Dehydration of Selenite Cleavage Faces

Initial dehydration of selenite cleavage surfaces start at temperature 86 °C. The dislocations are revealed by distilled water. Dislocations are mobile at dehydration temperature. Impurity centres may act as obstacles for dislocation movement. Dehydration figures are in probability formed at impurity centres.     

Eccentricity of symmetrical and asymmetrical etch pits on calcite cleavages

There are two types of chemical eccentric etch pits.

• (1) Deepest points are always lying on the shorter diagonal. – Symmetrical etch pits the deepest points of which lying on the diagonals show dislocation lines in the plane (110). Eccentricity of symmetrical etch pits along the [110] direction is depending on the concentration of the etchant and on the inclination of the dislocation line in the plane (110).
• (2) Depth points do not lie on any diagonals. Eccentricity of asymmetrical etch pits along the [110] direction is depending on the concentration of the etchant and on the inclination of the dislocation line in the plane (110).

     

Dose distribution in electron-irradiated PMMA: effect of dose and geometry

Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio 1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA.     

Gross dissolution of natural rhombohedral calcite crystal in nitric acid

Gross dissolution of natural calcite crystal in concentrated nitric acid give interesting results. The gross dissolution is maximum at 6 M concentration of HNO₃. The activation energy increases as the concentration of HNO₃ increases. Similarly pre-exponential factor is also increases as concentration increases. The combined effect of activation energy and pre-exponentail factor gives the peak at 6 M concentration of nitric acid.     

The effects of grain shape and frustration in a granular column near jamming

We investigate the full phase diagram of a column of grains near jamming, as a function of varying levels of frustration. Frustration is modelled by the effect of two opposing fields on a grain, due respectively to grains above and below it. The resulting four dynamical regimes (ballistic, logarithmic, activated and glassy) are characterised by means of the jamming time of zero-temperature dynamics, and of the statistics of attractors reached by the latter. Shape effects are most pronounced in the cases of strong and weak frustration, and essentially disappear around a mean-field point.     

The nature of marbled Terra Sigillata slips: a combined μXRF and μXRD investigation

In addition to the red terra sigillata production, the largest Gallic workshop (La Graufesenque) made a special type of terra sigillata, called “marbled” by the archaeologists. Produced exclusively at this site, this pottery is characterized by a surface finish made of a mixture of yellow and red slips. Because the two slips are intimately mixed, it is difficult to obtain the precise composition of one of the two constituents without contamination from the other. In order to obtain very precise correlation at the appropriate scale between the color aspect and the elemental and mineralogical phase distributions in the slip, combined electron microprobe, X-ray micro spectroscopies and micro diffraction on cross-sectional samples were performed. The aim of this study is to discover how potters were able to produce this unique type of terra sigillata and especially this particular slip of an intense yellow color. Results show that the yellow component of marbled sigillata was made from a titanium-rich clay preparation. The color is due to the formation of a pseudobrookite (TiFe₂O₅) phase in the yellow part of the slip, the main characteristics of that structure being considered nowadays as essential for the fabrication of stable yellow ceramic pigments. Its physical properties such as high refractive indices and a melting point higher than that of most silicates widely used as ceramic colorants are indeed determinant for this kind of application. Finally, the red parts have a similar composition (elementary and mineralogical) to the one of standard red slip.     

Hybrid systems through natural product leads: an approach towards new molecular entities

Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain integration of key structural/functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.     

Electrophilic additions to a 2-methylenebicyclo[2.1.1]hexane system: probing pi-face selectivity for electrostatic and orbital effects

[reaction: see text] 5-exo-Bicyclo[2.1.1]hexane derivatives with remote electron-withdrawing substituents exhibit very modest face selectivity during electrophilic additions due to interplay of several electronic factors. These experimental results have been probed through ab initio MESP maps, bond density calculations, and energetics involved in pre-reaction complexation.