Time-resolved method to distinguish protein/peptide oxidation during electrospray ionization mass spectrometry.

PubMed

Pei, Jiying; Hsu, Cheng-Chih; Yu, Kefu; Wang, Yinghui; Huang, Guangming

2018-06-29

Electrospray ionization mass spectrometry (ESI-MS) is one of the most prevalent techniques used to monitor protein/peptide oxidation induced by reactive oxygen species (ROSs). However, both corona discharge (CD) and electrochemistry (EC) can also lead to protein/peptide oxidation during ESI. Because the two types of oxidation occur almost simultaneously, determining the extent to which the two pathways contribute to protein/peptide oxidation is difficult. Herein, a time-resolved method was introduced to identify and differentiate CD- and EC-induced oxidation. Using this approach, we separated the instantaneous CD-induced oxidation from the hysteretic EC-induced oxidation, and the effects of the spray voltage and flow rate of the ESI source on both oxidation types were investigated with a homemade ESI source. For angiotensin II analogue (b-DRVYVHPF-y), the dehydrogenation and oxygenation species were the detected EC-induced oxidation products, while the oxygenation species were the major CD-induced oxidation products. This time-resolved approach was also applicable to a commercial HESI source, in which both CD and EC were responsible for hemoglobin and cytochrome c oxidation with upstream grounding while CD dominated the oxidation without upstream grounding. Copyright © 2018 Elsevier B.V. All rights reserved.

Grid Convergence of High Order Methods for Multiscale Complex Unsteady Viscous Compressible Flows

NASA Technical Reports Server (NTRS)

Sjoegreen, B.; Yee, H. C.

2001-01-01

Grid convergence of several high order methods for the computation of rapidly developing complex unsteady viscous compressible flows with a wide range of physical scales is studied. The recently developed adaptive numerical dissipation control high order methods referred to as the ACM and wavelet filter schemes are compared with a fifth-order weighted ENO (WENO) scheme. The two 2-D compressible full Navier-Stokes models considered do not possess known analytical and experimental data. Fine grid solutions from a standard second-order TVD scheme and a MUSCL scheme with limiters are used as reference solutions. The first model is a 2-D viscous analogue of a shock tube problem which involves complex shock/shear/boundary-layer interactions. The second model is a supersonic reactive flow concerning fuel breakup. The fuel mixing involves circular hydrogen bubbles in air interacting with a planar moving shock wave. Both models contain fine scale structures and are stiff in the sense that even though the unsteadiness of the flows are rapidly developing, extreme grid refinement and time step restrictions are needed to resolve all the flow scales as well as the chemical reaction scales.

Concentration-Discharge Relations in the Critical Zone: Implications for Resolving Critical Zone Structure, Function, and Evolution

NASA Astrophysics Data System (ADS)

Chorover, Jon; Derry, Louis A.; McDowell, William H.

2017-11-01

Critical zone science seeks to develop mechanistic theories that describe critical zone structure, function, and long-term evolution. One postulate is that hydrogeochemical controls on critical zone evolution can be inferred from solute discharges measured down-gradient of reactive flow paths. These flow paths have variable lengths, interfacial compositions, and residence times, and their mixing is reflected in concentration-discharge (C-Q) relations. Motivation for this special section originates from a U.S. Critical Zone Observatories workshop that was held at the University of New Hampshire, 20-22 July 2015. The workshop focused on resolving mechanistic CZ controls over surface water chemical dynamics across the full range of lithogenic (e.g., nonhydrolyzing and hydrolyzing cations and oxyanions) and bioactive solutes (e.g., organic and inorganic forms of C, N, P, and S), including dissolved and colloidal species that may cooccur for a given element. Papers submitted to this special section on "concentration-discharge relations in the critical zone" include those from authors who attended the workshop, as well as others who responded to the open solicitation. Submissions were invited that utilized information pertaining to internal, integrated catchment function (relations between hydrology, biogeochemistry, and landscape structure) to help illuminate controls on observed C-Q relations.

A numerical analysis for non-linear radiation in MHD flow around a cylindrical surface with chemically reactive species

NASA Astrophysics Data System (ADS)

Khan, Junaid Ahmad; Mustafa, M.

2018-03-01

Boundary layer flow around a stretchable rough cylinder is modeled by taking into account boundary slip and transverse magnetic field effects. The main concern is to resolve heat/mass transfer problem considering non-linear radiative heat transfer and temperature/concentration jump aspects. Using conventional similarity approach, the equations of motion and heat transfer are converted into a boundary value problem whose solution is computed by shooting method for broad range of slip coefficients. The proposed numerical scheme appears to improve as the strengths of magnetic field and slip coefficients are enhanced. Axial velocity and temperature are considerably influenced by a parameter M which is inversely proportional to the radius of cylinder. A significant change in temperature profile is depicted for growing wall to ambient temperature ratio. Relevant physical quantities such as wall shear stress, local Nusselt number and local Sherwood number are elucidated in detail.

On Spurious Numerics in Solving Reactive Equations

NASA Technical Reports Server (NTRS)

Kotov, D. V; Yee, H. C.; Wang, W.; Shu, C.-W.

2013-01-01

The objective of this study is to gain a deeper understanding of the behavior of high order shock-capturing schemes for problems with stiff source terms and discontinuities and on corresponding numerical prediction strategies. The studies by Yee et al. (2012) and Wang et al. (2012) focus only on solving the reactive system by the fractional step method using the Strang splitting (Strang 1968). It is a common practice by developers in computational physics and engineering simulations to include a cut off safeguard if densities are outside the permissible range. Here we compare the spurious behavior of the same schemes by solving the fully coupled reactive system without the Strang splitting vs. using the Strang splitting. Comparison between the two procedures and the effects of a cut off safeguard is the focus the present study. The comparison of the performance of these schemes is largely based on the degree to which each method captures the correct location of the reaction front for coarse grids. Here "coarse grids" means standard mesh density requirement for accurate simulation of typical non-reacting flows of similar problem setup. It is remarked that, in order to resolve the sharp reaction front, local refinement beyond standard mesh density is still needed.

Development of a Regional Structured and Unstructured Grid Methodology for Chemically Reactive Turbulent Flows

NASA Astrophysics Data System (ADS)

Stefanski, Douglas Lawrence

A finite volume method for solving the Reynolds Averaged Navier-Stokes (RANS) equations on unstructured hybrid grids is presented. Capabilities for handling arbitrary mixtures of reactive gas species within the unstructured framework are developed. The modeling of turbulent effects is carried out via the 1998 Wilcox k -- o model. This unstructured solver is incorporated within VULCAN -- a multi-block structured grid code -- as part of a novel patching procedure in which non-matching interfaces between structured blocks are replaced by transitional unstructured grids. This approach provides a fully-conservative alternative to VULCAN's non-conservative patching methods for handling such interfaces. In addition, the further development of the standalone unstructured solver toward large-eddy simulation (LES) applications is also carried out. Dual time-stepping using a Crank-Nicholson formulation is added to recover time-accuracy, and modeling of sub-grid scale effects is incorporated to provide higher fidelity LES solutions for turbulent flows. A switch based on the work of Ducros, et al., is implemented to transition from a monotonicity-preserving flux scheme near shocks to a central-difference method in vorticity-dominated regions in order to better resolve small-scale turbulent structures. The updated unstructured solver is used to carry out large-eddy simulations of a supersonic constrained mixing layer.

Spinal Nerve Root Haemangioblastoma Associated with Reactive Polycythemia

PubMed Central

Law, Eric K. C.; Lee, Ryan K. L.; Griffith, James F.; Siu, Deyond Y. W.; Ng, Ho Keung

2014-01-01

Haemangioblastomas are uncommon tumours that usually occur in the cerebellum and, less commonly, in the intramedullary spinal cord. The extramedullary spinal canal is an uncommon location for these tumours. Also haemangioblastoma at this site is not known to be associated with polycythemia. We present the clinical, imaging, and histological findings of an adult patient with extramedullary spinal haemangioblastoma and reactive polycythemia. Radiography and computed tomography (CT) revealed a medium-sized tumour that most likely arose from an extramedullary spinal nerve root. This tumour appeared to be slow growing as evidenced by the accompanying well-defined bony resorption with a sclerotic rim and mild neural foraminal widening. Magnetic resonance imaging revealed prominent flow voids consistent with tumoural hypervascularity. CT-guided biopsy was performed. Although preoperative angiographic embolisation was technically successful, excessive intraoperative tumour bleeding necessitated tumour debulking rather than complete tumour resection. Histology of the resected specimen revealed haemangioblastoma. Seven months postoperatively, the patients back pain and polycythemia have resolved. PMID:25431722

A Novel Multi-Scale Domain Overlapping CFD/STH Coupling Methodology for Multi-Dimensional Flows Relevant to Nuclear Applications

NASA Astrophysics Data System (ADS)

Grunloh, Timothy P.

The objective of this dissertation is to develop a 3-D domain-overlapping coupling method that leverages the superior flow field resolution of the Computational Fluid Dynamics (CFD) code STAR-CCM+ and the fast execution of the System Thermal Hydraulic (STH) code TRACE to efficiently and accurately model thermal hydraulic transport properties in nuclear power plants under complex conditions of regulatory and economic importance. The primary contribution is the novel Stabilized Inertial Domain Overlapping (SIDO) coupling method, which allows for on-the-fly correction of TRACE solutions for local pressures and velocity profiles inside multi-dimensional regions based on the results of the CFD simulation. The method is found to outperform the more frequently-used domain decomposition coupling methods. An STH code such as TRACE is designed to simulate large, diverse component networks, requiring simplifications to the fluid flow equations for reasonable execution times. Empirical correlations are therefore required for many sub-grid processes. The coarse grids used by TRACE diminish sensitivity to small scale geometric details such as Reactor Pressure Vessel (RPV) internals. A CFD code such as STAR-CCM+ uses much finer computational meshes that are sensitive to the geometric details of reactor internals. In turbulent flows, it is infeasible to fully resolve the flow solution, but the correlations used to model turbulence are at a low level. The CFD code can therefore resolve smaller scale flow processes. The development of a 3-D coupling method was carried out with the intention of improving predictive capabilities of transport properties in the downcomer and lower plenum regions of an RPV in reactor safety calculations. These regions are responsible for the multi-dimensional mixing effects that determine the distribution at the core inlet of quantities with reactivity implications, such as fluid temperature and dissolved neutron absorber concentration.

Combining Ambient Measurements of OH Radicals and OH Reactivity in a Tropical Rainforest during the OP-3 Project: Resolving the Magnitude of the Missing OH Sources and Sinks

NASA Astrophysics Data System (ADS)

Whalley, L. K.; Edwards, P.; Furneaux, K. L.; Goddard, A.; George, I. J.; Evans, M. J.; Heard, D. E.; Team Op-3

2010-12-01

The self cleansing capacity of the troposphere and the lifetime of key greenhouse gases are controlled to a large extent by the OH radical. In environments where biogenic VOC emissions are high and NOx concentrations are low, for example in tropical rainforests, the current understanding of tropospheric chemistry suggests that OH radical concentrations should be suppressed. OH measurements made in such regions, however, have highlighted higher than expected OH radical concentrations that cannot be replicated by chemical models constrained with the currently known OH formation pathways [1]. Here we report OH and OH reactivity measurements made during the OP-3 project that took place in the Borneo rainforest in 2008. Concentrations of OH displayed a clear diurnal cycle, peaking at solar noon, with significant concentrations observed: up to 8.7×106 molecule cm-3 (60 min average). Although j(O1D) levels and humidity were high, low O3 concentrations limited the rate of primary OH production from ozone photolysis. OH reactivity measurements were made using a sliding injector flow-tube reactor technique, with OH detection by LIF. Mean OH reactivities of 15.5 s-1 were observed with daily maximum OH reactivity of 24.7 ± 11.1 s-1 shortly after local solar noon, coinciding with peak isoprene concentrations. Minimum values of 7.2 ± 2.2 s-1 were observed just before sun rise. Using the measured OH and OH reactivity in a constrained box model containing detailed MCM chemistry we are able to fully resolve the magnitude of the missing OH source. We find that significant OH sources must be present - in addition to primary production - in order to maintain the elevated levels of OH levels recorded. Inclusion of an additional OH source formed as a recycled product of isoprene oxidation [2] improves the modelled OH agreement but reduces the modelled to measured HO2 agreement. To replicate both OH and HO2, a process that recycles HO2 to OH is required; equivalent to the OH recycling effect of 0.74 ppbv of NO. The model is unable to account for all of the OH reactivity; to simulate the OH reactivity a range of unmeasured sinks must be invoked. In general we believe that the simultaneous measurement of OH reactivity and OH concentration enables the separation of OH sources and sinks, allowing a more comprehensive test of our understanding of the radical chemistry occurring in this chemically complex environment. [1] J. Lelieveld, T. M. Butler, J. N. Crowley et al.: Nature, 2008, 452, p.737 - 740 [2] J. Peeters, T. L. Nguyen & L. Vereecken, PCCP, 2009, 11, p.5935 - 5939

Can we get a better knowledge on dissolution processes in chalk by using microfluidic chips?

NASA Astrophysics Data System (ADS)

Neuville, Amélie; Minde, Mona; Renaud, Louis; Vinningland, Jan Ludvig; Dysthe, Dag Kristian; Hiorth, Aksel

2017-04-01

This work has been initiated in the context of research on improving the oil recovery in chalk bedrocks. One of the methods to improve the oil recovery is to inject "smart water" (acidic water/brines). Experiments on core scale and field tests that have been carried out the last decade have clearly shown that water chemistry affects the final oil recovery. However, there is generally no consensus in the scientific community of why additional oil is released, and it is also still not understood what are the mineralogical and structural changes. Direct in situ observation of the structural changes that occur when chalk is flooded with brines could resolve many of the open questions that remain. One of the highlights of this work is thus the development of an innovative methodology where fluid/rock interactions are observed in-situ by microscopy. To do so, we create several types of custom-made microfluidic systems that embeds reactive materials like chalk and calcite. The methodology we develop can be applied to other reactive materials. We will present an experiment where a calcite window dissolves with a fluid, where we observe in-situ the topography features of the calcite window, as well as the dissolution rate [1]. The injected fluid circulates at controlled flowrates in a channel which is obtained by xurography: double sided tape is cut out with a cutter plotter and placed between the reactive window and a non-reactive support. While the calcite window reacts, its topography is measured in situ every 10 s using an interference microscope, with a pixel resolution of 4.9 μm and a vertical resolution of 50 nm. These experiments are also compared with reactive flow simulations done with Lattice Boltzmann methods. Then, we will present a dissolution experiment done with a microfluidic system that embeds chalk. In this experiment, the main flow takes place at the chalk surface, in contact with fluid flowing in a channel above the chalk sample. Thus the reaction mostly occurs at the surface of the sample. The reacting chalk surface is observed in situ by stereomicroscopy and by interferometry. The dissolution velocities are highly heterogeneous. To identify the mineral change of the surface, a posteriori measurements using field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). [1] Neuville et al, 2016, Xurography for microfluidics on a reactive solid, Lab on Chip, DOI: 10.1039/c6lc01253a

Multi-fluid Dynamics for Supersonic Jet-and-Crossflows and Liquid Plug Rupture

NASA Astrophysics Data System (ADS)

Hassan, Ezeldin A.

Multi-fluid dynamics simulations require appropriate numerical treatments based on the main flow characteristics, such as flow speed, turbulence, thermodynamic state, and time and length scales. In this thesis, two distinct problems are investigated: supersonic jet and crossflow interactions; and liquid plug propagation and rupture in an airway. Gaseous non-reactive ethylene jet and air crossflow simulation represents essential physics for fuel injection in SCRAMJET engines. The regime is highly unsteady, involving shocks, turbulent mixing, and large-scale vortical structures. An eddy-viscosity-based multi-scale turbulence model is proposed to resolve turbulent structures consistent with grid resolution and turbulence length scales. Predictions of the time-averaged fuel concentration from the multi-scale model is improved over Reynolds-averaged Navier-Stokes models originally derived from stationary flow. The response to the multi-scale model alone is, however, limited, in cases where the vortical structures are small and scattered thus requiring prohibitively expensive grids in order to resolve the flow field accurately. Statistical information related to turbulent fluctuations is utilized to estimate an effective turbulent Schmidt number, which is shown to be highly varying in space. Accordingly, an adaptive turbulent Schmidt number approach is proposed, by allowing the resolved field to adaptively influence the value of turbulent Schmidt number in the multi-scale turbulence model. The proposed model estimates a time-averaged turbulent Schmidt number adapted to the computed flowfield, instead of the constant value common to the eddy-viscosity-based Navier-Stokes models. This approach is assessed using a grid-refinement study for the normal injection case, and tested with 30 degree injection, showing improved results over the constant turbulent Schmidt model both in mean and variance of fuel concentration predictions. For the incompressible liquid plug propagation and rupture study, numerical simulations are conducted using an Eulerian-Lagrangian approach with a continuous-interface method. A reconstruction scheme is developed to allow topological changes during plug rupture by altering the connectivity information of the interface mesh. Rupture time is shown to be delayed as the initial precursor film thickness increases. During the plug rupture process, a sudden increase of mechanical stresses on the tube wall is recorded, which can cause tissue damage.

Antiviral prophylaxis during chemotherapy or immunosuppressive drug therapy to prevent HBV reactivation in patients with resolved HBV infection: a systematic review and meta-analysis.

PubMed

Su, Yi-Chia; Lin, Pei-Chin; Yu, Hsien-Chung; Wu, Chih-Chien

2018-05-29

Until recently, the role of antiviral prophylaxis in preventing hepatitis B virus (HBV) reactivation during immunosuppressive therapy or chemotherapy in patients with resolved HBV infection was unclear. The aim of the study reported here was to compare the efficacy of antiviral prophylaxis versus that of non-prophylaxis in resolved HBV-infected patients undergoing chemotherapy or immunosuppressive therapy. PubMed, the Cochrane library, and the ClinicalTrials.gov website were searched from inception until December 2017. Studies comparing reactivation in prophylaxis versus non-prophylaxis in patients undergoing immunosuppressive therapy or chemotherapy were included. The meta-analysis was performed to calculate the relative risk (RR) and the pooled estimates. A meta-analysis was conducted of 13 studies (2 randomized controlled trials [RCTs] and 11 cohort studies). The summary RR for HBV reactivation was 0.47 (95% confidence interval [CI] 0.13-1.69) for antiviral prophylaxis versus non-prophylaxis. Both of the RCTs included in the meta-analysis enrolled patients treated with rituximab. Subgroup analyses showed that the two RCTs ± high-quality cohort studies showed a decreased risk of HBV reactivation among the antiviral prophylaxis groups (RCT 1: RR 0.13, 95% CI 0.02-0.70; P = 0.02; RCT 2: 0.28, 95% CI 0.08-0.98; P = 0.05). Subgroup analyses further showed that the cohort studies did not support an association between the antiviral prophylaxis groups and HBV reactivation (RR 0.62, 95% CI 0.14-2.83; P = 0.54); adjusting for confounding factors, such as detectable anti-HBs antibodies, failed to produce a significant association (RR,0.29, 95% CI 0.07-1.28; P = 0.10). Our meta-analyses did not show an association between antiviral prophylaxis use and risk of HBV reactivation. As using only the RCTs ± high-quality cohort studies data rendered this association significant, clinicians can consider providing antiviral prophylaxis to patients with resolved HBV infection who are undergoing rituximab-based therapy.

Tracing the plasma interactions for pulsed reactive crossed-beam laser ablation

NASA Astrophysics Data System (ADS)

Chen, Jikun; Stender, Dieter; Pichler, Markus; Döbeli, Max; Pergolesi, Daniele; Schneider, Christof W.; Wokaun, Alexander; Lippert, Thomas

2015-10-01

Pulsed reactive crossed-beam laser ablation is an effective technique to govern the chemical activity of plasma species and background molecules during pulsed laser deposition. Instead of using a constant background pressure, a gas pulse with a reactive gas, synchronized with the laser beam, is injected into vacuum or a low background pressure near the ablated area of the target. It intercepts the initially generated plasma plume, thereby enhancing the physicochemical interactions between the gaseous environment and the plasma species. For this study, kinetic energy resolved mass-spectrometry and time-resolved plasma imaging were used to study the physicochemical processes occurring during the reactive crossed beam laser ablation of a partially 18O substituted La0.6Sr0.4MnO3 target using oxygen as gas pulse. The characteristics of the ablated plasma are compared with those observed during pulsed laser deposition in different oxygen background pressures.

Quantitative assessment of reactive hyperemia using laser speckle contrast imaging at multiple wavelengths

NASA Astrophysics Data System (ADS)

Young, Anthony; Vishwanath, Karthik

2016-03-01

Reactive hyperemia refers to an increase of blood flow in tissue post release of an occlusion in the local vasculature. Measuring the temporal response of reactive hyperemia, post-occlusion in patients has the potential to shed information about microvascular diseases such as systemic sclerosis and diabetes. Laser speckle contrast imaging (LSCI) is an imaging technique capable of sensing superficial blood flow in tissue which can be used to quantitatively assess reactive hyperemia. Here, we employ LSCI using coherent sources in the blue, green and red wavelengths to evaluate reactive hyperemia in healthy human volunteers. Blood flow in the forearms of subjects were measured using LSCI to assess the time-course of reactive hyperemia that was triggered by a pressure cuff applied to the biceps of the subjects. Raw speckle images were acquired and processed to yield blood-flow parameters from a region of interest before, during and after application of occlusion. Reactive hyperemia was quantified via two measures - (1) by calculating the difference between the peak LSCI flow during the hyperemia and baseline flow, and (2) by measuring the amount of time that elapsed between the release of the occlusion and peak flow. These measurements were acquired in three healthy human participants, under the three laser wavelengths employed. The studies shed light on the utility of in vivo LSCI-based flow sensing for non-invasive assessment of reactive hyperemia responses and how they varied with the choice source wavelength influences the measured parameters.

A Study of Strain Rate Effects for Turbulent Premixed Flames with Application to LES of a Gas Turbine Combustor Model

DOE PAGES

Kemenov, Konstantin A.; Calhoon, William H.

2015-03-24

Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the lineareddy model with a one-dimensional counter-flow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable,more » the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results suggest the necessity to represent the strain rate effects accurately in order to improve LES modeling of the turbulent flame speed.« less

Modeling non-Fickian dispersion by use of the velocity PDF on the pore scale

NASA Astrophysics Data System (ADS)

Kooshapur, Sheema; Manhart, Michael

2015-04-01

For obtaining a description of reactive flows in porous media, apart from the geometrical complications of resolving the velocities and scalar values, one has to deal with the additional reactive term in the transport equation. An accurate description of the interface of the reacting fluids - which is strongly influenced by dispersion- is essential for resolving this term. In REV-based simulations the reactive term needs to be modeled taking sub-REV fluctuations and possibly non-Fickian dispersion into account. Non-Fickian dispersion has been observed in strongly heterogeneous domains and in early phases of transport. A fully resolved solution of the Navier-Stokes and transport equations which yields a detailed description of the flow properties, dispersion, interfaces of fluids, etc. however, is not practical for domains containing more than a few thousand grains, due to the huge computational effort required. Through Probability Density Function (PDF) based methods, the velocity distribution in the pore space can facilitate the understanding and modelling of non-Fickian dispersion [1,2]. Our aim is to model the transition between non-Fickian and Fickian dispersion in a random sphere pack within the framework of a PDF based transport model proposed by Meyer and Tchelepi [1,3]. They proposed a stochastic transport model where velocity components of tracer particles are represented by a continuous Markovian stochastic process. In addition to [3], we consider the effects of pore scale diffusion and formulate a different stochastic equation for the increments in velocity space from first principles. To assess the terms in this equation, we performed Direct Numerical Simulations (DNS) for solving the Navier-Stokes equation on a random sphere pack. We extracted the PDFs and statistical moments (up to the 4th moment) of the stream-wise velocity, u, and first and second order velocity derivatives both independent and conditioned on velocity. By using this data and combining the Taylor expansion of velocity increments, du, and the Langevin equation for point particles we obtained the components of velocity fluxes which point to a drift and diffusion behavior in the velocity space. Thus a partial differential equation for the velocity PDF has been formulated that constitutes an advection-diffusion equation in velocity space (a Fokker-Planck equation) in which the drift and diffusion coefficients are obtained using the velocity conditioned statistics of the derivatives of the pore scale velocity field. This has been solved by both a Random Walk (RW) model and a Finite Volume method. We conclude that both, these methods are able to simulate the velocity PDF obtained by DNS. References [1] D. W. Meyer, P. Jenny, H.A.Tschelepi, A joint velocity-concentration PDF method for traqcer flow in heterogeneous porous media, Water Resour.Res., 46, W12522, (2010). [2] Nowak, W., R. L. Schwede, O. A. Cirpka, and I. Neuweiler, Probability density functions of hydraulic head and velocity in three-dimensional heterogeneous porous media, Water Resour.Res., 44, W08452, (2008) [3] D. W. Meyer, H. A. Tchelepi, Particle-based transport model with Markovian velocity processes for tracer dispersion in highly heterogeneous porous media, Water Resour. Res., 46, W11552, (2010)

Electron spin polarization (CIDEP) investigation of the interaction of reactive free radicals with polynitroxyl stable free radicals

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

Turro, N.J.; Khudyakov, I.V.; Dwyer, D.W.

1993-10-14

Time-resolved electron spin resonance (TR ESR) was employed to investigate the polarized ESR (CIDEP) spectra produced by interaction of mono- and polynitroxyls with reactive free radicals (r[sup [number sign

Kinetics of Reactive Fronts in Porous Media: quantification through a laboratory experiment

NASA Astrophysics Data System (ADS)

De Anna, P.; Jimenez-Martinez, J.; Turuban, R.; Tabuteau, H.; Derrien, M.; Le Borgne, T.; Meheust, Y.

2013-12-01

The kinetics of reaction fronts in heterogeneous flows is tightly linked to the mixing dynamics governed by the combined action of stretching, diffusion and dispersion. Focusing on porous media flows, with a new experimental setup we show that the invading solute is organized into stretched lamellae, whose deformation and coalescence control the effective reaction kinetics of the mixing limited bimolecular reaction A + B --> C. While the classic advection-dispersion theory predicts a scaling of the cumulative product mass of C as t^(0.5), we observe two distinct kinetics regimes, one characterized by the stretching and the other by the coalescence of the invading lamellae, in which the mass of C scales faster than t^(0.5). The proposed experimental set up allows for direct quantification of mixing and reactive transport in porous media with a high spatial resolution, at the pore scale. The analogous two dimensional porous medium consists in a Hele-Shaw cell containing a single layer of cylindrical solid grains built by soft lithography. On the one hand, the measurement of the local, intra-pore, conservative concentration field is done using a fluorescent tracer. On the other hand, considering a fast bimolecular advection-dispersion reaction A + B --> C occurring as A displaces B, we quantify the reaction kinetics from the spatially-resolved measurement of the pore scale reaction rate, using a chemiluminescent reaction.

A HYBRID MODELING APPROACH TO RESOLVE POLLUTANT CONCENTRATIONS IN AN URBAN AREA

EPA Science Inventory

A modeling tool that can resolve contributions from individual sources to the urban environment is critical for air-toxics exposure assessments. Air toxics are often chemically reactive and may have background concentrations originated from distant sources. Grid models are the be...

Non-normality and classification of amplification mechanisms in stability and resolvent analysis

NASA Astrophysics Data System (ADS)

Symon, Sean; Rosenberg, Kevin; Dawson, Scott T. M.; McKeon, Beverley J.

2018-05-01

Eigenspectra and pseudospectra of the mean-linearized Navier-Stokes operator are used to characterize amplification mechanisms in laminar and turbulent flows in which linear mechanisms are important. Success of mean flow (linear) stability analysis for a particular frequency is shown to depend on whether two scalar measures of non-normality agree: (1) the product between the resolvent norm and the distance from the imaginary axis to the closest eigenvalue and (2) the inverse of the inner product between the most amplified resolvent forcing and response modes. If they agree, the resolvent operator can be rewritten in its dyadic representation to reveal that the adjoint and forward stability modes are proportional to the forcing and response resolvent modes at that frequency. Hence the real parts of the eigenvalues are important since they are responsible for resonant amplification and the resolvent operator is low rank when the eigenvalues are sufficiently separated in the spectrum. If the amplification is pseudoresonant, then resolvent analysis is more suitable to understand the origin of observed flow structures. Two test cases are studied: low Reynolds number cylinder flow and turbulent channel flow. The first deals mainly with resonant mechanisms, hence the success of both classical and mean stability analysis with respect to predicting the critical Reynolds number and global frequency of the saturated flow. Both scalar measures of non-normality agree for the base and mean flows, and the region where the forcing and response modes overlap scales with the length of the recirculation bubble. In the case of turbulent channel flow, structures result from both resonant and pseudoresonant mechanisms, suggesting that both are necessary elements to sustain turbulence. Mean shear is exploited most efficiently by stationary disturbances while bounds on the pseudospectra illustrate how pseudoresonance is responsible for the most amplified disturbances at spatial wavenumbers and temporal frequencies corresponding to well-known turbulent structures. Some implications for flow control are discussed.

Chalk-calcite-microfluidic experiments: construction and flooding of microsystems with reactive fluids

NASA Astrophysics Data System (ADS)

Neuville, Amélie; Thuy Luu, Thi; Dysthe, Dag Kristian; Vinningland, Jan Ludvig; Hiorth, Aksel

2015-04-01

Direct in situ observation of the pore structure changes that occur when chalk is flooded with brines could resolve many of the open questions that remain about the interactions between mineralogical alterations and oil-liberating mechanisms. Experiments on core scale and field tests that have been carried out the last decade have clearly shown that water chemistry affects the final oil recovery. However, there is generally no consensus in the scientific community of why additional oil is released. In this work, our aim is to focus on in-situ observations of single phase flow and interactions at the pore scale. To do so, we create several types of custom-made microsystems with chalk and calcite crystals. We then do experiments with reacting fluids in these microsystems. During these experiments, we realize in-situ observations (geometrical characteristics, reaction rate) using microsopy techniques (white light vertical/phase shift interferometric microscopy, and classical microscopy), and show how they vary as function as the water chemistry. In simple systems made of calcite, we obtain reactive rates that are coherent with the litterature and with numerical simulations based on Lattice-Boltzmann methods.

Scaling of flow and transport behavior in heterogeneous groundwater systems

NASA Astrophysics Data System (ADS)

Scheibe, Timothy; Yabusaki, Steven

1998-11-01

Three-dimensional numerical simulations using a detailed synthetic hydraulic conductivity field developed from geological considerations provide insight into the scaling of subsurface flow and transport processes. Flow and advective transport in the highly resolved heterogeneous field were modeled using massively parallel computers, providing a realistic baseline for evaluation of the impacts of parameter scaling. Upscaling of hydraulic conductivity was performed at a variety of scales using a flexible power law averaging technique. A series of tests were performed to determine the effects of varying the scaling exponent on a number of metrics of flow and transport behavior. Flow and transport simulation on high-performance computers and three-dimensional scientific visualization combine to form a powerful tool for gaining insight into the behavior of complex heterogeneous systems. Many quantitative groundwater models utilize upscaled hydraulic conductivity parameters, either implicitly or explicitly. These parameters are designed to reproduce the bulk flow characteristics at the grid or field scale while not requiring detailed quantification of local-scale conductivity variations. An example from applied groundwater modeling is the common practice of calibrating grid-scale model hydraulic conductivity or transmissivity parameters so as to approximate observed hydraulic head and boundary flux values. Such parameterizations, perhaps with a bulk dispersivity imposed, are then sometimes used to predict transport of reactive or non-reactive solutes. However, this work demonstrates that those parameters that lead to the best upscaling for hydraulic conductivity and head do not necessarily correspond to the best upscaling for prediction of a variety of transport behaviors. This result reflects the fact that transport is strongly impacted by the existence and connectedness of extreme-valued hydraulic conductivities, in contrast to bulk flow which depends more strongly on mean values. It provides motivation for continued research into upscaling methods for transport that directly address advection in heterogeneous porous media. An electronic version of this article is available online at the journal's homepage at http://www.elsevier.nl/locate/advwatres or http://www.elsevier.com/locate/advwatres (see "Special section on vizualization". The online version contains additional supporting information, graphics, and a 3D animation of simulated particle movement. Limited. All rights reserved

T-REX on-demand redox targeting in live cells.

PubMed

Parvez, Saba; Long, Marcus J C; Lin, Hong-Yu; Zhao, Yi; Haegele, Joseph A; Pham, Vanha N; Lee, Dustin K; Aye, Yimon

2016-12-01

This protocol describes targetable reactive electrophiles and oxidants (T-REX)-a live-cell-based tool designed to (i) interrogate the consequences of specific and time-resolved redox events, and (ii) screen for bona fide redox-sensor targets. A small-molecule toolset comprising photocaged precursors to specific reactive redox signals is constructed such that these inert precursors specifically and irreversibly tag any HaloTag-fused protein of interest (POI) in mammalian and Escherichia coli cells. Syntheses of the alkyne-functionalized endogenous reactive signal 4-hydroxynonenal (HNE(alkyne)) and the HaloTag-targetable photocaged precursor to HNE(alkyne) (also known as Ht-PreHNE or HtPHA) are described. Low-energy light prompts photo-uncaging (t 1/2 <1-2 min) and target-specific modification. The targeted modification of the POI enables precisely timed and spatially controlled redox events with no off-target modification. Two independent pathways are described, along with a simple setup to functionally validate known targets or discover novel sensors. T-REX sidesteps mixed responses caused by uncontrolled whole-cell swamping with reactive signals. Modification and downstream response can be analyzed by in-gel fluorescence, proteomics, qRT-PCR, immunofluorescence, fluorescence resonance energy transfer (FRET)-based and dual-luciferase reporters, or flow cytometry assays. T-REX targeting takes 4 h from initial probe treatment. Analysis of targeted redox responses takes an additional 4-24 h, depending on the nature of the pathway and the type of readouts used.

T-REX on-demand redox targeting in live cells

PubMed Central

Parvez, Saba; Long, Marcus J C; Lin, Hong-Yu; Zhao, Yi; Haegele, Joseph A; Pham, Vanha N; Lee, Dustin K; Aye, Yimon

2017-01-01

This protocol describes targetable reactive electrophiles and oxidants (T-REX)—a live-cell-based tool designed to (i) interrogate the consequences of specific and time-resolved redox events, and (ii) screen for bona fide redox-sensor targets. A small-molecule toolset comprising photocaged precursors to specific reactive redox signals is constructed such that these inert precursors specifically and irreversibly tag any HaloTag-fused protein of interest (POI) in mammalian and Escherichia coli cells. Syntheses of the alkyne-functionalized endogenous reactive signal 4-hydroxynonenal (HNE (alkyne)) and the HaloTag-targetable photocaged precursor to HNE (alkyne) (also known as Ht-PreHNE or HtPHA) are described. Low-energy light prompts photo-uncaging (t1/2 <1–2 min) and target-specific modification. The targeted modification of the POI enables precisely timed and spatially controlled redox events with no off-target modification. Two independent pathways are described, along with a simple setup to functionally validate known targets or discover novel sensors. T-REX sidesteps mixed responses caused by uncontrolled whole-cell swamping with reactive signals. Modification and downstream response can be analyzed by in-gel fluorescence, proteomics, qRT-PCR, immunofluorescence, fluorescence resonance energy transfer (FRET)-based and dual-luciferase reporters, or flow cytometry assays. T-REX targeting takes 4 h from initial probe treatment. Analysis of targeted redox responses takes an additional 4–24 h, depending on the nature of the pathway and the type of readouts used. PMID:27809314

A Gas-Kinetic Scheme for Reactive Flows

NASA Technical Reports Server (NTRS)

Lian,Youg-Sheng; Xu, Kun

1998-01-01

In this paper, the gas-kinetic BGK scheme for the compressible flow equations is extended to chemical reactive flow. The mass fraction of the unburnt gas is implemented into the gas kinetic equation by assigning a new internal degree of freedom to the particle distribution function. The new variable can be also used to describe fluid trajectory for the nonreactive flows. Due to the gas-kinetic BGK model, the current scheme basically solves the Navier-Stokes chemical reactive flow equations. Numerical tests validate the accuracy and robustness of the current kinetic method.

High-Energy, High-Pulse-Rate Light Sources for Enhanced Time-Resolved Tomographic PIV of Unsteady and Turbulent Flows

DTIC Science & Technology

2017-07-31

Report: High-Energy, High-Pulse-Rate Light Sources for Enhanced Time -Resolved Tomographic PIV of Unsteady & Turbulent Flows The views, opinions and/or...reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching...High-Energy, High-Pulse-Rate Light Sources for Enhanced Time -Resolved Tomographic PIV of Unsteady & Turbulent Flows Report Term: 0-Other Email

Adjoint Sensitivity Analysis for Scale-Resolving Turbulent Flow Solvers

NASA Astrophysics Data System (ADS)

Blonigan, Patrick; Garai, Anirban; Diosady, Laslo; Murman, Scott

2017-11-01

Adjoint-based sensitivity analysis methods are powerful design tools for engineers who use computational fluid dynamics. In recent years, these engineers have started to use scale-resolving simulations like large-eddy simulations (LES) and direct numerical simulations (DNS), which resolve more scales in complex flows with unsteady separation and jets than the widely-used Reynolds-averaged Navier-Stokes (RANS) methods. However, the conventional adjoint method computes large, unusable sensitivities for scale-resolving simulations, which unlike RANS simulations exhibit the chaotic dynamics inherent in turbulent flows. Sensitivity analysis based on least-squares shadowing (LSS) avoids the issues encountered by conventional adjoint methods, but has a high computational cost even for relatively small simulations. The following talk discusses a more computationally efficient formulation of LSS, ``non-intrusive'' LSS, and its application to turbulent flows simulated with a discontinuous-Galkerin spectral-element-method LES/DNS solver. Results are presented for the minimal flow unit, a turbulent channel flow with a limited streamwise and spanwise domain.

Structure-Preserving Variational Multiscale Modeling of Turbulent Incompressible Flow with Subgrid Vortices

NASA Astrophysics Data System (ADS)

Evans, John; Coley, Christopher; Aronson, Ryan; Nelson, Corey

2017-11-01

In this talk, a large eddy simulation methodology for turbulent incompressible flow will be presented which combines the best features of divergence-conforming discretizations and the residual-based variational multiscale approach to large eddy simulation. In this method, the resolved motion is represented using a divergence-conforming discretization, that is, a discretization that preserves the incompressibility constraint in a pointwise manner, and the unresolved fluid motion is explicitly modeled by subgrid vortices that lie within individual grid cells. The evolution of the subgrid vortices is governed by dynamical model equations driven by the residual of the resolved motion. Consequently, the subgrid vortices appropriately vanish for laminar flow and fully resolved turbulent flow. As the resolved velocity field and subgrid vortices are both divergence-free, the methodology conserves mass in a pointwise sense and admits discrete balance laws for energy, enstrophy, and helicity. Numerical results demonstrate the methodology yields improved results versus state-of-the-art eddy viscosity models in the context of transitional, wall-bounded, and rotational flow when a divergence-conforming B-spline discretization is utilized to represent the resolved motion.

Critical cerebral perfusion pressure at high intracranial pressure measured by induced cerebrovascular and intracranial pressure reactivity.

PubMed

Bragin, Denis E; Statom, Gloria L; Yonas, Howard; Dai, Xingping; Nemoto, Edwin M

2014-12-01

The lower limit of cerebral blood flow autoregulation is the critical cerebral perfusion pressure at which cerebral blood flow begins to fall. It is important that cerebral perfusion pressure be maintained above this level to ensure adequate cerebral blood flow, especially in patients with high intracranial pressure. However, the critical cerebral perfusion pressure of 50 mm Hg, obtained by decreasing mean arterial pressure, differs from the value of 30 mm Hg, obtained by increasing intracranial pressure, which we previously showed was due to microvascular shunt flow maintenance of a falsely high cerebral blood flow. The present study shows that the critical cerebral perfusion pressure, measured by increasing intracranial pressure to decrease cerebral perfusion pressure, is inaccurate but accurately determined by dopamine-induced dynamic intracranial pressure reactivity and cerebrovascular reactivity. Cerebral perfusion pressure was decreased either by increasing intracranial pressure or decreasing mean arterial pressure and the critical cerebral perfusion pressure by both methods compared. Cortical Doppler flux, intracranial pressure, and mean arterial pressure were monitored throughout the study. At each cerebral perfusion pressure, we measured microvascular RBC flow velocity, blood-brain barrier integrity (transcapillary dye extravasation), and tissue oxygenation (reduced nicotinamide adenine dinucleotide) in the cerebral cortex of rats using in vivo two-photon laser scanning microscopy. University laboratory. Male Sprague-Dawley rats. At each cerebral perfusion pressure, dopamine-induced arterial pressure transients (~10 mm Hg, ~45 s duration) were used to measure induced intracranial pressure reactivity (Δ intracranial pressure/Δ mean arterial pressure) and induced cerebrovascular reactivity (Δ cerebral blood flow/Δ mean arterial pressure). At a normal cerebral perfusion pressure of 70 mm Hg, 10 mm Hg mean arterial pressure pulses had no effect on intracranial pressure or cerebral blood flow (induced intracranial pressure reactivity = -0.03 ± 0.07 and induced cerebrovascular reactivity = -0.02 ± 0.09), reflecting intact autoregulation. Decreasing cerebral perfusion pressure to 50 mm Hg by increasing intracranial pressure increased induced intracranial pressure reactivity and induced cerebrovascular reactivity to 0.24 ± 0.09 and 0.31 ± 0.13, respectively, reflecting impaired autoregulation (p < 0.05). By static cerebral blood flow, the first significant decrease in cerebral blood flow occurred at a cerebral perfusion pressure of 30 mm Hg (0.71 ± 0.08, p < 0.05). Critical cerebral perfusion pressure of 50 mm Hg was accurately determined by induced intracranial pressure reactivity and induced cerebrovascular reactivity, whereas the static method failed.

Continuous flow chemistry: a discovery tool for new chemical reactivity patterns.

PubMed

Hartwig, Jan; Metternich, Jan B; Nikbin, Nikzad; Kirschning, Andreas; Ley, Steven V

2014-06-14

Continuous flow chemistry as a process intensification tool is well known. However, its ability to enable chemists to perform reactions which are not possible in batch is less well studied or understood. Here we present an example, where a new reactivity pattern and extended reaction scope has been achieved by transferring a reaction from batch mode to flow. This new reactivity can be explained by suppressing back mixing and precise control of temperature in a flow reactor set up.

Time-resolved vibrational spectroscopy

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

Tokmakoff, Andrei; Champion, Paul; Heilweil, Edwin J.

2009-05-14

This document contains the Proceedings from the 14th International Conference on Time-Resolved Vibrational Spectroscopy, which was held in Meredith, NH from May 9-14, 2009. The study of molecular dynamics in chemical reaction and biological processes using time-resolved spectroscopy plays an important role in our understanding of energy conversion, storage, and utilization problems. Fundamental studies of chemical reactivity, molecular rearrangements, and charge transport are broadly supported by the DOE's Office of Science because of their role in the development of alternative energy sources, the understanding of biological energy conversion processes, the efficient utilization of existing energy resources, and the mitigation ofmore » reactive intermediates in radiation chemistry. In addition, time-resolved spectroscopy is central to all fiveof DOE's grand challenges for fundamental energy science. The Time-Resolved Vibrational Spectroscopy conference is organized biennially to bring the leaders in this field from around the globe together with young scientists to discuss the most recent scientific and technological advances. The latest technology in ultrafast infrared, Raman, and terahertz spectroscopy and the scientific advances that these methods enable were covered. Particular emphasis was placed on new experimental methods used to probe molecular dynamics in liquids, solids, interfaces, nanostructured materials, and biomolecules.« less

Effects of chewing rate and reactive hyperemia on blood flow in denture-supporting mucosa during simulated chewing.

PubMed

Ogino, Takamichi; Ueda, Takayuki; Ogami, Koichiro; Koike, Takashi; Sakurai, Kaoru

2017-01-01

We examined how chewing rate and the extent of reactive hyperemia affect the blood flow in denture-supporting mucosa during chewing. The left palatal mucosa was loaded under conditions of simulated chewing or simulated clenching for 30s, and the blood flow during loading was recorded. We compared the relative blood flow during loading under conditions that recreated different chewing rates by combining duration of chewing cycle (DCC) and occlusal time (OT): fast chewing group, typical chewing group, slow chewing group and clenching group. The relationship between relative blood flow during simulated chewing and the extent of reactive hyperemia was also analyzed. When comparing the different chewing rate, the relative blood flow was highest in fast chewing rate, followed by typical chewing rate and slow chewing rate. Accordingly, we suggest that fast chewing increases the blood flow more than typical chewing or slow chewing. There was a significant correlation between the amount of blood flow during simulated chewing and the extent of reactive hyperemia. Within the limitations of this study, we concluded that slow chewing induced less blood flow than typical or fast chewing in denture-supporting mucosa and that people with less reactive hyperemia had less blood flow in denture-supporting mucosa during chewing. Copyright © 2016 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering.

PubMed

Ehn, Andreas; Zhu, Jiajian; Li, Xuesong; Kiefer, Johannes

2017-03-01

Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

Large eddy simulation modelling of combustion for propulsion applications.

PubMed

Fureby, C

2009-07-28

Predictive modelling of turbulent combustion is important for the development of air-breathing engines, internal combustion engines, furnaces and for power generation. Significant advances in modelling non-reactive turbulent flows are now possible with the development of large eddy simulation (LES), in which the large energetic scales of the flow are resolved on the grid while modelling the effects of the small scales. Here, we discuss the use of combustion LES in predictive modelling of propulsion applications such as gas turbine, ramjet and scramjet engines. The LES models used are described in some detail and are validated against laboratory data-of which results from two cases are presented. These validated LES models are then applied to an annular multi-burner gas turbine combustor and a simplified scramjet combustor, for which some additional experimental data are available. For these cases, good agreement with the available reference data is obtained, and the LES predictions are used to elucidate the flow physics in such devices to further enhance our knowledge of these propulsion systems. Particular attention is focused on the influence of the combustion chemistry, turbulence-chemistry interaction, self-ignition, flame holding burner-to-burner interactions and combustion oscillations.

Reactive multiphase flow simulation workshop summary

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

VanderHeyden, W.B.

1995-09-01

A workshop on computer simulation of reactive multiphase flow was held on May 18 and 19, 1995 in the Computational Testbed for Industry at Los Alamos National Laboratory (LANL), Los Alamos, New Mexico. Approximately 35 to 40 people attended the workshop. This included 21 participants from 12 companies representing the petroleum, chemical, environmental and consumer products industries, two representatives from the DOE Office of Industrial Technologies and several from Los Alamos. The dialog at the meeting suggested that reactive multiphase flow simulation represents an excellent candidate for government/industry/academia collaborative research. A white paper on a potential consortium for reactive multiphasemore » flow with input from workshop participants will be issued separately.« less

Predictive value of reactive hyperemia for cardiovascular events in patients with peripheral arterial disease undergoing vascular surgery.

PubMed

Huang, Alex L; Silver, Annemarie E; Shvenke, Elena; Schopfer, David W; Jahangir, Eiman; Titas, Megan A; Shpilman, Alex; Menzoian, James O; Watkins, Michael T; Raffetto, Joseph D; Gibbons, Gary; Woodson, Jonathan; Shaw, Palma M; Dhadly, Mandeep; Eberhardt, Robert T; Keaney, John F; Gokce, Noyan; Vita, Joseph A

2007-10-01

Reactive hyperemia is the compensatory increase in blood flow that occurs after a period of tissue ischemia, and this response is blunted in patients with cardiovascular risk factors. The predictive value of reactive hyperemia for cardiovascular events in patients with atherosclerosis and the relative importance of reactive hyperemia compared with other measures of vascular function have not been previously studied. We prospectively measured reactive hyperemia and brachial artery flow-mediated dilation by ultrasound in 267 patients with peripheral arterial disease referred for vascular surgery (age 66+/-11 years, 26% female). Median follow-up was 309 days (range 1 to 730 days). Fifty patients (19%) had an event, including cardiac death (15), myocardial infarction (18), unstable angina (8), congestive heart failure (6), and nonhemorrhagic stroke (3). Patients with an event were older and had lower hyperemic flow velocity (75+/-39 versus 95+/-50 cm/s, P=0.009). Patients with an event also had lower flow-mediated dilation (4.5+/-3.0 versus 6.9+/-4.6%, P<0.001), and when these 2 measures of vascular function were included in the same Cox proportional hazards model, lower hyperemic flow (OR 2.7, 95% CI 1.2 to 5.9, P=0.018) and lower flow-mediated dilation (OR 4.2, 95% CI: 1.8 to 9.8, P=0.001) both predicted cardiovascular events while adjusting for other risk factors. Thus, lower reactive hyperemia is associated with increased cardiovascular risk in patients with peripheral arterial disease. Furthermore, flow-mediated dilation and reactive hyperemia incrementally relate to cardiovascular risk, although impaired flow-mediated dilation was the stronger predictor in this population. These findings further support the clinical relevance of vascular function measured in the microvasculature and conduit arteries in the upper extremity.

Two-photon laser-induced fluorescence of atomic hydrogen in a diamond-depositing dc arcjet.

PubMed

Juchmann, Wolfgang; Luque, Jorge; Jeffries, Jay B

2005-11-01

Atomic hydrogen in the plume of a dc-arcjet plasma is monitored by use of two-photon excited laser-induced fluorescence (LIF) during the deposition of diamond film. The effluent of a dc-arc discharge in hydrogen and argon forms a luminous plume as it flows through a converging-diverging nozzle into a reactor. When a trace of methane (< 2%) is added to the flow in the diverging part of the nozzle, diamond thin film grows on a water-cooled molybdenum substrate from the reactive mixture. LIF of atomic hydrogen in the arcjet plume is excited to the 3S and 3D levels with two photons near 205 nm, and the subsequent fluorescence is observed at Balmer-alpha near 656 nm. Spatially resolved LIF measurements of atomic hydrogen are made as a function of the ratio of hydrogen to argon feedstock gas, methane addition, and reactor pressure. At lower reactor pressures, time-resolved LIF measurements are used to verify our collisional quenching correction algorithm. The quenching rate coefficients for collisions with the major species in the arcjet (Ar, H, and H2) do not change with gas temperature variations in the plume (T < 2300 K). Corrections of the LIF intensity measurements for the spatial variation of collisional quenching are important to determine relative distributions of the atomic hydrogen concentration. The relative atomic hydrogen concentrations measured here are calibrated with an earlier calorimetric determination of the feedstock hydrogen dissociation to provide quantitative hydrogen-atom concentration distributions.

Variably Saturated Flow and Multicomponent Biogeochemical Reactive Transport Modeling of a Uranium Bioremediation Field Experiment

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

Yabusaki, Steven B.; Fang, Yilin; Williams, Kenneth H.

2011-11-01

Field experiments at a former uranium mill tailings site have identified the potential for stimulating indigenous bacteria to catalyze the conversion of aqueous uranium in the +6 oxidation state to immobile solid-associated uranium in the +4 oxidation state. This effectively removes uranium from solution resulting in groundwater concentrations below actionable standards. Three-dimensional, coupled variably-saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport rates and biogeochemical reaction rates that determine the location and magnitude of key reaction products. A comprehensive reaction network, developed largely throughmore » previous 1-D modeling studies, was used to simulate the impacts on uranium behavior of pulsed acetate amendment, seasonal water table variation, spatially-variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. A principal challenge is the mechanistic representation of biologically-mediated terminal electron acceptor process (TEAP) reactions whose products significantly alter geochemical controls on uranium mobility through increases in pH, alkalinity, exchangeable cations, and highly reactive reduction products. In general, these simulations of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado confirmed previously identified behaviors including (1) initial dominance by iron reducing bacteria that concomitantly reduce aqueous U(VI), (2) sulfate reducing bacteria that become dominant after {approx}30 days and outcompete iron reducers for the acetate electron donor, (3) continuing iron-reducer activity and U(VI) bioreduction during dominantly sulfate reducing conditions, and (4) lower apparent U(VI) removal from groundwater during dominantly sulfate reducing conditions. New knowledge on simultaneously active metal and sulfate reducers has been incorporated into the modeling. In this case, an initially small population of slow growing sulfate reducers is active from the initiation of biostimulation. Three-dimensional, variably saturated flow modeling was used to address impacts of a falling water table during acetate injection. These impacts included a significant reduction in aquifer saturated thickness and isolation of residual reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions; however, the ranges were sufficiently small to preserve general trends. Large computer memory and high computational performance were required to simulate the detailed coupled process models for multiple biogeochemical components in highly resolved heterogeneous materials for the 110-day field experiment and 50 days of post-biostimulation behavior. In this case, a highly-scalable subsurface simulator operating on 128 processor cores for 12 hours was used to simulate each realization. An equivalent simulation without parallel processing would have taken 60 days, assuming sufficient memory was available.« less

Development of Hydroxyl Tagging Velocimetry for Low Velocity Flows

NASA Technical Reports Server (NTRS)

Andre, Matthieu A.; Bardet, Philippe M.; Burns, Ross A.; Danehy, Paul M.

2016-01-01

Hydroxyl tagging velocimetry (HTV) is a molecular tagging technique that relies on the photo-dissociation of water vapor into OH radicals and their subsequent tracking using laser induced fluorescence. Velocities are then obtained from time-of-flight calculations. At ambient temperature in air, the OH species lifetime is relatively short (<50 µs), making it suited for high speed flows. Lifetime and radicals formation increases with temperature, which allows HTV to also probe low-velocity, high-temperature flows or reacting flows such as flames. The present work aims at extending the domain of applicability of HTV, particularly towards low-speed (<10 m/s) and moderate (<500 K) temperature flows. Results are compared to particle image velocimetry (PIV) measurements recorded in identical conditions. Single shot and averaged velocity profiles are obtained in an air jet at room temperature. By modestly raising the temperature (100-200 degC) the OH production increases, resulting in an improvement of the signal-to-noise ratio (SNR). Use of nitrogen - a non-reactive gas with minimal collisional quenching - extends the OH species lifetime (to over 500 µs), which allows probing of slower flows or, alternately, increases the measurement precision at the expense of spatial resolution. Instantaneous velocity profiles are resolved in a 100degC nitrogen jet (maximum jet-center velocity of 6.5 m/s) with an uncertainty down to 0.10 m/s (1.5%) at 68% confidence level. MTV measurements are compared with particle image velocimetry and show agreement within 2%.

Theoretical and computer models of detonation in solid explosives

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

Tarver, C.M.; Urtiew, P.A.

1997-10-01

Recent experimental and theoretical advances in understanding energy transfer and chemical kinetics have led to improved models of detonation waves in solid explosives. The Nonequilibrium Zeldovich - von Neumann - Doring (NEZND) model is supported by picosecond laser experiments and molecular dynamics simulations of the multiphonon up-pumping and internal vibrational energy redistribution (IVR) processes by which the unreacted explosive molecules are excited to the transition state(s) preceding reaction behind the leading shock front(s). High temperature, high density transition state theory calculates the induction times measured by laser interferometric techniques. Exothermic chain reactions form product gases in highly excited vibrational states,more » which have been demonstrated to rapidly equilibrate via supercollisions. Embedded gauge and Fabry-Perot techniques measure the rates of reaction product expansion as thermal and chemical equilibrium is approached. Detonation reaction zone lengths in carbon-rich condensed phase explosives depend on the relatively slow formation of solid graphite or diamond. The Ignition and Growth reactive flow model based on pressure dependent reaction rates and Jones-Wilkins-Lee (JWL) equations of state has reproduced this nanosecond time resolved experimental data and thus has yielded accurate average reaction zone descriptions in one-, two- and three- dimensional hydrodynamic code calculations. The next generation reactive flow model requires improved equations of state and temperature dependent chemical kinetics. Such a model is being developed for the ALE3D hydrodynamic code, in which heat transfer and Arrhenius kinetics are intimately linked to the hydrodynamics.« less

Using resolvent analysis for the design of separation control on a NACA 0012 airfoil

NASA Astrophysics Data System (ADS)

Yeh, Chi-An; Taira, Kunihiko

2017-11-01

A combined effort based on large-eddy simulation and resolvent analysis on the separated flow over a NACA 0012 airfoil is conducted to design active flow control for suppression of separation. This study considers the the airfoil at 6 deg. angle-of-attack and Reynolds number of 23000. The response mode obtained from the resolvent analysis about the baseline turbulent mean flow reveals modal structures that can be categorized into three families when sweeping through the resonant frequency: (1) von Karman wake structure for low frequency; (2) Kelvin-Helmholtz structure in the separation bubble for high frequency; (3) blended structure of (1) and (2) for the intermediate frequency. Leveraging the insights from resolvent analysis, unsteady thermal actuation is introduced to the flow near the leading-edge to examine the use of the frequencies from three families for separation control in LES. As indicated by the resolvent response modes, we find that the use of intermediate frequencies are most effective in suppressing the flow separation, since the shear layer over the separation bubble and the wake are both receptive to the perturbation at the these frequencies. The resolvent-analysis-based control strategy achieves 35% drag reduction and 9% lift increase with effective frequency. This work was supported by Office of Naval Research (N00014-15-R-FO13) and Army Research Office (W911NF-14-1-0224).

Characterization of Rare Reverse Flow Events in Adverse Pressure Gradient Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

Kaehler, Christian J.; Bross, Matthew; Fuchs, Thomas

2017-11-01

Time-resolved tomographic flow fields measured in the viscous sublayer region of a turbulent boundary layer subjected to an adverse pressure gradient (APG) are examined with the aim to resolve and characterize reverse flow events at Reτ = 5000. The fields were measured using a novel high resolution tomographic particle tracking technique. It is shown that this technique is able to fully resolve mean and time dependent features of the complex three-dimensional flow with high accuracy down to very near-wall distances ( 10 μm). From time resolved Lagrangian particle trajectories, statistical information as well as instantaneous topological features of near-wall flow events are deduced. Similar to the zero pressure gradient case (ZPG), it was found that individual events with reverse flow components still occur relatively rarely under the action of the pressure gradient investigated here. However, reverse flow events comprised of many individual events, are shown to appear in relatively organized groupings in both spanwise and streamise directions. Furthermore, instantaneous measurements of reverse flow events show that these events are associated with the motion of low-momentum streaks in the near-wall region. This work is supported by the Priority Programme SPP 1881 Turbulent Superstructures and the individual project Grant KA1808/8-2 of the Deutsche Forschungsgemeinschaft.

PDF methods for turbulent reactive flows

NASA Technical Reports Server (NTRS)

Hsu, Andrew T.

1995-01-01

Viewgraphs are presented on computation of turbulent combustion, governing equations, closure problem, PDF modeling of turbulent reactive flows, validation cases, current projects, and collaboration with industry and technology transfer.

Stability and Interaction of Coherent Structure in Supersonic Reactive Wakes

NASA Technical Reports Server (NTRS)

Menon, Suresh

1983-01-01

A theoretical formulation and analysis is presented for a study of the stability and interaction of coherent structure in reacting free shear layers. The physical problem under investigation is a premixed hydrogen-oxygen reacting shear layer in the wake of a thin flat plate. The coherent structure is modeled as a periodic disturbance and its stability is determined by the application of linearized hydrodynamic stability theory which results in a generalized eigenvalue problem for reactive flows. Detailed stability analysis of the reactive wake for neutral, symmetrical and antisymmetrical disturbance is presented. Reactive stability criteria is shown to be quite different from classical non-reactive stability. The interaction between the mean flow, coherent structure and fine-scale turbulence is theoretically formulated using the von-Kaman integral technique. Both time-averaging and conditional phase averaging are necessary to separate the three types of motion. The resulting integro-differential equations can then be solved subject to initial conditions with appropriate shape functions. In the laminar flow transition region of interest, the spatial interaction between the mean motion and coherent structure is calculated for both non-reactive and reactive conditions and compared with experimental data wherever available. The fine-scale turbulent motion determined by the application of integral analysis to the fluctuation equations. Since at present this turbulence model is still untested, turbulence is modeled in the interaction problem by a simple algebraic eddy viscosity model. The applicability of the integral turbulence model formulated here is studied parametrically by integrating these equations for the simple case of self-similar mean motion with assumed shape functions. The effect of the motion of the coherent structure is studied and very good agreement is obtained with previous experimental and theoretical works for non-reactive flow. For the reactive case, lack of experimental data made direct comparison difficult. It was determined that the growth rate of the disturbance amplitude is lower for reactive case. The results indicate that the reactive flow stability is in qualitative agreement with experimental observation.

Quantifying uncertainty and computational complexity for pore-scale simulations

NASA Astrophysics Data System (ADS)

Chen, C.; Yuan, Z.; Wang, P.; Yang, X.; Zhenyan, L.

2016-12-01

Pore-scale simulation is an essential tool to understand the complex physical process in many environmental problems, from multi-phase flow in the subsurface to fuel cells. However, in practice, factors such as sample heterogeneity, data sparsity and in general, our insufficient knowledge of the underlying process, render many simulation parameters and hence the prediction results uncertain. Meanwhile, most pore-scale simulations (in particular, direct numerical simulation) incur high computational cost due to finely-resolved spatio-temporal scales, which further limits our data/samples collection. To address those challenges, we propose a novel framework based on the general polynomial chaos (gPC) and build a surrogate model representing the essential features of the underlying system. To be specific, we apply the novel framework to analyze the uncertainties of the system behavior based on a series of pore-scale numerical experiments, such as flow and reactive transport in 2D heterogeneous porous media and 3D packed beds. Comparing with recent pore-scale uncertainty quantification studies using Monte Carlo techniques, our new framework requires fewer number of realizations and hence considerably reduce the overall computational cost, while maintaining the desired accuracy.

Transport and Reactive Flow Modelling Using A Particle Tracking Method Based on Continuous Time Random Walks

NASA Astrophysics Data System (ADS)

Oliveira, R.; Bijeljic, B.; Blunt, M. J.; Colbourne, A.; Sederman, A. J.; Mantle, M. D.; Gladden, L. F.

2017-12-01

Mixing and reactive processes have a large impact on the viability of enhanced oil and gas recovery projects that involve acid stimulation and CO2 injection. To achieve a successful design of the injection schemes an accurate understanding of the interplay between pore structure, flow and reactive transport is necessary. Dependent on transport and reactive conditions, this complex coupling can also be dependent on initial rock heterogeneity across a variety of scales. To address these issues, we devise a new method to study transport and reactive flow in porous media at multiple scales. The transport model is based on an efficient Particle Tracking Method based on Continuous Time Random Walks (CTRW-PTM) on a lattice. Transport is modelled using an algorithm described in Rhodes and Blunt (2006) and Srinivasan et al. (2010); this model is expanded to enable for reactive flow predictions in subsurface rock undergoing a first-order fluid/solid chemical reaction. The reaction-induced alteration in fluid/solid interface is accommodated in the model through changes in porosity and flow field, leading to time dependent transport characteristics in the form of transit time distributions which account for rock heterogeneity change. This also enables the study of concentration profiles at the scale of interest. Firstly, we validate transport model by comparing the probability of molecular displacement (propagators) measured by Nuclear Magnetic Resonance (NMR) with our modelled predictions for concentration profiles. The experimental propagators for three different porous media of increasing complexity, a beadpack, a Bentheimer sandstone and a Portland carbonate, show a good agreement with the model. Next, we capture the time evolution of the propagators distribution in a reactive flow experiment, where hydrochloric acid is injected into a limestone rock. We analyse the time-evolving non-Fickian signatures for the transport during reactive flow and observe an increase in transport heterogeneity at latter times, representing the increase in rock heterogeneity. Evolution of transit time distribution is associated with the evolution of concentration profiles, thus highlighting the impact of initial rock structure on the reactive transport for a range of Pe and Da numbers.

Predictive Value of Reactive Hyperemia for Cardiovascular Events in Patients With Peripheral Arterial Disease Undergoing Vascular Surgery

PubMed Central

Huang, Alex L.; Silver, Annemarie E.; Shvenke, Elena; Schopfer, David W.; Jahangir, Eiman; Titas, Megan A.; Shpilman, Alex; Menzoian, James O.; Watkins, Michael T.; Raffetto, Joseph D.; Gibbons, Gary; Woodson, Jonathan; Shaw, Palma M.; Dhadly, Mandeep; Eberhardt, Robert T.; Keaney, John F.; Gokce, Noyan; Vita, Joseph A.

2008-01-01

Objective Reactive hyperemia is the compensatory increase in blood flow that occurs after a period of tissue ischemia, and this response is blunted in patients with cardiovascular risk factors. The predictive value of reactive hyperemia for cardiovascular events in patients with atherosclerosis and the relative importance of reactive hyperemia compared with other measures of vascular function have not been previously studied. Methods and Results We prospectively measured reactive hyperemia and brachial artery flow-mediated dilation by ultrasound in 267 patients with peripheral arterial disease referred for vascular surgery (age 66±11 years, 26% female). Median follow-up was 309 days (range 1 to 730 days). Fifty patients (19%) had an event, including cardiac death (15), myocardial infarction (18), unstable angina (8), congestive heart failure (6), and nonhemorrhagic stroke (3). Patients with an event were older and had lower hyperemic flow velocity (75±39 versus 95±50 cm/s, P=0.009). Patients with an event also had lower flow-mediated dilation (4.5±3.0 versus 6.9±4.6%, P<0.001), and when these 2 measures of vascular function were included in the same Cox proportional hazards model, lower hyperemic flow (OR 2.7, 95% CI 1.2 to 5.9, P=0.018) and lower flow-mediated dilation (OR 4.2, 95% CI: 1.8 to 9.8, P=0.001) both predicted cardiovascular events while adjusting for other risk factors. Conclusions Thus, lower reactive hyperemia is associated with increased cardiovascular risk in patients with peripheral arterial disease. Furthermore, flow-mediated dilation and reactive hyperemia incrementally relate to cardiovascular risk, although impaired flow-mediated dilation was the stronger predictor in this population. These findings further support the clinical relevance of vascular function measured in the microvasculature and conduit arteries in the upper extremity. PMID:17717291

Resolving the Multi-scale Behavior of Geochemical Weathering in the Critical Zone Using High Resolution Hydro-geochemical Models

NASA Astrophysics Data System (ADS)

Pandey, S.; Rajaram, H.

2015-12-01

This work investigates hydrologic and geochemical interactions in the Critical Zone (CZ) using high-resolution reactive transport modeling. Reactive transport models can be used to predict the response of geochemical weathering and solute fluxes in the CZ to changes in a dynamic environment, such as those pertaining to human activities and climate change in recent years. The scales of hydrology and geochemistry in the CZ range from days to eons in time and centimeters to kilometers in space. Here, we present results of a multi-dimensional, multi-scale hydro-geochemical model to investigate the role of subsurface heterogeneity on the formation of mineral weathering fronts in the CZ, which requires consideration of many of these spatio-temporal scales. The model is implemented using the reactive transport code PFLOTRAN, an open source subsurface flow and reactive transport code that utilizes parallelization over multiple processing nodes and provides a strong framework for simulating weathering in the CZ. The model is set up to simulate weathering dynamics in the mountainous catchments representative of the Colorado Front Range. Model parameters were constrained based on hydrologic, geochemical, and geophysical observations from the Boulder Creek Critical Zone Observatory (BcCZO). Simulations were performed in fractured rock systems and compared with systems of heterogeneous and homogeneous permeability fields. Tracer simulations revealed that the mean residence time of solutes was drastically accelerated as fracture density increased. In simulations that include mineral reactions, distinct signatures of transport limitations on weathering arose when discrete flow paths were included. This transport limitation was related to both advective and diffusive processes in the highly heterogeneous systems (i.e. fractured media and correlated random permeability fields with σlnk > 3). The well-known time-dependence of mineral weathering rates was found to be the most pronounced in the fractured systems, with a departure from the maximum system-averaged dissolution rate occurring after ~100 kyr followed by a gradual decrease in the reaction rate with time that persists beyond 104 kyr.

Scale-Resolving simulations (SRS): How much resolution do we really need?

NASA Astrophysics Data System (ADS)

Pereira, Filipe M. S.; Girimaji, Sharath

2017-11-01

Scale-resolving simulations (SRS) are emerging as the computational approach of choice for many engineering flows with coherent structures. The SRS methods seek to resolve only the most important features of the coherent structures and model the remainder of the flow field with canonical closures. With reference to a typical Large-Eddy Simulation (LES), practical SRS methods aim to resolve a considerably narrower range of scales (reduced physical resolution) to achieve an adequate degree of accuracy at reasonable computational effort. While the objective of SRS is well-founded, the criteria for establishing the optimal degree of resolution required to achieve an acceptable level of accuracy are not clear. This study considers the canonical case of the flow around a circular cylinder to address the issue of `optimal' resolution. Two important criteria are developed. The first condition addresses the issue of adequate resolution of the flow field. The second guideline provides an assessment of whether the modeled field is canonical (stochastic) turbulence amenable to closure-based computations.

Characterization of argon direct-current glow discharge with a longitudinal electric field applied at ambient air

NASA Astrophysics Data System (ADS)

Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

2014-09-01

A direct-current-driven plasma jet is developed by applying a longitudinal electric field on the flowing argon at ambient air. This plasma shows a torch shape with its cross-section increased from the anode to the cathode. Comparison with its counterparts indicates that the gas flow plays a key role in variation of the plasma structure and contributes much to enlarging the plasma volume. It is also found that the circular hollow metal base promotes generation of plasma with a high-power volume density in a limited space. The optical emission spectroscopy (OES) diagnosis indicates that the plasma comprises many reactive species, such as OH, O, excited N2, and Ar metastables. Examination of the rotational and vibrational temperature indicates that the plasma is under nonequilibrium condition and the excited species OH(A 2Σ+), O(5P), and N2(C 3Πu) are partly generated by energy transfer from argon metastables. The spatially resolved OES of plasma reveals that the negative glow, Faraday dark space, and positive column are distributed across the gas gap. The absence of the anode glow is attributed to the fact that many electrons in the vicinity of the anode follow ions into the positive column due to the ambipolar diffusion in the flowing gas.

Time-Resolved Rayleigh Scattering Measurements in Hot Gas Flows

NASA Technical Reports Server (NTRS)

Mielke, Amy F.; Elam, Kristie A.; Sung, Chih-Jen

2008-01-01

A molecular Rayleigh scattering technique is developed to measure time-resolved gas velocity, temperature, and density in unseeded gas flows at sampling rates up to 32 kHz. A high power continuous-wave laser beam is focused at a point in an air flow field and Rayleigh scattered light is collected and fiber-optically transmitted to the spectral analysis and detection equipment. The spectrum of the light, which contains information about the temperature and velocity of the flow, is analyzed using a Fabry-Perot interferometer. Photomultipler tubes operated in the photon counting mode allow high frequency sampling of the circular interference pattern to provide time-resolved flow property measurements. Mean and rms velocity and temperature fluctuation measurements in both an electrically-heated jet facility with a 10-mm diameter nozzle and also in a hydrogen-combustor heated jet facility with a 50.8-mm diameter nozzle at NASA Glenn Research Center are presented.

Antecedent reactivation by surface and deep anaphora in Norwegian

PubMed Central

HESTVIK, ARILD; NORDBY, HELGE; KARLSEN, GEIR

2005-01-01

Anaphora are expressions in language that depend on other linguistic entities for their full meaning. They can furthermore be divided into two types according to the level of representation where they find their antecedents: Surface anaphora, which resolve their reference at the sentence representation level, and deep anaphora, which resolve their reference at the non-grammatical level of discourse representation. The linguistic theory of these two anaphor types, and recent findings about processing differences at these two levels, combine to predict that surface anaphora should show fast and immediate reactivation of their antecedents, whereas deep anaphora should have a slower time course of antecedent reaccess. These predictions were confirmed with two lexical decision task experiments with Norwegian stimuli. PMID:15842413

Study of Varying Boundary Layer Height on Turret Flow Structures

DTIC Science & Technology

2011-06-01

fluid dynamics. The difficulties of the problem arise in modeling several complex flow features including separation, reattachment, three-dimensional...impossible. In this case, the approach is to create a model to calculate the properties of interest. The main issue with resolving turbulent flows...operation and their effect is modeled through subgrid scale models . As a result, the the most important turbulent scales are resolved and the

Reactive Power Pricing Model Considering the Randomness of Wind Power Output

NASA Astrophysics Data System (ADS)

Dai, Zhong; Wu, Zhou

2018-01-01

With the increase of wind power capacity integrated into grid, the influence of the randomness of wind power output on the reactive power distribution of grid is gradually highlighted. Meanwhile, the power market reform puts forward higher requirements for reasonable pricing of reactive power service. Based on it, the article combined the optimal power flow model considering wind power randomness with integrated cost allocation method to price reactive power. Meanwhile, considering the advantages and disadvantages of the present cost allocation method and marginal cost pricing, an integrated cost allocation method based on optimal power flow tracing is proposed. The model realized the optimal power flow distribution of reactive power with the minimal integrated cost and wind power integration, under the premise of guaranteeing the balance of reactive power pricing. Finally, through the analysis of multi-scenario calculation examples and the stochastic simulation of wind power outputs, the article compared the results of the model pricing and the marginal cost pricing, which proved that the model is accurate and effective.

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET) Velocimetry in Flow and Combustion Diagnostics

NASA Technical Reports Server (NTRS)

Jiang, Naibo; Halls, Benjamin R.; Stauffer, Hans U.; Roy, Sukesh; Danehy, Paul M.; Gord, James R.

2016-01-01

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET), a non-seeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and non-reactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25-nm 100-fs light. STARFLEET greatly reduces the per-pulse energy required (30 µJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and non-reactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities and further demonstrate the significantly less-intrusive nature of STARFLEET.

Quantum-state resolved reactive scattering at the gas-liquid interface: F+squalane (C30H62) dynamics via high-resolution infrared absorption of nascent HF(v,J).

PubMed

Zolot, Alexander M; Dagdigian, Paul J; Nesbitt, David J

2008-11-21

Exothermic chemical reaction dynamics at the gas-liquid interface have been investigated by colliding a supersonic beam of F atoms [E(com)=0.7(3) kcalmol] with a continuously refreshed liquid hydrocarbon (squalane) surface under high vacuum conditions. Absolute HF(v,J) product densities are determined by infrared laser absorption spectroscopy, with velocity distributions along the probe axis derived from high resolution Dopplerimetry. Nascent HF(v

Quantum-state resolved reactive scattering at the gas-liquid interface: F +squalane (C30H62) dynamics via high-resolution infrared absorption of nascent HF(v,J)

NASA Astrophysics Data System (ADS)

Zolot, Alexander M.; Dagdigian, Paul J.; Nesbitt, David J.

2008-11-01

Exothermic chemical reaction dynamics at the gas-liquid interface have been investigated by colliding a supersonic beam of F atoms [Ecom=0.7(3)kcal/mol] with a continuously refreshed liquid hydrocarbon (squalane) surface under high vacuum conditions. Absolute HF(v,J) product densities are determined by infrared laser absorption spectroscopy, with velocity distributions along the probe axis derived from high resolution Dopplerimetry. Nascent HF(v ⩽3) products are formed in a highly nonequilibrium (inverted) vibrational distribution [⟨Evib⟩=13.2(2)kcal/mol], reflecting insufficient time for complete thermal accommodation with the surface prior to desorption. Colder, but still non-Boltzmann, rotational state populations [⟨Erot⟩=1.0(1)kcal/mol] indicate that some fraction of molecules directly scatter into the gas phase without rotationally equilibrating with the surface. Nascent HF also recoils from the liquid surface with excess translational energy, resulting in Doppler broadened linewidths that increase systematically with internal HF excitation. The data are consistent with microscopic branching in HF-surface dynamics following the reactive event, with (i) a direct reactive scattering fraction of newly formed product molecules leaving the surface promptly and (ii) a trapping desorption fraction that accommodates rotationally (though still not vibrationally) with the bulk liquid. Comparison with analogous gas phase F +hydrocarbon processes reveals that the liquid acts as a partial "heat sink" for vibrational energy flow on the time scale of the chemical reaction event.

Drug Treatment Combined with BCG Vaccination Reduces Disease Reactivation in Guinea Pigs Infected with Mycobacterium tuberculosis

PubMed Central

Shang, Shaobin; Shanley, Crystal A.; Caraway, Megan L.; Orme, Eileen A.; Henao-Tamayo, Marcela; Hascall-Dove, Laurel; Ackart, David; Orme, Ian M.; Ordway, Diane J.; Basaraba, Randall J.

2012-01-01

Bacillus-Calmette-Guerin (BCG), the only human tuberculosis vaccine, primes a partially protective immune response against M. tuberculosis infection in humans and animals. In guinea pigs, BCG vaccination slows the progression of disease and reduces the severity of necrotic granulomas, which harbor a population of drug-tolerant bacilli. The objective of this study was to determine if reducing disease severity by BCG vaccination of guinea pigs prior to M. tuberculosis challenge enhanced the efficacy of combination drug therapy. At 20 days of infection, treatment of vaccinated and non-vaccinated animals with rifampin, isoniazid, and pyrizinamide (RHZ) was initiated for 4 or 8 weeks. On days 50, 80 and 190 of infection (10 weeks after drug were withdrawn), treatment efficacy was evaluated by quantifying clinical condition, bacterial loads, lesion severity, and dynamic changes in peripheral blood and lung leukocyte numbers by flow cytometry. In a separate, long-term survival study, treatment efficacy was evaluated by determining disease reactivation frequency post-mortem. BCG vaccination alone delayed pulmonary and extra-pulmonary disease progression, but failed to prevent dissemination of bacilli and the formation of necrotic granulomas. Drug therapy either alone or in combination with BCG, was more effective at lessening clinical disease and lesion severity compared to control animals or those receiving BCG alone. Fewer residual lesions in BCG vaccinated and drug treated animals, equated to a reduced frequency of reactivation disease and improvement in survival even out to 500 days of infection. The combining of BCG vaccination and drug therapy was more effective at resolving granulomas such that fewer animals had evidence of residual infection and thus less reactivation disease. PMID:22244979

Reactive transport modeling in fractured rock: A state-of-the-science review

NASA Astrophysics Data System (ADS)

MacQuarrie, Kerry T. B.; Mayer, K. Ulrich

2005-10-01

The field of reactive transport modeling has expanded significantly in the past two decades and has assisted in resolving many issues in Earth Sciences. Numerical models allow for detailed examination of coupled transport and reactions, or more general investigation of controlling processes over geologic time scales. Reactive transport models serve to provide guidance in field data collection and, in particular, enable researchers to link modeling and hydrogeochemical studies. In this state-of-science review, the key objectives were to examine the applicability of reactive transport codes for exploring issues of redox stability to depths of several hundreds of meters in sparsely fractured crystalline rock, with a focus on the Canadian Shield setting. A conceptual model of oxygen ingress and redox buffering, within a Shield environment at time and space scales relevant to nuclear waste repository performance, is developed through a review of previous research. This conceptual model describes geochemical and biological processes and mechanisms materially important to understanding redox buffering capacity and radionuclide mobility in the far-field. Consistent with this model, reactive transport codes should ideally be capable of simulating the effects of changing recharge water compositions as a result of long-term climate change, and fracture-matrix interactions that may govern water-rock interaction. Other aspects influencing the suitability of reactive transport codes include the treatment of various reaction and transport time scales, the ability to apply equilibrium or kinetic formulations simultaneously, the need to capture feedback between water-rock interactions and porosity-permeability changes, and the representation of fractured crystalline rock environments as discrete fracture or dual continuum media. A review of modern multicomponent reactive transport codes indicates a relatively high-level of maturity. Within the Yucca Mountain nuclear waste disposal program, reactive transport codes of varying complexity have been applied to investigate the migration of radionuclides and the geochemical evolution of host rock around the planned disposal facility. Through appropriate near- and far-field application of dual continuum codes, this example demonstrates how reactive transport models have been applied to assist in constraining historic water infiltration rates, interpreting the sealing of flow paths due to mineral precipitation, and investigating post-closure geochemical monitoring strategies. Natural analogue modeling studies, although few in number, are also of key importance as they allow the comparison of model results with hydrogeochemical and paleohydrogeological data over geologic time scales.

Selective Catalytic Combustion Sensors for Reactive Organic Analysis

NASA Technical Reports Server (NTRS)

Innes, W. B.

1971-01-01

Sensors involving a vanadia-alumina catalyst bed-thermocouple assembly satisfy requirements for simple, reproducible and rapid continuous analysis or reactive organics. Responses generally increase with temperature to 400 C and increase to a maximum with flow rate/catalyst volume. Selectivity decreases with temperature. Response time decreases with flow rate and increases with catalyst volume. At chosen optimum conditions calculated response which is additive and linear agrees better with photochemical reactivity than other methods for various automotive sources, and response to vehicle exhaust is insensitive to flow rate. Application to measurement of total reactive organics in vehicle exhaust as well as for gas chromatography detection illustrate utility. The approach appears generally applicable to high thermal effect reactions involving first order kinetics.

Pore-scale study of multiphase reactive transport in fibrous electrodes of vanadium redox flow batteries

DOE PAGES

Chen, Li; He, YaLing; Tao, Wen -Quan; ...

2017-07-21

The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, pore-scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lowermore » porosities. Further, a pore-scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, V II/V III transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. Furthermore, the current pore-scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upscaled to improve the accuracy of the current continuum-scale models.« less

Effects of intermittent theta burst stimulation on cerebral blood flow and cerebral vasomotor reactivity.

PubMed

Pichiorri, Floriana; Vicenzini, Edoardo; Gilio, Francesca; Giacomelli, Elena; Frasca, Vittorio; Cambieri, Chiara; Ceccanti, Marco; Di Piero, Vittorio; Inghilleri, Maurizio

2012-08-01

To determine whether intermittent theta burst stimulation influences cerebral hemodynamics, we investigated changes induced by intermittent theta burst stimulation on the middle cerebral artery cerebral blood flow velocity and vasomotor reactivity to carbon dioxide (CO(2)) in healthy participants. The middle cerebral artery flow velocity and vasomotor reactivity were monitored by continuous transcranial Doppler sonography. Changes in cortical excitability were tested by transcranial magnetic stimulation. In 11 healthy participants, before and immediately after delivering intermittent theta burst stimulation, we tested cortical excitability measured by the resting motor threshold and motor evoked potential amplitude over the stimulated hemisphere and vasomotor reactivity to CO(2) bilaterally. The blood flow velocity was monitored in both middle cerebral arteries throughout the experimental session. In a separate session, we tested the effects of sham stimulation under the same experimental conditions. Whereas the resting motor threshold remained unchanged before and after stimulation, motor evoked potential amplitudes increased significantly (P = .04). During and after stimulation, middle cerebral artery blood flow velocities also remained bilaterally unchanged, whereas vasomotor reactivity to CO(2) increased bilaterally (P = .04). The sham stimulation left all variables unchanged. The expected intermittent theta burst stimulation-induced changes in cortical excitability were not accompanied by changes in cerebral blood flow velocities; however, the bilateral increased vasomotor reactivity suggests that intermittent theta burst stimulation influences the cerebral microcirculation, possibly involving subcortical structures. These findings provide useful information on hemodynamic phenomena accompanying intermittent theta burst stimulation, which should be considered in research aimed at developing this noninvasive, low-intensity stimulation technique for safe therapeutic applications.

Time Resolved Digital PIV Measurements of Flow Field Cyclic Variation in an Optical IC Engine

NASA Astrophysics Data System (ADS)

Jarvis, S.; Justham, T.; Clarke, A.; Garner, C. P.; Hargrave, G. K.; Halliwell, N. A.

2006-07-01

Time resolved digital particle image velocimetry (DPIV) experimental data is presented for the in-cylinder flow field development of a motored four stroke spark ignition (SI) optical internal combustion (IC) engine. A high speed DPIV system was employed to quantify the velocity field development during the intake and compression stroke at an engine speed of 1500 rpm. The results map the spatial and temporal development of the in-cylinder flow field structure allowing comparison between traditional ensemble average and cycle average flow field structures. Conclusions are drawn with respect to engine flow field cyclic variations.

Dynamic power flow controllers

DOEpatents

Divan, Deepakraj M.; Prasai, Anish

2017-03-07

Dynamic power flow controllers are provided. A dynamic power flow controller may comprise a transformer and a power converter. The power converter is subject to low voltage stresses and not floated at line voltage. In addition, the power converter is rated at a fraction of the total power controlled. A dynamic power flow controller controls both the real and the reactive power flow between two AC sources having the same frequency. A dynamic power flow controller inserts a voltage with controllable magnitude and phase between two AC sources; thereby effecting control of active and reactive power flows between two AC sources.

Mobile detection system to evaluate reactive hyperemia using radionuclide plethysmography.

PubMed

Harel, François; Ngo, Quam; Finnerty, Vincent; Hernandez, Edgar; Khairy, Paul; Dupuis, Jocelyn

2007-08-01

We validated a novel mobile detection system to evaluate reactive hyperemia using the radionuclide plethysmography technique. Twenty-six subjects underwent simultaneously radionuclide plethysmography with strain gauge plethysmography. Strain gauge and radionuclide methods showed excellent reproducibility with intraclass correlation coefficients of 0.96 and 0.89 respectively. There was also a good correlation of flows between the two methods during reactive hyperemia (r = 0.87). We conclude that radionuclide plethysmography using this mobile detection system is a non-invasive alternative to assess forearm blood flow and its dynamic variations during reactive hyperemia.

Time-resolved fluorescence decay measurements for flowing particles

DOEpatents

Deka, C.; Steinkamp, J.A.

1999-06-01

Time-resolved fluorescence decay measurements are disclosed for flowing particles. An apparatus and method for the measurement and analysis of fluorescence for individual cells and particles in flow are described, wherein the rapid measurement capabilities of flow cytometry and the robust measurement and analysis procedures of time-domain fluorescence lifetime spectroscopy are combined. A pulse-modulated CW laser is employed for excitation of the particles. The characteristics and the repetition rate of the excitation pulses can be readily adjusted to accommodate for fluorescence decays having a wide range of lifetimes. 12 figs.

Time-resolved fluorescence decay measurements for flowing particles

DOEpatents

Deka, Chiranjit; Steinkamp, John A.

1999-01-01

Time-resolved fluorescence decay measurements for flowing particles. An apparatus and method for the measurement and analysis of fluorescence for individual cells and particles in flow are described, wherein the rapid measurement capabilities of flow cytometry and the robust measurement and analysis procedures of time-domain fluorescence lifetime spectroscopy are combined. A pulse-modulated cw laser is employed for excitation of the particles. The characteristics and the repetition rate of the excitation pulses can be readily adjusted to accommodate for fluorescence decays having a wide range of lifetimes.

Influence of reactive gas admixture on transition metal cluster nucleation in a gas aggregation cluster source

NASA Astrophysics Data System (ADS)

Peter, Tilo; Polonskyi, Oleksandr; Gojdka, Björn; Mohammad Ahadi, Amir; Strunskus, Thomas; Zaporojtchenko, Vladimir; Biederman, Hynek; Faupel, Franz

2012-12-01

We quantitatively assessed the influence of reactive gases on the formation processes of transition metal clusters in a gas aggregation cluster source. A cluster source based on a 2 in. magnetron is used to study the production rate of titanium and cobalt clusters. Argon served as working gas for the DC magnetron discharge, and a small amount of reactive gas (oxygen and nitrogen) is added to promote reactive cluster formation. We found that the cluster production rate depends strongly on the reactive gas concentration for very small amounts of reactive gas (less than 0.1% of total working gas), and no cluster formation takes place in the absence of reactive species. The influence of discharge power, reactive gas concentration, and working gas pressure are investigated using a quartz micro balance in a time resolved manner. The strong influence of reactive gas is explained by a more efficient formation of nucleation seeds for metal-oxide or nitride than for pure metal.

Sparse Partial Equilibrium Tables in Chemically Resolved Reactive Flow

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

Vitello, P; Fried, L E; Pudliner, B

2003-07-14

The detonation of an energetic material is the result of a complex interaction between kinetic chemical reactions and hydrodynamics. Unfortunately, little is known concerning the detailed chemical kinetics of detonations in energetic materials. CHEETAH uses rate laws to treat species with the slowest chemical reactions, while assuming other chemical species are in equilibrium. CHEETAH supports a wide range of elements and condensed detonation products and can also be applied to gas detonations. A sparse hash table of equation of state values, called the ''cache'' is used in CHEETAH to enhance the efficiency of kinetic reaction calculations. For large-scale parallel hydrodynamicmore » calculations, CHEETAH uses MPI communication to updates to the cache. We present here details of the sparse caching model used in the CHEETAH. To demonstrate the efficiency of modeling using a sparse cache model we consider detonations in energetic materials.« less

Sparse Partial Equilibrium Tables in Chemically Resolved Reactive Flow

NASA Astrophysics Data System (ADS)

Vitello, Peter; Fried, Laurence E.; Pudliner, Brian; McAbee, Tom

2004-07-01

The detonation of an energetic material is the result of a complex interaction between kinetic chemical reactions and hydrodynamics. Unfortunately, little is known concerning the detailed chemical kinetics of detonations in energetic materials. CHEETAH uses rate laws to treat species with the slowest chemical reactions, while assuming other chemical species are in equilibrium. CHEETAH supports a wide range of elements and condensed detonation products and can also be applied to gas detonations. A sparse hash table of equation of state values is used in CHEETAH to enhance the efficiency of kinetic reaction calculations. For large-scale parallel hydrodynamic calculations, CHEETAH uses parallel communication to updates to the cache. We present here details of the sparse caching model used in the CHEETAH coupled to an ALE hydrocode. To demonstrate the efficiency of modeling using a sparse cache model we consider detonations in energetic materials.

Online kinetic studies on intermediates of laccase-catalyzed reaction in reversed micelle.

PubMed

Liu, Zhi-Hong; Shao, Mei; Cai, Ru-Xiu; Shen, Ping

2006-02-01

Using water/AOT/n-octane reversed micelle as the medium, the optical signal of the reactive intermediate of laccase-catalyzed oxidation of o-phenylenediamine, which was indetectable in aqueous solutions, was successfully captured. Thus online kinetic studies of the intermediate were accomplished. Two-way kinetic spectral data were acquired with stopped-flow technique. By resolving the data with global analysis software, both the kinetic curves and the absorption spectra of the components involved in the reaction process were simultaneously obtained. The whole reaction in the reversed micelle was proved to be composed of two successive steps, an enzymatic generation of the intermediate and a following nonenzymatic decay of the intermediate. A consecutive first-order kinetic model of the whole reaction was confirmed. The influences of microenvironmental factors of the medium (such as the pH value of the water pool and the water/AOT ratio) on the detection of the intermediate were also investigated.

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST.

PubMed

Stadlbauer, Andreas; van der Riet, Wilma; Crelier, Gerard; Salomonowitz, Erich

2010-07-01

To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves. Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R=2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers. Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach. We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping. Copyright 2009 Elsevier Ireland Ltd. All rights reserved.

Monitoring of Hepatitis B Virus (HBV) DNA and Risk of HBV Reactivation in B-Cell Lymphoma: A Prospective Observational Study.

PubMed

Kusumoto, Shigeru; Tanaka, Yasuhito; Suzuki, Ritsuro; Watanabe, Takashi; Nakata, Masanobu; Takasaki, Hirotaka; Fukushima, Noriyasu; Fukushima, Takuya; Moriuchi, Yukiyoshi; Itoh, Kuniaki; Nosaka, Kisato; Choi, Ilseung; Sawa, Masashi; Okamoto, Rumiko; Tsujimura, Hideki; Uchida, Toshiki; Suzuki, Sachiko; Okamoto, Masataka; Takahashi, Tsutomu; Sugiura, Isamu; Onishi, Yasushi; Kohri, Mika; Yoshida, Shinichiro; Sakai, Rika; Kojima, Minoru; Takahashi, Hiroyuki; Tomita, Akihiro; Maruyama, Dai; Atsuta, Yoshiko; Tanaka, Eiji; Suzuki, Takayo; Kinoshita, Tomohiro; Ogura, Michinori; Mizokami, Masashi; Ueda, Ryuzo

2015-09-01

There is no standard management of reactivation of hepatitis B virus (HBV) infection in HBV-resolved patients without hepatitis B surface antigen (HBsAg), but with antibodies against hepatitis B core antigen and/or antibodies against HBsAg (anti-HBs). We conducted a prospective observational study to evaluate the occurrence of HBV reactivation by serial monthly monitoring of HBV DNA and to establish preemptive therapy guided by this monitoring in B-cell non-Hodgkin lymphoma (B-NHL) treated with rituximab plus corticosteroid-containing chemotherapy (R-steroid-chemo). The primary endpoint was the incidence of HBV reactivation defined as quantifiable HBV DNA levels of ≥ 11 IU/mL. With a median HBV DNA follow-up of 562 days, HBV reactivation was observed in 21 of the 269 analyzed patients. The incidence of HBV reactivation at 1.5 years was 8.3% (95% confidence interval, 5.5-12.4). No hepatitis due to HBV reactivation was observed in patients who received antiviral treatment when HBV DNA levels were between 11 and 432 IU/mL. An anti-HBs titer of <10 mIU/mL and detectable HBV DNA remaining below the level of quantification at baseline were independent risk factors for HBV reactivation (hazard ratio, 20.6 and 56.2, respectively; P < .001). Even in 6 patients with a rapid increase of HBV due to mutations, the monthly HBV DNA monitoring was effective at preventing HBV-related hepatitis. Monthly monitoring of HBV DNA is useful for preventing HBV reactivation-related hepatitis among B-NHL patients with resolved HBV infection following R-steroid-chemo (UMIN000001299). © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Efficient non-hydrostatic modelling of 3D wave-induced currents using a subgrid approach

NASA Astrophysics Data System (ADS)

Rijnsdorp, Dirk P.; Smit, Pieter B.; Zijlema, Marcel; Reniers, Ad J. H. M.

2017-08-01

Wave-induced currents are an ubiquitous feature in coastal waters that can spread material over the surf zone and the inner shelf. These currents are typically under resolved in non-hydrostatic wave-flow models due to computational constraints. Specifically, the low vertical resolutions adequate to describe the wave dynamics - and required to feasibly compute at the scales of a field site - are too coarse to account for the relevant details of the three-dimensional (3D) flow field. To describe the relevant dynamics of both wave and currents, while retaining a model framework that can be applied at field scales, we propose a two grid approach to solve the governing equations. With this approach, the vertical accelerations and non-hydrostatic pressures are resolved on a relatively coarse vertical grid (which is sufficient to accurately resolve the wave dynamics), whereas the horizontal velocities and turbulent stresses are resolved on a much finer subgrid (of which the resolution is dictated by the vertical scale of the mean flows). This approach ensures that the discrete pressure Poisson equation - the solution of which dominates the computational effort - is evaluated on the coarse grid scale, thereby greatly improving efficiency, while providing a fine vertical resolution to resolve the vertical variation of the mean flow. This work presents the general methodology, and discusses the numerical implementation in the SWASH wave-flow model. Model predictions are compared with observations of three flume experiments to demonstrate that the subgrid approach captures both the nearshore evolution of the waves, and the wave-induced flows like the undertow profile and longshore current. The accuracy of the subgrid predictions is comparable to fully resolved 3D simulations - but at much reduced computational costs. The findings of this work thereby demonstrate that the subgrid approach has the potential to make 3D non-hydrostatic simulations feasible at the scale of a realistic coastal region.

Low cytomegalovirus-specific T-cell counts at reactivation are associated with progression to high-level viremia or disease in seropositive recipients of hematopoietic cell grafts from seropositive but not seronegative donors.

PubMed

Hoegh-Petersen, Mette; Roa, Lina; Liu, Yiping; Zhou, Feng; Ugarte-Torres, Alejandra; Louie, Polly; Fonseca, Kevin; Khan, Faisal; Russell, James A; Storek, Jan

2012-02-01

Identifying patients who spontaneously resolve cytomegalovirus (CMV) reactivation could spare these patients from the toxicity of antiviral drugs such as ganciclovir. The role of CMV-specific T cells in clearing CMV viremia in patients who do not receive ganciclovir has not been evaluated. We assessed this in patients with CMV viremia between 50 and 50 000 genome copies/mL, because our threshold for initiating ganciclovir is 50 000 copies/mL. We enumerated CMV-specific T cells in 39 CMV seropositive hematopoietic cell transplantation (HCT) recipients within 4 days of the first positive CMV polymerase chain reaction (PCR). CMV-specific T cells were defined as cells that upon stimulation with CMV lysate or pp65 overlapping peptides produced interferon (IFN)-γ, tumor necrosis factor (TNF)-α or interleukin (IL)-2, alone or in combination. Among Donor (D+), Recipient (R+) patients, unifunctional CMV-specific CD4 T-cells were higher in patients who spontaneously resolved CMV viremia (did not receive ganciclovir) versus those who progressed (received ganciclovir) (median 0.20 versus 0.02/μL lysate-stimulated cells, P < 0.05, and 0.26 versus 0.05/μL pp65 peptide-stimulated cells, P<0.05). Among D- R+ patients, there was no difference between patients with spontaneous resolution or progression; all subsets of CMV-specific T cells measured were barely detectable, in both patients with spontaneous resolution and those with progression. Among D+ R+ patients (but not D- R+ patients), high CMV-specific CD4 T-cell counts identify patients who can spontaneously resolve CMV reactivation. In D- R+ patients, immune mechanisms other than T cells may control the progression from reactivation to high-level viremia/disease.

Low incidence of hepatitis B virus reactivation and subsequent hepatitis in patients with chronic hepatitis C receiving direct-acting antiviral therapy.

PubMed

Tamori, A; Abiru, S; Enomoto, H; Kioka, K; Korenaga, M; Tani, J; Enomoto, M; Sugiyama, M; Masaki, T; Kawada, N; Yatsuhashi, H; Nishiguchi, S; Mizokami, M

2018-05-01

To determine the clinical characteristics of hepatitis B virus (HBV) reactivation in patients undergoing interferon-free antihepatitis C virus (HCV) therapy, we examined HBV DNA in 25 HBV co-infected patients and 765 patients with resolved HBV infection during and after treatment with direct-acting antiviral agents (DAAs). Among those with HCV genotype 1, asunaprevir plus daclatasvir was administered to 160 patients, sofosbuvir (SOF) plus ledipasvir to 438 patients and paritaprevir plus ombitasvir and ritonavir to 25 patients. In total, 167 patients with genotype 2 were treated with SOF plus ribavirin. Three patients with an HBV DNA level ≥2000 IU/mL were treated with entecavir before anti-HCV therapy, without reactivation of HBV. In 3 of 22 (12%) HBV surface antigen (HBsAg)-positive patients with an HBV DNA level <2000 IU/mL, the viral load increased during treatment. However, hepatitis flare did not occur in these patients. There was no significant difference in clinical history between patients with and without HBV reactivation. Among 765 patients with resolved HBV infection, HBV reactivation occurred in 1 (0.1%) patient after initial resolution, whose HBV DNA level spontaneously decreased after DAA therapy. We compared anti-HBs titres at baseline with those at post-DAA therapy in 123 patients without HBsAg. There was no significant difference in anti-HBs levels between the two points (P = .79). In conclusion, HBV reactivation was rare in HBsAg-negative patients treated with DAA therapy. Additionally, hepatitis did not occur in HBV-reactivated patients with a baseline HBV DNA level <2000 IU/mL before DAA therapy. © 2017 John Wiley & Sons Ltd.

Real rock-microfluidic flow cell: A test bed for real-time in situ analysis of flow, transport, and reaction in a subsurface reactive transport environment.

PubMed

Singh, Rajveer; Sivaguru, Mayandi; Fried, Glenn A; Fouke, Bruce W; Sanford, Robert A; Carrera, Martin; Werth, Charles J

2017-09-01

Physical, chemical, and biological interactions between groundwater and sedimentary rock directly control the fundamental subsurface properties such as porosity, permeability, and flow. This is true for a variety of subsurface scenarios, ranging from shallow groundwater aquifers to deeply buried hydrocarbon reservoirs. Microfluidic flow cells are now commonly being used to study these processes at the pore scale in simplified pore structures meant to mimic subsurface reservoirs. However, these micromodels are typically fabricated from glass, silicon, or polydimethylsiloxane (PDMS), and are therefore incapable of replicating the geochemical reactivity and complex three-dimensional pore networks present in subsurface lithologies. To address these limitations, we developed a new microfluidic experimental test bed, herein called the Real Rock-Microfluidic Flow Cell (RR-MFC). A porous 500μm-thick real rock sample of the Clair Group sandstone from a subsurface hydrocarbon reservoir of the North Sea was prepared and mounted inside a PDMS microfluidic channel, creating a dynamic flow-through experimental platform for real-time tracking of subsurface reactive transport. Transmitted and reflected microscopy, cathodoluminescence microscopy, Raman spectroscopy, and confocal laser microscopy techniques were used to (1) determine the mineralogy, geochemistry, and pore networks within the sandstone inserted in the RR-MFC, (2) analyze non-reactive tracer breakthrough in two- and (depth-limited) three-dimensions, and (3) characterize multiphase flow. The RR-MFC is the first microfluidic experimental platform that allows direct visualization of flow and transport in the pore space of a real subsurface reservoir rock sample, and holds potential to advance our understandings of reactive transport and other subsurface processes relevant to pollutant transport and cleanup in groundwater, as well as energy recovery. Copyright © 2017 Elsevier B.V. All rights reserved.

Sensitivity correction for the influence of the fat layer on muscle oxygenation and estimation of fat thickness by time-resolved spectroscopy

NASA Astrophysics Data System (ADS)

Ohmae, Etsuko; Nishio, Shinichiro; Oda, Motoki; Suzuki, Hiroaki; Suzuki, Toshihiko; Ohashi, Kyoichi; Koga, Shunsaku; Yamashita, Yutaka; Watanabe, Hiroshi

2014-06-01

Near-infrared spectroscopy (NIRS) has been used for noninvasive assessment of oxygenation in living tissue. For muscle measurements by NIRS, the measurement sensitivity to muscle (S) is strongly influenced by fat thickness (FT). In this study, we investigated the influence of FT and developed a correction curve for S with an optode distance (3 cm) sufficiently large to probe the muscle. First, we measured the hemoglobin concentration in the forearm (n=36) and thigh (n=6) during arterial occlusion using a time-resolved spectroscopy (TRS) system, and then FT was measured by ultrasound. The correction curve was derived from the ratio of partial mean optical path length of the muscle layer to observed mean optical path length . There was good correlation between FT and at rest, and could be used to estimate FT. The estimated FT was used to validate the correction curve by measuring the forearm blood flow (FBF) by strain-gauge plethysmography (SGP_FBF) and TRS (TRS_FBF) simultaneously during a reactive hyperemia test with 16 volunteers. The corrected TRS_FBF results were similar to the SGP_FBF results. This is a simple method for sensitivity correction that does not require use of ultrasound.

Cerebral blood flow modulations during cognitive control in major depressive disorder.

PubMed

Hoffmann, Alexandra; Montoro, Casandra I; Reyes Del Paso, Gustavo A; Duschek, Stefan

2018-09-01

This study investigated cerebral blood flow modulations during proactive and reactive cognitive control in major depressive disorder (MDD). Proactive control refers to preparatory processes during anticipation of a behaviorally relevant event; reactive control is activated after such an event to ensure goal attainment. Using functional transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries of both hemispheres were recorded in 40 MDD patients and 40 healthy controls during a precued Stroop task. The font color of color words, which appeared 5 s after an acoustic warning signal, had to be indicated while ignoring word meaning. Patients, as compared to controls, exhibited smaller bilateral blood flow increases during task preparation and larger increases after color word presentation. Response time was longer in patients irrespective of the match or mismatch between font color and word meaning. The blood flow increase after word presentation correlated positively with response time. Potential effects of psychotropic medication on cognition and cerebral blood flow could not be controlled. The study revealed evidence of reduced cortical activity during proactive and elevated activity that occurs during reactive control in MDD. Deficient implementation of proactive control in MDD may lead to increased reliance on reactive control. The association between the blood flow increase after color word presentation and poorer performance indicates that deficient response preparation cannot be compensated for by reactive strategies. The findings are clinically relevant, as they may contribute to our understanding of the mechanisms relevant to cognitive impairments in MDD. Copyright © 2018 Elsevier B.V. All rights reserved.

Mathematical Modeling of the Heat Transfer and Conditions of Ignition of a Turbulent Flow of a Reactive Gas

NASA Astrophysics Data System (ADS)

Matvienko, O. V.

2016-01-01

Results of investigations into the heat transfer and conditions of ignition of a turbulent flow of a chemically reactive gas have been presented. Approximation formulas have been obtained for determining the critical conditions of ignition of the turbulent flow, the length of the preflame zone, and the criterion of heat transfer in subcritical and supercritical reaction regimes.

40 CFR 1066.140 - Diluted exhaust flow calibration.

Code of Federal Regulations, 2014 CFR

2014-07-01

... whenever corrective action does not resolve a failure to meet the diluted exhaust flow verification (i.e... subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice, a laminar flow...

Modeling Coherent Structures in Canopy Flows

NASA Astrophysics Data System (ADS)

Luhar, Mitul

2017-11-01

It is well known that flows over vegetation canopies are characterized by the presence of energetic coherent structures. Since the mean profile over dense canopies exhibits an inflection point, the emergence of such structures is often attributed to a Kelvin-Helmholtz instability. However, though stability analyses provide useful mechanistic insights into canopy flows, they are limited in their ability to generate predictions for spectra and coherent structure. The present effort seeks to address this limitation by extending the resolvent formulation (McKeon and Sharma, 2010, J. Fluid Mech.) to canopy flows. Under the resolvent formulation, the turbulent velocity field is expressed as a superposition of propagating modes, identified via a gain-based (singular value) decomposition of the Navier-Stokes equations. A key advantage of this approach is that it reconciles multiple mechanisms that lead to high amplification in turbulent flows, including modal instability, transient growth, and critical-layer phenomena. Further, individual high-gain modes can be combined to generate more complete models for coherent structure and velocity spectra. Preliminary resolvent-based model predictions for canopy flows agree well with existing experiments and simulations.

Characteristics of Atmospheric Pressure Rotating Gliding Arc Plasmas

NASA Astrophysics Data System (ADS)

Zhang, Hao; Zhu, Fengsen; Tu, Xin; Bo, Zheng; Cen, Kefa; Li, Xiaodong

2016-05-01

In this work, a novel direct current (DC) atmospheric pressure rotating gliding arc (RGA) plasma reactor has been developed for plasma-assisted chemical reactions. The influence of the gas composition and the gas flow rate on the arc dynamic behaviour and the formation of reactive species in the N2 and air gliding arc plasmas has been investigated by means of electrical signals, high speed photography, and optical emission spectroscopic diagnostics. Compared to conventional gliding arc reactors with knife-shaped electrodes which generally require a high flow rate (e.g., 10-20 L/min) to maintain a long arc length and reasonable plasma discharge zone, in this RGA system, a lower gas flow rate (e.g., 2 L/min) can also generate a larger effective plasma reaction zone with a longer arc length for chemical reactions. Two different motion patterns can be clearly observed in the N2 and air RGA plasmas. The time-resolved arc voltage signals show that three different arc dynamic modes, the arc restrike mode, takeover mode, and combined modes, can be clearly identified in the RGA plasmas. The occurrence of different motion and arc dynamic modes is strongly dependent on the composition of the working gas and gas flow rate. supported by National Natural Science Foundation of China (No. 51576174), the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120101110099) and the Fundamental Research Funds for the Central Universities (No. 2015FZA4011)

Femtosecond, two-photon laser-induced-fluorescence imaging of atomic oxygen in an atmospheric-pressure plasma jet

NASA Astrophysics Data System (ADS)

Schmidt, Jacob B.; Sands, Brian L.; Kulatilaka, Waruna D.; Roy, Sukesh; Scofield, James; Gord, James R.

2015-06-01

Femtosecond, two-photon-absorption laser-induced-fluorescence (fs-TALIF) spectroscopy is employed to measure space- and time-resolved atomic-oxygen distributions in a nanosecond, repetitively pulsed, externally grounded, atmospheric-pressure plasma jet flowing helium with a variable oxygen admixture. The high-peak-intensity, low-average-energy femtosecond pulses result in increased TALIF signal with reduced photolytic inferences. This allows 2D imaging of absolute atomic-oxygen number densities ranging from 5.8   ×   1015 to 2.0   ×   1012cm-3 using a cooled CCD with an external intensifier. Xenon is used for signal and imaging-system calibrations to quantify the atomic-oxygen fluorescence signal. Initial results highlight a transition in discharge morphology from annular to filamentary, corresponding with a change in plasma chemistry from ozone to atomic oxygen production, as the concentration of oxygen in the feed gas is changed at a fixed voltage-pulse-repetition rate. In this configuration, significant concentrations of reactive oxygen species may be remotely generated by sustaining an active discharge beyond the confines of the dielectric capillary, which may benefit applications that require large concentrations of reactive oxygen species such as material processing or biomedical devices.

Acceleration methods for multi-physics compressible flow

NASA Astrophysics Data System (ADS)

Peles, Oren; Turkel, Eli

2018-04-01

In this work we investigate the Runge-Kutta (RK)/Implicit smoother scheme as a convergence accelerator for complex multi-physics flow problems including turbulent, reactive and also two-phase flows. The flows considered are subsonic, transonic and supersonic flows in complex geometries, and also can be either steady or unsteady flows. All of these problems are considered to be a very stiff. We then introduce an acceleration method for the compressible Navier-Stokes equations. We start with the multigrid method for pure subsonic flow, including reactive flows. We then add the Rossow-Swanson-Turkel RK/Implicit smoother that enables performing all these complex flow simulations with a reasonable CFL number. We next discuss the RK/Implicit smoother for time dependent problem and also for low Mach numbers. The preconditioner includes an intrinsic low Mach number treatment inside the smoother operator. We also develop a modified Roe scheme with a corresponding flux Jacobian matrix. We then give the extension of the method for real gas and reactive flow. Reactive flows are governed by a system of inhomogeneous Navier-Stokes equations with very stiff source terms. The extension of the RK/Implicit smoother requires an approximation of the source term Jacobian. The properties of the Jacobian are very important for the stability of the method. We discuss what the chemical physics theory of chemical kinetics tells about the mathematical properties of the Jacobian matrix. We focus on the implication of the Le-Chatelier's principle on the sign of the diagonal entries of the Jacobian. We present the implementation of the method for turbulent flow. We use a two RANS turbulent model - one equation model - Spalart-Allmaras and a two-equation model - k-ω SST model. The last extension is for two-phase flows with a gas as a main phase and Eulerian representation of a dispersed particles phase (EDP). We present some examples for such flow computations inside a ballistic evaluation rocket motor. The numerical examples in this work include transonic flow about a RAE2822 airfoil, about a M6 Onera wing, NACA0012 airfoil at very low Mach number, two-phase flow inside a Ballistic evaluation motor (BEM), a turbulent reactive shear layer and a time dependent Sod's tube problem.

Differential blood flow responses to CO2 in human internal and external carotid and vertebral arteries

PubMed Central

Sato, Kohei; Sadamoto, Tomoko; Hirasawa, Ai; Oue, Anna; Subudhi, Andrew W; Miyazawa, Taiki; Ogoh, Shigehiko

2012-01-01

Arterial CO2 serves as a mediator of cerebral blood flow (CBF), and its relative influence on the regulation of CBF is defined as cerebral CO2 reactivity. Our previous studies have demonstrated that there are differences in CBF responses to physiological stimuli (i.e. dynamic exercise and orthostatic stress) between arteries in humans. These findings suggest that dynamic CBF regulation and cerebral CO2 reactivity may be different in the anterior and posterior cerebral circulation. The aim of this study was to identify cerebral CO2 reactivity by measuring blood flow and examine potential differences in CO2 reactivity between the internal carotid artery (ICA), external carotid artery (ECA) and vertebral artery (VA). In 10 healthy young subjects, we evaluated the ICA, ECA, and VA blood flow responses by duplex ultrasonography (Vivid-e, GE Healthcare), and mean blood flow velocity in middle cerebral artery (MCA) and basilar artery (BA) by transcranial Doppler (Vivid-7, GE healthcare) during two levels of hypercapnia (3% and 6% CO2), normocapnia and hypocapnia to estimate CO2 reactivity. To characterize cerebrovascular reactivity to CO2, we used both exponential and linear regression analysis between CBF and estimated partial pressure of arterial CO2, calculated by end-tidal partial pressure of CO2. CO2 reactivity in VA was significantly lower than in ICA (coefficient of exponential regression 0.021 ± 0.008 vs. 0.030 ± 0.008; slope of linear regression 2.11 ± 0.84 vs. 3.18 ± 1.09% mmHg−1: VA vs. ICA, P < 0.01). Lower CO2 reactivity in the posterior cerebral circulation was persistent in distal intracranial arteries (exponent 0.023 ± 0.006 vs. 0.037 ± 0.009; linear 2.29 ± 0.56 vs. 3.31 ± 0.87% mmHg−1: BA vs. MCA). In contrast, CO2 reactivity in ECA was markedly lower than in the intra-cerebral circulation (exponent 0.006 ± 0.007; linear 0.63 ± 0.64% mmHg−1, P < 0.01). These findings indicate that vertebro-basilar circulation has lower CO2 reactivity than internal carotid circulation, and that CO2 reactivity of the external carotid circulation is markedly diminished compared to that of the cerebral circulation, which may explain different CBF responses to physiological stress. PMID:22526884

Gas-liquid Phase Distribution and Void Fraction Measurements Using the MRI

NASA Technical Reports Server (NTRS)

Daidzic, N. E.; Schmidt, E.; Hasan, M. M.; Altobelli, S.

2004-01-01

We used a permanent-magnet MRI system to estimate the integral and spatially- and/or temporally-resolved void-fraction distributions and flow patterns in gas-liquid two-phase flows. Air was introduced at the bottom of the stagnant liquid column using an accurate and programmable syringe pump. Air flow rates were varied between 1 and 200 ml/min. The cylindrical non-conducting test tube in which two-phase flow was measured was placed in a 2.67 kGauss MRI with MRT spectrometer/imager. Roughly linear relationship has been obtained for the integral void-fraction, obtained by volume-averaging of the spatially-resolved signals, and the air flow rate in upward direction. The time-averaged spatially-resolved void fraction has also been obtained for the quasi-steady flow of air in a stagnant liquid column. No great accuracy is claimed as this was an exploratory proof-of-concept type of experiment. Preliminary results show that MRI a non-invasive and non-intrusive experimental technique can indeed provide a wealth of different qualitative and quantitative data and is especially well suited for averaged transport processes in adiabatic and diabatic multi-phase and/or multi-component flows.

Validation of a numerical method for interface-resolving simulation of multicomponent gas-liquid mass transfer and evaluation of multicomponent diffusion models

NASA Astrophysics Data System (ADS)

Woo, Mino; Wörner, Martin; Tischer, Steffen; Deutschmann, Olaf

2018-03-01

The multicomponent model and the effective diffusivity model are well established diffusion models for numerical simulation of single-phase flows consisting of several components but are seldom used for two-phase flows so far. In this paper, a specific numerical model for interfacial mass transfer by means of a continuous single-field concentration formulation is combined with the multicomponent model and effective diffusivity model and is validated for multicomponent mass transfer. For this purpose, several test cases for one-dimensional physical or reactive mass transfer of ternary mixtures are considered. The numerical results are compared with analytical or numerical solutions of the Maxell-Stefan equations and/or experimental data. The composition-dependent elements of the diffusivity matrix of the multicomponent and effective diffusivity model are found to substantially differ for non-dilute conditions. The species mole fraction or concentration profiles computed with both diffusion models are, however, for all test cases very similar and in good agreement with the analytical/numerical solutions or measurements. For practical computations, the effective diffusivity model is recommended due to its simplicity and lower computational costs.

40 CFR 1065.340 - Diluted exhaust flow (CVS) calibration.

Code of Federal Regulations, 2010 CFR

2010-07-01

... action does not resolve a failure to meet the diluted exhaust flow verification (i.e., propane check) in... subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice, a laminar flow...

Experimental determination of sorption in fractured flow systems

NASA Astrophysics Data System (ADS)

Zimmerman, Mitchell D.; Bennett, Philip C.; Sharp, John M.; Choi, Wan-Joo

2002-09-01

Fracture "skins" are alteration zones on fracture surfaces created by a variety of biological, chemical, and physical processes. Skins increase surface area, where sorption occurs, compared to the unaltered rock matrix. This study examines the sorption of organic solutes on altered fracture surfaces in an experimental fracture-flow apparatus. Fracture skins containing abundant metal oxides, clays, and organic material from the Breathitt Formation (Kentucky, USA) were collected in a manner such that skin surface integrity was maintained. The samples were reassembled in the lab in a flow-through apparatus that simulated ˜2.7 m of a linear fracture "conduit." A dual-tracer injection scheme was utilized with the sorbing or reactive tracer compared to a non-reactive tracer (chloride) injected simultaneously. Sorption was assessed from the ratio of the first temporal moments of the breakthrough curves and from the loss of reactive tracer mass and evaluated as a function of flow velocity and solute type. The breakthrough curves suggest dual-flow regimes in the fracture with both sorbing and non-sorbing flow fields. Significant sorption occurs for the reactive components, and sorption increased with decreasing flow rate and decreasing compound solubility. Based on moment analysis, however, there was little retardation of the center of solute mass. These data suggest that non-equilibrium sorption processes dominate and that slow desorption and boundary layer diffusion cause extensive tailing in the breakthrough curves.

Prediction of Down-Gradient Impacts of DNAPL Source Depletion Using Tracer Techniques

NASA Astrophysics Data System (ADS)

Basu, N. B.; Fure, A. D.; Jawitz, J. W.

2006-12-01

Four simplified DNAPL source depletion models that have been discussed in the literature recently are evaluated for the prediction of long-term effects of source depletion under natural gradient flow. These models are simple in form (a power function equation is an example) but are shown here to serve as mathematical analogs to complex multiphase flow and transport simulators. One of the source depletion models, the equilibrium streamtube model, is shown to be relatively easily parameterized using non-reactive and reactive tracers. Non-reactive tracers are used to characterize the aquifer heterogeneity while reactive tracers are used to describe the mean DNAPL mass and its distribution. This information is then used in a Lagrangian framework to predict source remediation performance. In a Lagrangian approach the source zone is conceptualized as a collection of non-interacting streamtubes with hydrodynamic and DNAPL heterogeneity represented by the variation of the travel time and DNAPL saturation among the streamtubes. The travel time statistics are estimated from the non-reactive tracer data while the DNAPL distribution statistics are estimated from the reactive tracer data. The combined statistics are used to define an analytical solution for contaminant dissolution under natural gradient flow. The tracer prediction technique compared favorably with results from a multiphase flow and transport simulator UTCHEM in domains with different hydrodynamic heterogeneity (variance of the log conductivity field = 0.2, 1 and 3).

Influence of nitrogen admixture to argon on the ion energy distribution in reactive high power pulsed magnetron sputtering of chromium

NASA Astrophysics Data System (ADS)

Breilmann, W.; Maszl, C.; Hecimovic, A.; von Keudell, A.

2017-04-01

Reactive high power impulse magnetron sputtering (HiPIMS) of metals is of paramount importance for the deposition of various oxides, nitrides and carbides. The addition of a reactive gas such as nitrogen to an argon HiPIMS plasma with a metal target allows the formation of the corresponding metal nitride on the substrate. The addition of a reactive gas introduces new dynamics into the plasma process, such as hysteresis, target poisoning and the rarefaction of two different plasma gases. We investigate the dynamics for the deposition of chromium nitride by a reactive HiPIMS plasma using energy- and time-resolved ion mass spectrometry, fast camera measurements and temporal and spatially resolved optical emission spectroscopy. It is shown that the addition of nitrogen to the argon plasma gas significantly changes the appearance of the localized ionization zones, the so-called spokes, in HiPIMS plasmas. In addition, a very strong modulation of the metal ion flux within each HiPIMS pulse is observed, with the metal ion flux being strongly suppressed and the nitrogen molecular ion flux being strongly enhanced in the high current phase of the pulse. This behavior is explained by a stronger return effect of the sputtered metal ions in the dense plasma above the racetrack. This is best observed in a pure nitrogen plasma, because the ionization zones are mostly confined, implying a very high local plasma density and consequently also an efficient scattering process.

Reactive transport simulations of alternative flow pathways in the ambient unsaturated zone at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Browning, L.; Murphy, W.; Manepally, C.; Fedors, R.

2003-04-01

Uncertainties in simulated ambient system unsaturated zone flow could have a significant impact on performance evaluations of the proposed nuclear waste repository at Yucca Mountain, Nevada. In addition to determining variations in the quantity of water available to corrode engineered materials and transport radionuclides, model assumptions regarding flow pathways may significantly affect estimates of groundwater chemistry. The manner and extent to which groundwater compositions evolve along a flow pathway are determined mainly by thermohydrologic conditions, the types of reactive materials encountered, and the interaction times with those materials. Simulated groundwater compositions can thus vary significantly depending on whether or not the flow model includes lateral diversion of infiltrating waters, or preferential flow pathways in variably-saturated materials. To assist a regulatory review of a potential license application for a geologic repository for high-level waste, we developed a reactive transport model for the ambient hydrogeochemical system at Yucca Mountain. The model simulates two phase, nonisothermal, advective and diffusive flow and transport through a one dimensional, matrix and fracture continua (dual permeability) containing ten kinetically reactive hydrostatigraphic layers in the vicinity of the SD-9 borehole at Yucca Mountain. In this presentation, we describe how the model was used to evaluate alternative ambient unsaturated zone flow pathways proposed by the U.S. Department of Energy. This abstract is an independent product of the CNWRA and does not necessarily reflect the views or regulatory position of the NRC.

Reactivity of Nucleic Acid Radicals

PubMed Central

Greenberg, Marc M.

2016-01-01

Nucleic acid oxidation plays a vital role in the etiology and treatment of diseases, as well as aging. Reagents that oxidize nucleic acids are also useful probes of the biopolymers’ structure and folding. Radiation scientists have contributed greatly to our understanding of nucleic acid oxidation using a variety of techniques. During the past two decades organic chemists have applied the tools of synthetic and mechanistic chemistry to independently generate and study the reactive intermediates produced by ionizing radiation and other nucleic acid damaging agents. This approach has facilitated resolving mechanistic controversies and lead to the discovery of new reactive processes. PMID:28529390

Filming the invisible - time-resolved visualization of compressible flows

NASA Astrophysics Data System (ADS)

Kleine, H.

2010-04-01

Essentially all processes in gasdynamics are invisible to the naked eye as they occur in a transparent medium. The task to observe them is further complicated by the fact that most of these processes are also transient, often with characteristic times that are considerably below the threshold of human perception. Both difficulties can be overcome by combining visualization methods that reveal changes in the transparent medium, and high-speed photography techniques that “stop” the motion of the flow. The traditional approach is to reconstruct a transient process from a series of single images, each taken in a different experiment at a different instant. This approach, which is still widely used today, can only be expected to give reliable results when the process is reproducible. Truly time-resolved visualization, which yields a sequence of flow images in a single experiment, has been attempted for more than a century, but many of the developed camera systems were characterized by a high level of complexity and limited quality of the results. Recent advances in digital high-speed photography have changed this situation and have provided the tools to investigate, with relative ease and in sufficient detail, the true development of a transient flow with characteristic time scales down to one microsecond. This paper discusses the potential and the limitations one encounters when using density-sensitive visualization techniques in time-resolved mode. Several examples illustrate how this approach can reveal and explain a number of previously undetected phenomena in a variety of highly transient compressible flows. It is demonstrated that time-resolved visualization offers numerous advantages which normally outweigh its shortcomings, mainly the often-encountered loss in resolution. Apart from the capability to track the location and/or shape of flow features in space and time, adequate time-resolved visualization allows one to observe the development of deliberately introduced near-isentropic perturbation wavelets. This new diagnostic tool can be used to qualitatively and quantitatively determine otherwise inaccessible thermodynamic properties of a compressible flow.

Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

DTIC Science & Technology

2003-12-01

and Flame 117, 732. TSAI, K. & Fox, R. 0. 1998 The BMC/GIEM model for micromixing in non-premixed turbulent reacting flows. Industrial Engineering...L. & Fox, R. 0. 2003 Comparison of micromixing models for CFD simulation of nanoparticle formation by reactive precipitation. Submitted to AIChE

Effects of incomplete mixing on reactive transport in flows through heterogeneous porous media

NASA Astrophysics Data System (ADS)

Wright, Elise E.; Richter, David H.; Bolster, Diogo

2017-11-01

The phenomenon of incomplete mixing reduces bulk effective reaction rates in reactive transport. Many existing models do not account for these effects, resulting in the overestimation of reaction rates in laboratory and field settings. To date, most studies on incomplete mixing have focused on diffusive systems; here, we extend these to explore the role that flow heterogeneity has on incomplete mixing. To do this, we examine reactive transport using a Lagrangian reactive particle tracking algorithm in two-dimensional idealized heterogeneous porous media. Contingent on the nondimensional Peclet and Damköhler numbers in the system, it was found that near well-mixed behavior could be observed at late times in the heterogeneous flow field simulations. We look at three common flow deformation metrics that describe the enhancement of mixing in the flow due to velocity gradients: the Okubo-Weiss parameter (θ ), the largest eigenvalue of the Cauchy-Green strain tensor (λC), and the finite-time Lyapunov exponent (Λ ). Strong mixing regions in the heterogeneous flow field identified by these metrics were found to correspond to regions with higher numbers of reactions, but the infrequency of these regions compared to the large numbers of reactions occurring elsewhere in the domain imply that these strong mixing regions are insufficient in explaining the observed near well-mixed behavior. Since it was found that reactive transport in these heterogeneous flows could overcome the effects of incomplete mixing, we also search for a closure for the mean concentration. The conservative quantity u2¯, where u =CA-CB , was found to predict the late time scaling of the mean concentration, i.e., Ci¯˜u2¯ .

Numerical investigation of coupled density-driven flow and hydrogeochemical processes below playas

NASA Astrophysics Data System (ADS)

Hamann, Enrico; Post, Vincent; Kohfahl, Claus; Prommer, Henning; Simmons, Craig T.

2015-11-01

Numerical modeling approaches with varying complexity were explored to investigate coupled groundwater flow and geochemical processes in saline basins. Long-term model simulations of a playa system gain insights into the complex feedback mechanisms between density-driven flow and the spatiotemporal patterns of precipitating evaporites and evolving brines. Using a reactive multicomponent transport model approach, the simulations reproduced, for the first time in a numerical study, the evaporite precipitation sequences frequently observed in saline basins ("bull's eyes"). Playa-specific flow, evapoconcentration, and chemical divides were found to be the primary controls for the location of evaporites formed, and the resulting brine chemistry. Comparative simulations with the computationally far less demanding surrogate single-species transport models showed that these were still able to replicate the major flow patterns obtained by the more complex reactive transport simulations. However, the simulated degree of salinization was clearly lower than in reactive multicomponent transport simulations. For example, in the late stages of the simulations, when the brine becomes halite-saturated, the nonreactive simulation overestimated the solute mass by almost 20%. The simulations highlight the importance of the consideration of reactive transport processes for understanding and quantifying geochemical patterns, concentrations of individual dissolved solutes, and evaporite evolution.

Challenges in Scale-Resolving Simulations of turbulent wake flows with coherent structures

NASA Astrophysics Data System (ADS)

Pereira, Filipe S.; Eça, Luís; Vaz, Guilherme; Girimaji, Sharath S.

2018-06-01

The objective of this work is to investigate the challenges encountered in Scale-Resolving Simulations (SRS) of turbulent wake flows driven by spatially-developing coherent structures. SRS of practical interest are expressly intended for efficiently computing such flows by resolving only the most important features of the coherent structures and modelling the remainder as stochastic field. The success of SRS methods depends upon three important factors: i) ability to identify key flow mechanisms responsible for the generation of coherent structures; ii) determine the optimum range of resolution required to adequately capture key elements of coherent structures; and iii) ensure that the modelled part is comprised nearly exclusively of fully-developed stochastic turbulence. This study considers the canonical case of the flow around a circular cylinder to address the aforementioned three key issues. It is first demonstrated using experimental evidence that the vortex-shedding instability and flow-structure development involves four important stages. A series of SRS computations of progressively increasing resolution (decreasing cut-off length) are performed. An a priori basis for locating the origin of the coherent structures development is proposed and examined. The criterion is based on the fact that the coherent structures are generated by the Kelvin-Helmholtz (KH) instability. The most important finding is that the key aspects of coherent structures can be resolved only if the effective computational Reynolds number (based on total viscosity) exceeds the critical value of the KH instability in laminar flows. Finally, a quantitative criterion assessing the nature of the unresolved field based on the strain-rate ratio of mean and unresolved fields is examined. The two proposed conditions and rationale offer a quantitative basis for developing "good practice" guidelines for SRS of complex turbulent wake flows with coherent structures.

Cavitation erosion prediction based on analysis of flow dynamics and impact load spectra

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

Mihatsch, Michael S., E-mail: michael.mihatsch@aer.mw.tum.de; Schmidt, Steffen J.; Adams, Nikolaus A.

2015-10-15

Cavitation erosion is the consequence of repeated collapse-induced high pressure-loads on a material surface. The present paper assesses the prediction of impact load spectra of cavitating flows, i.e., the rate and intensity distribution of collapse events based on a detailed analysis of flow dynamics. Data are obtained from a numerical simulation which employs a density-based finite volume method, taking into account the compressibility of both phases, and resolves collapse-induced pressure waves. To determine the spectrum of collapse events in the fluid domain, we detect and quantify the collapse of isolated vapor structures. As reference configuration we consider the expansion ofmore » a liquid into a radially divergent gap which exhibits unsteady sheet and cloud cavitation. Analysis of simulation data shows that global cavitation dynamics and dominant flow events are well resolved, even though the spatial resolution is too coarse to resolve individual vapor bubbles. The inviscid flow model recovers increasingly fine-scale vapor structures and collapses with increasing resolution. We demonstrate that frequency and intensity of these collapse events scale with grid resolution. Scaling laws based on two reference lengths are introduced for this purpose. We show that upon applying these laws impact load spectra recorded on experimental and numerical pressure sensors agree with each other. Furthermore, correlation between experimental pitting rates and collapse-event rates is found. Locations of high maximum wall pressures and high densities of collapse events near walls obtained numerically agree well with areas of erosion damage in the experiment. The investigation shows that impact load spectra of cavitating flows can be inferred from flow data that captures the main vapor structures and wave dynamics without the need for resolving all flow scales.« less

Reactive oligoarthritis in a patient with Clostridium difficile pseudomembranous colitis. Review of the literature.

PubMed

Veillard, E; Guggenbuhl, P; Bello, S; Lamer, F; Chalès, G

1998-12-01

A 57-year-old man developed oligoarthritis of the right sacroiliac joint, knee and elbow in the wake of Clostridium difficile pseudomembranous colitis. He was HLA B27-positive and had a history of Reiter's syndrome. His joint manifestations resolved after a course of nonsteroidal antiinflammatory drug therapy and injection of the right knee with triamcinolone acetonide. Clostridium difficile should be recognized as a rare cause of reactive arthritis.

A Multi-domain Spectral Method for Supersonic Reactive Flows

NASA Technical Reports Server (NTRS)

Don, Wai-Sun; Gottlieb, David; Jung, Jae-Hun; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

This paper has a dual purpose: it presents a multidomain Chebyshev method for the solution of the two-dimensional reactive compressible Navier-Stokes equations, and it reports the results of the application of this code to the numerical simulations of high Mach number reactive flows in recessed cavity. The computational method utilizes newly derived interface boundary conditions as well as an adaptive filtering technique to stabilize the computations. The results of the simulations are relevant to recessed cavity flameholders.

Mechanism of Na+ binding to thrombin resolved by ultra-rapid kinetics

PubMed Central

Gianni, Stefano; Ivarsson, Ylva; Bah, Alaji; Bush-Pelc, Leslie A.; Di Cera, Enrico

2007-01-01

The interaction of Na+ and K+ with proteins is at the basis of numerous processes of biological importance. However, measurement of the kinetic components of the interaction has eluded experimentalists for decades because the rate constants are too fast to resolve with conventional stopped-flow methods. Using a continuous-flow apparatus with a dead time of 50 μs we have been able to resolve the kinetic rate constants and entire mechanism of Na+ binding to thrombin, an interaction that is at the basis of the procoagulant and prothrombotic roles of the enzyme in the blood. PMID:17935858

How to use your peak flow meter

MedlinePlus

Peak flow meter - how to use; Asthma - peak flow meter; Reactive airway disease - peak flow meter; Bronchial asthma - peak flow meter ... your airways are narrowed and blocked due to asthma, your peak flow values drop. You can check ...

A Fictitious Domain Method for Resolving the Interaction of Blood Flow with Clot Growth

NASA Astrophysics Data System (ADS)

Mukherjee, Debanjan; Shadden, Shawn

2016-11-01

Thrombosis and thrombo-embolism cause a range of diseases including heart attack and stroke. Closer understanding of clot and blood flow mechanics provides valuable insights on the etiology, diagnosis, and treatment of thrombotic diseases. Such mechanics are complicated, however, by the discrete and multi-scale phenomena underlying thrombosis, and the complex interactions of unsteady, pulsatile hemodynamics with a clot of arbitrary shape and microstructure. We have developed a computational technique, based on a fictitious domain based finite element method, to study these interactions. The method can resolve arbitrary clot geometries, and dynamically couple fluid flow with static or growing clot boundaries. Macroscopic thrombus-hemodynamics interactions were investigated within idealized vessel geometries representative of the common carotid artery, with realistic unsteady flow profiles as inputs. The method was also employed successfully to resolve micro-scale interactions using a model driven by in-vivo morphology data. The results provide insights into the flow structures and hemodynamic loading around an arbitrarily grown clot at arterial length-scales, as well as flow and transport within the interstices of platelet aggregates composing the clot. The work was supported by AHA Award No: 16POST27500023.

Depth-encoded dual beam phase-resolved Doppler OCT for Doppler-angle-independent flow velocity measurement

NASA Astrophysics Data System (ADS)

Qian, Jie; Cheng, Wei; Cao, Zhaoyuan; Chen, Xinjian; Mo, Jianhua

2017-02-01

Phase-resolved Doppler optical coherence tomography (PR-D-OCT) is a functional OCT imaging technique that can provide high-speed and high-resolution depth-resolved measurement on flow in biological materials. However, a common problem with conventional PR-D-OCT is that this technique often measures the flow motion projected onto the OCT beam path. In other words, it needs the projection angle to extract the absolute velocity from PR-D-OCT measurement. In this paper, we proposed a novel dual-beam PR-D-OCT method to measure absolute flow velocity without separate measurement on the projection angle. Two parallel light beams are created in sample arm and focused into the sample at two different incident angles. The images produced by these two beams are encoded to different depths in single B-scan. Then the Doppler signals picked up by the two beams together with the incident angle difference can be used to calculate the absolute velocity. We validated our approach in vitro on an artificial flow phantom with our home-built 1060 nm swept source OCT. Experimental results demonstrated that our method can provide an accurate measurement of absolute flow velocity with independency on the projection angle.

Assessment of swirl spray interaction in lab scale combustor using time-resolved measurements

NASA Astrophysics Data System (ADS)

Rajamanickam, Kuppuraj; Jain, Manish; Basu, Saptarshi

2017-11-01

Liquid fuel injection in highly turbulent swirling flows becomes common practice in gas turbine combustors to improve the flame stabilization. It is well known that the vortex bubble breakdown (VBB) phenomenon in strong swirling jets exhibits complicated flow structures in the spatial domain. In this study, the interaction of hollow cone liquid sheet with such coaxial swirling flow field has been studied experimentally using time-resolved measurements. In particular, much attention is focused towards the near field breakup mechanism (i.e. primary atomization) of liquid sheet. The detailed swirling gas flow field characterization is carried out using time-resolved PIV ( 3.5 kHz). Furthermore, the complicated breakup mechanisms and interaction of the liquid sheet are imaged with the help of high-speed shadow imaging system. Subsequently, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) is implemented over the instantaneous data sets to retrieve the modal information associated with the interaction dynamics. This helps to delineate more quantitative nature of interaction process between the liquid sheet and swirling gas phase flow field.

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

Chen, Li; He, YaLing; Tao, Wen -Quan

The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, pore-scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lowermore » porosities. Further, a pore-scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, V II/V III transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. Furthermore, the current pore-scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upscaled to improve the accuracy of the current continuum-scale models.« less

Applying flow chemistry: methods, materials, and multistep synthesis.

PubMed

McQuade, D Tyler; Seeberger, Peter H

2013-07-05

The synthesis of complex molecules requires control over both chemical reactivity and reaction conditions. While reactivity drives the majority of chemical discovery, advances in reaction condition control have accelerated method development/discovery. Recent tools include automated synthesizers and flow reactors. In this Synopsis, we describe how flow reactors have enabled chemical advances in our groups in the areas of single-stage reactions, materials synthesis, and multistep reactions. In each section, we detail the lessons learned and propose future directions.

Characterizing Reactive Flow Paths in Fractured Cement

NASA Astrophysics Data System (ADS)

Wenning, Q. C.; Huerta, N. J.; Hesse, M. A.; Bryant, S. L.

2011-12-01

Geologic carbon sequestration can be a viable method for reducing anthropogenic CO2 flux into the atmosphere. However, the technology must be economically feasible and pose acceptable risk to stakeholders. One key risk is CO2 leakage out of the storage reservoir. Potential driving forces for leakage are the overpressure due to CO2 injection and the buoyancy of free phase CO2. Potential hazards of leakage are contamination of Underground Sources of Drinking Water or the atmosphere and would be deemed an unacceptable risk. Wells potentially provide a fast path for leakage from the reservoir. While the well's cement casing is reactive with CO2 and CO2-saturated brine, the low cement matrix permeability and slow diffusion rate make it unlikely that CO2 will escape through a properly constructed wellbore. However, highly permeable fractures with micrometer scale apertures can occur in cement casings. Reactions that occur in the flow in these fractures can either be self-limiting or self-enhancing. Therefore, understanding the reactive flow is critical to understanding of leakage evolution through these fractures. The goal of our work is to characterize the modification of the flow paths in the fracture due to reaction with acidic brine. With this aim we have characterized both the initial flow path of un-reactive flow and the final flow path after introduction of low-pH acid along the same fracture. Class H cement cores 3-6 cm in length and 2.5 cm diameter are created and a single natural and unique fracture is produced in each core using the Brazilian method. Our experimental fluid is injected at a constant rate into the cement core housed in a Hassler Cell under confining pressure. A solution of red dye and deionized water is pumped through the fracture to stain the un-reactive flow paths. Deionized water is then pumped through the core to limit diffusion of the dye into non-flowing portions of the fracture. After staining the initial flow path, low pH water due to hydrochloric acid (HCL), is pumped through the core at the same rate as the dye. The low pH water is used as a proxy for acidic CO2-saturated brine. Both staining from the un-reactive dye and acid produce visible permanent color alterations on the cement fracture plane. Results show that nearly the entire fracture width is stained by the red dye, with only a few asperities un-dyed. However the low pH HCl forms restricted reacted channels that are a subset of the area open to un-reactive flow, occupying only 10-50% of the entire fracture width. Low pH HCl is believed to be the driving force for the reaction that causes channeling. As acid flows through the fracture, calcium is stripped from the low pH high velocity flow front and precipitates along of the edges of the channel where pH is higher due to the lower flow velocities outside the channel. It is hypothesized that this mineral precipitation restricts the flow into localized channels within the plane of fractures having apertures of tens of micrometers. Reactions restrict the flow path to a smaller fraction of the surface, which may be an indication of self-limiting behavior.

Evaluation of Collaterals and Clot Burden Using Time-Resolved C-Arm Conebeam CT Angiography in the Angiography Suite: A Feasibility Study.

PubMed

Yang, P; Niu, K; Wu, Y; Struffert, T; Doerfler, A; Holter, P; Aagaard-Kienitz, B; Strother, C; Chen, G-H

2017-04-01

The assessment of collaterals and clot burden in patients with acute ischemic stroke provides important information about treatment options and clinical outcome. Time-resolved C-arm conebeam CT angiography has the potential to provide accurate and reliable evaluations of collaterals and clot burden in the angiographic suite. Experience with this technique is extremely limited, and feasibility studies are needed to validate this technique. Our purpose was to present such a feasibility study. Ten C-arm conebeam CT perfusion datasets from 10 subjects with acute ischemic stroke acquired before endovascular treatment were retrospectively processed to generate time-resolved conebeam CTA. From time-resolved conebeam CTA, 2 experienced readers evaluated the clot burden and collateral flow in consensus by using previously reported scoring systems and assessed the clinical value of this novel imaging technique independently. Interobserver agreement was analyzed by using the intraclass correlation analysis method. Clot burden and collateral flow can be assessed by using the commonly accepted scoring systems for all eligible cases. Additional clinical information (eg, the quantitative dynamic information of collateral flow) can be obtained from this new imaging technique. Two readers agreed that time-revolved C-arm conebeam CTA is the preferred method for evaluating the clot burden and collateral flow compared with other conventional imaging methods. Comprehensive evaluations of clot burden and collateral flow are feasible by using time-resolved C-arm conebeam CTA data acquired in the angiography suite. This technique further enriches the imaging tools in the angiography suite to enable a "one-stop- shop" imaging workflow for patients with acute ischemic stroke. © 2017 by American Journal of Neuroradiology.

Safety and Convergence Analysis of Intersecting Aircraft Flows Under Decentralized Collision Avoidance

NASA Astrophysics Data System (ADS)

Dallal, Ahmed H.

Safety is an essential requirement for air traffic management and control systems. Aircraft are not allowed to get closer to each other than a specified safety distance, to avoid any conflicts and collisions between aircraft. Forecast analysis predicts a tremendous increase in the number of flights. Subsequently, automated tools are needed to help air traffic controllers resolve air born conflicts. In this dissertation, we consider the problem of conflict resolution of aircraft flows with the assumption that aircraft are flowing through a fixed specified control volume at a constant speed. In this regard, several centralized and decentralized resolution rules have been proposed for path planning and conflict avoidance. For the case of two intersecting flows, we introduce the concept of conflict touches, and a collaborative decentralized conflict resolution rule is then proposed and analyzed for two intersecting flows. The proposed rule is also able to resolved airborne conflicts that resulted from resolving another conflict via the domino effect. We study the safety conditions under the proposed conflict resolution and collision avoidance rule. Then, we use Lyapunov analysis to analytically prove the convergence of conflict resolution dynamics under the proposed rule. The analysis show that, under the proposed conflict resolution rule, the system of intersecting aircraft flows is guaranteed to converge to safe, conflict free, trajectories within a bounded time. Simulations are provided to verify the analytically derived conclusions and study the convergence of the conflict resolution dynamics at different encounter angles. Simulation results show that lateral deviations taken by aircraft in each flow, to resolve conflicts, are bounded, and aircraft converged to safe and conflict free trajectories, within a finite time.

Time-Resolved PIV for Space-Time Correlations in Hot Jets

NASA Technical Reports Server (NTRS)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is being used to characterize the decay of turbulence in jet flows a critical element for understanding the acoustic properties of the flow. A TR-PIV system, developed in-house at the NASA Glenn Research Center, is capable of acquiring planar PIV image frame pairs at up to 10 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

Resolvent analysis of exact coherent solutions

NASA Astrophysics Data System (ADS)

Rosenberg, Kevin; McKeon, Beverley

2017-11-01

Exact coherent solutions have been hypothesized to constitute the state-space skeleton of turbulent trajectories and thus are of interest as a means to better understand the underlying dynamics of turbulent flows. An asymptotic description of how these types of solutions self-sustain was provided by Hall & Sherwin. Here we offer a fully-nonlinear perspective on the self-sustainment of these solutions in terms of triadic scale interactions and use the resolvent framework of McKeon & Sharma to interpret these results from an input/output point of view. We analyze traveling wave solutions and periodic orbits in channel flow, and demonstrate how resolvent analysis can be used to obtain low-dimensional representations of these flows. We gratefully acknowledge funding from the AFOSR (FA9550-16-1-0361) and J.S. Park, M.D. Graham, and J.F. Gibson for providing data for the ECS solutions.

Experimental Characterization of the Jet Wiping Process

NASA Astrophysics Data System (ADS)

Mendez, Miguel Alfonso; Enache, Adriana; Gosset, Anne; Buchlin, Jean-Marie

2018-06-01

This paper presents an experimental characterization of the jet wiping process, used in continuous coating applications to control the thickness of a liquid coat using an impinging gas jet. Time Resolved Particle Image Velocimetry (TR-PIV) is used to characterize the impinging gas flow, while an automatic interface detection algorithm is developed to track the liquid interface at the impact. The study of the flow interaction is combined with time resolved 3D thickness measurements of the liquid film remaining after the wiping, via Time Resolved Light Absorption (TR-LAbs). The simultaneous frequency analysis of liquid and gas flows allows to correlate their respective instability, provide an experimental data set for the validation of numerical studies and allows for formulating a working hypothesis on the origin of the coat non-uniformity encountered in many jet wiping processes.

A Numerical Study on the Effects of Street‒canyon Aspect‒ratio on Reactive Pollutant Dispersion

NASA Astrophysics Data System (ADS)

Park, S. J.; Kim, J.

2014-12-01

In this study, the effects of street‒canyon aspect‒ratio on reactive pollutant dispersion were investigated using the coupled CFD‒chemistry model. For this, flow characteristics were analyzed first in street canyons with different aspect ratios and flow regimes were classified according to the building height. For each flow regime, dispersion characteristics were investigated in views of reactive pollutant concentration and VOCs‒NOX ratio. Finally, the relations between pollutant concentration and aspect ratio in urban street canyons were investigated. In the case of H/S = 1.0 (H is building height and S is street width), one clockwise‒rotating vortex appeared vertically and the reverse and outward flows were dominant near the street bottom. In the case of H/S = 2.0, two counter‒rotating vortices appeared vertically in the street canyon. The primary (secondary) vortex rotating clockwise (counterclockwise) was formed in upper (lower) layer. The flow patterns affected the reactive pollutant concentration in street canyons. As building height increased, mean concentration of NO decreased when one vortex was generated in street canyons and increased when two vortexes appeared in street canyons. O3 concentration showed almost contrasted tendency with those of NO because O3 was depleted by the NO titration.

Spatially Resolved Quantification of the Surface Reactivity of Solid Catalysts.

PubMed

Huang, Bing; Xiao, Li; Lu, Juntao; Zhuang, Lin

2016-05-17

A new property is reported that accurately quantifies and spatially describes the chemical reactivity of solid surfaces. The core idea is to create a reactivity weight function peaking at the Fermi level, thereby determining a weighted summation of the density of states of a solid surface. When such a weight function is defined as the derivative of the Fermi-Dirac distribution function at a certain non-zero temperature, the resulting property is the finite-temperature chemical softness, termed Fermi softness (SF ), which turns out to be an accurate descriptor of the surface reactivity. The spatial image of SF maps the reactive domain of a heterogeneous surface and even portrays morphological details of the reactive sites. SF analyses reveal that the reactive zones on a Pt3 Y(111) surface are the platinum sites rather than the seemingly active yttrium sites, and the reactivity of the S-dimer edge of MoS2 is spatially anisotropic. Our finding is of fundamental and technological significance to heterogeneous catalysis and industrial processes demanding rational design of solid catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acute Central Retinal Vein Occlusion Secondary to Reactive Thrombocytosis after Splenectomy

PubMed Central

Oncel Acir, Nursen; Borazan, Mehmet

2014-01-01

The diagnosis and treatment of central retinal vein occlusion was reported in a young patient. Central retinal vein occlusion was probably related to secondary to reactive thrombocytosis after splenectomy. The patient was treated with steroids for papilledema and administered coumadin and aspirin. The symptoms resolved, and the findings returned to normal within three weeks. Current paper emphasizes that, besides other well-known thrombotic events, reactive thrombocytosis after splenectomy may cause central retinal vein occlusion, which may be the principal symptom of this risky complication. Thus, it can be concluded that followup for thrombocytosis and antithrombotic treatment, when necessary, are essential for these cases. PMID:25276452

Reactive Transport in a Pipe in Soluble Rock: a Theoretical and Experimental Study

NASA Astrophysics Data System (ADS)

Li, W.; Opolot, M.; Sousa, R.; Einstein, H. H.

2015-12-01

Reactive transport processes within the dominant underground flow pathways such as fractures can lead to the widening or narrowing of rock fractures, potentially altering the flow and transport processes in the fractures. A flow-through experiment was designed to study the reactive transport process in a pipe in soluble rock to serve as a simplified representation of a fracture in soluble rock. Assumptions were made to formulate the problem as three coupled, one-dimensional partial differential equations: one for the flow, one for the transport and one for the radius change due to dissolution. Analytical and numerical solutions were developed to predict the effluent concentration and the change in pipe radius. The positive feedback of the radius increase is captured by the experiment and the numerical model. A comparison between the experiment and the simulation results demonstrates the validity of the analytical and numerical models.

Concept Demonstration of Dopant Selective Reactive Etching (DSRIE) in Silicon Carbide

NASA Technical Reports Server (NTRS)

Okojie, Robert S.

2015-01-01

Accurate quantification of combustor pressure dynamics for the primary purpose of experimental validation of computational fluid dynamics (CFD) codes requires the use of robust, reliable and sensitive pressure sensors that can resolve sub--pound-per-square-inch pressure levels in high temperature environments (i.e., combustor). The state of the art microfabricated piezoresistive silicon carbide (SiC) pressure sensors that we have developed are capable of operating reliably at 600 degrees Centigrade. This technology was used in support of the ARMD ISRP-ERA (NASA's Aeronautics Research Mission Directorate, Integrated System Research Project - Environmentally Responsible Aviation) program to quantify combustor thermoacoustic instabilities. The results showed that while the SiC pressure sensors survived the high temperature and measured instabilities, the diaphragm (force collector) was not thin enough to be sensitive in resolving sub-pound-per-square-inch pressures; 30 meters is the thinnest diaphragm achievable with conventional reactive ion etching (RIE) processes. Therefore, this precludes its use for sub-pound-per-square-inch pressure measurement with high fidelity. In order to effectively resolve sub-pound-per-square-inch pressures, a thinner more sensitive diaphragm (10 meters) is needed. To achieve this would require a new and innovative fabrication process technique.

Numerical optimization of Ignition and Growth reactive flow modeling for PAX2A

NASA Astrophysics Data System (ADS)

Baker, E. L.; Schimel, B.; Grantham, W. J.

1996-05-01

Variable metric nonlinear optimization has been successfully applied to the parameterization of unreacted and reacted products thermodynamic equations of state and reactive flow modeling of the HMX based high explosive PAX2A. The NLQPEB nonlinear optimization program has been recently coupled to the LLNL developed two-dimensional high rate continuum modeling programs DYNA2D and CALE. The resulting program has the ability to optimize initial modeling parameters. This new optimization capability was used to optimally parameterize the Ignition and Growth reactive flow model to experimental manganin gauge records. The optimization varied the Ignition and Growth reaction rate model parameters in order to minimize the difference between the calculated pressure histories and the experimental pressure histories.

Nuclear engine flow reactivity shim control

DOEpatents

Walsh, J.M.

1973-12-11

A nuclear engine control system is provided which automatically compensates for reactor reactivity uncertainties at the start of life and reactivity losses due to core corrosion during the reactor life in gas-cooled reactors. The coolant gas flow is varied automatically by means of specially provided control apparatus so that the reactor control drums maintain a predetermined steady state position throughout the reactor life. This permits the reactor to be designed for a constant drum position and results in a desirable, relatively flat temperature profile across the core. (Official Gazette)

Three-dimensional shape perception from chromatic orientation flows

PubMed Central

Zaidi, Qasim; Li, Andrea

2010-01-01

The role of chromatic information in 3-D shape perception is controversial. We resolve this controversy by showing that chromatic orientation flows are sufficient for accurate perception of 3-D shape. Chromatic flows required less cone contrast to convey shape than did achromatic flows, thus ruling out luminance artifacts as a problem. Luminance artifacts were also ruled out by a protanope’s inability to see 3-D shape from chromatic flows. Since chromatic orientation flows can only be extracted from retinal images by neurons that are responsive to color modulations and selective for orientation, the psychophysical results also resolve the controversy over the existence of such neurons. In addition, we show that identification of 3-D shapes from chromatic flows can be masked by luminance modulations, indicating that it is subserved by orientation-tuned neurons sensitive to both chromatic and luminance modulations. PMID:16961963

Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers

NASA Astrophysics Data System (ADS)

Kalpakli, Athanasia; Örlü, Ramis; Tillmark, Nils; Alfredsson, P. Henrik

2011-12-01

Turbulent pulsatile flows through pipe bends are prevalent in internal combustion engine components which consist of bent pipe sections and branching conduits. Nonetheless, most of the studies related to pulsatile flows in pipe bends focus on incompressible, low Womersley and low Dean number flows, primarily because they aim in modeling blood flow, while internal combustion engine related flows have mainly been addressed in terms of integral quantities and consist of single point measurements. The present study aims at bridging the gap between these two fields by means of time-resolved stereoscopic particle image velocimetry measurements in a pipe bend with conditions that are close to those encountered in exhaust manifolds. The time/phase-resolved three-dimensional cross-sectional flow-field 3 pipe diameters downstream the pipe bend is captured and the interplay between different secondary motions throughout a pulse cycle is discussed.

The state of the art of conventional flow visualization techniques for wind tunnel testing

NASA Technical Reports Server (NTRS)

Settles, G. S.

1982-01-01

Conventional wind tunnel flow visualization techniques which consist of surface flow methods, tracers, and optical methods are presented. Different surface flow methods are outlined: (1) liquid films (oil and fluorescent dye and UV lighting, renewable film via porous dispenser in model, volatile carrier fluid, cryogenic colored oil dots, oil film interferometry); (2) reactive surface treatment (reactive gas injection, reversible dye); (3) transition and heat transfer detectors (evaporation, sublimation, liquid crystals, phase change paints, IR thermography); and (4) tufts (fluorescent mini tufts, cryogenic suitability). Other methods are smoke wire techniques, vapor screens, and optical methods.

First continuous flow analysis results from the Greenland ReCAP project

NASA Astrophysics Data System (ADS)

Kjær, Helle Astrid

2016-04-01

The new Renland ice core was drilled in summer 2015 in Greenland and measured by means of Continuous flow analysis during the last 3 months of 2015. The Renland ice core was obtained as part of the ReCAP project, extending 584.11 meters to the bottom of the Renland ice cap located in east Greenland. The unique position on a mountain saddle above 2000 meters altitude, but close to the coast, ensures that the Renland ice core offers high accumulation, but also reaches far back in time. Preliminary results show that the record holds ice from the past warm interglacial period, the Eemian. The record was analyzed for multiple elements including the forest fire tracers NH4+ and black carbon, insoluble dust particles by means of Abakus laser particle counter and the dust ion Ca2+, sea salt Na and acidity useful for finding volcanic layers to date the core. Further H2O2, and the nutrients Fe and dissolved reactive phosphorus was analyzed as well as the temperature indicator δ18O all by means of continuous flow analysis (CFA). The core was melted at a rate of 3 cm/min providing a temporal resolution for most components determined sufficient to resolve annual layers through the Holocene. The glacial section is strongly thinned, but nonetheless due to the high resolution of the measurements all DO events could be identified. Below the glacial section another ˜20 meters of warm Eemian ice have been analysed. Here we present the first chemistry results as obtained by continuous flow analysis (CFA).

Microplasma array patterning of reactive oxygen and nitrogen species onto polystyrene

NASA Astrophysics Data System (ADS)

Szili, Endre J.; Dedrick, James; Oh, Jun-Seok; Bradley, James W.; Boswell, Roderick W.; Charles, Christine; Short, Robert D.; Al-Bataineh, Sameer A.

2017-02-01

We investigate an approach for the patterning of reactive oxygen and nitrogen species (RONS) onto polystyrene using atmospheric-pressure microplasma arrays. The spectrally integrated and time-resolved optical emission from the array is characterised with respect to the applied voltage, applied-voltage frequency and pressure; and the array is used to achieve spatially resolved modification of polystyrene at three pressures: 500 Torr, 760 Torr and 1000 Torr. As determined by time-of-flight secondary ion mass spectrometry (ToF-SIMS), regions over which surface modification occurs are clearly restricted to areas that are exposed to individual microplasma cavities. Analysis of the negative-ion ToF-SIMS mass spectra from the centre of the modified microspots shows that the level of oxidation is dependent on the operating pressure, and closely correlated with the spatial distribution of the optical emission. The functional groups that are generated by the microplasma array on the polystyrene surface are shown to readily participate in an oxidative reaction in phosphate buffered saline solution (pH 7.4). Patterns of oxidised and chemically reactive functionalities could potentially be applied to the future development of biomaterial surfaces, where spatial control over biomolecule or cell function is needed.

Shock-induced mechanochemistry in heterogeneous reactive powder mixtures

NASA Astrophysics Data System (ADS)

Gonzales, Manny; Gurumurthy, Ashok; Kennedy, Gregory; Neel, Christopher; Gokhale, Arun; Thadhani, Naresh

The bulk response of compacted powder mixtures subjected to high-strain-rate loading conditions in various configurations is manifested from behavior at the meso-scale. Simulations at the meso-scale can provide an additional confirmation of the possible origins of the observed response. This work investigates the bulk dynamic response of Ti +B +Al reactive powder mixtures under two extreme loading configurations - uniaxial stress and strain loading - leveraging highly-resolved in-situ measurements and meso-scale simulations. Modified rod-on-anvil impact tests on a reactive pellet demonstrate an optimized stoichiometry promoting reaction in Ti +B +Al. Encapsulated powders subjected to shock compression via flyer plate tests provide possible evidence of a shock-induced reaction at high pressures. Meso-scale simulations of the direct experimental configurations employing highly-resolved microstructural features of the Ti +B compacted mixture show complex inhomogeneous deformation responses and reveal the importance of meso-scale features such as particle size and morphology and their effects on the measured response. Funding is generously provided by DTRA through Grant No. HDTRA1-10-1-0038 (Dr. Su Peiris - Program Manager) and by the SMART (AFRL Wright Patterson AFB) and NDSEG fellowships (High Performance Computing and Modernization Office).

Scale separation for multi-scale modeling of free-surface and two-phase flows with the conservative sharp interface method

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

Han, L.H., E-mail: Luhui.Han@tum.de; Hu, X.Y., E-mail: Xiangyu.Hu@tum.de; Adams, N.A., E-mail: Nikolaus.Adams@tum.de

In this paper we present a scale separation approach for multi-scale modeling of free-surface and two-phase flows with complex interface evolution. By performing a stimulus-response operation on the level-set function representing the interface, separation of resolvable and non-resolvable interface scales is achieved efficiently. Uniform positive and negative shifts of the level-set function are used to determine non-resolvable interface structures. Non-resolved interface structures are separated from the resolved ones and can be treated by a mixing model or a Lagrangian-particle model in order to preserve mass. Resolved interface structures are treated by the conservative sharp-interface model. Since the proposed scale separationmore » approach does not rely on topological information, unlike in previous work, it can be implemented in a straightforward fashion into a given level set based interface model. A number of two- and three-dimensional numerical tests demonstrate that the proposed method is able to cope with complex interface variations accurately and significantly increases robustness against underresolved interface structures.« less

Approximation of traveling wave solutions in wall-bounded flows using resolvent modes

NASA Astrophysics Data System (ADS)

McKeon, Beverley; Graham, Michael; Moarref, Rashad; Park, Jae Sung; Sharma, Ati; Willis, Ashley

2014-11-01

Significant recent attention has been devoted to computing and understanding exact traveling wave solutions of the Navier-Stokes equations. These solutions can be interpreted as the state-space skeleton of turbulence and are attractive benchmarks for studying low-order models of wall turbulence. Here, we project such solutions onto the velocity response (or resolvent) modes supplied by the gain-based resolvent analysis outlined by McKeon & Sharma (JFM, 2010). We demonstrate that in both pipe (Pringle et al., Phil. Trans. R. Soc. A, 2009) and channel (Waleffe, JFM, 2001) flows, the solutions can be well-described by a small number of resolvent modes. Analysis of the nonlinear forcing modes sustaining these solutions reveals the importance of small amplitude forcing, consistent with the large amplifications admitted by the resolvent operator. We investigate the use of resolvent modes as computationally cheap ``seeds'' for the identification of further traveling wave solutions. The support of AFOSR under Grants FA9550-09-1-0701, FA9550-12-1-0469, FA9550-11-1-0094 and FA9550-14-1-0042 (program managers Rengasamy Ponnappan, Doug Smith and Gregg Abate) is gratefully acknowledged.

Assessment of the Partially Resolved Numerical Simulation (PRNS) Approach in the National Combustion Code (NCC) for Turbulent Nonreacting and Reacting Flows

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Liu, Nan-Suey

2008-01-01

This paper describes an approach which aims at bridging the gap between the traditional Reynolds-averaged Navier-Stokes (RANS) approach and the traditional large eddy simulation (LES) approach. It has the characteristics of the very large eddy simulation (VLES) and we call this approach the partially-resolved numerical simulation (PRNS). Systematic simulations using the National Combustion Code (NCC) have been carried out for fully developed turbulent pipe flows at different Reynolds numbers to evaluate the PRNS approach. Also presented are the sample results of two demonstration cases: nonreacting flow in a single injector flame tube and reacting flow in a Lean Direct Injection (LDI) hydrogen combustor.

Scaling laws and reduced-order models for mixing and reactive-transport in heterogeneous anisotropic porous media

NASA Astrophysics Data System (ADS)

Mudunuru, M. K.; Karra, S.; Nakshatrala, K. B.

2016-12-01

Fundamental to enhancement and control of the macroscopic spreading, mixing, and dilution of solute plumes in porous media structures is the topology of flow field and underlying heterogeneity and anisotropy contrast of porous media. Traditionally, in literature, the main focus was limited to the shearing effects of flow field (i.e., flow has zero helical density, meaning that flow is always perpendicular to vorticity vector) on scalar mixing [2]. However, the combined effect of anisotropy of the porous media and the helical structure (or chaotic nature) of the flow field on the species reactive-transport and mixing has been rarely studied. Recently, it has been experimentally shown that there is an irrefutable evidence that chaotic advection and helical flows are inherent in porous media flows [1,2]. In this poster presentation, we present a non-intrusive physics-based model-order reduction framework to quantify the effects of species mixing in-terms of reduced-order models (ROMs) and scaling laws. The ROM framework is constructed based on the recent advancements in non-negative formulations for reactive-transport in heterogeneous anisotropic porous media [3] and non-intrusive ROM methods [4]. The objective is to generate computationally efficient and accurate ROMs for species mixing for different values of input data and reactive-transport model parameters. This is achieved by using multiple ROMs, which is a way to determine the robustness of the proposed framework. Sensitivity analysis is performed to identify the important parameters. Representative numerical examples from reactive-transport are presented to illustrate the importance of the proposed ROMs to accurately describe mixing process in porous media. [1] Lester, Metcalfe, and Trefry, "Is chaotic advection inherent to porous media flow?," PRL, 2013. [2] Ye, Chiogna, Cirpka, Grathwohl, and Rolle, "Experimental evidence of helical flow in porous media," PRL, 2015. [3] Mudunuru, and Nakshatrala, "On enforcing maximum principles and achieving element-wise species balance for advection-diffusion-reaction equations under the finite element method," JCP, 2016. [4] Quarteroni, Manzoni, and Negri. "Reduced Basis Methods for Partial Differential Equations: An Introduction," Springer, 2016.

Guar gum coupled microscale ZVI for in situ treatment of CAHs: continuous-flow column study.

PubMed

Velimirovic, Milica; Simons, Queenie; Bastiaens, Leen

2014-01-30

A column study was performed under in situ conditions to evaluate to which extend the inactivation of the microscale zerovalent iron (mZVI) by guar gum occurs under continuous flow conditions. Five aquifer containing columns were set up under different conditions. Efficient removal of trichloroethene was observed for the column amended by mZVI. Stabilization of the mZVI with guar gum led to slightly reduced activity. More reduced reactivity was observed in the poisoned column containing guar gum stabilized mZVI. This confirms that soil microorganisms can degrade guar gum and that subsequent removal of the oligosaccharides by the groundwater flow (flushing effect) can reactivate the mZVI. After more than six months of continuous operation the columns were dismantled. DNA-based qPCR analysis revealed that mZVI does not significantly affect the bacterial community, while guar gum stabilized mZVI particles can even induce bacterial growth. Overall, this study suggests that the temporarily decreased mZVI reactivity due to guar gum, has a rather limited impact on the performance of in situ reactive zones. The presence of guar gum slightly reduced the reactivity of iron, but also slowed down the iron corrosion rate which prolongs the life time of reactive zone. Copyright © 2013 Elsevier B.V. All rights reserved.

Highly reactive light-dependent monoterpenes in the Amazon

NASA Astrophysics Data System (ADS)

Jardine, A. B.; Jardine, K. J.; Fuentes, J. D.; Martin, S. T.; Martins, G.; Durgante, F.; Carneiro, V.; Higuchi, N.; Manzi, A. O.; Chambers, J. Q.

2015-03-01

Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 profiles. Leaf level emissions of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis.

Use of three-dimensional time-resolved phase-contrast magnetic resonance imaging with vastly undersampled isotropic projection reconstruction to assess renal blood flow in a renal cell carcinoma patient treated with sunitinib: a case report.

PubMed

Takayama, Tatsuya; Takehara, Yasuo; Sugiyama, Masataka; Sugiyama, Takayuki; Ishii, Yasuo; Johnson, Kevin E; Wieben, Oliver; Wakayama, Tetsuya; Sakahara, Harumi; Ozono, Seiichiro

2014-08-14

New imaging modalities to assess the efficacy of drugs that have molecular targets remain under development. Here, we describe for the first time the use of time-resolved three-dimensional phase-contrast magnetic resonance imaging to monitor changes in blood supply to a tumor during sunitinib treatment in a patient with localized renal cell carcinoma. A 43-year-old Japanese woman with a tumor-bearing but functional single kidney presented at our hospital in July 2012. Computed tomography and magnetic resonance imaging revealed a cT1aN0M0 renal cell carcinoma embedded in the upper central region of the left kidney. She was prescribed sunitinib as neoadjuvant therapy for 8 months, and then underwent partial nephrectomy. Tumor monitoring during this time was done using time-resolved three-dimensional phase-contrast magnetic resonance imaging, a recent technique which specifically measures blood flow in the various vessels of the kidney. This imaging allowed visualization of the redistribution of renal blood flow during treatment, and showed that flow to the tumor was decreased and flows to other areas increased. Of note, this change occurred in the absence of any change in tumor size. The ability of time-resolved three-dimensional phase-contrast magnetic resonance imaging to provide quantitative information on blood supply to tumors may be useful in monitoring the efficacy of sunitinib treatment.

Development of a Rayleigh Scattering Diagnostic for Time-Resolved Gas Flow Velocity, Temperature, and Density Measurements in Aerodynamic Test Facilities

NASA Technical Reports Server (NTRS)

Mielke, Amy F.; Elam, Kristie A.; Sung, Chih-Jen

2007-01-01

A molecular Rayleigh scattering technique is developed to measure time-resolved gas velocity, temperature, and density in unseeded turbulent flows at sampling rates up to 32 kHz. A high power continuous-wave laser beam is focused at a point in an air flow field and Rayleigh scattered light is collected and fiber-optically transmitted to the spectral analysis and detection equipment. The spectrum of the light, which contains information about the temperature and velocity of the flow, is analyzed using a Fabry-Perot interferometer. Photomultiplier tubes operated in the photon counting mode allow high frequency sampling of the circular interference pattern to provide time-resolved flow property measurements. An acoustically driven nozzle flow is studied to validate velocity fluctuation measurements, and an asymmetric oscillating counterflow with unequal enthalpies is studied to validate the measurement of temperature fluctuations. Velocity fluctuations are compared with constant temperature anemometry measurements and temperature fluctuations are compared with constant current anemometry measurements at the same locations. Time-series and power spectra of the temperature and velocity measurements are presented. A numerical simulation of the light scattering and detection process was developed and compared with experimental data for future use as an experiment design tool.

Towards a Viscous Wall Model for Immersed Boundary Methods

NASA Technical Reports Server (NTRS)

Brehm, Christoph; Barad, Michael F.; Kiris, Cetin C.

2016-01-01

Immersed boundary methods are frequently employed for simulating flows at low Reynolds numbers or for applications where viscous boundary layer effects can be neglected. The primary shortcoming of Cartesian mesh immersed boundary methods is the inability of efficiently resolving thin turbulent boundary layers in high-Reynolds number flow application. The inefficiency of resolving the thin boundary is associated with the use of constant aspect ratio Cartesian grid cells. Conventional CFD approaches can efficiently resolve the large wall normal gradients by utilizing large aspect ratio cells near the wall. This paper presents different approaches for immersed boundary methods to account for the viscous boundary layer interaction with the flow-field away from the walls. Different wall modeling approaches proposed in previous research studies are addressed and compared to a new integral boundary layer based approach. In contrast to common wall-modeling approaches that usually only utilize local flow information, the integral boundary layer based approach keeps the streamwise history of the boundary layer. This allows the method to remain effective at much larger y+ values than local wall modeling approaches. After a theoretical discussion of the different approaches, the method is applied to increasingly more challenging flow fields including fully attached, separated, and shock-induced separated (laminar and turbulent) flows.

Time-resolved flow reconstruction with indirect measurements using regression models and Kalman-filtered POD ROM

NASA Astrophysics Data System (ADS)

Leroux, Romain; Chatellier, Ludovic; David, Laurent

2018-01-01

This article is devoted to the estimation of time-resolved particle image velocimetry (TR-PIV) flow fields using a time-resolved point measurements of a voltage signal obtained by hot-film anemometry. A multiple linear regression model is first defined to map the TR-PIV flow fields onto the voltage signal. Due to the high temporal resolution of the signal acquired by the hot-film sensor, the estimates of the TR-PIV flow fields are obtained with a multiple linear regression method called orthonormalized partial least squares regression (OPLSR). Subsequently, this model is incorporated as the observation equation in an ensemble Kalman filter (EnKF) applied on a proper orthogonal decomposition reduced-order model to stabilize it while reducing the effects of the hot-film sensor noise. This method is assessed for the reconstruction of the flow around a NACA0012 airfoil at a Reynolds number of 1000 and an angle of attack of {20}°. Comparisons with multi-time delay-modified linear stochastic estimation show that both the OPLSR and EnKF combined with OPLSR are more accurate as they produce a much lower relative estimation error, and provide a faithful reconstruction of the time evolution of the velocity flow fields.

Time resolved flow-field measurements of a turbulent mixing layer over a rectangular cavity

NASA Astrophysics Data System (ADS)

Bian, Shiyao; Driscoll, James F.; Elbing, Brian R.; Ceccio, Steven L.

2011-07-01

High Reynolds number, low Mach number, turbulent shear flow past a rectangular, shallow cavity has been experimentally investigated with the use of dual-camera cinematographic particle image velocimetry (CPIV). The CPIV had a 3 kHz sampling rate, which was sufficient to monitor the time evolution of large-scale vortices as they formed, evolved downstream and impinged on the downstream cavity wall. The time-averaged flow properties (velocity and vorticity fields, streamwise velocity profiles and momentum and vorticity thickness) were in agreement with previous cavity flow studies under similar operating conditions. The time-resolved results show that the separated shear layer quickly rolled-up and formed eddies immediately downstream of the separation point. The vortices convect downstream at approximately half the free-stream speed. Vorticity strength intermittency as the structures approach the downstream edge suggests an increase in the three-dimensionality of the flow. Time-resolved correlations reveal that the in-plane coherence of the vortices decays within 2-3 structure diameters, and quasi-periodic flow features are present with a vortex passage frequency of ~1 kHz. The power spectra of the vertical velocity fluctuations within the shear layer revealed a peak at a non-dimensional frequency corresponding to that predicted using linear, inviscid instability theory.

40 CFR 1065.340 - Diluted exhaust flow (CVS) calibration.

Code of Federal Regulations, 2013 CFR

2013-07-01

... initial CVS installation and whenever corrective action does not resolve a failure to meet the diluted... such as a subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice...

40 CFR 1065.340 - Diluted exhaust flow (CVS) calibration.

Code of Federal Regulations, 2012 CFR

2012-07-01

... initial CVS installation and whenever corrective action does not resolve a failure to meet the diluted... such as a subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice...

40 CFR 1065.340 - Diluted exhaust flow (CVS) calibration.

Code of Federal Regulations, 2014 CFR

2014-07-01

... initial CVS installation and whenever corrective action does not resolve a failure to meet the diluted... such as a subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice...

Comparison of reactivity in a flow reactor and a single cylinder engine

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

Natelson, Robert H.; Johnson, Rodney O.; Kurman, Matthew S.

2010-10-15

The relative reactivity of 2:1:1 and 1:1:1 mixtures of n-decane:n-butylcyclohexane:n-butylbenzene and an average sample of JP-8 were evaluated in a single cylinder engine and compared to results obtained in a pressurized flow reactor. At compression ratios of 14:1, 15:1, and 16:1, inlet temperature of 500 K, inlet pressure of 0.1 MPa, equivalence ratio of 0.23, and engine speed of 800 RPM, the autoignition delay times were, from shortest to longest, the 2:1:1, followed by the 1:1:1, and then the JP-8. This order corresponded with recent results in a pressurized flow reactor, where the preignition oxidation chemistry was monitored at temperaturesmore » of 600-800 K, 0.8 MPa pressure, and an equivalence ratio of 0.30, and where the preignition reactivity from highest to lowest was the 2:1:1, followed by the 1:1:1, and the JP-8. This shows that the relative reactivity at low temperatures in the flow reactor tracks the autoignition tendencies in the engine for these particular fuels. (author) the computed experimental error. (author)« less

4D blood flow mapping using SPIM-microPIV in the developing zebrafish heart

NASA Astrophysics Data System (ADS)

Zickus, Vytautas; Taylor, Jonathan M.

2018-02-01

Fluid-structure interaction in the developing heart is an active area of research in developmental biology. However, investigation of heart dynamics is mostly limited to computational uid dynamics simulations using heart wall structure information only, or single plane blood ow information - so there is a need for 3D + time resolved data to fully understand cardiac function. We present an imaging platform combining selective plane illumination microscopy (SPIM) with micro particle image velocimetry (μPIV) to enable 3D-resolved flow mapping in a microscopic environment, free from many of the sources of error and bias present in traditional epi uorescence-based μPIV systems. By using our new system in conjunction with optical heart beat synchronization, we demonstrate the ability obtain non-invasive 3D + time resolved blood flow measurements in the heart of a living zebrafish embryo.

Magnetomotive laser speckle imaging

PubMed Central

Kim, Jeehyun; Oh, Junghwan; Choi, Bernard

2010-01-01

Laser speckle imaging (LSI) involves analysis of reflectance images collected during coherent optical excitation of an object to compute wide-field maps of tissue blood flow. An intrinsic limitation of LSI for resolving microvascular architecture is that its signal depends on relative motion of interrogated red blood cells. Hence, with LSI, small-diameter arterioles, venules, and capillaries are difficult to resolve due to the slow flow speeds associated with such vasculature. Furthermore, LSI characterization of subsurface blood flow is subject to blurring due to scattering, further limiting the ability of LSI to resolve or quantify blood flow in small vessels. Here, we show that magnetic activation of superparamagnetic iron oxide (SPIO) nanoparticles modulate the speckle flow index (SFI) values estimated from speckle contrast analysis of collected images. With application of an ac magnetic field to a solution of stagnant SPIO particles, an apparent increase in SFI is induced. Furthermore, with application of a focused dc magnetic field, a focal decrease in SFI values is induced. Magnetomotive LSI may enable wide-field mapping of suspicious tissue regions, enabling subsequent high-resolution optical interrogation of these regions. Similarly, subsequent photoactivation of intravascular SPIO nanoparticles could then be performed to induce selective photothermal destruction of unwanted vasculature. PMID:20210436

Transitional hemodynamics in intracranial aneurysms - Comparative velocity investigations with high resolution lattice Boltzmann simulations, normal resolution ANSYS simulations, and MR imaging.

PubMed

Jain, Kartik; Jiang, Jingfeng; Strother, Charles; Mardal, Kent-André

2016-11-01

Blood flow in intracranial aneurysms has, until recently, been considered to be disturbed but still laminar. Recent high resolution computational studies have demonstrated, in some situations, however, that the flow may exhibit high frequency fluctuations that resemble weakly turbulent or transitional flow. Due to numerous assumptions required for simplification in computational fluid dynamics (CFD) studies, the occurrence of these events, in vivo, remains unsettled. The detection of these fluctuations in aneurysmal blood flow, i.e., hemodynamics by CFD, poses additional challenges as such phenomena cannot be captured in clinical data acquisition with magnetic resonance (MR) due to inadequate temporal and spatial resolutions. The authors' purpose was to address this issue by comparing results from highly resolved simulations, conventional resolution laminar simulations, and MR measurements, identify the differences, and identify their causes. Two aneurysms in the basilar artery, one with disturbed yet laminar flow and the other with transitional flow, were chosen. One set of highly resolved direct numerical simulations using the lattice Boltzmann method (LBM) and another with adequate resolutions under laminar flow assumption were conducted using a commercially available ANSYS Fluent solver. The velocity fields obtained from simulation results were qualitatively and statistically compared against each other and with MR acquisition. Results from LBM, ANSYS Fluent, and MR agree well qualitatively and quantitatively for one of the aneurysms with laminar flow in which fluctuations were <80 Hz. The comparisons for the second aneurysm with high fluctuations of > ∼ 600 Hz showed vivid differences between LBM, ANSYS Fluent, and magnetic resonance imaging. After ensemble averaging and down-sampling to coarser space and time scales, these differences became minimal. A combination of MR derived data and CFD can be helpful in estimating the hemodynamic environment of intracranial aneurysms. Adequately resolved CFD would suffice gross assessment of hemodynamics, potentially in a clinical setting, and highly resolved CFD could be helpful in a detailed and retrospective understanding of the physiological mechanisms.

A stochastic two-scale model for pressure-driven flow between rough surfaces

PubMed Central

Larsson, Roland; Lundström, Staffan; Wall, Peter; Almqvist, Andreas

2016-01-01

Seal surface topography typically consists of global-scale geometric features as well as local-scale roughness details and homogenization-based approaches are, therefore, readily applied. These provide for resolving the global scale (large domain) with a relatively coarse mesh, while resolving the local scale (small domain) in high detail. As the total flow decreases, however, the flow pattern becomes tortuous and this requires a larger local-scale domain to obtain a converged solution. Therefore, a classical homogenization-based approach might not be feasible for simulation of very small flows. In order to study small flows, a model allowing feasibly-sized local domains, for really small flow rates, is developed. Realization was made possible by coupling the two scales with a stochastic element. Results from numerical experiments, show that the present model is in better agreement with the direct deterministic one than the conventional homogenization type of model, both quantitatively in terms of flow rate and qualitatively in reflecting the flow pattern. PMID:27436975

Atomic oxygen production scaling in a nanosecond-pulsed externally grounded dielectric barrier plasma jet

NASA Astrophysics Data System (ADS)

Sands, Brian; Schmidt, Jacob; Ganguly, Biswa; Scofield, James

2014-10-01

Atomic oxygen production is studied in a capillary dielectric barrier plasma jet that is externally grounded and driven with a 20-ns risetime positive unipolar pulsed voltage at pulse repetition rates up to 25 kHz. The power coupled to the discharge can be easily increased by increasing the pulse repetition rate. At a critical turnover frequency, determined by the net energy density coupled to the discharge, the plasma chemistry abruptly changes. This is indicated by increased plasma conductance and a transition in reactive oxygen species production from an ozone-dominated production regime below the turnover frequency to atomic-oxygen-dominated production at higher pulse rates. Here, we characterize atomic oxygen production scaling using spatially- and temporally-resolved two-photon absorption laser-induced-fluorescence (TALIF). Quantitative results are obtained via calibration with xenon using a similar laser excitation and collection system. These results are compared with quantitative ozone and discharge power measurements using a helium gas flow with oxygen admixtures up to 3%.

Time Resolved PIV for Space-Time Correlations in Hot Jets

NASA Technical Reports Server (NTRS)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows -- a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number

Time Resolved Stereo Particle Image Velocimetry Measurements of the Instabilities Downstream of a Backward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Yao, Chung-Sheng

2017-01-01

Time-resolved particle image velocimetry (TRPIV) measurements are performed down-stream of a swept backward-facing step, with a height of 49% of the boundary-layer thickness. The results agree well qualitatively with previously reported hotwire measurements, though the amplitudes of the fluctuating components measured using TRPIV are higher. Nonetheless, the low-amplitude instabilities in the flow are fairly well resolved using TR- PIV. Proper orthogonal decomposition is used to study the development of the traveling cross flow and Tollmien-Schlichting (TS) instabilities downstream of the step and to study how they interact to form the large velocity spikes that ultimately lead to transition. A secondary mode within the traveling cross flow frequency band develops with a wavelength close to that of the stationary cross flow instability, so that at a certain point in the phase, it causes an increase in the spanwise modulation initially caused by the stationary cross flow mode. This increased modulation leads to an increase in the amplitude of the TS mode, which, itself, is highly modulated through interactions with the stationary cross flow. When the traveling cross flow and TS modes align in time and space, the large velocity spikes occur. Thus, these three instabilities, which are individually of low amplitude when the spikes start to occur (U'rms/Ue <0.03), interact and combine to cause a large flow disturbance that eventually leads to transition.

Simulations of reactive transport and precipitation with smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Tartakovsky, Alexandre M.; Meakin, Paul; Scheibe, Timothy D.; Eichler West, Rogene M.

2007-03-01

A numerical model based on smoothed particle hydrodynamics (SPH) was developed for reactive transport and mineral precipitation in fractured and porous materials. Because of its Lagrangian particle nature, SPH has several advantages for modeling Navier-Stokes flow and reactive transport including: (1) in a Lagrangian framework there is no non-linear term in the momentum conservation equation, so that accurate solutions can be obtained for momentum dominated flows and; (2) complicated physical and chemical processes such as surface growth due to precipitation/dissolution and chemical reactions are easy to implement. In addition, SPH simulations explicitly conserve mass and linear momentum. The SPH solution of the diffusion equation with fixed and moving reactive solid-fluid boundaries was compared with analytical solutions, Lattice Boltzmann [Q. Kang, D. Zhang, P. Lichtner, I. Tsimpanogiannis, Lattice Boltzmann model for crystal growth from supersaturated solution, Geophysical Research Letters, 31 (2004) L21604] simulations and diffusion limited aggregation (DLA) [P. Meakin, Fractals, scaling and far from equilibrium. Cambridge University Press, Cambridge, UK, 1998] model simulations. To illustrate the capabilities of the model, coupled three-dimensional flow, reactive transport and precipitation in a fracture aperture with a complex geometry were simulated.

Quantum-state-resolved reactivity of overtone excited CH 4 on Ni(111): Comparing experiment and theory

DOE PAGES

Hundt, P. Morten; van Reijzen, Maarten E.; Beck, Rainer D.; ...

2017-02-07

Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH 4 on Ni(111). IR-IR double resonance excitation in a molecular beam was used to prepare CH 4 in three different vibrational symmetry components A 1, E, and F 2 of the 2ν 32 antisymmetric stretch overtone vibration as well as in the ν1+ν3 symmetric plus antisymmetric C-H stretch combination band of F 2 symmetry. We measured the quantum state specific dissociation probability S 0 (sticking coefficient) for each of the four vibrational states by detecting chemisorbed carbon on Ni(111)more » as the product of CH 4 dissociation by Auger electron spectroscopy. We also observe strong mode specificity, where S 0 for the most reactive state ν 1+ν 3 is an order of magnitude higher than for the least reactive, more energetic 2ν 3-E state. Our first principles quantum scattering calculations show that as molecules in the ν1 state approach the surface, the vibrational amplitude becomes localized on the reacting C-H bond, making them very reactive. We found that this behavior results from the weakening of the reacting C-H bond as the molecule approaches the surface, decoupling its motion from the three non-reacting C-H stretches. Similarly, we find that overtone normal mode states with more ν 1 character are more reactive: S 0(2ν 1) > S 0(ν 1+ν 3) > S 0(2ν 3). The 2ν 3 eigenstates excited in the experiment can be written as linear combinations of these normal mode states. The highly reactive 2ν 1 and ν 1+ν 3 normal modes, being of A 1 and F 2 symmetry, can contribute to the 2ν 3-A 1 and 2ν 3-F 2 eigenstates, respectively, boosting their reactivity over the E component, which contains no ν 1 character due to symmetry.« less

Fictitious domain method for fully resolved reacting gas-solid flow simulation

NASA Astrophysics Data System (ADS)

Zhang, Longhui; Liu, Kai; You, Changfu

2015-10-01

Fully resolved simulation (FRS) for gas-solid multiphase flow considers solid objects as finite sized regions in flow fields and their behaviours are predicted by solving equations in both fluid and solid regions directly. Fixed mesh numerical methods, such as fictitious domain method, are preferred in solving FRS problems and have been widely researched. However, for reacting gas-solid flows no suitable fictitious domain numerical method has been developed. This work presents a new fictitious domain finite element method for FRS of reacting particulate flows. Low Mach number reacting flow governing equations are solved sequentially on a regular background mesh. Particles are immersed in the mesh and driven by their surface forces and torques integrated on immersed interfaces. Additional treatments on energy and surface reactions are developed. Several numerical test cases validated the method and a burning carbon particles array falling simulation proved the capability for solving moving reacting particle cluster problems.

Effect of reactivity loss on apparent reaction order of burning char particles

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

Murphy, Jeffrey J.; Shaddix, Christopher R.

Considerable debate still exists in the char combustion community over the expected and observed reaction orders of carbon reacting with oxygen. In particular, very low values of the reaction order (approaching zero) are commonly observed in char combustion experiments. These observations appear to conflict with porous catalyst theory as first expressed by Thiele, which suggests that the apparent reaction order must be greater than 0.5. In this work, we propose that this conflict may be resolved by considering the decrease in char reactivity with burnout due to ash effects, thermal annealing, or other phenomena. Specifically, the influence of ash dilutionmore » of the available surface area on the apparent reaction order is explored. Equations describing the ash dilution effect are combined with a model for particle burnout based on single-film nth-order Arrhenius char combustion and yield an analytical expression for the effective reaction order. When this expression is applied for experimental conditions reflecting combustion of individual pulverized coal particles in an entrained flow reactor, the apparent reaction order is shown to be lower than the inherent char matrix reaction order, even for negligible extents of char conversion. As char conversion proceeds and approaches completion, the apparent reaction order drops precipitously past zero to negative values. Conversely, the inclusion of the ash dilution model has little effect on the char conversion profile or char particle temperature until significant burnout has occurred. Taken together, these results suggest that the common experimental observation of low apparent reaction orders during char combustion is a consequence of the lack of explicit modeling of the decrease in char reactivity with burnout. (author)« less

Magnesite Dissolution Rates Across Scales: Role of Spatial Heterogeneity, Equilibrium Lengths, and Reactive Time Scales

NASA Astrophysics Data System (ADS)

Wen, H.; Li, L.

2017-12-01

This work develops a general rate law for magnesite dissolution in heterogeneous media under variable flow and length conditions, expanding the previous work under one particular flow and length conditions (Wen and Li, 2017). We aim to answer: 1) How does spatial heterogeneity influence the time and length scales to reach equilibrium? 2) How do relative timescales of advection, diffusion/dispersion, and reactions influence dissolution rates under variable flow and length conditions? We carried out 640 Monte-Carlo numerical experiments of magnesite dissolution within quartz matrix with heterogeneity characterized by permeability variance and correlation length under a range of length and flow velocity. A rate law Rhete = kAT(1-exp(τeq,m/τa))(1-exp(- Lβ))^α was developed. The former part is rates in equivalent homogeneous media kAT(1-exp(τeq,m/τa)), depending on rate constant k, magnesite surface area AT, and relative timescales of reactions τeq,m and advection τa. The latter term (1-exp(- Lβ))^α is the heterogeneity factor χ that quantifies the deviation of heterogeneous media from its homogeneous counterpart. The term has a scaling factor, called reactive transport number β=τa/(τad,r+τeq,m), for domain length L, and the geostatistical characteristics of heterogeneity α. The β quantifies the relative timescales of advection at the domain scale τa versus the advective-diffusive-dispersive transport time out of reactive zones τad,r and reaction time τeq,m. The χ is close to 1 and is insignificant under long residence time conditions (low flow velocity and / or long length) where the residence time is longer than the time needed for Mg to dissolve and transport out of reactive zones (τad,r+τeq,m) so that equilibrium is reached and homogenization occurs. In contrast, χ deviates from 1 and is significant only when β is small, which occurs at short length or fast flow where timescales of reactive transport in reactive zones are much longer than the global residence time so that reactive transport is the limiting step. These findings demonstrate that dissolution rates in heterogeneous media reach asymptotic values in homogeneous media at "sufficiently" long lengths. Wen, H. and Li, L. (2017) An upscaled rate law for magnesite dissolution in heterogeneous porous media. Geochimica et Cosmochimica Acta 210, 289-305.

Simulating dispersion in porous media and the influence of segmentation on stagnancy in carbonates

NASA Astrophysics Data System (ADS)

Gray, F.; Cen, J.; Shah, S. M.; Crawshaw, J. P.; Boek, E. S.

2016-11-01

Understanding the transport of chemical components in porous media is fundamentally important to many reservoir processes such as contaminant transport and reactive flows involved in CO2 sequestration. Carbonate rocks in particular present difficulties for pore-scale simulations because they contain large amounts of sub-micron porosity. In this work, we introduce a new hybrid simulation model to calculate hydrodynamic dispersion in pore-scale images of real porous media and use this to elucidate the origins and behaviour of stagnant zones arising in transport simulations using micro-CT images of carbonates. For this purpose a stochastic particle model for simulating the transport of a solute is coupled to a Lattice-Boltzmann algorithm to calculate the flow field. The particle method incorporates second order spatial and temporal resolution to resolve finer features of the domain. We demonstrate how dispersion coefficients can be accurately obtained in capillaries, where corresponding analytical solutions are available, even when these are resolved to just a few lattice units. Then we compute molecular displacement distributions for pore-spaces of varying complexity: a pack of beads; a Bentheimer sandstone; and a Portland carbonate. Our calculated propagator distributions are compared directly with recent experimental PFG-NMR propagator distributions (Scheven et al., 2005; Mitchell et al., 2008), the latter excluding spin relaxation mechanisms. We observe that the calculated transport propagators can be quantitatively compared with the experimental distribution, provided that spin relaxations in the experiment are excluded, and good agreement is found for both the sandstone and the carbonate. However, due to the absence of explicit micro-porosity from the carbonate pore space image used for flow field simulations we note that there are fundamental differences in the physical origins of the stagnant zones for micro-porous rocks between simulation and experiment. We show that for a given micro-CT image of a carbonate, small variations in the parameters chosen for the segmentation process lead to different amounts of stagnancy which diffuse away at different rates. Finally, we use a filtering method to show that this is due to the presence of spurious isolated pores which arise from the segmentation process and suggest an approach to overcome this limitation.

Optical properties of zirconium oxynitride films: The effect of composition, electronic and crystalline structures

NASA Astrophysics Data System (ADS)

Carvalho, P.; Borges, J.; Rodrigues, M. S.; Barradas, N. P.; Alves, E.; Espinós, J. P.; González-Elipe, A. R.; Cunha, L.; Marques, L.; Vasilevskiy, M. I.; Vaz, F.

2015-12-01

This work is devoted to the investigation of zirconium oxynitride (ZrOxNy) films with varied optical responses prompted by the variations in their compositional and structural properties. The films were prepared by dc reactive magnetron sputtering of Zr, using Ar and a reactive gas mixture of N2 + O2 (17:3). The colour of the films changed from metallic-like, very bright yellow-pale and golden yellow, for low gas flows to red-brownish for intermediate gas flows. Associated to this colour change there was a significant decrease of brightness. With further increase of the reactive gas flow, the colour of the samples changed from red-brownish to dark blue or even to interference colourations. The variations in composition disclosed the existence of four different zones, which were found to be closely related with the variations in the crystalline structure. XRD analysis revealed the change from a B1 NaCl face-centred cubic zirconium nitride-type phase for films prepared with low reactive gas flows, towards a poorly crystallized over-stoichiometric nitride phase, which may be similar to that of Zr3N4 with some probable oxygen inclusions within nitrogen positions, for films prepared with intermediate reactive gas flows. For high reactive gas flows, the films developed an oxynitride-type phase, similar to that of γ-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions, evolving to a ZrO2 monoclinic type structure within the zone where films were prepared with relatively high reactive gas flows. The analysis carried out by reflected electron energy loss spectroscopy (REELS) revealed a continuous depopulation of the d-band and an opening of an energy gap between the valence band (2p) and the Fermi level close to 5 eV. The ZrN-based coatings (zone I and II) presented intrinsic colourations, with a decrease in brightness and a colour change from bright yellow to golden yellow, red brownish and dark blue. Associated to these changes, there was also a shift of the reflectivity minimum to lower energies, with the increase of the non-metallic content. The samples lying in the two last zones (zone III, oxynitride and zone IV, oxide films) revealed a typical semi-transparent-optical behaviour showing interference-like colourations only due to the complete depopulation of the d band at the Fermi level. The samples lying in these zones presented also an increase of the optical bandgap from 2 to 3.6 eV.

Development of new flux splitting schemes. [computational fluid dynamics algorithms

NASA Technical Reports Server (NTRS)

Liou, Meng-Sing; Steffen, Christopher J., Jr.

1992-01-01

Maximizing both accuracy and efficiency has been the primary objective in designing a numerical algorithm for computational fluid dynamics (CFD). This is especially important for solutions of complex three dimensional systems of Navier-Stokes equations which often include turbulence modeling and chemistry effects. Recently, upwind schemes have been well received for their capability in resolving discontinuities. With this in mind, presented are two new flux splitting techniques for upwind differencing. The first method is based on High-Order Polynomial Expansions (HOPE) of the mass flux vector. The second new flux splitting is based on the Advection Upwind Splitting Method (AUSM). The calculation of the hypersonic conical flow demonstrates the accuracy of the splitting in resolving the flow in the presence of strong gradients. A second series of tests involving the two dimensional inviscid flow over a NACA 0012 airfoil demonstrates the ability of the AUSM to resolve the shock discontinuity at transonic speed. A third case calculates a series of supersonic flows over a circular cylinder. Finally, the fourth case deals with tests of a two dimensional shock wave/boundary layer interaction.

Using a bias aware EnKF to account for unresolved structure in an unsaturated zone model

NASA Astrophysics Data System (ADS)

Erdal, D.; Neuweiler, I.; Wollschläger, U.

2014-01-01

When predicting flow in the unsaturated zone, any method for modeling the flow will have to define how, and to what level, the subsurface structure is resolved. In this paper, we use the Ensemble Kalman Filter to assimilate local soil water content observations from both a synthetic layered lysimeter and a real field experiment in layered soil in an unsaturated water flow model. We investigate the use of colored noise bias corrections to account for unresolved subsurface layering in a homogeneous model and compare this approach with a fully resolved model. In both models, we use a simplified model parameterization in the Ensemble Kalman Filter. The results show that the use of bias corrections can increase the predictive capability of a simplified homogeneous flow model if the bias corrections are applied to the model states. If correct knowledge of the layering structure is available, the fully resolved model performs best. However, if no, or erroneous, layering is used in the model, the use of a homogeneous model with bias corrections can be the better choice for modeling the behavior of the system.

Identifying Coherent Structures in a 3-Stream Supersonic Jet Flow using Time-Resolved Schlieren Imaging

NASA Astrophysics Data System (ADS)

Tenney, Andrew; Coleman, Thomas; Berry, Matthew; Magstadt, Andy; Gogineni, Sivaram; Kiel, Barry

2015-11-01

Shock cells and large scale structures present in a three-stream non-axisymmetric jet are studied both qualitatively and quantitatively. Large Eddy Simulation is utilized first to gain an understanding of the underlying physics of the flow and direct the focus of the physical experiment. The flow in the experiment is visualized using long exposure Schlieren photography, with time resolved Schlieren photography also a possibility. Velocity derivative diagnostics are calculated from the grey-scale Schlieren images are analyzed using continuous wavelet transforms. Pressure signals are also captured in the near-field of the jet to correlate with the velocity derivative diagnostics and assist in unraveling this complex flow. We acknowledge the support of AFRL through an SBIR grant.

Estimating sources, sinks and fluxes of reactive atmospheric compounds within a forest canopy

EPA Science Inventory

While few dispute the significance of within-canopy sources or sinks of reactive gaseous and particulate compounds, their estimation continues to be the subject of active research and debate. Reactive species undergo turbulent dispersion within an inhomogeneous flow field, and ma...

[Latest Treatment of Viral Hepatitis--Overcoming Hepatitis C and Reactivation of Hepatitis B].

PubMed

Tanaka, Yasuhito

2016-02-01

Hepatitis B virus (HBV) and hepatitis C virus (HCV), discovered as causative viruses of post-transfusion hepatitis, become persistent infections, leading to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). For HCV, recent IFN-free direct-acting antiviral (DAA) therapies have increased sustained virological response (SVR) rates and reduced adverse events. IFN-based therapies, still the standard of care in Asian countries, are influenced by IL28B genetic variants and the liver fibrosis stage, but the DAA combinations obscure the influence of these factors. These new therapies can eradicate HCV and prevent HCC development. On the other hand, it is difficult to eradicate HBV completely. Although HBV infection can be prevented by vaccination, reactivation of HBV following anti-cancer chemotherapy and immunosuppressive therapy is a well-known complication. HBV reactivation has been reported to be associated with anti-CD20 monoclonal antibody rituximab-containing chemotherapy and TNF-α inhibitor-containing immunosuppressive therapy in HBV-resolved patients. Our prospective observational study revealed that monthly monitoring of HBV DNA was useful for preventing HBV reactivation-related hepatitis among B-cell non-Hodgkin lymphoma patients with resolved HBV infection following rituximab-steroid-chemo, suggesting that preemptive therapy guided by serial HBV DNA monitoring should be recommended. Recently, highly sensitive HBsAg detection by Lumipulse HBsAg-HQ may be useful for several clinical applications. The sensitivity of this assay (5 mIU/mL) was approximately 10-fold higher than Abbott ARCHITECT, but still lower than HBV-DNA assays. The convenient HBsAg-HQ may be useful for detecting occult HBV infection and HBV reactivation in relatively low-risk groups except for those receiving rituximab-steroid-chemo. [

Hybrid Multiscale Finite Volume method for multiresolution simulations of flow and reactive transport in porous media

NASA Astrophysics Data System (ADS)

Barajas-Solano, D. A.; Tartakovsky, A. M.

2017-12-01

We present a multiresolution method for the numerical simulation of flow and reactive transport in porous, heterogeneous media, based on the hybrid Multiscale Finite Volume (h-MsFV) algorithm. The h-MsFV algorithm allows us to couple high-resolution (fine scale) flow and transport models with lower resolution (coarse) models to locally refine both spatial resolution and transport models. The fine scale problem is decomposed into various "local'' problems solved independently in parallel and coordinated via a "global'' problem. This global problem is then coupled with the coarse model to strictly ensure domain-wide coarse-scale mass conservation. The proposed method provides an alternative to adaptive mesh refinement (AMR), due to its capacity to rapidly refine spatial resolution beyond what's possible with state-of-the-art AMR techniques, and the capability to locally swap transport models. We illustrate our method by applying it to groundwater flow and reactive transport of multiple species.

Experimental and numerical study of the relation between flow paths and fate of a pesticide in a riparian wetland

NASA Astrophysics Data System (ADS)

Kidmose, Jacob; Dahl, Mette; Engesgaard, Peter; Nilsson, Bertel; Christensen, Britt S. B.; Andersen, Stine; Hoffmann, Carl Christian

2010-05-01

SummaryA field-scale pulse-injection experiment with the herbicide Isoproturon was conducted in a Danish riparian wetland. A non-reactive tracer (bromide) experiment was also carried out to characterize the physical transport system. Groundwater flow and reactive transport modelling was used to simulate flow paths, residence times, as well as bromide and Isoproturon distributions. The wetland can be characterized by two distinct riparian flow paths; one flow path discharges 2/3 of the incoming groundwater directly to the free water surface of the wetland near the foot of the hillslope with an average residence time of 205 days, and another flow path diffusively discharging the remaining 1/3 of the incoming groundwater to the stream with an average residence time of 425 days. The reactive transport simulations reveal that Isoproturon is retarded by a factor of 2-4, which is explained by the high organic content in the peat layer of the wetland. Isoproturon was found to be aerobically degraded with a half-life in the order of 12-80 days. Based on the quantification of flow paths, residence times and half-lives it is estimated that about 2/3 of the injected Isoproturon is removed in the wetland. Thus, close to 1/3 may find its way to the stream through overland flow. It is also possible that high concentrations of metabolites will reach the stream.

Reactivation of a cryptobiotic stream ecosystem in the McMurdo Dry Valleys, Antarctica: A long-term geomorphological experiment

USGS Publications Warehouse

McKnight, Diane M.; Tate, C.M.; Andrews, E.D.; Niyogi, D.K.; Cozzetto, K.; Welch, K.; Lyons, W.B.; Capone, D.G.

2007-01-01

The McMurdo Dry Valleys of Antarctica contain many glacial meltwater streams that flow for 6 to 12??weeks during the austral summer and link the glaciers to the lakes on the valley floors. Dry valley streams gain solutes longitudinally through weathering reactions and microbial processes occurring in the hyporheic zone. Some streams have thriving cyanobacterial mats. In streams with regular summer flow, the mats are freeze-dried through the winter and begin photosynthesizing with the onset of flow. To evaluate the longer term persistence of cyanobacterial mats, we diverted flow to an abandoned channel, which had not received substantial flow for approximately two decades. Monitoring of specific conductance showed that for the first 3??years after the diversion, the solute concentrations were greater in the reactivated channel than in most other dry valley streams. We observed that cyanobacterial mats became abundant in the reactivated channel within a week, indicating that the mats had been preserved in a cryptobiotic state in the channel. Over the next several years, these mats had high rates of productivity and nitrogen fixation compared to mats from other streams. Experiments in which mats from the reactivated channel and another stream were incubated in water from both of the streams indicated that the greater solute concentrations in the reactivated channel stimulated net primary productivity of mats from both streams. These stream-scale experimental results indicate that the cryptobiotic preservation of cyanobacterial mats in abandoned channels in the dry valleys allows for rapid response of these stream ecosystems to climatic and geomorphological change, similar to other arid zone stream ecosystems. ?? 2006 Elsevier B.V. All rights reserved.

On the physics-based processes behind production-induced seismicity in natural gas fields

NASA Astrophysics Data System (ADS)

Zbinden, Dominik; Rinaldi, Antonio Pio; Urpi, Luca; Wiemer, Stefan

2017-05-01

Induced seismicity due to natural gas production is observed at different sites worldwide. Common understanding states that the pressure drop caused by gas production leads to compaction, which affects the stress field in the reservoir and the surrounding rock formations and hence reactivates preexisting faults and induces earthquakes. In this study, we show that the multiphase fluid flow involved in natural gas extraction activities should be included. We use a fully coupled fluid flow and geomechanics simulator, which accounts for stress-dependent permeability and linear poroelasticity, to better determine the conditions leading to fault reactivation. In our model setup, gas is produced from a porous reservoir, divided into two compartments that are offset by a normal fault. Results show that fluid flow plays a major role in pore pressure and stress evolution within the fault. Fault strength is significantly reduced due to fluid flow into the fault zone from the neighboring reservoir compartment and other formations. We also analyze scenarios for minimizing seismicity after a period of production, such as (i) well shut-in and (ii) gas reinjection. In the case of well shut-in, a highly stressed fault zone can still be reactivated several decades after production has ceased, although on average the shut-in results in a reduction in seismicity. In the case of gas reinjection, fault reactivation can be avoided if gas is injected directly into the compartment under depletion. However, gas reinjection into a neighboring compartment does not stop the fault from being reactivated.

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.

Flow in cerebral aneurysms: 4D Flow MRI measurements and CFD models

NASA Astrophysics Data System (ADS)

Rayz, Vitaliy; Schnell, Susanne

2017-11-01

4D Flow MRI is capable of measuring blood flow in vivo, providing time-resolved velocity fields in 3D. The dynamic range of the 4D Flow MRI is determined by a velocity sensitivity parameter (venc), set above the expected maximum velocity, which can result in noisy data for slow flow regions. A dual-venc 4D flow MRI technique, where both low- and high-venc data are acquired, can improve velocity-to-noise ratio and, therefore, quantification of clinically-relevant hemodynamic metrics. In this study, patient-specific CFD simulations were used to evaluate the advantages of the dual-venc approach for assessment of the flow in cerebral aneurysms. The flow in 2 cerebral aneurysms was measured in vivo with dual-venc 4D Flow MRI and simulated with CFD, using the MRI data to prescribe flow boundary conditions. The flow fields obtained with computations were compared to those measured with a single- and dual-venc 4D Flow MRI. The numerical models resolved small flow structures near the aneurysmal wall, that were not detected with a single-venc acquisition. Comparison of the numerical and imaging results shows that the dual-venc approach can improve the accuracy of the 4D Flow MRI measurements in regions characterized by high-velocity jets and slow recirculating flows.

Quantum State-Resolved Reactive and Inelastic Scattering at Gas-Liquid and Gas-Solid Interfaces

NASA Astrophysics Data System (ADS)

Grütter, Monika; Nelson, Daniel J.; Nesbitt, David J.

2012-06-01

Quantum state-resolved reactive and inelastic scattering at gas-liquid and gas-solid interfaces has become a research field of considerable interest in recent years. The collision and reaction dynamics of internally cold gas beams from liquid or solid surfaces is governed by two main processes, impulsive scattering (IS), where the incident particles scatter in a few-collisions environment from the surface, and trapping-desorption (TD), where full equilibration to the surface temperature (T{TD}≈ T{s}) occurs prior to the particles' return to the gas phase. Impulsive scattering events, on the other hand, result in significant rotational, and to a lesser extent vibrational, excitation of the scattered molecules, which can be well-described by a Boltzmann-distribution at a temperature (T{IS}>>T{s}). The quantum-state resolved detection used here allows the disentanglement of the rotational, vibrational, and translational degrees of freedom of the scattered molecules. The two examples discussed are (i) reactive scattering of monoatomic fluorine from room-temperature ionic liquids (RTILs) and (ii) inelastic scattering of benzene from a heated (˜500 K) gold surface. In the former experiment, rovibrational states of the nascent HF beam are detected using direct infrared absorption spectroscopy, and in the latter, a resonace-enhanced multi-photon-ionization (REMPI) scheme is employed in combination with a velocity-map imaging (VMI) device, which allows the detection of different vibrational states of benzene excited during the scattering process. M. E. Saecker, S. T. Govoni, D. V. Kowalski, M. E. King and G. M. Nathanson Science 252, 1421, 1991. A. M. Zolot, W. W. Harper, B. G. Perkins, P. J. Dagdigian and D. J. Nesbitt J. Chem. Phys 125, 021101, 2006. J. R. Roscioli and D. J. Nesbitt Faraday Disc. 150, 471, 2011.

Accurate Quantum Wave Packet Study of the Deep Well D+ + HD Reaction: Product Ro-vibrational State-Resolved Integral and Differential Cross Sections.

PubMed

He, Haixiang; Zhu, Weimin; Su, Wenli; Dong, Lihui; Li, Bin

2018-03-08

The H + + H 2 reaction and its isotopic variants as the simplest triatomic ion-molecule reactive system have been attracting much interests, however there are few studies on the titled reaction at state-to-state level until recent years. In this work, accurate state-to-state quantum dynamics studies of the titled reaction have been carried out by a reactant Jacobi coordinate-based time-dependent wave packet approach on diabatic potential energy surfaces constructed by Kamisaka et al. Product ro-vibrational state-resolved information has been calculated for collision energies up to 0.2 eV with maximal total angular momentum J = 40. The necessity of including all K-component for accounting the Coriolis coupling for the reaction has been illuminated. Competitions between the two product channels, (D + + HD' → D' + + HD and D + + HD' → H + + DD') were investigated. Total integral cross sections suggest that resonances enhance the reactivity of channel D + + HD'→ H + + DD', however, resonances depress the reactivity of the another channel D + + HD' → D' + + HD. The structures of the differential cross sections are complicated and depend strongly on collision energies of the two channels and also on the product rotational states. All of the product ro-vibrational state-resolved differential cross sections for this reaction do not exhibit rigorous backward-forward symmetry which may indicate that the lifetimes of the intermediate resonance complexes should not be that long. The dynamical observables of this deuterated isotopic reaction are quite different from the reaction of H + + H 2 → H 2 + H + reported previously.

Myocardial Blood Flow Distribution during Ischemia-Induced Coronary Vasodilation in the Unanesthetized Dog

PubMed Central

Bache, Robert J.; Cobb, Frederick R.; Greenfield, Joseph C.

1974-01-01

This study was designed to determine whether coronary vasodilation distal to a flow-limiting coronary artery stenosis could result in redistribution of myocardial blood flow to produce subendocardial underperfusion. Studies were performed in 10 awake dogs chronically prepared with electromagnetic flow-meters and hydraulic occluders on the left circumflex coronary artery. Regional myocardial blood flow was measured using radionuclide-labeled microspheres, 7-10 μm in diameter, injected into the left atrium. A 5-s coronary artery occlusion was followed by reactive hyperemia with excess inflow of arterial blood effecting 375±20% repayment of the blood flow debt incurred during occlusion. When, after a 5-s occlusion, the occluder was only partially released to hold arterial inflow to the preocclusion level for 20 s before complete release, the delayed reactive hyperemia was augmented (mean blood flow repayment = 610±45%, P < 0.01). This augmentation of the reactive hyperemia suggested that ischemia was continuing during the interval of coronary vasodilation when coronary inflow was at the preocclusion level. Measurements of regional myocardial blood flow demonstrated that endocardial flow slightly exceeded epicardial flow during control conditions. When arterial inflow was limited to the preocclusion rate during vasodilation after a 5-s total coronary artery occlusion, however, flow to the subepicardial myocardium was increased at the expense of underperfusion of the subendocardial myocardium. Thus, in the presence of a flow-limiting proximal coronary artery stenosis, ischemia-induced coronary vasodilation resulted in redistribution of myocardial blood flow with production of subendocardial ischemia in the presence of a net volume of arterial inflow which, if properly distributed, would have been adequate to prevent myocardial ischemia. Images PMID:4279928

Flow topologies and turbulence scales in a jet-in-cross-flow

DOE PAGES

Oefelein, Joseph C.; Ruiz, Anthony M.; Lacaze, Guilhem

2015-04-03

This study presents a detailed analysis of the flow topologies and turbulence scales in the jet-in-cross-flow experiment of [Su and Mungal JFM 2004]. The analysis is performed using the Large Eddy Simulation (LES) technique with a highly resolved grid and time-step and well controlled boundary conditions. This enables quantitative agreement with the first and second moments of turbulence statistics measured in the experiment. LES is used to perform the analysis since experimental measurements of time-resolved 3D fields are still in their infancy and because sampling periods are generally limited with direct numerical simulation. A major focal point is the comprehensivemore » characterization of the turbulence scales and their evolution. Time-resolved probes are used with long sampling periods to obtain maps of the integral scales, Taylor microscales, and turbulent kinetic energy spectra. Scalar-fluctuation scales are also quantified. In the near-field, coherent structures are clearly identified, both in physical and spectral space. Along the jet centerline, turbulence scales grow according to a classical one-third power law. However, the derived maps of turbulence scales reveal strong inhomogeneities in the flow. From the modeling perspective, these insights are useful to design optimized grids and improve numerical predictions in similar configurations.« less

Velocity-Resolved LES (VR-LES) technique for simulating turbulent transport of high Schmidt number passive scalars

NASA Astrophysics Data System (ADS)

Verma, Siddhartha; Blanquart, Guillaume; P. K. Yeung Collaboration

2011-11-01

Accurate simulation of high Schmidt number scalar transport in turbulent flows is essential to studying pollutant dispersion, weather, and several oceanic phenomena. Batchelor's theory governs scalar transport in such flows, but requires further validation at high Schmidt and high Reynolds numbers. To this end, we use a new approach with the velocity field fully resolved, but the scalar field only partially resolved. The grid used is fine enough to resolve scales up to the viscous-convective subrange where the decaying slope of the scalar spectrum becomes constant. This places the cutoff wavenumber between the Kolmogorov scale and the Batchelor scale. The subgrid scale terms, which affect transport at the supergrid scales, are modeled under the assumption that velocity fluctuations are negligible beyond this cutoff wavenumber. To ascertain the validity of this technique, we performed a-priori testing on existing DNS data. This Velocity-Resolved LES (VR-LES) technique significantly reduces the computational cost of turbulent simulations of high Schmidt number scalars, and yet provides valuable information of the scalar spectrum in the viscous-convective subrange.

Predictive model for convective flows induced by surface reactivity contrast

NASA Astrophysics Data System (ADS)

Davidson, Scott M.; Lammertink, Rob G. H.; Mani, Ali

2018-05-01

Concentration gradients in a fluid adjacent to a reactive surface due to contrast in surface reactivity generate convective flows. These flows result from contributions by electro- and diffusio-osmotic phenomena. In this study, we have analyzed reactive patterns that release and consume protons, analogous to bimetallic catalytic conversion of peroxide. Similar systems have typically been studied using either scaling analysis to predict trends or costly numerical simulation. Here, we present a simple analytical model, bridging the gap in quantitative understanding between scaling relations and simulations, to predict the induced potentials and consequent velocities in such systems without the use of any fitting parameters. Our model is tested against direct numerical solutions to the coupled Poisson, Nernst-Planck, and Stokes equations. Predicted slip velocities from the model and simulations agree to within a factor of ≈2 over a multiple order-of-magnitude change in the input parameters. Our analysis can be used to predict enhancement of mass transport and the resulting impact on overall catalytic conversion, and is also applicable to predicting the speed of catalytic nanomotors.

Patient-Specific Simulations of Reactivity in Models of the Pulmonary Vasculature: A 3-D Numerical Study with Fluid-Structure Interaction

NASA Astrophysics Data System (ADS)

Hunter, Kendall; Zhang, Yanhang; Lanning, Craig

2005-11-01

Insight into the progression of pulmonary hypertension may be obtained from thorough study of vascular flow during reactivity testing, an invasive diagnostic procedure which can dramatically alter vascular hemodynamics. Diagnostic imaging methods, however, are limited in their ability to provide extensive data. Here we present detailed flow and wall deformation results from simulations of pulmonary arteries undergoing this procedure. Patient-specific 3-D geometric reconstructions of the first four branches of the pulmonary vasculature were obtained clinically and meshed for use with computational software. Transient simulations in normal and reactive states were obtained from four such models were completed with patient-specific velocity inlet conditions and flow impedance exit conditions. A microstructurally based orthotropic hyperelastic model that simulates pulmonary artery mechanics under normotensive and hypoxic hypertensive conditions treated wall constitutive changes due to pressure reactivity and arterial remodeling. Pressure gradients, velocity fields, arterial deformation, and complete topography of shear stress were obtained. These models provide richer detail of hemodynamics than can be obtained from current imaging techniques, and should allow maximum characterization of vascular function in the clinical situation.

On the modelling of non-reactive and reactive turbulent combustor flows

NASA Technical Reports Server (NTRS)

Nikjooy, Mohammad; So, Ronald M. C.

1987-01-01

A study of non-reactive and reactive axisymmetric combustor flows with and without swirl is presented. Closure of the Reynolds equations is achieved by three models: kappa-epsilon, algebraic stress and Reynolds stress closure. Performance of two locally nonequilibrium and one equilibrium algebraic stress models is analyzed assuming four pressure strain models. A comparison is also made of the performance of a high and a low Reynolds number model for combustor flow calculations using Reynolds stress closures. Effects of diffusion and pressure-strain models on these closures are also investigated. Two models for the scalar transport are presented. One employs the second-moment closure which solves the transport equations for the scalar fluxes, while the other solves the algebraic equations for the scalar fluxes. In addition, two cases of non-premixed and one case of premixed combustion are considered. Fast- and finite-rate chemistry models are applied to non-premixed combustion. Both show promise for application in gas turbine combustors. However, finite rate chemistry models need to be examined to establish a suitable coupling of the heat release effects on turbulence field and rate constants.

Inside out: Speed-dependent barriers to reactive mixing

NASA Astrophysics Data System (ADS)

Kelley, Douglas; Nevins, Thomas

2015-11-01

Reactive mixing occurs wherever fluid flow and chemical or biological growth interact over time and space. Those interactions often lead to steep gradients in reactant and product concentration, arranged in complex spatial structures that can cause wide variation in the global reaction rate and concentrations. By simultaneously measuring fluid velocity and reaction front locations in laboratory experiments with the Belousov-Zhabotinsky reaction, we find that the barriers defining those structures vary dramatically with speed. In particular, we find that increasing flow speed causes reacted regions to move from vortex edges to vortex cores, thus turning the barriers ``inside out''. This observation has implications for reactive mixing of phytoplankton in global oceans.

Optically Guided Photoactivity: Coordinating Tautomerization, Photoisomerization, Inhomogeneity, and Reactive Intermediates within the RcaE Cyanobacteriochrome.

PubMed

Gottlieb, Sean M; Chang, Che-Wei; Martin, Shelley S; Rockwell, Nathan C; Lagarias, J Clark; Larsen, Delmar S

2014-05-01

The RcaE cyanobacteriochrome uses a linear tetrapyrrole chromophore to sense the ratio of green and red light to enable the Fremyella diplosiphon cyanobacterium to control the expression of the photosynthetic infrastructure for efficient utilization of incident light. The femtosecond photodynamics of the embedded phycocyanobilin chromophore within RcaE were characterized with dispersed femtosecond pump-dump-probe spectroscopy, which resolved a complex interplay of excited-state proton transfer, photoisomerization, multilayered inhomogeneity, and reactive intermediates. These reactions were integrated within a central model that incorporated a rapid (200 fs) excited-state Le Châtelier redistribution between parallel evolving populations ascribed to different tautomers. Three photoproducts were resolved and originates from four independent subpopulations, each with different dump-induced behavior: Lumi-Go was depleted, Lumi-Gr was unaffected, and Lumi-Gf was enhanced. This suggests that RcaE may be engineered to act either as an in vivo fluorescent probe (after single-pump excitation) or as an in vivo optogenetic sample (after pump and dump excitation).

Dissolved CO2 Increases Breakthrough Porosity in Natural Porous Materials.

PubMed

Yang, Y; Bruns, S; Stipp, S L S; Sørensen, H O

2017-07-18

When reactive fluids flow through a dissolving porous medium, conductive channels form, leading to fluid breakthrough. This phenomenon is caused by the reactive infiltration instability and is important in geologic carbon storage where the dissolution of CO 2 in flowing water increases fluid acidity. Using numerical simulations with high resolution digital models of North Sea chalk, we show that the breakthrough porosity is an important indicator of dissolution pattern. Dissolution patterns reflect the balance between the demand and supply of cumulative surface. The demand is determined by the reactive fluid composition while the supply relies on the flow field and the rock's microstructure. We tested three model scenarios and found that aqueous CO 2 dissolves porous media homogeneously, leading to large breakthrough porosity. In contrast, solutions without CO 2 develop elongated convective channels known as wormholes, with low breakthrough porosity. These different patterns are explained by the different apparent solubility of calcite in free drift systems. Our results indicate that CO 2 increases the reactive subvolume of porous media and reduces the amount of solid residual before reactive fluid can be fully channelized. Consequently, dissolved CO 2 may enhance contaminant mobilization near injection wellbores, undermine the mechanical sustainability of formation rocks and increase the likelihood of buoyance driven leakage through carbonate rich caprocks.

The resolvent of singular integral equations. [of kernel functions in mixed boundary value problems

NASA Technical Reports Server (NTRS)

Williams, M. H.

1977-01-01

The investigation reported is concerned with the construction of the resolvent for any given kernel function. In problems with ill-behaved inhomogeneous terms as, for instance, in the aerodynamic problem of flow over a flapped airfoil, direct numerical methods become very difficult. A description is presented of a solution method by resolvent which can be employed in such problems.

Highly reactive light-dependent monoterpenes in the Amazon

DOE PAGES

Jardine, A. B.; Jardine, K. J.; Fuentes, J. D.; ...

2015-03-06

Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 profiles. Leaf level emissionsmore » of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis.« less

Optimal reactive planning with security constraints

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

Thomas, W.R.; Cheng, D.T.Y.; Dixon, A.M.

1995-12-31

The National Grid Company (NGC) of England and Wales has developed a computer program, SCORPION, to help system planners optimize the location and size of new reactive compensation plant on the transmission system. The reactive power requirements of the NGC system have risen as a result of increased power flows and the shorter timescale on which power stations are commissioned and withdrawn from service. In view of the high costs involved, it is important that reactive compensation be installed as economically as possible, without compromising security. Traditional methods based on iterative use of a load flow program are labor intensivemore » and subjective. SCORPION determines a near-optimal pattern of new reactive sources which are required to satisfy voltage constraints for normal and contingent states of operation of the transmission system. The algorithm processes the system states sequentially, instead of optimizing all of them simultaneously. This allows a large number of system states to be considered with an acceptable run time and computer memory requirement. Installed reactive sources are treated as continuous, rather than discrete, variables. However, the program has a restart facility which enables the user to add realistically sized reactive sources explicitly and thereby work towards a realizable solution to the planning problem.« less

Advanced flow MRI: emerging techniques and applications

PubMed Central

Markl, M.; Schnell, S.; Wu, C.; Bollache, E.; Jarvis, K.; Barker, A. J.; Robinson, J. D.; Rigsby, C. K.

2016-01-01

Magnetic resonance imaging (MRI) techniques provide non-invasive and non-ionising methods for the highly accurate anatomical depiction of the heart and vessels throughout the cardiac cycle. In addition, the intrinsic sensitivity of MRI to motion offers the unique ability to acquire spatially registered blood flow simultaneously with the morphological data, within a single measurement. In clinical routine, flow MRI is typically accomplished using methods that resolve two spatial dimensions in individual planes and encode the time-resolved velocity in one principal direction, typically oriented perpendicular to the two-dimensional (2D) section. This review describes recently developed advanced MRI flow techniques, which allow for more comprehensive evaluation of blood flow characteristics, such as real-time flow imaging, 2D multiple-venc phase contrast MRI, four-dimensional (4D) flow MRI, quantification of complex haemodynamic properties, and highly accelerated flow imaging. Emerging techniques and novel applications are explored. In addition, applications of these new techniques for the improved evaluation of cardiovascular (aorta, pulmonary arteries, congenital heart disease, atrial fibrillation, coronary arteries) as well as cerebrovascular disease (intra-cranial arteries and veins) are presented. PMID:26944696

Determining Near-Bottom Fluxes of Passive Tracers in Aquatic Environments

NASA Astrophysics Data System (ADS)

Bluteau, Cynthia E.; Ivey, Gregory N.; Donis, Daphne; McGinnis, Daniel F.

2018-03-01

In aquatic systems, the eddy correlation method (ECM) provides vertical flux measurements near the sediment-water interface. The ECM independently measures the turbulent vertical velocities w' and the turbulent tracer concentration c' at a high sampling rate (> 1 Hz) to obtain the vertical flux w'c'¯ from their time-averaged covariance. This method requires identifying and resolving all the flow-dependent time (and length) scales contributing to w'c'¯. With increasingly energetic flows, we demonstrate that the ECM's current technology precludes resolving the smallest flux-contributing scales. To avoid these difficulties, we show that for passive tracers such as dissolved oxygen, w'c'¯ can be measured from estimates of two scalar quantities: the rate of turbulent kinetic energy dissipation ɛ and the rate of tracer variance dissipation χc. Applying this approach to both laboratory and field observations demonstrates that w'c'¯ is well resolved by the new method and can provide flux estimates in more energetic flows where the ECM cannot be used.

Feed artery role in blood flow control to rat hindlimb skeletal muscles.

PubMed Central

Williams, D A; Segal, S S

1993-01-01

1. Vasomotor tone and reactivity were investigated in feed arteries of the extensor digitorum longus and soleus muscles. Feed arteries are located external to the muscle and give rise to the microcirculation within each muscle. Resting diameter was smaller in feed arteries of the soleus muscle. 2. Feed arteries of both muscles dilated to similar peak values with sodium nitroprusside. 3. Micropressure measurements demonstrated resistance to blood flow in the feed arteries supplying both muscles. Feed arteries supplying soleus muscle demonstrated greater resistance to blood flow compared to feed arteries of extensor digitorum longus muscle. 4. Greater resting tone and larger pressure drop for feed arteries of soleus muscle suggest greater range of flow control compared to feed arteries of extensor digitorum longus muscle. 5. In both muscles, feed artery diameter increased with muscle contraction (functional dilatation) and in response to transient ischaemia (reactive dilatation). The magnitude of these responses varied between muscles. 6. Feed arteries are active sites of blood flow control in extensor digitorum longus and soleus muscles of the rat. These muscles differ in fibre type and recruitment properties. Differences in feed artery reactivity may contribute to differences in blood flow between these muscles observed at rest and during exercise. Images Fig. 2 Fig. 3 Fig. 4 Fig. 5 PMID:8246199

LONG-TERM GEOCHEMICAL BEHAVIOR OF A ZEROVALENT IRON PERMEABLE REACTIVE BARRIER FOR THE TREATMENT OF HEXAVALENT CHROMIUM IN GROUNDWATER

EPA Science Inventory

Passive, in-situ reactive barriers have proven to be viable, cost-effective systems for the remediation of Cr-contaminated groundwater at some sites. Permeable reactive barriers (PRBs) are installed in the flow-path of groundwater, most typically as vertical treatment walls. Re...

TRICHLOROETHYLENE REMOVAL FROM GROUNDWATER IN FLOW-THROUGH COLUMNS SIMULATING A PERMEABLE REACTIVE BARRIER CONSTRUCTED WITH PLANT MULCH

EPA Science Inventory

Ground water contaminated with TCE is commonly treated with a passive reactive barrier (PRB) constructed with zero-valence iron. The cost of iron as the reactive matrix has driven a search for less costly alternatives, and composted plant mulch has been used as an alternative re...

Phenotypic modulation of auto-reactive cells by insertion of tolerogenic molecules via MSC-derived exosomes.

PubMed

Mokarizadeh, Aram; Delirezh, Nowruz; Morshedi, Ahhmad; Mosayebi, Ghasem; Farshid, Amir-Abbas; Dalir-Naghadeh, Bahram

2012-01-01

Auto-reactive cells-mediated immune responses are responsible for the current tissue damages during autoimmunity. Accordingly, functional modulation of auto-reactive cells has been a pivotal aim in many of recent studies. In the current study, we investigated the possibility for insertion of regulatory molecules onto auto-reactive cells through exosomal nano-shuttles as a novel approach for phenotype modification of auto-reactive cells. The exosomes were isolated from supernatant of mesenchymal stem cells culture. Resultant exosomes co-cultured with lymphocytes were harvested from established EAE mice in the presence of antigenic MOG35-55 peptide. After 24 hr, insertion of exosomal tolerogenic molecules (PD-L1, TGF-β, galectin-1) onto auto-reactive cells were explored through flow cytometry. The potency of exosomal inserted membrane molecules to modulate phenotype of auto-reactive lymphocytes was assessed upon ELISA test for their-derived cytokines IFN-γ and IL-17. Incorporation of exosomal molecules into lymohocytes' membrane was confirmed by flow cytometric analyses for surface levels of mentioned molecules. Additionally, the decreased secretion of IFN-γ and IL-17 were detected in exosome pre-treated lymphocytes upon stimulation with MOG peptide. Mesenchymal stem cells -derived exosomes showed to be efficient organelles for insertion of bioactive tolerogenic molecules onto auto-reactive cells and modulation of their phenotypes.

Characterizing 3-D flow velocity in evolving pore networks driven by CaCO3 precipitation and dissolution

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Yoon, H.; Martinez, M. J.

2015-12-01

Understanding reactive flow in geomaterials is important for optimizing geologic carbon storage practices, such as using pore space efficiently. Flow paths can be complex in large degrees of geologic heterogeneities across scales. In addition, local heterogeneity can evolve as reactive transport processes alter the pore-scale morphology. For example, dissolved carbon dioxide may react with minerals in fractured rocks, confined aquifers, or faults, resulting in heterogeneous cementation (and/or dissolution) and evolving flow conditions. Both path and flow complexities are important and poorly characterized, making it difficult to determine their evolution with traditional 2-D transport models. Here we characterize the development of 3-D pore-scale flow with an evolving pore configuration due to calcium carbonate (CaCO3) precipitation and dissolution. A simple pattern of a microfluidic pore network is used initially and pore structures will become more complex due to precipitation and dissolution processes. At several stages of precipitation and dissolution, we directly visualize 3-D velocity vectors using micro particle image velocimetry and a laser scanning confocal microscope. Measured 3-D velocity vectors are then compared to 3-D simulated flow fields which will be used to simulate reactive transport. Our findings will highlight the importance of the 3-D flow dynamics and its impact on estimating reactive surface area over time. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114.

Generalized thick strip modelling for vortex-induced vibration of long flexible cylinders

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

Bao, Y., E-mail: ybao@sjtu.edu.cn; Department of Aeronautics, Imperial College London, South Kensington Campus, London; Palacios, R., E-mail: r.palacios@imperial.ac.uk

2016-09-15

We propose a generalized strip modelling method that is computationally efficient for the VIV prediction of long flexible cylinders in three-dimensional incompressible flow. In order to overcome the shortcomings of conventional strip-theory-based 2D models, the fluid domain is divided into “thick” strips, which are sufficiently thick to locally resolve the small scale turbulence effects and three dimensionality of the flow around the cylinder. An attractive feature of the model is that we independently construct a three-dimensional scale resolving model for individual strips, which have local spanwise scale along the cylinder's axial direction and are only coupled through the structural modelmore » of the cylinder. Therefore, this approach is able to cover the full spectrum for fully resolved 3D modelling to 2D strip theory. The connection between these strips is achieved through the calculation of a tensioned beam equation, which is used to represent the dynamics of the flexible body. In the limit, however, a single “thick” strip would fill the full 3D domain. A parallel Fourier spectral/hp element method is employed to solve the 3D flow dynamics in the strip-domain, and then the VIV response prediction is achieved through the strip–structure interactions. Numerical tests on both laminar and turbulent flows as well as the comparison against the fully resolved DNS are presented to demonstrate the applicability of this approach.« less

Development and Application of Numerical Models for Reactive Flows

DTIC Science & Technology

1990-08-15

Shear Layers: Ill. Effect of Convective Mach number Raafat H. Guirguis Abstract Model This paper addresses some of the fundamental We have made the...OTIC FILE COPY / 0 00 DTIC N~l 9 ELECTE D CbBA9-OI Development and Application of Numerical Models for Reactive Flows Berkeley Research Associates...Laboratory for Computa- tional Physics (LCP), hav focused on developing mathematical and computational models which accurately and efficiently describe the

High Pressure Combustion Experimental Facility(HPCEF) for Studies on Combustion in Reactive Flows

DTIC Science & Technology

2017-12-13

SECURITY CLASSIFICATION OF: 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6...Report: High Pressure Combustion Experimental Facility (HPCEF) for Studies on Combustion in Reactive Flows The views, opinions and/or findings... contained in this report are those of the author(s) and should not contrued as an official Department of the Army position, policy or decision, unless so

Smoothed Particle Hydrodynamics and its applications for multiphase flow and reactive transport in porous media

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

Tartakovsky, Alexandre M.; Trask, Nathaniel; Pan, K.

2016-03-11

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian method based on a meshless discretization of partial differential equations. In this review, we present SPH discretization of the Navier-Stokes and Advection-Diffusion-Reaction equations, implementation of various boundary conditions, and time integration of the SPH equations, and we discuss applications of the SPH method for modeling pore-scale multiphase flows and reactive transport in porous and fractured media.

Improving Advanced Inverter Control Convergence in Distribution Power Flow

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

Nagarajan, Adarsh; Palmintier, Bryan; Ding, Fei

Simulation of modern distribution system powerflow increasingly requires capturing the impact of advanced PV inverter voltage regulation on powerflow. With Volt/var control, the inverter adjusts its reactive power flow as a function of the point of common coupling (PCC) voltage. Similarly, Volt/watt control curtails active power production as a function of PCC voltage. However, with larger systems and higher penetrations of PV, this active/reactive power flow itself can cause significant changes to the PCC voltage potentially introducing oscillations that slow the convergence of system simulations. Improper treatment of these advanced inverter functions could potentially lead to incorrect results. This papermore » explores a simple approach to speed such convergence by blending in the previous iteration's reactive power estimate to dampen these oscillations. Results with a single large (5MW) PV system and with multiple 500kW advanced inverters show dramatic improvements using this approach.« less

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

NASA Astrophysics Data System (ADS)

Hemberger, Patrick; Custodis, Victoria B. F.; Bodi, Andras; Gerber, Thomas; van Bokhoven, Jeroen A.

2017-06-01

Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity and yield unsatisfactory conversion. Understanding the pyrolysis reaction mechanism at the molecular level may help to make this sustainable process more economic. Reactive intermediates are responsible for product branching and hold the key to unveiling these mechanisms, but are notoriously difficult to detect isomer-selectively. Here, we investigate the catalytic pyrolysis of guaiacol, a lignin model compound, using photoelectron photoion coincidence spectroscopy with synchrotron radiation, which allows for isomer-selective detection of reactive intermediates. In combination with ambient pressure pyrolysis, we identify fulvenone as the central reactive intermediate, generated by catalytic demethylation to catechol and subsequent dehydration. The fulvenone ketene is responsible for the phenol formation. This technique may open unique opportunities for isomer-resolved probing in catalysis, and holds the potential for achieving a mechanistic understanding of complex, real-life catalytic processes.

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

Jardine, A. B.; Jardine, K. J.; Fuentes, J. D.

Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 profiles. Leaf level emissionsmore » of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis.« less

Communication: Reactivity borrowing in the mode selective chemistry of H + CHD3 → H2 + CD3

NASA Astrophysics Data System (ADS)

Ellerbrock, Roman; Manthe, Uwe

2017-12-01

Quantum state-resolved reaction probabilities for the H + CHD3 → H2 + CD3 reaction are calculated by accurate full-dimensional quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree approach and the quantum transition state concept. Reaction probabilities of various ro-vibrational states of the CHD3 reactant are investigated for vanishing total angular momentum. While the reactivity of the different vibrational states of CHD3 mostly follows intuitive patterns, an unusually large reaction probability is found for CHD3 molecules triply excited in the CD3 umbrella-bending vibration. This surprising reactivity can be explained by a Fermi resonance-type mixing of the single CH-stretch excited and the triple CD3 umbrella-bend excited vibrational states of CHD3. These findings show that resonant energy transfer can significantly affect the mode-selective chemistry of CHD3 and result in counter-intuitive reactivity patterns.

Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows

NASA Astrophysics Data System (ADS)

Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Tittelmeier, Kai; Bromberger, Benjamin; Prasser, Horst-Michael

Neutron imaging, in general, is a useful technique for visualizing low-Z materials (such as water or plastics) obscured by high-Z materials. However, when significant amounts of both materials are present and full-bodied samples have to be examined, cold and thermal neutrons rapidly reach their applicability limit as the samples become opaque. In such cases one can benefit from the high penetrating power of fast neutrons. In this work we demonstrate the feasibility of time-resolved, fast neutron radiography of generic air-water two-phase flows in a 1.5 cm thick flow channel with Aluminum walls and rectangular cross section. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany. Exposure times down to 3.33 ms have been achieved at reasonable image quality and acceptable motion artifacts. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two-phase flow parameters like the volumetric gas fraction, bubble size and bubble velocities have been measured.

Global Skin-Friction Measurements Using Particle Image Surface FLow Visualization and a Luminescent Oil-Film

NASA Technical Reports Server (NTRS)

Husen, Nicholas; Roozeboom, Nettie; Liu, Tianshu; Sullivan, John P.

2015-01-01

A quantitative global skin-friction measurement technique is proposed. An oil-film is doped with a luminescent molecule and thereby made to fluoresce in order to resolve oil-film thickness, and Particle Image Surface Flow Visualization is used to resolve the velocity field of the surface of the oil-film. Skin-friction is then calculated at location x as (x )xh, where x is the displacement of the surface of the oil-film and is the dynamic viscosity of the oil. The data collection procedure and data analysis procedures are explained, and preliminary experimental skin-friction results for flow over the wing of the CRM are presented.

Fully resolved simulations of expansion waves propagating into particle beds

NASA Astrophysics Data System (ADS)

Marjanovic, Goran; Hackl, Jason; Annamalai, Subramanian; Jackson, Thomas; Balachandar, S.

2017-11-01

There is a tremendous amount of research that has been done on compression waves and shock waves moving over particles but very little concerning expansion waves. Using 3-D direct numerical simulations, this study will explore expansion waves propagating into fully resolved particle beds of varying volume fractions and geometric arrangements. The objectives of these simulations are as follows: 1) To fully resolve all (1-way coupled) forces on the particles in a time varying flow and 2) to verify state-of-the-art drag models for such complex flows. We will explore a range of volume fractions, from very low ones that are similar to single particle flows, to higher ones where nozzling effects are observed between neighboring particles. Further, we will explore two geometric arrangements: body centered cubic and face centered cubic. We will quantify the effects that volume fraction and geometric arrangement plays on the drag forces and flow fields experienced by the particles. These results will then be compared to theoretical predictions from a model based on the generalized Faxen's theorem. This work was supported in part by the U.S. Department of Energy under the Predictive Science Academic Alliance Program, under Contract No. DE-NA0002378.

Power flow controller with a fractionally rated back-to-back converter

DOEpatents

Divan, Deepakraj M.; Kandula, Rajendra Prasad; Prasai, Anish

2016-03-08

A power flow controller with a fractionally rated back-to-back (BTB) converter is provided. The power flow controller provide dynamic control of both active and reactive power of a power system. The power flow controller inserts a voltage with controllable magnitude and phase between two AC sources at the same frequency; thereby effecting control of active and reactive power flows between the two AC sources. A transformer may be augmented with a fractionally rated bi-directional Back to Back (BTB) converter. The fractionally rated BTB converter comprises a transformer side converter (TSC), a direct-current (DC) link, and a line side converter (LSC). By controlling the switches of the BTB converter, the effective phase angle between the two AC source voltages may be regulated, and the amplitude of the voltage inserted by the power flow controller may be adjusted with respect to the AC source voltages.

Influence of magnetic field on chemically reactive blood flow through stenosed bifurcated arteries

NASA Astrophysics Data System (ADS)

Hossain, Khan Enaet; Haque, Md. Mohidul

2017-06-01

Dynamic response of mass transfer in chemically reactive blood flow through bifurcated arteries under the stenotic condition is numerically studied in the present of a uniform magnetic field. The blood flowing through the artery is assumed an incompressible, fully developed and Newtonian. The nonlinear unsteady flow phenomena are governed by the Navier-Stokes and concentration equations. All these equations together with the appropriate boundary conditions describing the present biomechanical problem are transformed by using a radial transformation and the numerical results are obtained using a finite difference technique. Effects of stenosed bifurcation and externally applied magnetic field on the blood flow with chemical reaction are discussed with the help of graph. All the flow characteristics are found to be affected by the presence of chemical reaction and exposure of magnetic field of different intensities. Finally some important findings of the problem are concluded in this work.

Impact of microstructure evolution on the difference between geometric and reactive surface areas in natural chalk

NASA Astrophysics Data System (ADS)

Yang, Y.; Bruns, S.; Stipp, S. L. S.; Sørensen, H. O.

2018-05-01

The coupling between flow and mineral dissolution drives the evolution of many natural and engineered flow systems. Pore surface changes as microstructure evolves but this transient behaviour has traditionally been difficult to model. We combined a reactor network model with experimental, greyscale tomography data to establish the morphological grounds for differences among geometric, reactive and apparent surface areas in dissolving chalk. This approach allowed us to study the effects of initial geometry and macroscopic flow rate independently. The simulations showed that geometric surface, which represents a form of local transport heterogeneity, increases in an imposed flow field, even when the porous structure is chemically homogeneous. Hence, the fluid-reaction coupling leads to solid channelisation, which further results in fluid focusing and an increase in geometric surface area. Fluid focusing decreases the area of reactive surface and the residence time of reactant, both contribute to the over-normalisation of reaction rate. In addition, the growing and merging of microchannels, near the fluid entrance, contribute to the macroscopic, fast initial dissolution rate of rocks.

Toward Understanding Tip Leakage Flows in Small Compressor Cores Including Stator Leakage Flow

NASA Technical Reports Server (NTRS)

Berdanier, Reid A.; Key, Nicole L.

2017-01-01

The focus of this work was to provide additional data to supplement the work reported in NASA/CR-2015-218868 (Berdanier and Key, 2015b). The aim of that project was to characterize the fundamental flow physics and the overall performance effects due to increased rotor tip clearance heights in axial compressors. Data have been collected in the three-stage axial research compressor at Purdue University with a specific focus on analyzing the multistage effects resulting from the tip leakage flow. Three separate rotor tip clearances were studied with nominal tip clearance gaps of 1.5 percent, 3.0 percent, and 4.0 percent based on a constant annulus height. Overall compressor performance was previously investigated at four corrected speedlines (100 percent, 90 percent, 80 percent, and 68 percent) for each of the three tip clearance configurations. This study extends the previously published results to include detailed steady and time-resolved pressure data at two loading conditions, nominal loading (NL) and high loading (HL), on the 100 percent corrected speedline for the intermediate clearance level (3.0 percent). Steady detailed radial traverses of total pressure at the exit of each stator row are supported by flow visualization techniques to identify regions of flow recirculation and separation. Furthermore, detailed radial traverses of time-resolved total pressures at the exit of each rotor row have been measured with a fast-response pressure probe. These data were combined with existing three-component velocity measurements to identify a novel technique for calculating blockage in a multistage compressor. Time-resolved static pressure measurements have been collected over the rotor tips for all rotors with each of the three tip clearance configurations for up to five loading conditions along the 100 percent corrected speedline using fast-response piezoresistive pressure sensors. These time-resolved static pressure measurements reveal new knowledge about the trajectory of the tip leakage flow through the rotor passage. Further, these data extend previous measurements identifying a modulation of the tip leakage flow due to upstream stator wake propagation. Finally, a novel instrumentation technique has been implemented to measure pressures in the shrouded stator cavities. These data provide boundary conditions relating to the flow across the shrouded stator knife seal teeth. Moreover, the utilization of fast-response pressure sensors provides a new look at the time-resolved pressure field, leading to instantaneous differential pressures across the seal teeth. Ultimately, the data collected for this project represent a unique data set which contributes to build a better understanding of the tip leakage flow field and its associated loss mechanisms. These data will facilitate future engine design goals leading to small blade heights in the rear stages of high pressure compressors and aid in the development of new blade designs which are desensitized to the performance penalties attributed to rotor tip leakage flows.

Analysis of Massively Separated Flows of Aircraft Using Detached Eddy Simulation

NASA Astrophysics Data System (ADS)

Morton, Scott

2002-08-01

An important class of turbulent flows of aerodynamic interest are those characterized by massive separation, e.g., the flow around an aircraft at high angle of attack. Numerical simulation is an important tool for analysis, though traditional models used in the solution of the Reynolds-averaged Navier-Stokes (RANS) equations appear unable to accurately account for the time-dependent and three-dimensional motions governing flows with massive separation. Large-eddy simulation (LES) is able to resolve these unsteady three-dimensional motions, yet is cost prohibitive for high Reynolds number wall-bounded flows due to the need to resolve the small scale motions in the boundary layer. Spalart et. al. proposed a hybrid technique, Detached-Eddy Simulation (DES), which takes advantage of the often adequate performance of RANS turbulence models in the "thin," typically attached regions of the flow. In the separated regions of the flow the technique becomes a Large Eddy Simulation, directly resolving the time-dependent and unsteady features that dominate regions of massive separation. The current work applies DES to a 70 degree sweep delta wing at 27 degrees angle of attack, a geometrically simple yet challenging flowfield that exhibits the unsteady three-dimensional massively separated phenomena of vortex breakdown. After detailed examination of this basic flowfield, the method is demonstrated on three full aircraft of interest characterized by massive separation, the F-16 at 45 degrees angle of attack, the F-15 at 65 degree angle of attack (with comparison to flight test), and the C-130 in a parachute drop condition at near stall speed with cargo doors open.

A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow

NASA Technical Reports Server (NTRS)

Weinan, E.; Shu, Chi-Wang

1994-01-01

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved.

A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow

NASA Technical Reports Server (NTRS)

Weinan, E.; Shu, Chi-Wang

1992-01-01

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.

Towards Measurement of the Time-resolved Heat Release of Protein Conformation Dynamics

NASA Technical Reports Server (NTRS)

Puchalla, Jason; Adamek, Daniel; Austin, Robert

2004-01-01

We present a way to observe time-resolved heat release using a laminar flow diffusional mixer coupled with a highly sensitive infrared camera which measures the temperature change of the solvent. There are significant benefits to the use of laminar flow mixers for time-resolved calorimetry: (1) The thermal signal can be made position and time- stationary to allow for signal integration; (2) Extremely small volumes (nl/s) of sample are required for a measurement; (3) The same mixing environment can be observed spectroscopically to obtain state occupation information; (4) The mixer allows one to do out of equilibrium dynamic studies. The hope is that these measurements will allow us probe the non-equilibrium thermodynamics as a protein moves along a free energy trajectory from one state to another.

Reactive transport of CO2-rich fluids in simulated wellbore interfaces: Experiments and models exploring behaviour on length scales of 1 to 6 m

NASA Astrophysics Data System (ADS)

Wolterbeek, T. K. T.; Raoof, A.; Peach, C. J.; Spiers, C. J.

2016-12-01

Defects present at casing-cement interfaces in wellbores constitute potential pathways for CO2 to migrate from geological storage systems. It is essential to understand how the transport properties of such pathways evolve when penetrated by CO2-rich fluids. While numerous studies have explored this problem at the decimetre length-scale, the 1-10-100 m scales relevant for real wellbores have received little attention. The present work addresses the effects of long-range reactive transport on a length scale of 1-6 m. This is done by means of a combined experimental and modelling study. The experimental work consisted of flow-through tests, performed on cement-filled steel tubes, 1-6 m in length, containing artificially debonded cement-interfaces. Four tests were performed, at 60-80 °C, imposing flow-through of CO2-rich fluid at mean pressures of 10-15 MPa, controlling the pressure difference at 0.12-4.8 MPa, while measuring flow-rate. In the modelling work, we developed a numerical model to explore reactive transport in CO2-exposed defects on a similar length scale. The formulation adopted incorporates fluid flow, advective and diffusive solute transport, and CO2-cement chemical reactions. Our results show that long-range reactive transport strongly affects the permeability evolution of CO2-exposed defects. In the experiments, sample permeability decreased by 2-4 orders, which microstructural observations revealed was associated with downstream precipitation of carbonates, possibly aided by migration of fines. The model simulations show precipitation in initially open defects produces a sharp decrease in flow rate, causing a transition from advection to diffusion-dominated reactive transport. While the modelling results broadly reproduce the experimental observations, it is further demonstrated that non-uniformity in initial defect aperture has a profound impact on self-sealing behaviour and system permeability evolution on the metre scale. The implication is that future reactive transport models and wellbore scale analyses must include defects with variable aperture in order to obtain reliable upscaling relations.

On the physics-based processes behind production-induced seismicity in natural gas fields

NASA Astrophysics Data System (ADS)

Zbinden, Dominik; Rinaldi, Antonio Pio; Urpi, Luca; Wiemer, Stefan

2017-04-01

Induced seismicity due to natural gas production is observed at different sites around the world. Common understanding is that the pressure drop caused by gas production leads to compaction, which affects the stress field in the reservoir and the surrounding rock formations, hence reactivating pre-existing faults and inducing earthquakes. Previous studies have often assumed that pressure changes in the reservoir compartments and intersecting fault zones are equal, while neglecting multi-phase fluid flow. In this study, we show that disregarding fluid flow involved in natural gas extraction activities is often inappropriate. We use a fully coupled multiphase fluid flow and geomechanics simulator, which accounts for stress-dependent permeability and linear poroelasticity, to better determine the conditions leading to fault reactivation. In our model setup, gas is produced from a porous reservoir, cut in two compartments that are offset by a normal fault, and overlain by impermeable caprock. Results show that fluid flow plays a major role pertaining to pore pressure and stress evolution within the fault. Hydro-mechanical processes include rotation of the principal stresses due to reservoir compaction, as well as poroelastic effects caused by the pressure drop in the adjacent reservoir. Fault strength is significantly reduced due to fluid flow into the fault zone from the neighbouring reservoir compartment and other formations. We also analyze the case of production in both compartments, and results show that simultaneous production does not prevent the fault to be reactivated, but the magnitude of the induced event is smaller. Finally, we analyze scenarios for minimizing seismicity after a period of production, such as (i) well shut-in and (ii) gas re-injection. Results show that, in the case of well shut-in, a highly stressed fault zone can still be reactivated several decades after production stop, although in average the shut-in results in reduction of seismicity. In the case of gas re-injection, fault reactivation can be avoided if gas is injected directly into the compartment under depletion. However, accounting for continuous production at a given reservoir and gas re-injection at a neighbouring compartment does not stop the fault from being reactivated.

Resolvent analysis of shear flows using One-Way Navier-Stokes equations

NASA Astrophysics Data System (ADS)

Rigas, Georgios; Schmidt, Oliver; Towne, Aaron; Colonius, Tim

2017-11-01

For three-dimensional flows, questions of stability, receptivity, secondary flows, and coherent structures require the solution of large partial-derivative eigenvalue problems. Reduced-order approximations are thus required for engineering prediction since these problems are often computationally intractable or prohibitively expensive. For spatially slowly evolving flows, such as jets and boundary layers, the One-Way Navier-Stokes (OWNS) equations permit a fast spatial marching procedure that results in a huge reduction in computational cost. Here, an adjoint-based optimization framework is proposed and demonstrated for calculating optimal boundary conditions and optimal volumetric forcing. The corresponding optimal response modes are validated against modes obtained in terms of global resolvent analysis. For laminar base flows, the optimal modes reveal modal and non-modal transition mechanisms. For turbulent base flows, they predict the evolution of coherent structures in a statistical sense. Results from the application of the method to three-dimensional laminar wall-bounded flows and turbulent jets will be presented. This research was supported by the Office of Naval Research (N00014-16-1-2445) and Boeing Company (CT-BA-GTA-1).

Prevention and management of hepatitis B virus reactivation in patients with hematological malignancies treated with anticancer therapy

PubMed Central

Law, Man Fai; Ho, Rita; Cheung, Carmen K M; Tam, Lydia H P; Ma, Karen; So, Kent C Y; Ip, Bonaventure; So, Jacqueline; Lai, Jennifer; Ng, Joyce; Tam, Tommy H C

2016-01-01

Hepatitis due to hepatitis B virus (HBV) reactivation can be severe and potentially fatal, but is preventable. HBV reactivation is most commonly reported in patients receiving cancer chemotherapy, especially rituximab-containing therapy for hematological malignancies and those receiving stem cell transplantation. All patients with hematological malignancies receiving anticancer therapy should be screened for active or resolved HBV infection by blood tests for hepatitis B surface antigen (HBsAg) and antibody to hepatitis B core antigen (anti-HBc). Patients found to be positive for HBsAg should be given prophylactic antiviral therapy to prevent HBV reactivation. For patients with resolved HBV infection, no standard strategy has yet been established to prevent HBV reactivation. There are usually two options. One is pre-emptive therapy guided by serial HBV DNA monitoring, whereby antiviral therapy is given as soon as HBV DNA becomes detectable. However, there is little evidence regarding the optimal interval and period of monitoring. An alternative approach is prophylactic antiviral therapy, especially for patients receiving high-risk therapy such as rituximab, newer generation of anti-CD20 monoclonal antibody, obinutuzumab or hematopoietic stem cell transplantation. This strategy may effectively prevent HBV reactivation and avoid the inconvenience of repeated HBV DNA monitoring. Entecavir or tenofovir are preferred over lamivudine as prophylactic therapy. Although there is no well-defined guideline on the optimal duration of prophylactic therapy, there is growing evidence to recommend continuing prophylactic antiviral therapy for at least 12 mo after cessation of chemotherapy, and even longer for those who receive rituximab or who had high serum HBV DNA levels before the start of immunosuppressive therapy. Many novel agents have recently become available for the treatment of hematological malignancies, and these agents may be associated with HBV reactivation. Although there is currently limited evidence to guide the optimal preventive measures, we recommend antiviral prophylaxis in HBsAg-positive patients receiving novel treatments, especially the Bruton tyrosine kinase inhibitors and the phosphatidylinositol 3-kinase inhibitors, which are B-cell receptor signaling modulators and reduce proliferation of malignant B-cells. Further studies are needed to clarify the risk of HBV reactivation with these agents and the best prophylactic strategy in the era of targeted therapy for hematological malignancies. PMID:27605883

Diabetes enhances vulnerability to particulate air pollution-associated impairment in vascular reactivity and endothelial function.

PubMed

O'Neill, Marie S; Veves, Aristidis; Zanobetti, Antonella; Sarnat, Jeremy A; Gold, Diane R; Economides, Panayiotis A; Horton, Edward S; Schwartz, Joel

2005-06-07

Epidemiological studies suggest that people with diabetes are vulnerable to cardiovascular health effects associated with exposure to particle air pollution. Endothelial and vascular function is impaired in diabetes and may be related to increased cardiovascular risk. We examined whether endothelium-dependent and -independent vascular reactivity was associated with particle exposure in individuals with and without diabetes. Study subjects were 270 greater-Boston residents. We measured 24-hour average ambient levels of air pollution (fine particles [PM2.5], particle number, black carbon, and sulfates [SO4(2-)]) approximately 500 m from the patient examination site. Pollutant concentrations were evaluated for associations with vascular reactivity. Linear regressions were fit to the percent change in brachial artery diameter (flow mediated and nitroglycerin mediated), with the particulate pollutant index, apparent temperature, season, age, race, sex, smoking history, and body mass index as predictors. Models were fit to all subjects and then stratified by diagnosed diabetes versus at risk for diabetes. Six-day moving averages of all 4 particle metrics were associated with decreased vascular reactivity among patients with diabetes but not those at risk. Interquartile range increases in SO4(2-) were associated with decreased flow-mediated (-10.7%; 95% CI, -17.3 to -3.5) and nitroglycerin-mediated (-5.4%; 95% CI, -10.5 to -0.1) vascular reactivity among those with diabetes. Black carbon increases were associated with decreased flow-mediated vascular reactivity (-12.6%; 95% CI, -21.7 to -2.4), and PM2.5 was associated with nitroglycerin-mediated reactivity (-7.6%; 95% CI, -12.8 to -2.1). Effects were stronger in type II than type I diabetes. Diabetes confers vulnerability to particles associated with coal-burning power plants and traffic.

Case Studies of a Behavior Inclusion Model in an Elementary School District

ERIC Educational Resources Information Center

Santa Cruz, Margaret Escobar

2017-01-01

School discipline practices have traditionally been reactive and punitive in nature. Students violating a school district's code of conduct were often met with exclusionary discipline policies such as out-of-school suspensions, long-term suspensions, and expulsions. Districts attempted to resolve these practices by creating alternative education…

The direction of fluid flow during contact metamorphism of siliceous carbonate rocks: new data for the Monzoni and Predazzo aureoles, northern Italy, and a global review

NASA Astrophysics Data System (ADS)

Ferry, John M.; Wing, Boswell A.; Penniston-Dorland, Sarah C.; Rumble, Douglas

2002-03-01

Periclase formed in siliceous dolomitic marbles during contact metamorphism in the Monzoni and Predazzo aureoles, the Dolomites, northern Italy, by infiltration of the carbonate rocks by chemically reactive, H2O-rich fluids at 500 bar and 565-710 °C. The spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time-integrated flux ~5,000 and ~300 mol fluid/cm2 rock in the Monzoni and Predazzo aureoles, respectively. The new results for Monzoni and Predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction, amount, and controls on the geometry of reactive fluid flow during contact metamorphism of siliceous carbonate rocks. Flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton. Fluid flow in two of the other three was primarily horizontal, directed from the pluton into the aureole. The direction of flow in the remaining aureole is uncertain. Earlier suggestions that fluid flow is often horizontal, directed toward the pluton, are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions. With the exception of three samples from one aureole, time-integrated fluid flux was in the range 102-104 mol/cm2. Both the amount and direction of fluid flow are consistent with hydrodynamic models of contact metamorphism. The orientation of bedding and lithologic contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal. Other pre-metamorphic structures, including dikes, faults, fold hinges, and fracture zones, served to channel fluid flow as well.

The direction of fluid flow during contact metamorphism of siliceous carbonate rocks: new data for the Monzoni and Predazzo aureoles, northern Italy, and a global review

NASA Astrophysics Data System (ADS)

Ferry, John; Wing, Boswell; Penniston-Dorland, Sarah; Rumble, Douglas

2001-11-01

Periclase formed in siliceous dolomitic marbles during contact metamorphism in the Monzoni and Predazzo aureoles, the Dolomites, northern Italy, by infiltration of the carbonate rocks by chemically reactive, H2O-rich fluids at 500 bar and 565-710 °C. The spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time-integrated flux 5,000 and 300 mol fluid/cm2 rock in the Monzoni and Predazzo aureoles, respectively. The new results for Monzoni and Predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction, amount, and controls on the geometry of reactive fluid flow during contact metamorphism of siliceous carbonate rocks. Flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton. Fluid flow in two of the other three was primarily horizontal, directed from the pluton into the aureole. The direction of flow in the remaining aureole is uncertain. Earlier suggestions that fluid flow is often horizontal, directed toward the pluton, are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions. With the exception of three samples from one aureole, time-integrated fluid flux was in the range 102-104 mol/cm2. Both the amount and direction of fluid flow are consistent with hydrodynamic models of contact metamorphism. The orientation of bedding and lithologic contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal. Other pre-metamorphic structures, including dikes, faults, fold hinges, and fracture zones, served to channel fluid flow as well.

Large eddy simulation of forced ignition of an annular bluff-body burner

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

Subramanian, V.; Domingo, P.; Vervisch, L.

2010-03-15

The optimization of the ignition process is a crucial issue in the design of many combustion systems. Large eddy simulation (LES) of a conical shaped bluff-body turbulent nonpremixed burner has been performed to study the impact of spark location on ignition success. This burner was experimentally investigated by Ahmed et al. [Combust. Flame 151 (2007) 366-385]. The present work focuses on the case without swirl, for which detailed measurements are available. First, cold-flow measurements of velocities and mixture fractions are compared with their LES counterparts, to assess the prediction capabilities of simulations in terms of flow and turbulent mixing. Timemore » histories of velocities and mixture fractions are recorded at selected spots, to probe the resolved probability density function (pdf) of flow variables, in an attempt to reproduce, from the knowledge of LES-resolved instantaneous flow conditions, the experimentally observed reasons for success or failure of spark ignition. A flammability map is also constructed from the resolved mixture fraction pdf and compared with its experimental counterpart. LES of forced ignition is then performed using flamelet fully detailed tabulated chemistry combined with presumed pdfs. Various scenarios of flame kernel development are analyzed and correlated with typical flow conditions observed in this burner. The correlations between, velocities and mixture fraction values at the sparking time and the success or failure of ignition, are then further discussed and analyzed. (author)« less

Time-Resolved 3D Quantitative Flow MRI of the Major Intracranial Vessels: Initial Experience and Comparative Evaluation at 1.5T and 3.0T in Combination With Parallel Imaging

PubMed Central

Bammer, Roland; Hope, Thomas A.; Aksoy, Murat; Alley, Marcus T.

2012-01-01

Exact knowledge of blood flow characteristics in the major cerebral vessels is of great relevance for diagnosing cerebrovascular abnormalities. This involves the assessment of hemodynamically critical areas as well as the derivation of biomechanical parameters such as wall shear stress and pressure gradients. A time-resolved, 3D phase-contrast (PC) MRI method using parallel imaging was implemented to measure blood flow in three dimensions at multiple instances over the cardiac cycle. The 4D velocity data obtained from 14 healthy volunteers were used to investigate dynamic blood flow with the use of multiplanar reformatting, 3D streamlines, and 4D particle tracing. In addition, the effects of magnetic field strength, parallel imaging, and temporal resolution on the data were investigated in a comparative evaluation at 1.5T and 3T using three different parallel imaging reduction factors and three different temporal resolutions in eight of the 14 subjects. Studies were consistently performed faster at 3T than at 1.5T because of better parallel imaging performance. A high temporal resolution (65 ms) was required to follow dynamic processes in the intracranial vessels. The 4D flow measurements provided a high degree of vascular conspicuity. Time-resolved streamline analysis provided features that have not been reported previously for the intracranial vasculature. PMID:17195166

Forebody and base region real gas flow in severe planetary entry by a factored implicit numerical method. II - Equilibrium reactive gas

NASA Technical Reports Server (NTRS)

Davy, W. C.; Green, M. J.; Lombard, C. K.

1981-01-01

The factored-implicit, gas-dynamic algorithm has been adapted to the numerical simulation of equilibrium reactive flows. Changes required in the perfect gas version of the algorithm are developed, and the method of coupling gas-dynamic and chemistry variables is discussed. A flow-field solution that approximates a Jovian entry case was obtained by this method and compared with the same solution obtained by HYVIS, a computer program much used for the study of planetary entry. Comparison of surface pressure distribution and stagnation line shock-layer profiles indicates that the two solutions agree well.

Measurement of OH, O, and NO densities and their correlations with mouse melanoma cell death rate treated by a nanosecond pulsed streamer discharge

NASA Astrophysics Data System (ADS)

Yagi, Ippei; Shirakawa, Yuki; Hirakata, Kenta; Akiyama, Taketoshi; Yonemori, Seiya; Mizuno, Kazue; Ono, Ryo; Oda, Tetsuji

2015-10-01

Mouse melanoma cells in a culture medium are treated using a nanosecond pulsed streamer discharge plasma and the correlations between the rate of cell death and the densities of reactive species (OH, O, and NO) in the plasma are measured. The plasma is irradiated onto the culture medium surface with a vertical gas flow of an O2/N2 mixture from a glass tube at various gas flow rates and O2 concentrations. The densities of the reactive species are measured very close to the culture medium surface, where the reactive species interact with the culture medium, using laser-induced fluorescence. In the case of the N2 discharge (O2 = 0%), an increase in gas flow rate decreases OH density because it lowers the water vapor concentration by diluting the vapor, which is required for OH production. The increase in gas flow rate also leads to a decreased cell death rate. In the case of the O2/N2 discharge, on the other hand, an increase in O2 concentration at a fixed flow rate does not affect the rate of cell death, although it considerably changes the O and NO densities. These findings indicate that some reactive species derived from water vapor such as OH are responsible for the melanoma cell death, whereas those from O2, such as O and NO, are less likely responsible. They also indicate the importance of water evaporation from the culture medium surface in cell treatment.

Programmable flow system for automation of oxygen radical absorbance capacity assay using pyrogallol red for estimation of antioxidant reactivity.

PubMed

Ramos, Inês I; Gregório, Bruno J R; Barreiros, Luísa; Magalhães, Luís M; Tóth, Ildikó V; Reis, Salette; Lima, José L F C; Segundo, Marcela A

2016-04-01

An automated oxygen radical absorbance capacity (ORAC) method based on programmable flow injection analysis was developed for the assessment of antioxidant reactivity. The method relies on real time spectrophotometric monitoring (540 nm) of pyrogallol red (PGR) bleaching mediated by peroxyl radicals in the presence of antioxidant compounds within the first minute of reaction, providing information about their initial reactivity against this type of radicals. The ORAC-PGR assay under programmable flow format affords a strict control of reaction conditions namely reagent mixing, temperature and reaction timing, which are critical parameters for in situ generation of peroxyl radical from 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The influence of reagent concentrations and programmable flow conditions on reaction development was studied, with application of 37.5 µM of PGR and 125 mM of AAPH in the flow cell, guaranteeing first order kinetics towards peroxyl radicals and pseudo-zero order towards PGR. Peroxyl-scavenging reactivity of antioxidants, bioactive compounds and phenolic-rich beverages was estimated employing the proposed methodology. Recovery assays using synthetic saliva provided values of 90 ± 5% for reduced glutathione. Detection limit calculated using the standard antioxidant compound Trolox was 8 μM. RSD values were <3.4 and <4.9%, for intra and inter-assay precision, respectively. Compared to previous batch automated ORAC assays, the developed system also accounted for high sampling frequency (29 h(-1)), low operating costs and low generation of waste. Copyright © 2015 Elsevier B.V. All rights reserved.

Relation between digital peripheral arterial tonometry and brachial artery ultrasound measures of vascular function in patients with coronary artery disease and in healthy volunteers.

PubMed

Lee, Craig R; Bass, Almasa; Ellis, Kyle; Tran, Bryant; Steele, Savanna; Caughey, Melissa; Stouffer, George A; Hinderliter, Alan L

2012-03-01

Digital peripheral arterial tonometry (PAT) is an emerging, noninvasive method to assess vascular function. The physiology underlying this phenotype, however, remains unclear. Therefore, we evaluated the relation between digital PAT and established brachial artery ultrasound measures of vascular function under basal conditions and after reactive hyperemia. Using a cross-sectional study design, digital PAT and brachial artery ultrasonography with pulsed wave Doppler were simultaneously completed at baseline and after reactive hyperemia in both those with established coronary artery disease (n = 99) and healthy volunteers with low cardiovascular disease risk (n = 40). Under basal conditions, the digital pulse volume amplitude demonstrated a significant positive correlation with the brachial artery velocity-time integral that was independent of the arterial diameter, in both the healthy volunteer (r(s) = 0.64, p <0.001) and coronary artery disease (r(s) = 0.63, p <0.001) cohorts. Similar positive relations were observed with the baseline brachial artery blood flow velocity and blood flow. In contrast, no relation between the reactive hyperemia-evoked digital PAT ratio and either brachial artery flow-mediated dilation or shear stress was observed in either cohort (p = NS). In conclusion, these findings demonstrate that the digital PAT measures of vascular function more closely reflect basal blood flow in the brachial artery than reactive hyperemia-induced changes in the arterial diameter or flow velocity, and the presence of vascular disease does not modify the physiology underlying the digital PAT phenotype. Copyright © 2012 Elsevier Inc. All rights reserved.

Reaction front dynamics under shear flow for arbitrary Damköhler numbers

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Méheust, Yves; Le Borgne, Tanguy

2016-04-01

Reaction fronts where two reactive fluids displace one another play an important role in a range of applications, including contaminant plume transport and reaction, soil and aquifer remediation, CO2 sequestration, geothermal dipoles and the development of hotspots of reaction in mixing zones. The background flow induces enhanced mixing, and therefore reaction, through interfacial shear. Hence the coupling of fluid flow with chemical reactions is pivotal in understanding and quantifying effective reaction kinetics in reaction fronts. While this problem has been addressed in the limit of fast reactions (e.g. de Simoni 2005, Le Borgne 2014), in natural systems reactions can span a large range of Damköhler numbers since their characteristic reaction times vary over a large range of typical values. Here the coupling of shear flow and reversible chemical reactions is studied for a reaction front with initially separated reactants at arbitrary Damköhler numbers. Approximate analytical expressions for the global production rate are derived based on a reactive lamella approach. We observe three distinct regimes, each of them characterized by different scalings of the global production rate and width of the reactive zone. We describe the dependency of these scalings and the associated characteristic transition times as a function of Damköhler and Péclet numbers. These results are validated against 2D numerical simulations. The study is expected to shed light on the inherently complex cases of reactive mixing with varying reaction rates under the influence of an imposed flow. de Simoni et al. (2005) Water Resour. Res., 41, W11410 Le Borgne et al. (2014) GRL, 41(22), 7898

Adapting HYDRUS-1D to simulate overland flow and reactive transport during sheet flow deviations

USDA-ARS?s Scientific Manuscript database

The HYDRUS-1D code is a popular numerical model for solving the Richards equation for variably-saturated water flow and solute transport in porous media. This code was adapted to solve rather than the Richards equation for subsurface flow the diffusion wave equation for overland flow at the soil sur...

A comprehensive approach to reactive power scheduling in restructured power systems

NASA Astrophysics Data System (ADS)

Shukla, Meera

Financial constraints, regulatory pressure, and need for more economical power transfers have increased the loading of interconnected transmission systems. As a consequence, power systems have been operated close to their maximum power transfer capability limits, making the system more vulnerable to voltage instability events. The problem of voltage collapse characterized by a severe local voltage depression is generally believed to be associated with inadequate VAr support at key buses. The goal of reactive power planning is to maintain a high level of voltage security, through installation of properly sized and located reactive sources and their optimal scheduling. In case of vertically-operated power systems, the reactive requirement of the system is normally satisfied by using all of its reactive sources. But in case of different scenarios of restructured power systems, one may consider a fixed amount of exchange of reactive power through tie lines. Reviewed literature suggests a need for optimal scheduling of reactive power generation for fixed inter area reactive power exchange. The present work proposed a novel approach for reactive power source placement and a novel approach for its scheduling. The VAr source placement technique was based on the property of system connectivity. This is followed by development of optimal reactive power dispatch formulation which facilitated fixed inter area tie line reactive power exchange. This formulation used a Line Flow-Based (LFB) model of power flow analysis. The formulation determined the generation schedule for fixed inter area tie line reactive power exchange. Different operating scenarios were studied to analyze the impact of VAr management approach for vertically operated and restructured power systems. The system loadability, losses, generation and the cost of generation were the performance measures to study the impact of VAr management strategy. The novel approach was demonstrated on IEEE 30 bus system.

THC-MP: High performance numerical simulation of reactive transport and multiphase flow in porous media

NASA Astrophysics Data System (ADS)

Wei, Xiaohui; Li, Weishan; Tian, Hailong; Li, Hongliang; Xu, Haixiao; Xu, Tianfu

2015-07-01

The numerical simulation of multiphase flow and reactive transport in the porous media on complex subsurface problem is a computationally intensive application. To meet the increasingly computational requirements, this paper presents a parallel computing method and architecture. Derived from TOUGHREACT that is a well-established code for simulating subsurface multi-phase flow and reactive transport problems, we developed a high performance computing THC-MP based on massive parallel computer, which extends greatly on the computational capability for the original code. The domain decomposition method was applied to the coupled numerical computing procedure in the THC-MP. We designed the distributed data structure, implemented the data initialization and exchange between the computing nodes and the core solving module using the hybrid parallel iterative and direct solver. Numerical accuracy of the THC-MP was verified through a CO2 injection-induced reactive transport problem by comparing the results obtained from the parallel computing and sequential computing (original code). Execution efficiency and code scalability were examined through field scale carbon sequestration applications on the multicore cluster. The results demonstrate successfully the enhanced performance using the THC-MP on parallel computing facilities.

Reactivity of Iron Bearing Minerals and CO 2 Sequestration: A Multi-­Disciplinary and Experimental Approach

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

Schoonen, Martin A.

2014-12-22

The reactivity of sandstones was studied under conditions relevant to the injection of supercritical carbon dioxide in the context of carbon geosequestration. The emphasis of the study was on the reactivity of iron-­bearing minerals when exposed to supercritical CO 2 (scCO 2) and scCO 2 with commingled aqueous solutions containing H 2S and/or SO 2. Flow through and batch experiments were conducted. Results indicate that sandstones, irrespective of their mineralogy, are not reactive when exposed to pure scCO2 or scCO 2 with commingled aqueous solutions containing H 2S and/or SO 2 under conditions simulating the environment near the injection pointmore » (flow through experiments). However, sandstones are reactive under conditions simulating the edge of the injected CO 2 plume or ahead of the plume (batch experiments). Sandstones containing hematite (red sandstone) are particularly reactive. The composition of the reaction products is strongly dependent on the composition of the aqueous phase. The presence of dissolved sulfide leads to the conversion of hematite into pyrite and siderite. The relative amount of the pyrite and siderite is influenced by the ionic strength of the solution. Little reactivity is observed when sulfite is present in the aqueous phase. Sandstones without hematite (grey sandstones) show little reactivity regardless of the solution composition.« less

A spectral radius scaling semi-implicit iterative time stepping method for reactive flow simulations with detailed chemistry

NASA Astrophysics Data System (ADS)

Xie, Qing; Xiao, Zhixiang; Ren, Zhuyin

2018-09-01

A spectral radius scaling semi-implicit time stepping scheme has been developed for simulating unsteady compressible reactive flows with detailed chemistry, in which the spectral radius in the LUSGS scheme has been augmented to account for viscous/diffusive and reactive terms and a scalar matrix is proposed to approximate the chemical Jacobian using the minimum species destruction timescale. The performance of the semi-implicit scheme, together with a third-order explicit Runge-Kutta scheme and a Strang splitting scheme, have been investigated in auto-ignition and laminar premixed and nonpremixed flames of three representative fuels, e.g., hydrogen, methane, and n-heptane. Results show that the minimum species destruction time scale can well represent the smallest chemical time scale in reactive flows and the proposed scheme can significantly increase the allowable time steps in simulations. The scheme is stable when the time step is as large as 10 μs, which is about three to five orders of magnitude larger than the smallest time scales in various tests considered. For the test flames considered, the semi-implicit scheme achieves second order of accuracy in time. Moreover, the errors in quantities of interest are smaller than those from the Strang splitting scheme indicating the accuracy gain when the reaction and transport terms are solved coupled. Results also show that the relative efficiency of different schemes depends on fuel mechanisms and test flames. When the minimum time scale in reactive flows is governed by transport processes instead of chemical reactions, the proposed semi-implicit scheme is more efficient than the splitting scheme. Otherwise, the relative efficiency depends on the cost in sub-iterations for convergence within each time step and in the integration for chemistry substep. Then, the capability of the compressible reacting flow solver and the proposed semi-implicit scheme is demonstrated for capturing the hydrogen detonation waves. Finally, the performance of the proposed method is demonstrated in a two-dimensional hydrogen/air diffusion flame.

Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies

PubMed Central

Krishna, Katla Sai; Biswas, Sanchita; Navin, Chelliah V.; Yamane, Dawit G.; Miller, Jeffrey T.; Kumar, Challa S.S.R.

2013-01-01

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the first, synthesis of ultra-small copper nanoclusters is described. The second example provides their utility for investigating time resolved kinetics of chemical reactions by analyzing gold nanoparticle formation using in situ X-ray absorption spectroscopy. The final example demonstrates continuous flow catalysis of reactions inside millifluidic channel coated with nanostructured catalyst. PMID:24327099

Contrast-enhanced time-resolved MRA for follow-up of intracranial aneurysms treated with the pipeline embolization device.

PubMed

Boddu, S R; Tong, F C; Dehkharghani, S; Dion, J E; Saindane, A M

2014-01-01

Endovascular reconstruction and flow diversion by using the Pipeline Embolization Device is an effective treatment for complex cerebral aneurysms. Accurate noninvasive alternatives to DSA for follow-up after Pipeline Embolization Device treatment are desirable. This study evaluated the accuracy of contrast-enhanced time-resolved MRA for this purpose, hypothesizing that contrast-enhanced time-resolved MRA will be comparable with DSA and superior to 3D-TOF MRA. During a 24-month period, 37 Pipeline Embolization Device-treated intracranial aneurysms in 26 patients underwent initial follow-up by using 3D-TOF MRA, contrast-enhanced time-resolved MRA, and DSA. MRA was performed on a 1.5T unit by using 3D-TOF and time-resolved imaging of contrast kinetics. All patients underwent DSA a median of 0 days (range, 0-68) after MRA. Studies were evaluated for aneurysm occlusion, quality of visualization of the reconstructed artery, and measurable luminal diameter of the Pipeline Embolization Device, with DSA used as the reference standard. The sensitivity, specificity, and positive and negative predictive values of contrast-enhanced time-resolved MRA relative to DSA for posttreatment aneurysm occlusion were 96%, 85%, 92%, and 92%. Contrast-enhanced time-resolved MRA demonstrated superior quality of visualization (P = .0001) and a higher measurable luminal diameter (P = .0001) of the reconstructed artery compared with 3D-TOF MRA but no significant difference compared with DSA. Contrast-enhanced time-resolved MRA underestimated the luminal diameter of the reconstructed artery by 0.965 ± 0.497 mm (27% ± 13%) relative to DSA. Contrast-enhanced time-resolved MRA is a reliable noninvasive method for monitoring intracranial aneurysms following flow diversion and vessel reconstruction by using the Pipeline Embolization Device. © 2014 by American Journal of Neuroradiology.

Assessment of two-phase flow on the chemical alteration and sealing of leakage pathways in cemented wellbores

DOE PAGES

Iyer, Jaisree; Walsh, Stuart D. C.; Hao, Yue; ...

2018-01-08

Wellbore leakage tops the list of perceived risks to the long-term geologic storage of CO 2, because wells provide a direct path between the CO 2 storage reservoir and the atmosphere. In this paper, we have coupled a two-phase flow model with our original framework that combined models for reactive transport of carbonated brine, geochemistry of reacting cement, and geomechanics to predict the permeability evolution of cement fractures. Additionally, this makes the framework suitable for field conditions in geological storage sites, permitting simulation of contact between cement and mixtures of brine and supercritical CO 2. Due to lack of conclusivemore » experimental data, we tried both linear and Corey relative permeability models to simulate flow of the two phases in cement fractures. The model also includes two options to account for the inconsistent experimental observations regarding cement reactivity with two-phase CO 2-brine mixtures. One option assumes that the reactive surface area is independent of the brine saturation and the second option assumes that the reactive surface area is proportional to the brine saturation. We have applied the model to predict the extent of cement alteration, the conditions under which fractures seal, the time it takes to seal a fracture, and the leakage rates of CO 2 and brine when damage zones in the wellbore are exposed to two-phase CO 2-brine mixtures. Initial brine residence time and the initial fracture aperture are critical parameters that affect the fracture sealing behavior. We also evaluated the importance of the model assumptions regarding relative permeability and cement reactivity. These results illustrate the need to understand how mixtures of carbon dioxide and brine flow through fractures and react with cement to make reasonable predictions regarding well integrity. For example, a reduction in the cement reactivity with two-phase CO 2-brine mixture can not only significantly increase the sealing time for fractures but may also prevent fracture sealing.« less

Multi-scale modeling of multi-component reactive transport in geothermal aquifers

NASA Astrophysics Data System (ADS)

Nick, Hamidreza M.; Raoof, Amir; Wolf, Karl-Heinz; Bruhn, David

2014-05-01

In deep geothermal systems heat and chemical stresses can cause physical alterations, which may have a significant effect on flow and reaction rates. As a consequence it will lead to changes in permeability and porosity of the formations due to mineral precipitation and dissolution. Large-scale modeling of reactive transport in such systems is still challenging. A large area of uncertainty is the way in which the pore-scale information controlling the flow and reaction will behave at a larger scale. A possible choice is to use constitutive relationships relating, for example the permeability and porosity evolutions to the change in the pore geometry. While determining such relationships through laboratory experiments may be limited, pore-network modeling provides an alternative solution. In this work, we introduce a new workflow in which a hybrid Finite-Element Finite-Volume method [1,2] and a pore network modeling approach [3] are employed. Using the pore-scale model, relevant constitutive relations are developed. These relations are then embedded in the continuum-scale model. This approach enables us to study non-isothermal reactive transport in porous media while accounting for micro-scale features under realistic conditions. The performance and applicability of the proposed model is explored for different flow and reaction regimes. References: 1. Matthäi, S.K., et al.: Simulation of solute transport through fractured rock: a higher-order accurate finite-element finite-volume method permitting large time steps. Transport in porous media 83.2 (2010): 289-318. 2. Nick, H.M., et al.: Reactive dispersive contaminant transport in coastal aquifers: Numerical simulation of a reactive Henry problem. Journal of contaminant hydrology 145 (2012), 90-104. 3. Raoof A., et al.: PoreFlow: A Complex pore-network model for simulation of reactive transport in variably saturated porous media, Computers & Geosciences, 61, (2013), 160-174.

Assessment of two-phase flow on the chemical alteration and sealing of leakage pathways in cemented wellbores

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

Iyer, Jaisree; Walsh, Stuart D. C.; Hao, Yue

Wellbore leakage tops the list of perceived risks to the long-term geologic storage of CO 2, because wells provide a direct path between the CO 2 storage reservoir and the atmosphere. In this paper, we have coupled a two-phase flow model with our original framework that combined models for reactive transport of carbonated brine, geochemistry of reacting cement, and geomechanics to predict the permeability evolution of cement fractures. Additionally, this makes the framework suitable for field conditions in geological storage sites, permitting simulation of contact between cement and mixtures of brine and supercritical CO 2. Due to lack of conclusivemore » experimental data, we tried both linear and Corey relative permeability models to simulate flow of the two phases in cement fractures. The model also includes two options to account for the inconsistent experimental observations regarding cement reactivity with two-phase CO 2-brine mixtures. One option assumes that the reactive surface area is independent of the brine saturation and the second option assumes that the reactive surface area is proportional to the brine saturation. We have applied the model to predict the extent of cement alteration, the conditions under which fractures seal, the time it takes to seal a fracture, and the leakage rates of CO 2 and brine when damage zones in the wellbore are exposed to two-phase CO 2-brine mixtures. Initial brine residence time and the initial fracture aperture are critical parameters that affect the fracture sealing behavior. We also evaluated the importance of the model assumptions regarding relative permeability and cement reactivity. These results illustrate the need to understand how mixtures of carbon dioxide and brine flow through fractures and react with cement to make reasonable predictions regarding well integrity. For example, a reduction in the cement reactivity with two-phase CO 2-brine mixture can not only significantly increase the sealing time for fractures but may also prevent fracture sealing.« less

Unsteady, one-dimensional gas dynamics computations using a TVD type sequential solver

NASA Technical Reports Server (NTRS)

Thakur, Siddharth; Shyy, Wei

1992-01-01

The efficacy of high resolution convection schemes to resolve sharp gradient in unsteady, 1D flows is examined using the TVD concept based on a sequential solution algorithm. Two unsteady flow problems are considered which include the problem involving the interaction of the various waves in a shock tube with closed reflecting ends and the problem involving the unsteady gas dynamics in a tube with closed ends subject to an initial pressure perturbation. It is concluded that high accuracy convection schemes in a sequential solution framework are capable of resolving discontinuities in unsteady flows involving complex gas dynamics. However, a sufficient amount of dissipation is required to suppress oscillations near discontinuities in the sequential approach, which leads to smearing of the solution profiles.

Time dependent three-dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surface

NASA Technical Reports Server (NTRS)

Neuhauser, Daniel; Baer, Michael; Judson, Richard S.; Kouri, Donald J.

1989-01-01

The first successful application of the three-dimensional quantum body frame wave packet approach to reactive scattering is reported for the H + H2 exchange reaction on the LSTH potential surface. The method used is based on a procedure for calculating total reaction probabilities from wave packets. It is found that converged, vibrationally resolved reactive probabilities can be calculated with a grid that is not much larger than required for the pure inelastic calculation. Tabular results are presented for several energies.

The laser versus the lamp: Reactivity of the diphenyl ketyl radical in the ground and excited states

NASA Astrophysics Data System (ADS)

Baumann, H.; Merckel, C.; Timpe, H.-J.; Graness, A.; Kleinschmidt, J.; Gould, I. R.; Turro, N. J.

1984-01-01

The diphenyl ketyl radical which is formed upon photolysis of α-phenyl benzoin is produced in its excited state upon intense pulsed laser irradiation. Using the techniques of time-resolved absorption and emission spectroscopy, reaction rate constants for the ground and excited states of this radical were obtained. For the radical quenchers employed, the excited state reactivity is found to be typically several orders of magnitude greater than that of the ground state. It is concluded that the excited state of diphenyl ketyl radical reacts predominantly by electron transfer processes.

Fracture sealing caused by mineral precipitation: The role of aperture and mineral heterogeneity on precipitation-induced permeability loss

NASA Astrophysics Data System (ADS)

Jones, T.; Detwiler, R. L.

2017-12-01

Fractures act as dominant pathways for fluid flow in low-permeability rocks. However, in many subsurface environments, fluid rock reactions can lead to mineral precipitation, which alters fracture surface geometry and reduces fracture permeability. In natural fractures, surface mineralogy and roughness are often heterogeneous, leading to variations in both velocity and reactive surface area. The combined effects of surface roughness and mineral heterogeneity can lead to large disparities in local precipitation rates that are difficult to predict due to the strong coupling between dissolved mineral transport and reactions at the fracture surface. Recent experimental observations suggest that mineral precipitation in a heterogeneous fracture may promote preferential flow and focus large dissolved ion concentrations into regions with limited reactive surface area. Here, we build on these observations using reactive transport simulations. Reactive transport is simulated with a quasi-steady-state 2D model that uses a depth-averaged mass-transfer relationship to describe dissolved mineral transport across the fracture aperture and local precipitation reactions. Mineral precipitation-induced changes to fracture surface geometry are accounted for using two different approaches: (1) by only allowing reactive minerals to grow vertically, and (2) by allowing three-dimensional mineral growth at reaction sites. Preliminary results from simulations using (1) suggest that precipitation-induced aperture reduction focuses flow into thin flow paths. This flow focusing causes a reduction in the fracture-scale precipitation rate, and precipitation ceases when the reaction zone extends the entire length of the fracture. This approach reproduces experimental observations at early time reasonably well, but as precipitation proceeds, reaction sites can grow laterally along the fracture surfaces, which is not predicted by (1). To account for three-dimensional mineral growth (2), we have incorporated a level-set-method based approach for tracking the mineral interfaces in three dimensions. This provides a mechanistic approach for simulating the dynamics of the formation, and eventual closing, of preferential flow paths by precipitation-induced aperture alteration, that do not occur using (1).

PIV measurements and flow characteristics downstream of mangrove root models

NASA Astrophysics Data System (ADS)

Kazemi, Amirkhosro; Curet, Oscar

2016-11-01

Mangrove forests attracted attentions as a solution to protect coastal areas exposed to sea-level rising, frequent storms, and tsunamis. Mangrove forests found in tide-dominated flow regions are characterized by their massive and complex root systems, which play a prominent role in the structure of tidal flow currents. To understand the role of mangrove roots in flow structure, we modeled mangrove roots with rigid and flexible arrays of cylinders with different spacing between them as well as different configurations. In this work, we investigate the fluid dynamics downstream of the models using a 2-D time-resolved particle image velocimetry (PIV) and flow visualization. We carried out experiments for four different Reynolds number based on cylinder diameters ranges from 2200 to 12000. We present time-averaged and time-resolved flow parameters including velocity distribution, vorticity, streamline, Reynolds shear stress and turbulent kinetic energy. The results show that the flow structure has different vortex shedding downstream of the cylinders due to interactions of shear layers separating from cylinders surface. The spectral analysis of the measured velocity data is also performed to obtain Strouhal number of the unsteady flow in the cylinder wake.

Relationship between haemodynamic impairment and collateral blood flow in carotid artery disease.

PubMed

Hartkamp, Nolan S; Petersen, Esben T; Chappell, Michael A; Okell, Thomas W; Uyttenboogaart, Maarten; Zeebregts, Clark J; Bokkers, Reinoud Ph

2017-01-01

Collateral blood flow plays a pivotal role in steno-occlusive internal carotid artery (ICA) disease to prevent irreversible ischaemic damage. Our aim was to investigate the effect of carotid artery disease upon cerebral perfusion and cerebrovascular reactivity and whether haemodynamic impairment is influenced at brain tissue level by the existence of primary and/or secondary collateral. Eighty-eight patients with steno-occlusive ICA disease and 29 healthy controls underwent MR examination. The presence of collaterals was determined with time-of-flight, two-dimensional phase contrast MRA and territorial arterial spin labeling (ASL) imaging. Cerebral blood flow and cerebrovascular reactivity were assessed with ASL before and after acetazolamide. Cerebral haemodynamics were normal in asymptomatic ICA stenosis patients, as opposed to patients with ICA occlusion, in whom the haemodynamics in both hemispheres were compromised. Haemodynamic impairment in the affected brain region was always present in symptomatic patients. The degree of collateral blood flow was inversely correlated with haemodynamic impairment. Recruitment of secondary collaterals only occurred in symptomatic ICA occlusion patients. In conclusion, both CBF and cerebrovascular reactivity were found to be reduced in symptomatic patients with steno-occlusive ICA disease. The presence of collateral flow is associated with further haemodynamic impairment. Recruitment of secondary collaterals is associated with severe haemodynamic impairment.

Continuous flow hygroscopicity-resolved relaxed eddy accumulation (Hy-Res REA) method of measuring size-resolved sodium chloride particle fluxes

EPA Science Inventory

The accurate representation of aerosols in climate models requires direct ambient measurement of the size- and composition-dependent particle production fluxes. Here, we present the design, testing, and analysis of data collected through the first instrument capable of measuring ...

PDF calculation of scalar mixing layer with simple chemical reactions

NASA Astrophysics Data System (ADS)

Kanzaki, Takao; Pope, Stephen B.

1999-11-01

A joint velocity-composition-turbulent frequency PDF(JPDF) model is used to simulate reactive mixing layer in a grid-generated turbulence with the influence of second-order irreversible chemical reactions. To investigate the effects of molecular mixing, a gas flow and a liquid flow are simulated. For a gas flow, the oxidation reaction (NO+ O3 arrow NO2 +O2 ) between nitricoxide (NO) and ozone (O3 ) is used. For a liquid flow, the saponification reaction(NaOH+HCOOCH3 arrow HCOONa+CH_3OH) between sodiumhydroxide(NaOH) and methylformate(HCOOCH_3) is used. The both cases are moderately fast reactions. Therefore, reactive scalar statistics are affected by turbulent mixing. The results of caliculation are compared with experimental data of Komori et al.(1994) and Bilger et al.(1991)

Fluid mechanics and heat transfer spirally fluted tubing

NASA Astrophysics Data System (ADS)

Yampolsky, J. S.; Libby, P. A.; Launder, B. E.; Larue, J. C.

1984-12-01

The objective of this program is to develop an understanding of the fluid mechanics and heat transfer mechanisms that result in the demonstrated performance of the spiral fluted tubing under development at GA Technologies Inc. Particularly emphasized are the processes that result in the augmentation of the heat transfer coefficient without an increase in friction coefficient in the single-phase flow. Quantitative delineation of these processes would allow for their application to the optimal solution of heat transfer problems in general was well as to tubular heat exchanges using spiral fluted tubes. The experimental phase of the program consisted of the following: (1) Flow visualization studies using high-speed photography of dye injected into water flowing in a cast acrylic spiral fluted tube. (2) Time-resolved axial velocity measurements as a function of radius at the exit plane of a spiral fluted tube with water flowing through the tube. (3) Simultaneous time-resolved measurements of the axial and radial velocity components and temperature with heated air flowing through the tube cooled by a water jacket.

High sensitivity detection and sorting of infectious human immunodeficiency virus (HIV-1) particles by flow virometry

PubMed Central

Bonar, Micha M.; Tilton, John C.

2017-01-01

Detection of viruses by flow cytometry is complicated by their small size. Here, we characterized the ability of a standard (FACSAria II) and a sub-micron flow cytometer (A50 Micro) to resolve HIV-1 viruses. The A50 was superior at resolving small particles but did not reliably distinguish HIV-1, extracellular vesicles, and laser noise by light scatter properties alone. However, single fluorescent HIV-1 particles could readily be detected by both cytometers. Fluorescent particles were sorted and retained infectivity, permitting further exploration of the functional consequences of HIV-1 heterogeneity. Finally, flow cytometry had a limit of detection of 80 viruses/ml, nearly equal to PCR assays. These studies demonstrate the power of flow cytometry to detect and sort viral particles and provide a critical toolkit to validate methods to label wild-type HIV-1; quantitatively assess integrity and aggregation of viruses and virus-based therapeutics; and efficiently screen drugs inhibiting viral assembly and release. PMID:28235684

High sensitivity detection and sorting of infectious human immunodeficiency virus (HIV-1) particles by flow virometry.

PubMed

Bonar, Michał M; Tilton, John C

2017-05-01

Detection of viruses by flow cytometry is complicated by their small size. Here, we characterized the ability of a standard (FACSAria II) and a sub-micron flow cytometer (A50 Micro) to resolve HIV-1 viruses. The A50 was superior at resolving small particles but did not reliably distinguish HIV-1, extracellular vesicles, and laser noise by light scatter properties alone. However, single fluorescent HIV-1 particles could readily be detected by both cytometers. Fluorescent particles were sorted and retained infectivity, permitting further exploration of the functional consequences of HIV-1 heterogeneity. Finally, flow cytometry had a limit of detection of 80 viruses/ml, nearly equal to PCR assays. These studies demonstrate the power of flow cytometry to detect and sort viral particles and provide a critical toolkit to validate methods to label wild-type HIV-1; quantitatively assess integrity and aggregation of viruses and virus-based therapeutics; and efficiently screen drugs inhibiting viral assembly and release. Copyright © 2017 Elsevier Inc. All rights reserved.

Time resolved PIV and flow visualization of 3D sheet cavitation

NASA Astrophysics Data System (ADS)

Foeth, E. J.; van Doorne, C. W. H.; van Terwisga, T.; Wieneke, B.

2006-04-01

Time-resolved PIV was applied to study fully developed sheet cavitation on a hydrofoil with a spanwise varying angle of attack. The hydrofoil was designed to have a three-dimensional cavitation pattern closely related to propeller cavitation, studied for its adverse effects as vibration, noise, and erosion production. For the PIV measurements, fluorescent tracer particles were applied in combination with an optical filter, in order to remove the reflections of the laser lightsheet by the cavitation. An adaptive mask was developed to find the interface between the vapor and liquid phase. The velocity at the interface of the cavity was found to be very close to the velocity predicted by a simple streamline model. For a visualization of the global flow dynamics, the laser beam was expanded and used to illuminate the entire hydrofoil and cavitation structure. The time-resolved recordings reveal the growth of the attached cavity and the cloud shedding. Our investigation proves the viability of accurate PIV measurements around developed sheet cavitation. The presented results will further be made available as a benchmark for the validation of numerical simulations of this complicated flow.

Simultaneous temporally resolved DPIV and pressure measurements of symmetric oscillations in a scaled-up vocal fold model

NASA Astrophysics Data System (ADS)

Ringenberg, Hunter; Rogers, Dylan; Wei, Nathaniel; Krane, Michael; Wei, Timothy

2017-11-01

The objective of this study is to apply experimental data to theoretical framework of Krane (2013) in which the principal aeroacoustic source is expressed in terms of vocal fold drag, glottal jet dynamic head, and glottal exit volume flow, reconciling formal theoretical aeroacoustic descriptions of phonation with more traditional lumped-element descriptions. These quantities appear in the integral equations of motion for phonatory flow. In this way time resolved velocity field measurements can be used to compute time-resolved estimates of the relevant terms in the integral equations of motion, including phonation aeroacoustic source strength. A simplified 10x scale vocal fold model from Krane, et al. (2007) was used to examine symmetric, i.e. `healthy', oscillatory motion of the vocal folds. By using water as the working fluid, very high spatial and temporal resolution was achieved. Temporal variation of transglottal pressure was simultaneously measured with flow on the vocal fold model mid-height. Experiments were dynamically scaled to examine a range of frequencies corresponding to male and female voice. The simultaneity of the pressure and flow provides new insights into the aeroacoustics associated with vocal fold oscillations. Supported by NIH Grant No. 2R01 DC005642-11.

Interface-Resolving Simulation of Collision Efficiency of Cloud Droplets

NASA Astrophysics Data System (ADS)

Wang, Lian-Ping; Peng, Cheng; Rosa, Bodgan; Onishi, Ryo

2017-11-01

Small-scale air turbulence could enhance the geometric collision rate of cloud droplets while large-scale air turbulence could augment the diffusional growth of cloud droplets. Air turbulence could also enhance the collision efficiency of cloud droplets. Accurate simulation of collision efficiency, however, requires capture of the multi-scale droplet-turbulence and droplet-droplet interactions, which has only been partially achieved in the recent past using the hybrid direct numerical simulation (HDNS) approach. % where Stokes disturbance flow is assumed. The HDNS approach has two major drawbacks: (1) the short-range droplet-droplet interaction is not treated rigorously; (2) the finite-Reynolds number correction to the collision efficiency is not included. In this talk, using two independent numerical methods, we will develop an interface-resolved simulation approach in which the disturbance flows are directly resolved numerically, combined with a rigorous lubrication correction model for near-field droplet-droplet interaction. This multi-scale approach is first used to study the effect of finite flow Reynolds numbers on the droplet collision efficiency in still air. Our simulation results show a significant finite-Re effect on collision efficiency when the droplets are of similar sizes. Preliminary results on integrating this approach in a turbulent flow laden with droplets will also be presented. This work is partially supported by the National Science Foundation.

Nanofluidic fuel cell

NASA Astrophysics Data System (ADS)

Lee, Jin Wook; Kjeang, Erik

2013-11-01

Fuel cells are gaining momentum as a critical component in the renewable energy mix for stationary, transportation, and portable power applications. State-of-the-art fuel cell technology benefits greatly from nanotechnology applied to nanostructured membranes, catalysts, and electrodes. However, the potential of utilizing nanofluidics for fuel cells has not yet been explored, despite the significant opportunity of harnessing rapid nanoscale reactant transport in close proximity to the reactive sites. In the present article, a nanofluidic fuel cell that utilizes fluid flow through nanoporous media is conceptualized and demonstrated for the first time. This transformative concept captures the advantages of recently developed membraneless and catalyst-free fuel cell architectures paired with the enhanced interfacial contact area enabled by nanofluidics. When compared to previously reported microfluidic fuel cells, the prototype nanofluidic fuel cell demonstrates increased surface area, reduced activation overpotential, superior kinetic characteristics, and moderately enhanced fuel cell performance in the high cell voltage regime with up to 14% higher power density. However, the expected mass transport benefits in the high current density regime were constrained by high ohmic cell resistance, which could likely be resolved through future optimization studies.

Artificial Photosynthetic Reaction Center Exhibiting Acid-Responsive Regulation of Photoinduced Charge Separation

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

Pahk, Ian; Kodis, Gerdenis; Fleming, Graham R.

Charge separation (CS) is the primary light-driven reaction in photosynthesis whereas onphotochemical quenching (NPQ) is a photoprotective regulatory mechanism employed by many photosynthetic organisms to dynamically modulate energy flow within the photosynthetic apparatus in response to fluctuating light conditions. Activated by decreases in lumen pH produced during periods of high photon flux, NPQ induces rapid thermal dissipation of excess excitation energy. As a result, the rate of CS decreases, thereby limiting the accumulation of potentially deleterious reactive intermediates and byproducts. In this article, a molecular triad that functionally mimics the effects of NPQ associated with an artificial photosynthetic reaction centermore » is described. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies have been used to demonstrate a 1 order of magnitude reduction in the CS quantum yield via reversible protonation of an excited-state-quenching molecular switch moiety. As in the natural system, the populations of unquenched and quenched states and therefore the overall yields of CS were found to be dependent on acid concentration.« less

An efficient unstructured WENO method for supersonic reactive flows

NASA Astrophysics Data System (ADS)

Zhao, Wen-Geng; Zheng, Hong-Wei; Liu, Feng-Jun; Shi, Xiao-Tian; Gao, Jun; Hu, Ning; Lv, Meng; Chen, Si-Cong; Zhao, Hong-Da

2018-03-01

An efficient high-order numerical method for supersonic reactive flows is proposed in this article. The reactive source term and convection term are solved separately by splitting scheme. In the reaction step, an adaptive time-step method is presented, which can improve the efficiency greatly. In the convection step, a third-order accurate weighted essentially non-oscillatory (WENO) method is adopted to reconstruct the solution in the unstructured grids. Numerical results show that our new method can capture the correct propagation speed of the detonation wave exactly even in coarse grids, while high order accuracy can be achieved in the smooth region. In addition, the proposed adaptive splitting method can reduce the computational cost greatly compared with the traditional splitting method.

Modelling of reactive fluid transport in deformable porous rocks

NASA Astrophysics Data System (ADS)

Yarushina, V. M.; Podladchikov, Y. Y.

2009-04-01

One outstanding challenge in geology today is the formulation of an understanding of the interaction between rocks and fluids. Advances in such knowledge are important for a broad range of geologic settings including partial melting and subsequent migration and emplacement of a melt into upper levels of the crust, or fluid flow during regional metamorphism and metasomatism. Rock-fluid interaction involves heat and mass transfer, deformation, hydrodynamic flow, and chemical reactions, thereby necessitating its consideration as a complex process coupling several simultaneous mechanisms. Deformation, chemical reactions, and fluid flow are coupled processes. Each affects the others. Special effort is required for accurate modelling of the porosity field through time. Mechanical compaction of porous rocks is usually treated under isothermal or isoentropic simplifying assumptions. However, joint consideration of both mechanical compaction and reactive porosity alteration requires somewhat greater than usual care about thermodynamic consistency. Here we consider the modelling of multi-component, multi-phase systems, which is fundamental to the study of fluid-rock interaction. Based on the conservation laws for mass, momentum, and energy in the form adopted in the theory of mixtures, we derive a thermodynamically admissible closed system of equations describing the coupling of heat and mass transfer, chemical reactions, and fluid flow in a deformable solid matrix. Geological environments where reactive transport is important are located at different depths and accordingly have different rheologies. In the near surface, elastic or elastoplastic properties would dominate, whereas viscoplasticity would have a profound effect deeper in the lithosphere. Poorly understood rheologies of heterogeneous porous rocks are derived from well understood processes (i.e., elasticity, viscosity, plastic flow, fracturing, and their combinations) on the microscale by considering a representative volume element and subsequent averaging of microscopic constitutive laws. Micromechanical and thermodynamic modelling is performed in such a way that the consistency of the obtained rheology and thermodynamically admissible closed system of equations with the exact Gassman's relationship and Terzaghi effective stress law in the simplified case of poroelasticity is guaranteed. In such environments as subduction zones or mid-ocean ridge, metamorphic rocks exhibit a lack of chemical homogenisation. Geochemistry suggests that in order to produce chemical heterogeneity, the fluids generated during high-pressure metamorphism must have been strongly channelled. The following three major mechanisms of fluid flow focusing have been proposed: fluid flow in open fractures and two different types of flow instabilities that do not require the pre-existing fracture network. Of the latter, the first represents a purely mechanical instability of Darcian flow through the deformable porous rock while the second is reactive infiltration instability. Both mechanical and reactive instabilities are expected to occur in the mantle and should probably reinforce each other. However, little research has been done in this direction. In order to investigate how the focusing of a fluid flow occurs, how mechanical and reactive infiltration instabilities influence each other, and what their relative importance in rocks with different rheologies is, linear and non-linear stability analysis is applied to derived governing equations.

A Nonlinear Dynamic Subscale Model for Partially Resolved Numerical Simulation (PRNS)/Very Large Eddy Simulation (VLES) of Internal Non-Reacting Flows

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Liu, nan-Suey

2010-01-01

A brief introduction of the temporal filter based partially resolved numerical simulation/very large eddy simulation approach (PRNS/VLES) and its distinct features are presented. A nonlinear dynamic subscale model and its advantages over the linear subscale eddy viscosity model are described. In addition, a guideline for conducting a PRNS/VLES simulation is provided. Results are presented for three turbulent internal flows. The first one is the turbulent pipe flow at low and high Reynolds numbers to illustrate the basic features of PRNS/VLES; the second one is the swirling turbulent flow in a LM6000 single injector to further demonstrate the differences in the calculated flow fields resulting from the nonlinear model versus the pure eddy viscosity model; the third one is a more complex turbulent flow generated in a single-element lean direct injection (LDI) combustor, the calculated result has demonstrated that the current PRNS/VLES approach is capable of capturing the dynamically important, unsteady turbulent structures while using a relatively coarse grid.

Reactive flow calibration for diaminoazoxyfurazan (DAAF) and comparison with experiment

NASA Astrophysics Data System (ADS)

Johnson, Carl; Francois, Elizabeth Green; Morris, John

2012-03-01

Diaminoazoxyfurazan (DAAF) has a number of desirable properties; it is sensitive to shock while being insensitive to initiation by low level impact or friction, it has a small failure diameter, and its manufacturing process is inexpensive with minimal environmental impact. In light of its unique properties, DAAF based materials have gained interest for possible applications in insensitive munitions. In order to facilitate hydrocode modeling of DAAF and DAAF based formulations, we have developed a set of reactive flow parameters which were calibrated using published experimental data as well as recent experiments at LANL. Hydrocode calculations using the DAAF reactive flow parameters developed in the course of this work were compared to rate stick experiments, small scale gap tests, as well as the Onionskin experiment. Hydrocode calculations were compared directly to streak image results using numerous tracer points in conjunction with an external algorithm to match the data sets. The calculations display a reasonable agreement with experiment with the exception of effects related to shock desensitization of explosive.

TOUGHREACT Version 2.0: A simulator for subsurface reactive transport under non-isothermal multiphase flow conditions

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

Xu, T.; Spycher, N.; Sonnenthal, E.

2010-08-01

TOUGHREACT is a numerical simulation program for chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media, and was developed by introducing reactive chemistry into the multiphase fluid and heat flow simulator TOUGH2 V2. The first version of TOUGHREACT was released to the public through the U.S. Department of Energy's Energy Science and Technology Software Center (ESTSC) in August 2004. It is among the most frequently requested of ESTSC's codes. The code has been widely used for studies in CO{sub 2} geological sequestration, nuclear waste isolation, geothermal energy development, environmental remediation, and increasingly for petroleum applications. Over themore » past several years, many new capabilities have been developed, which were incorporated into Version 2 of TOUGHREACT. Major additions and improvements in Version 2 are discussed here, and two application examples are presented: (1) long-term fate of injected CO{sub 2} in a storage reservoir and (2) biogeochemical cycling of metals in mining-impacted lake sediments.« less

One-dimensional model for the intracranial pulse morphological analysis during hyperventilation and CO2 inhalation tests

NASA Astrophysics Data System (ADS)

Ryu, Jaiyoung; Hu, Xiao; Shadden, Shawn C.

2015-11-01

The brain's CO2 reactivity mechanism is coupled with cerebral autoregulation and other unique features of cerebral hemodynamics. We developed a one-dimensional nonlinear model of blood flow in the cerebral arteries coupled to lumped parameter (LP) networks. The LP networks incorporate cerebral autoregulation, CO2 reactivity, intracranial pressure, cerebrospinal fluid, and cortical collateral blood flow models. The model was used to evaluate hemodynamic variables (arterial deformation, blood velocity and pressure) in the cerebral vasculature during hyperventilation and CO2 inhalation test. Tests were performed for various arterial blood pressure (ABP) representing normal and hypotensive conditions. The increase of the cerebral blood flow rates agreed well with the published measurements for various ABP measurements taken during clinical CO2 reactivity tests. The changes in distal vasculature affected the reflected pulse wave energy, which caused the waveform morphological changes at the middle cerebral, common and internal carotid arteries. The pulse morphological analysis demonstrated agreement with previous clinical measurements for cerebral vasoconstriction and vasodilation.

Effect of gas flow ratio on the microstructure and mechanical properties of boron phosphide films prepared by reactive magnetron sputtering

NASA Astrophysics Data System (ADS)

Jia, Z. C.; Zhu, J. Q.; Jiang, C. Z.; Shen, W. X.; Han, J. C.; Chen, R. R.

2011-10-01

Boron phosphide films were grown on silicon substrate by radio frequency reactive magnetron sputtering using boron target and hydrogen phosphine at different gas flow ratios (PH 3/Ar) at lower temperature. The chemical composition, microstructure and mechanical properties were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectrum, FTIR spectrum, surface profilometer and nano-indenter. The results indicate that the atomic ratio (P/B) rises from 1.06 up to 1.52 with the gas flow ratio increasing from 3/50 to 15/50. Simultaneously, the hardness and Young's modulus decrease from 25.4 GPa to 22.5 GPa, and 250.4 GPa to 238.4 GPa, respectively. Microstructure transforms from microcrystalline state to amorphous state along with the gas flow ratio increasing. Furthermore higher gas flow ratio leads to lower stress. The BP film prepared at the gas flow ratio of 3/50 can be contributed with the best properties.

PERMEABLE REACTIVE BARRIERS FOR REMEDIATION OF INORGANIC CONTAMINANTS

EPA Science Inventory

The permeable reactive barrier (PRB) technology is an in-situ approach for groundwater remediation that couples subsurface flow management with a passive chemical or biochemical treatment zone. The development and application of the PRB technology has progressed over the last de...

SELECTION AND CALIBRATION OF SUBSURFACE REACTIVE TRANSPORT MODELS USING A SURROGATE-MODEL APPROACH

EPA Science Inventory

While standard techniques for uncertainty analysis have been successfully applied to groundwater flow models, extension to reactive transport is frustrated by numerous difficulties, including excessive computational burden and parameter non-uniqueness. This research introduces a...

COST ANALYSIS OF PERMEABLE REACTIVE BARRIERS FOR REMEDIATION OF GROUND WATER

EPA Science Inventory

ABSTRACT

Permeable reactive barriers (PRB's) are an emerging, alternative in-situ approach for remediating contaminated groundwater that combine subsurface fluid flow management with a passive chemical treatment zone. PRB's are a potentially more cost effective treatment...

Osimertinib reactivated immune-related colitis after treatment with anti-PD1 antibody for non-small cell lung cancer.

PubMed

Takenaka, Tomoyoshi; Yamazaki, Koji; Miura, Naoko; Harada, Naohiko; Takeo, Sadanori

2017-12-01

We reported a case of relapsing immune-related colitis (initially caused by nivolumab) following osimertinib therapy for lung adenocarcinoma. A 45-year-old female who had never smoked was diagnosed with adenocarcinoma of the lung and underwent surgical resection. Four years after surgical resection, she was diagnosed with recurrent disease and was eventually treated with nivolumab as third-line therapy. One month after the completion of nivolumab therapy, the patient reported abdominal pain and frequent diarrhea. We diagnosed immune-related colitis and started oral prednisolone. However, the steroid therapy was ineffective, so the patient was administered infliximab and an increased dose of prednisolone. Her symptoms subsequently resolved, and her mucosal lesions improved. Six months after the last administration of nivolumab, osimertinib was initiated as fourth-line therapy, but 3 days later, the patient developed blood in the stool and frequent diarrhea. Osimertinib treatment was discontinued, given the possibility that it had reactivated the patient's immune-related colitis. We subsequently re-administered oral prednisolone (2 mg/kg/day), and the colitis resolved within a few weeks.

A Noachian/Hesperian Hiatus and Erosive Reactivation of Martian Valley Networks

NASA Technical Reports Server (NTRS)

Irwin, R. P., III.; Maxwell, T. A.; Howard, A. D.; Craddock, R. A.; Moore, J. M.

2005-01-01

Despite new evidence for persistent flow and sedimentation on early Mars, it remains unclear whether valley networks were active over long geologic timescales (10(exp 5)-10(exp 8) yr), or if flows were persistent only during multiple discrete episodes of moderate (approx. 10(exp 4) yr) to short (<10 yr) duration. Understanding the long-term stability/variability of valley network hydrology would provide an important control on paleoclimate and groundwater models. Here we describe geologic evidence for a hiatus in highland valley network activity while the fretted terrain formed, followed by a discrete reactivation of persistent (but possibly variable) erosive flows. Additional information is included in the original extended abstract.

Stability of a laminar premixed supersonic free shear layer with chemical reactions

NASA Technical Reports Server (NTRS)

Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

1984-01-01

The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

Which Came First, the Yardang or the Platy Flow?

NASA Image and Video Library

2014-02-13

One of the great strengths of the HiRISE camera onboard NASA Mars Reconnaissance Orbiter is that its high resolution can help resolve interesting questions. Here, is the platy flow material younger than the yardang-forming material?

Temporally resolved electrocardiogram-triggered diffusion-weighted imaging of the human kidney: correlation between intravoxel incoherent motion parameters and renal blood flow at different time points of the cardiac cycle.

PubMed

Wittsack, Hans-Jörg; Lanzman, Rotem S; Quentin, Michael; Kuhlemann, Julia; Klasen, Janina; Pentang, Gael; Riegger, Caroline; Antoch, Gerald; Blondin, Dirk

2012-04-01

To evaluate the influence of pulsatile blood flow on apparent diffusion coefficients (ADC) and the fraction of pseudodiffusion (F(P)) in the human kidney. The kidneys of 6 healthy volunteers were examined by a 3-T magnetic resonance scanner. Electrocardiogram (ECG)-gated and respiratory-triggered diffusion-weighted imaging (DWI) and phase-contrast flow measurements were performed. Flow imaging of renal arteries was carried out to quantify the dependence of renal blood flow on the cardiac cycle. ECG-triggered DWI was acquired in the coronal plane with 16 b values in the range of 0 s/mm(2) and 750 s/mm(2) at the time of minimum (MIN) (20 milliseconds after R wave) and maximum renal blood flow (MAX) (197 ± 24 milliseconds after R wave). The diffusion coefficients were calculated using the monoexponential approach as well as the biexponential intravoxel incoherent motion model and correlated to phase-contrast flow measurements. Flow imaging showed pulsatile renal blood flow depending on the cardiac cycle. The mean flow velocity at MIN was 45 cm/s as compared with 61 cm/s at MAX. F(p) at MIN (0.29) was significantly lower than at MAX (0.40) (P = 0.001). Similarly, ADC(mono), derived from the monoexponential model, also showed a significant difference (P < 0.001) between MIN (ADC(mono) = 2.14 ± 0.08 × 10(-3) mm(2)/s) and MAX (ADC(mono) = 2.37 ± 0.04 × 10(-3) mm(2)/s). The correlation between renal blood flow and F(p) (r = 0.85) as well as ADC(mono) (r = 0.67) was statistically significant. Temporally resolved ECG-gated DWI enables for the determination of the diffusion coefficients at different time points of the cardiac cycle. ADC(mono) and FP vary significantly among acquisitions at minimum (diastole) and maximum (systole) renal blood flow. Temporally resolved ECG-gated DWI might therefore serve as a novel technique for the assessment of pulsatility in the human kidney.

Regional cerebral blood flow and cerebrovascular reactivity in Alzheimer's disease and vascular dementia assessed by arterial spinlabeling magnetic resonance imaging.

PubMed

Gao, Yong-Zhe; Zhang, Jun-Jian; Liu, Hui; Wu, Guang-Yao; Xiong, Li; Shu, Min

2013-02-01

Hemodynamic disturbance in cerebral blood flow (CBF) is common in both Alzheimer's disease (AD) and vascular dementia (VaD).The aim of this study is to investigate the different patterns of regional cerebral blood flow (rCBF) change and cerebrovascular reactivity (CVR) in these two types of dementia. Mean flow velocity (MFV) of middle cerebral artery and rCBF were measured by Transcranial Doppler ultrasound (TCD) and arterial spin-labeling (ASL) magnetic resonance, separately. CVR was evaluated by MFV or rCBF change in response to 5% CO2 inhalation. The ASL results showed that, rCBF was significantly lower in both the bilateral frontal and temporal lobes in AD group and lower in left frontal and temporal white matter in patients with VaD. CVR calculated by rCBF was impaired more severely in bilateral frontal cortices in AD. Conversely, TCD tests failed to demonstrate significant difference in MFV and CVR between the two groups. It is concluded that the different patterns detected by ASL in resting rCBF change and cerebrovascular reactivity in response to carbogen inhalation may serve as a potential marker to distinguish AD and VaD.

Porosity and Permeability Evolution in Cemented Rock Cores under Reactive Flowing Conditions: Comparative Analysis between Limestone and Sandstone Host Rocks

NASA Astrophysics Data System (ADS)

Cao, P.; Karpyn, Z.; Li, L.

2013-12-01

CO2-brine has the potential to alter wellbore cement in depleted oil and gas reservoirs under geological CO2 sequestration conditions. A better understanding of CO2-brine-cement-rock interaction is needed to evaluate the seal integrity of candidate sequestration formation in the long run. This work investigates possible alteration of wellbore cement when bonded by different host formation rock upon exposure to CO2-saturated brine. Composite cement-sandstone and cement-limestone core samples were created to perform reactive coreflood experiments. After an eight-day dynamic flow-through period, both cores had a similar extent of porosity increase, while the cement-limestone core experienced a ten-fold higher increase in permeability. With the aid of X-ray Micro-CT imaging and Scanning Electron Microscopy, it is observed that cement underwent greater degradation at the cement-sandstone interface. Degradation of cement-limestone core mainly took place on the host rock matrix. Worm holes were developed and a solution channel was formed in the limestone, creating a dominant flow path that altered both flow and reaction behavior. Limestone buffered the injected acidic brine preventing further deterioration of cement near the core outlet. Changes in fluid chemistry of limestone and sandstone coreflood effluents are compared. Results from this work are aimed at assisting the development and validation of robust reactive transport models through direct measurement of cemented rock core porosity and permeability evolution as well as the effluent aqueous chemistry change. This will subsequently improve predictive capabilities of reactive transport models associated with CO2 sequestration in geologic environments. Permeability Evolution of Cement-Rock Core Sample during Dynamic Flow of CO2-Brine

Mixing-controlled uncertainty in long-term predictions of acid rock drainage from heterogeneous waste-rock piles

NASA Astrophysics Data System (ADS)

Pedretti, D.; Beckie, R. D.; Mayer, K. U.

2015-12-01

The chemistry of drainage from waste-rock piles at mine sites is difficult to predict because of a number of uncertainties including heterogeneous reactive mineral content, distribution of minerals, weathering rates and physical flow properties. In this presentation, we examine the effects of mixing on drainage chemistry over timescales of 100s of years. We use a 1-D streamtube conceptualization of flow in waste rocks and multicomponent reactive transport modeling. We simplify the reactive system to consist of acid-producing sulfide minerals and acid-neutralizing carbonate minerals and secondary sulfate and iron oxide minerals. We create multiple realizations of waste-rock piles with distinct distributions of reactive minerals along each flow path and examine the uncertainty of drainage geochemistry through time. The limited mixing of streamtubes that is characteristic of the vertical unsaturated flow in many waste-rock piles, allows individual flowpaths to sustain acid or neutral conditions to the base of the pile, where the streamtubes mix. Consequently, mixing and the acidity/alkalinity balance of the streamtube waters, and not the overall acid- and base-producing mineral contents, control the instantaneous discharge chemistry. Our results show that the limited mixing implied by preferential flow and the heterogeneous distribution of mineral contents lead to large uncertainty in drainage chemistry over short and medium time scales. However, over longer timescales when one of either the acid-producing or neutralizing primary phases is depleted, the drainage chemistry becomes less controlled by mixing and in turn less uncertain. A correct understanding of the temporal variability of uncertainty is key to make informed long-term decisions in mining settings regarding the management of waste material.

Rate dependent fractionation of sulfur isotopes in through-flowing systems

NASA Astrophysics Data System (ADS)

Giannetta, M.; Sanford, R. A.; Druhan, J. L.

2017-12-01

The fidelity of reactive transport models in quantifying microbial activity in the subsurface is often improved through the use stable isotopes. However, the accuracy of current predictions for microbially mediated isotope fractionations within open through-flowing systems typically depends on nutrient availability. This disparity arises from the common application of a single `effective' fractionation factor assigned to a given system, despite extensive evidence for variability in the fractionation factor between eutrophic environments and many naturally occurring, nutrient-limited environments. Here, we demonstrate a reactive transport model with the capacity to simulate a variable fractionation factor over a range of microbially mediated reduction rates and constrain the model with experimental data for nutrient limited conditions. Two coupled isotope-specific Monod rate laws for 32S and 34S, constructed to quantify microbial sulfate reduction and predict associated S isotope partitioning, were parameterized using a series of batch reactor experiments designed to minimize microbial growth. In the current study, we implement these parameterized isotope-specific rate laws within an open, through-flowing system to predict variable fractionation with distance as a function of sulfate reduction rate. These predictions are tested through a supporting laboratory experiment consisting of a flow-through column packed with homogenous porous media inoculated with the same species of sulfate reducing bacteria used in the previous batch reactors, Desulfovibrio vulgaris. The collective results of batch reactor and flow-through column experiments support a significant improvement for S isotope predictions in isotope-sensitive multi-component reactive transport models through treatment of rate-dependent fractionation. Such an update to the model will better equip reactive transport software for isotope informed characterization of microbial activity within energy and nutrient limited environments.

Employing a Modified Diffuser Momentum Model to Simulate Ventilation of the Orion CEV

NASA Technical Reports Server (NTRS)

Straus, John; Lewis, John F.

2011-01-01

The Ansys CFX CFD modeling tool was used to support the design efforts of the ventilation system for the Orion CEV. CFD modeling was used to establish the flow field within the cabin for several supply configurations. A mesh and turbulence model sensitivity study was performed before the design studies. Results were post-processed for comparison with performance requirements. Most configurations employed straight vaned diffusers to direct and throw the flow. To manage the size of the models, the diffuser vanes were not resolved. Instead, a momentum model was employed to account for the effect of the diffusers. The momentum model was tested against a separate, vane-resolved side study. Results are presented for a single diffuser configuration for a low supply flow case.

Weighted Flow Algorithms (WFA) for stochastic particle coagulation

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

DeVille, R.E.L., E-mail: rdeville@illinois.edu; Riemer, N., E-mail: nriemer@illinois.edu; West, M., E-mail: mwest@illinois.edu

2011-09-20

Stochastic particle-resolved methods are a useful way to compute the time evolution of the multi-dimensional size distribution of atmospheric aerosol particles. An effective approach to improve the efficiency of such models is the use of weighted computational particles. Here we introduce particle weighting functions that are power laws in particle size to the recently-developed particle-resolved model PartMC-MOSAIC and present the mathematical formalism of these Weighted Flow Algorithms (WFA) for particle coagulation and growth. We apply this to an urban plume scenario that simulates a particle population undergoing emission of different particle types, dilution, coagulation and aerosol chemistry along a Lagrangianmore » trajectory. We quantify the performance of the Weighted Flow Algorithm for number and mass-based quantities of relevance for atmospheric sciences applications.« less

Capillary red blood cell velocimetry by phase-resolved optical coherence tomography.

PubMed

Tang, Jianbo; Erdener, Sefik Evren; Fu, Buyin; Boas, David A

2017-10-01

We present a phase-resolved optical coherence tomography (OCT) method to extend Doppler OCT for the accurate measurement of the red blood cell (RBC) velocity in cerebral capillaries. OCT data were acquired with an M-mode scanning strategy (repeated A-scans) to account for the single-file passage of RBCs in a capillary, which were then high-pass filtered to remove the stationary component of the signal to ensure an accurate measurement of phase shift of flowing RBCs. The angular frequency of the signal from flowing RBCs was then quantified from the dynamic component of the signal and used to calculate the axial speed of flowing RBCs in capillaries. We validated our measurement by RBC passage velocimetry using the signal magnitude of the same OCT time series data.

Weighted Flow Algorithms (WFA) for stochastic particle coagulation

NASA Astrophysics Data System (ADS)

DeVille, R. E. L.; Riemer, N.; West, M.

2011-09-01

Stochastic particle-resolved methods are a useful way to compute the time evolution of the multi-dimensional size distribution of atmospheric aerosol particles. An effective approach to improve the efficiency of such models is the use of weighted computational particles. Here we introduce particle weighting functions that are power laws in particle size to the recently-developed particle-resolved model PartMC-MOSAIC and present the mathematical formalism of these Weighted Flow Algorithms (WFA) for particle coagulation and growth. We apply this to an urban plume scenario that simulates a particle population undergoing emission of different particle types, dilution, coagulation and aerosol chemistry along a Lagrangian trajectory. We quantify the performance of the Weighted Flow Algorithm for number and mass-based quantities of relevance for atmospheric sciences applications.

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

PubMed Central

Hemberger, Patrick; Custodis, Victoria B. F.; Bodi, Andras; Gerber, Thomas; van Bokhoven, Jeroen A.

2017-01-01

Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity and yield unsatisfactory conversion. Understanding the pyrolysis reaction mechanism at the molecular level may help to make this sustainable process more economic. Reactive intermediates are responsible for product branching and hold the key to unveiling these mechanisms, but are notoriously difficult to detect isomer-selectively. Here, we investigate the catalytic pyrolysis of guaiacol, a lignin model compound, using photoelectron photoion coincidence spectroscopy with synchrotron radiation, which allows for isomer-selective detection of reactive intermediates. In combination with ambient pressure pyrolysis, we identify fulvenone as the central reactive intermediate, generated by catalytic demethylation to catechol and subsequent dehydration. The fulvenone ketene is responsible for the phenol formation. This technique may open unique opportunities for isomer-resolved probing in catalysis, and holds the potential for achieving a mechanistic understanding of complex, real-life catalytic processes. PMID:28660882

Scattering Resonances in the Simplest Chemical Reaction

NASA Astrophysics Data System (ADS)

Fernandez-Alonso, Felix; Zare, Richard N.

2002-10-01

Recent studies of state-resolved angular distributions show the participation of reactive scattering resonances in the simplest chemical reaction. This review is intended for those who wish to learn about the state-of-the-art in the study of the H + H2 reaction family that has made this breakthrough possible. This review is also intended for those who wish to gain insight into the nature of reactive scattering resonances. Following a tour across several fields of physics and chemistry where the concept of resonance has been crucial for the understanding of new phenomena, we offer an operational definition and taxonomy of reactive scattering resonances. We introduce simple intuitive models to illustrate each resonance type. We focus next on the last decade of H + H2 reaction dynamics. Emphasis is placed on the various experimental approaches that have been applied to the search for resonance behavior in the H + H2 reaction family. We conclude by sketching the road ahead in the study of H + H2 reactive scattering resonances.

LONG-TERM PERFORMANCE ASSESSMENT OF PERMEABLE REACTIVE BARRIERS TO REMEDIATE CONTAMINATED GROUND WATER

EPA Science Inventory

Permeable reactive barriers (PRBs) are an emerging, alternative in-situ approach for remediating groundwater contamination that combine subsurface fluid flow management with a passive chemical treatment zone. The few pilot and commercial installations which have been implemented ...

LONG-TERM PERFORMANCE MONITORING OF A PERMEABLE REACTIVE BARRIER TO REMEDIATE CONTAMINATED GROUND WATER

EPA Science Inventory

Permeable reactive barriers (PRB's) are an emerging, alternative in-situ approach for remediating groundwater contamination that combine subsurface fluid flow management with a passive chemical treatment zone. The few pilot and commercial installations which have been implemented...

Flow cytometry crossmatch reactivity with pronase-treated T cells induced by non-HLA autoantibodies in human immunodeficiency virus-infected patients.

PubMed

Szewczyk, Katarzyna; Barrios, Kelly; Magas, Daniel; Sieg, Kristin; Labuda, Bozena; Jendrisak, Martin D; Jaramillo, Andrés

2016-06-01

Pronase treatment is used in the flow cytometry crossmatch (FCXM) to prevent nonspecific antibody binding on B cells. However, we have observed unexpected positive results with pronase-treated T cells in human immunodeficiency virus (HIV)-infected patients. In this study, 25 HIV-infected patients without HLA antibodies were tested with pronase-treated and nontreated cells. HIV-positive sera were pretreated with reducing agents and preabsorbed with pronase-treated and nontreated T or B cells before crossmatching. All patients displayed FCXM reactivity with pronase-treated T cells but not with nontreated T cells. None of the patients exhibited FCXM reactivity with pronase-treated and nontreated B cells. These patients displayed FCXM reactivity with pronase-treated CD4+ and CD8+ T cells but not with their nontreated counterparts. Preabsorption with pronase-treated T cells reduced the T cell FCXM reactivity. Preabsorption with pronase-treated B cells or nontreated T and B cells did not have any effect on the T cell FCXM reactivity. Pretreatment with reducing agents did not affect the T cell FCXM reactivity. 15 of 21 HIV-infected kidney allograft recipients with pronase-treated T cell FCXM reactivity display long-term graft survival (1193±631days). These data indicate that HIV-infected patients have nondeleterious autoantibodies recognizing cryptic epitopes exposed by pronase on T cells. Copyright © 2016 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved.

A mobile-mobile transport model for simulating reactive transport in connected heterogeneous fields

NASA Astrophysics Data System (ADS)

Lu, Chunhui; Wang, Zhiyuan; Zhao, Yue; Rathore, Saubhagya Singh; Huo, Jinge; Tang, Yuening; Liu, Ming; Gong, Rulan; Cirpka, Olaf A.; Luo, Jian

2018-05-01

Mobile-immobile transport models can be effective in reproducing heavily tailed breakthrough curves of concentration. However, such models may not adequately describe transport along multiple flow paths with intermediate velocity contrasts in connected fields. We propose using the mobile-mobile model for simulating subsurface flow and associated mixing-controlled reactive transport in connected fields. This model includes two local concentrations, one in the fast- and the other in the slow-flow domain, which predict both the concentration mean and variance. The normalized total concentration variance within the flux is found to be a non-monotonic function of the discharge ratio with a maximum concentration variance at intermediate values of the discharge ratio. We test the mobile-mobile model for mixing-controlled reactive transport with an instantaneous, irreversible bimolecular reaction in structured and connected random heterogeneous domains, and compare the performance of the mobile-mobile to the mobile-immobile model. The results indicate that the mobile-mobile model generally predicts the concentration breakthrough curves (BTCs) of the reactive compound better. Particularly, for cases of an elliptical inclusion with intermediate hydraulic-conductivity contrasts, where the travel-time distribution shows bimodal behavior, the prediction of both the BTCs and maximum product concentration is significantly improved. Our results exemplify that the conceptual model of two mobile domains with diffusive mass transfer in between is in general good for predicting mixing-controlled reactive transport, and particularly so in cases where the transfer in the low-conductivity zones is by slow advection rather than diffusion.

Dielectric barrier structure with hollow electrodes and its recoil effect

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

Yu, Shuang; Chen, Qunzhi; Liu, Jiahui

2015-06-15

A dielectric barrier structure with hollow electrodes (HEDBS), in which gas flow oriented parallel to the electric field, was proposed. Results showed that with this structure, air can be effectively ignited, forming atmospheric low temperature plasma, and the proposed HEDBS could achieve much higher electron density (5 × 10{sup 15}/cm{sup 3}). It was also found that the flow condition, including outlet diameter and flow rate, played a key role in the evolution of electron density. Optical emission spectroscopy diagnostic results showed that the concentration of reactive species had the same variation trend as the electron density. The simulated distribution of discharge gasmore » flow indicated that the HEDBS had a strong recoil effect on discharge gas, and could efficiently promote generating electron density as well as reactive species.« less

Measures of total stress-induced blood pressure responses are associated with vascular damage.

PubMed

Nazzaro, Pietro; Seccia, Teresa; Vulpis, Vito; Schirosi, Gabriella; Serio, Gabriella; Battista, Loredana; Pirrelli, Anna

2005-09-01

The role of cardiovascular reactivity to study hypertension, and the assessment methods, are still controversial. We aimed to verify the association of hypertension and vascular damage with several measures of cardiovascular response. We studied 40 patients with normal-high (132 +/- 1/87 +/- 1 mm Hg) blood pressure (Group 1) and 80 untreated hypertensive subjects. Postischemic forearm vascular resistance (mFVR) served to differentiate hypertensive subjects (142 +/- 2/92 +/- 1 mm Hg v 143 +/- 2/94 +/- 2 mm Hg, P = NS) with a lower (Group 2) and higher (Group 3) hemodynamic index of vascular damage (4.8 +/- .05 v 6.3 +/- .09, P < .001). Reactivity was induced by Stroop (5') and cold pressor (90") tests. We measured muscular contraction and skin conductance as indices of emotional arousal, blood pressure, heart rate, forearm blood flow, and vascular resistance. Reactivity measures included: a) change from baseline, b) residualized score, c) cumulative change from baseline and residualized score, and d) total reactivity as area-under-the-curve (AUC), including changes occurring during baseline and recovery phases. The AUC of systolic blood pressure, diastolic blood pressure, and mFVR progressively increased in the groups (P < .001). Corrections of anthropometric and metabolic confounders were introduced in the Pearson equation between mFVR and reactivity measures. The AUC of SBP, DBP, and forearm blood flow and resistance demonstrated the highest (P < .001) correlation. On multiple regression analysis, AUC of SBP (beta = 0.634) and forearm blood flow (beta = -0.337) were predictive (P < .001) of vascular damage. Total blood pressure stress response, as AUC, including baseline and recovery phases, was significantly better associated with hypertension and vascular damage than the other reactivity measures studied.

Dynamically Consistent Parameterization of Mesoscale Eddies This work aims at parameterization of eddy effects for use in non-eddy-resolving ocean models and focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones.

NASA Astrophysics Data System (ADS)

Berloff, P. S.

2016-12-01

This work aims at developing a framework for dynamically consistent parameterization of mesoscale eddy effects for use in non-eddy-resolving ocean circulation models. The proposed eddy parameterization framework is successfully tested on the classical, wind-driven double-gyre model, which is solved both with explicitly resolved vigorous eddy field and in the non-eddy-resolving configuration with the eddy parameterization replacing the eddy effects. The parameterization focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones. The parameterization locally approximates transient eddy flux divergence by spatially localized and temporally periodic forcing, referred to as the plunger, and focuses on the linear-dynamics flow solution induced by it. The nonlinear self-interaction of this solution, referred to as the footprint, characterizes and quantifies the induced eddy forcing exerted on the large-scale flow. We find that spatial pattern and amplitude of each footprint strongly depend on the underlying large-scale flow, and the corresponding relationships provide the basis for the eddy parameterization and its closure on the large-scale flow properties. Dependencies of the footprints on other important parameters of the problem are also systematically analyzed. The parameterization utilizes the local large-scale flow information, constructs and scales the corresponding footprints, and then sums them up over the gyres to produce the resulting eddy forcing field, which is interactively added to the model as an extra forcing. Thus, the assumed ensemble of plunger solutions can be viewed as a simple model for the cumulative effect of the stochastic eddy forcing. The parameterization framework is implemented in the simplest way, but it provides a systematic strategy for improving the implementation algorithm.

Prediction of down-gradient impacts of DNAPL source depletion using tracer techniques: Laboratory and modeling validation

NASA Astrophysics Data System (ADS)

Jawitz, J. W.; Basu, N.; Chen, X.

2007-05-01

Interwell application of coupled nonreactive and reactive tracers through aquifer contaminant source zones enables quantitative characterization of aquifer heterogeneity and contaminant architecture. Parameters obtained from tracer tests are presented here in a Lagrangian framework that can be used to predict the dissolution of nonaqueous phase liquid (NAPL) contaminants. Nonreactive tracers are commonly used to provide information about travel time distributions in hydrologic systems. Reactive tracers have more recently been introduced as a tool to quantify the amount of NAPL contaminant present within the tracer swept volume. Our group has extended reactive tracer techniques to also characterize NAPL spatial distribution heterogeneity. By conceptualizing the flow field through an aquifer as a collection of streamtubes, the aquifer hydrodynamic heterogeneities may be characterized by a nonreactive tracer travel time distribution, and NAPL spatial distribution heterogeneity may be similarly described using reactive travel time distributions. The combined statistics of these distributions are used to derive a simple analytical solution for contaminant dissolution. This analytical solution, and the tracer techniques used for its parameterization, were validated both numerically and experimentally. Illustrative applications are presented from numerical simulations using the multiphase flow and transport simulator UTCHEM, and laboratory experiments of surfactant-enhanced NAPL remediation in two-dimensional flow chambers.

Using travel times to simulate multi-dimensional bioreactive transport in time-periodic flows.

PubMed

Sanz-Prat, Alicia; Lu, Chuanhe; Finkel, Michael; Cirpka, Olaf A

2016-04-01

In travel-time models, the spatially explicit description of reactive transport is replaced by associating reactive-species concentrations with the travel time or groundwater age at all locations. These models have been shown adequate for reactive transport in river-bank filtration under steady-state flow conditions. Dynamic hydrological conditions, however, can lead to fluctuations of infiltration velocities, putting the validity of travel-time models into question. In transient flow, the local travel-time distributions change with time. We show that a modified version of travel-time based reactive transport models is valid if only the magnitude of the velocity fluctuates, whereas its spatial orientation remains constant. We simulate nonlinear, one-dimensional, bioreactive transport involving oxygen, nitrate, dissolved organic carbon, aerobic and denitrifying bacteria, considering periodic fluctuations of velocity. These fluctuations make the bioreactive system pulsate: The aerobic zone decreases at times of low velocity and increases at those of high velocity. For the case of diurnal fluctuations, the biomass concentrations cannot follow the hydrological fluctuations and a transition zone containing both aerobic and obligatory denitrifying bacteria is established, whereas a clear separation of the two types of bacteria prevails in the case of seasonal velocity fluctuations. We map the 1-D results to a heterogeneous, two-dimensional domain by means of the mean groundwater age for steady-state flow in both domains. The mapped results are compared to simulation results of spatially explicit, two-dimensional, advective-dispersive-bioreactive transport subject to the same relative fluctuations of velocity as in the one-dimensional model. The agreement between the mapped 1-D and the explicit 2-D results is excellent. We conclude that travel-time models of nonlinear bioreactive transport are adequate in systems of time-periodic flow if the flow direction does not change. Copyright © 2016 Elsevier B.V. All rights reserved.

Reactive Flow Modeling of Liquid Explosives via ALE3D/Cheetah Simulations

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

Kuo, I W; Bastea, S; Fried, L E

2010-03-10

We carried out reactive flow simulations of liquid explosives such as nitromethane using the hydrodynamic code ALE3D coupled with equations of state and reaction kinetics modeled by the thermochemical code Cheetah. The simulation set-up was chosen to mimic cylinder experiments. For pure unconfined nitromethane we find that the failure diameter and detonation velocity dependence on charge diameter are in agreement with available experimental results. Such simulations are likely to be useful for determining detonability and failure behavior for a wide range of experimental conditions and explosive compounds.

Continuous real-time measurement of aqueous cyanide

DOEpatents

Rosentreter, Jeffrey J.; Gering, Kevin L.

2007-03-06

This invention provides a method and system capable of the continuous, real-time measurement of low concentrations of aqueous free cyanide (CN) using an on-line, flow through system. The system is based on the selective reactivity of cyanide anions and the characteristically nonreactive nature of metallic gold films, wherein this selective reactivity is exploited as an indirect measurement for aqueous cyanide. In the present invention the dissolution of gold, due to the solubilization reaction with the analyte cyanide anion, is monitored using a piezoelectric microbalance contained within a flow cell.

Magnetohydrodynamic stability of stochastically driven accretion flows.

PubMed

Nath, Sujit Kumar; Mukhopadhyay, Banibrata; Chattopadhyay, Amit K

2013-07-01

We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.

An Experimental Investigation of the Flow Physics Associated With End Wall Losses and Large Rotor Tip Clearances as Found in the Rear Stages of a High Pressure Compressor

NASA Technical Reports Server (NTRS)

Berdanier, Reid A.; Key, Nicole L.

2015-01-01

The focus of this work was to characterize the fundamental flow physics and the overall performance effects due to increased rotor tip clearance heights in axial compressors. Data have been collected in the three-stage axial research compressor at Purdue University with a specific focus on analyzing the multistage effects resulting from the tip leakage flow. Three separate rotor tip clearance heights were studied with nominal tip clearance heights of 1.5%, 3.0%, and 4.0% based on a constant annulus height. Overall compressor performance was investigated at four corrected speedlines (100%, 90%, 80%, and 68%) for each of the three tip clearance configurations using total pressure and total temperature rakes distributed throughout the compressor. The results have confirmed results from previous authors showing a decrease of total pressure rise, isentropic efficiency, and stall margin which is approximately linear with increasing tip clearance height. The stall inception mechanisms have also been evaluated at the same corrected speeds for each of the tip clearance configurations. Detailed flow field measurements have been collected at two loading conditions, nominal loading (NL) and high loading (HL), on the 100% corrected speedline for the smallest and largest tip clearance heights (1.5% and 4.0%). Steady detailed radial traverses of total pressure at the exit of each stator row have been supported by flow visualization techniques to identify regions of flow recirculation and separation. Furthermore, detailed radial traverses of time-resolved total pressures at the exit of each rotor row have been measured with a fast-response pressure probe. These data have helped to quantify the size of the leakage flow at the exit of each rotor. Thermal anemometry has also been implemented to evaluate the time-resolved three-dimensional components of velocity throughout the compressor and calculate blockage due to the rotor tip leakage flow throughout the compressor. These measurements have also been used to calculate streamwise vorticity. Time-resolved static pressure measurements have been collected over the rotor tips for all rotors with each of the three tip clearance configurations for up to five loading conditions along the 100% corrected speedline using fast-response piezoresistive pressure sensors. These time-resolved static pressure measurements, as well as the time-resolved total pressures and velocities have helped to reveal a profound influence of the upstream stator vane on the size and shape of the rotor tip leakage flow. Finally, a novel particle image velocimetry (PIV) technique has been developed as a proof-of- concept. In contrast to PIV methods that have been typically been utilized for turbomachinery applications in the past, the method used for this study introduced the laser light through the same access window that was also used to image the flow. This new method addresses potential concerns related to the intrusive laser-introducing techniques that have typically been utilized by other authors in the past. Ultimately, the data collected for this project represent a unique data set which contributes to build a better understanding of the tip leakage flow field and its associated loss mechanisms. These data will facilitate future engine design goals leading to small blade heights in the rear stages of high pressure compressors and aid in the development of new blade designs which are desensitized to the performance penalties attributed to rotor tip leakage flows.

LONG-TERM PERFORMANCE MONITORING OF PERMEABLE REACTIVE BARRIERS TO REMEDIATE CONTAMINATED GROUND WATER

EPA Science Inventory

Permeable reactive barriers (PRB's) are an alternative in-situ approach for remediating contaminated groundwater that combine subsurface fluid flow management with a passive chemical treatment zone. PRB's are being selected with increased frequency at waste sites (more than 40 f...

LONG-TERM PERFORMANCE OF IN-SITU PERMEABLE REACTIVE BARRIERS FOR REMEDIATION OF CONTAMINATED GROUND WATER

EPA Science Inventory

Permeable reactive barriers (PRB's) are an emerging, alternative in-situ approach for remediating groundwater contamination that combine subsurface fluid flow management with a passive chemical treatment zone. The few pilot and commercial installations which have been implemented...

GEOCHEMISTRY OF SUBSURFACE REACTIVE BARRIERS FOR REMEDIATION OF CONTAMINATED GROUND WATER

EPA Science Inventory

Reactive barriers that couple subsurface fluid flow with a passive chemical treatment zone are emerging, cost effective approaches for in-situ remediation of contaminated groundwater. Factors such as the build-up of surface precipitates, bio-fouling, and changes in subsurface tr...

CARBON AND SULFUR ACCUMULATION AND IRON MINERAL TRANSFORMATION IN PERMEABLE REACTIVE BARRIERS CONTAINING ZERO-VALENT IRON

EPA Science Inventory

Permeable reactive barrier technology is an in-situ approach for remediating groundwater contamination that combines subsurface fluid flow management with passive chemical treatment. Factors such as the buildup of mineral precipitates, buildup of microbial biomass (bio-fouling...

Cerebral vasomotor responsiveness to carbon dioxide is preserved during propofol and midazolam anesthesia in humans.

PubMed

Strebel, S; Kaufmann, M; Guardiola, P M; Schaefer, H G

1994-05-01

Carbon dioxide reactivity, as measured by transcranial Doppler ultrasonography, was determined during total intravenous anesthesia with propofol or midazolam in comparison with an awake control group. Thirty ASA physical status I neurosurgical patients undergoing lumbar laminectomy participated in the study. In randomized order they were subjected to a CO2 reactivity challenge, either under an intravenous anesthesia technique or in the awake state. CO2 reactivity was calculated in each study group as a relative change in middle cerebral artery (MCA) flow velocity per mm Hg change in end-tidal CO2 (PETCO2) (%/mm Hg). The cerebrovascular response to changes in CO2 was preserved during intravenous anesthesia. There was a significant difference (P < 0.05) in the reactivity slopes between the awake and the anesthetized patients with a small but not significant difference between the propofol and the midazolam group. We conclude that hypocarbia is effective in reducing cerebral blood flow velocity (CBFV) during intravenous anesthesia, either with propofol or midazolam.

Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

NASA Technical Reports Server (NTRS)

Raman, Venkatramanan; Pitsch, Heinz; Fox, Rodney O.

2003-01-01

A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.

Plasma reactivity in high-power impulse magnetron sputtering through oxygen kinetics

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

Vitelaru, Catalin; National Institute for Optoelectronics, Magurele-Bucharest, RO 077125; Lundin, Daniel

2013-09-02

The atomic oxygen metastable dynamics in a Reactive High-Power Impulse Magnetron Sputtering (R-HiPIMS) discharge has been characterized using time-resolved diode laser absorption in an Ar/O{sub 2} gas mixture with a Ti target. Two plasma regions are identified: the ionization region (IR) close to the target and further out the diffusion region (DR), separated by a transition region. The μs temporal resolution allows identifying the main atomic oxygen production and destruction routes, which are found to be very different during the pulse as compared to the afterglow as deduced from their evolution in space and time.

Dynamically consistent parameterization of mesoscale eddies. Part III: Deterministic approach

NASA Astrophysics Data System (ADS)

Berloff, Pavel

2018-07-01

This work continues development of dynamically consistent parameterizations for representing mesoscale eddy effects in non-eddy-resolving and eddy-permitting ocean circulation models and focuses on the classical double-gyre problem, in which the main dynamic eddy effects maintain eastward jet extension of the western boundary currents and its adjacent recirculation zones via eddy backscatter mechanism. Despite its fundamental importance, this mechanism remains poorly understood, and in this paper we, first, study it and, then, propose and test its novel parameterization. We start by decomposing the reference eddy-resolving flow solution into the large-scale and eddy components defined by spatial filtering, rather than by the Reynolds decomposition. Next, we find that the eastward jet and its recirculations are robustly present not only in the large-scale flow itself, but also in the rectified time-mean eddies, and in the transient rectified eddy component, which consists of highly anisotropic ribbons of the opposite-sign potential vorticity anomalies straddling the instantaneous eastward jet core and being responsible for its continuous amplification. The transient rectified component is separated from the flow by a novel remapping method. We hypothesize that the above three components of the eastward jet are ultimately driven by the small-scale transient eddy forcing via the eddy backscatter mechanism, rather than by the mean eddy forcing and large-scale nonlinearities. We verify this hypothesis by progressively turning down the backscatter and observing the induced flow anomalies. The backscatter analysis leads us to formulating the key eddy parameterization hypothesis: in an eddy-permitting model at least partially resolved eddy backscatter can be significantly amplified to improve the flow solution. Such amplification is a simple and novel eddy parameterization framework implemented here in terms of local, deterministic flow roughening controlled by single parameter. We test the parameterization skills in an hierarchy of non-eddy-resolving and eddy-permitting modifications of the original model and demonstrate, that indeed it can be highly efficient for restoring the eastward jet extension and its adjacent recirculation zones. The new deterministic parameterization framework not only combines remarkable simplicity with good performance but also is dynamically transparent, therefore, it provides a powerful alternative to the common eddy diffusion and emerging stochastic parameterizations.

Effects of inlet boundary conditions, on the computed flow in the Turbine-99 draft tube, using OpenFOAM and CFX

NASA Astrophysics Data System (ADS)

Nilsson, H.; Cervantes, M. J.

2012-11-01

The flow in the Turbine-99 Kaplan draft tube was thoroughly investigated at three workshops (1999, 2001, 2005), which aimed at determining the state of the art of draft tube simulations. The flow is challenging due to the different flow phenomena appearing simultaneously such as unsteadiness, separation, swirl, turbulence, and a strong adverse pressure gradient. The geometry and the experimentally determined inlet boundary conditions were provided to the Turbine-99 workshop participants. At the final workshop, angular resolved inlet velocity boundary conditions were provided. The rotating non-axi-symmetry of the inlet flow due to the runner blades was thus included. The effect of the rotating angular resolution was however not fully investigated at that workshop. The first purpose of this work is to further investigate this effect. Several different inlet boundary conditions are applied - the angular resolved experimental data distributed at the Turbine-99 workshop, the angular resolved results of a runner simulation with interpolated values using different resolution in the tangential and radial directions, and an axi-symmetric variant of the same numerical data. The second purpose of this work is to compare the results from the OpenFOAM and CFX CFD codes, using as similar settings as possible. The present results suggest that the experimental angular inlet boundary conditions proposed to the workshop are not adequate to simulate accurately the flow in the T-99 draft tube. The reason for this is that the experimental phase-averaged data has some important differences compared to the previously measured time-averaged data. Using the interpolated data from the runner simulation as inlet boundary condition however gives good results as long as the resolution of that data is sufficient. It is shown that the difference between the results using the angular-resolved and the corresponding symmetric inlet data is very small, suggesting that the importance of the angular resolution is small. The results from OpenFOAM and CFX are very similar as long as the inlet data resolution is fine enough. CFX seems to be more sensitive to that resolution.

The role of zonal flows in reactive fluid closures

NASA Astrophysics Data System (ADS)

Jan, WEILAND

2018-07-01

We will give an overview of results obtained by our reactive fluid model. It is characterised as a fluid model where all moments with sources in the experiment are kept. Furthermore, full account is taken for the highest moments appearing in unexpanded denominators also including full toroidicity. It has been demonstrated that the strength of zonal flows is dramatically larger in reactive fluid closures than in those which involve dissipation. This gives a direct connection between the fluid closure and the level of excitation of turbulence. This is because zonal flows are needed to absorb the inverse cascade in quasi 2D turbulence. This also explains the similarity in structure of the transport coefficients in our model with a reactive closure in the energy equation and models which have a reactive closure because of zero ion temperature such as the Hasegawa–Wakatani model. Our exact reactive closure unifies several well-known features of tokamak experiments such as the L–H transition, internal transport barriers and the nonlinear Dimits upshift of the critical gradient for onset of transport. It also gives transport of the same level as that in nonlinear gyrokinetic codes. Since these include the kinetic resonance this confirms the validity of the thermodynamic properties of our model. Furthermore, we can show that while a strongly nonlinear model is needed in kinetic theory a quasilinear model is sufficient in the fluid description. Thus our quasilinear fluid model will be adequate for treating all relevant problems in bulk transport. This is finally confirmed by the reproduction by the model of the experimental power scaling of the confinement time τ E ∼ P ‑2/3. This confirms the validity of our reactive fluid model. This also gives credibility to our ITER simulations including the H-mode barrier. A new result is here, that alpha heating strongly reduces the slope of the H-mode barrier. This should significantly reduce the effects of ELM’s.

Mass transfer in thin films under counter-current gas: experiments and numerical study

NASA Astrophysics Data System (ADS)

Lucquiaud, Mathieu; Lavalle, Gianluca; Schmidt, Patrick; Ausner, Ilja; Wehrli, Marc; O Naraigh, Lennon; Valluri, Prashant

2016-11-01

Mass transfer in liquid-gas stratified flows is strongly affected by the waviness of the interface. For reactive flows, the chemical reactions occurring at the liquid-gas interface also influence the mass transfer rate. This is encountered in several technological applications, such as absorption units for carbon capture. We investigate the absorption rate of carbon dioxide in a liquid solution. The experimental set-up consists of a vertical channel where a falling film is sheared by a counter-current gas flow. We measure the absorption occurring at different flow conditions, by changing the liquid solution, the liquid flow rate and the gas composition. With the aim to support the experimental results with numerical simulations, we implement in our level-set flow solver a novel module for mass transfer taking into account a variant of the ghost-fluid formalism. We firstly validate the pure mass transfer case with and without hydrodynamics by comparing the species concentration in the bulk flow to the analytical solution. In a final stage, we analyse the absorption rate in reactive flows, and try to reproduce the experimental results by means of numerical simulations to explore the active role of the waves at the interface.

A Gas-Kinetic Scheme for Multimaterial Flows and Its Application in Chemical Reaction

NASA Technical Reports Server (NTRS)

Lian, Yongsheng; Xu, Kun

1999-01-01

This paper concerns the extension of the multicomponent gas-kinetic BGK-type scheme to multidimensional chemical reactive flow calculations. In the kinetic model, each component satisfies its individual gas-kinetic BGK equation and the equilibrium states of both components are coupled in space and time due to the momentum and energy exchange in the course of particle collisions. At the same time, according to the chemical reaction rule one component can be changed into another component with the release of energy, where the reactant and product could have different gamma. Many numerical test cases are included in this paper, which show the robustness and accuracy of kinetic approach in the description of multicomponent reactive flows.

CHROTRAN, 1.0

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

Hansen, Scott K.; Pandey, Sachin; Karra, Satish

2017-04-13

CHROTRAN is a fork of the widely-used PFLOTRAN flow and reactive transport numerical simulation code. It implements custom physics and chemistry appropriate to the design of in-situ reduction of heavy metals such as Cr(VI) in groundwater. CHROTRAN includes full dynamics for five species: the metal to be remediated, an electron donor, biofilm, a nontoxic conservative bio-inhibitor, and a biocide. Direct abiotic reduction by donor-metal interaction as well as donor-driven biomass growth and bio-reduction are modeled, along with crucial processes such as donor sorption, and biofilm inactivation. The software implementation handles heterogeneous flow fields, arbitrarily many chemical species and amendment injectionmore » points, and features full coupling between flow and reactive transport, allowing for assessment of the effect of bio-fouling.« less

A numerical study of axisymmetric compressible non-isothermal and reactive swirling flow

NASA Astrophysics Data System (ADS)

Tavernetti, William E.; Hafez, Mohamed M.

2017-09-01

Non-linear dynamical phenomena in combustion processes is an active area of experimental and theoretical research. This is in large part due to increasingly strict environmental pressures to make gas turbine engines and industrial burners more efficient. Using numerical methods, for steady and unsteady confined and unconfined compressible flow, this study examines the modeling influence of compressibility for axisymmetric swirling flow. The compressible reactive Navier-Stokes equations in terms of stream function, vorticity, circulation are used. Results, details of the numerical algorithms, as well as numerical verification techniques and validation with sources from the literature will be presented. Understanding how vortex breakdown phenomena are affected by modeling reactant consumption with compressibility effect is the main goal of this study.

Time-dependent computational studies of flames in microgravity

NASA Technical Reports Server (NTRS)

Oran, Elaine S.; Kailasanath, K.

1989-01-01

The research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of the NASA Microgravity Science and Applications Program is described. The primary focus was on investigating fundamental questions concerning the propagation and extinction of premixed flames in Earth gravity and in microgravity environments. The approach was to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. A combination of one-dimensional and two-dimensional simulations was used to investigate the effects of curvature and dilution on ignition and propagation of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the mechanism leading to cellular instability, and to study the effects of gravity on the transition to cellular structure. A flame in a microgravity environment can be extinguished without external losses, and the mechanism leading to cellular structure is not preferential diffusion but a thermo-diffusive instability. The simulations have also lead to a better understanding of the interactions between buoyancy forces and the processes leading to thermo-diffusive instability.

Simultaneous Interfacial Reactivity and Topography Mapping with Scanning Ion Conductance Microscopy.

PubMed

Momotenko, Dmitry; McKelvey, Kim; Kang, Minkyung; Meloni, Gabriel N; Unwin, Patrick R

2016-03-01

Scanning ion conductance microscopy (SICM) is a powerful technique for imaging the topography of a wide range of materials and interfaces. In this report, we develop the use and scope of SICM, showing how it can be used for mapping spatial distributions of ionic fluxes due to (electro)chemical reactions occurring at interfaces. The basic idea is that there is a change of ion conductance inside a nanopipet probe when it approaches an active site, where the ionic composition is different to that in bulk solution, and this can be sensed via the current flow in the nanopipet with an applied bias. Careful tuning of the tip potential allows the current response to be sensitive to either topography or activity, if desired. Furthermore, the use of a distance modulation SICM scheme allows reasonably faithful probe positioning using the resulting ac response, irrespective of whether there is a reaction at the interface that changes the local ionic composition. Both strategies (distance modulation or tuned bias) allow simultaneous topography-activity mapping with a single channel probe. The application of SICM reaction imaging is demonstrated on several examples, including voltammetric mapping of electrocatalytic reactions on electrodes and high-speed electrochemical imaging at rates approaching 4 s per image frame. These two distinct approaches provide movies of electrochemical current as a function of potential with hundreds of frames (images) of surface reactivity, to reveal a wealth of spatially resolved information on potential- (and time) dependent electrochemical phenomena. The experimental studies are supported by detailed finite element method modeling that places the technique on a quantitative footing.

Electrical Detection of C-Reactive Protein Using a Single Free-Standing, Thermally Controlled Piezoresistive Microcantilever for Highly Reproducible and Accurate Measurements

PubMed Central

Yen, Yi-Kuang; Lai, Yu-Cheng; Hong, Wei-Ting; Pheanpanitporn, Yotsapoom; Chen, Chuin-Shan; Huang, Long-Sun

2013-01-01

This study demonstrates a novel method for electrical detection of C-reactive protein (CRP) as a means of identifying an infection in the body, or as a cardiovascular disease risk assay. The method uses a single free-standing, thermally controlled piezoresistive microcantilever biosensor. In a commonly used sensing arrangement of conventional dual cantilevers in the Wheatstone bridge circuit, reference and gold-coated sensing cantilevers that inherently have heterogeneous surface materials and different multilayer structures may yield independent responses to the liquid environmental changes of chemical substances, flow field and temperature, leading to unwanted signal disturbance for biosensing targets. In this study, the single free-standing microcantilever for biosensing applications is employed to resolve the dual-beam problem of individual responses in chemical solutions and, in a thermally controlled system, to maintain its sensor performance due to the sensitive temperature effect. With this type of single temperature-controlled microcantilever sensor, the electrical detection of various CRP concentrations from 1 μg/mL to 200 μg/mL was performed, which covers the clinically relevant range. Induced surface stresses were measured at between 0.25 N/m and 3.4 N/m with high reproducibility. Moreover, the binding affinity (KD) of CRP and anti-CRP interaction was found to be 18.83 ± 2.99 μg/mL, which agreed with results in previous reported studies. This biosensing technique thus proves valuable in detecting inflammation, and in cardiovascular disease risk assays. PMID:23899933

Experimental mycobacteriosis in striped bass Morone saxatilis

USGS Publications Warehouse

Gauthier, David T.; Rhodes, M.W.; Vogelbein, W.K.; Kator, H.; Ottinger, C.A.

2003-01-01

Striped bass Morone saxatilis were infected intraperitoneally with approximately 105 Mycobacterium marinum, M. shottsii sp. nov., or M. gordonae. Infected fish were maintained in a flow-through freshwater system at 18 to 21??C, and were examined histologically and bacteriologically at 2, 4, 6, 8, 17, 26, 36 and 45 wk post-infection (p.i.). M. marinum caused acute peritonitis, followed by extensive granuloma development in the mesenteries, spleen and anterior kidney. Granulomas in these tissues underwent a temporal progression of distinct morphological stages, culminating in well-circumscribed lesions surrounded by normal or healing tissue. Mycobacteria were cultured in high numbers from splenic tissue at all times p.i. Standard Ziehl-Neelsen staining, however, did not demonstrate acid-fast rods in most early inflammatory foci and granulomas. Large numbers of acid-fast rods were present in granulomas beginning at 8 wk p.i. Between 26 and 45 wk p.i., reactivation of disease was observed in some fish, with disintegration of granulomas, renewed inflammation, and elevated splenic bacterial densities approaching 109 colony-forming units g-1. Infection with M. shottsii or M. gordonae did not produce severe pathology. Mild peritonitis was followed by granuloma formation in the mesenteries, but, with 1 exception, granulomas were not observed in the spleen or anterior kidney. M. shottsii and M. gordonae both established persistent infections in the spleen, but were present at densities at least 2 orders of magnitude less than M. marinum at all time points observed. Granulomas in the mesenteries of M. shottsii- and M. gordonae-infected fish resolved over time, and no reactivation of disease was observed.

Flow temporal reconstruction from non-time-resolved data part I: mathematic fundamentals

NASA Astrophysics Data System (ADS)

Legrand, Mathieu; Nogueira, José; Lecuona, Antonio

2011-10-01

At least two circumstances point to the need of postprocessing techniques to recover lost time information from non-time-resolved data: the increasing interest in identifying and tracking coherent structures in flows of industrial interest and the high data throughput of global measuring techniques, such as PIV, for the validation of computational fluid dynamics (CFD) codes. This paper offers the mathematic fundamentals of a space--time reconstruction technique from non-time-resolved, statistically independent data. An algorithm has been developed to identify and track traveling coherent structures in periodic flows. Phase-averaged flow fields are reconstructed with a correlation-based method, which uses information from the Proper Orthogonal Decomposition (POD). The theoretical background shows that the snapshot POD coefficients can be used to recover flow phase information. Once this information is recovered, the real snapshots are used to reconstruct the flow history and characteristics, avoiding neither the use of POD modes nor any associated artifact. The proposed time reconstruction algorithm is in agreement with the experimental evidence given by the practical implementation proposed in the second part of this work (Legrand et al. in Exp Fluids, 2011), using the coefficients corresponding to the first three POD modes. It also agrees with the results on similar issues by other authors (Ben Chiekh et al. in 9 Congrès Francophone de Vélocimétrie Laser, Bruxelles, Belgium, 2004; Van Oudheusden et al. in Exp Fluids 39-1:86-98, 2005; Meyer et al. in 7th International Symposium on Particle Image Velocimetry, Rome, Italy, 2007a; in J Fluid Mech 583:199-227, 2007b; Perrin et al. in Exp Fluids 43-2:341-355, 2007). Computer time to perform the reconstruction is relatively short, of the order of minutes with current PC technology.

Spatially Resolved MR-Compatible Doppler Ultrasound: Proof of Concept for Triggering of Diagnostic Quality Cardiovascular MRI for Function and Flow Quantification at 3T.

PubMed

Crowe, Lindsey Alexandra; Manasseh, Gibran; Chmielewski, Aneta; Hachulla, Anne-Lise; Speicher, Daniel; Greiser, Andreas; Muller, Hajo; de Perrot, Thomas; Vallee, Jean-Paul; Salomir, Rares

2018-02-01

We demonstrate the use of a magnetic-resonance (MR)-compatible ultrasound (US) imaging probe using spatially resolved Doppler for diagnostic quality cardiovascular MR imaging (MRI) as an initial step toward hybrid US/MR fetal imaging. A newly developed technology for a dedicated MR-compatible phased array ultrasound-imaging probe acquired pulsed color Doppler carotid images, which were converted in near-real time to a trigger signal for cardiac cine and flow quantification MRI. Ultrasound and MR data acquired simultaneously were interference free. Conventional electrocardiogram (ECG) and the proposed spatially resolved Doppler triggering were compared in 10 healthy volunteers. A synthetic "false-triggered" image was retrospectively processed using metric optimized gating (MOG). Images were scored by expert readers, and sharpness, cardiac function and aortic flow were quantified. Four-dimensional (4-D) flow (two volunteers) showed feasibility of Doppler triggering over a long acquisition time. Imaging modalities were compatible. US probe positioning was stable and comfortable. Image quality scores and quantified sharpness were statistically equal for Doppler- and ECG-triggering (p ). ECG-, Doppler-triggered, and MOG ejection fractions were equivalent (p ), with false-triggered values significantly lower (p < 0.0005). Aortic flow showed no difference between ECG- and Doppler-triggered and MOG (p > 0.05). 4-D flow quantification gave consistent results between ECG and Doppler triggering. We report interference-free pulsed color Doppler ultrasound during MR data acquisition. Cardiovascular MRI of diagnostic quality was successfully obtained with pulsed color Doppler triggering. The hardware platform could further enable advanced free-breathing cardiac imaging. Doppler ultrasound triggering is applicable where ECG is compromised due to pathology or interference at higher magnetic fields, and where direct ECG is impossible, i.e., fetal imaging.

Resolving Low-Density Lipoprotein (LDL) on the Human Aortic Surface Using Large Eddy Simulation

NASA Astrophysics Data System (ADS)

Lantz, Jonas; Karlsson, Matts

2011-11-01

The prediction and understanding of the genesis of vascular diseases is one of the grand challenges in biofluid engineering. The progression of atherosclerosis is correlated to the build- up of LDL on the arterial surface, which is affected by the blood flow. A multi-physics simulation of LDL mass transport in the blood and through the arterial wall of a subject specific human aorta was performed, employing a LES turbulence model to resolve the turbulent flow. Geometry and velocity measurements from magnetic resonance imaging (MRI) were incorporated to assure physiological relevance of the simulation. Due to the turbulent nature of the flow, consecutive cardiac cycles are not identical, neither in vivo nor in the simulations. A phase average based on a large number of cardiac cycles is therefore computed, which is the proper way to get reliable statistical results from a LES simulation. In total, 50 cardiac cycles were simulated, yielding over 2.5 Billion data points to be post-processed. An inverse relation between LDL and WSS was found; LDL accumulated on locations where WSS was low and vice-versa. Large temporal differences were present, with the concentration level decreasing during systolic acceleration and increasing during the deceleration phase. This method makes it possible to resolve the localization of LDL accumulation in the normal human aorta with its complex transitional flow.

EFFECTS OF PORE STRUCTURE CHANGE AND MULTI-SCALE HETEROGENEITY ON CONTAMINANT TRANSPORT AND REACTION RATE UPSCALING

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

Lindquist, W. Brent; Jones, Keith W.; Um, Wooyong

2013-02-15

This project addressed the scaling of geochemical reactions to core and field scales, and the interrelationship between reaction rates and flow in porous media. We targeted reactive transport problems relevant to the Hanford site - specifically the reaction of highly caustic, radioactive waste solutions with subsurface sediments, and the immobilization of 90Sr and 129I through mineral incorporation and passive flow blockage, respectively. We addressed the correlation of results for pore-scale fluid-soil interaction with field-scale fluid flow, with the specific goals of (i) predicting attenuation of radionuclide concentration; (ii) estimating changes in flow rates through changes of soil permeabilities; and (iii)more » estimating effective reaction rates. In supplemental work, we also simulated reactive transport systems relevant to geologic carbon sequestration. As a whole, this research generated a better understanding of reactive transport in porous media, and resulted in more accurate methods for reaction rate upscaling and improved prediction of permeability evolution. These scientific advancements will ultimately lead to better tools for management and remediation of DOE’s legacy waste problems. We established three key issues of reactive flow upscaling, and organized this project in three corresponding thrust areas. 1) Reactive flow experiments. The combination of mineral dissolution and precipitation alters pore network structure and the subsequent flow velocities, thereby creating a complex interaction between reaction and transport. To examine this phenomenon, we conducted controlled laboratory experimentation using reactive flow-through columns. Results and Key Findings: Four reactive column experiments (S1, S3, S4, S5) have been completed in which simulated tank waste leachage (STWL) was reacted with pure quartz sand, with and without Aluminum. The STWL is a caustic solution that dissolves quartz. Because Al is a necessary element in the formation of secondary mineral precipitates (cancrinite), conducting experiments under conditions with and without Al allowed us to experimentally separate the conditions that lead to quartz dissolution from the conditions that lead to quartz dissolution plus cancrinite precipitation. Consistent with our expectations, in the experiments without Al, there was a substantial reduction in volume of the solid matrix. With Al there was a net increase in the volume of the solid matrix. The rate and extent of reaction was found to increase with temperature. These results demonstrate a successful effort to identify conditions that lead to increases and conditions that lead to decreases in solid matrix volume due to reactions of caustic tank wastes with quartz sands. In addition, we have begun to work with slightly larger, intermediate-scale columns packed with Hanford natural sediments and quartz. Similar dissolution and precipitation were observed in these colums. The measurements are being interpreted with reactive transport modeling using STOMP; preliminary observations are reported here. 2) Multi-Scale Imaging and Analysis. Mineral dissolution and precipitation rates within a porous medium will be different in different pores due to natural heterogeneity and the heterogeneity that is created from the reactions themselves. We used a combination of X-ray computed microtomography, backscattered electron and energy dispersive X-ray spectroscopy combined with computational image analysis to quantify pore structure, mineral distribution, structure changes and fluid-air and fluid-grain interfaces. Results and Key Findings: Three of the columns from the reactive flow experiments at PNNL (S1, S3, S4) were imaged using 3D X-ray computed microtomography (XCMT) at BNL and analyzed using 3DMA-rock at SUNY Stony Brook. The imaging results support the mass balance findings reported by Dr. Um’s group, regarding the substantial dissolution of quartz in column S1. An important observation is that of grain movement accompanying dissolution in the unconsolidated media. The resultant movement changes the anticipated findings for pore and throat size distributions. For column S3, with cancrinite precipitation accompanying quartz dissolution, the precitiation halts much of the grain movement and more systematic distributions are obtained. Column S4, which was sealed with caustic solution acted as a control sample to study reactive effects during periods when columns S1 and S3 were sealed between flow experiments. No significant changes are observed in S4 with time. At Princeton, the imaging and analysis work focused on the effects of mineral precipitation and advancing our understanding of the impacts of these reactions on reactive transport in subsurface sediments. These findings are described in detail below, and have been published in L.E. Crandell, C.A. Peters, W. Um, K.W. Jones, W.B. Lindquist, 2012. “Changes in the pore network structure of Hanford sediment after reaction with caustic tank wastes.” Journal of Contaminant Hydrology 131 (2012) 89–99. 3) Multi-Scale Modeling and Up-Scaling. Using an array of modeling approaches, we examined pore-scale variations in physical and mineralogical properties, flow velocities, and (for unsaturated conditions) wetting fluid/grain surface areas, and permeability evolution. Results and Key Findings: To predict the column permeability and estimate the impact of mineral precipitation, pore network models were informed using the pore and throat-size distributions from the imaging analyses. As a comparison, supplemental analyses were performed on Viking sandstone specimens from the Alberta sedimentary basin. In another part of this study we sought to understand how carbonate rocks in contact with CO2-rich brines change due to the precipitation or dissolution of fast-reacting minerals such as calcite and dolomite. Using a newly developed reactive-transport pore-network model we were able to identify the conditions that lead to significant permeability changes. These findings are presented below and are compiled in a publication that is under review: J.P. Nogues, J.P. Fitts, M.A. Celia, C.A. Peters. “Permeability evolution due to dissolution and precipitation of carbonates using reactive transport modeling in pore networks”, Submitted: Water Resources Research, 2013.« less

Cutaneous Microvascular Blood Flow and Reactivity in Hypoxia

PubMed Central

Treml, Benedikt; Kleinsasser, Axel; Stadlbauer, Karl-Heinz; Steiner, Iris; Pajk, Werner; Pilch, Michael; Burtscher, Martin; Knotzer, Hans

2018-01-01

As is known, hypoxia leads to an increase in microcirculatory blood flow of the skin in healthy volunteers. In this pilot study, we investigated microcirculatory blood flow and reactive hyperemia of the skin in healthy subjects in normobaric hypoxia. Furthermore, we examined differences in microcirculation between hypoxic subjects with and without short-term acclimatization, whether or not skin microvasculature can acclimatize. Fourty-six healthy persons were randomly allocated to either short-term acclimatization using intermittent hypoxia for 1 h over 7 days at an FiO2 0.126 (treatment, n = 23) or sham short-term acclimatization for 1 h over 7 days at an FiO2 0.209 (control, n = 23). Measurements were taken in normoxia and at 360 and 720 min during hypoxia (FiO2 0.126). Microcirculatory cutaneous blood flow was assessed with a laser Doppler flowmeter on the forearm. Reactive hyperemia was induced by an ischemic stimulus. Measurements included furthermore hemodynamics, blood gas analyses and blood lactate. Microcirculatory blood flow increased progressively during hypoxia (12.3 ± 7.1–19.0 ± 8.1 perfusion units; p = 0.0002) in all subjects. The magnitude of the reactive hyperemia was diminished during hypoxia (58.2 ± 14.5–40.3 ± 27.4 perfusion units; p = 0.0003). Short-term acclimatization had no effect on microcirculatory blood flow. When testing for a hyperemic response of the skin's microcirculation we found a diminished signal in hypoxia, indicative for a compromised auto-regulative circulatory capacity. Furthermore, hypoxic short-term acclimatization did not affect cutaneous microcirculatory blood flow. Seemingly, circulation of the skin was unable to acclimatize using a week-long short-term acclimatization protocol. A potential limitation of our study may be the 7 days between acclimatization and the experimental test run. However, there is evidence that the hypoxic ventilatory response, an indicator of acclimatization, is increased for 1 week after short-term acclimatization. Then again, 1 week is what one needs to get from home to a location at significant altitude. PMID:29559919

The Impact of the Flow Field Heterogeneity and of the Injection Rate on the Effective Reaction Rates in Carbonates: a Study at the Pore Scale

NASA Astrophysics Data System (ADS)

Nunes, J. P. P.; Bijeljic, B.; Blunt, M. J.

2015-12-01

Carbonate rocks are notoriously difficult to characterize. Their abrupt facies variations give rise to drastic changes in the petrophysical properties of the reservoir. Such heterogeneity, when further associated with variations in rock mineralogy due to diagenetic processes, result in a challenging scenario to model from the pore to the field scale. Micro-CT imaging is one of the most promising technologies to characterize porous rocks. The understanding at the pore scale of reactive and non-reactive transport is being pushed forward by recent developments in both imaging capability - 3D images with resolution of a few microns - and in modeling techniques - flow simulations in giga-cell models. We will present a particle-based method capable of predicting the evolution of petrophysical properties of carbonate cores subjected to CO2 injection at reservoir conditions (i.e. high pressures and temperatures). Reactive flow is simulated directly on the voxels of high resolution micro-CT images of rocks. Reactants are tracked using a semi-analytical streamline tracing algorithm and rock-fluid interaction is controlled by the diffusive flux of particles from the pores to the grains. We study the impact of the flow field heterogeneity and of the injection rate on the sample-averaged (i.e. effective) reaction rate of calcite dissolution in three rocks of increasing complexity: a beadpack, an oolitic limestone and a bioclastic limestone. We show how decreases in the overall dissolution rate depend on both the complexity of the pore space and also on the flow rate. This occurs even in chemically homogenous rocks. Our results suggest that the large differences observed between laboratory and field scale rates could, in part, be explained by the inhomogeneity in the flow field at the pore scale and the consequent transport-limited flux of reactants at the solid surface. Our results give valuable insight into the processes governing carbonate dissolution and provide a starting point to the refinement of upscaling techniques for reactive flows. Potential impacts for reservoir development and monitoring will also be discussed.

LONG-TERM PERFORMANCE OF PERMEABLE REACTIVE BARRIERS: AN UPDATE ON A U.S. MULTI-AGENCY INITIATIVE

EPA Science Inventory

Permeable reactive barriers (PRB's) are an emerging, alternative in-situ approach for remediating contaminated groundwater that combine subsurface fluid flow management with a passive chemical treatment zone. PRB's are a potentially more cost effective treatment option at seve...

Towards establishing the rheology of a sediment bed

NASA Astrophysics Data System (ADS)

Biegert, Edward; Vowinckel, Bernhard; Meiburg, Eckart

2017-11-01

In order to gain a better understanding of erosion, we have conducted numerical simulations of particle-resolved flows similar to the experiments of Aussillous et al. (2013), which involve laminar pressure-driven flows over erodible sediment beds. These simulations allow us to resolve velocity profiles and stresses of the fluid-particle mixtures within and above the sediment bed, which can be difficult or impossible to measure experimentally. Thus, we can begin investigating the rheology of the fluid-particle mixtures. In particular, we compare the effective viscosity as a function of volume fraction to existing models, such as those of Eilers (1943), Morris and Boulay (1999), and Boyer et al. (2011).

An engineering closure for heavily under-resolved coarse-grid CFD in large applications

NASA Astrophysics Data System (ADS)

Class, Andreas G.; Yu, Fujiang; Jordan, Thomas

2016-11-01

Even though high performance computation allows very detailed description of a wide range of scales in scientific computations, engineering simulations used for design studies commonly merely resolve the large scales thus speeding up simulation time. The coarse-grid CFD (CGCFD) methodology is developed for flows with repeated flow patterns as often observed in heat exchangers or porous structures. It is proposed to use inviscid Euler equations on a very coarse numerical mesh. This coarse mesh needs not to conform to the geometry in all details. To reinstall physics on all smaller scales cheap subgrid models are employed. Subgrid models are systematically constructed by analyzing well-resolved generic representative simulations. By varying the flow conditions in these simulations correlations are obtained. These comprehend for each individual coarse mesh cell a volume force vector and volume porosity. Moreover, for all vertices, surface porosities are derived. CGCFD is related to the immersed boundary method as both exploit volume forces and non-body conformal meshes. Yet, CGCFD differs with respect to the coarser mesh and the use of Euler equations. We will describe the methodology based on a simple test case and the application of the method to a 127 pin wire-wrap fuel bundle.

Fully Resolved Simulations of Particle-Bed-Turbulence Interactions in Oscillatory Flows

NASA Astrophysics Data System (ADS)

Apte, S.; Ghodke, C.

2017-12-01

Particle-resolved direct numerical simulations (DNS) are performed to investigate the behavior of an oscillatory flow field over a bed of closely packed fixed spherical particles for a range of Reynolds numbers in transitional and rough turbulent flow regime. Presence of roughness leads to a substantial modification of the underlying boundary layer mechanism resulting in increased bed shear stress, reduction in the near-bed anisotropy, modification of the near-bed sweep and ejection motions along with marked changes in turbulent energy transport mechanisms. Characterization of such resulting flow field is performed by studying statistical descriptions of the near-bed turbulence for different roughness parameters. A double-averaging technique is employed to reveal spatial inhomogeneities at the roughness scale that provide alternate paths of energy transport in the turbulent kinetic energy (TKE) budget. Spatio-temporal characteristics of unsteady particle forces by studying their spatial distribution, temporal auto-correlations, frequency spectra, cross-correlations with near-bed turbulent flow variables and intermittency intermittency in the forces using the concept of impulse are investigated in detail. These first principle simulations provide substantial insights into the modeling of incipient motion of sediments.

Wall-resolved spectral cascade-transport turbulence model

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

Brown, C. S.; Shaver, D. R.; Lahey, R. T.

A spectral cascade-transport model has been developed and applied to turbulent channel flows (Reτ= 550, 950, and 2000 based on friction velocity, uτ ; or ReδΜ= 8,500; 14,800 and 31,000, based on the mean velocity and channel half-width). This model is an extension of a spectral model previously developed for homogeneous single and two-phase decay of isotropic turbulence and uniform shear flows; and a spectral turbulence model for wall-bounded flows without resolving the boundary layer. Data from direct numerical simulation (DNS) of turbulent channel flow was used to help develop this model and to assess its performance in the 1Dmore » direction across the channel width. The resultant spectral model is capable of predicting the mean velocity, turbulent kinetic energy and energy spectrum distributions for single-phase wall-bounded flows all the way to the wall, where the model source terms have been developed to account for the wall influence. We implemented the model into the 3D multiphase CFD code NPHASE-CMFD and the latest results are within reasonable error of the 1D predictions.« less

Wall-resolved spectral cascade-transport turbulence model

DOE PAGES

Brown, C. S.; Shaver, D. R.; Lahey, R. T.; ...

2017-07-08

A spectral cascade-transport model has been developed and applied to turbulent channel flows (Reτ= 550, 950, and 2000 based on friction velocity, uτ ; or ReδΜ= 8,500; 14,800 and 31,000, based on the mean velocity and channel half-width). This model is an extension of a spectral model previously developed for homogeneous single and two-phase decay of isotropic turbulence and uniform shear flows; and a spectral turbulence model for wall-bounded flows without resolving the boundary layer. Data from direct numerical simulation (DNS) of turbulent channel flow was used to help develop this model and to assess its performance in the 1Dmore » direction across the channel width. The resultant spectral model is capable of predicting the mean velocity, turbulent kinetic energy and energy spectrum distributions for single-phase wall-bounded flows all the way to the wall, where the model source terms have been developed to account for the wall influence. We implemented the model into the 3D multiphase CFD code NPHASE-CMFD and the latest results are within reasonable error of the 1D predictions.« less

Prostaglandin control of renal circulation in the unanesthetized dog and baboon

NASA Technical Reports Server (NTRS)

Swain, J. A.; Vatner, S. F.; Heyndrickx, G. R.; Boettcher, D. H.

1975-01-01

Effects of indomethacin and meclofenamate, inhibitors of prostaglandin synthesis, were evaluated in the regulation of renal blood flow in conscious and anesthetized dogs and in tranquilized baboons, instrumented with arterial pressure catheters and renal blood flow probes. Indomethacin, 10 mg/kg, did not alter renal blood flow or resistance significantly in the conscious dog. In the anesthetized dog, however, indomethacin caused a reduction in renal blood flow and an elevation of renal vascular resistance. Meclofenamate, 4 mg/kg, reduced renal flow and increased renal vascular resistance in conscious dogs. In conscious dogs and tranquilized primates, indomethacin and meclofenamate reduced the reactive hyperemia in the renal bed. Methoxamine and angiotensin II infused in graded doses induced significantly greater renal vasoconstriction in conscious dogs in the presence of indomethacin. Thus, in the conscious animal, prostaglandins appear to play only a minor part in the control of renal circulation at rest, but they are of greater importance in mediating the renal responses to reactive hyperemia and to vasoconstriction.

Role of Coronary Myogenic Response in Pressure-Flow Autoregulation in Swine: A Meta-Analysis With Coronary Flow Modeling

PubMed Central

Dick, Gregory M.; Namani, Ravi; Patel, Bhavesh; Kassab, Ghassan S.

2018-01-01

Myogenic responses (pressure-dependent contractions) of coronary arterioles play a role in autoregulation (relatively constant flow vs. pressure). Publications on myogenic reactivity in swine coronaries vary in caliber, analysis, and degree of responsiveness. Further, data on myogenic responses and autoregulation in swine have not been completely compiled, compared, and modeled. Thus, it has been difficult to understand these physiological phenomena. Our purpose was to: (a) analyze myogenic data with standard criteria; (b) assign results to diameter categories defined by morphometry; and (c) use our novel multiscale flow model to determine the extent to which ex vivo myogenic reactivity can explain autoregulation in vivo. When myogenic responses from the literature are an input for our model, the predicted coronary autoregulation approaches in vivo observations. More complete and appropriate data are now available to investigate the regulation of coronary blood flow in swine, a highly relevant model for human physiology and disease. PMID:29875686

A quantification method for numerical dissipation in quasi-DNS and under-resolved DNS, and effects of numerical dissipation in quasi-DNS and under-resolved DNS of turbulent channel flows

NASA Astrophysics Data System (ADS)

Komen, E. M. J.; Camilo, L. H.; Shams, A.; Geurts, B. J.; Koren, B.

2017-09-01

LES for industrial applications with complex geometries is mostly characterised by: a) a finite volume CFD method using a non-staggered arrangement of the flow variables and second order accurate spatial and temporal discretisation schemes, b) an implicit top-hat filter, where the filter length is equal to the local computational cell size, and c) eddy-viscosity type LES models. LES based on these three main characteristics is indicated as industrial LES in this paper. It becomes increasingly clear that the numerical dissipation in CFD codes typically used in industrial applications with complex geometries may inhibit the predictive capabilities of explicit LES. Therefore, there is a need to quantify the numerical dissipation rate in such CFD codes. In this paper, we quantify the numerical dissipation rate in physical space based on an analysis of the transport equation for the mean turbulent kinetic energy. Using this method, we quantify the numerical dissipation rate in a quasi-Direct Numerical Simulation (DNS) and in under-resolved DNS of, as a basic demonstration case, fully-developed turbulent channel flow. With quasi-DNS, we indicate a DNS performed using a second order accurate finite volume method typically used in industrial applications. Furthermore, we determine and explain the trends in the performance of industrial LES for fully-developed turbulent channel flow for four different Reynolds numbers for three different LES mesh resolutions. The presented explanation of the mechanisms behind the observed trends is based on an analysis of the turbulent kinetic energy budgets. The presented quantitative analyses demonstrate that the numerical errors in the industrial LES computations of the considered turbulent channel flows result in a net numerical dissipation rate which is larger than the subgrid-scale dissipation rate. No new computational methods are presented in this paper. Instead, the main new elements in this paper are our detailed quantification method for the numerical dissipation rate, the application of this method to a quasi-DNS and under-resolved DNS of fully-developed turbulent channel flow, and the explanation of the effects of the numerical dissipation on the observed trends in the performance of industrial LES for fully-developed turbulent channel flows.

Using the Multipole Resonance Probe to Stabilize the Electron Density During a Reactive Sputter Process

NASA Astrophysics Data System (ADS)

Oberberg, Moritz; Styrnoll, Tim; Ries, Stefan; Bienholz, Stefan; Awakowicz, Peter

2015-09-01

Reactive sputter processes are used for the deposition of hard, wear-resistant and non-corrosive ceramic layers such as aluminum oxide (Al2O3) . A well known problem is target poisoning at high reactive gas flows, which results from the reaction of the reactive gas with the metal target. Consequently, the sputter rate decreases and secondary electron emission increases. Both parameters show a non-linear hysteresis behavior as a function of the reactive gas flow and this leads to process instabilities. This work presents a new control method of Al2O3 deposition in a multiple frequency CCP (MFCCP) based on plasma parameters. Until today, process controls use parameters such as spectral line intensities of sputtered metal as an indicator for the sputter rate. A coupling between plasma and substrate is not considered. The control system in this work uses a new plasma diagnostic method: The multipole resonance probe (MRP) measures plasma parameters such as electron density by analyzing a typical resonance frequency of the system response. This concept combines target processes and plasma effects and directly controls the sputter source instead of the resulting target parameters.

Final Report for''Numerical Methods and Studies of High-Speed Reactive and Non-Reactive Flows''

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

Schwendeman, D W

2002-11-20

The work carried out under this subcontract involved the development and use of an adaptive numerical method for the accurate calculation of high-speed reactive flows on overlapping grids. The flow is modeled by the reactive Euler equations with an assumed equation of state and with various reaction rate models. A numerical method has been developed to solve the nonlinear hyperbolic partial differential equations in the model. The method uses an unsplit, shock-capturing scheme, and uses a Godunov-type scheme to compute fluxes and a Runge-Kutta error control scheme to compute the source term modeling the chemical reactions. An adaptive mesh refinementmore » (AMR) scheme has been implemented in order to locally increase grid resolution. The numerical method uses composite overlapping grids to handle complex flow geometries. The code is part of the ''Overture-OverBlown'' framework of object-oriented codes [1, 2], and the development has occurred in close collaboration with Bill Henshaw and David Brown, and other members of the Overture team within CASC. During the period of this subcontract, a number of tasks were accomplished, including: (1) an extension of the numerical method to handle ''ignition and grow'' reaction models and a JWL equations of state; (2) an improvement in the efficiency of the AMR scheme and the error estimator; (3) an addition of a scheme of numerical dissipation designed to suppress numerical oscillations/instabilities near expanding detonations and along grid overlaps; and (4) an exploration of the evolution to detonation in an annulus and of detonation failure in an expanding channel.« less

Head and neck vascular malformations: time-resolved MR projection angiography.

PubMed

Ziyeh, S; Schumacher, M; Strecker, R; Rössler, J; Hochmuth, A; Klisch, J

2003-10-01

Extracranial vascular anomalies can be divided into haemangiomas and vascular malformations. The latter can be subdivided on the basis of the predominant type of vascular channels. Separation of high- and low-flow vascular malformations is of clinical importance. We report preliminary observations on time-resolved magnetic resonance projection angiography (MRPA) of vascular malformations of the head and neck. We examined eight patients with vascular anomalies of the head and neck. On MRPA the time between the early arterial phase and enhancement of the malformation could be used to distinguish high- and low-flow lesions. High-flow arteriovenous malformations showed early, intense enhancement. Venous malformations were either not visible on MRPA or showed late enhancement of veins. One patient was examined after embolisation of an arteriovenous fistula of the mandible. Normal MRPA was taken to indicate absence of a residual lesion.

Comparison of in-situ and optical current-meter estimates of rip-current circulation

NASA Astrophysics Data System (ADS)

Moulton, M.; Chickadel, C. C.; Elgar, S.; Raubenheimer, B.

2016-12-01

Rip currents are fast, narrow, seaward flows that transport material from the shoreline to the shelf. Spatially and temporally complex rip current circulation patterns are difficult to resolve with in-situ instrument arrays. Here, high spatial-resolution estimates of rip current circulation from remotely sensed optical images of the sea surface are compared with in-situ estimates of currents in and near channels ( 1- to 2-m deep and 30-m wide) dredged across the surf zone. Alongshore flows are estimated using the optical current-meter method, and cross-shore flows are derived with the assumption of continuity. The observations span a range of wave conditions, tidal elevations, and flow patterns, including meandering alongshore currents near and in the channel, and 0.5 m/s alongshore flows converging at a 0.8 m/s rip jet in the channel. In addition, the remotely sensed velocities are used to investigate features of the spatially complex flow patterns not resolved by the spatially sparse in-situ sensors, including the spatial extent of feeder current zones and the width, alongshore position, and cross-shore extent of rip current jets. Funded by ASD(R&E) and NSF.

Impeller tandem blade study with grid embedding for local grid refinement

NASA Technical Reports Server (NTRS)

Bache, George

1992-01-01

Flow non-uniformity at the discharge of high power density impellers can result in significant unsteady interactions between impeller blades and downstream diffuser vanes. These interactions result in degradation of both performance and pump reliability. The MSFC Pump Technology Team has recognized the importance of resolving this problem and has thus initiated the development and testing of a high head coefficient impeller. One of the primary goals of this program is to improve impeller performance and discharge flow uniformity. The objective of the present work is complimentary. Flow uniformity and performance gains were sought through the application of a tandem blade arrangement. The approach adopted was to numerically establish flow characteristics at the impeller discharge for the baseline MSFC impeller and then parametrically evaluate tandem blade configurations. A tandem design was sought that improves both impeller performance and discharge uniformity. The Navier-Stokes solver AEROVISC was used to conduct the study. Grid embedding is used to resolve local gradients while attempting to minimize model size. Initial results indicate that significant gains in flow uniformity can be achieved through the tandem blade concept and that blade clocking rather than slot location is the primary driver for flow uniformity.

A Level-set based framework for viscous simulation of particle-laden supersonic flows

NASA Astrophysics Data System (ADS)

Das, Pratik; Sen, Oishik; Jacobs, Gustaaf; Udaykumar, H. S.

2017-06-01

Particle-laden supersonic flows are important in natural and industrial processes, such as, volcanic eruptions, explosions, pneumatic conveyance of particle in material processing etc. Numerical study of such high-speed particle laden flows at the mesoscale calls for a numerical framework which allows simulation of supersonic flow around multiple moving solid objects. Only a few efforts have been made toward development of numerical frameworks for viscous simulation of particle-fluid interaction in supersonic flow regime. The current work presents a Cartesian grid based sharp-interface method for viscous simulations of interaction between supersonic flow with moving rigid particles. The no-slip boundary condition is imposed at the solid-fluid interfaces using a modified ghost fluid method (GFM). The current method is validated against the similarity solution of compressible boundary layer over flat-plate and benchmark numerical solution for steady supersonic flow over cylinder. Further validation is carried out against benchmark numerical results for shock induced lift-off of a cylinder in a shock tube. 3D simulation of steady supersonic flow over sphere is performed to compare the numerically obtained drag co-efficient with experimental results. A particle-resolved viscous simulation of shock interaction with a cloud of particles is performed to demonstrate that the current method is suitable for large-scale particle resolved simulations of particle-laden supersonic flows.

Modeling Intrajunction Dispersion at a Well-Mixed Tidal River Junction

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

Wolfram, Phillip J.; Fringer, Oliver B.; Monsen, Nancy E.

In this paper, the relative importance of small-scale, intrajunction flow features such as shear layers, separation zones, and secondary flows on dispersion in a well-mixed tidal river junction is explored. A fully nonlinear, nonhydrostatic, and unstructured three-dimensional (3D) model is used to resolve supertidal dispersion via scalar transport at a well-mixed tidal river junction. Mass transport simulated in the junction is compared against predictions using a simple node-channel model to quantify the effects of small-scale, 3D intrajunction flow features on mixing and dispersion. The effects of three-dimensionality are demonstrated by quantifying the difference between two-dimensional (2D) and 3D model results.more » An intermediate 3D model that does not resolve the secondary circulation or the recirculating flow at the junction is also compared to the 3D model to quantify the relative sensitivity of mixing on intrajunction flow features. Resolution of complex flow features simulated by the full 3D model is not always necessary because mixing is primarily governed by bulk flow splitting due to the confluence–diffluence cycle. Finally, results in 3D are comparable to the 2D case for many flow pathways simulated, suggesting that 2D modeling may be reasonable for nonstratified and predominantly hydrostatic flows through relatively straight junctions, but not necessarily for the full junction network.« less

Modeling Intrajunction Dispersion at a Well-Mixed Tidal River Junction

DOE PAGES

Wolfram, Phillip J.; Fringer, Oliver B.; Monsen, Nancy E.; ...

2016-08-01

In this paper, the relative importance of small-scale, intrajunction flow features such as shear layers, separation zones, and secondary flows on dispersion in a well-mixed tidal river junction is explored. A fully nonlinear, nonhydrostatic, and unstructured three-dimensional (3D) model is used to resolve supertidal dispersion via scalar transport at a well-mixed tidal river junction. Mass transport simulated in the junction is compared against predictions using a simple node-channel model to quantify the effects of small-scale, 3D intrajunction flow features on mixing and dispersion. The effects of three-dimensionality are demonstrated by quantifying the difference between two-dimensional (2D) and 3D model results.more » An intermediate 3D model that does not resolve the secondary circulation or the recirculating flow at the junction is also compared to the 3D model to quantify the relative sensitivity of mixing on intrajunction flow features. Resolution of complex flow features simulated by the full 3D model is not always necessary because mixing is primarily governed by bulk flow splitting due to the confluence–diffluence cycle. Finally, results in 3D are comparable to the 2D case for many flow pathways simulated, suggesting that 2D modeling may be reasonable for nonstratified and predominantly hydrostatic flows through relatively straight junctions, but not necessarily for the full junction network.« less

Multiphase, multicomponent simulations and experiments of reactive flow, relevant for combining geologic CO2 sequestration with geothermal energy capture

NASA Astrophysics Data System (ADS)

Saar, Martin O.

2011-11-01

Understanding the fluid dynamics of supercritical carbon dioxide (CO2) in brine- filled porous media is important for predictions of CO2 flow and brine displacement during geologic CO2 sequestration and during geothermal energy capture using sequestered CO2 as the subsurface heat extraction fluid. We investigate multiphase fluid flow in porous media employing particle image velocimetry experiments and lattice-Boltzmann fluid flow simulations at the pore scale. In particular, we are interested in the motion of a drop (representing a CO2 bubble) through an orifice in a plate, representing a simplified porous medium. In addition, we study single-phase/multicomponent reactive transport experimentally by injecting water with dissolved CO2 into rocks/sediments typically considered for CO2 sequestration to investigate how resultant fluid-mineral reactions modify permeability fields. Finally, we investigate numerically subsurface CO2 and heat transport at the geologic formation scale.

A Numerical Study on Characteristics of Flow and Reactive Pollutant Dispersion in Step‒up Street Canyons

NASA Astrophysics Data System (ADS)

Kim, E. R.; Kim, J.

2014-12-01

For decades, many metro‒ and/or mega‒cities have grown and densities of population and building have increased. Because pollutants released from sources near ground surface such as vehicles are not easy to escape from street canyons which are spaces between buildings standing along streets pedestrians, drivers and residents are likely to be exposed to high concentrations of hazardous pollutants. Therefore, it is important to understand characteristics of flow and pollutant dispersion in street canyons. In this study, step‒up street canyons with higher downwind buildings are considered for understanding flow and reactive pollutants' dispersion characteristics there as a basic step to understand the characteristics in wider urban areas. This study used a CFD model coupled to a chemistry module. Detailed flow and air pollutant concentration are analyzed in step‒up street canyons with different upwind building heights.

Methods of computing steady-state voltage stability margins of power systems

DOEpatents

Chow, Joe Hong; Ghiocel, Scott Gordon

2018-03-20

In steady-state voltage stability analysis, as load increases toward a maximum, conventional Newton-Raphson power flow Jacobian matrix becomes increasingly ill-conditioned so power flow fails to converge before reaching maximum loading. A method to directly eliminate this singularity reformulates the power flow problem by introducing an AQ bus with specified bus angle and reactive power consumption of a load bus. For steady-state voltage stability analysis, the angle separation between the swing bus and AQ bus can be varied to control power transfer to the load, rather than specifying the load power itself. For an AQ bus, the power flow formulation is only made up of a reactive power equation, thus reducing the size of the Jacobian matrix by one. This reduced Jacobian matrix is nonsingular at the critical voltage point, eliminating a major difficulty in voltage stability analysis for power system operations.

On-chip determination of C-reactive protein using magnetic particles in continuous flow.

PubMed

Phurimsak, Chayakom; Tarn, Mark D; Peyman, Sally A; Greenman, John; Pamme, Nicole

2014-11-04

We demonstrate the application of a multilaminar flow platform, in which functionalized magnetic particles are deflected through alternating laminar flow streams of reagents and washing solutions via an external magnet, for the rapid detection of the inflammatory biomarker, C-reactive protein (CRP). The two-step sandwich immunoassay was accomplished in less than 60 s, a vast improvement on the 80-300 min time frame required for enzyme-linked immunosorbent assays (ELISA) and the 50 min necessary for off-chip magnetic particle-based assays. The combination of continuous flow and a stationary magnet enables a degree of autonomy in the system, while a detection limit of 0.87 μg mL(-1) makes it suitable for the determination of CRP concentrations in clinical diagnostics. Its applicability was further proven by assaying real human serum samples and comparing those results to values obtained using standard ELISA tests.

3-D flow and scour near a submerged wing dike: ADCP measurements on the Missouri River

USGS Publications Warehouse

Jamieson, E.C.; Rennie, C.D.; Jacobson, R.B.; Townsend, R.D.

2011-01-01

Detailed mapping of bathymetry and three-dimensional water velocities using a boat-mounted single-beam sonar and acoustic Doppler current profiler (ADCP) was carried out in the vicinity of two submerged wing dikes located in the Lower Missouri River near Columbia, Missouri. During high spring flows the wing dikes become submerged, creating a unique combination of vertical flow separation and overtopping (plunging) flow conditions, causing large-scale three-dimensional turbulent flow structures to form. On three different days and for a range of discharges, sampling transects at 5 and 20 m spacing were completed, covering the area adjacent to and upstream and downstream from two different wing dikes. The objectives of this research are to evaluate whether an ADCP can identify and measure large-scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike; and whether or not moving-boat (single-transect) data are sufficient for resolving complex three-dimensional flow fields. Results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex (temporally and spatially variable) three-dimensional flow field than repeated single transects. Results also indicate a correspondence between the location of calculated vortex cores (resolved from the interpolated three-dimensional flow field) and the nearby scour holes, providing new insight into the connections between vertically oriented coherent structures and local scour, with the unique perspective of flow and morphology in a large river.

High-Speed Hopping: Time-Resolved Tomographic PIV Measurements of Water Flea Swimming

NASA Astrophysics Data System (ADS)

Murphy, D. W.; Webster, D. R.; Yen, J.

2012-11-01

Daphniids, also known as water fleas, are small, freshwater crustaceans that live in a low-to-intermediate Reynolds number regime. These plankters are equipped with a pair of branched, setae-bearing antennae that they beat to impulsively propel themselves, or ``hop,'' through the water. A typical hop carries the daphniid one body length forward and is followed by a period of sinking. We present time-resolved tomographic PIV measurements of swimming by Daphnia magna. The body kinematics and flow physics of the daphniid hop are quantified. It is shown that the flow generated by each stroking antenna resembles an asymmetric viscous vortex ring. It is proposed that the flow produced by the daphniid hop can be modeled as a double Stokeslet consisting of two impulsively applied point forces separated by the animal width. The flow physics are discussed in the context of other species operating in the same Reynolds number range of 10 to 100: sea butterfly swimming and flight by the smallest flying insects.

Deterministic and stochastic algorithms for resolving the flow fields in ducts and networks using energy minimization

NASA Astrophysics Data System (ADS)

Sochi, Taha

2016-09-01

Several deterministic and stochastic multi-variable global optimization algorithms (Conjugate Gradient, Nelder-Mead, Quasi-Newton and global) are investigated in conjunction with energy minimization principle to resolve the pressure and volumetric flow rate fields in single ducts and networks of interconnected ducts. The algorithms are tested with seven types of fluid: Newtonian, power law, Bingham, Herschel-Bulkley, Ellis, Ree-Eyring and Casson. The results obtained from all those algorithms for all these types of fluid agree very well with the analytically derived solutions as obtained from the traditional methods which are based on the conservation principles and fluid constitutive relations. The results confirm and generalize the findings of our previous investigations that the energy minimization principle is at the heart of the flow dynamics systems. The investigation also enriches the methods of computational fluid dynamics for solving the flow fields in tubes and networks for various types of Newtonian and non-Newtonian fluids.

High-order Two-Fluid Plasma Solver for Direct Numerical Simulations of Magnetic Flows with Realistic Transport Phenomena

NASA Astrophysics Data System (ADS)

Li, Zhaorui; Livescu, Daniel

2017-11-01

The two-fluid plasma equations with full transport terms, including temperature and magnetic field dependent ion and electron viscous stresses and heat fluxes, frictional drag force, and ohmic heating term have been solved by using the sixth-order non-dissipative compact scheme for plasma flows in several different regimes. In order to be able to fully resolve all the dynamically relevant time and length scales while maintaining computational feasibility, the assumptions of infinite speed of light and negligible electron inertia have been made. The accuracy and robustness of this two-fluid plasma solver in handling plasma flows have been tested against a series of canonical problems, such as Alfven-Whistler dispersion relation, electromagnetic plasma shock, magnetic reconnection, etc. For all test cases, grid convergence tests have been conducted to achieve fully resolved results. The roles of heat flux, viscosity, resistivity, Hall and Biermann battery effects, are investigated for the canonical flows studied.

Sensitivity analysis of conservative and reactive stream transient storage models applied to field data from multiple-reach experiments

USGS Publications Warehouse

Gooseff, M.N.; Bencala, K.E.; Scott, D.T.; Runkel, R.L.; McKnight, Diane M.

2005-01-01

The transient storage model (TSM) has been widely used in studies of stream solute transport and fate, with an increasing emphasis on reactive solute transport. In this study we perform sensitivity analyses of a conservative TSM and two different reactive solute transport models (RSTM), one that includes first-order decay in the stream and the storage zone, and a second that considers sorption of a reactive solute on streambed sediments. Two previously analyzed data sets are examined with a focus on the reliability of these RSTMs in characterizing stream and storage zone solute reactions. Sensitivities of simulations to parameters within and among reaches, parameter coefficients of variation, and correlation coefficients are computed and analyzed. Our results indicate that (1) simulated values have the greatest sensitivity to parameters within the same reach, (2) simulated values are also sensitive to parameters in reaches immediately upstream and downstream (inter-reach sensitivity), (3) simulated values have decreasing sensitivity to parameters in reaches farther downstream, and (4) in-stream reactive solute data provide adequate data to resolve effective storage zone reaction parameters, given the model formulations. Simulations of reactive solutes are shown to be equally sensitive to transport parameters and effective reaction parameters of the model, evidence of the control of physical transport on reactive solute dynamics. Similar to conservative transport analysis, reactive solute simulations appear to be most sensitive to data collected during the rising and falling limb of the concentration breakthrough curve. ?? 2005 Elsevier Ltd. All rights reserved.

Numerical modeling of coupled variably saturated fluid flow and reactive transport with fast and slow chemical reactions

NASA Astrophysics Data System (ADS)

Yeh, Gour-Tsyh (George); Siegel, Malcolm D.; Li, Ming-Hsu

2001-02-01

The couplings among chemical reaction rates, advective and diffusive transport in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution within fractures and in rock matrix are important for both nuclear waste disposal and remediation of contaminated sites. This paper describes the development and application of LEHGC2.0, a mechanistically based numerical model for simulation of coupled fluid flow and reactive chemical transport, including both fast and slow reactions in variably saturated media. Theoretical bases and numerical implementations are summarized, and two example problems are demonstrated. The first example deals with the effect of precipitation/dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between chemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions.

Solid phase evolution in the Biosphere 2 hillslope experiment as predicted by modeling of hydrologic and geochemical fluxes

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

Dontsova, K.; Steefel, C.I.; Desilets, S.

2009-07-15

A reactive transport geochemical modeling study was conducted to help predict the mineral transformations occurring over a ten year time-scale that are expected to impact soil hydraulic properties in the Biosphere 2 (B2) synthetic hillslope experiment. The modeling sought to predict the rate and extent of weathering of a granular basalt (selected for hillslope construction) as a function of climatic drivers, and to assess the feedback effects of such weathering processes on the hydraulic properties of the hillslope. Flow vectors were imported from HYDRUS into a reactive transport code, CrunchFlow2007, which was then used to model mineral weathering coupled tomore » reactive solute transport. Associated particle size evolution was translated into changes in saturated hydraulic conductivity using Rosetta software. We found that flow characteristics, including velocity and saturation, strongly influenced the predicted extent of incongruent mineral weathering and neo-phase precipitation on the hillslope. Results were also highly sensitive to specific surface areas of the soil media, consistent with surface reaction controls on dissolution. Effects of fluid flow on weathering resulted in significant differences in the prediction of soil particle size distributions, which should feedback to alter hillslope hydraulic conductivities.« less

Analytical solutions for flow fields near drain-and-gate reactive barriers.

PubMed

Klammler, Harald; Hatfield, Kirk; Kacimov, Anvar

2010-01-01

Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two-dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain-and-gate (DG) PRBs, which may possess a collector and a distributor drain ("full" configuration) or a collector drain only ("simple" configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner-friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel-and-gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances.

Occupational status and job stress in relation to cardiovascular stress reactivity in Japanese workers.

PubMed

Hirokawa, Kumi; Ohira, Tetsuya; Nagayoshi, Mako; Kajiura, Mitsugu; Imano, Hironori; Kitamura, Akihiko; Kiyama, Masahiko; Okada, Takeo; Iso, Hiroyasu

2016-12-01

This study aimed to investigate the effects of occupational status and job stress factors on cardiovascular stress reactivity in Japanese workers. In this baseline assessment between 2001 and 2009 in Osaka, Japan, we examined 928 healthy Japanese employees (330 men, 598 women) from two occupational statuses: managers/professionals and general workers. A brief job stress questionnaire was used to evaluate job stress levels. Systolic and diastolic blood pressure (SBP, DBP), heart rate, heart rate variability (high-frequency [HF], low-frequency [LF], LF/HF], and peripheral blood flow were measured at rest and during two stressful tasks. Changes in stress reactivity were calculated as the difference between the measured variables during the tasks and the rest period. Men showed inverse associations between quantitative job overload and DBP, heart rate, and LF/HF, between physical demands and blood pressure (SBP, DBP), and between a poor physical environment and HF. Men also had positive associations between qualitative job overload and heart rate, and between physical demands and peripheral blood flow (all p < 0.05). Women showed inverse associations between qualitative job overload and SBP, and showed positive associations between qualitative job overload and peripheral blood flow, and between a poor physical environment and SBP (all p < 0.05). When stratified by occupational status, significant associations between job stress and changes in stress reactivity were observed in male managers/professionals and female general workers (p < 0.05). Job stress levels are associated with changes in cardiovascular stress reactivity in men and women. Occupational status may modify these associations.

Modeling variably saturated multispecies reactive groundwater solute transport with MODFLOW-UZF and RT3D

USGS Publications Warehouse

Bailey, Ryan T.; Morway, Eric D.; Niswonger, Richard G.; Gates, Timothy K.

2013-01-01

A numerical model was developed that is capable of simulating multispecies reactive solute transport in variably saturated porous media. This model consists of a modified version of the reactive transport model RT3D (Reactive Transport in 3 Dimensions) that is linked to the Unsaturated-Zone Flow (UZF1) package and MODFLOW. Referred to as UZF-RT3D, the model is tested against published analytical benchmarks as well as other published contaminant transport models, including HYDRUS-1D, VS2DT, and SUTRA, and the coupled flow and transport modeling system of CATHY and TRAN3D. Comparisons in one-dimensional, two-dimensional, and three-dimensional variably saturated systems are explored. While several test cases are included to verify the correct implementation of variably saturated transport in UZF-RT3D, other cases are included to demonstrate the usefulness of the code in terms of model run-time and handling the reaction kinetics of multiple interacting species in variably saturated subsurface systems. As UZF1 relies on a kinematic-wave approximation for unsaturated flow that neglects the diffusive terms in Richards equation, UZF-RT3D can be used for large-scale aquifer systems for which the UZF1 formulation is reasonable, that is, capillary-pressure gradients can be neglected and soil parameters can be treated as homogeneous. Decreased model run-time and the ability to include site-specific chemical species and chemical reactions make UZF-RT3D an attractive model for efficient simulation of multispecies reactive transport in variably saturated large-scale subsurface systems.

A Tracer Test to Characterize Treatment of TCE in a Permeable Reactive Barrier

EPA Science Inventory

A tracer test was conducted to characterize the flow of ground water surrounding a permeable reactive barrier constructed with plant mulch (a biowall) at the OU-1 site on Altus Air Force Base, Oklahoma. This biowall is intended to intercept and treat ground water contaminated by ...

Bond Strength and Reactivity Scales for Lewis Superacid Adducts: A Comparative Study with In(OTf)3 and Al(OTf)3.

PubMed

Compain, Guillaume; Sikk, Lauri; Massi, Lionel; Gal, Jean-François; Duñach, Elisabet

2017-03-17

Metal triflates, often called Lewis superacids, are potent catalysts for organic synthesis. However, the reactivity of a given Lewis superacid toward a given base is difficult to anticipate. A systematic screening of catalysts is often necessary when developing synthetic methodologies. Presented herein is the development of quantitative reactivity and bond strength scales by using mass spectrometry (MS). By applying a collision-induced dissociation (CID) technique to the adducts formed between Lewis superacids Al(OTf) 3 or In(OTf) 3 with a series of amides bases, including monodentate and bidentate ligands, different dissociation pathways were observed. Quantitative relative energy scales were established by performing energy-resolved mass spectrometry (ERMS) analysis on the adducts. ERMS of the adducts affords a bond strength scale when the fragmentation leads to the loss of a ligand, and reactivity scales when the dissociation leads to the C-F bond activation of one triflate anion or the deprotonation of the ligand. Al(OTf) 3 was found to bind stronger to amides than In(OTf) 3 and to provide the most reactive adducts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vascular Dysfunction in Leukoaraiosis.

PubMed

Sam, K; Crawley, A P; Poublanc, J; Conklin, J; Sobczyk, O; Mandell, D M; Duffin, J; Venkatraghavan, L; Fisher, J A; Black, S E; Mikulis, D J

2016-12-01

The pathogenesis of leukoaraiosis has long been debated. This work addresses a less well-studied mechanism, cerebrovascular reactivity, which could play a leading role in the pathogenesis of this disease. Our aim was to evaluate blood flow dysregulation and its relation to leukoaraiosis. Cerebrovascular reactivity, the change in the blood oxygen level-dependent 3T MR imaging signal in response to a consistently applied step change in the arterial partial pressure of carbon dioxide, was measured in white matter hyperintensities and their contralateral spatially homologous normal-appearing white matter in 75 older subjects (age range, 50-91 years; 40 men) with leukoaraiosis. Additional quantitative evaluation of regions of leukoaraiosis was performed by using diffusion (n = 75), quantitative T2 (n = 54), and DSC perfusion MRI metrics (n = 25). When we compared white matter hyperintensities with contralateral normal-appearing white matter, cerebrovascular reactivity was lower by a mean of 61.2% ± 22.6%, fractional anisotropy was lower by 44.9 % ± 6.9%, and CBF was lower by 10.9% ± 11.9%. T2 was higher by 61.7% ± 13.5%, mean diffusivity was higher by 59.0% ± 11.7%, time-to-maximum was higher by 44.4% ± 30.4%, and TTP was higher by 6.8% ± 5.8% (all P < .01). Cerebral blood volume was lower in white matter hyperintensities compared with contralateral normal-appearing white matter by 10.2% ± 15.0% (P = .03). Not only were resting blood flow metrics abnormal in leukoaraiosis but there is also evidence of reduced cerebrovascular reactivity in these areas. Studies have shown that reduced cerebrovascular reactivity is more sensitive than resting blood flow parameters for assessing vascular insufficiency. Future work is needed to examine the sensitivity of resting-versus-dynamic blood flow measures for investigating the pathogenesis of leukoaraiosis. © 2016 by American Journal of Neuroradiology.

Numerical prediction of turbulent flame stability in premixed/prevaporized (HSCT) combustors

NASA Technical Reports Server (NTRS)

Winowich, Nicholas S.

1990-01-01

A numerical analysis of combustion instabilities that induce flashback in a lean, premixed, prevaporized dump combustor is performed. KIVA-II, a finite volume CFD code for the modeling of transient, multidimensional, chemically reactive flows, serves as the principal analytical tool. The experiment of Proctor and T'ien is used as a reference for developing the computational model. An experimentally derived combustion instability mechanism is presented on the basis of the observations of Proctor and T'ien and other investigators of instabilities in low speed (M less than 0.1) dump combustors. The analysis comprises two independent procedures that begin from a calculated stable flame: The first is a linear increase of the equivalence ratio and the second is the linear decrease of the inflow velocity. The objective is to observe changes in the aerothermochemical features of the flow field prior to flashback. It was found that only the linear increase of the equivalence ratio elicits a calculated flashback result. Though this result did not exhibit large scale coherent vortices in the turbulent shear layer coincident with a flame flickering mode as was observed experimentally, there were interesting acoustic effects which were resolved quite well in the calculation. A discussion of the k-e turbulence model used by KIVA-II is prompted by the absence of combustion instabilities in the model as the inflow velocity is linearly decreased. Finally, recommendations are made for further numerical analysis that may improve correlation with experimentally observed combustion instabilities.

High temporal resolution modelling of environmentally-dependent seabird ammonia emissions: Description and testing of the GUANO model

NASA Astrophysics Data System (ADS)

Riddick, S. N.; Blackall, T. D.; Dragosits, U.; Tang, Y. S.; Moring, A.; Daunt, F.; Wanless, S.; Hamer, K. C.; Sutton, M. A.

2017-07-01

Many studies in recent years have highlighted the ecological implications of adding reactive nitrogen (Nr) to terrestrial ecosystems. Seabird colonies represent a situation with concentrated sources of Nr, through excreted and accumulated guano, often occurring in otherwise nutrient-poor areas. To date, there has been little attention given to modelling N flows in this context, and particularly to quantifying the relationship between ammonia (NH3) emissions and meteorology. This paper presents a dynamic mass-flow model (GUANO) that simulates temporal variations in NH3 emissions from seabird guano. While the focus is on NH3 emissions, the model necessarily also treats the interaction with wash-off as far as this affects NH3. The model is validated using NH3 emissions measurements from seabird colonies across a range of climates, from sub-polar to tropical. In simulations for hourly time-resolved data, the model is able to capture the observed dependence of NH3 emission on environmental variables. With temperature and wind speed having the greatest effects on emission for the cases considered. In comparison with empirical data, the percentage of excreted nitrogen that volatilizes as NH3 is found to range from 2% to 67% (based on measurements), with the GUANO model providing a range of 2%-82%. The model provides a tool that can be used to investigate the meteorological dependence of NH3 emissions from seabird guano and provides a starting point to refine models of NH3 emissions from other sources.

Velocity landscape correlation resolves multiple flowing protein populations from fluorescence image time series.

PubMed

Pandžić, Elvis; Abu-Arish, Asmahan; Whan, Renee M; Hanrahan, John W; Wiseman, Paul W

2018-02-16

Molecular, vesicular and organellar flows are of fundamental importance for the delivery of nutrients and essential components used in cellular functions such as motility and division. With recent advances in fluorescence/super-resolution microscopy modalities we can resolve the movements of these objects at higher spatio-temporal resolutions and with better sensitivity. Previously, spatio-temporal image correlation spectroscopy has been applied to map molecular flows by correlation analysis of fluorescence fluctuations in image series. However, an underlying assumption of this approach is that the sampled time windows contain one dominant flowing component. Although this was true for most of the cases analyzed earlier, in some situations two or more different flowing populations can be present in the same spatio-temporal window. We introduce an approach, termed velocity landscape correlation (VLC), which detects and extracts multiple flow components present in a sampled image region via an extension of the correlation analysis of fluorescence intensity fluctuations. First we demonstrate theoretically how this approach works, test the performance of the method with a range of computer simulated image series with varying flow dynamics. Finally we apply VLC to study variable fluxing of STIM1 proteins on microtubules connected to the plasma membrane of Cystic Fibrosis Bronchial Epithelial (CFBE) cells. Copyright © 2018 Elsevier Inc. All rights reserved.

Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system

NASA Astrophysics Data System (ADS)

Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai

2015-07-01

In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.

Three-dimensional model for multi-component reactive transport with variable density groundwater flow

USGS Publications Warehouse

Mao, X.; Prommer, H.; Barry, D.A.; Langevin, C.D.; Panteleit, B.; Li, L.

2006-01-01

PHWAT is a new model that couples a geochemical reaction model (PHREEQC-2) with a density-dependent groundwater flow and solute transport model (SEAWAT) using the split-operator approach. PHWAT was developed to simulate multi-component reactive transport in variable density groundwater flow. Fluid density in PHWAT depends not on only the concentration of a single species as in SEAWAT, but also the concentrations of other dissolved chemicals that can be subject to reactive processes. Simulation results of PHWAT and PHREEQC-2 were compared in their predictions of effluent concentration from a column experiment. Both models produced identical results, showing that PHWAT has correctly coupled the sub-packages. PHWAT was then applied to the simulation of a tank experiment in which seawater intrusion was accompanied by cation exchange. The density dependence of the intrusion and the snow-plough effect in the breakthrough curves were reflected in the model simulations, which were in good agreement with the measured breakthrough data. Comparison simulations that, in turn, excluded density effects and reactions allowed us to quantify the marked effect of ignoring these processes. Next, we explored numerical issues involved in the practical application of PHWAT using the example of a dense plume flowing into a tank containing fresh water. It was shown that PHWAT could model physically unstable flow and that numerical instabilities were suppressed. Physical instability developed in the model in accordance with the increase of the modified Rayleigh number for density-dependent flow, in agreement with previous research. ?? 2004 Elsevier Ltd. All rights reserved.

The dependence of chlorine decay and DBP formation kinetics on pipe flow properties in drinking water distribution.

PubMed

Zhao, Yingying; Yang, Y Jeffrey; Shao, Yu; Neal, Jill; Zhang, Tuqiao

2018-04-27

Simultaneous chlorine decay and disinfection byproduct (DBP) formation have been discussed extensively because of their regulatory and operational significance. This study further examines chemical reaction variability in the water quality changes under various hydrodynamic conditions in drinking water distribution. The variations of kinetic constant for overall chlorine decay (k E ) and trihalomethane (THM) formation were determined under stagnant to turbulent flows using three devices of different wall demand and two types of natural organic matters (NOM) in water. The results from the comparative experiments and modeling analyses show the relative importance of wall demand (k w ), DBP-forming chlorine decay (k D ), and other bulk demand (k b ' ) for pipe flows of Re = 0-52500. It is found that chlorine reactivity of virgin NOM is the overriding factor. Secondly, for tap water NOM of lower reactivity, pipe flow properties (Re or u) can significantly affect k E , the THM yield (T), formation potential (Y), and the time to reach the maximum THM concentration (t max ) through their influence on kinetic ratio k D (k b ' +k w ). These observations, corroborating with turbidity variations during experiments, cannot be explained alone by chlorine dispersion to and from the pipe wall. Mass exchanges through deposition and scale detachment, most likely being flow-dependent, may have contributed to the overall chlorine decay and DBP formation rates. Thus for the simultaneous occurrence of chlorine decay and DBP formation, model considerations of NOM reactivity, pipe types (wall demand), flow hydraulics, and their interactions are essential. Copyright © 2018 Elsevier Ltd. All rights reserved.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

PubMed

Lee, Sang Joon; Park, Han Wook; Jung, Sung Yong

2014-09-01

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Literature Survey on Operational Voltage Control and Reactive Power Management on Transmission and Sub-Transmission Networks

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

Elizondo, Marcelo A.; Samaan, Nader A.; Makarov, Yuri V.

Voltage and reactive power system control is generally performed following usual patterns of loads, based on off-line studies for daily and seasonal operations. This practice is currently challenged by the inclusion of distributed renewable generation, such as solar. There has been focus on resolving this problem at the distribution level; however, the transmission and sub-transmission levels have received less attention. This paper provides a literature review of proposed methods and solution approaches to coordinate and optimize voltage control and reactive power management, with an emphasis on applications at transmission and sub-transmission level. The conclusion drawn from the survey is thatmore » additional research is needed in the areas of optimizing switch shunt actions and coordinating all available resources to deal with uncertain patterns from increasing distributed renewable generation in the operational time frame. These topics are not deeply explored in the literature.« less

Toward computational models of magma genesis and geochemical transport in subduction zones

NASA Astrophysics Data System (ADS)

Katz, R.; Spiegelman, M.

2003-04-01

The chemistry of material erupted from subduction-related volcanoes records important information about the processes that lead to its formation at depth in the Earth. Self-consistent numerical simulations provide a useful tool for interpreting this data as they can explore the non-linear feedbacks between processes that control the generation and transport of magma. A model capable of addressing such issues should include three critical components: (1) a variable viscosity solid flow solver with smooth and accurate pressure and velocity fields, (2) a parameterization of mass transfer reactions between the solid and fluid phases and (3) a consistent fluid flow and reactive transport code. We report on progress on each of these parts. To handle variable-viscosity solid-flow in the mantle wedge, we are adapting a Patankar-based FAS multigrid scheme developed by Albers (2000, J. Comp. Phys.). The pressure field in this scheme is the solution to an elliptic equation on a staggered grid. Thus we expect computed pressure fields to have smooth gradient fields suitable for porous flow calculations, unlike those of commonly used penalty-method schemes. Use of a temperature and strain-rate dependent mantle rheology has been shown to have important consequences for the pattern of flow and the temperature structure in the wedge. For computing thermal structure we present a novel scheme that is a hybrid of Crank-Nicholson (CN) and Semi-Lagrangian (SL) methods. We have tested the SLCN scheme on advection across a broad range of Peclet numbers and show the results. This scheme is also useful for low-diffusivity chemical transport. We also describe our parameterization of hydrous mantle melting [Katz et. al., G3, 2002 in review]. This parameterization is designed to capture the melting behavior of peridotite--water systems over parameter ranges relevant to subduction. The parameterization incorporates data and intuition gained from laboratory experiments and thermodynamic calculations yet it remains flexible and computationally efficient. Given accurate solid-flow fields, a parameterization of hydrous melting and a method for calculating thermal structure (enforcing energy conservation), the final step is to integrate these components into a consistent framework for reactive-flow and chemical transport in deformable porous media. We present preliminary results for reactive flow in 2-D static and upwelling columns and discuss possible mechanical and chemical consequences of open system reactive melting with application to arcs.

Hall effects on unsteady MHD reactive flow of second grade fluid through porous medium in a rotating parallel plate channel

NASA Astrophysics Data System (ADS)

Krishna, M. Veera; Swarnalathamma, B. V.

2017-07-01

We considered the transient MHD flow of a reactive second grade fluid through porous medium between two infinitely long horizontal parallel plates when one of the plate is set into uniform accelerated motion in the presence of a uniform transverse magnetic field under Arrhenius reaction rate. The governing equations are solved by Laplace transform technique. The effects of the pertinent parameters on the velocity, temperature are discussed in detail. The shear stress and Nusselt number at the plates are also obtained analytically and computationally discussed with reference to governing parameters.

Chemorheology of reactive systems: Finite element analysis

NASA Technical Reports Server (NTRS)

Douglas, C.; Roylance, D.

1982-01-01

The equations which govern the nonisothermal flow of reactive fluids are outlined, and the means by which finite element analysis is used to solve these equations for the sort of arbitrary boundary conditions encountered in industrial practice are described. The performance of the computer code is illustrated by several trial problems, selected more for their value in providing insight to polymer processing flows than as practical production problems. Although a good deal remains to be learned as to the performance and proper use of this numerical technique, it is undeniably useful in providing better understanding of today's complicated polymer processing problems.

Gas sampling system for reactive gas-solid mixtures

DOEpatents

Daum, Edward D.; Downs, William; Jankura, Bryan J.; McCoury, Jr., John M.

1989-01-01

An apparatus and method for sampling a gas containing a reactive particulate solid phase flowing through a duct and for communicating a representative sample to a gas analyzer. A sample probe sheath 32 with an angular opening 34 extends vertically into a sample gas duct 30. The angular opening 34 is opposite the gas flow. A gas sampling probe 36 concentrically located within sheath 32 along with calibration probe 40 partly extend in the sheath 32. Calibration probe 40 extends further in the sheath 32 than gas sampling probe 36 for purging the probe sheath area with a calibration gas during calibration.

Gas sampling system for reactive gas-solid mixtures

DOEpatents

Daum, Edward D.; Downs, William; Jankura, Bryan J.; McCoury, Jr., John M.

1990-01-01

An apparatus and method for sampling gas containing a reactive particulate solid phase flowing through a duct and for communicating a representative sample to a gas analyzer. A sample probe sheath 32 with an angular opening 34 extends vertically into a sample gas duct 30. The angular opening 34 is opposite the gas flow. A gas sampling probe 36 concentrically located within sheath 32 along with calibration probe 40 partly extends in the sheath 32. Calibration probe 40 extends further in the sheath 32 than gas sampling probe 36 for purging the probe sheath area with a calibration gas during calibration.

Reactive Orthotropic Lattice Diffuser for Noise Reduction

NASA Technical Reports Server (NTRS)

Khorrami, Mehdi R. (Inventor)

2016-01-01

An orthotropic lattice structure interconnects porous surfaces of the flap with internal lattice-structured perforations to equalize the steady pressure field on the flap surfaces adjacent to the end and to reduce the amplitude of the fluctuations in the flow field near the flap end. The global communication that exists within all of the perforations provides the mechanism to lessen the pressure gradients experienced by the end portion of the flap. In addition to having diffusive effects (diffusing the incoming flow), the three-dimensional orthogonal lattice structure is also reactive (acoustic wave phase distortion) due to the interconnection of the perforations.

A reactive flow model with coupled reaction kinetics for detonation and combustion in non-ideal explosives

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

Miller, P.J.

1996-07-01

A new reactive flow model for highly non-ideal explosives and propellants is presented. These compositions, which contain large amounts of metal, upon explosion have reaction kinetics that are characteristic of both fast detonation and slow metal combustion chemistry. A reaction model for these systems was incorporated into the two-dimensional, finite element, Lagrangian hydrodynamic code, DYNA2D. A description of how to determine the model parameters is given. The use of the model and variations are applied to AP, Al, and nitramine underwater explosive and propellant systems.

Biomonitoring of Organophosphorus Agent Exposure by Reactivation of Cholinesterase Enzyme Based on Carbon Nanotube-Enhanced Flow-Injection Amperometric Detection

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

Du, Dan; Wang, Jun; Smith, Jordan N.

2009-11-15

A portable, rapid, and sensitive assessment of sub-clinical organophosphorus (OPs) agent exposure based on reactivation of cholinesterase (ChE) from OP-inhibited ChE using rat saliva (in vitro) was developed using an electrochemical sensor coupled with a microflow-injection system. The sensor was based on a carbon nanotube (CNT)-modified screen printed carbon electrode (SPE), which was integrated into a flow cell. Due to the extent of inter-individual ChE activity variability, ChE biomonitoring often requires an initial base-line determination (non-inhibited) of enzyme activity which is then directly compared with activity after OP exposure. This manuscript described an alternative strategy where reactivation of the phosphorylatedmore » enzyme was exploited to enable measurement of both inhibited and baseline ChE activity (i.e. after reactivation) in the same sample. The use of CNT makes the electrochemical detection of the products from enzymatic reactions more feasible with extremely high sensitivity and at low potentials. Paraoxon was selected as a model OP compound for in vitro inhibition studies. Some experiment parameters, (e.g. inhibition and reactivation times), have been optimized such that, 92 - 95% ChE reactivation can be achieved over a broad range of ChE inhibition (5 - 94 %) with paraoxon. The extent of enzyme inhibition using this electrochemical sensor correlates well with conventional enzyme activity measurements.« less

Is cerebral vasomotor reactivity impaired in Parkinson disease?

PubMed

Hanby, Martha F; Panerai, Ronney B; Robinson, Thompson G; Haunton, Victoria J

2017-04-01

The ability of a blood vessel to change diameter in response to a change in carbon dioxide concentration is often referred to as vasomotor reactivity. This study aimed to determine whether vasomotor reactivity is impaired in patients with idiopathic Parkinson's Disease in comparison to healthy controls. Transcranial Doppler was used to measure cerebral blood flow velocity in the middle cerebral arteries at baseline and under hypocapnic conditions in 40 patients with idiopathic Parkinson's disease and 50 healthy controls. Vasomotor reactivity, assessed under hypocapnic conditions, is not impaired in patients with idiopathic Parkinson's Disease in comparison to healthy controls.

A weakly nonlinear theory for wave-vortex interactions in curved channel flow

NASA Technical Reports Server (NTRS)

Singer, Bart A.; Erlebacher, Gordon; Zang, Thomas A.

1992-01-01

A weakly nonlinear theory is developed to study the interaction of Tollmien-Schlichting (TS) waves and Dean vortices in curved channel flow. The predictions obtained from the theory agree well with results obtained from direct numerical simulations of curved channel flow, especially for low amplitude disturbances. Some discrepancies in the results of a previous theory with direct numerical simulations are resolved.

Core Dynamics Analysis for Reactivity Insertion and Loss of Coolant Flow Tests Using the High Temperature Engineering Test Reactor

NASA Astrophysics Data System (ADS)

Takamatsu, Kuniyoshi; Nakagawa, Shigeaki; Takeda, Tetsuaki

Safety demonstration tests using the High Temperature Engineering Test Reactor (HTTR) are in progress to verify its inherent safety features and improve the safety technology and design methodology for High-temperature Gas-cooled Reactors (HTGRs). The reactivity insertion test is one of the safety demonstration tests for the HTTR. This test simulates the rapid increase in the reactor power by withdrawing the control rod without operating the reactor power control system. In addition, the loss of coolant flow tests has been conducted to simulate the rapid decrease in the reactor power by tripping one, two or all out of three gas circulators. The experimental results have revealed the inherent safety features of HTGRs, such as the negative reactivity feedback effect. The numerical analysis code, which was named-ACCORD-, was developed to analyze the reactor dynamics including the flow behavior in the HTTR core. We have modified this code to use a model with four parallel channels and twenty temperature coefficients. Furthermore, we added another analytical model of the core for calculating the heat conduction between the fuel channels and the core in the case of the loss of coolant flow tests. This paper describes the validation results for the newly developed code using the experimental results. Moreover, the effect of the model is formulated quantitatively with our proposed equation. Finally, the pre-analytical result of the loss of coolant flow test by tripping all gas circulators is also discussed.

VS2DRTI: Simulating Heat and Reactive Solute Transport in Variably Saturated Porous Media.

PubMed

Healy, Richard W; Haile, Sosina S; Parkhurst, David L; Charlton, Scott R

2018-01-29

Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena, such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid-rock drainage, and the geologic sequestration of carbon dioxide. Up to now, our ability to simulate these processes simultaneously with fully coupled reactive transport models has been limited to complex and often difficult-to-use models. To address the need for a simple and easy-to-use model, the VS2DRTI software package has been developed for simulating water flow, heat transport, and reactive solute transport through variably saturated porous media. The underlying numerical model, VS2DRT, was created by coupling the flow and transport capabilities of the VS2DT and VS2DH models with the equilibrium and kinetic reaction capabilities of PhreeqcRM. Flow capabilities include two-dimensional, constant-density, variably saturated flow; transport capabilities include both heat and multicomponent solute transport; and the reaction capabilities are a complete implementation of geochemical reactions of PHREEQC. The graphical user interface includes a preprocessor for building simulations and a postprocessor for visual display of simulation results. To demonstrate the simulation of multiple processes, the model is applied to a hypothetical example of injection of heated waste water to an aquifer with temperature-dependent cation exchange. VS2DRTI is freely available public domain software. © 2018, National Ground Water Association.

Editorial

NASA Astrophysics Data System (ADS)

Bijeljic, Branko; Icardi, Matteo; Prodanović, Maša

2018-05-01

Substantial progress has been made over last few decades on understanding the physics of multiphase flow and reactive transport phenomena in subsurface porous media. Confluence of advances in experimental techniques (including micromodels, X-ray microtomography, Nuclear Magnetic Resonance (NMR)) as well as computational power have made it possible to observe static and dynamic multi-scale flow, transport and reactive processes, thus stimulating development of new generation of modelling tools from pore to field scale. One of the key challenges is to make experiment and models as complementary as possible, with continuously improving experimental methods in order to increase predictive capabilities of theoretical models across scales. This creates need to establish rigorous benchmark studies of flow, transport and reaction in porous media which can then serve as the basis for introducing more complex phenomena in future developments.

Energy transport in a shear flow of particles in a two-dimensional dusty plasma.

PubMed

Feng, Yan; Goree, J; Liu, Bin

2012-11-01

A shear flow of particles in a laser-driven two-dimensional (2D) dusty plasma is observed in a study of viscous heating and thermal conduction. Video imaging and particle tracking yields particle velocity data, which we convert into continuum data, presented as three spatial profiles: mean particle velocity (i.e., flow velocity), mean-square particle velocity, and mean-square fluctuations of particle velocity. These profiles and their derivatives allow a spatially resolved determination of each term in the energy and momentum continuity equations, which we use for two purposes. First, by balancing these terms so that their sum (i.e., residual) is minimized while varying viscosity η and thermal conductivity κ as free parameters, we simultaneously obtain values for η and κ in the same experiment. Second, by comparing the viscous heating and thermal conduction terms, we obtain a spatially resolved characterization of the viscous heating.

Development of a steady potential solver for use with linearized, unsteady aerodynamic analyses

NASA Technical Reports Server (NTRS)

Hoyniak, Daniel; Verdon, Joseph M.

1991-01-01

A full potential steady flow solver (SFLOW) developed explicitly for use with an inviscid unsteady aerodynamic analysis (LINFLO) is described. The steady solver uses the nonconservative form of the nonlinear potential flow equations together with an implicit, least squares, finite difference approximation to solve for the steady flow field. The difference equations were developed on a composite mesh which consists of a C grid embedded in a rectilinear (H grid) cascade mesh. The composite mesh is capable of resolving blade to blade and far field phenomena on the H grid, while accurately resolving local phenomena on the C grid. The resulting system of algebraic equations is arranged in matrix form using a sparse matrix package and solved by Newton's method. Steady and unsteady results are presented for two cascade configurations: a high speed compressor and a turbine with high exit Mach number.

Effects of combined xenon and hypothermia on cerebral blood flow and oxygen consumption in newborn piglets measured with a time-resolved near-infrared technique

NASA Astrophysics Data System (ADS)

Fazel Bakhsheshi, Mohammad; Hadway, Jennifer; Morrison, Laura B.; Diop, Mamadou; St. Lawrence, Keith; Lee, Ting-Yim

2013-02-01

Mild hypothermia (HT), in which the brain is cooled to 32-33°C, has been shown to be neuroprotective for neurological emergencies such as head trauma and neonatal asphyxia. Xenon (Xe), a scarce and expensive anesthetic gas, has also shown great promise as a neuroprotectant, particularly when combined with HT. The purpose of the present study was to investigate the combined effect of Xe and HT on the cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF). A closed circuit re-breathing system was used to deliver the Xe in order to make the treatment efficient and economical. A bolus-tracking method using indocyanine green (ICG) as a flow tracer with time-resolved near-infrared (TR-NIR) technique was used to measure CBF and CMRO2 in newborn piglets.

In microfluidico: Recreating in vivo hemodynamics using miniaturized devices

PubMed Central

Zhu, Shu; Herbig, Bradley A.; Li, Ruizhi; Colace, Thomas V.; Muthard, Ryan W.; Neeves, Keith B.; Diamond, Scott L.

2016-01-01

Microfluidic devices create precisely controlled reactive blood flows and typically involve: (i) validated anticoagulation/pharmacology protocols, (ii) defined reactive surfaces, (iii) defined flow-transport regimes, and (iv) optical imaging. An 8-channel device can be run at constant flow rate or constant pressure drop for blood perfusion over a patterned collagen, collagen/kaolin, or collagen/tissue factor (TF) to measure platelet, thrombin, and fibrin dynamics during clot growth. A membrane-flow device delivers a constant flux of platelet agonists or coagulation enzymes into flowing blood. A trifurcated device sheaths a central blood flow on both sides with buffer, an ideal approach for on-chip recalcification of citrated blood or drug delivery. A side-view device allows clotting on a porous collagen/TF plug at constant pressure differential across the developing clot. The core-shell architecture of clots made in mouse models can be replicated in this device using human blood. For pathological flows, a stenosis device achieves shear rates of >100,000 s−1 to drive plasma von Willebrand factor (VWF) to form thick long fibers on collagen. Similarly, a micropost-impingement device creates extreme elongational and shear flows for VWF fiber formation without collagen. Overall, microfluidics are ideal for studies of clotting, bleeding, fibrin polymerization/fibrinolysis, cell/clot mechanics, adhesion, mechanobiology, and reaction-transport dynamics. PMID:26600269

Strong Photothermoelectric Response and Contact Reactivity of the Dirac Semimetal ZrTe 5

DOE PAGES

Leonard, Francois; Yu, Wenlong; Collins, Kimberlee C.; ...

2017-10-03

The family of three-dimensional topological insulators opens new avenues to discover novel photophysics and to develop novel types of photodetectors. ZrTe 5 has been shown to be a Dirac semimetal possessing unique topological, electronic, and optical properties. Here, we present spatially resolved photocurrent measurements on devices made of nanoplatelets of ZrTe 5, demonstrating the photothermoelectric origin of the photoresponse. Because of the high electrical conductivity and good Seebeck coefficient, we obtain noise-equivalent powers as low as 42 pW/Hz 1/2, at room temperature for visible light illumination, at zero bias. We also show that these devices suffer from significant ambient reactivity,more » such as the formation of a Te-rich surface region driven by Zr oxidation as well as severe reactions with the metal contacts. This reactivity results in significant stresses in the devices, leading to unusual geometries that are useful for gaining insight into the photocurrent mechanisms. Lastly, our results indicate that both the large photothermoelectric response and reactivity must be considered when designing or interpreting photocurrent measurements in these systems.« less

CRISPR-Cas9-based target validation for p53-reactivating model compounds

PubMed Central

Wanzel, Michael; Vischedyk, Jonas B; Gittler, Miriam P; Gremke, Niklas; Seiz, Julia R; Hefter, Mirjam; Noack, Magdalena; Savai, Rajkumar; Mernberger, Marco; Charles, Joël P; Schneikert, Jean; Bretz, Anne Catherine; Nist, Andrea; Stiewe, Thorsten

2015-01-01

Inactivation of the p53 tumor suppressor by Mdm2 is one of the most frequent events in cancer, so compounds targeting the p53-Mdm2 interaction are promising for cancer therapy. Mechanisms conferring resistance to p53-reactivating compounds are largely unknown. Here we show using CRISPR-Cas9–based target validation in lung and colorectal cancer that the activity of nutlin, which blocks the p53-binding pocket of Mdm2, strictly depends on functional p53. In contrast, sensitivity to the drug RITA, which binds the Mdm2-interacting N terminus of p53, correlates with induction of DNA damage. Cells with primary or acquired RITA resistance display cross-resistance to DNA crosslinking compounds such as cisplatin and show increased DNA cross-link repair. Inhibition of FancD2 by RNA interference or pharmacological mTOR inhibitors restores RITA sensitivity. The therapeutic response to p53-reactivating compounds is therefore limited by compound-specific resistance mechanisms that can be resolved by CRISPR-Cas9-based target validation and should be considered when allocating patients to p53-reactivating treatments. PMID:26595461

Far-infrared observations of the exciting stars of Herbig-Haro objects. III - Circumstellar disks

NASA Technical Reports Server (NTRS)

Cohen, M.; Harvey, P. M.; Schwartz, R. D.

1985-01-01

Far-infrared observations of the exciting stars of Herbig-Haro objects are presented that (1) show these stars to be of low luminosity; (2) indicate that it is not usual for these objects themselves to be visible at far-infrared wavelengths; and (3) demonstrate the existence of spatially resolved, physically large, potentially disklike structures. These latter structures are resolved perpendicular to the directions of flow from the stars, but not parallel to the flows. In addition to these general properties, two new HH-exciting stars were discovered by searching along the extrapolated proper motion vectors for these HHs; and the jetlike object 'DG Tau B' was also detected.

Time-Domain Filtering for Spatial Large-Eddy Simulation

NASA Technical Reports Server (NTRS)

Pruett, C. David

1997-01-01

An approach to large-eddy simulation (LES) is developed whose subgrid-scale model incorporates filtering in the time domain, in contrast to conventional approaches, which exploit spatial filtering. The method is demonstrated in the simulation of a heated, compressible, axisymmetric jet, and results are compared with those obtained from fully resolved direct numerical simulation. The present approach was, in fact, motivated by the jet-flow problem and the desire to manipulate the flow by localized (point) sources for the purposes of noise suppression. Time-domain filtering appears to be more consistent with the modeling of point sources; moreover, time-domain filtering may resolve some fundamental inconsistencies associated with conventional space-filtered LES approaches.

Mid-infrared laser absorption tomography for quantitative 2D thermochemistry measurements in premixed jet flames

NASA Astrophysics Data System (ADS)

Wei, Chuyu; Pineda, Daniel I.; Paxton, Laurel; Egolfopoulos, Fokion N.; Spearrin, R. Mitchell

2018-06-01

A tomographic laser absorption spectroscopy technique, utilizing mid-infrared light sources, is presented as a quantitative method to spatially resolve species and temperature profiles in small-diameter reacting flows relevant to combustion systems. Here, tunable quantum and interband cascade lasers are used to spectrally resolve select rovibrational transitions near 4.98 and 4.19 μm to measure CO and {CO2}, respectively, as well as their vibrational temperatures, in piloted premixed jet flames. Signal processing methods are detailed for the reconstruction of axial and radial profiles of thermochemical structure in a canonical ethylene-air jet flame. The method is further demonstrated to quantitatively distinguish between different turbulent flow conditions.

INFLUENCE OF GROUNDWATER GEOCHEMISTRY ON THE LONG-TERM PERFORMANCE OF IN-SITU PERMEABLE REACTIVE BARRIERS CONTAINING ZERO-VALENT IRON

EPA Science Inventory

Reactive barriers that couple subsurface fluid flow with a passive chemical treatment zone are emerging, cost effective approaches for in-situ remediation of contaminated groundwater. Factors such as the build-up of surface precipitates, bio-fouling, and changes in subsurface tr...

Interest of HYPR flow dynamic MRA for characterization of cerebral arteriovenous malformations: comparison with TRICKS MRA and catheter DSA.

PubMed

Dautry, Raphaël; Edjlali, Myriam; Roca, Pauline; Rabrait, Cécile; Wu, Yijing; Johnson, Kevin; Wieben, Olivier; Trystram, Denis; Rodriguez-Régent, Christine; Alshareef, Fawaz; Turski, Patrick; Meder, Jean-François; Naggara, Olivier; Oppenheim, Catherine

2015-11-01

HYPR flow is a 3D dynamic contrast-enhanced MRA technique providing isotropic sub-millimetre resolution with half-second temporal resolution. We compared HYPR flow and time-resolved imaging of contrast kinetics (TRICKS) MRA for the characterization of cerebral arteriovenous malformations (cAVMs), using catheter DSA as reference. Twenty-two patients underwent HYPR flow and TRICKS MRA within 15 days of DSA. HYPR flow and TRICKS datasets were reviewed separately by two readers for image quality, Spetzler-Martin grade, venous ectasia, and deep venous drainage. Image quality was better for HYPR flow than for TRICKS (narrower full width at half maximum; larger arterial diagnostic window; greater number of arterial frames, P ≤ 0.05). Using HYPR flow, inter-reader agreement was excellent for all cAVM characteristics. The agreement with DSA for the overall Spetzler-Martin grade was excellent for HYPR flow (ICC = 0.96 and 0.98, depending on the reader) and TRICKS (ICC = 0.82 and 0.95). In comparison to TRICKS, HYPR flow showed higher concordance with DSA for the identification of venous ectasia and deep venous drainage. Owing to an excellent agreement with DSA with respect to depiction of the vascular architecture of cAVMs, HYPR flow could be useful for the non-invasive characterization of cAVMs. • Dynamic MRA is used for cerebral AVM depiction and follow-up • HYPR flow is a new, highly-resolved dynamic MRA sequence • HYPR flow provides whole brain coverage • HYPR flow provides excellent agreement with the Spetzler-Martin grade • Compared to TRICKS MRA, HYPR flow improves cerebral AVM characterization.

Forearm Vascular Reactivity and Arterial Stiffness in Asymptomatic Subjects from the Community

PubMed Central

Malik, A. Rauoof; Kondragunta, Venkateswarlu; Kullo, Iftikhar J.

2010-01-01

Vascular reactivity may affect the stiffness characteristics of the arterial wall. We investigated the association between forearm microcirculatory and conduit artery function and measures of arterial stiffness in 527 asymptomatic non-Hispanic white adults without known cardiovascular disease. High-resolution ultrasonography of the brachial artery (ba) was performed to assess forearm microcirculatory function (ba blood flow velocity, local shear stress, and forearm vascular resistance at rest and during reactive hyperemia) and conduit artery function (ba flow-mediated dilatation baFMD and ba nitroglycerin-mediated dilatation baNMD). Arterial stiffness was assessed by cuff-derived brachial pulse pressure and aortic pulse wave velocity (aPWV) measured by applanation tonometry. In regression analyses that adjusted for heart rate, mean arterial pressure, height, cardiovascular risk factors, and hypertension medication and statin use, higher baseline ba systolic velocity and systolic shear stress were associated with greater pulse pressure (P=0.0002 and P=0.006, respectively) and higher aPWV (each P<0.0001). During hyperemia, lower ba mean velocity and lower mean shear stress were associated with higher pulse pressure (P=0.045 and P=0.036, respectively) while both systolic and mean velocity (P<0.0001 and P=0.002, respectively) and systolic and mean shear stress (P<0.0001 and P=0.003, respectively) were inversely associated with aPWV. baFMD was not associated with pulse pressure but was inversely associated with aPWV (P=0.011). baNMD was inversely associated with pulse pressure (P=0.0002) and aPWV (P=0.008). Our findings demonstrate that impaired forearm microvascular function (in the form of elevated resting blood flow velocity and impaired flow reserve) and impaired brachial artery reactivity are associated with increased arterial stiffness. PMID:18426995

Velocity and Temperature Measurement in Supersonic Free Jets Using Spectrally Resolved Rayleigh Scattering

NASA Technical Reports Server (NTRS)

Panda, J.; Seasholtz, R. G.

2004-01-01

The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99, 1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the spectrally resolved application, laser light scattered by the air molecules is collected and analyzed using a Fabry-Perot interferometer (FPI). The difference between the incident laser frequency and the peak of the Rayleigh spectrum provides a measure of gas velocity. The temperature is measured from the spectral broadening caused by the random thermal motion and density is measured from the total light intensity. The present point measurement technique uses a CW laser, a scanning FPI and photon counting electronics. The 1 mm long probe volume is moved from point to point to survey the flow fields. Additional arrangements were made to remove particles from the main as well as the entrained flow and to isolate FPI from the high sound and vibration levels produced by the supersonic jets. In general, velocity is measured within +/- 10 m/s accuracy and temperature within +/- 10 K accuracy.

Time-resolved imaging of contrast kinetics does not improve performance of follow-up MRA of embolized intracranial aneurysms.

PubMed

Serafin, Zbigniew; Strześniewski, Piotr; Lasek, Władysław; Beuth, Wojciech

2012-07-01

The use of contrast media and the time-resolved imaging of contrast kinetics (TRICKS) technique have some theoretical advantages over time-of-flight magnetic resonance angiography (TOF-MRA) in the follow-up of intracranial aneurysms after endovascular treatment. We prospectively compared the diagnostic performance of TRICKS and TOF-MRA with digital subtracted angiography (DSA) in the assessment of occlusion of embolized aneurysms. Seventy-two consecutive patients with 72 aneurysms were examined 3 months after embolization. Test characteristics of TOF-MRA and TRICKS were calculated for the detection of residual flow. The results of quantification of flow were compared with weighted kappa. Intraobserver and interobserver reproducibility was determined. The sensitivity of TOF-MRA was 85% (95% CI, 65-96%) and of TRICKS, 89% (95% CI, 70-97%). The specificity of both methods was 91% (95% CI, 79-98%). The accuracy of the flow quantification ranged from 0.76 (TOF-MRA) to 0.83 (TRICKS). There was no significant difference between the methods in the area under the ROC curve regarding both the detection and the quantification of flow. Intraobserver reproducibility was very good with both techniques (kappa, 0.86-0.89). The interobserver reproducibility was moderate for TOF-MRA and very good for TRICKS (kappa, 0.74-0.80). In this study, TOF-MRA and TRICKS presented similar diagnostic performance; therefore, the use of time-resolved contrast-enhanced MRA is not justified in the follow-up of embolized aneurysms.

Space and time-resolved probing of heterogeneous catalysis reactions using lab-on-a-chip

NASA Astrophysics Data System (ADS)

Navin, Chelliah V.; Krishna, Katla Sai; Theegala, Chandra S.; Kumar, Challa S. S. R.

2016-03-01

Probing catalytic reactions on a catalyst surface in real time is a major challenge. Herein, we demonstrate the utility of a continuous flow millifluidic chip reactor coated with a nanostructured gold catalyst as an effective platform for in situ investigation of the kinetics of catalytic reactions by taking 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) conversion as a model reaction. The idea conceptualized in this paper can not only dramatically change the ability to probe the time-resolved kinetics of heterogeneous catalysis reactions but also used for investigating other chemical and biological catalytic processes, thereby making this a broad platform for probing reactions as they occur within continuous flow reactors.Probing catalytic reactions on a catalyst surface in real time is a major challenge. Herein, we demonstrate the utility of a continuous flow millifluidic chip reactor coated with a nanostructured gold catalyst as an effective platform for in situ investigation of the kinetics of catalytic reactions by taking 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) conversion as a model reaction. The idea conceptualized in this paper can not only dramatically change the ability to probe the time-resolved kinetics of heterogeneous catalysis reactions but also used for investigating other chemical and biological catalytic processes, thereby making this a broad platform for probing reactions as they occur within continuous flow reactors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06752a

Using a reactive transport model to elucidate differences between laboratory and field dissolution rates in regolith

NASA Astrophysics Data System (ADS)

Moore, Joel; Lichtner, Peter C.; White, Art F.; Brantley, Susan L.

2012-09-01

The reactive transport model FLOTRAN was used to forward-model weathering profiles developed on granitic outwash alluvium over 40-3000 ka from the Merced, California (USA) chronosequence as well as deep granitic regolith developed over 800 ka near Davis Run, Virginia (USA). Baseline model predictions that used laboratory rate constants (km), measured fluid flow velocities (v), and BET volumetric surface areas for the parent material (AB,mo) were not consistent with measured profiles of plagioclase, potassium feldspar, and quartz. Reaction fronts predicted by the baseline model are deeper and thinner than the observed, consistent with faster rates of reaction in the model. Reaction front depth in the model depended mostly upon saturated versus unsaturated hydrologic flow conditions, rate constants controlling precipitation of secondary minerals, and the average fluid flow velocity (va). Unsaturated hydrologic flow conditions (relatively open with respect to CO2(g)) resulted in the prediction of deeper reaction fronts and significant differences in the separation between plagioclase and potassium feldspar reaction fronts compared to saturated hydrologic flow (relatively closed with respect to CO2(g)). Under saturated or unsaturated flow conditions, the rate constant that controls precipitation rates of secondary minerals must be reduced relative to laboratory rate constants to match observed reaction front depths and measured pore water chemistry. Additionally, to match the observed reaction front depths, va was set lower than the measured value, v, for three of the four profiles. The reaction front gradients in mineralogy and pore fluid chemistry could only be modeled accurately by adjusting values of the product kmAB,mo. By assuming km values were constrained by laboratory data, field observations were modeled successfully with TST-like rate equations by dividing measured values of AB,mo by factors from 50 to 1700. Alternately, with sigmoidal or Al-inhibition rate models, this adjustment factor ranges from 5 to 170. Best-fit models of the wetter, hydrologically saturated Davis Run profile required a smaller adjustment to AB,mo than the drier hydrologically unsaturated Merced profiles. We attributed the need for large adjustments in va and AB,mo necessary for the Merced models to more complex hydrologic flow that decreased the reactive surface area in contact with bulk flow water, e.g., dead-end pore spaces containing fluids that are near or at chemical equilibrium. Thus, rate models from the laboratory can successfully predict weathering over millions of years, but work is needed to understand how to incorporate changes in what controls the relationship between reactive surface area and hydrologic flow.

Refinement Of Hexahedral Cells In Euler Flow Computations

NASA Technical Reports Server (NTRS)

Melton, John E.; Cappuccio, Gelsomina; Thomas, Scott D.

1996-01-01

Topologically Independent Grid, Euler Refinement (TIGER) computer program solves Euler equations of three-dimensional, unsteady flow of inviscid, compressible fluid by numerical integration on unstructured hexahedral coordinate grid refined where necessary to resolve shocks and other details. Hexahedral cells subdivided, each into eight smaller cells, as needed to refine computational grid in regions of high flow gradients. Grid Interactive Refinement and Flow-Field Examination (GIRAFFE) computer program written in conjunction with TIGER program to display computed flow-field data and to assist researcher in verifying specified boundary conditions and refining grid.

Planar temperature measurement in compressible flows using laser-induced iodine fluorescence

NASA Technical Reports Server (NTRS)

Hartfield, Roy J., Jr.; Hollo, Steven D.; Mcdaniel, James C.

1991-01-01

A laser-induced iodine fluorescence technique that is suitable for the planar measurement of temperature in cold nonreacting compressible air flows is investigated analytically and demonstrated in a known flow field. The technique is based on the temperature dependence of the broadband fluorescence from iodine excited by the 514-nm line of an argon-ion laser. Temperatures ranging from 165 to 245 K were measured in the calibration flow field. This technique makes complete, spatially resolved surveys of temperature practical in highly three-dimensional, low-temperature compressible flows.

Reactive power compensator

DOEpatents

El-Sharkawi, Mohamed A.; Venkata, Subrahmanyam S.; Chen, Mingliang; Andexler, George; Huang, Tony

1992-01-01

A system and method for determining and providing reactive power compensation for an inductive load. A reactive power compensator (50,50') monitors the voltage and current flowing through each of three distribution lines (52a, 52b, 52c), which are supplying three-phase power to one or more inductive loads. Using signals indicative of the current on each of these lines when the voltage waveform on the line crosses zero, the reactive power compensator determines a reactive power compensator capacitance that must be connected to the lines to maintain a desired VAR level, power factor, or line voltage. Alternatively, an operator can manually select a specific capacitance for connection to each line, or the capacitance can be selected based on a time schedule. The reactive power compensator produces control signals, which are coupled through optical fibers (102/106) to a switch driver (110, 110') to select specific compensation capacitors (112) for connections to each line. The switch driver develops triggering signals that are supplied to a plurality of series-connected solid state switches (350), which control charge current in one direction in respect to ground for each compensation capacitor. During each cycle, current flows from ground to charge the capacitors as the voltage on the line begins to go negative from its positive peak value. The triggering signals are applied to gate the solid state switches into a conducting state when the potential on the lines and on the capacitors reaches a negative peak value, thereby minimizing both the potential difference and across the charge current through the switches when they begin to conduct. Any harmonic distortion on the potential and current carried by the lines is filtered out from the current and potential signals used by the reactive power compensator so that it does not affect the determination of the required reactive compensation.

Reactive Power Compensator.

DOEpatents

El-Sharkawi, M.A.; Venkata, S.S.; Chen, M.; Andexler, G.; Huang, T.

1992-07-28

A system and method for determining and providing reactive power compensation for an inductive load. A reactive power compensator (50,50') monitors the voltage and current flowing through each of three distribution lines (52a, 52b, 52c), which are supplying three-phase power to one or more inductive loads. Using signals indicative of the current on each of these lines when the voltage waveform on the line crosses zero, the reactive power compensator determines a reactive power compensator capacitance that must be connected to the lines to maintain a desired VAR level, power factor, or line voltage. Alternatively, an operator can manually select a specific capacitance for connection to each line, or the capacitance can be selected based on a time schedule. The reactive power compensator produces control signals, which are coupled through optical fibers (102/106) to a switch driver (110, 110') to select specific compensation capacitors (112) for connections to each line. The switch driver develops triggering signals that are supplied to a plurality of series-connected solid state switches (350), which control charge current in one direction in respect to ground for each compensation capacitor. During each cycle, current flows from ground to charge the capacitors as the voltage on the line begins to go negative from its positive peak value. The triggering signals are applied to gate the solid state switches into a conducting state when the potential on the lines and on the capacitors reaches a negative peak value, thereby minimizing both the potential difference and across the charge current through the switches when they begin to conduct. Any harmonic distortion on the potential and current carried by the lines is filtered out from the current and potential signals used by the reactive power compensator so that it does not affect the determination of the required reactive compensation. 26 figs.

Hemodynamics in a giant intracranial aneurysm characterized by in vitro 4D flow MRI

PubMed Central

Schiavazzi, Daniele; Moen, Sean; Jagadeesan, Bharathi; Van de Moortele, Pierre-François; Coletti, Filippo

2018-01-01

Experimental and computational data suggest that hemodynamics play a critical role in the development, growth, and rupture of cerebral aneurysms. The flow structure, especially in aneurysms with a large sac, is highly complex and three-dimensional. Therefore, volumetric and time-resolved measurements of the flow properties are crucial to fully characterize the hemodynamics. In this study, phase-contrast Magnetic Resonance Imaging is used to assess the fluid dynamics inside a 3D-printed replica of a giant intracranial aneurysm, whose hemodynamics was previously simulated by multiple research groups. The physiological inflow waveform is imposed in a flow circuit with realistic cardiovascular impedance. Measurements are acquired with sub-millimeter spatial resolution for 16 time steps over a cardiac cycle, allowing for the detailed reconstruction of the flow evolution. Moreover, the three-dimensional and time-resolved pressure distribution is calculated from the velocity field by integrating the fluid dynamics equations, and is validated against differential pressure measurements using precision transducers. The flow structure is characterized by vortical motions that persist within the aneurysm sac for most of the cardiac cycle. All the main flow statistics including velocity, vorticity, pressure, and wall shear stress suggest that the flow pattern is dictated by the aneurysm morphology and is largely independent of the pulsatility of the inflow, at least for the flow regimes investigated here. Comparisons are carried out with previous computational simulations that used the same geometry and inflow conditions, both in terms of cycle-averaged and systolic quantities. PMID:29300738

User's Guide of TOUGH2-EGS. A Coupled Geomechanical and Reactive Geochemical Simulator for Fluid and Heat Flow in Enhanced Geothermal Systems Version 1.0

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

Fakcharoenphol, Perapon; Xiong, Yi; Hu, Litang

TOUGH2-EGS is a numerical simulation program coupling geomechanics and chemical reactions for fluid and heat flows in porous media and fractured reservoirs of enhanced geothermal systems. The simulator includes the fully-coupled geomechanical (THM) module, the fully-coupled geochemical (THC) module, and the sequentially coupled reactive geochemistry (THMC) module. The fully-coupled flow-geomechanics model is developed from the linear elastic theory for the thermo-poro-elastic system and is formulated with the mean normal stress as well as pore pressure and temperature. The chemical reaction is sequentially coupled after solution of flow equations, which provides the flow velocity and phase saturation for the solute transportmore » calculation at each time step. In addition, reservoir rock properties, such as porosity and permeability, are subjected to change due to rock deformation and chemical reactions. The relationships between rock properties and geomechanical and chemical effects from poro-elasticity theories and empirical correlations are incorporated into the simulator. This report provides the user with detailed information on both mathematical models and instructions for using TOUGH2-EGS for THM, THC or THMC simulations. The mathematical models include the fluid and heat flow equations, geomechanical equation, reactive geochemistry equations, and discretization methods. Although TOUGH2-EGS has the capability for simulating fluid and heat flows coupled with both geomechanical and chemical effects, it is up to the users to select the specific coupling process, such as THM, THC, or THMC in a simulation. There are several example problems illustrating the applications of this program. These example problems are described in details and their input data are presented. The results demonstrate that this program can be used for field-scale geothermal reservoir simulation with fluid and heat flow, geomechanical effect, and chemical reaction in porous and fractured media.« less

A flow-system comparison of the reactivities of calcium superoxide and potassium superoxide with carbon dioxide and water vapor

NASA Technical Reports Server (NTRS)

Wood, P. C.; Ballou, E. V.; Spitze, L. A.; Wydeven, T.

1982-01-01

A single pass flow system was used to test the reactivity of calcium superoxide with respiratory gases and the performance was compared to that of potassium superoxide. The KO2 system is used by coal miners as a self-contained unit in rescue operations. Particular attention was given to the reactivity with carbon dioxide and water vapor at different temperatures and partial pressures of oxygen, carbon dioxide, and water vapor. The calcium superoxide beds were found to absorb CO2 and H2O vapor, releasing O2. The KO2 bed, however, released O2 at twice the rate of CO2 absorption at 37 C. It is concluded that the calcium superoxide material is not a suitable replacement for the KO2 bed, although Ca(O2)2 may be added to the KO2 bed to enhance the CO2 absorption.

Structural isomers of C2N(+) - A selected-ion flow tube study

NASA Technical Reports Server (NTRS)

Knight, J. S.; Petrie, S. A. H.; Freeman, C. G.; Mcewan, M. J.; Mclean, A. D.

1988-01-01

Reactivities of the structural isomers CCN(+) and CNC(+) were examined in a selected-ion flow tube at 300 + or - 5 K. The less reactive CNC(+) isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC(+) can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN(+) and CNC(+); a saddle point for the reaction CCN(+) yielding CNC(+) is calculated to be 195 kJ/mol above CNC(+). The results provide evidence that the more reactive CCN(+) isomer is unlikely to be present in measurable densities in interstellar clouds.

Coupling lattice Boltzmann and continuum equations for flow and reactive transport in porous media.

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

Coon, Ethan; Porter, Mark L.; Kang, Qinjun

2012-06-18

In spatially and temporally localized instances, capturing sub-reservoir scale information is necessary. Capturing sub-reservoir scale information everywhere is neither necessary, nor computationally possible. The lattice Boltzmann Method for solving pore-scale systems. At the pore-scale, LBM provides an extremely scalable, efficient way of solving Navier-Stokes equations on complex geometries. Coupling pore-scale and continuum scale systems via domain decomposition. By leveraging the interpolations implied by pore-scale and continuum scale discretizations, overlapping Schwartz domain decomposition is used to ensure continuity of pressure and flux. This approach is demonstrated on a fractured medium, in which Navier-Stokes equations are solved within the fracture while Darcy'smore » equation is solved away from the fracture Coupling reactive transport to pore-scale flow simulators allows hybrid approaches to be extended to solve multi-scale reactive transport.« less

TiN films fabricated by reactive gas pulse sputtering: A hybrid design of multilayered and compositionally graded structures

NASA Astrophysics Data System (ADS)

Yang, Jijun; Zhang, Feifei; Wan, Qiang; Lu, Chenyang; Peng, Mingjing; Liao, Jiali; Yang, Yuanyou; Wang, Lumin; Liu, Ning

2016-12-01

Reactive gas pulse (RGP) sputtering approach was used to prepare TiN thin films through periodically changing the N2/Ar gas flow ratio. The obtained RGPsbnd TiN film possessed a hybrid architecture containing compositionally graded and multilayered structures, composed of hcp Ti-phase and fcc TiN-phase sublayers. Meanwhile, the RGP-TiN film exhibited a composition-oscillation along the film thickness direction, where the Ti-phase sublayer had a compositional gradient and the TiN-phase retained a constant stoichiometric ratio of Ti:N ≈ 1. The film modulation ratio λ (the thicknesses ratio of the Ti and TiN-phase sublayer) can be effectively tuned by controlling the undulation behavior of the N2 partial flow rate. Detailed analysis showed that this hybrid structure originated from a periodic transition of the film growth mode during the reactive sputtering process.

Reactivity of mouse antibodies against bromelain-treated mouse erythrocytes with thrombin-treated mouse platelets.

PubMed Central

Kawaguchi, S

1989-01-01

The reactivity of mouse antibodies against bromelain-treated mouse erythrocytes (BrMRBC) with mouse platelets before and after thrombin treatment was assessed by flow cytometry. Anti-BrMRBC antibodies could bind to thrombin-treated platelets, although normal platelets were also weakly reactive with the antibodies. The binding of anti-BrMRBC antibodies to platelets was confirmed by complement-dependent lysis. It is suggested that thrombin-activated platelets may be a real target for anti-BrMRBC antibodies. PMID:2467876

The rheology and composition of cryovolcanic flows on icy satellites

NASA Technical Reports Server (NTRS)

Kargel, Jeffrey S.

1993-01-01

The rheologic properties of terrestrial lavas have been related to morphologic features of their flows, such as levees, banked surfaces, multilobate structures, and compressible folds. These features also have been used to determine rheologies and constrain the compositions of extraterrestrial flows. However, with rare exceptions, such features are not resolvable in Voyager images of the satellites of outer planets. Often only flow length and edge thickness of cryovolcanic flows can be measured reasonably accurately from Voyager images. The semiempirical lava-flow model presented here is a renewed effort to extract useful information from such measurements.

IgA and IgG1 reactivities assessed by flow cytometry mirror clinical aspects of infants with ocular congenital toxoplasmosis.

PubMed

de Jesus, Laura Néspoli Nassar Pansini; Tonini, Aline de Castro Zacche; Barros, Geisa Baptista; Coelho-dos-Reis, Jordana Grazziela A; Béla, Samantha Ribeiro; Antonelli, Lis Ribeiro do Valle; Machado, Anderson Silva; Carneiro, Ana Carolina Aguiar Vasconcelos; Andrade, Gláucia Manzan Queiroz; Vasconcelos-Santos, Daniel Vitor; Januário, José Nélio; Teixeira-Carvalho, Andréa; Vitor, Ricardo Wagner Almeida; Ferro, Eloísa A V; Mineo, José Roberto; Bahia-Oliveira, Lilian Maria Garcia; Martins-Filho, Olindo Assis; Lemos, Elenice Moreira

2016-01-01

This study intended to apply the flow cytometric analysis of IgA and IgG reactivity and intracytoplasmic cytokine analysis to understand and decode the clinical aspects of infants with ocular congenital toxoplasmosis. The Toxoplasma gondii-infected infants (TOXO) were subdivided according to their clinical aspects based on the absence (NRL), presence of active (ARL), active/cicatricial (ACRL) or cicatricial retinochoroidal lesions (CRL) and compared to non-infected controls (NI). The reactivity of anti-T. gondii IgG subclasses resembles the clinical aspects of ocular lesions. IgG and IgG1 discriminate infants with cicatricial lesions (ACRL and CRL) from both ARL and NLR. IgG2 and IgG3 are particularly higher in ACRL and CRL as compared to NLR. No differences were observed when IgG4 reactivity was evaluated. Thus, the results indicated that the reactivity patterns of IgA, IgG and IgG subclasses are able to discriminate ARL, ACRL and CRL from NLR or NI. IgA and IgG subclasses are relevant serological biomarkers with diagnostic and prognostic applicability, respectively. Moreover, IgA and IgG1 were closely related to cytokine production by innate/adaptive immunity cells. IgA reactivity was directly associated to TNF-α-derived from neutrophils, monocytes and CD8(+) T-cells, while IgG1 was inversely correlated with IFN-γ-producing CD4(+) and CD8(+) T-cells but positively correlated with IL-10(+) B-cells. These findings provide insights on the relationship between the cytokine production by innate/adaptive immunity and the antibody pattern of infants with ocular congenital toxoplasmosis. In addition, the present study supports the use of flow cytometric serology as a potential tool for the diagnosis and monitoring of ocular lesions in T. gondii-infected infants in the clinical setting. Copyright © 2015 Elsevier B.V. All rights reserved.

Advancements in Dual-Pump Broadband CARS for Supersonic Combustion Measurements

NASA Technical Reports Server (NTRS)

Tedder, Sarah Augusta Umberger

2010-01-01

Space- and time-resolved measurements of temperature and species mole fractions of nitrogen, oxygen, and hydrogen were obtained with a dual-pump coherent anti-Stokes Raman spectroscopy (CARS) system in hydrogen-fueled supersonic combustion free jet flows. These measurements were taken to provide time-resolved fluid properties of turbulent supersonic combustion for use in the creation and verification of computational fluid dynamic (CFD) models. CFD models of turbulent supersonic combustion flow currently facilitate the design of air-breathing supersonic combustion ramjet (scramjet) engines. Measurements were made in supersonic axi-symmetric free jets of two scales. First, the measurement system was tested in a laboratory environment using a laboratory-scale burner (approx.10 mm at nozzle exit). The flow structures of the laboratory-burner were too small to be resolved with the CARS measurements volume, but the composition and temperature of the jet allowed the performance of the system to be evaluated. Subsequently, the system was tested in a burner that was approximately 6 times larger, whose length scales are better resolved by the CARS measurement volume. During both these measurements, weaknesses of the CARS system, such as sensitivity to vibrations and beam steering and inability to measure temperature or species concentrations in hydrogen fuel injection regions were indentified. Solutions were then implemented in improved CARS systems. One of these improved systems is a dual-pump broadband CARS technique called, Width Increased Dual-pump Enhanced CARS (WIDECARS). The two lowest rotational energy levels of hydrogen detectable by WIDECARS are H2 S(3) and H2 S(4). The detection of these lines gives the system the capability to measure temperature and species concentrations in regions of the flow containing pure hydrogen fuel at room temperature. WIDECARS is also designed for measurements of all the major species (except water) in supersonic combustion flows fueled with hydrogen and hydrogen/ethylene mixtures (N2, O2, H2, C2H4, CO, and CO2). This instrument can characterize supersonic combustion fueled with surrogate fuel mixtures of hydrogen and ethylene. This information can lead to a better understanding of the chemistry and performance of supersonic combustion fueled with cracked jet propulsion (JP)-type fuel.

A Dual-Line Detection Rayleigh Scattering Diagnostic Technique for the Combustion of Hydrocarbon Fuels and Filtered UV Rayleigh Scattering for Gas Velocity Measurements

NASA Technical Reports Server (NTRS)

Otugen, M. Volkan

1997-01-01

Non-intrusive techniques for the dynamic measurement of gas flow properties such as density, temperature and velocity, are needed in the research leading to the development of new generation high-speed aircraft. Accurate velocity, temperature and density data obtained in ground testing and in-flight measurements can help understand the flow physics leading to transition and turbulence in supersonic, high-altitude flight. Such non-intrusive measurement techniques can also be used to study combustion processes of hydrocarbon fuels in aircraft engines. Reliable, time and space resolved temperature measurements in various combustor configurations can lead to a better understanding of high temperature chemical reaction dynamics thus leading to improved modeling and better prediction of such flows. In view of this, a research program was initiated at Polytechnic University's Aerodynamics Laboratory with support from NASA Lewis Research Center through grants NAG3-1301 and NAG3-1690. The overall objective of this program has been to develop laser-based, non-contact, space- and time-resolved temperature and velocity measurement techniques. In the initial phase of the program a ND:YAG laser-based dual-line Rayleigh scattering technique was developed and tested for the accurate measurement of gas temperature in the presence of background laser glare. Effort was next directed towards the development of a filtered, spectrally-resolved Rayleigh/Mie scattering technique with the objective of developing an interferometric method for time-frozen velocity measurements in high-speed flows utilizing the uv line of an ND:YAG laser and an appropriate molecular absorption filter. This effort included both a search for an appropriate filter material for the 266 nm laser line and the development and testing of several image processing techniques for the fast processing of Fabry-Perot images for velocity and temperature information. Finally, work was also carried out for the development of a new laser-based strain-rate and vorticity technique for the time-resolved measurement of vorticity and strain-rates in turbulent flows.

An Image-based Micro-continuum Pore-scale Model for Gas Transport in Organic-rich Shale

NASA Astrophysics Data System (ADS)

Guo, B.; Tchelepi, H.

2017-12-01

Gas production from unconventional source rocks, such as ultra-tight shales, has increased significantly over the past decade. However, due to the extremely small pores ( 1-100 nm) and the strong material heterogeneity, gas flow in shale is still not well understood and poses challenges for predictive field-scale simulations. In recent years, digital rock analysis has been applied to understand shale gas transport at the pore-scale. An issue with rock images (e.g. FIB-SEM, nano-/micro-CT images) is the so-called "cutoff length", i.e., pores and heterogeneities below the resolution cannot be resolved, which leads to two length scales (resolved features and unresolved sub-resolution features) that are challenging for flow simulations. Here we develop a micro-continuum model, modified from the classic Darcy-Brinkman-Stokes framework, that can naturally couple the resolved pores and the unresolved nano-porous regions. In the resolved pores, gas flow is modeled with Stokes equation. In the unresolved regions where the pore sizes are below the image resolution, we develop an apparent permeability model considering non-Darcy flow at the nanoscale including slip flow, Knudsen diffusion, adsorption/desorption, surface diffusion, and real gas effect. The end result is a micro-continuum pore-scale model that can simulate gas transport in 3D reconstructed shale images. The model has been implemented in the open-source simulation platform OpenFOAM. In this paper, we present case studies to demonstrate the applicability of the model, where we use 3D segmented FIB-SEM and nano-CT shale images that include four material constituents: organic matter, clay, granular mineral, and pore. In addition to the pore structure and the distribution of the material constituents, we populate the model with experimental measurements (e.g. size distribution of the sub-resolution pores from nitrogen adsorption) and parameters from the literature and identify the relative importance of different physics on gas production. Overall, the micro-continuum model provides a novel tool for digital rock analysis of organic-rich shale.

Atmospheric Pressure Plasma Jet for Chem/Bio Warfare Decontamination

NASA Astrophysics Data System (ADS)

Herrmann, Hans W.; Henins, Ivars; Park, Jaeyoung; Selwyn, Gary S.

1999-11-01

Atmospheric Pressure Plasma Jet (APPJ) technology may provide a much needed method of CBW decontamination which, unlike traditional decon methods, is dry and nondestructive to sensitive equipment and materials. The APPJ discharge uses a high-flow feedgas consisting primarily of an inert carrier gas, such as He, and a small amount of a reactive additive, such as O2, which flows between capacitively-coupled electrodes powered at 13.56 MHz. The plasma generates highly reactive metastable and atomic species of oxygen which are then directed onto a contaminated surface. The reactive effluent of the APPJ has been shown to effectively neutralize VX nerve agent as well as simulants for anthrax and mustard blister agent. Research efforts are now being directed towards reducing He consumption and increasing the allowable stand-off distance. Recent results demonstrate that by replacing the O2 reactive additive with CO2, ozone formation is greatly reduced. This has the result of extending the lifetime of atomic oxygen by an order of magnitude or more. A recirculating APP Decon Chamber which combines heat, vacuum, forced convection and reactivity is currently being developed for enhanced decontamination of sensitive equipment. Several techniques are also being evaluated for use in an APP Decon Jet for decontamination of items which cannot be placed inside a chamber.

Comparative study of MacCormack and TVD MacCormack schemes for three-dimensional separation at wing/body junctions in supersonic flows

NASA Technical Reports Server (NTRS)

Lakshmanan, Balakrishnan; Tiwari, Surendra N.

1992-01-01

A robust, discontinuity-resolving TVD MacCormack scheme containing no dependent parameters requiring adjustment is presently used to investigate the 3D separation of wing/body junction flows at supersonic speeds. Many production codes employing MacCormack schemes can be adapted to use this method. A numerical simulation of laminar supersonic junction flow is found to yield improved separation location predictions, as well as the axial velocity profiles in the separated flow region.

An Immersed Boundary - Adaptive Mesh Refinement solver (IB-AMR) for high fidelity fully resolved wind turbine simulations

NASA Astrophysics Data System (ADS)

Angelidis, Dionysios; Sotiropoulos, Fotis

2015-11-01

The geometrical details of wind turbines determine the structure of the turbulence in the near and far wake and should be taken in account when performing high fidelity calculations. Multi-resolution simulations coupled with an immersed boundary method constitutes a powerful framework for high-fidelity calculations past wind farms located over complex terrains. We develop a 3D Immersed-Boundary Adaptive Mesh Refinement flow solver (IB-AMR) which enables turbine-resolving LES of wind turbines. The idea of using a hybrid staggered/non-staggered grid layout adopted in the Curvilinear Immersed Boundary Method (CURVIB) has been successfully incorporated on unstructured meshes and the fractional step method has been employed. The overall performance and robustness of the second order accurate, parallel, unstructured solver is evaluated by comparing the numerical simulations against conforming grid calculations and experimental measurements of laminar and turbulent flows over complex geometries. We also present turbine-resolving multi-scale LES considering all the details affecting the induced flow field; including the geometry of the tower, the nacelle and especially the rotor blades of a wind tunnel scale turbine. This material is based upon work supported by the Department of Energy under Award Number DE-EE0005482 and the Sandia National Laboratories.

Capillary red blood cell velocimetry by phase-resolved optical coherence tomography

NASA Astrophysics Data System (ADS)

Tang, Jianbo; Erdener, Sefik Evren; Fu, Buyin; Boas, David A.

2018-02-01

Quantitative measurement of blood flow velocity in capillaries is challenging due to their small size (around 5-10 μm), and the discontinuity and single-file feature of RBCs flowing in a capillary. In this work, we present a phase-resolved Optical Coherence Tomography (OCT) method for accurate measurement of the red blood cell (RBC) speed in cerebral capillaries. To account for the discontinuity of RBCs flowing in capillaries, we applied an M-mode scanning strategy that repeated A-scans at each scanning position for an extended time. As the capillary size is comparable to the OCT resolution size (3.5×3.5×3.5μm), we applied a high pass filter to remove the stationary signal component so that the phase information of the dynamic component (i.e. from the moving RBC) could be enhanced to provide an accurate estimate of the RBC axial speed. The phase-resolved OCT method accurately quantifies the axial velocity of RBC's from the phase shift of the dynamic component of the signal. We validated our measurements by RBC passage velocimetry using the signal magnitude of the same OCT time series data. These proposed method of capillary velocimetry proved to be a robust method of mapping capillary RBC speeds across the micro-vascular network.

Scalable Heuristics for Planning, Placement and Sizing of Flexible AC Transmission System Devices

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

Frolov, Vladmir; Backhaus, Scott N.; Chertkov, Michael

Aiming to relieve transmission grid congestion and improve or extend feasibility domain of the operations, we build optimization heuristics, generalizing standard AC Optimal Power Flow (OPF), for placement and sizing of Flexible Alternating Current Transmission System (FACTS) devices of the Series Compensation (SC) and Static VAR Compensation (SVC) type. One use of these devices is in resolving the case when the AC OPF solution does not exist because of congestion. Another application is developing a long-term investment strategy for placement and sizing of the SC and SVC devices to reduce operational cost and improve power system operation. SC and SVCmore » devices are represented by modification of the transmission line inductances and reactive power nodal corrections respectively. We find one placement and sizing of FACTs devices for multiple scenarios and optimal settings for each scenario simultaneously. Our solution of the nonlinear and nonconvex generalized AC-OPF consists of building a convergent sequence of convex optimizations containing only linear constraints and shows good computational scaling to larger systems. The approach is illustrated on single- and multi-scenario examples of the Matpower case-30 model.« less

4D Magnetic Resonance Velocimetry in a 3D printed brain aneurysm

NASA Astrophysics Data System (ADS)

Amili, Omid; Schiavazzi, Daniele; Coletti, Filippo

2016-11-01

Cerebral aneurysms are of great clinical importance. It is believed that hemodynamics play a critical role in the development, growth, and rupture of brain arteries with such condition. The flow structure in the aneurysm sac is complex, unsteady, and three-dimensional. Therefore the time-resolved measurement of the three-dimensional three-component velocity field is crucial to predict the clinical outcome. In this study magnetic resonance velocimetry is used to assess the fluid dynamics inside a 3D printed model of a giant intracranial aneurysm. We reach sub-millimeter resolution while resolving sixteen instances within the cardiac cycle. The physiological flow waveform is imposed using an in-house built pump in a flow circuit where the cardiovascular impedance is matched. The flow evolution over time is reconstructed in detail. The complex flow structure is characterized by vortical and helical motions that reside in the aneurysm for most part of the cycle. The 4D pressured distribution is also reconstructed from the velocity field. The present case study was used in a previous CFD challenge, therefore these results may provide useful experimental comparison for simulations performed by other research groups.

Flow-mediated transport around a macroscopic arterial thrombus

NASA Astrophysics Data System (ADS)

Mukherjee, Debanjan; Garduno, Jocelyn; Shadden, Shawn

2017-11-01

Pathological blood clotting (thrombosis) is the acute cause of most major cardiovascular events including heart attack and stroke. Local blood and plasma transport in the neighborhood of a clot is thought to govern the thrombotic process (e.g. growth and consolidation), embolization, and the effectiveness of pharmacological treatments. To better understand the fluid mechanics near a clot it is necessary to resolve the dynamic interactions between a realistic thrombus with arbitrary shape and microstructure, and viscous, pulsatile flow. Here, we describe a computational technique to characterize flow-mediated transport phenomena in the vicinity of macro-scale arterial clots. The technique comprises (a) resolving unsteady flow around a thrombus model using a discrete particle fictitious domain finite element method; (b) identifying coherent transport features using finite time Lyapunov exponent fields, and (c) characterizing mixing using a particle-based approach. Numerical examples are discussed using realistic thrombus aggregates derived from experimental data, and pulsatile flow typical in human arteries. The results indicate the existence of local transport barriers and coherent regions in the vicinity of the clot with potential influence to local biochemical mechanics. National Science Foundation Award: 1354541; American Heart Association Award: 16POST27500023.

Fourier-domain study of drift turbulence driven sheared flow in a laboratory plasma

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

Xu, M.; Tynan, G. R.; Holland, C.

2010-03-15

Frequency-resolved nonlinear internal and kinetic energy transfer rates have been measured in the Controlled Shear Decorrelation Experiment (CSDX) linear plasma device using a recently developed technique [Xu et al., Phys. Plasmas 16, 042312 (2009)]. The results clearly show a net kinetic energy transfer into the zonal flow frequency region, consistent with previous time-domain observations of turbulence-driven shear flows [Tynan et al., Plasma Phys. Controlled Fusion 48, S51 (2006)]. The experimentally measured dispersion relation has been used to map the frequency-resolved energy transfer rates into the wave number domain, which shows that the shear flow drive comes from midrange (k{sub t}hetarho{submore » S}>0.3) drift fluctuations, and the strongest flow drive comes from k{sub t}hetarho{sub S}approx =1 fluctuations. Linear growth rates have been inferred from a linearized Hasegawa-Wakatani model [Hasegawa et al., Phys. Fluids 22, 2122 (1979)], which indicates that the m=0 mode is linearly stable and the m=1-10 modes (corresponding to k{sub t}hetarho{sub S}>0.3) are linearly unstable for the n=1 and n=2 radial eigenmodes. This is consistent with our energy transfer measurements.« less

Numerical modelling of fault reactivation in carbonate rocks under fluid depletion conditions - 2D generic models with a small isolated fault

NASA Astrophysics Data System (ADS)

Zhang, Yanhua; Clennell, Michael B.; Delle Piane, Claudio; Ahmed, Shakil; Sarout, Joel

2016-12-01

This generic 2D elastic-plastic modelling investigated the reactivation of a small isolated and critically-stressed fault in carbonate rocks at a reservoir depth level for fluid depletion and normal-faulting stress conditions. The model properties and boundary conditions are based on field and laboratory experimental data from a carbonate reservoir. The results show that a pore pressure perturbation of -25 MPa by depletion can lead to the reactivation of the fault and parts of the surrounding damage zones, producing normal-faulting downthrows and strain localization. The mechanism triggering fault reactivation in a carbonate field is the increase of shear stresses with pore-pressure reduction, due to the decrease of the absolute horizontal stress, which leads to an expanded Mohr's circle and mechanical failure, consistent with the predictions of previous poroelastic models. Two scenarios for fault and damage-zone permeability development are explored: (1) large permeability enhancement of a sealing fault upon reactivation, and (2) fault and damage zone permeability development governed by effective mean stress. In the first scenario, the fault becomes highly permeable to across- and along-fault fluid transport, removing local pore pressure highs/lows arising from the presence of the initially sealing fault. In the second scenario, reactivation induces small permeability enhancement in the fault and parts of damage zones, followed by small post-reactivation permeability reduction. Such permeability changes do not appear to change the original flow capacity of the fault or modify the fluid flow velocity fields dramatically.

An interior penalty stabilised incompressible discontinuous Galerkin-Fourier solver for implicit large eddy simulations

NASA Astrophysics Data System (ADS)

Ferrer, Esteban

2017-11-01

We present an implicit Large Eddy Simulation (iLES) h / p high order (≥2) unstructured Discontinuous Galerkin-Fourier solver with sliding meshes. The solver extends the laminar version of Ferrer and Willden, 2012 [34], to enable the simulation of turbulent flows at moderately high Reynolds numbers in the incompressible regime. This solver allows accurate flow solutions of the laminar and turbulent 3D incompressible Navier-Stokes equations on moving and static regions coupled through a high order sliding interface. The spatial discretisation is provided by the Symmetric Interior Penalty Discontinuous Galerkin (IP-DG) method in the x-y plane coupled with a purely spectral method that uses Fourier series and allows efficient computation of spanwise periodic three-dimensional flows. Since high order methods (e.g. discontinuous Galerkin and Fourier) are unable to provide enough numerical dissipation to enable under-resolved high Reynolds computations (i.e. as necessary in the iLES approach), we adapt the laminar version of the solver to increase (controllably) the dissipation and enhance the stability in under-resolved simulations. The novel stabilisation relies on increasing the penalty parameter included in the DG interior penalty (IP) formulation. The latter penalty term is included when discretising the linear viscous terms in the incompressible Navier-Stokes equations. These viscous penalty fluxes substitute the stabilising effect of non-linear fluxes, which has been the main trend in implicit LES discontinuous Galerkin approaches. The IP-DG penalty term provides energy dissipation, which is controlled by the numerical jumps at element interfaces (e.g. large in under-resolved regions) such as to stabilise under-resolved high Reynolds number flows. This dissipative term has minimal impact in well resolved regions and its implicit treatment does not restrict the use of large time steps, thus providing an efficient stabilization mechanism for iLES. The IP-DG stabilisation is complemented with a Spectral Vanishing Viscosity (SVV) method, in the z-direction, to enhance stability in the continuous Fourier space. The coupling between the numerical viscosity in the DG plane and the SVV damping, provides an efficient approach to stabilise high order methods at moderately high Reynolds numbers. We validate the formulation for three turbulent flow cases: a circular cylinder at Re = 3900, a static and pitch oscillating NACA 0012 airfoil at Re = 10000 and finally a rotating vertical-axis turbine at Re = 40000, with Reynolds based on the circular diameter, airfoil chord and turbine diameter, respectively. All our results compare favourably with published direct numerical simulations, large eddy simulations or experimental data. We conclude that the DG-Fourier high order solver, with IP-SVV stabilisation, proves to be a valuable tool to predict turbulent flows and associated statistics for both static and rotating machinery.

Three Dimensional Energetics of Left Ventricle Flows Using Time-Resolved DPIV

NASA Astrophysics Data System (ADS)

Pierrakos, Olga; Vlachos, Pavlos

2006-11-01

Left ventricular (LV) flows in the human heart are very complex and in the presence of unhealthy or prosthetic heart valves (HV), the complexity of the flow is further increased. Yet to date, no study has documented the complex 3D hemodynamic characteristics and energetics of LV flows. We present high sampling frequency Time Resolved DPIV results obtained in a flexible, transparent LV documenting the evolution of eddies and turbulence. The purpose is to characterize the energetics of the LV flow field in the presence of four orientations of the most commonly implanted mechanical bileaflet HV and a porcine valve. By decomposing the energy scales of the flow field, the ultimate goal is to quantify the total energy losses associated with vortex ring formation and turbulence dissipation. The energies associated to vortex ring formation give a measure of the energy trapped within the structure while estimations of the turbulence dissipation rate (TDR) give a measure of the energy dissipated at the smaller scales. For the first time in cardiovascular applications, an LES-based PIV method, which overcomes the limitations of conventional TDR estimation methods that assume homogeneous isotropic turbulence, was employed. We observed that energy lost at the larger scales (vortex ring) is much higher than the energy lost at the smaller scales due to turbulence dissipation.

Micromixer-based time-resolved NMR: applications to ubiquitin protein conformation.

PubMed

Kakuta, Masaya; Jayawickrama, Dimuthu A; Wolters, Andrew M; Manz, Andreas; Sweedler, Jonathan V

2003-02-15

Time-resolved NMR spectroscopy is used to studychanges in protein conformation based on the elapsed time after a change in the solvent composition of a protein solution. The use of a micromixer and a continuous-flow method is described where the contents of two capillary flows are mixed rapidly, and then the NMR spectra of the combined flow are recorded at precise time points. The distance after mixing the two fluids and flow rates define the solvent-protein interaction time; this method allows the measurement of NMR spectra at precise mixing time points independent of spectral acquisition time. Integration of a micromixer and a microcoil NMR probe enables low-microliter volumes to be used without losing significant sensitivity in the NMR measurement. Ubiquitin, the model compound, changes its conformation from native to A-state at low pH and in 40% or higher methanol/water solvents. Proton NMR resonances of the His-68 and the Tyr-59 of ubiquitin are used to probe the conformational changes. Mixing ubiquitin and methanol solutions under low pH at microliter per minute flow rates yields both native and A-states. As the flow rate decreases, yielding longer reaction times, the population of the A-state increases. The micromixer-NMR system can probe reaction kinetics on a time scale of seconds.

Large-eddy simulation of flow past a circular cylinder

NASA Technical Reports Server (NTRS)

Mittal, R.

1995-01-01

Some of the most challenging applications of large-eddy simulation are those in complex geometries where spectral methods are of limited use. For such applications more conventional methods such as finite difference or finite element have to be used. However, it has become clear in recent years that dissipative numerical schemes which are routinely used in viscous flow simulations are not good candidates for use in LES of turbulent flows. Except in cases where the flow is extremely well resolved, it has been found that upwind schemes tend to damp out a significant portion of the small scales that can be resolved on the grid. Furthermore, it has been found that even specially designed higher-order upwind schemes that have been used successfully in the direct numerical simulation of turbulent flows produce too much dissipation when used in conjunction with large-eddy simulation. The objective of the current study is to perform a LES of incompressible flow past a circular cylinder at a Reynolds number of 3900 using a solver which employs an energy-conservative second-order central difference scheme for spatial discretization and compare the results obtained with those of Beaudan & Moin (1994) and with the experiments in order to assess the performance of the central scheme for this relatively complex geometry.

Effects of Langmuir Turbulence on Reactive Tracers in the Upper Ocean

NASA Astrophysics Data System (ADS)

Smith, K.; Hamlington, P.; Niemeyer, K.; Fox-Kemper, B.; Lovenduski, N. S.

2017-12-01

Reactive tracers such as carbonate chemical species play important roles in the oceanic carbon cycle, allowing the ocean to hold 60 times more carbon than the atmosphere. However, uncertainties in regional ocean sinks for anthropogenic CO2 are still relatively high. Many carbonate species are non-conserved, flux across the air-sea interface, and react on time scales similar to those of ocean turbulent processes, such as small-scale wave-driven Langmuir turbulence. All of this complexity gives rise to heterogeneous tracer distributions that are not fully understood and can greatly affect the rate at which CO2 fluxes across the air-sea interface. In order to more accurately model the biogeochemistry of the ocean in Earth system models (ESMs), a better understanding of the fundamental interactions between these reactive tracers and relevant turbulent processes is required. Research on reacting flows in other contexts has shown that the most significant tracer-flow couplings occur when coherent structures in the flow have timescales that rival reaction time scales. Langmuir turbulence, a 3D, small-scale, wave-driven process, has length and time scales on the order of O(1-100m) and O(1-10min), respectively. Once CO2 transfers across the air-sea interface, it reacts with seawater in a series of reactions whose rate limiting steps have time scales of 10-25s. This similarity in scales warrants further examination into interactions between these small-scale physical and chemical processes. In this presentation, large eddy simulations are used to examine the evolution of reactive tracers in the presence of realistic upper ocean wave- and shear-driven turbulence. The reactive tracers examined are those specifically involved in non-biological carbonate chemistry. The strength of Langmuir turbulence is varied in order to determine a relationship between the degree of enhancement (or reduction) of carbon that is fluxed across the air-sea interface due to the presence of Langmuir turbulence. By examining different reaction chemistry and surface forcing scenarios, the coupled turbulence-reactive tracer dynamics are connected with spatial and statistical properties of the resulting tracer fields. These results, along with implications for development of reduced order reactive tracer models, are discussed.

Hybrid Multiscale Simulation of Hydrologic and Biogeochemical Processes in the River-Groundwater Interaction Zone

NASA Astrophysics Data System (ADS)

Yang, X.; Scheibe, T. D.; Chen, X.; Hammond, G. E.; Song, X.

2015-12-01

The zone in which river water and groundwater mix plays an important role in natural ecosystems as it regulates the mixing of nutrients that control biogeochemical transformations. Subsurface heterogeneity leads to local hotspots of microbial activity that are important to system function yet difficult to resolve computationally. To address this challenge, we are testing a hybrid multiscale approach that couples models at two distinct scales, based on field research at the U. S. Department of Energy's Hanford Site. The region of interest is a 400 x 400 x 20 m macroscale domain that intersects the aquifer and the river and contains a contaminant plume. However, biogeochemical activity is high in a thin zone (mud layer, <1 m thick) immediately adjacent to the river. This microscale domain is highly heterogeneous and requires fine spatial resolution to adequately represent the effects of local mixing on reactions. It is not computationally feasible to resolve the full macroscale domain at the fine resolution needed in the mud layer, and the reaction network needed in the mud layer is much more complex than that needed in the rest of the macroscale domain. Hence, a hybrid multiscale approach is used to efficiently and accurately predict flow and reactive transport at both scales. In our simulations, models at both scales are simulated using the PFLOTRAN code. Multiple microscale simulations in dynamically defined sub-domains (fine resolution, complex reaction network) are executed and coupled with a macroscale simulation over the entire domain (coarse resolution, simpler reaction network). The objectives of the research include: 1) comparing accuracy and computing cost of the hybrid multiscale simulation with a single-scale simulation; 2) identifying hot spots of microbial activity; and 3) defining macroscopic quantities such as fluxes, residence times and effective reaction rates.

Time-resolved and Depth-dependent Photo-Degradation of Marine Dissolved Organic Matter Analyzed by Semi-continuous EEM Fluorescence Monitoring

NASA Astrophysics Data System (ADS)

Gonsior, M.; Timko, S.; Conte, M. H.; Schmitt-Kopplin, P.

2016-02-01

Ten liter water samples were collected at the Bermuda Atlantic Time Series Station (BATS) at 200 m intervals down to a maximum depth of 4530 m and solid-phase extracted. The methanol extracts were dried and re-dissolved in pure water and then used to determine the time-resolved photo-degradation of marine dissolved organic matter to be able to determine kinetic data. Excitation Emission Matrix (EEM) fluorescence spectra were recorded every 20 minutes using a custom-built flow-through photo-degradation system during 20 h of solar simulated light exposure. The resulting EEM spectra were modeled using Parallel Factor Analysis (PARAFAC) and results revealed reproducible and significant changes in the photo-degradation of marine FDOM originating from different depths. A five component model was fitted and the terrestrial-like components showed the expected high photo-reactivity, but surprisingly, the traditional marine-like peak showed slight photo-production in the surface layer, which might be the reason for its prevalence in the open ocean. Surface ocean waters were depleted in the highly photo-degradable components while protein-like fluorescent components were enriched, which was in agreement with previous studies. Ultrahigh resolution mass spectrometry confirmed unique aliphatic molecular ions in the Surface Ocean and hydrogen-deficient molecules at depth. Multivariate statistical analyses revealed strong correlations between unsaturated/aromatic molecular ions and depth, where aliphatic molecular ions were more prevalent in the Surface Ocean and aromatic molecular ions at depth. Strong correlations were also found between hydrogen-deficient molecular ions and the humic-like fluorescent components. The rapid photo-degradation of the deep-sea FDOM and the surface oceans relative depletion of aromatic molecular ions suggested that deep-ocean FDOM may be too photochemically labile to survive meridional overturning circulation.

Grid generation about complex three-dimensional aircraft configurations

NASA Technical Reports Server (NTRS)

Klopfer, Goetz H.

1991-01-01

The problem of obtaining three dimensional grids with sufficient resolution to resolve all the flow or other physical features of interest is addressed. The generation of a computational grid involves a series of compromises to resolve several conflicting requirements. On one hand, one would like the grid to be fine enough and not too skewed to reduce the numerical errors and to adequately resolve the pertinent physical features of the flow field about the aircraft. On the other hand, the capabilities of present or even future supercomputers are finite and the number of mesh points must be limited to a reasonable number: one which is usually much less than desired for numerical accuracy. One technique to overcome this limitation is the 'zonal' grid approach. In this method, the overall field is subdivided into smaller zones or blocks in each of which an independent grid is generated with enough grid density to resolve the flow features in that zone. The zonal boundaries or interfaces require special boundary conditions such that the conservation properties of the governing equations are observed. Much work was done in 3-D zonal approaches with nonconservative zonal interfaces. A 3-D zonal conservative interfacing method that is efficient and easy to implement was developed during the past year. During the course of the work, it became apparent that it would be much more feasible to do the conservative interfacing with cell-centered finite volume codes instead of the originally planned finite difference codes. Accordingly, the CNS code was converted to finite volume form. This new version of the code is named CNSFV. The original multi-zonal interfacing capability of the CNS code was enhanced by generalizing the procedure to allow for completely arbitrarily shaped zones with no mesh continuity between the zones. While this zoning capability works well for most flow situations, it is, however, still nonconservative. The conservative interface algorithm was also implemented but was not completely validated.

On modeling heterogeneous coastal sediment transport - A numerical study using multiphase Eulerian and Euler-Lagrangian approaches

NASA Astrophysics Data System (ADS)

Cheng, Z.; Yu, X.; Hsu, T. J.; Calantoni, J.; Chauchat, J.

2016-02-01

Regional scale coastal evolution models do not explicitly resolve wave-driven sediment transport and must rely on bedload/suspended modules that utilize empirical assumptions. Under extreme wave events or in regions of high sediment heterogeneity, these empirical bedload/suspended load modules may need to be reevaluated with detailed observation and more sophisticated small-scale models. In the past decade, significant research efforts have been devoted to modeling sediment transport using multiphase Eulerian or Euler-Lagrangian approaches. Recently, an open-source multi-dimensional Reynolds-averaged two-phase sediment transport model, SedFOAM is developed by the authors and it has been adopted by many researchers to study momentary bed failure, granular rheology in sheet flow and scour around structures. In this abstract, we further report our recent progress made in extending the model with 3D turbulence-resolving capability and to model the sediment phase with the Discrete Element method (DEM). Adopting the large-eddy simulation methodology, we validate the 3D model with measured fine sediment transport is oscillatory sheet flow and demonstrate that the model is able to resolve sediment burst events during flow reversals. To better resolve the intergranular interactions and to model heterogeneous properties of sediment (e.g., mixed grain sizes and grain shape), we use an Euler-Lagrangian solver called CFDEM, which couples OpenFOAM for the fluid phase and LIGGGHTS for the particle phase. We improve the model by better enforcing conservation of mass in the pressure solver. The modified CFDEM solver is validated with measured oscillatory sheet flow data for coarse sand and we demonstrated that the model can reproduce the well-known armoring effects. We show that under Stokes second-order wave forcing, the armoring effect is more significant during the energetic positive peak, and hence the net onshore transport is reduced. Preliminary results modeling the shape effects using composite particles will be presented. This research is supported by Office of Naval Research and National Science Foundation.

Chemical Energy Release in Several Recently Discovered Detonation and Deflagration Flows

NASA Astrophysics Data System (ADS)

Tarver, Craig M.

2010-10-01

Several recent experiments on complex detonation and deflagration flows are analyzed in terms of the chemical energy release required to sustain these flows. The observed double cellular structures in detonating gaseous nitromethane-oxygen and NO2-fuel (H2, CH4, and C2H6) mixtures are explained by the amplification of two distinct pressure wave frequencies by two exothermic reactions, the faster reaction forming vibrationally excited NO* and the slower reaction forming highly vibrationally excited N2**. The establishment of a Chapman-Jouguet (C-J) deflagration behind a weak shock wave, the C-J detonation established after a head-on collision with a shock front, and the C-J detonation conditions established in reactive supersonic flows are quantitatively calculated using the chemical energy release of a H2 + Cl2 mixture. For these three reactive flows, these calculations illustrate that different fractions of the exothermic chemical energy are used to sustain steady-state propagation. C-J detonation calculations on the various initial states using the CHEETAH chemical equilibrium code are shown to be in good agreement with experimental detonation velocity measurements for the head-on collision and supersonic flow detonations.

Flash chemistry: flow microreactor synthesis based on high-resolution reaction time control.

PubMed

Yoshida, Jun-ichi

2010-10-01

This article addresses a fascinating aspect of flash chemistry, high-resolution reaction-time control by virtue of a flow microreactor system, and its applications. The length of time that the solution remains inside the reactor is called the residence time. The residence time between the addition of a reagent and that of a quenching agent or the next reagent in a flow microreactor is the reaction time, and the reaction time can be greatly reduced by adjusting the length of a reaction channel in a flow microreactor. This feature is quite effective for conducting reactions involving short-lived reactive intermediates. A reactive species can be generated and transferred to another location to be used in the next reaction before it decomposes by adjusting the residence time in the millisecond to second timescale. The principle of such high-resolution reaction-time control, which can be achieved only by flow microreactors, and its applications to synthetic reactions including Swern-Moffatt-type oxidation, as well as the generation and reactions of aryllithium compounds bearing electrophilic substituents, such as alkoxycarbonyl groups, are presented. Integration of such reactions using integrated flow microreactor systems is also demonstrated. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Attempting to link hydro-morphology, transient storage and metabolism in streams: Insights from reactive tracer experiments

NASA Astrophysics Data System (ADS)

Kurz, Marie J.; Schmidt, Christian; Blaen, Phillip; Knapp, Julia L. A.; Drummond, Jennifer D.; Martí, Eugenia; Zarnetske, Jay P.; Ward, Adam S.; Krause, Stefan

2016-04-01

In-stream transient storage zones, including the hyporheic zone and vegetation beds, can be hotspots of biogeochemical processing in streams, enhancing ecosystem functions such as metabolism and nutrient uptake. The spatio-temporal dynamics and reactivity of these storage zones are influenced by multiple factors, including channel geomorphology, substrate composition and hydrology, and by anthropogenic modifications to flow regimes and nutrient loads. Tracer injections are a commonly employed method to evaluate solute transport and transient storage in streams; however, reactive tracers are needed to differentiate between metabolically active and inactive transient storage zones. The reactive stream tracer resazurin (Raz), a weakly fluorescent dye which irreversibly transforms to resorufin (Rru) under mildly reducing conditions, provides a proxy for aerobic respiration and an estimate of the metabolic activity associated with transient storage zones. Across a range of lotic ecosystems, we try to assess the influence of stream channel hydro-morphology, morphologic heterogeneity, and substrate type on reach (103 m) and sub-reach (102 m) scale transient storage, respiration, and nutrient uptake. To do so, we coupled injections of Raz and conservative tracers (uranine and/or salt) at each study site. The study sites included: vegetated mesocosms controlled for water depth; vegetated and un-vegetated sediment-filled mesocosms fed by waste-water effluent; a contrasting sand- vs. gravel-bedded lowland stream (Q = 0.08 m3/s); and a series of upland streams with varying size (Q = 0.1 - 1.5 m3/s) and prevalence of morphologic features. Continuous time-series of tracer concentrations were recorded using in-situ fluorometers and EC loggers. At the stream sites, time-series were recorded at multiple downstream locations in order to resolve sub-reach dynamics. Analyses yielded highly variable transport metrics and Raz-Rru transformation between study sites and between sub-reaches within stream sites. Higher Raz-Rru transformation rates were typically observed in smaller streams, in sub-reaches with higher prevalence of morphologic features known to promote hyporheic exchange, and in mesocosms with higher water depth, vegetation density and retention time. However, relationships between transformation rates and common metrics of transient storage were not consistent among study cases, indicating the existence of yet unrealized complexities in the relationships between water and solute transport and metabolism. Further insights were also gained related to the utility of Raz and improved tracer test practices.

Fundamental Physics and Practical Applications of Electromagnetic Local Flow Control in High Speed Flows (Rutgers)

DTIC Science & Technology

2010-02-16

field. Techniques utilizing this design use an open- loop control and no flow monitoring sensors are required. Conversely, reactive (or closed - loop ...and closed (dashed line) configuration. 38 closed configuration described above, the ambiguity in the critical limits of the transition...flow; a new vortex is then shed from the cavity leading edge, closing the feedback loop .[31] Open cavities with an L/D approximately greater than

Control of topography gradients on residence time distributions, mixing dynamics and reactive hotspot development

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Le Borgne, Tanguy; Davy, Philippe

2017-04-01

Topography-driven subsurface flows are thought to play a central role in determining solute turnover and biogeochemical processes at different scales in the critical zone, including river-hyporheic zone exchanges, hillslope solute transport and reactions, and catchment biogeochemical cycles. Hydraulic head gradients, induced by topography gradients at different scales, generate a distribution of streamlines at depth, dictating the spatial distribution of redox sensitive species, the magnitude of surface water - ground water exchanges and ultimately the source/sink function of the subsurface. Flow velocities generally decrease with depth, leading to broad residence time distributions, which have been shown to affect river chemistry and geochemical reactions in catchments. In this presentation, we discuss the impact of topography-driven flows on mixing processes and the formation of localized reactive hotspots. For this, we solve analytically the coupled flow, mixing and reaction equations in two-dimensional vertical cross-sections of subsurface domains with different topography gradients. For a given topography gradient, we derive the spatial distribution of subsurface velocities, the rates of solute mixing accross streamlines and the induced kinetics of redox, precipitation and dissolution reactions using a Lagrangian approach (Le Borgne et al. 2014). We demonstrate that vertical velocity profiles driven by topography variations, act effectively as shear flows, hence stretching continuously the mixing fronts between recently infiltrated and resident water (Bandopadhyay et al. 2017). We thus derive analytical expressions for residence time distributions, mixing rates and kinetics of chemical reactions as a function of the topography gradients. We show that the rates dissolution and precipitation reactions are significantly enhanced by the existence of vertical velocity gradients and that reaction rates reach a maximum in a localized subsurface reactive layer, whose location and intensity depends on topography gradients. As a consequence of these findings, we discuss the links between topography variations, subsurface velocity gradients and biogeochemical processes in the critical zone. References: Bandopadhyay A., T. Le Borgne, Y. Méheust and M. Dentz (2017) Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damkohler numbers, Adv. in Water Resour. Vol. 100, p. 78-95 Le Borgne T., T. Ginn and M. Dentz (2014) Impact of Fluid Deformation on Mixing-Induced Chemical Reactions in Heterogeneous Flows, Geophys. Res. Lett., Vol. 41, 22, p. 7898-790

Effect of mobile phone use on salivary concentrations of protein, amylase, lipase, immunoglobulin A, lysozyme, lactoferrin, peroxidase and C-reactive protein of the parotid gland.

PubMed

Hashemipour, M S; Yarbakht, M; Gholamhosseinian, A; Famori, H

2014-05-01

The possibility of side effects associated with the electromagnetic waves emitted from mobile phones is a controversial issue. The present study aimed to evaluate the effect of mobile phone use on parotid gland salivary concentrations of protein, amylase, lipase, immunoglobulin A, lysozyme, lactoferrin, peroxidase and C-reactive protein. Stimulated salivary samples were collected simultaneously from both parotid glands of 86 healthy volunteers. Salivary flow rate and salivary concentrations of proteins, amylase, lipase, lysozyme, lactoferrin, peroxidase, C-reactive protein and immunoglobulin A, were measured. Data were analysed using t-tests and one-way analyses of variance. Salivary flow rate and parotid gland salivary concentrations of protein were significantly higher on the right side compared to the left in those that predominantly held mobile phones on the right side. In addition, there was a decrease in concentrations of amylase, lipase, lysozyme, lactoferrin and peroxidase. The side of dominant mobile phone use was associated with differences in salivary flow rate and parotid gland salivary concentrations, in right-dominant users. Although mobile phone use influenced salivary composition, the relationship was not significant.

Fringe-controlled biodegradation under dynamic conditions: Quasi 2-D flow-through experiments and reactive-transport modeling

NASA Astrophysics Data System (ADS)

Eckert, Dominik; Kürzinger, Petra; Bauer, Robert; Griebler, Christian; Cirpka, Olaf A.

2015-01-01

Biodegradation in contaminated aquifers has been shown to be most pronounced at the fringe of contaminant plumes, where mixing of contaminated water and ambient groundwater, containing dissolved electron acceptors, stimulates microbial activity. While physical mixing of contaminant and electron acceptor by transverse dispersion has been shown to be the major bottleneck for biodegradation in steady-state plumes, so far little is known on the effect of flow and transport dynamics (caused, e.g., by a seasonally fluctuating groundwater table) on biodegradation in these systems. Towards this end we performed experiments in quasi-two-dimensional flow-through microcosms on aerobic toluene degradation by Pseudomonas putida F1. Plume dynamics were simulated by vertical alteration of the toluene plume position and experimental results were analyzed by reactive-transport modeling. We found that, even after disappearance of the toluene plume for two weeks, the majority of microorganisms stayed attached to the sediment and regained their full biodegradation potential within two days after reappearance of the toluene plume. Our results underline that besides microbial growth, also maintenance and dormancy are important processes that affect biodegradation performance under transient environmental conditions and therefore deserve increased consideration in future reactive-transport modeling.

Pore-scale simulation of CO2-water-rock interactions

NASA Astrophysics Data System (ADS)

Deng, H.; Molins, S.; Steefel, C. I.; DePaolo, D. J.

2017-12-01

In Geologic Carbon Storage (GCS) systems, the migration of scCO2 versus CO2-acidifed brine ultimately determines the extent of mineral trapping and caprock integrity, i.e. the long-term storage efficiency and security. While continuum scale multiphase reactive transport models are valuable for large scale investigations, they typically (over-)simplify pore-scale dynamics and cannot capture local heterogeneities that may be important. Therefore, pore-scale models are needed in order to provide mechanistic understanding of how fine scale structural variations and heterogeneous processes influence the transport and geochemistry in the context of multiphase flow, and to inform parameterization of continuum scale modeling. In this study, we investigate the interplay of different processes at pore scale (e.g. diffusion, reactions, and multiphase flow) through the coupling of a well-developed multiphase flow simulator with a sophisticated reactive transport code. The objectives are to understand where brine displaced by scCO2 will reside in a rough pore/fracture, and how the CO2-water-rock interactions may affect the redistribution of different phases. In addition, the coupled code will provide a platform for model testing in pore-scale multiphase reactive transport problems.

A Model to Couple Flow, Thermal and Reactive Chemical Transport, and Geo-mechanics in Variably Saturated Media

NASA Astrophysics Data System (ADS)

Yeh, G. T.; Tsai, C. H.

2015-12-01

This paper presents the development of a THMC (thermal-hydrology-mechanics-chemistry) process model in variably saturated media. The governing equations for variably saturated flow and reactive chemical transport are obtained based on the mass conservation principle of species transport supplemented with Darcy's law, constraint of species concentration, equation of states, and constitutive law of K-S-P (Conductivity-Degree of Saturation-Capillary Pressure). The thermal transport equation is obtained based on the conservation of energy. The geo-mechanic displacement is obtained based on the assumption of equilibrium. Conventionally, these equations have been implicitly coupled via the calculations of secondary variables based on primary variables. The mechanisms of coupling have not been obvious. In this paper, governing equations are explicitly coupled for all primary variables. The coupling is accomplished via the storage coefficients, transporting velocities, and conduction-dispersion-diffusion coefficient tensor; one set each for every primary variable. With this new system of equations, the coupling mechanisms become clear. Physical interpretations of every term in the coupled equations will be discussed. Examples will be employed to demonstrate the intuition and superiority of these explicit coupling approaches. Keywords: Variably Saturated Flow, Thermal Transport, Geo-mechanics, Reactive Transport.

Numerical simulations of the process of multiple shock-flame interactions

NASA Astrophysics Data System (ADS)

Jiang, Hua; Dong, Gang; chen, Xiao; Wu, Jin-Tao

2016-08-01

Based on a weighted essentially nonoscillatory scheme, the multiple interactions of a flame interface with an incident shock wave and its reshock waves are numerically simulated by solving the compressible reactive Navier-Stokes equations with a single-step Arrhenius chemical reaction. The two-dimensional sinusoidally perturbed premixed flames with different initial perturbed amplitudes are used to investigate the effect of the initial perturbation on the flame evolutions. The results show that the development of the flame interface is directly affected by the initial perturbed amplitudes before the passages of reshock waves, and the perturbation development is mainly controlled by the Richtmyer-Meshkov instability (RMI). After the successive impacts of multiple reshock waves, the chemical reaction accelerates the consumption of reactants and leads to a gradual disappearance of the initial perturbed information. The perturbation developments in frozen flows with the same initial interface as those in reactive flows are also demonstrated. Comparisons of results between the reactive and frozen flows show that a chemical reaction changes the perturbation pattern of the flame interface by decreasing the density gradient, thereby weakening the baroclinic torque in the flame mixing region, and therefore plays a dominant role after the passage of reshock waves.

Letter: Modeling reactive shock waves in heterogeneous solids at the continuum level with stochastic differential equations

NASA Astrophysics Data System (ADS)

Kittell, D. E.; Yarrington, C. D.; Lechman, J. B.; Baer, M. R.

2018-05-01

A new paradigm is introduced for modeling reactive shock waves in heterogeneous solids at the continuum level. Inspired by the probability density function methods from turbulent reactive flows, it is hypothesized that the unreacted material microstructures lead to a distribution of heat release rates from chemical reaction. Fluctuations in heat release, rather than velocity, are coupled to the reactive Euler equations which are then solved via the Riemann problem. A numerically efficient, one-dimensional hydrocode is used to demonstrate this new approach, and simulation results of a representative impact calculation (inert flyer into explosive target) are discussed.

Cerebral blood flow is reduced in patients with sepsis syndrome

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

Bowton, D.L.; Bertels, N.H.; Prough, D.S.

The relationship between sepsis-induced CNS dysfunction and changes in brain blood flow remains unknown, and animal studies examining the influence of sepsis on cerebral blood flow (CBF) do not satisfactorily address that relationship. We measured CBF and cerebrovascular reactivity to CO/sub 2/ in nine patients with sepsis syndrome using the /sup 133/Xe clearance technique. Mean CBF was 29.6 +/- 15.8 (SD) ml/100 g.min, significantly lower than the normal age-matched value in this laboratory of 44.9 +/- 6.2 ml/100 g.min (p less than .02). This depression did not correlate with changes in mean arterial pressure. Despite the reduction in CBF, themore » specific reactivity of the cerebral vasculature to changes in CO/sub 2/ was normal, 1.3 +/- 0.9 ml/100 g.min/mm Hg. Brain blood flow is reduced in septic humans; the contribution of this reduction to the metabolic and functional changes observed in sepsis requires further study.« less

Systematic development of reduced reaction mechanisms for dynamic modeling

NASA Technical Reports Server (NTRS)

Frenklach, M.; Kailasanath, K.; Oran, E. S.

1986-01-01

A method for systematically developing a reduced chemical reaction mechanism for dynamic modeling of chemically reactive flows is presented. The method is based on the postulate that if a reduced reaction mechanism faithfully describes the time evolution of both thermal and chain reaction processes characteristic of a more complete mechanism, then the reduced mechanism will describe the chemical processes in a chemically reacting flow with approximately the same degree of accuracy. Here this postulate is tested by producing a series of mechanisms of reduced accuracy, which are derived from a full detailed mechanism for methane-oxygen combustion. These mechanisms were then tested in a series of reactive flow calculations in which a large-amplitude sinusoidal perturbation is applied to a system that is initially quiescent and whose temperature is high enough to start ignition processes. Comparison of the results for systems with and without convective flow show that this approach produces reduced mechanisms that are useful for calculations of explosions and detonations. Extensions and applicability to flames are discussed.

Sea Butterfly Swimming: Time-resolved Tomographic PIV measurements

NASA Astrophysics Data System (ADS)

Murphy, David; Zheng, Lingxiao; Mittal, Rajat; Webster, Donald; Yen, Jeannette

2011-11-01

The planktonic sea butterfly Limacina helicina swims by flapping its flexible, wing-like parapodia. The appendage stroke kinematics of this shell-bearing pteropod are three-dimensional and likely contain elements of both drag-based (rowing) and lift-based (flapping) propulsion. Unsteady lift-generating mechanisms such as clap-and-fling may also be present. Upstroke and downstroke motions both propel the animal upward and roll it forwards and backwards, resulting in a sawtooth trajectory. We present time-resolved, tomographic PIV measurements of flow generated by free-swimming pteropods (Limacina helicina) moving upwards with average swimming speeds of 5 - 17 mm/s. The pteropods beat their appendages with a stroke frequency of 4 - 5 Hz. With a size range of 1 - 2 mm, the animals filmed in this study operate in a viscous environment with a Reynolds number of 5 to 20. The volumetric flow measurements provide insight into the three dimensional nature of the flow and into the relative importance of drag- and lift-based propulsion at this low Reynolds number. Preliminary results from Navier-Stokes simulations of the flow associated with the swimming of this organism will also be presented.

Retrieving accurate temporal and spatial information about Taylor slug flows from non-invasive NIR photometry measurements

NASA Astrophysics Data System (ADS)

Helmers, Thorben; Thöming, Jorg; Mießner, Ulrich

2017-11-01

In this article, we introduce a novel approach to retrieve spatial- and time-resolved Taylor slug flow information from a single non-invasive photometric flow sensor. The presented approach uses disperse phase surface properties to retrieve the instantaneous velocity information from a single sensor's time-scaled signal. For this purpose, a photometric sensor system is simulated using a ray-tracing algorithm to calculate spatially resolved near-infrared transmission signals. At the signal position corresponding to the rear droplet cap, a correlation factor of the droplet's geometric properties is retrieved and used to extract the instantaneous droplet velocity from the real sensor's temporal transmission signal. Furthermore, a correlation for the rear cap geometry based on the a priori known total superficial flow velocity is developed, because the cap curvature is velocity sensitive itself. Our model for velocity derivation is validated, and measurements of a first prototype showcase the capability of the device. Long-term measurements visualize systematic fluctuations in droplet lengths, velocities, and frequencies that could otherwise, without the observation on a larger timescale, have been identified as measurement errors and not systematic phenomenas.

A Runge-Kutta discontinuous Galerkin approach to solve reactive flows: The hyperbolic operator

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

Billet, G., E-mail: billet@onera.f; Ryan, J., E-mail: ryan@onera.f

2011-02-20

A Runge-Kutta discontinuous Galerkin method to solve the hyperbolic part of reactive Navier-Stokes equations written in conservation form is presented. Complex thermodynamics laws are taken into account. Particular care has been taken to solve the stiff gaseous interfaces correctly with no restrictive hypothesis. 1D and 2D test cases are presented.

RATE OF TCE DEGRADATION IN PASSIVE REACTIVE BARRIERS CONSTRUCTED WITH PLANT MULCH (BIOWALLS)

EPA Science Inventory

This presentation reviews a case study at Altus AFB on the extent of treatment of TCE in a passive reactive barrier constructed with plant mulch. It presents data from a tracer test to estimate the rate of ground water flow at the site, and the residence time of water and TCE in...

32-channel pyrometer with high dynamic range for studies of shocked nanothermites

NASA Astrophysics Data System (ADS)

Bassett, Will P.; Dlott, Dana D.

2017-01-01

A 32-channel optical pyrometer has been developed for studying temperature dynamics of shock-initiated reactive materials with one nanosecond time resolution and high dynamic range. The pyrometer consists of a prism spectrograph which directs the spectrally-resolved emission to 32 fiber optics and 32 photomultiplier tubes and digitizers. Preliminary results show shock-initiated reactions of a nanothermite composite, nano CuO/Al in nitrocellulose binder, consists of three stages. The first stage occurred at 30 ns, right after the shock unloaded, the second stage at 100 ns and the third at 1 μs, and the temperatures ranged from 2100K to 3000K. Time-resolved emission spectra suggest hot spots formed during shock unloading, which initiated the bulk thermite/nitrocellulose reaction.

Effects of Building‒roof Cooling on Flow and Distribution of Reactive Pollutants in street canyons

NASA Astrophysics Data System (ADS)

Park, S. J.; Choi, W.; Kim, J.; Jeong, J. H.

2016-12-01

The effects of building‒roof cooling on flow and dispersion of reactive pollutants were investigated in the framework of flow dynamics and chemistry using a coupled CFD‒chemistry model. For this, flow characteristics were analyzed first in street canyons in the presence of building‒roof cooling. A portal vortex was generated in street canyon, producing dominant reverse and outward flows near the ground in all the cases. The building‒roof cooling increased horizontal wind speeds at the building roof and strengthened the downward motion near the downwind building in the street canyon, resultantly intensifying street canyon vortex strength. The flow affected the distribution of primary and secondary pollutants. Concentrations of primary pollutants such as NOx, VOC and CO was high near the upwind building because the reverse flows were dominant at street level, making this area the downwind region of emission sources. Concentration of secondary pollutant such as O3 was lower than the background near the ground, where NOX concentrations were high. Building‒roof cooling decreased the concentration of primary pollutants in contrasted to those under non‒cooling conditions. In contrast, building‒roof cooling increased O3 by reducing NO concentrations in urban street canyon compared to concentrations under non‒cooling conditions.

Blood Flow Modulation of Vascular Dynamics

PubMed Central

Lee, Juhyun; Sevag Packard, René R.; Hsiai, Tzung K.

2015-01-01

Purpose of review Blood flow is intimately linked with cardiovascular development, repair, and dysfunction. The current review will build on the fluid mechanical principle underlying hemodynamic shear forces, mechanotransduction, and metabolic effects. Recent findings Pulsatile flow produces both time- (∂τ /∂t)and spatial-varying shear stress (∂τ /∂x) to modulate vascular oxidative stress and inflammatory response with pathophysiological significance to atherosclerosis. The characteristics of hemodynamic shear forces; namely, steady laminar (∂τ /∂t= 0), pulsatile (PSS: unidirectional forward flow), and oscillatory shear stress (OSS: bidirectional with a near net 0 forward flow) modulate mechano-signal transduction to influence metabolic effects on vascular endothelial function. Atheroprotective PSS promotes anti-oxidant, anti-inflammatory, and anti-thrombotic responses, whereas atherogenic OSS induces NADPH oxidase–JNK signaling to increase mitochondrial superoxide production, protein degradation of manganese superoxide dismutase (MnSOD), and post-translational protein modifications of LDL particles in the disturbed flow-exposed regions of vasculature. In the era of tissue regeneration, shear stress has been implicated in re-activation of developmental genes; namely, Wnt and Notch signaling, for vascular development and repair. Summary Blood flow imparts a dynamic continuum from vascular development to repair. Augmentation of PSS confers atheroprotection and re-activation of developmental signaling pathways for regeneration. PMID:26218416

Nonlinear dynamics of skin blood flow response to mechanical and thermal stresses in the plantar foot of diabetics with peripheral neuropathy.

PubMed

Liao, Fuyuan; Jan, Yih-Kuen

2017-01-01

Diabetic foot ulcers (DFU) are a major complication in diabetics. Impaired microvascular reactivity is a major contributor to the development of DFU and has been traditionally quantified by time-domain or frequency-domain measures of skin blood flow (SBF). These measures, however, are unable to characterize the changes of nonlinear dynamics of SBF associated with diabetes and peripheral neuropathy. The objective of this study was to investigate altered nonlinear dynamics of skin blood flow in the plantar foot of diabetics with peripheral neuropathy. 18 type 2 diabetics with peripheral neuropathy and 8 healthy controls were recruited. SBF at the first metatarsal head in response to a loading pressure of 300 mmHg and a local heating was measured using laser Doppler flowmetry. A sample entropy approach was used to quantify the degree of regularity of SBF. Our results showed that the regularity degree of SBF in the diabetic foot underwent only small changes during post-occlusive reactive hyperemia and thermally induced biphasic response compared to non-diabetics. SBF of the diabetic foot has higher degree of irregularity during reactive hyperemia because of attenuated myogenic activity, and demonstrated higher regularity during the biphasic response largely due to significantly enhanced cardiac activities. This study suggests that the regularity degree of SBF at the first metatarsal head could be used to assess impaired microvascular reactivity and thus may be used to assess the risk for DFU in diabetics with peripheralneuropathy.

The Hitchhiker's Guide to Flow Chemistry ∥.

PubMed

Plutschack, Matthew B; Pieber, Bartholomäus; Gilmore, Kerry; Seeberger, Peter H

2017-09-27

Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask. Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions. This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow. Until recently, however, the question, "Should we do this in flow?" has merely been an afterthought. This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts.

Direct analysis of Holliday junction resolving enzyme in a DNA origami nanostructure.

PubMed

Suzuki, Yuki; Endo, Masayuki; Cañas, Cristina; Ayora, Silvia; Alonso, Juan C; Sugiyama, Hiroshi; Takeyasu, Kunio

2014-06-01

Holliday junction (HJ) resolution is a fundamental step for completion of homologous recombination. HJ resolving enzymes (resolvases) distort the junction structure upon binding and prior cleavage, raising the possibility that the reactivity of the enzyme can be affected by a particular geometry and topology at the junction. Here, we employed a DNA origami nano-scaffold in which each arm of a HJ was tethered through the base-pair hybridization, allowing us to make the junction core either flexible or inflexible by adjusting the length of the DNA arms. Both flexible and inflexible junctions bound to Bacillus subtilis RecU HJ resolvase, while only the flexible junction was efficiently resolved into two duplexes by this enzyme. This result indicates the importance of the structural malleability of the junction core for the reaction to proceed. Moreover, cleavage preferences of RecU-mediated reaction were addressed by analyzing morphology of the reaction products. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

Computational study of collisions between O({sup 3}P) and NO({sup 2}Π) at temperatures relevant to the hypersonic flight regime

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

Castro-Palacio, Juan Carlos; Nagy, Tibor; Meuwly, Markus, E-mail: m.meuwly@unibas.ch

2014-10-28

Reactions involving N and O atoms dominate the energetics of the reactive air flow around spacecraft when reentering the atmosphere in the hypersonic flight regime. For this reason, the thermal rate coefficients for reactive processes involving O({sup 3}P) and NO({sup 2}Π) are relevant over a wide range of temperatures. For this purpose, a potential energy surface (PES) for the ground state of the NO{sub 2} molecule is constructed based on high-level ab initio calculations. These ab initio energies are represented using the reproducible kernel Hilbert space method and Legendre polynomials. The global PES of NO{sub 2} in the ground statemore » is constructed by smoothly connecting the surfaces of the grids of various channels around the equilibrium NO{sub 2} geometry by a distance-dependent weighting function. The rate coefficients were calculated using Monte Carlo integration. The results indicate that at high temperatures only the lowest A-symmetry PES is relevant. At the highest temperatures investigated (20 000 K), the rate coefficient for the “O1O2+N” channel becomes comparable (to within a factor of around three) to the rate coefficient of the oxygen exchange reaction. A state resolved analysis shows that the smaller the vibrational quantum number of NO in the reactants, the higher the relative translational energy required to open it and conversely with higher vibrational quantum number, less translational energy is required. This is in accordance with Polanyi's rules. However, the oxygen exchange channel (NO2+O1) is accessible at any collision energy. Finally, this work introduces an efficient computational protocol for the investigation of three-atom collisions in general.« less

Computational study of collisions between O(3P) and NO(2Π) at temperatures relevant to the hypersonic flight regime.

PubMed

Castro-Palacio, Juan Carlos; Nagy, Tibor; Bemish, Raymond J; Meuwly, Markus

2014-10-28

Reactions involving N and O atoms dominate the energetics of the reactive air flow around spacecraft when reentering the atmosphere in the hypersonic flight regime. For this reason, the thermal rate coefficients for reactive processes involving O((3)P) and NO((2)Π) are relevant over a wide range of temperatures. For this purpose, a potential energy surface (PES) for the ground state of the NO2 molecule is constructed based on high-level ab initio calculations. These ab initio energies are represented using the reproducible kernel Hilbert space method and Legendre polynomials. The global PES of NO2 in the ground state is constructed by smoothly connecting the surfaces of the grids of various channels around the equilibrium NO2 geometry by a distance-dependent weighting function. The rate coefficients were calculated using Monte Carlo integration. The results indicate that at high temperatures only the lowest A-symmetry PES is relevant. At the highest temperatures investigated (20,000 K), the rate coefficient for the "O1O2+N" channel becomes comparable (to within a factor of around three) to the rate coefficient of the oxygen exchange reaction. A state resolved analysis shows that the smaller the vibrational quantum number of NO in the reactants, the higher the relative translational energy required to open it and conversely with higher vibrational quantum number, less translational energy is required. This is in accordance with Polanyi's rules. However, the oxygen exchange channel (NO2+O1) is accessible at any collision energy. Finally, this work introduces an efficient computational protocol for the investigation of three-atom collisions in general.

Absorption Mode FT-ICR Mass Spectrometry Imaging

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

Smith, Donald F.; Kilgour, David P.; Konijnenburg, Marco

2013-12-03

Fourier transform ion cyclotron resonance mass spectrometry offers the highest mass resolving power for molecular imaging experiments. This high mass resolving power ensures that closely spaced peaks at the same nominal mass are resolved for proper image generation. Typically higher magnetic fields are used to increase mass resolving power. However, a gain in mass resolving power can also be realized by phase correction of the data for absorption mode display. In addition to mass resolving power, absorption mode offers higher mass accuracy and signal-to-noise ratio over the conventional magnitude mode. Here we present the first use of absorption mode formore » Fourier transform ion cyclotron resonance mass spectrometry imaging. The Autophaser algorithm is used to phase correct each spectrum (pixel) in the image and then these parameters are used by the Chameleon work-flow based data processing software to generate absorption mode ?Datacubes? for image and spectral viewing. Absorption mode reveals new mass and spatial features that are not resolved in magnitude mode and results in improved selected ion image contrast.« less

In vitro antigen-specific induction of IL-22 in human subjects that resolved HCV infection

PubMed Central

Cusick, Matthew F; Libbey, Jane E; Fujinami, Robert S; Eckels, David D

2012-01-01

Aims To determine if in vitro production of IL-22 and IL-17 correlated with resolution of HCV infection. Materials & methods Human peripheral blood cells isolated from a well-defined cohort of resolved and chronic HCV-infected subjects were used to measure HCV-, influenza- and mitogen-activated T-cell proliferation. In addition, IL-22 and IL-17 production was measured via ELISAs and flow cytometry. Results Resolved HCV subjects had a significantly higher T-cell proliferative response to recombinant NS3 protein compared with chronic HCV subjects. Resolved subjects had a dose-dependent IL-22 response to recombinant NS3 compared with chronic HCV subjects. Conclusion IL-22 production is associated with antigen-specific induction of CD4 + T cells in individuals that resolved HCV infection, suggesting a potential role for IL-22 in HCV clearance. PMID:23185211

Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

PubMed Central

Braaf, Boy; Vienola, Kari V.; Sheehy, Christy K.; Yang, Qiang; Vermeer, Koenraad A.; Tiruveedhula, Pavan; Arathorn, David W.; Roorda, Austin; de Boer, Johannes F.

2012-01-01

In phase-resolved OCT angiography blood flow is detected from phase changes in between A-scans that are obtained from the same location. In ophthalmology, this technique is vulnerable to eye motion. We address this problem by combining inter-B-scan phase-resolved OCT angiography with real-time eye tracking. A tracking scanning laser ophthalmoscope (TSLO) at 840 nm provided eye tracking functionality and was combined with a phase-stabilized optical frequency domain imaging (OFDI) system at 1040 nm. Real-time eye tracking corrected eye drift and prevented discontinuity artifacts from (micro)saccadic eye motion in OCT angiograms. This improved the OCT spot stability on the retina and consequently reduced the phase-noise, thereby enabling the detection of slower blood flows by extending the inter-B-scan time interval. In addition, eye tracking enabled the easy compounding of multiple data sets from the fovea of a healthy volunteer to create high-quality eye motion artifact-free angiograms. High-quality images are presented of two distinct layers of vasculature in the retina and the dense vasculature of the choroid. Additionally we present, for the first time, a phase-resolved OCT angiogram of the mesh-like network of the choriocapillaris containing typical pore openings. PMID:23304647

RAPID COMMUNICATION Time-resolved measurements with a vortex flowmeter in a pulsating turbulent flow using wavelet analysis

NASA Astrophysics Data System (ADS)

Laurantzon, F.; Örlü, R.; Segalini, A.; Alfredsson, P. H.

2010-12-01

Vortex flowmeters are commonly employed in technical applications and are obtainable in a variety of commercially available types. However their robustness and accuracy can easily be impaired by environmental conditions, such as inflow disturbances and/or pulsating conditions. Various post-processing techniques of the vortex signal have been used, but all of these methods are so far targeted on obtaining an improved estimate of the time-averaged bulk velocity. Here, on the other hand, we propose, based on wavelet analysis, a straightforward way to utilize the signal from a vortex shedder to extract the time-resolved and thereby the phase-averaged velocity under pulsatile flow conditions. The method was verified with hot-wire and laser Doppler velocimetry measurements.

Examining diseased states in a scaled-up vocal fold model using simultaneous temporally resolved DPIV and pressure measurements

NASA Astrophysics Data System (ADS)

Rogers, Dylan; Wei, Nathaniel; Ringenber, Hunter; Krane, Michael; Wei, Timothy

2017-11-01

This study builds on the parallel presentation of Ringenberg, et al. (APS-DFD 2017) involving simultaneous, temporally and spatially resolved flow and pressure measurements in a scaled-up vocal fold model. In this talk, data from experiments replicating characteristics of diseased vocal folds are presented. This begins with vocal folds that do not fully close and continues with asymmetric oscillations. Data are compared to symmetric, i.e. `healthy', oscillatory motions presented in the companion talk. Having pressure and flow data for individual as well as phase averaged oscillations for these diseased cases highlights the potential for aeroacoustic analysis in this complex system. Supported by NIH Grant No. 2R01 DC005642-11.

NASA-Chinese Aeronautical Establishment (CAE) Symposium

NASA Technical Reports Server (NTRS)

1986-01-01

Several topics relative to combustion research are discussed. A numerical study of combustion processes in afterburners; the modeling of turbulent, reactive flow; gas turbine research; modeling of dilution jet flow fields; and chemical shock tubes as tools for studying high-temperature chemical kinetics are among the topics covered.

Purely-elastic flow instabilities and elastic turbulence in microfluidic cross-slot devices

PubMed Central

Sousa, P. C.; Pinho, F. T.

2018-01-01

We experimentally investigate the dynamics of viscoelastic fluid flows in cross-slot microgeometries under creeping flow conditions. We focus on the unsteady flow regime observed at high Weissenberg numbers (Wi) with the purpose of understanding the underlying flow signature of elastic turbulence. The effects of the device aspect ratio and fluid rheology on the unsteady flow state are investigated. Visualization of the flow patterns and time-resolved micro-particle image velocimetry were carried out to study the fluid flow behavior for a wide range of Weissenberg numbers. A periodic flow behavior is observed at low Weissenberg numbers followed by a more complex dynamics as Wi increases, eventually leading to the onset of elastic turbulence for very high Weissenberg numbers. PMID:29376533

Validation of SIV measurements of turbulent characteristics in the separation region

NASA Astrophysics Data System (ADS)

Dushin, N. S.; Mikheev, N. I.; Dushina, O. A.; Zaripov, D. I.; Aslaev, A. K.

2017-11-01

Temporally and spatially resolved 2D measurements are important for the studies of complex turbulent flows. The recently developed SIV technique (Smoke Image Velocimetry), which is superior to PIV in some cases, can be used for this purpose. SIV validation results are presented for the steady turbulent backward-facing step flow measurements. Velocity profiles and Reynolds stress profiles are given for the regions of oncoming flow, reverse flow, flow reattachment and relaxation. The Reynolds number based on the step height and oncoming flow velocity at the boundary layer edge was Reh = 4834. The obtained data have been compared to LDA measurements and DNS.

Quantitative flow and velocity measurements of pulsatile blood flow with 4D-DSA

NASA Astrophysics Data System (ADS)

Shaughnessy, Gabe; Hoffman, Carson; Schafer, Sebastian; Mistretta, Charles A.; Strother, Charles M.

2017-03-01

Time resolved 3D angiographic data from 4D DSA provides a unique environment to explore physical properties of blood flow. Utilizing the pulsatility of the contrast waveform, the Fourier components can be used to track the waveform motion through vessels. Areas of strong pulsatility are determined through the FFT power spectrum. Using this method, we find an accuracy from 4D-DSA flow measurements within 7.6% and 6.8% RMSE of ICA PCVIPR and phantom flow probe validation measurements, respectively. The availability of velocity and flow information with fast acquisition could provide a more quantitative approach to treatment planning and evaluation in interventional radiology.

Continuous Flow Liquid Microjunction Surface Sampling Probe Connected On-line with HPLC/MS for Spatially Resolved Analysis of Small Molecules and Proteins

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

Van Berkel, Gary J; Kertesz, Vilmos

RATIONALE: A continuous flow liquid microjunction surface sampling probe extracts soluble material from surfaces for direct ionization and detection by MS. Demonstrated here is the on-line coupling of such a probe with HPLC/MS enabling extraction, separation and detection of small molecules and proteins from surfaces in a spatially resolved (~0.5 mm diameter spots) manner. Methods: A continuous flow liquid microjunction surface sampling probe was connected to a 6-port, 2-position valve for extract collection and injection to an HPLC column. A QTRAP 5500 hybrid triple quadrupole linear ion trap equipped with a Turbo V ion source operated in positive ESI modemore » was used for all experiments. System operation was tested with extraction, separation and detection of propranolol and associated metabolites from drug dosed tissues and proteins from dried sheep blood spots on paper. Results: Confirmed in the tissue were the parent drug and two different hydroxypropranolol glucuronides. The mass spectrometric response for these compounds from different locations in the liver showed an increase with increasing extraction time (5, 20 and 40 s extractions). For on-line separation and detection/identification of extracted proteins from dried sheep blood spots, two major protein peaks dominated the chromatogram and could be correlated with the expected masses for the hemoglobin and chains. Conclusions: Spatially resolved sampling, separation, and detection of small molecules and proteins from surfaces can be accomplished using a continuous flow liquid microjunction surface sampling probe coupled on-line with HPLC/MS detection.« less

Consideration of grain packing in granular iron treatability studies

NASA Astrophysics Data System (ADS)

Firdous, R.; Devlin, J. F.

2014-08-01

Commercial granular iron (GI) is light steel that is used in Permeable Reactive Barriers (PRBs). Investigations into the reactivity of GI have focused on its chemical nature and relatively little direct work has been done to account for the effects of grain shape and packing. Both of these factors are expected to influence available grain surface area, which is known to correlate to reactivity. Commercial granular iron grains are platy and therefore pack in preferential orientations that could affect solution access to the surface. Three packing variations were investigated using Connelly Iron and trichloroethylene (TCE). Experimental kinetic data showed reaction rates 2-4 times higher when grains were packed with long axes preferentially parallel to flow (VP) compared to packings with long axes preferentially perpendicular to flow (HP) or randomly arranged (RP). The variations were found to be explainable by variations in reactive sorption capacities, i.e., sorption to sites where chemical transformations took place. The possibility that the different reactive sorption capacities were related to physical pore-scale differences was assessed by conducting an image analysis of the pore structure of sectioned columns. The analyses suggested that pore-scale factors - in particular the grain surface availability, reflected in the sorption capacity terms of the kinetic model used - could only account for a fraction of the observed reactivity differences between packing types. It is concluded that packing does affect observable reaction rates but that micro-scale features on the grain surfaces, rather than the pore scale characteristics, account for most of the apparent reactivity differences. This result suggests that treatability tests should consider the packing of columns carefully if they are to mimic field performance of PRBs to the greatest extent possible.

Continuous Flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) Method of Measuring Size-Resolved Sea-Salt Particle Fluxes

NASA Astrophysics Data System (ADS)

Meskhidze, N.; Royalty, T. M.; Phillips, B.; Dawson, K. W.; Petters, M. D.; Reed, R.; Weinstein, J.; Hook, D.; Wiener, R.

2017-12-01

The accurate representation of aerosols in climate models requires direct ambient measurement of the size- and composition-dependent particle production fluxes. Here we present the design, testing, and analysis of data collected through the first instrument capable of measuring hygroscopicity-based, size-resolved particle fluxes using a continuous-flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) technique. The different components of the instrument were extensively tested inside the US Environmental Protection Agency's Aerosol Test Facility for sea-salt and ammoniums sulfate particle fluxes. The new REA system design does not require particle accumulation, therefore avoids the diffusional wall losses associated with long residence times of particles inside the air collectors of the traditional REA devices. The Hy-Res REA system used in this study includes a 3-D sonic anemometer, two fast-response solenoid valves, two Condensation Particle Counters (CPCs), a Scanning Mobility Particle Sizer (SMPS), and a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA). A linear relationship was found between the sea-salt particle fluxes measured by eddy covariance and REA techniques, with comparable theoretical (0.34) and measured (0.39) proportionality constants. The sea-salt particle detection limit of the Hy-Res REA flux system is estimated to be 6x105 m-2s-1. For the conditions of ammonium sulfate and sea-salt particles of comparable source strength and location, the continuous-flow Hy-Res REA instrument was able to achieve better than 90% accuracy of measuring the sea-salt particle fluxes. In principle, the instrument can be applied to measure fluxes of particles of variable size and distinct hygroscopic properties (i.e., mineral dust, black carbon, etc.).

Application of infrared thermography for online monitoring of wall temperatures in inductively coupled plasma torches with conventional and low-flow gas consumption

NASA Astrophysics Data System (ADS)

Engelhard, Carsten; Scheffer, Andy; Maue, Thomas; Hieftje, Gary M.; Buscher, Wolfgang

2007-10-01

Inductively coupled plasma (ICP) sources typically used for trace elemental determination and speciation were investigated with infrared (IR) thermography to obtain spatially resolved torch temperature distributions. Infrared thermographic imaging is an excellent tool for the monitoring of temperatures in a fast and non-destructive way. This paper presents the first application of IR thermography to inductively coupled plasma torches and the possibility to investigate temperatures and thermal patterns while the ICP is operating and despite background emission from the plasma itself. A fast and easy method is presented for the determination of temperature distributions and stress features within ICP torches. Two different ICP operating torches were studied: a commercially available Fassel-type ICP unit with 14 L min - 1 total Ar consumption and a SHIP torch with the unusually low Ar flow of 0.6 L min - 1 . Spatially resolved infrared images of both torches were obtained and laterally resolved temperature profiles were extracted. After temperature-resolved calibration of the emissivity (between 0.5 and 0.35 at 873-1323 K) and transmission (20% between 3.75 and 4.02 μm) of the fused quartz used in the torch construction, an image correction was applied. Inhomogeneous temperature distributions with locally defined stress areas in the conventional Fassel-type torch were revealed. As a general trend, it was found that the SHIP torch exhibited higher temperatures ( Tmax = 1580 K) than the conventional torch ( Tmax = 730 K). In the former case, torch sites with efficient and inefficient cooling were discovered and the external flow of cooling air (24-48 m s - 1 ) was identified as the limiting factor.

Reactivation of dead sulfide species in lithium polysulfide flow battery for grid scale energy storage.

PubMed

Jin, Yang; Zhou, Guangmin; Shi, Feifei; Zhuo, Denys; Zhao, Jie; Liu, Kai; Liu, Yayuan; Zu, Chenxi; Chen, Wei; Zhang, Rufan; Huang, Xuanyi; Cui, Yi

2017-09-06

Lithium polysulfide batteries possess several favorable attributes including low cost and high energy density for grid energy storage. However, the precipitation of insoluble and irreversible sulfide species on the surface of carbon and lithium (called "dead" sulfide species) leads to continuous capacity degradation in high mass loading cells, which represents a great challenge. To address this problem, herein we propose a strategy to reactivate dead sulfide species by reacting them with sulfur powder with stirring and heating (70 °C) to recover the cell capacity, and further demonstrate a flow battery system based on the reactivation approach. As a result, ultrahigh mass loading (0.125 g cm -3 , 2 g sulfur in a single cell), high volumetric energy density (135 Wh L -1 ), good cycle life, and high single-cell capacity are achieved. The high volumetric energy density indicates its promising application for future grid energy storage.Lithium polysulfide batteries suffer from the precipitation of insoluble and irreversible sulfide species on the surface of carbon and lithium. Here the authors show a reactivation strategy by a reaction with cheap sulfur powder under stirring and heating to recover the cell capacity.

Mineral transformation and biomass accumulation associated with uranium bioremediation at Rifle, Colorado

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

Li, L.; Steefel, C.I.; Williams, K.H.

2009-04-20

Injection of organic carbon into the subsurface as an electron donor for bioremediation of redox-sensitive contaminants like uranium often leads to mineral transformation and biomass accumulation, both of which can alter the flow field and potentially bioremediation efficacy. This work combines reactive transport modeling with a column experiment and field measurements to understand the biogeochemical processes and to quantify the biomass and mineral transformation/accumulation during a bioremediation experiment at a uranium contaminated site near Rifle, Colorado. We use the reactive transport model CrunchFlow to explicitly simulate microbial community dynamics of iron and sulfate reducers, and their impacts on reaction rates.more » The column experiment shows clear evidence of mineral precipitation, primarily in the form of calcite and iron monosulfide. At the field scale, reactive transport simulations suggest that the biogeochemical reactions occur mostly close to the injection wells where acetate concentrations are highest, with mineral precipitate and biomass accumulation reaching as high as 1.5% of the pore space. This work shows that reactive transport modeling coupled with field data can be an effective tool for quantitative estimation of mineral transformation and biomass accumulation, thus improving the design of bioremediation strategies.« less

Effects of the electrical parameters and gas flow rate on the generation of reactive species in liquids exposed to atmospheric pressure plasma jets

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

Baek, Eun Jeong; Joh, Hea Min; Kim, Sun Ja

2016-07-15

In this work, an atmospheric pressure plasma jet was fabricated and studied for plasma–liquid interactions. The plasma jet consists of a quartz-covered pin electrode and outer quartz tube with a tapered nozzle. Using the current–voltage (I-V) and optical emission characteristics of the plasma jet, the plasma density and the speed of the plume were investigated. The optical emission spectra clearly indicated the excited NO, O, OH, N{sub 2}, and N{sub 2}{sup +} in the plasma plumes. Then the plasma jets were applied to the deionized water. We investigated the effects of the operating parameters such as applied voltage, pulse frequency,more » and gas flow rate on the generation of reactive species in the gas and liquid phases. The densities of reactive species including OH radicals were obtained at the plasma–liquid surface and inside the plasma-treated liquids using ultraviolet absorption spectroscopy and chemical probe method. The nitrite concentration was detected by Griess assay. The data are very suggestive that there is a strong correlation among the production of reactive oxygen and nitrogen species (RONS) in the plasmas and liquids.« less

Mineral transformation and biomass accumulation associated with uranium bioremediation at Rifle, Colorado.

PubMed

Li, Li; Steefel, Carl I; Williams, Kenneth H; Wilkins, Michael J; Hubbard, Susan S

2009-07-15

Injection of organic carbon into the subsurface as an electron donor for bioremediation of redox-sensitive contaminants like uranium often leads to mineral transformation and biomass accumulation, both of which can alter the flow field and potentially bioremediation efficacy. This work combines reactive transport modeling with a column experiment and field measurements to understand the biogeochemical processes and to quantify the biomass and mineral transformation/accumulation during a bioremediation experiment at a uranium contaminated site near Rifle, Colorado. We use the reactive transport model CrunchFlow to explicitly simulate microbial community dynamics of iron and sulfate reducers, and their impacts on reaction rates. The column experiment shows clear evidence of mineral precipitation, primarily in the form of calcite and iron monosulfide. At the field scale, reactive transport simulations suggest that the biogeochemical reactions occur mostly close to the injection wells where acetate concentrations are highest, with mineral precipitate and biomass accumulation reaching as high as 1.5% of the pore space. This work shows that reactive transport modeling coupled with field data can bean effective tool for quantitative estimation of mineral transformation and biomass accumulation, thus improving the design of bioremediation strategies.

An overview of permeable reactive barriers for in situ sustainable groundwater remediation.

PubMed

Obiri-Nyarko, Franklin; Grajales-Mesa, S Johana; Malina, Grzegorz

2014-09-01

Permeable reactive barriers (PRBs) are one of the innovative technologies widely accepted as an alternative to the 'pump and treat' (P&T) for sustainable in situ remediation of contaminated groundwater. The concept of the technology involves the emplacement of a permeable barrier containing reactive materials across the flow path of the contaminated groundwater to intercept and treat the contaminants as the plume flows through it under the influence of the natural hydraulic gradient. Since the invention of PRBs in the early 1990s, a variety of materials has been employed to remove contaminants including heavy metals, chlorinated solvents, aromatic hydrocarbons, and pesticides. Contaminant removal is usually accomplished via processes such as adsorption, precipitation, denitrification and biodegradation. Despite wide acknowledgment, there are still unresolved issues about long term-performance of PRBs, which have somewhat affected their acceptability and full-scale implementation. The current paper presents an overview of the PRB technology, which includes the state of art, the merits and limitations, the reactive media used so far, and the mechanisms employed to transform or immobilize contaminants. The paper also looks at the design, construction and the long-term performance of PRBs. Copyright © 2014 Elsevier Ltd. All rights reserved.

Emerging biomedical applications of time-resolved fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Lakowicz, Joseph R.; Szmacinski, Henryk; Koen, Peter A.

1994-07-01

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods are resulting in the rapid migration of time-resolved fluorescence to the clinical chemistry lab, to the patient's bedside, to flow cytometers, to the doctor's office, and even to home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy, and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. In this overview paper we attempt to describe some of the opportunities available using chemical sensing based on fluorescence lifetimes, and to predict those applications of lifetime-based sensing which are most likely in the near future.

Fluid Flow Characterization of High Turbulent Intensity Compressible Flow Using Particle Image Velocimetry

DTIC Science & Technology

2015-08-01

completed in order to begin further experimentation. A 10 kHz Time Resolved Particle Image Velocimetry (TR-PIV) system and a 3 kHz Planer Laser ...9 2.3.2 Planar Laser Induced Fluorescence (PLIF...35 Figure 4.4: Solenoid valve (a), proportional control valve (b) and flowmeter (c) ...................................... 36 Figure 4.5

A stopped-flow calorimeter for biochemical applications.

PubMed Central

Howarth, J V; Millar, N C; Gutfreund, H

1987-01-01

A rapid-response stopped-flow calorimeter for small samples of reagents is described. The construction, performance characteristics and operational limitations are described, along with an example of its ability to resolve the kinetics of an enzyme-catalysed hydrolysis. It is thought likely that the method would find useful application in a variety of chemical and biochemical investigations. PMID:3435478

On the large eddy simulation of turbulent flows in complex geometry

NASA Technical Reports Server (NTRS)

Ghosal, Sandip

1993-01-01

Application of the method of Large Eddy Simulation (LES) to a turbulent flow consists of three separate steps. First, a filtering operation is performed on the Navier-Stokes equations to remove the small spatial scales. The resulting equations that describe the space time evolution of the 'large eddies' contain the subgrid-scale (sgs) stress tensor that describes the effect of the unresolved small scales on the resolved scales. The second step is the replacement of the sgs stress tensor by some expression involving the large scales - this is the problem of 'subgrid-scale modeling'. The final step is the numerical simulation of the resulting 'closed' equations for the large scale fields on a grid small enough to resolve the smallest of the large eddies, but still much larger than the fine scale structures at the Kolmogorov length. In dividing a turbulent flow field into 'large' and 'small' eddies, one presumes that a cut-off length delta can be sensibly chosen such that all fluctuations on a scale larger than delta are 'large eddies' and the remainder constitute the 'small scale' fluctuations. Typically, delta would be a length scale characterizing the smallest structures of interest in the flow. In an inhomogeneous flow, the 'sensible choice' for delta may vary significantly over the flow domain. For example, in a wall bounded turbulent flow, most statistical averages of interest vary much more rapidly with position near the wall than far away from it. Further, there are dynamically important organized structures near the wall on a scale much smaller than the boundary layer thickness. Therefore, the minimum size of eddies that need to be resolved is smaller near the wall. In general, for the LES of inhomogeneous flows, the width of the filtering kernel delta must be considered to be a function of position. If a filtering operation with a nonuniform filter width is performed on the Navier-Stokes equations, one does not in general get the standard large eddy equations. The complication is caused by the fact that a filtering operation with a nonuniform filter width in general does not commute with the operation of differentiation. This is one of the issues that we have looked at in detail as it is basic to any attempt at applying LES to complex geometry flows. Our principal findings are summarized.

Rapid on-site sensing aflatoxin B1 in food and feed via a chromatographic time-resolved fluoroimmunoassay.

PubMed

Zhang, Zhaowei; Tang, Xiaoqian; Wang, Du; Zhang, Qi; Li, Peiwu; Ding, Xiaoxia

2015-01-01

Aflatoxin B1 poses grave threats to food and feed safety due to its strong carcinogenesis and toxicity, thus requiring ultrasensitive rapid on-site determination. Herein, a portable immunosensor based on chromatographic time-resolved fluoroimmunoassay was developed for sensitive and on-site determination of aflatoxin B1 in food and feed samples. Chromatographic time-resolved fluoroimmunoassay offered a magnified positive signal and low signal-to-noise ratio in time-resolved mode due to the absence of noise interference caused by excitation light sources. Compared with the immunosensing performance in previous studies, this platform demonstrated a wider dynamic range of 0.2-60 μg/kg, lower limit of detection from 0.06 to 0.12 µg/kg, and considerable recovery from 80.5% to 116.7% for different food and feed sample matrices. It was found to be little cross-reactivity with other aflatoxins (B2, G1, G2, and M1). In the case of determination of aflatoxin B1 in peanuts, corn, soy sauce, vegetable oil, and mouse feed, excellent agreement was found when compared with aflatoxin B1 determination via the conversational high-performance liquid chromatography method. The chromatographic time-resolved fluoroimmunoassay affords a powerful alternative for rapid on-site determination of aflatoxin B1 and holds a promise for food safety in consideration of practical food safety and environmental monitoring.

Rapid On-Site Sensing Aflatoxin B1 in Food and Feed via a Chromatographic Time-Resolved Fluoroimmunoassay

PubMed Central

Wang, Du; Zhang, Qi; Li, Peiwu; Ding, Xiaoxia

2015-01-01

Aflatoxin B1 poses grave threats to food and feed safety due to its strong carcinogenesis and toxicity, thus requiring ultrasensitive rapid on-site determination. Herein, a portable immunosensor based on chromatographic time-resolved fluoroimmunoassay was developed for sensitive and on-site determination of aflatoxin B1 in food and feed samples. Chromatographic time-resolved fluoroimmunoassay offered a magnified positive signal and low signal-to-noise ratio in time-resolved mode due to the absence of noise interference caused by excitation light sources. Compared with the immunosensing performance in previous studies, this platform demonstrated a wider dynamic range of 0.2-60 μg/kg, lower limit of detection from 0.06 to 0.12 µg/kg, and considerable recovery from 80.5% to 116.7% for different food and feed sample matrices. It was found to be little cross-reactivity with other aflatoxins (B2, G1, G2, and M1). In the case of determination of aflatoxin B1 in peanuts, corn, soy sauce, vegetable oil, and mouse feed, excellent agreement was found when compared with aflatoxin B1 determination via the conversational high-performance liquid chromatography method. The chromatographic time-resolved fluoroimmunoassay affords a powerful alternative for rapid on-site determination of aflatoxin B1 and holds a promise for food safety in consideration of practical food safety and environmental monitoring. PMID:25874803

Hepatitis B Virus Reactivation in the Setting of Cancer Chemotherapy and Other Immunosuppressive Drug Therapy

PubMed Central

Gonzalez, Stevan A.; Perrillo, Robert P.

2016-01-01

Hepatitis B virus reactivation (HBVr) is an important complication of immunosuppressive drug therapy (ISDT). It can occur with active or resolved hepatitis B virus (HBV) infection with a clinical spectrum that ranges from mild elevations in liver tests to fulminant hepatic failure. The risk of it occurring is determined by the interplay between HBV serological status, level of viremia, and the immunosuppressive potency of the drug(s) used. Reactivation is most common during treatment of hematologic malignancies but also occurs with chemotherapy for breast cancer and numerous other solid organ malignancies, organ transplant, and immune suppression for nonmalignant conditions. The expansion of new biologic treatments for malignant and nonmalignant disorders has enlarged the population at risk. Increased awareness of HBVr among healthcare providers who prescribe ISDT, adoption of routine HBV screening, and linking the results of screening to antiviral prophylaxis are needed to reduce the incidence of this potentially fatal but preventable disorder. PMID:27190320

Remediating Contaminant Plumes in Groundwater with Shallow Excavations Containing Coarse Reactive Media.

PubMed

Hudak, Paul F

2018-02-01

A groundwater flow and mass transport model tested the capability of shallow excavations filled with coarse, reactive media to remediate a hypothetical unconfined aquifer with a maximum saturated thickness of 5 m. Modeled as contaminant sinks, the rectangular excavations were 10 m downgradient of an initial contaminant plume originating from a source at the top of the aquifer. The initial plume was approximately 259 m long, 23 m wide, and 5 m thick, with a downgradient tip located approximately 100 m upgradient of the site boundary. The smallest trench capable of preventing offsite migration was 11 m long (measured perpendicular to groundwater flow), 4 m wide (measured parallel to groundwater flow), and 3 m deep. Results of this study suggest that shallow trenches filled with coarse filter media that partially penetrate unconfined aquifers may be a viable alternative for remediating contaminated groundwater at some sites.

Photoredox activation of carbon dioxide for amino acid synthesis in continuous flow

NASA Astrophysics Data System (ADS)

Seo, Hyowon; Katcher, Matthew H.; Jamison, Timothy F.

2017-05-01

Although carbon dioxide (CO2) is highly abundant, its low reactivity has limited its use in chemical synthesis. In particular, methods for carbon-carbon bond formation generally rely on two-electron mechanisms for CO2 activation and require highly activated reaction partners. Alternatively, radical pathways accessed via photoredox catalysis could provide new reactivity under milder conditions. Here we demonstrate the direct coupling of CO2 and amines via the single-electron reduction of CO2 for the photoredox-catalysed continuous flow synthesis of α-amino acids. By leveraging the advantages of utilizing gases and photochemistry in flow, a commercially available organic photoredox catalyst effects the selective α-carboxylation of amines that bear various functional groups and heterocycles. The preliminary mechanistic studies support CO2 activation and carbon-carbon bond formation via single-electron pathways, and we expect that this strategy will inspire new perspectives on using this feedstock chemical in organic synthesis.

DC discharges in atmospheric air for bio-decontamination - spectroscopic methods for mechanism identification

NASA Astrophysics Data System (ADS)

Machala, Z.; Jedlovský, I.; Chládeková, L.; Pongrác, B.; Giertl, D.; Janda, M.; Ikurová, L. Å.; Polčic, P.

2009-08-01

Three types of DC electrical discharges in atmospheric air (streamer corona, transient spark and glow discharge) were tested for bio-decontamination of bacteria and yeasts in water solution, and spores on surfaces. Static vs. flowing treatment of contaminated water were compared, in the latter the flowing water either covered the grounded electrode or passed through the high voltage needle electrode. The bacteria were killed most efficiently in the flowing regime by transient spark. Streamer corona was efficient when the treated medium flew through the active corona region. The spores on plastic foil and paper surfaces were successfully inactivated by negative corona. The microbes were handled and their population evaluated by standard microbiology cultivation procedures. The emission spectroscopy of the discharges and TBARS (thiobarbituric acid reactive substances) absorption spectrometric detection of the products of lipid peroxidation of bacterial cell membranes indicated a major role of radicals and reactive oxygen species among the bio-decontamination mechanisms.

PDF methods for combustion in high-speed turbulent flows

NASA Technical Reports Server (NTRS)

Pope, Stephen B.

1995-01-01

This report describes the research performed during the second year of this three-year project. The ultimate objective of the project is extend the applicability of probability density function (pdf) methods from incompressible to compressible turbulent reactive flows. As described in subsequent sections, progress has been made on: (1) formulation and modelling of pdf equations for compressible turbulence, in both homogeneous and inhomogeneous inert flows; and (2) implementation of the compressible model in various flow configurations, namely decaying isotropic turbulence, homogeneous shear flow and plane mixing layer.

Varicella-Zoster-Mediated Radiculitis Reactivation following Cervical Spine Surgery: Case Report and Review of the Literature

PubMed Central

Drazin, Doniel; Hanna, George; Shweikeh, Faris; Jeswani, Sunil; Lovely, Leah; Sokolov, Richard; Liu, John C.

2013-01-01

Varicella-zoster virus and herpes simplex virus types 1 and 2 are neurotropic viruses that can be reactivated after a surgical or stressful intervention. Although such cases are uncommon, consequences can be debilitating, and variable treatment responses merit consideration. We describe a 41-year-old male with a history of varicella-mediated skin eruptions, who presented with continuing right arm pain, burning, and numbness in a C6 dermatomal distribution following a C5-6 anterior cervical discectomy and fusion and epidural steroid injections. The operative course was uncomplicated and he was discharged home on postoperative day 1. Approximately ten days after surgery, the patient presented to the emergency department complaining of severe pain in his right upper extremity and a vesicular rash from his elbow to his second digit. He was started on Acyclovir and discharged home. On outpatient follow-up, his rash had resolved though his pain continued. The patient was started on a neuromodulating agent for chronic pain. This case adds to the limited literature regarding this rare complication, brings attention to the symptoms for proper diagnosis and treatment, and emphasizes the importance of prompt antiviral therapy. We suggest adding a neuromodulating agent to prevent long-term sequelae and resolve acute symptoms. PMID:24251050

NO 2 oxidation reactivity and burning mode of diesel particulates

DOE PAGES

Strzelec, Andrea; Vander Wal, Randy L.; Thompson, Thomas N.; ...

2016-03-24

The NO 2 oxidation kinetics and burning mode for diesel particulate from light-duty and medium-duty engines fueled with either ultra low sulfur diesel or soy methyl ester biodiesel blends have been investigated and are shown to be significantly different from oxidation by O 2. Oxidation kinetics were measured using a flow-through packed bed microreactor for temperature programmed reactions and isothermal differential pulsed oxidation reactions. The burning mode was evaluated using the same reactor system for flowing BET specific surface area measurements and HR-TEM with fringe analysis to evaluate the nanostructure of the nascent and partially oxidized particulates. The low activationmore » energy measured, specific surface area progression with extent of oxidation, HR-TEM images and difference plots of fringe length and tortuosity paint a consistent picture of higher reactivity for NO 2, which reacts indiscriminately immediately upon contact with the surface, leading to the Zone I or shrinking core type oxidation. In comparison, O 2 oxidation is shown to have relatively lower reactivity, preferentially attacking highly curved lamella, which are more reactive due to bond strain, and short lamella, which have a higher proportion of more reactive edge sites. Furthermore, this preferential oxidation leads to Zone II type oxidation, where solid phase diffusion of oxygen via pores contributes significantly to slowing the overall oxidation rate, by comparison.« less

Clinico-immunochemical studies on airborne Areca catechu L. Pollen, a probable risk factor in emergency asthma hospitalization from Eastern India.

PubMed

Chakraborty, Pampa; Mandal, Jyotshna; Sarkar, Eva; Chowdhury, Indrani; Gupta-Bhattacharya, Swati

2009-01-01

The pollen grain of the Areca catechu L. tree is airborne and allergenic. This study aimed to know the role of this pollen as a source of aeroallergen with effect on emergency asthma hospitalization, to isolate its important allergic fraction and to check its cross-reaction with betel nut. Areca pollen was monitored with a Burkard sampler. Determination of allergenic activities was studied by in vivo and in vitro analyses. Asthma hospitalization data were collected from two nearby hospitals. The pollen extract was fractionated by a combination of DEAE-Sephadex and Sephacryl S-200 column. The protein components were observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-reactivity of Areca pollen and betel nut was shown by IgE enzyme-linked immunosorbent assay (ELISA) inhibition. The Areca pollen was perennially airborne. Skin test results of respiratory allergic patients showed 38.6% positivity. The detected aeroallergen spots in particle immunoblotting correlated significantly with airborne pollen count. Areca pollen showed a significant positive correlation with asthma hospitalization. There are 6 IgE-reactive protein components in the whole-pollen extract. IgE-reactive fraction 1 was resolved into 4 subfractions. Subfraction 1a showing IgE reactivity contained 3 protein components, among which 2 of 48 and 118 kDa were IgE reactive. The 48-kDa component was reported to be cross-reactive with other palm pollen types. In IgE ELISA inhibition, the betel nut extract showed 50% inhibition with about 110 ng/ml concentration. A. catechu pollen is a significant contributor to the aeroallergen load in India. Its partially purified IgE-reactive fraction may be useful in therapeutics. The betel nut extract showed remarkable cross-reactivity with Areca pollen. Copyright (C) 2009 S. Karger AG, Basel.

Evaluation of incremental reactivity and its uncertainty in Southern California.

PubMed

Martien, Philip T; Harley, Robert A; Milford, Jana B; Russell, Armistead G

2003-04-15

The incremental reactivity (IR) and relative incremental reactivity (RIR) of carbon monoxide and 30 individual volatile organic compounds (VOC) were estimated for the South Coast Air Basin using two photochemical air quality models: a 3-D, grid-based model and a vertically resolved trajectory model. Both models include an extended version of the SAPRC99 chemical mechanism. For the 3-D modeling, the decoupled direct method (DDM-3D) was used to assess reactivities. The trajectory model was applied to estimate uncertainties in reactivities due to uncertainties in chemical rate parameters, deposition parameters, and emission rates using Monte Carlo analysis with Latin hypercube sampling. For most VOC, RIRs were found to be consistent in rankings with those produced by Carter using a box model. However, 3-D simulations show that coastal regions, upwind of most of the emissions, have comparatively low IR but higher RIR than predicted by box models for C4-C5 alkenes and carbonyls that initiate the production of HOx radicals. Biogenic VOC emissions were found to have a lower RIR than predicted by box model estimates, because emissions of these VOC were mostly downwind of the areas of primary ozone production. Uncertainties in RIR of individual VOC were found to be dominated by uncertainties in the rate parameters of their primary oxidation reactions. The coefficient of variation (COV) of most RIR values ranged from 20% to 30%, whereas the COV of absolute incremental reactivity ranged from about 30% to 40%. In general, uncertainty and variability both decreased when relative rather than absolute reactivity metrics were used.

Hydraulic Jumps, Waves and Other Flow Features Found by Modeling Stably-Stratified Flows in the Salt Lake Valley

NASA Astrophysics Data System (ADS)

Chen, Y.; Ludwig, F.; Street, R.

2003-12-01

The Advanced Regional Prediction System (ARPS) was used to simulate weak synoptic wind conditions with stable stratification and pronounced drainage flow at night in the vicinity of the Jordan Narrows at the south end of Salt Lake Valley. The simulations showed the flow to be quite complex with hydraulic jumps and internal waves that make it essential to use a complete treatment of the fluid dynamics. Six one-way nested grids were used to resolve the topography; they ranged from 20-km grid spacing, initialized by ETA 40-km operational analyses down to 250-m horizontal resolution and 200 vertically stretched levels to a height of 20 km, beginning with a 10-m cell at the surface. Most of the features of interest resulted from interactions with local terrain features, so that little was lost by using one-way nesting. Canyon, gap, and over-terrain flows have a large effect on mixing and vertical transport, especially in the regions where hydraulic jumps are likely. Our results also showed that the effect of spatial resolution on simulation performance is profound. The horizontal resolution must be such that the smallest features that are likely to have important impact on the flow are spanned by at least a few grid points. Thus, the 250 m minimum resolution of this study is appropriate for treating the effects of features of about 1 km or greater extent. To be consistent, the vertical cell dimension must resolve the same terrain features resolved by the horizontal grid. These simulations show that many of the interesting flow features produce observable wind and temperature gradients at or near the surface. Accordingly, some relatively simple field measurements might be made to confirm that the mixing phenomena that were simulated actually take place in the real atmosphere, which would be very valuable for planning large, expensive field campaigns. The work was supported by the Atmospheric Sciences Program, Office of Biological and Environmental Research, U.S. Department of Energy. The National Energy Research Scientific Computing Center (NERSC) provided computational time. We thank Professor Ming Xue and others at the University of Oklahoma for their help.

Temporal and spatial evolution of EHD particle flow onset in air in a needle-to-plate negative DC corona discharge

NASA Astrophysics Data System (ADS)

Mizeraczyk, J.; Berendt, A.; Podlinski, J.

2016-05-01

In this paper we present images showing the temporal and spatial evolution of the electrohydrodynamic (EHD) flow of dust particles (cigarette smoke) suspended in still air in a needle-to-plate negative DC corona discharge arrangement just after the corona onset, i.e. in the first stage of development of the EHD particle flow. The experimental apparatus for our study of the EHD flow onset consisted of a needle-to-plate electrode arrangement, high voltage power supply and time-resolved EHD imaging system based on 2D time-resolved particle image velocimetry equipment. The time-resolved flow images clearly show the formation of a ball-like flow structure at the needle tip just after the corona discharge onset, and its evolution into a mushroom-like object moving to the collecting electrode. After a certain time, when the mushroom-like object is still present in the interelectrode gap a second mushroom-like object forms near the needle electrode and starts to move towards the collecting electrode. Before the first mushroom-like object reaches the collecting electrode several similar mushroom-like objects can be formed and presented simultaneously in the interelectrode gap. They look like a series of mushroom-like minijets shot from the needle electrode vicinity towards the collecting electrode. The simultaneous presence of mushroom-like minijets in the interelectrode gap in the corona discharge in particle-seeded air resembles the negative-ion-charged ‘clouds’ (induced by the Trichel pulses) traversing simultaneously the interelectrode gap of the corona discharge in air, predicted a long time ago by Loeb, and Lama and Gallo and recently by Dordizadeh et al. Analysing the time behaviours of the mushroom-like minijets and current waveform in the corona discharge in particle-seeded air, we found that the Trichel pulse trains, formed just after the corona onset initiates the mushroom-like minijets. The first stage of development of the EHD particle flow, the area of which is practically limited to the interelectrode duct, ends when the first mushroom-like minijet reaches the collecting electrode.

Resolved simulations of a granular-fluid flow through a check dam with a SPH-DCDEM model

NASA Astrophysics Data System (ADS)

Birjukovs Canelas, Ricardo; Domínguez, Jose; Crespo, Alejandro; Gómez-Gesteira, Moncho; Ferreira, Rui M. L.

2017-04-01

Debris flows represent some of the most relevant phenomena in geomorphological events. Due to the potential destructiveness of such flows, they are the target of a vast amount of research. Experimental research in laboratory facilities or in the field is fundamental to characterize the fundamental rheological properties of these flows and to provide insights on its structure. However, characterizing interparticle contacts and the structure of the motion of the granular phase is difficult, even in controlled laboratory conditions, and possible only for simple geometries. This work addresses the need for a numerical simulation tool applicable to granular-fluid mixtures featuring high spatial and temporal resolution, thus capable of resolving the motion of individual particles, including all interparticle contacts and susceptible to complement laboratory research. The DualSPHysics meshless numerical implementation based on Smoothed Particle Hydrodynamics (SPH) is expanded with a Distributed Contact Discrete Element Method (DCDEM) in order to explicitly solve the fluid and the solid phase. The specific objective is to test the SPH-DCDEM approach by comparing its results with experimental data. An experimental set-up for stony debris flows in a slit check dam is reproduced numerically, where solid material is introduced through a hopper assuring a constant solid discharge for the considered time interval. With each sediment particle possibly undergoing several simultaneous contacts, thousands of time-evolving interactions are efficiently treated due to the model's algorithmic structure and the HPC implementation of DualSPHysics. The results, comprising mainly of retention curves, are in good agreement with the measurements, correctly reproducing the changes in efficiency with slit spacing and density. The encouraging results, coupled with the prospect of so far unique insights into the internal dynamics of a debris flow show the potential of high-performance resolved approaches to the description of the flow and the study of its mitigation strategies. This research as partially supported by Portuguese and European funds, within programs COMPETE2020 and PORL-FEDER, through project PTDC/ECM-HID/6387/2014 granted by the National Foundation for Science and Technology (FCT).

Unsteady Transonic Flow Past Airfoils in Rigid Body Motion.

DTIC Science & Technology

1981-03-01

coordinate system. Numerical experiments show that the scheme is very stable and is able to resolve the highly non- linear transonic effects for flutter...Numerical experiments show that the scheme is very stable and is able to resolve the highly nonlinear transonic effects for flutter analysis within...of attack, the angle between the flight direction and the airfoil chord. The effect of chanqinthe angle of attack of a conventional symmetric airfoil

Extrahepatic portosystemic shunt in congenital absence of the portal vein depicted by time-resolved contrast-enhanced MR angiography.

PubMed

Goo, Hyun Woo

2007-07-01

Congenital absence of the portal vein is a rare malformation in which mesenteric and splenic venous flow bypasses the liver and drains into various sites in the systemic venous system via an extrahepatic portosystemic shunt. In an 11-year-old girl with congenital absence of the portal vein, the detailed anatomy of the extrahepatic portosystemic shunt is demonstrated by time-resolved contrast-enhanced MR angiography.

OH and CH luminescence in opposed flow methane oxy-flames

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

De Leo, Maurizio; Saveliev, Alexei; Kennedy, Lawrence A.

Emission spectroscopy is a 2-D nonintrusive diagnostic technique that offers spatially resolved data for combustion optimization and control. The UV and visible chemiluminescence of the excited radicals CH(A{sup 2}{delta},B{sup 2}{sigma}{sup -}) and OH(A{sup 2}{sigma}{sup +}) is studied experimentally and numerically in opposed-flow diffusion flames of methane and oxygen-enriched air. The oxidized oxygen content is varied from 21 to 100% while the range of the studied strain rates spans from 20 to 40 s{sup -1}. The spectrally resolved imaging is obtained by two different methods: scattering through a grating monochromator and interposition of interference filters along the optical path. Absolute measuredmore » chemiluminescence intensities, coupled with a numerical model based on the opposed flow flame code, are used to evaluate the chemical kinetics of the excited species. The predictions of the selected model are in good agreement with the experimental data over the range of the studied flame conditions. (author)« less