1,721,007 research outputs found
Prograde and retrograde chloritoid zoning in low temperature metamorphism, Alpi Apuane, Italy
No full textThe formation of fibrolite nodules in a package of melanocratic gneisses from the Hercynian basement of NE Sardinia, Italy
No full textMarble protection: An inorganic electrokinetic approach
No full textThe influence of an electric potential difference in an aqueous solution was studied as a method for depositing a calcium oxalate coating over a weathered carbonatic stone. Samples of weathered Carrara white marble were treated at 15 and 50 °C for five hours in an electrokinetic cell, specifically conceived for this study, containing a solution of ammonium oxalate (4% by weight), and were subsequently characterised by Scanning Electron Microscopy, X Ray Diffractometry, Thermogravimetric analysis and Mercury Intrusion porosimetry. The electrokinetic treatment proved to be a cost effective and time saving process, able to produce a thick and homogeneous calcium oxalate coating over the stone surface that improves its chemical and physical resistance in low pH environments, and is able to protect the stone from the by-products of urban pollution
Metakaolin in White Cement Mortars
No full textHere are presented the results of an experimental study conducted to investigate the physical- mechanical performance of white cement bound products. White cement is a key ingredient in buildings with unplastered concrete blockwork facades of special architectural value. A metakaolin pozzolan is used instead of the more commonly used dark grey silica fume. An acrylic product is used as superplasticizer, testing different concentrations in an effort to reduce the larger amount of water required by white cement pastes. The physical-mechanical properties of the examined mortars were found to depend decisively on the poor performance of the superplasticizer that proved to be unable to reduce the water-to-cement ratio significantly. On the other hand, the metakaolins tested, especially the products obtained by the calcination of Sardinian kaolinic clays, containing thermodynamically unstable silica phases, appeared to be more effective especially at short curing times
Specific surface area and chemical reactivity of quartz powders during mechanical processing
No full textThe present work focuses on the specific surface area increase, and on the related chemical reactivity enhancement of quartz powders submitted to mechanical processing. The mechanical treatment was carried out in a suitably developed ball mill allowing the control of the frequency and energy of the impacts between ball and reactor. The specific surface area was directly measured by nitrogen physisorption, whereas electron microscopy was used to determine the size distribution of powder particles. Based on the experimental results, a simplified mathematical model was developed to describe the process of specific surface area increase on a phenomenological basis. The model permits to gain valuable information on the amount of powder processed in individual impacts. The density of reactive centers at the surface of powder particles was also estimated by using the neutralization of a free radical as a test reaction. It is shown that the surface density of reactive centers increases with the energy of collisions
The origin of fibrolite-rich nodules in high grade melanocratic gneisses from NE Sardinia,Italy.
No full textAnatexis in the Hercynian basement of NE Sardinia, Italy: a case study of the migmatite of Porto Ottiolu
No full textMethodology to investigate the microclimate of a cultural heritage inserted in a semi-confined environment
No full textThe aim of the research has been to analyse the decay observed in the semi-confined
archaeological site in Cagliari. A multidisciplinary approach has been purposed. Differential
decay with zones with great damage for the structures (pulverization, detachments,
efflorescences) and other zones with less damage (only efflorescences) appeared from the
survey conducted in the site. Diagnostics have been carried out to reveal the decay forms and
their distribution; microclimatic monitoring has been carried out to detect temperature and
relative humidity, eventually harmful values for the conservation and possible differential
values of them inside the site. Sodium sulphate results the main decay agent and it is diffuse
homogeneously inside the site. Microclimatic monitoring has detected a microclimatic zoning
originated by the semi-confined environment. The zones closest to the outside have a trend
very similar to it, instead the most confined one have a great thermal and hygrometric inertia.
The comparison between the hygrothermal conditions monitored in the site and those
thermodynamic favourable to salt crystallization has finally revealed the reason of the
differential decay in site: different microclimatic conditions allow the sodium sulphate
crystallisation as efflorescences in the zones most confined, and cryptoefflorescences in the
closest to the outside one
Failure of acute diphenylhydantoin to affect the spontaneous electrical activity of dopamine cells.
No full textDiphenylhydantoin (DPH) has recently been reported to produce dopaminergic (DA) supersensitivity in animals. These results have suggested that the dyskinesias observed in humans after DPH, although rare, might be regarded as a neuroleptic-like effect. Indeed dyskinesias would be induced by an inactivation of post-synaptic DAergic receptors, operated by DPH, and therefore reminiscent of that observable in neuroleptic treatment. In order to investigate this matter, we studied the effects of i.v. DPH on the extracellular single unit activity of DAergic cells located in mid-brain areas of rats. DPH was injected alone or in combination with DA antagonists such as L-sulpiride (L-SULP) and haloperidol (HAL), or the DAergic agonist apomorphine (APO). Our results show that DPH did not affect spontaneous DAergic firing rate and also failed to modify the known action of the DA agonists and antagonists which were tested on these neurons
- …
