Axial crushing of metal-composite hybrid tubes: experimental analysis

In the automotive sector, special attention is paid to the study of the behavior of the structural components that make the car bodies. The continuous demands on the weight saving imply the car bodies to be assembled with components made in different materials and using different manufacturing processes. Considering the making of the sacrificial structures aimed to the energy absorption, composite materials are increasingly used to replace conventional metal materials. However, the use of composites is accompanied with a change in the type of deformation obtained during the impact phenomenon. Usually, with the conventional metal materials, the crushing behavior is a progressive buckling whereas the composite materials are characterized by a brittle fracture. The combination of the traditional metal materials with the composite ones can represent a good solution to obtain high levels of performance. In this context, the structural performance of metal-composite hybrid tubes subjected to quasi-static axial crushing is experimentally evaluated in this work. The specimens, with circular cross section, were obtained with tubes made in a fully thermoplastic composite internally reinforced with aluminum tubes. The composite material used were made in polypropylene both for the matrix and for the reinforcing fibers. This material has a good axial absorption capacity but irregular behavior during crushing. The addition of a conventional material as reinforcement allowed to increase the absorption capacity by ensuring a more progressive and controlled crush. The analysis was carried out by evaluating, for various geometric configurations, different parameters (mean load, average stress, specific energy, efficiency). The results, discussed in the work, showed how the energy absorption performance of a hybrid structure are higher than the sum of the performance of the single materials

Critical transitions in heterogeneous networks: Loss of low-degree nodes as an early warning signal.

A large number of real networks show abrupt phase transition phenomena in response to environmental changes. In this case, cascading phenomena can induce drastic and discontinuous changes in the system state and lead to collapse. Although complex network theory has been used to investigate these drastic events, we are still unable to predict them effectively. We here analyze collapse phenomena by proposing a minimal two-state dynamic on a complex network and introducing the effect of local connectivities on the evolution of network nodes. We find that a heterogeneous system of interconnected components presents a mixed response to stress and can serve as a control indicator. In particular, before the critical transition point is reached a severe loss of low-degree nodes is observed, masked by the minimal failure of higher-degree nodes. Accordingly, we suggest that a significant reduction in less connected nodes can indicate impending global failure

Unsupervised Acquisition of Verb Subcategorization Frames from Shallow-Parsed Corpora

In this paper, we reported experiments of unsupervised automatic acquisition of Italian and English verb subcategorization frames (SCFs) from general and domain corpora. The proposed technique operates on syntactically shallow-parsed corpora on the basis of a limited number of search heuristics not relying on any previous lexico-syntactic knowledge about SCFs. Although preliminary, reported results are in line with state-of-the-art lexical acquisition systems. The issue of whether verbs sharing similar SCFs distributions happen to share similar semantic properties as well was also explored by clustering verbs that share frames with the same distribution using the Minimum Description Length Principle (MDL). First experiments in this direction were carried out on Italian verbs with encouraging results

experimental and numerical analysis of a thermoplastic lamina for composite material

Abstract Thermoplastic composites nowadays belong to an interesting class of materials for different type of industries. Those materials present a considerable number of advantages compared to the thermosetting composites. Their low density, low production cost, recyclability, are some of the positive aspects encouraging their usage. The numerical simulation is still an open research field due to the peculiar behaviour of the thermoplastic composites. According to that, this works starts a detailed numerical study in which the main deformation mechanisms are simulated using different modelling approaches. In this overview, the object of this study is a fully polypropylene composites made up of woven polypropylene laminas. These laminas are stacked and hot pressed. Previous research showed a ductile and plastic crush behaviour of this material, in which the main failure mode is governed by the delamination. Firstly, an experimental campaign is carried out, in order to define the constitutive properties of the single lamina. Woven laminas are orthotropic composites responding differently according to the direction of the load. Yarn test was executed to capture the tensile modulus and the strength, whereas the Bias-Extension test was carried out to examine the in-plane shear properties. The definition of those properties required several considerations and a detailed analysis because the load applied in the test is directed neither along the weft nor along the wrap direction. For this reason, geometrical approximations and hypothesis about the boundary condition are necessary to evaluate the shear stress and the shear angle parameters. Hence, three different FE models were developed in LS-DYNA and results were validated against the experimental tests. Two geometry discretization method and three material models were implemented. The first numerical model was developed for fabric materials and it represents a macro-mechanics approach with low computationally cost. The second model instead accounts for the fabric architecture, allowing to evaluate the weave geometry and the reorientation effect of the yarns during the deformation. The third model represents the discrete architecture of the fabric, modelling the specimen at the tape level. The numerical results showed a good approximation of the experimental evidence, especially considering the second numerical model. This material model confirmed the geometrical assumptions used to define the mechanical properties. This work gives a first important step for the simulation of components made of thermoplastic composites and with more complex geometry using a mesoscopic approach

Multilevel synchronization of human β-cells networks

β-cells within the endocrine pancreas are fundamental for glucose, lipid and protein homeostasis. Gap junctions between cells constitute the primary coupling mechanism through which cells synchronize their electrical and metabolic activities. This evidence is still only partially investigated through models and numerical simulations. In this contribution, we explore the effect of combined electrical and metabolic coupling in β-cell clusters using a detailed biophysical model. We add heterogeneity and stochasticity to realistically reproduce β-cell dynamics and study networks mimicking arrangements of β-cells within human pancreatic islets. Model simulations are performed over different couplings and heterogeneities, analyzing emerging synchronization at the membrane potential, calcium, and metabolites levels. To describe network synchronization, we use the formalism of multiplex networks and investigate functional network properties and multiplex synchronization motifs over the structural, electrical, and metabolic layers. Our results show that metabolic coupling can support slow wave propagation in human islets, that combined electrical and metabolic synchronization is realized in small aggregates, and that metabolic long-range correlation is more pronounced with respect to the electrical one

NAFLD in Some Common Endocrine Diseases: Prevalence, Pathophysiology, and Principles of Diagnosis and Management

Secondary nonalcoholic fatty liver disease (NAFLD) defines those complex pathophysiological and clinical consequences that ensue when the liver becomes an ectopic site of lipid storage owing to reasons other than its mutual association with the metabolic syndrome. Disorders affecting gonadal hormones, thyroid hormones, or growth hormones (GH) may cause secondary forms of NAFLD, which exhibit specific pathophysiologic features and, in theory, the possibility to receive an effective treatment. Here, we critically discuss epidemiological and pathophysiological features, as well as principles of diagnosis and management of some common endocrine diseases, such as polycystic ovary syndrome (PCOS), hypothyroidism, hypogonadism, and GH deficiency. Collectively, these forms of NAFLD secondary to specific endocrine derangements may be envisaged as a naturally occurring disease model of NAFLD in humans. Improved understanding of such endocrine secondary forms of NAFLD promises to disclose novel clinical associations and innovative therapeutic approaches, which may potentially be applied also to selected cases of primary NAFLD