Hydroclimatic vulnerability of peat carbon in the central Congo Basin

The forested swamps of the central Congo Basin store approximately 30 billion metric tonnes of carbon in peat1,2. Little is known about the vulnerability of these carbon stocks. Here we investigate this vulnerability using peat cores from a large interfluvial basin in the Republic of the Congo and palaeoenvironmental methods. We find that peat accumulation began at least at 17,500 calibrated years before present (cal. yr BP; taken as AD 1950). Our data show that the peat that accumulated between around 7,500 to around 2,000 cal. yr BP is much more decomposed compared with older and younger peat. Hydrogen isotopes of plant waxes indicate a drying trend, starting at approximately 5,000 cal. yr BP and culminating at approximately 2,000 cal. yr BP, coeval with a decline in dominant swamp forest taxa. The data imply that the drying climate probably resulted in a regional drop in the water table, which triggered peat decomposition, including the loss of peat carbon accumulated prior to the onset of the drier conditions. After approximately 2,000 cal. yr BP, our data show that the drying trend ceased, hydrologic conditions stabilized and peat accumulation resumed. This reversible accumulation–loss–accumulation pattern is consistent with other peat cores across the region, indicating that the carbon stocks of the central Congo peatlands may lie close to a climatically driven drought threshold. Further research should quantify the combination of peatland threshold behaviour and droughts driven by anthropogenic carbon emissions that may trigger this positive carbon cycle feedback in the Earth system

Generalized Toeplitz operators and cyclic vectors

We give in this paper some asymptotic Von Neumann inequalities for power bounded operators in the class C subrho intersection C sub 1. and some spacial von Neumann inequalities associated with non zero elements of the point spectrum, when it is non void, of generalized Toeplitz operators. Introducing perturbed kernel, we consider classes C sub R which extend the classical classes C subrho. We give results about absolute continuity with respect to the Haar measure for operators in class C sub R intersection C sub 1. This allows us to give new results on cyclic vectors for such operators and provides invariant subspaces for their powers. Relationships between cyclic vectors for T and T* involving generalized Toeplitz operators are given and the commutativity of left brace T right brace', the commutant of T is discussed

Preliminary Acoustic Study of 3D Localization of Buried Polyethylene Pipe

International audienceAcoustic waves are commonly used to locate buried polyethylene pipes. In this preliminary study we are particularly interested in pipes depth. To obtain depth information we are moving towards a multi-sensor solution. Several estimators are implemented and tested on real data. A depth estimator according to the relative delays between sensors is proposed. We compare two relative delays estimators : the method using the cross-correlation and the one using the coherence function. We will verify on real measurements that the second method is much more efficient than the first one. Before discussing the results we will present another approach which consists in adapting the MUSIC (MUltiple SIgnals Classification) algorithm to our problem

High resolution paleo-hydrological record from carbonate deposits in the Roman aqueduct of Traconnade (Aix-en-Provence, SE France)

International audienc

Information sharing and the stability of cooperation in research joint ventures*

The model studies information sharing and the stability of cooperation in cost reducing Research Joint Ventures (RJVs). In a three-stage game-theoretic framework, firms decide on participation in a RJV, information sharing along with R&D expenditures, and output. An important feature of the model is that voluntary information sharing between cooperating firms increases information leakage from the RJV to outsiders. It is found that RJVs representing a larger portion of firms in the industry are more likely to share information. It is also found that when sharing information is costless, firms generally don't choose intermediate levels of information sharing: they share all the information or none at all. The size of the RJV is found to depend on three effects: a coordination effect, an information sharing effect, and a competition effect. Depending on the relative magnitudes of these effects, the size of the RJV may increase or decrease with spillovers. In response to an increase in leakages, RJV members reduce their R&D spending. In addition, they either increase the RJV size while maintaining information sharing unchanged (when leakages are low), or they reduce both information sharing and RJV size (when leakages are high).Endogenous R&D Spillovers, Information Sharing, R&D Cooperation, Research Joint Ventures,