Glacial uplift: fluid injection beneath an elastic sheet on a poroelastic substrate

NASA Astrophysics Data System (ADS)

Neufeld, Jerome; Hewitt, Duncan; Chini, Greg

2016-11-01

Supraglacial lakes can drain to the base of glaciers extremely rapidly, causing localised uplift of the surrounding glacier and affecting its sliding velocity. The means by which large volumes of drained water interact with and leak into the subglacial hydrological system is unclear, as is the role of the basal till. A theoretical study of the spread of fluid injected below an elastic sheet (the ice) is presented, where the ice lies above, and initially compresses, a deformable poroelastic layer. As pressurized fluid is injected, the deformable layer swells to accommodate more fluid. If sufficient fluid is injected, a 'blister' of fluid forms above the layer, causing the overburden to lift off the base. The flow is controlled by the local pressure drop across the tip of this blister, which depends subtly on both the flow of fluid through the porous layer below the tip, and on poroelastic deformation in the till ahead of the tip. The spreading behaviour and dependence on key parameters is analysed. Predictions of the model are compared to field measurements of uplift from draining glacial lakes in Greenland.

Impact of inward turbulence spreading on energy loss of edge-localized modes

DOE PAGES

Ma, C. H.; Xu, X. Q.; Xi, P. W.; ...

2015-05-18

Nonlinear two-fluid and gyrofluid simulations show that an edge localized modes(ELM) crash has two phases: fast initial crash of ion temperature perturbation on the Alfvén time scale and slow turbulence spreading. The turbulencetransport phase is a slow encroachment of electron temperature perturbation due to the ELM event into pedestal region. Because of the inward turbulence spreading effect, the energy loss of an ELM decreases when density pedestal height increases. The Landau resonance yields the different cross phase-shift of ions and electrons. A 3 + 1 gyro-Landau-fluid model is implemented in BOUT++ framework. As a result, the gyrofluid simulations show thatmore » the kinetic effects have stabilizing effects on the ideal ballooning mode and the energy loss increases with the pedestal height.« less

Gyro-Landau-Fluid Theory and Simulations of Edge-Localized-Modes

NASA Astrophysics Data System (ADS)

Xu, X. Q.

2012-10-01

We report on the theory and simulations of edge-localized-modes (ELMs) using a gyro-Landau-fluid (GLF) extension of the BOUT++ code. Consistent with the two-fluid model (including 1st order FLR corrections), large ELMs, which are low-to-intermediate toroidal mode number (n) peeling-ballooning (P-B) modes, are suppressed by finite Larmor radius (FLR) effects as the ion temperature increases, while small ELMs (at intermediate n's) remain unstable. This result is good news for high ion temperatures in ITER due to the large stabilizing effects of FLR. Because the FLR effects are proportional to both Ti and n, the maximum growth rate is inversely proportional to Ti and the P-B mode is stabilized at high n. Nonlinear gyro-fluid simulations show results similar to those from the two-fluid model, namely that the P-B modes trigger magnetic reconnection, which drives the collapse of the pedestal pressure. Hyper-resistivity limits the radial spreading of ELMs by facilitating magnetic reconnection. The gyro-fluid ion model further limits the radial spreading of ELMs due to FLR-corrected nonlinear ExB convection of the ion gyro-center density. A gyro-fluid ETG model is being developed to self-consistently calculate the hyper-resistivity. Zonal magnetic fields arise from an ELM event and finite beta drift-wave turbulence when electron inertia effects are included. These lead to current generation and self-consistent current transport as a result of ExB convection in the generalized Ohm's law. Because edge plasmas have significant spatial inhomogeneities and complicated boundary conditions, we have developed a fast non-Fourier method for the computation of Landau-fluid closure terms based on an accurate and tunable approximation. The accuracy and the fast computational scaling of the method are demonstrated.

Numerical Temperature And Fluid-Flow Modelling For The Topographic Effects On Hydrothermal Circulation; A case study in Lucy Strike Vent Field

NASA Astrophysics Data System (ADS)

Erçetin, Engin; Düşünür Doǧan, Doǧa

2017-04-01

The aim of the study is to present a numerical temperature and fluid-flow modelling for the topographic effects on hydrothermal circulation. Bathymetry can create a major disturbance on fluid flow pattern. ANSYS Fluent Computational fluid dynamics software is used for simulations. Coupled fluid flow and temperature quations are solved using a 2-Dimensional control volume finite difference approach. Darcy's law is assumed to hold, the fluid is considered to be anormal Boussinesq incompressible fluid neglecting inertial effects. Several topographic models were simulated and both temperature and fluid flow calculations obtained for this study. The preliminary simulations examine the effect of a ingle bathymetric high on a single plume and the secondary study of simulations investigates the effect of multiple bathymetric highs on multiple plume. The simulations were also performed for the slow spreading Lucky Strike segment along the Mid-Atlantic Ridge (MAR), one of the best studied regions along the MAR, where a 3.4 km deep magma chamber extending 6 km along-axis is found at its center. The Lucky Strike segment displays a transitional morphology between that of the FAMOUS - North FAMOUS segments, which are characterized by well-developed axial valleys typical of slow-spreading segments, and that of the Menez Gwen segment, characterized by an axial high at the segment center. Lucky Strike Segment hosts a central volcano and active vent field located at the segment center and thus constitutes an excellent case study to simulate the effects of bathymetry on fluid flow. Results demonstrate that bathymetric relief has an important influence on hydrothermal flow. Subsurface pressure alterations can be formed by bathymetric highs, for this reason, bathymetric relief ought to be considered while simulating hydrothermal circulation systems. Results of this study suggest the dominant effect of bathymetric highs on fluid flow pattern and Darcy velocities will be presented. Keywords: Hydrothermal Circulation, Lucky Strike, Bathymetry - Topography, Vent Location, Fluid Flow, Numerical Modelling

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun

Here, an entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace’s law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results.more » Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.« less

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

NASA Astrophysics Data System (ADS)

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; Derome, Dominique; Carmeliet, Jan

2018-03-01

An entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace's law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results. Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.

Entropic multiple-relaxation-time multirange pseudopotential lattice Boltzmann model for two-phase flow

DOE PAGES

Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; ...

2018-03-22

Here, an entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace’s law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results.more » Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.« less

Shock-induced bubble jetting into a viscous fluid with application to tissue injury in shock-wave lithotripsy.

PubMed

Freund, J B; Shukla, R K; Evan, A P

2009-11-01

Shock waves in liquids are known to cause spherical gas bubbles to rapidly collapse and form strong re-entrant jets in the direction of the propagating shock. The interaction of these jets with an adjacent viscous liquid is investigated using finite-volume simulation methods. This configuration serves as a model for tissue injury during shock-wave lithotripsy, a medical procedure to remove kidney stones. In this case, the viscous fluid provides a crude model for the tissue. It is found that for viscosities comparable to what might be expected in tissue, the jet that forms upon collapse of a small bubble fails to penetrate deeply into the viscous fluid "tissue." A simple model reproduces the penetration distance versus viscosity observed in the simulations and leads to a phenomenological model for the spreading of injury with multiple shocks. For a reasonable selection of a single efficiency parameter, this model is able to reproduce in vivo observations of an apparent 1000-shock threshold before wide-spread tissue injury occurs in targeted kidneys and the approximate extent of this injury after a typical clinical dose of 2000 shock waves.

Shock-induced bubble jetting into a viscous fluid with application to tissue injury in shock-wave lithotripsy

PubMed Central

Freund, J. B.; Shukla, R. K.; Evan, A. P.

2009-01-01

Shock waves in liquids are known to cause spherical gas bubbles to rapidly collapse and form strong re-entrant jets in the direction of the propagating shock. The interaction of these jets with an adjacent viscous liquid is investigated using finite-volume simulation methods. This configuration serves as a model for tissue injury during shock-wave lithotripsy, a medical procedure to remove kidney stones. In this case, the viscous fluid provides a crude model for the tissue. It is found that for viscosities comparable to what might be expected in tissue, the jet that forms upon collapse of a small bubble fails to penetrate deeply into the viscous fluid “tissue.” A simple model reproduces the penetration distance versus viscosity observed in the simulations and leads to a phenomenological model for the spreading of injury with multiple shocks. For a reasonable selection of a single efficiency parameter, this model is able to reproduce in vivo observations of an apparent 1000-shock threshold before wide-spread tissue injury occurs in targeted kidneys and the approximate extent of this injury after a typical clinical dose of 2000 shock waves. PMID:19894850

Toward direct pore-scale modeling of three-phase displacements

NASA Astrophysics Data System (ADS)

Mohammadmoradi, Peyman; Kantzas, Apostolos

2017-12-01

A stable spreading film between water and gas can extract a significant amount of bypassed non-aqueous phase liquid (NAPL) through immiscible three-phase gas/water injection cycles. In this study, the pore-scale displacement mechanisms by which NAPL is mobilized are incorporated into a three-dimensional pore morphology-based model under water-wet and capillary equilibrium conditions. The approach is pixel-based and the sequence of invasions is determined by the fluids' connectivity and the threshold capillary pressure of the advancing interfaces. In addition to the determination of three-phase spatial saturation profiles, residuals, and capillary pressure curves, dynamic finite element simulations are utilized to predict the effective permeabilities of the rock microtomographic images as reasonable representations of the geological formations under study. All the influential features during immiscible fluid flow in pore-level domains including wetting and spreading films, saturation hysteresis, capillary trapping, connectivity, and interface development strategies are taken into account. The capabilities of the model are demonstrated by the successful prediction of saturation functions for Berea sandstone and the accurate reconstruction of three-phase fluid occupancies through a micromodel.

Modeling of Rapid Solidification with Undercooling Effect During Droplet Flattening on a Substrate in Coating Formation

NASA Astrophysics Data System (ADS)

Shukla, Rajesh Kumar; Patel, Virendra; Kumar, Arvind

2018-02-01

The coating deposit on the substrate in thermal spray coating process develops by solidification of individual molten particle which impacts, flattens and solidifies on the surface of the substrate. Droplet flattening and solidification typically involves rapid cooling. In this paper, a model for non-equilibrium rapid solidification of a molten droplet spreading onto a substrate is presented. Transient flow during droplet impact and its subsequent spreading is considered using the volume of fluid surface tracking method which was fully coupled with the rapid solidification model. The rapid solidification model includes undercooling, nucleation, interface tracking, non-equilibrium solidification kinetics and combined heat transfer and fluid flow as required to treat a non-stagnant splat formed from droplet flattening. The model is validated with the literature results on stagnant splats. Subsequently, using the model the characteristics of the rapidly solidifying interface for non-stagnant splat, such as interface velocity and interface temperature, are described and the effect of undercooling and interfacial heat transfer coefficient are highlighted. In contrast to the stagnant splat, the non-stagnant splat considered in this study displays interesting features in the rapidly solidifying interface. These are attributed to droplet thinning and droplet recoiling that occur during the droplet spreading process.

Construction of Fluid - solid Coupling Model with Improved Richards - BP & Its Engineering Application

NASA Astrophysics Data System (ADS)

Xie, Chengyu; Jia, Nan; Shi, Dongping; Lu, Hao

2017-10-01

In order to study the slurry diffusion law during grouting, Richards unsaturated-saturated model was introduced, the definition of the grouting model is clear, the Richards model control equation was established, And the BP neural network was introduced, the improved fluid-solid coupling model was constructed, Through the use of saturated - unsaturated seepage flow model, As well as the overflow boundary iterative solution of the mixed boundary conditions, the free surface is calculated. Engineering practice for an example, with the aid of multi - field coupling analysis software, the diffusion law of slurry was simulated numerically. The results show that the slurry diffusion rule is affected by grouting material, initial pressure and other factors. When the slurry starts, it flows in the cracks along the upper side of the grouting hole, when the pressure gradient is reduced to the critical pressure, that is, to the lower side of the flow, when the slurry diffusion stability, and ultimately its shape like an 8. The slurry is spread evenly from the overall point of view, from the grouting mouth toward the surrounding evenly spread, it gradually reaches saturation by non-saturation, and it is not a purely saturated flow, when the slurry spread and reach a saturated state, the diffusion time is the engineering grouting time.

Dissipative-particle-dynamics model of biofilm growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zhijie; Meakin, Paul; Tartakovsky, Alexandre M.

2011-06-13

A dissipative particle dynamics (DPD) model for the quantitative simulation of biofilm growth controlled by substrate (nutrient) consumption, advective and diffusive substrate transport, and hydrodynamic interactions with fluid flow (including fragmentation and reattachment) is described. The model was used to simulate biomass growth, decay, and spreading. It predicts how the biofilm morphology depends on flow conditions, biofilm growth kinetics, the rheomechanical properties of the biofilm and adhesion to solid surfaces. The morphology of the model biofilm depends strongly on its rigidity and the magnitude of the body force that drives the fluid over the biofilm.

Coating flow of an anti-HIV microbicide gel: boundary dilution and yield stress

NASA Astrophysics Data System (ADS)

Szeri, Andrew J.; Tasoglu, Savas; Park, Su Chan; Katz, David F.

2010-11-01

A recent study has confirmed, for the first time, that a vaginal gel formulation of the antiretroviral drug Tenofovir, when topically applied, significantly inhibits sexual HIV transmission to women [1]. However, the gel for this drug, and anti-HIV microbicide gels in general, have not been designed using an understanding of how gel spreading govern successful drug delivery. Elastohydrodynamic lubrication theory can be applied to model spreading of microbicide gels [2]. Here, we extend our initial analysis: we incorporate a yield stress, and we model the effects of gel dilution due to contact with vaginal fluid produced at the gel-tissue interface. Our model developed in [2] is supplemented with a convective-diffusive transport equation to characterize dilution, and solved using a multi-step scheme in a moving domain. The association between local dilution of gel and rheological properties is obtained experimentally. To model the common yield stress property of gels, we proceed by scaling analysis first. This establishes the conditions for validity of lubrication theory of a shear thinning yield stress fluid. This involves further development of the model in [2], incorporating a biviscosity model.[4pt] [1] Karim, et al., Science, 2010.[0pt] [2] Szeri, et al., Phy. of Fluids, 2008.

Prediction of fire growth on furniture using CFD

NASA Astrophysics Data System (ADS)

Pehrson, Richard David

A fire growth calculation method has been developed that couples a computational fluid dynamics (CFD) model with bench scale cone calorimeter test data for predicting the rate of flame spread on compartment contents such as furniture. The commercial CFD code TASCflow has been applied to solve time averaged conservation equations using an algebraic multigrid solver with mass weighted skewed upstream differencing for advection. Closure models include k-e for turbulence, eddy breakup for combustion following a single step irreversible reaction with Arrhenius rate constant, finite difference radiation transfer, and conjugate heat transfer. Radiation properties are determined from concentrations of soot, CO2 and H2O using the narrow band model of Grosshandler and exponential wide band curve fit model of Modak. The growth in pyrolyzing area is predicted by treating flame spread as a series of piloted ignitions based on coupled gas-fluid boundary conditions. The mass loss rate from a given surface element follows the bench scale test data for input to the combustion prediction. The fire growth model has been tested against foam-fabric mattresses and chairs burned in the furniture calorimeter. In general, agreement between model and experiment for peak heat release rate (HRR), time to peak HRR, and total energy lost is within +/-20%. Used as a proxy for the flame spread velocity, the slope of the HRR curve predicted by model agreed with experiment within +/-20% for all but one case.

The effects of inhomogeneous boundary dilution on the coating flow of an anti-HIV microbicide vehicle

NASA Astrophysics Data System (ADS)

Tasoglu, Savas; Peters, Jennifer J.; Park, Su Chan; Verguet, Stéphane; Katz, David F.; Szeri, Andrew J.

2011-09-01

A recent study in South Africa has confirmed, for the first time, that a vaginal gel formulation of the antiretroviral drug Tenofovir, when topically applied, significantly inhibits sexual HIV transmission to women [Karim et al., Science 329, 1168 (2010)]. However, the gel for this drug and anti-HIV microbicide gels in general have not been designed using an understanding of how gel spreading and retention in the vagina govern successful drug delivery. Elastohydrodynamic lubrication theory can be applied to model spreading of microbicide gels [Szeri et al., Phys. Fluids 20, 083101 (2008)]. This should incorporate the full rheological behavior of a gel, including how rheological properties change due to contact with, and dilution by, ambient vaginal fluids. Here, we extend our initial analysis, incorporating the effects of gel dilution due to contact with vaginal fluid produced at the gel-tissue interface. Our original model is supplemented with a convective-diffusive transport equation to characterize water transport into the gel and, thus, local gel dilution. The problem is solved using a multi-step scheme in a moving domain. The association between local dilution of gel and rheological properties is obtained experimentally, delineating the way constitutive parameters of a shear-thinning gel are modified by dilution. Results show that dilution accelerates the coating flow by creating a slippery region near the vaginal wall akin to a dilution boundary layer, especially if the boundary flux exceeds a certain value. On the other hand, if the diffusion coefficient of boundary fluid is increased, the slippery region diminishes in extent and the overall rate of gel spreading decreases.

Strontium isotope constraints on fluid flow in the sheeted dike complex of fast spreading crust: Pervasive fluid flow at Pito Deep

NASA Astrophysics Data System (ADS)

Barker, A. K.; Coogan, L. A.; Gillis, K. M.; Weis, D.

2008-06-01

Fluid flow through the axial hydrothermal system at fast spreading ridges is investigated using the Sr-isotopic composition of upper crustal samples recovered from a tectonic window at Pito Deep (NE Easter microplate). Samples from the sheeted dike complex collected away from macroscopic evidence of channelized fluid flow, such as faults and centimeter-scale hydrothermal veins, show a range of 87Sr/86Sr from 0.7025 to 0.7030 averaging 0.70276 relative to a protolith with 87Sr/86Sr of ˜0.7024. There is no systematic variation in 87Sr/86Sr with depth in the sheeted dike complex. Comparison of these new data with the two other localities that similar data sets exist for (ODP Hole 504B and the Hess Deep tectonic window) reveals that the extent of Sr-isotope exchange is similar in all of these locations. Models that assume that fluid-rock reaction occurs during one-dimensional (recharge) flow lead to significant decreases in the predicted extent of isotopic modification of the rock with depth in the crust. These model results show systematic misfits when compared with the data that can only be avoided if the fluid flow is assumed to be focused in isolated channels with very slow fluid-rock exchange. In this scenario the fluid at the base of the crust is little modified in 87Sr/86Sr from seawater and thus unlike vent fluids. Additionally, this model predicts that some rocks should show no change from the fresh-rock 87Sr/86Sr, but this is not observed. Alternatively, models in which fluid-rock reaction occurs during upflow (discharge) as well as downflow, or in which fluids are recirculated within the hydrothermal system, can reproduce the observed lack of variation in 87Sr/86Sr with depth in the crust. Minimum time-integrated fluid fluxes, calculated from mass balance, are between 1.5 and 2.6 × 106 kg m-2 for all areas studied to date. However, new evidence from both the rocks and a compilation of vent fluid compositions demonstrates that some Sr is leached from the crust. Because this leaching lowers the fluid 87Sr/86Sr without changing the rock 87Sr/86Sr, these mass balance models must underestimate the time-integrated fluid flux. Additionally, these values do not account for fluid flow that is channelized within the crust.

A mixed boundary representation to simulate the displacement of a biofluid by a biomaterial in porous media.

PubMed

Widmer, René P; Ferguson, Stephen J

2011-05-01

Characterization of the biomaterial flow through porous bone is crucial for the success of the bone augmentation process in vertebroplasty. The biofluid, biomaterial, and local morphological bone characteristics determine the final shape of the filling, which is important both for the post-treatment mechanical loading and the risk of intraoperative extraosseous leakage. We have developed a computational model that describes the flow of biomaterials in porous bone structures by considering the material porosity, the region-dependent intrinsic permeability of the porous structure, the rheological properties of the biomaterial, and the boundary conditions of the filling process. To simulate the process of the substitution of a biofluid (bone marrow) by a biomaterial (bone cement), we developed a hybrid formulation to describe the evolution of the fluid boundary and properties and coupled it to a modified version of Darcy's law. The apparent rheological properties are derived from a fluid-fluid interface tracking algorithm and a mixed boundary representation. The region- specific intrinsic permeability of the bone is governed by an empirical relationship resulting from a fitting process of experimental data. In a first step, we verified the model by studying the displacement process in spherical domains, where the spreading pattern is known in advance. The mixed boundary model demonstrated, as expected, that the determinants of the spreading pattern are the local intrinsic permeability of the porous matrix and the ratio of the viscosity of the fluids that are contributing to the displacement process. The simulations also illustrate the sensitivity of the mixed boundary representation to anisotropic permeability, which is related to the directional dependent microstructural properties of the porous medium. Furthermore, we compared the nonlinear finite element model to different published experimental studies and found a moderate to good agreement (R(2)=0.9895 for a one-dimensional bone core infiltration test and a 10.94-16.92% relative error for a three-dimensional spreading pattern study, respectively) between computational and experimental results.

Osmosis-driven viscous fingering of oil-in-water emulsions

NASA Astrophysics Data System (ADS)

Liu, Ying; Rallabandi, Bhargav; Baskaran, Mrudhula; Stone, Howard

2017-11-01

Viscous fingering occurs when a low viscosity fluid invades a more viscous fluid. Fingering of two miscible fluids is more complicated than that of immiscible fluids in that there is no sharp fluid-fluid interface and diffusion occurs between the phases. We experimentally studied the fingering of two miscible fluids: an oil-in-water emulsion and a sodium chloride solution. When the concentration of sodium chloride in the water phase in the emulsion exceeds that in the sodium chloride solution, the consequent osmotic flow automatically facilitates the occurrence of the fingering. On the contrary, when the sodium chloride solution has higher concentration, the spreading of emulsion is more uniform than the case without the concentration difference. We provide a model to rationalize and quantify these observations.

Along-axis hydrothermal flow at the axis of slow spreading Mid-Ocean Ridges: Insights from numerical models of the Lucky Strike vent field (MAR)

NASA Astrophysics Data System (ADS)

Fontaine, Fabrice J.; Cannat, Mathilde; Escartin, Javier; Crawford, Wayne C.

2014-07-01

processes and efficiency of hydrothermal heat extraction along the axis of mid-ocean ridges are controlled by lithospheric thermal and permeability structures. Hydrothermal circulation models based on the structure of fast and intermediate spreading ridges predict that hydrothermal cell organization and vent site distribution are primarily controlled by the thermodynamics of high-temperature mid-ocean ridge hydrothermal fluids. Using recent constraints on shallow structure at the slow spreading Lucky Strike segment along the Mid-Atlantic Ridge, we present a physical model of hydrothermal cooling that incorporates the specificities of a magma-rich slow spreading environment. Using three-dimensional numerical models, we show that, in contrast to the aforementioned models, the subsurface flow at Lucky Strike is primarily controlled by across-axis permeability variations. Models with across-axis permeability gradients produce along-axis oriented hydrothermal cells and an alternating pattern of heat extraction highs and lows that match the distribution of microseismic clusters recorded at the Lucky Strike axial volcano. The flow is also influenced by temperature gradients at the base of the permeable hydrothermal domain. Although our models are based on the structure and seismicity of the Lucky Strike segment, across-axis permeability gradients are also likely to occur at faster spreading ridges and these results may also have important implications for the cooling of young crust at fast and intermediate spreading centers.

Numerical study of drop spreading on a flat surface

NASA Astrophysics Data System (ADS)

Wang, Sheng; Desjardins, Olivier

2017-11-01

In this talk, we perform a numerical study of a droplet on a flat surface with special emphasis on capturing the spreading dynamics. The computational methodology employed is tailored for simulating large-scale two-phase flows within complex geometries. It combines a conservative level-set method to capture the liquid-gas interface, a conservative immersed boundary method to represent the solid-fluid interface, and a sub-grid curvature model at the triple-point to implicitly impose the contact angle of the liquid-gas interface. The performance of the approach is assessed in the inertial droplet spreading regime, the viscous spreading regime of high viscosity drops, and with the capillary oscillation of low viscosity droplets.

Monolayer Adsorption of Ar and Kr on Graphite: Theoretical Isotherms and Spreading Pressures

PubMed

Mulero; Cuadros

1997-02-01

The validity of analytical equations for two-dimensional fluids in the prediction of monolayer adsorption isotherms and spreading pressures of rare gases on graphite is analyzed. The statistical mechanical theory of Steele is used to relate the properties of the adsorbed and two-dimensional fluids. In such theory the model of graphite is a perfectly flat surface, which means that only the first order contribution of the fluid-solid interactions are taken into account. Two analytical equations for two-dimensional Lennard-Jones fluids are used: one proposed by Reddy-O'Shea, based in the fit on pressure and potential energy computer simulated results, and other proposed by Cuadros-Mulero, based in the fit of the Helmholtz free energy calculated from computer simulated results of the radial distribution function. The theoretical results are compared with experimental results of Constabaris et al. (J. Chem. Phys. 37, 915 (1962)) for Ar and of Putnam and Fort (J. Phys. Chem. 79, 459 (1975)) for Kr. Good agreement is found using both equations in both cases.

Moving contact lines in partial wetting: bridging the gap across the scales

NASA Astrophysics Data System (ADS)

Pahlavan, Amir; Cueto-Felgueroso, Luis; McKinley, Gareth; Juanes, Ruben

2017-11-01

The spreading and dewetting of liquid films on solid substrates is a common phenomenon in nature and industry from a snail secreting a mucosal film to printing and coating processes. A quantitative description of these phenomena, however, requires a detailed understanding of the flow physics at the nanoscale as the intermolecular interactions become important close to the contact line. Classical hydrodynamic theory describes wetting as an interplay between viscous and interfacial forces, neglecting the intermolecular interactions, leading to a paradox known as the moving contact line singularity. By contrast, molecular kinetic theory describes wetting as an activated process, neglecting the bulk hydrodynamics in the spreading viscous fluid film altogether. Here, we show that our recently developed model for thin liquid films in partial wetting, which properly incorporates the role of van der Waals interactions in a thin spreading fluid layer into a height-dependent surface tension, bridges the gap between these two approaches and leads to a unified framework for the description of wetting phenomena. We further use our model to investigate the instability and dewetting of nanometric liquid films, and show that it brings theoretical predictions closer to experimental observations.

Hybrid Spreading Mechanisms and T Cell Activation Shape the Dynamics of HIV-1 Infection

PubMed Central

Zhang, Changwang; Zhou, Shi; Groppelli, Elisabetta; Pellegrino, Pierre; Williams, Ian; Borrow, Persephone; Chain, Benjamin M.; Jolly, Clare

2015-01-01

HIV-1 can disseminate between susceptible cells by two mechanisms: cell-free infection following fluid-phase diffusion of virions and by highly-efficient direct cell-to-cell transmission at immune cell contacts. The contribution of this hybrid spreading mechanism, which is also a characteristic of some important computer worm outbreaks, to HIV-1 progression in vivo remains unknown. Here we present a new mathematical model that explicitly incorporates the ability of HIV-1 to use hybrid spreading mechanisms and evaluate the consequences for HIV-1 pathogenenesis. The model captures the major phases of the HIV-1 infection course of a cohort of treatment naive patients and also accurately predicts the results of the Short Pulse Anti-Retroviral Therapy at Seroconversion (SPARTAC) trial. Using this model we find that hybrid spreading is critical to seed and establish infection, and that cell-to-cell spread and increased CD4+ T cell activation are important for HIV-1 progression. Notably, the model predicts that cell-to-cell spread becomes increasingly effective as infection progresses and thus may present a considerable treatment barrier. Deriving predictions of various treatments’ influence on HIV-1 progression highlights the importance of earlier intervention and suggests that treatments effectively targeting cell-to-cell HIV-1 spread can delay progression to AIDS. This study suggests that hybrid spreading is a fundamental feature of HIV infection, and provides the mathematical framework incorporating this feature with which to evaluate future therapeutic strategies. PMID:25837979

The OSCAR experiment: using full-waveform inversion in the analysis of young oceanic crust

NASA Astrophysics Data System (ADS)

Silverton, Akela; Morgan, Joanna; Wilson, Dean; Hobbs, Richard

2017-04-01

The OSCAR experiment aims to derive an integrated model to better explain the effects of heat loss and alteration by hydrothermal fluids, associated with the cooling of young oceanic crust at an axial ridge. High-resolution seismic imaging of the sediments and basaltic basement can be used to map fluid flow pathways between the oceanic crust and the surrounding ocean. To obtain these high-resolution images, we undertake full-waveform inversion (FWI), an advanced seismic imaging technique capable of resolving velocity heterogeneities at a wide range of length scales, from background trends to fine-scale geological/crustal detail, in a fully data-driven automated manner. This technology is widely used within the petroleum sector due to its potential to obtain high-resolution P-wave velocity models that lead to improvements in migrated seismic images of the subsurface. Here, we use the P-wave velocity model obtained from travel-time tomography as the starting model in the application of acoustic, time-domain FWI to a multichannel streamer field dataset acquired in the east Pacific along a profile between the Costa Rica spreading centre and the Ocean Drilling Program (ODP) borehole 504B, where the crust is approximately six million years old. FWI iteratively improves the velocity model by minimizing the misfit between the predicted data and the field data. It seeks to find a high-fidelity velocity model that is capable of matching individual seismic waveforms of the original raw field dataset, with an initial focus on matching the low-frequency components of the early arriving energy. Quality assurance methods adopted during the inversion ensure convergence in the direction of the global minimum. We demonstrate that FWI is able to recover fine-scale, high-resolution velocity heterogeneities within the young oceanic crust along the profile. The highly resolved FWI velocity model is useful in the identification of the layer 2A/2B interface and low-velocity layers that may represent zones of enhanced fluid movement. With FWI we are able to better explain the non-linear changes in velocity as the crust evolves with distance from the spreading centre and image the effects of any alteration by hydrothermal fluids. This model provides valuable insight and new constraints on the thermal processes involved, at spreading centres, setting a new benchmark for integrated multi-physics experiments at similar ocean ridge systems. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Bacillus subtilis spreads by surfing on waves of surfactant

PubMed Central

Angelini, Thomas E.; Roper, Marcus; Kolter, Roberto; Weitz, David A.; Brenner, Michael P.

2009-01-01

The bacterium Bacillus subtilis produces the molecule surfactin, which is known to enhance the spreading of multicellular colonies on nutrient substrates by lowering the surface tension of the surrounding fluid, and to aid in the formation of aerial structures. Here we present experiments and a mathematical model that demonstrate how the differential accumulation rates induced by the geometry of the bacterial film give rise to surfactant waves. The spreading flux increases with increasing biofilm viscosity. Community associations are known to protect bacterial populations from environmental challenges such as predation, heat, or chemical stresses, and enable digestion of a broader range of nutritive sources. This study provides evidence of enhanced dispersal through cooperative motility, and points to nonintuitive methods for controlling the spread of biofilms. PMID:19826092

Analysis of flame spread over multicomponent combustibles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohtani, H.; Sato, J.

1985-01-01

A theoretical model of volatile component diffusion in the condensed phase is carried out in order to form a basis for predicting the flame spread rate in thermally thick multicomponent combustibles in a non-fluid condensed phase. The fuels could be, e.g., crude oil, heavy oil, or light oil. Mass transfer occurs only by diffusion so the gas phase volatile concentration at the surface is estimated from the condensed phase volatile concentration and the surface temperature, which increases close to the leading flame edge. The flame spread rate is assumed steady. The velocity of the flame spread is shown to bemore » a function of the initial condensed phase temperature and the temperature at the leading flame edge.« less

Axisymmetric Lattice Boltzmann Model of Droplet Impact on Solid Surfaces

NASA Astrophysics Data System (ADS)

Dalgamoni, Hussein; Yong, Xin

2017-11-01

Droplet impact is a ubiquitous fluid phenomena encountered in scientific and engineering applications such as ink-jet printing, coating, electronics manufacturing, and many others. It is of great technological importance to understand the detailed dynamics of drop impact on various surfaces. The lattice Boltzmann method (LBM) emerges as an efficient method for modeling complex fluid systems involving rapidly evolving fluid-fluid and fluid-solid interfaces with complex geometries. In this work, we model droplet impact on flat solid substrates with well-defined wetting behavior using a two-phase axisymmetric LBM with high density and viscosity contrasts. We extend the two-dimensional Lee and Liu model to capture axisymmetric effect in the normal impact. First we compare the 2D axisymmetric results with the 2D and 3D results reported by Lee and Liu to probe the effect of axisymmetric terms. Then, we explore the effects of Weber number, Ohnesorge number, and droplet-surface equilibrium contact angle on the impact. The dynamic contact angle and spreading factor of the droplet during impact are investigated to qualitatively characterize the impact dynamics.

Saltstone SDU6 Modeling Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Si Y.; Hyun, Sinjae

2013-01-10

A new disposal unit, designated as Saltstone Disposal Unit 6 (SDU6), is being designed for support of site accelerated closure goals and salt waste projections identified in the new Liquid Waste System Plan. The unit is a cylindrical disposal cell of 375 ft in diameter and 43 ft in height, and it has a minimum 30 million gallons of capacity. SRNL was requested to evaluate the impact of an increased grout placement height on the flow patterns radially spread on the floor and to determine whether grout quality is impacted by the height. The primary goals of the work aremore » to develop the baseline Computational Fluid Dynamics (CFD) model and to perform the evaluations for the flow patterns of grout material in SDU6 as a function of elevation of grout discharge port and grout rheology. Two transient grout models have been developed by taking a three-dimensional multiphase CFD approach to estimate the domain size of the grout materials radially spread on the facility floor and to perform the sensitivity analysis with respect to the baseline design and operating conditions such as elevation height of the discharge port and fresh grout properties. For the CFD modeling calculations, air-grout Volume of Fluid (VOF) method combined with Bingham plastic and time-dependent grout models were used for examining the impact of fluid spread performance for the initial baseline configurations and to evaluate the impact of grout pouring height on grout quality. The grout quality was estimated in terms of the air volume fraction for the grout layer formed on the SDU6 floor, resulting in the change of grout density. The study results should be considered as preliminary scoping analyses since benchmarking analysis is not included in this task scope. Transient analyses with the Bingham plastic model were performed with the FLUENTTM code on the high performance parallel computing platform in SRNL. The analysis coupled with a transient grout aging model was performed by using ANSYS-CFX code in the parallel computing platform in Mercer University. Recommended operational guidance was developed assuming that local shear rates and flow patterns related to radial spread along the SDU floor can be used as a measure of grout performance and spatial dispersion affected by the grout height and viscosity. The 5 ft height baseline results show that when the 150 gpm grout flow with a 5 Pa yield stress and a 60 cp viscosity is poured down through a 3 inch discharge port, the grout is spread radially up to about 64 ft distance from the pouring center after 2 hours' pouring time. The air volume fraction of the grout layer is about 29% at 5 minutes' transient time, and it is reduced by about 9% in 2 hours' pouring time, resulting in the grout density consisting of about 80% grout and 20% air volume fractions. The sensitivity results show that when the discharge port is located at a higher position, a larger amount of air is trapped inside the layer formed below the discharge port at the early transient time of less than 30 minutes because of the higher impinging momentum of the grout flow on the floor, resulting in the formation of less smooth layer. The results clearly indicate that the radial spread for the 43 ft discharge port is about 10% faster than that of the 5 ft discharge port for the early transient period of 5 minutes. However, for the pouring time longer than half an hour, the discharge port height does not affect the radial distance spread on the disposal floor. When grout quality is related to grout volume fraction, the grout volume fraction for the 43 ft discharge port has lower volume fraction than the 5 ft discharge port for the transient period of the first 5 minutes. However, for the pouring time longer than half an hour, the discharge port height does not affect the grout volume fraction for the layer accumulated on the disposal floor. A modified Bingham plastic model coupled with time-dependent viscosity behavior was developed for conducting the initial scoping calculations to assess the impact of fluid residence time on radial spreading and basic flow patterns. The results for the transient viscosity model show that when grout material becomes more viscous, the thickness of the grout layer accumulated on the floor becomes higher, but the radial distance spread on the horizontal floor becomes smaller. The early transient results for the grout density with about 32% air volume fractions are in reasonable agreement with those of the idealized Bingham plastic model. It is recommended that the current models developed here be benchmarked against the experimental results for critical applications of the modeling results.« less

Buoyant miscible displacement flows in a nonuniform Hele-Shaw cell

NASA Astrophysics Data System (ADS)

Walling, E.; Mollaabbasi, R.; Taghavi, S. M.

2018-03-01

Miscible displacement flows within the gap of a nonuniform Hele-Shaw cell are considered, theoretically and experimentally. The cell is vertical and it can be diverging or converging. A light fluid displaces a heavy fluid downwards. The displacement imposed velocity is sufficiently large so that diffusive effects are negligible within our time scale of interest. For certain flow parameters, the displacement flow is characterized by a symmetric, two-dimensional penetration of the light fluid into the heavy one, for which a lubrication approximation approach is developed to simplify the governing equations and find a semianalytical solution for the flux functions. The solutions reveal how the cell nonuniformity may affect the propagation of the interface between the two fluids, versus the other flow parameters, i.e., the viscosity ratio (m ) and a buoyancy number (χ ), for which a detailed flow regime classification is presented. Our results demonstrate that the presence of nonuniformity adds a unique spatiotemporal nature to these displacements which is not the case for uniform cell flows. The combination of the model and experiments reveals the existence of self-spreading, spike, and unstable (viscous fingering) flow regimes, which may occur at various spatial positions within the cell. A converging cell may allow a transition from spike to self-spreading or unstable regime, whereas a diverging cell may offer a transition from self-spreading or unstable to spike regime. Our work demonstrates that the novel spatiotemporal nature of nonuniform cell flows must be considered through the numerical solution of the interface propagation equation, to yield accurate predictions about the flow behaviors at various spatial positions.

The Effect of Surface Tension on the Gravity-driven Thin Film Flow of Newtonian and Power-law Fluids.

PubMed

Hu, Bin; Kieweg, Sarah L

2012-07-15

Gravity-driven thin film flow is of importance in many fields, as well as for the design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. There have been many prior works on gravity-driven thin films. However, the incorporation of surface tension effect has not been well studied for non-Newtonian fluids. After surface tension effect was incorporated into our 2D (i.e. 1D spreading) power-law model, we found that surface tension effect not only impacted the spreading speed of the microbicide gel, but also had an influence on the shape of the 2D spreading profile. We observed a capillary ridge at the front of the fluid bolus. Previous literature shows that the emergence of a capillary ridge is strongly related to the contact line fingering instability. Fingering instabilities during epithelial coating may change the microbicide gel distribution and therefore impact how well it can protect the epithelium. In this study, we focused on the capillary ridge in 2D flow and performed a series of simulations and showed how the capillary ridge height varies with other parameters, such as surface tension coefficient, inclination angle, initial thickness, and power-law parameters. As shown in our results, we found that capillary ridge height increased with higher surface tension, steeper inclination angle, bigger initial thickness, and more Newtonian fluids. This study provides the initial insights of how to optimize the flow and prevent the appearance of a capillary ridge and fingering instability.

Droplet impact dynamics for two liquids impinging on anisotropic superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Pearson, John T.; Maynes, Daniel; Webb, Brent W.

2012-09-01

Droplet impingement experiments were performed on grooved hydrophobic surfaces with cavity fractions of 0, 80, and 93 % using droplets of water and a 50 %/50 % water/glycerol mixture. The influence of liquid viscosity, cavity fraction, and spreading direction, relative to the surface grooves, is explored qualitatively and quantitatively. The maximum droplet spread diameter, velocity of the rebounding jet, and the time delay between droplet impact and jet emission were characterized for Weber numbers, We, based on droplet impact speed and diameter, up to 500. The unequal shear stresses and contact angles influence the maximum spread diameters in the two primary spread directions. At We > 100, the ratio of the spread diameter along the direction of the grooves to the spread diameter perpendicular to the grooves increases above unity with increasing We. The maximum droplet spread diameter is compared to recent predictive models, and the data reveal differing behavior for the two fluids considered. The results also reveal the existence of very high relative jet velocities in the range 5 ≤ We ≤ 15 for water droplets, while such jets were not observed for the more viscous mixture. Further, in the range 115 ≤ We ≤ 265, the water/glycerol jet formation dynamics are radically different from the water behavior. Most evident is the existence of two-pronged jets, which arise from the anisotropy of the surface and the unequal shear stresses and contact angles that prevail on the surfaces. It is these influences that give rise to differences in the maximum spread diameters in the two primary spread directions. Similar two-pronged jet emission was observed for water over the very narrow range of We from 91 to 96. The issuing jet velocities were also observed to increase with increasing cavity fraction for both fluids and over the entire range of We explored. Lastly, the elapsed time between droplet impact and jet emission decreased with increasing cavity fraction.

Laws of spreading: When hydrodynamic equations are not enough

NASA Astrophysics Data System (ADS)

Kavehpour, Pirouz; Mohammad Karim, Alireza; Rothstein, Jonathan; Davis, Stephen

2017-11-01

For nearly 50 years, most of the researchers in the area of wetting and spreading have used a relationship between the dynamics contact angle and velocity and the equilibrium contact angle. Different forms of this relationship are known as Tanner's law, Hoffman-Voinov-Tanner law or Cox model, all of them are derived based on hydrodynamics assumptions. In this talk, we will discuss several common situations that this relationship is not valid and we propose a new way to look at spreading problem and its underlying physics. Our experimental result agrees with this interpretation of spreading dynamics. In addition, the experimental study has been performed using forced spreading with tensiometer to obtain the dependence of dynamic contact angle to the contact line velocity to describe the spreading dynamics of Newtonian liquids on the micro-textured surfaces. The effect of the geometrical descriptions of the micro-posts along with the physical properties of liquids on the spreading dynamics on micro-textured Teflon plates have been also studied. It was shown that hydrodynamic results are not valid for certain combination of fluid/solid systems.

Fault Weakening due to Erosion by Fluids: A Possible Origin of Intraplate Earthquake Swarms

NASA Astrophysics Data System (ADS)

Vavrycuk, V.; Hrubcova, P.

2016-12-01

The occurrence and specific properties of earthquake swarms in geothermal areas are usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes their opening and subsequent shear-tensile rupture. The spreading and evolution of the seismic activity is controlled by fluid flow due to diffusion in a permeable rock and/or by the redistribution of Coulomb stress. The `fluid-injection model', however, is not valid universally. We provide evidence that this model is inconsistent with observations of earthquake swarms in West Bohemia, Czech Republic. Full seismic moment tensors of micro-earthquakes in the 1997 and 2008 swarms in West Bohemia indicate that fracturing at the starting phase of the swarm was not associated with fault openings caused by pressurized fluids but rather with fault compactions. This can physically be explained by a `fluid-erosion model', when the essential role in the swarm triggering is attributed to chemical and hydrothermal fluid-rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2-saturated fluids, the walls of fractures are weakened by dissolving and altering various minerals. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers and a new cycle begins.

Modeling the release, spreading, and burning of LNG, LPG, and gasoline on water.

PubMed

Johnson, David W; Cornwell, John B

2007-02-20

Current interest in the shipment of liquefied natural gas (LNG) has renewed the debate about the safety of shipping large volumes of flammable fuels. The size of a spreading pool following a release of LNG from an LNG tank ship has been the subject of numerous papers and studies dating back to the mid-1970s. Several papers have presented idealized views of how the LNG would be released and spread across a quiescent water surface. There is a considerable amount of publicly available material describing these idealized releases, but little discussion of how other flammable fuels would behave if released from similar sized ships. The purpose of this paper is to determine whether the models currently available from the United States Federal Energy Regulatory Commission (FERC) can be used to simulate the release, spreading, vaporization, and pool fire impacts for materials other than LNG, and if so, identify which material-specific parameters are required. The review of the basic equations and principles in FERC's LNG release, spreading, and burning models did not reveal a critical fault that would prevent their use in evaluating the consequences of other flammable fluid releases. With the correct physical data, the models can be used with the same level of confidence for materials such as LPG and gasoline as they are for LNG.

Numerical simulations of hydrothermal circulation resulting from basalt intrusions in a buried spreading center

USGS Publications Warehouse

Fisher, A.T.; Narasimhan, T.N.

1991-01-01

A two-dimensional, one by two-kilometer section through the seafloor was simulated with a numerical model to investigate coupled fluid and heat flow resulting from basalt intrusions in a buried spreading center. Boundary and initial conditions and physical properties of both sediments and basalt were constrained by field surveys and drilling in the Guaymas Basin, central Gulf of California. Parametric variations in these studies included sediment and basalt permeability, anisotropy in sediment permeability, and the size of heat sources. Faults were introduced through new intrusions both before and after cooling.Background heat input caused fluid convection at velocities ≤ 3 cm a−1 through shallow sediments. Eighty to ninety percent of the heat introduced at the base of the simulations exited through the upper, horizontal surface, even when the vertical boundaries were made permeable to fluid flow. The simulated injection of a 25–50 m thick basalt intrusion at a depth of 250 m resulted in about 10 yr of pore-fluid expulsion through the sea-floor in all cases, leaving the sediments above the intrusions strongly underpressured. A longer period of fluid recharge followed, sometimes accompanied by reductions in total seafloor heat output of 10% in comparison to pre-intrusion values. Additional discharge-recharge events were dispersed chaotically through the duration of the cooling period. These cycles in heat and fluid flow resulted from the response of the simulated system to a thermodynamic shock, the sudden emplacement of a large heat source, and not from mechanical displacement of sediments and pore fluids, which was not simulated.Water/rock mass ratios calculated from numerical simulations are in good agreement with geochemical estimates from materials recovered from the Guaymas Basin, assuming a bulk basalt permeability value of at least 10−17 m2/(10−2 mD). The addition of faults through intrusions and sediments in these simulations did not facilitate continuous, rapid venting. Increased heat input at the base of the faults resulted in temporarily greater fluid discharge, but the flow could not be sustained because the modeled system could not recharge cold fluid quickly enough to remove sufficient heat through the vents.

Capillary Flow of Liquid Metals in Brazing

NASA Astrophysics Data System (ADS)

Dehsara, Mohammad

Capillary flow is driven or controlled by capillary forces, exerted at the triple line where the fluid phases meet the solid boundary. Phase field (PF) models naturally accommodate diffusive triple line motion with variable contact angle, thus allowing for the no-slip boundary condition without the stress singularities. Moreover, they are uniquely suited for modeling of topological discontinuities which often arise during capillary flows. In this study, we consider diffusive triple line motion within two PF models: the compositionally compressible (CC) and the incompressible (IC) models. We derive the IC model as a systematic approximation to the CC model, based on a suitable choice of continuum velocity field. The CC model, applied to the fluids of dissimilar mass densities, exhibits a computational instability at the triple line. The IC model perfectly represents the analytic equilibria. We develop the parameter identification procedure and show that the triple line kinetics can be well represented by the IC model's diffusive boundary condition. The IC model is first tested by benchmarking the phase-field and experimental kinetics of water, and silicone oil spreading over the glass plates in which two systems do not interact with the substrate. Then, two high-temperature physical settings involving spreading of the molten Al-Si alloy: one over a rough wetting substrate, the other over a non-wetting substrate are modeled in a T-joint structure which is a typical geometric configuration for many brazing and soldering applications. Surface roughness directly influences the spreading of the molten metal by causing break-ups of the liquid film and trapping the liquid away from the joint. In the early stages of capillary flow over non-wetting surface, the melting and flow are concurrent, so that the kinetics of wetting is strongly affected by the variations in effective viscosity of the partially molten metal. We define adequate time-dependent functions for the variations of Al-Si alloy viscosity and triple line mobility to describe the wetting kinetics.

Identification of Regime Transitions in Umbrella Cloud Growth for Short- and Long-Lived Eruptions

NASA Astrophysics Data System (ADS)

Pouget, S.; Bursik, M. I.; Johnson, C. G.; Hogg, A. J.; Sparks, R. S. J.; Phillips, J.

2014-12-01

The ability to characterize the transition between fluid dynamic regimes in an umbrella cloud as it spreads as a gravity current is important for volcanologists and atmospheric scientists. It would allow a better understanding of how ash behaves and spreads in the atmosphere and therefore better estimate the location and propagation of the ash during an eruption. We tested a new gravity current model that allows us to study the transition from one flow regime to another in data plume growth data from several eruptions. It was found that previous asymptotic models of umbrella cloud growth only treat one part of the evolution of the cloud. The new model allows for the study of the duration of different regimes and the timing of transitions during growth of the umbrella cloud. It was found, by testing the effect of the different input parameters of the model, that the duration of release from the volcanic source has a larger impact than the drag force and the initial radius of the intrusion on the initial and downwind spreading.

Faulting and off-axis submarine massive sulfide accumulation at slow spreading mid-ocean ridges: A numerical modeling perspective

NASA Astrophysics Data System (ADS)

Andersen, C.; Theissen-Krah, S.; Hannington, M.; Rüpke, L.; Petersen, S.

2017-06-01

The potential of mining seafloor massive sulfide deposits for metals such as Cu, Zn, and Au is currently debated. One key challenge is to predict where the largest deposits worth mining might form, which in turn requires understanding the pattern of subseafloor hydrothermal mass and energy transport. Numerical models of heat and fluid flow are applied to illustrate the important role of fault zone properties (permeability and width) in controlling mass accumulation at hydrothermal vents at slow spreading ridges. We combine modeled mass-flow rates, vent temperatures, and vent field dimensions with the known fluid chemistry at the fault-controlled Logatchev 1 hydrothermal field of the Mid-Atlantic Ridge. We predict that the 135 kilotons of SMS at this site (estimated by other studies) can have accumulated with a minimum depositional efficiency of 5% in the known duration of hydrothermal venting (58,200 year age of the deposit). In general, the most productive faults must provide an efficient fluid pathway while at the same time limit cooling due to mixing with entrained cold seawater. This balance is best met by faults that are just wide and permeable enough to control a hydrothermal plume rising through the oceanic crust. Model runs with increased basal heat input, mimicking a heat flow contribution from along-axis, lead to higher mass fluxes and vent temperatures, capable of significantly higher SMS accumulation rates. Nonsteady state conditions, such as the influence of a cooling magmatic intrusion beneath the fault zone, also can temporarily increase the mass flux while sustaining high vent temperatures.

Alteration heterogeneities in peridotites tectonically exhumed along slow-spreading ridges

NASA Astrophysics Data System (ADS)

Rouméjon, S.; Frueh-Green, G. L.; Williams, M. J.

2017-12-01

Serpentinized peridotites associated with mafic lithologies commonly outcrop along slow-spreading ridges. They are exhumed along large offset normal faults, called detachment faults, that uplift fresh peridotites and gabbros from the base of the brittle lithosphere to shallower levels where they are hydrothermally altered. Numerous petrological studies in these environments reveal that peridotites are variably altered depending on factors such as the temperature, redox state, intensity of hydrothermal fluid input and the chemistry of these fluids. It follows that the detachment footwalls are heterogeneous at scales less than a kilometer, reflecting initial distribution of primary lithologies and later variable alteration. Here we investigate the nature, distribution and typical length scales of alteration heterogeneities. We primarily focus on samples drilled at five sites across the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during IODP Exp. 357 (Nov. 2015, RRS James Cook) and on samples dredged along the easternmost Southwest Indian Ridge (Smoothseafloor cruise, Oct. 2010, N/O Marion Dufresne). Multiple petrological observations are combined: hand sample description, sequences of textures and the associated mineralogical assemblages identifiable in thin section, in situ major and trace elements data as well as bulk rock and in situ oxygen isotopes ratios in serpentine textures. We show that all serpentinized peridotites develop serpentine mesh textures. However, some domains of the footwall are overprinted by further serpentine recrystallization and veins (mostly chrysotile- or antigorite-bearing) as a result of localized fluid-rock interaction and evolving fluids. Other domains are impacted by the alteration of the surrounding mafic bodies that influences both the mineralogy and chemistry of the altered peridotites. Using these results, we propose a conceptual model for the development of alteration heterogeneities during exhumation at slow-spreading ridges.

A mathematical model of the coupled mechanisms of cell adhesion, contraction and spreading

PubMed Central

Vernerey, Franck J.; Farsad, Mehdi

2013-01-01

Recent research has shown that cell spreading is highly dependent on the contractililty of its cytoskeleton and the mechanical properties of the environment it is located in. The dynamics of such process is critical for the development of tissue engineering strategy but is also a key player in wound contraction, tissue maintenance and angiogenesis. To better understand the underlying physics of such phenomena, the paper describes a mathematical formulation of cell spreading and contraction that couples the processes of stress fiber formation, protrusion growth through actin polymerization at the cell edge and dynamics of cross-membrane protein (integrins) enabling cell-substrate attachment. The evolving cell’s cytoskeleton is modeled as a mixture of fluid, proteins and filaments that can exchange mass and generate contraction. In particular, besides self-assembling into stress fibers, actin monomers able to polymerize into an actin meshwork at the cell’s boundary in order to push the membrane forward and generate protrusion. These processes are possible via the development of cell-substrate attachment complexes that arise from the mechano-sensitive equilibrium of membrane proteins, known as integrins. After deriving the governing equation driving the dynamics of cell evolution and spreading, we introduce a numerical solution based on the extended finite element method, combined with a level set formulation. Numerical simulations show that the proposed model is able to capture the dependency of cell spreading and contraction on substrate stiffness and chemistry. The very good agreement between model predictions and experimental observations suggests that mechanics plays a strong role into the coupled mechanisms of contraction, adhesion and spreading of adherent cells. PMID:23463540

Predictions of hydrothermal alteration within near-ridge oceanic crust from coordinated geochemical and fluid flow models

USGS Publications Warehouse

Wetzel, L.R.; Raffensperger, Jeff P.; Shock, E.L.

2001-01-01

Coordinated geochemical and hydrological calculations guide our understanding of the composition, fluid flow patterns, and thermal structure of near-ridge oceanic crust. The case study presented here illustrates geochemical and thermal changes taking place as oceanic crust ages from 0.2 to 1.0 Myr. Using a finite element code, we model fluid flow and heat transport through the upper few hundred meters of an abyssal hill created at an intermediate spreading rate. We use a reaction path model with a customized database to calculate equilibrium fluid compositions and mineral assemblages of basalt and seawater at 500 bars and temperatures ranging from 150 to 400??C. In one scenario, reaction path calculations suggest that volume increases on the order of 10% may occur within portions of the basaltic basement. If this change in volume occurred, it would be sufficient to fill all primary porosity in some locations, effectively sealing off portions of the oceanic crust. Thermal profiles resulting from fluid flow simulations indicate that volume changes along this possible reaction path occur primarily within the first 0.4 Myr of crustal aging. ?? 2001 Elsevier Science B.V. All rights reserved.

Fluid simulations of plasma turbulence at ion scales: Comparison with Vlasov-Maxwell simulations

NASA Astrophysics Data System (ADS)

Perrone, D.; Passot, T.; Laveder, D.; Valentini, F.; Sulem, P. L.; Zouganelis, I.; Veltri, P.; Servidio, S.

2018-05-01

Comparisons are presented between a hybrid Vlasov-Maxwell (HVM) simulation of turbulence in a collisionless plasma and fluid reductions. These include Hall-magnetohydrodynamics (HMHD) and Landau fluid (LF) or finite Larmor radius-Landau fluid (FLR-LF) models that retain pressure anisotropy and low-frequency kinetic effects such as Landau damping and, for the last model, finite Larmor radius (FLR) corrections. The problem is considered in two space dimensions, when initial conditions involve moderate-amplitude perturbations of a homogeneous equilibrium plasma subject to an out-of-plane magnetic field. LF turns out to provide an accurate description of the velocity field up to the ion Larmor radius scale, and even to smaller scales for the magnetic field. Compressibility nevertheless appears significantly larger at the sub-ion scales in the fluid models than in the HVM simulation. High frequency kinetic effects, such as cyclotron resonances, not retained by fluid descriptions, could be at the origin of this discrepancy. A significant temperature anisotropy is generated, with a bias towards the perpendicular component, the more intense fluctuations being rather spread out and located in a broad vicinity of current sheets. Non-gyrotropic pressure tensor components are measured and are shown to reach a significant fraction of the total pressure fluctuations, with intense regions closely correlated with current sheets.

Magnetic fluid control for viscous loss reduction of high-speed MRF brakes and clutches with well-defined fail-safe behavior

NASA Astrophysics Data System (ADS)

Güth, Dirk; Schamoni, Markus; Maas, Jürgen

2013-09-01

No-load losses within brakes and clutches based on magnetorheological fluids are unavoidable and represent a major barrier towards their wide-spread commercial adoption. Completely torque free rotation is not yet possible due to persistent fluid contact within the shear gap. In this paper, a novel concept is presented that facilitates the controlled movement of the magnetorheological fluid from an active, torque-transmitting region into an inactive region of the shear gap. This concept enables complete decoupling of the fluid engaging surfaces such that viscous drag torque can be eliminated. In order to achieve the desired effect, motion in the magnetorheological fluid is induced by magnetic forces acting on the fluid, which requires an appropriate magnetic circuit design. In this investigation, we propose a methodology to determine suitable magnetic circuit designs with well-defined fail-safe behavior. The magnetically induced motion of magnetorheological fluids is modeled by the use of the Kelvin body force, and a multi-physics domain simulation is performed to elucidate various transitions between an engaged and disengaged operating mode. The modeling approach is validated by captured high-speed video frames which show the induced motion of the magnetorheological fluid due to the magnetic field. Finally, measurements performed with a prototype actuator prove that the induced viscous drag torque can be reduced significantly by the proposed magnetic fluid control methodology.

Effects of lower limb neurodynamic mobilization on intraneural fluid dispersion of the fourth lumbar nerve root: an unembalmed cadaveric investigation

PubMed Central

Gilbert, Kerry K.; Smith, Michael P.; Sobczak, Stéphane; James, C. Roger; Sizer, Phillip S.; Brismée, Jean-Michel

2015-01-01

Objectives Manual and physical therapists incorporate neurodynamic mobilisation (NDM) to improve function and decrease pain. Little is known about the mechanisms by which these interventions affect neural tissue. The objective of this research was to assess the effects of repetitive straight leg raise (SLR) NDM on the fluid dynamics within the fourth lumbar nerve root in unembalmed cadavers. Methods A biomimetic solution (Toluidine Blue Stock 1% and Plasma) was injected intraneurally, deep to the epineurium, into the L4 nerve roots of seven unembalmed cadavers. The initial dye spread was allowed to stabilise and measured with a digital calliper. Once the initial longitudinal dye spread stabilised, an intervention strategy (repetitive SLR) was applied incorporating NDMs (stretch/relax cycles) at a rate of 30 repetitions per minute for 5 minutes. Post-intervention calliper measurements of the longitudinal dye spread were measured. Results The mean experimental posttest longitudinal dye spread measurement (1.1 ± 0.9 mm) was significantly greater (P = 0.02) than the initial stabilised pretest longitudinal dye spread measurement. Increases ranged from 0.0 to 2.6 mm and represented an average of 7.9% and up to an 18.1% increase in longitudinal dye spread. Discussion Passive NDM in the form of repetitive SLR induced a significant increase in longitudinal fluid dispersion in the L4 nerve root of human cadaveric specimen. Lower limb NDM may be beneficial in promoting nerve function by limiting or altering intraneural fluid accumulation within the nerve root, thus preventing the adverse effects of intraneural oedema. PMID:26955255

Spreading of a pendant liquid drop underneath a textured substrate

NASA Astrophysics Data System (ADS)

Mistry, Aashutosh; Muralidhar, K.

2018-04-01

A pendant drop spreading underneath a partially wetting surface from an initial shape to its final equilibrium configuration and contact angle is studied. A mathematical formulation that quantifies spreading behavior of liquid drops over textured surfaces is discussed. The drop volume and the equilibrium contact angle are treated as parameters in the study. The unbalanced force at the three-phase contact line is modeled as being proportional to the degree of departure from the equilibrium state. Model predictions are verified against the available experimental data in the literature. Results show that the flow dynamics is strongly influenced by the fluid properties, drop volume, and contact angle of the liquid with the partially wetting surface. The drop exhibits rich dynamical behavior including inertial oscillations and gravitational instability, given that gravity tries to detach the drop against wetting contributions. Flow characteristics of drop motion, namely, the radius of the footprint, slip length, and dynamic contact angle in the pendant configuration are presented. Given the interplay among the competing time-dependent forces, a spreading drop can momentarily be destabilized and not achieve a stable equilibrium shape. Instability is then controlled by the initial drop shape as well. The spreading model is used to delineate stable and unstable regimes in the parameter space. Predictions of the drop volume based on the Young-Laplace equation are seen to be conservative relative to the estimates of the dynamical model discussed in the present study.

Predictive models for moving contact line flows

NASA Technical Reports Server (NTRS)

Rame, Enrique; Garoff, Stephen

2003-01-01

Modeling flows with moving contact lines poses the formidable challenge that the usual assumptions of Newtonian fluid and no-slip condition give rise to a well-known singularity. This singularity prevents one from satisfying the contact angle condition to compute the shape of the fluid-fluid interface, a crucial calculation without which design parameters such as the pressure drop needed to move an immiscible 2-fluid system through a solid matrix cannot be evaluated. Some progress has been made for low Capillary number spreading flows. Combining experimental measurements of fluid-fluid interfaces very near the moving contact line with an analytical expression for the interface shape, we can determine a parameter that forms a boundary condition for the macroscopic interface shape when Ca much les than l. This parameter, which plays the role of an "apparent" or macroscopic dynamic contact angle, is shown by the theory to depend on the system geometry through the macroscopic length scale. This theoretically established dependence on geometry allows this parameter to be "transferable" from the geometry of the measurement to any other geometry involving the same material system. Unfortunately this prediction of the theory cannot be tested on Earth.

The effect of sediments on turbulent plume dynamics in a stratified fluid

NASA Astrophysics Data System (ADS)

Stenberg, Erik; Ezhova, Ekaterina; Brandt, Luca

2017-11-01

We report large eddy simulation results of sediment-loaded turbulent plumes in a stratified fluid. The configuration, where the plume is discharged from a round source, provides an idealized model of subglacial discharge from a submarine tidewater glacier and is a starting point for understanding the effect of sediments on the dynamics of the rising plume. The transport of sediments is modeled by means of an advection-diffusion equation where sediment settling velocity is taken into account. We initially follow the experimental setup of Sutherland (Phys. Rev. Fluids, 2016), considering uniformly stratified ambients and further extend the work to pycnocline-type stratifications typical of Greenland fjords. Apart from examining the rise height, radial spread and intrusion of the rising plume, we gain further insights of the plume dynamics by extracting turbulent characteristics and the distribution of the sediments inside the plume.

Splashing Droplets

NASA Technical Reports Server (NTRS)

VanderWal, Randall L.; Kizito, John Patrick; Berger, Gordon M.; Iwan, J.; Alexander, D.; Tryggvason, Gretar

2002-01-01

Current data on droplet breakup is scarce for the sizes and velocities typical of practical applications such as in spray combustion processes and coating processes. While much more representative of practical applications, the small spatial scales and rapid time-scales prevent detailed measurement of the internal fluid dynamics and liquid property gradients produced by impinging upon surfaces. Realized through the extended spatial and temporal scales afforded by a microgravity environment, an improved understanding of drop breakup dynamics is sought to understand and ultimately control the impingement dynamics of droplets upon surfaces in practical situations. The primary objective of this research will be to mark the onset of different 'splashing modes' and to determine their temperature, pressure and angle dependence for impinging droplets representative of practical fluids. In addition, we are modeling the evolution of droplets that do not initially splash but rather undergo a 'fingering' evolution observed on the spreading fluid front and the transformation of these fingers into splashed products. An example of our experimental data is presented below. These images are of Isopar V impacting a mirror-polished surface. They were acquired using a high-speed camera at 1000 frames per second. They show the spreading of a single droplet after impact and ensuing finger instabilities. Normal gravity experimental data such as this will guide low gravity measurements in the 2.2 second drop tower and KC-135 aircraft as available. Presently we are in the process of comparing the experimental data of droplet shape evolution to numerical models, which can also capture the internal fluid dynamics and liquid property gradients such as produced by impingement upon a heated surface. To-date isothermal numerical data has been modeled using direct numerical simulations of representative splashing droplets. The data obtained so far indicates that the present model describes well the droplet wall interactions to a point in time just before splash. Additional information is included in the original extended abstract.

Dynamics and linear stability of thermocapillary spreading films on homogeneous and micropatterned surfaces

NASA Astrophysics Data System (ADS)

Davis, Jeffrey Michael

The recent focus on microfluidic devices has generated substantial interest in small-scale transport phenomena. Because the surface to volume ratio scales inversely with the characteristic length scale, surface forces dominate in microscale systems. In particular, these forces can be manipulated to regulate the motion of thin liquid films. The dynamics and stability of thermocapillary spreading films are theoretically investigated in this dissertation for flow on homogeneous and chemically or topographically patterned substrates. Because the governing equations for spreading films driven by other forces are analogous, the approach and results are valid for general lubrication flows. Experiments have shown that films spreading on homogeneous substrates can undergo a flow transition from a uniform front at the advancing solid-liquid-vapor contact line to an array of parallel rivulets. This instability is investigated via a non-modal, transient analysis because the relevant linearized disturbance operators for spatially inhomogeneous thin films are nonnormal. Stability results for three different contact line models are compared. This investigation of thermocapillary driven spreading is also pursued in the context of characterizing a novel, open-architecture microfluidic device based on flow confinement to completely wetting microstripes through chemical micropatterning of the substrate. The resulting lateral curvature of the fluid significantly influences the dynamics of the liquid. Applied to the dip coating of these patterned substrates, hydrodynamic scaling arguments are used to derive a replacement for the classical Landau-Levich result for homogeneous substrates. Thermocapillary flow along wetting microstripes is then characterized. The lateral curvature modifies the expected spreading velocity and film profile and also suppresses the capillary ridge and instability observed at the advancing contact line on homogeneous surfaces. In addition, a lubrication-based model is derived to quantify the significant effects of lateral film curvature and fluid confinement on the transverse diffusive broadening in two microstreams merging at a ⋎ -junction. Finally, the analysis is extended to lubrication flow over chemically uniform but topographically patterned substrates. A transient analysis is employed to determine the evolution of disturbances to the capillary ridges induced by the substrate topography.

Impact, Fire, and Fluid Spread Code Coupling for Complex Transportation Accident Environment Simulation.

PubMed

Brown, Alexander L; Wagner, Gregory J; Metzinger, Kurt E

2012-06-01

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that are necessary to resolve for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been described for modeling the impact and subsequent liquid spread. Because the environment is difficult to instrument and costly to test, the existing validation data are of limited scope and quality. A comparatively well instrumented test involving a rocket propelled cylindrical tank of water was performed, the results of which are helpful to understand the adequacy of the modeling methods. Existing data include estimates of drop sizes at several locations, final liquid surface deposition mass integrated over surface area regions, and video evidence of liquid cloud spread distances. Comparisons are drawn between the experimental observations and the predicted results of the modeling methods to provide evidence regarding the accuracy of the methods, and to provide guidance on the application and use of these methods.

Voxelized Computational Model for Convection-Enhanced Delivery in the Rat Ventral Hippocampus: Comparison with In Vivo MR Experimental Studies

PubMed Central

Kim, Jung Hwan; Astary, Garrett W.; Kantorovich, Svetlana; Mareci, Thomas H.; Carney, Paul R.; Sarntinoranont, Malisa

2012-01-01

Convection-enhanced delivery (CED) is a promising local delivery technique for overcoming the blood–brain barrier (BBB) and treating diseases of the central nervous system (CNS). For CED, therapeutics are infused directly into brain tissue and the drug agent is spread through the extracellular space, considered to be highly tortuous porous media. In this study, 3D computational models developed using magnetic resonance (MR) diffusion tensor imaging data sets were used to predict CED transport in the rat ventral hippocampus using a voxelized modeling previously developed by our group. Predicted albumin tracer distributions were compared with MR-measured distributions from in vivo CED in the ventral hippocampus up to 10 μL of Gd-DTPA albumin tracer infusion. Predicted and measured tissue distribution volumes and distribution patterns after 5 and 10 μL infusions were found to be comparable. Tracers were found to occupy the underlying landmark structures with preferential transport found in regions with less fluid resistance such as the molecular layer of the dentate gyrus. Also, tracer spread was bounded by high fluid resistance layers such as the granular cell layer and pyramidal cell layer of dentate gyrus. Leakage of tracers into adjacent CSF spaces was observed towards the end of infusions. PMID:22532321

Controlling droplet spreading with topography

NASA Astrophysics Data System (ADS)

Kant, P.; Hazel, A. L.; Dowling, M.; Thompson, A. B.; Juel, A.

2017-09-01

We present an experimental system that can be used to study the dynamics of a picoliter droplet (in-flight radius of 12.2 μ m ) as it spreads over substrates with topographic variations. We concentrate on the spreading of a droplet within a recessed stadium-shaped pixel, with applications to the manufacture of polymer organic light-emitting-diode displays, and find that the sloping sidewall of the pixel can either locally enhance or hinder spreading depending on whether the topography gradient ahead of the contact line is positive or negative, respectively. Locally enhanced spreading occurs via the formation of thin pointed rivulets along the sidewalls of the pixel through a mechanism similar to capillary rise in sharp corners. We demonstrate that a simplified model involving quasistatic surface-tension effects within the framework of a thin-film approximation combined with an experimentally measured dynamic spreading law, relating the speed of the contact line to the contact angle, provides excellent predictions of the evolving liquid morphologies. A key feature of the liquid-substrate interaction studied here is the presence of significant contact angle hysteresis, which enables the persistence of noncircular fluid morphologies. We also show that the spreading law for an advancing contact line can be adequately approximated by a Cox-Voinov law for the majority of the evolution. The model does not include viscous effects in the bulk of the droplet and hence the time scales for the propagation of the thin pointed rivulets are not captured. Nonetheless, this simple model can be used very effectively to predict the areas covered by the liquid and may serve as a useful design tool for systems that require precise control of liquid on substrates.

Refining the Subseafloor Circulation Model of the Middle Valley Hydrothermal System Using Fluid Geochemistry

NASA Astrophysics Data System (ADS)

Inderbitzen, K. E.; Wheat, C. G.; Baker, P. A.; Fisher, A. T.

2014-12-01

Currently, fluid circulation patterns and the evolution of rock/fluid compositions as circulation occurs in subseafloor hydrothermal systems are poorly constrained. Sedimented spreading centers provide a unique opportunity to study subsurface flow because sediment acts as an insulating blanket that traps heat from the cooling magma body and limits: (a) potential flow paths for seawater to recharge the aquifer in permeable upper basaltic basement and (b) points of altered fluid egress. This also allows for a range of thermal and geochemical gradients to exist near the sediment-water interface. Models of fluid circulation patterns in this type of hydrologic setting have been generated (eg. Stein and Fisher, 2001); however fluid chemistry datasets have not previously been used to test the model's viability. We address this issue by integrating the existing circulation model with fluid compositional data collected from sediment pore waters and high temperature hydrothermal vents located in Middle Valley on the Juan de Fuca Ridge. Middle Valley hosts a variety of hydrologic regimes: including areas of fluid recharge (Site 855), active venting (Site 858/1036; Dead Dog vent field), recent venting (Site 856/1035; Bent Hill Massive Sulfide deposit) and a section of heavily sedimented basement located between recharge and discharge sites (Site 857). We will present new results based on thermal and geochemical data from the area of active venting (Sites 858 and 1036), that was collected during Ocean Drilling Program Legs 139 and 169 and a subsequent heat flow/gravity coring effort. These results illuminate fine scale controls on secondary recharge and fluid flow within the sediment section at Site 858/1036. The current status of high temperature vents in this area (based on observations made in July, 2014) will also be outlined.

Effects of the endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae) parasitism, venom, and calyx fluid on cellular and humoral immunity of its host Chilo suppressalis (Lepidoptera: Crambidae) larvae.

PubMed

Teng, Zi-Wen; Xu, Gang; Gan, Shi-Yu; Chen, Xuan; Fang, Qi; Ye, Gong-Yin

2016-02-01

The larval endoparasitoid Cotesia chilonis injects venom and bracoviruses into its host Chilo suppressalis during oviposition. Here we study the effects of the polydnavirus (PDV)-carrying endoparasitoid C. chilonis (Hymenoptera: Braconidae) parasitism, venom and calyx fluid on host cellular and humoral immunity, specifically hemocyte composition, cellular spreading, encapsulation and melanization. Total hemocyte counts (THCs) were higher in parasitized larvae than in unparasitized larvae in the late stages following parasitization. While both plasmatocyte and granulocyte fractions and hemocyte mortality did not differ between parasitized and unparasitized hosts, in vitro spreading behavior of hemocytes was inhibited significantly by parasitism throughout the course of parasitoid development. C. chilonis parasitism suppressed the encapsulation response and melanization in the early stages. Venom alone did not alter cellular immune responses, including effects on THCs, mortality, hemocyte composition, cell spreading and encapsulation, but venom did inhibit humoral immunity by reducing melanization within 6h after injection. In contrast to venom, calyx fluid had a significant effect on cell spreading, encapsulation and melanization from 6h after injection. Dose-response injection studies indicated the effects of venom and calyx fluid synergized, showing a stronger and more persistent reduction in immune system responses than the effect of either injected alone. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

VOF simulations of the contact angle dynamics during the drop spreading: standard models and a new wetting force model.

PubMed

Malgarinos, Ilias; Nikolopoulos, Nikolaos; Marengo, Marco; Antonini, Carlo; Gavaises, Manolis

2014-10-01

In this study,a novel numerical implementation for the adhesion of liquid droplets impacting normally on solid dry surfaces is presented. The advantage of this new approach, compared to the majority of existing models, is that the dynamic contact angle forming during the surface wetting process is not inserted as a boundary condition, but is derived implicitly by the induced fluid flow characteristics (interface shape) and the adhesion physics of the gas-liquid-surface interface (triple line), starting only from the advancing and receding equilibrium contact angles. These angles are required in order to define the wetting properties of liquid phases when interacting with a solid surface. The physical model is implemented as a source term in the momentum equation of a Navier-Stokes CFD flow solver as an "adhesion-like" force which acts at the triple-phase contact line as a result of capillary interactions between the liquid drop and the solid substrate. The numerical simulations capture the liquid-air interface movement by considering the volume of fluid (VOF) method and utilizing an automatic local grid refinement technique in order to increase the accuracy of the predictions at the area of interest, and simultaneously minimize numerical diffusion of the interface. The proposed model is validated against previously reported experimental data of normal impingement of water droplets on dry surfaces at room temperature. A wide range of impact velocities, i.e. Weber numbers from as low as 0.2 up to 117, both for hydrophilic (θadv=10°-70°) and hydrophobic (θadv=105°-120°) surfaces, has been examined. Predictions include in addition to droplet spreading dynamics, the estimation of the dynamic contact angle; the latter is found in reasonable agreement against available experimental measurements. It is thus concluded that theimplementation of this model is an effective approach for overcoming the need of a pre-defined dynamic contact angle law, frequently adopted as an approximate boundary condition for such simulations. Clearly, this model is mostly influential during the spreading phase for the cases of low We number impacts (We<˜80) since for high impact velocities, inertia dominates significantly over capillary forces in the initial phase of spreading. Copyright © 2014 Elsevier B.V. All rights reserved.

Ebola virus disease

MedlinePlus

... body fluids of infected animals Contact with infected bats Ebola does NOT spread through: Air Water Food ... who has died from Ebola. Avoid contact with bats and nonhuman primates or blood, fluids, and raw ...

Computation of three-phase capillary entry pressures and arc menisci configurations in pore geometries from 2D rock images: A combinatorial approach

NASA Astrophysics Data System (ADS)

Zhou, Yingfang; Helland, Johan Olav; Hatzignatiou, Dimitrios G.

2014-07-01

We present a semi-analytical, combinatorial approach to compute three-phase capillary entry pressures for gas invasion into pore throats with constant cross-sections of arbitrary shapes that are occupied by oil and/or water. For a specific set of three-phase capillary pressures, geometrically allowed gas/oil, oil/water and gas/water arc menisci are determined by moving two circles in opposite directions along the pore/solid boundary for each fluid pair such that the contact angle is defined at the front circular arcs. Intersections of the two circles determine the geometrically allowed arc menisci for each fluid pair. The resulting interfaces are combined systematically to allow for all geometrically possible three-phase configuration changes. The three-phase extension of the Mayer and Stowe - Princen method is adopted to calculate capillary entry pressures for all determined configuration candidates, from which the most favorable gas invasion configuration is determined. The model is validated by comparing computed three-phase capillary entry pressures and corresponding fluid configurations with analytical solutions in idealized triangular star-shaped pores. It is demonstrated that the model accounts for all scenarios that have been analyzed previously in these shapes. Finally, three-phase capillary entry pressures and associated fluid configurations are computed in throat cross-sections extracted from segmented SEM images of Bentheim sandstone. The computed gas/oil capillary entry pressures account for the expected dependence of oil/water capillary pressure in spreading and non-spreading fluid systems at the considered wetting conditions. Because these geometries are irregular and include constrictions, we introduce three-phase displacements that have not been identified previously in pore-network models that are based on idealized pore shapes. However, in the limited number of pore geometries considered in this work, we find that the favorable displacements are not generically different from those already encountered in network models previously, except that the size and shape of oil layers that are surrounded by gas and water are described more realistically. The significance of the results for describing oil connectivity in porous media accurately can only be evaluated by including throats with more complex cross-sections in three-phase pore-network models.

Prediction of the low-velocity distribution from the pore structure in simple porous media

NASA Astrophysics Data System (ADS)

de Anna, Pietro; Quaife, Bryan; Biros, George; Juanes, Ruben

2017-12-01

The macroscopic properties of fluid flow and transport through porous media are a direct consequence of the underlying pore structure. However, precise relations that characterize flow and transport from the statistics of pore-scale disorder have remained elusive. Here we investigate the relationship between pore structure and the resulting fluid flow and asymptotic transport behavior in two-dimensional geometries of nonoverlapping circular posts. We derive an analytical relationship between the pore throat size distribution fλ˜λ-β and the distribution of the low fluid velocities fu˜u-β /2 , based on a conceptual model of porelets (the flow established within each pore throat, here a Hagen-Poiseuille flow). Our model allows us to make predictions, within a continuous-time random-walk framework, for the asymptotic statistics of the spreading of fluid particles along their own trajectories. These predictions are confirmed by high-fidelity simulations of Stokes flow and advective transport. The proposed framework can be extended to other configurations which can be represented as a collection of known flow distributions.

Slope effects on the fluid dynamics of a fire spreading across a fuel bed: PIV measurements and OH* chemiluminescence imaging

NASA Astrophysics Data System (ADS)

Morandini, F.; Silvani, X.; Honoré, D.; Boutin, G.; Susset, A.; Vernet, R.

2014-08-01

Slope is among the most influencing factor affecting the spread of wildfires. A contribution to the understanding of the fluid dynamics of a fire spreading in these terrain conditions is provided in the present paper. Coupled optical diagnostics are used to study the slope effects on the flow induced by a fire at laboratory scale. Optical diagnostics consist of particle image velocimetry, for investigating the 2D (vertical) velocity field of the reacting flow and chemiluminescence imaging, for visualizing the region of spontaneous emission of OH radical occurring during gaseous combustion processes. The coupling of these two techniques allows locating accurately the contour of the reaction zone within the computed velocity field. The series of experiments are performed across a bed of vegetative fuel, under both no-slope and 30° upslope conditions. The increase in the rate of fire spread with increasing slope is attributed to a significant change in fluid dynamics surrounding the flame. For horizontal fire spread, flame fronts exhibit quasi-vertical plume resulting in the buoyancy forces generated by the fire. These buoyancy effects induce an influx of ambient fresh air which is entrained laterally into the fire, equitably from both sides. For upward flame spread, the induced flow is strongly influenced by air entrainment on the burnt side of the fire and fire plume is tilted toward unburned vegetation. A particular attention is paid to the induced air flow ahead of the spreading flame. With increasing the slope angle beyond a threshold, highly dangerous conditions arise because this configuration induces wind blows away from the fire rather than toward it, suggesting the presence of convective heat transfers ahead of the fire front.

Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles.

PubMed

Paulatto, Michele; Laigle, Mireille; Galve, Audrey; Charvis, Philippe; Sapin, Martine; Bayrakci, Gaye; Evain, Mikael; Kopp, Heidrun

2017-07-10

Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60-100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120-160 km depth suggests that the slab's mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics.

Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles

PubMed Central

Paulatto, Michele; Laigle, Mireille; Galve, Audrey; Charvis, Philippe; Sapin, Martine; Bayrakci, Gaye; Evain, Mikael; Kopp, Heidrun

2017-01-01

Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60–100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120–160 km depth suggests that the slab’s mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics. PMID:28691714

Model for the Evolution of an Oceanic Core Complex and its Hydrothermal Vent on the Ultraslow-Spreading Mid Cayman Spreading Center

NASA Astrophysics Data System (ADS)

Harding, J.; Van Avendonk, H. J.; Hayman, N. W.; Grevemeyer, I.; Peirce, C.

2016-12-01

The Mid Cayman Spreading Center (MCSC) is an ultraslow-spreading center (15 mm yr-1 full rate) along the Caribbean-North American plate boundary. Despite the paradigm that ultraslow-spreading centers are amagmatic and cold, two hydrothermal vent fields have recently been discovered along the MCSC. The Beebe Vent Field is a black smoker in the northern axial deep, and the Von Damm Vent Field (VDVF) is a moderate-temperature, talc precipitating vent found atop an oceanic core complex (OCC). This OCC, "Mt. Dent", is a large (3 km high) massif that formed beneath a detachment fault, which exhumed lower crustal and upper mantle material. The CaySeis Experiment was conducted in April, 2015 in order to collect wide-angle refraction data of the MCSC crust and upper mantle. We modeled the across-axis crustal structure of Mt. Dent as well as the surrounding lithosphere using 2.5D P-wave tomography. Using this tomographic model, along with geochemistry, we propose a model for the formation and evolution of the OCC Mt. Dent and the VDVF. A detachment fault formed in a magma-poor environment due to a pulse of magmatism, producing a large gabbro body that was then exhumed and rotated into the OCC footwall. Once magmatism waned and the gabbroic body cooled, the OCC was faulted and fractured due to plate flexure and increased tectonic extensional stress in the naturally cold and thick lithosphere. These faults provide a permeable and deep network of hydrothermal pathways that mine deep lithospheric heat and expose gabbro and fresh mantle peridotite. This model is consistent with the basalt geochemistry, hydrothermal fluid geochemistry, and the distribution of brittle vs. ductile structures along the detachment shear zone. The VDVF is therefore a product of a pulse of magmatism in an overall melt-poor environment, conditions that may be found at other ultraslow-spreading ridges.

On multiscale moving contact line theory.

PubMed

Li, Shaofan; Fan, Houfu

2015-07-08

In this paper, a multiscale moving contact line (MMCL) theory is presented and employed to simulate liquid droplet spreading and capillary motion. The proposed MMCL theory combines a coarse-grained adhesive contact model with a fluid interface membrane theory, so that it can couple molecular scale adhesive interaction and surface tension with hydrodynamics of microscale flow. By doing so, the intermolecular force, the van der Waals or double layer force, separates and levitates the liquid droplet from the supporting solid substrate, which avoids the shear stress singularity caused by the no-slip condition in conventional hydrodynamics theory of moving contact line. Thus, the MMCL allows the difference of the surface energies and surface stresses to drive droplet spreading naturally. To validate the proposed MMCL theory, we have employed it to simulate droplet spreading over various elastic substrates. The numerical simulation results obtained by using MMCL are in good agreement with the molecular dynamics results reported in the literature.

An Immersed Boundary method with divergence-free velocity interpolation and force spreading

NASA Astrophysics Data System (ADS)

Bao, Yuanxun; Donev, Aleksandar; Griffith, Boyce E.; McQueen, David M.; Peskin, Charles S.

2017-10-01

The Immersed Boundary (IB) method is a mathematical framework for constructing robust numerical methods to study fluid-structure interaction in problems involving an elastic structure immersed in a viscous fluid. The IB formulation uses an Eulerian representation of the fluid and a Lagrangian representation of the structure. The Lagrangian and Eulerian frames are coupled by integral transforms with delta function kernels. The discretized IB equations use approximations to these transforms with regularized delta function kernels to interpolate the fluid velocity to the structure, and to spread structural forces to the fluid. It is well-known that the conventional IB method can suffer from poor volume conservation since the interpolated Lagrangian velocity field is not generally divergence-free, and so this can cause spurious volume changes. In practice, the lack of volume conservation is especially pronounced for cases where there are large pressure differences across thin structural boundaries. The aim of this paper is to greatly reduce the volume error of the IB method by introducing velocity-interpolation and force-spreading schemes with the properties that the interpolated velocity field in which the structure moves is at least C1 and satisfies a continuous divergence-free condition, and that the force-spreading operator is the adjoint of the velocity-interpolation operator. We confirm through numerical experiments in two and three spatial dimensions that this new IB method is able to achieve substantial improvement in volume conservation compared to other existing IB methods, at the expense of a modest increase in the computational cost. Further, the new method provides smoother Lagrangian forces (tractions) than traditional IB methods. The method presented here is restricted to periodic computational domains. Its generalization to non-periodic domains is important future work.

Predictive Model for Particle Residence Time Distributions in Riser Reactors. Part 1: Model Development and Validation

DOE PAGES

Foust, Thomas D.; Ziegler, Jack L.; Pannala, Sreekanth; ...

2017-02-28

Here in this computational study, we model the mixing of biomass pyrolysis vapor with solid catalyst in circulating riser reactors with a focus on the determination of solid catalyst residence time distributions (RTDs). A comprehensive set of 2D and 3D simulations were conducted for a pilot-scale riser using the Eulerian-Eulerian two-fluid modeling framework with and without sub-grid-scale models for the gas-solids interaction. A validation test case was also simulated and compared to experiments, showing agreement in the pressure gradient and RTD mean and spread. For simulation cases, it was found that for accurate RTD prediction, the Johnson and Jackson partialmore » slip solids boundary condition was required for all models and a sub-grid model is useful so that ultra high resolutions grids that are very computationally intensive are not required. Finally, we discovered a 2/3 scaling relation for the RTD mean and spread when comparing resolved 2D simulations to validated unresolved 3D sub-grid-scale model simulations.« less

Geochemistry of hydrothermal vent fluids and its implications for subsurface processes at the active Longqi hydrothermal field, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Ji, Fuwu; Zhou, Huaiyang; Yang, Qunhui; Gao, Hang; Wang, Hu; Lilley, Marvin D.

2017-04-01

The Longqi hydrothermal field at 49.6°E on the Southwest Indian Ridge was the first active hydrothermal field found at a bare-rock ultra-slow spreading mid-ocean ridge. Here we report the chemistry of the hydrothermal fluids, for the first time, that were collected from the S zone and the M zone of the Longqi field by gas-tight isobaric samplers by the HOV "Jiaolong" diving cruise in January 2015. According to H2, CH4 and other chemical data of the vent fluid, we suggest that the basement rock at the Longqi field is dominantly mafic. This is consistent with the observation that the host rock of the active Longqi Hydrothermal field is dominated by extensively distributed basaltic rock. It was very interesting to detect simultaneously discharging brine and vapor caused by phase separation at vents DFF6, DFF20, and DFF5 respectively, in a distance of about 400 m. Based on the end-member fluid chemistry and distance between the vents, we propose that there is a single fluid source at the Longqi field. The fluid branches while rising to the seafloor, and two of the branches reach S zone and M zone and phase separate at similar conditions of about 28-30.2 MPa and 400.6-408.3 °C before they discharge from the vents. The end-member fluid compositions of these vents are comparable with or within the range of variation of known global seafloor hydrothermal fluid chemical data from fast, intermediate and slow spreading ridges, which confirms that the spreading rate is not the key factor that directly controls hydrothermal fluid chemistry. The composition of basement rock, water-rock interaction and phase separation are the major factors that control the composition of the vent fluids in the Longqi field.

Characterization of Magma-Driven Hydrothermal Systems at Oceanic Spreading Centers

NASA Astrophysics Data System (ADS)

Farough, A.; Lowell, R. P.; Corrigan, R.

2012-12-01

Fluid circulation in high-temperature hydrothermal systems involves complex water-rock chemical reactions and phase separation. Numerical modeling of reactive transport in multi-component, multiphase systems is required to obtain a full understanding of the characteristics and evolution of hydrothermal vent systems. We use a single-pass parameterized model of high-temperature hydrothermal circulation at oceanic spreading centers constrained by observational parameters such as vent temperature, heat output, and vent field area, together with surface area and depth of the sub-axial magma chamber, to deduce fundamental hydrothermal parameters such as mass flow rate, bulk permeability, conductive boundary layer thickness at the base of the system, magma replenishment rate, and residence time in the discharge zone. All of these key subsurface characteristics are known for fewer than 10 sites out of 300 known hydrothermal systems. The principal limitations of this approach stem from the uncertainty in heat output and vent field area. For systems where data are available on partitioning of heat and chemical output between focused and diffuse flow, we determined the fraction of high-temperature vent fluid incorporated into diffuse flow using a two-limb single pass model. For EPR 9°50` N and ASHES, the diffuse flow temperatures calculated assuming conservative mixing are nearly equal to the observed temperatures indicating that approximately 80%-90% of the hydrothermal heat output occurs as high-temperature flow derived from magmatic heat even though most of the heat output appears as low-temperature diffuse discharge. For the Main Endeavour Field and Lucky Strike, diffuse flow fluids show significant conductive cooling and heating respectively. Finally, we calculate the transport of various geochemical constituents in focused and diffuse flow at the vent field scale and compare the results with estimates of geochemical transports from the Rainbow hydrothermal field where diffuse flow is absent.

Modeling fire-induced smoke spread and carbon monoxide transportation in a long channel: Fire Dynamics Simulator comparisons with measured data.

PubMed

Hu, L H; Fong, N K; Yang, L Z; Chow, W K; Li, Y Z; Huo, R

2007-02-09

Smoke and toxic gases, such as carbon monoxide, are the most fatal factors in fires. This paper models fire-induced smoke spread and carbon monoxide transportation in an 88m long channel by Fire Dynamics Simulator (FDS) with large eddy simulation (LES). FDS is now a well-founded fire dynamics computational fluid dynamic (CFD) program, which was developed by National Institute of Standards and Technology (NIST). Two full scale experiments with fire sizes of 0.75 and 1.6MW were conducted in this channel to validate the program. The spread of the fire-induced smoke flow together with the smoke temperature distribution along the channel, and the carbon monoxide concentration at an assigned position were measured. The FDS simulation results were compared with experimental data with fairly good agreement demonstrated. The validation work is then extended to numerically study the carbon monoxide concentration distribution, both vertically and longitudinally, in this long channel. Results showed that carbon monoxide concentration increase linearly with the height above the floor and decreases exponentially with the distance away from the fire source.

Progressive serpentinization of the oceanic lithosphere from ridge to ridge flank: Consequences for biogeochemical cycles

NASA Astrophysics Data System (ADS)

Frueh-Green, G. L.; Boschi, C.

2011-12-01

Exposure of mantle rocks is an integral process of slow- and ultra-slow spreading ridges and ridge-flanks. Mantle-dominated lithosphere is a highly reactive chemical and thermal system, in which progressive interaction with seawater during serpentinization has significant geophysical, geochemical and biological consequences for the global marine system. This presentation is intended to provide an overview of serpentinization processes as fundamental to understanding the evolution of oceanic lithosphere formed at slow spreading ridges, fluid flow and the consequences of serpentinization for biogeochemical cycles. Seawater progressively reacts with peridotite, commonly as detachment faults unroof mantle material to the seafloor and serpentinites become dominant components of the ridge flanks. The mineral assemblages and textures of abyssal serpentinites typically record progressive, static hydration reactions that take place under a wide range of temperatures, lithospheric depths, fluid compositions and redox conditions. The products and sequence of serpentinization reactions are influenced by the time-integrated flux of seawater, bulk protolith compositions, the presence or absence of magmatic intrusions and/or trapped gabbroic melts, and structure (e.g., detachment faults, cataclastic fault zones). In turn, these factors influence mineral assemblages, fluid chemistry, and volatile contents. Serpentinization processes have major consequences for long-term, global geochemical fluxes by acting as a sink for H2O, Cl, B, U, S, and C from seawater and a source of Ca, Ni and possibly Cr to hydrothermal fluids, and by producing hydrogen-rich reduced fluids that are critical to sustain microbial communities. Seafloor weathering of serpentinized abyssal peridotites may also result in Mg loss and enhanced B uptake during clay mineral formation. The production of hydrogen during serpentinization is generally attributed to the formation of magnetite during olivine hydration and is described by simplified reactions with end-member phases. In reality, serpentinization involves solid solutions and metastable reactions governed by local variations in bulk chemistry, fluid-rock ratios and the activities of elements such as Si, Mg, Fe, Ca, and C. Serpentinization at temperatures below ~200°C produces high alkaline, Ca-rich fluids with elevated concentrations of abiotic hydrocarbons and formate, as exemplified by the Lost City hydrothermal system [1,2]. The high pH and reducing conditions dictate that any carbonate species in the fluids are either reduced or precipitated as carbonate before fluid discharge on the seafloor, and thus represents an important sink of dissolved (inorganic and organic) carbon from seawater [2,3]. In contrast to basalt-dominated ridge flank systems, where conceptual models of the fluid pathways and subsequent reactions and element uptake are relatively well constrained, less is known of the fluid flow and reaction paths in serpentinite-dominated portions of ridge flanks at slow- and ultra-slow spreading environments. [1] Kelley et al. (2005) Science 307, 1428-1434. [2] Proskurowski et al. (2008) Science 319, 604-607. [3] Delacour et al. (2008) GCA 72, 3681-3702.

Ice-lubricated gravity spreading of the Olympus Mons aureole deposits

USGS Publications Warehouse

Tanaka, K.L.

1985-01-01

Gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of Olympus Mons. Detachment sliding could have occurred around the volcano if either pore-fluid pressures were exceptionally high (greater than 90%) or the rocks had very low resistance to shear (about 1 ?? 105 Pa or 1 bar). Because of the vast areal extent and probable shallow depth of the detachment zone, development of ubiquitous, high pore-fluid pressures beneath aureole-forming material was unlikely. However, a zone of sufficiently weak material consisting of about 10% interstitial or interbedded ice could have been present. If so, a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer. According to this model, extensional deformation would have occurred near the shield and compressional deformation in its distal parts. Proximal grabens and distal corrugations on aureole surfaces support this model. A submarine slide at Kitimat Arm, British Columbia, is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits. Ground-ice processes have been considered the cause of many geologic features on Mars; a 3% average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere. Ice may have been deposited in higher concentrations below the aureole-forming material; the source of the ice could have been juvenile water circulated hydrothermally by Olympus Mons volcanism. The basal scarp of Olympus Mons apparently demarcates the transition between the upper, stable part of the shield and its lower part that decoupled and formed the aureole deposits. This transition may reflect a change in the bulk shear strength of the shield, caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano. Other Martian volcanoes exhibit virtually no evidence of similar large-scale gravity spreading and basal scarps. Perhaps such evidence, if it existed, has been buried by lava flows, or perhaps the smaller size of other volcanoes did not permit the development of these features. ?? 1985.

Mobility of Yield-Stress Fluids on Lubricant-Impregnated Surface

NASA Astrophysics Data System (ADS)

Rapoport, Leonid; Solomon, Brian; Varanasi, Kripa; Varanasi Research Group Team

2017-11-01

Assuring the flow of yield-stress fluids is an essential problem for various industries such as consumer products, health care, and energy. Elimination of wall-induced pinning forces can potentially save power and cleaning costs as well as enable the flow of yield-stress fluids in channels previously considered too narrow. Lubricant-Impregnated Surfaces (LIS) have been demonstrated to change the dynamic behavior of yield-stress fluids and enable them to move as bulk without shearing at all. However, despite the wide applicability of this technology and its general appeal, the fundamental principles governing the performance of yield stress fluids on LIS have not yet been fully explained. In this work, we explore the mobility of yield stress fluids on a wide range of LIS, and explain the connection between macroscale behavior and the microscale properties of the LIS. Specifically, we show a striking difference in mobility between an LIS that contains a lubricant which fully spreads on the rough micro-features of the surface, and an LIS that contains a lubricant which only imbibes these features but does spread over them

Nanodroplet impact onto solid platinum surface: Spreading and bouncing

NASA Astrophysics Data System (ADS)

Lussier, Daniel; Ventikos, Yiannis

2009-11-01

The impact of droplets onto solid surfaces is found in a huge variety of natural and technological applications, from rain drops splashing on the pavement, to material manufacturing by molten droplet deposition. Taking inspiration from existing microfluidic technologies (i.e. lab-on-chip), there is increasing interest in the use of nanodroplets (D < 100 nm) for a number of applications such as drug delivery and semiconductor device manufacturing. However, as the size of the droplet is reduced into the nanoscale, the direct use of previously obtained macroscopic results is not guaranteed. At the nanoscale, important effects due to the molecular nature of the fluid, thermal fluctuations and reduced dimensionality can play a critical role in determining system dynamics. In this paper we present the results of large-scale, fully atomistic, three-dimensional molecular dynamics (MD) simulation of an argon nanodroplet (D = 18 nm, 54 000 atoms) impact onto a solid platinum surface, using the LAMMPS software package. The fluid argon is modeled using the well-known Lennard-Jones (LJ) potential, while the embedded-atom model (EAM) potential is used for the solid platinum. By varying both the impact velocities (10-1000 m/s) and the wettability of the solid surface a wide range of impact behaviors is observed, from smooth spreading, to bouncing recoil, pointing towards a wide array of potential applications.

Jet Penetration into a Scaled Microfabricated Stirling Cycle Regenerator

NASA Technical Reports Server (NTRS)

Sun, Liyong; Simon, Terrence W.; Mantell, Susan; Ibrahim, Mournir; Gedeon, David; Tew, Roy

2008-01-01

The cooler and heater adjacent to the regenerator of a Stirling cycle engine have tubes or channels which form jets that pass into the regenerator while diffusing within the matrix. An inactive part of the matrix, beyond the cores of these jets, does not participate fully in the heat transfer between the flow of working fluid and the regenerator matrix material, weakening the regenerator s ability to exchange heat with the working fluid. The objective of the present program is to document this effect on the performance of the regenerator and to develop a model for generalizing the results. However, the small scales of actual Stirling regenerator matrices (on the order of tens of microns) make direct measurements of this effect very difficult. As a result, jet spreading within a regenerator matrix has not been characterized well and is poorly understood. Also, modeling is lacking experimental verification. To address this, a large-scale mockup of thirty times actual scale was constructed and operated under conditions that are dynamically similar to the engine operation. Jet penetration with round jets and slot jets into the microfabricated regenerator geometry are then measured by conventional means. The results are compared with those from a study of spreading of round jets within woven screen regenerator for further documentation of the comparative performance of the microfabricated regenerator geometry.

Temperature Field During Flame Spread over Alcohol Pools: Measurements and Modelling

NASA Technical Reports Server (NTRS)

Miller, Fletcher J.; Ross, Howard D.; Schiller, David N.

1994-01-01

A principal difference between flame spread over solid fuels and over liquid fuels is, in the latter case, the presence of liquid-phase convection ahead of the leading edge of the flame. The details of the fluid dynamics and heat transfer mechanisms in both the pulsating and uniform flame spread regimes were heavily debated, without resolution, in the 1960s and 1970s; recently, research on flame spread over pools was reinvigorated by the advent of enhanced diagnostic techniques and computational power. Temperature fields in the liquid, which enable determination of the extent of preheating ahead of the flame, were determined previously by the use of thermocouples and repetitive tests, and suggested that the surface temperature does not decrease monotonically ahead of the pulsating flame front, but that there exists a surface temperature valley. Recent predictions support this suggestion. However, others' thermocouple measurements and the recent field measurements using Holographic Interferometry (HI) did not find a similar valley. In this work we examine the temperature field using Rainbow Schlieren Deflectometry (RSD), with a measurement threshold exceeding that of conventional interferometry by a factor of 20:1, for uniform and pulsating flame spread using propanol and butanol as fuels. This technique was not applied before to flame spread over liquid pools, except in some preliminary measurements reported earlier. Noting that HI is sensitive to the refractive index while RSD responds to refractive index gradients, and that these two techniques might therefore be difficult to compare, we utilized a numerical simulation, described below, to predict and compare both types of field for the uniform and pulsating spread regimes. The experimental data also allows a validation of the model at a level of detail greater than has been attempted before.

Tribology Experiment in Zero Gravity

NASA Technical Reports Server (NTRS)

Pan, C. H. T.; Gause, R. L.; Whitaker, A. F.; Finckenor, M. M.

2015-01-01

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates observation of such motions as controlled by interfacial and capillary forces. Two experimental configurations were used. One deals with the liquid on one solid surface, and the other with the liquid between a pair of closed spaced surfaces. Time sequence photographs of fluid motion on a solid surface yielded spreading rate data of several fluid-surface combinations. In general, a slow spreading process as governed by the tertiary junction can be distinguished from a more rapid process which is driven by surface tension controlled internal fluid pressure. Photographs were also taken through the transparent bushings of several experimental journal bearings. Morphology of incomplete fluid films and its fluctuation with time suggest the presence or absence of unsteady phenomena of the bearing-rotor system in various arrangements.

Impact of a complex fluid droplet on wettable and non wettable surfaces

NASA Astrophysics Data System (ADS)

Bolleddula, Daniel; Aliseda, Alberto

2008-11-01

The impact of liquid droplets is a phenomenon prevalent in many natural and industrial processes. Such events include rain drops, fuel injection, and ink-jet printing. To date, research in atomization and droplet impact has been focused on Newtonian fluids. In the coating of pharmaceutical tablets, the coating solutions contain polymers, surfactants, and large concentrations of insoluble solids in suspension which inherently exhibit non-Newtonian behavior. In this work, we will present ongoing droplet impact experiments using complex rheology fluids under a wide range of Weber and Ohnesorge numbers. Both hydrophilic and hydrophobic surfaces are been studied, and the effect of surface roughness has also been considered. We will describe the limits of bouncing, spreading, and splashing for these complex fluids. We will also discuss quantitative information such as spreading rates and contact angle measurements on wettable and non-wettable surfaces obtained from high speed images.

Sulphide mineralization and wall-rock alteration in ophiolites and modern oceanic spreading centres

USGS Publications Warehouse

Koski, R.A.

1983-01-01

Massive and stockwork Fe-Cu-Zn (Cyprus type) sulphide deposits in the upper parts of ophiolite complexes represent hydrothermal mineralization at ancient accretionary plate boundaries. These deposits are probable metallogenic analogues of the polymetallic sulphide deposits recently discovered along modern oceanic spreading centres. Genetic models for these deposits suggest that mineralization results from large-scale circulation of sea-water through basaltic basement along the tectonically active axis of spreading, a zone of high heat flow. The high geothermal gradient above 1 to 2 km deep magma chambers emplaced below the ridge axis drives the convective circulation cell. Cold oxidizing sea-water penetrating the crust on the ridge flanks becomes heated and evolves into a highly reduced somewhat acidic hydrothermal solvent during interaction with basaltic wall-rock. Depending on the temperature and water/rock ratio, this fluid is capable of leaching and transporting iron, manganese, and base metals; dissolved sea-water sulphate is reduced to sulphide. At the ridge axis, the buoyant hydrothermal fluid rises through permeable wall-rocks, and fluid flow may be focussed along deep-seated fractures related to extensional tectonic processes. Metal sulphides are precipitated along channelways as the ascending fluid undergoes adiabatic expansion and then further cooling during mixing with ambient sub-sea-floor water. Vigorous fluid flow results in venting of reduced fluid at the sea-floor/sea-water interface and deposition of massive sulphide. A comparison of sulphide mineralization and wall-rock alteration in ancient and modern spreading centre environments supports this genetic concept. Massive sulphide deposits in ophiolites generally occur in clusters of closely spaced (< 1-5 km) deposits. Individual deposits are a composite of syngenetic massive sulphide and underlying epigenetic stockwork-vein mineralization. The massive sulphide occurs as concordant tabular, lenticular, or saucer-shaped bodies in pillow lavas and pillow-lava breccia; massive lava flows, hyalcoclastite, tuff, and bedded radolarian chert are less commonly associated rock types. These massive sulphide zones are as much as 700 m long, 200 m wide, and 50 m thick. The pipe-, funnel-, or keel-shaped stockwork zone may extend to a dehpth of 1 km in the sheeted-dike complex. Several deposits in Cyprus are confined to grabens or the hanging wall of premineralization normal faults. Polymetallic massive sulphide deposits and active hydrothermal vents at medium- to fast-rate spreading centres (the East Pacific Rise at lat. 21??N, the Galapagos Spreading Centre at long. 86??W, the Juan de Fuca Ridge at lat. 45??N., and the Southern Trough of Guaymas Basin, Gulf of California) have interdeposit spacings on a scale of tens or hundreds of metres, and are spatially associated with structural ridges or grabens within the narrow (< 5 km) axial valleys of the rift zones. Although the most common substrate for massive sulphide accumulations is stacked sequences of pillow basalt and sheet flows, the sea-floor underlying numerous deposits in Guaymas Basin consists of diatomaceous ooze and terrigenous clastic sediment that is intruded by diabase sills. Mound-like massive sulphide deposits, as much as 30 m wide and 5m high, occur over actively discharging vents on the East Pacific Rise, and many of these deposits serve as the base for narrow chimneys and spires of equal or greater height. Sulphides on the Juan de Fuca Ridge appear to form more widespread blanket deposits in the shallow axial-valley depression. The largest deposit found to date, along the axial ridge of the Galapagos Spreading Centre, has a tabular form and a length of 1000 m, a width of 200 m, and a height of 30 m. The sulphide assemblage in both massive and vein mineralization in Cyprus type deposits is characteristically simple: abundant pyrite or, less commonly, pyrrhotite accompanied by minor marcasite, chalcopyrite

A new statistical dispersion model for tracer tests and contaminant spread in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ates, H.; Kasap, E.

Dispersion of solutes moving in permeable media is an essential control to describe fluid flow in permeable media. Dispersion can be thought of as a spreading of a solute caused by the presence of microscopic inhomogeneities. An accurate model for dispersion is needed for accurate estimation of oil recovery efficiencies and clean up costs of subsurface contaminants. Current approaches utilizing the fickian assumption fall short in describing the real physics of spreading during a solute transport process. Numerous field investigations have shown that dispersivities measured in the field are much larger than those measured in the lab for the samemore » type of porous material. Moreover, field measured dispersivities have been shown to be scale dependent, that is, a tracer test conducted over a longer travel path will yield a larger dispersivity value than a tracer test conducted in the same geologic formation over a shorter travel path. Numerous approaches to address this problem have been developed yet none attempted to go beyond the Fickian dispersion assumption. In this study, a convective dispersivity is introduced. New model assumes that dispersion is dimensionless and mainly determined by pore size distribution. The new model results in a spread that increases linearly with time contrary to conventional model, which predicts a mixing zone length that increases with square root of time. Therefore, new model explains the field test results that indicate increasing dispersivity with distance. The model validations are in perfect agreement with experimental results, which include; Ganapathy et al.`s slug experiment on Antolini sandstone, Handy`s radioactive tracer experiment on Alhambra sandstone, and CT experiment conducted at BDM-OK/NIPER facilities on Tallant sandstone.« less

Water reservoir maintained by cell growth fuels the spreading of a bacterial swarm

PubMed Central

Wu, Yilin; Berg, Howard C.

2012-01-01

Flagellated bacteria can swim across moist surfaces within a thin layer of fluid, a means for surface colonization known as swarming. This fluid spreads with the swarm, but how it does so is unclear. We used micron-sized air bubbles to study the motion of this fluid within swarms of Escherichia coli. The bubbles moved diffusively, with drift. Bubbles starting at the swarm edge drifted inward for the first 5 s and then moved outward. Bubbles starting 30 μm from the swarm edge moved inward for the first 20 s, wandered around in place for the next 40 s, and then moved outward. Bubbles starting at 200 or 300 μm from the edge moved outward or wandered around in place, respectively. So the general trend was inward near the outer edge of the swarm and outward farther inside, with flows converging on a region about 100 μm from the swarm edge. We measured cellular metabolic activities with cells expressing a short-lived GFP and cell densities with cells labeled with a membrane fluorescent dye. The fluorescence plots were similar, with peaks about 80 μm from the swarm edge and slopes that mimicked the particle drift rates. These plots suggest that net fluid flow is driven by cell growth. Fluid depth is largest in the multilayered region between approximately 30 and 200 μm from the swarm edge, where fluid agitation is more vigorous. This water reservoir travels with the swarm, fueling its spreading. Intercellular communication is not required; cells need only grow. PMID:22371567

Water reservoir maintained by cell growth fuels the spreading of a bacterial swarm.

PubMed

Wu, Yilin; Berg, Howard C

2012-03-13

Flagellated bacteria can swim across moist surfaces within a thin layer of fluid, a means for surface colonization known as swarming. This fluid spreads with the swarm, but how it does so is unclear. We used micron-sized air bubbles to study the motion of this fluid within swarms of Escherichia coli. The bubbles moved diffusively, with drift. Bubbles starting at the swarm edge drifted inward for the first 5 s and then moved outward. Bubbles starting 30 μm from the swarm edge moved inward for the first 20 s, wandered around in place for the next 40 s, and then moved outward. Bubbles starting at 200 or 300 μm from the edge moved outward or wandered around in place, respectively. So the general trend was inward near the outer edge of the swarm and outward farther inside, with flows converging on a region about 100 μm from the swarm edge. We measured cellular metabolic activities with cells expressing a short-lived GFP and cell densities with cells labeled with a membrane fluorescent dye. The fluorescence plots were similar, with peaks about 80 μm from the swarm edge and slopes that mimicked the particle drift rates. These plots suggest that net fluid flow is driven by cell growth. Fluid depth is largest in the multilayered region between approximately 30 and 200 μm from the swarm edge, where fluid agitation is more vigorous. This water reservoir travels with the swarm, fueling its spreading. Intercellular communication is not required; cells need only grow.

Examination of Wildland Fire Spread at Small Scales Using Direct Numerical Simulations and High-Speed Laser Diagnostics

NASA Astrophysics Data System (ADS)

Wimer, N. T.; Mackoweicki, A. S.; Poludnenko, A. Y.; Hoffman, C.; Daily, J. W.; Rieker, G. B.; Hamlington, P.

2017-12-01

Results are presented from a joint computational and experimental research effort focused on understanding and characterizing wildland fire spread at small scales (roughly 1m-1mm) using direct numerical simulations (DNS) with chemical kinetics mechanisms that have been calibrated using data from high-speed laser diagnostics. The simulations are intended to directly resolve, with high physical accuracy, all small-scale fluid dynamic and chemical processes relevant to wildland fire spread. The high fidelity of the simulations is enabled by the calibration and validation of DNS sub-models using data from high-speed laser diagnostics. These diagnostics have the capability to measure temperature and chemical species concentrations, and are used here to characterize evaporation and pyrolysis processes in wildland fuels subjected to an external radiation source. The chemical kinetics code CHEMKIN-PRO is used to study and reduce complex reaction mechanisms for water removal, pyrolysis, and gas phase combustion during solid biomass burning. Simulations are then presented for a gaseous pool fire coupled with the resulting multi-step chemical reaction mechanisms, and the results are connected to the fundamental structure and spread of wildland fires. It is anticipated that the combined computational and experimental approach of this research effort will provide unprecedented access to information about chemical species, temperature, and turbulence during the entire pyrolysis, evaporation, ignition, and combustion process, thereby permitting more complete understanding of the physics that must be represented by coarse-scale numerical models of wildland fire spread.

Subduction and dehydration of slow-spread oceanic lithosphere

NASA Astrophysics Data System (ADS)

Paulatto, M.; Laigle, M.; Galve, A.; Charvis, P.

2016-12-01

Water transported by subducting slabs affects the dynamics of subduction zones and is a major gateway in the global geochemical water cycle. During subduction much of the water stored in the slab is released via pore fluid escape and through metamorphic reactions that depend on the thermal regime. The most notable are eclogitization of hydrated basalt and gabbro and breakdown of serpentinite. Most constraints to date have been obtained at Pacific subduction zones, and have contributed to a model of slab dehydration applicable to normal fast-spread oceanic lithosphere with a mafic crust. Slow-spread crust however, is heterogeneous in thickness and composition and has a different water distribution than fast-spread crust. We use P-wave traveltimes from several active source seismic experiments and P- and S-wave traveltimes from shallow and intermediate depth (< 160 km) local earthquakes recorded on a vast amphibious array of OBSs and land seismometers to recover the 3D Vp and Vp/Vs structure of the central Lesser Antilles subduction zone from the surface to 160 km depth. This slab was formed by slow accretion at the Mid-Atlantic ridge and represents the global slow accretion rate end-member. We image the dipping low-Vp layer at the top of the slab corresponding to the hydrated slab crust penetrating to about 100 km depth. High Vp/Vs ratio on the slab top and in the forearc crust is interpreted as evidence of elevated fluid content either as free fluids or as bound water in hydrated minerals. A local minimum in Vp is observed on the slab top at 50 km depth, and forms an elongated trench-parallel anomaly. This anomaly is interrupted at the projection of the Marathon fracture zone. We suggest that this is the result of lateral variations in slab crust composition from normal mafic oceanic crust to tectonized oceanic crust consisting to a large extent of serpentinized peridotite near the fracture zone. Slab regions with normal mafic oceanic crust likely undergo eclogitization, resulting in voluminous water release over a narrow depth range. Serpentinized ultramafic crust, in contrast, may release water at a more constant rate. We infer that subduction of slow-spread lithosphere may result in heterogeneous water transport and release at subduction zones with implications for seismicity, magma generation and the geochemical budget.

Single-bubble dynamics in pool boiling of one-component fluids.

PubMed

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013)]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Collisional Evolution of the Enceladus Neutral Cloud

NASA Technical Reports Server (NTRS)

Cassidy, T. A.; Johnson, R. E.; Hendrix, A. R.

2011-01-01

Water vapor ejected from Saturn's small moon Enceladus easily escapes its meager gravity to form a Saturn-encircling cloud with a low collision rate. Observations show that the cloud is quite broad in the radial direction, and we show here that collisions, though quite rare, may be largely responsible for this radial spreading. We modeled this cloud using the Direct Simulation Monte Carlo method, as fluid methods would be inappropriate for such a tenuous gas.

Influences of coupled fire-atmosphere interaction on wildfire behavior

NASA Astrophysics Data System (ADS)

Linn, R.; Winterkamp, J.; Jonko, A. K.; Runde, I.; Canfield, J.; Parsons, R.; Sieg, C.

2017-12-01

Two-way interactions between fire and the environment affect fire behavior at scales ranging from buoyancy-induced mixing and turbulence to fire-scale circulations that retard or increase fire spread. Advances in computing have created new opportunities for the exploration of coupled fire-atmosphere behavior using numerical models that represent interactions between the dominant processes driving wildfire behavior, including convective and radiative heat transfer, aerodynamic drag and buoyant response of the atmosphere to heat released by the fire. Such models are not practical for operational, faster-than-real-time fire prediction due to their computational and data requirements. However, they are valuable tools for exploring influences of fire-atmosphere feedbacks on fire behavior as they explicitly simulate atmospheric motions surrounding fires from meter to kilometer scales. We use the coupled fire-atmosphere model FIRETEC to gain new insights into aspects of fire behavior that have been observed in the field and laboratory, to carry out sensitivity analysis that is impractical through observations and to pose new hypotheses that can be tested experimentally. Specifically, we use FIRETEC to study the following multi-scale coupled fire-atmosphere interactions: 1) 3D fire-atmosphere interaction that dictates multi-scale fire line dynamics; 2) influence of vegetation heterogeneity and variability in wind fields on predictability of fire spread; 3) fundamental impacts of topography on fire spread. These numerical studies support new conceptual models for the dominant roles of multi-scale fluid dynamics in determining fire spread, including the roles of crosswind fire line-intensity variations on heat transfer to unburned fuels and the role of fire line depth expansion in upslope acceleration of fires.

Droplet spreading and capillary imbibition in a porous medium: A coupled IB-VOF method based numerical study

NASA Astrophysics Data System (ADS)

Das, Saurish; Patel, H. V.; Milacic, E.; Deen, N. G.; Kuipers, J. A. M.

2018-01-01

We investigate the dynamics of a liquid droplet in contact with a surface of a porous structure by means of the pore-scale level, fully resolved numerical simulations. The geometrical details of the solid porous matrix are resolved by a sharp interface immersed boundary method on a Cartesian computational grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid method. The numerical simulations are performed considering a model porous structure that is approximated by a 3D cubical scaffold with cylindrical struts. The effect of the porosity and the equilibrium contact angle (between the gas-liquid interface and the solid struts) on the spreading behavior, liquid imbibition, and apparent contact angle (between the gas-liquid interface and the porous base) are studied. We also perform several simulations for droplet spreading on a flat surface as a reference case. Gas-liquid systems of the Laplace number, La = 45 and La = 144 × 103 are considered neglecting the effect of gravity. We report the time exponent (n) and pre-factor (C) of the power law describing the evolution of the spreading diameter (S = Ctn) for different equilibrium contact angles and porosity. Our simulations reveal that the apparent or macroscopic contact angle varies linearly with the equilibrium contact angle and increases with porosity. Not necessarily for all the wetting porous structures, a continuous capillary drainage occurs, and we find that the rate of the capillary drainage very much depends on the fluid inertia. At La = 144 × 103, numerically we capture the capillary wave induced pinch-off and daughter droplet ejection. We observe that on the porous structure the pinch-off is weak compared to that on a flat plate.

Dispersion effects in the miscible displacement of two fluids in a duct of large aspect ratio

NASA Astrophysics Data System (ADS)

Zhang, J.; Frigaard, I. A.

We study miscible displacements in long ducts in the dispersive limit of small \\varepsilon Pe, where \\varepsilon ≪ 1 is the inverse aspect ratio and Pe the Péclet number. We consider the class of generalized Newtonian fluids, with specified closure laws for the fluid properties of the concentration-dependent mixture. Regardless of viscosity ratio and the constitutive laws of the pure fluids, for sufficiently small \\varepsilon Pe these displacements are characterized by rapid cross-stream diffusion and slow streamwise dispersion, i.e. the concentration appears to be near-uniform across the duct and spreads slowly as it translates. Using the multiple-scales method we derive the leading-order asymptotic approximation to the average fluid concentration bar{c}_0. We show that bar{c}_0 evolves on the slow timescale t ˜ (\\varepsilon Pe)^{-1}, and satisfies a nonlinear diffusion equation in a frame of reference moving with the mean speed of the flow. In the case that the two fluids have identical rheologies and the concentration represents a passive tracer, the diffusion equation is linear. For Newtonian fluids we recover the classical results of Taylor (l953), Aris (1956), and for power-law fluids those of Vartuli et al. (1995). In the case that the fluids differ and/or that mixing is non-passive, bar{c}_0 satisfies a nonlinear diffusion equation in the moving frame of reference. Given a specific mixing/closure law for the rheological properties, we are able to compute the dispersive diffusivity D_T(bar{c}_0) and predict spreading along the channel. We show that D_T(bar{c}_0) can vary significantly with choice of mixing law and discuss why. This also opens the door to possibilities of controlling streamwise spreading by the rheological design of reactive mixtures, i.e. including chemical additives such that the rheology of the mixture behaves very differently to the rheology of either pure fluid. Computed examples illustrate the potential effects that might be achieved.

Characterization and experimental validation of a squeeze film damper with MR fluid in a rotor-bearing system

NASA Astrophysics Data System (ADS)

Dominguez-Nuñez, L. A.; Silva-Navarro, G.

2014-04-01

The general study and applications of Magneto-Rhelogical (MR) dampers have been spread in the lasts years but only some studies have been focusing on the vibration control problems on rotor-bearings systems. Squeeze-Film Dampers (SFD) are now commonly used to passively control the vibration response on rotor-bearing systems because they can provide flexibility, damping and extend the so-called stability thresholds in rotating machinery. More recently, SFD are combined with MR or Electro-Rheological (ER) fluids to introduce a semiactive control mechanism to modify the rotordynamic coefficients and deal with the robust performance of the overall system response for higher operating speeds. There are, however, some theoretical and technological problems that complicate their extensive use, like the relationship between the centering spring flexibility and the rheological behavior of the smart fluid to produce the SFD forces. In this work it is considered a SFD with MR fluid and a set of circular section beams in a squirrel cage arrangement in combination with latex seals as centering springs. The mathematical model analysis includes the controllable viscoelastic properties associated to the MR fluid. The characterization of the SFD is made by the determination of some coefficients associated with a modified Choi-Lee-Park polynomial model. During the analysis is considered a rotor-bearing system modeled using finite element methods. The SFD with MR fluid is connected to an experimental platform to validate and experimentally evaluate the overall system. Finally, to improve the open-loop system performance, a methodology for the use of different control schemes is proposed.

The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges

NASA Astrophysics Data System (ADS)

Knight, Robert D.; Roberts, Stephen; Webber, Alexander P.

2018-01-01

Seafloor massive sulphide (SMS) deposits are variably enriched in precious metals including gold. However, the processes invoked to explain the formation of auriferous deposits do not typically apply to mid-ocean ridge settings. Here, we show a statistically significant, negative correlation between the average gold concentration of SMS deposits with spreading rate, at non-sedimented mid-ocean ridges. Deposits located at slow spreading ridges (20-40 mm/a) have average gold concentrations of between 850 and 1600 ppb; however, with increasing spreading rate (up to 140 mm/a), gold concentrations gradually decrease to between 50 and 150 ppb. This correlation of gold content with spreading rate may be controlled by the degree and duration of fluid-rock interaction, which is a function of the heat flux, crustal structure (faulting) and the permeability of the source rocks. Deposits at ultraslow ridges, including ultramafic-hosted deposits, are particularly enriched in gold. This is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals, combined with relatively high gold concentrations in peridotite compared with mid-ocean ridge basalt. Variations in fluid chemistry, such as reducing conditions and the potential for increased sulphur availability at ultramafic-hosted sites, may also contribute to the high concentrations observed. Beehive chimneys, which offer more favourable conditions for gold precipitation, may be more prevalent at ultramafic-hosted sites due to diffuse low-velocity venting compared with more focussed venting at basalt-hosted sites.

Time-dependent changes in magmatic and hydrothermal activity at the Costa Rica Rift recorded by variations in oceanic crustal structure

NASA Astrophysics Data System (ADS)

Wilson, D. J.; Peirce, C.; Hobbs, R. W.; Gregory, E. P. M.; Zhang, L.

2016-12-01

Geophysical studies of crustal structure at a diverse range of ridges have provided evidence that the balance between spreading rate and magma supply determines whether spreading predominantly occurs by magmatic accretion of new oceanic crust or through tectonic stretching of the whole lithosphere. Asymmetric spreading, patterns of on- and off-axis volcanism, the evolution of oceanic core complexes and the distribution of hydrothermal systems all indicate that the process of spreading is not constant over geologically short timescales. The structure of the resulting crust reflects this complexity in origin. Studies along flow-lines across ridges spreading at intermediate rates suggest variations in topographic style and crustal structure have periodically occurred, controlled by the interplay between magmatic accretion and tectonic stretching, and coupled to the degree of hydrothermal activity. Seismic reflection images and tomographic models derived from wide-angle seismic data have enabled a detailed examination of the oceanic crust that formed at the fast-to-intermediate-spreading (36 mm yr-1) Costa Rica Rift over the last 6 Ma, to look for any temporal variation in basement topography, upper crust (layer 2) P-wave velocity/density structure and crustal thickness. Coincident marine gravity and magnetic data not only allow us to test the validity of the final velocity-density model but also review variability in half-spreading rate, respectively. Collectively our analyses allow us to investigate the timescale and cyclicity of crustal structure variations and, having determined the spreading rate over time, consider how this may reflect changes in magma supply and/or hydrothermal activity at the Costa Rica Rift, using borehole 504B as the ground-truth. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

A numerical analysis of forces exerted by laminar flow on spreading cells in a parallel plate flow chamber assay.

PubMed

Olivier, L A; Truskey, G A

1993-10-01

Exposure of spreading anchorage-dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two-dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm(2), whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area. (c) 1993 John Wiley & Sons, Inc.

On the relationship between kinetic and fluid formalisms for convection in the inner magnetosphere

NASA Astrophysics Data System (ADS)

Song, Yang; Sazykin, Stanislav; Wolf, Richard A.

2008-08-01

In the inner magnetosphere, the plasma flows are mostly slow compared to thermal or Alfvén speeds, but the convection is far away from the ideal magnetohydrodynamic regime since the gradient/curvature drifts become significant. Both kinetic (Wolf, 1983) and two-fluid (Peymirat and Fontaine, 1994; Heinemann, 1999) formalisms have been used to describe plasma dynamics, but it is not fully understood how they relate to each other. We explore the relations among kinetic, fluid, and recently developed "average" (Liu, 2006) models in an attempt to find the simplest yet realistic way to describe the convection. First, we prove analytically that the model of (Liu, 2006), when closed with the assumption of a Maxwellian distribution, is equivalent to the fluid model of (Heinemann, 1999). Second, we analyze the transport of both one-dimensional and two-dimensional Gaussian-shaped blob of hot plasma. For the kinetic case, it is known that the time evolution of such a blob is gradual spreading in time. For the fluid case, Heinemann and Wolf (2001a, 2001b) showed that in a one-dimensional idealized case, the blob separates into two drifting at different speeds. We present a fully nonlinear solution of this case, confirming this behavior but demonstrating what appears to be a shocklike steepening of the faster drifting secondary blob. A new, more realistic two-dimensional example using the dipole geometry with a uniform electric field confirms the one-dimensional solutions. Implications for the numerical simulations of magnetospheric dynamics are discussed.

Recombinant Canine Distemper Virus Strain Snyder Hill Expressing Green or Red Fluorescent Proteins Causes Meningoencephalitis in the Ferret

PubMed Central

Ludlow, M.; Nguyen, D. T.; Silin, D.; Lyubomska, O.; de Vries, R. D.; von Messling, V.; McQuaid, S.; De Swart, R. L.

2012-01-01

The propensity of canine distemper virus (CDV) to spread to the central nervous system is one of the primary features of distemper. Therefore, we developed a reverse genetics system based on the neurovirulent Snyder Hill (SH) strain of CDV (CDVSH) and show that this virus rapidly circumvents the blood-brain and blood-cerebrospinal fluid (CSF) barriers to spread into the subarachnoid space to induce dramatic viral meningoencephalitis. The use of recombinant CDVSH (rCDVSH) expressing enhanced green fluorescent protein (EGFP) or red fluorescent protein (dTomato) facilitated the sensitive pathological assessment of routes of virus spread in vivo. Infection of ferrets with these viruses led to the full spectrum of clinical signs typically associated with distemper in dogs during a rapid, fatal disease course of approximately 2 weeks. Comparison with the ferret-adapted CDV5804P and the prototypic wild-type CDVR252 showed that hematogenous infection of the choroid plexus is not a significant route of virus spread into the CSF. Instead, viral spread into the subarachnoid space in rCDVSH-infected animals was triggered by infection of vascular endothelial cells and the hematogenous spread of virus-infected leukocytes from meningeal blood vessels into the subarachnoid space. This resulted in widespread infection of cells of the pia and arachnoid mater of the leptomeninges over large areas of the cerebral hemispheres. The ability to sensitively assess the in vivo spread of a neurovirulent strain of CDV provides a novel model system to study the mechanisms of virus spread into the CSF and the pathogenesis of acute viral meningitis. PMID:22553334

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simmons, Stuart F.; Spycher, Nicolas; Sonnenthal, Eric

This report summarizes the results of Phase I work for a go/no go decision on Phase II funding. In the first objective, we assessed the extent to which fluid-mineral equilibria controlled deep water compositions in geothermal systems across the Great Basin. Six systems were evaluated: Beowawe; Desert Peak; Dixie Valley; Mammoth; Raft River; Roosevelt. These represent a geographic spread of geothermal resources, in different geological settings and with a wide range of fluid compositions. The results were used for calibration/reformulation of chemical geothermometers that reflect the reservoir temperatures in producing reservoirs. In the second objective, we developed a reactive -transportmore » model of the Desert Peak hydrothermal system to evaluate the processes that affect reservoir fluid geochemistry and its effect on solute geothermometry. This included testing geothermometry on “reacted” thermal water originating from different lithologies and from near-surface locations where the temperature is known from the simulation. The integrated multi-component geothermometer (GeoT, relying on computed mineral saturation indices) was tested against the model results and also on the systems studied in the first objective.« less

PREFACE: Dynamics of wetting Dynamics of wetting

NASA Astrophysics Data System (ADS)

Grest, Gary S.; Oshanin, Gleb; Webb, Edmund B., III

2009-11-01

Capillary phenomena associated with fluids wetting other condensed matter phases have drawn great scientific interest for hundreds of years; consider the recent bicentennial celebration of Thomas Young's paper on equilibrium contact angles, describing the geometric shape assumed near a three phase contact line in terms of the relevant surface energies of the constituent phases [1]. Indeed, nearly a century has passed since the seminal papers of Lucas and Washburn, describing dynamics of capillary imbibition [2, 3]. While it is generally appreciated that dynamics of fluid wetting processes are determined by the degree to which a system is out of capillary equilibrium, myriad complications exist that challenge the fundamental understanding of dynamic capillary phenomena. The topic has gathered much interest from recent Nobel laureate Pierre-Gilles de Gennes, who provided a seminal review of relevant dissipation mechanisms for fluid droplets spreading on solid surfaces [4] Although much about the dynamics of wetting has been revealed, much remains to be learned and intrinsic technological and fundamental interest in the topic drives continuing high levels of research activity. This is enabled partly by improved experimental capabilities for resolving wetting processes at increasingly finer temporal, spatial, and chemical resolution. Additionally, dynamic wetting research advances via higher fidelity computational modeling capabilities, which drive more highly refined theory development. The significance of this topic both fundamentally and technologically has resulted in a number of reviews of research activity in wetting dynamics. One recent example addresses the evaluation of existing wetting dynamics theories from an experimentalist's perspective [5]. A Current Opinion issue was recently dedicated to high temperature capillarity, including dynamics of high temperature spreading [6]. New educational tools have recently emerged for providing instruction in wetting dynamics and the broader field of fluid dynamics [7-9]. Such an active field requires an occasional collective examination of current research to highlight both recent successes and remaining challenges. Herein, we have collected a range of articles to illustrate the broad nature of research associated with understanding dynamics of moving condensed matter three phase contact lines. Despite the breadth of topics examined, certain unifying themes emerge. The role of the substrate surface is critical in determining kinetics of wetting; this is evidenced by the attention given to this in articles herein. McHale et al investigate the role of surface topography on wetting kinetics and how its effect can be incorporated in existing theories describing contact line dynamics. Moosavi et al examine surface topography effects via a mesoscopic hydrodynamics approach. The capillary driven motion of fluid through structures on a surface bears tremendous importance for microfluidics studies and the emerging field of nanofluidics. Blow et al examine this phenomena for liquid imbibition into a geometric array of structures on a solid surface, while Shen et al analyze the effects of surface temperature during boiling and non-boiling conditionson droplet impingement dynamics. Finally, Pesika et al discover a wonderful world of smart surfaces, like gecko adhesion pads. A number of papers utilize computational modeling to explore phenomena underlying wetting dynamics and to consider relevant mechanisms in terms of existing theory for contact line dynamics. Winter et al utilize Monte Carlo simulation techniques and thermodynamic integration methods to test classical theory describing heterogeneous nucleation at a wall near a wetting transition. Qian et al briefly review the Onsager principle of minimum energy dissipation underlying many descriptions of dissipative systems; they then provide a variational approach description of hydrodynamics of moving contact lines and demonstrate the validity of their continuum model via comparison with molecular dynamics simulations.Bertrand et al use large scale molecular dynamics simulations to examine fundamental questions about wetting dynamics and how they depend upon interactions between a liquid drop and solid substrate; in particular, atomic scale mechanisms directly associated with the molecular kinetic theory of wetting are observed and quantified. Sun et al explore, by molecular dynamics simulations, atomistic mechanisms of high temperature contact line advancement for a rapidly spreading liquid droplet. Starov et al discuss general aspects of surface forces and wetting phenomena, while Courbin et al present anoverview of diverse dynamical processes ranging from inertial spreading to viscous imbibition. Mukhopadhyay et al examine the effect of Marangoni and centrifugal forces on the wetting dynamics of thin liquid films and drops. Willis et al analyze an enhanced droplet spreading due to thermal fluctuations. How wetting and contact line dynamics depend upon the complexity of the structure in the liquid is interesting both academically and technologically; Delabre et al illustrate this with a study of wetting of liquid crystals and the role of molecular scale organization. In addition, Mechkov et al explore this realm by studying post-Tanner spreading for nematic droplets and, in general, post-Tanner spreading of liquid droplets governed by the contact line-tension effects. Liang et al focus on spreading dynamics of power-law fluid droplets, while Wei et al discuss dynamics of wetting in viscous Newtonian and non-Newtonian fluids. Yin et al discuss an important issue of reactive wetting in metal-metal systems. We hope that the articles gathered here will permit readers to understand the wide range of condensed matter systems impacted by wetting kinetics and the many complicating factors that emerge in describing contact line dynamics for realistic materials. We wish to thank all the contributing authors for their effort and support of our endeavour. References [1] Young T 1805 Phil. Trans. R. Soc. A 95 65 [2] Lucas R 1918 Kolloidn. Zh. 23 15 [3] Washburn E W 1921 Phys. Rev. 17 273 [4] de Gennes P G 1985 Rev. Mod. Phys. 57 827 [5] Ralston J, Popescu M and Sedev R 2008 Annu. Rev. Mater. Res.38 23 [6] High Temperature Capillarity Focus Issue 2005 Current Opinion in Solid State and Materials Science 9 149-254 [7] Starov V M, Velarde M G and Radke C J 2007 Wetting and Spreading Dynamics (Boca Raton, FL: CRC Press) [8] Golub J 2008 Phys. Today 61 8 [9] Homsby G M (ed) 2008 Multimedia Fluid Mechanics 2nd edn (New York: Cambridge University Press) (Also see www.efluids.com)

Biomechanics of Tetrahymena escaping from dead ends

NASA Astrophysics Data System (ADS)

Ishikawa, Takuji; Kikuchi, Kenji

2017-11-01

Behaviors of swimming microorganisms in complex environments are important in understanding cells' distribution in nature and in industries. Although cell's swimming and spreading in an infinite fluid has been intensively investigated, that in a narrow region bounded by walls is still unclear. Thus, in this study, we used Tetrahymena thermophila as a model microorganism, and experimentally investigated its behavior between flat plates with an angle. The results showed that the cells tended to escape from the narrow region, and the swimming velocity and the radius of curvature of the trajectories decreased as they swam narrower region. We then developed a computational model of swimming Tetrahymena. The results showed that the escaping behavior could be well explained by fluid mechanics. The obtained knowledge is useful in understanding cells' behaviors in complex environments, such as in porous media and in a granular matter. This research was supported by JSPS KAKENHI Grants, numbers 25000008 and 17H00853.

A Two-length Scale Turbulence Model for Single-phase Multi-fluid Mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarzkopf, J. D.; Livescu, D.; Baltzer, J. R.

2015-09-08

A two-length scale, second moment turbulence model (Reynolds averaged Navier-Stokes, RANS) is proposed to capture a wide variety of single-phase flows, spanning from incompressible flows with single fluids and mixtures of different density fluids (variable density flows) to flows over shock waves. The two-length scale model was developed to address an inconsistency present in the single-length scale models, e.g. the inability to match both variable density homogeneous Rayleigh-Taylor turbulence and Rayleigh-Taylor induced turbulence, as well as the inability to match both homogeneous shear and free shear flows. The two-length scale model focuses on separating the decay and transport length scales,more » as the two physical processes are generally different in inhomogeneous turbulence. This allows reasonable comparisons with statistics and spreading rates over such a wide range of turbulent flows using a common set of model coefficients. The specific canonical flows considered for calibrating the model include homogeneous shear, single-phase incompressible shear driven turbulence, variable density homogeneous Rayleigh-Taylor turbulence, Rayleigh-Taylor induced turbulence, and shocked isotropic turbulence. The second moment model shows to compare reasonably well with direct numerical simulations (DNS), experiments, and theory in most cases. The model was then applied to variable density shear layer and shock tube data and shows to be in reasonable agreement with DNS and experiments. Additionally, the importance of using DNS to calibrate and assess RANS type turbulence models is highlighted.« less

Computational And Experimental Studies Of Three-Dimensional Flame Spread Over Liquid Fuel Pools

NASA Technical Reports Server (NTRS)

Ross, Howard D. (Technical Monitor); Cai, Jinsheng; Liu, Feng; Sirignano, William A.; Miller, Fletcher J.

2003-01-01

Schiller, Ross, and Sirignano (1996) studied ignition and flame spread above liquid fuels initially below the flashpoint temperature by using a two-dimensional computational fluid dynamics code that solves the coupled equations of both the gas and the liquid phases. Pulsating flame spread was attributed to the establishment of a gas-phase recirculation cell that forms just ahead of the flame leading edge because of the opposing effect of buoyancy-driven flow in the gas phase and the thermocapillary-driven flow in the liquid phase. Schiller and Sirignano (1996) extended the same study to include flame spread with forced opposed flow in the gas phase. A transitional flow velocity was found above which an originally uniform spreading flame pulsates. The same type of gas-phase recirculation cell caused by the combination of forced opposed flow, buoyancy-driven flow, and thermocapillary-driven concurrent flow was responsible for the pulsating flame spread. Ross and Miller (1998) and Miller and Ross (1998) performed experimental work that corroborates the computational findings of Schiller, Ross, and Sirignano (1996) and Schiller and Sirignano (1996). Cai, Liu, and Sirignano (2002) developed a more comprehensive three-dimensional model and computer code for the flame spread problem. Many improvements in modeling and numerical algorithms were incorporated in the three-dimensional model. Pools of finite width and length were studied in air channels of prescribed height and width. Significant three-dimensional effects around and along the pool edge were observed. The same three-dimensional code is used to study the detailed effects of pool depth, pool width, opposed air flow velocity, and different levels of air oxygen concentration (Cai, Liu, and Sirignano, 2003). Significant three-dimensional effects showing an unsteady wavy flame front for cases of wide pool width are found for the first time in computation, after being noted previously by experimental observers (Ross and Miller, 1999). Regions of uniform and pulsating flame spread are mapped for the flow conditions of pool depth, opposed flow velocity, initial pool temperature, and air oxygen concentration under both normal and microgravity conditions. Details can be found in Cai et al. (2002, 2003). Experimental results recently performed at NASA Glenn of flame spread across a wide, shallow pool as a function of liquid temperature are also presented here.

Fingering, Fracturing and Dissolution in Granular Media

NASA Astrophysics Data System (ADS)

Juanes, R.; Cueto-Felgueroso, L.; Trojer, M.; Zhao, B.; Fu, X.

2014-12-01

The displacement of one fluid by another in a porous medium give rise to a rich variety of hydrodynamic instabilities. Beyond their scientific value as fascinating models of pattern formation, unstable porous-media flows are essential to understanding many natural and man-made processes, including water infiltration in the vadose zone, carbon dioxide injection and storage in deep saline aquifers, and hydrocarbon recovery. Here, we review the pattern-selection mechanisms of a wide spectrum of porous-media flows that develop hydrodynamic instabilities, discuss their origin and the mathematical models that have been used to describe them. We point out many challenges that remain to be resolved in the context of multiphase flows, and suggest modeling approaches that may offer new quantitative understanding. In particular, I will present experimental, theoretical and computational results for: (1) fluid spreading under partial wetting; (2) the impact of wettability on viscously unstable multiphase flow in porous media; (3) capillary fracturing in granular media; and (4) rock dissolution during convective mixing in porous media.

Falling drops skating on a film of air

NASA Astrophysics Data System (ADS)

Rubinstein, Shmuel

2012-02-01

When a raindrop hits a window, the surface immediately becomes wet as the water spreads. Indeed, this common observation of a drop impacting a surface is ubiquitous in our everyday experience. I will show that the impact of a drop on a surface is a much richer, more complex phenomenon than our simple experience may suggests: To completely wet the surface the drop must first expel all the air beneath it; however, this does not happened instantaneously. Instead, a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the fluid spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate laterally outward at strikingly high velocities. Simultaneously, the wetting fluid spreads inward at a much slower velocity, trapping a bubble of air within the drop. However, these events occur at diminutive length scales and fleeting time scales; therefore, to visualize them we develop new imaging modalities that are sensitive to the behavior right at the surface and that have time resolution superior to even the very fastest cameras. These imaging techniques reveal that the ultimate wetting of the surface occurs through a completely new mechanism, the breakup of the thin film of air through a spinodal like dewetting process that breaks the cylindrical symmetry of the impact and drives an anomalously rapid spreading of a wetting front. These results are in accord with recent theoretical predictions and challenge the prevailing paradigm in which contact between the liquid and solid occurs immediately, and spreading is dominated by the dynamics of a single contact line.

Single-bubble dynamics in pool boiling of one-component fluids

NASA Astrophysics Data System (ADS)

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007), 10.1103/PhysRevE.75.036304], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013), 10.1016/j.ijheatmasstransfer.2012.10.080]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Controls on mid-ocean ridge segmentation and transform fault formation from laboratory experiments using fluids of complex rheology.

NASA Astrophysics Data System (ADS)

Sibrant, A.; Mittelstaedt, E. L.; Davaille, A.

2017-12-01

Mid-ocean ridges are tectonically segmented at scales of 10s to 100s of kilometers by several types of offsets including transform faults (TF), overlapping spreading centers (OSC), and slow-spreading non-transform offsets (NTO). Differences in segmentation along axis have been attributed to changes in numerous processes including magma supply from the upwelling mantle, viscous flow in the asthenosphere, ridge migration, and plate spreading direction. The wide variety of proposed mechanisms demonstrate that the origin of tectonic offsets and their relationship to segment-scale magmatic processes remain actively debated; each of the above processes, however, invoke combinations of tectonic and magmatic processes to explain changes in segmentation. To address the role of tectonic deformation and magmatic accretion on the development of ridge offsets, we present a series of analogue experiments using colloidal silica dispersions as an Earth analogue. Saline water solutions placed in contact with these fluids, cause formation of a skin through salt diffusion, whose rheology evolves from purely viscous to elastic and brittle with increasing salinity. Experiments are performed in a Plexiglas tank with two Plexiglas plates suspended above the base of the tank. The tank is filled with the colloidal fluid to just above the suspended plates, a thin layer of saline water is spread across the surface, and spreading initiated by moving the suspended Plexiglas plates apart at a fixed rate. Results show formation of OSCs, NTOs, and TFs. For parameters corresponding to the Earth, TF offsets are < 5 mm and form at all spreading velocities, corresponding to transform offsets of < 100 km on Earth. Measured TF offset size and ridge segment lengths exhibit a Poisson-type distribution with no apparent dependence on spreading rate. Observations of TF offset size on Earth show a similar distribution for TFs <100 km long and supports the hypothesis that TFform spontaneously through a mechanical instability of the axis. Here, we present an analysis of the magmatic and tectonic controls on axis instability leading to the formation of TFs, OSCs, and NTOs, and their implications for the evolution of mid-ocean ridges.

The electromagnetic interchange mode in a partially ionized collisional plasma. [spread F region

NASA Technical Reports Server (NTRS)

Hudson, M. K.; Kennel, C. F.

1974-01-01

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.

Capillary Flow in an Interior Corner

NASA Technical Reports Server (NTRS)

Weislogel, Mark Milton

1996-01-01

The design of fluids management processes in the low-gravity environment of space requires an accurate model and description of capillarity-controlled flow in containers of irregular geometry. Here we consider the capillary rise of a fluid along an interior corner of a container following a rapid reduction in gravity. The analytical portion of the work presents an asymptotic formulation in the limit of a slender fluid column, slight surface curvature along the corner, small inertia, and low gravity. New similarity solutions are found and a list of closed form expressions is provided for flow rate and column length. In particular, it is found that the flow is proportional to t(exp 1/2) for a constant height boundary condition, t(exp 2/5) for a spreading drop, and t(exp 3/5) for constant flow. In the experimental portion of the work, measurements from a 2.2s drop tower are reported. An extensive data set, collected over a previously unexplored range of flow parameters, includes estimates of repeatability and accuracy, the role of inertia and column slenderness, and the effects of corner angle, container geometry, and fluid properties. Comprehensive comparisons are made which illustrate the applicability of the analytic results to low-g fluid systems design.

Determining the Extent of Hydrothermal Interaction on the Southern Costa Rica Rift Ridge Flank During the Past 8 Ma from Joint Inversion of Geophysical Data

NASA Astrophysics Data System (ADS)

Wilson, D. J.; Moorkamp, M.; Hobbs, R. W.; Peirce, C.; Harris, R. N.; Morgan, J. V.

2017-12-01

Advective hydrothermal systems preferentially develop in zones of high porosity and permeability, driven by a local heat source. Associated chemical reactions lead to changes in the bulk physical properties, so variations in velocity and density, and the relationship connecting them, may provide a record of alteration by hydrothermal fluids. Oceanic crust accreted at intermediate rate ridges displays a range of characteristics between those typical for fast and slow spreading rates so changes in crustal porosity and permeability are sensitive to the interplay between tectonic stretching, magmatic supply and plate motions. Hence, changes in spreading style and sediment cover will influence the extent of the hydrothermal interaction that occurs and the mode of heat loss as evidenced by heat flow measurements. Using a variety of geophysical data we determine where hydrothermal circulation has been active in young oceanic crust that was accreted at an intermediate spreading rate. Results from traveltime tomography along a 300 km profile across the southern flank of the Costa Rica Rift reveal several variations in the P-wave velocity structure of the upper crust (layer 2). Following an initial increase in P-wave velocity near the ridge axis there is a section of the model 80 km in length that has lower P-wave velocity (up to 0.5 km s-1) compared to adjacent crust. This section has shallower bathymetry, by up to 500 m, than predicted by the subsidence curve and the top basement surface is rougher with a greater amount of faulting and larger throws. This zone is preceded by crust with significantly faster P-wave velocities (up to 1.0 km s-1) that was sampled by DSDP/ODP 504B. We characterise these changes in the shallow crustal structure by jointly inverting travel-time data and gravity data with deeper control from coincident magnetotelluric data. Using a cross-gradient approach allows us to search for models with a structural match, thus determining the relationship between P-wave velocity and density models from which we infer the likely hydrothermal regimes at the time of formation at the spreading ridge. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Effect of Spreading Time on Contact Angle of Nanofluid on the Surface of Stainless Steel AISI 316 and Zircalloy 4

NASA Astrophysics Data System (ADS)

Prajitno, D. H.; Trisnawan, V.; Syarif, D. G.

2017-05-01

The solid surface tension plays an important role in the heat and mass transfer system for heat exchanger equipment. In the nuclear power plant industry, the stainless steel AISI 316 and Zircalloy 4 have been used for long time as structure materials. The purpose of the experimental is to study solid state surface tension behavior by measure contact angle Nano fluid contain nano particle alumina on metal surface of stainless steel AISI 316 and Zircalloy 4 by sessile drop method. The experiment is to measure the static contact angle and drop nano fluid contains nano particle alumina on stainless steel 316 and zircalloy 4 with different spreading time from 1 to 30 minute. It was observed that stainless steel 316 and zircalloy 4 lose their hydrophobic properties with increasing elapsed time during drop of nano fluid on the surface of alloy. As a result the contact angle of nano fluid on surface of metal is decrease with increasing elapsed time. While the magnitude diameter of drop nano fluid and wetting surface is increase with increasing elapsed time on the surface of the stainless steel SS 316 and Zircalloy 4.

Subsurface conditions in hydrothermal vents inferred from diffuse flow composition, and models of reaction and transport

NASA Astrophysics Data System (ADS)

Larson, B. I.; Houghton, J. L.; Lowell, R. P.; Farough, A.; Meile, C. D.

2015-08-01

Chemical gradients in the subsurface of mid-ocean ridge hydrothermal systems create an environment where minerals precipitate and dissolve and where chemosynthetic organisms thrive. However, owing to the lack of easy access to the subsurface, robust knowledge of the nature and extent of chemical transformations remains elusive. Here, we combine measurements of vent fluid chemistry with geochemical and transport modeling to give new insights into the under-sampled subsurface. Temperature-composition relationships from a geochemical mixing model are superimposed on the subsurface temperature distribution determined using a heat flow model to estimate the spatial distribution of fluid composition. We then estimate the distribution of Gibb's free energies of reaction beneath mid oceanic ridges and by combining flow simulations with speciation calculations estimate anhydrite deposition rates. Applied to vent endmembers observed at the fast spreading ridge at the East Pacific Rise, our results suggest that sealing times due to anhydrite formation are longer than the typical time between tectonic and magmatic events. The chemical composition of the neighboring low temperature flow indicates relatively uniform energetically favorable conditions for commonly inferred microbial processes such as methanogenesis, sulfate reduction and numerous oxidation reactions, suggesting that factors other than energy availability may control subsurface microbial biomass distribution. Thus, these model simulations complement fluid-sample datasets from surface venting and help infer the chemical distribution and transformations in subsurface flow.

Recombinant canine distemper virus strain Snyder Hill expressing green or red fluorescent proteins causes meningoencephalitis in the ferret.

PubMed

Ludlow, M; Nguyen, D T; Silin, D; Lyubomska, O; de Vries, R D; von Messling, V; McQuaid, S; De Swart, R L; Duprex, W P

2012-07-01

The propensity of canine distemper virus (CDV) to spread to the central nervous system is one of the primary features of distemper. Therefore, we developed a reverse genetics system based on the neurovirulent Snyder Hill (SH) strain of CDV (CDV(SH)) and show that this virus rapidly circumvents the blood-brain and blood-cerebrospinal fluid (CSF) barriers to spread into the subarachnoid space to induce dramatic viral meningoencephalitis. The use of recombinant CDV(SH) (rCDV(SH)) expressing enhanced green fluorescent protein (EGFP) or red fluorescent protein (dTomato) facilitated the sensitive pathological assessment of routes of virus spread in vivo. Infection of ferrets with these viruses led to the full spectrum of clinical signs typically associated with distemper in dogs during a rapid, fatal disease course of approximately 2 weeks. Comparison with the ferret-adapted CDV(5804P) and the prototypic wild-type CDV(R252) showed that hematogenous infection of the choroid plexus is not a significant route of virus spread into the CSF. Instead, viral spread into the subarachnoid space in rCDV(SH)-infected animals was triggered by infection of vascular endothelial cells and the hematogenous spread of virus-infected leukocytes from meningeal blood vessels into the subarachnoid space. This resulted in widespread infection of cells of the pia and arachnoid mater of the leptomeninges over large areas of the cerebral hemispheres. The ability to sensitively assess the in vivo spread of a neurovirulent strain of CDV provides a novel model system to study the mechanisms of virus spread into the CSF and the pathogenesis of acute viral meningitis.

Role of upwelling hydrothermal fluids in the development of alteration patterns at fast spreading ridges: Evidence from the sheeted dike complex at Pito Deep

NASA Astrophysics Data System (ADS)

Heft, Kerri L.; Gillis, Kathryn M.; Pollock, Megan A.; Karson, Jeffery A.; Klein, Emily M.

2008-05-01

Alteration of sheeted dikes exposed along submarine escarpments at the Pito Deep Rift (NE edge of the Easter microplate) provides constraints on the crustal component of axial hydrothermal systems at fast spreading mid-ocean ridges. Samples from vertical transects through the upper crust constrain the temporal and spatial scales of hydrothermal fluid flow and fluid-rock reaction. The dikes are relatively fresh (average extent of alteration is 27%), with the extent of alteration ranging from 0 to >80%. Alteration is heterogeneous on scales of tens to hundreds of meters and displays few systematic spatial trends. Background alteration is amphibole-dominated, with chlorite-rich dikes sporadically distributed throughout the dike complex, indicating that peak temperatures ranged from <300°C to >450°C and did not vary systematically with depth. Dikes locally show substantial metal mobility, with Zn and Cu depletion and Mn enrichment. Amphibole and chlorite fill fractures throughout the dike complex, whereas quartz-filled fractures and faults are only locally present. Regional variability in alteration characteristics is found on a scale of <1-2 km, illustrating the diversity of fluid-rock interaction that can be expected in fast spreading crust. We propose that much of the alteration in sheeted dike complexes develops within broad, hot upwelling zones, as the inferred conditions of alteration cannot be achieved in downwelling zones, particularly in the shallow dikes. Migration of circulating cells along rides axes and local evolution of fluid compositions produce sections of the upper crust with a distinctive character of alteration, on a scale of <1-2 km and <5-20 ka.

Ballistic Motion of Enzymes that Catalyze Highly Exothermic Reactions

NASA Astrophysics Data System (ADS)

Tsekouras, Konstantinos; Pressé, Steve

Recently we proposed that the experimentally observed enhanced diffusion of enzymes catalyzing highly exothermic reactions is a consequence of their mechanism for dissipating reaction energy. More specifically, we proposed that reaction energy spreads out from the reaction site in the form of an acoustic wave which causes the enzyme to asymmetrically deform into the solvent. The solvent reaction propels the enzyme. However, it has been noted that in water, high viscosity should reduce enzyme momentum to zero within a few ps, so any diffusion increase should not be observable. Here we provide a model explaining how small volumetric expansions of biomolecules inside water may cause fluid compression that in turn creates regions of low fluid density around the biomolecule. We then investigate the dynamics of the biomolecule in the presence of these perturbations.

A model of transluminal flow of an anti-HIV microbicide vehicle: Combined elastic squeezing and gravitational sliding

NASA Astrophysics Data System (ADS)

Szeri, Andrew J.; Park, Su Chan; Verguet, Stéphane; Weiss, Aaron; Katz, David F.

2008-08-01

Elastohydrodynamic lubrication over soft substrates is of importance in a number of biomedical problems: From lubrication of the eye surface by the tear film, to lubrication of joints by synovial fluid, to lubrication between the pleural surfaces that protect the lungs and other organs. Such flows are also important for the drug delivery functions of vehicles for anti-HIV topical microbicides. These are intended to inhibit transmission into vulnerable mucosa, e.g., in the vagina. First generation prototype microbicides have gel vehicles, which spread after insertion and coat luminal surfaces. Effectiveness derives from potency of the active ingredients and completeness and durability of coating. Delivery vehicle rheology, luminal biomechanical properties, and the force due to gravity influence the coating mechanics. We develop a framework for understanding the relative importance of boundary squeezing and body forces on the extent and speed of the coating that results. A single dimensionless number, independent of viscosity, characterizes the relative influences of squeezing and gravitational acceleration on the shape of spreading in the Newtonian case. A second scale, involving viscosity, determines the spreading rate. In the case of a shear-thinning fluid, the Carreau number also plays a role. Numerical solutions were developed for a range of the dimensionless parameter and compared well with asymptotic theory in the limited case where such results can be obtained. Results were interpreted with respect to trade-offs between wall elasticity, longitudinal forces, bolus viscosity, and bolus volume. These provide initial insights of practical value for formulators of gel delivery vehicles for anti-HIV microbicidal formulations.

The influence of isotropic and anisotropic crustal permeability on hydrothermal flow at fast spreading ridges

NASA Astrophysics Data System (ADS)

Hasenclever, Jörg; Rüpke, Lars; Theissen-Krah, Sonja; Morgan, Jason

2016-04-01

We use 3-D numerical models of hydrothermal fluid flow to assess the magnitude and spatial distribution of hydrothermal mass and energy fluxes within the upper and lower oceanic crust. A better understanding of the hydrothermal flow pattern (e.g. predominantly on-axis above the axial melt lens vs. predominantly off-axis and ridge-perpendicular over the entire crustal thickness) is essential for quantifying the volume of oceanic crust exposed to high-temperature fluid flow and the associated leaching and redistribution of economically interesting metals. The initial setup of all 3-D models is based on our previous 2-D studies (Theissen-Krah et al., 2011), in which we have coupled numerical models for crustal accretion and hydrothermal fluid flow. One result of these 2-D calculations is a crustal permeability field that leads to a thermal structure in the crust that matches seismic tomography data at the East Pacific Rise. Our reference 3-D model for hydrothermal flow at fast-spreading ridges predicts the existence of a hybrid hydrothermal system (Hasenclever et al., 2014) with two interacting flow components that are controlled by different physical mechanisms. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittle-ductile transition. About ˜60% of the discharging fluid mass is replenished on-axis by warm (up to 300oC) recharge flow surrounding the hot thermal plumes. The remaining ˜40%, however, occurs as colder and broader recharge up to several kilometres away from the ridge axis that feeds hot (500-700oC) deep off-axis flow in the lower crust towards the ridge. Both flow components merge above the melt lens to feed ridge-centred vent sites. In a suite of 3-D model calculations we vary the isotropic crustal permeability to quantify its influence on on-axis vs. off-axis hydrothermal fluxes as well as on along-axis hydrothermal activity. We also explore the effect of anisotropic permeability that is likely to be a feature of the diking region above the melt lens where the repeated emplacement of meter-size dikes should lead to higher permeability in vertical and along-ridge direction and to lower permeability across the ridge. We further study the effect of along-ridge depth-variations of the axial melt lens on the distribution of hydrothermal vent sites.

Fluid-solid coupled simulation of the ignition transient of solid rocket motor

NASA Astrophysics Data System (ADS)

Li, Qiang; Liu, Peijin; He, Guoqiang

2015-05-01

The first period of the solid rocket motor operation is the ignition transient, which involves complex processes and, according to chronological sequence, can be divided into several stages, namely, igniter jet injection, propellant heating and ignition, flame spreading, chamber pressurization and solid propellant deformation. The ignition transient should be comprehensively analyzed because it significantly influences the overall performance of the solid rocket motor. A numerical approach is presented in this paper for simulating the fluid-solid interaction problems in the ignition transient of the solid rocket motor. In the proposed procedure, the time-dependent numerical solutions of the governing equations of internal compressible fluid flow are loosely coupled with those of the geometrical nonlinearity problems to determine the propellant mechanical response and deformation. The well-known Zeldovich-Novozhilov model was employed to model propellant ignition and combustion. The fluid-solid coupling interface data interpolation scheme and coupling instance for different computational agents were also reported. Finally, numerical validation was performed, and the proposed approach was applied to the ignition transient of one laboratory-scale solid rocket motor. For the application, the internal ballistics were obtained from the ground hot firing test, and comparisons were made. Results show that the integrated framework allows us to perform coupled simulations of the propellant ignition, strong unsteady internal fluid flow, and propellant mechanical response in SRMs with satisfactory stability and efficiency and presents a reliable and accurate solution to complex multi-physics problems.

Topography and tectonics of mid-oceanic ridge axes

NASA Technical Reports Server (NTRS)

Sleep, N. H.; Rosendahl, B. R.

1979-01-01

Numerical fluid dynamic models of mid-oceanic ridge axes were constructed using distributions of material properties constrained by seismic studies and thermal calculations. The calculations indicate that spreading is passive except for forces caused by density differences due to thermal expansion and partial melt. Except for geometric differences due to temperature distribution, one set of mechanical properties can adequately explain central rifts of slow ridges and central peaks of fast ridges. Viscous head loss in the upwelling material dominates at low spreading rates where material ascends through a narrow conduit. Thermal expansion and partial melting dominate at high spreading rates where a wide low viscosity crustal magma chamber is present. The preferred rheology is 10 to the 20th poise for the upwelling lithosphere; less than 5 x 10 to the 17th for the crustal magma chamber and axial intrusion zone at fast ridges, and a yield stress of 200 bars for the lithosphere. The calculation correctly predicts the existence of central peaks at 'hot-spot' ridges, where seismic evidence indicates a large magma chamber.

Transient swelling, spreading, and drug delivery by a dissolved anti-HIV microbicide-bearing film

NASA Astrophysics Data System (ADS)

Tasoglu, Savas; Rohan, Lisa C.; Katz, David F.; Szeri, Andrew J.

2013-03-01

There is a widespread agreement that more effective drug delivery vehicles with more alternatives, as well as better active pharmaceutical ingredients (APIs), must be developed to improve the efficacy of microbicide products. For instance, in tropical regions, films are more appropriate than gels due to better stability of drugs at extremes of moisture and temperature. Here, we apply fundamental fluid mechanical and physicochemical transport theory to help better understand how successful microbicide API delivery depends upon properties of a film and the human reproductive tract environment. Several critical components of successful drug delivery are addressed. Among these are: elastohydrodynamic flow of a dissolved non-Newtonian film; mass transfer due to inhomogeneous dilution of the film by vaginal fluid contacting it along a moving boundary (the locally deforming vaginal epithelial surface); and drug absorption by the epithelium. Local rheological properties of the film are dependent on local volume fraction of the vaginal fluid. We evaluated this experimentally, delineating the way that constitutive parameters of a shear-thinning dissolved film are modified by dilution. To develop the mathematical model, we integrate the Reynolds lubrication equation with a mass conservation equation to model diluting fluid movement across the moving vaginal epithelial surface and into the film. This is a complex physicochemical phenomenon that is not well understood. We explore time- and space-varying boundary flux model based upon osmotic gradients. Results show that the model produces fluxes that are comparable to experimental data. Further experimental characterization of the vaginal wall is required for a more precise set of parameters and a more sophisticated theoretical treatment of epithelium.

Integrating Cloud-Computing-Specific Model into Aircraft Design

NASA Astrophysics Data System (ADS)

Zhimin, Tian; Qi, Lin; Guangwen, Yang

Cloud Computing is becoming increasingly relevant, as it will enable companies involved in spreading this technology to open the door to Web 3.0. In the paper, the new categories of services introduced will slowly replace many types of computational resources currently used. In this perspective, grid computing, the basic element for the large scale supply of cloud services, will play a fundamental role in defining how those services will be provided. The paper tries to integrate cloud computing specific model into aircraft design. This work has acquired good results in sharing licenses of large scale and expensive software, such as CFD (Computational Fluid Dynamics), UG, CATIA, and so on.

Coughing and sneezing

NASA Astrophysics Data System (ADS)

Bourouiba, Lydia; Tasissa, Abiy; Bush, John

2010-11-01

The emergence and explosive spread of virulent viral (e.g., H1N1, SARS) and bacterial (e.g., Tuberculosis) infections is a problem of global interest with enormous human and economic consequences. The nature of contact between infected and non-infected persons greatly influences the outcomes of the disease epidemic; nevertheless, the definition and mechanisms leading to contact remain nebulous. We here examine the manner in which fluid dynamics modeling can assist in our understanding of contact and transmission of respiratory diseases. Particular attention is given to modeling the effluent of discrete exhalation events (e.g., coughing, sneezing) as multiphase thermals, and to predicting the range of pathogen-bearing droplets.

Gravity-Driven Flow of non-Newtonian Fluids in Heterogeneous Porous Media: a Theoretical and Experimental Analysis

NASA Astrophysics Data System (ADS)

Di Federico, V.; Longo, S.; Ciriello, V.; Chiapponi, L.

2015-12-01

A theoretical and experimental analysis of non-Newtonian gravity-driven flow in porous media with spatially variable properties is presented. The motivation for our study is the rheological complexity exhibited by several environmental contaminants (wastewater sludge, oil pollutants, waste produced by the minerals and coal industries) and remediation agents (suspensions employed to enhance the efficiency of in-situ remediation). Natural porous media are inherently heterogeneous, and this heterogeneity influences the extent and shape of the porous domain invaded by the contaminant or remediation agent. To grasp the combined effect of rheology and spatial heterogeneity, we consider: a) the release of a thin current of non-Newtonian power-law fluid into a 2-D, semi-infinite and saturated porous medium above a horizontal bed; b) perfectly stratified media, with permeability and porosity varying along the direction transverse (vertical) or parallel (horizontal) to the flow direction. This continuous variation of spatial properties is described by two additional parameters. In order to represent several possible spreading scenarios, we consider: i) instantaneous injection with constant mass; ii) continuous injection with time-variable mass; iii) instantaneous release of a mound of fluid, which can drain freely out of the formation at the origin (dipole flow). Under these assumptions, scalings for current length and thickness are derived in self similar form. An analysis of the conditions on model parameters required to avoid an unphysical or asymptotically invalid result is presented. Theoretical results are validated against multiple sets of experiments, conducted for different combinations of spreading scenarios and types of stratification. Two basic setups are employed for the experiments: I) direct flow simulation in an artificial porous medium constructed superimposing layers of glass beads of different diameter; II) a Hele-Shaw (HS) analogue made of two parallel plates set at an angle. The HS analogy is extended to power-law fluid flow in porous media with variable properties parallel or transverse to the flow direction. Comparison with experimental results show that the proposed models capture the propagation of the current front and the current profile at intermediate and late time.

Impinging Water Droplets on Inclined Glass Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armijo, Kenneth Miguel; Lance, Blake; Ho, Clifford K.

Multiphase computational models and tests of falling water droplets on inclined glass surfaces were developed to investigate the physics of impingement and potential of these droplets to self-clean glass surfaces for photovoltaic modules and heliostats. A multiphase volume-of-fluid model was developed in ANSYS Fluent to simulate the impinging droplets. The simulations considered different droplet sizes (1 mm and 3 mm), tilt angles (0°, 10°, and 45°), droplet velocities (1 m/s and 3 m/s), and wetting characteristics (wetting=47° contact angle and non-wetting = 93° contact angle). Results showed that the spread factor (maximum droplet diameter during impact divided by the initialmore » droplet diameter) decreased with increasing inclination angle due to the reduced normal force on the surface. The hydrophilic surface yielded greater spread factors than the hydrophobic surface in all cases. With regard to impact forces, the greater surface tilt angles yielded lower normal forces, but higher shear forces. Experiments showed that the experimentally observed spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) was significantly larger than the simulated spread factor. Observed spread factors were on the order of 5 - 6 for droplet velocities of ~3 m/s, whereas the simulated spread factors were on the order of 2. Droplets were observed to be mobile following impact only for the cases with 45° tilt angle, which matched the simulations. An interesting phenomenon that was observed was that shortly after being released from the nozzle, the water droplet oscillated (like a trampoline) due to the "snapback" caused by the surface tension of the water droplet being released from the nozzle. This oscillation impacted the velocity immediately after the release. Future work should evaluate the impact of parameters such as tilt angle and surface wettability on the impact of particle/soiling uptake and removal to investigate ways that photovoltaic modules and heliostats can be designed to maximize self-cleaning.« less

High-temperature hydrothermal circulation in the lower oceanic crust at fast spreading ridges: Reconciling geophysical and geochemical constraints

NASA Astrophysics Data System (ADS)

Wilcock, W.

2003-04-01

Hydrothermal circulation is the dominant mechanism for cooling young oceanic crust and knowledge of its depth, extent and timing is critical for our understanding of crustal accretion. At fast-spreading ridges there is considerable controversy regarding the importance of this process in the lower crust. Geochemical data indicate that high-temperature hydrothermal fluids react with the lower crust but they also suggest that the reactions are limited to a narrow temperature interval and involve relatively small volumes of fluid. As a result many geochemical studies conclude that high-temperature hydrothermal circulation plays a relatively small role in heat transport in the lower crust and occurs in a closed system that is isolated from upper crustal hydrothermal cells. In contrast, seismic observations on the fast spreading East Pacific Rise show that the mid-crustal axial magma chamber is underlain by a low velocity zone which is no more than 5-8 km wide throughout the lower crust and is interpreted as a region of elevated temperatures containing relatively low average melt fractions. Irrespective of the style of lower crustal accretion, simple physical considerations suggest that this structure is only thermally feasible if the lower crust cools by extensive hydrothermal circulation. Modeling studies indicate that this requires the permeability of the lower crust to temporarily reach at least ~10-13 m2. In order to reconcile the geochemical and geophysical data it is important to recognize that the thermal constraints do not require pervasive seawater circulation in the lower crust and can be satisfied by focused flow through narrow permeable zones spaced as far as about 1 km apart. Widely spaced regions of flow might be difficult to find in the field especially if the sampling strategies focus on the freshest outcrops. There is a tendency to overestimate the volume of fluid that must circulate through an open single-pass system. The fluid-rock ratios (0.2 - 1) inferred from oxygen isotope studies are often cited as evidence of limited circulation but when interpreted physically they are actually sufficient to transport a substantial proportion of the heat required to solidify and cool the lower crust. Nevertheless the geophysical constraints are also compatible with circulation in a two-layer double diffusive system favored by many researchers, in which the lower crust is cooled by a recirculating brine cell.

STOCHASTICITY AND EFFICIENCY IN SIMPLIFIED MODELS OF CORE-COLLAPSE SUPERNOVA EXPLOSIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cardall, Christian Y.; Budiardja, Reuben D., E-mail: cardallcy@ornl.gov, E-mail: reubendb@utk.edu

2015-11-01

We present an initial report on 160 simulations of a highly simplified model of the post-bounce core-collapse supernova environment in three spatial dimensions (3D). We set different values of a parameter characterizing the impact of nuclear dissociation at the stalled shock in order to regulate the post-shock fluid velocity, thereby determining the relative importance of convection and the stationary accretion shock instability (SASI). While our convection-dominated runs comport with the paradigmatic notion of a “critical neutrino luminosity” for explosion at a given mass accretion rate (albeit with a nontrivial spread in explosion times just above threshold), the outcomes of ourmore » SASI-dominated runs are much more stochastic: a sharp threshold critical luminosity is “smeared out” into a rising probability of explosion over a ∼20% range of luminosity. We also find that the SASI-dominated models are able to explode with 3–4 times less efficient neutrino heating, indicating that progenitor properties, and fluid and neutrino microphysics, conducive to the SASI would make the neutrino-driven explosion mechanism more robust.« less

Influence of the impact energy on the pattern of blood drip stains

NASA Astrophysics Data System (ADS)

Smith, F. R.; Nicloux, C.; Brutin, D.

2018-01-01

The maximum spreading diameter of complex fluid droplets has been extensively studied and explained by numerous physical models. This research focuses therefore on a different aspect, the bulging outer rim observed after evaporation on the final dried pattern of blood droplets. A correlation is found between the inner diameter, the maximum outer diameter, and the impact speed. This shows how the drying mechanism of a blood drip stain is influenced by the impact energy, which induces a larger spreading diameter and thus a different redistribution of red blood cells inside the droplet. An empirical relation is established between the final dried pattern of a passive bloodstain and its impact speed, yielding a possible forensic application. Indeed, being able to relate accurately the energy of the drop with its final pattern would give a clue to investigators, as currently no such simple and accurate tool exists.

Sedimentation from particle-bearing plumes in a stratified ambient

NASA Astrophysics Data System (ADS)

Sutherland, Bruce R.; Hong, Youn Sub Dominic

2016-11-01

Laboratory experiments are performed to examine the sedimentation of particles that initially rise in a plume, then spread radially and settle in uniformly stratified fluid. Using light attenuation, the depth of the sediment bed is measured nonintrusively as a function of radius from the center of the plume. To gain some insight into these dynamics, an idealized model is developed by adapting well-established plume theory and a theory that accounts for sedimentation from surface gravity currents emanating from a plume impacting a rigid lid. We also account for recycling of falling particles that are re-entrained into the plume. With a suitable choice of parameters determining the intrusion height, entrainment during fountain collapse, and the radius at which settling from the intrusion begins, in most cases for which particles are predicted to be drawn back into the plume and recycled. The predictions for intrusion height, particle mound height, and spread agree within 20% of observations.

Molecular Determinants of Human T-lymphotropic Virus Type 1 Transmission and Spread

PubMed Central

Lairmore, Michael D.; Anupam, Rajaneesh; Bowden, Nadine; Haines, Robyn; Haynes, Rashade A. H.; Ratner, Lee; Green, Patrick L.

2011-01-01

Human T-lymphotrophic virus type-1 (HTLV-1) infects approximately 15 to 20 million people worldwide, with endemic areas in Japan, the Caribbean, and Africa. The virus is spread through contact with bodily fluids containing infected cells, most often from mother to child through breast milk or via blood transfusion. After prolonged latency periods, approximately 3 to 5% of HTLV-1 infected individuals will develop either adult T-cell leukemia/lymphoma (ATL), or other lymphocyte-mediated disorders such as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The genome of this complex retrovirus contains typical gag, pol, and env genes, but also unique nonstructural proteins encoded from the pX region. These nonstructural genes encode the Tax and Rex regulatory proteins, as well as novel proteins essential for viral spread in vivo such as, p30, p12, p13 and the antisense encoded HBZ. While progress has been made in the understanding of viral determinants of cell transformation and host immune responses, host and viral determinants of HTLV-1 transmission and spread during the early phases of infection are unclear. Improvements in the molecular tools to test these viral determinants in cellular and animal models have provided new insights into the early events of HTLV-1 infection. This review will focus on studies that test HTLV-1 determinants in context to full length infectious clones of the virus providing insights into the mechanisms of transmission and spread of HTLV-1. PMID:21994774

Measurement of nanoscale molten polymer droplet spreading using atomic force microscopy

NASA Astrophysics Data System (ADS)

Soleymaniha, Mohammadreza; Felts, Jonathan R.

2018-03-01

We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures using atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μm diameters at 115-175 °C on sapphire, silicon oxide, and mica. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The contact angle evolution follows a power law with time with experimentally determined values of -0.29 ± 0.01, -0.08 ± 0.02, and -0.21 ± 0.01 for sapphire, silicon oxide, and mica, respectively. The non-zero steady state contact angles result in a slower evolution of contact angle with time consistent with theories combining molecular kinetic and hydrodynamic models. Monitoring the cantilever phase provides additional information about the local mechanics of the droplet surface. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 °C to 175 °C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means.

Rise of a variable-viscosity fluid in a steadily spreading wedge-shaped conduit with accreting walls

USGS Publications Warehouse

Lachenbruch, Arthur H.; Nathenson, Manuel

1976-01-01

Relatively rigid plates making up the outer 50 to 100 km of the Earth are steadily separating from one another along narrow globe-circling zones of submarine volcanism, the oceanic spreading centers. Continuity requires that the viscous underlying material rise beneath spreading centers and accrete onto the steadily diverging plates. It is likely that during the rise the viscosity changes systematically and that the viscous tractions exerted on the plates contribute to the unique pattern of submarine mountains and earthquake faults observed at spreading centers. The process is modeled by viscous creep in a wedge-shaped conduit (with apex at the sea floor) in which the viscosity varies as rm where r is distance from the apex and m is a parameter. For these conditions, the governing differential equations take a simple form. The solution for the velocity is independent of r and of the sign of m. As viscous stresses vary as rm-1, the pattern of stress on the conduit wall is sensitive to viscosity variation. For negative m, the viscous pressure along the base of the conduit is quite uniform; for positive m, it falls toward zero in the axial region as the conduit base widens. For small opening angles, viscous forces push the plates apart, and for large ones, they oppose plate separation. Though highly idealized, the solution provides a tool for investigating tectonic processes at spreading centers.

Cinema Fire Modelling by FDS

NASA Astrophysics Data System (ADS)

Glasa, J.; Valasek, L.; Weisenpacher, P.; Halada, L.

2013-02-01

Recent advances in computer fluid dynamics (CFD) and rapid increase of computational power of current computers have led to the development of CFD models capable to describe fire in complex geometries incorporating a wide variety of physical phenomena related to fire. In this paper, we demonstrate the use of Fire Dynamics Simulator (FDS) for cinema fire modelling. FDS is an advanced CFD system intended for simulation of the fire and smoke spread and prediction of thermal flows, toxic substances concentrations and other relevant parameters of fire. The course of fire in a cinema hall is described focusing on related safety risks. Fire properties of flammable materials used in the simulation were determined by laboratory measurements and validated by fire tests and computer simulations

Textural, Rheological and Sensory Properties and Oxidative Stability of Nut Spreads—A Review

PubMed Central

Shakerardekani, Ahmad; Karim, Roselina; Ghazali, Hasanah Mohd; Chin, Nyuk Ling

2013-01-01

Tree nuts are rich in macro and micronutrients, phytochemicals, tocopherols and phenolic compounds. The development of nut spreads would potentially increase the food uses of nuts and introduce consumers with a healthier, non-animal breakfast snack food. Nut spreads are spreadable products made from nuts that are ground into paste. Roasting and milling (particle size reduction) are two important stages for the production of nut spreads that affected the textural, rheological characteristic and overall quality of the nut spread. Textural, color, and flavor properties of nut spreads play a major role in consumer appeal, buying decisions and eventual consumption. Stability of nut spreads is influenced by its particle size. Proper combination of ingredients (nut paste, sweetener, vegetable oil and protein sources) is also required to ensure a stable nut spread product is produced. Most of the nut spreads behaved like a non-Newtonian pseudo-plastic fluid under yield stress which help the producers how to start pumping and stirring of the nut spreads. Similar to other high oil content products, nut spreads are susceptible to autoxidation. Their oxidation can be controlled by application of antioxidants, using processing techniques that minimize tocopherol and other natural antioxidant losses. PMID:23429239

Chromosomal studies on 2 mL of celomic fluid obtained during the fifth week of development in the timed-pregnant baboon model.

PubMed

Santolaya-Forgas, Joaquin; De Leon-Luis, Juan; Shen, Zhion; McCorquodale, Maureen

2005-09-01

To determine if chromosomal studies could be performed using 2 mL of celomicfluid obtained during the fifth postfertilization week in pregnant baboons. Nine ultrasound-guided celocenteses were performed. The initial 0.5 mL of celomic fluid was discarded to decrease maternal cell contamination. Approximately 2 mL of celomic fluid was then collected. The fluid was centrifuged and the supernatant removed to a final volume of 0.5 mL. The celomic fluid sample was placed in either a small plastic flaskette chamber slide with a mix of 0.5 mL celomic fluid, 1 mL of Amniomax, and 1 mL of usedfibroblast culture medium to spread on the entire surface (n=4), or a 3.5 x 1-cm plastic Petri dish with a 24 x 30-mm glass coverslip to keep the 0.5 mL celomic fluid mixed with 1 mL of Amniomax (Invitrogen, Carlsbad, California) within a 1 cm2 area (n=5). The medium was changed on day 5 and thereafter every second to third day. The cells were harvested when the number of cells appeared sufficient for chromosomal analysis. Standard chromosomal studies were possible in 5 of the 9 celomicfluid samples. Mean (+/-SD) celomic fluid volume used for culture was 1.85 +/- 0.3 mL. Mean (+/-SD) time to karyotype result was 18.8 +/- 1.8 days. The findings of this study suggest that there are living cells at 36-42 days of embryonic development in the extraembryonic celomic fluid of primates and that they can be cultured for chromosomal studies. However, significant improvements in understanding the biology of cells present at 5 weeks after fertilization in celomic fluid are needed to improve culture conditions.

Geologic setting of the Snake Pit hydrothermal site: An active vent field on the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Karson, Jeffrey A.; Brown, Jennifer R.

1988-03-01

The Snake Pit Hydrothermal Site lies on the axis of the Mid-Atlantic Ridge at 23°22' N latitude, about 30 km south of the Kane Transform Intersection. Active ‘black smoker’ vents and a surrounding field of hydrothermal sediment occur at the crest of a laterally extensive neovolcanic ridge. It is one of the first active hydrothermal vent fields to be found on a slow-spreading ridge axis and despite significant differences in its geologic setting from those of the East Pacific Rise, has many similarities to its fast-spreading counterparts. Although preliminary reports have documented many interesting aspects of these vents and their surroundings, new data collected from the manned submersible ALVIN and the deep-towed ANGUS camera system define the regional tectonic setting as well as the local geologic environment of this fascinating area. The Snake Pit vents are located on a local peak of a volcanic constructional ridge at a depth of 3450 m, 700 800 m deeper than vents known from the East Pacific Rise, Galapagos, or Juan de Fuca spreading centers. The vent field is at least 600 m long and up to 200 m wide and is covered by a thick blanket of greenish to yellow-orange hydrothermal sediment. Both active and extinct vents are perched along the crests of steep-sided sulfide mounds that reach heights of over 40 m. High-temperature (350° C) fluids are vented from black smoker chimneys and low-temperature (226° C) fluids seep from sulphide domes and subordinate anhydrite constructions. Water temperatures, flow rates, fluid chemistries, and mineralization are strikingly similar to vents of faster spreading ridge crests; however, a somewhat distinct fauna inhabit the area.

Simulation of solid-liquid flows in a stirred bead mill based on computational fluid dynamics (CFD)

NASA Astrophysics Data System (ADS)

Winardi, S.; Widiyastuti, W.; Septiani, E. L.; Nurtono, T.

2018-05-01

The selection of simulation model is an important step in computational fluid dynamics (CFD) to obtain an agreement with experimental work. In addition, computational time and processor speed also influence the performance of the simulation results. Here, we report the simulation of solid-liquid flow in a bead mill using Eulerian model. Multiple Reference Frame (MRF) was also used to model the interaction between moving (shaft and disk) and stationary (chamber exclude shaft and disk) zones. Bead mill dimension was based on the experimental work of Yamada and Sakai (2013). The effect of shaft rotation speed of 1200 and 1800 rpm on the particle distribution and the flow field was discussed. For rotation speed of 1200 rpm, the particles spread evenly throughout the bead mill chamber. On the other hand, for the rotation speed of 1800 rpm, the particles tend to be thrown to the near wall region resulting in the dead zone and found no particle in the center region. The selected model agreed well to the experimental data with average discrepancies less than 10%. Furthermore, the simulation was run without excessive computational cost.

Quantifying solute spreading and mixing in rocks using 3D X-ray CT and PET imaging

NASA Astrophysics Data System (ADS)

Kurotori, T.; Zahasky, C.; Benson, S. M.; Pini, R.

2016-12-01

Geological structures are heterogeneous with key transport properties varying over a wide range of scales. This limits our current capability to accurately predict fluid transport in the subsurface and therefore represents a major challenge for technologies, such as the sequestration of CO2in deep reservoirs. In this project, a novel experimental approach is proposed that is at the forefront of current practices for reservoir core analysis. Conventional pulse-tracer tests are combined with the simultaneous imaging of flows, thus including X-ray CT and Positron Emission Tomography (PET), so as to obtain real-time dynamic 3D images during tracer transport. The ability to directly visualize tracer flows with such level of observational detail is key to improve our understanding on the effects of heterogeneity in natural complex systems. A set of pulse-tracer tests has been carried out using two distinct porous systems, namely an unconsolidated glass beadpack and a consolidated Ketton carbonate to quantify hydrodynamic dispersion at various Péclet numbers. Tracer spreading and mixing is investigated by analysing breakthrough curves and 2D spatial distribution at various control planes within the rock sample. The experiments with beadpacks confirm observations from earlier studies where homogeneous spatial and temporal spreading of the tracer was reported. Although various studies exist on experiments with beadpacks, only few have gathered a multidimensional data set. In that respect, the results presented here are very important to "calibrate" the system for sub-core scale (mm-scale) observations, in view of the inherent heterogeneity of rock sample at the same scale and noise that comes with images acquired from non-invasive techniques. Interestingly, results with Ketton exhibit a non-Fickian behaviour. We anticipate that the former is not only caused by the presence of sub-core scale heterogeneities, but also due to the mass transfer effects between the bulk fluid and the stagnant fluid in the micropores that represent a significant portion (50%) of the pore space. So-called capacitance (or multi-rate mass transfer, MRMT) models have been used to account for the additional mechanism that contributes to the anomalous transport.

Hepatitis A

MedlinePlus

... travel, especially to Asia, South or Central America, Africa and the Middle East IV drug use Living ... or other bodily fluid. Avoid unclean food and water. The virus may spread more rapidly through day ...

Cytomegalovirus

MedlinePlus

... other body fluids. CMV is rarely spread by blood transfusion or organ transplantation. If a pregnant woman passes ... Aid and Injury Prevention Crisis Situations Pets and Animals myhealthfinder Food and Nutrition Healthy Food Choices Weight ...

New Method Developed to Measure Contact Angles of a Sessile Drop

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Nengli

2002-01-01

The spreading of an evaporating liquid on a solid surface occurs in many practical processes and is of importance in a number of practical situations such as painting, textile dyeing, coating, gluing, and thermal engineering. Typical processes involving heat transfer where the contact angle plays an important role are film cooling, boiling, and the heat transfer through heat pipes. The biological phenomenon of cell spreading also is analogous to a drop spreading (ref. 1). In the study of spreading, the dynamic contact angle describes the interfacial properties on solid substrates and, therefore, has been studied by physicists and fluid mechanics investigators. The dynamic contact angle of a spreading nonvolatile liquid drop provides a simple tool in the study of the free-boundary problem, but the study of the spreading of a volatile liquid drop is of more practical interest because the evaporation of common liquids is inevitable in practical processes. The most common method to measure the contact angle, the contact radius, and the height of a sessile drop on a solid surface is to view the drop from its edge through an optical microscope. However, this method gives only local information in the view direction. Zhang and Yang (ref. 2) developed a laser shadowgraphy method to investigate the evaporation of sessile drop on a glass plate. As described here, Zhang and Chao (refs. 3 and 4) improved the method and suggested a new optical arrangement to measure the dynamic contact angle and the instant evaporation rate of a sessile drop with much higher accuracy (less than 1 percent). With this method, any fluid motion in the evaporating drop can be visualized through shadowgraphy without using a tracer, which often affects the field under investigation.

Influences of the Tonga Subduction Zone on seafloor massive sulfide deposits along the Eastern Lau Spreading Center and Valu Fa Ridge

NASA Astrophysics Data System (ADS)

Evans, Guy N.; Tivey, Margaret K.; Seewald, Jeffrey S.; Wheat, C. Geoff

2017-10-01

This study investigates the morphology, mineralogy, and geochemistry of seafloor massive sulfide (SMS) deposits from six back-arc hydrothermal vent fields along the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the context of endmember vent fluid chemistry and proximity to the Tonga Subduction Zone. To complement deposit geochemistry, vent fluid analyses of Cu, Zn, Ba, Pb and H2,(aq) were completed to supplement existing data and enable thermodynamic calculations of mineral saturation states at in situ conditions. Results document southward increases in the abundance of mantle-incompatible elements in hydrothermal fluids (Ba and Pb) and SMS deposits (Ba, Pb, As, and Sb), which is also expressed in the abundance of barite (BaSO4) and galena (PbS) in SMS deposits. These increases correspond to a decrease in distance between the ELSC/VFR and the Tonga Subduction Zone that correlates with a change in crustal lithology from back-arc basin basalt in the north to mixed andesite, rhyolite, and dacite in the south. Barite influences deposit morphology, contributing to the formation of horizontal flanges and squat terraces. Results are also consistent with a regional-scale lowering of hydrothermal reaction zone temperatures from north to south (except at the southernmost Mariner vent field) that leads to lower-temperature, higher-pH vent fluids relative to mid-ocean ridges of similar spreading rates (Mottl et al., 2011). These fluids are Cu- and Zn-poor and the deposits formed from these fluids are Cu-poor but Zn-rich. In contrast, at the Mariner vent field, higher-temperature and lower pH vent fluids are hypothesized to result from higher reaction zone temperatures and the localized addition of acidic magmatic volatiles (Mottl et al., 2011). The Mariner fluids are Cu- and Zn-rich and vent from SMS deposits that are rich in Cu but poor in Zn with moderate amounts of Pb. Thermodynamic calculations indicate that the contrasting metal contents of vent fluids and SMS deposits can be accounted for by vent fluid pH. Wurtzite/sphalerite ((Zn, Fe)S) and galena (PbS) are saturated at higher temperatures in higher-pH, Zn-, Cu-, and Pb-poor ELSC/VFR vent fluids, but are undersaturated at similar temperatures in low-pH, Zn-, Cu-, and Pb-rich vent fluids from the Mariner vent field. Indicators of pH in the ELSC and VFR SMS deposits include the presence of co-precipitated wurtzite and chalcopyrite along conduit linings in deposits formed from higher pH fluids, and different correlations between concentrations of Zn and Ag in bulk geochemical analyses. Significant positive bulk geochemical Zn:Ag correlations occur for deposits at vent fields where hydrothermal fluids have a minimum pH (at 25 °C) < 3.3, while correlations of Zn:Ag are weak or negative for deposits at vent fields where the minimum vent fluid pH (at 25 °C) > 3.6. Data show that the compositions of the mineral linings of open conduit chimneys (minerals present, mol% FeS in (Zn,Fe)S) that precipitate directly from hydrothermal fluids closely reflect the temperature and sulfur fugacity of sampled hydrothermal fluids. These mineral lining compositions thus can be used as indicators of hydrothermal fluid temperature and composition (pH, metal content, sulfur fugacity).

Computational Study of Ventilation and Disease Spread in Poultry Houses

NASA Astrophysics Data System (ADS)

Cimbala, John; Pawar, Sourabh; Wheeler, Eileen; Lindberg, Darla

2006-11-01

The air flow in and around poultry houses has been studied numerically with the goal of determining disease spread characteristics and comparing ventilation schemes. A typical manure-belt layer egg production facility is considered. The continuity, momentum, and energy equations are solved for flow both inside and outside poultry houses using the commercial computational fluid dynamics (CFD) code FLUENT. Both simplified two-dimensional and fully three-dimensional geometries are modeled. The spread of virus particles is considered to be analogous to diffusion of a tracer contaminant gas, in this case ammonia. The effect of thermal plumes produced by the hens in the poultry house is also considered. Two ventilation schemes with opposite flow directions are compared. Contours of temperature and ammonia mass fraction for both cases are obtained and compared. The analysis shows that ventilation and air quality characteristics are much better for the case in which the air flow is from bottom to top (enhancing the thermal plume) instead of from top to bottom (fighting the thermal plume) as in most poultry houses. This has implications in air quality control in the event of epidemic outbreaks of avian flu or other infectious diseases.

Developing a Control Strategy for Jets in Crossflow Using Direct Numerical Simulation

DTIC Science & Technology

2010-03-29

the total volume of scalar–containing fluid ( Vsc ) for stroke ratios equal to 2 and 6. Vsc is computed as the sum of all volume elements which have...concentration allows the difference between the scalar containing fluid and unmixed ambient fluid to be represented. Vsc can be considered as a measure of the...spread of the scalar in the flow–field. Figure 2.10(a) shows that Vsc increases nearly linearly (at a rate of 1.7) until t∗ ∼ 2. In general, Vsc

Tribology experiment. [journal bearings and liquid lubricants

NASA Technical Reports Server (NTRS)

Wall, W. A.

1981-01-01

A two-dimensional concept for Spacelab rack 7 was developed to study the interaction of liquid lubricants and surfaces under static and dynamic conditions in a low-gravity environment fluid wetting and spreading experiments of a journal bearing experiments, and means to accurately measure and record the low-gravity environment during experimentation are planned. The wetting and spreading process of selected commercial lubricants on representative surface are to the observes in a near-zero gravity environment.

LUNAR ACCRETION FROM A ROCHE-INTERIOR FLUID DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salmon, Julien; Canup, Robin M., E-mail: julien@boulder.swri.edu, E-mail: robin@boulder.swri.edu

2012-11-20

We use a hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk, consisting of a fluid model for the disk inside the Roche limit and an N-body code to describe accretion outside the Roche limit. As the inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body simulation. Contrary to an accretion timescale of a few months obtained with prior pure N-body codes, here the final stage of the Moon's growth is controlled by the slow spreading of themore » inner disk, resulting in a total lunar accretion timescale of {approx}10{sup 2} years. It has been proposed that the inner disk may compositionally equilibrate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon. However, the mass fraction of the final Moon that is derived from the inner disk is limited by resonant torques between the disk and exterior growing moons. For initial disks containing <2.5 lunar masses (M{sub Last-Quarter-Moon }), we find that a final Moon with mass > 0.8 M{sub Last-Quarter-Moon} contains {<=}60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.« less

Reaction of seawater with fresh mid-ocean ridge gabbro creates ';atypical' REE pattern and high REE fluid fluxes: Experiments at 425 and 475 °C, 400 and 1000 bar

NASA Astrophysics Data System (ADS)

Beermann, O.; Garbe-Schönberg, D.; Holzheid, A. D.

2013-12-01

High-temperature MOR hydrothermalism significantly affects ocean chemistry. The Sisters Peak (SP) hydrothermal field at 5°S on the slow-spreading Mid-Atlantic Ridge (MAR) emanates fluids >400°C [1] that have high concentrations of H2, transition metals, and rare earth elements (REE) exhibiting ';atypical' REE pattern characterized by depletions of LREE and HREE relative to MREE and no Eu anomaly [2]. This is in contrast to the ';typical' LREE enrichment and strong positive Eu anomaly known from many MOR vent fluids observed world-wide [e.g., 3]. Besides temperature, the seawater-to-rock ratio (w/r ratio) has significant control on the fluid chemistry [e.g., 4, 5]. To understand how vent fluid REE-signatures are generated during water-rock interaction processes we reacted unaltered gabbro with natural bottom seawater at 425 °C and 400 bar and at 425 and 475 °C at 1000 bar at variable w/r (mass) ratios ranging from 0.5-10 by using cold seal pressure vessels (CSPV). The run durations varied from 3-72 h. Reacted fluids were analysed for major and trace elements by ICP-OES and ICP-MS. In our experiments, ';atypical' REE fluid pattern similar to those of SP fluids were obtained at high w/r ratio (5 and 10) that might be characteristic for focused fluid-flow along e.g., detachment faults at slow-spreading MOR [6]. In contrast, more ';typical'-like REE pattern with elevated LREE and slightly positive Eu anomalies have been reproduced at low w/r ratio (0.5-1). Results of numerical simulations imply that strong positive Eu anomalies of fluids and altered gabbro from high temperature MOR hydrothermal systems can be created by intense rock leaching processes at high w/r ratio (5-10). This suggests that hydrothermal circulation through the ocean crust creates ';typical' REE fluid pattern with strong positive Eu anomalies if seawater reacts with gabbroic host rock that has been already leached in REE at high fluid fluxes. Simulations of the temporal chemical evolution of high temperature MOR hydrothermal systems reveal that rock and fluid REE contents can rapidly decrease within several months particularly at high fluid fluxes. In contrast, the reaction with ';fresh', unaltered rock is evident from the high REE concentration of SP fluids. Both, fluid access to fresh rock and the fluid flux should therefore significantly control chemical fluxes to the ocean. Thus, high chemical fluxes can be expected in particular from early stage high-temperature MOR hydrothermal systems that are assumed to be not uncommon along the slow-spreading MAR. [1] Koschinsky A., Garbe-Schönberg D., Sander S., Schmidt K., Gennerich H.-H., and Strauss H. (2008) Geology 36, 615-618. [2] Schmidt K., Garbe-Schönberg D., Bau M., and Koschinsky A. (2010) Geochim. Cosmochim. Acta 74, 4058-4077. [3] Douville E., Bienvenu P., Charlou J. L., Donval J. P., Fouquet Y., Appriou P., and Gamo T. (1999). Geochim. Cosmochim. Acta 63, 627-643. [4] Seyfried [Jr.] W. E. and Bischoff J. L. (1977) Earth. Planet. Sci. Lett. 34, 71-77. [5] Hajash A. and Chandler G. W. (1981) Contrib. Mineral. Petrol. 78, 240-254. [6] McCaig A.M. and Harris M. (2012) Geology 40, 367-370.

Application of Compressible Volume of Fluid Model in Simulating the Impact and Solidification of Hollow Spherical ZrO2 Droplet on a Surface

NASA Astrophysics Data System (ADS)

Safaei, Hadi; Emami, Mohsen Davazdah; Jazi, Hamidreza Salimi; Mostaghimi, Javad

2017-12-01

Applications of hollow spherical particles in thermal spraying process have been developed in recent years, accompanied by attempts in the form of experimental and numerical studies to better understand the process of impact of a hollow droplet on a surface. During such process, volume and density of the trapped gas inside droplet change. The numerical models should be able to simulate such changes and their consequent effects. The aim of this study is to numerically simulate the impact of a hollow ZrO2 droplet on a flat surface using the volume of fluid technique for compressible flows. An open-source, finite-volume-based CFD code was used to perform the simulations, where appropriate subprograms were added to handle the studied cases. Simulation results were compared with the available experimental data. Results showed that at high impact velocities ( U 0 > 100 m/s), the compression of trapped gas inside droplet played a significant role in the impact dynamics. In such velocities, the droplet splashed explosively. Compressibility effects result in a more porous splat, compared to the corresponding incompressible model. Moreover, the compressible model predicted a higher spread factor than the incompressible model, due to planetary structure of the splat.

Simulation of Oil Slick Transport in Great Lakes Connecting Channels. Volume 1. Theory and Model Formulation

DTIC Science & Technology

1986-03-01

attempted to analyze in detail the 3 hydrodynamic problem defined above (Kerr and Babu, 1970; 5 15 U DePietio and Cox, 1979; and Foda and Cox, 1980...coefficient ET can be related to the magnitude of V’ by the random walk analysis (Fischer, et al., 1979), whereI V’ = (4E T/6t)2 (27) 3 in which 5t = time...Water Management and Planning Branch.. Foda , M. and R.G. Cox, (1980). "The spreading of thin liquid films on a water-air interface," Journal of Fluid

Development of an Evaporation Sub-model and Simulation of Multiple Droplet Impingement in Volume of Fluid Method

NASA Astrophysics Data System (ADS)

Potham, Sathya Prasad

Droplet collision and impingement on a substrate are widely observed phenomenon in many applications like spray injection of Internal Combustion Engines, spray cooling, spray painting and atomizers used in propulsion applications. Existing Lagrangian models do not provide a comprehensive picture of the outcome of these events and may involve model constants requiring experimental data for validation. Physics based models like Volume of Fluid (VOF) method involve no parametric tuning and are more accurate. The aim of this thesis is to extend the basic VOF method with an evaporation sub-model and implement in an open source Computational Fluid Dynamics (CFD) software, OpenFOAM. The new model is applied to numerically study the evaporation of spherical n-heptane droplets impinging on a hot wall at atmospheric pressure and a temperature above the Leidenfrost temperature. An additional vapor phase is introduced apart from the liquid and gas phases to understand the mixing and diffusion of vapor and gas phases. The evaporation model is validated quantitatively and qualitatively with fundamental problems having analytical solutions and published results. The effect of droplet number and arrangement on evaporation is studied by three cases with one (Case 1), two (Case 2) and four (Case 3) droplets impinging on hot wall in film boiling regime at a fixed temperature of wall and a constant non-dimensional distance between droplets. Droplet lift and spread, surface temperature, heat transfer, and evaporation rate are examined. It was observed that more liquid mass evaporated in Case 1 compared to the other cases. Droplet levitation begins early in Case 1 and very high levitation observed was partially due to contraction of its shape from elongated to a more circular form. Average surface temperature was also considerably reduced in Case 1 due to high droplet levitation.

Determining the spill flow discharge of combined sewer overflows using rating curves based on computational fluid dynamics instead of the standard weir equation.

PubMed

Fach, S; Sitzenfrei, R; Rauch, W

2009-01-01

It is state of the art to evaluate and optimise sewer systems with urban drainage models. Since spill flow data is essential in the calibration process of conceptual models it is important to enhance the quality of such data. A wide spread approach is to calculate the spill flow volume by using standard weir equations together with measured water levels. However, these equations are only applicable to combined sewer overflow (CSO) structures, whose weir constructions correspond with the standard weir layout. The objective of this work is to outline an alternative approach to obtain spill flow discharge data based on measurements with a sonic depth finder. The idea is to determine the relation between water level and rate of spill flow by running a detailed 3D computational fluid dynamics (CFD) model. Two real world CSO structures have been chosen due to their complex structure, especially with respect to the weir construction. In a first step the simulation results were analysed to identify flow conditions for discrete steady states. It will be shown that the flow conditions in the CSO structure change after the spill flow pipe acts as a controlled outflow and therefore the spill flow discharge cannot be described with a standard weir equation. In a second step the CFD results will be used to derive rating curves which can be easily applied in everyday practice. Therefore the rating curves are developed on basis of the standard weir equation and the equation for orifice-type outlets. Because the intersection of both equations is not known, the coefficients of discharge are regressed from CFD simulation results. Furthermore, the regression of the CFD simulation results are compared with the one of the standard weir equation by using historic water levels and hydrographs generated with a hydrodynamic model. The uncertainties resulting of the wide spread use of the standard weir equation are demonstrated.

Bacterial invasion of the inner ear in association with pneumococcal meningitis.

PubMed

Møller, Martin Nue; Brandt, Christian; Østergaard, Christian; Caye-Thomasen, Per

2014-06-01

To examine the pathways of bacterial invasion and subsequent spreading in the inner ear during pneumococcal meningitis. A well-established adult rat model of Streptococcus pneumoniae meningitis was used. Thirty rats were inoculated intrathecally with S. pneumoniae serotype 1, 3 or 9 V and received no additional treatment. The rats were sacrificed when reaching terminal illness or on Day 7 and then prepared for serial sectioning and PAS-Alcian blue staining for light microscopy. During the first few days after inoculation, bacteria invade the inner ear through the cochlear aqueduct, into the scala tympani of the cochlea (perilymphatic space). From here, bacteria spreads apically toward the helicotrema and subsequently basally through the scala vestibuli, toward the vestibule and the vestibular system. When the bacteria after 5 to 6 days had reached scala vestibuli of the basal turn of the cochlea, hematogenous spreading occurred to the spiral ligament and into the cochlear endolymph, subsequently to the vestibular endolymph. We found no evidence of alternative routes for bacterial invasion in the inner ear. Several internal barriers to bacterial spreading were found within the inner ear. Bacterial elimination was evidenced by engulfment by macrophages within the inner ear. From the meninges, pneumococci invade the inner ear through the cochlear aqueduct during the first days of infection, whereas hematogenous invasion via the spiral ligament capillary bed occur at later stages. Although internal barriers exist within the inner ear, the spreading of bacteria occurs via the natural pathways of the fluid compartments. Bacterial elimination occurs by local macrophage engulfment.

Intrascleral Drug Delivery to the Eye Using Hollow Microneedles

PubMed Central

Jiang, Jason; Moore, Jason S.; Edelhauser, Henry F.; Prausnitz, Mark R.

2010-01-01

Purpose This study tested the hypothesis that hollow microneedles can infuse solutions containing soluble molecules, nanoparticles, and microparticles into sclera in a minimally invasive manner. Methods Individual hollow microneedles were inserted into, but not across, human cadaver sclera and aqueous solutions containing sulforhodamine or fluorescently-tagged nanoparticles or microparticles were infused into sclera at constant pressure. The infused volume of fluid was measured and imaged histologically as a function of scleral thickness, infusion pressure, needle retraction depth and the presence of spreading enzymes (hyaluronidase and collagenase). Results Individual hollow microneedles were able to insert into sclera. Fluid infusion was extremely slow after microneedle insertion into the sclera without retraction, but partial retraction of the microneedle over a distance of 200–300 μm enabled infusion of 10–35 μl of fluid into the tissue. Scleral thickness and infusion pressure had insignificant effects on fluid delivery. Nanoparticle suspensions were also delivered into sclera, but microparticles were delivered only in the presence of hyaluronidase and collagenase spreading enzymes, which suggested the role of scleral glycosaminoglycans and collagen fibers as rate-limiting barriers. Conclusion This study shows that hollow microneedles can infuse solutions into the sclera for minimally invasive delivery of soluble molecules, nanoparticles and microparticles. PMID:18979189

Fifth disease

MedlinePlus

Parvovirus B19; Erythema infectiosum; Slapped cheek rash ... Fifth disease is caused by human parvovirus B19. It often affects preschoolers or school-age children during the spring. The disease spreads through the fluids in the nose and mouth ...

A model of concurrent flow flame spread over a thin solid fuel

NASA Technical Reports Server (NTRS)

Ferkul, Paul V.

1993-01-01

A numerical model is developed to examine laminar flame spread and extinction over a thin solid fuel in lowspeed concurrent flows. The model provides a more precise fluid-mechanical description of the flame by incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point. Parabolic equations are used to treat the downstream flame, which has a higher flow Reynolds number. The parabolic and elliptic regions are coupled smoothly by an appropriate matching of boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Steady spread with constant flame and pyrolysis lengths is found possible for thin fuels and this facilitates the adoption of a moving coordinate system attached to the flame with the flame spread rate being an eigen value. Calculations are performed in purely forced flow in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Both quenching and blowoff extinction are observed. The results show that as flow velocity or oxygen percentage is reduced, the flame spread rate, the pyrolysis length, and the flame length all decrease, as expected. The flame standoff distance from the solid and the reaction zone thickness, however, first increase with decreasing flow velocity, but eventually decrease very near the quenching extinction limit. The short, diffuse flames observed at low flow velocities and oxygen levels are consistent with available experimental data. The maximum flame temperature decreases slowly at first as flow velocity is reduced, then falls more steeply close to the quenching extinction limit. Low velocity quenching occurs as a result of heat loss. At low velocities, surface radiative loss becomes a significant fraction of the total combustion heat release. In addition, the shorter flame length causes an increase in the fraction of conduction downstream compared to conduction to the fuel. These heat losses lead to lower flame temperatures, and ultimately, extinction. This extinction mechanism differs from that of blowoff, where the flame is unable to be stabilized due to the high flow velocity.

Stochasticity and efficiency of convection-dominated vs. SASI-dominated supernova explosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cardall, Christian Y.; Budiardja, Reuben D.

2015-10-22

We present an initial report on 160 simulations of a highly simplified model of the post-bounce supernova environment in three position space dimensions (3D). We set different values of a parameter characterizing the impact of nuclear dissociation at the stalled shock in order to regulate the post-shock fluid velocity, thereby determining the relative importance of convection and the stationary accretion shock instability (SASI). While our convection-dominated runs comport with the paradigmatic notion of a `critical neutrino luminosity' for explosion at a given mass accretion rate (albeit with a nontrivial spread in explosion times just above threshold), the outcomes of our SASI-dominated runs are more stochastic: a sharp threshold critical luminosity is `smeared out' into a rising probability of explosion over amore » $$\\sim 20\\%$$ range of luminosity. We also find that the SASI-dominated models are able to explode with 3 to 4 times less efficient neutrino heating, indicating that progenitor properties, and fluid and neutrino microphysics, conducive to the SASI would make the neutrino-driven explosion mechanism more robust.« less

Fluid Management of and Flame Spread Across Liquid Pools

NASA Technical Reports Server (NTRS)

Ross, H. D.; Miller, F. J.

2001-01-01

The goal of our research on flame spread across pools of liquid fuel remains the quantitative identification of the mechanisms that control the rate and nature of flame spread when the initial temperature of the liquid pool is below the fuel's flash point temperature. As described in, four microgravity (mu-g) sounding rocket flights examined the effect of forced opposed airflow over a 2.5 cm deep x 2 cm wide x 30 cm long pool of 1-butanol. Among many unexpected findings, it was observed that the flame spread is much slower and steadier than in 1g where flame spread has a pulsating character. Our numerical model, restricted to two dimensions, had predicted faster, pulsating flame spread in mu-g. In a test designed to achieve a more 2-D experiment, our investigation of a shallow, wide pool (2 mm deep x 78 mm wide x 30 cm long) was unsuccessful in mu-g, due to an unexpectedly long time required to fill the tray. As such, the most recent Spread Across Liquids (SAL) sounding rocket experiment had two principal objectives: 1) determine if pulsating flame spread in deep fuel trays would occur under the conditions that a state-of-the-art computational combustion code and short-duration drop tower tests predict; and 2) determine if a long, rectangular, shallow fuel tray could achieve a visibly flat liquid surface across the whole tray without spillage in the mu-g time allotted. If the second objective was met, the shallow tray was to be ignited to determine the nature of flame spread in mu-g for this geometry. For the first time in the experiment series, two fuel trays - one deep (30 cm long x 2 cm wide x 25 mm deep) and one shallow (same length and width, but 2 mm deep)-- were flown. By doing two independent experiments in a single flight, a significant cost savings was realized. In parallel, the computational objective was to modify the code to improve agreement with earlier results. This last objective was achieved by modifying the fuel mass diffusivity and adding a parameter to correct for radiative and lateral heat loss.

On ice rifts and the stability of non-Newtonian extensional flows on a sphere

NASA Astrophysics Data System (ADS)

Sayag, Roiy

2017-11-01

Rifts that form at the fronts of floating ice shelves that spread into the ocean can trigger major calving events in the ice. The deformation of ice can be modeled as a thin viscous film driven by buoyancy. The front of such a viscous film that propagates over a flat surface with no-slip basal conditions is known to have stable axisymmetric solutions. In contrast, when the fluid propagates under free-slip conditions at the substrate, the front can become unstable to small perturbations if the fluid is sufficiently strain-rate softening. Consequently, the front will develop tongues with a characteristic wavelength that coarsens over time, a pattern that is reminiscent of ice rifts. Here we investigate the stability of a spherical sheet of power-law fluids under free-slip basal conditions. The fluid is discharged at constant flux and axisymmetrically with respect to the pole, and propagates towards the equator. The propagating front in such a situation may become unstable due to its failure to sustain large extensional forces, resulting in the formation of rifts. This study has implications to understanding the cause of patterns that are observed on shells of floating ice in a range of planetary objects, and whether open rifts that sustain life were feasible in snowball earth. Israel Science Foundation 1368/16.

Fluid Mechanics and Homeland Security

NASA Astrophysics Data System (ADS)

Settles, Gary S.

2006-01-01

Homeland security involves many applications of fluid mechanics and offers many opportunities for research and development. This review explores a wide selection of fluids topics in counterterrorism and suggests future directions. Broad topics range from preparedness and deterrence of impending terrorist attacks to detection, response, and recovery. Specific topics include aircraft hardening, blast mitigation, sensors and sampling, explosive detection, microfluidics and labs-on-a-chip, chemical plume dispersal in urban settings, and building ventilation. Also discussed are vapor plumes and standoff detection, nonlethal weapons, airborne disease spread, personal protective equipment, and decontamination. Involvement in these applications requires fluid dynamicists to think across the traditional boundaries of the field and to work with related disciplines, especially chemistry, biology, aerosol science, and atmospheric science.

Experimentally Modeling Black and White Hole Event Horizons via Fluid Flow

NASA Astrophysics Data System (ADS)

Manheim, Marc E.; Lindner, John F.; Manz, Niklas

We will present a scaled down experiment that hydrodynamically models the interaction between electromagnetic waves and black/white holes. It has been mathematically proven that gravity waves in water can behave analogously to electromagnetic waves traveling through spacetime. In this experiment, gravity waves will be generated in a water tank and propagate in a direction opposed to a flow of varying rate. We observe a noticeable change in the wave's spreading behavior as it travels through the simulated horizon with decreased wave speeds up to standing waves, depending on the opposite flow rate. Such an experiment has already been performed in a 97.2 cubic meter tank. We reduced the size significantly to be able to perform the experiment under normal lab conditions.

Model of large pool fires.

PubMed

Fay, J A

2006-08-21

A two zone entrainment model of pool fires is proposed to depict the fluid flow and flame properties of the fire. Consisting of combustion and plume zones, it provides a consistent scheme for developing non-dimensional scaling parameters for correlating and extrapolating pool fire visible flame length, flame tilt, surface emissive power, and fuel evaporation rate. The model is extended to include grey gas thermal radiation from soot particles in the flame zone, accounting for emission and absorption in both optically thin and thick regions. A model of convective heat transfer from the combustion zone to the liquid fuel pool, and from a water substrate to cryogenic fuel pools spreading on water, provides evaporation rates for both adiabatic and non-adiabatic fires. The model is tested against field measurements of large scale pool fires, principally of LNG, and is generally in agreement with experimental values of all variables.

A Reference Section through the Lower Fast-spreading Oceanic Crust in the Wadi Gideah (Sumail ophiolite, Sultanate Oman): Drill Sites GT1A and GT2A within the ICDP Oman Drilling Project

NASA Astrophysics Data System (ADS)

Mueller, S.; Koepke, J.; Garbe-Schoenberg, C. D.; Müller, T.; Mock, D.; Strauss, H.; Schuth, S.; Ildefonse, B.

2017-12-01

In the absence of a complete profile through fast-spreading oceanic crust in modern oceans, we established a reference profile through the whole paleocrust of the Sumail Ophiolite (Oman), which is regarded as the best analogue for fast-spreading oceanic crust on land. For establishing a coherent data set, we sampled the Wadi Gideah in the Wadi-Tayin massif from the mantle section up to the pillow basalts and performed different analytical and structural investigations on the same suite of samples (pool sample concept). The whole sample set contains about 400 samples focusing on both primary magmatic rocks and hydrothermal fault zones to characterize initial formation processes and cooling of the crust. The Wadi Gideah hosts the sites GT1A (lower crust) and GT2A (foliated / layered gabbro transition) where 400 m long cores have been drilled in the frame of the ICDP Oman Drilling Project (OmanDP). Thus, the Wadi Gideah crustal transect is well-suited for providing a reference frame for these two drill cores. Major and trace element data on minerals and rocks reveal in-situ crystallization in the deep crust, thus strongly supporting a hybrid accretion model that is characterized by sheeted sill intrusion in the lower part of the plutonic crust and gabbro glacier features in the upper section. This hybrid model is also supported by results on crystallographic preferred orientations (CPO) of the minerals within the gabbros, which call for distinct formation mechanisms in the upper and lower gabbro sections. A requirement for our hybrid model is significant hydrothermal cooling in the lower crust for the consumption of the latent heat of crystallization. This was facilitated by channelled hydrothermal flow zones, preserved today in faulted zones of extensively altered gabbro cutting both layered and foliated gabbros. These gabbros show higher Sr87/Sr86 ratios if compared to the background gabbro, the presence of late stage minerals (amphibole, oxides, orthopyroxene, apatite) and evidence for hydrous partial melting, as consequence of fluid / rock interaction at very high temperatures. Obviously, these fault zones remained active for channelled fluid flow during the entire cooling stage of the oceanic crust down to low-temperature mineral assemblages.

Influence of Turbulence on the Restraint of Liquid Jets by Surface Tension in Microgravity Investigated

NASA Technical Reports Server (NTRS)

Chato, David J.

2002-01-01

Microgravity poses many challenges to the designer of spacecraft tanks. Chief among these are the lack of phase separation and the need to supply vapor-free liquid or liquidfree vapor to the spacecraft processes that require fluid. One of the principal problems of phase separation is the creation of liquid jets. A jet can be created by liquid filling, settling of the fluid to one end of the tank, or even closing a valve to stop the liquid flow. Anyone who has seen a fountain knows that jets occur in normal gravity also. However, in normal gravity, the gravity controls and restricts the jet flow. In microgravity, with gravity largely absent, surface tension forces must contain jets. To model this phenomenon, a numerical method that tracks the fluid motion and the surface tension forces is required. Jacqmin has developed a phase model that converts the discrete surface tension force into a barrier function that peaks at the free surface and decays rapidly away. Previous attempts at this formulation were criticized for smearing the interface. This can be overcome by sharpening the phase function, double gridding the fluid function, and using a higher order solution for the fluid function. The solution of this equation can be rewritten as two coupled Poisson equations that also include the velocity. After the code was implemented in axisymmetric form and verified by several test cases at the NASA Glenn Research Center, the drop tower runs of Aydelott were modeled. Work last year with a laminar model was found to overpredict Aydelott's results, except at the lowest Reynolds number conditions of 400. This year, a simple turbulence model was implemented by adding a turbulent viscosity based on the mixing-length hypothesis and empirical measurements of previous works. Predictions made after this change was implemented have been much closer to experimentally observed flow patterns and geyser heights. Two model runs is shown. The first, without any turbulence correction, breaks through the free surface and strikes the far end of the tank. In the second, the turbulence spreads the jet momentum over more of the free surface, enabling the surface tension forces to turn the jet back into the bulk liquid. The model geyser height with the second model is 1.1 cm. This is quite close to the 1.5-cm geyser height measured by Aydelott.

Frequency dependent Qα and Qβ in the Umbria-Marche (Italy) region using a quadratic approximation of the coda-normalization method

NASA Astrophysics Data System (ADS)

de Lorenzo, Salvatore; Bianco, Francesca; Del Pezzo, Edoardo

2013-06-01

The coda normalization method is one of the most used methods in the inference of attenuation parameters Qα and Qβ. Since, in this method, the geometrical spreading exponent γ is an unknown model parameter, the most part of studies assumes a fixed γ, generally equal to 1. However γ and Q could be also jointly inferred from the non-linear inversion of coda-normalized logarithms of amplitudes, but the trade-off between γ and Q could give rise to unreasonable values of these parameters. To minimize the trade-off between γ and Q, an inversion method based on a parabolic expression of the coda-normalization equation has been developed. The method has been applied to the waveforms recorded during the 1997 Umbria-Marche seismic crisis. The Akaike criterion has been used to compare results of the parabolic model with those of the linear model, corresponding to γ = 1. A small deviation from the spherical geometrical spreading has been inferred, but this is accompanied by a significant variation of Qα and Qβ values. For almost all the considered stations, Qα smaller than Qβ has been inferred, confirming that seismic attenuation, in the Umbria-Marche region, is controlled by crustal pore fluids.

Coupled Viscous Fluid Flow and Joint Deformation Analysis for Grout Injection in a Rock Joint

NASA Astrophysics Data System (ADS)

Kim, Hyung-Mok; Lee, Jong-Won; Yazdani, Mahmoud; Tohidi, Elham; Nejati, Hamid Reza; Park, Eui-Seob

2018-02-01

Fluid flow modeling is a major area of interest within the field of rock mechanics. The main objective of this study is to gain insight into the performance of grout injection inside jointed rock masses by numerical modeling of grout flow through a single rock joint. Grout flow has been widely simulated using non-Newtonian Bingham fluid characterized by two main parameters of dynamic viscosity and shear yield strength both of which are time dependent. The increasing value of these properties with injection time will apparently affect the parameters representing the grouting performance including grout penetration length and volumetric injection rate. In addition, through hydromechanical coupling a mutual influence between the injection pressure from the one side and the joint opening/closing behavior and the aperture profile variation on the other side is anticipated. This is capable of producing a considerable impact on grout spread within the rock joints. In this study based on the Bingham fluid model, a series of numerical analysis has been conducted using UDEC to simulate the flow of viscous grout in a single rock joint with smooth parallel surfaces. In these analyses, the time-dependent evolution of the grout fluid properties and the hydromechanical coupling have been considered to investigate their impact on grouting performance. In order to verify the validity of these simulations, the results of analyses including the grout penetration length and the injection flow rate were compared with a well-known analytical solution which is available for the simple case of constant grout properties and non-coupled hydraulic analysis. The comparison demonstrated that the grout penetration length can be overestimated when the time-dependent hardening of grout material is not considered. Moreover, due to the HM coupling, it was shown that the joint opening induced by injection pressure may have a considerable increasing impression on the values of penetration length and injected grout volume.

Diffusion tensor magnetic resonance imaging driven growth modeling for radiotherapy target definition in glioblastoma.

PubMed

Jensen, Morten B; Guldberg, Trine L; Harbøll, Anja; Lukacova, Slávka; Kallehauge, Jesper F

2017-11-01

The clinical target volume (CTV) in radiotherapy is routinely based on gadolinium contrast enhanced T1 weighted (T1w + Gd) and T2 weighted fluid attenuated inversion recovery (T2w FLAIR) magnetic resonance imaging (MRI) sequences which have been shown to over- or underestimate the microscopic tumor cell spread. Gliomas favor spread along the white matter fiber tracts. Tumor growth models incorporating the MRI diffusion tensors (DTI) allow to account more consistently for the glioma growth. The aim of the study was to investigate the potential of a DTI driven growth model to improve target definition in glioblastoma (GBM). Eleven GBM patients were scanned using T1w, T2w FLAIR, T1w + Gd and DTI. The brain was segmented into white matter, gray matter and cerebrospinal fluid. The Fisher-Kolmogorov growth model was used assuming uniform proliferation and a difference in white and gray matter diffusion of a ratio of 10. The tensor directionality was tested using an anisotropy weighting parameter set to zero (γ0) and twenty (γ20). The volumetric comparison was performed using Hausdorff distance, Dice similarity coefficient (DSC) and surface area. The median of the standard CTV (CTVstandard) was 180 cm 3 . The median surface area of CTVstandard was 211 cm 2 . The median surface area of respective CTV γ0 and CTV γ20 significantly increased to 338 and 376 cm 2 , respectively. The Hausdorff distance was greater than zero and significantly increased for both CTV γ0 and CTV γ20 with respective median of 18.7 and 25.2 mm. The DSC for both CTV γ0 and CTV γ20 were significantly below one with respective median of 0.74 and 0.72, which means that 74 and 72% of CTVstandard were included in CTV γ0 and CTV γ20, respectively. DTI driven growth models result in CTVs with a significantly increased surface area, a significantly increased Hausdorff distance and decreased overlap between the standard and model derived volume.

Entropy-driven motility of Sinorhizobium meliloti on a semi-solid surface

PubMed Central

Dilanji, Gabriel E.; Teplitski, Max; Hagen, Stephen J.

2014-01-01

Sinorhizobium meliloti growing on soft agar can exhibit an unusual surface spreading behaviour that differs from other bacterial surface motilities. Bacteria in the colony secrete an exopolysaccharide-rich mucoid fluid that expands outward on the surface, carrying within it a suspension of actively dividing cells. The moving slime disperses the cells in complex and dynamic patterns indicative of simultaneous bacterial growth, swimming and aggregation. We find that while flagellar swimming is required to maintain the cells in suspension, the spreading and the associated pattern formation are primarily driven by the secreted exopolysaccharide EPS II, which creates two entropy-increasing effects: an osmotic flow of water from the agar to the mucoid fluid and a crowding or depletion attraction between the cells. Activation of these physical/chemical phenomena may be a useful function for the high molecular weight EPS II, a galactoglucan whose biosynthesis is tightly regulated by the ExpR/SinI/SinR quorum-sensing system: unlike bacterial colonies that spread via bacterium-generated, physical propulsive forces, S. meliloti under quorum conditions may use EPS II to activate purely entropic forces within its environment, so that it can disperse by passively ‘surfing’ on those forces. PMID:24741008

Wetting dynamics of a collapsing fluid hole

NASA Astrophysics Data System (ADS)

Bostwick, J. B.; Dijksman, J. A.; Shearer, M.

2017-01-01

The collapse dynamics of an axisymmetric fluid cavity that wets the bottom of a rotating bucket bound by vertical sidewalls are studied. Lubrication theory is applied to the governing field equations for the thin film to yield an evolution equation that captures the effect of capillary, gravitational, and centrifugal forces on this converging flow. The focus is on the quasistatic spreading regime, whereby contact-line motion is governed by a constitutive law relating the contact-angle to the contact-line speed. Surface tension forces dominate the collapse dynamics for small holes with the collapse time appearing as a power law whose exponent compares favorably to experiments in the literature. Gravity accelerates the collapse process. Volume dependence is predicted and compared with experiment. Centrifugal forces slow the collapse process and lead to complex dynamics characterized by stalled spreading behavior that separates the large and small hole asymptotic regimes.

Hydrothermal plumes over spreading-center axes: Global distributions and geological inferences

NASA Astrophysics Data System (ADS)

Baker, Edward T.; German, Christopher R.; Elderfield, Henry

Seafloor hydrothermal circulation is the principal agent of energy and mass exchange between the ocean and the earth's crust. Discharging fluids cool hot rock, construct mineral deposits, nurture biological communities, alter deep-sea mixing and circulation patterns, and profoundly influence ocean chemistry and biology. Although the active discharge orifices themselves cover only a minuscule percentage of the ridge-axis seafloor, the investigation and quantification of their effects is enhanced as a consequence of the mixing process that forms hydrothermal plumes. Hydrothermal fluids discharged from vents are rapidly diluted with ambient seawater by factors of 104-105 [Lupton et al., 1985]. During dilution, the mixture rises tens to hundreds of meters to a level of neutral buoyancy, eventually spreading laterally as a distinct hydrographic and chemical layer with a spatial scale of tens to thousands of kilometers [e.g., Lupton and Craig, 1981; Baker and Massoth, 1987; Speer and Rona, 1989].

Numerical study of liquid film rupture after droplet spreading on a superhydrophilic surface

NASA Astrophysics Data System (ADS)

Guo, Yisen; Lian, Yongsheng

2017-11-01

When a droplet impacts onto a solid surface, different outcomes can be observed, such as rebound, spreading and splashing. We present numerical simulation results on liquid film rupture after spreading of a droplet impact on a smooth superhydrophilic surface. The Navier-Stokes equations are solved using the variable density pressure projection method and the moment-of-fluid method is used to track the droplet interface. A superhydrophilic or superwetting surface has strong affinity to liquid and we assume the contact angle between solid and liquid is almost zero degree. The droplet spreading and film rupture process occurs in two stages: the droplet first spreads onto the surface and flattens into a thin film as it reaches the maximum diameter, then the film rim becomes unstable and the film rupture initiates from the rim toward the center gradually until the entire film breaks up into secondary droplets. The duration of the film rupture stage is much shorter than the spreading stage. The simulation result is compared with experiment and good agreement is achieved. We investigate the film thickness evolution during spreading and the effect of surface wettability on film rupture.

Accretion mode of oceanic ridges governed by axial mechanical strength

NASA Astrophysics Data System (ADS)

Sibrant, A. L. R.; Mittelstaedt, E.; Davaille, A.; Pauchard, L.; Aubertin, A.; Auffray, L.; Pidoux, R.

2018-04-01

Oceanic spreading ridges exhibit structural changes as a function of spreading rate, mantle temperature and the balance of tectonic and magmatic accretion. The role that these or other processes have in governing the overall shape of oceanic ridges is unclear. Here, we use laboratory experiments to simulate ridge spreading in colloidal aqueous dispersions whose rheology evolves from purely viscous to elastic and brittle when placed in contact with a saline water solution. We find that ridge shape becomes increasingly linear with spreading rate until reaching a minimum tortuosity. This behaviour is predicted by the axial failure parameter ΠF, a dimensionless number describing the balance of brittle and plastic failure of axial lithosphere. Slow-spreading, fault-dominated and fast-spreading, fluid intrusion-dominated ridges on Earth and in the laboratory are separated by the same critical ΠF value, suggesting that the axial failure mode governs ridge geometry. Values of ΠF can also be calculated for different mantle temperatures and applied to other planets or the early Earth. For higher mantle temperatures during the Archaean, our results preclude the predicted formation of large tectonic plates at high spreading velocity.

Plume capture by a migrating ridge: Analog geodynamic experiments

NASA Astrophysics Data System (ADS)

Mendez, J. S.; Hall, P.

2010-12-01

Paleomagnetic data from the Hawaii-Emperor Seamount Chain (HESC) suggests that the Hawaiian hotspot moved rapidly (~40 mm/yr) between 81 - 47 Ma but has remained relatively stationary since that time. This implies that the iconic bend in the HESC may in fact reflect the transition from a period of rapid hotspot motion to a stationary state, rather than a change in motion of the Pacific plate. Tarduno et al. (2009) have suggested that this period of rapid hotspot motion might be the surface expression of a plume conduit returning to a largely vertical orientation after having been “captured” and tilted by a migrating mid-ocean ridge. We report on a series of analog fluid dynamic experiments designed to characterize the interaction between a migrating spreading center and a thermally buoyant mantle plume. Experiments were conducted in a clear acrylic tank (100 cm x 70 cm x 50 cm) filled with commercial grade high-fructose corn syrup. Plate-driven flow is modeled by dragging two sheets of Mylar film (driven by independent DC motors) in opposite directions over the surface of the fluid. Ridge migration is achieved by moving the point at which the mylar sheets diverge using a separate motor drive. Buoyant plume flow is modeled using corn syrup introduced into the bottom of the tank from an external, heated, pressurized reservoir. Small (~2 mm diameter), neutrally buoyant Delrin spheres are mixed into reservoir of plume material to aid in visualization. Plate velocities and ridge migration rate are controlled and plume temperature monitored using LabView software. Experiments are recorded using digital video which is then analyzed using digital image analysis software to track the position and shape of the plume conduit throughout the course of the experiment. The intersection of the plume conduit with the surface of the fluid is taken as an analog for the locus of hotspot volcanism and tracked as a function of time to obtain a hotspot migration rate. Experiments are scaled to the Earth's mantle through a combination of a Peclet number and a plume buoyancy number. A range of spreading rates, ridge migration rates, and plume excess temperatures representative of the Earth are considered.

Does serpentinite carbonation occur during recharge or discharge of hydrothermal fluids? A case of study from the Newfoundland margin

NASA Astrophysics Data System (ADS)

Picazo, Suzanne; Malvoisin, Benjamin; Baumgartner, Lukas P.; Bouvier, Anne-Sophie

2017-04-01

Hydrothermal fluid circulation in extensional systems occurrs along the spreading axis of passive, hyper-extended margins and mid-ocean ridges. The most studied feature resulting from hydrothermal circulation is the sub-seafloor chimneys because of their accessibility. Here we focus on the less studied carbonation process of the associated serpentinites. Carbonation of partially to totally serpentinized peridotite i.e. peridotite/serpentinite replacement by carbonate is usually described as a process of veining or matrix formation but not direct replacement of serpentinite. Carbonates that crystallize in veins or as a matrix in a sedimentary setting is known in near-surface environments like Oman (Kelemen et al, 2011), however the processes and timing of carbonation are still not well understood. This study is examins in detail the onset of carbonation in the footwall of the detachment faults responsible for mantle exhumation in hyper-extended rifted margins. It is based on drilled samples from ODP Leg 210 Site 1277 in the Newfoundland margin. We observed calcite grains in the mesh core replacing serpentine and we measured δ18O from core to rim of the calcite grain using the Secondary Ion Mass Spectrometer (SIMS, SwissSIMS facility, University of Lausanne). Ultimately δ18O measurements lead us to infer the temperature of calcite growth. We suplement the study with equilibrium thermodynamic modeling in an open system where fluid can be transported either upwards or downwards. The model allows us determining the influence of fluid flow direction, temperature, pressure and fluid/rock ratio on the stability of carbonates and serpentine, and thus to discuss if carbonation occurs during recharge or discharge of the fluids. Kelemen, P. B., Matter, J., Streit, E. E., Rudge, J. F., Curry, W. B., & Blusztajn, J. (2011). Rates and mechanisms of mineral carbonation in peridotite: natural processes and recipes for enhanced, in situ CO2 capture and storage. Annual Review of Earth and Planetary Sciences, 39, 545-576.

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review.

PubMed

Ai, Z T; Melikov, A K

2018-07-01

This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Fluid and chemical fluxes along a buried-basement ridge in the eastern Juan de Fuca Ridge flank

NASA Astrophysics Data System (ADS)

Hulme, S.; Wheat, C. G.

2010-12-01

Hydrothermal fluid circulation within oceanic crust at low temperatures affects global biogeochemical cycles, with the volume of fluid circulation rivaling that of the world’s water flux to the oceans from rivers. Our work focuses on the best studied low temperature hydrothermal system on the eastern flank of the Juan de Fuca Ridge where a buried basement ridge 100 km from the active spreading axis has been sampled with a variety of mediums. We use data from deep sea drilling, gravity coring, and submersible operations from five sites along-strike of the buried ridge to better constrain the chemical and fluid fluxes along this transect. A transport (advection-diffusion) model is applied to the data, constraining the volumetric fluid flux per unit length within the oceanic crust from 0.05 and 0.2 m3 y-1 cm-1 and identifying conservative elements within this system. Using an average fluid flux, reactive fluxes are determined for non-conservative elements within basaltic crust for twenty-four chemical species. Conservative species include K, Cl, SO4, Ba, Sr, Cs, Mo, and Y. Only Ca and the rare earth elements Ce and Gd are produced by basaltic basement. The remaining chemical species Mg, Na, ammonium, Li, Rb, Mn, Fe, Co, Zn, Cd, U, La and Yb are all consumed within upper basaltic basement. Fluxes of potentially-bioavailable redox species ammonium, Fe, and Mn into the upper basaltic basement are 3 to 20 nmol y-1cm-2. Possible mechanisms of removal are suggested, placing constraints on microbial metabolic activity and biomineralization.

Rapid spread and association of Schmallenberg virus with ruminant abortions and foetal death in Austria in 2012/2013.

PubMed

Steinrigl, Adolf; Schiefer, Peter; Schleicher, Corina; Peinhopf, Walter; Wodak, Eveline; Bagó, Zoltán; Schmoll, Friedrich

2014-10-15

Schmallenberg virus (SBV) has emerged in summer-autumn 2011 in north-western Europe. Since then, SBV has been continuously spreading over Europe, including Austria, where antibodies to SBV, as well as SBV genome, were first detected in autumn 2012. This study was performed to demonstrate the dynamics of SBV spread within Austria, after its probable first introduction in summer 2012. True seroprevalence estimates for cattle and small ruminates were calculated to demonstrate temporal and regional differences of infection. Furthermore, the probability of SBV genome detection in foetal tissues of aborted or stillborn cattle and small ruminants as well as in allantoic fluid samples from cows with early foetal losses was retrospectively assessed. SBV first reached Austria most likely in July-August 2012, as indicated by retrospective detection of SBV antibodies and SBV genome in archived samples. From August to October 2012, a rapid increase in seroprevalence to over 98% in cattle and a contemporaneous peak in the detection of SBV genome in foetal tissues and allantoic fluid samples was noted, indicating widespread acute infections. Notably, foetal malformations were absent in RT-qPCR positive foetuses at this time of the epidemic. SBV spread within Austrian cattle reached a plateau phase as early as October 2012, without significant regional differences in SBV seroprevalence (98.4-100%). Estimated true seroprevalences among small ruminates were comparatively lower than in cattle and regionally different (58.3-95.6% in October 2012), potentially indicating an eastward spread of the infection, as well as different infection dynamics between cattle and small ruminants. Additionally, the probability of SBV genome detection over time differed significantly between small ruminant and cattle samples subjected to RT-qPCR testing. Copyright © 2014 Elsevier B.V. All rights reserved.

Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Coaxial Supersonic Free-Jet Experiment

NASA Technical Reports Server (NTRS)

Baurle, Robert A.; Edwards, Jack R.

2010-01-01

Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment was designed to study compressible mixing flow phenomenon under conditions that are representative of those encountered in scramjet combustors. The experiment utilized either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state-of-the-art for each modeling approach, and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The initial value chosen for this parameter resulted in an over-prediction of the mixing layer spreading rate for the helium case, but the opposite trend was observed when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid Reynolds-averaged/large-eddy simulations also over-predicted the mixing layer spreading rate for the helium case, while under-predicting the rate of mixing when argon was used as the injectant. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions were suggested as a remedy to this dilemma. Second-order turbulence statistics were also compared to their modeled Reynolds-averaged counterparts to evaluate the effectiveness of common turbulence closure assumptions.

Loki's Castle: Discovery and geology of a black smoker vent field at the Arctic Mid-Ocean Ridge

NASA Astrophysics Data System (ADS)

Pedersen, R.; Thorseth, I. H.; Lilley, M. D.; Barriga, F. J.; Früh-Green, G.; Nakamura, K.

2010-12-01

Previous attempts to locate hydrothermal vent fields and unravel the nature of venting at the ultraslow spreading and magma starved parts of the Arctic Mid Ocean Ridge (AMOR) have been unsuccessful. A black smoker vent field was eventually discovered at the Mohns-Knipovich bend at 73.5°N in 2008, and the field was revisited in 2009 and 2010. The Loki’s Castle vent field is located on the crest of an axial volcanic ridge that is bordered by a tectonic terrain dominated by core complexes to the NW, and a ridge flank that is buried by sediments from the Bear Island Fan to the SE. Fluid compositions are anomalous to other basalt-hosted fields and indicate interactions with sediments at depths. The vent field is associated with an unusually large hydrothermal deposit, which documents that extensive venting occurs at ultraslow spreading ridges despite the strongly reduced magmatic heat budget. ROV surveys have shown that venting occurs in two areas separated by around 100 m. Micro-bathymetry acquired by a Hugin AUV documents that two 20-30 tall mounds that coalesce at the base have developed around the vent sites. The micro-bathymetry also shows that the venting is located above two normal faults that define the NW margin of a rift that runs along the crest of the volcano. The black smoker fluids reach 317 °C, with an end-member SiO2 content of 16 mmol/kg. End-member chlorinity is around 85% of seawater suggesting that the fluids have phase-separated at depth. The fluid compositions indicate that the rock-water reactions occur around 2 km below the seafloor. The crustal thickness is estimated to be 4 +/- 0.5 km in the area. Whereas the depth of the reaction zone is comparable with faster spreading ridges, the fraction of crust cooled convectively by hydrothermal circulation is two times that of vent fields at ridges with normal crustal thickness.

Sedimentation from Particle-Laden Plumes in Stratified Fluid

NASA Astrophysics Data System (ADS)

Sutherland, Bruce; Hong, Youn Sub

2015-11-01

Laboratory experiments are performed in which a mixture of particles, water and a small amount of dye is continuously injected upwards from a localized source into a uniformly stratified ambient. The particle-fluid mixture initially rises as a forced plume (which in most cases is buoyant, though in some cases due to high particle concentration is negative-buoyant at the source), reaches a maximum height, collapses upon itself and then spreads as a radial intrusion. The particles are observed to rain out of the descending intrusion and settle upon the floor of the tank. Using light attenuation, the depth of the particle mound is measured after the experiment has run for a fixed amount of time. In most experiments the distribution of particles is found to be approximately axisymmetric about the source with a near Gaussian structure for height as a function of radius. The results are compared with a code that combines classical plume theory with an adaptation to stratified fluids of the theory of Carey, Sigurdsson and Sparks (JGR, 1988) for the spread and fall of particles from a particle-laden plume impacting a rigid ceiling. Re-entrainment of particles into the plume is also taken into account.

The positive impact of general vitamin D food fortification policy on vitamin D status in a representative adult Finnish population: evidence from an 11-y follow-up based on standardized 25-hydroxyvitamin D data.

PubMed

Jääskeläinen, Tuija; Itkonen, Suvi T; Lundqvist, Annamari; Erkkola, Maijaliisa; Koskela, Tapani; Lakkala, Kaisa; Dowling, Kirsten G; Hull, George Lj; Kröger, Heikki; Karppinen, Jaro; Kyllönen, Eero; Härkänen, Tommi; Cashman, Kevin D; Männistö, Satu; Lamberg-Allardt, Christel

2017-06-01

Background: A systematic vitamin D fortification of fluid milk products and fat spreads was started in 2003 in Finland to improve vitamin D status. Objective: We investigated the effects of the vitamin D fortification policy on vitamin D status in Finland between 2000 and 2011. Design: Serum 25-hydroxyvitamin D [S-25(OH)D] concentrations of a nationally representative sample comprising 6134 and 4051 adults aged ≥30 y from the Health 2000 and Health 2011 surveys, respectively, were standardized according to the Vitamin D Standardization Program with the use of liquid chromatography-tandem mass spectrometry. Linear and logistic regression models were used to assess the change in S-25(OH)D concentrations. Results: Between 2000 and 2011, the mean S-25(OH)D increased from 48 nmol/L (95% CI: 47, 48 nmol/L) to 65 nmol/L (95% CI: 65, 66 nmol/L) ( P < 0.001). The prevalence of vitamin D supplement users increased from 11% to 41% ( P < 0.001). When analyzing the effect of fortification of fluid milk products, we focused on supplement nonusers. The mean increase in S-25(OH)D in daily fluid milk consumers ( n = 1017) among supplement nonusers was 20 nmol/L (95% CI: 19, 21 nmol/L), which was 6 nmol/L higher than nonconsumers ( n = 229) (14 nmol/L; 95% CI: 12, 16 nmol/L) ( P < 0.001). In total, 91% of nonusers who consumed fluid milk products, fat spreads, and fish based on Finnish nutrition recommendations reached S-25(OH)D concentrations >50 nmol/L in 2011. Conclusions: The vitamin D status of the Finnish adult population has improved considerably during the time period studied. The increase is mainly explained by food fortification, especially of fluid milk products, and augmented vitamin D supplement use. Other factors, such as the difference in the ultraviolet radiation index between 2000 and 2011, may partly explain the results. When consuming vitamin D sources based on the nutritional recommendations, vitamin D status is sufficient [S-25(OH)D ≥50 nmol/L], and supplementation is generally not needed. © 2017 American Society for Nutrition.

The basal part of the Oman ophiolitic mantle: a fossil Mantle Wedge?

NASA Astrophysics Data System (ADS)

Prigent, Cécile; Guillot, Stéphane; Agard, Philippe; Godard, Marguerite; Chauvet, Alain; Dubacq, Benoit; Monié, Patrick; Yamato, Philippe

2014-05-01

Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. Fluids involved in the hydration of the oceanic lithosphere and in the presence of a secondary boninitic and andesitic volcanism may provide a way to discriminate between these two interpretations: are they descending near-axis hydrothermal fluxes (first model) or ascending from a subducting slab (second model)? We herein focus on the base of the ophiolitic mantle in order to characterize the origin of fluids and decipher hydration processes. Samples were taken along hecto- to kilometre-long sections across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that, unlike the generally refractory character of Oman harzburgites, all the basal mantle rocks display secondary crystallization of clinopyroxene and amphibole through metasomatic processes. The microstructures and the chronology of these secondary mineralizations (clinopyroxene, pargasitic amphibole, antigorite and then lizardite/chrysotile) suggest that these basal rocks have been affected by cooling from mantle temperatures (<1200°C) to low-T serpentinisation (<300°C). Furthermore, major elements required to crystallize these minerals and the observed fluid-mobile elements (FMEs) enrichments in the clinopyroxenes and in the amphiboles (B, Pb, Sr), as well as in the serpentines (B, Sr, Rb, Ba, As), are consistent with amphibolite-derived fluids (Ishikawa et al., 2005) and cannot be easily explained by other sources. Based on these observations, we propose a geodynamic model in which intense and continuous metasomatism of the cooling base of the ophiolitic mantle is due to the release of fluids coming from the progressive dehydration of underlying amphibolitic rocks. This process is compatible with the progressive subduction of the Arabian margin during the Upper Cretaceous (e.g., HP-LT units history, and tectonic structures observed on top of it). The basal part of the Oman ophiolite would thus represent a fossil incipient mantle wedge.

The effects of capillary forces on the axisymmetric propagation of two-phase, constant-flux gravity currents in porous media

NASA Astrophysics Data System (ADS)

Golding, Madeleine J.; Huppert, Herbert E.; Neufeld, Jerome A.

2013-03-01

The effects of capillary forces on the propagation of two-phase, constant-flux gravity currents in a porous medium are studied analytically and numerically in an axisymmetric geometry. The fluid within a two-phase current generally only partially saturates the pore space it invades. For long, thin currents, the saturation distribution is set by the vertical balance between gravitational and capillary forces. The capillary pressure and relative permeability of the fluid in the current depend on this saturation. The action of capillary forces reduces the average saturation, thereby decreasing the relative permeability throughout the current. This results in a thicker current, which provides a steeper gradient to drive flow, and a more blunt-nose profile. The relative strength of gravity and capillary forces remains constant within a two-phase gravity current fed by a constant flux and spreading radially, due to mass conservation. For this reason, we use an axisymmetric representation of the framework developed by Golding et al. ["Two-phase gravity currents in porous media," J. Fluid Mech. 678, 248-270 (2011)], 10.1017/jfm.2011.110, to investigate the effect on propagation of varying the magnitude of capillary forces and the pore-size distribution. Scaling analysis indicates that axisymmetric two-phase gravity currents fed by a constant flux propagate like t1/2, similar to their single-phase counterparts [S. Lyle, H. E. Huppert, M. Hallworth, M. Bickle, and A. Chadwick, "Axisymmetric gravity currents in a porous medium," J. Fluid Mech. 543, 293-302 (2005)], 10.1017/S0022112005006713, with the effects of capillary forces encapsulated in the constant of proportionality. As a practical application of our new concepts and quantitative evaluations, we discuss the implications of our results for the process of carbon dioxide (CO2) sequestration, during which gravity currents consisting of supercritical CO2 propagate in rock saturated with aqueous brine. We apply our two-phase model including capillary forces to quantitatively assess seismic images of CO2 spreading at Sleipner underneath the North Sea.

Shallow velocity structure across the Mariana arc

NASA Astrophysics Data System (ADS)

Tait, S.; Kaminski, E. C.; Carazzo, G.; Limare, A.

2016-12-01

Atmospheric injection of volcanic ash during explosive eruptions is controlled by the dynamics of a volcanic column and associated umbrella cloud, which are subject to a wind field, and are connected by a turbulent fountain which initiates horizontal spreading at the neutral buoyancy level. We present a new theoretical and experimental study of an axisymmetric turbulent umbrella cloud intruding horizontally at its neutral buoyancy level into a static environment linearly stratified in density. The intrusion is fed by a constant horizontal volume flux (Q0) at a finite radius (R0), where it has a constant thickness (2H0). The characteristics of the fountain (R0, H0, Q0) derive from a vertical forced plume (source momentum and buoyancy fluxes Mi , Fi) and environmental stratification N. Buoyancy drives horizontal flow but, despite high Reynolds number, impedes entrainment of ambient fluid into the umbrella cloud. Turbulent stresses are nevertheless crucial in the momentum balance. Our theory highlights the vertical profiles of density and velocity within the current of which we present experimental measurements. Initially, current buoyancy is opposed by the inertia of the ambient fluid, and current radius (RN(t)) grows linearly in time. Subsequently, turbulent drag opposes buoyancy, and the current breaks down into two parts: i) between the source and a transition radius (R0T(t)), a steady region where current thickness (2H) and mean velocity (U) are time-independent and decreasing functions of r ; ii), a contiguous unsteady « frontal » region, between the transition radius and the front (RTN), in which the current thickens. The theory predicts current shape and an asymptotic spreading behaviour (RN t^5/9) which agree well with experimental data. Our analysis of satellite observations of several sustained plinian events including the Pinatubo 1991 climactic eruption shows that both the initial and asymptotic spreading regimes predicted by the model are present.

The Dynamics of Volcanic Umbrella Clouds

NASA Astrophysics Data System (ADS)

Tait, S.; Kaminski, E. C.; Carazzo, G.; Limare, A.

2017-12-01

Atmospheric injection of volcanic ash during explosive eruptions is controlled by the dynamics of a volcanic column and associated umbrella cloud, which are subject to a wind field, and are connected by a turbulent fountain which initiates horizontal spreading at the neutral buoyancy level. We present a new theoretical and experimental study of an axisymmetric turbulent umbrella cloud intruding horizontally at its neutral buoyancy level into a static environment linearly stratified in density. The intrusion is fed by a constant horizontal volume flux (Q0) at a finite radius (R0), where it has a constant thickness (2H0). The characteristics of the fountain (R0, H0, Q0) derive from a vertical forced plume (source momentum and buoyancy fluxes Mi , Fi) and environmental stratification N. Buoyancy drives horizontal flow but, despite high Reynolds number, impedes entrainment of ambient fluid into the umbrella cloud. Turbulent stresses are nevertheless crucial in the momentum balance. Our theory highlights the vertical profiles of density and velocity within the current of which we present experimental measurements. Initially, current buoyancy is opposed by the inertia of the ambient fluid, and current radius (RN(t)) grows linearly in time. Subsequently, turbulent drag opposes buoyancy, and the current breaks down into two parts: i) between the source and a transition radius (R0T(t)), a steady region where current thickness (2H) and mean velocity (U) are time-independent and decreasing functions of r ; ii), a contiguous unsteady « frontal » region, between the transition radius and the front (RTN), in which the current thickens. The theory predicts current shape and an asymptotic spreading behaviour (RN t^5/9) which agree well with experimental data. Our analysis of satellite observations of several sustained plinian events including the Pinatubo 1991 climactic eruption shows that both the initial and asymptotic spreading regimes predicted by the model are present.

The Multibasic Cleavage Site in H5N1 Virus Is Critical for Systemic Spread along the Olfactory and Hematogenous Routes in Ferrets

PubMed Central

Schrauwen, Eefje J. A.; Herfst, Sander; Leijten, Lonneke M.; van Run, Peter; Bestebroer, Theo M.; Linster, Martin; Bodewes, Rogier; Kreijtz, Joost H. C. M.; Rimmelzwaan, Guus F.; Osterhaus, Albert D. M. E.; Fouchier, Ron A. M.; Kuiken, Thijs

2012-01-01

The route by which highly pathogenic avian influenza (HPAI) H5N1 virus spreads systemically, including the central nervous system (CNS), is largely unknown in mammals. Especially, the olfactory route, which could be a route of entry into the CNS, has not been studied in detail. Although the multibasic cleavage site (MBCS) in the hemagglutinin (HA) of HPAI H5N1 viruses is a major determinant of systemic spread in poultry, the association between the MBCS and systemic spread in mammals is less clear. Here we determined the virus distribution of HPAI H5N1 virus in ferrets in time and space—including along the olfactory route—and the role of the MBCS in systemic replication. Intranasal inoculation with wild-type H5N1 virus revealed extensive replication in the olfactory mucosa, from which it spread to the olfactory bulb and the rest of the CNS, including the cerebrospinal fluid (CSF). Virus spread to the heart, liver, pancreas, and colon was also detected, indicating hematogenous spread. Ferrets inoculated intranasally with H5N1 virus lacking an MBCS demonstrated respiratory tract infection only. In conclusion, HPAI H5N1 virus can spread systemically via two different routes, olfactory and hematogenous, in ferrets. This systemic spread was dependent on the presence of the MBCS in HA. PMID:22278228

Revisiting Temporal Markov Chains for Continuum modeling of Transport in Porous Media

NASA Astrophysics Data System (ADS)

Delgoshaie, A. H.; Jenny, P.; Tchelepi, H.

2017-12-01

The transport of fluids in porous media is dominated by flow­-field heterogeneity resulting from the underlying permeability field. Due to the high uncertainty in the permeability field, many realizations of the reference geological model are used to describe the statistics of the transport phenomena in a Monte Carlo (MC) framework. There has been strong interest in working with stochastic formulations of the transport that are different from the standard MC approach. Several stochastic models based on a velocity process for tracer particle trajectories have been proposed. Previous studies have shown that for high variances of the log-conductivity, the stochastic models need to account for correlations between consecutive velocity transitions to predict dispersion accurately. The correlated velocity models proposed in the literature can be divided into two general classes of temporal and spatial Markov models. Temporal Markov models have been applied successfully to tracer transport in both the longitudinal and transverse directions. These temporal models are Stochastic Differential Equations (SDEs) with very specific drift and diffusion terms tailored for a specific permeability correlation structure. The drift and diffusion functions devised for a certain setup would not necessarily be suitable for a different scenario, (e.g., a different permeability correlation structure). The spatial Markov models are simple discrete Markov chains that do not require case specific assumptions. However, transverse spreading of contaminant plumes has not been successfully modeled with the available correlated spatial models. Here, we propose a temporal discrete Markov chain to model both the longitudinal and transverse dispersion in a two-dimensional domain. We demonstrate that these temporal Markov models are valid for different correlation structures without modification. Similar to the temporal SDEs, the proposed model respects the limited asymptotic transverse spreading of the plume in two-dimensional problems.

Infective factors of male infertility among Nigerians.

PubMed

Ogunbanjo, B O; Osoba, A O; Ochei, J

1989-03-01

Seminal fluid from 782 Nigerian males with complaints of infertility were examined with respect to infective agents and indices such as sperm count, motility and the presence of a significant number of pus cells. Various infective agents were recovered from 54 (7%) of the patients, while in 25% of the remaining patients, a significant number of pus cells was present, with associated abnormal seminal fluid indices. Our findings indicate that seminal fluids constitute an important medium for the spread of various infective agents, and that genital infections by these infective agents, sexually and non-sexually transmitted, may be responsible for a good percentage of infertility cases in Nigerian males.

On the role of radiation and dimensionality in predicting flow opposed flame spread over thin fuels

NASA Astrophysics Data System (ADS)

Kumar, Chenthil; Kumar, Amit

2012-06-01

In this work a flame-spread model is formulated in three dimensions to simulate opposed flow flame spread over thin solid fuels. The flame-spread model is coupled to a three-dimensional gas radiation model. The experiments [1] on downward spread and zero gravity quiescent spread over finite width thin fuel are simulated by flame-spread models in both two and three dimensions to assess the role of radiation and effect of dimensionality on the prediction of the flame-spread phenomena. It is observed that while radiation plays only a minor role in normal gravity downward spread, in zero gravity quiescent spread surface radiation loss holds the key to correct prediction of low oxygen flame spread rate and quenching limit. The present three-dimensional simulations show that even in zero gravity gas radiation affects flame spread rate only moderately (as much as 20% at 100% oxygen) as the heat feedback effect exceeds the radiation loss effect only moderately. However, the two-dimensional model with the gas radiation model badly over-predicts the zero gravity flame spread rate due to under estimation of gas radiation loss to the ambient surrounding. The two-dimensional model was also found to be inadequate for predicting the zero gravity flame attributes, like the flame length and the flame width, correctly. The need for a three-dimensional model was found to be indispensable for consistently describing the zero gravity flame-spread experiments [1] (including flame spread rate and flame size) especially at high oxygen levels (>30%). On the other hand it was observed that for the normal gravity downward flame spread for oxygen levels up to 60%, the two-dimensional model was sufficient to predict flame spread rate and flame size reasonably well. Gas radiation is seen to increase the three-dimensional effect especially at elevated oxygen levels (>30% for zero gravity and >60% for normal gravity flames).

Lectures on combustion theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burstein, S.Z.; Lax, P.D.; Sod, G.A.

1978-09-01

Eleven lectures are presented on mathematical aspects of combustion: fluid dynamics, deflagrations and detonations, chemical kinetics, gas flows, combustion instability, flame spread above solids, spark ignition engines, burning rate of coal particles and hydrocarbon oxidation. Separate abstracts were prepared for three of the lectures. (DLC)

Experiments on point plumes in a rotating environment

NASA Astrophysics Data System (ADS)

Frank, Daria; Landel, Julien; Dalziel, Stuart; Linden, Paul

2016-11-01

Motivated by the Deepwater Horizon oil spill in the Gulf of Mexico we study the dynamics of point plumes in a stratified and homogeneous rotating environment. To this end, we conduct small-scale experiments in the laboratory on salt water and bubble plumes over a wide range of Rossby numbers. The rotation modifies the entrainment into the plume and also inhibits the lateral spreading of the plume fluid which leads to various instabilities in the flow. In particular, we focus on the plume behaviour in the near-source region (where the plume is dominated by the source conditions) and at intermediate water depths, e.g., lateral intrusions at the neutral buoyancy level in the stratified environment. One of the striking features in the rotating environment is the anticyclonic precession of the plume axis which leads to an enhanced dispersion of the plume fluid in the ambient and which is absent in the non-rotating system. In this talk, we present our experimental results and develop simple models to explain the observed plume dynamics.

Geochemical Tracers of Processes Affecting the Formation of Seafloor Hydrothermal Fluids and Deposits in the Manus Back-Arc Basin

DTIC Science & Technology

2009-02-01

21 ° N East Pacific Rise . In Hydrothermal Processes at Seafloor Spreading Centers (ed. P. Rona, K. Boström, L. Laubier, and K. L. Smith), pp... hydrothermal fluids ( 21 ° N East Pacific Rise ) are taken from Mitra et al (1994) and Klinkhammer et al. (1994). The chemical composition...Measures C. I., Walden B., and Weiss R. F. (1985) Chemistry of submarine hydrothermal solutions at 21 ° N , East

Modeling and simulation of dense cloud dispersion in urban areas by means of computational fluid dynamics.

PubMed

Scargiali, F; Grisafi, F; Busciglio, A; Brucato, A

2011-12-15

The formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tank cars, may occur inside urban areas so the problem arises of their consequences evaluation. Due to the semi-confined nature of the dispersion site simplified models may often be inappropriate. As an alternative, computational fluid dynamics (CFD) has the potential to provide realistic simulations even for geometrically complex scenarios since the heavy gas dispersion process is described by basic conservation equations with a reduced number of approximations. In the present work a commercial general purpose CFD code (CFX 4.4 by Ansys(®)) is employed for the simulation of dense cloud dispersion in urban areas. The simulation strategy proposed involves a stationary pre-release flow field simulation followed by a dynamic after-release flow and concentration field simulations. In order to try a generalization of results, the computational domain is modeled as a simple network of straight roads with regularly distributed blocks mimicking the buildings. Results show that the presence of buildings lower concentration maxima and enlarge the side spread of the cloud. Dispersion dynamics is also found to be strongly affected by the quantity of heavy-gas released. Copyright © 2011 Elsevier B.V. All rights reserved.

Spreading of a surfactant monolayer on a thin liquid film: Onset and evolution of digitated structures.

PubMed

Matar, Omar K.; Troian, Sandra M.

1999-03-01

We describe the response of an insoluble surfactant monolayer spreading on the surface of a thin liquid film to small disturbances in the film thickness and surfactant concentration. The surface shear stress, which derives from variations in surfactant concentration at the air-liquid interface, rapidly drives liquid and surfactant from the source toward the distal region of higher surface tension. A previous linear stability analysis of a quasi-steady state solution describing the spreading of a finite strip of surfactant on a thin Newtonian film has predicted only stable modes. [Dynamics in Small Confining Systems III, Materials Research Society Symposium Proceedings, edited by J. M. Drake, J. Klafter, and E. R. Kopelman (Materials Research Society, Boston, 1996), Vol. 464, p. 237; Phys. Fluids A 9, 3645 (1997); O. K. Matar Ph.D. thesis, Princeton University, Princeton, NJ, 1998]. A perturbation analysis of the transient behavior, however, has revealed the possibility of significant amplification of disturbances in the film thickness within an order one shear time after the onset of flow [Phys. Fluids A 10, 1234 (1998); "Transient response of a surfactant monolayer spreading on a thin liquid film: Mechanism for amplification of disturbances," submitted to Phys. Fluids]. In this paper we describe the linearized transient behavior and interpret which physical parameters most strongly affect the disturbance amplification ratio. We show how the disturbances localize behind the moving front and how the inclusion of van der Waals forces further enhances their growth and lifetime. We also present numerical solutions to the fully nonlinear 2D governing equations. As time evolves, the nonlinear system sustains disturbances of longer and longer wavelength, consistent with the quasi-steady state and transient linearized descriptions. In addition, for the parameter set investigated, disturbances consisting of several harmonics of a fundamental wavenumber do not couple significantly. The system eventually singles out the smallest wavenumber disturbance in the chosen set. The summary of results to date seems to suggest that the fingering process may be a transient response which nonetheless has a dramatic influence on the spreading process since the digitated structures redirect the flux of liquid and surfactant to produce nonuniform surface coverage. (c) 1999 American Institute of Physics.

Towards a Model of Reactive-Cracking: the Role of Reactions, Elasticity and Surface Energy Driven Flow in Poro-elastic Media

NASA Astrophysics Data System (ADS)

Evans, O.; Spiegelman, M. W.; Wilson, C. R.; Kelemen, P. B.

2016-12-01

Many critical processes can be described by reactive fluid flow in brittle media, including hydration/alteration of oceanic plates near spreading ridges, chemical weathering, and dehydration/decarbonation of subducting plates. Such hydration reactions can produce volume changes that may induce stresses large enough to drive fracture in the rock, in turn exposing new reactive surface and modifying the permeability. A better understanding of this potentially rich feedback could also be critical in the design of engineered systems for geologic carbon sequestration. To aid understanding of these processes we have developed a macroscopic continuum description of reactive fluid flow in an elastically deformable porous media. We explore the behaviour of this model by considering a simplified hydration reaction (e.g. olivine + H20 -> serpentine + brucite). In a closed system, these hydration reactions will continue to consume available fluids until the permeability reaches zero, leaving behind it a highly stressed residuum. Our model demonstrates this limiting behaviour, and that the elastic stresses generated are large enough to cause failure/fracture of the host rock. Whilst it is understood that `reactive fracture' is an important mechanism for the continued evolution of this process, it is also proposed that imbibition/surface energy driven flow may play a role. Through a simplified set of computational experiments, we investigate the relative roles of elasticity and surface energy in both a non-reactive purely poro-elastic framework, and then in the presence of reaction. We demonstrate that surface energy can drive rapid diffusion of porosity, thus allowing the reaction to propagate over larger areas. As we expect both surface energy and fracture/failure to be of importance in these processes, we plan to integrate the current model into one that allows for fracture once critical stresses are exceeded.

Computational Fluid Dynamics Modeling of Supersonic Coherent Jets for Electric Arc Furnace Steelmaking Process

NASA Astrophysics Data System (ADS)

Alam, Morshed; Naser, Jamal; Brooks, Geoffrey; Fontana, Andrea

2010-12-01

Supersonic coherent gas jets are now used widely in electric arc furnace steelmaking and many other industrial applications to increase the gas-liquid mixing, reaction rates, and energy efficiency of the process. However, there has been limited research on the basic physics of supersonic coherent jets. In the present study, computational fluid dynamics (CFD) simulation of the supersonic jet with and without a shrouding flame at room ambient temperature was carried out and validated against experimental data. The numerical results show that the potential core length of the supersonic oxygen and nitrogen jet with shrouding flame is more than four times and three times longer, respectively, than that without flame shrouding, which is in good agreement with the experimental data. The spreading rate of the supersonic jet decreased dramatically with the use of the shrouding flame compared with a conventional supersonic jet. The present CFD model was used to investigate the characteristics of the supersonic coherent oxygen jet at steelmaking conditions of around 1700 K (1427 °C). The potential core length of the supersonic coherent oxygen jet at steelmaking conditions was 1.4 times longer than that at room ambient temperature.

Not spreading in reverse: The dewetting of a liquid film into a single drop

PubMed Central

Edwards, Andrew M. J.; Ledesma-Aguilar, Rodrigo; Newton, Michael I.; Brown, Carl V.; McHale, Glen

2016-01-01

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet—a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction. PMID:27704042

Not spreading in reverse: The dewetting of a liquid film into a single drop.

PubMed

Edwards, Andrew M J; Ledesma-Aguilar, Rodrigo; Newton, Michael I; Brown, Carl V; McHale, Glen

2016-09-01

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet-a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.

Propagation of a viscous thin film over an elastic membran

NASA Astrophysics Data System (ADS)

Zheng, Zhong; Griffiths, Ian; Stone, Howard

2016-11-01

We study the buoyancy-driven spreading of a thin viscous film over a thin elastic membrane. Neglecting the effects of membrane bending and the membrane weight, we study the case of constant fluid injection and obtain a system of coupled partial differential equations to describe the shape of the air-liquid interface, and the deformation and the radial tension of the stretched membrane. We obtain self-similar solutions to describe the dynamics. In particular, in the early time period, the dynamics is dominated by buoyancy-driven spreading of the liquid film, and membrane stretching is a response to the buoyancy-controlled distribution of liquid weight; the location of the liquid front obeys the power-law form rf (t) t 1 / 2 . However, in the late time period, the system is quasi-steady, the air-liquid interface is flat, and membrane stretching, due to the liquid weight, causes the spreading of the liquid front; the location of the front obeys a different power-law form rf (t) t 1 / 4 before the edge effects of the membrane become significant. In addition, we report laboratory experiments for constant fluid injection using different viscous liquids and thin elastic membranes. Very good agreement is obtained between the theory and experiments.

Morphology-Patterned Anisotropic Wetting Surface for Fluid Control and Gas-Liquid Separation in Microfluidics.

PubMed

Wang, Shuli; Yu, Nianzuo; Wang, Tieqiang; Ge, Peng; Ye, Shunsheng; Xue, Peihong; Liu, Wendong; Shen, Huaizhong; Zhang, Junhu; Yang, Bai

2016-05-25

This article shows morphology-patterned stripes as a new platform for directing flow guidance of the fluid in microfluidic devices. Anisotropic (even unidirectional) spreading behavior due to anisotropic wetting of the underlying surface is observed after integrating morphology-patterned stripes with a Y-shaped microchannel. The anisotropic wetting flow of the fluid is influenced by the applied pressure, dimensions of the patterns, including the period and depth of the structure, and size of the channels. Fluids with different surface tensions show different flowing anisotropy in our microdevice. Moreover, the morphology-patterned surfaces could be used as a microvalve, and gas-water separation in the microchannel was realized using the unidirectional flow of water. Therefore, benefiting from their good performance and simple fabrication process, morphology-patterned surfaces are good candidates to be applied in controlling the fluid behavior in microfluidics.

Information spreading dynamics in hypernetworks

NASA Astrophysics Data System (ADS)

Suo, Qi; Guo, Jin-Li; Shen, Ai-Zhong

2018-04-01

Contact pattern and spreading strategy fundamentally influence the spread of information. Current mathematical methods largely assume that contacts between individuals are fixed by networks. In fact, individuals are affected by all his/her neighbors in different social relationships. Here, we develop a mathematical approach to depict the information spreading process in hypernetworks. Each individual is viewed as a node, and each social relationship containing the individual is viewed as a hyperedge. Based on SIS epidemic model, we construct two spreading models. One model is based on global transmission, corresponding to RP strategy. The other is based on local transmission, corresponding to CP strategy. These models can degenerate into complex network models with a special parameter. Thus hypernetwork models extend the traditional models and are more realistic. Further, we discuss the impact of parameters including structure parameters of hypernetwork, spreading rate, recovering rate as well as information seed on the models. Propagation time and density of informed nodes can reveal the overall trend of information dissemination. Comparing these two models, we find out that there is no spreading threshold in RP, while there exists a spreading threshold in CP. The RP strategy induces a broader and faster information spreading process under the same parameters.

Low Reynolds number suspension gravity currents.

PubMed

Saha, Sandeep; Salin, Dominique; Talon, Laurent

2013-08-01

The extension of a gravity current in a lock-exchange problem, proceeds as square root of time in the viscous-buoyancy phase, where there is a balance between gravitational and viscous forces. In the presence of particles however, this scenario is drastically altered, because sedimentation reduces the motive gravitational force and introduces a finite distance and time at which the gravity current halts. We investigate the spreading of low Reynolds number suspension gravity currents using a novel approach based on the Lattice-Boltzmann (LB) method. The suspension is modeled as a continuous medium with a concentration-dependent viscosity. The settling of particles is simulated using a drift flux function approach that enables us to capture sudden discontinuities in particle concentration that travel as kinematic shock waves. Thereafter a numerical investigation of lock-exchange flows between pure fluids of unequal viscosity, reveals the existence of wall layers which reduce the spreading rate substantially compared to the lubrication theory prediction. In suspension gravity currents, we observe that the settling of particles leads to the formation of two additional fronts: a horizontal front near the top that descends vertically and a sediment layer at the bottom which aggrandises due to deposition of particles. Three phases are identified in the spreading process: the final corresponding to the mutual approach of the two horizontal fronts while the laterally advancing front halts indicating that the suspension current stops even before all the particles have settled. The first two regimes represent a constant and a decreasing spreading rate respectively. Finally we conduct experiments to substantiate the conclusions of our numerical and theoretical investigation.

Serpentinization of Olivine by Seawater: A Flow-Through Experiment

NASA Astrophysics Data System (ADS)

Gouze, P.; Luquot, L.; Andreani, M.; Godard, M.; Gibert, B.

2011-12-01

The mantle exposed at slow spreading ridges is pervasively serpentinized, down to ca. 5km according to geophysical data. The onset and durability of this hydration process require efficient penetration and renewal of fluids at the mineral-fluid interface. However, the mechanisms of fluid penetration are still poorly understood. Moreover, serpentinization is exovolumic, if a mass-conservative system is assumed, or chemical elements are leached out to conserve rock volume. Thus, the extent of serpentinization depends of the system capacity to create space and/or to drive mass transfers. In order to investigate these hydrodynamic and chemical mechanisms, we did a laboratory experiment during which seawater was injected in a sintered San Carlos olivine sample at conditions representative of low temperature ultramafic hydrothermal systems. The percolation-reaction experiment was carried out at 19 MPa and 190°C; the initial water flow was set at 0.2 mL/h then decreased down to 0.06 mL/h after 8 days. During the experiment (23 days), permeability decreased continuously. The composition of the outlet fluid varied strongly during the first 24h of the experiment, then reached equilibrium values. The high Si concentrations in outlet fluids indicated steady olivine dissolution, while their low Fe and Mg concentrations suggested precipitation of Fe- and Mg-rich mineral phases. The reacted sample acquired a reddish brown color, indicating oxidation reactions occurred. Optical observation and SEM imaging revealed the presence of a soft white material filling the pores of the reacted sample. It was identified as a poorly crystallized serpentine type material by AEM/TEM analyses. This proto-serpentine is intimately associated to <100 nm Fe-oxide patches (probably hematite) growing on the olivine surface. We interpret the precipitation of this proto-serpentine together with Fe-oxides throughout the sample as marking the early stages of serpentinization. The fluid composition not being modified by changes in fluid flow, we posit that olivine serpentinization is not controlled by elemental transport and/or by chemical kinetics, but takes place at-equilibrium; the reaction velocity is very fast and independent on the changes in the reaction surface area. Indeed, mass balance calculations indicate that more than 15 wt. % olivine was dissolved while the same mass of proto-serpentine was formed; concurrently, porosity decreased from ˜ 12% to 5 %. We infer that the structure of the newly formed proto-serpentine resulted in the clogging of fluid paths and explain the decrease of permeability during experiments. Yet the loose structure of the proto-serpentine allows maintaining a connected pore structure ensuring the perennial renewing (diffusion and/or advection) of the reactants at the reaction surfaces. These experimental results are used to constrain numerical reactive transport models and better understand the scale and efficiency of serpentinization reactions (effective reaction rates in porous/fractured media) at the scale of spreading ridges.

Boundaries of the thoracic paravertebral space: potential risks and benefits of the thoracic paravertebral block from an anatomical perspective.

PubMed

Bouman, Esther A C; Sieben, Judith M; Balthasar, Andrea J R; Joosten, Elbert A; Gramke, Hans-Fritz; van Kleef, Maarten; Lataster, Arno

2017-10-01

Thoracic paravertebral block (TPVB) may be an alternative to thoracic epidural analgesia. A detailed knowledge of the anatomy of the TPV-space (TPVS), content and adnexa is essential in understanding the clinical consequences of TPVB. The exploration of the posterior TPVS accessibility in this study allows (1) determination of the anatomical boundaries, content and adnexa, (2) description of an ultrasound-guided spread of low and high viscous liquid. In two formalin-fixed specimens, stratification of the several layers and the 3D-architecture of the TPVS were dissected, observed and photographed. In a third unembalmed specimen, ultrasound-guided posterolateral injections at several levels of the TPVS were performed with different fluids. TPVS communicated with all surrounding spaces including the segmental dorsal intercostal compartments (SDICs) and the prevertebral space. TPVS transitions to the SDICs were wide, whereas the SDICs showed narrowed transitions to the lateral intercostal spaces at the costal angle. Internal subdivision of the TPVS in a subendothoracic and an extra-pleural compartment by the endothoracic fascia was not observed. Caudally injected fluids spread posteriorly to the costodiaphragmatic recess, showing segmental intercostal and slight prevertebral spread. Our detailed anatomical study shows that TPVS is a potential space continuous with the SDICs. The separation of the TPVS in a subendothoracic and an extra-pleural compartment by the endothoracic fascia was not observed. Based on the ultrasound-guided liquid spread we conclude that the use of a more lateral approach might increase the probability of intravascular puncture or catheter position.

Landslide Spreading, Impulse Water Waves and Modelling of the Vajont Rockslide

NASA Astrophysics Data System (ADS)

Crosta, Giovanni B.; Imposimato, Silvia; Roddeman, Dennis

2016-06-01

Landslides can occur in different environments and can interact with or fall into water reservoirs or open sea with different characteristics. The subaerial evolution and the transition from subaerial to subaqueous conditions can strongly control the landslide evolution and the generated impulse waves, and consequently the final hazard zonation. We intend to model the landslide spreading, the impact with the water surface and the generation of the impulse wave under different 2D and 3D conditions and settings. We verify the capabilities of a fully 2D and 3D FEM ALE approach to model and analyse near-field evolution. To this aim we validate the code against 2D laboratory experiments for different Froude number conditions (Fr = 1.4, 3.2). Then the Vajont rockslide (Fr = 0.26-0.75) and the consequent impulse wave are simulated in 2D and 3D. The sliding mass is simulated as an elasto-plastic Mohr-Coulomb material and the lake water as a fully inviscid low compressibility fluid. The rockslide model is validated against field observations, including the total duration, the profile and internal geometry of the final deposit, the maximum water run-up on the opposite valley flank and on the rockslide mass. 2D models are presented for both the case of a dry valley and that of the impounded lake. The set of fully 3D simulations are the first ones available and considering the rockslide evolution, propagation and interaction with the water reservoir. Advantages and disadvantages of the modelling approach are discussed.

Containment of subsurface contaminants

DOEpatents

Corey, John C.

1994-01-01

A barrier for reducing the spread of a plume of subsurface contaminants. The apparatus includes a well system for injecting a fluid, such as air, just outside and below the periphery of the plume. The fluid is injected at a pressure sufficient to lower the hydraulic conductivity of the soil from the point of injection to the surface thus establishing a curtain-like barrier to groundwater movement. The barrier is established upgradient of the plume to divert groundwater away, or preferably completely around the plume to reduce the flow of groundwater into or out of the plume. The barrier enables the remediation of the confined contamination and then, when the injection of the fluid is halted, the barrier quickly dissipates.

Numerical modeling of the effects of fire-induced convection and fire-atmosphere interactions on wildfire spread and fire plume dynamics

NASA Astrophysics Data System (ADS)

Sun, Ruiyu

It is possible due to present day computing power to produce a fluid dynamical physically-based numerical solution to wildfire behavior, at least in the research mode. This type of wildfire modeling affords a flexibility and produces details that are not available in either current operational wildfire behavior models or field experiments. However before using these models to study wildfire, validation is necessary, and model results need to be systematically and objectively analyzed and compared to real fires. Plume theory and data from the Meteotron experiment, which was specially designed to provide results from measurements for the theoretical study of a convective plume produced by a high heat source at the ground, are used here to evaluate the fire plume properties simulated by two numerical wildfire models, the Fire Dynamics Simulator or FDS, and the Clark coupled atmosphere-fire model. The study indicates that the FDS produces good agreement with the plume theory and the Meteotron results. The study also suggests that the coupled atmosphere-fire model, a less explicit and ideally less computationally demanding model than the FDS; can produce good agreement, but that the agreement is sensitive to the method of putting the energy released from the fire into the atmosphere. The WFDS (Wildfire and wildland-urban interface FDS), an extension of the FDS to the vegetative fuel, and the Australian grass fire experiments are used to evaluate and improve the UULES-wildfire coupled model. Despite the simple fire parameterization in the UULES-wildfire coupled model, the fireline is fairly well predicted in terms of both shape and location in the simulation of Australian grass fire experiment F19. Finally, the UULES-wildfire coupled model is used to examine how the turbulent flow in the atmospheric boundary layer (ABL) affects the growth of the grass fires. The model fires showed significant randomness in fire growth: Fire spread is not deterministic in the ABL, and a probabilistic prediction method is warranted. Of the two contributors to the variability in fire growth in the grass fire simulations in the ABL, fire-induced convection, as opposed to the turbulent ABL wind, appears to be the more important one. One mechanism associated with enhanced fire-induced flow is the downdraft behind the frontal fireline. The downdraft is the direct result of the random interaction between the fire plume and the large eddies in the ABL. This study indicates a connection between fire variability in rate of spread and area burnt and so-called convective velocity scale, and it may be possible to use this boundary-layer scale parameter to account for the effects of ABL turbulence on fire spread and fire behavior in today's operational fire prediction systems.

Computational Study of Droplet Trains Impacting a Smooth Solid Surface

NASA Astrophysics Data System (ADS)

Markt, David, Jr.; Pathak, Ashish; Raessi, Mehdi; Lee, Seong-Young; Zhao, Emma

2017-11-01

The study of droplet impingement is vital to understanding the fluid dynamics of fuel injection in modern internal combustion engines. One widely accepted model was proposed by Yarin and Weiss (JFM, 1995), developed from experiments of single trains of ethanol droplets impacting a substrate. The model predicts the onset of splashing and the mass ejected upon splashing. In this study, using an in-house 3D multiphase flow solver, the experiments of Yarin and Weiss were computationally simulated. The experimentally observed splashing threshold was captured by the simulations, thus validating the solver's ability to accurately simulate the splashing dynamics. Then, we performed simulations of cases with multiple droplet trains, which have high relevance to dense fuel sprays, where droplets impact within the spreading diameters of their neighboring droplets, leading to changes in splashing dynamics due to interactions of spreading films. For both single and multi-train simulations the amount of splashed mass was calculated as a function of time, allowing a quantitative comparison between the two cases. Furthermore, using a passive scalar the amount of splashed mass per impinging droplet was also calculated. This work is supported by the Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) and the Department of Defense, Tank and Automotive Research, Development, and Engineering Center (TARDEC), under Award Number DE-EE0007292.

Modeling of non-stationary local response on impurity penetration in plasma

NASA Astrophysics Data System (ADS)

Tokar, M. Z.; Koltunov, M.

2012-04-01

In fusion devices, strongly localized intensive sources of impurities may arise unexpectedly, e.g., if the wall is excessively demolished by hot plasma particles, or can be created deliberately through impurity seeding. The spreading of impurities from such sources both along and perpendicular to the magnetic field is affected by coulomb collisions with background particles, ionization, acceleration by electric field, etc. Simultaneously, the plasma itself can be significantly disturbed by these interactions. To describe self-consistently the impurity spreading process and the plasma response, three-dimensional fluid equations for the particle, parallel momentum, and energy balances of various plasma components are solved by reducing them to ordinary differential equations for the time evolution of several parameters characterizing the solutions in principal details: the maximum densities of impurity ions of different charges, the dimensions both along and across the magnetic field of the shells occupied by these particles, the characteristic temperatures of all plasma components, and the densities of the main ions and electrons in different shells. The results of modeling for penetration of lithium singly charged particles in tokamak edge plasma are presented. A new mechanism for the condensation phenomenon and formation of cold dense plasma structures, implying an outstanding role of coulomb collisions between main and impurity ions, is proposed.

Analysis of zolpidem in postmortem fluids and tissues using ultra-performance liquid chromatography-mass spectrometry.

DOT National Transportation Integrated Search

2014-02-01

Zolpidem is a nonbenzodiazepine sedative hypnotic drug used for the short-term treatment of insomnia. Its : use is common and wide-spread. While quite effective in producing sedation, zolpidem has potentially : hazardous side effects when put in the ...

Impact of scaling and body movement on contaminant transport in airliner cabins

NASA Astrophysics Data System (ADS)

Mazumdar, Sagnik; Poussou, Stephane B.; Lin, Chao-Hsin; Isukapalli, Sastry S.; Plesniak, Michael W.; Chen, Qingyan

2011-10-01

Studies of contaminant transport have been conducted using small-scale models. This investigation used validated Computational Fluid Dynamics (CFD) to examine if a small-scale water model could reveal the same contaminant transport characteristics as a full-scale airliner cabin. But due to similarity problems and the difficulty of scaling the geometry, a perfect scale up from a small water model to an actual air model was found to be impossible. The study also found that the seats and passengers tended to obstruct the lateral transport of the contaminants and confine their spread to the aisle of the cabin. The movement of a crew member or a passenger could carry a contaminant in its wake to as many rows as the crew member or passenger passed. This could be the reason why a SARS infected passenger could infect fellow passengers who were seated seven rows away. To accurately simulate the contaminant transport, the shape of the moving body should be a human-like model.

The geochemical controls on vent fluids from the Lucky Strike vent field, Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Von Damm, K. L.; Bray, A. M.; Buttermore, L. G.; Oosting, S. E.

1998-08-01

Hydrothermal vent fluids were collected from the Lucky Strike site at 37°17'N on the Mid-Atlantic Ridge in both 1993 and 1996. Seven vents were sampled with the DSV Alvin in 1993 and six vents were sampled in 1996 using the ROV Jason during the LUSTRE '96 Cruise. As three of the vents were sampled in both 1993 and in 1996, a time series of vent fluid chemistry is also reported. Measured temperatures ranged from 202 to 333°C at the 1618-1726 m depth of the vent field, which is located on Lucky Strike Seamount. These fluids are either equal to or less than the local bottom seawater in chlorinity. While the range in fluid compositions at Lucky Strike is generally within that observed elsewhere, the unusual aspects of the fluid chemistries are the relatively high pH and low Fe, Mn, Li and Zn. We attribute this, as well as an usually low Sr/Ca ratio, to reaction with a highly altered substrate. The high Si and Cu contents suggest a deep, as well as hot, source for these fluids. The fluid compositions therefore suggest formation by super-critical phase separation at a depth not less than 1300 m below the seafloor, and reaction with a relatively oxic, and previously altered, substrate. There is temporal variability in some of the vent fluid compositions as Li, K, Ca and Fe concentrations have increased in some of the vents, as has the Fe/Mn (molar) ratio, although the chlorinities have remained essentially constant from 1993 to 1996. While there is not a simple relationship between vent fluid compositions (or temperatures) and distance from the lava lake at the summit of the seamount, the vent fluids from many of the vents can be shown to be related to others, often at distances >200 m. The most southeasterly vents (Eiffel Tower and the Marker/Mounds vents) are distinct in chlorinity and other chemical parameters from the rest of the vents, although closely related to each other within the southeastern area. Similarly all of the vents not in this one area, appear closely related to each other. This suggests one or two source fluids for many of the vents, as is also inferred to be the case at TAG, but which is in contrast to observations on faster spreading ridges. This may suggest inherently different plumbing for hydrothermal systems at slower versus faster spreading ridges.

A new method for the analysis of fire spread modeling errors

Treesearch

Francis M. Fujioka

2002-01-01

Fire spread models have a long history, and their use will continue to grow as they evolve from a research tool to an operational tool. This paper describes a new method to analyse two-dimensional fire spread modeling errors, particularly to quantify the uncertainties of fire spread predictions. Measures of error are defined from the respective spread distances of...

An exploration for hydrothermal plume evolution using the AUV "URASHIMA" with fluid sampling system at southern Mariana Trough

NASA Astrophysics Data System (ADS)

Noguchi, T.; Sunamura, M.; Yamamoto, H.; Fukuba, T.; Okino, K.; Sugiyama, T.; Okamura, K.

2009-12-01

Hydrothermal fluids contain high concentration of anoxic chemical species, i.e. methane and hydrogen sulfide, helium-3, and heavy metals derived from the rock-water interaction. During the hydothermal plume spreading, it is known that several chemical species are oxidized which include available energy source for microorganism, however, few results have been reported on the spatial variation of both of chemical and microbiological concentration and species. In the southern Mariana Trough, some site surveys have been conducted with CTD hydrocasts, the manned submersible, and ROVs since 2003. In this field, three hydrothermal vent sites were discovered within the small area, where the chemistry of each hydrothermal fluid was different from each other. These differences of chemistry are prospected to affect the individual plume evolution. In order to discuss the each hydrothermal plume evolution, we conducted high-resolution plume mapping by the AUV "URASHIMA" with some chemical sensors. Additionally, we loaded 24 bottles of water sampler for the geochemical and microbial analysis. During this cruise, we detected hydrothermal plume anomalies derived from each hydrothermal site with the highly precise topographic results. Based on the results, we will discuss the relationships between the spreading of hydrothermal plume (geochemical evolution) and the ecology of plume microbes.

Experimental and theoretical study of the spread of fluid from a point source on an inclined incontinence bed-pad.

PubMed

Eames, I; Small, I; Frampton, A; Cottenden, A M

2003-01-01

The spread of fluid from a localized source on to a flat fibrous sheet is studied. The sheet is inclined at an angle, alpha, to the horizontal, and the areal flux of the fluid released is Qa. A new experimental study is described where the dimensions of the wetted region are measured as a function of time t, Qa and alpha (>0). The down-slope length, Y, grows according to Y approximately (Qa t)(2/3) (sin alpha)(1/3); for high discharge rates and low angles of inclination, the cross-slope width, X, grows as approximately (Qa t)(1/2), while for low discharge rates or high angles of inclination, the cross-slope transport is dominated by infiltration and X approximately 2(2Ks psi* t)(1/2), where Ks is the saturated permeability and psi* is the characteristic value of capillary pressure. A scaling analysis of the underlying non-linear advection diffusion equation describing the infiltration process confirms many of the salient features of the flow observed. Good agreement is observed between the collapse of the numerical solutions and experimental results. The broader implications of these results for incontinence bed-pad research are briefly discussed.

Effects of rewiring strategies on information spreading in complex dynamic networks

NASA Astrophysics Data System (ADS)

Ally, Abdulla F.; Zhang, Ning

2018-04-01

Recent advances in networks and communication services have attracted much interest to understand information spreading in social networks. Consequently, numerous studies have been devoted to provide effective and accurate models for mimicking information spreading. However, knowledge on how to spread information faster and more widely remains a contentious issue. Yet, most existing works are based on static networks which limit the reality of dynamism of entities that participate in information spreading. Using the SIR epidemic model, this study explores and compares effects of two rewiring models (Fermi-Dirac and Linear functions) on information spreading in scale free and small world networks. Our results show that for all the rewiring strategies, the spreading influence replenishes with time but stabilizes in a steady state at later time-steps. This means that information spreading takes-off during the initial spreading steps, after which the spreading prevalence settles toward its equilibrium, with majority of the population having recovered and thus, no longer affecting the spreading. Meanwhile, rewiring strategy based on Fermi-Dirac distribution function in one way or another impedes the spreading process, however, the structure of the networks mimic the spreading, even with a low spreading rate. The worst case can be when the spreading rate is extremely small. The results emphasize that despite a big role of such networks in mimicking the spreading, the role of the parameters cannot be simply ignored. Apparently, the probability of giant degree neighbors being informed grows much faster with the rewiring strategy of linear function compared to that of Fermi-Dirac distribution function. Clearly, rewiring model based on linear function generates the fastest spreading across the networks. Therefore, if we are interested in speeding up the spreading process in stochastic modeling, linear function may play a pivotal role.

Proteomic analysis of cerebrospinal fluid from children with central nervous system tumors identifies candidate proteins relating to tumor metastatic spread.

PubMed

Spreafico, Filippo; Bongarzone, Italia; Pizzamiglio, Sara; Magni, Ruben; Taverna, Elena; De Bortoli, Maida; Ciniselli, Chiara M; Barzanò, Elena; Biassoni, Veronica; Luchini, Alessandra; Liotta, Lance A; Zhou, Weidong; Signore, Michele; Verderio, Paolo; Massimino, Maura

2017-07-11

Central nervous system (CNS) tumors are the most common solid tumors in childhood. Since the sensitivity of combined cerebrospinal fluid (CSF) cytology and radiological neuroimaging in detecting meningeal metastases remains relatively low, we sought to characterize the CSF proteome of patients with CSF tumors to identify biomarkers predictive of metastatic spread. CSF samples from 27 children with brain tumors and 13 controls (extra-CNS non-Hodgkin lymphoma) were processed using core-shell hydrogel nanoparticles, and analyzed with reverse-phase liquid chromatography/electrospray tandem mass spectrometry (LC-MS/MS). Candidate proteins were identified with Fisher's exact test and/or a univariate logistic regression model. Reverse phase protein array (RPPA), Western blot (WB), and ELISA were used in the training set and in an independent set of CFS samples (60 cases, 14 controls) to validate our discovery findings. Among the 558 non-redundant proteins identified by LC-MS/MS, 147 were missing from the CSF database at http://www.biosino.org. Fourteen of the 26 final top-candidate proteins were chosen for validation with WB, RPPA and ELISA methods. Six proteins (type 1 collagen, insulin-like growth factor binding protein 4, procollagen C-endopeptidase enhancer 1, glial cell-line derived neurotrophic factor receptor α2, inter-alpha-trypsin inhibitor heavy chain 4, neural proliferation and differentiation control protein-1) revealed the ability to discriminate metastatic cases from controls. Combining a unique dataset of CSFs from pediatric CNS tumors with a novel enabling nanotechnology led us to identify CSF proteins potentially related to metastatic status.

Ocean acidification affects parameters of immune response and extracellular pH in tropical sea urchins Lytechinus variegatus and Echinometra luccunter.

PubMed

Leite Figueiredo, Débora Alvares; Branco, Paola Cristina; Dos Santos, Douglas Amaral; Emerenciano, Andrews Krupinski; Iunes, Renata Stecca; Shimada Borges, João Carlos; Machado Cunha da Silva, José Roberto

2016-11-01

The rising concentration of atmospheric CO 2 by anthropogenic activities is changing the chemistry of the oceans, resulting in a decreased pH. Several studies have shown that the decrease in pH can affect calcification rates and reproduction of marine invertebrates, but little attention has been drawn to their immune response. Thus this study evaluated in two adult tropical sea urchin species, Lytechinus variegatus and Echinometra lucunter, the effects of ocean acidification over a period of 24h and 5days, on parameters of the immune response, the extracellular acid base balance, and the ability to recover these parameters. For this reason, the phagocytic capacity (PC), the phagocytic index (PI), the capacity of cell adhesion, cell spreading, cell spreading area of phagocytic amebocytes in vitro, and the coelomic fluid pH were analyzed in animals exposed to a pH of 8.0 (control group), 7.6 and 7.3. Experimental pH's were predicted by IPCC for the future of the two species. Furthermore, a recovery test was conducted to verify whether animals have the ability to restore these physiological parameters after being re-exposed to control conditions. Both species presented a significant decrease in PC, in the pH of coelomic fluid and in the cell spreading area. Besides that, Echinometra lucunter showed a significant decrease in cell spreading and significant differences in coelomocyte proportions. The recovery test showed that the PC of both species increased, also being below the control values. Even so, they were still significantly higher than those exposed to acidified seawater, indicating that with the re-establishment of the pH value the phagocytic capacity of cells tends to restore control conditions. These results demonstrate that the immune system and the coelomic fluid pH of these animals can be affected by ocean acidification. However, the effects of a short-term exposure can be reversible if the natural values ​​are re-established. Thus, the effects of ocean acidification could lead to consequences for pathogen resistance and survival of these sea urchin species. Copyright © 2016 Elsevier B.V. All rights reserved.

Potential for Carbon Dioxide Sequestration and Enhanced Oil Recovery in the Vedder Formation, Greeley Field, San Joaquin Valley, California.

NASA Astrophysics Data System (ADS)

Jameson, S.

2015-12-01

Most scientists agree that greenhouse gases (GHG) such as carbon dioxide (CO2), Methane (CH4), and nitrous oxide (N2O) are major contributors to the global warming trend and climate change. One effort to mitigate anthropogenic sourced CO2 is through carbon capture and sequestration. Depleted oil and gas reservoirs due to their known trapping capability, in-place infrastructure, and proximity to carbon emission sources are good candidates for possible CO2 storage. The Vedder formation is one of three reservoirs identified in the San Joaquin Basin that meets standards for possible storage. An analysis of net fluid production data (produced minus injected) from discovery to the present is used to determine the reservoir volume available for CO2 storage. Data regarding reservoir pressure response to injection and production of fluids include final shut-in pressures from drill stem test, static bottom-hole pressure measurements from well completion histories, and idle well fluid level measurements for recent pressure data. Proprietary experimental pressure, volume and temperature data (PVT), gas oil ratios (GOR), well by well permeability, porosity, and oil gravity, and relative permeability and perforation intervals are used to create static and dynamic multiphase fluid flow models. All data collected was logged and entered into excel spreadsheets and mapping software to create subsurface structure, reservoir thickness and pressure maps, cross sections, production/injection charts on a well-by-well basis, and both static and dynamic flow models. This data is used to determine storage capacity and the amount of pressure variance within the field to determine how the reservoir will react to CO2 injection and to gain insight into the subsurface fluid movement of CO2. Results indicate a homogenous field with a storage capacity of approximately 26 Million Metric Tons of CO2. Analysis of production by stream and pressure change through time indicates a strong water drive. The connection to a large and active aquifer allows pressure changes to be spread over large areas. Flow modeling will help to determine the impact that the water influx will have on storage capacity and EOR production potential.

Numerical simulation of tidal dispersion around a coastal headland

USGS Publications Warehouse

Signell, R.P.; Geyer, W. Rockwell; Cheng, Ralph T.

1990-01-01

Tidal flows around headlands can exhibit strong spatial gradients in the Eulerian currents, resulting in complex Lagrangian trajectories and dispersion of the vertically integrated flow. This typically occurs when the horizontal length scale of the headland is comparable to or smaller than the tidal excursion. The effects of these headlands on dispersion are investigated using a depthaveraged hydrodynamic model combined with a particle tracking model. The dispersion of patches of fluid is found to vary by more than an order of magnitude, depending both on position and tidal phase at the time of release. This is due to the infrequent interaction of material with the strongly sheared flow at the tip of the headland, where flow separation occurs during times of maximum tidal flow. Spreading of these patches over many tidal cycles is not Gaussian, but rather shows a patchy, streaky structure.

Deterministic ripple-spreading model for complex networks.

PubMed

Hu, Xiao-Bing; Wang, Ming; Leeson, Mark S; Hines, Evor L; Di Paolo, Ezequiel

2011-04-01

This paper proposes a deterministic complex network model, which is inspired by the natural ripple-spreading phenomenon. The motivations and main advantages of the model are the following: (i) The establishment of many real-world networks is a dynamic process, where it is often observed that the influence of a few local events spreads out through nodes, and then largely determines the final network topology. Obviously, this dynamic process involves many spatial and temporal factors. By simulating the natural ripple-spreading process, this paper reports a very natural way to set up a spatial and temporal model for such complex networks. (ii) Existing relevant network models are all stochastic models, i.e., with a given input, they cannot output a unique topology. Differently, the proposed ripple-spreading model can uniquely determine the final network topology, and at the same time, the stochastic feature of complex networks is captured by randomly initializing ripple-spreading related parameters. (iii) The proposed model can use an easily manageable number of ripple-spreading related parameters to precisely describe a network topology, which is more memory efficient when compared with traditional adjacency matrix or similar memory-expensive data structures. (iv) The ripple-spreading model has a very good potential for both extensions and applications.

Titanite chronology, thermometry, and speedometry of ultrahigh-temperature (UHT) calc-silicates from south Madagascar: U-Pb dates, Zr temperatures, and lengthscales of trace-element diffusion

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2017-12-01

Calc-silicate rocks are often overlooked as sources of pressure-temperature-time data in granulite-UHT metamorphic terranes due to the strong dependence of calc-silicate mineral assemblages on complex fluid compositions and a lack of thermodynamic data on common high-temperature calc-silicate minerals such as scapolite. In the Ediacaran-Cambrian UHT rocks of southern Madagascar, clinopyroxene-scapolite-feldspar-quartz-zircon-titanite calc-silicate rocks are wide-spread. U-Pb dates of 540-520 Ma from unaltered portions of titanite correspond to cooling of the rocks through upper-amphibolite facies and indicate UHT metamorphism occurred before 540 Ma. Zr concentrations in these domains preserve growth temperatures of 900-950 °C, consistent with peak temperatures calculated by pseudosection modeling of nearby osumilite-bearing gneisses. Younger U-Pb dates (510-490 Ma) correspond to fluid-mediated Pb loss from titanite grains, which occurred below their diffusive Pb-closure temperature, along fractures. The extent of fluid alteration is seen clearly in back-scattered electron images and Zr-, Al-, Fe-, Ce-, and Nb-concentration maps. Laser-ablation depth profiling of idioblastic titanite grains shows preserved Pb diffusion profiles at grain rims, but there is no evidence for Zr diffusion, indicating that it was effectively immobile even at UHT.

Analogue Models Of Volcanic Spreading At Mt. Vesuvius

NASA Astrophysics Data System (ADS)

De Matteo, Ada; Castaldo, Raffaele; D'Auria, Luca; James, Michael; Lane, Steve; Massa, Bruno; Pepe, Susi; Tizzani, Pietro

2015-04-01

Somma-Vesuvius is a quiescent strato-volcano of the Neapolitan district, southern Italy, for which various geophysical and geological evidences (e.g. geodetic measurements, geological and structural data, seismic profiles interpretations and surface deformation analysis with Differential Interferometric Synthetic Aperture Radar (DInSAR)) indicate ongoing spreading deformation. In this research we investigate the spreading deformation and associated surface deformation pattern by performing analogue experiments and comparing the results with actual ground deformation as measured using DInSAR data recorded between 1992 and 2010. Somma-Vesuvius consists of a volcanic cone (Gran Cono) lying within an asymmetric caldera (Somma). The Somma caldera is the result of at least 7 Plinian eruptions, the last of which was the 79 CE. Pompeii eruption. The current cone of Mt. Vesuvius grew within the caldera in the following centuries as the effect of continued explosive and effusive activity of the volcano. The volcano lies on a substratum consisting of a Mesozoic carbonatic basement, overlapped by Holocene clastic sediments and volcanic rocks. Our analogue models were built to simulate the shape of the Somma-Vesuvius top a scale of about 1:100000, emplaced on a sand layer (brittle behaviour) laid on a silicone layer (ductile behaviour). Models are based on the Fluid-dynamics Dimensionless Analysis (FDA), according to the Buckingham-Π theorem. In this context, we considered few dimensionless parameters that allowed the setting of a reliable scaled model. To represent the complex Somma-Vesuvius geometry, an asymmetric model was built by setting a truncated cone (mimicking the topography of Somma edifice) topped by another small cone (mimicking the Gran Cono) shifted off the axis of the main cone. Different experiments were carried out in which the thickness of the basal sand layer and of the silicone one were varied. To quantify the vertical and horizontal displacements the models were monitored with three synchronised digital cameras, enabling sequential 3-D models to be derived using a photogrammetric technique. Finally, our models were compared with the 1992 - 2010 SBAS DInSAR measurements of ground deformations obtained using ERS-ENVISAT satellite images. The results show that analogue models are able to reproduce different styles of volcanic spreading and to reproduce the observed surface and deformation pattern. At the end our models show a deformation rather similar to the actual deformation pattern of the Somma-Vesuvius, both in the direction and in the intensity. Further studies will be devoted at find the best combination of parameters (silicone layer thickness and viscosity) to fit observations and to introduce a tridimensional rigid based topography. These studies will be implemented also with new structural and surface deformation (DinSAR) data and will be integrated with a numerical modelling.

Rumor spreading model with the different attitudes towards rumors

NASA Astrophysics Data System (ADS)

Hu, Yuhan; Pan, Qiuhui; Hou, Wenbing; He, Mingfeng

2018-07-01

Rumor spreading has a profound influence on people's well-being and social stability. There are many factors influencing rumor spreading. In this paper, we recommended an assumption that among the common mass there are three attitudes towards rumors: to like rumor spreading, to dislike rumor spreading, and to be hesitant (or neutral) to rumor spreading. Based on such an assumption, a Susceptible-Hesitating-Affected-Resistant(SHAR) model is established, which considered individuals' different attitudes towards rumor spreading. We also analyzed the local and global stability of rumor-free equilibrium and rumor-existence equilibrium, calculated the basic reproduction number of our model. With numerical simulations, we illustrated the effect of parameter changes on rumor spreading, analyzing the parameter sensitivity of the model. The results of the theoretical analysis and numerical simulations illustrated the conclusions of this study. People having different attitudes towards rumors may play different roles in the process of rumor spreading. It was surprising to find, in our research, that people who hesitate to spread rumors have a positive effect on the spread of rumors.

Microseismicity Induced by Fluid Pressure Drop (Laboratory Study)

NASA Astrophysics Data System (ADS)

Turuntaev, Sergey; Zenchenko, Evgeny; Melchaeva, Olga

2013-04-01

Pore pressure change in saturated porous rocks may result in its fracturing (Maury et Fourmaintraux, 1993) and corresponding microseismic event occurrences. Microseismicity due to fluid injection is considered in numerous papers (Maxwell, 2010, Shapiro et al., 2005). Another type of the porous medium fracturing is related with rapid pore pressure drop at some boundary. The mechanism of such fracturing was considered by (Khristianovich, 1985) as a model of sudden coal blowing and by (Alidibirov, Panov, 1998) as a model of volcano eruptions. If the porous saturated medium has a boundary where it directly contacted with fluid under the high pressure (in a hydraulic fracture or in a borehole), and the pressure at that boundary is dropped, the conditions for tensile cracks can be achieved at some distance from the boundary. In the paper, the results of experimental study of saturated porous sample fracturing due to pore pressure rapid drop are discussed. The samples (82 mm high, ∅60 mm) were made of quartz sand, which was cemented by "liquid glass" glue with mass fraction 1%. The sample (porosity 35%, uniaxial unconfined compression strength 2.5 MPa) was placed in a mould and saturated by oil. The upper end of the sample contacted with the mould upper lid, the lower end contacted with fluid. The fluid pressure was increased to 10 MPa and then discharged through the bottom nipple. The pressure increases/drops were repeated 30-50 times. Pore pressure and acoustic emission (AE) were registered by transducers mounted into upper and bottom lids of the mould. It was found, that AE sources (corresponded to microfracturing) were spreading from the open end to the closed end of the sample, and that maximal number of AE events was registered at some distance from the opened end. The number of AE pulses increased with every next pressure drop, meanwhile the number of pulses with high amplitudes diminished. It was found that AE maximal rate corresponded to the fluid pressure gradient maximal values. The model of AE relation with the pore pressure gradient was considered based on the following assumptions: AE event occurred when the pore pressure gradient reaches some critical value; the critical value varies and can be described by Weibull distribution. Permeability variation during the fluid pressure drop was estimated by means of fluid pressure data and pore-elastic equation solution for small time intervals (0.01 sec). The study showed possibility to solve both a direct problem of microseismicity variation relation with fluid pressure changes and an inverse problem of defining permeability by registering microseismic activity variation in particular volume of porous medium alongside with pore pressure measurements at some point.

Estimating wildland fire rate of spread in a spatially nonuniform environment

Treesearch

Francis M Fujioka

1985-01-01

Estimating rate of fire spread is a key element in planning for effective fire control. Land managers use the Rothermel spread model, but the model assumptions are violated when fuel, weather, and topography are nonuniform. This paper compares three averaging techniques--arithmetic mean of spread rates, spread based on mean fuel conditions, and harmonic mean of spread...

Isotopic constraints on ice age fluids in active geothermal systems: Reykjanes, Iceland

NASA Astrophysics Data System (ADS)

Pope, Emily C.; Bird, Dennis K.; Arnórsson, Stefán; Fridriksson, Thráinn; Elders, Wilfred A.; Fridleifsson, Gudmundur Ó.

2009-08-01

The Reykjanes geothermal system is located on the landward extension of the Mid-Atlantic Ridge in southwest Iceland, and provides an on-land proxy to high-temperature hydrothermal systems of oceanic spreading centers. Previous studies of elemental composition and salinity have shown that Reykjanes geothermal fluids are likely hydrothermally modified seawater. However, δD values of these fluids are as low as -23‰, which is indicative of a meteoric water component. Here we constrain the origin of Reykjanes hydrothermal solutions by analysis of hydrogen and oxygen isotope compositions of hydrothermal epidote from geothermal drillholes at depths between 1 and 3 km. δDEPIDOTE values from wells RN-8, -9, -10 and -17 collectively range from -60 to -78‰, and δ18OEPIDOTE in these wells are between -3.0 and 2.3‰. The δD values of epidote generally increase along a NE trend through the geothermal field, whereas δ18O values generally decrease, suggesting a southwest to northeast migration of the geothermal upflow zone with time that is consistent with present-day temperatures and observed hydrothermal mineral zones. For comparative analysis, the meteoric-water dominated Nesjavellir and Krafla geothermal systems, which have a δDFLUID of ˜ -79‰ and -89‰, respectively, show δDEPIDOTE values of -115‰ and -125‰. In contrast, δDEPIDOTE from the mixed meteoric-seawater Svartsengi geothermal system is -68‰; comparable to δDEPIDOTE from well RN-10 at Reykjanes. Stable isotope compositions of geothermal fluids in isotopic equilibrium with the epidotes at Reykjanes are computed using published temperature dependent hydrogen and oxygen isotope fractionation curves for epidote-water, measured isotope composition of the epidotes and temperatures approximated from the boiling point curve with depth. Calculated δD and δ18O of geothermal fluids are less than 0‰, suggesting that fluids of meteoric or glacial origin are a significant component of the geothermal solutions. Additionally, δDFLUID values in equilibrium with geothermal epidote are lower than those of modern-day fluids, whereas calculated δ18OFLUID values are within range of the observed fluid isotope composition. We propose that modern δDEPIDOTE and δDFLUID values are the result of diffusional exchange between hydrous alteration minerals that precipitated from glacially-derived fluids early in the evolution of the Reykjanes system and modern seawater-derived geothermal fluids. A simplified model of isotope exchange in the Reykjanes geothermal system, in which the average starting δDROCK value is -125‰ and the water to rock mass ratio is 0.25, predicts a δDFLUID composition within 1‰ of average measured values. This model resolves the discrepancy between fluid salinity and isotope composition of Reykjanes geothermal fluids, explains the observed disequilibrium between modern fluids and hydrothermal epidote, and suggests that rock-fluid interaction is the dominant control over the evolution of fluid isotope composition in the hydrothermal system.

Omega-3 fatty acids enriched chocolate spreads using soybean and coconut oils.

PubMed

Jeyarani, T; Banerjee, T; Ravi, R; Krishna, A G Gopala

2015-02-01

Chocolate spreads were developed by incorporating two different soybean oil margarines, fat phases prepared using 85 % soybean oil (M1) and 1:1 blend of soybean oil and coconut oil (M2) with commercial palm stearin. Eight formulations were tried by varying skim milk powder (SMP)/fluid skimmed milk (FSM), type of fats (M1, M2, a commercial margarine and a table spread), sugar and cocoa powder and their quality characteristics were compared with a commercial hazelnut cocoa spread. The moisture and fat content were 5-6.1 % and 31.4-32.8 % for formulations with SMP and 21.5-24.7 % and 15.6-21.4 % respectively for those with FSM. Rheological studies of FSM spreads showed higher G″ value (loss modulus) than G' (storage modulus) indicating better spreadability. Descriptive sensory analysis revealed that the products had acceptability score of 8.3 to 10.5 (maximum score: 15). Fat extracted from spreads prepared using M1 and M2 was found to contain 43.9 and 22.3 % linoleic acid and 2.1 and 4.4 % linolenic acid respectively, were free from trans fat while the commercial hazelnut spread had 9.8 % linoleic acid but did not contain linolenic acid. Hence, the developed chocolate spreads have the potential to overcome ω-3 deficiency, ω-6/ω-3 imbalance and to enhance the health standard of people.

Numerical modeling of water spray suppression of conveyor belt fires in a large-scale tunnel.

PubMed

Yuan, Liming; Smith, Alex C

2015-05-01

Conveyor belt fires in an underground mine pose a serious life threat to miners. Water sprinkler systems are usually used to extinguish underground conveyor belt fires, but because of the complex interaction between conveyor belt fires and mine ventilation airflow, more effective engineering designs are needed for the installation of water sprinkler systems. A computational fluid dynamics (CFD) model was developed to simulate the interaction between the ventilation airflow, the belt flame spread, and the water spray system in a mine entry. The CFD model was calibrated using test results from a large-scale conveyor belt fire suppression experiment. Simulations were conducted using the calibrated CFD model to investigate the effects of sprinkler location, water flow rate, and sprinkler activation temperature on the suppression of conveyor belt fires. The sprinkler location and the activation temperature were found to have a major effect on the suppression of the belt fire, while the water flow rate had a minor effect.

Numerical modeling of water spray suppression of conveyor belt fires in a large-scale tunnel

PubMed Central

Yuan, Liming; Smith, Alex C.

2015-01-01

Conveyor belt fires in an underground mine pose a serious life threat to miners. Water sprinkler systems are usually used to extinguish underground conveyor belt fires, but because of the complex interaction between conveyor belt fires and mine ventilation airflow, more effective engineering designs are needed for the installation of water sprinkler systems. A computational fluid dynamics (CFD) model was developed to simulate the interaction between the ventilation airflow, the belt flame spread, and the water spray system in a mine entry. The CFD model was calibrated using test results from a large-scale conveyor belt fire suppression experiment. Simulations were conducted using the calibrated CFD model to investigate the effects of sprinkler location, water flow rate, and sprinkler activation temperature on the suppression of conveyor belt fires. The sprinkler location and the activation temperature were found to have a major effect on the suppression of the belt fire, while the water flow rate had a minor effect. PMID:26190905

RESIDENCE TIME DISTRIBUTION OF FLUIDS IN STIRRED ANNULAR PHOTOREACTORS

EPA Science Inventory

When gases flow through an annular photoreactor at constant rate, some of the gas spends more or less than the average residence time in the reactor. This spread of residence time can have an important effect on the performance of the reactor. this study tested how the residence...

Fluid dynamics structures in a fire environment observed in laboratory-scale experiments

Treesearch

J. Lozano; W. Tachajapong; D.R. Weise; S. Mahalingam; M. Princevac

2010-01-01

Particle Image Velocimetry (PIV) measurements were performed in laboratory-scale experimental fires spreading across horizontal fuel beds composed of aspen (Populus tremuloides Michx) excelsior. The continuous flame, intermittent flame, and thermal plume regions of a fire were investigated. Utilizing a PIV system, instantaneous velocity fields for...

The Plague Generation.

ERIC Educational Resources Information Center

Jones, Richard C.

1993-01-01

Describes an activity to simulate the geometries of a spreading pathogen such as HIV throughout a generation. Students exchange "bodily fluids" three times and are then tested for the presence of "infection." Materials used include base solutions (NaOH or KOH), phenolphthalein (pH indicator), clear plastic cups, and an eye dropper. (PR)

Impact dynamics of particle-coated droplets

NASA Astrophysics Data System (ADS)

Supakar, T.; Kumar, A.; Marston, J. O.

2017-01-01

We present findings from an experimental study of the impact of liquid marbles onto solid surfaces. Using dual-view high-speed imaging, we reveal details of the impact dynamics previously not reported. During the spreading stage it is observed that particles at the surface flow rapidly to the periphery of the drop, i.e., the lamella. We characterize the spreading with the maximum spread diameter, comparing to impacts of pure liquid droplets. The principal result is a power-law scaling for the normalized maximum spread in terms of the impact Weber number, Dmax/D0˜Weα , with α ≈1 /3 . However, the best description of the spreading is obtained by considering a total energy balance, in a similar fashion to Pasandideh-Fard et al. [Phys. Fluids 8, 650 (1996)], 10.1063/1.868850. By using hydrophilic target surfaces, the marble integrity is lost even for moderate impact speeds as the particles at the surface separate and allow liquid-solid contact to occur. Remarkably, however, we observe no significant difference in the maximum spread between hydrophobic and hydrophilic targets, which is rationalized by the presence of the particles. Finally, for the finest particles used, we observe the formation of nonspherical arrested shapes after retraction and rebound from hydrophobic surfaces, which is quantified by a circularity measurement of the side profiles.

Understanding Thiel Embalming in Pig Kidneys to Develop a New Circulation Model

PubMed Central

Willaert, Wouter; De Vos, Marie; Van Hoof, Tom; Delrue, Louke; Pattyn, Piet; D’Herde, Katharina

2015-01-01

The quality of tissue preservation in Thiel embalmed bodies varies. Research on the administered embalming volume and its vascular distribution may elucidate one of the mechanisms of tissue preservation and allow for new applications of Thiel embalming. Vascular embalming with (group 1, n = 15) or without (group 2, n = 20) contrast agent was initiated in pig kidneys. The distribution of Thiel embalming solution in group 1 was visualized using computed tomography. The kidneys in both groups were then immersed in concentrated salt solutions to reduce their weight and volume. Afterwards, to mimic a lifelike circulation in the vessels, group 2 underwent pump-driven reperfusion for 120 minutes with either paraffinum perliquidum or diluted polyethylene glycol. The circulation was imaged with computed tomography. All of the kidneys were adequately preserved. The embalming solution spread diffusely in the kidney, but fluid accumulation was present. Subsequent immersion in concentrated salt solutions reduced weight (P < 0.01) and volume (P < 0.01). Reperfusion for 120 minutes was established in group 2. Paraffinum perliquidum filled both major vessels and renal tissue, whereas diluted polyethylene glycol spread widely in the kidney. There were no increases in weight (P = 0.26) and volume (P = 0.79); and pressure further decreased (P = 0.032) after more than 60 minutes of reperfusion with paraffinum perliquidum, whereas there were increases in weight (P = 0.005), volume (P = 0.032) and pressure (P < 0.0001) after reperfusion with diluted polyethylene glycol. Arterial embalming of kidneys results in successful preservation due to complete parenchymatous spreading. More research is needed to determine whether other factors affect embalming quality. Dehydration is an effective method to regain the organs’ initial status. Prolonged vascular reperfusion with paraffinum perliquidum can be established in this model without increases in weight, volume and pressure. PMID:25806527

Normal versus anomalous self-diffusion in two-dimensional fluids: memory function approach and generalized asymptotic Einstein relation.

PubMed

Shin, Hyun Kyung; Choi, Bongsik; Talkner, Peter; Lee, Eok Kyun

2014-12-07

Based on the generalized Langevin equation for the momentum of a Brownian particle a generalized asymptotic Einstein relation is derived. It agrees with the well-known Einstein relation in the case of normal diffusion but continues to hold for sub- and super-diffusive spreading of the Brownian particle's mean square displacement. The generalized asymptotic Einstein relation is used to analyze data obtained from molecular dynamics simulations of a two-dimensional soft disk fluid. We mainly concentrated on medium densities for which we found super-diffusive behavior of a tagged fluid particle. At higher densities a range of normal diffusion can be identified. The motion presumably changes to sub-diffusion for even higher densities.

Normal versus anomalous self-diffusion in two-dimensional fluids: Memory function approach and generalized asymptotic Einstein relation

NASA Astrophysics Data System (ADS)

Shin, Hyun Kyung; Choi, Bongsik; Talkner, Peter; Lee, Eok Kyun

2014-12-01

Based on the generalized Langevin equation for the momentum of a Brownian particle a generalized asymptotic Einstein relation is derived. It agrees with the well-known Einstein relation in the case of normal diffusion but continues to hold for sub- and super-diffusive spreading of the Brownian particle's mean square displacement. The generalized asymptotic Einstein relation is used to analyze data obtained from molecular dynamics simulations of a two-dimensional soft disk fluid. We mainly concentrated on medium densities for which we found super-diffusive behavior of a tagged fluid particle. At higher densities a range of normal diffusion can be identified. The motion presumably changes to sub-diffusion for even higher densities.

Containment of subsurface contaminants

DOEpatents

Corey, J.C.

1994-09-06

A barrier is disclosed for reducing the spread of a plume of subsurface contaminants. The apparatus includes a well system for injecting a fluid, such as air, just outside and below the periphery of the plume. The fluid is injected at a pressure sufficient to lower the hydraulic conductivity of the soil from the point of injection to the surface thus establishing a curtain-like barrier to groundwater movement. The barrier is established upgradient of the plume to divert groundwater away, or preferably completely around the plume to reduce the flow of groundwater into or out of the plume. The barrier enables the remediation of the confined contamination and then, when the injection of the fluid is halted, the barrier quickly dissipates. 5 figs.

Influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure

NASA Astrophysics Data System (ADS)

Pechereau, François; Bonaventura, Zdeněk; Bourdon, Anne

2016-08-01

This paper presents simulations of an atmospheric pressure air discharge in a point-to-plane geometry with a dielectric layer parallel to the cathode plane. Experimentally, a discharge reignition in the air gap below the dielectrics has been observed. With a 2D fluid model, it is shown that due to the fast rise of the high voltage applied and the sharp point used, a first positive spherical discharge forms around the point. Then this discharge propagates axially and impacts the dielectrics. As the first discharge starts spreading on the upper dielectric surface, in the second air gap with a low preionization density of {{10}4}~\\text{c}{{\\text{m}}-3} , the 2D fluid model predicts a rapid reignition of a positive discharge. As in experiments, the discharge reignition is much slower, a discussion on physical processes to be considered in the model to increase the reignition delay is presented. The limit case with no initial seed charges in the second air gap has been studied. First, we have calculated the time to release an electron from the cathode surface by thermionic and field emission processes for a work function φ \\in ≤ft[3,4\\right] eV and an amplification factor β \\in ≤ft[100,220\\right] . Then a 3D Monte Carlo model has been used to follow the dynamics of formation of an avalanche starting from a single electron emitted at the cathode. Due to the high electric field in the second air gap, we have shown that in a few nanoseconds, a Gaussian cloud of seed charges is formed at a small distance from the cathode plane. This Gaussian cloud has been used as the initial condition of the 2D fluid model in the second air gap. In this case, the propagation of a double headed discharge in the second air gap has been observed and the reignition delay is in rather good agreement with experiments.

Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution

NASA Astrophysics Data System (ADS)

Derby, Brian

2010-08-01

Inkjet printing is viewed as a versatile manufacturing tool for applications in materials fabrication in addition to its traditional role in graphics output and marking. The unifying feature in all these applications is the dispensing and precise positioning of very small volumes of fluid (1-100 picoliters) on a substrate before transformation to a solid. The application of inkjet printing to the fabrication of structures for structural or functional materials applications requires an understanding as to how the physical processes that operate during inkjet printing interact with the properties of the fluid precursors used. Here we review the current state of understanding of the mechanisms of drop formation and how this defines the fluid properties that are required for a given liquid to be printable. The interactions between individual drops and the substrate as well as between adjacent drops are important in defining the resolution and accuracy of printed objects. Pattern resolution is limited by the extent to which a liquid drop spreads on a substrate and how spreading changes with the overlap of adjacent drops to form continuous features. There are clearly defined upper and lower bounds to the width of a printed continuous line, which can be defined in terms of materials and process variables. Finer-resolution features can be achieved through appropriate patterning and structuring of the substrate prior to printing, which is essential if polymeric semiconducting devices are to be fabricated. Low advancing and receding contact angles promote printed line stability but are also more prone to solute segregation or “coffee staining” on drying.

Low-gravity fluid dynamics and transport phenomena. Progress in Astronautics and Aeronautics. Vol. 130

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koster, J.N.; Sani, R.L.

1990-01-01

Various papers on low-gravity fluid dynamics and transport phenomena are presented. Individual topics addressed include: fluid management in low gravity, nucleate pool boiling in variable gravity, application of energy-stability theory to problems in crystal growth, thermosolutal convection in liquid HgCdTe near the liquidus temperature, capillary surfaces in microgravity, thermohydrodynamic instabilities and capillary flows, interfacial oscillators, effects of gravity jitter on typical fluid science experiments and on natural convection in a vertical cylinder. Also discussed are: double-diffusive convection and its effects under reduced gravity, segregation and convection in dendritic alloys, fluid flow and microstructure development, analysis of convective situations with themore » Soret effect, complex natural convection in low Prandtl number metals, separation physics, phase partitioning in reduced gravity, separation of binary alloys with miscibility gap in the melt, Ostwald ripening in liquids, particle cloud combustion in reduced gravity, opposed-flow flame spread with implications for combustion at microgravity.« less

Velocity relaxation of a particle in a confined compressible fluid

NASA Astrophysics Data System (ADS)

Tatsumi, Rei; Yamamoto, Ryoichi

2013-05-01

The velocity relaxation of an impulsively forced spherical particle in a fluid confined by two parallel plane walls is studied using a direct numerical simulation approach. During the relaxation process, the momentum of the particle is transmitted in the ambient fluid by viscous diffusion and sound wave propagation, and the fluid flow accompanied by each mechanism has a different character and affects the particle motion differently. Because of the bounding walls, viscous diffusion is hampered, and the accompanying shear flow is gradually diminished. However, the sound wave is repeatedly reflected and spreads diffusely. As a result, the particle motion is governed by the sound wave and backtracks differently in a bulk fluid. The time when the backtracking of the particle occurs changes non-monotonically with respect to the compressibility factor ɛ = ν/ac and is minimized at the characteristic compressibility factor. This factor depends on the wall spacing, and the dependence is different at small and large wall spacing regions based on the different mechanisms causing the backtracking.

Studies on the population dynamics of a rumor-spreading model in online social networks

NASA Astrophysics Data System (ADS)

Dong, Suyalatu; Fan, Feng-Hua; Huang, Yong-Chang

2018-02-01

This paper sets up a rumor spreading model in online social networks based on the European fox rabies SIR model. The model considers the impact of changing number of online social network users, combines the transmission dynamics to set up a population dynamics of rumor spreading model in online social networks. Simulation is carried out on online social network, and results show that the new rumor spreading model is in accordance with the real propagation characteristics in online social networks.

SICR rumor spreading model in complex networks: Counterattack and self-resistance

NASA Astrophysics Data System (ADS)

Zan, Yongli; Wu, Jianliang; Li, Ping; Yu, Qinglin

2014-07-01

Rumor is an important form of social interaction. However, spreading of harmful rumors could have a significant negative impact on the well-being of the society. In this paper, considering the counterattack mechanism of the rumor spreading, we introduce two new models: Susceptible-Infective-Counterattack-Refractory (SICR) model and adjusted-SICR model. We then derive mean-field equations to describe their dynamics in homogeneous networks and conduct the steady-state analysis. We also introduce the self-resistance parameter τ, and study the influence of this parameter on rumor spreading. Numerical simulations are performed to compare the SICR model with the SIR model and the adjusted-SICR model, respectively, and we investigate the spreading peak of the rumor and the final size of the rumor with various parameters. Simulation results are congruent exactly with the theoretical analysis. The experiment reveals some interesting patterns of rumor spreading involved with counterattack force.

Dynamic interaction of two-phase debris flow with pyramidal defense structures: An optimal strategy to efficiently protecting the desired area

NASA Astrophysics Data System (ADS)

Kattel, Parameshwari; Kafle, Jeevan; Fischer, Jan-Thomas; Mergili, Martin; Tuladhar, Bhadra Man; Pudasaini, Shiva P.

2017-04-01

In this work we analyze the dynamic interaction of two phase debris flows with pyramidal obstacles. To simulate the dynamic interaction of two-phase debris flow (a mixture of solid particles and viscous fluid) with obstacles of different dimensions and orientations, we employ the general two-phase mass flow model (Pudasaini, 2012). The model consists of highly non-linear partial differential equations representing the mass and momentum conservations for both solid and fluid. Besides buoyancy, the model includes some dominant physical aspects of the debris flows such as generalized drag, virtual mass and non-Newtonian viscous stress as induced by the gradient of solid-volume-fraction. Simulations are performed with high-resolution numerical schemes to capture essential dynamics, including the strongly re-directed flow with multiple stream lines, mass arrest and debris-vacuum generation when the rapidly cascading debris mass suddenly encounters the obstacle. The solid and fluid phases show fundamentally different interactions with obstacles, flow spreading and dispersions, run-out dynamics, and deposition morphology. A forward-facing pyramid deflects the mass wider, and a rearward-facing pyramid arrests a portion of solid-mass at its front. Our basic study reveals that appropriately installed obstacles, their dimensions and orientations have a significant influence on the flow dynamics, material redistribution and redirection. The precise knowledge of the change in dynamics is of great importance for the optimal and effective protection of designated areas along the mountain slopes and the runout zones. Further important results are, that specific installations lead to redirect either solid, or fluid, or both, in the desired amounts and directions. The present method of the complex interactions of real two-phase mass flows with the obstacles may help us to construct defense structures and to design advanced and physics-based engineering solutions for the prevention and mitigation of natural hazards caused by geophysical mass flows. References: Pudasaini, S. P. (2012): A general two-phase debris flow model. J. Geophys. Res. 117, F03010, doi: 10.1029/ 2011JF002186.

Flow regimes for fluid injection into a confined porous medium

DOE PAGES

Zheng, Zhong; Guo, Bo; Christov, Ivan C.; ...

2015-02-24

We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governingmore » equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.« less

Human vaginal fluid contains exosomes that have an inhibitory effect on an early step of the HIV-1 life cycle.

PubMed

Smith, Johanna A; Daniel, Rene

2016-11-13

Vaginal transmission is crucial to the spread of HIV-1 around the world. It is not yet clear what type (s) of innate defenses against HIV-1 infection are present in the vagina. Here, we aimed to determine whether human vaginal fluid contains exosomes that may possess anti-HIV-1 activity. The exosomal fraction was isolated from samples of vaginal fluids. The presence of exosomes was confirmed by flow cytometry and western blotting. The newly discovered exosomes were tested for their ability to block early steps of HIV-1 infection in vitro using established cell culture systems and real time PCR-based methods. Vaginal fluid contains exosomes expressing CD9, CD63, and CD81 exosomal markers. The exosomal fraction of the fluid-reduced transmission of HIV-1 vectors by 60%, the efficiency of reverse transcription step by 58.4%, and the efficiency of integration by 47%. Exosomes had no effect on the entry of HIV-1 vectors. Human vaginal fluid exosomes are newly discovered female innate defenses that may protect women against HIV-1 infection.

SEIR Model of Rumor Spreading in Online Social Network with Varying Total Population Size

NASA Astrophysics Data System (ADS)

Dong, Suyalatu; Deng, Yan-Bin; Huang, Yong-Chang

2017-10-01

Based on the infectious disease model with disease latency, this paper proposes a new model for the rumor spreading process in online social network. In this paper what we establish an SEIR rumor spreading model to describe the online social network with varying total number of users and user deactivation rate. We calculate the exact equilibrium points and reproduction number for this model. Furthermore, we perform the rumor spreading process in the online social network with increasing population size based on the original real world Facebook network. The simulation results indicate that the SEIR model of rumor spreading in online social network with changing total number of users can accurately reveal the inherent characteristics of rumor spreading process in online social network. Supported by National Natural Science Foundation of China under Grant Nos. 11275017 and 11173028

Peeling without precursors

NASA Astrophysics Data System (ADS)

Lister, John; Skinner, Dominic; Large, Tim

2017-11-01

The peeling by fluid injection of an elastic sheet away from a substrate is often regularised by invoking a thin prewetting film or a low-viscosity phase in the tip. Here we analyse fluid-driven peeling without such precursors, and consider an elastic sheet either bonded to, or simply laid on, an elastic substrate. To resolve the `elastic contact-line problem' that arises from viscous flow and beam theory, we determine the near-tip behaviour from lubrication theory coupled to the full equations of elasticity and fracture. The result is a law for the tip propagation speed in terms of the remote loading and the toughness of the sheet-substrate bonding (which might be zero). There are distinct modes of failure, according to whether there is slip ahead of the fluid front. The propagation-speed law gives rise to new similarity solutions for the spread of a fluid-filled blister in different regimes.

Using hyperbolic Lagrangian coherent structures to investigate vortices in bioinspired fluid flows

PubMed Central

Green, Melissa A.; Rowley, Clarence W.; Smits, Alexander J.

2010-01-01

We use direct Lyapunov exponents to identify Lagrangian coherent structures (LCSs) in a bioinspired fluid flow: the wakes of rigid pitching panels with a trapezoidal planform geometry chosen to model idealized fish caudal fins. When compared with commonly used Eulerian criteria, the Lagrangian method has previously exhibited the ability to define structure boundaries without relying on a preselected threshold. In addition, qualitative changes in the LCS have previously been shown to correspond to physical changes in the vortex structure. For this paper, digital particle image velocimetry experiments were performed to obtain the time-resolved velocity fields for Strouhal numbers of 0.17 and 0.27. A classic reverse von Kármán vortex street pattern was observed along the midspan of the near wake at low Strouhal number, but at higher Strouhal number the complexity of the wake increased downstream of the trailing edge. The spanwise vortices spread transversely across the wake and lose coherence, and this event was shown to correspond to a qualitative change in the LCS at the same time and location. PMID:20370300

Effect of mitral orifice shape on intra-ventricular filling fluid dynamics

NASA Astrophysics Data System (ADS)

Okafor, Ikechukwu; Angirish, Yagna; Yoganathan, Ajit; Santhanakrishnan, Arvind

2013-11-01

The natural geometry of the mitral orifice is D-shaped. However, most current designs of prosthetic valves employ O-shaped orifice geometry. The goal of this study was to compare the effect of geometrical modification between the D and O orifice on the intra-ventricular fluid dynamics during diastolic filling. The different mitral orifice geometries were incorporated into an in vitro left heart simulator consisting of a flexible-walled anatomical left ventricle (LV) physical model enclosed in an acrylic housing. Physiological flow rates and pressures were obtained via tuning systemic resistance and compliance elements in the flow loop. A programmable piston pump was used to generate the LV model wall motion. 2D Particle image velocimetry measurements were conducted along multiple longitudinal planes perpendicular to the annulus plane. During peak diastole, the incoming jet width at the LV central plane was smaller for the D-orifice than that of the O-orifice. Further, the core of the vortex ring in the D-orifice was reduced in size compared to that of the O-orifice. The spatiotemporal spreading of the inflow jet as well as the propagation of the vortex ring will be discussed. This study was funded by a grant from the National Heart, Lung and Blood Institute (RO1HL70262).

Modeling cell-substrate de-adhesion dynamics under fluid shear

NASA Astrophysics Data System (ADS)

Maan, Renu; Rani, Garima; Menon, Gautam I.; Pullarkat, Pramod A.

2018-07-01

Changes in cell-substrate adhesion are believed to signal the onset of cancer metastasis, but such changes must be quantified against background levels of intrinsic heterogeneity between cells. Variations in cell-substrate adhesion strengths can be probed through biophysical measurements of cell detachment from substrates upon the application of an external force. Here, we investigate, theoretically and experimentally, the detachment of cells adhered to substrates when these cells are subjected to fluid shear. We present a theoretical framework within which we calculate the fraction of detached cells as a function of shear stress for fast ramps as well as the decay in this fraction at fixed shear stress as a function of time. Using HEK and 3T3 fibroblast cells as experimental model systems, we extract characteristic force scales for cell adhesion as well as characteristic detachment times. We estimate force-scales of  ∼500 pN associated to a single focal contact, and characteristic time-scales of s representing cell-spread-area dependent mean first passage times to the detached state at intermediate values of the shear stress. Variations in adhesion across cell types are especially prominent when cell detachment is probed by applying a time-varying shear stress. These methods can be applied to characterizing changes in cell adhesion in a variety of contexts, including metastasis.

Stochastic analysis of transverse dispersion in density‐coupled transport in aquifers

USGS Publications Warehouse

Welty, Claire; Kane, Allen C.; Kauffman, Leon J.

2003-01-01

Spectral perturbation techniques have been used previously to derive integral expressions for dispersive mixing in concentration‐dependent transport in three‐dimensional, heterogeneous porous media, where fluid density and viscosity are functions of solute concentration. Whereas earlier work focused on evaluating longitudinal dispersivity in isotropic media and incorporating the result in a mean one‐dimensional transport model, the emphasis of this paper is on evaluation of the complete dispersion tensor, including the more general case of anisotropic media. Approximate analytic expressions for all components of the macroscopic dispersivity tensor are derived, and the tensor is shown to be asymmetric. The tensor is separated into its symmetric and antisymmetric parts, where the symmetric part is used to calculate the principal components and principal directions of dispersivity, and the antisymmetric part of the tensor is shown to modify the velocity of the solute body compared to that of the background fluid. An example set of numerical simulations incorporating the tensor illustrates the effect of density‐coupled dispersivity on a sinking plume in an aquifer. The simulations show that the effective transverse vertical spreading in a sinking plume to be significantly greater than would be predicted by a standard density‐coupled transport model that does not incorporate the coupling in the dispersivity tensor.

Composition of hydrothermal fluids and mineralogy of associated chimney material on the East Scotia Ridge back-arc spreading centre

NASA Astrophysics Data System (ADS)

James, Rachael H.; Green, Darryl R. H.; Stock, Michael J.; Alker, Belinda J.; Banerjee, Neil R.; Cole, Catherine; German, Christopher R.; Huvenne, Veerle A. I.; Powell, Alexandra M.; Connelly, Douglas P.

2014-08-01

The East Scotia Ridge is an active back-arc spreading centre located to the west of the South Sandwich island arc in the Southern Ocean. Initial exploration of the ridge by deep-tow surveys provided the first evidence for hydrothermal activity in a back-arc setting outside of the western Pacific, and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments E2 and E9. Here we report the chemical and isotopic composition of high- and low-temperature vent fluids, and the mineralogy of associated high-temperature chimney material, for two sites at E2 (Dog’s Head and Sepia), and four sites at E9 (Black & White, Ivory Tower, Pagoda and Launch Pad). The chemistry of the fluids is highly variable between the ridge segments. Fluid temperatures were ∼350 °C at all vent sites except Black & White, which was significantly hotter (383 °C). End-member chloride concentrations in E2 fluids (532-536 mM) were close to background seawater (540 mM), whereas Cl in E9 fluids was much lower (98-220 mM) indicating that these fluids are affected by phase separation. Concentrations of the alkali elements (Na, Li, K and Cs) and the alkaline earth elements (Ca, Sr and Ba) co-vary with Cl, due to charge balance constraints. Similarly, concentrations of Mn and Zn are highest in the high Cl fluids but, by contrast, Fe/Cl ratios are higher in E9 fluids (3.8-8.1 × 10-3) than they are in E2 fluids (1.5-2.4 × 10-3) and fluids with lowest Cl have highest Cu. Although both ridge segments are magmatically inflated, there is no compelling evidence for input of magmatic gases to the vent fluids. Fluid δD values range from 0.2‰ to 1.5‰, pH values (3.02-3.42) are not especially low, and F concentrations (34.6-54.4 μM) are lower than bottom seawater (62.8 μM). The uppermost sections of conjugate chimney material from E2, and from Ivory Tower and Pagoda at E9, typically exhibit inner zones of massive chalcopyrite enclosed within an outer zone of disseminated sulphide, principally sphalerite and pyrite, in an anhydrite matrix. By contrast, the innermost part of the chimneys that currently vent fluids with lowest Cl (Black & White and Launch Pad), is dominated by anhydrite. By defining and assessing the controls on the chemical composition of these vent fluids, and associated mineralisation, this study provides new information for evaluating the significance of hydrothermal processes at back-arc basins for ocean chemistry and the formation of seafloor mineral deposits.

Spreading in online social networks: the role of social reinforcement.

PubMed

Zheng, Muhua; Lü, Linyuan; Zhao, Ming

2013-07-01

Some epidemic spreading models are usually applied to analyze the propagation of opinions or news. However, the dynamics of epidemic spreading and information or behavior spreading are essentially different in many aspects. Centola's experiments [Science 329, 1194 (2010)] on behavior spreading in online social networks showed that the spreading is faster and broader in regular networks than in random networks. This result contradicts with the former understanding that random networks are preferable for spreading than regular networks. To describe the spreading in online social networks, a unknown-known-approved-exhausted four-status model was proposed, which emphasizes the effect of social reinforcement and assumes that the redundant signals can improve the probability of approval (i.e., the spreading rate). Performing the model on regular and random networks, it is found that our model can well explain the results of Centola's experiments on behavior spreading and some former studies on information spreading in different parameter space. The effects of average degree and network size on behavior spreading process are further analyzed. The results again show the importance of social reinforcement and are accordant with Centola's anticipation that increasing the network size or decreasing the average degree will enlarge the difference of the density of final approved nodes between regular and random networks. Our work complements the former studies on spreading dynamics, especially the spreading in online social networks where the information usually requires individuals' confirmations before being transmitted to others.

From rifting to subduction: the role of inheritance in the Wilson Cycle

NASA Astrophysics Data System (ADS)

Beaussier, Stéphane; Gerya, Taras; Burg, Jean-Pierre

2017-04-01

The Wilson Cycle entails that oceans close and reopen. This cycle is a fundamental principle in plate tectonics, inferring continuity from divergence to convergence and that continental rifting takes place along former suture zones. This view questions the role of inherited structures at each stage of the Wilson Cycle. Using the 3D thermo-mechanical code, I3ELVIS (Gerya and Yuen 2007) we present a high-resolution continuous model of the Wilson cycle from continental rifting, breakup and oceanic spreading to convergence and spontaneous subduction initiation. Therefore, all lateral and longitudinal structures of the lithospheres are generated self-consistently and are consequences of the initial continental structure, tectono-magmatic inheritance and material rheology. In the models, subduction systematically initiates off-ridge and is controlled by the convergence-induced swelling of the ridge. Geometry and dynamics of the developing off-ridge subduction is controlled by four main factors: (1) the obliquity of the ridge with respect to the convergence direction; (2) fluid-induced weakening of the oceanic crust; (3) irregularity of ridge and margins inherited from rifting and spreading; (4) strain localization at transform faults formed during ocean floor spreading. Further convergence can lead to obduction of the oceanic crust and segments of ridge after the oceanic lithosphere is entrained into subduction. We show that the main parameters controlling the occurrence and geometry of obducted ophiolite are the convergence rate and the inherited structure of the passive margins and ridge. Our numerical experiments results show the essential role played by inheritance during the Wilson Cycle and are consistent with nature observations such as the tectonic history of the Oman subduction-obduction system. REFERENCES Gerya, T. V., and D. A. Yuen. 2007: "Robust Characteristics Method for Modelling Multiphase Visco-Elasto-Plastic Thermo-Mechanical Problems, Physics of the Earth and Planetary Interiors, 163 (1-4), 83-105.

Modeling Electrically Evoked Otoacoustic Emissions

NASA Astrophysics Data System (ADS)

Grosh, K.; Deo, N.; Parthasarathi, A. A.; Nuttall, A. L.; Zheng, J. F.; Ren, T. Y.

2003-02-01

Electrical evoked otoacoustic emissions (EEOAE) are used to investigate in vivo cochlear electromechanical function. Round window electrical stimulation gives rise to a broad frequency EEOAE response, from 100 Hz or below to 40 kHz in guinea pigs. Placing bipolar electrodes very close to the basilar membrane (in the scala vestibuli and scala tympani) gives rise to a much narrower frequency range of EEOAE, limited to around 20 kHz when the electrodes are placed near the 18 kHz best frequency place. Model predictions using a three dimensional fluid model in conjunction with a simple model for outer hair cell (OHC) activity are used to interpret the experimental results. The model is solved using a 2.5D finite-element formulation. Predictions show that the high-frequency limit of the excitation is determined by the spatial extent of the current stimulus (also called the current spread). The global peaks in the EEOAE spectra are interpreted as constructive interference between electrically evoked backward traveling waves and forward traveling waves reflected from the stapes. Steady-state response predictions of the model are presented.

Pulsating jet-like structures in magnetized plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goncharov, V. P.; Pavlov, V. I.

The formation of pulsating jet-like structures has been studied in the scope of the nonhydrostatic model of a magnetized plasma with horizontally nonuniform density. We discuss two mechanisms which are capable of stopping the gravitational spreading appearing to grace the Rayleigh-Taylor instability and to lead to the formation of stationary or oscillating localized structures. One of them is caused by the Coriolis effect in the rotating frames, and another is connected with the Lorentz effect for magnetized fluids. Magnetized jets/drops with a positive buoyancy must oscillate in transversal size and can manifest themselves as “radio pulsars.” The estimates of theirmore » frequencies are made for conditions typical for the neutron star's ocean.« less

Plume Splitting in a Two-layer Stratified Ambient Fluid

NASA Astrophysics Data System (ADS)

Ma, Yongxing; Flynn, Morris; Sutherland, Bruce

2017-11-01

A line-source plume descending into a two-layer stratified ambient fluid in a finite sized tank is studied experimentally. Although the total volume of ambient fluid is fixed, lower- and upper-layer fluids are respectively removed and added at a constant rate mimicking marine outfall through diffusers and natural and hybrid ventilated buildings. The influence of the plume on the ambient depends on the value of λ, defined as the ratio of the plume buoyancy to the buoyancy loss of the plume as it crosses the ambient interface. Similar to classical filling-box experiments, the plume can always reach the bottom of the tank if λ > 1 . By contrast, if λ < 1 , an intermediate layer eventually forms as a result of plume splitting. Eventually all of the plume fluid spreads within the intermediate layer. The starting time, tv, and the ending time, tt, of the transition process measured from experiments correlate with the value of λ. A three-layer ambient fluid is observed after transition, and the mean value of the measured densities of the intermediate layer fluid is well predicted using plume theory. Acknowledgments: Funding for this study was provided by NSERC.

Guatemala jadeitites and albitites were formed by deuterium-rich serpentinizing fluids deep within a subduction zone

USGS Publications Warehouse

Johnson, C.A.; Harlow, G.E.

1999-01-01

Jadeitites and albitites from the Motagua Valley, Guatemala, are high-pressure-low-temperature metasomatic rocks that occur as tectonic inclusions in serpentinite-matrix melange. Metasomatism was driven by a fluid with a ??18OH2O value of 6???, and a ??DH2O value that is high in comparison with metamorphic fluids at other high-pressure-low-temperature localities of similar grade. We infer that the fluid was originally seawater that was entrained during subduction either as mineral-bound H2O or as free pore waters. The fluid drove serpentinization reactions in ultramafic rocks, possibly leading to deuterium enrichment of H2O, prior to forming the Jadeitites and albitites at a depth of 29 ?? 11 km. There are isotopic and fluid-inclusion similarities to rodingites, which are Ca-rich metasomatites found at other serpentinite localities. Our results suggest that the serpentinization process, whether it occurs within subduction zones or on the flanks of oceanic spreading ridges, may produce residual fluids that are H2O rich, have 1-8 wt% equivalent NaCl, and have high, perhaps sea water-like, ??D values.

Mathematical Models of Seafloor Hydrothermal Systems Driven by Serpentinization of Peridotite

NASA Astrophysics Data System (ADS)

Lowell, R. P.; Rona, P. A.; Germanovich, L. N.

2001-12-01

Most seafloor hydrothermal systems are driven by heat transfer from subsurface magma bodies. At slow spreading ridges of the Atlantic and Indian oceans, however, magma supply is low; and tectonic activity brings mantle rocks to shallow depths in the crust. Then, the heat of formation released upon serpentinization of peridotite provides the energy source for hydrothermal circulation. This latter class of system has been relatively unstudied, but recent discoveries of peridotite-hosted hydrothermal systems along the Mid-Atlantic Ridge suggest that such systems may play an important role in geochemical cycling and biogeochemical processes. The likelihood that peridotite-hosted hydrothermal systems was more prevalent during the Archean further suggests that such systems may have played a role in the origin of life. We present the first mathematical models of seafloor hydrothermal systems driven by heat released upon serpentinization of peridotite. We assume seawater circulates through a major crack network in the host-peridotite and that cooling of the host-rock leads to the formation of microcracks through which the fluid infiltrates. Reaction of the fluid in microcracks with the host rock results in serpentinization and the heat released upon serpentinization is transported to the seafloor by the fluid circulating in the main crack network. The temperature and heat output of the resulting hydrothermal system is a function of the main network permeability and the rate at which the serpentinization reaction proceeds via diffusion and propagation of the microcracks. Although the temperature of such a system can be quite variable, vent temperatures between 10° C and 100° C are likely for typical crustal parameters.

Collection of Oral Fluids Using Cotton Ropes as a Sampling Method to Detect Foot-and-Mouth Disease Virus Infection in Pigs.

PubMed

Vosloo, W; Morris, J; Davis, A; Giles, M; Wang, J; Nguyen, H T T; Kim, P V; Quach, N V; Le, P T T; Nguyen, P H N; Dang, H; Tran, H X; Vu, P P; Hung, V V; Le, Q T; Tran, T M; Mai, T M T; Le, Q T V; Singanallur, N B

2015-10-01

In high-density farming practices, it is important to constantly monitor for infectious diseases, especially diseases that have the potential to spread rapidly between holdings. Pigs are known to amplify foot-and-mouth disease (FMD) by excreting large amounts of virus, and it is therefore important to detect the virus quickly and accurately to minimize the spread of disease. Ropes were used to collect oral fluid samples from pigs, and each sample was compared to saliva samples collected from individual animals by detecting FMD virus RNA using real-time PCR. Two different experiments are described where groups of pigs were infected with different serotypes of FMD virus, either with or without vaccination, and unvaccinated pigs were kept in aerosol contact. The sensitivity of the rope sampling varied between 0.67 and 0.92, and the statistical agreement between this method and individual sampling ranged from substantial to moderate for the two different serotypes. The ease of collecting oral fluids using ropes together with the high sensitivity of subsequent FMD detection through PCR indicates that this could be a useful method to monitor pig populations for FMD virus infection. With further validation of the sensitivity of detection of FMD virus RNA, this can be a cost-effective, non-invasive diagnostic tool. © 2013 Blackwell Verlag GmbH.

A simple physical model for forest fire spread

Treesearch

E. Koo; P. Pagni; J. Woycheese; S. Stephens; D. Weise; J. Huff

2005-01-01

Based on energy conservation and detailed heat transfer mechanisms, a simple physical model for fire spread is presented for the limit of one-dimensional steady-state contiguous spread of a line fire in a thermally-thin uniform porous fuel bed. The solution for the fire spread rate is found as an eigenvalue from this model with appropriate boundary conditions through a...

Impact of the plasma response in three-dimensional edge plasma transport modelling for RMP ELM control scenarios at ITER

NASA Astrophysics Data System (ADS)

Schmitz, Oliver

2014-10-01

The constrains used in magneto-hydrodynamic (MHD) modeling of the plasma response to external resonant magnetic perturbation (RMP) fields have a profound impact on the three-dimensional (3-D) shape of the plasma boundary induced by RMP fields. In this contribution, the consequences of the plasma response on the actual 3D boundary structure and transport during RMP application at ITER are investigated. The 3D fluid plasma and kinetic neutral transport code EMC3-Eirene is used for edge transport modeling. Plasma response modeling is conducted with the M3D-C1 code using a single fluid, non-linear and a two fluid, linear MHD constrain. These approaches are compared to results with an ideal MHD like plasma response. A 3D plasma boundary is formed for all cases consisting of magnetic finger structures at the X-point intersecting the divertor surface in a helical footprint pattern. The width of the helical footprint pattern is largely reduced compared to vacuum magnetic fields when using the ideal MHD like screening model. This yields increasing peak heat fluxes in contrast to a beneficial heat flux spreading seen with vacuum fields. The particle pump out as well as loss of thermal energy is reduced by a factor of two compared to vacuum fields. In contrast, the impact of the plasma response obtained from both MHD constrains in M3D-C1 is nearly negligible at the plasma boundary and only a small modification of the magnetic footprint topology is detected. Accordingly, heat and particle fluxes on the target plates as well as the edge transport characteristics are comparable to the vacuum solution. This span of modeling results with different plasma response models highlights the importance of thoroughly validating both, plasma response and 3D edge transport models for a robust extrapolation towards ITER. Supported by ITER Grant IO/CT/11/4300000497 and F4E Grant GRT-055 (PMS-PE) and by Start-Up Funds of the University of Wisconsin - Madison.

Spray and High-Pressure Flow Computations in the National Combustion Code (NCC) Improved

NASA Technical Reports Server (NTRS)

Raju, Manthena S.

2002-01-01

Sprays occur in a wide variety of industrial and power applications and in materials processing. A liquid spray is a two-phase flow with a gas as the continuous phase and a liquid as the dispersed phase in the form of droplets or ligaments. The interactions between the two phases--which are coupled through exchanges of mass, momentum, and energy--can occur in different ways at disparate time and length scales involving various thermal, mass, and fluid dynamic factors. An understanding of the flow, combustion, and thermal properties of a rapidly vaporizing spray requires careful modeling of the ratecontrolling processes associated with turbulent transport, mixing, chemical kinetics, evaporation, and spreading rates of the spray, among many other factors. With the aim of developing an efficient solution procedure for use in multidimensional combustor modeling, researchers at the NASA Glenn Research Center have advanced the state-of-the-art in spray computations in several important ways.

A set of constitutive relationships accounting for residual NAPL in the unsaturated zone.

PubMed

Wipfler, E L; van der Zee, S E

2001-07-01

Although laboratory experiments show that non-aqueous phase liquid (NAPL) is retained in the unsaturated zone, no existing multiphase flow model has been developed to account for residual NAPL after NAPL drainage in the unsaturated zone. We developed a static constitutive set of saturation-capillary pressure relationships for water, NAPL and air that accounts for both this residual NAPL and entrapped NAPL. The set of constitutive relationships is formulated similarly to the set of scaled relationships that is frequently applied in continuum models. The new set consists of three fluid-phase systems: a three-phase system and a two-phase system, that both comply with the original constitutive model, and a newly introduced residual NAPL system. The new system can be added relatively easily to the original two- and three-phase systems. Entrapment is included in the model. The constitutive relationships of the non-drainable residual NAPL system are based on qualitative fluid behavior derived from a pore scale model. The pore scale model reveals that the amount of residual NAPL depends on the spreading coefficient and the water saturation. Furthermore, residual NAPL is history-dependent. At the continuum scale, a critical NAPL pressure head defines the transition from free, mobile NAPL to residual NAPL. Although the Pc-S relationships for water and total liquid are not independent in case of residual NAPL, two two-phase Pc-S relations can represent a three-phase residual system of Pc-S relations. A newly introduced parameter, referred to as the residual oil pressure head, reflects the mutual dependency of water and oil. Example calculations show consistent behavior of the constitutive model. Entrapment and retention in the unsaturated zone cooperate to retain NAPL. Moreover, the results of our constitutive model are in agreement with experimental observations.

Enhanced Amendment Delivery to Subsurface Using Shear Thinning Fluid and Aqueous Foam for Metal, Radionuclide, and NAPL Remediation

NASA Astrophysics Data System (ADS)

Zhong, L.; Szecsody, J.; Li, X.; Oostrom, M.; Truex, M.

2010-12-01

In many contamination sites, removal of contaminants by any active remediation efforts is not practical due to the high cost and technological limitations. Alternatively, in situ remediation is expected to be the most important remediation strategy. Delivery of reactive amendment to the contamination zone is essential for the reactions between the contaminants and remedial amendments to proceed in situ. It is a challenge to effectively deliver remedial amendment to the subsurface contamination source areas in both aquifer and vadose zone. In aquifer, heterogeneity induces fluid bypassing the low-permeability zones, resulting in certain contaminated areas inaccessible to the remedial amendment delivered by water injection, thus inhibiting the success of remedial operations. In vadose zone in situ remediation, conventional solution injection and infiltration for amendment delivery have difficulties to achieve successful lateral spreading and uniform distribution of the reactive media. These approaches also tend to displace highly mobile metal and radionuclide contaminants such as hexavalent chromium [Cr(VI)] and technetium (Tc-99), causing spreading of contaminations. Shear thinning fluid and aqueous foam can be applied to enhance the amendment delivery and improve in situ subsurface remediation efficiency under aquifer and vadose zone conditions, respectively. Column and 2-D flow cell experiments were conducted to demonstrate the enhanced delivery and improved remediation achieved by the application of shear thinning fluid and foam injection at the laboratory scale. Solutions of biopolymer xanthan gum were used as the shear thinning delivering fluids. Surfactant sodium lauryl ether sulfate (STEOL CS-330) was the foaming agent. The shear thinning fluid delivery (STFD) considerably improved the sweeping efficiency over a heterogeneous system and enhanced the non-aqueous liquid phase (NAPL) removal. The delivery of amendment into low-perm zones (LPZs) by STFD also increased the persistence of amendment solution in the LPZs after injection. Immobilization of Tc-99 was improved when a reductant was delivered by foam versus by water-based solution to contaminated vadose zone sediments. Foam delivery remarkably improved the lateral distribution of fluids compared to direct liquid injection. In heterogeneous vadose zone formation, foam injection increased the liquid flow in the high permeable zones into which very limited fluid was distributed during liquid infiltration, demonstrating improved amendment distribution uniformity in the heterogeneous system by foam delivery.

Methane Distribution In Plumes Of The South Mariana Back-arc Spreading Center

NASA Astrophysics Data System (ADS)

Toki, T.; Hirota, A.; Tsunogai, U.; Gamo, T.; Nakamura, K.; Noguchi, T.; Taira, N.; Oomori, T.; Ishibashi, J.; Utsumi, M.

2004-12-01

In the South Mariana Back-arc Spreading Center, two methane plumes were observed in water column based on analysis of methane in seawater samples collected during the R/V Thompson expeditions in 2003 around water depth of 2,700 m over the Fryer site on the ridge-axis seamount (12\\deg57.22N, 143\\deg37.16E, depth: 2,850 m). The estimated end-member isotopic compositions of methane in the two plumes are \\delta13C_{CH4} = -5‰ PDB and -50‰ PDB. These values indicated that the two plumes were originated from the different sources. During YK03-09 cruise using the submersible Shinkai 6500 from October to November in 2003, detailed seafloor observation discovered sulfide chimneys emitting black and clear hydrothermal fluid on the off-axis seamount at Pika site (12°55.15N, 143°36.96E, depth: 2,773 m). The result of analysis of isotopic composition of methane in the hydrothermal fluids recovered from the off-axis hydrothermal vents using WHATS (Water and Hydrothermal Atsuryoku Tight Sampler) was averaged value of -4‰ PDB (standard deviation = 1‰ PDB, n = 3). Hydrothermal fluids from the Fryer site were also sampled and were measured: average value = -6.7‰ PDB, standard deviation = 0.3‰ PDB, n = 3. During the R/V Thompson expeditions in March 2004 using ROV ROPOS, 11 ROPOS dives and CTD-RMS plume surveys were conducted, and newly discovered a huge hydrothermal structure with active fluid venting at Achaean site on the ridge skirt (12°56.37N, 143°37.92E, depth: 2,990 m). The δ ^{13}C_{CH4} value of the fluid sample from the site using ROCS (Rotary Clean Seawater sampler) was -14.7‰ PDB. Analysis of isotopic composition of methane in the plume samples collected using the CTD-hydrocast at water depth of 2,500 m over the Archaean site showed -45‰ PDB. Source of methane (δ ^{13}C_{CH4} = -50‰ PDB), however, in the two plumes of the South Mariana Back-arc Spreading Center has been missing. The δ ^{13}C of methane cannot be considered in sediment-starved seafloor hydrothermal fluids as the results from an abiogenic reaction in magma. Alternative explanation would be the secondary stimulated plume of methane that is formed in invertebrate guts of zooplankton swarmed about microbes in the plume, as proposed about a subsurface CH_{4} maximum in the upper oceanic water column. The secondary methane plume may be associated with methane plume without a corresponding enrichment in ^{3}He, observed in the Mariana Trough Back-arc basin at 14° N.

Modeling the potential of different countries for pandemic spread over the global air network

NASA Astrophysics Data System (ADS)

Sun, Zhe; Lv, Baolei; Xu, Bing

2017-04-01

Air network plays an important role in the spread of global epidemics due to its superior speed and range. Understanding the disease transmission pattern via network is the foundation for the prevention and control of future pandemics. In this study, we measured the potential of different countries for the pandemic spread by using a disease transmission model which integrated inter-country air traffic flow and geographic distance. The model was verified on the spread pattern of 2003 SARS, 2009 H1N1 influenza and 2014 Ebola by setting starting point at China, Mexico and Guinea respectively. Results showed that the model well reproduced the spread direction during the early stage as the time course were in good agreement with the reported arrival dates. Then the model was used to simulate the potential risk of each country in spreading the disease as the origin country. We observed that countries in North America, Europe and East Asia had the highest risk of transmission considering their high degree in the air network. We also found that for most starting countries, United States, United Kingdom, Germany and France would become the most-important spreading cores. Compared with empirical Susceptible-Infectious-Recover model, this model could respond much faster to the disease spread with no need for empirical disease transmission parameters.

Gossip spread in social network Models

NASA Astrophysics Data System (ADS)

Johansson, Tobias

2017-04-01

Gossip almost inevitably arises in real social networks. In this article we investigate the relationship between the number of friends of a person and limits on how far gossip about that person can spread in the network. How far gossip travels in a network depends on two sets of factors: (a) factors determining gossip transmission from one person to the next and (b) factors determining network topology. For a simple model where gossip is spread among people who know the victim it is known that a standard scale-free network model produces a non-monotonic relationship between number of friends and expected relative spread of gossip, a pattern that is also observed in real networks (Lind et al., 2007). Here, we study gossip spread in two social network models (Toivonen et al., 2006; Vázquez, 2003) by exploring the parameter space of both models and fitting them to a real Facebook data set. Both models can produce the non-monotonic relationship of real networks more accurately than a standard scale-free model while also exhibiting more realistic variability in gossip spread. Of the two models, the one given in Vázquez (2003) best captures both the expected values and variability of gossip spread.

Validation of the gravity model in predicting the global spread of influenza.

PubMed

Li, Xinhai; Tian, Huidong; Lai, Dejian; Zhang, Zhibin

2011-08-01

The gravity model is often used in predicting the spread of influenza. We use the data of influenza A (H1N1) to check the model's performance and validation, in order to determine the scope of its application. In this article, we proposed to model the pattern of global spread of the virus via a few important socio-economic indicators. We applied the epidemic gravity model for modelling the virus spread globally through the estimation of parameters of a generalized linear model. We compiled the daily confirmed cases of influenza A (H1N1) in each country as reported to the WHO and each state in the USA, and established the model to describe the relationship between the confirmed cases and socio-economic factors such as population size, per capita gross domestic production (GDP), and the distance between the countries/states and the country where the first confirmed case was reported (i.e., Mexico). The covariates we selected for the model were all statistically significantly associated with the global spread of influenza A (H1N1). However, within the USA, the distance and GDP were not significantly associated with the number of confirmed cases. The combination of the gravity model and generalized linear model provided a quick assessment of pandemic spread globally. The gravity model is valid if the spread period is long enough for estimating the model parameters. Meanwhile, the distance between donor and recipient communities has a good gradient. Besides, the spread should be at the early stage if a single source is taking into account.

Bloodborne Pathogens: HIV and HBV Contagion Risks at Camp.

ERIC Educational Resources Information Center

Skaros, Susan

1996-01-01

AIDS and hepatitis B are diseases caused by the viruses HIV and HBV, respectively, which are spread in blood and body fluids. HBV is 100 times more contagious than HIV. Diligent implementation of universal precautions, an exposure control plan, use of personal protective equipment, a vaccination program, and ongoing staff and camper education can…

Effect of Heterogeneous Interest Similarity on the Spread of Information in Mobile Social Networks

NASA Astrophysics Data System (ADS)

Zhao, Narisa; Sui, Guoqin; Yang, Fan

2018-06-01

Mobile social networks (MSNs) are important platforms for spreading news. The fact that individuals usually forward information aligned with their own interests inevitably changes the dynamics of information spread. Thereby, first we present a theoretical model based on the discrete Markov chain and mean field theory to evaluate the effect of interest similarity on the information spread in MSNs. Meanwhile, individuals' interests are heterogeneous and vary with time. These two features result in interest shift behavior, and both features are considered in our model. A leveraging simulation demonstrates the accuracy of our model. Moreover, the basic reproduction number R0 is determined. Further extensive numerical analyses based on the model indicate that interest similarity has a critical impact on information spread at the early spreading stage. Specifically, the information always spreads more quickly and widely if the interest similarity between an individual and the information is higher. Finally, five actual data sets from Sina Weibo illustrate the validity of the model.

Modification of electron beam ion source instability by longitudinal kinetic effects

NASA Astrophysics Data System (ADS)

Krafft, G. A.; Mark, J. W.-K.

1982-07-01

The electron beam ion source (EBIS) was proposed and subsequently realized by Donets. Further development has been done by the Orsay group and by the Berkeley group. Much theoretical work has been done on EBIS and, in particular, Litwin, Vella, and Sessler find that an electrostatic mode of the electron beam-ion system is unstable using a fluid calculation. The present work indicates that the inclusion of a longitudinal velocity spread in the electron beam decreases the instability growth rate, but their conclusions are not significantly modified. Numerically it is shown that substantial linear instability remains, even when sizeable longitudinal velocity spread is included. The principal result of the work is fig. 1; it gives the complex frequency of the mode as a function of σ/ υ0 z, σ being the spread and υ0 z being the average electron axial velocity.

A laboratory-scale comparison of rate of spread model predictions using chaparral fuel beds – preliminary results

Treesearch

D.R. Weise; E. Koo; X. Zhou; S. Mahalingam

2011-01-01

Observed fire spread rates from 240 laboratory fires in horizontally-oriented single-species live fuel beds were compared to predictions from various implementations and modifications of the Rothermel rate of spread model and a physical fire spread model developed by Pagni and Koo. Packing ratio of the laboratory fuel beds was generally greater than that observed in...

Validation of the Gravity Model in Predicting the Global Spread of Influenza

PubMed Central

Li, Xinhai; Tian, Huidong; Lai, Dejian; Zhang, Zhibin

2011-01-01

The gravity model is often used in predicting the spread of influenza. We use the data of influenza A (H1N1) to check the model’s performance and validation, in order to determine the scope of its application. In this article, we proposed to model the pattern of global spread of the virus via a few important socio-economic indicators. We applied the epidemic gravity model for modelling the virus spread globally through the estimation of parameters of a generalized linear model. We compiled the daily confirmed cases of influenza A (H1N1) in each country as reported to the WHO and each state in the USA, and established the model to describe the relationship between the confirmed cases and socio-economic factors such as population size, per capita gross domestic production (GDP), and the distance between the countries/states and the country where the first confirmed case was reported (i.e., Mexico). The covariates we selected for the model were all statistically significantly associated with the global spread of influenza A (H1N1). However, within the USA, the distance and GDP were not significantly associated with the number of confirmed cases. The combination of the gravity model and generalized linear model provided a quick assessment of pandemic spread globally. The gravity model is valid if the spread period is long enough for estimating the model parameters. Meanwhile, the distance between donor and recipient communities has a good gradient. Besides, the spread should be at the early stage if a single source is taking into account. PMID:21909295

Continuous flow electrophoresis system experiments on shuttle flights STS-6 and STS-7

NASA Technical Reports Server (NTRS)

Snyder, Robert S.; Rhodes, Percy H.; Miller, Teresa Y.

1987-01-01

A space continuous flow electrophoresis system (CFES) was developed that would incorporate specific modifications to laboratory instruments to take advantage of weightlessness. The specific objectives were to use a model sample material at a high concentration to evaluate the continuous flow electrophoresis process in the CFES instrument and compare its separation resolution and sample throughput with related devices on Earth and to expand the basic knowledge of the limitations imposed by fluid flows and particle concentration effects on the electrophoresis process by careful design and evaluation of the space experiment. Hemoglobin and polysaccharide were selected as primary samples. The results from space show a large band spread of the high concentration of the single species of hemoglobin that was due to the mismatch of electrical conductivity between the sample and the buffer. On STS-7 the major objective was to evaluate the influence of the electrical properties of the sample constituents on the resolution of the CFES. As expected, the polystyrene latex microspheres dispersed in a solution with 3 times the electrical conductivity of the curtain buffer separated with a larger band spread than in the 2nd experiment.

Source Evolution After Subduction Initiation as Recorded in the Izu-Bonin-Mariana Fore-arc Crust

NASA Astrophysics Data System (ADS)

Shervais, J. W.; Reagan, M. K.; Pearce, J. A.; Shimizu, K.

2015-12-01

Drilling in the Izu-Bonin-Mariana (IBM) fore-arc during IODP Expedition 352 and DSDP Leg 60 recovered consistent stratigraphic sequences of volcanic rocks reminiscent of those found in many ophiolites. The oldest lavas in these sections are "fore-arc basalts" (FAB) with ~51.5 Ma ages. Boninites began eruption approximately 2-3 m.y. later (Ishizuka et al., 2011, EPSL; Reagan et al., 2013, EPSL) and further from the trench. First results from IODP Expedition 352 and preliminary post-cruise data suggest that FAB at Sites U1440 and U1441 were generated by decompression melting during near-trench sea-floor spreading, and that fluids from the subducting slab were not involved in their genesis. Temperatures appear to have been unusually high and pressures of melting appear to have been unusually low compared to mid-ocean ridges. Spreading rates at this time appear to have been robust enough to maintain a stable melt lens. Incompatible trace element abundances are low in FAB compared to even depleted MORB. Nd and Hf Isotopic compositions published before the expedition suggest that FAB were derived from typical MORB source mantle. Thus, their extreme deletion resulted from unusually high degrees of melting immediately after subduction initiation. The oldest boninites from DSDP Site 458 and IODP Sites U1439 and U1442 have relatively high concentrations of fluid-soluble elements, low concentrations of REE, and light depleted REE patterns. Younger boninites, have even lower REE concentrations, but have U-shaped REE patterns. Our first major and trace element compositions for the FAB through boninite sequence suggests that melting pressures and temperatures decreased through time, mantle became more depleted though time, and spreading rates waned during boninite genesis. Subduction zone fluids involved in boninite genesis appear to have been derived from progressively higher temperatures and pressures over time as the subducting slab thermally matured.

Bioactivity of Y2O3 and CeO2 doped SiO2-SrO-Na2O glass-ceramics.

PubMed

Placek, L M; Keenan, T J; Wren, A W

2016-08-01

The bioactivity of yttrium and cerium are investigated when substituted for Sodium (Na) in a 0.52SiO2-0.24SrO-0.24-xNa2O-xMO glass-ceramics (where x = 0.08 and MO = Y2O3 or CeO2). Bioactivity is monitored through pH and inductively coupled plasma-optical emission spectrometry where pH of simulated body fluid ranged from 7.5 to 7.6 and increased between 8.2 and 10.0 after 14-day incubation with the glass-ceramic disks. Calcium (Ca) and phosphorus (P) levels in simulated body fluid after incubation with yttrium and cerium containing disks show a continual decline over the 14-day period. In contrast, Con disks (not containing yttrium or cerium) caused the elimination of Ca in solution after 1 day and throughout the incubation period, and initially showed a decline in P levels followed by an increase at 14 days. Scanning electron microscopy and energy dispersive spectroscopy confirmed the presence of Ca and P on the surface of the simulated body fluid-incubated disks and showed precipitates on Con and HCe (8 mol% cerium) samples. Cell viability of MC3T3 osteoblasts was not significantly affected at a 9% extract concentration. Optical microscopy after 24 h cell incubation with disks showed that Con samples do not support osteoblast or Schwann cell growth, while all yttrium and cerium containing disks have direct contact with osteoblasts spread across the wells. Schwann cells attached in all wells, but only showed spreading with the HY-S (8 mol% yttrium, heated to sintering temperature) and YCe (4 mol% yttrium and cerium) disks. Scanning electron microscopy of the compatible disks shows osteoblast and sNF96.2 Schwann cells attachment and spreading directly on the disk surfaces. © The Author(s) 2016.

Low-order modelling of a drop on a highly-hydrophobic substrate: statics and dynamics

NASA Astrophysics Data System (ADS)

Wray, Alexander W.; Matar, Omar K.; Davis, Stephen H.

2017-11-01

We analyse the behaviour of droplets resting on highly-hydrophobic substrates. This problem is of practical interest due to its appearance in many physical contexts involving the spreading, wetting, and dewetting of fluids on solid substrates. In mathematical terms, it exhibits an interesting challenge as the interface is multi-valued as a function of the natural Cartesian co-ordinates, presenting a stumbling block to typical low-order modelling techniques. Nonetheless, we show that in the static case, the interfacial shape is governed by the Young-Laplace equation, which may be solved explicitly in terms of elliptic functions. We present simple low-order expressions that faithfully reproduce the shapes. We then consider the dynamic case, showing that the predictions of our low-order model compare favourably with those obtained from direct numerical simulations. We also examine the characteristic flow regimes of interest. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM).

Computing fluid-particle interaction forces for nano-suspension droplet spreading: molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Zhou, Weizhou; Shi, Baiou; Webb, Edmund

2017-11-01

Recently, there are many experimental and theoretical studies to understand and control the dynamic spreading of nano-suspension droplets on solid surfaces. However, fundamental understanding of driving forces dictating the kinetics of nano-suspension wetting and spreading, especially capillary forces that manifest during the process, is lacking. Here, we present results from atomic scale simulations that were used to compute forces between suspended particles and advancing liquid fronts. The role of nano-particle size, particle loading, and interaction strength on forces computed from simulations will be discussed. Results demonstrate that increasing the particle size dramatically changes observed wetting behavior from depinning to pinning. From simulations on varying particle size, a relationship between computed forces and particle size is advanced and compared to existing expressions in the literature. High particle loading significantly slowed spreading kinetics, by introducing tortuous transport paths for liquid delivery to the advancing contact line. Lastly, we show how weakening the interaction between the particle and the underlying substrate can change a system from exhibiting pinning behavior to de-pinning.

The Effects of Ultra Thin Films on Dynamic Wetting

NASA Astrophysics Data System (ADS)

Chen, Xia; Garoff, Stephen; Rame, Enrique

2002-11-01

Dynamic wetting, the displacement of one fluid by another immiscible fluid on a surface, controls many natural and technological phenomena, such as coating, printing, spray painting and lubricating. Particularly in coating and spraying applications, contact lines advance across pre-existing fluid films. Most previous work has focused on contact lines advancing across films sufficiently thick that they behave as simple Newtonian fluids. Ultrathin films, where the film thickness may impinge on fundamental length scales in the fluid, have received less attention. In this talk, we will discuss the effects of ultrathin polymer films on dynamic wetting. We measure the interface shape within microns of moving contact lines advancing across preexisting films and compare the measurements to existing models of viscous bending for interfaces advancing across dry surfaces and 'thick' (in the sense that they behave as liquids) films. In the experiments, we advance a contact line of 10-poise and 1-poise polydimethylsiloxane (silicone oil) across pre-coated films of the same fluid with thickness from a single chain thickness (approx. 10 A) through a couple of radii of gyration (100-200 A) to films so thick they are likely bulk in behavior (103 A). All films are physisorbed, i.e. they readily rinse from the surface. Thus, molecules in the film are not anchored to the surface and can move within the film if the hydrodynamics dictate such motion. For films of the thickness of a single chain (approx. 10 A), our experiments indicate that the advancing fluid behaves just as it would if it advanced over a dry surface. For the thicker films (103 A), we find behavior indicating that the molecules in the film are acting as a fluid with the bulk properties. In this regime, results for the two different fluids are identical when the experiments are performed at the same pre-existing film thickness and advancing capillary number, Ca. For film of thickness of a few radii of gyration (approx. 100-200 A), the behavior depends on Ca of the advancing meniscus. At low Ca, the viscous bending of the interface near the contact line does not behave as it would on a dry surface. It has a lower curvature than expected. However, at higher Ca, the viscous bending is described by the model for spreading over a dry surface. These results show that the fluid flow in the film does behave differently than bulk as the film thickness becomes comparable to molecular length scale. But even more intriguing is the unusual velocity dependence of that behavior where the film behaves more solid-like at higher contact line speeds. We will discuss these results in terms of the properties of confined polymer melts.

The Effects of Ultra Thin Films on Dynamic Wetting

NASA Technical Reports Server (NTRS)

Chen, Xia; Garoff, Stephen; Rame, Enrique

2002-01-01

Dynamic wetting, the displacement of one fluid by another immiscible fluid on a surface, controls many natural and technological phenomena, such as coating, printing, spray painting and lubricating. Particularly in coating and spraying applications, contact lines advance across pre-existing fluid films. Most previous work has focused on contact lines advancing across films sufficiently thick that they behave as simple Newtonian fluids. Ultrathin films, where the film thickness may impinge on fundamental length scales in the fluid, have received less attention. In this talk, we will discuss the effects of ultrathin polymer films on dynamic wetting. We measure the interface shape within microns of moving contact lines advancing across preexisting films and compare the measurements to existing models of viscous bending for interfaces advancing across dry surfaces and 'thick' (in the sense that they behave as liquids) films. In the experiments, we advance a contact line of 10-poise and 1-poise polydimethylsiloxane (silicone oil) across pre-coated films of the same fluid with thickness from a single chain thickness (approx. 10 A) through a couple of radii of gyration (100-200 A) to films so thick they are likely bulk in behavior (10(exp 3) A). All films are physisorbed, i.e. they readily rinse from the surface. Thus, molecules in the film are not anchored to the surface and can move within the film if the hydrodynamics dictate such motion. For films of the thickness of a single chain (approx. 10 A), our experiments indicate that the advancing fluid behaves just as it would if it advanced over a dry surface. For the thicker films (10(exp 3) A), we find behavior indicating that the molecules in the film are acting as a fluid with the bulk properties. In this regime, results for the two different fluids are identical when the experiments are performed at the same pre-existing film thickness and advancing capillary number, Ca. For film of thickness of a few radii of gyration (approx. 100-200 A), the behavior depends on Ca of the advancing meniscus. At low Ca, the viscous bending of the interface near the contact line does not behave as it would on a dry surface. It has a lower curvature than expected. However, at higher Ca, the viscous bending is described by the model for spreading over a dry surface. These results show that the fluid flow in the film does behave differently than bulk as the film thickness becomes comparable to molecular length scale. But even more intriguing is the unusual velocity dependence of that behavior where the film behaves more solid-like at higher contact line speeds. We will discuss these results in terms of the properties of confined polymer melts.

Heat flow in the flanks of the Oceanographer-Hayes segment of the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Le Gal, V.; Lucazeau, F.; Cannat, M.; Battani, A.; Poort, J.; Guichet, X.; Monnin, C.; Fontaine, F. J.; Leroy, S. D.

2016-12-01

It is currently estimated that a third of the oceanic heat loss is due to fluid circulation in the oceanic crust. Besides high and low temperature fluid discharge at ridge axis, off-axis low temperature fluid circulations can affect large volumes of the oceanic crust. Long term investigations of the Eastern Juan de Fuca ridge flank (Hutnak et al.2006) have established a circulation pattern where hydrothermal discharge and recharge occur at basement outcrops and where sediment is mostly impermeable. Here, we present results from the recent Oceanograflu cruise (2013), on the Oceanographer-Hayes segment ridge flanks of the Mid-Atlantic ridge in crust 5 and 12 myrs in age. On both flanks, we obtained 185 temperature gradients and conductivities in-situ, 30 Küllenberg cores (3 to 5 meters long) coupled with temperature gradients in-situ and conductivity measurements onboard. These data are interpreted in terms of heat flow values and are generally lower than the conductive cooling model. Several temperature-depth profiles don't show linear gradients, but rather sigmoid shapes or inverse gradients suggesting superficial circulations through the first meters of sediments. The corresponding heat flow pattern is not similar to the one observed at Juan de Fuca. No systematic links have been observed between basement outcrops and lower or higher heat flow which would point to discharge or recharge sites. Instead, the pattern recalls studies in the North Pond area (Langseth et al.1992), with a clear predominance of low heat flow values over the site. We propose that the North Pond circulation model is applicable to large portions of slow-spreading ridge flanks such as the Atlantic. In this model, seawater cools the uppermost crust below sediments in basins that are typically tens of kms wide, reducing the surface heat flow under cooling model values. Based on subsidence rates, these shallow hydrothermal circulations have a minor impact on the cooling of the diverging plates.

A Monte Carlo model for 3D grain evolution during welding

NASA Astrophysics Data System (ADS)

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

2017-09-01

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bézier curves, which allow for the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. The model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.

A qualitative comparison of fire spread models incorporating wind and slope effects

Treesearch

David R. Weise; Gregory S. Biging

1997-01-01

Wind velocity and slope are two critical variables that affect wildland fire rate of spread. The effects of these variables on rate of spread are often combined in rate-of-spread models using vector addition. The various methods used to combine wind and slope effects have seldom been validated or compared due to differences in the models or to lack of data. In this...

Effects of compressional waves on the response of quartz crystal microbalance in contact with silicone oil droplets

NASA Astrophysics Data System (ADS)

Zhuang, Han; Lim, Siak Piang; Lee, Heow Pueh

2009-06-01

Droplet quartz crystal microbalance has been demonstrated to be a promising tool for accessing material properties of fluids as well as the diverse solid-fluid interface phenomena. However, a microliter droplet localized on the surface of the electrodes of finite lateral size may cause a nonuniform distribution of the plane velocity, which may lead to surface normal fluid flow and generate the compressional waves above the crystal surface. In the present article, we report systematical investigation on both resonance frequency and dissipation measurements with reference to the small droplets of silicone oils spreading on the surface of the quartz crystal microbalance. Significant cyclical variations in the resonant frequency and resistance of the crystal have been observed as the characteristic sizes of the silicone oil droplets are close to specific values known to favor compressional wave generation. The experimental results have been compared with the theoretical values predicted by the finite element computation associated with a simple hydrodynamic model. Good agreement between theory and experiment has been obtained. The finding indicates that the small droplets on the crystal surface can act as resonant cavities for the compressional wave generation and that the greatest propensity to exhibit periodical resonance behavior in the frequency and dissipation measurements is at droplet height of λc/2 above the crystal surface.

Formation of Hydro-acoustic Waves in Dissipative Coupled Weakly Compressible Fluids

NASA Astrophysics Data System (ADS)

Abdolali, A.; Kirby, J. T., Jr.; Bellotti, G.

2014-12-01

Recent advances in deep sea measurement technology provide an increasing opportunity to detect and interpret hydro-acoustic waves as a component in improved Tsunami Early Warning Systems (TEWS). For the idealized case of a homogeneous water column above a moving but otherwise rigid bottom (in terms of assessing acoustic wave interaction), the description of the infinite family of acoustic modes is characterized by local water depth at source area; i.e. the period of the first acoustic mode is given by four times the required time for sound to travel from the seabed to the surface. Spreading off from earthquake zone, the dominant spectrum is filtered and enriched by seamounts and barriers. This study focuses on the characteristics of hydro-acoustic waves generated by sudden sea bottom motion in a weakly compressible fluid coupled with an underlying sedimentary layer, where the added complexity of the sediment layer rheology leads to both the lowering of dominant spectral peaks and wave attenuation across the full spectrum. To overcome the computational difficulties of three-dimensional models, we derive a depth integrated equation valid for varying water depth and sediment thickness. Damping behavior of the two layered system is initially taken into account by introducing the viscosity of fluid-like sedimentary layer. We show that low frequency pressure waves which are precursor components of tsunamis contain information of seafloor motion.

Maximum spreading of liquid drop on various substrates with different wettabilities

NASA Astrophysics Data System (ADS)

Choudhury, Raihan; Choi, Junho; Yang, Sangsun; Kim, Yong-Jin; Lee, Donggeun

2017-09-01

This paper describes a novel model developed for a priori prediction of the maximal spread of a liquid drop on a surface. As a first step, a series of experiments were conducted under precise control of the initial drop diameter, its falling height, roughness, and wettability of dry surfaces. The transient liquid spreading was recorded by a high-speed camera to obtain its maximum spreading under various conditions. Eight preexisting models were tested for accurate prediction of the maximum spread; however, most of the model predictions were not satisfactory except one, in comparison with our experimental data. A comparative scaling analysis of the literature models was conducted to elucidate the condition-dependent prediction characteristics of the models. The conditioned bias in the predictions was mainly attributed to the inappropriate formulations of viscous dissipation or interfacial energy of liquid on the surface. Hence, a novel model based on energy balance during liquid impact was developed to overcome the limitations of the previous models. As a result, the present model was quite successful in predicting the liquid spread in all the conditions.

Fingering dynamics on the adsorbed solute with influence of less viscous and strong sample solvent.

PubMed

Rana, Chinar; Mishra, Manoranjan

2014-12-07

Viscous fingering is a hydrodynamic instability that sets in when a low viscous fluid displaces a high viscous fluid and creates complex patterns in porous media flows. Fundamental facets of the displacement process, such as the solute concentration distribution, spreading length, and the solute mixing, depend strongly on the type of pattern created by the unstable interface of the underlying fluids. In the present study, the frontal interface of the sample shows viscous fingering and the strong solvent causes the retention of the solute to depend on the solvent concentration. This work presents a computational investigation to explore the effect of the underlying physico-chemical phenomena, (i.e., the combined effects of solvent strength, retention, and viscous fingering) on the dynamics of the adsorbed solute. A linear adsorption isotherm has been assumed between the mobile and stationary phases of the solute. We carried out the numerical simulations by considering a rectangular Hele-Shaw cell as an analog to 2D-porous media containing a three component system (displacing fluid, sample solvent, solute) to map out the evolution of the solute concentration. We observed that viscous fingering at the frontal interface of the strong sample solvent intensifies the band broadening of the solute zone. Also notable increase in the spreading dynamics of the solute has been observed for less viscous and strong sample solvent as compared to the high viscous sample slices or in the pure dispersive case. On the contrary, the solute gets intensively mixed at early times for more viscous sample in comparison to less viscous one. The results of the simulations are in qualitative agreement with the behavior observed in the liquid chromatography column experiments.

The penalty immersed boundary method and its application to aerodynamics

NASA Astrophysics Data System (ADS)

Kim, Yongsam

The Immersed Boundary (IB) method has been widely applied to problems involving a moving elastic boundary that is immersed in fluid and interacting with it. But most applications of the IB method have involved a massless elastic boundary. Extending the method to cover the case of a massive boundary has required spreading the boundary mass out onto the fluid grid and then solving the Navier-Stokes equations with a variable mass density. The variable mass density makes Fourier transform methods inapplicable, and requires a multigrid solver. Here we propose a new and simple way to give mass to the elastic boundary. The key idea of the method is to introduce two representations of each boundary: one is a massive boundary which does not interact with the fluid, and the other is messless and plays the same role as the boundary of the IB method with the massless assumption. Although they are almost the same, we allow these two representations of the boundary to be different as long as the gap between them is small. This can be ensured by connecting them with a stiff spring with a zero rest length which generates force acting on both boundaries and pulling them together. We call this the 'Penalty IB method'. It does not spread mass to the fluid grid, retains the use of Fourier transform methodology, and is easy to implement in the context of an existing IB method code for the massless case. This thesis introduces the Penalty IB method and applies it to several problems in which the mass of the boundary is important. These problems are filaments in a flowing soap film, flows past a cylinder, windsocks, flags, and parachutes.

Organic matter in hydrothermal metal ores and hydrothermal fluids

USGS Publications Warehouse

Orem, W.H.; Spiker, E. C.; Kotra, R.K.

1990-01-01

Massive polymetallic sulfides are currently being deposited around active submarine hydrothermal vents associated with spreading centers. Chemoautolithotrophic bacteria are responsible for the high production of organic matter also associated with modern submarine hydrothermal activity. Thus, there is a significant potential for organic matter/metal interactions in these systems. We have studied modern and ancient hydrothermal metal ores and modern hydrothermal fluids in order to establish the amounts and origin of the organic matter associated with the metal ores. Twenty-six samples from modern and ancient hydrothermal systems were surveyed for their total organic C contents. Organic C values ranged from 0.01% to nearly 4.0% in these samples. Metal ores from modern and ancient sediment-covered hydrothermal systems had higher organic C values than those from modern and ancient hydrothermal systems lacking appreciable sedimentary cover. One massive pyrite sample from the Galapagos spreading center (3% organic C) had stable isotope values of -27.4% (??13C) and 2.1% (??15N), similar to those in benthic siphonophors from active vents and distinct from seep sea sedimentary organic matter. This result coupled with other analyses (e.g. 13C NMR, pyrolysis/GC, SEM) of this and other samples suggests that much of the organic matter may originate from chemoautolithotrophic bacteria at the vents. However, the organic matter in hydrothermal metal ores from sediment covered vents probably arises from complex sedimentary organic matter by hydrothermal pyrolysis. The dissolved organic C concentrations of hydrothermal fluids from one site (Juan de Fuca Ridge) were found to be the same as that of background seawater. This result may indicate that dissolved organic C is effectively scavenged from hydrothermal fluids by biological activity or by co-precipitation with metal ores. ?? 1990.

Event ambiguity fuels the effective spread of rumors

NASA Astrophysics Data System (ADS)

Xu, Jiuping; Zhang, Yi

2015-08-01

In this paper, a new rumor spreading model which quantifies a specific rumor spreading feature is proposed. The specific feature focused on is the important role the event ambiguity plays in the rumor spreading process. To study the impact of this event ambiguity on the spread of rumors, the probability p(t) that an individual becomes a rumor spreader from an initially unaware person at time t is built. p(t) reflects the extent of event ambiguity, and a parameter c of p(t) is used to measure the speed at which the event moves from ambiguity to confirmation. At the same time, a principle is given to decide on the correct value for parameter c A rumor spreading model is then developed with this function added as a parameter to the traditional model. Then, several rumor spreading model simulations are conducted with different values for c on both regular networks and ER random networks. The simulation results indicate that a rumor spreads faster and more broadly when c is smaller. This shows that if events are ambiguous over a longer time, rumor spreading appears to be more effective, and is influenced more significantly by parameter c in a random network than in a regular network. We then determine parameters of this model through data fitting of the missing Malaysian plane, and apply this model to an analysis of the missing Malaysian plane. The simulation results demonstrate that the most critical time for authorities to control rumor spreading is in the early stages of a critical event.

Enhanced and asymmetric melting beneath the southern Mariana back-arc spreading ridge under the influence of the Pacific plate subduction

NASA Astrophysics Data System (ADS)

Matsuno, T.; Seama, N.; Shindo, H.; Nogi, Y.; Okino, K.

2017-12-01

Back-arc spreading ridges in the southern Mariana Trough are slow-spreading ridges but have features suggesting enhanced melting beneath the ridges and influences on seafloor spreading processes by fluid derived from the subducted Pacific slab underlying the ridges. To reveal melting and dehydration processes and dynamics in the upper mantle in the southern Mariana Trough, we conducted a marine magnetotelluric (MT) experiment along a 120 km-length transect across a ridge segment at 13°N. We obtained electromagnetic field data at 9 stations along the transect, and analyzed them for estimating MT responses, striping seafloor topographic distortion from the responses, and imaging a 2-D electrical resistivity structure by 2-D inversion of TM-mode responses. A resultant 2-D inversion model showed 1) a conductive area at 10-20 km depth beneath the ridge center, the center of which slightly offsets to the trench side, 2) a moderately conductive area expanding asymmetrically around and under the conductor of 1), 3) a resistive area thickening from the ridge center up to about 40 km on the remnant arc side, and 4) a resistive area with a constant thickness of about 150 km on the trench side. These model features suggest 1) a melt body beneath the ridge center, possibly containing slab-derived water 2) water- and melt-retained mantle area produced by hydration of the back-arc mantle wedge and asymmetric passive decompression melting in the hydrous mantle wedge, 3) cooled and residual lithospheric mantle off the ridge center, and 4) mantle wedge and subducted Pacific lithospheric mantle that are both cold and depleted. The electrical resistivity structure obtained in the southern Mariana Trough, which clearly contrasts with the structure of the central Mariana Trough at 18°N in that this lacks a conductor beneath the ridge center, provides insights on the mantle dynamics and its relation to the characteristic tectonics and many kinds of observational results in the southern Mariana Trough.

Physical inter-relationships between hydrothermal activity, faulting and magmatic processes at the center of a slow-spreading, magma-rich mid-ocean ridge segment: A case study of the Lucky Strike segment (MAR, 37°03'-37‧N)

NASA Astrophysics Data System (ADS)

Fontaine, F. J.; Cannat, M.; Escartin, J.; Crawford, W. C.; Singh, S. C.

2012-12-01

The modalities and efficiency of hydrothermal heat evacuation at mid-ocean ridges (25% of the global heat loss) are controlled by the lithosphere thermal and permeability structures for which we had robust constraints only for fast/intermediate spreading axis until the last past few years during which integrated geophysical, geological and geochemical studies focused on some hydrothermal sites at slow-spreading ridges. At the Lucky Strike vent field of the mid-atlantic ridge - a hydrothermal complex composed of high-temperature (maximum T=340°C), smoker-like vents and associated diffuse flow and extracting a few hundreds MW from the oceanic lithosphere - a seafloor observatory which installation started in 2005 highlights local interactions between hydrothermal, tectonic and magmatic processes. Detailed geophysical and geological investigations stress the role of the local axial fault system on localizing high- and low-temperature ventings around the faulted rim of a paleo lava lake. Microseismic studies bring constraints on the subseafloor hydrology and suggest an along-axis flow pattern, with a privileged recharge area located about a kilometer north off the active discharges. Seismic reflection studies image a central magma chamber fueling the hydrothermal sites and also reveal its along-axis depth variations likely influencing hydrothermal cell organization and flow focusing. Such linkages among hydrothermal dynamics, heat source and crustal permeability geometries usually lack quantitative constraints at mid-ocean ridges in general, and the Lucky Strike segment settings offers a unique opportunity to couple high-resolution geophysical data to hydrodynamic model. Here we develop a series of original two- and three-dimensional numerical and physical models of hydrothermal activity, tailored to this slow-spreading environment. Our results highlight physical linkages among magmatism, tectonics and crustal hydrology stressing the key role of faulting and magma chamber roof-topology in focusing fluid flow at the center of the Lucky Strike segment. They also help identifying some causes of variations in the modalities of hydrothermal heat extraction along the global ridge network.

Flows in films and over flippers

NASA Astrophysics Data System (ADS)

van Nierop, Ernst Adriaan

Three topics in fluid mechanics are dealt with in this dissertation, namely (i) reactive spreading and recoil of oil on water, (ii) free film formation theory and experiment, and (iii) how humpback whale flippers delay stall. Reactive spreading of an oil droplet on water is described in Chapter 1. Small amounts of acid and base were added to the oil and water respectively, such that a surfactant was produced at the interface between the oil and the water, greatly enhancing spreading rates. After the oil drop spreads out to some maximum radius, the drop recoils on a timescale that is indicative of a diffusive process redistributing the surfactant over the entire volume of water. In Chapter 2, the theory of soap film formation by withdrawal from a bath of soapy liquid is reviewed, and the assumptions supporting Frankel's law are challenged. Stress balances that describe film evolution in either extensional or shear flow are rigorously derived and we find that the strength of surface stress terms pick the resulting flow type. With this background in mind, we describe in Chapter 3 how films were made using aqueous solutions of poly(ethylene oxide) or PEO with and without surfactant. The initial thickness of these films agrees well with existing data in the literature for overlapping ranges of the capillary number Ca. For larger Ca numbers, we observe that (i) the addition of SDS results in thinner films, (ii) films can be made that are thicker than the wire thickness, and (iii) films swell in thickness when the withdrawal process stops. Some potential mechanisms are described to explain the novel swelling phenomenon. Finally, in Chapter 4, we model the bumpy flipper of a humpback whale as a perturbed elliptic wing with Joukowski profiles of varying chord length, and combine this with lifting line theory as well as experimental stall characteristics of smooth wings. This model shows that the perturbations rearrange the downwash distribution on the wing, smoothing the transition to stall. Bump amplitude dominates the smoothing, while the wavelength of the bumps plays only a small role.

A model of spreading of sudden events on social networks

NASA Astrophysics Data System (ADS)

Wu, Jiao; Zheng, Muhua; Zhang, Zi-Ke; Wang, Wei; Gu, Changgui; Liu, Zonghua

2018-03-01

Information spreading has been studied for decades, but its underlying mechanism is still under debate, especially for those ones spreading extremely fast through the Internet. By focusing on the information spreading data of six typical events on Sina Weibo, we surprisingly find that the spreading of modern information shows some new features, i.e., either extremely fast or slow, depending on the individual events. To understand its mechanism, we present a susceptible-accepted-recovered model with both information sensitivity and social reinforcement. Numerical simulations show that the model can reproduce the main spreading patterns of the six typical events. By this model, we further reveal that the spreading can be speeded up by increasing either the strength of information sensitivity or social reinforcement. Depending on the transmission probability and information sensitivity, the final accepted size can change from continuous to discontinuous transition when the strength of the social reinforcement is large. Moreover, an edge-based compartmental theory is presented to explain the numerical results. These findings may be of significance on the control of information spreading in modern society.

Computational study of a self-cleaning process on superhydrophobic surface

NASA Astrophysics Data System (ADS)

Farokhirad, Samaneh

All substances around us are bounded by interfaces. In general, interface between different phases of materials are categorized as fluid-fluid, solid-fluid, and solid-solid. Fluid-fluid interfaces exhibit a distinct behavior by adapting their shape in response to external stimulus. For example, a liquid droplet on a substrate can undergo different wetting morphologies depending on topography and chemical composition of the surface. Fundamentally, interfacial phenomena arise at the limit between two immiscible phases, namely interface. The interface dynamic governs, to a great extent, physical processes such as impact and spreading of two immiscible media, and stabilization of foams and emulsions from break-up and coalescence. One of the recent challenging problems in the interface-driven fluid dynamics is the self-propulsion mechanism of droplets by means of different types of external forces such as electrical potential, or thermal Marangoni effect. Rapid removal of self-propelled droplet from the surface is an essential factor in terms of expense and efficiency for many applications including self-cleaning and enhanced heat and mass transfer to save energy and natural resources. A recent study on superhydrophobic nature of micro- and nanostructures of cicada wings offers a unique way for the self-propulsion process with no external force, namely coalescence-induced self-propelled jumping of droplet which can act effectively at any orientation. The biological importance of this new mechanism is associated with protecting such surfaces from long term exposure to colloidal particles such as microbial colloids and virus particles. Different interfacial phenomena can occur after out-of-plane jumping of droplet. If the departed droplet is landed back by gravity, it may impact and spread on the surface or coalesce with another droplet and again self-peopled itself to jump away from the surface. The complete removal of the propelled droplet to a sufficient distance beyond the boundary layer of the surface can be accomplished with a surface-parallel shear flow. This thesis presents an investigation of the physics involved in the mechanism of coalescence-induced self-propelled jumping of droplet with and without particle presence, through the use of numerical simulation. (Abstract shortened by ProQuest.).

Morphology of oceanic ridges in spreading colloidal suspensions: Influence of spreading rate and lithospheric thickness

NASA Astrophysics Data System (ADS)

Sibrant, A.; Davaille, A.; Mittelstaedt, E. L.

2016-12-01

Oceanic ridges exhibit significant changes in their structural, morphological, and volcanic characteristics with changes in spreading velocity. However, separating the role of correlated affects such as spreading rate and lithospheric thickness on the segmentation of the ridge axis is difficult with only field data. The goal of this study is (a) to conduct properly scaled laboratory simulations of oceanic ridges, and (b) to investigate how the morphology and geometry of spreading-normal oceanic ridges vary separately with extension rate and lithospheric thickness. We present a series of analogue experiments using colloidal silica dispersions as an Earth analogue. Saline water solutions placed in contact with these fluids, cause formation of a skin through salt diffusion, whose rheology evolves from purely viscous to elastic and brittle with increasing salinity. Applying a fixed spreading rate to this pre-formed, brittle plate resulting in cracks, faults and axial ridge structures. Lithospheric (skin) thickness at a given extension rate is varied by changing salinity of the surface water layer. With increasing spreading rate, we observe several regimes: (1) at the slowest spreading rates, the spreading axis is composed of several segments separated by non-transform offsets and has a fault-bounded, deep, U-shaped axial valley. The axis has a large sinuosity, rough topography, and jumps repeatedly. (2) At intermediate spreading rates, the spreading axis shows low sinuosity, overlapping spreading centers (OSC) , a smooth axial morphology, and very few to no jumps. The axial valley is shallow and shows a V-shape morphology. The OSCs have a ratio of length to width of 3 to 1. (3) At faster spreading rates, the axis is continuous and presents an axial high topography. (4) At the fastest spreading rates tested, the spreading axis is again segmented. Each segment is offset by well developed transform faults and the axis has a sinuosity comparable to those of regimes 2 and 3. Rotating and growing microplates are also observed in regimes 3 and 4. For the first time, we are able to independently control spreading rate, lithospheric thickness, and mechanical properties of a simulated ridge axis in the laboratory. We present results of these experiments and discuss the implications for oceanic ridges on Earth.

Axial crustal structure of the Costa Rica Rift: Implications for along-axis hydrothermal circulation

NASA Astrophysics Data System (ADS)

Zhang, L.; Tong, V.; Hobbs, R. W.; Peirce, C.; Lowell, R. P.; Haughton, G.; Murton, B. J.; Morales Maqueda, M. A.; Harris, R. N.; Robinson, A. H.

2017-12-01

In 2015, a multidisciplinary geophysical cruise surveyed the Costa Rica Rift (CRR) in the Panama Basin of the equatorial East Pacific, acquiring a grid of multichannel seismic and wide-angle profiles to determine the mode of oceanic crustal accretion at intermediate-spreading ridges, and how the crustal structure may be influenced by hydrothermal fluid flow. Analysis of 69,000 P-wave first arrivals recorded by 25 ocean-bottom seismographs deployed over a 20 × 20 km area that straddles the ridge axis, reveals a 3D velocity-depth model of upper crustal structure. In particular, the model shows a low velocity anomaly that extends to 2 km below seabed centred on a small-offset non-transform discontinuity (NTD), and a pattern of increasing velocity with distance off-axis that may reflect changes in porosity and permeability in layer 2 of the crust. Assuming the upper crustal velocity anomalies are linked with porosity and hence represent the ability of fluid to flow, comparison of the tomographic model with the volcanic seabed morphology suggests that the broad low velocity zone beneath the NTD may be a region of extensive fracturing. Hence, we infer that this region may provide a primary pathway for the recharge of seawater into the crust. Further west along the axis, beneath the bathymetric dome, which is the shallowest portion along the axis, the low-velocity anomaly is less pronounced, suggesting that fractures are less open and that fluid-rock interaction has encouraged mineral precipitation and alteration, as a result of a longer established hydrothermal fluid flow driven by the axial magma lens observed beneath it. This interpretation is supported by the presence of a plume from an active hydrothermal vent system. Hence, we infer that the variable velocity structure of the upper crust of the CRR is a proxy that reflects the primary porosity, faulting and fracturing related to phases of magma-driven accretion and/or ridge geometry re-adjustment, and that there is along-axis hydrothermal circulation transferring heat and impacting the properties of newly accreted oceanic crust. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Interactive Electronic Technical Manuals (IETMs) Annotated Bibliography

DTIC Science & Technology

2002-10-22

translated from their graphical counterparts. This paper examines a set of challenging issues facing speech interface designers and describes approaches...spreading network, combined with visual design techniques, such as typography , color, and transparency, enables the system to fluidly respond to...However, most research and design guidelines address typography and color separately without considering their spatial context or their function as

Strain Partitioning and Accumulation across Overlapping Spreading Centers: Geodetic GPS Measurements in South Iceland

NASA Astrophysics Data System (ADS)

La Femina, P. C.; Dixon, T. H.; Malservisi, R.; Árnadóttir, T.; Sigmundsson, F.; Sturkell, E.

2004-12-01

Overlapping spreading centers (OSCs) and propagating ridges are important classes of mid-ocean ridges. Kinematic models of OSCs predict along strike variability in spreading rate associated with the propagation of one center and deactivation of the other. Iceland offers a unique opportunity to investigate strain accumulation and partitioning across slow, overlapping spreading centers, and the influence of a ridge centered hotspot on ridge kinematics and morphology. We present results of detailed GPS observations across the Eastern and Western Volcanic Zones, south Iceland, spanning a seven to nine year inter-rifting period, and compare our observations with two-dimensional elastic half-space models that simulate the long-term spreading process. We then compare the elastic half-space models with simple viscoelastic coupling models. We model three velocity profiles across the EVZ-WVZ system, solving for the spreading rate, locking depth and horizontal location of each spreading center. Our spreading rate estimates indicate along strike variations as expected in an OSC system and total spreading rates consistent with geodetic and geologic plate motion models. Spreading rates in the WVZ increase from northeast (3 ±1 mm/yr) to southwest (7 ±1 mm/yr). Spreading rates in the southwest propagating EVZ decrease from northeast (17 ±1 mm/yr) to southwest (12 ±1 mm/yr). These results are consistent with a model whereby the WVZ is deactivating in the direction of EVZ propagation. The morphology of the two spreading centers reflects the spreading rate differences and their location relative to the Iceland hotspot. The predicted locations of the spreading axis for each zone are consistent with mapped Holocene fissure swarms. The neovolcanic zone of the slower WVZ consists of a narrow (10-20 km wide) axial graben and has had few Holocene eruptions. The faster EVZ consists of two parallel neovolcanic zones separated by a 20 km gap of inactivity, little normal faulting, higher topography and five historical fissure eruptions, reflecting its proximity to the hotspot. The maximum velocity gradient in the EVZ is located on the Veidivotn fissure swarm, which had a small volume eruption in 1864. The last major fissure eruption in the EVZ was the 1783 Lakagigar, located 20 km to the east. This pattern of current and past strain accumulation and release suggests intra-ridge jumping of activity and crustal accretion across a 60 km wide area.

Modeling universal dynamics of cell spreading on elastic substrates.

PubMed

Fan, Houfu; Li, Shaofan

2015-11-01

A three-dimensional (3D) multiscale moving contact line model is combined with a soft matter cell model to study the universal dynamics of cell spreading over elastic substrates. We have studied both the early stage and the late stage cell spreading by taking into account the actin tension effect. In this work, the cell is modeled as an active nematic droplet, and the substrate is modeled as a St. Venant Kirchhoff elastic medium. A complete 3D simulation of cell spreading has been carried out. The simulation results show that the spreading area versus spreading time at different stages obeys specific power laws, which is in good agreement with experimental data and theoretical prediction reported in the literature. Moreover, the simulation results show that the substrate elasticity may affect force dipole distribution inside the cell. The advantage of this approach is that it combines the hydrodynamics of actin retrograde flow with moving contact line model so that it can naturally include actin tension effect resulting from actin polymerization and actomyosin contraction, and thus it might be capable of simulating complex cellular scale phenomenon, such as cell spreading or even crawling.

The latent heat of vaporization of supercritical fluids

NASA Astrophysics Data System (ADS)

Banuti, Daniel; Raju, Muralikrishna; Hickey, Jean-Pierre; Ihme, Matthias

2016-11-01

The enthalpy of vaporization is the energy required to overcome intermolecular attractive forces and to expand the fluid volume against the ambient pressure when transforming a liquid into a gas. It diminishes for rising pressure until it vanishes at the critical point. Counterintuitively, we show that a latent heat is in fact also required to heat a supercritical fluid from a liquid to a gaseous state. Unlike its subcritical counterpart, the supercritical pseudoboiling transition is spread over a finite temperature range. Thus, in addition to overcoming intermolecular attractive forces, added energy simultaneously heats the fluid. Then, considering a transition from a liquid to an ideal gas state, we demonstrate that the required enthalpy is invariant to changes in pressure for 0 < p < 3pcr . This means that the classical pressure-dependent latent heat is merely the equilibrium part of the phase transition. The reduction at higher pressures is compensated by an increase in a nonequilibrium latent heat required to overcome residual intermolecular forces in the real fluid vapor during heating. At supercritical pressures, all of the transition occurs at non-equilibrium; for p -> 0 , all of the transition occurs at equilibrium.

Visualization of sneeze ejecta: steps of fluid fragmentation leading to respiratory droplets

NASA Astrophysics Data System (ADS)

Scharfman, B. E.; Techet, A. H.; Bush, J. W. M.; Bourouiba, L.

2016-02-01

Coughs and sneezes feature turbulent, multiphase flows that may contain pathogen-bearing droplets of mucosalivary fluid. As such, they can contribute to the spread of numerous infectious diseases, including influenza and SARS. The range of contamination of the droplets is largely determined by their size. However, major uncertainties on the drop size distributions persist. Here, we report direct observation of the physical mechanisms of droplet formation at the exit of the mouth during sneezing. Specifically, we use high-speed imaging to directly examine the fluid fragmentation at the exit of the mouths of healthy subjects. We reveal for the first time that the breakup of the fluid into droplets continues to occur outside of the respiratory tract during violent exhalations. We show that such breakup involves a complex cascade of events from sheets, to bag bursts, to ligaments, which finally break into droplets. Finally, we reveal that the viscoelasticity of the mucosalivary fluid plays an important role in delaying fragmentation by causing the merger of the droplet precursors that form along stretched filaments; thereby affecting the final drop size distribution farther downstream.

Diving, Jumping and Drinking: instabilities during water entry and exit

NASA Astrophysics Data System (ADS)

Jung, Sunghwan

2017-11-01

All organisms interact with fluids in one way or another, and some have presumably adapted their behaviors or features in response to fluid-mechanical forces. Particularly, fluid forces are of great importance when organisms or their body parts move in and out of water. In this talk, I will discuss three problems in which fluid mechanics principles affect form and function of animals. The first problem is how several seabirds (e.g. Gannets and Boobies) dive into water at up to 24 m/s without any injuries. This study examines the effects of their beak shape and dense feathers during water entry to reduce or spread the impact force on the body. The second problem is how animals jump out of water, from plankton to whales. Some aquatic animals generate enough force to exit the water surface as an effective method of capturing prey or escaping from predators. Finally, I will discuss about lapping animals (e.g. dog and cat) as a combined water entry and exit. During the tongue-lapping, associated fluid forces and pinch-off instability will be discussed.

Epidemic spreading with activity-driven awareness diffusion on multiplex network.

PubMed

Guo, Quantong; Lei, Yanjun; Jiang, Xin; Ma, Yifang; Huo, Guanying; Zheng, Zhiming

2016-04-01

There has been growing interest in exploring the interplay between epidemic spreading with human response, since it is natural for people to take various measures when they become aware of epidemics. As a proper way to describe the multiple connections among people in reality, multiplex network, a set of nodes interacting through multiple sets of edges, has attracted much attention. In this paper, to explore the coupled dynamical processes, a multiplex network with two layers is built. Specifically, the information spreading layer is a time varying network generated by the activity driven model, while the contagion layer is a static network. We extend the microscopic Markov chain approach to derive the epidemic threshold of the model. Compared with extensive Monte Carlo simulations, the method shows high accuracy for the prediction of the epidemic threshold. Besides, taking different spreading models of awareness into consideration, we explored the interplay between epidemic spreading with awareness spreading. The results show that the awareness spreading can not only enhance the epidemic threshold but also reduce the prevalence of epidemics. When the spreading of awareness is defined as susceptible-infected-susceptible model, there exists a critical value where the dynamical process on the awareness layer can control the onset of epidemics; while if it is a threshold model, the epidemic threshold emerges an abrupt transition with the local awareness ratio α approximating 0.5. Moreover, we also find that temporal changes in the topology hinder the spread of awareness which directly affect the epidemic threshold, especially when the awareness layer is threshold model. Given that the threshold model is a widely used model for social contagion, this is an important and meaningful result. Our results could also lead to interesting future research about the different time-scales of structural changes in multiplex networks.

Epidemic spreading with activity-driven awareness diffusion on multiplex network

NASA Astrophysics Data System (ADS)

Guo, Quantong; Lei, Yanjun; Jiang, Xin; Ma, Yifang; Huo, Guanying; Zheng, Zhiming

2016-04-01

There has been growing interest in exploring the interplay between epidemic spreading with human response, since it is natural for people to take various measures when they become aware of epidemics. As a proper way to describe the multiple connections among people in reality, multiplex network, a set of nodes interacting through multiple sets of edges, has attracted much attention. In this paper, to explore the coupled dynamical processes, a multiplex network with two layers is built. Specifically, the information spreading layer is a time varying network generated by the activity driven model, while the contagion layer is a static network. We extend the microscopic Markov chain approach to derive the epidemic threshold of the model. Compared with extensive Monte Carlo simulations, the method shows high accuracy for the prediction of the epidemic threshold. Besides, taking different spreading models of awareness into consideration, we explored the interplay between epidemic spreading with awareness spreading. The results show that the awareness spreading can not only enhance the epidemic threshold but also reduce the prevalence of epidemics. When the spreading of awareness is defined as susceptible-infected-susceptible model, there exists a critical value where the dynamical process on the awareness layer can control the onset of epidemics; while if it is a threshold model, the epidemic threshold emerges an abrupt transition with the local awareness ratio α approximating 0.5. Moreover, we also find that temporal changes in the topology hinder the spread of awareness which directly affect the epidemic threshold, especially when the awareness layer is threshold model. Given that the threshold model is a widely used model for social contagion, this is an important and meaningful result. Our results could also lead to interesting future research about the different time-scales of structural changes in multiplex networks.

Characterizing super-spreading in microblog: An epidemic-based information propagation model

NASA Astrophysics Data System (ADS)

Liu, Yu; Wang, Bai; Wu, Bin; Shang, Suiming; Zhang, Yunlei; Shi, Chuan

2016-12-01

As the microblogging services are becoming more prosperous in everyday life for users on Online Social Networks (OSNs), it is more favorable for hot topics and breaking news to gain more attraction very soon than ever before, which are so-called "super-spreading events". In the information diffusion process of these super-spreading events, messages are passed on from one user to another and numerous individuals are influenced by a relatively small portion of users, a.k.a. super-spreaders. Acquiring an awareness of super-spreading phenomena and an understanding of patterns of wide-ranged information propagations benefits several social media data mining tasks, such as hot topic detection, predictions of information propagation, harmful information monitoring and intervention. Taking into account that super-spreading in both information diffusion and spread of a contagious disease are analogous, in this study, we build a parameterized model, the SAIR model, based on well-known epidemic models to characterize super-spreading phenomenon in tweet information propagation accompanied with super-spreaders. For the purpose of modeling information diffusion, empirical observations on a real-world Weibo dataset are statistically carried out. Both the steady-state analysis on the equilibrium and the validation on real-world Weibo dataset of the proposed model are conducted. The case study that validates the proposed model shows that the SAIR model is much more promising than the conventional SIR model in characterizing a super-spreading event of information propagation. In addition, numerical simulations are carried out and discussed to discover how sensitively the parameters affect the information propagation process.

Assessment of CO2 Storage Potential in Naturally Fractured Reservoirs With Dual-Porosity Models

NASA Astrophysics Data System (ADS)

March, Rafael; Doster, Florian; Geiger, Sebastian

2018-03-01

Naturally Fractured Reservoirs (NFR's) have received little attention as potential CO2 storage sites. Two main facts deter from storage projects in fractured reservoirs: (1) CO2 tends to be nonwetting in target formations and capillary forces will keep CO2 in the fractures, which typically have low pore volume; and (2) the high conductivity of the fractures may lead to increased spatial spreading of the CO2 plume. Numerical simulations are a powerful tool to understand the physics behind brine-CO2 flow in NFR's. Dual-porosity models are typically used to simulate multiphase flow in fractured formations. However, existing dual-porosity models are based on crude approximations of the matrix-fracture fluid transfer processes and often fail to capture the dynamics of fluid exchange accurately. Therefore, more accurate transfer functions are needed in order to evaluate the CO2 transfer to the matrix. This work presents an assessment of CO2 storage potential in NFR's using dual-porosity models. We investigate the impact of a system of fractures on storage in a saline aquifer, by analyzing the time scales of brine drainage by CO2 in the matrix blocks and the maximum CO2 that can be stored in the rock matrix. A new model to estimate drainage time scales is developed and used in a transfer function for dual-porosity simulations. We then analyze how injection rates should be limited in order to avoid early spill of CO2 (lost control of the plume) on a conceptual anticline model. Numerical simulations on the anticline show that naturally fractured reservoirs may be used to store CO2.

Fire spread estimation on forest wildfire using ensemble kalman filter

NASA Astrophysics Data System (ADS)

Syarifah, Wardatus; Apriliani, Erna

2018-04-01

Wildfire is one of the most frequent disasters in the world, for example forest wildfire, causing population of forest decrease. Forest wildfire, whether naturally occurring or prescribed, are potential risks for ecosystems and human settlements. These risks can be managed by monitoring the weather, prescribing fires to limit available fuel, and creating firebreaks. With computer simulations we can predict and explore how fires may spread. The model of fire spread on forest wildfire was established to determine the fire properties. The fire spread model is prepared based on the equation of the diffusion reaction model. There are many methods to estimate the spread of fire. The Kalman Filter Ensemble Method is a modified estimation method of the Kalman Filter algorithm that can be used to estimate linear and non-linear system models. In this research will apply Ensemble Kalman Filter (EnKF) method to estimate the spread of fire on forest wildfire. Before applying the EnKF method, the fire spread model will be discreted using finite difference method. At the end, the analysis obtained illustrated by numerical simulation using software. The simulation results show that the Ensemble Kalman Filter method is closer to the system model when the ensemble value is greater, while the covariance value of the system model and the smaller the measurement.

Characteristics of Hydrothermal Mineralization in Ultraslow Spreading Ridges

NASA Astrophysics Data System (ADS)

Zhou, H.; Yang, Q.; Ji, F.; Dick, H. J.

2014-12-01

Hydrothermal activity is a major component of the processes that shape the composition and structure of the ocean crust, providing a major pathway for the exchange of heat and elements between the Earth's crust and oceans, and a locus for intense biological activity on the seafloor and underlying crust. In other hand, the structure and composition of hydrothermal systems are the result of complex interactions between heat sources, fluids, wall rocks, tectonic controls and even biological processes. Ultraslow spreading ridges, including the Southwest Indian Ridge, the Gakkel Ridge, are most remarkable end member in plate-boundary structures (Dick et al., 2003), featured with extensive tectonic amagmatic spreading and frequent exposure of peridotite and gabbro. With intensive surveys in last decades, it is suggested that ultraslow ridges are several times more effective than faster-spreading ridges in sustaining hydrothermal activities. This increased efficiency could attributed to deep mining of heat and even exothermic serpentinisation (Baker et al., 2004). Distinct from in faster spreading ridges, one characteristics of hydrothermal mineralization on seafloor in ultraslow spreading ridges, including the active Dragon Flag hydrothermal field at 49.6 degree of the Southwest Indian Ridge, is abundant and pervasive distribution of lower temperature precipitated minerals ( such as Fe-silica or silica, Mn (Fe) oxides, sepiolite, pyrite, marcasite etc. ) in hydrothermal fields. Structures formed by lower temperature activities in active and dead hydrothermal fields are also obviously. High temperature precipitated minerals such as chalcopyrite etc. are rare or very limited in hydrothermal chimneys. Distribution of diverse low temperature hydrothermal activities is consistence with the deep heating mechanisms and hydrothermal circulations in the complex background of ultraslow spreading tectonics. Meanwhile, deeper and larger mineralization at certain locations along the ultraslow spreading ridges is also presumable.

Lattice model for influenza spreading with spontaneous behavioral changes.

PubMed

Fierro, Annalisa; Liccardo, Antonella

2013-01-01

Individual behavioral response to the spreading of an epidemic plays a crucial role in the progression of the epidemic itself. The risk perception induces individuals to adopt a protective behavior, as for instance reducing their social contacts, adopting more restrictive hygienic measures or undergoing prophylaxis procedures. In this paper, starting with a previously developed lattice-gas SIR model, we construct a coupled behavior-disease model for influenza spreading with spontaneous behavioral changes. The focus is on self-initiated behavioral changes that alter the susceptibility to the disease, without altering the contact patterns among individuals. Three different mechanisms of awareness spreading are analyzed: the local spreading due to the presence in the neighborhood of infective individuals; the global spreading due to the news published by the mass media and to educational campaigns implemented at institutional level; the local spreading occurring through the "thought contagion" among aware and unaware individuals. The peculiarity of the present approach is that the awareness spreading model is calibrated on available data on awareness and concern of the population about the risk of contagion. In particular, the model is validated against the A(H1N1) epidemic outbreak in Italy during the 2009/2010 season, by making use of the awareness data gathered by the behavioral risk factor surveillance system (PASSI). We find that, increasing the accordance between the simulated awareness spreading and the PASSI data on risk perception, the agreement between simulated and experimental epidemiological data improves as well. Furthermore, we show that, within our model, the primary mechanism to reproduce a realistic evolution of the awareness during an epidemic, is the one due to globally available information. This result highlights how crucial is the role of mass media and educational campaigns in influencing the epidemic spreading of infectious diseases.

Variable Seawater-Peridotite Interactions - First Insights From ODP Leg 209, MAR 15° N

NASA Astrophysics Data System (ADS)

Bach, W.; Garrido, C. J.; Harvey, J.; Paulick, H.; Rosner, M.; Odp Leg 193 Shipboard Science Party

2003-12-01

Serpentinization of peridotites at slow-spreading mid-ocean ridges has important consequences for the rheology of the oceanic lithosphere, geochemical budgets of the oceans, and microbial processes within, at, and above the seafloor. ODP Leg 209 recovered peridotites that show a remarkable variability of hydrothermal alteration reactions and intensities, including talc-tremolite alteration of pyroxenes associated with incipient serpentinization of olivine, complete alteration of peridotites to serpentine and magnetite followed by the destruction of magnetite and replacement of serpentine by talc, variable degrees of serpentine-brucite alteration, and replacement of brucite by iowaite. These rocks provide a unique opportunity to calibrate our observations against recent results from experimental/theoretical geochemical studies and further our understanding of serpentinization and its role in tectonic accretion and microbial colonization of oceanic lithosphere at slow and ultraslow spreading ridges. We propose that at temperatures above 250° C, pyroxenes react to form serpentine, talc, and tremolite, releasing Ca, Si, H2, and acidity to the reacting fluids that may cause rodingitization in adjacent gabbro bodies. Overall however, rodingites are rare, which may reflect the depleted nature of the mantle protoliths. In the absence of pyroxenes (in dunites) - or at temperatures below 250° C, where pyroxenes react very slowly - the fluids do not become enriched in Ca and Si and serpentine, magnetite, and brucite will form. Many serpentinites lack brucite, tremolite, and talc, because changes in fluid pH and silica activity of the interacting fluids, following the exhaustion of either olivine or pyroxene, caused reaction of these phases to serpentine. Extensive talc alteration of serpentinites and gabbros is usually observed at the intrusive contacts, but large-scale silica metasomatism (or Mg-loss) must be invoked to explain the overall abundance of talc at Site 1268. Significant pyrite/marcasite/hematite veining at Site 1268 indicates fairly oxidizing conditions consistent with the presence of sulfate in the interacting fluids. The first discovery of iowaite in mid-ocean ridge serpentinites (at Site 1272) and the abundant carbonate/Fe-oxyhydroxide alteration, locally extending down to 90 meters below seafloor, indicate that water-rock reactions continue at low temperatures and under strongly oxidizing conditions. Pore fluids from nontronite-bearing serpentine muds in fault gouges may provide information about the nature of these late-stage circulating fluids and potential microbial activity.

Flame Spread and Extinction Over a Thick Solid Fuel in Low-Velocity Opposed and Concurrent Flows

NASA Astrophysics Data System (ADS)

Zhu, Feng; Lu, Zhanbin; Wang, Shuangfeng

2016-05-01

Flame spread and extinction phenomena over a thick PMMA in purely opposed and concurrent flows are investigated by conducting systematical experiments in a narrow channel apparatus. The present tests focus on low-velocity flow regime and hence complement experimental data previously reported for high and moderate velocity regimes. In the flow velocity range tested, the opposed flame is found to spread much faster than the concurrent flame at a given flow velocity. The measured spread rates for opposed and concurrent flames can be correlated by corresponding theoretical models of flame spread, indicating that existing models capture the main mechanisms controlling the flame spread. In low-velocity gas flows, however, the experimental results are observed to deviate from theoretical predictions. This may be attributed to the neglect of radiative heat loss in the theoretical models, whereas radiation becomes important for low-intensity flame spread. Flammability limits using oxygen concentration and flow velocity as coordinates are presented for both opposed and concurrent flame spread configurations. It is found that concurrent spread has a wider flammable range than opposed case. Beyond the flammability boundary of opposed spread, there is an additional flammable area for concurrent spread, where the spreading flame is sustainable in concurrent mode only. The lowest oxygen concentration allowing concurrent flame spread in forced flow is estimated to be approximately 14 % O2, substantially below that for opposed spread (18.5 % O2).

Cronobacter sakazakii DNA Detection in Cerebrospinal Fluid of a Patient with Amyotrophic Lateral Sclerosis Mimic Syndrome

PubMed Central

Piombo, Marianna; Chiarello, Daniela; Corbetto, Marzia; Di Pino, Giovanni; Dicuonzo, Giordano; Angeletti, Silvia; Riva, Elisabetta; De Florio, Lucia; Capone, Fioravante; Di Lazzaro, Vincenzo

2015-01-01

A 45-year-old male noticed progressive weakness of the right lower limb with gait disturbance. Over the following months, motor deficits worsened, spreading to the right upper limb. Electromyography showed active denervation in the upper and lower limb muscles. A diagnosis of amyotrophic lateral sclerosis (ALS) was made. About 2 years after symptom onset, gradual improvement occurred. Cerebrospinal fluid analysis performed about 3 years after the beginning of symptoms identified Cronobacter sakazakii. Since no other possible causes were identified, we suggest that an almost completely reversible ALS-like syndrome had been triggered by Cronobacter infection in our immunocompetent patient. PMID:26955334

Computational-hydrodynamic studies of the Noh compressible flow problem using non-ideal equations of state

NASA Astrophysics Data System (ADS)

Honnell, Kevin; Burnett, Sarah; Yorke, Chloe'; Howard, April; Ramsey, Scott

2017-06-01

The Noh problem is classic verification problem in the field of compressible flows. Simple to conceptualize, it is nonetheless difficult for numerical codes to predict correctly, making it an ideal code-verification test bed. In its original incarnation, the fluid is a simple ideal gas; once validated, however, these codes are often used to study highly non-ideal fluids and solids. In this work the classic Noh problem is extended beyond the commonly-studied polytropic ideal gas to more realistic equations of state (EOS) including the stiff gas, the Nobel-Abel gas, and the Carnahan-Starling hard-sphere fluid, thus enabling verification studies to be performed on more physically-realistic fluids. Exact solutions are compared with numerical results obtained from the Lagrangian hydrocode FLAG, developed at Los Alamos. For these more realistic EOSs, the simulation errors decreased in magnitude both at the origin and at the shock, but also spread more broadly about these points compared to the ideal EOS. The overall spatial convergence rate remained first order.

Running and tumbling with E. coli in polymeric solutions

PubMed Central

Patteson, A. E.; Gopinath, A.; Goulian, M.; Arratia, P. E.

2015-01-01

Run-and-tumble motility is widely used by swimming microorganisms including numerous prokaryotic and eukaryotic organisms. Here, we experimentally investigate the run-and-tumble dynamics of the bacterium E. coli in polymeric solutions. We find that even small amounts of polymer in solution can drastically change E. coli dynamics: cells tumble less and their velocity increases, leading to an enhancement in cell translational diffusion and a sharp decline in rotational diffusion. We show that suppression of tumbling is due to fluid viscosity while the enhancement in swimming speed is mainly due to fluid elasticity. Visualization of single fluorescently labeled DNA polymers reveals that the flow generated by individual E. coli is sufficiently strong to stretch polymer molecules and induce elastic stresses in the fluid, which in turn can act on the cell in such a way to enhance its transport. Our results show that the transport and spread of chemotactic cells can be independently modified and controlled by the fluid material properties. PMID:26507950

Running and tumbling with E. coli in polymeric solutions

NASA Astrophysics Data System (ADS)

Patteson, A. E.; Gopinath, A.; Goulian, M.; Arratia, P. E.

2015-10-01

Run-and-tumble motility is widely used by swimming microorganisms including numerous prokaryotic and eukaryotic organisms. Here, we experimentally investigate the run-and-tumble dynamics of the bacterium E. coli in polymeric solutions. We find that even small amounts of polymer in solution can drastically change E. coli dynamics: cells tumble less and their velocity increases, leading to an enhancement in cell translational diffusion and a sharp decline in rotational diffusion. We show that suppression of tumbling is due to fluid viscosity while the enhancement in swimming speed is mainly due to fluid elasticity. Visualization of single fluorescently labeled DNA polymers reveals that the flow generated by individual E. coli is sufficiently strong to stretch polymer molecules and induce elastic stresses in the fluid, which in turn can act on the cell in such a way to enhance its transport. Our results show that the transport and spread of chemotactic cells can be independently modified and controlled by the fluid material properties.

[In Situ Analysis of Element Geochemistry in Submarine Basalt in Hydrothermal Areas from Ultraslow Spreading Southwest Indian Ridge].

PubMed

Wang, Yan; Sun, Xiao-ming; Xu, Li; Liang, Ye-heng; Wu, Zhong-wei; Fu, Yu; Huang, Yi

2015-03-01

In this study, we analyze element geochemistry of submarine basalt in situ, which is sampled in hydrothermal areas from ultraslow spreading Southwest Indian Ridge, including the fresh basalt rocks (B19-9, B15-13) and altered basalt (B5-2). And we can confirm that altered mineral in B5-2 is celadonite by microscope and Raman Spectrum. Furthermore, amygdaloidal celadonites are analyzed by electron microprobe (EPMA) and EDS-line scanning. The results show that K-contents decrease and Na-contents increase from the core to the edge in these altered minerals, indicating the transition from celadonite to saponite. Celadonite is an altered minerals, forming in low temperature (< 50 degrees C) and oxidizing condition, while saponite form in low water/rock and more reducing condition. As a result, the transition from celadonite to saponite suggests environment change from oxidizing to reducing condition. Using the result of EPMA as internal standard, we can analyze rare earth elements (REE) in altered mineral in situ. Most of result show positive Eu anomaly (Δ(Eu)), indicating hydrothermal fluid transform from oxidizing to reducing, and reducing fluid rework on the early altered minerals. Comparison with REE in matrix feldspar both in altered and unaltered zoning, we find that reducing fluid can leach REE from the matrix feldspar, leading to lower total REE concentrations and positive Eu anomaly. So leaching process play an important role in hydrothermal system.

Modeling of combustion processes of stick propellants via combined Eulerian-Lagrangian approach

NASA Technical Reports Server (NTRS)

Kuo, K. K.; Hsieh, K. C.; Athavale, M. M.

1988-01-01

This research is motivated by the improved ballistic performance of large-caliber guns using stick propellant charges. A comprehensive theoretical model for predicting the flame spreading, combustion, and grain deformation phenomena of long, unslotted stick propellants is presented. The formulation is based upon a combined Eulerian-Lagrangian approach to simulate special characteristics of the two phase combustion process in a cartridge loaded with a bundle of sticks. The model considers five separate regions consisting of the internal perforation, the solid phase, the external interstitial gas phase, and two lumped parameter regions at either end of the stick bundle. For the external gas phase region, a set of transient one-dimensional fluid-dynamic equations using the Eulerian approach is obtained; governing equations for the stick propellants are formulated using the Lagrangian approach. The motion of a representative stick is derived by considering the forces acting on the entire propellant stick. The instantaneous temperature and stress fields in the stick propellant are modeled by considering the transient axisymmetric heat conduction equation and dynamic structural analysis.

Earthquake rupture process recreated from a natural fault surface

USGS Publications Warehouse

Parsons, Thomas E.; Minasian, Diane L.

2015-01-01

What exactly happens on the rupture surface as an earthquake nucleates, spreads, and stops? We cannot observe this directly, and models depend on assumptions about physical conditions and geometry at depth. We thus measure a natural fault surface and use its 3D coordinates to construct a replica at 0.1 m resolution to obviate geometry uncertainty. We can recreate stick-slip behavior on the resulting finite element model that depends solely on observed fault geometry. We clamp the fault together and apply steady state tectonic stress until seismic slip initiates and terminates. Our recreated M~1 earthquake initiates at contact points where there are steep surface gradients because infinitesimal lateral displacements reduce clamping stress most efficiently there. Unclamping enables accelerating slip to spread across the surface, but the fault soon jams up because its uneven, anisotropic shape begins to juxtapose new high-relief sticking points. These contacts would ultimately need to be sheared off or strongly deformed before another similar earthquake could occur. Our model shows that an important role is played by fault-wall geometry, though we do not include effects of varying fluid pressure or exotic rheologies on the fault surfaces. We extrapolate our results to large fault systems using observed self-similarity properties, and suggest that larger ruptures might begin and end in a similar way, though the scale of geometrical variation in fault shape that can arrest a rupture necessarily scales with magnitude. In other words, fault segmentation may be a magnitude dependent phenomenon and could vary with each subsequent rupture.

Geochemistry of hydrothermal fluids from the PACMANUS, Northeast Pual and Vienna Woods hydrothermal fields, Manus Basin, Papua New Guinea

USGS Publications Warehouse

Reeves, Eoghan P.; Seewald, Jeffrey S.; Saccocia, Peter; Bach, Wolfgang; Craddock, Paul R.; Shanks, Wayne C.; Sylva, Sean P.; Walsh, Emily; Pichler, Thomas; Rosner, Martin

2011-01-01

Processes controlling the composition of seafloor hydrothermal fluids in silicic back-arc or near-arc crustal settings remain poorly constrained despite growing evidence for extensive magmatic-hydrothermal activity in such environments. We conducted a survey of vent fluid compositions from two contrasting sites in the Manus back-arc basin, Papua New Guinea, to examine the influence of variations in host rock composition and magmatic inputs (both a function of arc proximity) on hydrothermal fluid chemistry. Fluid samples were collected from felsic-hosted hydrothermal vent fields located on Pual Ridge (PACMANUS and Northeast (NE) Pual) near the active New Britain Arc and a basalt-hosted vent field (Vienna Woods) located farther from the arc on the Manus Spreading Center. Vienna Woods fluids were characterized by relatively uniform endmember temperatures (273-285 degrees C) and major element compositions, low dissolved CO2 concentrations (4.4 mmol/kg) and high measured pH (4.2-4.9 at 25 degrees C). Temperatures and compositions were highly variable at PACMANUS/NE Pual and a large, newly discovered vent area (Fenway) was observed to be vigorously venting boiling (358 degrees C) fluid. All PACMANUS fluids are characterized by negative delta DH2O values, in contrast to positive values at Vienna Woods, suggesting substantial magmatic water input to circulating fluids at Pual Ridge. Low measured pH (25 degrees C) values (~2.6-2.7), high endmember CO2 (up to 274 mmol/kg) and negative delta 34SH2S values (down to -2.7 permille) in some vent fluids are also consistent with degassing of acid-volatile species from evolved magma. Dissolved CO2 at PACMANUS is more enriched in 13C (-4.1 permille to -2.3 permille) than Vienna Woods (-5.2 permille to -5.7 permille), suggesting a contribution of slab-derived carbon. The mobile elements (e.g. Li, K, Rb, Cs and B) are also greatly enriched in PACMANUS fluids reflecting increased abundances in the crust there relative to the Manus Spreading Center. Variations in alkali and dissolved gas abundances with Cl at PACMANUS and NE Pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents. In further contrast to Vienna Woods, substantial modification of PACMANUS/NE Pual fluids has taken place as a result of seawater ingress into the upflow zone. Consistently high measured Mg concentrations as well as trends of increasingly non-conservative SO4 behavior, decreasing endmember Ca/Cl and Sr/Cl ratios with increased Mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment. Decreased pH and endmember Fe/Mn ratios in higher Mg fluids indicate that the associated mixing/cooling gives rise to sulfide deposition and secondary acidity production. Several low temperature (< or = 80 degrees C) fluids at PACMANUS/NE Pual also show evidence for anhydrite dissolution and water-rock interaction (fixation of B) subsequent to seawater entrainment. Hence, the evolution of fluid compositions at Pual Ridge reflects the cumulative effects of water/rock interaction, admixing and reaction of fluids exsolved from silicic magma, phase separation/segregation and seawater ingress into upflow zones.

Can high-temperature, high-heat flux hydrothermal vent fields be explained by thermal convection in the lower crust along fast-spreading Mid-Ocean Ridges?

NASA Astrophysics Data System (ADS)

Fontaine, Fabrice J.; Rabinowicz, M.; Cannat, M.

2017-05-01

We present numerical models to explore possible couplings along the axis of fast-spreading ridges, between hydrothermal convection in the upper crust and magmatic flow in the lower crust. In an end-member category of models corresponding to effective viscosities μM lower than 1013 Pa.s in a melt-rich lower crustal along-axis corridor and permeability k not exceeding ˜10-16 m2 in the upper crust, the hot, melt-rich, gabbroic lower crust convects as a viscous fluid, with convection rolls parallel to the ridge axis. In these models, we show that the magmatic-hydrothermal interface settles at realistic depths for fast ridges, i.e., 1-2 km below seafloor. Convection cells in both horizons are strongly coupled and kilometer-wide hydrothermal upflows/plumes, spaced by 8-10 km, arise on top of the magmatic upflows. Such magmatic-hydrothermal convective couplings may explain the distribution of vent fields along the East (EPR) and South-East Pacific Rise (SEPR). The lower crustal plumes deliver melt locally at the top of the magmatic horizon possibly explaining the observed distribution of melt-rich regions/pockets in the axial melt lenses of EPR and SEPR. Crystallization of this melt provides the necessary latent heat to sustain permanent ˜100 MW vents fields. Our models also contribute to current discussions on how the lower crust forms at fast ridges: they provide a possible mechanism for focused transport of melt-rich crystal mushes from moho level to the axial melt lens where they further crystallize, feed eruptions, and are transported both along and off-axis to produce the lower crust.

Cooperative spreading processes in multiplex networks.

PubMed

Wei, Xiang; Chen, Shihua; Wu, Xiaoqun; Ning, Di; Lu, Jun-An

2016-06-01

This study is concerned with the dynamic behaviors of epidemic spreading in multiplex networks. A model composed of two interacting complex networks is proposed to describe cooperative spreading processes, wherein the virus spreading in one layer can penetrate into the other to promote the spreading process. The global epidemic threshold of the model is smaller than the epidemic thresholds of the corresponding isolated networks. Thus, global epidemic onset arises in the interacting networks even though an epidemic onset does not arise in each isolated network. Simulations verify the analysis results and indicate that cooperative spreading processes in multiplex networks enhance the final infection fraction.

An effective wind speed for models of fire spread

Treesearch

Ralph M. Nelson

2002-01-01

In previous descriptions of wind-slope interaction and the spread rate of wildland fires it is assumed that the separate effects of wind and slope are independent and additive and that corrections for these effects may be applied to spread rates computed from existing rate of spread models. A different approach is explored in the present paper in which the upslope...

Propagation dynamics for a spatially periodic integrodifference competition model

NASA Astrophysics Data System (ADS)

Wu, Ruiwen; Zhao, Xiao-Qiang

2018-05-01

In this paper, we study the propagation dynamics for a class of integrodifference competition models in a periodic habitat. An interesting feature of such a system is that multiple spreading speeds can be observed, which biologically means different species may have different spreading speeds. We show that the model system admits a single spreading speed, and it coincides with the minimal wave speed of the spatially periodic traveling waves. A set of sufficient conditions for linear determinacy of the spreading speed is also given.

Plume-Ridge Interaction on the Cocos Plate (ODP Leg 205, Costa Rica): Implication for Fluid Circulation

NASA Astrophysics Data System (ADS)

Dreyer, B.; Chavagnac, V.; Font, L.; Morris, J.; Schramm, B.; Chavagnac, V.; Font, L.; Schramm, B.; Dreyer, B.; Morris, J. D.

2004-12-01

At subduction zone, the permeability and hydrology of the down-going igneous section play a key role on the behaviour of the seismogenic zone, which produces earthquake and tsunamis. We present, here, evidence of fluid circulation pathways in the igneous section being subducted at the Central American convergent margin (Site 1253 ODP Leg 205, Costa Rica). The geological evolution of the Cocos plate over the last 25 Ma is complicated as a result of plate boundaries re-arrangement (Silver et al., 1998). The Cocos-Nazca spreading centre (CNS) interacted with the Galapagos hotspot, which simultaneously deposited volcanic material on both side of the CNS, on the Cocos and Nazca plates. The oceanic crust of the Cocos and Nazca plates was formed along four spreading centres (Meschede et al., 1998) and the East Pacific Rise (EPR). The EPR oceanic crust has the featureless morphology and low-amplitude magnetic anomalies common to fast spreading ridge (Wilson & Hey, 1995) while the CNS oceanic crust presents a rough topography and high-amplitude magnetic anomalies (Wilson & Hey, 1995). We wish to focus on the ODP 1253 Site drilled in the Cocos plate because it samples the igneous input (rock, heat and fluid) to the Central American subduction zone. Coring at Site 1253 penetrated two separate igneous Units of which the upper one is a sill (Unit 4A) separated from the lower Unit (Unit 4B) by sediment. Both Unit 4A and 4B present similar texture, structure and mineralogy apart from the thin basaltic interval at 513 mbsf, below which Unit 4B becomes more glass-rich and altered. Unit 4B is either a sill complex with multiple intrusions related to the Galapagos volcanic activity or a series of thick slowly cooled lava flows formed at the EPR. Some of these characteristics of Unit 4B are similar to those seen in horizons recovered at Site 1256, which intersected thick-ponded lava flows. Analyses of marine magnetic anomalies indicate that the crust at Site 1253 was formed at EPR 25 Ma ago. However, its thermal gradients and conductivity yield surface heat flow anomalies of 10-40 mWm2, which is ˜70% lower than normal cooling lithosphere of that age (Fisher et al., 2003). Off-axis magmatic and tectonic activity associated with the formation of the Cocos Ridge may have increased fluid circulation pathways within the basement structure. Mobile trace element (Ba, Sr) and Sr isotope variations in conjunction with petrographic observation help identify horizons of fluid/rock interaction, e.g. fluid circulation pathways within Unit 4A and 4B. Based on veins, fractures, and void occurrences, the Unit 4A and 4B were subdivided into two and seven subunits respectively. Along the core-depth profile, mobile element concentrations and 87Sr/86Sr ratios vary mainly in a narrow range (0.703245 and 0.703503) but are still higher than those of EPR or the Galapagos hotspot (<0.703). At sub-unit interface, we observe drastic increases in Ba and Sr content and more radiogenic Sr isotope signature (up to 0.705106), especially above the thin basaltic horizon. This reflects exchange of Sr with seawater or hydrothermal fluids during alteration. Further work will determine fluid flux estimate at Site 1253. The origin, nature and structure of the oceanic crust at Site 1253 will be presented in two additional abstracts (see Dreyer and Moe, this session).

An efficient immersed boundary-lattice Boltzmann method for the hydrodynamic interaction of elastic filaments

PubMed Central

Tian, Fang-Bao; Luo, Haoxiang; Zhu, Luoding; Liao, James C.; Lu, Xi-Yun

2012-01-01

We have introduced a modified penalty approach into the flow-structure interaction solver that combines an immersed boundary method (IBM) and a multi-block lattice Boltzmann method (LBM) to model an incompressible flow and elastic boundaries with finite mass. The effect of the solid structure is handled by the IBM in which the stress exerted by the structure on the fluid is spread onto the collocated grid points near the boundary. The fluid motion is obtained by solving the discrete lattice Boltzmann equation. The inertial force of the thin solid structure is incorporated by connecting this structure through virtual springs to a ghost structure with the equivalent mass. This treatment ameliorates the numerical instability issue encountered in this type of problems. Thanks to the superior efficiency of the IBM and LBM, the overall method is extremely fast for a class of flow-structure interaction problems where details of flow patterns need to be resolved. Numerical examples, including those involving multiple solid bodies, are presented to verify the method and illustrate its efficiency. As an application of the present method, an elastic filament flapping in the Kármán gait and the entrainment regions near a cylinder is studied to model fish swimming in these regions. Significant drag reduction is found for the filament, and the result is consistent with the metabolic cost measured experimentally for the live fish. PMID:23564971

An efficient immersed boundary-lattice Boltzmann method for the hydrodynamic interaction of elastic filaments

NASA Astrophysics Data System (ADS)

Tian, Fang-Bao; Luo, Haoxiang; Zhu, Luoding; Liao, James C.; Lu, Xi-Yun

2011-08-01

We have introduced a modified penalty approach into the flow-structure interaction solver that combines an immersed boundary method (IBM) and a multi-block lattice Boltzmann method (LBM) to model an incompressible flow and elastic boundaries with finite mass. The effect of the solid structure is handled by the IBM in which the stress exerted by the structure on the fluid is spread onto the collocated grid points near the boundary. The fluid motion is obtained by solving the discrete lattice Boltzmann equation. The inertial force of the thin solid structure is incorporated by connecting this structure through virtual springs to a ghost structure with the equivalent mass. This treatment ameliorates the numerical instability issue encountered in this type of problems. Thanks to the superior efficiency of the IBM and LBM, the overall method is extremely fast for a class of flow-structure interaction problems where details of flow patterns need to be resolved. Numerical examples, including those involving multiple solid bodies, are presented to verify the method and illustrate its efficiency. As an application of the present method, an elastic filament flapping in the Kármán gait and the entrainment regions near a cylinder is studied to model fish swimming in these regions. Significant drag reduction is found for the filament, and the result is consistent with the metabolic cost measured experimentally for the live fish.

Self-organization of hydrothermal outflow and recharge in young oceanic crust: Constraints from open-top porous convection analog experiments

NASA Astrophysics Data System (ADS)

Mittelstaedt, E. L.; Olive, J. A. L.; Barreyre, T.

2016-12-01

Hydrothermal circulation at the axis of mid-ocean ridges has a profound effect on chemical and biological processes in the deep ocean, and influences the thermo-mechanical state of young oceanic lithosphere. Yet, the geometry of fluid pathways beneath the seafloor and its relation to spatial gradients in crustal permeability remain enigmatic. Here we present new laboratory models of hydrothermal circulation aimed at constraining the self-organization of porous convection cells in homogeneous as well as highly heterogeneous crust analogs. Oceanic crust analogs of known permeability are constructed using uniform glass spheres and 3-D printed plastics with a network of mutually perpendicular tubes. These materials are saturated with corn syrup-water mixtures and heated at their base by a resistive silicone strip heater to initiate thermal convection. A layer of pure fluid (i.e., an analog ocean) overlies the porous medium and allows an "open-top" boundary condition. Areas of fluid discharge from the crust into the ocean are identified by illuminating microscopic glass particles carried by the fluid, using laser sheets. Using particle image velocimetry, we estimate fluid discharge rates as well as the location and extent of fluid recharge. Thermo-couples distributed throughout the crust provide insights into the geometry of convection cells at depth, and enable estimates of convective heat flux, which can be compared to the heat supplied at the base of the system. Preliminary results indicate that in homogeneous crust, convection is largely confined to the narrow slot overlying the heat source. Regularly spaced discharge zones appear focused while recharge areas appear diffuse, and qualitatively resemble the along-axis distribution of hydrothermal fields at oceanic spreading centers. By varying the permeability of the crustal analogs, the viscosity of the convecting fluid, and the imposed basal temperature, our experiments span Rayleigh numbers between 10 and 10,000. This allows us to precisely map the conditions of convection initiation, and test scaling relations between the Nusselt and Rayleigh numbers. Finally, we investigate how these scalings and convection geometry change when a slot of high-permeability material (i.e., an analog fault) is introduced in the middle of the porous domain.

Coupled charge migration and fluid mixing in reactive fronts

NASA Astrophysics Data System (ADS)

Ghosh, Uddipta; Bandopadhyay, Aditya; Jougnot, Damien; Le Borgne, Tanguy; Meheust, Yves

2017-04-01

Quantifying fluid mixing in subsurface environments and its consequence on biogeochemical reactions is of paramount importance owing to its role in processes such as contaminant migration, aquifer remediation, CO2 sequestration or clogging processes, to name a few (Dentz et al. 2011). The presence of strong velocity gradients in porous media is expected to lead to enhanced diffusive mixing and augmented reaction rates (Le Borgne et al. 2014). Accurate in situ imaging of subsurface reactive solute transport and mixing remains to date a challenging proposition: the opacity of the medium prevents optical imaging and field methods based on tracer tests do not provide spatial information. Recently developed geophysical methods based on the temporal monitoring of electrical conductivity and polarization have shown promises for mapping and monitoring biogeochemical reactions in the subsurface although it remains challenging to decipher the multiple sources of electrical signals (e.g. Knight et al. 2010). In this work, we explore the coupling between fluid mixing, reaction and charge migration in porous media to evaluate the potential of mapping reaction rates from electrical measurements. To this end, we develop a new theoretical framework based on a lamellar mixing model (Le Borgne et al. 2013) to quantify changes in electrical mobility induced by chemical reactions across mixing fronts. Electrical conductivity and induced polarization are strongly dependent on the concentration of ionic species, which in turn depend on the local reaction rates. Hence, our results suggest that variation in real and complex electrical conductivity may be quantitatively related to the mixing and reaction dynamics. Thus, the presented theory provides a novel upscaling framework for quantifying the coupling between mixing, reaction and charge migration in heterogeneous porous media flows. References: Dentz. et al., Mixing, spreading and reaction in heterogeneous media: A brief review J. Contam. Hydrol. 120-121, 1 (2011). Le Borgne et al. Impact of Fluid Deformation on Mixing-Induced Chemical Reactions in heterogeneous Flows, Geophys. Res. Lett. 41, 7898 (2014). Knight, et al., Geophysics at the interface: Response of geophysical properties to solid-fluid, fluid-fluid, and solid-solid interfaces. Rev. Geophys. 48, (2010). Le Borgne et al. (2013) Stretching, coalescence and mixing in porous media, Phys. Rev. Lett., 110, 204501

Theory of rumour spreading in complex social networks

NASA Astrophysics Data System (ADS)

Nekovee, M.; Moreno, Y.; Bianconi, G.; Marsili, M.

2007-01-01

We introduce a general stochastic model for the spread of rumours, and derive mean-field equations that describe the dynamics of the model on complex social networks (in particular, those mediated by the Internet). We use analytical and numerical solutions of these equations to examine the threshold behaviour and dynamics of the model on several models of such networks: random graphs, uncorrelated scale-free networks and scale-free networks with assortative degree correlations. We show that in both homogeneous networks and random graphs the model exhibits a critical threshold in the rumour spreading rate below which a rumour cannot propagate in the system. In the case of scale-free networks, on the other hand, this threshold becomes vanishingly small in the limit of infinite system size. We find that the initial rate at which a rumour spreads is much higher in scale-free networks than in random graphs, and that the rate at which the spreading proceeds on scale-free networks is further increased when assortative degree correlations are introduced. The impact of degree correlations on the final fraction of nodes that ever hears a rumour, however, depends on the interplay between network topology and the rumour spreading rate. Our results show that scale-free social networks are prone to the spreading of rumours, just as they are to the spreading of infections. They are relevant to the spreading dynamics of chain emails, viral advertising and large-scale information dissemination algorithms on the Internet.

The effects of global awareness on the spreading of epidemics in multiplex networks

NASA Astrophysics Data System (ADS)

Zang, Haijuan

2018-02-01

It is increasingly recognized that understanding the complex interplay patterns between epidemic spreading and human behavioral is a key component of successful infection control efforts. In particular, individuals can obtain the information about epidemics and respond by altering their behaviors, which can affect the spreading dynamics as well. Besides, because the existence of herd-like behaviors, individuals are very easy to be influenced by the global awareness information. Here, in this paper, we propose a global awareness controlled spreading model (GACS) to explore the interplay between the coupled dynamical processes. Using the global microscopic Markov chain approach, we obtain the analytical results for the epidemic thresholds, which shows a high accuracy by comparison with lots of Monte Carlo simulations. Furthermore, considering other classical models used to describe the coupled dynamical processes, including the local awareness controlled contagion spreading (LACS) model, Susceptible-Infected-Susceptible-Unaware-Aware-Unaware (SIS-UAU) model and the single layer occasion, we make a detailed comparisons between the GACS with them. Although the comparisons and results depend on the parameters each model has, the GACS model always shows a strong restrain effects on epidemic spreading process. Our results give us a better understanding of the coupled dynamical processes and highlights the importance of considering the spreading of global awareness in the control of epidemics.

Rumor spreading model with consideration of forgetting mechanism: A case of online blogging LiveJournal

NASA Astrophysics Data System (ADS)

Zhao, Laijun; Wang, Qin; Cheng, Jingjing; Chen, Yucheng; Wang, Jiajia; Huang, Wei

2011-07-01

Rumor is an important form of social interaction, and its spreading has a significant impact on people’s lives. In the age of Web, people are using electronic media more frequently than ever before, and blog has become one of the main online social interactions. Therefore, it is essential to learn the evolution mechanism of rumor spreading on homogeneous network in consideration of the forgetting mechanism of spreaders. Here we study a rumor spreading model on an online social blogging platform called LiveJournal. In comparison with the Susceptible-Infected-Removed (SIR) model, we provide a more detailed and realistic description of rumor spreading process with combination of forgetting mechanism and the SIR model of epidemics. A mathematical model has been presented and numerical solutions of the model were used to analyze the impact factors of rumor spreading, such as the average degree, forgetting rate and stifling rate. Our results show that there exist a threshold of the average degree of LiveJournal and above which the influence of rumor reaches saturation. Forgetting mechanism and stifling rate exert great influence on rumor spreading on online social network. The analysis results can guide people’s behaviors in view of the theoretical and practical aspects.

Coupling effects on turning points of infectious diseases epidemics in scale-free networks.

PubMed

Kim, Kiseong; Lee, Sangyeon; Lee, Doheon; Lee, Kwang Hyung

2017-05-31

Pandemic is a typical spreading phenomenon that can be observed in the human society and is dependent on the structure of the social network. The Susceptible-Infective-Recovered (SIR) model describes spreading phenomena using two spreading factors; contagiousness (β) and recovery rate (γ). Some network models are trying to reflect the social network, but the real structure is difficult to uncover. We have developed a spreading phenomenon simulator that can input the epidemic parameters and network parameters and performed the experiment of disease propagation. The simulation result was analyzed to construct a new marker VRTP distribution. We also induced the VRTP formula for three of the network mathematical models. We suggest new marker VRTP (value of recovered on turning point) to describe the coupling between the SIR spreading and the Scale-free (SF) network and observe the aspects of the coupling effects with the various of spreading and network parameters. We also derive the analytic formulation of VRTP in the fully mixed model, the configuration model, and the degree-based model respectively in the mathematical function form for the insights on the relationship between experimental simulation and theoretical consideration. We discover the coupling effect between SIR spreading and SF network through devising novel marker VRTP which reflects the shifting effect and relates to entropy.

Estimation of liquefaction-induced lateral spread from numerical modeling and its application

NASA Astrophysics Data System (ADS)

Meng, Xianhong

A noncoupled numerical procedure was developed using a scheme of pore water generation that causes shear modulus degradation and shear strength degradation resulting from earthquake cyclic motion. The designed Fast Lagrangian Analysis of Continua (FLAC) model procedure was tested using the liquefaction-induced lateral spread and ground response for Wildlife and Kobe sites. Sixteen well-documented case histories of lateral spread were reviewed and modeled using the modeling procedure. The dynamic residual strength ratios were back-calculated by matching the predicted displacement with the measured lateral spread, or with the displacement predicted by the Yound et al. model. Statistical analysis on the modeling results and soil properties show that most significant parameters governing the residual strength of the liquefied soil are the SPT blow count, fine content and soil particle size of the lateral spread layer. A regression equation was developed to express the residual strength values with these soil properties. Overall, this research demonstrated that a calibrated numerical model can predict the first order effectiveness of liquefaction-induced lateral spread using relatively simple parameters obtained from routine geotechnical investigation. In addition, the model can be used to plan a soil improvement program for cases where liquefaction remediation is needed. This allows the model to be used for design purposes at bridge approaches structured on liquefiable materials.

Piezoelectric control of needle-free transdermal drug delivery.

PubMed

Stachowiak, Jeanne C; von Muhlen, Marcio G; Li, Thomas H; Jalilian, Laleh; Parekh, Sapun H; Fletcher, Daniel A

2007-12-04

Transdermal drug delivery occurs primarily through hypodermic needle injections, which cause pain, require a trained administrator, and may contribute to the spread of disease. With the growing number of pharmaceutical therapies requiring transdermal delivery, an effective, safe, and simple needle-free alternative is needed. We present and characterize a needle-free jet injector that employs a piezoelectric actuator to accelerate a micron-scale stream of fluid (40-130 microm diameter) to velocities sufficient for skin penetration and drug delivery (50-160 m/s). Existing jet injectors, powered by compressed springs and gases, are not widely used due to painful injections and poor reliability in skin penetration depth and dose. In contrast, our device offers electronic control of the actuator expansion rate, resulting in direct control of jet velocity and thus the potential for more precise injections. We apply a simple fluid-dynamic model to predict the device response to actuator expansion. Further, we demonstrate that injection parameters including expelled volume, jet pressure, and penetration depth in soft materials vary with actuator expansion rate, but are highly coupled. Finally, we discuss how electronically-controlled jet injectors may enable the decoupling of injection parameters such as penetration depth and dose, improving the reliability of needle-free transdermal drug delivery.

Using HFire for spatial modeling of fire in shrublands

Treesearch

Seth H. Peterson; Marco E. Morais; Jean M. Carlson; Philip E. Dennison; Dar A. Roberts; Max A. Moritz; David R. Weise

2009-01-01

An efficient raster fire-spread model named HFire is introduced. HFire can simulate single-fire events or long-term fire regimes, using the same fire-spread algorithm. This paper describes the HFire algorithm, benchmarks the model using a standard set of tests developed for FARSITE, and compares historical and predicted fire spread perimeters for three southern...

Spreading gossip in social networks.

PubMed

Lind, Pedro G; da Silva, Luciano R; Andrade, José S; Herrmann, Hans J

2007-09-01

We study a simple model of information propagation in social networks, where two quantities are introduced: the spread factor, which measures the average maximal reachability of the neighbors of a given node that interchange information among each other, and the spreading time needed for the information to reach such a fraction of nodes. When the information refers to a particular node at which both quantities are measured, the model can be taken as a model for gossip propagation. In this context, we apply the model to real empirical networks of social acquaintances and compare the underlying spreading dynamics with different types of scale-free and small-world networks. We find that the number of friendship connections strongly influences the probability of being gossiped. Finally, we discuss how the spread factor is able to be applied to other situations.

Spreading gossip in social networks

NASA Astrophysics Data System (ADS)

Lind, Pedro G.; da Silva, Luciano R.; Andrade, José S., Jr.; Herrmann, Hans J.

2007-09-01

We study a simple model of information propagation in social networks, where two quantities are introduced: the spread factor, which measures the average maximal reachability of the neighbors of a given node that interchange information among each other, and the spreading time needed for the information to reach such a fraction of nodes. When the information refers to a particular node at which both quantities are measured, the model can be taken as a model for gossip propagation. In this context, we apply the model to real empirical networks of social acquaintances and compare the underlying spreading dynamics with different types of scale-free and small-world networks. We find that the number of friendship connections strongly influences the probability of being gossiped. Finally, we discuss how the spread factor is able to be applied to other situations.

Chemical compositions and precipitation timing of basement carbonate vein from fossil spreading ridge of South China Sea

NASA Astrophysics Data System (ADS)

Ding, W.; Chen, Y.

2016-12-01

Eighteen calcium carbonate veins within the igneous basement recovered close to the fossil spreading ridge of the South China Sea during the Integrated Ocean Drilling Program (IODP) Expedition 349 were investigated. These carbonates are of primarily either calcite or aragonite, or some mixed aragonite and calcite, with rarely ankerite. The chemical (Ca, Mg, Sr, Mn, Fe) contents and isotopic (87Sr/86Sr, δ18O, δ18C) compositions of the veins were determined to study the evolving chemistry of hydrothermal fluids and to constrain the timing of vein formation. The carbonate δ18O values range from -5.0 to -0.2 ‰ PDB, indicating these are typical low temperature basement carbonates. Chemical analyses show distinct Mg/Ca and Sr/Ca ratios for aragonite and calcite. 87Sr/86Sr ratios show negative correlations with both the depth and δ18O-calculated formation temperature, and are independent of mineralogy with both aragonite and calcite, indicating more geochemically evolved carbonated have precipitated from warmer fluids. The hightest 87Sr/86Sr ratios of vein samples at each drill site are believed to reflect the contemporaneous seawater compositions when carbonates precipitated. No unambiguous precipitation ages can be constrained by correlating 87Sr/86Sr ratios with the global seawater Sr isotope evolution. However, based on correlations of vein chemical composition with depth and formation temperature, as well as the Neogene post-spreading magmatism, we hypothesize 10 Ma is a particular time favoring the formation of carbonate veins in our study area.

THE PATHOGENESIS OF HERPES VIRUS ENCEPHALITIS

PubMed Central

Johnson, Richard T.

1964-01-01

The pathogenesis of herpes simplex virus encephalitis and myelitis was studied in suckling mice using routine titration procedures and fluorescent antibody staining for the identification of infected cells. After intracerebral inoculation virus was shown to disperse rapidly in the cerebrospinal fluid (CSF), multiply in meninges and ependyma, and then invade the underlying parenchyma infecting both neurons and glia. Following extraneural inoculation virus gained access to the central nervous system (CNS) by both hematogenous and neural pathways. After intraperitoneal and intranasal inoculation virus was found to multiply in viscera and produce viremia; foci of CNS infection then developed around small cerebral vessels. After subcutaneous and intranasal inoculation neural spread of virus was demonstrated along corresponding peripheral and cranial nerves. This spread resulted from the centripetal infection of endoneural cells (Schwann cells and fibroblasts). Antigen was not found in axons even after infection of the corresponding ganglion cell perikaryon. Subsequent spread within the CNS was unrelated to neural tracts, and there was no evidence of axonal spread of virus in the host-virus system studied. These findings are discussed in relation to previous and current theories of the viral "blood-brain barrier" and neural pathways of infection. PMID:14164487

Modelling the spread of Ebola virus with Atangana-Baleanu fractional operators

NASA Astrophysics Data System (ADS)

Koca, Ilknur

2018-03-01

The model of Ebola spread within a targeted population is extended to the concept of fractional differentiation and integration with non-local and non-singular fading memory introduced by Atangana and Baleanu. It is expected that the proposed model will show better approximation than the models established before. The existence and uniqueness of solutions for the spread of Ebola disease model is given via the Picard-Lindelof method. Finally, numerical solutions for the model are given by using different parameter values.

Epidemic spreading in time-varying community networks.

PubMed

Ren, Guangming; Wang, Xingyuan

2014-06-01

The spreading processes of many infectious diseases have comparable time scale as the network evolution. Here, we present a simple networks model with time-varying community structure, and investigate susceptible-infected-susceptible epidemic spreading processes in this model. By both theoretic analysis and numerical simulations, we show that the efficiency of epidemic spreading in this model depends intensively on the mobility rate q of the individuals among communities. We also find that there exists a mobility rate threshold qc. The epidemic will survive when q > qc and die when q < qc. These results can help understanding the impacts of human travel on the epidemic spreading in complex networks with community structure.

A novel information cascade model in online social networks

NASA Astrophysics Data System (ADS)

Tong, Chao; He, Wenbo; Niu, Jianwei; Xie, Zhongyu

2016-02-01

The spread and diffusion of information has become one of the hot issues in today's social network analysis. To analyze the spread of online social network information and the attribute of cascade, in this paper, we discuss the spread of two kinds of users' decisions for city-wide activities, namely the "want to take part in the activity" and "be interested in the activity", based on the users' attention in "DouBan" and the data of the city-wide activities. We analyze the characteristics of the activity-decision's spread in these aspects: the scale and scope of the cascade subgraph, the structure characteristic of the cascade subgraph, the topological attribute of spread tree, and the occurrence frequency of cascade subgraph. On this basis, we propose a new information spread model. Based on the classical independent diffusion model, we introduce three mechanisms, equal probability, similarity of nodes, and popularity of nodes, which can generate and affect the spread of information. Besides, by conducting the experiments in six different kinds of network data set, we compare the effects of three mechanisms above mentioned, totally six specific factors, on the spread of information, and put forward that the node's popularity plays an important role in the information spread.

In-situ seismic record of potential sill intrusion at the ultraslow spreading Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Meier, M.; Schlindwein, V. S. N.

2017-12-01

Ultraslow spreading mid-ocean ridges with full spreading rates up to 15 mm/yr are described as the melt poor endmember of the entire mid-ocean ridge system. The melt supply along ultraslow spreading ridges is uneven resulting in the formation of volcanic centres and amagmatic segments. Amagmatic segments show thicker brittle lithosphere of up to 30 km, whereas magmatic segments have much thinner lithosphere of up to less than 15 km. It is supposed that melt travels along the lithosphere asthenosphere boundary from amagmatic segments to magmatic segments, where it can reach the seafloor and erupt. These spreading events are rare at ultraslow spreading ridges compared to faster spreading ridges and insitu observations hardly exist. During an ocean bottom seismometer (OBS) experiment at the eastern Southwest Indian Ridge two earthquake swarms were accidentally recorded. The swarms occurred in January and April 2013 and both lasted for a few days. The events of the earthquake swarms were relatively located with HypoDD for better spatial resolution. This unique dataset allowed for studying active spreading processes at an ultraslow spreading ridge. The earthquakes occurred in depths, where the magma chamber of the nearby Segment-8 volcano is located. This magma chamber potentially fed a sill intrusion, which was recorded as earthquake swarms. During the first hours of the first earthquake swarm a migration pattern was identified. The hypocentres migrated away from the Segment-8 volcanic centre and slightly downwards. Later events occurred more randomly in the active area. Simultaneously seismic tremor was recorded at the station closest to the swarm locations. The tremor lasted longer for the shorter earthquake swarm in April. During both tremor phases the signal was modulated with a 12 hour period. We speculate that a hydrothermal system was affected by the intrusion and fluid flow modulated by the tides produced the tremor signal.

Suppressing disease spreading by using information diffusion on multiplex networks.

PubMed

Wang, Wei; Liu, Quan-Hui; Cai, Shi-Min; Tang, Ming; Braunstein, Lidia A; Stanley, H Eugene

2016-07-06

Although there is always an interplay between the dynamics of information diffusion and disease spreading, the empirical research on the systemic coevolution mechanisms connecting these two spreading dynamics is still lacking. Here we investigate the coevolution mechanisms and dynamics between information and disease spreading by utilizing real data and a proposed spreading model on multiplex network. Our empirical analysis finds asymmetrical interactions between the information and disease spreading dynamics. Our results obtained from both the theoretical framework and extensive stochastic numerical simulations suggest that an information outbreak can be triggered in a communication network by its own spreading dynamics or by a disease outbreak on a contact network, but that the disease threshold is not affected by information spreading. Our key finding is that there is an optimal information transmission rate that markedly suppresses the disease spreading. We find that the time evolution of the dynamics in the proposed model qualitatively agrees with the real-world spreading processes at the optimal information transmission rate.

Modeling potential Emerald Ash Borer spread through GIS/cell-based/gravity models with data bolstered by web-based inputs

Treesearch

Louis R. Iverson; Anantha M. Prasad; Davis Sydnor; Jonathan Bossenbroek; Mark W. Schwartz; Mark W. Schwartz

2006-01-01

We model the susceptibility and potential spread of the organism across the eastern United States and especially through Michigan and Ohio using Forest Inventory and Analysis (FIA) data. We are also developing a cell-based model for the potential spread of the organism. We have developed a web-based tool for public agencies and private individuals to enter the...

A network model for Ebola spreading.

PubMed

Rizzo, Alessandro; Pedalino, Biagio; Porfiri, Maurizio

2016-04-07

The availability of accurate models for the spreading of infectious diseases has opened a new era in management and containment of epidemics. Models are extensively used to plan for and execute vaccination campaigns, to evaluate the risk of international spreadings and the feasibility of travel bans, and to inform prophylaxis campaigns. Even when no specific therapeutical protocol is available, as for the Ebola Virus Disease (EVD), models of epidemic spreading can provide useful insight to steer interventions in the field and to forecast the trend of the epidemic. Here, we propose a novel mathematical model to describe EVD spreading based on activity driven networks (ADNs). Our approach overcomes the simplifying assumption of homogeneous mixing, which is central to most of the mathematically tractable models of EVD spreading. In our ADN-based model, each individual is not bound to contact every other, and its network of contacts varies in time as a function of an activity potential. Our model contemplates the possibility of non-ideal and time-varying intervention policies, which are critical to accurately describe EVD spreading in afflicted countries. The model is calibrated from field data of the 2014 April-to-December spreading in Liberia. We use the model as a predictive tool, to emulate the dynamics of EVD in Liberia and offer a one-year projection, until December 2015. Our predictions agree with the current vision expressed by professionals in the field, who consider EVD in Liberia at its final stage. The model is also used to perform a what-if analysis to assess the efficacy of timely intervention policies. In particular, we show that an earlier application of the same intervention policy would have greatly reduced the number of EVD cases, the duration of the outbreak, and the infrastructures needed for the implementation of the intervention. Copyright © 2016 Elsevier Ltd. All rights reserved.

Varicella infection modeling.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, Katherine A.; Finley, Patrick D.; Moore, Thomas W.

2013-09-01

Infectious diseases can spread rapidly through healthcare facilities, resulting in widespread illness among vulnerable patients. Computational models of disease spread are useful for evaluating mitigation strategies under different scenarios. This report describes two infectious disease models built for the US Department of Veteran Affairs (VA) motivated by a Varicella outbreak in a VA facility. The first model simulates disease spread within a notional contact network representing staff and patients. Several interventions, along with initial infection counts and intervention delay, were evaluated for effectiveness at preventing disease spread. The second model adds staff categories, location, scheduling, and variable contact rates tomore » improve resolution. This model achieved more accurate infection counts and enabled a more rigorous evaluation of comparative effectiveness of interventions.« less

Prediction of Time Response of Electrowetting

NASA Astrophysics Data System (ADS)

Lee, Seung Jun; Hong, Jiwoo; Kang, Kwan Hyoung

2009-11-01

It is very important to predict the time response of electrowetting-based devices, such as liquid lenses, reflective displays, and optical switches. We investigated the time response of electrowetting, based on an analytical and a numerical method, to find out characteristic scales and a scaling law for the switching time. For this, spreading process of a sessile droplet was analyzed based on the domain perturbation method. First, we considered the case of weakly viscous fluids. The analytical result for the spreading process was compared with experimental results, which showed very good agreement in overall time response. It was shown that the overall dynamics is governed by P2 shape mode. We derived characteristic scales combining the droplet volume, density, and surface tension. The overall dynamic process was scaled quite well by the scales. A scaling law was derived from the analytical solution and was verified experimentally. We also suggest a scaling law for highly viscous liquids, based on results of numerical analysis for the electrowetting-actuated spreading process.

Simulation studies of vestibular macular afferent-discharge patterns using a new, quasi-3-D finite volume method

NASA Technical Reports Server (NTRS)

Ross, M. D.; Linton, S. W.; Parnas, B. R.

2000-01-01

A quasi-three-dimensional finite-volume numerical simulator was developed to study passive voltage spread in vestibular macular afferents. The method, borrowed from computational fluid dynamics, discretizes events transpiring in small volumes over time. The afferent simulated had three calyces with processes. The number of processes and synapses, and direction and timing of synapse activation, were varied. Simultaneous synapse activation resulted in shortest latency, while directional activation (proximal to distal and distal to proximal) yielded most regular discharges. Color-coded visualizations showed that the simulator discretized events and demonstrated that discharge produced a distal spread of voltage from the spike initiator into the ending. The simulations indicate that directional input, morphology, and timing of synapse activation can affect discharge properties, as must also distal spread of voltage from the spike initiator. The finite volume method has generality and can be applied to more complex neurons to explore discrete synaptic effects in four dimensions.

Continuous versus Arrested Spreading of Biofilms at Solid-Gas Interfaces: The Role of Surface Forces

NASA Astrophysics Data System (ADS)

Trinschek, Sarah; John, Karin; Lecuyer, Sigolène; Thiele, Uwe

2017-08-01

We introduce and analyze a model for osmotically spreading bacterial colonies at solid-air interfaces that includes wetting phenomena, i.e., surface forces. The model is based on a hydrodynamic description for liquid suspensions which is supplemented by bioactive processes. We show that surface forces determine whether a biofilm can expand laterally over a substrate and provide experimental evidence for the existence of a transition between continuous and arrested spreading for Bacillus subtilis biofilms. In the case of arrested spreading, the lateral expansion of the biofilm is confined, albeit the colony is biologically active. However, a small reduction in the surface tension of the biofilm is sufficient to induce spreading. The incorporation of surface forces into our hydrodynamic model allows us to capture this transition in biofilm spreading behavior.

Exploring the Morphology of oceanic ridges with experiments using colloidal dispersions

NASA Astrophysics Data System (ADS)

Davaille, Anne; Sibrant, Aurore; Mittelstaedt, Eric; Aubertin, Alban; Auffray, Lionel; Pidoux, Raphael

2017-04-01

Mid-ocean ridges exhibit significant changes in their structural, morphological, and volcanic characteristics with changes in lithospheric thickness and/or spreading velocity. However, to separate the respective roles of those two partly correlated effects is difficult with only field data. We therefore designed a series of laboratory experiments using colloidal silica dispersions as an Earth analogue. Saline water solutions placed in contact with these fluids, cause formation of a skin through salt diffusion, whose rheology evolves from purely viscous to elastic and brittle with increasing salinity. Applying a fixed spreading rate to this pre- formed, brittle plate results in cracks, faults and axial ridge structures. Lithospheric (skin) thickness at a given extension rate can be varied by changing the surface water layer salinity. Moreover, the mechanical properties of the skin can also be independently controlled by changing the type of colloid. We focus here on cases where the spreading direction is perpendicular to the ridge axis. For a given dispersion and salinity, we observe four regimes as the spreading rate increases: (1) at the slowest spreading rates, the spreading axis is composed of several segments separated by non-transform offsets and has a fault-bounded, deep, U-shaped axial valley. The axis has a large sinuosity, rough topography, and jumps repeatedly. (2) At intermediate spreading rates, the spreading axis shows low sinuosity, overlapping spreading centers (OSC) , a smooth axial morphology, and very few to no jumps. The axial valley is shallow and shows a V-shape morphology. The OSCs have a ratio of length to width of 3 to 1. (3) At faster spreading rates, the axis is continuous and presents an axial high topography. (4) At the fastest spreading rates tested, the spreading axis is again segmented. Each segment is offset by well developed transform faults and the axis has a sinuosity comparable to those of regimes 2 and 3. Rotating and growing microplates are also observed in regimes 3 and 4. These four regimes, as well as the decrease in sinuosity with increasing spreading rate (regime 1) down to a critical value (regimes 2 to 4), present strong similarities with natural cases. This is predicted by a new dimensionless number ΠF comparing the maximum fracture length attainable without plasticity to the axial thickness. Slow spreading, fault-dominated ridges and fast spreading, dike-dominated ridges on Earth and in the laboratory are separated by the same critical ΠF value. Moreover, our results suggests that the fraction M of spreading rate accomodated by magmatic dyke opening is closely related to ΠF.

Exploring the Complex Pattern of Information Spreading in Online Blog Communities

PubMed Central

Pei, Sen; Muchnik, Lev; Tang, Shaoting; Zheng, Zhiming; Makse, Hernán A.

2015-01-01

Information spreading in online social communities has attracted tremendous attention due to its utmost practical values in applications. Despite that several individual-level diffusion data have been investigated, we still lack the detailed understanding of the spreading pattern of information. Here, by comparing information flows and social links in a blog community, we find that the diffusion processes are induced by three different spreading mechanisms: social spreading, self-promotion and broadcast. Although numerous previous studies have employed epidemic spreading models to simulate information diffusion, we observe that such models fail to reproduce the realistic diffusion pattern. In respect to users behaviors, strikingly, we find that most users would stick to one specific diffusion mechanism. Moreover, our observations indicate that the social spreading is not only crucial for the structure of diffusion trees, but also capable of inducing more subsequent individuals to acquire the information. Our findings suggest new directions for modeling of information diffusion in social systems, and could inform design of efficient propagation strategies based on users behaviors. PMID:25985081

Exploring the complex pattern of information spreading in online blog communities.

PubMed

Pei, Sen; Muchnik, Lev; Tang, Shaoting; Zheng, Zhiming; Makse, Hernán A

2015-01-01

Information spreading in online social communities has attracted tremendous attention due to its utmost practical values in applications. Despite that several individual-level diffusion data have been investigated, we still lack the detailed understanding of the spreading pattern of information. Here, by comparing information flows and social links in a blog community, we find that the diffusion processes are induced by three different spreading mechanisms: social spreading, self-promotion and broadcast. Although numerous previous studies have employed epidemic spreading models to simulate information diffusion, we observe that such models fail to reproduce the realistic diffusion pattern. In respect to users behaviors, strikingly, we find that most users would stick to one specific diffusion mechanism. Moreover, our observations indicate that the social spreading is not only crucial for the structure of diffusion trees, but also capable of inducing more subsequent individuals to acquire the information. Our findings suggest new directions for modeling of information diffusion in social systems, and could inform design of efficient propagation strategies based on users behaviors.

A novel method for sensing metastatic cells in the CSF of pediatric population with medulloblastoma by frequency domain FLIM system

NASA Astrophysics Data System (ADS)

Yahav, Gilad; Fixler, Dror; Gershanov, Sivan; Goldenberg-Cohen, Nitza

2016-03-01

Brain tumors are the second leading cause of cancer-related deaths in children, after leukemia. Patients with cancer in the central nervous system have a very low recovery rate. Today known imaging and cytology techniques are not always sensitive enough for an early detection of both tumor and its metastatic spread, moreover the detection is generally limited, reviewer dependent and takes a relatively long time. Medulloblastoma (MB) is the most common malignant brain tumor in children. The aim of our talk is to present the frequency domain fluorescence lifetime imaging microscopy system as a possible method for an early detection of MB and its metastatic spread in the cerebrospinal fluids within the pediatric population.

Using Concurrent Cardiovascular Information to Augment Survival Time Data from Orthostatic Tilt Tests

NASA Technical Reports Server (NTRS)

Feiveson, Alan H.; Fiedler, James; Lee, Stuart M. M.; Westby, Christian M.; Stenger, Michael B.; Platts, Steven H.

2014-01-01

Orthostatic Intolerance (OI) is the propensity to develop symptoms of fainting during upright standing. OI is associated with changes in heart rate, blood pressure and other measures of cardiac function. Problem: NASA astronauts have shown increased susceptibility to OI on return from space missions. Current methods for counteracting OI in astronauts include fluid loading and the use of compression garments. Multivariate trajectory spread is greater as OI increases. Pairwise comparisons at the same time within subjects allows incorporation of pass/fail outcomes. Path length, convex hull area, and covariance matrix determinant do well as statistics to summarize this spread Missing data problems Time series analysis need many more time points per OTT session treatment of trend? how incorporate survival information?

Clearing Extracellular Alpha-Synuclein from Cerebrospinal Fluid: A New Therapeutic Strategy in Parkinson’s Disease

PubMed Central

Padilla-Zambrano, Huber S.; Tomás-Zapico, Cristina; García, Benjamin Fernández

2018-01-01

This concept article aims to show the rationale of targeting extracellular α-Synuclein (α-Syn) from cerebrospinal fluid (CSF) as a new strategy to remove this protein from the brain in Parkinson’s disease (PD). Misfolding and intracellular aggregation of α-synuclein into Lewy bodies are thought to be crucial in the pathogenesis of PD. Recent research has shown that small amounts of monomeric and oligomeric α-synuclein are released from neuronal cells by exocytosis and that this extracellular alpha-synuclein contributes to neurodegeneration, progressive spreading of alpha-synuclein pathology, and neuroinflammation. In PD, extracellular oligomeric-α-synuclein moves in constant equilibrium between the interstitial fluid (ISF) and the CSF. Thus, we expect that continuous depletion of oligomeric-α-synuclein in the CSF will produce a steady clearance of the protein in the ISF, preventing transmission and deposition in the brain. PMID:29570693

Clearing Extracellular Alpha-Synuclein from Cerebrospinal Fluid: A New Therapeutic Strategy in Parkinson's Disease.

PubMed

Menéndez-González, Manuel; Padilla-Zambrano, Huber S; Tomás-Zapico, Cristina; García, Benjamin Fernández

2018-03-23

This concept article aims to show the rationale of targeting extracellular α-Synuclein (α-Syn) from cerebrospinal fluid (CSF) as a new strategy to remove this protein from the brain in Parkinson's disease (PD). Misfolding and intracellular aggregation of α-synuclein into Lewy bodies are thought to be crucial in the pathogenesis of PD. Recent research has shown that small amounts of monomeric and oligomeric α-synuclein are released from neuronal cells by exocytosis and that this extracellular alpha-synuclein contributes to neurodegeneration, progressive spreading of alpha-synuclein pathology, and neuroinflammation. In PD, extracellular oligomeric-α-synuclein moves in constant equilibrium between the interstitial fluid (ISF) and the CSF. Thus, we expect that continuous depletion of oligomeric-α-synuclein in the CSF will produce a steady clearance of the protein in the ISF, preventing transmission and deposition in the brain.

Structural Transformation in the Northern Continental Margin of the South China Sea During Syn- and Post-Spreading Stages: Based on Study of Baiyun Sag in Pearl River Mouth Basin

NASA Astrophysics Data System (ADS)

Deng, P.; Mei, L.; Liu, J.; Liu, M.

2016-12-01

During the post-rift period, the northern continental margin of the South China Sea experienced syn-spreading stage related to the seafloor spreading from 32-15.5 Ma and post-spreading stage from 15.5-0 Ma. To recognize the structural difference and transformation between the syn- and post-spreading stags, we based on the interpretation of the high quality of 3D seismic data and comprehensively analyze the geometry and kinematics of faults, volcanism, magmatic diapirs and fluid actions of post-rift in Baiyun sag. The analysis reveals the syn-spreading stage can be divided into three episodes, namely Nanhai Episode One (32-29Ma), Nanhai Episode Two (24.4-21Ma) and Nanhai Episode Three (18.5-16.5Ma). Each of the three episodes has different geodynamic background: the first one is response to weak extensional structural environment at the beginning of the seafloor spreading, the second one is response to northward migration of the shelf slope-break in Baiyun sag, and the third one is response to strong subsidence of the Main Baiyun sag. During the syn-spreading stage, amount of effusive magma and polygonal faults developed, and the dynamics of the seafloor spreading shows migratory direction from south to north. The Post-spreading stage, which is response to the subduction compression from the Philippine plate in the east, can be divided into two episodes: Dongsha Episode One (12.5-10.5Ma) and Dongsha Episode Two (5.33-3.6Ma). During the post-spreading stage, each of episode has similar structural property and shows dynamic migration direction from east to west, besides there are much strong tectonism which are different from that of the syn-spreading stage's, such as magmatic diapirs and gas chimney. The structure has obvious transformation from syn- to post-spreading stage in Baiyun sag: faults plane pattern's transformation from dispersive and weak belt-like to X-shaped conjugated shear zone; tectonic evolution migration's transformation from northward migration to westward migration; structural type's transformation from effusive magma and polygonal faults to magmatic diapirs and gas chimney. This study has an enlightening significance of the recognition of structural characteristics in the northern continental margin of the South China Sea during the post-rift period.

Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere.

PubMed

Schlindwein, Vera; Schmid, Florian

2016-07-14

Along ultraslow-spreading ridges, where oceanic tectonic plates drift very slowly apart, conductive cooling is thought to limit mantle melting and melt production has been inferred to be highly discontinuous. Along such spreading centres, long ridge sections without any igneous crust alternate with magmatic sections that host massive volcanoes capable of strong earthquakes. Hence melt supply, lithospheric composition and tectonic structure seem to vary considerably along the axis of the slowest-spreading ridges. However, owing to the lack of seismic data, the lithospheric structure of ultraslow ridges is poorly constrained. Here we describe the structure and accretion modes of two end-member types of oceanic lithosphere using a detailed seismicity survey along 390 kilometres of ultraslow-spreading ridge axis. We observe that amagmatic sections lack shallow seismicity in the upper 15 kilometres of the lithosphere, but unusually contain earthquakes down to depths of 35 kilometres. This observation implies a cold, thick lithosphere, with an upper aseismic zone that probably reflects substantial serpentinization. We find that regions of magmatic lithosphere thin dramatically under volcanic centres, and infer that the resulting topography of the lithosphere-asthenosphere boundary could allow along-axis melt flow, explaining the uneven crustal production at ultraslow-spreading ridges. The seismicity data indicate that alteration in ocean lithosphere may reach far deeper than previously thought, with important implications towards seafloor deformation and fluid circulation.

Web malware spread modelling and optimal control strategies

NASA Astrophysics Data System (ADS)

Liu, Wanping; Zhong, Shouming

2017-02-01

The popularity of the Web improves the growth of web threats. Formulating mathematical models for accurate prediction of malicious propagation over networks is of great importance. The aim of this paper is to understand the propagation mechanisms of web malware and the impact of human intervention on the spread of malicious hyperlinks. Considering the characteristics of web malware, a new differential epidemic model which extends the traditional SIR model by adding another delitescent compartment is proposed to address the spreading behavior of malicious links over networks. The spreading threshold of the model system is calculated, and the dynamics of the model is theoretically analyzed. Moreover, the optimal control theory is employed to study malware immunization strategies, aiming to keep the total economic loss of security investment and infection loss as low as possible. The existence and uniqueness of the results concerning the optimality system are confirmed. Finally, numerical simulations show that the spread of malware links can be controlled effectively with proper control strategy of specific parameter choice.

Web malware spread modelling and optimal control strategies.

PubMed

Liu, Wanping; Zhong, Shouming

2017-02-10

The popularity of the Web improves the growth of web threats. Formulating mathematical models for accurate prediction of malicious propagation over networks is of great importance. The aim of this paper is to understand the propagation mechanisms of web malware and the impact of human intervention on the spread of malicious hyperlinks. Considering the characteristics of web malware, a new differential epidemic model which extends the traditional SIR model by adding another delitescent compartment is proposed to address the spreading behavior of malicious links over networks. The spreading threshold of the model system is calculated, and the dynamics of the model is theoretically analyzed. Moreover, the optimal control theory is employed to study malware immunization strategies, aiming to keep the total economic loss of security investment and infection loss as low as possible. The existence and uniqueness of the results concerning the optimality system are confirmed. Finally, numerical simulations show that the spread of malware links can be controlled effectively with proper control strategy of specific parameter choice.

InterSpread Plus: a spatial and stochastic simulation model of disease in animal populations.

PubMed

Stevenson, M A; Sanson, R L; Stern, M W; O'Leary, B D; Sujau, M; Moles-Benfell, N; Morris, R S

2013-04-01

We describe the spatially explicit, stochastic simulation model of disease spread, InterSpread Plus, in terms of its epidemiological framework, operation, and mode of use. The input data required by the model, the method for simulating contact and infection spread, and methods for simulating disease control measures are described. Data and parameters that are essential for disease simulation modelling using InterSpread Plus are distinguished from those that are non-essential, and it is suggested that a rational approach to simulating disease epidemics using this tool is to start with core data and parameters, adding additional layers of complexity if and when the specific requirements of the simulation exercise require it. We recommend that simulation models of disease are best developed as part of epidemic contingency planning so decision makers are familiar with model outputs and assumptions and are well-positioned to evaluate their strengths and weaknesses to make informed decisions in times of crisis. Copyright © 2012 Elsevier B.V. All rights reserved.

Web malware spread modelling and optimal control strategies

PubMed Central

Liu, Wanping; Zhong, Shouming

2017-01-01

The popularity of the Web improves the growth of web threats. Formulating mathematical models for accurate prediction of malicious propagation over networks is of great importance. The aim of this paper is to understand the propagation mechanisms of web malware and the impact of human intervention on the spread of malicious hyperlinks. Considering the characteristics of web malware, a new differential epidemic model which extends the traditional SIR model by adding another delitescent compartment is proposed to address the spreading behavior of malicious links over networks. The spreading threshold of the model system is calculated, and the dynamics of the model is theoretically analyzed. Moreover, the optimal control theory is employed to study malware immunization strategies, aiming to keep the total economic loss of security investment and infection loss as low as possible. The existence and uniqueness of the results concerning the optimality system are confirmed. Finally, numerical simulations show that the spread of malware links can be controlled effectively with proper control strategy of specific parameter choice. PMID:28186203

Climate model diversity in the Northern Hemisphere Polar vortex response to climate change.

NASA Astrophysics Data System (ADS)

Simpson, I.; Seager, R.; Hitchcock, P.; Cohen, N.

2017-12-01

Global climate models vary widely in their predictions of the future of the Northern Hemisphere stratospheric polar vortex, with some showing a significant strengthening of the vortex, some showing a significant weakening and others displaying a response that is not outside of the range expected from internal variability alone. This inter-model spread in stratospheric predictions may account for some inter-model spread in tropospheric predictions with important implications for the storm tracks and regional climate change, particularly for the North Atlantic sector. Here, our current state of understanding of this model spread and its tropospheric impacts will be reviewed. Previous studies have proposed relationships between a models polar vortex response to climate change and its present day vortex climatology while others have demonstrated links between a models polar vortex response and changing wave activity coming up from the troposphere below under a warming climate. The extent to which these mechanisms can account for the spread in polar vortex changes exhibited by the Coupled Model Intercomparison Project, phase 5 models will be assessed. In addition, preliminary results from a series of idealized experiments with the Community Atmosphere Model will be presented. In these experiments, nudging of the stratospheric zonal mean state has been imposed to mimic the inter-model spread in the polar vortex response to climate change so that the downward influence of the spread in zonal mean stratospheric responses on the tropospheric circulation can be assessed within one model.

Numerical simulation study on impact of slope on smoke temperature distribution and smoke spread pattern in spiral tunnel fires

NASA Astrophysics Data System (ADS)

Li, Tao; Xie, Wei

2017-04-01

The spiral tunnel arises as a new form of tunnel, with great differences in fire development pattern when compared with traditional straight line tunnel, this paper takes method of numerical simulation, based on computation fluid dynamics theory and fire-turbulence numerical simulation theory, establishing a full-scale spiral tunnel model, and applies CFX simulation software to research full-scale spiral tunnel fire and its ventilation condition. The results indicate that with increasing tunnel slope, high temperature area gradually extends to downstream area, high temperature mainly distributes near fire source area, and symmetrically distributes among the fire center point; With increasing tunnel slope, the highest temperature underneath tunnel arch rises first followed by a downward trend and then rising again, which strengthens chimney effect, and promotes more fresh cold air flow into the tunnel, suppressing fire smoke backflow and simultaneously accelerating fire smoke spread to downstream area; Fire plume presents vertical slender shape with 1% or 3% tunnel slope, and burning flame hits tunnel arch and then extending all around into the ceiling jet flow, when tunnel slope increases to 5% or 7%, fire plume cross section grows bigger and wider with unstable burning flame swaying in all directions, integrally incline to fire downstream.

Insights Into the Causes of Arc Rifting From 2-D Dynamic Models of Subduction

NASA Astrophysics Data System (ADS)

Billen, Magali I.

2017-11-01

Back-arc spreading centers initiate as fore-arc or arc rifting events when extensional forces localize within lithosphere weakened by hydrous fluids or melting. Two models have been proposed for triggering fore-arc/arc rifting: rollback of the subducting plate causing trench retreat or motion of the overriding plate away from the subduction zone. This paper demonstrates that there is a third mechanism caused by an in situ instability that occurs when the thin high-viscosity boundary, which separates the weak fore arc from the hot buoyant mantle wedge, is removed. Buoyant upwelling mantle causes arc rifting, drives the overriding plate away from the subducting plate, and there is sufficient heating of the subducting plate crust and overriding plate lithosphere to form adakite or boninite volcanism. For spontaneous fore-arc/arc rifting to occur a broad region of weak material must be present and one of the plates must be free to respond to the upwelling forces.

Non-aqueous phase liquid spreading during soil vapor extraction

PubMed Central

Kneafsey, Timothy J.; Hunt, James R.

2010-01-01

Many non-aqueous phase liquids (NAPLs) are expected to spread at the air – water interface, particularly under non-equilibrium conditions. In the vadose zone, this spreading should increase the surface area for mass transfer and the efficiency of volatile NAPL recovery by soil vapor extraction (SVE). Observations of spreading on water wet surfaces led to a conceptual model of oil spreading vertically above a NAPL pool in the vadose zone. Analysis of this model predicts that spreading can enhance the SVE contaminant recovery compared to conditions where the liquid does not spread. Experiments were conducted with spreading volatile oils hexane and heptane in wet porous media and capillary tubes, where spreading was observed at the scale of centimeters. Within porous medium columns up to a meter in height containing stagnant gas, spreading was less than ten centimeters and did not contribute significantly to hexane volatilization. Water film thinning and oil film pinning may have prevented significant oil film spreading, and thus did not enhance SVE at the scale of a meter. The experiments performed indicate that volatile oil spreading at the field scale is unlikely to contribute significantly to the efficiency of SVE. PMID:14734243

A Monte Carlo model for 3D grain evolution during welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bezier curves, which allow formore » the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. Furthermore, the model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.« less

A Monte Carlo model for 3D grain evolution during welding

DOE PAGES

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

2017-08-04

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bezier curves, which allow formore » the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. Furthermore, the model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.« less

Global stability of a two-mediums rumor spreading model with media coverage

NASA Astrophysics Data System (ADS)

Huo, Liang'an; Wang, Li; Song, Guoxiang

2017-09-01

Rumor spreading is a typical form of social communication and plays a significant role in social life, and media coverage has a great influence on the spread of rumor. In this paper, we present a new model with two media coverage to investigate the impact of the different mediums on rumor spreading. Then, we calculate the equilibria of the model and construct the reproduction number ℜ0. And we prove the global asymptotic stability of equilibria by using Lyapunov functions. Finally, we can conclude that the transition rate of the ignorants between two mediums has a direct effect on the scale of spreaders, and different media coverage has significant effects on the dynamics behaviors of rumor spreading.

Epidemic spreading in time-varying community networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Guangming, E-mail: wangxy@dlut.edu.cn, E-mail: ren-guang-ming@163.com; Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024; Wang, Xingyuan, E-mail: wangxy@dlut.edu.cn, E-mail: ren-guang-ming@163.com

2014-06-15

The spreading processes of many infectious diseases have comparable time scale as the network evolution. Here, we present a simple networks model with time-varying community structure, and investigate susceptible-infected-susceptible epidemic spreading processes in this model. By both theoretic analysis and numerical simulations, we show that the efficiency of epidemic spreading in this model depends intensively on the mobility rate q of the individuals among communities. We also find that there exists a mobility rate threshold q{sub c}. The epidemic will survive when q > q{sub c} and die when q < q{sub c}. These results can help understanding the impacts of human travel onmore » the epidemic spreading in complex networks with community structure.« less

Hybrid epidemics--a case study on computer worm conficker.

PubMed

Zhang, Changwang; Zhou, Shi; Chain, Benjamin M

2015-01-01

Conficker is a computer worm that erupted on the Internet in 2008. It is unique in combining three different spreading strategies: local probing, neighbourhood probing, and global probing. We propose a mathematical model that combines three modes of spreading: local, neighbourhood, and global, to capture the worm's spreading behaviour. The parameters of the model are inferred directly from network data obtained during the first day of the Conficker epidemic. The model is then used to explore the tradeoff between spreading modes in determining the worm's effectiveness. Our results show that the Conficker epidemic is an example of a critically hybrid epidemic, in which the different modes of spreading in isolation do not lead to successful epidemics. Such hybrid spreading strategies may be used beneficially to provide the most effective strategies for promulgating information across a large population. When used maliciously, however, they can present a dangerous challenge to current internet security protocols.

Spreading-vanishing dichotomy in a diffusive logistic model with a free boundary, II

NASA Astrophysics Data System (ADS)

Du, Yihong; Guo, Zongming

We study the diffusive logistic equation with a free boundary in higher space dimensions and heterogeneous environment. Such a model may be used to describe the spreading of a new or invasive species, with the free boundary representing the expanding front. For simplicity, we assume that the environment and the solution are radially symmetric. In the special case of one space dimension and homogeneous environment, this free boundary problem was investigated in Du and Lin (2010) [10]. We prove that the spreading-vanishing dichotomy established in Du and Lin (2010) [10] still holds in the more general and ecologically realistic setting considered here. Moreover, when spreading occurs, we obtain best possible upper and lower bounds for the spreading speed of the expanding front. When the environment is asymptotically homogeneous at infinity, these two bounds coincide. Our results indicate that the asymptotic spreading speed determined by this model does not depend on the spatial dimension.

Climate change alters diffusion of forest pest: A model study

NASA Astrophysics Data System (ADS)

Jo, Woo Seong; Kim, Hwang-Yong; Kim, Beom Jun

2017-01-01

Population dynamics with spatial information is applied to understand the spread of pests. We introduce a model describing how pests spread in discrete space. The number of pest descendants at each site is controlled by local information such as temperature, precipitation, and the density of pine trees. Our simulation leads to a pest spreading pattern comparable to the real data for pine needle gall midge in the past. We also simulate the model in two different climate conditions based on two different representative concentration pathways scenarios for the future. We observe that after an initial stage of a slow spread of pests, a sudden change in the spreading speed occurs, which is soon followed by a large-scale outbreak. We found that a future climate change causes the outbreak point to occur earlier and that the detailed spatio-temporal pattern of the spread depends on the source position from which the initial pest infection starts.

Hybrid Epidemics—A Case Study on Computer Worm Conficker

PubMed Central

Zhang, Changwang; Zhou, Shi; Chain, Benjamin M.

2015-01-01

Conficker is a computer worm that erupted on the Internet in 2008. It is unique in combining three different spreading strategies: local probing, neighbourhood probing, and global probing. We propose a mathematical model that combines three modes of spreading: local, neighbourhood, and global, to capture the worm’s spreading behaviour. The parameters of the model are inferred directly from network data obtained during the first day of the Conficker epidemic. The model is then used to explore the tradeoff between spreading modes in determining the worm’s effectiveness. Our results show that the Conficker epidemic is an example of a critically hybrid epidemic, in which the different modes of spreading in isolation do not lead to successful epidemics. Such hybrid spreading strategies may be used beneficially to provide the most effective strategies for promulgating information across a large population. When used maliciously, however, they can present a dangerous challenge to current internet security protocols. PMID:25978309

Influence of trust in the spreading of information

NASA Astrophysics Data System (ADS)

Wu, Hongrun; Arenas, Alex; Gómez, Sergio

2017-01-01

The understanding and prediction of information diffusion processes on networks is a major challenge in network theory with many implications in social sciences. Many theoretical advances occurred due to stochastic spreading models. Nevertheless, these stochastic models overlooked the influence of rational decisions on the outcome of the process. For instance, different levels of trust in acquaintances do play a role in information spreading, and actors may change their spreading decisions during the information diffusion process accordingly. Here, we study an information-spreading model in which the decision to transmit or not is based on trust. We explore the interplay between the propagation of information and the trust dynamics happening on a two-layer multiplex network. Actors' trustable or untrustable states are defined as accumulated cooperation or defection behaviors, respectively, in a Prisoner's Dilemma setup, and they are controlled by a memory span. The propagation of information is abstracted as a threshold model on the information-spreading layer, where the threshold depends on the trustability of agents. The analysis of the model is performed using a tree approximation and validated on homogeneous and heterogeneous networks. The results show that the memory of previous actions has a significant effect on the spreading of information. For example, the less memory that is considered, the higher is the diffusion. Information is highly promoted by the emergence of trustable acquaintances. These results provide insight into the effect of plausible biases on spreading dynamics in a multilevel networked system.

Electrical signal transmission and gap junction regulation in a bone cell network: a cable model for an osteon

NASA Technical Reports Server (NTRS)

Zhang, D.; Cowin, S. C.; Weinbaum, S.

1997-01-01

A cable model is formulated to estimate the spatial distribution of intracellular electric potential and current, from the cement line to the lumen of an osteon, as the frequency of the loading and the conductance of the gap junction are altered. The model predicts that the characteristic diffusion time for the spread of current along the membrane of the osteocytic processes, 0.03 sec, is nearly the same as the predicted pore pressure relaxation time in Zeng et al. (Annals of Biomedical Engineering. 1994) for the draining of the bone fluid into the osteonal canal. This approximate equality of characteristic times causes the cable to behave as a high-pass, low-pass filter cascade with a maximum in the spectral response for the intracellular potential at approximately 30 Hz. This behavior could be related to the experiments of Rubin and McLeod (Osteoporosis, Academic Press, 1996) which show that live bone appears to be selectively responsive to mechanical loading in a specific frequency range (15-30 Hz) for several species.

A coupled DEM-CFD method for impulse wave modelling

NASA Astrophysics Data System (ADS)

Zhao, Tao; Utili, Stefano; Crosta, GiovanBattista

2015-04-01

Rockslides can be characterized by a rapid evolution, up to a possible transition into a rock avalanche, which can be associated with an almost instantaneous collapse and spreading. Different examples are available in the literature, but the Vajont rockslide is quite unique for its morphological and geological characteristics, as well as for the type of evolution and the availability of long term monitoring data. This study advocates the use of a DEM-CFD framework for the modelling of the generation of hydrodynamic waves due to the impact of a rapid moving rockslide or rock-debris avalanche. 3D DEM analyses in plane strain by a coupled DEM-CFD code were performed to simulate the rockslide from its onset to the impact with still water and the subsequent wave generation (Zhao et al., 2014). The physical response predicted is in broad agreement with the available observations. The numerical results are compared to those published in the literature and especially to Crosta et al. (2014). According to our results, the maximum computed run up amounts to ca. 120 m and 170 m for the eastern and western lobe cross sections, respectively. These values are reasonably similar to those recorded during the event (i.e. ca. 130 m and 190 m respectively). In these simulations, the slope mass is considered permeable, such that the toe region of the slope can move submerged in the reservoir and the impulse water wave can also flow back into the slope mass. However, the upscaling of the grains size in the DEM model leads to an unrealistically high hydraulic conductivity of the model, such that only a small amount of water is splashed onto the northern bank of the Vajont valley. The use of high fluid viscosity and coarse grain model has shown the possibility to model more realistically both the slope and wave motions. However, more detailed slope and fluid properties, and the need for computational efficiency should be considered in future research work. This aspect has also been investigated by Crosta et al. (2014) via 2D and 3D FEM ALE modelling without considering the water seepage in the slope mass has been used. Their results can be a good way to estimate the slope and wave motion for fast sliding conditions. The 3D modelling can also clarify the lateral motion of water and estimate the potential risk of water overtopping the dam crest. The DEM and FEM ALE modelling can be used together to analyse fast moving rockslides (i.e. flowslides, rockslides, rock and debris avalanches) both in dry conditions and for their interaction with water basins. References Zhao, T., Utili, S., Crosta, G.B. Rockslide and impulse wave modelling in the Vajont reservoir by DEM-CFD analyses. Rock Mechanics and rock Engineering, under review. Crosta, G.B., Imposimato, S. & Roddeman, D. 2014. Landslide spreading, impulse waves and modelling of the Vajont rockslide. Rock Mechanics and Rock Engineering, under review.

Continuous flow electrophoresis system experiments on shuttle flights STS-6 and STS-7

NASA Technical Reports Server (NTRS)

Snyder, Robert S.; Rhodes, Percy H.; Miller, Teresa Y.

1988-01-01

The development of a space continuous flow electrophoresis system (CFES) is discussed. The objectives of the experiment were: (1) to use a model sample material at a high concentration to evaluate the continuous flow electrophoresis process in the McDonnell Douglass CFES instrument and compare its separation resolution and sample throughput with related devices on Earth, and (2) to expand the basic knowledge of the limitations imposed by fluid flows and particle concentration effects on the electrophoresis process by careful design and evaluation of the space experiment. Hemoglobin and polysaccharide were selected as samples of concentration effects. The results from space show a large band spread of the high concentration of the single species of hemoglobin that was principally due to the mismatch of electrical conductivity between the sample and buffer.

Glymphatic fluid transport controls paravascular clearance of AAV vectors from the brain

PubMed Central

Murlidharan, Giridhar; Crowther, Andrew; Reardon, Rebecca A.; Song, Juan

2016-01-01

Adeno-associated viruses (AAV) are currently being evaluated in clinical trials for gene therapy of CNS disorders. However, host factors that influence the spread, clearance, and transduction efficiency of AAV vectors in the brain are not well understood. Recent studies have demonstrated that fluid flow mediated by aquaporin-4 (AQP4) channels located on astroglial end feet is essential for exchange of solutes between interstitial and cerebrospinal fluid. This phenomenon, which is essential for interstitial clearance of solutes from the CNS, has been termed glial-associated lymphatic transport or glymphatic transport. In the current study, we demonstrate that glymphatic transport profoundly affects various aspects of AAV gene transfer in the CNS. Altered localization of AQP4 in aged mouse brains correlated with significantly increased retention of AAV vectors in the parenchyma and reduced systemic leakage following ventricular administration. We observed a similar increase in AAV retention and transgene expression upon i.c.v. administration in AQP4–/– mice. Consistent with this observation, fluorophore-labeled AAV vectors showed markedly reduced flux from the ventricles of AQP4–/– mice compared with WT mice. These results were further corroborated by reduced AAV clearance from the AQP4-null brain, as demonstrated by reduced transgene expression and vector genome accumulation in systemic organs. We postulate that deregulation of glymphatic transport in aged and diseased brains could markedly affect the parenchymal spread, clearance, and gene transfer efficiency of AAV vectors. Assessment of biomarkers that report the kinetics of CSF flux in prospective gene therapy patients might inform variable treatment outcomes and guide future clinical trial design. PMID:27699236

Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Co-Axial Supersonic Free-Jet Experiment

NASA Technical Reports Server (NTRS)

Baurle, R. A.; Edwards, J. R.

2009-01-01

Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment utilized either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state-of-the-art for each modeling approach, and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The baseline value chosen for this parameter resulted in an over-prediction of the mixing layer spreading rate for the helium case, but the opposite trend was noted when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid simulation results showed the same trends as the baseline Reynolds-averaged predictions. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions are suggested as a remedy to this dilemma. Comparisons between resolved second-order turbulence statistics and their modeled Reynolds-averaged counterparts were also performed.

Probabilistic 3-D time-lapse inversion of magnetotelluric data: application to an enhanced geothermal system

NASA Astrophysics Data System (ADS)

Rosas-Carbajal, M.; Linde, N.; Peacock, J.; Zyserman, F. I.; Kalscheuer, T.; Thiel, S.

2015-12-01

Surface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved. We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north-south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

Probabilistic 3-D time-lapse inversion of magnetotelluric data: Application to an enhanced geothermal system

USGS Publications Warehouse

Rosas-Carbajal, Marina; Linde, Nicolas; Peacock, Jared R.; Zyserman, F. I.; Kalscheuer, Thomas; Thiel, Stephan

2015-01-01

Surface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved.We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north-south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

A fuzzy rumor spreading model based on transmission capacity

NASA Astrophysics Data System (ADS)

Zhang, Yi; Xu, Jiuping; Wu, Yue

This paper proposes a rumor spreading model that considers three main factors: the event importance, event ambiguity, and the publics critical sense, each of which are defined by decision makers using linguistic descriptions and then transformed into triangular fuzzy numbers. To calculate the resultant force of these three factors, the transmission capacity and a new parameter category with fuzzy variables are determined. A rumor spreading model is then proposed which has fuzzy parameters rather than the fixed parameters in traditional models. As the proposed model considers the comprehensive factors affecting rumors from three aspects rather than examining special factors from a particular aspect. The proposed rumor spreading model is tested using different parameters for several different conditions on BA networks and three special cases are simulated. The simulation results for all three cases suggested that events of low importance, those that are only clarifying facts, and those that are strongly critical do not result in rumors. Therefore, the model assessment results were proven to be in agreement with reality. Parameters for the model were then determined and applied to an analysis of the 7.23 Yong-Wen line major transportation accident (YWMTA). When the simulated data were compared with the real data from this accident, the results demonstrated that the interval for the rumor spreading key point in the model was accurate, and that the key point for the YWMTA rumor spread fell into the range estimated by the model.

An agent-based computational model of the spread of tuberculosis

NASA Astrophysics Data System (ADS)

de Espíndola, Aquino L.; Bauch, Chris T.; Troca Cabella, Brenno C.; Souto Martinez, Alexandre

2011-05-01

In this work we propose an alternative model of the spread of tuberculosis (TB) and the emergence of drug resistance due to the treatment with antibiotics. We implement the simulations by an agent-based model computational approach where the spatial structure is taken into account. The spread of tuberculosis occurs according to probabilities defined by the interactions among individuals. The model was validated by reproducing results already known from the literature in which different treatment regimes yield the emergence of drug resistance. The different patterns of TB spread can be visualized at any time of the system evolution. The implementation details as well as some results of this alternative approach are discussed.

Analysis of Initial Cell Spreading Using Mechanistic Contact Formulations for a Deformable Cell Model

PubMed Central

Odenthal, Tim; Smeets, Bart; Van Liedekerke, Paul; Tijskens, Engelbert; Van Oosterwyck, Hans; Ramon, Herman

2013-01-01

Adhesion governs to a large extent the mechanical interaction between a cell and its microenvironment. As initial cell spreading is purely adhesion driven, understanding this phenomenon leads to profound insight in both cell adhesion and cell-substrate interaction. It has been found that across a wide variety of cell types, initial spreading behavior universally follows the same power laws. The simplest cell type providing this scaling of the radius of the spreading area with time are modified red blood cells (RBCs), whose elastic responses are well characterized. Using a mechanistic description of the contact interaction between a cell and its substrate in combination with a deformable RBC model, we are now able to investigate in detail the mechanisms behind this universal power law. The presented model suggests that the initial slope of the spreading curve with time results from a purely geometrical effect facilitated mainly by dissipation upon contact. Later on, the spreading rate decreases due to increasing tension and dissipation in the cell's cortex as the cell spreads more and more. To reproduce this observed initial spreading, no irreversible deformations are required. Since the model created in this effort is extensible to more complex cell types and can cope with arbitrarily shaped, smooth mechanical microenvironments of the cells, it can be useful for a wide range of investigations where forces at the cell boundary play a decisive role. PMID:24146605

A suite of models to support the quantitative assessment of spread in pest risk analysis.

PubMed

Robinet, Christelle; Kehlenbeck, Hella; Kriticos, Darren J; Baker, Richard H A; Battisti, Andrea; Brunel, Sarah; Dupin, Maxime; Eyre, Dominic; Faccoli, Massimo; Ilieva, Zhenya; Kenis, Marc; Knight, Jon; Reynaud, Philippe; Yart, Annie; van der Werf, Wopke

2012-01-01

Pest Risk Analyses (PRAs) are conducted worldwide to decide whether and how exotic plant pests should be regulated to prevent invasion. There is an increasing demand for science-based risk mapping in PRA. Spread plays a key role in determining the potential distribution of pests, but there is no suitable spread modelling tool available for pest risk analysts. Existing models are species specific, biologically and technically complex, and data hungry. Here we present a set of four simple and generic spread models that can be parameterised with limited data. Simulations with these models generate maps of the potential expansion of an invasive species at continental scale. The models have one to three biological parameters. They differ in whether they treat spatial processes implicitly or explicitly, and in whether they consider pest density or pest presence/absence only. The four models represent four complementary perspectives on the process of invasion and, because they have different initial conditions, they can be considered as alternative scenarios. All models take into account habitat distribution and climate. We present an application of each of the four models to the western corn rootworm, Diabrotica virgifera virgifera, using historic data on its spread in Europe. Further tests as proof of concept were conducted with a broad range of taxa (insects, nematodes, plants, and plant pathogens). Pest risk analysts, the intended model users, found the model outputs to be generally credible and useful. The estimation of parameters from data requires insights into population dynamics theory, and this requires guidance. If used appropriately, these generic spread models provide a transparent and objective tool for evaluating the potential spread of pests in PRAs. Further work is needed to validate models, build familiarity in the user community and create a database of species parameters to help realize their potential in PRA practice.

A Suite of Models to Support the Quantitative Assessment of Spread in Pest Risk Analysis

PubMed Central

Robinet, Christelle; Kehlenbeck, Hella; Kriticos, Darren J.; Baker, Richard H. A.; Battisti, Andrea; Brunel, Sarah; Dupin, Maxime; Eyre, Dominic; Faccoli, Massimo; Ilieva, Zhenya; Kenis, Marc; Knight, Jon; Reynaud, Philippe; Yart, Annie; van der Werf, Wopke

2012-01-01

Pest Risk Analyses (PRAs) are conducted worldwide to decide whether and how exotic plant pests should be regulated to prevent invasion. There is an increasing demand for science-based risk mapping in PRA. Spread plays a key role in determining the potential distribution of pests, but there is no suitable spread modelling tool available for pest risk analysts. Existing models are species specific, biologically and technically complex, and data hungry. Here we present a set of four simple and generic spread models that can be parameterised with limited data. Simulations with these models generate maps of the potential expansion of an invasive species at continental scale. The models have one to three biological parameters. They differ in whether they treat spatial processes implicitly or explicitly, and in whether they consider pest density or pest presence/absence only. The four models represent four complementary perspectives on the process of invasion and, because they have different initial conditions, they can be considered as alternative scenarios. All models take into account habitat distribution and climate. We present an application of each of the four models to the western corn rootworm, Diabrotica virgifera virgifera, using historic data on its spread in Europe. Further tests as proof of concept were conducted with a broad range of taxa (insects, nematodes, plants, and plant pathogens). Pest risk analysts, the intended model users, found the model outputs to be generally credible and useful. The estimation of parameters from data requires insights into population dynamics theory, and this requires guidance. If used appropriately, these generic spread models provide a transparent and objective tool for evaluating the potential spread of pests in PRAs. Further work is needed to validate models, build familiarity in the user community and create a database of species parameters to help realize their potential in PRA practice. PMID:23056174

Spatial spreading model and dynamics of West Nile virus in birds and mosquitoes with free boundary.

PubMed

Lin, Zhigui; Zhu, Huaiping

2017-12-01

In this paper, a reaction-diffusion system is proposed to model the spatial spreading of West Nile virus in vector mosquitoes and host birds in North America. Transmission dynamics are based on a simplified model involving mosquitoes and birds, and the free boundary is introduced to model and explore the expanding front of the infected region. The spatial-temporal risk index [Formula: see text], which involves regional characteristic and time, is defined for the simplified reaction-diffusion model with the free boundary to compare with other related threshold values, including the usual basic reproduction number [Formula: see text]. Sufficient conditions for the virus to vanish or to spread are given. Our results suggest that the virus will be in a scenario of vanishing if [Formula: see text], and will spread to the whole region if [Formula: see text] for some [Formula: see text], while if [Formula: see text], the spreading or vanishing of the virus depends on the initial number of infected individuals, the area of the infected region, the diffusion rate and other factors. Moreover, some remarks on the basic reproduction numbers and the spreading speeds are presented and compared.

Dynamic behavior of the interaction between epidemics and cascades on heterogeneous networks

NASA Astrophysics Data System (ADS)

Jiang, Lurong; Jin, Xinyu; Xia, Yongxiang; Ouyang, Bo; Wu, Duanpo

2014-12-01

Epidemic spreading and cascading failure are two important dynamical processes on complex networks. They have been investigated separately for a long time. But in the real world, these two dynamics sometimes may interact with each other. In this paper, we explore a model combined with the SIR epidemic spreading model and a local load sharing cascading failure model. There exists a critical value of the tolerance parameter for which the epidemic with high infection probability can spread out and infect a fraction of the network in this model. When the tolerance parameter is smaller than the critical value, the cascading failure cuts off the abundance of paths and blocks the spreading of the epidemic locally. While the tolerance parameter is larger than the critical value, the epidemic spreads out and infects a fraction of the network. A method for estimating the critical value is proposed. In simulations, we verify the effectiveness of this method in the uncorrelated configuration model (UCM) scale-free networks.

Spatial spread of the West Africa Ebola epidemic.

PubMed

Kramer, Andrew M; Pulliam, J Tomlin; Alexander, Laura W; Park, Andrew W; Rohani, Pejman; Drake, John M

2016-08-01

Controlling Ebola outbreaks and planning an effective response to future emerging diseases are enhanced by understanding the role of geography in transmission. Here we show how epidemic expansion may be predicted by evaluating the relative probability of alternative epidemic paths. We compared multiple candidate models to characterize the spatial network over which the 2013-2015 West Africa epidemic of Ebola virus spread and estimate the effects of geographical covariates on transmission during peak spread. The best model was a generalized gravity model where the probability of transmission between locations depended on distance, population density and international border closures between Guinea, Liberia and Sierra Leone and neighbouring countries. This model out-performed alternative models based on diffusive spread, the force of infection, mobility estimated from cell phone records and other hypothesized patterns of spread. These findings highlight the importance of integrated geography to epidemic expansion and may contribute to identifying both the most vulnerable unaffected areas and locations of maximum intervention value.

Spatial spread of the West Africa Ebola epidemic

PubMed Central

Pulliam, J. Tomlin; Alexander, Laura W.; Rohani, Pejman; Drake, John M.

2016-01-01

Controlling Ebola outbreaks and planning an effective response to future emerging diseases are enhanced by understanding the role of geography in transmission. Here we show how epidemic expansion may be predicted by evaluating the relative probability of alternative epidemic paths. We compared multiple candidate models to characterize the spatial network over which the 2013–2015 West Africa epidemic of Ebola virus spread and estimate the effects of geographical covariates on transmission during peak spread. The best model was a generalized gravity model where the probability of transmission between locations depended on distance, population density and international border closures between Guinea, Liberia and Sierra Leone and neighbouring countries. This model out-performed alternative models based on diffusive spread, the force of infection, mobility estimated from cell phone records and other hypothesized patterns of spread. These findings highlight the importance of integrated geography to epidemic expansion and may contribute to identifying both the most vulnerable unaffected areas and locations of maximum intervention value. PMID:27853607

Membrane materials for storing biological samples intended for comparative nanotoxicological testing

NASA Astrophysics Data System (ADS)

Metelkin, A.; Kuznetsov, D.; Kolesnikov, E.; Chuprunov, K.; Kondakov, S.; Osipov, A.; Samsonova, J.

2015-11-01

The study is aimed at identifying the samples of most promising membrane materials for storing dry specimens of biological fluids (Dried Blood Spots, DBS technology). Existing sampling systems using cellulose fiber filter paper have a number of drawbacks such as uneven distribution of the sample spot, dependence of the spot spreading area on the individual biosample properties, incomplete washing-off of the sample due to partially inconvertible sorption of blood components on cellulose fibers, etc. Samples of membrane materials based on cellulose, polymers and glass fiber with applied biosamples were studied using methods of scanning electron microscopy, FT-IR spectroscopy and surface-wetting measurement. It was discovered that cellulose-based membrane materials sorb components of biological fluids inside their structure, while membranes based on glass fiber display almost no interaction with the samples and biological fluid components dry to films in the membrane pores between the structural fibers. This characteristic, together with the fact that membrane materials based on glass fiber possess sufficient strength, high wetting properties and good storage capacity, attests them as promising material for dry samples of biological fluids storage systems.

Wind-Mediated Spread of Low-Pathogenic Avian Influenza Virus into the Environment during Outbreaks at Commercial Poultry Farms.

PubMed

Jonges, Marcel; van Leuken, Jeroen; Wouters, Inge; Koch, Guus; Meijer, Adam; Koopmans, Marion

2015-01-01

Avian influenza virus-infected poultry can release a large amount of virus-contaminated droppings that serve as sources of infection for susceptible birds. Much research so far has focused on virus spread within flocks. However, as fecal material or manure is a major constituent of airborne poultry dust, virus-contaminated particulate matter from infected flocks may be dispersed into the environment. We collected samples of suspended particulate matter, or the inhalable dust fraction, inside, upwind and downwind of buildings holding poultry infected with low-pathogenic avian influenza virus, and tested them for the presence of endotoxins and influenza virus to characterize the potential impact of airborne influenza virus transmission during outbreaks at commercial poultry farms. Influenza viruses were detected by RT-PCR in filter-rinse fluids collected up to 60 meters downwind from the barns, but virus isolation did not yield any isolates. Viral loads in the air samples were low and beyond the limit of RT-PCR quantification except for one in-barn measurement showing a virus concentration of 8.48 x 10(4) genome copies/m(3). Air samples taken outside poultry barns had endotoxin concentrations of ~50 EU/m(3) that declined with increasing distance from the barn. Atmospheric dispersion modeling of particulate matter, using location-specific meteorological data for the sampling days, demonstrated a positive correlation between endotoxin measurements and modeled particulate matter concentrations, with an R(2) varying from 0.59 to 0.88. Our data suggest that areas at high risk for human or animal exposure to airborne influenza viruses can be modeled during an outbreak to allow directed interventions following targeted surveillance.

The Solution to Pollution is Distribution: Design Your Own Chaotic Flow

NASA Astrophysics Data System (ADS)

Tigera, R. G.; Roth, E. J.; Neupauer, R.; Mays, D. C.

2015-12-01

Plume spreading promotes the molecular mixing that drives chemical reactions in porous media in general, and remediation reactions in groundwater aquifers in particular. Theoretical analysis suggests that engineered injection and extraction, a specific sequence of pumping through wells surrounding a contaminant plume, can improve groundwater remediation through chaotic advection. Selection of an engineered injection and extraction scheme is difficult, however, because the engineer is faced with the difficulty of recommending a pumping scheme for a contaminated site without having any previous knowledge of how the scheme will perform. To address this difficulty, this presentation describes a Graphical User Interface (GUI) designed to help engineers develop, test, and observe pumping schemes as described in previous research (Mays, D.C. and Neupauer, R.M., 2012, Plume spreading in groundwater by stretching and folding, Water Resour. Res., 48, W07501, doi:10.1029/2011WR011567). The inputs allow the user to manipulate the model conditions such as number of wells, plume size, and pumping scheme. Plume evolution is modeled, assuming no diffusion or dispersion, using analytical solutions for injection or extraction through individual wells or pairs or wells (i.e., dipoles). Using the GUI, an engineered injection and extraction scheme can be determined that best fits the remediation needs of the contaminated site. By creating multiple injection and extraction schemes, the user can learn about the plume shapes created from different schemes and, ultimately, recommend a pumping scheme based on some experience of fluid flow as shown in the GUI. The pumping schemes developed through this GUI are expected to guide more advanced modeling and laboratory studies that account for the crucial role of dispersion in groundwater remediation.

Fire spread in chaparral – a comparison of laboratory data and model predictions in burning live fuels

Treesearch

David R. Weise; Eunmo Koo; Xiangyang Zhou; Shankar Mahalingam; Frédéric Morandini; Jacques-Henri Balbi

2016-01-01

Fire behaviour data from 240 laboratory fires in high-density live chaparral fuel beds were compared with model predictions. Logistic regression was used to develop a model to predict fire spread success in the fuel beds and linear regression was used to predict rate of spread. Predictions from the Rothermel equation and three proposed changes as well as two physically...

The Bee Fire: a case study validation of BEHAVE in chaparral fuels

Treesearch

David Weise; A. Gelobter; J. Regelbrugge; J. Millar

2002-01-01

The Bee Fire burned 9,620 acres of grass and chaparral in the San Bernardino National Forest in southern California from June 29 to July 2, 1996. Rate of spread data were determined from successive fire perimeters and compared with rate of spread predicted by the Rothermel rate of spread model using fuel model 4 (heavy brush) and a custom fuel model for chamise...

Modelling the influence of human behaviour on the spread of infectious diseases: a review.

PubMed

Funk, Sebastian; Salathé, Marcel; Jansen, Vincent A A

2010-09-06

Human behaviour plays an important role in the spread of infectious diseases, and understanding the influence of behaviour on the spread of diseases can be key to improving control efforts. While behavioural responses to the spread of a disease have often been reported anecdotally, there has been relatively little systematic investigation into how behavioural changes can affect disease dynamics. Mathematical models for the spread of infectious diseases are an important tool for investigating and quantifying such effects, not least because the spread of a disease among humans is not amenable to direct experimental study. Here, we review recent efforts to incorporate human behaviour into disease models, and propose that such models can be broadly classified according to the type and source of information which individuals are assumed to base their behaviour on, and according to the assumed effects of such behaviour. We highlight recent advances as well as gaps in our understanding of the interplay between infectious disease dynamics and human behaviour, and suggest what kind of data taking efforts would be helpful in filling these gaps.

Modelling the influence of human behaviour on the spread of infectious diseases: a review

PubMed Central

Funk, Sebastian; Salathé, Marcel; Jansen, Vincent A. A.

2010-01-01

Human behaviour plays an important role in the spread of infectious diseases, and understanding the influence of behaviour on the spread of diseases can be key to improving control efforts. While behavioural responses to the spread of a disease have often been reported anecdotally, there has been relatively little systematic investigation into how behavioural changes can affect disease dynamics. Mathematical models for the spread of infectious diseases are an important tool for investigating and quantifying such effects, not least because the spread of a disease among humans is not amenable to direct experimental study. Here, we review recent efforts to incorporate human behaviour into disease models, and propose that such models can be broadly classified according to the type and source of information which individuals are assumed to base their behaviour on, and according to the assumed effects of such behaviour. We highlight recent advances as well as gaps in our understanding of the interplay between infectious disease dynamics and human behaviour, and suggest what kind of data taking efforts would be helpful in filling these gaps. PMID:20504800

Numerical analysis of single tank thermocline thermal storage system for concentrated solar power plant

NASA Astrophysics Data System (ADS)

Afrin, Samia

The overall efficiency of a Concentrating Solar Power (CSP) plant depends on the effectiveness of Thermal Energy Storage (TES) system. A Single tank TES system has potential to provide effective solution. In a single tank TES system, a thermocline region, which produces the temperature gradient between hot and cold storage fluid by density difference, is used. Preservation of this thermocline region in the tank during charging and discharging cycles depends on the uniformity of the velocity profile at any horizontal plane. One of the major challenges for the single tank thermocline is actually maintaining the thermocline region in the tank, so that it does not spread out to occupy the entire tank. Since the thermocline is a horizontal surface, the hot and cold fluid must be introduce in such a way that it does not disturb the thermocline. If the fluid is introduced in a jet stream, it will disturb the thermocline and mix the hot and cold fluids into a homogeneous medium. So the objective of this thesis is to preserve the thermocline region by maximizing the uniformity of the velocity distribution. An ideal distributor will minimize the thermocline spreading and hence maximize the useable form of thermal energy storage in a single tank system. The performance of two different types of distributors: pipe flow distributor and honeycomb distributor, were checked. The effectiveness of the pipe flow distributor was checked by varying the dimension of the geometry i.e. number of holes, distance between the holes, position of the holes and number of distributor pipes. Thermal energy storage system from solar power relies on high temperature thermal storage units for continuous operation. The storage units should have facilitated with high thermal conductivity and heat capacity storage fluid. Hence it is necessary to find a better performing heat transfer fluid at higher operating temperature. Novel materials such as nanomaterial additives can become cost effective and can increase the operating range of the storage facilities to higher range of temperatures. In this work HitecRTM molten salt is considered as the heat transfer fluid (HTF). The operating temperature of this HTF is 300-500°C. So to increase the thermal properties of this HTF nanomaterial has been added. The effective thermal conductivity and specific heat capacity of the nanofluid were calculated and the thermal effect of this nanofluid was observed from the simulation result.

Low- and High-Pathogenic Avian Influenza H5 and H7 Spread Risk Assessment Within and Between Australian Commercial Chicken Farms

PubMed Central

Scott, Angela Bullanday; Toribio, Jenny-Ann L. M. L.; Singh, Mini; Groves, Peter; Barnes, Belinda; Glass, Kathryn; Moloney, Barbara; Black, Amanda; Hernandez-Jover, Marta

2018-01-01

This study quantified and compared the probability of avian influenza (AI) spread within and between Australian commercial chicken farms via specified spread pathways using scenario tree mathematical modeling. Input values for the models were sourced from scientific literature, expert opinion, and a farm survey conducted during 2015 and 2016 on Australian commercial chicken farms located in New South Wales (NSW) and Queensland. Outputs from the models indicate that the probability of no establishment of infection in a shed is the most likely end-point after exposure and infection of low-pathogenic avian influenza (LPAI) in one chicken for all farm types (non-free range meat chicken, free range meat chicken, cage layer, barn layer, and free range layer farms). If LPAI infection is established in a shed, LPAI is more likely to spread to other sheds and beyond the index farm due to a relatively low probability of detection and reporting during LPAI infection compared to high-pathogenic avian influenza (HPAI) infection. Among farm types, the median probability for HPAI spread between sheds and between farms is higher for layer farms (0.0019, 0.0016, and 0.0031 for cage, barn, and free range layer, respectively) than meat chicken farms (0.00025 and 0.00043 for barn and free range meat chicken, respectively) due to a higher probability of mutation in layer birds, which relates to their longer production cycle. The pathway of LPAI spread between sheds with the highest average median probability was spread via equipment (0.015; 5–95%, 0.0058–0.036) and for HPAI spread between farms, the pathway with the highest average median probability was spread via egg trays (3.70 × 10−5; 5–95%, 1.47 × 10−6–0.00034). As the spread model did not explicitly consider volume and frequency of the spread pathways, these results provide a comparison of spread probabilities per pathway. These findings highlight the importance of performing biosecurity practices to limit spread of the AI virus. The models can be updated as new information on the mechanisms of the AI virus and on the volume and frequency of movements shed-to-shed and of movements between commercial chicken farms becomes available. PMID:29686993

Low- and High-Pathogenic Avian Influenza H5 and H7 Spread Risk Assessment Within and Between Australian Commercial Chicken Farms.

PubMed

Scott, Angela Bullanday; Toribio, Jenny-Ann L M L; Singh, Mini; Groves, Peter; Barnes, Belinda; Glass, Kathryn; Moloney, Barbara; Black, Amanda; Hernandez-Jover, Marta

2018-01-01

This study quantified and compared the probability of avian influenza (AI) spread within and between Australian commercial chicken farms via specified spread pathways using scenario tree mathematical modeling. Input values for the models were sourced from scientific literature, expert opinion, and a farm survey conducted during 2015 and 2016 on Australian commercial chicken farms located in New South Wales (NSW) and Queensland. Outputs from the models indicate that the probability of no establishment of infection in a shed is the most likely end-point after exposure and infection of low-pathogenic avian influenza (LPAI) in one chicken for all farm types (non-free range meat chicken, free range meat chicken, cage layer, barn layer, and free range layer farms). If LPAI infection is established in a shed, LPAI is more likely to spread to other sheds and beyond the index farm due to a relatively low probability of detection and reporting during LPAI infection compared to high-pathogenic avian influenza (HPAI) infection. Among farm types, the median probability for HPAI spread between sheds and between farms is higher for layer farms (0.0019, 0.0016, and 0.0031 for cage, barn, and free range layer, respectively) than meat chicken farms (0.00025 and 0.00043 for barn and free range meat chicken, respectively) due to a higher probability of mutation in layer birds, which relates to their longer production cycle. The pathway of LPAI spread between sheds with the highest average median probability was spread via equipment (0.015; 5-95%, 0.0058-0.036) and for HPAI spread between farms, the pathway with the highest average median probability was spread via egg trays (3.70 × 10 -5 ; 5-95%, 1.47 × 10 -6 -0.00034). As the spread model did not explicitly consider volume and frequency of the spread pathways, these results provide a comparison of spread probabilities per pathway. These findings highlight the importance of performing biosecurity practices to limit spread of the AI virus. The models can be updated as new information on the mechanisms of the AI virus and on the volume and frequency of movements shed-to-shed and of movements between commercial chicken farms becomes available.

Rumor Spreading Model with Trust Mechanism in Complex Social Networks

NASA Astrophysics Data System (ADS)

Wang, Ya-Qi; Yang, Xiao-Yuan; Han, Yi-Liang; Wang, Xu-An

2013-04-01

In this paper, to study rumor spreading, we propose a novel susceptible-infected-removed (SIR) model by introducing the trust mechanism. We derive mean-field equations that describe the dynamics of the SIR model on homogeneous networks and inhomogeneous networks. Then a steady-state analysis is conducted to investigate the critical threshold and the final size of the rumor spreading. We show that the introduction of trust mechanism reduces the final rumor size and the velocity of rumor spreading, but increases the critical thresholds on both networks. Moreover, the trust mechanism not only greatly reduces the maximum rumor influence, but also postpones the rumor terminal time, which provides us with more time to take measures to control the rumor spreading. The theoretical results are confirmed by sufficient numerical simulations.

Dynamics for a diffusive prey-predator model with different free boundaries

NASA Astrophysics Data System (ADS)

Wang, Mingxin; Zhang, Yang

2018-03-01

To understand the spreading and interaction of prey and predator, in this paper we study the dynamics of the diffusive Lotka-Volterra type prey-predator model with different free boundaries. These two free boundaries, which may intersect each other as time evolves, are used to describe the spreading of prey and predator. We investigate the existence and uniqueness, regularity and uniform estimates, and long time behaviors of global solution. Some sufficient conditions for spreading and vanishing are established. When spreading occurs, we provide the more accurate limits of (u , v) as t → ∞, and give some estimates of asymptotic spreading speeds of u , v and asymptotic speeds of g , h. Some realistic and significant spreading phenomena are found.

New models of hematogenous ovarian cancer metastasis demonstrate preferential spread to the ovary and a requirement for the ovary for abdominal dissemination.

PubMed

Coffman, Lan G; Burgos-Ojeda, Daniela; Wu, Rong; Cho, Kathleen; Bai, Shoumei; Buckanovich, Ronald J

2016-09-01

Emerging evidence suggest that many high-grade serous "ovarian" cancers (HGSOC) start in the fallopian tube. Cancer cells are then recruited to the ovary and then spread diffusely through the abdomen. The mechanism of ovarian cancer spread was thought to be largely due to direct shedding of tumor cells into the peritoneal cavity with vascular spread being of limited importance. Recent work challenges this dogma, suggesting hematogenous spread of ovarian cancer may play a larger role in ovarian cancer cell metastasis than previously thought. One reason the role of vascular spread of ovarian cancer has not been fully elucidated is the lack of easily accessible models of vascular ovarian cancer metastasis. Here, we present 3 metastatic models of ovarian cancer which confirm the ability of ovarian cancer to hematogenously spread. Strikingly, we observe a high rate of metastasis to the ovary with the development of ascites in these models. Interestingly, oophorectomy resulted in a complete loss of peritoneal metastases and ascites. Taken together, our data indicate that hematogenously disseminated HGSOC cells have a unique tropism for the ovary and that hematogenous spread in ovarian cancer may be more common than appreciated. Furthermore, our studies support a critical role for the ovary in promoting HGSOC cell metastasis to the abdomen. The models developed here represent important new tools to evaluate both the mechanism of cancer cell recruitment to the ovary and understand and target key steps in ovarian cancer metastasis. Copyright © 2016 Elsevier Inc. All rights reserved.

New models of hematogenous ovarian cancer metastasis demonstrate preferential spread to the ovary and a requirement for the ovary for abdominal dissemination

PubMed Central

Coffman, Lan G; Burgos-Ojeda, Daniela; Wu, Rong; Cho, Kathleen; Bai, Shoumei; Buckanovich, Ronald J

2016-01-01

Emerging evidence suggest that many high grade serous ‘ovarian’ cancers (HGSOC) start in the fallopian tube. Cancer cells are then recruited to the ovary and then spread diffusely through the abdomen. The mechanism of ovarian cancer spread was thought to be largely due to direct shedding of tumor cells into the peritoneal cavity with vascular spread being of limited importance. Recent work challenges this dogma, suggesting hematogenous spread of ovarian cancer may play a larger role in ovarian cancer cell metastasis than previously thought. One reason the role of vascular spread of ovarian cancer has not been fully elucidated is the lack of easily accessible models of vascular ovarian cancer metastasis. Here we present three metastatic models of ovarian cancer which confirm the ability of ovarian cancer to hematogenously spread. Strikingly, we observe a high rate of metastasis to the ovary with the development of ascites in these models. Interestingly, oophorectomy resulted in a complete loss of peritoneal metastases and ascites. Taken together our data indicates that hematogenously disseminated HGSOC cells have a unique tropism for the ovary and that hematogenous spread in ovarian cancer may be more common than appreciated. Furthermore our studies support a critical role for the ovary in promoting HGSOC cell metastasis to the abdomen. The models developed here represent important new tools to evaluate both the mechanism of cancer cell recruitment to the ovary and to understand and target key steps in ovarian cancer metastasis. PMID:27083386

Solid Surface Combustion Experiment Completes a Series of Eight Successful Flights

NASA Technical Reports Server (NTRS)

1996-01-01

The Solid Surface Combustion Experiment (SSCE) was the first combustion experiment to fly in the space shuttle and the first such experiment in the NASA spaceflight program since Skylab. SSCE was actually a series of experiments designed to begin to characterize flame spreading over solid fuels in microgravity and the differences of this flame spreading from normal gravity behavior. These experiments should lead to a better understanding of the physical processes involved--increasing our understanding of fire behavior, both in space and on Earth. SSCE results will help researchers evaluate spacecraft fire hazards. These experiments were conceived by the principal investigator, Professor Robert A. Altenkirch, Dean of Engineering at Washington State University. In the first five flights, the fuel sample--ashless filter paper instrumented with three thermocouples--was mounted in a sealed chamber filled with a 50-percent or 35-percent mixture of oxygen in nitrogen at pressures of 1.0, 1.5, and 2.0 atm. In the next three flights, a polymethyl methacrylate (plexiglass) fuel was instrumented with three thermocouples and tested in a 70-percent or 50-percent mixture of oxygen and nitrogen at pressures of 1.0 and 2.0 atm. SSCE is a self-contained, battery-operated experiment that can be flown either in the shuttle middeck or in the Spacelab module. More information about the hardware configuration have been published. This past year, the final two of eight flights were completed on STS-64 and STS-63. The NASA Lewis Research Center designed and built the SSCE payload and performed engineering, testing, scientific, and flight operations support. The SSCE project was supported in some way by nearly every major sector of Lewis' organization. Professor Altenkirch developed a numerical simulation of the flame-spreading process from first principles (of fluid mechanics, heat transfer, and reaction kinetics). The spread rates, flame shape, and thermodynamic data from the SSCE flights are being compared directly with the results of the computational model. Results from the eight flights will be used to formulate an improved solid-phase pyrolysis model. In addition, some results of the flights have been published and presented at international combustion symposiums. Additional solid fuel combustion experiments are being investigated for future tests with the existing hardware.

Nonlinear model for an optical read-only-memory disk readout channel based on an edge-spread function.

PubMed

Kobayashi, Seiji

2002-05-10

A point-spread function (PSF) is commonly used as a model of an optical disk readout channel. However, the model given by the PSF does not contain the quadratic distortion generated by the photo-detection process. We introduce a model for calculating an approximation of the quadratic component of a signal. We show that this model can be further simplified when a read-only-memory (ROM) disk is assumed. We introduce an edge-spread function by which a simple nonlinear model of an optical ROM disk readout channel is created.

A Patient-Specific Anisotropic Diffusion Model for Brain Tumour Spread.

PubMed

Swan, Amanda; Hillen, Thomas; Bowman, John C; Murtha, Albert D

2018-05-01

Gliomas are primary brain tumours arising from the glial cells of the nervous system. The diffuse nature of spread, coupled with proximity to critical brain structures, makes treatment a challenge. Pathological analysis confirms that the extent of glioma spread exceeds the extent of the grossly visible mass, seen on conventional magnetic resonance imaging (MRI) scans. Gliomas show faster spread along white matter tracts than in grey matter, leading to irregular patterns of spread. We propose a mathematical model based on Diffusion Tensor Imaging, a new MRI imaging technique that offers a methodology to delineate the major white matter tracts in the brain. We apply the anisotropic diffusion model of Painter and Hillen (J Thoer Biol 323:25-39, 2013) to data from 10 patients with gliomas. Moreover, we compare the anisotropic model to the state-of-the-art Proliferation-Infiltration (PI) model of Swanson et al. (Cell Prolif 33:317-329, 2000). We find that the anisotropic model offers a slight improvement over the standard PI model. For tumours with low anisotropy, the predictions of the two models are virtually identical, but for patients whose tumours show higher anisotropy, the results differ. We also suggest using the data from the contralateral hemisphere to further improve the model fit. Finally, we discuss the potential use of this model in clinical treatment planning.

Assessing adverse effects of intra-articular botulinum toxin A in healthy Beagle dogs: A placebo-controlled, blinded, randomized trial

PubMed Central

Jokinen, Tarja S.; Syrjä, Pernilla; Junnila, Jouni; Hielm-Björkman, Anna; Laitinen-Vapaavuori, Outi

2018-01-01

Objective To investigate the clinical, cytological, and histopathological adverse effects of intra-articularly injected botulinum toxin A in dogs and to study whether the toxin spreads from the joint after the injection. Methods A longitudinal, placebo-controlled, randomized clinical trial was conducted with six healthy laboratory Beagle dogs. Stifle joints were randomized to receive either 30 IU of onabotulinum toxin A or placebo in a 1:1 ratio. Adverse effects and spread of the toxin were examined by evaluating dynamic and static weight-bearing of the injected limbs, by assessing painless range of motion and pain on palpation of joints, and by performing synovial fluid analysis, neurological examination, and electrophysiological recordings at different examination time-points in a 12-week period after the injections. The dogs were then euthanized and autopsy and histopathological examination of joint structures and adjacent muscles and nerves were performed. Results Intra-articular botulinum toxin A did not cause local weakness or injection site pain. Instead, static weight-bearing and painless range of motion of stifle joints decreased in the placebo limbs. No clinically significant abnormalities associated with intra-articular botulinum toxin A were detected in the neurological examinations. Electrophysiological recordings showed low compound muscle action potentials in two dogs in the botulinum toxin A-injected limb. No significant changes were detected in the synovial fluid. Autopsy and histopathological examination of the joint and adjacent muscles and nerves did not reveal histopathological adverse effects of the toxin. Conclusion Intra-articular botulinum toxin A does not produce significant clinical, cytological, or histopathological adverse effects in healthy dogs. Based on the electrophysiological recordings, the toxin may spread from the joint, but its clinical impact seems to be low. PMID:29320549

Comprehensive Review on Ebola (EBOV) Virus: Future Prospects.

PubMed

Khan, Sajad; Muhammad; Rauf, Abdur; Khan, Ahsan; Rizwan, Muhammad; Patel, Seema; Khan, Haroon; Mahasneh, Adel M; Mubarak, Mohammad S

2018-01-01

Ebola virus (EBOV) was discovered for the first time in 1976. It belongs to the family Filoviridae, which causes hemorrhagic fever that could lead to death in a few days. West Africa faced a major outbreak where symptoms appeared in the form of chills, myalgia, fever, diarrhea, and vomiting, and the disease finally reached a severe state as a result of hemorrhagic complications and failure of multiple organs. EBOV spreads by contact with body fluids of an infected person such as blood, saliva, urine, and seminal fluid, and also spreads by a contact with contaminated surfaces. Viral infection depends on the virus and host defenses. When the virus invades the body, the immune system becomes activated in an attempt to neutralize it. However, if this fails, EBOV viral infection spreads and leads to impaired innate and adaptive immune responses and uncontrollable viral replication. Consequently, the symptomatic patient is isolated and various medicinal regimens such as BCX-4430n TKM- EBOV are used, to cure EBOV, though, a specific treatment is not available. Accordingly, the aim of the present review is to survey and summarize the recent literature pertaining to the outbreak of EBOV, systematic infection of the human body, along with transmission and treatment. In addition, the review also aims to identify areas that need more research and development in combatting this dangerous virus. In the meantime, it should be noted that there is no fully FDA approved drug to treat infections by this virus. Therefore, there is a pressing need to focus on drug discovery along with public awareness to effectively manage any outbreaks in the future. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Contagion of Cooperation in Static and Fluid Social Networks.

PubMed

Jordan, Jillian J; Rand, David G; Arbesman, Samuel; Fowler, James H; Christakis, Nicholas A

2013-01-01

Cooperation is essential for successful human societies. Thus, understanding how cooperative and selfish behaviors spread from person to person is a topic of theoretical and practical importance. Previous laboratory experiments provide clear evidence of social contagion in the domain of cooperation, both in fixed networks and in randomly shuffled networks, but leave open the possibility of asymmetries in the spread of cooperative and selfish behaviors. Additionally, many real human interaction structures are dynamic: we often have control over whom we interact with. Dynamic networks may differ importantly in the goals and strategic considerations they promote, and thus the question of how cooperative and selfish behaviors spread in dynamic networks remains open. Here, we address these questions with data from a social dilemma laboratory experiment. We measure the contagion of both cooperative and selfish behavior over time across three different network structures that vary in the extent to which they afford individuals control over their network ties. We find that in relatively fixed networks, both cooperative and selfish behaviors are contagious. In contrast, in more dynamic networks, selfish behavior is contagious, but cooperative behavior is not: subjects are fairly likely to switch to cooperation regardless of the behavior of their neighbors. We hypothesize that this insensitivity to the behavior of neighbors in dynamic networks is the result of subjects' desire to attract new cooperative partners: even if many of one's current neighbors are defectors, it may still make sense to switch to cooperation. We further hypothesize that selfishness remains contagious in dynamic networks because of the well-documented willingness of cooperators to retaliate against selfishness, even when doing so is costly. These results shed light on the contagion of cooperative behavior in fixed and fluid networks, and have implications for influence-based interventions aiming at increasing cooperative behavior.

Assessing adverse effects of intra-articular botulinum toxin A in healthy Beagle dogs: A placebo-controlled, blinded, randomized trial.

PubMed

Heikkilä, Helka M; Jokinen, Tarja S; Syrjä, Pernilla; Junnila, Jouni; Hielm-Björkman, Anna; Laitinen-Vapaavuori, Outi

2018-01-01

To investigate the clinical, cytological, and histopathological adverse effects of intra-articularly injected botulinum toxin A in dogs and to study whether the toxin spreads from the joint after the injection. A longitudinal, placebo-controlled, randomized clinical trial was conducted with six healthy laboratory Beagle dogs. Stifle joints were randomized to receive either 30 IU of onabotulinum toxin A or placebo in a 1:1 ratio. Adverse effects and spread of the toxin were examined by evaluating dynamic and static weight-bearing of the injected limbs, by assessing painless range of motion and pain on palpation of joints, and by performing synovial fluid analysis, neurological examination, and electrophysiological recordings at different examination time-points in a 12-week period after the injections. The dogs were then euthanized and autopsy and histopathological examination of joint structures and adjacent muscles and nerves were performed. Intra-articular botulinum toxin A did not cause local weakness or injection site pain. Instead, static weight-bearing and painless range of motion of stifle joints decreased in the placebo limbs. No clinically significant abnormalities associated with intra-articular botulinum toxin A were detected in the neurological examinations. Electrophysiological recordings showed low compound muscle action potentials in two dogs in the botulinum toxin A-injected limb. No significant changes were detected in the synovial fluid. Autopsy and histopathological examination of the joint and adjacent muscles and nerves did not reveal histopathological adverse effects of the toxin. Intra-articular botulinum toxin A does not produce significant clinical, cytological, or histopathological adverse effects in healthy dogs. Based on the electrophysiological recordings, the toxin may spread from the joint, but its clinical impact seems to be low.

Epidemic spreading and global stability of an SIS model with an infective vector on complex networks

NASA Astrophysics Data System (ADS)

Kang, Huiyan; Fu, Xinchu

2015-10-01

In this paper, we present a new SIS model with delay on scale-free networks. The model is suitable to describe some epidemics which are not only transmitted by a vector but also spread between individuals by direct contacts. In view of the biological relevance and real spreading process, we introduce a delay to denote average incubation period of disease in a vector. By mathematical analysis, we obtain the epidemic threshold and prove the global stability of equilibria. The simulation shows the delay will effect the epidemic spreading. Finally, we investigate and compare two major immunization strategies, uniform immunization and targeted immunization.

Hybrid shallow on-axis and deep off-axis hydrothermal circulation at fast-spreading ridges.

PubMed

Hasenclever, Jörg; Theissen-Krah, Sonja; Rüpke, Lars H; Morgan, Jason P; Iyer, Karthik; Petersen, Sven; Devey, Colin W

2014-04-24

Hydrothermal flow at oceanic spreading centres accounts for about ten per cent of all heat flux in the oceans and controls the thermal structure of young oceanic plates. It also influences ocean and crustal chemistry, provides a basis for chemosynthetic ecosystems, and has formed massive sulphide ore deposits throughout Earth's history. Despite this, how and under what conditions heat is extracted, in particular from the lower crust, remains largely unclear. Here we present high-resolution, whole-crust, two- and three-dimensional simulations of hydrothermal flow beneath fast-spreading ridges that predict the existence of two interacting flow components, controlled by different physical mechanisms, that merge above the melt lens to feed ridge-centred vent sites. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittle-ductile transition. About 60 per cent of the discharging fluid mass is replenished on-axis by warm (up to 300 degrees Celsius) recharge flow surrounding the hot thermal plumes, and the remaining 40 per cent or so occurs as colder and broader recharge up to several kilometres away from the axis that feeds hot (500-700 degrees Celsius) deep-rooted off-axis flow towards the ridge. Despite its lower contribution to the total mass flux, this deep off-axis flow carries about 70 per cent of the thermal energy released at the ridge axis. This combination of two flow components explains the seismically determined thermal structure of the crust and reconciles previously incompatible models favouring either shallower on-axis or deeper off-axis hydrothermal circulation.

Edge turbulence and divertor heat flux width simulations of Alcator C-Mod discharges using an electromagnetic two-fluid model

NASA Astrophysics Data System (ADS)

Chen, B.; Xu, X. Q.; Xia, T. Y.; Porkolab, M.; Edlund, E.; LaBombard, B.; Terry, J.; Hughes, J. W.; Mao, S. F.; Ye, M. Y.; Wan, Y. X.

2017-11-01

The BOUT++ code has been exploited in order to improve the understanding of the role of turbulent modes in controlling edge transport and resulting scaling of the scrape-off layer (SOL) heat flux width. For the C-Mod enhanced D_α (EDA) H-mode discharges, BOUT++ six-field two-fluid nonlinear simulations show a reasonable agreement of upstream turbulence and divertor target heat flux behavior: (a) the simulated quasi-coherent modes show consistent characteristics of the frequency versus poloidal wave number spectra of the electromagnetic fluctuations when compared with experimental measurements: frequencies are around 60-120 kHz (experiment: about 70-110 kHz), k_θ are around 2.0 cm-1 which is similar to the phase contrast imaging data; (b) linear spectrum analysis is consistent with the nonlinear phase relationship calculation which indicates the dominance of resistive-ballooning modes and drift-Alfven wave instabilities; (c) the SOL heat flux width λq versus current I p scaling is reproduced by turbulent transport: the simulations yield similar λq to experimental measurements within a factor of 2. However the magnitudes of divertor heat fluxes can be varied, depending on the physics models, sources and sinks, sheath boundary conditions, or flux limiting coefficient; (d) Simple estimate by the ‘2-point model’ for λq is consistent with simulation. Moreover, blobby turbulent spreading is confirmed for these relatively high B p shots.

Spreading Speed of Magnetopause Reconnection X-Lines Using Ground-Satellite Coordination

NASA Astrophysics Data System (ADS)

Zou, Ying; Walsh, Brian M.; Nishimura, Yukitoshi; Angelopoulos, Vassilis; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

2018-01-01

Conceptual and numerical models predict that magnetic reconnection starts at a localized region and then spreads out of the reconnection plane. At the Earth's magnetopause this spreading would occur primarily in local time along the boundary. Different simulations have found the spreading to occur at different speeds such as the Alfvén speed and speed of the current carriers. We use conjugate Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and Super Dual Auroral Radar Network (SuperDARN) radar measurements to observationally determine the X-line spreading speed at the magnetopause. THEMIS probes the reconnection parameters locally, and SuperDARN tracks the reconnection development remotely. Spreading speeds under different magnetopause boundary conditions are obtained and compared with model predictions. We find that while spreading under weak guide field could be explained by either the current carriers or the Alfvén waves, spreading under strong guide field is consistent only with the current carriers.

Complicated acute appendicitis presenting as a rapidly progressive soft tissue infection of the abdominal wall: a case report.

PubMed

Beerle, Corinne; Gelpke, Hans; Breitenstein, Stefan; Staerkle, Ralph F

2016-12-01

We report a case of a rare complication of acute appendicitis with perforation through the abdominal wall. The case points out that an intraabdominal origin should be considered in patients presenting with rapidly spreading soft tissue infections of the trunk. A 58-year-old European woman presented to our hospital with a 1-week history of severe abdominal pain accompanied by rapidly spreading erythema and emphysema of the lower abdomen. On admission, the patient was in septic shock with leukocytosis and elevation of C-reactive protein. Among other diagnoses, necrotizing fasciitis was suspected. Computed tomography showed a large soft tissue infection with air-fluid levels spreading through the lower abdominal wall. During the operation, we found a perforated appendicitis breaking through the fascia and causing a rapidly progressive soft tissue infection of the abdominal wall. Appendicitis was the origin of the soft tissue infection. The abdominal wall was only secondarily involved. Even though perforated appendicitis as an etiology of a rapidly progressive soft tissue infection of the abdominal wall is very rare, it should be considered in the differential diagnosis of abdominal wall cellulitis. The distinction between rapidly spreading subcutaneous infection with abscess formation and early onset of necrotizing fasciitis is often difficult and can be confirmed only by surgical intervention.

How the government's punishment and individual's sensitivity affect the rumor spreading in online social networks

NASA Astrophysics Data System (ADS)

Li, Dandan; Ma, Jing

2017-03-01

We explore the impact of punishment of governments and sensitivity of individuals on the rumor spreading in this paper. Considering the facts that some rumors that relate to the hot events could be disseminated repeatedly, however, some other rumors will never be disseminated after they have been popular for some time. Therefore, we investigate two types (SIS and SIR) of rumor spreading models in which the punishment of government and sensitivity of individuals are considered. Based on the mean-field method, we have calculated the spreading threshold of SIS and SIR model, respectively. Furthermore, we perform the rumor spreading process in the Facebook and POK social networks, and achieve that there is an excellent agreement between the theoretical and numerical results of spreading threshold. The results indicate that improving the punishment of government and increasing the sensitivity of individuals could control the spreading of rumor effectively.

Multiscale biomechanics of brain tumours favours cancer invasion by cell softening and tissue stiffening

NASA Astrophysics Data System (ADS)

Kas, Josef; Fritsch, Anatol; Grosser, Steffen; Friebe, Sabrina; Reiss-Zimmermann, Martin; Müller, Wolf; Hoffmann, Karl-Titus; Sack, Ingolf

Cancer progression needs two contradictory mechanical prerequisites. For metastasis individual cancer cells or small clusters have to flow through the microenvironment by overcoming the yield stress exerted by the surrounding. On the other hand a tumour has to behave as a solid to permit cell proliferation and spreading of the tumour mass against its surrounding. We determine that the high mechanical adaptability of cancer cells and the scale controlled viscoelastic properties of tissues reconcile both conflicting properties, fluid and solid, simultaneously in brain tumours. We resolve why different techniques that assess cell and tissue mechanics have produced apparently conflicting results by our finding that tumours generate different viscoelastic behaviours on different length scales, which are in concert optimal for tumour spreading and metastasis. Single cancer cells become very soft in their elastic behavior which promotes cell unjamming. On the level of direct cell-to-cell interactions cells feel their micro-environment as rigid elastic substrate that stimulates cancer on the molecular level. All over a tumour has predominately a stiff elastic character in terms of viscoelastic behaviour caused by a solid backbone. Simultaneously, the tumour mass is characterized by a large local variability in the storage and loss modulus that is caused by areas of a more fluid nature.

A Particle Model for Prediction of Cement Infiltration of Cancellous Bone in Osteoporotic Bone Augmentation.

PubMed

Basafa, Ehsan; Murphy, Ryan J; Kutzer, Michael D; Otake, Yoshito; Armand, Mehran

2013-01-01

Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks - osteoporotic cancellous bone surrogates - and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R(2) = 0.86) and normalized pressure (R(2) = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.

Dependence of credit spread and macro-conditions based on an alterable structure model.

PubMed

Xie, Yun; Tian, Yixiang; Xiao, Zhuang; Zhou, Xiangyun

2018-01-01

The fat-tail financial data and cyclical financial market makes it difficult for the fixed structure model based on Gaussian distribution to characterize the dynamics of corporate bonds spreads. Using a flexible structure model based on generalized error distribution, this paper focuses on the impact of macro-level factors on the spreads of corporate bonds in China. It is found that in China's corporate bonds market, macroeconomic conditions have obvious structural transformational effects on bonds spreads, and their structural features remain stable with the downgrade of bonds ratings. The impact of macroeconomic conditions on spreads is significant for different structures, and the differences between the structures increase as ratings decline. For different structures, the persistent characteristics of bonds spreads are obviously stronger than those of recursive ones, which suggest an obvious speculation in bonds market. It is also found that the structure switching of bonds with different ratings is not synchronous, which indicates the shift of investment between different grades of bonds.

Dependence of credit spread and macro-conditions based on an alterable structure model

PubMed Central

2018-01-01

The fat-tail financial data and cyclical financial market makes it difficult for the fixed structure model based on Gaussian distribution to characterize the dynamics of corporate bonds spreads. Using a flexible structure model based on generalized error distribution, this paper focuses on the impact of macro-level factors on the spreads of corporate bonds in China. It is found that in China's corporate bonds market, macroeconomic conditions have obvious structural transformational effects on bonds spreads, and their structural features remain stable with the downgrade of bonds ratings. The impact of macroeconomic conditions on spreads is significant for different structures, and the differences between the structures increase as ratings decline. For different structures, the persistent characteristics of bonds spreads are obviously stronger than those of recursive ones, which suggest an obvious speculation in bonds market. It is also found that the structure switching of bonds with different ratings is not synchronous, which indicates the shift of investment between different grades of bonds. PMID:29723295

Diffusion in Colocation Contact Networks: The Impact of Nodal Spatiotemporal Dynamics.

PubMed

Thomas, Bryce; Jurdak, Raja; Zhao, Kun; Atkinson, Ian

2016-01-01

Temporal contact networks are studied to understand dynamic spreading phenomena such as communicable diseases or information dissemination. To establish how spatiotemporal dynamics of nodes impact spreading potential in colocation contact networks, we propose "inducement-shuffling" null models which break one or more correlations between times, locations and nodes. By reconfiguring the time and/or location of each node's presence in the network, these models induce alternative sets of colocation events giving rise to contact networks with varying spreading potential. This enables second-order causal reasoning about how correlations in nodes' spatiotemporal preferences not only lead to a given contact network but ultimately influence the network's spreading potential. We find the correlation between nodes and times to be the greatest impediment to spreading, while the correlation between times and locations slightly catalyzes spreading. Under each of the presented null models we measure both the number of contacts and infection prevalence as a function of time, with the surprising finding that the two have no direct causality.

The spread model of food safety risk under the supply-demand disturbance.

PubMed

Wang, Jining; Chen, Tingqiang

2016-01-01

In this paper, based on the imbalance of the supply-demand relationship of food, we design a spreading model of food safety risk, which is about from food producers to consumers in the food supply chain. We use theoretical analysis and numerical simulation to describe the supply-demand relationship and government supervision behaviors' influence on the risk spread of food safety and the behaviors of the food producers and the food retailers. We also analyze the influence of the awareness of consumer rights protection and the level of legal protection of consumer rights on the risk spread of food safety. This model contributes to the explicit investigation of the influence relationship among supply-demand factors, the regulation behavioral choice of government, the behavioral choice of food supply chain members and food safety risk spread. And this paper provides a new viewpoint for considering food safety risk spread in the food supply chain, which has a great reference for food safety management.

Circulation of carbon dioxide in the mantle: multiscale modeling

NASA Astrophysics Data System (ADS)

Morra, G.; Yuen, D. A.; Lee, S.

2012-12-01

Much speculation has been put forward on the quantity and nature of carbon reservoirs in the deep Earth, because of its involvement in the evolution of life at the surface and inside planetary interiors. Carbon penetrates into the Earth's mantle mostly during subduction of oceanic crust, which contains carbonate deposits [1], however the form that it assumes at lower mantle depths is scarcely understood [2], hampering our ability to estimate the amount of carbon in the entire mantle by orders of magnitude. We present simulations of spontaneous degassing of supercritical CO2 using in-house developed novel implementations of the Fast-Multipole Boundary Element Method suitable for modeling two-phase flow (here mantle mineral and free CO2 fluid) through disordered materials such as porous rocks. Because the mutual interaction of droplets immersed either in a fluid or a solid matrix and their weakening effect to the host rock alters the strength of the mantle rocks, at the large scale the fluid phases in the mantle may control the creeping of mantle rocks [3]. In particular our study focuses on the percolation of supercritical CO2, estimated through the solution of the Laplace equation in a porous system, stochastically generated through a series of random Karhunen-Loeve decomposition. The model outcome is employed to extract the transmissivity of supercritical fluids in the mantle from the lowest scale up to the mantle scale and in combination with the creeping flow of the convecting mantle. The emerging scenarios on the global carbon cycle are finally discussed. [1] Boulard, E., et al., New host for carbon in the deep Earth. Proceedings of the National Academy of Sciences, 2011. 108(13): p. 5184-5187. [2] Walter, M.J., et al., Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions. Science, 2011. 334(6052): p. 54-57. [3] Morra, G., et al., Ascent of Bubbles in Magma Conduits Using Boundary Elements and Particles. Procedia Computer Science, 2011.; Boundary Element solution of a flow through a porous. Left boxes represent the the matrix associated with the integrals. The flow enters below and emerges at the top, the amount of flow is identical. The flow is spread in the porous and is viscousless (Laplace equation).

Oceanic transform faults: how and why do they form? (Invited)

NASA Astrophysics Data System (ADS)

Gerya, T.

2013-12-01

Oceanic transform faults at mid-ocean ridges are often considered to be the direct product of plate breakup process (cf. review by Gerya, 2012). In contrast, recent 3D thermomechanical numerical models suggest that transform faults are plate growth structures, which develop gradually on a timescale of few millions years (Gerya, 2010, 2013a,b). Four subsequent stages are predicted for the transition from rifting to spreading (Gerya, 2013b): (1) crustal rifting, (2) multiple spreading centers nucleation and propagation, (3) proto-transform faults initiation and rotation and (4) mature ridge-transform spreading. Geometry of the mature ridge-transform system is governed by geometrical requirements for simultaneous accretion and displacement of new plate material within two offset spreading centers connected by a sustaining rheologically weak transform fault. According to these requirements, the characteristic spreading-parallel orientation of oceanic transform faults is the only thermomechanically consistent steady state orientation. Comparison of modeling results with the Woodlark Basin suggests that the development of this incipient spreading region (Taylor et al., 2009) closely matches numerical predictions (Gerya, 2013b). Model reproduces well characteristic 'rounded' contours of the spreading centers as well as the presence of a remnant of the broken continental crustal bridge observed in the Woodlark basin. Similarly to the model, the Moresby (proto)transform terminates in the oceanic rather than in the continental crust. Transform margins and truncated tip of one spreading center present in the model are documented in nature. In addition, numerical experiments suggest that transform faults can develop gradually at mature linear mid-ocean ridges as the result of dynamical instability (Gerya, 2010). Boundary instability from asymmetric plate growth can spontaneously start in alternate directions along successive ridge sections; the resultant curved ridges become transform faults. Offsets along the transform faults change continuously with time by asymmetric plate growth and discontinuously by ridge jumps. The ridge instability is governed by rheological weakening of active fault structures. The instability is most efficient for slow to intermediate spreading rates, whereas ultraslow and (ultra)fast spreading rates tend to destabilize transform faults (Gerya, 2010; Püthe and Gerya, 2013) References Gerya, T. (2010) Dynamical instability produces transform faults at mid-ocean ridges. Science, 329, 1047-1050. Gerya, T. (2012) Origin and models of oceanic transform faults. Tectonophys., 522-523, 34-56 Gerya, T.V. (2013a) Three-dimensional thermomechanical modeling of oceanic spreading initiation and evolution. Phys. Earth Planet. Interiors, 214, 35-52. Gerya, T.V. (2013b) Initiation of transform faults at rifted continental margins: 3D petrological-thermomechanical modeling and comparison to the Woodlark Basin. Petrology, 21, 1-10. Püthe, C., Gerya, T.V. (2013) Dependence of mid-ocean ridge morphology on spreading rate in numerical 3-D models. Gondwana Res., DOI: http://dx.doi.org/10.1016/j.gr.2013.04.005 Taylor, B., Goodliffe, A., Martinez, F. (2009) Initiation of transform faults at rifted continental margins. Comptes Rendus Geosci., 341, 428-438.

Analysis of the Yule-Nielsen effect with the multiple-path point spread function in a frequency-modulated halftone.

PubMed

Rogers, Geoffrey

2018-06-01

The Yule-Nielsen effect is an influence on halftone color caused by the diffusion of light within the paper upon which the halftone ink is printed. The diffusion can be characterized by a point spread function. In this paper, a point spread function for paper is derived using the multiple-path model of reflection. This model treats the interaction of light with turbid media as a random walk. Using the multiple-path point spread function, a general expression is derived for the average reflectance of light from a frequency-modulated halftone, in which dot size is constant and the number of dots is varied, with the arrangement of dots random. It is also shown that the line spread function derived from the multiple-path model has the form of a Lorentzian function.

Modeling emerald ash borer spread in Ohio and Michigan

Treesearch

Anantha Prasad; Louis Iverson; Matthew Peters; Jonathan Bossenbroek; Davis Sydnor; Mark Schwartz

2008-01-01

Our group has been modelling the spread of emerald ash borer (EAB) in Ohio using a spatially explicit cell-based model that takes into account the insect's flight characteristics (Insect Flight Model) as well as external factors that enable the insects to travel passively (Insect Ride Model).

Optimal control strategy for a novel computer virus propagation model on scale-free networks

NASA Astrophysics Data System (ADS)

Zhang, Chunming; Huang, Haitao

2016-06-01

This paper aims to study the combined impact of reinstalling system and network topology on the spread of computer viruses over the Internet. Based on scale-free network, this paper proposes a novel computer viruses propagation model-SLBOSmodel. A systematic analysis of this new model shows that the virus-free equilibrium is globally asymptotically stable when its spreading threshold is less than one; nevertheless, it is proved that the viral equilibrium is permanent if the spreading threshold is greater than one. Then, the impacts of different model parameters on spreading threshold are analyzed. Next, an optimally controlled SLBOS epidemic model on complex networks is also studied. We prove that there is an optimal control existing for the control problem. Some numerical simulations are finally given to illustrate the main results.

Prize to a Faculty Member for Research in an Undergraduate: Chaotic mixing and front propagation

NASA Astrophysics Data System (ADS)

Solomon, Tom

2014-03-01

We present results from a series of experiments - all done with undergraduate students - on chaotic fluid mixing and the effects of fluid flows on the behavior of reaction systems. Simple, well-ordered laminar fluid flows can give rise to fluid mixing with complexity far beyond that of the underlying flow, with tracers that separate exponentially in time and invariant manifolds that act as barriers to transport. Recently, we have studied how fluid mixing affects the propagation of reaction fronts in a flow. This is an issue with applications to a wide range of systems including microfluidic chemical reactors, blooms of phytoplankton in the oceans, and the spreading of a disease in a moving population. To analyze and predict the behavior of the fronts, we generalize tools developed to describe passive mixing. In particular, the concept of an invariant manifold is expanded to account for reactive burning. ``Burning invariant manifolds'' (BIMs) are predicted and measured experimentally as structures in the flow that act as one-way barriers that block the motion of reaction fronts. We test these ideas experimentally in three fluid flows: (a) and chain of alternating vortices; (b) an extended, spatially-random pattern of vortices; and (c) a time-independent, three-dimensional, nested vortex flow. The reaction fronts are produced chemically with variations of the well-known Belousov-Zhabotinsky reaction. Supported by Research Corporation and the National Science Foundation.

Mantle Flow and Melting Processes Beneath Back-Arc Basins

NASA Astrophysics Data System (ADS)

Hall, P. S.

2007-12-01

The chemical systematics of back-arc basin basalts suggest that multiple mechanisms of melt generation and transport operate simultaneously beneath the back-arc, resulting in a continuum of melts ranging from a relatively dry, MORB-like end-member to a wet, slab-influenced end-member [e.g., Kelley et al., 2006; Langmuir et al., 2006]. Potential melting processes at work include adiabatic decompression melting akin to that at mid-ocean ridges, diapiric upwelling of hydrous and/or partially molten mantle from above the subducting lithospheric slab [e.g., Marsh, 1979; Hall and Kincaid, 2001; Gerya and Yuen, 2003], and melting of back-arc mantle due to a continuous flux of slab-derived hydrous fluid [Kelley et al., 2006]. In this study, we examine the potential for each of these melting mechanisms to contribute to the observed distribution of melts in back-arc basins within the context of upper mantle flow (driven by plate motions) beneath back-arcs, which ultimately controls temperatures within the melting region. Mantle velocities and temperatures are derived from numerical geodynamic models of subduction with back-arc spreading that explicitly include adiabatic decompression melting through a Lagrangian particle scheme and a parameterization of hydrous melting. Dynamical feedback from the melting process occurs through latent heating and viscosity increases related to dehydration. A range of parameters, including subduction rate and trench-back-arc separation distances, is explored. The thermal evolution of individual diapirs is modeled numerically as they traverse the mantle, from nucleation above the subducting slab to melting beneath the back-arc spreading center, and a range of diapir sizes and densities and considered.

Modeling the coupled return-spread high frequency dynamics of large tick assets

NASA Astrophysics Data System (ADS)

Curato, Gianbiagio; Lillo, Fabrizio

2015-01-01

Large tick assets, i.e. assets where one tick movement is a significant fraction of the price and bid-ask spread is almost always equal to one tick, display a dynamics in which price changes and spread are strongly coupled. We present an approach based on the hidden Markov model, also known in econometrics as the Markov switching model, for the dynamics of price changes, where the latent Markov process is described by the transitions between spreads. We then use a finite Markov mixture of logit regressions on past squared price changes to describe temporal dependencies in the dynamics of price changes. The model can thus be seen as a double chain Markov model. We show that the model describes the shape of the price change distribution at different time scales, volatility clustering, and the anomalous decrease of kurtosis. We calibrate our models based on Nasdaq stocks and we show that this model reproduces remarkably well the statistical properties of real data.

A network-patch methodology for adapting agent-based models for directly transmitted disease to mosquito-borne disease.

PubMed

Manore, Carrie A; Hickmann, Kyle S; Hyman, James M; Foppa, Ivo M; Davis, Justin K; Wesson, Dawn M; Mores, Christopher N

2015-01-01

Mosquito-borne diseases cause significant public health burden and are widely re-emerging or emerging. Understanding, predicting, and mitigating the spread of mosquito-borne disease in diverse populations and geographies are ongoing modelling challenges. We propose a hybrid network-patch model for the spread of mosquito-borne pathogens that accounts for individual movement through mosquito habitats, extending the capabilities of existing agent-based models (ABMs) to include vector-borne diseases. The ABM are coupled with differential equations representing 'clouds' of mosquitoes in patches accounting for mosquito ecology. We adapted an ABM for humans using this method and investigated the importance of heterogeneity in pathogen spread, motivating the utility of models of individual behaviour. We observed that the final epidemic size is greater in patch models with a high risk patch frequently visited than in a homogeneous model. Our hybrid model quantifies the importance of the heterogeneity in the spread of mosquito-borne pathogens, guiding mitigation strategies.

Using landscape epidemiological models to understand the distribution of chronic wasting disease in the Midwestern USA

USGS Publications Warehouse

Robinson, Stacie J.; Samuel, Michael D.; Rolley, Robert E.; Shelton, Paul

2013-01-01

Animal movement across the landscape plays a critical role in the ecology of infectious wildlife diseases. Dispersing animals can spread pathogens between infected areas and naïve populations. While tracking free-ranging animals over the geographic scales relevant to landscape-level disease management is challenging, landscape features that influence gene flow among wildlife populations may also influence the contact rates and disease spread between populations. We used spatial diffusion and barriers to white-tailed deer gene flow, identified through landscape genetics, to model the distribution of chronic wasting disease (CWD) in the infected region of southern Wisconsin and northern Illinois, USA. Our generalized linear model showed that risk of CWD infection declined exponentially with distance from current outbreaks, and inclusion of gene flow barriers dramatically improved fit and predictive power of the model. Our results indicate that CWD is spreading across the Midwestern landscape from these two endemic foci, but spread is strongly influenced by highways and rivers that also reduce deer gene flow. We used our model to plot a risk map, providing important information for CWD management by identifying likely routes of disease spread and providing a tool for prioritizing disease monitoring and containment efforts. The current analysis may serve as a framework for modeling future disease risk drawing on genetic information to investigate barriers to spread and extending management and monitoring beyond currently affected regions.

A simple and complete model for wind turbine wakes over complex terrain

NASA Astrophysics Data System (ADS)

Rommelfanger, Nick; Rajborirug, Mai; Luzzatto-Fegiz, Paolo

2017-11-01

Simple models for turbine wakes have been used extensively in the wind energy community, both as independent tools, as well as to complement more refined and computationally-intensive techniques. These models typically prescribe empirical relations for how the wake radius grows with downstream distance x and obtain the wake velocity at each x through the application of either mass conservation, or of both mass and momentum conservation (e.g. Katić et al. 1986; Frandsen et al. 2006; Bastankhah & Porté-Agel 2014). Since these models assume a global behavior of the wake (for example, linear spreading with x) they cannot respond to local changes in background flow, as may occur over complex terrain. Instead of assuming a global wake shape, we develop a model by relying on a local assumption for the growth of the turbulent interface. To this end, we introduce to wind turbine wakes the use of the entrainment hypothesis, which has been used extensively in other areas of geophysical fluid dynamics. We obtain two coupled ordinary differential equations for mass and momentum conservation, which can be readily solved with a prescribed background pressure gradient. Our model is in good agreement with published data for the development of wakes over complex terrain.

Fluid models and simulations of biological cell phenomena

NASA Technical Reports Server (NTRS)

Greenspan, H. P.

1982-01-01

The dynamics of coated droplets are examined within the context of biofluids. Of specific interest is the manner in which the shape of a droplet, the motion within it as well as that of aggregates of droplets can be controlled by the modulation of surface properties and the extent to which such fluid phenomena are an intrinsic part of cellular processes. From the standpoint of biology, an objective is to elucidate some of the general dynamical features that affect the disposition of an entire cell, cell colonies and tissues. Conventionally averaged field variables of continuum mechanics are used to describe the overall global effects which result from the myriad of small scale molecular interactions. An attempt is made to establish cause and effect relationships from correct dynamical laws of motion rather than by what may have been unnecessary invocation of metabolic or life processes. Several topics are discussed where there are strong analogies droplets and cells including: encapsulated droplets/cell membranes; droplet shape/cell shape; adhesion and spread of a droplet/cell motility and adhesion; and oams and multiphase flows/cell aggregates and tissues. Evidence is presented to show that certain concepts of continuum theory such as suface tension, surface free energy, contact angle, bending moments, etc. are relevant and applicable to the study of cell biology.

A Spatial Modeling Approach to Predicting the Secondary Spread of Invasive Species Due to Ballast Water Discharge

PubMed Central

Sieracki, Jennifer L.; Bossenbroek, Jonathan M.; Chadderton, W. Lindsay

2014-01-01

Ballast water in ships is an important contributor to the secondary spread of invasive species in the Laurentian Great Lakes. Here, we use a model previously created to determine the role ballast water management has played in the secondary spread of viral hemorrhagic septicemia virus (VHSV) to identify the future spread of one current and two potential invasive species in the Great Lakes, the Eurasian Ruffe (Gymnocephalus cernuus), killer shrimp (Dikerogammarus villosus), and golden mussel (Limnoperna fortunei), respectively. Model predictions for Eurasian Ruffe have been used to direct surveillance efforts within the Great Lakes and DNA evidence of ruffe presence was recently reported from one of three high risk port localities identified by our model. Predictions made for killer shrimp and golden mussel suggest that these two species have the potential to become rapidly widespread if introduced to the Great Lakes, reinforcing the need for proactive ballast water management. The model used here is flexible enough to be applied to any species capable of being spread by ballast water in marine or freshwater ecosystems. PMID:25470822

Using the Gravity Model to Estimate the Spatial Spread of Vector-Borne Diseases

PubMed Central

Barrios, José Miguel; Verstraeten, Willem W.; Maes, Piet; Aerts, Jean-Marie; Farifteh, Jamshid; Coppin, Pol

2012-01-01

The gravity models are commonly used spatial interaction models. They have been widely applied in a large set of domains dealing with interactions amongst spatial entities. The spread of vector-borne diseases is also related to the intensity of interaction between spatial entities, namely, the physical habitat of pathogens’ vectors and/or hosts, and urban areas, thus humans. This study implements the concept behind gravity models in the spatial spread of two vector-borne diseases, nephropathia epidemica and Lyme borreliosis, based on current knowledge on the transmission mechanism of these diseases. Two sources of information on vegetated systems were tested: the CORINE land cover map and MODIS NDVI. The size of vegetated areas near urban centers and a local indicator of occupation-related exposure were found significant predictors of disease risk. Both the land cover map and the space-borne dataset were suited yet not equivalent input sources to locate and measure vegetated areas of importance for disease spread. The overall results point at the compatibility of the gravity model concept and the spatial spread of vector-borne diseases. PMID:23202882

Using the gravity model to estimate the spatial spread of vector-borne diseases.

PubMed

Barrios, José Miguel; Verstraeten, Willem W; Maes, Piet; Aerts, Jean-Marie; Farifteh, Jamshid; Coppin, Pol

2012-11-30

The gravity models are commonly used spatial interaction models. They have been widely applied in a large set of domains dealing with interactions amongst spatial entities. The spread of vector-borne diseases is also related to the intensity of interaction between spatial entities, namely, the physical habitat of pathogens’ vectors and/or hosts, and urban areas, thus humans. This study implements the concept behind gravity models in the spatial spread of two vector-borne diseases, nephropathia epidemica and Lyme borreliosis, based on current knowledge on the transmission mechanism of these diseases. Two sources of information on vegetated systems were tested: the CORINE land cover map and MODIS NDVI. The size of vegetated areas near urban centers and a local indicator of occupation-related exposure were found significant predictors of disease risk. Both the land cover map and the space-borne dataset were suited yet not equivalent input sources to locate and measure vegetated areas of importance for disease spread. The overall results point at the compatibility of the gravity model concept and the spatial spread of vector-borne diseases.

A trait-based approach for predicting species responses to environmental change from sparse data: how well might terrestrial mammals track climate change?

PubMed

Santini, Luca; Cornulier, Thomas; Bullock, James M; Palmer, Stephen C F; White, Steven M; Hodgson, Jenny A; Bocedi, Greta; Travis, Justin M J

2016-07-01

Estimating population spread rates across multiple species is vital for projecting biodiversity responses to climate change. A major challenge is to parameterise spread models for many species. We introduce an approach that addresses this challenge, coupling a trait-based analysis with spatial population modelling to project spread rates for 15 000 virtual mammals with life histories that reflect those seen in the real world. Covariances among life-history traits are estimated from an extensive terrestrial mammal data set using Bayesian inference. We elucidate the relative roles of different life-history traits in driving modelled spread rates, demonstrating that any one alone will be a poor predictor. We also estimate that around 30% of mammal species have potential spread rates slower than the global mean velocity of climate change. This novel trait-space-demographic modelling approach has broad applicability for tackling many key ecological questions for which we have the models but are hindered by data availability. © 2016 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

The impact of antibiotic use on transmission of resistant bacteria in hospitals: Insights from an agent-based model.

PubMed

Almagor, Jonatan; Temkin, Elizabeth; Benenson, Itzhak; Fallach, Noga; Carmeli, Yehuda

2018-01-01

Extensive antibiotic use over the years has led to the emergence and spread of antibiotic resistant bacteria (ARB). Antibiotic resistance poses a major threat to public health since for many infections antibiotic treatment is no longer effective. Hospitals are focal points for ARB spread. Antibiotic use in hospitals exerts selective pressure, accelerating the spread of ARB. We used an agent-based model to explore the impact of antibiotics on the transmission dynamics and to examine the potential of stewardship interventions in limiting ARB spread in a hospital. Agents in the model consist of patients and health care workers (HCW). The transmission of ARB occurs through contacts between patients and HCW and between adjacent patients. In the model, antibiotic use affects the risk of transmission by increasing the vulnerability of susceptible patients and the contagiousness of colonized patients who are treated with antibiotics. The model shows that increasing the proportion of patients receiving antibiotics increases the rate of acquisition non-linearly. The effect of antibiotics on the spread of resistance depends on characteristics of the antibiotic agent and the density of antibiotic use. Antibiotic's impact on the spread increases when the bacterial strain is more transmissible, and decreases as resistance prevalence rises. The individual risk for acquiring ARB increases in parallel with antibiotic density both for patients treated and not treated with antibiotics. Antibiotic treatment in the hospital setting plays an important role in determining the spread of resistance. Interventions to limit antibiotic use have the potential to reduce the spread of resistance, mainly by choosing an agent with a favorable profile in terms of its impact on patient's vulnerability and contagiousness. Methods to measure these impacts of antibiotics should be developed, standardized, and incorporated into drug development programs and approval packages.

Using a network model to assess risk of forest pest spread via recreational travel

Treesearch

Frank H. Koch; Denys Yemshanov; Robert A. Haack; Roger D. Magarey

2014-01-01

Long-distance dispersal pathways, which frequently relate to human activities, facilitate the spread of alien species. One pathway of concern in North America is the possible spread of forest pests in firewood carried by visitors to campgrounds or recreational facilities. We present a network model depicting the movement of campers and, by extension, potentially...

Modelling indirect interactions during failure spreading in a project activity network.

PubMed

Ellinas, Christos

2018-03-12

Spreading broadly refers to the notion of an entity propagating throughout a networked system via its interacting components. Evidence of its ubiquity and severity can be seen in a range of phenomena, from disease epidemics to financial systemic risk. In order to understand the dynamics of these critical phenomena, computational models map the probability of propagation as a function of direct exposure, typically in the form of pairwise interactions between components. By doing so, the important role of indirect interactions remains unexplored. In response, we develop a simple model that accounts for the effect of both direct and subsequent exposure, which we deploy in the novel context of failure propagation within a real-world engineering project. We show that subsequent exposure has a significant effect in key aspects, including the: (a) final spreading event size, (b) propagation rate, and (c) spreading event structure. In addition, we demonstrate the existence of 'hidden influentials' in large-scale spreading events, and evaluate the role of direct and subsequent exposure in their emergence. Given the evidence of the importance of subsequent exposure, our findings offer new insight on particular aspects that need to be included when modelling network dynamics in general, and spreading processes specifically.

Improving Agent Based Models and Validation through Data Fusion

PubMed Central

Laskowski, Marek; Demianyk, Bryan C.P.; Friesen, Marcia R.; McLeod, Robert D.; Mukhi, Shamir N.

2011-01-01

This work is contextualized in research in modeling and simulation of infection spread within a community or population, with the objective to provide a public health and policy tool in assessing the dynamics of infection spread and the qualitative impacts of public health interventions. This work uses the integration of real data sources into an Agent Based Model (ABM) to simulate respiratory infection spread within a small municipality. Novelty is derived in that the data sources are not necessarily obvious within ABM infection spread models. The ABM is a spatial-temporal model inclusive of behavioral and interaction patterns between individual agents on a real topography. The agent behaviours (movements and interactions) are fed by census / demographic data, integrated with real data from a telecommunication service provider (cellular records) and person-person contact data obtained via a custom 3G Smartphone application that logs Bluetooth connectivity between devices. Each source provides data of varying type and granularity, thereby enhancing the robustness of the model. The work demonstrates opportunities in data mining and fusion that can be used by policy and decision makers. The data become real-world inputs into individual SIR disease spread models and variants, thereby building credible and non-intrusive models to qualitatively simulate and assess public health interventions at the population level. PMID:23569606

Improving Agent Based Models and Validation through Data Fusion.

PubMed

Laskowski, Marek; Demianyk, Bryan C P; Friesen, Marcia R; McLeod, Robert D; Mukhi, Shamir N

2011-01-01

This work is contextualized in research in modeling and simulation of infection spread within a community or population, with the objective to provide a public health and policy tool in assessing the dynamics of infection spread and the qualitative impacts of public health interventions. This work uses the integration of real data sources into an Agent Based Model (ABM) to simulate respiratory infection spread within a small municipality. Novelty is derived in that the data sources are not necessarily obvious within ABM infection spread models. The ABM is a spatial-temporal model inclusive of behavioral and interaction patterns between individual agents on a real topography. The agent behaviours (movements and interactions) are fed by census / demographic data, integrated with real data from a telecommunication service provider (cellular records) and person-person contact data obtained via a custom 3G Smartphone application that logs Bluetooth connectivity between devices. Each source provides data of varying type and granularity, thereby enhancing the robustness of the model. The work demonstrates opportunities in data mining and fusion that can be used by policy and decision makers. The data become real-world inputs into individual SIR disease spread models and variants, thereby building credible and non-intrusive models to qualitatively simulate and assess public health interventions at the population level.

An agent-based computational model for tuberculosis spreading on age-structured populations

NASA Astrophysics Data System (ADS)

Graciani Rodrigues, C. C.; Espíndola, Aquino L.; Penna, T. J. P.

2015-06-01

In this work we present an agent-based computational model to study the spreading of the tuberculosis (TB) disease on age-structured populations. The model proposed is a merge of two previous models: an agent-based computational model for the spreading of tuberculosis and a bit-string model for biological aging. The combination of TB with the population aging, reproduces the coexistence of health states, as seen in real populations. In addition, the universal exponential behavior of mortalities curves is still preserved. Finally, the population distribution as function of age shows the prevalence of TB mostly in elders, for high efficacy treatments.

An intraorganizational model for developing and spreading quality improvement innovations.

PubMed

Kellogg, Katherine C; Gainer, Lindsay A; Allen, Adrienne S; OʼSullivan, Tatum; Singer, Sara J

Recent policy reforms encourage quality improvement (QI) innovations in primary care, but practitioners lack clear guidance regarding spread inside organizations. We designed this study to identify how large organizations can facilitate intraorganizational spread of QI innovations. We conducted ethnographic observation and interviews in a large, multispecialty, community-based medical group that implemented three QI innovations across 10 primary care sites using a new method for intraorganizational process development and spread. We compared quantitative outcomes achieved through the group's traditional versus new method, created a process model describing the steps in the new method, and identified barriers and facilitators at each step. The medical group achieved substantial improvement using its new method of intraorganizational process development and spread of QI innovations: standard work for rooming and depression screening, vaccine error rates and order compliance, and Pap smear error rates. Our model details nine critical steps for successful intraorganizational process development (set priorities, assess the current state, develop the new process, and measure and refine) and spread (develop support, disseminate information, facilitate peer-to-peer training, reinforce, and learn and adapt). Our results highlight the importance of utilizing preexisting organizational structures such as established communication channels, standardized roles, common workflows, formal authority, and performance measurement and feedback systems when developing and spreading QI processes inside an organization. In particular, we detail how formal process advocate positions in each site for each role can facilitate the spread of new processes. Successful intraorganizational spread is possible and sustainable. Developing and spreading new QI processes across sites inside an organization requires creating a shared understanding of the necessary process steps, considering the barriers that may arise at each step, and leveraging preexisting organizational structures to facilitate intraorganizational process development and spread.

An intraorganizational model for developing and spreading quality improvement innovations

PubMed Central

Kellogg, Katherine C.; Gainer, Lindsay A.; Allen, Adrienne S.; O'Sullivan, Tatum; Singer, Sara J.

2017-01-01

Background: Recent policy reforms encourage quality improvement (QI) innovations in primary care, but practitioners lack clear guidance regarding spread inside organizations. Purpose: We designed this study to identify how large organizations can facilitate intraorganizational spread of QI innovations. Methodology/Approach: We conducted ethnographic observation and interviews in a large, multispecialty, community-based medical group that implemented three QI innovations across 10 primary care sites using a new method for intraorganizational process development and spread. We compared quantitative outcomes achieved through the group’s traditional versus new method, created a process model describing the steps in the new method, and identified barriers and facilitators at each step. Findings: The medical group achieved substantial improvement using its new method of intraorganizational process development and spread of QI innovations: standard work for rooming and depression screening, vaccine error rates and order compliance, and Pap smear error rates. Our model details nine critical steps for successful intraorganizational process development (set priorities, assess the current state, develop the new process, and measure and refine) and spread (develop support, disseminate information, facilitate peer-to-peer training, reinforce, and learn and adapt). Our results highlight the importance of utilizing preexisting organizational structures such as established communication channels, standardized roles, common workflows, formal authority, and performance measurement and feedback systems when developing and spreading QI processes inside an organization. In particular, we detail how formal process advocate positions in each site for each role can facilitate the spread of new processes. Practice Implications: Successful intraorganizational spread is possible and sustainable. Developing and spreading new QI processes across sites inside an organization requires creating a shared understanding of the necessary process steps, considering the barriers that may arise at each step, and leveraging preexisting organizational structures to facilitate intraorganizational process development and spread. PMID:27428788

Spread prediction model of continuous steel tube based on BP neural network

NASA Astrophysics Data System (ADS)

Zhai, Jian-wei; Yu, Hui; Zou, Hai-bei; Wang, San-zhong; Liu, Li-gang

2017-07-01

According to the geometric pass of roll and technological parameters of three-roller continuous mandrel rolling mill in a factory, a finite element model is established to simulate the continuous rolling process of seamless steel tube, and the reliability of finite element model is verified by comparing with the simulation results and actual results of rolling force, wall thickness and outer diameter of the tube. The effect of roller reduction, roller rotation speed and blooming temperature on the spread rule is studied. Based on BP(Back Propagation) neural network technology, a spread prediction model of continuous rolling tube is established for training wall thickness coefficient and spread coefficient of the continuous rolling tube, and the rapid and accurate prediction of continuous rolling tube size is realized.

Modelling the effects of treatment and quarantine on measles

NASA Astrophysics Data System (ADS)

Beay, Lazarus Kalvein

2018-03-01

Treatment and quarantine are efforts to cure as well as to overcome the spread of diseases including measles. The spread of measles can be expressed by mathematical modelling in the form of nonlinear dynamical systems. In this study was conducted on the spread of measles by considering the effect of treatment and quarantine on the infected individuals. By using the basic reproduction number of the model, can be analyzed the effects of treatment and quarantine to reduce the spread of measles. Basic reproduction number of models is monotonically descreasing as treatment and quarantine increasing. Numerical simulations conducted on the analysis of the results. The results showed that treatment and quarantine was given to infected individuals who were infectious has a major influence to eliminate measles from the system.

Theoretical Analysis of Novel Quasi-3D Microscopy of Cell Deformation

PubMed Central

Qiu, Jun; Baik, Andrew D.; Lu, X. Lucas; Hillman, Elizabeth M. C.; Zhuang, Zhuo; Guo, X. Edward

2012-01-01

A novel quasi-three-dimensional (quasi-3D) microscopy technique has been developed to enable visualization of a cell under dynamic loading in two orthogonal planes simultaneously. The three-dimensional (3D) dynamics of the mechanical behavior of a cell under fluid flow can be examined at a high temporal resolution. In this study, a numerical model of a fluorescently dyed cell was created in 3D space, and the cell was subjected to uniaxial deformation or unidirectional fluid shear flow via finite element analysis (FEA). Therefore, the intracellular deformation in the simulated cells was exactly prescribed. Two-dimensional fluorescent images simulating the quasi-3D technique were created from the cell and its deformed states in 3D space using a point-spread function (PSF) and a convolution operation. These simulated original and deformed images were processed by a digital image correlation technique to calculate quasi-3D-based intracellular strains. The calculated strains were compared to the prescribed strains, thus providing a theoretical basis for the measurement of the accuracy of quasi-3D and wide-field microscopy-based intracellular strain measurements against the true 3D strains. The signal-to-noise ratio (SNR) of the simulated quasi-3D images was also modulated using additive Gaussian noise, and a minimum SNR of 12 was needed to recover the prescribed strains using digital image correlation. Our computational study demonstrated that quasi-3D strain measurements closely recovered the true 3D strains in uniform and fluid flow cellular strain states to within 5% strain error. PMID:22707985

The Role of Node Heterogeneity in the Coupled Spreading of Epidemics and Awareness.

PubMed

Guo, Quantong; Lei, Yanjun; Xia, Chengyi; Guo, Lu; Jiang, Xin; Zheng, Zhiming

2016-01-01

Exploring the interplay between information spreading and epidemic spreading is a topic that has been receiving increasing attention. As an efficient means of depicting the spreading of information, which manifests as a cascade phenomenon, awareness cascading is utilized to investigate this coupled transmission. Because in reality, different individuals facing the same epidemic will exhibit distinct behaviors according to their own experiences and attributes, it is important for us to consider the heterogeneity of individuals. Consequently, we propose a heterogeneous spreading model. To describe the heterogeneity, two of the most important but radically different methods for this purpose, the degree and k-core measures, are studied in this paper through three models based on different assumptions. Adopting a Markov chain approach, we succeed in predicting the epidemic threshold trend. Furthermore, we find that when the k-core measure is used to classify individuals, the spreading process is robust to these models, meaning that regardless of the model used, the spreading process is nearly identical at the macroscopic level. In addition, the k-core measure leads to a much larger final epidemic size than the degree measure. These results are cross-checked through numerous simulations, not only of a synthetic network but also of a real multiplex network. The presented findings provide a better understanding of k-core individuals and reveal the importance of considering network structure when investigating various dynamic processes.

Nonlinear model of epidemic spreading in a complex social network.

PubMed

Kosiński, Robert A; Grabowski, A

2007-10-01

The epidemic spreading in a human society is a complex process, which can be described on the basis of a nonlinear mathematical model. In such an approach the complex and hierarchical structure of social network (which has implications for the spreading of pathogens and can be treated as a complex network), can be taken into account. In our model each individual has one of the four permitted states: susceptible, infected, infective, unsusceptible or dead. This refers to the SEIR model used in epidemiology. The state of an individual changes in time, depending on the previous state and the interactions with other individuals. The description of the interpersonal contacts is based on the experimental observations of the social relations in the community. It includes spatial localization of the individuals and hierarchical structure of interpersonal interactions. Numerical simulations were performed for different types of epidemics, giving the progress of a spreading process and typical relationships (e.g. range of epidemic in time, the epidemic curve). The spreading process has a complex and spatially chaotic character. The time dependence of the number of infective individuals shows the nonlinear character of the spreading process. We investigate the influence of the preventive vaccinations on the spreading process. In particular, for a critical value of preventively vaccinated individuals the percolation threshold is observed and the epidemic is suppressed.

The Role of Node Heterogeneity in the Coupled Spreading of Epidemics and Awareness

PubMed Central

2016-01-01

Exploring the interplay between information spreading and epidemic spreading is a topic that has been receiving increasing attention. As an efficient means of depicting the spreading of information, which manifests as a cascade phenomenon, awareness cascading is utilized to investigate this coupled transmission. Because in reality, different individuals facing the same epidemic will exhibit distinct behaviors according to their own experiences and attributes, it is important for us to consider the heterogeneity of individuals. Consequently, we propose a heterogeneous spreading model. To describe the heterogeneity, two of the most important but radically different methods for this purpose, the degree and k-core measures, are studied in this paper through three models based on different assumptions. Adopting a Markov chain approach, we succeed in predicting the epidemic threshold trend. Furthermore, we find that when the k-core measure is used to classify individuals, the spreading process is robust to these models, meaning that regardless of the model used, the spreading process is nearly identical at the macroscopic level. In addition, the k-core measure leads to a much larger final epidemic size than the degree measure. These results are cross-checked through numerous simulations, not only of a synthetic network but also of a real multiplex network. The presented findings provide a better understanding of k-core individuals and reveal the importance of considering network structure when investigating various dynamic processes. PMID:27517715

Current Results and Proposed Activities in Microgravity Fluid Dynamics

NASA Technical Reports Server (NTRS)

Polezhaev, V. I.

1996-01-01

The Institute for Problems in Mechanics' Laboratory work in mathematical and physical modelling of fluid mechanics develops models, methods, and software for analysis of fluid flow, instability analysis, direct numerical modelling and semi-empirical models of turbulence, as well as experimental research and verification of these models and their applications in technological fluid dynamics, microgravity fluid mechanics, geophysics, and a number of engineering problems. This paper presents an overview of the results in microgravity fluid dynamics research during the last two years. Nonlinear problems of weakly compressible and compressible fluid flows are discussed.

Flow visualization by mobile phone cameras

NASA Astrophysics Data System (ADS)

Cierpka, Christian; Hain, Rainer; Buchmann, Nicolas A.

2016-06-01

Mobile smart phones were completely changing people's communication within the last ten years. However, these devices do not only offer communication through different channels but also devices and applications for fun and recreation. In this respect, mobile phone cameras include now relatively fast (up to 240 Hz) cameras to capture high-speed videos of sport events or other fast processes. The article therefore explores the possibility to make use of this development and the wide spread availability of these cameras in the terms of velocity measurements for industrial or technical applications and fluid dynamics education in high schools and at universities. The requirements for a simplistic PIV (particle image velocimetry) system are discussed. A model experiment of a free water jet was used to prove the concept and shed some light on the achievable quality and determine bottle necks by comparing the results obtained with a mobile phone camera with data taken by a high-speed camera suited for scientific experiments.

3-D numerical investigation of the mantle dynamics associated with the breakup of Pangea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baumgardner, J.R.

1992-01-01

Three-dimensional finite element calculations in spherical geometry are performed to study the response of the mantle with platelike blocks at its surface to an initial condition corresponding to subduction along the margins of Pangea. The mantle is treated as an infinite Prandtl number Boussinesq fluid inside a spherical shell with isothermal, undeformable, free-slip boundaries. Nonsubducting rigid blocks to model continental lithosphere are included in the topmost layer of the computational mesh. At the beginning of the numerical experiments these blocks represent the present continents mapped to their approximate Pangean positions. Asymmetrical downwelling at the margins of these nonsubducting blocks resultsmore » in a pattern of stresses that acts to pull the supercontinent apart. The calculations suggest that the breakup of Pangea and the subsequent global pattern of seafloor spreading was driven largely by the subduction at the Pangean margins.« less

3-D numerical investigation of the mantle dynamics associated with the breakup of Pangea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baumgardner, J.R.

1992-10-01

Three-dimensional finite element calculations in spherical geometry are performed to study the response of the mantle with platelike blocks at its surface to an initial condition corresponding to subduction along the margins of Pangea. The mantle is treated as an infinite Prandtl number Boussinesq fluid inside a spherical shell with isothermal, undeformable, free-slip boundaries. Nonsubducting rigid blocks to model continental lithosphere are included in the topmost layer of the computational mesh. At the beginning of the numerical experiments these blocks represent the present continents mapped to their approximate Pangean positions. Asymmetrical downwelling at the margins of these nonsubducting blocks resultsmore » in a pattern of stresses that acts to pull the supercontinent apart. The calculations suggest that the breakup of Pangea and the subsequent global pattern of seafloor spreading was driven largely by the subduction at the Pangean margins.« less

High volume hydraulic fracturing operations: potential impacts on surface water and human health.

PubMed

Mrdjen, Igor; Lee, Jiyoung

2016-08-01

High volume, hydraulic fracturing (HVHF) processes, used to extract natural gas and oil from underground shale deposits, pose many potential hazards to the environment and human health. HVHF can negatively affect the environment by contaminating soil, water, and air matrices with potential pollutants. Due to the relatively novel nature of the process, hazards to surface waters and human health are not well known. The purpose of this article is to link the impacts of HVHF operations on surface water integrity, with human health consequences. Surface water contamination risks include: increased structural failure rates of unconventional wells, issues with wastewater treatment, and accidental discharge of contaminated fluids. Human health risks associated with exposure to surface water contaminated with HVHF chemicals include increased cancer risk and turbidity of water, leading to increased pathogen survival time. Future research should focus on modeling contamination spread throughout the environment, and minimizing occupational exposure to harmful chemicals.

SSIC model: A multi-layer model for intervention of online rumors spreading

NASA Astrophysics Data System (ADS)

Tian, Ru-Ya; Zhang, Xue-Fu; Liu, Yi-Jun

2015-06-01

SIR model is a classical model to simulate rumor spreading, while the supernetwork is an effective tool for modeling complex systems. Based on the Opinion SuperNetwork involving Social Sub-network, Environmental Sub-network, Psychological Sub-network, and Viewpoint Sub-network, drawing from the modeling idea of SIR model, this paper designs super SIC model (SSIC model) and its evolution rules, and also analyzes intervention effects on public opinion of four elements of supernetwork, which are opinion agent, opinion environment, agent's psychology and viewpoint. Studies show that, the SSIC model based on supernetwork has effective intervention effects on rumor spreading. It is worth noting that (i) identifying rumor spreaders in Social Sub-network and isolating them can achieve desired intervention results, (ii) improving environmental information transparency so that the public knows as much information as possible to reduce the rumors is a feasible way to intervene, (iii) persuading wavering neutrals has better intervention effects than clarifying rumors already spread everywhere, so rumors should be intervened in properly in time by psychology counseling.

Spread of Ebola disease with susceptible exposed infected isolated recovered (SEIIhR) model

NASA Astrophysics Data System (ADS)

Azizah, Afina; Widyaningsih, Purnami; Retno Sari Saputro, Dewi

2017-06-01

Ebola is a deadly infectious disease and has caused an epidemic on several countries in West Africa. Mathematical modeling to study the spread of Ebola disease has been developed, including through models susceptible infected removed (SIR) and susceptible exposed infected removed (SEIR). Furthermore, susceptible exposed infected isolated recovered (SEIIhR) model has been derived. The aims of this research are to derive SEIIhR model for Ebola disease, to determine the patterns of its spread, to determine the equilibrium point and stability of the equilibrium point using phase plane analysis, and also to apply the SEIIhR model on Ebola epidemic in Sierra Leone in 2014. The SEIIhR model is a differential equation system. Pattern of ebola disease spread with SEIIhR model is solution of the differential equation system. The equilibrium point of SEIIhR model is unique and it is a disease-free equilibrium point that stable. Application of the model is based on the data Ebola epidemic in Sierra Leone. The free-disease equilibrium point (Se; Ee; Ie; Ihe; Re )=(5743865, 0, 0, 0, 0) is stable.

South Asian monsoon precipitation in CMIP 5: a link between inter-model spread and the representations of tropical convection

DOE PAGES

Hagos, Samson; Leung, L. Ruby; Ashfaq, Moetasim; ...

2018-03-20

CMIP 5 models exhibit a mean dry bias and a large inter-model spread in simulating South Asian monsoon precipitation but the origins of the bias and spread are not well understood. Using moisture and energy budget analysis that exploits the weak temperature gradients in the tropics, we derived a non-linear relationship between the normalized precipitation and normalized precipitable water that is similar to the non-linear relationship between precipitation and precipitable water found in previous observational studies. About half of the 21 models analyzed fall in the steep gradient of the non-linear relationship where small differences in the normalized precipitable watermore » in the equatorial Indian Ocean (EIO) manifest in large differences in normalized precipitation in the region. Models with larger normalized precipitable water in the EIO during spring contribute disproportionately to the large inter-model spread and multi-model mean dry bias in monsoon precipitation through perturbations of the large-scale winds. Thus the intermodel spread in precipitable water over EIO leads to the dry bias in the multi-model mean South Asian monsoon precipitation. The models with high normalized precipitable water over EIO also project larger response to warming and dominate the inter-model spread in the multi-model projections of monsoon rainfall. Conversely, models on the flat side of the relationship between normalized precipitation and precipitable water are in better agreement with each other and with observations. On average these models project a smaller increase in the projected monsoon precipitation than that from multi-model mean. As a result, this study identified the normalized precipitable water over EIO, which is determined by the relationship between the profiles of convergence and moisture and therefore is an essential outcome of the treatment of convection, as a key metric for understanding model biases and differentiating model skill in simulating South Asian monsoon precipitation.« less

South Asian monsoon precipitation in CMIP 5: a link between inter-model spread and the representations of tropical convection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagos, Samson; Leung, L. Ruby; Ashfaq, Moetasim

CMIP 5 models exhibit a mean dry bias and a large inter-model spread in simulating South Asian monsoon precipitation but the origins of the bias and spread are not well understood. Using moisture and energy budget analysis that exploits the weak temperature gradients in the tropics, we derived a non-linear relationship between the normalized precipitation and normalized precipitable water that is similar to the non-linear relationship between precipitation and precipitable water found in previous observational studies. About half of the 21 models analyzed fall in the steep gradient of the non-linear relationship where small differences in the normalized precipitable watermore » in the equatorial Indian Ocean (EIO) manifest in large differences in normalized precipitation in the region. Models with larger normalized precipitable water in the EIO during spring contribute disproportionately to the large inter-model spread and multi-model mean dry bias in monsoon precipitation through perturbations of the large-scale winds. Thus the intermodel spread in precipitable water over EIO leads to the dry bias in the multi-model mean South Asian monsoon precipitation. The models with high normalized precipitable water over EIO also project larger response to warming and dominate the inter-model spread in the multi-model projections of monsoon rainfall. Conversely, models on the flat side of the relationship between normalized precipitation and precipitable water are in better agreement with each other and with observations. On average these models project a smaller increase in the projected monsoon precipitation than that from multi-model mean. As a result, this study identified the normalized precipitable water over EIO, which is determined by the relationship between the profiles of convergence and moisture and therefore is an essential outcome of the treatment of convection, as a key metric for understanding model biases and differentiating model skill in simulating South Asian monsoon precipitation.« less

Geodiversity of hydrothermal processes along the Mid-Atlantic Ridge and ultramafic-hosted mineralization: A new type of oceanic Cu-Zn-Co-Au volcanogenic massive sulfide deposit

NASA Astrophysics Data System (ADS)

Fouquet, Yves; Cambon, Pierre; Etoubleau, Joël; Charlou, Jean Luc; Ondréas, Hélène; Barriga, Fernando J. A. S.; Cherkashov, Georgy; Semkova, Tatiana; Poroshina, Irina; Bohn, M.; Donval, Jean Pierre; Henry, Katell; Murphy, Pamela; Rouxel, Olivier

Several hydrothermal deposits associated with ultramafic rocks have recently been found along slow spreading ridges with a low magmatic budget. Three preferential settings are identified: (1) rift valley walls near the amagmatic ends of ridge segments; (2) nontransform offsets; and (3) ultramafic domes at inside corners of ridge transform-fault intersections. The exposed mantle at these sites is often interpreted to be a detachment fault. Hydrothermal cells in ultramafic rocks may be driven by regional heat flow, cooling gabbroic intrusions, and exothermic heat produced during serpentinization. Along the Mid-Atlantic Ridge (MAR), hydrothermal deposits in ultramafic rocks include the following: (1) sulfide mounds related to high-temperature low-pH fluids (Logatchev, Rainbow, and Ashadze); (2) carbonate chimneys related to low-temperature, high-pH fluids (Lost City); (3) low-temperature diffuse venting and high-methane discharge associated with silica, minor sulfides, manganese oxides, and pervasive alteration (Saldanha); and (4) stockwork quartz veins with sulfides at the base of detachment faults (15°05'N). These settings are closely linked to preferential circulation of fluid along permeable detachment faults. Compared to mineralization in basaltic environments, sulfide deposits associated with ultramafic rocks are enriched in Cu, Zn, Co, Au, and Ni. Gold has a bimodal distribution in low-temperature Zn-rich and in high-temperature Cu-rich mineral assemblages. The Cu-Zn-Co-Au deposits along the MAR seem to be more abundant than in ophiolites on land. This may be because ultramafic-hosted volcanogenic massive sulfide deposits on slow spreading ridges are usually not accreted to continental margins during obduction and may constitute a specific marine type of mineralization.

Congenital Abnormalities: Consequence of Maternal Zika Virus Infection: A Narrative Review.

PubMed

Hassan, Fatima I; Niaz, Kamal; Maqbool, Faheem; Khan, Fazlullah; Abdollahi, Mohammad

2017-01-01

Zika virus (ZIKV) is a deadly flavivirus that has spread from Africa to Asia and European countries. The virus is associated with other viruses in the same genus or family, transmitted by the same mosquito species with known history of fatality. A sudden increase in the rate of infection from ZIKV has made it a global health concern, which necessitates close symptom monitoring, enhancing treatment options, and vaccine production. This paper reviewed current reports on birth defects associated with ZIKV, mode of transmission, body fluids containing the virus, diagnosis, possible preventive measures or treatments, and vaccine development. Google scholar was used as the major search engine for research and review articles, up to July, 2016. Search terms such as "ZIKV", "ZIKV infection", "ZIKV serotypes", "treatment of ZIKV infection", "co-infection with zika virus", "flavivirus", "microcephaly and zika", "birth defects and Zika", as well as "ZIKV vaccine" were used. ZIKV has been detected in several body fluids such as saliva, semen, blood, and amniotic fluid. This reveals the possibility of sexual and mother to child transmission. The ability of the virus to cross the placental barrier and the blood brain barrier (BBB) has been associated with birth defects such as microcephaly, ocular defects, and Guillian Barre syndrome (GBS). Preventive measures can reduce the spread and risk of the infection. Available treatments only target symptoms while vaccines are still under development. Birth defects are associated with ZIKV infection in pregnant women; hence the need for development of standard treatments, employment of strict preventive measures and development of effective vaccines. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

On solar geoengineering and climate uncertainty

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacMartin, Douglas; Kravitz, Benjamin S.; Rasch, Philip J.

2015-09-03

Uncertainty in the climate system response has been raised as a concern regarding solar geoengineering. Here we show that model projections of regional climate change outcomes may have greater agreement under solar geoengineering than with CO2 alone. We explore the effects of geoengineering on one source of climate system uncertainty by evaluating the inter-model spread across 12 climate models participating in the Geoengineering Model Intercomparison project (GeoMIP). The model spread in regional temperature and precipitation changes is reduced with CO2 and a solar reduction, in comparison to the case with increased CO2 alone. That is, the intermodel spread in predictionsmore » of climate change and the model spread in the response to solar geoengineering are not additive but rather partially cancel. Furthermore, differences in efficacy explain most of the differences between models in their temperature response to an increase in CO2 that is offset by a solar reduction. These conclusions are important for clarifying geoengineering risks.« less

Spreading the Word on Safety

NASA Technical Reports Server (NTRS)

2004-01-01

Beginning with the Apollo Program in the early 1960s, the NASA White Sands Test Facility (WSTF) has supported every U.S. human exploration space flight program to date. Located in Las Cruces, New Mexico, WSTF is part of Johnson Space Center. The facility's primary mission is to provide the expertise and infrastructure to test and evaluate spacecraft materials, components, and rocket propulsion systems to enable the safe human exploration and utilization of space. WSTF stores, tests, and disposes of Space Shuttle and International Space Station propellants. Since aerospace fluids can have harmful reactions with the construction materials of the systems containing them, a major component of WSTF's work is the study of propellants and hazardous materials. WSTF has a wide variety of resources to draw upon in assessing the fire, explosion, compatibility, and safety hazards of these fluids, which include hydrogen, oxygen, hydrazine fuels, and nitrogen tetroxide. In addition to developing new test methods, WSTF has created technical manuals and training courses for the safe use of aerospace fluids.

Spatial spreading of infectious disease via local and national mobility networks in South Korea

NASA Astrophysics Data System (ADS)

Kwon, Okyu; Son, Woo-Sik

2017-12-01

We study the spread of infectious disease based on local- and national-scale mobility networks. We construct a local mobility network using data on urban bus services to estimate local-scale movement of people. We also construct a national mobility network from orientation-destination data of vehicular traffic between highway tollgates to evaluate national-scale movement of people. A metapopulation model is used to simulate the spread of epidemics. Thus, the number of infected people is simulated using a susceptible-infectious-recovered (SIR) model within the administrative division, and inter-division spread of infected people is determined through local and national mobility networks. In this paper, we consider two scenarios for epidemic spread. In the first, the infectious disease only spreads through local-scale movement of people, that is, the local mobility network. In the second, it spreads via both local and national mobility networks. For the former, the simulation results show infected people sequentially spread to neighboring divisions. Yet for the latter, we observe a faster spreading pattern to distant divisions. Thus, we confirm the national mobility network enhances synchronization among the incidence profiles of all administrative divisions.

Examination of the wind speed limit function in the Rothermel surface fire spread model

Treesearch

Patricia L. Andrews; Miguel G. Cruz; Richard C. Rothermel

2013-01-01

The Rothermel surface fire spread model includes a wind speed limit, above which predicted rate of spread is constant. Complete derivation of the wind limit as a function of reaction intensity is given, along with an alternate result based on a changed assumption. Evidence indicates that both the original and the revised wind limits are too restrictive. Wind limit is...

Being Ethnically Fluid in Post-Brexit Britain: How Teaching English Literature in England Made Me Want--Momentarily--to Return to Russia and Join Putin's Party

ERIC Educational Resources Information Center

Protopopova, Darya

2018-01-01

A descendant of Chekhov's extended family, Darya Protopopova has always loved all things literary. When she found out that Chekhov was popular with British modernist writers, she decided to do a master's and then a doctorate in English modernism at the University of Oxford. Having completed both, she chose to spread her love for English literary…

Implications of the spatial dynamics of fire spread for the bistability of savanna and forest.

PubMed

Schertzer, E; Staver, A C; Levin, S A

2015-01-01

The role of fire in expanding the global distribution of savanna is well recognized. Empirical observations and modeling suggest that fire spread has a threshold response to fuel-layer continuity, which sets up a positive feedback that maintains savanna-forest bistability. However, modeling has so far failed to examine fire spread as a spatial process that interacts with vegetation. Here, we use simple, well-supported assumptions about fire spread as an infection process and its effects on trees to ask whether spatial dynamics qualitatively change the potential for savanna-forest bistability. We show that the spatial effects of fire spread are the fundamental reason that bistability is possible: because fire spread is an infection process, it exhibits a threshold response to fuel continuity followed by a rapid increase in fire size. Other ecological processes affecting fire spread may also contribute including temporal variability in demography or fire spread. Finally, including the potential for spatial aggregation increases the potential both for savanna-forest bistability and for savanna and forest to coexist in a landscape mosaic.

Hydrothermal activity at slow-spreading ridges: variability and importance of magmatic controls

NASA Astrophysics Data System (ADS)

Escartin, Javier

2016-04-01

Hydrothermal activity along mid-ocean ridge axes is ubiquitous, associated with mass, chemical, and heat exchanges between the deep lithosphere and the overlying envelopes, and sustaining chemiosynthetic ecosystems at the seafloor. Compared with hydrothermal fields at fast-spreading ridges, those at slow spreading ones show a large variability as their location and nature is controlled or influenced by several parameters that are inter-related: a) tectonic setting, ranging from 'volcanic systems' (along the rift valley floor, volcanic ridges, seamounts), to 'tectonic' ones (rift-bounding faults, oceanic detachment faults); b) the nature of the host rock, owing to compositional heterogeneity of slow-spreading lithosphere (basalt, gabbro, peridotite); c) the type of heat source (magmatic bodies at depth, hot lithosphere, serpentinization reactions); d) and the associated temperature of outflow fluids (high- vs.- low temperature venting and their relative proportion). A systematic review of the distribution and characteristics of hydrothermal fields along the slow-spreading Mid-Atlantic Ridge suggests that long-lived hydrothermal activity is concentrated either at oceanic detachment faults, or along volcanic segments with evidence of robust magma supply to the axis. A detailed study of the magmatically robust Lucky Strike segment suggests that all present and past hydrothermal activity is found at the center of the segment. The association of these fields to central volcanos, and the absence of indicators of hydrothermal activity along the remaining of the ridge segment, suggests that long-lived hydrothermal activity in these volcanic systems is maintained by the enhanced melt supply and the associated magma chamber(s) required to build these volcanic edifices. In this setting, hydrothermal outflow zones at the seafloor are systematically controlled by faults, indicating that hydrothermal fluids in the shallow crust exploit permeable fault zones to circulate. While less studied, similar hydrothermal systems are found elsewhere associated to other central volcanoes along the ridge axis (e.g., Menez Gwenn at the Mid-Atlantic Ridge and Soria Mornia or Troll Wall at the Arctic Ridges). Long-lived hydrothermal activity plays an important role in controlling the thermal structure of the lithosphere and its accretion at and near-axis, and also determining the distribution and biogeography of vent communities. Along slow-spreading segments, long-lived hydrothermal activity can be provided both by volcanic systems (e.g., Lucky Strike) and tectonic systems (oceanic detachment faults). While magmatic and hydrothermal activity is relatively well understood now in volcanic systems (e.g., Lucky Strike), tectonic systems (oceanic detachment faults) require further integrated studies to constrain the links between long-lived localization of deformation along oceanic detachment faults, hydrothermal activity, and origin and nature of off-axis heat sources animating hydrothermal circulation.

Geodynamics of seafloor spreading extinction: Constraints from the South China Sea

NASA Astrophysics Data System (ADS)

Zhang, X.; Lin, J.; Behn, M. D.

2016-12-01

We investigate magmatism and mantle thermal structure beneath fossil spreading centers in the South China Sea (SCS), focusing on two aspects: (1) mantle thermal structure and melting, and (2) magmatism associated with seamounts. We carried out 3D geodynamic models to study thermal structure beneath the SCS during the process from initiation to cessation of seafloor spreading. Modeling results suggested that the overall mantle temperatures of the East Subbasin were significantly greater than that of the Southwest Subbasin when the seafloor spreading of both subbasins ceased at about 15-16 Ma. However, the differences in thermal structure between the two subbasins were calculated to have decreased with time. Work is in progress to couple geochemical and geophysical constraints with geodynamic modeling to investigate melt generation, fractional crystallization, and melt extraction at the fossil spreading centers in the SCS. Among the seamounts that can be identified on multi-beam bathymetry data, about half of them are located along the fossil spreading centers while the remaining located off axis. This is in contrast to fossil spreading ridges in the West Scotia Sea and Phoenix Ridge, where most seamounts are located off axis. The off-axis seamounts in the SCS also show strong asymmetry about the fossil spreading centers with most seamounts concentrated in the northern flank. Work is in progress to investigate the melting processes associated with seamounts.

Spreading of Cholera through Surface Water

NASA Astrophysics Data System (ADS)

Bertuzzo, E.; Casagrandi, R.; Gatto, M.; Rodriguez-Iturbe, I.; Rinaldo, A.

2009-12-01

Cholera epidemics are still a major public health concern to date in many areas of the world. In order to understand and forecast cholera outbreaks, one of the most important factors is the role played by the environmental matrix in which the disease spreads. We study how river networks, acting as environmental corridors for pathogens, affect the spreading of cholera epidemics. The environmental matrix in which the disease spreads is constituted by different human communities and their hydrologic interconnections. Each community is characterized by its spatial position, population size, water resources availability and hygiene conditions. By implementing a spatially explicit cholera model we seek the effects on epidemic dynamics of: i) the topology and metrics of the pathogens pathways that connect different communities; ii) the spatial distribution of the population size; and iii) the spatial distributions and quality of surface water resources and public health conditions, and how they vary with population size. The model has been applied to study the space-time evolution of a well documented cholera epidemic occurred in the KwaZulu-Natal province of South Africa. The epidemic lasted for two years and involved about 140,000 confirmed cholera cases. The model does well in reproducing the distribution of the cholera cases during the two outbreaks as well as their spatial spreading. We further extend the model by deriving the speed of propagation of traveling fronts in the case of uniformly distributed systems for different topologies: one and two dimensional lattices and river networks. The derivation of the spreading celerity proves instrumental in establishing the overall conditions for the relevance of spatially explicit models. The conditions are sought by comparison between spreading and disease timescales. Consider a cholera epidemic that starts from a point and spreads throughout a finite size system, it is possible to identify two different timescales: i) the spreading timescale, that is the time needed for the disease to spread and involve all the communities in the system; and ii) the epidemic timescale, defined by the duration of the epidemic in a single community. Our results suggest that in many cases of real-life epidemiological interest, timescales of disease dynamics may trigger outbreaks that significantly depart from the predictions of classical space-implicit compartmental models.

Droplet-Surface Impingement Dynamics for Intelligent Spray Design

NASA Technical Reports Server (NTRS)

Wal, Randy L. Vander; Kizito, John P.; Tryggvason, Gretar

2004-01-01

Spray cooling has high potential in thermal management and life support systems by overcoming the deleterious effect of microgravity upon two-phase heat transfer. In particular spray cooling offers several advantages in heat flux removal that include the following: 1) By maintaining a wetted surface, spray droplets impinge upon a thin fluid film rather than a dry solid surface; 2. Most heat transfer surfaces will not be smooth but rough. Roughness can enhance conductive cooling, aid liquid removal by flow channeling; and 3. Spray momentum can be used to a) substitute for gravity delivering fluid to the surface, b) prevent local dryout and potential thermal runaway and c) facilitate liquid and vapor removal. Yet high momentum results in high We and Re numbers characterizing the individual spray droplets. Beyond an impingement threshold, droplets splash rather than spread. Heat flux declines and spray cooling efficiency can markedly decrease. Accordingly we are investigating droplet impingement upon a) dry solid surfaces, b) fluid films, c) rough surfaces and determining splashing thresholds and relationships for both dry surfaces and those covered by fluid films. We are presently developing engineering correlations delineating the boundary between splashing and non-splashing regions. Determining the splash/non-splash boundary is important for many practical applications. Coating and cooling processes would each benefit from near-term empirical relations and subsequent models. Such demonstrations can guide theoretical development by providing definitive testing of its predictive capabilities. Thus, empirical relations describing the boundary between splash and non-splash are given for drops impinging upon a dry solid surface and upon a thin fluid film covering a similar surface. Analytical simplification of the power laws describing the boundary between the splash and non-splash regions yields insight into the engineering parameters governing the splash and non-splash outcomes of the fluid droplets. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a dry solid surface. Splashing upon a dry surface is reasonably described by Ca greater than 0.85, reflecting the competing roles of surface tension and viscosity. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a thin fluid film covering the solid surface. Splashing upon a thin fluid film, as described by v (pd/s) greater than 63, is governed by fluid density and surface tension, but is rather independent of viscosity. Finally, the data presented here suggests that a more direct dependence upon the surface tension and viscosity, given a better understanding of their interplay, would allow accurate description of the droplet-surface impacts for more complicated situations involving non-Newtonian fluids, specifically those exhibiting viscoelastic behavior.

Modeling the spatial spread of infectious diseases: the GLobal Epidemic and Mobility computational model

PubMed Central

Balcan, Duygu; Gonçalves, Bruno; Hu, Hao; Ramasco, José J.; Colizza, Vittoria

2010-01-01

Here we present the Global Epidemic and Mobility (GLEaM) model that integrates sociodemographic and population mobility data in a spatially structured stochastic disease approach to simulate the spread of epidemics at the worldwide scale. We discuss the flexible structure of the model that is open to the inclusion of different disease structures and local intervention policies. This makes GLEaM suitable for the computational modeling and anticipation of the spatio-temporal patterns of global epidemic spreading, the understanding of historical epidemics, the assessment of the role of human mobility in shaping global epidemics, and the analysis of mitigation and containment scenarios. PMID:21415939

Contrasting Hydrodynamic and Environmental Effects of Hurricanes Harvey and Ike in a Highly Industrialized Estuary

NASA Astrophysics Data System (ADS)

Kiaghadi, A.; Rifai, H. S.

2017-12-01

It is commonly believed that storm surge is the most destructive aspect of hurricanes. However, massive rainfall with a return period of 100 years or more induced by hurricanes can cause more catastrophic damage than losses caused by storm surge as demonstrated recently by hurricanes Harvey, Irma and Maria. In this study the hydrodynamics and environmental effects of hurricanes Ike and Harvey were compared and contrasted by linking hydrodynamic flow models with water quality models to simulate spills from storage tanks located in the Houston Ship Channel (HSC). Hurricane Ike with a maximum surge of 5.3 meters in Galveston Bay and Harvey with a maximum rainfall of 1.25 meters both struck the HSC region in Texas in 2008 and 2017, respectively. Both events resulted in numerous spills from municipal and industrial facilities, hazardous waste sites, superfund sites, and landfills. The Environmental Fluid Dynamic Code (EFDC) was coupled with the SWAN+ADCIRC hurricane simulation model to simulate Hurricane Ike and EFDC was coupled with USGS flow boundary conditions to model Hurricane Harvey. A conservative dye release was used to simulate a chemical release during each event. The results showed Hurricane Harvey caused higher water surface elevations within the HSC accompanied by longer and wider-spread land inundation. In contrast, higher water surface elevations were observed within the shallow side bays during Hurricane Ike that caused sediment resuspension and repartitioning of pollutants. Rapid spill mass transportation was observed for both hurricanes; 50% of total spill mass reached Galveston Bay in 20 and 22 hours after a spill event for Hurricane Harvey and Ike, respectively, and more than 90% of the spill mass reached the bay in 36 and 48 hours, respectively. Unlike Hurricane Harvey, the conservative tracer was spread almost 2.5 km upstream of the releasing point for Hurricane Ike due to surge. However, during Harvey, 35% more land was affected by the spilled mass with five times more remained mass on the land.

Modeling the effects of social impact on epidemic spreading in complex networks

NASA Astrophysics Data System (ADS)

Ni, Shunjiang; Weng, Wenguo; Zhang, Hui

2011-11-01

We investigate by mean-field analysis and extensive simulations the effects of social impact on epidemic spreading in various typical networks with two types of nodes: active nodes and passive nodes, of which the behavior patterns are modeled according to the social impact theory. In this study, nodes are not only the media to spread the virus, but also disseminate their opinions on the virus-whether there is a need for certain self-protection measures to be taken to reduce the risk of being infected. Our results indicate that the interaction between epidemic spreading and opinion dynamics can have significant influences on the spreading of infectious diseases and related applications, such as the implementation of prevention and control measures against the infectious diseases.

Autoimmune Neurological Conditions Associated With Zika Virus Infection.

PubMed

Acosta-Ampudia, Yeny; Monsalve, Diana M; Castillo-Medina, Luis F; Rodríguez, Yhojan; Pacheco, Yovana; Halstead, Susan; Willison, Hugh J; Anaya, Juan-Manuel; Ramírez-Santana, Carolina

2018-01-01

Zika virus (ZIKV) is an emerging flavivirus rapidly spreading throughout the tropical Americas. Aedes mosquitoes is the principal way of transmission of the virus to humans. ZIKV can be spread by transplacental, perinatal, and body fluids. ZIKV infection is often asymptomatic and those with symptoms present minor illness after 3 to 12 days of incubation, characterized by a mild and self-limiting disease with low-grade fever, conjunctivitis, widespread pruritic maculopapular rash, arthralgia and myalgia. ZIKV has been linked to a number of central and peripheral nervous system injuries such as Guillain-Barré syndrome (GBS), transverse myelitis (TM), meningoencephalitis, ophthalmological manifestations, and other neurological complications. Nevertheless, mechanisms of host-pathogen neuro-immune interactions remain incompletely elucidated. This review provides a critical discussion about the possible mechanisms underlying the development of autoimmune neurological conditions associated with Zika virus infection.

Universal inverse power-law distribution for temperature and rainfall in the UK region

NASA Astrophysics Data System (ADS)

Selvam, A. M.

2014-06-01

Meteorological parameters, such as temperature, rainfall, pressure, etc., exhibit selfsimilar space-time fractal fluctuations generic to dynamical systems in nature such as fluid flows, spread of forest fires, earthquakes, etc. The power spectra of fractal fluctuations display inverse power-law form signifying long-range correlations. A general systems theory model predicts universal inverse power-law form incorporating the golden mean for the fractal fluctuations. The model predicted distribution was compared with observed distribution of fractal fluctuations of all size scales (small, large and extreme values) in the historic month-wise temperature (maximum and minimum) and total rainfall for the four stations Oxford, Armagh, Durham and Stornoway in the UK region, for data periods ranging from 92 years to 160 years. For each parameter, the two cumulative probability distributions, namely cmax and cmin starting from respectively maximum and minimum data value were used. The results of the study show that (i) temperature distributions (maximum and minimum) follow model predicted distribution except for Stornowy, minimum temperature cmin. (ii) Rainfall distribution for cmin follow model predicted distribution for all the four stations. (iii) Rainfall distribution for cmax follows model predicted distribution for the two stations Armagh and Stornoway. The present study suggests that fractal fluctuations result from the superimposition of eddy continuum fluctuations.

Bursty communication patterns facilitate spreading in a threshold-based epidemic dynamics.

PubMed

Takaguchi, Taro; Masuda, Naoki; Holme, Petter

2013-01-01

Records of social interactions provide us with new sources of data for understanding how interaction patterns affect collective dynamics. Such human activity patterns are often bursty, i.e., they consist of short periods of intense activity followed by long periods of silence. This burstiness has been shown to affect spreading phenomena; it accelerates epidemic spreading in some cases and slows it down in other cases. We investigate a model of history-dependent contagion. In our model, repeated interactions between susceptible and infected individuals in a short period of time is needed for a susceptible individual to contract infection. We carry out numerical simulations on real temporal network data to find that bursty activity patterns facilitate epidemic spreading in our model.