The Posthumous Depiction of Youths in Late Hellenistic and Early Imperial Gymnasia

Dieser Beitrag untersucht posthume Ehrungen und Darstellungen von jungen Männern im Gymnasion, die in der Forschung bislang nicht umfassend untersucht worden sind. Nach einem Überblick über das bekannte Skulpturenrepertoire in Gymnasia werden die epigraphischen Quellen posthumer Ehrungen von jungen Männern diskutiert, die im Gymnasion trainierten und vorzeitig verstarben. Der Fokus liegt dann auf der Identifizierung von Skulpturen die, dem Kontext und der Ikonographie zufolge, als posthume Ehrungen von Jugendlichen gedient haben könnten. Darunter ist z.B. die Statue des Kleoneikos von Eretria. Es wird dargelegt, dass drei verschiedene ikonographische Typen für diese Ehrungen verwendet wurden: der nackte ‚heroische‘ Typ, der Himation-Typ und die Herme

Computational haemodynamics in arterial geometries in relation to obesity-induced cardiovascular diseases

Childhood and adolescent obesity, primarily a dietary disease, has become a major challenge of the modern society. Obesity is known to accelerate endothelial dysfunction, one of the key biological indicators of lesions of atherosclerosis that underlie most cardiovascular diseases. Early vascular changes can be clinically assessed with measurements of the aortic and carotid intima-media thickness (IMT), and flow-mediated dilatation (FMD) of the brachial, radial, femoral, or popliteal artery, induced by transient hyperaemia. The haemodynamic environment in high-risk patients is likely to be altered in a way that has not yet been clearly understood. This work will discuss the design and mesh generation challenges of idealised and anatomically-realistic vascular geometries, with the use of the ANSA® pre-processor (BETA CAE Systems SA), for the assessment of early signs of cardiovascular diseases in relation to obese children and adolescents. It will also present arterial models that attempt to clarify some of the flow-related mechanisms that are believed to contribute to early vascular changes. Numerical simulations of the time-dependent, incompressible Navier-Stokes equations will be presented utilising a high-fidelity finite volume solver in OpenFOAM®. The models help evaluate the haemodynamic shear stresses along the arterial walls and the possible location of early atherosclerotic lesions. Further work is ongoing on multi-scale computational modelling in patient-specific three-dimensional anatomies combining blood flow computations with macroscopic and microscopic features

Computational studies of blood flow at arterial branches in relation to the localisation of atherosclerosis

Atherosclerotic lesions are non-uniformly distributed at arterial bends and branch sites, suggesting an important role for haemodynamic factors, particularly wall shear stress (WSS), in their development. Using computational flow simulations in idealised and anatomically realistic models of aortic branches, this thesis investigates the role of haemodynamics in the localisation of atherosclerosis. The pattern of atherosclerotic lesions is different between species and ages. Such differences have been most completely documented for the origins of intercostal arteries within the descending thoracic aorta. The first part of the thesis deals with the analysis of wall shear stresses and flow field near the wall in the vicinity of model intercostal branch ostia using high-order spectral/hp element methods. An idealised model of an intercostal artery emerging perpendicularly from the thoracic aorta was developed, initially, to study effects of Reynolds number and flow division under steady flow conditions. Patterns of flow and WSS were strikingly dependent on these haemodynamic parameters. Incorporation of more realistic geometrical features had only minor effects. The WSS distribution in an anatomically correct geometry of a pair of intercostal arteries resembled in character the pattern seen in the idealised geometry. Under unsteady and non-reversing flow conditions, the effect of pulsatility was small. However, significantly different patterns were generated for reversing aortic near-wall flow and reversing side branch flow. The work was extended to study the wall shear stress distribution within the aortic arch and proximal branches of mice, in comparison to that of men. Mice are increasingly used as models to study atherosclerosis and it has been shown that, in knockout mice lacking the low density lipoprotein receptor and apolipoprotein E, lesions develop in vivo at the proximal wall of the entrance to the brachiocephalic artery. Three aortic arch geometries from wild-type mice were reconstructed from MRI images using in-house and commercial software, and the WSS distribution was calculated under steady flow conditions to establish the mouse haemodynamic environment and mouse-to-mouse variability. Approximated human aortic arch geometries were further considered to enable comparison of the flow and WSS fields with that of mice. The haemodynamic environment of the aortic arch varied between the two species. The overall distribution of wall shear stress was more heterogeneous in the human aortic arch than in the mouse arch, although some features were similar. Intraspecies differences in mice were small and influenced primarily by the detailed anatomical geometry and the Reynolds number. A number of simplifications were made in the above flow analyses, and clearly, relaxing these assumptions would increase complexity. Nonetheless, this thesis demonstrates the fundamental features of flow, which underlie the disparate patterns of WSS in different species and/or ages, for simplified cases, and the results are expected to be relevant to more complex ones. Aspects of the observed WSS patterns in the simplified model of intercostal artery correlate with, and may explain, some of the lesion patterns in human, rabbit and mouse aortas. WSS distributions in the aortic arch of wild-type mice associate with lesion locations seen in diseased mice.Open acces

Blood flow simulations in the aortic arch in relation to haemodynamic wall shear stress and obesity-induced vascular changes

Introduction The aorta is the largest artery in the human body, with a complex geometry and flow dynamics. Locations of arterial curvature and bifurcation are known to be prone to endothelial dysfunction, one of the early biological markers for atherosclerotic lesions that underlie most cardiovascular diseases [1]-[2]. However, the influence of local anatomical and haemodynamic factors, such as wall shear stress (WSS), on lesion development is not well established [3]. This is particularly relevant to conditions of obesity, which is believed to accelerate the initiation and progression of vascular changes, and may be associated with vascular remodelling, inducing increased vessel diameters and wall thickness [4]. In this study, we hypothesize normal and obesity-altered arterial conditions to investigate the effect of a range of anatomical and flow parameters on the haemodynamic environment. To that end, we utilised 3D computational fluid dynamic (CFD) modelling methods; such methods have become an essential tool in the study of cardiovascular diseases and can be indirectly incorporated into clinical practice by improving our understanding of the underlying mechanisms of such diseases. Methods Simplified three-dimensional aortic arch geometries were created using the ANSA pre-processor (BETA CAE Systems), while numerical simulations were performed with the open source platform OpenFOAM®, using physiological parameters adopted from the literature [5]. Preliminary results consider both steady and timedependent (pulsatile) flow for the solution of the incompressible Newtonian Navier-Stokes equations. The boundary conditions studied include different inlet profiles with both steady and pulsatile flow. Computational fluid dynamic analysis focussed on the variance of flow parameters, specifically velocity, pressure, and wall shear stress, for the different boundary conditions. Results & Discussion The results demonstrate the importance of normal and obesity-altered arterial conditions for aortic arch models. The branch flow splits in both steady-state and unsteady calculations influence the shear stresses developed on the aortic wall. Time-dependent metrics such as the time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI), indicate locations of disturbed flow. Conclusion In this work, simulations were conducted on simplified aortic arch configurations for various boundary conditions that could quantify the impact of such parameters and find associations with early signs of vascular changes in obese patients. The future direction of this work is to improve the accuracy of the simulations by implementing more complex boundary conditions, namely the windkessel model to account for the resistance and capacitance of peripheral arteries. The investigation will then be extended to patient-specific aortic models to confirm the results of this work. Acknowledgments This work is supported in part from the University of Strathclyde Research Studentship Scheme (SRSS) Student Excellence Awards (SEA) Project No 1619, and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 749185. References 1. Caro C., Fitz-Gerald J., Schroter R. Proceedings of the Royal Society of London Series B 1971; 177(46):109-159. 2. M. E. DeBakey, G. M. Lawrie, and D. H. Glaeser. Annals of Surgery 1985; 201(2): 115–131. 3. Kazakidi A, Sherwin SJ, Weinberg PD. J R Soc Interface 2009; 6(35):539-548 4. Wildman RP. et al. Diabetes Care 2004; 27(12):2997-2999. 5. Vasava P. et al., Comput Math Methods Med. 2012; 861837

Blood flow simulations in the human aortic arch in relation to obesity

The global obesity epidemic is worsening with 10% of the world’s population now classified as obese [1]. In 2015, obesity contributed to 4 million deaths globally, 41% of which were due to cardiovascular disease. The healthy human aorta has a complex anatomy often associated with disturbed flow dynamics, while in obese individuals structural and functional changes to the cardiovascular system lead to abnormal aortic function [2]. Such changes are also associated with coronary artery disease, hypertension, and diabetes; disorders which themselves are thought to be accelerated by obesity. In this study, we utilised computational fluid dynamic (CFD) methods to examine various haemodynamic parameters, namely blood flow velocity, blood pressure, and wall shear stress (WSS), in the aortic arch and proximal branches. Two idealised three-dimensional geometries of the human aortic arch, based on anatomically-correct data from two different patient groups [3], were created using the ANSA pre-processor (BETA CAE Systems). A mesh independence study was completed to determine the optimum number of elements for the geometries. CFD simulations were performed in the open-source library OpenFOAM®, with the material properties of the working fluid, blood, in accordance with current literature [4]. Preliminary results considered both steady and time-dependent (pulsatile) flow for the solution of the incompressible Newtonian Navier-Stokes equations. The initial focus of the flow analysis was on the distribution of wall shear stress. Flow patterns observed for both models showed regions of considerable flow disturbance. The results demonstrate low shear stresses at locations on the aortic wall which are known to be susceptible to the development of atherosclerotic plaques. Blood flow parameters are significantly affected by the local anatomy of the aortic arch, highlighting important differences between the two models. The future direction of this work is to improve the accuracy of the simulations by implementing more complex boundary conditions. The investigation will then be extended to patient-specific aortic models to confirm the results of this work

Computational mechanics in pediatric medicine : an overview

From foetuses, to newborns, to children and adolescents there is a large number of pediatric patients in need of computational strategies to improve the treatment of their conditions. In fact, the pediatric age is characterized by very rapid and sudden changes, which make it extremely difficult to test standardized paradigms of care. In turn, this makes pediatric treatments highly personalized, especially when it comes to surgeries and prosthetics. While on the one hand there is the difficulty of conducting wide clinical trials on large patient populations for each stage of growth and development, especially when it comes to rare congenital disease; on the other hand there is the need to treat these conditions as soon as possible, sometimes even in the womb, to ensure a good quality of life in these subjects. The growing use of computational mechanics as patient-specific predictive tools for adult treatments has spurred interest in engineers, researchers and physicians for the use of computational methods in predicting the outcome of highly personalized pediatric treatments, for which the need of prognostic tools is high and vital. The translation of established computational methods used in adults to pediatric patients has its own challenges, from the lack of high-quality images, as children are often spared CT-scans and X-rays, to the need of an accurate predictions in very rapid times. In this minisymposium we aim to explore the state of the art of this novel, interdisciplinary area of application of computational mechanics, continuing the success of a similar minisymposium in WCCM18. Therefore, it will include a review of the computational strategies applied to pediatric care: from fluid dynamic models applied to the identification of the best surgeries to correct congenital heart defect, to biomechanical computational approaches to assess growth in children, to numerical models of fetal development, to simulations of pediatric medical device treatments. The outcome of this minisymposium will be a productive gathering of minds, where experts from different areas of pediatric computational mechanics will gather together and exchange thoughts on strategies to overcome the challenges of this area of study and ideas to further the application of computational mechanics as a clinical tool for pediatric medicine

Investigating the role of haematocrit in foetal circulation : a multi-compartment lumped parameter model

Foetal circulation is a complex system that differs from the corresponding neonatal and adult system. Current understanding of the foetal haemodynamics is limited1, while the role of haematocrit at different gestational ages has not yet been investigated extensively. Computational models can aid elucidate circulation haemodynamics2. To this end, this contribution proposes a multi-compartment lumped parameter model of the foetal circulatory system to investigate the effect of haematocrit variations on the systemic arterial flow

Fluid-structure interaction simulation of flow-mediated dilation of a straight arterial conduit

Introduction Flow-mediated dilation (FMD) is a key non-invasive clinical assessment of endothelial dysfunction, an indicator of early atherosclerosis and cardiovascular diseases. FMD involves the measurement of an artery dilation, e.g. of the brachial, radial, femoral, or popliteal artery, induced by transient hyperaemia, following a temporary ischemic occlusion of a distal arterial segment. Such transient conditions, however, may also involve changes in the wall shear stress (WSS), blood pressure, and wall stiffness which have not been clearly established in relation to early vascular changes. This work aims to clarify the role of these flow-related mechanisms by investigating the haemodynamic environment of a straight arterial conduit with compliant walls during FMD. Methods By implementing a strongly-coupled fluid-structure interaction (FSI) solver within the open-source OpenFOAMextend library [1], the arterial vessel was modelled as a quarter cylinder with an in-vivo measured hyperaemic inflow condition (by [2]). The FSI solver follows a partitioned approach with separated solvers for fluid and structure, and an implicit coupling method between fluid and solid, with interface values being passed from one solver to the other. The solution of the fluid flow is based on the finite volume method (FVM), while the solid is solved by a Lagrangian FVM solver. The mesh motion for both the fluid and the solid, due to the interface displacement, is updated at every timestep using a dynamic mesh solver in OpenFOAM based on the Laplace equation discretisation. Prior examples of FSI simulations in OpenFOAM and the foam-extend project have demonstrated its use for cardiovascular flows [3]. Results & Discussion The results demonstrate the diameter change during FMD, while haemodynamic shear stresses and pressure values are also analysed. Current results are being used for correlating the displacement of the arterial walls and the prescribed in-vivo inlet velocity. Conclusion The methodology has been established for subsequent simulations. Future work will investigate the FMD in idealised and anatomically-correct bifurcated arterial models with prescribed ischemic occlusion of the distal branching arteries. It will also include the investigation of further haemodynamic metrics, such as the timeaveraged wall shear stress, the oscillatory shear index, and the transverse WSS, in comparison with in-vivo data. Acknowledgments This work is supported in part from the University of Strathclyde International Strategic Partner (ISP) Research Studentships, and the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 749185. References 1. Extend-Project (2018) The foam-extend. https://sourceforge.net/projects/foam-extend/ 2. van Bussel, FCG et al. A control systems approach to quantify wall shear stress normalization by flowmediated dilation in the brachial artery. PloS one (2015) 10:e0115977 3. Tukovic, Zeljko, Karaˇc, Aleksandar, Cardiff, Philip, Jasak, Hrvoje and Ivankovic, Alojz. (2018). OpenFOAM Finite Volume Solver for Fluid-Solid Interaction. Transactions of FA- MENA. 42. 1-31. 10.21278/TOF.42301

Octopus-inspired multi-arm robotic swimming

The outstanding locomotor and manipulation characteristics of the octopus have recently inspired the development, by our group, of multi-functional robotic swimmers, featuring both manipulation and locomotion capabilities, which could be of significant engineering interest in underwater applications. During its little-studied arm-swimming behavior, as opposed to the better known jetting via the siphon, the animal appears to generate considerable propulsive thrust and rapid acceleration, predominantly employing movements of its arms. In this work, we capture the fundamental characteristics of the corresponding complex pattern of arm motion by a sculling profile, involving a fast power stroke and a slow recovery stroke. We investigate the propulsive capabilities of a multi-arm robotic system under various swimming gaits, namely patterns of arm coordination, which achieve the generation of forward, as well as backward, propulsion and turning. A lumped-element model of the robotic swimmer, which considers arm compliance and the interaction with the aquatic environment, was used to study the characteristics of these gaits, the effect of various kinematic parameters on propulsion, and the generation of complex trajectories. This investigation focuses on relatively high-stiffness arms. Experiments employing a compliant-body robotic prototype swimmer with eight compliant arms, all made of polyurethane, inside a water tank, successfully demonstrated this novel mode of underwater propulsion. Speeds of up to 0.26 body lengths per second (approximately 100 mm s(-1)), and propulsive forces of up to 3.5 N were achieved, with a non-dimensional cost of transport of 1.42 with all eight arms and of 0.9 with only two active arms. The experiments confirmed the computational results and verified the multi-arm maneuverability and simultaneous object grasping capability of such systems

A computational fluid dynamic investigation of the obesity-altered hemodynamics in children and adolescents

Childhood obesity has become one of the major challenges of our century, taking epidemic proportions. Obesity, mainly a dietary disease, is known to advance endothelial dysfunction [1], an early sign of atherosclerotic lesions underling most cardiovascular diseases. Endothelial damage in high-risk paediatric patients can be clinically assessed with measurements of the aortic and carotid intima-media thickness (IMT), and flow-mediated dilatation (FMD) of the brachial, radial, and femoral arteries [2]. However, it is not yet clear how the haemodynamic environment is altered in this particular group of patients and which flow-related mechanisms contribute to early vascular changes. This work will discuss a computational model of an arterial conduit with compliant walls during FDM that attempts to clarify some of these aspects. Solutions to the time-dependent, incompressible Navier-Stokes equations are based on high-fidelity finite volume and hybrid Cartesian/immersed-boundary (HCIB) methods [3] that overcome several of the shortcomings of conventional computational fluid dynamic methods and provide increased spatial flow analysis. The codes have previously been validated and used extensively in various applications. Implementation of wall motion is particularly easy with HCIB methods, which are inherently capable of handling arbitrarily large body motions and allow for effective solutions of wall configuration. The model provides an evaluation of the haemodynamic shear stresses, a common indicator of early atherosclerotic lesion localisation. Future work will include multi-scale modelling that combines highresolution 3D blood flow computations, with macroscopic and microscopic features of the vascular environment. Further haemodynamic metrics, such as the time-averaged wall shear stress (TAWSS), the oscillatory shear index (OSI), and the transverse WSS will also be assessed, in conjunction with patient data