Fast exopolysaccharide secretion of Pseudomonas aeruginosa on polar polymer surfaces

The influence of the surface chemical structure and related physicochemical properties on the adhesion of P. aeruginosa has been studied for moderately hydrophobic polymers and for hydrophilic surfaces obtained by O2-plasma treatments and 50 keV Ar+ beam irradiation of poly(hydroxymethylsiloxane) and poly(ethyleneterephthalate). The surface chemical structure has been obtained by X-ray photoelectron spectroscopy, the roughness was measured by atomic force microscopy, and the surface free energy was evaluated from contact angle measurements for all the polymer substrates before and after the irradiation treatments. It is shown that a massive and unusually fast secretion of exopolysaccharides onto highly polar surfaces, corresponding to the formation of complex three-dimensional multilayers (i.e., biofilm-like structures), occurs already after 2 h of incubation. It is suggested that such highly polar surfaces can operate either by promoting, by means of a still unknown biomolecular mechanism, an early gene expression process or by mimicking the P. aeruginosa cellular walls.     

Mott-insulator-SF transition lobe in the presence of a second superfluid component

Laser Physics - A two-component bosonic mixture loaded in a two-dimensional optical lattice is analyzed. By means of Mean-Field techniques and Worm algorithm Monte Carlo simulations, we study the...     

On the effect of gravity on the bifurcation of rectangular closed-loop thermosyphon

Closed-loop thermosyphons are systems in which heat is transferred from a source to a sink by means of a natural convective flow, i.e. without the help of mechanical pumping. In fact, the dynamics of such systems strongly depend both on the thermal boundary conditions and on the gravitational field in which they operate. While the effect of variations of the boundary conditions has been extensively analysed in the last decades, the dependence on gravity has never been explicitly studied.The aim of this paper is to examine the effect of variations of gravity as well as that of thermal boundary conditions on the dynamics of natural circulation loops. Such an analysis might point out some useful applications for the cooling of a generic source in reduced gravity conditions.To this purpose an experimental campaign was performed on a natural circulation operating under a gravity field varying in the range between 10^–2 g and 1.8 g, with g = 9.81 ms^–2. The dynamical behaviour detected during the experiment was used for the validation of a mathematical model, previously validated under terrestrial gravity conditions. Model simulations were found to satisfactorily reproduce the dynamics of the system under variable gravity. This proved the possibility to use the model for the construction of bifurcation diagrams describing the behaviours of natural circulation loops under variations of both the gravitational field and the thermal boundaries.     

Sulle equazioni paraboliche del secondo ordine di tipo non variazionale

Sunto Come nell'introduzione. Lavoro eseguito nell'ambito dell'attività dei Gruppi di ricerca matematici del Consiglio nazionale delle ricerche.     

Antimicrobial Effect and Cytotoxic Evaluation of Mg-Doped Hydroxyapatite Functionalized with Au-Nano Rods

Hydroxyapatite (HA) is the main inorganic mineral that constitutes bone matrix and represents the most used biomaterial for bone regeneration. Over the years, it has been demonstrated that HA exhibits good biocompatibility, osteoconductivity, and osteoinductivity both in vitro and in vivo, and can be prepared by synthetic and natural sources via easy fabrication strategies. However, its low antibacterial property and its fragile nature restricts its usage for bone graft applications. In this study we functionalized a MgHA scaffold with gold nanorods (AuNRs) and evaluated its antibacterial effect against S. aureus and E. coli in both suspension and adhesion and its cytotoxicity over time (1 to 24 days). Results show that the AuNRs nano-functionalization improves the antibacterial activity with 100% bacterial reduction after 24 h. The toxicity study, however, indicates a 4.38-fold cell number decrease at 24 days. Although further optimization on nano-functionalization process are needed for cytotoxicity, these data indicated that Au-NRs nano-functionalization is a very promising method for improving the antibacterial properties of HA.     

On the Control of the Friction Force

This paper tackles the problem of controlling the Coulomb friction force in order to achieve damping characteristics which can be advantageous in engineering applications, particularly in the area of vibration control, for example, vehicle suspensions, rotating machinery foundations or earthquake protection systems. The control schemes employed belong to the family of variable structure controllers (VSC), a class of robust control algorithms, namely sliding mode control (SMC) and switched state feedback (SSF). The schemes perform force tracking control, aiming at making the friction force track a reference force in order to reduce the acceleration experienced by a suspended mass. The plant investigated is a 2-degree of freedom system and in this study represents a quarter car. The controller performances are investigated both numerically and experimentally.     

Analysis of Pseudo-Lyapunov Exponents of Solar Convection Using State-of-the-Art Observations

The solar photosphere and the outer layer of the Sun’s interior are characterized by convective motions, which display a chaotic and turbulent character. In this work, we evaluated the pseudo-Lyapunov exponents of the overshooting convective motions observed on the Sun’s surface by using a method employed in the literature to estimate those exponents, as well as another technique deduced from their definition. We analyzed observations taken with state-of-the-art instruments at ground- and space-based telescopes, and we particularly benefited from the spectro-polarimetric data acquired with the Interferometric Bidimensional Spectrometer, the Crisp Imaging SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following previous studies in the literature, we computed maps of four quantities which were representative of the physical properties of solar plasma in each observation, and estimated the pseudo-Lyapunov exponents from the residuals between the values of the quantities computed at any point in the map and the mean of values over the whole map. In contrast to previous results reported in the literature, we found that the computed exponents hold negative values, which are typical of a dissipative regime, for all the quantities derived from our observations. The values of the estimated exponents increase with the spatial resolution of the data and are almost unaffected by small concentrations of magnetic field. Finally, we showed that similar results were also achieved by estimating the exponents from residuals between the values at each point in maps derived from observations taken at different times. The latter estimation technique better accounts for the definition of these exponents than the method employed in previous studies.     

Dynamic control for a natural circulation loop

In the present paper a control strategy is outlined to avoid instabilities in a rectangular natural circulation loop. A mathematical model linearized using the stationary solutions was used together with a standard P.I.D. control to counteract the birth of the instabilities inside the loop. The proposed strategy was tested both with numerical simulation and with experimental tests. In both cases the strategy control was suitable to avoid the flow inversion of the working fluid inside the loop.