Structural and optical characterization of self-assembled InAs-GaAs quantum dots grown on high index surfaces

The structural and the optical properties of InAs layers grown on high index GaAs surfaces by molecular beam epitaxy are investigated in order to understand the formation and the self-organization of quantum dots (QDs) on novel index surfaces. Four different GaAs substrate orientations have been examined, namely, (111)B, (311)A, (311)B and (100). The (100) surface was used as a reference sample. STM pictures exhibit a uniform QD coverage for all the samples with the exception of (111)B, which displays a surface characterized by very large islands and where STM pictures give no evidence of QD formation. The photoluminescence (PL) spectra of GaAs (100) and (311) samples show typical QD features with PL peaks in the energy range 1.15-1.35 eV with comparable efficiency. No significant quenching of PL up to temperatures as high as 70K was observed. These results suggest that the high index substrates are promising candidates for production of high quality self-assembled QD materials for application to photonics.     

A transformed gamma process for bounded degradation phenomena

Most of the stochastic models adopted to describe the evolution over time of degradation phenomena of technological units assume that their degradation level can increase indeterminately. However, these degradation phenomena are typically subjected to obvious bounds, if only because technological units have finite size. In fact, very often, this inconsistency does not significantly affect the effectiveness of unbounded degradation models, since degrading units are usually assumed to fail when their degradation level exceeds a failure threshold that is much smaller than the obvious bounds. Nevertheless, in some cases, due to the very nature of the underlying degradation mechanism, less obvious bounds could exist, which are not necessarily far from the failure thresholds. The question that arises is whether the use of a bounded degradation model, in this latter type of experimental situations, could be beneficial. For this purpose, since a bounded degradation process should necessarily have dependent increments, in this paper we investigate the potential of a new bounded transformed gamma (TG) process to adequately describe bounded degradation phenomena and predict their future evolution. Differently from other existing gamma process based bounded degradation models, here the upper bound is treated as an unknown parameter that has to be estimated from the available degradation data. A numerical example is presented where the parameters of the proposed model are estimated from simulated data. Then the model is applied to a set of wear measures of cylinder liners that equip a diesel engine for marine propulsion, which have also stimulated this study. Model parameters are estimated by using the maximum likelihood (ML) method. The fitting ability of the proposed new bounded process is compared to that of an unbounded gamma process, which was previously adopted to analyze the same liner wear data. Obtained results are critically discussed in the paper.     

The role played by the alpha-helix in the unfolding pathway and stability of azurin: switching between hierarchic and nonhierarchic folding

The role played by the alpha-helix in determining the structure, the stability and the unfolding mechanism of azurin was addressed by studying a helix-depleted azurin variant produced by site-directed mutagenesis. The protein structure was investigated by CD, 1D (1)H NMR, fluorescence spectroscopy measurements and MD simulations, whilst EPR, UV-visible and cyclic voltammetry experiments were carried out to investigate the geometry and the properties of the Cu(II) site. The effects of the alpha-helix depletion on the thermal stability and the unfolding pathway of the protein were determined by DSC, UV/visible and fluorescence measurements at increasing temperature. The results show that, in the absence of the alpha-helix segment, the overall protein structure is maintained, and that only the Cu site is slightly modified. In contrast, the protein stability is diminished by about 60% with respect to the wild-type azurin. Moreover, the unfolding pathway of the mutant azurin involves the presence of detectable intermediates. In comparison with previous studies concerning other small beta-sheet cupredoxins, the results as a whole support the hypothesis that the presence of the alpha-helix can switch the folding of azurin from a hierarchic to a nonhierarchic mechanism in which the highly conserved beta-sheet core provides a scaffold for cooperative folding of the wild-type protein.     

Glass and wine: a good example of the deep relationship between drinkware and beverage

As the choice of the drinkware could deeply affect consumer perception during beverage consumption, an experimental research was carried out by expert testers to investigate the evolution of chemical–physical and sensory profiles of a typical rosé wine maintained in different types of glasses. The aim of this research was to select some parameters to well correlate beverage sensory properties with glass characteristics which can be used for drinkware design. The different sensorial profiles, obtained as a function of the geometric characteristics of glasses, were compared with one another. In order to find any significant parameter useful to represent the time evolution of the wine inside each vessel, the wine poured in all glasses was also characterized at different times from a chemical and physical point of view. As the design parameters are now guided more by aesthetic reasons rather than by functional ones, this new ‘integrated approach’, deriving from the merging of chemical, physical and sensorial data, can be used to design the optimum vessel for the enjoyment of the consumer during assessing sessions. This innovative procedure could be easily adapted for every beverage such as fruit juices, sparkling wines or beer.     

Heat and mass transfer modeling during continuous flow processing of fluid food by direct steam injection

Fluid food products, in the agri-food industry, are commonly subject to thermal treatments to ensure their safety and quality characteristics. Therefore, these treatments must be accurately selected and monitored to avoid over-processing, as consumer safety and product acceptability must be preserved.