Synergistic interaction between the Arp2/3 complex and cofilin drives stimulated lamellipod extension

Both the Arp2/3 complex and cofilin are believed to be important for the generation of protrusive force at the leading edge; however, their relative contributions have not been explored in vivo. Our results with living cells show that cofilin enters the leading edge immediately before the start of lamellipod extension, slightly earlier than Arp2/3, which begins to be recruited slightly later as the lamellipod is extended. Blocking either the Arp2/3 complex or cofilin function in cells results in failure to extend broad lamellipods and inhibits free barbed ends, suggesting that neither factor on its own can support actin polymerization-mediated protrusion in response to growth factor stimulation. High-resolution analysis of the actin network at the leading edge supports the idea that both the severing activity of cofilin and the specific branching activity of the Arp2/3 complex are essential for lamellipod protrusion. These results are the first to document the relative contributions of cofilin and Arp2/3 complex in vivo and indicate that cofilin begins to initiate the generation of free barbed ends that act in synergy with the Arp2/3 complex to create a large burst in nucleation activity

Mesoscale modeling of the rheology of pressure sensitive adhesives through inclusion of transient forces

For optimal application, pressure-sensitive adhesives must have rheological properties in between those of a viscoplastic solid and those of a viscoelastic liquid. Such adhesives can be produced by emulsion polymerisation, resulting in latex particles which are dispersed in water and contain long-chain acrylic polymers. When the emulsion is dried, the latex particles coalesce and an adhesive film is formed. The rheological properties of the dried samples are believed to be dominated by the interface regions between the original latex particles, but the relation between rheology and latex particle properties is poorly understood. In this paper we show that it is possible to describe the bulk rheology of a pressure-sensitive adhesive by means of a mesoscale simulation model. To reach experimental time and length scales, each latex particle is represented by just one simulated particle. The model is subjected to oscillatory shear flow and extensional flow. Simple order of magnitude estimates of the model parameters already lead to semi-quantitative agreement with experimental results. We show that inclusion of transient forces in the model, i.e. forces with memory of previous configurations, is essential to correctly predict the linear and nonlinear properties.Comment: 29 pages, 8 figure

Reduced dimension modeling of leading edge turbulent interaction noise

A computational aeroacoustics approach is used to model the effects of real airfoil geometry on leading edge turbulent interaction noise for symmetric airfoils at zero angle of attack. For the first time, one-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulent disturbances are modeled instead of single frequency transverse gusts, which previous computational studies of leading edge noise have been confined to. The effects of the inclusion of streamwise and spanwise disturbances on the noise are assessed, and it is shown that accurate noise predictions for symmetric airfoils can be made by modeling only the transverse disturbances, which reduces the computational expense of simulations. Additionally, the two-component turbulent synthesis method is used to model the effects of airfoil thickness on the noise for thicknesses ranging from 2% to 12%. By using sufficient airfoil thicknesses to show trends, it is found that airfoil thickness will reduce the noise at high frequency, and that the sound power P will reduce linearly with increasing airfoil thickness

Protention and retention in biological systems

This paper proposes an abstract mathematical frame for describing some features of cognitive and biological time. We focus here on the so called "extended present" as a result of protentional and retentional activities (memory and anticipation). Memory, as retention, is treated in some physical theories (relaxation phenomena, which will inspire our approach), while protention (or anticipation) seems outside the scope of physics. We then suggest a simple functional representation of biological protention. This allows us to introduce the abstract notion of "biological inertia".Comment: This paper was made possible only as part of an extended collaboration with Francis Bailly (see references), a dear friend and "ma\^itre \'a penser", who contributed to the key ideas. Francis passed away in february 2008: we continue here our inspiring discussions and joint wor

Assessing optical earth observation systems for mapping and monitoring temporary ponds in arid areas

Remote sensing methods for locating and monitoring temporary ponds over large areas in arid lands were tested on a study site in Northern Senegal. Three main results are presented, validated with field data and intended to highlight different spectral, spatial and temporal characteristics of the methods: (1) Among several water indices tested, two Middle Infrared-based indices (MNDWIModified Normalized Difference Water Index and NDWI1Normalized Difference Water Index) are found to be most efficient; (2) an objective method is given prescribing the necessary sensor spatial resolution in terms of minimal detected pond area; and (3) the potential of multi-temporal MODIS imagery for tracking the filling phases of small ponds is illustrated. These results should assist in epidemiological studies of vector-borne diseases that develop around these ponds, but also more generally for land and water management and preservation of threatened ecosystems in arid areas

New determinations of gamma-ray line intensities of the Ep = 550 keV and Ep = 1747 keV resonances of the 13-C(p,gamma)14-N reaction

Gamma-ray angular distributions for the resonances at Ep = 550 keV and 1747 keV of the radiative capture reaction 13-C(p,g)14-N have been measured, using intense proton beams on isotopically pure 13-C targets. Relative intensities for the strongest transitions were extracted with an accuracy of typically five per cent, making these resonances new useful gamma-ray standards for efficiency calibration in the energy range Egamma = 1.6 to 9 MeV.Comment: 17 pages, 6 figures, Nuclear Instruments and Methods, Sec. A, accepte

Simulating geometric uncertainties of impervious areas based on image segmentation accuracy metrics

International audienceUrban sprawl monitoring is important for developing land management policies at various spatial scales. Segmentation and classification of satellite images allows obtaining polygons of impervious areas regularly over large areas, e.g. as has been implemented for the region Languedoc‐Roussillon in the south of France using 5 m RapidEye images. Starting from the results of this previous study, we aim to: i) evaluate the geometric and thematic accuracy of the impervious polygons (S) using segmentation accuracy metrics, and ii) use these metrics to simulate polygons having the same level of uncertainty. A manual segmentation (M) was used to evaluate the accuracy. After matching the polygons, the distance (d) and azimuth (a) of each vertex of M to the closest segment of the boundary of S was calculated. Spherically correlated random fields of d and a were used to randomly move the vertices of S. Realistic simulations of impervious polygons were obtained

Coupling potential of ICESat/GLAS and SRTM for the discrimination of forest landscape types in French Guiana

The Shuttle Radar Topography Mission (SRTM) has produced the most accurate nearly global elevation dataset to date. Over vegetated areas, the measured SRTM elevations are the result of a complex interaction between radar waves and tree crowns. In this study, waveforms acquired by the Geoscience Laser Altimeter System (GLAS) were combined with SRTM elevations to discriminate the five forest landscape types (LTs) in French Guiana. Two differences were calculated: (1) penetration depth, defined as the GLAS highest elevations minus the SRTM elevations, and (2) the GLAS centroid elevations minus the SRTM elevations. The results show that these differences were similar for the five LTs, and they increased as a function of the GLAS canopy height and of the SRTM roughness index. Next, a Random Forest (RF) classifier was used to analyze the coupling potential of GLAS and SRTM in the discrimination of forest landscape types in French Guiana. The parameters used in the RF classification were the GLAS canopy height, the SRTM roughness index, the difference between the GLAS highest elevations and the SRTM elevations and the difference between the GLAS centroid elevations and the SRTM elevations. Discrimination of the five forest landscape types in French Guiana was possible, with an overall classification accuracy of 81.3% and a kappa coefficient of 0.75. All forest LTs were well classified with an accuracy varying from 78.4% to 97.5%. Finally, differences of near coincident GLAS waveforms, one from the wet season and one from the dry season, were analyzed. The results showed that the open forest LT (LT12), in some locations, contains trees that lose leaves during the dry season. These trees allow LT12 to be easily discriminated from the other LTs that retain their leaves using the following three criteria: (1) difference between the GLAS centroid elevations and the SRTM elevations, (2) ratio of top energy in the wet season to top energy in the dry season, or (3) ratio of ground energy in the wet season to ground energy in the dry season

Regional scale rain-forest height mapping using regression-kriging of spaceborneand airborne lidar data: application on French Guiana

IGARSS 2015, Milan, ITA, 26-/07/2015 - 31/07/2015International audienceLiDAR remote sensing has been shown to be a good technique for the estimation of forest parameters such as canopy heights and aboveground biomass. Whilst airborne LiDAR data are in general very dense but only available over small areas due to the cost of their acquisition, spaceborne LiDAR data acquired from the Geoscience Laser Altimeter System (GLAS) have a coarser acquisition density associated with a global cover. It is therefore valuable to analyze the integration relevance of canopy heights estimated from LiDAR sensors with ancillary data such as geological, meteorological, and phenological variables in order to propose a forest canopy height map with good precision and high spatial resolution.In this study, canopy heights extracted from both airborne and spaceborne LiDAR, were first extrapolated from available environmental data. The estimated canopy height maps using random forest (RF) regression from the airborne or GLAS calibration datasets showed similar precisions (RMSE better than 6.5 m). In order to improve the precision of the canopy height estimates regression-kriging (kriging of RF regression residuals) was used. Results indicated an improvement in the RMSE (decrease from 6.5 to 4.2 m) for the regression-kriging maps from the GLAS dataset, and from 5.8 to 1.8 m for the regression-kriging map from the airborne LiDAR dataset