Papers from the Joint Meeting of the Dutch and Belgian Societies for Electron Microscopy and the Belgian Society for Cell Biology. Antwerp, December 10-11, 1992.
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Animals↗
Biomedical subjects
G Van Tendeloo
Publications and source records attributed to G Van Tendeloo.
Real space modulation in Bi2Sr2CanCun + 1O6+2n and Tl2Ba2CuO6 superconductors derived from electron diffraction information.
We will try to illustrate here that, simply from the geometry of the electron diffraction pattern of an incommensurably modulated structure, conclusive information can be obtained on the real space shape of this modulation. The method applied here is based on the 3 + 1 dimensional description of symmetry operations and can be summarized as follows: 1) reconstruct the three-dimensional reciprocal space geometry of the modulated structure from electron diffraction information along different zone axes; 2) deduce the complete Bravais type symbol of the four-dimensional structure from the general reflection conditions; and 3) derive the modulation function for each atom type from the superspace symmetry elements which result from the information of both modulation and basic structure. This method will be applied here in short on the Bi2Sr2CanCun + 1O6+2n strucutre, for which system the results are in agreement with the ones recently obtained from neutron diffraction. For Tl2Ba2CuO6 where no data from other diffraction techniques are available, a more complete calculation will be performed, in order to determine the shape of the displacement function for the different atom types; the results are in agreement with the observed High Resolution Electron Microscopy (HREM) images.
Bismuth↗
Age-hardening mechanisms in a commercial dental gold alloy containing platinum and palladium.
The age-hardening mechanism of a commercial dental gold alloy containing platinum and palladium (in wt.%, 15 Cu, 6 Ag, 5 Pt, 3 Pd, 3 Zn, with the balance as gold) was elucidated by means of electrical resistivity, hardness tests, x-ray and electron diffraction and electron microscopy, as well as high-resolution electron microscopy. The sequence of phase transformations during isothermal aging below the critical temperature, Tc = 825 K, was described as follows: disordered solid solution alpha 0 (FCC)----metastable AuCu I' ordered phase (FCT)----metastable alpha 2 disordered phase (FCC) equilibrium AuCu I ordered phase (FCT) + equilibrium alpha 2 disordered phase (FCC). The hardening was due to the introduction of coherency strain at the interface between the AuCu I' platelet and the matrix. These ordered platelets had mutually perpendicular c-axes to compensate for the strain introduced by their tetragonality. A loss of coherency at the interface brought about softening of the alloy, i.e., over-aging.
Electric Conductivity↗
Defect structure of superconducting YBa2Cu3O7-delta.
The superconducting material Y1Ba2Cu3O7-delta has been investigated by electron microscopy. Special attention has been paid to the defects occurring in the material. Twinning on (110) or (110) planes is intrinsically related to the orthorhombicity, and when cooled slowly the twin bands are pseudoperiodic with an average width of approximately 50 nm. The orthorhombic-tetragonal transition is reversible and diffusion controlled. Under particular conditions and in slightly reduced material a 2a0 x b0 superstructure resulting from vacancy ordering is formed. When kept in air under powder form the material seems to be unstable. Planar defects along (001) accompany the degeneration of the material.
Crystallography↗
High-resolution electron microscopic study of age-hardening in a commercial dental gold alloy.
High-resolution electron microscopy and electron diffraction were applied to elucidate the hardening mechanism in an 18-carat gold commercial dental alloy, Au-31.7 at.%,Cu-8.1 at.%,Pd-5.3 at.%,Ag-54.9 at.%. The interface between the AuCu-I ordered platelets and the surrounding Au3Cu ordered phase was analyzed down to the atomic scale. A geometric model for the interface was deduced directly from the high-resolution electron micrographs. No evidence was found for the presence of a FCC phase at the interface between AuCu-I and Au3Cu.
Chemical Phenomena↗
Metacarpal bone mass and upper-extremity strength in 18-year-old boys.
The relation between bone mass and upper-extremity strength in 106 18-year-old boys was investigated. Bone mass was measured radiogrammetrically at the second metacarpal bone, and upper-extremity strength was measured by three power ability tests: vertical jump height, arm pull strength, and bent arm hang time. A significant correlation between arm pull strength and cortical thickness and cortical area was found. There was also a significant correlation between body weight, bone mass, and power tests. After partial correlation study, leaving out weight, a significant correlation between bone mass indices and arm pull strength remained. The larger bone mass in the above-average-fit boy is due to a larger periosteal diameter and smaller endosteal diameter. This study suggests that static strength is one of the determinants of bone gain before maturity.
Adolescent↗