De la logique philosophique à la logique mathématique. Introduction

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From Scientific Philosophy to Absolute Positivism: Abel Rey and the Vienna Circle

On associe généralement l’expression de philosophie scientifique au positivisme logique, lequel se signale par son recours à la logique mathématique dans l’analyse des problèmes philosophiques. Or il apparaît à plus proche examen que cette expression est employée dès 1848 par Ernest Renan. La tentative d’élaborer une philosophie scientifique fait l’objet d’un long débat. Au tournant du xxe siècle, Abel Rey reprend cette question. Or, son livre, La Théorie de la physique chez les physiciens contemporains, exercera une influence forte sur le Cercle de Vienne. Le positivisme absolu que propose Rey présente à la fois des analogies frappantes et des différences notables avec le positivisme logique. Si on y trouve le même souci de clarté et de précision, la logique n’est pas au centre de la démarche philosophique. Les diverses sciences, des mathématiques à la psychologie, sont mises à contribution. Il n’y a pas de hiérarchie, mais un encyclopédisme visant à inclure toutes les données fournies par la recherche scientifique. À travers l’étude comparée de la conception d’Abel Rey et de celle du Cercle de Vienne, il s’agit ici d’interroger la possibilité d’une philosophie scientifique.The concept of scientific philosophy is generally associated with logical positivism or logical empiricism, which is characterized by its recourse to mathematical logic in tackling philosophical problems. But on closer inspection it appears that this concept was employed as early as 1848 by Ernest Renan. The attempt to elaborate a scientific philosophy gave rise to a lengthy debate. At the turn of the twentieth century, Abel Rey took up the issue again. His book, La Théorie de la physique chez les physiciens contemporains, exerted a strong influence on the Vienna Circle. Rey’s absolute positivism reveals striking analogies and sharp contrasts with logical positivism. If we find the same requirement for clearness and precision, logic for Rey is not the main focus of philosophical method. The various sciences, from mathematics to psychology, are called on. There is no hierarchy but an encyclopedia, whose aim is to encompass all results of scientific research. By way of a comparative study of Abel Rey and the Vienna Circle, I seek to question the possibility of a scientific philosophy

Epistémologie d'une science de la nature

Publication de l'IREM de Montpellier - production du groupe Mathématiques et PhilosophieCette ressource présente une activité menée en cours de philosophie en classe de Terminale. Un débat sur l’épistémologie d’une science de la nature précède l’exploitation d’une analyse d’un texte de Popper qui conduit à une institutionnalisation des concepts suivans : Théorie scientifique / raison / réel / vérité / Connaissance / interprétation. La ressource inclut également deux fichiers satellites : l'un qui questionne les démarches de classification des sciences, en lien avec leurs épistémologies ; l'autre qui vise à éclairer le concept de falsification de Popper du point de vue de la logique. Ces documents sont rédigés à destination des professeurs de philosophie et de sciences, en tant que ressource pour la classe et pour l'auto-formation des enseignants

Single-shot temporal characterization of XUV pulses with duration from ~10 fs to ~350 fs at FLASH

Ultra-short extreme ultraviolet pulses from the free-electron laser FLASH are characterized using terahertz-field driven streaking. Measurements at different ultra-short extreme ultraviolet wavelengths and pulse durations as well as numerical simulations were performed to explore the application range and accuracy of the method. For the simulation of streaking, a standard classical approach is used which is compared to quantum mechanical theory, based on strong field approximation. Various factors limiting the temporal resolution of the presented terahertz streaking setup are investigated and discussed. Special attention is paid to the cases of very short (similar to 10 fs) and long (up to similar to 350 fs) pulses.We want to acknowledge the work of the scientific and technical team at FLASH. NMK acknowledges the hospitality and financial support from DESY and from the theory group in cooperation with the SQS research group of the European XFEL (Hamburg). KW and MD acknowledge support by the SFB925-A1. UF and AD acknowledge support by the excellence cluster `The Hamburg Center for Ultrafast Imaging-Structure, Dynamics and Control of Matter at the Atomic Scale' (DFG)-EXC 1074 project ID 194651731. SW acknowledges support by the DFG Forschergruppe FOR 1789. Editoria

Noise Reduction and Image Quality Improvement of Low Dose and Ultra Low Dose Brain Perfusion CT by HYPR-LR Processing

To evaluate image quality and signal characteristics of brain perfusion CT (BPCT) obtained by low-dose (LD) and ultra-low-dose (ULD) protocols with and without post-processing by highly constrained back-projection (HYPR)–local reconstruction (LR) technique.Simultaneous BPCTs were acquired in 8 patients on a dual-source-CT by applying LD (80 kV,200 mAs,14×1.2 mm) on tube A and ULD (80 kV,30 mAs,14×1.2 mm) on tube B. Image data from both tubes was reconstructed with identical parameters and post-processed using the HYPR-LR. Correlation coefficients between mean and maximum (MAX) attenuation values within corresponding ROIs, area under attenuation curve (AUC), and signal to noise ratio (SNR) of brain parenchyma were assessed. Subjective image quality was assessed on a 5-point scale by two blinded observers (1:excellent, 5:non-diagnostic).Radiation dose of ULD was more than six times lower compared to LD. SNR was improved by HYPR: ULD vs. ULD+HYPR: 1.9±0.3 vs. 8.4±1.7, LD vs. LD+HYPR: 5.0±0.7 vs. 13.4±2.4 (both p<0.0001). There was a good correlation between the original datasets and the HYPR-LR post-processed datasets: r = 0.848 for ULD and ULD+HYPR and r = 0.933 for LD and LD+HYPR (p<0.0001 for both). The mean values of the HYPR-LR post-processed ULD dataset correlated better with the standard LD dataset (r = 0.672) than unprocessed ULD (r = 0.542), but both correlations were significant (p<0.0001). There was no significant difference in AUC or MAX. Image quality was rated excellent (1.3) in LD+HYPR and non-diagnostic (5.0) in ULD. LD and ULD+HYPR images had moderate image quality (3.3 and 2.7).SNR and image quality of ULD-BPCT can be improved to a level similar to LD-BPCT when using HYPR-LR without distorting attenuation measurements. This can be used to substantially reduce radiation dose. Alternatively, LD images can be improved by HYPR-LR to higher diagnostic quality

Duhemian Themes in Expected Utility Theory

This monographic chapter explains how expected utility (EU) theory arose in von Neumann and Morgenstern, how it was called into question by Allais and others, and how it gave way to non-EU theories, at least among the specialized quarters of decion theory. I organize the narrative around the idea that the successive theoretical moves amounted to resolving Duhem-Quine underdetermination problems, so they can be assessed in terms of the philosophical recommendations made to overcome these problems. I actually follow Duhem's recommendation, which was essentially to rely on the passing of time to make many experiments and arguments available, and evebntually strike a balance between competing theories on the basis of this improved knowledge. Although Duhem's solution seems disappointingly vague, relying as it does on "bon sens" to bring an end to the temporal process, I do not think there is any better one in the philosophical literature, and I apply it here for what it is worth. In this perspective, EU theorists were justified in resisting the first attempts at refuting their theory, including Allais's in the 50s, but they would have lacked "bon sens" in not acknowledging their defeat in the 80s, after the long process of pros and cons had sufficiently matured. This primary Duhemian theme is actually combined with a secondary theme - normativity. I suggest that EU theory was normative at its very beginning and has remained so all along, and I express dissatisfaction with the orthodox view that it could be treated as a straightforward descriptive theory for purposes of prediction and scientific test. This view is usually accompanied with a faulty historical reconstruction, according to which EU theorists initially formulated the VNM axioms descriptively and retreated to a normative construal once they fell threatened by empirical refutation. From my historical study, things did not evolve in this way, and the theory was both proposed and rebutted on the basis of normative arguments already in the 1950s. The ensuing, major problem was to make choice experiments compatible with this inherently normative feature of theory. Compability was obtained in some experiments, but implicitly and somewhat confusingly, for instance by excluding overtly incoherent subjects or by creating strong incentives for the subjects to reflect on the questions and provide answers they would be able to defend. I also claim that Allais had an intuition of how to combine testability and normativity, unlike most later experimenters, and that it would have been more fruitful to work from his intuition than to make choice experiments of the naively empirical style that flourished after him. In sum, it can be said that the underdetermination process accompanying EUT was resolved in a Duhemian way, but this was not without major inefficiencies. To embody explicit rationality considerations into experimental schemes right from the beginning would have limited the scope of empirical research, avoided wasting resources to get only minor findings, and speeded up the Duhemian process of groping towards a choice among competing theories

Un positivisme nouveau en France au début du XXe siècle : Milhaud, Le Roy, Duhem et Poincaré

Nouvelle édition de l'ouvrage paru aux PUF en 2006International audienc

Histoire et logique dans l'écriture encyclopédique

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La transformation des valeurs scientifiques au XVIIe siècle

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Les textes fondateurs de l'épistémologie française : Duhem, Poincaré, Brunschvicg et autres philosophes

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