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We consider a 2D spin crossover (SCO) nanoparticles configuration under the influence of an external environment. Each nanoparticle is at the vertex of a triangular lattice leading to hexagonal-shaped systems. Each molecule located in the bulk is then connected to six nearest-neighbours (nn) while those situated at the surface have three or four nn.Adapting the entropic sampling Monte Carlo method, using three parameters: nHS (the total high spin fraction), s (the correlation: the sum of nn interactions the molecules) and nsHS (the high-spin fraction at the surface), we determined the density of macrostates D(nHS, nsHS ,s) by scanning the full spin configurations. This information is then used to analyse the thermal behaviour of the system taking into account for the short- (J) and long-range (G) interactions as well for the interactions (L) between the molecules at the surface and the matrix (environment). The present contribution is devoted to the investigations of the required physical conditions which allow this triangular 2D lattice to exhibit a re-entrant phase transition, in particular when the size of the nanoparticles is reduced. International audience

In this report first we show, in a framework of the Ising-like model, a numerical simulation of a typical two step thermal transition obtained for a square lattice 12x12: a "first-step hysteresis" for a high spin fraction Nhs between 0 - 0,5 and at a higher temperature a "second-step hysteresis" with Nhs between 0.5 and 1. As long as we decrease the number of molecules the temperature range of the "second-step hysteresis" moves to a lower temperature, until is obtained, for a square of 4x4, a clear overlapped case with a three state behaviour. A detailed analys is on the role of the size system (4x4, 5x5, 6x6, 8x8 and 12x12) on the stability of this "Three state behaviour" is presented in this contribution. We study the influence of the surrounding environment for this specific thermal hysteresis. To solve the self-consistent equation related to the average value of the spin-operator , we use the density of the states calculated using a dynamic programming algorithm that will be presented in this paper. International audience

First-principle molecular dynamics simulations of methane hydrate MH-III, including the quantum properties of the hydrogen nuclei, were carried out at pressures in the 5-65 GPa range, in order to observe the H-bond symmetrization at high pressure and at room temperature. According to our simulations, the symmetrization transition takes place around 40 GPa and is little dependent on isotope substitution. We find that, consistently with the rather complex crystal structure of MH-III, the transition is much more convoluted in the hydrate than in ices VII and X. In methane hydrate, due to the presence of non equivalent O ions with distinct O-O distances, the dissimilar H bonds symmetrize in a pressure domain rather than at a single critical pressure. International audience

Louis Poinsot est un mathématicien surtout connu pour ses travaux en mécanique et géométrie. Il est pourtant cité à plusieurs reprises dans des textes du xixe siècle comme mathématicien ayant joué un rôle dans l'histoire de la théorie des nombres et de l'algèbre. Dans cet article, nous étudions les travaux de Poinsot dans ces deux domaines à partir de ses publications et d'un manuscrit sur la théorie des permutations et nous essayons de montrer en quoi un examen du travail de Poinsot peut éclairer la période séparant les Disquisitiones Arithmeticae de Gauss de l'œuvre de Galois. The mathematician Louis Poinsot is principally known today for his contributions to mechanics and Geometry. In texts from the nineteenth century, however, he is frequently mentioned for his influence in the development of number theory and algebra. In this paper, we study Poinsot's work in these two domains through his publications and a manuscript of his on the theory of permutations. We then discuss how such a study may help to understand the transition from Gauss's Disquisitiones Arithmeticae to Galois's work. International audience

The topic of this paper is, on the one hand to introduce algebraic analysis results of Étienne Bézout (1730- 1783) not as we know them today but as he found them in his time, and on the other hand to emphasize his innovating viewpoints. We will be concerned with Bezout special way of reducing elimination for any degree systems to finding conditions for linear systems solutions, with his typical use of indeterminate coefficients that he doesn't compute but looks only for existence and number, with his idea to work on set of polynomials products sums, and with a very personal method to found two equations resultant. International audience 76 pages

The flat oyster, Ostrea edulis, was consumed as a luxury dish by the Romans in antiquity. Numerous shells are found in archaeological sites in the Lyon region, Central France. This area is located over 250 km away from the nearest coastline (the Mediterranean Sea) and little is known about the origin of these oysters prior to transport for consumption. The chemistry of biogenic carbonates reflects that of the fluid they precipitate from at the time of formation. Stable isotopes and Mg/Ca ratios in oyster shells have previously been used as palaeoenvironmental proxies. As Mg/Ca ratio amplitude in bivalve shells has been reported to differ according to local hydrologic settings, we suggest that geochemical differences observed in each shell can be used to identify the type of environment (e.g. estuary, lagoon or marine) from which the specimens originated. International audience

Our aim is to derive the symmetries of the space-time, i.e. the Lorentz transformations, from discrete symmetries of the interactions between the most fundamental constituents of matter, in particular quarks and leptons. The role of Pauli’s exclusion principle in the derivation of the SL(2,C), symmetry is put forward as the source of the macroscopically observed Lorentz symmetry. Then Pauli’s principle is generalized for the case of the Z 3 grading replacing the usual Z 2 grading, leading to ternary commutation relations for quantum operator algebras. In the case of lowest dimension, with two generators only, it is shown how the cubic combinations Z 3-graded elements behave like Lorentz spinors, and the binary product of elements of this algebra with an element of the conjugate algebra behave like Lorentz vectors. International audience

Over 60 years ago, stone tools and remains of megafauna were discovered on the Southeast Asian islands of Flores, Sulawesi and Luzon, and a Middle Pleistocene colonization by Homo erectus was initially proposed to have occurred on these islands 1-4. However, until the discovery of Homo floresiensis in 2003, claims of the presence of archaic hominins on Wallacean islands were hypothetical owing to the absence of in situ fossils and/or stone artefacts that were excavated from well-documented stratigraphic contexts, or because secure numerical dating methods of these sites were lacking. As a consequence, these claims were generally treated with scepticism 5. Here we describe the results of recent excavations at Kalinga in the Cagayan Valley of northern Luzon in the Philippines that have yielded 57 stone tools associated with an almost-complete disarticulated skeleton of Rhinoceros philippinensis, which shows clear signs of butchery, together with other fossil fauna remains attributed to stegodon, Philippine brown deer, freshwater turtle and monitor lizard. All finds originate from a clay-rich bone bed that was dated to between 777 and 631 thousand years ago using electron-spin resonance methods that were applied to tooth enamel and fluvial quartz. This evidence pushes back the proven period of colonization 6 of the Philippines by hundreds of thousands of years, and furthermore suggests that early overseas dispersal in Island South East Asia by premodern hominins took place several times during the Early and Middle Pleistocene stages 1-4. The Philippines therefore may have had a central role in southward movements into Wallacea, not only of Pleistocene megafauna 7 , but also of archaic hominins. The most recent recoveries in Flores 8,9 and Sulawesi 10 (Indonesia) provide a unique documentation of overseas hominin dispersal during the early Middle Pleistocene epoch. An early presence in the Philippine archipelago has been hypothesized since the 1950s, with the reporting of presumably Pleistocene megafaunal remains and 'Palaeolithic' industries consisting of chopping tools and flakes (the 'Cabalwanian' and 'Liwanian' industries, respectively) from surface finds and excavations in the Cagayan Valley basin of northern Luzon 3,4. Despite the fact that these early discoveries took place more than 60 years ago, no direct association between megafauna and lithic industries has been documented since then, and no secure numerical dating of both fossil fauna and lithics has been available for this region 11. To date, the discovery of a human metatarsal in Callao Cave in northern Luzon 6 , directly dated to 66.7 ± 1.0 thousand years ago (ka), represented the oldest evidence of the peopling of the Philippines. International audience