1,721,010 research outputs found
Computational strategies for discrete modeling of Cultural Heritage structures
Get PDFLo scopo di questo lavoro di ricerca è presentare lo sviluppo di approcci discontinui e l'influenza della stereotomia per simulare il comportamento dinamico non lineare di strutture storiche in muratura di grandi dimensioni. Gli obiettivi sono quindi le valutazioni qualitative e quantitative dei diversi approcci esistenti e delle principali leggi costitutive, l'analisi e la calibrazione dei parametri meccanici e fornire forti indicazioni sul miglior livello di discretizzazione necessario per questo tipo di approcci. Pertanto, lo studio prevede l'utilizzo di schemi di integrazione temporale implicita ed esplicita per la dinamica strutturale, rispettivamente nel metodo della Dinamica di Contatto Non Regolare e Modello di Zona Coesiva implementati nel codice LMGC90©, dove i moti di scorrimento sono governati dalla condizione di impenetrabilità di Signorini e dalla legge di attrito di Coulomb, e nel Metodo degli Elementi Discreti con comportamenti coesivi e di resistenza a trazione dei giunti nel codice 3DEC©. Una serie di casi studio di strutture esistenti è stata rappresentata adottando quattro diversi modelli geometrici che andavano da quello più complesso, comprese le pareti in muratura a geometria piena e disordinata (a sacco), a quello più semplice, includendo le murature con singolo paramento come semplificazione delle opere murarie esistenti. I risultati numerici hanno evidenziato le modalità di cedimento dipendenti dalla forma, dimensione e tessitura della muratura e le modalità di danneggiamento progressivo sotto azioni dinamiche. Inoltre, gli approcci numerici presentati si sono dimostrati in grado di simulare grandi spostamenti e separazioni complete di blocchi, riprodurre comportamenti meccanici complessi e fare previsioni sulla valutazione di vulnerabilità degli edifici storici in muratura. I risultati discussi sono positivi e preziosi nell'ottica della preservazione del patrimonio culturale da danni futuri proponendo linee guida per il rinforzo e l'adeguamento sismico delle strutture.The aim of this research work is to present the development of discontinuous approaches and the influence of stereotomy to simulate the nonlinear dynamic behavior of historical large-scale masonry structures. Thus, the objectives are the qualitative and quantitative evaluations on the different existing approaches and the main constitutive laws, the analyses and calibration of mechanical parameters, and providing strong indications on the best level of discretization needed for these kinds of approaches. Thus, the study involves the use of implicit and explicit time integration schemes for structural dynamics, respectively in the Non-Smooth Contact Dynamics method and Cohesive Zone Model implemented in the LMGC90© code, where sliding motions are governed by Signorini's impenetrability condition and dry-friction Coulomb's law, and in the Discrete Element Method with cohesive and tensional behaviors at the joints in the 3DEC© code. A set of case studies from real structures was represented adopting four different geometric models ranged from the most complex one, including the full geometry and multi-leaf masonry walls, to the simplest one, including the single-leaf walls as a simplification of the real masonry. The numerical results highlighted the failure modes depending on the shape, size and texture of the masonry and the modalities of progressive damage under dynamic actions. Moreover, the numerical approaches presented have proven to be capable of simulating large displacements and complete block separations, reproducing complex mechanical behaviors and making predictions on the vulnerability assessment of the historical masonry buildings. The results discussed are successful and valuable in view of preservation of the cultural heritage from future damages proposing guidelines for strengthening and seismic retrofitting of structures.
An evaluation on management of carotid body tumour (CBT). A twelve years experience
No full textObjectives. Carotid Body Tumor (CBT) is a rare lesion of the neuroendocrine system but it is the most common form of head and neck paraganglioma (PGL). Our objective is to discuss the optimal management of these lesions to provide the best outcome of patients treated by surgical resection. Patients and Methods. A retrospective evaluation was obtained by review of the records of 20 patients with 26 CBT treated at our institution between 2000 and 2012. Primary tumor characteristics, diagnostic protocols, surgical treatment, short and long-term outcomes were collected and analyzed. Results. A total of 26 CBTs resections were performed on 20 patients; the age range was 21-89 years. There was a female prevalence (14 women-80% and 6 men-20%). Familial cases occurred in 6 patients (30%); of these, 3 patients had bilateral lesions and 1 patient multiple paragangliomas. In all cases no lymph node metastasis was found. All lesions were grouped into three groups according to the latero-lateral diameter: Group I 5cm; Group III >5cm. All patients were managed by surgical resection of the CBT. There were no operative deaths. Overall we found transitory neurological impairment in 15,3% and permanent neurological deficit in 7,6% of cases. No complications occurred in all resections of Group I tumors. In Group II only 1 resection was followed by dysphonia by recurrent nerve palsy (after vagal nerve en-bloc resection). In Group III only 1 resection was followed by permanent vagus nerve palsy. Conclusions. Surgical removal of the tumor is the only treatment that can ensure a complete eradication of the disease. Family screening is of great importance in patients with hereditary forms. Careful preoperative planning of surgical procedure by integrated diagnostic imaging and a full mastery of the surgical technique can minimize the risk of the most common postoperative complications. Lifelong follow-up is mandatory to make early diagnosis of recurrent disease
Late patency of reconstructed visceral arteries after open repair of thoracoabdominal aortic aneurysm
Get PDFBackground: In the era of rising endovascular treatment of thoracoabdominal aortic aneurysms (TAAAs), the analysis of visceral vessel (VV) patency after open surgical repair is crucial to provide a future benchmark between these different approaches. This study reports the late outcomes of a single-center experience with open TAAA repair, focusing on the results of different techniques adopted for renal and splanchnic revascularization. Methods: Data were analyzed for 382 consecutive open TAAA repairs performed between January 2009 and July 2015 (284 men; mean age, 66 ± 10 years). Follow-up of surviving patients was carried out by computed tomography angiography and office checkups at 3 and 12 months and yearly afterward. Kaplan-Meier analysis was performed for overall survival, patency of reconstructed VVs (celiac trunk, superior mesenteric artery, right renal artery, left renal artery), and reinterventions on visceral arteries. Furthermore, VV long-term patency was analyzed in subgroups of patients according to the revascularization strategy (patch inclusion of all vessels, group 1; one-vessel separate reattachment and patch inclusion of the remaining vessels, group 2; separate reattachment of all VVs, group 3). Results: In-hospital mortality and paraparesis/paraplegia occurred in 7.6% and 8.1% of patients, respectively. Among the 353 survivors, 338 complied with the follow-up protocol, and adequate computed tomography angiography images were available in 247 patients (952 VVs were analyzed). Overall follow-up survival was 94%, 91%, and 70% at 1 year, 2 years, and 5 years, respectively. At the same time points, VV patency was 99%, 98%, and 98% for celiac trunk; 100%, 100%, and 100% for superior mesenteric artery; 100%, 96%, and 96% for right renal artery; and 91%, 87%, and 82% for left renal artery (log-rank test, P < .0001). Estimates for reinterventions on VVs were 1.2%, 6.3%, and 17% at the same time points. Freedom from occlusion of any VV at 1 year and 3 years was 95% and 87% for group 1, 89% and 79% for group 2, and 92% and 92% for group 3, respectively (log-rank test, P = .13). Conclusions: Long-term patency of VVs after open TAAA repair performed in high-volume centers is high, regardless of the technique employed for revascularization. The left renal artery appears to be most prone to occlusion over time
FE modelling for the nonlinear dynamics of a historic tower in Central Italy
No full textThe dynamics of a medieval tower, on the upper side of San Severino Marche (Central Italy), subjected to transversal dynamic loadings was analysed. An advanced numerical model is utilised to have an insight into the modalities of progressive damage of the structure under strong nonlinear dynamic excitations, namely the FE concrete damage plasticity (CDP) model. A full 3D detailed discretisation is adopted. From the numerical results, both the role played by the actual geometries and the insufficient resistance of the constituent materials are envisaged, showing a good match with crack patterns observed after the seismic sequence of 2016-2017
Infections of the aorta and iliac arteries. Report of 20 years experience in a single centre
No full textAim: Retrospective review of aorto-iliac infections in a single vascular surgery center.
Methods: From a retrospective review of their experience in the last 20 years, the authors analyze a series of 12 cases of aorto-iliac infection. Prognostic factors, surgical options and results are discussed and compared with the literature.
Results: Infections of the aorta eventually associated with aneurysmal degeneration are uncommon (less than 3% of all aortic aneurysms) but still a life-threatening condition with high hospital mortality (25%). No statistical evaluation can be drawn from small series; however, early results are apparently influenced by emergency surgery and comorbidities affecting the immune response; in-situ reconstruction is associated with better long-term results (patency 100%, recurrent infection 0%).
Conclusions: In our experience, in situ aortic grafting reconstruction associated with proper antibiotic therapy obtained satisfactory results in terms of mortality and long-term survival. Endovascular treatment can be adopted in critical patients with prohibitive surgical risk
Damage assessment of cultural heritage affected by last Italian earthquakes
No full textIn the present work, the importance of considering the exact nonlinear and three-dimensional behavior of masonry structures is shown to study the damage assessment of complex structures. For this purpose, three churches damaged by the last earthquake are taken as cases study. The exact geometries of the structures are reconstructed, while information regarding the mechanical properties of materials is derived from previous investigations and literature references. Based on this information, the Finite Elements numerical models are realized. The models are used to performing static and dynamic analysis. The eigenvalue analyses are turn out to be good to identify, with low computational time, the elements more prone to be damaged, meanwhile the non-linear static analyses allowed to follow the damage evolution beyond the elastic field and to extract the seismic capacity
Dynamic characterisation and numerical model updating of a historical complex
No full textThe world is full of historical structures that must be preserved. Given their considerable value, nothing or minimally invasive techniques must be adopted to monitor their health and improve their structural capacity. The Operation Modal Analysis (OMA) is currently the most popular non-invasive methodology to monitor them. Indeed, it allows to derive the dynamic characteristics of the structures through acceleration appropriately positioned sensors. The OMA is employed in the current paper to study a historical complex in the Marche region hinterland (central Italy). First, the dynamic monitoring is carried out to extract the dynamic parameters of the structure. The obtained data are then employed to realize a realistic numerical model by acting on uncertain parameters such as boundary conditions and material parameters
The non-smooth tale of multiple leaf masonry walls
No full textIn the present paper has been reported the Non-Smooth Contact Dynamics method (NSCD) used for the damage evaluation of the multiple leaf masonry walls of the medieval fortress of Arquata del Tronto, strongly affected by the last Centre Italy earthquakes of August and October 2016. Pursuing this approach, a system of rigid blocks has been used for the assembly of the masonry structure. By means of contacts between blocks, which are governed by the Signorini’s impenetrability condition and by dry-friction Coulomb’s law, the building exhibits discontinuous dynamics. Finally, the NSCD method has proved to be an effective instrument for investigating the dynamical behavior of the masonry structures under the ground seismic accelerations. Indeed, several possible failure mechanisms have been confirmed through the numerical results, which have given a deep insight into the seismic vulnerability of this damaged medieval fortress
Pentraxins PTX3 and CRP recruit C1q to cholesterol crystals and co-localize with the terminal complement complex in human atherosclerotic plaques
Get PDFBackground: The pentraxins PTX3 and C-reactive protein (CRP)
are acute-phase proteins associated with increased risk of cardiovascular
events and are known to interact with the complement
system. Cholesterol crystals (CC) are found in atherosclerotic
plaques, where inflammation is a part of the initial process leading
to atherosclerosis. CC induce complement activation but the role of
the pentraxins PTX3, CRP and serum amyloid P component (SAP)
in CC mediated inflammation remains unknown.
Materials and methods: Binding and interaction of recombinant
and native PTX3, CRP or SAP with the complement pattern
recognition molecule C1q on CC was investigated in vitro by flow
cytometry and fluorescence microscopy. The role of C1q in phagocytosis
of CC was investigated by flow cytometry using hirudin
whole blood. Furthermore, co-localization of PTX3, CRP, and SAP
with complement activation product C5b-9 was investigated in vivo
inhumanatherosclerotic plaques by immunofluorescence and confocal
microscopy.
Results and conclusions: In the present study we report a
novel link between the presence of pentraxins in atherosclerotic
lesions and the known complement activation and inflammatory
response induced by CC. Recombinant and native PTX3, CRP and
SAP bound to CC in a concentration dependent manner. PTX3 and
CRP interacted with the complement pattern recognition molecule
C1q on CC by increasing the binding of both purified C1q and C1q
in plasma. Furthermore, CRP binding to CC increased C1q mediate complement activation and deposition of C5b-9. In a phagocytic
assay using whole blood we showed that phagocytosis of CC is
complement dependent and initiated by C1q mediated activation.
The pathophysiological relevance of the in vitro observations was
examined in vivo in human atherosclerotic plaques. PTX3, CRP, and
SAP were found in atherosclerotic plaques and were located mainly
in the cholesterol-rich necrotic core where they show partial colocalization
with complement activation product C5b-9.
In conclusion, this study identifies interaction between PTX3 or
CRP and C1q on CC as a new mechanism in the CC induced inflammation,
which may be highly important in the pathophysiology of
atherosclerosis
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