Synthetic models for the analysis and control of composite and sandwich aerospace structures in critical conditions

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Nonlinear static response analysis of sandwich beams using the Refined Zigzag Theory

The Refined Zigzag Theory (RZT) is assessed for the buckling and nonlinear static response analysis of multilayered composite and sandwich beams. A nonlinear formulation of the RZT is developed taking into account geometric imperfections and nonlinearities using the Von Kármán nonlinear strain-displacement relations. FE analyses are conducted employing C0-beam elements based on the RZT and the Timoshenko Beam Theory (TBT) to model three sandwich beams with different core materials and slenderness ratios, in both simply supported and cantilever configurations. The reference solutions are obtained by high-fidelity FE commercial codes, Abaqus® and Nastran®. The first two buckling loads and mode shapes are evaluated for the beams without initial imperfections. Several shapes are then assumed as geometric imperfections to calculate the beams nonlinear response to axial-compressive loads. The comparisons show the very high accuracy of the RZT (comparable to high-fidelity FE commercial codes) for both the buckling and nonlinear static analyses and its superior capability with respect to the TBT to deal with sandwich beams with low slenderness ratio and higher face-to-core stiffness ratio

Nonlinear static analysis of composite beams with piezoelectric actuator patches using the Refined Zigzag Theory

Piezoelectric actuators have been highly successful in a wide range of structural control applications. Assuch, there is an ongoing need for rapid and accurate structural analysis techniques, particularly for highlyheterogeneous composite materials and accounting for the actuator as a patch.Here, a new model based on the Refined Zigzag Theory (RZT) formulation that includes geometricnonlinearities is proposed for buckling, postbuckling and nonlinear static response analyses of geometricallyimperfect composite beams with piezoelectric actuators.Both the analytical and the finite element (FE) formulation are presented for symmetrically and non-symmetrically laminated beams. The FE approximation is further generalised to the case of beams withgeometric discontinuities to model composite beams with piezoelectric actuator patches. The new RZT modelis numerically verified through comparisons to Abaqus solutions for buckling and postbuckling analyses andfor the geometrically nonlinear response to an applied voltage of geometrically imperfect composite beamswith piezoelectric actuator patches.This work presents a new model for composite beams with piezoelectric actuators and confirms theremarkable advantages of RZT in terms of accuracy and computational efficiency also for challenging nonlinearanalyses, where the RZT computational time is generally less than half the time required by the FE commercial code

Free vibration analysis of sandwich beams using the Refined Zigzag Theory: an experimental assessment

The paper is devoted to the experimental assessment of the Refined Zigzag Theory (RZT) for the free-vibration analysis of sandwich beams. To investigate the model performance, the effect of the face-to-core stiffness and thickness ratios as well as beam slenderness are taken into consideration. For comparison purposes, the results obtained by using the Timoshenko's beam model, adopting an adequate shear correction factor, are given. The RZT demonstrates its remarkable accuracy with respect to the Timoshenko's beam theory even when the latter is used with the ad-hoc calculated shear correction factor

Isolated Intramural Hematoma of Superior Mesenteric Artery: Case Reports and a Review of Literature

(1) Background: Spontaneous isolated intramural hematoma of the superior mesenteric artery (SIHSMA) is a rare entity often considered as a subset of spontaneous isolated dissection of the superior mesenteric artery (SIDSMA). It is characterized by a completely thrombosed false lumen with or without an ulcer-like projection with computed tomography (CT) imaging. The recent literature describes few reports with a relatively short-term follow-up. The natural course, prognosis, and treatment options for SIHSMA still lack consensus. We present two cases of acute abdominal pain in a young man due to IMH of the superior mesenteric artery with an extensive literature review. (2) Case report: A 46-year-old male patient was submitted to an urgent CTA for acute abdominal pain, showing the presence of an isolated dissection of the superior mesenteric artery, determining significant stenosis of the vessel with collateral vessel patency. The patient referred to a recent COVID-19 infection, whose course was paucisymptomatic. He was conservatively treated with antiplatelet therapy and corticosteroid treatments, and, after a few days, the symptomatology completely regressed; also, the 2-month-control CTA showed complete IMH regression and the absence of any signs of residual stenosis. The second patient was a 61-year-old male patient who was submitted to an urgent CTA for acute abdominal pain, showing the presence of an isolated dissection of the superior mesenteric artery, not determining significant vessel stenosis. He was conservatively treated with antiplatelet therapy and corticosteroid treatment, and after a few days, the symptomatology completely regressed and the radiological control showed complete dissection regression. (3) Conclusion: SISHSMA is a rare entity of vascular pathology, and conservative management represents the best medical strategy. We propose corticosteroid treatment as one of the most appropriate tools in the conservative treatment of SISHSMA

Exposure of Toll-like receptors 4 to bacterial lipopolysaccharide (LPS) impairs human colonic smooth muscle cell function.

Endotoxemia by bacterial lipopolysaccharide (LPS) has been reported to affect gut motility specifically depending on Toll-like receptor 4 activation (TLR4). However, the direct impact of LPS ligation to TLR4 on human smooth muscle cells (HSMC) activity still remains to be elucidated. The present study shows that TLR4, its associated molecule MD2, and TLR2 are constitutively expressed on cultured HSMC and that, once activated, they impair HSMC function. The stimulation of TLR4 by LPS induced a time- and dose-dependent contractile dysfunction, which was associated with a decrease of TLR2 messenger, a rearrangement of microfilament cytoskeleton and an oxidative imbalance, i.e., the formation of reactive oxygen species (ROS) together with the depletion of GSH content. An alteration of mitochondria, namely a hyperpolarization of their membrane potential, was also detected. Most of these effects were partially prevented by the NADPH oxidase inhibitor apocynin or the NF kappa B inhibitor MG132. Finally, a 24 h washout in LPS-free medium almost completely restored morphofunctional and biochemical HSMC resting parameters, even if GSH levels remained significantly lower and no recovery was observed in TLR2 expression. Thus, the exposure to bacterial endotoxin directly and persistently impaired gastrointestinal smooth muscle activity indicating that HSMC actively participate to dysmotility during infective burst. The knowledge of these interactions might provide novel information on the pathogenesis of infection-associated gut dysmotility and further clues for the development of new therapeutic strategies. J. Cell. Physiol. 223: 442-450, 2010. (C) 2010 Wiley-Liss, Inc

Hot topics on vertebral osteomyelitis from the International Society of Antimicrobial Chemotherapy

reserved19mixedSaeed K.; Esposito S.; Ascione T.; Bassetti M.; Bonnet E.; Carnelutti A.; Chan M.; Lye D.C.; Cortes N.; Dryden M.; Fernando S.; Gottlieb T.; Gould I.; Hijazi K.; Madonia S.; Pagliano P.; Pottinger P.S.; Segreti J.; Spera A.M.Saeed, K.; Esposito, S.; Ascione, T.; Bassetti, M.; Bonnet, E.; Carnelutti, A.; Chan, M.; Lye, D. C.; Cortes, N.; Dryden, M.; Fernando, S.; Gottlieb, T.; Gould, I.; Hijazi, K.; Madonia, S.; Pagliano, P.; Pottinger, P. S.; Segreti, J.; Spera, A. M