“Fenomeni di danneggiamento e problematiche di progettazione di perni fissaggio stralli per grosse imbarcazioni a vela”

L’obiettivo del presente lavoro è quello di condurre un’approfondita failure analysis su tre perni di aggancio per le sartie di posizionamento e pre-compressione dell’albero di maestra su un’imbarcazione della Perini Navi. I tre perni, rispettivamente di Genoa, Backstay e Trinchetta sono tutti realizzati in acciaio inossidabile indurente per precipitazione ARMCO 17- 4 PH allo stato di fornitura H1075. L’attività sperimentale è stata suddivisa in quattro fasi principali. Durante la prima parte è stata condotta una verifica strutturale dei perni mediante analisi agli elementi finiti per controllare le tensioni interne di lavoro. Nella seconda fase sperimentale è stata effettuata un’analisi macroscopica a basso ingrandimento mediante stereo microscopio e analisi metallografiche per verificare le caratteristiche microstrutturali dell’acciaio. Si sono poi condotte analisi frattografiche su tutti i perni impiegando un Microscopio Elettronico a Scansione (SEM) interfacciato con microsonda a dispersione di energia (EDS) per il rilievo delle chimiche semiquantitative su aree superficiali ristrette. Si è infine proceduto al rilievo del contenuto di idrogeno nei perni, impiegando un sensore a termo conducibilità. Sulla base di queste analisi e delle relative evidenze sperimentali, si è ritenuto importante procedere ad una terza fase per accertarsi della corretta composizione chimica dei perni e si sono condotte misure di durezza Vickers per controllare il relativo stato di fornitura. In tal modo, l’insieme dei risultati ottenuti ha permesso di individuare le regioni di innesco e le modalità di propagazione della frattura. La quarta e ultima fase ha riguardato lo studio delle possibili alternative all’acciaio 17-4 PH e le modifiche da dover apportare nel montaggio dei perni sull’albero di maestra. Dai dati sperimentali ottenuti è emerso che la struttura di questo materiale è di fatto quella attesa per l’acciaio, ovvero una matrice martensitica con all’interno una dispersione indurente di fasi intermetalliche. Le durezze dei perni però risultano in tutti e tre i casi superiori ai valori massimi previsti per la condizione H1075, avvicinandosi molto di più ai valori di durezza di uno stato di fornitura H900 (maggiore resistenza a snervamento e a rottura). Le superfici di frattura dei perni, macroscopicamente piane, presentano uno stato ossidativo decrescente partendo dalla zona più esterna, innesco della cricca con propagazione sub-critica della frattura intergranulare, verso il centro, rottura finale di schianto con caratteristiche transgranulari. La propagazione fragile intergranulare della rottura, l’evidenza di innesco corrosivo superficiale e la formazione di abbondanti prodotti di corrosione in avanzamento sub-critico, hanno portato ad identificare un fenomeno di danneggiamento per tensocorrosione – fatica, favorito dall’idrogeno prodotto per corrosione all’interno della cricca (causa dell’infragilimento lungo gli ex bordi di grano austenitico dell’acciaio), dalla lenta velocità delle deformazioni durante la navigazione e dagli elevati carichi di rottura (>1000 MPa) del materiale costitutivo. L’acciaio inox 17-4 PH, infatti, per sua natura può essere soggetto a questo tipo di danneggiamento, soprattutto quando esibisce elevati valori di durezza e alti limiti resistenziali (come nello stato di fornitura dei suddetti perni). La rottura finale dei perni si è verificata ben prima di raggiungere il carico di rottura del materiale, in particolare in corrispondenza del fattore critico di intensificazione degli sforzi all’apice della cricca, nonostante la flessione indotta dal largo e non corretto GAP di montaggio tra spallette e forcella. Appare dunque evidente il forte sovradimensionamento dei perni nel carico di pre-compressione trasmesso per progetto all’albero. Per ridurre il rischio di ulteriori rotture di questi perni sarà necessario sia utilizzare dei materiali come gli acciai duplex, superduplex o PH austenitici che presentano una migliore resistenza meccanica, a tensocorrosione e ad infragilimento da idrogeno, sia apportare delle modiche sul montaggio dei perni riducendo il GAP esistente tra le guance e la forcella diminuendo così le sollecitazioni imposte al componente

The Evaluation of the Effects of Dietary Vitamin E or Selenium on Lipid Oxidation in Rabbit Hamburgers: Comparing TBARS and Hexanal SPME-GC Analyses

The effects and specificity of dietary supplementation of EconomasETM (EcoE), mainly consisting of organic selenium (0.15 or 0.30 mg/kg feed; Se) or of vitamin E (100 or 200 mg/kg feed; VE), on lipid oxidation were evaluated in rabbit hamburgers during refrigerated storage. Oxidation data obtained by thiobarbituric acid-reactive substances (TBARS) spectrophotometric analysis and solid-phase microextraction (SPME) coupled with gas chromatography (GC) to determine hexanal content were compared. The relationships between oxidation levels, colour and pH and the discriminability of EcoE- or VE-treatment compared with control were also examined. TBARS content decreased in both VE and EcoE groups, while hexanal showed lower values only in the VE100 dietary group. The colour parameters were compatible with acceptable product quality and seemed to parallel the TBARS values up to the second day storage. Both VE and EcoE improved oxidative stability without affecting the sensory properties, but the VE effect appeared to more specifically hamper lipid oxidation, as evidenced by the determination and quantification of hexanal, a specific product of fatty acid peroxidation

In vivo and in vitro effects of selected antioxidants on rabbit meat microbiota

The purpose of this study was to investigate the effect of dietary vitamin E or EconomasE™ supplementation on the growth of several background/pathogenic bacteria on rabbit carcasses and hamburgers during refrigerated storage. For 51days, 270 New Zealand rabbits received either a basal diet, or experimental diets enriched with 100 or 200mg/kg of vitamin E or EconomasE™. The bacteria studied were Salmonella, Listeria monocytogenes, Pseudomonas, Enterobacteriaceae, Escherichia coli, coagulase-positive staphylococci, plus both mesophilic and psychrotrophic aerobes. The growth of Listeria monocytogenes on contaminated patties was evaluated through a challenge test. The potential protective or antimicrobial effect of vitamin E or EconomasE™ on Listeria monocytogenes or Pseudomonas aeruginosa was assessed in vitro. Diet did not influence the concentrations of bacteria found on rabbit carcasses and developing on hamburgers. Vitamin E (in vivo and in vitro) and EconomasE™ in vivo had a protective antioxidant role, while EconomasE™ in vitro had strong antibacterial activity against Listeria monocytogenes, but not against Pseudomonas aeruginosa

Transcriptional Repressors of Fetal Globin Genes as Novel Therapeutic Targets in Beta-Thalassemia

During development the human β-globin gene cluster undergoes two switching processes at the embryo-fetal and fetal-adult stages, respectively, involving changes in chromatin remodeling and in transcriptional regulatory networks. In particular, during the perinatal period, the switch from fetal-to-adult globin gene expression leads to fetal globin genes silencing and progressive decline of fetal hemoglobin (HbF). Impaired hemoglobin switching is associated with hereditary persistence of HbF (HPFH), a condition in which the fetal globin genes fail to be completely silenced in adult red blood cells. This condition, when co-inherited with hemoglobinopathies, has great therapeutic potential because elevated HbF levels can ameliorate β-thalassemia and sickle cell anemia. Therefore, there is a growing interest about the complex network of factors that regulate fetal globin genes expression. Here we discuss the activity of transcriptional repressors of fetal globin genes and their potential role as novel therapeutic targets in β-thalassemia

MiR-137 Targets the 3′ Untranslated Region of MSH2: Potential Implications in Lynch Syndrome-Related Colorectal Cancer

Mismatch Repair (MMR) gene dysregulation plays a fundamental role in Lynch Syndrome (LS) pathogenesis, a form of hereditary colorectal cancer. Loss or overexpression of key MMR genes leads to genome instability and tumorigenesis; however, the mechanisms controlling MMR gene expression are unknown. One such gene, MSH2, exerts an important role, not only in MMR, but also in cell proliferation, apoptosis, and cell cycle control. In this study, we explored the functions and underlying molecular mechanisms of increased MSH2 expression related to a c.*226A>G variant in the 3′untranslated (UTR) region of MSH2 that had been previously identified in a subject clinically suspected of LS. Bioinformatics identified a putative binding site for miR-137 in this region. To verify miRNA targeting specificity, we performed luciferase gene reporter assays using a MSH2 3′UTR psiCHECK-2 vector in human SW480 cells over-expressing miR-137, which showed a drastic reduction in luciferase activity (p > 0.0001). This effect was abolished by site-directed mutagenesis of the putative miR-137 seed site. Moreover, in these cells we observed that miR-137 levels were inversely correlated with MSH2 expression levels. These results were confirmed by results in normal and tumoral tissues from the patient carrying the 3′UTR c.*226A>G variant in MSH2. Finally, miR-137 overexpression in SW480 cells significantly suppressed cell proliferation in a time- and dose-dependent manner (p < 0.0001), supporting a role for MSH2 in apoptosis and cell proliferation processes. Our findings suggest miR-137 helps control MSH2 expression via its 3′UTR and that dysregulation of this mechanism appears to promote tumorigenesis in colon cells

Hereditary Colorectal Cancer: State of the Art in Lynch Syndrome.

Hereditary non-polyposis colorectal cancer is also known as Lynch syndrome. Lynch syndrome is associated with pathogenetic variants in one of the mismatch repair (MMR) genes. In addition to colorectal cancer, the inefficiency of the MMR system leads to a greater predisposition to cancer of the endometrium and other cancers of the abdominal sphere. Molecular diagnosis is performed to identify pathogenetic variants in MMR genes. However, for many patients with clinically suspected Lynch syndrome, it is not possible to identify a pathogenic variant in MMR genes. Molecular diagnosis is essential for referring patients to specific surveillance to prevent the development of tumors related to Lynch syndrome. This review summarizes the main aspects of Lynch syndrome and recent advances in the field and, in particular, emphasizes the factors that can lead to the loss of expression of MMR genes

Recently identified viruses contribute significantly to acute respiratory infections in children.

Oral presentatio

Hereditary Colorectal Cancer: State of the Art in Lynch Syndrome

Hereditary non-polyposis colorectal cancer is also known as Lynch syndrome. Lynch syndrome is associated with pathogenetic variants in one of the mismatch repair (MMR) genes. In addition to colorectal cancer, the inefficiency of the MMR system leads to a greater predisposition to cancer of the endometrium and other cancers of the abdominal sphere. Molecular diagnosis is performed to identify pathogenetic variants in MMR genes. However, for many patients with clinically suspected Lynch syndrome, it is not possible to identify a pathogenic variant in MMR genes. Molecular diagnosis is essential for referring patients to specific surveillance to prevent the development of tumors related to Lynch syndrome. This review summarizes the main aspects of Lynch syndrome and recent advances in the field and, in particular, emphasizes the factors that can lead to the loss of expression of MMR genes