A novel framework for fluid/structure interaction in rapid subjectspecific simulations of blood flow in coronary artery bifurcations

Background/Aim. Practical difficulties, particularly long model development time, have limited the types and applicability of computational fluid dynamics simulations in numerical modeling of blood flow in serial manner. In these simulations, the most revealing flow parameters are the endothelial shear stress distribution and oscillatory shear index. The aim of this study was analyze their role in the diagnosis of the occurrence and prognosis of plaque development in coronary artery bifurcations. Methods. We developed a novel modeling technique for rapid cardiovascular hemodynamic simulations taking into account interactions between fluid domain (blood) and solid domain (artery wall). Two numerical models that represent the observed subdomains of an arbitrary patient-specific coronary artery bifurcation were created using multi-slice computed tomography (MSCT) coronagraphy and ultrasound measurements of blood velocity. Coronary flow using an in-house finite element solver PAK-FS was solved. Results. Overall behavior of coronary artery bifurcation during one cardiac cycle is described by: velocity, pressure, endothelial shear stress, oscillatory shear index, stress in arterial wall and nodal displacements. The places where (a) endothelial shear stress is less than 1.5, and (b) oscillatory shear index is very small (close or equal to 0) are prone to plaque genesis. Conclusion. Finite element simulation of fluid-structure interaction was used to investigate patient-specific flow dynamics and wall mechanics at coronary artery bifurcations. Simulation model revealed that lateral walls of the main branch and lateral walls distal to the carina are exposed to low endothelial shear stress which is a predilection site for development of atherosclerosis. This conclusion is confirmed by the low values of oscillatory shear index in those places

Computational investigations of copper oxides for solar cell applications

Photovoltaic (PV) technology which makes use of the superabundant and freely available Sun’s energy to generate electricity has obvious economic, environmental and societal benefits. However, to achieve significant market penetration PV devices have to be efficient and composed of cheap and readily available material. Semiconducting copper oxide compounds are formed from comparatively inexpensive and non-toxic elements, emerge in abundant quantities, demonstrate ease of fabrication and are environmentally friendly – which makes them attractive for large-scale PV applications. Using quantum mechanical theoretical calculations based on density functional theory (DFT), distinct copper oxide compounds were investigated to asses, quantify, revise and boost their overall PV potential. First, the search for a set of unique parameters that would describe all three oxides of copper (Cu2O, Cu4O3, and CuO) simultaneously at a desired accuracy was undertaken. On top of that, the usual metric, upon which PV absorbers are addressed as suitable or not, was extended in order to include simulated absorption spectra as well as selection rules besides the commonly employed electronic band gap value. Using a hybrid-DFT approach, first row transition metal extrinsic dopants were introduced substitutionally on the cation site in Cu2O. Furthermore, additional vacancies in the proximity of the dopant site were included in order to match the experimentally observed natural presence of copper vacancies. This has lead to an increase in the overall PV conversion efficiencies of Cu2O, which is one of the key factors when a material is sought for real time applications. The occurrence of intrinsic defects in a material was proven crucial for its longlasting and stable performance. After validating the computational parameters used within DFT against available experimental values for the ground state of CuO and Cu4O3, the energetics of intrinsic defects materializing in both compounds were found and proven to be in good agreement with available experimental data

Non-linear transient heat conduction analysis of insulation wall of tank for transportation of liquid aluminum

This paper deals with transient non-linear heat conduction through the insulation wall of the tank for transportation of liquid aluminum. Tanks designed for this purpose must satisfy certain requirements regarding temperature of loading and unloading, duringtransport. Basic theoretical equations are presented, which describe the problem of heat conduction finite element analysis, starting from the differential equation of energy balance, taking into account the initial and boundary conditions of the problem. General 3-D problem for heat conduction is considered, from which solutions for two- and one-dimensional heat conduction can be obtained, as special cases. Forming of the finite element matrices using Galerkin method is briefly described. The procedure for solving equations of energy balance is discussed, by methods of resolving iterative processes of non-linear transient heat conduction. Solution of this problem illustrates possibilities of PAK-T software package, such as materials properties, given as tabular data, or analytical functions. Software alsooffers the possibility to solve non-linear and transient problems with incremental methods. Obtained results for different thicknesses of the tank wall insulation materials enable its comparison in regards to given conditions

Modeling of thermoelectric module operation in inhomogeneous transient temperature field using finite element method

This paper is the result of research and operation modeling of the new systems for cooling of cutting tools based on thermoelectric module. A copper inlay with thermoelectric module on the back side was added to a standard turning tool for metal processing. For modeling and simulating the operation of thermoelectric module, finite element method was used as a method for successful solving the problems of inhomogeneous transient temperature field on the cutting tip of lathe knives. Developed mathematical model is implemented in the software package PAK-T through which numerical results are obtained. Experimental research was done in different conditions of thermoelectric module operation. Cooling of the hot module side was done by a heat exchanger based on fluid using automatic temperature regulator. After the calculation is done, numerical results are in good agreement with experimental. It can be concluded that developed mathe-matical model can be used successfully for modeling of cooling of cutting tools

Computer-Vision Unmanned Aerial Vehicle Detection System Using YOLOv8 Architectures

Abstract: This work aims to test the performance of the you only look once version 8 (YOLOv8) model for the problem of drone detection. Drones are very slightly regulated and standards need to be established. With a robust system for detecting drones the possibilities for regulating their usage are becoming realistic. Five different sizes of the model were tested to determine the best architecture size for this problem. The results indicate high performance across all models and that each model is to be used for a specific case. Smaller models are suited for lightweight system approaches where some false identification is tolerable, while the largest models are to be used with stationary systems that require the best precision

Tuning the electronic band gap of Cu2O via transition metal doping for improved photovoltaic applications

Cu 2 O is a widely known p -type semiconductor with a band-gap value suitable for photovoltaic applications. However, due to its parity-forbidden nature of the first interband transition and high carrier recombination currents, Cu 2 O has failed to reach commercial application. Hybrid density functional theory has been used to study the effect of transition metal dopants on the electronic and optical properties of Cu 2 O . Substitutional transition metal dopants, incorporated on the copper site, allow band-gap tunability by creating a range of defect states in the electronic structure, from shallow levels to deep intermediate bands. The preferred position of the dopants is in the vicinity of copper vacancies, which are naturally found in Cu 2 O and are responsible for its p -type conductivity. Impurity levels created via extrinsic transition metal dopants increase substantially the capacity of Cu 2 O to absorb light, reaching values close to 10%. First row transition metal dopants thus show potential for considerable improvement of the overall photovoltaic performance of Cu 2 O

Comparative Analysis of SPH and FVM Numerical Simulations of Bloodflow through Left Ventricle

The purpose of this research was to compare blood flow modeling inside the heart’s left ventricle using commercial smoothed particle hydrodynamics (SPH) and finite volume method (FVM) solvers. These two methods are both based on continuum mechanics, and while FVM uses Eulerian material framework, SPH uses a Lagrangian formulation. In this study, the focus was only on CFD analysis of blood flow through the left ventricle using the two mentioned methods. Therefore, in the numerical analysis using FVM, walls were modeled as boundary conditions where fluid velocity was set to zero. The ventricle wall in the SPH was modeled using larger, fixed fluid particles, so at this point, there is no need for a specific contact definition. LS-DYNA software was used for modeling the left ventricle using the SPH method. In order to generate realistic fluid flow injection particles at the mitral valve and deactivation planes at the aortic semilunar valve were used where particle velocity was defined by time functions. Ansys Fluent software was used for modeling the left ventricle using FVM, within which a finite volume mesh was generated. Velocities at the inlet and outlet of the model are defined by functions using User Defined Function (UDF) so that the fluid flow corresponds to the realistic blood flow through the left ventricle. The results obtained by FVM were used as a verification of the results obtained using the SPH method. In the results section of the paper, the velocity field obtained by SPH and FVM methods is shown and compared. SPH offers greater possibilities to study FSI phenomena like the effects of wall deformations, or tracking the movement of solid particle inclusion, all within the single numerical domain. On the other hand, it requires elaborate contact definition, and prolonged analysis time in comparison to the finite volume CFD analysis.Publishe

Experimental and Numerical Strength Analysis of Wagon for Transporting Bulk Material

This paper presents comparative experimental and numerical strength analysis of wagon for transporting bulk material according to the TSI standard and norm EN 12663:2000. The aim of this analysis is to show that results of stresses obtained by measuring with strain gauges and stresses obtained by FEM calculation gives good agreement. Based on the results and their good match, it can be concluded that the numerical FEM analysis can be reliably used for structural analysis. According to this fact, FEM analysis can reduce number of the testing new products. This leads to great savings in the design of new prototypes, in order to immediately start the process of mass production. This would lead to significantly less cost of products.Publishe

Cytidine-5-diphosphocholine reduces microvascular permeability during experimental endotoxemia

Background: Microvascular permeability and leukocyte adhesion are pivotal mechanisms in sepsis pathophysiology contributing to the development of shock and mortality. No effective pharmacological therapy is currently available to restore microvascular barrier function in sepsis. Cholinergic mediators have been demonstrated to exert anti-inflammatory effects during inflammation. Cytidine-5-diphosphocholine (CDP-choline) is an extensively studied cholinergic drug due to its brain protective characteristics in cerebrovascular diseases. This study evaluated the effect of CDP-choline on microvascular permeability and leukocyte adhesion during endotoxemia. Methods: Macromolecular leakage, leukocyte adhesion, and venular wall shear rate were examined in mesenteric postcapillary venules of rats by using intravital microscopy (IVM). Lipopolysaccharide (LPS) (4 mg/kg/h) or equivalent volumes of saline were continuously infused following baseline IVM at 0 min. IVM was repeated after 60 and 120 min in endotoxemic and nonendotoxemic animals. CDP-choline (100 mg/kg) was applied as an i.v. bolus. Animals received either saline alone, CDP-choline alone, CDP-choline 10 min before or 30 min after LPS administration, or LPS alone. Due to nonparametric data distribution, Wilcoxon test and Dunn's multiple comparisons test were used for data analysis. Data were considered statistically significant at p < 0.05. Results: Treatment with LPS alone significantly increased microvascular permeability and leukocyte adhesion and decreased venular wall shear rate. CDP-choline significantly reduced microvascular permeability in animals treated with LPS. Leukocyte adhesion and venular wall shear rate were not affected by CDP-choline during endotoxemia. Conclusion: CDP-choline has a protective effect on microvascular barrier function during endotoxemia. Considering the excellent pharmacologic safety profile of CDP-choline, its use could be an approach for the treatment of capillary leakage in sepsis