CFD Analysis of Pulsatile Flow and Non-Newtonian Behavior of Blood in Arteries

CFD analysis plays an important role in the area of analysis of blood flow as in-vivo measurements of blood flow is costly and easily not accessible. This paper presents simulation of blood flow in healthy and stenosed coronary artery 2- D models. The simulation was done considering non-Newtonian behavior of blood and pulsatile nature of blood flow which is close to physical scenario. Pressure distribution, velocity distribution and wall shear were examined to understand their effect on Atherosclerosis.     

Non-Newtonian Blood Flow in Left Coronary Arteries with Varying Stenosis: A Comparative Study

This paper presents Computational fluid dynamic (CFD) analysis of blood flow in three different 3-D models of left coronary artery (LCA). A comparative study of flow parameters (pressure distribution, velocity distribution and wall shear stress) in each of the models is done for a non-Newtonian (Carreau) as well as the Newtonian nature of blood viscosity over a complete cardiac cycle. The difference between these two types of behavior of blood is studied for both transient and steady states of flow. Additionally, flow parameters are compared for steady and transient boundary conditions considering blood as non-Newtonian fluid. The study shows that the highest wall shear stress (WSS), velocity and pressure are found in artery having stenosis in all the three branches of LCA. The use of Newtonian blood model is a good approximation for steady as well as transient blood flow boundary conditions if shear rate is above 100 s-1. However, the assumption of steady blood flow results in underestimating the values of flow parameters such as wall shear stress, pressure and velocity.     

A Mathematical Study on Three Layered Oscillatory Blood Flow Through Stenosed Arteries

A mathematical model is constructed to examine the characteristics of three layered blood flow through the oscillatory cylindrical tube (stenosed arteries).The proposed model basically consists three layers of blood (viscous fluids with different viscosities) named as core layer (red blood cells),intermediate layer (platelets/white blood cells) and peripheral layer (plasma).The analysis was restricted to propagation of small-amplitude harmonic waves,generated due to blood flow whose wave length is larger compared to the radius of the arterial segment.The impacts of viscosity of fluid in peripheral layer and intermediate layer on the interfaces,average flow rate,mechanical efficiency,trapping and reflux are discussed with the help of numerical and computational results.This model is the generalized form of the preceding models.On the basis of present discussion,it is found that the size of intermediate and peripheral layers reduces in expanded region and enhances in contracted region with the increasing viscosity of fluid in peripheral layer,whereas,opposite effect is observed for viscosity of fluid in intermediate layer.Final conclusion is that the average flow rate and mechanical efficiency increase with the increasing viscosity of fluid in both layers,however,the effects of the viscosity of fluid in both layers on trapping and reflux are opposite to each other.     

Robustness of Oscillatory Behavior in Correlated Networks

Understanding network robustness against failures of network units is useful for preventing large-scale breakdowns and damages in real-world networked systems. The tolerance of networked systems whose functions are maintained by collective dynamical behavior of the network units has recently been analyzed in the framework called dynamical robustness of complex networks. The effect of network structure on the dynamical robustness has been examined with various types of network topology, but the role of network assortativity, or degree–degree correlations, is still unclear. Here we study the dynamical robustness of correlated (assortative and disassortative) networks consisting of diffusively coupled oscillators. Numerical analyses for the correlated networks with Poisson and power-law degree distributions show that network assortativity enhances the dynamical robustness of the oscillator networks but the impact of network disassortativity depends on the detailed network connectivity. Furthermore, we theoretically analyze the dynamical robustness of correlated bimodal networks with two-peak degree distributions and show the positive impact of the network assortativity.     

A Stochastic Model of Oscillatory Blood Testosterone Levels

A continuous-time, discrete-state stochastic model of testosterone secretion in men is considered. Blood levels of testosterone in men fluctuate periodically with a period of 2–3 h. The deterministic model, on which the stochastic model considered here is based, is well studied and has been shown to have a globally stable fixed point. Thus, no sustained oscillations are possible in the deterministic case. However, the stochastic model does observe periodic, pulsatile behavior. This demonstrates how oscillations can occur due to a switching behavior dependent on the random degradation of testosterone molecules in the system. The Gillespie algorithm is used to simulate the hormone secretion model. Important parameters of the model are discussed and results from the model are compared to experimental observations.     

Flow Loading Induces Oscillatory Trajectories in a Bloodstream Parasite

The dynamics of isolated microswimmers are studied in bounded flow using the African trypanosome, a unicellular parasite, as the model organism. With the help of a microfluidics platform, cells are subjected to flow and found to follow an oscillatory path that is well fit by a sine wave. The frequency and amplitudes of the oscillatory trajectories are dependent on the flow velocity and cell orientation. When traveling in such a manner, trypanosomes orient upstream while downstream-facing cells tumble within the same streamline. A comparison with immotile trypanosomes demonstrates that self-propulsion is essential to the trajectories of trypanosomes even at flow velocities up to ～40 times higher than their own swimming speed. These studies reveal important swimming dynamics that may be generally pertinent to the transport of microswimmers in flow and may be relevant to microbial pathogenesis.     

酒精酵母在连续发酵中的振荡行为研究

初步分析酒精酵母在连续发酵中的振荡行为的产生条件及产生机理。通过改变稀释率、pH值、溶氧和进料葡萄糖浓度等条件 ,观察不同操作条件对酒精酵母菌生长和代谢行为的影响。在 10～ 15 g/L的较低葡萄糖浓度 ,0 .10～ 0 .2 0h-1的较低稀释率 ,以及 70 %左右的适度的溶氧浓度等发酵条件下 ,酒精酵母会出现同步的代谢振荡现象。一定条件下 ,菌体浓度处于振荡状态 ,残余葡萄糖浓度不可测或在很低水平振荡 ,这些发现预示着控制机制的新发展。     

A Model of Oscillatory Blood Cell Counts in Chronic Myelogenous Leukaemia

In certain blood diseases, oscillations are found in blood cell counts. Particularly, such oscillations are sometimes found in chronic myelogenous leukaemia, and then occur in all the derived blood cell types: red blood cells, white blood cells, and platelets. It has been suggested that such oscillations arise because of an instability in the pluri-potential stem cell population, associated with its regulatory control system. In this paper, we consider how such oscillations can arise in a model of competition between normal (S) and genetically altered abnormal (A) stem cells, as the latter population grows at the expense of the former. We use an analytic model of long period oscillations to describe regions of oscillatory behaviour in the S–A phase plane, and give parametric criteria to describe when such oscillations will occur. We also describe a mechanism which can explain dynamically how the transformation from chronic phase to acute phase and blast crisis can occur.     

含阻尼项二阶泛函差分方程的振动性质

从解的渐近状态入手,应用分类讨论方法和Raccati技巧,讨论了一类广泛的二阶泛函差分方程解的振动性与非振动性,建立了四个新的振动性定理,推广并改进了已有文献中的相关结果.     

高阶线性泛函方程解的振动性

考虑一类高阶线性泛函方程解的振动性,我们获得一些新的振动准则.这些振动准则,推广或改进了一些文献中的某些结果.     

The Role of Actin Cytoskeletal Tension in Oscillatory Fluid Flow Induced Osteogenesis

This article has no abstract.     

微生物细胞连续培养过程中振荡和混沌行为的研究进展

本文对微生物细胞连续培养过程中产生振荡现象的条件,影响振荡特征（振幅和周期）的因素,振荡机理的研究和振荡行为的应用等进行了全面的论述,并指出了振荡研究的发展方向。