Automatic Scheduling for a Ground Segment as a Service Platform Dedicated to Small Satellites

Together with the development of nano, micro, and small satellite missions and constellations, the necessity for efficient and tailored ground segments is raising. The peculiarities of the market together with the technological developments of the recent years have led to the idea of ground segment as a service. To meet these needs Leaf Space introduced Leaf Line. An essential part of such service consists of scheduling contact windows over the worldwide-deployed network of ground stations. This is an NP-hard problem, which is often solved with methods belonging to the class of operational research. Generally, the orbits of small satellites are very low, characterized by short-timed contact windows. This condition leads to needs way different from those associated to long-lived high-orbit satellites, which most of the literature on scheduling algorithms for telecommunication systems is focused on. Furthermore, a service dedicated to SMEs and NewSpace startups brings additional challenges linked to customer needs. These peculiarities require the development of new, tailored, scheduling algorithms. In the proposed strategy it is assumed to have no information about the state of the satellite (stored data and available energy), and that start and end of contact windows are fixed. In this work, the scheduling is treated as a highly constrained combinatorial optimization problem; various approaches are described and then compared. Such algorithms are iterative, and they all leverage the structure of the problem; specifically, many efforts are made to appropriately reduce the search space. Although optimality cannot be guaranteed, good solutions that are reasonably close to optimal can be obtained. It is found that depending on the problem settings, different algorithms can stand out as the best ones. This paper presents the work done on the scheduling library that is currently powering the Leaf Line network: this platform is offering an easy-to-use, cloud-based and high-availability ground segment service for small satellites operators

A diffuse interface approach for disperse two-phase flows involving dual-scale kinematics of droplet deformation based on geometrical variables

The purpose of this contribution is to derive a reduced-order two-phase flow model in- cluding interface subscale modeling through geometrical variables based on Stationary Action Principle (SAP) and Second Principle of Thermodynamics in the spirit of [6, 14]. The derivation is conducted in the disperse phase regime for the sake of clarity but the resulting paradigm can be used in a more general framework. One key issue is the definition of the proper potential and kinetic energies in the Lagrangian of the system based on geometrical variables (Interface area density, mean and Gauss curvatures...), which will drive the subscale kinematics and dissipation, and their coupling with large scales of the flow. While [14] relied on bubble pulsation, that is normal deformation of the interface with shape preservation related to pressure changes, we aim here at tackling inclusion deformation at constant volume, thus describing self-sustained oscillations. In order to identify the proper energies, we use Direct Numerical Simulations (DNS) of oscillating droplets using ARCHER code and recently devel- oped library, Mercur(v)e, for mean geometrical variable evaluation and analysis preserving topological invariants. This study is combined with historical analytical studies conducted in the small perturba- tion regime and shows that the proper potential energy is related to the surface difference compared to the spherical minimal surface. A geometrical quasi-invariant is also identified and a natural definition of subscale momentum is proposed. The set of Partial Differential Equations (PDEs) including the conservation equations as well as dissipation source terms are eventually derived leading to an original two-scale diffuse interface model involving geometrical variables

Mapping genomic loci implicates genes and synaptic biology in schizophrenia

Schizophrenia has a heritability of 60-80%1, much of which is attributable to common risk alleles. Here, in a two-stage genome-wide association study of up to 76,755 individuals with schizophrenia and 243,649 control individuals, we report common variant associations at 287 distinct genomic loci. Associations were concentrated in genes that are expressed in excitatory and inhibitory neurons of the central nervous system, but not in other tissues or cell types. Using fine-mapping and functional genomic data, we identify 120 genes (106 protein-coding) that are likely to underpin associations at some of these loci, including 16 genes with credible causal non-synonymous or untranslated region variation. We also implicate fundamental processes related to neuronal function, including synaptic organization, differentiation and transmission. Fine-mapped candidates were enriched for genes associated with rare disruptive coding variants in people with schizophrenia, including the glutamate receptor subunit GRIN2A and transcription factor SP4, and were also enriched for genes implicated by such variants in neurodevelopmental disorders. We identify biological processes relevant to schizophrenia pathophysiology; show convergence of common and rare variant associations in schizophrenia and neurodevelopmental disorders; and provide a resource of prioritized genes and variants to advance mechanistic studies

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Vers une modélisation eulérienne unifiée pour les écoulements diphasiques : phénomènes géométriques à petite échelle et stratégies de calcul flexibles associées

In current times we are witnessing a “second space race”: private companies like SpaceX are paving the way to a new generation of space launcher systems optimized for cost effectiveness and extreme performances that will bring humankind to Mars for the first time in its existence. A key aspect of those systems is to provide a high level of reusability leading to a drastic drop of launch costs. This translates into propulsion systems that need to operate on wider flight envelopes, with more advantageous propellant pairs like cryogenic methane and liquid oxygen, therefore requiring tighter designs for the injection systems. The injectors are responsible for the correct nebulization of fuel and oxidizer and they have a direct impact on the performance of the engines. These kind of problems are shared across different applications and are somehow generic The current state of the art modeling strategies fail at predicting the correct distributions of droplets in the combustion chamber. Therefore, the target of this thesis is to contribute to the design of a unified modeling framework addressing the derivation of system of equations governing two-phase flow systems characterized by a sound mathematical structure via a variational approach named Stationary Action Principle (SAP) coupled to the second principle of thermodynamics. This effort is backed by a tailored computational toolset that allows the rational choice of modeling assumptions and the effective simulations of the developed models, possibly on modern computing architectures. This work identifies three main points of improvement: the development of reduced-order models via a variational procedure named the Stationary Action Principle (SAP) featuring a set of equations that include geometrical properties such as the interfacial surface density and the mean and Gauss curvatures; the implementation of a geometric DNS post-processing tool that is used to collect useful insight from high-fidelity simulations in order to craft an accurate reducedorder model, and the development of a Python library that acts as a prototyping playbook aimed at quickly testing ideas in the context of numerical schemes, boundary conditions, domain configurations, with the potential ability of leveraging modern computational architectures such as GPUs.Nous assistons actuellement à une “deuxième course à l'espace” : des entreprises privées comme SpaceX ouvrent la voie à une nouvelle génération de systèmes de lanceurs spatiaux optimisés pour leur rentabilité et leurs performances extrêmes, qui permettront à l'humanité d'atteindre Mars pour la première fois dans son existence. L'un des aspects essentiels de ces systèmes est d'offrir un niveau élevé de réutilisation, ce qui entraîne une baisse drastique des coûts de lancement. Cela se traduit par des systèmes de propulsion qui doivent fonctionner dans des enveloppes de vol plus larges, avec des paires d'ergols plus avantageuses comme le méthane et l'oxygène liquides, ce qui exige une conception plus rigoureuse des systèmes d'injection. Les injecteurs sont responsables de la nébulisation correcte des ergols et ils ont un impact direct sur les performances des moteurs. Les stratégies de modélisation actuelles ne parviennent pas à prédire les distributions correctes de gouttelettes dans la chambre de combustion. L'objectif de cette thèse est donc d'offrir un cadre de modélisation unifié permettant la dérivation de systèmes d'équations pour les écoulements diphasique, caractérisé par une structure mathématique solide obtenue avec un principe variationnel appelé “Principe d'Action stationnaire” (SAP). Cet effort est soutenu par un ensemble d'outils informatiques adaptés qui permettent le choix rationnel des hypothèses de modélisation et la simulation efficace des modèles développés, éventuellement sur des architectures modernes. Ce travail identifie trois points principaux d'amélioration : le développement de modèles d'ordre réduit avec le SAP, comportant un ensemble d'équations qui incluent des propriétés géométriques telles que la densité de la surface interfaciale et les courbures moyenne et de Gauss ; la mise en œuvre d'un outil de post-traitement géométrique pour les simulations à haute-fidelité utilisé pour recueillir des informations utiles afin d'élaborer un modèle d'ordre réduit précis, et le développement d'une bibliothèque Python qui agit comme un outil de prototypage rapide visant à tester rapidement des idées dans le contexte des schémas numériques, des conditions limites, des configurations de domaine, avec la possibilité d'exploiter des architectures de calcul modernes comme les GPU

Vers une modélisation eulérienne unifiée pour les écoulements diphasiques : phénomènes géométriques à petite échelle et stratégies de calcul flexibles associées

Nous assistons actuellement à une “deuxième course à l'espace” : des entreprises privées comme SpaceX ouvrent la voie à une nouvelle génération de systèmes de lanceurs spatiaux optimisés pour leur rentabilité et leurs performances extrêmes, qui permettront à l'humanité d'atteindre Mars pour la première fois dans son existence. L'un des aspects essentiels de ces systèmes est d'offrir un niveau élevé de réutilisation, ce qui entraîne une baisse drastique des coûts de lancement. Cela se traduit par des systèmes de propulsion qui doivent fonctionner dans des enveloppes de vol plus larges, avec des paires d'ergols plus avantageuses comme le méthane et l'oxygène liquides, ce qui exige une conception plus rigoureuse des systèmes d'injection. Les injecteurs sont responsables de la nébulisation correcte des ergols et ils ont un impact direct sur les performances des moteurs. Les stratégies de modélisation actuelles ne parviennent pas à prédire les distributions correctes de gouttelettes dans la chambre de combustion. L'objectif de cette thèse est donc d'offrir un cadre de modélisation unifié permettant la dérivation de systèmes d'équations pour les écoulements diphasique, caractérisé par une structure mathématique solide obtenue avec un principe variationnel appelé “Principe d'Action stationnaire” (SAP). Cet effort est soutenu par un ensemble d'outils informatiques adaptés qui permettent le choix rationnel des hypothèses de modélisation et la simulation efficace des modèles développés, éventuellement sur des architectures modernes. Ce travail identifie trois points principaux d'amélioration : le développement de modèles d'ordre réduit avec le SAP, comportant un ensemble d'équations qui incluent des propriétés géométriques telles que la densité de la surface interfaciale et les courbures moyenne et de Gauss ; la mise en œuvre d'un outil de post-traitement géométrique pour les simulations à haute-fidelité utilisé pour recueillir des informations utiles afin d'élaborer un modèle d'ordre réduit précis, et le développement d'une bibliothèque Python qui agit comme un outil de prototypage rapide visant à tester rapidement des idées dans le contexte des schémas numériques, des conditions limites, des configurations de domaine, avec la possibilité d'exploiter des architectures de calcul modernes comme les GPU.In current times we are witnessing a “second space race”: private companies like SpaceX are paving the way to a new generation of space launcher systems optimized for cost effectiveness and extreme performances that will bring humankind to Mars for the first time in its existence. A key aspect of those systems is to provide a high level of reusability leading to a drastic drop of launch costs. This translates into propulsion systems that need to operate on wider flight envelopes, with more advantageous propellant pairs like cryogenic methane and liquid oxygen, therefore requiring tighter designs for the injection systems. The injectors are responsible for the correct nebulization of fuel and oxidizer and they have a direct impact on the performance of the engines. These kind of problems are shared across different applications and are somehow generic The current state of the art modeling strategies fail at predicting the correct distributions of droplets in the combustion chamber. Therefore, the target of this thesis is to contribute to the design of a unified modeling framework addressing the derivation of system of equations governing two-phase flow systems characterized by a sound mathematical structure via a variational approach named Stationary Action Principle (SAP) coupled to the second principle of thermodynamics. This effort is backed by a tailored computational toolset that allows the rational choice of modeling assumptions and the effective simulations of the developed models, possibly on modern computing architectures. This work identifies three main points of improvement: the development of reduced-order models via a variational procedure named the Stationary Action Principle (SAP) featuring a set of equations that include geometrical properties such as the interfacial surface density and the mean and Gauss curvatures; the implementation of a geometric DNS post-processing tool that is used to collect useful insight from high-fidelity simulations in order to craft an accurate reducedorder model, and the development of a Python library that acts as a prototyping playbook aimed at quickly testing ideas in the context of numerical schemes, boundary conditions, domain configurations, with the potential ability of leveraging modern computational architectures such as GPUs

Derivation of a two-phase flow model with two-scale kinematics and surface tension by means of variational calculus

International audienceThe present paper proposes a definition of a two-phase interface that relies on a probability density function. This definition enables to introduce a scale separation in the definition this interface and to define fields that characterize the geometry of the interface. Relying on these fields, we propose a two-phase flow model that is able to account for small and large scale separation of the interface description by means of supplementary convected geometric variables. The model accounts for two-scale kinematics and two-scale surface tension. At large scale, the flow and the full geometry of the interface may be retrieved thanks to the bulk variables and the volume fraction, while at small scale the interface dynamics is accurately recovered through the interfacial area density fluctuation and the mean curvature

Numerical Study of an Isothermal Slush Flow for Aerospace Propulsion Applications

status: Published onlin

Derivation of a two-phase flow model with two-scale kinematics, geometric variables and surface tension using variational calculus

International audienceThe present paper proposes a two-phase flow model that is able to account for two-scale kinematics and two-scale surface tension effects based on geometric variables at small scale. At large scale, the flow and the full geometry of the interface may be retrieved thanks to the bulk variables, while at small scale the interface is accurately described by volume fraction, interfacial area density and mean curvature, called the geometric variables. Our work mainly relies on the Least Action Principle. The resulting system is an extension of a previous work modeling small scale pulsation in which surface tension was not taken into account at large or small scale. Whereas the original derivation assumes a cloud of monodispersed spherical bubbles, the present context allows for polydispersed, non-spherical bubbles. The resulting system of equations solely involves small scale geometric variables, thus contributing in the construction of a unified model describing both large and small scales

Post-processing of two-phase DNS simulations exploiting geometrical features and topological invariants to extract flow statistics: application to canonical objects and the collision of two droplets

International audienceThis work presents a methodology to collect useful flow statistics over DNS simulations exploiting geometrical properties maps and topological invariants. The procedure is based on estimating curvatures on triangulated surfaces as as averaged values around a given point and its first neighbours (the 1-ring of such a point). In the case of two-phase flow high-fidelity simulations, the surfaces are obtained after an iso-contouring procedure of the volumetric level-set field. The estimation of the curvatures on the surface allows the possibility of characterizing the 3D objects that are created in a high-fidelity simulation in terms of their area-weighted geometrical maps. In this work we provide an assessment of the robustness of the curvature estimation algorithm applied to some canonical 3D objects and to the Direct Numerical Simulation of the collision of two droplets. We provide the tracking of the topological evolution of such objects in terms of geometrical maps and we highlight the effect of mesh resolution on those topological changes