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1

Correlation analysis of vertical total electron content

Arslan N.

Acta Geophysica

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2011

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Vol. 59, no. 2

377-397

EN

It is necessary to model and analyze the ionospheric effects due to a direct relationship between Global Positioning System (GPS) applications and changes in the ionosphere. In order to monitor these changes, the ionosphere can be represented by the vertical total electron content (VTEC) which can be used to analyze ionospheric conditions from a variety of stations. In this study, 21 stations were used to carry out analysis and estimation of VTEC. Three days during a geomagnetic storm, namely, 7, 8, and 9 January 2005, are chosen for investigation. In addition, the de-correlation time of the VTEC was estimated to define ionospheric variations in time using autocorrelation analysis. The de-correlation time of the ionosphere is based on correlation times estimated by using autocorrelation functions. From the high-latitude stations, the mean of the correlation times decreased from 8 to 6 epochs during a storm. In this time period, it was found from the station results that the ionosphere was more affected at the high-latitude than at the mid-latitude region.

2

Steady and disturbed flow effects on human umbilical vein endothelial cells (HUVECs) in vascular system: an experimental study

Arslan N., Isik S., Uykan O.

Acta of Bioengineering and Biomechanics

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2010

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Vol. 12, no. 4

3-9

EN

Coronary artery disease is still one of the most important reasons of the death in the world. The endothelium is the membrane of special cells which lines the interior surface of blood vessels forming an interface between circulating blood in the lumen and the rest of the vessel wall. Endothelial cells (ECs) line the entire circulatory system, from the heart to the smallest capillary. ECs dysfunction has been linked with atherosclerosis through their response to fluid forces. ECs change their morphology when exposed to mechanical stresses. The morphological responses include reorientation, elongation, and rearrangement of adhering molecules. Atherosclerotic lesions are formed in specific arterial regions, where low and oscillatory endothelial shear stress (ESS) occur. In this study, the effects of steady and disturbed flow over human umbilical vein endothelial cells (HUVECs) at different flow rates and periods were determined. Steady flow experiments were performed at flow rate of 1000 cm3/min for twenty four hours. Disturbed flow experiments simulating the flow in branching regions of arterial systems were carried out at flow rates of 250 cm3/min for five hours. The results obtained testified to the morphological changes easily observed. The directional alignment of the cells was determined in the steady flow experiments. Under disturbed flow conditions we observed not only the cell movement at the stagnation point but also the polygonal cell shape downstream the flow field.

3

Mathematical analysis of the flow over endothelial glycocalyx

Arslan N.

International Journal of Applied Mechanics and Engineering

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2007

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Vol. 12, no 4

1165-1171

EN

Mathematical modeling of the flow over the glycocalyx located on the endothelial cells (EC) was investigated. Flow regions are considered as a core flow region which is the flow in the lumen of the vessel which are simiIar flow to the Poiseuille flow inside the straight pipe and the flow over the glycocalyx located on the EC which are considered as flow through the porous media. Solutions were found in both regions and also wall shear stresses (WSS) and drag forces were calculated.