1,721,253 research outputs found
Numerical and analytical analyses of high-strength steel cellular beams: A discerning approach
No full textThe behaviour of cellular beams made from normal and high strength steel with various geometries is investigated through a large number of finite element analyses and a simple mechanical model for the Web-Post Buckling (WPB) failure is developed and analysed in order to highlight the factors which influence its occurrence and development for both normal and High-Strength (HS) steels. The performed FE analyses and the proposed modelling, once calibrated, allow to shed some light on the characteristics of the phenomenon and to provide the basis of a reliable design method to predict shear buckling of web-post of cellular beams made both of mild and HS steel
Terapia intensiva in chirurgia cardiovascolare
No full textIl progresso compiuto negli ultimi anni dalla Cardiochirurgia ha consentito di estendere l’indicazione al trattamento a pazienti con maggiori comorbidità e profilo di rischio globale più elevato. Ciò ha richiesto un consensuale sviluppo di tecniche di terapia intensiva postoperatoria progressivamente più avanzate.
Questo volume, indirizzato a tutti i Medici che operano nelle Unità di Terapia Intensiva Cardiovascolare, quali cardioanestesisti, cardiochirurghi, cardiologi, rianimatori ed intensivisti, analizza il complesso scenario perioperatorio del paziente cardochirurgico, valutando l’impatto di questa chirurgia specialistica sui vari organi ed apparati.
Il manuale si propone come una guida per l’inquadramento del paziente cardiochirurgico, per la sua gestione postoperatoria e per il trattamento delle specifiche complicanze, descrivendo inoltre le modalità di cura necessarie al supporto ed alla sostituzione delle diverse funzioni d’organo.
● Il volume, illustrato da oltre 150 fotografie e disegni, è suddiviso in 21 capitoli e due sezioni: 1. La gestione della fase acuta; 2. Problematiche con decorso complicato.
● La prima parte analizza in modo sistematico tutte le fasi della gestione del paziente cardochirurgico, sin dall’arrivo presso l’Unità di Terapia Intensiva, e prende in considerazione tutti i supporti necessari al mantenimento delle funzioni vitali.
● Nella seconda parte vengono esaminati gli scenari clinici caratterizzati da un decorso complicato come le infezioni nel paziente cronico, il problema nutrizionale, la tracheostomia, le tecniche depurative nel paziente settico, la sedazione nel decorso complicato
Commentary: Perceval S bioprosthesis valve and platelets: The thrombocytopenia is behind the corner and the mystery continues
No full textRevisitation of elastic buckling of circular rings: Some analytical and numerical issues
No full textElastic buckling of circular rings under external pressure is one of the oldest and most ubiquitous problems in structural engineering and the first meaningful solution to it was proposed by Levy (1884). This basic solution, based on the Euler–Bernoulli beam model, can be found in the vast majority of textbooks on stability. However, there are a number of subtleties in the formulation of the problem which need to be taken into account so and one should always be well aware of the underlying analytical fundamentals, especially in the current world which strongly relies on numerical analyses. Therefore, starting from the general nonlinear kinematics of the problem, the buckling load is revisited by means of a direct energy approach and on the basis of an in-depth discussion of the classic kinematic hypotheses. Possibly different outcomes are pointed out and remarked. Finally, some inconsistencies which unexpectedly arise in pursuing the solution by means of commercial FE packages are presented and commented
From static buckling to nonlinear dynamics of circular rings
No full textThe dynamic buckling of circular rings is a pervasive instability problem with a major impact in various fields, such as structural, nuclear and offshore engineering, robotics, electromechanics, and biomechanics. This phenomenon may be simply seen as the complex motion that occurs deviating from the original circular shape under, for instance, any kind of time-dependent forcing load. Despite the fact that this topic has progressively gained importance since the mid-20th century, it seems that the same points have not been made completely clear. In fact, even some subtleties in the derivation of classical static buckling load may still give rise to misinterpretations and lead to misleading results. A fortiori, research concerning the nonlinear dynamics of rings still suffers the inherent difficulties associated with different possible analytical formulations of post-buckling dynamics. Advancement in this respect would be relevant, both from a theoretical and a practical point of view, since the applications are endless, with countless possibilities, especially in the biomedical and biotechnological fields: buckling-driven transformations of thin-film materials for applications in electronic microsystems, self-excited oscillations in collapsible tubes and pliable fluid-carrying shells, vocal-fold oscillations during phonation and snoring, pulse wave propagation in arteries, closure and reopening of pulmonary airways, stability of cardiac and venous valves during vascular surgery, stability of annuloplasty devices, flow-induced deformation and ultimate rupture of a cerebral aneurysm, and much more. The present article, in the framework of a critical review of the classic formulation of elastic ring buckling, proposes a straightforward approach for the nonlinear dynamics of an elastic ring that leads to a Mathieu–Duffing equation. In such a manner, some possible evolutions of the system under pulsing loads are analyzed and discussed, showing the inherent complexity of its dynamic behavior
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