Diffusion of Li in olivine. Part I: Experimental observations and a multi species diffusion model
NASA Astrophysics Data System (ADS)
Dohmen, Ralf; Kasemann, Simone A.; Coogan, Laurence; Chakraborty, Sumit
2010-01-01
There are an increasing number of studies that focus on the systematics of the distribution of Li and its isotopes among different geochemical reservoirs. These studies have found that Li is relatively mobile compared to many other elements (e.g., Fe, Mg), and diffusion has been considered as a mechanism to generate large isotopic fractionations even at high temperatures. In order to quantify some of these aspects, we have measured Li diffusion rates experimentally along [0 0 1] of single crystals of olivines from San Carlos, Arizona and Pakistan, at 800-1200 °C at a total pressure of 100 kPa and fO 2 ≈ WM buffer. A complex diffusion behavior of Li is observed, indicating that two mechanisms of diffusion (a fast and a slower one) operate simultaneously. The behavior is well described by a model that partitions Li between two different sites in olivine - an octahedral site (Li Me) and an interstitial site (Li i). Transport of Li is a combination of hopping within and between each of these kinds of sites involving also vacancies on the octahedral site (V Me). It is assumed that the homogeneous reaction (Li Me = V Me + Li i) that maintains equilibrium distribution of Li between the sites is instantaneous compared to the timescales of all other processes associated with diffusive transport. One consequence of this mode of transport of Li in olivine is that the shape and length of diffusion profiles depend on the boundary conditions imposed at the surface of a crystal; i.e., the chemical environment (e.g., fO 2, aLi 4SiO 4), in addition to temperature and pressure. Our model describes the variable experimentally determined Li-profile shapes produced at different temperatures and with different boundary conditions, as well as their time evolution, quantitatively. Modeling the observed isotopic fractionation shows that 6Li diffuses about 5% faster than 7Li on the interstitial site. Inspection of published data on Li distribution in natural olivines that are available
Amato, Francesco; Cosentino, Carlo; Pricl, Sabrina; Ferrone, Marco; Fermeglia, Maurizio; Cheng, Mark Ming-Cheng; Walczak, Robert; Ferrari, Mauro
2006-12-01
Transport and surface interactions of proteins in nanopore membranes play a key role in many processes of biomedical importance. Although the use of porous materials provides a large surface-to-volume ratio, the efficiency of the operations is often determined by transport behavior, and this is complicated by the fact that transport paths (i.e., the pores) are frequently of molecular dimensions. Under these conditions, a protein diffusion can be slower than predicted from Fick law. The main contribution of this paper is the development of a mathematical model of this phenomenon, whose parameters are computed via molecular modeling, as described Part 1. Our multiscale modeling methodology, validated by using experimental results related to the diffusion of lysozyme molecules, constitutes an "ab initio" recipe, for which no experimental data are needed to predict the protein release, and can be tailored in principle to match any different protein and any different surface, thus filling gap between the nano and the macroscale. PMID:17003963
NASA Astrophysics Data System (ADS)
Al-Shakran, Mohammad; Kibler, Ludwig A.; Jacob, Timo; Ibach, Harald; Beltramo, Guillermo L.; Giesen, Margret
2016-09-01
This is Part I of two closely related papers, where we show that the specific adsorption of anions leads to a failure of the nearest-neighbor Ising model to describe island perimeter curvatures on Au(100) electrodes in dilute KBr, HCl and H2SO4 electrolytes and the therewith derived step diffusivity vs. step orientation. This result has major consequences for theoretical studies aiming at the understanding of growth, diffusion and degradation phenomena. Part I focuses on the experimental data. As shown theoretically in detail in Part II (doi:10.1016/j.susc.2016.03.022), a set of nearest-neighbor and next-nearest-neighbor interaction energies (ɛNN, ɛNNN) can uniquely be derived from the diffusivity of steps along <100> and <110>. We find strong repulsive next-nearest neighbor (NNN) interaction in KBr and HCl, whereas NNN interaction is negligibly for H2SO4. The NNN repulsive interaction energy ɛNNN therefore correlates positively with the Gibbs adsorption energy of the anions. We find furthermore that ɛNNN increases with increasing Br- and Cl- coverage. The results for ɛNN and ɛNNN are quantitatively consistent with the coverage dependence of the step line tension. We thereby establish a sound experimental base for theoretical studies on the energetics of steps in the presence of specific adsorption.
UPDATING APPLIED DIFFUSION MODELS
Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Socie...
Wilkinson, P; Dimbylow, P J
1985-10-01
A mathematical model has been developed that examines the ingress of radon into houses, through a vertical crack in an otherwise impervious concrete floor. Initially, the model considered the diffusive flow of radon from its soil source and this simulation has highlighted the dependency of the flux of radon into the house on the magnitude of various parameters, such as the diffusion coefficient of radon in soil. A preliminary investigation of the modelling of pressure-driven flow into a building is presented, and the potential of this type of analysis is discussed. PMID:4081719
Pivovarov, Sergey
2009-04-01
This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson-Boltzmann equation, the Gaines-Thomas selectivity coefficient for uni-bivalent exchange on clay, K(GT)(Me(2+)/M(+))=(Q(Me)(0.5)/Q(M)){M(+)}/{Me(2+)}(0.5), (Q is the equivalent fraction of cation in the exchange capacity, and {M(+)} and {Me(2+)} are the ionic activities in solution) may be calculated as [surface charge, mueq/m(2)]/0.61. The obtained solution of the Poisson-Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01-6 M NaCl solutions. In addition, a new model of acid-base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson-Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model. PMID:19159896
Diffuse Cystic Lung Disease. Part II.
Gupta, Nishant; Vassallo, Robert; Wikenheiser-Brokamp, Kathryn A; McCormack, Francis X
2015-07-01
The diffuse cystic lung diseases have a broad differential diagnosis. A wide variety of pathophysiological processes spanning the spectrum from airway obstruction to lung remodeling can lead to multifocal cyst development in the lung. Although lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis are perhaps more frequently seen in the clinic, disorders such as Birt-Hogg-Dubé syndrome, lymphocytic interstitial pneumonia, follicular bronchiolitis, and light-chain deposition disease are increasingly being recognized. Obtaining an accurate diagnosis can be challenging, and management approaches are highly disease dependent. Unique imaging features, genetic tests, serum studies, and clinical features provide invaluable clues that help clinicians distinguish among the various etiologies, but biopsy is often required for definitive diagnosis. In part II of this review, we present an overview of the diffuse cystic lung diseases caused by lymphoproliferative disorders, genetic mutations, or aberrant lung development and provide an approach to aid in their diagnosis and management. PMID:25906201
A two-dimensional, finite-difference model simulating a highway has been developed which is able to handle linear and nonlinear chemical reactions. Transport of the pollutants is accomplished by use of an upstream-flux-corrected algorithm developed at the Naval Research Laborator...
NASA Astrophysics Data System (ADS)
Han, Xuebing; Ouyang, Minggao; Lu, Languang; Li, Jianqiu
2015-03-01
Now the lithium ion batteries are widely used in electrical vehicles (EV). The battery modeling and state estimation is of great significance. The rigorous physic based electrochemical model is too complicated for on-line simulation in vehicle. In this work, the simplification of physics-based model lithium ion battery for application in battery management system (BMS) on real electrical vehicle is proposed. Approximate method for solving the solid phase diffusion and electrolyte concentration distribution problems is introduced. The approximate result is very close to the rigorous model but fewer computations are needed. An extended single particle model is founded based on these approximated results and the on-line state of charge (SOC) estimation algorithm using the extended Kalman filter with this single particle model is discussed. This SOC estimation algorithm could be used in the BMS in real vehicle.
Diffuse Cystic Lung Disease. Part I.
Gupta, Nishant; Vassallo, Robert; Wikenheiser-Brokamp, Kathryn A; McCormack, Francis X
2015-06-15
The diffuse cystic lung diseases (DCLDs) are a group of pathophysiologically heterogenous processes that are characterized by the presence of multiple spherical or irregularly shaped, thin-walled, air-filled spaces within the pulmonary parenchyma. Although the mechanisms of cyst formation remain incompletely defined for all DCLDs, in most cases lung remodeling associated with inflammatory or infiltrative processes results in displacement, destruction, or replacement of alveolar septa, distal airways, and small vessels within the secondary lobules of the lung. The DCLDs can be broadly classified according to underlying etiology as those caused by low-grade or high-grade metastasizing neoplasms, polyclonal or monoclonal lymphoproliferative disorders, infections, interstitial lung diseases, smoking, and congenital or developmental defects. In the first of a two-part series, we present an overview of the cystic lung diseases caused by neoplasms, infections, smoking-related diseases, and interstitial lung diseases, with a focus on lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis. PMID:25906089
Multispecies diffusion models: A study of uranyl species diffusion
NASA Astrophysics Data System (ADS)
Liu, Chongxuan; Shang, Jianying; Zachara, John M.
2011-12-01
Rigorous numerical description of multispecies diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication in imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multispecies diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multispecies diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multispecies U(VI) diffusion under a steady state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that for multispecies U(VI) diffusion under transient chemical conditions, a fully coupled diffusion model could be well approximated by a component-based diffusion model when the diffusion coefficient for each chemical component was properly selected. The component-based diffusion model considers the difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be enforced, if necessary, by adding a secondary migration term resulting from model simplification. The effect of ion activity coefficient gradients on multispecies diffusion is also discussed. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from U.S. Department of Energy's Hanford 300A
DiffuseModel: Modeling the diffuse ultraviolet background
NASA Astrophysics Data System (ADS)
Murthy, Jayant
2015-12-01
DiffuseModel calculates the scattered radiation from dust scattering in the Milky Way based on stars from the Hipparcos catalog. It uses Monte Carlo to implement multiple scattering and assumes a user-supplied grid for the dust distribution. The output is a FITS file with the diffuse light over the Galaxy. It is intended for use in the UV (900 - 3000 A) but may be modified for use in other wavelengths and galaxies.
Yang, L.H.; Ding, Y.M.
2009-07-01
The aim of this article is to discuss the distribution law of the gasification agent concentration in a deep-going way during underground coal gasification and the new method of solving the problem for the convection diffusion of the gas. In this paper, the basic features of convection diffusion for the gas produced in underground coal gasification are studied. On the basis of the model experiment, through the analysis of the distribution and patterns of variation for the fluid concentration field in the process of the combustion and gasification of the coal seams within the gasifier, the 3-D non-linear unstable mathematical models on the convection diffusion for oxygen are established. In order to curb such pseudo-physical effects as numerical oscillation and surfeit which frequently occurred in the solution of the complex mathematical models, the novel finite unit algorithm, the upstream weighted multi-cell balance method is advanced in this article, and its main derivation process is introduced.
In Vivo Facilitated Diffusion Model
Bauer, Maximilian; Metzler, Ralf
2013-01-01
Under dilute in vitro conditions transcription factors rapidly locate their target sequence on DNA by using the facilitated diffusion mechanism. However, whether this strategy of alternating between three-dimensional bulk diffusion and one-dimensional sliding along the DNA contour is still beneficial in the crowded interior of cells is highly disputed. Here we use a simple model for the bacterial genome inside the cell and present a semi-analytical model for the in vivo target search of transcription factors within the facilitated diffusion framework. Without having to resort to extensive simulations we determine the mean search time of a lac repressor in a living E. coli cell by including parameters deduced from experimental measurements. The results agree very well with experimental findings, and thus the facilitated diffusion picture emerges as a quantitative approach to gene regulation in living bacteria cells. Furthermore we see that the search time is not very sensitive to the parameters characterizing the DNA configuration and that the cell seems to operate very close to optimal conditions for target localization. Local searches as implied by the colocalization mechanism are only found to mildly accelerate the mean search time within our model. PMID:23349772
NASA Astrophysics Data System (ADS)
Ryazhskikh, A. V.; Boger, A. A.; Slyusarev, M. I.; Ryazhskikh, V. I.
2016-01-01
The authors have developed a convective-diffusion model of sedimentation of solid Stokesian particles from a dispersed phase moving in an ideal-mixing regime in a plane channel as the initial boundary-value problem for the particle size function, whose solution was obtained in analytical form. The mixing coefficient has been found from the hydrodynamic analogy with turbulent viscosity, and the kinetic coefficients of settling on "wetted" surfaces have been determined on condition that the particles near the walls lose the convective velocity component but preserve the Brownian and Stokesian components. The obtained calculation results are consistent with the universally accepted ideas of separation of the solid phase of suspensions from flows on the settling surface.
Finite-dimensional models of diffusion chaos
NASA Astrophysics Data System (ADS)
Glyzin, S. D.; Kolesov, A. Yu.; Rozov, N. Kh.
2010-05-01
Some parabolic systems of the reaction-diffusion type exhibit the phenomenon of diffusion chaos. Specifically, when the diffusivities decrease proportionally, while the other parameters of a system remain fixed, the system exhibits a chaotic attractor whose dimension increases indefinitely. Various finite-dimensional models of diffusion chaos are considered that represent chains of coupled ordinary differential equations and similar chains of discrete mappings. A numerical analysis suggests that these chains with suitably chosen parameters exhibit chaotic attractors of arbitrarily high dimensions.
Estimating the UV diffuse fraction of solar radiation under partly cloudy skies
NASA Astrophysics Data System (ADS)
Grant, Richard H.; Gao, Wei
2002-01-01
A major limitation in predicting the ultraviolet-B (UVB) irradiance on humans, plant leaves and flowers and aquatic organisms is the difficulty in determining the UVB under partly cloudy sky conditions. This study analyzes the UV diffuse fractions under partly cloudy and clear conditions for nine locations in the USA over a period of 1997 through 1999. Radiation measurements, made as part of the United States Department of Agriculture UVB Monitoring Program using multi-filter rotating shadow band radiometers, were paired with cloud cover and other atmospheric measurements made with National Weather Service Automated Surface Observation Systems within 30 km of the radiation measurement location to evaluate the accuracy of using a relatively simple model to describe the diffuse fraction of UV radiation under partly-cloudy skies. The diffuse fraction was modeled as the summation of clear and overcast sky diffuse fractions, weighted by the probability of the sun's direct beam being obstructed or not for a given cloud cover fraction. For the nine locations evaluated, the model had a mean bias error (MBE) of 0.0037 and a root mean squared error (RMSE) of 0.0361. Simplifying the model by assuming a diffuse fraction of 1 for the overcast sky resulted in a slightly higher error (MBE error of -0.0045 and an RMSE of 0.0387). Model errors were greatest for low solar zenith angles and high cloud fractions. The greatest error, associated with overcast sky conditions, appeared to be a result of scattering off the clouds during the period of time where the sun's beam was unobstructed. Error analysis also showed that the diffuse fraction of partly cloudy skies when the sun's beam was not obstructed is well approximated by the clear sky condition to within approximately 0.1, supporting the use of aerosol optical thickness estimates by Langley plot under partly cloudy skies.
This research program was initiated with the overall objective of gaining understanding of the flow and diffusion of pollutants in complex terrain under both neutral and stably stratified conditions. This report covers the first phase of the project; it describes the flow structu...
Deniz, S.; Greitzer, E.M.; Cumpsty, N.A.
2000-01-01
This is Part 2 of an examination of the influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of a straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity on diffuser pressure recovery and operating range are addressed. The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The ranges of the overall pressure recovery coefficients were 0.50--0.78 for the straight-channel diffuser and 0.50--0.70 for the discrete-passage diffuser, except when the diffuser was choked. In other words, the maximum pressure recovery of the straight-channel diffuser was found to be roughly 10% higher than that of the discrete-passage diffuser investigated. The two types of diffuser showed similar behavior regarding the dependence of pressure recovery on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers, was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, {alpha}{sub crit} = 70 {+-} 0.5 deg. The background, nomenclature, and description of the facility and method are all given in Part 1.
Stress diffusion in models for shear banding
NASA Astrophysics Data System (ADS)
Masnada, Elian; Olmsted, Peter
Understanding shear banding is of utmost importance from both theoretical and experimental point of view and consequently it has been studied for several decades. Despite this study numerous aspects of shear banding remains poorly understood. Because of the intrinsic inhomogeneity in the shear banded state, applicable constitutive models must be include spatial inhomogeneities, leading to a so-called 'diffusive' term in the equation of motion for the slow variables that carry stress. Such terms are also vital in describing the interaction of bulk shear banding flows with walls and incorporation of wall slip. In this work, we consider different sources of 'diffusion' in polymer models in which concentration degrees of freedom are negligible. The simplest models used are consistent with diffusive terms whose origin is intrinsically dissipative, such as due to hydrodynamic interactions. By contrast, models in which elastic effects such as finite chain stiffness contribute to stress diffusion are inconsistent with simple diffusive models, and we propose alternative consistent models
Filipenco, V.G.; Deniz, S.; Johnston, J.M.; Greitzer, E.M.; Cumpsty, N.A.
2000-01-01
This is Part 1 of a two-part paper considering the performance of radial diffusers for use in a high-performance centrifugal compressor. Part 1 reports on discrete-passage diffusers, while Part 2 describes a test of a straight-channel diffuser designed for equivalent duty. Two builds of discrete-passage diffuser were tested, with 30 and 38 separate passages. Both the 30 and 38 passage diffusers investigated showed comparable range of unstalled operation and similar level of overall diffuser pressure recovery. The paper concentrates on the influence of inlet flow conditions on the pressure recovery and operating range of radial diffusers for centrifugal compressor stages. The flow conditions examined include diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. The facility can provide a wide range of diffuser inlet velocity profile distortion and skew with Mach numbers up to unity and flow angles of 63 to 75 deg from the radical direction. The consequences of different averaging methods for the inlet total pressure distributions, which are needed in the definition of diffuser pressure recovery coefficient for nonuniform diffuser inlet conditions, were also assessed. The overall diffuser pressure recovery coefficient, based on suitably averaged inlet total pressure, was found to correlate well with the momentum-averaged flow angle into the diffuser. It is shown that the generally accepted sensitivity of diffuser pressure recovery performance to inlet flow distortion and boundary layer blockage can be largely attributed to inappropriate quantification of the average dynamic pressure at diffuser inlet. Use of an inlet dynamic pressure based on availability or mass-averaging in combination with definition of inlet flow angle based on mass average of the radial and tangential velocity at diffuser inlet
NASA Astrophysics Data System (ADS)
Correia, Teresa; Arridge, Simon
2016-02-01
Fluorescence diffuse optical tomography (fDOT) provides 3D images of fluorescence distributions in biological tissue, which represent molecular and cellular processes. The image reconstruction problem is highly ill-posed and requires regularisation techniques to stabilise and find meaningful solutions. Quadratic regularisation tends to either oversmooth or generate very noisy reconstructions, depending on the regularisation strength. Edge preserving methods, such as anisotropic diffusion regularisation (AD), can preserve important features in the fluorescence image and smooth out noise. However, AD has limited ability to distinguish an edge from noise. In this two-part paper, we propose a patch-based anisotropic diffusion regularisation (PAD), where regularisation strength is determined by a weighted average according to the similarity between patches around voxels within a search window, instead of a simple local neighbourhood strategy. However, this method has higher computational complexity and, hence, we wavelet compress the patches (PAD-WT) to speed it up, while simultaneously taking advantage of the denoising properties of wavelet thresholding. The proposed method combines the nonlocal means (NLM), AD and wavelet shrinkage methods, which are image processing methods. Therefore, in this first paper, we used a denoising test problem to analyse the performance of the new method. Our results show that the proposed PAD-WT method provides better results than the AD or NLM methods alone. The efficacy of the method for fDOT image reconstruction problem is evaluated in part 2.
Modeling of hydrogen diffusion in metals
Yang, K.; Cao, M.Z.; Wan, X.J.; Shi, C.X.
1989-02-01
The study of the diffusion of hydrogen in metals is very important to further understand the hydrogen embrittlement of metals. To describe the diffusion of hydrogen in metals the diffusion equation deduced from Fick's law under an ideal condition has been generally used and the effect of hydrogen trapping in metals has been neglected. In the process of hydrogen diffusion through a metal, hydrogen fills the traps continuously and the fraction of the traps filled by hydrogen, which have only little effect on the diffusion of hydrogen, may be different at different places because the distribution of hydrogen concentration may be different at different places. Thus the hydrogen diffusion coefficient in the metal may also be different at different positions, i.e., the diffusion coefficient should be affected by time in a dynamic process of hydrogen diffusion through a metal. But in the previous analyses, the above fact is not considered and the hydrogen diffusion coefficient is generally taken as a constant. In the present paper a new model of hydrogen diffusion in metals in which the effect of time is taken into account is developed.
Models, Part IV: Inquiry Models.
ERIC Educational Resources Information Center
Callison, Daniel
2002-01-01
Discusses models for information skills that include inquiry-oriented activities. Highlights include WebQuest, which uses Internet resources supplemented with videoconferencing; Minnesota's Inquiry Process based on the Big Six model for information problem-solving; Indiana's Student Inquiry Model; constructivist learning models for inquiry; and…
NASA Technical Reports Server (NTRS)
Opila, Elizabeth J.; Smialek, James L.; Robinson, Raymond C.; Fox, Dennis S.; Jacobson, Nathan S.
1998-01-01
In combustion environments, volatilization of SiO2 to Si-O-H(g) species is a critical issue. Available thermochemical data for Si-O-H(g) species were used to calculate boundary layer controlled fluxes from SiO2. Calculated fluxes were compared to volatilization rates Of SiO2 scales grown on SiC which were measured in Part 1 of this paper. Calculated volatilization rates were also compared to those measured in synthetic combustion gas furnace tests. Probable vapor species were identified in both fuel-lean and fuel-rich combustion environments based on the observed pressure, temperature and velocity dependencies as well as the magnitude of the volatility rate. Water vapor is responsible for the degradation of SiO2 in the fuel-lean environment. Silica volatility in fuel-lean combustion environments is attributed primarily to the formation of Si(OH)4(g) with a small contribution of SiO(OH)2(g).
Diffusion Decision Model: Current Issues and History.
Ratcliff, Roger; Smith, Philip L; Brown, Scott D; McKoon, Gail
2016-04-01
There is growing interest in diffusion models to represent the cognitive and neural processes of speeded decision making. Sequential-sampling models like the diffusion model have a long history in psychology. They view decision making as a process of noisy accumulation of evidence from a stimulus. The standard model assumes that evidence accumulates at a constant rate during the second or two it takes to make a decision. This process can be linked to the behaviors of populations of neurons and to theories of optimality. Diffusion models have been used successfully in a range of cognitive tasks and as psychometric tools in clinical research to examine individual differences. In this review, we relate the models to both earlier and more recent research in psychology. PMID:26952739
Modeling mammary gland morphogenesis as a reaction-diffusion process.
Grant, Mark R; Hunt, C Anthony; Xia, Lan; Fata, Jimmie E; Bissell, Mina J
2004-01-01
Mammary ducts are formed through a process of branching morphogenesis. We present results of experiments using a simulation model of this process, and discuss their implications for understanding mammary duct extension and bifurcation. The model is a cellular automaton approximation of a reaction-diffusion process in which matrix metalloproteinases represent the activator, inhibitors of matrix metalloproteinases represent the inhibitor, and growth factors serve as a substrate. We compare results from the simulation model with those from in-vivo experiments as part of an assessment of whether duct extension and bifurcation during morphogenesis may be a consequence of a reaction-diffusion mechanism mediated by MMPs and TIMPs. PMID:17271768
Stochastic models for surface diffusion of molecules
Shea, Patrick Kreuzer, Hans Jürgen
2014-07-28
We derive a stochastic model for the surface diffusion of molecules, starting from the classical equations of motion for an N-atom molecule on a surface. The equation of motion becomes a generalized Langevin equation for the center of mass of the molecule, with a non-Markovian friction kernel. In the Markov approximation, a standard Langevin equation is recovered, and the effect of the molecular vibrations on the diffusion is seen to lead to an increase in the friction for center of mass motion. This effective friction has a simple form that depends on the curvature of the lowest energy diffusion path in the 3N-dimensional coordinate space. We also find that so long as the intramolecular forces are sufficiently strong, memory effects are usually not significant and the Markov approximation can be employed, resulting in a simple one-dimensional model that can account for the effect of the dynamics of the molecular vibrations on the diffusive motion.
NASA Astrophysics Data System (ADS)
Correia, Teresa; Koch, Maximilian; Ale, Angelique; Ntziachristos, Vasilis; Arridge, Simon
2016-02-01
Fluorescence diffuse optical tomography (fDOT) provides 3D images of fluorescence distributions in biological tissue, which represent molecular and cellular processes. The image reconstruction problem is highly ill-posed and requires regularisation techniques to stabilise and find meaningful solutions. Quadratic regularisation tends to either oversmooth or generate very noisy reconstructions, depending on the regularisation strength. Edge preserving methods, such as anisotropic diffusion regularisation (AD), can preserve important features in the fluorescence image and smooth out noise. However, AD has limited ability to distinguish an edge from noise. We propose a patch-based anisotropic diffusion regularisation (PAD), where regularisation strength is determined by a weighted average according to the similarity between patches around voxels within a search window, instead of a simple local neighbourhood strategy. However, this method has higher computational complexity and, hence, we wavelet compress the patches (PAD-WT) to speed it up, while simultaneously taking advantage of the denoising properties of wavelet thresholding. Furthermore, structural information can be incorporated into the image reconstruction with PAD-WT to improve image quality and resolution. In this case, the weights used to average voxels in the image are calculated using the structural image, instead of the fluorescence image. The regularisation strength depends on both structural and fluorescence images, which guarantees that the method can preserve fluorescence information even when it is not structurally visible in the anatomical images. In part 1, we tested the method using a denoising problem. Here, we use simulated and in vivo mouse fDOT data to assess the algorithm performance. Our results show that the proposed PAD-WT method provides high quality and noise free images, superior to those obtained using AD.
Mathematical modeling of molecular diffusion through mucus
Cu, Yen; Saltzman, W. Mark
2008-01-01
The rate of molecular transport through the mucus gel can be an important determinant of efficacy for therapeutic agents delivered by oral, intranasal, intravaginal/rectal, and intraocular routes. Transport through mucus can be described by mathematical models based on principles of physical chemistry and known characteristics of the mucus gel, its constituents, and of the drug itself. In this paper, we review mathematical models of molecular diffusion in mucus, as well as the techniques commonly used to measure diffusion of solutes in the mucus gel, mucus gel mimics, and mucosal epithelia. PMID:19135488
Analytical boron diffusivity model in silicon for thermal diffusion from boron silicate glass film
NASA Astrophysics Data System (ADS)
Kurachi, Ikuo; Yoshioka, Kentaro
2015-09-01
An analytical boron diffusivity model in silicon for thermal diffusion from a boron silicate glass (BSG) film has been proposed in terms of enhanced diffusion due to boron-silicon interstitial pair formation. The silicon interstitial generation is considered to be a result of the silicon kick-out mechanism by the diffused boron at the surface. The additional silicon interstitial generation in the bulk silicon is considered to be the dissociation of the diffused pairs. The former one causes the surface boron concentration dependent diffusion. The latter one causes the local boron concentration dependent diffusion. The calculated boron profiles based on the diffusivity model are confirmed to agree with the actual diffusion profiles measured by secondary ion mass spectroscopy (SIMS) for a wide range of the BSG boron concentration. This analytical diffusivity model is a helpful tool for p+ boron diffusion process optimization of n-type solar cell manufacturing.
MODIS Solar Diffuser: Modelled and Actual Performance
NASA Technical Reports Server (NTRS)
Waluschka, Eugene; Xiong, Xiao-Xiong; Esposito, Joe; Wang, Xin-Dong; Krebs, Carolyn (Technical Monitor)
2001-01-01
The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument's solar diffuser is used in its radiometric calibration for the reflective solar bands (VIS, NTR, and SWIR) ranging from 0.41 to 2.1 micron. The sun illuminates the solar diffuser either directly or through a attenuation screen. The attenuation screen consists of a regular array of pin holes. The attenuated illumination pattern on the solar diffuser is not uniform, but consists of a multitude of pin-hole images of the sun. This non-uniform illumination produces small, but noticeable radiometric effects. A description of the computer model used to simulate the effects of the attenuation screen is given and the predictions of the model are compared with actual, on-orbit, calibration measurements.
Trivett, D.A.
1994-09-01
This paper focuses on modeling the fate of effluent from diffuse seafloor hydrothermal activity after it has been vented into the water column. The model was formulated using a number of simplifying assumptions which permit direct application of this model to field measurements. I have limited the configurations to those where the hydrothermal outflow velocities are smaller than horizontal current. I assume that the entrainment of ambient seawater into the plume is constant over the length of the plume. This permits formulation of a first-order relation for the rise height and dilution in a diffuse hydrothermal plume as a function of downstream distance. The analytic model is compared with a simple laboratory simulation of the hydrothermal flow. The results suggest that diffuse hydrothermal effluent will penetrate to a height in the water column that is proportional to the overall dimension of the diffuse vent patch, multiplied by a dimensionless plume intensity parameter. I also ahow relations for plume dilution which will be compared with field data in part 2 of this work.
Assessment of diffuse radiation models in Azores
NASA Astrophysics Data System (ADS)
Magarreiro, Clarisse; Brito, Miguel; Soares, Pedro; Azevedo, Eduardo
2014-05-01
Measured irradiance databases usually consist of global solar radiation data with limited spatial coverage. Hence, solar radiation models have been developed to estimate the diffuse fraction from the measured global irradiation. This information is critical for the assessment of the potential of solar energy technologies; for example, the decision to use photovoltaic systems with tracking system. The different solar radiation models for this purpose differ on the parameters used as input. The simplest, and most common, are models which use global radiation information only. More sophisticated models require meteorological parameters such as information from clouds, atmospheric turbidity, temperature or precipitable water content. Most of these models comprise correlations with the clearness index, kt (portion of horizontal extra-terrestrial radiation reaching the Earth's surface) to obtain the diffuse fraction kd (portion of diffuse component from global radiation). The applicability of these different models is related to the local atmospheric conditions and its climatic characteristics. The models are not of general validity and can only be applicable to locations where the albedo of the surrounding terrain and the atmospheric contamination by dust are not significantly different from those where the corresponding methods were developed. Thus, models of diffuse fraction exhibit a relevant degree of location dependence: e.g. models developed considering data acquired in Europe are mainly linked to Northern, Central or, more recently, Mediterranean areas. The Azores Archipelago, with its particular climate and cloud cover characteristics, different from mainland Europe, has not yet been considered for the development of testing of such models. The Azorean climate reveals large amounts of cloud cover in its annual cycle, with spatial and temporal variabilities more complex than the common Summer/Winter pattern. This study explores the applicability of different
Modelling Diffusion of a Personalized Learning Framework
ERIC Educational Resources Information Center
Karmeshu; Raman, Raghu; Nedungadi, Prema
2012-01-01
A new modelling approach for diffusion of personalized learning as an educational process innovation in social group comprising adopter-teachers is proposed. An empirical analysis regarding the perception of 261 adopter-teachers from 18 schools in India about a particular personalized learning framework has been made. Based on this analysis,…
Effects of microscopic diffusion and rotational mixing on stellar models
NASA Astrophysics Data System (ADS)
Chaboyer, Brian Charles
1993-01-01
We have calculated evolutionary tracks for halo stars and constructed isochrones with alpha-enhanced compositions which cover the entire globular cluster metallicity range and include the effects of the diffusion of He-4. We find that including the effects of helium diffusion has a negligible effect (less than 0.5 Gyr) on the derived ages of globular clusters. Regardless of the inclusion of helium diffusion, we find a significant age spread of 5 Gyr among the globular clusters. The oldest globular cluster studied was M92 with an age of 17 +/- 2 Gyr old. The stellar models may be tested by comparing the Li-7 depletion and surface rotation rates to observations in young clusters stars. The observed Li-7 abundances clearly indicate that standard or diffusive models do not deplete enough Li-7. Instabilities induced by rotation provide an additional mixing mechanism. For this reason the stellar evolution code was modified to include the combined effects of diffusion and rotational mixing of H-1, He-4 and the trace elements He-3, Li-7 and Be-9. The calibrated solar models have a convection zone depth of 0.709-0.714 solar radius, in excellent agreement with the observed depth of (0.713 +/- 0.003) solar radius. The rotational mixing inhibits the diffusion in the outer parts of the models, leading to a decrease in the envelope diffusion by 50-80 percent. These models are able to reproduce the Li-7 abundances and rotation velocities observed in young cluster stars. Observations of Li-7 abundances in extremely metal poor halo stars provide another test of the stellar models. Standard models do a good job of fitting the observed Li-7 abundances and predict a primordial Li-7 abundance of log N(Li) = 2.24 +/- 0.03. Models of hot stars which include microscopic diffusion, but not rotational mixing, deplete too much Li-7. The (Fe/H) = 2.28 stellar models which include both diffusion and rotational mixing provide an excellent match to the observations, and predict a primordial Li-7
Results from Modeling the Diffuse Ultraviolet Background
NASA Astrophysics Data System (ADS)
Murthy, Jayant
2016-07-01
I have used a Monte Carlo model for dust scattering in our Galaxy with multiple scattering to study the diffuse emission seen by the GALEX mission. I find that the emission at low and mid latitudes is fit well by scattering from dust grains with an albedo of 0.4. However, only about 30% of the diffuse radiation at high Galactic latitudes is due to dust scattering. There is an additional component of 500 - 600 ph cm^{-2} s^{-1} sr^{-1} Å^{-1} at all latitudes of an unknown origin.
Generalized Drift-Diffusion Model In Semiconductors
Mesbah, S.; Bendib-Kalache, K.; Bendib, A.
2008-09-23
A new drift-diffusion model is proposed based on the computation of the stationary nonlocal current density. The semi classical Boltzmann equation is solved keeping all the anisotropies of the distribution function with the use of the continued fractions. The conductivity is calculated in the linear approximation and for arbitrary collision frequency with respect to Kv{sub t} where K{sup -1} is the characteristic length scale of the system and V{sub t} is the thermal velocity. The nonlocal conductivity can be used to close the generalized drift-diffusion equations valid for arbitrary collisionality.
Anomalous Diffusion in a Trading Model
NASA Astrophysics Data System (ADS)
Khidzir, Sidiq Mohamad; Wan Abdullah, Wan Ahmad Tajuddin
2009-07-01
The result of the trading model by Chakrabarti et al. [1] is the wealth distribution with a mixed exponential and power law distribution. Based on the motivation of studying the dynamics behind the flow of money similar to work done by Brockmann [2, 3] we track the flow of money in this trading model to observe anomalous diffusion in the form of long waiting times and Levy Flights.
Measuring Psychometric Functions with the Diffusion Model
Ratcliff, Roger
2014-01-01
The diffusion decision model (Ratcliff, 1978) was used to examine discrimination for a range of perceptual tasks: numerosity discrimination, number discrimination, brightness discrimination, motion discrimination, speed discrimination, and length discrimination. The model produces a measure of the quality of the information that drives decision processes, a measure termed “drift rate” in the model. As drift rate varies across experimental conditions that differ in difficulty, a psychometric function that plots drift rate against difficulty can be constructed. Psychometric functions for the tasks in this article usually plot accuracy against difficulty, but for some levels of difficulty, accuracy can be at ceiling. The diffusion model extends the range of difficulty that can be evaluated because drift rates depend on response times (RTs) as well as accuracy and when RTs decrease across conditions that are all at ceiling in accuracy, then drift rates will distinguish among the conditions. Signal detection theory assumes that the variable driving performance is the z-transform of the accuracy value and somewhat surprisingly, this closely matches drift rate extracted from the diffusion model when accuracy is not at ceiling, but not sometimes when accuracy is high. Even though the functions are similar in the middle of the range, the interpretations of the variability in the models (e.g., perceptual variability, decision process variability) are incompatible. PMID:24446719
Modeling Demic and Cultural Diffusion: An Introduction.
Fort, Joaquim; Crema, Enrico R; Madella, Marco
2015-07-01
Identifying the processes by which human cultures spread across different populations is one of the most topical objectives shared among different fields of study. Seminal works have analyzed a variety of data and attempted to determine whether empirically observed patterns are the result of demic and/or cultural diffusion. This special issue collects articles exploring several themes (from modes of cultural transmission to drivers of dispersal mechanisms) and contexts (from the Neolithic in Europe to the spread of computer programming languages), which offer new insights that will augment the theoretical and empirical basis for the study of demic and cultural diffusion. In this introduction we outline the state of art in the modeling of these processes, briefly discuss the pros and cons of two of the most commonly used frameworks (equation-based models and agent-based models), and summarize the significance of each article in this special issue. PMID:26932566
NASA Astrophysics Data System (ADS)
Morgan, D. J.; Chamberlain, K. J.; Kahl, M.; Potts, N. J.; Pankhurst, M. J.; Wilson, C. J. N.
2014-12-01
Over the past 20 years, diffusion chronometers have evolved from a niche tool into one of routine application, with more practitioners, new tools and increasingly large datasets. As we expand the horizons of diffusional geochronometry, it is worth taking stock of developments in methodologies and data acquisition, and taking time to revisit the underpinnings of the technique. Data collected as part of recent projects on Campi Flegrei, the Bishop Tuff and Fimmvörðuháls-Eyjafjallajökull are here used to investigate the initial state assumption, an absolutely vital aspect underpinning most diffusional work and one that is rarely evaluated despite its fundamental importance. To illustrate the nature of the problem we consider two widely-used element-mineral systems for felsic and mafic systems, respectively. First, barium and strontium profiles within sanidine crystals, modelled independently, can give strongly contrasting timescales from the same crystal zone. We can reconcile the datasets only for a situation where the initial boundary within the crystal was not a sharp step function, but relatively fuzzy before diffusion onset. This fuzziness effectively starts both chronometers off with an apparent, and false, pre-existing timescale, impacting the slower-diffusing barium much more strongly than the faster-diffusing strontium, yielding thousands of years of non-existent diffusion history. By combining both elements, a starting width of tens of microns can be shown, shortening the true diffusive timescales from tens of thousands of years to hundreds. Second, in olivine, we encounter different growth-related problems. Here, Fe-Mg interdiffusion occurs at a rate comparable to growth, with the compound nature of zonation making it difficult to extract the diffusion component. This requires a treatment of changing boundary conditions and sequential growth to generate the curvature seen in natural data, in order to recover timescales for anything but the outermost
A Stochastic Cellular Automaton Model of Non-linear Diffusion and Diffusion with Reaction
NASA Astrophysics Data System (ADS)
Brieger, Leesa M.; Bonomi, Ernesto
1991-06-01
This article presents a stochastic cellular automaton model of diffusion and diffusion with reaction. The master equations for the model are examined, and we assess the difference between the implementation in which a single particle at a time moves (asynchronous dynamics) and one implementation in which all particles move simultaneously (synchronous dynamics). Biasing locally each particle's random walk, we alter the diffusion coefficients of the system. By appropriately choosing the biasing function, we can impose a desired non-linear diffusive behaviour in the model. We present an application of this model, adapted to include two diffusing species, two static species, and a chemical reaction in a prototypical simulation of carbonation in concrete.
A Diffuse Interface Model with Immiscibility Preservation
Tiwari, Arpit; Freund, Jonathan B.; Pantano, Carlos
2013-01-01
A new, simple, and computationally efficient interface capturing scheme based on a diffuse interface approach is presented for simulation of compressible multiphase flows. Multi-fluid interfaces are represented using field variables (interface functions) with associated transport equations that are augmented, with respect to an established formulation, to enforce a selected interface thickness. The resulting interface region can be set just thick enough to be resolved by the underlying mesh and numerical method, yet thin enough to provide an efficient model for dynamics of well-resolved scales. A key advance in the present method is that the interface regularization is asymptotically compatible with the thermodynamic mixture laws of the mixture model upon which it is constructed. It incorporates first-order pressure and velocity non-equilibrium effects while preserving interface conditions for equilibrium flows, even within the thin diffused mixture region. We first quantify the improved convergence of this formulation in some widely used one-dimensional configurations, then show that it enables fundamentally better simulations of bubble dynamics. Demonstrations include both a spherical bubble collapse, which is shown to maintain excellent symmetry despite the Cartesian mesh, and a jetting bubble collapse adjacent a wall. Comparisons show that without the new formulation the jet is suppressed by numerical diffusion leading to qualitatively incorrect results. PMID:24058207
A diffusion model for tungsten powder carburization
NASA Astrophysics Data System (ADS)
McCarty, Lewis V.; Donelson, Richard; Hehemann, Robert f.
1991-01-01
A mathematical model describes the carburization kinetics of tungsten powders mixed with carbon and heated in hydrogen. It is based on diffusion of carbon through a shell of WC growing into particles which are modeled as spheres. The activation energy is 58 kcal/mole in the temperature range 1056 to 1833 °C. Hydrogen gas is important to transport carbon as methane or acetylene, but increased hydrogen pressure increases the rate of carburization so little that an adsorbed species such as CH probably controls the carbon concentration at the particle surface.
Radiosity diffusion model in 3D
NASA Astrophysics Data System (ADS)
Riley, Jason D.; Arridge, Simon R.; Chrysanthou, Yiorgos; Dehghani, Hamid; Hillman, Elizabeth M. C.; Schweiger, Martin
2001-11-01
We present the Radiosity-Diffusion model in three dimensions(3D), as an extension to previous work in 2D. It is a method for handling non-scattering spaces in optically participating media. We present the extension of the model to 3D including an extension to the model to cope with increased complexity of the 3D domain. We show that in 3D more careful consideration must be given to the issues of meshing and visibility to model the transport of light within reasonable computational bounds. We demonstrate the model to be comparable to Monte-Carlo simulations for selected geometries, and show preliminary results of comparisons to measured time-resolved data acquired on resin phantoms.
Distributed Energy Resources Market Diffusion Model
Maribu, Karl Magnus; Firestone, Ryan; Marnay, Chris; Siddiqui,Afzal S.
2006-06-16
Distributed generation (DG) technologies, such as gas-fired reciprocating engines and microturbines, have been found to be economically beneficial in meeting commercial-sector electrical, heating, and cooling loads. Even though the electric-only efficiency of DG is lower than that offered by traditional central stations, combined heat and power (CHP) applications using recovered heat can make the overall system energy efficiency of distributed energy resources (DER) greater. From a policy perspective, however, it would be useful to have good estimates of penetration rates of DER under various economic and regulatory scenarios. In order to examine the extent to which DER systems may be adopted at a national level, we model the diffusion of DER in the US commercial building sector under different technical research and technology outreach scenarios. In this context, technology market diffusion is assumed to depend on the system's economic attractiveness and the developer's knowledge about the technology. The latter can be spread both by word-of-mouth and by public outreach programs. To account for regional differences in energy markets and climates, as well as the economic potential for different building types, optimal DER systems are found for several building types and regions. Technology diffusion is then predicted via two scenarios: a baseline scenario and a program scenario, in which more research improves DER performance and stronger technology outreach programs increase DER knowledge. The results depict a large and diverse market where both optimal installed capacity and profitability vary significantly across regions and building types. According to the technology diffusion model, the West region will take the lead in DER installations mainly due to high electricity prices, followed by a later adoption in the Northeast and Midwest regions. Since the DER market is in an early stage, both technology research and outreach programs have the potential to increase
Modelling of the pressure-velocity correlation in turbulence diffusion
NASA Astrophysics Data System (ADS)
Fu, Song
1993-05-01
In the context of second-moment closure, the mechanism of turbulence diffusion consists of mainly two parts: a triple velocity correlation and a pressure-velocity correlation. The first correlation is measurable and can be analyzed theoretically through its transport equation. The second correlation cannot, however, be obtained directly from experiments and knowledge about it is comparatively limited. Most current computations of turbulent flows adopt diffusion models which neglect the effect of the pressure-velocity correlation in the diffusion process. The importance of this correlation effect is elucidated; the neglect of this effect constitutes some of the major defects in the application of the second-moment closures. Through the relation between the two correlations, established by Lumley (1978), we propose a new type of turbulence diffusion model which takes into account the pressure effect. Application of this new model in the computation of the turbulence shearless mixing layer and plane- and round-jet flows shows that the spreading rates of these flows can be captured satisfactorily.
Diffusion through thin membranes: Modeling across scales
NASA Astrophysics Data System (ADS)
Aho, Vesa; Mattila, Keijo; Kühn, Thomas; Kekäläinen, Pekka; Pulkkinen, Otto; Minussi, Roberta Brondani; Vihinen-Ranta, Maija; Timonen, Jussi
2016-04-01
From macroscopic to microscopic scales it is demonstrated that diffusion through membranes can be modeled using specific boundary conditions across them. The membranes are here considered thin in comparison to the overall size of the system. In a macroscopic scale the membrane is introduced as a transmission boundary condition, which enables an effective modeling of systems that involve multiple scales. In a mesoscopic scale, a numerical lattice-Boltzmann scheme with a partial-bounceback condition at the membrane is proposed and analyzed. It is shown that this mesoscopic approach provides a consistent approximation of the transmission boundary condition. Furthermore, analysis of the mesoscopic scheme gives rise to an expression for the permeability of a thin membrane as a function of a mesoscopic transmission parameter. In a microscopic model, the mean waiting time for a passage of a particle through the membrane is in accordance with this permeability. Numerical results computed with the mesoscopic scheme are then compared successfully with analytical solutions derived in a macroscopic scale, and the membrane model introduced here is used to simulate diffusive transport between the cell nucleus and cytoplasm through the nuclear envelope in a realistic cell model based on fluorescence microscopy data. By comparing the simulated fluorophore transport to the experimental one, we determine the permeability of the nuclear envelope of HeLa cells to enhanced yellow fluorescent protein.
Distributed Wind Diffusion Model Overview (Presentation)
Preus, R.; Drury, E.; Sigrin, B.; Gleason, M.
2014-07-01
Distributed wind market demand is driven by current and future wind price and performance, along with several non-price market factors like financing terms, retail electricity rates and rate structures, future wind incentives, and others. We developed a new distributed wind technology diffusion model for the contiguous United States that combines hourly wind speed data at 200m resolution with high resolution electricity load data for various consumer segments (e.g., residential, commercial, industrial), electricity rates and rate structures for utility service territories, incentive data, and high resolution tree cover. The model first calculates the economics of distributed wind at high spatial resolution for each market segment, and then uses a Bass diffusion framework to estimate the evolution of market demand over time. The model provides a fundamental new tool for characterizing how distributed wind market potential could be impacted by a range of future conditions, such as electricity price escalations, improvements in wind generator performance and installed cost, and new financing structures. This paper describes model methodology and presents sample results for distributed wind market potential in the contiguous U.S. through 2050.
Diffuse Interface Model for Microstructure Evolution
NASA Astrophysics Data System (ADS)
Nestler, Britta
A phase-field model for a general class of multi-phase metallic alloys is proposed which describes both, multi-phase solidification phenomena as well as polycrystalline grain structures. The model serves as a computational method to simulate the motion and kinetics of multiple phase boundaries and enables the visualization of the diffusion processes and of the phase transitions in multi-phase systems. Numerical simulations are presented which illustrate the capability of the phase-field model to recover a variety of complex experimental growth structures. In particular, the phase-field model can be used to simulate microstructure evolutions in eutectic, peritectic and monotectic alloys. In addition, polycrystalline grain structures with effects such as wetting, grain growth, symmetry properties of adjacent triple junctions in thin film samples and stability criteria at multiple junctions are described by phase-field simulations.
Multilayer model of photon diffusion in skin
Schmitt, J.M.; Zhou, G.X.; Walker, E.C.; Wall, R.T. )
1990-11-01
A diffusion model describing the propagation of photon flux in the epidermal, dermal, and subcutaneous tissue layers of the skin is presented. Assuming that the skin is illuminated by a collimated, finite-aperture source, we develop expressions relating photon flux density within the skin and intensities re-emitted from the skin surface to the optical properties of the individual layers. Model simulations show that the rate at which re-emitted intensities diminish with radial distance away from the source can provide information about absorption and scattering in underlying tissues. Re-emitted intensities measured from homogeneous and two-layer tissue phantoms compare favorably with model predictions. We demonstrate potential applications of the model by estimating the absorption (sigma a) and transport-corrected scattering (sigma's) coefficients of dermis and subcutis from intensities measured from intact skin and by predicting the magnitude of the optical-density variations measured by a photoplethysmograph.
A diffusion-diffusion model for percutaneous drug absorption.
Kubota, K; Ishizaki, T
1986-08-01
Several theories describing percutaneous drug absorption have been proposed, incorporating the mathematical solutions of differential equations describing percutaneous drug absorption processes where the vehicle and skin are regarded as simple diffusion membranes. By a solution derived from Laplace transforms, the mean residence time MRT and the variance of the residence time VRT in the vehicle are expressed as simple elementary functions of the following five pharmacokinetic parameters characterizing the percutaneous drug absorption: kd, which is defined as the normalized diffusion coefficient of the skin, kc, which is defined as the normalized skin-capillary boundary clearance, the apparent length of diffusion of the skin 1d, the effective length of the vehicle lv, and the diffusion coefficient of the vehicle Dv. All five parameters can be obtained by the methods proposed here. Results of numerical computation indicate that: concentration-distance curves in the vehicle and skin approximate two curves which are simply expressed using trigonometric functions when sufficient time elapses after an ointment application; the most suitable condition for the assumption that the concentration of a drug in the uppermost epidermis can be considered unchanged is the case where the partition coefficient between vehicle and skin is small, and the constancy of drug concentration is even more valid when the effective length of the vehicle is large; and the amount of a drug in the vehicle or skin and the flow rate of the drug from vehicle into skin or from skin into blood becomes linear on a semilogarithmic scale, and the slopes of those lines are small when Dv is small, when the partition coefficient between vehicle and skin is small, when lv is large, or when kc is small. A simple simulation method is also proposed using a biexponential for the concentration-time curve for the skin near the skin-capillary boundary, that is, the flow rate-time curve for drug passing from skin
Effects of Microscopic Diffusion and Rotational Mixing on Stellar Models
NASA Astrophysics Data System (ADS)
Chaboyer, Brian
1994-02-01
Evolutionary tracks and isochrones were calculated with alpha-enhanced compositions which cover the entire globular cluster metallicity range and include the effects of the diffusion of ^4He. Including the effects of helium diffusion has a negligible effect (< 0.5 Gyr) on the derived ages of globular clusters. Regardless of the inclusion of helium diffusion, a significant age spread of ~5$ Gyr exists among the globular clusters. The oldest globular cluster studied was M92 with an age of 17 +/- 2 Gyr old. The stellar models may be tested by comparing the Li depletion and surface rotation rates to observations in young clusters stars. The observed Li abundances clearly indicate that standard or diffusive models do not deplete enough Li. Instabilities induced by rotation provide an additional mixing mechanism. For this reason the stellar evolution code was modified to include the combined effects of diffusion and rotational mixing on ^1H, ^4He and the trace elements ^3He, ^6Li, ^7Li, and ^9Be. The calibrated solar models have a convection zone depth of 0.709 - 0.714~R_odot, in excellent agreement with the observed depth of (0.713 +/- 0.003)~R_odot. The rotational mixing inhibits the diffusion in the outer parts of the models, leading to a decrease in the envelope diffusion by 30 - 50%. The combined models are able to simultaneously match the Li abundances observed in the Pleiades, UMaG, Hyades, NGC 752 and M67. They also match the observed rotation periods in the Hyades. However, these models are unable to explain the presence of the rapidly rotating G and K stars in the Pleiades. Observations of Li abundances in extremely metal poor halo stars provide another test of the stellar models. All models which use Kurucz (1992) model atmospheres to determine the surface boundary conditions are unable to match the observed Li depletion in cool halo stars. Models which use the gray atmosphere approximation provide a much better fit to the data. Standard models do a good job
Databases for Computational Thermodynamics and Diffusion Modeling
NASA Astrophysics Data System (ADS)
Kattner, U. R.; Boettinger, W. J.; Morral, J. E.
2002-11-01
Databases for computational thermodynamics and diffusion modeling can be applied to predict phase diagrams for alloy design and alloy behavior during processing and service. Databases that are currently available to scientists, engineers and students need to be expanded and improved. The approach of the workshop was to first identify the database and information delivery tool needs of industry and education. The workshop format was a series of invited talks given to the group as a whole followed by general discussions of needs and benefits to provide a roadmap of future activities.
Relation between the diffusion curve and the roughness of a tilting diffuser: part II
NASA Astrophysics Data System (ADS)
Rebollo, M. A.; Perez Quintian, F.; Landau, Monica R.; Hogert, Elsa N.; Gaggioli, Nestor G.
1996-02-01
We have studied the diffusion curve evolution in variable translucent rough surfaces. In order to carry on these studies, we used cells having an internal diffuser face. Inside these cells, we place a liquid of controllable refraction index. In this way, we are able to obtain a great range of roughness values without changing the correlation length. In this paper we extend the results obtained in another work presented in the II Iberoamerican Optical Meeting. We verify the existence of a similar phenomenon and its relation with the surface roughness. Moreover, we must note that this work has been done with coherent, but we think that we deal with a predominantly geometric phenomenon, not quite in agreement with most of the authors that are studying this subject.
Diffusion model for lightning radiative transfer
NASA Technical Reports Server (NTRS)
Koshak, William J.; Solakiewicz, Richard J.; Phanord, Dieudonne D.; Blakeslee, Richard J.
1994-01-01
A one-speed Boltzmann transport theory, with diffusion approximations, is applied to study the radiative transfer properties of lightning in optically thick thunderclouds. Near-infrared (lambda = 0.7774 micrometers) photons associated with a prominent oxygen emission triplet in the lightning spectrum are considered. Transient and spatially complex lightning radiation sources are placed inside a rectangular parallelepiped thundercloud geometry and the effects of multiple scattering are studied. The cloud is assumed to be composed of a homogeneous collection of identical spherical water droplets, each droplet a nearly conservative, anisotropic scatterer. Conceptually, we treat the thundercloud like a nuclear reactor, with photons replaced by neutrons, and utilize standard one-speed neutron diffusion techniques common in nuclear reactor analyses. Valid analytic results for the intensity distribution (expanded in spherical harmonics) are obtained for regions sufficiently far from sources. Model estimates of the arrival-time delay and pulse width broadening of lightning signals radiated from within the cloud are determined and the results are in good agreement with both experimental data and previous Monte Carlo estimates. Additional model studies of this kind will be used to study the general information content of cloud top lightning radiation signatures.
Azimi, Mohammad; Jamali, Yousef; Mofrad, Mohammad R. K.
2011-01-01
Diffusion plays a key role in many biochemical reaction systems seen in nature. Scenarios where diffusion behavior is critical can be seen in the cell and subcellular compartments where molecular crowding limits the interaction between particles. We investigate the application of a computational method for modeling the diffusion of molecules and macromolecules in three-dimensional solutions using agent based modeling. This method allows for realistic modeling of a system of particles with different properties such as size, diffusion coefficients, and affinity as well as the environment properties such as viscosity and geometry. Simulations using these movement probabilities yield behavior that mimics natural diffusion. Using this modeling framework, we simulate the effects of molecular crowding on effective diffusion and have validated the results of our model using Langevin dynamics simulations and note that they are in good agreement with previous experimental data. Furthermore, we investigate an extension of this framework where single discrete cells can contain multiple particles of varying size in an effort to highlight errors that can arise from discretization that lead to the unnatural behavior of particles undergoing diffusion. Subsequently, we explore various algorithms that differ in how they handle the movement of multiple particles per cell and suggest an algorithm that properly accommodates multiple particles of various sizes per cell that can replicate the natural behavior of these particles diffusing. Finally, we use the present modeling framework to investigate the effect of structural geometry on the directionality of diffusion in the cell cytoskeleton with the observation that parallel orientation in the structural geometry of actin filaments of filopodia and the branched structure of lamellipodia can give directionality to diffusion at the filopodia-lamellipodia interface. PMID:21966493
Extended source model for diffusive coupling.
González-Ochoa, Héctor O; Flores-Moreno, Roberto; Reyes, Luz M; Femat, Ricardo
2016-01-01
Motivated by the prevailing approach to diffusion coupling phenomena which considers point-like diffusing sources, we derived an analogous expression for the concentration rate of change of diffusively coupled extended containers. The proposed equation, together with expressions based on solutions to the diffusion equation, is intended to be applied to the numerical solution of systems exclusively composed of ordinary differential equations, however is able to account for effects due the finite size of the coupled sources. PMID:26802012
Modeling of diffusion controlled drug delivery.
Siepmann, Juergen; Siepmann, Florence
2012-07-20
Mathematical modeling of drug release can be very helpful to speed up product development and to better understand the mechanisms controlling drug release from advanced delivery systems. Ideally, in silico simulations can quantitatively predict the impact of formulation and processing parameters on the resulting drug release kinetics. The aim of this article is to give an overview on the current state of the art of modeling drug release from delivery systems, which are predominantly controlled by diffusional mass transport. The inner structure of the device, the ratio "initial drug concentration:drug solubility" as well as the device geometry determine which type of mathematical equation must be applied. A straightforward "road map" is given, explaining how to identify the appropriate equation for a particular type of drug delivery system. The respective equations for a broad range of devices are indicated, including reservoir and matrix systems, exhibiting or not an initial excess of drug and the geometry of slabs, spheres and cylinders. The assumptions the models are based on as well as their limitations are pointed out. Practical examples illustrate the usefulness of mathematical modeling of diffusion controlled drug delivery. Due to the advances in information technology the importance of in silico optimization of advanced drug delivery systems can be expected to significantly increase in the future. PMID:22019555
Extending the diffusion approximation to the boundary using an integrated diffusion model
NASA Astrophysics Data System (ADS)
Chen, Chen; Du, Zhidong; Pan, Liang
2015-06-01
The widely used diffusion approximation is inaccurate to describe the transport behaviors near surfaces and interfaces. To solve such stochastic processes, an integro-differential equation, such as the Boltzmann transport equation (BTE), is typically required. In this work, we show that it is possible to keep the simplicity of the diffusion approximation by introducing a nonlocal source term and a spatially varying diffusion coefficient. We apply the proposed integrated diffusion model (IDM) to a benchmark problem of heat conduction across a thin film to demonstrate its feasibility. We also validate the model when boundary reflections and uniform internal heat generation are present.
Modeling of hydrogen-air diffusion flame
NASA Technical Reports Server (NTRS)
Isaac, K. M.
1988-01-01
Work performed during the first six months of the project duration for NASA Grant (NAG-1-861) is reported. An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies attempted so far are described.
Some Problems in Using Diffusion Models for New Products
ERIC Educational Resources Information Center
Bernhardt, Irwin; Mackenzie, Kenneth D.
1972-01-01
Analyzes some of the problems involved in using diffusion models to formulate marketing strategies for introducing new products. Six models, which remove some of the theoretical and methodological restrictions inherent in current models of the adoption and diffusion process, are presented. (Author/JH)
Radon diffusion through multilayer earthen covers: models and simulations
Mayer, D.W.; Oster, C.A.; Nelson, R.W.; Gee, G.W.
1981-09-01
A capability to model and analyze the fundamental interactions that influence the diffusion of radon gas through uranium mill tailings and cover systems has been investigated. The purpose of this study is to develop the theoretical basis for modeling radon diffusion and to develop an understanding of the fundamental interactions that influence radon diffusion. This study develops the theoretical basis for modeling radon diffusion in one, two and three dimensions. The theory has been incorporated into three computer models that are used to analyze several tailings and cover configurations. This report contains a discussion of the theoretical basis for modeling radon diffusion, a discussion of the computer models used to analyze uranium mill tailings and multilayered cover systems, and presents the results that have been obtained.
A Comparison of Competing Models of the News Diffusion Process.
ERIC Educational Resources Information Center
Mayer, Michael E.; And Others
1990-01-01
Investigates the diffusion of information about the space shuttle Challenger explosion by comparing loglinear models of the diffusion process. Finds that the most parsimonious model with adequate goodness of fit was a linear one in which a person's location affected how the information was heard, which in turn affected when the information was…
Parameter Variability and Distributional Assumptions in the Diffusion Model
ERIC Educational Resources Information Center
Ratcliff, Roger
2013-01-01
If the diffusion model (Ratcliff & McKoon, 2008) is to account for the relative speeds of correct responses and errors, it is necessary that the components of processing identified by the model vary across the trials of a task. In standard applications, the rate at which information is accumulated by the diffusion process is assumed to be normally…
Modeling realistic breast lesions using diffusion limited aggregation
NASA Astrophysics Data System (ADS)
Rashidnasab, Alaleh; Elangovan, Premkumar; Dance, David R.; Young, Kenneth C.; Diaz, Oliver; Wells, Kevin
2012-03-01
Synthesizing the appearance of malignant masses and inserting these into digital mammograms can be used as part of a wider framework for investigating the radiological detection task in X-ray mammography. However, the randomness associated with cell division within cancerous masses and the associated complex morphology challenges the realism of the modeling process. In this paper, Diffusion Limited Aggregation (DLA), a type of fractal growth process is proposed and utilized for modeling breast lesions. Masses of different sizes, shapes and densities were grown by controlling DLA growth parameters either prior to growth, or dynamically updating these during growth. A validation study was conducted by presenting 30 real and 30 simulated masses in a random order to a team of radiologists. The results from the validation study suggest that the observers found it difficult to differentiate between the real and simulated lesions.
Diffusion in Condensed Matter: Methods, Materials, Models
NASA Astrophysics Data System (ADS)
Heitjans, Paul; Kärger, Jög
This comprehensive, handbook-style survey of diffusion in condensed matter gives detailed insight into diffusion as the process of particle transport due to stochastic movement. It is understood and presented as a phenomenon of crucial relevance for a large variety of processes and materials. In this book, all aspects of the theoretical fundamentals, experimental techniques, highlights of current developments and results for solids, liquids and interfaces are presented.
Dynamic hysteresis modeling including skin effect using diffusion equation model
NASA Astrophysics Data System (ADS)
Hamada, Souad; Louai, Fatima Zohra; Nait-Said, Nasreddine; Benabou, Abdelkader
2016-07-01
An improved dynamic hysteresis model is proposed for the prediction of hysteresis loop of electrical steel up to mean frequencies, taking into account the skin effect. In previous works, the analytical solution of the diffusion equation for low frequency (DELF) was coupled with the inverse static Jiles-Atherton (JA) model in order to represent the hysteresis behavior for a lamination. In the present paper, this approach is improved to ensure the reproducibility of measured hysteresis loops at mean frequency. The results of simulation are compared with the experimental ones. The selected results for frequencies 50 Hz, 100 Hz, 200 Hz and 400 Hz are presented and discussed.
Diffusion model of the non-stoichiometric uranium dioxide
NASA Astrophysics Data System (ADS)
Moore, Emily; Guéneau, Christine; Crocombette, Jean-Paul
2013-07-01
Uranium dioxide (UO2), which is used in light water reactors, exhibits a large range of non-stoichiometry over a wide temperature scale up to 2000 K. Understanding diffusion behavior of uranium oxides under such conditions is essential to ensure safe reactor operation. The current understanding of diffusion properties is largely limited by the stoichiometric deviations inherent to the fuel. The present DICTRA-based model considers diffusion across non-stoichiometric ranges described by experimentally available data. A vacancy and interstitial model of diffusion is applied to the U-O system as a function of its defect structure derived from CALPHAD-type thermodynamic descriptions. Oxygen and uranium self and tracer diffusion coefficients are assessed for the construction of a mobility database. Chemical diffusion coefficients of oxygen are derived with respect to the Darken relation and migration energies of defects are evaluated as a function of stoichiometric deviation.
Modeling diffusion and adsorption in compacted bentonite: a critical review.
Bourg, Ian C; Bourg, Alain C M; Sposito, Garrison
2003-03-01
The current way of describing diffusive transport through compacted clays is a simple diffusion model coupled to a linear adsorption coefficient (K(d)). To fit the observed results of cation diffusion, this model is usually extended with an adjustable "surface diffusion" coefficient. Description of the negative adsorption of anions calls for a further adjustment through the use of an "effective porosity". The final model thus includes many fitting parameters. This is inconvenient where predictive modeling is called for (e.g., for waste confinement using compacted clay liners). The diffusion/adsorption models in current use have been derived from the common hydrogeological equation of advection/dispersion/adsorption. However, certain simplifications were also borrowed without questioning their applicability to the case of compacted clays. Among these simplifications, the assumption that the volume of the adsorbed phase is negligible should be discussed. We propose a modified diffusion/adsorption model that accounts for the volume of the adsorbed phase. It suggests that diffusion through highly compacted clay takes place through the interlayers (i.e., in the adsorbed phase). Quantitative prediction of the diffusive flux will necessitate more detailed descriptions of surface reactivity and of the mobility of interlayer species. PMID:12598111
A new indirect measure of diffusion model error
Kumar, A.; Morel, J. E.; Adams, M. L.
2013-07-01
We define a new indirect measure of the diffusion model error called the diffusion model error source. When this model error source is added to the diffusion equation, the transport solution for the angular-integrated intensity is obtained. This source represents a means by which a transport code can be used to generate information relating to the adequacy of diffusion theory for any given problem without actually solving the diffusion equation. The generation of this source does not relate in any way to acceleration of the iterative convergence of transport solutions. Perhaps the most well-known indirect measure of the diffusion model error is the variable-Eddington tensor. This tensor provides a great deal of information about the angular dependence of the angular intensity solution, but it is not always simple to interpret. In contrast, our diffusion model error source is a scalar that is conceptually easy to understand. In addition to defining the diffusion model error source analytically, we show how to generate this source numerically relative to the S{sub n} radiative transfer equations with linear-discontinuous spatial discretization. This numerical source is computationally tested and shown to reproduce the Sn solution for a Marshak-wave problem. (authors)
Exact curvilinear diffusion coefficients in the repton model
NASA Astrophysics Data System (ADS)
Buhot, A.
2005-10-01
The Rubinstein-Duke or repton model is one of the simplest lattice model of reptation for the diffusion of a polymer in a gel or a melt. Recently, a slightly modified model with hardcore interactions between the reptons has been introduced. The curvilinear diffusion coefficients of both models are exactly determined for all chain lengths. The case of periodic boundary conditions is also considered.
Modeling Diffusion Induced Stresses for Lithium-Ion Battery Materials
NASA Astrophysics Data System (ADS)
Chiu Huang, Cheng-Kai
rate (C-rate) during charging/discharging affects diffusion induced stresses inside electrode materials. For the experimental part we first conduct charging/discharging under different C-rates to observe the voltage responses for commercial LiFePO4 batteries. Then Time-of-Flight Secondary Ion Mass Spectrometry technique is applied to measure the lithium ion intensities in different C-rate charged/discharged samples. These experimental results could be used to support that a more significant voltage fluctuation under high C-rates is due to different lithium insertion mechanisms, rather than the amount of lithium ions intercalated into electrode materials. Thus the investigation of C-rate-dependent stress evolution is required for the development of a more durable lithium ion battery. In this dissertation, we extend the single particle finite element model to investigate the C-rate-dependent diffusion induced stresses in a multi-particle system. Concentration dependent anisotropic material properties, C-rate-dependent volume misfits and concentration dependent Li-ion diffusivity are incorporated in the model. The concentration gradients, diffusion induced stresses, and strain energies under different C-rates are discussed in this study. Particle fractures have been observed in many experimental results, in this study we further discuss the effect of the crack surface orientation on the lithium concentration profile and stress level in cathode materials. The results of this dissertation provide a better understanding of diffusion induced stresses in electrode materials and contribute to our fundamental knowledge of interplay between lithium intercalations, stress evolutions, particle fractures and the capacity fade in lithium-ion batteries.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 10 Energy 2 2013-01-01 2013-01-01 false Illustrative List of Gaseous Diffusion Enrichment Plant... Appendix C to Part 110—Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components... for gaseous diffusion enrichment plants are the systems of plant needed to feed UF6 to the...
Code of Federal Regulations, 2014 CFR
2014-01-01
... 10 Energy 2 2014-01-01 2014-01-01 false Illustrative List of Gaseous Diffusion Enrichment Plant... Appendix C to Part 110—Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components... for gaseous diffusion enrichment plants are the systems of plant needed to feed UF6 to the...
Modeling atomic hydrogen diffusion in GaAs
NASA Astrophysics Data System (ADS)
Kagadei, Valerii A.; Nefyodtsev, E.
2004-05-01
The hydrogen diffusion model in GaAs in conditions of an intense flow of penetrating atoms has been developed. It is shown that the formation undersurface diffusion barrier layer from immobile interstitial molecules of hydrogen reduce probability of atoms penetration into crystal and rate of their diffusion in GaAs, and influence on the process of shallow- and/or deep-centers passivation. It is exhibited that the influence of diffusion barrier should be taken into account at optimum mode selection of GaAs structure hydrogenation.
Modeling complex diffusion mechanisms in L1 2 -structured compounds
NASA Astrophysics Data System (ADS)
Zacate, M. O.; Lape, M.; Stufflebeam, M.; Evenson, W. E.
2010-04-01
We report on a procedure developed to create stochastic models of hyperfine interactions for complex diffusion mechanisms and demonstrate its application to simulate perturbed angular correlation spectra for the divacancy and 6-jump cycle diffusion mechanisms in L12-structured compounds.
A computational kinetic model of diffusion for molecular systems
Teo, Ivan; Schulten, Klaus
2013-01-01
Regulation of biomolecular transport in cells involves intra-protein steps like gating and passage through channels, but these steps are preceded by extra-protein steps, namely, diffusive approach and admittance of solutes. The extra-protein steps develop over a 10–100 nm length scale typically in a highly particular environment, characterized through the protein's geometry, surrounding electrostatic field, and location. In order to account for solute energetics and mobility of solutes in this environment at a relevant resolution, we propose a particle-based kinetic model of diffusion based on a Markov State Model framework. Prerequisite input data consist of diffusion coefficient and potential of mean force maps generated from extensive molecular dynamics simulations of proteins and their environment that sample multi-nanosecond durations. The suggested diffusion model can describe transport processes beyond microsecond duration, relevant for biological function and beyond the realm of molecular dynamics simulation. For this purpose the systems are represented by a discrete set of states specified by the positions, volumes, and surface elements of Voronoi grid cells distributed according to a density function resolving the often intricate relevant diffusion space. Validation tests carried out for generic diffusion spaces show that the model and the associated Brownian motion algorithm are viable over a large range of parameter values such as time step, diffusion coefficient, and grid density. A concrete application of the method is demonstrated for ion diffusion around and through the Eschericia coli mechanosensitive channel of small conductance ecMscS. PMID:24089741
A computational kinetic model of diffusion for molecular systems
NASA Astrophysics Data System (ADS)
Teo, Ivan; Schulten, Klaus
2013-09-01
Regulation of biomolecular transport in cells involves intra-protein steps like gating and passage through channels, but these steps are preceded by extra-protein steps, namely, diffusive approach and admittance of solutes. The extra-protein steps develop over a 10-100 nm length scale typically in a highly particular environment, characterized through the protein's geometry, surrounding electrostatic field, and location. In order to account for solute energetics and mobility of solutes in this environment at a relevant resolution, we propose a particle-based kinetic model of diffusion based on a Markov State Model framework. Prerequisite input data consist of diffusion coefficient and potential of mean force maps generated from extensive molecular dynamics simulations of proteins and their environment that sample multi-nanosecond durations. The suggested diffusion model can describe transport processes beyond microsecond duration, relevant for biological function and beyond the realm of molecular dynamics simulation. For this purpose the systems are represented by a discrete set of states specified by the positions, volumes, and surface elements of Voronoi grid cells distributed according to a density function resolving the often intricate relevant diffusion space. Validation tests carried out for generic diffusion spaces show that the model and the associated Brownian motion algorithm are viable over a large range of parameter values such as time step, diffusion coefficient, and grid density. A concrete application of the method is demonstrated for ion diffusion around and through the Eschericia coli mechanosensitive channel of small conductance ecMscS.
Liu, Yanfeng; Zhou, Xiaojun; Wang, Dengjia; Song, Cong; Liu, Jiaping
2015-12-15
Most building materials are porous media, and the internal diffusion coefficients of such materials have an important influences on the emission characteristics of volatile organic compounds (VOCs). The pore structure of porous building materials has a significant impact on the diffusion coefficient. However, the complex structural characteristics bring great difficulties to the model development. The existing prediction models of the diffusion coefficient are flawed and need to be improved. Using scanning electron microscope (SEM) observations and mercury intrusion porosimetry (MIP) tests of typical porous building materials, this study developed a new diffusivity model: the multistage series-connection fractal capillary-bundle (MSFC) model. The model considers the variable-diameter capillaries formed by macropores connected in series as the main mass transfer paths, and the diameter distribution of the capillary bundles obeys a fractal power law in the cross section. In addition, the tortuosity of the macrocapillary segments with different diameters is obtained by the fractal theory. Mesopores serve as the connections between the macrocapillary segments rather than as the main mass transfer paths. The theoretical results obtained using the MSFC model yielded a highly accurate prediction of the diffusion coefficients and were in a good agreement with the VOC concentration measurements in the environmental test chamber. PMID:26291782
Modeling anomalous diffusion of dense fluids in carbon nanotubes
NASA Astrophysics Data System (ADS)
Wang, Gerald; Hadjiconstantinou, Nicolas
2015-11-01
Molecular diffusive mechanisms exhibited under nanoconfinement can differ considerably from the Fickian self-diffusion expected in a bulk fluid. We propose a theoretical description of this phenomenon in a nanofluidic system of considerable interest - namely, a dense fluid confined within a carbon nanotube (CNT). We show that the anomalous diffusion reported in the literature is closely related to the fluid layering widely observed in this system and recently theoretically described [Wang and Hadjiconstantinou, Physics of Fluids, 052006, 2015]. In particular, we find that the key to describing the anomalous molecular diffusion (within sufficiently large CNTs) lies in recognizing that the diffusion mechanism is spatially dependent: while fluid in the center of the nanotube (at least three molecular diameters away from the wall) exhibits Fickian diffusion, fluid near the CNT wall can demonstrate non-Fickian diffusive behavior. The previously reported anomalous diffusive behavior can be reproduced, to a good approximation level, by appropriately combining the bulk and near-wall behavior to form a model for the overall diffusion rate within the nanotube. Such models produce results in quantitative agreement with molecular dynamics simulations.
Comparison of Turbulent Thermal Diffusivity and Scalar Variance Models
NASA Technical Reports Server (NTRS)
Yoder, Dennis A.
2016-01-01
This paper will include a detailed comparison of heat transfer models that rely upon the thermal diffusivity. The goals are to inform users of the development history of the various models and the resulting differences in model formulations, as well as to evaluate the models on a variety of validation cases so that users might better understand which models are more broadly applicable.
Model calculations for diffuse molecular clouds. [interstellar hydrogen cloud model
NASA Technical Reports Server (NTRS)
Glassgold, A. E.; Langer, W. D.
1974-01-01
A steady state isobaric cloud model is developed. The pressure, thermal, electrical, and chemical balance equations are solved simultaneously with a simple one dimensional approximation to the equation of radiative transfer appropriate to diffuse clouds. Cooling is mainly by CII fine structure transitions, and a variety of heating mechanisms are considered. Particular attention is given to the abundance variation of H2. Inhomogeneous density distributions are obtained because of the attenuation of the interstellar UV field and the conversion from atomic to molecular hyrodgen. The effects of changing the model parameters are described and the applicability of the model to OAO-3 observations is discussed. Good qualitative agreement with the fractional H2 abundance determinations has been obtained. The observed kinetic temperatures near 80 K can also be achieved by grain photoelectron heating. The problem of the electron density is solved taking special account of the various hydrogen ions as well as heavier ones.
What can the diffusion model tell us about prospective memory?
Horn, Sebastian S; Bayen, Ute J; Smith, Rebekah E
2011-03-01
Cognitive process models, such as Ratcliff's (1978) diffusion model, are useful tools for examining cost or interference effects in event-based prospective memory (PM). The diffusion model includes several parameters that provide insight into how and why ongoing-task performance may be affected by a PM task and is ideally suited to analyse performance because both reaction time and accuracy are taken into account. Separate analyses of these measures can easily yield misleading interpretations in cases of speed-accuracy trade-offs. The diffusion model allows us to measure possible criterion shifts and is thus an important methodological improvement over standard analyses. Performance in an ongoing lexical-decision task was analysed with the diffusion model. The results suggest that criterion shifts play an important role when a PM task is added, but do not fully explain the cost effect on reaction time. PMID:21443332
Nonequilibrium drift-diffusion model for organic semiconductor devices
NASA Astrophysics Data System (ADS)
Felekidis, Nikolaos; Melianas, Armantas; Kemerink, Martijn
2016-07-01
Two prevailing formalisms are currently used to model charge transport in organic semiconductor devices. Drift-diffusion calculations, on the one hand, are time effective but assume local thermodynamic equilibrium, which is not always realistic. Kinetic Monte Carlo models, on the other hand, do not require this assumption but are computationally expensive. Here, we present a nonequilibrium drift-diffusion model that bridges this gap by fusing the established multiple trap and release formalism with the drift-diffusion transport equation. For a prototypical photovoltaic system the model is shown to quantitatively describe, with a single set of parameters, experiments probing (1) temperature-dependent steady-state charge transport—space-charge limited currents, and (2) time-resolved charge transport and relaxation of nonequilibrated photocreated charges. Moreover, the outputs of the developed kinetic drift-diffusion model are an order of magnitude, or more, faster to compute and in good agreement with kinetic Monte Carlo calculations.
Improved knowledge diffusion model based on the collaboration hypernetwork
NASA Astrophysics Data System (ADS)
Wang, Jiang-Pan; Guo, Qiang; Yang, Guang-Yong; Liu, Jian-Guo
2015-06-01
The process for absorbing knowledge becomes an essential element for innovation in firms and in adapting to changes in the competitive environment. In this paper, we present an improved knowledge diffusion hypernetwork (IKDH) model based on the idea that knowledge will spread from the target node to all its neighbors in terms of the hyperedge and knowledge stock. We apply the average knowledge stock V(t) , the variable σ2(t) , and the variance coefficient c(t) to evaluate the performance of knowledge diffusion. By analyzing different knowledge diffusion ways, selection ways of the highly knowledgeable nodes, hypernetwork sizes and hypernetwork structures for the performance of knowledge diffusion, results show that the diffusion speed of IKDH model is 3.64 times faster than that of traditional knowledge diffusion (TKDH) model. Besides, it is three times faster to diffuse knowledge by randomly selecting "expert" nodes than that by selecting large-hyperdegree nodes as "expert" nodes. Furthermore, either the closer network structure or smaller network size results in the faster knowledge diffusion.
Diffusion models for Jupiter's radiation belt
NASA Technical Reports Server (NTRS)
Jacques, S. A.; Davis, L., Jr.
1972-01-01
Solutions are given for the diffusion of trapped particles in a planetary magnetic field in which the first and second adiabatic invariants are preserved but the third is not, using as boundary conditions a fixed density at the outer boundary (the magnetopause) and a zero density at an inner boundary (the planetary surface). Losses to an orbiting natural satellite are included and an approximate evaluation is made of the effects of the synchrotron radiation on the energy of relativistic electrons. Choosing parameters appropriate to Jupiter, the electrons required to produce the observed synchrotron radiation are explained. If a speculative mechanism in which the diffusion is driven by ionospheric wind is the true explanation of the electrons producing the synchrotron emission it can be concluded that Jupiter's inner magnetosphere is occupied by an energetic proton flux that would be a serious hazard to spacecraft.
Diffusion coefficient and shear viscosity of rigid water models.
Tazi, Sami; Boţan, Alexandru; Salanne, Mathieu; Marry, Virginie; Turq, Pierre; Rotenberg, Benjamin
2012-07-18
We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC/E with three sites, and TIP4P/2005 with four sites) and a polarizable one (Dang-Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also provides an estimate of the viscosity of all water models, which we compare to the Green-Kubo result. In all cases, a good agreement is found. The TIP4P/2005 model is in better agreement with the experimental data for both diffusion and viscosity. The SPC/E and Dang-Chang models overestimate the diffusion coefficient and underestimate the viscosity. PMID:22739097
Addition of Diffusion Model to MELCOR and Comparison with Data
Brad Merrill; Richard Moore; Chang Oh
2004-06-01
A chemical diffusion model was incorporated into the thermal-hydraulics package of the MELCOR Severe Accident code (Reference 1) for analyzing air ingress events for a very high temperature gas-cooled reactor.
Postural control model interpretation of stabilogram diffusion analysis
NASA Technical Reports Server (NTRS)
Peterka, R. J.
2000-01-01
Collins and De Luca [Collins JJ. De Luca CJ (1993) Exp Brain Res 95: 308-318] introduced a new method known as stabilogram diffusion analysis that provides a quantitative statistical measure of the apparently random variations of center-of-pressure (COP) trajectories recorded during quiet upright stance in humans. This analysis generates a stabilogram diffusion function (SDF) that summarizes the mean square COP displacement as a function of the time interval between COP comparisons. SDFs have a characteristic two-part form that suggests the presence of two different control regimes: a short-term open-loop control behavior and a longer-term closed-loop behavior. This paper demonstrates that a very simple closed-loop control model of upright stance can generate realistic SDFs. The model consists of an inverted pendulum body with torque applied at the ankle joint. This torque includes a random disturbance torque and a control torque. The control torque is a function of the deviation (error signal) between the desired upright body position and the actual body position, and is generated in proportion to the error signal, the derivative of the error signal, and the integral of the error signal [i.e. a proportional, integral and derivative (PID) neural controller]. The control torque is applied with a time delay representing conduction, processing, and muscle activation delays. Variations in the PID parameters and the time delay generate variations in SDFs that mimic real experimental SDFs. This model analysis allows one to interpret experimentally observed changes in SDFs in terms of variations in neural controller and time delay parameters rather than in terms of open-loop versus closed-loop behavior.
BF{sub 3} PIII modeling: Implantation, amorphisation and diffusion
Essa, Z.; Cristiano, F.; Spiegel, Y.; Boulenc, P.; Qiu, Y.; Quillec, M.; Taleb, N.; Burenkov, A.; Hackenberg, M.; Bedel-Pereira, E.; Mortet, V.; Torregrosa, Frank; Tavernier, C.
2012-11-06
In the race for highly doped ultra-shallow junctions (USJs) in complementary metal oxide semi-conductor (CMOS) technologies, plasma immersion ion implantation (PIII) is a promising alternative to traditional beamline implantation. Currently, no commercial technology computer aided design (TCAD) process simulator allows modeling the complete USJ fabrication process by PIII, including as-implanted dopant profiles, damage formation, dopant diffusion and activation. In this work, a full simulation of a p-type BF{sub 3} PIII USJ has been carried out. In order to investigate the various physical phenomena mentioned above, process conditions included a high energy/high dose case (10 kV, 5 Multiplication-Sign 10{sup 15} cm{sup -2}), specifically designed to increase damage formation, as well as more technology relevant implant conditions (0.5 kV) for comparison. All implanted samples were annealed at different temperatures and times. As implanted profiles for both boron and fluorine in BF{sub 3} implants were modeled and compared to Secondary Ion Mass Spectrometry (SIMS) measurements. Amorphous/crystalline (a/c) interface depths were measured by transmission electron microscopy (TEM) and successfully simulated. Diffused profiles simulations agreed with SIMS data at low thermal budgets. A boron peak behind the a/c interface was observed in all annealed SIMS profiles for the 10 kV case, indicating boron trapping from EOR defects in this region even after high thermal budgets. TEM measurements on the annealed samples showed an end of range (EOR) defects survival behind the a/c interface, including large dislocation loops (DLs) lying on (001) plane parallel to the surface. In the last part of this work, activation simulations were compared to Hall measurements and confirmed the need to develop a (001) large BICs model.
Modelling oxygen self-diffusion in UO2 under pressure
Cooper, Michael William D.; Grimes, R. W.; Fitzpatrick, M. E.; Chroneos, A.
2015-10-22
Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO2 is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO2 over a range of pressures (0–10 GPa) and temperatures (300–1900 K). Furthermore, the significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.
A model for diffusive systems: Beyond the Arrhenius mechanism
NASA Astrophysics Data System (ADS)
Rosa, A. C. P.; Vaveliuk, Pablo; Mundim, Kleber C.; Moret, M. A.
2016-05-01
Diffusivity in supercooled liquids was observed to exhibit a non-Arrhenius behavior near the glass-transition temperature. This process, which occurs where the activation energy depends on the temperature, suggests the possibility of a metastable equilibrium. This peculiar phenomenon cannot be explained using the usual Markovian stochastic models. Based on a non-linear Fokker-Planck equation, we propose a diffusion coefficient that is proportional to the supercooled-liquid concentration. The proposed model allows us to explain the anomalous behavior of the diffusivity robustly. We demonstrate that this new approach is consistent with experimental patterns. Besides, it could be applied to non-Arrhenius chemical kinetics.
Mathematical modelling of diffusion and reaction in blocked zeolite catalysts
Sundaresan, S.; Hall, C.K.
1985-01-01
A mathematical model for diffusion and reaction in blocked zeolites is developed which takes into account nonidealities arising from interaction between sorbed molecules as well as the effect of pore and surface blocking. The model combines a microscopic approach, in which expressions for chemical potential and diffusive fluxes are calculated within the lattice-gas framework, with the more traditional continuum approach which takes into account the effect of surface blocking. The effect of pore blocking on the diffusive fluxes is accounted for through an effective medium approximation.
NASA Astrophysics Data System (ADS)
McMillen, Laura; Vavylonis, Dimitrios; Vavylonis Group Team
It is debated whether transport of actin across the cell by diffusion alone is sufficiently fast to account for the rapid reorganization of actin filaments at the leading edge of motile cells. In order to investigate this question, we created a 3D model of the whole cell that includes reaction and diffusion of actin using a particle Monte Carlo method. For the lamellipodium of the simulated cell we use the model by Smith et al. Biophys. J 104:247 (2013), which includes two diffuse pools of actin, one which is slowly diffusing and the other which diffuses more quickly, as well as a pool of filamentous actin undergoing retrograde flow towards the cell center. We adjusted this model to fit a circular geometry around the whole cell. We also consider actin in the cell center which is either diffusing or in stationary filamentous form, representing cortical actin or actin in stress fibers. The local rates of polymerization and the lifetime distributions of polymerized actin were estimated from single molecule speckle microscopy experiments by the group of N. Watanabe. With this model we are able to simulate prior experiments that monitored the redistribution of actin after photoactivation or fluorescence recovery after photobleaching in various parts of the cell. We find that transport by diffusion is sufficient to fit these data, without the need for an active transport mechanism, however significant concentration gradients may develop at steady state.
A discrete time random walk model for anomalous diffusion
NASA Astrophysics Data System (ADS)
Angstmann, C. N.; Donnelly, I. C.; Henry, B. I.; Nichols, J. A.
2015-07-01
The continuous time random walk, introduced in the physics literature by Montroll and Weiss, has been widely used to model anomalous diffusion in external force fields. One of the features of this model is that the governing equations for the evolution of the probability density function, in the diffusion limit, can generally be simplified using fractional calculus. This has in turn led to intensive research efforts over the past decade to develop robust numerical methods for the governing equations, represented as fractional partial differential equations. Here we introduce a discrete time random walk that can also be used to model anomalous diffusion in an external force field. The governing evolution equations for the probability density function share the continuous time random walk diffusion limit. Thus the discrete time random walk provides a novel numerical method for solving anomalous diffusion equations in the diffusion limit, including the fractional Fokker-Planck equation. This method has the clear advantage that the discretisation of the diffusion limit equation, which is necessary for numerical analysis, is itself a well defined physical process. Some examples using the discrete time random walk to provide numerical solutions of the probability density function for anomalous subdiffusion, including forcing, are provided.
Scaling in the Diffusion Limited Aggregation Model
NASA Astrophysics Data System (ADS)
Menshutin, Anton
2012-01-01
We present a self-consistent picture of diffusion limited aggregation (DLA) growth based on the assumption that the probability density P(r,N) for the next particle to be attached within the distance r to the center of the cluster is expressible in the scale-invariant form P[r/Rdep(N)]. It follows from this assumption that there is no multiscaling issue in DLA and there is only a single fractal dimension D for all length scales. We check our assumption self-consistently by calculating the particle-density distribution with a measured P(r/Rdep) function on an ensemble with 1000 clusters of 5×107 particles each. We also show that a nontrivial multiscaling function D(x) can be obtained only when small clusters (N<10000) are used to calculate D(x). Hence, multiscaling is a finite-size effect and is not intrinsic to DLA.
Update on Advection-Diffusion Purge Flow Model
NASA Technical Reports Server (NTRS)
Brieda, Lubos
2015-01-01
Gaseous purge is commonly used in sensitive spacecraft optical or electronic instruments to prevent infiltration of contaminants and/or water vapor. Typically, purge is sized using simplistic zero-dimensional models that do not take into account instrument geometry, surface effects, and the dependence of diffusive flux on the concentration gradient. For this reason, an axisymmetric computational fluid dynamics (CFD) simulation was recently developed to model contaminant infiltration and removal by purge. The solver uses a combined Navier-Stokes and Advection-Diffusion approach. In this talk, we report on updates in the model, namely inclusion of a particulate transport model.
SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.
Hromadka, T.V., II; Lai, Chintu
1985-01-01
A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. To investigate its capability, the numerical model using the diffusion approach is applied to a hypothetical failure problem of a regional water reservoir. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by a popular home computer which supports 64K FORTRAN. Though simple, the 2-D model can simulate some interesting flooding effects that a 1-D full dynamic model cannot.
Innovation Diffusion Model in Higher Education: Case Study of E-Learning Diffusion
ERIC Educational Resources Information Center
Buc, Sanjana; Divjak, Blaženka
2015-01-01
The diffusion of innovation (DOI) is critical for any organization and especially nowadays for higher education institutions (HEIs) in the light of vast pressure of emerging educational technologies as well as of the demand of economy and society. DOI takes into account the initial and the implementation phase. The conceptual model of DOI in…
Gas-phase diffusion in porous media: Comparison of models
Webb, S.W.
1998-09-01
Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.
Modeling cation diffusion in compacted water-saturated sodium bentonite at low ionic strength.
Bourg, Ian C; Sposito, Garrison; Bourg, Alain C M
2007-12-01
Sodium bentonites are used as barrier materials for the isolation of landfills and are under consideration for a similar use in the subsurface storage of high-level radioactive waste. The performance of these barriers is determined in large part by molecular diffusion in the bentonite pore space. We tested two current models of cation diffusion in bentonite against experimental data on the relative apparent diffusion coefficients of two representative cations, sodium and strontium. On the "macropore/nanopore" model, solute molecules are divided into two categories, with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer nanopores. On the "surface diffusion" model, solute molecules are divided into categories based on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite gel) to 1.7 kg dm(-3) (a highly compacted bentonite with most of its pore space located in interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry densities greater than about 1.3 kg dm(-3). PMID:18186346
Modeling cation diffusion in compacted water-saturatedNa-bentonite at low ionic strength
Bourg, Ian C.; Sposito, Garrison; Bourg, Alain C.M.
2007-08-28
Sodium bentonites are used as barrier materials for the isolation of landfills and are under consideration for a similar use in the subsurface storage of high-level radioactive waste. The performance of these barriers is determined in large part by molecular diffusion in the bentonite pore space. We tested two current models of cation diffusion in bentonite against experimental data on the relative apparent diffusion coefficients of two representative cations, sodium and strontium. On the 'macropore/nanopore' model, solute molecules are divided into two categories, with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer nanopores. On the 'surface diffusion' model, solute molecules are divided into categories based on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite gel) to 1.7 kg dm{sup -3} (a highly compacted bentonite with most of its pore space located in interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry densities greater than about 1.2 kg dm{sup -3}.
Measurement and prediction of the oxygen diffusion coefficient in partly saturated media
NASA Astrophysics Data System (ADS)
Aachib, M.; Mbonimpa, M.; Aubertin, M.; Bussiere, B.
2004-05-01
Molecular diffusion is an important mechanism for gas transport in various natural and man-made systems. This is particularly the case with soil covers installed on acid generating mine tailings, where oxygen availability has to be controlled. One of the most important roles of such covers is to limit gas flux, which depends on the effective diffusion coefficient De of the cover materials. This paper presents an experimental procedure and results from oxygen diffusion tests performed on different types of materials, at various degrees of saturation. The determination of De in the laboratory from the test data is based on solutions to Fick's laws. The ensuing values of De are compared to values calculated from available models that relate De to basic material properties, including porosity and degree of saturation. Statistical indicators are used to evaluate the accuracy of selected models, individually and on a comparative basis. It is shown that modified versions of the Millington-Quirk and Millington-Shearer models provide De values close to the measured data. A semi-empirical expression, ensuing from these models and measurements, is proposed as a simple means of estimating De.
Scaling in the diffusion limited aggregation model.
Menshutin, Anton
2012-01-01
We present a self-consistent picture of diffusion limited aggregation (DLA) growth based on the assumption that the probability density P(r,N) for the next particle to be attached within the distance r to the center of the cluster is expressible in the scale-invariant form P[r/R{dep}(N)]. It follows from this assumption that there is no multiscaling issue in DLA and there is only a single fractal dimension D for all length scales. We check our assumption self-consistently by calculating the particle-density distribution with a measured P(r/R{dep}) function on an ensemble with 1000 clusters of 5×10{7} particles each. We also show that a nontrivial multiscaling function D(x) can be obtained only when small clusters (N<10 000) are used to calculate D(x). Hence, multiscaling is a finite-size effect and is not intrinsic to DLA. PMID:22304265
Cohabitation reaction-diffusion model for virus focal infections
NASA Astrophysics Data System (ADS)
Amor, Daniel R.; Fort, Joaquim
2014-12-01
The propagation of virus infection fronts has been typically modeled using a set of classical (noncohabitation) reaction-diffusion equations for interacting species. However, for some single-species systems it has been recently shown that noncohabitation reaction-diffusion equations may lead to unrealistic descriptions. We argue that previous virus infection models also have this limitation, because they assume that a virion can simultaneously reproduce inside a cell and diffuse away from it. For this reason, we build a several-species cohabitation model that does not have this limitation. Furthermore, we perform a sensitivity analysis for the most relevant parameters of the model, and we compare the predicted infection speed with observed data for two different strains of the T7 virus.
A Novel Restricted Diffusion Model of Evoked Dopamine
2015-01-01
In vivo fast-scan cyclic voltammetry provides high-fidelity recordings of electrically evoked dopamine release in the rat striatum. The evoked responses are suitable targets for numerical modeling because the frequency and duration of the stimulus are exactly known. Responses recorded in the dorsal and ventral striatum of the rat do not bear out the predictions of a numerical model that assumes the presence of a diffusion gap interposed between the recording electrode and nearby dopamine terminals. Recent findings, however, suggest that dopamine may be subject to restricted diffusion processes in brain extracellular space. A numerical model cast to account for restricted diffusion produces excellent agreement between simulated and observed responses recorded under a broad range of anatomical, stimulus, and pharmacological conditions. The numerical model requires four, and in some cases only three, adjustable parameters and produces meaningful kinetic parameter values. PMID:24983330
GUIDELINE FOR FLUID MODELING OF ATMOSPHERIC DIFFUSION
The fundamental principles for fluid modeling of flow and dispersion of pollutants in the atmospheric boundary layer are reviewed. The usefulness of fluid models are evaluated from both scientific and engineering viewpoints. Because many detailed decisions must be made during the...
Toxicological Models Part B: Environmental Models
NASA Astrophysics Data System (ADS)
Garric, Jeanne; Thybaud, Eric
Assessment of ecotoxicological risks due to chemical substances is based in part on establishing concentration-response relationships for different organisms, including plants, invertebrates, and vertebrates living on land, fresh water, or sea water. European regulations for assessing the risks due to chemical products thus recommend the measurement of toxic effects on at least three taxons (algae, crustacea, fish) [1]. The assessment becomes more relevant when based upon a variety of different organisms, with a range of different biological and ecological features (autotrophic or heterotrophic, benthic or pelagic habitat, and different modes of reproduction, growth, respiration, or feeding, etc.), but also when it describes the effects of contaminants on sensitive physiological functions such as growth and reproduction, which determine the balance of populations of terrestrial and aquatic species in their environment.
A Combinatorial Model of Malware Diffusion via Bluetooth Connections
Merler, Stefano; Jurman, Giuseppe
2013-01-01
We outline here the mathematical expression of a diffusion model for cellphones malware transmitted through Bluetooth channels. In particular, we provide the deterministic formula underlying the proposed infection model, in its equivalent recursive (simple but computationally heavy) and closed form (more complex but efficiently computable) expression. PMID:23555677
An Urban Diffusion Simulation Model for Carbon Monoxide
ERIC Educational Resources Information Center
Johnson, W. B.; And Others
1973-01-01
A relatively simple Gaussian-type diffusion simulation model for calculating urban carbon (CO) concentrations as a function of local meteorology and the distribution of traffic is described. The model can be used in two ways: in the synoptic mode and in the climatological mode. (Author/BL)
TURBULENT DIFFUSION BEHIND VEHICLES: EXPERIMENTS AND VERIFICATION OF ROADWAY MODELS
Tracer gas was released behind model vehicles in a moving floor wind tunnel and sampled extensively at various downwind distances. A numerical model was used to test various expressions for the eddy diffusion coefficients. The best formulation has been incorporated into the ROADW...
Diffusion approximation for modeling of 3-D radiation distributions
Zardecki, A.; Gerstl, S.A.W.; De Kinder, R.E. Jr.
1985-01-01
A three-dimensional transport code DIF3D, based on the diffusion approximation, is used to model the spatial distribution of radiation energy arising from volumetric isotropic sources. Future work will be concerned with the determination of irradiances and modeling of realistic scenarios, relevant to the battlefield conditions. 8 refs., 4 figs.
A combinatorial model of malware diffusion via bluetooth connections.
Merler, Stefano; Jurman, Giuseppe
2013-01-01
We outline here the mathematical expression of a diffusion model for cellphones malware transmitted through Bluetooth channels. In particular, we provide the deterministic formula underlying the proposed infection model, in its equivalent recursive (simple but computationally heavy) and closed form (more complex but efficiently computable) expression. PMID:23555677
A three-dimensional spin-diffusion model for micromagnetics
Abert, Claas; Ruggeri, Michele; Bruckner, Florian; Vogler, Christoph; Hrkac, Gino; Praetorius, Dirk; Suess, Dieter
2015-01-01
We solve a time-dependent three-dimensional spin-diffusion model coupled to the Landau-Lifshitz-Gilbert equation numerically. The presented model is validated by comparison to two established spin-torque models: The model of Slonzewski that describes spin-torque in multi-layer structures in the presence of a fixed layer and the model of Zhang and Li that describes current driven domain-wall motion. It is shown that both models are incorporated by the spin-diffusion description, i.e., the nonlocal effects of the Slonzewski model are captured as well as the spin-accumulation due to magnetization gradients as described by the model of Zhang and Li. Moreover, the presented method is able to resolve the time dependency of the spin-accumulation. PMID:26442796
A three-dimensional spin-diffusion model for micromagnetics.
Abert, Claas; Ruggeri, Michele; Bruckner, Florian; Vogler, Christoph; Hrkac, Gino; Praetorius, Dirk; Suess, Dieter
2015-01-01
We solve a time-dependent three-dimensional spin-diffusion model coupled to the Landau-Lifshitz-Gilbert equation numerically. The presented model is validated by comparison to two established spin-torque models: The model of Slonzewski that describes spin-torque in multi-layer structures in the presence of a fixed layer and the model of Zhang and Li that describes current driven domain-wall motion. It is shown that both models are incorporated by the spin-diffusion description, i.e., the nonlocal effects of the Slonzewski model are captured as well as the spin-accumulation due to magnetization gradients as described by the model of Zhang and Li. Moreover, the presented method is able to resolve the time dependency of the spin-accumulation. PMID:26442796
A three-dimensional spin-diffusion model for micromagnetics
NASA Astrophysics Data System (ADS)
Abert, Claas; Ruggeri, Michele; Bruckner, Florian; Vogler, Christoph; Hrkac, Gino; Praetorius, Dirk; Suess, Dieter
2015-10-01
We solve a time-dependent three-dimensional spin-diffusion model coupled to the Landau-Lifshitz-Gilbert equation numerically. The presented model is validated by comparison to two established spin-torque models: The model of Slonzewski that describes spin-torque in multi-layer structures in the presence of a fixed layer and the model of Zhang and Li that describes current driven domain-wall motion. It is shown that both models are incorporated by the spin-diffusion description, i.e., the nonlocal effects of the Slonzewski model are captured as well as the spin-accumulation due to magnetization gradients as described by the model of Zhang and Li. Moreover, the presented method is able to resolve the time dependency of the spin-accumulation.
Langevin equation with fluctuating diffusivity: A two-state model
NASA Astrophysics Data System (ADS)
Miyaguchi, Tomoshige; Akimoto, Takuma; Yamamoto, Eiji
2016-07-01
Recently, anomalous subdiffusion, aging, and scatter of the diffusion coefficient have been reported in many single-particle-tracking experiments, though the origins of these behaviors are still elusive. Here, as a model to describe such phenomena, we investigate a Langevin equation with diffusivity fluctuating between a fast and a slow state. Namely, the diffusivity follows a dichotomous stochastic process. We assume that the sojourn time distributions of these two states are given by power laws. It is shown that, for a nonequilibrium ensemble, the ensemble-averaged mean-square displacement (MSD) shows transient subdiffusion. In contrast, the time-averaged MSD shows normal diffusion, but an effective diffusion coefficient transiently shows aging behavior. The propagator is non-Gaussian for short time and converges to a Gaussian distribution in a long-time limit; this convergence to Gaussian is extremely slow for some parameter values. For equilibrium ensembles, both ensemble-averaged and time-averaged MSDs show only normal diffusion and thus we cannot detect any traces of the fluctuating diffusivity with these MSDs. Therefore, as an alternative approach to characterizing the fluctuating diffusivity, the relative standard deviation (RSD) of the time-averaged MSD is utilized and it is shown that the RSD exhibits slow relaxation as a signature of the long-time correlation in the fluctuating diffusivity. Furthermore, it is shown that the RSD is related to a non-Gaussian parameter of the propagator. To obtain these theoretical results, we develop a two-state renewal theory as an analytical tool.
Langevin equation with fluctuating diffusivity: A two-state model.
Miyaguchi, Tomoshige; Akimoto, Takuma; Yamamoto, Eiji
2016-07-01
Recently, anomalous subdiffusion, aging, and scatter of the diffusion coefficient have been reported in many single-particle-tracking experiments, though the origins of these behaviors are still elusive. Here, as a model to describe such phenomena, we investigate a Langevin equation with diffusivity fluctuating between a fast and a slow state. Namely, the diffusivity follows a dichotomous stochastic process. We assume that the sojourn time distributions of these two states are given by power laws. It is shown that, for a nonequilibrium ensemble, the ensemble-averaged mean-square displacement (MSD) shows transient subdiffusion. In contrast, the time-averaged MSD shows normal diffusion, but an effective diffusion coefficient transiently shows aging behavior. The propagator is non-Gaussian for short time and converges to a Gaussian distribution in a long-time limit; this convergence to Gaussian is extremely slow for some parameter values. For equilibrium ensembles, both ensemble-averaged and time-averaged MSDs show only normal diffusion and thus we cannot detect any traces of the fluctuating diffusivity with these MSDs. Therefore, as an alternative approach to characterizing the fluctuating diffusivity, the relative standard deviation (RSD) of the time-averaged MSD is utilized and it is shown that the RSD exhibits slow relaxation as a signature of the long-time correlation in the fluctuating diffusivity. Furthermore, it is shown that the RSD is related to a non-Gaussian parameter of the propagator. To obtain these theoretical results, we develop a two-state renewal theory as an analytical tool. PMID:27575079
Modelling of monovacancy diffusion in W over wide temperature range
Bukonte, L. Ahlgren, T.; Heinola, K.
2014-03-28
The diffusion of monovacancies in tungsten is studied computationally over a wide temperature range from 1300 K until the melting point of the material. Our modelling is based on Molecular Dynamics technique and Density Functional Theory. The monovacancy migration barriers are calculated using nudged elastic band method for nearest and next-nearest neighbour monovacancy jumps. The diffusion pre-exponential factor for monovacancy diffusion is found to be two to three orders of magnitude higher than commonly used in computational studies, resulting in attempt frequency of the order 10{sup 15} Hz. Multiple nearest neighbour jumps of monovacancy are found to play an important role in the contribution to the total diffusion coefficient, especially at temperatures above 2/3 of T{sub m}, resulting in an upward curvature of the Arrhenius diagram. The probabilities for different nearest neighbour jumps for monovacancy in W are calculated at different temperatures.
Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells
Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain
2014-06-06
It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately
Numerical modelling of swirling diffusive flames
NASA Astrophysics Data System (ADS)
Parra-Santos, Teresa; Perez, Ruben; Szasz, Robert Z.; Gutkowski, Artur N.; Castro, Francisco
2016-03-01
Computational Fluid Dynamics has been used to study the mixing and combustion of two confined jets whose setup and operating conditions are those of the benchmark of Roback and Johnson. Numerical model solves 3D transient Navier Stokes for turbulent and reactive flows. Averaged velocity profiles using RNG swirl dominated k-epsilon model have been validated with experimental measurements from other sources for the non reactive case. The combustion model is Probability Density Function. Bearing in mind the annular jet has swirl number over 0.5, a vortex breakdown appears in the axis of the burner. Besides, the sudden expansion with a ratio of 2 in diameter between nozzle exits and the test chamber produces the boundary layer separation with the corresponding torus shape recirculation. Contrasting the mixing and combustion models, the last one produces the reduction of the vortex breakdown.
Modelling on cavitation in a diffuser with vortex generator
NASA Astrophysics Data System (ADS)
Jablonská, J.
2013-04-01
Based on cavitation modelling in Laval nozzle results and experience, problem with the diffuser with vortex generator was defined. The problem describes unsteady multiphase flow of water. Different cavitation models were used when modelling in Fluent, flow condition is inlet and pressure condition is outlet. Boundary conditions were specified by Energy Institute, Victor Kaplan's Department of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Numerical modelling is compared with experiment.
Notes on the Langevin model for turbulent diffusion of ``marked`` particles
Rodean, H.C.
1994-01-26
Three models for scalar diffusion in turbulent flow (eddy diffusivity, random displacement, and on the Langevin equation) are briefly described. These models random velocity increment based Fokker-Planck equation is introduced as are then examined in more detail in the reverse order. The Fokker-Planck equation is the Eulerian equivalent of the Lagrangian Langevin equation, and the derivation of e outlined. The procedure for obtaining the deterministic and stochastic components of the Langevin equation from Kolmogorov`s 1941 inertial range theory and the Fokker-Planck equation is described. it is noted that a unique form of the Langevin equation can be determined for diffusion in one dimension but not in two or three. The Langevin equation for vertical diffusion in the non-Gaussian convective boundary layer is presented and successively simplified for Gaussian inhomogeneous turbulence and Gaussian homogeneous turbulence in turn. The Langevin equation for Gaussian inhomogeneous turbulence is mathematically transformed into the random displacement model. It is shown how the Fokker-Planck equation for the random displacement model is identical in form to the partial differential equation for the eddy diffusivity model. It is noted that the Langevin model is applicable in two cases in which the other two are not valid: (1) very close in time and distance to the point of scalar release and (2) the non-Gaussian convective boundary layer. The two- and three-dimensional cases are considered in Part III.
Evaluating the accuracy of diffusion MRI models in white matter.
Rokem, Ariel; Yeatman, Jason D; Pestilli, Franco; Kay, Kendrick N; Mezer, Aviv; van der Walt, Stefan; Wandell, Brian A
2015-01-01
Models of diffusion MRI within a voxel are useful for making inferences about the properties of the tissue and inferring fiber orientation distribution used by tractography algorithms. A useful model must fit the data accurately. However, evaluations of model-accuracy of commonly used models have not been published before. Here, we evaluate model-accuracy of the two main classes of diffusion MRI models. The diffusion tensor model (DTM) summarizes diffusion as a 3-dimensional Gaussian distribution. Sparse fascicle models (SFM) summarize the signal as a sum of signals originating from a collection of fascicles oriented in different directions. We use cross-validation to assess model-accuracy at different gradient amplitudes (b-values) throughout the white matter. Specifically, we fit each model to all the white matter voxels in one data set and then use the model to predict a second, independent data set. This is the first evaluation of model-accuracy of these models. In most of the white matter the DTM predicts the data more accurately than test-retest reliability; SFM model-accuracy is higher than test-retest reliability and also higher than the DTM model-accuracy, particularly for measurements with (a) a b-value above 1000 in locations containing fiber crossings, and (b) in the regions of the brain surrounding the optic radiations. The SFM also has better parameter-validity: it more accurately estimates the fiber orientation distribution function (fODF) in each voxel, which is useful for fiber tracking. PMID:25879933
Evaluating the Accuracy of Diffusion MRI Models in White Matter
Rokem, Ariel; Yeatman, Jason D.; Pestilli, Franco; Kay, Kendrick N.; Mezer, Aviv; van der Walt, Stefan; Wandell, Brian A.
2015-01-01
Models of diffusion MRI within a voxel are useful for making inferences about the properties of the tissue and inferring fiber orientation distribution used by tractography algorithms. A useful model must fit the data accurately. However, evaluations of model-accuracy of commonly used models have not been published before. Here, we evaluate model-accuracy of the two main classes of diffusion MRI models. The diffusion tensor model (DTM) summarizes diffusion as a 3-dimensional Gaussian distribution. Sparse fascicle models (SFM) summarize the signal as a sum of signals originating from a collection of fascicles oriented in different directions. We use cross-validation to assess model-accuracy at different gradient amplitudes (b-values) throughout the white matter. Specifically, we fit each model to all the white matter voxels in one data set and then use the model to predict a second, independent data set. This is the first evaluation of model-accuracy of these models. In most of the white matter the DTM predicts the data more accurately than test-retest reliability; SFM model-accuracy is higher than test-retest reliability and also higher than the DTM model-accuracy, particularly for measurements with (a) a b-value above 1000 in locations containing fiber crossings, and (b) in the regions of the brain surrounding the optic radiations. The SFM also has better parameter-validity: it more accurately estimates the fiber orientation distribution function (fODF) in each voxel, which is useful for fiber tracking. PMID:25879933
Hierarchical set of models to estimate soil thermal diffusivity
NASA Astrophysics Data System (ADS)
Arkhangelskaya, Tatiana; Lukyashchenko, Ksenia
2016-04-01
Soil thermal properties significantly affect the land-atmosphere heat exchange rates. Intra-soil heat fluxes depend both on temperature gradients and soil thermal conductivity. Soil temperature changes due to energy fluxes are determined by soil specific heat. Thermal diffusivity is equal to thermal conductivity divided by volumetric specific heat and reflects both the soil ability to transfer heat and its ability to change temperature when heat is supplied or withdrawn. The higher soil thermal diffusivity is, the thicker is the soil/ground layer in which diurnal and seasonal temperature fluctuations are registered and the smaller are the temperature fluctuations at the soil surface. Thermal diffusivity vs. moisture dependencies for loams, sands and clays of the East European Plain were obtained using the unsteady-state method. Thermal diffusivity of different soils differed greatly, and for a given soil it could vary by 2, 3 or even 5 times depending on soil moisture. The shapes of thermal diffusivity vs. moisture dependencies were different: peak curves were typical for sandy soils and sigmoid curves were typical for loamy and especially for compacted soils. The lowest thermal diffusivities and the smallest range of their variability with soil moisture were obtained for clays with high humus content. Hierarchical set of models will be presented, allowing an estimate of soil thermal diffusivity from available data on soil texture, moisture, bulk density and organic carbon. When developing these models the first step was to parameterize the experimental thermal diffusivity vs. moisture dependencies with a 4-parameter function; the next step was to obtain regression formulas to estimate the function parameters from available data on basic soil properties; the last step was to evaluate the accuracy of suggested models using independent data on soil thermal diffusivity. The simplest models were based on soil bulk density and organic carbon data and provided different
NASA Astrophysics Data System (ADS)
Mizia, Ronald E.; Clark, Denis E.; Glazoff, Michael V.; Lister, Tedd E.; Trowbridge, Tammy L.
2013-01-01
A research effort was made to evaluate the usefulness of modern thermodynamic and diffusion computational tools, Thermo-Calc and Dictra (Thermo_Calc Software, Inc., McMurray, PA), in optimizing the parameters for diffusion welding of Alloy 800H. This would achieve a substantial reduction in the overall number of experiments required to achieve optimal welding and post-weld heat treatment conditions. This problem is important because diffusion-welded components of Alloy 800H are being evaluated for use in assembling compact, micro-channel heat exchangers that are being proposed in the design of a high-temperature, gas-cooled reactor by the U.S. Department of Energy. The modeling was done in close contact with experimental work. The latter included using the Gleeble 3500 System (Dynamic Systems, Inc., Poestenkill, NY) for welding simulation, mechanical property measurement, and light optical and scanning electron microscopy. The modeling efforts suggested a temperature of 1423 K (1150 °C) for 1 hour with an applied pressure of 5 MPa using a 15- μm Ni foil as joint filler to reduce chromium oxidation on the welded surfaces. Good agreement between modeled and experimentally determined concentration gradients was achieved, and model refinements to account for the complexity of actual alloy materials are suggested.
A multiple mapping conditioning model for differential diffusion
NASA Astrophysics Data System (ADS)
Dialameh, L.; Cleary, M. J.; Klimenko, A. Y.
2014-02-01
This work introduces modeling of differential diffusion within the multiple mapping conditioning (MMC) turbulent mixing and combustion framework. The effect of differential diffusion on scalar variance decay is analyzed and, following a number of publications, is found to scale as Re-1/2. The ability to model the differential decay rates is the most important aim of practical differential diffusion models, and here this is achieved in MMC by introducing what is called the side-stepping method. The approach is practical and, as it does not involve an increase in the number of MMC reference variables, economical. In addition we also investigate the modeling of a more refined and difficult to reproduce differential diffusion effect - the loss of correlation between the different scalars. For this we develop an alternative MMC model with two reference variables but which also makes use of the side-stepping method. The new models are successfully validated against DNS results available in literature for homogenous, isotropic two scalar mixing.
Models of geochemical systems from mixture theory: diffusion
Kirwan, A.D. Jr; Kump, L.R.
1987-05-01
The problem of diffusion of a geochemical component in a natural environment is investigated from the standpoint of mixture theory. The approach here differs from previous diffusion studies in that both the conservation of mass and momentum for the component is considered. This approach avoids parameterizing the diffusive flux in the mass equation by Fick's law. It is shown that when the momentum equation is included with the mass equation, the linear approximation for the space-time distribution of a solute in a binary system is the telegraph equation, well known from electrodynamics. This contrasts with the diffusion equation, which relies on introducing the Fick's law assumption into the conservation of mass equation for the solute. Solutions for both the diffusion and telegraph equation models are obtained and compared for the case of migration of a minor component into the sea bed when the sediment-water interface concentration is a prescribed function of time. Although the stationary, steady state solutions of the telegraph and diffusion equations are identical, the former has a transient solution in which fluctuations propagate at finite speed. The Fickian assumption, in contrast, requires an infinite speed of propagation.
Modeling of slow glutamate diffusion and AMPA receptor activation in the cerebellar glomerulus.
Saftenku, E E
2005-06-01
Synaptic conductances are influenced markedly by the geometry of the space surrounding the synapse since the transient glutamate concentration in the synaptic cleft is determined by this geometry. Our paper is an attempt to understand the reasons for slow glutamate diffusion in the cerebellar glomerulus, a structure situated around the enlarged mossy fiber terminal in the cerebellum and surrounded by a glial sheath. For this purpose, analytical expressions for glutamate diffusion in the glomerulus were considered in models with two-, three-, and fractional two-three-dimensional (2D-3D) geometry with an absorbing boundary. The time course of average glutamate concentration in the synaptic cleft of the mossy fiber-granule cell connection was calculated for both direct release of glutamate from the same synaptic unit, and for cumulative spillover of glutamate from neighboring release sites. Several kinetic schemes were examined, and the parameters of the diffusion models were estimated by identifying theoretical activation of AMPA receptors with direct release and spillover components of published experimental AMPA receptor-mediated EPSCs. For model selection, the correspondence of simulated paired-pulse ratio and EPSC increase after prevention of desensitization to experimental values were also taken into consideration. Our results suggest at least a 7- to 10-fold lower apparent diffusion coefficient of glutamate in the porous medium of the glomerulus than in water. The modeling of glutamate diffusion in the 2D-3D geometry gives the best fit of experimental EPSCs. We show that it could be only partly explained by normal diffusion of glutamate in the complex geometry of the glomerulus. We assume that anomalous diffusion of glutamate occurs in the glomerulus. A good match of experimental estimations and theoretical parameters, obtained in the simulations that use an approximation of anomalous diffusion by a solution for fractional Brownian motion, confirms our
Evaluation of the Diffusive Equilibrium Models by the IMAGE RPI
NASA Astrophysics Data System (ADS)
Ozhogin, Pavel; Reinisch, Bodo W.; Song, Paul; Tu, Jiannan
2013-04-01
Using measured field-aligned electron density profiles, this study investigates the validity of the diffusive equilibrium model in Earth's plasmasphere. This model which describes the electron and ion densities along a magnetic field line in the plasmasphere has been widely used for ray tracing and pitch-angle scattering calculations. It is based on the hydrostatic equilibrium with the electrostatic force that acts on ions and electrons along geomagnetic field lines while actually there is no motion or diffusion of the plasma involved. The model requires multiple input parameters: electron density and ion composition (H+, He+, O+) at a base level for a magnetic field line in the ionosphere, and the (electron or ion) temperature in the plasmasphere. It has been recognized that these input parameters have to be flexible from one field line to another so that the model output does not contradict some known observed relationships. However, while the flexibility provides the possibility to fit any individual observed density distribution which is measured across many different field lines, the model prediction becomes questionable along a single field line. Before the launch of the IMAGE satellite in 2000 no plasma density measurements along a single field line were available, and therefore the validity of the diffusive equilibrium models had not been independently verified. Our qualitative and quantitative analysis shows that the fundamental functional form of the diffusive equilibrium model is inconsistent with the large database of field-aligned electron density distributions obtained by the radio plasma imager (RPI) instrument onboard the IMAGE satellite. Review of the procedures used in the derivation of the original diffusive equilibrium model suggests that the physical processes described by the mathematical procedures are fundamentally incorrect.
NASA Technical Reports Server (NTRS)
Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.; Paloski, William H. (Technical Monitor)
2000-01-01
A three-region mathematical model of gas bubble dynamics has been shown suitable for describing diffusion-limited dynamics of more than one bubble in a given volume of extravascular tissue. The model is based on the dynamics of gas exchange between a bubble and a well-stirred tissue region through an intervening unperfused diffusion region previously assumed to have constant thickness and uniform gas diffusivity. As a result, the gas content of the diffusion region remains constant as the volume of the region increases with bubble growth, causing dissolved gas in the region to violate Henry's law. Earlier work also neglected the relationship between the varying diffusion region volume and the fixed total tissue volume, because only cases in which the diffusion region volume is a small fraction of the overall tissue volume were considered. We herein extend the three-region model to correct these theoretical inconsistencies by allowing both the thickness and gas content of the diffusion region to vary during bubble evolution. A postulated difference in gas diffusivity between an infinitesimally thin layer at the bubble surface and the remainder of the diffusion region leads to variation in diffusion region gas content and thickness during bubble growth and resolution. This variable thickness, differential diffusivity (VTDD) model can yield bubble lifetimes considerably longer than those yielded by earlier three-region models for given model and decompression parameters, and meets a need for theoretically consistent but relatively simple bubble dynamics models for use in studies of decompression sickness (DCS) in human subjects, Keywords: decompression sickness, gas diffusion in tissue, diffusivity
Some Approaches to Modeling Diffuse Flow at Mid-Ocean Ridges
NASA Astrophysics Data System (ADS)
Farough, A.; Lowell, R. P.; Craft, K.; Germanovich, L. N.
2011-12-01
To obtain a sound understanding of subsurface temperatures and the extent of the subsurface biosphere in young oceanic crust, one must understand the mechanisms of diffuse flow at oceanic spreading centers. Mathematical modeling of diffuse flow at oceanic spreading centers has received relatively little attention compared to high-temperature black smoker discharge, in part because the temperature and fluid flow data required to constrain the models are scarce. We review a number of different approaches to modelling diffuse flow: (1) The simplest method considers 1-D steady-state uniform upflow from below subject to a heat transfer boundary condition at the surface, which represents the effects of mixing of hydrothermal fluid with seawater. These models, in which the heat transfer coefficient and the velocity of the ascending fluid are constrained by observed diffuse flow vent temperature and heat flux, typically result in a steep temperature gradient near the seafloor and subsurface biological activity may be limited to the upper few cm of the crust. (2) A related method uses data on the partitioning of heat flux between focused and diffuse flow and chemical data from the focused and diffuse flow components in a two-limb single pass modeling approach to determine the fraction of high-temperature fluid that is incorporated in the diffuse flow. Using data available from EPR 950', the Main Endeavour Field, and ASHES vent field at Axial Volcano on the Juan de Fuca Ridge in conjunction with Mg as a passive tracer, we find that the mixing ratio of high temperature in diffuse flow is <10%. The high-temperature contribution to the diffuse heat flux remains large, however, and high-temperature vent fluid ultimately contributes ~ 90% of the total heat output from the vent field. In these models mixing between high-temperature fluid and seawater may occur over a considerable depth, and the subsurface biosphere may be ~ 100 m deep beneath diffuse flow sites. (3) Finally, in
Computer modelling of nanoscale diffusion phenomena at epitaxial interfaces
NASA Astrophysics Data System (ADS)
Michailov, M.; Ranguelov, B.
2014-05-01
The present study outlines an important area in the application of computer modelling to interface phenomena. Being relevant to the fundamental physical problem of competing atomic interactions in systems with reduced dimensionality, these phenomena attract special academic attention. On the other hand, from a technological point of view, detailed knowledge of the fine atomic structure of surfaces and interfaces correlates with a large number of practical problems in materials science. Typical examples are formation of nanoscale surface patterns, two-dimensional superlattices, atomic intermixing at an epitaxial interface, atomic transport phenomena, structure and stability of quantum wires on surfaces. We discuss here a variety of diffusion mechanisms that control surface-confined atomic exchange, formation of alloyed atomic stripes and islands, relaxation of pure and alloyed atomic terraces, diffusion of clusters and their stability in an external field. The computational model refines important details of diffusion of adatoms and clusters accounting for the energy barriers at specific atomic sites: smooth domains, terraces, steps and kinks. The diffusion kinetics, integrity and decomposition of atomic islands in an external field are considered in detail and assigned to specific energy regions depending on the cluster stability in mass transport processes. The presented ensemble of diffusion scenarios opens a way for nanoscale surface design towards regular atomic interface patterns with exotic physical features.
GIS-BASED 1-D DIFFUSIVE WAVE OVERLAND FLOW MODEL
KALYANAPU, ALFRED; MCPHERSON, TIMOTHY N.; BURIAN, STEVEN J.
2007-01-17
This paper presents a GIS-based 1-d distributed overland flow model and summarizes an application to simulate a flood event. The model estimates infiltration using the Green-Ampt approach and routes excess rainfall using the 1-d diffusive wave approximation. The model was designed to use readily available topographic, soils, and land use/land cover data and rainfall predictions from a meteorological model. An assessment of model performance was performed for a small catchment and a large watershed, both in urban environments. Simulated runoff hydrographs were compared to observations for a selected set of validation events. Results confirmed the model provides reasonable predictions in a short period of time.
Cosmic ray anisotropy in fractional differential models of anomalous diffusion
Uchaikin, V. V.
2013-06-15
The problem of galactic cosmic ray anisotropy is considered in two versions of the fractional differential model for anomalous diffusion. The simplest problem of cosmic ray propagation from a point instantaneous source in an unbounded medium is used as an example to show that the transition from the standard diffusion model to the Lagutin-Uchaikin fractional differential model (with characteristic exponent {alpha} = 3/5 and a finite velocity of free particle motion), which gives rise to a knee in the energy spectrum at 10{sup 6} GeV, increases the anisotropy coefficient only by 20%, while the anisotropy coefficient in the Lagutin-Tyumentsev model (with exponents {alpha} = 0.3 and {beta} = 0.8, a long stay of particles in traps, and an infinite velocity of their jumps) is close to one. This is because the parameters of the Lagutin-Tyumentsev model have been chosen improperly.
Turing instability in reaction-diffusion models on complex networks
NASA Astrophysics Data System (ADS)
Ide, Yusuke; Izuhara, Hirofumi; Machida, Takuya
2016-09-01
In this paper, the Turing instability in reaction-diffusion models defined on complex networks is studied. Here, we focus on three types of models which generate complex networks, i.e. the Erdős-Rényi, the Watts-Strogatz, and the threshold network models. From analysis of the Laplacian matrices of graphs generated by these models, we numerically reveal that stable and unstable regions of a homogeneous steady state on the parameter space of two diffusion coefficients completely differ, depending on the network architecture. In addition, we theoretically discuss the stable and unstable regions in the cases of regular enhanced ring lattices which include regular circles, and networks generated by the threshold network model when the number of vertices is large enough.
NASA Astrophysics Data System (ADS)
Chau, J. F.; Or, D.; Jones, S.; Sukop, M.
2004-05-01
Liquid distribution in unsaturated porous media under different gravitational forces and resulting gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. Different fluid behavior in plant growth media under microgravity conditions as compared to earth presents a challenge to plant growth in long duration space exploration missions. Our primary objective was to provide qualitative description and quantitative measures of the role of reduced gravity on hydraulic and gaseous transport properties in simulated porous media. We implemented a multi-phase lattice Boltzmann code for equilibrium distribution of liquid in an idealized two-dimensional porous medium under microgravity and "normal" gravity conditions. The information was then used to provide boundary conditions for simulation of gaseous diffusion through the equilibrium domains (considering diffusion through liquid phase negligibly small). The models were tested by comparison with several analytical solutions to the diffusion equation, with excellent results. The relative diffusion coefficient for both series of simulations (with and without gravity) as functions of air-filled porosity was in good agreement with established models of Millington-Quirk. Liquid distribution under earth's gravity featured increased water content at the lower part of the medium relative to the distribution in reduced gravity, which resulted in decreased gas diffusion through a vertically oriented column of a porous medium. Simulation results for larger domains under various orientations will be presented.
Final Report - Experiments and Models for Chemical Diffusion in Silicate Melts
Richter, Frank
1999-10-01
The final report describes experimental measurements of chemical diffusion and self-diffusion in silicate melts. The data are then used to validate a theoretical model for calculating the diffusion matrix of non-ideal liquids.
A Mixed-Culture Biofilm Model with Cross-Diffusion.
Rahman, Kazi A; Sudarsan, Rangarajan; Eberl, Hermann J
2015-11-01
We propose a deterministic continuum model for mixed-culture biofilms. A crucial aspect is that movement of one species is affected by the presence of the other. This leads to a degenerate cross-diffusion system that generalizes an earlier single-species biofilm model. Two derivations of this new model are given. One, like cellular automata biofilm models, starts from a discrete in space lattice differential equation where the spatial interaction is described by microscopic rules. The other one starts from the same continuous mass balances that are the basis of other deterministic biofilm models, but it gives up a simplifying assumption of these models that has recently been criticized as being too restrictive in terms of ecological structure. We show that both model derivations lead to the same PDE model, if corresponding closure assumptions are introduced. To investigate the role of cross-diffusion, we conduct numerical simulations of three biofilm systems: competition, allelopathy and a mixed system formed by an aerobic and an anaerobic species. In all cases, we find that accounting for cross-diffusion affects local distribution of biomass, but it does not affect overall lumped quantities such as the total amount of biomass in the system. PMID:26582360
Modeling intragranular diffusion in low-connectivity granular media
NASA Astrophysics Data System (ADS)
Ewing, Robert P.; Liu, Chongxuan; Hu, Qinhong
2012-03-01
Characterizing the diffusive exchange of solutes between bulk water in an aquifer and water in the intragranular pores of the solid phase is still challenging despite decades of study. Many disparities between observation and theory could be attributed to low connectivity of the intragranular pores. The presence of low connectivity indicates that a useful conceptual framework is percolation theory. The present study was initiated to develop a percolation-based finite difference (FD) model, and to test it rigorously against both random walk (RW) simulations of diffusion starting from nonequilibrium, and data on Borden sand published by Ball and Roberts (1991a,b) and subsequently reanalyzed by Haggerty and Gorelick (1995) using a multirate mass transfer (MRMT) approach. The percolation-theoretical model is simple and readily incorporated into existing FD models. The FD model closely matches the RW results using only a single fitting parameter, across a wide range of pore connectivities. Simulation of the Borden sand experiment without pore connectivity effects reproduced the MRMT analysis, but including low pore connectivity effects improved the fit. Overall, the theory and simulation results show that low intragranular pore connectivity can produce diffusive behavior that appears as if the solute had undergone slow sorption, despite the absence of any sorption process, thereby explaining some hitherto confusing aspects of intragranular diffusion.
Modeling development of inhibition zones in an agar diffusion bioassay.
Chandrasekar, Vaishnavi; Knabel, Stephen J; Anantheswaran, Ramaswamy C
2015-09-01
A two-temperature agar diffusion bioassay is commonly used to quantify the concentration of nisin using Micrococcus luteus as the indicator microorganism. A finite element computational model based on Fick's second law of diffusion was used to predict the radius of the inhibition zone in this diffusion bioassay. The model developed was used to calculate nisin concentration profiles as a function of time and position within the agar. The minimum inhibitory concentration (MIC) of nisin against M. luteus was determined experimentally. The critical time (T c) for growth of M. luteus within the agar diffusion bioassay was experimentally determined using incubation studies with nisin. The radius of the inhibition zone was predicted from the computational model as the location where the predicted nisin concentration at T c was equal to MIC. The MIC was experimentally determined to be 0.156 μg mL(-1), and T c was determined to be 7 h. Good agreement (R (2) = 0.984) was obtained between model-predicted and experimentally determined inhibition zone radii. PMID:26405525
Reaction Diffusion Modeling of Calcium Dynamics with Realistic ER Geometry
Means, Shawn; Smith, Alexander J.; Shepherd, Jason; Shadid, John; Fowler, John; Wojcikiewicz, Richard J. H.; Mazel, Tomas; Smith, Gregory D.; Wilson, Bridget S.
2006-01-01
We describe a finite-element model of mast cell calcium dynamics that incorporates the endoplasmic reticulum's complex geometry. The model is built upon a three-dimensional reconstruction of the endoplasmic reticulum (ER) from an electron tomographic tilt series. Tetrahedral meshes provide volumetric representations of the ER lumen, ER membrane, cytoplasm, and plasma membrane. The reaction-diffusion model simultaneously tracks changes in cytoplasmic and ER intraluminal calcium concentrations and includes luminal and cytoplasmic protein buffers. Transport fluxes via PMCA, SERCA, ER leakage, and Type II IP3 receptors are also represented. Unique features of the model include stochastic behavior of IP3 receptor calcium channels and comparisons of channel open times when diffusely distributed or aggregated in clusters on the ER surface. Simulations show that IP3R channels in close proximity modulate activity of their neighbors through local Ca2+ feedback effects. Cytoplasmic calcium levels rise higher, and ER luminal calcium concentrations drop lower, after IP3-mediated release from receptors in the diffuse configuration. Simulation results also suggest that the buffering capacity of the ER, and not restricted diffusion, is the predominant factor influencing average luminal calcium concentrations. PMID:16617072
Modeling development of inhibition zones in an agar diffusion bioassay
Chandrasekar, Vaishnavi; Knabel, Stephen J; Anantheswaran, Ramaswamy C
2015-01-01
A two-temperature agar diffusion bioassay is commonly used to quantify the concentration of nisin using Micrococcus luteus as the indicator microorganism. A finite element computational model based on Fick's second law of diffusion was used to predict the radius of the inhibition zone in this diffusion bioassay. The model developed was used to calculate nisin concentration profiles as a function of time and position within the agar. The minimum inhibitory concentration (MIC) of nisin against M. luteus was determined experimentally. The critical time (Tc) for growth of M. luteus within the agar diffusion bioassay was experimentally determined using incubation studies with nisin. The radius of the inhibition zone was predicted from the computational model as the location where the predicted nisin concentration at Tc was equal to MIC. The MIC was experimentally determined to be 0.156 μg mL−1, and Tc was determined to be 7 h. Good agreement (R2 = 0.984) was obtained between model-predicted and experimentally determined inhibition zone radii. PMID:26405525
ANALYTICAL DIFFUSION MODEL FOR LONG DISTANCE TRANSPORT OF AIR POLLUTANTS
A steady-state two-dimensional diffusion model suitable for predicting ambient air pollutant concentrations averaged over a long time period (e.g., month, season, or year) and resulting from the transport of pollutants for distances greater than about 100 km from the source is de...
Decomposing Task-Switching Costs with the Diffusion Model
ERIC Educational Resources Information Center
Schmitz, Florian; Voss, Andreas
2012-01-01
In four experiments, task-switching processes were investigated with variants of the alternating runs paradigm and the explicit cueing paradigm. The classical diffusion model for binary decisions (Ratcliff, 1978) was used to dissociate different components of task-switching costs. Findings can be reconciled with the view that task-switching…
User's Manual for the APRAC-1A Urban Diffusion Model Computer Program.
ERIC Educational Resources Information Center
Mancuso, R. L.; And Others
The APRAC-1A diffusion model was developed as a versatile and practical model for computing the concentrations of pollutants at any point within a city. The model calculates pollutant contributions from diffusion on various scales, including: extra-urban diffusion, mainly from sources in upwind cities; intra-urban diffusion from freeway, arterial,…
Plaque fluid and diffusion: study of the cariogenic challenge by computer modeling.
Dibdin, G H
1990-06-01
Every cariogenic challenge involves a mixture of convective transport, diffusive transport, and biochemical reactions, plus physico-chemical reactions (including charge-coupling of diffusion), all of which together require numerical methods for their analysis. This presentation describes a one-dimensional finite-difference computer model of the cariogenic process, and some conclusions obtained from it. Sugar clearance from the mouth, together with site-dependent exchange between the bulk saliva and plaque surface via a salivary film, is combined with a finite-difference model of events occurring within the dental plaque. The latter includes: sugar diffusion and pH-dependent acid production; diffusion and dissociation equilibria for two acid end-products of fermentation and their anions (acetate and lactate); diffusion and dissociation equilibria of phosphate buffer; diffusion of potassium and chloride; diffusion of protons and simultaneous equilibration with fixed and mobile buffers. So that proper concentration distributions consistent with local charge neutrality can be ensured, an algorithm called Q-couple is used to impose charge-coupling between the fluxes of different ions including fixed charges. Mineral dissolution and precipitation are modeled as part of the same equilibrium calculations. The predictions of the model are compared with those of an earlier, much simpler one, in which fixed buffers were not included. It is shown that the known concentration of fixed buffer greatly extends the low pH of a Stephan curve. The isoelectric point of the plaque bacteria also appears to be of importance. The effects of various concentrations of mobile buffers, including acetate, are investigated. It is also shown that varying plaque/saliva contact over the known range derived from published studies has a profound effect on the modeled cariogenic challenge. PMID:2355127
Auto-stratification in drying colloidal dispersions: a diffusive model.
Trueman, R E; Lago Domingues, E; Emmett, S N; Murray, M W; Routh, A F
2012-07-01
The mechanism by which the particles in a drying film come into close packing during solvent evaporation has an important role to play in the final film morphology. During drying the particles can develop non-uniform concentrations across the vertical height of the film, depending on their diffusion rate. By applying the principles of classical diffusion mechanics to a hard sphere system, a theory for this novel method of stratification during drying of a two component film has been derived. The model is dependent on the particle Peclet numbers and when one is above unity and the other below, maximum stratification is observed. PMID:22503626
Modeling the diffusion of phosphorus in silicon in 3-D
Baker, K.R.
1994-12-31
The use of matrix preconditioning in semiconductor process simulation is examined. The simplified nonlinear single-species model for the diffusion of phosphorus into silicon is considered. The experimental three-dimensional simulator, PEPPER3, which uses finite differences and the numerical method of lines to implement the reaction-diffusion equation is modified to allow NSPCG to be called to solve the linear system in the inner Newton loop. Use of NSPCG allowed various accelerators such as Generalized Minimal Residual (GMRES) and Conjugate Gradient (CG) to be used in conjunction with preconditioners such as Richardson, Jacobi, and Incomplete Cholesky.
Reaction-diffusion modelling of bacterial colony patterns
NASA Astrophysics Data System (ADS)
Mimura, Masayasu; Sakaguchi, Hideo; Matsushita, Mitsugu
2000-07-01
It is well known from experiments that bacterial species Bacillus subtilis exhibit various colony patterns. These are essentially classified into five types in the morphological diagram, depending on the substrate softness and nutrient concentration. (A) diffusion-limited aggregation-like; (B) Eden-like; (C) concentric ring-like; (D) disk-like; and (E) dense branching morphology-like. There arises the naive question of whether the diversity of colony patterns observed in experiments is caused by different effects or governed by the same underlying principles. Our research has led us to propose reaction-diffusion models to describe the morphological diversity of colony patterns except for Eden-like ones.
Transport Corrections in Nodal Diffusion Codes for HTR Modeling
Abderrafi M. Ougouag; Frederick N. Gleicher
2010-08-01
The cores and reflectors of High Temperature Reactors (HTRs) of the Next Generation Nuclear Plant (NGNP) type are dominantly diffusive media from the point of view of behavior of the neutrons and their migration between the various structures of the reactor. This means that neutron diffusion theory is sufficient for modeling most features of such reactors and transport theory may not be needed for most applications. Of course, the above statement assumes the availability of homogenized diffusion theory data. The statement is true for most situations but not all. Two features of NGNP-type HTRs require that the diffusion theory-based solution be corrected for local transport effects. These two cases are the treatment of burnable poisons (BP) in the case of the prismatic block reactors and, for both pebble bed reactor (PBR) and prismatic block reactor (PMR) designs, that of control rods (CR) embedded in non-multiplying regions near the interface between fueled zones and said non-multiplying zones. The need for transport correction arises because diffusion theory-based solutions appear not to provide sufficient fidelity in these situations.
Atomic scale modeling of boron transient diffusion in silicon
Caturla, M. J.; Diaz de la Rubia, T.; Foad, M.; Giles, M.; Johnson, M. D.; Law, M.; Lilak, A.
1998-06-17
We presents results from a predictive atomic level simulation of Boron diffusion in Silicon under a wide variety of implant and annealing conditions. The parameters for this simulation have been extracted from first principle approximation models and molecular dynamics simulations. The results are compared with experiments showing good agreement in all cases. The parameters and reactions used have been implemented into a continuum-level model simulator.
Fitting degradation of shoreline scarps by a nonlinear diffusion model
Andrews, D.J.; Buckna, R.C.
1987-01-01
The diffusion model of degradation of topographic features is a promising means by which vertical offsets on Holocene faults might be dated. In order to calibrate the method, we have examined present-day profiles of wave-cut shoreline scarps of late Pleistocene lakes Bonneville and Lahontan. A table is included that allows easy application of the model to scarps with simple initial shape. -from Authors
NASA Astrophysics Data System (ADS)
Ben, Igor; Layosh, Yonatan Y.; Granot, Er'el
2016-06-01
A Monte Carlo simulation was utilized to investigate a simple model for the transition between the ballistic and the diffusive regimes in diffusive media. The simulation focuses on the propagation of visible and near-infrared light in biological tissues. This research has mainly two findings: (1) the transition can be described, as was found experimentally, with good accuracy by only two terms (ballistic and diffusive). (2) The model can be utilized for cases where the absorption coefficient is not negligible compared to the scattering coefficient by adding a power-law prefactor to the diffusive term.
Stellar models with microscopic diffusion and rotational mixing. 1: Application to the Sun
NASA Technical Reports Server (NTRS)
Chaboyer, Brian; Demarque, P.; Pinsonneault, M. H.
1995-01-01
The Yale stellar evolution code has been modified to include the combined effects of diffusion and rotational mixing on H-1, H-4, and the trace elements He, Li-6, Li-7, and Be-9. The interaction between rotational mixing and diffusion is studied by calculating a number of calibrated solar models. The rotational mixing inhibits the diffusion in the outer parts of the models, leading to a decrease in the envelope diffusion by 25%-50%. Conversely, diffusion leads to gradients in mean molecular weight which can inhibit the rotational mixing. The degree to which gradients in mean molecular weight inhibit the rotational mixing is somewhat uncertain. A comparison with the observed solar oblateness suggests that gradients in the mean molecular weight play a smaller role in inhibiting the rotational mixing than previously believed. This is reinforced by the fact that the model with the standard value for the inhibiting effect of mean molecular weight on the rotational mixing depletes no Li on the main sequence. This is clear in contrast to the observations. A reduction in the inhibiting effect of mean molecular weight gradients by a factor of 10 loads to noticeable main-sequence Li depletion.
Modeling aerosol formation in opposed-flow diffusion flames.
Violi, Angela; D'Anna, Andrea; D'Alessio, Antonio; Sarofim, Adel F
2003-06-01
The microstructures of atmospheric pressure, counter-flow, sooting, flat, laminar ethylene diffusion flames have been studied numerically by using a new kinetic model developed for hydrocarbon oxidation and pyrolysis. Modeling results are in reasonable agreement with experimental data in terms of concentration profiles of stable species and gas-phase aromatic compounds. Modeling results are used to analyze the controlling steps of aromatic formation and soot growth in counter-flow configurations. The formation of high molecular mass aromatics in diffusion controlled conditions is restricted to a narrow area close to the flame front where these species reach a molecular weight of about 1000 u. Depending on the flame configuration, soot formation is controlled by the coagulation of nanoparticles or by the addition of PAH to soot nuclei. PMID:12718969
A model of the diffuse galactic gamma ray emission
NASA Technical Reports Server (NTRS)
Sreekumar, Parameswaran
1990-01-01
The galaxy was observed to be a source of high energy gamma rays as shown by the two successful satellite experiments, SAS-2 and COS-B. It is generally understood that these diffuse gamma rays result from interactions between energetic cosmic rays and interstellar gas. This work makes use of the most recent data on the distribution of atomic and molecular hydrogen in the galaxy along with new estimates of gamma ray production functions to model the diffuse galactic gamma ray emission. The model allows various spatial distributions for cosmic rays in the Galaxy including non-axisymmetric ones. In the light of the expected data from EGRET (Energetic Gamma-Ray Experiment Telescope), an improved model of cosmic ray-matter-gamma ray interaction will provide new insights into the distribution of cosmic rays and the strength of its coupling to matter.
Numerical modelling and image reconstruction in diffuse optical tomography
Dehghani, Hamid; Srinivasan, Subhadra; Pogue, Brian W.; Gibson, Adam
2009-01-01
The development of diffuse optical tomography as a functional imaging modality has relied largely on the use of model-based image reconstruction. The recovery of optical parameters from boundary measurements of light propagation within tissue is inherently a difficult one, because the problem is nonlinear, ill-posed and ill-conditioned. Additionally, although the measured near-infrared signals of light transmission through tissue provide high imaging contrast, the reconstructed images suffer from poor spatial resolution due to the diffuse propagation of light in biological tissue. The application of model-based image reconstruction is reviewed in this paper, together with a numerical modelling approach to light propagation in tissue as well as generalized image reconstruction using boundary data. A comprehensive review and details of the basis for using spatial and structural prior information are also discussed, whereby the use of spectral and dual-modality systems can improve contrast and spatial resolution. PMID:19581256
Code of Federal Regulations, 2011 CFR
2011-01-01
... 10 Energy 2 2011-01-01 2011-01-01 false Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC Export Licensing Authority C Appendix C to Part 110 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) EXPORT AND IMPORT OF NUCLEAR EQUIPMENT AND MATERIAL Pt. 110, App. C Appendix C to Part 110—Illustrative List...
Assessment of a Molecular Diffusion Model in MELCOR
Chang OH; Richard Moore
2005-06-01
The MELCOR (version 1.8.5) [1] computer code with INEEL revisions is being improved for the analysis of very high temperature gas-cooled reactors [2]. Following a loss-of-coolant accident, flow through the reactor vessel may initially stagnate due to a non-uniform concentration of helium and air. However, molecular diffusion will eventually result in a uniform concentration of air and helium. The differences in fluid temperatures within the reactor vessel will then result in the establishment of a natural circulation flow that can supply significant amounts of air to the reactor core. The heat released by the resulting oxidation of graphite in the reactor core has the potential to increase the peak fuel temperature. In order to analyze the effects of oxidation on the response of the reactor during accidents, a molecular diffusion model was added to MELCOR. The model is based on Fick's Second Law for spatially uniform pressure and temperature. This paper describes equimolal counter diffusion experiments in a two bulb diffusion cell and the results of the assessment calculations.
Cauchy graph embedding based diffusion model for salient object detection.
Tan, Yihua; Li, Yansheng; Chen, Chen; Yu, Jin-Gang; Tian, Jinwen
2016-05-01
Salient object detection has been a rather hot research topic recently, due to its potential applications in image compression, scene classification, image registration, and so forth. The overwhelming majority of existing computational models are designed based on computer vision techniques by using lots of image cues and priors. Actually, salient object detection is derived from the biological perceptual mechanism, and biological evidence shows that the spread of the spatial attention generates the object attention. Inspired by this, we attempt to utilize the emerging spread mechanism of object attention to construct a new computational model. A novel Cauchy graph embedding based diffusion (CGED) model is proposed to fulfill the spread process. Combining the diffusion model and attention prediction model, a salient object detection approach is presented through perceptually grouping the multiscale diffused attention maps. The effectiveness of the proposed approach is validated on the salient object dataset. The experimental results show that the CGED process can obviously improve the performance of salient object detection compared with the input spatial attention map, and the proposed approach can achieve performance comparable to that of state-of-the-art approaches. PMID:27140886
Characterization and modeling of thermal diffusion and aggregation in nanofluids.
Gharagozloo, Patricia E.; Goodson, Kenneth E.
2010-05-01
Fluids with higher thermal conductivities are sought for fluidic cooling systems in applications including microprocessors and high-power lasers. By adding high thermal conductivity nanoscale metal and metal oxide particles to a fluid the thermal conductivity of the fluid is enhanced. While particle aggregates play a central role in recent models for the thermal conductivity of nanofluids, the effect of particle diffusion in a temperature field on the aggregation and transport has yet to be studied in depth. The present work separates the effects of particle aggregation and diffusion using parallel plate experiments, infrared microscopy, light scattering, Monte Carlo simulations, and rate equations for particle and heat transport in a well dispersed nanofluid. Experimental data show non-uniform temporal increases in thermal conductivity above effective medium theory and can be well described through simulation of the combination of particle aggregation and diffusion. The simulation shows large concentration distributions due to thermal diffusion causing variations in aggregation, thermal conductivity and viscosity. Static light scattering shows aggregates form more quickly at higher concentrations and temperatures, which explains the increased enhancement with temperature reported by other research groups. The permanent aggregates in the nanofluid are found to have a fractal dimension of 2.4 and the aggregate formations that grow over time are found to have a fractal dimension of 1.8, which is consistent with diffusion limited aggregation. Calculations show as aggregates grow the viscosity increases at a faster rate than thermal conductivity making the highly aggregated nanofluids unfavorable, especially at the low fractal dimension of 1.8. An optimum nanoparticle diameter for these particular fluid properties is calculated to be 130 nm to optimize the fluid stability by reducing settling, thermal diffusion and aggregation.
Anomalous Impact in Reaction-Diffusion Financial Models
NASA Astrophysics Data System (ADS)
Mastromatteo, I.; Tóth, B.; Bouchaud, J.-P.
2014-12-01
We generalize the reaction-diffusion model A +B → /0 in order to study the impact of an excess of A (or B ) at the reaction front. We provide an exact solution of the model, which shows that the linear response breaks down: the average displacement of the reaction front grows as the square root of the imbalance. We argue that this model provides a highly simplified but generic framework to understand the square-root impact of large orders in financial markets.
Reactive radical facilitated reaction-diffusion modeling for holographic photopolymerization
Liu Jianhua; Pu Haihui; Gao Bin; Gao Hongyue; Yin Dejin; Dai Haitao
2010-02-08
A phenomenological concentration of reactive radical is proposed to take the role of curing light intensity in explicit proportion to the reaction rate for the conventional reaction-diffusion model. This revision rationally eliminates the theoretical defect of null reaction rate in modeling of the postcuring process, and facilitates the applicability of the model in the whole process of holographic photopolymerizations in photocurable monomer and nematic liquid crystal blend system. Excellent consistencies are obtained in both curing and postcuring processes between simulated and experimentally measured evolutions of the first order diffraction efficiency of the formed composite Bragg gratings.
Model-free simulation approach to molecular diffusion tensors.
Chevrot, Guillaume; Hinsen, Konrad; Kneller, Gerald R
2013-10-21
In the present work, we propose a simple model-free approach for the computation of molecular diffusion tensors from molecular dynamics trajectories. The method uses a rigid body trajectory of the molecule under consideration, which is constructed a posteriori by an accumulation of quaternion-based superposition fits of consecutive conformations. From the rigid body trajectory, we compute the translational and angular velocities of the molecule and by integration of the latter also the corresponding angular trajectory. All quantities can be referred to the laboratory frame and a molecule-fixed frame. The 6 × 6 diffusion tensor is computed from the asymptotic slope of the tensorial mean square displacement and, for comparison, also from the Kubo integral of the velocity correlation tensor. The method is illustrated for two simple model systems - a water molecule and a lysozyme molecule in bulk water. We give estimations of the statistical accuracy of the calculations. PMID:24160503
Social influence and perceptual decision making: a diffusion model analysis.
Germar, Markus; Schlemmer, Alexander; Krug, Kristine; Voss, Andreas; Mojzisch, Andreas
2014-02-01
Classic studies on social influence used simple perceptual decision-making tasks to examine how the opinions of others change individuals' judgments. Since then, one of the most fundamental questions in social psychology has been whether social influence can alter basic perceptual processes. To address this issue, we used a diffusion model analysis. Diffusion models provide a stochastic approach for separating the cognitive processes underlying speeded binary decisions. Following this approach, our study is the first to disentangle whether social influence on decision making is due to altering the uptake of available sensory information or due to shifting the decision criteria. In two experiments, we found consistent evidence for the idea that social influence alters the uptake of available sensory evidence. By contrast, participants did not adjust their decision criteria. PMID:24154917
Model-free simulation approach to molecular diffusion tensors
NASA Astrophysics Data System (ADS)
Chevrot, Guillaume; Hinsen, Konrad; Kneller, Gerald R.
2013-10-01
In the present work, we propose a simple model-free approach for the computation of molecular diffusion tensors from molecular dynamics trajectories. The method uses a rigid body trajectory of the molecule under consideration, which is constructed a posteriori by an accumulation of quaternion-based superposition fits of consecutive conformations. From the rigid body trajectory, we compute the translational and angular velocities of the molecule and by integration of the latter also the corresponding angular trajectory. All quantities can be referred to the laboratory frame and a molecule-fixed frame. The 6 × 6 diffusion tensor is computed from the asymptotic slope of the tensorial mean square displacement and, for comparison, also from the Kubo integral of the velocity correlation tensor. The method is illustrated for two simple model systems - a water molecule and a lysozyme molecule in bulk water. We give estimations of the statistical accuracy of the calculations.
Thermomechanics of damageable materials under diffusion: modelling and analysis
NASA Astrophysics Data System (ADS)
Roubíček, Tomáš; Tomassetti, Giuseppe
2015-12-01
We propose a thermodynamically consistent general-purpose model describing diffusion of a solute or a fluid in a solid undergoing possible phase transformations and damage, beside possible visco-inelastic processes. Also heat generation/consumption/transfer is considered. Damage is modelled as rate-independent. The applications include metal-hydrogen systems with metal/hydride phase transformation, poroelastic rocks, structural and ferro/para-magnetic phase transformation, water and heat transport in concrete, and if diffusion is neglected, plasticity with damage and viscoelasticity, etc. For the ensuing system of partial differential equations and inclusions, we prove existence of solutions by a carefully devised semi-implicit approximation scheme of the fractional-step type.
Consistent flamelet modeling of differential molecular diffusion for turbulent non-premixed flames
NASA Astrophysics Data System (ADS)
Wang, Haifeng
2016-03-01
Treating differential molecular diffusion correctly and accurately remains as a great challenge to the modeling of turbulent non-premixed combustion. The aim of this paper is to develop consistent modeling strategies for differential molecular diffusion in flamelet models. Two types of differential molecular diffusion models are introduced, linear differential diffusion models and nonlinear differential diffusion models. A multi-component turbulent mixing layer problem is analyzed in detail to gain insights into differential molecular diffusion and its characteristics, particularly the dependence of differential molecular diffusion on the Reynolds number and the Lewis number. These characteristics are then used to validate the differential molecular diffusion models. Finally, the new models are applied to the modeling of a series of laboratory-scale turbulent non-premixed jet flames with different Reynolds number (Sandia Flames B, C, and D) to further assess the models' performance.
Modeling diffusive transport with a fractional derivative without singular kernel
NASA Astrophysics Data System (ADS)
Gómez-Aguilar, J. F.; López-López, M. G.; Alvarado-Martínez, V. M.; Reyes-Reyes, J.; Adam-Medina, M.
2016-04-01
In this paper we present an alternative representation of the diffusion equation and the diffusion-advection equation using the fractional calculus approach, the spatial-time derivatives are approximated using the fractional definition recently introduced by Caputo and Fabrizio in the range β , γ ∈(0 ; 2 ] for the space and time domain respectively. In this representation two auxiliary parameters σx and σt are introduced, these parameters related to equation results in a fractal space-time geometry provide an entire new family of solutions for the diffusion processes. The numerical results showed different behaviors when compared with classical model solutions. In the range β , γ ∈(0 ; 1) , the concentration exhibits the non-Markovian Lévy flights and the subdiffusion phenomena; when β = γ = 1 the classical case is recovered; when β , γ ∈(1 ; 2 ] the concentration exhibits the Markovian Lévy flights and the superdiffusion phenomena; finally when β = γ = 2 the concentration is anomalous dispersive and we found ballistic diffusion.
Modeling of Diffuse-Diffuse Photon Coupling via a Nonscattering Region: a Comparative Study
NASA Astrophysics Data System (ADS)
Lee, Jae Hoon; Kim, Seunghwan; Kim, Youn Tae
2004-06-01
It is well established that diffusion approximation is valid for light propagation in highly scattering media, but it breaks down in nonscattering regions. The previous methods that manipulate nonscattering regions are essentially boundary-to-boundary coupling (BBC) methods through a nonscattering void region based on the radiosity theory. We present a boundary-to-interior coupling (BIC) method. BIC is based on the fact that the collimated pencil beam incident on the medium can be replaced by an isotropic point source positioned at one reduced scattering length inside the medium from an illuminated point. A similar replacement is possible for the nondiffuse lights that enter the diffuse medium through the void, and it is formulated as the BIC method. We implemented both coupling methods using the finite element method (FEM) and tested for the circle with a void gap and for a four-layer adult head model. For mean time of flight, the BIC shows better agreement with Monte Carlo (MC) simulation results than BBC. For intensity, BIC shows a comparable match with MC data compared with that of BBC. The effect of absorption of the clear layer in the adult head model was investigated. Both mean time and intensity decrease as absorption of the clear layer increases.
Modeling of diffuse-diffuse photon coupling via a nonscattering region: a comparative study.
Lee, Jae Hoon; Kim, Seunghwan; Kim, Youn Tae
2004-06-20
It is well established that diffusion approximation is valid for light propagation in highly scattering media, but it breaks down in nonscattering regions. The previous methods that manipulate nonscattering regions are essentially boundary-to-boundary coupling (BBC) methods through a nonscattering void region based on the radiosity theory. We present a boundary-to-interior coupling (BIC) method. BIC is based on the fact that the collimated pencil beam incident on the medium can be replaced by an isotropic point source positioned at one reduced scattering length inside the medium from an illuminated point. A similar replacement is possible for the nondiffuse lights that enter the diffuse medium through the void, and it is formulated as the BIC method. We implemented both coupling methods using the finite element method (FEM) and tested for the circle with a void gap and for a four-layer adult head model. For mean time of flight, the BIC shows better agreement with Monte Carlo (MC) simulation results than BBC. For intensity, BIC shows a comparable match with MC data compared with that of BBC. The effect of absorption of the clear layer in the adult head model was investigated. Both mean time and intensity decrease as absorption of the clear layer increases. PMID:15218604
Pricing turbo warrants under mixed-exponential jump diffusion model
NASA Astrophysics Data System (ADS)
Yu, Jianfeng; Xu, Weidong
2016-06-01
Turbo warrant is a special type of barrier options in which the rebate is calculated as another exotic option. In this paper, using Laplace transforms we obtain the valuation of turbo warrant under the mixed-exponential jump diffusion model, which is able to approximate any jump size distribution. The numerical Laplace inversion examples verify that the analytical solutions are accurate. The results of simulation confirm the argument that jump risk should not be ignored in the valuation of turbo warrants.
Tracking a terrain bounce jammer with a diffuse scattering model
NASA Astrophysics Data System (ADS)
Nguyen, Joseph H.; Bowyer, Duane E.
1994-07-01
This paper presents a simulation model for an air-to-air missile to measure the power losses due to specular and diffuse scattering on various terrains. This includes a range of surfaces from a sea surface of different root-mean-square surface roughness slopes to desert sand. This paper also presents the correlation between theoretical and empirical data for specular scattering on dry land and moist sand.
Modeling of Diffusion in Liquid Ge and Its Alloys
NASA Technical Reports Server (NTRS)
Stroud, David G.
1998-01-01
This report summarizes progress made on NASA Grant NAG3-1437, Modeling of diffusion in Liquid Ge and Its Alloys, which was in effect from January 15, 1993 through July 10, 1997. It briefly describes the purpose of the grant, and the work accomplished in simulations and other studies of thermophysical properties of liquid semiconductors and related materials. A list of publications completed with the support of the grant is also given.
Most current electrostatic surface complexation models describing ionic binding at the particle/water interface rely on the use of Poisson - Boltzmann (PB) theory for relating diffuse layer charge densities to diffuse layer electrostatic potentials. PB theory is known to contain ...
Computer modeling of Earthshine contamination on the VIIRS solar diffuser
NASA Astrophysics Data System (ADS)
Mills, Stephen P.; Agravante, Hiroshi; Hauss, Bruce; Klein, James E.; Weiss, Stephanie C.
2005-10-01
The Visible/Infrared Imager Radiometer Suite (VIIRS), built by Raytheon Santa Barbara Remote Sensing (SBRS) will be one of the primary earth-observing remote-sensing instruments on the National Polar-Orbiting Operational Environmental Satellite System (NPOESS). It will also be installed on the NPOESS Preparatory Project (NPP). These satellite systems fly in near-circular, sun-synchronous low-earth orbits at altitudes of approximately 830 km. VIIRS has 15 bands designed to measure reflectance with wavelengths between 412 nm and 2250 nm, and an additional 7 bands measuring primarily emissive radiance between 3700nm and 11450 nm. The calibration source for the reflective bands is a solar diffuser (SD) that is illuminated once per orbit as the satellite passes from the dark side to the light side of the earth near the poles. Sunlight enters VIIRS through an opening in the front of the instrument. An attenuation screen covers the opening, but other than this there are no other optical elements between the SD and the sun. The BRDF of the SD and the transmittance of the attenuation screen is measured pre-flight, and so with knowledge of the angles of incidence, the radiance of the sun can be computed and is used as a reference to produce calibrated reflectances and radiances. Unfortunately, the opening also allows a significant amount of reflected earthshine to illuminate part of the SD, and this component introduces radiometric error to the calibration process, referred to as earthshine contamination (ESC). The VIIRS radiometric error budget allocated a 0.3% error based on modeling of the ESC done by SBRS during the design phase. This model assumes that the earth has Lambertian BRDF with a maximum top-of-atmosphere albedo of 1. The Moderate Resolution Imaging Spectroradiometer (MODIS) has an SD with a design similar to VIIRS, and in 2003 the MODIS Science Team reported to Northrop Grumman Space Technology (NGST), the prime contractor for NPOESS, their suspicion that ESC
An epidemic model of rumor diffusion in online social networks
NASA Astrophysics Data System (ADS)
Cheng, Jun-Jun; Liu, Yun; Shen, Bo; Yuan, Wei-Guo
2013-01-01
So far, in some standard rumor spreading models, the transition probability from ignorants to spreaders is always treated as a constant. However, from a practical perspective, the case that individual whether or not be infected by the neighbor spreader greatly depends on the trustiness of ties between them. In order to solve this problem, we introduce a stochastic epidemic model of the rumor diffusion, in which the infectious probability is defined as a function of the strength of ties. Moreover, we investigate numerically the behavior of the model on a real scale-free social site with the exponent γ = 2.2. We verify that the strength of ties plays a critical role in the rumor diffusion process. Specially, selecting weak ties preferentially cannot make rumor spread faster and wider, but the efficiency of diffusion will be greatly affected after removing them. Another significant finding is that the maximum number of spreaders max( S) is very sensitive to the immune probability μ and the decay probability v. We show that a smaller μ or v leads to a larger spreading of the rumor, and their relationships can be described as the function ln(max( S)) = Av + B, in which the intercept B and the slope A can be fitted perfectly as power-law functions of μ. Our findings may offer some useful insights, helping guide the application in practice and reduce the damage brought by the rumor.
Impact Acceleration Model of Diffuse Traumatic Brain Injury.
Hellewell, Sarah C; Ziebell, Jenna M; Lifshitz, Jonathan; Morganti-Kossmann, M Cristina
2016-01-01
The impact acceleration (I/A) model of traumatic brain injury (TBI) was developed to reliably induce diffuse traumatic axonal injury in rats in the absence of skull fractures and parenchymal focal lesions. This model replicates a pathophysiology that is commonly observed in humans with diffuse axonal injury (DAI) caused by acceleration-deceleration forces. Such injuries are typical consequences of motor vehicle accidents and falls, which do not necessarily require a direct impact to the closed skull. There are several desirable characteristics of the I/A model, including the extensive axonal injury produced in the absence of a focal contusion, the suitability for secondary insult modeling, and the adaptability for mild/moderate injury through alteration of height and/or weight. Furthermore, the trauma device is inexpensive and readily manufactured in any laboratory, and the induction of injury is rapid (~45 min per animal from weighing to post-injury recovery) allowing multiple animal experiments per day. In this chapter, we describe in detail the methodology and materials required to produce the rat model of I/A in the laboratory. We also review current adaptations to the model to alter injury severity, discuss frequent complications and technical issues encountered using this model, and provide recommendations to ensure technically sound injury induction. PMID:27604723
THE LOS ALAMOS NATIONAL LABORATORY ATMOSPHERIC TRANSPORT AND DIFFUSION MODELS
M. WILLIAMS
1999-08-01
The LANL atmospheric transport and diffusion models are composed of two state-of-the-art computer codes. The first is an atmospheric wind model called HOThlAC, Higher Order Turbulence Model for Atmospheric circulations. HOTMAC generates wind and turbulence fields by solving a set of atmospheric dynamic equations. The second is an atmospheric diffusion model called RAPTAD, Random Particle Transport And Diffusion. RAPTAD uses the wind and turbulence output from HOTMAC to compute particle trajectories and concentration at any location downwind from a source. Both of these models, originally developed as research codes on supercomputers, have been modified to run on microcomputers. Because the capability of microcomputers is advancing so rapidly, the expectation is that they will eventually become as good as today's supercomputers. Now both models are run on desktop or deskside computers, such as an IBM PC/AT with an Opus Pm 350-32 bit coprocessor board and a SUN workstation. Codes have also been modified so that high level graphics, NCAR Graphics, of the output from both models are displayed on the desktop computer monitors and plotted on a laser printer. Two programs, HOTPLT and RAPLOT, produce wind vector plots of the output from HOTMAC and particle trajectory plots of the output from RAPTAD, respectively. A third CONPLT provides concentration contour plots. Section II describes step-by-step operational procedures, specifically for a SUN-4 desk side computer, on how to run main programs HOTMAC and RAPTAD, and graphics programs to display the results. Governing equations, boundary conditions and initial values of HOTMAC and RAPTAD are discussed in Section III. Finite-difference representations of the governing equations, numerical solution procedures, and a grid system are given in Section IV.
Saeed, Muhanned; Probst, Leila; Betz, Gabriele
2011-03-01
Near-infrared spectroscopy offers tremendous advantages for pharmaceutical manufacturing as a fast and nondestructive method of quantitative and qualitative analysis. Content uniformity (end-product analytics) and process analytics are two important applications of the method. Diffuse reflection (DR) information depth (vertical sampling span) assessment is of equal importance in content prediction applications and to understand the effect of inhomogeneities in the sample. Three experiments were conducted: (a) 0.5 to 10.0 mm incremental thickness MCC tablets with constant porosity, (b) MCC/phenylbutazone (PBZ) double-layered (DL) tablets (PBZ layer 0%-100% in 0.5 mm steps), and (c) Comparison of placebo and 30% caffeine tablet cores with incremental film coating (film thickness of 0-0.35 mm). Incremental thickness and cluster analysis of DL tablets showed that DR information depth was <0.5 mm, whereas the data fitting from incremental coating showed that signal drop reached 50% at 0.05 to 0.07 mm, depending on the wavenumber and 90% signal drop (10% information content) can be seen between 0.20 and 0.25 mm without extrapolation. These results mean that DR mode for pharmaceutical tablets obtains spectral information from the very surface, and radiation is barely reflected back from beyond thin-film coatings, making it less useful than diffuse transmission mode for core content analysis, especially for thick-coated, multilayer, multicore, or highly inhomogeneous tablets. PMID:20862671
A pore-pressure diffusion model for estimating landslide-inducing rainfall
Reid, M.E.
1994-01-01
Many types of landslide movement are induced by large rainstorms, and empirical rainfall intensity/duration thresholds for initiating movement have been determined for various parts of the world. In this paper, I present a simple pressure diffusion model that provides a physically based hydrologic link between rainfall intensity/duration at the ground surface and destabilizing pore-water pressures at depth. The model approximates rainfall infiltration as a sinusoidally varying flux over time and uses physical parameters that can be determined independently. Using a comprehensive data set from an intensively monitored landslide, I demonstrate that the model is capable of distinguishing movement-inducing rainstorms. -Author
A Temporal Model of Technology Diffusion into Small Firms in Wales.
ERIC Educational Resources Information Center
Thomas, Brychan; Packham, Gary; Miller, Chris
2001-01-01
Discusses technology diffusion through formal and informal networks. Develops a model that includes channels and mechanisms involved in transferring technology into innovative small businesses. The model depicts influences that increase or slow the rate of diffusion. (SK)
Super-Resolution Image Reconstruction Using Diffuse Source Models
Ellis, Michael A.; Viola, Francesco; Walker, William F.
2010-01-01
Image reconstruction is central to many scientific fields, from medical ultrasound and sonar to computed tomography and computer vision. While lenses play a critical reconstruction role in these fields, digital sensors enable more sophisticated computational approaches. A variety of computational methods have thus been developed, with the common goal of increasing contrast and resolution to extract the greatest possible information from raw data. This paper describes a new image reconstruction method named the Diffuse Time-domain Optimized Near-field Estimator (dTONE). dTONE represents each hypothetical target in the system model as a diffuse region of targets rather than a single discrete target, which more accurately represents the experimental data that arise from signal sources in continuous space, with no additional computational requirements at the time of image reconstruction. Simulation and experimental ultrasound images of animal tissues show that dTONE achieves image resolution and contrast far superior to those of conventional image reconstruction methods. We also demonstrate the increased robustness of the diffuse target model to major sources of image degradation, through the addition of electronic noise, phase aberration, and magnitude aberration to ultrasound simulations. Using experimental ultrasound data from a tissue-mimicking phantom containing a 3 mm diameter anechoic cyst, the conventionally reconstructed image has a cystic contrast of −6.3 dB whereas the dTONE image has a cystic contrast of −14.4 dB. PMID:20447760
Super-resolution image reconstruction using diffuse source models.
Ellis, Michael A; Viola, Francesco; Walker, William F
2010-06-01
Image reconstruction is central to many scientific fields, from medical ultrasound and sonar to computed tomography and computer vision. Although lenses play a critical reconstruction role in these fields, digital sensors enable more sophisticated computational approaches. A variety of computational methods have thus been developed, with the common goal of increasing contrast and resolution to extract the greatest possible information from raw data. This paper describes a new image reconstruction method named the Diffuse Time-domain Optimized Near-field Estimator (dTONE). dTONE represents each hypothetical target in the system model as a diffuse region of targets rather than a single discrete target, which more accurately represents the experimental data that arise from signal sources in continuous space, with no additional computational requirements at the time of image reconstruction. Simulation and experimental ultrasound images of animal tissues show that dTONE achieves image resolution and contrast far superior to those of conventional image reconstruction methods. We also demonstrate the increased robustness of the diffuse target model to major sources of image degradation through the addition of electronic noise, phase aberration and magnitude aberration to ultrasound simulations. Using experimental ultrasound data from a tissue-mimicking phantom containing a 3-mm-diameter anechoic cyst, the conventionally reconstructed image has a cystic contrast of -6.3 dB, whereas the dTONE image has a cystic contrast of -14.4 dB. PMID:20447760
Measurements and modeling of explosive vapor diffusion in snow
NASA Astrophysics Data System (ADS)
Albert, Mary R.; Cragin, James H.; Leggett, Daniel C.
2000-08-01
The detection of buried mines is important to both for humanitarian and military strategic de-mining both at home and abroad, and recent efforts in chemical detection show promise for definitive identification of buried miens. The impact of weather has a large effect on the fate and transport of the explosives vapor that these systems sense. In many areas of military conflict, and at Army military training grounds in cold regions, winter weather affects military operations for many months of the year. In cold regions, the presence of freezing ground or a snow cover may provide increased temporary storage of the explosive, potentially leading to opportunities for more optimal sensing conditions later. This paper discusses the result of a controlled laboratory experiment to investigate explosives diffusion through snow, quantitative microscopy measurements of snow microstructure including specific surface, and verifications of our transport model using this data. In experiments measuring 1,3-DNB, 2,4-DNT and 2,4,6-TNT we determined an effective diffusion coefficient of 1.5 X 10-6 cm2/s from measurements through isothermal sieved snow with equivalent sphere radius of 0.11 mm. Adsorption is a major factor in diffusive transport of these explosives through snow. The data was used to verify our finite element mole of explosives transport. Measurements and model results show close agreement.
Influence Diffusion Model in Text-Based Communication
NASA Astrophysics Data System (ADS)
Matsumura, Naohiro; Ohsawa, Yukio; Ishizuka, Mitsuru
Business people, especially marketing researchers, are keen to understand peoples' potential sense of value to create fascinating topics stimulating peoples' interest. In this paper, we aim at finding influential people, comments, and terms contributing the discovery of such topics. For this purpose, we propose an Influence Diffusion Model in text-based communication, where the influence of people, comments, and terms are defined as the degree of text-based relevance of messages. We apply this model to Bulletin Board Service(BBS) on the Internet, and present our discoveries on experimental evaluations.
Diffusion model to describe osteogenesis within a porous titanium scaffold.
Schmitt, M; Allena, R; Schouman, T; Frasca, S; Collombet, J M; Holy, X; Rouch, P
2016-01-01
In this study, we develop a two-dimensional finite element model, which is derived from an animal experiment and allows simulating osteogenesis within a porous titanium scaffold implanted in ewe's hemi-mandible during 12 weeks. The cell activity is described through diffusion equations and regulated by the stress state of the structure. We compare our model to (i) histological observations and (ii) experimental data obtained from a mechanical test done on sacrificed animal. We show that our mechano-biological approach provides consistent numerical results and constitutes a useful tool to predict osteogenesis pattern. PMID:25573031
Diffuse-interface modeling of three-phase interactions
NASA Astrophysics Data System (ADS)
Park, Jang Min; Anderson, Patrick D.
2016-05-01
In this work, a numerical model is developed to study the three-phase interactions which take place when two immiscible drops suspended in a third immiscible liquid are brought together. The diffuse-interface model coupled with the hydrodynamic equations is solved by a standard finite element method. Partial and complete engulfing between two immiscible drops is studied, and the effects of several parameters are discussed. In the partial-engulfing case, two stages of wetting and pulling are identified, which qualitatively agrees with the experiment. In the complete-engulfing case, three stages of wetting and/or penetration, pulling, and spreading are identified.
Effective Diffusivity and Spalling Models for Slagging Coal Gasifiers
Williford, Rick E.; Johnson, Kenneth I.; Sundaram, S. K.; Pilli, Siva Prasad
2008-01-08
A major impact on the economics of coal gasification is the spalling degradation of hot-face refractories in slagging coal gasifiers. Two predictive models for spalling have been previously proposed and benchmarked. Both models express molten slag ingress into the porous refractory in terms of an effective diffusivity, a formulation for which is developed in the present Communication. The results appear useful for predicting the lifetimes of refractories in slagging coal gasifiers, and for determining whether the spall originated from tensile or compressive mechanisms.
Diffusion of innovations in Axelrod’s model
NASA Astrophysics Data System (ADS)
Tilles, Paulo F. C.; Fontanari, José F.
2015-11-01
Axelrod's model for the dissemination of culture contains two key factors required to model the process of diffusion of innovations, namely, social influence (i.e., individuals become more similar when they interact) and homophily (i.e., individuals interact preferentially with similar others). The strength of these social influences are controlled by two parameters: $F$, the number of features that characterizes the cultures and $q$, the common number of states each feature can assume. Here we assume that the innovation is a new state of a cultural feature of a single individual -- the innovator -- and study how the innovation spreads through the networks among the individuals. For infinite regular lattices in one (1D) and two dimensions (2D), we find that initially the successful innovation spreads linearly with the time $t$, but in the long-time limit it spreads diffusively ($\\sim t^{1/2}$) in 1D and sub-diffusively ($\\sim t/\\ln t$) in 2D. For finite lattices, the growth curves for the number of adopters are typically concave functions of $t$. For random graphs with a finite number of nodes $N$, we argue that the classical S-shaped growth curves result from a trade-off between the average connectivity $K$ of the graph and the per feature diversity $q$. A large $q$ is needed to reduce the pace of the initial spreading of the innovation and thus delimit the early-adopters stage, whereas a large $K$ is necessary to ensure the onset of the take-off stage at which the number of adopters grows superlinearly with $t$. In an infinite random graph we find that the number of adopters of a successful innovation scales with $t^\\gamma$ with $\\gamma =1$ for $K> 2$ and $1/2 < \\gamma < 1$ for $K=2$. We suggest that the exponent $\\gamma$ may be a useful index to characterize the process of diffusion of successful innovations in diverse scenarios.
A Discrete Model to Study Reaction-Diffusion-Mechanics Systems
Weise, Louis D.; Nash, Martyn P.; Panfilov, Alexander V.
2011-01-01
This article introduces a discrete reaction-diffusion-mechanics (dRDM) model to study the effects of deformation on reaction-diffusion (RD) processes. The dRDM framework employs a FitzHugh-Nagumo type RD model coupled to a mass-lattice model, that undergoes finite deformations. The dRDM model describes a material whose elastic properties are described by a generalized Hooke's law for finite deformations (Seth material). Numerically, the dRDM approach combines a finite difference approach for the RD equations with a Verlet integration scheme for the equations of the mass-lattice system. Using this framework results were reproduced on self-organized pacemaking activity that have been previously found with a continuous RD mechanics model. Mechanisms that determine the period of pacemakers and its dependency on the medium size are identified. Finally it is shown how the drift direction of pacemakers in RDM systems is related to the spatial distribution of deformation and curvature effects. PMID:21804911
Anomalous behavior of the coherent light diffusion by a tilted translucent rough surface: part I
NASA Astrophysics Data System (ADS)
Rebollo, M. A.; Perez Quintian, F.; Hogert, Elsa N.; Landau, Monica R.; Gaggioli, Nestor G.
1996-02-01
When a translucent rough surface is illuminated, light is diffused in different directions. The envelope the intensity distribution is called diffusion curve. As the diffuser is rotated with respect to the incident beam, the diffuser curve changes its appearance: the maximum suffers a displacement and changes its shape. Some authors have studied this phenomenon, but none of them explained it properly. In this work we make an additional contribution to address the problem, showing experimentally that the maximum displacement depends on the incident angle and the diffuser ratio T/(sigma) . We compare our experimental results with those that can be calculated with the reformulated Beckmann's theory. We could observe important agreements and differences. For example, Beckmann's theory predicts that the diffusion results are asymmetric, while our measured results are indefectibly symmetric.
Marinak, M. )
1990-02-01
The problem of deducing {chi}{sub e} from measurements of the propagation of a monopole heatpulse is considered. An extended diffusive model, which takes into account perturbed sources and sinks is extended to the case of a monopole heat input. {chi}{sub e} is expressed as a function of two observables, the heat pulse velocity and the radial damping rate. Two simple expressions valid for two different ranges of the radius of the poloidal waist of the beam power profile are given. The expressions are valid in the heat pulse measurement region, extending radially 0.05a beyond the beam power waist to near 0.6a. The inferred {chi}{sub e} is a local value, not an average value of the radial {chi}{sub e} profile. 7 refs., 6 figs., 1 tab.
Bayesian Model Selection with Network Based Diffusion Analysis.
Whalen, Andrew; Hoppitt, William J E
2016-01-01
A number of recent studies have used Network Based Diffusion Analysis (NBDA) to detect the role of social transmission in the spread of a novel behavior through a population. In this paper we present a unified framework for performing NBDA in a Bayesian setting, and demonstrate how the Watanabe Akaike Information Criteria (WAIC) can be used for model selection. We present a specific example of applying this method to Time to Acquisition Diffusion Analysis (TADA). To examine the robustness of this technique, we performed a large scale simulation study and found that NBDA using WAIC could recover the correct model of social transmission under a wide range of cases, including under the presence of random effects, individual level variables, and alternative models of social transmission. This work suggests that NBDA is an effective and widely applicable tool for uncovering whether social transmission underpins the spread of a novel behavior, and may still provide accurate results even when key model assumptions are relaxed. PMID:27092089
A multiphase solute diffusion model for dendritic alloy solidification
Wang, C.Y.; Beckermann, C.
1993-12-01
A solute diffusion model, aimed at predicting microstructure formation in metal castings, is proposed for dendritic solidification of alloys. The model accounts for the different length scales existing in a dendritic structure. This is accomplished by utilizing a multiphase approach, in which not only the various physical phases but also phases associated with different length scales are considered separately. The macroscopic conservation equations are derived for each phase using the volume averaging technique, with constitutive relations developed for the interfacial transfer terms. It is shown that the multiphase model can rigorously incorporate the growth of dendrite tips and coarsening of dendrite arms. In addition, the distinction of different length scales enables the inclusion of realistic descriptions of the dendrite topology and relations to key metallurgical parameters. Another novel aspect of the model is that a single set of conservation equations for solute diffusion is developed for both equiaxed and columnar dendritic solidification. Finally, illustrative calculations for equiaxed, columnar, and mixed columnar-equiaxed solidification are carried out to provide quantitative comparisons with previous studies, and a variety of fundamental phenomena such as recalescence, dendrite tip undercooling, and columnar-to-equiaxed transition (CET) are predicted.
Subgrid models for mass and thermal diffusion in turbulent mixing
NASA Astrophysics Data System (ADS)
Lim, H.; Yu, Y.; Glimm, J.; Li, X.-L.; Sharp, D. H.
2010-12-01
We propose a new method for the large eddy simulation (LES) of turbulent mixing flows. The method yields convergent probability distribution functions (PDFs) for temperature and concentration and a chemical reaction rate when applied to reshocked Richtmyer-Meshkov (RM) unstable flows. Because such a mesh convergence is an unusual and perhaps original capability for LES of RM flows, we review previous validation studies of the principal components of the algorithm. The components are (i) a front tracking code, FronTier, to control numerical mass diffusion and (ii) dynamic subgrid scale (SGS) models to compensate for unresolved scales in the LES. We also review the relevant code comparison studies. We compare our results to a simple model based on 1D diffusion, taking place in the geometry defined statistically by the interface (the 50% isoconcentration surface between the two fluids). Several conclusions important to physics could be drawn from our study. We model chemical reactions with no closure approximations beyond those in the LES of the fluid variables itself, and as with dynamic SGS models, these closures contain no adjustable parameters. The chemical reaction rate is specified by the joint PDF for temperature and concentration. We observe a bimodal distribution for the PDF and we observe significant dependence on fluid transport parameters.
A Reaction-Diffusion Model of Cholinergic Retinal Waves
Lansdell, Benjamin; Ford, Kevin; Kutz, J. Nathan
2014-01-01
Prior to receiving visual stimuli, spontaneous, correlated activity in the retina, called retinal waves, drives activity-dependent developmental programs. Early-stage waves mediated by acetylcholine (ACh) manifest as slow, spreading bursts of action potentials. They are believed to be initiated by the spontaneous firing of Starburst Amacrine Cells (SACs), whose dense, recurrent connectivity then propagates this activity laterally. Their inter-wave interval and shifting wave boundaries are the result of the slow after-hyperpolarization of the SACs creating an evolving mosaic of recruitable and refractory cells, which can and cannot participate in waves, respectively. Recent evidence suggests that cholinergic waves may be modulated by the extracellular concentration of ACh. Here, we construct a simplified, biophysically consistent, reaction-diffusion model of cholinergic retinal waves capable of recapitulating wave dynamics observed in mice retina recordings. The dense, recurrent connectivity of SACs is modeled through local, excitatory coupling occurring via the volume release and diffusion of ACh. In addition to simulation, we are thus able to use non-linear wave theory to connect wave features to underlying physiological parameters, making the model useful in determining appropriate pharmacological manipulations to experimentally produce waves of a prescribed spatiotemporal character. The model is used to determine how ACh mediated connectivity may modulate wave activity, and how parameters such as the spontaneous activation rate and sAHP refractory period contribute to critical wave size variability. PMID:25474327
Bayesian Model Selection with Network Based Diffusion Analysis
Whalen, Andrew; Hoppitt, William J. E.
2016-01-01
A number of recent studies have used Network Based Diffusion Analysis (NBDA) to detect the role of social transmission in the spread of a novel behavior through a population. In this paper we present a unified framework for performing NBDA in a Bayesian setting, and demonstrate how the Watanabe Akaike Information Criteria (WAIC) can be used for model selection. We present a specific example of applying this method to Time to Acquisition Diffusion Analysis (TADA). To examine the robustness of this technique, we performed a large scale simulation study and found that NBDA using WAIC could recover the correct model of social transmission under a wide range of cases, including under the presence of random effects, individual level variables, and alternative models of social transmission. This work suggests that NBDA is an effective and widely applicable tool for uncovering whether social transmission underpins the spread of a novel behavior, and may still provide accurate results even when key model assumptions are relaxed. PMID:27092089
Anomalous diffusion in neutral evolution of model proteins
NASA Astrophysics Data System (ADS)
Nelson, Erik D.; Grishin, Nick V.
2015-06-01
Protein evolution is frequently explored using minimalist polymer models, however, little attention has been given to the problem of structural drift, or diffusion. Here, we study neutral evolution of small protein motifs using an off-lattice heteropolymer model in which individual monomers interact as low-resolution amino acids. In contrast to most earlier models, both the length and folded structure of the polymers are permitted to change. To describe structural change, we compute the mean-square distance (MSD) between monomers in homologous folds separated by n neutral mutations. We find that structural change is episodic, and, averaged over lineages (for example, those extending from a single sequence), exhibits a power-law dependence on n . We show that this exponent depends on the alignment method used, and we analyze the distribution of waiting times between neutral mutations. The latter are more disperse than for models required to maintain a specific fold, but exhibit a similar power-law tail.
On Large Time Behavior and Selection Principle for a Diffusive Carr-Penrose Model
NASA Astrophysics Data System (ADS)
Conlon, Joseph G.; Dabkowski, Michael; Wu, Jingchen
2016-04-01
This paper is concerned with the study of a diffusive perturbation of the linear LSW model introduced by Carr and Penrose. A main subject of interest is to understand how the presence of diffusion acts as a selection principle, which singles out a particular self-similar solution of the linear LSW model as determining the large time behavior of the diffusive model. A selection principle is rigorously proven for a model which is a semiclassical approximation to the diffusive model. Upper bounds on the rate of coarsening are also obtained for the full diffusive model.
Diffusive spatio-temporal noise in a first-passage time model for intracellular calcium release
NASA Astrophysics Data System (ADS)
Flegg, Mark B.; Rüdiger, Sten; Erban, Radek
2013-04-01
The intracellular release of calcium from the endoplasmic reticulum is controlled by ion channels. The resulting calcium signals exhibit a rich spatio-temporal signature, which originates at least partly from microscopic fluctuations. While stochasticity in the gating transition of ion channels has been incorporated into many models, the distribution of calcium is usually described by deterministic reaction-diffusion equations. Here we test the validity of the latter modeling approach by using two different models to calculate the frequency of localized calcium signals (calcium puffs) from clustered IP3 receptor channels. The complexity of the full calcium system is here limited to the basic opening mechanism of the ion channels and, in the mathematical reduction simplifies to the calculation of a first passage time. Two models are then studied: (i) a hybrid model, where channel gating is treated stochastically, while calcium concentration is deterministic and (ii) a fully stochastic model with noisy channel gating and Brownian calcium ion motion. The second model utilises the recently developed two-regime method [M. B. Flegg, S. J. Chapman, and R. Erban, "The two-regime method for optimizing stochastic reaction-diffusion simulations," J. R. Soc., Interface 9, 859-868 (2012)], 10.1098/rsif.2011.0574 in order to simulate a large domain with precision required only near the Ca2+ absorbing channels. The expected time for a first channel opening that results in a calcium puff event is calculated. It is found that for a large diffusion constant, predictions of the interpuff time are significantly overestimated using the model (i) with a deterministic non-spatial calcium variable. It is thus demonstrated that the presence of diffusive noise in local concentrations of intracellular Ca2+ ions can substantially influence the occurrence of calcium signals. The presented approach and results may also be relevant for other cell-physiological first-passage time problems with
12 CFR Appendix A to Part 573 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 571, subpart... 12 Banks and Banking 6 2013-01-01 2012-01-01 true Model Privacy Form A Appendix A to Part 573... INFORMATION Pt. 573, App. A Appendix A to Part 573—Model Privacy Form A. The Model Privacy Form...
12 CFR Appendix A to Part 573 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 571, subpart... 12 Banks and Banking 5 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 573... INFORMATION Pt. 573, App. A Appendix A to Part 573—Model Privacy Form A. The Model Privacy Form...
12 CFR Appendix A to Part 573 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 571, subpart... 12 Banks and Banking 6 2012-01-01 2012-01-01 false Model Privacy Form A Appendix A to Part 573... INFORMATION Pt. 573, App. A Appendix A to Part 573—Model Privacy Form A. The Model Privacy Form...
12 CFR Appendix A to Part 573 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 571, subpart... 12 Banks and Banking 6 2014-01-01 2012-01-01 true Model Privacy Form A Appendix A to Part 573... INFORMATION Pt. 573, App. A Appendix A to Part 573—Model Privacy Form A. The Model Privacy Form...
12 CFR Appendix A to Part 573 - Model Privacy Form
Code of Federal Regulations, 2010 CFR
2010-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 571, subpart... 12 Banks and Banking 5 2010-01-01 2010-01-01 false Model Privacy Form A Appendix A to Part 573... INFORMATION Pt. 573, App. A Appendix A to Part 573—Model Privacy Form A. The Model Privacy Form...
Reading and a Diffusion Model Analysis of Reaction Time
Naples, Adam; Katz, Leonard; Grigorenko, Elena L.
2012-01-01
Processing speed is associated with reading performance. However, the literature is not clear either on the definition of processing speed or on why and how it contributes to reading performance. In this study we demonstrated that processing speed, as measured by reaction time, is not a unitary construct. Using the diffusion model of two-choice reaction time, we assessed processing speed in a series of same-different reaction time tasks for letter and number strings. We demonstrated that the association between reaction time and reading performance is driven by processing speed for reading-related information, but not motor or sensory encoding speed. PMID:22612543
A study of hydrogen diffusion flames using PDF turbulence model
NASA Technical Reports Server (NTRS)
Hsu, Andrew T.
1991-01-01
The application of probability density function (pdf) turbulence models is addressed in this work. For the purpose of accurate prediction of turbulent combustion, an algorithm that combines a conventional CFD flow solver with the Monte Carlo simulation of the pdf evolution equation has been developed. The algorithm has been validated using experimental data for a heated turbulent plane jet. The study of H2-F2 diffusion flames has been carried out using this algorithm. Numerical results compared favorably with experimental data. The computuations show that the flame center shifts as the equivalence ratio changes, and that for the same equivalence ratio, similarity solutions for flames exist.
A study of hydrogen diffusion flames using PDF turbulence model
NASA Technical Reports Server (NTRS)
Hsu, Andrew T.
1991-01-01
The application of probability density function (pdf) turbulence models is addressed. For the purpose of accurate prediction of turbulent combustion, an algorithm that combines a conventional computational fluid dynamic (CFD) flow solver with the Monte Carlo simulation of the pdf evolution equation was developed. The algorithm was validated using experimental data for a heated turbulent plane jet. The study of H2-F2 diffusion flames was carried out using this algorithm. Numerical results compared favorably with experimental data. The computations show that the flame center shifts as the equivalence ratio changes, and that for the same equivalence ratio, similarity solutions for flames exist.
Modeling the Determinants Influencing the Diffusion of Mobile Internet
NASA Astrophysics Data System (ADS)
Alwahaishi, Saleh; Snášel, Václav
2013-04-01
Understanding individual acceptance and use of Information and Communication Technology (ICT) is one of the most mature streams of information systems research. In Information Technology and Information System research, numerous theories are used to understand users' adoption of new technologies. Various models were developed including the Innovation Diffusion Theory, Theory of Reasoned Action, Theory of Planned Behavior, Technology Acceptance Model, and recently, the Unified Theory of Acceptance and Use of Technology. This research composes a new hybrid theoretical framework to identify the factors affecting the acceptance and use of Mobile Internet -as an ICT application- in a consumer context. The proposed model incorporates eight constructs: Performance Expectancy (PE), Effort Expectancy (EE), Facilitating Conditions (FC), Social Influences (SI), Perceived Value (PV), Perceived Playfulness (PP), Attention Focus (AF), and Behavioral intention (BI). Individual differences-namely, age, gender, education, income, and experience are moderating the effects of these constructs on behavioral intention and technology use.
A polarizable continuum model for molecules at spherical diffuse interfaces
NASA Astrophysics Data System (ADS)
Di Remigio, Roberto; Mozgawa, Krzysztof; Cao, Hui; Weijo, Ville; Frediani, Luca
2016-03-01
We present an extension of the Polarizable Continuum Model (PCM) to simulate solvent effects at diffuse interfaces with spherical symmetry, such as nanodroplets and micelles. We derive the form of the Green's function for a spatially varying dielectric permittivity with spherical symmetry and exploit the integral equation formalism of the PCM for general dielectric environments to recast the solvation problem into a continuum solvation framework. This allows the investigation of the solvation of ions and molecules in nonuniform dielectric environments, such as liquid droplets, micelles or membranes, while maintaining the computationally appealing characteristics of continuum solvation models. We describe in detail our implementation, both for the calculation of the Green's function and for its subsequent use in the PCM electrostatic problem. The model is then applied on a few test systems, mainly to analyze the effect of interface curvature on solvation energetics.
A polarizable continuum model for molecules at spherical diffuse interfaces.
Di Remigio, Roberto; Mozgawa, Krzysztof; Cao, Hui; Weijo, Ville; Frediani, Luca
2016-03-28
We present an extension of the Polarizable Continuum Model (PCM) to simulate solvent effects at diffuse interfaces with spherical symmetry, such as nanodroplets and micelles. We derive the form of the Green's function for a spatially varying dielectric permittivity with spherical symmetry and exploit the integral equation formalism of the PCM for general dielectric environments to recast the solvation problem into a continuum solvation framework. This allows the investigation of the solvation of ions and molecules in nonuniform dielectric environments, such as liquid droplets, micelles or membranes, while maintaining the computationally appealing characteristics of continuum solvation models. We describe in detail our implementation, both for the calculation of the Green's function and for its subsequent use in the PCM electrostatic problem. The model is then applied on a few test systems, mainly to analyze the effect of interface curvature on solvation energetics. PMID:27036423
Innovation Diffusion: A Deterministic Model of Space-Time Integration with Physical Analog
ERIC Educational Resources Information Center
Haynes, Kingsley E.; And Others
1977-01-01
Extends a fundamental temporal diffusion model to integrate space and time dimensions of innovation diffusion. Compares analogous developments in the physical sciences and argues that the proposed model may help link the concepts of catalysts in physical science diffusion processes to the role of change agents in social science systems. (Author/JG)
Hybrid approaches for multiple-species stochastic reaction–diffusion models
Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K.; Byrne, Helen
2015-10-15
Reaction–diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction–diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model. - Highlights: • A novel hybrid stochastic/deterministic reaction–diffusion simulation method is given. • Can massively speed up stochastic simulations while preserving stochastic effects. • Can handle multiple reacting species. • Can handle moving boundaries.
A Microscopic Multiphase Diffusion Model of Viable Epidermis Permeability
Nitsche, Johannes M.; Kasting, Gerald B.
2013-01-01
A microscopic model of passive transverse mass transport of small solutes in the viable epidermal layer of human skin is formulated on the basis of a hexagonal array of cells (i.e., keratinocytes) bounded by 4-nm-thick, anisotropic lipid bilayers and separated by 1-μm layers of extracellular fluid. Gap junctions and tight junctions with adjustable permeabilities are included to modulate the transport of solutes with low membrane permeabilities. Two keratinocyte aspect ratios are considered to represent basal and spinous cells (longer) and granular cells (more flattened). The diffusion problem is solved in a unit cell using a coordinate system conforming to the hexagonal cross section, and an efficient two-dimensional treatment is applied to describe transport in both the cell membranes and intercellular spaces, given their thinness. Results are presented in terms of an effective diffusion coefficient, D¯epi, and partition coefficient, K¯epi/w, for a homogenized representation of the microtransport problem. Representative calculations are carried out for three small solutes—water, L-glucose, and hydrocortisone—covering a wide range of membrane permeability. The effective transport parameters and their microscopic interpretation can be employed within the context of existing three-layer models of skin transport to provide more realistic estimates of the epidermal concentrations of topically applied solutes. PMID:23708370
SCIMAP: Modelling Diffuse Pollution in Large River Basins
NASA Astrophysics Data System (ADS)
Milledge, D.; Heathwaite, L.; Lane, S. N.; Reaney, S. M.
2009-12-01
Polluted rivers are a problem for the plants and animals that require clean water to survive. Watershed scale processes can influence instream aquatic ecosystems by delivering fine sediment, solutes and organic matter from diffuse sources. To improve our rivers we need to identify the pollution sources. Models can help us to do this but these rarely address the extent to which risky land uses are hydrologically-connected, and hence able to deliver, to the drainage network. Those that do tend to apply a full hydrological scheme, which is unfeasible for large watersheds. Here we develop a risk-based modelling framework, SCIMAP, for diffuse pollution from agriculture (Nitrate, Phosphate and Fine Sediment). In each case the basis of the analysis is the joint consideration of the probability of a unit of land (25 m2 cell) producing a particular environmental risk and then of that risk reaching the river. The components share a common treatment of hydrological connectivity but differ in their treatment of each pollution type. We test and apply SCIMAP using spatially-distributed instream water quality data for some of the UK’s largest catchments to infer the processes and the associated process parameters that matter in defining their concentrations. We use these to identify a series of risky field locations, where this land use is readily connected to the river system by overland flow.
The Approximate Number System Acuity Redefined: A Diffusion Model Approach
Park, Joonkoo; Starns, Jeffrey J.
2015-01-01
While all humans are capable of non-verbally representing numerical quantity using so-called the approximate number system (ANS), there exist considerable individual differences in its acuity. For example, in a non-symbolic number comparison task, some people find it easy to discriminate brief presentations of 14 dots from 16 dots while others do not. Quantifying individual ANS acuity from such a task has become an essential practice in the field, as individual differences in such a primitive number sense is thought to provide insights into individual differences in learned symbolic math abilities. However, the dominant method of characterizing ANS acuity—computing the Weber fraction (w)—only utilizes the accuracy data while ignoring response times (RT). Here, we offer a novel approach of quantifying ANS acuity by using the diffusion model, which accounts both accuracy and RT distributions. Specifically, the drift rate in the diffusion model, which indexes the quality of the stimulus information, is used to capture the precision of the internal quantity representation. Analysis of behavioral data shows that w is contaminated by speed-accuracy tradeoff, making it problematic as a measure of ANS acuity, while drift rate provides a measure more independent from speed-accuracy criterion settings. Furthermore, drift rate is a better predictor of symbolic math ability than w, suggesting a practical utility of the measure. These findings demonstrate critical limitations of the use of w and suggest clear advantages of using drift rate as a measure of primitive numerical competence. PMID:26733929
Modeling viscosity and diffusion of plasma mixtures across coupling regimes
NASA Astrophysics Data System (ADS)
Arnault, Philippe
2014-10-01
Viscosity and diffusion of plasma for pure elements and multicomponent mixtures are modeled from the high-temperature low-density weakly coupled regime to the low-temperature high-density strongly coupled regime. Thanks to an atom in jellium modeling, the effect of electron screening on the ion-ion interaction is incorporated through a self-consistent definition of the ionization. This defines an effective One Component Plasma, or an effective Binary Ionic Mixture, that is representative of the strength of the interaction. For the viscosity and the interdiffusion of mixtures, approximate kinetic expressions are supplemented by mixing laws applied to the excess viscosity and self-diffusion of pure elements. The comparisons with classical and quantum molecular dynamics results reveal deviations in the range 20--40% on average with almost no predictions further than a factor of 2 over many decades of variation. Applications in the inertial confinement fusion context could help in predicting the growth of hydrodynamic instabilities.
Diffusion dynamics in the disordered Bose Hubbard model
NASA Astrophysics Data System (ADS)
Wadleigh, Laura; Russ, Philip; Demarco, Brian
2016-05-01
We explore the dynamics of diffusion for out-of-equilibrium superfluid, Mott insulator, and Bose glass states using an atomic realization of the disordered Bose Hubbard (DBH) model. Dynamics in strongly correlated systems, especially far from equilibrium, are not well understood. The introduction of disorder further complicates these systems. We realize the DBH model--which has been central to our understanding of quantum phase transitions in disordered systems--using ultracold Rubidium-87 atoms trapped in a cubic disordered optical lattice. By tightly focusing a beam into the center of the gas, we create a hole in the atomic density profile. We achieve Mott insulator, superfluid, or Bose glass states by varying the interaction and disorder strength, and measure the time evolution of the density profile after removing the central barrier. This allows us to infer diffusion rates from the velocities at the edge of the hole and to look for signatures of superfluid puddles in the Bose glass state. We acknowledge funding from NSF Grant PHY 15-05468, NSF Grant DGE-1144245, and ARO Grant W911NF-12-1-0462.
Desmet, Gert; Deridder, Sander
2011-01-01
Using the permeability analogue of the diffusion and partitioning processes occurring in a chromatographic column, the different Effective Medium Theory (EMT) models that exist in literature for the electrical and thermal conductivity have been transformed into expressions that accurately predict the B-term band broadening in chromatographic columns. The expressions are written in such a form that they hold for both fully porous and porous-shell particles, and both spherical and cylindrical particles are considered. Mutually comparing the established EMT-expressions, it has been found that the most basic variant, i.e., the Maxwell-based expression, is already accurate to within 5% for the typical conditions encountered in liquid phase chromatography, independently of the exact microscopic morphology of the packing. For most typical values of the intra-particle diffusion rate and the species retention factors, it is even accurate to within 1%. If even higher accuracies are needed, more elaborate EMT-expressions are available. The modelling accuracy of all explicit EMT-expressions is much better than the residence time weighted (RTW) B-term expressions that have been used up to now in the field of chromatography, where the error is typically on the order of 10% and more. The EMT-models have also been used to establish expressions for the obstruction and tortuosity factor in packings of non-porous particles. The EMT has also been applied to the meso-porous zone only, yielding an expression for the intra-particle diffusion coefficient that can be used without having to specify any obstruction factor. It has also been shown that the EMT also provides a very simple but exact expression to represent the way in which the solid core obstructs the effective intra-particle diffusion in the case of porous-shell particles. This obstruction factor is given by γ(part)=2/(2+ρ³) for spherical particles and γ(part)=1/(1+ρ³) for cylinders. Back-transforming the obtained
NASA Astrophysics Data System (ADS)
Liang, L. Z. J.; Lemmens, D.; Tempere, J.
2010-06-01
Path integral techniques for the pricing of financial options are mostly based on models that can be recast in terms of a Fokker-Planck differential equation and that, consequently, neglect jumps and only describe drift and diffusion. We present a method to adapt formulas for both the path-integral propagators and the option prices themselves, so that jump processes are taken into account in conjunction with the usual drift and diffusion terms. In particular, we focus on stochastic volatility models, such as the exponential Vasicek model, and extend the pricing formulas and propagator of this model to incorporate jump diffusion with a given jump size distribution. This model is of importance to include non-Gaussian fluctuations beyond the Black-Scholes model, and moreover yields a lognormal distribution of the volatilities, in agreement with results from superstatistical analysis. The results obtained in the present formalism are checked with Monte Carlo simulations.
Comparison of Turbulent Thermal Diffusivity and Scalar Variance Models
NASA Technical Reports Server (NTRS)
Yoder, Dennis A.
2016-01-01
In this study, several variable turbulent Prandtl number formulations are examined for boundary layers, pipe flow, and axisymmetric jets. The model formulations include simple algebraic relations between the thermal diffusivity and turbulent viscosity as well as more complex models that solve transport equations for the thermal variance and its dissipation rate. Results are compared with available data for wall heat transfer and profile measurements of mean temperature, the root-mean-square (RMS) fluctuating temperature, turbulent heat flux and turbulent Prandtl number. For wall-bounded problems, the algebraic models are found to best predict the rise in turbulent Prandtl number near the wall as well as the log-layer temperature profile, while the thermal variance models provide a good representation of the RMS temperature fluctuations. In jet flows, the algebraic models provide no benefit over a constant turbulent Prandtl number approach. Application of the thermal variance models finds that some significantly overpredict the temperature variance in the plume and most underpredict the thermal growth rate of the jet. The models yield very similar fluctuating temperature intensities in jets from straight pipes and smooth contraction nozzles, in contrast to data that indicate the latter should have noticeably higher values. For the particular low subsonic heated jet cases examined, changes in the turbulent Prandtl number had no effect on the centerline velocity decay.
Pre-Clinical Models of Diffuse Intrinsic Pontine Glioma
Misuraca, Katherine L.; Cordero, Francisco J.; Becher, Oren J.
2015-01-01
Diffuse intrinsic pontine glioma (DIPG) is a rare and incurable brain tumor that arises in the brainstem of children predominantly between the ages of 6 and 8. Its intricate morphology and involvement of normal pons tissue precludes surgical resection, and the standard of care today remains fractionated radiation alone. In the past 30 years, there have been no significant advances made in the treatment of DIPG. This is largely because we lack good models of DIPG and therefore have little biological basis for treatment. In recent years, however, due to increased biopsy and acquisition of autopsy specimens, research is beginning to unravel the genetic and epigenetic drivers of DIPG. Insight gleaned from these studies has led to improvements in approaches to both model these tumors in the lab and to potentially treat them in the clinic. This review will detail the initial strides toward modeling DIPG in animals, which included allograft and xenograft rodent models using non-DIPG glioma cells. Important advances in the field came with the development of in vitro cell and in vivo xenograft models derived directly from autopsy material of DIPG patients or from human embryonic stem cells. Finally, we will summarize the progress made in the development of genetically engineered mouse models of DIPG. Cooperation of studies incorporating all of these modeling systems to both investigate the unique mechanisms of gliomagenesis in the brainstem and to test potential novel therapeutic agents in a preclinical setting will result in improvement in treatments for DIPG patients. PMID:26258075
Five forest harvesting simulation models, part 1: modeling characteristics
Goulet, D.V.; Iff, R.H.; Sirois, D.L.
1980-01-01
This paper is the first of two describing the conclusions from a study to determine the state of the art in timber harvesting computer simulation modeling. Five models were evaluated -- Forest Harvesting Simulation Model (FHSM), Full Tree Field Chipping (FTFC), Harvesting System Simulator (HSS), Simulation Applied to Logging Systems (SAPLOS), and Timber Harvesting and Transport Simulator (THATS) -- for their potential use in southern forest harvesting operations. In Part I, modeling characteristics and overall model philosophy are identified and illustrated. This includes a detailed discussion of the wood flow process in each model, accounting strategies for productive/non-productive times, performance variables, and the different types of harvesting systems modelable. In Part II we discuss user implementation problems. Those dealt with in detail are: What questions can be asked of the model. What are the modeling tradeoffs, and how do they impact on the analysis. What are the computer skills necessary to effectively work with the model. What computer support is needed. Are the models operational. The results provide a good picture of the state of the art in timber harvesting computer simulation. Much learning has occurred in the generation of these models, and many modeling and implementation problems have been uncovered, some of which remain unsolved. Hence, the user needs to examine closely the model and the intended application so that results will represent usable, valid data. It is recommended that the development of timber harvesting computer simulation modeling continue, so that existing and proposed timber harvesting strategies can be adequately evaluated. A set of design criteria are proposed. (Refs. 21).
12 CFR Appendix A to Part 716 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 717, subpart... 12 Banks and Banking 7 2012-01-01 2012-01-01 false Model Privacy Form A Appendix A to Part 716... CONSUMER FINANCIAL INFORMATION Pt. 716, App. A Appendix A to Part 716—Model Privacy Form A.The...
12 CFR Appendix A to Part 716 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 717, subpart... 12 Banks and Banking 7 2013-01-01 2013-01-01 false Model Privacy Form A Appendix A to Part 716... CONSUMER FINANCIAL INFORMATION Pt. 716, App. A Appendix A to Part 716—Model Privacy Form A.The...
12 CFR Appendix A to Part 716 - Model Privacy Form
Code of Federal Regulations, 2010 CFR
2010-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 717, subpart... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Model Privacy Form A Appendix A to Part 716... CONSUMER FINANCIAL INFORMATION Pt. 716, App. A Appendix A to Part 716—Model Privacy Form A.The...
12 CFR Appendix A to Part 716 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... the model form under this part, must comply with section 624 of the FCRA and 12 CFR part 717, subpart... 12 Banks and Banking 6 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 716... CONSUMER FINANCIAL INFORMATION Pt. 716, App. A Appendix A to Part 716—Model Privacy Form A.The...
JPEG-2000 Part 10 Verification Model
2003-03-04
VM10 is a research software implementation of the ISO/IEC JPEG-2000 Still Image Coding standard (ISO international Standard 15444). JPEG-2000 image coding involves subband codiing and compression of digital raster images to facilitate storage and transmission of such imagery. Images are decomposed into space/scale subbands using cascades of two-dimensional (tensor product) discrete wavelet transforms. The wavelet transforms can be either reversible (integer-to-integer) transforms or irreversible (integer-to-float). The subbands in each resolution level are quantized by uniformmore » scalar quantization in the irreversible case. The resulting integer subbands in each resolution level are partitioned into spatially localized code blocks to facilitate localized entropy decoding. Code blocks are encoded and packaged into an embedded bitstream using binary arithmetic bitplane coding (the MQ Coder algorithm applied to hierarchical bitplane coding (the MQ coder algorithm applied to hierachical bitplane context modeling). The resultant compressed bitstream is configured for use with the JPIP interactive client-server protocol (JPEG-2000 part 9). VM10 is written in ANSI C++ using the Biltz++ array class library. To enable development of multidimensional image coding algorithms, VM10 is templated on the dimension of the array containers. It was developed with the GNU g++ compiler on both Linux (Red Hat) and Windows/cygwin platforms, although it should compile and run under other ANSI C++ compilers as well. Software design is highly modular and object-oriented in order to facilitate rapid development and frequent revision and experimentation. No attempt has been made to optimize the run-time performance of the code. The software performs both the encoding and decoding operations involved in JPEG-2000 image coding, as implemented in apps/compress/main.cpp and apps/expand/main.cpp. VM10 implements all of the JPEG-2000 baseline (Part 1, ISO 15444-1) and portions of the
JPEG-2000 Part 10 Verification Model
Mniszewski, Susan; Rivenburgh, Reid; Brislawn, Chris
2003-03-04
VM10 is a research software implementation of the ISO/IEC JPEG-2000 Still Image Coding standard (ISO international Standard 15444). JPEG-2000 image coding involves subband codiing and compression of digital raster images to facilitate storage and transmission of such imagery. Images are decomposed into space/scale subbands using cascades of two-dimensional (tensor product) discrete wavelet transforms. The wavelet transforms can be either reversible (integer-to-integer) transforms or irreversible (integer-to-float). The subbands in each resolution level are quantized by uniform scalar quantization in the irreversible case. The resulting integer subbands in each resolution level are partitioned into spatially localized code blocks to facilitate localized entropy decoding. Code blocks are encoded and packaged into an embedded bitstream using binary arithmetic bitplane coding (the MQ Coder algorithm applied to hierarchical bitplane coding (the MQ coder algorithm applied to hierachical bitplane context modeling). The resultant compressed bitstream is configured for use with the JPIP interactive client-server protocol (JPEG-2000 part 9). VM10 is written in ANSI C++ using the Biltz++ array class library. To enable development of multidimensional image coding algorithms, VM10 is templated on the dimension of the array containers. It was developed with the GNU g++ compiler on both Linux (Red Hat) and Windows/cygwin platforms, although it should compile and run under other ANSI C++ compilers as well. Software design is highly modular and object-oriented in order to facilitate rapid development and frequent revision and experimentation. No attempt has been made to optimize the run-time performance of the code. The software performs both the encoding and decoding operations involved in JPEG-2000 image coding, as implemented in apps/compress/main.cpp and apps/expand/main.cpp. VM10 implements all of the JPEG-2000 baseline (Part 1, ISO 15444-1) and portions of the published
On Modeling Viral Diffusion in Heterogeneous Wireless Networks
NASA Astrophysics Data System (ADS)
Nguyen, Hoai-Nam; Shinoda, Yoichi
Smart phones and computers now are able to co-work in a wireless environment where malware can propagate. Although many investigations have modeled the spread of malware, little has been done to take into account different characteristics of items to see how they affect disease diffusion in an ad hoc network. We have therefore developed a novel framework, consisting of two models, which consider diversity of objects as well as interactions between their different classes. Our framework is able to produce a huge result space thus makes it appropriate to describe many viral proliferating scenarios. Additionally, we have developed a formula to calculate the possible average number of newly infected devices in the considered system. An important contribution of our work is the comprehension of item diversity, which states that a mixture of device types causes a bigger malware spread as the number of device types in the network increases.
A Lattice Boltzmann Model for Oscillating Reaction-Diffusion
NASA Astrophysics Data System (ADS)
Rodríguez-Romo, Suemi; Ibañez-Orozco, Oscar; Sosa-Herrera, Antonio
2016-07-01
A computational algorithm based on the lattice Boltzmann method (LBM) is proposed to model reaction-diffusion systems. In this paper, we focus on how nonlinear chemical oscillators like Belousov-Zhabotinsky (BZ) and the chlorite-iodide-malonic acid (CIMA) reactions can be modeled by LBM and provide with new insight into the nature and applications of oscillating reactions. We use Gaussian pulse initial concentrations of sulfuric acid in different places of a bidimensional reactor and nondiffusive boundary walls. We clearly show how these systems evolve to a chaotic attractor and produce specific pattern images that are portrayed in the reactions trajectory to the corresponding chaotic attractor and can be used in robotic control.
NASA Astrophysics Data System (ADS)
Morgan, D. J.; Chamberlain, K. J.; Wilson, C. J. N.
2014-12-01
Diffusion modelling of elemental gradients across compositional zones within crystals is frequently used to investigate timescales of various magmatic processes. In most cases, however, only a single crystal phase is used for this modelling. The ~0.76 Ma Bishop Tuff (Long Valley, eastern California) in later parts of its eruptive sequence has zoned orthopyroxene, quartz and sanidine. It thus provides an unusual opportunity to compare the modelled timescales from each phase, and assess the limitations of single-phase diffusion modelling in lower-temperature, rhyolitic volcanic systems. The presence of a late-stage compositionally distinct melt (the 'bright-rim' melt) mixing into the lower parts of the Bishop magma chamber has been noted by many authors [e.g. Wark et al. 2007, Geology 35, 235; Roberge et al. 2013, CMP 165, 237; Chamberlain et al. 2014, J Petrol 55, 395] in later-erupted material discharged from vents along the northern ring fracture of the caldera. Here we present the results of 1D diffusion modelling of Ba and Sr in sanidine, Ti in quartz and Fe-Mg interdiffusion in orthopyroxene in samples from later-erupted ignimbrite packages in the tuff. Timescales from diffusion modelling of Fe-Mg interdiffusion in orthopyroxene are <20 years; Ti in quartz <150 years and from Ba and Sr in sanidine <10000 years. The orders of magnitude variance between different crystal phases can be attributed to either distinct differences in the timing of interaction with the 'bright-rim' melt, or to uncertainties in the diffusion coefficient (orthopyroxene) and incorrect assumptions about the initial conditions for diffusion modelling (sanidine), or some combination of these factors. By combined modelling of Ba and Sr diffusion in sanidine the diffusion timescales are reduced to <1000 years, implying that interaction of the 'bright-rim' melt may have occurred over more extended timescales, and was not necessarily a direct eruptive trigger for the Bishop Tuff eruption. We
Rule-based spatial modeling with diffusing, geometrically constrained molecules
2010-01-01
Background We suggest a new type of modeling approach for the coarse grained, particle-based spatial simulation of combinatorially complex chemical reaction systems. In our approach molecules possess a location in the reactor as well as an orientation and geometry, while the reactions are carried out according to a list of implicitly specified reaction rules. Because the reaction rules can contain patterns for molecules, a combinatorially complex or even infinitely sized reaction network can be defined. For our implementation (based on LAMMPS), we have chosen an already existing formalism (BioNetGen) for the implicit specification of the reaction network. This compatibility allows to import existing models easily, i.e., only additional geometry data files have to be provided. Results Our simulations show that the obtained dynamics can be fundamentally different from those simulations that use classical reaction-diffusion approaches like Partial Differential Equations or Gillespie-type spatial stochastic simulation. We show, for example, that the combination of combinatorial complexity and geometric effects leads to the emergence of complex self-assemblies and transportation phenomena happening faster than diffusion (using a model of molecular walkers on microtubules). When the mentioned classical simulation approaches are applied, these aspects of modeled systems cannot be observed without very special treatment. Further more, we show that the geometric information can even change the organizational structure of the reaction system. That is, a set of chemical species that can in principle form a stationary state in a Differential Equation formalism, is potentially unstable when geometry is considered, and vice versa. Conclusions We conclude that our approach provides a new general framework filling a gap in between approaches with no or rigid spatial representation like Partial Differential Equations and specialized coarse-grained spatial simulation systems like
NASA Astrophysics Data System (ADS)
Yolcu, Cem; Memiç, Muhammet; Şimşek, Kadir; Westin, Carl-Fredrik; Özarslan, Evren
2016-05-01
We study the influence of diffusion on NMR experiments when the molecules undergo random motion under the influence of a force field and place special emphasis on parabolic (Hookean) potentials. To this end, the problem is studied using path integral methods. Explicit relationships are derived for commonly employed gradient waveforms involving pulsed and oscillating gradients. The Bloch-Torrey equation, describing the temporal evolution of magnetization, is modified by incorporating potentials. A general solution to this equation is obtained for the case of parabolic potential by adopting the multiple correlation function (MCF) formalism, which has been used in the past to quantify the effects of restricted diffusion. Both analytical and MCF results were found to be in agreement with random walk simulations. A multidimensional formulation of the problem is introduced that leads to a new characterization of diffusion anisotropy. Unlike the case of traditional methods that employ a diffusion tensor, anisotropy originates from the tensorial force constant, and bulk diffusivity is retained in the formulation. Our findings suggest that some features of the NMR signal that have traditionally been attributed to restricted diffusion are accommodated by the Hookean model. Under certain conditions, the formalism can be envisioned to provide a viable approximation to the mathematically more challenging restricted diffusion problems.
Gleeson, Michael R.; Sheridan, John T.
2009-09-15
The photochemical processes present during free-radical-based holographic grating formation are examined. A kinetic model is presented, which includes, in a more nearly complete and physically realistic way, most of the major photochemical and nonlocal photopolymerization-driven diffusion effects. These effects include: (i) non-steady-state kinetics (ii) spatially and temporally nonlocal polymer chain growth (iii) time varying photon absorption (iv) diffusion controlled viscosity effects (v) multiple termination mechanisms, and (vi) inhibition. The convergence of the predictions of the resulting model is then examined. Comparisons with experimental results are carried out in Part II of this series of papers [J. Opt. Soc. Am. B 26, 1746 (2009)].
NASA Astrophysics Data System (ADS)
Yoshida, Masayuki; Morooka, Masami; Takahashi, Manabu; Tomokage, Hajime
2000-05-01
Based on the pair diffusion models of vacancy and interstitial (V and I) mechanisms, the V and I components of effective P diffusion coefficient, DP^+,Veff and DP^+,Ieff, and the controlling process of P diffusion in Si are obtained. Assuming that the I mechanism is dominant, not only the I- concentration, CI^-, but also its gradient, d CI^-/d λ , is effective on DP^+,Ieff at high CP^+. DP^+,Ieff is large at d CI^-/d λ <0 and small at d CI^-/d λ >0. P+ and I- are generated by the dissociation of P-I pair. When excess I- thus generated is removed, d CI^-/d λ <0 is obtained. d CI^-/d λ <0 is also obtained by the decrease in quasi self-interstitial formation energy. Several diffusion models simulate the P diffusion profile well under an inert atmosphere. Applying the controlling process to them, the reason why they simulate the P profile well is investigated. Because all of them simulate the P profile well, it is difficult to conclude which model is correct. It is suggested that it is possible to conclude which model is correct from the P profile under oxidation at CP^+s >1× 1020 cm-3 (s: surface).
Photoionized Mixing Layer Models of the Diffuse Ionized Gas
NASA Astrophysics Data System (ADS)
Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe
2009-04-01
It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/Hα, [O I]/Hα, [N II]/[S II], and [O III]/Hβ reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.
NASA Astrophysics Data System (ADS)
Dawson, Joanne; Mcclure-Griffiths, Naomi; Jones, Paul; Dickey, John; Cunningham, Maria; Jones, Courtney
2011-10-01
The condensation of molecular clouds from the atomic ISM is a key link in the lifecycle of material in galactic systems, but one that remains poorly observationally constrained. This project will obtain HI, OH and CO line data at parsec and sub-parsec resolutions in order to form a comprehensive picture of the anatomy of a region in which this atomic-molecular transition is occurring. This combination of complementary tracers will reveal the medium throughout this evolutionary process, providing an unparalleled dataset for comparison with theoretical models, and allowing the testing of key predictions such as structure formation size scales and the degree of interpenetration of the molecular and atomic phases. This proposal requests 25 hours to obtain sensitive diffuse OH 18cm line data with Parkes, in order to bridge the gap between the fully atomic and molecular regimes probed by HI and CO. This data will be used to estimate the mass fraction of transition-state gas, investigate its global distribution, and will provide short-spacing correction to high-resolution ATCA data. This document comprises one of a set of three observing proposals submitted this semester as part of this project.
Mukhopadhyay, B; Bhattacharyya, R
2006-02-01
The paper is concerned with the effect of variable dispersal rates on Turing instability of a non-Lotka-Volterra reaction-diffusion system. In ecological applications, the dispersal rates of different species tends to oscillate in time. This oscillation is modeled by temporal variation in the diffusion coefficient with large as well as small periodicity. The case of large periodicity is analyzed using the theory of Floquet multipliers and that of the small periodicity by using Hill's equation. The effect of such variation on the resulting Turing space is studied. A comparative analysis of the Turing spaces with constant diffusivity and variable diffusivities is performed. Numerical simulations are carried out to support analytical findings. PMID:16794932
LHC Beam Diffusion Dependence on RF Noise: Models And Measurements
Mastorides, T.; Rivetta, C.; Fox, J.D.; Van Winkle, D.; Baudrenghien, P.; Butterworth, A.; Molendijk, J.; /CERN
2010-09-14
Radio Frequency (RF) accelerating system noise and non-idealities can have detrimental impact on the LHC performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and RF loop dynamics with the bunch length growth [1]. Measurements were conducted at LHC to validate the formalism, determine the performance limiting RF components, and provide the foundation for beam diffusion estimates for higher energies and intensities. A brief summary of these results is presented in this work. During a long store, the relation between the energy lost to synchrotron radiation and the noise injected to the beam by the RF accelerating voltage determines the growth of the bunch energy spread and longitudinal emittance. Since the proton synchrotron radiation in the LHC is very low, the beam diffusion is extremely sensitive to RF perturbations. The theoretical formalism presented in [1], suggests that the noise experienced by the beam depends on the cavity phase noise power spectrum, filtered by the beam transfer function, and aliased due to the periodic sampling of the accelerating voltage signal V{sub c}. Additionally, the dependence of the RF accelerating cavity noise spectrum on the Low Level RF (LLRF) configurations has been predicted using time-domain simulations and models [2]. In this work, initial measurements at the LHC supporting the above theoretical formalism and simulation predictions are presented.
Magnetic field diffusion modeling of a small enclosed firing system
Warne, L.K.; Merewether, K.O.
1996-01-01
Intense magnetic fields exist in the immediate vicinity of a lightning strike (and near power lines). Conducting barriers increase the rise time (and thus decrease the rise rate) interior to the barrier, but typically do not prevent penetration of the magnetic field, since the lightning current fall time may be larger than the barrier diffusion time. Thus, substantial energy is present in the interior field, although the degradation of rise rate makes it more difficult to couple into electrical circuits. This report assesses the threat posed by the diffusive magnetic field to interior components and wire loops (where voltages are induced). Analytical and numerical bounding analyses are carried out on a pill box shaped conducting barrier to develop estimates for the worst case magnetic field threats inside the system. Worst case induced voltages and energies are estimated and compared with threshold charge voltages and energies on the output capacitor of the system. Variability of these quantities with respect to design parameters are indicated. The interior magnetic field and induced voltage estimates given in this report can be used as excitations for more detailed interior and component models.
Analytical model of diffuse reflectance spectrum of skin tissue
Lisenko, S A; Kugeiko, M M; Firago, V A; Sobchuk, A N
2014-01-31
We have derived simple analytical expressions that enable highly accurate calculation of diffusely reflected light signals of skin in the spectral range from 450 to 800 nm at a distance from the region of delivery of exciting radiation. The expressions, taking into account the dependence of the detected signals on the refractive index, transport scattering coefficient, absorption coefficient and anisotropy factor of the medium, have been obtained in the approximation of a two-layer medium model (epidermis and dermis) for the same parameters of light scattering but different absorption coefficients of layers. Numerical experiments on the retrieval of the skin biophysical parameters from the diffuse reflectance spectra simulated by the Monte Carlo method show that commercially available fibre-optic spectrophotometers with a fixed distance between the radiation source and detector can reliably determine the concentration of bilirubin, oxy- and deoxyhaemoglobin in the dermis tissues and the tissue structure parameter characterising the size of its effective scatterers. We present the examples of quantitative analysis of the experimental data, confirming the correctness of estimates of biophysical parameters of skin using the obtained analytical expressions. (biophotonics)
Analytical model of diffuse reflectance spectrum of skin tissue
NASA Astrophysics Data System (ADS)
Lisenko, S. A.; Kugeiko, M. M.; Firago, V. A.; Sobchuk, A. N.
2014-01-01
We have derived simple analytical expressions that enable highly accurate calculation of diffusely reflected light signals of skin in the spectral range from 450 to 800 nm at a distance from the region of delivery of exciting radiation. The expressions, taking into account the dependence of the detected signals on the refractive index, transport scattering coefficient, absorption coefficient and anisotropy factor of the medium, have been obtained in the approximation of a two-layer medium model (epidermis and dermis) for the same parameters of light scattering but different absorption coefficients of layers. Numerical experiments on the retrieval of the skin biophysical parameters from the diffuse reflectance spectra simulated by the Monte Carlo method show that commercially available fibre-optic spectrophotometers with a fixed distance between the radiation source and detector can reliably determine the concentration of bilirubin, oxy- and deoxyhaemoglobin in the dermis tissues and the tissue structure parameter characterising the size of its effective scatterers. We present the examples of quantitative analysis of the experimental data, confirming the correctness of estimates of biophysical parameters of skin using the obtained analytical expressions.
Complex Geometric Models of Diffusion and Relaxation in Healthy and Damaged White Matter
Farrell, Jonathan A.D.; Smith, Seth A.; Reich, Daniel S.; Calabresi, Peter A.; van Zijl, Peter C.M.
2010-01-01
Which aspects of tissue microstructure affect diffusion weighted MRI signals? Prior models, many of which use Monte-Carlo simulations, have focused on relatively simple models of the cellular microenvironment and have not considered important anatomic details. With the advent of higher-order analysis models for diffusion imaging, such as high-angular-resolution diffusion imaging (HARDI), more realistic models are necessary. This paper presents and evaluates the reproducibility of simulations of diffusion in complex geometries. Our framework is quantitative, does not require specialized hardware, is easily implemented with little programming experience, and is freely available as open-source software. Models may include compartments with different diffusivities, permeabilities, and T2 time constants using both parametric (e.g., spheres and cylinders) and arbitrary (e.g., mesh-based) geometries. Three-dimensional diffusion displacement-probability functions are mapped with high reproducibility, and thus can be readily used to assess reproducibility of diffusion-derived contrasts. PMID:19739233
A model for the diffuse attenuation coefficient of downwelling irradiance
NASA Astrophysics Data System (ADS)
Lee, Zhong-Ping; Du, Ke-Ping; Arnone, Robert
2005-02-01
The diffuse attenuation coefficient for downwelling irradiance (Kd) is an important parameter for ocean studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color remote sensing. At present, values of Kd from remote sensing are estimated using empirical algorithms. Such an approach is insufficient to provide an understanding regarding the variation of Kd and contains large uncertainties in the derived values. In this study a semianalytical model for Kd is developed based on the radiative transfer equation, with values of the model parameters derived from Hydrolight simulations using the averaged particle phase function. The model is further tested with data simulated using significantly different particle phase functions, and the modeled Kd are found matching Hydrolight Kd very well (˜2% average error and ˜12% maximum error). Such a model provides an improved interpretation about the variation of Kd and a basis to more accurately determine Kd (especially using data from remote sensing).
A seed-diffusion model for tropical tree diversity patterns
NASA Astrophysics Data System (ADS)
Derzsi, A.; Néda, Z.
2012-10-01
Diversity patterns of tree species in a tropical forest community are approached by a simple lattice model and investigated by Monte Carlo simulations using a backtracking method. Our spatially explicit neutral model is based on a simple statistical physics process, namely the diffusion of seeds. The model has three parameters: the speciation rate, the size of the meta-community in which the studied tree-community is embedded, and the average surviving time of the seeds. By extensive computer simulations we aim towards the reproduction of relevant statistical measures derived from the experimental data of the Barro Colorado Island tree census in 1995. The first two parameters of the model are fixed to known values, characteristic of the studied community, thus obtaining a model with only one freely adjustable parameter. As a result of this, the average number of species in the considered territory, the relative species abundance distribution, the species-area relationship and the spatial auto-correlation function of the individuals in abundant species are simultaneously fitted with only one parameter which is the average surviving time of the seeds.
Ohashi, Hidenori; Tamaki, Takanori; Yamaguchi, Takeo
2011-12-29
Molecular collisions, which are the microscopic origin of molecular diffusive motion, are affected by both the molecular surface area and the distance between molecules. Their product can be regarded as the free space around a penetrant molecule defined as the "shell-like free volume" and can be taken as a characteristic of molecular collisions. On the basis of this notion, a new diffusion theory has been developed. The model can predict molecular diffusivity in polymeric systems using only well-defined single-component parameters of molecular volume, molecular surface area, free volume, and pre-exponential factors. By consideration of the physical description of the model, the actual body moved and which neighbor molecules are collided with are the volume and the surface area of the penetrant molecular core. In the present study, a semiempirical quantum chemical calculation was used to calculate both of these parameters. The model and the newly developed parameters offer fairly good predictive ability. PMID:22082054
A kinetic model for molecular diffusion through pores.
D'Agostino, Tommaso; Salis, Samuele; Ceccarelli, Matteo
2016-07-01
The number of pathogens developing multiple drug resistance is ever increasing. The impact on healthcare systems is huge and the need for novel antibiotics as well a new way to develop them is urgent, especially against Gram-negative bacteria. The first defense of these bacteria is the outer membrane, where unspecific protein channels (porins) modulate nutrients passive diffusion. Also polar antibiotics enter through this path and down-regulation and/or mutation of porins are very common in drug resistant strains. Our inability to come up with novel effective antibiotics mostly relies upon the insufficient comprehension of the key molecular features enabling better penetration through porins. Molecular dynamics simulations offer an extraordinary tool in the study of the dynamics of biological systems; however, one of the major drawbacks of this method is that its use is currently restricted to study time scales of the order of microsecond. Enhanced sampling methods like Metadynamics have been recently used to investigate the diffusion of antibiotics through bacterial porins. The main limitation is that dynamical properties cannot be estimated because of the different potential that the systems under study are experiencing. Recently, the scope of Metadynamics has been extended. By applying an a posteriori analysis one can obtain rates of transitions and rate-limiting steps of the process under study, directly comparable with kinetic data extracted from electrophysiology experiments. In this work, we apply this method to the study of the permeability of Escherichia coli's OmpF with respect to Meropenem, finding good agreement with the residence time obtained analyzing experimental current noise. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov. PMID:26796683
NASA Astrophysics Data System (ADS)
Martelli, Fabrizio; Ninni, Paola Di; Zaccanti, Giovanni; Contini, Davide; Spinelli, Lorenzo; Torricelli, Alessandro; Cubeddu, Rinaldo; Wabnitz, Heidrun; Mazurenka, Mikhail; Macdonald, Rainer; Sassaroli, Angelo; Pifferi, Antonio
2014-07-01
We present the experimental implementation and validation of a phantom for diffuse optical imaging based on totally absorbing objects for which, in the previous paper [J. Biomed. Opt. 18(6), 066014, (2013)], we have provided the basic theory. Totally absorbing objects have been manufactured as black polyvinyl chloride (PVC) cylinders and the phantom is a water dilution of intralipid-20% as the diffusive medium and India ink as the absorber, filled into a black scattering cell made of PVC. By means of time-domain measurements and of Monte Carlo simulations, we have shown the reliability, the accuracy, and the robustness of such a phantom in mimicking typical absorbing perturbations of diffuse optical imaging. In particular, we show that such a phantom can be used to generate any absorption perturbation by changing the volume and position of the totally absorbing inclusion.
Diffusion bonding and its application to manufacturing. [for joining of metal parts
NASA Technical Reports Server (NTRS)
Spurgeon, W. M.
1972-01-01
In its simplest form diffusion bonding is accomplished by placing clean metal surfaces together under a sufficient load and heating. The natural interatomic attractive force between atoms transforms the interface into a natural grain boundary. Therefore, in principle, the properties of the bond area are identical to those of the parent metal. Other advantages of diffusion bonding over conventional methods of bonding include freedom from residual stresses, excessive deformation, foreign metals, or changed crystal structures. Stainless steels, nickel-base superalloys, and aluminum alloys have all been successfully joined. Complex hardware, including integrated flueric devices, jet engine servovalves, and porous woven structures have been fabricated. The processing involved is discussed, along with such theoretical considerations as the role of metal surfaces, the formation of metal contact junctions, and the mechanisms of material transport in diffusion bonding.
NASA Astrophysics Data System (ADS)
Araruna, F. D.; Braz e Silva, P.; Carvalho, R. R.; Rojas-Medar, M. A.
2015-06-01
We consider the motion of a viscous incompressible fluid consisting of two components with a diffusion effect obeying Fick's law in ℝ3. We prove that there exists a small time interval where the fluid variables converge uniformly as the viscosity and the diffusion coefficient tend to zero. In the limit, we find a non-homogeneous, non-viscous, incompressible fluid governed by an Euler-like system.
The small ice cap instability in diffusive climate models
NASA Technical Reports Server (NTRS)
North, G. R.
1984-01-01
Simple climate models which invoke diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a radius of about 20 deg on a great circle. Attention is presently given to a solution of this phenomenon which is physically appealing. The ice-free solution has a thermal minimum, and if the minimum temperature is just above the critical value for ice formation, then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature. A second stable solution will then exist whose spatial extent is determined by the range of the influence function of a point sink of heat, due to the albedo shift in the patch.
Individual differences in emotion word processing: A diffusion model analysis.
Mueller, Christina J; Kuchinke, Lars
2016-06-01
The exploratory study investigated individual differences in implicit processing of emotional words in a lexical decision task. A processing advantage for positive words was observed, and differences between happy and fear-related words in response times were predicted by individual differences in specific variables of emotion processing: Whereas more pronounced goal-directed behavior was related to a specific slowdown in processing of fear-related words, the rate of spontaneous eye blinks (indexing brain dopamine levels) was associated with a processing advantage of happy words. Estimating diffusion model parameters revealed that the drift rate (rate of information accumulation) captures unique variance of processing differences between happy and fear-related words, with highest drift rates observed for happy words. Overall emotion recognition ability predicted individual differences in drift rates between happy and fear-related words. The findings emphasize that a significant amount of variance in emotion processing is explained by individual differences in behavioral data. PMID:26860908
Energy efficient engine diffuser/combustor model technology
NASA Technical Reports Server (NTRS)
Gardner, W.
1980-01-01
A full scale, full annular diffuser/combustor model test rig was tested to investigate how configurational changes affect pressure loss and flow separation characteristics. The rig was characterized by five major modules: inlet; prediffuser; strut; simulated combustor; and full combustor. The prediffuser featured a short, curved wall dump design. Performance goals included: (1) a separation-free prediffuser flow field; (2) total pressure loss limited to 3.0 percent in the prediffuser and shrouds; and (3) an overall section pressure loss of 5.5 percent P sub T3 at the design airflow distribution. The results indicated that the prediffuser configurations operate well within the program goals for pressure loss and demonstrate separation free operation over a wide range of inlet conditions.
Directional entropy based model for diffusivity-driven tumor growth.
de Oliveira, Marcelo E; Neto, Luiz M G
2016-04-01
In this work, we present and investigate a multiscale model to simulate 3D growth of glioblastomas (GBMs) that incorporates features of the tumor microenvironment and derives macroscopic growth laws from microscopic tissue structure information. We propose a normalized version of the Shannon entropy as an alternative measure of the directional anisotropy for an estimation of the diffusivity tensor in cases where the latter is unknown. In our formulation, the tumor aggressiveness and morphological behavior is tissue-type dependent, i.e. alterations in white and gray matter regions (which can e.g. be induced by normal aging in healthy individuals or neurodegenerative diseases) affect both tumor growth rates and their morphology. The feasibility of this new conceptual approach is supported by previous observations that the fractal dimension, which correlates with the Shannon entropy we calculate, is a quantitative parameter that characterizes the variability of brain tissue, thus, justifying the further evaluation of this new conceptual approach. PMID:27105991
A diffuse interface model of grain boundary faceting
NASA Astrophysics Data System (ADS)
Abdeljawad, F.; Medlin, D. L.; Zimmerman, J. A.; Hattar, K.; Foiles, S. M.
2016-06-01
Interfaces, free or internal, greatly influence the physical properties and stability of materials microstructures. Of particular interest are the processes that occur due to anisotropic interfacial properties. In the case of grain boundaries (GBs) in metals, several experimental observations revealed that an initially flat GB may facet into hill-and-valley structures with well defined planes and corners/edges connecting them. Herein, we present a diffuse interface model that is capable of accounting for strongly anisotropic GB properties and capturing the formation of hill-and-valley morphologies. The hallmark of our approach is the ability to independently examine the various factors affecting GB faceting and subsequent facet coarsening. More specifically, our formulation incorporates higher order expansions to account for the excess energy due to facet junctions and their non-local interactions. As a demonstration of the modeling capability, we consider the Σ5 <001 > tilt GB in body-centered-cubic iron, where faceting along the {210} and {310} planes was experimentally observed. Atomistic calculations were utilized to determine the inclination-dependent GB energy, which was then used as an input in our model. Linear stability analysis and simulation results highlight the role of junction energy and associated non-local interactions on the resulting facet length scales. Broadly speaking, our modeling approach provides a general framework to examine the microstructural stability of polycrystalline systems with highly anisotropic GBs.
Anomalous diffusion in neutral evolution of model proteins.
Nelson, Erik D; Grishin, Nick V
2015-06-01
Protein evolution is frequently explored using minimalist polymer models, however, little attention has been given to the problem of structural drift, or diffusion. Here, we study neutral evolution of small protein motifs using an off-lattice heteropolymer model in which individual monomers interact as low-resolution amino acids. In contrast to most earlier models, both the length and folded structure of the polymers are permitted to change. To describe structural change, we compute the mean-square distance (MSD) between monomers in homologous folds separated by n neutral mutations. We find that structural change is episodic, and, averaged over lineages (for example, those extending from a single sequence), exhibits a power-law dependence on n. We show that this exponent depends on the alignment method used, and we analyze the distribution of waiting times between neutral mutations. The latter are more disperse than for models required to maintain a specific fold, but exhibit a similar power-law tail. PMID:26172648
Stochastic fire-diffuse-fire model with realistic cluster dynamics
NASA Astrophysics Data System (ADS)
Calabrese, Ana; Fraiman, Daniel; Zysman, Daniel; Ponce Dawson, Silvina
2010-09-01
Living organisms use waves that propagate through excitable media to transport information. Ca2+ waves are a paradigmatic example of this type of processes. A large hierarchy of Ca2+ signals that range from localized release events to global waves has been observed in Xenopus laevis oocytes. In these cells, Ca2+ release occurs trough inositol 1,4,5-trisphosphate receptors (IP3Rs) which are organized in clusters of channels located on the membrane of the endoplasmic reticulum. In this article we construct a stochastic model for a cluster of IP3R ’s that replicates the experimental observations reported in [D. Fraiman , Biophys. J. 90, 3897 (2006)10.1529/biophysj.105.075911]. We then couple this phenomenological cluster model with a reaction-diffusion equation, so as to have a discrete stochastic model for calcium dynamics. The model we propose describes the transition regimes between isolated release and steadily propagating waves as the IP3 concentration is increased.
The theoretical bases and computational techniques are presented for U.S. and Russian complex terrain diffusion models developed for engineering applications. hile the U.S. model is based on the modified Gaussian diffusion model, the Russian model is based on the analytical appro...
31 CFR Appendix A to Part 132 - Model Notice
Code of Federal Regulations, 2010 CFR
2010-07-01
... one another can be found at part 233 of title 12 of the U.S. Code of Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations (31 CFR part 132). ... INTERNET GAMBLING Pt. 132, App. A Appendix A to Part 132—Model Notice Re: U.S. Unlawful Internet...
12 CFR Appendix A to Part 233 - Model Notice
Code of Federal Regulations, 2010 CFR
2010-01-01
... Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations (31 CFR part 132). ... FUNDING OF UNLAWFUL INTERNET GAMBLING (REGULATION GG) Part 233, App. A Appendix A to Part 233—Model...
12 CFR Appendix A to Part 233 - Model Notice
Code of Federal Regulations, 2011 CFR
2011-01-01
... Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations (31 CFR part 132). ... FUNDING OF UNLAWFUL INTERNET GAMBLING (REGULATION GG) Part 233, App. A Appendix A to Part 233—Model...
NASA/MSFC multilayer diffusion models and computer programs, version 5
NASA Technical Reports Server (NTRS)
Dumbauld, R. K.; Bjorklund, J. R.
1975-01-01
The transport and diffusion models and algorithms developed for use by NASA in predicting concentrations and dosages downwind from normal and abnormal launches of rocket vehicles are described along with the associated computer programs for use in performing the calculations. Topics discussed include: the mathematical specifications and procedures used in the Preprocessor Program to calculate rocket exhaust cloud rise, cloud dimensions, and other input parameters to the transport and diffusion models; the revised mathematical specifications for the Multilayer Diffusion Models; users' instructions for implementing the Preprocessor and Multilayer Diffusion Models Programs; and worked example problems illustrating the use of the models and computer programs.
Protein folding dynamics: the diffusion-collision model and experimental data.
Karplus, M.; Weaver, D. L.
1994-01-01
The diffusion-collision model of protein folding is assessed. A description is given of the qualitative aspects and quantitative results of the diffusion-collision model and their relation to available experimental data. We consider alternative mechanisms for folding and point out their relationship to the diffusion-collision model. We show that the diffusion-collision model is supported by a growing body of experimental and theoretical evidence, and we outline future directions for developing the model and its applications. PMID:8003983
Dynamics of velocity gradient invariants in turbulence: Restricted Euler and linear diffusion models
NASA Astrophysics Data System (ADS)
Martín, Jesús; Dopazo, César; Valiño, Luis
1998-08-01
A complete system of dynamical equations for the invariants of the velocity gradient, the strain rate, and the rate-of-rotation tensors is deduced for an incompressible flow. The equations for the velocity gradient invariants R and Q were first deduced by Cantwell [Phys. Fluids A 4, 782 (1992)] in terms of Hij, the tensor containing the anisotropic part of the pressure Hessian and the viscous diffusion term in the velocity gradient equation. These equations are extended here for the strain rate tensor invariants, RS and QS, and for the rate-of-rotation tensor invariant, QW, using HijS and HijW, the symmetric and the skew-symmetric parts of Hij, respectively. In order to obtain a complete system, an equation for the square of the vortex stretching vector, Vi≡Sijωj, is required. The resulting dynamical system of invariants is closed using a simple model for the velocity gradient evolution: an isotropic approximation for the pressure term and a linear model for the viscous diffusion term. The local topology and the resulting statistics implied by this model reproduce a number of trends similar to known results from numerical experiments for the small scales of turbulence.
Lamminmäki, T T; Kettle, J P; Puukko, P J T; Ridgway, C J; Gane, P A C
2012-01-01
The structures of inkjet coatings commonly contain a high concentration of fine diameter pores together with a large pore volume capacity. To clarify the interactive role of the porous structure and the coincidentally occurring swelling of binder during inkjet ink vehicle imbibition, coating structures were studied in respect to their absorption behaviour for polar and non-polar liquid. The absorption measurement was performed using compressed pigment tablets, based on a range of pigment types and surface charge polarity, containing either polyvinyl alcohol (PVOH) or styrene acrylic latex (SA) as the binder, by recording the liquid uptake with a microbalance. The results indicate that, at the beginning of liquid uptake, at times less than 2 s, the small pores play the dominant role with respect to the inkjet ink vehicle imbibition. Simultaneously, water molecules diffuse into and within the hydrophilic PVOH binder causing binder swelling, which diminishes the number of active small pores and reduces the diameter of remaining pores, thus slowing the capillary flow as a function of time. The SA latex does not absorb the vehicle, and therefore the dominating phenomenon is then capillary absorption. However, the diffusion coefficient of the water vapour across separately prepared PVOH and SA latex films seems to be quite similar. In the PVOH, the polar liquid diffuses into the polymer network, whereas in the SA latex the hydrophobic nature prevents the diffusion into the polymer matrix and there exists surface diffusion. At longer timescale, permeation flow into the porous coating dominates as the resistive term controlling the capillary driven liquid imbibition rate. PMID:21981972
An efficient method for model refinement in diffuse optical tomography
NASA Astrophysics Data System (ADS)
Zirak, A. R.; Khademi, M.
2007-11-01
Diffuse optical tomography (DOT) is a non-linear, ill-posed, boundary value and optimization problem which necessitates regularization. Also, Bayesian methods are suitable owing to measurements data are sparse and correlated. In such problems which are solved with iterative methods, for stabilization and better convergence, the solution space must be small. These constraints subject to extensive and overdetermined system of equations which model retrieving criteria specially total least squares (TLS) must to refine model error. Using TLS is limited to linear systems which is not achievable when applying traditional Bayesian methods. This paper presents an efficient method for model refinement using regularized total least squares (RTLS) for treating on linearized DOT problem, having maximum a posteriori (MAP) estimator and Tikhonov regulator. This is done with combination Bayesian and regularization tools as preconditioner matrices, applying them to equations and then using RTLS to the resulting linear equations. The preconditioning matrixes are guided by patient specific information as well as a priori knowledge gained from the training set. Simulation results illustrate that proposed method improves the image reconstruction performance and localize the abnormally well.
Reaction–diffusion model of hair-bundle morphogenesis
Jacobo, Adrian; Hudspeth, A. J.
2014-01-01
The hair bundle, an apical specialization of the hair cell composed of several rows of regularly organized stereocilia and a kinocilium, is essential for mechanotransduction in the ear. Its precise organization allows the hair bundle to convert mechanical stimuli to electrical signals; mutations that alter the bundle’s morphology often cause deafness. However, little is known about the proteins involved in the process of morphogenesis and how the structure of the bundle arises through interactions between these molecules. We present a mathematical model based on simple reaction–diffusion mechanisms that can reproduce the shape and organization of the hair bundle. This model suggests that the boundary of the cell and the kinocilium act as signaling centers that establish the bundle’s shape. The interaction of two proteins forms a hexagonal Turing pattern—a periodic modulation of the concentrations of the morphogens, sustained by local activation and long-range inhibition of the reactants—that sets a blueprint for the location of the stereocilia. Finally we use this model to predict how different alterations to the system might impact the shape and organization of the hair bundle. PMID:25313064
Collective Diffusion Model for Ion Conduction through Microscopic Channels
Liu, Yingting; Zhu, Fangqiang
2013-01-01
Ion conduction through microscopic channels is of central importance in both biology and nanotechnology. To better understand the current-voltage (I-V) dependence of ion channels, here we describe and prove a collective diffusion model that quantitatively relates the spontaneous ion permeation at equilibrium to the stationary ionic fluxes driven by small voltages. The model makes it possible to determine the channel conductance in the linear I-V range from equilibrium simulations without the application of a voltage. To validate the theory, we perform molecular-dynamics simulations on two channels—a conical-shaped nanopore and the transmembrane pore of an α-hemolysin—under both equilibrium and nonequilibrium conditions. The simulations reveal substantial couplings between the motions of cations and anions, which are effectively captured by the collective coordinate in the model. Although the two channels exhibit very different linear ranges in the I-V curves, in both cases the channel conductance at small voltages is in reasonable agreement with the prediction from the equilibrium simulation. The simulations also suggest that channel charges, rather than geometric asymmetry, play a more prominent role in current rectification. PMID:23442858
12 CFR Appendix A to Part 704 - Model Forms
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 6 2011-01-01 2011-01-01 false Model Forms A Appendix A to Part 704 Banks and... Pt. 704, App. A Appendix A to Part 704—Model Forms This appendix contains sample forms intended for... Prioritization and Model Forms Part I—Optional Capital Prioritization Notwithstanding any other provision in...
Development of Spray on Bag for manufacturing of large composites parts: Diffusivity analysis
NASA Astrophysics Data System (ADS)
Dempah, Maxime Joseph
Bagging materials are utilized in many composites manufacturing processes. The selection is mainly driven by cost, temperature requirements, chemical compatibility and tear properties of the bag. The air barrier properties of the bag are assumed to be adequate or in many cases are not considered at all. However, the gas barrier property of a bag is the most critical parameter, as it can negatively affect the quality of the final laminate. The barrier property is a function of the bag material, uniformity, thickness and temperature. Improved barrier properties are needed for large parts, high pressure consolidated components and structures where air stays entrapped on the part surface. The air resistance property of the film is defined as permeability and is investigated in this thesis. A model was developed to evaluate the gas transport through the film and an experimental cell was implemented to characterize various commercial films. Understanding and characterizing the transport phenomena through the film allows optimization of the bagging material for various manufacturing processes. Spray-on-Bag is a scalable alternative bagging method compared to standard films. The approach allows in-situ fabrication of the bag on large and complex geometry structures where optimization of the bag properties can be varied on a local level. An experimental setup was developed and implemented using a six axis robot and an automated spraying system. Experiments were performed on a flat surface and specimens were characterized and compared to conventional films. Air barrier properties were within range of standard film approaches showing the potential to fabricate net shape bagging structures in an automated process.
NASA Astrophysics Data System (ADS)
Shilpakar, P.; Oldow, J. S.
2015-12-01
Morphological dating of fault scarps has the potential to provide a fast and cost-effective means of determining the spatial and temporal pattern of paleo-seismic events over broad regions. Scarp-morphology dating algorithms are based on diffusion degradation relations but have not been adequately calibrated for sensitivity or repeatability. Using Terrestrial Laser Scanner (TLS) images to characterize geomorphic surfaces at centimeter scale, we characterize fault scarps of known and differing ages ( 20 to 13,500 years) to evaluate the applicability of morphology-degradation models in estimating ages of fault scarps. We acquired TLS images of five Quaternary fault scarp surfaces formed in unconsolidated sediments in different parts of the western Basin and Range in western Nevada and southeastern California. Diffusion models assess the initial and final configuration of a scarp to yield the product of a diffusivity constant (K) and the scarp age (T). With known T we can solve for K and vice versa. Our sensitivity analysis of the diffusion models demonstrate that small variations in the measurable parameters such as maximum slope angle (θ), far field slope angle (α), and surface offset (d) can produce large variations in the calculated age of scarp formation. Even a 0.5° uncertainty in the value of θ or α will cause 10 to 20 percent variability in K, and a 25 cm uncertainty in d will make a 20 percent difference in calculated K. This uncertainty in K value will yield ± 3000 year variation in the estimated scarp age. Using 10 cm resolution digital elevation models of fault scarps acquired with TLS, we best fit profiles and digitally measure the geometric parameters. The ages of the scarps are known via historical records or through age brackets establish in trenching studies. Using the known ages and the modeled morphology, we compute K for the various scarps formed in similarly material and environments. Estimates of K range from 1.57 m2/kyr to 13.74 m2/kyr and
Diffusively anisotropic model for the deflagration-to-detonation transition
NASA Astrophysics Data System (ADS)
Kagan, Leonid; Sivashinsky, Gregory
2014-03-01
To elucidate the key mechanisms responsible for the transition from deflagrative to detonative combustion in smooth-walled channels, a reactive flow with anisotropic thermal and molecular diffusivities is considered. Setting the transverse diffusivities large compared to longitudinal diffusivities, the initially formed deflagration (despite no-slip boundary conditions) appears to be nearly planar and not accelerating. This, however, does not prevent its eventual abrupt transition to Chapman-Jouguet detonation.
Performance of a TKE diffusion scheme in ECMWF IFS Single Column Model
NASA Astrophysics Data System (ADS)
Svensson, Jacob; Bazile, Eric; Sandu, Irina; Svensson, Gunilla
2015-04-01
Numerical Weather Prediction models (NWP) as well as climate models are used for decision making on all levels in society and their performance and accuracy are of great importance for both economical and safety reasons. Today's extensive use of weather apps and websites that directly uses model output even more highlights the importance of realistic output parameters. The turbulent atmospheric boundary layer (ABL) includes many physical processes which occur on a subgrid scale and need to be parameterized. As the absolute major part of the biosphere is located in the ABL, it is of great importance that these subgrid processes are parametrized so that they give realistic values of e.g. temperature and wind on the levels close to the surface. GEWEX (Global Energy and Water Exchange Project) Atmospheric Boundary Layer Study (GABLS), has the overall objective to improve the understanding and the representation of the atmospheric boundary layers in climate models. The study has pointed out that there is a need for a better understanding and representation of stable atmospheric boundary layers (SBL). Therefore four test cases have been designed to highlight the performance of and differences between a number of climate models and NWP:s in SBL. In the experiments, most global NWP and climate models have shown to be too diffusive in stable conditions and thus give too weak temperature gradients, too strong momentum mixing and too weak ageostrophic Ekman flow. The reason for this is that the models need enhanced diffusion to create enough friction for the large scale weather systems, which otherwise would be too fast and too active. In the GABLS test cases, turbulence schemes that use Turbulent Kinetic Energy (TKE) have shown to be more skilful than schemes that only use stability and gradients. TKE as a prognostic variable allows for advection both vertically and horizontally and gives a "memory" from previous time steps. Therefore, e.g. the ECMWF-GABLS workshop in 2011
Occupational lung disease. Part 2. Discovering the cause of diffuse parenchymal lung disease.
Kuschner, Ware G; Stark, Paul
2003-04-01
Diffuse parenchymal lung disease (also known as interstitial lung disease) and acute irritant reactions are much less commonly managed by primary care physicians than asthma. Acute irritant reactions are typically readily recognized because of the immediate exposure-response relationship. As with asthma, a diagnosis of diffuse parenchymal lung disease should prompt a careful review of the patient's work history. Findings from history taking and radiography provide most of the data needed to establish a diagnosis of asbestosis or silicosis. A pulmonologist should be consulted about lung disease that eludes diagnosis. In cases in which a link between work and illness is strongly suspected, an occupational medicine specialist may be consulted for assistance with preparing reports for a workers' compensation claim as well as characterizing and quantifying impairment. Various government agencies provide extensive information about specific toxic exposures and occupational lung diseases by telephone and on the World Wide Web. PMID:12718237
NASA Astrophysics Data System (ADS)
Debure, Mathieu; De Windt, Laurent; Frugier, Pierre; Gin, Stéphane
2013-11-01
The influence of diffusion of reactive species in aqueous solutions on the alteration rate of borosilicate glass of nuclear interest in the presence of magnesium carbonate (hydromagnesite: 4MgCO3·Mg(OH)2·4H2O) is investigated together with the ability of coupled chemistry/transport models to simulate the processes involved. Diffusion cells in which the solids are separated by an inert stainless steel sintered filter were used to establish parameters for direct comparison with batch experiments in which solids are intimately mixed. The chemistry of the solution and solid phases was monitored over time by various analytical techniques including ICP-AES, XRD, and SEM. The primary mechanism controlling the geochemical evolution of the system remains the consumption of silicon from the glass by precipitation of magnesium silicates. The solution chemistry and the dissolution and precipitation of solid phases are correctly described by 2D modeling with the GRAAL model implemented in the HYTEC reactive transport code. The spatial symmetry of the boron concentrations in both compartments of the cells results from dissolution coupled with simple diffusion, whereas the spatial asymmetry of the silicon and magnesium concentrations is due to strong coupling between dissolution, diffusion, and precipitation of secondary phases. A sensitivity analysis on the modeling of glass alteration shows that the choice of these phases and their thermodynamic constants have only a moderate impact whereas the thickness of the filter has a greater barrier effect.
Armatas, G S; Petrakis, D E; Pomonis, P J
2005-05-13
The diffusion parameters of binary gas mixture He (tracer gas)-N2 (carrier gas) in hybrid organic-inorganic SiO2-X porous solids which have suffered gradual functionalization with functional groups X of increasing length (X = psi, [triple bond]Si-H, [triple bond]Si-CH2OH, [triple bond]Si-(CH2)3OH, [triple bond]Si-(CH2)11CH3) are reported. The effective diffusivities Deff, the Henry law constants K as well as the tortuosity factors tau for the examined solids were estimated by a typical pulse gas chromatographic method. Analysis of the experimental results was carried out by the well-known method of linearization of moments. The moments s analysis provides a powerful means for extracting diffusion parameters from the experimental response curves The proposed methodology is simple compared to other similar studies and provides rapidly reliable data. The results of this work indicate that the effective diffusivity Deff in porous networks drops markedly as the initial porosity of the parent SiO2 sample is blocked by the functionalization of the pore surfaces with functional groups of increasing size, [triple bond]Si-H, [triple bond]Si-CH2OH, [triple bond]Si-(CH2)3OH and [triple bond]Si-(CH2)11CH3. The low values of the Henry law constants K found indicate that the adsorption of He on the porous surfaces for all the solids is weak. Also, the tortuosity factor r is proportionally correlated to the pore blocking effects and the percolation phenomena of gases flowing into the porous network. PMID:15941039
Hybrid approaches for multiple-species stochastic reaction–diffusion models
Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K.; Byrne, Helen
2015-01-01
Reaction–diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction–diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model. PMID:26478601
Hybrid approaches for multiple-species stochastic reaction-diffusion models
NASA Astrophysics Data System (ADS)
Spill, Fabian; Guerrero, Pilar; Alarcon, Tomas; Maini, Philip K.; Byrne, Helen
2015-10-01
Reaction-diffusion models are used to describe systems in fields as diverse as physics, chemistry, ecology and biology. The fundamental quantities in such models are individual entities such as atoms and molecules, bacteria, cells or animals, which move and/or react in a stochastic manner. If the number of entities is large, accounting for each individual is inefficient, and often partial differential equation (PDE) models are used in which the stochastic behaviour of individuals is replaced by a description of the averaged, or mean behaviour of the system. In some situations the number of individuals is large in certain regions and small in others. In such cases, a stochastic model may be inefficient in one region, and a PDE model inaccurate in another. To overcome this problem, we develop a scheme which couples a stochastic reaction-diffusion system in one part of the domain with its mean field analogue, i.e. a discretised PDE model, in the other part of the domain. The interface in between the two domains occupies exactly one lattice site and is chosen such that the mean field description is still accurate there. In this way errors due to the flux between the domains are small. Our scheme can account for multiple dynamic interfaces separating multiple stochastic and deterministic domains, and the coupling between the domains conserves the total number of particles. The method preserves stochastic features such as extinction not observable in the mean field description, and is significantly faster to simulate on a computer than the pure stochastic model.
Diffusion Models of the Flanker Task: Discrete versus Gradual Attentional Selection
ERIC Educational Resources Information Center
White, Corey N.; Ratcliff, Roger; Starns, Jeffrey J.
2011-01-01
The present study tested diffusion models of processing in the flanker task, in which participants identify a target that is flanked by items that indicate the same (congruent) or opposite response (incongruent). Single- and dual-process flanker models were implemented in a diffusion-model framework and tested against data from experiments that…
Applicability of an Adoption-Diffusion Model to Resource Conservation: A Supporting View.
ERIC Educational Resources Information Center
Nowak, Peter J.
At issue is the extent to which one can employ an adoption and diffusion of innovations model(s) to explain and predict the use of soil and water conservation practices. Much, however, can be gained from using models in this area. Four dimensions that should be present in any research design if it is to account for adoption and diffusion of…
A diffuse interface model of grain boundary faceting
NASA Astrophysics Data System (ADS)
Abdeljawad, Fadi; Medlin, Douglas; Zimmerman, Jonathan; Hattar, Khalid; Foiles, Stephen
Incorporating anisotropy into thermodynamic treatments of interfaces dates back to over a century ago. For a given orientation of two abutting grains in a pure metal, depressions in the grain boundary (GB) energy may exist as a function of GB inclination, defined by the plane normal. Therefore, an initially flat GB may facet resulting in a hill-and-valley structure. Herein, we present a diffuse interface model of GB faceting that is capable of capturing anisotropic GB energies and mobilities, and accounting for the excess energy due to facet junctions and their non-local interactions. The hallmark of our approach is the ability to independently examine the role of each of the interface properties on the faceting behavior. As a demonstration, we consider the Σ 5 < 001 > tilt GB in iron, where faceting along the { 310 } and { 210 } planes was experimentally observed. Linear stability analysis and numerical examples highlight the role of junction energy and associated non-local interactions on the resulting facet length scales. On the whole, our modeling approach provides a general framework to examine the spatio-temporal evolution of highly anisotropic GBs in polycrystalline metals. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Subgrid models for mass and thermal diffusion in turbulent mixing
Sharp, David H; Lim, Hyunkyung; Li, Xiao - Lin; Gilmm, James G
2008-01-01
We are concerned with the chaotic flow fields of turbulent mixing. Chaotic flow is found in an extreme form in multiply shocked Richtmyer-Meshkov unstable flows. The goal of a converged simulation for this problem is twofold: to obtain converged solutions for macro solution features, such as the trajectories of the principal shock waves, mixing zone edges, and mean densities and velocities within each phase, and also for such micro solution features as the joint probability distributions of the temperature and species concentration. We introduce parameterized subgrid models of mass and thermal diffusion, to define large eddy simulations (LES) that replicate the micro features observed in the direct numerical simulation (DNS). The Schmidt numbers and Prandtl numbers are chosen to represent typical liquid, gas and plasma parameter values. Our main result is to explore the variation of the Schmidt, Prandtl and Reynolds numbers by three orders of magnitude, and the mesh by a factor of 8 per linear dimension (up to 3200 cells per dimension), to allow exploration of both DNS and LES regimes and verification of the simulations for both macro and micro observables. We find mesh convergence for key properties describing the molecular level of mixing, including chemical reaction rates between the distinct fluid species. We find results nearly independent of Reynolds number for Re 300, 6000, 600K . Methodologically, the results are also new. In common with the shock capturing community, we allow and maintain sharp solution gradients, and we enhance these gradients through use of front tracking. In common with the turbulence modeling community, we include subgrid scale models with no adjustable parameters for LES. To the authors' knowledge, these two methodologies have not been previously combined. In contrast to both of these methodologies, our use of Front Tracking, with DNS or LES resolution of the momentum equation at or near the Kolmogorov scale, but without resolving the
Ndanou, S. Favrie, N. Gavrilyuk, S.
2015-08-15
We extend the model of diffuse solid–fluid interfaces developed earlier by authors of this paper to the case of arbitrary number of interacting hyperelastic solids. Plastic transformations of solids are taken into account through a Maxwell type model. The specific energy of each solid is given in separable form: it is the sum of a hydrodynamic part of the energy depending only on the density and the entropy, and an elastic part of the energy which is unaffected by the volume change. It allows us to naturally pass to the fluid description in the limit of vanishing shear modulus. In spite of a large number of governing equations, the model has a quite simple mathematical structure: it is a duplication of a single visco-elastic model. The model is well posed both mathematically and thermodynamically: it is hyperbolic and compatible with the second law of thermodynamics. The resulting model can be applied in the situations involving an arbitrary number of fluids and solids. In particular, we show the ability of the model to describe spallation and penetration phenomena occurring during high velocity impacts.
Regularized lattice Boltzmann model for a class of convection-diffusion equations.
Wang, Lei; Shi, Baochang; Chai, Zhenhua
2015-10-01
In this paper, a regularized lattice Boltzmann model for a class of nonlinear convection-diffusion equations with variable coefficients is proposed. The main idea of the present model is to introduce a set of precollision distribution functions that are defined only in terms of macroscopic moments. The Chapman-Enskog analysis shows that the nonlinear convection-diffusion equations can be recovered correctly. Numerical tests, including Fokker-Planck equations, Buckley-Leverett equation with discontinuous initial function, nonlinear convection-diffusion equation with anisotropic diffusion, are carried out to validate the present model, and the results show that the present model is more accurate than some available lattice Boltzmann models. It is also demonstrated that the present model is more stable than the traditional single-relaxation-time model for the nonlinear convection-diffusion equations. PMID:26565368
Monte Carlo Modeling of Diffuse Scattering from Single Crystals: The Program ZMC
Goossens, D.J.; Heerdegen, A.P.; Chan, E.J.; Welberry, T.R.
2012-04-30
Diffuse scattering probes the local ordering in a crystal, whereas Bragg peaks are descriptive of the average long-range ordering. The population of local configurations can be explored by modeling the three-dimensional distribution of diffuse scattering. Local configurations are not constrained by the average crystallographic symmetry, so one way of modeling diffuse scattering is by modeling a disordered (short-range-ordered) structure and then calculating its diffuse scattering. The structure must contain enough unit cells to give a statistically valid model of the populations of local configurations, and so requirements for a program to model this ordering are very different from programs that model average crystal structures (used to fit the Bragg diffraction). ZMC is a program that has been developed to model diffuse scattering, particularly from molecular crystals. The strategies used to tackle the problem and the way in which they are implemented will be discussed.
NASA Astrophysics Data System (ADS)
Verdecchia, K.; Diop, M.; St. Lawrence, K.
2015-03-01
Diffuse correlation spectroscopy (DCS) is a non-invasive optical technique capable of monitoring tissue perfusion changes, particularly in the brain. The normalized temporal intensity autocorrelation function generated by DCS is typically characterized by assuming that the movement of erythrocytes can be modeled as a Brownian diffusion-like process instead of the expected random flow model. Carp et al. [Biomedical Optics Express, 2011] proposed a hybrid model, referred to as the hydrodynamic diffusion model, to capture both the random ballistic and diffusive nature of erythrocyte motion. The purpose of this study was to compare how well the Brownian diffusion and the hydrodynamic diffusion models characterized DCS data acquired directly on the brain, avoiding the confounding effects of scalp and skull. Data were acquired from seven pigs during normocapnia (39.9 +/- 0.7 mmHg) and hypocapnia (22.1 +/- 1.6 mmHg) with the DCS fibers placed 7 mm apart, directly on the cerebral cortex. The hydrodynamic diffusion model was found to provide a consistently better fit to the autocorrelation functions compared to the Brownian diffusion model and was less sensitive to the chosen start and end time points used in the fitting. However, the decrease in cerebral blood flow from normocapnia to hypocapnia determined was similar for the two models (-42.6 +/- 8.6 % for the Brownian model and -42.2 +/- 10.2 % for the hydrodynamic model), suggesting that the latter is reasonable for monitoring flow changes.
Reaction time in ankle movements: a diffusion model analysis
Michmizos, Konstantinos P.; Krebs, Hermano Igo
2015-01-01
Reaction time (RT) is one of the most commonly used measures of neurological function and dysfunction. Despite the extensive studies on it, no study has ever examined the RT in the ankle. Twenty-two subjects were recruited to perform simple, 2- and 4-choice RT tasks by visually guiding a cursor inside a rectangular target with their ankle. RT did not change with spatial accuracy constraints imposed by different target widths in the direction of the movement. RT increased as a linear function of potential target stimuli, as would be predicted by Hick–Hyman law. Although the slopes of the regressions were similar, the intercept in dorsal–plantar (DP) direction was significantly smaller than the intercept in inversion–eversion (IE) direction. To explain this difference, we used a hierarchical Bayesian estimation of the Ratcliff's (Psychol Rev 85:59, 1978) diffusion model parameters and divided processing time into cognitive components. The model gave a good account of RTs, their distribution and accuracy values, and hence provided a testimony that the non-decision processing time (overlap of posterior distributions between DP and IE < 0.045), the boundary separation (overlap of the posterior distributions < 0.1) and the evidence accumulation rate (overlap of the posterior distributions < 0.01) components of the RT accounted for the intercept difference between DP and IE. The model also proposed that there was no systematic change in non-decision processing time or drift rate when spatial accuracy constraints were altered. The results were in agreement with the memory drum hypothesis and could be further justified neurophysiologically by the larger innervation of the muscles controlling DP movements. This study might contribute to assessing deficits in sensorimotor control of the ankle and enlighten a possible target for correction in the framework of our on-going effort to develop robotic therapeutic interventions to the ankle of children with cerebral palsy
Developing A Laser Shockwave Model For Characterizing Diffusion Bonded Interfaces
James A. Smith; Jeffrey M. Lacy; Barry H. Rabin
2014-07-01
12. Other advances in QNDE and related topics: Preferred Session Laser-ultrasonics Developing A Laser Shockwave Model For Characterizing Diffusion Bonded Interfaces 41st Annual Review of Progress in Quantitative Nondestructive Evaluation Conference QNDE Conference July 20-25, 2014 Boise Centre 850 West Front Street Boise, Idaho 83702 James A. Smith, Jeffrey M. Lacy, Barry H. Rabin, Idaho National Laboratory, Idaho Falls, ID ABSTRACT: The US National Nuclear Security Agency has a Global Threat Reduction Initiative (GTRI) which is assigned with reducing the worldwide use of high-enriched uranium (HEU). A salient component of that initiative is the conversion of research reactors from HEU to low enriched uranium (LEU) fuels. An innovative fuel is being developed to replace HEU. The new LEU fuel is based on a monolithic fuel made from a U-Mo alloy foil encapsulated in Al-6061 cladding. In order to complete the fuel qualification process, the laser shock technique is being developed to characterize the clad-clad and fuel-clad interface strengths in fresh and irradiated fuel plates. The Laser Shockwave Technique (LST) is being investigated to characterize interface strength in fuel plates. LST is a non-contact method that uses lasers for the generation and detection of large amplitude acoustic waves to characterize interfaces in nuclear fuel plates. However the deposition of laser energy into the containment layer on specimen’s surface is intractably complex. The shock wave energy is inferred from the velocity on the backside and the depth of the impression left on the surface from the high pressure plasma pulse created by the shock laser. To help quantify the stresses and strengths at the interface, a finite element model is being developed and validated by comparing numerical and experimental results for back face velocities and front face depressions with experimental results. This paper will report on initial efforts to develop a finite element model for laser
NASA Astrophysics Data System (ADS)
Bultinck, E.; Mahieu, S.; Depla, D.; Bogaerts, A.
2010-07-01
'Bohm diffusion' causes the electrons to diffuse perpendicularly to the magnetic field lines. However, its origin is not yet completely understood: low and high frequency electric field fluctuations are both named to cause Bohm diffusion. The importance of including this process in a Monte Carlo (MC) model is demonstrated by comparing calculated ionization rates with particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations. A good agreement is found with a Bohm diffusion parameter of 0.05, which corresponds well to experiments. Since the PIC/MCC method accounts for fast electric field fluctuations, we conclude that Bohm diffusion is caused by fast electric field phenomena.
An electrodynamics-based model for ion diffusion in microbial polysaccharides.
Liu, Chongxuan; Zachara, John M; Felmy, Andrew; Gorby, Yuri
2004-10-10
An electrodynamics-based model was formulated for simulation of ion diffusion in microbial polysaccharides. The fixed charges and electrostatic double layers that may associate with microbial polysaccharides and their effects on ion diffusion were explicitly built into the model. The model extends a common multicomponent ion diffusion formulation that is based on irreversible thermodynamics under a zero ionic charge flux condition, which is only applicable to the regions without fixed charges and electrostatic double layers. An efficient numerical procedure was presented to solve the differential equations in the model. The model well described key features of experimental observations of ion diffusion in negatively charged microbial polysaccharides including accelerated diffusive transport of cations, exclusion of anions, and increased rate of cation transport with increasing negative charge density. The simulated diffusive fluxes of cations and anions were consistent with a cation exchange diffusion concept in negatively charged polysaccharides at the interface of plant roots and soils; and the developed model allows to mathematically study such diffusion phenomena. An illustrative example was also provided to simulate dynamic behavior of ionic current during ion diffusion within a charged bacterial cell wall polysaccharide and the effects of the ionic current on the compression or expansion of the bacterial electrostatic double layer at the interface of the cell wall and bulk solution. PMID:15465305
Poupon, Cyril; Rieul, Bernard; Kezele, Irina; Perrin, Muriel; Poupon, Fabrice; Mangin, Jean-François
2008-12-01
We present new diffusion phantoms dedicated to the study and validation of high-angular-resolution diffusion imaging (HARDI) models. The phantom design permits the application of imaging parameters that are typically employed in studies of the human brain. The phantoms were made of small-diameter acrylic fibers, chosen for their high hydrophobicity and flexibility that ensured good control of the phantom geometry. The polyurethane medium was filled under vacuum with an aqueous solution that was previously degassed, doped with gadolinium-tetraazacyclododecanetetraacetic acid (Gd-DOTA), and treated by ultrasonic waves. Two versions of such phantoms were manufactured and tested. The phantom's applicability was demonstrated on an analytical Q-ball model. Numerical simulations were performed to assess the accuracy of the phantom. The phantom data will be made accessible to the community with the objective of analyzing various HARDI models. PMID:19030160
A generalized diffusion model for growth of nanoparticles synthesized by colloidal methods.
Wen, Tianlong; Brush, Lucien N; Krishnan, Kannan M
2014-04-01
A nanoparticle growth model is developed to predict and guide the syntheses of monodisperse colloidal nanoparticles in the liquid phase. The model, without any a priori assumptions, is based on the Fick's law of diffusion, conservation of mass and the Gibbs-Thomson equation for crystal growth. In the limiting case, this model reduces to the same expression as the currently accepted model that requires the assumption of a diffusion layer around each nanoparticle. The present growth model bridges the two limiting cases of the previous model i.e. complete diffusion controlled and adsorption controlled growth of nanoparticles. Specifically, the results show that a monodispersion of nanoparticles can be obtained both with fast monomer diffusion and with surface reaction under conditions of small diffusivity to surface reaction constant ratio that results is growth 'focusing'. This comprehensive description of nanoparticle growth provides new insights and establishes the required conditions for fabricating monodisperse nanoparticles critical for a wide range of applications. PMID:24491334
NASA Technical Reports Server (NTRS)
Allgood, Daniel C.; Graham, Jason S.; Ahuja, Vineet; Hosangadi, Ashvin
2008-01-01
Simulation technology can play an important role in rocket engine test facility design and development by assessing risks, providing analysis of dynamic pressure and thermal loads, identifying failure modes and predicting anomalous behavior of critical systems. Advanced numerical tools assume greater significance in supporting testing and design of high altitude testing facilities and plume induced testing environments of high thrust engines because of the greater inter-dependence and synergy in the functioning of the different sub-systems. This is especially true for facilities such as the proposed A-3 facility at NASA SSC because of a challenging operating envelope linked to variable throttle conditions at relatively low chamber pressures. Facility designs in this case will require a complex network of diffuser ducts, steam ejector trains, fast operating valves, cooling water systems and flow diverters that need to be characterized for steady state performance. In this paper, we will demonstrate with the use of CFD analyses s advanced capability to evaluate supersonic diffuser and steam ejector performance in a sub-scale A-3 facility at NASA Stennis Space Center (SSC) where extensive testing was performed. Furthermore, the focus in this paper relates to modeling of critical sub-systems and components used in facilities such as the A-3 facility. The work here will address deficiencies in empirical models and current CFD analyses that are used for design of supersonic diffusers/turning vanes/ejectors as well as analyses for confined plumes and venting processes. The primary areas that will be addressed are: (1) supersonic diffuser performance including analyses of thermal loads (2) accurate shock capturing in the diffuser duct; (3) effect of turning duct on the performance of the facility (4) prediction of mass flow rates and performance classification for steam ejectors (5) comparisons with test data from sub-scale diffuser testing and assessment of confidence
NASA Technical Reports Server (NTRS)
Allgood, Daniel C.; Graham, Jason S.; Ahuja, Vineet; Hosangadi, Ashvin
2010-01-01
Simulation technology can play an important role in rocket engine test facility design and development by assessing risks, providing analysis of dynamic pressure and thermal loads, identifying failure modes and predicting anomalous behavior of critical systems. Advanced numerical tools assume greater significance in supporting testing and design of high altitude testing facilities and plume induced testing environments of high thrust engines because of the greater inter-dependence and synergy in the functioning of the different sub-systems. This is especially true for facilities such as the proposed A-3 facility at NASA SSC because of a challenging operating envelope linked to variable throttle conditions at relatively low chamber pressures. Facility designs in this case will require a complex network of diffuser ducts, steam ejector trains, fast operating valves, cooling water systems and flow diverters that need to be characterized for steady state performance. In this paper, we will demonstrate with the use of CFD analyses s advanced capability to evaluate supersonic diffuser and steam ejector performance in a sub-scale A-3 facility at NASA Stennis Space Center (SSC) where extensive testing was performed. Furthermore, the focus in this paper relates to modeling of critical sub-systems and components used in facilities such as the A-3 facility. The work here will address deficiencies in empirical models and current CFD analyses that are used for design of supersonic diffusers/turning vanes/ejectors as well as analyses for confined plumes and venting processes. The primary areas that will be addressed are: (1) supersonic diffuser performance including analyses of thermal loads (2) accurate shock capturing in the diffuser duct; (3) effect of turning duct on the performance of the facility (4) prediction of mass flow rates and performance classification for steam ejectors (5) comparisons with test data from sub-scale diffuser testing and assessment of confidence
Modeling simple driving tasks with a one-boundary diffusion model.
Ratcliff, Roger; Strayer, David
2014-06-01
A one-boundary diffusion model was applied to the data from two experiments in which subjects were performing a simple simulated driving task. In the first experiment, the same subjects were tested on two driving tasks using a PC-based driving simulator and the psychomotor vigilance test. The diffusion model fit the response time distributions for each task and individual subject well. Model parameters were found to correlate across tasks, which suggests that common component processes were being tapped in the three tasks. The model was also fit to a distracted driving experiment of Cooper and Strayer (Human Factors, 50, 893-902, 2008). Results showed that distraction altered performance by affecting the rate of evidence accumulation (drift rate) and/or increasing the boundary settings. This provides an interpretation of cognitive distraction whereby conversing on a cell phone diverts attention from the normal accumulation of information in the driving environment. PMID:24297620
Moustafa, Ahmed A; Kéri, Szabolcs; Somlai, Zsuzsanna; Balsdon, Tarryn; Frydecka, Dorota; Misiak, Blazej; White, Corey
2015-09-15
In this study, we tested reward- and punishment learning performance using a probabilistic classification learning task in patients with schizophrenia (n=37) and healthy controls (n=48). We also fit subjects' data using a Drift Diffusion Model (DDM) of simple decisions to investigate which components of the decision process differ between patients and controls. Modeling results show between-group differences in multiple components of the decision process. Specifically, patients had slower motor/encoding time, higher response caution (favoring accuracy over speed), and a deficit in classification learning for punishment, but not reward, trials. The results suggest that patients with schizophrenia adopt a compensatory strategy of favoring accuracy over speed to improve performance, yet still show signs of a deficit in learning based on negative feedback. Our data highlights the importance of applying fitting models (particularly drift diffusion models) to behavioral data. The implications of these findings are discussed relative to theories of schizophrenia and cognitive processing. PMID:26005124
Modeling of surface myoelectric signals--Part I: Model implementation.
Merletti, R; Lo Conte, L; Avignone, E; Guglielminotti, P
1999-07-01
The relationships between the parameters of active motor units (MU's) and the features of surface electromyography (EMG) signals have been investigated using a mathematical model that represents the surface EMG as a summation of contributions from the single muscle fibers. Each MU has parallel fibers uniformly scattered within a cylindrical volume of specified radius embedded in an anisotropic medium. Two action potentials, each modeled as a current tripole, are generated at the neuromuscular junction, propagate in opposite directions and extinguish at the fiber-tendon endings. The neuromuscular junctions and fiber-tendon endings are uniformly scattered within regions of specified width. Muscle fiber conduction velocity and average fiber length to the right and left of the center of the innervation zone are also specified. The signal produced by MU's with different geometries and conduction velocities are superimposed. Monopolar, single differential and double differential signals are computed from electrodes placed in equally spaced locations on the surface of the muscle and are displayed as functions of any of the model's parameters. Spectral and amplitude variables and conduction velocity are estimated from the surface signals and displayed as functions of any of the model's parameters. The influence of fiber-end effects, electrode misalignment, tissue anisotropy, MU's location and geometry are discussed. Part II of this paper will focus on the simulation and interpretation of experimental signals. PMID:10396899
Modeling bioluminescent photon transport in tissue based on Radiosity-diffusion model
NASA Astrophysics Data System (ADS)
Sun, Li; Wang, Pu; Tian, Jie; Zhang, Bo; Han, Dong; Yang, Xin
2010-03-01
Bioluminescence tomography (BLT) is one of the most important non-invasive optical molecular imaging modalities. The model for the bioluminescent photon propagation plays a significant role in the bioluminescence tomography study. Due to the high computational efficiency, diffusion approximation (DA) is generally applied in the bioluminescence tomography. But the diffusion equation is valid only in highly scattering and weakly absorbing regions and fails in non-scattering or low-scattering tissues, such as a cyst in the breast, the cerebrospinal fluid (CSF) layer of the brain and synovial fluid layer in the joints. A hybrid Radiosity-diffusion model is proposed for dealing with the non-scattering regions within diffusing domains in this paper. This hybrid method incorporates a priori information of the geometry of non-scattering regions, which can be acquired by magnetic resonance imaging (MRI) or x-ray computed tomography (CT). Then the model is implemented using a finite element method (FEM) to ensure the high computational efficiency. Finally, we demonstrate that the method is comparable with Mont Carlo (MC) method which is regarded as a 'gold standard' for photon transportation simulation.
A Numerical Model for Coupling of Neutron Diffusion and Thermomechanics in Fast Burst Reactors
Samet Y. Kadioglu; Dana A. Knoll; Cassiano De Oliveira
2008-11-01
We develop a numerical model for coupling of neutron diffusion adn termomechanics in order to stimulate transient behavior of a fast burst reactor. The problem involves solving a set of non-linear different equations which approximate neutron diffusion, temperature change, and material behavior. With this equation set we will model the transition from a supercritical to subcritical state and possible mechanical vibration.
NASA Astrophysics Data System (ADS)
Ashworth, J. R.; Sheplev, V. S.
1997-09-01
Layered coronas between two reactant minerals can, in many cases, be attributed to diffusion-controlled growth with local equilibrium. This paper clarifies and unifies the previous approaches of various authors to the simplest form of modelling, which uses no assumed values for thermochemical quantities. A realistic overall reaction must be estimated from measured overall proportions of minerals and their major element compositions. Modelling is not restricted to a particular number of components S, relative to the number of phases Φ. IfΦ > S + 1, the overall reaction is a combination of simultaneous reactions. The stepwise method, solving for the local reaction at each boundary in turn, is extended to allow for recurrence of a mineral (its presence in two parts of the layer structure separated by a gap). The equations are also given in matrix form. A thermodynamic stability criterion is derived, determining which layer sequence is truly stable if several are computable from the same inputs. A layer structure satisfying the stability criterion has greater growth rate (and greater rate of entropy production) than the other computable layer sequences. This criterion of greatest entropy production is distinct from Prigogine's theorem of minimum entropy production, which distinguishes the stationary or quasi-stationary state from other states of the same layer sequence. The criterion leads to modification of previous results for coronas comprising hornblende, spinel, and orthopyroxene between olivine (Ol) and plagioclase (Pl). The outcome supports the previous inference that Si, and particularly Al, commonly behave as immobile relative to other cation-forming major elements. The affinity (-ΔG) of a corona-forming reaction is estimated, using previous estimates of diffusion coefficient and the duration t of reaction, together with a new model quantity (-ΔG) *. For an example of the Ol + Pl reaction, a rough calculation gives (-ΔG) > 1.7RT (per mole of P1 consumed
Mekkaoui, Imen; Moulin, Kevin; Croisille, Pierre; Pousin, Jerome; Viallon, Magalie
2016-08-01
Cardiac motion presents a major challenge in diffusion weighted MRI, often leading to large signal losses that necessitate repeated measurements. The diffusion process in the myocardium is difficult to investigate because of the unqualified sensitivity of diffusion measurements to cardiac motion. A rigorous mathematical formalism is introduced to quantify the effect of tissue motion in diffusion imaging. The presented mathematical model, based on the Bloch-Torrey equations, takes into account deformations according to the laws of continuum mechanics. Approximating this mathematical model by using finite elements method, numerical simulations can predict the sensitivity of the diffusion signal to cardiac motion. Different diffusion encoding schemes are considered and the diffusion weighted MR signals, computed numerically, are compared to available results in literature. Our numerical model can identify the existence of two time points in the cardiac cycle, at which the diffusion is unaffected by myocardial strain and cardiac motion. Of course, these time points depend on the type of diffusion encoding scheme. Our numerical results also show that the motion sensitivity of the diffusion sequence can be reduced by using either spin echo technique with acceleration motion compensation diffusion gradients or stimulated echo acquisition mode with unipolar and bipolar diffusion gradients. PMID:27385441
NASA Astrophysics Data System (ADS)
Mekkaoui, Imen; Moulin, Kevin; Croisille, Pierre; Pousin, Jerome; Viallon, Magalie
2016-08-01
Cardiac motion presents a major challenge in diffusion weighted MRI, often leading to large signal losses that necessitate repeated measurements. The diffusion process in the myocardium is difficult to investigate because of the unqualified sensitivity of diffusion measurements to cardiac motion. A rigorous mathematical formalism is introduced to quantify the effect of tissue motion in diffusion imaging. The presented mathematical model, based on the Bloch–Torrey equations, takes into account deformations according to the laws of continuum mechanics. Approximating this mathematical model by using finite elements method, numerical simulations can predict the sensitivity of the diffusion signal to cardiac motion. Different diffusion encoding schemes are considered and the diffusion weighted MR signals, computed numerically, are compared to available results in literature. Our numerical model can identify the existence of two time points in the cardiac cycle, at which the diffusion is unaffected by myocardial strain and cardiac motion. Of course, these time points depend on the type of diffusion encoding scheme. Our numerical results also show that the motion sensitivity of the diffusion sequence can be reduced by using either spin echo technique with acceleration motion compensation diffusion gradients or stimulated echo acquisition mode with unipolar and bipolar diffusion gradients.
Boundedness in a chemotaxis-haptotaxis model with nonlinear diffusion
NASA Astrophysics Data System (ADS)
Li, Yan; Lankeit, Johannes
2016-05-01
This article deals with an initial-boundary value problem for the coupled chemotaxis-haptotaxis system with nonlinear diffusion under homogeneous Neumann boundary conditions in a bounded smooth domain Ω \\subset {{{R}}n} , n = 2, 3, 4, where χ,ξ and μ are given nonnegative parameters. The diffusivity D(u) is assumed to satisfy D(u)≥slant δ {{u}m-1} for all u > 0 with some δ >0 . It is proved that for sufficiently regular initial data global bounded solutions exist whenever m>2-\\frac{2}{n} . For the case of non-degenerate diffusion (i.e. D(0) > 0) the solutions are classical; for the case of possibly degenerate diffusion (D(0)≥slant 0 ), the existence of bounded weak solutions is shown.
NASA Astrophysics Data System (ADS)
Ge, J.; Everett, M. E.; Weiss, C. J.
2012-12-01
A 2.5D finite difference (FD) frequency-domain modeling algorithm based on the theory of fractional diffusion of electromagnetic (EM) fields generated by a loop source lying above a fractured geological medium is addressed in this paper. The presence of fractures in the subsurface, usually containing highly conductive pore fluids, gives rise to spatially hierarchical flow paths of induced EM eddy currents. The diffusion of EM eddy currents in such formations is anomalous, generalizing the classical Gaussian process described by the conventional Maxwell equations. Based on the continuous time random walk (CTRW) theory, the diffusion of EM eddy currents in a rough medium is governed by the fractional Maxwell equations. Here, we model the EM response of a 2D subsurface containing fractured zones, with a 3D loop source, which results the so-called 2.5D model geometry. The governing equation in the frequency domain is converted using Fourier transform into k domain along the strike direction (along which the model conductivity doesn't vary). The resulting equation system is solved by the multifrontal massively parallel solver (MUMPS). The data obtained is then converted back to spatial domain and the time domain. We find excellent agreement between the FD and analytic solutions for a rough halfspace model. Then FD solutions are calculated for a 2D fault zone model with variable conductivity and roughness. We compare the results with responses from several classical models and explore the relationship between the roughness and the spatial density of the fracture distribution.
Diffusion-controlled reactions modeling in Geant4-DNA
NASA Astrophysics Data System (ADS)
Karamitros, M.; Luan, S.; Bernal, M. A.; Allison, J.; Baldacchino, G.; Davidkova, M.; Francis, Z.; Friedland, W.; Ivantchenko, V.; Ivantchenko, A.; Mantero, A.; Nieminem, P.; Santin, G.; Tran, H. N.; Stepan, V.; Incerti, S.
2014-10-01
Context Under irradiation, a biological system undergoes a cascade of chemical reactions that can lead to an alteration of its normal operation. There are different types of radiation and many competing reactions. As a result the kinetics of chemical species is extremely complex. The simulation becomes then a powerful tool which, by describing the basic principles of chemical reactions, can reveal the dynamics of the macroscopic system. To understand the dynamics of biological systems under radiation, since the 80s there have been on-going efforts carried out by several research groups to establish a mechanistic model that consists in describing all the physical, chemical and biological phenomena following the irradiation of single cells. This approach is generally divided into a succession of stages that follow each other in time: (1) the physical stage, where the ionizing particles interact directly with the biological material; (2) the physico-chemical stage, where the targeted molecules release their energy by dissociating, creating new chemical species; (3) the chemical stage, where the new chemical species interact with each other or with the biomolecules; (4) the biological stage, where the repairing mechanisms of the cell come into play. This article focuses on the modeling of the chemical stage. Method This article presents a general method of speeding-up chemical reaction simulations in fluids based on the Smoluchowski equation and Monte-Carlo methods, where all molecules are explicitly simulated and the solvent is treated as a continuum. The model describes diffusion-controlled reactions. This method has been implemented in Geant4-DNA. The keys to the new algorithm include: (1) the combination of a method to compute time steps dynamically with a Brownian bridge process to account for chemical reactions, which avoids costly fixed time step simulations; (2) a k-d tree data structure for quickly locating, for a given molecule, its closest reactants. The
Diffusion-controlled reactions modeling in Geant4-DNA
Karamitros, M.; Luan, S.; Bernal, M.A.; Allison, J.; Baldacchino, G.; Davidkova, M.; Francis, Z.; Friedland, W.; Ivantchenko, V.; Ivantchenko, A.; Mantero, A.; Nieminem, P.; Santin, G.; Tran, H.N.; Stepan, V.; Incerti, S.
2014-10-01
Context Under irradiation, a biological system undergoes a cascade of chemical reactions that can lead to an alteration of its normal operation. There are different types of radiation and many competing reactions. As a result the kinetics of chemical species is extremely complex. The simulation becomes then a powerful tool which, by describing the basic principles of chemical reactions, can reveal the dynamics of the macroscopic system. To understand the dynamics of biological systems under radiation, since the 80s there have been on-going efforts carried out by several research groups to establish a mechanistic model that consists in describing all the physical, chemical and biological phenomena following the irradiation of single cells. This approach is generally divided into a succession of stages that follow each other in time: (1) the physical stage, where the ionizing particles interact directly with the biological material; (2) the physico-chemical stage, where the targeted molecules release their energy by dissociating, creating new chemical species; (3) the chemical stage, where the new chemical species interact with each other or with the biomolecules; (4) the biological stage, where the repairing mechanisms of the cell come into play. This article focuses on the modeling of the chemical stage. Method This article presents a general method of speeding-up chemical reaction simulations in fluids based on the Smoluchowski equation and Monte-Carlo methods, where all molecules are explicitly simulated and the solvent is treated as a continuum. The model describes diffusion-controlled reactions. This method has been implemented in Geant4-DNA. The keys to the new algorithm include: (1) the combination of a method to compute time steps dynamically with a Brownian bridge process to account for chemical reactions, which avoids costly fixed time step simulations; (2) a k–d tree data structure for quickly locating, for a given molecule, its closest reactants. The
12 CFR Appendix B to Part 202 - Model Application Forms
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 2 2013-01-01 2013-01-01 false Model Application Forms B Appendix B to Part... CREDIT OPPORTUNITY ACT (REGULATION B) Pt. 202, App. B Appendix B to Part 202—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a...
12 CFR Appendix A to Part 213 - Model Forms
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Model Forms A Appendix A to Part 213 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM CONSUMER LEASING (REGULATION M) Pt. 213, App. A Appendix A to Part 213—Model Forms A-1Model Open-End or Finance Vehicle...
12 CFR Appendix B to Part 1002 - Model Application Forms
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 8 2013-01-01 2013-01-01 false Model Application Forms B Appendix B to Part... B) Pt. 1002, App. B Appendix B to Part 1002—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a particular type of consumer...
12 CFR Appendix B to Part 202 - Model Application Forms
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 2 2014-01-01 2014-01-01 false Model Application Forms B Appendix B to Part... CREDIT OPPORTUNITY ACT (REGULATION B) Pt. 202, App. B Appendix B to Part 202—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a...
12 CFR Appendix A to Part 213 - Model Forms
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 2 2013-01-01 2013-01-01 false Model Forms A Appendix A to Part 213 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM CONSUMER LEASING (REGULATION M) Pt. 213, App. A Appendix A to Part 213—Model Forms A-1Model Open-End or Finance Vehicle...
12 CFR Appendix A to Part 213 - Model Forms
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 2 2014-01-01 2014-01-01 false Model Forms A Appendix A to Part 213 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM CONSUMER LEASING (REGULATION M) Pt. 213, App. A Appendix A to Part 213—Model Forms A-1Model Open-End or Finance Vehicle...
12 CFR Appendix B to Part 1002 - Model Application Forms
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 8 2014-01-01 2014-01-01 false Model Application Forms B Appendix B to Part... B) Pt. 1002, App. B Appendix B to Part 1002—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a particular type of consumer...
12 CFR Appendix A to Part 213 - Model Forms
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 2 2012-01-01 2012-01-01 false Model Forms A Appendix A to Part 213 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM CONSUMER LEASING (REGULATION M) Pt. 213, App. A Appendix A to Part 213—Model Forms A-1Model Open-End or Finance Vehicle...
12 CFR Appendix B to Part 1002 - Model Application Forms
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 8 2012-01-01 2012-01-01 false Model Application Forms B Appendix B to Part... B) Pt. 1002, App. B Appendix B to Part 1002—Model Application Forms 1. This Appendix contains five model credit application forms, each designated for use in a particular type of consumer...
12 CFR Appendix B to Part 202 - Model Application Forms
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 2 2012-01-01 2012-01-01 false Model Application Forms B Appendix B to Part... CREDIT OPPORTUNITY ACT (REGULATION B) Pt. 202, App. B Appendix B to Part 202—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a...
12 CFR Appendix B to Part 202 - Model Application Forms
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Model Application Forms B Appendix B to Part... CREDIT OPPORTUNITY ACT (REGULATION B) Pt. 202, App. B Appendix B to Part 202—Model Application Forms 1. This appendix contains five model credit application forms, each designated for use in a...
10 CFR Appendix K to Part 50 - ECCS Evaluation Models
Code of Federal Regulations, 2011 CFR
2011-01-01
... 10 Energy 1 2011-01-01 2011-01-01 false ECCS Evaluation Models K Appendix K to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. K Appendix K to Part 50—ECCS Evaluation Models I. Required and Acceptable Features of Evaluation Models. II. Required Documentation. I. Required...
12 CFR Appendix B to Part 202 - Model Application Forms
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 2 2010-01-01 2010-01-01 false Model Application Forms B Appendix B to Part 202 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM EQUAL CREDIT OPPORTUNITY ACT (REGULATION B) Pt. 202, App. B Appendix B to Part 202—Model Application Forms 1. This appendix contains five model...
Comparison of homogenized and enhanced diffusion solutions of model PWR problems
Lewis, E. E.; Smith, M. A.
2012-07-01
Model problem comparisons in slab geometry are made between two forms of homogenized diffusion theory and enhanced diffusion theory. The pin-cell discontinuity factors for homogenized diffusion calculations are derived from homogenized variational nodal P1 response matrices and from standard finite differencing. Enhanced diffusion theory consists of applying quasi-reflected interface conditions to reduce variational nodal Pn response matrices to one degree of freedom per interface, without homogenization within the cell. As expected both homogenized diffusion methods preserve reaction rates exactly if the discontinuity factors are derived from the P 11 reference solutions. If no reference lattice solution is available, discontinuity factors may be approximated from single cells with reflected boundary conditions; the computational effort is then comparable to calculating the enhanced diffusion response matrices. In this situation enhanced diffusion theory gives the most accurate results and finite difference discontinuity factors the least accurate. (authors)
NASA Astrophysics Data System (ADS)
Wang, Xiping; Guo, Yan; Li, Baoguo; Wang, Xiyong; Ma, Yuntao
2006-07-01
Diffuse photosynthetically active radiation (DPAR) is important during overcast days and for plant parts shaded from the direct beam radiation. Simulation of DPAR interception by individual plant parts of a canopy, separately from direct beam photosynthetically active radiation (PAR), may give important insights into plant ecology. This paper presents a model to simulate the interception of DPAR in plant canopies. A sub-model of a virtual maize canopy was reconstructed. Plant surfaces were represented as small triangular facets positioned according to three-dimensionally (3D) digitized data collected in the field. Then a second sub-model to simulate the 3D DPAR distribution in the canopy was developed by dividing the sky hemisphere into a grid of fine cells that allowed for the anisotropic distribution of DPAR over the sky hemisphere. This model, DSHP (Dividing Sky Hemisphere with Projecting), simulates which DSH (Divided Sky Hemisphere) cells are directly visible from a facet in the virtual canopy, i.e. not obscured by other facets. The DPAR reaching the center of a facet was calculated by summing the amounts of DPAR present in every DSH cell. The distribution of DPAR in a canopy was obtained from the calculated DPARs intercepted by all facets in the canopy. This DSHP model was validated against DPAR measurements made in an actual maize ( Zea mays L.) canopy over selected days during the early filling stage. The simulated and measured DPAR at different canopy depths showed a good agreement with a R 2 equaling 0.78 ( n=120).
12 CFR Appendix A to Part 1013 - Model Forms
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 8 2014-01-01 2014-01-01 false Model Forms A Appendix A to Part 1013 Banks and... A to Part 1013—Model Forms A-1—Model Open-End or Finance Vehicle Lease Disclosures A-2—Model Closed-End or Net Vehicle Lease Disclosures A-3—Model Furniture Lease Disclosures ER19DE11.010...
12 CFR Appendix to Part 1016 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 8 2014-01-01 2014-01-01 false Model Privacy Form Appendix to Part 1016 Banks... (REGULATION P) Pt. 1016, App. Appendix to Part 1016—Model Privacy Form A. The Model Privacy Form ER21DE11.058.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix A to Part 40 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 1 2014-01-01 2014-01-01 false Model Privacy Form A Appendix A to Part 40... INFORMATION Pt. 40, App. A Appendix A to Part 40—Model Privacy Form A. The Model Privacy Form ER01DE09.000.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix A to Part 1013 - Model Forms
Code of Federal Regulations, 2013 CFR
2013-01-01
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12 CFR Appendix to Part 1016 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 8 2012-01-01 2012-01-01 false Model Privacy Form Appendix to Part 1016 Banks... (REGULATION P) Pt. 1016, App. Appendix to Part 1016—Model Privacy Form A. The Model Privacy Form ER21DE11.058.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix A to Part 1013 - Model Forms
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 8 2012-01-01 2012-01-01 false Model Forms A Appendix A to Part 1013 Banks and... A to Part 1013—Model Forms A-1—Model Open-End or Finance Vehicle Lease Disclosures A-2—Model Closed-End or Net Vehicle Lease Disclosures A-3—Model Furniture Lease Disclosures ER19DE11.010...
12 CFR Appendix A to Part 40 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 1 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 40... INFORMATION Pt. 40, App. A Appendix A to Part 40—Model Privacy Form A. The Model Privacy Form ER01DE09.000.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix A to Part 40 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 1 2012-01-01 2012-01-01 false Model Privacy Form A Appendix A to Part 40... INFORMATION Pt. 40, App. A Appendix A to Part 40—Model Privacy Form A. The Model Privacy Form ER01DE09.000.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix A to Part 40 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 1 2013-01-01 2013-01-01 false Model Privacy Form A Appendix A to Part 40... INFORMATION Pt. 40, App. A Appendix A to Part 40—Model Privacy Form A. The Model Privacy Form ER01DE09.000.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
12 CFR Appendix to Part 1016 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 8 2013-01-01 2013-01-01 false Model Privacy Form Appendix to Part 1016 Banks... (REGULATION P) Pt. 1016, App. Appendix to Part 1016—Model Privacy Form A. The Model Privacy Form ER21DE11.058.... How the Model Privacy Form Is Used (a) The model form may be used, at the option of a...
Model for radon diffusion through the lunar regolith.
NASA Technical Reports Server (NTRS)
Friesen, L. J.; Heymann, D.
1972-01-01
Description of a model for radon diffusion through the lunar regolith in which the atom migrates by random walk. The regolith is represented by a system of randomly oriented baffles in which the mean distance which the atom travels between two collisions takes on the role of a mean free path. The effective mean time between two collisions depends on two entities: the actual mean time-of-flight and the mean sticking time on grain surfaces for one collision. The latter depends strongly on the temperature and the heat of adsorption of radon on regolith materials. Both the mean free path as well as the heat of adsorption are either poorly known or unknown for the lunar regolith; hence these quantities are treated as free parameters. Because of the greatly different mean lifetimes against radioactive decay of Rn219, Rn220, and Rn222, the regolith acts as a powerful 'filter' for these species. Rn222 escape is significant (32%) even for a mean free path of 1 micron, a heat of adsorption of 7.0 kcal/mole and a regolith depth of 4 m. Calculations of radon escape from a 4 m thick regolith, using mean free paths of 1, 10, and 80 microns and heats of adsorption of 4.0, 5.2, and 7.0 kcal/mole show that the Rn222/Rn220 escape ratio can be as small as 7.7 and as large as, or larger than 47. The small value of 7.7 is of particular interest, because it is nearly equal to the escape ratio inferred by Turkevich et al. (1970) from their Surveyor 5 results.
An Electrodynamics-Based Model for Ion Diffusion in Microbial Polysaccharides
Liu, Chongxuan; Zachara, John M.; Felmy, Andrew R.; Gorby, Yuri A.
2004-08-03
An electrodynamics-based model was formulated for simulation of ion diffusion in microbial polysaccharides with fixed charges and electrostatic double layers. The model extends a common multicomponent ion diffusion model that is based on irreversible thermodynamics under a zero ionic charge flux condition, which is only applicable to the regions without fixed charges and electrostatic double layers. An efficient numerical procedure was presented to solve the differential equations in the model. The model well described key features of experimental observations of ion diffusion in negatively charged microbial polysaccharides including accelerated diffusive transport of cations, exclusion of anions, and increased rate of cation transport with increasing negative charge density. The simulated diffusive fluxes of cations and anions were consistent with a classic exchange diffusion concept in negatively charged polysaccharides at the interface of plant roots and soils; and the developed model allows to mathematically study such diffusion phenomena. Numerical simulations also showed that ion diffusive transport within a bacterial cell wall polysaccharide may induce an ionic current that compresses or expands the bacterial electrostatic double layer at the interface of the cell wall and bulk solution.
NASA Astrophysics Data System (ADS)
Huber, Markus; Tailleux, Remi; Ferreira, David; Kuhlbrodt, Till; Gregory, Jonathan
2015-04-01
The classic vertical advection-diffusion (VAD) balance is a central concept in studying the ocean heat budget, in particular in simple climate models (SCMs). Here we present a new framework to calibrate the parameters of the VAD equation to the vertical ocean heat balance of two fully-coupled climate models that is traceable to the models' circulation as well as to vertical mixing and diffusion processes. Based on temperature diagnostics, we derive an effective vertical velocity w∗ and turbulent diffusivity kν∗ for each individual physical process. In steady state, we find that the residual vertical velocity and diffusivity change sign in middepth, highlighting the different regional contributions of isopycnal and diapycnal diffusion in balancing the models' residual advection and vertical mixing. We quantify the impacts of the time evolution of the effective quantities under a transient 1% CO2 simulation and make the link to the parameters of currently employed SCMs.
Laser perforated fuel cell diffusion media. Part I: Related changes in performance and water content
NASA Astrophysics Data System (ADS)
Manahan, M. P.; Hatzell, M. C.; Kumbur, E. C.; Mench, M. M.
In this study, cathode-side, bi-layered diffusion media (DM) samples with micro-porous layer were perforated with 300 μm laser-cut holes (covering 15% of the surface area in a homogenous pattern) using a ytterbium fiber laser to investigate the effect of structural changes on the gas and water transport. Under reduced humidity conditions (50% inlet relative humidity on the anode and cathode), the perforated DM were observed to increase the potential by an average of 6% for current densities ranging from 0.2 to 1.4 A cm -2. However, the perforated DM showed reduced performance for current densities greater than 1.4 A cm -2 and at all currents under high-humidity conditions. Neutron radiography experiments were also performed to understand the changes in liquid water retention characteristics of DM due to the laser perforations. Significant water accumulation and water redistribution were observed in the perforated DM, which helps explain the observed performance behavior. The results indicate that the perforations act as water pooling and possible channeling locations, which significantly alter the water condensation, storage, and transport scheme within the fuel cell. These observations suggest that proper tailoring of fuel cell DM possesses significant potential to enable fuel cell operations with reduce liquid overhead and high performance.
Utrillas, María P; Marín, María J; Esteve, Anna R; Estellés, Victor; Tena, Fernando; Cañada, Javier; Martínez-Lozano, José A
2009-01-01
Values of measured and modeled diffuse UV erythemal irradiance (UVER) for all sky conditions are compared on planes inclined at 40 degrees and oriented north, south, east and west. The models used for simulating diffuse UVER are of the geometric-type, mainly the Isotropic, Klucher, Hay, Muneer, Reindl and Schauberger models. To analyze the precision of the models, some statistical estimators were used such as root mean square deviation, mean absolute deviation and mean bias deviation. It was seen that all the analyzed models reproduce adequately the diffuse UVER on the south-facing plane, with greater discrepancies for the other inclined planes. When the models are applied to cloud-free conditions, the errors obtained are higher because the anisotropy of the sky dome acquires more importance and the models do not provide the estimation of diffuse UVER accurately. PMID:19496991
Modeling the flow in diffuse interface methods of solidification
NASA Astrophysics Data System (ADS)
Subhedar, A.; Steinbach, I.; Varnik, F.
2015-08-01
Fluid dynamical equations in the presence of a diffuse solid-liquid interface are investigated via a volume averaging approach. The resulting equations exhibit the same structure as the standard Navier-Stokes equation for a Newtonian fluid with a constant viscosity, the effect of the solid phase fraction appearing in the drag force only. This considerably simplifies the use of the lattice Boltzmann method as a fluid dynamics solver in solidification simulations. Galilean invariance is also satisfied within this approach. Further, we investigate deviations between the diffuse and sharp interface flow profiles via both quasiexact numerical integration and lattice Boltzmann simulations. It emerges from these studies that the freedom in choosing the solid-liquid coupling parameter h provides a flexible way of optimizing the diffuse interface-flow simulations. Once h is adapted for a given spatial resolution, the simulated flow profiles reach an accuracy comparable to quasiexact numerical simulations.
Modeling the flow in diffuse interface methods of solidification.
Subhedar, A; Steinbach, I; Varnik, F
2015-08-01
Fluid dynamical equations in the presence of a diffuse solid-liquid interface are investigated via a volume averaging approach. The resulting equations exhibit the same structure as the standard Navier-Stokes equation for a Newtonian fluid with a constant viscosity, the effect of the solid phase fraction appearing in the drag force only. This considerably simplifies the use of the lattice Boltzmann method as a fluid dynamics solver in solidification simulations. Galilean invariance is also satisfied within this approach. Further, we investigate deviations between the diffuse and sharp interface flow profiles via both quasiexact numerical integration and lattice Boltzmann simulations. It emerges from these studies that the freedom in choosing the solid-liquid coupling parameter h provides a flexible way of optimizing the diffuse interface-flow simulations. Once h is adapted for a given spatial resolution, the simulated flow profiles reach an accuracy comparable to quasiexact numerical simulations. PMID:26382542
Parra-Robles, Juan; Wild, Jim M
2014-02-01
Our extensive investigation of the cylinder model theory through numerical modelling and purpose-designed experiments has demonstrated that it does produce inaccurate estimates of airway dimensions at all diffusion times currently used. This is due to a variety of effects: incomplete treatment of non-Gaussian effects, finite airway size, branching geometry, background susceptibility gradients and diffusion time dependence of the (3)He MR diffusion behaviour in acinar airways. The cylinder model is a good starting point for the development of a lung morphometry technique from (3)He diffusion MR but its limitations need to be understood and documented in the interest of reliable clinical interpretation. PMID:24342570
Modeling diffuse phosphorus emissions to assist in best management practice designing
NASA Astrophysics Data System (ADS)
Kovacs, Adam; Zessner, Matthias; Honti, Mark; Clement, Adrienne
2010-05-01
A diffuse emission modeling tool has been developed, which is appropriate to support decision-making in watershed management. The PhosFate (Phosphorus Fate) tool allows planning best management practices (BMPs) in catchments and simulating their possible impacts on the phosphorus (P) loads. PhosFate is a simple fate model to calculate diffuse P emissions and their transport within a catchment. The model is a semi-empirical, catchment scale, distributed parameter and long-term (annual) average model. It has two main parts: (a) the emission and (b) the transport model. The main input data of the model are digital maps (elevation, soil types and landuse categories), statistical data (crop yields, animal numbers, fertilizer amounts and precipitation distribution) and point information (precipitation, meteorology, soil humus content, point source emissions and reservoir data). The emission model calculates the diffuse P emissions at their source. It computes the basic elements of the hydrology as well as the soil loss. The model determines the accumulated P surplus of the topsoil and distinguishes the dissolved and the particulate P forms. Emissions are calculated according to the different pathways (surface runoff, erosion and leaching). The main outputs are the spatial distribution (cell values) of the runoff components, the soil loss and the P emissions within the catchment. The transport model joins the independent cells based on the flow tree and it follows the further fate of emitted P from each cell to the catchment outlets. Surface runoff and P fluxes are accumulated along the tree and the field and in-stream retention of the particulate forms are computed. In case of base flow and subsurface P loads only the channel transport is taken into account due to the less known hydrogeological conditions. During the channel transport, point sources and reservoirs are also considered. Main results of the transport algorithm are the discharge, dissolved and sediment
A fractional Fokker-Planck model for anomalous diffusion
Anderson, Johan; Kim, Eun-jin; Moradi, Sara
2014-12-15
In this paper, we present a study of anomalous diffusion using a Fokker-Planck description with fractional velocity derivatives. The distribution functions are found using numerical means for varying degree of fractionality of the stable Lévy distribution. The statistical properties of the distribution functions are assessed by a generalized normalized expectation measure and entropy in terms of Tsallis statistical mechanics. We find that the ratio of the generalized entropy and expectation is increasing with decreasing fractionality towards the well known so-called sub-diffusive domain, indicating a self-organising behavior.
12 CFR Appendix A to Part 213 - Model Forms
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 2 2010-01-01 2010-01-01 false Model Forms A Appendix A to Part 213 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM CONSUMER LEASING (REGULATION M) Pt. 213, App. A Appendix A to Part 213—Model Forms A-1Model Open-End or Finance Vehicle Lease Disclosures A-2Model Closed-End or...
Integrating O/S models during conceptual design, part 2
NASA Technical Reports Server (NTRS)
Ebeling, Charles E.
1994-01-01
This report documents the procedures for utilizing and maintaining the Reliability & Maintainability Model (RAM) developed by the University of Dayton for the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) under NASA research grant NAG-1-1327. The purpose of the grant is to provide support to NASA in establishing operational and support parameters and costs of proposed space systems. As part of this research objective, the model described here was developed. Additional documentation concerning the development of this model may be found in Part 1 of this report. This is the 2nd part of a 3 part technical report.
12 CFR Appendix A to Part 704 - Model Forms
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 6 2010-01-01 2010-01-01 false Model Forms A Appendix A to Part 704 Banks and Banking NATIONAL CREDIT UNION ADMINISTRATION REGULATIONS AFFECTING CREDIT UNIONS CORPORATE CREDIT UNIONS Pt. 704, App. A Appendix A to Part 704—Model Forms This appendix contains sample forms intended...
29 CFR Appendix A to Part 4011 - Model Participant Notice
Code of Federal Regulations, 2011 CFR
2011-07-01
... 29 Labor 9 2011-07-01 2011-07-01 false Model Participant Notice A Appendix A to Part 4011 Labor Regulations Relating to Labor (Continued) PENSION BENEFIT GUARANTY CORPORATION CERTAIN REPORTING AND DISCLOSURE REQUIREMENTS DISCLOSURE TO PARTICIPANTS Pt. 4011, App. A Appendix A to Part 4011—Model...
Modeling of the magnetic free energy of self-diffusion in bcc Fe
NASA Astrophysics Data System (ADS)
Sandberg, N.; Chang, Z.; Messina, L.; Olsson, P.; Korzhavyi, P.
2015-11-01
A first-principles based approach to calculating self-diffusion rates in bcc Fe is discussed with particular focus on the magnetic free energy associated with diffusion activation. First, the enthalpies and entropies of vacancy formation and migration in ferromagnetic bcc Fe are calculated from standard density functional theory methods in combination with transition state theory. Next, the shift in diffusion activation energy when going from the ferromagnetic to the paramagnetic state is estimated by averaging over random spin states. Classical and quantum mechanical Monte Carlo simulations within the Heisenberg model are used to study the effect of spin disordering on the vacancy formation and migration free energy. Finally, a quasiempirical model of the magnetic contribution to the diffusion activation free energy is applied in order to connect the current first-principles results to experimental data. The importance of the zero-point magnon energy in modeling of diffusion in bcc Fe is stressed.
31 CFR Appendix A to Part 132 - Model Notice
Code of Federal Regulations, 2014 CFR
2014-07-01
... 31 Money and Finance: Treasury 1 2014-07-01 2014-07-01 false Model Notice A Appendix A to Part 132... 132—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S... U.S. Code of Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code...
12 CFR Appendix A to Part 233 - Model Notice
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 4 2012-01-01 2012-01-01 false Model Notice A Appendix A to Part 233 Banks and...—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S. government... Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations...
12 CFR Appendix A to Part 233 - Model Notice
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 4 2014-01-01 2014-01-01 false Model Notice A Appendix A to Part 233 Banks and...—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S. government... Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations...
31 CFR Appendix A to Part 132 - Model Notice
Code of Federal Regulations, 2012 CFR
2012-07-01
... 31 Money and Finance: Treasury 1 2012-07-01 2012-07-01 false Model Notice A Appendix A to Part 132... 132—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S... U.S. Code of Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code...
31 CFR Appendix A to Part 132 - Model Notice
Code of Federal Regulations, 2013 CFR
2013-07-01
... 31 Money and Finance: Treasury 1 2013-07-01 2013-07-01 false Model Notice A Appendix A to Part 132... 132—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S... U.S. Code of Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code...
12 CFR Appendix A to Part 233 - Model Notice
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 4 2013-01-01 2013-01-01 false Model Notice A Appendix A to Part 233 Banks and...—Model Notice Re: U.S. Unlawful Internet Gambling Enforcement Act Notice Dear : On , U.S. government... Federal Regulations (12 CFR part 233) and part 132 of title 31 of the U.S. Code of Federal Regulations...
Employing a Modified Diffuser Momentum Model to Simulate Ventilation of the Orion CEV
NASA Technical Reports Server (NTRS)
Straus, John; Lewis, John F.
2011-01-01
The Ansys CFX CFD modeling tool was used to support the design efforts of the ventilation system for the Orion CEV. CFD modeling was used to establish the flow field within the cabin for several supply configurations. A mesh and turbulence model sensitivity study was performed before the design studies. Results were post-processed for comparison with performance requirements. Most configurations employed straight vaned diffusers to direct and throw the flow. To manage the size of the models, the diffuser vanes were not resolved. Instead, a momentum model was employed to account for the effect of the diffusers. The momentum model was tested against a separate, vane-resolved side study. Results are presented for a single diffuser configuration for a low supply flow case.
Diffusion versus network models as descriptions for the spread of prion diseases in the brain.
Matthäus, Franziska
2006-05-01
In this paper we will discuss different modeling approaches for the spread of prion diseases in the brain. Firstly, we will compare reaction-diffusion models with models of epidemic diseases on networks. The solutions of the resulting reaction-diffusion equations exhibit traveling wave behavior on a one-dimensional domain, and the wave speed can be estimated. The models can be tested for diffusion-driven (Turing) instability, which could present a possible mechanism for the formation of plaques. We also show that the reaction-diffusion systems are capable of reproducing experimental data on prion spread in the mouse visual system. Secondly, we study classical epidemic models on networks, and use these models to study the influence of the network topology on the disease progression. PMID:16219329
Primary migration by diffusion through kerogen: I. Model experiments with organic-coated rocks
Thomas, M.M.; Clouse, J.A. )
1990-10-01
Laboratory experiments were performed to assess diffusion through kerogen as a mechanism of hydrocarbon transport through fine-grained rocks. Such transport can be important in primary migration within source rocks and in leakage through seals. To test the concept of diffusion through organic matter networks, model experiments were performed in which hydrocarbon diffusion was measured through Austin chalk cores that had been coated with a monolayer of fatty acids. Hydrocarbon fluxes through the coated cores were compared to hydrocarbon fluxes through uncoated Austin chalk cores. Results showed that the organic coating enhanced transport through the core by a hundredfold over diffusion through its water-filled pore space alone.
SIMPLE PDF MODELS FOR CONVECTIVELY DRIVEN VERTICAL DIFFUSION
The mode of vertical velocity in convective boundary layers is usually negative and the probability distribution function(PDF) of w, pw is rarely symmetrlc. Consequently, vertical diffusion from elevated sources is usually asymmetric and exhibits a descending mode of concentratio...
NASA Astrophysics Data System (ADS)
Boyer, D.; Romo-Cruz, J. C. R.
2014-10-01
Motivated by studies on the recurrent properties of animal and human mobility, we introduce a path-dependent random-walk model with long-range memory for which not only the mean-square displacement (MSD) but also the propagator can be obtained exactly in the asymptotic limit. The model consists of a random walker on a lattice, which, at a constant rate, stochastically relocates at a site occupied at some earlier time. This time in the past is chosen randomly according to a memory kernel, whose temporal decay can be varied via an exponent parameter. In the weakly non-Markovian regime, memory reduces the diffusion coefficient from the bare value. When the mean backward jump in time diverges, the diffusion coefficient vanishes and a transition to an anomalous subdiffusive regime occurs. Paradoxically, at the transition, the process is an anticorrelated Lévy flight. Although in the subdiffusive regime the model exhibits some features of the continuous time random walk with infinite mean waiting time, it belongs to another universality class. If memory is very long-ranged, a second transition takes place to a regime characterized by a logarithmic growth of the MSD with time. In this case the process is asymptotically Gaussian and effectively described as a scaled Brownian motion with a diffusion coefficient decaying as 1 /t .
First Principles Modeling of Bimolecular Reactions with Diffusion
NASA Astrophysics Data System (ADS)
Hansen, S. K.; Scher, H.; Berkowitz, B.
2013-12-01
We consider three approaches to modeling A + B → C irreversible reactions in natural media: 1) a discretized diffusion-reaction equation (DRE), 2) a particle tracking (PT) scheme in which reaction occurs if and only if an A and B particle pair are within a fixed distance, r (the "reaction radius"), and 3) a PT scheme using an alternative to the fixed reaction radius: a collocation probability distribution derived directly from first principles. Each approach has advantages. In some cases a discretized DRE may be the most computationally efficient method. For PT simulations, robust codes exist based on use of a fixed reaction radius. And finally, collocation probabilities may be derived directly from the Fick's Law constant, D, which is a well-established property for most species. In each approach, a single parameter governs the 'promiscuity' of the reaction (i.e. the thermodynamic favorability of reaction, predicated on the particles being locally well mixed). For the DRE, fixed-reaction-radius PT, and collocation-based PT, these parameters are, respectively: a second-order decay rate, r, and D. We established a number of new results enhancing these approaches and relating them to each other (and to nature). In particular, a thought experiment concerning a simple system in which the predictions of each approach can be computed analytically was used to derive formulas establishing a universal one-to-one correspondence among each of the governing parameters. We thus showed the conditions for equivalence of the three approaches, and grounded both the DRE approach and the fixed-radius PT approach in the Fick's Law D. We further showed that the existing collocation-based PT theory is based on a probability distribution that is only correct for infinitesimally small times, but which can be modified to be accurate for larger times by means of continuous time random walk analysis and first-passage probability distributions. Finally, we employed a novel mathematical
Ho, C.K.; Webb, S.W.
1996-05-01
A review of mechanisms, models, and data relevant to the postulated phenomenon of enhanced vapor-phase diffusion in porous media is presented. Information is obtained from literature spanning two different disciplines (soil science and engineering) to gain a diverse perspective on this topic. Findings indicate that while enhanced vapor diffusion tends to correct the discrepancies observed between past theory and experiments, no direct evidence exists to support the postulated processes causing enhanced vapor diffusion. Numerical modeling analyses of experiments representative of the two disciplines are presented in this paper to assess the sensitivity of different systems to enhanced vapor diffusion. Pore-scale modeling is also performed to evaluate the relative significance of enhanced vapor diffusion mechanisms when compared to Fickian diffusion. The results demonstrate the need for additional experiments so that more discerning analyses can be performed.
Kee, Kerk F; Sparks, Lisa; Struppa, Daniele C; Mannucci, Mirco A; Damiano, Alberto
2016-01-01
By integrating the simplicial model of social aggregation with existing research on opinion leadership and diffusion networks, this article introduces the constructs of simplicial diffusers (mathematically defined as nodes embedded in simplexes; a simplex is a socially bonded cluster) and simplicial diffusing sets (mathematically defined as minimal covers of a simplicial complex; a simplicial complex is a social aggregation in which socially bonded clusters are embedded) to propose a strategic approach for information diffusion of cancer screenings as a health intervention on Facebook for community cancer prevention and control. This approach is novel in its incorporation of interpersonally bonded clusters, culturally distinct subgroups, and different united social entities that coexist within a larger community into a computational simulation to select sets of simplicial diffusers with the highest degree of information diffusion for health intervention dissemination. The unique contributions of the article also include seven propositions and five algorithmic steps for computationally modeling the simplicial model with Facebook data. PMID:26362453
NASA Astrophysics Data System (ADS)
Liang, Yingjie; Ye, Allen Q.; Chen, Wen; Gatto, Rodolfo G.; Colon-Perez, Luis; Mareci, Thomas H.; Magin, Richard L.
2016-10-01
Non-Gaussian (anomalous) diffusion is wide spread in biological tissues where its effects modulate chemical reactions and membrane transport. When viewed using magnetic resonance imaging (MRI), anomalous diffusion is characterized by a persistent or 'long tail' behavior in the decay of the diffusion signal. Recent MRI studies have used the fractional derivative to describe diffusion dynamics in normal and post-mortem tissue by connecting the order of the derivative with changes in tissue composition, structure and complexity. In this study we consider an alternative approach by introducing fractal time and space derivatives into Fick's second law of diffusion. This provides a more natural way to link sub-voxel tissue composition with the observed MRI diffusion signal decay following the application of a diffusion-sensitive pulse sequence. Unlike previous studies using fractional order derivatives, here the fractal derivative order is directly connected to the Hausdorff fractal dimension of the diffusion trajectory. The result is a simpler, computationally faster, and more direct way to incorporate tissue complexity and microstructure into the diffusional dynamics. Furthermore, the results are readily expressed in terms of spectral entropy, which provides a quantitative measure of the overall complexity of the heterogeneous and multi-scale structure of biological tissues. As an example, we apply this new model for the characterization of diffusion in fixed samples of the mouse brain. These results are compared with those obtained using the mono-exponential, the stretched exponential, the fractional derivative, and the diffusion kurtosis models. Overall, we find that the order of the fractal time derivative, the diffusion coefficient, and the spectral entropy are potential biomarkers to differentiate between the microstructure of white and gray matter. In addition, we note that the fractal derivative model has practical advantages over the existing models from the
Redox response model for partly substituted cuprates
Oesterreicher, H. . Dept. of Chemistry)
1994-05-01
Inhomogeneous substitutions (e.g. clustering and preferential site occupations) in compounds such as YBa[sub 2](Cu[sub 1[minus]x]M[sub x])[sub 3]O[sub y] with M = Fe, Co, Ni, etc. are an unavoidable response to the changing redox environments in these O intercalation compounds. The authors collect here experimental evidence for various types of inhomogeneous distributions predicted on a thermodynamic model which considers the preferential desorption'' of O from various local environments. The parameter organizing the redox environment is [Delta]H* (incremental enthalpy of oxygen desorption per mol O[sub 2]). Theory suggests a sequence of discernible states represented by the acronym CLUSTER. With decreasing [Delta]H*, indications for several of these states are obtained from Moessbauer and other experiments. These states are characteristically shifted in [Delta]H* for different M. Also, further substitutions according to (YX)(BaZ)[sub 2](CuM)[sub 3]O[sub y] with X = Ca, Z = Sr, La can change the relevant [Delta]H* for these states, allowing prediction of their preparation conditions. Aspects of the complex electronic phase diagram as a function of redox preparation are discussed.
Diffusion on a hypersphere: application to the Wright-Fisher model
NASA Astrophysics Data System (ADS)
Maruyama, Kishiko; Itoh, Yoshiaki
2016-04-01
The eigenfunction expansion by Gegenbauer polynomials for the diffusion on a hypersphere is transformed into the diffusion for the Wright-Fisher model with a particular mutation rate. We use the Ito calculus considering stochastic differential equations. The expansion gives a simple interpretation of the Griffiths eigenfunction expansion for the Wright-Fisher model. Our representation is useful to simulate the Wright-Fisher model as well as Brownian motion on a hypersphere.
NASA Astrophysics Data System (ADS)
Haxhimali, Tomorr; Rudd, Robert; Jackson, Julie; Surh, Michael; Cabot, William; Caspersen, Kyle; Greenough, Jeffrey; Graziani, Frank; Miller, Paul
2012-10-01
We employ classical molecular dynamics (MD) to investigate species diffusivity in binary Yukawa mixtures. The Yukawa potential is used to describe the screened Coulomb interaction between the ions, providing the basis for models of dense stellar materials, inertial confined plasmas, and colloidal particles in electrolytes. We use Green-Kubo techniques to calculate self-diffusivities and the Maxwell-Stefan diffusivities, and evaluate the validity of the Darken relation over a range of thermodynamic conditions of the mixture. The inter-diffusivity (or mutual diffusivity) can then be related to the Maxwell-Stefan diffusivities through the thermodynamic factor. The latter requires knowledge of the equation of state of the mixture. To test these Green-Kubo approaches and to estimate the activity contribution we have also employed large-scale non-equilibrium MD. In these simulations we can extract the inter-diffusivity value by calculating the rate of broadening of the interface in a diffusion couple. We also explore thermodynamic conditions for possible non-Fickian diffusivity. The main motivation in this work is to build a model that describes the transport coefficients in binary Yukawa mixtures over a broad range of thermodynamic conditions up to 1keV.
An efficient wavelet analysis method to film-pore diffusion model arising in mathematical chemistry.
Hariharan, G
2014-04-01
In this paper, we have established an efficient Legendre wavelet based approximation method to solve film-pore diffusion model arising in engineering. Film-pore diffusion model is widely used to determine study the kinetics of adsorption systems. The use of Legendre wavelet based approximation method is found to be accurate, simple, fast, flexible, convenient, and computationally attractive. It is shown that film-pore diffusion model satisfactorily describe kinetics of methylene blue adsorption onto the three low-cost adsorbents, Guava, teak and gulmohar plant leaf powders, used in this study. PMID:24562792
A Computational Model for Diffusion Weighted Imaging of Myelinated White Matter
Baxter, Gregory T.; Frank, Lawrence R.
2013-01-01
The signal for diffusion weighted magnetic resonance imaging has previously been represented analytically and simulated numerically for a variety of model problems with idealized geometries. Numerical simulations hold the promise of computing the diffusion weighted MR signal for more complex realistic tissue architectures and physiological models. This paper investigates a white matter model consisting of a matrix of coated cylinders with distinct diffusion coefficients and spin concentrations for each of the cylinder core, the coating, and the surrounding bath and compares results with an the analytical solution developed by Sen and Basser for the long diffusion time limit. Numerical simulations of diffusion weighted imaging experiments are performed for the three-medium model using a Monte Carlo diffusion simulation. Experiments are carried out for model parameters representing normal white matter. Pulse sequence parameters range from a low b value, long time limit, short pulse approximation to realistic clinical values. For simulations in the short pulse width, long diffusion time limit, numerical simulations agree with the Sen-Basser analytical result. When tested with realistic pulse sequence parameters, numerical simulations show lower anisotropy than the analytical model predicts. PMID:23507381
Modeling of band-3 protein diffusion in the normal and defective red blood cell membrane.
Li, He; Zhang, Yihao; Ha, Vi; Lykotrafitis, George
2016-04-13
We employ a two-component red blood cell (RBC) membrane model to simulate lateral diffusion of band-3 proteins in the normal RBC and in the RBC with defective membrane proteins. The defects reduce the connectivity between the lipid bilayer and the membrane skeleton (vertical connectivity), or the connectivity of the membrane skeleton itself (horizontal connectivity), and are associated with the blood disorders of hereditary spherocytosis (HS) and hereditary elliptocytosis (HE) respectively. Initially, we demonstrate that the cytoskeleton limits band-3 lateral mobility by measuring the band-3 macroscopic diffusion coefficients in the normal RBC membrane and in a lipid bilayer without the cytoskeleton. Then, we study band-3 diffusion in the defective RBC membrane and quantify the relation between band-3 diffusion coefficients and percentage of protein defects in HE RBCs. In addition, we illustrate that at low spectrin network connectivity (horizontal connectivity) band-3 subdiffusion can be approximated as anomalous diffusion, while at high horizontal connectivity band-3 diffusion is characterized as confined diffusion. Our simulations show that the band-3 anomalous diffusion exponent depends on the percentage of protein defects in the membrane cytoskeleton. We also confirm that the introduction of attraction between the lipid bilayer and the spectrin network reduces band-3 diffusion, but we show that this reduction is lower than predicted by the percolation theory. Furthermore, we predict that the attractive force between the spectrin filament and the lipid bilayer is at least 20 times smaller than the binding forces at band-3 and glycophorin C, the two major membrane binding sites. Finally, we explore diffusion of band-3 particles in the RBC membrane with defects related to vertical connectivity. We demonstrate that in this case band-3 diffusion can be approximated as confined diffusion for all attraction levels between the spectrin network and the lipid bilayer
Modelling the Mach bands illusion by means of a diffusion model.
Geier, Janos; Hudák, Mariann
2014-01-01
First, we criticize the validity of the principle of lateral inhibition. Second, on the basis of illusory phenomena and stabilized retinal images, we point out that the retina does not code the absolute luminance; the retina forwards a relative luminance sketch towards higher levels of the visual system. However, at the level of conscious processing the perceptual counterpart of absolute luminance, brightness, is available. Therefore, it is reasonable to assume that a reconstruction process is carried out by the visual system, which recovers the inner representation that corresponds to the retinal light distribution from the coded relative luminance sketch. We provide an illustrative description of a computational model of this reconstruction process. The basis of the reconstruction is a mathematically provable theorem, according to which if image P is produced from image I by Laplacian filtering, and then P is used as the sources and sinks of a homogeneous linear diffusion process, then the equilibrium of the diffusion will be identical to the original image I. We have illustrated this by a one-dimensional heat diffusion example, and by a series of test tubes connected to each other, also in one dimension. Brightness illusions are considered as a side effect of this diffusion-based reconstruction process. If the diffusion process deviates from the principle of homogeneous linearity, then the result of the reconstruction will deviate from the original image I. We showed a concrete illustration of this with regards to the Mach bands illusion: here we violated the principle of homogeneous linearity by means of inserting a small vertical tube serving as a serial resistance between each test tube and the horizontal connecting tube. This violation resulted in a change of water level in the source and the sink test tubes corresponding to the Mach bands illusion. PMID:25420330
Modelling the Mach bands illusion by means of a diffusion model.
Geier, Janos; Hudák, Mariann
2014-01-01
First, we criticize the validity of the principle of lateral inhibition. Second, on the basis of illusory phenomena and stabilized retinal images, we point out that the retina does not code the absolute luminance; the retina forwards a relative luminance sketch towards higher levels of the visual system. However, at the level of conscious processing the perceptual counterpart of absolute luminance, brightness, is available. Therefore, it is reasonable to assume that a reconstruction process is carried out by the visual system, which recovers the inner representation that corresponds to the retinal light distribution from the coded relative luminance sketch. We provide an illustrative description of a computational model of this reconstruction process. The basis of the reconstruction is a mathematically provable theorem, according to which if image P is produced from image I by Laplacian filtering, and then P is used as the sources and sinks of a homogeneous linear diffusion process, then the equilibrium of the diffusion will be identical to the original image I. We have illustrated this by a one-dimensional heat diffusion example, and by a series of test tubes connected to each other, also in one dimension. Brightness illusions are considered as a side effect of this diffusion-based reconstruction process. If the diffusion process deviates from the principle of homogeneous linearity, then the result of the reconstruction will deviate from the original image I. We showed a concrete illustration of this with regards to the Mach bands illusion: here we violated the principle of homogeneous linearity by means of inserting a small vertical tube serving as a serial resistance between each test tube and the horizontal connecting tube. This violation resulted in a change of water level in the source and the sink test tubes corresponding to the Mach bands illusion. PMID:25507314
Goossens, D. J.
2015-01-01
Diffuse scattering from a crystal contains valuable information about the two-body correlations (related to the nanoscale order) in the material. Despite years of development, the detailed analysis of single crystal diffuse scattering (SCDS) has yet to become part of the everyday toolbox of the structural scientist. Recent decades have seen the pair distribution function approach to diffuse scattering (in fact, total scattering) from powders become a relatively routine tool. However, analysing the detailed, complex, and often highly anisotropic three-dimensional distribution of SCDS remains valuable yet rare because there is no routine method for undertaking the analysis. At present, analysis requiresmore » significant investment of time to develop specialist expertise, which means that the analysis of diffuse scattering, which has much to offer, is not incorporated thorough studies of many compounds even though it has the potential to be a very useful adjunct to existing techniques. This article endeavours to outline in some detail how the diffuse scattering from a molecular crystal can be modelled relatively quickly and largely using existing software tools. It is hoped this will provide a template for other studies. To enable this, the entire simulation is included as deposited material.« less
12 CFR Appendix A to Part 216 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
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12 CFR Appendix A to Part 332 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 4 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 332... PRIVACY OF CONSUMER FINANCIAL INFORMATION Pt. 332, App. A Appendix A to Part 332—Model Privacy Form A. The Model Privacy Form ER01DE09.014 ER01DE09.015 ER01DE09.016 ER01DE09.017 ER01DE09.018...
12 CFR Appendix A to Part 216 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 216... CONSUMER FINANCIAL INFORMATION (REGULATION P) Pt. 216, App. A Appendix A to Part 216—Model Privacy Form A. The Model Privacy Form ER01DE09.007 ER01DE09.008 ER01DE09.009 ER01DE09.010 ER01DE09.011...
12 CFR Appendix A to Part 332 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 5 2013-01-01 2013-01-01 false Model Privacy Form A Appendix A to Part 332... PRIVACY OF CONSUMER FINANCIAL INFORMATION Pt. 332, App. A Appendix A to Part 332—Model Privacy Form A. The Model Privacy Form ER01DE09.014 ER01DE09.015 ER01DE09.016 ER01DE09.017 ER01DE09.018...
12 CFR Appendix A to Part 332 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 5 2014-01-01 2014-01-01 false Model Privacy Form A Appendix A to Part 332... PRIVACY OF CONSUMER FINANCIAL INFORMATION Pt. 332, App. A Appendix A to Part 332—Model Privacy Form A. The Model Privacy Form ER01DE09.014 ER01DE09.015 ER01DE09.016 ER01DE09.017 ER01DE09.018...
12 CFR Appendix A to Part 216 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 2 2013-01-01 2013-01-01 false Model Privacy Form A Appendix A to Part 216... CONSUMER FINANCIAL INFORMATION (REGULATION P) Pt. 216, App. A Appendix A to Part 216—Model Privacy Form A. The Model Privacy Form ER01DE09.007 ER01DE09.008 ER01DE09.009 ER01DE09.010 ER01DE09.011...
12 CFR Appendix A to Part 216 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 2 2014-01-01 2014-01-01 false Model Privacy Form A Appendix A to Part 216... CONSUMER FINANCIAL INFORMATION (REGULATION P) Pt. 216, App. A Appendix A to Part 216—Model Privacy Form A. The Model Privacy Form ER01DE09.007 ER01DE09.008 ER01DE09.009 ER01DE09.010 ER01DE09.011...
12 CFR Appendix A to Part 332 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 5 2012-01-01 2012-01-01 false Model Privacy Form A Appendix A to Part 332... PRIVACY OF CONSUMER FINANCIAL INFORMATION Pt. 332, App. A Appendix A to Part 332—Model Privacy Form A. The Model Privacy Form ER01DE09.014 ER01DE09.015 ER01DE09.016 ER01DE09.017 ER01DE09.018...
Diffusive flux in a model of stochastically gated oxygen transport in insect respiration
NASA Astrophysics Data System (ADS)
Berezhkovskii, Alexander M.; Shvartsman, Stanislav Y.
2016-05-01
Oxygen delivery to insect tissues is controlled by transport through a branched tubular network that is connected to the atmosphere by valve-like gates, known as spiracles. In certain physiological regimes, the spiracles appear to be randomly switching between open and closed states. Quantitative analysis of this regime leads a reaction-diffusion problem with stochastically switching boundary condition. We derive an expression for the diffusive flux at long times in this problem. Our approach starts with the derivation of the passage probability for a single particle that diffuses between a stochastically gated boundary, which models the opening and closing spiracle, and the perfectly absorbing boundary, which models oxygen absorption by the tissue. This passage probability is then used to derive an expression giving the diffusive flux as a function of the geometric parameters of the tube and characteristic time scales of diffusion and gate dynamics.
Turing pattern dynamics and adaptive discretization for a super-diffusive Lotka-Volterra model.
Bendahmane, Mostafa; Ruiz-Baier, Ricardo; Tian, Canrong
2016-05-01
In this paper we analyze the effects of introducing the fractional-in-space operator into a Lotka-Volterra competitive model describing population super-diffusion. First, we study how cross super-diffusion influences the formation of spatial patterns: a linear stability analysis is carried out, showing that cross super-diffusion triggers Turing instabilities, whereas classical (self) super-diffusion does not. In addition we perform a weakly nonlinear analysis yielding a system of amplitude equations, whose study shows the stability of Turing steady states. A second goal of this contribution is to propose a fully adaptive multiresolution finite volume method that employs shifted Grünwald gradient approximations, and which is tailored for a larger class of systems involving fractional diffusion operators. The scheme is aimed at efficient dynamic mesh adaptation and substantial savings in computational burden. A numerical simulation of the model was performed near the instability boundaries, confirming the behavior predicted by our analysis. PMID:26219250
Atomistic modeling of the self-diffusion in γ-U and γ-U-Mo
NASA Astrophysics Data System (ADS)
Smirnova, D. E.; Kuksin, A. Yu.; Starikov, S. V.; Stegailov, V. V.
2015-05-01
Results of investigations of the self-diffusion in gamma-uranium and metallic U-Mo alloys are presented. Calculations are performed using the method of atomistic modeling with the help of interatomic potentials based on the embedded-atom model and its modifications. Proposed potentials are verified by calculating thermodynamic and mechanical properties of uranium and U-Mo alloys. The formation energies of point defects and atomic diffusivities due to the diffusion of defects are calculated for gamma-uranium and alloy containing 9 wt % molybdenum. Self-diffusion coefficients of uranium and molybdenum are evaluated. Based on the data obtained, it has been concluded that the experimentally observed features of the self-diffusion in gamma-uranium can be explained by the prevalence of the interstitial mechanism.
Numerical study of a cylinder model of the diffusion MRI signal for neuronal dendrite trees.
Van Nguyen, Dang; Grebenkov, Denis; Le Bihan, Denis; Li, Jing-Rebecca
2015-03-01
We study numerically how the neuronal dendrite tree structure can affect the diffusion magnetic resonance imaging (dMRI) signal in brain tissue. For a large set of randomly generated dendrite trees, synthetic dMRI signals are computed and fitted to a cylinder model to estimate the effective longitudinal diffusivity D(L) in the direction of neurites. When the dendrite branches are short compared to the diffusion length, D(L) depends significantly on the ratio between the average branch length and the diffusion length. In turn, D(L) has very weak dependence on the distribution of branch lengths and orientations of a dendrite tree, and the number of branches per node. We conclude that the cylinder model which ignores the connectivity of the dendrite tree, can still be adapted to describe the apparent diffusion coefficient in brain tissue. PMID:25681802
Diffusive flux in a model of stochastically gated oxygen transport in insect respiration.
Berezhkovskii, Alexander M; Shvartsman, Stanislav Y
2016-05-28
Oxygen delivery to insect tissues is controlled by transport through a branched tubular network that is connected to the atmosphere by valve-like gates, known as spiracles. In certain physiological regimes, the spiracles appear to be randomly switching between open and closed states. Quantitative analysis of this regime leads a reaction-diffusion problem with stochastically switching boundary condition. We derive an expression for the diffusive flux at long times in this problem. Our approach starts with the derivation of the passage probability for a single particle that diffuses between a stochastically gated boundary, which models the opening and closing spiracle, and the perfectly absorbing boundary, which models oxygen absorption by the tissue. This passage probability is then used to derive an expression giving the diffusive flux as a function of the geometric parameters of the tube and characteristic time scales of diffusion and gate dynamics. PMID:27250273
Numerical study of a cylinder model of the diffusion MRI signal for neuronal dendrite trees
NASA Astrophysics Data System (ADS)
Van Nguyen, Dang; Grebenkov, Denis; Le Bihan, Denis; Li, Jing-Rebecca
2015-03-01
We study numerically how the neuronal dendrite tree structure can affect the diffusion magnetic resonance imaging (dMRI) signal in brain tissue. For a large set of randomly generated dendrite trees, synthetic dMRI signals are computed and fitted to a cylinder model to estimate the effective longitudinal diffusivity DL in the direction of neurites. When the dendrite branches are short compared to the diffusion length, DL depends significantly on the ratio between the average branch length and the diffusion length. In turn, DL has very weak dependence on the distribution of branch lengths and orientations of a dendrite tree, and the number of branches per node. We conclude that the cylinder model which ignores the connectivity of the dendrite tree, can still be adapted to describe the apparent diffusion coefficient in brain tissue.
Modeling of TCE diffusion to the atmosphere and distribution in plant stems.
Ma, Xingmao; Burken, Joel
2004-09-01
Fate of chlorinated solvents in phytoremediation has been delineated by many discoveries made in recent years. Plant uptake, metabolism, rhizosphere degradation, accumulation, and volatilization were shown to occur to differing degrees for many organic contaminants including chlorinated solvents. Among these mechanistic findings, recent research confirmed that volatile organic compounds (VOCs) volatilize from stems and that the resulting diffusive flux to the atmosphere is related to exposure concentration and to height up the stem. A comprehensive model was developed based upon all identified fate and transport mechanisms for VOCs, including translocation in the xylem flow and diffusion. The dispersion and diffusion in the radial direction were considered as one process (effective diffusion) as the two could not be investigated individually. The mechanism-based model mathematically indicates an exponential decrease of concentrations with height. While an analytic solution for the comprehensive model was not attained, it can serve as a starting point for other modeling efforts. The comprehensive model was simplified in this work for practical application to experimentally obtained data on trichloroethylene (TCE) fate. Model output correlated well with experimental results, and effective diffusivities for TCE in plant tissues were obtained through the model calibrations. The simplified model approximated TCE concentrations in the transpiration stream as well as TCE volatilization to the atmosphere. Xylem transport, including advection, dispersion, and diffusion through cell walls with subsequent volatilization to the atmosphere, is a major fate for VOCs in phytoremediation. PMID:15461166
Ages estimated from a diffusion equation model for scarp degradation
Colman, Steven M.; Watson, K.E.N.
1983-01-01
The diffusion equation derived from the continuity equation for hillslopes is applied to scarp erosion in unconsolidated materials. Solutions to this equation allow direct calculation of the product of the rate coefficient and the age of the scarp from measurements of scarp morphology. Where the rate coefficient can be estimated or can be derived from scarps of known age, this method allows direct calculation of unknown ages of scarps.
Nie, Qi-Yang; Maurer, Mara; Müller, Hermann J; Conci, Markus
2016-05-01
Illusory Kanizsa figures demonstrate that a perceptually completed whole is more than the sum of its composite parts. In the current study, we explored part/whole relationships in object completion using the configural superiority effect (CSE) with illusory figures (Pomerantz & Portillo, 2011). In particular, we investigated to which extent the CSE is modulated by closure in target and distractor configurations. Our results demonstrated a typical CSE, with detection of a configural whole being more efficient than the detection of a corresponding part-level target. Moreover, the CSE was more pronounced when grouped objects were presented in distractors rather than in the target. A follow-up experiment systematically manipulated closure in whole target or, respectively, distractor configurations. The results revealed the effect of closure to be again stronger in distractor, rather than in target configurations, suggesting that closure primarily affects the inhibition of distractors, and to a lesser extent the selection of the target. In addition, a drift-diffusion model analysis of our data revealed that efficient distractor inhibition expedites the rate of evidence accumulation, with closure in distractors particularly speeding the drift toward the decision boundary. In sum, our findings demonstrate that the CSE in Kanizsa figures derives primarily from the inhibition of closed distractor objects, rather than being driven by a conspicuous target configuration. Altogether, these results support a fundamental role of inhibition in driving configural superiority effects in visual search. PMID:26896900
Measuring and modeling diffuse scattering in protein X-ray crystallography
Van Benschoten, Andrew H.; Liu, Lin; Gonzalez, Ana; Brewster, Aaron S.; Sauter, Nicholas K.; Fraser, James S.; Wall, Michael E.
2016-03-28
X-ray diffraction has the potential to provide rich information about the structural dynamics of macromolecules. To realize this potential, both Bragg scattering, which is currently used to derive macromolecular structures, and diffuse scattering, which reports on correlations in charge density variations, must be measured. Until now, measurement of diffuse scattering from protein crystals has been scarce because of the extra effort of collecting diffuse data. Here, we present 3D measurements of diffuse intensity collected from crystals of the enzymes cyclophilin A and trypsin. The measurements were obtained from the same X-ray diffraction images as the Bragg data, using best practicesmore » for standard data collection. To model the underlying dynamics in a practical way that could be used during structure refinement, we tested translation–libration–screw (TLS), liquid-like motions (LLM), and coarse-grained normal-modes (NM) models of protein motions. The LLM model provides a global picture of motions and was refined against the diffuse data, whereas the TLS and NM models provide more detailed and distinct descriptions of atom displacements, and only used information from the Bragg data. Whereas different TLS groupings yielded similar Bragg intensities, they yielded different diffuse intensities, none of which agreed well with the data. In contrast, both the LLM and NM models agreed substantially with the diffuse data. In conclusion, these results demonstrate a realistic path to increase the number of diffuse datasets available to the wider biosciences community and indicate that dynamics-inspired NM structural models can simultaneously agree with both Bragg and diffuse scattering.« less
Measuring and modeling diffuse scattering in protein X-ray crystallography.
Van Benschoten, Andrew H; Liu, Lin; Gonzalez, Ana; Brewster, Aaron S; Sauter, Nicholas K; Fraser, James S; Wall, Michael E
2016-04-12
X-ray diffraction has the potential to provide rich information about the structural dynamics of macromolecules. To realize this potential, both Bragg scattering, which is currently used to derive macromolecular structures, and diffuse scattering, which reports on correlations in charge density variations, must be measured. Until now, measurement of diffuse scattering from protein crystals has been scarce because of the extra effort of collecting diffuse data. Here, we present 3D measurements of diffuse intensity collected from crystals of the enzymes cyclophilin A and trypsin. The measurements were obtained from the same X-ray diffraction images as the Bragg data, using best practices for standard data collection. To model the underlying dynamics in a practical way that could be used during structure refinement, we tested translation-libration-screw (TLS), liquid-like motions (LLM), and coarse-grained normal-modes (NM) models of protein motions. The LLM model provides a global picture of motions and was refined against the diffuse data, whereas the TLS and NM models provide more detailed and distinct descriptions of atom displacements, and only used information from the Bragg data. Whereas different TLS groupings yielded similar Bragg intensities, they yielded different diffuse intensities, none of which agreed well with the data. In contrast, both the LLM and NM models agreed substantially with the diffuse data. These results demonstrate a realistic path to increase the number of diffuse datasets available to the wider biosciences community and indicate that dynamics-inspired NM structural models can simultaneously agree with both Bragg and diffuse scattering. PMID:27035972
Measuring and modeling diffuse scattering in protein X-ray crystallography
Van Benschoten, Andrew H.; Liu, Lin; Gonzalez, Ana; Brewster, Aaron S.; Sauter, Nicholas K.; Wall, Michael E.
2016-01-01
X-ray diffraction has the potential to provide rich information about the structural dynamics of macromolecules. To realize this potential, both Bragg scattering, which is currently used to derive macromolecular structures, and diffuse scattering, which reports on correlations in charge density variations, must be measured. Until now, measurement of diffuse scattering from protein crystals has been scarce because of the extra effort of collecting diffuse data. Here, we present 3D measurements of diffuse intensity collected from crystals of the enzymes cyclophilin A and trypsin. The measurements were obtained from the same X-ray diffraction images as the Bragg data, using best practices for standard data collection. To model the underlying dynamics in a practical way that could be used during structure refinement, we tested translation–libration–screw (TLS), liquid-like motions (LLM), and coarse-grained normal-modes (NM) models of protein motions. The LLM model provides a global picture of motions and was refined against the diffuse data, whereas the TLS and NM models provide more detailed and distinct descriptions of atom displacements, and only used information from the Bragg data. Whereas different TLS groupings yielded similar Bragg intensities, they yielded different diffuse intensities, none of which agreed well with the data. In contrast, both the LLM and NM models agreed substantially with the diffuse data. These results demonstrate a realistic path to increase the number of diffuse datasets available to the wider biosciences community and indicate that dynamics-inspired NM structural models can simultaneously agree with both Bragg and diffuse scattering. PMID:27035972
Degenerate mobilities in phase field models are insufficient to capture surface diffusion
NASA Astrophysics Data System (ADS)
Lee, Alpha A.; Münch, Andreas; Süli, Endre
2015-08-01
Phase field models frequently provide insight into phase transitions and are robust numerical tools to solve free boundary problems corresponding to the motion of interfaces. A body of prior literature suggests that interface motion via surface diffusion is the long-time, sharp interface limit of microscopic phase field models such as the Cahn-Hilliard equation with a degenerate mobility function. Contrary to this conventional wisdom, we show that the long-time behaviour of degenerate Cahn-Hilliard equation with a polynomial free energy undergoes coarsening, reflecting the presence of bulk diffusion, rather than pure surface diffusion. This reveals an important limitation of phase field models that are frequently used to model surface diffusion.
A Functional Model for Teaching Osmosis-Diffusion to Biology Students
ERIC Educational Resources Information Center
Olsen, Richard W.; Petry, Douglas E.
1976-01-01
Described is a maternal-fetal model, operated by the student, to teach osmosis-diffusion to biology students. Included are materials needed, assembly instructions, and student operating procedures. (SL)
Wang, Zhiwu; Hamilton-Brehm, Scott; Lochner, Adriane; Elkins, James G; Morrell-Falvey, Jennifer L
2011-01-01
Abstract: The morphological and structural properties of microbial biofilms are influenced by internal substrate diffusion and utilization processes. In the case of microbial hydrolysis of plant cell walls, only thin and uniform biofilm structures are typically formed by cellulolytic microorganisms. In this study, we develop a hydrolysate diffusion and utilization model system to examine factors influencing cellulolytic biofilm formation. Model simulations using Caldicellulosiruptor obsidiansis as a representative organism, reveal that the growth of the cellulolytic biofilm is limited by hydrolysate utilization but not diffusion. As a consequence, the cellulolytic biofilm has a uniform growth rate, and there is a hydrolysate surplus that diffuses through the cellulolytic biofilm into the bulk solution where it is consumed by planktonic cells. Predictions based on the model were tested in a cellulose fermentation study and the results are consistent with the model and previously reported experimental data. The factors determining the rate-limiting step of biofilm growth are also analyzed.
Improved oxygen mass transfer modeling for diffused or subsurface aeration systems
McWhirter, J.R.; Hutter, J.C. . Dept. of Chemical Engineering)
1988-01-01
The mass transfer analysis of the oxygen transfer performance of diffused air or subsurface mechanical aeration systems has progressed very little over the past twenty years. The ASCE Standard Method for determination of the oxygen mass transfer performance as applied to a diffused or subsurface aeration systems is based on a greatly over-simplified mass transfer model. Although the ASCE Standard can be used to empirically evaluate point performance conditions, it is not suitable for prediction of the performance of diffused aeration systems under changing operating or environmental conditions. A new oxygen mass transfer model has been developed which is a fundamentally more rigorous description of the actual mass transfer process in diffused aeration systems. This model can be confidently used to predict aerator performance under changing operation and environmental conditions and is easily adapted to numerical solution on a computer for routing aeration system performance evaluation as well as process design. The model is presented in this book.
A modified multiple-relaxation-time lattice Boltzmann model for convection-diffusion equation
NASA Astrophysics Data System (ADS)
Huang, Rongzong; Wu, Huiying
2014-10-01
A modified lattice Boltzmann model with multiple relaxation times (MRT) for the convection-diffusion equation (CDE) is proposed. By modifying the relaxation matrix, as well as choosing the corresponding equilibrium distribution function properly, the present model can recover the CDE with anisotropic diffusion coefficient with no deviation term even when the velocity vector varies generally with space or time through the Chapman-Enskog analysis. This model is firstly validated by simulating the diffusion of a Gaussian hill, which demonstrates it can handle the anisotropic diffusion problem correctly. Then it is adopted to calculate the longitudinal dispersion coefficient of the Taylo-Aris dispersion. Numerical results show that the present model can further reduce the numerical error under the condition of non-zero velocity vector, especially when the dimensionless relaxation time is relatively large.
Woo, Jiyoung; Chen, Hsinchun
2016-01-01
As social media has become more prevalent, its influence on business, politics, and society has become significant. Due to easy access and interaction between large numbers of users, information diffuses in an epidemic style on the web. Understanding the mechanisms of information diffusion through these new publication methods is important for political and marketing purposes. Among social media, web forums, where people in online communities disseminate and receive information, provide a good environment for examining information diffusion. In this paper, we model topic diffusion in web forums using the epidemiology model, the susceptible-infected-recovered (SIR) model, frequently used in previous research to analyze both disease outbreaks and knowledge diffusion. The model was evaluated on a large longitudinal dataset from the web forum of a major retail company and from a general political discussion forum. The fitting results showed that the SIR model is a plausible model to describe the diffusion process of a topic. This research shows that epidemic models can expand their application areas to topic discussion on the web, particularly social media such as web forums. PMID:26839759
A novel tensor distribution model for the diffusion-weighted MR signal.
Jian, Bing; Vemuri, Baba C; Ozarslan, Evren; Carney, Paul R; Mareci, Thomas H
2007-08-01
Diffusion MRI is a non-invasive imaging technique that allows the measurement of water molecule diffusion through tissue in vivo. The directional features of water diffusion allow one to infer the connectivity patterns prevalent in tissue and possibly track changes in this connectivity over time for various clinical applications. In this paper, we present a novel statistical model for diffusion-weighted MR signal attenuation which postulates that the water molecule diffusion can be characterized by a continuous mixture of diffusion tensors. An interesting observation is that this continuous mixture and the MR signal attenuation are related through the Laplace transform of a probability distribution over symmetric positive definite matrices. We then show that when the mixing distribution is a Wishart distribution, the resulting closed form of the Laplace transform leads to a Rigaut-type asymptotic fractal expression, which has been phenomenologically used in the past to explain the MR signal decay but never with a rigorous mathematical justification until now. Our model not only includes the traditional diffusion tensor model as a special instance in the limiting case, but also can be adjusted to describe complex tissue structure involving multiple fiber populations. Using this new model in conjunction with a spherical deconvolution approach, we present an efficient scheme for estimating the water molecule displacement probability functions on a voxel-by-voxel basis. Experimental results on both simulations and real data are presented to demonstrate the robustness and accuracy of the proposed algorithms. PMID:17570683
Xu, X.; Sumption, M. D.
2016-01-01
In this work we explore the compositions of non-stoichiometric intermediate phases formed by diffusion reactions: a mathematical framework is developed and tested against the specific case of Nb3Sn superconductors. In the first part, the governing equations for the bulk diffusion and inter-phase interface reactions during the growth of a compound are derived, numerical solutions to which give both the composition profile and growth rate of the compound layer. The analytic solutions are obtained with certain approximations made. In the second part, we explain an effect that the composition characteristics of compounds can be quite different depending on whether it is the bulk diffusion or grain boundary diffusion that dominates in the compounds, and that “frozen” bulk diffusion leads to unique composition characteristics that the bulk composition of a compound layer remains unchanged after its initial formation instead of varying with the diffusion reaction system; here the model is modified for the case of grain boundary diffusion. Finally, we apply this model to the Nb3Sn superconductors and propose approaches to control their compositions. PMID:26754774
NASA Astrophysics Data System (ADS)
Wu, Qiong; Li, Shu-Suo; Ma, Yue; Gong, Sheng-Kai
2012-10-01
The diffusion coefficients of several alloying elements (Al, Mo, Co, Ta, Ru, W, Cr, Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory. The correlation factors provided by the five-frequency model are explicitly calculated. The calculated diffusion coefficients show their excellent agreement with the available experimental data. Both the diffusion pre-factor (D0) and the activation energy (Q) of impurity diffusion are obtained. The diffusion coefficients above 700 K are sorted in the following order: DAl > DCr > DCo > DTa > DMo > DRu > DW > DRe. It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair (E1). The value of E2-E1 (E2 is the solute diffusion energy) and the correlation factor each also show a positive correlation. The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.
NASA Astrophysics Data System (ADS)
Casalegno, A.; Bresciani, F.; Groppi, G.; Marchesi, R.
Water management is widely investigated because it affects both the performance and the lifetime of polymer electrolyte fuel cells. Membrane hydration is necessary to ensure the high proton conductivity, but too much water can cause flooding and pore obstruction within the cathode gas diffusion layer and the electrode. Experimental studies prove that the characteristics of the diffusion layer have great influence on water transport; the introduction of a micro-porous layer between the gas diffusion layer and the electrode reduces flooding and stabilizes the performance of the fuel cell, although the reason is not fully explained. A quantitative method to characterize water transport through the diffusion layers was proposed in our previous work, and the present work aims to further understand the flooding phenomenon and the role of the micro-porous layer. The improved experimental setup and methodology allow an accurate and reliable evaluation of water transport through the diffusion layer in a wide range of operating conditions. The proposed 1D + 1D model faithfully reproduces the experimental data adopting effective diffusivity values in agreement with literature. The presented experimental and modelling analysis allows us to evaluate the influence of pore obstruction on the effective diffusivity, the overall transport coefficient and water flow through the diffusion layer, elucidating the effect of the micro-porous layer on fuel cell performance and operation stability.
Modelling oxygen self-diffusion in UO_{2} under pressure
Cooper, Michael William D.; Grimes, R. W.; Fitzpatrick, M. E.; Chroneos, A.
2015-10-22
Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO_{2} is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO_{2} over a range of pressures (0–10 GPa) and temperatures (300–1900 K). Furthermore, the significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.
Diffusion in a generalized Rubinstein-Duke model of electrophoresis with kinematic disorder
NASA Astrophysics Data System (ADS)
Willmann, Richard D.; Schütz, Gunter M.; Jain, Kavita
2003-06-01
Using a generalized Rubinstein-Duke model, we prove rigorously that kinematic disorder leaves the prediction of the standard reptation theory for the scaling of the diffusion constant in the limit for long polymer chains D∝L-2 unaffected. Based on an analytical calculation as well as on Monte Carlo simulations, we predict kinematic disorder to affect the center-of-mass diffusion constant of an entangled polymer in the limit for long chains by the same factor as single particle diffusion in a random barrier model.
Efficient simulation of diffusion-based choice RT models on CPU and GPU.
Verdonck, Stijn; Meers, Kristof; Tuerlinckx, Francis
2016-03-01
In this paper, we present software for the efficient simulation of a broad class of linear and nonlinear diffusion models for choice RT, using either CPU or graphical processing unit (GPU) technology. The software is readily accessible from the popular scripting languages MATLAB and R (both 64-bit). The speed obtained on a single high-end GPU is comparable to that of a small CPU cluster, bringing standard statistical inference of complex diffusion models to the desktop platform. PMID:25761391
NASA Astrophysics Data System (ADS)
Klapp, Jaime; di G Sigalotti, Leonardo; Troconis, Jorge; Sira, Eloy; Pena, Franklin; ININ-IVIC Team; Cinvestav-UAM-A Team
2014-11-01
We study numerically liquid-vapor phase separation in two-dimensional, nonisothermal, van der Waals (vdW) liquid drops using the method of Smoothed Particle Hydrodynamics (SPH). In contrast to previous SPH simulations of drop formation, our approach is fully adaptive and follows the diffuse interface model for a single-component fluid, where a reversible, capillary (Korteweg) force is added to the equations of motion to model the rapid but smooth transition of physical quantities through the interface separating the bulk phases. Surface tension arises naturally from the cohesive part of the vdW equation of state and the capillary forces. The drop models all start from a square-shaped liquid and spinodal decomposition is investigated for a range of initial densities and temperatures. The simulations predict the formation of stable, subcritical liquid drops with a vapor atmosphere, with the densities and temperatures of coexisting liquid and vapor in the vdW phase diagram closely matching the binodal curve. We find that the values of surface tension, as determined from the Young-Laplace equation, are in good agreement with the results of independent numerical simulations and experimental data. The models also predict the increase of the vapor pressure with temperature and the fitting to the numerical data reproduces very well the Clausius-Clapeyron relation, thus allowing for the calculation of the vaporization pressure for this vdW fluid. Cinvestav-Abacus.
NASA Astrophysics Data System (ADS)
Sigalotti, Leonardo Di G.; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime
2014-07-01
We study numerically liquid-vapor phase separation in two-dimensional, nonisothermal, van der Waals (vdW) liquid drops using the method of smoothed particle hydrodynamics (SPH). In contrast to previous SPH simulations of drop formation, our approach is fully adaptive and follows the diffuse-interface model for a single-component fluid, where a reversible, capillary (Korteweg) force is added to the equations of motion to model the rapid but smooth transition of physical quantities through the interface separating the bulk phases. Surface tension arises naturally from the cohesive part of the vdW equation of state and the capillary forces. The drop models all start from a square-shaped liquid and spinodal decomposition is investigated for a range of initial densities and temperatures. The simulations predict the formation of stable, subcritical liquid drops with a vapor atmosphere, with the densities and temperatures of coexisting liquid and vapor in the vdW phase diagram closely matching the binodal curve. We find that the values of surface tension, as determined from the Young-Laplace equation, are in good agreement with the results of independent numerical simulations and experimental data. The models also predict the increase of the vapor pressure with temperature and the fitting to the numerical data reproduces very well the Clausius-Clapeyron relation, thus allowing for the calculation of the vaporization pressure for this vdW fluid.
Sigalotti, Leonardo Di G; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime
2014-07-01
We study numerically liquid-vapor phase separation in two-dimensional, nonisothermal, van der Waals (vdW) liquid drops using the method of smoothed particle hydrodynamics (SPH). In contrast to previous SPH simulations of drop formation, our approach is fully adaptive and follows the diffuse-interface model for a single-component fluid, where a reversible, capillary (Korteweg) force is added to the equations of motion to model the rapid but smooth transition of physical quantities through the interface separating the bulk phases. Surface tension arises naturally from the cohesive part of the vdW equation of state and the capillary forces. The drop models all start from a square-shaped liquid and spinodal decomposition is investigated for a range of initial densities and temperatures. The simulations predict the formation of stable, subcritical liquid drops with a vapor atmosphere, with the densities and temperatures of coexisting liquid and vapor in the vdW phase diagram closely matching the binodal curve. We find that the values of surface tension, as determined from the Young-Laplace equation, are in good agreement with the results of independent numerical simulations and experimental data. The models also predict the increase of the vapor pressure with temperature and the fitting to the numerical data reproduces very well the Clausius-Clapeyron relation, thus allowing for the calculation of the vaporization pressure for this vdW fluid. PMID:25122383
Shaviv, Avi; Raban, Smadar; Zaidel, Elina
2003-05-15
A comprehensive model describing the complex and "non-Fickian" (mathematically nonlinear) nature of the release from single granules of membrane coated, controlled release fertilizers (CRFs) is proposed consisting of three stages: i. a lag period during which water penetrates the coating of the granule dissolving part of the solid fertilizer in it ii. a period of linear release during which water penetration into and release out occur concomitantly while the total volume of the granules remains practically constant; and iii. a period of "decaying release", starting as the concentration inside the granule starts to decrease. A mathematical model was developed based on vapor and nutrient diffusion equations. The model predicts the release stages in terms of measurable geometrical and chemophysical parameters such as the following: the product of granule radius and coating thickness, water and solute permeability, saturation concentration of the fertilizer, and its density. The model successfully predicts the complex and "sigmoidal" pattern of release that is essential for matching plant temporal demand to ensure high agronomic and environmental effectiveness. It also lends itself to more complex statistical formulations which account for the large variability within large populations of coated CRFs and can serve for further improving CRF production and performance. PMID:12785532
NASA Astrophysics Data System (ADS)
Sysun, V. I.; Bute, I. V.; Boriskov, P. P.
2016-09-01
The transition process from the low resistance state into the high resistance state in a Pt/NiO/Pt memory switching structure has been studied by numerical modeling. Detailed analysis shows, that thermally induced diffusion oxidation by nickel vacancies is the key factor for distortion of the channel metallic conductivity. Spatial dynamics of the process of oxidation defines channel narrowing mainly in its central part, and also sets the critical current through the structure sufficient for final rupture of the channel and the transition to high resistance state. The increase in critical current above the limit even by 10% reduces the switching time by an order of magnitude, which is in agreement with experiments. The developed radial diffusion model of conductive channel (or filaments) oxidation may be suitable for the analysis of switching effect a number of other ReRAM oxide structures.
Delay-induced Turing-like waves for one-species reaction-diffusion model on a network
NASA Astrophysics Data System (ADS)
Petit, Julien; Carletti, Timoteo; Asllani, Malbor; Fanelli, Duccio
2015-09-01
A one-species time-delay reaction-diffusion system defined on a complex network is studied. Traveling waves are predicted to occur following a symmetry-breaking instability of a homogeneous stationary stable solution, subject to an external nonhomogeneous perturbation. These are generalized Turing-like waves that materialize in a single-species populations dynamics model, as the unexpected byproduct of the imposed delay in the diffusion part. Sufficient conditions for the onset of the instability are mathematically provided by performing a linear stability analysis adapted to time-delayed differential equations. The method here developed exploits the properties of the Lambert W-function. The prediction of the theory are confirmed by direct numerical simulation carried out for a modified version of the classical Fisher model, defined on a Watts-Strogatz network and with the inclusion of the delay.
Modification of TOUGH2 to Include the Dusty Gas Model for Gas Diffusion
WEBB, STEPHEN W.
2001-10-01
The GEO-SEQ Project is investigating methods for geological sequestration of CO{sub 2}. This project, which is directed by LBNL and includes a number of other industrial, university, and national laboratory partners, is evaluating computer simulation methods including TOUGH2 for this problem. The TOUGH2 code, which is a widely used code for flow and transport in porous and fractured media, includes simplified methods for gas diffusion based on a direct application of Fick's law. As shown by Webb (1998) and others, the Dusty Gas Model (DGM) is better than Fick's Law for modeling gas-phase diffusion in porous media. In order to improve gas-phase diffusion modeling for the GEO-SEQ Project, the EOS7R module in the TOUGH2 code has been modified to include the Dusty Gas Model as documented in this report. In addition, the liquid diffusion model has been changed from a mass-based formulation to a mole-based model. Modifications for separate and coupled diffusion in the gas and liquid phases have also been completed. The results from the DGM are compared to the Fick's law behavior for TCE and PCE diffusion across a capillary fringe. The differences are small due to the relatively high permeability (k = 10{sup -11} m{sup 2}) of the problem and the small mole fraction of the gases. Additional comparisons for lower permeabilities and higher mole fractions may be useful.
Diffusion parameters of indium for silicon process modeling
NASA Astrophysics Data System (ADS)
Kizilyalli, I. C.; Rich, T. L.; Stevie, F. A.; Rafferty, C. S.
1996-11-01
The diffusion parameters of indium in silicon are investigated. Systematic diffusion experiments in dry oxidizing ambients at temperatures ranging from 800 to 1050 °C are conducted using silicon wafers implanted with indium. Secondary-ion-mass spectrometry (SIMS) is used to analyze the dopant distribution before and after heat treatment. The oxidation-enhanced diffusion parameter [R. B. Fair, in Semiconductor Materials and Process Technology Handbook, edited by G. E. McGuire (Noyes, Park Ridge, NJ, 1988); A. M. R. Lin, D. A. Antoniadis, and R. W. Dutton, J. Electrochem. Soc. Solid-State Sci. Technol. 128, 1131 (1981); D. A. Antoniadis and I. Moskowitz, J. Appl. Phys. 53, 9214 (1982)] and the segregation coefficient at the Si/SiO2 interface [R. B. Fair and J. C. C. Tsai, J. Electrochem. Soc. Solid-State Sci. Technol. 125, 2050 (1978)] (ratio of indium concentration in silicon to that in silicon dioxide) are extracted as a function of temperature using SIMS depth profiles and the silicon process simulator PROPHET [M. Pinto, D. M. Boulin, C. S. Rafferty, R. K. Smith, W. M. Coughran, I. C. Kizilyalli, and M. J. Thoma, in IEDM Technical Digest, 1992, p. 923]. It is observed that the segregation coefficient of indium at the Si/SiO2 interface is mIn≪1, similar to boron; however, unlike boron, the segregation coefficient of indium at the Si/SiO2 interface decreases with increasing temperature. Extraction results are summarized in analytical forms suitable for incorporation into other silicon process simulators. Finally, the validity of the extracted parameters is verified by comparing the simulated and measured SIMS profiles for an indium implanted buried-channel p-channel metal-oxide-semiconductor field-effect-transistor [I. C. Kizilyalli, F. A. Stevie, and J. D. Bude, IEEE Electron Device Lett. (1996)] process that involves a gate oxidation and various other thermal processes.
Kidney Tumor Growth Prediction by Coupling Reaction-Diffusion and Biomechanical Model
Chen, Xinjian; Summers, Ronald M.; Yao, Jianhua
2014-01-01
It is desirable to predict the tumor growth rate so that appropriate treatment can be planned in the early stage. Previously, we proposed a finite element method (FEM)-based 3D kidney tumor growth prediction system using longitudinal images. A reaction-diffusion model was applied as the tumor growth model. In this paper, we not only improve the tumor growth model by coupling the reaction-diffusion model with a biomechanical model, but also take the surrounding tissues into account. Different diffusion and biomechanical properties are applied for different tissue types. FEM is employed to simulate the coupled tumor growth model. Model parameters are estimated by optimizing an objective function of overlap accuracy using a hybrid optimization parallel search package (HOPSPACK). The proposed method was tested with kidney CT images of eight tumors from five patients with seven time points. The experimental results showed the performance of the proposed method improved greatly compared to our previous work. PMID:23047857
NASA Astrophysics Data System (ADS)
Zhu, Haochen; Ghoufi, Aziz; Szymczyk, Anthony; Balannec, Béatrice; Morineau, Denis
2012-06-01
We report the self-diffusion coefficients and hindrance factor for the diffusion of ions into cylindrical hydrophilic silica nanopores (hydrated silica) determined from molecular dynamics (MD) simulations. We make a comparison with the hindered diffusion coefficients used in continuum-based models of nanofiltration (NF). Hindrance factors for diffusion estimated from the macroscopic hydrodynamic theory were found to be in fair quantitative agreement with MD simulations for a protonated pore, but they strongly overestimate diffusion inside a deprotonated pore.
A diffuse plate boundary model for Indian Ocean tectonics
NASA Technical Reports Server (NTRS)
Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.
1985-01-01
It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.
Cosmic-ray diffusion modeling: Solutions using variational methods
NASA Astrophysics Data System (ADS)
Tautz, R. C.; Lerche, I.
2013-05-01
The diffusion of energetic particles in turbulent magnetic fields is usually described via the two-point, two-time velocity correlation function. A variational principle is used to determine the characteristic function that results from the Fourier-transformed correlation function. Both for a linear approximation and for the wave vector set to zero, explicit solutions are derived that depend on the Fokker-Planck coefficient of pitch-angle scattering. It is shown that, for an isotropic form of the Fokker-Planck coefficient, the characteristic function is divergent, which can be remedied only by using a Fokker-Planck coefficient that is finite at all pitch angles.
A joint model for boundaries of multiple anatomical parts
NASA Astrophysics Data System (ADS)
Kerr, Grégoire; Kurtek, Sebastian; Srivastava, Anuj
2011-03-01
The use of joint shape analysis of multiple anatomical parts is a promising area of research with applications in medical diagnostics, growth evaluations, and disease characterizations. In this paper, we consider several features (shapes, orientations, scales, and locations) associated with anatomical parts and develop probability models that capture interactions between these features and across objects. The shape component is based on elastic shape analysis of continuous boundary curves. The proposed model is a second order model that considers principal coefficients in tangent spaces of joint manifolds as multivariate normal random variables. Additionally, it models interactions across objects using area-interaction processes. Using given observations of four anatomical parts: caudate, hippocampus, putamen and thalamus, on one side of the brain, we first estimate the model parameters and then generate random samples from them using the Metropolis-Hastings algorithm. The plausibility of these random samples validates the proposed models.
Radiation transport phenomena and modeling. Part A: Codes; Part B: Applications with examples
Lorence, L.J. Jr.; Beutler, D.E.
1997-09-01
This report contains the notes from the second session of the 1997 IEEE Nuclear and Space Radiation Effects Conference Short Course on Applying Computer Simulation Tools to Radiation Effects Problems. Part A discusses the physical phenomena modeled in radiation transport codes and various types of algorithmic implementations. Part B gives examples of how these codes can be used to design experiments whose results can be easily analyzed and describes how to calculate quantities of interest for electronic devices.
Measurement and modeling of CO2 diffusion coefficient in Saline Aquifer at reservoir conditions
NASA Astrophysics Data System (ADS)
Azin, Reza; Mahmoudy, Mohamad; Raad, Seyed; Osfouri, Shahriar
2013-12-01
Storage of CO2 in deep saline aquifers is a promising techniques to mitigate global warming and reduce greenhouse gases (GHG). Correct measurement of diffusivity is essential for predicting rate of transfer and cumulative amount of trapped gas. Little information is available on diffusion of GHG in saline aquifers. In this study, diffusivity of CO2 into a saline aquifer taken from oil field was measured and modeled. Equilibrium concentration of CO2 at gas-liquid interface was determined using Henry's law. Experimental measurements were reported at temperature and pressure ranges of 32-50°C and 5900-6900 kPa, respectively. Results show that diffusivity of CO2 varies between 3.52-5.98×10-9 m2/s for 5900 kPa and 5.33-6.16×10-9 m2/s for 6900 kPa initial pressure. Also, it was found that both pressure and temperature have a positive impact on the measures of diffusion coefficient. Liquid swelling due to gas dissolution and variations in gas compressibility factor as a result of pressure decay was found negligible. Measured diffusivities were used model the physical model and develop concentration profile of dissolved gas in the liquid phase. Results of this study provide unique measures of CO2 diffusion coefficient in saline aquifer at high pressure and temperature conditions, which can be applied in full-field studies of carbon capture and sequestration projects.
Quasilinear model for energetic particle diffusion in radial and velocity space
Waltz, R. E.; Staebler, G. M.; Bass, E. M.
2013-04-15
A quasilinear model for passive energetic particle (EP) turbulent diffusion in radial and velocity space is fitted and tested against nonlinear gyrokinetic tokamak simulations with the GYRO code [J. Candy and R. E. Waltz, Phys. Rev. Lett. 91, 045001 (2003)]. Off diagonal elements of a symmetric positive definite 2 Multiplication-Sign 2 EP diffusion matrix account for fluxes up radial (energy) gradients driven by energy (radial) gradients of the EP velocity space distribution function. The quasilinear ratio kernel of the model is provided by a simple analytic formula for the EP radial and velocity space EP diffusivity relative to radial thermal ion energy diffusivity at each linear mode of the turbulence driven by the thermal plasma. The TGLF [G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 14, 0055909 (2007); ibid. 15, 0055908 (2008)] tokamak transport model provides the linear mode frequency and growth rates to the kernel as well as the nonlinear spectral weight for each mode.
Quasilinear model for energetic particle diffusion in radial and velocity space
NASA Astrophysics Data System (ADS)
Waltz, R. E.; Bass, E. M.; Staebler, G. M.
2013-04-01
A quasilinear model for passive energetic particle (EP) turbulent diffusion in radial and velocity space is fitted and tested against nonlinear gyrokinetic tokamak simulations with the GYRO code [J. Candy and R. E. Waltz, Phys. Rev. Lett. 91, 045001 (2003)]. Off diagonal elements of a symmetric positive definite 2×2 EP diffusion matrix account for fluxes up radial (energy) gradients driven by energy (radial) gradients of the EP velocity space distribution function. The quasilinear ratio kernel of the model is provided by a simple analytic formula for the EP radial and velocity space EP diffusivity relative to radial thermal ion energy diffusivity at each linear mode of the turbulence driven by the thermal plasma. The TGLF [G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 14, 0055909 (2007); ibid. 15, 0055908 (2008)] tokamak transport model provides the linear mode frequency and growth rates to the kernel as well as the nonlinear spectral weight for each mode.
NASA Astrophysics Data System (ADS)
Ziemys, A.; Kojic, M.; Milosevic, M.; Kojic, N.; Hussain, F.; Ferrari, M.; Grattoni, A.
2011-06-01
We present a successful hierarchical modeling approach which accounts for interface effects on diffusivity, ignored in classical continuum theories. A molecular dynamics derived diffusivity scaling scheme is incorporated into a finite element method to model transport through a nanochannel. In a 5 nm nanochannel, the approach predicts 2.2 times slower mass release than predicted by Fick's law by comparing time spent to release 90% of mass. The scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. We show robustness of our discrete continuum model in addressing complex diffusion phenomena in biomedical and engineering applications by providing flexible hierarchical coupling of molecular scale effects and preserving computational finite element method speed.
Convergence of the binomial tree method for Asian options in jump-diffusion models
NASA Astrophysics Data System (ADS)
Kim, Kwang Ik; Qian, Xiao-Song
2007-06-01
The binomial tree methods (BTM), first proposed by Cox, Ross and Rubinstein [J. Cox, S. Ross, M. Rubinstein, Option pricing: A simplified approach, J. Finan. Econ. 7 (1979) 229-264] in diffusion models and extended by Amin [K.I. Amin, Jump diffusion option valuation in discrete time, J. Finance 48 (1993) 1833-1863] to jump-diffusion models, is one of the most popular approaches to pricing options. In this paper, we present a binomial tree method for Asian options in jump-diffusion models and show its equivalence to certain explicit difference scheme. Employing numerical analysis and the notion of viscosity solution, we prove the uniform convergence of the binomial tree method for European-style and American-style Asian options.
Symmetry breaking in a bulk-surface reaction-diffusion model for signalling networks
NASA Astrophysics Data System (ADS)
Rätz, Andreas; Röger, Matthias
2014-08-01
Signalling molecules play an important role for many cellular functions. We investigate here a general system of two membrane reaction-diffusion equations coupled to a diffusion equation inside the cell by a Robin-type boundary condition and a flux term in the membrane equations. A specific model of this form was recently proposed by the authors for the GTPase cycle in cells. We investigate here a putative role of diffusive instabilities in cell polarization. By a linearized stability analysis, we identify two different mechanisms. The first resembles a classical Turing instability for the membrane subsystem and requires (unrealistically) large differences in the lateral diffusion of activator and substrate. On the other hand, the second possibility is induced by the difference in cytosolic and lateral diffusion and appears much more realistic. We complement our theoretical analysis by numerical simulations that confirm the new stability mechanism and allow us to investigate the evolution beyond the regime where the linearization applies.
The Diffuse Galactic Gamma-Ray Emission Model for GLAST LAT
Porter, T.A.; Digel, S.W.; Grenier, I.A.; Moskalenko, I.V.; Strong, A.W.; /Garching, Max Planck Inst., MPE
2007-06-13
Diffuse emission from the Milky Way dominates the gamma-ray sky. About 80% of the high-energy luminosity of the Milky Way comes from processes in the interstellar medium. The Galactic diffuse emission traces interactions of energetic particles, primarily protons and electrons, with the interstellar gas and radiation field, thus delivering information about cosmic-ray spectra and interstellar mass in distant locations. Additionally, the Galactic diffuse emission is the celestial foreground for the study of gamma-ray point sources and the extragalactic diffuse gamma-ray emission. We will report on the latest developments in the modeling of the Galactic diffuse emission, which will be used for the Gamma Ray Large Area Space Telescope (GLAST) investigations.
Bellassai, Debora; Spinazzola, Antonio; Silvestri, Stefano
2015-01-01
In absence of results of environmental monitoring to proceed with the assessment of occupational exposure, it was developed a model that retraces the one of Pasquill and Gifford, currently used for the estimation of concentrations of pollutants at certain distances from the source in outdoor environment. Purpose of the study is the quantitative estimate of the diffusion of airborne asbestos fibers in function of the distance from the source in an factory where railway carriages were produced during the period when asbestos was sprayed as insulator of the body. The treatment was carried out in a large shed without separation from other operations. The application of the model, given the characteristics of the emitting source, has allowed us to estimate the diffusion of particles inside the shed with an expected decrease in concentration inversely proportional to the distance from the source. By appropriate calculations the concentration by weight has been converted into number offibers by volume, the unit of measure currently used for the definition of asbestos pollution. PMID:26193738
NASA Astrophysics Data System (ADS)
Chen, Xueli; Yang, Defu; Qu, Xiaochao; Hu, Hao; Liang, Jimin; Gao, Xinbo; Tian, Jie
2012-06-01
Bioluminescence tomography (BLT) has been successfully applied to the detection and therapeutic evaluation of solid cancers. However, the existing BLT reconstruction algorithms are not accurate enough for cavity cancer detection because of neglecting the void problem. Motivated by the ability of the hybrid radiosity-diffusion model (HRDM) in describing the light propagation in cavity organs, an HRDM-based BLT reconstruction algorithm was provided for the specific problem of cavity cancer detection. HRDM has been applied to optical tomography but is limited to simple and regular geometries because of the complexity in coupling the boundary between the scattering and void region. In the provided algorithm, HRDM was first applied to three-dimensional complicated and irregular geometries and then employed as the forward light transport model to describe the bioluminescent light propagation in tissues. Combining HRDM with the sparse reconstruction strategy, the cavity cancer cells labeled with bioluminescent probes can be more accurately reconstructed. Compared with the diffusion equation based reconstruction algorithm, the essentiality and superiority of the HRDM-based algorithm were demonstrated with simulation, phantom and animal studies. An in vivo gastric cancer-bearing nude mouse experiment was conducted, whose results revealed the ability and feasibility of the HRDM-based algorithm in the biomedical application of gastric cancer detection.
Chen, Xueli; Yang, Defu; Qu, Xiaochao; Hu, Hao; Liang, Jimin; Gao, Xinbo; Tian, Jie
2012-06-01
Bioluminescence tomography (BLT) has been successfully applied to the detection and therapeutic evaluation of solid cancers. However, the existing BLT reconstruction algorithms are not accurate enough for cavity cancer detection because of neglecting the void problem. Motivated by the ability of the hybrid radiosity-diffusion model (HRDM) in describing the light propagation in cavity organs, an HRDM-based BLT reconstruction algorithm was provided for the specific problem of cavity cancer detection. HRDM has been applied to optical tomography but is limited to simple and regular geometries because of the complexity in coupling the boundary between the scattering and void region. In the provided algorithm, HRDM was first applied to three-dimensional complicated and irregular geometries and then employed as the forward light transport model to describe the bioluminescent light propagation in tissues. Combining HRDM with the sparse reconstruction strategy, the cavity cancer cells labeled with bioluminescent probes can be more accurately reconstructed. Compared with the diffusion equation based reconstruction algorithm, the essentiality and superiority of the HRDM-based algorithm were demonstrated with simulation, phantom and animal studies. An in vivo gastric cancer-bearing nude mouse experiment was conducted, whose results revealed the ability and feasibility of the HRDM-based algorithm in the biomedical application of gastric cancer detection. PMID:22734771
16 CFR Appendix A to Part 313 - Model Privacy Form
Code of Federal Regulations, 2014 CFR
2014-01-01
... 16 Commercial Practices 1 2014-01-01 2014-01-01 false Model Privacy Form A Appendix A to Part 313... FINANCIAL INFORMATION Pt. 313, App. A Appendix A to Part 313—Model Privacy Form A. The Model Privacy Form ER01DE09.035 ER01DE09.036 ER01DE09.037 ER01DE09.038 ER01DE09.039 ER01DE09.041 1. How the Model Privacy...
16 CFR Appendix A to Part 313 - Model Privacy Form
Code of Federal Regulations, 2010 CFR
2010-01-01
... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Model Privacy Form A Appendix A to Part 313... FINANCIAL INFORMATION Pt. 313, App. A Appendix A to Part 313—Model Privacy Form A. The Model Privacy Form ER01DE09.035 ER01DE09.036 ER01DE09.037 ER01DE09.038 ER01DE09.039 ER01DE09.041 1. How the Model Privacy...
16 CFR Appendix A to Part 313 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-01-01
... 16 Commercial Practices 1 2013-01-01 2013-01-01 false Model Privacy Form A Appendix A to Part 313... FINANCIAL INFORMATION Pt. 313, App. A Appendix A to Part 313—Model Privacy Form A. The Model Privacy Form ER01DE09.035 ER01DE09.036 ER01DE09.037 ER01DE09.038 ER01DE09.039 ER01DE09.041 1. How the Model Privacy...
16 CFR Appendix A to Part 313 - Model Privacy Form
Code of Federal Regulations, 2012 CFR
2012-01-01
... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Model Privacy Form A Appendix A to Part 313... FINANCIAL INFORMATION Pt. 313, App. A Appendix A to Part 313—Model Privacy Form A. The Model Privacy Form ER01DE09.035 ER01DE09.036 ER01DE09.037 ER01DE09.038 ER01DE09.039 ER01DE09.041 1. How the Model Privacy...
16 CFR Appendix A to Part 313 - Model Privacy Form
Code of Federal Regulations, 2011 CFR
2011-01-01
... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Model Privacy Form A Appendix A to Part 313... FINANCIAL INFORMATION Pt. 313, App. A Appendix A to Part 313—Model Privacy Form A. The Model Privacy Form ER01DE09.035 ER01DE09.036 ER01DE09.037 ER01DE09.038 ER01DE09.039 ER01DE09.041 1. How the Model Privacy...
Lateral diffusion of small compounds in human stratum corneum and model lipid bilayer systems.
Johnson, M E; Berk, D A; Blankschtein, D; Golan, D E; Jain, R K; Langer, R S
1996-01-01
An image-based technique of fluorescence recovery after photobleaching (video-FRAP) was used to measure the lateral diffusion coefficients of a series of nine fluorescent probes in two model lipid bilayer systems, dimyristoylphosphatidylcholine (DMPC) and DMPC/cholesterol (40 mol%), as well as in human stratum corneum-extracted lipids. The probes were all lipophilic, varied in molecular weight from 223 to 854 Da, and were chosen to characterize the lateral diffusion of small compounds in these bilayer systems. A clear molecular weight dependence of the lateral diffusion coefficients in DMPC bilayers was observed. Values ranged from 6.72 x 10(-8) to 16.2 x 10(-8) cm2/s, with the smaller probes diffusing faster than the larger ones. Measurements in DMPC/cholesterol bilayers, which represent the most thorough characterization of small-solute diffusion in this system, exhibited a similar molecular weight dependence, although the diffusion coefficients were lower, ranging from 1.62 x 10(-8) to 5.60 x 10(-8) cm2/s. Lateral diffusion measurements in stratum corneum-extracted lipids, which represent a novel examination of diffusion in this unique lipid system, also exhibited a molecular weight dependence, with values ranging from 0.306 x 10(-8) to 2.34 x 10(-8) cm2/s. Literature data showed that these strong molecular weight dependencies extend to even smaller compounds than those examined in this study. A two-parameter empirical expression is presented that describes the lateral diffusion coefficient in terms of the solute's molecular weight and captures the size dependence over the range examined. This study illustrates the degree to which small-molecule lateral diffusion in stratum corneum-extracted lipids can be represented by diffusion in DMPC and DMPC/cholesterol bilayer systems, and may lead to a better understanding of small-solute transport across human stratum corneum. PMID:8913603
Integrating O/S models during conceptual design, part 1
NASA Technical Reports Server (NTRS)
Ebeling, Charles E.
1994-01-01
The University of Dayton is pleased to submit this report to the National Aeronautics and Space Administration (NASA), Langley Research Center, which integrates a set of models for determining operational capabilities and support requirements during the conceptual design of proposed space systems. This research provides for the integration of the reliability and maintainability (R&M) model, both new and existing simulation models, and existing operations and support (O&S) costing equations in arriving at a complete analysis methodology. Details concerning the R&M model and the O&S costing model may be found in previous reports accomplished under this grant (NASA Research Grant NAG1-1327). In the process of developing this comprehensive analysis approach, significant enhancements were made to the R&M model, updates to the O&S costing model were accomplished, and a new simulation model developed. This is the 1st part of a 3 part technical report.
Modelling the effect of diffuse light on canopy photosynthesis in controlled environments
NASA Technical Reports Server (NTRS)
Cavazzoni, James; Volk, Tyler; Tubiello, Francesco; Monje, Oscar; Janes, H. W. (Principal Investigator)
2002-01-01
A layered canopy model was used to analyze the effects of diffuse light on canopy gross photosynthesis in controlled environment plant growth chambers, where, in contrast to the field, highly diffuse light can occur at high irradiance. The model suggests that high diffuse light fractions (approximately 0.7) and irradiance (1400 micromoles m-2 s-1) may enhance crop life-cycle canopy gross photosynthesis for hydroponic wheat by about 20% compared to direct light at the same irradiance. Our simulations suggest that high accuracy is not needed in specifying diffuse light fractions in chambers between approximately 0.7 and 1, because simulated photosynthesis for closed canopies plateau in this range. We also examined the effect of leaf angle distribution on canopy photosynthesis under growth chamber conditions, as these distributions determine canopy extinction coefficients for direct and diffuse light. We show that the spherical leaf angle distribution is not suitable for modeling photosynthesis of planophile canopies (e.g., soybean and peanut) in growth chambers. Also, the absorption of the light reflected from the surface below the canopy should generally be included in model simulations, as the corresponding albedo values in the photosynthetically active range may be quite high in growth chambers (e.g., approximately 0.5). In addition to the modeling implications, our results suggest that diffuse light conditions should be considered when drawing conclusions from experiments in controlled environments.
Modelling the effect of diffuse light on canopy photosynthesis in controlled environments.
Cavazzoni, James; Volk, Tyler; Tubiello, Francesco; Monje, Oscar
2002-01-01
A layered canopy model was used to analyze the effects of diffuse light on canopy gross photosynthesis in controlled environment plant growth chambers, where, in contrast to the field, highly diffuse light can occur at high irradiance. The model suggests that high diffuse light fractions (approximately 0.7) and irradiance (1400 micromoles m-2 s-1) may enhance crop life-cycle canopy gross photosynthesis for hydroponic wheat by about 20% compared to direct light at the same irradiance. Our simulations suggest that high accuracy is not needed in specifying diffuse light fractions in chambers between approximately 0.7 and 1, because simulated photosynthesis for closed canopies plateau in this range. We also examined the effect of leaf angle distribution on canopy photosynthesis under growth chamber conditions, as these distributions determine canopy extinction coefficients for direct and diffuse light. We show that the spherical leaf angle distribution is not suitable for modeling photosynthesis of planophile canopies (e.g., soybean and peanut) in growth chambers. Also, the absorption of the light reflected from the surface below the canopy should generally be included in model simulations, as the corresponding albedo values in the photosynthetically active range may be quite high in growth chambers (e.g., approximately 0.5). In addition to the modeling implications, our results suggest that diffuse light conditions should be considered when drawing conclusions from experiments in controlled environments. PMID:12882223
A Bayesian hierarchical diffusion model decomposition of performance in Approach–Avoidance Tasks
Krypotos, Angelos-Miltiadis; Beckers, Tom; Kindt, Merel; Wagenmakers, Eric-Jan
2015-01-01
Common methods for analysing response time (RT) tasks, frequently used across different disciplines of psychology, suffer from a number of limitations such as the failure to directly measure the underlying latent processes of interest and the inability to take into account the uncertainty associated with each individual's point estimate of performance. Here, we discuss a Bayesian hierarchical diffusion model and apply it to RT data. This model allows researchers to decompose performance into meaningful psychological processes and to account optimally for individual differences and commonalities, even with relatively sparse data. We highlight the advantages of the Bayesian hierarchical diffusion model decomposition by applying it to performance on Approach–Avoidance Tasks, widely used in the emotion and psychopathology literature. Model fits for two experimental data-sets demonstrate that the model performs well. The Bayesian hierarchical diffusion model overcomes important limitations of current analysis procedures and provides deeper insight in latent psychological processes of interest. PMID:25491372
Diffusive to quasi-ballistic random laser: incoherent and coherent models
NASA Astrophysics Data System (ADS)
Guerin, W.; Chong, Y. D.; Baudouin, Q.; Liertzer, M.; Rotter, S.; Kaiser, R.
2016-09-01
We study the crossover between the diffusive and quasi-ballistic regimes of random lasers. In particular, we compare incoherent models based on the diffusion equation and the radiative transfer equation (RTE), which neglect all wave effects, with a coherent wave model for the random laser threshold. We show that both the incoherent and the coherent models predict qualitatively similar thresholds, with a smooth transition from a diffuse to a quasi-ballistic regime. The shape of the intensity distribution in the sample as predicted by the RTE model at threshold is also in good agreement with the coherent model. The approximate incoherent models thus provide useful analytical predictions for the threshold of random lasers as well as the shape of the random laser modes at threshold.
King, M.D.; Burkardt, N.; Clark, B.T.
2006-01-01
Recent literature on the diffusion of innovations concentrates either specifically on public adoption of policy, where social or environmental conditions are the dependent variables for adoption, or on private adoption of an innovation, where emphasis is placed on the characteristics of the innovation itself. This article uses both the policy diffusion literature and the diffusion of innovation literature to assess watershed management councils' decisions to adopt, or not adopt, scientific models. Watershed management councils are a relevant case study because they possess both public and private attributes. We report on a survey of councils in the United States that was conducted to determine the criteria used when selecting scientific models for studying watershed conditions. We found that specific variables from each body of literature play a role in explaining the choice to adopt scientific models by these quasi-public organizations. The diffusion of innovation literature contributes to an understanding of how organizations select models by confirming the importance of a model's ability to provide better data. Variables from the policy diffusion literature showed that watershed management councils that employ consultants are more likely to use scientific models. We found a gap between those who create scientific models and those who use these models. We recommend shrinking this gap through more communication between these actors and advancing the need for developers to provide more technical assistance.
17 CFR Appendix A to Part 160 - Model Privacy Form
Code of Federal Regulations, 2013 CFR
2013-04-01
... 17 Commodity and Securities Exchanges 1 2013-04-01 2013-04-01 false Model Privacy Form A Appendix... Part 160—Model Privacy Form A. The Model Privacy Form ER28DE12.003 ER28DE12.004 ER28DE12.005 ER28DE12.006 ER28DE12.007 ER28DE12.008 ER28DE12.009 B. General Instructions 1. How the Model Privacy Form...
Balcom, B J; Petersen, N O
1993-01-01
We have systematically investigated the probe size and shape dependence of lateral diffusion in model dimyristoyl phosphatidylcholine membranes. Linear hydrophobic polymers, which differ in length by an order of magnitude, were used to explore the effect on the lateral diffusion coefficient of hydrodynamic restrictions in the bilayer interior. The polymers employed are isoprenoid alcohols--citronellol, solanesol, and dolichol. Tracer lateral diffusion coefficients were measured by fluorescence photobleaching recovery. Despite the large difference in lengths, the nitrobenzoxadiazole labelled alcohols all diffuse at the rate of lipid self-diffusion (5.0 x 10(-12) m2 s-1, 29 degrees C) in the liquid crystal phase. Companion measurements in isotropic polymer solution, in gel phase lipid membranes and with nonpolar fluorescent polyaromatic hydrocarbons, show a marked dependence of the lateral diffusion coefficient on the probe molecule size. Our results in the liquid crystal phase are in accord with free area theory which asserts that lateral diffusion in the membrane is restricted by the surface-free area. Probe molecules which are significantly longer than the host phospholipid, seven times longer in the case of dolichol, are still restricted in their lateral motion by the surface properties of the bilayer in the liquid crystal phase. Fluorescence quenching experiments indicate that the nitrobenzoxadiazole label does not reside at the aqueous interface, although it must reside in close proximity according to the diffusion measurements. PMID:8218892
Diffusion of a Sustainable Farming Technique in Sri Lanka: An Agent-Based Modeling Approach
NASA Astrophysics Data System (ADS)
Jacobi, J. H.; Gilligan, J. M.; Carrico, A. R.; Truelove, H. B.; Hornberger, G.
2012-12-01
We live in a changing world - anthropogenic climate change is disrupting historic climate patterns and social structures are shifting as large scale population growth and massive migrations place unprecedented strain on natural and social resources. Agriculture in many countries is affected by these changes in the social and natural environments. In Sri Lanka, rice farmers in the Mahaweli River watershed have seen increases in temperature and decreases in precipitation. In addition, a government led resettlement project has altered the demographics and social practices in villages throughout the watershed. These changes have the potential to impact rice yields in a country where self-sufficiency in rice production is a point of national pride. Studies of the climate can elucidate physical effects on rice production, while research on social behaviors can illuminate the influence of community dynamics on agricultural practices. Only an integrated approach, however, can capture the combined and interactive impacts of these global changes on Sri Lankan agricultural. As part of an interdisciplinary team, we present an agent-based modeling (ABM) approach to studying the effects of physical and social changes on farmers in Sri Lanka. In our research, the diffusion of a sustainable farming technique, the system of rice intensification (SRI), throughout a farming community is modeled to identify factors that either inhibit or promote the spread of a more sustainable approach to rice farming. Inputs into the ABM are both physical and social and include temperature, precipitation, the Palmer Drought Severity Index (PDSI), community trust, and social networks. Outputs from the ABM demonstrate the importance of meteorology and social structure on the diffusion of SRI throughout a farming community.
MO-G-BRF-07: Anomalously Fast Diffusion of Carbon Nanotubes Carriers in 3D Tissue Model
Wang, Y; Bahng, J; Kotov, N
2014-06-15
Purpose: We aim to investigate and understand diffusion process of carbon nanotubes (CNTs) and other nanoscale particles in tissue and organs. Methods: In this research, we utilized a 3D model tissue of hepatocellular carcinoma (HCC)cultured in inverted colloidal crystal (ICC) scaffolds to compare the diffusivity of CNTs with small molecules such as Rhodamine and FITC in vitro, and further investigated the transportation of CNTs with and without targeting ligand, TGFβ1. The real-time permeation profiles of CNTs in HCC tissue model with high temporal and spatial resolution was demonstrated by using standard confocal microscopy. Quantitative analysis of the diffusion process in 3D was carried out using luminescence intensity in a series of Z-stack images obtained for different time points of the diffusion process after initial addition of CNTs or small molecules to the cell culture and the image data was analyzed by software ImageJ and Mathematica. Results: CNTs display diffusion rate in model tissues substantially faster than small molecules of the similar charge such as FITC, and the diffusion rate of CNTs are significantly enhanced with targeting ligand, TGFβ1. Conclusion: In terms of the advantages of in-vitro model, we were able to have access to measuring the rate of CNT penetration at designed conditions with variable parameters. And the findings by using this model, changed our understanding about advantages of CNTs as nanoscale drug carriers and provides design principles for making new drug carriers for both treatment and diagnostics. Additionally the fast diffusion opens the discussion of the best possible drug carriers to reach deep parts of cancerous tissues, which is often a prerequisite for successful cancer treatment. This work was supported by the Center for Photonic and Multiscale Nanomaterials funded by National Science Foundation Materials Research Science and Engineering Center program DMR 1120923. The work was also partially supported by NSF
Diffusion transport model for pelagic sediments on the Mid-Atlantic Ridge
NASA Astrophysics Data System (ADS)
Mitchell, Neil C.
1995-10-01
The diffusion model is potentially useful for quantifying the effect of downslope gravity transport on sedimentation rate variations, which are commonly found between Deep Sea Drilling Project and Ocean Drilling Program sites. If appropriate, the model and stratigraphy could be used, for example, to constrain the amount and timing of fault block rotation. Deep Tow profiler records from the French-American Mid-Ocean Undersea Study area of the Mid-Atlantic Ridge are examined to determine whether they are consistent with a diffusion model. Sedimentary contacts with basement show that a variety of processes may be operating, some of which are inconsistent with the diffusion model. For example, there are moats around some contacts which are typical of scouring or nondeposition due to high current velocities. More than half of the contacts, however, show onlapping, which is qualitatively consistent with the diffusion model. Sediments generally fill low areas of the topography and have smooth surfaces, as expected from a diffusion model. Where the fluxes of sediment entering a basin are constant, the diffusion model predicts that the sediment surface should evolve to a parabola (the steady state solution). Some 20 curved surfaces in the profiler data were digitized and least squares parabolas fitted to them with rms errors of less than 1 m. The slopes of the model parabolas provide values for the ratio of sediment flux to diffusivity at the edges of the basins (steep surfaces are produced by low diffusivity or high fluxes). This ratio is combined with estimates of the fluxes to determine the apparent sediment diffusivity, Kapp, for eacri basin. Flux is estimated by assuming the abyssal hill topography acts as a simple sediment trap, so that the lateral flux equals the width of a basin's pelagic catchment area times the area's mean sedimentation rate S. Using this method, median Kapp is 0.04-0.11 m2 yr-1 (assuming S = 10-30 m m.y.-1). Variations in Kapp and the assumptions
A model for diffuse and global irradiation on horizontal surfaces
Jain, P.C. )
1990-01-01
The intensity of the direct radiation and the diffuse radiation at any time on a horizontal surface are each expressed as fractions of the intensity of the extraterrestrial radiation. Using these and assuming a random distribution of the bright sunshine hours and not too wide variations in the values of the transmission coefficients, a number of relations for estimating the global and the diffuse irradiation are derived. Two of the relations derived, including the Angstroem correlation for estimating the global irradiation, are already known empirically while several new correlations have been derived. The relations derived in this paper are: (i) H{sub d}/H{sub o} = a{sub 1} + b{sub 1} (S/S{sub o}); (ii) H/H{sub o} = A{sub 2} + b{sub 2} (S/S{sub o}); (iii) H{sub D}/H{sub o} = a{sub 3} + b{sub 3} (H/H{sub o}); (iv) H{sub D}/H = a{sub 4} + b{sub 4} (h{sub o}/) (v) H/(H{minus}H{sub D}) = a{sub 5} + b{sub 5} (S{sub o}/S); (vi) H{sub D}/(H{minus}H{sub D}) = A{sub 6} + b{sub 6} (S{sub o}/S); (vii) H/H{sub D} = a{sub 7} + b{sub 7} (S/S{sub o}); (viii) H/H{sub D} = A{sub 1} + A{sub 2} (S/S{sub o}) + A{sub 3} (S/S{sub o}){sup 2}. The study identifies three independent basic parameters and the constants appearing in the various equations as simple functions of these three basic parameters. This provides unification and inter-relationships between the various constants. Experimental data for the diffuse irradiation, the global irradiation and the bright sunshine duration for Macerata (Italy), Salisbury and Bulawayo (Zimbabwe) is found to show good correlation for the linear eqns (i) to (vii), and the nature and the interrelationships of the constants is found to be as predicted by theory.
Wang, Jing
2013-01-11
We analyze the spatiotemporal behavior of species concentrations in a diffusion-mediated conversion reaction which occurs at catalytic sites within linear pores of nanometer diameter. A strict single-file (no passing) constraint occurs in the diffusion within such narrow pores. Both transient and steady-state behavior is precisely characterized by kinetic Monte Carlo simulations of a spatially discrete lattice–gas model for this reaction–diffusion process considering various distributions of catalytic sites. Exact hierarchical master equations can also be developed for this model. Their analysis, after application of mean-field type truncation approximations, produces discrete reaction–diffusion type equations (mf-RDE). For slowly varying concentrations, we further develop coarse-grained continuum hydrodynamic reaction–diffusion equations (h-RDE) incorporating a precise treatment of single-file diffusion (SFD) in this multispecies system. Noting the shortcomings of mf-RDE and h-RDE, we then develop a generalized hydrodynamic (GH) formulation of appropriate gh-RDE which incorporates an unconventional description of chemical diffusion in mixed-component quasi-single-file systems based on a refined picture of tracer diffusion for finite-length pores. The gh-RDE elucidate the non-exponential decay of the steady-state reactant concentration into the pore and the non-mean-field scaling of the reactant penetration depth. Then an extended model of a catalytic conversion reaction within a functionalized nanoporous material is developed to assess the effect of varying the reaction product – pore interior interaction from attractive to repulsive. The analysis is performed utilizing the generalized hydrodynamic formulation of the reaction-diffusion equations which can reliably capture the complex interplay between reaction and restricted transport for both irreversible and reversible reactions.
Nowacki, P.; Samson, P.J.; Sillman, S.
1996-10-01
It is shown that Urban Airshed Model (UAM-IV) calculated air pollutant concentrations during photochemical smog episodes in Atlanta, Georgia, depend strongly on the numerical parameterization of the daytime vertical diffusivity. Results found suggest that vertical mixing is overestimated by the UAM-IV during unstable daytime conditions, as calculated vertical diffusivity values exceed measured and comparable literature values. Although deviations between measured and UAM-IV calculated air pollutant concentrations may only in part be due the UAM-IV diffusivity parameterization, results indicate the large error potential in vertical diffusivity parameterization. Easily implemented enhancements to UAM-IV algorithms are proposed, thus improving UAM-IV modeling performance during unstable stratification. 38 refs., 14 figs., 1 tab.
Plimpton, Steven J.; Sershen, Cheryl L.; May, Elebeoba E.
2015-01-01
This paper describes a method for incorporating a diffusion field modeling oxygen usage and dispersion in a multi-scale model of Mycobacterium tuberculosis (Mtb) infection mediated granuloma formation. We implemented this method over a floating-point field to model oxygen dynamics in host tissue during chronic phase response and Mtb persistence. The method avoids the requirement of satisfying the Courant-Friedrichs-Lewy (CFL) condition, which is necessary in implementing the explicit version of the finite-difference method, but imposes an impractical bound on the time step. Instead, diffusion is modeled by a matrix-based, steady state approximate solution to the diffusion equation. Moreover, presented in figure 1 is the evolution of the diffusion profiles of a containment granuloma over time.
Plimpton, Steven J.; Sershen, Cheryl L.; May, Elebeoba E.
2015-01-01
This paper describes a method for incorporating a diffusion field modeling oxygen usage and dispersion in a multi-scale model of Mycobacterium tuberculosis (Mtb) infection mediated granuloma formation. We implemented this method over a floating-point field to model oxygen dynamics in host tissue during chronic phase response and Mtb persistence. The method avoids the requirement of satisfying the Courant-Friedrichs-Lewy (CFL) condition, which is necessary in implementing the explicit version of the finite-difference method, but imposes an impractical bound on the time step. Instead, diffusion is modeled by a matrix-based, steady state approximate solution to the diffusion equation. Moreover, presented in figuremore » 1 is the evolution of the diffusion profiles of a containment granuloma over time.« less
A model of space-fractional-order diffusion in the glial scar.
Prodanov, Dimiter; Delbeke, Jean
2016-08-21
Implantation of neuroprosthetic electrodes induces a stereotypical state of neuroinflammation, which is thought to be detrimental for the neurons surrounding the electrode. Mechanisms of this type of neuroinflammation are still poorly understood. Recent experimental and theoretical results point to a possible role of the diffusing species in this process. The paper considers a model of anomalous diffusion occurring in the glial scar around a chronic implant in two simple geometries - a separable rectilinear electrode and a cylindrical electrode, which are solvable exactly. We describe a hypothetical extended source of diffusing species and study its concentration profile in steady-state conditions. Diffusion transport is assumed to obey a fractional-order Fick law, derivable from physically realistic assumptions using a fractional calculus approach. Presented fractional-order distribution morphs into integer-order diffusion in the case of integral fractional exponents. The model demonstrates that accumulation of diffusing species can occur and the scar properties (i.e. tortuosity, fractional order, scar thickness) and boundary conditions can influence such accumulation. The observed shape of the concentration profile corresponds qualitatively with GFAP profiles reported in the literature. The main difference with respect to the previous studies is the explicit incorporation of the apparatus of fractional calculus without assumption of an ad hoc tortuosity parameter. The approach can be adapted to other studies of diffusion in biological tissues, for example of biomolecules or small drug molecules. PMID:27179458
The utility of diffusion chambers as models for the description of drug disposition.
Ganzinger, U; Schiel, H; Georgopoulos, A; Gumhold, G
1986-07-01
Tissue cages were employed to explore the diffusion processes of several cephalosporins into extravascular fluids. Concentrations of cefotaxime in serum and in subcutaneous chambers increased proportionally to the amount of the drug injected. Administration of single equal doses of cephalothin, cephaloridine and cefotaxime resulted in different concentration-time courses in the serum and in diffusion chambers. These observations suggest that diffusion chambers are linked to the tissue at the implantation site. None of the classical compartmental approaches can be applied to evaluate the kinetics of drug diffusion into tissue cages. Correlations of total or non-protein bound drug concentrations in tissue cages to those in the peripheral compartment assumed concentration and time dependent diffusion processes. No specific diffusion constant based on the law of Fick could be derived for the diffusion chambers used in this study. Concentration-time courses in serum and interstitial fluid can be simultaneously evaluated according to pharmacokinetic-pharmacodynamic models. Based on the equation describing the effect site this model can be used to simulate drug concentrations in tissue cages by varying the dose size or the dose interval. PMID:3759726
A novel rumor diffusion model considering the effect of truth in online social media
NASA Astrophysics Data System (ADS)
Sun, Ling; Liu, Yun; Zeng, Qing-An; Xiong, Fei
2015-12-01
In this paper, we propose a model to investigate how truth affects rumor diffusion in online social media. Our model reveals a relation between rumor and truth — namely, when a rumor is diffusing, the truth about the rumor also diffuses with it. Two patterns of the agents used to identify rumor, self-identification and passive learning are taken into account. Combining theoretical proof and simulation analysis, we find that the threshold value of rumor diffusion is negatively correlated to the connectivity between nodes in the network and the probability β of agents knowing truth. Increasing β can reduce the maximum density of the rumor spreaders and slow down the generation speed of new rumor spreaders. On the other hand, we conclude that the best rumor diffusion strategy must balance the probability of forwarding rumor and the probability of agents losing interest in the rumor. High spread rate λ of rumor would lead to a surge in truth dissemination which will greatly limit the diffusion of rumor. Furthermore, in the case of unknown λ, increasing β can effectively reduce the maximum proportion of agents who do not know the truth, but cannot narrow the rumor diffusion range in a certain interval of β.
A hybrid transport-diffusion model for radiative transfer in absorbing and scattering media
Roger, M.; Caliot, C.; Crouseilles, N.; Coelho, P.J.
2014-10-15
A new multi-scale hybrid transport-diffusion model for radiative transfer is proposed in order to improve the efficiency of the calculations close to the diffusive regime, in absorbing and strongly scattering media. In this model, the radiative intensity is decomposed into a macroscopic component calculated by the diffusion equation, and a mesoscopic component. The transport equation for the mesoscopic component allows to correct the estimation of the diffusion equation, and then to obtain the solution of the linear radiative transfer equation. In this work, results are presented for stationary and transient radiative transfer cases, in examples which concern solar concentrated and optical tomography applications. The Monte Carlo and the discrete-ordinate methods are used to solve the mesoscopic equation. It is shown that the multi-scale model allows to improve the efficiency of the calculations when the medium is close to the diffusive regime. The proposed model is a good alternative for radiative transfer at the intermediate regime where the macroscopic diffusion equation is not accurate enough and the radiative transfer equation requires too much computational effort.
A hybrid transport-diffusion model for radiative transfer in absorbing and scattering media
NASA Astrophysics Data System (ADS)
Roger, M.; Caliot, C.; Crouseilles, N.; Coelho, P. J.
2014-10-01
A new multi-scale hybrid transport-diffusion model for radiative transfer is proposed in order to improve the efficiency of the calculations close to the diffusive regime, in absorbing and strongly scattering media. In this model, the radiative intensity is decomposed into a macroscopic component calculated by the diffusion equation, and a mesoscopic component. The transport equation for the mesoscopic component allows to correct the estimation of the diffusion equation, and then to obtain the solution of the linear radiative transfer equation. In this work, results are presented for stationary and transient radiative transfer cases, in examples which concern solar concentrated and optical tomography applications. The Monte Carlo and the discrete-ordinate methods are used to solve the mesoscopic equation. It is shown that the multi-scale model allows to improve the efficiency of the calculations when the medium is close to the diffusive regime. The proposed model is a good alternative for radiative transfer at the intermediate regime where the macroscopic diffusion equation is not accurate enough and the radiative transfer equation requires too much computational effort.
Assessing cognitive processes with diffusion model analyses: a tutorial based on fast-dm-30
Voss, Andreas; Voss, Jochen; Lerche, Veronika
2015-01-01
Diffusion models can be used to infer cognitive processes involved in fast binary decision tasks. The model assumes that information is accumulated continuously until one of two thresholds is hit. In the analysis, response time distributions from numerous trials of the decision task are used to estimate a set of parameters mapping distinct cognitive processes. In recent years, diffusion model analyses have become more and more popular in different fields of psychology. This increased popularity is based on the recent development of several software solutions for the parameter estimation. Although these programs make the application of the model relatively easy, there is a shortage of knowledge about different steps of a state-of-the-art diffusion model study. In this paper, we give a concise tutorial on diffusion modeling, and we present fast-dm-30, a thoroughly revised and extended version of the fast-dm software (Voss and Voss, 2007) for diffusion model data analysis. The most important improvement of the fast-dm version is the possibility to choose between different optimization criteria (i.e., Maximum Likelihood, Chi-Square, and Kolmogorov-Smirnov), which differ in applicability for different data sets. PMID:25870575
Uncertainty quantification in modeling of microfluidic T-sensor based diffusion immunoassay.
Jha, Aman Kumar; Bahga, Supreet Singh
2016-01-01
Comparison of experimental data with modeling predictions is essential for making quantitative measurements of species properties, such as diffusion coefficients and species concentrations using a T-sensor. To make valid comparisons between experimental data and model predictions, it is necessary to account for uncertainty in model predictions due to uncertain values of model parameters. We present an analysis of uncertainty induced in model predictions of a T-sensor based competitive diffusion immunoassay due to uncertainty in diffusion constants, binding reaction rate constants, and inlet flow speed. We use a non-intrusive stochastic uncertainty quantification method employing polynomial chaos expansions to represent the dependence of uncertain species concentrations on the uncertainty in model parameters. Our simulations show that the uncertainties in model parameters lead to significant spatially varying uncertainty in predicted concentration. In particular, the diffusivity of fluorescently labeled probe antigen dominates the overall uncertainty. The predicted uncertainty in fluorescence intensity is minimum near the centerline of T-sensor and relatively high in the regions with gradients in fluorescence intensity. We show that using centerline fluorescence intensity instead of first derivative of fluorescence intensity as the system response for measuring sample antigen concentration in T-sensor based competitive diffusion immunoassay leads to lower uncertainty and higher detection sensitivity. PMID:26858817
Using a Quasipotential Transformation for Modeling Diffusion Media inPolymer-Electrolyte Fuel Cells
Weber, Adam Z.; Newman, John
2008-08-29
In this paper, a quasipotential approach along with conformal mapping is used to model the diffusion media of a polymer-electrolyte fuel cell. This method provides a series solution that is grid independent and only requires integration along a single boundary to solve the problem. The approach accounts for nonisothermal phenomena, two-phase flow, correct placement of the electronic potential boundary condition, and multilayer media. The method is applied to a cathode diffusion medium to explore the interplay between water and thermal management and performance, the impact of the rib-to-channel ratio, and the existence of diffusion under the rib and flooding phenomena.
NASA Astrophysics Data System (ADS)
Ingo, Carson; Sui, Yi; Chen, Yufen; Parrish, Todd; Webb, Andrew; Ronen, Itamar
2015-03-01
In this paper, we provide a context for the modeling approaches that have been developed to describe non-Gaussian diffusion behavior, which is ubiquitous in diffusion weighted magnetic resonance imaging of water in biological tissue. Subsequently, we focus on the formalism of the continuous time random walk theory to extract properties of subdiffusion and superdiffusion through novel simplifications of the Mittag-Leffler function. For the case of time-fractional subdiffusion, we compute the kurtosis for the Mittag-Leffler function, which provides both a connection and physical context to the much-used approach of diffusional kurtosis imaging. We provide Monte Carlo simulations to illustrate the concepts of anomalous diffusion as stochastic processes of the random walk. Finally, we demonstrate the clinical utility of the Mittag-Leffler function as a model to describe tissue microstructure through estimations of subdiffusion and kurtosis with diffusion MRI measurements in the brain of a chronic ischemic stroke patient.
Modeling and Uncertainty Quantification of Vapor Sorption and Diffusion in Heterogeneous Polymers.
Sun, Yunwei; Harley, Stephen J; Glascoe, Elizabeth A
2015-10-01
A high-fidelity model of kinetic and equilibrium sorption and diffusion is developed and exercised. The gas-diffusion model is coupled with a triple-sorption mechanism: Henry's law absorption, Langmuir adsorption, and pooling or clustering of molecules at higher partial pressures. Sorption experiments are conducted and span a range of relative humidities (0-95 %) and temperatures (30-60 °C). Kinetic and equilibrium sorption properties and effective diffusivity are determined by minimizing the absolute difference between measured and modeled uptakes. Uncertainty quantification and sensitivity analysis methods are described and exercised herein to demonstrate the capability of this modeling approach. Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networks is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors. PMID:26274619
Modeling and Uncertainty Quantification of Vapor Sorption and Diffusion in Heterogeneous Polymers
Sun, Yunwei; Harley, Stephen J.; Glascoe, Elizabeth A.
2015-08-13
A high-fidelity model of kinetic and equilibrium sorption and diffusion is developed and exercised. The gas-diffusion model is coupled with a triple-sorption mechanism: Henry’s law absorption, Langmuir adsorption, and pooling or clustering of molecules at higher partial pressures. Sorption experiments are conducted and span a range of relative humidities (0-95 %) and temperatures (30-60 °C). Kinetic and equilibrium sorption properties and effective diffusivity are determined by minimizing the absolute difference between measured and modeled uptakes. Uncertainty quantification and sensitivity analysis methods are described and exercised herein to demonstrate the capability of this modeling approach. Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networks is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors.
Global stability of equilibrium of multi-species model with cross diffusion
NASA Astrophysics Data System (ADS)
Anguelov, R.; Tenkam, H. M. D.
2015-10-01
In this work, we study a model of the interaction of N species (N > 2) which involves cross-diffusion. The model generalizes the model introduced in 1979 by Shigesada, Kawasaki and Teramoto for two species (SKT). All species are assumed to exhibit a functional response of the same form similar to SKT model. By constructing a Lyapunov functional of the system, we establish the global stability of the equilibrium, subject to some conditions on the cross-diffusion matrix and the diffusion vector. A sufficient condition is also derived for the coexistence of a large number of interacting species. Particular cases of the model for two species are considered extensively in the literature. Most of these results are shown to follow as consequences of the general theory developed here.
Fast and accurate Monte Carlo sampling of first-passage times from Wiener diffusion models
Drugowitsch, Jan
2016-01-01
We present a new, fast approach for drawing boundary crossing samples from Wiener diffusion models. Diffusion models are widely applied to model choices and reaction times in two-choice decisions. Samples from these models can be used to simulate the choices and reaction times they predict. These samples, in turn, can be utilized to adjust the models’ parameters to match observed behavior from humans and other animals. Usually, such samples are drawn by simulating a stochastic differential equation in discrete time steps, which is slow and leads to biases in the reaction time estimates. Our method, instead, facilitates known expressions for first-passage time densities, which results in unbiased, exact samples and a hundred to thousand-fold speed increase in typical situations. In its most basic form it is restricted to diffusion models with symmetric boundaries and non-leaky accumulation, but our approach can be extended to also handle asymmetric boundaries or to approximate leaky accumulation. PMID:26864391
Development of a Diffusion-Based Mathematical Model for Predicting Chemotherapy Effects
Wang, Zhihui; Kerketta, Romica; Chuang, Yao-Li; Cristini, Vittorio
2016-01-01
Mathematical modeling of drug transport can complement current experimental and clinical investigations to understand drug resistance mechanisms, which eventually will help to develop patient-specific chemotherapy treatments. In this paper, we present a general time- and space-dependent mathematical model based on diffusion theory for predicting chemotherapy outcome. This model has two important parameters: the blood volume fraction and radius of blood vessels divided by drug diffusion penetration length. Model analysis finds that a larger ratio of the radius of blood vessel to diffusion penetration length resulted in to a larger fraction of tumor killed, thereby leading to a better treatment outcome. Clinical translation of the model can help quantify and predict the optimal dosage size and frequency of chemotherapy for individual patients. PMID:25570493
Intergenerational Educational Encounters: Part 2--Counseling Implications of the Model
ERIC Educational Resources Information Center
Gamliel, Tova; Reichental, Yael; Eyal, Nitza
2007-01-01
This second paper commences where Part 1 concluded in volume 33, number 1, 2006. The paper describes the relations reflected in the Model-of-Knowledge between all partners of the intergenerational encounters at school--children, old adults, and teachers. The Model-of-Knowledge represents a relatively balanced approach toward the generations'…
NASA Astrophysics Data System (ADS)
O'Malley, S. M.; Alvidrez, V., Jr.; Ling, A. G.; Albert, J.; Colman, J. J.; Quinn, R. A.; Selcher, C. A.; Starks, M. J.
2014-12-01
Two of the largest contributors to electron pitch angle diffusion in the plasmasphere are plasmaspheric hiss and lightning-generated whistler mode waves. Several modeling efforts have been made to describe the interaction between electrons and waves associated with these natural processes, most notably by Abel and Thorne [1998] and Meredith et al [2007,2009]. We present an additional lightning-generated whistler diffusion model based on the recent VLF spectral density climatology of Colman and Starks [2013]. Monthly averages of the wave power distribution used to develop this model are provided. A polynomial fit to the spectral intensity profiles is used to describe the power distribution instead of the normal Gaussian formalization. Comparisons between these models are facilitated via a program based on quasi-linear theory, using input parameters that are representative of each model. Diffusion coefficients are presented as a function of equatorial pitch angle and L-shell for L-shells in the range 2.5-4.0 at electron energies of 0.1, 0.5, 1.0, and 5.0 MeV. The diffusion coefficients are applied to the CRRESELE radiation belt model to determine electron loss timescales. The diffused electron flux pitch angle distributions are presented for CRRESELE energies of 0.65, 2.0, 3.15, and 5.75 MeV and at elapsed times of 30 days, 90 days, 1 year, and 4 years after the start of diffusion. Our results are found to be consistent with prior modeling determinations for small wave normal angle propagation, but less diffusive for large wave normal angles.
3D modeling for solving forward model of no-contact fluorescence diffuse optical tomography method
NASA Astrophysics Data System (ADS)
Nouizi, F.; Chabrier, R.; Torregrossa, M.; Poulet, P.
2009-07-01
This paper presents detailed computational aspects of a new 3D modeling for solving the direct problem in a no-contact time-resolved Fluorescent Diffuse Optical Tomography (FDOT) method that rely on near-infrared scattered and fluorescent photons to image the optical properties and distribution of fluorescent probes in small laboratory animals. An optical scanner allowing performing in-vivo measurements in no-contact scheme was built in our laboratory and is presented. We use the three-dimensional Finite Element Method (FEM) to solve the coupled diffusion equations of excitation and fluorescence photons in highly scattering objects. The computed results allowed yielding photon density maps and the temporal profiles of photons on the surface of the small animal. Our 3D modeling of propagation of photons in the void space between the surface of the object and the detectors allows calculating the quantity of photons reaching the optodes. Simulations were carried-out on two test objects: a resin cylinder and a mouse phantom. The results demonstrate the potential applications of the method to pre-clinical imaging.
NASA Astrophysics Data System (ADS)
Ver Eecke, H. C.; Oslowski, D. M.; Butterfield, D. A.; Olson, E. J.; Lilley, M. D.; Holden, J. F.
2009-12-01
In 2008 and 2009, 534 hydrothermal fluid samples and 5 actively-venting black smoker chimneys were collected using Alvin for correlative microbiological and chemical analyses as part of the Endeavour Segment and Axial Volcano Geochemistry and Ecology Research (EAGER) program. Hyperthermophilic, autotrophic Fe(III) oxide reducers, methanogens, and sulfur-reducing heterotrophs were enriched for at 85 and 95°C using most-probable-number estimates from 28 diffuse fluid and 8 chimney samples. Heterotrophs were the most abundant of the three groups in both diffuse fluids and black-smoker chimneys. Iron reducers were more abundant than methanogens, and more abundant in sulfide-hosted vents than in basalt-hosted vents. Fluid chemistry suggests that there is net biogenic methanogenesis at the Marker 113/62 diffuse vent at Axial Volcano but nowhere else sampled. The growth of hyperthermophilic methanogens and heterotrophs was modeled in the lab using pure cultures. Methanocaldococcus jannaschii grew at 82°C in a 2-liter reactor with continuous gas flow at H2 concentrations between 20 and 225 µM with a H2 km of 100 µM. Correlating H2 end-member mixing curves from vent fluids and seawater with our laboratory modeling study suggests that H2 concentrations are limiting for Methanocaldococcus growth at most Mothra, Main Field, and High Rise vent sites at Endeavour but sufficient to support growth at some Axial Volcano vents. Therefore, hyperthermophilic methanogens may depend on H2 syntrophy at low H2 sites. Twenty-one pure hyperthermophilic heterotroph strains each grew on α-1,4 and β-1,4 linked sugars and polypeptides with concomitant H2 production. The H2 production rate (cell-1 doubling-1) for Pyrococcus furiosus at 95°C without sulfur was 29 fmol, 36 fmol, and 53 fmol for growth on α-1,4 sugars, β-1,4 sugars, and peptides, respectively. The CH4 production rate for M. jannaschii was 390 fmol cell-1 doubling-1; therefore, we estimate that it would take approximately
Hierarchical Diffusion Models for Two-Choice Response Times
ERIC Educational Resources Information Center
Vandekerckhove, Joachim; Tuerlinckx, Francis; Lee, Michael D.
2011-01-01
Two-choice response times are a common type of data, and much research has been devoted to the development of process models for such data. However, the practical application of these models is notoriously complicated, and flexible methods are largely nonexistent. We combine a popular model for choice response times--the Wiener diffusion…
Technological Diffusion within Educational Institutions: Applying the Technology Acceptance Model.
ERIC Educational Resources Information Center
Wolski, Stacy; Jackson, Sally
Expectancy models of behavior such as the Theory of Reasoned Action (TRA) and the Technology Acceptance Model (TAM) offer guidelines that aid efforts to facilitate use of new technology. These models remind us that both acceptance of and resistance to technology use are grounded in beliefs and norms regarding the technology. Although TAM is widely…
Yuste, S B; Abad, E; Baumgaertner, A
2016-07-01
We address the problem of diffusion on a comb whose teeth display varying lengths. Specifically, the length ℓ of each tooth is drawn from a probability distribution displaying power law behavior at large ℓ,P(ℓ)∼ℓ^{-(1+α)} (α>0). To start with, we focus on the computation of the anomalous diffusion coefficient for the subdiffusive motion along the backbone. This quantity is subsequently used as an input to compute concentration recovery curves mimicking fluorescence recovery after photobleaching experiments in comblike geometries such as spiny dendrites. Our method is based on the mean-field description provided by the well-tested continuous time random-walk approach for the random-comb model, and the obtained analytical result for the diffusion coefficient is confirmed by numerical simulations of a random walk with finite steps in time and space along the backbone and the teeth. We subsequently incorporate retardation effects arising from binding-unbinding kinetics into our model and obtain a scaling law characterizing the corresponding change in the diffusion coefficient. Finally, we show that recovery curves obtained with the help of the analytical expression for the anomalous diffusion coefficient cannot be fitted perfectly by a model based on scaled Brownian motion, i.e., a standard diffusion equation with a time-dependent diffusion coefficient. However, differences between the exact curves and such fits are small, thereby providing justification for the practical use of models relying on scaled Brownian motion as a fitting procedure for recovery curves arising from particle diffusion in comblike systems. PMID:27575088
NASA Astrophysics Data System (ADS)
Yuste, S. B.; Abad, E.; Baumgaertner, A.
2016-07-01
We address the problem of diffusion on a comb whose teeth display varying lengths. Specifically, the length ℓ of each tooth is drawn from a probability distribution displaying power law behavior at large ℓ ,P (ℓ ) ˜ℓ-(1 +α ) (α >0 ). To start with, we focus on the computation of the anomalous diffusion coefficient for the subdiffusive motion along the backbone. This quantity is subsequently used as an input to compute concentration recovery curves mimicking fluorescence recovery after photobleaching experiments in comblike geometries such as spiny dendrites. Our method is based on the mean-field description provided by the well-tested continuous time random-walk approach for the random-comb model, and the obtained analytical result for the diffusion coefficient is confirmed by numerical simulations of a random walk with finite steps in time and space along the backbone and the teeth. We subsequently incorporate retardation effects arising from binding-unbinding kinetics into our model and obtain a scaling law characterizing the corresponding change in the diffusion coefficient. Finally, we show that recovery curves obtained with the help of the analytical expression for the anomalous diffusion coefficient cannot be fitted perfectly by a model based on scaled Brownian motion, i.e., a standard diffusion equation with a time-dependent diffusion coefficient. However, differences between the exact curves and such fits are small, thereby providing justification for the practical use of models relying on scaled Brownian motion as a fitting procedure for recovery curves arising from particle diffusion in comblike systems.
A finite element model of region-specific response for mild diffuse brain injury.
Fijalkowski, Ronald J; Yoganandan, Narayan; Zhang, Jiangyue; Pintar, Frank A
2009-11-01
It is well known that rotational loading is responsible for a spectrum of diffuse brain injuries spanning from concussion to diffuse axonal trauma. Many experimental studies have been performed to understand the pathological and biomechanical factors associated with diffuse brain injuries. Finite element models have also been developed to correlate experimental findings with intrinsic variables such as strain. However, a paucity of studies exist examining the combined role of the strain-time parameter. Consequently, using the principles of finite element analysis, the present study introduced the concept of sustained maximum principal strain (SMPS) criterion and explored its potential applicability to diffuse brain injury. An algorithm was developed to determine if the principal strain in a finite element of the brain exceeded a specified magnitude over a specific time interval. The anatomical and geometrical details of the rat for the two-dimensional model were obtained from published data. Using material properties from literature and iterative techniques, the model was validated under three distinct rotational loading conditions indicative of non-injury, concussion, and diffuse axonal trauma. Validation results produced a set of material properties to define the model and were deemed appropriate to examine the role of sustained strain as an indicator of the mechanics of mild diffuse brain injury at the local level. Using a separate set of histological data obtained from graded mild diffuse brain injury experimental studies in rats, different formulations of SMPS criterion were evaluated. For the hippocampus and parietal cortex regions, 4-4 SMPS criterion was found to most closely match with the pattern of histological results. This was further verified by correlating the fractional areas to the time of unconsciousness for each animal group. Although not fully conclusive, these results are valuable in the understanding of diffuse brain injury pathologies
Ocean Turbulence I: One-Point Closure Model Momentum and Heat Vertical Diffusivities
NASA Technical Reports Server (NTRS)
Canuto, V. M.; Howard, A.; Cheng, Y.; Dubovikov, M. S.
1999-01-01
Since the early forties, one-point turbulence closure models have been the canonical tools used to describe turbulent flows in many fields. In geophysics, Mellor and Yamada applied such models using the 1980 state-of-the art. Since then, no improvements were introduced to alleviate two major difficulties: 1) closure of the pressure correlations, which affects the correct determination of the critical Richardson number Ri(sub cr) above which turbulent mixing is no longer possible and 2) the need to express the non-local third-order moments (TOM) in terms of lower order moments rather than via the down-gradient approximation as done thus far, since the latter seriously underestimates the TOMs. Since 1) and 2) are still being dealt with adjustable parameters which weaken the credibility of the models, alternative models, not based on turbulence modeling, have been suggested. The aim of this paper is to show that new information, partly derived from the newest 2-point closure model discussed, can be used to solve these shortcomings. The new one-point closure model, which in its simplest form is algebraic and thus simple to implement, is first shown to reproduce a variety of data. Then, it is used in a Ocean-General Circulation Model (O-GCM) where it reproduces well a large variety of ocean data. While phenomenological models are specifically tuned to ocean turbulence, the present model is not. It is first tested against laboratory data on stably stratified flows and then used in an O-GCM. It is more general, more predictive and more resilient, e.g., it can incorporate phenomena like wave-breaking at the surface, salinity diffusivity, non-locality, etc. One important feature that naturally comes out of the new model is that the predicted Richardson critical value Ri(sub cr) is Ri (sub cr approx. = 1) in agreement with both Large Eddy Simulations (LES) and empirical evidence while all previous models predicted Ri (sub cr approx. = 0.2) which led to a considerable
Multi-view and 3D deformable part models.
Pepik, Bojan; Stark, Michael; Gehler, Peter; Schiele, Bernt
2015-11-01
As objects are inherently 3D, they have been modeled in 3D in the early days of computer vision. Due to the ambiguities arising from mapping 2D features to 3D models, 3D object representations have been neglected and 2D feature-based models are the predominant paradigm in object detection nowadays. While such models have achieved outstanding bounding box detection performance, they come with limited expressiveness, as they are clearly limited in their capability of reasoning about 3D shape or viewpoints. In this work, we bring the worlds of 3D and 2D object representations closer, by building an object detector which leverages the expressive power of 3D object representations while at the same time can be robustly matched to image evidence. To that end, we gradually extend the successful deformable part model [1] to include viewpoint information and part-level 3D geometry information, resulting in several different models with different level of expressiveness. We end up with a 3D object model, consisting of multiple object parts represented in 3D and a continuous appearance model. We experimentally verify that our models, while providing richer object hypotheses than the 2D object models, provide consistently better joint object localization and viewpoint estimation than the state-of-the-art multi-view and 3D object detectors on various benchmarks (KITTI [2] , 3D object classes [3] , Pascal3D+ [4] , Pascal VOC 2007 [5] , EPFL multi-view cars[6] ). PMID:26440264
NASA Astrophysics Data System (ADS)
Porth, O.; Vorster, M. J.; Lyutikov, M.; Engelbrecht, N. E.
2016-08-01
We study the transport of high-energy particles in pulsar wind nebulae (PWN) using three-dimensional magnetohydrodynamic (MHD) and test-particle simulations, as well as a Fokker-Planck particle transport model. The latter includes radiative and adiabatic losses, diffusion, and advection on the background flow of the simulated MHD nebula. By combining the models, the spatial evolution of flux and photon index of the X-ray synchrotron emission is modelled for the three nebulae G21.5-0.9, the inner regions of Vela, and 3C 58, thereby allowing us to derive governing parameters: the magnetic field strength, average flow velocity, and spatial diffusion coefficient. For comparison, the nebulae are also modelled with the semi-analytic Kennel & Coroniti model but the Porth et al. model generally yields better fits to the observational data. We find that high velocity fluctuations in the turbulent nebula (downstream of the termination shock) give rise to efficient diffusive transport of particles, with average Péclet number close to unity, indicating that both advection and diffusion play an important role in particle transport. We find that the diffusive transport coefficient of the order of ˜ 2 × 1027(Ls/0.42 Ly) cm2 s- 1 (Ls is the size of the termination shock) is independent of energy up to extreme particle Lorentz factors of γp ˜ 1010.
Tone-dependent error diffusion based on an updated blue-noise model
NASA Astrophysics Data System (ADS)
Fung, Yik-Hing; Chan, Yuk-Hee
2016-01-01
The conventional blue-noise model that specifies the desired noise characteristics of an ideal halftone has been updated recently, and simulation results showed that the updated model can serve as a better guideline for developing halftone algorithms. At the moment, only a feature-preserving multiscale error diffusion-based algorithm was developed based on the updated noise model. As the algorithm does not support real-time applications, a tone-dependent error diffusion (TDED) algorithm is developed based on the updated noise model. To support the proposed TDED algorithm, we optimize a diffusion filter and a quantizer threshold for each possible input gray level based on the updated noise model, such that the algorithm can adapt its diffusion filter and quantizer according to the input intensity value of a pixel to produce a halftone. Simulation results showed that the proposed TDED algorithm can successfully produce halftones bearing the desired noise characteristics as specified by the updated noise model. As a consequence, it provides better performance than conventional error diffusion-based algorithms in terms of various measures including radially averaged power spectrum density and anisotropy. When processing real images, it can eliminate directional artifacts, regular structure patterns, and unintended sharpening effects in its halftoning outputs.
NASA Astrophysics Data System (ADS)
Porth, O.; Vorster, M. J.; Lyutikov, M.; Engelbrecht, N. E.
2016-08-01
We study the transport of high-energy particles in pulsar wind nebulae (PWN) using three-dimensional MHD (see Porth et al. (2014) for details) and test-particle simulations, as well as a Fokker-Planck particle transport model. The latter includes radiative and adiabatic losses, diffusion, and advection on the background flow of the simulated MHD nebula. By combining the models, the spatial evolution of flux and photon index of the X-ray synchrotron emission is modelled for the three nebulae G21.5-0.9, the inner regions of Vela, and 3C 58, thereby allowing us to derive governing parameters: the magnetic field strength, average flow velocity and spatial diffusion coefficient. For comparison, the nebulae are also modelled with the semi-analytic Kennel & Coroniti (1984) model but the Porth et al. (2014) model generally yields better fits to the observational data. We find that high velocity fluctuations in the turbulent nebula (downstream of the termination shock) give rise to efficient diffusive transport of particles, with average P\\'eclet number close to unity, indicating that both advection and diffusion play an important role in particle transport. We find that the diffusive transport coefficient of the order of $\\sim2\\times 10^{27} (L_{\\rm s}/0.42\\rm Ly) cm^{2}s^{-1}$ ($L_{\\rm s}$ is the size of the termination shock) is independent of energy up to extreme particle Lorentz factors of $\\gamma_{p}\\sim10^{10}$.
Dynamic Recrystallization (DRX) as the Mechanism for Sn Whisker Development. Part I: A Model
NASA Astrophysics Data System (ADS)
Vianco, P. T.; Rejent, J. A.
2009-09-01
A model is proposed that attributes whisker growth in metals and alloys to dynamic recrystallization (DRX) and, in particular, DRX at the material surface. Each step in the DRX process was correlated to the development of whiskers. The DRX model depends upon the details of the deformation process(es) responsible for new grain initiation and growth. The dependencies exhibited by DRX as a function of deformation strain rate, temperature, and microstructure correlate with the behaviors of whisker development. Anomalous or ultrafast diffusion mechanisms, either by themselves or associated with the deformation structures, provide the means of mass transport necessary to grow whiskers. In Part II of this study, the strain and rate kinetics data are determined for Sn. Parts I and II, together, provide a critical step towards developing a capability to predict the conditions that are likely to cause whisker growth in engineering applications.
Experimental and Modeling Study of Retarded Diffusive Transport of Uranium(VI) in a Hanford Sediment
NASA Astrophysics Data System (ADS)
Bai, J.; Ball, W. P.
2006-12-01
Uranium(VI) is a common contaminant at sites of nuclear material processing and uranium mining. U(VI) fate and transport is of great concern at the U.S. Department of Energy (DOE) Hanford Site due to the high probability of discharging into the nearby Columbia River. While large-scale U migration in the subsurface is generally determined by advection along permeable pathways, local scale transport in less permeable regions, such as rock matrices or fine-grained (e.g. clayey) soils is controlled by diffusion. In this work, a single reservoir diffusion cell (in-diffusion method) was designed to study U(VI) diffusion in the fully saturated silt/clay fraction of a composite Hanford sediment material, under strictly controlled chemical conditions (pH 8.0, I = 0.02M, PCO2=10-3.5atm, saturated with calcite). Time-variant concentrations of tritiated water tracer (3H2O) and U(VI) in the reservoir were monitored during the diffusion phase and used as a measure of diffusion flux into the porous medium of the cell. U(VI) profiles in the pore water and in the solid phase along the cell length were also obtained at the end of the diffusion phase, by using high speed centrifugation and a specially designed extraction procedure. The 3H2O data were used to determine the tortuosity factor of the cell sediment. A retarded diffusive transport model for U(VI) was developed and numerically solved assuming local equilibrium and using a Freundlich sorption isotherm that was independently obtained from batch sorption experiments. The effective diffusion coefficient of U(VI) was determined by fitting the modeling results to experimental data (Optimization Toolbox, Matlab). The U(VI) diffusion showed less sorption retardation than expected based on batch results, indicating either reduced retardation capacity of the sediment, or invalidity of the local equilibrium assumption due to kinetic processes such as intra-particle diffusion at the grain scale. An improved model using first
NASA Technical Reports Server (NTRS)
Canuto, V. M.; Dubovikov, M. S.; Howard, A.; Cheng, Y.
1999-01-01
In papers 1 and 2 we have presented the results of the most updated 1-point closure model for the turbulent vertical diffusivities of momentum, heat and salt, K(sub m,h,s). In this paper, we derive the analytic expressions for K(sub m,h,s) using a new 2-point closure model that has recently been developed and successfully tested against some approx. 80 turbulence statistics for different flows. The new model has no free parameters. The expressions for K(sub m, h. s) are analytical functions of two stability parameters: the Turner number R(sub rho) (salinity gradient/temperature gradient) and the Richardson number R(sub i) (temperature gradient/shear). The turbulent kinetic energy K and its rate of dissipation may be taken local or non-local (K-epsilon model). Contrary to all previous models that to describe turbulent mixing below the mixed layer (ML) have adopted three adjustable "background diffusivities" for momentum. heat and salt, we propose a model that avoids such adjustable diffusivities. We assume that below the ML, K(sub m,h,s) have the same functional dependence on R(sub i) and R(sub rho) derived from the turbulence model. However, in order to compute R(sub i) below the ML, we use data of vertical shear due to wave-breaking measured by Gargett et al. (1981). The procedure frees the model from adjustable background diffusivities and indeed we use the same model throughout the entire vertical extent of the ocean. Using the new K(sub m,h, s), we run an O-GCM and present a variety of results that we compare with Levitus and the KPP model. Since the traditional 1-point (used in papers 1 and 2) and the new 2-point closure models used here represent different modeling philosophies and procedures, testing them in an O-GCM is indispensable. The basic motivation is to show that the new 2-point closure model gives results that are overall superior to the 1-point closure in spite of the fact that the latter rely on several adjustable parameters while the new 2-point
Diffusion of Innovation: A Plea for Indigenous Models
ERIC Educational Resources Information Center
Rubdy, Rani
2008-01-01
Much of curriculum innovation in English language teaching in the context of former colonial countries has been derivative rather than generative, imitative rather than self-initiated or self-regulatory. This trend is in part the result of historical exigencies that made the importation of ELT approaches, methods, and techniques for classroom…
A comparison between the fission matrix method, the diffusion model and the transport model
Dehaye, B.; Hugot, F. X.; Diop, C. M.
2013-07-01
The fission matrix method may be used to solve the critical eigenvalue problem in a Monte Carlo simulation. This method gives us access to the different eigenvalues and eigenvectors of the transport or fission operator. We propose to compare the results obtained via the fission matrix method with those of the diffusion model, and an approximated transport model. To do so, we choose to analyse the mono-kinetic and continuous energy cases for a Godiva-inspired critical sphere. The first five eigenvalues are computed with TRIPOLI-4{sup R} and compared to the theoretical ones. An extension of the notion of the extrapolation distance is proposed for the modes other than the fundamental one. (authors)
Tourlomousis, Filippos; Chang, Robert C
2016-03-01
The dynamic nature of in vitro drug metabolism models demands reliable numerical tools to determine key design parameter values towards high-fidelity cell-based platforms of in vivo drug metabolism. This paper represents the first of a two-part model-based investigation of a 3D dynamic microorgan device (DMD). The prescribed tissue model in this paper is precisely embedded within a DMD by 3D bioprinting hydrogel encapsulated liver cells into a patterned array of microchannels. A perfusing drug substrate is biotransformed by liver cells encapsulated within porous hydrogel walls. Therefore, the free and porous flow regime equations are first solved in tandem to derive the laminar velocity profile and wall shear stresses in the entire shear-mediated flow regime. These equations are then coupled with a convection-diffusion equation and Michaelis-Menten reaction terms, resulting in an effective convection-diffusion-cell kinetics model. A key consideration addressed herein is mechanotransduction where shear stresses on the encapsulated cells alter subcellular liver enzyme reaction rates. Cells are incorporated into the geometric model implicitly (macroscale) as enzyme reaction structures uniformly distributed throughout the DMD length. Transient simulations enable effluent drug metabolite profile determination wherein the proposed macroscale modeling approach is validated with an experimental drug flow study. PMID:26332859
Tariné Gombkŏtö, Z; Molnár, J; Farkasné Gunics, G; Regdon, G; Selmeczi, B
1992-11-01
After the physical parameters had been determined, the in vitro drug liberation from vaginal suppositories containing 100 mg of antibacterial agent (sulphadimine, chloramphenicol, gentamicin-sulphate) was studied by membrane diffusion and microbiological methods. Among the vehicles available in Hungary the hydrophylic Massa macrogoli was found to be the best for this purpose. Among the lipophilic bases the in vitro drug liberation of the French Suppocire NA product was significantly better (p < 0.05) compared to the other lipophilic bases. This vehicle is recommended by the authors for the topical treatment of vaginitis, as these suppositories have the further advantage that they can easily be produced on a magistral, galenical or industrial scale as well. In the first part of the publication the formulation and some important physical parameters of lipophilic and hydrophilic antibacterial suppositories for vaginal use were described. In the present paper the drug liberation ability of the compositions with proper physical parameters was studied. The published results were obtained from measurements performed 1 week after formulation. PMID:1488916
Simulating watercolor by modeling diffusion, pigment, and paper fibers
NASA Astrophysics Data System (ADS)
Small, David
1991-08-01
This paper explores a parallel approach to the problem of predicting the actions of pigment and water when applied to paper fibers. This work was done on the Connection Machine II, whose parallel architecture allows one to cast the problem as that of a complex cellular automata. One defines simple rules for the behavior of each cell based on the state of that cell and its immediate neighbors. By repeating the computation for each cell in the paper over many time steps, elaborate and realistic behaviors can be achieved. The simulation takes into account diffusion, surface tension, gravity, humidity, paper absorbency and the molecular weight of each pigment. At each time step a processor associated with each fiber in the paper computes water and pigment gradients, surface tension and gravitational forces, and decides if there should be any movement of material. Pigment and water can be applied and removed (blotting) with masks created from type or scanned images. Use of a parallel processor simplifies the creation and testing of software, and variables can be stored and manipulated at highprecision. The resulting simulation runs at approximately one-tenth real time.
Modeling of aircraft unsteady aerodynamic characteristics. Part 1: Postulated models
NASA Technical Reports Server (NTRS)
Klein, Vladislav; Noderer, Keith D.
1994-01-01
A short theoretical study of aircraft aerodynamic model equations with unsteady effects is presented. The aerodynamic forces and moments are expressed in terms of indicial functions or internal state variables. The first representation leads to aircraft integro-differential equations of motion; the second preserves the state-space form of the model equations. The formulations of unsteady aerodynamics is applied in two examples. The first example deals with a one-degree-of-freedom harmonic motion about one of the aircraft body axes. In the second example, the equations for longitudinal short-period motion are developed. In these examples, only linear aerodynamic terms are considered. The indicial functions are postulated as simple exponentials and the internal state variables are governed by linear, time-invariant, first-order differential equations. It is shown that both approaches to the modeling of unsteady aerodynamics lead to identical models.
Bilayer mass transport model for determining swelling and diffusion in coated, ultrathin membranes.
Nadermann, Nichole K; Chan, Edwin P; Stafford, Christopher M
2015-02-18
Water transport and swelling properties of an ultrathin, selective polyamide layer with a hydrophilic polymer coating, i.e., a polymer bilayer, are studied using quartz crystal microbalance with dissipation (QCM-D). Specifically, QCM-D is used to measure the dynamic and equilibrium change in mass in a series of differential sorption experiments to determine the dependence of the apparent diffusion coefficient and equilibrium swelling of the bilayer as a function of the water vapor activity. To determine transport properties specific to the polyamide layer, sorption kinetics of the bilayer was modeled with a bilayer mass transport model. The swelling and water diffusion coefficients are interpreted according to the Painter-Shenoy polymer network swelling model and the solution-diffusion model, respectively. PMID:25597964
Aurela, B; Ketoja, J A
2002-01-01
Predictive migration models for polymers are already so well established that the European Commission intends to allow the use of the models as one quality assurance tool in product safety assessment of plastic materials and articles for food contact. The inhomogeneity of fibre-based materials makes modelling difficult--thus, little research has been done in this area. The authors compare experiments on the diffusion of certain volatile compounds through laboratory kraft pulp sheets with computer simulations in which the fibre network structure is modelled explicitly. The major advantage of the present random walk simulation is that it gives an estimate of the effective diffusion constant for the fibre network. For most compounds, the agreement between the experiments and simulations is good. The experiments and simulations indicate that gas diffusion rate is very sensitive to sheet porosity. PMID:11962715
NASA Astrophysics Data System (ADS)
Gallego, Sergi; Ortuño, Manuel; Neipp, Cristian; Márquez, Andrés; Beléndez, Augusto; Pascual, Inmaculada
2005-10-01
Several theoretical models have been proposed to predict the behavior of photopolymers as holographic recording materials. Basically these models have been applied to study thin layers (around 100 µm thick). The increasing importance of holographic memories recorded in photopolymers (thickness of >500 µm) makes it necessary to extend the ideas proposed by these models to study thick photopolymer layers. We calculate the temporal evolution of the diffraction efficiencies for thick layers using a first-harmonic diffusion model, and the results obtained are compared with the corresponding values for thin layers. Furthermore, the values of the average diffusivity of the polymer chains after the grating is formed are also obtained. In general, we find that the monomer and polymer diffusivity increases when higher values of thickness are used.
Modeling Convective Core Overshoot and Diffusion in Procyon Constrained by Asteroseismic Data
NASA Astrophysics Data System (ADS)
Guenther, D. B.; Demarque, P.; Gruberbauer, M.
2014-06-01
We compare evolved stellar models, which match Procyon's mass and position in the HR diagram, to current ground-based asteroseismic observations. Diffusion of helium and metals along with two conventional core overshoot descriptions and the Kuhfuss nonlocal theory of convection are considered. We establish that one of the two published asteroseismic data reductions for Procyon, which mainly differ in their identification of even versus odd l values, is a significantly more probable and self-consistent match to our models than the other. The most probable models according to our Bayesian analysis have evolved to just short of turnoff, still retaining a hydrogen convective core. Our most probable models include Y and Z diffusion and have conventional core overshoot between 0.9 and 1.5 pressure scale heights, which increases the outer radius of the convective core by between 36% and 43%, respectively. We discuss the significance of this comparatively higher than expected core overshoot amount in terms of internal mixing during evolution. The parameters of our most probable models are similar regardless of whether adiabatic or nonadiabatic model p-mode frequencies are compared to the observations, although, the Bayesian probabilities are greater when the nonadiabatic model frequencies are used. All the most probable models (with or without core overshoot, adiabatic or nonadiabatic model frequencies, diffusion or no diffusion, including priors for the observed HRD location and mass or not) have masses that are within 1σ of the observed mass 1.497 ± 0.037 M ⊙.
Modeling convective core overshoot and diffusion in Procyon constrained by asteroseismic data
Guenther, D. B.; Gruberbauer, M.; Demarque, P.
2014-06-01
We compare evolved stellar models, which match Procyon's mass and position in the HR diagram, to current ground-based asteroseismic observations. Diffusion of helium and metals along with two conventional core overshoot descriptions and the Kuhfuss nonlocal theory of convection are considered. We establish that one of the two published asteroseismic data reductions for Procyon, which mainly differ in their identification of even versus odd l values, is a significantly more probable and self-consistent match to our models than the other. The most probable models according to our Bayesian analysis have evolved to just short of turnoff, still retaining a hydrogen convective core. Our most probable models include Y and Z diffusion and have conventional core overshoot between 0.9 and 1.5 pressure scale heights, which increases the outer radius of the convective core by between 36% and 43%, respectively. We discuss the significance of this comparatively higher than expected core overshoot amount in terms of internal mixing during evolution. The parameters of our most probable models are similar regardless of whether adiabatic or nonadiabatic model p-mode frequencies are compared to the observations, although, the Bayesian probabilities are greater when the nonadiabatic model frequencies are used. All the most probable models (with or without core overshoot, adiabatic or nonadiabatic model frequencies, diffusion or no diffusion, including priors for the observed HRD location and mass or not) have masses that are within 1σ of the observed mass 1.497 ± 0.037 M {sub ☉}.
Effect of a protection zone in the diffusive Leslie predator-prey model
NASA Astrophysics Data System (ADS)
Du, Yihong; Peng, Rui; Wang, Mingxin
In this paper, we consider the diffusive Leslie predator-prey model with large intrinsic predator growth rate, and investigate the change of behavior of the model when a simple protection zone Ω for the prey is introduced. As in earlier work [Y. Du, J. Shi, A diffusive predator-prey model with a protection zone, J. Differential Equations 229 (2006) 63-91; Y. Du, X. Liang, A diffusive competition model with a protection zone, J. Differential Equations 244 (2008) 61-86] we show the existence of a critical patch size of the protection zone, determined by the first Dirichlet eigenvalue of the Laplacian over Ω and the intrinsic growth rate of the prey, so that there is fundamental change of the dynamical behavior of the model only when Ω is above the critical patch size. However, our research here reveals significant difference of the model's behavior from the predator-prey model studied in [Y. Du, J. Shi, A diffusive predator-prey model with a protection zone, J. Differential Equations 229 (2006) 63-91] with the same kind of protection zone. We show that the asymptotic profile of the population distribution of the Leslie model is governed by a standard boundary blow-up problem, and classical or degenerate logistic equations.
A novel approach to modelling water transport and drug diffusion through the stratum corneum
2010-01-01
Background The potential of using skin as an alternative path for systemically administering active drugs has attracted considerable interest, since the creation of novel drugs capable of diffusing through the skin would provide a great step towards easily applicable -and more humane- therapeutic solutions. However, for drugs to be able to diffuse, they necessarily have to cross a permeability barrier: the stratum corneum (SC), the uppermost set of skin layers. The precise mechanism by which drugs penetrate the skin is generally thought to be diffusion of molecules through this set of layers following a "tortuous pathway" around corneocytes, i.e. impermeable dead cells. Results In this work, we simulate water transport and drug diffusion using a three-dimensional porous media model. Our numerical simulations show that diffusion takes place through the SC regardless of the direction and magnitude of the fluid pressure gradient, while the magnitude of the concentrations calculated are consistent with experimental studies. Conclusions Our results support the possibility for designing arbitrary drugs capable of diffusing through the skin, the time-delivery of which is solely restricted by their diffusion and solubility properties. PMID:20716360
A reversible mesoscopic model of diffusion in liquids: from giant fluctuations to Fick’s law
NASA Astrophysics Data System (ADS)
Donev, Aleksandar; Fai, Thomas G.; Vanden-Eijnden, Eric
2014-04-01
We study diffusive mixing in the presence of thermal fluctuations under the assumption of large Schmidt number. In this regime we obtain a limiting equation that contains a diffusive stochastic drift term with diffusion coefficient obeying a Stokes-Einstein relation, in addition to the expected advection by a random velocity. The overdamped limit correctly reproduces both the enhanced diffusion in the ensemble-averaged mean and the long-range correlated giant fluctuations in individual realizations of the mixing process, and is amenable to efficient numerical solution. Through a combination of Eulerian and Lagrangian numerical methods we demonstrate that diffusion in liquids is not most fundamentally described by Fick’s irreversible law; rather, diffusion is better modeled as reversible random advection by thermal velocity fluctuations. We find that the diffusion coefficient is effectively renormalized to a value that depends on the scale of observation. Our work reveals somewhat unexpected connections between flows at small scales, dominated by thermal fluctuations, and flows at large scales, dominated by turbulent fluctuations.