Comment regarding "On the theoretical determination of the Prigogine-Defay ratio in glass transition"

International audienceGenerally, experimentally determined values of the Prigogine-Defay (PD) ratio are different from unity. This can be explained if one considers that more than one single order parameter are involved in the thermodynamics of the glass transition process. Against the consensual view, Tropin et al. demonstrated that PD ratios can be different from unity even if one single order parameter is involved. This "Comment" aims to discuss fundamental mistakes leading to this conclusion in the recent article "On the theoretical determination of the Prigogine-Defay ratio in glass transition" [ J. Chem. Phys. 136, 124502 (2012)] by Tropin et al

Temperature of systems out of thermodynamic equilibrium

Two phenomenological approaches are currently used in the study of the vitreous state. One is based on the concept of fictive temperature introduced by Tool [Jour. Research Nat. Bur. Standards 34, 199 (1945)] and recently revisited by Nieuwenhuizen [Phys. Rev. Lett. 80, 5580 (1998)]. The other is based on the thermodynamics of irreversible processes initiated by De Donder at the beginning of the last century [L'Affinit\'e (Gauthier-Villars, Paris, 1927)] and recently used by M\"oller and co-workers for a thorough study of the glass transition [J. Chem. Phys. 125, 094505 (2006)]. This latter approach leads to the possibility of describing the glass transition by means of the freezing-in of one or more order parameters connected to the internal structural degrees of freedom involved in the vitrification process. In this paper, the equivalence of the two preceding approaches is demonstrated, not only for glasses, but in a very general way for any system undergoing an irreversible transformation. This equivalence allows the definition of an effective temperature for all systems departed from equilibrium generating a positive amount of entropy. In fact, the initial fictive temperature concept of Tool leads to the generalization of the notion of temperature for systems out of thermodynamic equilibrium, for which glasses are just particular cases

Active Control of Silicon Nanotweezers Detects Enzymatic Reaction at the Molecular Level

International audienceThis work achieved the control of micromachined tweezers for the enhancement of the sensing of DNA molecules and related enzymatic reactions. The mechanical stiffness of the silicon nanotweezers is decreased by feedback design and the sensitivity of the system is drastically improved

The size of plume heterogeneities constrained by Marquesas isotopic stripes

International audienceThe scale and geometry of chemical and isotopic heterogeneities in the source of plumes have important scientific implications on the nature, composition and origin of plumes and on the dynamics of mantle mixing over time. Here, we address these issues through the study of Marquesas Islands, one of the Archipelagoes in Polynesia. We present new Sr, Nd, Pb, Hf isotopes as well as trace element data on lavas from several Marquesas Islands and demonstrate that this archipelago consists of two adjacent and distinct rows of islands with significantly different isotopic compositions. For the entire 5.5 Ma construction period, the northern islands, hereafter called the Ua Huka group, has had systematically higher 87Sr/86Sr and lower 206Pb/204Pb ratios than the southern Fatu Hiva group at any given 143Nd/144Nd value. The shape and curvature of mixing arrays preclude the ambient depleted MORB mantle as one of the mixing end-members. We believe therefore that the entire isotopic heterogeneity originates in the plume itself. We suggest that the two Marquesas isotopic stripes originate from partial melting of two adjacent filaments contained in small plumes or "plumelets" that came from a large dome structure located deep in the mantle under Polynesia. Low-degree partial melting under Marquesas and other "weak" Polynesian hot spot chains (Pitcairn-Gambier, Austral-Cook, Society) sample small areas of the dome and preserve source heterogeneities. In contrast, more productive hot spots build up large islands such as Big Island in Hawaii or Réunion Island, and the higher degrees of melting blur the isotopic variability of the plume source

Closed-loop Control of Silicon Nanotweezers for Improvement of Sensitivity to Mechanical Stiffness Measurement and Bio-Sensing on DNA Molecules

International audienceIn this work we show that implementation of closed loop control to silicon nanotweezers improves the sensitivity of the tool for mechanical characterizations of biological molecules. Micromachined tweezers have already been used for the characterizations of mechanical properties of DNA molecules as well as for the sensing of enzymatic reactions on DNA bundle. However the resolution of the experiments does not allow the sensing on single molecules. Hereafter we show theoretically and experimentally that, reducing the resonance frequency of the system by the implementation of a state feedback, the sensitivity to stiffness variation is enhanced. Such improvement leads to better resolution for detection of enzymatic reactions on DNA

The eruptive chronology of the Yucamane-Calientes compound volcano: a potentially active edifice of the Central Andes (Southern Peru)

We have reconstructed the eruptive chronology of the Yucamane–Calientes compound volcano in southern Peru based on extensive fieldwork and a large dataset of geochronological (40K–40Ar, 40Ar–39Ar, U-Pb and 14C) and geochemical (major and trace element) analyses. This compound volcano is composed of two edifices that have experienced discontinuous volcanic activity from the Middle Pleistocene to the Holocene. The Calientes volcano has been constructed in four successive stages: Calientes I is composed of andesitic lava flows that were dated at ~500 ka. Then, the Callazas ignimbrite (Calientes II stage) was emplaced (~160-190 ka), followed by the main cone-building stage (Calientes III), which was dated at ~125 ka. Finally, the Holocene Caliente domes were emplaced and represent the last eruptive products of this edifice. The Yucamane volcano has been constructed in three stages: Yucamane I stage consists of a sequence of andesitic lava flows exposed at the base of the volcano with an age older than 37-40 ka. Yucamane II stage (~36-24 ka) comprises a thick sequence of block-and-ash deposits that represents a dome-growth episode that predates the younger Yucamane cone (Yucamane III stage) since 20-25 ka. During the Holocene, the Yucamane had shown vulcanian to sub-Plinian activity resulting in the emplacement of tephra fallout and pyroclastic density current deposits. The last sub-Plinian eruption occurred ca. 3085 ± 35 aBP and emitted a pumice fall deposit associated with a pumice flow deposit. Most samples from the Calientes volcano are andesites and dacites (60.1-67.7 wt.% SiO2), while rocks of the Yucamane volcano correspond to basic andesites to dacites (53.4-66.9 wt.% SiO2). These rocks show a mineral assemblage of plagioclase, amphibole, biotite, ortho- and clino-pyroxene, olivine, and Fe-Ti oxides. All of the analyzed samples belong to a high-K, calc-alkaline series. Calientes volcano erupted mostly andesitic magmas and is punctuated by rare eruptions involving silica-rich magmas. In contrast, Yucamane volcano displays a different pattern, characterized by a gradual decrease of silica content through post-glacial time, from moderate (VEI <=2) vulcanian events comprising basic andesitic magmas to the large (VEI 3) sub-Plinian eruption of ~3 ka, involving andesitic magma. On the basis of this recurrent low-to-moderate explosive activity, Yucamane must be considered as an active and potentially threatening volcano, which may affect the province of Candarave with about 12 000 inhabitants

Thermodynamics of small systems by nanocalorimetry: from physical to biological nano-objects

Membrane based nanocalorimeters have been developed for ac calorimetry experiments. It has allowed highly sensitive measurements of heat capacity from solid state physics to complex systems like polymers and proteins. In this article we review what has been developed in ac calorimetry toward the measurement of very small systems. Firstly, at low temperature ac calorimetry using silicon membrane permits the measurement of superconducting sample having geometry down to the nanometer scale. New phase transitions have been found in these nanosystems illustrated by heat capacity jumps versus the applied magnetic field. Secondly, a sensor based on ultra-thin polymer membrane will be presented. It has been devoted to thermal measurements of nanomagnetic systems at intermediate temperature (20K to 300K). Thirdly, three specific polyimide membrane based sensors have been designed for room temperature measurements. One is devoted to phase transitions detection in polymer, the second one to protein folding/unfolding studies and the third one will be used for the study of heat release in living cells. The possibility of measuring systems out of equilibrium will be emphasized