GENERALIZED FORCES AND DISSIPATION FUNCTIONS IN THE CONTEXT OF AN INTERNAL VARIABLE APPROACH APPLIED TO THE SOLUTION OF ELASTIC-PLASTIC PROBLEMS

A non-traditional approach to the numerical analysis of elastic-plastic systems is discussed by focusing on a formulation that makes use of internal variables and dissipation functions. These functions are used in order to enforce the constitutive law, so that they play the role of the yield functions in the framework of the classical theory of plasticity. With reference to finite element discrete models, it is shown that the solution of an elastic-plastic problem corresponds to the minimum point of a convex function (when the material is stable in Drucker\u2019s sense) and that convergence is guaranteed when a convenient time integration method (usually known as backward-difference scheme) is applied. As a matter of fact, it can be proved that the value of that function progressively decreases (iteration by iteration) when a proper time integration strategy is implemented. Elastic-plastic systems will be considered, which are subjected to uniaxial and multiaxial stress states (by assuming Mises\u2019 yield condition for two-dimensional and three-dimensional finite elements). In all cases, it will be easily noticed that the dissipation functions depend on convenient generalized forces, whose features are obvious in the presence of uniaxial stress states. Instead, when the structural system is subjected to multiaxial stress states, the actual meaning of the generalized forces must be properly understood in order to define convenient dissipation functions and/or yield functions: this is the main issue of the present paper and represents a topic which, to the authors\u2019 knowledge, has not been adequately investigated, yet

An Iterative Procedure for the Analysis of Nonlinear Elastic Systems Subjected to Uniaxial Loading and Large Displacements

The paper deals with an iterative procedure for the solution of elastic problems, for which the large displacement theory must be considered. It is shown that the algorithm, based upon a non-traditional iterative scheme, tends to converge to the correct solution and some numerical tests are considered, by assuming a linear and piecewise-linear material model

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

A simple approach to the large-displacement analysis of elastic framed structures

The paper is centered on an iterative procedure, which can be adopted for the structural analysis of elastic frames subjected to large displacements. In consequence, the equilibrium equations are written by considering the deformed configuration. The algorithm is based on the finite element method and essentially requires the solution of a sequence of linear elastic problems. At each iteration, the nodal displacements are updated according to the small displacement theory. Thus, the numerical approach discussed here makes use of the usual tools, which are typical of a simple linear elastic analysis. More specifically, after a preliminary analysis that is performed by considering a given set of external loads and by imposing equilibrium with respect to the initial configuration, the actual curvatures of the beam elements are determined and convenient equivalent nodal loads are computed. Next, a new mesh is generated in order to account for the deformed configuration of the framed structure and further incremental displacements are found by applying a set of nodal loads, which represent the difference between the given loads and the loads determined at the end of the previous analysis. The process continues until a convenient measure of the discrepancy between the displacements computed at the last iteration and the displacements estimated at the previous iteration is below a given tolerance. To this aim, it is possible to compare the Euclidean norms of the displacement vectors evaluated at two subsequent iterations. Some preliminary numerical tests on simple plane systems show that the approach presented in this paper does give results, which are consistent with analytical and/or experimental solutions

A Discrete Direct Formulation for Nonlinear Structural Analysis

The paper deals with a discrete formulation that makes use of primal and dual meshes. While the first mesh is needed to introduce a compatible set of displacements, the second one is utilised to enforce equilibrium by taking into account the forces concerned with each polygon (dual cell) of this mesh: body forces acting on the cell, applied external surface loads and tractions exchanged with contiguous cells. Typical meshes can be generated by considering the Delaunay network (a set of triangles) and the Voronoi tessellation (a set of polygons). Possible applications to basic elastic-plastic problems are briefly discussed. Next, some emphasis is given to the possibility of modelling crack propagation through a nontraditional approach. In fact, the particula pattern of the Voronoi tessellation (dual mesh) provides a discrete number of zig-zag paths, since the interface course (where equilibrium conditions must be satisfied) tends to turn left and right, up and down, repeatedly in a sharp way. Therefore, interfaces can be recognized as potential crack paths and a convenient criterion can be introduced in order to define critical loads beyond which cracks start to propagate. Finally, some numerical examples are briefly discussed in order to show possible applications of the proposed procedure

A discrete direct formulation for elastic-plastic analysis

The paper deals with a direct discrete formulation (applicable to a large class of physical problems) that allows one to directly derive discrete equations without using differential equations. General applications to plane elastic-plastic systems are presented by using a non-traditional modelling technique (the cell method). A classical von Mises problem is solved and coupling with boundary elements is discussed. Next, a novel approach to the discretization of cracking phenomena is introduced on the basis of Coulomb friction law. Finally, numerical results concerned with plane problems are reported

Persistence of chromosomal abnormalities additional to the Philadelphia chromosome after Philadelphia chromosome disappearance during imatinib therapy for chronic myeloid leukemia

Five Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML) patients with additional chromosome abnormalities at diagnosis have been followed during Imatinib therapy. In all, the Ph chromosome disappeared, while the 5 cases, additional abnormalities [dup(1); del(5), +8 (2 patients) and +14] persisted in the subsequent studies, performed over a period of 11 to 49 months, either alone or together with a karyotypically normal cell population. This finding is consistent with a secondary origin of the Ph chromosome in these patients. It is still to early to evaluate the possible prognostic value of these additional abnormalities

Imaging diagnosis of a rare case of intermittent intestinal pneumatosis: A consequence of ileocecal valve clip dysfunction?

ABSTRACT: Pneumatosis intestinalis is a condition characterized by the presence of gas or air pockets within the walls of the intestines. It can occur in any section of the gastrointestinal tract but it is most commonly found in the colon. Etiology and pathogenesis of PI are not yet fully understood, but several potential factors have been suggested to play a pivotal role in the development of this pathologic condition. Pneumatosis intestinalis seems to arise from a complex interplay between various factors, such as the integrity of the intestinal lining, pressure within the portal vein, the composition of the microbiological flora in the gut. Pneumatosis intestinalis can be caused by a variety of underlying conditions, such as bowel obstruction, intestinal ischemia, infection, inflammatory bowel disease, or certain medications. Symptoms may include abdominal pain, bloating, diarrhea, vomiting, and bloody stools. We present a case report of a 63-year-old male patient who underwent laparoscopic cholecystectomy for symptomatic cholelithiasis with recurrent cholecystitis. Following the surgery, the patient experienced a rapid drop in hemoglobin levels, necessitating an urgency regimen laparoscopic abdominal exploration which revealed Meckel's diverticulitis with active bleeding leading to diverticulectomy. The next day, the patient developed a radiological condition characterized by the co-presence of intermittent pneumatosis intestinalis, Portal pneumatosis and intermittent small bowel obstruction