The mechanical resistance of saturated stones

This paper aims at investigating the effect of the presence of water on the mechanical resistance of stones. The presence of water, connected to the intrinsic properties of the stone (mineralogical composition, fabric, texture, etc.) and to the conditions of use (anchoring systems, climatic parameters, etc ), is the main cause of stone decay. However, the presence of water alone inside stone could cause a decrease in mechanical resistance . The obtained data could in fact be useful to correct the safety coefficient and should be taken into account in the planning of structural stonework. Moreover, useful suggestions can be drawn for the in situ monitoring, taking into account that non destructive tests, together with conventional mechanical methods, are influenced by the presence of water in stones and should be corrected. Three kinds of stones, which have historically been used for structural purposes, have been studied: Pietra di Luserna (gneiss, Piedmont, Italy), Pietra Verde Argento (gneiss, Piedmont, Italy) and Pietra di Courtil (mica-schist, Aosta Valley, Italy). The flexural strength, rupture energy, open porosity and ultrasonic pulse velocity (UPV) have been determined on specimens in dried and saturated conditions at different accelerated ageing steps. As far as the UPV test is concerned, its results are well correlated with the flexural strength values but, without other parameters, it cannot give information on whether the specimen is filled with water, therefore suitable procedures to correct the UPV value obtained in situ are suggested. Destructive methods, and in particular the flexural strength method, instead, give lower resistance values for saturated specimens than dried ones, thus confirming the weakness of the stone due to the water insid

Monopolistic competition, expected inflation and contract length

Monopoly

Ambiguity resolution for satellite Doppler positioning systems

A test for ambiguity resolution was derived which was the most powerful in the sense that it maximized the probability of a correct decision. When systematic error sources were properly included in the least squares reduction process to yield an optimal solution, the test reduced to choosing the solution which provided the smaller valuation of the least squares loss function. When systematic error sources were ignored in the least squares reduction, the most powerful test was a quadratic form comparison with the weighting matrix of the quadratic form obtained by computing the pseudo-inverse of a reduced rank square matrix. A formula is presented for computing the power of the most powerful test. A numerical example is included in which the power of the test is computed for a situation which may occur during an actual satellite aided search and rescue mission

Anomalous temperature dependence of the band-gap in Black Phosphorus

Black Phosphorus (BP) has gained renewed attention due to its singular anisotropic electronic and optical properties that might be exploited for a wide range of technological applications. In this respect, the thermal properties are particularly important both to predict its room temperature operation and to determine its thermoelectric potential. From this point of view, one of the most spectacular and poorly understood phenomena is, indeed, the BP temperature-induced band-gap opening: when temperature is increased the fundamental band-gap increases instead of decreasing. This anomalous thermal dependence has also been observed, recently, in its monolayer counterpart. In this work, based on \textit{ab-initio} calculations, we present an explanation for this long known, and yet not fully explained, effect. We show that it arises from a combination of harmonic and lattice thermal expansion contributions, which are, in fact, highly interwined. We clearly narrow down the mechanisms that cause this gap opening by identifying the peculiar atomic vibrations that drive the anomaly. The final picture we give explains both the BP anomalous band-gap opening and the frequency increase with increasing volume (tension effect).Comment: Published in Nano Letter

Growth in systems of vesicles and membranes

We present a theoretical study for the intermediate stages of the growth of membranes and vesicles in supersaturated solutions of amphiphilic molecules. The problem presents important differences with the growth of droplets in the classical theory of Lifshitz-Slyozov-Wagner, because the aggregates are extensive only in two dimensions, but still grow in a three dimensional bath. The balance between curvature and edge energy favours the nucleation of small planar membranes, but as they grow beyond a critical size they close themselves to form vesicles. We obtain a system of coupled equations describing the growth of planar membranes and vesicles, which is solved numerically for different initial conditions. Finally, the range of parameters relevant in experimental situations is discussed.Comment: 13 pages and 5 postscript figures. To appear in Phys. Rev

Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices

Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation