1,721,180 research outputs found
Virtual collapse of true lumen in acute type A aortic dissection
No full textTrue lumen collapse may be a dynamic process. It predominates during diastole but is reduced during the ejection phase to allow distal true lumen perfusion. In our patient, the filling with contrast medium of both true and false lumens in the descending aorta supports this hypothesis
Conservative management of left ventricle cardiac fibroma in an adult asymptomatic patient
No full textPrimary cardiac tumours are rare with an autopsy frequency of 0.001–0.03% and approximately 90% of them are benign. Among these, cardiac fibromas represent a minority and, together with rhabdomyomas, are the most common benign cardiac tumours in paediatric patients. However, their occurrence in the adult patient is uncommon. Most originate from the left ventricle (LV) or interventricular septum.
Patients with cardiac fibroma usually present with chest discomfort or pain, syncope, heart failure, cyanosis, arrhythmias or even sudden death but approximately one third of patients diagnosed with cardiac fibroma are asymptomatic and the tumour is discovered incidentally. There is a general agreement that surgical treatment should be performed whenever the cardiac fibroma is causing symptoms. In these patients, surgical options include complete surgical excision, partial resection or orthotopic heart transplantation. Indication for surgical treatment remains controversial in patients who are strictly asymptomatic. We report the case of an asymptomatic adult patient presenting with a giant LV cardiac fibroma and for whom we have opted for a conservative management. Conservative management of LV cardiac fibroma in an
adult patient who is strictly asymptomatic seems to be an acceptable strategy when the risks of complete surgical resection outweigh the benefits. Close clinical and instrumental follow-up is mandatory and the implantation of an ICD might be a reasonable precaution
Exploring Plasticity Material Models in Level-Set Topology Optimization
No full textThis work investigates various elastoplastic material models in topology optimization. A novel topology optimization framework using the level-set method and COMSOL Multiphysics is proposed to handle the complexities introduced by nonlinear material behaviors. This method broadens the range of applicable plasticity models and streamlines nonlinear analysis in topology optimization
Unravelling correlation between electrolyte composition and surface finishing in electropolishing of AISI 316 L stainless steel in H3PO4 - H2SO4 mixtures
No full textA systematic study on AISI 316 L electropolishing (EP) in H3PO4-H2SO4-based electrolytes is presented, aiming to investigate correlations between electrolyte physico-chemical properties and surface finishing and to clarify interfacial phenomena occurring during EP. The effect of electrolyte concentration, [H3PO4]/[H2SO4] ratio and organic additives was considered. Electrical conductivity, density, and viscosity were measured; cyclic voltammetry was run to evaluate EP potential window and plateau current density. Surface finishing was characterised by roughness and brightness measurements; morphology was investigated by optical and electronic microscopy; composition was assessed by energy dispersive X-ray spectroscopy. Best results were obtained in concentrated electrolytes showing lower electrical conductivity, higher viscosity, a wider EP potential window and a lower plateau current density. Lower roughness was obtained when [H3PO4]/[H2SO4] = [H2SO4]/[H3PO4] ≈ 4. Regardless [H3PO4]/[H2SO4] ratio, EP surfaces revealed well-defined crystalline grains, showing different intra-granular microstructure depending on electrolyte composition. Finally, hypotheses on interfacial phenomena governing the process were made
Surgical treatment of chronic constrictive pericarditis
No full textObjectives. Chronic constrictive pericarditis is an uncommon disease, which diagnosis and treatment are still difficult. Here we present our recent experience with the surgical treatment of chronic constrictive pericarditis.
Methods. Between January 2000 and December 2009, we have operated on 70 patients. Mean age at the time of operation was 54 ± 17 years (range 15-79 years) and there was a prevalence of male sex (65.7%). The etiology was as follows: undetermined (52.8%), post radiation therapy (15.7%), post cardiac surgery (14.3%), tuberculous (14.3%), viral (1.4%) and autoimmune (1.5%). Subtotal pericardiectomy, limited by the phrenic nerves, was always performed via median sternotomy. Redo operation was performed in 13 patients (18.5%) and combined surgery in 11 patients (15.7%; valvular surgery: n=7, coronary artery bypass grafting surgery: n=4).
Results. Elective cardiopulmonary bypass was used in 10 patients. In-hospital mortality was 11% (n = 8). At univariate analysis the use of cardiopulmonary bypass (p <0.001) and the presence of other cardiac surgery procedures (p <0.001) were predictors of in-hospital mortality. One-year and 5-year survival was 95% and 79%, respectively.
Conclusion. The etiology of chronic constrictive pericarditis remains unknown in about half the cases. Pericardiectomy is still the surgical treatment of choice. Operative mortality is low but it increases significantly when associated to other cardiac surgery procedures
Topology optimization of nonlinear structural dynamics with invariant manifold-based reduced order models
Full text linkWe present a structural topology optimization method to tailor the hardening/softening dynamic response of nonlinear mechanical systems. The coefficient that controls this behavior is computed analytically using the third-order normal-form parametrization of the Lyapunov subcenter manifold, which eliminates the need for expensive full-order simulations and numerical continuation to approximate the so-called backbone curve of the system. The method further leverages the adjoint method for efficiently computing sensitivities of the objective function and constraints, while the explicit formulation of nonlinear internal elastic forces through tensor notation simplifies these evaluations. Notably, this tensorial approach is computationally efficient, especially when applied to a regular grid of elements. Consequently, the proposed approach offers a robust and efficient framework for optimizing the dynamic performance of nonlinear mechanical structures modeled with high-dimensional finite element models. The findings are corroborated through examples of two geometrically nonlinear systems, a Messerschmitt-Bölkow-Blohm (MBB) beam and a microelectro-mechanical system (MEMS) inertial resonator
Chronic thromboembolic pulmonary hypertension: uncomun cases and long term results of pulmonary endarterectomy.
No full textBackbone curve tailoring via Lyapunov subcenter manifold optimization
No full textWe present a technique for the direct optimization of conservative backbone curves in nonlinear mechanical systems. The periodic orbits on the conservative backbone are computed analytically using the reduced dynamics of the corresponding Lyapunov subcenter manifold (LSM). In this manner, we avoid expensive full-system simulations and numerical continuation to approximate the nonlinear response. Our method aims at tailoring the shape of the backbone curve using a gradient-based optimization with respect to the system’s parameters. To this end, we formulate the optimization problem by imposing constraints on the frequency-amplitude relation. Sensitivities are computed analytically by differentiating the backbone expression and the corresponding LSM. At each iteration, only the reduced-order model construction and sensitivity computation are performed, making our approach robust and efficient
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