91 research outputs found
Pierre Varignon, un membre du « groupe malebranchiste » ?
No full textInternational audienceP. Varignon has sometimes been considered as a member of the “malebranchist group”: this term refers to a group of scientists grouped around N. Malebranche and whose activity was oriented towards the dissemination of infinitesimal calculus in France. However, his ties to this group of mathematicians have not often been studied in detail : are they limited to the promotion of Leibnizian calculus, and if so, to which audience? We propose to examine this question in focusing particularly on the role that Varignon played in the publication of the Analyse démontrée by the oratorian C. Reyneau and in trying to determine the influence of the former on the latter in the writing of this book. This perspective allows us to highlight the common conceptions on which the two mathematicians rely to conceive the calculus and its novelty, but also the differences relating to the analytical treatment of instantaneous speed in particular, and more generally to the use of the infinitesimal analysis in relationship with mechanical hypotheses. Varignon thus appears in an obvious proximity with the Malebranchists but also committed to a more analytical conception of mechanics than they were
Nouvelle mécanique, ou Statique, dont le projet fut donné en M. DC. LXXXVII. Tome 1 / ; ouvrage posthume de M. Varignon,...
No full textAppartient à l’ensemble documentaire : GTextes1Contient une table des matièresAvec mode texteOuvrages avant 180
Nouvelle mécanique, ou Statique, dont le projet fut donné en M. DC. LXXXVII. Tome 2 / ; ouvrage posthume de M. Varignon,...
No full textAppartient à l’ensemble documentaire : GTextes1Ouvrages avant 180
Measurement of the neutron-induced deuteron breakup reaction cross-section between 5 and 25 MeV
No full textThis article presents a full program devoted to the calculation and the measurement of the neutron-induced deuteron break-up reaction cross-section between 5 and 10 MeV, and between 20 and 25 MeV. Measurements are compared with theoretical calculations based on the solution of the Faddeev equations for a realistic nuclear Hamiltonian. The experiments were performed at the Tandem 7 MV accelerator at CEA, DAM, DIF, France. The measurements were carried out with a C6D6 detector as active deuterium target located at the center of a 4π neutron counter (see C. Varignon et al., Nucl. Instrum. Methods B 248, 329 (2006)) which allows to count the two neutrons emitted in the 2H(n, 2n)p reaction. Comparisons of the new data and calculations are made with the existing data as well as the CENDL2, JENDL3.3 and ENDF/B-VII evaluations
Coexistence and coupling of ferroelectricity and magnetism in an oxide two-dimensional electron gas
No full textContribution a l'etude experimentale des neutrons de spallation produits par des protons dans des cibles epaisses
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Electric Field Control of Jahn-Teller Distortions in Bulk Perovskites
No full textpeer reviewedThe Jahn-Teller distortion, by its very nature, is often at the heart of the various electronic properties displayed by perovskites and related materials. Despite the Jahn-Teller mode being nonpolar, we devise and demonstrate, in the present Letter, an electric field control of Jahn-Teller distortions in bulk perovskites. The electric field control is enabled through an anharmonic lattice mode coupling between the Jahn-Teller distortion and a polar mode. We confirm this coupling and quantify it through first-principles calculations. The coupling will always exist within the Pb21m space group, which is found to be the favored ground state for various perovskites under sufficient tensile epitaxial strain. Intriguingly, the calculations reveal that this mechanism is not only restricted to Jahn-Teller active systems, promising a general route to tune or induce novel electronic functionality in perovskites as a whole
Lavoro, meccanica e «arti meccaniche» nell'età dell'Encyclopédie (1751-1794)
No full textIn questo intervento, attraverso la lettura dell' Enciclopedia di Diderot e d'Alembert (1751-1780), intendo reperire alcuni nessi esistenti — al di là dei complessi problemi relativi alle fonti (Chambers, Varignon, Bernouilli ecc.) — tra la scienza meccanica e la Description des Arts et Métiers, quel vasto progetto di rendicontazione dello stato di avanzamento delle tecniche nel secolo XVIII, affiancato dal lavoro di commento e di rappresentazione letteraria delle «arti» svolto negli undici volumi di Tavole dell'Enciclopedia, in cui vengono raffigurate, in sequenza, le diverse fasi di lavoro e descritte le macchine, strumenti e utensili usati.
Si tratta di vedere come e in che misura le concezioni teoriche degli enciclopedisti, in fatto di macchine e di meccanica, abbiano trovato riscontro nella parte pratica del Dictionnaire, relativa alle tecniche e alla descrizione di macchine adibite alla produzione. Vedere, cioè, se è reperibile o meno accordo tra intenti teorici e risultati pratici, indagando, infine, se il nesso di teoria e prassi, punto forte del programma enciclopedico, agisca effettivamente nelle rappresentazioni offerte dai testi e dalle tavole. Questi sembrano voler dare atto, ante litteram, dell'affermazione di Ernst Mach (1883) che «le conoscenze meccaniche siano nate da un processo di chiarificazione intellettuale com¬piuto sulle esperienze che si erano accumulate nell'esercizio del lavoro artigianale»
Nouveaux matériaux multiferroïques à partir de calculs de premiers principes
No full textpeer reviewedInterest in first-principles calculations within the multiferroic community has been rapidly on the rise over the last decade. Initially considered as a powerful support to explain experimentally observed behaviours, the trend has evolved and, nowadays, density functional theory calculations have become also an essential predicting tool for identifying original rules to achieve multiferroism and design new magneto-electric compounds. This chapter aims at highlighting the key advances in the field of multiferroics, to which first-principles methods have contributed significantly. The essential theoretical developments that made this research possible are also briefly presented
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