Low Velocity Gradient Research Articles

Experimental and simulation study of flow field characteristics of a disturbing rotary centrifugal air classifier

In the present study, a new disturbing rotary centrifugal classifier was designed and a method was proposed to characterize its pressure signals. The models for evaluating the classification effects were established based on multi-zones. It was found that the flow field, processing parameters, and material properties significantly affected on the particle force and classification performance. The pressure with high amplitude and energy analyzed using Hilbert-Huang Transform (HHT) concentrated within 200–400 Hz, and the screening cage facilitated energy transfer to lower frequency bands. Correlation analysis demonstrated the correlation coefficients (A5 and A6) between adjacent measurement points increased with frequency, further enhanced by the screening cage. The flow field of simulation was characterized by a low-pressure, high-velocity gradient at the center and a high-pressure, low-velocity gradient at the sidewalls and the gas velocity and flow for experiment achieved the maximum at z = 0.50 m, while the magnitude of pressure change was significant at the inlet end and discharge end, where the velocity gradient and pressure drop had the same trend and small errors for experiments and simulation. The flow field affected the competing relationship between centrifugal and drag forces on the particles with different kinematic behavior during the classification process. The errors between the predicted values of the theoretical, simulated, and experimental cut particle size models and the true values were all within 10 %, based on which the multi-zone classification efficiency model applicable to the disturbing centrifugal classifier was established, and it was found that the models all had high prediction accuracy and suitability. The article delves into the correlation between pressure signals, flow field characteristics and particle behavior, aiming to provide an important reference for the internal flow field and classification performance of air classifiers.

Computational investigations of the effects of wall surface temperature on a hypersonic inlet isolator

Flow and shock train development in a hypersonic inlet isolator at various wall surface temperatures, Tw, and freestream static temperatures, T?, were studied through numerical simulations. A non-dimensional parameter, Tw /T?, is used to characterize flow behaviors in hypersonic isolator. With the increase of Tw /T?, boundary-layer thickness increases and boundary-layer momentum thickness decreases at the entrance of isolator. Inside the isolator without the presence of backpressure, skin friction decreases with the increase of Tw /T?. The main cause is a lower velocity gradient near the wall at high temperature. A lower skin friction on high wall temperature results in a stronger separation with shock impingement. Under backpressure conditions, with the increase of Tw /T?, an upstream movement of the starting position of the shock train inside the isolator, an increase in the length of the shock train, and an increase in pressure coefficient on the wall surface are observed.

Study on the mechanism of hydrodynamic manipulation of floc structure to achieve high-flux of coagulation macro-filtration for the rapid removal of Aphanizomenonflos-aquae

Coagulation-filtration hybrid process has been widely used in algae removal treatment to improve the water quality and alleviate the membrane fouling. However, the intricate interplay of how floc structure induced by coagulation hydraulic shear influences the cake layer and filtration performance in coagulation macro-filtration of microalgae remains unexplored. In this study, a novel coagulation filtration with macro-pore of 75 μm was first adopted for the rapid removal of Aphanizomenonflos-aquae, and the floc structure was artificially manipulated through various velocity gradients to explore the effect mechanism of the coagulation hydrodynamic shear on the macro-filtration performance from the perspectives of floc characteristics (size and fractal dimension) and cake layer structure (thickness and roughness). The results showed that an optimal average flux of 31257.64 ± 2776.28 L·m−2·h−1 can be achieved at a manipulated appropriate velocity gradient (19 s−1), which is 1.1–2.3 times the flux achieved at higher or non-velocity gradients. The flocs formed at low velocity gradient were large and loose, while those formed at high velocity gradient were small and compact. Subsequently, the cake layer stacked by loose flocs was thicker and coarser than that by compact flocs, and exhibited a lower specific cake resistance, yielding a higher average flux. Moreover, a theoretical model for average flux was developed by introducing the velocity gradient, which directly elucidates how hydrodynamic shear affects floc characteristic, cake structure and filtration flux for the coagulation macro-filtration of Aphanizomenonflos-aquae. This study lays a theoretical foundation for the optimization of coagulation macro-filtration performance of microalgae and provides a new solution for the large flux removal of cyanobacteria by artificially regulating the coagulation hydrodynamic shear.

Investigation of the influence of the bluff-body temperature on a lean premixed DME/air flame approaching blowoff

In flames stabilized by a two-dimensional (2D) bluff body, the lean blowoff (LBO) limit can be extended by increasing the bluff-body temperature, which is verified experimentally in premixed dimethyl ether (DME)/air flames in this work. Two bluff-body temperatures of 573 K and 773 K are tested, respectively. High-speed OH* chemiluminescence (CL) imaging is applied to record the spatial distribution of the heat release. Particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) are performed simultaneously to explore the flow field and the combustion characteristics. Based on the results of OH*-CL, the heat release of the area near the bluff body is strengthened in the case of higher bluff-body temperature, and the enhanced chemical reactivity will further influence the downstream area. The turbulent flame speed obtained by OH-PLIF is increased in the entire area of interest. Due to the higher velocity gradient adjacent to the bluff body in the upstream region (y < 35 mm), the flame surface density (FSD), brush thickness, and flame wrinkling ratio are not sensitive to the bluff-body temperature. However, in the downstream region (y > 35 mm), a noticeable change can be found in these three parameters due to a higher turbulent flame speed and a much lower velocity gradient. Based on the PIV results, a limited effect on the velocity field by increasing the bluff-body temperature by 200 K. Furthermore, the probability density functions (PDF) of the vorticity and strain rate on the flame front are computed. The results indicate that the enhanced flame stability leads to a more pronounced overlapping between the flame front and the high-vorticity region, further increasing the values of these two parameters.

From the Lebombo Monocline to the Mozambique Deep Basin, using combined wide-angle and reflection seismic data

The North Natal valley (NNV), South Mozambique margin, is a key area for the understanding of the SW Indian Ocean history since the Gondwana break-up as its crustal nature and geometry strongly impacted the reconstruction of the paleogeography before the rifting. It is also of considerable importance for the understanding of the evolution of a margin system as the NNV is situated at the transition between divergent and strike-slip segments and at the conjunction of Oxfordian-Kimmeridgian Indian Ocean and the Valanginian-Aptian Atlantic one. As one part of the PAMELA project (PAssive Margins Exploration Laboratories), the NNV and the East Limpopo margin have been investigated during the MOZ3/5 cruise (2016), through the acquisition of 7 intersecting wide-angle profiles and coincident marine multichannel (720 traces) seismic as well as potential field data. Simultaneously, land seismometers were deployed in the Mozambique coastal plain (MCP), extending six of those profiles on land for about 100 km in order to provide information on the onshore-offshore transition. Wide-angle seismic data are of major importance as they can highlight constraints on the crustal structure of the margin and the position of the continent-ocean boundary in an area where the crustal nature is poorly known and largely controversial. The MOZ3/5 data set therefore reveals new essential constraints for kinematic reconstructions. This work presents results on the crustal structure from P-waves velocity modeling along two E-W wide-angle profiles (MZ1 and MZ2) through the NNV, from the Lebombo Monocline to the Mozambique Basin (MB), and crossing the Mozambique Fracture Zone (MFZ).The new geophysical data reveals an upper sedimentary sequence characterized by low velocities generally not exceeding 3 km/s, and up to 3 km thick where a major contouritic structure was observed. This feature formes together with several other contouritic structures, a N-S alignment just west of the MFZ, which produces high positive gravity anomalies, previously thought to be related to the magmatism that built the Galathea and Dana Plateaus. High velocity lenses are locally identified through the sedimentary layers and interpreted as inter-bedded volcanic sills. Furthermore, from the NNV to the MFZ, the underlying sequence is formed of a 3.0–3.5 km thick volcano-sedimentary sequence presenting important lateral changes in its seismic signature and characterized by a large velocity range (4.4 to 5.8 km/s), which partly reflects variations in the volcanic/sedimentary ratio laterally and with depth. At depth, an initially smoother and reduced eastward thinning of the crust occurs to the West below the continental shelf, from 34 to 31 km thick. The crustal thickness remains relatively constant of about 28–29 km along the Central Domain (CD), whereas a second and major region of thinning (26 to 12 km thick) is imaged West of the MFZ, in the southward prolongation of the Limpopo Corridor (LC). By contrast, as the eastern extremity, the crust is <10 km thick when reaching the MB. Crustal velocities reveal low velocity gradients, with atypical high velocities, increasing to 7.3 to 7.6 km/s at the base of the crust, and globally in the whole crust in the LC, just West of the MFZ. We interpreted the velocity architecture combined with the evidence of volcanism at shallower depths as indicative of an intensively intruded continental crust in the NNV, and discuss the particular segmentation of the longest profile (MZ1) in the kinematic context of both divergent and strike-slipe segments offshore Mozambique.Combining wide-angle and reflection seismic observations along these two profiles and the other MOZ3/5 lines, the data shows a coherent segmentation of the E-W crustal architecture off South Mozambique. These results along MZ1 and MZ2 profiles, combined with the previously published profiles, gives a 3D-view of the NNV, which becomes one of the most passive margins covered in the world by deep wide-angle seismic data.

Evaluation of the sensitivity on mesoscale eddy associated with the sea surface height anomaly forecasting in the Kuroshio Extension

The sensitivity of the sea surface height anomaly (SSHA) forecasting on the accuracy of mesoscale eddies over the Kuroshio Extension region, which was determined by the conditional non-linear optimal perturbation (CNOP) method using a two-layer quasigeostrophic model, is evaluated by adopting multiply realistic marine datasets through an advanced particle filter assimilation method. It is shown that, if additional observations are preferentially assimilated to the sensitive area of mesoscale eddies identified by the CNOP, where the eddies present a clear high- to low-velocity gradient along the eddy rotation, the forecasting skill of the SSHA can be more significantly improved. It is also demonstrated that the forecasts of the SSHA in the region where the large-scale mean flow possesses much stronger barotropic and/or baroclinic instability tend to exhibit stronger sensitivity to the accuracy of the initial field in the sensitive area of mesoscale eddies. Therefore, more attention should be preferentially paid to the assimilation of the additional observations of the mesoscale eddies for the SSHA forecast in the region with a strong velocity shear of ocean circulation. The present study verifies the sensitivity on mesoscale eddies of SSHA forecasts derived by the two-layer quasigeostrophic model using multiply sets of realistic oceanic data, especially including observation and reanalysis data, which further additionally demonstrates the importance of targeted observations of mesoscale eddies to the SSHA forecast in the regions of strong velocity shear of ocean circulation and provides a more credible scientific basis for the field campaign of the targeted observations for mesoscale eddies associated with the SSHA forecasting.

Gas kinematics around filamentary structures in the Orion B cloud

Context. Understanding the initial properties of star-forming material and how they affect the star formation process is key. From an observational point of view, the feedback from young high-mass stars on future star formation properties is still poorly constrained. Aims. In the framework of the IRAM 30m ORION-B large program, we obtained observations of the translucent (2 ≤ AV &lt; 6 mag) and moderately dense gas (6 ≤ AV &lt; 15 mag), which we used to analyze the kinematics over a field of 5 deg2 around the filamentary structures. Methods. We used the Regularized Optimization for Hyper-Spectral Analysis (ROHSA) algorithm to decompose and de-noise the C18O(1–0) and 13CO(1–0) signals by taking the spatial coherence of the emission into account. We produced gas column density and mean velocity maps to estimate the relative orientation of their spatial gradients. Results. We identified three cloud velocity layers at different systemic velocities and extracted the filaments in each velocity layer. The filaments are preferentially located in regions of low centroid velocity gradients. By comparing the relative orientation between the column density and velocity gradients of each layer from the ORION-B observations and synthetic observations from 3D kinematic toy models, we distinguish two types of behavior in the dynamics around filaments: (i) radial flows perpendicular to the filament axis that can be either inflows (increasing the filament mass) or outflows and (ii) longitudinal flows along the filament axis. The former case is seen in the Orion B data, while the latter is not identified. We have also identified asymmetrical flow patterns, usually associated with filaments located at the edge of an H II region. Conclusions. This is the first observational study to highlight feedback from H II regions on filament formation and, thus, on star formation in the Orion B cloud. This simple statistical method can be used for any molecular cloud to obtain coherent information on the kinematics.

A Semi-Empirical Model to Estimate Maximum Floc Size in a Turbulent Flow.

The basic model for agglomerate breakage under the effect of hydrodynamic stress (dmax = C.G−γ) is only applicable for low velocity gradients (<500 s−1) and is often used for shear rates that are not representative of the global phenomenon. This paper presents a semi-empirical model that is able to predict mean floc size in a very broad shear range spanning from aggregation to floc fragmentation. Theoretical details and modifications relating to the orthokinetic flocculation output are also provided. Modelling changes in turbidity in relation to the velocity gradient with this model offer a mechanistic approach and provide kinetic agglomeration and breakage index ka and kb. The floc breakage mode is described by the relationship between the floc size and the Kolmogorov microscale. Shear-related floc restructuring is analysed by monitoring the fractal dimension. These models, as well as those used to determine floc porosity, density and volume fraction, are validated by the experimental results obtained from several flocculation operations conducted on ultrafine kaolin in a 4-litre reactor tank compliant with laws of geometric similarity. The velocity gradient range explored was from 60 to 6000 s−1.

Flow Velocity Gradient of Refined Hydrocarbon and Viscous Fluid in A Single Stage Symmetrical Bifurcated Channel

A single stage bifurcated system in its wide spectrum of applications in the petroleum and gas processing industry, chemical industry and civil engineering industry, in the distribution and recovery of processed and unprocessed fluid and materials. Considered in this experimental investigation of the impact of a single stage symmetrical bifurcated system on the flow of viscous fluid and refined hydrocarbon to truly establish a relationship between specific dimensions of symmetrical bifurcated flow channels and the physical properties of various classes of fluid samples. Peanut oil and diesel were selected to respectively represent viscous fluid and refined hydrocarbon, as they are allowed to flow through some selected angles of a single stage symmetrical bifurcated channel until designated volumes of each of the fluid samples are recovered into a recovery beaker. Profile of results presented from the experimental study reveals a trend with a sharp negative velocity gradient for small flow time corresponding to smaller&#x0D; recovery volume and a much lower velocity gradient for relatively higher flow time for higher recovery volume for less viscous and dense diesel oil representing refined hydrocarbon and a more viscous and dense peanut oil represented by the trend with a lower negative velocity gradient. The implication of the results obtained is that bifurcated systems offer flow stability in a continuous flow situation, and also observed from the results is the confirmation of the existence of velocity gradient between opposite wall of the branched channels, which further reveals where the flow state will eventually begin to graduate into turbulence. The study can be extended by investigating the impact of two-stage or multiple level bifurcated network system on flow structure and stability, and how the pressure based on the level of fluid in the reservoir is related to the flow velocity and stability.

The most sensitive initial error of sea surface height anomaly forecasts and its implication for target observations of mesoscale eddies

Abstract We used the conditional nonlinear optimal perturbation (CNOP) approach to investigate the most sensitive initial error of sea surface height anomaly (SSHA) forecasts by using a two-layer quasigeostrophic model and revealed the importance of mesoscale eddies in initialization of the SSHA forecasts. Then, the CNOP-type initial errors for individual mesoscale eddies were calculated, revealing that the errors tend to occur in locations where the eddies present a clear high-to low-velocity gradient along the eddy rotation and the errors often have a shear SSHA structure present. Physically, we interpreted the rationality of the particular location and shear structure of the CNOP-type errors by barotropic instability from the perspective of the Lagrange expression of fluid motions. Numerically, we examined the sensitivity of the CNOP-type errors by using observing system simulation experiments (OSSEs). We concluded that if additional observations are preferentially implemented in the location where CNOP-type errors occur, especially with a particular array indicated by their shear structure, the forecast ability of the SSHA can be significantly improved. These results provide scientific guidance for the target observation of mesoscale eddies and therefore are very instructive for improving ocean state SSHA forecasts.

Effect of blowing ratio on film-cooling effectiveness of ginkgo shaped holes: a numerical approach

Modern gas turbine engines operate at high temperatures to improve thermal efficiency and power output. Increased rotor inlet temperatures increase the rate of heat transfer to the turbine blades, which requires sophisticated cooling schemes to keep the blade temperature at acceptable levels. This work is a numerical investigation of film cooling techniques as applied to gas turbines. The cooling performance of two differently shaped holes, namely, Ginkgo Forward and Ginkgo Reverse, were investigated in terms of centerline and local lateral cooling effectiveness, and a comprehensive comparison was made with the cooling performance of a cylindrical hole. The investigations were performed at a constant density ratio (DR = 2.0) and three different blowing ratios (BR = 1.0, 1.5, and 2.0). Under all of the operating conditions, the results demonstrated significant augmentation in centerline and lateral cooling effectiveness when the Ginkgo Reverse shaped hole was used, followed by the Ginkgo Forward and cylindrical cooling holes. For the shaped cooling holes, the low velocity gradient through the film alleviated the jet lift-off and turbulence, resulting in decreased entrainment of hot gas to the bottom surface. To conclude, the prominent lateral dispersal of the coolant due to the shaped cooling holes significantly enhanced thermal protection and the overall cooling performance.

Crustal Structure of the Northern Hikurangi Margin, New Zealand: Variable Accretion and Overthrusting Plate Strength Influenced by Rough Subduction

AbstractExploring the structure of convergent margins is key to understanding megathrust slip behavior and tsunami generation. We present new wide‐angle and marine multichannel seismic data that constrain the crustal structure and accretion dynamics of the northern Hikurangi margin. The top of the basement of the Hikurangi Plateau is overlain by a rough, 2–3 km thick layer of volcanic cover with P‐wave velocities (VP) between 3 and 5 km/s. This volcanic cover contributes significantly to seismic reflectivity beneath the shallow subduction plate boundary. The frontal prism structure varies along‐strike from ∼25 km wide with imbricate thrust faults where accretion of trench sediments is undisrupted, to narrower (∼14 km) with slumps and branching, irregular thrust fault geometries, which may reflect lower sediment supply or past seamount collisions. A large thrust fault network in the inner prism with a seismically fast hanging wall indicates a mechanical boundary between a seismically faster deforming backstop and the seismically slower frontal prism. Near the coastline, VP increases between 2.8 and 4 km/s at 2–8 km depth and is 0.5–1.7 km/s slower than the southern Hikurangi margin. Low seismic wavespeeds and low vertical velocity gradients in the inner prism support the hypothesis that a weak overthrusting plate contributes to historic tsunami‐earthquakes and long duration seismic ground motion.

Deep Structure of the North Natal Valley (Mozambique) Using Combined Wide‐Angle and Reflection Seismic Data

AbstractThe North Natal Valley (NNV) and the Mozambique Coastal Plain (MCP) are key areas for the understanding of the SW Indian Ocean history since the Gondwana break‐up. Nevertheless, the deep structures and the nature of the NNV and MCP remain discussed in the absence of deep geophysical data. In 2016, the NNV, MCP and Limpopo margin (LM) have been investigated along seven wide‐angle and MCS profiles. The combined wide‐angle and reflection seismic interpretation along the N‐S MZ7 profile reveals an upper sedimentary sequence characterized by low velocities generally not exceeding 3 km/s, with thicknesses varying from 0.150 km in the central part to ∼2.8 km in the south. The underlying sequence is formed of a 2.53.0 km thick volcano‐sedimentary sequence which presents important lateral and with depth changes and presence of high velocity lenses, indicating inter‐bedded volcanic sills and recurrent magmatic episodes. The south of the NNV including the Naude Ridge (NR) presents a disturbed sedimentary cover with structural highs and southward‐dipping reflectors and sub‐basins. The crust, reaching 35–40 km onshore below the MCP, gently thins below the continental shelf to a regular thickness of ∼29 km below the NNV. Crustal velocities reveal low velocity gradients, with atypical high velocities. South the ND, the crust thins to 15 km. We interpret the velocity architecture combined with the evidences of volcanism at shallower depths as indicating an intensively intruded continental crust. Contrary to what is proposed in most geodynamic models, the Mozambique Coastal plain and the Natal Valley are both of continental nature, with an abrupt necking zone located south of NR. The Antarctica plate was therefore situated at the eastern limit of these two domains before the Gondwana breakup.

Composition and Seismic Properties of the Oceanic Lithosphere: A Synthesis of Ophiolites and Core Samples of the IODP

AbstractOur knowledge of the oceanic lithosphere largely comes from analogy with ophiolite complexes and the direct scientific drilling of the present‐day oceanic crust (e.g., Christensen and Salisbury, 1975, 1989; Smith and Vine, 1989; Dilek and Furnes, 2011, 2014). In this study, we summarized previous experimental results on seismic properties of oceanic lower crust and upper mantle according to different tectonic settings. The results are used to highlight the compositional heterogeneity and the nature of the oceanic Moho. Observation in different ophiolites reveal an ideal oceanic lithosphere profile with ideal petrologic units and seismic units (Dilek and Furnes, 2011, 2014). The lithospheric mantle beneath ocean basins is composed of tectonized peridotites, which include layered lherzolites and harzburgites and lenses of dunites with chromitites and nearly correspond to the seismic Layer 4. The overlying layered gabbros and mafic sheeted dike complex equal to the seismic Layer 3, as a result of crystallization from a magma chamber. The transitional unit between the former two petrologic units consists of layered ultramafic and mafic rocks, corresponds to the petrological Moho. The seismic Layer 2 and 1 are well defined by pillow lavas and massive flows, and the overlying abyssal sediments, respectively. Compared these results with the refraction seismic profiles, the oceanic crust and upper mantle show different composition and structure. The P‐wave velocities of the Layer 3 gabbros varies from 6.7 to 7.0 km s‐1 and have low velocity gradients of &lt;0.1 km s‐1. Although the gradual increase of P‐ and S‐wave velocities with depth can be attributed to the increasing proportion of mafic minerals from the top to the bottom, prehnite‐pumpellyite facies alteration of basalts, greenschist‐faces metamorphism to epidote‐amphibolite facies metamorphism of gabbros will decrease the velocities of the Layer 2 and Layer 3 (Christensen and Salisbury, 1975, 1989), because the P‐wave velocities of chlorite and hornblende are 6.00 and 7.00 km s‐1, respectively, lower than those of plagioclase and pyroxene, respectively (Carlson, 2004). In addition, local velocity anomalies near the petrologic Moho can be related serpentinization of ultramafic rocks (Salisbury and Christensen, 1978;Carlson et al., 2009). In the Layer 4, the characteristic P‐wave velocities of the upper mantle should fall in the range of 7.8 to 8.2 km s‐1. Poisson's ratios of chrysotile and lizardite, which are stable in oceanic crustal environments according to the phase diagram, is 0.267 and 0.359, respectively, higher than those of olivine and pyroxene (Wang et al., 2013). Serpentinization will significantly decreased velocities and densities of peridotites and is the main reason for the variation of the Moho reflectivity beneath oceans.

Wall temperature effects on shock wave/turbulent boundary layer interaction via direct numerical simulation

Shockwave/turbulent boundary layer interaction on flat plate are investigated by using direct numerical simulation at different wall temperature of Tw/Tr=0.5,1.0,2.0 respectively. Responses of skin friction, velocity profile and root mean square velocity profile are examined. Analysis on velocity profiles indicate that streamwise velocity in the outer part of boundary layer experiences a reduction with wall temperature going up. Skin friction decreases while wall is heating mainly caused by a lower velocity gradient near the wall at a high temperature. A lower skin friction on high wall temperature results in a stronger separation. The comparison of root mean square velocity profile shows turbulent kinetic energy is augmented on a heating wall. The maximum value moves closer to the wall with wall temperature increasing. The scale of separation bubble is amplified with wall temperature increasing. Near-wall streaks become unstable and get an increment in spanwise distance. The process of near-wall strip vortices evolving to complicated 3-dimonsional structures is accelerated and amplified in a high wall temperature. Counter-rotating vortex in reattachment process is evaluated in the three cases. The scale of such vortex gets larger when wall temperature gets higher. The spanwise distance between counter-rotating vortices rises obviously and break down to smaller coherent structures quicker.

Deposition and oxidation behavior of atmospheric laminar plasma sprayed Mo coatings from 200 mm to 400 mm under 20 kW: Numerical and experimental analyses

A stable laminar plasma jet with a jet length of above 600 mm was adopted to deposit molybdenum coatings to investigate the behavior of high-melting point metal, molybdenum, and particles during laminar plasma spraying process. The temperature, velocity, and species distribution of the plasma jet were calculated by numerical simulation. In the experiment, the temperature and velocity distribution of the in-flight particles were measured, and the microstructure and properties of the coatings were analyzed. Combining the results of the simulation and experimental results, the deposition behavior and oxidation mechanism of the coatings prepared at the spray distance from 200 mm to 400 mm were discussed. The results indicate that both the laminar plasma jet and injected particles exhibit high temperature and low velocity, and low temperature and velocity gradients. The microstructure of the coatings shows a high similarity and hardly changes when the spray distance exceeds 250 mm. When the spray distance is 200 mm, post-deposition oxidation occurs due to the heating effect of the long plasma jet on the substrate. In contrast, when the spray distance is longer, the particles undergo severe in-flight oxidation, and the oxide formed is uniformly distributed in the coating improving the hardness from 500 HV0.3 to 700 HV0.3.

Obstacles, Interfacial Forms, and Turbulence: A Numerical Analysis of Soil\u2013Water Evaporation Across Different Interfaces

Exchange processes between a turbulent free flow and a porous media flow are sensitive to the flow dynamics in both flow regimes, as well as to the interface that separates them. Resolving these complex exchange processes across irregular interfaces is key in understanding many natural and engineered systems. With soil–water evaporation as the natural application of interest, the coupled behavior and exchange between flow regimes are investigated numerically, considering a turbulent free flow as well as interfacial forms and obstacles. Interfacial forms and obstacles will alter the flow conditions at the interface, creating flow structures that either enhance or reduce exchange rates based on their velocity conditions and their mixing with the main flow. To evaluate how these interfacial forms change the exchange rates, interfacial conditions are isolated and investigated numerically. First, different flow speeds are compared for a flat surface. Second, a porous obstacle of varied height is introduced at the interface, and the effects the flow structures that develop have on the interface are analyzed. The flow parameters of this obstacle are then varied and the interfacial exchange rates investigated. Next, to evaluate the interaction of flow structures between obstacles, a second obstacle is introduced, separated by a varied distance. Finally, the shape of these obstacles is modified to create different wave forms. Each of these interfacial forms and obstacles is shown to create different flow structures adjacent to the surface which alter the mass, momentum, and energy conditions at the interface. These changes will enhance the exchange rate in locations where higher velocity gradients and more mixing with the main flow develop, but will reduce the exchange rate in locations where low velocity gradients and limited mixing with the main flow occur.

A multi-diagnostic spectral analysis of penumbral microjets

Context. Penumbral microjets (PMJs) are short-lived, jet-like objects found in the penumbra of sunspots. They were first discovered in chromospheric lines and have later also been shown to exhibit signals in transition region (TR) lines. Their origin and manner of evolution is not yet settled. Aims. We perform a comprehensive analysis of PMJs through the use of spectral diagnostics that span from photospheric to TR temperatures to constrain PMJ properties. Methods We employed high-spatial-resolution Swedish 1-m Solar Telescope observations in the Ca II 8542 Å and H α lines, IRIS slit-jaw images, and IRIS spectral observations in the Mg II h &amp; k lines, the Mg II 2798.75 Å &amp; 2798.82 Å triplet blend, the C II 1334 Å &amp; 1335 Å lines, and the Si IV 1394 Å &amp; 1403 Å lines. We derived a wide range of spectral diagnostics from these and investigated other secondary phenomena associated with PMJs. Results. We find that PMJs exhibit varying degrees of signal in all of our studied spectral lines. We find low or negligible Doppler velocities and velocity gradients throughout our diagnostics and all layers of the solar atmosphere associated with these. Dark features in the inner wings of H α and Ca II 8542 Å imply that PMJs form along pre-existing fibril structures. We find evidence for upper photospheric heating in a subset of PMJs through emission in the wings of the Mg II triplet lines. There is little evidence for ubiquitous twisting motion in PMJs. There is no marked difference in onset-times for PMJ brightenings in different spectral lines. Conclusions. PMJs most likely exhibit only very modest mass-motions, contrary to earlier suggestions. We posit that PMJs form at upper photospheric or chromospheric heights at pre-existing fibril structures.

Genesis of Antibiotic Resistance LIX: Fluid Resuscitation Induced Aberrant Intracranial Pressure (“Monroe‐Kellie” Doctrine (MKD) Contort Tethered Leucocytes / Platelets Crest “Critical Closing Pressure” (CCP)

NCT01663701 noted that the median volume of iv fluid administered within 6 hours of presenting to ER in the sepsis intervention group was 3.5 L. The mean volume administered during the similar time interval in prior sepsis resuscitation trials were 5.0 L (EGDT); 5.1 L (ProCESS); and 4.5 L (ARISE). Criticisms of NCT01663701 such as a. the suggested vs administered median volume of fluid administered during the initial phase of resuscitation in the sepsis protocol group (3.5L) may have been higher than the 30 mL/kg recommended by SSC guidelines; b.”Each 1‐hour delay in antibiotic administration was associated with an absolute increase in mortality in the range of 5% to 10%”; and c. the median volume of iv fluid administered between ER presentation and 6 hours for BMI 18.5 kg/m2 ~ 70 mL/kg, here we present a plausible pathophysiological sequel as a contributing factor for mortality rate. Within the six hrs. of fluid resuscitation, a surge of fluid bolus mounted an adverse pressure gradient on the sphincters in metarterioles deregulating the pulsatile blood flow into the capillary bed. Based on the “Whole Brain Fluid and Osmolyte Network Model or” or “The whole brain network” approach a mechanistic model inclusive of major cranial compartments simulated the effect of osmotic therapy predicted that critical intracranial pressure (ICP) increased to &gt;30 mmHg, with insufficient cerebral perfusion, and ventriculomegaly. The ventricular enlargement, in turn, reduces extracellular milieu for fluid exchange lead to a chronic increase in ventricular size shifts attributed to osmolyte administered. It is our hypothesis that after fluid resuscitation blood flows against an adverse pressure gradient in the capillary bed. The fluid particles such as activated and/or aggregating Cellular Aggregates near to the endothelial layer due to their low kinetic energy, “Cellular Aggregates” flows in the opposite direction. Such Cellular Aggregates cannot surmount the adverse pressure, lead to the formation of eddies. Such eddies in the arterial end are likely to cause local flow reversal zone and which retard the velocity concurrently the pressure of the blood flow. Under the low velocity and pressure gradient, the cellular eddies start separating from the endothelium referred to as boundary layer separation causing the blood flow to decelerate against an adverse pressure gradient. Then in the upstream part which is the venous end of the capillary bed, where the cellular eddies achieve boundary layer separation, causing blood pressure to drop from that of the arterial end creating the eddies to drag. At this stage, the pressure distribution in the capillary bed is at the stagnation point, where the velocity becomes zero at which cellular eddies form DIC. Sustained fluid bolus with vasopressor likely to form a non‐pulsatile flow pattern forming turbulent eddies in the venous end and disseminate the coagulated eddies leading to an aberration in the “MKD”. Dysregulated ICP, in turn, alter the ARGR leading to hypoperfusion subsequently coma.Support or Funding InformationSupported by pd funds and in part CME activities of Subburaj Kannan MD PhD for www.aaets.org

The Cloud Factory I: Generating resolved filamentary molecular clouds from galactic-scale forces

ABSTRACT We introduce a new suite of simulations, ‘The Cloud Factory’, which self-consistently forms molecular cloud complexes at high enough resolution to resolve internal substructure (up to 0.25 M⊙ in mass) all while including galactic-scale forces. We use a version of the arepo code modified to include a detailed treatment of the physics of the cold molecular ISM, and an analytical galactic gravitational potential for computational efficiency. The simulations have nested levels of resolution, with the lowest layer tied to tracer particles injected into individual cloud complexes. These tracer refinement regions are embedded in the larger simulation so continue to experience forces from outside the cloud. This allows the simulations to act as a laboratory for testing the effect of galactic environment on star formation. Here we introduce our method and investigate the effect of galactic environment on filamentary clouds. We find that cloud complexes formed after a clustered burst of feedback have shorter lengths and are less likely to fragment compared to quiescent clouds (e.g. the Musca filament) or those dominated by the galactic potential (e.g. Nessie). Spiral arms and differential rotation preferentially align filaments, but strong feedback randomizes them. Long filaments formed within the cloud complexes are necessarily coherent with low internal velocity gradients, which has implications for the formation of filamentary star-clusters. Cloud complexes formed in regions dominated by supernova feedback have fewer star-forming cores, and these are more widely distributed. These differences show galactic-scale forces can have a significant impact on star formation within molecular clouds.