Influence of absorption level on mechanisms of Braggdiffracted x-ray beam formation in real silicon crystals

The methods of numerical calculations based on the formulae of the X-ray dynamic scattering theory by real crystals and of the Takagi-Topin equations were used for investigation of the basic regularities of inherent to the Bragg diffraction in conditions of a strong and weak absorption. The mechanisms of profile formation of a spatial intensity distribution of diffracted beams depending on an energy of radiation and on structural perfection parameters of crystals are discussed. The formulae for an analytical description of spatial intensity distribution profiles which take into account the dynamical corrections (coefficients of extinction) for coherent and incoherent components of the total reflectivity were used

Surface state atoms and their contribution to the surface tension of quantum liquids

We investigate the new type of excitations on the surface of liquid helium. These excitations, called surfons, appear because helium atoms have discrete energy level at the liquid surface, being attracted to the surface by the van der Waals force and repulsed at a hard-core interatomic distance. The concentration of the surfons increases with temperature. The surfons propagate along the surface and form a two-dimensional gas. Basing on the simple model of the surfon microscopic structure, we estimate the surfon activation energy and effective mass for both helium isotopes. We also calculate the contribution of the surfons to the temperature dependence of the surface tension. This contribution explains the great and long-standing discrepancy between theory and experiment on this temperature dependence in both helium isotopes. The achieved agreement between our theory and experiment is extremely high. The comparison with experiment allows to extract the surfon activation energy and effective mass. The values of these surfon microscopic parameters are in a reasonable agreement with the calculated from the proposed simple model of surfon structure.Comment: 10 pages, 6 figure

Ionospheric photoelectrons at Venus: Initial observations by ASPERA-4

Abstract We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 nm photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks in energy for such photoelectrons have been predicted by Venus atmosphere/ionosphere models. The ELS energy resolution (DE/E$7%) means that these are the first detailed measurements of such electrons. Considerations of ion production and transport in the atmosphere of Venus suggest that the observed photoelectron peaks are due primarily to ionization of atomic oxygen.

Preparation of pickering-emulsion-based capsules with shells composed of titanium dioxide nanoparticles and polyelectrolyte layers

A procedure has been proposed for the preparation of capsules with shells composed of titanium dioxide nanoparticles and polymers via the formation of Pickering emulsions (colloidosomes) followed by layer-by-layer deposition of polyelectrolytes. The feasibility of stabilizing oil droplets of emulsions by spontaneous adsorption of partly hydrophobized nanoparticles of anatase-form titanium dioxide at the oil/water interface has been studied. Conditions have been determined for the formation of stable colloidosomes and the subsequent layer-by-layer deposition of oppositely charged polyelectrolytes onto their surfaces. It has been shown that hydrophobic dyes may be encapsulated using the procedure developed for the preparation of the capsules. The photocatalytic activity of TiO2 particles occurring in the shell has been demonstrated by the example of degradation of Nile red which is incorporated in the oil core of a capsule

Transition from Spherical to Irregular Dispersed Phase in Water/Oil Emulsions

Bulk properties of transparent and dilute water in paraffin oil emulsions stabilized with sodium dodecyl sulfate (SDS) are analyzed by optical scanning tomography. Each scanning shot of the considered emulsions has a precision of 1 mu m. The influence of aluminum oxide nanoparticles in the structure of the water droplets is investigated. Depending on concentrations of SDS and nanoparticles, a transition occurs in their shape that changes from spherical to polymorphous. This transition is controlled by the SDS/alumina nanoparticles mixing ratio and is described using an identification procedure of the topology of the gray level contours extracted from each images. The transition occurs for a critical mixing ratio of R-crit approximate to 0.05 which does not significantly depend on temperature and electrolyte concentration. This structural change seems to be a general feature when emulsifying dispersions and most probably involves both interfacial and bulk phenomena

Split of the magnetic and crystallographic states in Fe1−Rh Ge

International audienceWe report on a comprehensive experimental and theoretical study of the Fe 1−x Rh x Ge compounds, within the entire concentration range x ∈ [0.0 − 1.0], using X-Ray diffraction, small-angle neutron scattering, magnetometry and theoretical calculations. While FeGe and RhGe are single phase helimagnet and unconventional superconductor, respectively, an internal splitting of the crystallographic and magnetic states is found for intermediate compositions x ∈ [0.2 − 0.9]. A theoretical analysis of the stability of the two detected phases, together with the experimental data, indicate that this splitting preserves a common space group and occurs within single crystallites. Despite their apparent similarity, these two phases however display different magnetic structures, with distinct ferro-and helimagnetic character