A longitudinal analysis of the occupational status of the graduates of the University of Palermo

The availability of a large amount of longitudinal data provided by the surveys carried out by STELLA (Statistics about Graduates and Labour Market) allowed us to describe the occupational paths of graduates of the University of Palermo. In this paper we refer to a disproportionate stratified sample of graduates in 2009, interviewed three dierent times: one year (2010), three years (2012), ve years (2014) after the graduation. In such a global economic crises context, our aims are describing the labour market of the Palermitan graduates, identifying the variables that influence most their occupational status and nally outlining a transition probability structure among the states: Work, Sear…

Influence of M23C6 carbides on the heterogeneous strain development in annealed 420 stainless steel

Understanding the local strain enhancement and lattice distortion resulting from different microstructure features in metal alloys is crucial in many engineering processes. The development of heterogeneous strain not only plays an important role in the work hardening of the material but also in other processes such as recrystallization and damage inheritance and fracture. Isolating the contribution of precipitates to the development of heterogeneous strain can be challenging due to the presence of grain boundaries or other microstructure features that might cause ambiguous interpretation. In this work a statistical analysis of local strains measured by electron back scatter diffraction and …

Accurate representation of the distributions of the 3D Poisson-Voronoi typical cell geometrical features

Understanding the intricate and complex materials microstructure and how it is related to materials properties is an important problem in the Materials Science field. For a full comprehension of this relation, it is fundamental to be able to describe the main characteristics of the 3-dimensional microstructure. The most basic model used for approximating steel microstructure is the Poisson-Voronoi diagram. Poisson-Voronoi diagrams have interesting mathematical properties, and they are used as a good model for single-phase materials. In this paper we exploit the scaling property of the underlying Poisson process to derive the distribution of the main geometrical features of the grains for ev…

A Data-Driven Approach for Studying the Influence of Carbides on Work Hardening of Steel

This study proposes a new approach to determine phenomenological or physical relations between microstructure features and the mechanical behavior of metals bridging advanced statistics and materials science in a study of the effect of hard precipitates on the hardening of metal alloys. Synthetic microstructures were created using multi-level Voronoi diagrams in order to control microstructure variability and then were used as samples for virtual tensile tests in a full-field crystal plasticity solver. A data-driven model based on Functional Principal Component Analysis (FPCA) was confronted with the classical Voce law for the description of uniaxial tensile curves of synthetic AISI 420 ste…

Prima, durante e dopo: il percorso degli studenti dall’immatricolazione fino a cinque anni dopo la laurea

Does taking additional Maths classes in high school affect academic outcomes?

Several studies in the mathematical education literature show the effect of students’ high school skills in maths on their success at higher levels of education and work. In particular, the importance of maths course taking in US high schools is highlighted to be important for college enrolment and completion. The choice of taking additional maths courses or, as in Italy, of choosing a high-school curriculum with more maths, is not random: it depends on several substantial factors such as gender and socio-economic status. This selection bias implies that the differences in the academic outcomes might be traceable not only to mathematics ability and knowledge. In this paper, the aim is to es…

Microstructure–property relation and machine learning prediction of hole expansion capacity of high-strength steels

Abstract The relationship between microstructure features and mechanical properties plays an important role in the design of materials and improvement of properties. Hole expansion capacity plays a fundamental role in defining the formability of metal sheets. Due to the complexity of the experimental procedure of testing hole expansion capacity, where many influencing factors contribute to the resulting values, the relationship between microstructure features and hole expansion capacity and the complexity of this relation is not yet fully understood. In the present study, an experimental dataset containing the phase constituents of 55 microstructures as well as corresponding properties, su…

General framework for testing Poisson-Voronoi assumption for real microstructures

Modeling microstructures is an interesting problem not just in Materials Science but also in Mathematics and Statistics. The most basic model for steel microstructure is the Poisson-Voronoi diagram. It has mathematically attractive properties and it has been used in the approximation of single phase steel microstructures. The aim of this paper is to develop methods that can be used to test whether a real steel microstructure can be approximated by such a model. Therefore, a general framework for testing the Poisson-Voronoi assumption based on images of 2D sections of real metals is set out. Following two different approaches, according to the use or not of periodic boundary conditions, thre…

A new measure for the attitude to mobility of Italian students and graduates: a topological data analysis approach

AbstractStudents’ and graduates’ mobility is an interesting topic of discussion especially for the Italian education system and universities. The main reasons for migration and for the so called brain drain, can be found in the socio-economic context and in the famous North–South divide. Measuring mobility and understanding its dynamic over time and space are not trivial tasks. Most of the studies in the related literature focus on the determinants of such phenomenon, in this paper, instead, combining tools coming from graph theory and Topological Data Analysis we propose a new measure for the attitude to mobility. Each mobility trajectory is represented by a graph and the importance of the…

Statistical analysis of the relation between metallic microstructures and mechanical properties

This thesis aims at the development of physical relations between the intricate 3D features of metallic microstructures and the mechanical properties of the material. For understanding which are the microstructural determinants of the resultingmechanical behaviour of metals, a deep quantitative characterisation of the microstructure is needed. The main steps of quantitative characterisation of the microstructures are: identification of the phases distribution and their chemical composition, study of the microstructure morphology (geometrical arrangement of grains, grain boundaries, grain orientations, grain size and grain shape). An accurate description of the microstructure features enrich…

Topology-based goodness-of-fit tests for sliced spatial data

In materials science and many other application domains, 3D information can often only be extrapolated by taking 2D slices. In topological data analysis, persistence vineyards have emerged as a powerful tool to take into account topological features stretching over several slices. In the present paper, we illustrate how persistence vineyards can be used to design rigorous statistical hypothesis tests for 3D microstructure models based on data from 2D slices. More precisely, by establishing the asymptotic normality of suitable longitudinal and cross-sectional summary statistics, we devise goodness-of-fit tests that become asymptotically exact in large sampling windows. We illustrate the test…

Does taking additional Maths classes improve university performance?

Several recent studies in educational literature showed how students’ skills in maths affect their success at higher levels of education. The aim of this paper is to evaluate the effect of taking additional maths class at high school on first-year performance of Italian university students. However, university performance and the choice of the high-school depend on several factors that make this evaluation challenging. Using information coming from three different sources, we carry out a multilevel propensity score procedure to estimate the average treatment effect between the applied sciences track and the traditional scientific one. After balancing for school- and student-level covariates…

A new bipartite matching approach for record linkage: the case of two big Italian databases

In recent years, university student mobility in Italy has worsened the north-south economic divide. Therefore, studying this phenomenon and its determinants is necessary to provide helpful information to support socio-economic policies. Thus, this paper aims at integrating two big databases about university students in Italy: the first one is provided by the Ministry of University and Research, concerning the university careers of student cohorts; the second one is provided by the AlmaLaurea consortium, concerning the university experiences of graduates and their success in the labour market. Both databases contain socio-demographic information that complements each other. The proposed meth…

Isotonic regression for metallic microstructure data: estimation and testing under order restrictions

Investigating the main determinants of the mechanical performance of metals is not a simple task. Already known physical inspired qualitative relations between 2D microstructure characteristics and 3D mechanical properties can act as the starting point of the investigation. Isotonic regression allows to take into account ordering relations and leads to more efficient and accurate results when the underlying assumptions actually hold. The main goal in this paper is to test order relations in a model inspired by a materials science application. The statistical estimation procedure is described considering three different scenarios according to the knowledge of the variances: known variance ra…

The combined influence of grain size distribution and dislocation density on hardness of interstitial free steel

Abstract Understanding the relationship between microstructure features and mechanical properties is of great significance for the improvement and specific adjustment of steel properties. The relationship between mean grain size and yield strength is established by the well-known Hall-Petch equation. But due to the complexity of the grain configuration within materials, considering only the mean value is unlikely to give a complete representation of the mechanical behavior. The classical Taylor equation is often used to account for the effect of dislocation density, but not thoroughly tested in combination with grain size influence. In the present study, systematic heat treatment routes and…