Streak Formation Research Articles

Phase-space dynamics of near-wall streaks in wall-bounded turbulence with spanwise oscillation

This work presents systematical investigations on the skin-friction drag reduction (DR) of turbulent channel flow subjected to spanwise wall oscillation using direct numerical simulation. Altogether 12 different oscillatory cases have been studied with a reference at Reτ = 200, varying the controlling parameters characterized by maximum wall velocity Wm+ and oscillation period T+. Some of the previously established facts have been reproduced by our analysis with a new focus on the phase-space dynamics of the near-wall streaks, on the basis of statistical data over entire oscillation periods and over phasewise variations. It is revealed that streamwise vortices are generated in the vicinity of oscillation walls, disrupting the formation of near-wall low-speed streaks. Although the overall turbulence is weakened, the Stokes layer is thicker within wall acceleration phases for larger Wm+, which causes the turbulence intensity to increase in the upper viscous sublayer. In addition, regarding the effect of T+, a long oscillation period promotes the formation of energetic near-wall structures, while for short T+, the streak-generation time scale preferentially restricts the growth of spanwise streaks. From a new vorticity-transport perspective of the Reynolds shear stress, our results further indicate that high drag-reducing phenomena are connected to the near-wall sweep events, and the shear stress variation is principally driven by the distortion of the spanwise transport of wall-normal vorticity, i.e., vortex tilting/stretching. The DR process is seen to be linked to the increase in enstrophy and turbulence-energy dissipation in the near-wall region.

Anti-Atherosclerotic and Anti-Inflammatory Effects of Curcumin on Hypercholesterolemic Male Rabbits.

Curcumin has a potent antioxidant and anti-inflammatory properties that may suppress inflammatory component of atherosclerosis. It has been demonstrated that curcumin derivatives can reduce the formation of arterial fatty streaks in cholesterol-fed rabbits. Therefore in this study we evaluated the protective effects of Curcumin on the progression of atherosclerosis. 20 mature rabbits were included for this study; they were randomly divided into four groups each of 5. Group 1: (normal control) were fed corn pellets diet and tab water, group 2: (high cholesterol diet control) were kept on cholesterol rich diet (2% cholesterol) and tab water. Group 3: (cholesterol and rosuvastatin treated group) were kept on cholesterol rich diet (2% cholesterol) and 2.5mg/kg/day Rosuvastatin dispersed in DW and given orally, group 4: (cholesterol and curcumin treated group) were kept on cholesterol rich diet (2% cholesterol) and 0.2% curcumin added with corn pellets. The study continued for 12weeks then assessment of serum level of high sensitive C-reactive protein, ICAM1, VCAM1 and PCSK9 was carried out at the end of the study. Total antioxidant activity of curcumin was also determined. Histopathological examination of aortic tissues for atherosclerotic changes was also carried out. Atherogenic (cholesterol rich diet) induced an increment in serum level of TC, LDL, VLDL and TG with concomitant decrement in serum level of HDL and increased atherogenic index. Treatment with curcumin produced substantial reduction in serum TC, LDL, TG with no effect on HDL level thus decreased atherogenic index. Rabbits treated with curcumin showed a significant reduction in the serum level of high sensitive C-reactive protein, ICAM1, VCAM, PCSK9 serum expression and aortic total antioxidant capacity. Curcumin has a potent anti-inflammatory and anti- oxidant effects against atherosclerosis so exerts a protective role by decreasing lipid oxidation and inflammatory markers.

P3447Multimodal assessment and phenomapping of early atherosclerosis in children with chronic disease

Abstract Background Childhood survival of chronic disease steadily increased over the last decades. However, accumulating evidence suggests that survivors are at risk for early atherosclerosis. The “Cardiovascular Disease in Children with chronic disease” (CDC) study has two aims. First, multimodal assessment of early atherosclerosis was performed in adolescents with chronic inflammatory- and metabolic disorders in order to develop new diagnostic approaches. As fatty streak formation starts in the abdominal aorta, aortic wall thickness (AWT) and pulse wave velocity (PWV) were measured using cardiovascular magnetic resonance imaging (MRI), and compared with traditional carotid intima-media thickness (cIMT) and echocardiography. Second, comprehensive risk profiling was performed, including phenomapping of early risk factors, in order to establish cardiovascular risk profiles in childhood. Methods 113 adolescents aged 12–19 years old were enrolled*. The study population includes adolescents with juvenile idiopathic arthritis (JIA, n=19), cystic fibrosis (CF, n=24), obesity (n=20), corrected coarctation of the aorta (CoA, n=25), and corrected atrial septal defect as control group (ASD, n=25). The aorta was imaged on a 3.0 Tesla MR system using the 3D-T1-BB-VISTA sequence. Aortic PWV was assessed using velocity-encoded MRI. cIMT was measured in three directions for both the right- and left carotid artery using echography. Unbiased hierarchical clustering was performed on phenotypic data (phenomapping), including anthropomorphic-, metabolic-, and inflammatory parameters. Results* Aortic pulse wave velocity on MRI was highest in the obese group compared to controls (p=0.002), yet JIA patients (p=0.015), CoA patients (p=0.029), and CF patients (p=0.044) also showed increased PWV compared to controls. Aortic wall thickness was highest in obese adolescents (p=0.020) and in CF patients (p=0.043). cIMT was only increased in CoA patients (p=0.000). While PWV and AWT showed correlation with inflammatory- and metabolic parameters such as lymphocyte count (PWV, p=0.043), monocyte count (PWV, p=0.002; AWT, p=0.036), CRP (AWT, p=0.032), and QUICKI (PWV, p=0.026), cIMT correlated with systolic blood pressure (p=0.017). Phenomapping of risk factors will further define distinct cardiovascular risk profiles*. Conclusion Multimodal assessment of early atherosclerosis in children with chronic disease reveals differential vascular changes. While traditional cIMT is associated with increased systolic blood pressure in young CoA patients, aortic PWV and aortic wall thickness reflect early systemic inflammatory- and metabolic derangement. Phenomapping traditional risk factors alongside inflammatory- and metabolic parameters bears promise to establish early cardiovascular risk profiles in childhood chronic disease*. *Patient inclusion finishes May 2019, followed by phenomapping of patient characteristics. At the ESC, final data will be presented. Acknowledgement/Funding Wilhelmina Children's Hospital Research Fund, Dutch Topsector Life Sciences and Health TKI fund, Nutricia Research fund. HS was supported by VENI-NWO.

Analysis of the Interconnections between Classic Vortex Models of Coherent Structures Based on DNS Data

Low- and high-speed streaks (ejection, Q2, and sweep, Q4, events in quadrant analysis) are significant features of coherent structures in turbulent flow. Streak formation is closely related to turbulent structures in several vortex models, such as attached eddy models, streamwise vortex analysis models, and hairpin vortex models, which are all standard models. Vortex models are complex, whereby the relationships among the different vortex models are unclear; thus, further studies are still needed to complete our understanding of vortices. In this study, 30 sets of direct numerical simulation (DNS) data were obtained to analyze the mechanics of the formation of coherent structures. Image processing techniques and statistical analysis were used to identify and quantify streak characteristics. We used a method of vortex recognition to extract spanwise vortices in the x–z plane. Analysis of the interactions among coherent structures showed that the three standard vortex models all gave reasonably close results. The attached eddy vortex model provides a good explanation of the linear dimensions of streaky structures with respect to the water depth and Q2 and Q4 events, whereby it can be augmented to form the quasi-streamwise vortex model. The legs of a hairpin vortex envelop low-speed streaky structures and so move in the streamwise direction; lower-velocity vortex legs also gradually accumulate into a streamwise vortex. Statistical analysis allowed us to combine our present results with some previous research results to propose a mechanism for the formation of streaky structures. This study provides a deeper understanding of the interrelationships among different vortex models.

Hydroentangled polymer nonwovens: Prediction of jet streaks and surface roughness

Here, the dynamic model of polymer fibers in hydroentanglement is used to predict the appearance of the so-called jet streaks and surface roughness. The mechanism of formation of jet streaks is explained. It is shown that the staggered two-row water jets which are widely used in industry help to optimize surface roughness and reduce the jet streaks. It is also shown that the jet width ratio plays an important role in minimizing the surface roughness at different jet pressures. Furthermore, a novel numerical method of re-construction of the 3-D surface topography from discrete data is developed to visualize the jet streaks. Also, in the experiments of this work, the optical images of jet streaks on hydroentangled polymer nonwovens are analyzed. The streaks period is measured by using the Fast Fourier Transform (FFT) and the surface topography is visualized by using optical profilometer. The predicted optimal jet width ratio is compared to the experimental results and a good agreement is found.

Turbulent spots in an oscillatory flow over a rough wall

Abstract We describe the results of a direct numerical simulation inspired by laboratory experiments (Carstensen et al., 2012), which showed the formation of turbulent spots in an oscillatory boundary layer over a rough wall. Even though, differently from the experiments, the wall we consider is characterized by a regular roughness, turbulent spots with similar characteristics are observed. The numerical results provide information on transition to turbulence and on the early stages of formation of the turbulent spots. In particular, the formation of low-speed streaks and the subsequent generation of turbulent spots are described. The speed of the extreme points of the spots is obtained from the numerical results. Moreover, the effects of the wall roughness on the speed of the turbulent spots are discussed.

Total Body Photography and Sequential Digital Dermoscopy in Pregnant Women.

Melanocytic nevi can vary in size and number in pregnant women, and the differential diagnosis with melanoma may be challenging. To describe changes in total body photography of pregnant women and dermoscopy aspects of their nevi. A prospective cohort study with 703 melanocytic nevi from 18 women was performed, comparing them in the first and third trimester of pregnancy. Images were analyzed between the 2 periods for changes in dermoscopic aspects. Total body photography images indicated that 44% of patients had new lesions. Regarding the observed changes, there were symmetric or regular changes of the network (23% of cases), occurrence of new globules/dots (12.4%), new vascular structures (3.2%), new streaks (1.7%), and new structureless area (1.0%). Moreover, 55.0% of the nevi increased in size. Enlarging of the nevi was observed mostly on the abdomen (87.1%; P < 0.001) and showed more network changes (27.1%; P = 0.014) and formation of new globules and dots (16.0%; P < 0.001). Patients with a risk of developing melanoma presented more frequently enlarged nevi (45%; P = 0.019). The association between streak formation and skin type was significant (P = 0.012) and was more frequent in skin type II (2.7%), when compared with skin types III (1.3%) and IV (0%). Development of new melanocytic nevi may occur in pregnant women. The majority of the preexisting melanocytic nevi showed enlarging, and most of them presented with benign dermoscopic changes. The appearance of new streaks is more frequent in fair skin types. Patients with a personal or family history of melanoma in first-degree relatives presented more nevi with changes in size.

Potential Cardio-Protective Effects of Green Grape Juice: A Review

Unripe grape juice (verjuice) may offer health benefits, including the treatment of cardiovascular disease. The presence of bioactive compounds in verjuice influences blood pressure, inflammatory markers, oxidative stress, endothelial function, fatty streak formation and glycemic level. Studies have shown that the bioactive compounds also affect serum lipid profile, raising LDL cholesterol under certain circumstances. The health-promoting effects of verjuice have been investigated through human and animal trials. This review paper provides a comprehensive summary of the literature on the pharmacological and phytochemical properties of green grape juice. Further research on this juice is needed to quantify the phytochemical composition and support the current findings. Furthermore, future studies are needed to determine the exact amount of verjuice required to exhibit the optimal health effects on humans, as this is currently unknown.

SAT-001 Supra-Physiological Testosterone Treatment Reduces Aortic Atheroma but Increases Markers of Cardiac Hypertrophy

Supra-physiological Testosterone Treatment Reduces Aortic Atheroma but Increases Markers of Cardiac Hypertrophy The impact of testosterone on the cardiovascular system is controversial and concerns have been raised in regard to the safety of testosterone replacement therapy (TTh) in hypogonadal men with cardiovascular disease. We have examined the effects of supra-physiological concentrations of testosterone upon aortic fatty streak formation in high-fat diet-fed testicular feminized (Tfm) mice, which exhibit non-functional androgen receptors (AR) and low circulating testosterone levels. Tfm mice were fed a high-cholesterol diet ad libitum for 28 weeks and received fortnightly intramuscular injections of either saline (Tfm, n=8, XY, n=8), 10uL of 250mg/mL testosterone alone (Tfm, n=8, XY, n=8), or in conjunction with either a 30uL intramuscular injection of 50mg/ml estrogen receptor-alpha antagonist fulvestrant (Tfm, n=8), or with 10mg/kg/day of aromatase inhibitor anastrazole in drinking water (Tfm, n=7). Cardiac tissue mRNA was analysed by qPCR for markers of hypertrophy (ANP, BNP, alpha-actin, MYH7, Gsk3-beta, SM22-alpha). A significant reduction in aortic fatty streak formation was observed in Tfm mice receiving supra-physiological testosterone compared to those receiving saline; 1.25+0.36% versus 2.85+0.37% respectively (p<0.01). No significant increase in aortic lipid deposition was observed in XY littermates administered supra-physiological testosterone compared to those receiving saline; 0.22+0.13% versus 0.32+0.12% respectively (p=ns). Aortic fatty streak formation in Tfm mice receiving supra-physiological testosterone in conjunction with fulvestrant or anastrazole was similar to that observed in Tfm mice receiving supra-physiological testosterone therapy alone; 0.71+0.18% and 1.09+0.81% respectively versus 1.25+0.36% (both p=ns) indicating non-genomic actions of testosterone. Hypertrophic markers and heart weights were elevated in XY littermates receiving supra-physiological testosterone but not in Tfm mice compared to placebo suggesting AR-dependent actions. This evidence suggests that supra-physiological levels of testosterone protect against diet induced aortic atheroma formation, at least in part, via non-genomic mechanisms but incur increased cardiovascular risk by potentially inducing cardiac hypertrophy via AR-dependent actions. Dose titration to physiological levels and careful monitoring of patients throughout treatment is key to eliciting the beneficial cardiovascular effects of TTh in hypogonadal men.

A wave of WNT signaling balanced by secreted inhibitors controls primitive streak formation in micropattern colonies of human embryonic stem cells.

Long-range signaling by morphogens and their inhibitors define embryonic patterning yet quantitative data and models are rare, especially in humans. Here, we use a human embryonic stem cell micropattern system to model formation of the primitive streak (PS) by WNT. In the pluripotent state, E-cadherin (E-CAD) transduces boundary forces to focus WNT signaling to the colony border. Following application of WNT ligand, E-CAD mediates a front or wave of epithelial-to-mesenchymal (EMT) conversion analogous to PS extension in an embryo. By knocking out the secreted WNT inhibitors active in our system, we show that DKK1 alone controls the extent and duration of patterning. The NODAL inhibitor cerberus 1 acts downstream of WNT to refine the endoderm versus mesoderm fate choice. Our EMT wave is a generic property of a bistable system with diffusion and we present a single quantitative model that describes both the wave and our knockout data.

Hot Streak Characterization of High-Performance Double-Serpentine Exhaust Nozzles at Design Conditions

The characterization and mitigation of hot streak phenomena in double-serpentine exhaust nozzles have strategic, operational, and tactical implications for future airborne weapon systems. However, airframe integration increases the risk for material failure due to exposure of downstream components to high-temperature gases from the high-performance convergent-divergent nozzle. The formation of hot streaks must be understood if mitigation strategies are to be developed. To that end, this paper establishes a set of novel characterization parameters based on the temperature distribution and flow conditions at the nozzle exit. Hot streak phenomena observed for a set of serpentine exhaust nozzles with varying geometries are compared using a modified Dean number (called the White number) that accounts for arbitrary cross-sectional area and streamline curvature changes. Using these parameters and computational fluid dynamics, quantifiable differences are observed in the distribution and intensity of hot flow at the nozzle exit. The results show that hot steak phenomena are most prominent for nozzles with a lower White number. The results also provide insight into flow physics acting as primary drivers of hot streak phenomena. The effects of bulk engine swirl are considered and exhibit a significant impact on surface temperature distribution and the formation of hot streaks.

Recent Advances in Understanding the Pathogenesis of Cardiovascular Diseases and Development of Treatment Modalities.

Cardiovascular Diseases (CVDs) are a leading cause of morbidity and mortality worldwide. The underlying pathology for cardiovascular disease is largely atherosclerotic in nature and the steps include fatty streak formation, plaque progression and plaque rupture. While there is optimal drug therapy available for patients with CVD, there are also underlying drug delivery obstacles that must be addressed. Challenges in drug delivery warrant further studies for the development of novel and more efficacious medical therapies. An extensive understanding of the molecular mechanisms of disease in combination with current challenges in drug delivery serves as a platform for the development of novel drug therapeutic targets for CVD. The objective of this article is to review the pathogenesis of atherosclerosis, first-line medical treatment for CVD, and key obstacles in an efficient drug delivery.

Seasonal formation rates of martian slope streaks

Slope streaks are gravity-driven dark or light-toned features that form throughout the martian year in high-albedo and low-thermal inertia equatorial regions on Mars. These distinctive features have never been observed in a terrestrial environment although some analogs have been proposed. Based on diverse orbital observations, a number of mechanisms including granular and aqueous flows have been proposed to explain their formation. Using multi-temporal images taken by the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO), we identified newly formed streaks in multiple martian years and estimated seasonal streak formation rates at intermediate latitudes, as well as at the equator. We found seasonal variations in streak activity in multiple consecutive martian years, including high formation rates during autumn (solar longitude LS ~190°). During this time, slope streak activity exceeds the long-term formation rate multiple times. The highest seasonal formation rate of 0.16% per streak per martian day was observed in the Olympus Mons aureole in autumn (LS ~210°) of Mars year 30. In some sites, slope streak formation rate at slopes of opposite orientation peaks at different seasons. The seasonal variations of the formation rate are inconsistent with sporadic trigger mechanisms and revealed that changing conditions at the slopes affect the formation of the streaks throughout the martian year. Modelled environmental parameters at the streak-bearing slopes indicate a correlation between seasonal streak activity and surface temperature, as well as wind velocity. Seasonal variations of streak activity could be a result of varying intensities of both dry and wet mechanisms or could be explained by the interaction of multiple mechanisms.

Are Slope Streaks Indicative of Global‐Scale Aqueous Processes on Contemporary Mars?

AbstractSlope streaks are prevalent and intriguing dark albedo surface features on contemporary Mars. Slope streaks are readily observed in the equatorial and subequatorial dusty regolith regions with low thermal inertia. They gradually fade over decadal timescales. The proposed mechanisms for their formation vary widely based on several physicochemical and geomorphological explanations. The scientific community is divided in proposing both dry and wet mechanisms for the formation of slope streaks. Here we perform a systematic evaluation of the literature for these wet and dry mechanisms. We discuss the probable constraints on the various proposed mechanisms and provide perspectives on the plausible process driving global‐scale slope streak formation on contemporary Mars. Although per our understanding, a thorough consideration of the global distribution of slope streaks, their morphology and topography, flow characteristics, physicochemical and atmospheric coincidences, and terrestrial analogies weighs more in favor of several wet mechanisms, we acknowledge that such wet mechanisms cannot explain all the reported morphological and terrain variations of slope streaks. Thus, we suggest that explanations considering both dry and wet processes can more holistically describe all the observed morphological variations among slope streaks. We further acknowledge the constraints on the resolutions of remote sensing data and on our understanding of the Martian mineralogy, climate, and atmosphere and recommend continuous investigations in this direction using future remote sensing acquisitions and simulations. In this regard, finding more wet and dry terrestrial analogs for Martian slope streaks and studying them at high spatiotemporal resolutions can greatly improve our understanding.

Streak formation in flow over biomimetic fish scale arrays.

The surface topology of the scale pattern from the European sea bass (Dicentrarchus labrax) was measured using a digital microscope and geometrically reconstructed using computer assisted design modelling. Numerical flow simulations and experiments with a physical model of the surface pattern in a flow channel mimic the flow over the fish surface with a laminar boundary layer. The scale array produces regular rows of alternating, streamwise low-speed and high-speed streaks inside the boundary layer close to the surface, with maximum velocity difference of approximately 9%. Low velocity streaks are formed in the central region of the scales whereas the high velocity streaks originated in the overlapping region between the scales. Thus, those flow patterns are linked to the arrangement and the size of the overlapping scales within the array. Because of the velocity streaks, total drag reduction is observed when the scale height is small relative to the boundary layer thickness, i.e. less than 10%. Flow simulations were compared with surface oil-flow visualisations on the physical model of the biomimetic surface placed in a flow channel. The results show an excellent agreement in the size and arrangement of the streaky structures. The existence of streaks is also shown on sea bass and common carp (Cyprinus carpio) by surface flow visualisation. From comparisons with recent literature on micro-roughness effects on laminar boundary layer flows, it is hypothesised that the fish scales could delay transition, which would further reduce the drag.

Effects of Rotation on Turbulence Production

Direct numerical simulations (DNS) of non-rotating and rotating turbulent channel flow were conducted. The data base obtained from these DNS simulations was used to investigate the prominent coherent structures involved in the turbulence generation cycle. Predictions from three theoretical models concerning the formation and evolution of sublayer streaks, three-dimensional hairpin vortices and propagating plane waves were validated using visualizations from the present DNS data. Quadrant analysis was used to determine a phase shift between the fluctuating streamwise and wall-normal velocities as a characteristic of turbulence production in the suction region at a low rotation number.

Haemodynamic stress-induced breaches of the arterial intima trigger inflammation and drive atherogenesis.

Inflammatory mediators, including blood cells and their products, contribute critically to atherogenesis, but the igniting triggers of inflammation remain elusive. Atherosclerosis develops at sites of flow perturbation, where the enhanced haemodynamic stress could initiate the atherogenic inflammatory process due to the occurrence of mechanic injury. We investigated the role of haemodynamic stress-induced breaches, allowing the entry of blood cells in the arterial intima, in triggering inflammation-driven atherogenesis. Human coronary samples isolated from explanted hearts, (n = 47) displayed signs of blood entry (detected by the presence of iron, ferritin, and glycophorin A) in the subintimal space (54%) as assessed by histology, immunofluorescence, high resolution episcopic microscopy, and scanning electron microscopy. Computational flow dynamic analysis showed that intimal haemorrhagic events occurred at sites of flow disturbance. Experimental carotid arteries from Apoe deficient mice showed discrete endothelial breaches and intimal haemorrhagic events specifically occurring at the site of flow perturbation, within 3 days after the exacerbation of the local haemodynamic stress. Endothelial tearing was associated with increased VCAM-1 expression and, within 7 days, substantial Ly6G+ leucocytes accumulated at the sites of erythrocyte-derived iron and lipids droplets accumulation, pathological intimal thickening and positive oil red O staining. The formation of fatty streaks at the sites of intimal breaches was prevented by the depletion of Ly6G+ leucocytes, suggesting that the local injury driven by haemodynamic stress-induced breaches triggers atherogenic inflammation. Haemodynamic-driven breaches of the arterial intima drive atherogenic inflammation by triggering the recruitment of leucocyte at sites of disturbed arterial flow.

Receptivity to Freestream Acoustic Noise in Hypersonic Flow over a Generic Forebody

Direct numerical simulations of the Navier–Stokes equations have been performed to investigate the receptivity and breakdown mechanisms in a Mach 6 flow over a generic forebody geometry with freestream acoustic disturbances. The simulations are based on transition experiments carried out in April 2015 in the Boeing/U.S. Air Force Office of Scientific Research Mach 6 facility at Purdue University. A three-dimensional model for both fast and slow freestream acoustic waves with multiple frequencies and spanwise wave numbers has been adopted in the numerical simulations, for which high-amplitude disturbances have been considered in order to simulate noisy wind-tunnel conditions. The numerical results revealed similarities in comparison to the experimental observations, especially when slow acoustic waves were considered as freestream disturbances. In particular, slow acoustic waves have been found to induce the breakdown process via crossflow instabilities located in the off-centerline region, with formation of streamwise streaks. Fast acoustic waves, in contrast, appeared more efficient in inducing earlier nonlinear growth through destabilization of the boundary layer along the symmetry plane of the body.

Dyslipidemia in pregnancy and maternal-fetal outcome.

Hyperlipidemia is a known cause of atherosclerosis and directly contributes to the current epidemic in cardio-vascular disease. Pregnancy is typified by an increase in serum levels of total cholesterol and triglycerides pushed by the rise in estrogen, progesterone and lactogen. Mobilization of stored fat depots in late pregnancy may provide a reservoir of fatty acids for fetal growth and placental tissue steroid synthesis. This physiologic increase in lipids performs an essential role during pregnancy; however, elevated levels of lipids in predisposed women or with familiar forms of hyperlipidemia can carry increased risk for maternal-fetal complications. The present treatment of pregnant women with hyperlipidemia is the suspension of medications. However, hyperlipidemia during pregnancy is associated with preeclampsia, preterm birth and gestational diabetes and offspring of these mothers show a propensity to enhanced fatty streak formation and an increased risk of progressive atherosclerosis. This current evidence may motivate the further study on the potential benefits of treatment of hyperlipidemia in pregnancy and its effects on maternal-fetal outcomes.

Maintenance of Oscillations in Three-Dimensional Traveling Waves in Plane Poiseuille Flows

Two solutions of three-dimensional Navier–Stokes equations are studied numerically. These solutions describe the fluid motion in a plane channel, are of the traveling-wave form, and are periodic in the streamwise and spanwise directions. It is shown that, in each solution, the oscillations arise as a result of linear instability in the streamwise averaged velocity field. This instability is due to the existence of streamwise streaks known as the regions where the velocity is higher or lower than the mean velocity. A mechanism for the maintenance of streamwise vortices causing the formation of streaks is revealed. The obtained results confirm and extend the existing knowledge about the mechanism for the formation of near-wall turbulent structures.