du processus de stockage et des changements saisonniers

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Fingerprint of lactic acid bacteria population in beef carpaccio is influenced by storage process and seasonal changes

We have investigated the population structure of lactic acid bacteria (LAB) for several beef carpaccio available on the market with the purpose of comparing the effect of storage process (modified-atmosphere packaging and vacuum-packaging) and of seasonal changes on this microbial population. Out of 60 samples we have characterised 214 isolates accounting for 10 Lspecies and 35 isolates accounting for 11 non-Lspecies. Lactobacillus sakei, Leuconostoc carnosum and Leuconostoc mesenteroides were the most prevailing Lspecies with a frequency of identification within 66%, 62% and 52% of the samples respectively. These 3 species were also characterised by a phenotypic intra-species diversity of isolates based on colony morphology. We showed that the prevalence was increased 1.5 fold for L. sakei and L. mesenteroides during the summer sampling in comparison to the spring or the fall sampling suggesting an environmental origin of these two species. Seasonal variations were also observed for the prevalence of Lactobacillus fuchuensis and L. carnosum in spring (2- and 1.5-fold increase, respectively) and of Brochothrix thermosphacta in fall (6-fold increase). Finally, we demonstrated that the growth potential after the sell-by-date was favourable of 1.25 log(10) cfu g(-1) to Leuconostoc spp. in modified-atmosphere packaging and of 1.38 log(10) cfu g(-1) to Lactobacillus spp. in vacuum-packaging. In conclusion, we show that important and unsuspected traits in bacterial population dynamics can be unravelled by large sampling strategies. We discuss about the need to take this assessment into account for further studies on bacterial ecosystems of meat. (C) 2011 Elsevier Ltd. All rights reserved

Combination of DNA markers for characterizing and fingerprinting a Lactobacillus sakei isolate

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