NMR relaxation evidence for solute-induced nanosized superstructures in ultramolecular aqueous dilutions of silica-lactose

We investigated 20 MHz water proton NMR longitudinal (T1) and transverse (T2) relaxation in ultrahigh dilutions (range 10 − 7 M-10 − 47 M) of a mixture of silica-lactose (Sil/Lac) in various media (water, 0.15 M NaCl, 0.15 M LiCl) and in various containers (glass, polyethylene). The samples were prepared by iterative centesimal dilutions under vigorous agitation and rigorously controlled laboratory conditions. Water and salt media were similarly and simultaneously treated, as controls. No significant effect on relaxation times was induced by the iterative dilution/agitation process in pure water and salt controls. By contrast, a slight increase in T1 and decrease in T2 was observed with increasing dilution in silica-lactose solutions, resulting in a marked progressive increase in T1/T2, especially in LiCl medium, distinguishable up to the ultrahigh dilution level. Cross-correlation analyses between T1, T2 and T1/T2 managed to demonstrate opposite behaviours of controls and Sil/Lac dilutions, even in the ultramolecular range of dilution. The effect seemed dependent on the medium (LiCl N NaCl N Water), and was observed in the glassware and polyethylene series as well. After a heating/cooling cycle directly in the sealed NMR tubes, the relaxation variations observed as a function of dilution totally vanished, and the T1/T2 ratio dropped, indicating a less ordered structure. These findings were interpreted in terms of nanosized superstructures with motional correlation time greater than 5.10 − 9 s, nucleated around the solute, and composed of water, ions and nanobubbles generated during the vigorous mechanical process. Incidentally, a striking catalytic enhancement of silica leaching was observed during the preparation of silica-lactose dilutions in glassware; but this did not influence the NMR relaxation results

Electronic structure and optical properties of TaC from the first principles calculation

Abstract.: The electronic and optical properties of tantalum carbide TaC have been calculated using the full-potential linearized augmented-plane-wave method within the local density approximation scheme for the exchange-correlation potential. We find that the optical spectra can be extremely sensitive to the Brillouin zone sampling. The influence of relativistic effects on the dielectric function is investigated. It is shown that the scalar-relativistic correction is much more important than spin-orbit coupling. Our results are found to be in good agreement with the available experimental data. The determinant role of a band structure computation with respect to the analysis of optical properties is discusse

Does As(III) interact with Fe(II), Fe(III) and organic matter through ternary complexes?

International audienceUp until now, only a small number of studies have been dedicated to the binding processes of As(III) with organic matter (OM) via ionic Fe(III) bridges; none was interested in Fe (II). Complexation isotherms were carried out with As(III), Fe(II) or Fe(III) and Leonardite humic acid (HA). Although PHREEQC/Model VI, implemented with OM thiol groups, reproduced the experimental datasets with Fe(III), the poor fit between the experimental and modeled Fe(II) data suggested another binding mechanism for As(III) to OM. PHREEQC/Model VI was modified to take various possible As(III)-Fe(II)-OM ternary complex conformations into account. The complexation of As(III) as a mononuclear bidentate complex to a bidentate Fe(II)-HA complex was evidenced. However, the model needed to be improved since the distribution of the bidentate sites appeared to be unrealistic with regards to the published XAS data. In the presence of Fe(III), As(III) was bound to thiol groups which are more competitive with regards to the low density of formed Fe(III)-HA complexes. Based on the new data and previously published results, we propose a general scheme describing the various As(III)-Fe-MO complexes that are able to form in Fe and OM-rich waters

Preferential arrangement of uniform Mn nanodots on Si(111)-7x7 surface

Under proper growth conditions, ordered and uniform Mn nanodots were fabricated on the Si(111)-7x7 surface without the presence of a wetting layer. Furthermore, the Mn nanodots deposited onto the elevated substrates were observed to occupy preferentially on the faulted half unit cells (FHUCs) of the Si(111)-7x7 surface. This phenomenon implies that the Mn dots adsorbed on the FHUCs is more stable than those adsorbed on the unfaulted half unit cells (UFHUCs). Within the framework of quasiequilibrium thermodynamics, the energy difference between adsorption on the UFHUCs and the FHUCs was estimated to be 0.05eV. The intrinsic attractive potential wells on the FHUCs effectively trap the outdiffusion of Mn atoms, and consequently result in a preferential arrangement of islands with well-defined sizes

Structure peculiarities of cementite and their influence on the magnetic characteristics

The iron carbide $Fe_3C$ is studied by the first-principle density functional theory. It is shown that the crystal structure with the carbon disposition in a prismatic environment has the lowest total energy and the highest energy of magnetic anisotropy as compared to the structure with carbon in an octahedron environment. This fact explains the behavior of the coercive force upon annealing of the plastically deformed samples. The appearance of carbon atoms in the octahedron environment can be revealed by Mossbauer experiment.Comment: 10 pages, 3 figures, 3 tables. submitted to Phys.Rev.

Exploring input modalities for interacting with augmented paper maps

International audienceInteractive geographic maps are today widely available, but remain mostly limited to standard interaction contexts. We introduce a spatial augmented reality map, in which a virtual map is projected on a physical piece of paper. In a preliminary study we compared interaction techniques based on multi-touch, tangible and spatial modalities for three common map functions: zooming, panning, and changing the basemap. Our results suggest that object-based and spatial interaction may be advantageous over multi-touch in our augmented reality setup

In Vitro Acquisition of Specific Small Interfering RNAs Inhibits the Expression of Some Target Genes in the Plant Ectoparasite Xiphinema index

Xiphinema index is an important plant parasitic nematode that induces direct damages and specifically transmits the Grapevine fanleaf virus, which is particularly harmful for grapevines. Genomic resources of this nematode species are still limited and no functional gene validation technology is available. RNA interference (RNAi) is a powerful technology to study gene function and here we describe the application of RNAi on several genes in X. index. Soaking the nematodes for 48 h in a suspension containing specific small interfering RNAs resulted in a partial inhibition of the accumulation of some targeted mRNA. However, low reproducible silencing efficiency was observed which could arise from X. index silencing pathway deficiencies. Indeed, essential accustomed proteins for these pathways were not found in the X. index proteome predicted from transcriptomic data. The most reproducible silencing effect was obtained when targeting the piccolo gene potentially involved in endo-exocytosis of synaptic molecules. This represents the first report of gene silencing in a nematode belonging to the Longidoridae family

Exploration input modalities for interacting with augmented paper maps

National audienceInteractive geographic maps are today widely available, but remain mostly limited to standard interaction contexts. We introduce a spatial augmented reality map, in which a virtual map is projected on a physical piece of paper. In a preliminary study we compared interaction techniques based on multi-touch, tangible and spatial modalities for three common map functions: zooming, panning, and changing the basemap. Our results suggest that object-based and spatial interaction may be advantageous over multi-touch in our augmented reality setup

Postural Optimization for an Ergonomic Human-Robot Interaction

International audienceIn human-robot collaboration the robot's behavior impacts the worker's safety, comfort and acceptance of the robotic system. In this paper we address the problem of how to improve the worker's posture during human-robot collaboration. Using postural assessment techniques, and a personalized human kinematic model, we optimize the model body posture to fulfill a task while avoiding uncomfortable or unsafe postures. We then derive a robotic behavior that leads the worker towards that improved posture. We validate our approach in an experiment involving a joint task with 39 human subjects and a Baxter torso-humanoid robot