On the fatigue improvement of railways superstructure components due to cold expansion – Part I: Experimental analysis

The fatigue strength improvement of materials and structures has always been the subject of studies, as a consequence of the rapid development of technologies and strictive safety requirements. In the railway field the fatigue resistance problem is thoroughly studied due to high transportation safety standard. Fatigue cracking is a major issue, in particular at rail-end-bolt holes. Cold Expansion is a common technique to induce beneficial residual compressive stresses around the holes, with the aim to improve the fatigue life of the rail. This paper is the first of a two part-series dealing with the study of the residual stress-strain field induced by the cold expansion process around rail-end-bolt holes. In Part I of this series, a contribution to better understanding the whole strain field distribution arising around rail-end-bolt holes during and after cold expansion is presented. Strains were experimentally measured using both electrical strain gauges and 2D-Digital Image Correlation. Contrary to common literature, strain-time history during the entire cold expansion process was investigated, in order to capture the highly non-linear elasto-plastic response of the material; the results of this study has been used in Part II of this series for the validation of the finite element model described there. The cold expansion process was applied to three rail holes, having equal nominal diameter. At first, the experimental results concerning each expanded hole are analysed. Then, all the results are compared, in order to evaluate the repeatability: - of the measurements; - of the Cold Expansion process; - of the adopted experimental technique, and, above all, to extrapolate the distribution of the hoop and radial residual strains as a function of the distance from the hole edge. At the end, results obtained by strain gauges and 2D-Digital Image Correlation are compared: a good agreement is found on the central flat surface of the rail web, which guarantees the availability of a robust and valuable highly non-linear reference result that has been used for the validation of the finite element model presented in Part II of this series

On the fatigue improvement of railways superstructure components due to cold expansion – Part I: Experimental analysis

The fatigue strength improvement of materials and structures has always been the subject of studies, as a consequence of the rapid development of technologies and strictive safety requirements. In the railway field the fatigue resistance problem is thoroughly studied due to high transportation safety standard. Fatigue cracking is a major issue, in particular at rail-end-bolt holes. Cold Expansion is a common technique to induce beneficial residual compressive stresses around the holes, with the aim to improve the fatigue life of the rail. This paper is the first of a two part-series dealing with the study of the residual stress-strain field induced by the cold expansion process around rail-end-bolt holes. In Part I of this series, a contribution to better understanding the whole strain field distribution arising around rail-end-bolt holes during and after cold expansion is presented. Strains were experimentally measured using both electrical strain gauges and 2D-Digital Image Correlation. Contrary to common literature, strain-time history during the entire cold expansion process was investigated, in order to capture the highly non-linear elasto-plastic response of the material; the results of this study has been used in Part II of this series for the validation of the finite element model described there. The cold expansion process was applied to three rail holes, having equal nominal diameter. At first, the experimental results concerning each expanded hole are analysed. Then, all the results are compared, in order to evaluate the repeatability: - of the measurements; - of the Cold Expansion process; - of the adopted experimental technique, and, above all, to extrapolate the distribution of the hoop and radial residual strains as a function of the distance from the hole edge. At the end, results obtained by strain gauges and 2D-Digital Image Correlation are compared: a good agreement is found on the central flat surface of the rail web, which guarantees the availability of a robust and valuable highly non-linear reference result that has been used for the validation of the finite element model presented in Part II of this series

Fault-trapped waves depict continuity of the fault system responsible for the 6 April 2009 MW 6.3 L’Aquila earthquake, central Italy

We investigate fault-trapped waves observed at a permanent broad-band station (FAGN) installed on the San Demetrio Fault, about 20 km southeast of L'Aquila. This fault has the same strike of the Paganica Fault which was responsible for the MW 6.3, 6 April 2009 earthquake. The two faults display an en-echelon pattern with a few km offset. We have found that events causing efficient trapped waves are clustered at the northwestern and southeastern bottom ends of the ruptured Paganica fault plane. The efficiency of trapped waves at FAGN, which is located about 5 km far from the ruptured fault plane, indicates that the two faults are linked at depth. This suggests that fault segments in the study area can be part of a longer and continuous fault system which controls the seismic hazard of the region. Moreover, we have found that the two earthquake clusters generating the most efficient trapped waves occur in portions of the fault system with the highest fluid pressure

Hepatitis C virus production requires apolipoprotein A-I and affects its association with nascent low-density lipoproteins

Background/aims The life cycle of hepatitis C virus (HCV) is intimately linked to the lipid metabolism of the host. In particular, HCV exploits the metabolic machinery of the lipoproteins in several steps of its life cycle such as circulation in the bloodstream, cell attachment and entry, assembly and release of viral particles. However, the details of how HCV interacts with and influences the metabolism of the host lipoproteins are not well understood. A study was undertaken to investigate whether HCV directly affects the protein composition of host circulating lipoproteins. Methods A proteomic analysis of circulating very low-, low- and high-density lipoproteins (VLDL, LDL and HDL), isolated from either in-treatment naive HCV-infected patients or healthy donors (HD), was performed using two-dimensional gel electrophoresis and tandem mass spectrometry (MALDI-TOF/TOF). The results obtained were further investigated using in vitro models of HCV infection and replication. Results A decreased level of apolipoprotein A-I (apoA-I) was found in the LDL fractions of HCV-infected patients. This result was confirmed by western blot and ELISA analysis. HCV cellular models (JFH1 HCV cell culture system (HCVcc) and HCV subgenomic replicons) showed that the decreased apoA-I/LDL association originates from hepatic biogenesis rather than lipoprotein catabolism occurring in the circulation, and is not due to a downregulation of the apoA-I protein concentration. The sole non-structural viral proteins were sufficient to impair the apoA-I/LDL association. Functional evidence was obtained for involvement of apoA-I in the viral life cycle such as RNA replication and virion production. The specific siRNA-mediated downregulation of apoA-I led to a reduction in both HCV RNA and viral particle levels in culture. Conclusions This study shows that HCV induces lipoprotein structural modification and that its replication and production are linked to the host lipoprotein metabolism, suggesting apoA-I as a new possible target for antiviral therapy

Experimental and numerical study on the fatigue behaviour of the shot-earth 772

The present research work is devoted to the mechanical, fracture and fatigue experimental characterization of the shot-earth 772, with a particular attention to its fatigue behaviour. To such an aim, an extensive experimental program has been carried out, consisting of: (i) flexural and compression tests, (ii) three-point bending fracture tests, and (iii) bending and compression cyclic tests. Moreover, a FE numerical model is employed to simulate both the above bending and compression cyclic tests, after the input data validation performed by simulating the above fracture tests. The numerical fatigue lifetimes are compared with the corresponding experimental ones for both pulsating bending and compression, highlighting the model accuracy. Finally, the contours of both the damage parameter and the reduced Young modulus are plotted showing the evolution of fatigue damage

Lymphocyte distribution and intrahepatic compartmentalization during HCV infection: a main role for MHC-unrestricted T cells

Hepatitis C virus (HCV) infection induces an acute and chronic liver inflammation through an immune-mediated pathway that may lead to cirrhosis and liver failure. Indeed, HCV-related hepatitis is characterized by a dramatic lymphocyte infiltrate into the liver which is mainly composed by HCV non-specific cells. Several data indicated that interferon (IFN)-gamma secretion by intrahepatic lymphocytes (IHL) may drive non-specific cell homing to the liver, inducing interferon inducible protein-10 (IP-10) production. An interesting hallmark of these IHL is the recruitment of lymphocytes associated with mechanisms of innate immunity, such as natural killer (NK), natural killer T (NKT) and gamma delta T lymphocytes. CD81 triggering on NK cell surface by the HCV envelope glycoprotein E2 was recently shown to inhibit NK cell function in the liver of HCV-infected persons, resulting in a possible mechanism contributing to the lack of virus clearance and to the establishment of chronic infection. In contrast, intrahepatic NKT cells restricted to CD1d molecules expressed on the hepatocyte surface may contribute to a large extent to liver damage. Finally, an increased frequency of T cells expressing the gamma delta T cell receptor (TCR) was observed in HCV-infected liver and recent observations indicate that intrahepatic gamma delta T cell activation could be directly induced by the HCV/E2 particle through CD81 triggering. These cells are not HCV specific, are able to kill target cells including primary hepatocytes and their ability to produce T helper (Th)1 cytokines is associated with a higher degree of liver disease. Together, CD1d/NKT and/or E2/CD81 interactions may play a major role in the establishment of HCV immunopathogenesis. In the absence of virus clearance, the chemokine-driven recruitment of lymphocytes with an innate cytotoxic behavior in the liver of HCV-infected patients may boost itself, leading to necroinflammatory and fibrotic liver disease

Analisi della risposta sismica di un edificio campione nel Comune di Ariano Irpino (AV)

Nella pratica ingegneristica vengono usate correlazioni derivate da regressioni statistiche tra numero dei piani degli edifici e frequenze di risonanza. Tuttavia la discrepanza tra comportamento reale e valori aspettati può essere talvolta significativa, e solo l’acquisizione di dati sperimentali consente di comprendere il reale comportamento dinamico di una struttura. La sperimentazione, in situazioni anche complesse, e la raccolta di nuovi dati possono essere molto importanti nel campo dell’ingegneria strutturale. In questo articolo vengono presentati i risultati del monitoraggio sismico effettuato su un edificio campione in muratura (il municipio di Ariano Irpino), tipologia costruttiva largamente diffusa tra gli edifici pubblici strategici (ad esempio scuole, caserme ed ospedali). Sono state utilizzate 7 stazioni sismologiche a sei canali equipaggiate con sismometri ed accelerometri. I dati sismici sono stati acquisiti in modalità continua, in punti strategici della struttura, su diversi livelli, dal gennaio 2006 a dicembre 2007. Sono stati selezionati una ventina di terremoti di magnitudo bassa o intermedia (1.5 ≤ M ≤ 4.8) avvenuti a distanze epicentrali variabili da 4 a 116 km. Le registrazioni sono state analizzate sia mediante la tecnica dei rapporti spettrali rispetto alla base dell’edificio sia calcolando i rapporti spettrali tra componente orizzontale e verticale di ogni sensore. L’analisi svolta ha consentito di evidenziare numerose frequenze di vibrazione dell’edificio. Mediante simulazioni numeriche su un modello tridimensionale rappresentativo della struttura in esame è stato possibile associare i picchi in frequenza ai modi propri in campo lineare. In particolare, sono stati ben identificati i primi 3 modi di vibrazione (due flessionali ed uno rotazionale)

Mast cells counteract regulatory T-cell suppression through interleukin-6 and OX40/OX40L axis toward Th17-cell differentiation

The development of inflammatory diseases implies inactivation of regulatory T (Treg) cells through mechanisms that still are largely unknown. Here we showed that mast cells (MCs), an early source of inflammatory mediators, are able to counteract Treg inhibition over effector T cells. To gain insight into the molecules involved in their interplay, we set up an in vitro system in which all 3 cellular components were put in contact. Reversal of Treg suppression required T cell-derived interleukin-6 (IL-6) and the OX40/OX40L axis. In the presence of activated MCs, concomitant abundance of IL-6 and paucity of Th1/Th2 cytokines skewed Tregs and effector T cells into IL-17-producing T cells (Th17). In vivo analysis of lymph nodes hosting T-cell priming in experimental autoimmune encephalomyelitis revealed activated MCs, Tregs, and Th17 cells displaying tight spatial interactions, further supporting the occurrence of an MC-mediated inhibition of Treg suppression in the establishment of Th17-mediated inflammatory responses. © 2009 by The American Society of Hematology

FORTI EFFETTI DI AMPLIFICAZIONE DEL MOTO IN ZONA DI FAGLIA DURANTE LA SEQUENZA SISMICA DEL 2009 IN ABRUZZO

Negli anni 1997-1998, durante la sequenza dell’Umbria-Marche, la stazione accelerometrica di Nocera Umbra superò ripetutamente, per terremoti di magnitudo > 5, il picco di accelerazione di 0.5 g. Tali valori furono i maggiori mai registrati in Italia, e apparvero subito inusuali per terremoti di faglia normale a magnitudo moderate. Una serie di studi del sito della stazione permise di attribuire l’ampiezza anomala a un forte effetto di amplificazione locale prodotto dalle variazioni verticali della velocità delle onde di taglio nella roccia danneggiata di una faglia sub-verticale in prossimità della stazione. Anche durante i terremoti della sequenza Aquilana si sono trovate evidenze di effetti analoghi. La stazione a banda larga FAGN, in prossimità della faglia di San Demetrio, ha mostrato una accentuata variabilità dell’ampiezza delle sue registrazioni, con valori che superano fino ad un fattore 10 le ampiezze delle stazioni vicine. Mediante un’analisi su 350 terremoti si è trovato che le massime amplificazioni avvengono per terremoti localizzati a sud-ovest della stazione, in posizione favorevole alla propagazione nella zona di faglia dalla sorgente al ricevitore. Utilizzando metodi sia analitici che numerici è stato possibile attribuire gli effetti osservati alle eterogeneità di una zona di faglia larga 300-400 m e profonda 3 km, approssimativamente, con una riduzione di velocità di circa il 30% rispetto alla roccia non deformata. Anche il forte impulso di spostamento di 40 cm picco-picco registrato durante la scossa principale a Castello d’Ocre da una stazione GPS (CADO) con campionamento a 10 Hz non trova giustificazione plausibile se non modellando un effetto di risonanza in prossimità dello strumento. In questo caso è possibile generare modelli che riproducano l’osservazione usando valori della larghezza della zona di faglia di qualche centinaio di metri con forti riduzioni della velocità delle onde di taglio rispetto ai blocchi rigidi adiacenti. Queste osservazioni confermano la potenziale pericolosità del territorio in prossimità delle zone di faglia, nonostante non siano emerse durante il terremoto dell’Aquila chiare evidenze di anomalie del danno persistenti lungo le faglie. Recenti studi in California sembrano mettere in luce l’estrema variabilità delle onde intrappolate nelle zone di faglia, per cui l’effetto appare sporadicamente sia per quanto riguarda le stazioni di registrazione lungo la faglia che per quanto riguarda le zone-sorgenti nella faglia capaci di generare onde intrappolate.PublishedPrato3.1. Fisica dei terremotiope