Mechanics and polarity in cell motility

The motility of a fish keratocyte on a flat substrate exhibits two distinct regimes: the non-migrating and the migrating one. In both configurations the shape is fixed in time and, when the cell is moving, the velocity is constant in magnitude and direction. Transition from a stable configuration to the other one can be produced by a mechanical or chemotactic perturbation. In order to point out the mechanical nature of such a bistable behaviour, we focus on the actin dynamics inside the cell using a minimal mathematical model. While the protein diffusion, recruitment and segregation govern the polarization process, we show that the free actin mass balance, driven by diffusion, and the polymerized actin retrograde flow, regulated by the active stress, are sufficient ingredients to account for the motile bistability. The length and velocity of the cell are predicted on the basis of the parameters of the substrate and of the cell itself. The key physical ingredient of the theory is the exchange among actin phases at the edges of the cell, that plays a central role both in kinematics and in dynamics

Time-resolved lidar fluorosensor for sea pollution detection

A contemporary time and spectral analysis of oil fluorescence is useful for the detection and the characterization of oil spills on the sea surface. Nevertheless the fluorosensor lidars, which were realized up to now, have only partial capability to perform this double analysis. The main difficulties are the high resolution required (of the order of 1 nanosecond) and the complexity of the detection system for the recording of a two-dimensional matrix of data for each laser pulse. An airborne system whose major specifications were: time range, 30 to 75 ns; time resolution, 1 ns; spectral range, 350 to 700 nm; and spectral resolution, 10 nm was designed and constructed. The designed system of a short pulse ultraviolet laser source and a streak camera based detector are described

Hybrid organic/inorganic nanotubes of imogolite type

The aim of the present PhD project is to describe the developments obtained in imogolite research field, concerning the synthesis and characterization of two new modified imogolite nanotubes, either by direct or post-synthesis reactions, as compared to unmodified synthetic imogolite. Using a methylated Si precursor instead of TEOS, methyl-imogolite (Me-IMO), a nanotube material with formula (OH)3Al2O3SiCH3, is obtained in place of the standard imogolite (OH)3Al2O3SiOH (IMO) (I. Bottero et al. PCCP 7(13), 2011, 744 -750). Post-synthesis grafting of the outer surface of Me-IMO with 3-aminopropyltriethoxysilane (3-APS) yields a new hybrid material (Me-IMO-NH2) (C.Zanzottera et al. JPCC, DOI: 10.1021/jp301177q) with an entirely hydrophobic inner surface and a largely aminated outer surface. Me-IMO-NH2 structure was studied in detail and compared with those of Me-IMO and IMO by means of: i) 1H, 13C, 27Al, 29Si and HETCOR 1H-13C MAS NMR experiments, providing evidence for the occurrence of grafting and yielding an estimate of its extent; ii) XPS analysis, confirming the surface chemical composition of Me-IMO-NH2; iii) IR spectroscopy, showing that most terminal -NH2 groups are protonated; iv) XRD measurements and FE-SEM microscopy yielding information on the long-range order and morphology; v) N2 adsorption at -196°C, yielding specific surface area and pore size distribution. Adsorptive properties were tested towards CH4 and CO2 by means of volumetric measurments. Curve-fits obtained by assuming a Langmuir model of CH4 adsorption in the 0-35 bar pressure range, show good agreement with experimental points: both the maximum adsorbed volumes (76.81 and 29.65 cm3/g for Me-IMO and IMO, respectively) and equilibrium constants (0.03 and 0.06 bar-1 for Me-IMO and IMO, respectively), were calculated. With CO2, the preliminary results available at low pressure and weighted by the corresponding surface area values, confirm that the interaction, as expected, is stronger in case of IMO, according to the following sequence, IMO > Me-IMO-NH2 > Me-IMO, being Me-IMO the less polar material. Stability of imogolite-like nanotubes was studied by combining MAS NMR, XRD and TGA-Mass techniques. Collapsing of the structure is evidenced by the formation of a lamellar phase at 500 °C. With IMO, the mechanism proposed wants the cleavage of nanotubes to happen across their diameter, causing the formation of the following repeating sequence, Al-O-Si-O-Si-O-Al. With hybrid imogolite-like samples the mechanism is much more complex. Two processes seem to act subsequently: the first one, when methyl groups are removed at high temperature (above 300 °C); the second one, if methyl groups of two close nanotubes are able to create Si-CH2-O-Al links, by the reaction with terminal aluminol groups. Surface properties were studied by FT-IR spectroscopy of adsorbed probe molecules, namely CO2, NH3 (adsorbed at room temperature) and CO (adsorbed at nominal -196°C). IMO and Me-IMO interact reversibly with carbon dioxide showing the presence of physisorbed gas as well as of carbonate-like species. With Me-IMO-NH2, besides the two aforementioned species, carbamic species are also present, thus confirming the successful amination of the outer surface. NH3 adsorption evidenced that pores among aligned tubes of IMO are too narrow to be accessible by the gas. Thus, for geometrical reasons, that is the larger nanotubes diameter external -Al(OH)Al species are detectable only in case of Me-IMO and Me-IMO-NH2. CO adsorption indicated a weak electrostatic interaction. Particularly, with IMO pre-treated at 150 °C, IMO-150, CO interacts with water molecules still adsorbed and removed only by outgassing at a higher temperature; with Me-IMO-150, the slightly shifted 2146 cm-1 band indicates instead a weak perturbation of the gas; Me-IMO-NH2 showed both contributions. In agreement with MAS NMR results, lamellar imogolite phase is obtained at 500 °C. In fact, both NH3 and CO interaction confirmed that with IMO-500, hydroxyls more acidic than silanols are formed. On the contrary, with lamellar Me-IMO and Me-IMO-NH2, physisorbed CO as well as heterogeneous acidic sites are found, analogously to Al-rich microporous silicates. Finally, in spite of their shared fibrous nature, according to the preliminary study performed, imogolite nanotubes were proposed as candidate as a low-toxicity reference material for in vitro toxicological studies on HARNs, High Aspect Ratio Nanomaterials. Moreover, the substantial inertness of macrophages towards the tubes, may ensure high bio-compatibility as a scaffold for cell growth in different medical settings (O. Bussolati et al, manuscript in preparation). As a general conclusion, it is worth noting that, in contrast with the more famous carbon nanotubes, Imo-derived nanotubes may be functionalized under mild conditions by means of direct or post-synthesis procedure. In particular, properties of both the inner and the outer surface may be properly changed, and the hydrophilicity of the material may be modulated as well as porosity and thermal stability. This may open the way to new and promising application

Intermittency in crystal plasticity informed by lattice symmetry

We develop a nonlinear, three-dimensional phase field model for crystal plasticity which accounts for the infinite and discrete symmetry group G of the underlying periodic lattice. This generates a complex energy landscape with countably-many G-related wells in strain space, whereon the material evolves by energy minimization under the loading through spontaneous slip processes inducing the creation and motion of dislocations without the need of auxiliary hypotheses. Multiple slips may be activated simultaneously, in domains separated by a priori unknown free boundaries. The wells visited by the strain at each position and time, are tracked by the evolution of a G-valued discrete plastic map, whose non-compatible discontinuities identify lattice dislocations. The main effects in the plasticity of crystalline materials at microscopic scales emerge in this framework, including the long-range elastic fields of possibly interacting dislocations, lattice friction, hardening, band-like vs. complex spatial distributions of dislocations. The main results concern the scale-free intermittency of the flow, with power-law exponents for the slip avalanche statistics which are significantly affected by the symmetry and the compatibility properties of the activated fundamental shears.Comment: 13 pages, 4 figure

Economic and social policies of Argentina (1911-1924)

Entre fines del siglo XIX y principios del siglo XX la noción de economía social formó parte del debate de los reformadores sociales. A principios del siglo XX un grupo de intelectuales y profesionales argentinos intentaron introducir estas ideas en la sociedad con el fin de atenuar la conflictividad social. La fundación en 1911 del Museo Social Argentino, entidad promotora del mutualismo y el Cooperativismo, formó parte de ese movimiento, que el artículo se propone analizar.Entre o fim do século XIX e início do século XX a noção de economia social participou do debate dos reformadores sociais. No início do século XX, um grupo de intelectuais e professionais argentinos tentaram introduzir estas ideias na sociedade com o fim de atenuar os conflitos sociais. O Museu Social Argentino, entidade promotora do mutualismo, foi fundado em 1911. Participou do movimento Cooperativo, que o artigo se propõe a analisar.Between late nineteenth century and early twentieth century the notion of social economy was part of the discussion of social reformers. At the beginning of twentieth century, a group of Argentine intellectuals and professionals tried to introduce these ideas in society in order to mitigate social conflict. The foundation in 1911 of the Argentine Social Museum, promoter of mutualism and Cooperatives, was part of that movement, that the article analyzes.Fil: Zanzottera, Maria Guillermina. Universidad de Buenos Aires. Facultad de Arquitectura y Urbanismo. Instituto de Arte Americano e Investigación Estéticas "Mario Buschiazzo"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

La vivienda en la ciudad reformada: los debates en el Primer Congreso Argentino de la Habitación (1920)

Para este trabajo nos centraremos en analizar, desde una perspectiva histórica, las Actas del Primer Congreso Argentino de la Habitación. El examen de los debates que se promovieron en ese evento de alcance nacional, realizado en Buenos Aires entre el 5 y el 13 de septiembre de 1920, dan cuenta de los temas que, sobre vivienda y ciudad, se estaban constituyendo como problema y nos permiten observar el pasaje de las intervenciones aisladas a un proyecto reformador de la ciudad en su conjunto. En ese sentido, nuestra hipótesis se vincula a que el análisis de esa fuente particular nos permite iluminar los modos de pensar la reforma de la vivienda y la ciudad en el año 20, posibilitándonos observar las “nuevas” representaciones sobre la que se cimentarán las intervención y discusiones que configurarán los debates de los años siguientes.For this work we will focus on analyzing, from a historical perspective, the Proceedings of the Primer Congreso Argentino de la Habitación The discussion of the debates that were promoted in that event of national scope, made in Buenos Aires between September 5 and 13, 1920, give an account of the issues that, on housing and city, were constituting a problem and allow us to observe the passage of the isolated interventions to a reforming project of the city as a whole. In this sense, our hypothesis is linked to the fact that the analysis of that particular source allows us to illuminate the ways of thinking the reform of housing and the city in the year 20, making it possible to observe the "new" representations on which will be based the intervention and discussions that will shape the debates of the following years

A multiregional extension of the SIR model, with application to the COVID-19 spread in Italy

The paper concerns a new forecast model that includes the class of undiagnosed infected people, and has a multiregion extension, to cope with the in-time and in-space heterogeneity of an epidemic. The model is applied to the SARS-CoV2 (COVID-19) pandemic that, starting from the end of February 2020, began spreading along the Italian peninsula, by first attacking small communities in north regions, and then extending to the center and south of Italy, including the two main islands. It has proved to be a robust and reliable tool for the forecast of the total and active cases, which can be also used to simulate different scenarios. In particular, the model is able to address a number of issues, such as assessing the adoption of the lockdown in Italy, started from March 11, 2020; the estimate of the actual attack rate; and how to employ a rapid screening test campaign for containing the epidemic

L’efficacia di nuove tecnologie nella valorizzazione del paesaggio della Brianza - The new technologies ability for landscape’s enhancement of the Brianza

In the 20th century the Brianza, 'the idyllic region more rich and fertile in all Lombardy' (Richard Bagot, 19th century), was hit by a crushing unit that had characterized its development and identity. The alteration of the values and the rapid shift from agricultural to industrial reality generated a loss of specific identity’s awareness and a violent drop of the cultural heritage. With the support of local institutions (Lombardy Region, municipalities, Institute for the History of Lombard Art) were developed communication strategies, with the use of current technologies for the recovery of collective memory, also offered to the international public of EXPO. By participating at the all communication process, I learned the ability of the latest technologies to enhance the plots that still exist between landscape, craftsmanship, heritage, monuments, as I’ll show in my report