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We study both experimentally and theoretically the dynamics of chemically self-propelled Janus colloids moving atop a two-dimensional crystalline surface. The surface is a hexagonally close-packed monolayer of colloidal particles of the same size as the mobile one. The dynamics of the self-propelled colloid reflects the competition between hindered diffusion due to the periodic surface and enhanced diffusion due to active motion. Which contribution dominates depends on the propulsion strength, which can be systematically tuned by changing the concentration of a chemical fuel. The mean-square displacements (MSDs) obtained from the experiment exhibit enhanced diffusion at long lag times. Our experimental data are consistent with a Langevin model for the effectively two-dimensional translational motion of an active Brownian particle in a periodic potential, combining the confining effects of gravity and the crystalline surface with the free rotational diffusion of the colloid. Approximate analytical predictions are made for theMSDdescribing the crossover from free Brownian motion at short times to active diffusion at long times. The results are in semi-quantitative agreement with numerical results of a refined Langevin model that treats translational and rotational degrees of freedom on the same footing. [ABSTRACT FROM AUTHOR]

The synthesis of ruby from an Al2O3-Cr2O3 mixture compacted in pellets of different density by layer-by-layer selective laser sintering (SLS) has been investigated depending on the irradiation power and the traverse speed of a laser beam. It has been established that a formed track consists of crystallites textured: vertical texturing is inherent to volume layers and horizontal texturing is proper to surface layer. The morphology of the surface of the track is determined by the irradiation conditions. [ABSTRACT FROM AUTHOR]

The presence of crystalline inclusions in plasma cell myeloma is a rare phenomenon and cases have been reported with rod, needle, and rectangular shaped crystals. Here, we present a case of IgG lambda restricted plasma cell myeloma with rhomboid shaped intracellular crystalline inclusions and extracellular crystal depositions in the bone marrow. Since rhomboid crystal depositions can be seen in other clinical conditions such as pseudogout, this case invites consideration of plasma cell myeloma in the differential diagnosis of patients with rhomboid crystalline deposition in the bone marrow and in sites/organs other than the bone marrow. [ABSTRACT FROM AUTHOR]

The present paper describes an opto-electronic humidity sensor based on thin film of zinc oxide prepared by pulsed laser deposition method. Being optical in nature it gives electromagnetic disturbance-free monitoring. The sensing element is a right-angled isosceles prism with its base coated with ZnO thin film. Films have been characterized by XRD, SEM, and optical transmission. Film grown with substrate at room temperature is amorphous whereas that grown at elevated temperature is single crystalline with grain size 38.52 nm. Film deposited at room temperature is sensitive to humidity over a wide range i.e. 5–90RH% while that deposited at elevated temperature is found to be insensitive to humidity. The sensor shows better sensitivity for higher range of humidity. The response and recovery time of the sensor element have also been evaluated. This sensor configuration can be used for on-line applications and in-situ monitoring. [ABSTRACT FROM AUTHOR]

The dissociation of CO serves both as a model test reaction on single crystals and as a relevant reaction step for industrial methanation. We combined extensive density functional theory calculations, ultra-high vacuum experiments on well-defined single crystals, and catalytic activity measurements on supported catalysts in a study of the dissociation mechanism of CO on Ni surfaces. We found that this process is highly structure-sensitive and also is sensitive to the presence of hydrogen: Under ultra-high vacuum, with no hydrogen present, the dissociation proceeds through a direct route in which only undercoordinated sites (e.g., steps) are active. Under methanation conditions, the dissociation also proceeds most favorably over undercoordinated sites, but through a COH species. [Copyright &y& Elsevier]

Both the approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. Extending earlier work, an hierarchical set of criteria for the separation of isopointal structures into isoconfigurational structure types is used. It is shown how these criteria, which include the space group (number), Wyckoff sequence and Pearson symbol, c/ a ratio, β ranges, ANX formulae and, in certain cases, the necessary elements and forbidden elements, may be used to uniquely identify the representative structure types of the compounds contained in the ICSD database. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of the new ternary compound TmCu4−x Sb2 (x =1.065) was determined by direct methods from X-ray powder data (diffractometer DRON-3M, Cu Kα-radiation). It crystallizes with the orthorhombic structure type ErFe4Ge2 (low-temperature modification) and is the first representative of this structure type among known antimonides: space group Pnnm, Pearson code oP14-2.13, a =7.00565(6)Å, b =7.83582(6)Å, c =4.25051(3)Å, Z =2. Investigated structure is an orthorhombically deformed derivative of the ZrFe4Si2 structure type. [Copyright &y& Elsevier]

Extensive theoretical analysis and experimental observations show surface roughening transitions of crystals. The surface roughening is characterized by step free energy, which gradually decreases to 0 at the roughening transition temperature. For a crystal of finite size, the surface roughening transition is manifested by gradual increase of the curved edge and corner areas. In alloys, the interfaces between the solid and the liquid phases can be either singular, partially rough, or completely rough at different temperatures. Their thermally induced roughening transitions are similar to those of the solid-vapor interfaces. The interface roughening and the reverse transition to singular structures can also be induced by additives. The grain boundaries of any misorientation angles in oxides and metals also show roughening transitions. The singular grain boundaries have either flat, hill-and-valley, or kinked shapes, and with temperature increase or composition changes, they become defaceted to curved shapes. These defaceted grain boundaries are rough. It is thus possible to produce either singular or rough grain boundaries by heat-treatment or additives to vary their properties. [ABSTRACT FROM AUTHOR]

Abstract: . A crystalline interface is often covered by a dense network of linear defects with a (pseudo) biperiodic geometry. The elastic field of this network is calculated by thinking the interface as paved by adjacent Somigliana dislocations. The analysis of a portion of an erratic zigzag line of a (001)Si low angle twist boundary, observed in two-beam transmission electron microscopy, is given as an example. To cite this article: A. Boussaid et al., C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Reports on the detailed comparison of the one-dimensional paracrystalline and perturbed lattice models of disordered crystals and their diffraction. Calculation of diffraction patterns showing that with an appropriate choice of parameters, the two models give essentially identical diffraction for small crystallites and very similar diffraction for larger crystallites.