This paper presents a computational study characterizing the swirl intensity distribution and Internal Recirculation zone (IRZ) formed in a cylindrical domain with tangential injections and isothermal flow. The range of inlet boundary conditions investigated is 5o to 25o for the injection angle and 7190 to 100711 for the bulk flow Reynolds number. The evolution of swirl intensity is presented with and without incorporating effects of the accompanying pressure variations. The Shear Stress Transport (SST) k-ω is used to model turbulence. Results show that the Swirl strength created by such tangential injections strongly depends on the injection angle but does not vary with bulk flow Reynolds number (Re), except for low Re values. The swirling flow is shown to result in IRZ formation at injection angles 6o and above or when asymptotic value of the maximum Swirl Number in the domain exceeds approximately 0. 6, same as the transition value of inlet Swirl Number in swirling flows with axial injections. The IRZ length increases with injection angle and varies with Re for lower values of Re at a given injection angle but asymptotes for higher values above 40000. The conventional Swirl Number rises rapidly downstream of the injection plane followed by a slow decline. On the other hand, an alternative Swirl Number, which incorporates the gauge pressure variation, shows slow and consistent decay all the way downstream of the injection plane. The Swirl Number incorporated with gauge pressure term subsumes interconversions between the axial momentum and pressure in the regions of vortex breakdown and IRZ formation, thereby presenting an alternative picture of swirl intensity evolution in swirling flows.

The dispersion of solid particles in zones of turbulent Recirculation flow is of interest in various technological applications. Many experimental studies have been developed in order to know the contribution of Stokes numbers and mean drift parameter on the entering and dispersion of particles in the Recirculation zone however to our knowledge there are not numerical studies reported about it. In this work, we made a numerical study of the incompressible turbulent flow laden with solid particles in sudden expansion pipes with different expansion ratios and different Reynolds number upstream of the pipe, using LES and Germano dynamic model with JetCode program for the continuous phase (air). The solid particles movement (different diameters were considered) was solved by using a Lagrangian tracking algorithm coupled to JetCode taking into account only drag and gravity forces supposing one way coupling. Finally, we calculated Stokes numbers based on the different fluid time scales and the mean drift parameter for all the solved cases and studied their isolated effect on the solid particle dispersion in the Recirculation zones by computing the concentration by means of the particle number within the Recirculation zones. Our results coincided with the experimental findings reported by others authors: the particle concentration exhibits a maximum value as the Reynolds number upstream in the pipe is decreased, the pipe expansion ratio is increased and particle size is decreased. Regarding the results obtained numerically about the solid particle dispersion within turbulent Recirculation zones in terms of Stokes numbers and the mean drift parameters, coincided adequately with the experimental results.

Dear Editor: Recently, with great interest we read the review article by Zeraati et al. entitled "A review article: access Recirculation among end stage renal disease patients undergoing maintenance hemodialysis" in your most valuable journal. The author summarized some of observations about causes and clinical significance of arteriovenous (AV) fistula Recirculation, techniques for accurate assessment and main source of pitfall in calculation of access Recirculation (AR). Hemodialysis AR occurs when the blood urea concentration in arterial line is lower than that of systemic circulation, indicating that dialyzed blood returning through the venous needle reenters the HD machine through the arterial needle.

In order to study biozones of the Pabdeh Formation in the Northeast Kazerun, Murdak section was selected. In this section, Pabdeh Formation is mainly consists of marl, shale and marly limestone. The study of calcareous nannofossils led to the recognition of 70 species and 28 genera. According to the first and last occurrence of index species and assemblages fossil, the following biozones based on global standard zonations are identified: Discoaster multiradiatus zone (NP9/ CNP11), Tribrachiatus contortus zone (NP10/ CNE1-CNE2), Discoaster binodosus zone (NP11/ CNE3), Tribrachiatus orthostylus zone (NP12/ CNE4), Discoaster lodoensis zone (NP13/ CNE5), Discoaster sunlodoensis zone (NP14/ CNE6-CNE8), Nannotetrina fulgens zone (NP15/ CNE9-CNE11), Discoaster tanii nodifer zone (NP16/ CNE12-CNE15), Discoaster saipanensis zone (NP17/ CNE15-CNE16), Chiasmolithus oamaruensis zone (NP18/ CNE17-CNE18), Isthmolithus recurvus zone (NP19/ CNE18-CNE19), Sphenolithus pseudoradians zone (NP20/ CNE20), Ericsonia Subdisticha zone (NP21/ CNE21-CNO1), Helicosphaera reticulate zone (NP22/ CNO2), Sphenolithus predistintus zone (NP23/ CNO3-CNO4). As a result of this study and based on the obtained biozones, the age of Pabdeh Formation in Murdak section, is Late Paleocene (Thanetian) to Oligocene (Rupelian-Chatian).

Background and Objective: Degeneration of neurons in the central nervous system occurs during aging. Transplantation of neural stem cells (NSCs) can be preventing the degeneration of neurons. In addition to neuronal replacement, with the production of neurotrophic factors, increased survival and proliferation of endogenous cells. This study was done to compare the cell proliferation, neurotrophic factors expression and features of NSCs harvested from different areas of the central nervous system in vitro.Materials and Methods: In this laboratory study NSCs have been harvested from subgranular zone (SGZ), subventricular zone (SVZ) and central canal of spinal cord from adult Wistar rats with mechanical, enzymatical digestion and subsequently was cultured in α-MEM medium supplemented with serum as monolayer or adherent conditions and passaged for 13 times. Immunocytochemistry was used to determine expression of the nestin and GFAP markers. Semi-quantitative RT–PCR was used to confirm genes expression (NGF, CNTF, NT3, NT4.5, GDNF and BDNF).Results: Morphological features of stem cells extracted from different regions of the central nervous system were similar in the culture. Doubling time NSCs in the SVZ (37.45 hr) is shorter than in the SGZ (44.04 hr) and central canal of spinal cord (57.22 hr). The culture conditions as well as monolayer neural stem cells are capable of producing neurospheres. Also, nestin and GFAP markers, expressed by NSCs. Neurotrophic gene expression pattern profiles were similar to each other in stem cells extracted from the SGZ, SVZ and central canal of spinal cord.Conclusion: Neurotrophic gene expression in stem cells extracted from different regions of the central nervous system were similar, but proliferation capacity was higher in NSCs, which have been harvested from the SVZ.

This paper introduces a new type of flame holder. Flow field is investigated, using PIV measurements in cold flow regime. The experiments on two types of V-shape flame holder: one with smooth edges and the other with wavy edges. The instantaneous velocity fields, Strouhal number, average velocity, vorticity, and Recirculation zone length were among the parameters affected by the flame holder geometry. In this work, we examined the influence of these characteristics. Complex structure and unsteadiness of the flow was obtained with high accuracy. The results indicate an increase in length and width of the Recirculation zone when using the wavy edges instead of smooth edges. For both geometries, a symmetrical flow structure was observed behind the flame holder. Also, higher static pressure drop was detected behind the flame holder for geometry with wavy edges.

Hemodialysis access Recirculation occurs when dialyzed blood returning through the venous needle reenters the extracorporeal circuit through the arterial needle rather than returning to the systemic circulation. It is important to meausre hemodialysis access Recirculation for two reasons: The reentry of dialyzed blood into the extracorporeal circuite reduces solute concentration gradients across the dialysis membrane by mixing already dialyzed with undialyzed blood. As a result, the efficiency of dialysis is reduced. High degrees of Recirculation can lead to a significant discrepancy between the amount of hemodialysis prescribed (prescribed Kt/V urea) and the amount of hemodialysis delivdred (delivered Kt/V urea). High degrees of access Recirculation indicate the presence of access stenoses, the most common cause of access thrombosis. Prospective identification and treamtnet of access stenoses improves long-term access patency rate.

Background: Prior investigators have demonstrated that determining Recirculation in aterovenous fistula is a reliable tool for evaluation of hemodialysis. Dialysis patients were reported to be 22000 cases in our country, for whom aterovenous fistula were prepared with different techniques. To our knowledge, there is not any study clarifying the quality of hemodialysis in the affected subjects. Materials and methods: A descriptive study was conducted on 97 patients in Hasheminejad Dialysis Center in Tehran, all of whom had native aterovenous fistula. Recirculation was determined by low blood flow technique. Type and site of the fistula were compared according to the Recirculation rate. Results: Recirculation varied from zero to 16% with the mean of 2.5%. The highest mean of Recirculation was found in end to side proximal fistulas and the lowest was reported in side to side proximal fistulas. Conclusion: Recirculation was within the normal range. It does not show correlation with site and type of fistula at flow of 300 ml/min.

Treatment for end stage renal disease patients is based on dialysis; however, the presence of access Recirculation (AR) decreases dialysis efficiency and adequacy. This study was conducted to determine the Recirculation rate in dialysis patients undergoing hemodialysis through using a permanent catheter. 60 patients including 23 males and 37 females were enrolled. Mean age of the participants was 57. 66 (± 14. 08) years. Mean AR in the subjects was 9. 36%, and 16 (27%) of patients had mean AR above 10%. Moreover, there was a significant correlation between AR and catheter longevity (P <. 001). It is suggested to limit the use of permanent catheters to specific cases and not to use them in place of arteriovenous fistulas.