MapRDD : finer grained resilient distributed dataset for machine learning

The Resilient Distributed Dataset (RDD) is the core memory abstraction behind the popular data-analytic framework Apache Spark. We present an extension to the Resilient Distributed Dataset for map transformations, that we call MapRDD, which takes advantage of the underlying relations between records in the parent and child datasets, in order to achieve random-access of individual records in a partition. The design is complemented by a new MemoryStore, which manages data sampling and data transfers asynchronously. We use the ImageNet dataset to demonstrate that: (I) The initial data loading phase is redundant and can be completely avoided; (II) Sampling on the CPU can be entirely overlapped with training on the GPU to achieve near full occupancy; (III) CPU processing cycles and memory usage can be reduced by more than 90%, allowing other applications to be run simultaneously; (IV) Constant training step time can be achieved, regardless of the size of the partition, for up to 1.3 million records in our experiments. We expect to obtain the same improvements in other RDD transformations via further research on finer-grained implicit & explicit dataset relations

Virtual imaging trials improved the transparency and reliability of AI systems in COVID-19 imaging

The credibility of AI models in medical imaging is often challenged by reproducibility issues and obscured clinical insights, a reality highlighted during the COVID-19 pandemic by many reports of near-perfect artificial intelligence (AI) models that all failed to generalize. To address these concerns, we propose a virtual imaging trial framework, employing a diverse collection of medical images that are both clinical and simulated. In this study, COVID-19 serves as a case example to unveil the intrinsic and extrinsic factors influencing AI performance. Our findings underscore a significant impact of dataset characteristics on AI efficacy. Even when trained on large, diverse clinical datasets with thousands of patients, AI performance plummeted by up to 20% in generalization. However, virtual imaging trials offer a robust platform for objective assessment, unveiling nuanced insights into the relationships between patient- and physics-based factors and AI performance. For instance, disease extent markedly influenced AI efficacy, computed tomography (CT) out-performed chest radiography (CXR), while imaging dose exhibited minimal impact. Using COVID-19 as a case study, this virtual imaging trial study verified that radiology AI models often suffer from a reproducibility crisis. Virtual imaging trials not only offered a solution for objective performance assessment but also extracted several clinical insights. This study illuminates the path for leveraging virtual imaging to augment the reliability, transparency, and clinical relevance of AI in medical imaging.Comment: 3 tables, 4 figures, 1 Supplemen

Discovery of a new M32-like "Compact Elliptical" galaxy in the halo of the Abell 496 cD galaxy

Aims: ``Compact ellipticals'' are so rare that a search for M32 analogs is needed to ensure the very existence of this class. Methods: We report here the discovery of A496cE, a M32 twin in the cluster Abell 496, located in the halo of the central cD. Results: Based on CFHT and HST imaging we show that the light profile of A496cE requires a two component fit: a Sersic bulge and an exponential disc. The spectrum of A496cE obtained with the ESO-VLT FLAMES/Giraffe spectrograph can be fit by a stellar synthesis spectrum dominated by old stars, with high values of [Mg/Fe] and velocity dispersion. Conclusions: The capture of A496cE by the cD galaxy and tidal stripping of most of its disc are briefly discussed.Comment: 4 pages, 4 figures, accepted for publication in A&A Letter

Proceedings Virtual Imaging Trials in Medicine 2024

This submission comprises the proceedings of the 1st Virtual Imaging Trials in Medicine conference, organized by Duke University on April 22-24, 2024. The listed authors serve as the program directors for this conference. The VITM conference is a pioneering summit uniting experts from academia, industry and government in the fields of medical imaging and therapy to explore the transformative potential of in silico virtual trials and digital twins in revolutionizing healthcare. The proceedings are categorized by the respective days of the conference: Monday presentations, Tuesday presentations, Wednesday presentations, followed by the abstracts for the posters presented on Monday and Tuesday

Revealing the Mechanism for Covalent Inhibition of Glycoside Hydrolases by Carbasugars at an Atomic Level

Mechanism-based glycoside hydrolase inhibitors are carbohydrate analogs that mimic the natural substrate’s structure. Their covalent bond formation with the glycoside hydrolase makes these compounds excellent tools for chemical biology and potential drug candidates. Here we report the synthesis of cyclohexene-based α-galactopyranoside mimics and the kinetic and structural characterization of their inhibitory activity toward an α-galactosidase from Thermotoga maritima (TmGalA). By solving the structures of several enzyme-bound species during mechanism-based covalent inhibition of TmGalA, we show that the Michaelis complexes for intact inhibitor and product have half-chair (2H3) conformations for the cyclohexene fragment, while the covalently linked intermediate adopts a flattened half-chair (2H3) conformation. Hybrid QM/MM calculations confirm the structural and electronic properties of the enzyme-bound species and provide insight into key interactions in the enzyme-active site. These insights should stimulate the design of mechanism-based glycoside hydrolase inhibitors with tailored chemical properties

Disk Galaxy Evolution Along the Hubble Sequence

Galaxy disks are characterised by star formation histories that vary systematically along the Hubble sequence. We study global star formation, incorporating supernova feedback, gas accretion and enriched outflows in disks modelled by a multiphase interstellar medium in a fixed gravitational potential. The star formation histories, gas distributions and chemical evolution can be explained in a simple sequence of models which are primarily regulated by the cold gas accretion history.Comment: 12 pages, 12 figure

Kinematics and Stellar Populations of Low-Luminosity Early-Type Galaxies in the Abell 496 Cluster

The morphology and stellar populations of low-luminosity early-type galaxies in clusters have until now been limited to a few relatively nearby clusters such as Virgo or Fornax. Scenarii for the formation and evolution of dwarf galaxies in clusters are therefore not well constrained. We investigate here the morphology and stellar populations of low-luminosity galaxies in the relaxed cluster Abell 496 (z=0.0330). Deep multiband imaging obtained with the CFHT Megacam allowed us to select a sample of faint galaxies (-18.8<M_B<-15.1 mag). We observed 118 galaxies spectroscopically with the ESO VLT FLAMES/Giraffe spectrograph (R=6300). We present structural analysis and colour maps for the 48 galaxies belonging to the cluster. We fit the spectra of 46 objects with PEGASE.HR synthetic spectra to estimate the ages, metallicities, and velocity dispersions. We computed values of $\alpha$/Fe abundance ratios from the measurements of Lick indices. High-precision estimates of stellar population properties have been obtained for a large sample of faint galaxies in a cluster, allowing for the extension of relations between stellar populations and internal kinematics to the low-velocity dispersion regime. We have revealed a peculiar population of elliptical galaxies in the core of the cluster, resembling massive early-type galaxies by their stellar population properties and velocity dispersions, but having luminosities of about 2 mag fainter. External mechanisms of gas removal (ram pressure stripping and gravitational harassment) are more likely to have occurred than internal mechanisms such as supernova-driven winds. The violent tidal stripping of intermediate-luminosity, early-type galaxies in the cluster core can explain the properties of the peculiar elliptical galaxies surrounding the cD galaxy.Comment: Accepted to A&A, 48 pages, 62 figures, 3 tables. This version contains low-resolution figures. We encourage you to get the full-resolution PDF (16Mb) from http://voplus.obspm.fr/DataCollections/Abell0496

The Current Status of Galaxy Formation

Understanding galaxy formation is one of the most pressing issues in cosmology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarise the prospects for future advances.Comment: Minor change in Sect. 6 (resolution of ERIS simulation). Note that the figures of the arXiv version are typically sharper than on the published versio