20 research outputs found
Quantities in Nature : the Applicability of mathematics and its ontological conditions
Si nos thĂ©ories physiques peuvent dĂ©crire les traits les plus gĂ©nĂ©raux de la rĂ©alitĂ©, on sait aussi que pour le faire, elles utilisent le langage des mathĂ©matiques. On peut alors lĂ©gitimement se demander si notre capacitĂ© Ă dĂ©crire, sinon la nature intime des objets et phĂ©nomĂšnes physiques, du moins les relations et structures quâils instancient, ne vient pas de cette application des mathĂ©matiques. Dans cette thĂšse, nous soutenons que les mathĂ©matiques sont si efficacement applicables en physique tout simplement parce que la rĂ©alitĂ© dĂ©crite par les physiciens est de nature quantitative. Pour cela, nous proposons dâabord une ontologie des quantitĂ©s, puis des lois de la nature, qui sâinscrit dans les dĂ©bats contemporains sur la nature des propriĂ©tĂ©s (thĂ©orie des universaux, thĂ©orie des tropes, ou nominalisme), et des lois (rĂ©gularitĂ©s, ou relations entre universaux). Ensuite, nous examinons deux sortes dâapplication des mathĂ©matiques : la mathĂ©matisation des phĂ©nomĂšnes par la mesure, puis la formulation mathĂ©matique des Ă©quations reliant des grandeurs physiques. Nous montrons alors que les propriĂ©tĂ©s et les lois doivent ĂȘtre comme notre ontologie les dĂ©crit, pour que les mathĂ©matiques soient lĂ©gitimement, et si efficacement, applicables. LâintĂ©rĂȘt de ce travail est dâarticuler des discussions purement ontologiques (et trĂšs anciennes, comme la querelle des universaux) avec des exigences Ă©pistĂ©mologiques rigoureuses qui Ă©manent de la physique actuelle. Cette articulation est conçue de maniĂšre transcendantale, car la nature quantitative de la rĂ©alitĂ© (des propriĂ©tĂ©s et des lois) y est dĂ©fendue comme condition dâapplicabilitĂ© des mathĂ©matiques en physique.Assuming that our best physical theories succeed in describing the most general features of reality, one can only be struck by the effectiveness of mathematics in physics, and wonder whether our ability to describe, if not the very nature of physical entities, at least their relations and the fundamental structures they enter, does not result from applying mathematics. In this dissertation, we claim that mathematical theories are so effectively applicable in physics merely because physical reality is of quantitative nature. We begin by displaying and supporting an ontology of quantities and laws of nature, in the context of current philosophical debates on the nature of properties (universals, classes of tropes, or even nominalistic resemblance classes) and of laws (as mere regularities or as relations among universals). Then we consider two main ways mathematics are applied: first, the way measurement mathematizes physical phenomena, second, the way mathematical concepts are used to formulate equations linking physical quantities. Our reasoning has eventually a transcendental flavor: properties and laws of nature must be as described by the ontology we first support with purely a priori arguments, if mathematical theories are to be legitimately and so effectively applied in measurements and equations. What could make this work valuable is its attempt to link purely ontological (and often very ancient) discussions with rigorous epistemological requirements of modern and contemporary physics. The quantitative nature of being (properties and laws) is thus supported on a transcendental basis: as a necessary condition for mathematics to be legitimately applicable in physics
LâĂ©nigme de Goodman face Ă lâindistinction nomologique
Lorsque Goodman expose sa « nouvelle Ă©nigme de lâinduction », il veut la distinguer dâun vieux problĂšme, celui de la justification du principe dâuniformitĂ© de la nature : peut-on montrer que le futur ressemblera au passĂ©, et que ce qui vaut jusquâaujourd'hui comme loi de la nature continuera de valoir comme tel Ă lâavenir ? Câest avec toutes ces vieilles questions que Goodman entend rompre, en posant la question des gĂ©nĂ©ralisations lĂ©gitimes et des prĂ©dicats projectibles. A quelles conditions, et pour quelles raisons, peut-on dire que certaines gĂ©nĂ©ralisations sont confirmables par leurs instances observĂ©es (i.e. nomologiques), contrairement Ă dâautres qui sont pourtant empiriquement Ă©quivalentes ? Il ne sâagit plus de donner un fondement Ă lâinduction, mais de trouver un critĂšre prĂ©cis pour distinguer les hypothĂšses quâon peut lĂ©gitimement induire de celles dont lâinduction serait absurde. Ainsi prĂ©sentĂ©e, la thĂšse de Goodman apparaĂźt double. (A) Dâune part, il existe un second problĂšme de lâinduction, distinct de lâancien, mais qui reste un authentique problĂšme de lâinduction. (B) Dâautre part, ce problĂšme est soluble par la dĂ©finition dâun critĂšre de confirmation empirique, qui permet de distinguer les gĂ©nĂ©ralisations susceptibles dâĂȘtre confirmĂ©es par leurs instances, des gĂ©nĂ©ralisations non-nomologiques. Nous voulons montrer quâon ne peut pas Ă la fois (A) poser le nouveau problĂšme de lâinduction et (B) chercher un critĂšre de distinction des hypothĂšses nomologiques et non nomologiques. En effet, si lâon confronte plusieurs hypothĂšses ou gĂ©nĂ©ralisations Ă partir des mĂȘmes observations, alors elles doivent ĂȘtre toutes aussi nomologiques les unes que les autres. Inversement, si lâon se donne des hypothĂšses ou gĂ©nĂ©ralisations qui ne sont pas toutes nomologiques, on ne peut pas les comparer au sein dâune mĂȘme induction, ni donc poser lâĂ©nigme de Goodman. Le problĂšme posĂ© en (A) ne trouve donc pas de solution adĂ©quate en (B). Et comme nous acceptons la thĂšse (A) et lâexistence dâun problĂšme goodmanien de lâinduction, nous nierons quâon puisse le rĂ©soudre par le type de solutions envisagĂ©es en (B). Nous finirons donc par formuler ce problĂšme et le type de solution que, selon nous, il appelle
Les quantités dans la nature: Les conditions ontologiques de l'applicabilité des mathématiques
Assuming that our best physical theories succeed in describing the most general features of reality, one can only be struck by the effectiveness of mathematics in physics, and wonder whether our ability to describe, if not the very nature of physical entities, at least their relations and the fundamental structures they enter, does not result from applying mathematics. In this dissertation, we claim that mathematical theories are so effectively applicable in physics merely because physical reality is of quantitative nature. We begin by displaying and supporting an ontology of quantities and laws of nature, in the context of current philosophical debates on the nature of properties (universals, classes of tropes, or even nominalistic resemblance classes) and of laws (as mere regularities or as relations among universals). Then we consider two main ways mathematics are applied: first, the way measurement mathematizes physical phenomena, second, the way mathematical concepts are used to formulate equations linking physical quantities. Our reasoning has eventually a transcendental flavor: properties and laws of nature must be as described by the ontology we first support with purely a priori arguments, if mathematical theories are to be legitimately and so effectively applied in measurements and equations. What could make this work valuable is its attempt to link purely ontological (and often very ancient) discussions with rigorous epistemological requirements of modern and contemporary physics. The quantitative nature of being (properties and laws) is thus supported on a transcendental basis: as a necessary condition for mathematics to be legitimately applicable in physics.Si nos thĂ©ories physiques peuvent dĂ©crire les traits les plus gĂ©nĂ©raux de la rĂ©alitĂ©, on sait aussi que pour le faire, elles utilisent le langage des mathĂ©matiques. On peut alors lĂ©gitimement se demander si notre capacitĂ© Ă dĂ©crire, sinon la nature intime des objets et phĂ©nomĂšnes physiques, du moins les relations et structures quâils instancient, ne vient pas de cette application des mathĂ©matiques. Dans cette thĂšse, nous soutenons que les mathĂ©matiques sont si efficacement applicables en physique tout simplement parce que la rĂ©alitĂ© dĂ©crite par les physiciens est de nature quantitative. Pour cela, nous proposons dâabord une ontologie des quantitĂ©s, puis des lois de la nature, qui sâinscrit dans les dĂ©bats contemporains sur la nature des propriĂ©tĂ©s (thĂ©orie des universaux, thĂ©orie des tropes, ou nominalisme), et des lois (rĂ©gularitĂ©s, ou relations entre universaux). Ensuite, nous examinons deux sortes dâapplication des mathĂ©matiques : la mathĂ©matisation des phĂ©nomĂšnes par la mesure, puis la formulation mathĂ©matique des Ă©quations reliant des grandeurs physiques. Nous montrons alors que les propriĂ©tĂ©s et les lois doivent ĂȘtre comme notre ontologie les dĂ©crit, pour que les mathĂ©matiques soient lĂ©gitimement, et si efficacement, applicables. LâintĂ©rĂȘt de ce travail est dâarticuler des discussions purement ontologiques (et trĂšs anciennes, comme la querelle des universaux) avec des exigences Ă©pistĂ©mologiques rigoureuses qui Ă©manent de la physique actuelle. Cette articulation est conçue de maniĂšre transcendantale, car la nature quantitative de la rĂ©alitĂ© (des propriĂ©tĂ©s et des lois) y est dĂ©fendue comme condition dâapplicabilitĂ© des mathĂ©matiques en physique
Light induced modulation of charge transport phenomena across the bistability region in [Fe(Htrz) 2 (trz)](BF 4 ) spin crossover micro-rods
International audienceWe studied the effect of light irradiation on the electrical conductance of micro-rods of the spin crossover [Fe(Htrz)2(trz)](BF4) network, organized between interdigitated gold electrodes. By irradiating the sample with different wavelengths (between 295 and 655 nm) either in air or under a nitrogen atmosphere we observed both a reversible and an irreversible change of the current flowing in the device. The reversible process consists of an abrupt decrease of the current intensity (ca. 10â50%) upon light irradiation, while the irreversible process is characterized by a slow, but continuous increase in time of the current, which persists also in the dark. These photo-induced processes were only detected in the high conductance low-spin (LS) state of the complex. On switching the rods to the high spin (HS) state the conductance decreases two orders of magnitude (at the same temperature) and â as a consequence â the photo-effect vanishes
On the stability of spin crossover materials: From bulk samples to electronic devices
International audienceIn this paper we report on the integration of micro-rods of the [Fe(Htrz)2(trz)](BF4) spin crossover compound into an electronic switch-type device. The device has been fabricated by organizing the micrometric particles between interdigitated gold electrodes using dielectrophoresis and the influence of dielectrophoresis parameters on their integration is also examined. A particular attention was devoted to the investigation of the stability of the spin transition and the associated device properties. The stability of the particles before dielectrophoresis was investigated using variable temperature diffuse reflectivity experiments, which revealed a remarkable stability of the spin crossover even after performing 3000 switching cycles. We show also that the spin transition is not influenced by the solvents used for device fabrication, neither by the atmosphere (ambient air or vacuum) in which the device is used. The spin transition remains reproducible over several tens of cycles even at the device level, but the current in the device decreases continuously
Unidirectional electric field-induced spin-state switching in spin crossover based microelectronic devices
International audienceWe report on a molecular spin-state switching phenomenon induced by an electric field in micrometric objects of the [Fe(Htrz)2(trz)](BF4) spin crossover complex, organized between interdigitated electrodes. By applying an electric field step of 40 kV/cm at temperatures within the thermal hysteresis region of the first-order spin transition, the iron(II) ions are switched from the metastable high spin to the stable low spin state obtaining a rather incomplete transition but perfectly reversible by heating. A model based on the interaction between the electric field and the electric dipolar moment of spin crossover complexes, grasps the main features of the experimental data