Arboreal ants use the "Velcro® principle" to capture very large prey

Plant-ants live in a mutualistic association with host plants known as "myrmecophytes" that provide them with a nesting place and sometimes with extra-floral nectar (EFN) and/or food bodies (FBs); the ants can also attend sap-sucking Hemiptera for their honeydew. In return, plant-ants, like most other arboreal ants, protect their host plants from defoliators. To satisfy their nitrogen requirements, however, some have optimized their ability to capture prey in the restricted environment represented by the crowns of trees by using elaborate hunting techniques. In this study, we investigated the predatory behavior of the ant Azteca andreae which is associated with the myrmecophyte Cecropia obtusa. We noted that up to 8350 ant workers per tree hide side-by-side beneath the leaf margins of their host plant with their mandibles open, waiting for insects to alight. The latter are immediately seized by their extremities, and then spread-eagled; nestmates are recruited to help stretch, carve up and transport prey. This group ambush hunting technique is particularly effective when the underside of the leaves is downy, as is the case for C. obtusa. In this case, the hook-shaped claws of the A. andreae workers and the velvet-like structure of the underside of the leaves combine to act like natural VelcroH that is reinforced by the group ambush strategy of the workers, allowing them to capture prey of up to 13,350 times the mean weight of a single worker

Inferring river properties with SWOT like data

Inverse problems in hydraulics are still open questions such as the estimation of river discharges. Remotely sensed measurements of hydrosystems can provide valuable information but adequate methods are still required to exploit it. The future Surface Water and Ocean Topography (SWOT) mission would provide new cartographic measurements of inland water surfaces. The highlight of SWOT will be its almost global coverage and temporal revisits on the order of 1 to 4 times per 22 days repeat cycle [1]. Lots of studies have shown the possibility of retrieving discharge given the river bathymetry or roughness and/or in situ time series. The new challenge is to use SWOT type data to inverse the triplet formed by the roughness, the bathymetry and the discharge. The method presented here is composed of two steps: following an inverse formulation from [2], the first step consists in retrieving an equivalent bathymetry profile of a river given one in situ depth measurement and SWOT like data of the water surface, that is to say water elevation, free surface slope and width. From this equivalent bathymetry, the second step consists in solving mass and Manning equation in the least square sense [3]. Nevertheless, for cases where no in situ measurement of water depth is available, it is still possible to solve a system formed by mass and Manning equations in the least square sense (or with other methods such as Bayesian ones, see e.g. [4]). We show that a good a priori knowledge of bathymetry and roughness is compulsory for such methods. Depending on this a priori knowledge, the inversion of the triplet (roughness, bathymetry, discharge) in SWOT context was evaluated on the Garonne River [5, 6]. The results are presented on 80 km of the Garonne River downstream of Toulouse in France [7]. An equivalent bathymetry is retrieved with less than 10% relative error with SWOT like observations. After that, encouraging results are obtained with less than 10% relative error on the identified discharge

Modification des fibres cellulosiques. Amélioration des propriétés hydrophiles des pâtes bisulfites

This works focus on the sorption properties improvement of bisulfite fibres. The cellulose is modified by middle oxidation to increase the intra-fibres cross-linking. Two approaches are studied to manage the oxidation. The first concerns a physical approach with plasma treatment and the second a chemical approach with chemical oxidants in aqueous medium. Two different systems of plasma generation have been used, corona discharges under atmospheric pressure and the cold oxygen plasma under reduced pressure. The both processes lead to an improvement of the wettability of fibres with decrease of contact angle fibre. The chemical oxidation of the cellulose is realized by transformation of primary or secondary alcohol groups in carboxylic acid groups. The oxidation of secondary alcohol groups is obtained by a sequence in two steps of sodium periodate following by sodium chlorite and hydrogen peroxide. Concerning primary alcohol, the one step oxidation is obtained by an electrochemical process using TEMPO derivatives. In the both processes, the modification induce by the treatment is significant and the compromise between fibrous properties and acidic group ratio is a key factor. The tests of intra-fibres cross-linking show an improvement of sorption properties. Modified fibres characteristics are evaluated by chemical and spectrometric analysis, and the performance by the specific tests related to the absorption and the retention of liquids in fibrous network.This works focus on the sorption properties improvement of bisulfite fibres. The cellulose is modified by middle oxidation to increase the intra-fibres cross-linking. Two approaches are studied to manage the oxidation. The first concerns a physical approach with plasma treatment and the second a chemical approach with chemical oxidants in aqueous medium. Two different systems of plasma generation have been used, corona discharges under atmospheric pressure and the cold oxygen plasma under reduced pressure. The both processes lead to an improvement of the wettability of fibres with decrease of contact angle fibre. The chemical oxidation of the cellulose is realized by transformation of primary or secondary alcohol groups in carboxylic acid groups. The oxidation of secondary alcohol groups is obtained by a sequence in two steps of sodium periodate following by sodium chlorite and hydrogen peroxide. Concerning primary alcohol, the one step oxidation is obtained by an electrochemical process using TEMPO derivatives. In the both processes, the modification induce by the treatment is significant and the compromise between fibrous properties and acidic group ratio is a key factor. The tests of intra-fibres cross-linking show an improvement of sorption properties. Modified fibres characteristics are evaluated by chemical and spectrometric analysis, and the performance by the specific tests related to the absorption and the retention of liquids in fibrous network

Revision of the Pentacrinid Stalked Crinoids of the Genus Endoxocrinus (Echinodermata, Crinoidea), with a Study of Environmental Control of Characters and Its Consequences for Taxonomy

A revision of the stalked crinoid species attributed to the genus Endoxocrinus A.H. Clark, 1908 (Diplocrininae, Pentacrinitidae, Crinoidea, Echinodermata) is conducted using studies on phenotype variation and its relation with environment. Specimens collected via submersible at five sites in the Bahamas exhibit distinct phenotypes that correlate with different apparent ecological niches and serve as references for interpreting specimens dredged in Atlantic and Pacific Oceans where detailed information on their benthic environment is unknown. Documentation of ecophenotypic convergences or divergences allows us to distinguish between adaptive characters and those revealing genetic affinities, and to discuss allopatric evolution and bathymetric zonation. The results suggest the following taxonomy: the genus Endoxocrinus is subdivided into two subgenera, i.e., Endoxocrinus A.H. Clark, 1908 and Diplocrinus Döderlein, 1912 (Annacrinus A. H. Clark, 1923 becomes a junior synonym of Diplocrinus); the subgenus Endoxocrinus is monospecific with E. (E.) parrae [Gervais (in Guérin, 1835)] from the western tropical Atlantic; the subgenus Diplocrinus includes E. (D.) alternicirrus (Carpenter, 1882) from the western and central Pacific, E. (D.) maclearanus (Thomson, 1872) from the western tropical Atlantic, and E. (D.) wyvillethomsoni (Jeffreys, 1870) from the northeastern Atlantic. Endoxocrinus (E.) parrae includes three subspecies adapted to different habitats and depths: E. (E.) parrae parrae usually in 154–518 m with moderate to high current velocity and moderate turbulence to laminar flow, E. (E.) parrae carolinae (A.H. Clark, 1934) in 504–724 m with moderate current velocity and high turbulence, and E. (E.) parrae prionodes H.L. Clark, 1941 in 402–832 m with high current velocity in laminar flow. E. (D.) alternicirrus includes two subspecies, E. (D.) alternicirrus alternicirrus in 625–1476 m and E. (D.) alternicirrus sibogae (Döderlein, 1907) usually in 364–800 m. E. (D.) maclearanus has a depth range of 432–878 m and occurs as a dwarf variety minimus n. var. in high current velocities and high turbulence. E. (D.) wyvillethomsoni from depths of 1214–2070 m lives on various substrates under a variety of hydrodynamic conditions

On the assimilation of altimetric data in 1D Saint-Venant river flow models

Given altimetry measurements, the identification capability of time varying inflow discharge Qin(t) and the Strickler coefficient K (defined as a power-law in h the water depth) of the 1D river Saint-Venant model is investigated. Various altimetry satellite missions provide water level elevation measurements of wide rivers, in particular the 21 future Surface Water and Ocean Topography (SWOT) mission. An original and synthetic reading of all the available information (data, wave propagation and the Manning-Strickler’s law residual) are represented on the so-called identifiability map. The latter provides in the space-time plane a comprehensive overview of the inverse problem features. Inferences based on Variational Data Assimilation (VDA) are investigated at the limit of the data-model inversion capability : relatively short river portions, relatively infrequent observations, that is inverse problems presenting a low identifiability index . The inflow discharge Qin(t) is infered simultaneously with the varying coefficient K(h). The bed level is either given or infered from a lower complexity model. The experiments and analysis are conducted for different scenarios (SWOT-like or multi-sensors-like). The scenarios differ by the observation frequency and by the identifiability index. Sensitivity analyses with respect to the observation errors and to the first guess values demonstrate the robustness of the VDA inferences. Finally this study aiming at fusing relatively sparse altimetric data and the 1D Saint-Venant river flow model highlights the spatiotemporal resolution lower limit, also the great potential in terms of discharge inference including for a single river reach

Three-dimensional analysis of a tensile test on a propellant with digital volume correlation

International audienceA full three-dimensional study of a tensile test on a sample made of polymerbonded propellant is presented. The analysis combines different tools, namely, X-ray microtomography of an in situ experiment, image acquisition and treatment, 3D volume correlation to measure three-dimensional displacement fields. It allows for global and local strain analyses prior to and after the peak load. By studying the correlation residuals, it is also possible to analyze the damage activity during the experiment

Variationnal data assimilation of AirSWOT and SWOT data into the 2D shallow water model Dassflow, method and test case on the Garonne river (France)

For river hydraulic studies, water level measurements are fundamental information, yet they are currently mostly provided by gauging stations mostly located on the main river channel. That is why they are sparsely distributed in space and can have gaps in their time series (because of floods damages on sensors or sensors failures). These issues can be compensated by remote sensing data, which have considerably contributed to improve the observation of physical processes in hydrology and hydraulics in general and, in particular, in flood hydrodynamic. Indeed, the new generation of satellites is equipped with sensors of metric resolution. Remotely-sensed images from satellites such as SWOT (Surface Water and Ocean Topography) would give spatially distributed information on water elevations with a high accuracy (able to observe river wider than100m with a vertical precision ~dm) and periodic in time (revisiting ~week at mid-latitude). Gathering pre-mission data over specific and varied science targets is the purpose of the AirSWOT airborne campaign in order to implement and test SWOT products retrieval algorithms. A reach of the Garonne River, downstream of Toulouse (FRANCE), is a proposed study area for AirSWOT flights. This choice is motivated by previous hydraulic and thermal studies (Larnier et al., 2010) already performed on this section of 100km reach of the river. Moreover, on this highly instrumented and studied portion of river many typical free surface flow modelling issue has been encountered, and this river reach represents the limit of SWOT observation capability. The 2DH (vertically integrated) free surface flow model Dassflow (Honnorat et al., 2005; Honnorat et al., 2007; Honnorat et al., 2009; Hostache et al., 2010; Lai and Monnier, 2009) especially designed for variational data assimilation, will be used on this portion of the Garonne River. Mathematical methodologies such as twin experiments (Roux and Dartus, 2005; Roux and Dartus, 2006) will be performed on several modelling hypothesis in order to identify main characteristic of the river. An identification strategy would allow to retrieve spatial roughness along the main channel, variation of the local topographic slope or else temporal evolution of the streamflow

Encuesta Cuantitativa Bogotá METAL 2009. Resultados preliminares

En el marco del programa METAL Metrópolis de América Latina en la globalización :reconfiguraciones territoriales, movilidad espacial, acción pública" que se desarrolla desde finales de 2007 con el apoyo financiero de la Agencia francesa de investigación (ANR) y de la Agencia francesa interinstitucional de investigación para el desarrollo (AIRD), hemos diseñado y aplicado en Bogotá, Santiago y São Paulo un sistema de encuestas que tiene como objetivo permitir un análisis fino de las diferentes formas de movilidad de la población y de las transformaciones que ellas ejercen en las tres metrópolis.Con el presente informe, nos esforzamos en poner a disposición de las personas o instituciones interesadas una serie de cuadros que abarquen los principales temas de la encuesta: características demográficas generales, acceso a la vivienda, movilidad residencial, movilidad cotidiana hasta el lugar de trabajo y el lugar de estudio, educación y actividad económica. Esta información no representa sino una pequeña parte de la información recolectada, procesada con el objetivo de mejorar, aun parcialmente, el conocimiento sobre los mecanismos actuales de poblamiento de Bogotá, a través de una serie de datos sobre la situación demográfica y los procesos actuales de movilidad espacial, tales como fueron observados en junio de 2009 en unas 11 zonas de Bogotá y de la periferia metropolitana."Características demográficas -Vivienda - Migración - Movilidad residencial -Movilidad cotidiana - Educación - Actividad económica.

An Overlooked Mandibular-Rubbing Behavior Used during Recruitment by the African Weaver Ant, Oecophylla longinoda

In Oecophylla, an ant genus comprising two territorially dominant arboreal species, workers are known to (1) use anal spots to mark their territories, (2) drag their gaster along the substrate to deposit short-range recruitment trails, and (3) drag the extruded rectal gland along the substrate to deposit the trails used in long-range recruitment. Here we study an overlooked but important marking behavior in which O. longinoda workers first rub the underside of their mandibles onto the substrate, and then—in a surprising posture—tilt their head and also rub the upper side of their mandibles. We demonstrate that this behavior is used to recruit nestmates. Its frequency varies with the rate at which a new territory, a sugary food source, a prey item, or an alien ant are discovered. Microscopy analyses showed that both the upper side and the underside of the mandibles possess pores linked to secretory glands. So, by rubbing their mandibles onto the substrate, the workers probably spread a secretion from these glands that is involved in nestmate recruitment

A temporary social parasite of tropical plant-ants improves the fitness of a myrmecophyte

Myrmecophytes offer plant-ants a nesting place in exchange for protection from their enemies, particularly defoliators. These obligate ant-plant mutualisms are common model systems for studying factors that allow horizontally transmitted mutualisms to persist since parasites of ant-myrmecophyte mutualisms exploit the rewards provided by host plants whilst providing no protection in return. In pioneer formations in French Guiana, Azteca alfari and Azteca ovaticeps are known to be mutualists of myrmecophytic Cecropia (Cecropia ants). Here, we show that Azteca andreae, whose colonies build carton nests on myrmecophytic Cecropia, is not a parasite of Azteca-Cecropia mutualisms nor is it a temporary social parasite of A. alfari; it is, however, a temporary social parasite of A. ovaticeps. Contrarily to the two mutualistic Azteca species that are only occasional predators feeding mostly on hemipteran honeydew and food bodies provided by the host trees, A. andreae workers, which also attend hemipterans, do not exploit the food bodies. Rather, they employ an effective hunting technique where the leaf margins are fringed with ambushing workers, waiting for insects to alight. As a result, the host trees' fitness is not affected as A. andreae colonies protect their foliage better than do mutualistic Azteca species resulting in greater fruit production. Yet, contrarily to mutualistic Azteca, when host tree development does not keep pace with colony growth, A. andreae workers forage on surrounding plants; the colonies can even move to a non-Cecropia tree