Comparison of Six Highway Air Pollution Dispersion Models Using Synthetic Data

DOT National Transportation Integrated Search

1977-09-01

This is the second of two studies conducted by the Transportation Systems Center (TSC) to test the performance of highway air pollution dispersion models, using synthetic data (i.e., either measured or artificially constructed input data for models, ...

Development of a Geographic Information System Based Dust Dispersion Modeling System For Use In the Planning and Implementation of Military Training Exercises

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

Crandall, Duard W; Rutz, Frederick C

2004-08-12

Military maneuvers and training exercises are essential for national and world defense. These maneuvers must however be performed in a manner that will have a minimal effect on the environment and local civilians. As residential areas continue to develop near military sites, possible impacts from military traffic and exercises to these areas begin to become of greater concern. Concerns facing the military include the effects of particulate air quality and atmospheric dust dispersion caused by such maneuvers. To aid the Department of Defense with this problem, Pacific Northwest National Laboratory proposed a plan to develop, document and test a modelingmore » system for use in dust dispersion reduction and management near government sites. To accomplish this task a user interface was developed that would be user friendly yet sophisticated enough to accommodate the needs of the client. One such need is to integrate a geographic information system (GIS) with the dust dispersion modeling software. This allows the user to enter the point, area, or line source required for the model runs. Incorporating the GIS with the software will also allow the user to view plume rise and expansion over actual data maps of the desired site. Data collected during previous field studies will be used to verify the results generated by the dust dispersion models. Thus utilizing historical, current, and user defined data, near real-time dust dispersion models will be able to aid in estimating and minimizing the effects of military exercises on the environment and nonmilitary personnel.« less

Dispersion, sorption and photodegradation of petroleum hydrocarbons in dispersant-seawater-sediment systems.

PubMed

Zhao, Xiao; Liu, Wen; Fu, Jie; Cai, Zhengqing; O'Reilly, S E; Zhao, Dongye

2016-08-15

This work examined effects of model oil dispersants on dispersion, sorption and photodegradation of petroleum hydrocarbons in simulated marine systems. Three dispersants (Corexit 9500A, Corexit 9527A and SPC 1000) were used to prepare dispersed water accommodated oil (DWAO). While higher doses of dispersants dispersed more n-alkanes and PAHs, Corexit 9500A preferentially dispersed C11-C20 n-alkanes, whereas Corexit 9527A was more favorable for smaller alkanes (C10-C16), and SPC 1000 for C12-C28 n-alkanes. Sorption of petroleum hydrocarbons on sediment was proportional to TPH types/fractions in the DWAOs. Addition of 18mg/L of Corexit 9500A increased sediment uptake of 2-3 ring PAHs, while higher dispersant doses reduced the uptake, due to micelle-enhanced solubilization effects. Both dispersed n-alkanes and PAHs were susceptible to photodegradation under simulated sunlight. For PAHs, both photodegradation and photo-facilitated alkylation were concurrently taking place. The information can facilitate sounder assessment of fate and distribution of dispersed oil hydrocarbons in marine systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Factors regulating early life history dispersal of Atlantic cod (Gadus morhua) from coastal Newfoundland.

PubMed

Stanley, Ryan R E; deYoung, Brad; Snelgrove, Paul V R; Gregory, Robert S

2013-01-01

To understand coastal dispersal dynamics of Atlantic cod (Gadus morhua), we examined spatiotemporal egg and larval abundance patterns in coastal Newfoundland. In recent decades, Smith Sound, Trinity Bay has supported the largest known overwintering spawning aggregation of Atlantic cod in the region. We estimated spawning and dispersal characteristics for the Smith Sound-Trinity Bay system by fitting ichthyoplankton abundance data to environmentally-driven, simplified box models. Results show protracted spawning, with sharply increased egg production in early July, and limited dispersal from the Sound. The model for the entire spawning season indicates egg export from Smith Sound is 13%•day(-1) with a net mortality of 27%•day(-1). Eggs and larvae are consistently found in western Trinity Bay with little advection from the system. These patterns mirror particle tracking models that suggest residence times of 10-20 days, and circulation models indicating local gyres in Trinity Bay that act in concert with upwelling dynamics to retain eggs and larvae. Our results are among the first quantitative dispersal estimates from Smith Sound, linking this spawning stock to the adjacent coastal waters. These results illustrate the biophysical interplay regulating dispersal and connectivity originating from inshore spawning of coastal northwest Atlantic.

Evaluation of the Regional Atmospheric Modeling System in the Eastern Range Dispersion Assessment System

NASA Technical Reports Server (NTRS)

Case, Jonathan

2000-01-01

The Applied Meteorology Unit is conducting an evaluation of the Regional Atmospheric Modeling System (RAMS) contained within the Eastern Range Dispersion Assessment System (ERDAS). ERDAS provides emergency response guidance for operations at the Cape Canaveral Air Force Station and the Kennedy Space Center in the event of an accidental hazardous material release or aborted vehicle launch. The prognostic data from RAMS is available to ERDAS for display and is used to initialize the 45th Range Safety (45 SW/SE) dispersion model. Thus, the accuracy of the 45 SW/SE dispersion model is dependent upon the accuracy of RAMS forecasts. The RAMS evaluation task consists of an objective and subjective component for the Florida warm and cool seasons of 1999-2000. The objective evaluation includes gridded and point error statistics at surface and upper-level observational sites, a comparison of the model errors to a coarser grid configuration of RAMS, and a benchmark of RAMS against the widely accepted Eta model. The warm-season subjective evaluation involves a verification of the onset and movement of the Florida east coast sea breeze and RAMS forecast precipitation. This interim report provides a summary of the RAMS objective and subjective evaluation for the 1999 Florida warm season only.

Evolution of the mating system in colonizing plants.

PubMed

Pannell, John R

2015-05-01

Colonization is likely to be more successful for species with an ability to self-fertilize and thus to establish new populations as single individuals. As a result, self-compatibility should be common among colonizing species. This idea, labelled 'Baker's law', has been influential in discussions of sexual-system and mating-system evolution. However, its generality has been questioned, because models of the evolution of dispersal and the mating system predict an association between high dispersal rates and outcrossing rather than selfing, and because of many apparent counter examples to the law. The contrasting predictions made by models invoking Baker's law versus those for the evolution of the mating system and dispersal urges a reassessment of how we should view both these traits. Here, I review the literature on the evolution of mating and dispersal in colonizing species, with a focus on conceptual issues. I argue for the importance of distinguishing between the selfing or outcrossing rate and a simple ability to self-fertilize, as well as for the need for a more nuanced consideration of dispersal. Colonizing species will be characterized by different phases in their life pattern: dispersal to new habitat, implying an ecological sieve on dispersal traits; establishment and a phase of growth following colonization, implying a sieve on reproductive traits; and a phase of demographic stasis at high density, during which new trait associations can evolve through local adaptation. This dynamic means that the sorting of mating-system and dispersal traits should change over time, making simple predictions difficult. © 2015 John Wiley & Sons Ltd.

Effect of tubing length on the dispersion correction of an arterially sampled input function for kinetic modeling in PET.

PubMed

O'Doherty, Jim; Chilcott, Anna; Dunn, Joel

2015-11-01

Arterial sampling with dispersion correction is routinely performed for kinetic analysis of PET studies. Because of the the advent of PET-MRI systems, non-MR safe instrumentation will be required to be kept outside the scan room, which requires the length of the tubing between the patient and detector to increase, thus worsening the effects of dispersion. We examined the effects of dispersion in idealized radioactive blood studies using various lengths of tubing (1.5, 3, and 4.5 m) and applied a well-known transmission-dispersion model to attempt to correct the resulting traces. A simulation study was also carried out to examine noise characteristics of the model. The model was applied to patient traces using a 1.5 m acquisition tubing and extended to its use at 3 m. Satisfactory dispersion correction of the blood traces was achieved in the 1.5 m line. Predictions on the basis of experimental measurements, numerical simulations and noise analysis of resulting traces show that corrections of blood data can also be achieved using the 3 m tubing. The effects of dispersion could not be corrected for the 4.5 m line by the selected transmission-dispersion model. On the basis of our setup, correction of dispersion in arterial sampling tubing up to 3 m by the transmission-dispersion model can be performed. The model could not dispersion correct data acquired using a 4.5 m arterial tubing.

Trajectory-Based Loads for the Ares I-X Test Flight Vehicle

NASA Technical Reports Server (NTRS)

Vause, Roland F.; Starr, Brett R.

2011-01-01

In trajectory-based loads, the structural engineer treats each point on the trajectory as a load case. Distributed aero, inertial, and propulsion forces are developed for the structural model which are equivalent to the integrated values of the trajectory model. Free-body diagrams are then used to solve for the internal forces, or loads, that keep the applied aero, inertial, and propulsion forces in dynamic equilibrium. There are several advantages to using trajectory-based loads. First, consistency is maintained between the integrated equilibrium equations of the trajectory analysis and the distributed equilibrium equations of the structural analysis. Second, the structural loads equations are tied to the uncertainty model for the trajectory systems analysis model. Atmosphere, aero, propulsion, mass property, and controls uncertainty models all feed into the dispersions that are generated for the trajectory systems analysis model. Changes in any of these input models will affect structural loads response. The trajectory systems model manages these inputs as well as the output from the structural model over thousands of dispersed cases. Large structural models with hundreds of thousands of degrees of freedom would execute too slowly to be an efficient part of several thousand system analyses. Trajectory-based loads provide a means for the structures discipline to be included in the integrated systems analysis. Successful applications of trajectory-based loads methods for the Ares I-X vehicle are covered in this paper. Preliminary design loads were based on 2000 trajectories using Monte Carlo dispersions. Range safety loads were tied to 8423 malfunction turn trajectories. In addition, active control system loads were based on 2000 preflight trajectories using Monte Carlo dispersions.

The Evaluation of the Regional Atmospheric Modeling System in the Eastern Range Dispersion Assessment System

NASA Technical Reports Server (NTRS)

Case, Jonathan

2001-01-01

The Applied Meteorology Unit (AMU) evaluated the Regional Atmospheric Modeling System (RAMS) contained within the Eastern Range Dispersion Assessment System (ERDAS). ERDAS provides emergency response guidance for Cape Canaveral Air Force Station and Kennedy Space Center operations in the event of an accidental hazardous material release or aborted vehicle launch. The RAMS prognostic data are available to ERDAS for display and are used to initialize the 45th Space Wing/Range Safety dispersion model. Thus, the accuracy of the dispersion predictions is dependent upon the accuracy of RAMS forecasts. The RAMS evaluation consisted of an objective and subjective component for the 1999 and 2000 Florida warm seasons, and the 1999-2000 cool season. In the objective evaluation, the AMU generated model error statistics at surface and upper-level observational sites, compared RAMS errors to a coarser RAMS grid configuration, and benchmarked RAMS against the nationally-used Eta model. In the subjective evaluation, the AMU compared forecast cold fronts, low-level temperature inversions, and precipitation to observations during the 1999-2000 cool season, verified the development of the RAMS forecast east coast sea breeze during both warm seasons, and examined the RAMS daily thunderstorm initiation and precipitation patterns during the 2000 warm season. This report summarizes the objective and subjective verification for all three seasons.

Solute transport along a single fracture in a porous rock: a simple analytical solution and its extension for modeling velocity dispersion

NASA Astrophysics Data System (ADS)

Liu, Longcheng; Neretnieks, Ivars; Shahkarami, Pirouz; Meng, Shuo; Moreno, Luis

2018-02-01

A simple and robust solution is developed for the problem of solute transport along a single fracture in a porous rock. The solution is referred to as the solution to the single-flow-path model and takes the form of a convolution of two functions. The first function is the probability density function of residence-time distribution of a conservative solute in the fracture-only system as if the rock matrix is impermeable. The second function is the response of the fracture-matrix system to the input source when Fickian-type dispersion is completely neglected; thus, the effects of Fickian-type dispersion and matrix diffusion have been decoupled. It is also found that the solution can be understood in a way in line with the concept of velocity dispersion in fractured rocks. The solution is therefore extended into more general cases to also account for velocity variation between the channels. This leads to a development of the multi-channel model followed by detailed statistical descriptions of channel properties and sensitivity analysis of the model upon changes in the model key parameters. The simulation results obtained by the multi-channel model in this study fairly well agree with what is often observed in field experiments—i.e. the unchanged Peclet number with distance, which cannot be predicted by the classical advection-dispersion equation. In light of the findings from the aforementioned analysis, it is suggested that forced-gradient experiments can result in considerably different estimates of dispersivity compared to what can be found in natural-gradient systems for typical channel widths.

Traveling waves in a delayed SIR model with nonlocal dispersal and nonlinear incidence

NASA Astrophysics Data System (ADS)

Zhang, Shou-Peng; Yang, Yun-Rui; Zhou, Yong-Hui

2018-01-01

This paper is concerned with traveling waves of a delayed SIR model with nonlocal dispersal and a general nonlinear incidence. The existence and nonexistence of traveling waves of the system are established respectively by Schauder's fixed point theorem and two-sided Laplace transform. It is also shown that the spread speed c is influenced by the dispersal rate of the infected individuals and the delay τ.

Factors Regulating Early Life History Dispersal of Atlantic Cod (Gadus morhua) from Coastal Newfoundland

PubMed Central

Stanley, Ryan R. E.; deYoung, Brad; Snelgrove, Paul V. R.; Gregory, Robert S.

2013-01-01

To understand coastal dispersal dynamics of Atlantic cod (Gadus morhua), we examined spatiotemporal egg and larval abundance patterns in coastal Newfoundland. In recent decades, Smith Sound, Trinity Bay has supported the largest known overwintering spawning aggregation of Atlantic cod in the region. We estimated spawning and dispersal characteristics for the Smith Sound-Trinity Bay system by fitting ichthyoplankton abundance data to environmentally-driven, simplified box models. Results show protracted spawning, with sharply increased egg production in early July, and limited dispersal from the Sound. The model for the entire spawning season indicates egg export from Smith Sound is 13%•day−1 with a net mortality of 27%•day–1. Eggs and larvae are consistently found in western Trinity Bay with little advection from the system. These patterns mirror particle tracking models that suggest residence times of 10–20 days, and circulation models indicating local gyres in Trinity Bay that act in concert with upwelling dynamics to retain eggs and larvae. Our results are among the first quantitative dispersal estimates from Smith Sound, linking this spawning stock to the adjacent coastal waters. These results illustrate the biophysical interplay regulating dispersal and connectivity originating from inshore spawning of coastal northwest Atlantic. PMID:24058707

Lagrangian predictability characteristics of an Ocean Model

NASA Astrophysics Data System (ADS)

Lacorata, Guglielmo; Palatella, Luigi; Santoleri, Rosalia

2014-11-01

The Mediterranean Forecasting System (MFS) Ocean Model, provided by INGV, has been chosen as case study to analyze Lagrangian trajectory predictability by means of a dynamical systems approach. To this regard, numerical trajectories are tested against a large amount of Mediterranean drifter data, used as sample of the actual tracer dynamics across the sea. The separation rate of a trajectory pair is measured by computing the Finite-Scale Lyapunov Exponent (FSLE) of first and second kind. An additional kinematic Lagrangian model (KLM), suitably treated to avoid "sweeping"-related problems, has been nested into the MFS in order to recover, in a statistical sense, the velocity field contributions to pair particle dispersion, at mesoscale level, smoothed out by finite resolution effects. Some of the results emerging from this work are: (a) drifter pair dispersion displays Richardson's turbulent diffusion inside the [10-100] km range, while numerical simulations of MFS alone (i.e., without subgrid model) indicate exponential separation; (b) adding the subgrid model, model pair dispersion gets very close to observed data, indicating that KLM is effective in filling the energy "mesoscale gap" present in MFS velocity fields; (c) there exists a threshold size beyond which pair dispersion becomes weakly sensitive to the difference between model and "real" dynamics; (d) the whole methodology here presented can be used to quantify model errors and validate numerical current fields, as far as forecasts of Lagrangian dispersion are concerned.

Analytical nuclear gradients for the range-separated many-body dispersion model of noncovalent interactions.

PubMed

Blood-Forsythe, Martin A; Markovich, Thomas; DiStasio, Robert A; Car, Roberto; Aspuru-Guzik, Alán

2016-03-01

An accurate treatment of the long-range electron correlation energy, including van der Waals (vdW) or dispersion interactions, is essential for describing the structure, dynamics, and function of a wide variety of systems. Among the most accurate models for including dispersion into density functional theory (DFT) is the range-separated many-body dispersion (MBD) method [A. Ambrosetti et al. , J. Chem. Phys. , 2014, 140 , 18A508], in which the correlation energy is modeled at short-range by a semi-local density functional and at long-range by a model system of coupled quantum harmonic oscillators. In this work, we develop analytical gradients of the MBD energy with respect to nuclear coordinates, including all implicit coordinate dependencies arising from the partitioning of the charge density into Hirshfeld effective volumes. To demonstrate the efficiency and accuracy of these MBD gradients for geometry optimizations of systems with intermolecular and intramolecular interactions, we optimized conformers of the benzene dimer and isolated small peptides with aromatic side-chains. We find excellent agreement with the wavefunction theory reference geometries of these systems (at a fraction of the computational cost) and find that MBD consistently outperforms the popular TS and D3(BJ) dispersion corrections. To demonstrate the performance of the MBD model on a larger system with supramolecular interactions, we optimized the C 60 @C 60 H 28 buckyball catcher host-guest complex. In our analysis, we also find that neglecting the implicit nuclear coordinate dependence arising from the charge density partitioning, as has been done in prior numerical treatments, leads to an unacceptable error in the MBD forces, with relative errors of ∼20% (on average) that can extend well beyond 100%.

High-order FDTD methods for transverse electromagnetic systems in dispersive inhomogeneous media.

PubMed

Zhao, Shan

2011-08-15

This Letter introduces a novel finite-difference time-domain (FDTD) formulation for solving transverse electromagnetic systems in dispersive media. Based on the auxiliary differential equation approach, the Debye dispersion model is coupled with Maxwell's equations to derive a supplementary ordinary differential equation for describing the regularity changes in electromagnetic fields at the dispersive interface. The resulting time-dependent jump conditions are rigorously enforced in the FDTD discretization by means of the matched interface and boundary scheme. High-order convergences are numerically achieved for the first time in the literature in the FDTD simulations of dispersive inhomogeneous media. © 2011 Optical Society of America

Microcomputer pollution model for civilian airports and Air Force bases. Model description

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

Segal, H.M.; Hamilton, P.L.

1988-08-01

This is one of three reports describing the Emissions and Dispersion Modeling System (EDMS). EDMS is a complex source emissions/dispersion model for use at civilian airports and Air Force bases. It operates in both a refined and a screening mode and is programmed for an IBM-XT (or compatible) computer. This report--MODEL DESCRIPTION--provides the technical description of the model. It first identifies the key design features of both the emissions (EMISSMOD) and dispersion (GIMM) portions of EDMS. It then describes the type of meteorological information the dispersion model can accept and identifies the manner in which it preprocesses National Climatic Centermore » (NCC) data prior to a refined-model run. The report presents the results of running EDMS on a number of different microcomputers and compares EDMS results with those of comparable models. The appendices elaborate on the information noted above and list the source code.« less

Reactive solute transport in an asymmetric aquifer-aquitard system with scale-dependent dispersion

NASA Astrophysics Data System (ADS)

Zhou, R.; Zhan, H.

2017-12-01

Abstract: The understanding of reactive solute transport in an aquifer-aquitard system is important to study transport behavior in the more complex porous media. When transport properties are asymmetric in the upper and lower aquitards, reactive solute transport in such an aquifer-aquitard system becomes a coupled three domain problem that is more complex than the symmetric case in which the upper and lower aquitards have identical transport properties. Meanwhile, the dispersivity of transport in the aquifer is considered as a linear or exponential function of travel distance due to the heterogeneity of aquifer. This study proposed new transport models to describe reactive solute transport in such an asymmetric aquifer-aquitard system with scale-dependent dispersion. Mathematical models were developed for such problems under the first-type and third-type boundary conditions to analyze the spatial-temporal concentration and mass distribution in the aquifer and aquitards with the help of Laplace transform technique and the de Hoog numerical Laplace inversion method. Breakthrough curves (BTCs) and residence time distribution curves (RTDs) obtained from the models with scale-dependent dispersion, constant dispersion and constant effective dispersivity were compared to reflect the lumped scale-dispersion effect in the aquifer-aquitard system. The newly acquired solutions were then tested extensively against previous analytical and numerical solutions and were proven to be robust and accurate. Furthermore, to study the back diffusion of contaminant mass in aquitards, a zero-contaminant mass concentration boundary condition was imposed on the inlet boundary of the system after a certain time, which is also called the process of water flushing. The diffusion loss alone the aquifer/aquitard interfaces and mass stored ratio change in each of three domains (upper aquitard, aquifer, and lower aquitard) after water flushing provided an insightful and comprehensive analysis of transport behavior with asymmetric distribution of transport properties.

PHYSICAL AND NUMERICAL MODELING OF ASD EXHAUST DISPERSION AROUND HOUSES

EPA Science Inventory

The report discusses the use of a wind tunnel to physically model the dispersion of exhaust plumes from active soil depressurization (ASD) radon mitigation systems in houses. he testing studied the effects of exhaust location (grade level vs. above the eave), as house height, roo...

Dispersal, patch Leaving, and distribution of Homalodisca vitripennis (Hemiptera: Cicadellidae)

USDA-ARS?s Scientific Manuscript database

Influences on the dispersal, distribution, and residence times of the glassy-winged sharpshooter leafhopper, Homalodisca vitripennis (Germar), were measured to establish a model of leafhopper behavior. This model aids in the management and design of cropping systems to reduce Pierce’s disease in gr...

Effects of vertical shear in modelling horizontal oceanic dispersion

NASA Astrophysics Data System (ADS)

Lanotte, A. S.; Corrado, R.; Palatella, L.; Pizzigalli, C.; Schipa, I.; Santoleri, R.

2016-02-01

The effect of vertical shear on the horizontal dispersion properties of passive tracer particles on the continental shelf of the South Mediterranean is investigated by means of observation and model data. In situ current measurements reveal that vertical gradients of horizontal velocities in the upper mixing layer decorrelate quite fast ( ˜ 1 day), whereas an eddy-permitting ocean model, such as the Mediterranean Forecasting System, tends to overestimate such decorrelation time because of finite resolution effects. Horizontal dispersion, simulated by the Mediterranean sea Forecasting System, is mostly affected by: (1) unresolved scale motions, and mesoscale motions that are largely smoothed out at scales close to the grid spacing; (2) poorly resolved time variability in the profiles of the horizontal velocities in the upper layer. For the case study we have analysed, we show that a suitable use of deterministic kinematic parametrizations is helpful to implement realistic statistical features of tracer dispersion in two and three dimensions. The approach here suggested provides a functional tool to control the horizontal spreading of small organisms or substance concentrations, and is thus relevant for marine biology, pollutant dispersion as well as oil spill applications.

Highly Anisotropic Magnon Dispersion in Ca_{2}RuO_{4}: Evidence for Strong Spin Orbit Coupling.

PubMed

Kunkemöller, S; Khomskii, D; Steffens, P; Piovano, A; Nugroho, A A; Braden, M

2015-12-11

The magnon dispersion in Ca_{2}RuO_{4} has been determined by inelastic neutron scattering on single crytals containing 1% of Ti. The dispersion is well described by a conventional Heisenberg model suggesting a local moment model with nearest neighbor interaction of J=8  meV. Nearest and next-nearest neighbor interaction as well as interlayer coupling parameters are required to properly describe the entire dispersion. Spin-orbit coupling induces a very large anisotropy gap in the magnetic excitations in apparent contrast with a simple planar magnetic model. Orbital ordering breaking tetragonal symmetry, and strong spin-orbit coupling can thus be identified as important factors in this system.

Ensemble Simulations with Coupled Atmospheric Dynamic and Dispersion Models: Illustrating Uncertainties in Dosage Simulations.

NASA Astrophysics Data System (ADS)

Warner, Thomas T.; Sheu, Rong-Shyang; Bowers, James F.; Sykes, R. Ian; Dodd, Gregory C.; Henn, Douglas S.

2002-05-01

Ensemble simulations made using a coupled atmospheric dynamic model and a probabilistic Lagrangian puff dispersion model were employed in a forensic analysis of the transport and dispersion of a toxic gas that may have been released near Al Muthanna, Iraq, during the Gulf War. The ensemble study had two objectives, the first of which was to determine the sensitivity of the calculated dosage fields to the choices that must be made about the configuration of the atmospheric dynamic model. In this test, various choices were used for model physics representations and for the large-scale analyses that were used to construct the model initial and boundary conditions. The second study objective was to examine the dispersion model's ability to use ensemble inputs to predict dosage probability distributions. Here, the dispersion model was used with the ensemble mean fields from the individual atmospheric dynamic model runs, including the variability in the individual wind fields, to generate dosage probabilities. These are compared with the explicit dosage probabilities derived from the individual runs of the coupled modeling system. The results demonstrate that the specific choices made about the dynamic-model configuration and the large-scale analyses can have a large impact on the simulated dosages. For example, the area near the source that is exposed to a selected dosage threshold varies by up to a factor of 4 among members of the ensemble. The agreement between the explicit and ensemble dosage probabilities is relatively good for both low and high dosage levels. Although only one ensemble was considered in this study, the encouraging results suggest that a probabilistic dispersion model may be of value in quantifying the effects of uncertainties in a dynamic-model ensemble on dispersion model predictions of atmospheric transport and dispersion.

Epidemiology and population biology of pseudoperonospora cubensis: a model system for management of downy mildews

USDA-ARS?s Scientific Manuscript database

The resurgence of cucurbit downy mildew has dramatically influenced production of cucurbits and disease management systems at multiple scales. Long-distance dispersal is a fundamental aspect of epidemic development that influences the timing and extent of disease outbreaks. Dispersal potential of th...

Dynamics and profiles of a diffusive host-pathogen system with distinct dispersal rates

NASA Astrophysics Data System (ADS)

Wu, Yixiang; Zou, Xingfu

2018-04-01

In this paper, we investigate a diffusive host-pathogen model with heterogeneous parameters and distinct dispersal rates for the susceptible and infected hosts. We first prove that the solution of the model exists globally and the model system possesses a global attractor. We then identify the basic reproduction number R0 for the model and prove its threshold role: if R0 ≤ 1, the disease free equilibrium is globally asymptotically stable; if R0 > 1, the solution of the model is uniformly persistent and there exists a positive (pathogen persistent) steady state. Finally, we study the asymptotic profiles of the positive steady state as the dispersal rate of the susceptible or infected hosts approaches zero. Our result suggests that the infected hosts concentrate at certain points which can be characterized as the pathogen's most favoured sites when the mobility of the infected host is limited.

Simulating Sustainment for an Unmanned Logistics System Concept of Operation in Support of Distributed Operations

DTIC Science & Technology

2017-06-01

designed experiment to model and explore a ship-to-shore logistics process supporting dispersed units via three types of ULSs, which vary primarily in...systems, simulation, discrete event simulation, design of experiments, data analysis, simplekit, nearly orthogonal and balanced designs 15. NUMBER OF... designed experiment to model and explore a ship-to-shore logistics process supporting dispersed units via three types of ULSs, which vary primarily

Evaluation of a Mesoscale Atmospheric Dispersion Modeling System with Observations from the 1980 Great Plains Mesoscale Tracer Field Experiment. Part I: Datasets and Meteorological Simulations.

NASA Astrophysics Data System (ADS)

Moran, Michael D.; Pielke, Roger A.

1996-03-01

The Colorado State University mesoscale atmospheric dispersion (MAD) numerical modeling system, which consists of a prognostic mesoscale meteorological model coupled to a mesoscale Lagrangian particle dispersion model, has been used to simulate the transport and diffusion of a perfluorocarbon tracer-gas cloud for one afternoon surface release during the July 1980 Great Plains mesoscale tracer field experiment. Ground-level concentration (GLC) measurements taken along arcs of samplers 100 and 600 km downwind of the release site at Norman, Oklahoma, up to three days after the tracer release were available for comparison. Quantitative measures of a number of significant dispersion characteristics obtained from analysis of the observed tracer cloud's moving GLC `footprint' have been used to evaluate the modeling system's skill in simulating this MAD case.MAD is more dependent upon the spatial and temporal structure of the transport wind field than is short-range atmospheric dispersion. For the Great Plains mesoscale tracer experiment, the observations suggest that the Great Plains nocturnal low-level jet played an important role in transporting and deforming the tracer cloud. A suite of ten two- and three-dimensional numerical meteorological experiments was devised to investigate the relative contributions of topography, other surface inhomogeneities, atmospheric baroclinicity, synoptic-scale flow evolution, and meteorological model initialization time to the structure and evolution of the low-level mesoscale flow field and thus to MAD. Results from the ten mesoscale meteorological simulations are compared in this part of the paper. The predicted wind fields display significant differences, which give rise in turn to significant differences in predicted low-level transport. The presence of an oscillatory ageostrophic component in the observed synoptic low-level winds for this case is shown to complicate initialization of the meteorological model considerably and is the likely cause of directional errors in the predicted mean tracer transport. A companion paper describes the results from the associated dispersion simulations.

Dispersion Modeling in Complex Urban Systems

EPA Science Inventory

Models are used to represent real systems in an understandable way. They take many forms. A conceptual model explains the way a system works. In environmental studies, for example, a conceptual model may delineate all the factors and parameters for determining how a particle move...

Anisotropic Shear Dispersion Parameterization for Mesoscale Eddy Transport

NASA Astrophysics Data System (ADS)

Reckinger, S. J.; Fox-Kemper, B.

2016-02-01

The effects of mesoscale eddies are universally treated isotropically in general circulation models. However, the processes that the parameterization approximates, such as shear dispersion, typically have strongly anisotropic characteristics. The Gent-McWilliams/Redi mesoscale eddy parameterization is extended for anisotropy and tested using 1-degree Community Earth System Model (CESM) simulations. The sensitivity of the model to anisotropy includes a reduction of temperature and salinity biases, a deepening of the southern ocean mixed-layer depth, and improved ventilation of biogeochemical tracers, particularly in oxygen minimum zones. The parameterization is further extended to include the effects of unresolved shear dispersion, which sets the strength and direction of anisotropy. The shear dispersion parameterization is similar to drifter observations in spatial distribution of diffusivity and high-resolution model diagnosis in the distribution of eddy flux orientation.

Analysis of pressure spectra measurements in a ducted combustion system. Ph.D. Thesis - Toledo Univ.

NASA Technical Reports Server (NTRS)

Miles, J. H.

1980-01-01

Combustion noise propagation in an operating ducted liquid fuel combustion system is studied in relation to the development of combustion noise prediction and suppression techniques. The presence of combustor emissions in the duct is proposed as the primary mechanism producing the attenuation and dispersion of combustion noise propagating in an operating liquid fuel combustion system. First, a complex mathematical model for calculating attenuation and dispersion taking into account mass transfer, heat transfer, and viscosity effects due to the presence of liquid fuel droplets or solid soot particles is discussed. Next, a simpler single parameter model for calculating pressure auto-spectra and cross-spectra which takes into account dispersion and attenuation due to heat transfer between solid soot particles and air is developed. Then, auto-spectra and cross-spectra obtained from internal pressure measurements in a combustion system consisting of a J-47 combustor can, a spool piece, and a long duct are presented. Last, analytical results obtained with the single parameter model are compared with the experimental measurements. The single parameter model results are shown to be in excellent agreement with the measurements.

Analysis of pressure spectra measurements in a ducted combustion system

NASA Astrophysics Data System (ADS)

Miles, J. H.

1980-11-01

Combustion noise propagation in an operating ducted liquid fuel combustion system is studied in relation to the development of combustion noise prediction and suppression techniques. The presence of combustor emissions in the duct is proposed as the primary mechanism producing the attenuation and dispersion of combustion noise propagating in an operating liquid fuel combustion system. First, a complex mathematical model for calculating attenuation and dispersion taking into account mass transfer, heat transfer, and viscosity effects due to the presence of liquid fuel droplets or solid soot particles is discussed. Next, a simpler single parameter model for calculating pressure auto-spectra and cross-spectra which takes into account dispersion and attenuation due to heat transfer between solid soot particles and air is developed. Then, auto-spectra and cross-spectra obtained from internal pressure measurements in a combustion system consisting of a J-47 combustor can, a spool piece, and a long duct are presented. Last, analytical results obtained with the single parameter model are compared with the experimental measurements. The single parameter model results are shown to be in excellent agreement with the measurements.

Ecological systems as computer networks: Long distance sea dispersal as a communication medium between island plant populations.

PubMed

Sanaa, Adnen; Ben Abid, Samir; Boulila, Abdennacer; Messaoud, Chokri; Boussaid, Mohamed; Ben Fadhel, Najeh

2016-06-01

Ecological systems are known to exchange genetic material through animal species migration and seed dispersal for plants. Isolated plant populations have developed long distance dispersal as a means of propagation which rely on meteorological such as anemochory and hydrochory for coast, island and river bank dwelling species. Long distance dispersal by water, in particular, in the case of water current bound islands, calls for the analogy with computer networks, where each island and nearby mainland site plays the role of a network node, the water currents play the role of a transmission channel, and water borne seeds as data packets. In this paper we explore this analogy to model long distance dispersal of seeds among island and mainland populations, when traversed with water currents, in order to model and predict their future genetic diversity. The case of Pancratium maritimum L. populations in Tunisia is used as a proof of concept, where their genetic diversity is extrapolated. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Determining the turnover time of groundwater systems with the aid of environmental tracers. 1. Models and their applicability

NASA Astrophysics Data System (ADS)

Małoszewski, P.; Zuber, A.

1982-06-01

Three new lumped-parameter models have been developed for the interpretation of environmental radioisotope data in groundwater systems. Two of these models combine other simpler models, i.e. the piston flow model is combined either with the exponential model (exponential distribution of transit times) or with the linear model (linear distribution of transit times). The third model is based on a new solution to the dispersion equation which more adequately represents the real systems than the conventional solution generally applied so far. The applicability of models was tested by the reinterpretation of several known case studies (Modry Dul, Cheju Island, Rasche Spring and Grafendorf). It has been shown that two of these models, i.e. the exponential-piston flow model and the dispersive model give better fitting than other simpler models. Thus, the obtained values of turnover times are more reliable, whereas the additional fitting parameter gives some information about the structure of the system. In the examples considered, in spite of a lower number of fitting parameters, the new models gave practically the same fitting as the multiparameter finite state mixing-cell models. It has been shown that in the case of a constant tracer input a prior physical knowledge of the groundwater system is indispensable for determining the turnover time. The piston flow model commonly used for age determinations by the 14C method is an approximation applicable only in the cases of low dispersion. In some cases the stable-isotope method aids in the interpretation of systems containing mixed waters of different ages. However, when 14C method is used for mixed-water systems a serious mistake may arise by neglecting the different bicarbonate contents in particular water components.

A comparison of coupled freshwater-saltwater sharp-interface and convective-dispersive models of saltwater intrusion in a layered aquifer system

USGS Publications Warehouse

Hill, Mary C.

1988-01-01

Simulated results of the coupled freshwater-saltwater sharp interface and convective-dispersive numerical models are compared by using steady-state cross-sectional simulations. The results indicate that in some aquifers the calculated sharp interface is located further landward than would be expected.

RE-ENTRAINMENT AND DISPERSION OF EXHAUSTS FROM INDOOR RADON REDUCTION SYSTEMS: ANALYSIS OF TRACER GAS DATA

EPA Science Inventory

Tracer gas studies were conducted around four model houses in a wind tunnel, and around one house in the field, to quantify re-entrainment and dispersion of exhaust gases released from residential indoor radon reduction systems. Re-entrainment tests in the field suggest that acti...

Wave turbulence in shallow water models.

PubMed

Clark di Leoni, P; Cobelli, P J; Mininni, P D

2014-06-01

We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to 2048{2} points. In all simulations, the Froude number varies between 0.015 and 0.05, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, nonlinear waves are nondispersive and the spectrum of potential energy is compatible with ∼k{-2} scaling. For deeper (Boussinesq) flows, the nonlinear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, ∼k{-4/3}. In this latter case, the nonlinear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution.

Integration of AERMOD into EDMS

DOT National Transportation Integrated Search

2003-06-22

The Federal Aviation Administration (FAA) requires the use of the Emissions and : Dispersion Modeling System (EDMS) for air quality analysis involving aviation sources. : Dispersion in EDMS has previously been computed by CALINE3 and PAL2. With the :...

NEXT Ion Thruster Performance Dispersion Analyses

NASA Technical Reports Server (NTRS)

Soulas, George C.; Patterson, Michael J.

2008-01-01

The NEXT ion thruster is a low specific mass, high performance thruster with a nominal throttling range of 0.5 to 7 kW. Numerous engineering model and one prototype model thrusters have been manufactured and tested. Of significant importance to propulsion system performance is thruster-to-thruster performance dispersions. This type of information can provide a bandwidth of expected performance variations both on a thruster and a component level. Knowledge of these dispersions can be used to more conservatively predict thruster service life capability and thruster performance for mission planning, facilitate future thruster performance comparisons, and verify power processor capabilities are compatible with the thruster design. This study compiles the test results of five engineering model thrusters and one flight-like thruster to determine unit-to-unit dispersions in thruster performance. Component level performance dispersion analyses will include discharge chamber voltages, currents, and losses; accelerator currents, electron backstreaming limits, and perveance limits; and neutralizer keeper and coupling voltages and the spot-to-plume mode transition flow rates. Thruster level performance dispersion analyses will include thrust efficiency.

Amphibian sacculus and the forced Kuramoto model with intrinsic noise and frequency dispersion

NASA Astrophysics Data System (ADS)

Ji, Seung; Bozovic, Dolores; Bruinsma, Robijn

2018-04-01

The amphibian sacculus (AS) is an end organ that specializes in the detection of low-frequency auditory and vestibular signals. In this paper, we propose a model for the AS in the form of an array of phase oscillators with long-range coupling, subject to a steady load that suppresses spontaneous oscillations. The array is exposed to significant levels of frequency dispersion and intrinsic noise. We show that such an array can be a sensitive and robust subthreshold detector of low-frequency stimuli, though without significant frequency selectivity. The effects of intrinsic noise and frequency dispersion are contrasted. Intermediate levels of intrinsic noise greatly enhance the sensitivity through stochastic resonance. Frequency dispersion, on the other hand, only degrades detection sensitivity. However, frequency dispersion can play a useful role in terms of the suppression of spontaneous activity. As a model for the AS, the array parameters are such that the system is poised near a saddle-node bifurcation on an invariant circle. However, by a change of array parameters, the same system also can be poised near an emergent Andronov-Hopf bifurcation and thereby function as a frequency-selective detector.

Droplet size in flow: Theoretical model and application to polymer blends

NASA Astrophysics Data System (ADS)

Fortelný, Ivan; Jůza, Josef

2017-05-01

The paper is focused on prediction of the average droplet radius, R, in flowing polymer blends where the droplet size is determined by dynamic equilibrium between the droplet breakup and coalescence. Expressions for the droplet breakup frequency in systems with low and high contents of the dispersed phase are derived using available theoretical and experimental results for model blends. Dependences of the coalescence probability, Pc, on system parameters, following from recent theories, is considered and approximate equation for Pc in a system with a low polydispersity in the droplet size is proposed. Equations for R in systems with low and high contents of the dispersed phase are derived. Combination of these equations predicts realistic dependence of R on the volume fraction of dispersed droplets, φ. Theoretical prediction of the ratio of R to the critical droplet radius at breakup agrees fairly well with experimental values for steadily mixed polymer blends.

Simplified method for numerical modeling of fiber lasers.

PubMed

Shtyrina, O V; Yarutkina, I A; Fedoruk, M P

2014-12-29

A simplified numerical approach to modeling of dissipative dispersion-managed fiber lasers is examined. We present a new numerical iteration algorithm for finding the periodic solutions of the system of nonlinear ordinary differential equations describing the intra-cavity dynamics of the dissipative soliton characteristics in dispersion-managed fiber lasers. We demonstrate that results obtained using simplified model are in good agreement with full numerical modeling based on the corresponding partial differential equations.

Derivation of a Multiparameter Gamma Model for Analyzing the Residence-Time Distribution Function for Nonideal Flow Systems as an Alternative to the Advection-Dispersion Equation

DOE PAGES

Embry, Irucka; Roland, Victor; Agbaje, Oluropo; ...

2013-01-01

A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less

STS-1 operational flight profile. Volume 5: Descent, cycle 3. Appendix C: Monte Carlo dispersion analysis

NASA Technical Reports Server (NTRS)

1980-01-01

The results of three nonlinear the Monte Carlo dispersion analyses for the Space Transportation System 1 Flight (STS-1) Orbiter Descent Operational Flight Profile, Cycle 3 are presented. Fifty randomly selected simulation for the end of mission (EOM) descent, the abort once around (AOA) descent targeted line are steep target line, and the AOA descent targeted to the shallow target line are analyzed. These analyses compare the flight environment with system and operational constraints on the flight environment and in some cases use simplified system models as an aid in assessing the STS-1 descent flight profile. In addition, descent flight envelops are provided as a data base for use by system specialists to determine the flight readiness for STS-1. The results of these dispersion analyses supersede results of the dispersion analysis previously documented.

Testing fundamental physics with distant star clusters: theoretical models for pressure-supported stellar systems

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Baumgardt, Holger; Kroupa, Pavel; Grebel, Eva K.; Hilker, Michael; Jordi, Katrin

2009-05-01

We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N-body code N-MODY, which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 104 to 109Msolar and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime (ai, ae << a0), where the motion of stars is either dominated by internal accelerations (ai >> ae) or constant external accelerations (ae >> ai). In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime (ai ~ ae ~ a0). This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.

Atmospheric Dispersion about a Heavy Gas Vapor Detention System.

NASA Astrophysics Data System (ADS)

Shin, Seong-Hee

Dispersion of liquefied natural gas (LNG) in the event of an accidental spill is a major concern in LNG storage and transport safety planning, hazard response, and facility siting. Falcon Series large scale LNG spill experiments were planned by Lawrence Livermore National Laboratory (LLNL) for the Department of Transportation (DOT) and the Gas Research Institute (GRI) as part of a joint government/industry study in 1987 to evaluate the effectiveness of vapor fences as a mitigating technique for accidental release of LNG and to assist in validating wind tunnel and numerical methods for vapor dispersion simulation. Post-field-spill wind-tunnel experiments were performed in Environmental Wind Tunnel (EWT) (1988, 1989) to augment the LNG Vapor Fence Program data obtained during the Falcon Test Series. The program included four different model length scales and two different simulant gases. The purpose of this program is to provide a basis for the analysis of the simulation of physical modeling tests using proper physical modeling techniques and to assist in the development and verification of analytical models. Field data and model data were compared and analyzed by surface pattern comparisons and statistical methods. A layer-averaged slab model developed by Meroney et al. (1988) (FENC23) was expanded to evaluate an enhanced entrainment model proposed for dense gas dispersion including the effect of vapor barriers, and the numerical model was simulated for Falcon tests without the fence and with the vapor fence to examine the effectiveness of vapor detention system on heavy gas dispersion. Model data and the field data were compared with the numerical model data, and degree of similarity between data were assessed.

Molecular surface area based predictive models for the adsorption and diffusion of disperse dyes in polylactic acid matrix.

PubMed

Xu, Suxin; Chen, Jiangang; Wang, Bijia; Yang, Yiqi

2015-11-15

Two predictive models were presented for the adsorption affinities and diffusion coefficients of disperse dyes in polylactic acid matrix. Quantitative structure-sorption behavior relationship would not only provide insights into sorption process, but also enable rational engineering for desired properties. The thermodynamic and kinetic parameters for three disperse dyes were measured. The predictive model for adsorption affinity was based on two linear relationships derived by interpreting the experimental measurements with molecular structural parameters and compensation effect: ΔH° vs. dye size and ΔS° vs. ΔH°. Similarly, the predictive model for diffusion coefficient was based on two derived linear relationships: activation energy of diffusion vs. dye size and logarithm of pre-exponential factor vs. activation energy of diffusion. The only required parameters for both models are temperature and solvent accessible surface area of the dye molecule. These two predictive models were validated by testing the adsorption and diffusion properties of new disperse dyes. The models offer fairly good predictive ability. The linkage between structural parameter of disperse dyes and sorption behaviors might be generalized and extended to other similar polymer-penetrant systems. Copyright © 2015 Elsevier Inc. All rights reserved.

Operational atmospheric modeling system CARIS for effective emergency response associated with hazardous chemical releases in Korea.

PubMed

Kim, Cheol-Hee; Park, Jin-Ho; Park, Cheol-Jin; Na, Jin-Gyun

2004-03-01

The Chemical Accidents Response Information System (CARIS) was developed at the Center for Chemical Safety Management in South Korea in order to track and predict the dispersion of hazardous chemicals in the case of an accident or terrorist attack involving chemical companies. The main objective of CARIS is to facilitate an efficient emergency response to hazardous chemical accidents by rapidly providing key information in the decision-making process. In particular, the atmospheric modeling system implemented in CARIS, which is composed of a real-time numerical weather forecasting model and an air pollution dispersion model, can be used as a tool to forecast concentrations and to provide a wide range of assessments associated with various hazardous chemicals in real time. This article introduces the components of CARIS and describes its operational modeling system. Some examples of the operational modeling system and its use for emergency preparedness are presented and discussed. Finally, this article evaluates the current numerical weather prediction model for Korea.

Toward an Integrated Solution to Mitigate the Impact of Volcanic Ash to Aviation

NASA Technical Reports Server (NTRS)

Murray, John J.; Dezitter, Fabien; Fairlie, T. Duncan; Krotkov, Nickolay; Lekki, John; Lindsay, Francis; Pavolonis, Mike; Pieri, David; Prata, Fred; Vernier, Jean-Paul

2015-01-01

The science community is making a concerted effort to improve the reliability of dispersion models for the forecasting of volcanic ash plumes. Toward this end, it has been observed that the assimilation of diverse, accurate and frequent surface, airborne and satellite observations of the source and distal ash plumes may hold the key. Various international research organizations and operational agencies make these observations using a variety of active and passive remote sensing systems and use them to initialize atmospheric trajectory and dispersion models. These observation systems range from surface LIDAR and ceilometers, to airborne radiometers and nephelometers, to satellite radiometers, multi-spectral imagers, LIDAR and UV-photometers. None of these systems alone is a panacea, however, their synergistic application holds great promise toward solving this complex problem. Additionally, the aeronautical and science communities are working to better understand the quantitative thresholds and tolerances of aviation systems to volcanic ash to better inform scientists of the accuracy requirements for dispersion model forecasts. A number of the most recent and promising efforts in all of these area are discussed in this presentation.

Chaotic Lagrangian models for turbulent relative dispersion.

PubMed

Lacorata, Guglielmo; Vulpiani, Angelo

2017-04-01

A deterministic multiscale dynamical system is introduced and discussed as a prototype model for relative dispersion in stationary, homogeneous, and isotropic turbulence. Unlike stochastic diffusion models, here trajectory transport and mixing properties are entirely controlled by Lagrangian chaos. The anomalous "sweeping effect," a known drawback common to kinematic simulations, is removed through the use of quasi-Lagrangian coordinates. Lagrangian dispersion statistics of the model are accurately analyzed by computing the finite-scale Lyapunov exponent (FSLE), which is the optimal measure of the scaling properties of dispersion. FSLE scaling exponents provide a severe test to decide whether model simulations are in agreement with theoretical expectations and/or observation. The results of our numerical experiments cover a wide range of "Reynolds numbers" and show that chaotic deterministic flows can be very efficient, and numerically low-cost, models of turbulent trajectories in stationary, homogeneous, and isotropic conditions. The mathematics of the model is relatively simple, and, in a geophysical context, potential applications may regard small-scale parametrization issues in general circulation models, mixed layer, and/or boundary layer turbulence models as well as Lagrangian predictability studies.

Chaotic Lagrangian models for turbulent relative dispersion

NASA Astrophysics Data System (ADS)

Lacorata, Guglielmo; Vulpiani, Angelo

2017-04-01

A deterministic multiscale dynamical system is introduced and discussed as a prototype model for relative dispersion in stationary, homogeneous, and isotropic turbulence. Unlike stochastic diffusion models, here trajectory transport and mixing properties are entirely controlled by Lagrangian chaos. The anomalous "sweeping effect," a known drawback common to kinematic simulations, is removed through the use of quasi-Lagrangian coordinates. Lagrangian dispersion statistics of the model are accurately analyzed by computing the finite-scale Lyapunov exponent (FSLE), which is the optimal measure of the scaling properties of dispersion. FSLE scaling exponents provide a severe test to decide whether model simulations are in agreement with theoretical expectations and/or observation. The results of our numerical experiments cover a wide range of "Reynolds numbers" and show that chaotic deterministic flows can be very efficient, and numerically low-cost, models of turbulent trajectories in stationary, homogeneous, and isotropic conditions. The mathematics of the model is relatively simple, and, in a geophysical context, potential applications may regard small-scale parametrization issues in general circulation models, mixed layer, and/or boundary layer turbulence models as well as Lagrangian predictability studies.

Density-Dependent Formulation of Dispersion-Repulsion Interactions in Hybrid Multiscale Quantum/Molecular Mechanics (QM/MM) Models.

PubMed

Curutchet, Carles; Cupellini, Lorenzo; Kongsted, Jacob; Corni, Stefano; Frediani, Luca; Steindal, Arnfinn Hykkerud; Guido, Ciro A; Scalmani, Giovanni; Mennucci, Benedetta

2018-03-13

Mixed multiscale quantum/molecular mechanics (QM/MM) models are widely used to explore the structure, reactivity, and electronic properties of complex chemical systems. Whereas such models typically include electrostatics and potentially polarization in so-called electrostatic and polarizable embedding approaches, respectively, nonelectrostatic dispersion and repulsion interactions are instead commonly described through classical potentials despite their quantum mechanical origin. Here we present an extension of the Tkatchenko-Scheffler semiempirical van der Waals (vdW TS ) scheme aimed at describing dispersion and repulsion interactions between quantum and classical regions within a QM/MM polarizable embedding framework. Starting from the vdW TS expression, we define a dispersion and a repulsion term, both of them density-dependent and consistently based on a Lennard-Jones-like potential. We explore transferable atom type-based parametrization strategies for the MM parameters, based on either vdW TS calculations performed on isolated fragments or on a direct estimation of the parameters from atomic polarizabilities taken from a polarizable force field. We investigate the performance of the implementation by computing self-consistent interaction energies for the S22 benchmark set, designed to represent typical noncovalent interactions in biological systems, in both equilibrium and out-of-equilibrium geometries. Overall, our results suggest that the present implementation is a promising strategy to include dispersion and repulsion in multiscale QM/MM models incorporating their explicit dependence on the electronic density.

Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors

NASA Astrophysics Data System (ADS)

Kerr, Benjamin; Riley, Margaret A.; Feldman, Marcus W.; Bohannan, Brendan J. M.

2002-07-01

One of the central aims of ecology is to identify mechanisms that maintain biodiversity. Numerous theoretical models have shown that competing species can coexist if ecological processes such as dispersal, movement, and interaction occur over small spatial scales. In particular, this may be the case for non-transitive communities, that is, those without strict competitive hierarchies. The classic non-transitive system involves a community of three competing species satisfying a relationship similar to the children's game rock-paper-scissors, where rock crushes scissors, scissors cuts paper, and paper covers rock. Such relationships have been demonstrated in several natural systems. Some models predict that local interaction and dispersal are sufficient to ensure coexistence of all three species in such a community, whereas diversity is lost when ecological processes occur over larger scales. Here, we test these predictions empirically using a non-transitive model community containing three populations of Escherichia coli. We find that diversity is rapidly lost in our experimental community when dispersal and interaction occur over relatively large spatial scales, whereas all populations coexist when ecological processes are localized.

Microsatellite DNA Suggests that Group Size Affects Sex-biased Dispersal Patterns in Red Colobus Monkeys

PubMed Central

Miyamoto, Michael M.; Allen, Julie M.; Gogarten, Jan F.; Chapman, Colin A.

2013-01-01

Dispersal is a major life history trait of social organisms influencing the behavioral and genetic structure of their groups. Unfortunately, primate dispersal is difficult to quantify, because of the rarity of these events and our inability to ascertain if individuals dispersed or died when they disappear. Socioecological models have been partially developed to understand the ecological causes of different dispersal systems and their social consequences. However, these models have yielded confusing results when applied to folivores. The folivorous red colobus monkey (Procolobus rufomitratus) in Kibale National Park, Uganda is thought to exhibit female-biased dispersal, although both sexes have been observed to disperse and there remains considerable debate over the selective pressures favoring the transfers of males and females and the causes of variation in the proportion of each sex to leave the natal group. We circumvent this problem by using microsatellite DNA data to investigate the prediction that female dispersal will be more frequent in larger groups as compared to smaller ones. The rationale for this prediction is that red colobus exhibit increased within-group competition in bigger groups, which should favor higher female dispersal rates and ultimately lower female relatedness. Genetic data from two unequally sized neighboring groups of red colobus demonstrate increased female relatedness within the smaller group, suggesting females are less likely to disperse when there is less within-group competition. We suggest that the dispersal system is mediated to some degree by scramble competition and group size. Since red colobus group sizes have increased throughout Kibale by over 50% in the last decade, these changes may have major implications for the genetic structure and ultimately the population viability of this endangered primate. PMID:23307485

A coupled "AB" system: Rogue waves and modulation instabilities.

PubMed

Wu, C F; Grimshaw, R H J; Chow, K W; Chan, H N

2015-10-01

Rogue waves are unexpectedly large and localized displacements from an equilibrium position or an otherwise calm background. For the nonlinear Schrödinger (NLS) model widely used in fluid mechanics and optics, these waves can occur only when dispersion and nonlinearity are of the same sign, a regime of modulation instability. For coupled NLS equations, rogue waves will arise even if dispersion and nonlinearity are of opposite signs in each component as new regimes of modulation instability will appear in the coupled system. The same phenomenon will be demonstrated here for a coupled "AB" system, a wave-current interaction model describing baroclinic instability processes in geophysical flows. Indeed, the onset of modulation instability correlates precisely with the existence criterion for rogue waves for this system. Transitions from "elevation" rogue waves to "depression" rogue waves are elucidated analytically. The dispersion relation as a polynomial of the fourth order may possess double pairs of complex roots, leading to multiple configurations of rogue waves for a given set of input parameters. For special parameter regimes, the dispersion relation reduces to a cubic polynomial, allowing the existence criterion for rogue waves to be computed explicitly. Numerical tests correlating modulation instability and evolution of rogue waves were conducted.

SPRAYTRAN USER'S GUIDE: A GIS-BASED ATMOSPHERIC SPRAY DROPLET DISPERSION MODELING SYSTEM

EPA Science Inventory

The offsite drift of pesticide from spray operations is an ongoing source of concern. The SPRAY TRANsport (SPRAYTRAN) system, documented in this report, incorporates the near-field spray application model, AGDISP, into a meso-scale atmospheric transport model. The AGDISP model ...

Axial dispersion, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column by radiotracer residence time distribution analysis.

PubMed

Din, Ghiyas Ud; Chughtai, Imran Rafiq; Inayat, Mansoor Hameed; Khan, Iqbal Hussain

2008-12-01

Axial dispersion, holdup and slip velocity of dispersed phase have been investigated for a range of dispersed and continuous phase superficial velocities in a pulsed sieve plate extraction column using radiotracer residence time distribution (RTD) analysis. Axial dispersion model (ADM) was used to simulate the hydrodynamics of the system. It has been observed that increase in dispersed phase superficial velocity results in a decrease in its axial dispersion and increase in its slip velocity while its holdup increases till a maximum asymptotic value is achieved. An increase in superficial velocity of continuous phase increases the axial dispersion and holdup of dispersed phase until a maximum value is obtained, while slip velocity of dispersed phase is found to decrease in the beginning and then it increases with increase in superficial velocity of continuous phase.

Error estimates for (semi-)empirical dispersion terms and large biomacromolecules.

PubMed

Korth, Martin

2013-10-14

The first-principles modeling of biomaterials has made tremendous advances over the last few years with the ongoing growth of computing power and impressive developments in the application of density functional theory (DFT) codes to large systems. One important step forward was the development of dispersion corrections for DFT methods, which account for the otherwise neglected dispersive van der Waals (vdW) interactions. Approaches at different levels of theory exist, with the most often used (semi-)empirical ones based on pair-wise interatomic C6R(-6) terms. Similar terms are now also used in connection with semiempirical QM (SQM) methods and density functional tight binding methods (SCC-DFTB). Their basic structure equals the attractive term in Lennard-Jones potentials, common to most force field approaches, but they usually use some type of cutoff function to make the mixing of the (long-range) dispersion term with the already existing (short-range) dispersion and exchange-repulsion effects from the electronic structure theory methods possible. All these dispersion approximations were found to perform accurately for smaller systems, but error estimates for larger systems are very rare and completely missing for really large biomolecules. We derive such estimates for the dispersion terms of DFT, SQM and MM methods using error statistics for smaller systems and dispersion contribution estimates for the PDBbind database of protein-ligand interactions. We find that dispersion terms will usually not be a limiting factor for reaching chemical accuracy, though some force fields and large ligand sizes are problematic.

Boussinesq equations and other systems for small-amplitude long waves in nonlinear dispersive media: II. The nonlinear theory

NASA Astrophysics Data System (ADS)

Bona, J. L.; Chen, M.; Saut, J.-C.

2004-05-01

In part I of this work (Bona J L, Chen M and Saut J-C 2002 Boussinesq equations and other systems for small-amplitude long waves in nonlinear dispersive media I: Derivation and the linear theory J. Nonlinear Sci. 12 283-318), a four-parameter family of Boussinesq systems was derived to describe the propagation of surface water waves. Similar systems are expected to arise in other physical settings where the dominant aspects of propagation are a balance between the nonlinear effects of convection and the linear effects of frequency dispersion. In addition to deriving these systems, we determined in part I exactly which of them are linearly well posed in various natural function classes. It was argued that linear well-posedness is a natural necessary requirement for the possible physical relevance of the model in question. In this paper, it is shown that the first-order correct models that are linearly well posed are in fact locally nonlinearly well posed. Moreover, in certain specific cases, global well-posedness is established for physically relevant initial data. In part I, higher-order correct models were also derived. A preliminary analysis of a promising subclass of these models shows them to be well posed.

Quantum Drude oscillator model of atoms and molecules: Many-body polarization and dispersion interactions for atomistic simulation

NASA Astrophysics Data System (ADS)

Jones, Andrew P.; Crain, Jason; Sokhan, Vlad P.; Whitfield, Troy W.; Martyna, Glenn J.

2013-04-01

Treating both many-body polarization and dispersion interactions is now recognized as a key element in achieving the level of atomistic modeling required to reveal novel physics in complex systems. The quantum Drude oscillator (QDO), a Gaussian-based, coarse grained electronic structure model, captures both many-body polarization and dispersion and has linear scale computational complexity with system size, hence it is a leading candidate next-generation simulation method. Here, we investigate the extent to which the QDO treatment reproduces the desired long-range atomic and molecular properties. We present closed form expressions for leading order polarizabilities and dispersion coefficients and derive invariant (parameter-free) scaling relationships among multipole polarizability and many-body dispersion coefficients that arise due to the Gaussian nature of the model. We show that these “combining rules” hold to within a few percent for noble gas atoms, alkali metals, and simple (first-row hydride) molecules such as water; this is consistent with the surprising success that models with underlying Gaussian statistics often exhibit in physics. We present a diagrammatic Jastrow-type perturbation theory tailored to the QDO model that serves to illustrate the rich types of responses that the QDO approach engenders. QDO models for neon, argon, krypton, and xenon, designed to reproduce gas phase properties, are constructed and their condensed phase properties explored via linear scale diffusion Monte Carlo (DMC) and path integral molecular dynamics (PIMD) simulations. Good agreement with experimental data for structure, cohesive energy, and bulk modulus is found, demonstrating a degree of transferability that cannot be achieved using current empirical models or fully ab initio descriptions.

Modeling emulsification processes in rotary-disk mixers

NASA Astrophysics Data System (ADS)

Laponov, S. V.; Shulaev, N. S.; Ivanov, S. P.; Bondar', K. E.; Suleimanov, D. F.

2017-10-01

This article presents the experimental studies results of emulsification processes in liquid-liquid systems in rotary-disk mixers, allowing regulating the distribution of dispersed particles by changing the process conditions and the ratio of the dispersed phase. It is shown that with the increase of mixer’s revolutions per minute (RPM), both the size of dispersed particles and the deviation of dispersed particles sizes from the average decrease. The increase of the dispersed particles part results in the increase of particles average sizes at the current energy consumption. Discovered relationships can be used in the design of industrial equipment and laboratory research.

Velocity mapping and models of the elliptical galaxies NGC 720, NGC 1052, and NGC 4697

NASA Technical Reports Server (NTRS)

Binney, J. J.; Davies, Roger L.; Illingworth, Garth D.

1990-01-01

CCD surface photometry and extensive long-slit spectroscopy are used to construct detailed models of the flattened ellipticals NGC 720, 1052, and 4697. The models are combined with the Jeans equations to yield predicted fields of line-of-sight velocity dispersion and streaming velocity. By comparing these fields with observed velocities, it is concluded that none of these systems can have isotropic velocity dispersion tensors, and diminishing the assumed inclination of any given galaxy tends to decrease the line-of-sight velocity dispersion and, counterintuitively, to increase the line-of-sight rotation speeds. The ratio of the line-of-sight velocity dispersion along the minor axis to that along the major axis is found to be a sensitive diagnostic of the importance of a third integral for the galaxy's structure.

A necessary condition for dispersal driven growth of populations with discrete patch dynamics.

PubMed

Guiver, Chris; Packman, David; Townley, Stuart

2017-07-07

We revisit the question of when can dispersal-induced coupling between discrete sink populations cause overall population growth? Such a phenomenon is called dispersal driven growth and provides a simple explanation of how dispersal can allow populations to persist across discrete, spatially heterogeneous, environments even when individual patches are adverse or unfavourable. For two classes of mathematical models, one linear and one non-linear, we provide necessary conditions for dispersal driven growth in terms of the non-existence of a common linear Lyapunov function, which we describe. Our approach draws heavily upon the underlying positive dynamical systems structure. Our results apply to both discrete- and continuous-time models. The theory is illustrated with examples and both biological and mathematical conclusions are drawn. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Filling the Gaps: The Synergistic Application of Satellite Data for the Volcanic Ash Threat to Aviation

NASA Technical Reports Server (NTRS)

Murray, John; Vernier, Jean-Paul; Fairlie, T. Duncan; Pavolonis, Michael; Krotkov, Nickolay A.; Lindsay, Francis; Haynes, John

2013-01-01

Although significant progress has been made in recent years, estimating volcanic ash concentration for the full extent of the airspace affected by volcanic ash remains a challenge. No single satellite, airborne or ground observing system currently exists which can sufficiently inform dispersion models to provide the degree of accuracy required to use them with a high degree of confidence for routing aircraft in and near volcanic ash. Toward this end, the detection and characterization of volcanic ash in the atmosphere may be substantially improved by integrating a wider array of observing systems and advancements in trajectory and dispersion modeling to help solve this problem. The qualitative aspect of this effort has advanced significantly in the past decade due to the increase of highly complementary observational and model data currently available. Satellite observations, especially when coupled with trajectory and dispersion models can provide a very accurate picture of the 3-dimensional location of ash clouds. The accurate estimate of the mass loading at various locations throughout the entire plume, however improving, remains elusive. This paper examines the capabilities of various satellite observation systems and postulates that model-based volcanic ash concentration maps and forecasts might be significantly improved if the various extant satellite capabilities are used together with independent, accurate mass loading data from other observing systems available to calibrate (tune) ash concentration retrievals from the satellite systems.

Model-Based IN SITU Parameter Estimation of Ultrasonic Guided Waves in AN Isotropic Plate

NASA Astrophysics Data System (ADS)

Hall, James S.; Michaels, Jennifer E.

2010-02-01

Most ultrasonic systems employing guided waves for flaw detection require information such as dispersion curves, transducer locations, and expected propagation loss. Degraded system performance may result if assumed parameter values do not accurately reflect the actual environment. By characterizing the propagating environment in situ at the time of test, potentially erroneous a priori estimates are avoided and performance of ultrasonic guided wave systems can be improved. A four-part model-based algorithm is described in the context of previous work that estimates model parameters whereby an assumed propagation model is used to describe the received signals. This approach builds upon previous work by demonstrating the ability to estimate parameters for the case of single mode propagation. Performance is demonstrated on signals obtained from theoretical dispersion curves, finite element modeling, and experimental data.

A preliminary estimate of future communications traffic for the electric power system

NASA Technical Reports Server (NTRS)

Barnett, R. M.

1981-01-01

Diverse new generator technologies using renewable energy, and to improve operational efficiency throughout the existing electric power systems are presented. A description of a model utility and the information transfer requirements imposed by incorporation of dispersed storage and generation technologies and implementation of more extensive energy management are estimated. An example of possible traffic for an assumed system, and an approach that can be applied to other systems, control configurations, or dispersed storage and generation penetrations is provided.

Simulation of tracer dispersion from elevated and surface releases in complex terrain

NASA Astrophysics Data System (ADS)

Hernández, J. F.; Cremades, L.; Baldasano, J. M.

A new version of an advanced mesoscale dispersion modeling system for simulating passive air pollutant dispersion in the real atmospheric planetary boundary layer (PBL), is presented. The system comprises a diagnostic mass-consistent meteorological model and a Lagrangian particle dispersion model (LADISMO). The former version of LADISMO, developed according to Zannetti (Air pollution modelling, 1990), was based on the Monte Carlo technique and included calculation of higher-order moments of vertical random forcing for convective conditions. Its ability to simulate complex flow dispersion has been stated in a previous paper (Hernández et al. 1995, Atmospheric Environment, 29A, 1331-1341). The new version follows Thomson's scheme (1984, Q. Jl Roy. Met. Soc.110, 1107-1120). It is also based on Langevin equation and follows the ideas given by Brusasca et al. (1992, Atmospheric Environment26A, 707-723) and Anfossi et al. (1992, Nuovo Cemento 15c, 139-158). The model is used to simulate the dispersion and predict the ground level concentration (g.l.c.) of a tracer (SF 6) released from both an elevated source ( case a) and a ground level source ( case b) in a highly complex mountainous terrain during neutral and synoptically dominated conditions ( case a) and light and apparently stable conditions ( case b). The last case is considered as being a specially difficult task to simulate. In fact, few works have reported situations with valley drainage flows in complex terrains and real stable atmospheric conditions with weak winds. The model assumes that nearly calm situations associated to strong stability and air stagnation, make the lowest layers of PBL poorly diffusive (Brusasca et al., 1992, Atmospheric Environment26A, 707-723). Model results are verified against experimental data from Guardo-90 tracer experiments, an intensive field campaign conducted in the Carrion river valley (Northern Spain) to study atmospheric diffusion within a steep walled valley in mountainous terrain (Ibarra, 1992, Energia, No. 1, 74-85).

Three atmospheric dispersion experiments involving oil fog plumes measured by lidar

NASA Technical Reports Server (NTRS)

Eberhard, W. L.; Mcnice, G. T.; Troxel, S. W.

1986-01-01

The Wave Propagation Lab. participated with the U.S. Environmental Protection Agency in a series of experiments with the goal of developing and validating dispersion models that perform substantially better that models currently available. The lidar systems deployed and the data processing procedures used in these experiments are briefly described. Highlights are presented of conclusions drawn thus far from the lidar data.

Kinetics of the addition of olefins to Si-centered radicals: the critical role of dispersion interactions revealed by theory and experiment.

PubMed

Johnson, Erin R; Clarkin, Owen J; Dale, Stephen G; DiLabio, Gino A

2015-06-04

Solution-phase rate constants for the addition of selected olefins to the triethylsilyl and tris(trimethylsilyl)silyl radicals are measured using laser-flash photolysis and competition kinetics. The results are compared with predictions from density functional theory (DFT) calculations, both with and without dispersion corrections obtained from the exchange-hole dipole moment (XDM) model. Without a dispersion correction, the rate constants are consistently underestimated; the errors increase with system size, up to 10(6) s(-1) for the largest system considered. Dispersion interactions preferentially stabilize the transition states relative to the separated reactants and bring the DFT-calculated rate constants into excellent agreement with experiment. Thus, dispersion interactions are found to play a key role in determining the kinetics for addition reactions, particularly those involving sterically bulky functional groups.

The magnetotelluric response over 2D media with resistivity frequency dispersion

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

Mauriello, P.; Patella, D.; Siniscalchi, A.

1996-09-01

The authors investigate the magnetotelluric response of two-dimensional bodies, characterized by the presence of low-frequency dispersion phenomena of the electrical parameters. The Cole-Cole dispersion model is assumed to represent the frequency dependence of the impedivity complex function, defined as the inverse of Stoyer`s admittivity complex parameter. To simulate real geological situations, they consider three structural models, representing a sedimentary basin, a geothermal system and a magma chamber, assumed to be partially or totally dispersive. From a detailed study of the frequency and space behaviors of the magnetotelluric parameters, taking known non-dispersive results as reference, they outline the main peculiarities ofmore » the local distortion effects, caused by the presence of dispersion in the target media. Finally, they discuss the interpretive errors which can be made by neglecting the dispersion phenomena. The apparent dispersion function, which was defined in a previous paper to describe similar effects in the one-dimensional case, is again used as a reliable indicator of location, shape and spatial extent of the dispersive bodies. The general result of this study is a marked improvement in the resolution power of the magnetotelluric method.« less

Modelling threats to water quality from fire suppression chemicals and post-fire erosion

NASA Astrophysics Data System (ADS)

Hyde, Kevin; Ziemniak, Chris; Elliot, William; Samuels, William

2014-05-01

Misapplication of fire retardant chemicals into streams and rivers may threaten aquatic life. The possible threat depends on the contaminant concentration that, in part, is controlled by dispersion within flowing water. In the event of a misapplication, methods are needed to rapidly estimate the chemical mass entering the waterway and the dispersion and transport within the system. Here we demonstrate a new tool that calculates the chemical mass based on aircraft delivery system, fire chemical type, and stream and intersect geometry. The estimated mass is intended to be transferred into a GIS module that uses real-time stream data to map and simulate the dispersion and transport downstream. This system currently accounts only for aqueous transport. We envision that the GIS module can be modified to incorporate sediment transport, specifically to model movement of sediments from post-fire erosion. This modification could support assessment of threats of post-fire erosion to water quality and water supply systems.

Numerical model of the circulation and dispersion in the east Adriatic coastal waters

NASA Astrophysics Data System (ADS)

Beg Paklar, Gordana; Dzoic, Tomislav; Koracin, Darko; Matijevic, Slavica; Grbec, Branka; Ivatek-Sahdan, Stjepan

2017-04-01

The Regional Ocean Modeling System (ROMS) was implemented to reproduce physical properties of the area around submarine outlet Stobrec in the middle Adriatic coastal area. ROMS model run was forced with realistic atmospheric fields obtained from meteorological model Aladin, climatological river discharges, tides and dynamics of the surrounding area imposed at the open boundaries. Atmospheric forcing included momentum, heat and water fluxes calculated interactively from the Aladin surface fields during ROMS model simulations. Simulated fields from the Adriatic and shelf scale models were used to prescribe the initial and open boundary conditions for fine resolution coastal domain. Model results were compared with available CTD measurements and discussed in the light of the climatological circulation and thermohaline properties of the middle Adriatic coastal area. Variability in the circulation is related to the prevailing atmospheric conditions, changes in the hydrological conditions and water mass exchange at the open boundaries. Basic features of the coastal circulation are well reproduced by the ROMS model, as well as temperatures and salinities which are within corresponding seasonal intervals, although with lower stratification than measured ones. In order to reproduce dispersion of the passive tracer the ROMS model was coupled with Lagrangian dispersion model. Multiyear monitoring of the physical, chemical and biological parameters around the sewage outlet was used to assess the quality of the dispersion model results. Among measured parameters, redox potential of the surface sediment layer was selected to be compared with model results as its negative values are direct consequence of increased organic matter input that can be attributed to the sewage system inflow.

Dispersion-convolution model for simulating peaks in a flow injection system.

PubMed

Pai, Su-Cheng; Lai, Yee-Hwong; Chiao, Ling-Yun; Yu, Tiing

2007-01-12

A dispersion-convolution model is proposed for simulating peak shapes in a single-line flow injection system. It is based on the assumption that an injected sample plug is expanded due to a "bulk" dispersion mechanism along the length coordinate, and that after traveling over a distance or a period of time, the sample zone will develop into a Gaussian-like distribution. This spatial pattern is further transformed to a temporal coordinate by a convolution process, and finally a temporal peak image is generated. The feasibility of the proposed model has been examined by experiments with various coil lengths, sample sizes and pumping rates. An empirical dispersion coefficient (D*) can be estimated by using the observed peak position, height and area (tp*, h* and At*) from a recorder. An empirical temporal shift (Phi*) can be further approximated by Phi*=D*/u2, which becomes an important parameter in the restoration of experimental peaks. Also, the dispersion coefficient can be expressed as a second-order polynomial function of the pumping rate Q, for which D*(Q)=delta0+delta1Q+delta2Q2. The optimal dispersion occurs at a pumping rate of Qopt=sqrt[delta0/delta2]. This explains the interesting "Nike-swoosh" relationship between the peak height and pumping rate. The excellent coherence of theoretical and experimental peak shapes confirms that the temporal distortion effect is the dominating reason to explain the peak asymmetry in flow injection analysis.

Steady Shear Viscosities of Two Hard Sphere Colloidal Dispersions

NASA Astrophysics Data System (ADS)

Cheng, Zhengdong; Chaikin, Paul M.; Phan, See-Eng; Russel, William B.; Zhu, Jixiang

1996-03-01

Though hard spheres have the simplest inter-particle potential, the many body hydrodynamic interactions are complex and the rheological properties of dispersions are not fully understood in the concentrated regime. We studied two model systems: colloidal poly-(Methyl Methacrylate) spheres with a grafted layer of poly-(12-hydroxy stearic acid) (PMMA/PHSA) and spherical Silica particles (PST-5, Nissan Chemical Industries, Ltd, Tokyo, Japan). Steady shear viscosities were measured by a Zimm viscometer. The high shear relative viscosity of the dispersions compares well with other hard sphere systems, but the low shear relative viscosity of PMMA/PHSA dispersions is η / η 0 = 50 at φ = 0.5 , higher than η / η 0 = 22 for other hard sphere systems, consistent with recently published data (Phys. Rev. Lett. 75(1995)958). Bare Silica spheres are used to clarify the effect of the grafted layer. With the silica spheres, volume fraction can be determined independent of intrinsic viscosity measurements; also, higher concentrated dispersions can be made.

Longitudinal dispersion coefficients for numerical modeling of groundwater solute transport in heterogeneous formations

NASA Astrophysics Data System (ADS)

Lee, Jonghyun; Rolle, Massimo; Kitanidis, Peter K.

2018-05-01

Most recent research on hydrodynamic dispersion in porous media has focused on whole-domain dispersion while other research is largely on laboratory-scale dispersion. This work focuses on the contribution of a single block in a numerical model to dispersion. Variability of fluid velocity and concentration within a block is not resolved and the combined spreading effect is approximated using resolved quantities and macroscopic parameters. This applies whether the formation is modeled as homogeneous or discretized into homogeneous blocks but the emphasis here being on the latter. The process of dispersion is typically described through the Fickian model, i.e., the dispersive flux is proportional to the gradient of the resolved concentration, commonly with the Scheidegger parameterization, which is a particular way to compute the dispersion coefficients utilizing dispersivity coefficients. Although such parameterization is by far the most commonly used in solute transport applications, its validity has been questioned. Here, our goal is to investigate the effects of heterogeneity and mass transfer limitations on block-scale longitudinal dispersion and to evaluate under which conditions the Scheidegger parameterization is valid. We compute the relaxation time or memory of the system; changes in time with periods larger than the relaxation time are gradually leading to a condition of local equilibrium under which dispersion is Fickian. The method we use requires the solution of a steady-state advection-dispersion equation, and thus is computationally efficient, and applicable to any heterogeneous hydraulic conductivity K field without requiring statistical or structural assumptions. The method was validated by comparing with other approaches such as the moment analysis and the first order perturbation method. We investigate the impact of heterogeneity, both in degree and structure, on the longitudinal dispersion coefficient and then discuss the role of local dispersion and mass transfer limitations, i.e., the exchange of mass between the permeable matrix and the low permeability inclusions. We illustrate the physical meaning of the method and we show how the block longitudinal dispersivity approaches, under certain conditions, the Scheidegger limit at large Péclet numbers. Lastly, we discuss the potential and limitations of the method to accurately describe dispersion in solute transport applications in heterogeneous aquifers.

A dispersion model for predicting the extent of starch liquefaction by Bacillus licheniformis alpha-amylase during reactive extrusion.

PubMed

Komolprasert, V; Ofoli, R Y

1991-03-25

A Baker-Perkins corotating twin screw extruder was used as a bioreactor to hydrolyze pregelantinized corn starch by themophilic Bacillus licheniformis alpha-amylase. The extruder was modeled as a tube, and characterized as a closed system. This characterization is not in the thermodynamic sense; rather, it relates to the profile of a tracer fluid upon entry to and exit from the reaction zone. The reaction kinetics were modeled by a modified first-order equation, which allowed the dispersion equation to be solved analytically with the Danckwerts boundary condition. Data from several extrusion runs were super-imposed to obtain a profile to evaluate the model. The dispersion number, determined from the first and second moments of the RTD curve, was primarily a function of the length of the reaction zone. There was good agreement between predictions and experimental data, especially at low dispersion numbers. In general, the axial dispersion model appears to be suitable for analysis of enzymatic reactions of up to 30% conversion. At a fixed flow rate and constant temperature, the extent of starch conversion depends significantly on moisture content, residence time and enzyme dosage, but not on screw speed.

Vibration suppression in flexible structures via the sliding-mode control approach

NASA Technical Reports Server (NTRS)

Drakunov, S.; Oezguener, Uemit

1994-01-01

Sliding mode control became very popular recently because it makes the closed loop system highly insensitive to external disturbances and parameter variations. Sliding algorithms for flexible structures have been used previously, but these were based on finite-dimensional models. An extension of this approach for differential-difference systems is obtained. That makes if possible to apply sliding-mode control algorithms to the variety of nondispersive flexible structures which can be described as differential-difference systems. The main idea of using this technique for dispersive structures is to reduce the order of the controlled part of the system by applying an integral transformation. We can say that transformation 'absorbs' the dispersive properties of the flexible structure as the controlled part becomes dispersive.

Modeling and simulations of carbon nanotube (CNT) dispersion in water/surfactant/polymer systems

NASA Astrophysics Data System (ADS)

Uddin, Nasir Mohammad

An innovative multiscale (atomistic to mesoscale) model capable of predicting carbon nanotube (CNT) interactions and dispersion in water/surfactant/polymer systems was developed. The model was verified qualitatively with available experimental data in the literature. It can be used to computationally screen potential surfactants, solvents, polymers, and CNT with appropriate diameter and length to obtain improved CNT dispersion in aqueous medium. Thus the model would facilitate the reduction of time and cost required to produce CNT dispersed homogeneous solutions and CNT reinforced materials. CNT dispersion in any water/surfactant/polymer system depends on interactions between CNTs and surrounding molecules. Central to the study was the atomistic scale model which used the atomic structure of the surfactant, solvent, polymer, and CNT. The model was capable of predicting the CNT interactions in terms of potential of mean force (PMF) between CNTs under the influence of surrounding molecules in an aqueous solution. On the atomistic scale, molecular dynamics method was used to compute the PMF as a function of CNT separation and CNT alignment. An adaptive biasing force (ABF) method was used to speed up the calculations. Correlations were developed to determine the effective interactions between CNTs as a function of their any inter-atomic distance and orientation angle in water as well as in water/surfactant by fitting the calculated PMF data. On the mesoscale, the fitted PMF correlations were used as input in the Monte Carlo simulations to determine the degree of dispersion of CNTs in water and water/surfactant system. The distribution of CNT cluster size was determined for the CNTs dispersed in water with and without surfactant addition. The entropie and enthalpie contributions to the CNT interactions in water were determined to understand the dispersion mechanism of CNTs in water. The effects of CNT orientation, length, diameter, chirality and surfactant concentrations and structures on CNT interactions in water were investigated at room conditions. CNT interactions in polymer solution were also investigated with polyethylene oxide (PEO) polymer and water as a solvent. In all cases, the atomic arrangement of molecules was discussed in detailed. Simulations revealed that CNT orientation, length, diameter, and addition of surfactant and its structures can significantly affect CNT interactions (i.e., PMFs varied significantly) and in-turn the degree of CNT dispersion in aqueous solution. For all simulation cases, a uniform sampling was achieved by using the ABF method to calculate the governing PMF between CNTs indicating the effectiveness and convergence of the adaptive sampling scheme. The surfactant molecules were shown to adsorb at the CNT surface and contribute to weaker interactions between CNTs which resulted less CNT aggregate size at the mesoscale. Surfactant consisting with a benzene ring contributed much weaker interactions between CNTs as compared with that of without benzene ring. The increase in CNT length contributed the stronger CNT interactions where the increase in CNT diameter caused weaker CNT interactions in water. The interfacial characteristics between the CNT, surfactant and the polymer were also predicted and discussed. The model can be expanded for more solvents, surfactants, and polymers.

Pharmaceutical grade phyllosilicate dispersions: the influence of shear history on floc structure.

PubMed

Viseras, C; Meeten, G H; Lopez-Galindo, A

1999-05-10

The effect of mixing conditions on the flow curves of some clay-water dispersions was studied. Two Spanish fibrous phyllosilicates (sepiolite from Vicálvaro and palygorskite from Turón) and a commercial bentonite (Bentopharm Copyright, UK) were selected as model clays. The disperse systems were made up using a rotor-stator mixer working at two different mixing rates (1000 and 8000 rpm), for periods of 1 and 10 min. Rheological measurements were taken and the corresponding flow curves obtained immediately after interposition and then after a period of 24 h under low shear caused by a roller apparatus. Aqueous sepiolite dispersions showed the highest viscosity and were easily interposed, whereas palygorskite dispersions were more difficult to obtain, resulting in low to medium viscosity gels. Bentonite dispersions provided medium viscosity systems, which greatly increased their viscosity after the low shear treatment (as a result of swelling), whereas the viscosity of the fibrous clays stayed at approximately the same values or even decreased. A linear relation was found between mixing energy and apparent viscosity in the bentonite systems, while apparent viscosity in the sepiolite samples was related to mixing power, with minor influence of mixing times. All the systems studied had thixotropic behaviour, changing from clearly positive to even negative thixotropy in some palygorskite systems. Finally, we studied the effect of drastic pH changes on the system structure. Results showed that rheological properties were highly sensitive to pH in the fibrous dispersions, but less sensitive behaviour was found in the laminar clay systems. Copyright.

Average dispersal success: linking home range, dispersal, and metapopulation dynamics to reserve design.

PubMed

Fagan, William F; Lutscher, Frithjof

2006-04-01

Spatially explicit models for populations are often difficult to tackle mathematically and, in addition, require detailed data on individual movement behavior that are not easily obtained. An approximation known as the "average dispersal success" provides a tool for converting complex models, which may include stage structure and a mechanistic description of dispersal, into a simple matrix model. This simpler matrix model has two key advantages. First, it is easier to parameterize from the types of empirical data typically available to conservation biologists, such as survivorship, fecundity, and the fraction of juveniles produced in a study area that also recruit within the study area. Second, it is more amenable to theoretical investigation. Here, we use the average dispersal success approximation to develop estimates of the critical reserve size for systems comprising single patches or simple metapopulations. The quantitative approach can be used for both plants and animals; however, to provide a concrete example of the technique's utility, we focus on a special case pertinent to animals. Specifically, for territorial animals, we can characterize such an estimate of minimum viable habitat area in terms of the number of home ranges that the reserve contains. Consequently, the average dispersal success framework provides a framework through which home range size, natal dispersal distances, and metapopulation dynamics can be linked to reserve design. We briefly illustrate the approach using empirical data for the swift fox (Vulpes velox).

Analysis of an anisotropic coastal aquifer system using variable-density flow and solute transport simulation

USGS Publications Warehouse

Souza, W.R.; Voss, C.I.

1987-01-01

The groundwater system in southern Oahu, Hawaii consists of a thick, areally extensive freshwater lens overlying a zone of transition to a thick saltwater body. This system is analyzed in cross section with a variable-density groundwater flow and solute transport model on a regional scale. The simulation is difficult, because the coastal aquifer system has a saltwater transition zone that is broadly dispersed near the discharge area, but is very sharply defined inland. Steady-state simulation analysis of the transition zone in the layered basalt aquifer of southern Oahu indicates that a small transverse dispersivity is characteristic of horizontal regional flow. Further, in this system flow is generally parallel to isochlors and steady-state behavior is insensitive to the longitudinal dispersivity. Parameter analysis identifies that only six parameters control the complex hydraulics of the system: horizontal and vertical hydraulic conductivity of the basalt aquifer; hydraulic conductivity of the confining "caprock" layer; leakance below the caprock; specific yield; and aquifer matrix compressibility. The best-fitting models indicate the horizontal hydraulic conductivity is significantly greater than the vertical hydraulic conductivity. These models give values for specific yield and aquifer compressibility which imply a considerable degree of compressive storage in the water table aquifer. ?? 1987.

Temporal self-splitting of optical pulses

NASA Astrophysics Data System (ADS)

Ding, Chaoliang; Koivurova, Matias; Turunen, Jari; Pan, Liuzhan

2018-05-01

We present mathematical models for temporally and spectrally partially coherent pulse trains with Laguerre-Gaussian and Hermite-Gaussian Schell-model statistics as extensions of the standard Gaussian Schell model for pulse trains. We derive propagation formulas of both classes of pulsed fields in linearly dispersive media and in temporal optical systems. It is found that, in general, both types of fields exhibit time-domain self-splitting upon propagation. The Laguerre-Gaussian model leads to multiply peaked pulses, while the Hermite-Gaussian model leads to doubly peaked pulses, in the temporal far field (in dispersive media) or at the Fourier plane of a temporal system. In both model fields the character of the self-splitting phenomenon depends both on the degree of temporal and spectral coherence and on the power spectrum of the field.

Short-term emergency response planning and risk assessment via an integrated modeling system for nuclear power plants in complex terrain

NASA Astrophysics Data System (ADS)

Chang, Ni-Bin; Weng, Yu-Chi

2013-03-01

Short-term predictions of potential impacts from accidental release of various radionuclides at nuclear power plants are acutely needed, especially after the Fukushima accident in Japan. An integrated modeling system that provides expert services to assess the consequences of accidental or intentional releases of radioactive materials to the atmosphere has received wide attention. These scenarios can be initiated either by accident due to human, software, or mechanical failures, or from intentional acts such as sabotage and radiological dispersal devices. Stringent action might be required just minutes after the occurrence of accidental or intentional release. To fulfill the basic functions of emergency preparedness and response systems, previous studies seldom consider the suitability of air pollutant dispersion models or the connectivity between source term, dispersion, and exposure assessment models in a holistic context for decision support. Therefore, the Gaussian plume and puff models, which are only suitable for illustrating neutral air pollutants in flat terrain conditional to limited meteorological situations, are frequently used to predict the impact from accidental release of industrial sources. In situations with complex terrain or special meteorological conditions, the proposing emergency response actions might be questionable and even intractable to decisionmakers responsible for maintaining public health and environmental quality. This study is a preliminary effort to integrate the source term, dispersion, and exposure assessment models into a Spatial Decision Support System (SDSS) to tackle the complex issues for short-term emergency response planning and risk assessment at nuclear power plants. Through a series model screening procedures, we found that the diagnostic (objective) wind field model with the aid of sufficient on-site meteorological monitoring data was the most applicable model to promptly address the trend of local wind field patterns. However, most of the hazardous materials being released into the environment from nuclear power plants are not neutral pollutants, so the particle and multi-segment puff models can be regarded as the most suitable models to incorporate into the output of the diagnostic wind field model in a modern emergency preparedness and response system. The proposed SDSS illustrates the state-of-the-art system design based on the situation of complex terrain in South Taiwan. This system design of SDSS with 3-dimensional animation capability using a tailored source term model in connection with ArcView® Geographical Information System map layers and remote sensing images is useful for meeting the design goal of nuclear power plants located in complex terrain.

Ultrafine particles dispersion modeling in a street canyon: development and evaluation of a composite lattice Boltzmann model.

PubMed

Habilomatis, George; Chaloulakou, Archontoula

2013-10-01

Recently, a branch of particulate matter research concerns on ultrafine particles found in the urban environment, which originate, to a significant extent, from traffic sources. In urban street canyons, dispersion of ultrafine particles affects pedestrian's short term exposure and resident's long term exposure as well. The aim of the present work is the development and the evaluation of a composite lattice Boltzmann model to study the dispersion of ultrafine particles, in urban street canyon microenvironment. The proposed model has the potential to penetrate into the physics of this complex system. In order to evaluate the model performance against suitable experimental data, ultrafine particles levels have been monitored on an hourly basis for a period of 35 days, in a street canyon, in Athens area. The results of the comparative analysis are quite satisfactory. Furthermore, our modeled results are in a good agreement with the results of other computational and experimental studies. This work is a first attempt to study the dispersion of an air pollutant by application of the lattice Boltzmann method. Copyright © 2013 Elsevier B.V. All rights reserved.

Finite-element time-domain modeling of electromagnetic data in general dispersive medium using adaptive Padé series

NASA Astrophysics Data System (ADS)

Cai, Hongzhu; Hu, Xiangyun; Xiong, Bin; Zhdanov, Michael S.

2017-12-01

The induced polarization (IP) method has been widely used in geophysical exploration to identify the chargeable targets such as mineral deposits. The inversion of the IP data requires modeling the IP response of 3D dispersive conductive structures. We have developed an edge-based finite-element time-domain (FETD) modeling method to simulate the electromagnetic (EM) fields in 3D dispersive medium. We solve the vector Helmholtz equation for total electric field using the edge-based finite-element method with an unstructured tetrahedral mesh. We adopt the backward propagation Euler method, which is unconditionally stable, with semi-adaptive time stepping for the time domain discretization. We use the direct solver based on a sparse LU decomposition to solve the system of equations. We consider the Cole-Cole model in order to take into account the frequency-dependent conductivity dispersion. The Cole-Cole conductivity model in frequency domain is expanded using a truncated Padé series with adaptive selection of the center frequency of the series for early and late time. This approach can significantly increase the accuracy of FETD modeling.

Decoupling of epitaxial graphene via gold intercalation probed by dispersive Raman spectroscopy

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

Pillai, P. B., E-mail: p.pillai@sheffield.ac.uk, E-mail: m.desouza@sheffield.ac.uk; DeSouza, M., E-mail: p.pillai@sheffield.ac.uk, E-mail: m.desouza@sheffield.ac.uk; Narula, R.

Signatures of a superlattice structure composed of a quasi periodic arrangement of atomic gold clusters below an epitaxied graphene (EG) layer are examined using dispersive Raman spectroscopy. The gold-graphene system exhibits a laser excitation energy dependant red shift of the 2D mode as compared to pristine epitaxial graphene. The phonon dispersions in both the systems are mapped using the experimentally observed Raman signatures and a third-nearest neighbour tight binding electronic band structure model. Our results reveal that the observed excitation dependent Raman red shift in gold EG primarily arise from the modifications of the phonon dispersion in gold-graphene and showsmore » that the extent of decoupling of graphene from the underlying SiC substrate can be monitored from the dispersive nature of the Raman 2D modes. The intercalated gold atoms restore the phonon band structure of epitaxial graphene towards free standing graphene.« less

Modelling of pollen dispersion in the atmosphere: evaluation with a continuous 1β+1δ lidar

NASA Astrophysics Data System (ADS)

Sicard, Michaël; Izquierdo, Rebeca; Jorba, Oriol; Alarcón, Marta; Belmonte, Jordina; Comerón, Adolfo; De Linares, Concepción; Baldasano, José Maria

2018-04-01

Pollen allergenicity plays an important role on human health and wellness. It is thus of large public interest to increase our knowledge of pollen grain behavior in the atmosphere (source, emission, processes involved during their transport, etc.) at fine temporal and spatial scales. First simulations with the Barcelona Supercomputing Center NMMB/BSC-CTM model of Platanus and Pinus dispersion in the atmosphere were performed during a 5-day pollination event observed in Barcelona, Spain, between 27 - 31 March, 2015. The simulations are compared to vertical profiles measured with the continuous Barcelona Micro Pulse Lidar system. First results show that the vertical distribution is well reproduced by the model in shape, but not in intensity, the model largely underestimating in the afternoon. Guidelines are proposed to improve the dispersion of airborne pollen by numerical prediction models.

Engineering ultra-flattened normal dispersion photonic crystal fiber with silica material

NASA Astrophysics Data System (ADS)

Ferhat, Mohamed Lamine; Cherbi, Lynda; Bahloul, Lies; Hariz, Abdelhafid

2017-05-01

The tailoring of the group velocity dispersion (GVD) of an optical fiber is critical in many applications, influence on the bandwidth of information transmission in optical communication systems, successful utilization of nonlinear optical properties in applications such as supercontinuum generation, wavelength conversion and harmonic generation via stimulated Raman scattering ...In this work, we propose a design of ultra-flattened photonic crystal fiber by changing the diameter of the air holes of the cladding rings. The geometry is composed of only four rings, hexagonal structure of air holes and silica as background of the solid core. As a result, we present structures with broadband flat normal dispersion on many wavelengths bands useful for several applications. We obtain flat normal dispersion over 1000 nm broadband flat normal dispersion below -7 [ps/nm.km], and ultra-flat near zero normal dispersion below -0.2 [ps/nm.km] over 150 nm. The modeled photonic crystal fiber would be valuable for the fabrication of ultra-flattened-dispersion fibers, and have potential applications in wide-band high-speed optical communication systems, supercontinuum generation and many other applications.

Neutral Evolution and Dispersal Limitation Produce Biogeographic Patterns in Microcystis aeruginosa Populations of Lake Systems.

PubMed

Shirani, Sahar; Hellweger, Ferdi L

2017-08-01

Molecular observations reveal substantial biogeographic patterns of cyanobacteria within systems of connected lakes. An important question is the relative role of environmental selection and neutral processes in the biogeography of these systems. Here, we quantify the effect of genetic drift and dispersal limitation by simulating individual cyanobacteria cells using an agent-based model (ABM). In the model, cells grow (divide), die, and migrate between lakes. Each cell has a full genome that is subject to neutral mutation (i.e., the growth rate is independent of the genome). The model is verified by simulating simplified lake systems, for which theoretical solutions are available. Then, it is used to simulate the biogeography of the cyanobacterium Microcystis aeruginosa in a number of real systems, including the Great Lakes, Klamath River, Yahara River, and Chattahoochee River. Model output is analyzed using standard bioinformatics tools (BLAST, MAFFT). The emergent patterns of nucleotide divergence between lakes are dynamic, including gradual increases due to accumulation of mutations and abrupt changes due to population takeovers by migrant cells (coalescence events). The model predicted nucleotide divergence is heterogeneous within systems, and for weakly connected lakes, it can be substantial. For example, Lakes Superior and Michigan are predicted to have an average genomic nucleotide divergence of 8200 bp or 0.14%. The divergence between more strongly connected lakes is much lower. Our results provide a quantitative baseline for future biogeography studies. They show that dispersal limitation can be an important factor in microbe biogeography, which is contrary to the common belief, and could affect how a system responds to environmental change.

Development of a fine scale smoke dispersion modeling system. Part II: Case study of a prescribed burn in the New Jersey Pine Barrens

Treesearch

Michael T. Kiefer; Warren E. Heilman; Shiyuan Zhong; Joseph J. Charney; X. Bian; Ryan P. Shadbolt; John Hom; Kenneth Clark; Nicholas Skowronski; Michael Gallagher; Matthew Patterson

2011-01-01

Smoke dispersion from wildland fires is a critical health and safety issue, impacting air quality and visibility across a broad range of space and time scales. Predicting the dispersion of smoke from low-intensity fires is particularly challenging due to the fact that it is highly sensitive to factors such as near-surface meteorological conditions, local topography,...

The Ship Tethered Aerostat Remote Sensing System (STARRS): Observations of Small-Scale Surface Lateral Transport During the LAgrangian Submesoscale ExpeRiment (LASER)

NASA Astrophysics Data System (ADS)

Carlson, D. F.; Novelli, G.; Guigand, C.; Özgökmen, T.; Fox-Kemper, B.; Molemaker, M. J.

2016-02-01

The Consortium for Advanced Research on the Transport of Hydrocarbon in the Environment (CARTHE) will carry out the LAgrangian Submesoscale ExpeRiment (LASER) to study the role of small-scale processes in the transport and dispersion of oil and passive tracers. The Ship-Tethered Aerostat Remote Sensing System (STARRS) will observe small-scale surface dispersion in the open ocean. STARRS is built around a high-lift-capacity (30 kg) helium-filled aerostat. STARRS is equipped with a high resolution digital camera. An integrated GNSS receiver and inertial navigation system permit direct geo-rectification of the imagery. Consortium for Advanced Research on the Transport of Hydrocarbon in the Environment (CARTHE) will carry out the LAgrangian Submesoscale ExpeRiment (LASER) to study the role of small-scale processes in the transport and dispersion of oil and passive tracers. The Ship-Tethered Aerostat Remote Sensing System (STARRS) was developed to produce observational estimates of small-scale surface dispersion in the open ocean. STARRS is built around a high-lift-capacity (30 kg) helium-filled aerostat. STARRS is equipped with a high resolution digital camera. An integrated GNSS receiver and inertial navigation system permit direct geo-rectification of the imagery. Thousands of drift cards deployed in the field of view of STARRS and tracked over time provide the first observational estimates of small-scale (1-500 m) surface dispersion in the open ocean. The STARRS imagery will be combined with GPS-tracked surface drifter trajectories, shipboard observations, and aerial surveys of sea surface temperature in the DeSoto Canyon. In addition to obvious applications to oil spill modelling, the STARRS observations will provide essential benchmarks for high resolution numerical modelsDrift cards deployed in the field of view of STARRS and tracked over time provide the first observational estimates of small-scale (1-100 m) surface dispersion in the open ocean. The STARRS imagery will be combined with GPS-tracked surface drifter trajectories, shipboard observations, and aerial surveys of sea surface temperature in the DeSoto Canyon. In addition to obvious applications to oil spill modelling, the STARRS observations will provide essential benchmarks for high resolution numerical models

Computing dispersion curves of elastic/viscoelastic transversely-isotropic bone plates coupled with soft tissue and marrow using semi-analytical finite element (SAFE) method.

PubMed

Nguyen, Vu-Hieu; Tran, Tho N H T; Sacchi, Mauricio D; Naili, Salah; Le, Lawrence H

2017-08-01

We present a semi-analytical finite element (SAFE) scheme for accurately computing the velocity dispersion and attenuation in a trilayered system consisting of a transversely-isotropic (TI) cortical bone plate sandwiched between the soft tissue and marrow layers. The soft tissue and marrow are mimicked by two fluid layers of finite thickness. A Kelvin-Voigt model accounts for the absorption of all three biological domains. The simulated dispersion curves are validated by the results from the commercial software DISPERSE and published literature. Finally, the algorithm is applied to a viscoelastic trilayered TI bone model to interpret the guided modes of an ex-vivo experimental data set from a bone phantom. Copyright © 2017 Elsevier Ltd. All rights reserved.

The dispersal of planet-forming discs: theory confronts observations.

PubMed

Ercolano, Barbara; Pascucci, Ilaria

2017-04-01

Discs of gas and dust around million-year-old stars are a by-product of the star formation process and provide the raw material to form planets. Hence, their evolution and dispersal directly impact what type of planets can form and affect the final architecture of planetary systems. Here, we review empirical constraints on disc evolution and dispersal with special emphasis on transition discs, a subset of discs that appear to be caught in the act of clearing out planet-forming material. Along with observations, we summarize theoretical models that build our physical understanding of how discs evolve and disperse and discuss their significance in the context of the formation and evolution of planetary systems. By confronting theoretical predictions with observations, we also identify the most promising areas for future progress.

The dispersal of planet-forming discs: theory confronts observations

PubMed Central

Pascucci, Ilaria

2017-01-01

Discs of gas and dust around million-year-old stars are a by-product of the star formation process and provide the raw material to form planets. Hence, their evolution and dispersal directly impact what type of planets can form and affect the final architecture of planetary systems. Here, we review empirical constraints on disc evolution and dispersal with special emphasis on transition discs, a subset of discs that appear to be caught in the act of clearing out planet-forming material. Along with observations, we summarize theoretical models that build our physical understanding of how discs evolve and disperse and discuss their significance in the context of the formation and evolution of planetary systems. By confronting theoretical predictions with observations, we also identify the most promising areas for future progress. PMID:28484640

Modelling larval dispersal dynamics of common sole (Solea solea) along the western Iberian coast

NASA Astrophysics Data System (ADS)

Tanner, Susanne E.; Teles-Machado, Ana; Martinho, Filipe; Peliz, Álvaro; Cabral, Henrique N.

2017-08-01

Individual-based coupled physical-biological models have become the standard tool for studying ichthyoplankton dynamics and assessing fish recruitment. Here, common sole (Solea solea L.), a flatfish of high commercial importance in Europe was used to evaluate transport of eggs and larvae and investigate the connectivity between spawning and nursery areas along the western Iberian coast as spatio-temporal variability in dispersal and recruitment patterns can result in very strong or weak year-classes causing large fluctuations in stock size. A three-dimensional particle tracking model coupled to Regional Ocean Modelling System model was used to investigate variability of sole larvae dispersal along the western Iberian coast over a five-year period (2004-2009). A sensitivity analysis evaluating: (1) the importance of diel vertical migrations of larvae and (2) the size of designated recruitment areas was performed. Results suggested that connectivity patterns of sole larvae dispersal and their spatio-temporal variability are influenced by the configuration of the coast with its topographical structures and thus the suitable recruitment area available as well as the wind-driven mesoscale circulation along the Iberian coast.

The role of vertical shear on the horizontal oceanic dispersion

NASA Astrophysics Data System (ADS)

Lanotte, A. S.; Corrado, R.; Lacorata, G.; Palatella, L.; Pizzigalli, C.; Schipa, I.; Santoleri, R.

2015-09-01

The effect of vertical shear on the horizontal dispersion properties of passive tracer particles on the continental shelf of South Mediterranean is investigated by means of observative and model data. In-situ current measurements reveal that vertical velocity gradients in the upper mixed layer decorrelate quite fast (∼ 1 day), whereas basin-scale ocean circulation models tend to overestimate such decorrelation time because of finite resolution effects. Horizontal dispersion simulated by an eddy-permitting ocean model, like, e.g., the Mediterranean Forecasting System, is mosty affected by: (1) unresolved scale motions, and mesoscale motions that are largely smoothed out; (2) poorly resolved time variability of vertical velocity profiles in the upper layer. For the case study we have analysed, we show that a suitable use of kinematic parameterisations is helpful to implement realistic statistical features of tracer dispersion in two and three dimensions. The approach here suggested provides a functional tool to control the horizontal spreading of small organisms or substance concentrations, and is thus relevant for marine biology, pollutant dispersion as well as oil spill applications.

Development of Adaptive Management Tools to Guide Habitat Allocations for At-Risk Species

DTIC Science & Technology

2014-01-01

Results indicated that the mating system assumptions can have a large impact on the ability of the model to approximate data collected in the field...indicated that strength of habitat preferences during dispersal for juvenile and subadult male dispersal also significantly impacted model fit. Certainly...the influence of habitat loss, as these structural (or geometric) changes are often confounded in real landscapes, the impact of fragmentation is

Analytical solutions for a soil vapor extraction model that incorporates gas phase dispersion and molecular diffusion

NASA Astrophysics Data System (ADS)

Huang, Junqi; Goltz, Mark N.

2017-06-01

To greatly simplify their solution, the equations describing radial advective/dispersive transport to an extraction well in a porous medium typically neglect molecular diffusion. While this simplification is appropriate to simulate transport in the saturated zone, it can result in significant errors when modeling gas phase transport in the vadose zone, as might be applied when simulating a soil vapor extraction (SVE) system to remediate vadose zone contamination. A new analytical solution for the equations describing radial gas phase transport of a sorbing contaminant to an extraction well is presented. The equations model advection, dispersion (including both mechanical dispersion and molecular diffusion), and rate-limited mass transfer of dissolved, separate phase, and sorbed contaminants into the gas phase. The model equations are analytically solved by using the Laplace transform with respect to time. The solutions are represented by confluent hypergeometric functions in the Laplace domain. The Laplace domain solutions are then evaluated using a numerical Laplace inversion algorithm. The solutions can be used to simulate the spatial distribution and the temporal evolution of contaminant concentrations during operation of a soil vapor extraction well. Results of model simulations show that the effect of gas phase molecular diffusion upon concentrations at the extraction well is relatively small, although the effect upon the distribution of concentrations in space is significant. This study provides a tool that can be useful in designing SVE remediation strategies, as well as verifying numerical models used to simulate SVE system performance.

Dispersed Fringe Sensing Analysis - DFSA

NASA Technical Reports Server (NTRS)

Sigrist, Norbert; Shi, Fang; Redding, David C.; Basinger, Scott A.; Ohara, Catherine M.; Seo, Byoung-Joon; Bikkannavar, Siddarayappa A.; Spechler, Joshua A.

2012-01-01

Dispersed Fringe Sensing (DFS) is a technique for measuring and phasing segmented telescope mirrors using a dispersed broadband light image. DFS is capable of breaking the monochromatic light ambiguity, measuring absolute piston errors between segments of large segmented primary mirrors to tens of nanometers accuracy over a range of 100 micrometers or more. The DFSA software tool analyzes DFS images to extract DFS encoded segment piston errors, which can be used to measure piston distances between primary mirror segments of ground and space telescopes. This information is necessary to control mirror segments to establish a smooth, continuous primary figure needed to achieve high optical quality. The DFSA tool is versatile, allowing precise piston measurements from a variety of different optical configurations. DFSA technology may be used for measuring wavefront pistons from sub-apertures defined by adjacent segments (such as Keck Telescope), or from separated sub-apertures used for testing large optical systems (such as sub-aperture wavefront testing for large primary mirrors using auto-collimating flats). An experimental demonstration of the coarse-phasing technology with verification of DFSA was performed at the Keck Telescope. DFSA includes image processing, wavelength and source spectral calibration, fringe extraction line determination, dispersed fringe analysis, and wavefront piston sign determination. The code is robust against internal optical system aberrations and against spectral variations of the source. In addition to the DFSA tool, the software package contains a simple but sophisticated MATLAB model to generate dispersed fringe images of optical system configurations in order to quickly estimate the coarse phasing performance given the optical and operational design requirements. Combining MATLAB (a high-level language and interactive environment developed by MathWorks), MACOS (JPL s software package for Modeling and Analysis for Controlled Optical Systems), and DFSA provides a unique optical development, modeling and analysis package to study current and future approaches to coarse phasing controlled segmented optical systems.

A maximally particle-hole asymmetric spectrum emanating from a semi-Dirac point.

PubMed

Quan, Yundi; Pickett, Warren E

2018-02-21

Tight binding models have proven an effective means of revealing Dirac (massless) dispersion, flat bands (infinite mass), and intermediate cases such as the semi-Dirac (sD) dispersion. This approach is extended to a three band model that yields, with chosen parameters in a two-band limit, a closed line with maximally asymmetric particle-hole dispersion: infinite mass holes, zero mass particles. The model retains the sD points for a general set of parameters. Adjacent to this limiting case, hole Fermi surfaces are tiny and needle-like. A pair of large electron Fermi surfaces at low doping merge and collapse at half filling to a flat (zero energy) closed contour with infinite mass along the contour and enclosing no carriers on either side, while the hole Fermi surface has shrunk to a point at zero energy, also containing no carriers. The tight binding model is used to study several characteristics of the dispersion and density of states. The model inspired generalization of sD dispersion to a general  ±[Formula: see text] form, for which analysis reveals that both n and m must be odd to provide a diabolical point with topological character. Evolution of the Hofstadter spectrum of this three band system with interband coupling strength is presented and discussed.

A maximally particle-hole asymmetric spectrum emanating from a semi-Dirac point

NASA Astrophysics Data System (ADS)

Quan, Yundi; Pickett, Warren E.

2018-02-01

Tight binding models have proven an effective means of revealing Dirac (massless) dispersion, flat bands (infinite mass), and intermediate cases such as the semi-Dirac (sD) dispersion. This approach is extended to a three band model that yields, with chosen parameters in a two-band limit, a closed line with maximally asymmetric particle-hole dispersion: infinite mass holes, zero mass particles. The model retains the sD points for a general set of parameters. Adjacent to this limiting case, hole Fermi surfaces are tiny and needle-like. A pair of large electron Fermi surfaces at low doping merge and collapse at half filling to a flat (zero energy) closed contour with infinite mass along the contour and enclosing no carriers on either side, while the hole Fermi surface has shrunk to a point at zero energy, also containing no carriers. The tight binding model is used to study several characteristics of the dispersion and density of states. The model inspired generalization of sD dispersion to a general  ± \\sqrt{k_x2n +k_y2m} form, for which analysis reveals that both n and m must be odd to provide a diabolical point with topological character. Evolution of the Hofstadter spectrum of this three band system with interband coupling strength is presented and discussed.

Simple equations to simulate closed-loop recycling liquid-liquid chromatography: Ideal and non-ideal recycling models.

PubMed

Kostanyan, Artak E

2015-12-04

The ideal (the column outlet is directly connected to the column inlet) and non-ideal (includes the effects of extra-column dispersion) recycling equilibrium-cell models are used to simulate closed-loop recycling counter-current chromatography (CLR CCC). Simple chromatogram equations for the individual cycles and equations describing the transport and broadening of single peaks and complex chromatograms inside the recycling closed-loop column for ideal and non-ideal recycling models are presented. The extra-column dispersion is included in the theoretical analysis, by replacing the recycling system (connecting lines, pump and valving) by a cascade of Nec perfectly mixed cells. To evaluate extra-column contribution to band broadening, two limiting regimes of recycling are analyzed: plug-flow, Nec→∞, and maximum extra-column dispersion, Nec=1. Comparative analysis of ideal and non-ideal models has shown that when the volume of the recycling system is less than one percent of the column volume, the influence of the extra-column processes on the CLR CCC separation may be neglected. Copyright © 2015 Elsevier B.V. All rights reserved.

Modified sedimentation-dispersion model for solids in a three-phase slurry column

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

Smith, D.N.; Ruether, J.A.; Shah, Y.T.

1986-03-01

Solids distribution data for a three-phase, batch-fluidized slurry bubble column (SBC) are presented, using air as the gas phase, pure liquids and solutions as the liquid phase, and glass beads and carborundum catalyst powder as the solid phase. Solids distribution data for the three-phase SBC operated in a continuous mode of operation are also presented, using nitrogen as the gas phase, water as the liquid phase, and glass beads as the solid phase. A new model to provide a reasonable approach to predict solids concentration distributions for systems containing polydispersed solids is presented. The model is a modification of standardmore » sedimentation-dispersion model published earlier. Empirical correlations for prediction of hindered settling velocity and solids dispersion coefficient for systems containing polydispersed solids are presented. A new method of evaluating critical gas velocity (CGV) from concentrations of the sample withdrawn at the same port of the SBC is presented. Also presented is a new mapping for CGV which separates the two regimes in the SBC, namely, incomplete fluidization and complete fluidization.« less

Interhost dispersal alters microbiome assembly and can overwhelm host innate immunity in an experimental zebrafish model.

PubMed

Burns, Adam R; Miller, Elizabeth; Agarwal, Meghna; Rolig, Annah S; Milligan-Myhre, Kathryn; Seredick, Steve; Guillemin, Karen; Bohannan, Brendan J M

2017-10-17

The diverse collections of microorganisms associated with humans and other animals, collectively referred to as their "microbiome," are critical for host health, but the mechanisms that govern their assembly are poorly understood. This has made it difficult to identify consistent host factors that explain variation in microbiomes across hosts, despite large-scale sampling efforts. While ecological theory predicts that the movement, or dispersal, of individuals can have profound and predictable consequences on community assembly, its role in the assembly of animal-associated microbiomes remains underexplored. Here, we show that dispersal of microorganisms among hosts can contribute substantially to microbiome variation, and is able to overwhelm the effects of individual host factors, in an experimental test of ecological theory. We manipulated dispersal among wild-type and immune-deficient myd88 knockout zebrafish and observed that interhost dispersal had a large effect on the diversity and composition of intestinal microbiomes. Interhost dispersal was strong enough to overwhelm the effects of host factors, largely eliminating differences between wild-type and immune-deficient hosts, regardless of whether dispersal occurred within or between genotypes, suggesting dispersal can independently alter the ecology of microbiomes. Our observations are consistent with a predictive model that assumes metacommunity dynamics and are likely mediated by dispersal-related microbial traits. These results illustrate the importance of microbial dispersal to animal microbiomes and motivate its integration into the study of host-microbe systems.

Longitudinal dispersion coefficients for numerical modeling of groundwater solute transport in heterogeneous formations.

PubMed

Lee, Jonghyun; Rolle, Massimo; Kitanidis, Peter K

2017-09-15

Most recent research on hydrodynamic dispersion in porous media has focused on whole-domain dispersion while other research is largely on laboratory-scale dispersion. This work focuses on the contribution of a single block in a numerical model to dispersion. Variability of fluid velocity and concentration within a block is not resolved and the combined spreading effect is approximated using resolved quantities and macroscopic parameters. This applies whether the formation is modeled as homogeneous or discretized into homogeneous blocks but the emphasis here being on the latter. The process of dispersion is typically described through the Fickian model, i.e., the dispersive flux is proportional to the gradient of the resolved concentration, commonly with the Scheidegger parameterization, which is a particular way to compute the dispersion coefficients utilizing dispersivity coefficients. Although such parameterization is by far the most commonly used in solute transport applications, its validity has been questioned. Here, our goal is to investigate the effects of heterogeneity and mass transfer limitations on block-scale longitudinal dispersion and to evaluate under which conditions the Scheidegger parameterization is valid. We compute the relaxation time or memory of the system; changes in time with periods larger than the relaxation time are gradually leading to a condition of local equilibrium under which dispersion is Fickian. The method we use requires the solution of a steady-state advection-dispersion equation, and thus is computationally efficient, and applicable to any heterogeneous hydraulic conductivity K field without requiring statistical or structural assumptions. The method was validated by comparing with other approaches such as the moment analysis and the first order perturbation method. We investigate the impact of heterogeneity, both in degree and structure, on the longitudinal dispersion coefficient and then discuss the role of local dispersion and mass transfer limitations, i.e., the exchange of mass between the permeable matrix and the low permeability inclusions. We illustrate the physical meaning of the method and we show how the block longitudinal dispersivity approaches, under certain conditions, the Scheidegger limit at large Péclet numbers. Lastly, we discuss the potential and limitations of the method to accurately describe dispersion in solute transport applications in heterogeneous aquifers. Copyright © 2017. Published by Elsevier B.V.

DEVELOPMENT OF A RATIONALLY BASED DESIGN PROTOCOL FOR THE ULTRAVIOLET LIGHT DISINFECTION PROCESS

EPA Science Inventory

A protocol is demonstrated for the design and evaluation of ultraviolet (UV) disinfection systems based on a mathematical model. The disinfection model incorporates the system's physical dimensions, the residence time distribution of the reactor and dispersion characteristics, th...

A theoretical study of complexes formed between cations and curved aromatic systems: electrostatics does not always control cation-π interaction.

PubMed

Carrazana-García, Jorge A; Cabaleiro-Lago, Enrique M; Rodríguez-Otero, Jesús

2017-04-19

The present work studies the interaction of two extended curved π-systems (corannulene and sumanene) with various cations (sodium, potassium, ammonium, tetramethylammonium, guanidinium and imidazolium). Polyatomic cations are models of groups found in important biomolecules in which cation-π interaction plays a fundamental role. The results indicate an important size effect: with extended π systems and cations of the size of potassium and larger, dispersion is much more important than has been generally recognized for cation-π interactions. In most of the systems studied here, the stability of the cation-π complexes is the result of a balanced combination of electrostatic, induction and dispersion contributions. None of the systems studied here owes its stability to the electrostatic interaction more than 42%. Induction dominates stabilization in complexes with sodium, and in some of the potassium and ammonium complexes. In complexes with large cations and with flat cations dispersion is the major stabilizing contribution and can provide more than 50% of the stabilization energy. This implies that theoretical studies of the cation-π interaction involving large or even medium-size fragments require a level of calculation capable of properly modelling dispersion. The separation between the cation and the π system is another important factor to take into account, especially when the fragments of the cation-π complex are bound (for example, to a protein backbone) and cannot interact at the most favourable distance.

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

NASA Astrophysics Data System (ADS)

Ebrahimi, Ali N.; Or, Dani

2014-09-01

The dispersal rates of self-propelled microorganisms affect their spatial interactions and the ecological functioning of microbial communities. Microbial dispersal rates affect risk of contamination of water resources by soil-borne pathogens, the inoculation of plant roots, or the rates of spoilage of food products. In contrast with the wealth of information on microbial dispersal in water replete systems, very little is known about their dispersal rates in unsaturated porous media. The fragmented aqueous phase occupying complex soil pore spaces suppress motility and limits dispersal ranges in unsaturated soil. The primary objective of this study was to systematically evaluate key factors that shape microbial dispersal in model unsaturated porous media to quantify effects of saturation, pore space geometry, and chemotaxis on characteristics of principles that govern motile microbial dispersion in unsaturated soil. We constructed a novel 3-D angular pore network model (PNM) to mimic aqueous pathways in soil for different hydration conditions; within the PNM, we employed an individual-based model that considers physiological and biophysical properties of motile and chemotactic bacteria. The effects of hydration conditions on first passage times in different pore networks were studied showing that fragmentation of aquatic habitats under dry conditions sharply suppresses nutrient transport and microbial dispersal rates in good agreement with limited experimental data. Chemotactically biased mean travel speed of microbial cells across 9 mm saturated PNM was ˜3 mm/h decreasing exponentially to 0.45 mm/h for the PNM at matric potential of -15 kPa (for -35 kPa, dispersal practically ceases and the mean travel time to traverse the 9 mm PNM exceeds 1 year). Results indicate that chemotaxis enhances dispersal rates by orders of magnitude relative to random (diffusive) motions. Model predictions considering microbial cell sizes relative to available liquid pathways sizes were in good agreement with experimental results for unsaturated soils. The new modeling platform enables quantitative consideration of key biophysical factors (e.g., pore space heterogeneities and hydration conditions) governing microbial interactions in 3-D soil pore spaces.

FDTD modelling of induced polarization phenomena in transient electromagnetics

NASA Astrophysics Data System (ADS)

Commer, Michael; Petrov, Peter V.; Newman, Gregory A.

2017-04-01

The finite-difference time-domain scheme is augmented in order to treat the modelling of transient electromagnetic signals containing induced polarization effects from 3-D distributions of polarizable media. Compared to the non-dispersive problem, the discrete dispersive Maxwell system contains costly convolution operators. Key components to our solution for highly digitized model meshes are Debye decomposition and composite memory variables. We revert to the popular Cole-Cole model of dispersion to describe the frequency-dependent behaviour of electrical conductivity. Its inversely Laplace-transformed Debye decomposition results in a series of time convolutions between electric field and exponential decay functions, with the latter reflecting each Debye constituents' individual relaxation time. These function types in the discrete-time convolution allow for their substitution by memory variables, annihilating the otherwise prohibitive computing demands. Numerical examples demonstrate the efficiency and practicality of our algorithm.

Increased persistence via asynchrony in oscillating ecological populations with long-range interaction

NASA Astrophysics Data System (ADS)

Gupta, Anubhav; Banerjee, Tanmoy; Dutta, Partha Sharathi

2017-10-01

Understanding the influence of the structure of a dispersal network on the species persistence and modeling a realistic species dispersal in nature are two central issues in spatial ecology. A realistic dispersal structure which favors the persistence of interacting ecological systems was studied [M. D. Holland and A. Hastings, Nature (London) 456, 792 (2008), 10.1038/nature07395], where it was shown that a randomization of the structure of a dispersal network in a metapopulation model of prey and predator increases the species persistence via clustering, prolonged transient dynamics, and amplitudes of population fluctuations. In this paper, by contrast, we show that a deterministic network topology in a metapopulation can also favor asynchrony and prolonged transient dynamics if species dispersal obeys a long-range interaction governed by a distance-dependent power law. To explore the effects of power-law coupling, we take a realistic ecological model, namely, the Rosenzweig-MacArthur model in each patch (node) of the network of oscillators, and show that the coupled system is driven from synchrony to asynchrony with an increase in the power-law exponent. Moreover, to understand the relationship between species persistence and variations in power-law exponent, we compute a correlation coefficient to characterize cluster formation, a synchrony order parameter, and median predator amplitude. We further show that smaller metapopulations with fewer patches are more vulnerable to extinction as compared to larger metapopulations with a higher number of patches. We believe that the present work improves our understanding of the interconnection between the random network and the deterministic network in theoretical ecology.

Solvability of the Initial Value Problem to the Isobe-Kakinuma Model for Water Waves

NASA Astrophysics Data System (ADS)

Nemoto, Ryo; Iguchi, Tatsuo

2017-09-01

We consider the initial value problem to the Isobe-Kakinuma model for water waves and the structure of the model. The Isobe-Kakinuma model is the Euler-Lagrange equations for an approximate Lagrangian which is derived from Luke's Lagrangian for water waves by approximating the velocity potential in the Lagrangian. The Isobe-Kakinuma model is a system of second order partial differential equations and is classified into a system of nonlinear dispersive equations. Since the hypersurface t=0 is characteristic for the Isobe-Kakinuma model, the initial data have to be restricted in an infinite dimensional manifold for the existence of the solution. Under this necessary condition and a sign condition, which corresponds to a generalized Rayleigh-Taylor sign condition for water waves, on the initial data, we show that the initial value problem is solvable locally in time in Sobolev spaces. We also discuss the linear dispersion relation to the model.

EDMS Multi-year Validation Plan

DOT National Transportation Integrated Search

2001-06-01

The Emissions and Dispersion Modeling System (EDMS) is the air quality model required for use on airport projects by the Federal Aviation Administration (FAA). This model has continued to be improved and recently has included several important enhanc...

Statistical mechanics of two-dimensional shuffled foams: Geometry-topology correlation in small or large disorder limits

NASA Astrophysics Data System (ADS)

Durand, Marc; Kraynik, Andrew M.; van Swol, Frank; Käfer, Jos; Quilliet, Catherine; Cox, Simon; Ataei Talebi, Shirin; Graner, François

2014-06-01

Bubble monolayers are model systems for experiments and simulations of two-dimensional packing problems of deformable objects. We explore the relation between the distributions of the number of bubble sides (topology) and the bubble areas (geometry) in the low liquid fraction limit. We use a statistical model [M. Durand, Europhys. Lett. 90, 60002 (2010), 10.1209/0295-5075/90/60002] which takes into account Plateau laws. We predict the correlation between geometrical disorder (bubble size dispersity) and topological disorder (width of bubble side number distribution) over an extended range of bubble size dispersities. Extensive data sets arising from shuffled foam experiments, surface evolver simulations, and cellular Potts model simulations all collapse surprisingly well and coincide with the model predictions, even at extremely high size dispersity. At moderate size dispersity, we recover our earlier approximate predictions [M. Durand, J. Kafer, C. Quilliet, S. Cox, S. A. Talebi, and F. Graner, Phys. Rev. Lett. 107, 168304 (2011), 10.1103/PhysRevLett.107.168304]. At extremely low dispersity, when approaching the perfectly regular honeycomb pattern, we study how both geometrical and topological disorders vanish. We identify a crystallization mechanism and explore it quantitatively in the case of bidisperse foams. Due to the deformability of the bubbles, foams can crystallize over a larger range of size dispersities than hard disks. The model predicts that the crystallization transition occurs when the ratio of largest to smallest bubble radii is 1.4.

Secondary flow measurements and passive tracer dispersion in multi-generational models of conducting airways of the lung

NASA Astrophysics Data System (ADS)

Fresconi, Frank; Prasad, Ajay

2006-11-01

A detailed knowledge of the flow and dispersion within the human respiratory tract is desirable for numerous reasons. Both risk assessments of exposure to toxic particles in the environment and the design of medical delivery systems targeting both lung-specific conditions (asthma, cystic fibrosis, and chronic obstructive pulmonary disease (COPD)) and system-wide ailments (diabetes, cancer, hormone replacement) would profit from such an understanding. The present work features experimental efforts aimed at elucidating the fluid mechanics of the lung. Particle image velocimetry (PIV) and laser induced fluorescence (LIF) measurements of steady and oscillatory flows were undertaken in anatomically accurate models (single and multi-generational) of the conductive region of the lung. PIV results captured primary and secondary velocity fields. LIF allowed visualization of the time-dependent deformation of a passive tracer and also quantified convective dispersion through the usage of a transport profile.

Modeling self-consistent multi-class dynamic traffic flow

NASA Astrophysics Data System (ADS)

Cho, Hsun-Jung; Lo, Shih-Ching

2002-09-01

In this study, we present a systematic self-consistent multiclass multilane traffic model derived from the vehicular Boltzmann equation and the traffic dispersion model. The multilane domain is considered as a two-dimensional space and the interaction among vehicles in the domain is described by a dispersion model. The reason we consider a multilane domain as a two-dimensional space is that the driving behavior of road users may not be restricted by lanes, especially motorcyclists. The dispersion model, which is a nonlinear Poisson equation, is derived from the car-following theory and the equilibrium assumption. Under the concept that all kinds of users share the finite section, the density is distributed on a road by the dispersion model. In addition, the dynamic evolution of the traffic flow is determined by the systematic gas-kinetic model derived from the Boltzmann equation. Multiplying Boltzmann equation by the zeroth, first- and second-order moment functions, integrating both side of the equation and using chain rules, we can derive continuity, motion and variance equation, respectively. However, the second-order moment function, which is the square of the individual velocity, is employed by previous researches does not have physical meaning in traffic flow. Although the second-order expansion results in the velocity variance equation, additional terms may be generated. The velocity variance equation we propose is derived from multiplying Boltzmann equation by the individual velocity variance. It modifies the previous model and presents a new gas-kinetic traffic flow model. By coupling the gas-kinetic model and the dispersion model, a self-consistent system is presented.

Effects of oil dispersants on photodegradation of pyrene in marine water.

PubMed

Gong, Yanyan; Fu, Jie; O'Reilly, S E; Zhao, Dongye

2015-04-28

This work investigated effects of a popular oil dispersant (Corexit EC9500A) on UV- or sunlight-mediated photodegradation of pyrene (a model polycyclic aromatic hydrocarbon) in seawater. The presence of 18 and 180mg/L of the dispersant increased the first-order photodegradation rate by 5.5% and 16.7%, respectively, and reduced or ceased pyrene volatilization. By combining individual first-order rate laws for volatilization and photodegradation, we proposed an integrated kinetic model that can adequately predict the overall dissipation of pyrene from seawater. Mechanistic studies indicated that superoxide radicals played a predominant role in pyrene photodegradation, and the dispersant enhanced formation of superoxide radicals. 1-Hydroxypyrene was the main intermediate regardless of the dispersant, suggesting that electrons were transferred from excited pyrene to oxygen. In the presence of 18mg/L of the dispersant, the photodegradation rate increased with increasing ionic strength and temperature, but decreased with increasing HA concentration, and remained independent of solution pH. The results are important in understanding roles of oil dispersants on environmental fate of persistent oil components in natural and engineered systems. Copyright © 2015 Elsevier B.V. All rights reserved.

Asymmetric patch size distribution leads to disruptive selection on dispersal.

PubMed

Massol, François; Duputié, Anne; David, Patrice; Jarne, Philippe

2011-02-01

Numerous models have been designed to understand how dispersal ability evolves when organisms live in a fragmented landscape. Most of them predict a single dispersal rate at evolutionary equilibrium, and when diversification of dispersal rates has been predicted, it occurs as a response to perturbation or environmental fluctuation regimes. Yet abundant variation in dispersal ability is observed in natural populations and communities, even in relatively stable environments. We show that this diversification can operate in a simple island model without temporal variability: disruptive selection on dispersal occurs when the environment consists of many small and few large patches, a common feature in natural spatial systems. This heterogeneity in patch size results in a high variability in the number of related patch mates by individual, which, in turn, triggers disruptive selection through a high per capita variance of inclusive fitness. Our study provides a likely, parsimonious and testable explanation for the diversity of dispersal rates encountered in nature. It also suggests that biological conservation policies aiming at preserving ecological communities should strive to keep the distribution of patch size sufficiently asymmetric and variable. © 2010 The Author(s). Evolution© 2010 The Society for the Study of Evolution.

The use of deconvolution techniques to identify the fundamental mixing characteristics of urban drainage structures.

PubMed

Stovin, V R; Guymer, I; Chappell, M J; Hattersley, J G

2010-01-01

Mixing and dispersion processes affect the timing and concentration of contaminants transported within urban drainage systems. Hence, methods of characterising the mixing effects of specific hydraulic structures are of interest to drainage network modellers. Previous research, focusing on surcharged manholes, utilised the first-order Advection-Dispersion Equation (ADE) and Aggregated Dead Zone (ADZ) models to characterise dispersion. However, although systematic variations in travel time as a function of discharge and surcharge depth have been identified, the first order ADE and ADZ models do not provide particularly good fits to observed manhole data, which means that the derived parameter values are not independent of the upstream temporal concentration profile. An alternative, more robust, approach utilises the system's Cumulative Residence Time Distribution (CRTD), and the solute transport characteristics of a surcharged manhole have been shown to be characterised by just two dimensionless CRTDs, one for pre- and the other for post-threshold surcharge depths. Although CRTDs corresponding to instantaneous upstream injections can easily be generated using Computational Fluid Dynamics (CFD) models, the identification of CRTD characteristics from non-instantaneous and noisy laboratory data sets has been hampered by practical difficulties. This paper shows how a deconvolution approach derived from systems theory may be applied to identify the CRTDs associated with urban drainage structures.

Statistical analysis for improving data precision in the SPME GC-MS analysis of blackberry (Rubus ulmifolius Schott) volatiles.

PubMed

D'Agostino, M F; Sanz, J; Martínez-Castro, I; Giuffrè, A M; Sicari, V; Soria, A C

2014-07-01

Statistical analysis has been used for the first time to evaluate the dispersion of quantitative data in the solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis of blackberry (Rubus ulmifolius Schott) volatiles with the aim of improving their precision. Experimental and randomly simulated data were compared using different statistical parameters (correlation coefficients, Principal Component Analysis loadings and eigenvalues). Non-random factors were shown to significantly contribute to total dispersion; groups of volatile compounds could be associated with these factors. A significant improvement of precision was achieved when considering percent concentration ratios, rather than percent values, among those blackberry volatiles with a similar dispersion behavior. As novelty over previous references, and to complement this main objective, the presence of non-random dispersion trends in data from simple blackberry model systems was evidenced. Although the influence of the type of matrix on data precision was proved, the possibility of a better understanding of the dispersion patterns in real samples was not possible from model systems. The approach here used was validated for the first time through the multicomponent characterization of Italian blackberries from different harvest years. Copyright © 2014 Elsevier B.V. All rights reserved.

Mars Exploration Rovers Landing Dispersion Analysis

NASA Technical Reports Server (NTRS)

Knocke, Philip C.; Wawrzyniak, Geoffrey G.; Kennedy, Brian M.; Desai, Prasun N.; Parker, TImothy J.; Golombek, Matthew P.; Duxbury, Thomas C.; Kass, David M.

2004-01-01

Landing dispersion estimates for the Mars Exploration Rover missions were key elements in the site targeting process and in the evaluation of landing risk. This paper addresses the process and results of the landing dispersion analyses performed for both Spirit and Opportunity. The several contributors to landing dispersions (navigation and atmospheric uncertainties, spacecraft modeling, winds, and margins) are discussed, as are the analysis tools used. JPL's MarsLS program, a MATLAB-based landing dispersion visualization and statistical analysis tool, was used to calculate the probability of landing within hazardous areas. By convolving this with the probability of landing within flight system limits (in-spec landing) for each hazard area, a single overall measure of landing risk was calculated for each landing ellipse. In-spec probability contours were also generated, allowing a more synoptic view of site risks, illustrating the sensitivity to changes in landing location, and quantifying the possible consequences of anomalies such as incomplete maneuvers. Data and products required to support these analyses are described, including the landing footprints calculated by NASA Langley's POST program and JPL's AEPL program, cartographically registered base maps and hazard maps, and flight system estimates of in-spec landing probabilities for each hazard terrain type. Various factors encountered during operations, including evolving navigation estimates and changing atmospheric models, are discussed and final landing points are compared with approach estimates.

Habitat heterogeneity hypothesis and edge effects in model metacommunities.

PubMed

Hamm, Michaela; Drossel, Barbara

2017-08-07

Spatial heterogeneity is an inherent property of any living environment and is expected to favour biodiversity due to a broader niche space. Furthermore, edges between different habitats can provide additional possibilities for species coexistence. Using computer simulations, this study examines metacommunities consisting of several trophic levels in heterogeneous environments in order to explore the above hypotheses on a community level. We model heterogeneous landscapes by using two different sized resource pools and evaluate the combined effect of dispersal and heterogeneity on local and regional species diversity. This diversity is obtained by running population dynamics and evaluating the robustness (i.e., the fraction of surviving species). The main results for regional robustness are in agreement with the habitat heterogeneity hypothesis, as the largest robustness is found in heterogeneous systems with intermediate dispersal rates. This robustness is larger than in homogeneous systems with the same total amount of resources. We study the edge effect by arranging the two types of resources in two homogeneous blocks. Different edge responses in diversity are observed, depending on dispersal strength. Local robustness is highest for edge habitats that contain the smaller amount of resource in combination with intermediate dispersal. The results show that dispersal is relevant to correctly identify edge responses on community level. Copyright © 2017 Elsevier Ltd. All rights reserved.

1998 Technology Showcase. JOAP International Condition Monitoring Conference.

DTIC Science & Technology

1998-04-01

Systems using Automated SEM/ EDX and New Diagnostic Routines 276 N. W Farrant & T. Luckhurst ADVANCED DIAGNOSTIC SYSTEMS Model-Based Diagnostics of Gas...Microscopy with Energy Dispersive X-Ray (SEM/ EDX ) micro analysis packages and Energy Dispersive X-Ray Fluorescence (EDXRF) analytical equipment. Therqfore...wear particles separated by ferrogram method. a- I WEAR PARTICLE A SLAS 97 (HOME PAGE) Fig I Home Page NONFE;RROUS MATERIAL A wW~ a48 -1, rV fr , ý b

Effect of dispersion forces on squeezing with Rydberg atoms

NASA Technical Reports Server (NTRS)

Ng, S. K.; Muhamad, M. R.; Wahiddin, M. R. B.

1994-01-01

We report exact results concerning the effect of dipole-dipole interaction (dispersion forces) on dynamic and steady-state characteristics of squeezing in the emitted fluorescent field from two identical coherently driven two-level atoms. The atomic system is subjected to three different damping baths in particular the normal vacuum, a broad band thermal field and a broad band squeezed vacuum. The atomic model is the Dicke model, hence possible experiments are most likely to agree with theory when performed on systems of Rydberg atoms making microwave transitions. The presence of dipole-dipole interaction can enhance squeezing for realizable values of the various parameters involved.

The statistical evaluation and comparison of ADMS-Urban model for the prediction of nitrogen dioxide with air quality monitoring network.

PubMed

Dėdelė, Audrius; Miškinytė, Auksė

2015-09-01

In many countries, road traffic is one of the main sources of air pollution associated with adverse effects on human health and environment. Nitrogen dioxide (NO2) is considered to be a measure of traffic-related air pollution, with concentrations tending to be higher near highways, along busy roads, and in the city centers, and the exceedances are mainly observed at measurement stations located close to traffic. In order to assess the air quality in the city and the air pollution impact on public health, air quality models are used. However, firstly, before the model can be used for these purposes, it is important to evaluate the accuracy of the dispersion modelling as one of the most widely used method. The monitoring and dispersion modelling are two components of air quality monitoring system (AQMS), in which statistical comparison was made in this research. The evaluation of the Atmospheric Dispersion Modelling System (ADMS-Urban) was made by comparing monthly modelled NO2 concentrations with the data of continuous air quality monitoring stations in Kaunas city. The statistical measures of model performance were calculated for annual and monthly concentrations of NO2 for each monitoring station site. The spatial analysis was made using geographic information systems (GIS). The calculation of statistical parameters indicated a good ADMS-Urban model performance for the prediction of NO2. The results of this study showed that the agreement of modelled values and observations was better for traffic monitoring stations compared to the background and residential stations.

Anisotropic shear dispersion parameterization for ocean eddy transport

NASA Astrophysics Data System (ADS)

Reckinger, Scott; Fox-Kemper, Baylor

2015-11-01

The effects of mesoscale eddies are universally treated isotropically in global ocean general circulation models. However, observations and simulations demonstrate that the mesoscale processes that the parameterization is intended to represent, such as shear dispersion, are typified by strong anisotropy. We extend the Gent-McWilliams/Redi mesoscale eddy parameterization to include anisotropy and test the effects of varying levels of anisotropy in 1-degree Community Earth System Model (CESM) simulations. Anisotropy has many effects on the simulated climate, including a reduction of temperature and salinity biases, a deepening of the southern ocean mixed-layer depth, impacts on the meridional overturning circulation and ocean energy and tracer uptake, and improved ventilation of biogeochemical tracers, particularly in oxygen minimum zones. A process-based parameterization to approximate the effects of unresolved shear dispersion is also used to set the strength and direction of anisotropy. The shear dispersion parameterization is similar to drifter observations in spatial distribution of diffusivity and high-resolution model diagnosis in the distribution of eddy flux orientation.

Shall we upgrade one-dimensional secondary settler models used in WWTP simulators? - An assessment of model structure uncertainty and its propagation.

PubMed

Plósz, Benedek Gy; De Clercq, Jeriffa; Nopens, Ingmar; Benedetti, Lorenzo; Vanrolleghem, Peter A

2011-01-01

In WWTP models, the accurate assessment of solids inventory in bioreactors equipped with solid-liquid separators, mostly described using one-dimensional (1-D) secondary settling tank (SST) models, is the most fundamental requirement of any calibration procedure. Scientific knowledge on characterising particulate organics in wastewater and on bacteria growth is well-established, whereas 1-D SST models and their impact on biomass concentration predictions are still poorly understood. A rigorous assessment of two 1-DSST models is thus presented: one based on hyperbolic (the widely used Takács-model) and one based on parabolic (the more recently presented Plósz-model) partial differential equations. The former model, using numerical approximation to yield realistic behaviour, is currently the most widely used by wastewater treatment process modellers. The latter is a convection-dispersion model that is solved in a numerically sound way. First, the explicit dispersion in the convection-dispersion model and the numerical dispersion for both SST models are calculated. Second, simulation results of effluent suspended solids concentration (XTSS,Eff), sludge recirculation stream (XTSS,RAS) and sludge blanket height (SBH) are used to demonstrate the distinct behaviour of the models. A thorough scenario analysis is carried out using SST feed flow rate, solids concentration, and overflow rate as degrees of freedom, spanning a broad loading spectrum. A comparison between the measurements and the simulation results demonstrates a considerably improved 1-D model realism using the convection-dispersion model in terms of SBH, XTSS,RAS and XTSS,Eff. Third, to assess the propagation of uncertainty derived from settler model structure to the biokinetic model, the impact of the SST model as sub-model in a plant-wide model on the general model performance is evaluated. A long-term simulation of a bulking event is conducted that spans temperature evolution throughout a summer/winter sequence. The model prediction in terms of nitrogen removal, solids inventory in the bioreactors and solids retention time as a function of the solids settling behaviour is investigated. It is found that the settler behaviour, simulated by the hyperbolic model, can introduce significant errors into the approximation of the solids retention time and thus solids inventory of the system. We demonstrate that these impacts can potentially cause deterioration of the predictive power of the biokinetic model, evidenced by an evaluation of the system's nitrogen removal efficiency. The convection-dispersion model exhibits superior behaviour, and the use of this type of model thus is highly recommended, especially bearing in mind future challenges, e.g., the explicit representation of uncertainty in WWTP models.

Automated system for smoke dispersion prediction due to wild fires in Alaska

NASA Astrophysics Data System (ADS)

Kulchitsky, A.; Stuefer, M.; Higbie, L.; Newby, G.

2007-12-01

Community climate models have enabled development of specific environmental forecast systems. The University of Alaska (UAF) smoke group was created to adapt a smoke forecast system to the Alaska region. The US Forest Service (USFS) Missoula Fire Science Lab had developed a smoke forecast system based on the Weather Research and Forecasting (WRF) Model including chemistry (WRF/Chem). Following the successful experience of USFS, which runs their model operationally for the contiguous U.S., we develop a similar system for Alaska in collaboration with scientists from the USFS Missoula Fire Science Lab. Wildfires are a significant source of air pollution in Alaska because the climate and vegetation favor annual summer fires that burn huge areas. Extreme cases occurred in 2004, when an area larger than Maryland (more than 25000~km2) burned. Small smoke particles with a diameter less than 10~μm can penetrate deep into lungs causing health problems. Smoke also creates a severe restriction to air transport and has tremendous economical effect. The smoke dispersion and forecast system for Alaska was developed at the Geophysical Institute (GI) and the Arctic Region Supercomputing Center (ARSC), both at University of Alaska Fairbanks (UAF). They will help the public and plan activities a few days in advance to avoid dangerous smoke exposure. The availability of modern high performance supercomputers at ARSC allows us to create and run high-resolution, WRF-based smoke dispersion forecast for the entire State of Alaska. The core of the system is a Python program that manages the independent pieces. Our adapted Alaska system performs the following steps \\begin{itemize} Calculate the medium-resolution weather forecast using WRF/Met. Adapt the near real-time satellite-derived wildfire location and extent data that are received via direct broadcast from UAF's "Geographic Information Network of Alaska" (GINA) Calculate fuel moisture using WRF forecasts and National Fire Danger Rating System (NFDRS) fuel maps Calculate smoke emission components using a first order fire emission model Model the smoke plume rise yielding a vertically distribution that accounts for one-dimensional (vertical) concentrations of smoke constituents in the atmosphere above the fire Run WRF/Chem at high resolution for the forecast Use standard graphical tools to provide accessible smoke dispersion The system run twice each day at ARSC. The results will be freely available from a dedicated wildfire smoke web portal at ARSC.

The Effects of Polymer Carrier, Hot Melt Extrusion Process and Downstream Processing Parameters on the Moisture Sorption Properties of Amorphous Solid Dispersions

PubMed Central

Feng, Xin; Vo, Anh; Patil, Hemlata; Tiwari, Roshan V.; Alshetaili, Abdullah S.; Pimparade, Manjeet B.; Repka, Michael A.

2017-01-01

Objective The aim of this study was to evaluate the effect of polymer carrier, hot melt extrusion (HME) and downstream processing parameters on the water uptake properties of amorphous solid dispersions. Methods Three polymers and a model drug were used to prepare amorphous solid dispersions utilizing HME technology. The sorption-desorption isotherms of solid dispersions and their physical mixtures were measured by the Dynamic Vapor Sorption system, and the effect of polymer hydrophobicity, hygroscopicity, molecular weight and the HME process were investigated. FTIR imaging was performed to understand the phase separation driven by the moisture. Key findings Solid dispersions with polymeric carriers with lower hydrophilicity, hygroscopicity, and higher molecular weight could sorb less moisture under the high RH conditions. The water uptake ability of polymer-drug solid dispersion systems were decreased compared to the physical mixture after HME, which might be due to the decreased surface area and porosity. The FTIR imaging indicated the homogeneity of the drug molecularly dispersed within the polymer matrix was changed after exposure to high RH. Conclusion Understanding the effect of formulation and processing on the moisture sorption properties of solid dispersions is essential for the development of drug products with desired physical and chemical stability. PMID:26589107

Directed electromagnetic wave propagation in 1D metamaterial: Projecting operators method

NASA Astrophysics Data System (ADS)

Ampilogov, Dmitrii; Leble, Sergey

2016-07-01

We consider a boundary problem for 1D electrodynamics modeling of a pulse propagation in a metamaterial medium. We build and apply projecting operators to a Maxwell system in time domain that allows to split the linear propagation problem to directed waves for a material relations with general dispersion. Matrix elements of the projectors act as convolution integral operators. For a weak nonlinearity we generalize the linear results still for arbitrary dispersion and derive the system of interacting right/left waves with combined (hybrid) amplitudes. The result is specified for the popular metamaterial model with Drude formula for both permittivity and permeability coefficients. We also discuss and investigate stationary solutions of the system related to some boundary regimes.

A discontinuous Galerkin approach for conservative modeling of fully nonlinear and weakly dispersive wave transformations

NASA Astrophysics Data System (ADS)

Sharifian, Mohammad Kazem; Kesserwani, Georges; Hassanzadeh, Yousef

2018-05-01

This work extends a robust second-order Runge-Kutta Discontinuous Galerkin (RKDG2) method to solve the fully nonlinear and weakly dispersive flows, within a scope to simultaneously address accuracy, conservativeness, cost-efficiency and practical needs. The mathematical model governing such flows is based on a variant form of the Green-Naghdi (GN) equations decomposed as a hyperbolic shallow water system with an elliptic source term. Practical features of relevance (i.e. conservative modeling over irregular terrain with wetting and drying and local slope limiting) have been restored from an RKDG2 solver to the Nonlinear Shallow Water (NSW) equations, alongside new considerations to integrate elliptic source terms (i.e. via a fourth-order local discretization of the topography) and to enable local capturing of breaking waves (i.e. via adding a detector for switching off the dispersive terms). Numerical results are presented, demonstrating the overall capability of the proposed approach in achieving realistic prediction of nearshore wave processes involving both nonlinearity and dispersion effects within a single model.

On valuing patches: Estimating contributions to metapopulation growth with reverse-time capture-recapture modelling

USGS Publications Warehouse

Sanderlin, J.S.; Waser, P.M.; Hines, J.E.; Nichols, J.D.

2012-01-01

Metapopulation ecology has historically been rich in theory, yet analytical approaches for inferring demographic relationships among local populations have been few. We show how reverse-time multi-state capture-recapture models can be used to estimate the importance of local recruitment and interpopulation dispersal to metapopulation growth. We use 'contribution metrics' to infer demographic connectedness among eight local populations of banner-tailed kangaroo rats, to assess their demographic closure, and to investigate sources of variation in these contributions. Using a 7 year dataset, we show that: (i) local populations are relatively independent demographically, and contributions to local population growth via dispersal within the system decline with distance; (ii) growth contributions via local survival and recruitment are greater for adults than juveniles, while contributions involving dispersal are greater for juveniles; (iii) central populations rely more on local recruitment and survival than peripheral populations; (iv) contributions involving dispersal are not clearly related to overall metapopulation density; and (v) estimated contributions from outside the system are unexpectedly large. Our analytical framework can classify metapopulations on a continuum between demographic independence and panmixia, detect hidden population growth contributions, and make inference about other population linkage forms, including rescue effects and source-sink structures. Finally, we discuss differences between demographic and genetic population linkage patterns for our system. ?? 2011 The Royal Society.

SEARCH: Spatially Explicit Animal Response to Composition of Habitat.

PubMed

Pauli, Benjamin P; McCann, Nicholas P; Zollner, Patrick A; Cummings, Robert; Gilbert, Jonathan H; Gustafson, Eric J

2013-01-01

Complex decisions dramatically affect animal dispersal and space use. Dispersing individuals respond to a combination of fine-scale environmental stimuli and internal attributes. Individual-based modeling offers a valuable approach for the investigation of such interactions because it combines the heterogeneity of animal behaviors with spatial detail. Most individual-based models (IBMs), however, vastly oversimplify animal behavior and such behavioral minimalism diminishes the value of these models. We present program SEARCH (Spatially Explicit Animal Response to Composition of Habitat), a spatially explicit, individual-based, population model of animal dispersal through realistic landscapes. SEARCH uses values in Geographic Information System (GIS) maps to apply rules that animals follow during dispersal, thus allowing virtual animals to respond to fine-scale features of the landscape and maintain a detailed memory of areas sensed during movement. SEARCH also incorporates temporally dynamic landscapes so that the environment to which virtual animals respond can change during the course of a simulation. Animals in SEARCH are behaviorally dynamic and able to respond to stimuli based upon their individual experiences. Therefore, SEARCH is able to model behavioral traits of dispersing animals at fine scales and with many dynamic aspects. Such added complexity allows investigation of unique ecological questions. To illustrate SEARCH's capabilities, we simulated case studies using three mammals. We examined the impact of seasonally variable food resources on the weight distribution of dispersing raccoons (Procyon lotor), the effect of temporally dynamic mortality pressure in combination with various levels of behavioral responsiveness in eastern chipmunks (Tamias striatus), and the impact of behavioral plasticity and home range selection on disperser mortality and weight change in virtual American martens (Martes americana). These simulations highlight the relevance of SEARCH for a variety of applications and illustrate benefits it can provide for conservation planning.

The Multimedia Environmental Pollutant Assessment System (MEPAS){reg_sign}: Atmospheric pathway formulations. Revision

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

Droppo, J.G.; Buck, J.W.

1996-03-01

The Multimedia Environmental Pollutant Assessment System (MEPAS) is an integrated software implementation of physics-based fate and transport models for health and environmental risk assessments of both radioactive and hazardous pollutants. This atmospheric component report is one of a series of formulation reports that document the MEPAS mathematical models. MEPAS is a multimedia model; pollutant transport is modeled within, through, and between multiple media (air, soil, groundwater, and surface water). The estimated concentrations in the various media are used to compute exposures and impacts to the environment, to maximum individuals, and to populations. The MEPAS atmospheric component for the air mediamore » documented in this report includes models for emission from a source to the air, initial plume rise and dispersion, airborne pollutant transport and dispersion, and deposition to soils and crops. The material in this report is documentation for MEPAS Versions 3.0 and 3.1 and the MEPAS version used in the Remedial Action Assessment System (RAAS) Version 1.0.« less

Antagonism between local dispersal and self-incompatibility systems in a continuous plant population.

PubMed

Cartwright, Reed A

2009-06-01

Many self-incompatible plant species exist in continuous populations in which individuals disperse locally. Local dispersal of pollen and seeds facilitates inbreeding because pollen pools are likely to contain relatives. Self-incompatibility promotes outbreeding because relatives are likely to carry incompatible alleles. Therefore, populations can experience an antagonism between these forces. In this study, a novel computational model is used to explore the effects of this antagonism on gene flow, allelic diversity, neighbourhood sizes, and identity by descent. I confirm that this antagonism is sensitive to dispersal levels and linkage. However, the results suggest that there is little to no difference between the effects of gametophytic and sporophytic self-incompatibility systems (GSI and SSI) on unlinked loci. More importantly, both GSI and SSI affect unlinked loci in a manner similar to obligate outcrossing without mating types. This suggests that the primary evolutionary impact of self-incompatibility systems may be to prevent selfing, and prevention of biparental inbreeding might be a beneficial side-effect.

Power loss of an oscillating electric dipole in a quantum plasma

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

Ghaderipoor, L.; Mehramiz, A.

2012-12-15

A system of linearized quantum plasma equations (quantum hydrodynamic model) has been used for investigating the dispersion equation for electrostatic waves in the plasma. Furthermore, dispersion relations and their modifications due to quantum effects are used for calculating the power loss of an oscillating electric dipole. Finally, the results are compared in quantum and classical regimes.

Cosmological test using strong gravitational lensing systems

NASA Astrophysics Data System (ADS)

Yuan, C. C.; Wang, F. Y.

2015-09-01

As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay Δτ of images, the velocity dispersion σ of the lensing galaxies and the combination of these two effects, Δτ/σ2. In this paper, in order to carry out one-on-one comparisons between ΛCDM universe and Rh = ct universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the Sloan Lens Advanced Camera for Surveys (SLACS) and Lens Structure and Dynamic survey (LSD) survey. Concerning the time-delay effect, 12 two-image lensing systems with Δτ are also used. In addition, Monte Carlo simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the 99.7 per cent confidence level. Comparing with constraints from Δτ and the velocity dispersion σ, we find that using Δτ/σ2 can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between Δτ/σ2 and σ, Δτ/σ2 could be considered as an improved method of σ if more data samples are available.

CONTRIBUTIONS OF CHEMICAL EXCHANGE TO T1ρ DISPERSION IN A TISSUE MODEL

PubMed Central

Cobb, Jared G.; Xie, Jingping; Gore, John C.

2015-01-01

Variations in T1ρ with locking-field strength (T1ρ dispersion) may be used to estimate proton exchange rates. We developed a novel approach utilizing the second derivative of the dispersion curve to measure exchange in a model system of cross-linked polyacrylamide gels. These gels were varied in relative composition of co-monomers, increasing stiffness, and in pH, modifying exchange rates. MR images were recorded with a spin-locking sequence as described by Sepponen et al. These measurements were fit to a mono-exponential decay function yielding values for T1ρ at each locking-field measured. These values were then fit to a model by Chopra et al. for estimating exchange rates. For low stiffness gels, the calculated exchange values increased by a factor of 4 as pH increased, consistent with chemical exchange being the dominant contributor to T1ρ dispersion. Interestingly, calculated chemical exchange rates also increased with stiffness, likely due to modified side-chain exchange kinetics as the composition varied. This paper demonstrates a new method to assess the structural and chemical effects on T1ρ relaxation dispersion with a suitable model. These phenomena may be exploited in an imaging context to emphasize the presence of nuclei of specific exchange rates, rather than chemical shifts. PMID:21590720

Estimating dispersion from a tornado vortex and mesocyclone

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

Weber, A.H.; Hunter, C.H.

Atmospheric dispersion modeling is required to ensure that a postulated breach in radionuclide storage containers at the Savannah River Site (SRS) from a tornado strike of Fujita-scale intensity F2 or higher will not result in an unacceptable dose to individuals. Fujita-scale tornado descriptions are included in Appendix A of this report. Dispersion models previously used at SRS for estimating dispersion following a tornado strike were developed by D.W. Pepper in 1975 (DP-1387, Dispersion of Small Particles) and H.R. Haynes and D.W. Taylor in 1983 (DPST-82-982, Estimating Doses from Tornado Winds). Research conducted in 1983 on the formation and evolution ofmore » tornadic thunderstorms has lead to a more complete understanding of the tornado vortex and associated persistent updraft and downdraft regions within the parent thunderstorm. To ensure that appropriate, contemporary methods are used for safety analysis, the Pepper model and the Haynes and Taylor model were evaluated with respect to current knowledge of circulations within tornadic thunderstorms. Pepper`s model is complex numerically but contains most of the desired physical parameterizations. Haynes and Taylor`s model is used with the Puff-Plume model (an emergency response model on the Weather INformation and Display System at SRS) and has provisions for radionuclide deposition and rainout. Haynes and Taylor assumed heavy rain following the tornado for a period of ten minutes, followed by a lighter rain for another ten minutes, then no rain for the period when the material is transported to 100 km downwind. However, neither model incorporates the effects of a nearby thunderstorm downdraft.« less

Assessing implicit models for nonpolar mean solvation forces: The importance of dispersion and volume terms

PubMed Central

Wagoner, Jason A.; Baker, Nathan A.

2006-01-01

Continuum solvation models provide appealing alternatives to explicit solvent methods because of their ability to reproduce solvation effects while alleviating the need for expensive sampling. Our previous work has demonstrated that Poisson-Boltzmann methods are capable of faithfully reproducing polar explicit solvent forces for dilute protein systems; however, the popular solvent-accessible surface area model was shown to be incapable of accurately describing nonpolar solvation forces at atomic-length scales. Therefore, alternate continuum methods are needed to reproduce nonpolar interactions at the atomic scale. In the present work, we address this issue by supplementing the solvent-accessible surface area model with additional volume and dispersion integral terms suggested by scaled particle models and Weeks–Chandler–Andersen theory, respectively. This more complete nonpolar implicit solvent model shows very good agreement with explicit solvent results and suggests that, although often overlooked, the inclusion of appropriate dispersion and volume terms are essential for an accurate implicit solvent description of atomic-scale nonpolar forces. PMID:16709675

Early detection of emerging forest disease using dispersal estimation and ecological niche modeling.

PubMed

Meentemeyer, Ross K; Anacker, Brian L; Mark, Walter; Rizzo, David M

2008-03-01

Distinguishing the manner in which dispersal limitation and niche requirements control the spread of invasive pathogens is important for prediction and early detection of disease outbreaks. Here, we use niche modeling augmented by dispersal estimation to examine the degree to which local habitat conditions vs. force of infection predict invasion of Phytophthora ramorum, the causal agent of the emerging infectious tree disease sudden oak death. We sampled 890 field plots for the presence of P. ramorum over a three-year period (2003-2005) across a range of host and abiotic conditions with variable proximities to known infections in California, USA. We developed and validated generalized linear models of invasion probability to analyze the relative predictive power of 12 niche variables and a negative exponential dispersal kernel estimated by likelihood profiling. Models were developed incrementally each year (2003, 2003-2004, 2003-2005) to examine annual variability in model parameters and to create realistic scenarios for using models to predict future infections and to guide early-detection sampling. Overall, 78 new infections were observed up to 33.5 km from the nearest known site of infection, with slightly increasing rates of prevalence across time windows (2003, 6.5%; 2003-2004, 7.1%; 2003-2005, 9.6%). The pathogen was not detected in many field plots that contained susceptible host vegetation. The generalized linear modeling indicated that the probability of invasion is limited by both dispersal and niche constraints. Probability of invasion was positively related to precipitation and temperature in the wet season and the presence of the inoculum-producing foliar host Umbellularia californica and decreased exponentially with distance to inoculum sources. Models that incorporated niche and dispersal parameters best predicted the locations of new infections, with accuracies ranging from 0.86 to 0.90, suggesting that the modeling approach can be used to forecast locations of disease spread. Application of the combined niche plus dispersal models in a geographic information system predicted the presence of P. ramorum across approximately 8228 km2 of California's 84785 km2 (9.7%) of land area with susceptible host species. This research illustrates how probabilistic modeling can be used to analyze the relative roles of niche and dispersal limitation in controlling the distribution of invasive pathogens.

Forecasting volcanic ash dispersal and coeval resuspension during the April-May 2015 Calbuco eruption

NASA Astrophysics Data System (ADS)

Reckziegel, F.; Bustos, E.; Mingari, L.; Báez, W.; Villarosa, G.; Folch, A.; Collini, E.; Viramonte, J.; Romero, J.; Osores, S.

2016-07-01

Atmospheric dispersion of volcanic ash from explosive eruptions or from subsequent fallout deposit resuspension causes a range of impacts and disruptions on human activities and ecosystems. The April-May 2015 Calbuco eruption in Chile involved eruption and resuspension activities. We overview the chronology, effects, and products resulting from these events, in order to validate an operational forecast strategy for tephra dispersal. The modelling strategy builds on coupling the meteorological Weather Research and Forecasting (WRF/ARW) model with the FALL3D dispersal model for eruptive and resuspension processes. The eruption modelling considers two distinct particle granulometries, a preliminary first guess distribution used operationally when no field data was available yet, and a refined distribution based on field measurements. Volcanological inputs were inferred from eruption reports and results from an Argentina-Chilean ash sample data network, which performed in-situ sampling during the eruption. In order to validate the modelling strategy, results were compared with satellite retrievals and ground deposit measurements. Results indicate that the WRF-FALL3D modelling system can provide reasonable forecasts in both eruption and resuspension modes, particularly when the adjusted granulometry is considered. The study also highlights the importance of having dedicated datasets of active volcanoes furnishing first-guess model inputs during the early stages of an eruption.

Modeling and Simulation of Shuttle Launch and Range Operations

NASA Technical Reports Server (NTRS)

Bardina, Jorge; Thirumalainambi, Rajkumar

2004-01-01

The simulation and modeling test bed is based on a mockup of a space flight operations control suitable to experiment physical, procedural, software, hardware and psychological aspects of space flight operations. The test bed consists of a weather expert system to advise on the effect of weather to the launch operations. It also simulates toxic gas dispersion model, impact of human health risk, debris dispersion model in 3D visualization. Since all modeling and simulation is based on the internet, it could reduce the cost of operations of launch and range safety by conducting extensive research before a particular launch. Each model has an independent decision making module to derive the best decision for launch.

Simulation and validation of larval sucker dispersal and retention through the restored Williamson River Delta and Upper Klamath Lake system, Oregon

USGS Publications Warehouse

Wood, Tamara M.; Hendrixson, Heather A.; Markle, Douglas F.; Erdman, Charles S.; Burdick, Summer M.; Ellsworth, Craig M.

2014-01-01

A hydrodynamic model with particle tracking was used to create individual-based simulations to describe larval fish dispersal through the restored Williamson River Delta and into Upper Klamath Lake, Oregon. The model was verified by converting particle ages to larval lengths and comparing these lengths to lengths of larvae in net catches. Correlations of simulated lengths with field data were moderate and suggested a species-specific difference in model performance. Particle trajectories through the delta were affected by wind speed and direction, lake elevation, and shoreline configuration. Once particles entered the lake, transport was a function of current speed and whether behavior enhanced transport (swimming aligned with currents) or countered transport through greater dispersal (faster random swimming). We tested sensitivity to swim speed (higher speeds led to greater dispersal and more retention), shoreline configuration (restoration increased retention relative to pre-restoration conditions), and lake elevation (retention was maximized at an intermediate elevation). The simulations also highlight additional biological questions, such as the extent to which spatially heterogeneous mortality or fish behavior and environmental cues could interact with wind-driven currents and contribute to patterns of dispersal.

A Near-Road Modeling System for Community-Scale Assessments of Traffic-Related AirPollution in the United States

EPA Science Inventory

The Community Line Source (C-LINE) modeling system estimates emissions and dispersion of toxic air pollutants for roadways within the continental United States. It accesses publicly available traffic and meteorological datasets, and is optimized for use on community-sized areas (...

Incorporating a Full-Physics Meteorological Model into an Applied Atmospheric Dispersion Modeling System

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

Berg, Larry K.; Allwine, K Jerry; Rutz, Frederick C.

2004-08-23

A new modeling system has been developed to provide a non-meteorologist with tools to predict air pollution transport in regions of complex terrain. This system couples the Penn State/NCAR Mesoscale Model 5 (MM5) with Earth Tech’s CALMET-CALPUFF system using a unique Graphical User Interface (GUI) developed at Pacific Northwest National Laboratory. This system is most useful in data-sparse regions, where there are limited observations to initialize the CALMET model. The user is able to define the domain of interest, provide details about the source term, and enter a surface weather observation through the GUI. The system then generates initial conditionsmore » and time constant boundary conditions for use by MM5. MM5 is run and the results are piped to CALPUFF for the dispersion calculations. Contour plots of pollutant concentration are prepared for the user. The primary advantages of the system are the streamlined application of MM5 and CALMET, limited data requirements, and the ability to run the coupled system on a desktop or laptop computer. In comparison with data collected as part of a field campaign, the new modeling system shows promise that a full-physics mesoscale model can be used in an applied modeling system to effectively simulate locally thermally-driven winds with minimal observations as input. An unexpected outcome of this research was how well CALMET represented the locally thermally-driven flows.« less

Attenuation and velocity dispersion in the exploration seismic frequency band

NASA Astrophysics Data System (ADS)

Sun, Langqiu

In an anelastic medium, seismic waves are distorted by attenuation and velocity dispersion, which depend on petrophysical properties of reservoir rocks. The effective attenuation and velocity dispersion is a combination of intrinsic attenuation and apparent attenuation due to scattering, transmission response, and data acquisition system. Velocity dispersion is usually neglected in seismic data processing partly because of insufficient observations in the exploration seismic frequency band. This thesis investigates the methods of measuring velocity dispersion in the exploration seismic frequency band and interprets the velocity dispersion data in terms of petrophysical properties. Broadband, uncorrelated vibrator data are suitable for measuring velocity dispersion in the exploration seismic frequency band, and a broad bandwidth optimizes the observability of velocity dispersion. Four methods of measuring velocity dispersion in uncorrelated vibrator VSP data are investigated, which are the sliding window crosscorrelation (SWCC) method, the instantaneous phase method, the spectral decomposition method, and the cross spectrum method. Among them, the SWCC method is a new method and has satisfactory robustness, accuracy, and efficiency. Using the SWCC method, velocity dispersion is measured in the uncorrelated vibrator VSP data from three areas with different geological settings, i.e., Mallik gas hydrate zone, McArthur River uranium mines, and Outokumpu crystalline rocks. The observed velocity dispersion is fitted to a straight line with respect to log frequency for a constant (frequency-independent) Q value. This provides an alternative method for calculating Q. A constant Q value does not directly link to petrophysical properties. A modeling study is implemented for the Mallik and McArthur River data to interpret the velocity dispersion observations in terms of petrophysical properties. The detailed multi-parameter petrophysical reservoir models are built according to the well logs; the models' parameters are adjusted by fitting the synthetic data to the observed data. In this way, seismic attenuation and velocity dispersion provide new insight into petrophysics properties at the Mallik and McArthur River sites. Potentially, observations of attenuation and velocity dispersion in the exploration seismic frequency band can improve the deconvolution process for vibrator data, Q-compensation, near-surface analysis, and first break picking for seismic data.

Discrete element method study of fuel relocation and dispersal during loss-of-coolant accidents

NASA Astrophysics Data System (ADS)

Govers, K.; Verwerft, M.

2016-09-01

The fuel fragmentation, relocation and dispersal (FFRD) during LOCA transients today retain the attention of the nuclear safety community. The fine fragmentation observed at high burnup may, indeed, affect the Emergency Core Cooling System performance: accumulation of fuel debris in the cladding ballooned zone leads to a redistribution of the temperature profile, while dispersal of debris might lead to coolant blockage or to debris circulation through the primary circuit. This work presents a contribution, by discrete element method, towards a mechanistic description of the various stages of FFRD. The fuel fragments are described as a set of interacting particles, behaving as a granular medium. The model shows qualitative and quantitative agreement with experimental observations, such as the packing efficiency in the balloon, which is shown to stabilize at about 55%. The model is then applied to study fuel dispersal, for which experimental parametric studies are both difficult and expensive.

Statistical methods for launch vehicle guidance, navigation, and control (GN&C) system design and analysis

NASA Astrophysics Data System (ADS)

Rose, Michael Benjamin

A novel trajectory and attitude control and navigation analysis tool for powered ascent is developed. The tool is capable of rapid trade-space analysis and is designed to ultimately reduce turnaround time for launch vehicle design, mission planning, and redesign work. It is streamlined to quickly determine trajectory and attitude control dispersions, propellant dispersions, orbit insertion dispersions, and navigation errors and their sensitivities to sensor errors, actuator execution uncertainties, and random disturbances. The tool is developed by applying both Monte Carlo and linear covariance analysis techniques to a closed-loop, launch vehicle guidance, navigation, and control (GN&C) system. The nonlinear dynamics and flight GN&C software models of a closed-loop, six-degree-of-freedom (6-DOF), Monte Carlo simulation are formulated and developed. The nominal reference trajectory (NRT) for the proposed lunar ascent trajectory is defined and generated. The Monte Carlo truth models and GN&C algorithms are linearized about the NRT, the linear covariance equations are formulated, and the linear covariance simulation is developed. The performance of the launch vehicle GN&C system is evaluated using both Monte Carlo and linear covariance techniques and their trajectory and attitude control dispersion, propellant dispersion, orbit insertion dispersion, and navigation error results are validated and compared. Statistical results from linear covariance analysis are generally within 10% of Monte Carlo results, and in most cases the differences are less than 5%. This is an excellent result given the many complex nonlinearities that are embedded in the ascent GN&C problem. Moreover, the real value of this tool lies in its speed, where the linear covariance simulation is 1036.62 times faster than the Monte Carlo simulation. Although the application and results presented are for a lunar, single-stage-to-orbit (SSTO), ascent vehicle, the tools, techniques, and mathematical formulations that are discussed are applicable to ascent on Earth or other planets as well as other rocket-powered systems such as sounding rockets and ballistic missiles.

A novel osmotic pump-based controlled delivery system consisting of pH-modulated solid dispersion for poorly soluble drug flurbiprofen: in vitro and in vivo evaluation.

PubMed

Li, Shujuan; Wang, Xiaoyu; Wang, Yingying; Zhao, Qianqian; Zhang, Lina; Yang, Xinggang; Liu, Dandan; Pan, Weisan

2015-01-01

In this study, a novel controlled release osmotic pump capsule consisting of pH-modulated solid dispersion for poorly soluble drug flurbiprofen (FP) was developed to improve the solubility and oral bioavailability of FP and to minimize the fluctuation of plasma concentration. The pH-modulated solid dispersion containing FP, Kollidon® 12 PF and Na2CO3 at a weight ratio of 1/4.5/0.02 was prepared using the solvent evaporation method. The osmotic pump capsule was assembled by semi-permeable capsule shell of cellulose acetate (CA) prepared by the perfusion method. Then, the solid dispersion, penetration enhancer, and suspending agents were tableted and filled into the capsule. Central composite design-response surface methodology was used to evaluate the influence of factors on the responses. A second-order polynomial model and a multiple linear model were fitted to correlation coefficient of drug release profile and ultimate cumulative release in 12 h, respectively. The actual response values were in good accordance with the predicted ones. The optimized formulation showed a complete drug delivery and zero-order release rate. Beagle dogs were used to be conducted in the pharmacokinetic study. The in vivo study indicated that the relative bioavailability of the novel osmotic pump system was 133.99% compared with the commercial preparation. The novel controlled delivery system with combination of pH-modulated solid dispersion and osmotic pump system is not only a promising strategy to improve the solubility and oral bioavailability of poorly soluble ionizable drugs but also an effective way to reduce dosing frequency and minimize the plasma fluctuation.

Atmospheric Dispersal and Dispostion of Tephra From a Potential Volcanic Eruption at Yucca Mountain, Nevada

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

G. Keating; W.Statham

2004-02-12

The purpose of this model report is to provide documentation of the conceptual and mathematical model (ASHPLUME) for atmospheric dispersal and subsequent deposition of ash on the land surface from a potential volcanic eruption at Yucca Mountain, Nevada. This report also documents the ash (tephra) redistribution conceptual model. The ASHPLUME conceptual model accounts for incorporation and entrainment of waste fuel particles associated with a hypothetical volcanic eruption through the Yucca Mountain repository and downwind transport of contaminated tephra. The ASHPLUME mathematical model describes the conceptual model in mathematical terms to allow for prediction of radioactive waste/ash deposition on the groundmore » surface given that the hypothetical eruptive event occurs. This model report also describes the conceptual model for tephra redistribution from a basaltic cinder cone. Sensitivity analyses and model validation activities for the ash dispersal and redistribution models are also presented. Analyses documented in this model report will improve and clarify the previous documentation of the ASHPLUME mathematical model and its application to the Total System Performance Assessment (TSPA) for the License Application (TSPA-LA) igneous scenarios. This model report also documents the redistribution model product outputs based on analyses to support the conceptual model.« less

Modeling of dispersed-drug delivery from planar polymeric systems: optimizing analytical solutions.

PubMed

Helbling, Ignacio M; Ibarra, Juan C D; Luna, Julio A; Cabrera, María I; Grau, Ricardo J A

2010-11-15

Analytical solutions for the case of controlled dispersed-drug release from planar non-erodible polymeric matrices, based on Refined Integral Method, are presented. A new adjusting equation is used for the dissolved drug concentration profile in the depletion zone. The set of equations match the available exact solution. In order to illustrate the usefulness of this model, comparisons with experimental profiles reported in the literature are presented. The obtained results show that the model can be employed in a broad range of applicability. Copyright © 2010 Elsevier B.V. All rights reserved.

Spatial resolution of transport parameters in a subtropical karst conduit system during dry and wet seasons

NASA Astrophysics Data System (ADS)

Ender, Anna; Goeppert, Nadine; Goldscheider, Nico

2018-04-01

Karst aquifers are characterized by a high degree of hydrologic variability and spatial heterogeneity of transport parameters. Tracer tests allow the quantification of these parameters, but conventional point-to-point experiments fail to capture spatiotemporal variations of flow and transport. The goal of this study was to elucidate the spatial distribution of transport parameters in a karst conduit system at different flow conditions. Therefore, six tracer tests were conducted in an active and accessible cave system in Vietnam during dry and wet seasons. Injections and monitoring were done at five sites along the flow system: a swallow hole, two sites inside the cave, and two springs draining the system. Breakthrough curves (BTCs) were modeled with CXTFIT software using the one-dimensional advection-dispersion model and the two-region nonequilibrium model. In order to obtain transport parameters in the individual sections of the system, a multi-pulse injection approach was used, which was realized by using the BTCs from one section as input functions for the next section. Major findings include: (1) In the entire system, mean flow velocities increase from 183 to 1,043 m/h with increasing discharge, while (2) the proportion of immobile fluid regions decrease; (3) the lowest dispersivity was found at intermediate discharge; (4) in the individual cave sections, flow velocities decrease along the flow direction, related to decreasing gradients, while (5) dispersivity is highest in the middle section of the cave. The obtained results provide a valuable basis for the development of an adapted water management strategy for a projected water-supply system.

In vitro characterization of a novel polymeric system for preparation of amorphous solid drug dispersions.

PubMed

Mahmoudi, Zahra N; Upadhye, Sampada B; Ferrizzi, David; Rajabi-Siahboomi, Ali R

2014-07-01

Preparation of amorphous solid dispersions using polymers is a commonly used formulation strategy for enhancing the solubility of poorly water-soluble drugs. However, often a single polymer may not bring about a significant enhancement in solubility or amorphous stability of a poorly water-soluble drug. This study describes application of a unique and novel binary polymeric blend in preparation of solid dispersions. The objective of this study was to investigate amorphous solid dispersions of glipizide, a BCS class II model drug, in a binary polymeric system of polyvinyl acetate phthalate (PVAP) and hypromellose (hydroxypropyl methylcellulose, HPMC). The solid dispersions were prepared using two different solvent methods: rotary evaporation (rotavap) and fluid bed drug layering on sugar spheres. The performance and physical stability of the dispersions were evaluated with non-sink dissolution testing, powder X-ray diffraction (PXRD), and modulated differential scanning calorimetry (mDSC). PXRD analysis demonstrated an amorphous state for glipizide, and mDSC showed no evidence of phase separation. Non-sink dissolution testing in pH 7.5 phosphate buffer indicated more than twofold increase in apparent solubility of the drug with PVAP-HPMC system. The glipizide solid dispersions demonstrated a high glass transition temperature (Tg) and acceptable chemical and physical stability during the stability period irrespective of the manufacturing process. In conclusion, the polymeric blend of PVAP-HPMC offers a unique formulation approach for developing amorphous solid dispersions with the flexibility towards the use of these polymers in different ratios and combined quantities depending on drug properties.

Near Real{time Data Assimilation for the HYSPLIT Aerosol Dispersion Model

NASA Astrophysics Data System (ADS)

Kalpakis, K.; Yang, S.; Yesha, Y.

2010-12-01

Konstantinos Kalpakis, Shiming Yang, and Yaacov Yesha Department of Computer Science and Electrical Engineering University of Maryland Baltimore County 1000 Hilltop Circle, Baltimore, MD, U.S.A. {kalpakis, shiming1, yayeshag}@csee.umbc.edu ABSTRACT We are working on an IBM-funded project seeking to develop a prototype system for real-time plume dispersion and fire and smoke detection and monitoring. Our prototype system utilizes HYSPLIT and observation data from various sources. HYSPLIT is a model developed by NOAA's Air Resources Laboratory for forecasting aerosol trajectories, dispersion, and concentration from emission sources. It is used extensively by NOAA to routinely provide a number of data products. We develop a data assimilation system for assimilating observational data into the forecasting model in order to improve its forecasting accuracy. Our system is based on the Local Ensemble Transform Kalman Filter (LETKF) algorithm and it is computationally efficient. We evaluate our data assimilation system with real in-situ observational data, and find that our system improves upon HYSPLIT's forecast by reducing the normalized mean squared error and the bias. We are also experimenting with assimilating MODIS data with HYSPLIT model forecasts. To this end, we extrapolate ground concentrations from MODIS Aerosol Optical Depth (AOD) data. Our extrapolation approach relies on spatially localized linear regressions of aerosol concentrations from ground stations in the Air Quality System (AQS) network and MODIS AOD data. We expect that assimilating the extrapolated concentrations leads into further improvements of HYSPLIT forecasts. Furthermore, we are investigating using additional sources of in-situ and remotely sensed observations, such as GOES AOD 30-minute data, and UAV data from the Ikhana AMS fire missions. These sources provide higher spatial resolution and more frequent temporal coverage. Moreover, GOES and UAVs provide near-real time data which should be useful in improving HYSPLIT forecasts of smoke from wildfires. Currently, the Ikhana AMS fire missions team provides L1B data which are very useful in themselves, but no level 2 to the best of our knowledge. For our application, it would very useful to have an AOD data product for these datasets. A possible path for deriving AOD data the AMS sensor onboard UAVs would be to utilize the DRL code for deriving the MODIS AOD from MODIS L1B data, due to the sensor similarities. Developing such code would be very useful for wildfire smoke prediction applications. Our near real-time data assimilation system helps in bridging the gap between predictions and real-time observations, for more accurate and timely aerosol dispersion forecasts. Keywords: data assimilation, HYSPLIT, forecast model performance, real-time, ensemble Kalman filter, aerosol dispersion and concentration.

Symmetries, chirp-free points, and bistability in dispersion-managed fiber lines.

PubMed

Turitsyn, S K; Nijhof, J H; Mezentsev, V K; Doran, N J

1999-12-15

We show from an elementary symmetry analysis that, in dispersion-compensated systems for which a lossless model is valid, nonlinearity requires a chirp-free point at the center of symmetry (if such exists) of the map for any kind of unique periodic solution. We also present an example of a more-complex map when the periodic solution is not unique.

Charge-dependent many-body exchange and dispersion interactions in combined QM/MM simulations

NASA Astrophysics Data System (ADS)

Kuechler, Erich R.; Giese, Timothy J.; York, Darrin M.

2015-12-01

Accurate modeling of the molecular environment is critical in condensed phase simulations of chemical reactions. Conventional quantum mechanical/molecular mechanical (QM/MM) simulations traditionally model non-electrostatic non-bonded interactions through an empirical Lennard-Jones (LJ) potential which, in violation of intuitive chemical principles, is bereft of any explicit coupling to an atom's local electronic structure. This oversight results in a model whereby short-ranged exchange-repulsion and long-ranged dispersion interactions are invariant to changes in the local atomic charge, leading to accuracy limitations for chemical reactions where significant atomic charge transfer can occur along the reaction coordinate. The present work presents a variational, charge-dependent exchange-repulsion and dispersion model, referred to as the charge-dependent exchange and dispersion (QXD) model, for hybrid QM/MM simulations. Analytic expressions for the energy and gradients are provided, as well as a description of the integration of the model into existing QM/MM frameworks, allowing QXD to replace traditional LJ interactions in simulations of reactive condensed phase systems. After initial validation against QM data, the method is demonstrated by capturing the solvation free energies of a series of small, chlorine-containing compounds that have varying charge on the chlorine atom. The model is further tested on the SN2 attack of a chloride anion on methylchloride. Results suggest that the QXD model, unlike the traditional LJ model, is able to simultaneously obtain accurate solvation free energies for a range of compounds while at the same time closely reproducing the experimental reaction free energy barrier. The QXD interaction model allows explicit coupling of atomic charge with many-body exchange and dispersion interactions that are related to atomic size and provides a more accurate and robust representation of non-electrostatic non-bonded QM/MM interactions.

Superluminal propagation in a poly-chromatically driven gain assisted four-level N-type atomic system

NASA Astrophysics Data System (ADS)

Amin Bacha, Bakht; Ahmad, Iftikhar; Ullah, Arif; Ali, Hazrat

2013-10-01

We investigate the behavior of light propagation in an N-type four-level gain assisted model (Agarwal and Dasgupta 2004 Phys. Rev. A 70 023802) under poly-chromatic pump fields. The system exhibits interesting results of multiple controllable pairs of the gain doublet profile with changes in the intensity of the control field. We observe multiple anomalous dispersive regions for superluminal propagation in the medium. A negative group velocity of -37.50 m s-1 with a negative time delay of -8 ms is observed between each gain doublet in anomalous dispersive regions. This generalized model and its predictions can be tested with existing experimental setups.

The Rb 780-nanometer Faraday anomalous dispersion optical filter: Theory and experiment

NASA Technical Reports Server (NTRS)

Yin, B.; Alvarez, L. S.; Shay, T. M.

1994-01-01

The Faraday anomalous dispersion optical filter may provide ultra-high background noise rejection for free-space laser communications systems. The theoretical model for the filter is reported. The experimental measurements and their comparison with theoretical results are discussed. The results show that the filter can provide a 56-dB solar background noise rejection with about a 2-GHz transmission bandwidth and no image degradation. To further increase the background noise rejection, a composite Zeeman and Faraday anomalous dispersion optical filter is designed and experimentally demonstrated.

NASA Agricultural Aircraft Research Program in the Langley Vortex Research Facility and the Langley Full Scale Wind Tunnel

NASA Technical Reports Server (NTRS)

Jordan, F. L., Jr.; Mclemore, H. C.; Bragg, M. B.

1978-01-01

The current status of aerial applications technology research at the Langley's Vortex Research Facility and Full-Scale Wind Tunnel is reviewed. Efforts have been directed mainly toward developing and validating the required experimental and theoretical research tools. A capability to simulate aerial dispersal of materials from agricultural airplanes with small-scale airplane models, numerical methods, and dynamically scaled test particles was demonstrated. Tests on wake modification concepts have proved the feasibility of tailoring wake properties aerodynamically to produce favorable changes in deposition and to provide drift control. An aerodynamic evaluation of the Thrush Commander 800 agricultural airplane with various dispersal systems installed is described. A number of modifications intended to provide system improvement to both airplane and dispersal system are examined, and a technique for documenting near-field spray characteristics is evaluated.

Evaluation of an urban vegetative canopy scheme and impact on plume dispersion

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

Nelson, Matthew A; Williams, Michael D; Zajic, Dragan

2009-01-01

The Quick Urban and Industrial Complex (QUIC) atmospheric dispersion modeling system attempts to fill an important gap between the fast, but nonbuilding-aware Gaussian plume models and the building-aware but slow computational fluid dynamics (CFD) models. While Gaussian models have the ability to give answers quickly to emergency responders, they are unlikely to be able to adequately account for the effects of the building-induced complex flow patterns on the near-source dispersion of contaminants. QUIC uses a diagnostic massconsistent empirical wind model called QUIC-URB that is based on the methodology of Rockle (1990), (see also Kaplan and Dinar 1996). In this approach,more » the recirculation zones that form around and between buildings are inserted into the flow using empirical parameterizations and then the wind field is forced to be mass consistent. Although not as accurate as CFD codes, this approach is several orders of magnitude faster and accounts for the bulk effects of buildings.« less

Use of Remote Sensing and Dust Modelling to Evaluate Ecosystem Phenology and Pollen Dispersal

NASA Technical Reports Server (NTRS)

Luvall, Jeffrey C.; Sprigg, William A.; Watts, Carol; Shaw, Patrick

2007-01-01

The impact of pollen release and downwind concentrations can be evaluated utilizing remote sensing. Previous NASA studies have addressed airborne dust prediction systems PHAiRS (Public Health Applications in Remote Sensing) which have determined that pollen forecasts and simulations are possible. By adapting the deterministic dust model (as an in-line system with the National Weather Service operational forecast model) used in PHAiRS to simulate downwind dispersal of pollen, initializing the model with pollen source regions from MODIS, assessing the results a rapid prototype concept can be produced. We will present the results of our effort to develop a deterministic model for predicting and simulating pollen emission and downwind concentration to study details or phenology and meteorology and their dependencies, and the promise of a credible real time forecast system to support public health and agricultural science and service. Previous studies have been done with PHAiRS research, the use of NASA data, the dust model and the PHAiRS potential to improve public health and environmental services long into the future.

Landscape characteristics of Rhizophora mangle forests and propagule deposition in coastal environments of Florida (USA)

USGS Publications Warehouse

Sengupta, R.; Middleton, B.; Yan, C.; Zuro, M.; Hartman, H.

2005-01-01

Field dispersal studies are seldom conducted at regional scales even though reliable information on mid-range dispersal distance is essential for models of colonization. The purpose of this study was to examine the potential distance of dispersal of Rhizophora mangle propagules by comparing deposition density with landscape characteristics of mangrove forests. Propagule density was estimated at various distances to mangrove sources (R. mangle) on beaches in southwestern Florida in both high-and low-energy environments, either facing open gulf waters vs. sheltered, respectively. Remote sensing and Geographic Information Systems were used to identify source forests and to determine their landscape characteristics (forest size and distance to deposition area) for the regression analyses. Our results indicated that increasing density of propagules stranded on beaches was related negatively to the distance of the deposition sites from the nearest stands of R. mangle and that deposition was greatly diminished 2 km or more from the source. Measures of fragmentation such as the area of the R. mangle forests were related to propagule deposition but only in low-energy environments. Our results suggest that geographic models involving the colonization of coastal mangrove systems should include dispersal dynamics at mid-range scales, i.e., for our purposes here, beyond the local scale of the forest and up to 5 km distant. Studies of mangrove propagule deposition at various spatial scales are key to understanding regeneration limitations in natural gaps and restoration areas. Therefore, our study of mid-range propagule dispersal has broad application to plant ecology, restoration, and modeling. ?? Springer 2005.

Male-killing endosymbionts: influence of environmental conditions on persistence of host metapopulation

PubMed Central

2008-01-01

Background Male killing endosymbionts manipulate their arthropod host reproduction by only allowing female embryos to develop into infected females and killing all male offspring. Because of the reproductive manipulation, we expect them to have an effect on the evolution of host dispersal rates. In addition, male killing endosymbionts are expected to approach fixation when fitness of infected individuals is larger than that of uninfected ones and when transmission from mother to offspring is nearly perfect. They then vanish as the host population crashes. High observed infection rates and among-population variation in natural systems can consequently not be explained if defense mechanisms are absent and when transmission efficiency is perfect. Results By simulating the host-endosymbiont dynamics in an individual-based metapopulation model we show that male killing endosymbionts increase host dispersal rates. No fitness compensations were built into the model for male killing endosymbionts, but they spread as a group beneficial trait. Host and parasite populations face extinction under panmictic conditions, i.e. conditions that favor the evolution of high dispersal in hosts. On the other hand, deterministic 'curing' (only parasite goes extinct) can occur under conditions of low dispersal, e.g. under low environmental stochasticity and high dispersal mortality. However, high and stable infection rates can be maintained in metapopulations over a considerable spectrum of conditions favoring intermediate levels of dispersal in the host. Conclusion Male killing endosymbionts without explicit fitness compensation spread as a group selected trait into a metapopulation. Emergent feedbacks through increased evolutionary stable dispersal rates provide an alternative explanation for both, the high male-killing endosymbiont infection rates and the high among-population variation in local infection rates reported for some natural systems. PMID:18764948

Development and Utilization of Regional Oceanic Modeling System (ROMS). Delicacy, Imprecision, and Uncertainty of Oceanic Simulations: An Investigation with the Regional Oceanic Modeling System (ROMS). Mixing in the Ocean Surface Layer Using the Regional Oceanic Modeling System (ROMS).

DTIC Science & Technology

2011-09-30

community use for ROMS is biogeochemisty: chemical cycles, water quality, blooms , micro-nutrients, larval dispersal, biome transitions, and coupling to...J.C. McWilliams, X. Capet, and J. Kurian, 2010: Heat balance and eddies in the Peru- Chile Current System. Climate Dynamics, 37, in press. doi10.1007

Mate-finding as an overlooked critical determinant of dispersal variation in sexually-reproducing animals.

PubMed

Gilroy, James J; Lockwood, Julie L

2012-01-01

Dispersal is a critically important process in ecology, but robust predictive models of animal dispersal remain elusive. We identify a potentially ubiquitous component of variation in animal dispersal that has been largely overlooked until now: the influence of mate encounters on settlement probability. We use an individual-based model to simulate dispersal in sexually-reproducing organisms that follow a simple set of movement rules based on conspecific encounters, within an environment lacking spatial habitat heterogeneity. We show that dispersal distances vary dramatically with fluctuations in population density in such a model, even in the absence of variation in dispersive traits between individuals. In a simple random-walk model with promiscuous mating, dispersal distributions become increasingly 'fat-tailed' at low population densities due to the increasing scarcity of mates. Similar variation arises in models incorporating territoriality. In a model with polygynous mating, we show that patterns of sex-biased dispersal can even be reversed across a gradient of population density, despite underlying dispersal mechanisms remaining unchanged. We show that some widespread dispersal patterns found in nature (e.g. fat tailed distributions) can arise as a result of demographic variability in the absence of heterogeneity in dispersive traits across the population. This implies that models in which individual dispersal distances are considered to be fixed traits might be unrealistic, as dispersal distances vary widely under a single dispersal mechanism when settlement is influenced by mate encounters. Mechanistic models offer a promising means of advancing our understanding of dispersal in sexually-reproducing organisms.

Mycelium-Like Networks Increase Bacterial Dispersal, Growth, and Biodegradation in a Model Ecosystem at Various Water Potentials.

PubMed

Worrich, Anja; König, Sara; Miltner, Anja; Banitz, Thomas; Centler, Florian; Frank, Karin; Thullner, Martin; Harms, Hauke; Kästner, Matthias; Wick, Lukas Y

2016-05-15

Fungal mycelia serve as effective dispersal networks for bacteria in water-unsaturated environments, thereby allowing bacteria to maintain important functions, such as biodegradation. However, poor knowledge exists on the effects of dispersal networks at various osmotic (Ψo) and matric (Ψm) potentials, which contribute to the water potential mainly in terrestrial soil environments. Here we studied the effects of artificial mycelium-like dispersal networks on bacterial dispersal dynamics and subsequent effects on growth and benzoate biodegradation at ΔΨo and ΔΨm values between 0 and -1.5 MPa. In a multiple-microcosm approach, we used a green fluorescent protein (GFP)-tagged derivative of the soil bacterium Pseudomonas putida KT2440 as a model organism and sodium benzoate as a representative of polar aromatic contaminants. We found that decreasing ΔΨo and ΔΨm values slowed bacterial dispersal in the system, leading to decelerated growth and benzoate degradation. In contrast, dispersal networks facilitated bacterial movement at ΔΨo and ΔΨm values between 0 and -0.5 MPa and thus improved the absolute biodegradation performance by up to 52 and 119% for ΔΨo and ΔΨm, respectively. This strong functional interrelationship was further emphasized by a high positive correlation between population dispersal, population growth, and degradation. We propose that dispersal networks may sustain the functionality of microbial ecosystems at low osmotic and matric potentials. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Enhanced global Radionuclide Source Attribution for the Nuclear-Test-Ban Verification by means of the Adjoint Ensemble Dispersion Modeling Technique applied at the IDC/CTBTO.

NASA Astrophysics Data System (ADS)

Becker, A.; Wotawa, G.; de Geer, L.

2006-05-01

The Provisional Technical Secretariat (PTS) of the CTBTO Preparatory Commission maintains and permanently updates a source-receptor matrix (SRM) describing the global monitoring capability of a highly sensitive 80 stations radionuclide (RN) network in order to verify states signatories' compliance of the comprehensive nuclear-test-ban treaty (CTBT). This is done by means of receptor-oriented Lagrangian particle dispersion modeling (LPDM) to help determine the region from which suspicious radionuclides may originate. In doing so the LPDM FLEXPART5.1 is integrated backward in time based on global analysis wind fields yielding global source-receptor sensitivity (SRS) fields stored in three-hour frequency and at 1º horizontal resolution. A database of these SRS fields substantially helps in improving the interpretation of the RN samples measurements and categorizations because it enables the testing of source-hypothesis's later on in a pure post-processing (SRM inversion) step being feasible on hardware with specifications comparable to currently sold PC's or Notebooks and at any place (decentralized), provided access to the SRS fields is warranted. Within the CTBT environment it is important to quickly achieve decision-makers confidence in the SRM based backtracking products issued by the PTS in the case of the occurrence of treaty relevant radionuclides. Therefore the PTS has set up a highly automated response system together with the Regional Specialized Meteorological Centers of the World Meteorological Organization in the field of dispersion modeling who committed themselves to provide the PTS with the same standard SRS fields as calculated by their systems for CTBT relevant cases. This system was twice utilized in 2005 in order to perform adjoint ensemble dispersion modeling (EDM) and demonstrated the potential of EDM based backtracking to improve the accuracy of the source location related to singular nuclear events thus serving the backward analogue to the findings of the ensemble dispersion modeling (EDM) technique No. 5 efforts performed by Galmarini et al, 2004 (Atmos. Env. 38, 4607-4617). As the scope of the adjoint EDM methodology is not limited to CTBT verification but can be applied to any kind of nuclear event monitoring and location it bears the potential to improve the design of manifold emergency response systems towards preparedness concepts as needed for mitigation of disasters (like Chernobyl) and pre-emptive estimation of pollution hazards.

Numerical modelling of the work of a pulsed aerosol system for fire fighting at the ignitions of liquid hydrocarbon fuels

NASA Astrophysics Data System (ADS)

Rychkov, A. D.

2009-06-01

The work of a pulsed aerosol system for fire fighting is modelled, which is designed for fire fighting at oil storages and at the spills of oil products, whose vapors were modelled by gaseous methane. The system represents a device for separate installation, which consists of a charge of solid propellant (the gas generator) and a container with fine-dispersed powder of the flame-damper substance. The methane combustion was described by a one-stage gross-reaction, the influence of the concentration of vapors of the flame-damper substance on the combustion process was taken into account by reducing the pre-exponent factor in the Arrhenius law and was described by an empirical dependence. The computational experiment showed that the application of the pulsed aerosol system for fire fighting ensures an efficient transport of fine-dispersed aerosol particles of the flame-damping substance and its forming vapors to the combustion zone; the concentration of particles ensures the damping of the heat source.

Evaluation of high-resolution GRAMM-GRAL (v15.12/v14.8) NOx simulations over the city of Zürich, Switzerland

NASA Astrophysics Data System (ADS)

Berchet, Antoine; Zink, Katrin; Oettl, Dietmar; Brunner, Jürg; Emmenegger, Lukas; Brunner, Dominik

2017-09-01

Hourly NOx concentrations were simulated for the city of Zürich, Switzerland, at 10 m resolution for the years 2013-2014. The simulations were generated with the nested mesoscale meteorology and micro-scale dispersion model system GRAMM-GRAL (versions v15.12 and v14.8) by applying a catalogue-based approach. This approach was specifically designed to enable long-term city-wide building-resolving simulations with affordable computation costs. It relies on a discrete set of possible weather situations and corresponding steady-state flow and dispersion patterns that are pre-computed and then matched hourly with actual meteorological observations. The modelling system was comprehensively evaluated using eight sites continuously monitoring NOx concentrations and 65 passive samplers measuring NO2 concentrations on a 2-weekly basis all over the city. The system was demonstrated to fulfil the European Commission standards for air pollution modelling at nearly all sites. The average spatial distribution was very well represented, despite a general tendency to overestimate the observed concentrations, possibly due to a crude representation of traffic-induced turbulence and to underestimated dispersion in the vicinity of buildings. The temporal variability of concentrations explained by varying emissions and weather situations was accurately reproduced on different timescales. The seasonal cycle of concentrations, mostly driven by stronger vertical dispersion in summer than in winter, was very well captured in the 2-year simulation period. Short-term events, such as episodes of particularly high and low concentrations, were detected in most cases by the system, although some unrealistic pollution peaks were occasionally generated, pointing at some limitations of the steady-state approximation. The different patterns of the diurnal cycle of concentrations observed in the city were generally well captured as well. The evaluation confirmed the adequacy of the catalogue-based approach in the context of city-scale air pollution modelling. The ability to reproduce not only the spatial gradients but also the hourly temporal variability over multiple years makes the model system particularly suitable for investigating individualized air pollution exposure in the city.

The effects of polymer carrier, hot melt extrusion process and downstream processing parameters on the moisture sorption properties of amorphous solid dispersions.

PubMed

Feng, Xin; Vo, Anh; Patil, Hemlata; Tiwari, Roshan V; Alshetaili, Abdullah S; Pimparade, Manjeet B; Repka, Michael A

2016-05-01

The aim of this study was to evaluate the effect of polymer carrier, hot melt extrusion and downstream processing parameters on the water uptake properties of amorphous solid dispersions. Three polymers and a model drug were used to prepare amorphous solid dispersions utilizing the hot melt extrusion technology. The sorption-desorption isotherms of solid dispersions and their physical mixtures were measured by the dynamic vapour sorption system, and the effects of polymer hydrophobicity, hygroscopicity, molecular weight and the hot melt extrusion process were investigated. Fourier transform infrared (FTIR) imaging was performed to understand the phase separation driven by the moisture. Solid dispersions with polymeric carriers with lower hydrophilicity, hygroscopicity and higher molecular weight could sorb less moisture under the high relative humidity (RH) conditions. The water uptake ability of polymer-drug solid dispersion systems were decreased compared with the physical mixture after hot melt extrusion, which might be due to the decreased surface area and porosity. The FTIR imaging indicated that the homogeneity of the drug molecularly dispersed within the polymer matrix was changed after exposure to high RH. Understanding the effect of formulation and processing on the moisture sorption properties of solid dispersions is essential for the development of drug products with desired physical and chemical stability. © 2015 Royal Pharmaceutical Society.

Experimental investigation of gas hydrate formation, plugging and transportability in partially dispersed and water continuous systems

NASA Astrophysics Data System (ADS)

Vijayamohan, Prithvi

As oil/gas subsea fields mature, the amount of water produced increases significantly due to the production methods employed to enhance the recovery of oil. This is true especially in the case of oil reservoirs. This increase in the water hold up increases the risk of hydrate plug formation in the pipelines, thereby resulting in higher inhibition cost strategies. A major industry concern is to reduce the severe safety risks associated with hydrate plug formation, and significantly extending subsea tieback distances by providing a cost effective flow assurance management/safety tool for mature fields. Developing fundamental understanding of the key mechanistic steps towards hydrate plug formation for different multiphase flow conditions is a key challenge to the flow assurance community. Such understanding can ultimately provide new insight and hydrate management guidelines to diminish the safety risks due to hydrate formation and accumulation in deepwater flowlines and facilities. The transportability of hydrates in pipelines is a function of the operating parameters, such as temperature, pressure, fluid mixture velocity, liquid loading, and fluid system characteristics. Specifically, the hydrate formation rate and plugging onset characteristics can be significantly different for water continuous, oil continuous, and partially dispersed systems. The latter is defined as a system containing oil/gas/water, where the water is present both as a free phase and partially dispersed in the oil phase (i.e., entrained water in the oil). Since hydrate formation from oil dispersed in water systems and partially dispersed water systems is an area which is poorly understood, this thesis aims to address some key questions in these systems. Selected experiments have been performed at the University of Tulsa flowloop to study the hydrate formation and plugging characteristics for the partially dispersed water/oil/gas systems as well as systems where the oil is completely dispersed in water. These experiments indicate that the partially dispersed systems tend to be problematic and are more severe cases with respect to flow assurance when compared to systems where the water is completely dispersed in oil. We have found that the partially dispersed systems are distinct, and are not an intermediate case between water dominated, and water-in-oil emulsified systems. Instead the experiments indicate that the hydrate formation and plugging mechanism for these systems are very complex. Hydrate growth is very rapid for such systems when compared to 100% water cut systems. The plugging mechanism for these systems is a combination of various phenomena (wall growth, agglomeration, bedding/settling, etc). Three different oils with different viscosities have been used to investigate the transportability of hydrates with respect to oil properties. The experiments indicate that the transportability of hydrates increases with increase in oil viscosity. The data from the tests performed provide the basis for a mechanistic model for hydrate formation and plugging in partially dispersed systems. It is found that in systems that were in stratified flow regime before hydrate onset, the hydrates eventually settled on the pipe walls thereby decreasing the flow area for the flow of fluids. In systems that were in the slug flow regime before hydrate formation, moving beds of hydrates were the main cause for plugging. In both the flow regimes, the systems studied entered a plugging regime beyond a certain hydrate concentration. This is termed as φplugging onset and can be used as an indicator to calculate the amount of hydrates that can be transported safely without requiring any additional treatment for a given set of flow characteristics. A correlation to calculate this hydrate concentration based on easily accessible parameters is developed in terms of flow characteristics and oil properties. The work performed in this thesis has enhanced the understanding of the hydrate plug mechanism in pipelines having high amounts of water. This work has also shown the effect of hydrate formation in different flow regimes thereby shedding light on the effects of hydrates on multiphase flow and vice versa. Lessons resulting from this work could be incorporated into flow assurance models, as well as operating company production strategies to reduce or mitigate hydrate plugging risks in complex multiphase systems.

Microcomputer pollution model for civilian airports and Air Force Bases. Model application and background

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

Segal, H.M.

1988-08-01

This is one of three reports describing the Emissions and Dispersion Modeling System (EDMS). All reports use the same main title--A MICROCOMPUTER MODEL FOR CIVILIAN AIRPORTS AND AIR FORCE BASES--but different subtitles. The subtitles are: (1) USER'S GUIDE - ISSUE 2 (FAA-EE-88-3/ESL-TR-88-54); (2) MODEL DESCRIPTION (FAA-EE-88-4/ESL-TR-88-53); (S) MODEL APPLICATION AND BACKGROUND (FAA-EE-88-5/ESL-TR-88-55). The first and second reports above describe the EDMS model and provide instructions for its use. This is the third report. IT consists of an accumulation of five key documents describing the development and use of the EDMS model. This report is prepared in accordance with discussions withmore » the EPA and requirements outlined in the March 27, 1980 Federal Register for submitting air-quality models to the EPA. Contents: Model Development and Use - Its Chronology and Reports; Monitoring Concorde EMissions; The Influence of Aircraft Operations on Air Quality at Airports; Simplex A - A simplified Atmospheric Dispersion Model for Airport Use -(User's Guide); Microcomputer Graphics in Atmospheric Dispersion Modeling; Pollution from Motor Vehicles and Aircraft at Stapleton International Airport (Abbreviated Report).« less

Optimisation of dispersion parameters of Gaussian plume model for CO₂ dispersion.

PubMed

Liu, Xiong; Godbole, Ajit; Lu, Cheng; Michal, Guillaume; Venton, Philip

2015-11-01

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the 'Gaussian' dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the 'dispersion parameters' in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different 'source strengths' and degrees of ground roughness. The performance of the CFD models was validated against the 'Kit Fox' field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained.

A DGTD method for the numerical modeling of the interaction of light with nanometer scale metallic structures taking into account non-local dispersion effects

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

Schmitt, Nikolai; Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder; Scheid, Claire

2016-07-01

The interaction of light with metallic nanostructures is increasingly attracting interest because of numerous potential applications. Sub-wavelength metallic structures, when illuminated with a frequency close to the plasma frequency of the metal, present resonances that cause extreme local field enhancements. Exploiting the latter in applications of interest requires a detailed knowledge about the occurring fields which can actually not be obtained analytically. For the latter mentioned reason, numerical tools are thus an absolute necessity. The insight they provide is very often the only way to get a deep enough understanding of the very rich physics at play. For the numericalmore » modeling of light-structure interaction on the nanoscale, the choice of an appropriate material model is a crucial point. Approaches that are adopted in a first instance are based on local (i.e. with no interaction between electrons) dispersive models, e.g. Drude or Drude–Lorentz models. From the mathematical point of view, when a time-domain modeling is considered, these models lead to an additional system of ordinary differential equations coupled to Maxwell's equations. However, recent experiments have shown that the repulsive interaction between electrons inside the metal makes the response of metals intrinsically non-local and that this effect cannot generally be overlooked. Technological achievements have enabled the consideration of metallic structures in a regime where such non-localities have a significant influence on the structures' optical response. This leads to an additional, in general non-linear, system of partial differential equations which is, when coupled to Maxwell's equations, significantly more difficult to treat. Nevertheless, dealing with a linearized non-local dispersion model already opens the route to numerous practical applications of plasmonics. In this work, we present a Discontinuous Galerkin Time-Domain (DGTD) method able to solve the system of Maxwell's equations coupled to a linearized non-local dispersion model relevant to plasmonics. While the method is presented in the general 3D case, numerical results are given for 2D simulation settings.« less

Dispersal and deposition of river sediments in coastal seas: Models from Asia and the tropics

NASA Astrophysics Data System (ADS)

Wright, L. D.

The diverse mechanisms by which river-borne sediments are dispersed into coastal oceans and the associated patterns of deposition are considered for some tropical and Asian river mouth dispersal systems: the Huanghe (Yellow River), which enters the Bohai Gulf (China), the Purari River which enters the Gulf of Papua (Papua New Guinea) and the Jaba River, which enters Empress Augusta Bay (Bougainville, Papua New Guinea). These models contrast sharply with 'conventional' models such as that of the Mississippi, although in different respects. Extremely high suspended sediment concentrations off the Huanghe mouth cause sinking, gravity-driven plumes which produce rapid deposition very near the mouth; extremely rapid seaward growth of the subaqueous delta results. Although the average water discharge of the Purari exceeds that of the Huanghe, the average sediment discharge from the Purari is an order of magnitude less than that of the Huanghe. Suspended sediments transported via buoyant plumes from the Purari mouth are trapped inshore by the southeasterly trades and have their ultimate sink in the tidal estuaries to the west of the mouths rather than offshore. The Jaba is a small river with a very steep gradient and an extremely high bed load relative to water discharge. It has constructed a protruding and rapidly evolving delta. Literature on the Indonesian rivers Solo and Porong dispersal systems suggests that those systems may, at different times, be subject to processes similar to those which operate off the mouths of the Huanghe, Purari and Jaba although no single, direct analogies can be made.

Numerical simulation of disperse particle flows on a graphics processing unit

NASA Astrophysics Data System (ADS)

Sierakowski, Adam J.

In both nature and technology, we commonly encounter solid particles being carried within fluid flows, from dust storms to sediment erosion and from food processing to energy generation. The motion of uncountably many particles in highly dynamic flow environments characterizes the tremendous complexity of such phenomena. While methods exist for the full-scale numerical simulation of such systems, current computational capabilities require the simplification of the numerical task with significant approximation using closure models widely recognized as insufficient. There is therefore a fundamental need for the investigation of the underlying physical processes governing these disperse particle flows. In the present work, we develop a new tool based on the Physalis method for the first-principles numerical simulation of thousands of particles (a small fraction of an entire disperse particle flow system) in order to assist in the search for new reduced-order closure models. We discuss numerous enhancements to the efficiency and stability of the Physalis method, which introduces the influence of spherical particles to a fixed-grid incompressible Navier-Stokes flow solver using a local analytic solution to the flow equations. Our first-principles investigation demands the modeling of unresolved length and time scales associated with particle collisions. We introduce a collision model alongside Physalis, incorporating lubrication effects and proposing a new nonlinearly damped Hertzian contact model. By reproducing experimental studies from the literature, we document extensive validation of the methods. We discuss the implementation of our methods for massively parallel computation using a graphics processing unit (GPU). We combine Eulerian grid-based algorithms with Lagrangian particle-based algorithms to achieve computational throughput up to 90 times faster than the legacy implementation of Physalis for a single central processing unit. By avoiding all data communication between the GPU and the host system during the simulation, we utilize with great efficacy the GPU hardware with which many high performance computing systems are currently equipped. We conclude by looking forward to the future of Physalis with multi-GPU parallelization in order to perform resolved disperse flow simulations of more than 100,000 particles and further advance the development of reduced-order closure models.

Dynamical and statistical behavior of discrete combustion waves: a theoretical and numerical study.

PubMed

Bharath, Naine Tarun; Rashkovskiy, Sergey A; Tewari, Surya P; Gundawar, Manoj Kumar

2013-04-01

We present a detailed theoretical and numerical study of combustion waves in a discrete one-dimensional disordered system. The distances between neighboring reaction cells were modeled with a gamma distribution. The results show that the random structure of the microheterogeneous system plays a crucial role in the dynamical and statistical behavior of the system. This is a consequence of the nonlinear interaction of the random structure of the system with the thermal wave. An analysis of the experimental data on the combustion of a gasless system (Ti + xSi) and a wide range of thermite systems was performed in view of the developed model. We have shown that the burning rate of the powder system sensitively depends on its internal structure. The present model allows for reproducing theoretically the experimental data for a wide range of pyrotechnic mixtures. We show that Arrhenius' macrokinetics at combustion of disperse systems can take place even in the absence of Arrhenius' microkinetics; it can have a purely thermal nature and be related to their heterogeneity and to the existence of threshold temperature. It is also observed that the combustion of disperse systems always occurs in the microheterogeneous mode according to the relay-race mechanism.

Dynamical and statistical behavior of discrete combustion waves: A theoretical and numerical study

NASA Astrophysics Data System (ADS)

Bharath, Naine Tarun; Rashkovskiy, Sergey A.; Tewari, Surya P.; Gundawar, Manoj Kumar

2013-04-01

We present a detailed theoretical and numerical study of combustion waves in a discrete one-dimensional disordered system. The distances between neighboring reaction cells were modeled with a gamma distribution. The results show that the random structure of the microheterogeneous system plays a crucial role in the dynamical and statistical behavior of the system. This is a consequence of the nonlinear interaction of the random structure of the system with the thermal wave. An analysis of the experimental data on the combustion of a gasless system (Ti + xSi) and a wide range of thermite systems was performed in view of the developed model. We have shown that the burning rate of the powder system sensitively depends on its internal structure. The present model allows for reproducing theoretically the experimental data for a wide range of pyrotechnic mixtures. We show that Arrhenius’ macrokinetics at combustion of disperse systems can take place even in the absence of Arrhenius’ microkinetics; it can have a purely thermal nature and be related to their heterogeneity and to the existence of threshold temperature. It is also observed that the combustion of disperse systems always occurs in the microheterogeneous mode according to the relay-race mechanism.

Thermal niche estimators and the capability of poor dispersal species to cope with climate change

NASA Astrophysics Data System (ADS)

Sánchez-Fernández, David; Rizzo, Valeria; Cieslak, Alexandra; Faille, Arnaud; Fresneda, Javier; Ribera, Ignacio

2016-03-01

For management strategies in the context of global warming, accurate predictions of species response are mandatory. However, to date most predictions are based on niche (bioclimatic) models that usually overlook biotic interactions, behavioral adjustments or adaptive evolution, and assume that species can disperse freely without constraints. The deep subterranean environment minimises these uncertainties, as it is simple, homogeneous and with constant environmental conditions. It is thus an ideal model system to study the effect of global change in species with poor dispersal capabilities. We assess the potential fate of a lineage of troglobitic beetles under global change predictions using different approaches to estimate their thermal niche: bioclimatic models, rates of thermal niche change estimated from a molecular phylogeny, and data from physiological studies. Using bioclimatic models, at most 60% of the species were predicted to have suitable conditions in 2080. Considering the rates of thermal niche change did not improve this prediction. However, physiological data suggest that subterranean species have a broad thermal tolerance, allowing them to stand temperatures never experienced through their evolutionary history. These results stress the need of experimental approaches to assess the capability of poor dispersal species to cope with temperatures outside those they currently experience.

Contributions of chemical exchange to T1ρ dispersion in a tissue model.

PubMed

Cobb, Jared G; Xie, Jingping; Gore, John C

2011-12-01

Variations in T(1ρ) with locking-field strength (T(1ρ) dispersion) may be used to estimate proton exchange rates. We developed a novel approach utilizing the second derivative of the dispersion curve to measure exchange in a model system of cross-linked polyacrylamide gels. These gels were varied in relative composition of comonomers, increasing stiffness, and in pH, modifying exchange rates. Magnetic resonance images were recorded with a spin-locking sequence as described by Sepponen et al. These measurements were fit to a mono-exponential decay function yielding values for T(1ρ) at each locking-field measured. These values were then fit to a model by Chopra et al. for estimating exchange rates. For low stiffness gels, the calculated exchange values increased by a factor of 4 as pH increased, consistent with chemical exchange being the dominant contributor to T(1ρ) dispersion. Interestingly, calculated chemical exchange rates also increased with stiffness, likely due to modified side-chain exchange kinetics as the composition varied. This article demonstrates a new method to assess the structural and chemical effects on T(1ρ) relaxation dispersion with a suitable model. These phenomena may be exploited in an imaging context to emphasize the presence of nuclei of specific exchange rates, rather than chemical shifts. Copyright © 2011 Wiley Periodicals, Inc.

Decadal climate predictions improved by ocean ensemble dispersion filtering

NASA Astrophysics Data System (ADS)

Kadow, C.; Illing, S.; Kröner, I.; Ulbrich, U.; Cubasch, U.

2017-06-01

Decadal predictions by Earth system models aim to capture the state and phase of the climate several years in advance. Atmosphere-ocean interaction plays an important role for such climate forecasts. While short-term weather forecasts represent an initial value problem and long-term climate projections represent a boundary condition problem, the decadal climate prediction falls in-between these two time scales. In recent years, more precise initialization techniques of coupled Earth system models and increased ensemble sizes have improved decadal predictions. However, climate models in general start losing the initialized signal and its predictive skill from one forecast year to the next. Here we show that the climate prediction skill of an Earth system model can be improved by a shift of the ocean state toward the ensemble mean of its individual members at seasonal intervals. We found that this procedure, called ensemble dispersion filter, results in more accurate results than the standard decadal prediction. Global mean and regional temperature, precipitation, and winter cyclone predictions show an increased skill up to 5 years ahead. Furthermore, the novel technique outperforms predictions with larger ensembles and higher resolution. Our results demonstrate how decadal climate predictions benefit from ocean ensemble dispersion filtering toward the ensemble mean.