Results 1 - 10 of 264988
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[en] We investigate the motional resonances of dual-species Coulomb crystals comprised of 9Be+ and 24Mg+ ions held in a 4-rod linear Paul trap. Our experimental data and simulations show that the secular motion of such mixed crystals has rich dynamics. Their secular spectra can differ significantly from those of pure ion crystals. We propose a simple model based on mechanical coupling with Coulomb interactions between the two different ion species that explains many features of the secular spectrum. Our findings contribute to a more reliable identification of the ion species in mixed crystals. (paper)
[en] Anharmonic contribution to the second-order Doppler shift of the Moessbauer line has been theoretically evaluated for a cubic crystal containing point defect pairs by employing double time Green's function technique. It has been found that even a weak anharmonicity produces a qualitative change in the time dependence of the correlation function, and results in the appearance of additional terms (which are proportional to temperature) in the expression for the energy shift of the Moessbauer line. The anharmonic contributions are evaluated for a Bravais crystal with nearest neighbour central-force interactions and are discussed for zero-phonon process. (author)
[en] The adequacy of numerical sequence accelerative transforms in providing accurate estimates of Coulomb sums is considered, referring particularly to distorted lattices. Performance of diagonal Pade approximants (DPA) in this context is critically assessed. Failure in the case of lattice vacancies is also demonstrated. The method of multiple-point Pade approximants (MPA) has been introduced for slowly convergent sequences and is shown to work well for both regular and distorted lattices, the latter being due either to impurities or vacancies. Viability of the two methods is also compared. In divergent situations with distortions owing to vacancies, a strategy of obtaining reliable results by separate applications of both DPA and MPA at appropriate places is also sketched. Representative calculations involve two basic cubic-lattice sums, one slowly convergent and the other divergent, from which very good quality estimates of Madelung constants for a number of common lattices follow
[en] Salient features of various parameterizations of cubic-cubic misorientation are discussed. It is proposed that the quaternion representation of rotations, as a pair of antipodal points on the surface of a four-dimensional sphere, encompasses the most desirable properties of other proposed representations, viz rectilinearity, a closed form for the composition of successive rotations, and an equivalence between the Euclidean measure on its parameter space and the invariant measure in the space of rotations. The classification of cubic-cubic misorientations according to group multiplicity is described in Euler angle and quaternion representations. A correspondence between coincidence site lattice (CSL) boundaries (Σ≤49), Euler angles and axis-angle parameters is given. (orig.)
[en] This paper introduces a novel shape and texture recognizing technique based on the design of bionic whisker. Whisker arrays are installed on both sides of the robot. In the experiment, the whisker sweeps around to detect the unidentified object. The center wavelength of fiber Bragg grating (FBG) pasted on the whisker shifts when the whisker touches the obstacle. Shape recognition is realized by processing and further calculating the wavelength shift data. At the same time, the whisker sweeps over the surface texture, and the texture information is obtained by processing the wavelength shift data with the time-frequency analysis method. The results show that the whisker sensor can identify the three-dimensional profile shapes of contacted objects and the texture features of touched surfaces effectively.
[en] The structure of monocrystals of the NiMn intermetallic compound containing small copper additions and being a stabilizer of the γ-phase is investigated by the methods of electron microscopy, X-ray and neutron diffraction. After 900 deg C quenching the monocrystals are shown to possess the ordered structure according to the L10 FCT type with ratio c/a0.95. The alloy contains three types of domains with mutually perpendicular axes c, and the alloy volume is divided into the regions containing two orientations of c-domains out of three possible ones conjugating in planes (110) and being at twin orientation relative to them. These regions, in its turn, are distorted tetragonally (c/a=0.97) and are formed according to the same diagram that c-domains do, forming polydomain plates separated by twin type boundaries. The character of diffuse scattering by main nodes testifies to the indistinct character of boundaries between c-domains in the intermetallics investigated
[en] The self-assembled colloidal crystals with structure transitions were realized experimentally on substrates with polymer brushes. Such polymer-mediated colloidal crystals were found to experience a series of in-layer structure transitions including stable columnar, polycrystalline, mixed square-hexagonal, square, hexagonal structures when the mass ratio of colloidal particles to free polymers was adjusted from 0.125 to 10. Among these structures, a large area interfacial square structure was proved to be a body-centered tetragonal (BCT) structure in three dimensions in the polymer-mediated colloidal crystals.
[en] The method for synthesis and neutron-diffraction study of Ge4Cs compound is developed. The results of neutron-diffraction analysis of Ge4Cs compound have shown that it crystallizes in the sp. gr. Pm3n and has an elementary cubical lattice with parameter a=(0.658 ± 0.03) nm