An automatic correction of Ma's thinning algorithm based on P -simple points

International audienceThe notion of P -simple points has been introduced by Bertrand to conceive parallel thinning algorithms. In 'A 3D fully parallel thinning algorithm for generating medial faces', Ma has proposed an algorithm for which there exists objects whose topology is not preserved. In this paper, we propose a new application of P -simple points: to automatically correct Ma's algorithm

Automatic correction of Ma and Sonka's thinning algorithm using P-simple points

International audienceMa and Sonka proposed a fully parallel 3D thinning algorithm which does not always preserve topology. We propose an algorithm based on P-simple points which automatically corrects Ma and Sonka's Algorithm. As far as we know, our algorithm is the only fully parallel curve thinning algorithm which preserves topology

Contribution à la caractérisation fonctionnelle de protéines de contrôle de la sécrétion d'effecteurs de type III chez la bactérie phytopathogène Ralstonia solanacearum : chaperonnes et protéine à domaine T3S4

La bactérie phytopathogène Ralstonia solanacearum est l'agent responsable du flétrissement bactérien sur plus de 200 espèces végétales, dont des espèces agronomiques, faisant de cette bactériose une des plus importantes dans le monde. Le pouvoir pathogène de la bactérie repose en grande partie sur sa capacité à injecter des protéines, appelées effecteurs de type III (ET3s), via le système de sécrétion de type III (SST3). La dernière décennie a été notamment marquée par la découverte chez les bactéries pathogènes de nombreuses protéines impliquées dans le contrôle du processus de sécrétion de type III. Chez R. solanacearum, ces mécanismes de contrôle de la sécrétion restent méconnus, contrairement aux mécanismes de régulation transcriptionnelle. Au cours de ces travaux, nous nous sommes attachés à caractériser les fonctions des protéines HpaB (RSp0853), HpaD (RSp0848) et FliT-like (RSc2897) pour lesquelles plusieurs éléments suggèrent un potentiel rôle comme chaperonnes de type III (CT3s), ainsi que de la protéine HpaP (RSp0862) qui présente un domaine T3S4 (Type III Secretion Substrate Specificity Switch). Nous avons pu mettre en évidence la capacité de certaines CT3s à interagir entre elles et, pour HpaB et HpaD, à interagir avec de nombreux ET3s. De plus, les trois CT3s putatives semblent impliquées dans le pouvoir pathogène de R. solanacearum, HpaB s'avérant même indispensable à la virulence de la bactérie. D'autre part, nos travaux mettent en exergue l'importance de la protéine HpaP pour le pouvoir pathogène de la bactérie et son implication dans le contrôle de la sécrétion de substrats du SST3. Les résultats suggèrent notamment que HpaP promeut la sécrétion de l'ET3 PopP1 en interagissant physiquement avec ce dernier. Finalement, la caractérisation de séquences conservées du domaine T3S4 révèle l'importance de cette région pour la fonction de la protéine HpaP. L'ensemble de ces travaux suggère l'implication de plusieurs protéines de R. solanacearum dans le contrôle du processus de sécrétion de type III et souligne la diversité des mécanismes mis en jeu impliquant les protéines de type T3S4 chez les bactéries pathogènes.The plant pathogenic bacterium Ralstonia solanacearum is the causative agent of the bacterial wilt on more than 200 plant species, including agronomic species, making it one of the most important bacterial disease in the world. The pathogenicity of the bacteria is largely based on its ability to inject proteins, called type III effectors (T3Es) via the type III secretion system (T3SS) . The last decade has been particularly marked by the discovery of many proteins involved in the control of the type III secretion process in pathogenic bacteria. In R. solanacearum , these control mechanisms remain unknown , unlike the transcriptional regulatory mechanisms. In this work, we focused on the functional characterization of the proteins HpaB (Rsp0853), HpaD (RSp0848) and FliT-like (RSc2897) for which several elements suggest a potential role as type III chaperones (T3Cs). We also focused on the HpaP protein (Rsp0862) which harbors a T3S4 domain (Type III Secretion Substrate Specificity Switch). We showed the ability of some CT3s to interact with each other and, concerning HpaB and HpaD, to interact with many T3Es. In addition, the three putative T3Cs seem to be involved in the pathogenicity of R. solanacearum, HpaB being even strictly required for bacterial virulence. Furthermore, our work highlights the importance of HpaP in pathogenicity and its involvement in the control of the secretion of T3SS substrates. The results suggest in particular that HpaP promotes the secretion of the T3E PopP1 by physically interacting with the latter. Finally, the characterization of conserved sequences in the T3S4 domain reveals the importance of this region for the function of the HpaP protein. On the whole, this work suggests the involvement of several proteins of R. solanacearum in the control of the type III secretion process and highlights the diversity of mechanisms in which T3S4 proteins are involved in pathogenic bacteria

Internet advertising to recruit respondents for a web-based survey on the mobility of teenagers. Effectiveness in five European countries

To study mobility behaviours and images of transport modes of teenagers in Europe, we organized a web-based survey in 2016. The population concerned is composed of teenagers (14-17 years old) living in five European countries (France, Germany, Great-Britain, Italy and Spain). Knowing the difficulty to reach teenagers through telephone and postal surveys, especially in five different countries, we decided to create a web-based survey. To recruit respondants, we paid for targeting advertising on Facebook, with a Facebook page for each country. To measure the impacts of advertising, we used several tools, from Facebook and from the survey platform. This poster aims at drawing lessons of this methodological experience and making some propositions for future surveys. We

What controls the formation of nocturnal low-level stratus clouds over southern West Africa during the monsoon season?

Nocturnal low-level stratus clouds (LLCs) are frequently observed in the atmospheric boundary layer (ABL) over southern West Africa (SWA) during the summer monsoon season. Considering the effect these clouds have on the surface energy and radiation budgets as well as on the diurnal cycle of the ABL, they are undoubtedly important for the regional climate. However, an adequate representation of LLCs in the state-of-the-art weather and climate models is still a challenge, which is largely due to the lack of high-quality observations in this region and gaps in understanding of underlying processes. In several recent studies, a unique and comprehensive data set collected in summer 2016 during the DACCIWA (Dynamics-aerosol-chemistry-cloud interactions in West Africa) ground-based field campaign was used for the first observational analyses of the parameters and physical processes relevant for the LLC formation over SWA. However, occasionally stratus-free nights occur during the monsoon season as well. Using observations and ERA5 reanalysis, we investigate differences in the boundary-layer conditions during 6 stratus-free and 20 stratus nights observed during the DACCIWA campaign. Our results suggest that the interplay between three major mechanisms is crucial for the formation of LLCs during the monsoon season: (i) the onset time and strength of the nocturnal low-level jet (NLLJ), (ii) horizontal cold-air advection, and (iii) background moisture level. Namely, weaker or later onset of NLLJ leads to a reduced contribution from horizontal cold-air advection. This in turn results in weaker cooling, and thus saturation is not reached. Such deviation in the dynamics of the NLLJ is related to the arrival of a cold air mass propagating northwards from the coast, called Gulf of Guinea maritime inflow. Additionally, stratus-free nights occur when the intrusions of dry air masses, originating from, for example, central or south Africa, reduce the background moisture over large parts of SWA. Backward-trajectory analysis suggests that another possible reason for clear nights is descending air, which originated from drier levels above the marine boundary layer

Conceptual model of diurnal cycle of low-level stratiform clouds over southern West Africa

The DACCIWA (Dynamics Aerosol Chemistry Cloud Interactions in West Africa) project and the associated ground-based field experiment, which took place during summer 2016, provided a comprehensive dataset on the low-level stratiform clouds (LLSCs), which develop almost every night over southern West Africa. The LLSCs, inaccurately represented in climate and weather forecasts, form in the monsoon flow during the night and break up during the following morning or afternoon, affecting considerably the radiation budget. Several published studies give an overview of the measurements during the campaign, analyse the dynamical features in which the LLSCs develop, and quantify the processes involved in the LLSC formation. Based on the main results of these studies and new analyses, we propose in this paper a conceptual model of the diurnal cycle of the LLSCs over southern West Africa. Four main phases compose the diurnal cycle of the LLSC. The stable and the jet phases are the two steps during which the relative humidity increases, due to cooling of the air, until the air is saturated and the LLSCs form. Horizontal advection of cold air from the Guinean coast by the maritime inflow and the nocturnal low-level jet (NLLJ) represents 50% of the local total cooling. The remaining half is mainly due to divergence of net radiation and turbulence flux. The third step of the LLSC diurnal cycle is the stratus phase, which starts during the night and lasts until the onset of surface-buoyancy-driven turbulence on the following day. During the stratus phase, interactions between the LLSCs and the NLLJ lead to a modification of the wind speed vertical profile in the cloud layer, and a mixing of the sub-cloud layer by shear-driven turbulence below the NLLJ core. The breakup of the LLSC occurs during the convective phase and follows three different scenarios which depend on the intensity of the turbulence observed during the night in the sub-cloud layer. The breakup time has a considerable impact on the energy balance of the Earth’s surface and, consequently, on the depth of the convective boundary layer, which could vary by a factor of 2 from day-to-day

Histolocalization and physico-chemical characterization of dihydrochalcones: Insight into the role of apple major flavonoids

Flavonoids, like other metabolites synthesized via the phenylpropanoid pathway, possess a wide range of biological activities including functions in plant development and its interaction with the environment. Dihydrochalcones (mainly phloridzin, sieboldin, trilobatin, phloretin) represent the major flavonoid subgroup in apple green tissues. Although this class of phenolic compounds is found in very large amounts in some tissues (≈200 mg/g of leaf DW), their physiological significance remains unclear. In the present study, we highlight their tissue-specific localization in young growing shoots suggesting a specific role in important physiological processes, most notably in response to biotic stress. Indeed, dihydrochalcones could constitute a basal defense, in particular phloretin which exhibits a strong broad-range bactericidal and fungicidal activity. Our results also indicate that sieboldin forms complexes with iron with strong affinity, reinforcing its antioxidant properties and conferring to this dihydrochalcone a potential for iron seclusion and/or storage. The importance of localization and biochemical properties of dihydrochalcones are discussed in view of the apple tree defense strategy against both biotic and abiotic stresses

Low-level stratiform clouds and dynamical features observed within the southern West African monsoon

During the boreal summer, the monsoon season that takes place in West Africa is accompanied by low stratus clouds over land that stretch from the Guinean coast several hundred kilometers inland. Numerical climate and weather models need finer description and knowledge of cloud macrophysical characteristics and of the dynamical and thermodynamical structures occupying the lowest troposphere, in order to be properly evaluated in this region. The Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) field experiment, which took place in summer 2016, addresses this knowledge gap. Low-level atmospheric dynamics and stratiform low-level cloud macrophysical properties are analyzed using in situ and remote sensing measurements continuously collected from 20 June to 30 July at Savè, Benin, roughly 180 km from the coast. The macrophysical characteristics of the stratus clouds are deduced from a ceilometer, an infrared cloud camera, and cloud radar. Onset times, evolution, dissipation times, base heights, and thickness are evaluated. The data from an ultra-high-frequency (UHF) wind profiler, a microwave radiometer, and an energy balance station are used to quantify the occurrence and characteristics of the monsoon flow, the nocturnal low-level jet, and the cold air mass inflow propagating northward from the coast of the Gulf of Guinea. The results show that these dynamical structures are very regularly observed during the entire 41 d documented period. Monsoon flow is observed every day during our study period. The so-called “maritime inflow” and the nocturnal low-level jet are also systematic features in this area. According to synoptic atmospheric conditions, the maritime inflow reaches Savè around 18:00–19:00 UTC on average. This timing is correlated with the strength of the monsoon flow. This time of arrival is close to the time range of the nocturnal low-level jet settlement. As a result, these phenomena are difficult to distinguish at the Savè site. The low-level jet occurs every night, except during rain events, and is associated 65 % of the time with low stratus clouds. Stratus clouds form between 22:00 and 06:00 UTC at an elevation close to the nocturnal low-level jet core height. The cloud base height, 310±30 m above ground level (a.g.l.), is rather stationary during the night and remains below the jet core height. The cloud top height, at 640±100 m a.g.l., is typically found above the jet core. The nocturnal low-level jet, low-level stratiform clouds, monsoon flow, and maritime inflow reveal significant day-to-day and intra-seasonal variability during the summer given the importance of the different monsoon phases and synoptic atmospheric conditions. Distributions of strength, depth, onset time, breakup time, etc. are quantified here. These results contribute to satisfy the main goals of DACCIWA and allow a conceptual model of the dynamical structures in the lowest troposphere over the southern part of West Africa

Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season

Within the framework of the DACCIWA (Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa) project and based on a field experiment conducted in June and July 2016, we analyze the daytime breakup of continental low-level stratiform clouds in southern West Africa. We use the observational data gathered during 22 precipitation-free occurrences at Savè, Benin. Our analysis, which starts from the stratiform cloud formation usually at night, focuses on the role played by the coupling between cloud and surface in the transition towards shallow convective clouds during daytime. It is based on several diagnostics, including the Richardson number and various cloud macrophysical properties. The distance between the cloud base height and lifting condensation level is used as a criterion of coupling. We also make an attempt to estimate the most predominant terms of the liquid water path budget in the early morning. When the nocturnal low-level stratiform cloud forms, it is decoupled from the surface except in one case. In the early morning, the cloud is found coupled with the surface in 9 cases and remains decoupled in the 13 other cases. The coupling, which occurs within the 4 h after cloud formation, is accompanied by cloud base lowering and near-neutral thermal stability in the subcloud layer. Further, at the initial stage of the transition, the stratiform cloud base is slightly cooler, wetter and more homogeneous in coupled cases. The moisture jump at the cloud top is usually found to be lower than 2 g kg−1 and the temperature jump within 1–5 K, which is significantly smaller than typical marine stratocumulus and explained by the monsoon flow environment in which the stratiform cloud develops over West Africa. No significant difference in liquid water path budget terms was found between coupled and decoupled cases. In agreement with previous numerical studies, we found that the stratiform cloud maintenance before sunrise results from the interplay between the predominant radiative cooling, entrainment and large-scale subsidence at its top. Three transition scenarios were observed depending on the state of coupling at the initial stage. In coupled cases, the low-level stratiform cloud remains coupled until its breakup. In five of the decoupled cases, the cloud couples with the surface as the lifting condensation level rises. In the eight remaining cases, the stratiform cloud remains hypothetically decoupled from the surface throughout its life cycle since the height of its base remains separated from the condensation level. In cases of coupling during the transition, the stratiform cloud base lifts with the growing convective boundary layer roughly between 06:30 and 08:00 UTC. The cloud deck breakup, occurring at 11:00 UTC or later, leads to the formation of shallow convective clouds. When the decoupling subsists, shallow cumulus clouds form below the stratiform cloud deck between 06:30 and 09:00 UTC. The breakup time in this scenario has a stronger variability and occurs before 11:00 UTC in most cases. Thus, we argue that the coupling with the surface during daytime hours has a crucial role in the low-level stratiform cloud maintenance and its transition towards shallow convective clouds