Instabilities of advection-dominated accretion flows
Chen, X
1996-01-01
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.
Instabilities of Advection-Dominated Accretion Flows
Chen, Xingming
1996-01-01
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.
Preheated Advection Dominated Accretion Flow
Park, M G; Park, Myeong-Gu; Ostriker, Jeremiah P.
2001-01-01
All high temperature accretion solutions including ADAF are physically thick, so outgoing radiation interacts with the incoming flow, sharing as much or more resemblance with classical spherical accretion flows as with disk flows. We examine this interaction for the popular ADAF case. We find that without allowance for Compton preheating, a very restricted domain of ADAF solution is permitted and with Compton preheating included a new high temperature PADAF branch appears in the solution space. In the absence of preheating, high temperature flows do not exist when the mass accretion rate mdot == Mdot c^2 / L_E >~ 10^-1.5. Below this mass accretion rate, a roughly conical region around the hole cannot sustain high temperature ions and electrons for all flows having mdot >~ 10^-4, which may lead to a funnel possibly filled with a tenuous hot outgoing wind. If the flow starts at large radii with the usual equilibrium temperature ~10^4 K, the critical mass accretion rate is much lower, mdot exist. However, above ...
Vertical structure of Advection dominated Accretion Flows
Zeraatgari, Fateme Zahra
2015-01-01
We solve the set of hydrodynamic (HD) equations for optically thin Advection Dominated Accretion Flows (ADAFs) by assuming radially self-similar in spherical coordinate system $ (r, \\theta, \\phi) $. The disk is considered to be steady state and axi-symmetric. We define the boundary conditions at the pole and the equator of the disk and to avoid singularity at the rotation axis, the disk is taken to be symmetric with respect to this axis. Moreover, only the $ \\tau_{r \\phi} $ component of viscous stress tensor is assumed and we have set $ v_{\\theta} = 0 $. The main purpose of this study is to investigate the variation of dynamical quantities of the flow in the vertical direction by finding an analytical solution. As a consequence, we found that the advection parameter, $ f^{adv} $, varies along the $ \\theta $ direction and reaches to its maximum near the rotation axis. Our results also show that, in terms of no-outflow solution, thermal equilibrium still exists and consequently advection cooling can balance vis...
Advecting Procedural Textures for 2D Flow Animation
Kao, David; Pang, Alex; Moran, Pat (Technical Monitor)
2001-01-01
This paper proposes the use of specially generated 3D procedural textures for visualizing steady state 2D flow fields. We use the flow field to advect and animate the texture over time. However, using standard texture advection techniques and arbitrary textures will introduce some undesirable effects such as: (a) expanding texture from a critical source point, (b) streaking pattern from the boundary of the flowfield, (c) crowding of advected textures near an attracting spiral or sink, and (d) absent or lack of textures in some regions of the flow. This paper proposes a number of strategies to solve these problems. We demonstrate how the technique works using both synthetic data and computational fluid dynamics data.
Intermittent distribution of tracers advected by a compressible random flow
Bec, Jeremie; Gawedzki, Krzysztof; Horvai, Peter
2003-01-01
Multifractal properties of a tracer density passively advected by a compressible random velocity field are characterized. A relationship is established between the statistical properties of mass on the dynamical fractal attractor towards which the trajectories converge and large deviations of the stretching rates of the flow. In the framework of the compressible Kraichnan model, this result is illustrated by analytical calculations and confirmed by numerical simulations.
Advection of nematic liquid crystals by chaotic flow
O'Naraigh, Lennon
2016-01-01
Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar two-dimensional geometry. The Landau-de Gennes equation coupled to an externally-prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation of motion for the uid velocity. The numerical simulations demonstrate that the coarsening of the liquid-crystal domains is arrested by the ow. The nature of the arrest is different depending on whether the flow is regular or chaotic. For the specific case where tumbling is important, the flow has a strong effect on the the liquid-crystal morphology: this provides a mechanism for controlling the shape of the liquid-crystal domains.
Is the accretion flow in NGC 4258 advection-dominated?
Lasota, J P; Chen, X; Krolik, J H; Narayan, R; Yi, I
1995-01-01
The mass of the central black hole in the active galaxy NGC 4258 (M106) has been measured to be M=3.6\\times10^7\\Msun (Miyoshi et al. 1995). The Eddington luminosity corresponding to this mass is L_E=4.5\\times10^{45} erg s^{-1}. By contrast the X-ray luminosity of the nucleus of NGC 4258 between 2-10 keV is (4\\pm 1)\\times10^{40}~{\\rm erg\\,s^{-1}} while the optical/UV luminosity is less than 1.5\\times10^{42} ~{\\rm erg\\,s^{-1}}. The luminosity of NGC 4258 is therefore extremely sub-Eddington, L\\sim10^{-5}L_E in X-rays and L\\sim3\\times10^{-4} L_E even if we take the maximum optical/UV luminosity. Assuming the usual accretion efficiency of 0.1 would imply accretion rates orders of magnitude lower than in Seyfert galaxies and quasars. We show that the properties of the AGN in NGC 4258 can be explained by an accretion flow in the form of a very hot, optically-thin plasma which advects most of the viscously generated thermal energy into the central black hole and radiates only a small fraction of the energy. In this ...
Particle transport in flow through porous media: advection, longitudinal dispersion, and filtration
Mau, Russell Edgar
1992-01-01
A theoretical and experimental investigation of the transport parameters of particles flowing through porous media has been made. These parameters are the particle advective velocity, longitudinal dispersion coefficient, and filter coefficient. Both theoretical and experimental results are limited to flows with low Reynolds number (linear, laminar flow) and high Peclet number (advection dominates diffusion). The theoretical development used dimensionless numbers to define the transport par...
Subsurface barrier design alternatives for confinement and controlled advection flow
Various technologies and designs are being considered to serve as subsurface barriers to confine or control contaminant migration from underground waste storage or disposal structures containing radioactive and hazardous wastes. Alternatives including direct-coupled flood and controlled advection designs are described as preconceptual examples. Prototype geotechnical equipment for testing and demonstration of these alternative designs tested at the Hanford Geotechnical Development and Test Facility and the Hanford Small-Tube Lysimeter Facility include mobile high-pressure injectors and pumps, mobile transport and pumping units, vibratory and impact pile drivers, and mobile batching systems. Preliminary laboratory testing of barrier materials and additive sequestering agents have been completed and are described
A global spectral element model for poisson equations and advective flow over a sphere
Mei, Huan; Wang, Faming; Zeng, Zhong; Qiu, Zhouhua; Yin, Linmao; Li, Liang
2016-03-01
A global spherical Fourier-Legendre spectral element method is proposed to solve Poisson equations and advective flow over a sphere. In the meridional direction, Legendre polynomials are used and the region is divided into several elements. In order to avoid coordinate singularities at the north and south poles in the meridional direction, Legendre-Gauss-Radau points are chosen at the elements involving the two poles. Fourier polynomials are applied in the zonal direction for its periodicity, with only one element. Then, the partial differential equations are solved on the longitude-latitude meshes without coordinate transformation between spherical and Cartesian coordinates. For verification of the proposed method, a few Poisson equations and advective flows are tested. Firstly, the method is found to be valid for test cases with smooth solution. The results of the Poisson equations demonstrate that the present method exhibits high accuracy and exponential convergence. Highprecision solutions are also obtained with near negligible numerical diffusion during the time evolution for advective flow with smooth shape. Secondly, the results of advective flow with non-smooth shape and deformational flow are also shown to be reasonable and effective. As a result, the present method is proved to be capable of solving flow through different types of elements, and thereby a desirable method with reliability and high accuracy for solving partial differential equations over a sphere.
Accretion discs around black holes two dimensional, advection cooled flows
Igumenshchev, I V; Abramowicz, M A; Igumenshchev, Igor V; Chen, Xingming; Abramowicz, Marek Artur
1995-01-01
Two-dimensional accretion flows near black holes have been investigated by time-dependent hydrodynamical calculations. We assume that the flow is axisymmetric and that radiative losses of internal energy are negligible, so that the disc is geometrically thick and hot. Accretion occurs due to the overflow of the effective potential barrier near the black hole, similar to the case of the Roche lobe overflowing star in a binary system. We make no pre-assumptions on the properties of the flow, instead our models evolve self-consistently from an initially non-accreting state. The viscosity is due to the the small-scale turbulence and it is described by the \\alpha-viscosity prescription. We confirm earlier suggestions that viscous accretion flows are convectively unstable. We found that the instability produces transient eddies of various length-scales. The eddies contribute to the strength of the viscosity in the flow by redistributing the angular momentum. They also introduce low amplitude oscillatory variations ...
Manmoto, T; Kusunose, M
1997-01-01
The global structure of optically thin advection dominated accretion flows which are composed of two-temperature plasma around black holes is calculated. We adopt the full set of basic equations including the advective energy transport in the energy equation for the electrons. The spectra emitted by the optically thin accretion flows are also investigated. The radiation mechanisms which are taken into accout are bremsstrahlung, synchrotron emission, and Comptonization. The calculation of the spectra and that of the structure of the accretion flows are made to be completely consistent by calculating the radiative cooling rate at each radius. As a result of the advection domination for the ions, the heat transport from the ions to the electrons becomes practically zero and the radiative cooling balances with the advective heating in the energy equation of the electrons. Following up on the successful work of Narayan et al. (1995), we applied our model to the spectrum of Sgr A*. We find that the spectrum of Sgr ...
Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman
2013-01-01
Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.
Study of an Advection-Reaction-Diffusion equation in a compressible flow field
Bianco, Federico; Prud'homme, Roger
2011-01-01
We have studied the front propagation in a one dimensional case of combustion by solving numerically an advection-reaction-diffusion equation. The physical model is simplified so that no coupling phenomena are considered and the reacting fluid is a binary mixture of gases. The compressible flow field is given analytically. We analyse the differences between popular models used in fundamental studies of compressible combustion and biological problems. Then, we investigate the effects of compressibility on the front interface dynamics for different reaction types and we characterise the conditions for which the reaction stops before its completion.
Structuring the hot advective accretion flow, as a result interaction of plasma with magnetic field
Yankova, Krasimira
2014-01-01
We present a magneto-hydrodynamic model developed for investigations of advective non-stationary, asymmetric Keplerian accretion disks in the normal magnetic field. The introduced model allows us to trace the evolution in different fixed moments and to get detailed description of the self-structuring of the disk. We have introduced "meeting coefficients" that define the feedback. It determines the impact from nonlinear effects have over the structure of the flow. We have obtained solutions for the radial structure of the disk for two crucial moments of its evolution.
Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows
Kazem Faghei
2012-03-01
In this paper, self-similar solutions of resistive advection dominated accretion flows (ADAF) in the presence of a pure azimuthal magnetic field are investigated. The mechanism of energy dissipation is assumed to be the viscosity and the magnetic diffusivity due to turbulence in the accretion flow. It is assumed that the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and -prescription is used for them. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. The solutions show that the structure of accretion flow depends on the magnetic field and the magnetic diffusivity. As the radial infall velocity and the temperature of the flow increase by magnetic diffusivity, the rotational velocity decreases. Also, the rotational velocity for all selected values of magnetic diffusivity and magnetic field is sub-Keplerian. The solutions show that there is a certain amount of magnetic field for which rotational velocity of the flow becomes zero. This amount of the magnetic field depends upon the gas properties of the disc, such as adiabatic index and viscosity, magnetic diffusivity, and advection parameters. The mass accretion rate increases by adding the magnetic diffusivity and the solutions show that in high magnetic pressure, the ratio of the mass accretion rate to the Bondi accretion rate is reduced with an increase in magnetic pressure. Also, the study of Lundquist and magnetic Reynolds numbers based on resistivity indicates that the linear growth of magnetorotational instability (MRI) of the flow reduces by resistivity. This property is qualitatively consistent with resistive magnetohydrodynamics (MHD) simulations.
Advection diffusion model for particles deposition in Rayleigh-Benard turbulent flows
In this paper, Direct Numerical Simulation (DNS) and Lagrangian Particle Tracking are used to precisely investigate the turbulent thermally driven flow and particles dispersion in a closed, slender cylindrical domain. The numerical simulations are carried out for Rayleigh (Ra) and Prandtl numbers (Pr) equal to Ra = 2X108 and Pr = 0.7, considering three sets of particles with Stokes numbers, based on Kolmogorov scale, equal to Stk 1.3, Stk 0.65 and Stk = 0.13. This data are used to calculate a priori the drift velocity and the turbulent diffusion coefficient for the Advection Diffusion model. These quantities are function of the Stokes, Froude, Rayleigh and Prandtl numbers only. One dimensional, time dependent, Advection- Diffusion Equation (ADE) is presented to predict particles deposition in Rayleigh-Benard flow in the cylindrical domain. This archetype configuration models flow and aerosol dynamics, produced in case of accident in the passive containment cooling system (PCCS) of a nuclear reactor. ADE results show a good agreement with DNS data for all the sets of particles investigated. (author)
Correlation networks from flows. The case of forced and time-dependent advection-diffusion dynamics
Tupikina, Liubov; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our r...
On a Flow-Based Paradigm in Modeling and Programming
Sabah Al-Fedaghi
2015-01-01
In computer science, the concept of flow is reflected in many terms such as data flow, control flow, message flow, information flow, and so forth. Many fields of study utilize the notion, including programming, communication (e.g., Shannon-Weaver communication model), software modeling, artificial intelligence, and knowledge representation. This paper focuses on two approaches that explicitly assert a flow-based paradigm: flow-based programming (FBP) and flowthing modeling (FM). The first is ...
Chakrabarti, Sandip K
2016-01-01
An accretion flow around a black hole has a saddle type sonic point just outside the event horizon to guarantee that the flow enters the black hole supersonically. This feature exclusively present in strong gravity limit makes its marks in every observation of black hole candidates. Another physical sonic point is present (as in a Bondi flow) even in weak gravity. Every aspect of spectral or temporal properties of every black hole can be understood using this transonic or advective flow having more than one saddle type points. This most well known and generalized solution with viscosity and radiative transfer has been verified by numerical simulations also. Spectra, computed for various combinations of the standard Keplerian, and advective sub-Keplerian components match accurately with those from satellite observations. Standing, oscillating and propagatory oscillating shocks are produced due to centrifugal barrier of the advective component. The post-shock region acts as the Compton cloud producing the power...
Mukhopadhyay, Banibrata
2016-01-01
We show that the removal of angular momentum is possible in the presence of large scale magnetic stresses, arisen by fields much stronger than that required for magnetorotational instability, in geometrically thick, advective, sub-Keplerian accretion flows around black holes in steady-state, in the complete absence of alpha-viscosity. The efficiency of such angular momentum transfer via Maxwell stress, with the field well below its equipartition value, could be equivalent to that of alpha-viscosity, arisen via Reynolds stress, with $\\alpha=0.01-0.08$. We find in our simpler vertically averaged advective disk model that stronger the magnetic field and/or larger the vertical-gradient of azimuthal component of magnetic field, stronger the rate of angular momentum transfer is, which in turn may lead to a faster rate of outflowing matter, which has important implications to describe the hard spectral states of black hole sources. When the generic origin of alpha-viscosity is still being explored, mechanism of effi...
Chakrabarti, Sandip K.
2016-01-01
An accretion flow around a black hole has a saddle type sonic point just outside the event horizon to guarantee that the flow enters the black hole supersonically. This feature exclusively present in strong gravity limit makes its marks in every observation of black hole candidates. Another physical sonic point is present (as in a Bondi flow) even in weak gravity. Every aspect of spectral or temporal properties of every black hole can be understood using this transonic or advective flow havin...
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Liubov Tupikina
Full Text Available Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet.
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Tupikina, Liubov; Molkenthin, Nora; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet. PMID:27128846
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics
Tupikina, Liubov; Molkenthin, Nora; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network’s structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet. PMID:27128846
In this study, two passive techniques are simultaneously investigated for heat transfer improvement (i.e. chaotic advection and nanofluids) in coiled heat exchangers. Performance of these two different coils (one with normal configuration and another with chaotic configuration) is numerically analyzed and compared for both water and nanofluid as fluid. Effects of different parameters such as geometry, types of nanofluids, nanoparticle volumetric concentration and Reynolds number on heat transfer and pressure drop are studied. The CuO and Al2O3 base water nanofluids with different nanoparticle concentrations 1–3% were simulated. Equations of conservation of mass, momentum and energy were discretized using a finite element based technique and were solved using ANSYS software. Numerical results showed that heat transfer in the chaotic coil with water as fluid was higher than that in the normal coil with nanofluids at various volumetric concentrations and addition small amount of nanofluid in the chaotic coil flow resulted in significant enhancement of heat transfer. - Highlights: • Nanofluids in a chaotic coil were investigated for heat transfer improvement. • Chaotic flow with water was more efficient than normal coil with nanofluids. • Nanofluid in chaotic flow resulted in significant enhancement of heat transfer. • Heat transfer improvement increased with higher concentration of nanoparticles
On a Flow-Based Paradigm in Modeling and Programming
Sabah Al-Fedaghi
2015-06-01
Full Text Available In computer science, the concept of flow is reflected in many terms such as data flow, control flow, message flow, information flow, and so forth. Many fields of study utilize the notion, including programming, communication (e.g., Shannon-Weaver communication model, software modeling, artificial intelligence, and knowledge representation. This paper focuses on two approaches that explicitly assert a flow-based paradigm: flow-based programming (FBP and flowthing modeling (FM. The first is utilized in programming and the latter in modeling (e.g., software development. Each produces a diagrammatic representation, and these are compared. The purpose is to promote progress in a flow-based paradigm and its utilization in the area of computer science. The resultant analysis highlights the fact that FBP and FM can benefit from each other’s methodology.
Volume of Fluid (VOF) type advection methods in two-phase flow: a comparative study
Aniszewski, Wojciech; Marek, Maciej
2014-01-01
In this paper, four distinct approaches to Volume of Fluid (VOF) computational method are compared. Two of the methods are the 'simplified' VOF formulations, in that they do not require geometrical interface reconstruction. The assessment is made possible by implementing all four approaches into the same code as a switchable options. This allows to rule out possible influence of other parts of numerical scheme, be it the discretisation of Navier-Stokes equations or chosen approximation of curvature, so that we are left with conclusive arguments because only one factor differs the compared methods. The comparison is done in the framework of CLSVOF (Coupled Level Set Volume of Fluid), so that all four methods are coupled with Level Set interface, which is used to compute pressure jump via the GFM (Ghost-Fluid Method). Results presented include static advections, full N-S solutions in laminar and turbulent flows. The paper is aimed at research groups who are implementing VOF methods in their computations or inte...
Kemner, K. M.; Boyanov, M.; Flynn, T. M.; O'Loughlin, E. J.; Antonopoulos, D. A.; Kelly, S.; Skinner, K.; Mishra, B.; Brooks, S. C.; Watson, D. B.; Wu, W. M.
2015-12-01
FeIII- and SO42--reducing microorganisms and the mineral phases they produce have profound implications for many processes in aquatic and terrestrial systems. In addition, many of these microbially-catalysed geochemical transformations are highly dependent upon introduction of reactants via advective and diffusive hydrological transport. We have characterized microbial communities from a set of static microcosms to test the effect of ethanol diffusion and sulfate concentration on UVI-contaminated sediment. The spatial distribution, valence states, and speciation of both U and Fe were monitored in situ throughout the experiment by synchrotron x-ray absorption spectroscopy, in parallel with solution measurements of pH and the concentrations of sulfate, ethanol, and organic acids. After reaction initiation, a ~1-cm thick layer of sediment near the sediment-water (S-W) interface became visibly dark. Fe XANES spectra of the layer were consistent with the formation of FeS. Over the 4 year duration of the experiment, U LIII-edge XANES indicated reduction of U, first in the dark layer and then throughout the sediment. Next, the microcosms were disassembled and samples were taken from the overlying water and different sediment regions. We extracted DNA and characterized the microbial community by sequencing 16S rRNA gene amplicons with the Illumina MiSeq platform and found that the community evolved from its originally homogeneous composition, becoming significantly spatially heterogeneous. We have also developed an x-ray accessible column to probe elemental transformations as they occur along the flow path in a porous medium with the purpose of refining reactive transport models (RTMs) that describe coupled physical and biogeochemical processes in environmental systems. The elemental distribution dynamics and the RTMs of the redox driven processes within them will be presented.
Wang, Jian-Min; Cheng, Cheng; Li, Yan-Rong
2012-04-01
We investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAFs), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting the angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong- and weak-coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and are mainly determined by the black hole potential, respectively. We propose the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong-coupling case. For the weak-coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to an accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to a collapse of the ADAF, and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, low ionization nuclear emission regions, and BL Lac objects.
Fan, Yi; Schlick, Conor; Isner, Austin; Ottino, Julio; Umbanhowar, Paul; Richard, Lueptow
2014-01-01
Segregation of granular materials composed of different-sized particles has important repercussions in various industrial processes and natural phenomena, but predicting size segregation remains a challenging problem. To address this problem, we have developed a theoretical model that captures the interplay between advection, segregation, and diffusion in size bidisperse granular materials. The fluxes associated with these three driving factors depend on the underlying kinematics, whose chara...
Mignone, A; Stute, M; Kolb, S M; Muscianisi, G
2012-01-01
Explicit numerical computations of super-fast differentially rotating disks are subject to the time-step constraint imposed by the Courant condition. When the bulk orbital velocity largely exceeds any other wave speed the time step is considerably reduced and a large number of steps may be necessary to complete the computation. We present a robust numerical scheme to overcome the Courant limitation by extending the algorithm previously known as FARGO (Fast Advection in Rotating Gaseous Objects) to the equations of magnetohydrodynamics (MHD). The proposed scheme conserves total angular momentum and energy to machine precision and works in Cartesian, cylindrical, or spherical coordinates. The algorithm is implemented in the PLUTO code for astrophysical gasdynamics and is suitable for local or global simulations of accretion or proto-planetary disk models. By decomposing the total velocity into an average azimuthal contribution and a residual term, the algorithm solves the MHD equations through a linear transpor...
Hornby, P. G.
2005-12-01
Understanding chemical and thermal processes taking place in hydrothermal mineral deposition systems could well be a key to unlocking new mineral reserves through improved targeting of exploration efforts. To aid in this understanding it is very helpful to be able to model such processes with sufficient fidelity to test process hypotheses. To gain understanding, it is often sufficient to obtain semi-quantitative results that model the broad aspects of the complex set of thermal and chemical effects taking place in hydrothermal systems. For example, it is often sufficient to gain an understanding of where thermal, geometric and chemical factors converge to precipitate gold (say) without being perfectly precise about how much gold is precipitated. The traditional approach is to use incompressible Darcy flow together with the Boussinesq approximation. From the flow field, the heat equation is used to advect-conduct the heat. The flow field is also used to transport solutes by solving an advection-dispersion-diffusion equation. The reactions in the fluid and between fluid and rock act as source terms for these advection-dispersion equations. Many existing modelling systems that are used for simulating such systems use explicit time marching schemes and finite differences. The disadvantage of this approach is the need to work on rectilinear grids and the number of time steps required by the Courant condition in the solute transport step. The second factor can be particularly significant if the chemical system is complex, requiring (at a minimum) an equilibrium calculation at each grid point at each time step. In the approach we describe, we use finite elements rather than finite differences, and the pressure, heat and advection-dispersion equations are solved implicitly. The general idea is to put unconditional numerical stability of the time integration first, and let accuracy assume a secondary role. It is in this sense that the method is semi-quantiative. However
Debnath, Dipak; Mondal, Santanu; Chakrabarti, Sandip K.
2015-02-01
We study spectral properties of GX 339-4 during its 2010-11 outburst with two component advective flow (TCAF) model after its inclusion in XSPEC as a table model. We compare results fitted by TCAF model with combined disc blackbody and power-law model. For a spectral fit, we use 2.5-25 keV spectral data of the Proportional Counter Array instrument onboard RXTE satellite. From our fit, accretion flow parameters such as Keplerian (disc) rate, sub-Keplerian (halo) rate, location and strength of shock are extracted. We quantify how the disc and the halo rates vary during the entire outburst. We study how the halo to disc accretion rate ratio (ARR), quasi-periodic oscillations (QPOs), shock locations and its strength vary when the system passes through hard, hard-intermediate, soft-intermediate and soft states. We find pieces of evidence of monotonically increasing and decreasing nature of QPO frequencies depending on the variation of ARR during rising and declining phases. Interestingly, on days of transition from hard state to hard-intermediate spectral state (during the rising phase) or vice-versa (during decline phase), ARR is observed to be locally maximum. Non-constancy of ARR while obtaining reasonable fits points to the presence of two independent components in the flow.
Mukhopadhyay, Banibrata
2015-01-01
We show that the removal of angular momentum is possible in the presence of large scale magnetic stresses in geometrically thick, advective, sub-Keplerian accretion flows around black holes in steady-state, in the complete absence of alpha-viscosity. The efficiency of such an angular momentum transfer could be equivalent to that of alpha-viscosity with alpha=0.01-0.08. Nevertheless, required field is well below its equipartition value, leading to a magnetically stable disk flow. This is essentially important in order to describe the hard spectral state of the sources, when the flow is non/sub-Keplerian. We show in our simpler 1.5-dimensional, vertically averaged disk model that larger the vertical-gradient of azimuthal component of magnetic field, stronger the rate of angular momentum transfer is, which in turn may lead to a faster rate of outflowing matter. Finding efficient angular momentum transfer, in black hole disks, via magnetic stresses alone is very interesting, when the generic origin of alpha-visco...
Debnath, Dipak; Chakrabarti, Sandip K
2013-01-01
We study the spectral properties of the Galactic transient black hole candidate (BHC) GX 339-4 during its 2010-11 outburst with Two Component (Keplerian and sub-Keplerian) Advective Flow (TCAF) model after its inclusion in XSPEC as a local model. We also compare our TCAF model fitted results with combined disk black body (DBB) and power-law (PL) model fitted spectral results and find similar types of smooth variation in thermal (Keplerian or disk black body) as well as non-thermal (power-law or sub-Keplerian) fluxes. For spectral fit, we use 2.5-25 keV spectral data of PCA instrument onboard RXTE satellite. From the TCAF model fit, accretion flow parameters, such as the Keplerian (disk) rate, sub-Keplerian (halo) rate, location of the shock and strength of the shock are extracted. Our study provides a comprehensive understanding of the mass accretion processes and properties of the accretion disk around the BHC during the outburst phases. Based on the comparison of the halo to disk accretion rate ratio (ARR) ...
Frontiers of chaotic advection
Aref, Hassan; Budišić, Marko; Cartwright, Julyan H E; Clercx, Herman J H; Feudel, Ulrike; Golestanian, Ramin; Gouillart, Emmanuelle; Guer, Yves Le; van Heijst, GertJan F; Krasnopolskaya, Tatyana S; MacKay, Robert S; Meleshko, Vyacheslav V; Metcalfe, Guy; Mezić, Igor; de Moura, Alessandro P S; Omari, Kamal El; Piro, Oreste; Speetjens, Michel F M; Sturman, Rob; Thiffeault, Jean-Luc; Tuval, Idan
2014-01-01
We review the present position of and survey future perspectives in the physics of chaotic advection; the field that emerged three decades ago at the intersection of fluid mechanics and nonlinear dynamics, which encompasses a range of applications with length scales ranging from micrometers to hundreds of kilometers, including systems as diverse as mixing and thermal processing of viscous fluids, micro-fluidics, biological flows, and large-scale dispersion of pollutants in oceanographic and atmospheric flows.
Optimal power flow application issues in the Pool paradigm
This paper focuses on the application of the Optimal Power Flow (OPF) to competitive markets. Since the OPF is a central decision-making tool its application to the more decentralized decision-making in the competitive electricity markets requires considerable care. There are some intrinsic challenges associated with the effective OPF application in the competitive environment due to the inherent characteristics of the OPF formulation. Two such characteristics are the flatness of the optimum surface and the consequent continuum associated with the optimum. In addition to these OPF structural characteristics, the level of authority vested in the central decision-making entity has major ramifications. These factors have wide ranging economic impacts, whose implications are very pronounced due to the fact that, unlike in the old vertically integrated utility environment, various market players are affected differently. The effects include price volatility, financial health of various players and the integrity of the market itself. We apply appropriate metrics to evaluate market efficiency and how the various players fare. We study the impacts of OPF applications in the Pool paradigm, with both supply and demand side explicitly modeled, and provide extensive numerical results on systems based on IEEE 30-bus and 118-bus networks. The results show the variability of nodal prices and the skew possible in different 'optimal' allocations among competing suppliers. Such variability in the results may lead to serious disputes among the players and the central decision-making authority. Directions for future research are discussed. (author)
Kurylyk, Barret L.; McKenzie, Jeffrey M; MacQuarrie, Kerry T. B.; Voss, Clifford I.
2014-01-01
Numerous cold regions water flow and energy transport models have emerged in recent years. Dissimilarities often exist in their mathematical formulations and/or numerical solution techniques, but few analytical solutions exist for benchmarking flow and energy transport models that include pore water phase change. This paper presents a detailed derivation of the Lunardini solution, an approximate analytical solution for predicting soil thawing subject to conduction, advection, and phase change. Fifteen thawing scenarios are examined by considering differences in porosity, surface temperature, Darcy velocity, and initial temperature. The accuracy of the Lunardini solution is shown to be proportional to the Stefan number. The analytical solution results obtained for soil thawing scenarios with water flow and advection are compared to those obtained from the finite element model SUTRA. Three problems, two involving the Lunardini solution and one involving the classic Neumann solution, are recommended as standard benchmarks for future model development and testing.
Liu; Yuan; Meyer; Meyer-Hofmeister; Xie
1999-12-10
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region. PMID:10566989
Lester, D R; Metcalfe, Guy
2016-01-01
The macroscopic spreading and mixing of solute plumes in saturated porous media is ultimately controlled by processes operating at the pore scale. Whilst the conventional picture of pore-scale mechanical dispersion and molecular diffusion leading to persistent hydrodynamic dispersion is well accepted, this paradigm is inherently two-dimensional (2D) in nature and neglects important three-dimensional (3D) phenomena. We discuss how the kinematics of steady 3D flow at the porescale generate chaotic advection, involving exponential stretching and folding of fluid elements,the mechanisms by which it arises and implications of microscopic chaos for macroscopic dispersion and mixing. Prohibited in steady 2D flow due to topological constraints, these phenomena are ubiquitous due to the topological complexity inherent to all 3D porous media. Consequently 3D porous media flows generate profoundly different fluid deformation and mixing processes to those of 2D flow. The interplay of chaotic advection and broad transit t...
Cao, Xinwu
2010-01-01
The broad-line region (BLR) disappears in many low-luminosity AGNs, the reason of which is still controversial. The BLRs in AGNs are believed to be associated with the outflows from the accretion disks. Most of the low-luminosity AGNs (LLAGNs) contain advection dominated accretion flows (ADAFs), which are very hot and have a positive Bernoulli parameter. ADAFs are therefore associated with strong outflows. We estimate the cooling of the outflows from the ADAFs, and find that the gases in such hot outflows always cannot be cooled efficiently by bremsstrahlung radiation. The ADAF may co-exist with the standard disk, i.e., the inner ADAF connects to the outer thin accretion disk at radius R_tr, in the sources accreting at slightly lower than the critical rate. For the ADAFs with >0.001 L_edd, a secondary small inner cold disk is suggested to co-exist with the ADAF due to the condensation process. We estimate the Compton cooling of the outflow, of which the soft seed photons either come from the outer cold disk o...
A New Paradigm for Flow Analyses and a Novel Technique to Enhance the Thrust from Scarfed Nozzles
Chang, I-Shih; Chang, Sin-Chung; Glick, Robert L.; Chang, Chau-Lyan; Glick, Mailyn P.
2008-01-01
A new flow analysis paradigm and a novel technique to enhance scarfed nozzle thrust are presented. The new paradigm, the space-time Conservation Element and Solution Element (CESE) method, a truly unsteady and genuinely multi-dimensional flow solver that provides accurate solutions for Euler and Navier-Stokes flows, is well suited for next generation flow analyses.In this study, the space-time CESE method was applied to solve scarfed nozzles flow-fields. Nozzle scarfing is frequently used for vectoring control of a space propulsion sub-system; it reduces nozzle weight and length and lowers nozzle thrust. A novel technique to enhance scarfed nozzles' thrust is discussed and investigated. Results of 2D and 3D flow analyses are presented.
Ya-Di Xu; Xin-Wu Cao
2009-01-01
It was found that advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SEDs) of two low- luminosity active galactic nuclei (AGNs), provided they are accreting at ～ 0.01 - 0.03 Eddington rates and the thin disks are truncated to ADAFs at～ 100Rs (Rs is the Schwarzschild radius) for M81 and NGC 4579 (Quataert et al. 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two low- luminosity AGNs, if the black hole is accreting at 2.5 × 10-4 Eddington rates with the thin disk truncated at Rtr = 120Rs for M81 ((m) = 3.3 × 10-3 and Rtr = 80Rs are required for NGC 4579). The transition zones with temperature from the thin disk with 104 - 105 to～109 - 1010 K in the ADAF will inevitably emit thermal X-ray lines, which provides a useful diagnosis of their physical properties. The observed widths of the thermal X-ray iron lines at(～)6.8 keV are consistent with Doppler broadening by Keplerian motion of the gases in the transition zones at～100Rs. We use the structure of the transition zone between the ADAF and the thin disk derived by assuming the turbulent diffusive heat mechanism to calculate their thermal X-ray line emission with the standard software package Astrophysical Plasma Emission Code (APEC). Comparing them with the equivalent widths of the observed thermal X-ray iron lines in these two sources, we find that the turbulent diffusive heat mechanism seems to be unable to reproduce the ob- served thermal X-ray line emission. The test of the evaporation model for the accretion mode transition with the observed thermal X-ray line emission is briefly discussed.
Passive advection in nonlinear medium
Chertkov, M
1998-01-01
Forced advection of passive tracer, $\\theta $, in nonlinear relaxational medium by large scale (Batchelor problem) incompressible velocity field at scales less than the correlation length of the flow and larger than the diffusion scale is considered. Effective theory explaining small scale scalar fluctuations is proven to be linear, asymptotic free (downscales from the scale of the pumping) and universal. Only three parameters are required to decribe exhaustively the small scale statistics of scalar difference: two velocity-dependent ones, average and dispersion ($\\bar{\\lambda}$ and $\\Delta $ respectively) of the exponential stretching rate of a trial line element, and fluctuations. $\\alpha $ is an explicit functional of potential chracterized medium nonlinearity and amplitude of $\\theta ^{2}$ flux pumped into the system. Structure functions show an extremely anomalous, intermittent behavior: $ \\sim r^{\\xi_{q}}, \\xi_{q} = \\min {q,\\sqrt{[
Using the Statecharts paradigm for simulation of patient flow in surgical care.
Sobolev, Boris; Harel, David; Vasilakis, Christos; Levy, Adrian
2008-03-01
Computer simulation of patient flow has been used extensively to assess the impacts of changes in the management of surgical care. However, little research is available on the utility of existing modeling techniques. The purpose of this paper is to examine the capacity of Statecharts, a system of graphical specification, for constructing a discrete-event simulation model of the perioperative process. The Statecharts specification paradigm was originally developed for representing reactive systems by extending the formalism of finite-state machines through notions of hierarchy, parallelism, and event broadcasting. Hierarchy permits subordination between states so that one state may contain other states. Parallelism permits more than one state to be active at any given time. Broadcasting of events allows one state to detect changes in another state. In the context of the peri-operative process, hierarchy provides the means to describe steps within activities and to cluster related activities, parallelism provides the means to specify concurrent activities, and event broadcasting provides the means to trigger a series of actions in one activity according to transitions that occur in another activity. Combined with hierarchy and parallelism, event broadcasting offers a convenient way to describe the interaction of concurrent activities. We applied the Statecharts formalism to describe the progress of individual patients through surgical care as a series of asynchronous updates in patient records generated in reaction to events produced by parallel finite-state machines representing concurrent clinical and managerial activities. We conclude that Statecharts capture successfully the behavioral aspects of surgical care delivery by specifying permissible chronology of events, conditions, and actions. PMID:18390170
Advection around ventilated U-shaped burrows: A model study
Brand, Andreas; Lewandowski, JöRg; Hamann, Enrico; Nützmann, Gunnar
2013-05-01
Advective transport in the porous matrix of sediments surrounding burrows formed by fauna such as Chironomus plumosus has been generally neglected. A positron emission tomography study recently revealed that the pumping activity of the midge larvae can indeed induce fluid flow in the sediment. We present a numerical model study which explores the conditions at which advective transport in the sediment becomes relevant. A 0.15 m deep U-shaped burrow with a diameter of 0.002 m within the sediment was represented in a 3-D domain. Fluid flow in the burrow was calculated using the Navier-Stokes equation for incompressible laminar flow in the burrow, and flow in the sediment was described by Darcy's law. Nonreactive and reactive transport scenarios were simulated considering diffusion and advection. The pumping activity of the model larva results in considerable advective flow in the sediment at reasonable high permeabilities with flow velocities of up to 7.0 × 10-6 m s-1 close to the larva for a permeability of 3 × 10-12 m2. At permeabilities below 7 × 10-13 m2 advection is negligible compared to diffusion. Reactive transport simulations using first-order kinetics for oxygen revealed that advective flux into the sediment downstream of the pumping larva enhances sedimentary uptake, while the advective flux into the burrow upstream of the larvae inhibits diffusive sedimentary uptake. Despite the fact that both effects cancel each other with respect to total solute uptake, the advection-induced asymmetry in concentration distribution can lead to a heterogeneous solute and redox distribution in the sediment relevant to complex reaction networks.
Advection-Dominated Accretion with Infall and Outflows
Beckert, Thomas
2000-01-01
We present self-similar solutions for advection-dominated accretion flows with radial viscous force in the presence of outflows from the accretion flow or infall. The axisymmetric flow is treated in variables integrated over polar sections and the effects of infall and outflows on the accretion flow are parametrised for possible configurations compatible with the self-similar solution. We investigate the resulting accretion flows for three different viscosity laws and derive upper limits on t...
How to Determine Losses in a Flow Field: A Paradigm Shifttowards the Second Law Analysis
Heinz Herwig
2014-05-01
Full Text Available Assuming that CFD solutions will be more and more used to characterizelosses in terms of drag for external flows and head loss for internal flows, we suggest toreplace single-valued data, like the drag force or a pressure drop, by field information aboutthe losses. These information are gained when the entropy generation in the flow field isanalyzed, an approach that often is called second law analysis (SLA, referring to the secondlaw of thermodynamics. We show that this SLA approach is straight-forward, systematicand helpful when it comes to the physical interpretation of the losses in a flow field. Variousexamples are given, including external and internal flows, two phase flow, compressible flowand unsteady flow. Finally, we show that an energy transfer within a certain process can beput into a broader perspective by introducing the entropic potential of an energy.
Depletion of advection in turbulent scalar mixing
Bos, Wouter J T; Fang, Le [LMFA, CNRS, Ecole centrale de Lyon, Universite de Lyon, Ecully (France); Rubinstein, Robert, E-mail: wouter.bos@ec-lyon.fr [Newport News, VA (United States)
2011-12-22
In turbulent scalar mixing the mean square advection is strongly suppressed with respect to its Gaussian estimate. This effect is particularly important in the small scales and related to the scales in which diffusion plays a role. The link with the generation of passive scalar fronts is discussed and it is argued that scalar fronts are the consequence of the underlying suppression of nonlinearity observed in a wide class of flows for which the dynamics are governed by quadratic nonlinearities or pseudo-nonlinearities.
A generalized advection dispersion equation
Abdon Atangana
2014-02-01
This paper examines a possible effect of uncertainties, variability or heterogeneity of any dynamic system when being included in its evolution rule; the notion is illustrated with the advection dispersion equation, which describes the groundwater pollution model. An uncertain derivative is defined; some properties of the operator are presented. The operator is used to generalize the advection dispersion equation. The generalized equation differs from the standard equation in four properties. The generalized equation is solved via the variational iteration technique. Some illustrative figures are presented.
Fast multigrid solution of the advection problem with closed characteristics
Yavneh, I. [Israel Inst. of Technology, Haifa (Israel); Venner, C.H. [Univ. of Twente, Enschede (Netherlands); Brandt, A. [Weizmann Inst. of Science, Rehovot (Israel)
1996-12-31
The numerical solution of the advection-diffusion problem in the inviscid limit with closed characteristics is studied as a prelude to an efficient high Reynolds-number flow solver. It is demonstrated by a heuristic analysis and numerical calculations that using upstream discretization with downstream relaxation-ordering and appropriate residual weighting in a simple multigrid V cycle produces an efficient solution process. We also derive upstream finite-difference approximations to the advection operator, whose truncation terms approximate {open_quotes}physical{close_quotes} (Laplacian) viscosity, thus avoiding spurious solutions to the homogeneous problem when the artificial diffusivity dominates the physical viscosity.
Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes
Mukhopadhyay, B
1998-01-01
We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.
Measuring groundwater transport through lake sediments by advection and diffusion
A method for estimating low rates of groundwater inflow and outflow through the bottom sediments of surface waters was developed and tested. A one-dimensional advection-diffusion model was fitted to measured pore water profiles of two nonreactive solutes, tritiated water and chloride, and the advection rate was calculated by a nonlinear least squares technique. Using 3H profiles measured 0-0.5 m below the sediment-water interface, rates of groundwater advection into a lake through interbedded sands and gyttja were estimated to be about 1.0 m/year. In midlake locations underlain by soft organic gyttja, rates of advection were much lower (<0.1 m/year). Knowledge of the rate and direction of groundwater flow substantially altered the interpretation of pore water profiles within the sediments and the fluxes of solutes. This technique can be used to estimate flow rates less than 2 m/annum with minimal disturbance, without enclosing the sediments in a container, in a diversity of systems. (author)
Topology preserving advection of implicit interfaces on Cartesian grids
Qin, Zhipeng; Delaney, Keegan; Riaz, Amir; Balaras, Elias
2015-06-01
Accurate representation of implicit interface topology is important for the numerical computation of two phase flow on Cartesian grids. A new method is proposed for the construction of signed distance function by geometrically projecting interface topology onto the Cartesian grid using a multi-level projection framework. The method involves a stepwise improvement in the approximation to the signed distance function based on pointwise, piecewise and locally smooth reconstructions of the interface. We show that this approach provides accurate representation of the projected interface and its topology on the Cartesian grid, including the distance from the interface and the interface normal and curvature. The projected interface can be in the form of either a connected set of marker particles that evolve with Lagrangian advection, or a discrete set of points associated with an implicit interface that evolves with the advection of a scalar function. The signed distance function obtained with geometric projection is independent of the details of the scaler field, in contrast to the conventional approach where advection and reinitialization cannot be decoupled. As a result, errors introduced by reinitialization do not amplify advection errors, which leads to substantial improvement in both volume conservation and topology representation.
Oceanic heat advection to the Arctic in the last Millennium
Spielhagen, Robert F.; Werner, Kirstin; Aagaard-Sørensen, Steffen; Zamelczyk, Katarzyna; Kandiano, Evguenia; Budeus, Gereon; Husum, Katrine; Marchitto, Thomas M.; Hald, Morten
2011-01-01
EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its ...
NONE
1998-12-31
This conference day was jointly organized by the `university group of thermal engineering (GUT)` and the French association of thermal engineers. This book of proceedings contains 7 papers entitled: `energy spectra of a passive scalar undergoing advection by a chaotic flow`; `analysis of chaotic behaviours: from topological characterization to modeling`; `temperature homogeneity by Lagrangian chaos in a direct current flow heat exchanger: numerical approach`; ` thermal instabilities in a mixed convection phenomenon: nonlinear dynamics`; `experimental characterization study of the 3-D Lagrangian chaos by thermal analogy`; `influence of coherent structures on the mixing of a passive scalar`; `evaluation of the performance index of a chaotic advection effect heat exchanger for a wide range of Reynolds numbers`. (J.S.)
Cellwise conservative unsplit advection for the volume of fluid method
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2015-02-01
We present a cellwise conservative unsplit (CCU) advection scheme for the volume of fluid method (VOF) in 2D. Contrary to other schemes based on explicit calculations of the flux balances, the CCU advection adopts a cellwise approach where the pre-images of the control volumes are traced backwards through the flow map. The donating regions of the fluxes are calculated via the streaklines of the grid intersections, represented as polygonal chains whose vertices are determined by backward tracing of particles injected in the flow at different times. High order accuracy is obtained from the fourth-order Runge-Kutta method, where intermediate velocities along pathlines are determined with quadratic temporal and bicubic spatial interpolations. The volumes of the donating regions are corrected in order to fulfill the discrete continuity of incompressible flows. Consequently, the calculation produces non-overlapping donating regions and pre-images with conforming edges to their neighbors, resulting in the conservativeness and the boundedness (liquid volume fraction inside the interval [ 0 , 1 ]) of the CCU advection scheme. Finally, the update of the liquid volume fractions is computed from the intersections of the pre-image polygons with the reconstructed interfaces. The CCU scheme is tested on several benchmark tests for the VOF advection, together with the standard piecewise linear interface calculation (PLIC). The geometrical errors of the CCU compare favorably with other unsplit VOF-PLIC schemes. Finally, potential improvements of the VOF method with the use of more precise interface representation techniques and the future extension of the CCU scheme to 3D are discussed.
Verification of Advective Bar Elements Implemented in the Aria Thermal Response Code.
Mills, Brantley [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
A verification effort was undertaken to evaluate the implementation of the new advective bar capability in the Aria thermal response code. Several approaches to the verification process were taken : a mesh refinement study to demonstrate solution convergence in the fluid and the solid, visually examining the mapping of the advective bar element nodes to the surrounding surfaces, and a comparison of solutions produced using the advective bars for simple geometries with solutions from commercial CFD software . The mesh refinement study has shown solution convergence for simple pipe flow in both temperature and velocity . Guidelines were provided to achieve appropriate meshes between the advective bar elements and the surrounding volume. Simulations of pipe flow using advective bars elements in Aria have been compared to simulations using the commercial CFD software ANSYS Fluent (r) and provided comparable solutions in temperature and velocity supporting proper implementation of the new capability. Verification of Advective Bar Elements iv Acknowledgements A special thanks goes to Dean Dobranich for his guidance and expertise through all stages of this effort . His advice and feedback was instrumental to its completion. Thanks also goes to Sam Subia and Tolu Okusanya for helping to plan many of the verification activities performed in this document. Thank you to Sam, Justin Lamb and Victor Brunini for their assistance in resolving issues encountered with running the advective bar element model. Finally, thanks goes to Dean, Sam, and Adam Hetzler for reviewing the document and providing very valuable comments.
Kinetics and spatial organization in reactive systems with nonpassively advected reactants
A reactive system under the influence of a turbulent flow leads to a diversity of kinetic regimes that result from the interplay between reaction, advection and drag forces. Inertial bias collects reactants preferentially in certain regions of the flow depending on their density, and this fact strongly determines the overall kinetic behaviour and the spatial organization of the reactive mixture. We present a Eulerian scheme for the advection terms in a kinetic mean-field model that is better suited to the study of nonpassively advected reactive systems than the original Lagrangian approach. We show two examples of these systems: first, a formal study of the typical binary diffusion-controlled reaction A+B →0, when the reactants are nonpassively advected; second, application to the study of plankton dynamics in the ocean that reproduces the well-known periodically sustained plankton blooms
Cellwise conservative unsplit advection for the volume of fluid method
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2015-01-01
We present a cellwise conservative unsplit (CCU) advection scheme for the volume of fluid method (VOF) in 2D. Contrary to other schemes based on explicit calculations of the flux balances, the CCU advection adopts a cellwise approach where the pre-images of the control volumes are traced...... improvements of the VOF method with the use of more precise interface representation techniques and the future extension of the CCU scheme to 3D are discussed. ©2014 Elsevier Inc. All rights reserved.......-order Runge–Kutta method, where intermediate velocities along pathlines are determined with quadratic temporal and bicubic spatial interpolations. The volumes of the donating regions are corrected in order to fulfill the discrete continuity of incompressible flows. Consequently, the calculation produces non...
Turbulent dynamo with advective magnetic helicity flux
Del Sordo, Fabio; Brandenburg, Axel
2012-01-01
Many astrophysical bodies harbor magnetic fields that are thought to be sustained by dynamo processes. However, it has been argued that the production of large-scale magnetic fields by a mean-field dynamo is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of magnetic helicity. This phenomenon is known as catastrophic quenching. Advection of magnetic field toward the outer boundaries and away from the dynamo is expected to alleviate such quenching. Examples are stellar and galactic winds. Such advection might be able to overcome the constraint imposed by the conservation of magnetic helicity, transporting a fraction of it outside the domain in which the dynamo operates. We study how the dynamo process is affected by advection. In particular, we study the relative roles played by advective and diffusive fluxes of magnetic helicity. We do this by performing direct numerical simulations of a turbulent dynamo of alpha^2 type driven by forced turbulence in a Cartesian domain in the ...
Besancenot, Damien; Dogguy, Habib
2011-01-01
This paper analyses the consequences of young researchers' scientifc choice on the dynamics of sciences. We develop a simple two state mean field game model to analyze the competition between two paradigms based on Kuhn's theory of scientifc revolutions. At the beginning of their career, young researchers choose the paradigm in which they want to work according to social and personal motivations. Despite the possibility of multiple equilibria the model exhibits at least one stable solution in...
Effect of Ionic Advection on Electroosmosis over Charge Surfaces: Beyond the Weak Field Limit
Ghosh, Uddipta
2015-01-01
The present study deals with the effect of ionic advection on electroosmotic flow over charge modulated surfaces in a generalized paradigm when the classically restrictive "weak field" limit may be relaxed. Going beyond the commonly portrayed weak field limit (i.e, the externally applied electric field is over-weighed by the surface-induced electrical potential, towards charge distribution in an electrified wall-adhering layer) for electroosmotic transport, we numerically solve the coupled full set of Poisson-Nernst-Planck (PNP) and Navier-Stokes equations, in a semi-infinite domain, bounded at the bottom by a charged wall. Further, in an effort to obtain deeper physical insight, we solve the simplified forms of the relevant governing equations for low surface potential in two separate asymptotic limits: (i) a regular perturbation solution for Low Ionic Peclet number (Pe), where Pe is employed as the gauge function and (ii) a matched asymptotic solution for O(1) Pe in the Thin Electric Double Layer (EDL) limi...
In this paper advected invariants and conservation laws in ideal magnetohydrodynamics (MHD) and gas dynamics are obtained using Lie dragging techniques. There are different classes of invariants that are advected or Lie dragged with the flow. Simple examples are the advection of the entropy S (a 0-form), and the conservation of magnetic flux (an invariant 2-form advected with the flow). The magnetic flux conservation law is equivalent to Faraday's equation. The gauge condition for the magnetic helicity to be advected with the flow is determined. Different variants of the helicity in ideal fluid dynamics and MHD including: fluid helicity, cross helicity and magnetic helicity are investigated. The fluid helicity conservation law and the cross-helicity conservation law in MHD are derived for the case of a barotropic gas. If the magnetic field lies in the constant entropy surface, then the gas pressure can depend on both the entropy and the density. In these cases the conservation laws are local conservation laws. For non-barotropic gases, we obtain nonlocal conservation laws for fluid helicity and cross helicity by using Clebsch variables. These nonlocal conservation laws are the main new results of the paper. Ertel's theorem and potential vorticity, the Hollman invariant, and the Godbillon–Vey invariant for special flows for which the magnetic helicity is zero are also discussed. (paper)
Waste dissolution with chemical reaction, diffusion and advection
This paper extends the mass-transfer analysis to include the effect of advective transport in predicting the steady-state dissolution rate, with a chemical-reaction-rate boundary condition at the surface of a waste form of arbitrary shape. This new theory provides an analytic means of predicting the ground-water velocities at which dissolution rate in a geologic environment will be governed entirely to the chemical reaction rate. As an illustration, we consider the steady-state potential flow of ground water in porous rock surrounding a spherical waste solid. 3 refs., 2 figs
Discrete Lie Advection of Differential Forms
Mullen, P; Pavlov, D; Durant, L; Tong, Y; Kanso, E; Marsden, J E; Desbrun, M
2009-01-01
In this paper, we present a numerical technique for performing Lie advection of arbitrary differential forms. Leveraging advances in high-resolution finite volume methods for scalar hyperbolic conservation laws, we first discretize the interior product (also called contraction) through integrals over Eulerian approximations of extrusions. This, along with Cartan's homotopy formula and a discrete exterior derivative, can then be used to derive a discrete Lie derivative. The usefulness of this operator is demonstrated through the numerical advection of scalar fields and 1-forms on regular grids.
Dense-gas dispersion advection-diffusion model
A dense-gas version of the ADPIC particle-in-cell, advection- diffusion model was developed to simulate the atmospheric dispersion of denser-than-air releases. In developing the model, it was assumed that the dense-gas effects could be described in terms of the vertically-averaged thermodynamic properties and the local height of the cloud. The dense-gas effects were treated as a perturbation to the ambient thermodynamic properties (density and temperature), ground level heat flux, turbulence level (diffusivity), and windfield (gravity flow) within the local region of the dense-gas cloud. These perturbations were calculated from conservation of energy and conservation of momentum principles along with the ideal gas law equation of state for a mixture of gases. ADPIC, which is generally run in conjunction with a mass-conserving wind flow model to provide the advection field, contains all the dense-gas modifications within it. This feature provides the versatility of coupling the new dense-gas ADPIC with alternative wind flow models. The new dense-gas ADPIC has been used to simulate the atmospheric dispersion of ground-level, colder-than-ambient, denser-than-air releases and has compared favorably with the results of field-scale experiments
Voltrová, Svatava; Šrogl, Jiří
2014-01-01
Roč. 1, č. 9 (2014), s. 1067-1071. ISSN 2052-4129 R&D Projects: GA MŠk LH12013 Institutional support: RVO:61388963 Keywords : Sonogashira * cross-coupling * flow chemistry Subject RIV: CC - Organic Chemistry
Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample
Ebner, Pirmin Philipp; Schneebeli, Martin; Steinfeld, Aldo
2016-04-01
Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m-1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.
Binning, Philip John; Postma, Diederik Jan; Russel, T.F.;
2007-01-01
Pyrite oxidation in unsaturated mine waste rock dumps and soils is limited by the supply of oxygen from the atmosphere. In models, oxygen transport through the subsurface is often assumed to be driven by diffusion. However, oxygen comprises 23.2% by mass of dry air, and when oxygen is consumed at...... depth in the unsaturated zone, a pressure gradient is created between the reactive zone and the ground surface, causing a substantial advective air flow into the subsurface. To determine the balance between advective and diffusive transport, a one-dimensional multicomponent unsaturated zone gas...... flows at steady state. However, greater pressure gradients are found in low-permeability soils. In transient cases, advective fluxes depend on the initial conditions and can be far greater than diffusive fluxes. In contrast to steady state conditions the transient case is sensitive to other model...
LIVIU GABRIEL CREŢU
2006-01-01
Full Text Available In the industrial age of the twenty century small firms or mass-production giants have been all organized on the classic principles defined by Smith, Taylor and Fayol. Lately, new organization theories have emerged to describe modern enterprises, process-oriented and much more agile in the new highly collaborative business landscape. Information and knowledge became the most important organizational assets as well as the basic concepts in enterprise architecture. This paper will provide an overview of organizational paradigms with respect to information and knowledge role in the business structure equation.
Asymmetric spreading in highly advective, disordered environments
Carpenter, John H.; Dahmen, Karin A.
2005-01-01
Spreading of bacteria in a highly advective, disordered environment is examined. Predictions of super-diffusive spreading for a simplified reaction-diffusion equation are tested. Concentration profiles display anomalous growth and super-diffusive spreading. A perturbation analysis yields a crossover time between diffusive and super-diffusive behavior. The time's dependence on the convection velocity and disorder is tested. Like the simplified equation, the full linear reaction-diffusion equat...
Distributed Parallel Particle Advection using Work Requesting
Muller, Cornelius; Camp, David; Hentschel, Bernd; Garth, Christoph
2013-09-30
Particle advection is an important vector field visualization technique that is difficult to apply to very large data sets in a distributed setting due to scalability limitations in existing algorithms. In this paper, we report on several experiments using work requesting dynamic scheduling which achieves balanced work distribution on arbitrary problems with minimal communication overhead. We present a corresponding prototype implementation, provide and analyze benchmark results, and compare our results to an existing algorithm.
Accuracy of spectral and finite difference schemes in 2D advection problems
Naulin, V.; Nielsen, A.H.
2003-01-01
In this paper we investigate the accuracy of two numerical procedures commonly used to solve 2D advection problems: spectral and finite difference (FD) schemes. These schemes are widely used, simulating, e.g., neutral and plasma flows. FD schemes have long been considered fast, relatively easy to...
A cryogenic circulating advective multi-pass absorption cell
A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 107 cm-3. A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.
A cryogenic circulating advective multi-pass absorption cell
Stockett, M. H.; Lawler, J. E. [Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706 (United States)
2012-03-15
A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 10{sup 7} cm{sup -3}. A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.
Chaotic advection in 2D anisotropic porous media
Varghese, Stephen; Speetjens, Michel; Trieling, Ruben; Toschi, Federico
2015-11-01
Traditional methods for heat recovery from underground geothermal reservoirs employ a static system of injector-producer wells. Recent studies in literature have shown that using a well-devised pumping scheme, through actuation of multiple injector-producer wells, can dramatically enhance production rates due to the increased scalar / heat transport by means of chaotic advection. However the effect of reservoir anisotropy on kinematic mixing and heat transport is unknown and has to be incorporated and studied for practical deployment in the field. As a first step, we numerically investigate the effect of anisotropy (both magnitude and direction) on (chaotic) advection of passive tracers in a time-periodic Darcy flow within a 2D circular domain driven by periodically reoriented diametrically opposite source-sink pairs. Preliminary results indicate that anisotropy has a significant impact on the location, shape and size of coherent structures in the Poincare sections. This implies that the optimal operating parameters (well spacing, time period of well actuation) may vary strongly and must be carefully chosen so as to enhance subsurface transport. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of Netherlands Organisation for Scientific Research (NWO). This research program is co-financed by Shell Global Solutions International B.V.
Happé, C M; Szulcek, R; Voelkel, N F; Bogaard, H J
2016-08-01
In pulmonary arterial hypertension (PAH) structural and functional abnormalities of the small lung vessels interact and lead to a progressive increase in pulmonary vascular resistance and right heart failure. A current pathobiological concept characterizes PAH as a 'quasi-malignant' disease focusing on cancer-like alterations in endothelial cells (EC) and the importance of their acquired apoptosis-resistant, hyper-proliferative phenotype in the process of vascular remodeling. While changes in pulmonary blood flow (PBF) have been long-since recognized and linked to the development of PAH, little is known about a possible relationship between an altered PBF and the quasi-malignant cell phenotype in the pulmonary vascular wall. This review summarizes recognized and hypothetical effects of an abnormal PBF on the pulmonary vascular bed and links these to quasi-malignant changes found in the pulmonary endothelium. Here we describe that abnormal PBF does not only trigger a pulmonary vascular cell growth program, but may also maintain the cancer-like phenotype of the endothelium. Consequently, normalization of PBF and EC response to abnormal PBF may represent a treatment strategy in patients with established PAH. PMID:26804008
Gjesdal, Thor
1997-12-31
This thesis discusses the development and application of efficient numerical methods for the simulation of fluid flows, in particular the flow of incompressible fluids. The emphasis is on practical aspects of algorithm development and on application of the methods either to linear scalar model equations or to the non-linear incompressible Navier-Stokes equations. The first part deals with cell centred multigrid methods and linear correction scheme and presents papers on (1) generalization of the method to arbitrary sized grids for diffusion problems, (2) low order method for advection-diffusion problems, (3) attempt to extend the basic method to advection-diffusion problems, (4) Fourier smoothing analysis of multicolour relaxation schemes, and (5) analysis of high-order discretizations for advection terms. The second part discusses a multigrid based on pressure correction methods, non-linear full approximation scheme, and papers on (1) systematic comparison of the performance of different pressure correction smoothers and some other algorithmic variants, low to moderate Reynolds numbers, and (2) systematic study of implementation strategies for high order advection schemes, high-Re flow. An appendix contains Fortran 90 data structures for multigrid development. 160 refs., 26 figs., 22 tabs.
MECHANISM OF OUTFLOWS IN ACCRETION SYSTEM: ADVECTIVE COOLING CANNOT BALANCE VISCOUS HEATING?
Based on the no-outflow assumption, we investigate steady-state, axisymmetric, optically thin accretion flows in spherical coordinates. By comparing the vertically integrated advective cooling rate with the viscous heating rate, we find that the former is generally less than 30% of the latter, which indicates that the advective cooling itself cannot balance the viscous heating. As a consequence, for radiatively inefficient flows with low accretion rates such as M-dot ≲10−3 M-dot Edd, where M-dot Edd is the Eddington accretion rate, the viscous heating rate will be larger than the sum of the advective cooling rate and the radiative cooling one. Thus, no thermal equilibrium can be established under the no-outflow assumption. We therefore argue that in such cases outflows ought to occur and take away more than 70% of the thermal energy generated by viscous dissipation. Similarly, for optically thick flows with extremely large accretion rates such as M-dot ≳10 M-dot Edd, outflows should also occur owing to the limited advection and the low efficiency of radiative cooling. Our results may help to understand the mechanism of outflows found in observations and numerical simulations
A Computational Method for Sharp Interface Advection
Roenby, Johan; Jasak, Hrvoje
2016-01-01
We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists in two parts: First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face-interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple 2D and 3D interface advection problems ...
Clarifying the Narrative Paradigm.
Fisher, Walter R.
1989-01-01
Replies to Rowland's article (same issue) on Fisher's views of the narrative paradigm. Clarifies the narrative paradigm by discussing three senses in which "narration" can be understood, and by indicating what the narrative paradigm is not. (SR)
Wu, Fan; Vainchtein, Dmitri; Ward, Thomas
2015-08-01
A drop translating in the presence of an electric field is studied analytically. The flow is a combination of a Hadamard-Rybczynski and a Taylor circulation due to the translation and electric field, respectively. We consider chaotic advection that is generated by (1) tilting and (2) time-dependent modulation of the electric field. For the analysis we consider small perturbations in time and space to what is otherwise an integrable flow. By using a robust analytical technique we find an adiabatic invariant (AI) for the system by averaging the equations of motion. The chaotic advection is due to quasirandom jumps of the AI after crossing the separatrix of the unperturbed flow. We demonstrate that the asymptotic analysis leads to a set of criteria that can be used to optimize stirring in these systems.
Rolle, Massimo
2015-01-01
advection-dominated flow through conditions. When the solutes are charged species, besides the magnitude of their aqueous diffusion coefficients also their electrostatic interactions play a significant role in the displacement of the different species. Under flow-through conditions this leads to...... under different advection-dominated conditions and in homogeneous and heterogeneous porous media. The interpretation of the experimental results requires a multicomponent modeling approach with an accurate description of local hydrodynamic dispersion and explicitly accounting for the cross-coupling of...... dispersive fluxes due to the Coulombic interactions between the charged species....
Transmission pricing: paradigms and methodologies
Shirmohammadi, Dariush [Pacific Gas and Electric Co., San Francisco, CA (United States); Vieira Filho, Xisto; Gorenstin, Boris [Centro de Pesquisas de Energia Eletrica (CEPEL), Rio de Janeiro, RJ (Brazil); Pereira, Mario V.P. [Power System Research, Rio de Janeiro, RJ (Brazil)
1994-12-31
In this paper we describe the principles of several paradigms and methodologies for pricing transmission services. The paper outlines some of the main characteristics of these paradigms and methodologies such as where they may be used for best results. Due to their popularity, power flow based MW-mile and short run marginal cost pricing methodologies will be covered in some detail. We conclude the paper with examples of the application of these two pricing methodologies for pricing transmission services in Brazil. (author) 25 refs., 2 tabs.
Memory effects in chaotic advection of inertial particles
A systematic investigation of the effect of the history force on particle advection is carried out for both heavy and light particles. General relations are given to identify parameter regions where the history force is expected to be comparable with the Stokes drag. As an illustrative example, a paradigmatic two-dimensional flow, the von Kármán flow is taken. For small (but not extremely small) particles all investigated dynamical properties turn out to heavily depend on the presence of memory when compared to the memoryless case: the history force generates a rather non-trivial dynamics that appears to weaken (but not to suppress) inertial effects, it enhances the overall contribution of viscosity. We explore the parameter space spanned by the particle size and the density ratio, and find a weaker tendency for accumulation in attractors and for caustics formation. The Lyapunov exponent of transients becomes larger with memory. Periodic attractors are found to have a very slow, t−1/2 type convergence towards the asymptotic form. We find that the concept of snapshot attractors is useful to understand this slow convergence: an ensemble of particles converges exponentially fast towards a snapshot attractor, which undergoes a slow shift for long times. (paper)
A generalized advection formalism for relativistic fluid simulations
Call, Jay M; Tohline, Joel E [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Lehner, Luis, E-mail: tohline@lsu.ed [Perimeter Institute for Theoretical Physics, 31 Caroline St N Waterloo, Ontario N2 L 2Y5 (Canada)
2010-09-07
While it is possible to numerically evolve the relativistic fluid equations using any chosen coordinate mesh, typically there will be computational advantages associated with certain choices. For example, astrophysical flows that are governed by rotation tend to give rise to advection variables that are naturally conserved when a cylindrical mesh is used. On the other hand, Cartesian-like coordinates afford a more straightforward implementation of adaptive mesh refinement and avoid the appearance of coordinate singularities. Here we show how it may be possible to reap the benefits associated with multiple coordinate systems simultaneously in numerical simulations. This could be accomplished by implementing a hybrid numerical scheme: one that evolves a set of state variables adapted to one set of coordinates on a mesh defined by an alternative set of coordinates. We provide a formalism (a generalization of the much-used Valencia formulation) by which this can be done. We suggest that a preferred approach to modeling astrophysical flows that are dominated by rotation involves the evolution of inertial-frame cylindrical momenta (i.e. radial momentum, angular momentum and vertical momentum) and the Jacobi energy on a corotating Cartesian coordinate grid.
Directed percolation process advected by the compressible flow
Lučivjanský, T.; Antonov, N. V.; Hnatič, M.; Kapustin, A. S.; Mižišin, L.
2015-01-01
It will be shown how the directed percolation process in the presence of compressible velocity fluctuations could be formulated within the means of field-theoretic formalism, which is suitable for the renormalization group treatment.
Emery, W. J.; Thomas, A. C.; Collins, M. J.; Crawford, W. R.; Mackas, D. L.
1986-11-01
Using cross correlations between sequential infrared satellite images, an objective technique is developed to compute advective sea surface velocities. Cross correlations are computed in 32 × 32 pixel search (second image) and 22 × 22 template (first image) windows from gradients of sea surface temperature computed from the satellite images. Velocity vectors, computed from sequential images of the British Columbia coastal ocean, generally appear coherent and consistent with the seasonal surface current in the region. During periods of strong wind forcing, as indicated by maps of sea level pressure, the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients; when winds are weaker, the advective velocities correspond better with the infrared temperature patterns, suggesting the increased contribution of the geostrophic current to the surface flow. Velocities determined from coincident, near-surface drogued (5-10 m) buoys, positioned every half hour by internal LORAN-C units in mid-June, show excellent agreement with the image advective velocities. In addition, conductivity, temperature, and depth (CTD) measurements (taken during the buoy tracking) confirm the homogeneity of the upper 10 m, and CTD-derived geostrophic currents are consistent with both buoy and sequential image displacement velocities.
The role of a delay time on the spatial structure of chaotically advected reactive scalars
Tzella, Alexandra; Haynes, Peter H.
2009-01-01
The stationary-state spatial structure of reacting scalar fields, chaotically advected by a two-dimensional large-scale flow, is examined for the case for which the reaction equations contain delay terms. Previous theoretical investigations have shown that, in the absence of delay terms and in a regime where diffusion can be neglected (large P\\'eclet number), the emergent spatial structures are filamental and characterized by a single scaling regime with a H\\"older exponent that depends on th...
Thermal instability of advection-dominated disks against local perturbations
Kato, S; Chen, X; Kato, Shoji; Abramowicz, Marek Artur; Chen, Xingming
1995-01-01
Thermal instability is examined for advection-dominated one-temperature accretion disks. We consider axisymmetric perturbations with short wavelength in the radial direction. The viscosity is assumed to be sufficiently small for the vertical hydrostatic balance to hold in perturbed states. The type of viscosity is given either by the \\alpha-viscosity or by a diffusion-type stress tensor. Optically thick disks are found to be in general more unstable than optically thin ones. When the thermal diffusion is present, the optically thin disks become stable, but the optically thick disks are still unstable. The instability of the advection-dominated disks is different from that of the geometrically thin disks without advection. In the case of no advection, the thermal mode behaves under no appreciable surface density change. In the case of advection-dominated disks, however, the thermal mode occurs with no appreciable pressure change (compared with the density change), when local perturbations are considered. The v...
Didaktiske paradigmer og refleksion
Christensen, Torben Spanget
2014-01-01
The article discusses the proposal of a didactic reflection paradigm set forward by Ellen Krogh in this issue of CURSIV. In CURSIV 9, Krogh proposed the paradigm in a discussion of possible links between the phenomenological analysis of subject didactics by Frede V. Nielsen and the semiotic......’s proposal is discussed in some detail and it is argued that a reflection paradigm does not live up to the criterion provided by Nielsen that a didactic paradigm must refer to a naturalistic phenomenon to be applicable for selection of content, at least in the interpretation of Nielsen that underlies this...... article. A possible utilitarian didactical paradigm, already indicated by Krogh as a historical paradigm prominent in our time, is also discussed. It is suggested that reflection could be seen as a normative response to the utilitarian paradigm, and not as a paradigm in its own right. It is concluded that...
Sediment transport in a surface-advected estuarine plume
Yao, H. Y.; Leonardi, N.; Li, J. F.; Fagherazzi, S.
2016-03-01
The interplay between suspended-sediment transport and plume hydrodynamics in a surface-advected estuarine plume is studied using a three-dimensional numerical model. Our analysis focuses on the formation of a sediment-rich alongshore current and on the effect of sediments on the structure of the recirculating freshwater bulge. We introduce the ratio Y between the traveling time of sediment along the bulge edge and the settling timescale. When Y 1 the sediments are deposited within the bulge. We find that a critical range of settling velocities exist above which no transport in the costal current is allowed. Critical settling-velocity values increase with river discharge. Therefore, low magnitude and long-lasting floods promote sediment sorting in the continental shelf. We further find that, for a given flood duration, intermediate flood magnitudes at the limit between subcritical and supercritical flow maximize the alongshore sediment transport. Similarly, for a fixed input of water and sediments, intermediate discharge durations maximize alongshore sediment transport.
Paradigms of Intelligent Systems
Dana Ramona ANDRISESCU
2007-01-01
This paper approaches the subject of paradigms for the categories of intelligent systems. First we can look at the term paradigm in its scientific meaning and then we make acquaintance with the main categories of intelligent systems (expert systems, intelligent systems based on genetic algorithms, artificial neuronal systems, fuzzy systems, hybrid intelligent systems). We will see that every system has one or more paradigms, but hybrid intelligent systems combine paradigms because they are ma...
Positioning Theory in Paradigms
FU Xiao-qiu
2015-01-01
This article discusses the importance of theory and paradigm to a researcher. It starts from introducing and analyzing the definition of the two terms, by using the theories in the field of intercultural communication as examples. To a good researcher, he needs not only clarifying the paradigm his research is positioned, but also integrating the theories in his paradigm.
Cook, Perran L. M.; Wenzhofer, Frank; Glud, Ronnie N.;
2007-01-01
proceeded predominantly through sulfate reduction when benthic mineralization rates were high and advective pore-water flow low as a result of poorly developed topography. Previous studies of benthic mineralization in shallow sandy sediments have generally ignored these dynamics and, hence, have overlooked...
Contribution of Advective and Non-advective Heat Fluxes to the Heat Budget of a Shallow Lagoon
Rodríguez-Rodríguez Miguel
2005-01-01
Full Text Available The heat budget in a shallow lagoon has been established from field measurements at a bihourly scale. Information on the main advective and non-advective heat fluxes were collected during year 2003 at Nueva lagoon (AlmerÃa, Southern Spain. Heat storage data was obtained from a thermistor chain located in the deepest part of the lagoon and meteorological information was acquired using an automatic meteorological station placed near the lagoon's shore. In addition, estimation of evaporation was inferred from climatic approaches. Inputs of heat energy were dominated by radiative fluxes, with received net radiation accounting on average for around 95% of the non-advective total gains and radiation losses accounting for around 70% of the non-advective total losses. Sensible heat transfer from/to the atmosphere constituted the second energy input (4% and output (20%, although heat losses by evaporation were also significant. Conduction of heat into the sediments was a relatively constant form of energy loss but constitutes a minor contribution on the overall heat budget. Considerable variability was evident in non-advective heat fluxes at different time scales, from diel to seasonal. In relation to advective heat fluxes, groundwater and irrigation surpluses added to the heat storage of Nueva lagoon, whereas heat advected via precipitation was negligible.
A Hybrid Advection Scheme for Conserving Angular Momentum on a Refined Cartesian Mesh
Byerly, Zachary D; Tohline, Joel E; Marcello, Dominic C
2014-01-01
We test a new "hybrid" scheme for simulating dynamical fluid flows in which cylindrical components of the momentum are advected across a rotating Cartesian coordinate mesh. This hybrid scheme allows us to conserve angular momentum to machine precision while capitalizing on the advantages offered by a Cartesian mesh, such as a straightforward implementation of mesh refinement. Our test focuses on measuring the real and imaginary parts of the eigenfrequency of unstable axisymmetric modes that naturally arise in massless polytropic tori having a range of different aspect ratios, and quantifying the uncertainty in these measurements. Our measured eigenfrequencies show good agreement with the results obtained from the linear stability analysis of Kojima (1986) and from nonlinear hydrodynamic simulations performed on a cylindrical coordinate mesh by Woodward et al. (1994). When compared against results conducted with a traditional Cartesian advection scheme, the hybrid scheme achieves qualitative convergence at the...
New complex variable meshless method for advection-diffusion problems
Wang Jian-Fei; Cheng Yu-Min
2013-01-01
In this paper,an improved complex variable meshless method (ICVMM) for two-dimensional advection-diffusion problems is developed based on improved complex variable moving least-square (ICVMLS) approximation.The equivalent functional of two-dimensional advection-diffusion problems is formed,the variation method is used to obtain the equation system,and the penalty method is employed to impose the essential boundary conditions.The difference method for two-point boundary value problems is used to obtain the discrete equations.Then the corresponding formulas of the ICVMM for advection-diffusion problems are presented.Two numerical examples with different node distributions are used to validate and investigate the accuracy and efficiency of the new method in this paper.It is shown that ICVMM is very effective for advection-diffusion problems,and has a good convergent character,accuracy,and computational efficiency.
Anomalous scaling of a scalar field advected by turbulence
Kraichnan, R.H. [Robert H. Kraichnan, Inc., Santa Fe, NM (United States)
1995-12-31
Recent work leading to deduction of anomalous scaling exponents for the inertial range of an advected passive field from the equations of motion is reviewed. Implications for other turbulence problems are discussed.
Driessen, B.J.; Dohner, J.L.
1998-08-01
In this paper a hybrid, finite element--boundary element method which can be used to solve for particle advection-diffusion in infinite domains with variable advective fields is presented. In previous work either boundary element, finite element, or difference methods have been used to solve for particle motion in advective-diffusive domains. These methods have a number of limitations. Due to the complexity of computing spatially dependent Green`s functions, the boundary element method is limited to domains containing only constant advective fields, and due to their inherent formulation, finite element and finite difference methods are limited to only domains of finite spatial extent. Thus, finite element and finite difference methods are limited to finite space problems for which the boundary element method is not, and the boundary element method is limited to constant advection field problems for which finite element and finite difference methods are not. In this paper it is proposed to split a domain into two sub-domains, and for each of these sub domains, apply the appropriate solution method; thereby, producing a method for the total infinite space, variable advective field domain.
Reaction-diffusion fronts under stochastic advection
Martí, A C; Sancho, J M
1997-01-01
We study front propagation in stirred media using a simplified modelization of the turbulent flow. Computer simulations reveal the existence of the two limiting propagation modes observed in recent experiments with liquid phase isothermal reactions. These two modes respectively correspond to a wrinkled although sharp propagating interface and to a broadened one. Specific laws relative to the enhancement of the front velocity in each regime are confirmed by our simulations.
Anisotropic Turbulent Advection of a Passive Vector Field: Effects of the Finite Correlation Time
Antonov, N. V.; Gulitskiy, N. M.
2016-02-01
The turbulent passive advection under the environment (velocity) field with finite correlation time is studied. Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is investigated by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and prescribed pair correlation function. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to nontrivial fixed points of the RG equations and depend on the relation between the exponents in the energy energy spectrum ɛ ∝ k⊥1-ξ and the dispersion law ω ∝ k⊥2-η . The corresponding anomalous exponents are associated with the critical dimensions of tensor composite operators built solely of the passive vector field itself. In contrast to the well-known isotropic Kraichnan model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale L has a logarithmic behavior: instead of power-like corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of L. Due to the presence of the anisotropy in the model, all multiloop diagrams are equal to zero, thus this result is exact.
Heat transfer enhancement utilizing chaotic advection in coiled tube heat exchangers
The present study introduced a novel chaotic coil heat exchanger utilizing chaotic advection to enhance heat transfer at low Reynolds numbers. Using Lagrangian tracing of fluid particles and their sensitivity to the initial condition and fluid element calculations, it was shown that mixing was significantly increased due to the chaotic advection. Heat transfer performance in the coil and chaotic configuration was visualized by isotherms contours of temperature in different cross-sections. In order to evaluate the hydraulic-thermal performance of heat exchangers, Nusselt numbers and friction factor were calculated and comparison was made between the two configurations. Numerical calculations revealed that the chaotic coil configuration displayed heat transfer enhancement of 4–26% relative to the fully developed Nusselt numbers in the regular coil with only 5–8% change in the pressure drop. - Highlights: • A novel chaotic coil heat exchanger is introduced in this study. • It is shown that mixing is increased significantly due to the altered chaotic advection mechanism. • By increasing the Reynolds number, results show impressive enhancement in chaotic heat exchanger performance. • Reorientation in chaotic flow leads to higher pressure loss than that in the normal helical coil
Advection-condensation of water vapor with coherent stirring: a stochastic approach
Tsang, Yue-Kin; Vanneste, Jacques; Vallis, Geoffrey
2015-11-01
The dynamics of atmospheric water is an essential ingredient of weather and climate. Water vapor, in particular, is an important greenhouse gas whose distribution has a strong impact on climate. To gain insight into the factors controlling the distribution of atmospheric moisture, we study an advection-condensation model in which water vapor is passively advected by a prescribed velocity and condensation acts as a sink that maintains the specific humidity below a prescribed, spatially dependent saturation value. The velocity consists of two parts: a single vortex representing large-scale coherent flow (e.g. the Hadley cell) and a white noise component mimicking small-scale turbulence. Steady-state is achieved in the presence of a moisture source at a boundary. We formulate this model as a set of stochastic differential equations. In the fast advection limit, analytical expression for the water vapor distribution is obtained by matched asymptotics. This allows us to make various predictions including the dependence of total precipitation on the vortex strength. These analytical results are verified by Monte Carlo simulations. This work is supported by the UK EPSRC Grant EP/I028072/1 and the Feasibility Fund from the UK EPSRC Network ReCoVER.
Clay with Desiccation Cracks is an Advection Dominated Environment
Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.
2012-04-01
, indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.
Effect of advection on variations in zooplankton at a single location near Cabo Nazca, Peru
Smith, S L; Brink, K H; Santander, H; Cowles, T J; Huyer, A
1980-04-01
Temporal variations in the biomass and species composition of zooplankton at a single midshelf station in an upwelling area off Peru can be explained to a large extent by onshore-offshore advection in the upper 20 m of the water column. During periods of strong or sustained near-surface onshore flow, peaks in biomass of zooplankton were observed at midshelf and typically oceanic species of copepod were collected. In periods of offshore flow at the surface, a copepod capable of migrating into oxygen-depleted layers deeper than 30 m was collected. A simple translocation model of advection applied to the cross-shelf distribution of Paracalanus parvus suggests that the fluctuations in P. pavus observed in the midshelf time-series were closely related to onshore-offshore flow in the upper 20 m. Fluctuations in abundance of the numerically dominant copepod, Acartia tonsa, were apparently affected by near surface flow also. The population age-structure suggests that A. tonsa was growing at maximal rates, due in part to its positive feeding response to the dinoflagellate/diatom assemblage of phytoplankton.
Gheorghe Lepadatu
2013-01-01
Statement of cash flows presents useful information about changing the company's financial position, allowing assessing the enterprise’s ability to generate future cash flows and cash equivalents in the operating, investing and financing activities and their appropriate use. Treasury forecasts are intended to contribute to financial security and enterprise profitability by reducing financial costs. Treasury of an economic entity can be considered its strong point. The manner in which they man...
Advective-diffusive transport of D2O in unsaturated media under evaporation condition
Advective-diffusive transport of HTO in unsaturated media was investigated empirically using deuterated water (D2O) and columns filled with glass beads. The tortuosity factor was evaluated by numerical model calculations corresponding to first experiment for diffusion under no-evaporation condition. Temporal variations in depth profiles of D2O concentrations in the columns were observed by second experiment, which considers the transferring and spreading of D2O by pore-water flow caused by evaporation. Measurements and model calculations indicated that diffusion was about two times more efficient than dispersion for D2O spreading process under this evaporation condition. (author)
Measurements on, and modelling of diffusive and advective radon transport in soil
Graff, E.R. van der; Witteman, G.A.A.; Spoel, W.H. van der;
1994-01-01
Results are presented of measurements on radon transport in soil under controlled conditions with a laboratory facility consisting of a stainless steel vessel (height and diameter 2 m) filled with a uniform column of sand. At several depths under the sand surface, probes are radially inserted into...... the vessel to measure the radon concentration in the soil gas. To study advective radon transport a perforated circular box is placed in the sand close to the bottom of the vessel. By pressurising this box, an air flow through the sand column is induced. Radon concentration profiles were measured...
Santos, Isaac R.; Eyre, Bradley D.; Glud, Ronnie N.
2012-01-01
Porewater flow enhances mineralization rates in organic-poor permeable sands. Here, a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from Heron Island (Great Barrier Reef...... consumption and N-2 production. The N:O-2 slope of 0.114 implied that about 75% of all the nitrogen mineralized was denitrified. A 4-fold increase in sediment column length (from 10 to 40 cm) resulted in an overall increase in oxygen consumption (1.6-fold), TCO2 production (1.8-fold), and denitrification (1...
Measurements on, and modelling of diffusive and advective radon transport in soil
Graff, E.R. van der; Witteman, G.A.A.; Spoel, W.H. van der; Andersen, C.E.; Meijer, R.J. de
the vessel to measure the radon concentration in the soil gas. To study advective radon transport a perforated circular box is placed in the sand close to the bottom of the vessel. By pressurising this box, an air flow through the sand column is induced. Radon concentration profiles were measured......Results are presented of measurements on radon transport in soil under controlled conditions with a laboratory facility consisting of a stainless steel vessel (height and diameter 2 m) filled with a uniform column of sand. At several depths under the sand surface, probes are radially inserted into...
Features of a rare advection-radiation fog event
2008-01-01
To investigate effects of atmospheric pollutants on fog nature, a comprehensive in situ observation project was implemented in the northern suburb of Nanjing, in December of 2006. For December 24-27 there occurred a heavy fog lasting 4 d in succession. This event is of rare characteristics, namely long persistence, high concentration, tall fog top, acid fog water and explosive growth. Detailed analysis along with the causes of the fog was presented. The evidence suggests that the fog was generated by nighttime radiative cooling, maintained and developed under effects of warm, wet advection. As a result, it is an advection-radiation fog event.
Methods to assess radioisotope migration in cementitious media using radial diffusion and advection
One of the primary aims of this project is to understand how a range of isotopes associated with radioactive wastes, move through the cementitious media potentially present in a geological disposal facility (GDF). This paper describes the development of experimental methods that use radial flow from intact cylinders of cementitious material to evaluate the potential for diffusion and advection of relevant isotopes through Nirex reference vault backfill (NRVB). The small scale and cost effectiveness of the approach means that multiple experiments can be undertaken encompassing the full range of physical (and chemical) variations. The radial flow experimental method uses small pre-cast cylinders of the matrix under investigation. For diffusion an appropriate concentration of the isotope of interest (90Sr in the present experiments) is introduced into a cavity in the centre of the cylinder, which is then sealed, and placed in a solution previously equilibrated with the matrix. The increase in concentration of the isotope in the external solution is then determined at defined time intervals. For advection 90Sr is similarly introduced into the central core of the cylinder and then equilibrated water is forced under nitrogen pressure, from the central core to the outside of the cylinder where it is collected in a tray prior to analysis. Both experimental set ups and results have been modelled using conventional numerical solutions and the simulation package GoldSim. Concerning diffusion experiments the modelled data reproduces the observed data effectively with a right diffusivity value of 9*10-11 m2/s. Concerning advection results are more mitigated and need further investigation
Paradigms for machine learning
Schlimmer, Jeffrey C.; Langley, Pat
1991-01-01
Five paradigms are described for machine learning: connectionist (neural network) methods, genetic algorithms and classifier systems, empirical methods for inducing rules and decision trees, analytic learning methods, and case-based approaches. Some dimensions are considered along with these paradigms vary in their approach to learning, and the basic methods are reviewed that are used within each framework, together with open research issues. It is argued that the similarities among the paradigms are more important than their differences, and that future work should attempt to bridge the existing boundaries. Finally, some recent developments in the field of machine learning are discussed, and their impact on both research and applications is examined.
Fractional gradient and its application to the fractional advection equation
D'Ovidio, M; Garra, R.
2013-01-01
In this paper we provide a definition of fractional gradient operators, related to directional derivatives. We develop a fractional vector calculus, providing a probabilistic interpretation and mathematical tools to treat multidimensional fractional differential equations. A first application is discussed in relation to the d-dimensional fractional advection-dispersion equation. We also study the connection with multidimensional L\\'evy processes.
Dilru R. Ratnaweera
2015-03-01
Full Text Available The effects of chaotic advection on the in situ assembly of a hierarchal nanocomposite of Poly Amide 6, (nylon 6 or PA6 and platelet shape nanoparticles (NPs were studied. The assemblies were formed by chaotic advection, where melts of pristine PA6 and a mixture of PA6 with NPs were segregated into discrete layers and extruded into film in a continuous process. The process assembles the nanocomposite into alternating pristine-polymer and oriented NP/polymer layers. The structure of these hierarchal assemblies was probed by X-rays as a processing parameter, N, was varied. This parameter provides a measure of the extent of in situ structuring by chaotic advection. We found that all assemblies are semi-crystalline at room temperature. Increasing N impacts the ratio of α to γ crystalline forms. The effects of the chaotic advection vary with the concentration of the NPs. For nanocomposites with lower NP concentrations the amount of the γ crystalline form increased with N. However, at higher NP concentrations, interfacial effects of the NP play a significant role in determining the structure, where the NPs oriented along the melt flow direction and the polymer chains oriented perpendicular to the NP surfaces.
Milgrom, Mordehai
2008-01-01
I review briefly different aspects of the MOND paradigm, with emphasis on phenomenology, epitomized here by many MOND laws of galactic motion--analogous to Kepler's laws of planetary motion. I then comment on the possible roots of MOND in cosmology, possibly the deepest and most far reaching aspect of MOND. This is followed by a succinct account of existing underlying theories. I also reflect on the implications of MOND's successes for the dark matter (DM) paradigm: MOND predictions imply tha...
HUANG Rui Xin
2014-01-01
Gravitational potential energy (GPE) source and sink due to stirring and cabbeling associated with sigma dif-fusion/advection is analyzed. It is shown that GPE source and sink is too big, and they are not closely linked to physical property distribution, such as temperature, salinity and velocity. Although the most frequently quoted advantage of sigma coordinate models are their capability of dealing with topography;the exces-sive amount of GPE source and sink due to stirring and cabbeling associated with sigma diffusion/advec-tion diagnosed from our analysis raises a very serious question whether the way lateral diffusion/advection simulated in the sigma coordinates model is physically acceptable. GPE source and sink in three coordinates is dramatically different in their magnitude and patterns. Overall, in terms of simulating lateral eddy diffu-sion and advection isopycnal coordinates is the best choice and sigma coordinates is the worst. The physical reason of the excessive GPE source and sink in sigma coordinates is further explored in details. However, even in the isopycnal coordinates, simulation based on the Eulerian coordinates can be contaminated by the numerical errors associated with the advection terms.
When transport in porous media is advection-dominated, the classical convection-dispersion equation behaves like an hyperbolic partial differential equation. Special numerical methods are then necessary to reduce numerical dispersion and/or spurious oscillations. Discontinuous Galerkin finite element methods are good candidates to solve this problem. At the discontinuities between two adjacent elements, numerical advective fluxes are calculated using one-dimensional approximate Riemann solvers. The method is stabilized with a multidimensional slope limiter which introduces small amounts of numerical diffusion when sharp concentration fronts occur. For a 2-dimensional domain and quadrangular elements, two space approximations are compared: a linear approximation (P1) based on average concentration value and average gradients (i.e. 3 degrees of freedom) and a bilinear approximation (Q1) based on nodal values of the concentration (i.e. 4 degrees of freedom). Numerical experiments based on structured or unstructured meshes and unidirectional or rotating flow have been run. For the same number of unknowns we show that: 1) the P1 approximation provides more accurate results than the Q1 approximation in simple configuration (structured meshes and unidirectional flow); 2) both approximations provide the same results for not too complicated configurations like structured meshes and rotating flow; 3) Q1 approximation provides more accurate results in complex situations like rotating flow on a unstructured mesh. However, because the required CPU time for the P1 approximation is much less than for the Q1 approximation, the P1 approximation was always found to be more efficient (in terms of CPU time for a given error) compared to the Q1 approximation. (authors)
Influences of tidal energy advection on the surface energy balance in a mangrove forest
J. G. Barr
2012-08-01
Full Text Available Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL. Forest-atmosphere energy exchanges were quantified with an eddy covariance system deployed on a flux tower. The lateral energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, tidal flows reduced the impact of high radiational loads on the mangrove forest. Including tidal energy advection in the surface energy balance improved the 30-min daytime energy closure from 73% to 82% over the study period. Also, the cumulative sum of energy output improved from 79% to 91% of energy input during the study period. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem response to changing climate and
About hypotheses and paradigms: exploring the Discreetness-Chance Paradigm.
Kaellis, Eugene
2006-01-01
Hypotheses generally conform to paradigms which, over time, change, usually tardily, after they have become increasingly difficult to sustain under the impact of non-conforming evidence and alternative hypotheses, but more important, when they no longer are comfortably ensconced in the surrounding social-economic-political-cultural milieu. It is asserted that this milieu is the most important factor in shaping scientific theorizing. Some examples are cited: the rejection of the evidence that the world orbits around the sun (suspected by Pythagoras) in favor of centuries-long firm adherence to the Ptolemaic geocentric system; the early acceptance of Natural Selection in spite of its tautological essence and only conjectural supporting evidence, because it justified contemporaneous social-political ideologies as typified by, e.g., Spencer and Malthus. Economic, social, and cultural factors are cited as providing the ground, i.e., ideational substrate, for what is cited as the Discreetness-Chance Paradigm (DCP), that has increasingly dominated physics, biology, and medicine for over a century and which invokes small, discrete packets of energy/matter (quanta, genes, microorganisms, aberrant cells) functioning within an environment of statistical, not determined, causality. There is speculation on a possible paradigmatic shift from the DCP, which has fostered the proliferation, parallel with ("splitting") taxonomy, of alleged individual disease entities, their diagnoses, and, when available, their specific remedies, something particularly prominent in, e.g., psychiatry's Diagnostic and Statistical Manual, a codified compendium of alleged mental and behavioral disorders, but evident in any textbook of diagnosis and treatment of physical ailments. This presumed paradigm shift may be reflected in Western medicine, presently increasingly empirical and atomized, towards a growing acceptance of a more generalized, subject-oriented, approach to health and disease, a non
Advection equation analysed by two-timing method
Vladimirov, V A
2016-01-01
The aim of this paper is to study and classify the multiplicity of distinguished limits and asymptotic solutions for the advection equation with a general oscillating velocity field with the systematic use of the two-timing method. Our results are: (i) the dimensionless advection equation contains two independent small parameters, which represent the ratio of two characteristic time-scales and the spatial amplitudes of oscillations; the scaling of the variables and parameters contains Strouhal number; (ii) an infinite sequence of distinguished limits has been identified; this sequence corresponds to the successive degenerations of a drift velocity; (iii) we have derived the averaged and oscillatory equations for the first four distinguished limits; derivations are performed up to the forth orders in small parameters; (v) we have shown, that each distinguish limit solution generates an infinite number of parametric solutions; these solutions differ from each other by the slow time-scale and the amplitude of pr...
Anomalous diffusion of a tracer advected by wave turbulence
Balk, Alexander M.
2001-02-01
We consider the advection of a passive tracer when the velocity field is a superposition of random waves. Green's function for the turbulent transport (turbulent diffusion and turbulent drift) is derived. This Green's function is shown to imply sub-diffusive or super-diffusive behavior of the tracer. For the analysis we introduce the statistical near-identity transformation. The results are confirmed by numerical simulations.
Oscillatory convection in binary mixtures: thermodiffusion, solutal buoyancy, and advection
Jung, D.; Matura, P.; Luecke, M.
2005-01-01
The role of thermodiffusive generation of concentration fluctuations via the Soret effect, their contribution to the buoyancy forces that drive convection, the advective mixing effect of the latter, and the diffusive homogenisation are compared and elucidated for oscillatory convection. Numerically obtained solutions of the field equations in the form of spatially extended relaxed traveling waves, of standing waves, and of the transient growth of standing waves and their transition to traveli...
Lattice Boltzmann method for the fractional advection-diffusion equation
Zhou, J. G.; Haygarth, P. M.; Withers, P. J. A.; Macleod, C. J. A.; Falloon, P. D.; Beven, K. J.; Ockenden, M. C.; Forber, K. J.; Hollaway, M. J.; Evans, R.; Collins, A. L.; Hiscock, K. M.; Wearing, C.; Kahana, R.; Villamizar Velez, M. L.
2016-04-01
Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β , the fractional order α , and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.
HYBRID EXISTENCE. THREE PARADIGMS
Lukasz Trzcinski
2010-01-01
Full Text Available The main problem of this text concerns the question of duality of human existence, and its relation with humans body. In the animistic paradigm body of a man is an “implement” unifying with the world, made by contact with sprits and ancestors. In the mechanical approach body is separate from consciousness, mind and spirit. It is a machine. In the holistic paradigm body is a part of the universe, and nowadays this universe is the informatics web. The man – golem, homunculus and automaton becomes part of total information. In this new situation the problem concerns psychological and moral attitude of man.
Spielhagen, Robert F.; Bauch, Henning A.; Maudrich, Martin; Not, Christelle; Telesinski, Maciej M.; Werner, Kirstin
2015-04-01
The Arctic Gateway between Greenland and Svalbard is the main passage for the advection of Atlantic Water to the Arctic Ocean. Water temperature and intensity of this advection largely determine the degree of ice coverage which is fed by sea ice export from the north. Supported by a maximum in insolation, the Early Holocene was a period of extraordinarily strong advection and relatively high near-surface water temperatures in the eastern Nordic Seas (cf. Risebrobakken et al., 2011, Paleoceanography v. 26). Here we present a synthesis of radiocarbon-dated records from the northern and western part of this area, reaching from the SW Greenland Sea (73°N) to the Yermak Plateau (81°N) and revealing temporal and spatial differences in the development of the so-called Holocene Thermal Maximum (HTM). In the northern part of this region, the HTM started ca. 11-10.5 ka as indicated by rapidly increasing amounts of subpolar planktic foraminifers in the sediments. In the eastern Fram Strait and on the Yermak Plateau, our records of (sub)millennial scale resolution show that the maximum influx terminated already 2,000 years later (9-8 ka). Most likely, this development went along with a N-S relocation of the sea ice margin. According to the current stratigraphic model for a core with submillennial-scale resolution from Vesterisbanken seamount (73°N) in the Greenland Sea, the timing was different there. Increasing total amounts of planktic foraminifers in the sediment indicate an early (11-10 ka) reduction in sea ice coverage also in this region. However, evidence from subpolar planktic foraminifers for maximum Atlantic Water advection is younger (9-6 ka) than in the north. Apparently, the site in the SW Greenland Sea was affected by Atlantic Water in the Greenland Gyre that decoupled from the northward flowing Norwegian Atlantic Current/Westspitsbergen Current south of the Fram Strait. Thus, in a suite of events, strong Atlantic Water advection first affected the
Ancey, Christophe; Bohorquez, Patricio; Heyman, Joris
2016-04-01
The advection-diffusion equation arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Stochastic models can also be used to derive this equation, with the significant advantage that they provide information on the statistical properties of particle activity. Stochastic models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. We develop an approach based on birth-death Markov processes, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received little attention. We show that particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due to velocity fluctuations), with the important consequence that local measurements depend on both the intrinsic properties of particle displacement and the dimensions of the measurement system.
Driessen, B.J.; Dohner, J.L.
1998-08-01
In this paper a hybrid, finite element/boundary element method which can be used to solve for particle diffusion in semi-infinite domains containing geometric obstructions and a variable advective field is presented. In previous work either boundary element or finite element/difference methods were used to solve for particle concentrations in an advective domain. These methods of solution had a number of limitations. Due to limitations in computing spatially dependent Green`s functions, the boundary element method of solution was limited to domains containing only constant advective fields, and due to its inherent formulation, finite element/difference methods were limited to only domains of finite spatial extent. Thus, where the finite element solution was limited, the boundary element solution was not, and where the boundary element solution was limited, the finite element solution was not. In this paper it is proposed to split the total domain into two sub-domains where each method of solution is applicable. For each of these sub-domains, the appropriate solution method is used; thereby, producing a general method of solution for the total semi-infinite domain.
Bernabé, Y.; Wang, Y.; Qi, T.; Li, M.
2016-02-01
The main purpose of this work is to investigate the relationship between passive advection-dispersion and permeability in porous materials presumed to be statistically homogeneous at scales larger than the pore scale but smaller than the reservoir scale. We simulated fluid flow through pipe network realizations with different pipe radius distributions and different levels of connectivity. The flow simulations used periodic boundary conditions, allowing monitoring of the advective motion of solute particles in a large periodic array of identical network realizations. In order to simulate dispersion, we assumed that the solute particles obeyed Taylor dispersion in individual pipes. When a particle entered a pipe, a residence time consistent with local Taylor dispersion was randomly assigned to it. When exiting the pipe, the particle randomly proceeded into one of the pipes connected to the original one according to probabilities proportional to the outgoing volumetric flow in each pipe. For each simulation we tracked the motion of at least 6000 solute particles. The mean fluid velocity was 10-3 ms-1, and the distance traveled was on the order of 10 m. Macroscopic dispersion was quantified using the method of moments. Despite differences arising from using different types of lattices (simple cubic, body-centered cubic, and face-centered cubic), a number of general observations were made. Longitudinal dispersion was at least 1 order of magnitude greater than transverse dispersion, and both strongly increased with decreasing pore connectivity and/or pore size variability. In conditions of variable hydraulic radius and fixed pore connectivity and pore size variability, the simulated dispersivities increased as power laws of the hydraulic radius and, consequently, of permeability, in agreement with previously published experimental results. Based on these observations, we were able to resolve some of the complexity of the relationship between dispersivity and permeability.
Paradigms and pragmatic constructivism
Nørreklit, Hanne; Nørreklit, Lennart; Mitchell, Falconer
2010-01-01
the analysis of the comment on their past paper. Findings - In addressing each of the issues in turn the authors clarify their analysis. Originality/value - The paper provides an argument for the development of a paradigm for accounting practice derived from the use of pragmatic constructivism....
The "New Environmental Paradigm"
Dunlap, Riley E.; Van Liere, Kent D.
2008-01-01
The "New Environmental Paradigm" or NEP appears to have gained considerable popularity in academic and intellectual circles, as well as among many college students; however, very little is known concerning the degree to which the general public has come to accept the ideas embodied in it. Thus, although there have been dozens of studies of…
Wrigley, Terry
2011-01-01
This short paper points to some paradigm issues in the field of school development (leadership, effectiveness, improvement) and their relationship to social justice. It contextualises the dominant School Effectiveness and School Improvement models within neo-liberal marketisation, paying attention to their transformation through a "marriage of…
Dias, Alcina Portugal
2013-01-01
In this short contribution a reflection on the evolution of the the Total Quality Management paradigm is pesented. The main differences between the three perspectives of Quality Management are analyzed, together with a set of changes and improvements to the practice of TQM that are likely to take place.
Paradigms in object recognition
A broad range of approaches has been proposed and applied for the complex and rather difficult task of object recognition that involves the determination of object characteristics and object classification into one of many a priori object types. Our paper revises briefly the three main different paradigms in pattern recognition, namely Bayesian statistics, neural networks, and expert systems. (author)
Programming Language Paradigms
Bartoníček Jan
2014-01-01
Full Text Available This paper's goal is to briefly explain the basic theory behind programming languages and their history while taking a close look at different programming paradigms that are used today as well as describing their differences, benefits, and drawbacks
The role of phase dynamics in a stochastic model of a passively advected scalar
Moradi, Sara
2016-01-01
Collective synchronous motion of the phases is introduced in a model for the stochastic passive advection-diffusion of a scalar with external forcing. The model for the phase coupling dynamics follows the well known Kuramoto model paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto model are assumed to obey a given scale dependence through a dispersion relation of the drift-wave form $-\\beta\\frac{k}{1+k^2}$, where $\\beta$ is a constant representing the typical strength of the gradient. The present aim is to study the importance of collective phase dynamics on the characteristic time evolution of the fluctuation energy and the formation of coherent structures. Our results show that the assumption of a fully stochastic phase state of turbulence is more relevant for high values of $\\beta$, where we find that the energy spectrum follows a $k^{-7/2}$ scaling. Whereas for lower $\\beta$ there is a significant difference between a-synchronised and synchronised phase states, and one could expe...
New Paradigms For Asteroid Formation
Johansen, Anders; Cuzzi, Jeffrey N; Morbidelli, Alessandro; Gounelle, Matthieu
2015-01-01
Asteroids and meteorites provide key evidence on the formation of planetesimals in the Solar System. Asteroids are traditionally thought to form in a bottom-up process by coagulation within a population of initially km-scale planetesimals. However, new models challenge this idea by demonstrating that asteroids of sizes from 100 to 1000 km can form directly from the gravitational collapse of small particles which have organised themselves in dense filaments and clusters in the turbulent gas. Particles concentrate passively between eddies down to the smallest scales of the turbulent gas flow and inside large-scale pressure bumps and vortices. The streaming instability causes particles to take an active role in the concentration, by piling up in dense filaments whose friction on the gas reduces the radial drift compared to that of isolated particles. In this chapter we review new paradigms for asteroid formation and compare critically against the observed properties of asteroids as well as constraints from meteo...
The Nature of Paradigms and Paradigm Shifts in Music Education
Panaiotidi, Elvira
2005-01-01
In this paper, the author attempts to extend the paradigm approach into the philosophy of music education and to build upon this basis a model for structuring music education discourse. The author begins with an examination of Peter Abbs' account of paradigms and paradigm shifts in arts education. Then she turns to Kuhn's conception and to his…
A rational function based scheme for solving advection equation
Xiao, Feng [Gunma Univ., Kiryu (Japan). Faculty of Engineering; Yabe, Takashi
1995-07-01
A numerical scheme for solving advection equations is presented. The scheme is derived from a rational interpolation function. Some properties of the scheme with respect to convex-concave preserving and monotone preserving are discussed. We find that the scheme is attractive in surpressinging overshoots and undershoots even in the vicinities of discontinuity. The scheme can also be easily swicthed as the CIP (Cubic interpolated Pseudo-Particle) method to get a third-order accuracy in smooth region. Numbers of numerical tests are carried out to show the non-oscillatory and less diffusive nature of the scheme. (author).
Advection and diffusion in random media implications for sea surface temperature anomalies
Piterbarg, Leonid I
1997-01-01
The book presents the foundations of the theory of turbulent transport within the context of stochastic partial differential equations. It serves to establish a firm connection between rigorous and non-rigorous results concerning turbulent diffusion. Mathematically all of the issues addressed in this book are concentrated around a single linear equation: stochastic advection-diffusion (transport) equation. There is no attempt made to derive universal statistics for turbulent flow. Instead emphasis is placed on a statistical description of a passive scalar (tracer) under given velocity statistics. An application concerning transport of sea surface temperature anomalies reconciles the developed theory and a highly practical issue of modern physical oceanography by using the newly designed inversion techniques which take advantage of powerful maximum likelihood and autoregressive estimators. Audience: Graduate students and researchers in mathematics, fluid dynamics, and physical oceanography.
Research Paradigm of Displaced Aggression
Tanno, Syota
2013-01-01
A review of research paradigm of displaced aggression is presented. The author arranged the Japanese wording of displaced aggression, summarized the historical transition of research on displaced aggression, and reviewed research paradigm of displaced aggression.
Andersen, Anna Bjerning Berg; Nielsen, Anna Sabine; Zunda, Daniella
2014-01-01
Our focal point and core concepts in this paper are science, health and yoga. Our main concern is to shed light on the understanding of these three concepts and how it varies, depending on the scientific approach these concepts are dealt with. The problem statement of this paper is thereby: How is it possible to argue, based on Kuhn's paradigm theory, that yoga/ayurveda and medical science represent fundamentally different views on health, yoga and science? We choose two scientific ap...
Multiple anisotropic collisions for advection-diffusion Lattice Boltzmann schemes
Ginzburg, Irina
2013-01-01
This paper develops a symmetrized framework for the analysis of the anisotropic advection-diffusion Lattice Boltzmann schemes. Two main approaches build the anisotropic diffusion coefficients either from the anisotropic anti-symmetric collision matrix or from the anisotropic symmetric equilibrium distribution. We combine and extend existing approaches for all commonly used velocity sets, prescribe most general equilibrium and build the diffusion and numerical-diffusion forms, then derive and compare solvability conditions, examine available anisotropy and stable velocity magnitudes in the presence of advection. Besides the deterioration of accuracy, the numerical diffusion dictates the stable velocity range. Three techniques are proposed for its elimination: (i) velocity-dependent relaxation entries; (ii) their combination with the coordinate-link equilibrium correction; and (iii) equilibrium correction for all links. Two first techniques are also available for the minimal (coordinate) velocity sets. Even then, the two-relaxation-times model with the isotropic rates often gains in effective stability and accuracy. The key point is that the symmetric collision mode does not modify the modeled diffusion tensor but it controls the effective accuracy and stability, via eigenvalue combinations of the opposite parity eigenmodes. We propose to reduce the eigenvalue spectrum by properly combining different anisotropic collision elements. The stability role of the symmetric, multiple-relaxation-times component, is further investigated with the exact von Neumann stability analysis developed in diffusion-dominant limit.
Moisture advection to the Arctic : forecasted, analysed and observed
Dufour, Ambroise; Zolina, Olga
2015-04-01
Besides its contribution to the Arctic hydrological budget, moisture imports from mid-latitudes are also influential on shorter time scales since water vapour advection tends to occur together with extratropical cyclones. Influx of moisture to the Arctic cause the formation of clouds that have an immediate impact on the surface energy budget especially in winter. In the long run, inaccuracies in the description of cloud cover and phase lead to temperature biases in CMIP5 models. The ECMWF workshop on polar prediction has highlighted moisture advection as one of the problematic physical processes limiting the quality of forecasts. Verifying the accuracy of medium-term forecasts is of interest beyond weather prediction : it points to the ability of models to bring adequate quantities of moisture to the Arctic when they are less constrained by observations than in analyses. In this study, we have compared forecasted moisture flux fields with analyses and observations over the period 2000-2010. ECMWF's ERA-Interim provided the forecasts, extending to ten days. For the analyses, in addition to ERA-Interim, we used the Arctic System Reanalysis whose forecast model is optimized for the polar regions and runs at high resolution (30 km). Finally, the Integrated Global Radiosonde Archive data over the Arctic allowed a validation by observations.
Horizontal advection, diffusion and plankton spectra at the sea surface.
Bracco, A.; Clayton, S.; Pasquero, C.
2009-04-01
Plankton patchiness is ubiquitous in the oceans, and various physical and biological processes have been proposed as its generating mechanisms. However, a coherent statement on the problem is missing, due to both a small number of suitable observations and to an incomplete understanding of the properties of reactive tracers in turbulent media. Abraham (1998) suggested that horizontal advection may be the dominant process behind the observed distributions of phytoplankton and zooplankton, acting to mix tracers with longer reaction times (Rt) down to smaller scales. Conversely, Mahadevan and Campbell (2002) attributed the relative distributions of sea surface temperature and phytoplankton to small scale upwelling, where tracers with longer Rt are able to homogenize more than those with shorter reaction times. Neither of the above mechanisms can explain simultaneously the (relative) spectral slopes of temperature, phytoplankton and zooplankton. Here, with a simple advection model and a large suite of numerical experiments, we concentrate on some of the physical processes influencing the relative distributions of tracers at the ocean surface, and we investigate: 1) the impact of the spatial scale of tracer supply; 2) the role played by coherent eddies on the distribution of tracers with different Rt; 3) the role of diffusion (so far neglected). We show that diffusion determines the distribution of temperature, regardless of the nature of the forcing. We also find that coherent structures together with differential diffusion of tracers with different Rt impact the tracer distributions. This may help in understanding the highly variable nature of observed plankton spectra.
Super-diffusion versus competitive advection: a simulation
Del Moro, D; Berrilli, F; Consolini, G; Lepreti, F; Gosic, M
2015-01-01
Magnetic element tracking is often used to study the transport and diffusion of the magnetic field on the solar photosphere. From the analysis of the displacement spectrum of these tracers, it has been recently agreed that a regime of super-diffusivity dominates the solar surface. Quite habitually this result is discussed in the framework of fully developed turbulence. But the debate whether the super-diffusivity is generated by a turbulent dispersion process, by the advection due to the convective pattern, or by even another process, is still open, as is the question about the amount of diffusivity at the scales relevant to the local dynamo process. To understand how such peculiar diffusion in the solar atmosphere takes places, we compared the results from two different data-sets (ground-based and space-borne) and developed a simulation of passive tracers advection by the deformation of a Voronoi network. The displacement spectra of the magnetic elements obtained by the data-sets are consistent in retrieving...
Thermally driven advection for radioxenon transport from an underground nuclear explosion
Sun, Yunwei; Carrigan, Charles R.
2016-05-01
Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.
Johnson, Joel P. L.; Delbecq, Katie; Kim, Wonsuck; Mohrig, David
2016-01-01
A goal of paleotsunami research is to quantitatively reconstruct wave hydraulics from sediment deposits in order to better understand coastal hazards. Simple models have been proposed to predict wave heights and velocities, based largely on deposit grain size distributions (GSDs). Although seemingly consistent with some recent tsunamis, little independent data exist to test these equations. We conducted laboratory experiments to evaluate inversion assumptions and uncertainties. A computer-controlled lift gate instantaneously released ~ 6.5 m3 of water into a 32 m flume with shallow ponded water, creating a hydraulic bore that transported sand from an upstream source dune. Differences in initial GSDs and ponded water depths influenced entrainment, transport, and deposition. While the source dune sand was fully suspendable based on size alone, experimental tsunamis produced deposits dominated by bed load sand transport in the upstream ~ 1/3 of the flume and suspension-dominated transport downstream. The suspension deposits exhibited downstream fining and thinning. At 95% confidence, a published advection-settling model predicts time-averaged flow depths to approximately a factor of two, and time-averaged downstream flow velocities to within a factor of 1.5. Finally, reasonable scaling is found between flume and field cases by comparing flow depths, inundation distances, Froude numbers, Rouse numbers and grain size trends in suspension-dominated tsunami deposits, justifying laboratory study of sediment transport and deposition by tsunamis.
SUSTAINABLE DEVELOPMENT PARADIGM - SYNOPSIS
Constantinescu Andreea
2014-07-01
Full Text Available Even if sustainable development is a concept that gained quite recently its scientific prestige, through contribution of researchers its content has upgraded to a high degree of conceptual luggage and, through contribution from governance representatives, has gained an impressive good-practice background. Allowing the use of different methodological premises and conceptual tools, sustainable development paradigm is equipped with all the elements that would allow the opening of new horizons of knowledge. Based on the facility which can operate the concept of sustainable development, the European Union aims to develop both a more competitive economy based on environmental protection as well as a new governance of economic policy. This on one hand demonstrates the sustainable development ability to irradiate creativity towards the establishment of interdisciplinary bridges and on the other hand explains the growing interest of researchers interested in the problem of analyzing in detail this fruitful concept. Launched first as a theoretical framework to serve justify actions responsible for weighting economic growth, the concept of Sustainable Development has quickly become a topic of ethical debate circumscribed to the area of perfectibility of human nature to the necessity registry. In this regard, the philosophical content of this paradigm could not remain outside researchers concerns, who want to provide both policy makers and the general public a wide range of evidence to demonstrate the viability of this paradigm. Academia waits until maximization of the contribution of governance to achieve sustainable economic development, which consists in conjunction of this upward path with the momentum given by public policy sync, perfectly adapted for globalization era and all crises to come. However, because this concept based its structure and composition on three pillars, equally important economy, society and environment any attempt to strengthen
Challenging the Innovation Paradigm
Sveiby, Karl Erik; Segercrantz, Beata
2012-01-01
Innovation is almost always seen as a "good thing". Challenging the Innovation Paradigm is a critical analysis of the innovation frenzy and contemporary innovation research. The one-sided focus on desirable effects of innovation misses many opportunities to reduce the undesirable consequences. Authors in this book show how systemic effects outside the innovating firms reduce the net benefits of innovation for individual employees, customers, as well as for society as a whole - also the innovators' own organizations. This book analyzes the dominant discourses that construct and recons
Liu, G.; Knobbe, S.; Butler, J. J., Jr.
2015-12-01
Direct measurement of groundwater flux is difficult to obtain in the field so hydrogeologists often use easily-detectable environmental tracers, such as heat or chemicals, as an indirect way to characterize flux. Previously, we developed a groundwater flux characterization (GFC) probe by using distributed temperature sensing (DTS) to monitor the temperature responses to active heating in a well. The temperature responses were consistent with the hydraulic conductivity profiles determined at the same location, and provided high-resolution information (approx. 1.5 cm) about vertical variations in horizontal flux through the screen. One of the key assumptions in the previous GFC approach was that the vertical variations in the thermal conductivity of the aquifer materials near the well are negligible, so that the temperature differences with depth are primarily a result of groundwater flux instead of thermal conduction. Although this assumption is likely valid for wells constructed with an artificial filter pack, it might become questionable for wells with natural filter packs (such as the wells constructed by direct push where the sediments are allowed to directly collapse onto the well screen). In this work, we develop a new procedure for separating advection from thermal conduction during GFC measurement. In addition to the normal open-screen GFC profiling, an impermeable sleeve was used so that heating tests could be performed without advective flow entering the well. The heating tests under sleeved conditions were primarily controlled by the thermal conduction around the well, and therefore could be used to remove the impact of thermal conduction from the normal GFC results obtained under open-screen conditions. This new procedure was tested in a laboratory sandbox, where a series of open-screen and sleeved GFC tests were performed under different flow rates. Results indicated that for the tested range of rates (Darcy velocity 0 - 0.78 m/d), the relation between
Air Pollution Steady-State Advection-Diffusion Equation: The General Three-Dimensional Solution
Bardo Bodmann; Tiziano Tirabassi; Marco Túllio Vilhena; Daniela Buske
2012-01-01
Atmospheric air pollution turbulent fluxes can be assumed to be proportional to the mean concentration gradient. This assumption, along with the equation of continuity, leads to the advection-diffusion equation. Many models simulating air pollution dispersion are based upon the solution (numerical or analytical) of the advection-diffusion equation as- suming turbulence parameterization for realistic physical scenarios. We present the general steady three-dimensional solution of the advection-...
X-ray Variability as a Probe of Advection-Dominated Accretion in Low-Luminosity AGN
Ptak, A.; Yaqoob, T.; Mushotzky, R.; Serlemitsos, P.; Griffiths, R.
1998-01-01
As a class, LINERs and Low-Luminosity AGN tend to show little or no significant short-term variability (i.e., with time-scales less than a day). This is a marked break for the trend of increased variability in Seyfert 1 galaxies with decreased luminosity. We propose that this difference is due to the lower accretion rate in LINERs and LLAGN which is probably causing the accretion flow to be advection-dominated. This results in a larger characteristic size for the X-ray producing region than i...
wake, and it is compared to the predictions from the Dynamic Wake Meandering model, for a selected 10 minutes dataset. Secondly, the average wake expansion in the fixed frame of reference is determined from measurements and compared to results from CFD simulations. The CFD simulations were conducted...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....
Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels;
2013-01-01
wake, and it is compared to the predictions from the Dynamic Wake Meandering model, for a selected 10 minutes dataset. Secondly, the average wake expansion in the fixed frame of reference is determined from measurements and compared to results from CFD simulations. The CFD simulations were conducted...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....
On the Structure of Advective Accretion Disks At High Luminosity
Artemova, I V; Igumenshchev, I V; Novikov, I D; Artemova, Ioulia V.; Bisnovatyi-Kogan, Gennadi S.; Igumenshchev, Igor V.; Novikov, Igor D.
2001-01-01
Global solutions of optically thick advective accretion disks around blackholes are constructed. The solutions are obtained by solving numerically a setof ordinary differential equations corresponding to a steady axisymmetricgeometrically thin disk. We pay special attention to consistently satisfy theregularity conditions at singular points of the equations. For this reason weanalytically expand a solution at the singular point, and use coefficients ofthe expansion in our iterative numerical procedure. We obtain consistenttransonic solutions in a wide range of values of the viscosity parameter alphaand mass acretion rate. We compare two different form of viscosity: one takesthe shear stress to be proportional to the pressure, while the other uses theangular velocity gradient-dependent stress. We find that there are two singular points in solutions corresponding to thepressure-proportional shear stress. The inner singular point locates close tothe last stable orbit around black hole. This point changes its typ...
HUANG; Guanhua; HUANG; Quanzhong; ZHAN; Hongbin
2005-01-01
The newly developed Fractional Advection-Dispersion Equation (FADE), which is FADE was extended and used in this paper for modelling adsorbing contaminant transport by adding an adsorbing term. A parameter estimation method and its corresponding FORTRAN based program named FADEMain were developed on the basis of Nonlinear Least Square Algorithm and the analytical solution for one-dimensional FADE under the conditions of step input and steady state flow. Data sets of adsorbing contaminants Cd and NH4+-N transport in short homogeneous soil columns and conservative solute NaCI transport in a long homogeneous soil column, respectively were used to estimate the transport parameters both by FADEMain and the advection-dispersion equation (ADE) based program CXTFIT2.1. Results indicated that the concentration simulated by FADE agreed well with the measured data. Compared to the ADE model, FADE can provide better simulation for the concentration in the initial lower concentration part and the late higher concentration part of the breakthrough curves for both adsorbing contaminants. The dispersion coefficients for ADE were from 0.13 to 7.06 cm2/min, while the dispersion coefficients for FADE ranged from 0.119 to 3.05 cm1.856/min for NaCI transport in the long homogeneous soil column. We found that the dispersion coefficient of FADE increased with the transport distance, and the relationship between them can be quantified with an exponential function. Less scale-dependent was also found for the dispersion coefficient of FADE with respect to ADE.
Huang, Y.H.; Saiers, J.E.; Harvey, J.W.; Noe, G.B.; Mylon, S.
2008-01-01
The movement of particulate matter within wetland surface waters affects nutrient cycling, contaminant mobility, and the evolution of the wetland landscape. Despite the importance of particle transport in influencing wetland form and function, there are few data sets that illuminate, in a quantitative way, the transport behavior of particulate matter within surface waters containing emergent vegetation. We report observations from experiments on the transport of 1 ??m latex microspheres at a wetland field site located in Water Conservation Area 3A of the Florida Everglades. The experiments involved line source injections of particles inside two 4.8-m-long surface water flumes constructed within a transition zone between an Eleocharis slough and Cladium jamaicense ridge and within a Cladium jamaicense ridge. We compared the measurements of particle transport to calculations of two-dimensional advection-dispersion model that accounted for a linear increase in water velocities with elevation above the ground surface. The results of this analysis revealed that particle spreading by longitudinal and vertical dispersion was substantially greater in the ridge than within the transition zone and that particle capture by aquatic vegetation lowered surface water particle concentrations and, at least for the timescale of our experiments, could be represented as an irreversible, first-order kinetics process. We found generally good agreement between our field-based estimates of particle dispersion and water velocity and estimates determined from published theory, suggesting that the advective-dispersive transport of particulate matter within complex wetland environments can be approximated on the basis of measurable properties of the flow and aquatic vegetation. Copyright 2008 by the American Geophysical Union.
Deosir Flávio Lobo de Castro Júnior
2015-09-01
Full Text Available The quantitative- qualitative debate is not a new discussion. The aim of this study therefore is to check through the concept of paradigm, new perspectives to understand the academic research in marketing, developments of marketing thinking and methodologies used in the studies of quality of service. Without pretending to exhaust the subject and present a final conclusion, studies that point to the need and importance of qualitative research, as it helps the researcher to better understand the complex nature of the social world in which we live are presented. According to Santana and Gomes (2007, after examining the discussion of Hegel and Kant, reason and conclude that epistemology itself are historical buildings and evolve from contradictions. This article is divided into five moments. The first part presents besides introducing the constitution of the goals of this theoretical essay. The second part presents a brief discussion of the concept of paradigm and marketing. The third part presents a historical retrospective of marketing and its evolution from its schools from studies of Miranda and Arruda (2004. The fourth part presents the methodology of the studies on quality of services and finally the fifth part presents the final considerations.
Stefano L. Russo
2010-01-01
Full Text Available Problem statement: The increasing diffusion of low-enthalpy geothermal open-loop Groundwater Heat Pumps (GWHP providing buildings air conditioning requires a careful assessment of the overall effects on groundwater system, especially in the urban areas. The impact on the groundwater temperature in the surrounding area of the re-injection well is directly linked to the aquifer properties. Physical processes affecting heat transport within an aquifer include advection (or convection and hydrodynamic thermodispersion (diffusion and mechanical dispersion. If the groundwater flows, the advective components tend to dominate the heat transfer process within the aquifer and the diffusion can be considered negligible. This study illustrates the experimental results derived from the groundwater monitoring in the surrounding area of an injection well connected to an open-loop GWHP plant which has been installed in the "Politecnico di Torino" (NW Italy for cooling some of the university buildings. Groundwater pumping and injection interfere only with the upper unconfined aquifer. Approach: After the description of the hydrogeological setting the authors examined the data deriving from multiparameter probes installed inside the pumping well (P2, the injection well (P4 and a downgradient piezometer (S2. Data refers to the summer 2009. To control the aquifer thermal stratification some multi-temporal temperature logs have been performed in the S2. Results: After the injection of warm water in P4 the plume arrived after 30 days in the S2. That delay is compatible with the calculated plume migration velocity (1.27 m d-1 and their respective distance (35 m. The natural temperature in the aquifer due to the switching-off of the GWHP plant has been reached after two month. The Electrical Conductivity (EC values tend to vary out of phase with the temperature. The temperature logs in the S2 highlighted a thermal stratification in the aquifer due to a low vertical
Bachand, P.A.M., E-mail: Philip.Bachand@Tetratech.com [Tetra Tech, Davis, CA (United States); Bachand, S. [Tetra Tech, Davis, CA (United States); Fleck, J.; Anderson, F. [U.S. Geological Survey, California Water Science Center, Sacramento, CA (United States); Windham-Myers, L. [U.S. Geological Survey, National Research Program, Menlo Park, CA (United States)
2014-06-01
The current state of science and engineering related to analyzing wetlands overlooks the importance of transpiration and risks data misinterpretation. In response, we developed hydrologic and mass budgets for agricultural wetlands using electrical conductivity (EC) as a natural conservative tracer. We developed simple differential equations that quantify evaporation and transpiration rates using flow rates and tracer concentrations at wetland inflows and outflows. We used two ideal reactor model solutions, a continuous flow stirred tank reactor (CFSTR) and a plug flow reactor (PFR), to bracket real non-ideal systems. From those models, estimated transpiration ranged from 55% (CFSTR) to 74% (PFR) of total evapotranspiration (ET) rates, consistent with published values using standard methods and direct measurements. The PFR model more appropriately represents these non-ideal agricultural wetlands in which check ponds are in series. Using a flux model, we also developed an equation delineating the root zone depth at which diffusive dominated fluxes transition to advective dominated fluxes. This relationship is similar to the Peclet number that identifies the dominance of advective or diffusive fluxes in surface and groundwater transport. Using diffusion coefficients for inorganic mercury (Hg) and methylmercury (MeHg) we calculated that during high ET periods typical of summer, advective fluxes dominate root zone transport except in the top millimeters below the sediment–water interface. The transition depth has diel and seasonal trends, tracking those of ET. Neglecting this pathway has profound implications: misallocating loads along different hydrologic pathways; misinterpreting seasonal and diel water quality trends; confounding Fick's First Law calculations when determining diffusion fluxes using pore water concentration data; and misinterpreting biogeochemical mechanisms affecting dissolved constituent cycling in the root zone. In addition, our
The current state of science and engineering related to analyzing wetlands overlooks the importance of transpiration and risks data misinterpretation. In response, we developed hydrologic and mass budgets for agricultural wetlands using electrical conductivity (EC) as a natural conservative tracer. We developed simple differential equations that quantify evaporation and transpiration rates using flow rates and tracer concentrations at wetland inflows and outflows. We used two ideal reactor model solutions, a continuous flow stirred tank reactor (CFSTR) and a plug flow reactor (PFR), to bracket real non-ideal systems. From those models, estimated transpiration ranged from 55% (CFSTR) to 74% (PFR) of total evapotranspiration (ET) rates, consistent with published values using standard methods and direct measurements. The PFR model more appropriately represents these non-ideal agricultural wetlands in which check ponds are in series. Using a flux model, we also developed an equation delineating the root zone depth at which diffusive dominated fluxes transition to advective dominated fluxes. This relationship is similar to the Peclet number that identifies the dominance of advective or diffusive fluxes in surface and groundwater transport. Using diffusion coefficients for inorganic mercury (Hg) and methylmercury (MeHg) we calculated that during high ET periods typical of summer, advective fluxes dominate root zone transport except in the top millimeters below the sediment–water interface. The transition depth has diel and seasonal trends, tracking those of ET. Neglecting this pathway has profound implications: misallocating loads along different hydrologic pathways; misinterpreting seasonal and diel water quality trends; confounding Fick's First Law calculations when determining diffusion fluxes using pore water concentration data; and misinterpreting biogeochemical mechanisms affecting dissolved constituent cycling in the root zone. In addition, our understanding of
2009-01-01
Flow er en positiv, koncentreret tilstand, hvor al opmærksomhed er samlet om en bestemt aktivitet, som er så krævende og engagerende, at man må anvende mange mentale ressourcer for at klare den. Tidsfornemmelsen forsvinder, og man glemmer sig selv. 'Flow' er den første af en række udsendelser om...
Paradigms for parasite conservation.
Dougherty, Eric R; Carlson, Colin J; Bueno, Veronica M; Burgio, Kevin R; Cizauskas, Carrie A; Clements, Christopher F; Seidel, Dana P; Harris, Nyeema C
2016-08-01
Parasitic species, which depend directly on host species for their survival, represent a major regulatory force in ecosystems and a significant component of Earth's biodiversity. Yet the negative impacts of parasites observed at the host level have motivated a conservation paradigm of eradication, moving us farther from attainment of taxonomically unbiased conservation goals. Despite a growing body of literature highlighting the importance of parasite-inclusive conservation, most parasite species remain understudied, underfunded, and underappreciated. We argue the protection of parasitic biodiversity requires a paradigm shift in the perception and valuation of their role as consumer species, similar to that of apex predators in the mid-20th century. Beyond recognizing parasites as vital trophic regulators, existing tools available to conservation practitioners should explicitly account for the unique threats facing dependent species. We built upon concepts from epidemiology and economics (e.g., host-density threshold and cost-benefit analysis) to devise novel metrics of margin of error and minimum investment for parasite conservation. We define margin of error as the risk of accidental host extinction from misestimating equilibrium population sizes and predicted oscillations, while minimum investment represents the cost associated with conserving the additional hosts required to maintain viable parasite populations. This framework will aid in the identification of readily conserved parasites that present minimal health risks. To establish parasite conservation, we propose an extension of population viability analysis for host-parasite assemblages to assess extinction risk. In the direst cases, ex situ breeding programs for parasites should be evaluated to maximize success without undermining host protection. Though parasitic species pose a considerable conservation challenge, adaptations to conservation tools will help protect parasite biodiversity in the face of
McGraw R.
2012-03-01
Moment methods are finding increasing usage for simulations of particle population balance in box models and in more complex flows including two-phase flows. These highly efficient methods have nevertheless had little impact to date for multi-moment representation of aerosols and clouds in atmospheric models. There are evidently two reasons for this: First, atmospheric models, especially if the goal is to simulate climate, tend to be extremely complex and take many man-years to develop. Thus there is considerable inertia to the implementation of novel approaches. Second, and more fundamental, the nonlinear transport algorithms designed to reduce numerical diffusion during advection of various species (tracers) from cell to cell, in the typically coarse grid arrays of these models, can and occasionally do fail to preserve correlations between the moments. Other correlated tracers such as isotopic abundances, composition of aerosol mixtures, hydrometeor phase, etc., are subject to this same fate. In the case of moments, this loss of correlation can and occasionally does give rise to unphysical moment sets. When this happens the simulation can come to a halt. Following a brief description and review of moment methods, the goal of this paper is to present two new approaches that both test moment sequences for validity and correct them when they fail. The new approaches work on individual grid cells without requiring stored information from previous time-steps or neighboring cells.
We present a combination of experiment, theory, and modelling on laminar mixing at large Péclet number. The flow is produced by oscillating electromagnetic forces in a thin electrolytic fluid layer, leading to oscillating dipoles, quadrupoles, octopoles, and disordered flows. The numerical simulations are based on the Diffusive Strip Method (DSM) which was recently introduced (P. Meunier and E. Villermaux, “The diffusive strip method for scalar mixing in two-dimensions,” J. Fluid Mech. 662, 134–172 (2010)) to solve the advection-diffusion problem by combining Lagrangian techniques and theoretical modelling of the diffusion. Numerical simulations obtained with the DSM are in reasonable agreement with quantitative dye visualization experiments of the scalar fields. A theoretical model based on log-normal Probability Density Functions (PDFs) of stretching factors, characteristic of homogeneous turbulence in the Batchelor regime, allows to predict the PDFs of scalar in agreement with numerical and experimental results. This model also indicates that the PDFs of scalar are asymptotically close to log-normal at late stages, except for the large concentration levels which correspond to low stretching factors
Application of GPU to Multi-interfaces Advection and Reconstruction Solver (MARS)
In the nuclear engineering fields, a high performance computer system is necessary to perform the large scale computations. Recently, a Graphics Processing Unit (GPU) has been developed as a rendering computational system in order to reduce a Central Processing Unit (CPU) load. In the graphics processing, the high performance computing is needed to render the high-quality 3D objects in some video games. Thus the GPU consists of many processing units and a wide memory bandwidth. In this study, the Multi-interfaces Advection and Reconstruction Solver (MARS) which is one of the interface volume tracking methods for multi-phase flows has been performed. The multi-phase flow computation is very important for the nuclear reactors and other engineering fields. The MARS consists of two computing parts: the interface tracking part and the fluid motion computing part. As for the interface tracking part, the performance of GPU (GTX280) was 6 times faster than that of the CPU (Dual-Xeon 5040), and in the fluid motion computing part the Poisson Solver by the GPU (GTX285) was 22 times faster than that by the CPU(Core i7). As for the Dam Breaking Problem, the result of GPU-MARS showed slightly different from the experimental result. Because the GPU-MARS was developed using the single-precision GPU, it can be considered that the round-off error might be accumulated. (author)
Analytical solution for the advection-dispersion transport equation in layered media
The advection-dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection-diffusion eigenvalue problem that had the same form and coef...
Algebraic dynamics solution to and algebraic dynamics algorithm for nonlinear advection equation
2008-01-01
Algebraic dynamics approach and algebraic dynamics algorithm for the solution of nonlinear partial differential equations are applied to the nonlinear advection equa-tion. The results show that the approach is effective for the exact analytical solu-tion and the algorithm has higher precision than other existing algorithms in nu-merical computation for the nonlinear advection equation.
Cox, T.J.; Runkel, R.L.
2008-01-01
Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.
Naturalistic Inquiry: Paradigm and Method.
Lotto, Linda S.
Despite the rhetoric acclaiming it as a new paradigm, educational researchers have tended to treat naturalistic inquiry as a new or alternative method employed within the dominant, rationalistic paradigm. Spokespersons for naturalistic inquiry tend to concentrate on what one does differently rather than how one perceives what one is doing…
Knoop, Hans Henrik
2006-01-01
FLOW. Orden i hovedet på den fede måde Oplevelsesmæssigt er flow-tilstanden kendetegnet ved at man er fuldstændig involveret, fokuseret og koncentreret; at man oplever stor indre klarhed ved at vide hvad der skal gøres, og i hvilket omfang det lykkes; at man ved at det er muligt at løse opgaven...
Mass loss from advective accretion disc around rotating black holes
Aktar, Ramiz; Nandi, Anuj
2015-01-01
We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter, PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (${\\mathcal E}$) and specific angular momentum ($\\lambda$) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole ($a_k$) plays an important role in deciding the outflow rate $R_{\\dot m}$ (ratio of mass flux of outflow and inflow), in particular, $R_{\\dot m}$ is directly correlated with $a_k$ for the same set of inflow parameters. It is found that ...
Bachand, P.A.M.; S. Bachand; Fleck, Jacob A.; Anderson, Frank E.; Windham-Myers, Lisamarie
2014-01-01
The current state of science and engineering related to analyzing wetlands overlooks the importance of transpiration and risks data misinterpretation. In response, we developed hydrologic and mass budgets for agricultural wetlands using electrical conductivity (EC) as a natural conservative tracer. We developed simple differential equations that quantify evaporation and transpiration rates using flowrates and tracer concentrations atwetland inflows and outflows. We used two ideal reactormodel solutions, a continuous flowstirred tank reactor (CFSTR) and a plug flow reactor (PFR), to bracket real non-ideal systems. From those models, estimated transpiration ranged from 55% (CFSTR) to 74% (PFR) of total evapotranspiration (ET) rates, consistent with published values using standard methods and direct measurements. The PFR model more appropriately represents these nonideal agricultural wetlands in which check ponds are in series. Using a fluxmodel, we also developed an equation delineating the root zone depth at which diffusive dominated fluxes transition to advective dominated fluxes. This relationship is similar to the Peclet number that identifies the dominance of advective or diffusive fluxes in surface and groundwater transport. Using diffusion coefficients for inorganic mercury (Hg) and methylmercury (MeHg) we calculated that during high ET periods typical of summer, advective fluxes dominate root zone transport except in the top millimeters below the sediment–water interface. The transition depth has diel and seasonal trends, tracking those of ET. Neglecting this pathway has profound implications: misallocating loads along different hydrologic pathways; misinterpreting seasonal and diel water quality trends; confounding Fick's First Law calculations when determining diffusion fluxes using pore water concentration data; and misinterpreting biogeochemicalmechanisms affecting dissolved constituent cycling in the root zone. In addition,our understanding of internal
Summertime influences of tidal energy advection on the surface energy balance in a mangrove forest
J. G. Barr
2013-01-01
Full Text Available Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive 10-day study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL, USA. Forest–atmosphere turbulent exchanges of energy were quantified with an eddy covariance system installed on a 30-m-tall flux tower. Energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, flood waters reduced the impact of high radiational loads on the mangrove forest. Also, the regression slope of available energy versus sink terms increased from 0.730 to 0.754 and from 0.798 to 0.857, including total enthalpy change in the water column in the surface energy balance for 30-min periods and daily daytime sums, respectively. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem
Convection-Dominated Accretion Flows
Quataert, Eliot; Gruzinov, Andrei
1999-01-01
Non-radiating, advection-dominated, accretion flows are convectively unstable. We calculate the two-dimensional (r-theta) structure of such flows assuming that (1) convection transports angular momentum inwards, opposite to normal viscosity and (2) viscous transport by other mechanisms (e.g., magnetic fields) is weak (alpha
The contiguous domains of Arctic Ocean advection: Trails of life and death
Wassmann, P.; Kosobokova, K. N.; Slagstad, D.; Drinkwater, K. F.; Hopcroft, R. R.; Moore, S. E.; Ellingsen, I.; Nelson, R. J.; Carmack, E.; Popova, E.; Berge, J.
2015-12-01
The central Arctic Ocean is not isolated, but tightly connected to the northern Pacific and Atlantic Oceans. Advection of nutrient-, detritus- and plankton-rich waters into the Arctic Ocean forms lengthy contiguous domains that connect subarctic with the arctic biota, supporting both primary production and higher trophic level consumers. In turn, the Arctic influences the physical, chemical and biological oceanography of adjacent subarctic waters through southward fluxes. However, exports of biomass out of the Arctic Ocean into both the Pacific and Atlantic Oceans are thought to be far smaller than the northward influx. Thus, Arctic Ocean ecosystems are net biomass beneficiaries through advection. The biotic impact of Atlantic- and Pacific-origin taxa in arctic waters depends on the total supply of allochthonously-produced biomass, their ability to survive as adults and their (unsuccessful) reproduction in the new environment. Thus, advective transport can be thought of as trails of life and death in the Arctic Ocean. Through direct and indirect (mammal stomachs, models) observations this overview presents information about the advection and fate of zooplankton in the Arctic Ocean, now and in the future. The main zooplankton organisms subjected to advection into and inside the Arctic Ocean are (a) oceanic expatriates of boreal Atlantic and Pacific origin, (b) oceanic Arctic residents and (c) neritic Arctic expatriates. As compared to the Pacific gateway the advective supply of zooplankton biomass through the Atlantic gateways is 2-3 times higher. Advection characterises how the main planktonic organisms interact along the contiguous domains and shows how the subarctic production regimes fuel life in the Arctic Ocean. The main differences in the advective regimes through the Pacific and Atlantic gateways are presented. The Arctic Ocean is, at least in some regions, a net heterotrophic ocean that - during the foreseeable global warming trend - will more and more rely
The role of a delay time on the spatial structure of chaotically advected reactive scalars
Tzella, Alexandra
2009-01-01
The stationary-state spatial structure of reacting scalar fields, chaotically advected by a two-dimensional large-scale flow, is examined for the case for which the reaction equations contain delay terms. Previous theoretical investigations have shown that, in the absence of delay terms and in a regime where diffusion can be neglected (large P\\'eclet number), the emergent spatial structures are filamental and characterized by a single scaling regime with a H\\"older exponent that depends on the rate of convergence of the reactive processes and the strength of the stirring measured by the average stretching rate. In the presence of delay terms, we show that for sufficiently small scales all interacting fields should share the same spatial structure, as found in the absence of delay terms. Depending on the strength of the stirring and the magnitude of the delay time, two further scaling regimes that are unique to the delay system may appear at intermediate length scales. An expression for the transition length s...
Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence
Schekochihin, A A; Highcock, E G; Dellar, P J; Dorland, W; Hammett, G W
2015-01-01
A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g., drift-wave turbulence driven by temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating ExB flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. A consistent theory is constructed in which very little free energy leaks into high velocity moments of the distribution, rendering the turbulent cascade in the energetically relevant part of the wave-number space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also i...
On-site testing of advective flux probes for enlarging the range of soil hydrocarbon analysis
The success of soil vapor as a means of assessing subsurface conditions depends upon the volatility of the compounds and the ability of the vapor to migrate through soil pores. Normally, soil gas techniques are not considered valid for poorly volatile compounds or tight soils. Both of these factors can be overcome by simultaneous application of heat and vacuum, combined with a means of creating an artificially porous substrate out of compacted poorly permeable soils. A special rock bit was devised to fit on a miniature hollow stem shaft. The bit receives a continuous flow of heated air or liquid which removes organics from the pulverized soil as the bit penetrates. The recirculation of hot air then transports the gas or liquid to the surface for chromatographic analysis. A comparison of vapor pressures of different organics versus absolute temperatures can be used to extrapolate the extension of soil gas detection. Heavy oils, petroleum, coal, creosotes, naphthalenes, turpenes and quinolines, all compounds whose boiling points exist in excess of 200 degree C, can be analyzed by soil vapor techniques. Samples of the volatile organic can be obtained by either: direct injection onto a heated column, bubbling the vapor through a solvent or adsorption-desorption tubes. The use of solvents allows the technique to extend to fluorometric or IR analysis. The paper compares current vacuum procedures with those obtained from the advective flux procedure for selected sites on Cape Cod
A diffusive Fisher-KPP equation with free boundaries and time-periodic advections
Sun, Ningkui; Lou, Bendong; Zhou, Maolin
2016-01-01
We consider a reaction-diffusion-advection equation of the form: $u_t=u_{xx}-\\beta(t)u_x+f(t,u)$ for $x\\in (g(t),h(t))$, where $\\beta(t)$ is a $T$-periodic function representing the intensity of the advection, $f(t,u)$ is a Fisher-KPP type of nonlinearity, $T$-periodic in $t$, $g(t)$ and $h(t)$ are two free boundaries satisfying Stefan conditions. This equation can be used to describe the population dynamics in time-periodic environment with advection. Its homogeneous version (that is, both $...
Functional reactive paradigm advantages for Android development
SUTULA ALEXANDER
2015-01-01
This article describes conceptual difference between imperative, reactive paradigms and functional reactive style advantages in Android development. Solutions of imperative paradigm main problems are described.
Antonov, N V; Gulitskiy, N M
2015-10-01
In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015)] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n, all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E∝k(⊥)(1-ξ) and the dispersion law ω∝k(⊥)(2-η). In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L. PMID:26565343
Horizontal Advection and Mixing of Pollutants in the Urban Atmospheric Environment
Magnusson, S. P.; Entekhabi, D.; Britter, R.; Norford, L.; Fernando, H. J.
2013-12-01
Although urban air quality and its impacts on the public health have long been studied, the increasing urbanization is raising concerns on how to better control and mitigate these health impacts. A necessary element in predicting exposure levels is fundamental understanding of flow and dispersion in urban canyons. The complex topology of building structures and roads requires the resolution of turbulence phenomena within urban canyons. The use of dense and low porosity construction material can lead to rapid heating in response to direct solar exposure due to large thermal mass. Hence thermal and buoyancy effects may be as important as mechanically-forced or shear-induced flows. In this study, the transport of pollutants within the urban environment, as well as the thermal and advection effects, are investigated. The focus is on the horizontal transport or the advection effects within the urban environment. With increased urbanization and larger and more spread cities, concern about how the upstream air quality situation can affect downstream areas. The study also examines the release and the dispersion of hazardous material. Due to the variety and complexity of urban areas around the world, the urban environment is simplified into adjacent two-dimensional urban street canyons. Pollutants are released inside each canyon. Computational Fluid Dynamics (CFD) simulations are applied to evaluate and quantify the flow rate out of each canyon and also the exchange of pollutants between the canyons. Imagine a row of ten adjacent urban street canyons of aspect ratio 1 with horizontal flow perpendicular to it as shown in the attached figure. C is the concentration of pollutants. The first digit indicates in what canyon the pollutant is released and the second digit indicates the location of that pollutant. For example, C3,4 is the concentration of pollutant released inside canyon 3 measured in canyon 4. The same amount of pollution is released inside the ten street canyons
Boundary value problemfor multidimensional fractional advection-dispersion equation
Khasambiev Mokhammad Vakhaevich
2015-05-01
authors first considered the boundary value problem for stationary equation for mass transfer in super-diffusion conditions and abnormal advection. Then the solution of the problem is explicitly given. The solution is obtained by the Fourier’s method.The obtained results will be useful in liquid filtration theory in fractal medium and for modeling the temperature variations in the heated bar.
Site use of advective flux probes for soil gas and soil analysis
The success of soil vapor as a means of assessing subsurface conditions depends upon the volatility of the compounds and the ability of the vapor to migrate through soil pores. Normally, soil gas techniques are not considered valid for poorly volatile compounds or tight soils. Both of these factors can be overcome by a simultaneous application of heat and vacuum with heated gas streams or use of a liquid solution, combined with a means of creating an artificially porous substrate out of compacted poorly permeable soils. Special points and bits have been devised to fit on a miniature hollow stem shaft. The point receives a continuous flow of heated air or liquid which volatilises or dissolves organics from porous or pulverized soil as the point penetrates. The re-circulation of gas or fluid then transports the adsorbed organics to the surface for chromatographic analysis. A comparison of vapor pressures of different organics versus absolute temperatures can be used to extrapolate the extension of soil gas detection. Heavy oils, creosotes, naphthalenes, turpenes, and quinolines, all compounds whose boiling points exist in excess of 200 degrees C, can be analyzed by soil vapor techniques. Samples of the organic were obtained by either direct injection on to a heated GC column or by liquid chromatographic processing. The paper compares current vacuum procedures with those obtained from the advective flux procedure. The compounds are plotted on a grid of boiling point, vapor pressure, and aqueous solubility. A site containing soil contaminated with a mixture of light to heavy petroleum products was analyzed with enhanced hot gas and liquid flow. A comparison between the compounds analyzed is presented for both techniques
Rigorous upper bounds for fluid and plasma transport due to passive advection
The formulation of variational principles for transport due to passive advection is described. A detailed account of the work has been published elsewhere. In the present paper, the motivations, philosophy, and implications of the method are briefly discussed. 15 refs
Sensitivity of Gcm Inm Ras To The Change of Humidity Advection Scheme
Kostrykin, S. V.
We study the influence of change the numerical scheme used for humidity advection in the GCM INM RAS on the model results. The previously used advection scheme of the second order leap-frog was changed on the semi-lagrangian cip scheme of the third order. It has shown that the last scheme has excelent numerical properties among other common semi-lagrangian schemes dealing with precise advection of sharp gra- dients. The numerical expriments with GCM has shown that the main changes in the humidity and temperature fields has happend near tropopause. More closeness of the model fields obtained with new advection of humidity to the NCAR/NCEP reanalyses fields are shown.
EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION
Many numerical methods use characteristic analysis to accommodate the advective component of transport. uch characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. eneralization of characteristic...
AN EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION
Many numerical methods use characteristic analysis to accommodate the advective component of transport. Such characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. A generalization of characteri...
A zoomable and adaptable hidden fine-mesh approach to solving advection-dispersion equations
A zoomable and adaptable hidden fine-mesh approach (ZAHFMA), that can be used with either finite element or finite difference methods, is proposed to solve the advection-dispersion equation. The approach is based on automatic adaptation of zooming a hidden fine-mesh in the place where the sharp front locates. Preliminary results indicate that ZAHFMA used with finite element methods can handle the advection-dispersion problems with Peclet number ranging from 0 to ∞. 5 refs., 2 figs
Numerical methods for advection-diffusion-reaction equations and medical applications
Montecinos, Gino Ignacio
2014-01-01
The purpose of this thesis is twofold, firstly, the study of a relaxation procedure for numerically solving advection-diffusion-reaction equations, and secondly, a medical application. Concerning the first topic, we extend the applicability of the Cattaneo relaxation approach to reformulate time-dependent advection-diffusion-reaction equations, that may include stiff reactive terms, as hyperbolic balance laws with stiff source terms. The resulting systems of hyperbolic balance laws are solved...
Backeberg, B. C.; Bertino, L.; J. A. Johannessen
2009-01-01
A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism...
Cornaton, Fabien; Perrochet, Pierre
2004-01-01
The main objective of this dissertation consisted in the elaboration of a methodology to determine reservoir groundwater age, life expectancy, and transit time probability distributions in a deterministic manner, considering advective-dispersive transport in steady velocity fields. In the first section, it is shown that by modelling the statistical distribution of groundwater age at aquifer scale by means of the classical advection-dispersion equation (ADE) for a conservative and non-reactive...
Planktonic interactions and chaotic advection in Langmuir circulation
Bees, Martin Alan; Mezic, I.; McGlade, J.
1998-01-01
The role of unsteady laminar flows for planktonic communities is investigated. Langmuir circulation is used, as a typical medium-scale structure, to illustrate mechanisms for the generation of plankton patches. Two behaviours are evident: chaotic regions that help to spread plankton and locally...
Scheck, L; Foglizzo, T; Kifonidis, K
2007-01-01
By 2D hydrodynamic simulations including a detailed equation of state and neutrino transport, we investigate the interplay between different non-radial hydrodynamic instabilities that play a role during the postbounce accretion phase of collapsing stellar cores. The convective mode of instability, which is driven by negative entropy gradients caused by neutrino heating or by time variations of the shock strength, can be identified clearly by the development of typical Rayleigh-Taylor mushrooms. However, in cases where the gas in the postshock region is rapidly advected towards the gain radius, the growth of such a buoyancy instability can be suppressed. In such a situation the shocked flow nevertheless can develop non-radial asymmetry with an oscillatory growth of the amplitude. This phenomenon was previously termed ``standing accretion shock instability'' (SASI) by Blondin et al. (2003). It is shown here that the oscillation period of the SASI observed in our simulations agrees well with the one estimated fo...
Towards reduction of Paradigm coordination models
Andova, S.; Groenewegen, L. P. J.; Vink, de, E.P.; Aceto, Luca; Mousavi, M.R.
2011-01-01
The coordination modelling language Paradigm addresses collaboration between components in terms of dynamic constraints. Within a Paradigm model, component dynamics are consistently specified at a detailed and a global level of abstraction. To enable automated verification of Paradigm models, a translation of Paradigm into process algebra has been defined in previous work. In this paper we investigate, guided by a client-server example, reduction of Paradigm models based on a notion of global...
Elevated tritium, helium-3 and chloride concentrations have been measured in groundwaters in a shallow sandy aquifer draining a small lake at the Chalk River Laboratories (CRL), Ontario, Canada. The chloride in the lakewater recharge is 25 times greater than precipitation recharge and forms a continuous, concentrated source of contamination to the aquifer. Tritium (3H) concentrations in both lake and precipitation recharge are elevated owing to the operation of a research reactor on the CRL site and form a continuous spatially distributed source of contamination. The transport of tritium and chloride over the 600 m groundwater flowpath from the lake to the discharge zone are simulated using a 3-D advection-dispersion model. The model requires information on the contaminant input concentrations, the velocity field, dispersion parameters, hydrostratigraphy and boundary conditions. The two independent sets of concentration data provide complementary information to minimize problems associated with the unknown input concentration. The velocity field was estimated from a 3-D simulation of the groundwater flow system; dispersion parameters were estimated from analysis of a controlled natural-gradient tracer test performed previously at the site. The hydrostratigraphy and boundary geometry was characterized by visual logging of borehole sediments, grain size analyses and ground penetrating radar surveys. The abundance of hydrogeologic and geophysical information allowed simulation of the spatial distribution of chloride concentrations with a remarkable degree of accuracy. Simulated and measured peak chloride concentrations differed by less than 15%. The excellent agreement between the simulated and observed chloride concentrations facilitated further modelling of the source and migrational behavior of 3H within this aquifer. We have solved the inverse problem for the 3H source function and successfully modelled the 3H source as a stepwise function. Estimates of
Cultural Paradigms in Management Sciences
Lukasz Sulkowski
2013-09-01
Full Text Available Purpose: The purpose of this paper is to present an idea for understanding cultural processes in the organizational discourse from the perspective of four paradigms in management sciences based on the concept of G. Burrell and G. Morgan.Methodology: The author has elaborated a valuable list of structures of the scientifi c theory based on the respective paradigms and has compared cultural paradigms in management sciences. The methodology involves an analysis of classical and recent world literature. Nowadays there is no consensus on the defi nitions, types or research models of organizational culture.Originality: In the literature on the subject we can fi nd many, sometimes contradictory cultural research studies that require further analysis. Precisely because of the diversity and complexity of cultural issues in management sciences a multi-paradigmatic analysis is necessary. The paper presents a proposal for a pluralistic approach to the theory and methodology of cultural studies in management sciences.
Bayesian test and Kuhn's paradigm
Chen Xiaoping
2006-01-01
Kuhn's theory of paradigm reveals a pattern of scientific progress,in which normal science alternates with scientific revolution.But Kuhn underrated too much the function of scientific test in his pattern,because he focuses all his attention on the hypothetico-deductive schema instead of Bayesian schema.This paper employs Bayesian schema to re-examine Kuhn's theory of paradigm,to uncover its logical and rational components,and to illustrate the tensional structure of logic and belief,rationality and irrationality,in the process of scientific revolution.
Paradigms in Physics Education Research
Robertson, Amy D; McKagan, Sarah B
2013-01-01
Physics education research (PER) includes three distinct paradigms: quantitative research, qualitative research, and question-driven research. Quantitative PER seeks reproducible, representative patterns and relationships; human behavior is seen as dictated by lawful (albeit probabilistic) relationships. Qualitative PER seeks to refine and develop theory by linking theory to cases; human action is seen as shaped by the meanings that participants make of their local environments. Question-driven physics education researchers prioritize questions over the pursuit of local meanings or abstract relationships. We illustrate each paradigm with interviews with physics education researchers and examples of published PER.
Chua, Leon O
1998-01-01
Revolutionary and original, this treatise presents a new paradigm of EMERGENCE and COMPLEXITY, with applications drawn from numerous disciplines, including artificial life, biology, chemistry, computation, physics, image processing, information science, etc.CNN is an acronym for Cellular Neural Networks when used in the context of brain science, or Cellular Nonlinear Networks, when used in the context of emergence and complexity. A CNN is modeled by cells and interactions: cells are defined as dynamical systems and interactions are defined via coupling laws. The CNN paradigm is a universal Tur
Planktonic interactions and chaotic advection in Langmuir circulation
Bees, Martin Alan; Mezic, I.; McGlade, J.
1998-01-01
The role of unsteady laminar flows for planktonic communities is investigated. Langmuir circulation is used, as a typical medium-scale structure, to illustrate mechanisms for the generation of plankton patches. Two behaviours are evident: chaotic regions that help to spread plankton and locally...... coherent regions that do not mix with the chaotic regions and which persist for long periods of time. The interaction of populations of phytoplankton with zooplankton is discussed, taking into account the variations in plankton buoyancy....
Advection of the salt wedge and evolution of the internal flow structure in the Rotterdam Waterway
De Nijs, M.A.J.; Pietrzak, J.D.; Winterwerp, J.C.
2011-01-01
An analysis of field measurements recorded over a tidal cycle in the Rotterdam Waterway is presented. These measurements are the first to elucidate the processes influencing the along-channel current structure and the excursion of the salt wedge in this estuary. The salt wedge structure remained sta
Phase dependent advection-diffusion in drift wave - zonal flow turbulence
Moradi, Sara
2016-01-01
In plasma turbulence theory, due to the complexity of the system with many non-linearly interacting waves, the dynamics of the phases is often disregarded and the so-called random-phase approximation (RPA) is used assuming the existence of a Chirikov-like criterion for the onset of wave stochasticity. The dynamical amplitudes are represented as complex numbers, $\\psi = \\psi_r + i\\psi_i = ae^{i\\theta}$, with the amplitudes slowly varying whereas the phases are rapidly varying and, in particular, distributed uniformly over the interval $[0;2\\pi)$. However, one could expect that the phase dynamics can play a role in the self-organisation and the formation of coherent structures. In the same manner it is also expected that the RPA falls short to take coherent interaction between phases into account. In this work therefore, we studied the role of phase dynamics and the coupling of phases between different modes on the characteristic time evolution of the turbulent. We assume a simple turbulent system where the so-...
Paradigms of mangroves in treatment of anthropogenic wastewater pollution.
Ouyang, Xiaoguang; Guo, Fen
2016-02-15
Mangroves have been increasingly recognized for treating wastewater from aquaculture, sewage and other sources with the overwhelming urbanization trend. This study clarified the three paradigms of mangroves in disposing wastewater contaminants: natural mangroves, constructed wetlands (including free water surface and subsurface flow) and mangrove-aquaculture coupling systems. Plant uptake is the common major mechanism for nutrient removal in all the paradigms as mangroves are generally nitrogen and phosphorus limited. Besides, sediments accrete and provide substrates for microbial activities, thereby removing organic matter and nutrients from wastewater in natural mangroves and constructed wetlands. Among the paradigms, the mangrove-aquaculture coupling system was determined to be the optimal alternative for aquaculture wastewater treatment by multi-criterion decision making. Sensitivity analysis shows variability of alternative ranking but underpins the coupling system as the most environment-friendly and cost-efficient option. Mangrove restoration is expected to be achievable if aquaculture ponds are planted with mangrove seedlings, creating the coupling system. PMID:26706768
The New Environmental Paradigm Scale.
Albrecht, Don; And Others
1982-01-01
Reports the reliability, validity, and unidimensionality of New Environmental Paradigm (NEP) scale, an instrument designed to measure how people feel about nature. Based on statewide samples of farmers (N=348) and metropolitan residents (N=407) of Iowa, the NEP was determined to be valid, reliable, and multidimensional, measuring three distinct…
Artificial life, the new paradigm
A chronological synthesis of the most important facts is presented in the theoretical development and computational simulation that they have taken to the formation of a new paradigm that is known as artificial life; their characteristics and their main investigation lines are analyzed. Finally, a description of its work is made in the National University of Colombia
Transplant rejection and paradigms lost
Strom, Terry B.
2013-01-01
During transplant rejection, migrating T cells infiltrate the grafted organ, but the signals that direct this migration are incompletely understood. In this issue of the JCI, Walch et al. debunk two classical paradigms concerning transplant rejection, with important consequences for the design of antirejection therapeutics. PMID:23676457
Transplant rejection and paradigms lost
Strom, Terry B.
2013-01-01
During transplant rejection, migrating T cells infiltrate the grafted organ, but the signals that direct this migration are incompletely understood. In this issue of the JCI, Walch et al. debunk two classical paradigms concerning transplant rejection, with important consequences for the design of antirejection therapeutics.
The emerging land management paradigm
Enemark, Stig
2006-01-01
Manchet: This paper was first presented by Professor Enemark at the RICS Christmas Lecture in December last year. It provides a cogent and detailed reference point for the current state of land management in developed countries, charts a course for the future and looks at how education must chang...... to meet the new paradigm....
The Paradigm of Distributed Creativity
Glaveanu, Vlad Petre
This presentation aims to focus on and develop the notion of distributed creativity from a cultural psychological perspective. It will start by outlining the need for a cultural psychological paradigm of creative expression and argue that this perspective is primarily concerned with what can be...
Paradigms, Exemplars and Social Change
Lawson, Hal A.
2009-01-01
Researchers' social-cultural organization influences the scope, quality, quantity, coherence, dissemination, utilization and impact of research-based, theoretically sound knowledge. Five concepts--paradigm, exemplar, segment, network and gatekeeper--are salient to research on researchers' organization. Autobiographical reflections signal these…
Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events
WU Xiandu; RAN Lingkun; CHU Yanli
2011-01-01
A moist thermodynamic advection parameter, defined as an absolute value of the dot product of horizontal gradients of three-dimensional potential temperature advection and general potential temperature, is introduced to diagnose frontal heavy rainfall events in the north of China. It is shown that the parameter is closely related to observed 6-h accumulative surface rainfall and simulated cloud hydrometeors. Since the parameter is capable of describing the typical vertical structural characteristics of dynamic, thermodynamic and water vapor fields above a strong precipitation region near the front surface, it may serve as a physical tracker to detect precipitable weather systems near to a front.A tendency equation of the parameter was derived in Cartesian coordinates and calculated with the simulation output data of a heavy rainfall event. Results revealed that the advection of the parameter by the three-dimensional velocity vector, the covariance of potential temperature advection by local change of the velocity vector and general potential temperature, and the interaction between potential temperature advection and the source or sink of general potential temperature, accounted for local change in the parameter. This indicated that the parameter was determined by a combination of dynamic processes and cloud microphysical processes.
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
Mazaheri, Alireza; Nishikawa, Hiroaki
2014-01-01
A time-dependent extension of the first-order hyperbolic system method for advection-diffusion problems is introduced. Diffusive/viscous terms are written and discretized as a hyperbolic system, which recovers the original equation in the steady state. The resulting scheme offers advantages over traditional schemes: a dramatic simplification in the discretization, high-order accuracy in the solution gradients, and orders-of-magnitude convergence acceleration. The hyperbolic advection-diffusion system is discretized by the second-order upwind residual-distribution scheme in a unified manner, and the system of implicit-residual-equations is solved by Newton's method over every physical time step. The numerical results are presented for linear and nonlinear advection-diffusion problems, demonstrating solutions and gradients produced to the same order of accuracy, with rapid convergence over each physical time step, typically less than five Newton iterations.
Advective transport observations with MODPATH-OBS--documentation of the MODPATH observation process
Hanson, R.T.; Kauffman, L.K.; Hill, M.C.; Dickinson, J.E.; Mehl, S.W.
2013-01-01
The MODPATH-OBS computer program described in this report is designed to calculate simulated equivalents for observations related to advective groundwater transport that can be represented in a quantitative way by using simulated particle-tracking data. The simulated equivalents supported by MODPATH-OBS are (1) distance from a source location at a defined time, or proximity to an observed location; (2) time of travel from an initial location to defined locations, areas, or volumes of the simulated system; (3) concentrations used to simulate groundwater age; and (4) percentages of water derived from contributing source areas. Although particle tracking only simulates the advective component of conservative transport, effects of non-conservative processes such as retardation can be approximated through manipulation of the effective-porosity value used to calculate velocity based on the properties of selected conservative tracers. This program can also account for simple decay or production, but it cannot account for diffusion. Dispersion can be represented through direct simulation of subsurface heterogeneity and the use of many particles. MODPATH-OBS acts as a postprocessor to MODPATH, so that the sequence of model runs generally required is MODFLOW, MODPATH, and MODPATH-OBS. The version of MODFLOW and MODPATH that support the version of MODPATH-OBS presented in this report are MODFLOW-2005 or MODFLOW-LGR, and MODPATH-LGR. MODFLOW-LGR is derived from MODFLOW-2005, MODPATH 5, and MODPATH 6 and supports local grid refinement. MODPATH-LGR is derived from MODPATH 5. It supports the forward and backward tracking of particles through locally refined grids and provides the output needed for MODPATH_OBS. For a single grid and no observations, MODPATH-LGR results are equivalent to MODPATH 5. MODPATH-LGR and MODPATH-OBS simulations can use nearly all of the capabilities of MODFLOW-2005 and MODFLOW-LGR; for example, simulations may be steady-state, transient, or a combination
Methods and Algorithms for Solving Inverse Problems for Fractional Advection-Dispersion Equations
Aldoghaither, Abeer
2015-11-12
Fractional calculus has been introduced as an e cient tool for modeling physical phenomena, thanks to its memory and hereditary properties. For example, fractional models have been successfully used to describe anomalous di↵usion processes such as contaminant transport in soil, oil flow in porous media, and groundwater flow. These models capture important features of particle transport such as particles with velocity variations and long-rest periods. Mathematical modeling of physical phenomena requires the identification of pa- rameters and variables from available measurements. This is referred to as an inverse problem. In this work, we are interested in studying theoretically and numerically inverse problems for space Fractional Advection-Dispersion Equation (FADE), which is used to model solute transport in porous media. Identifying parameters for such an equa- tion is important to understand how chemical or biological contaminants are trans- ported throughout surface aquifer systems. For instance, an estimate of the di↵eren- tiation order in groundwater contaminant transport model can provide information about soil properties, such as the heterogeneity of the medium. Our main contribution is to propose a novel e cient algorithm based on modulat-ing functions to estimate the coe cients and the di↵erentiation order for space FADE, which can be extended to general fractional Partial Di↵erential Equation (PDE). We also show how the method can be applied to the source inverse problem. This work is divided into two parts: In part I, the proposed method is described and studied through an extensive numerical analysis. The local convergence of the proposed two-stage algorithm is proven for 1D space FADE. The properties of this method are studied along with its limitations. Then, the algorithm is generalized to the 2D FADE. In part II, we analyze direct and inverse source problems for a space FADE. The problem consists of recovering the source term using final
Evaporative loss from irrigated interrows in a highly advective semi-arid agricultural area
Agam, Nurit; Evett, Steven R.; Tolk, Judy A.; Kustas, William P.; Colaizzi, Paul D.; Alfieri, Joseph G.; McKee, Lynn G.; Copeland, Karen S.; Howell, Terry A.; Chávez, Jose L.
2012-12-01
Agricultural productivity has increased in the Texas High Plains at the cost of declining water tables, putting at risk the sustainability of the Ogallala Aquifer as a principal source of water for irrigated agriculture. This has led area producers to seek alternative practices that can increase water use efficiency (WUE) through more careful management of water. One potential way of improving WUE is by reducing soil evaporation (E), thus reducing overall evapotranspiration (ET). Before searching for ways to reduce E, it is first important to quantify E and understand the factors that determine its magnitude. The objectives of this study were (1) to quantify E throughout part of the growing season for irrigated cotton in a strongly advective semi-arid region; (2) to study the effects of LAI, days after irrigation, and measurement location within the row on the E/ET fraction; and (3) to study the ability of microlysimeter (ML) measures of E combined with sap flow gage measures of transpiration (T) to accurately estimate ET when compared with weighing lysimeter ET data and to assess the E/T ratio. The research was conducted in an irrigated cotton field at the Conservation & Production Research Laboratory of the USDA-ARS, Bushland, TX. ET was measured by a large weighing lysimeter, and E was measured by 10 microlysimeters that were deployed in two sets of 5 across the interrow. In addition, 10 heat balance sap flow gages were used to determine T. A moderately good agreement was found between the sum E + T and ET (SE = 1 mm or ˜10% of ET). It was found that E may account for >50% of ET during early stages of the growing season (LAI < 0.2), significantly decreasing with increase in LAI to values near 20% at peak LAI of three. Measurement location within the north-south interrows had a distinct effect on the diurnal pattern of E, with a shift in time of peak E from west to east, a pattern that was governed by the solar radiation reaching the soil surface. However, total
To assess the effectiveness of mitigative measures against radon (222Rn) entry into houses, experiments were conducted in a crawl-space house where the dirt floor of the crawl space was covered with sheets of 0.23 mm polyethylene foil fixed to the walls. The radon concentration was measured below the foil and in the crawl space together with environmental variables such as indoor-outdoor pressure differences. The experimental data was analyzed using various types of models including a simplistic mass-balance model, a regression model, and a two-dimensional numerical model based on Darcy flow or soil gas and combined diffusive and advective transport of radon. The main outcome of the work was that: (i) The soil-gas entry rate per pascal depressurization was at the order of 1 m3 h-1, (ii) the stack-related part of the depressurization of the crawl space (approx. 0.1 Pa deg. C-1) was controlled by the temperature difference between the living room of the house and the outdoors (not by the difference between the crawl space and the outdoors), (iii) that part of the wind-related depressurization that was measured by the pressure transducers seemed to force radon into the crawl space in the same proportion as the stack-related part of the depressurization, (iv) the ratio of advective and diffusive entry was approx. 0.7, when the crawl space was depressurized 1.5 Pa, (v) the effective diffusivity of the foil was found to be three orders of magnitude larger than that measured in the laboratory (the enhanced diffusivity was most likely caused by leaks in the foil and by mixing fans located in the crawl space), and (vi) there was no measurable mitigative impact of having the sheets of foil on the crawl-space floor even if the crawl space was artificially pressurized or depressurized. (au) 28 tabs., 36 ills., 61 refs
Advection-diffusion model for the stagnation of normal grain growth in thin films
Lou, C.; Player, M.A. [Department of Engineering, University of Aberdeen, Aberdeen (United Kingdom)
2002-07-21
This paper presents an advection-diffusion model to describe the stagnation of normal grain growth in thin films. The underlying advection-diffusion model describes grain growth in a two-dimensional topological-class/size space. Grain boundary grooving and the correlation between neighbouring grains are introduced into the model to represent stagnation. Grain boundary grooving causes the stagnation of grain growth, and the correlation between neighbouring grains accelerates the effects of stagnation. Numerical solution of continuity equations gives a grain size distribution that is close to log-normal, and fits experiments well. The time development of average grain size also shows the stagnation of grain growth. (author)
Towards reduction of Paradigm coordination models
Suzana Andova
2011-08-01
Full Text Available The coordination modelling language Paradigm addresses collaboration between components in terms of dynamic constraints. Within a Paradigm model, component dynamics are consistently specified at a detailed and a global level of abstraction. To enable automated verification of Paradigm models, a translation of Paradigm into process algebra has been defined in previous work. In this paper we investigate, guided by a client-server example, reduction of Paradigm models based on a notion of global inertness. Representation of Paradigm models as process algebraic specifications helps to establish a property-preserving equivalence relation between the original and the reduced Paradigm model. Experiments indicate that in this way larger Paradigm models can be analyzed.
Black hole evaporation: a paradigm
A paradigm describing black hole evaporation in non-perturbative quantum gravity is developed by combining two sets of detailed results: (i) resolution of the Schwarzschild singularity using quantum geometry methods and (ii) time evolution of black holes in the trapping and dynamical horizon frameworks. Quantum geometry effects introduce a major modification in the traditional spacetime diagram of black hole evaporation, providing a possible mechanism for recovery of information that is classically lost in the process of black hole formation. The paradigm is developed directly in the Lorentzian regime and necessary conditions for its viability are discussed. If these conditions are met, much of the tension between expectations based on spacetime geometry and structure of quantum theory would be resolved
Towards reduction of Paradigm coordination models
Andova, S.; Groenewegen, L.P.J.; Vink, E.P. de; Aceto, L.; Mousavi, M.R.
2011-01-01
The coordination modelling language Paradigm addresses collaboration between components in terms of dynamic constraints. Within a Paradigm model, component dynamics are consistently specified at a detailed and a global level of abstraction. To enable automated verification of Paradigm models, a tran
Storytelling, advertising and paradigm fusion
Anderson, David
2012-01-01
'The art of storytelling in the modern age is fundamentally important. So, how we create stories for a screen-based culture is vitally important to master' (Hegarty, 2011, p.96-97). This paper explores the potential benefit of fusing aspects of creative writing with the curriculum of the BA Creative Advertising programme (BACAP) at Leeds College of Art (LCA) in order to address Sir John Hegarty's assertion. In particular it will focus on the characteristics of the 'classical paradigms' us...
Membrane Paradigm and Holographic Hydrodynamics
Eling, Christopher; Oz, Yaron
2010-01-01
We discuss recent work showing that in certain cases the membrane paradigm equations governing the dynamics of black hole horizons can be recast as relativistic conservation law equations. In the context of gauge/gravity dualities, these equations are interpreted as defining the viscous hydrodynamics of a holographically dual relativistic field theory. Using this approach, one can derive the viscous transport coefficients and the form of the entropy current for field theories dual to gravity plus matter fields.
Translation Definitions in Different Paradigms
Jixing LONG
2013-01-01
In the field of translation studies, owing to the factors such as the interests of scholar, cultural and historical reasons, scholars usually choose a definition of translation as the research orientation in a certain period of time. That is, as a scholastic community, they study under the same paradigm. Since the definition of translation not only describes and interprets the basic properties of translation, but also determines its connotation and extension, it is the core and basic part of ...
Crises and paradigms in macroeconomics
Malcolm Sawyer
2010-01-01
Contrasts are drawn between mainstream macroeconomics (with the 'New Consensus in Macroeconomics' taken as the current manifestation) and heterodox macroeconomics and their abilities to comprehend the financial crises and world wide recession of 2007 â€“ 09 for macroeconomic paradigms is discussed. Specifically, the contrasting ways in which the two schools of thought treat unemployment, human behaviour, aggregate and money and credit are discussed. It is concluded that the events of 2007 â€“...
Understanding the land management paradigm
Enemark, Stig
2006-01-01
There is a worldwide need to build understanding of the land management paradigm and for institutional development to establish sustainable national concepts. This includes creation and adoption of a policy on land development, and an approach that combines the land administration/cadastre/land r....../cadastre/land registration function with topographic mapping. The author seeks to awaken more awareness of global trends in this area, recognising that the systems design involved is always unique....
Political Market. Paradigms and Realities
Vasile Macoviciuc
2012-06-01
Full Text Available The paper Political Market. Paradigms and Realities, by Simona Busoi, is an important contribution and a spadework within our specialized literature. Recently issued by Editura ASE (The Bucharest Academy of Economic Studies Publishing House, in the collection “Et in Arcadia ego”, it offers to the readers a synthesis of the literature destined to the study of political phenomena from an economic point of view, but also a lucid analysis of the Romanian political market.
Poverty eradication: a new paradigm.
Pethe, V P
1998-08-01
This article offers a new paradigm for eradicating poverty in India. It was assumed incorrectly by Mahatma Gandhi that a good society without mass poverty would follow after independence. India copied Western models of development and developed giant factories, big dams, and megacities. Agriculture did not expand the number of jobs for people. The Western paradigm failed in India because of the false assumption of "trickle down" of income to the masses. The targeted programs to the poor did not directly benefit enough of the poor. Mega-industrialization led to reduced employment and higher skill needs. The model failed mainly because it was a proxy and relied on indirect ways of reaching the poor. The models failed to be adapted to conditions in India. The Swadeshi paradigm is a direct model for addressing mass poverty. Poverty is affected by immediate, intermediate, and ultimate determinants. Poverty begets social and economic problems, such as ignorance, ill health, high fertility, unemployment, and crime. In India and developing countries, mass poverty results from under use of human resources; lack of equal opportunities; and an outdated non-egalitarian social structure, an unjust global economic order, human cruelty, and erosion of ethical values. Indians are squandering their precious resources mimicking Western consumerism. Poverty leads to rapid population growth. People become productive assets with universal literacy, compulsory and free education, health services and sanitation, vocational training, and work ethics. India needs people-oriented policies with less emphasis on capital accumulation. PMID:12294462
Orphism as a scientific paradigm
Biernat Przemyslaw
2012-01-01
Full Text Available In my essay I would like to examine current interpretative paradigm, which western scholarship cast on heterogenous and ambiguous data first to create and then to modify the notion of ‘orphism’. In case of paradigms preceding the actual one, the role which ‘orphism’ played in contemporary theories and controversies centered around the question of its significance for emergence of Christianity is well known. That is why in my work I would like to focus on deconstruction of interpretative consensus, elaborated in recent years, which is to be found in such works as Martin West’s The Orphic Poems (1983, Ritual Texts for the Afterlife. Orpheus and the Bacchic Gold Tablets by Fritz Graf and Sarah Iles-Johnston (2007 or monumental Orfeo y la tradición órfica. Un reencuentro (2008 edited by Alberto Bernabé. What is significant, inasmuch as we can write the history of Athenian religion or the history of Hellenistic kings’ worship, we still cannot write the history of orphism. In formulation of all these scholars it is an ahistorical phenomenon, a hidden constant in the sphere of Greek religion, never expressed directly and entirely, but always alluded to y ancient authors. I find difficult to agree with such a statement. The aim of my inquiry is to reveal assumptions of current paradigm, which are hidden in it, but leave a distinct impression on data.
ADVECTION, EDGE, AND OASIS EFFECTS ON SPATIAL MOISTURE AND FLUX FIELDS FROM LIDAR
Relatively narrow forest stands such as the riparian Tamarisk bordering the Rio Grande are subject to dry air advection from the adjacent semi-desert environment. The transport of warm dry air into the canopy has a profound effect upon the spatial properties of the moisture field and associated lat...
General Solution of a Fractional Diffusion-Advection Equation for Solar Cosmic-Ray Transport
Rocca, M C; Plastino, A; De Paoli, A L
2016-01-01
In this effort we exactly solve the fractional diffusion-advection equation for solar cosmic-ray transport proposed in \\cite{LE2014} and give its {\\it general solution} in terms of hypergeometric distributions. Also, we regain all the results and approximations given in \\cite{LE2014} as {\\it particular cases} of our general solution.
New Solution of a Fractional Diffusion-Advection Equation Using Ultradistributions
Rocca, M C; Plastino, A R; De Paoli, A L
2014-01-01
In this paper we exactly solve the fractional diffusion-advection equation. For this purpose we use the Theoy of Ultradistributions of J. Sebastiao e Silva, to give a general solution for this equation. From this solution, we obtain several approximations as limiting cases of various situations of physical and astrophysical interest. One of them involves cosmic rays' diffusion.
Analytical solutions of the advection-dispersion equation and related models are indispensable for predicting or analyzing contaminant transport processes in streams and rivers, as well as in other surface water bodies. Many useful analytical solutions originated in disciplines other than surface-w...
A multicomponent solution is considered in advective diffusion chambers between two half-permeable barriers. A mathematical model is developed to calculate the concentration fields in the chamber. A new enrichment process is proposed and assessed using a digital simulation of space-time dynamics, based on the analytical solution of the model
Digital simulation of an enrichment process for solutions by means of an advection-diffusion chamber
An ab-initio digital simulation of the space-time dynamics of the concentration field of a solute in an advection-diffusion chamber is done. Some questions related to the digital simulation of the concentration field using the analytical solution obtained in a previous paper are discussed
Isoline retrieval: An optimal sounding method for validation of advected contours
Mills, Peter
2012-01-01
The study of chaotic mixing is important for its potential to improve our understanding of fluid systems. Contour advection simulations provide a good model of the phenomenon by tracking the evolution of one or more contours or isolines of a trace substance to a high level of precision. The most accurate method of validating an advected contour is to divide the tracer concentration into discrete ranges and perform a maximum likelihood classification, a method that we term, "isoline retrieval." Conditional probabilities generated as a result provide excellent error characterization. In this study, a water vapour isoline of 0.001 mass-mixing-ratio is advected over five days in the upper troposphere and compared with high-resolution AMSU (Advanced Microwave Sounding Unit) satellite retrievals. The goal is to find the same fine-scale, chaotic mixing in the isoline retrievals as seen in the advection simulations. Some of the filaments generated by the simulations show up in the conditional probabilities as areas o...
Rogers, M. A.
2015-12-01
Using satellite observations from GOES-E and GOES-W platforms in concert with GFS-derived cloud-level winds and a standalone radiative transfer model, an advection-derived forecast for surface GHI over the continental United States, with intercomparison between forecasts for four zones over the CONUS and Central Pacific with SURFRAD results. Primary sources for error in advection-based forecasts, primarily driven by false- or mistimed ramp events are discussed, with identification of error sources quantified along with techniques used to improve advection-based forecasts to approximately 10% MAE for designated surface locations. Development of a blended steering wind product utilizing NWP output combined with satellite-derived winds from AMV techniques to improve 0-1 hour advection forecasts will be discussed. Additionally, the use of two years' of solar forecast observations in the development of a prototype probablistic forecast for ramp events will be shown, with the intent of increasing the use of satellite-derived forecasts for grid operators and optimizing integration of renewable resources into the power grid. Elements of the work were developed under the 'Public-Private-Academic Partnership to Advance Solar Power Forecasting' project spearheaded by the National Center for Atmospheric Research.
Shell model for time-correlated random advection of passive scalars
Andersen, Ken Haste; Muratore-Ginanneschi, P.
1999-01-01
We study a minimal shell model for the advection of a passive scalar by a Gaussian time-correlated velocity field. The anomalous scaling properties of the white noise limit are studied analytically. The effect of the time correlations are investigated using perturbation theory around the white...
Hoedjes, J.C.B.; Zuurbier, R.M.; Watts, J.C.
2002-01-01
Scintillometer measurements were collected over an irrigated wheat field in a semi-arid region in northwest Mexico. Conditions were unstable in the morning and stable during the afternoon, while latent heat fluxes remained high throughout the day. Regional advection was observed during near-neutral
Boundary value problem for one-dimensional fractional differential advection-dispersion equation
Khasambiev Mokhammad Vakhaevich
2014-07-01
Full Text Available An equation commonly used to describe solute transport in aquifers has attracted more attention in recent years. After a formal study of some aspects of the advection-diffusion equation, basically from the mathematical point of view with the solution of a differential equation with fractional derivative, the main interest to this problem shifted onto physical aspects of the dynamical system, such as the total energy and the dynamical response. In this regard it should be pointed out that the interaction with environment is expressed in terms of stochastic arrow of time. This allows one also to reach a progress in one more issue. Formerly the equation of advection-diffusion was not obtained from any physical principles. However, mainly the success concerns linear fractional systems. In fact, there are many cases in which linear treatments are not sufficient. The more general systems described by nonlinear fractional differential equations have not been studied enough. The ordinary calculus brings out clearly that essentially new phenomena occur in nonlinear systems, which generally cannot occur in linear systems. Due to vast range of application of the fractional advection-dispersion equation, a lot of work has been done to find numerical solution and fundamental solution of this equation. The research on the analytical solution of initial-boundary problem for space-fractional advection-dispersion equation is relatively new and is still at an early stage of development. In this paper, we will take use of the method of variable separation to solve space-fractional advection-dispersion equation with initial boundary data.
Continuous time series of dissolved oxygen (DO) have been used to compute estimates of metabolism in aquatic ecosystems. Central to this open water or "Odum" method is the assumption that the DO time is not strongly affected by advection and that effects due to advection or mixin...
Analytical solutions of the advection-dispersion solute transport equation remain useful for a large number of applications in science and engineering. In this paper we extend the Duhamel theorem, originally established for diffusion type problems, to the case of advective-dispersive transport subj...
Seo, Bong-Chul; Krajewski, Witold F.
2015-12-01
This study offers a method to correct for the radar temporal sampling error when determining radar-rainfall accumulations. The authors evaluate the correction effect with respect to multiple factors associated with storm advection, rainfall characteristics, and different rainfall accumulation time scales. The advection method presented in this study uses linear interpolation of static rain storm locations observed at two intermittent radar sampling times to correct for the missed rainfall accumulations. The advection correction is applied to the high space (0.5 km) and time (5-min) resolution radar-rainfall products provided by the Iowa Flood Center. We use the ground reference data from a high quality and high density rain gauge network distributed over the Turkey River basin in Iowa to evaluate the advection corrected rain fields. We base our evaluation on six rain events and examine the correction performance/improvement with respect to the advection discretization, spatial grid aggregation, rainfall basin coverage, and conditional average rainfall intensity. The results show that the 1-min advection discretization is sufficient to represent the observed distribution of storm velocities for the presented cases. Grid aggregation that is motivated by the need to expedite the computation may induce errors in estimating advection vectors. The authors found that while the advection correction tends to enhance the QPE accuracy for intense rain storms over small or isolated areas, it has little impact on the improvement of light rain estimation.
Scalar transport in compressible flow
Vergassola, M.; Avellaneda, M.
1996-01-01
Transport of scalar fields in compressible flow is investigated. The effective equations governing the transport at scales large compared to those of the advecting flow are derived by using multi-scale techniques. Ballistic transport generally takes place when both the solenoidal and the potential components of the velocity do not vanish, despite of the fact that it has zero average value. The calculation of the effective ballistic velocity $V_b$ is reduced to the solution of one auxiliary eq...