Laboratoire de Tribologie et Dynamique des Systèmes

We present here a new solution for the astronomical computation of the insolation quantities on Earth spanning from -250 Myr to 250 Myr. This solution has been improved with respect to La93 (Laskar et al. [CITE]) by using a direct integration of the gravitational equations for the orbital motion, and by improving the dissipative contributions, in particular in the evolution of the Earth–Moon System. The orbital solution has been used for the calibration of the Neogene period (Lourens et al. [CITE]), and is expected to be used for age calibrations of paleoclimatic data over 40 to 50 Myr, eventually over the full Palaeogene period (65 Myr) with caution. Beyond this time span, the chaotic evolution of the orbits prevents a precise determination of the Earth's motion. However, the most regular components of the orbital solution could still be used over a much longer time span, which is why we provide here the solution over 250 Myr. Over this time interval, the most striking feature of the obliquity solution, apart from a secular global increase due to tidal dissipation, is a strong decrease of about 0.38 degree in the next few millions of years, due to the crossing of the resonance (Laskar et al. [CITE]). For the calibration of the Mesozoic time scale (about 65 to 250 Myr), we propose to use the term of largest amplitude in the eccentricity, related to , with a fixed frequency of /yr, corresponding to a period of 405 000 yr. The uncertainty of this time scale over 100 Myr should be about , and over the full Mesozoic era.

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

The OMEGA/Mars Express hyperspectral imager identified hydrated sulfates on light-toned layered terrains on Mars. Outcrops in Valles Marineris, Margaritifer Sinus, and Terra Meridiani show evidence for kieserite, gypsum, and polyhydrated sulfates. This identification has its basis in vibrational absorptions between 1.3 and 2.5 micrometers. These minerals constitute direct records of the past aqueous activity on Mars.

The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.

In Pseudomonas aeruginosa, the production of many virulence factors and secondary metabolites is regulated in concert with cell density through quorum sensing. Two quorum-sensing regulons have been identified in which the LuxR homologues LasR and RhlR are activated by N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) and N-butanoyl-L-homoserine lactone (BHL) respectively. The lasR and rhlR genes are linked to the luxl homologues lasl and rhll, which are responsible for synthesis of OdDHL and BHL, respectively. As lasRl and rhlRl are both involved in regulating synthesis of exoenzymes such as elastase, we sought to determine the nature of their interrelationship. By using lacZ transcriptional fusions in both homologous (P. aeruginosa) and heterologous (Escherichia coli) genetic backgrounds we provide evidence that (i) lasR is expressed constitutively throughout the growth cycle, (ii) rhlR expression is regulated by LasR/OdDHL, and (iii) that RhlR/BHL regulates rhll. We also show that expression of the stationary-phase sigma factor gene rpoS is abolished in a P. aeruginosa lasR mutant and in the pleiotropic BHL-negative mutant PANO67. Furthermore, our data reveal that kin E. coli, an rpoS-lacZ fusion is regulated directly by RhlR/BHL. Taken together, these results indicate that P. aeruginosa employs a multilayered hierarchical quorum-sensing cascade involving RhlR/BHL and LasR/OdDHL, interlinked via RpoS, to integrate the regulation of virulence determinants and secondary metabolites with adaptation and survival in the stationary phase.

Knowledge about the human skin mechanical properties is essential in several domains, particularly for dermatology, cosmetic or to detect some cutaneous pathology. This study proposes a new method to determine the human skin mechanical properties in vivo using the indentation test. Usually, the skin mechanical parameters obtained with this method are influenced by the mechanical properties of the subcutaneous layers, like muscles. In this study, different mechanical models were used to evaluate the effect of the subcutaneous layers on the measurements and to extract the skin elastic properties from the global mechanical response. The obtained results demonstrate that it is necessary to take into account the effect of the subcutaneous layers to correctly estimate the skin Young's modulus. Moreover, the results illustrate that the variation of the measured Young's modulus at low penetration depth cannot be correctly described with usual one-layer mechanical models. Thus a two-layer elastic model was proposed, which highly improved the measurement of the skin mechanical properties.

ADVERTISEMENT RETURN TO ISSUEPREVArticleA New Intermolecular Interaction: UnconventionalHydrogen Bonds with Element−Hydride Bonds as ProtonAcceptorRobert H. Crabtree, Per E. M. Siegbahn, Odile Eisenstein, Arnold L. Rheingold, and Thomas F. KoetzleView Author Information Yale Chemistry Department, 225 Prospect Street, New Haven, Connecticut 06520-8107 Department of Physics, University of Stockholm, Box 6730, S-113 85 Stockholm, Sweden Laboratoire de Structure et Dynamique des Systèmes Moléculaires et Solides (UMR 5636), Bât. 15,Université de Montpellier, 34095 Montpellier Cedex 05, France Department of Chemistry, University of Delaware, Newark, Delaware 19716 Department of Chemistry, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973 In papers with more than one author, the asterisk indicates thename of the author to whom inquiries about the paper should be addressed.Cite this: Acc. Chem. Res. 1996, 29, 7, 348–354Publication Date (Web):January 11, 1996Publication History Received27 November 1995Published online11 January 1996Published inissue 11 July 1996https://doi.org/10.1021/ar950150sCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views3380Altmetric-Citations576LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (321 KB) Get e-AlertsSUBJECTS:Anions,Chemical structure,Indoles,Metals,Reaction mechanisms Get e-Alerts

We have studied the atomistic origins of the ultralow friction coefficient of a molybdenum disulphide (${\mathrm{MoS}}_{2}$) coating in ultrahigh vacuum conditions. A friction coefficient in the ${10}^{\mathrm{\ensuremath{-}}3}$ range is associated with friction-induced orientation of ``easy shear'' basal planes of the ${\mathrm{MoS}}_{2}$ crystal structure parallel to the sliding direction. In addition to this basal plane orientation, an orientation disorder around the c axis is observed, indicating that frictional anisotropy during intercrystallite slip could be at the origin of the vanishing of the friction force. Experimental HRTEM lattice fringe imaging of ${\mathrm{MoS}}_{2}$ wear particles clearly show the existence of characteristic Moir\'e patterns. We have simulated TEM lattice fringe images of a [0001] ${\mathrm{MoS}}_{2}$ crystal and produced rotational Moir\'e patterns by superimposing two such images. A qualitative agreement between experimental and simulated Moir\'e patterns is demonstrated, which gives credence that ultralow friction of ${\mathrm{MoS}}_{2}$ in high vacuum can be attributed to a superlubric situation, by frictional anisotropy of sulphur-rich basal planes during intercrystallite slip.

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and microscales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.

Considering the increase of urban population and traffic congestion, smart parking is always a strategic issue to work on, not only in the research field, but also from economic interests. Thanks to information and communication technology evolution, drivers can more efficiently find satisfying parking spaces with smart parking services. The existing and ongoing works on smart parking are complicated and transdisciplinary. While deploying a smart parking system, cities, as well as urban engineers, need to spend a very long time to survey and inspect all the possibilities. Moreover, many varied works involve multiple disciplines, which are closely linked and inseparable. To give a clear overview, we introduce a smart parking ecosystem and propose a comprehensive and thoughtful classification by identifying their functionalities and problematic focuses. We go through the literature over the period of 2000-2016 on parking solutions as they were applied to smart parking development and evolution, and propose three macro-themes: information collection, system deployment, and service dissemination. In each macro-theme, we explain and synthesize the main methodologies used in the existing works and summarize their common goals and visions to solve current parking difficulties. Finally, we give our engineering insights and show some challenges and open issues. Our survey gives an exhaustive study and a prospect in a multidisciplinary approach. Besides, the main findings of the current state-of-the-art throw out recommendations for future research on smart cities and the Internet architecture.

In Pseudomonas aeruginosa PAO1, expression of elastase is dependent upon an interaction between the positive transcriptional activator LasR and the auto-inducer molecule N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), the synthesis of which is directed by LasI. Previously we have shown that in PAN067, an elastase-negative mutant of PAO1, elastase production can be restored to some extent by addition of exogenous N-(3-oxohexanoyl)-L-homoserine lactone (OHHL). Here we report that PAN067 is also defective in the production of alkaline protease, haemolysin, cyanide, pyocyanin and autoinducer(s). As neither addition of exogenous OdDHL nor introduction of lasR restored PAN067 to the parental phenotype, we sought to complement PAN067 with PAO1 DNA. From a cosmid library, a 2 kb DNA fragment was identified which re-established production of autoinducer(s) and exoproducts in PAN067. From the nucleotide sequence of this fragment, two genes termed rhIR and rhII were identified. RhII is responsible for autoinducer synthesis and shares 31% homology with LasI; RhIR has been previously identified in P. aeruginosa strain DSM2659 as a regulator of rhamnolipid biosynthesis and shares 28% identity with LasR. These data provide clear evidence that multiple families of quorum-sensing modulons interactively regulate gene expression in P. aeruginosa.

In this paper we argue that the new availability of digital data sets allows one to revisit Gabriel Tarde's (1843-1904) social theory that entirely dispensed with using notions such as individual or society. Our argument is that when it was impossible, cumbersome or simply slow to assemble and to navigate through the masses of information on particular items, it made sense to treat data about social connections by defining two levels: one for the element, the other for the aggregates. But once we have the experience of following individuals through their connections (which is often the case with profiles) it might be more rewarding to begin navigating datasets without making the distinction between the level of individual component and that of aggregated structure. It becomes possible to give some credibility to Tarde's strange notion of 'monads'. We claim that it is just this sort of navigational practice that is now made possible by digitally available databases and that such a practice could modify social theory if we could visualize this new type of exploration in a coherent way.

Switched systems constitute an important modeling paradigm faithfully describing many engineering systems in which software interacts with the physical world. Despite considerable progress on stability and stabilization of switched systems, the constant evolution of technology demands that we make similar progress with respect to different, and perhaps more complex, objectives. This paper describes one particular approach to address these different objectives based on the construction of approximately equivalent (bisimilar) symbolic models for switched systems. The main contribution of this paper consists in showing that under standard assumptions ensuring incremental stability of a switched system (i.e., existence of a common Lyapunov function, or multiple Lyapunov functions with dwell time), it is possible to construct a finite symbolic model that is approximately bisimilar to the original switched system with a precision that can be chosen <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> . To support the computational merits of the proposed approach, we use symbolic models to synthesize controllers for two examples of switched systems, including the boost dc-dc converter.

Electrosynthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) films was performed in a micellar aqueous solution containing sodium dodecyl sulfate (SDS) by cyclic voltammetry, chronoamperometry, and chronopotentiometry on a platinum electrode. The electrocatalytic effect of SDS was characterized by a significant decrease of the EDOT oxidation potential (Ep) in the micellar medium relative to 0.1 M LiClO4 acetonitrile as well as aqueous solutions. Linear variation of Ep with SDS concentration indicated the formation of a pseudocomplex (Keq = 5.4 × 103 M-1). PEDOT films were characterized electrochemically and spectroscopically (UV−visible, X-ray photoelectron spectroscopy, IR, Raman spectra). Regular, well-ordered, and adherent films were obtained in SDS medium. The PEDOT film morphologies investigated by atomic force microscopy suggested the possible presence of columnar structures when the electrosynthesis is performed in the micellar medium.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransition Metal Polyhydrides: From Qualitative Ideas to Reliable Computational Studies†Feliu Maseras, Agustí Lledós, Eric Clot, and Odile EisensteinView Author Information Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra Barcelona, Spain LSDSMS (UMR 5636) CC 014, Université de Montpellier II, 34095 Montpellier Cedex 05, France Cite this: Chem. Rev. 2000, 100, 2, 601–636Publication Date (Web):January 20, 2000Publication History Received30 April 1999Published online20 January 2000Published inissue 1 February 2000https://pubs.acs.org/doi/10.1021/cr980397dhttps://doi.org/10.1021/cr980397dresearch-articleACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views2149Altmetric-Citations323LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Anions,Chemical calculations,Chemical structure,Ligands,Metals Get e-Alerts

The participation of 4f electrons in the bonding of the lanthanide complexes Ln(NR2)3; R = H, SiH3, has been investigated at the DFT level. Structural parameters obtained with small core (f electrons in the valence) and large core (f electrons in the core) effective core potentials (ECPs) suggest the nonparticipation of the f electrons to the Ln−N bonding. A methodological study has been carried out on the lanthanide contraction with various ab initio methods using large core ECPs. The calculated lanthanide contraction (0.180 Å) is in excellent agreement with the experimental value (0.179 Å). Comparison of calculated structural parameters with available X-ray data shows that calculations with large core ECPs and density functional methods quantitatively reproduce the bonding at the lanthanide.

1. The hypothesis was tested that intermediate connectivity to a river results in propagule inputs to wetlands, whereas excessive connectivity impedes recruitment, and insufficient connectivity causes less competitive species to be eliminated, with no recruitment of new species. As a consequence, very low or very high nutrient levels should decrease species richness by selecting specialized species, whereas intermediate nutrient levels should favour the co‐occurrence of species with contrasting nutrient requirements. 2. Among cut‐off channels with high sinuosity and which are infrequently flooded by the river (low flood scouring), one example possesses high species richness because most species are saved from extinction by long‐term isolation of the channel and cold groundwater supplies. Other channels are poorly supplied with groundwater and show a lower richness of species, because of low propagule inputs and low recruitment potential. 3. Cut‐off channels with low sinuosity and which are flooded at intermediate frequencies were divided into three groups. The first group was species‐poor, being closely connected to the river through downstream backflows which maintain nutrient‐rich and turbid waters, in keeping with the hypothesis. The second group presents intermediate richness caused by: (i) lower river backflows; and (ii) floods that partly scour substrate and plants, and afford regeneration niches for transported propagules. The third group was species‐poor because of excessive groundwater supplies, which probably acted as a limiting factor for species growth and recruitment. 4. The most frequently flooded channel shows the highest species richness, and occurrence of rare and fugitive species, because of floods which compensate competition by scouring sediments and plants, and afford regeneration niches for propagules. In this case, conservation of biodiversity necessitates propagule sources at the level of the river landscape.

Here we characterized the effect of the ectomycorrhizal symbiosis on the genotypic and functional diversity of soil Pseudomonas fluorescens populations and analysed its possible consequences in terms of plant nutrition, development and health. Sixty strains of P. fluorescens were isolated from the bulk soil of a forest nursery, the ectomycorrhizosphere and the ectomycorrhizas of the Douglas fir (Pseudostuga menziesii) seedlings-Laccaria bicolor S238N. They were characterized in vitro with the following criteria: ARDRA, phosphate solubilization, siderophore, HCN and AIA production, genes of N2-fixation and antibiotic synthesis, in vitro confrontation with a range of phytopathogenic and ectomycorrhizal fungi, effect on the Douglas fir-L. bicolor symbiosis. For most of these criteria, we demonstrated that the ectomycorrhizosphere significantly structures the P. fluorescens populations and selects strains potentially beneficial to the symbiosis and to the plant. This prompts us to propose the ectomycorrhizal symbiosis as a true microbial complex where multitrophic interactions take place. Moreover it underlines the fact that this symbiosis has an indirect positive effect on plant growth, via its selective pressure on bacterial communities, in addition to its known direct positive effect.

We propose a simple model, supported by contact-dynamics simulations as well as rheology and friction measurements, that links the transition from continuous to discontinuous shear thickening in dense granular pastes to distinct lubrication regimes in the particle contacts. We identify a local Sommerfeld number that determines the transition from Newtonian to shear-thickening flows, and then show that the suspension's volume fraction and the boundary lubrication friction coefficient control the nature of the shear-thickening transition, both in simulations and experiments.

The calculated (DFT, B3PW91) A1 ν(CO) frequency in LNi(CO)3 defines an electronic parameter that reliably predicts the relative donor powers of a wide variety of cationic, neutral, and negatively charged ligands. These calculated parameters correlate very well with the available Tolman and Lever parameters, and also with Hammett's σm, where available. The method avoids any experimental limitations and, in particular, can be used for proposed ligands not yet experimentally available.