Onset Of Fluid Flow Research Articles

Numerical Investigation of the Transient Nature of a Laminar Separation Bubble in Hypersonic Flow

Shock-wave/boundary-layer interaction is a prime research topic in the design of hypersonic vehicles. For the proper designing of hypersonic vehicles, especially, their thermal protection systems, it is necessary to understand the time-dependent behavior of the wall properties and the corresponding pressure and thermal loads. Hence investigation is carried out to understand the unsteady nature of shock-induced laminar boundary layer separation for a simple canonical configuration of a two-dimensional ramp. A density-based non-reactive Navier-Stokes solver named rhoCentralFoam in openFOAM is employed in the present investigation. The detailed physics of laminar boundary layer separation in hypersonic flow is investigated through timewise behavior of the streamline patterns and the surface properties, such as the pressure, heat flux, and friction coefficients. It is found that at the onset of fluid flow it is its inviscid characteristics that are predominant and there is occurrence of very small separation bubble. The separation bubble grows, as the involvement of viscous characteristics increases gradually, and ultimately it attains a steady state. Because of separated boundary layer the heat flux and skin friction coefficients are found to follow the diffused V and deformed W shapes, respectively. The peaks of pressure and thermal loads are found to exist in the vicinity of the reattachment region. These peaks are higher in the initial stage of the process and attain steady state eventually. The high pressure and thermal loads may cause structural damage to the vehicle and hence their correct prediction is necessary. Thus, the current investigation is helpful in the design of thermal protection systems of hypersonic vehicles.

Support Epidemiology and Prognosis of Premature Rupture of Membranes in Pikine National Hospital Center

Premature rupture of membranes (PROM) complicates 3% of preterm pregnancies and occurs in 60% to 80% of term pregnancies. However, its management remains largely controversial. The objective of this study was to establish the epidemiological profile, to study the management and the prognosis of Premature rupture of membranes (PROM) in our practice. Patients and methods: It was a prospective, descriptive and analytical study from May 1st 2016 to January 31st 2017 at the Pikine National Hospital Center. The target population consisted of all patients received at the hospital with premature rupture of membranes and who had given birth in the structure. The variables studied were: marital status, mode and reason for admission; risk factors; antecedents; prenatal care; the clinical and paraclinical examinations; support and immediate maternal and fetal neonatal complications. Results and comments: The mean maternal age was 27.34 years and the majority of women were aged between 18 and 39 years (94.4%). Fifty-one point three percent of patients were primiparous, large multiparous represented only 2.5%. The majority of patients (385 patients or 66.9%) had consulted in the first 12 hours following the onset of fluid flow. For 20.1% of them this flow was associated with uterine contractions. Hidden risk factors were dominated by the twin pregnancy. The blood count showed that 38.8% of patients had leukocytosis and CRP was positive in 18.3% of patients. An ampicillin-based antibiotics was established in 42.6% of cases, corticosteroid therapy in 5.2% and 1% in tocolysis. An expectation was adopted in 65.7% of cases, induction of labor in 7.3% and a cesarean section immediately in 27% of cases. In total, 65.7% of patients had vaginal delivery and 34.3% cesarean. The perinatal mortality rate was 3.6% or 22 newborns on 610. Two cases of endometritis were observed and one case of immediate postpartum hemorrhage. No maternal deaths were recorded. Conclusion: These results show that the prognosis of premature rupture of membranes remains favorable in our practice. To improve this prognosis, we recommend sensitization of patients during prenatal care regarding signs of danger, a systematic bacteriological sample from all pregnant at the end of their pregnancy and the health personnel to direct patients’ references to structures in case of PROM.

Collective Cell Migration Drives Morphogenesis of the Kidney Nephron

Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis.

Matrix-specific p21-activated kinase activation regulates vascular permeability in atherogenesis

Elevated permeability of the endothelium is thought to be crucial in atherogenesis because it allows circulating lipoproteins to access subendothelial monocytes. Both local hemodynamics and cytokines may govern endothelial permeability in atherosclerotic plaque. We recently found that p21-activated kinase (PAK) regulates endothelial permeability. We now report that onset of fluid flow, atherogenic flow profiles, oxidized LDL, and proatherosclerotic cytokines all stimulate PAK phosphorylation and recruitment to cell–cell junctions. Activation of PAK is higher in cells plated on fibronectin (FN) compared to basement membrane proteins in all cases. In vivo, PAK is activated in atherosclerosis-prone regions of arteries and correlates with FN in the subendothelium. Inhibiting PAK in vivo reduces permeability in atherosclerosis-prone regions. Matrix-specific PAK activation therefore mediates elevated vascular permeability in atherogenesis.

Rowers coupled hydrodynamically. Modeling possible mechanisms for the cooperation of cilia

We introduce a model system of stochastic entities, called 'rowers' which include some essentialities of the behavior of real cilia. We introduce and discuss the problem of symmetry breaking for these objects and its connection with the onset of macroscopic, directed flow in the fluid. We perform a mean field-like calculation showing that hydrodynamic interaction may provide for the symmetry breaking mechanism and the onset of fluid flow. Finally, we discuss the problem of the metachronal wave in a stochastic context.

POROSITY AND PERMEABILITY EVOLUTION ACCOMPANYING HOT FLUID INJECTION INTO DIATOMITE

An experimental study of silica dissolution was performed to probe the evolution of permeability and porosity in siliceous diatomite during hot fluid injection such as water or steam flooding. Two competing mechanisms were identified. Silica solubility in water at elevated temperature causes rock dissolution thereby increasing permeability; however, the rock is mechanically weak leading to compression of the solid matrix during injection. Permeability and porosity can decrease at the onset of fluid flow. A laboratory flow apparatus was designed and built to examine these processes in diatomite core samples. At the core level, we measured the pressure drop as a function of time for fixed injection rates to determine permeability variation and utilized an X-ray Computerized Tomography (CT) scanner to measure in-situ porosity. At the pore level, a scanning electron microscope (SEM) was used to observe changes in pore morphology. We found that porosity decreased initially due to compaction caused by the imposed pressure drop across the core. Later, porosity increased as silica dissolved. Dissolution of the rock matrix appeared to be relatively uniform; wormholes were not observed even after tens of pore volumes of fluid injection.