A Stochastic Method for Solving Time-Fractional Differential Equations

We present a stochastic method for efficiently computing the solution of time-fractional partial differential equations (fPDEs) that model anomalous diffusion problems of the subdiffusive type. After discretizing the fPDE in space, the ensuing system of fractional linear equations is solved resorting to a Monte Carlo evaluation of the corresponding Mittag-Leffler matrix function. This is accomplished through the approximation of the expected value of a suitable multiplicative functional of a stochastic process, which consists of a Markov chain whose sojourn times in every state are Mittag-Leffler distributed. The resulting algorithm is able to calculate the solution at conveniently chosen points in the domain with high efficiency. In addition, we present how to generalize this algorithm in order to compute the complete solution. For several large-scale numerical problems, our method showed remarkable performance in both shared-memory and distributed-memory systems, achieving nearly perfect scalability up to 16,384 CPU cores.Comment: Submitted to the Journal of Computational Physic

A Fast Monte Carlo algorithm for evaluating matrix functions with application in complex networks

We propose a novel stochastic algorithm that randomly samples entire rows and columns of the matrix as a way to approximate an arbitrary matrix function. This contrasts with the "classical" Monte Carlo method which only works with one entry at a time, resulting in a significant better convergence rate than the "classical" approach. To assess the applicability of our method, we compute the subgraph centrality and total communicability of several large networks. In all benchmarks analyzed so far, the performance of our method was significantly superior to the competition, being able to scale up to 64 CPU cores with a remarkable efficiency.Comment: Submitted to the Journal of Scientific Computin

OmpSs-2 and OpenACC interoperation

We propose an interoperation mechanism to enable novel composability across pragma-based programming models. We study and propose a clear separation of duties and implement our approach by augmenting the OmpSs-2 programming model, compiler and runtime system to support OmpSs-2 + OpenACC programming. To validate our proposal we port ZPIC, a kinetic plasma simulator, to leverage our hybrid OmpSs-2 + OpenACC implementation. We compare our approach against OpenACC versions of ZPIC on a multi-GPU HPC system. We show that our approach manages to provide automatic asynchronous and multi-GPU execution, removing significant burden from the application’s developer, while also being able to outperform manually programmed versions, thanks to a better utilization of the hardware.This work has been part of the EPEEC project. The EPEEC project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 801051. This paper was also partially funded by the Ministerio de Ciencia e Innovación Agencia Estatal de Investigación (PID2019-107255GB-C21/AEI/10.13039/501100011033). We gratefully acknowledge the support of NVIDIA AI Technology Center (NVAITC) Europe who provided us the remote access to NVIDIA DGX-1Peer ReviewedPostprint (author's final draft

Towards OmpSs-2 and OpenACC interoperation

The increasing demand in HPC to utilize accelerators has motivated the development of pragma-based directives to target these devices. OmpSs-2 and OpenACC are both directive-based solutions that allow application programmers to utilize accelerators. The two leverage distinct types of parallelism: task parallelism and data parallelism, respectively. Non-trivial scientific applications can benefit from both types of available parallelism. However, the combination of pragma-based models is difficult to coordinate, as both assume full control and are unaware of each other at runtime. We propose an interoperation mechanism to enable novel composability across pragma-based programming models. We study and propose a clear separation of duties and implement our approach by augmenting the OmpSs-2 programming model, compiler and runtime to support OmpSs-2 + OpenACC programmingPeer ReviewedPostprint (author's final draft

Particle-In-Cell Simulation using Asynchronous Tasking

Recently, task-based programming models have emerged as a prominent alternative among shared-memory parallel programming paradigms. Inherently asynchronous, these models provide native support for dynamic load balancing and incorporate data flow concepts to selectively synchronize the tasks. However, tasking models are yet to be widely adopted by the HPC community and their effective advantages when applied to non-trivial, real-world HPC applications are still not well comprehended. In this paper, we study the parallelization of a production electromagnetic particle-in-cell (EM-PIC) code for kinetic plasma simulations exploring different strategies using asynchronous task-based models. Our fully asynchronous implementation not only significantly outperforms a conventional, synchronous approach but also achieves near perfect scaling for 48 cores.Comment: To be published on the 27th European Conference on Parallel and Distributed Computing (Euro-Par 2021

Particle-in-cell simulation using asynchronous tasking

Recently, task-based programming models have emerged as a prominent alternative among shared-memory parallel programming paradigms. Inherently asynchronous, these models provide native support for dynamic load balancing and incorporate data flow concepts to selectively synchronize the tasks. However, tasking models are yet to be widely adopted by the HPC community and their effective advantages when applied to non-trivial, real-world HPC applications are still not well comprehended. In this paper, we study the parallelization of a production electromagnetic particle-in-cell (EM-PIC) code for kinetic plasma simulations exploring different strategies using asynchronous task-based models. Our fully asynchronous implementation not only significantly outperforms a conventional, synchronous approach but also achieves near perfect scaling for 48 cores.Peer ReviewedPostprint (author's final draft

THE EFESTO PROJECT: FLEXIBLE TPS DESIGN AND TESTING FOR ADVANCED EUROPEAN RE-ENTRY SYSTEM BASED ON INFLATABLE HEAT SHIELDS

The European Union H2020 project EFESTO has been implemented with the main objective to improve the technology readiness level (TRL) of flexible inflatable heat shields for re-entry vehicles in Europe from 3 to 4 or 5. For this purpose, two reference missions with atmospheric entry to Earth and Mars were selected. Both missions were designed to make best use of the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) concept. Multidisciplinary design loops allowed prediction of the entry flight trajectory and identification of the aerothermodynamic environment on the exterior of the system. These results were the primary inputs to the design and testing of the Flexible Thermal Protection System (FTPS) layup and the underlying inflatable structure. This paper provides an insight into the efforts related to design, testing and numerical modelling of the FTPS for both applications. Advanced flexible materials were selected, some of which never had been considered in Europe before. These materials allow for a significant improvement upon previous design in system weight and maximum heat loads. Several multi-layer layups were developed for both applications, each of them allowing to keep the surface temperature below the material-specific upper limit. The most promising layups were selected for experimental simulation in DLR's arc-heated facilities LBK at flight relevant high-enthalpy conditions in realistic thermochemical environment. This testing covered both stagnation flow and tangential flow conditions in Mars and Earth atmospheres. Extensive numerical efforts were carried out to perform test rebuilding and allow cross-correlation between numerical and experimental simulations. The numerical models were calibrated with the wind tunnel data and further assisted in the analysis of the experimental results and the derivation of material specific properties and uncertainties. The project allowed to validate numerical models and simulations tools. This enables Europe to reliably design FTPS layups in future initiatives in the strategic field of re-entry solutions based on inflatable heat shields. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 821801

MICROSCOPE mission: first results of a space test of the equivalence principle

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10−15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[−1±9(stat)±9(syst)]×10−15 (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations

Progéniteurs luminaux prostatiques

Les traitements médicaux de l’hyperplasie bénigne et du cancer de la prostate reposent essentiellement sur l’inhibition de la signalisation androgénique. Bien qu’initialement efficaces, ces traitements sont tôt ou tard confrontés à une résistance thérapeutique. Des données récentes de séquençage d’ARN sur cellules uniques montrent que les cellules luminales survivant à la déprivation androgénique dans ces contextes pathologiques présentent un profil moléculaire semblable à celui de cellules luminales progénitrices, présentes en faible quantité dans un contexte physiologique. Ce profil moléculaire pourrait constituer un hub de résistance à la castration et résulter, en partie, de la reprogrammation des cellules luminales tumorales. L’inhibition thérapeutique de cette plasticité cellulaire constitue une piste prometteuse pour limiter la progression du cancer prostatique

Encyclopédie, ou Dictionnaire raisonné des sciences, des arts et des métiers, par une société de gens de lettres. Tome sixieme ET=FN

Mis en ordre & publié par m. Diderot, ... & quant à la partie mathématique, par m. d'Alembert, ...Seconde édition enrichie de notes, & donnée au public par M. Octavien Diodati noble lucquoi