[en] Quantitative analysis of electron microscope autoradiographs aims at extracting the maximum amount of information from ones material. It helps to identify labelled structures from micrographs with low grain densities and can provide numerical estimates for their relative activities. These values will only be estimates because of the low resolution of the technique compared with the resolving power of the electron microscope. The silver grains and the cellular structures they lie over may be well resolved, but it should be remembered that the position of the developed silver grain does not necessarily represent the source of radioactivity in the cell or tissue. This is because the β particles emitted after nuclear disintegration may travel for some distance in the tissue or in the emulsion before a grain is formed. The more energetic the emission the greater this scatter becomes. It is possible, therefore, that a grain lying over one structure may have originated from a nuclear disintegration in a neighbouring one. To analyse the grain distribution it is essential that such possibilities are taken into account by a statistical procedure. Analytical methods are described

[en] The measuring methods of optical density essential for X-ray images are briefly described. The value of the medium optical density should lie in that interval (ca. 0.9 ≤ D ≤ 1.25) which is a prerequisite for good detail rendition. The present contribution discusses conditions and methods for determining and adjusting this medium optical density. (orig.)

[en] The objective of this study was to throw some light on ammonium uranates precipitated from uranyl nitrate solution using ammonia or urea. The effect of washing the uranates, thickness of their layers on the trays during subsequent calcination, temperature and duration, on the densities of powders formed during thermal decomposition was studied. (author)

[en] The testing program described in this report was carried out to study the liquefaction behavior of a clean, uniform, medium sand. Horizontal beds of this sand, 42 inches by 90 inches by 4 inches were prepared by pluviation with a special sand spreader, saturated, and tested in a shaking table system designed for this program, which applied a horizontal cyclic shear stress to the specimens. Specimen size was selected to reduce boundary effects as much as possible. Values of pore pressures and shear strains developed during the tests are presented for sand specimens at relative densities of 54, 68, 82, and 90 percent, and the results interpreted to determine the values of the stress ratio causing liquefaction at the various relative densities

[en] The fundamental issue of reconstructing a porous medium is examined anew in this paper, thanks to a sample of low-porosity Fontainebleau sandstone that has been analyzed by computed microtomography. Various geometric properties are determined on the experimental sample. A statistical property, namely, the probability density of the covering radius, is determined. This is used in order to reconstruct a porous medium by means of a Poissonian generation of polydisperse spheres. In a second part, the properties of the real experimental sample and of the reconstructed one are compared. The most important success of the present reconstruction technique is the fact that the numerical sample percolates despite its low porosity. Moreover, other geometrical features and conductivity are found to be in good agreement

[en] A cloud consisting of a finite number of dust grains in a plasma is considered. It is shown that the absorption of the plasma by the dust grains gives rise to the formation of a plasma flow toward to the cloud. The drag force produced by this flow acts upon the dust grains and counterbalances the electrostatic repulsing force. The distribution of the grain density inside the cloud is determined. The characteristic size of the cloud is estimated as r_D^3/2/a^1/2, where r_D is the plasma Debye radius, and a is the size of the dust grains

No abstract available

[en] The results of sieve analyses may be interpreted in the best manner by approximate functions which permit the exact description of the grain size distributions by two parameters. This fact facilitates the comparison of results of size analyses essentially and enables their graphical representation in form of linear size-distributions curves. The deviations of the linearity refer to irregularities in the powder preparation or in the powder processing. Investigations of UO²-powders by dry sieve analysis have shown that it is possible to classify such powders in the range of grain sizes of more than 63 micrometers, in which specific sieving conditions must be find out for each special material. (author)

[en] Grain and pore growth are observed during sintering of SnO₂ without any densification for temperature up to 1500⁰C. This behaviour is due to mass transport through vapor phase. In order to favor densifying mechanism several concentrations of Nb₂O₅ were added to SnO₂ (1.0, 3.0, 5.0 and 10.0 mol%). Sintering of Nb₂O₅ doped SnO₂ pellets in the range of 1000 to 1450⁰C indicate that Nb₂O₅ inhibits SnO₂ evaporation allowing some densification at 1450⁰C. (author)

No abstract available