The crystal structure of BaNiOa has been determined by single-crystal analysis. The space group is P63/mmc and lattice constants are a= 5.629 (3) and c=4"811 (3) A, with Z= 2. The structure has been refined by the block-diagonal least-squares technique to a final R value of 0-049. The structure is characteristic with linear chains of nickel atoms having a Ni-Ni distance of 2"405 (2) A,; the NiO6 octahedron is trigonally distorted.

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Effects of various elemental additives on the electrical resistivity of hot‐pressed SiC ceramics were studied. The electrical resistivity at room temperature of dense SiC ceramics varied greatly depending on the additives used. SiC ceramics with added Be had an extremely high electrical resistivity of 3 × 1012°.cm. On the other hand, SiC ceramics with added B and Al had electrical resistivities of 2 × 10 and 0.8 °cm, respectively. The differences in the electrical resistivity of the dense SiC ceramics were considered to be due to different solubilities of the additives in SiC grains. SiC ceramics with added Be had a low level of impurities in the SiC grains as a result of the low solubility of Be in these grains.

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This paper presents an analysis of a novel 3-SPR parallel manipulator with 3 degrees-of-freedom that is characterized by a mobile platform consisting of a single point where all the three open-loop kinematic chains converge. The constraint singularity problem of the mechanism is solved in closed form by computing the Jacobian of the manipulator. Then, the expression of the transmission index is obtained for the 3-SPR manipulator by using the pressure angle definition. In order to evaluate the influence of secondary parameters, an equivalent 6-SPS mechanism is analyzed and its transmission index is computed in the parameter space. Finally, the proposed manipulator is compared to a standard 3-SPR parallel mechanism to investigate the influence of the mobile platform radius over transmission index and workspace volume. The results are discussed in order to highlight the advantages and disadvantages of the proposed structure of parallel manipulator.

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For kinematic calibration of robots, we proposed using a low order Fourier series obtained by transforming the data for circular measurements paths. The paths were measured using a Double-Ball-Bar (DBB) system. Two nondimensional indices were proposed for evaluating the orthogonalities of the measurement paths and calibration parameters. An index was also proposed to evaluate the accuracy of the calibration with regard to measurement error. An algorithm for determining adequate measurement paths and an optimal set of a specified number of paths using these indices was also proposed. The effectivenesss of the porposed method, indices, and algorithm was investigated through simulations and experiments of kinematic calibration with an experimental in-parallel actuated worktable which we developed.

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