Monte Carlo versus molecular dynamics simulations in heterogeneous systems: an application to the n-pentane liquid-vapor interface

The Monte Carlo (MC) and molecular dynamics (MD) methodologies are now well established for computing equilibrium properties in homogeneous fluids. This is not yet the case for the direct simulation of two-phase systems, which exhibit nonuniformity of the density distribution across the interface. We have performed direct MC and MD simulations of the liquid-gas interface of n-pentane using a standard force-field model. We obtained density and pressure components profiles along the direction normal to the interface that can be very different, depending on the truncation and long range correction strategies. We discuss the influence on predicted properties of different potential truncation schemes implemented in both MC and MD simulations. We show that the MD and MC profiles can be made in agreement by using a Lennard-Jones potential truncated via a polynomial function that makes the first and second derivatives of the potential continuous at the cutoff distance. In this case however, the predicted thermodynamic properties (phase envelope, surface tension) deviate from experiments, because of the changes made in the potential. A further readjustment of the potential parameters is needed if one wants to use this method. We conclude that a straightforward use of bulk phase force fields in MD simulations may lead to some physical inconsistencies when computing interfacial properties.     

Un modèle hyperbolique diphasique bi-fluide en milieu poreux

We introduce an hyperbolic two-fluid two-pressure model to compute unsteady two-phase flows in porous media. The closure laws comply with the entropy inequality, and a unique set of jump conditions holds within each field. To cite this article: J.-M. Hérard, C. R. Mecanique 336 (2008).     

A Novel Allenic Epoxycyclohexane and Related Compounds from Eutypa lata (Pers: F.) Tul

The novel allenic epoxycyclohexanes 1 , and related compounds 2 and 3 have been isolated from the culture medium of Eutypa lata. Their structures were established by combination of spectroscopic and chemical techniques. Biogenetic origin and biological activity of these compounds are also discussed.     

Noncovalent associations in fluorous fluids

Perfluorocarbons (PFCs) are emerging as a new type of liquid phase in which molecular recognition processes can effectively take place. The combination of perfluorocarbons (PFCs) and noncovalent associations, mostly hydrogen bonds, ion pairing, halogen bonds or coordination bonds, has already been successfully exploited for applications in organic synthesis (catalyst recycling, by-product removal), electrochemical sensing, selective extraction/titration processes or to prepare gels. Due to the extreme solvophobic effect in PFCs, the least polar existing fluids, noncovalent associations tend to be enhanced. For instance, quantitative data on the increase in association strength occurring in PFCs have recently been reported for ion-pairing interactions or encapsulation processes. Moreover, several examples show that confining a receptor in a fluorous phase leads to recognition processes with improved selectivity.     

Small strain behavior of polyethylene: In situ SAXS measurements

Stack lamella deformation depends on their orientation with respect to the loading axis, the intrinsic properties of the lamellae, and the mechanical coupling between crystalline and amorphous phases. The aim of this work is to investigate the influence of the stress transmitter (ST) density and the crystallinity X_c on the local deformation. A wide experimental campaign has been undertaken on several polyethylenes with controlled molecular parameters and subjected to different thermal treatments. The ST density has been evaluated by the natural draw ratio and calculated by the Brown's model. The local deformation was measured by SAXS along a tensile test by using the long period stretching of the equatorial lamella stacks. The ratio ε_local/ε_macro was found to be a constant close to 0.5. This surprising low value has highlighted that the equatorial regions could be either the stiffest zone of the spherulite or submitted to a lower stress. It is proposed that the stability of the ratio ε_local/ε_macro is the result of two opposite phenomena: On one hand, the increase of X_c leads to unload the equatorial regions due to partial percolation of the crystalline phase and so decreases the stresses. On the other hand, when increasing X_c, the ST density decreases which causes the decrease in the local equatorial modulus. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1535–1542, 2010     

Self-induced "electroclick" immobilization of a copper complex onto self-assembled monolayers on a gold electrode

We report the self-induced "electroclick" immobilization of the [Cu(II)(6-ethynyl-TMPA)(H(2)O)](2+) complex, by its simple electro-reduction, onto a mixed azidoundodecane-/decane-thiol modified gold electrode. The redox response of the grafted [Cu(II/I)(TMPA)] at the modified electrode is fully reversible indicating no Cu coordination change and a fast electron transfer.     

Glycerol and glycerol carbonate as ultraviscous solvents for mixture analysis by NMR

NMR of weakly polar analytes in an apolar ultraviscous solvent has recently been proposed for mixture analysis as a pertinent alternative to the DOSY experiment. The present article reports the first use of glycerol and glycerol carbonate as polar solvents for the NMR analysis of a model mixture of dipeptides. This work demonstrates the high potentiality of these solvents for the analysis of mixtures made of polar and potentially bioactive compounds. Medium-sized molecules slowly reorient in glycerol and glycerol carbonate under particular temperature conditions, so that solute resonances may show spin diffusion in NOESY spectra, thus opening the way to mixture analysis. Glycerol and glycerol carbonate have turned out to be ultraviscous solvents of choice for the individualization of four structurally close mixed dipeptides: Leu-Val, Leu-Tyr, Gly-Tyr and Ala-Tyr by means of 1D and 2D NOESY experiments. Selective sample excitation and signal detection were implemented to eliminate the intense proton signals of the non-deuterated solvents. Moreover, the recording of a multiplet selective 2D NOESY-TOCSY has shown that the analytical power of NMR in highly viscous solvents is not limited to the extraction of mixture component 1D subspectra but may also yield some supplementary information about atom connectivity within components.     

Ultrafast and bias-free all-optical wavelength conversion using III-V-on-silicon technology

Using a 7.5 μm diameter disk fabricated with III-V-on-silicon fabrication technology, we demonstrate bias-free all-optical wavelength conversion for non-return-to-zero on-off keyed pseudorandom bit sequence (PRBS) data at the speed of 10 Gbits/s with an extinction ratio of more than 12 dB. The working principle of such a wavelength converter is based on free-carrier-induced refractive index modulation in a pump-probe configuration. We believe it to be the first bias-free on-chip demonstration of all-optical wavelength conversion using PRBS data. All-optical gating measurements in the pump-probe configuration with the same device have revealed that it is possible to achieve wavelength conversion beyond 20 Gbits/s.     

A new distance measure including the weak preference relation: Application to the multiple criteria aggregation procedure for mixed evaluations

We introduce a new distance measure between two preorders that captures indifference, strict preference, weak preference and incomparability relations. This measure is the first to capture weak preference relations. We illustrate how this distance measure affords decision makers greater modeling power to capture their preferences, or uncertainty and ambiguity around them, by using our proposed distance measure in a multiple criteria aggregation procedure for mixed evaluations.     

中温固体氧化物燃料电池阴极材料LaBiMn2O6的制备与性能研究

采用固相法合成了中温固体氧化物燃料电池(IT-SOFCs)阴极材料LaBiMn₂O₆,并利用X射线衍射(XRD)和电化学阻抗谱(EIS)进行表征.结果表明该材料与电解质Ce_0.7Bi_0.3O_1.85(CBO)在1 000 ℃烧结12 h不发生反应.交流阻抗和直流极化测试结果发现,阴极极化电阻随测试温度的增加而逐渐减小,700 ℃空气中的极化电阻为0.71 Ω·cm²;氧分压测试结果显示,在600~700 ℃范围内,电极反应的速率控制步骤为电极上发生的电荷转移反应.电极过电位为85 mV时,700 ℃的阴极电流密度达到 216 mA·cm^-2 ,表明LaBiMn₂O₆是一种潜在的中温固体氧化物燃料电池(IT-SOFCs)阴极材料.