A computational model of ureteral peristalsis and an investigation into ureteral reflux.

The aim of this study is to create a computational model of the human ureteral system that accurately replicates the peristaltic movement of the ureter for a variety of physiological and pathological functions. The objectives of this research are met using our in-house fluid-structural dynamics code (CgLes-Y code). A realistic peristaltic motion of the ureter is modelled using a novel piecewise linear force model. The urodynamic responses are investigated under two conditions of a healthy and a depressed contraction force. A ureteral pressure during the contraction shows a very good agreement with corresponding clinical data. The results also show a dependency of the wall shear stresses on the contraction velocity and it confirms the presence of a high shear stress at the proximal part of the ureter. Additionally, it is shown that an inefficient lumen contraction can increase the possibility of a continuous reflux during the propagation of peristalsis.

[PRESSURE ULCER TREATMENT EXPERIENCE AT CLINICAL DEPARTMENT OF PLASTIC, RECONSTRUCTIVE AND AESTHETIC SURGERY, DUBRAVA UNIVERSITY HOSPITAL: COMPARISON OF RESULTS RECORDED IN THE 2011-2016 AND 2003-2008 PERIOD].

Results of this clinical study on surgical treatment of pressure ulcers at Department of Plastic, Reconstructive and Aesthetic Surgery, Dubrava University Hospital showed that there was no difference between the 2011-2016 and 2003-2008 periods, indicating continuation of good surgical treatment planning and appropriate postoperative care. Despite the smaller number of hospitalized patients in the 2011-2016 period (31 patients and 42 reconstructive procedures), the number of reconstructive procedure was similar to the recent 2003-2008 period (47 patients and 57 reconstructive procedures). The best results of reconstruction of sacral region pressure ulcer were achieved with fasciocutaneous and musculocutaneous flaps. Whenever possible, depending on the extent of the defect, musculocutaneous flaps should be preferred for reconstruction. It is especially suitable for pressure ulcer recurrence. For ischial region reconstruction, good results can be obtained by mobilizing the semimembranosus and/or semitendinosus in defect gap. For trochanteric region, the tensor fascia lata flap is a good choice. For maximal functional and reconstructive results, a multidisciplinary approach in pressure ulcer treatment has the leading role in the modern concept of wound healing. Surgical treatment should always include radical debridement, ostectomy and well planned defect reconstruction. Conservative treatment should be support to surgical treatment with a focus on patient health care and high hygiene measures. In recent years (2011-2016), the usage of better conservative treatment led to reduction of patient hospital stay and surgical treatment of pressure ulcer. Further 'wound care' nurses training in Croatia can lead the trend towards advanced practice nursing in pressure ulcer prevention and conservative treatment.

Simulation of the upper urinary system.

The ureter and its peristalsis motions have long been of significant interest in biomechanics. In this article we review experimental, theoretical, and numerical studies of the behavior of the ureter together with its mechanical properties, emphasizing studies that contain information of importance in building a virtual simulation tool of the complete ureter that includes its complex geometry, nonlinear material properties, and interaction with urine flow. A new technique to model the contraction of a ureter, which directly applies wall forces to model pacemaker activities, is presented. The required further steps to capture the full complex movement of the peristalsis are discussed, aiming to construct a computational platform that will provide a reliable tool to assist in the investigation and design of material devices (stents) for the renal system.

Some computational and algorithmic developments in computational mechanics of discontinua.

Discontinua simulations are becoming an important part of computational mechanics to the extent that computational mechanics of discontinua is becoming a separate sub-discipline of computational mechanics. Among the most widely used methods of computational mechanics of discontinua are discrete-element methods, combined finite-discrete-element methods and discontinuum deformation analysis methods. A range of key algorithmic procedures is common to most of these methods. These include contact detection, explicit solvers, fracture and fragmentation models, handling of complex geometric considerations when processing interaction in three dimensions (contact kinematics) and fluid coupling. In recent years, there have been major breakthroughs in almost all of these key algorithmic aspects. These include linear contact-detection procedures (NBS, C-grid), discretized contact solutions, fracture and fragmentation solutions, together with fluid pressure driven fracture process and three-dimensional explicit solvers incorporating finite rotations. Many of these breakthroughs have not yet been applied across the full range of relevant discontinuum problems. The major reason for this is that discrete-element method, discontinuum deformation analysis and combined finite-discrete-element method publications are spread over a wide range of specialist journals and conferences. Thus in this paper, the main features of a selection of algorithmic breakthroughs are reviewed for the first time, enabling researchers in different fields to apply these compatible developments to their specific applications.

The modelling of particle systems with real shapes.

The numerical modelling of particulate processes in environmental science increasingly requires an ability to represent the properties of individual natural particles. Considerable advances have been made in discontinuum modelling using spheres to represent particles. In this paper, we discuss recent developments that illustrate a way forward for tackling the complexity of realistically shaped bodies such as those exhibited by rock fragments. To address the validation of such approaches, we present a comparison of cube-packing experiments and their equivalent numerical simulation. Sensitivity to initial conditions, highlighted for non-spherical bodies, enters the discussion of problems with validation of numerical simulation. The algorithmic details behind these advances in modelling large systems of realistically shaped particles are summarized in our companion paper in this volume.