289 research outputs found
MORTARS AND PLASTERS PRODUCED WITH EARTH-BASED SUSTAINABLE MIXES: A METHODOLOGY PROPOSAL FOR RECOVERY OF VERNACULAR ARCHITECTURE IN ROERO, PIEDMONT (ITALY)
Abstract. The work presented is the achievement of a master degree project, developed at Politecnico di Torino. The paper aims to provide standards for the formulation and mixing of earth-based mortars, for the rehabilitation of historic buildings of the Roero area, in Piemonte region. Roero presents a large architectural heritage, consisting mainly of fired or earth bricks rural and residential buildings, which was anciently protected using lime or earth-based plasters perfectly integrated with local landscape and environment colours appearance. In recent decades (and still to present days), vernacular plasters are frequently replaced by cement-based products, resulting hardly compatible with local bearing walls materials and landscape aesthetic features. While Roero traditional buildings plasters were produced using local earth and sands coming from streams, today, aggregates extraction in watercourses proximity is not allowed, or strictly regulated by rules and regional regulations. The paper presents a classification of the characteristics of different soils from Roero area, through different types of particle distribution size analysis and diffractometric tests, and propose a method for the production of local earth-based plasters stabilized with lime, making use of earth and rocks from local excavation sites, considered in Italy as secondary raw materials or special waste. Produced plasters compressive and bending strength have been tested, while their suitability for building maintenance and restoration, as their compatibility with Roero architecture and landscape, have been verified through spectrophotometric measures
Nucleation dynamics in 2d cylindrical Ising models and chemotaxis
The aim of our work is to study the effect of geometry variation on
nucleation times and to address its role in the context of eukaryotic
chemotaxis (i.e. the process which allows cells to identify and follow a
gradient of chemical attractant). As a first step in this direction we study
the nucleation dynamics of the 2d Ising model defined on a cylindrical lattice
whose radius changes as a function of time. Geometry variation is obtained by
changing the relative value of the couplings between spins in the compactified
(vertical) direction with respect to the horizontal one. This allows us to keep
the lattice size unchanged and study in a single simulation the values of the
compactification radius which change in time. We show, both with theoretical
arguments and numerical simulations that squeezing the geometry allows the
system to speed up nucleation times even in presence of a very small energy gap
between the stable and the metastable states. We then address the implications
of our analysis for directional chemotaxis. The initial steps of chemotaxis can
be modelled as a nucleation process occurring on the cell membrane as a
consequence of the external chemical gradient (which plays the role of energy
gap between the stable and metastable phases). In nature most of the cells
modify their geometry by extending quasi-onedimensional protrusions (filopodia)
so as to enhance their sensitivity to chemoattractant. Our results show that
this geometry variation has indeed the effect of greatly decreasing the
timescale of the nucleation process even in presence of very small amounts of
chemoattractants.Comment: 27 pages, 6 figures and 2 table
Tunable topological edge modes in Su–Schrieffer–Heeger arrays
A potential weakness of topological waveguides is that they act on a fixed narrow band of frequencies. However, by 3D printing samples from a photo-responsive polymer, we can obtain a device whose operating frequency can be fine-tuned dynamically using laser excitation. This greatly enhances existing static tunability strategies, typically based on modifying the geometry. We use a version of the classical Su–Schrieffer–Heeger model to demonstrate our approach
Hierarchical auxetic and isotropic porous medium with extremely negative Poisson's ratio
We propose a novel two-dimensional hierarchical auxetic structure consisting of a porous medium in which a homogeneous matrix includes a rank-two set of cuts characterised by different scales. The six-fold symmetry of the perforations makes the medium isotropic in the plane. Remarkably, the mesoscale interaction between the first- and second-level cuts enables the attainment of a value of the Poisson’s ratio close to the minimum reachable limit of -1. The effective properties of the hierarchical auxetic structure are determined numerically, considering both a unit cell with periodic boundary conditions and a finite structure containing a large number of repeating cells. Further, results of the numerical study are validated experimentally on a polymeric specimen with appropriately arranged rank-two cuts, tested under uniaxial tension. We envisage that the proposed hierarchical design can be useful in numerous engineering applications exploiting an extreme auxetic effect
Cochlea-inspired tonotopic resonators
The cochlea has long been the subject of investigation in various research fields due to its intriguing spiral architecture and unique sensing characteristics. One of its most interesting features is tonotopy, the ability to sense acoustic waves at different spatial locations based on their frequency content. In this work, we propose a novel design for a tonotopic resonator, based on a cochlea-inspired spiral, which can discriminate the frequency content of elastic waves without the use of sub-wavelength resonators. The structure is the result of an optimization process to display a uniform distribution of displacement maxima along its centreline for frequencies spanning nearly a two-decade range, while maintaining a compact design. Numerical simulations are performed to demonstrate the concept and experimental measurements to validate it on a 3D printed structure. The resulting frequency-dependent distribution is also shown to be a viable means to discriminate signals with various frequency components. We also show that for appropriate parameter ranges, the tonotopic behaviour can be inverted, i.e., lower frequencies can be made to concentrate in narrower regions, as happens in the real cochlea. The harnessed tonotopic features can be used as a fundamental principle to design structures with applications in areas such as non-destructive testing and vibration attenuation
Engineering Design of the ITER RF Systems
Parallel conceptual design efforts for auxiliary heating systems on ITER are being carried out in both the electron cyclotron range of frequencies (ECRF) and ion cyclotron range of frequencies (ICRF). These systems are required to deliver a minimum of 50 MW of CW power to the plasma for the primary purpose of heating and the secondary purpose of current drive. Current designs of the two systems are presented and the primary design issues are discussed
Hierarchical auxetic and isotropic porous medium with extremely negative Poisson's ratio
We propose a novel two-dimensional hierarchical auxetic structure consisting of a porous medium in which a homogeneous matrix includes a rank-two set of cuts characterised by different scales. The six-fold symmetry of the perforations makes the medium isotropic in the plane. Remarkably, the mesoscale interaction between the first- and second-level cuts enables the attainment of a value of the Poisson's ratio close to the minimum reachable limit of -1. The effective properties of the hierarchical auxetic structure are determined numerically, considering both a unit cell with periodic boundary conditions and a finite structure containing a large number of repeating cells. Further, results of the numerical study are validated experimentally on a polymeric specimen with appropriately arranged rank-two cuts, tested under uniaxial tension. We envisage that the proposed hierarchical design can be useful in numerous engineering applications exploiting an extreme auxetic effect
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