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Despite major advances in the understanding of the formation and dynamics of nano-clusters in the past decades, theoretical bases for the control of their shape are still lacking. We investigate strategies for driving fluctuating few-particle clusters to an arbitrary target shape in minimum time with or without an external field. This question is recast into a first passage problem, solved numerically, and discussed within a high temperature expansion. Without field, large-enough low-energy target shapes exhibit an optimal temperature at which they are reached in minimum time. We then compute the optimal way to set an external field to minimize the time to reach the target, leading to a gain of time that grows when increasing cluster size or decreasing temperature. This gain can shift the optimal temperature or even create one. Our results could apply to clusters of atoms at equilibrium, and colloidal or nanoparticle clusters under thermo- or electrophoresis., Comment: Accepted for publication in Phys. Rev. Lett

PURPOSE In cardiovascular imaging, the numerous contrast injection protocols used to enhance structures make it difficult to gather training datasets for deep learning applications supporting diverse protocols. Moreover, creating annotations on non-contrast scans is extremely tedious. Recently, spectral CT's virtual-non-contrast images (VNC) have been used as data augmentation to train segmentation networks performing on enhanced and true-non-contrast (TNC) scans alike, while improving results on protocols absent of their training dataset. However, spectral data are not widely available, making it difficult to gather specific datasets for each task. As a solution, we present a data augmentation workflow based on a trained image translation network, to bring spectral-like augmentation to any conventional CT dataset. METHOD The HU-to-spectral image translation network (HUSpecNet) was first trained to generate VNC from HU images, using an unannotated spectral dataset of 1830 patients. It was then tested on a second dataset of 300 spectral CT scans, by comparing generated VNC (VNCDL ) to their true counterparts. To illustrate and compare our workflow's efficiency with true spectral augmentation, HUSpecNet was applied to a third dataset of 112 spectral scans to generate VNCDL along HU and VNC images. Three different 3D networks (U-Net, X-Net, U-Net++) were trained for multi-label heart segmentation, following four augmentation strategies. As baselines, trainings were performed on contrasted images without (HUonly) and with conventional gray-values augmentation (HUaug). Then, the same networks were trained using a proportion of contrasted and VNC/VNCDL images (TrueSpec/GenSpec). Each training strategy applied to each architecture was evaluated using Dice coefficients on a fourth multi-centric multi-vendor single-energy CT dataset of 121 patients, including different contrast injection protocols and unenhanced scans. The U-Net++ results were further explored with distance metrics on every label. RESULTS Tested on 300 full scans, our HUSpectNet translation network shows a mean absolute error of 6.70±2.83 HU between VNCDL and VNC, while peak-signal-to-noise-ratio reaches 43.89 dB. GenSpec and TrueSpec show very close results regardless of the protocol and used architecture: mean Dice coefficients (DSCmean ) are equal with a margin of 0.006, ranging from 0.879 to 0.938. Their performances significantly increase on TNC scans (p-values

International audience

National audience; Au moment de leur conception, les systèmes d'exploitation modernes implémentent une stratégie de sécurité et d'isolation bien précise reposant sur un ou plusieurs mécanismes logiciels ou matériels. Pour des raisons de coût, ce choix est rarement revisité après déploiement. Cette approche classique est limitée lorsque les protections matérielles viennent à casser, lorsque le matériel devient hétérogène, ou lorsque l'on cherche à spécialiser dynamiquement le système pour un cas d'usage précis. Nous présentons FlexOS, un système d'exploitation permettant de facilement spécialiser la stratégie d'isolation du noyau à la compilation et non à la conception. FlexOS est un LibOS modulable incluant des composants isolables à des granularités variables via de multiples mécanismes, d'un langage de description permettant à l'utilisateur de détailler les besoins en sécurité du système, et d'un framework d'exploration automatique des compromis de sécurité et performance offerts par FlexOS pour une application donnée. Nous évaluons FlexOS et démontrons le vaste espace de conception qu'il permet d'explorer.

Purpose This work presents our contribution to a data challenge organized by the French Radiology Society during the Journees Francophones de Radiologie in October 2018. This challenge consisted in classifying MR images of the knee with respect to the presence of tears in the knee menisci, on meniscal tear location, and meniscal tear orientation. Materials and methods We trained a mask region-based convolutional neural network (R-CNN) to explicitly localize normal and torn menisci, made it more robust with ensemble aggregation, and cascaded it into a shallow ConvNet to classify the orientation of the tear. Results Our approach predicted accurately tears in the database provided for the challenge. This strategy yielded a weighted AUC score of 0.906 for all three tasks, ranking first in this challenge. Conclusion The extension of the database or the use of 3D data could contribute to further improve the performances especially for non-typical cases of extensively damaged menisci or multiple tears.

Grain boundary (GB) roughness can affect electronic and mechanical properties of two-dimensional materials. This roughness depends crucially on the growth process by which the two-dimensional material is formed. To investigate the key mechanisms that govern the GB roughening, we have performed kinetic Monte Carlo simulations of a simple model that includes particle attachment, detachment, and diffusion. We have studied the closure of the gap between two flakes during growth, and the subsequent formation of the GB for a broad range of model parameters. The well-known near-equilibrium (attachment-limited) and unstable (diffusion-limited) growth regimes are identified, but we also observe a third regime when the precursor flux is sufficiently high to saturate the gap between the edges with diffusing species. This high deposition rate regime forms GBs with spatially uncorrelated roughness, which quickly relax to smoother configurations. Extrapolating the numerical results (with support from a theoretical approach) to edge lengths and gap widths of some micrometres, we confirm the advantage of this regime to produce GBs with minimal roughness faster than near-equilibrium conditions. This suggests an unexpected route towards efficient growth of two-dimensional materials with smooth GBs.

Blooms of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations affecting the recreational use and the tourism economy along southern Brittany (NE-Atlantic, France). Hypoxic conditions associated with phytoplankton biomass recycling are suspected to cause fauna mortalities. An in situ monitoring was performed in 2019 to characterise the seasonal variability of L. chlorophorum. This species was observed from May to November, with a maximum abundance in June–July. Specific bloom sampling demonstrated a dominance of L. chlorophorum within microphytoplankton, and documented its vertical distribution. Satellite observation was used to compute the surface extent of the bloom and to highlight the importance of small-scale temporal variability, with tidal currents being a primary driver of surface distribution of the bloom. Stratification contributed to promoting the bloom of L. chlorophorum. High concentrations of phosphate and ammonium, together with transparent exopolymer particles (TEP), were recorded within the bloom. Bacterial stimulation, leading to nutrient remineralisation or mucus facilitating mixotrophy, is suggested to sustain bloom development. Hence, TEP production might provide an ecological advantage for the dinoflagellate, conversely causing negative effects on the environment and biological resources through hypoxia. These first insights constitute a baseline for further studies in other ecosystems impacted by this species.

This paper describes the study and design of a 1 DoF attitude control system for a 1U CubeSat based on reaction wheel with the aim of implementing it on a PCB along with a magnetorquers system. This thesis takes place in the frame of the PLATHON project which aims to develop a simulation platform for optical communications between nanosatellites by regrouping many students and teacher from the Polytechnical University of Catalonia (UPC). To do this, a complete state of the art presents the features of nanosatellites and the existing technology to control the attitude of a CubeSat. Then, the method used for reading and controlling the attitude of a CubeSat is explained. To be more precise, the principle of operation of two Inertial Measurement Unit (IMU) is shown to understand how the attitude can be red. Along with this, the controlling program of the reaction wheel system is detailed to have an overview of the different functions required to impose a certain positioning to the CubeSat. The design of the hardware components of the project is then presented. Most of the pieces have been drawn under Solidworks software and manufactured by a 3D printer. Finally, the result of some experiments made at the university laboratory with an air bearing system are presented. Those results are discussed and highlight the different problems encountered over the project.

The growth of crystals confined in porous or cellular materials is ubiquitous in Nature and forms the basis of many industrial processes. Confinement affects the formation of biominerals in living organisms, of minerals in the Earth’s crust and of salt crystals damaging porous limestone monuments, and is also used to control the growth of artificial crystals. However, the mechanisms by which confinement alters crystal shapes and growth rates are still not elucidated. Based on novel in situ optical observations of (001) surfaces of NaClO3 and CaCO3 crystals at nanometric distances from a glass substrate, we demonstrate that new molecular layers can nucleate homogeneously and propagate without interruption even when in contact with other solids, raising the macroscopic crystal above them. Confined growth is governed by the peculiar dynamics of these molecular layers controlled by the two-dimensional transport of mass through the liquid film from the edges to the center of the contact, with distinctive features such as skewed dislocation spirals, kinetic localization of nucleation in the vicinity of the contact edge, and directed instabilities. Confined growth morphologies can be predicted from the values of three main dimensionless parameters.

We model the nonlinear response of a lubricated contact composed of a two-dimensional lipid membrane immersed in a simple fluid between two parallel flat and porous walls under shear. The nonlinear dynamics of the membrane gives rise to a rich dynamical behavior depending on the shear velocity. In quiescent conditions (i.e., absence of shear), the membrane freezes into a disordered labyrinthine wrinkle pattern. In the presence of shear, we find four different regimes depending on the shear rate. Regime I. For small shear, the labyrinthine pattern is still frozen, but exhibits a small drift which is mainly along the shear direction. In this regime, the tangential forces on the walls due to the presence of the membrane increase linearly with the shear rate. Regime II. When the shear rate is increased above a critical value, the membrane rearranges, and wrinkles start to align along the shear direction. This regime is accompanied by a sharp drop of the tangential forces on the wall. Regime III. For larger shear rates, the wrinkles align strongly along the shear direction, with a set of dislocation defects which assemble in pairs. The tangential forces are then controlled by the number of dislocations, and by the number of wrinkles between the two dislocations within each dislocation pairs. In this dislocation-dominated regime, the tangential forces in the transverse direction most often exceed those in the shear direction. Regime IV. For even larger shear, the membrane organizes into a perfect array of parallel stripes with no defects. The wavelength of the wrinkles is still identical to the wavelength in the absence of shear. In this final regime, the tangential forces due to the membrane vanish. These behaviors give rise to a non-linear rheological behavior of lubricated contacts containing membranes., Soft Matter (2021)

Legume-rhizobium symbiosis is a major ecological process in the nitrogen cycle, responsible for the main input of fixed nitrogen into the biosphere. The efficiency of this symbiosis relies on the coevolution of the partners., Legume plants can form root organs called nodules where they house intracellular symbiotic rhizobium bacteria. Within nodule cells, rhizobia differentiate into bacteroids, which fix nitrogen for the benefit of the plant. Depending on the combination of host plants and rhizobial strains, the output of rhizobium-legume interactions varies from nonfixing associations to symbioses that are highly beneficial for the plant. Bradyrhizobium diazoefficiens USDA110 was isolated as a soybean symbiont, but it can also establish a functional symbiotic interaction with Aeschynomene afraspera. In contrast to soybean, A. afraspera triggers terminal bacteroid differentiation, a process involving bacterial cell elongation, polyploidy, and increased membrane permeability, leading to a loss of bacterial viability while plants increase their symbiotic benefit. A combination of plant metabolomics, bacterial proteomics, and transcriptomics along with cytological analyses were used to study the physiology of USDA110 bacteroids in these two host plants. We show that USDA110 establishes a poorly efficient symbiosis with A. afraspera despite the full activation of the bacterial symbiotic program. We found molecular signatures of high levels of stress in A. afraspera bacteroids, whereas those of terminal bacteroid differentiation were only partially activated. Finally, we show that in A. afraspera, USDA110 bacteroids undergo atypical terminal differentiation hallmarked by the disconnection of the canonical features of this process. This study pinpoints how a rhizobium strain can adapt its physiology to a new host and cope with terminal differentiation when it did not coevolve with such a host. IMPORTANCE Legume-rhizobium symbiosis is a major ecological process in the nitrogen cycle, responsible for the main input of fixed nitrogen into the biosphere. The efficiency of this symbiosis relies on the coevolution of the partners. Some, but not all, legume plants optimize their return on investment in the symbiosis by imposing on their microsymbionts a terminal differentiation program that increases their symbiotic efficiency but imposes a high level of stress and drastically reduces their viability. We combined multi-omics with physiological analyses to show that the symbiotic couple formed by Bradyrhizobium diazoefficiens USDA110 and Aeschynomene afraspera, in which the host and symbiont did not evolve together, is functional but displays a low symbiotic efficiency associated with a disconnection of terminal bacteroid differentiation features.

International audience; We propose a method for segmenting two unregistered images from different modalities of the same patient and study at once, while enforcing a similarity constraint between the two segmentation masks. Our method relies on a segmentation network and a registration network, cooperating to get accurate and consistent segmentation masks across modalities, while forcing the segmentor to use all information available. Experiments on a dataset of T1 and T2-weighted liver MRI show that our method enables to get more similar segmentation masks across modalities than manual annotations, without deteriorating the performance (Dice =0.95 for T1, 0.92 for T2).

Biomembranes experience out-of-equilibrium conditions in living cells. Their undulation spectra are different from those in thermal equilibrium. Here, we report on the undulation of a fluid membrane pushed by the stepwise growth of filaments as in the leading edge of migrating cells, using three-dimensional Monte Carlo simulations. The undulations are largely modified from equilibrium behavior. When the tension is constrained, the low-wave-number modes are suppressed or enhanced at small or large growth step sizes, respectively, for high membrane surface tensions. In contrast, they are always suppressed for the tensionless membrane , wherein the wave-number range of the suppression depends on the step size. When the membrane area is constrained, in addition to these features, a specific mode is excited for zero and low surface tensions. The reduction of the undulation first induces membrane buckling at the lowest wave-number, and subsequently, other modes are excited, leading to a steady state.

The quantitative knowledge of interface anisotropy in lattice models is a major issue, both for the parametrization of continuum interface models, and for the analysis of experimental observations. In this paper, we focus on the anisotropy of line tension and stiffness, which plays a major role both in equilibrium shapes and fluctuations, and in the selection of nonequilibrium growth patterns. We consider a 2D Ising Hamiltonian on a square lattice with first and second-nearest-neighbor interactions. The surface stiffness and line tension are calculated by means of a broken-bond model for arbitrary orientations. The analysis of the interface energy allows us to determine the conditions under which stiffness anisotropy is minimal. These results are supported by a quantitative comparison with kinetic Monte Carlo simulations, based on the coupling of a field of mobile atoms to a condensed phase. Furthermore, we introduce a generic smoothing parameter which allows one to mimic the finite resolution of experimental microscopy techniques. Our results provide a method to fine-tune the interface energy in models of nanoscale non-equilibrium processes, where anisotropy and fluctuations combine and give rise to non-trivial morphologies.

We report on the influence of elastic strain on solid-state dewetting. Using continuum modeling, we first study the consequences of elastic stress on the pinching of the film away from the triple line during dewetting. We find that elastic stress in the solid film decreases both the time and the distance at which the film pinches in such a way that the dewetting front is accelerated. In addition, the spatial organization of islands emerging from the dewetting process is affected by strain. As an example, we demonstrate that ordered arrays of quantum dots can be achieved from solid-state dewetting of a square island in the presence of elastic stress.

Spectral CT scanner is an emerging technology in the clinical field, which al-lows to generate from a single scan conventional HU images, virtual non-contrast images (VNC) corresponding to unenhanced CT images on conventional CT scanners, and virtual mono-energetic (monoE) images at different keV that mimics low (at high keV) to high (at low keV) iodine-based contrast-enhanced studies. It has been demonstrated that these spectral images could be used as data augmentation for cardiovascular structures segmentation, improving dice scores on contrasted images, and enabling to segment true non-contrast (TNC) conventional scans. However, as of now, spectral CT are not widely distributed, making this data augmentation process not widely available.To overcome this limitation, we propose in this study CASPER, a full data augmentation workflow to provide any conventional CT training dataset with spectral CT augmentation capabilities. We trained on an unannotated data-base of 2500 spectral scans an image translation network (HUSpecNet) to create monoEs and VNC from conventional HU images. Any conventional CT scan exam can then be translated to mimic different contrast agent injection protocols.We evaluated our CASPER methodology by training a 3D U-net to segment the aorta, both with and without data augmentation on 143 annotated conventional scans. The network performances were compared on a testing dataset of 70 patients, including pulmonary embolism (PE) early enhancement scans, full chest-abdominal-pelvic delayed enhancement scans and TNC scans. The network trained using CASPER outperformed significantly the network trained without it, on every imaging protocols, and especially on TNC.

We report on the orientation and morphology of solid-state dewetting holes obtained from a kinetic Monte Carlo model with nearest neighbor and next nearest neighbor interactions on a cubic lattice. The morphologies found in simulations share strong similarities with those of diffusion-limited crystal growth: We find compact shapes, isotropic and anisotropic seaweed shapes, and dendritic shapes. Some of these shapes have been observed in solid-state dewetting experiments with various semi-conductors or metals on insulating substrates. The sides of the fingers can exhibit two types of zigzag instabilities with ${90}^{\ensuremath{\circ}}$ or ${45}^{\ensuremath{\circ}}$. Due to fourfold symmetry, dewetting hole shapes are found to exhibit two possible orientations with fingers along the (110) or (100) directions. We find that the rotation transition from one orientation to the other can be observed in our model by varying anisotropy, temperature, or dewetting strength. The two orientations correspond, respectively, to experimental observations of dewetting for silicon and germanium on insulator and to the dewetting of metal films with different reducing gas flow rate.

The unikernel is an emerging operating system model offering lightweightness, security and performance benefits. In this paperwe argue that a fundamental design principle of unikernels, the fact that one instance is viewed as a single unit of trust, is not suitable for the high security requirements of today’s cloud applications. We advocate for the introduction of intra-unikernel isolation. We observe that some unikernel benefits derive from another fundamental design principle: the presence of a single address space .We investigate bringing intra-unikernel isolation without breaking that principle with the help of hardware technologies in the form of modern (Intel Memory Protection Keys) and future (hardware capabilities) Instruction Set Architecture extensions.

International audience; Surface-diffusion mediated solid-state dewetting has been observed and studied in a number of different systems during the past two decades. This process can be accompanied by the pinching of the film at a finite distance from the retracting triple line. The repetition of this pinching is often referred to as periodic mass shedding. We show that the disjoining pressure of the film can accelerate mass shedding by orders of magnitude in ultrathin films with nanometric thickness. In the presence of power-law disjoining pressures induced by van der Waals forces, the mass shedding time exhibits an approximate power-law dependence on film thickness $t_{ms}∼¯h^ν$, with $ν≈6$. Exponentially decaying disjoining forces also give rise to a strong acceleration of mass shedding. However, due to the finite range of the exponential potential, the mass shedding time does not exhibit a simple power-law dependence on the thickness, and is controlled by a cutoff thickness. In addition, two-dimensional simulations indicate that, within the range of thicknesses that we have studied and for isotropic dynamics, the transversal instability of a straight front does not lead to fingering, and mass shedding is the dominant instability of the dewetting front. Finally, we also show that no significant difference is observed in the dewetting dynamics between simulations based on a model with a wetting potential integrated over the film surface area, or over the projected substrate area.

Under nitrogen-limiting conditions, legumes are able to interact symbiotically with bacteria of the Rhizobiaceae family. This interaction gives rise to a new organ, named a root nodule. Root nodules are characterized by an increased glutathione (GSH) and homoglutathione (hGSH) content compared to roots. These low molecular thiols are very important in the biological nitrogen fixation. In order to characterize the modification of nodule activity induced by the microsymbiont glutathione deficiency, physiological, biochemical, and gene expression modifications were analyzed in nodules after the inoculation of Medicago truncatula with the SmgshB mutant of Sinorhizobium meliloti which is deficient in GSH production. The decline in nitrogen fixation efficiency was correlated to the reduction in plant shoot biomass. Flow cytometry analysis showed that SmgshB bacteroids present a higher DNA content than free living bacteria. Live/dead microscopic analysis showed an early bacteroid degradation in SmgshB nodules compared to control nodules which is correlated to a lower bacteroid content at 20 dpi. Finally, the expression of two marker genes involved in nitrogen fixation metabolism, Leghemoglobin and Nodule Cysteine Rich Peptide 001, decreased significantly in mutant nodules at 20 dpi. In contrast, the expression of two marker genes involved in the nodule senescence, Cysteine Protease 6 and Purple Acid Protease, increased significantly in mutant nodules at 10 dpi strengthening the idea that an early senescence process occurs in SmgshB nodules. In conclusion, our results showed that bacterial GSH deficiency does not impair bacterial differentiation but induces an early nodule senescence.

Macrophage Migration Inhibitory Factors (MIF) are pivotal cytokines/chemokines for vertebrate immune systems. MIFs are typically soluble single-domain proteins that are conserved across plant, fungal, protist, and metazoan kingdoms but their functions have not been determined in most phylogenetic groups. Here we describe an atypical multidomain MIF protein. The marine dinoflagellate Lingulodinium polyedra produces a transmembrane protein with an extra-cytoplasmic MIF domain, which localizes to cell wall-associated membranes and vesicular bodies. This protein is also present in the membranes of extracellular vesicles accumulating at the secretory pores of the cells. Upon exposure to biotic stress, L. polyedra exhibits reduced expression of the MIF gene and reduced abundance of the surface-associated protein. These findings indicate that the transmembrane MIF may contribute to intercellular communication and/or interactions between free-living organisms in multispecies planktonic communities and raise the question of possible analogies in MIF functions between cells of metazoan organisms and protist communities.