• Journal of computational fluids engineering
• /
• v.9 no.4
• /
• pp.20-33
• /
• 2004

In this study a stretching-mapping method is proposed for calculating the materials' stretching exponents, which are to be used in quantification of the mixing effect. In this method, the mapping tensor associated with the deformation of each fluid material is first obtained. Then deformations of a lot of materials are obtained by applying the mapping tensor. The local stretching rates and their space-average values are next computed with the mapped deformations. Application to a simple time-periodic flow within a cavity shows that the method is indeed effective compared with the conventional method; i.e. the mapping method is fast and yields the same results as the conventional one.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.04a
• /
• pp.1-13
• /
• 2005

Fluid flows within microchannels are characterized by low Reynolds numbers. Therefore the effect of mixing is a crucial factor in design of the channels. Since the action of the electro-osmotic or magnetic forces used in the mixing enhancement is usually periodic in the three-dimensional channel configuration, use of the various concepts of chaotic advection is reasonable in the quantification of the stirring effect. In this paper, the details of the method of material-stretching mapping is explained. The actual application of the method to the screw extruder is also presented.

• Journal of computational fluids engineering
• /
• v.9 no.4
• /
• pp.55-63
• /
• 2004

The three-dimensional Stokes flow within a staggered screw channel is obtained by using a finite volume method. The geometry is intended to mimic the single screw extruder having staggered arrangement of flights. The flow solution is then subjected to the analysis of the stirring performance. In the analysis of the stirring performance, the stretching-mapping method developed by the author is employed for calculating the materials' stretching exponents, which are to be used in quantification of the mixing effect. The numerical results Indicate that the staggered geometry gives indeed far much better stirring-performance than the standard (nonstaggered) flight geometry. It was also shown that care must be given to the selection of the basis planes for evaluating the local stretching rate, and it turns out that the best method (H-method) has its basis plane just on the half way between the past and future evolution of fluid particles subjected to the defromation. In evaluating the stretching exponent, the expansion ratio must be considered which is one of the characteristic differences of the actual three-dimensional flows from the two-dimensionmal counterparts. The larger axial pressure-difference causes in general the smaller stirring performance while the flow rate is increased. The smaller channel length also increases the stirring performance.

• Childhood Kidney Diseases
• /
• v.5 no.2
• /
• pp.188-195
• /
• 2001

Type II membranoproliferative glomerulonephritis (Dense deposit disease) is an acquired primary glomerular disease characterized by electron microscopic evidence of a continuous dense membrane deposition replacing the lamina densa. It is a subtype of idiopathic membra- noproliferative glomerulonephritis, and was described as a separate entity by Berger and Galle in 1963. It frequently occurs in older chilren and young adults and the clinical course is variable, but is generally progressive. The presenting feature is nephrotic syndrome in many patients, and proteinuria and hematuria are also seen frequently. The purpose of this paper is to present a case of DDD (Dense deposit disease) from a 10 year old boy who was diagnosed as a acute poststreptococcal glomurulonephritis with protenuria, hematuria, and facial edema by renal biopsy 4 years ago. (J, Korean Soc Pediatr Nephrol 2001 ; 5 : 188-95)

• Childhood Kidney Diseases
• /
• v.2 no.2
• /
• pp.138-144
• /
• 1998

Purpose : The use of cyclosporine and mitomycin in various immunologic or neoplastic disorders has been known to cause wide-ranged nephrotoxic effects including thrombotic microangiopathy. However, the mechanism of nephrotoxicity of these drugs has not been studied adequately, so that present experimental study has been undertaken to find out whether these drugs can cause direct damage to the kidney and to clarify the pathogenetic mechanism of nephrotoxic effect of these drugs. Materials and methods : Sprague-Dawley rats weighing 250-300 gm were used for experimental animals and unilateral renal perfusion technique, modified from the method described by Hoyer et al was used. Isolation of left kidney from systemic circulation was made by clamping aorta and left renal vein and a hole was punctured in the anterior wall of the left renal vein. Cyclosporine (2.5 mg in 4 ml solution) and mitomycin (1.6 mg in 4ml solution) were infused through left renal artery and normal saline was used in control rats. Forty-eight hours after infusion of the drugs, animals were sacrificed and left kidney removed and processed for histologic examination. Total ischemic time of left kidney was less than 15 minutes: Results : Cyclosporine-perfused group showed severe swelling of glomerular endothelial ceil along with swelling of glomerular epithelial cell and interstitial vascular endothelial cell. Mitomycin-perfused group also showed severe swelling of glomerular endothelial and epithelial cells. And in addition to these findings, they demonstrated platelets aggregation, swelling and degranulation of platelets and fibrin accumulation in some of the capillaries, indicating occurrance of thrombotic microangiopathy. Conclusion : present experiment indicates that cyclosporine and mitomycin can cause direct toxic injury to renal endothelial cell. And this direct toxic damage to endothelial cell seems to be an important initiating event for the development of thrombotic microangiopathy.

• Childhood Kidney Diseases
• /
• v.18 no.1
• /
• pp.36-41
• /
• 2014

Purpose: Urinary tract infections (UTIs) are the most common source of bacterial infections in infants and young children. Accurate diagnosis and treatment is important because of their association with renal scarring, which can lead to complications. Urine endothelin-1 (ET-1) is the major renal isoform produced and released by renal mesangial cells in response to glomerular injury. This study aimed to investigate whether urinary levels of ET-1 can be used as a biomarker for UTI diagnosis. Method: We conducted a prospective study using medical records of 70 patients below the age of 18 years, who visited Chung-Ang University Hospital from July 2012 to July 2013. We classified the patients into the UTI and control groups based on urine culture studies. The UTI group was further divided into upper and lower UTI groups using 99m-Technetium dimercaptosuccinic acid scintigraphy. Urine ET-1 was measured using enzyme linked immunosorbent assay with 0.3 mL urine. Results: The UTI and control groups were comprised of 45 and 25 patients, respectively. Mean urine ET-1 levels were significantly higher in the UTI group than in the control group ($1.41{\pm}0.35$ pg/mL vs. $0.33{\pm}0.07$ pg/mL, P =0.04). There was no significance difference in the quantitative value between the upper and lower UTI groups (P =0.552). There was no correlation between urine ET-1 and serum C-reactive protein (Pearson correlation [R]=0.24), urine ET-1 and serum white blood cell count (R=0.19). Conclusion: Our study suggests that urine ET-1 can be used for early diagnosis of UTI in children.