Probing the nanohydrodynamics at liquid-solid interfaces using thermal motion

We report on a new method to characterize nano-hydrodynamic properties at the liquid/solid interface relying solely on the measurement of the thermal motion of confined colloids. Using Fluorescence Correlation Spectroscopy (FCS) to probe the diffusion of the colloidal tracers, this optical technique --equivalent in spirit to the microrheology technique used for bulk properties-- is able to achieve nanometric resolution on the slip length measurement. It confirms the no-slip boundary condition on wetting surfaces and shows a partial slip b=18 +/- 5 nm on non-wetting ones. Moreover, in the absence of external forcing, we do not find any evidence for large nano-bubble promoted slippage on moderately rough non-wetting surfaces.Comment: 4 pages, 3 figure

The implications of resonant x-ray scattering data on the physics of the insulating phase of V_2O_3

We have performed a quantitative analysis of recent resonant x-ray scattering experiments carried out in the antiferromagnetic phase of V_2O_3 by means of numerical ab-initio simulations. In order to treat magnetic effects, we have developed a method based on multiple scattering theory (MST) and a relativistic extension of the Schr\"{o}dinger Equation, thereby working with the usual non relativistic set of quantum numbers $l,m,\sigma$ for angular and spin momenta. Electric dipole-dipole (E1-E1), dipole-quadrupole (E1-E2) and quadrupole-quadrupole (E2-E2) transition were considered altogether. We obtain satisfactory agreement with experiments, both in energy and azimuthal scans. All the main features of the V K edge Bragg-forbidden reflections with $h+k+l=$odd can be interpreted in terms of the antiferromagnetic ordering only, {\it ie}, they are of magnetic origin. In particular the ab-initio simulation of the energy scan around the (1,1,1)-monoclinic reflection excludes the possibility of any symmetry reduction due to a time-reversal breaking induced by orbital ordering.Comment: 11 pages, 6 figure

Willingness to pay for environmental attributes of non-food agricultural products: a real choice experiment

This paper investigates consumers’ willingness to pay (WTP) a price premium for two environmental attributes of a non-food agricultural product. We study individual preferences for roses associated with an eco-label and a carbon footprint using an economic experiment combining discrete choice questions and real economic incentives involving real purchases of roses against cash. The data are analyzed with a mixed logit model and reveal significant premiums for both environmental attributes of the product.WILLINGNESS TO PAY;ENVIRONMENTAL ATTRIBUTES;NON-FOOD PRODUCT;REAL CHOICE EXPERIMENT;MIXED LOGIT

Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes

Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of fused silica while being free of Raman scattering. It also has a much higher optical damage threshold and a transparency window that extends from the UV to the infrared. We report the observation of nonlinear phenomena, such as self-phase modulation, in hollow-core photonic crystal fiber filled with supercritical Xe. In the subcritical regime, intermodal four-wave-mixing resulted in the generation of UV light in the HE12 mode. The normal dispersion of the fiber at high pressures means that spectral broadening can clearly obtained without influence from soliton effects or material damage

Host galaxies of AGN

The relationship of an AGN to its host galaxy is a crucial question in the study of galaxy evolution. We perform stellar population synthesis in the central regions of galaxies of different activity levels. A large number of stellar features are measured both in the optical and near-infrared. We find the nuclear stellar population to be related to the level of activity. These differences are no more conspicuous further away in the bulge of the galaxy

Manual of Quaternions

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Les Américains ont-ils accepté les OGM ?: Analyse comparée de la construction des OGM comme problème public en France et aux Etats-Unis

How can one explain that the use of genetically-modified organisms (GMOs) in food and agriculture poses a problem in France, where they are hardly used, yet seems to be taken for granted in the US, where their use is widespread ? Many observers see this as a sign that American consumers have accepted transgenic foods, due to a different attitude to risks, food and nature. The present article rejects that explanation. It presents a comparative analysis of the trajectory of GMOs as a public problem in France and the US, showing that very similar arguments were put forward by opponents to GMOs on both sides of the Atlantic, and that conflicts between opponents and defenders have focussed on the same issues : (i) food labeling ; (ii) the link between the choice of a technique (GMOs) and that of an economic system (intensive agriculture, capitalism) ; and (iii) the appropriate framework for evaluating risks. But whereas in France (and more generally in Europe), opponents’ arguments crystallized during specific key controversies, and contributed towards the definition of the cognitive and normative dimensions of GMOs as a public problem, this did not occur in the US. Three factors seem to explain this difference : (i) very different regulatory choices made in the late 1980s (based on processes in Europe and on products in the US) ; (ii) the fact that the usefulness of transgenic plants is perceived negatively in France whereas their association with the intensive export agriculture project is perceived positively in the US ; and (iii) the growing influence of a broader, “constructive” framework for risk analysis in Europe, whereas in the US regulatory authorities continue to base their legitimacy on the ideology of “sound science

Inelastic X-ray scattering from valence electrons near absorption edges of FeTe and TiSe2_2

We study resonant inelastic x-ray scattering (RIXS) peaks corresponding to low energy particle-hole excited states of metallic FeTe and semi-metallic TiSe$_2$ for photon incident energy tuned near the $L_{3}$ absorption edge of Fe and Ti respectively. We show that the cross section amplitudes are well described within a renormalization group theory where the effect of the core electrons is captured by effective dielectric functions expressed in terms of the the atomic scattering parameters $f_1$ of Fe and Ti. This method can be used to extract the dynamical structure factor from experimental RIXS spectra in metallic systems.Comment: 6 pages, 4 figure

Communication: Truncated non-bonded potentials can yield unphysical behavior in molecular dynamics simulations of interfaces

Non-bonded potentials are included in most force fields and therefore widely used in classical molecular dynamics simulations of materials and interfacial phenomena. It is commonplace to truncate these potentials for computational efficiency based on the assumption that errors are negligible for reasonable cutoffs or compensated for by adjusting other interaction parameters. Arising from a metadynamics study of the wetting transition of water on a solid substrate, we find that the influence of the cutoff is unexpectedly strong and can change the character of the wetting transition from continuous to first order by creating artificial metastable wetting states. Common cutoff corrections such as the use of a force switching function, a shifted potential, or a shifted force do not avoid this. Such a qualitative difference urges caution and suggests that using truncated non-bonded potentials can induce unphysical behavior that cannot be fully accounted for by adjusting other interaction parameters