A 1D continuum model for beams with pantographic microstructure: asymptotic micro-macro identification and numerical results

In the standard asymptotic micro-macro identification theory, starting from a De Saint-Venant cylinder, it is possible to prove that, in the asymptotic limit, only flexible, inextensible, beams can be obtained at the macro-level. In the present paper we address the following problem: is it possible to find a microstructure producing in the limit, after an asymptotic micro-macro identification procedure, a continuum macro-model of a beam which can be both extensible and flexible? We prove that under certain hypotheses, exploiting the peculiar features of a pantographic microstructure, this is possible. Among the most remarkable features of the resulting model we find that the deformation energy is not of second gradient type only because it depends, like in the Euler beam model, upon the Lagrangian curvature, i.e. the projection of the second gradient of the placement function upon the normal vector to the deformed line, but also because it depends upon the projection of the second gradient of the placement on the tangent vector to the deformed line, which is the elongation gradient. Thus, a richer set of boundary conditions can be prescribed for the pantographic beam model. Phase transition and elastic softening are exhibited as well. Using the resulting planar 1D continuum limit homogenized macro-model, by means of FEM analyses, we show some equilibrium shapes exhibiting highly non-standard features. Finally, we conceive that pantographic beams may be used as basic elements in double scale metamaterials to be designed in future

Feasibility study on manganese nodules recovery in the Clarion-Clipperton Zone

The sea occupies three quarters of the area on the earth and provides various kinds of resources to mankind in the form of minerals, food, medicines and even energy. “Seabed exploitation” specifically deals with recovery of the resources that are found on the seabed, in the form of solids, liquids and gasses (methane hydrates, oil and natural gas). The resources are abundant; nevertheless the recovery process from the seabed, poses various challenges to mankind. This study starts with a review on three types of resources: polymetallic manganese nodules, polymetallic manganese crusts and massive sulphides deposits. Each of them are rich in minerals, such as manganese, cobalt, nickel, copper and some rare earth elements. They are found at many locations in the deep seas and are potentially a big source of minerals. No commercial seabed mining activity has been accomplished to date due to the great complexities in recovery. This book describes the various challenges associated with a potential underwater mineral recovery operation, reviews and analyses the existing recovery techniques, and provides an innovative engineering system. It further identifies the associated risks and a suitable business model.Chapter 1 presents a brief background about the past and present industrial trends of seabed mining. A description of the sea, seabed and the three types of seabed mineral resources are also included. A section on motivations for deep sea mining follows which also compares the latter with terrestrial mining.Chapter 2 deals with the decision making process, including a market analysis, for selecting manganese nodules as the resource of interest. This is followed by a case study specific to the location of interest: West COMRA in the Clarion-Clipperton Zone. Specific site location is determined in order to estimate commercial risk, environmental impact assessment and logistic challenge.Chapter 3 lists the existing techniques for nodule recovery operation. The study identifies the main components of a nodules recovery system, and organizes them into: collector, propulsion and vertical transport systems.Chapter 4 discusses various challenges posed by manganese nodules recovery, in terms of the engineering and environment. The geo-political and legal-social issues have also been considered. This chapter plays an important role in defining the proposed engineering system, as addressing the identified challenges will better shape the proposed solution.Chapter 5 proposes an engineering system, by considering the key components in greater details. An innovative component, the black box is introduced, which is intended to be an environmentally-friendly solution for manganese nodules recovery. Other auxiliary components, such as the mother ship and metallurgical processing, are briefly included. A brief power supply analysis is also provided.Chapter 6 assesses the associated risks, which are divided into sections namely commercial viability, logistic challenges, environmental impact assessment and safety assessment. The feasibility of the proposed solution is also dealt with.Chapter 7 provides a business model for the proposed engineering system. Potential customers are identified, value proposition is determined, costumer relation is also suggested. Public awareness is then discussed and finally a SWOT analysis is presented. This business model serves as an important bridge to reach both industry and research institutes.Finally, Chapter 8 provides some conclusions and recommendation for future work

Urban boundary layers over dense and tall canopies

Wind tunnel experiments were carried out on four urban morphologies: two tall canopies with uniform-height and two super-tall canopies with a large variation in element heights (where the maximum element height is more than double the average canopy height, $h_{max}$=2.5 $h_{avg}$). {The average canopy height and packing density were fixed across the surfaces to $h_{avg} = 80$ mm, and $\lambda_{p} = 0.44$, respectively.} A combination of laser doppler anemometry and direct drag measurements were used to calculate and scale the mean velocity profiles {within the boundary layer depth, $\delta$}. In the uniform-height experiment, the high packing density resulted in a `skimming flow' regime with very little flow penetration into the canopy. This led to a surprisingly shallow roughness sublayer ($z\approx1.15h_{avg}$), and a well-defined inertial sublayer above it. {In the heterogeneous-height canopies, despite the same packing density and average height, the flow features were significantly different.} {The height heterogeneity enhanced mixing thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer was found to exist and extend up to just above the tallest element height (corresponding to $z/h_{avg} = 2.85$)}, which was found to be the dominant lengthscale controlling the flow behaviour. {Results points toward the existence of an inertial sublayer for all surfaces considered herein despite the severity of the surface roughness ($\delta/h_{avg} = 3 - 6.25$)}. This contrasts with previous literature.Comment: 25 pages, 12 figures. Revised submission to Boundary-Layer Meteorolog

Modelling turbulence in axisymmetric wakes: an application to wind turbine wakes

A novel fast-running model is developed to predict the three-dimensional (3D) distribution of turbulent kinetic energy (TKE) in axisymmetric wake flows. This is achieved by mathematically solving the partial differential equation of the TKE transport using the Green's function method. The developed solution reduces to a double integral that can be computed numerically for a wake prescribed by any arbitrary velocity profile. It is shown that the solution can be further simplified to a single integral for wakes with Gaussian-like velocity-deficit profiles. Model results are compared and validated against detailed 3D laser Doppler anemometry data measured within the wake flow of a model wind turbine in a laboratory environment. This shows a remarkably good agreement in both the magnitude and shape of the radial TKE profiles at the turbine hub height. The wind-tunnel data also provide insights into the evolution of important turbulent flow quantities such as turbulent viscosity, mixing length, and the TKE dissipation rate within a wind turbine wake

A machine learning approach to estimating preterm infants survival: development of the Preterm Infants Survival Assessment (PISA) predictor

Estimation of mortality risk of very preterm neonates is carried out in clinical and research settings. We aimed at elaborating a prediction tool using machine learning methods. We developed models on a cohort of 23747 neonates <30 weeks gestational age, or <1501 g birth weight, enrolled in the Italian Neonatal Network in 2008–2014 (development set), using 12 easily collected perinatal variables. We used a cohort from 2015–2016 (N = 5810) as a test set. Among several machine learning methods we chose artificial Neural Networks (NN). The resulting predictor was compared with logistic regression models. In the test cohort, NN had a slightly better discrimination than logistic regression (P < 0.002). The differences were greater in subgroups of neonates (at various gestational age or birth weight intervals, singletons). Using a cutoff of death probability of 0.5, logistic regression misclassified 67/5810 neonates (1.2 percent) more than NN. In conclusion our study – the largest published so far – shows that even in this very simplified scenario, using only limited information available up to 5 minutes after birth, a NN approach had a small but significant advantage over current approaches. The software implementing the predictor is made freely available to the community

Acoustic excitation of Tollmien–Schlichting waves due to localised surface roughness

Experiments on the receptivity of two-dimensional boundary layers to acoustic disturbances from two-dimensional roughness strips were performed in a low-turbulence wind tunnel on a flat plate model. The free stream was subjected to a plane acoustic wave so that a Stokes layer (SL) was created on the plate, thus generating a Tollmien-Schlichting (T-S) wave through the receptivity process. An improved technique to measure the T-S component is described based on a retracting two-dimensional roughness, which allowed for phase-locked measurements at the acoustic wave frequency to be made. This improved technique enables both protuberances and cavities to be explored in the range < |h| (equivalent to 0.025 < |h|/ γ B ∗) in relative roughness height to the local unperturbed Blasius boundary layer displacement thickness). These depths are designed to cover both the predicted linear and nonlinear response of the T-S excitation. Experimentally, cavities had not previously been explored. Results show that a linear regime is identifiable for both positive and negative roughness heights up to ≈ 150 μm (|h| γ B ∗ ≈ 0.126). The departure from the linear behaviour is, however, dependent on the geometry of the surface imperfection. For cavities of significant depth, the nonlinear behaviour is found to be milder than in the case of protuberances - this is attributed to the flow physics in the near field of the surface features. Nonetheless, results for positive heights agree well with previous theoretical work which predicted a linear disturbance response for small-height perturbations

Advanced active pixel architectures in standard CMOS technology

This paper aims at exploring and validating the adoption of standard fabrication processes for the realization of CMOS active pixel sensors, for particle detection purposes. The goal is to implement a single-chip, complete radiation sensor system, including on a CMOS integrated circuit the sensitive devices, read-out and signal processing circuits. A prototype chip (RAPS01) based on these principles has been already fabricated, and a chip characterization has been carried out; in particular, the evaluation of the sensitivity of the sensor response on the actual operating conditions was estimated, as well as the response uniformity. Optimization and tailoring of the sensor structures for High Energy Physics applications are being evaluated in the design of the next generation chip (RAPS02). Basic features of the new chip includes digitally configurable readout and multi-mode access (i.e., either sparse of line-scan readout). © 2005 IEEE

Interface formation during the growth of phase change material heterostructures based on Ge-Rich Ge-Sb-Te alloys

In this study, we present a full characterization of the electronic properties of phase change material (PCM) double-layered heterostructures deposited on silicon substrates. Thin films of amorphous Ge-rich Ge-Sb-Te (GGST) alloys were grown by physical vapor deposition on Sb2Te3 and on Ge2Sb2Te5 layers. The two heterostructures were characterized in situ by X-ray and ultraviolet photoemission spectroscopies (XPS and UPS) during the formation of the interface between the first and the second layer (top GGST film). The evolution of the composition across the heterostructure interface and information on interdiffusion were obtained. We found that, for both cases, the final composition of the GGST layer was close to Ge2SbTe2 (GST212), which is a thermodynamically favorable off-stoichiometry GeSbTe alloy in the Sb-GeTe pseudobinary of the ternary phase diagram. Density functional theory calculations allowed us to calculate the density of states for the valence band of the amorphous phase of GST212, which was in good agreement with the experimental valence bands measured in situ by UPS. The same heterostructures were characterized by X-ray diffraction as a function of the annealing temperature. Differences in the crystallization process are discussed on the basis of the photoemission results