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1
Tayachi, M., A. Rousseau, E. Blayo, N. Goutal, and V. Martin. "Design and analysis of a Schwarz coupling method for a dimensionally heterogeneous problem." International Journal for Numerical Methods in Fluids 75, no. 6 (2014): 446–65. http://dx.doi.org/10.1002/fld.3902.
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Menke, William, Arthur L. Lerner-Lam, Bruce Dubendorff, and Javier Pacheco. "Polarization and coherence of 5 to 30 Hz seismic wave fields at a hard-rock site and their relevance to velocity heterogeneities in the crust." Bulletin of the Seismological Society of America 80, no. 2 (1990): 430–49. http://dx.doi.org/10.1785/bssa0800020430.
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Abstract Except for its very onset, the P wave of earthquakes and chemical explosions observed at two narrow-aperture arrays on hard-rock sites in the Adirondack Mountains have a nearly random polarization. The amount of energy on the vertical, radial, and transverse components is about equal over the frequency range 5 to 30 Hz, for the entire seismogram. The spatial coherence of the seismograms is approximately exp(−cfΔx), where c is in the range 0.4 to 0.7 km−1Hz−1, f is frequency and Δx is the distance between array elements. Vertical, radial, and transverse components were quite coherent over the aperture of the array, indicating that the transverse motion of the compressional wave is a property of relatively large (106 m3) volumes of rock, and not just an anomaly caused by a malfunctioning instrument, poor instrument-rock coupling, or out-crop-scale effects. The spatial coherence is approximately independent of component, epicentral azimuth and range, and whether P- or S-wave coda is being considered, at least for propagation distances between 5 and 170 km. These results imply a strongly and three-dimensionally heterogeneous crust, with near-receiver scattering in the uppermost crust controlling the coherence properties of the waves.
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Dong, Bin, Songlei Jian, and Ke Zuo. "CDE++: Learning Categorical Data Embedding by Enhancing Heterogeneous Feature Value Coupling Relationships." Entropy 22, no. 4 (2020): 391. http://dx.doi.org/10.3390/e22040391.
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Categorical data are ubiquitous in machine learning tasks, and the representation of categorical data plays an important role in the learning performance. The heterogeneous coupling relationships between features and feature values reflect the characteristics of the real-world categorical data which need to be captured in the representations. The paper proposes an enhanced categorical data embedding method, i.e., CDE++, which captures the heterogeneous feature value coupling relationships into the representations. Based on information theory and the hierarchical couplings defined in our previous work CDE (Categorical Data Embedding by learning hierarchical value coupling), CDE++ adopts mutual information and margin entropy to capture feature couplings and designs a hybrid clustering strategy to capture multiple types of feature value clusters. Moreover, Autoencoder is used to learn non-linear couplings between features and value clusters. The categorical data embeddings generated by CDE++ are low-dimensional numerical vectors which are directly applied to clustering and classification and achieve the best performance comparing with other categorical representation learning methods. Parameter sensitivity and scalability tests are also conducted to demonstrate the superiority of CDE++.
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Liu, Rugeng, Chun Hong Mak, Xu Han, et al. "Efficient electronic coupling and heterogeneous charge transport of zero-dimensional Cs4PbBr6 perovskite emitters." Journal of Materials Chemistry A 8, no. 45 (2020): 23803–11. http://dx.doi.org/10.1039/d0ta06076c.
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Zero-dimensional Cs<sub>4</sub>PbBr<sub>6</sub> perovskite emitters exhibit efficient electrogenerated chemiluminescence by virtue of stronger electronic coupling and effective heterogeneous charge transfer.
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Camelliti, Patrizia, Andrew D. McCulloch, and Peter Kohl. "Microstructured Cocultures of Cardiac Myocytes and Fibroblasts: A Two-DimensionalIn VitroModel of Cardiac Tissue." Microscopy and Microanalysis 11, no. 3 (2005): 249–59. http://dx.doi.org/10.1017/s1431927605050506.
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Cardiac myocytes and fibroblasts are essential elements of myocardial tissue structure and function.In vivo, myocytes constitute the majority of cardiac tissue volume, whereas fibroblasts dominate in numbers.In vitro, cardiac cell cultures are usually designed to exclude fibroblasts, which, because of their maintained proliferative potential, tend to overgrow the myocytes. Recent advances in microstructuring of cultures and cell growth on elastic membranes have greatly enhancedin vitropreservation of tissue properties and offer a novel platform technology for producing morein vivo-like models of myocardium. We used microfluidic techniques to grow two-dimensional structured cardiac tissue models, containing both myocytes and fibroblasts, and characterized cell morphology, distribution, and coupling using immunohistochemical techniques.In vitrofindings were compared within vivoventricular cyto-architecture. Cardiac myocytes and fibroblasts, cultured on intersecting 30-μm-wide collagen tracks, acquire anin vivo-like phenotype. Their spatial arrangement closely resembles that observed in native tissue: Strands of highly aligned myocytes are surrounded by parallel threads of fibroblasts. In thisin vitrosystem, fibroblasts form contacts with other fibroblasts and myocytes, which can support homogeneous and heterogeneous gap junctional coupling, as observedin vivo. We conclude that structured cocultures of cardiomyocytes and fibroblasts mimicin vivoventricular tissue organization and provide a novel tool forin vitroresearch into cardiac electromechanical function.
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McGregor, M., and M. A. Wheel. "On the coupling number and characteristic length of micropolar media of differing topology." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2169 (2014): 20140150. http://dx.doi.org/10.1098/rspa.2014.0150.
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In planar micropolar elasticity theory, the degree of micropolarity exhibited by a loaded heterogeneous material is quantified by a dimensionless constitutive parameter, the coupling number. Theoretical predictions of this parameter derived by considering the mechanical behaviour of regular, two-dimensional lattices with straight connectors suggest that its value is dependent on the connectivity or topology of the lattice with the coupling number in a square lattice predicted to be notably higher than in its hexagonal counterpart. A second constitutive parameter reflecting the intrinsic lattice size scale, the characteristic length, is also predicted to be topology-dependent. In this paper, we compare the behaviour of alternative two-dimensional heterogeneous materials in the context of micropolar elasticity. These materials consist of periodic arrays of circular voids within a polymeric matrix rather than a lattice of straight connectors. Two material variants that differ only in their matrix topology are investigated in particular. Values of the additional micropolar constitutive parameters are obtained for each material from both experimental tests and finite-element analyses. The values determined for these parameters, particularly the coupling number, suggest that their topological dependence differs appreciably from the theoretical predictions of the lattice models.
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CAILLERIE, D., and E. SANCHEZ-PALENCIA. "ELASTIC THIN SHELLS: ASYMPTOTIC THEORY IN THE ANISOTROPIC AND HETEROGENEOUS CASES." Mathematical Models and Methods in Applied Sciences 05, no. 04 (1995): 473–96. http://dx.doi.org/10.1142/s0218202595000280.
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Asymptotic (two-scale) methods are used to derive thin shell theory from three-dimensional elasticity. The asymptotic process is done directly for the variational formulations, and existence and uniqueness theorems are given for the shell problem. The asymptotic behavior is the same as that recently derived by the authors using classical hypotheses of shell theory. The role of the subspace G of pure bendings (inextensional motions) appears in a natural way. The asymptotic is basically described by a leading order term contained in G and a lower order term contained in the orthogonal to G. As in anisotropic heterogeneous plates, which exhibit a coupling between flexion and traction, in heterogeneous shells there is coupling between the terms in G and in its orthogonal.
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Salama, Guy, and Bum-Rak Choi. "Images of Action Potential Propagation in Heart." Physiology 15, no. 1 (2000): 33–41. http://dx.doi.org/10.1152/physiologyonline.2000.15.1.33.
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Activation and repolarization across mammalian hearts follow complex three-dimensional pathways that are governed by fiber structure, intercellular coupling, and action potentials (APs) with spatially heterogeneous properties. Voltage-sensitive dyes and imaging techniques offer new insights on how spatiotemporal heterogeneities of APs govern propagation, repolarization, and AV node conduction and help us visualize arrhythmias with previously unattainable details.
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Gigante, Giacomo, and Christian Vergara. "Optimized Schwarz methods for the coupling of cylindrical geometries along the axial direction." ESAIM: Mathematical Modelling and Numerical Analysis 52, no. 4 (2018): 1597–615. http://dx.doi.org/10.1051/m2an/2018039.
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In this work, we focus on the Optimized Schwarz Method for circular flat interfaces and geometric heterogeneous coupling arising when cylindrical geometries are coupled along the axial direction. In the first case, we provide a convergence analysis for the diffusion-reaction problem and jumping coefficients and we apply the general optimization procedure developed in Gigante and Vergara (Numer. Math. 131 (2015) 369–404). In the numerical simulations, we discuss how to choose the range of frequencies in the optimization and the influence of the Finite Element and projection errors on the convergence. In the second case, we consider the coupling between a three-dimensional and a one-dimensional diffusion-reaction problem and we develop a new optimization procedure. The numerical results highlight the suitability of the theoretical findings.
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Miao, Hui, Kelong Ma, Shiwei Hu, Ruiqian Li, Lin Sun, and Yumin Cui. "Aerobic Oxidative Coupling of Aniline Catalyzed by One-Dimensional Manganese Hydroxide Nanomaterials." Synlett 30, no. 05 (2019): 552–56. http://dx.doi.org/10.1055/s-0037-1612108.
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The aerobic oxidative coupling of aniline is an effective process for producing aromatic azo compounds, which are widely used in the organic chemical industry. The development of heterogeneous catalysts for this reaction would be advantageous because of their recyclability and convenience in posttreatment. In this work, one-dimensional Mn(OH)2 nanostructure with various shapes were synthesized through the adjustment of various surfactants. The as-synthesized Mn(OH)2 nanobelts and nanowires showed superior catalytic activity in the activation of oxygen and aniline. Aromatic azo compounds with a variety of substituents were produced through the coupling of the corresponding anilines without additives under ambient conditions.
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Tramontana, Fabio, Laura Gardini, Roberto Dieci, and Frank Westerhoff. "The Emergence ofBull and BearDynamics in a Nonlinear Model of Interacting Markets." Discrete Dynamics in Nature and Society 2009 (2009): 1–30. http://dx.doi.org/10.1155/2009/310471.
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We develop a three-dimensional nonlinear dynamic model in which the stock markets of two countries are linked through the foreign exchange market. Connections are due to the trading activity of heterogeneous speculators. Using analytical and numerical tools, we seek to explore how the coupling of the markets may affect the emergence ofbull and bearmarket dynamics. The dimension of the model can be reduced by restricting investors' trading activity, which enables the dynamic analysis to be performed stepwise, from low-dimensional cases up to the full three-dimensional model. In our paper we focus mainly on the dynamics of the one- and two- dimensional cases, with numerical experiments and some analytical results, and also show that the main features persist in the three-dimensional model.
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Qu, Zhilin. "Dynamical effects of diffusive cell coupling on cardiac excitation and propagation: a simulation study." American Journal of Physiology-Heart and Circulatory Physiology 287, no. 6 (2004): H2803—H2812. http://dx.doi.org/10.1152/ajpheart.00299.2004.
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Cell coupling is considered to be important for cardiac action potential propagation and arrhythmogenesis. We carried out computer simulations to investigate the effects of stimulation strength and cell-to-cell coupling on action potential duration (APD) restitution, APD alternans, and stability of reentry in models of isolated cell, one-dimensional cable, and two-dimensional tissue. Phase I formulation of the Luo and Rudy action potential model was used. We found that stronger stimulation resulted in a shallower APD restitution curve and onset of APD alternans at a faster pacing rate. Reducing diffusive coupling between cells prolonged APD. Weaker diffusive currents along the direction of propagation steepened APD restitution and caused APD alternans to occur at a slower pacing rate in tissue. Diffusive current due to curvature changed APD but had little effect on APD restitution slope and onset of instability. Heterogeneous cell coupling caused APD inhomogeneities in space. Reduction in coupling strength either uniformly or randomly had little effect on the rotation period and stability of a reentry, but random cell decoupling slowed the rotation period and, thus, stabilized the reentry, preventing it from breaking up into multiple waves. Therefore, in addition to its effects on action potential conduction velocity, diffusive cell coupling also affects APD in a rate-dependent manner, causes electrophysiological heterogeneities, and thus modulates the dynamics of cardiac excitation. These effects are brought about by the modulation of ionic current activation and inactivation.
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Grabmaier, Sebastian, Matthias Jüttner, and Wolfgang Rucker. "Coupling of finite element method and integral formulation for vector Helmholtz equation." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 37, no. 4 (2018): 1405–17. http://dx.doi.org/10.1108/compel-08-2017-0346.
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Purpose Considering the vector Helmholtz equation in three dimensions, this paper aims to present a novel approach for coupling the finite element method and a boundary integral formulation. It is demonstrated that the method is well-suited for many realistic three-dimensional problems in high-frequency engineering. Design/methodology/approach The formulation is based on partial solutions fulfilling the global boundary conditions and the iterative interaction between them. In comparison to other coupling formulation, this approach avoids the typical singularity in the integral kernels. The approach applies ideas from domain decomposition techniques and is implemented for a parallel calculation. Findings Using confirming elements for the trace space and default techniques to realize the infinite domain, no additional loss in accuracy is introduced compared to a monolithic finite element method approach. Furthermore, the degree of coupling between the finite element method and the integral formulation is reduced. The accuracy and convergence rate are demonstrated on a three-dimensional antenna model. Research limitations/implications This approach introduces additional degrees of freedom compared to the classical coupling approach. The benefit is a noticeable reduction in the number of iterations when the arising linear equation systems are solved separately. Practical implications This paper focuses on multiple heterogeneous objects surrounded by a homogeneous medium. Hence, the method is suited for a wide range of applications. Originality/value The novelty of the paper is the proposed formulation for the coupling of both methods.
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Chen, Junjie, and Baofang Liu. "CFD Modeling and Operation Strategies for Hetero-/Homogeneous Combustion of Methane-Air Mixtures in Catalytic Microreactors Using Detailed Chemical Kinetics." Chemical Product and Process Modeling 11, no. 4 (2016): 291–304. http://dx.doi.org/10.1515/cppm-2015-0053.
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Abstract The hetero-/homogeneous combustion of methane-air mixtures in platinum-coated microreactors was investigated by means of two-dimensional CFD (computational fluid dynamics) simulations with detailed chemical reaction schemes, detailed species transport, and heat transfer mechanisms in the solid wall. Detailed homogeneous and heterogeneous chemical kinetic mechanisms are employed to describe the chemistry. The effects of the reactor size, inlet velocity and feed composition were elucidated. Operation strategies for controlling the heterogeneous and homogeneous chemistry in heterogeneous-homogeneous microreactors were developed. Simulations using these mechanisms suggested that homogeneous chemistry can be sustained for gaps well below the quenching distance because of enhanced catalyst-induced heating. This finding has very important ramifications for catalyst safety and lifetime, as well as can be used to produce chemicals, e. g. in oxidative coupling and oxidative dehydrogenation reactions. The proportion of heterogeneous and homogeneous contributions depends strongly upon the reactor operating conditions. Reactor size plays a vital role in the homogeneous chemistry contribution. Smaller reactors result in reduced homogeneous chemistry contribution. Pure heterogeneous chemistry can occur under certain proper conditions, such as heat loss/heat exchange rates, feed compositions, and flow rates. The competition or synergism between homogeneous and heterogeneous chemistry was delineated.
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Fonteyn, D., and N. Larsen. "Detailed PSC formation in a two-dimensional chemical transport model of the stratosphere." Annales Geophysicae 14, no. 3 (1996): 315–28. http://dx.doi.org/10.1007/s00585-996-0315-0.
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Abstract. A new two-dimensional zonal model of the stratosphere, based on a formulation in an isentropic framework, with complete chemistry has been coupled with a high resolution detailed microphysical model for polar stratospheric clouds (PSCs). The 2D model chemistry includes all presently known heterogeneous processes on sulfate aerosols and PSCs. The coupling of these two models, with inherently different time scales, is discussed. It is demonstrated that in order to obtain a realistic interrelationship between NOy and N2O an accurate simulation of the sedimentation by PSC particles is necessary. A good agreement of model PSC presence and observations is found for the Antarctic polar winter without the need to impose additional artificial temperature variations in the model. The calculated occurrence of polar stratospheric clouds and resulting heterogeneous chemistry during the Antarctic winter are discussed. Sensitivity of the polar stratospheric chemical composition and cloud formation for different perturbations is investigated by studying the effects of transport across the polar vortex boundary and heterogeneous processing by an enhanced sulfate aerosol load. The importance of including sedimentation for all cases is also discussed.
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Cascio, Marco Lo, Marco Grifò, Alberto Milazzo, and Ivano Benedetti. "Computational Homogenization of Heterogeneous Materials by a Novel Hybrid Numerical Scheme." Journal of Multiscale Modelling 11, no. 04 (2020): 2050008. http://dx.doi.org/10.1142/s1756973720500080.
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The Virtual Element Method (VEM) is a recent numerical technique capable of dealing with very general polygonal and polyhedral mesh elements, including irregular or non-convex ones. Because of this feature, the VEM ensures noticeable simplification in the data preparation stage of the analysis, especially for problems whose analysis domain features complex geometries, as in the case of computational micro-mechanics problems. The Boundary Element Method (BEM) is a well known, extensively used and effective numerical technique for the solution of several classes of problems in science and engineering. Due to its underlying formulation, the BEM allows reducing the dimensionality of the problem, resulting in substantial simplification of the pre-processing stage and in the reduction of the computational effort, without jeopardizing the solution accuracy. In this contribution, we explore the possibility of a coupling VEM and BEM for computational homogenization of heterogeneous materials with complex microstructures. The test morphologies consist of unit cells with irregularly shaped inclusions, representative e.g., of a fiber-reinforced polymer composite. The BEM is used to model the inclusions, while the VEM is used to model the surrounding matrix material. Benchmark finite element solutions are used to validate the analysis results.
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Borcea, L., J. Garnier, and K. Sølna. "Onset of energy equipartition among surface and body waves." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2246 (2021): 20200775. http://dx.doi.org/10.1098/rspa.2020.0775.
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We derive a radiative transfer equation that accounts for coupling from surface waves to body waves and the other way around. The model is the acoustic wave equation in a two-dimensional waveguide with reflecting boundary. The waveguide has a thin, weakly randomly heterogeneous layer near the top surface, and a thick homogeneous layer beneath it. There are two types of modes that propagate along the axis of the waveguide: those that are almost trapped in the thin layer, and thus model surface waves, and those that penetrate deep in the waveguide, and thus model body waves. The remaining modes are evanescent waves. We introduce a mathematical theory of mode coupling induced by scattering in the thin layer, and derive a radiative transfer equation which quantifies the mean mode power exchange. We study the solution of this equation in the asymptotic limit of infinite width of the waveguide. The main result is a quantification of the rate of convergence of the mean mode powers toward equipartition.
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Baum, Jennifer R., Biao Long, Candido Cabo, and Heather S. Duffy. "Myofibroblasts cause heterogeneous Cx43 reduction and are unlikely to be coupled to myocytes in the healing canine infarct." American Journal of Physiology-Heart and Circulatory Physiology 302, no. 3 (2012): H790—H800. http://dx.doi.org/10.1152/ajpheart.00498.2011.
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Following myocardial infarction (MI) inflammatory responses transform cardiac fibroblasts to myofibroblasts, which in vitro studies show form heterocellular gap junctions with cardiac myocytes via Connexin43 (Cx43). The ability to form heterocellular junctions in the intact heart and the impact of these junctions on propagation is unclear. We used a canine model of MI and characterized the distribution and quantity of myofibroblasts in surviving epicardial cells [epicardial border zone (EBZ)]. We found a significant increase in myofibroblasts within the EBZ and no gap junction plaques between myofibroblasts and myocytes. Because myofibroblasts produce IL-1β, which downregulates Cx43, we asked whether myofibroblast proliferation causes loss of Cx43 near myofibroblast clusters. In vitro studies showed that IL-1β caused loss of Cx43 and reduced coupling. Western blot showed a significant increase of IL-1β in the EBZ, and immunohistochemistry showed a loss of Cx43 in regions of myofibroblasts in the intact heart. Additionally, dye studies in intact heart showed no coupling between myocytes and myofibroblasts. To quantify the effect of myofibroblasts on propagation we used a two-dimensional subcellular computer model of the EBZ, which showed that heterogeneities in myofibroblast density lead to conduction abnormalities. In conclusion, an increase of myofibroblasts in the infarcted heart causes heterogeneous Cx43 levels, possibly as a result of the release of IL-1β and decreased cell-cell communication, which leads to conduction abnormalities following MI.
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Xie, Yuanfang, Alan Garfinkel, James N. Weiss, and Zhilin Qu. "Cardiac alternans induced by fibroblast-myocyte coupling: mechanistic insights from computational models." American Journal of Physiology-Heart and Circulatory Physiology 297, no. 2 (2009): H775—H784. http://dx.doi.org/10.1152/ajpheart.00341.2009.
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Recent experimental studies have shown that fibroblasts can electrotonically couple to myocytes via gap junctions. In this study, we investigated how this coupling affects action potential and intracellular calcium (Cai) cycling dynamics in simulated fibroblast-myocyte pairs and in two-dimensional tissue with random fibroblast insertions. We show that a fibroblast coupled with a myocyte generates a gap junction current flowing to the myocyte with two main components: an early pulse of transient outward current, similar to the fast transient outward current, and a later background current during the repolarizing phase. Depending on the relative prominence of the two components, fibroblast-myoycte coupling can 1) prolong or shorten action potential duration (APD), 2) promote or suppress APD alternans due to steep APD restitution (voltage driven) and also result in a novel mechanism of APD alternans at slow heart rates, 3) promote Cai-driven alternans and electromechanically discordant alternans, and 4) promote spatially discordant alternans by two mechanisms: by altering conduction velocity restitution and by heterogeneous fibroblast distribution causing electromechanically concordant and discordant alternans in different regions of the tissue. Thus, through their coupling with myocytes, fibroblasts alter repolarization and Cai cycling alternans at both the cellular and tissue scales, which may play important roles in arrhythmogenesis in diseased cardiac tissue with fibrosis.
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Van Gorder, Robert A., Hyunyeon Kim, and Andrew L. Krause. "Diffusive instabilities and spatial patterning from the coupling of reaction–diffusion processes with Stokes flow in complex domains." Journal of Fluid Mechanics 877 (August 27, 2019): 759–823. http://dx.doi.org/10.1017/jfm.2019.620.
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We study spatial and spatio-temporal pattern formation emergent from reaction–diffusion–advection systems formed by considering reaction–diffusion systems coupled to prescribed fluid flows. While there have been a number of studies on the planar dynamics of such systems and the resulting instabilities and spatio-temporal patterning in the plane, less has been done on complicated flows in complex domains. We consider a general approach for the study of bounded domains in order to model two- and three-dimensional geometries which are more likely to be of relevance for modelling dynamics within fluid vessels used in experiments. Considering a variety of problem geometries with finite cross-sections, such as two-dimensional channels, three-dimensional ducts and three-dimensional pipes, we demonstrate the role cross-section geometry plays in pattern formation under such systems. We find that the generic instability is that of an oscillatory or wave Turing instability, resulting in patterns which change in time, often being advected with the fluid flow. As in previous works, we observe a change in patterns formed when progressing from zero to weak to strong advection for uniform advection across the domain, with particularly strong advection destroying patterns. One novel finding is that heterogeneous fluid flow can induce qualitatively different patterns across the domain. For instance, Poiseuille flow with maximal advection in the centre of a vessel and zero advection at the boundary of a vessel is shown to exhibit patterns in the centre of the vessel which are different from patterns near the boundary, with differences attributed to the differential local advection within each region of the vessel. Additionally, we observe sheared patterns, which appear due to gradients in the fluid velocity, and cannot be obtained via any kind of uniform flow. Finally we also explore flow in more complex domains, including wavy-walled channels, continuous stirred-tank reactors, U-shaped pipes and a toroidal domain, in order to demonstrate behaviours when the flow is both heterogeneous and bidirectional, as well as to demonstrate that our results still apply for complex finite domains. Our analysis suggests that such non-trivial advection results in moving patterns which are more complex than observed in simpler reaction–diffusion–advection, and may be more characteristic of realistic flow regimes in biological media.
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LIN, HAO, BRIAN D. STOREY, and JUAN G. SANTIAGO. "A depth-averaged electrokinetic flow model for shallow microchannels." Journal of Fluid Mechanics 608 (July 11, 2008): 43–70. http://dx.doi.org/10.1017/s0022112008001869.
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Electrokinetic flows with heterogeneous conductivity configuration occur widely in microfluidic applications such as sample stacking and multidimensional assays. Electromechanical coupling in these flows may lead to complex flow phenomena, such as sample dispersion due to electro-osmotic velocity mismatch, and electrokinetic instability (EKI). In this work we develop a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow-channel geometry. An asymptotic analysis is performed with the channel depth-to-width ratio as a smallness parameter, and the three-dimensional equations are reduced to a set of depth-averaged equations governing in-plane flow dynamics. The momentum equation uses a Darcy–Brinkman–Forchheimer-type formulation, and the convective–diffusive transport of the conductivity field in the depth direction manifests itself as a dispersion effect on the in-plane conductivity field. The validity of the model is assessed by comparing the numerical results with full three-dimensional direct numerical simulations, and experimental data. The depth-averaged equations provide the accuracy of three-dimensional modelling with a convenient two-dimensional equation set applicable to a wide class of microfluidic devices.
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de Boer, Gregory, and Andreas Almqvist. "On the Two-Scale Modelling of Elastohydrodynamic Lubrication in Tilted-Pad Bearings." Lubricants 6, no. 3 (2018): 78. http://dx.doi.org/10.3390/lubricants6030078.
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A two-scale method for modelling the Elastohydrodynamic Lubrication (EHL) of tilted-pad bearings is derived and a range of solutions are presented. The method is developed from previous publications and is based on the Heterogeneous Multiscale Methods (HMM). It facilitates, by means of homogenization, incorporating the effects of surface topography in the analysis of tilted-pad bearings. New to this article is the investigation of three-dimensional bearings, including the effects of both ideal and real surface topographies, micro-cavitation, and the metamodeling procedure used in coupling the problem scales. Solutions for smooth bearing surfaces, and under pure hydrodynamic operating conditions, obtained with the present two-scale EHL model, demonstrate equivalence to those obtained from well-established homogenization methods. Solutions obtained for elastohydrodynamic operating conditions, show a dependency of the solution to the pad thickness and load capacity of the bearing. More precisely, the response for the real surface topography was found to be stiffer in comparison to the ideal. Micro-scale results demonstrate periodicity of the flow and surface topography and this is consistent with the requirements of the HMM. The means of selecting micro-scale simulations based on intermediate macro-scale solutions, in the metamodeling approach, was developed for larger dimensionality and subsequent calibration. An analysis of the present metamodeling approach indicates improved performance in comparison to previous studies.
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Hansen, Scott K., Sachin Pandey, Satish Karra, and Velimir V. Vesselinov. "CHROTRAN 1.0: A mathematical and computational model for in situ heavy metal remediation in heterogeneous aquifers." Geoscientific Model Development 10, no. 12 (2017): 4525–38. http://dx.doi.org/10.5194/gmd-10-4525-2017.
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Abstract. Groundwater contamination by heavy metals is a critical environmental problem for which in situ remediation is frequently the only viable treatment option. For such interventions, a multi-dimensional reactive transport model of relevant biogeochemical processes is invaluable. To this end, we developed a model, chrotran, for in situ treatment, which includes full dynamics for five species: a heavy metal to be remediated, an electron donor, biomass, 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, bio-fouling, and biomass death. Our software implementation handles heterogeneous flow fields, as well as arbitrarily many chemical species and amendment injection points, and features full coupling between flow and reactive transport. We describe installation and usage and present two example simulations demonstrating its unique capabilities. One simulation suggests an unorthodox approach to remediation of Cr(VI) contamination.
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Amir, Laila, and Michel Kern. "Jacobian Free Methods for Coupling Transport with Chemistry in Heterogenous Porous Media." Water 13, no. 3 (2021): 370. http://dx.doi.org/10.3390/w13030370.
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Reactive transport plays an important role in various subsurface applications, including carbon dioxide sequestration, nuclear waste storage, biogeochemistry and the simulation of hydro–thermal reservoirs. The model couples a set of partial differential equations, describing the transport of chemical species, to nonlinear algebraic or differential equations, describing the chemical reactions. Solution methods for the resulting large nonlinear system can be either fully coupled or can iterate between transport and chemistry. This paper extends previous work by the authors where an approach based on the Newton–Krylov method applied to a reduced system has been developed. The main feature of the approach is to solve the nonlinear system in a fully coupled manner while keeping transport and chemistry modules separate. Here we extend the method in two directions. First, we take into account mineral precipitation and dissolution reactions by using an interior point Newton method, so as to avoid the usual combinatorial approach. Second, we study two-dimensional heterogeneous geometries. We show how the method can make use of an existing transport solver, used as a black box. We detail the methods and algorithms for the individual modules, and for the coupling step. We show the performance of the method on synthetic examples.
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Kpogan, Kekeli, Yendoubouam Tampango, Hamid Zahrouni, Michel Potier-Ferry, and Hachmi Ben Dhia. "Computing Flatness Defects in Sheet Rolling by Arlequin and Asymptotic Numerical Methods." Key Engineering Materials 611-612 (May 2014): 186–93. http://dx.doi.org/10.4028/www.scientific.net/kem.611-612.186.
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Rolling of thin sheets generally induces flatness defects due to thermo-elastic deformation of rolls. This leads to heterogeneous plastic deformations throughout the strip width and then to out of plane displacements to relax residual stresses. In this work we present a new numerical technique to model the buckling phenomena under residual stresses induced by rolling process. This technique consists in coupling two finite element models: the first one consists in a three dimensional model based on 8-node tri-linear hexahedron which is used to model the three dimensional behaviour of the sheet in the roll bite; we introduce in this model, residual stresses from a full simulation of rolling (a plane-strain elastoplastic finite element model) or from an analytical profile. The second model is based on a shell formulation well adapted to large displacements and rotations; it will be used to compute buckling of the strip out of the roll bite. We propose to couple these two models by using Arlequin method. The originality of the proposed algorithm is that in the context of Arlequin method, the coupling area varies during the rolling process. Furthermore we use the asymptotic numerical method (ANM) to perform the buckling computations taking into account geometrical nonlinearities in the shell model. This technique allows one to solve nonlinear problems using high order algorithms well adapted to problems in the presence of instabilities. The proposed algorithm is applied to some rolling cases where “edges-waves” and “center-waves” defects of the sheet are observed.
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Poelzing, Steven, Bradley J. Roth, and David S. Rosenbaum. "Optical measurements reveal nature of intercellular coupling across ventricular wall." American Journal of Physiology-Heart and Circulatory Physiology 289, no. 4 (2005): H1428—H1435. http://dx.doi.org/10.1152/ajpheart.01245.2004.
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Previously, we showed that intercellular uncoupling through gap junctions is an important mechanism for maintaining transmural heterogeneities of repolarization that are responsible for ventricular arrhythmias in disease states such as heart failure. However, rotational anisotropy between transmural muscle layers also may influence coupling. To determine the effect of rotational anisotropy on transmural coupling, we developed a numerical three-dimensional model of passive cardiac tissue in which rotational anisotropy was varied in a controlled fashion. Simulations of optical mapping demonstrated that spatial averaging produced a voltage decay in space best fit by a single decaying exponential compared with the theoretically predicted decay. As fiber orientation varied by 90° with respect to the transmural surface, the effective transmural space constant (λTM) changed by only 0.31% in simulations. In contrast, reducing intercellular conductivity by 24% decreased λTM by 7.7%. In the canine wedge preparation ( n = 5), λ measured by optical mapping of the epicardial and subepicardial surface was similar transverse (λTV = 0.73 ± 0.10 mm) and transmural (λTM = 0.70 ± 0.08 mm) to subepicardial fibers. We confirmed previous findings that λTM in subepicardial layers was significantly reduced by 14 ± 2% compared with deeper layers of myocardium, providing evidence for transmural uncoupling in the epicardial-midmyocardial interface. These data establish the theoretical and experimental basis for measuring intercellular coupling between muscle layers spanning the ventricular wall with optical mapping techniques. Furthermore, this study demonstrates that transmural uncoupling at the epicardial-midmyocardial interface may be attributable to heterogeneous expression of cardiac gap junctions and not rotational anisotropy.
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Abbasi, Mohsen, Mehdi Farniaei, Sedigheh Kabiri, Mohammad Reza Rahimpour, and Saeid Abbasi. "Performance Study of a Thermally Double Coupled Multi-Tubular Reactor by Considering the Effect of Flow Type Patterns." International Journal of Chemical Reactor Engineering 14, no. 1 (2016): 63–78. http://dx.doi.org/10.1515/ijcre-2015-0098.
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AbstractIn this study, a steady-state heterogeneous one-dimensional model predicts the performance of a thermally double coupled auto-thermal multi-tubular reactor for simultaneous production of hydrogen, benzene, methanol and dimethyether (DME) in an economical approach for both co- and counter- current modes of operation. Reversed flow of cyclohexane has been considered for the counter-current flow regime. The simulation results for co- and counter-current modes have been investigated and compared with corresponding predictions for conventional methanol reactor and traditional coupled methanol reactor. In addition, various operating parameters along the reactor have been studied. The simulation results present that methanol yield in co- and counter- current modes are reached to 0.3735 and 0.3363 in a thermally double coupled reactor, respectively. Also, results for counter-current mode show a superior performance in hydrogen and benzene production. Finally, the results of simulation illustrate that the coupling of these reactions could be beneficial.
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Liu, Benhua, Hao Zhan, Yiran Liu, et al. "Effects of Slip Length and Inertia on the Permeability of Fracture with Slippery Boundary Condition." International Journal of Environmental Research and Public Health 17, no. 11 (2020): 3817. http://dx.doi.org/10.3390/ijerph17113817.
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Although the slippery boundary condition (BC) has been validated to enhance fracture permeability (k), the coupling effects of heterogeneous slippery BC and inertia on k remain less understood. We used computational fluid dynamics to investigate the competing roles of slippery BC and inertial forces in controlling k evolution with increasing pressure gradient by designing six cases with different slip length scenarios for a two-dimensional natural fracture. Our results suggest that pronounced inertial effects were directly related to and demonstrated by the growth of recirculation zone (RZ); this caused flow regimes transitioning from Darcy to non-Darcy and significantly reduced k, with an identical tailing slope for six cases, regardless of the variability in slip lengths. Moreover, the slippery BC dominantly determine the magnitude of k with orders depending on the slip length. Lastly, our study reveals that the specific k evolution path for the case with a varying slip length was significantly different from other cases with a homogeneous one, thus encouraging more efforts in determining the slip length for natural fractures via experiments.
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Amaziane, Brahim, Mikhail Panfilov, and Leonid Pankratov. "Homogenized Model of Two-Phase Flow with Local Nonequilibrium in Double Porosity Media." Advances in Mathematical Physics 2016 (2016): 1–13. http://dx.doi.org/10.1155/2016/3058710.
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We consider two-phase flow in a heterogeneous porous medium with highly permeable fractures and low permeable periodic blocks. The flow in the blocks is assumed to be in local capillary disequilibrium and described by Barenblatt’s relaxation relationships for the relative permeability and capillary pressure. It is shown that the homogenization of such equations leads to a new macroscopic model that includes two kinds of long-memory effects: the mass transfer between the blocks and fractures and the memory caused by the microscopic Barenblatt disequilibrium. We have obtained a general relationship for the double nonequilibrium capillary pressure which represents great interest for applications. Due to the nonlinear coupling and the nonlocality in time, the macroscopic model remains incompletely homogenized in general case. The completely homogenized model was obtained for two different regimes. The first case corresponds to a linearized flow in the blocks. In the second case, we assume a low contrast in the block-fracture permeability. Numerical results for the two-dimensional problem are presented for two test cases to demonstrate the effectiveness of the methodology.
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Paul, Anup, Luísa M. D. R. S. Martins, Anirban Karmakar, Maxim L. Kuznetsov, M. Fátima C. Guedes da Silva, and Armando J. L. Pombeiro. "Zn(II)-to-Cu(II) Transmetalation in an Amide Functionalized Complex and Catalytic Applications in Styrene Oxidation and Nitroaldol Coupling." Molecules 25, no. 11 (2020): 2644. http://dx.doi.org/10.3390/molecules25112644.
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The mononuclear zinc(II) complex cis-[ZnL2(H2O)2] (1; L = 4-(pyridin-3-ylcarbamoyl)benzoate) was synthesized and characterized. By soaking crystals of 1 in a mixture of DMF-H2O solution containing a slight excess of Cu(NO3)2 × 3H2O a transmetalation reaction occurred affording the related copper(II) complex trans-[CuL2(H2O)2] (2). The structures of the compounds were authenticated by single crystal X-ray diffraction revealing, apart from a change in the isomerism, an alteration in the relative orientation of the chelating carboxylate groups and of the pyridine moieties. H-bond interactions stabilize both geometries and expand them into two-dimensional (2D) networks. The transmetalation was confirmed by SEM–EDS analysis. Moreover, the thermodynamic feasibility of the transmetalation is demonstrated by density-functional theory (DFT) studies. The catalytic activities of 1 and 2 for the oxidation of styrene and for the nitroaldol (Henry) C-C coupling reaction were investigated. The copper(II) compound 2 acts as heterogeneous catalyst for the microwave-assisted oxidation of styrene with aqueous hydrogen peroxide, yielding selectively (>99%) benzaldehyde up to 66% of conversion and with a turnover frequency (TOF) of 132 h−1. The zinc(II) complex 1 is the most active catalyst (up to 87% yield) towards the nitroaldol (Henry) coupling reaction between benzaldehyde and nitro-methane or -ethane to afford the corresponding β-nitro alcohols. The reaction of benzaldehyde with nitroethane in the presence of 1 produced 2-nitro-1-phenylpropanol in the syn and the anti diastereoisomeric forms, with a considerable higher selectivity towards the former (66:34).
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Li, Yanjun, Lanxing Du, Zhen Zhang, and Qinglin Wu. "High-Density Polyethylene and Heat-Treated Bamboo Fiber Composites: Nonisothermal Crystallization Properties." International Journal of Polymer Science 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/658584.
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The effect of heat-treated bamboo fibers (BFs) on nonisothermal crystallization of high-density polyethylene (HDPE) was investigated using differential scanning calorimetry under nitrogen. The Avrami-Jeziorny model was used to fit the measured crystallization data of the HDPE/BF composites and to obtain the model parameters for the crystallization process. The heat flow curves of neat HDPE and HDPE/heat-treated BF composites showed similar trends. Their crystallization mostly occurred within a temperature range between 379 K and 399 K, where HDPE turned from the liquid phase into the crystalline phase. Values of the Avrami exponent (n) were in the range of 2.8~3.38. Lamellae of neat HDPE and their composites grew in a three-dimensional manner, which increased with increased heat-treatment temperature and could be attributed to the improved ability of heterogeneous nucleation and crystallization completeness. The values of the modified kinetic rate constant (KJ) first increased and then decreased with increased cooling rate because the supercooling was improved by the increased number of nucleating sites. Heat-treated BF and/or a coupling agent could act as a nucleator for the crystallization of HDPE.
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Fan, Suoya, and Michael A. Murphy. "Three-dimensional strain accumulation and partitioning in an arcuate orogenic wedge: An example from the Himalaya." GSA Bulletin 133, no. 1-2 (2020): 3–18. http://dx.doi.org/10.1130/b35528.1.
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Abstract In this study, we use published geologic maps and cross-sections to construct a three-dimensional geologic model of major shear zones that make up the Himalayan orogenic wedge. The model incorporates microseismicity, megathrust coupling, and various derivatives of the topography to address several questions regarding observed crustal strain patterns and how they are expressed in the landscape. These questions include: (1) How does vertical thickening vary along strike of the orogen? (2) What is the role of oblique convergence in contributing to along-strike thickness variations and the style of deformation? (3) How do variations in the coupling along the megathrust affect the overlying structural style? (4) Do lateral ramps exist along the megathrust? (5) What structural styles underlie and are possibly responsible for the generation of high-elevation, low-relief landscapes? Our model shows that the orogenic core of the western and central Himalaya displays significant along-strike variation in its thickness, from ∼25–26 km in the western Himalaya to ∼34–42 km in the central Himalaya. The thickness of the orogenic core changes abruptly across the western bounding shear zone of the Gurla Mandhata metamorphic core complex, demonstrating a change in the style of strain there. Pressure-temperature-time results indicate that the thickness of the orogenic core at 37 Ma is 17 km. Assuming this is constant along strike from 81°E to 85°E indicates that, the western and central Nepal Himalaya have been thickened by 0.5 and 1–1.5 times, respectively. West of Gurla Mandhata the orogenic core is significantly thinner and underlies a large 11,000 km2 Neogene basin (Zhada). A broad, thick orogenic core associated with thrust duplexing is collocated with an 8500 km2 high-elevation, low-relief surface in the Mugu-Dolpa region of west Nepal. We propose that these results can be explained by oblique convergence along a megathrust with an along-strike and down-dip heterogeneous coupling pattern influenced by frontal and oblique ramps along the megathrust.
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Malenica, Luka, Hrvoje Gotovac, Grgo Kamber, Srdjan Simunovic, Srikanth Allu, and Vladimir Divic. "Groundwater Flow Modeling in Karst Aquifers: Coupling 3D Matrix and 1D Conduit Flow via Control Volume Isogeometric Analysis—Experimental Verification with a 3D Physical Model." Water 10, no. 12 (2018): 1787. http://dx.doi.org/10.3390/w10121787.
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A novel numerical model for groundwater flow in karst aquifers is presented. A discrete-continuum (hybrid) approach, in which a three-dimensional matrix flow is coupled with a one-dimensional conduit flow, was used. The laminar flow in the karst matrix is described by a variably saturated flow equation to account for important hydrodynamic effects in both the saturated and unsaturated zones. Turbulent conduit flow for both free surface and pressurized flow conditions was captured via the noninertia wave equation, whereas the coupling of two flow domains was established through an exchange term proportional to head differences. The novel numerical approach based on Fup basis functions and control-volume formulation enabled us to obtain smooth and locally conservative numerical solutions. Due to its similarity to the isogeometric analysis concept (IGA), we labeled it as control-volume isogeometric analysis (CV-IGA). Since realistic verification of the karst flow models is an extremely difficult task, the particular contribution of this work is the construction of a specially designed 3D physical model ( dimensions: 5.66 × 2.95 × 2.00 m) in order to verify the developed numerical model under controlled laboratory conditions. Heterogeneous porous material was used to simulate the karst matrix, and perforated pipes were used as karst conduits. The model was able to capture many flow characteristics, such as the interaction between the matrix and conduit, rainfall infiltration through the unsaturated zone, direct recharge through sinkholes, and both free surface and pressurized flow in conduits. Two different flow experiments are presented, and comparison with numerical results confirmed the validity of the developed karst flow model under complex laboratory conditions.
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Khatmullina, Liliya, and Irina Chubarenko. "Transport of marine microplastic particles: why is it so difficult to predict?" Anthropocene Coasts 2, no. 1 (2019): 293–305. http://dx.doi.org/10.1139/anc-2018-0024.
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Marine microplastic particles (MPs, <5 mm) exhibit wide ranges of densities, sizes, and shapes, so that the entire MPs “ensemble” at every time instant can be characterized by continuous distributions of these parameters. Accordingly, this community of particles demonstrates distributions of dynamical properties, such as sinking or rising velocity, critical shear stress, and the re-suspension threshold. Moreover, all the MPs’ properties vary significantly with the time spent in marine environment and with particular conditions experienced by the particle on its journey. A brief review of the present-day numerical efforts towards prediction of MPs transport shows the prevalence of the Lagrangian particle tracking approach, especially for floating litter. In a broader context, the present practice of MPs transport modelling follows the “selective” strategy (e.g., only a certain sub-class of MPs, or specific processes, are considered, sometimes in only one- or two-dimensional setting). The heterogeneous nature of MPs, their enormous longevity and movability in marine environment, and the wide spectrum of the involved environmental processes suggest further integration (or coupling) of different models in future, as well as application of other types of models (ensemble modeling, chaos theory approaches, machine learning, etc.) to the problems of MPs transport and fate in the marine environment.
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Cabo, Candido, and Penelope A. Boyden. "Heterogeneous gap junction remodeling stabilizes reentrant circuits in the epicardial border zone of the healing canine infarct: a computational study." American Journal of Physiology-Heart and Circulatory Physiology 291, no. 6 (2006): H2606—H2616. http://dx.doi.org/10.1152/ajpheart.00346.2006.
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The ventricular tachycardias (VTs) that originate in the 5-day epicardial border zone (EBZ) of the healing canine infarcted heart are due to reentrant excitation. In cells surviving in the EBZ, both sarcolemmal ionic channels and gap junction conductance and distribution are remodeled. We previously showed that the heterogeneities in sodium current ( INa) and L-type calcium channel current ( ICaL) of the center and outer pathway cells result in a homogenization of the refractory period that in turn stabilizes reentrant VTs for ∼10 beats. To understand how heterogeneities in transverse gap junctional conductance remodeling reported experimentally contribute to the stability of these tachycardias, we studied the dynamics of reentering waves in two-dimensional computer models of the EBZ. First we used a computer model with homogeneous ionic channel properties [infarcted border zone cell model (IZ)]. These simulations show that, in the absence of heterogeneities in ionic channel properties, reentrant waves tend to drift to localized regions of uncoupling and stabilize there. Second, we used a computer model with a more realistic representation of the heterogeneous EBZ, including cellular models for both the center (IZc) and outer (IZo) pathway cells. These simulations show that neither a region of uniform uncoupling nor a step transition between two regions with different side-to-side (transverse) cell coupling stabilizes reentry in this substrate. However, an area of localized uncoupling did stabilize reentry in such a model. We propose that in addition to the heterogeneities in INa and ICaL properties, heterogeneities in gap junctional conductance in the EBZ causing regions of localized uncoupling stabilize VT in the EBZ. Previous experimental in situ activation maps of the 5-day EBZ show that the lines of block form in regions of slow transverse propagation. This is consistent with our findings that areas of localized uncoupling stabilize reentry.
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Donnellan Barraclough, Alicia, Roman Zweifel, Jarrod Cusens, and Sebastian Leuzinger. "Disentangling the net: concomitant xylem and over-bark size measurements reveal the phloem-generated turgor signal behind daytime stem swelling in the mangrove Avicennia marina." Functional Plant Biology 46, no. 5 (2019): 393. http://dx.doi.org/10.1071/fp18155.
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Daytime stem shrinking is a well recorded phenomenon: trees dip into their internal water stores to meet imbalances between water supply and demand. Uncertainty surrounds the mechanisms behind the unusual pattern of daytime stem swelling, presented by species like the mangrove Avicennia marina (Forssk.) Vierh., and which is thought to originate in the osmotic adjustment of storage tissues. We performed on-xylem radius change (XRC) and whole-stem radius change (SRC) measurements with point dendrometers to ascertain if the swelling of the stem is due to an increase in the thickness of the phloem and inner-bark (BRC). We measured leaf water potential (ψleaf), sap flow, leaf turgor and microclimate to understand the coupling between BRC and transpiration-driven changes in XRC. Our results present direct evidence of the type of mechanism responsible for daytime stem swelling. Inner-bark thickness increase concurrent with XRC decrease, sap-flow increase and leaf turgor loss, reveals a phloem-generated turgor signal behind daytime stem swelling of tree stems. On-xylem measurements were highly heterogeneous due to the variability in the three dimensional fish-net wood structure of the stem of A. marina. As daytime decreases in XRC were compensated by BRC and correlated with conditions of high water demand, we suggest a potential role of daytime stem swelling in the hydraulic safety of A. marina.
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Ercan, Ali, and M. Kavvas. "Numerical Evaluation of Fractional Vertical Soil Water Flow Equations." Water 13, no. 4 (2021): 511. http://dx.doi.org/10.3390/w13040511.
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Significant deviations from standard Boltzmann scaling, which corresponds to normal or Fickian diffusion, have been observed in the literature for water movement in porous media. However, as demonstrated by various researchers, the widely used conventional Richards equation cannot mimic anomalous diffusion and ignores the features of natural soils which are heterogeneous. Within this framework, governing equations of transient water flow in porous media in fractional time and multi-dimensional fractional soil space in anisotropic media were recently introduced by the authors by coupling Brooks–Corey constitutive relationships with the fractional continuity and motion equations. In this study, instead of utilizing Brooks–Corey relationships, empirical expressions, obtained by least square fits through hydraulic measurements, were utilized to show the suitability of the proposed fractional approach with other constitutive hydraulic relations in the literature. Next, a finite difference numerical method was proposed to solve the fractional governing equations. The applicability of the proposed fractional governing equations was investigated numerically in comparison to their conventional counterparts. In practice, cumulative infiltration values are observed to deviate from conventional infiltration approximation, or the wetting front through time may not be consistent with the traditional estimates of Richards equation. In such cases, fractional governing equations may be a better alternative for mimicking the physical process as they can capture sub-, super-, and normal-diffusive soil water flow processes during infiltration.
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Miltenberger, Annette K., Tim Lüttmer, and Christoph Siewert. "Secondary Ice Formation in Idealised Deep Convection—Source of Primary Ice and Impact on Glaciation." Atmosphere 11, no. 5 (2020): 542. http://dx.doi.org/10.3390/atmos11050542.
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Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than −10 °C have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation.
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Hubbard, Marjorie Letitia, and Craig S. Henriquez. "A microstructural model of reentry arising from focal breakthrough at sites of source-load mismatch in a central region of slow conduction." American Journal of Physiology-Heart and Circulatory Physiology 306, no. 9 (2014): H1341—H1352. http://dx.doi.org/10.1152/ajpheart.00385.2013.
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Regions of cardiac tissue that have a combination of focal activity and poor, heterogeneous gap junction coupling are often considered to be arrhythmogenic; however, the relationship between the properties of the cardiac microstructure and patterns of abnormal propagation is not well understood. The objective of this study was to investigate the effect of microstructure on the initiation of reentry from focal stimulation inside a poorly coupled region embedded in more well-coupled tissue. Two-dimensional discrete computer models of ventricular monolayers (1 × 1 cm) were randomly generated to represent heterogeneity in the cardiac microstructure. A small, central poorly coupled patch (0.40 × 0.40 cm) was introduced to represent the site of focal activity. Simulated unipolar electrogram recordings were computed at various points in the tissue. As the gap conductance of the patch decreased, conduction slowed and became increasingly complex, marked by fractionated electrograms with reduced amplitude. Near the limit of conduction block, isolated breakthrough sites occurred at single cells along the patch boundary and were marked by long cell-to-cell delays and negative deflections on electrogram recordings. The strongest determinant of the site of wavefront breakthrough was the connectivity of the brick wall architecture, which enabled current flow through small regions of overlapping cells to drive propagation into the well-coupled zone. In conclusion, breakthroughs at the size scale of a single cell can occur at the boundary of source-load mismatch allowing focal activations from slow conducting regions to produce reentry. These breakthrough regions, identifiable by distinct asymmetric, reduced amplitude electrograms, are sensitive to tissue architecture and may be targets for ablation.
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Jeong, Da Un, Jiyeong Lee, and Ki Moo Lim. "Computational Study to Identify the Effects of the KCNJ2 E299V Mutation in Cardiac Pumping Capacity." Computational and Mathematical Methods in Medicine 2020 (March 31, 2020): 1–11. http://dx.doi.org/10.1155/2020/7194275.
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The KCNJ2 gene mutations induce short QT syndrome (SQT3) by directly increasing the IK1 current. There have been many studies on the electrophysiological effects of mutations such as the KCNJ2 D172N that cause the SQT3. However, the KCNJ2 E299V mutation is distinguished from other representative gene mutations that can induce the short QT syndrome (SQT3) in that it increased IK1 current by impairing the inward rectification of K+ channels. The studies of the electromechanical effects on myocardial cells and mechanisms of E299V mutations are limited. Therefore, we investigated the electrophysiological changes and the concomitant mechanical responses according to the expression levels of the KCNJ2 E299V mutation during sinus rhythm and ventricular fibrillation. We performed excitation-contraction coupling simulations using a human ventricular model with both electrophysiological and mechanical properties. In order to observe the electromechanical changes due to the expression of KCNJ2 E299V mutation, the simulations were performed under normal condition (WT), heterogeneous mutation condition (WT/E299V), and pure mutation condition (E299V). First, a single-cell simulation was performed in three types of ventricular cells (endocardial cell, midmyocardial cell, and epicardial cell) to confirm the electrophysiological changes and arrhythmogenesis caused by the KCNJ2 E299V mutation. In three-dimensional sinus rhythm simulations, we compared electrical changes and the corresponding changes in mechanical performance caused by the expression level of E299V mutation. Then, we observed the electromechanical properties of the E299V mutation during ventricular fibrillation using the three-dimensional reentry simulation. The KCNJ2 E299V mutation accelerated the opening of the IK1 channel and increased IK1 current, resulting in a decrease in action potential duration. Accordingly, the QT interval was reduced by 48% and 60% compared to the WT condition, for the WT/E299V and E299V conditions, respectively. During sustained reentry, the wavelength was reduced due to the KCNJ2 E299V mutation. Furthermore, there was almost no ventricular contraction in both WT/E299V and E299V conditions. We concluded that in both sinus rhythm and fibrillation, the KCNJ2 E299V mutation results in very low contractility regardless of the expression level of mutation and increases the risk of cardiac arrest and cardiac death.
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Tomek, Jakub, Blanca Rodriguez, Gil Bub та Jordi Heijman. "β-Adrenergic receptor stimulation inhibits proarrhythmic alternans in postinfarction border zone cardiomyocytes: a computational analysis". American Journal of Physiology-Heart and Circulatory Physiology 313, № 2 (2017): H338—H353. http://dx.doi.org/10.1152/ajpheart.00094.2017.
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The border zone (BZ) of the viable myocardium adjacent to an infarct undergoes extensive autonomic and electrical remodeling and is prone to repolarization alternans-induced cardiac arrhythmias. BZ remodeling processes may promote or inhibit Ca2+ and/or repolarization alternans and may differentially affect ventricular arrhythmogenesis. Here, we used a detailed computational model of the canine ventricular cardiomyocyte to study the determinants of alternans in the BZ and their regulation by β-adrenergic receptor (β-AR) stimulation. The BZ model developed Ca2+ transient alternans at slower pacing cycle lengths than the control model, suggesting that the BZ may promote spatially heterogeneous alternans formation in an infarcted heart. β-AR stimulation abolished alternans. By evaluating all combinations of downstream β-AR stimulation targets, we identified both direct (via ryanodine receptor channels) and indirect [via sarcoplasmic reticulum (SR) Ca2+ load] modulation of SR Ca2+ release as critical determinants of Ca2+ transient alternans. These findings were confirmed in a human ventricular cardiomyocyte model. Cell-to-cell coupling indirectly modulated the likelihood of alternans by affecting the action potential upstroke, reducing the trigger for SR Ca2+ release in one-dimensional strand simulations. However, β-AR stimulation inhibited alternans in both single and multicellular simulations. Taken together, these data highlight a potential antiarrhythmic role of sympathetic hyperinnervation in the BZ by reducing the likelihood of alternans and provide new insights into the underlying mechanisms controlling Ca2+ transient and repolarization alternans. NEW & NOTEWORTHY We integrated, for the first time, postmyocardial infarction electrical and autonomic remodeling in a detailed, validated computer model of β-adrenergic stimulation in ventricular cardiomyocytes. Here, we show that β-adrenergic stimulation inhibits alternans and provide novel insights into underlying mechanisms, adding to a recent controversy about pro-/antiarrhythmic effects of postmyocardial infarction hyperinnervation. Listen to this article’s corresponding podcast at http://ajpheart.podbean.com/e/%CE%B2-ar-stimulation-and-alternans-in-border-zone-cardiomyocytes/ .
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Owen, Leanna M., Arjun S. Adhikari, Mohak Patel, et al. "A cytoskeletal clutch mediates cellular force transmission in a soft, three-dimensional extracellular matrix." Molecular Biology of the Cell 28, no. 14 (2017): 1959–74. http://dx.doi.org/10.1091/mbc.e17-02-0102.
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The ability of cells to impart forces and deformations on their surroundings underlies cell migration and extracellular matrix (ECM) remodeling and is thus an essential aspect of complex, metazoan life. Previous work has resulted in a refined understanding, commonly termed the molecular clutch model, of how cells adhering to flat surfaces such as a microscope coverslip transmit cytoskeletally generated forces to their surroundings. Comparatively less is known about how cells adhere to and exert forces in soft, three-dimensional (3D), and structurally heterogeneous ECM environments such as occur in vivo. We used time-lapse 3D imaging and quantitative image analysis to determine how the actin cytoskeleton is mechanically coupled to the surrounding matrix for primary dermal fibroblasts embedded in a 3D fibrin matrix. Under these circumstances, the cytoskeletal architecture is dominated by contractile actin bundles attached at their ends to large, stable, integrin-based adhesions. Time-lapse imaging reveals that α-actinin-1 puncta within actomyosin bundles move more quickly than the paxillin-rich adhesion plaques, which in turn move more quickly than the local matrix, an observation reminiscent of the molecular clutch model. However, closer examination did not reveal a continuous rearward flow of the actin cytoskeleton over slower moving adhesions. Instead, we found that a subset of stress fibers continuously elongated at their attachment points to integrin adhesions, providing stable, yet structurally dynamic coupling to the ECM. Analytical modeling and numerical simulation provide a plausible physical explanation for this result and support a picture in which cells respond to the effective stiffness of local matrix attachment points. The resulting dynamic equilibrium can explain how cells maintain stable, contractile connections to discrete points within ECM during cell migration, and provides a plausible means by which fibroblasts contract provisional matrices during wound healing.
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Miyauchi, Mizuho, Zhilin Qu, Yasushi Miyauchi, et al. "Chronic nicotine in hearts with healed ventricular myocardial infarction promotes atrial flutter that resembles typical human atrial flutter." American Journal of Physiology-Heart and Circulatory Physiology 288, no. 6 (2005): H2878—H2886. http://dx.doi.org/10.1152/ajpheart.01165.2004.
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The potential of chronic nicotine exposure for atrial fibrillation (AF) and atrial flutter (AFL) in hearts with and without chronic myocardial infarction (MI) remains poorly explored. MI was created in dogs by permanent occlusion of the left anterior descending coronary artery, and dogs were administered nicotine (5 mg·kg−1·day−1 sc) for 1 mo using osmotic minipumps. High-resolution epicardial (1,792 bipolar electrodes) and endocardial Halo catheters were used to map activation during induced atrial rhythms. Nicotine promoted inducible sustained AFL at a mean cycle length of 134 ± 10 ms in all MI dogs ( n = 6) requiring pacing and electrical shocks for termination. No AFL could be induced in MI dogs ( n = 6), control (non-MI) dogs ( n = 3) not exposed to nicotine, and dogs with no MI and exposed to nicotine ( n = 3). Activation maps during AFL showed a single reentrant wavefront in the right atrium that rotated either clockwise (60%) or counterclockwise (40%) around the crista terminalis and through the isthmus. Ablation of the isthmus prevented the induction of AFL. Nicotine caused a significant ( P < 0.01) but highly heterogeneous increase in atrial interstitial fibrosis (2- to 10-fold increase in left and right atria, respectively) in the MI group but only a 2-fold increase in the right atrium in the non-MI group. Nicotine also flattened ( P < 0.05) the slope of the epicardial monophasic action potential duration (electrical restitution) curve of both atria in the MI but not in non-MI dogs. Two-dimensional simulation in an excitable matrix containing an isthmus and nicotine's restitutional and reduced gap junctional coupling (fibrosis) parameters replicated the experiments. Chronic nicotine in hearts with MI promotes AFL that closely resembles typical human AFL. Increased atrial interstitial fibrosis and flattened electrical restitution are important substrates for the AFL.
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Wennerberg, Leif, and Gary Glassmoyer. "Absorption effects on plane waves in layered media." Bulletin of the Seismological Society of America 76, no. 5 (1986): 1407–32. http://dx.doi.org/10.1785/bssa0760051407.
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Abstract We present equations which can be used in conjunction with estimates of material properties to determine whether exact linear viscoelastic modeling will give significantly different results from elastic ray calculations. We apply the viscoelastic version of Snell's law to assess the effects of anelasticity on phase velocities, attenuation coefficients, transmission angles, and travel times for a plane wave propagating through a stack of plane viscoelastic layers described by the velocity and Q for a homogeneous wave in each layer. We include a survey of the viscoelastic theory of plane waves to provide a context for the results. Our analysis shows that the most general version of Snell's law leads to a complex two-dimensional vector ray parameter in which case plane P-wave motion does not decouple from horizontal transverse S-wave motion. We show that in a layered medium the fields generated by a symmetric point source, a vector point force, a double-couple point force, or a plane of tractions corresponding to a complex vector parameter, as well as other “reasonable” sources, can be calculated by integrating over real ray parameters, but in all of these cases, one must consider the coupling in laterally heterogeneous media. Differences from elastic ray behavior are found to be well correlated with the behavior of the parameter χ≡1+Q-2cos2γ where γ is the angle of inhomogeneity of the wave. We present equations for χ in terms of layer parameters and both the vector ray parameter and incident wave parameters. Examples presented to illustrate the method show significant (5 to 10 per cent) deviations from elastic travel times, and offsets in a given layer may be possible in very lossy layered materials.
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Hara, Tatsuhiko, and Robert J. Geller. "Anomalously large near-field Rayleight waves excited by the 1992 Landers, California, earthquake." Bulletin of the Seismological Society of America 84, no. 3 (1994): 751–60. http://dx.doi.org/10.1785/bssa0840030751.
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Abstract The epicenter of the Landers, California, earthquake (28 June 1992; MW = 7.3) was located near the TERRAscope network of broadband seismic stations. The direct Rayleigh wave arrivals, R1, were clipped, and the first two later arrivals, R2 and R3, were contaminated by the waves from a large aftershock, but, as reported by Kanamori et al. (1992a), the amplitudes of R4 and later great circle Rayleigh wave arrivals (fundamental mode spheroidal free oscillations) are about 10 times larger than predicted by synthetic seismograms for a spherically symmetric earth model. We show that, for the moment tensor of the Landers event (predominantly vertical strike slip), the amplitudes of synthetics at the TERRAscope stations for a laterally heterogeneous, rotating, elliptical model are about 10 times greater than those for a spherically symmetric model. Because the anomaly ratio is sensitive to both the source model and the three-dimensional (3D) earth model, we do not attempt to reproduce the exact anomaly ratios recorded by the various stations. To explain the existence of near-field amplitude anomalies in general, we use the first-order Born approximation to find the perturbation to the synthetic seismogram resulting from lateral heterogeneity, ellipticity, and the earth's rotation. In a coordinate system with the source on the z axis a point-source strike-slip earthquake on a vertical fault plane in a spherically symmetric medium excites Rayleigh waves with azimuthal order ±2 only; these waves have a near-field vertical displacement of zero at the source; the displacement increases with the square of epicentral distance for any given azimuth. Coupling as a result of asphericity allows such a source to excite Rayleigh waves with azimuthal order zero, whose near-field amplitude is independent of epicentral distance, thereby generating large near-field amplitude anomalies. We conduct numerical experiments to study the influence of various parameters on near-field amplitude anomalies.
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Xiao, Shangbin, Liu Liu, Wei Wang, Andreas Lorke, Jason Woodhouse, and Hans-Peter Grossart. "A Fast-Response Automated Gas Equilibrator (FaRAGE) for continuous in situ measurement of CH<sub>4</sub> and CO<sub>2</sub> dissolved in water." Hydrology and Earth System Sciences 24, no. 7 (2020): 3871–80. http://dx.doi.org/10.5194/hess-24-3871-2020.
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Abstract. Biogenic greenhouse gas emissions, e.g., of methane (CH4) and carbon dioxide (CO2) from inland waters, contribute substantially to global warming. In aquatic systems, dissolved greenhouse gases are highly heterogeneous in both space and time. To better understand the biological and physical processes that affect sources and sinks of both CH4 and CO2, their dissolved concentrations need to be measured with high spatial and temporal resolution. To achieve this goal, we developed the Fast-Response Automated Gas Equilibrator (FaRAGE) for real-time in situ measurement of dissolved CH4 and CO2 concentrations at the water surface and in the water column. FaRAGE can achieve an exceptionally short response time (t95 %=12 s when including the response time of the gas analyzer) while retaining an equilibration ratio of 62.6 % and a measurement accuracy of 0.5 % for CH4. A similar performance was observed for dissolved CO2 (t95 %=10 s, equilibration ratio 67.1 %). An equilibration ratio as high as 91.8 % can be reached at the cost of a slightly increased response time (16 s). The FaRAGE is capable of continuously measuring dissolved CO2 and CH4 concentrations in the nM-to-sub mM (10−9–10−3 mol L−1) range with a detection limit of sub-nM (10−10 mol L−1), when coupling with a cavity ring-down greenhouse gas analyzer (Picarro GasScouter). FaRAGE allows for the possibility of mapping dissolved concentration in a “quasi” three-dimensional manner in lakes and provides an inexpensive alternative to other commercial gas equilibrators. It is simple to operate and suitable for continuous monitoring with a strong tolerance for suspended particles. While the FaRAGE is developed for inland waters, it can be also applied to ocean waters by tuning the gas–water mixing ratio. The FaRAGE is easily adapted to suit other gas analyzers expanding the range of potential applications, including nitrous oxide and isotopic composition of the gases.
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Zhang, Wenjuan, and Mohammed Al Kobaisi. "Nonlinear Finite Volume Method for 3D Discrete Fracture-Matrix Simulations." SPE Journal 25, no. 04 (2020): 2079–97. http://dx.doi.org/10.2118/201098-pa.
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Summary We present a lower dimensional discrete fracture-matrix (DFM) model for general nonorthogonal meshes populated by anisotropic permeability tensors in 3D spatial dimension. The discrete fractures are represented as 2D planes embedded in a 3D matrix domain and serve as internal boundaries for conforming meshing of the entire computational domain. The nonlinear finite volume method (FVM) is used to derive flux for both matrix-matrix connections and fracture-fracture connections to account for permeability anisotropy in the matrix and inside the fracture planes, whereas the linear two-point flux approximation (TPFA) is used to couple the matrix and fracture together. The nonlinear method proceeds by first constructing two one-sided fluxes for a connection, and then a unique flux is obtained by a convex combination of the two one-sided fluxes. Construction of one-sided fluxes requires introducing the so-called harmonic averaging points as auxiliary points. While the nonlinear FVM can be applied to derive the flux for matrix-matrix connections in a straightforward way, difficulties arise for fracture-fracture connections because of the presence of fracture intersections. Therefore, to construct the one-sided fluxes for fracture-fracture connections, we first present a novel generalization of the concept of harmonic averaging point so that auxiliary points can be calculated at fracture intersections. Unique nonlinear fluxes are then derived for fracture-fracture connections and fracture intersections. Results of the numerical examples demonstrate that the linear TPFA coupling of matrix and fracture seems to be adequate even for relatively strong anisotropy on a non-K-orthogonal grid, and the new DFM model can accurately capture the permeability anisotropy effect inside the fracture planes as well as the permeability anisotropy in the matrix domain compared with the equidimensional models in which the fractures are gridded explicitly. Finally, the DFM model is applied successfully to deal with complex fracture networks embedded in a heterogeneous matrix domain or fracture network with challenging geometric features.
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Sullivan, Peter P., and James C. McWilliams. "Langmuir turbulence and filament frontogenesis in the oceanic surface boundary layer." Journal of Fluid Mechanics 879 (October 1, 2019): 512–53. http://dx.doi.org/10.1017/jfm.2019.655.
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Submesoscale currents, small-scale turbulence and surface gravity waves co-exist in the upper ocean and interact in complex ways. To expose the couplings, the frontogenetic life cycle of an idealized cold dense submesoscale filament interacting with upper ocean Langmuir turbulence is investigated in large-eddy simulations (LESs) based on the incompressible wave-averaged equations. The simulations utilize large domains and fine meshes with $6.4\times 10^{9}$ grid points. Case studies are made with surface winds or surface cooling with waves oriented in across-filament (perpendicular) or down-filament (parallel) directions relative to the two-dimensional filament axis. The currents $u$, $v$ and $w$ are aligned with the across-filament, down-filament and vertical directions, respectively. Frontogenesis is induced by across-filament Lagrangian secondary circulations in the boundary layer, and it is shown to be strongly impacted by surface waves, in particular the propagation direction relative to the filament axis. In a horizontally heterogeneous boundary layer, surface waves induce both mean and fluctuating Stokes-drift vortex forces that modify a linear, hydrostatic turbulent thermal wind (TTW) approximation for momentum. Down-filament winds and waves are found to be especially impactful, they significantly reduce the peak level of frontogenesis by fragmenting the filament into primary and secondary down-welling sites in a broad frontal zone over a width ${\sim}500~\text{m}$. At peak frontogenesis, opposing down-filament jets $\langle v\rangle$ overlie each other resulting in a vigorous vertical shear layer $\unicode[STIX]{x2202}_{z}\langle v\rangle$ with large vertical momentum flux $\langle v^{\prime }w^{\prime }\rangle$. Filament arrest is induced by a lateral shear instability that generates horizontal momentum flux $\langle u^{\prime }v^{\prime }\rangle$ at low wavenumbers. The turbulent vertical velocity patterns, indicative of coherent Langmuir cells, change markedly across the horizontal domain with both across-filament and down-filament winds under the action of submesoscale currents.
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Leiva, Jorge S., Pablo J. Blanco, and Gustavo C. Buscaglia. "Iterative strong coupling of dimensionally heterogeneous models." International Journal for Numerical Methods in Engineering, 2009, n/a. http://dx.doi.org/10.1002/nme.2741.
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Ganine, Vladislav, John W. Chew, Nicholas Hills, Sulfi Noor Mohamed, and Matthew Miller. "Transient Aero-Thermo-Mechanical Multidimensional Analysis of a High Pressure Turbine Assembly Through a Square Cycle." Journal of Engineering for Gas Turbines and Power, January 4, 2021. http://dx.doi.org/10.1115/1.4049498.
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Abstract Better understanding and more accurate prediction of heat transfer and cooling flows in aero engine components in steady and transient operating regimes are essential to modern engine designs aiming at reduced cooling air consumption and improved engine efficiencies. This paper presents a simplified coupled transient analysis methodology that allows assessment of the aerothermal and thermomechanical responses of engine components together with cooling air mass flow, pressure and temperature distributions in an automatic fully integrated way. This is achieved by assembling a fluid network with contribution of components of different geometrical dimensions coupled to each other through dimensionally heterogeneous interfaces. More accurate local flow conditions, heat transfer and structural displacement are resolved on a smaller area of interest with multidimensional surface coupled CFD/FE codes. Contributions of the whole engine air-system are predicted with a faster mono dimensional flow network code. Matching conditions at the common interfaces are enforced at each time step exactly by employing an efficient iterative scheme. The coupled simulation is performed on an industrial high pressure turbine disk component run through a square cycle. Predictions are compared against the available experimental data. The paper proves the reliability and performance of the multidimensional coupling technique in a realistic industrial setting. The results underline the importance of including more physical details into transient thermal modelling of turbine engine components.