An in vitro, in utero and in silico framework of oxygen diffusion in intricate vascular networks of the placenta

The placenta is a temporary and complex organ critical for fetal development through its subtle but convoluted harmonization of endocrine, vascular, haemodynamic and exchange adaptations. Yet, due to experimental, technological and ethical constraints, this unique organ remains poorly understood. In silico tools are emerging as a powerful means to overcome these challenges and have the potential to actualize novel breakthroughs. Here, we present an interdisciplinary framework combining in vitro experiments used to develop an elegant and scalable in silico model of oxygen diffusion. We then use in utero imaging of placental perfusion and oxygenation in both control and growth-restricted rodent placentas for validation of our in silico model. Our framework revealed the structure-function relationship in the feto-placental vasculature; oxygen diffusion is impaired in growth-restricted placentas, due to the diminished arborization of growth-restricted feto-placental vasculature and the lack of decelerated flow for adequate oxygen diffusion and exchange. We highlight the mechanisms of impairment in a rat model of growth restriction, underpinned by placental vascular impairment. Our framework reports and validates the prediction of blood flow deceleration impairment in growth restricted placentas with the placenta's oxygen transfer capability being significantly impaired, both globally and locally. Key words: Placenta; fetal growth restriction; oxygen diffusion; computational fluid dynamics; MRI

Teaching Limiting Behavior of Plane Oblique Shocks

Plane oblique shocks are formed in supersonic flows that cause abrupt flow deceleration, compression and turning. This behavior persists up to a maximum flow turning angle, θmax and a corresponding shock angle βmax for any upstream Mach number M1 with corresponding Mach angle, μ1. Beyond the maximum turning angle, the oblique shock becomes detached from the body and forms a bow shock. In teaching limiting behavior of plane oblique shocks, over a broad Mach range, from 1.5 to 5.0, we discover two interesting correlations. The first is on βmax which remains nearly invariant and the second is (μ1 + θmax) that remains nearly constant. In air with γ = 1.4, βmax is nearly 65.64° with 0.67° standard deviation and (μ1 + θmax) is nearly 53.24° with 0.32° standard deviation angle. Rankine-Hugoniot and Prandtl oblique shock relations are used in theoretical demonstrations of limiting behavior of plane oblique shocks.

Effects of Trade Wind Strength on Airflow and Cloudiness over O‘ahu

Satellite observations and high-resolution modeling during July–August 2013 are used to study the effects of trade wind strength on island wake circulations and cloudiness over O‘ahu, Hawai‘i. O‘ahu is composed of two northwest–southeast orientated mountain ranges: the Wai‘anae Range (~1227 m) along the western leeside coast and the Ko‘olau Range (~944 m) along the eastern windward coast. At night, the flow deceleration of the incoming northeasterly trade winds on the eastern windward side is more significant when trades are stronger.In the afternoon hours, effective albedo and simulated cloud water are greater over the Ko‘olau Range when trades are stronger, and clouds are advected downstream by the trade winds aloft. Over the Wai‘anae Range, orographic clouds are more significant when trades are weaker due to less moisture removal by orographic precipitation over the Ko‘olau Range and the development of both upslope flow on the eastern slope and upslope/sea-breeze flow along the western coast, the latter of which brings in warm, moist air from the ocean. When trades are weaker, cloudiness off the western leeside coast is more extensive and originates from orographic cloud development over the Wai‘anae Range, which drifts downstream due to a combination of trade winds and the easterly return flow aloft. The latter is associated with the low-level sea-breeze/upslope flow.

Fundamentals of the Theory of Power Pulse Device

The article discusses a mathematical model of a power impulse device, which allows you to select the characteristics of the ejected liquid jet, such as the velocity at the moment of ejection, the pressure created in the nozzle of the power impulse device, etc., by changing the parameters of the device. A feature of the proposed mathematical model, which significantly distinguishes it from the previously considered models, is that the model was considered for the case of unsteady motion. This state of the medium in a power impulse device is the most characteristic, therefore the results obtained are more general. It is shown that, in contrast to the steady motion of a liquid, in the case of unsteady motion, an additional term appears, which can be defined as a head having an inertial character. It can be seen from the proposed mathematical model that the presence of an inertial head leads to the appearance of a flow deceleration effect, which, in turn, leads to an increase in the total liquid head in the direction of the flow. The pressure generated in the barrel acts against the direction of the hydraulic resistance. All of the above is applicable only for a certain moment in time or for the case when the acceleration of the fluid is constant. If the acceleration changes, then the action of the heads along the fluid flow is a function of time. This circumstance makes it possible to apply the result obtained with unsteady motion to create devices that form a high-pressure jet. A distinctive feature of the considered model is that it analyzes the behavior of the fluid in the power impulse device for two cases: 1. the volume of fluid in the barrel of the power impulse unit is greater than the volume of the nozzle; 2. the volume of fluid in the barrel is less than or equal to the volume of the nozzle. The results of the analysis showed that in the first case, the initial velocity of liquid ejection significantly exceeds this velocity in the second case. That is, it is the first case that is of practical importance.

The architecture and evolution of shallow water delta mouth bars: examples from the Lower Cretaceous of Spain

<p>Improved understanding of delta mouth bar morphodynamics, and the resulting stratigraphic architectures, is important for predicting the loci of deposition of different sediment fractions, coastal geomorphic change and heterogeneity in mouth bar reservoirs. Facies and architectural analysis of exceptionally well-exposed shallow water (ca. 5 m depth) mouth bars and associated distributaries, from the Xert Formation (Lower Cretaceous), of the Maestrat Basin (east-central Spain), reveal that they grew via a succession of repeated autogenic cycles. The formation is part of a mixed clastic-carbonate succession deposited during a time of active faulting and incipient salt tectonism, but in an area away from their direct influence and where wave and tidal reworking were minimal.</p><p>An initial mouth bar accretion element forms after avulsion of a distributary into shallow standing water. Turbulent expansion of the fluvial jet and high bed friction results in rapid flow deceleration, and deposition of sediment in an aggradational to expansional bar-form. Vertical bar growth causes flattening and acceleration of the jet. The accelerated flow scours channels on the bar top, which focuses further expansion of the mouth bar at individual loci where the channels break through the front of the mouth bar. Here, new mouth bar accretion elements form, downlapping and onlapping against a readily recognizable surface of mouth bar reorganization. Vertical growth of the new mouth bar accretion elements causes flattening and re-acceleration of the jet, leading to channelization, and initiation of the next generation of mouth bar accretion elements. Thus the mouth bar grows, until bed-friction effects cause backwater deceleration and superelevation of flow in the feeding distributary. Within-channel sedimentation, choking and upstream avulsion of the feeding channel, results in mouth bar abandonment. In this study, mouth bars are formed of at least two to three accretion elements, before abandonment happened. The results of this study contrast with the notion that mouth bars form by simple vertical aggradation and radial expansion. However, the architecture and facies distributions of shallow water mouth bars are a predictable product of intrinsic processes that operate to deposit them.</p>

Numerical Study on the Effect of an Off-Surface Micro-Rod Vortex Generator Placed Upstream NACA0012 Aerofoil

In this paper, 3D numerical simulations have been carried out to enhance the understanding of a flow over a passive control device composed of micro cylinder with, d/c = 1.34% placed in the vicinity of NACA0012 aerofoil wing, by means of γ–Reθt transition sensitive turbulence model meant to predict the separation induced by transition achieved for aerofoils operating at moderate Reynolds number (Re = 4.45×105). Results show that the separation of the boundary layer has been eliminated by the passive static vortex generator at stall regime due to the injection of free-stream momentum to the boundary layer. The early transition to turbulent state overcomes the local flow deceleration of an adverse pressure gradient and remains sticked to the wall the boundary layer. Furthermore, the wing aerodynamic performance are improved as drag is reduced and lift is enhanced which is straight forward linked to the lift to drag ratio gain that varies from 22.68% to 134.17% at post stall angles of attack.

Characterization of anisotropic turbulence behavior in pulsatile blood flow

Turbulent-like hemodynamics with prominent cycle-to-cycle flow variations have received increased attention as a potential stimulus for cardiovascular diseases. These turbulent conditions are typically evaluated in a statistical sense from single scalars extracted from ensemble-averaged tensors (such as the Reynolds stress tensor), limiting the amount of information that can be used for physical interpretations and quality assessments of numerical models. In this study, barycentric anisotropy invariant mapping was used to demonstrate an efficient and comprehensive approach to characterize turbulence-related tensor fields in patient-specific cardiovascular flows, obtained from scale-resolving large eddy simulations. These techniques were also used to analyze some common modeling compromises as well as MRI turbulence measurements through an idealized constriction. The proposed method found explicit sites of elevated turbulence anisotropy, including a broad but time-varying spectrum of characteristics over the flow deceleration phase, which was different for both the steady inflow and Reynolds-averaged Navier–Stokes modeling assumptions. Qualitatively, the MRI results showed overall expected post-stenotic turbulence characteristics, however, also with apparent regions of unrealizable or conceivably physically unrealistic conditions, including the highest turbulence intensity ranges. These findings suggest that more detailed studies of MRI-measured turbulence fields are needed, which hopefully can be assisted by more comprehensive evaluation tools such as the once described herein.

The different flavors of extragalactic jets: The role of relativistic flow deceleration

We perform three-dimensional numerical simulations of relativistic (with a Lorentz factor of 10), non-magnetized jets propagating in a uniform density environment in order to study the effect of the entrainment and the consequent deceleration. Our simulations investigate the jet propagation inside the galaxy core, where the deceleration most likely occurs more efficiently. We compare cases with different density and pressure ratios with respect to the ambient medium and find that low density jets are efficiently decelerated and reach a quasi-steady state in which, over a length of 600 jet radii, they slow down from highly relativistic to sub-relativistic velocities. Conversely, denser jets keep highly relativistic velocities over the same length. We discuss these results in relation to the Faranoff Riley (FR) radio source classification. We infer that lower density jets can give rise to FR 0 and FR I radio sources, while higher density jets may be connected to FR II radio sources.

TB or not TB: banding in turbidite sandstones

ABSTRACT Recognition and interpretation of sedimentary structures is fundamental to understanding sedimentary processes. Banded sandstones are an enigmatic sedimentary facies comprising alternating mud-rich (as matrix and/or mud clasts) and cleaner sand layers. The juxtaposition of hydrodynamically different grain sizes contradicts established models of cleaner-sand bedform development. Here, outcrop, subsurface core, and petrographic data from three deep-water systems, with well-constrained paleogeographic contexts, are used to describe the range of sedimentary textures, bedform morphologies, and facies associations, and to quantify the mud content of banding. Banding can occur in any part of a bed (base, middle, or top), but it typically overlies a structureless basal sandstone or mud-clast conglomerate lag, and is overlain by clean parallel-laminated sandstone and/or ripple cross-lamination. Banding morphology ranges from sub-parallel to bedforms that comprise low-angle laminae with discontinuous lenses of mudstone, or asymmetric bedforms comprising steeply dipping foresets that transition downstream into low-amplitude bedwaves, or steeply dipping ripple-like bedforms with heterolithic foresets. This style of banding is interpreted as a range of bedforms that form progressively in the upper-stage plane-bed flow regime via tractional reworking beneath mud-laden transitional plug flows. The balance of cohesive and turbulent forces, and the rate of flow deceleration (aggradation rate), govern the style of deposit. Banded sandstones and linked debrites are rarely found juxtaposed together in the same bed because they are distributed preferentially in proximal and distal settings, respectively. Understanding the origins of banding in turbidite sandstones, the conditions under which it forms, and its distribution across deep-water systems and relationship to linked debrites, is important for it to be used effectively as a tool to interpret the geological record.