Downstream Distributions Research Articles

Spatiotemporal Analysis of Particle Spread to Assess the Hybrid Particle-Flow CFD Model of Radioembolization of HCC Tumors.

Computational fluid dynamics (CFD) models can potentially aid in pre-operative planning of transarterial radioactive microparticle injections to treat hepatocellular carcinoma, but these models are computationally very costly. Previously, we introduced the hybrid particle-flow model as a surrogate, less costly modelling approach for the full particle distribution in truncated hepatic arterial trees. We hypothesized that higher cross-sectional particle spread could increase the match between flow and particle distribution. Here, we investigate whether truncation is still reliable for selective injection scenarios, and if spread is an important factor to consider for reliable truncation. Moderate and severe up- and downstream truncation for selective injection served as input for the hybrid model to compare downstream particle distributions with non-truncated models. In each simulation, particle cross-sectional spread was quantified for 5-6 planes. Severe truncation gave maximum differences in particle distribution of ∼4-11% and ∼8-9% for down- and upstream truncation, respectively. For moderate truncation, these differences were only ∼1-1.5% and ∼0.5-2%. Considering all particles, spread increased downstream of the tip to 80-90%. However, spread was found to be much lower at specific timepoints, indicating high time-dependency. Combining domain truncation with hybrid particle-flow modelling is an effective method to reduce computational complexity, but moderate truncation is more reliable than severe truncation. Time-dependent spread measures show where differences might arise between flow and particle modelling. The hybrid particle-flow model cuts down computational time significantly by reducing the physical domain, paving the way towards future clinical applications.

Controls on distributions of aluminium, manganese and cobalt in the South Atlantic Ocean along GEOTRACES transect GA10

Trace metals (TMs) manganese (Mn), cobalt (Co), and aluminium (Al) have important geochemical and biological roles in the ocean. Here, we present full depth profiles of dissolved (d) and particulate Al, Mn, and Co along the latitude of 40 °S in the South Atlantic Ocean from the GEOTRACES GA10 cruises that operated in austral spring 2010 and summer 2011. The region is characterized by enhanced primary productivity and forms a key transition zone between the Southern Ocean and South Atlantic Subtropical Gyre. The mean concentrations of dAl, dCo, and dMn (±standard deviation) were 3.36 ± 2.65 nmol kg−1, 35.3 ± 17.6 pmol kg−1, and 0.624 ± 1.08 nmol kg−1, respectively. Their distributions in surface waters were determined by external sources and complex internal biogeochemical processes. Specifically, surface ocean dCo was controlled by the interplay between phytoplankton uptake, remineralization and external inputs; dMn was likely determined by the formation and photoreduction of Mn-oxides; and dAl was supplied by atmospheric deposition and removed by scavenging onto particles. Fluvial and sedimentary inputs near the Rio de La Plata estuary and benthic sources from the Agulhas Bank resulted in elevated dTM concentrations in near-shore surface waters. These externally sourced dTMs were effectively delivered to the open ocean by offshore diffusion and/or advection, and potentially facilitated enhanced primary productivity along the transect.The distributions of dTMs at depth were predominantly controlled by the mixing of North Atlantic Deep Water (NADW) and waters of Antarctic origin (e.g., Upper Circumpolar Water (UCDW) and Antarctic Bottom Water (AABW)). The calculated endmember concentrations of dAl and dCo in NADW showed minor decreases in the SASTG following north–south transport, suggesting removal rates of 0.064 nM/year and 0.035–0.075 pM/year, respectively. The endmember concentration of dCo in AABW was maintained at ∼30 pmol kg−1 without evidence for scavenging removal in the Southern Ocean and SASTG (time frame >400 years). The concentrations of dMn in NADW and AABW were between 0.1 and 0.16 nmol kg−1, and any elevated dMn concentrations were ascribed to local external inputs (e.g., from sediments in the Argentine Basin and hydrothermal activity near the Mid-Atlantic Ridge). Hence, four controlling factors (sources, internal cycling, water mass mixing and time) need to be considered when assessing TM distributions in the global ocean, even for TMs that are vulnerable to scavenging removal processes. Because the deep waters formed in high latitude oceans are crucial components of the global thermohaline overturning system, any processes (e.g., glacier melting, upwelling and sinking, and biological activity) that impact the preformed dTM concentrations in high latitude oceans will determine the downstream dTM distributions. Therefore, the sources and sinks of TMs and associated biological activity in high latitude oceans could engender basin to global scale impacts on seawater distributions of Al, Co, and Mn and their stoichiometric relationships with macronutrients, and the global biogeochemical cycles of these scavenged-type TMs.

Scattering of Superthermal Ions at Shocks: Dependence on Energy

Diffusive shock acceleration requires the production of backstreaming superthermal ions (injection) as a first step. Such ions can be generated in the process of scattering of ions in the superthermal tail off the shock front. Knowledge of the scattering of high-energy ions is essential for matching conditions of upstream and downstream distributions at the shock transition. Here we analyze the generation of backstreaming ions as a function of their initial energy in a model stationary shock and in a similar rippled shock. Rippling substantially enhances ion reflection and the generation of backstreaming ions for slightly and moderately superthermal energies, and thus is capable of ensuring ion injection into a further diffusive shock acceleration process. For high-energy ions, there is almost no difference in the fraction of backstreaming ions produced and the ion distributions between the planar stationary shock and the rippled shock.

Experimental study of downstream local heat flux of pool fires under relatively strong cross flows

Pool fire is the common form of combustion posing hazard to surroundings by thermal heat transfer. The local heat flux of pool fire under relatively small cross flow has been widely studied. However, none work investigates the influence of relatively strong cross flow to the local heat flux of pool fires. In this study, experiments are carried out to reveal the effect of strong cross flow on the downstream heat flux distributions of pool fires. Four square quartz sand boxes with the side lengths of 8 cm, 10 cm, 15 cm, and 20 cm are applied to simulate the pool fires. The cross flow speed ranges from 0 to 5.0 m/s. Eight local heat flux gauges are aligned downstream with 6 cm interval. In still air or when the flame base drag is smaller than the distance (6 cm) between the closest heat gauge and downstream pool rim, the heat flux decreases monotonically with the downstream distance. For other conditions, the local heat flux firstly increases then decreases with the downstream distance. And the location of peak local heat flux is the same as the flame base drag length. For a given pool size and heat release rate, the evolution of local heat flux with cross flow speed is complicated and shows three trends. Local heat flux is determined by the flame base drag representing the influence of pool dimension, cross flow speed, heat release rate and side entrainment, as well as downstream distance. Two regions of local heat flux are observed based on the different physics of heat transfer. Correlations are obtained for the two regions respectively and agree well with the experimental data.

Scattering of Ions at a Rippled Shock

In a collisionless shock the energy of the directed flow is converted to heating and acceleration of charged particles, and to magnetic compression. In low-Mach number shocks the downstream ion distribution is made of directly transmitted ions. In higher-Mach number shocks ion reflection is important. With the increase of the Mach number, rippling develops, which is expected to affect ion dynamics. Using ion tracing in a model shock front, downstream distributions of ions are analyzed and compared for a planar stationary shock with an overshoot and a similar shock with ripples propagating along the shock front. It is shown that rippling results in the distributions, which are substantially broader and more diffuse in the phase space. Gyrotropization is sped up. Rippling is able to generate backstreaming ions, which are absent in the planar stationary case.

Resiliency of Apache Trout habitats in a warmer and drier climate future

AbstractObjectiveThe Southwest has the hottest and driest climate in the United States, and projections show that it will only get hotter and drier into the 2100s. The Apache Trout Oncorhynchus apache is native to the Southwest and is currently listed as threatened under the U.S. Endangered Species Act. Our goals were to understand how climate factors influence the distribution of juvenile Apache Trout (<125 mm TL) and how climate change will influence the suitability of Apache Trout habitat into the 2080s.MethodsWe used a species distribution model to evaluate how climatic and other factors influence the distribution of juvenile Apache Trout. We used predictions from the model to evaluate how climate change might impact the suitability of streams designated for recovery of the species into the 2080s.ResultJuvenile Apache Trout occurrence was predicted well by mean July stream temperature (°C), mean annual precipitation (dm), stream slope (%), and the presence of nonnative trout (area under the receiver operating characteristic curve = 0.85). Standardized parameter estimates showed that Rainbow Trout O. mykiss presence and annual precipitation influenced occupancy the most. Model predictions for the 2080s showed suitable habitat (occurrence probability ≥ 0.25) to increase for 11 (of 45) Apache Trout streams in the increased temperature (+3°C) only scenario (scenario 1), as headwater reaches that are currently too cold warmed to become more suitable. When we also included projected declines in annual precipitation (−5%) for the 2080s (scenario 2), the amount of suitable habitat decreased for eight Apache Trout streams and remained unchanged in all other streams.ConclusionMost Apache Trout populations are isolated upstream of barriers to nonnative trout in stream reaches that are currently thermally suitable with respect to mean July temperatures and would remain suitable into the 2080s. Cold headwater reaches are projected to warm, becoming more suitable in the 2080s. Thus, intentional isolation and the resultant truncated downstream distributions of Apache Trout populations in headwater streams explain the nominal effect of projected temperature increases due to climate change on this cold‐adapted salmonid. Standardized model parameters suggest that future declines in precipitation, manifested through reduced snowpack and its influence on streamflows, will play a larger role than temperature in the suitability—and, thus, resiliency—of Apache Trout habitats at least into the 2080s.

A fluid–structure interaction model for large wind turbines based on flexible multibody dynamics and actuator line method

With higher demand of affordable electricity and rapid development of wind turbine technology, scale of wind turbines has been upsizing. As a consequence, blades grow longer and slender. Large geometrically nonlinear deformation and vibration of the blades lead to more challenges in the structural design. In the aerodynamic analysis, traditional blade element momentum theory cannot predict the complicated behavior of these modern blades while fully resolved Navier–Stokes equation methods cost much time modeling and refinement. To overcome these challenges, this paper proposes a new numerical method to analyze turbine aeroelastic performance and fluid–structure interaction based on flexible multibody dynamics and large eddy simulation with anisotropic actuator line method. By comparing the results with various existing numerical methods, we show that the newly proposed method can effectively predict the performance of the wind turbine, such as deformation and power output. We find that blade flexibility poses noticeable impact on the performance of large scale turbines in normal working conditions. The location of nascent vortex is postponed by blade deflection. The max difference between rigid and flexible blades in downstream velocity distributions reaches 10% and occurs at a radial distance around 0.55D. The new method also takes the fluid–structure coupling effect and momentum interaction into consideration and eliminates the non-physical oscillations caused by uncoupled methods. Also, blades deflection and vibration are found to accelerate momentum exchange, which facilitates the wake recovery process. Furthermore,compared to the rigid-blade model, the turbulent kinetic energy obtained by the newly developed flexible-blade model is higher in the low-frequency region, in which large-scale vortices develop and the turbulent mixing effect is strong. This paper is expected to provide a framework for researchers and technology developers to design or estimate the performance of modern large wind turbines.

Pressure Loss Coefficients of Ductwork Fitting Combinations With and Without Vanes (Baffles)

Abstract Ductwork components in ventilation systems are often installed in close proximity to each other due to space constraints. Published pressure loss coefficients are, however, only valid if there are sufficient distances between components. In this work, pressure losses of common combinations of two, three, and four bends and the addition of internal vanes were investigated with computational fluid dynamic simulations and validated with reference data. Pressure losses of combinations of bends without vanes were higher or lower than the sum of the single pressure losses of the components (combination effect), depending on the components and orientation. For bends with abrupt deflections, strong combination effects occurred; in some cases, pressure losses doubled. The spacing between the components was also a relevant factor. Combination effects were most pronounced for spacing lengths of the same order as the length of the flow separation region of the upstream bends. Consequently, certain spacer lengths were particularly unfavorable. Combination effects were found to be complex to predict and fluid simulations proved to be useful for analyzing the interactions. Adding vanes was found to be very useful. For bends and combinations with sharp deflections, the pressure loss coefficients were reduced by a factor of ten with vanes. Vanes also effectively reduced detrimental combination effects. The combination pressure losses with vanes were in all cases lower than the sum of the single components pressure losses. Pressure loss coefficients for combinations with vanes had a strong dependency on the Reynolds number. Furthermore, the downstream flow distributions were more homogeneous with vanes.

Different heating of Maxwellian and kappa distributions at shocks

Ion heating in collisionless shocks is non-adiabatic and efficient. The amount of heating and the downstream distributions depend on the shock parameters and on the incident ion distribution. The number of reflected ions and their distribution depend on the detailed shape of the tail of the distribution. In supercritical shocks the reflected ion contribution is significant. Kappa distributed ions are heated more strongly and have a larger fraction of reflected ions than Maxwellian distributed ions with the same upstream temperature and the same shock parameters. For kappa distributions the phase space dips are shallower.

Probabilities of ion scattering at the shock front

Collisionless shocks efficiently convert the energy of the directed ion flow into their thermal energy. Ion distributions change drastically at the magnetized shock crossing. Even in the absence of collisions, ion dynamics within the shock front is non-integrable and gyrophase dependent. The downstream distributions just behind the shock are not gyrotropic but become so quickly due to the kinematic gyrophase mixing even in laminar shocks. During the gyrotropization all information about gyrophases is lost. Here we develop a mapping of upstream and downstream gyrotropic distributions in terms of scattering probabilities at the shock front. An analytical expression for the probability is derived for directly transmitted ions in the narrow shock approximation. The dependence of the probability on the magnetic compression and the cross-shock potential is demonstrated.

Effects of burner aspect ratio on heat flux distributions beneath unconfined ceilings with different inclination angles

The present study experimentally investigated the heat flux distributions produced by rectangular fire sources under unconfined inclined ceilings, which have not been quantified in previous studies. The source–ceiling heights, heat release rates, inclination angles of the ceilings (from 0∘ to 20∘ ), and aspect ratios of the rectangular burners (from 1 to 10) were considered comprehensively for a total of 160 sets of test conditions. The results showed that the ceiling heat fluxes in the upstream and downstream areas decreased with an increase in the radial distance. However, with an increase in the ceiling's inclination angle, the attenuation rate of the upstream ceiling heat flux decreased, while the attenuation rate of the downstream ceiling heat flux increased. The upstream and downstream heat flux distributions beneath the ceiling under all the experimental conditions could be well described by a modified model. This study provided quantitative data and a basic understanding of the heat flux distributions under an inclined ceiling induced by different rectangular-source fire impingements, which were essentially different from other previously reported ceiling jets.

Effect of Geometric Accuracy at the Proximal Landing Zone on Simulation Results for Thoracic Endovascular Repair Patients.

Existing hemodynamic studies on aortic dissection after thoracic endovascular aortic repair (TEVAR) apply geometric simplifications. This study aims to evaluate the necessity of more accurate geometries at the proximal landing zone in computational fluid dynamic (CFD) studies. Three patient-specific 3D aortic dissection models with different geometric accuracies at the proximal landing zone were manually fabricated for CFD simulations: (i) model 1 without the stent graft (SG), (ii) model 2 with the metal stent, and (iii) model 3 with the SG. The flow distribution, flow pattern, and wall shear stress (WSS)-related indicators in these three models were compared. The flow distributions were quite similar for the three models, with a maximum absolute difference of 0.27% at the left suclavian artery (LSA) between models 1 and 3 because of partial coverage. A more chaotic flow pattern was observed at the proximal landing zone in model 3, with significant regional differences in the WSS-related indicator distributions. The upstream and downstream WSS-related indicator distributions were quite similar for the three models. The flow pattern and hemodynamic parameter distributions were affected by the geometric accuracy only in a small region near the proximal landing zone. The flow split was hardly affected by the LSA partial coverage, indicating that the coverage may have slight effects on short-term blood perfusion. However, this conclusion needs to be verified in future studies with larger sample sizes.

PROTRIP: Probabilistic Risk-Aware Optimal Transit Planner.

Optimal routing in urban transit networks, where variable congestion levels often lead to stochastic travel times, is usually studied with the least expected travel time (LET) as the performance criteria under the assumption of travel time independence on different road segments. However, a LET path might be subjected to high variability of travel time and therefore might not be desirable to transit users seeking a predictable arrival time. Further, there exists a spatial correlation in urban travel times due to the cascading effect of congestion across the road network. In this work, we propose a methodology and a tool that, given an origin-destination pair, a travel time budget, and a measure of the passenger's tolerance for uncertainty, provide the optimal online route choice in a transit network by balancing the objectives of maximizing on-time arrival probability and minimizing expected travel time. Our framework takes into account the correlation between travel time of different edges along a route and updates downstream distributions by taking advantage of upstream real-time information. We demonstrate the utility and performance of our algorithm with the help of realistic numerical experiments conducted on a fixed-route bus system that serves the residents of the Champaign-Urbana metropolitan area.

MMS Observations of Accelerated Interstellar Pickup He+ Ions at an Interplanetary Shock

Abstract Interstellar pickup ions (PUI) are interstellar neutrals that have been ionized in transit through the heliosphere via charge exchange or photoionization. These new PUIs then “freeze” into the solar wind (SW) and move with the bulk SW velocity (V SW). They also begin to gyrate around the local magnetic field with V SW, resulting in a maximum PUI velocity of 2 ∗ V SW. Understanding how He+ PUIs are accelerated at shocks in space provides valuable insights into shock dynamics and shock acceleration mechanisms. On 2018 January 8, while the Magnetospheric Multiscale (MMS) Mission was in the SW, it observed the forward shock of a corotating interaction region. In this work, we analyze the upstream and downstream velocity distributions of He+ for this quasiperpendicular, marginally supercritical (θ Bn = 67°, M A = 2.8) interplanetary shock. We derive average two-dimensional pitch-angle distributions in the field-aligned SW frame, as well as reduced one-dimensional velocity distributions for selected upstream and downstream intervals. We find that the shock accelerates He+ largely perpendicular to the magnetic field, consistent with shock reflection. Furthermore, we derive a measured ratio of accelerated He+ ions by estimating a maximum speed in the downstream frame, above which we assume that He+ ions have been accelerated by their interaction with the shock. The measured acceleration ratio, R Measured = 0.14, is then compared to a theoretical ratio derived from a simple model of the upstream distribution, R Theoretical = 0.06.

Inactivation of airborne porcine reproductive and respiratory syndrome virus (PRRSv) by a packed bed dielectric barrier discharge non-thermal plasma

Porcine reproductive and respiratory syndrome virus (PRRSv) is one of the most significant airborne viruses impacting the pork industry in the US. Non-thermal plasmas (NTPs) are electrical discharges comprised of reactive radicals and excited species that inactivate viruses and bacteria. Our previous experiments using a packed bed NTP reactor demonstrated effective inactivation of bacteriophage MS2 as a function of applied voltage and power. The present study examined the effectiveness of the same reactor in inactivating aerosolized PRRSv. A PRRSv solution containing ∼105 TCID50/ml of PRRSv VR2332 strain was aerosolized at 3 ml/min by an air-jet nebulizer and introduced into 5 or 12 cfm air flow followed by NTP exposure in the reactor. Twin impingers upstream and downstream of the reactor collected samples of the virus-laden air flow for subsequent TCID50 assay and qPCR analyses. An optical particle sizer measured upstream and downstream aerosol size distributions, giving estimates of aerosol filtration by the reactor. The results showed that PRRSv was inactivated to a similar degree as MS2 at the same conditions, with the maximum 1.3-log inactivation of PRRSv achieved at 20 kV and 12 cfm air flow rate. The results demonstrate the potential of properly optimized NTPs in controlling PRRSv transmission.

Rankine–Hugoniot Relations Including Pickup Ions

Abstract The Rankine–Hugoniot relations are consequences of the global, magnetohydrodynamic conservation laws of mass, momentum, energy, and magnetic flux at shocks in plasma. They provide us with the boundary conditions, although these are insufficient to quantify the energy partition in substantially non-Maxwellian plasmas in the presence of nonthermal, pickup ions (PUIs). Ion dynamics inside the shock front is essentially nonadiabatic and gyrophase-dependent. The shock jump conditions are typically evaluated using the upstream and downstream distributions in the regions where they already become gyrotropic. The relation between the gyrophase-dependent motion inside the shock front and the gyrophase-averaged moments of the ion distributions is established using numerical ion tracing across a model shock profile, which includes the major basic features of a collisionless shock. The upstream distribution of PUIs is taken to be a filled shell. The obtained moments of the PUI distribution function are used to construct the Rankine–Hugoniot relations for a gyrotropic plasma regime. The quality of numerical ion tracing is checked by comparing it with full particle simulations. The moments of the distribution in the isotropic region are estimated.

Characterization of pleated filter media using particle image velocimetry

Use of pleated filter media for removing particles is required in industrial and residential sectors encompassing many applications. Pressure drop is an important factor used to evaluate the performance of pleated filter media. Research has been focused on examining the effects of pleated filter properties and pleat geometries on pressure drop and filtration efficiency but air velocity distributions. In this study, a noninvasive particle image velocimetry (PIV) technique was used to characterize the velocity distributions downstream of pleated filters. A custom filter containing a singular rectangular pleat was constructed for comparison between a computational fluid dynamics (CFD) numerical model and experimentally obtained PIV results. Results indicated that the trend between PIV and CFD was similar in general. Special attention is needed when modeling porous media as some discrepancies were observed near the corners of the pleated filter where the filter medium is less permeable due to compression of the fibers. Subsequently, the PIV technique was used with commercial pleated filters to study the effects of pleat geometry on the downstream velocity distributions. Air velocity distributions were affected by both the pleat geometry and the pleat stabilizing technique, which is commonly applied to pleated filters to maintain pleat shape and gaps between pleats. Results suggest that in addition to pleated filter geometry such as shape, density, and height, the geometric effects of pleat lock or pleat stabilizing techniques, should be also considered for estimating flow effects more realistically.

Acceleration of Interstellar Pickup He+ at Earth's Perpendicular Bow Shock

AbstractOn 05 December 2015 the Magnetospheric MultiScale constellation observed interstellar pickup ion distributions during an inbound crossing of Earth's perpendicular bow shock near the subsolar point, which provides new insights into shock acceleration of pickup ions throughout the heliosphere. In this study we analyze the upstream and downstream velocity distributions of H+ and He+ using data from the Hot Plasma Composition Analyzer on Magnetospheric MultiScale. We derive average two‐dimensional pitch angle distributions in the upstream and downstream field‐aligned bulk plasma frame, as well as integrated one‐dimensional velocity distributions. By comparing the upstream and downstream distributions, we find evidence of accelerated H+ and He+ downstream of the shock. By comparing measured and theoretical reflection ratios for He+, we attribute a significant part of this acceleration to a single reflection at the shock.

Kinematic Collisionless Relaxation of Ions in Supercritical Shocks

We show that kinematic collisionless relaxation in the macroscopic electric and magnetic fields plays the main role in the formation of the downstream ion distributions in a super-critical shock with ion reflection present. It is done by comparison of a theoretically predicted magnetic profile with the magnetic profile of a shocks observed by MMS mission. It is shown that pressure balance remains the main constraint for the shock stability.

The Impact of Large-Scale Orography on Northern Hemisphere Winter Synoptic Temperature Variability

Abstract The impact of large-scale orography on wintertime near-surface (850 hPa) temperature variability on daily and synoptic time scales (from days to weeks) in the Northern Hemisphere is investigated. Using a combination of theory, idealized modeling work, and simulations with a comprehensive climate model, it is shown that large-scale orography reduces upstream temperature gradients, in turn reducing upstream temperature variability, and enhances downstream temperature gradients, enhancing downstream temperature variability. Hence, the presence of the Rockies on the western edge of the North American continent increases temperature gradients over North America and, consequently, increases North American temperature variability. By contrast, the presence of the Tibetan Plateau and the Himalayas on the eastern edge of the Eurasian continent damps temperature variability over most of Eurasia. However, Tibet and the Himalayas also interfere with the downstream development of storms in the North Pacific storm track, and thus damp temperature variability over North America, by approximately as much as the Rockies enhance it. Large-scale orography is also shown to impact the skewness of downstream temperature distributions, as temperatures to the north of the enhanced temperature gradients are more positively skewed while temperatures to the south are more negatively skewed. This effect is most clearly seen in the northwest Pacific, off the east coast of Japan.