Using a dynamic point-source percolation model to simulate bubble growth.
Zimmerman, Jonathan A.; Zeigler, David A.; Cowgill, Donald F.
2004-05-01
Accurate modeling of nucleation, growth and clustering of helium bubbles within metal tritide alloys is of high scientific and technological importance. Of interest is the ability to predict both the distribution of these bubbles and the manner in which these bubbles interact at a critical concentration of helium-to-metal atoms to produce an accelerated release of helium gas. One technique that has been used in the past to model these materials, and again revisited in this research, is percolation theory. Previous efforts have used classical percolation theory to qualitatively and quantitatively model the behavior of interstitial helium atoms in a metal tritide lattice; however, higher fidelity models are needed to predict the distribution of helium bubbles and include features that capture the underlying physical mechanisms present in these materials. In this work, we enhance classical percolation theory by developing the dynamic point-source percolation model. This model alters the traditionally binary character of site occupation probabilities by enabling them to vary depending on proximity to existing occupied sites, i.e. nucleated bubbles. This revised model produces characteristics for one and two dimensional systems that are extremely comparable with measurements from three dimensional physical samples. Future directions for continued development of the dynamic model are also outlined.
An autoregressive point source model for spatial processes
Hughes-Oliver, Jacqueline M.; Heo, Tae-Young; Ghosh, Sujit K.
2009-01-01
We suggest a parametric modeling approach for nonstationary spatial processes driven by point sources. Baseline near-stationarity, which may be reasonable in the absence of a point source, is modeled using a conditional autoregressive (CAR) Markov random field. Variability due to the point source is captured by our proposed autoregressive point source (ARPS) model. Inference proceeds according to the Bayesian hierarchical paradigm, and is implemented using Markov chain Monte Carlo (MCMC) methods. The parametric approach allows a formal test of effectiveness of the point source. Application is made to a real dataset on electric potential measurements in a field containing a metal pole and the finding is that our approach captures the pole’s impact on small-scale variability of the electric potential process. PMID:19936263
NASA Astrophysics Data System (ADS)
Kanai, Yasuhiro; Abe, Keiji; Seki, Yoichi
2015-06-01
We propose a price percolation model to reproduce the price distribution of components used in industrial finished goods. The intent is to show, using the price percolation model and a component category as an example, that percolation behaviors, which exist in the matter system, the ecosystem, and human society, also exist in abstract, random phenomena satisfying the power law. First, we discretize the total potential demand for a component category, considering it a random field. Second, we assume that the discretized potential demand corresponding to a function of a finished good turns into actual demand if the difficulty of function realization is less than the maximum difficulty of the realization. The simulations using this model suggest that changes in a component category's price distribution are due to changes in the total potential demand corresponding to the lattice size and the maximum difficulty of realization, which is an occupation probability. The results are verified using electronic components' sales data.
NASA Astrophysics Data System (ADS)
Solomon, Sorin; Weisbuch, Gerard; de Arcangelis, Lucilla; Jan, Naeem; Stauffer, Dietrich
2000-03-01
We here relate the occurrence of extreme market shares, close to either 0 or 100%, in the media industry to a percolation phenomenon across the social network of customers. We further discuss the possibility of observing self-organized criticality when customers and cinema producers adjust their preferences and the quality of the produced films according to previous experience. Comprehensive computer simulations on square lattices do indeed exhibit self-organized criticality towards the usual percolation threshold and related scaling behaviour.
Point source moment tensor inversion through a Bayesian hierarchical model
NASA Astrophysics Data System (ADS)
Mustać, Marija; Tkalčić, Hrvoje
2016-01-01
Characterization of seismic sources is an important aspect of seismology. Parameter uncertainties in such inversions are essential for estimating solution robustness, but are rarely available. We have developed a non-linear moment tensor inversion method in a probabilistic Bayesian framework that also accounts for noise in the data. The method is designed for point source inversion using waveform data of moderate-size earthquakes and explosions at regional distances. This probabilistic approach results in an ensemble of models, whose density is proportional to parameter probability distribution and quantifies parameter uncertainties. Furthermore, we invert for noise in the data, allowing it to determine the model complexity. We implement an empirical noise covariance matrix that accounts for interdependence of observational errors present in waveform data. After we demonstrate the feasibility of the approach on synthetic data, we apply it to a Long Valley Caldera, CA, earthquake with a well-documented anomalous (non-double-couple) radiation from previous studies. We confirm a statistically significant isotropic component in the source without a trade-off with the compensated linear vector dipoles component.
Electromagnetic modeling of foliage-obscured point source response
NASA Astrophysics Data System (ADS)
Hsu, Chih-Chien; Kong, Jin A.; Toups, Michael F.; Fleischman, Jack G.; Ayasli, Serpil; Shin, Robert T.
1993-11-01
This paper investigates the attenuation and phase fluctuations of electromagnetic waves propagating through foliage. These fluctuations are important in determining how well an object obscured by foliage can be imaged with synthetic aperture radar. A theoretical model is developed to calculate the mean attenuation and the amplitude and phase fluctuations. The attenuation of average received field is obtained from the sum of absorption loss and scattering loss. The amplitude fluctuation of electromagnetic wave is calculated from the bistatic scattering coefficients using the radiative transfer theory. The phase fluctuation is obtained from the amplitude fluctuation assuming the phase of the fluctuation field is uniformly distributed from -(pi) to (pi) . The average received power is obtained from the sum of the power of average field and the power of fluctuation field. The attenuation is then obtained by comparing the radiated power from a source under foliage to the received power from a source in free space. Theoretical results are compared with experimental data collected by MIT Lincoln Laboratory during the 1990 Foliage Penetration Experiment. This theoretical model is also used to illustrate the polarization and angular dependencies of attenuation and phase fluctuations.
HYDROLOGY AND SEDIMENT MODELING USING THE BASINS NON-POINT SOURCE MODEL
The Non-Point Source Model (Hydrologic Simulation Program-Fortran, or HSPF) within the EPA Office of Water's BASINS watershed modeling system was used to simulate streamflow and total suspended solids within Contentnea Creek, North Carolina, which is a tributary of the Neuse Rive...
Simulation of Non-point Source Pollution in the Songhua River Basin Using GBNP Model
NASA Astrophysics Data System (ADS)
Pan, J.; Tang, L.; Chen, Y. D.
2015-12-01
China is facing increasingly severe water pollution issue with rapid socio-economic development. Non-point source pollution, which is rarely monitored, has become the main forms of water pollution in China. In this study, the Geomorphology-Based Non-point source Pollution (GBNP) model was used to simulate the processes of rain-runoff, soil erosion, sediment routing and pollutant transport in the Songhua River basin from 2001 to 2010. The spatio-temporal variation of non-point source pollution and river water quality were analyzed based on the simulation outputs. In the entire basin, the annual mean loading of TN, TP and soil erosion are 270,000 ton/a, 42,200 ton/a and 55,900,000 ton/a, respectively. The point and non-point source pollution respectively account for 44.9% and 55.1% in TN loading. For TP loading, the proportions of point and non-point source pollution are 14.4% and 85.6%, respectively. It suggests that the non-point source pollution control and treatments should be paid more attention in the Songhua River basin. The inter-annual and intra-annual variations of non-point source pollution components and potential driving mechanisms are further examined. The annual loading of soil erosion, TN and TP are highly correlated with annual runoff, with the correlation coefficients of 0.75, 0.91 and 0.92, respectively, which implies that rain-runoff could be the main driving force of non-point pollution. The monthly sediment concentration in the watercourse is high in flood season and low in non-flood season, which agrees well with the seasonality of monthly runoff. By contrast, the concentrations of TN and TP in watercourse show the opposite features.
A Percolation Model for Fracking
NASA Astrophysics Data System (ADS)
Norris, J. Q.; Turcotte, D. L.; Rundle, J. B.
2014-12-01
Developments in fracking technology have enabled the recovery of vast reserves of oil and gas; yet, there is very little publicly available scientific research on fracking. Traditional reservoir simulator models for fracking are computationally expensive, and require many hours on a supercomputer to simulate a single fracking treatment. We have developed a computationally inexpensive percolation model for fracking that can be used to understand the processes and risks associated with fracking. In our model, a fluid is injected from a single site and a network of fractures grows from the single site. The fracture network grows in bursts, the failure of a relatively strong bond followed by the failure of a series of relatively weak bonds. These bursts display similarities to micro seismic events observed during a fracking treatment. The bursts follow a power-law (Gutenburg-Richter) frequency-size distribution and have growth rates similar to observed earthquake moment rates. These are quantifiable features that can be compared to observed microseismicity to help understand the relationship between observed microseismicity and the underlying fracture network.
NASA Astrophysics Data System (ADS)
Zhang, Tianhe C.; Grill, Warren M.
2010-12-01
Deep brain stimulation (DBS) has emerged as an effective treatment for movement disorders; however, the fundamental mechanisms by which DBS works are not well understood. Computational models of DBS can provide insights into these fundamental mechanisms and typically require two steps: calculation of the electrical potentials generated by DBS and, subsequently, determination of the effects of the extracellular potentials on neurons. The objective of this study was to assess the validity of using a point source electrode to approximate the DBS electrode when calculating the thresholds and spatial distribution of activation of a surrounding population of model neurons in response to monopolar DBS. Extracellular potentials in a homogenous isotropic volume conductor were calculated using either a point current source or a geometrically accurate finite element model of the Medtronic DBS 3389 lead. These extracellular potentials were coupled to populations of model axons, and thresholds and spatial distributions were determined for different electrode geometries and axon orientations. Median threshold differences between DBS and point source electrodes for individual axons varied between -20.5% and 9.5% across all orientations, monopolar polarities and electrode geometries utilizing the DBS 3389 electrode. Differences in the percentage of axons activated at a given amplitude by the point source electrode and the DBS electrode were between -9.0% and 12.6% across all monopolar configurations tested. The differences in activation between the DBS and point source electrodes occurred primarily in regions close to conductor-insulator interfaces and around the insulating tip of the DBS electrode. The robustness of the point source approximation in modeling several special cases—tissue anisotropy, a long active electrode and bipolar stimulation—was also examined. Under the conditions considered, the point source was shown to be a valid approximation for predicting excitation
In this paper, results of Eulerian grid and Lagrangian photochemical model simulations of emissions from a major elevated point source are presented. eries of simulations with grid sizes varying from 30 km to 2 km were performed with the Urban Airshed Model, a photochemical grid ...
PHOTOCHEMICAL SIMULATIONS OF POINT SOURCE EMISSIONS WITH THE MODELS-3 CMAQ PLUME-IN-GRID APPROACH
A plume-in-grid (PinG) approach has been designed to provide a realistic treatment for the simulation the dynamic and chemical processes impacting pollutant species in major point source plumes during a subgrid scale phase within an Eulerian grid modeling framework. The PinG sci...
Simulation of ultrasonic surface waves with multi-Gaussian and point source beam models
Zhao, Xinyu; Schmerr, Lester W. Jr.; Li, Xiongbing; Sedov, Alexander
2014-02-18
In the past decade, multi-Gaussian beam models have been developed to solve many complicated bulk wave propagation problems. However, to date those models have not been extended to simulate the generation of Rayleigh waves. Here we will combine Gaussian beams with an explicit high frequency expression for the Rayleigh wave Green function to produce a three-dimensional multi-Gaussian beam model for the fields radiated from an angle beam transducer mounted on a solid wedge. Simulation results obtained with this model are compared to those of a point source model. It is shown that the multi-Gaussian surface wave beam model agrees well with the point source model while being computationally much more efficient.
Stochastic point-source modeling of ground motions in the Cascadia region
Atkinson, G.M.; Boore, D.M.
1997-01-01
A stochastic model is used to develop preliminary ground motion relations for the Cascadia region for rock sites. The model parameters are derived from empirical analyses of seismographic data from the Cascadia region. The model is based on a Brune point-source characterized by a stress parameter of 50 bars. The model predictions are compared to ground-motion data from the Cascadia region and to data from large earthquakes in other subduction zones. The point-source simulations match the observations from moderate events (M 100 km). The discrepancy at large magnitudes suggests further work on modeling finite-fault effects and regional attenuation is warranted. In the meantime, the preliminary equations are satisfactory for predicting motions from events of M < 7 and provide conservative estimates of motions from larger events at distances less than 100 km.
An infrared sky model based on the IRAS point source data
NASA Technical Reports Server (NTRS)
Cohen, Martin; Walker, Russell; Wainscoat, Richard; Volk, Kevin; Walker, Helen; Schwartz, Deborah
1990-01-01
A detailed model for the infrared point source sky is presented that comprises geometrically and physically realistic representations of the galactic disk, bulge, spheroid, spiral arms, molecular ring, and absolute magnitudes. The model was guided by a parallel Monte Carlo simulation of the Galaxy. The content of the galactic source table constitutes an excellent match to the 12 micrometer luminosity function in the simulation, as well as the luminosity functions at V and K. Models are given for predicting the density of asteroids to be observed, and the diffuse background radiance of the Zodiacal cloud. The model can be used to predict the character of the point source sky expected for observations from future infrared space experiments.
Atmospheric Modeling and Verification of Point Source Fossil Fuel CO2 Emissions
NASA Astrophysics Data System (ADS)
Keller, E. D.; Turnbull, J. C.; Baisden, W. T.; Brailsford, G. W.; Bromley, T.; Norris, M. W.; Zondervan, A.
2014-12-01
Emissions from large point sources (electricity generation and large-scale industry) of fossil fuel CO2 (CO2ff) emissions are currently determined from self-reported "bottom-up" inventory data, with an uncertainty of about 20% for individual power plants. As the world moves towards a regulatory environment, there is a need for independent, objective measurements of these emissions both to improve the accuracy of and to verify the reported amounts. "Top-down" atmospheric methods have the potential to independently constrain point source emissions, combining observations with atmospheric transport modeling to derive emission estimates. We use the Kapuni Gas Treatment Plant to examine methodologies and model sensitivities for atmospheric monitoring of point source fossil fuel CO2 (CO2ff) emissions. The Kapuni plant, located in rural New Zealand, removes and vents CO2 from locally extracted natural gas at a rate of ~0.1 Tg carbon per year. We measured the CO2ff content in three different types of observations: air samples collected in flasks over a period of a few minutes, sodium hydroxide solution exposed the atmosphere, and grass samples from the surrounding farmland, the latter two representing ~1 week integrated averages. We use the WindTrax Lagrangian plume dispersion model to compare these atmospheric observations with "expected" values given the emissions reported by the Kapuni plant. The model has difficulty accurately capturing the short-term variability in the flask samples but does well in representing the longer-term averages from grass samples, suggesting that passive integrated-sampling methods have the potential to monitor long-term emissions. Our results indicate that using this method, point source emissions can be verified to within about 30%. Further improvements in atmospheric transport modelling are needed to reduce uncertainties. In view of this, we discuss model strengths and weaknesses and explore model sensitivity to meteorological conditions
Percolation in a kinetic opinion exchange model
NASA Astrophysics Data System (ADS)
Chandra, Anjan Kumar
2012-02-01
We study the percolation transition of the geometrical clusters in the square-lattice LCCC model [a kinetic opinion exchange model introduced by Lallouache, Chakrabarti, Chakraborti, and Chakrabarti, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.82.056112 82, 056112 (2010)] with the change in conviction and influencing parameter. The cluster is comprised of the adjacent sites having an opinion value greater than or equal to a prefixed threshold value of opinion (Ω). The transition point is different from that obtained for the transition of the order parameter (average opinion value) found by Lallouache Although the transition point varies with the change in the threshold value of the opinion, the critical exponents for the percolation transition obtained from the data collapses of the maximum cluster size, the cluster size distribution, and the Binder cumulant remain the same. The exponents are also independent of the values of conviction and influencing parameters, indicating the robustness of this transition. The exponents do not match any other known percolation exponents (e.g., the static Ising, dynamic Ising, and standard percolation). This means that the LCCC model belongs to a separate universality class.
Double point source W-phase inversion: Real-time implementation and automated model selection
NASA Astrophysics Data System (ADS)
Nealy, Jennifer L.; Hayes, Gavin P.
2015-12-01
Rapid and accurate characterization of an earthquake source is an extremely important and ever evolving field of research. Within this field, source inversion of the W-phase has recently been shown to be an effective technique, which can be efficiently implemented in real-time. An extension to the W-phase source inversion is presented in which two point sources are derived to better characterize complex earthquakes. A single source inversion followed by a double point source inversion with centroid locations fixed at the single source solution location can be efficiently run as part of earthquake monitoring network operational procedures. In order to determine the most appropriate solution, i.e., whether an earthquake is most appropriately described by a single source or a double source, an Akaike information criterion (AIC) test is performed. Analyses of all earthquakes of magnitude 7.5 and greater occurring since January 2000 were performed with extended analyses of the September 29, 2009 magnitude 8.1 Samoa earthquake and the April 19, 2014 magnitude 7.5 Papua New Guinea earthquake. The AIC test is shown to be able to accurately select the most appropriate model and the selected W-phase inversion is shown to yield reliable solutions that match published analyses of the same events.
Double point source W-phase inversion: Real-time implementation and automated model selection
Nealy, Jennifer; Hayes, Gavin
2015-01-01
Rapid and accurate characterization of an earthquake source is an extremely important and ever evolving field of research. Within this field, source inversion of the W-phase has recently been shown to be an effective technique, which can be efficiently implemented in real-time. An extension to the W-phase source inversion is presented in which two point sources are derived to better characterize complex earthquakes. A single source inversion followed by a double point source inversion with centroid locations fixed at the single source solution location can be efficiently run as part of earthquake monitoring network operational procedures. In order to determine the most appropriate solution, i.e., whether an earthquake is most appropriately described by a single source or a double source, an Akaike information criterion (AIC) test is performed. Analyses of all earthquakes of magnitude 7.5 and greater occurring since January 2000 were performed with extended analyses of the September 29, 2009 magnitude 8.1 Samoa earthquake and the April 19, 2014 magnitude 7.5 Papua New Guinea earthquake. The AIC test is shown to be able to accurately select the most appropriate model and the selected W-phase inversion is shown to yield reliable solutions that match published analyses of the same events.
Powerful model for the point source sky: Far-ultraviolet and enhanced midinfrared performance
NASA Technical Reports Server (NTRS)
Cohen, Martin
1994-01-01
I report further developments of the Wainscoat et al. (1992) model originally created for the point source infrared sky. The already detailed and realistic representation of the Galaxy (disk, spiral arms and local spur, molecular ring, bulge, spheroid) has been improved, guided by CO surveys of local molecular clouds, and by the inclusion of a component to represent Gould's Belt. The newest version of the model is very well validated by Infrared Astronomy Satellite (IRAS) source counts. A major new aspect is the extension of the same model down to the far ultraviolet. I compare predicted and observed far-utraviolet source counts from the Apollo 16 'S201' experiment (1400 A) and the TD1 satellite (for the 1565 A band).
MODELING PHOTOCHEMISTRY AND AEROSOL FORMATION IN POINT SOURCE PLUMES WITH THE CMAQ PLUME-IN-GRID
Emissions of nitrogen oxides and sulfur oxides from the tall stacks of major point sources are important precursors of a variety of photochemical oxidants and secondary aerosol species. Plumes released from point sources exhibit rather limited dimensions and their growth is gradu...
Scaling properties of percolation models for multifragmentation
NASA Astrophysics Data System (ADS)
Ngô, H.; Ngô, C.; Ighezou, F. Z.; Desbois, J.; Leray, S.; Zheng, Y.-M.
1990-03-01
We have used scaling properties of nuclear multifragmentation, which have been observed with emulsion data, to investigate the properties of some approaches based on percolation. We have studied different percolation models on a cubic lattice and shown that they can rather well reproduce the data except for binary break up. We have described what the mean field approximation would give in this context and showed that it cannot reproduce the experimental results. Most of the paper is focused on the restructured aggregation model introduced earlier which allows to well reproduce the scaling properties observed experimentally. This model has been studied in details and extended to take account of bonds breaking. It is shown that, in some cases, a nucleus can break up in two pieces. This process cannot be obtained in conventional percolation or aggregation but is observed experimentally in the emulsion data. Other features like the dimensionality of the aggregation model, the restructuration of the clusters and a schematic constraint in momentum space have also been investigated.
Modified Invasion Percolation Models for Multiphase Processes
Karpyn, Zuleima
2015-01-31
This project extends current understanding and modeling capabilities of pore-scale multiphase flow physics in porous media. High-resolution X-ray computed tomography imaging experiments are used to investigate structural and surface properties of the medium that influence immiscible displacement. Using experimental and computational tools, we investigate the impact of wetting characteristics, as well as radial and axial loading conditions, on the development of percolation pathways, residual phase trapping and fluid-fluid interfacial areas.
Percolation properties in a traffic model
NASA Astrophysics Data System (ADS)
Wang, Feilong; Li, Daqing; Xu, Xiaoyun; Wu, Ruoqian; Havlin, Shlomo
2015-11-01
As a dynamical complex system, traffic is characterized by a transition from free flow to congestions, which is mostly studied in highways. However, despite its importance in developing congestion mitigation strategies, the understanding of this common traffic phenomenon in a city scale is still missing. An open question is how the traffic in the network collapses from a global efficient traffic to isolated local flows in small clusters, i.e. the question of traffic percolation. Here we study the traffic percolation properties on a lattice by simulation of an agent-based model for traffic. A critical traffic volume in this model distinguishes the free state from the congested state of traffic. Our results show that the threshold of traffic percolation decreases with increasing traffic volume and reaches a minimum value at the critical traffic volume. We show that this minimal threshold is the result of longest spatial correlation between traffic flows at the critical traffic volume. These findings may help to develop congestion mitigation strategies in a network view.
Validation of a bulk turbulence model with thermal images of a point source
NASA Astrophysics Data System (ADS)
Kunz, Gerard J.; Moerman, Marcel M.; Fritz, Peter J.; de Leeuw, Gerrit
1996-10-01
A model was developed for the prediction of turbulence in the marine surface layer. The model requires standard meteorological values of air temperature, air humidity, wind speed each from any given height from within the surface layer and the sea surface temperature. Internally, the model is controlled by the exchange coefficients for momentum, heat and water vapor. A variant using the surface roughness length instead of the drag coefficient has also been implemented. The micrometeorological output parameters of the model are used to predict vertical profiles of the refractive index -- to predict refractivity effects -- and profiles of the refractive index structure function parameter C(subscript n)(superscript 2)(z). The latter is the controlling parameters to calculate optical turbulence effects such as scintillation and blurring. Experimental data were obtained from images taken of a point source over a 19 km path over the North Sea at a frame rate of 25 Hz using a 3 - 5 micrometer infrared camera system. The images were analyzed for scintillation, blur and image dancing. Predicted and measured turbulence effects are compared.
Economic-environmental modeling of point source pollution in Jefferson County, Alabama, USA.
Kebede, Ellene; Schreiner, Dean F; Huluka, Gobena
2002-05-01
This paper uses an integrated economic-environmental model to assess the point source pollution from major industries in Jefferson County, Northern Alabama. Industrial expansion generates employment, income, and tax revenue for the public sector; however, it is also often associated with the discharge of chemical pollutants. Jefferson County is one of the largest industrial counties in Alabama that experienced smog warnings and ambient ozone concentration, 1996-1999. Past studies of chemical discharge from industries have used models to assess the pollution impact of individual plants. This study, however, uses an extended Input-Output (I-O) economic model with pollution emission coefficients to assess direct and indirect pollutant emission for several major industries in Jefferson County. The major findings of the study are: (a) the principal emission by the selected industries are volatile organic compounds (VOC) and these contribute to the ambient ozone concentration; (b) the direct and indirect emissions are significantly higher than the direct emission by some industries, indicating that an isolated analysis will underestimate the emission by an industry; (c) while low emission coefficient industries may suggest industry choice they may also emit the most hazardous chemicals. This study is limited by the assumptions made, and the data availability, however it provides a useful analytical tool for direct and cumulative emission estimation and generates insights on the complexity in choice of industries. PMID:12173425
Modied invasion percolation model for fracking
NASA Astrophysics Data System (ADS)
Norris, J.; Turcotte, D. L.; Rundle, J. B.
2013-12-01
Recent developments in hydraulic fracturing (fracking) have enabled the recovery of large reserves of natural gas and oil. These developments include a change from low-volume, high-viscosity fluid injection to high-volume, low-viscosity injection. We consider new models of Invasion Percolation, (IP) which are models that were originally introduced to represent the injection of an invading fluid into a fluid filled porous medium. A primary difference between our model and the original model is the elimination of any unbroken bonds whose end sites are both filled with fluid. While the original model was found to have statistics nearly identical to traditional percolation, we find significant statistical differences. In particular, the distribution of broken bond strengths displays a strong roll-over near the critical point. Another difference between traditional percolation clusters and clusters generated using our model is the absence of internal loops. The modified growth rule prevents the formation of internal loops making the growing cluster ramified. Other ramified networks include drainage basins and DLA clusters. The study of drainage basins led to the development of Horton-Strahler and Tokunaga network statistics. We used both Horton-Strahler and Tokunaga network statistics to characterize simulated clusters using and found that the clusters generated by our model are statistically self-similar fractals. In addition to fractal clusters, IP also displays burst dynamics, in which the cluster extends rapidly through a spontaneous extension of percolating bonds. We define a burst to be a consecutive series of broken bonds whose strengths are all below a specified value. Using this definition of bursts we found good agreement with a power-law frequency-area distribution. Our model displays many of the characteristics of an energy landscape, and shows many similarities to DLA, neural networks, ecological landscapes, and the world wide web. We anticipate that this
NASA Astrophysics Data System (ADS)
Juodis, Laurynas; Filistovič, Vitold; Maceika, Evaldas; Remeikis, Vidmantas
2016-03-01
An analytical model for dispersion of air pollutants released from a point source forming a secondary pollutant (e.g. chemical transformation or parent-daughter radionuclide chain) is formulated considering the constant wind speed and eddy diffusivities as an explicit function of downwind distance from the source in Cauchy (reflection-deposition type) boundary conditions. The dispersion of pollutants has been investigated by using the Gaussian plume dispersion parameters σy and σz instead of the diffusivity parameters Ky and Kz. For primary pollutant it was proposed to use the derived dry deposition factor instead of the source depletion alternative. An analytical solution for steady-state two-dimensional pollutant transport in the atmosphere is presented. Derived formulas include dependency from effective release height, gravitational and dry deposition velocities of primary and secondary pollutants, advection, surface roughness length and empirical dispersion parameters σy and σz. Demonstration of analytical solution application is provided by calculation of 135Xe and 135C air activity concentrations and the applicability of the model for the solution of atmospheric pollution transport problems.
A land use regression model incorporating data on industrial point source pollution.
Chen, Li; Wang, Yuming; Li, Peiwu; Ji, Yaqin; Kong, Shaofei; Li, Zhiyong; Bai, Zhipeng
2012-01-01
Advancing the understanding of the spatial aspects of air pollution in the city regional environment is an area where improved methods can be of great benefit to exposure assessment and policy support. We created land use regression (LUR) models for SO2, NO2 and PM10 for Tianjin, China. Traffic volumes, road networks, land use data, population density, meteorological conditions, physical conditions and satellite-derived greenness, brightness and wetness were used for predicting SO2, NO2 and PM10 concentrations. We incorporated data on industrial point sources to improve LUR model performance. In order to consider the impact of different sources, we calculated the PSIndex, LSIndex and area of different land use types (agricultural land, industrial land, commercial land, residential land, green space and water area) within different buffer radii (1 to 20 km). This method makes up for the lack of consideration of source impact based on the LUR model. Remote sensing-derived variables were significantly correlated with gaseous pollutant concentrations such as SO2 and NO2. R2 values of the multiple linear regression equations for SO2, NO2 and PM10 were 0.78, 0.89 and 0.84, respectively, and the RMSE values were 0.32, 0.18 and 0.21, respectively. Model predictions at validation monitoring sites went well with predictions generally within 15% of measured values. Compared to the relationship between dependent variables and simple variables (such as traffic variables or meteorological condition variables), the relationship between dependent variables and integrated variables was more consistent with a linear relationship. Such integration has a discernable influence on both the overall model prediction and health effects assessment on the spatial distribution of air pollution in the city region. PMID:23513446
Evaluation of a non-point source pollution model, AnnAGNPS, in a tropical watershed
Polyakov, V.; Fares, A.; Kubo, D.; Jacobi, J.; Smith, C.
2007-01-01
Impaired water quality caused by human activity and the spread of invasive plant and animal species has been identified as a major factor of degradation of coastal ecosystems in the tropics. The main goal of this study was to evaluate the performance of AnnAGNPS (Annualized Non-Point Source Pollution Model), in simulating runoff and soil erosion in a 48 km2 watershed located on the Island of Kauai, Hawaii. The model was calibrated and validated using 2 years of observed stream flow and sediment load data. Alternative scenarios of spatial rainfall distribution and canopy interception were evaluated. Monthly runoff volumes predicted by AnnAGNPS compared well with the measured data (R2 = 0.90, P < 0.05); however, up to 60% difference between the actual and simulated runoff were observed during the driest months (May and July). Prediction of daily runoff was less accurate (R2 = 0.55, P < 0.05). Predicted and observed sediment yield on a daily basis was poorly correlated (R2 = 0.5, P < 0.05). For the events of small magnitude, the model generally overestimated sediment yield, while the opposite was true for larger events. Total monthly sediment yield varied within 50% of the observed values, except for May 2004. Among the input parameters the model was most sensitive to the values of ground residue cover and canopy cover. It was found that approximately one third of the watershed area had low sediment yield (0-1 t ha-1 y-1), and presented limited erosion threat. However, 5% of the area had sediment yields in excess of 5 t ha-1 y-1. Overall, the model performed reasonably well, and it can be used as a management tool on tropical watersheds to estimate and compare sediment loads, and identify "hot spots" on the landscape. ?? 2007 Elsevier Ltd. All rights reserved.
Modeling non-point source pollutants in the vadose zone: Back to the basics
NASA Astrophysics Data System (ADS)
Corwin, Dennis L.; Letey, John, Jr.; Carrillo, Marcia L. K.
More than ever before in the history of scientific investigation, modeling is viewed as a fundamental component of the scientific method because of the relatively recent development of the computer. No longer must the scientific investigator be confined to artificially isolated studies of individual processes that can lead to oversimplified and sometimes erroneous conceptions of larger phenomena. Computer models now enable scientists to attack problems related to open systems such as climatic change, and the assessment of environmental impacts, where the whole of the interactive processes are greater than the sum of their isolated components. Environmental assessment involves the determination of change of some constituent over time. This change can be measured in real time or predicted with a model. The advantage of prediction, like preventative medicine, is that it can be used to alter the occurrence of potentially detrimental conditions before they are manifest. The much greater efficiency of preventative, rather than remedial, efforts strongly justifies the need for an ability to accurately model environmental contaminants such as non-point source (NPS) pollutants. However, the environmental modeling advances that have accompanied computer technological development are a mixed blessing. Where once we had a plethora of discordant data without a holistic theory, now the pendulum has swung so that we suffer from a growing stockpile of models of which a significant number have never been confirmed or even attempts made to confirm them. Modeling has become an end in itself rather than a means because of limited research funding, the high cost of field studies, limitations in time and patience, difficulty in cooperative research and pressure to publish papers as quickly as possible. Modeling and experimentation should be ongoing processes that reciprocally enhance one another with sound, comprehensive experiments serving as the building blocks of models and models
Modelling plume dispersion pattern from a point source using spatial auto-correlational analysis
NASA Astrophysics Data System (ADS)
Ujoh, F.; Kwabe, D.
2014-02-01
The main objective of the study is to estimate the rate and model the pattern of plume rise from Dangote Cement Plc. A handheld Garmin GPS was employed for collection of coordinates at a single kilometre graduation from the centre of the factory to 10 kilometres. Plume rate was estimated using the Gaussian model while Kriging, using ArcGIS, was adopted for modelling the pattern of plume dispersion over a 10 kilometre radius around the factory. ANOVA test was applied for statistical analysis of the plume coefficients. The results indicate that plume dispersion is generally high with highest values recorded for the atmospheric stability classes A and B, while the least values are recorded for the atmospheric stability classes F and E. The variograms derived from the Kriging reveal that the pattern of plume dispersion is outwardly radial and omni-directional. With the exception of 3 stability sub-classes (DH, EH and FH) out of a total of 12, the 24-hour average of particulate matters (PM10 and PM2.5) within the study area is outrageously higher (highest value at 21392.3) than the average safety limit of 150 ug/m3 - 230 ug/m3 prescribed by the 2006 WHO guidelines. This indicates the presence of respirable and non-respirable pollutants that create poor ambient air quality. The study concludes that the use of geospatial technology can be adopted in modelling dispersion of pollutants from a point source. The study recommends ameliorative measures to reduce the rate of plume emission at the factory.
A Percolation Model of the Streamer Discharges
NASA Astrophysics Data System (ADS)
Sasaki, Akira; Kato, Susumu; Takahashi, Eiichi; Kanazawa, Seiji
A percolation model of discharge is presented. The model can reproduce stochastic behaviors of initial partial discharge to the growth of a stepped leader. The model uses macroscopic cells, from which a network of electric circuits is defined, and the spatial and temporal evolutions of the electric field and current in the discharge medium are calculated. For each cell, one of two states, either insulator or conductor, which corresponds to neutral gas or ionized plasmas, respectively, is decided. The decision is made on the basis of probability for each calculation cell at each time step, taking the effects of local electric field and current, which enhance ionization and sustain the discharge channel, respectively, into account.
Godowitch, J.M.; Gillani, N.V.; Biazar, A.; Wu, Y.; Imhoff, R.E.
1998-12-31
A cooperative research and development effort has been conducted to design and implement a plume-in-grid (PinG) modeling techniques into the Models-3 Community Multiscale Air Quality (CMAQ) modeling system in order to address the need for an improved modeling approach to treat major point source emissions. Objectives are to provide an improved characterization of the near-source concentration field and a better far-field regional pollutant pattern due to the impact of the plume-in-grid approach. The conceptual design and an overview of the science processes contained in the PDM in PinG algorithms are briefly presented. Test simulations with and without the PinG treatment for a major NO{sub x} point source are described, and an O{sub 3} concentration pattern from the grid model reveals the impact of the plume-in-grid approach. Subgrid scale plume cell O{sub 3} concentrations are also shown.
Modelling of point and non-point source pollution of nitrate with SWAT in the river Dill, Germany
NASA Astrophysics Data System (ADS)
Pohlert, T.; Huisman, J. A.; Breuer, L.; Frede, H.-G.
2005-12-01
We used the Soil and Water Assessment Tool (SWAT) to simulate point and non-point source pollution of nitrate in a mesoscale mountainous catchment. The results show that the model efficiency for daily discharge is 0.81 for the calibration period (November 1990 to December 1993) and 0.56 for the validation period (April 2000 to January 2003). The model efficiency for monthly nitrate load is 0.66 and 0.77 for the calibration period (April 2000 to March 2002) and validation period (April 2002 to January 2003), respectively. However, the model efficiency for daily loads is low (0.15), which cannot only be attributed to the quality of input data of point source effluents. An analysis of the internal fluxes and cycles of nitrogen pointed out considerable weaknesses in the models conceptualisation of the nitrogen modules which will be improved in future research.
Two exactly soluble models of rigidity percolation
Thorpe, M. F.; Stinchcombe, R. B.
2014-01-01
We summarize results for two exactly soluble classes of bond-diluted models for rigidity percolation, which can serve as a benchmark for numerical and approximate methods. For bond dilution problems involving rigidity, the number of floppy modes F plays the role of a free energy. Both models involve pathological lattices with two-dimensional vector displacements. The first model involves hierarchical lattices where renormalization group calculations can be used to give exact solutions. Algebraic scaling transformations produce a transition of the second order, with an unstable critical point and associated scaling laws at a mean coordination 〈r〉=4.41, which is above the ‘mean field’ value 〈r〉=4 predicted by Maxwell constraint counting. The order parameter exponent associated with the spanning rigid cluster geometry is β=0.0775 and that associated with the divergence of the correlation length and the anomalous lattice dimension d is dν=3.533. The second model involves Bethe lattices where the rigidity transition is massively first order by a mean coordination 〈r〉=3.94 slightly below that predicted by Maxwell constraint counting. We show how a Maxwell equal area construction can be used to locate the first-order transition and how this result agrees with simulation results on larger random-bond lattices using the pebble game algorithm. PMID:24379428
Modeling a point-source release of 1,1,1-trichloroethane using EPA`s SCREEN model
Henriques, W.D.; Dixon, K.R.
1994-12-31
Using data from the Environmental Protection Agency`s Toxic Release Inventory 1988 (EPA TRI88), pollutant concentration estimates were modeled for a point source air release of 1,1,1-trichloroethane at the Savannah River Plant located in Aiken, South Carolina. Estimates were calculating using the EPA`s SCREEN model utilizing typical meteorological conditions to determine maximum impact of the plume under different mixing conditions for locations within 100 meters of the stack. Input data for the SCREEN model were then manipulated to simulate the impact of the release under urban conditions (for the purpose of assessing future landuse considerations) and under flare release options to determine if these parameters lessen or increase the probability of human or wildlife exposure to significant concentrations. The results were then compared to EPA reference concentrations (RfC) in order to assess the size of the buffer around the stack which may potentially have levels that exceed this level of safety.
NASA Technical Reports Server (NTRS)
Diamante, J. M.; Englar, T. S., Jr.; Jazwinski, A. H.
1977-01-01
Estimation theory, which originated in guidance and control research, is applied to the analysis of air quality measurements and atmospheric dispersion models to provide reliable area-wide air quality estimates. A method for low dimensional modeling (in terms of the estimation state vector) of the instantaneous and time-average pollutant distributions is discussed. In particular, the fluctuating plume model of Gifford (1959) is extended to provide an expression for the instantaneous concentration due to an elevated point source. Individual models are also developed for all parameters in the instantaneous and the time-average plume equations, including the stochastic properties of the instantaneous fluctuating plume.
Percolation Model for Slow Dynamics in Glass-Forming Materials
NASA Astrophysics Data System (ADS)
Lois, Gregg; Blawzdziewicz, Jerzy; O'Hern, Corey S.
2009-01-01
We identify a link between the glass transition and percolation of regions of mobility in configuration space. We find that many hallmarks of glassy dynamics, for example, stretched-exponential response functions and a diverging structural relaxation time, are consequences of the critical properties of mean-field percolation. Specific predictions of the percolation model include the range of possible stretching exponents 1/3≤β≤1 and the functional dependence of the structural relaxation time τα and exponent β on temperature, density, and wave number.
Percolation model for selective dissolution of multi-component glasses
Kale, R.P.; Brinker, C.J.
1995-03-01
A percolation model is developed which accounts for most known features of the process of porous glass membrane preparation by selective dissolution of multi-component glasses. The model is founded within tile framework of the classical percolation theory, wherein the components of a glass are represented by random sites on a suitable lattice. Computer simulation is used to mirror the generation of a porous structure during the dissolution process, reproducing many of the features associated with the phenomenon. Simulation results evaluate the effect of the initial composition of the glass on the kinetics of the leaching process as well as the morphology of the generated porous structure. The percolation model establishes the porous structure as a percolating cluster of unreachable constituents in the glass. The simulation algorithm incorporates removal of both, the accessible leachable components in the glass as well as the independent clusters of unreachable components not attached to the percolating cluster. The dissolution process thus becomes limited by the conventional site percolation thresholds of the unreachable components (which restricts the formation of the porous network), as well as the leachable components (which restricts the accessibility of the solvating medium into the glass). The simulation results delineate the range of compositional variations for successful porous glass preparation and predict the variation of porosity, surface area, dissolution rates and effluent composition with initial composition and time. Results compared well with experimental studies and improved upon similar models attempted in die past.
Luo, Xiaolin; Zheng, Yi; Lin, Zhongrong; Wu, Bin; Han, Feng; Tian, Yong; Zhang, Wei; Wang, Xuejun
2015-01-01
Soils contaminated by Polycyclic Aromatic Hydrocarbons (PAHs) are subject to significant non-point source (NPS) pollution during rainfall events. Recent studies revealed that the classic enrichment ratio (ER) approach may not be applicable to PAHs. This study developed a model to estimate the ER of PAHs which innovatively applies the fugacity concept. The ER model has been validated with experimental data, which suggested that the transport of PAHs not only depends on their physicochemical properties, but on the sediment composition and how the composition evolves during the event. The modeling uncertainty was systematically examined, and found to be highly compound-dependent. Based on the ER model, a strategy was proposed to practically evaluate the potential NPS loading of PAHs in watersheds with heterogeneous soils. The study results have important implications to modeling and managing the NPS pollution of PAHs (or other chemicals alike) at a watershed scale. PMID:25282126
EVALUATION OF SHORT-TERM NO2 PLUME MODELS FOR POINT SOURCES. VOLUME 1: TECHNICAL DISCUSSION
Models for predicting short-term NO2 concentrations are discussed, and several (RPM-II, TCM, OLM, and CNOM) are selected for evaluation. The MISTT data, collected in 1976, were to be used to evaluate the models, but careful scrutiny of the data base revealed certain deficiencies ...
User's Guide for the Agricultural Non-Point Source (AGNPS) Pollution Model Data Generator
Finn, Michael P.; Scheidt, Douglas J.; Jaromack, Gregory M.
2003-01-01
BACKGROUND Throughout this user guide, we refer to datasets that we used in conjunction with developing of this software for supporting cartographic research and producing the datasets to conduct research. However, this software can be used with these datasets or with more 'generic' versions of data of the appropriate type. For example, throughout the guide, we refer to national land cover data (NLCD) and digital elevation model (DEM) data from the U.S. Geological Survey (USGS) at a 30-m resolution, but any digital terrain model or land cover data at any appropriate resolution will produce results. Another key point to keep in mind is to use a consistent data resolution for all the datasets per model run. The U.S. Department of Agriculture (USDA) developed the Agricultural Nonpoint Source (AGNPS) pollution model of watershed hydrology in response to the complex problem of managing nonpoint sources of pollution. AGNPS simulates the behavior of runoff, sediment, and nutrient transport from watersheds that have agriculture as their prime use. The model operates on a cell basis and is a distributed parameter, event-based model. The model requires 22 input parameters. Output parameters are grouped primarily by hydrology, sediment, and chemical output (Young and others, 1995.) Elevation, land cover, and soil are the base data from which to extract the 22 input parameters required by the AGNPS. For automatic parameter extraction, follow the general process described in this guide of extraction from the geospatial data through the AGNPS Data Generator to generate input parameters required by the pollution model (Finn and others, 2002.)
ArcEGMO-URBAN--hydrological model for point sources in river basins.
Biegel, M; Schanze, J; Krebs, P
2005-01-01
The new model ArcEGMO-URBAN aims at deterministic and spatiotemporal modelling of water, nitrogen and phosphorus fluxes from all urbanised areas of a river basin considering all potential sources. Pollution loads are calculated for discrete urban patches and balanced on the level of hydrological subbasins. Modelling results can be defined by the user of any level of spatial and/or temporal aggregation, e.g. matter balances for river basins or river sections and years or months, respectively. To process spatial data, a Geographic Information System is linked to the model. Information on urban land use and general characteristics of river basins is based on digital coverages, partly generated from remote-sensing data. Moreover, statistical data, e.g. on population, sewer systems, wastewater treatment plants etc. are included. Stormwater runoff from impervious surfaces is calculated as one input to the sewer network. Wastewater is considered with its main sewer system, pumping stations and treatment plants. Finally, the discharge is balanced for discrete river sections. Modelling results attest ArcEGMO-URBAN its ability to realistically quantify matter fluxes and major pollution sources as well as their seasonal variation. This makes the model an applicable tool for the analysis of scenarios with e.g. varying population distribution or climatic and technological conditions. PMID:16248202
The transport exponent in percolation models with additional loops
NASA Astrophysics Data System (ADS)
Babalievski, F.
1994-10-01
Several percolation models with additional loops were studied. The transport exponents for these models were estimated numerically by means of a transfer-matrix approach. It was found that the transport exponent has a drastically changed value for some of the models. This result supports some previous numerical studies on the vibrational properties of similar models (with additional loops).
Correlated percolation models of structured habitat in ecology
NASA Astrophysics Data System (ADS)
Huth, Géraldine; Lesne, Annick; Munoz, François; Pitard, Estelle
2014-12-01
Percolation offers acknowledged models of random media when the relevant medium characteristics can be described as a binary feature. However, when considering habitat modeling in ecology, a natural constraint comes from nearest-neighbor correlations between the suitable/unsuitable states of the spatial units forming the habitat. Such constraints are also relevant in the physics of aggregation where underlying processes may lead to a form of correlated percolation. However, in ecology, the processes leading to habitat correlations are in general not known or very complex. As proposed by Hiebeler (2000), these correlations can be captured in a lattice model by an observable aggregation parameter q, supplementing the density p of suitable sites. We investigate this model as an instance of correlated percolation. We analyze the phase diagram of the percolation transition and compute the cluster size distribution, the pair-connectedness function C(r) and the correlation function g(r). We find that while g(r) displays a power-law decrease associated with long-range correlations in a wide domain of parameter values, critical properties are compatible with the universality class of uncorrelated percolation. We contrast the correlation structures obtained respectively for the correlated percolation model and for the Ising model, and show that the diversity of habitat configurations generated by the Hiebeler model is richer than the archetypal Ising model. We also find that emergent structural properties are peculiar to the implemented algorithm, leading to questioning the notion of a well-defined model of aggregated habitat. We conclude that the choice of model and algorithm has strong consequences on what insights ecological studies can get using such models of species habitat.
Concentrator optical characterization using computer mathematical modelling and point source testing
NASA Technical Reports Server (NTRS)
Dennison, E. W.; John, S. L.; Trentelman, G. F.
1984-01-01
The optical characteristics of a paraboloidal solar concentrator are analyzed using the intercept factor curve (a format for image data) to describe the results of a mathematical model and to represent reduced data from experimental testing. This procedure makes it possible not only to test an assembled concentrator, but also to evaluate single optical panels or to conduct non-solar tests of an assembled concentrator. The use of three-dimensional ray tracing computer programs to calculate the mathematical model is described. These ray tracing programs can include any type of optical configuration from simple paraboloids to array of spherical facets and can be adapted to microcomputers or larger computers, which can graphically display real-time comparison of calculated and measured data.
Bach, M; Letzel, M; Kaul, U; Forstner, S; Metzner, G; Klasmeier, J; Reichenberger, S; Frede, H G
2010-06-01
A Water Framework Directive pilot project combines measured data and model approaches to calculate fluxes and mass balance of the pesticide bentazone in an 81 km section of the river Main (Germany). During the study period (six weeks in spring 2004) the observed bentazone inflow and outflow in the river section amounted to 52.8 and 53.1 kg, respectively; the maximum concentrations reached 220 and 290 ng l(-1). Based on sampling of seven sewage treatment plants a specific loss of 0.87 g bentazone per farm was calculated. Extrapolation to the entire sub-basin results in 2.6 kg bentazone in total as point source contribution from farms. Diffuse input into the surface water network occurred after an intensive rainfall event on May 7th. Total bentazone load was simulated with the pesticide emission model DRIPS to be 23.2 kg. One third of this load was estimated to be degraded by photolysis before reaching the main waterway, the river Main. The ATV water quality model was applied to predict the concentration profile of bentazone in river Main between Schweinfurt and Würzburg with reasonable results. The difference between total measured and modeled fluxes amounted to 1.5 kg corresponding to 2% of the overall input. The combined approach of monitoring and modeling appears to be a valuable strategy to quantify the relevance of point and non-point sources and to focus effective mitigation measures to the most relevant origins within a river basin. PMID:20546837
Percolation model with an additional source of disorder.
Kundu, Sumanta; Manna, S S
2016-06-01
The ranges of transmission of the mobiles in a mobile ad hoc network are not uniform in reality. They are affected by the temperature fluctuation in air, obstruction due to the solid objects, even the humidity difference in the environment, etc. How the varying range of transmission of the individual active elements affects the global connectivity in the network may be an important practical question to ask. Here a model of percolation phenomena, with an additional source of disorder, is introduced for a theoretical understanding of this problem. As in ordinary percolation, sites of a square lattice are occupied randomly with probability p. Each occupied site is then assigned a circular disk of random value R for its radius. A bond is defined to be occupied if and only if the radii R_{1} and R_{2} of the disks centered at the ends satisfy a certain predefined condition. In a very general formulation, one divides the R_{1}-R_{2} plane into two regions by an arbitrary closed curve. One defines a point within one region as representing an occupied bond; otherwise it is a vacant bond. The study of three different rules under this general formulation indicates that the percolation threshold always varies continuously. This threshold has two limiting values, one is p_{c}(sq), the percolation threshold for the ordinary site percolation on the square lattice, and the other is unity. The approach of the percolation threshold to its limiting values are characterized by two exponents. In a special case, all lattice sites are occupied by disks of random radii R∈{0,R_{0}} and a percolation transition is observed with R_{0} as the control variable, similar to the site occupation probability. PMID:27415234
Percolation model with an additional source of disorder
NASA Astrophysics Data System (ADS)
Kundu, Sumanta; Manna, S. S.
2016-06-01
The ranges of transmission of the mobiles in a mobile ad hoc network are not uniform in reality. They are affected by the temperature fluctuation in air, obstruction due to the solid objects, even the humidity difference in the environment, etc. How the varying range of transmission of the individual active elements affects the global connectivity in the network may be an important practical question to ask. Here a model of percolation phenomena, with an additional source of disorder, is introduced for a theoretical understanding of this problem. As in ordinary percolation, sites of a square lattice are occupied randomly with probability p . Each occupied site is then assigned a circular disk of random value R for its radius. A bond is defined to be occupied if and only if the radii R1 and R2 of the disks centered at the ends satisfy a certain predefined condition. In a very general formulation, one divides the R1-R2 plane into two regions by an arbitrary closed curve. One defines a point within one region as representing an occupied bond; otherwise it is a vacant bond. The study of three different rules under this general formulation indicates that the percolation threshold always varies continuously. This threshold has two limiting values, one is pc(sq) , the percolation threshold for the ordinary site percolation on the square lattice, and the other is unity. The approach of the percolation threshold to its limiting values are characterized by two exponents. In a special case, all lattice sites are occupied by disks of random radii R ∈{0 ,R0} and a percolation transition is observed with R0 as the control variable, similar to the site occupation probability.
NASA Astrophysics Data System (ADS)
Attanayake, Januka; Fonseca, João F. B. D.
2016-05-01
The February 22nd 2006 Mw = 7 Machaze earthquake is one of the largest, if not the largest, earthquakes reported since 1900 within Continental Africa. This large continental intraplate event has important implications to our understanding of tectonics and strong ground motion prediction locally and in the global context. Thus, accurate estimates of source parameters of this earthquake are important. In this study, we inverted the complete azimuthally distributed high frequency (0.05-2 Hz) P waveform dataset available for a best-fitting point source model and obtained stress drop estimates assuming different theoretical rupture models from spectral fitting. Our best-fitting point source model confirms steep normal faulting, has strike = 173° (309°), dip = 73° (23°), rake = -72° (-132°), and shows a 12%-4% improvement in waveform fit compared to previous models, which translates into an error minimization. We attribute this improvement to higher order reverberations near the source region that we took in to account and the excellent azimuthal coverage of the dataset. Preferred stress drop estimates assuming a rupture velocity = 0.9 x shear wave velocity (Vs) are between 11 and 15 MPa though, even higher stress drop estimates are possible for rupture velocities lower than 0.9Vs. The estimated stress drop is significantly higher than the global stress drop average of intraplate earthquakes, but is consistent with stress drop estimated for some intra-continental earthquakes elsewhere. The detection of a new active structure that appears to terminate in Machaze, its step-like geometry, and lithospheric strength all favors a hypothesis of stress concentration in the source region, which is likely the cause of this event and the higher than average stress drop.
Explosive percolation: Unusual transitions of a simple model
NASA Astrophysics Data System (ADS)
Bastas, N.; Giazitzidis, P.; Maragakis, M.; Kosmidis, K.
In this paper we review the recent advances in explosive percolation, a very sharp phase transition first observed by Achlioptas et al. (2009). There a simple model was proposed, which changed slightly the classical percolation process so that the emergence of the spanning cluster is delayed. This slight modification turns out to have a great impact on the percolation phase transition. The resulting transition is so sharp that it was termed explosive, and it was at first considered to be discontinuous. This surprising fact stimulated considerable interest in “Achlioptas processes”. Later work, however, showed that the transition is continuous (at least for Achlioptas processes on Erdös networks), but with very unusual finite size scaling. We present a review of the field, indicate open “problems” and propose directions for future research.
Truncated Connectivities in a Highly Supercritical Anisotropic Percolation Model
NASA Astrophysics Data System (ADS)
Couto, Rodrigo G.; de Lima, Bernardo N. B.; Sanchis, Rémy
2013-12-01
We consider an anisotropic bond percolation model on , with p=( p h , p v )∈[0,1]2, p v > p h , and declare each horizontal (respectively vertical) edge of to be open with probability p h (respectively p v ), and otherwise closed, independently of all other edges. Let with 0< x 1< x 2, and . It is natural to ask how the two point connectivity function behaves, and whether anisotropy in percolation probabilities implies the strict inequality . In this note we give an affirmative answer in the highly supercritical regime.
Chapman, Elaine G.; Gustafson, William I.; Easter, Richard C.; Barnard, James C.; Ghan, Steven J.; Pekour, Mikhail S.; Fast, Jerome D.
2009-02-01
The local and regional influence of elevated point sources on summertime aerosol forcing and cloud-aerosol interactions in northeastern North America was investigated using the WRF-Chem community model. The direct effects of aerosols on incoming solar radiation were simulated using existing modules to relate aerosol sizes and chemical composition to aerosol optical properties. Indirect effects were simulated by adding a prognostic treatment of cloud droplet number and adding modules that activate aerosol particles to form cloud droplets, simulate aqueous phase chemistry, and tie a two-moment treatment of cloud water (cloud water mass and cloud droplet number) to an existing radiation scheme. Fully interactive feedbacks thus were created within the modified model, with aerosols affecting cloud droplet number and cloud radiative properties, and clouds altering aerosol size and composition via aqueous processes, wet scavenging, and gas-phase-related photolytic processes. Comparisons of a baseline simulation with observations show that the model captured the general temporal cycle of aerosol optical depths (AODs) and produced clouds of comparable thickness to observations at approximately the proper times and places. The model slightly overpredicted SO2 mixing ratios and PM2.5 mass, but reproduced the range of observed SO2 to sulfate aerosol ratios, suggesting that atmospheric oxidation processes leading to aerosol sulfate formation are captured in the model. The baseline simulation was compared to a sensitivity simulation in which all emissions at model levels above the surface layer were set to zero, thus removing stack emissions. Instantaneous, site-specific differences for aerosol and cloud related properties between the two simulations could be quite large, as removing above-surface emission sources influenced when and where clouds formed within the modeling domain. When summed spatially over the finest resolution model domain (the extent of which corresponds to
Network representation of pore scale imagery for percolation models
NASA Astrophysics Data System (ADS)
Klise, K. A.; McKenna, S. A.; Read, E.; Karpyn, Z. T.; Celauro, J.
2012-12-01
Multiphase flow under capillary dominated flow regimes is driven by an intricate relationship between pore geometry, material and fluid properties. In this research, high-resolution micro-computed tomography (CT) imaging experiments are used to investigate structural and surface properties of bead packs, and how they influence percolation pathways. Coreflood experiments use a mix of hydrophilic and hydrophobic beads to track the influence of variable contact angle on capillary flow. While high-resolution CT images can render micron scale representation of the pore space, data must be upscaled to capture pore and pore throat geometry for use in percolation models. In this analysis, the pore space is upscaled into a network representation based on properties of the medial axis. Finding the medial axis using micron scale images is computationally expensive. Here, we compare the efficiency and accuracy of medial axes using erosion-based and watershed algorithms. The resulting network representation is defined as a ball-and-stick model which represents pores and pore throats. The ball-and-stick model can be further reduced by eliminating sections of the network that fall below a capillary pressure threshold. In a system of mixed hydrophilic and hydrophobic beads, capillary pressure can change significantly throughout the network based on the interaction between surface and fluid properties. The upscaled network representations are used in percolation models to estimate transport pathway. Current results use a basic percolation model that sequentially fills neighboring pores with the highest potential. Future work will expand the percolation model to include additional mechanics, such as trapping, vacating pores, and viscous fingering. Results from the coreflood experiments will be used to validate upscaling techniques and percolation models. Preliminary results show that the relative strength of water-wet and oil-wet surfaces has a significant impact on percolation
Correlated Percolation Models of Jamming and Glass Transitions
NASA Astrophysics Data System (ADS)
Jeng, Monwhea; Schwarz, Jennifer
2007-03-01
Toninelli, Biroli, and Fisher recently introduced a model of correlated percolation called the Knight model, which they claimed to prove underwent a dynamical glass transition. This transition had novel properties, with a discontinuous jump in the order parameter, but with diverging time scales and correlation lengths. We show that their proof misidentified the critical point, so that these properties are currently unproven for this model. However, we show that these novel properties can in fact be proven for suitably modified models of correlated percolation, with qualitatively similar culling rules. We discuss the features of the models necessary for a rigorous proof to be possible. We also discuss properties of models such as the force balance model and the original Knight model, which appear to undergo novel transitions despite the lack of a rigorous proof of such a transition.
NASA Astrophysics Data System (ADS)
Runkle, B. R.; Liang, X.; Hao, F.
2005-12-01
Hydrological behavior is a central factor in deciding the fate of agricultural pollutants, yet the exact functions of hydrology and the scales at which they are most important are understudied. A physically based hydrological model was developed to examine the transport of common agricultural pollutants (nitrogen, phosphorus, pesticides) and problems of soil salinity. This model looks to uncover the effects of different spatial and temporal scales on the dynamics of non-point source pollution loading, transport, and distribution. The principal geochemical and physical transport mechanisms such as dissolution, adsorption, advection and mass transfer from pore water to overland flow will be characterized as functions of irrigation input and soil moisture. The model is used to examine emergent behaviors at different scales and to determine which hydrological processes and conditions are most sensitive for pollutant transport. The model will be validated by comparison with data in the Inner Mongolia Irrigation District, a 5000 km2 region along the north bank of the Yellow River in northern China. The region receives very little (<200 mm) rainfall and relies heavily on irrigation water from the Yellow River and groundwater. Polluted drainage water is threatening the ecology of nearby Wuliangsuhai Lake, a wetlands ecosystem important for bird habitat. This project is supported in part by the National Natural Science Foundation of China.
NASA Astrophysics Data System (ADS)
Acero, F.; Ackermann, M.; Ajello, M.; Albert, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cuoco, A.; Cutini, S.; D’Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Venere, L.; Drell, P. S.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hayashi, K.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Hou, X.; Jogler, T.; Jóhannesson, G.; Kamae, T.; Kuss, M.; Landriu, D.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Maldera, S.; Malyshev, D.; Manfreda, A.; Martin, P.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mirabal, N.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Remy, Q.; Renault, N.; Sánchez-Conde, M.; Schaal, M.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; Werner, M.; Wood, K. S.; Wood, M.; Zaharijas, G.; Zimmer, S.
2016-04-01
Most of the celestial γ rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20° and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within ∼4° of the Galactic Center.
Wada, Yuji; Kundu, Tribikram; Nakamura, Kentaro
2014-08-01
The distributed point source method (DPSM) is extended to model wave propagation in viscous fluids. Appropriate estimation on attenuation and boundary layer formation due to fluid viscosity is necessary for the ultrasonic devices used for acoustic streaming or ultrasonic levitation. The equations for DPSM modeling in viscous fluids are derived in this paper by decomposing the linearized viscous fluid equations into two components-dilatational and rotational components. By considering complex P- and S-wave numbers, the acoustic fields in viscous fluids can be calculated following similar calculation steps that are used for wave propagation modeling in solids. From the calculations reported the precision of DPSM is found comparable to that of the finite element method (FEM) for a fundamental ultrasonic field problem. The particle velocity parallel to the two bounding surfaces of the viscous fluid layer between two rigid plates (one in motion and one stationary) is calculated. The finite element results agree well with the DPSM results that were generated faster than the transient FEM results. PMID:25096081
NASA Astrophysics Data System (ADS)
Xu, Fei; Dong, Guangxia; Wang, Qingrui; Liu, Lumeng; Yu, Wenwen; Men, Cong; Liu, Ruimin
2016-09-01
The impacts of different digital elevation model (DEM) resolutions, sources and resampling techniques on nutrient simulations using the Soil and Water Assessment Tool (SWAT) model have not been well studied. The objective of this study was to evaluate the sensitivities of DEM resolutions (from 30 m to 1000 m), sources (ASTER GDEM2, SRTM and Topo-DEM) and resampling techniques (nearest neighbor, bilinear interpolation, cubic convolution and majority) to identification of non-point source (NPS) critical source area (CSA) based on nutrient loads using the SWAT model. The Xiangxi River, one of the main tributaries of Three Gorges Reservoir in China, was selected as the study area. The following findings were obtained: (1) Elevation and slope extracted from the DEMs were more sensitive to DEM resolution changes. Compared with the results of the 30 m DEM, 1000 m DEM underestimated the elevation and slope by 104 m and 41.57°, respectively; (2) The numbers of subwatersheds and hydrologic response units (HRUs) were considerably influenced by DEM resolutions, but the total nitrogen (TN) and total phosphorus (TP) loads of each subwatershed showed higher correlations with different DEM sources; (3) DEM resolutions and sources had larger effects on CSAs identifications, while TN and TP CSAs showed different response to DEM uncertainties. TN CSAs were more sensitive to resolution changes, exhibiting six distribution patterns at all DEM resolutions. TP CSAs were sensitive to source and resampling technique changes, exhibiting three distribution patterns for DEM sources and two distribution patterns for DEM resampling techniques. DEM resolutions and sources are the two most sensitive SWAT model DEM parameters that must be considered when nutrient CSAs are identified.
NASA Astrophysics Data System (ADS)
Kale, Sohan; Sabet, Fereshteh A.; Jasiuk, Iwona; Ostoja-Starzewski, Martin
2016-07-01
In this study, we examine the effect of filler alignment on percolation behavior of polymer nanocomposites using Monte Carlo simulations of monodisperse prolate and oblate hard-core soft-shell ellipsoids representing carbon nanotubes and graphene nanoplatelets, respectively. The percolation threshold is observed to increase with increasing extent of alignment as expected. For a highly aligned system of rod-like fillers, the simulation results are shown to be in good agreement with the second virial approximation based predictions. However, for a highly aligned system of disk-like fillers, the second virial approximation based results are observed to significantly deviate from the simulations, even for higher aspect ratios. The effect of filler alignment on anisotropy in percolation behavior is also studied by predicting the percolation threshold along different directions. The anisotropy in percolation threshold is found to vanish even for highly aligned systems of fillers with increasing system size.
Loopless nontrapping invasion-percolation model for fracking
NASA Astrophysics Data System (ADS)
Norris, J. Quinn; Turcotte, Donald L.; Rundle, John B.
2014-02-01
Recent developments in hydraulic fracturing (fracking) have enabled the recovery of large quantities of natural gas and oil from old, low-permeability shales. These developments include a change from low-volume, high-viscosity fluid injection to high-volume, low-viscosity injection. The injected fluid introduces distributed damage that provides fracture permeability for the extraction of the gas and oil. In order to model this process, we utilize a loopless nontrapping invasion percolation previously introduced to model optimal polymers in a strongly disordered medium and for determining minimum energy spanning trees on a lattice. We performed numerical simulations on a two-dimensional square lattice and find significant differences from other percolation models. Additionally, we find that the growing fracture network satisfies both Horton-Strahler and Tokunaga network statistics. As with other invasion percolation models, our model displays burst dynamics, in which the cluster extends rapidly into a connected region. We introduce an alternative definition of bursts to be a consecutive series of opened bonds whose strengths are all below a specified value. Using this definition of bursts, we find good agreement with a power-law frequency-area distribution. These results are generally consistent with the observed distribution of microseismicity observed during a high-volume frack.
Loopless nontrapping invasion-percolation model for fracking.
Norris, J Quinn; Turcotte, Donald L; Rundle, John B
2014-02-01
Recent developments in hydraulic fracturing (fracking) have enabled the recovery of large quantities of natural gas and oil from old, low-permeability shales. These developments include a change from low-volume, high-viscosity fluid injection to high-volume, low-viscosity injection. The injected fluid introduces distributed damage that provides fracture permeability for the extraction of the gas and oil. In order to model this process, we utilize a loopless nontrapping invasion percolation previously introduced to model optimal polymers in a strongly disordered medium and for determining minimum energy spanning trees on a lattice. We performed numerical simulations on a two-dimensional square lattice and find significant differences from other percolation models. Additionally, we find that the growing fracture network satisfies both Horton-Strahler and Tokunaga network statistics. As with other invasion percolation models, our model displays burst dynamics, in which the cluster extends rapidly into a connected region. We introduce an alternative definition of bursts to be a consecutive series of opened bonds whose strengths are all below a specified value. Using this definition of bursts, we find good agreement with a power-law frequency-area distribution. These results are generally consistent with the observed distribution of microseismicity observed during a high-volume frack. PMID:25353434
Continuous percolation transition in suppressed random cluster growth model
NASA Astrophysics Data System (ADS)
Roy, Bappaditya; Santra, S. B.
2016-05-01
A new suppressed cluster growth model on 2D square lattice combining Hoshen-Kopelman and Leath approaches is studied here. The lattice sites are initially occupied randomly with probability (ρ). The empty perimeter sites of the clusters of occupied sites are grown with a cluster size dependent probability. The growth probability is then lowest for the largest cluster and highest for the smallest cluster. At the end of growth process all the cluster related quantities are estimated and they are found to display power law scaling as in percolation transition. However, the values of the critical exponents vary continuously with ρ, the initial seed concentration. At higher values of ρ, the model belongs the percolation universality class.
Fractal structure of equipotential curves on a continuum percolation model
NASA Astrophysics Data System (ADS)
Matsutani, Shigeki; Shimosako, Yoshiyuki; Wang, Yunhong
2012-12-01
We numerically investigate the electric potential distribution over a two-dimensional continuum percolation model between the electrodes. The model consists of overlapped conductive particles on the background with an infinitesimal conductivity. Using the finite difference method, we solve the generalized Laplace equation and show that in the potential distribution, there appear quasi-equipotential clusters which approximately and locally have the same values as steps and stairs. Since the quasi-equipotential clusters have the fractal structure, we compute the fractal dimension of equipotential curves and its dependence on the volume fraction over [0,1]. The fractal dimension in [1.00, 1.246] has a peak at the percolation threshold pc.
Technology Transfer Automated Retrieval System (TEKTRAN)
Today, non-point source pollution (NPS) is one of the major sources of water quality impairments globally (UNEP, 2007). In the US, nutrient pollution is the leading cause of water quality issues in lakes and estuaries (USEPA, 2002). The maximum concentration of nutrients in streams is found to be in...
The membrane skeleton of erythrocytes. A percolation model.
Saxton, M J
1990-01-01
The spectrin network on the cytoplasmic surface of the erythrocyte membrane is modeled as a triangular lattice of spectrin tetramers. This network obstructs lateral diffusion of proteins and provides mechanical reinforcement to the membrane. These effects are treated in a systematic and unified manner in terms of a percolation model. The diffusion coefficient is obtained as a function of the fraction of normal spectrin tetramers for both static and fluctuating barriers. The elasticity of the network is calculated as a function of the fraction of normal spectrin and the ratio of bending to stretching energies. For static barriers, elasticity and lateral diffusion are incompatible: if a network is connected enough to be elastic, it is connected enough to block long-range lateral diffusion. The elasticity and the force required for mechanical breakdown go to zero at the percolation threshold; experimental evidence suggests the existence of a stability threshold at or near the percolation threshold. The model is qualitatively applicable to other cells with membrane skeletons, such as epithelial cells, in which localization of membrane proteins is essential to differentiation. PMID:2393702
Modeling fractal cities using the correlated percolation model.
NASA Astrophysics Data System (ADS)
Makse, Hernán A.; Havlin, Shlomo; Stanley, H. Eugene
1996-03-01
Cities grow in a way that might be expected to resemble the growth of two-dimensional aggregates of particles, and this has led to recent attempts to model urban growth using ideas from the statistical physics of clusters. In particular, the model of diffusion limited aggregation (DLA) has been invoked to rationalize the apparently fractal nature of urban morphologies(M. Batty and P. Longley, Fractal Cities) (Academic, San Diego, 1994). The DLA model predicts that there should exist only one large fractal cluster, which is almost perfectly screened from incoming 'development units' (representing, for example, people, capital or resources), so that almost all of the cluster growth takes place at the tips of the cluster's branches. We show that an alternative model(H. A. Makse, S. Havlin, H. E. Stanley, Nature 377), 608 (1995), in which development units are correlated rather than being added to the cluster at random, is better able to reproduce the observed morphology of cities and the area distribution of sub-clusters ('towns') in an urban system, and can also describe urban growth dynamics. Our physical model, which corresponds to the correlated percolation model in the presence of a density gradient, is motivated by the fact that in urban areas development attracts further development. The model offers the possibility of predicting the global properties (such as scaling behavior) of urban morphologies.
Effect of threshold disorder on the quorum percolation model.
Monceau, Pascal; Renault, Renaud; Métens, Stéphane; Bottani, Samuel
2016-07-01
We study the modifications induced in the behavior of the quorum percolation model on neural networks with Gaussian in-degree by taking into account an uncorrelated Gaussian thresholds variability. We derive a mean-field approach and show its relevance by carrying out explicit Monte Carlo simulations. It turns out that such a disorder shifts the position of the percolation transition, impacts the size of the giant cluster, and can even destroy the transition. Moreover, we highlight the occurrence of disorder independent fixed points above the quorum critical value. The mean-field approach enables us to interpret these effects in terms of activation probability. A finite-size analysis enables us to show that the order parameter is weakly self-averaging with an exponent independent on the thresholds disorder. Last, we show that the effects of the thresholds and connectivity disorders cannot be easily discriminated from the measured averaged physical quantities. PMID:27575157
Effect of threshold disorder on the quorum percolation model
NASA Astrophysics Data System (ADS)
Monceau, Pascal; Renault, Renaud; Métens, Stéphane; Bottani, Samuel
2016-07-01
We study the modifications induced in the behavior of the quorum percolation model on neural networks with Gaussian in-degree by taking into account an uncorrelated Gaussian thresholds variability. We derive a mean-field approach and show its relevance by carrying out explicit Monte Carlo simulations. It turns out that such a disorder shifts the position of the percolation transition, impacts the size of the giant cluster, and can even destroy the transition. Moreover, we highlight the occurrence of disorder independent fixed points above the quorum critical value. The mean-field approach enables us to interpret these effects in terms of activation probability. A finite-size analysis enables us to show that the order parameter is weakly self-averaging with an exponent independent on the thresholds disorder. Last, we show that the effects of the thresholds and connectivity disorders cannot be easily discriminated from the measured averaged physical quantities.
Technology Transfer Automated Retrieval System (TEKTRAN)
This study evaluated the performance of two water quality models in accordance to specific tasks designated in the USDA Agricultural Research Service Conservation Effects Assessment Project. The Soil and Water Assessment Tool (SWAT) and the Annualized Agricultural Non-Point Source (AnnAGNPS) models ...
NASA Astrophysics Data System (ADS)
Valentine, A. P.; Kaeufl, P.; De Wit, R. W. L.; Trampert, J.
2014-12-01
Obtaining knowledge about source parameters in (near) real-time during or shortly after an earthquake is essential for mitigating damage and directing resources in the aftermath of the event. Therefore, a variety of real-time source-inversion algorithms have been developed over recent decades. This has been driven by the ever-growing availability of dense seismograph networks in many seismogenic areas of the world and the significant advances in real-time telemetry. By definition, these algorithms rely on short time-windows of sparse, local and regional observations, resulting in source estimates that are highly sensitive to observational errors, noise and missing data. In order to obtain estimates more rapidly, many algorithms are either entirely based on empirical scaling relations or make simplifying assumptions about the Earth's structure, which can in turn lead to biased results. It is therefore essential that realistic uncertainty bounds are estimated along with the parameters. A natural means of propagating probabilistic information on source parameters through the entire processing chain from first observations to potential end users and decision makers is provided by the Bayesian formalism.We present a novel method based on pattern recognition allowing us to incorporate highly accurate physical modelling into an uncertainty-aware real-time inversion algorithm. The algorithm is based on a pre-computed Green's functions database, containing a large set of source-receiver paths in a highly heterogeneous crustal model. Unlike similar methods, which often employ a grid search, we use a supervised learning algorithm to relate synthetic waveforms to point source parameters. This training procedure has to be performed only once and leads to a representation of the posterior probability density function p(m|d) --- the distribution of source parameters m given observations d --- which can be evaluated quickly for new data.Owing to the flexibility of the pattern
Interacting damage models mapped onto ising and percolation models
Toussaint, Renaud; Pride, Steven R.
2004-03-23
The authors introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasistatic fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, they obtain the probability distribution of each damage configuration at any level of the imposed external deformation. They demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, they show that damage models with global load sharing are isomorphic to standard percolation theory, that damage models with local load sharing rule are isomorphic to the standard ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. they also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, they also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model
Interacting damage models mapped onto Ising and percolation models.
Toussaint, Renaud; Pride, Steven R
2005-04-01
We introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasi-static fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, we obtain the probability distribution of each damage configuration at any level of the imposed external deformation. We demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, we show that damage models with global load sharing are isomorphic to standard percolation theory and that damage models with a local load sharing rule are isomorphic to the standard Ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. We also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, we also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model to standard
NASA Astrophysics Data System (ADS)
Toll, D.; Engman, T.; Edward, P.; Magness, A.; Townsend, P.; N-Meister, W.; Nigro, J.; Lee, S.
2007-12-01
The Environmental Protection Agency (EPA) estimates that over 20,000 bodies of water throughout the country do not meet water quality standards. Nonpoint sources -- pollution from urban, agricultural, and forest land that is transported by runoff -- typically cause 90 percent of impairments. EPA has developed the BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) modeling system for performing numerous water quality studies. The key to this suite of models is the Hydrological Simulation Program - Fortran (HSPF), which calculates daily stream flow rates and the corresponding pollutant concentrations at the watershed outlet. EPA has partnered with NASA to use high spatial and temporal hydrological variables (e.g., precipitation, evaporation, etc.) from the NASA Land Information System (LIS) and land cover/vegetative indices derived from primarily MODIS and Landsat satellite data non-point source water quality for the Chesapeake Bay Basin. For the precipitation and evaporation data, EPA-based BASINS-HSPF streamflow runs were conducted on seven study watersheds in the Chesapeake Bay Basin. Sets of runs using precipitation from default weather stations, the NASA LIS 1/8th degree precipitation, NOAA Stage IV precipitation, NASA LIS Noah land surface model evapotranspiration datasets were conducted for each watershed. The output statistics summarized reveal that for 74% of the runs, the NASA LIS 1/8th degree and Stage IV precipitation-based runs performed better than when using only the default EPA precipitation station data. In addition, an automatic calibration method ('PEST') and Noah land surface model evapotranspiration (ET) being further incorporated. The empirical ability of generalized spectral indices and land cover derived from Landsat and MODIS was tested for predicting stream water nitrogen export from predominately forested watersheds undergoing disturbance. The disturbance index, a summary index that is easily computed from Landsat
RAPID COMMUNICATION: Percolation modelling for highly aligned polycrystalline superconducting tapes
NASA Astrophysics Data System (ADS)
Rutter, N. A.; Glowacki, B. A.; Evetts, J. E.
2000-11-01
Surface and bulk texture measurements have been carried out on highly aligned NiFe tapes, suitable for use as coated conductor substrates. Data from small-area electron backscatter diffraction measurements are compared with those from bulk x-ray analysis in the development of a two-dimensional percolation model, and the two are shown to give very similar results. No evidence of grain-to-grain correlation is found. The model is then developed to assess how the properties of a superconducting layer grown epitaxially on buffered tapes will depend on parameters such as sample size, grain size and the extent of grain alignment.
Percolation and coarsening in the bidimensional voter model
NASA Astrophysics Data System (ADS)
Tartaglia, Alessandro; Cugliandolo, Leticia F.; Picco, Marco
2015-10-01
We study the bidimensional voter model on a square lattice with numerical simulations. We demonstrate that the evolution takes place in two distinct dynamic regimes; a first approach towards critical site percolation and a further approach towards full consensus. We calculate the time dependence of the two growing lengths, finding that they are both algebraic but with different exponents (apart from possible logarithmic corrections). We analyze the morphology and statistics of clusters of voters with the same opinion. We compare these results to the ones for curvature driven two-dimensional coarsening.
Percolation phase diagrams for multi-phase models built on the overlapping sphere model
NASA Astrophysics Data System (ADS)
Garboczi, E. J.
2016-01-01
The overlapping sphere (OS) percolation model gives a two-phase microstructure (matrix plus inclusions) that is useful for testing composite material ideas and other applications, as well as serving as a paradigm of overlapping object percolation and phase transitions. Real materials often have more than two phases, so it is of interest to extend the applicability of the OS model. A flexible variant of the OS model can be constructed by randomly assigning the spheres different phase labels, according to a uniform probability distribution, as they are inserted one by one into the matrix. The resulting three or more phase models can have different amounts of percolating and non-percolating phases, depending on the volume fraction of each phase and the total OS volume fraction. A three-dimensional digital image approach is used to approximately map out the percolation phase diagram of such models, explicitly up to four phases (one matrix plus three spherical inclusion phases) and implicitly for N > 4 phases. For the three phase model, it was found that a single OS sub-phase has a percolation threshold that ranges from about a volume fraction of 0.16, when the matrix volume fraction is about 0.01, to about 0.30, at a matrix volume fraction of about 0.7. The approximate analytical dependence of this sub-phase percolation threshold on the defining model parameters serves to guide the building of the percolation phase diagram for the N-phase model, and is used to determine the maximum value of N(N = 6) at which all N phases can be simultaneously percolated.
Electron percolation in realistic models of carbon nanotube networks
Simoneau, Louis-Philippe Villeneuve, Jérémie Rochefort, Alain
2015-09-28
The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models.
Electron percolation in realistic models of carbon nanotube networks
NASA Astrophysics Data System (ADS)
Simoneau, Louis-Philippe; Villeneuve, Jérémie; Rochefort, Alain
2015-09-01
The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models.
NASA Astrophysics Data System (ADS)
Kumari, Pato; Sharma, Vikash Kumar; Modi, Chitra
2016-04-01
In the present study, propagation of magnetoelastic shear wave due to a momentary point source in a viscoelastic crustal layer over inhomogeneous viscoelastic half space has been discussed. Green's function technique and Fourier transform along with method of successive approximation are used to find the closed-form solutions for displacement and generalized shear wave period equation. Attenuation of the resultant shear wave is computed and effects of magnetic field, width of the layer, complex wave number, viscosity, and inhomogeneity parameters are distinctly marked on dissipation curves using two-dimensional and surface plots. It is found that effect of layer's magnetoelastic coupling parameter on attenuation pattern of shear wave is just the reverse of half space magnetoelastic coupling parameter. Similarly, internal friction of layer has somewhat different effect on shear wave angular frequency than lower half space viscosity. Certain published results are also derived as special cases to the present study.
The Community Multiscale Air Quality (CMAQ) / Plume-in-Grid (PinG) model was applied on a domain encompassing the greater Nashville, Tennessee region. Model simulations were performed for selected days in July 1995 during the Southern Oxidant Study (SOS) field study program wh...
Percolation and Burgers' dynamics in a model of capillary formation
NASA Astrophysics Data System (ADS)
Coniglio, A.; de Candia, A.; di Talia, S.; Gamba, A.
2004-05-01
Capillary networks are essential in vertebrates to supply tissues with nutrients. Experiments of in vitro capillary formation show that cells randomly spread on a gel matrix autonomously organize to form vascular networks. Cells form disconnected networks at low densities and connected ones above a critical density. Above the critical density the network is characterized by a typical mesh size ˜200 μm , which is approximately constant on a wide range of density values. In this paper we present a full characterization of a recently proposed model which reproduces the main features of the biological system, focusing on its dynamical properties, on the fractal properties of patterns, and on the percolative phase transition. We discuss the relevance of the model in relation with some experiments in living beings and proposed diagnostic methods based on the measurement of the fractal dimension of vascular networks.
Modelling heterogeneous meltwater percolation on the Greenland Ice Sheet
NASA Astrophysics Data System (ADS)
Ligtenberg, S.
2015-12-01
The Greenland Ice Sheet (GrIS) has experienced an increase of surface meltwater production over the last decades, with the latest record set in the summer of 2012. For current and future ice sheet mass balance assessments, it is important to quantify what part of this meltwater reaches the ocean and contributes to sea level change. Meltwater produced at the surface has several options: it can infiltrate the local firn pack, where it is either stored temporarily or refrozen, or it can run off along the surface or via en-glacial drainage systems. In this study, we focus on the first; more specifically, in which manner meltwater percolates the firn column. Over the past years, GrIS research has shown that meltwater does not infiltrate the firn pack homogeneously (i.e. matrix flow), but that inhomogeneities in horizontal firn layers causes preferential flow paths for meltwater (i.e. piping). Although this process has been observed and studied on a few isolated sites, it has never been examined on the entire GrIS. To do so, we use the firn model IMAU-FDM with new parameterizations for preferential flow, impermeable ice lenses and sub-surface runoff. At the surface, IMAU-FDM is forced with realistic climate data from the regional climate model RACMO2.3. The model results are evaluated with temperatures and density measurements from firn cores across the GrIS. By allowing for heterogeneous meltwater percolation, the model is able to store heat and mass much deeper in the firn column. This is, however, in part counteracted by the inclusion of impermeability of ice lenses, which causes part of the meltwater to run off horizontally.
Series Expansion Method for Asymmetrical Percolation Models with Two Connection Probabilities
NASA Astrophysics Data System (ADS)
Inui, Norio; Komatsu, Genichi; Kameoka, Koichi
2000-01-01
In order to study the solvability of the percolation model based on Guttmann and Enting's conjecture, the power series for the percolation probability in the form of ∑nHn(q)pn is examined. Although the power series is given by calculating inverse of the transfer-matrix in principle, it is very hard to obtain the inverse matrix containing many complex polynomials as elements. We introduce a new series expansion technique which does not necessitate inverse operation for the transfer-matrix.By using the new procedure, we derive the series of the asymmetrical percolation probability including the isotropic percolation probability as a special case.
Non-point source pollution is a diffuse source that is difficult to measure and is highly variable due to different rain patterns and other climatic conditions. In many areas, however, non-point source pollution is the greatest source of water quality degradation. Presently, stat...
NASA Astrophysics Data System (ADS)
Usery, E. Lynn; Finn, Michael P.; Scheidt, Douglas J.; Ruhl, Sheila; Beard, Thomas; Bearden, Morgan
2004-10-01
Researchers have been coupling geographic information systems (GIS) data handling and processing capability to watershed and water-quality models for many years. This capability is suited for the development of databases appropriate for water modeling. However, it is rare for GIS to provide direct inputs to the models. To demonstrate the logical procedure of coupling GIS for model parameter extraction, we selected the Agricultural Non-Point Source (AGNPS) pollution model. Investigators can generate data layers at various resolutions and resample to pixel sizes to support models at particular scales. We developed databases of elevation, land cover, and soils at various resolutions in four watersheds. The ability to use multiresolution databases for the generation of model parameters is problematic for grid-based models. We used database development procedures and observed the effects of resolution and resampling on GIS input datasets and parameters generated from those inputs for AGNPS. Results indicate that elevation values at specific points compare favorably between 3- and 30-m raster datasets. Categorical data analysis indicates that land cover classes vary significantly. Derived parameters parallel the results of the base GIS datasets. Analysis of data resampled from 30-m to 60-, 120-, 210-, 240-, 480-, 960-, and 1920-m pixels indicates a general degradation of both elevation and land cover correlations as resolution decreases. Initial evaluation of model output values for soluble nitrogen and phosphorous indicates similar degradation with resolution.
Usery, E.L.; Finn, M.P.; Scheidt, D.J.; Ruhl, S.; Beard, T.; Bearden, M.
2004-01-01
Researchers have been coupling geographic information systems (GIS) data handling and processing capability to watershed and waterquality models for many years. This capability is suited for the development of databases appropriate for water modeling. However, it is rare for GIS to provide direct inputs to the models. To demonstrate the logical procedure of coupling GIS for model parameter extraction, we selected the Agricultural Non-Point Source (AGNPS) pollution model. Investigators can generate data layers at various resolutions and resample to pixel sizes to support models at particular scales. We developed databases of elevation, land cover, and soils at various resolutions in four watersheds. The ability to use multiresolution databases for the generation of model parameters is problematic for grid-based models. We used database development procedures and observed the effects of resolution and resampling on GIS input datasets and parameters generated from those inputs for AGNPS. Results indicate that elevation values at specific points compare favorably between 3- and 30-m raster datasets. Categorical data analysis indicates that land cover classes vary significantly. Derived parameters parallel the results of the base GIS datasets. Analysis of data resampled from 30-m to 60-, 120-, 210-, 240-, 480-, 960-, and 1920-m pixels indicates a general degradation of both elevation and land cover correlations as resolution decreases. Initial evaluation of model output values for soluble nitrogen and phosphorous indicates similar degradation with resolution. ?? Springer-Verlag 2004.
Ma, Denglong; Zhang, Zaoxiao
2016-07-01
Gas dispersion model is important for predicting the gas concentrations when contaminant gas leakage occurs. Intelligent network models such as radial basis function (RBF), back propagation (BP) neural network and support vector machine (SVM) model can be used for gas dispersion prediction. However, the prediction results from these network models with too many inputs based on original monitoring parameters are not in good agreement with the experimental data. Then, a new series of machine learning algorithms (MLA) models combined classic Gaussian model with MLA algorithm has been presented. The prediction results from new models are improved greatly. Among these models, Gaussian-SVM model performs best and its computation time is close to that of classic Gaussian dispersion model. Finally, Gaussian-MLA models were applied to identifying the emission source parameters with the particle swarm optimization (PSO) method. The estimation performance of PSO with Gaussian-MLA is better than that with Gaussian, Lagrangian stochastic (LS) dispersion model and network models based on original monitoring parameters. Hence, the new prediction model based on Gaussian-MLA is potentially a good method to predict contaminant gas dispersion as well as a good forward model in emission source parameters identification problem. PMID:27035273
Anisotropy in Fracking: A Percolation Model for Observed Microseismicity
NASA Astrophysics Data System (ADS)
Norris, J. Quinn; Turcotte, Donald L.; Rundle, John B.
2015-01-01
Hydraulic fracturing (fracking), using high pressures and a low viscosity fluid, allow the extraction of large quantiles of oil and gas from very low permeability shale formations. The initial production of oil and gas at depth leads to high pressures and an extensive distribution of natural fractures which reduce the pressures. With time these fractures heal, sealing the remaining oil and gas in place. High volume fracking opens the healed fractures allowing the oil and gas to flow to horizontal production wells. We model the injection process using invasion percolation. We use a 2D square lattice of bonds to model the sealed natural fractures. The bonds are assigned random strengths and the fluid, injected at a point, opens the weakest bond adjacent to the growing cluster of opened bonds. Our model exhibits burst dynamics in which the clusters extend rapidly into regions with weak bonds. We associate these bursts with the microseismic activity generated by fracking injections. A principal object of this paper is to study the role of anisotropic stress distributions. Bonds in the y-direction are assigned higher random strengths than bonds in the x-direction. We illustrate the spatial distribution of clusters and the spatial distribution of bursts (small earthquakes) for several degrees of anisotropy. The results are compared with observed distributions of microseismicity in a fracking injection. Both our bursts and the observed microseismicity satisfy Gutenberg-Richter frequency-size statistics.
A spatial model to aggregate point-source and nonpoint-source water-quality data for large areas
White, D.A.; Smith, R.A.; Price, C.V.; Alexander, R.B.; Robinson, K.W.
1992-01-01
More objective and consistent methods are needed to assess water quality for large areas. A spatial model, one that capitalizes on the topologic relationships among spatial entities, to aggregate pollution sources from upstream drainage areas is described that can be implemented on land surfaces having heterogeneous water-pollution effects. An infrastructure of stream networks and drainage basins, derived from 1:250,000-scale digital-elevation models, define the hydrologic system in this spatial model. The spatial relationships between point- and nonpoint pollution sources and measurement locations are referenced to the hydrologic infrastructure with the aid of a geographic information system. A maximum-branching algorithm has been developed to simulate the effects of distance from a pollutant source to an arbitrary downstream location, a function traditionally employed in deterministic water quality models. ?? 1992.
Johnson, Andrew C; Ternes, Thomas; Williams, Richard J; Sumpter, John P
2008-08-01
To carry out meaningful ecotoxicity studies on novel polar organic microcontaminants, it is essential to know what concentrations wildlife may be exposed to. Traditionally these values were obtained by analytical chemistry, but in recent years GIS water quality models have been developed which may offer a quick and reliable way of getting the same information. Thus, two ways of obtaining basically the same information now exist, and an issue, therefore, arises as to which method is the most appropriate to use in which situation. To address this issue we have critically reviewed and compared measuring and modeling approaches for the determination of sewage effluent and river water concentrations of organic microcontaminants. Where model predictions and chemical measurements can be directly compared in sewage effluents, receiving waters, and across catchments, reported model mean values have all been within 1 order of magnitude of the measured values, with typically no more than a 3- or 4-fold difference. Interlaboratory chemical analysis of some organic microcontaminants in effluents in the challenging ng/L range have provided results which have varied from one another by a similar margin. No such comparison has been carried out yet for GIS water quality models to determine variation in predicted concentrations. As the level of ecotoxicological effects of many chemicals is often considerably higher than the reported measured or modeled values, such errors that might occur will often be of no consequence. But due to their extraordinary potency, much more accuracy is required with some natural and synthetic hormones. Significantly, modeling is no more complex to conduct when dealing with contaminants at ng/L compared with mg/L concentrations, but the same cannot be said for chemical analysis. A combination of modeling and measuring techniques will give the greatest confidence in risk assessment. PMID:18754451
NASA Astrophysics Data System (ADS)
Day, C. A.
2014-12-01
Urban streams are often characterized by diminished water quality resulting from an increase in polluted runoff from impervious surfaces. Storm activity further reduces urban stream water quality by temporarily increasing stormwater discharge from sewer overflows. This will often manifest itself in rapid declines of dissolved oxygen and peaks in specific conductivity in response to a rising biochemical oxygen demand which slowly recovers as the pollution load is washed through the stream system. This research developed a GIS-based model to track potential sources of pollution based on the dissolved oxygen and specific conductivity response of urban streams to a series of storm events, within the city of Louisville, Kentucky. Watershed outlet hydrographs were first obtained to determine the lag time of dissolved oxygen drops and specific conductivity peaks in response to set of storm events. Using a digital elevation model and the National Landcover Database, 10m resolution rasters were then created which calculated slope and flow direction/accumulation for both open channel and overland flow conditions across the watersheds. The rasters were merged and converted to flow velocities using a series of storms with different intensities. The final step utilized the Flow Length tool in ArcGIS which calculated the travel time to the watershed outlets from each pixel weighted by the open channel and overland flow conditions. Potential pollution sources could then be located by matching the dissolved oxygen and specific conductivity response lag times to the associated watershed travel times.
Percolation models for boiling and bubble growth in porous media
Yortsos, Y.C.
1991-05-01
We analyze the liquid-to-vapor phase change in single-component fluids in porous media at low superheats. Conditions typical to steam injection in porous media are taken. We examine nucleation, phase equilibria and their stability, and the growth of vapor bubbles. Effects of pore structure are emphasized. It is shown that at low supersaturations, bubble growth can be described as a percolation process. In the absence of spatial gradients, macroscopic flow properties are calculated in terms of nucleation parameters. A modification of gradient percolation is also proposed in the case of spatial temperature gradients, when solid conduction predominates. 22 refs., 10 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Domínguez, C. G.; Pryet, A.; García Vera, M.; Gonzalez, A.; Chaumont, C.; Tournebize, J.; Villacis, M.; d'Ozouville, N.; Violette, S.
2016-01-01
A Rutter-type canopy interception model is combined with a 1-D physically-based soil water flow model to compare deep percolation rates below distinct land covers. The joint model allows the quantification of both evaporation and transpiration rates as well as deep percolation from vegetation and soil characteristics. Experimental observations are required to constitute the input and calibration datasets. An appropriate monitoring design is described which consists in meteorological monitoring together with throughfall and soil water tension measurements. The methodology is illustrated in Santa Cruz Island in the Galapagos Archipelago, which has been affected by significant land use changes. Two adjacent study plots are investigated: a secondary forest and a pasture. The results of the model reveal that evaporation of canopy interception is higher in the pasture due to the bigger canopy storage capacity, which promotes evaporation against canopy drainage. This is however compensated by higher transpiration in the secondary forest, due to the smaller surface resistance. As a consequence, total evapotranspiration is similar for the two plots and no marked difference in deep percolation can be observed. In both cases, deep percolation reaches ca. 2 m/year which corresponds to 80% of the incoming rainfall. This methodology not only allows the quantification of deep percolation, but can also be used to identify the controlling factors of deep percolation under contrasting land covers.
Luo, B; Li, J B; Huang, G H; Li, H L
2006-05-15
This study presents a simulation-based interval two-stage stochastic programming (SITSP) model for agricultural non-point source (NPS) pollution control through land retirement under uncertain conditions. The modeling framework was established by the development of an interval two-stage stochastic program, with its random parameters being provided by the statistical analysis of the simulation outcomes of a distributed water quality approach. The developed model can deal with the tradeoff between agricultural revenue and "off-site" water quality concern under random effluent discharge for a land retirement scheme through minimizing the expected value of long-term total economic and environmental cost. In addition, the uncertainties presented as interval numbers in the agriculture-water system can be effectively quantified with the interval programming. By subdividing the whole agricultural watershed into different zones, the most pollution-related sensitive cropland can be identified and an optimal land retirement scheme can be obtained through the modeling approach. The developed method was applied to the Swift Current Creek watershed in Canada for soil erosion control through land retirement. The Hydrological Simulation Program-FORTRAN (HSPF) was used to simulate the sediment information for this case study. Obtained results indicate that the total economic and environmental cost of the entire agriculture-water system can be limited within an interval value for the optimal land retirement schemes. Meanwhile, a best and worst land retirement scheme was obtained for the study watershed under various uncertainties. PMID:16242757
What are cirrus point sources?
NASA Technical Reports Server (NTRS)
Heiles, Carl; Mccarthy, Patrick J.; Reach, William; Strauss, Michael A.
1987-01-01
Most cirrus point sources are associated with interstellar gas. A subset of these was isolated, together with other sources showing large band 4 to 3 flux density ratios, that are not associated with interstellar gas. Most of the point sources are associated with diffuse cirrus emissions. The sources appear to be distributed randomly on the sky, with the exception of six clusters, one of which is not associated with any known object. Six sources out of seventeen that were observed for redshifted H I at Arecibo were found to be associated with relatively nondescript external galaxies. Most of the sources do not appear on the Palomar Sky Survey. Deep optical observations of eight fields revealed some fairly distant galaxies, one object with a very peculiar optical spectrum, and several blank fields.
Silva, Nayana G M; von Sperling, Marcos
2008-01-01
Downstream of Capim Branco I hydroelectric dam (Minas Gerais state, Brazil), there is the need of keeping a minimum flow of 7 m3/s. This low flow reach (LFR) has a length of 9 km. In order to raise the water level in the low flow reach, the construction of intermediate dikes along the river bed was decided. The LFR has a tributary that receives the discharge of treated wastewater. As part of this study, water quality of the low-flow reach was modelled, in order to gain insight into its possible behaviour under different scenarios (without and with intermediate dikes). QUAL2E equations were implemented in FORTRAN code. The model takes into account point-source pollution and diffuse pollution. Uncertainty analysis was performed, presenting probabilistic results and allowing identification of the more important coefficients in the LFR water-quality model. The simulated results indicate, in general, very good conditions for most of the water quality parameters The variables of more influence found in the sensitivity analysis were the conversion coefficients (without and with dikes), the initial conditions in the reach (without dikes), the non-point incremental contributions (without dikes) and the hydraulic characteristics of the reach (with dikes). PMID:18469404
Kuentz, M; Leuenberger, H
1998-02-01
The purpose of this investigation was to analyze the modified Young's modulus of microcrystalline cellulose tablets at comparatively low relative densities, based on concepts of percolation theory. Tablets were prepared and tested using a Zwick 1478 universal testing instrument. For statistical evaluation a new method is introduced for power laws, which exhibits highly correlated model parameters. According to our results the model Leuenberger, Leu is consistent with an Effective Medium Approximation which exhibits an exponent equal to one far away from the percolation threshold. In addition, the results show that it is essential to evaluate the elastic behavior of tablets close to the percolation threshold. For the different types of MCC a critical exponent q = 3.95 +/- 0.14 was obtained. This result is very essential, as it is in good agreement with the theoretically expected value of 3.9 from an elastic network (central force model). The proposed model describes the modified Young's modulus better than former model equations taking into account the relative density. Thus, the process during uniaxial compaction can be imagined as a directed continuum percolation and the relative density of compacts can be identified as a space-occupation probability density phi yielding reasonable percolation thresholds. PMID:9532596
NASA Astrophysics Data System (ADS)
Tasdighi, A.; Arabi, M.
2015-12-01
reducing them was assessed and bands of uncertainty around BMP efficiencies were determined. Moreover, using the predicted cumulative distribution functions (CDFs) for nonpoint loads (Agriculture) and CDFs of observed loads for point sources (WWTPs), trading ratios for specific trades were determined under uncertainty.
Beyond the percolation universality class: the vertex split model for tetravalent lattices
NASA Astrophysics Data System (ADS)
Nachtrab, Susan; Hoffmann, Matthias J. F.; Kapfer, Sebastian C.; Schröder-Turk, Gerd E.; Mecke, Klaus
2015-04-01
We propose a statistical model defined on tetravalent three-dimensional lattices in general and the three-dimensional diamond network in particular where the splitting of randomly selected nodes leads to a spatially disordered network, with decreasing degree of connectivity. The terminal state, that is reached when all nodes have been split, is a dense configuration of self-avoiding walks on the diamond network. Starting from the crystallographic diamond network, each of the four-coordinated nodes is replaced with probability p by a pair of two edges, each connecting a pair of the adjacent vertices. For all values 0≤slant p≤slant 1 the network percolates, yet the fraction fp of the system that belongs to a percolating cluster drops sharply at pc = 1 to a finite value fpc. This transition is reminiscent of a percolation transition yet with distinct differences to standard percolation behaviour, including a finite mass fpc\\gt 0 of the percolating clusters at the critical point. Application of finite size scaling approach for standard percolation yields scaling exponents for p\\to {{p}c} that are different from the critical exponents of the second-order phase transition of standard percolation models. This transition significantly affects the mechanical properties of linear-elastic realizations (e.g. as custom-fabricated models for artificial bone scaffolds), obtained by replacing edges with solid circular struts to give an effective density ϕ. Finite element methods demonstrate that, as a low-density cellular structure, the bulk modulus K shows a cross-over from a compression-dominated behaviour, K(φ )\\propto {{φ }κ } with κ ≈ 1, at p = 0 to a bending-dominated behaviour with κ ≈ 2 at p = 1.
Liu, Ruimin; Dong, Guangxia; Xu, Fei; Wang, Xiujuan; He, Mengchang
2015-01-01
In this paper, the spatial changes and trends in non-point source (NPS) total phosphorus (TP) pollution were analyzed by land and non-land uses in the Songliao River Basin from 1986 to 2000 (14 years). A grid-based export coefficient model was used in the process of analysis based on to a geographic information system. The Songliao Basin is divided in four regions: Liaoning province, Jilin province (JL), Heilongjiang province and the eastern part of the Inner Mongolia (IM) Autonomous Region. Results indicated that the NPS phosphorus load caused by land use and non-land use increased steadily from 3.11×10(4) tons in 1986 to 3.49×10(4) tons in 2000. The southeastern region of the Songliao Plain was the most important NPS pollution contributor of all the districts. Although the TP load caused by land use decreased during the studied period in the Songliao River Basin, the contribution of land use to the TP load was dominant compared to non-land uses. The NPS pollution caused by non-land use steadily increased over the studied period. The IM Autonomous Region and JL province had the largest mean annual rate of change among all districts (more than 30%). In this area, livestock and poultry breeding had become one of the most important NPS pollution sources. These areas will need close attention in the future. PMID:26038937
3D self-consistent percolative model for networks of randomly aligned carbon nanotubes
NASA Astrophysics Data System (ADS)
Colasanti, S.; Deep Bhatt, V.; Abdellah, A.; Lugli, P.
2015-10-01
A numerical percolative model for simulations of random networks of carbon nanotubes is presented. This algorithm takes into account the real 3D nature of these networks, allowing for a better understanding of their electrical properties. The nanotubes are modeled as non-rigid bendable cylinders with geometrical properties derived according to some statistical distributions inferred from the experiments. For the transport mechanisms we refer to the theory of one-dimensional ballistic channels which is based on the computation of the density of states. The behavior of the entire network is then simulated by coupling a SPICE program with an iterative algorithm that calculates self-consistently the electrostatic potential and the current flow in each node of the network. We performed several simulations on the resistivity of networks with different thicknesses and over different simulation domains. Our results confirm the percolative nature of the electrical transport, which are more pronounced in films close to their percolation threshold.
Point Source Location Sensitivity Analysis
NASA Astrophysics Data System (ADS)
Cox, J. Allen
1986-11-01
This paper presents the results of an analysis of point source location accuracy and sensitivity as a function of focal plane geometry, optical blur spot, and location algorithm. Five specific blur spots are treated: gaussian, diffraction-limited circular aperture with and without central obscuration (obscured and clear bessinc, respectively), diffraction-limited rectangular aperture, and a pill box distribution. For each blur spot, location accuracies are calculated for square, rectangular, and hexagonal detector shapes of equal area. The rectangular detectors are arranged on a hexagonal lattice. The two location algorithms consist of standard and generalized centroid techniques. Hexagonal detector arrays are shown to give the best performance under a wide range of conditions.
The Herschel Point Source Catalogue
NASA Astrophysics Data System (ADS)
Marton, Gabor; Schulz, Bernhard; Altieri, Bruno; Calzoletti, Luca; Kiss, Csaba; Lim, Tanya; Lu, Nanyao; Paladini, Roberta; Papageorgiou, Andreas; Pearson, Chris; Rector, John; Shupe, David; Valtchanov, Ivan; Verebélyi, Erika; Xu, Kevin
2015-08-01
The Herschel Space Observatory was the fourth cornerstone mission in the European Space Agency (ESA) science programme with excellent broad band imaging capabilities in the submillimetre and far-infrared part of the spectrum. Although the spacecraft finished its observations in 2013, it left a large legacy dataset that is far from having been fully scrutinized and still has potential for new scientific discoveries. This is specifically true for the photometric observations of the PACS and SPIRE instruments that scanned >10% of the sky at 70, 100, 160, 250, 350 and 500 microns. Some source catalogs have already been produced by individual observing programs, but there are many observations that would never be analyzed for their full source content. To maximize the science return of the SPIRE and PACS data sets, our international team of instrument experts is in the process of building the Herschel Point Source Catalog (HPSC) from all scan map observations. Our homogeneous source extraction enables a systematic and unbiased comparison of sensitivity across the different Herschel fields that single programs will generally not be able to provide. The extracted point sources will contain individual YSOs of our Galaxy, unresolved YSO clusters in resolved nearby galaxies and unresolved galaxies of the local and distant Universe that are related to star formation. Such a huge dataset will help scientists better understand the evolution from interstellar clouds to individual stars. Furthermore the analysis of stellar clusters and the star formation on galactic scales will add more details to the understanding of star formation laws through time.We present our findings on comparison of different source detection and photometric tools. First results of the extractions are shown along with the description of our pipelines and catalogue entries. We also provide an additional science product, the structure noise map, that is used for the quality assessment of the catalogue in
Modeling stock price dynamics by continuum percolation system and relevant complex systems analysis
NASA Astrophysics Data System (ADS)
Xiao, Di; Wang, Jun
2012-10-01
The continuum percolation system is developed to model a random stock price process in this work. Recent empirical research has demonstrated various statistical features of stock price changes, the financial model aiming at understanding price fluctuations needs to define a mechanism for the formation of the price, in an attempt to reproduce and explain this set of empirical facts. The continuum percolation model is usually referred to as a random coverage process or a Boolean model, the local interaction or influence among traders is constructed by the continuum percolation, and a cluster of continuum percolation is applied to define the cluster of traders sharing the same opinion about the market. We investigate and analyze the statistical behaviors of normalized returns of the price model by some analysis methods, including power-law tail distribution analysis, chaotic behavior analysis and Zipf analysis. Moreover, we consider the daily returns of Shanghai Stock Exchange Composite Index from January 1997 to July 2011, and the comparisons of return behaviors between the actual data and the simulation data are exhibited.
NASA Astrophysics Data System (ADS)
Donado-Garzon, L. D.; Pardo, Y.
2013-12-01
Fractured media are very heterogeneous systems where occur complex physical and chemical processes to model. One of the possible approaches to conceptualize this type of massifs is the Discrete Fracture Network (DFN). Donado et al., modeled flow and transport in a granitic batholith based on this approach and found good fitting with hydraulic and tracer tests, but the computational cost was excessive due to a gigantic amount of elements to model. We present in this work a methodology based on percolation theory for reducing the number of elements and in consequence, to reduce the bandwidth of the conductance matrix and the execution time of each network. DFN poses as an excellent representation of all the set of fractures of the media, but not all the fractures of the media are part of the conductive network. Percolation theory is used to identify which nodes or fractures are not conductive, based on the occupation probability or percolation threshold. In a fractured system, connectivity determines the flow pattern in the fractured rock mass. This volume of fluid is driven through connection paths formed by the fractures, when the permeability of the rock is negligible compared to the fractures. In a population of distributed fractures, each of this that has no intersection with any connected fracture do not contribute to generate a flow field. This algorithm also permits us to erase these elements however they are water conducting and hence, refine even more the backbone of the network. We used 100 different generations of DFN that were optimized in this study using percolation theory. In each of the networks calibrate hydrodynamic parameters as hydraulic conductivity and specific storage coefficient, for each of the five families of fractures, yielding a total of 10 parameters to estimate, at each generation. Since the effects of the distribution of fault orientation changes the value of the percolation threshold, but not the universal laws of classical
NASA Astrophysics Data System (ADS)
Ha, Dong-Gwang; Kim, Jang-Joo; Baldo, Marc A.
2016-04-01
Mixed host compositions that combine charge transport materials with luminescent dyes offer superior control over exciton formation and charge transport in organic light emitting devices (OLEDs). Two approaches are typically used to optimize the fraction of charge transport materials in a mixed host composition: either an empirical percolative model, or a hopping transport model. We show that these two commonly-employed models are linked by an analytic expression which relates the localization length to the percolation threshold and critical exponent. The relation is confirmed both numerically and experimentally through measurements of the relative conductivity of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) :1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPb) mixtures with different concentrations, where the TCTA plays a role as hole conductor and the BmPyPb as hole insulator. The analytic relation may allow the rational design of mixed layers of small molecules for high-performance OLEDs.
Ductile damage modeling based on void coalescence and percolation theories
Tonks, D.L.; Zurek, A.K.; Thissell, W.R.
1995-09-01
A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included, and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.
Lattice Boltzmann modeling of permeability in porous materials with partially percolating voxels.
Li, Ruru; Yang, Y Sam; Pan, Jinxiao; Pereira, Gerald G; Taylor, John A; Clennell, Ben; Zou, Caineng
2014-09-01
A partial-bounce-back lattice Boltzmann model has been used to simulate flow on a lattice consisting of cubic voxels with a locally varying effective percolating fraction. The effective percolating fraction of a voxel is the total response to the partial-bounce-back techniques for porous media flow due to subvoxel fine structures. The model has been verified against known analytic solutions on two- and three-dimensional regular geometries, and has been applied to simulate flow and permeabilities of two real-world rock samples. This enables quantitative determination of permeability for problems where voxels cannot be adequately segmented as discrete compositions. The voxel compositions are represented as volume fractions of various material phases and void. The numerical results have shown that, for the tight-sandstone sample, the bulk permeability is sensitive to the effective percolating fraction of calcite. That is, the subvoxel flow paths in the calcite phase are important for bulk permeability. On the other hand, flow in the calcite phase in the sandstone sample makes an insignificant contribution to the bulk permeability. The calculated permeability value for the sandstone sample is up to two orders of magnitude greater than the tight sandstone. This model is generic and could be applied to other oil and gas reservoir media or to material samples. PMID:25314558
NASA Astrophysics Data System (ADS)
Clerc, J. P.; Giraud, G.; Laugier, J. M.; Luck, J. M.
1990-05-01
We review theoretical and experimental studies of the AC dielectric response of inhomogeneous materials, modelled as bond percolation networks, with a binary (conductor-dielectric) distribution of bond conductances. We first summarize the key results of percolation theory, concerning mostly geometrical and static (DC) transport properties, with emphasis on the scaling properties of the critical region around the percolation threshold. The frequency-dependent (AC) response of a general binary model is then studied by means of various approaches, including the effective-medium approximation, a scaling theory of the critical region, numerical computations using the transfer-matrix algorithm, and several exactly solvable deterministic fractal models. Transient regimes, related to singularities in the complex-frequency plane, are also investigated. Theoretical predictions are made more explicit in two specific cases, namely R-C and RL-C networks, and compared with a broad variety of experimental results, concerning, for example, granular composites, thin films, powders, microemulsions, cermets, porous ceramics and the viscoelastic properties of gels.
Franović, Igor; Miljković, Vladimir
2009-06-01
Spike packet propagation is modeled in mesoscopic-scale networks, composed of locally and recurrently coupled neural pools, and embedded in a two-dimensional lattice. Site dynamics is governed by three key parameters--pool connectedness probability, synaptic strength (following the steady-state distribution of some realizations of spike-timing-dependent plasticity learning rule), and the neuron refractoriness. Formation of spatiotemporal patterns in our model, synfire chains, exhibits critical behavior, with the emerging percolation phase transition controlled by the probability for nonzero synaptic strength value. Applying the finite-size scaling method, we infer the critical probability dependence on synaptic strength and refractoriness and determine the effects of connection topology on the pertaining percolation clusters fractal dimensions. We find that the directed percolation and the pair contact process with diffusion constitute the relevant universality classes of phase transitions observed in a class of mesoscopic-scale network models, which may be related to recently reported data on in vitro cultures. PMID:19658540
Reentry Near the Percolation Threshold in a Heterogeneous Discrete Model for Cardiac Tissue
NASA Astrophysics Data System (ADS)
Alonso, Sergio; Bär, Markus
2013-04-01
Arrhythmias in cardiac tissue are related to irregular electrical wave propagation in the heart. Cardiac tissue is formed by a discrete cell network, which is often heterogeneous. A localized region with a fraction of nonconducting links surrounded by homogeneous conducting tissue can become a source of reentry and ectopic beats. Extensive simulations in a discrete model of cardiac tissue show that a wave crossing a heterogeneous region of cardiac tissue can disintegrate into irregular patterns, provided the fraction of nonconducting links is close to the percolation threshold of the cell network. The dependence of the reentry probability on this fraction, the system size, and the degree of excitability can be inferred from the size distribution of nonconducting clusters near the percolation threshold.
NASA Astrophysics Data System (ADS)
Pawłowski, G.
2009-04-01
The problem of order-order and order-disorder transitions in the system described by the 2D antiferromagnetic Blume-Capel model in the presence of a magnetic field is studied by the Wang and Landau flat-histogram simulation method and by the classical Monte Carlo. Anomalous thermodynamic characteristics in low temperatures indicate different type orderings in finite temperatures. The existence of pure antiferromagnetic phases as well as mixed state is shown by detailed phenomenological analysis of the system. The border lines on the phase diagram between various orderings are determined by the complementary microscopic study of the percolation problem for c(2×2) elementary structures of antiferromagnetic ordered phases. This new approach has also shown a full agreement between the percolation threshold for the cluster of mixed phase and the critical temperature of the ordered system.
NASA Astrophysics Data System (ADS)
Xu, S.; Rezvanian, O.; Peters, K.; Zikry, M. A.
2013-04-01
A new modeling method has been proposed to investigate how the electrical conductivity of carbon nanotube (CNT) reinforced polymer composites are affected by tunneling distance, volume fraction, and tube aspect ratios. A search algorithm and an electrical junction identification method was developed with a percolation approach to determine conductive paths for three-dimensional (3D) carbon nanotube arrangements and to account for electron tunneling effects. The predicted results are used to understand the limitations of percolation theory and experimental measurements and observations, and why percolation theory breaks down for specific CNT arrangements.
On chemical distances and shape theorems in percolation models with long-range correlations
NASA Astrophysics Data System (ADS)
Drewitz, Alexander; Ráth, Balázs; Sapozhnikov, Artëm
2014-08-01
In this paper, we provide general conditions on a one parameter family of random infinite subsets of {{Z}}^d to contain a unique infinite connected component for which the chemical distances are comparable to the Euclidean distance. In addition, we show that these conditions also imply a shape theorem for the corresponding infinite connected component. By verifying these conditions for specific models, we obtain novel results about the structure of the infinite connected component of the vacant set of random interlacements and the level sets of the Gaussian free field. As a byproduct, we obtain alternative proofs to the corresponding results for random interlacements in the work of Černý and Popov ["On the internal distance in the interlacement set," Electron. J. Probab. 17(29), 1-25 (2012)], and while our main interest is in percolation models with long-range correlations, we also recover results in the spirit of the work of Antal and Pisztora ["On the chemical distance for supercritical Bernoulli percolation," Ann Probab. 24(2), 1036-1048 (1996)] for Bernoulli percolation. Finally, as a corollary, we derive new results about the (chemical) diameter of the largest connected component in the complement of the trace of the random walk on the torus.
On chemical distances and shape theorems in percolation models with long-range correlations
Drewitz, Alexander; Ráth, Balázs; Sapozhnikov, Artëm
2014-08-01
In this paper, we provide general conditions on a one parameter family of random infinite subsets of Z{sup d} to contain a unique infinite connected component for which the chemical distances are comparable to the Euclidean distance. In addition, we show that these conditions also imply a shape theorem for the corresponding infinite connected component. By verifying these conditions for specific models, we obtain novel results about the structure of the infinite connected component of the vacant set of random interlacements and the level sets of the Gaussian free field. As a byproduct, we obtain alternative proofs to the corresponding results for random interlacements in the work of Cerný and Popov [“On the internal distance in the interlacement set,” Electron. J. Probab. 17(29), 1–25 (2012)], and while our main interest is in percolation models with long-range correlations, we also recover results in the spirit of the work of Antal and Pisztora [“On the chemical distance for supercritical Bernoulli percolation,” Ann Probab. 24(2), 1036–1048 (1996)] for Bernoulli percolation. Finally, as a corollary, we derive new results about the (chemical) diameter of the largest connected component in the complement of the trace of the random walk on the torus.
A percolation cluster model of the temperature dependent dielectric properties of hydrated proteins
NASA Astrophysics Data System (ADS)
Suherman, Phe Man; Smith, Geoff
2003-02-01
This study investigates the temperature dependence of the low frequency dielectric properties (0.1 Hz-1 MHz) of hydrated globular proteins (namely, ovalbumin, lysozyme and pepsin). The study aims to reveal the mechanisms of water-protein interaction from the dielectric response of these model proteins. Two principle dielectric responses were observed for each hydrated protein, namely, an anomalous low frequency dispersion and a dielectric loss peak at higher frequency (called the varepsilon3 dispersion). The low frequency response conformed to a fractional power low of frequency, while the higher frequency response conformed to a Davidson-Cole model. The strength of both processes reached a maximum at a certain temperature within the experimental temperature range. This temperature is referred to as the percolation threshold (PT) and is thought to be associated with the percolation of protons between hydrogen-bonded water molecules. The relaxation times of the varepsilon3 dispersion conformed to Arrhenius behaviour at temperatures below the PT, from which an activation energy (DeltaH) could be calculated. This activation energy is thought to be a measure of the concentration of available charged sites through which proton transport is facilitated. The structural fractal dimension in the hydrated protein system was also calculated, and enabled the approximation of the pathway for charge percolation in the protein matrix.
NASA Astrophysics Data System (ADS)
Szczygieł, Bartłomiej; Dudyński, Marek; Kwiatkowski, Kamil; Lewenstein, Maciej; Lapeyre, Gerald John; Wehr, Jan
2016-02-01
We introduce a class of discrete-continuous percolation models and an efficient Monte Carlo algorithm for computing their properties. The class is general enough to include well-known discrete and continuous models as special cases. We focus on a particular example of such a model, a nanotube model of disintegration of activated carbon. We calculate its exact critical threshold in two dimensions and obtain a Monte Carlo estimate in three dimensions. Furthermore, we use this example to analyze and characterize the efficiency of our algorithm, by computing critical exponents and properties, finding that it compares favorably to well-known algorithms for simpler systems.
Modelling of percolation rate of stormwater from underground infiltration systems.
Burszta-Adamiak, Ewa; Lomotowski, Janusz
2013-01-01
Underground or surface stormwater storage tank systems that enable the infiltration of water into the ground are basic elements used in Sustainable Urban Drainage Systems (SUDS). So far, the design methods for such facilities have not taken into account the phenomenon of ground clogging during stormwater infiltration. Top layer sealing of the filter bed influences the infiltration rate of water into the ground. This study presents an original mathematical model describing changes in the infiltration rate variability in the phases of filling and emptying the storage and infiltration tank systems, which enables the determination of the degree of top ground layer clogging. The input data for modelling were obtained from studies conducted on experimental sites on objects constructed on a semi-technological scale. The experiment conducted has proven that the application of the model developed for the phase of water infiltration enables us to estimate the degree of module clogging. However, this method is more suitable for reservoirs embedded in more permeable soils than for those located in cohesive soils. PMID:24292460
Vaccaro, J.J.
2007-01-01
A daily water-budget model for estimating ground-water recharge, the Deep Percolation Model, was modularized for inclusion into the U.S. Geological Survey's Modular Modeling System. The model was modularized in order to facilitate estimation of ground-water recharge under a large range in climatic, landscape, and land-use and land-cover conditions. The model can be applied to areas as large as regions or as small as a field plot. An overview of the Modular Modeling System and the Deep Percolation Model is presented. Data requirements, parameters, and variables for the model are described. The modules that compose the Deep Percolation Model are documented.
Research Trends in Non Point Source during 1975-2010
NASA Astrophysics Data System (ADS)
Yanhua, Zhuang; Thuminh, Nguyen; Beibei, Niu; ei, Shao; Song, Hong
According to the samples of 2924 articles about non point source of SCI and SSCI databases from 1975 to 2010, this study analysed the articles in the growth trend of article outputs, subject categories and journals, international collaborations, geographic distribution and scientific research issues by using bibliometric analysis. The results showed that non point source research steadily increased over the past 35 years and the annual number of articles published in 2010 was 79 times of that in 1975. Non point source was involved into 67 kinds of subjects and appeared in 451 journals. The main study area was concentrated in North America and Europe, following by East Asia. There were 79 countries/territories participated in non point source research, and USA was the largest contributor in non point source research and had a central position in collaboration networks. A keyword analysis indicated that water quality, non point pollutions, and watershed were the hottest issues of non point source research; "GIS, "watershed management", "modeling", "simulation", "monitoring", and "remote sensing" were the most popular research methods; and "agriculture", "land use", "runoff", and "pollution" were the leading causes of non point pollution.
Patterns in the English language: phonological networks, percolation and assembly models
NASA Astrophysics Data System (ADS)
Stella, Massimo; Brede, Markus
2015-05-01
In this paper we provide a quantitative framework for the study of phonological networks (PNs) for the English language by carrying out principled comparisons to null models, either based on site percolation, randomization techniques, or network growth models. In contrast to previous work, we mainly focus on null models that reproduce lower order characteristics of the empirical data. We find that artificial networks matching connectivity properties of the English PN are exceedingly rare: this leads to the hypothesis that the word repertoire might have been assembled over time by preferentially introducing new words which are small modifications of old words. Our null models are able to explain the ‘power-law-like’ part of the degree distributions and generally retrieve qualitative features of the PN such as high clustering, high assortativity coefficient and small-world characteristics. However, the detailed comparison to expectations from null models also points out significant differences, suggesting the presence of additional constraints in word assembly. Key constraints we identify are the avoidance of large degrees, the avoidance of triadic closure and the avoidance of large non-percolating clusters.
Unstable supercritical discontinuous percolation transitions
NASA Astrophysics Data System (ADS)
Chen, Wei; Cheng, Xueqi; Zheng, Zhiming; Chung, Ning Ning; D'Souza, Raissa M.; Nagler, Jan
2013-10-01
The location and nature of the percolation transition in random networks is a subject of intense interest. Recently, a series of graph evolution processes have been introduced that lead to discontinuous percolation transitions where the addition of a single edge causes the size of the largest component to exhibit a significant macroscopic jump in the thermodynamic limit. These processes can have additional exotic behaviors, such as displaying a “Devil's staircase” of discrete jumps in the supercritical regime. Here we investigate whether the location of the largest jump coincides with the percolation threshold for a range of processes, such as Erdős-Rényipercolation, percolation via edge competition and via growth by overtaking. We find that the largest jump asymptotically occurs at the percolation transition for Erdős-Rényiand other processes exhibiting global continuity, including models exhibiting an “explosive” transition. However, for percolation processes exhibiting genuine discontinuities, the behavior is substantially richer. In percolation models where the order parameter exhibits a staircase, the largest discontinuity generically does not coincide with the percolation transition. For the generalized Bohman-Frieze-Wormald model, it depends on the model parameter. Distinct parameter regimes well in the supercritical regime feature unstable discontinuous transitions—a novel and unexpected phenomenon in percolation. We thus demonstrate that seemingly and genuinely discontinuous percolation transitions can involve a rich behavior in supercriticality, a regime that has been largely ignored in percolation.
Documentation of a deep percolation model for estimating ground-water recharge
Bauer, H.H.; Vaccaro, J.J.
1987-01-01
A deep percolation model, which operates on a daily basis, was developed to estimate long-term average groundwater recharge from precipitation. It has been designed primarily to simulate recharge in large areas with variable weather, soils, and land uses, but it can also be used at any scale. The physical and mathematical concepts of the deep percolation model, its subroutines and data requirements, and input data sequence and formats are documented. The physical processes simulated are soil moisture accumulation, evaporation from bare soil, plant transpiration, surface water runoff, snow accumulation and melt, and accumulation and evaporation of intercepted precipitation. The minimum data sets for the operation of the model are daily values of precipitation and maximum and minimum air temperature, soil thickness and available water capacity, soil texture, and land use. Long-term average annual precipitation, actual daily stream discharge, monthly estimates of base flow, Soil Conservation Service surface runoff curve numbers, land surface altitude-slope-aspect, and temperature lapse rates are optional. The program is written in the FORTRAN 77 language with no enhancements and should run on most computer systems without modifications. Documentation has been prepared so that program modifications may be made for inclusions of additional physical processes or deletion of ones not considered important. (Author 's abstract)
Modeling gravity-driven fingering in rough-walled fractures using modified percolation theory
Glass, R.J.
1992-12-31
Pore scale invasion percolation theory is modified for imbibition of.wetting fluids into fractures. The effects of gravity, local aperture field geometry, and local in-plane air/water interfacial curvatureare included in the calculation of aperture filling potential which controls wetted structure growth within the fracture. The inclusion of gravity yields fingers oriented in the direction of the gravitational gradient. These fingers widen and tend to meander and branch more as the gravitational gradient decreases. In-plane interfacial curvature also greatly affects the wetted structure in both horizontal and nonhorizontal fractures causing the formation of macroscopic wetting fronts. The modified percolation model is used to simulate imbibition into an analogue rough-walled fracture where both fingering and horizontal imbibition experiments were previously conducted. Comparison of numerical and experimental results showed reasonably good agreement. This process oriented physical and numerical modeling is-a necessary step toward including gravity-driven fingering in models of flow and transport through unsaturated, fractured rock.
Ha, Dong -Gwang; Kim, Jang -Joo; Baldo, Marc A.
2016-04-29
Mixed host compositions that combine charge transport materials with luminescent dyes offer superior control over exciton formation and charge transport in organic light emitting devices (OLEDs). Two approaches are typically used to optimize the fraction of charge transport materials in a mixed host composition: either an empirical percolative model, or a hopping transport model. We show that these two commonly-employed models are linked by an analytic expression which relates the localization length to the percolation threshold and critical exponent. The relation is confirmed both numerically and experimentally through measurements of the relative conductivity of Tris(4-carbazoyl-9-ylphenyl) amine (TCTA) :1,3-bis(3,5-dipyrid-3-yl-phenyl) benzene (BmPyPb)more » mixtures with different concentrations, where the TCTA plays a role as hole conductor and the BmPyPb as hole insulator. Furthermore, the analytic relation may allow the rational design of mixed layers of small molecules for high-performance OLEDs.« less
Oxide thinning percolation statistical model for soft breakdown in ultrathin gate oxides
NASA Astrophysics Data System (ADS)
Chen, Ming-Jer; Kang, Ting-Kuo; Liu, Chuan-Hsi; Chang, Yih J.; Fu, Kuan-Yu
2000-07-01
An existing cell-based percolation model with parameter correlation can find its potential applications in assessing soft-breakdown (BD) statistics as long as the oxide thinning due to the localized physical damage near the SiO2/Si interface is accounted for. The resulting model is expressed explicitly with the critical trap number per cell nBD and the remaining oxide thickness tox' both as parameters. Reproduction of time-to-bimodal (soft- and hard-) breakdown statistical data from 3.3-nm-thick gate-oxide samples yields nBD of 3 and 4 for soft and hard breakdown, respectively. The extracted tox' of 1.0 nm for soft breakdown, plus the transition layer thickness of 0.5 nm in the model, is fairly comparable with literature values from current-voltage fitting. The dimension and area of the localized physically damaged region or percolation path (cell) are quantified as well. Based on the work, the origins of soft and hard breakdown are clarified in the following: (i) soft breakdown behaves intrinsically as hard breakdown, that is, they share the same defect (neutral trap) generation process and follow Poisson random statistics; (ii) both are independent events corresponding to different tox' requirements; and (iii) hard breakdown takes place in a certain path located differently from that for the first soft breakdown.
Percolation Model of Sensory Transmission and Loss of Consciousness Under General Anesthesia
NASA Astrophysics Data System (ADS)
Zhou, David W.; Mowrey, David D.; Tang, Pei; Xu, Yan
2015-09-01
Neurons communicate with each other dynamically; how such communications lead to consciousness remains unclear. Here, we present a theoretical model to understand the dynamic nature of sensory activity and information integration in a hierarchical network, in which edges are stochastically defined by a single parameter p representing the percolation probability of information transmission. We validate the model by comparing the transmitted and original signal distributions, and we show that a basic version of this model can reproduce key spectral features clinically observed in electroencephalographic recordings of transitions from conscious to unconscious brain activities during general anesthesia. As p decreases, a steep divergence of the transmitted signal from the original was observed, along with a loss of signal synchrony and a sharp increase in information entropy in a critical manner; this resembles the precipitous loss of consciousness during anesthesia. The model offers mechanistic insights into the emergence of information integration from a stochastic process, laying the foundation for understanding the origin of cognition.
Percolation Model of Sensory Transmission and Loss of Consciousness under General Anesthesia
Zhou, David W.; Mowrey, David D.; Tang, Pei; Xu, Yan
2015-01-01
Neurons communicate with each other dynamically. How such communications lead to consciousness remains unclear. Here, we present a theoretical model to understand the dynamic nature of sensory activity and information integration in a hierarchical network, in which edges are stochastically defined by a single parameter, p, representing percolation probability of information transmission. We validate the model by comparing the transmitted and original signal distributions and show that a basic version of this model can reproduce key spectral features clinically observed in electroencephalographic recordings of transitions from conscious to unconscious brain activities during general anesthesia. As p decreases, a steep divergence of the transmitted signal from the original was observed, along with a loss of signal synchrony and a sharp increase in information entropy in a critical manner, resembling the precipitous loss of consciousness during anesthesia. The model offers mechanistic insights into the emergence of information integration from a stochastic process, laying the foundation to understand the origin of cognition. PMID:26382705
Percolation on Sparse Networks
NASA Astrophysics Data System (ADS)
Karrer, Brian; Newman, M. E. J.; Zdeborová, Lenka
2014-11-01
We study percolation on networks, which is used as a model of the resilience of networked systems such as the Internet to attack or failure and as a simple model of the spread of disease over human contact networks. We reformulate percolation as a message passing process and demonstrate how the resulting equations can be used to calculate, among other things, the size of the percolating cluster and the average cluster size. The calculations are exact for sparse networks when the number of short loops in the network is small, but even on networks with many short loops we find them to be highly accurate when compared with direct numerical simulations. By considering the fixed points of the message passing process, we also show that the percolation threshold on a network with few loops is given by the inverse of the leading eigenvalue of the so-called nonbacktracking matrix.
NASA Astrophysics Data System (ADS)
Pohlert, T.
2007-12-01
The aim of this paper is to present recent developments of an integrated water- and N-balance model for the assessment of land use changes on water and N-fluxes for meso-scale river catchments. The semi-distributed water-balance model SWAT was coupled with algorithms of the bio-geochemical model DNDC as well as the model CropSyst. The new model that is further denoted as SWAT-N was tested with leaching data from a long- term lysimeter experiment as well as results from a 5-years sampling campaign that was conducted at the outlet of the meso-scale catchment of the River Dill (Germany). The model efficiency for N-load as well as the spatial representation of N-load along the river channel that was tested with results taken from longitudinal profiles show that the accuracy of the model has improved due to the integration of the aforementioned process-oriented models. After model development and model testing, SWAT-N was then used for the assessment of the EU agricultural policy (CAP reform) on land use change and consequent changes on N-fluxes within the Dill Catchment. giessen.de/geb/volltexte/2007/4531/
Self-organization with equilibration: a model for the intermediate phase in rigidity percolation.
Chubynsky, M V; Brière, M-A; Mousseau, Normand
2006-07-01
Recent experimental results for covalent glasses suggest the existence of an intermediate phase attributed to the self-organization of the glass network resulting from the tendency to minimize its internal stress. However, the exact nature of this experimentally measured phase remains unclear. We modified a previously proposed model of self-organization by generating a uniform sampling of stress-free networks. In our model, studied on a diluted triangular lattice, an unusual intermediate phase appears, in which both rigid and floppy networks have a chance to occur, a result also observed in a related model on a Bethe lattice by Barré et al[Phys. Rev. Lett. 94, 208701 (2005)]. Our results for the bond-configurational entropy of self-organized networks, which turns out to be only about 2% lower than that of random networks, suggest that a self-organized intermediate phase could be common in systems near the rigidity percolation threshold. PMID:16907160
NASA Astrophysics Data System (ADS)
Lu, Nianduan; Li, Ling; Liu, Ming
2015-05-01
Recent measurements conducted over a large range of temperature and carrier density have found that the Seebeck coefficient exhibits an approaching disorder-free transport feature in high-mobility conjugated polymers [D. Venkateshvaran et al., Nature 515, 384 (2014), 10.1038/nature13854]. It is difficult for the current Seebeck coefficient model to interpret the feature of the charge transport approaching disorder-free transport. We present a general analytical model to describe the Seebeck effect for organic semiconductors based on the hopping transport and percolation theory. The proposed model can well explain the Seebeck feature of the polymers with approaching disorder-free transport, as well as that of the organic semiconductors with the general disorder. The simulated results imply that the Seebeck coefficient in the organic semiconductors would happen to transfer from temperature dependence to temperature independence with the decrease of the energetic disorder.
NASA Astrophysics Data System (ADS)
Whitehead, P. G.; Heathwaite, A. L.; Flynn, N. J.; Wade, A. J.; Quinn, P. F.
2007-01-01
A semi-distributed model, INCA, has been developed to determine the fate and distribution of nutrients in terrestrial and aquatic systems. The model simulates nitrogen and phosphorus processes in soils, groundwaters and river systems and can be applied in a semi-distributed manner at a range of scales. In this study, the model has been applied at field to sub-catchment to whole catchment scale to evaluate the behaviour of biosolid-derived losses of P in agricultural systems. It is shown that process-based models such as INCA, applied at a wide range of scales, reproduce field and catchment behaviour satisfactorily. The INCA model can also be used to generate generic information for risk assessment. By adjusting three key variables: biosolid application rates, the hydrological connectivity of the catchment and the initial P-status of the soils within the model, a matrix of P loss rates can be generated to evaluate the behaviour of the model and, hence, of the catchment system. The results, which indicate the sensitivity of the catchment to flow paths, to application rates and to initial soil conditions, have been incorporated into a Nutrient Export Risk Matrix (NERM).
Fraga, I; Charters, F J; O'Sullivan, A D; Cochrane, T A
2016-02-01
Stormwater runoff in urban catchments contains heavy metals (zinc, copper, lead) and suspended solids (TSS) which can substantially degrade urban waterways. To identify these pollutant sources and quantify their loads the MEDUSA (Modelled Estimates of Discharges for Urban Stormwater Assessments) modelling framework was developed. The model quantifies pollutant build-up and wash-off from individual impervious roof, road and car park surfaces for individual rain events, incorporating differences in pollutant dynamics between surface types and rainfall characteristics. This requires delineating all impervious surfaces and their material types, the drainage network, rainfall characteristics and coefficients for the pollutant dynamics equations. An example application of the model to a small urban catchment demonstrates how the model can be used to identify the magnitude of pollutant loads, their spatial origin and the response of the catchment to changes in specific rainfall characteristics. A sensitivity analysis then identifies the key parameters influencing each pollutant load within the stormwater given the catchment characteristics, which allows development of a targeted calibration process that will enhance the certainty of the model outputs, while minimizing the data collection required for effective calibration. A detailed explanation of the modelling framework and pre-calibration sensitivity analysis is presented. PMID:26613353
In the EPA document Predicting Attenuation of Viruses During Percolation in Soils 1. Probabilistic Model the conceptual, theoretical, and mathematical foundations for a predictive screening model were presented. In this current volume we present a User's Guide for the computer mo...
Variational Formulas and Cocycle solutions for Directed Polymer and Percolation Models
NASA Astrophysics Data System (ADS)
Georgiou, Nicos; Rassoul-Agha, Firas; Seppäläinen, Timo
2016-03-01
We discuss variational formulas for the law of large numbers limits of certain models of motion in a random medium: namely, the limiting time constant for last-passage percolation and the limiting free energy for directed polymers. The results are valid for models in arbitrary dimension, steps of the admissible paths can be general, the environment process is ergodic under spatial translations, and the potential accumulated along a path can depend on the environment and the next step of the path. The variational formulas come in two types: one minimizes over gradient-like cocycles, and another one maximizes over invariant measures on the space of environments and paths. Minimizing cocycles can be obtained from Busemann functions when these can be proved to exist. The results are illustrated through 1+1 dimensional exactly solvable examples, periodic examples, and polymers in weak disorder.
Mean-field behavior of the negative-weight percolation model on random regular graphs.
Melchert, Oliver; Hartmann, Alexander K; Mézard, Marc
2011-10-01
We investigate both analytically and numerically the ensemble of minimum-weight loops in the negative-weight percolation model on random graphs with fixed connectivity and bimodal weight distribution. This allows us to study the mean-field behavior of this model. The analytical study is based on a conjectured equivalence with the problem of self-avoiding walks in a random medium. The numerical study is based on a mapping to a standard minimum-weight matching problem for which fast algorithms exist. Both approaches yield results that are in agreement on the location of the phase transition, on the value of critical exponents, and on the absence of any sizable indications of a glass phase. By these results, the previously conjectured upper critical dimension of d(u)=6 is confirmed. PMID:22181086
Point source detection in infrared astronomical surveys
NASA Technical Reports Server (NTRS)
Pelzmann, R. F., Jr.
1977-01-01
Data processing techniques useful for infrared astronomy data analysis systems are reported. This investigation is restricted to consideration of data from space-based telescope systems operating as survey instruments. In this report the theoretical background for specific point-source detection schemes is completed, and the development of specific algorithms and software for the broad range of requirements is begun.
IMPACT OF POINT SOURCE CONTROL STRATEGIES ON NO2 LEVELS
The report gives final results of a study of the effect of two point source NOx control strategies in the Chicago Air Quality Control Region (AQCR): combustion modification and flue gas treatment. The study involved the dispersion modeling of essentially all point and area source...
NASA Astrophysics Data System (ADS)
Jiang, Yefang; Somers, George
2009-05-01
Intensification of potato farming has contaminated groundwater with nitrate in many cases in Prince Edward Island, Canada, which raises concerns for drinking water quality and associated ecosystem protection. Numerical models were developed to simulate nitrate-N transport in groundwater and enhance understanding of the impacts of farming on water quality in the Wilmot River watershed. Nitrate is assumed non-reactive based on δ15N and δ18O in nitrate and geochemical information. The source functions were reconstructed from tile drain measurements, N budget and historical land-use information. The transport model was calibrated to long-term nitrate-N observations in the Wilmot River and verified against nitrate-N measurements in two rivers from watersheds with similar physical conditions. Simulations show groundwater flow is stratified and vertical flux decreases exponentially with depth. While it would take several years to reduce the nitrate-N in the shallow portion of the aquifer, it would take several decades or even longer to restore water quality in the deeper portions of the aquifer. Elevated nitrate-N concentrations in base flow are positively correlated with potato cropping intensity and significant reductions in nitrate-N loading are required if the nitrate level of surface water is to recover to the standard in the Canadian Water Quality Guidelines.
NASA Astrophysics Data System (ADS)
Gao, Nan; Li, Ling; Lu, Nianduan; Xie, Changqing; Liu, Ming; Bässler, Heinz
2016-08-01
The fact that in organic semiconductors the Hubbard energy is usually positive appears to be at variance with a bipolaron model to explain magnetoresistance (MR) in those systems. Employing percolation theory, we demonstrate that a moderately positive U is indeed compatible with the bipolaron concept for MR in unipolar current flow, provided that the system is energetically disordered, and the density of states (DOS) distribution is partially filled, so that the Fermi level overlaps with tail states of the DOS. By exploring a broad parameter space, we show that MR becomes maximal around U =0 and even diminishes at large negative values of U because of spin independent bipolaron dissociation. Trapping effects and reduced dimension enhance MR.
High-precision percolation thresholds and Potts-model critical manifolds from graph polynomials
NASA Astrophysics Data System (ADS)
>Jesper Lykke Jacobsen,
2014-04-01
The critical curves of the q-state Potts model can be determined exactly for regular two-dimensional lattices G that are of the three-terminal type. This comprises the square, triangular, hexagonal and bow-tie lattices. Jacobsen and Scullard have defined a graph polynomial PB(q, v) that gives access to the critical manifold for general lattices. It depends on a finite repeating part of the lattice, called the basis B, and its real roots in the temperature variable v = eK - 1 provide increasingly accurate approximations to the critical manifolds upon increasing the size of B. Using transfer matrix techniques, these authors computed PB(q, v) for large bases (up to 243 edges), obtaining determinations of the ferromagnetic critical point vc > 0 for the (4, 82), kagome, and (3, 122) lattices to a precision (of the order 10-8) slightly superior to that of the best available Monte Carlo simulations. In this paper we describe a more efficient transfer matrix approach to the computation of PB(q, v) that relies on a formulation within the periodic Temperley-Lieb algebra. This makes possible computations for substantially larger bases (up to 882 edges), and the precision on vc is hence taken to the range 10-13. We further show that a large variety of regular lattices can be cast in a form suitable for this approach. This includes all Archimedean lattices, their duals and their medials. For all these lattices we tabulate high-precision estimates of the bond percolation thresholds pc and Potts critical points vc. We also trace and discuss the full Potts critical manifold in the (q, v) plane, paying special attention to the antiferromagnetic region v < 0. Finally, we adapt the technique to site percolation as well, and compute the polynomials PB(p) for certain Archimedean and dual lattices (those having only cubic and quartic vertices), using very large bases (up to 243 vertices). This produces the site percolation thresholds pc to a precision of the order of 10-9.
NASA Astrophysics Data System (ADS)
Xu, Hao; Yang, Hong; Wang, Yan-Rong; Wang, Wen-Wu; Luo, Wei-Chun; Qi, Lu-Wei; Li, Jun-Feng; Zhao, Chao; Chen, Da-Peng; Ye, Tian-Chun
2016-08-01
High-k metal gate stacks are being used to suppress the gate leakage due to tunneling for sub-45 nm technology nodes. The reliability of thin dielectric films becomes a limitation to device manufacturing, especially to the breakdown characteristic. In this work, a breakdown simulator based on a percolation model and the kinetic Monte Carlo method is set up, and the intrinsic relation between time to breakdown and trap generation rate R is studied by TDDB simulation. It is found that all degradation factors, such as trap generation rate time exponent m, Weibull slope β and percolation factor s, each could be expressed as a function of trap density time exponent α. Based on the percolation relation and power law lifetime projection, a temperature related trap generation model is proposed. The validity of this model is confirmed by comparing with experiment results. For other device and material conditions, the percolation relation provides a new way to study the relationship between trap generation and lifetime projection. Project supported by the National High Technology Research and Development Program of China (Grant No. SS2015AA010601), the National Natural Science Foundation of China (Grant Nos. 61176091 and 61306129), and the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of MicroElectronics of Chinese Academy of Sciences.
NASA Astrophysics Data System (ADS)
Wiśniowski, R.; Olchawa, W.; Frączek, D.; Piasecki, R.
2016-02-01
Recently, the effective medium approach (EMA) using 2×2 basic cluster of model lattice sites to predict the conductivity of interacting microemulsion droplets has been presented by Hattori et al. To make a step aside from pure applications, we studied earlier a multi-scale percolation, employing any k× k basic cluster for non-interacting particles. Here, with interactions included, we examine in what way they alter the percolation threshold for any cluster case. We found that at a fixed length scale k, the interaction reduces the range of shifts of the percolation threshold. To determine the critical concentrations, the simplified EMA-model is used. It diminishes the number of local conductivities into two main ones. In the presence of a dominance of the repulsive interaction over the thermal energy, the exact percolation thresholds at two small scales can be revealed from analytical formulas. Furthermore, at large scales, the highest possible value of the estimated threshold can be obtained.
2D numerical modelling of fluid percolation in the subduction zone
NASA Astrophysics Data System (ADS)
Dymkova, D.; Gerya, T.; Podladchikov, Y.
2012-04-01
Subducting slab dehydration and resulting aqueous fluid percolation triggers partial melting in the mantle wedge and is accompanied with the further melt percolation through the porous space to the region above the slab. This problem is a complex coupled chemical, thermal and mechanical process responsible for the magmatic arcs formation and change of the mantle wedge properties. We have created a two-dimensional model of a two-phase flow in a porous media solving a coupled Darcy-Stokes system of equations for two incompressible media for the case of nonlinear visco-plastic rheology of solid matrix. Our system of equation is expanded for the high-porosity limits and stabilized for the case of high porosity contrasts. We use a finite-difference method with fully staggered grid in a combination with marker-in-cell technique for advection of fluid and solid phase. We performed a comparison with a benchmark of a thermal convection in a porous media in a bottom-heated box to verify the interdependency of Rayleigh and Nusselt numbers with earlier obtained ones (Cherkaoui & Wilcock, 1999). We have demonstrated the stability and robustness of the algorithm in case of strongly non-linear visco-plastic rheology of solid including cases with localization of both deformation and porous flow along spontaneously forming shear bands. We have checked our model for the forming of localized porous channels under a simple shear stress (Katz et al, 2006). We have developed a setup of a self-initiating due to gravitational instability subduction. With our coupled fluid-solid flow we have achieved a self-consistent water downward suction by a slab bending predicted by the other models with a simplified fluid kinematical motion implementation (Faccenda et al, 2009). With this setup we have obtained a self-consistent upper crust weakening by a porous fluid pressure which was theoretically assumed in the previously existing subduction models (Gerya & Meilick, 2011; Faccenda et al, 2009
Critical behavior of a tumor growth model: directed percolation with a mean-field flavor.
Lipowski, Adam; Ferreira, António Luis; Wendykier, Jacek
2012-10-01
We examine the critical behavior of a lattice model of tumor growth where supplied nutrients are correlated with the distribution of tumor cells. Our results support the previous report [Ferreira et al., Phys. Rev. E 85, 010901(R) (2012)], which suggested that the critical behavior of the model differs from the expected directed percolation (DP) universality class. Surprisingly, only some of the critical exponents (β, α, ν([perpendicular]), and z) take non-DP values while some others (β', ν(||), and spreading-dynamics exponents Θ, δ, z') remain very close to their DP counterparts. The obtained exponents satisfy the scaling relations β=αν(||), β'=δν(||), and the generalized hyperscaling relation Θ+α+δ=d/z, where the dynamical exponent z is, however, used instead of the spreading exponent z'. Both in d=1 and d=2 versions of our model, the exponent β most likely takes the mean-field value β=1, and we speculate that it might be due to the roulette-wheel selection, which is used to choose the site to supply a nutrient. PMID:23214560
Universal energy spectrum from point sources
NASA Technical Reports Server (NTRS)
Tomozawa, Yukio
1992-01-01
The suggestion is made that the energy spectrum from point sources such as galactic black hole candidates (GBHC) and active galactic nuclei (AGN) is universal on the average, irrespective of the species of the emitted particles, photons, nucleons, or others. The similarity between the observed energy spectra of cosmic rays, gamma-rays, and X-rays is discussed. In other words, the existing data for gamma-rays and X-rays seem to support the prediction. The expected data from the Gamma Ray Observatory are to provide a further test.
Percolation-Continuum Model of Evaporative Drying: Homogeneous or Patchy Saturation?
Wang, H F; Strand, T E; Berryman, J G
2005-02-18
Porous rock on the earth's surface often contains more than one fluid phase, and an important case is partial saturation with air and water. We implemented a pore-scale, percolation model coupled with a continuum model for water vapor diffusion in order to create a simulated tomographic image of water distribution within a rock core during drying. As drying proceeds, the initial, continuous water cluster breaks up into smaller and smaller clusters with an increasing surface-area-to-volume ratio. Drying times are a function of the number and location of boundary surfaces, but the surface-area-to-volume ratio is approximately the same for a given saturation. By applying a Voigt volume average of the elastic properties of water-filled and air-filled cells, and by introducing the ad hoc rule that water-filled pores on the air-water interface of a cluster behave in a drained manner, we find elastic moduli as a function of saturation that mimic laboratory experimental data.
Percolation model for growth rates of aggregates and its application for business firm growth
NASA Astrophysics Data System (ADS)
Fu, Dongfeng; Buldyrev, Sergey V.; Salinger, Michael A.; Stanley, H. Eugene
2006-09-01
Motivated by recent empirical studies of business firm growth, we develop a dynamic percolation model which captures some of the features of the economical system—i.e., merging and splitting of business firms—represented as aggregates on a d -dimensional lattice. We find the steady-state distribution of the aggregate size and explore how this distribution depends on the model parameters. We find that at the critical threshold, the standard deviation of the aggregate growth rates, σ , increases with aggregate size S as σ˜Sβ , where β can be explained in terms of the connectedness length exponent ν and the fractal dimension df , with β=1/(2νdf)≈0.20 for d=2 and 0.125 for d→∞ . The distributions of aggregate growth rates have a sharp peak at the center and pronounced wings extending over many standard deviations, giving the distribution a tent-shape form—the Laplace distribution. The distributions for different aggregate sizes scaled by their standard deviations collapse onto the same curve.
NASA Astrophysics Data System (ADS)
Lebovka, Nikolai I.; Tarasevich, Yuri Yu.; Dubinin, Dmitri O.; Laptev, Valeri V.; Vygornitskii, Nikolai V.
2015-12-01
The jamming and percolation for two generalized models of random sequential adsorption (RSA) of linear k -mers (particles occupying k adjacent sites) on a square lattice are studied by means of Monte Carlo simulation. The classical RSA model assumes the absence of overlapping of the new incoming particle with the previously deposited ones. The first model is a generalized variant of the RSA model for both k -mers and a lattice with defects. Some of the occupying k adjacent sites are considered as insulating and some of the lattice sites are occupied by defects (impurities). For this model even a small concentration of defects can inhibit percolation for relatively long k -mers. The second model is the cooperative sequential adsorption one where, for each new k -mer, only a restricted number of lateral contacts z with previously deposited k -mers is allowed. Deposition occurs in the case when z ≤(1 -d ) zm where zm=2 (k +1 ) is the maximum numbers of the contacts of k -mer, and d is the fraction of forbidden contacts. Percolation is observed only at some interval kmin≤k ≤kmax where the values kmin and kmax depend upon the fraction of forbidden contacts d . The value kmax decreases as d increases. A logarithmic dependence of the type log10(kmax) =a +b d , where a =4.04 ±0.22 ,b =-4.93 ±0.57 , is obtained.
Constantin, Julian Gelman; Schneider, Matthias; Corti, Horacio R
2016-06-01
The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model. It was found that the behavior of the water molar volume in trehalose-water mixtures at low temperatures can be obtained by assuming that the FVPM holds for this mixture. The temperature dependence of the water molar volume in the supercooled region of interest seems to be compatible with the recent hypothesis on the existence of two structure of liquid water, being the high density liquid water the state of water in the sugar solutions. The idealized FVPM describes the measured glass transition temperature of sucrose, glucose, and fructose aqueous solutions, with much better accuracy than both the Gordon-Taylor model based on an empirical kGT constant dependent on the saccharide glass transition temperature and the Couchman-Karasz model using experimental heat capacity changes of the components at the glass transition temperature. Thus, FVPM seems to be an excellent tool to predict the glass transition temperature of other aqueous saccharides and polyols solutions by resorting to volumetric information easily available. PMID:27176640
NASA Astrophysics Data System (ADS)
Srivastava, Brijesh K.
2011-07-01
Possible phase transition of strongly interacting matter from hadron to a Quark-Gluon Plasma (QGP) state have in the past received considerable interest. It has been suggested that this problem might be treated by percolation theory. The Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the QGP produced in central Au-Au collisions at RHIC energies. The bulk thermodynamic quantities - energy density, entropy density and the sound velocity - are obtained in the framework of CSPM. It is shown that the results are in excellent agreement with the recent lattice QCD calculations(LQCD).
Ding, Chengxiang; Fu, Zhe; Guo, Wenan; Wu, F Y
2010-06-01
In the preceding paper, one of us (F. Y. Wu) considered the Potts model and bond and site percolation on two general classes of two-dimensional lattices, the triangular-type and kagome-type lattices, and obtained closed-form expressions for the critical frontier with applications to various lattice models. For the triangular-type lattices Wu's result is exact, and for the kagome-type lattices Wu's expression is under a homogeneity assumption. The purpose of the present paper is twofold: First, an essential step in Wu's analysis is the derivation of lattice-dependent constants A,B,C for various lattice models, a process which can be tedious. We present here a derivation of these constants for subnet networks using a computer algorithm. Second, by means of a finite-size scaling analysis based on numerical transfer matrix calculations, we deduce critical properties and critical thresholds of various models and assess the accuracy of the homogeneity assumption. Specifically, we analyze the q -state Potts model and the bond percolation on the 3-12 and kagome-type subnet lattices (n×n):(n×n) , n≤4 , for which the exact solution is not known. Our numerical determination of critical properties such as conformal anomaly and magnetic correlation length verifies that the universality principle holds. To calibrate the accuracy of the finite-size procedure, we apply the same numerical analysis to models for which the exact critical frontiers are known. The comparison of numerical and exact results shows that our numerical values are correct within errors of our finite-size analysis, which correspond to 7 or 8 significant digits. This in turn infers that the homogeneity assumption determines critical frontiers with an accuracy of 5 decimal places or higher. Finally, we also obtained the exact percolation thresholds for site percolation on kagome-type subnet lattices (1×1):(n×n) for 1≤n≤6 . PMID:20866382
Point source solutions and coupling parameters in cratering mechanics
NASA Technical Reports Server (NTRS)
Holsapple, K. A.; Schmidt, R. M.
1987-01-01
The use of a point source of an impactor energy and momentum to replace the effects of the impactor is examined. The general framework and notation of the impact cratering problems are described; it is determined that the cratering phenomena are governed by Froude, Cauchy, and Reynolds numbers. The coupling parameter concept is defined mathematically as the measure that governs limit point source solutions. Examples of cases where coupling parameters are used are presented. The relationships of the coupling parameter concept with steady flow and the Z-model of cratering of Maxwell (1973, 1977) are studied. Crater size, ejecta distributions, growth histories, time of formation, melt volume, and shock decay for various scale factors for impact cratering mechanics are calculated, and the applicability of the coupling parameter to the study of cratering mechanics is revealed.
Weak percolation on multiplex networks
NASA Astrophysics Data System (ADS)
Baxter, Gareth J.; Dorogovtsev, Sergey N.; Mendes, José F. F.; Cellai, Davide
2014-04-01
Bootstrap percolation is a simple but nontrivial model. It has applications in many areas of science and has been explored on random networks for several decades. In single-layer (simplex) networks, it has been recently observed that bootstrap percolation, which is defined as an incremental process, can be seen as the opposite of pruning percolation, where nodes are removed according to a connectivity rule. Here we propose models of both bootstrap and pruning percolation for multiplex networks. We collectively refer to these two models with the concept of "weak" percolation, to distinguish them from the somewhat classical concept of ordinary ("strong") percolation. While the two models coincide in simplex networks, we show that they decouple when considering multiplexes, giving rise to a wealth of critical phenomena. Our bootstrap model constitutes the simplest example of a contagion process on a multiplex network and has potential applications in critical infrastructure recovery and information security. Moreover, we show that our pruning percolation model may provide a way to diagnose missing layers in a multiplex network. Finally, our analytical approach allows us to calculate critical behavior and characterize critical clusters.
Weak percolation on multiplex networks.
Baxter, Gareth J; Dorogovtsev, Sergey N; Mendes, José F F; Cellai, Davide
2014-04-01
Bootstrap percolation is a simple but nontrivial model. It has applications in many areas of science and has been explored on random networks for several decades. In single-layer (simplex) networks, it has been recently observed that bootstrap percolation, which is defined as an incremental process, can be seen as the opposite of pruning percolation, where nodes are removed according to a connectivity rule. Here we propose models of both bootstrap and pruning percolation for multiplex networks. We collectively refer to these two models with the concept of "weak" percolation, to distinguish them from the somewhat classical concept of ordinary ("strong") percolation. While the two models coincide in simplex networks, we show that they decouple when considering multiplexes, giving rise to a wealth of critical phenomena. Our bootstrap model constitutes the simplest example of a contagion process on a multiplex network and has potential applications in critical infrastructure recovery and information security. Moreover, we show that our pruning percolation model may provide a way to diagnose missing layers in a multiplex network. Finally, our analytical approach allows us to calculate critical behavior and characterize critical clusters. PMID:24827287
Surface growth on percolation networks by a conserved-noise restricted solid-on-solid growth model
NASA Astrophysics Data System (ADS)
Lee, Sang Bub
2016-02-01
Surface growth by the conserved-noise restricted solid-on-solid model is investigated on diluted lattices, i.e., on percolation networks that are embedded in two spatial dimensions. The growth exponent β and the roughness exponent α are defined, respectively, by the mean-square surface width via W2(t ) ˜t2 β and the mean-square saturated width via Wsat2(L ) ˜L2 α , where L is the system size. These are measured on both an infinite network and a backbone network and the results are compared with power-counting predictions obtained using the fractional Langevin equation. While the Monte Carlo results on deterministic fractal substrates show excellent agreement with the predictions [D. H. Kim and J. M. Kim, Phys. Rev. E 84, 011105 (2011), 10.1103/PhysRevE.84.011105], the results on critical percolation networks deviate by 8%-12% from these predictions.
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Cheng, Ping
2016-03-01
Percolation theory is used to model intrinsic and relative permeabilities as well as tortuosity in anisotropic carbon paper gas diffusion layers (GDL) and compared with existing results from lattice-Boltzmann (LB) simulations and experimental measurements. Although single- and two-phase characteristics of the carbon paper GDL are mainly affected by medium geometrical and topological properties, e.g., pore-size distribution, connectivity, and pore geometry, analyzing capillary pressure curves implies that the pore-size distribution of the carbon paper GDL is very narrow. This suggests that its effect on tortuosity and wetting- and nonwetting-phase relative permeabilities is trivial. However, integrated effects of pore geometry, surface area, connectivity, and tortuosity on intrinsic permeability might be substantial. Universal power laws from percolation theory predict the tortuosity-porosity and relative permeability-saturation curves accurately, indicating both characteristics not affected by the pore-size distribution. The permeability-porosity relationship, however, conforms to nonuniversality.
Surface growth on percolation networks by a conserved-noise restricted solid-on-solid growth model.
Lee, Sang Bub
2016-02-01
Surface growth by the conserved-noise restricted solid-on-solid model is investigated on diluted lattices, i.e., on percolation networks that are embedded in two spatial dimensions. The growth exponent β and the roughness exponent α are defined, respectively, by the mean-square surface width via W(2)(t)∼t(2β) and the mean-square saturated width via W(sat)(2)(L)∼L(2α), where L is the system size. These are measured on both an infinite network and a backbone network and the results are compared with power-counting predictions obtained using the fractional Langevin equation. While the Monte Carlo results on deterministic fractal substrates show excellent agreement with the predictions [D. H. Kim and J. M. Kim, Phys. Rev. E 84, 011105 (2011)], the results on critical percolation networks deviate by 8%-12% from these predictions. PMID:26986299
Percolation testing and hydraulic conductivity of soils for percolation areas.
Mulqueen, J; Rodgers, M
2001-11-01
The results of specific percolation tests are expressed in terms of field saturated hydraulic conductivity (Kfs) of the soil. The specific tests comprise the Irish SR 6 and the UK BS 6297 standard tests and the inversed auger hole and square hole tests employed for the design of land drainage. Percolation times from these tests are converted to Kfs values using unit gradient theory and the Elrick and Reynolds (Soil Sci. 142(5) (1986) 308) model which takes into account gravitational, pressure head and matric potential gradients. Kfs is then expressed as the inverse of the percolation rate times a constant, in this way the percolation rate can be directly related to Kfs of the soil. A plot of Kfs against percolation rate for the Irish SR 6 and the UK BS 6297 standard tests is asymptotic at Kfs values less than 0.2 m/d and greater than 0.8 m/d. This behaviour creates difficulty in setting limits for percolation rates in standards. Curves are provided which enable Kfs values to be read off from percolation tests without the restrictions of head range currently enforced, for example in the Irish SR 6 and BS 6297 standards. Experimental measurements of percolation rates and Kfs were carried out on two sands in the laboratory and in the field on two soils. Kfs of these four materials was also measured using a tension infiltrometer and the Guelph permeameter. The saturated hydraulic conductivities (Ks) of the sands were also estimated in a falling head laboratory apparatus and by the Hazen formula. There was good agreement between the different tests for Kfs on each material. Because percolation time continued to increase significantly in consecutive tests in the same test hole while Kfs became constant, the latter is a better measure of the suitability of soils for percolation. PMID:12230173
Is a wind turbine a point source? (L).
Makarewicz, Rufin
2011-02-01
Measurements show that practically all noise of wind turbine noise is produced by turbine blades, sometimes a few tens of meters long, despite that the model of a point source located at the hub height is commonly used. The plane of rotating blades is the critical location of the receiver because the distances to the blades are the shortest. It is shown that such location requires certain condition to be met. The model is valid far away from the wind turbine as well. PMID:21361413
NASA Astrophysics Data System (ADS)
Boadh, Rahul; Satyanarayana A. N., V.; Ramakrishna T. V. B. P., S.; Madala, Srikanth
2015-04-01
The deterioration of air quality may be attributed to the rapid industrialization, consequent urbanization and increased growth of vehicular traffic. In urban areas, the day to day increase in vehicular traffic has provided the impetus for comprehensive monitoring/modeling of air quality. In the present study, vehicular traffic as area sources and power plant as point source, the two major sources of oxides of nitrogen (NOX), was has considered. Gaussian plume air dispersion model, AERMOD is used for assessment of NOX dispersion over Nagpur city, Maharashtra. The processes within the planetary boundary layer (PBL) play an important role in the dispersion of air pollutants. AERMOD requires surface and upper air meteorological observations and various PBL parameters with good temporal resolution in the stand alone mode and mostly the data on PBL parameters is not available routinely over India. In the present study, an attempt has been made to simulate the necessary boundary layer parameters from WRF-ARW model and then offline coupled with AERMOD dispersion model. High resolution simulations with triple nested domain (horizontal resolution of 27, 9 and 3 km; 27 vertical levels) are carried out with WRF-ARW model. The surface and upper air meteorological data along with the computed PBL parameters of winter and pre-monsoon seasons representing January and April respectively in the year 2009 are considered for dispersion of the NOX over Nagpur. Experiments are conducted with two best PBL parameterization schemes over study region, non-local Yonsei University (YSU) and local Mellor-Yamada-Janjic (MYJ) schemes. AERMOD with 1 km resolution has been used for predicting the concentrations of NOX over Nagpur city. NOX observations from six monitoring stations of Central Pollution Control Board are used for validation of model predicted concentrations. The NOX concentrations are found to have over-predicted in both seasons. Close examination of the computed statistical errors
Conductivity of continuum percolating systems
NASA Astrophysics Data System (ADS)
Stenull, Olaf; Janssen, Hans-Karl
2001-11-01
We study the conductivity of a class of disordered continuum systems represented by the Swiss-cheese model, where the conducting medium is the space between randomly placed spherical holes, near the percolation threshold. This model can be mapped onto a bond percolation model where the conductance σ of randomly occupied bonds is drawn from a probability distribution of the form σ-a. Employing the methods of renormalized field theory we show to arbitrary order in ɛ expansion that the critical conductivity exponent of the Swiss-cheese model is given by tSC(a)=(d-2)ν+max[φ,(1-a)-1], where d is the spatial dimension and ν and φ denote the critical exponents for the percolation correlation length and resistance, respectively. Our result confirms a conjecture that is based on the ``nodes, links, and blobs'' picture of percolation clusters.
Signature of Thermal Rigidity Percolation
NASA Astrophysics Data System (ADS)
Huerta, Adrián
2013-12-01
To explore the role that temperature and percolation of rigidity play in determining the macroscopic properties, we propose a model that adds translational degrees of freedom to the spins of the well known Ising hamiltonian. In particular, the Ising model illustrate the longstanding idea that the growth of correlations on approach to a critical point could be describable in terms of the percolation of some sort of "physical cluster". For certain parameters of this model we observe two well defined peaks of CV, that suggest the existence of two kinds of "physical percolation", namely connectivity and rigidity percolation. Thermal fluctuations give rise to two different kinds of elementary excitations, i.e. droplets and configuron, as suggested by Angell in the framework of a bond lattice model approach. The later is reflected in the fluctuations of redundant constraints that gives stability to the structure and correlate with the order parameter.
NASA Astrophysics Data System (ADS)
Jha, Anjani K.
Particulate materials are routinely handled in large quantities by industries such as, agriculture, electronic, ceramic, chemical, cosmetic, fertilizer, food, nutraceutical, pharmaceutical, power, and powder metallurgy. These industries encounter segregation due to the difference in physical and mechanical properties of particulates. The general goal of this research was to study percolation segregation in multi-size and multi-component particulate mixtures, especially measurement, sampling, and modeling. A second generation primary segregation shear cell (PSSC-II), an industrial vibrator, a true cubical triaxial tester, and two samplers (triers) were used as primary test apparatuses for quantifying segregation and flowability; furthermore, to understand and propose strategies to mitigate segregation in particulates. Toward this end, percolation segregation in binary, ternary, and quaternary size mixtures for two particulate types: urea (spherical) and potash (angular) were studied. Three coarse size ranges 3,350-4,000 mum (mean size = 3,675 mum), 2,800-3,350 mum (3,075 mum), and 2,360-2,800 mum (2,580 mum) and three fines size ranges 2,000-2,360 mum (2,180 mum), 1,700-2,000 mum (1,850 mum), and 1,400-1,700 mum (1,550 mum) for angular-shaped and spherical-shaped were selected for tests. Since the fines size 1,550 mum of urea was not available in sufficient quantity; therefore, it was not included in tests. Percolation segregation in fertilizer bags was tested also at two vibration frequencies of 5 Hz and 7Hz. The segregation and flowability of binary mixtures of urea under three equilibrium relative humidities (40%, 50%, and 60%) were also tested. Furthermore, solid fertilizer sampling was performed to compare samples obtained from triers of opening widths 12.7 mm and 19.1 mm and to determine size segregation in blend fertilizers. Based on experimental results, the normalized segregation rate (NSR) of binary mixtures was dependent on size ratio, mixing ratio
Lebovka, Nikolai I; Tarasevich, Yuri Yu; Dubinin, Dmitri O; Laptev, Valeri V; Vygornitskii, Nikolai V
2015-12-01
The jamming and percolation for two generalized models of random sequential adsorption (RSA) of linear k-mers (particles occupying k adjacent sites) on a square lattice are studied by means of Monte Carlo simulation. The classical RSA model assumes the absence of overlapping of the new incoming particle with the previously deposited ones. The first model is a generalized variant of the RSA model for both k-mers and a lattice with defects. Some of the occupying k adjacent sites are considered as insulating and some of the lattice sites are occupied by defects (impurities). For this model even a small concentration of defects can inhibit percolation for relatively long k-mers. The second model is the cooperative sequential adsorption one where, for each new k-mer, only a restricted number of lateral contacts z with previously deposited k-mers is allowed. Deposition occurs in the case when z≤(1-d)z(m) where z(m)=2(k+1) is the maximum numbers of the contacts of k-mer, and d is the fraction of forbidden contacts. Percolation is observed only at some interval k(min)≤k≤k(max) where the values k(min) and k(max) depend upon the fraction of forbidden contacts d. The value k(max) decreases as d increases. A logarithmic dependence of the type log(10)(k(max))=a+bd, where a=4.04±0.22,b=-4.93±0.57, is obtained. PMID:26764641
Explosive percolation in thresholded networks
NASA Astrophysics Data System (ADS)
Hayasaka, Satoru
2016-06-01
Explosive percolation in a network is a phase transition where a large portion of nodes becomes connected with an addition of a small number of edges. Although extensively studied in random network models and reconstructed real networks, explosive percolation has not been observed in a more realistic scenario where a network is generated by thresholding a similarity matrix describing between-node associations. In this report, I examine construction schemes of such thresholded networks, and demonstrate that explosive percolation can be observed by introducing edges in a particular order.
Dithering Strategies and Point-Source Photometry
Samsing, Johan; Kim, Alex G
2011-02-22
The accuracy in the photometry of a point source depends on the point-spread function (PSF), detector pixelization, and observing strategy. The PSF and pixel response describe the spatial blurring of the source, the pixel scale describes the spatial sampling of a single exposure, and the observing strategy determines the set of dithered exposures with pointing offsets from which the source flux is inferred. In a wide-field imaging survey, sources of interest are randomly distributed within the field of view and hence are centered randomly within a pixel. A given hardware configuration and observing strategy therefore have a distribution of photometric uncertainty for sources of fixed flux that fall in the field. In this article we explore the ensemble behavior of photometric and position accuracies for different PSFs, pixel scales, and dithering patterns. We find that the average uncertainty in the flux determination depends slightly on dither strategy, whereas the position determination can be strongly dependent on the dithering. For cases with pixels much larger than the PSF, the uncertainty distributions can be non-Gaussian, with rms values that are particularly sensitive to the dither strategy. We also find that for these configurations with large pixels, pointings dithered by a fractional pixel amount do not always give minimal average uncertainties; this is in contrast to image reconstruction for which fractional dithers are optimal. When fractional pixel dithering is favored, a pointing accuracy of better than {approx}0.15 {approx}0.15 pixel width is required to maintain half the advantage over random dithers.
Atmospheric Verification of Point Source Fossil Fuel CO2 Emissions
NASA Astrophysics Data System (ADS)
Turnbull, J. C.; Keller, E. D.; Norris, M. W.; Wiltshire, R.; Baisden, W. T.; Brailsford, G. W.; Bromley, T.
2015-12-01
Large point sources (electricity generation and large-scale industry) make up roughly one third of all fossil fuel CO2 (CO2ff) emissions. Currently, these emissions are determined from self-reported inventory data, and sometimes from smokestack emissions monitoring, and the uncertainty in emissions from individual power plants is about 20%. We examine the utility of atmospheric 14C measurements combined with atmospheric transport modelling as a tool for independently quantifying point source CO2ff emissions, to both improve the accuracy of the reported emissions and for verification as we move towards a regulatory environment. We use the Kapuni Gas Treatment Facility as a test case. It is located in rural New Zealand with no other significant fossil fuel CO2 sources nearby, and emits CO2ff at ~0.1 Tg carbon per year. We use several different sampling methods to determine the 14C and hence the CO2ff content downwind of the emission source: grab flask samples of whole air; absorption of CO2 into sodium hydroxide integrated over many hours; and plant material which faithfully records the 14C content of assimilated CO2. We use a plume dispersion model to compare the reported emissions with our observed CO2ff mole fractions. We show that the short-term variability in plume dispersion makes it difficult to interpret the grab flask sample results, whereas the variability is averaged out in the integrated samples and we obtain excellent agreement between the reported and observed emissions, indicating that the 14C method can reliably be used to evaluated point source emissions.
NASA Astrophysics Data System (ADS)
Ding, Chengxiang; Fu, Zhe; Guo, Wenan; Wu, F. Y.
2010-06-01
In the preceding paper, one of us (F. Y. Wu) considered the Potts model and bond and site percolation on two general classes of two-dimensional lattices, the triangular-type and kagome-type lattices, and obtained closed-form expressions for the critical frontier with applications to various lattice models. For the triangular-type lattices Wu’s result is exact, and for the kagome-type lattices Wu’s expression is under a homogeneity assumption. The purpose of the present paper is twofold: First, an essential step in Wu’s analysis is the derivation of lattice-dependent constants A,B,C for various lattice models, a process which can be tedious. We present here a derivation of these constants for subnet networks using a computer algorithm. Second, by means of a finite-size scaling analysis based on numerical transfer matrix calculations, we deduce critical properties and critical thresholds of various models and assess the accuracy of the homogeneity assumption. Specifically, we analyze the q -state Potts model and the bond percolation on the 3-12 and kagome-type subnet lattices (n×n):(n×n) , n≤4 , for which the exact solution is not known. Our numerical determination of critical properties such as conformal anomaly and magnetic correlation length verifies that the universality principle holds. To calibrate the accuracy of the finite-size procedure, we apply the same numerical analysis to models for which the exact critical frontiers are known. The comparison of numerical and exact results shows that our numerical values are correct within errors of our finite-size analysis, which correspond to 7 or 8 significant digits. This in turn infers that the homogeneity assumption determines critical frontiers with an accuracy of 5 decimal places or higher. Finally, we also obtained the exact percolation thresholds for site percolation on kagome-type subnet lattices (1×1):(n×n) for 1≤n≤6 .
Monte Carlo study of the site-percolation model in two and three dimensions.
Deng, Youjin; Blöte, Henk W J
2005-07-01
We investigate the site-percolation problem on the square and simple-cubic lattices by means of a Monte Carlo algorithm that in fact simulates systems with size L(d-1) x infinity, where L specifies the linear system size. This algorithm can be regarded either as an extension of the Hoshen-Kopelman method or as a special case of the transfer-matrix Monte Carlo technique. Various quantities, such as the magnetic correlation function, are sampled in the finite directions of the above geometry. Simulations are arranged such that both bulk and surface quantities can be sampled. On the square lattice, we locate the percolation threshold at p(c) =0.592 746 5 (4) , and determine two universal quantities as Q(gbc) =0.930 34 (1) and Q(gsc) =0.793 72 (3) , which are associated with bulk and surface correlations, respectively. These values agree well with the exact values 2(-5/48) and 2(-1/3) , respectively, which follow from conformal invariance. On the simple-cubic lattice, we locate the percolation threshold at p(c) =0.311 607 7 (4) . We further determine the bulk thermal and magnetic exponents as y(t) =1.1437 (6) and y(h) =2.5219 (2) , respectively, and the surface magnetic exponent at the ordinary phase transition as y (o)(hs) =1.0248 (3) . PMID:16090055
Monte Carlo study of the site-percolation model in two and three dimensions
NASA Astrophysics Data System (ADS)
Deng, Youjin; Blöte, Henk W. J.
2005-07-01
We investigate the site-percolation problem on the square and simple-cubic lattices by means of a Monte Carlo algorithm that in fact simulates systems with size Ld-1×∞ , where L specifies the linear system size. This algorithm can be regarded either as an extension of the Hoshen-Kopelman method or as a special case of the transfer-matrix Monte Carlo technique. Various quantities, such as the magnetic correlation function, are sampled in the finite directions of the above geometry. Simulations are arranged such that both bulk and surface quantities can be sampled. On the square lattice, we locate the percolation threshold at pc=0.5927465(4) , and determine two universal quantities as Qgbc=0.93034(1) and Qgsc=0.79372(3) , which are associated with bulk and surface correlations, respectively. These values agree well with the exact values 2-5/48 and 2-1/3 , respectively, which follow from conformal invariance. On the simple-cubic lattice, we locate the percolation threshold at pc=0.3116077(4) . We further determine the bulk thermal and magnetic exponents as yt=1.1437(6) and yh=2.5219(2) , respectively, and the surface magnetic exponent at the ordinary phase transition as yhs(o)=1.0248(3) .
Wang, Yang; Weng, George J.; Meguid, Shaker A.; Hamouda, Abdel Magid
2014-05-21
A continuum model that possesses several desirable features of the electrical conduction process in carbon-nanotube (CNT) based nanocomposites is developed. Three basic elements are included: (i) percolation threshold, (ii) interface effects, and (iii) tunneling-assisted interfacial conductivity. We approach the first one through the selection of an effective medium theory. We approach the second one by the introduction of a diminishing layer of interface with an interfacial conductivity to build a 'thinly coated' CNT. The third one is introduced through the observation that interface conductivity can be enhanced by electron tunneling which in turn can be facilitated with the formation of CNT networks. We treat this last issue in a continuum fashion by taking the network formation as a statistical process that can be represented by Cauchy's probability density function. The outcome is a simple and yet widely useful model that can simultaneously capture all these fundamental characteristics. It is demonstrated that, without considering the interface effect, the predicted conductivity would be too high, and that, without accounting for the additional contribution from the tunneling-assisted interfacial conductivity, the predicted conductivity beyond the percolation threshold would be too low. It is with the consideration of all three elements that the theory can fully account for the experimentally measured data. We further use the developed model to demonstrate that, despite the anisotropy of the intrinsic CNT conductivity, it is its axial component along the CNT direction that dominates the overall conductivity. This theory is also proved that, even with a totally insulating matrix, it is still capable of delivering non-zero conductivity beyond the percolation threshold.
A New Proof of the Sharpness of the Phase Transition for Bernoulli Percolation and the Ising Model
NASA Astrophysics Data System (ADS)
Duminil-Copin, Hugo; Tassion, Vincent
2016-04-01
We provide a new proof of the sharpness of the phase transition for Bernoulli percolation and the Ising model. The proof applies to infinite-range models on arbitrary locally finite transitive infinite graphs. For Bernoulli percolation, we prove finiteness of the susceptibility in the subcritical regime {β < β_c}, and the mean-field lower bound {{P}_β[0longleftrightarrow infty ]ge (β-β_c)/β} for {β > β_c}. For finite-range models, we also prove that for any {β < β_c}, the probability of an open path from the origin to distance n decays exponentially fast in n. For the Ising model, we prove finiteness of the susceptibility for {β < β_c}, and the mean-field lower bound {< σ_0rangle_β^+ge sqrt{(β^2-β_c^2)/β^2}} for {β > β_c}. For finite-range models, we also prove that the two-point correlation functions decay exponentially fast in the distance for {β < β_c}.
NASA Astrophysics Data System (ADS)
Bautista, I.; Téllez, A. Fernandez; Ghosh, Premomoy
2015-10-01
We analyze high-multiplicity proton-proton (p p ) collision data in the framework of the string percolation model that has been successful in describing several phenomena of multiparticle production, including the signatures of recent discovery of strongly interacting partonic matter, the quark-gluon plasma, in relativistic heavy-ion collisions. Our study in terms of the ratio of shear viscosity and entropy density (η /s ) and the [Lattice Quantum Chromodinamics (LQCD)] predicted signature of QCD change of phase, in terms of the effective number of degrees of freedom (ɛ /T4), reiterates the possibility of a strongly interacting collective medium in these events.
Locally self-organized quasicritical percolation in a multiple-disease model.
Juul, Jeppe; Sneppen, Kim
2011-09-01
Diseases emerge, persist, and vanish in an ongoing battle for available hosts. Hosts, on the other hand, defend themselves by developing immunity that limits the ability of pathogens to reinfect them. We here explore a multidisease system with emphasis on mutual exclusion. We demonstrate that such a system develops toward a steady state, where the spread of individual diseases self-organizes to a state close to that of critical percolation, without any global control mechanism or separation of time scale. For a broad range of introduction rates of new diseases, the likelihood of transmitting diseases remains approximately constant. PMID:22060468
Deep Percolation in Devegetated Hillslopes
NASA Astrophysics Data System (ADS)
Ebel, B. A.; Hinckley, E. S.
2011-12-01
Deep percolation has recently been recognized as a critical component in hillslope hydrology studies. In devegetated hillslopes where vegetation is killed and, in some cases, removed, deep percolation may be substantially enhanced beyond pre-disturbance magnitudes. We discuss two examples of devegetated hillslopes where water balance partitioning shifted to favor increased deep percolation fluxes for some hydrologic conditions. The first is the Coos Bay Experimental Catchment in Oregon, USA, where commercial forestry resulted in the complete removal of trees. An intensive field campaign in the 1990's resulted in a long term record of precipitation, discharge, piezometric response, and groundwater levels. Hydrologic response modeling confirms hypotheses from the field-data analysis and points to unresolved questions regarding feedbacks between deep percolation and near-surface hydrologic processes. The second example is the area burned by the Fourmile Canyon Fire in Colorado, USA, where a severe wildland fire removed all vegetation from a north-aspect hillslope in 2010. Precipitation, atmospheric conditions, soil-water content, matric potential, and runoff have been measured since the fire devegetated the site. Subsurface sampling of the vadose zone is accomplished using suction lysimeters to capture total nitrate, ammonium, and dissolved organic carbon concentrations. Darcian flux calculations of net infiltration from the shallow soil into fractured granodiorite bedrock are used to estimate solute fluxes to a deeper groundwater system. Virtual experiments using numerical models of unsaturated fluid flow and solute transport further elucidate the temporal dynamics of deep percolation and associated solute fluxes during spring snowmelt and frontal rainstorms, which are the major hydrologic drivers of deep percolation in this fire-impacted system. Together, these examples serve to illustrate the critical importance of deep percolation in disturbed landscapes. The
Semi-directed percolation in two dimensions
NASA Astrophysics Data System (ADS)
Knežević, Dragica; Knežević, Milan
2016-02-01
We studied a model of semi-directed percolation on finite strips of the square and triangular lattices. Using the transfer-matrix method, combined with phenomenological renormalization group approach, we obtain good numerical estimates for critical probabilities and correlation lengths critical exponents. Our results confirm the conjecture that semi-directed percolation belongs to the universality class of the usual fully-directed percolation model.
Gönci, Balázs; Németh, Valéria; Balogh, Emeric; Szabó, Bálint; Dénes, Ádám; Környei, Zsuzsanna; Vicsek, Tamás
2010-01-01
Because of its relevance to everyday life, the spreading of viral infections has been of central interest in a variety of scientific communities involved in fighting, preventing and theoretically interpreting epidemic processes. Recent large scale observations have resulted in major discoveries concerning the overall features of the spreading process in systems with highly mobile susceptible units, but virtually no data are available about observations of infection spreading for a very large number of immobile units. Here we present the first detailed quantitative documentation of percolation-type viral epidemics in a highly reproducible in vitro system consisting of tens of thousands of virtually motionless cells. We use a confluent astroglial monolayer in a Petri dish and induce productive infection in a limited number of cells with a genetically modified herpesvirus strain. This approach allows extreme high resolution tracking of the spatio-temporal development of the epidemic. We show that a simple model is capable of reproducing the basic features of our observations, i.e., the observed behaviour is likely to be applicable to many different kinds of systems. Statistical physics inspired approaches to our data, such as fractal dimension of the infected clusters as well as their size distribution, seem to fit into a percolation theory based interpretation. We suggest that our observations may be used to model epidemics in more complex systems, which are difficult to study in isolation. PMID:21187920
NASA Astrophysics Data System (ADS)
Harris, Jamie; Connaughton, Colm; Bustamante, Miguel D.
2013-08-01
We study the kinematics of nonlinear resonance broadening of interacting Rossby waves as modelled by the Charney-Hasegawa-Mima equation on a biperiodic domain. We focus on the set of wave modes which can interact quasi-resonantly at a particular level of resonance broadening and aim to characterize how the structure of this set changes as the level of resonance broadening is varied. The commonly held view that resonance broadening can be thought of as a thickening of the resonant manifold is misleading. We show that in fact the set of modes corresponding to a single quasi-resonant triad has a non-trivial structure and that its area in fact diverges for a finite degree of broadening. We also study the connectivity of the network of modes which is generated when quasi-resonant triads share common modes. This network has been argued to form the backbone for energy transfer in Rossby wave turbulence. We show that this network undergoes a percolation transition when the level of resonance broadening exceeds a critical value. Below this critical value, the largest connected component of the quasi-resonant network contains a negligible fraction of the total number of modes in the system whereas above this critical value a finite fraction of the total number of modes in the system are contained in the largest connected component. We argue that this percolation transition should correspond to the transition to turbulence in the system.
Noise scaling in continuum percolating films
NASA Astrophysics Data System (ADS)
Garfunkel, G. A.; Weissman, M. B.
1985-07-01
Measurements of the scaling of 1/f noise magnitude versus resistance were made in metal films as the metal was removed by sandblasting. This procedure gives an approximate experimental realization of a Swiss-cheese continuum-percolation model, for which theory indicates some scaling properties very different from lattice percolation. The ratio of the resistance and noise exponents was in strong disagreement with lattice-percolation predictions and agreed approximately with simple continuum predictions.
Great lakes eutrophication: the effect of point source control of total phosphorus.
Chapra, S C; Robertson, A
1977-06-24
A mathematical model of the Great Lakes total phosphorus budgets indicates that a 1 milligram per liter effluent restriction for point sources would result in significant improvement in the trophic status of most of the system. However, because large areas of their drainage basins are devoted to agriculture or are urbanized, western Lake Erie, lower Green Bay, and Saginaw Bay may require non-point source controls to effect significant improvements in their trophic status. PMID:17776924
NASA Astrophysics Data System (ADS)
Ovaska, M.; Alava, M. J.
2015-10-01
Nuclear fuel material is an example of a sintered, porous ceramic material. We formulate a two-dimensional model which couples three physical mechanisms in the material: (scalar) damage accumulation by thermal creep and radiation effects, porosity changes due to the damage, and the time-dependent diffusion of (radiation-induced) gases in the pore system thus created. The most important effect in the dynamics arises from the process where the pore system is swept through the percolation transition. The main conclusions that can be drawn concern the fractional gas release and its dependence on the three effects present in the damage dynamics: creep, radiation-induced bubble formation, and recovery due to bubble closure. In the main, the model reproduces the experimentally observed quick gas release phenomenon qualitatively.
Russ, Stefanie
2014-08-01
It is shown that a two-component percolation model on a simple cubic lattice can explain an experimentally observed behavior [Savage et al., Sens. Actuators B 79, 17 (2001); Sens. Actuators B 72, 239 (2001).], namely, that a network built up by a mixture of sintered nanocrystalline semiconducting n and p grains can exhibit selective behavior, i.e., respond with a resistance increase when exposed to a reducing gas A and with a resistance decrease in response to another reducing gas B. To this end, a simple model is developed, where the n and p grains are simulated by overlapping spheres, based on realistic assumptions about the gas reactions on the grain surfaces. The resistance is calculated by random walk simulations with nn, pp, and np bonds between the grains, and the results are found in very good agreement with the experiments. Contrary to former assumptions, the np bonds are crucial to obtain this accordance. PMID:25215722
Inference of Dim Gamma-Ray Point Sources Using Probabilistic Catalogues
NASA Astrophysics Data System (ADS)
Daylan, Tansu; Portillo, Stephen K. N.; Finkbeiner, Douglas P.
2016-07-01
Poisson regression of the Fermi-LAT data in the inner Milky Way reveals an extended gamma-ray excess. The anomalous emission falls steeply away from the galactic center and has an energy spectrum that peaks at 1-2 GeV. An important question is whether the signal is coming from a collection of unresolved point sources, possibly recycled pulsars, or constitutes a truly diffuse emission component. Previous analyses have relied on non-Poissonian template fits or wavelet decomposition of the Fermi-LAT data, which find evidence for a population of dim point sources just below the 3FGL flux limit. In order to draw conclusions about a potentially dim population, we propose to sample from the catalog space of point sources, where the model dimensionality, i.e., the number of sources, is unknown. Although being a computationally expensive sampling problem, this approach allows us to infer the number, flux and radial distribution of the point sources consistent with the observed count data. Probabilistic cataloging is specifically useful in the crowded field limit, such as in the galactic disk, where the typical separation between point sources is comparable to the PSF. Using this approach, we recover the results of the deterministic Fermi-LAT 3FGL catalog, as well as sub-detection threshold information and fold the point source parameter degeneracies into the model-choice problem of whether an emission is coming from unresolved MSPs or dark matter annihilation.
Inference of Dim Gamma-Ray Point Sources Using Probabilistic Catalogues
NASA Astrophysics Data System (ADS)
Daylan, Tansu; Portillo, Stephen; Finkbeiner, Douglas P.
2016-01-01
Poisson regression of the Fermi-LAT data in the inner Milky Way reveals an extended gamma-ray excess. The anomalous emission falls steeply away from the galactic center and has an energy spectrum that peaks at 1-2 GeV. An important question is whether the signal is coming from a collection of unresolved point sources, possibly recycled pulsars, or constitutes a truly diffuse emission component. Previous analyses have relied on non-Poissonian template fits or wavelet decomposition of the Fermi-LAT data, which find evidence for a population of dim point sources just below the 3FGL flux limit. In order to be able to make conclusions about such a dim population we propose to sample from the catalogue space of point sources in the inner galaxy, where the model dimensionality, i.e., the number of sources, is unknown. Although being a computationally expensive sampling problem, this approach allows us to infer the number, luminosity and radial distribution of the point source population that is consistent with the data while providing a Bayesian evidence for the point source hypothesis, which is independent of the model indicator. This talk will focus on the method of trans-dimensional sampling using the reversible-jump formalism and its application to the inference of a mock point source population. See the poster by Stephen K. N. Portillo for the inferred catalogue using the high latitude Fermi-LAT data.
NASA Astrophysics Data System (ADS)
Pfeffer, Michael; Kumar, Praveen; Eibl, Oliver
2016-08-01
Resistive losses corresponding to the front-side metallization limit the efficiency of Si solar cells. At the front-side contact, the Si emitter is covered by a glass layer that is less than 1 μm thick embedded with Ag colloids to volume fraction >20%. Bulk Ag fingers are arranged on top of the glass layer. A similar microstructure is found for both n-type and p-type cells showing high efficiency. The Ag colloids constitute current filaments with reduced resistance in the glass layer, thereby introducing a percolative current which is the basis of the proposed model. This model is new and differs from the classical percolation model in its direct reliance on the macroscopic resistance of these filaments, and in considering the matrix as semiconducting rather than insulating. For periodically arranged Ag colloids of fixed diameter, the percolative limit of 13% in two dimensions (2D) and 15% in three dimensions (3D) depends only on the volume fraction of colloids but not their size. The resistance of randomly arranged and sized Ag colloids confirms the analytical results. The model explains quantitatively, consistent with microstructural analyses, why low contact resistances are found in solar cells with high colloid density. The introduced percolation model is also relevant for other systems in which metallic precipitates are found in a semiconducting matrix.
NASA Astrophysics Data System (ADS)
Moriya, Masataka; Huong, Tran Thi Thu; Matsumoto, Kazuhiko; Shimada, Hiroshi; Kimura, Yasuo; Hirano-Iwata, Ayumi; Mizugaki, Yoshinao
2016-08-01
We calculated the connection probability, P C, between electrodes on the basis of the triangular lattice percolation model for investigating the effect of distance variation between electrodes and the electrode width on fabricated capacitively coupled single-electron transistors. Single-electron devices were fabricated via the dispersion of gold nanoparticles (NPs). The NPs were dispersed via the repeated dropping of an NP solution onto a chip. The experimental results were fitted to the calculated values, and the fitting parameters were compared with the occupation probability, P O, which was estimated for one drop of the NP solution. On the basis of curves of the drain current versus the drain-source voltage ( I D- V DS) measured at 77 K, the current was suppressed at approximately 0 V.
NASA Astrophysics Data System (ADS)
Métens, S.; Monceau, P.; Renault, R.; Bottani, S.
2016-03-01
We start from a continuous extension of a mean field approach of the quorum percolation model, accounting for the response of in vitro neuronal cultures, to carry out a normal form analysis of the critical behavior. We highlight the effects of nonlinearities associated with this mean field approach even in the close vicinity of the critical point. Statistical properties of random networks with Gaussian in-degree are related to the outcoming links distribution. Finite size analysis of explicit Monte Carlo simulations enables us to confirm the relevance of the mean field approach on such networks and to show that the order parameter is weakly self-averaging; dynamical relaxation is investigated. Furthermore we derive a mean field equation taking into account the effect of inhibitory neurons and discuss the equivalence with a purely excitatory network.
Point source searches with the IceCube Neutrino Observatory
NASA Astrophysics Data System (ADS)
Feintzeig, Jacob
2013-04-01
Observing a point source of astrophysical neutrinos would be a ``smoking gun'' signature of a cosmic ray accelerator. Here we discuss past and future searches for point sources using IceCube, a cubic kilometer Cherenkov detector at the South Pole. Results from three years of partial-detector data will be shown. I will then describe how upcoming analyses will improve IceCube's sensitivity to point sources by including two years of full-detector data and incorporating new event reconstruction techniques.
Percolation transitions in two dimensions.
Feng, Xiaomei; Deng, Youjin; Blöte, Henk W J
2008-09-01
We investigate bond- and site-percolation models on several two-dimensional lattices numerically, by means of transfer-matrix calculations and Monte Carlo simulations. The lattices include the square, triangular, honeycomb kagome, and diced lattices with nearest-neighbor bonds, and the square lattice with nearest- and next-nearest-neighbor bonds. Results are presented for the bond-percolation thresholds of the kagome and diced lattices, and the site-percolation thresholds of the square, honeycomb, and diced lattices. We also include the bond- and site-percolation thresholds for the square lattice with nearest- and next-nearest-neighbor bonds. We find that corrections to scaling behave according to the second temperature dimension X_{t2}=4 predicted by the Coulomb gas theory and the theory of conformal invariance. In several cases there is evidence for an additional term with the same exponent, but modified by a logarithmic factor. Only for the site-percolation problem on the triangular lattice does such a logarithmic term appear to be small or absent. The amplitude of the power-law correction associated with X_{t2}=4 is found to be dependent on the orientation of the lattice with respect to the cylindrical geometry of the finite systems. PMID:18851022
Percolation transitions in two dimensions
NASA Astrophysics Data System (ADS)
Feng, Xiaomei; Deng, Youjin; Blöte, Henk W. J.
2008-09-01
We investigate bond- and site-percolation models on several two-dimensional lattices numerically, by means of transfer-matrix calculations and Monte Carlo simulations. The lattices include the square, triangular, honeycomb kagome, and diced lattices with nearest-neighbor bonds, and the square lattice with nearest- and next-nearest-neighbor bonds. Results are presented for the bond-percolation thresholds of the kagome and diced lattices, and the site-percolation thresholds of the square, honeycomb, and diced lattices. We also include the bond- and site-percolation thresholds for the square lattice with nearest- and next-nearest-neighbor bonds. We find that corrections to scaling behave according to the second temperature dimension Xt2=4 predicted by the Coulomb gas theory and the theory of conformal invariance. In several cases there is evidence for an additional term with the same exponent, but modified by a logarithmic factor. Only for the site-percolation problem on the triangular lattice does such a logarithmic term appear to be small or absent. The amplitude of the power-law correction associated with Xt2=4 is found to be dependent on the orientation of the lattice with respect to the cylindrical geometry of the finite systems.
ESTIMATION OF VIABLE AIRBORNE MICROBES DOWNWIND FROM A POINT SOURCE
Modification of the Pasquill atmospheric diffusion equations for estimating viable microbial airborne cell concentrations downwind from a continuous point source is presented. A graphical method is given to estimate the ground level cell concentration given (1) microbial death ra...
Scattering of point source illumination by an arbitrary configuration
NASA Technical Reports Server (NTRS)
Solakiewicz, Richard
1994-01-01
The problem of electromagnetic scattering of an incident plane wave by an arbitrary configuration of obstacles was solved by Twersky. In this report, the results are extended to point source incidence corresponding to a Hertz dipole. Knowledge of the response of a fixed configuration of scatterers excited by a point source may provide insight to improve the accuracy of the values of bulk parameters for clouds which have been found using plane wave excitation.
Point-source imbibition into dry aqueous foams
NASA Astrophysics Data System (ADS)
Mensire, Rémy; Ault, Jesse T.; Lorenceau, Elise; Stone, Howard A.
2016-02-01
We use experiments, modeling and numerics to study the imbibition dynamics from a point source into a homogeneous dry aqueous foam. A distinctive feature of foams compared to solid porous material is that imbibition occurs in the liquid microchannels of the foam called Plateau borders, which have a volume varying in space and time. Dynamics is driven by the capillary pressure and resisted by the viscous and gravity forces in the liquid microchannels. Assuming a constant pressure in the imbibing liquid reservoir, we show that the imbibition front advances and flattens out in time due to gravity, the effect of which is quantified by introducing the Bond number B, which compares the gravitational effects to the capillary pressure using the mean bubble radius as the characteristic length. This evolution describes both miscible and immiscible imbibing liquids. For the latter, we introduce the idea of an effective interfacial tension γ\\textit{eff} to take the oil-water interfacial energy into account. The details of the imbibition process are confirmed by experiments and numerics using foams with tangentially immobile interfaces in the channel-dominated model.
Identifying populations at risk from environmental contamination from point sources
Williams, F; Ogston, S
2002-01-01
Objectives: To compare methods for defining the population at risk from a point source of air pollution. A major challenge for environmental epidemiology lies in correctly identifying populations at risk from exposure to environmental pollutants. The complexity of today's environment makes it essential that the methods chosen are accurate and sensitive. Methods: Environmental and mathematical methods were used to identify the population potentially exposed to a point source of airborne pollution emanating from a waste incinerator. Soil sampling was undertaken at 83 sites throughout the city and environs. The concentrations of arsenic and copper were measured at each site. Computer software produced smoothed contour plots of the distribution of arsenic and copper in the soil based on the information derived from the sampling sites. The population at risk was also identified using concentric rings of varying radii, with the source of pollution at the centre. Lastly, we used the sites that had previously been selected and measured the frequency of wind direction, speed and distance from the source of pollution at each site. Theoretical contour plots were constructed using the distance from the source of pollution at each site, with and without incorporating wind frequency as a function of direction. Results: Each method identified different populations at risk from airborne pollution. The use of circles was a very imprecise way of identifying exposed populations. Mathematical modelling that incorporated wind direction was better. Soil sampling at many sites was accurate, as the method is direct; but it is very costly and the close proximity of high and low concentrations hindered interpretation. The smoothed contour plots derived from the soil sampling sites identified an exposed population that was similar to that derived from the spot sampling. Conclusions: Using circles as the only means of identifying the exposed population leads to dilution of the potential
NASA Astrophysics Data System (ADS)
Ordway, Stephen; King, Dawn; Bahar, Sonya
Reaction-diffusion processes, such as branching-coalescing random walks, can be used to describe the underlying dynamics of nonequilibrium phase transitions. In an agent-based, neutral model of evolutionary dynamics, we have previously shown that our system undergoes a continuous, nonequilibrium phase transition, from extinction to survival, as various system parameters were tuned. This model was shown to belong to the directed percolation (DP) universality class, by measuring the critical exponents corresponding to correlation length ξ⊥, correlation time ξ| |, and particle density β. The fourth critical exponent that defines the DP universality class is β', which measures the survival probability of growth from a single seed organism. Since DP universality is theorized to have time-reversal symmetry, it is assumed that β = β '. In order to confirm the existence of time-reversal symmetry in our model, we evaluate the system growth from a single asexually reproducing organism. Importantly, the critical exponent β' could be useful for comparison to experimental studies of phase transitions in biological systems, since observing growth of microbial populations is significantly easier than observing death. This research was supported by funding from the James S. McDonnell Foundation.
NASA Astrophysics Data System (ADS)
Sasaki, Akira; Kato, Susumu; Takahashii, Eiichi; Kishimoto, Yasuaki; Fujii, Takashi; Kanazawa, Seiji
2016-02-01
We show a cell simulation of a discharge in an insulating gas from the initial partial discharge to leader inception until breakdown, based on the percolation model. In the model, we consider that the propagation of the leader occurs when connections between randomly produced ionized regions in the discharge medium are established. To determine the distribution of ionized regions, the state of each simulation cell is decided by evaluating the probability of ionization in SF6, which depends on the local electric field. The electric field as well as the discharge current are calculated by solving circuit equations for the network of simulation cells. Both calculations are coupled to each other and the temporal evolution of discharge is self-consistently calculated. The model dependence of the features of the discharge is investigated. It is found that taking the suppression of attachment in the presence of a discharge current into account, the calculation reproduces the behavior of experimental discharges. It is shown that for a strong electric field, the inception of a stepped leader causes immediate breakdown. For an electric field of 30-50% of the critical field, the initial partial discharge persists for a stochastic time lag and then the propagation of a leader takes place. As the strength of the electric field decreases, the time lag increases rapidly and eventually only a partial discharge with a short arrested leader occurs, as observed in experiments.
Chandra Spectra of the Cassiopeia A Point Source
NASA Astrophysics Data System (ADS)
Stage, Michael D.; Joss, Paul C.
2001-09-01
We present the first Chandra High Energy Transmission Grating (HETG) spectra of the X-ray point source (XPS) at the center of the Cassiopeia A supernova remnant, using our recent HETGS observation of Cas A (Obsid 1046), as well as spectra extracted from the long duration archival 50 ksec ACIS-S3 observation (Obsid 114). Discovered in the Chandra first light image, the flux and spectrum of XPS strongly indicate that it is associated with the remnant, but it has been difficult to classify the point source unambiguously. The assertion that the XPS is a weakly magnetized neutron star (B <= 1010 G) radiating primarily via thermal emission is supported by the recent discovery of weak X-ray pulsations with a 13 ms period (H. Tananbaum, talk presented at 198th Mtg. AAS). Such a source is an ideal candidate to fit with our new theoretical atmosphere models (Joss, Madej, and Stage, these proceedings). Early data fit well to a variety of spectral forms, including power laws, model neutron star atmospheres, pure blackbody, and thermal bremsstrahlung (Chakrabarty et al., ApJ 548: 800; Pavlov et al., ApJ 531: L53). With our longer duration and higher resolution observations, we have greater ability to discriminate among the possible spectral models. We have previously carried out model atmosphere fits to a spectrum extracted from the archival 50 ksec observation. Our results yielded effective temperatures (kTeff ~= 0.2 keV) and radii (Reff ~= 2 km) that are comparable to those obtained in earlier fits to neutron-star model atmospheres (Chakrabarty et. al.). The lack of detection of radio pulsations or of a synchrotron nebula from the location of the XPS (McLaughlin et al., ApJ 547: L41) suggests that the XPS is not a classical young pulsar, a result with which we agree. The quality of our model atmosphere fits is superior to those we obtained using simple power law or blackbody models. Furthermore, recent upper limits on the emission from the XPS at near infrared and optical
NASA Astrophysics Data System (ADS)
Nichols, J. M.; Waterman, J. R.
2016-07-01
This work derives the modeling and detection theory required to predict the performance of an infrared focal plane array in detecting point source targets. Specifically, we focus on modeling the uncertainty associated with the location of the point source on the array. In the process we derive several new expressions related to pixel-averaged detection performance under a variety of problem assumptions. The resulting predictions are compared to standard approaches where the location is assumed fixed and known. It is further shown how to incorporate these predictions into multi-frame detection strategies.
A guide to differences between stochastic point-source and stochastic finite-fault simulations
Atkinson, G.M.; Assatourians, K.; Boore, D.M.; Campbell, K.; Motazedian, D.
2009-01-01
Why do stochastic point-source and finite-fault simulation models not agree on the predicted ground motions for moderate earthquakes at large distances? This question was posed by Ken Campbell, who attempted to reproduce the Atkinson and Boore (2006) ground-motion prediction equations for eastern North America using the stochastic point-source program SMSIM (Boore, 2005) in place of the finite-source stochastic program EXSIM (Motazedian and Atkinson, 2005) that was used by Atkinson and Boore (2006) in their model. His comparisons suggested that a higher stress drop is needed in the context of SMSIM to produce an average match, at larger distances, with the model predictions of Atkinson and Boore (2006) based on EXSIM; this is so even for moderate magnitudes, which should be well-represented by a point-source model. Why? The answer to this question is rooted in significant differences between point-source and finite-source stochastic simulation methodologies, specifically as implemented in SMSIM (Boore, 2005) and EXSIM (Motazedian and Atkinson, 2005) to date. Point-source and finite-fault methodologies differ in general in several important ways: (1) the geometry of the source; (2) the definition and application of duration; and (3) the normalization of finite-source subsource summations. Furthermore, the specific implementation of the methods may differ in their details. The purpose of this article is to provide a brief overview of these differences, their origins, and implications. This sets the stage for a more detailed companion article, "Comparing Stochastic Point-Source and Finite-Source Ground-Motion Simulations: SMSIM and EXSIM," in which Boore (2009) provides modifications and improvements in the implementations of both programs that narrow the gap and result in closer agreement. These issues are important because both SMSIM and EXSIM have been widely used in the development of ground-motion prediction equations and in modeling the parameters that control
Emergence of coexisting percolating clusters in networks.
Faqeeh, Ali; Melnik, Sergey; Colomer-de-Simón, Pol; Gleeson, James P
2016-06-01
It is commonly assumed in percolation theories that at most one percolating cluster can exist in a network. We show that several coexisting percolating clusters (CPCs) can emerge in networks due to limited mixing, i.e., a finite and sufficiently small number of interlinks between network modules. We develop an approach called modular message passing (MMP) to describe and verify these observations. We demonstrate that the appearance of CPCs is an important source of inaccuracy in previously introduced percolation theories, such as the message passing (MP) approach, which is a state-of-the-art theory based on the belief propagation method. Moreover, we show that the MMP theory improves significantly over the predictions of MP for percolation on synthetic networks with limited mixing and also on several real-world networks. These findings have important implications for understanding the robustness of networks and in quantifying epidemic outbreaks in the susceptible-infected-recovered (SIR) model of disease spread. PMID:27415281
Emergence of coexisting percolating clusters in networks
NASA Astrophysics Data System (ADS)
Faqeeh, Ali; Melnik, Sergey; Colomer-de-Simón, Pol; Gleeson, James P.
2016-06-01
It is commonly assumed in percolation theories that at most one percolating cluster can exist in a network. We show that several coexisting percolating clusters (CPCs) can emerge in networks due to limited mixing, i.e., a finite and sufficiently small number of interlinks between network modules. We develop an approach called modular message passing (MMP) to describe and verify these observations. We demonstrate that the appearance of CPCs is an important source of inaccuracy in previously introduced percolation theories, such as the message passing (MP) approach, which is a state-of-the-art theory based on the belief propagation method. Moreover, we show that the MMP theory improves significantly over the predictions of MP for percolation on synthetic networks with limited mixing and also on several real-world networks. These findings have important implications for understanding the robustness of networks and in quantifying epidemic outbreaks in the susceptible-infected-recovered (SIR) model of disease spread.
Atmospheric measurement of point source fossil fuel CO2 emissions
NASA Astrophysics Data System (ADS)
Turnbull, J. C.; Keller, E. D.; Baisden, W. T.; Brailsford, G.; Bromley, T.; Norris, M.; Zondervan, A.
2013-11-01
We use the Kapuni Gas Treatment Plant to examine methodologies for atmospheric monitoring of point source fossil fuel CO2 (CO2ff) emissions. The Kapuni plant, located in rural New Zealand, removes CO2 from locally extracted natural gas and vents that CO2 to the atmosphere, at a rate of ~0.1 Tg carbon per year. The plant is located in a rural dairy farming area, with no other significant CO2ff sources nearby, but large, diurnally varying, biospheric CO2 fluxes from the surrounding highly productive agricultural grassland. We made flask measurements of CO2 and 14CO2 (from which we derive the CO2ff component) and in situ measurements of CO2 downwind of the Kapuni plant, using a Helikite to sample transects across the emission plume from the surface up to 100 m a.g.l. We also determined the surface CO2ff content averaged over several weeks from the 14CO2 content of grass samples collected from the surrounding area. We use the WindTrax plume dispersion model to compare the atmospheric observations with the emissions reported by the Kapuni plant, and to determine how well atmospheric measurements can constrain the emissions. The model has difficulty accurately capturing the fluctuations and short-term variability in the Helikite samples, but does quite well in representing the observed CO2ff in 15 min averaged surface flask samples and in ~1 week integrated CO2ff averages from grass samples. In this pilot study, we found that using grass samples, the modeled and observed CO2ff emissions averaged over one week agreed to within 30%. The results imply that greater verification accuracy may be achieved by including more detailed meteorological observations and refining 14CO2 sampling strategies.
NASA Astrophysics Data System (ADS)
Scala, Antonio
2015-03-01
We introduce the concept of self-healing in the field of complex networks modelling; in particular, self-healing capabilities are implemented through distributed communication protocols that exploit redundant links to recover the connectivity of the system. Self-healing is a crucial in implementing the next generation of smart grids allowing to ensure a high quality of service to the users. We then map our self-healing procedure in a percolation problem and analyse the interplay between redundancies and topology in improving the resilience of networked infrastructures to multiple failures. We find exact results both for planar lattices and for random lattices, hinting the role of duality in the design of resilient networks. Finally, we introduce a cavity method approach to study the recovery of connectivity after damage in self-healing networks. CNR-PNR National Project ``Crisis-Lab,'' EU HOME/2013/CIPS/AG/4000005013 project CI2C and EU FET project MULTIPLEX nr.317532.
Power-Law Template for IR Point Source Clustering
NASA Technical Reports Server (NTRS)
Addison, Graeme E.; Dunkley, Joanna; Hajian, Amir; Viero, Marco; Bond, J. Richard; Das, Sudeep; Devlin, Mark; Halpern, Mark; Hincks, Adam; Hlozek, Renee; Marriage, Tobias A.; Moodley, Kavilan; Page, Lyman A.; Reese, Erik D.; Scott, Douglass; Spergel, David N.; Staggs,Suzanne T.; Wollack, Edward
2011-01-01
We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217,353,545 and 857 GHz, over angular scales 100 < I < 2200), the Balloonborne Large-Aperture Submillimeter Telescope (BLAST; 250, 350 and 500 microns; 1000 < I < 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fit by a simple power law of the form C_l\\propto I(sup -n) with n = 1.25 +/- 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, nu(sup beta) B(nu,T_eff), with a single emissivity index beta = 2.20 +/- 0.07 and effective temperature T_eff= 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be alpha_150-220 = 3.68 +/- 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in Cosmic Microwave Background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.
Power-Law Template for Infrared Point-Source Clustering
NASA Technical Reports Server (NTRS)
Addison, Graeme E; Dunkley, Joanna; Hajian, Amir; Viero, Marco; Bond, J. Richard; Das, Sudeep; Devlin, Mark J.; Halpern, Mark; Hincks, Adam D; Hlozek, Renee; Marriage, Tobias A.; Moodley, Kavilan; Page, Lyman A.; Reese, Erik D.; Scott, Douglas; Spergel, David N.; Staggs, Suzanne T.; Wollack, Edward
2012-01-01
We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217, 353, 545, and 857 GHz, over angular scales 100 approx < l approx < 2200), the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST; 250, 350, and 500 micron; 1000 approx < l approx < 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fitted by a simple power law of the form C(sup clust)(sub l) varies as l (sub -n) with n = 1.25 +/- 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, ?(sup Beta)B(?, T(sub eff) ), with a single emissivity index Beta = 2.20 +/- 0.07 and effective temperature T(sub eff) = 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be alpha(sub 150-220) = 3.68 +/- 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in cosmic microwave background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.
POWER-LAW TEMPLATE FOR INFRARED POINT-SOURCE CLUSTERING
Addison, Graeme E.; Dunkley, Joanna; Hajian, Amir; Das, Sudeep; Hincks, Adam D.; Page, Lyman A.; Staggs, Suzanne T.; Viero, Marco; Bond, J. Richard; Devlin, Mark J.; Reese, Erik D.; Halpern, Mark; Scott, Douglas; Hlozek, Renee; Marriage, Tobias A.; Spergel, David N.; Moodley, Kavilan; Wollack, Edward
2012-06-20
We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217, 353, 545, and 857 GHz, over angular scales 100 {approx}< l {approx}< 2200), the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST; 250, 350, and 500 {mu}m; 1000 {approx}< l {approx}< 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fitted by a simple power law of the form C{sup clust}{sub l}{proportional_to}l{sup -n} with n = 1.25 {+-} 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, {nu}{sup {beta}} B({nu}, T{sub eff}), with a single emissivity index {beta} = 2.20 {+-} 0.07 and effective temperature T{sub eff} = 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be {alpha}{sub 150-220} = 3.68 {+-} 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in cosmic microwave background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.
Coalescence and percolation in thin metal films
Yu, X.; Duxbury, P.M.; Jeffers, G.; Dubson, M.A. Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824-1116 )
1991-12-15
Metals thermally evaporated onto warm insulating substrates evolve to the thin-film state via the morphological sequence: compact islands, elongated islands, percolation, hole filling, and finally the thin-film state. The coverage at which the metal percolates ({ital p}{sub {ital c}}) is often considerably higher than that predicted by percolation models, such as inverse swiss cheese or lattice percolation. Using a simple continuum model, we show that high-{ital p}{sub {ital c}}'s arise naturally in thin films that exhibit a crossover from full coalescence of islands at early stages of growth to partial coalescence at later stages. In this interrupted-coalescence model, full coalescence of islands occurs up to a critical island radius {ital R}{sub {ital c}}, after which islands overlap, but do not fully coalesce. We present the morphology of films and the critical area coverages generated by this model.
ENERGY CONSERVATION THROUGH POINT SOURCE RECYCLE WITH HIGH TEMPERATURE HYPERFILTRATION
The report gives results of a study of energy conservation effects of point source recycle with high-temperature hyperfiltration (HF) in the textile industry. (HF and ultrafiltration (UF) are pressure-driven membrane processes which have potential for recycle of water, energy, an...
Radio Point Sources Toward Galaxy Clusters at 30 GHz
NASA Technical Reports Server (NTRS)
Coble, K.; Carlstrom, J. E.; Bonamente, M.; Dawson, K.; Holzapfel, W.; Joy, M.; LaRoque, S.; Reese, E. D.
2006-01-01
Extra-galactic point sources are a significant contaminant in cosmic microwave background and Sunyaev-Zel'dovich effect experiments. Deep interferometric observations with the BIMA and OVRO arrays are used to characterize the spatial, spectral, and flux distributions of radio point sources toward galaxy clusters at 28.5 GHz. We compute counts of mJy point source fluxes from 90 fields centered on known massive galaxy clusters and 8 non-cluster fields. Counts in the non-cluster fields are consistent with extrapolations from the results of other surveys. We also compute counts towards clusters as a function of luminosity in three redshift bins out to z = 1.0 and see no clear evidence for evolution with redshift. We compute spectral indices of mJy sources in cluster fields between 1.4 and 28.5 GHz. The distribution is skewed, with a median spectral index of 0.76 and 25th and 75th percentiles of 0.55 and 0.95, respectively. This is steeper than the spectral indices of brighter field point sources measured by other surveys.
TMDLS: AFTER POINT SOURCES, WHAT CAN WE DO NEXT?
Section 303(d) of the Clean Water Act required TMDLs (total maximum daily loads) for all waters for which effluent or point source limitations are insufficient to meet water quality standards. Concerns may arise regarding the manner by which TMDLs are established, the corrective ...
Anomalous critical and supercritical phenomena in explosive percolation
NASA Astrophysics Data System (ADS)
D'Souza, Raissa M.; Nagler, Jan
2015-07-01
The emergence of large-scale connectivity on an underlying network or lattice, the so-called percolation transition, has a profound impact on the system’s macroscopic behaviours. There is thus great interest in controlling the location of the percolation transition to either enhance or delay its onset and, more generally, in understanding the consequences of such control interventions. Here we review explosive percolation, the sudden emergence of large-scale connectivity that results from repeated, small interventions designed to delay the percolation transition. These transitions exhibit drastic, unanticipated and exciting consequences that make explosive percolation an emerging paradigm for modelling real-world systems ranging from social networks to nanotubes.
Reversible first-order transition in Pauli percolation
NASA Astrophysics Data System (ADS)
Maksymenko, Mykola; Moessner, Roderich; Shtengel, Kirill
2015-06-01
Percolation plays an important role in fields and phenomena as diverse as the study of social networks, the dynamics of epidemics, the robustness of electricity grids, conduction in disordered media, and geometric properties in statistical physics. We analyze a new percolation problem in which the first-order nature of an equilibrium percolation transition can be established analytically and verified numerically. The rules for this site percolation model are physical and very simple, requiring only the introduction of a weight W (n )=n +1 for a cluster of size n . This establishes that a discontinuous percolation transition can occur with qualitatively more local interactions than in all currently considered examples of explosive percolation; and that, unlike these, it can be reversible. This greatly extends both the applicability of such percolation models in principle and their reach in practice.
Reversible first-order transition in Pauli percolation.
Maksymenko, Mykola; Moessner, Roderich; Shtengel, Kirill
2015-06-01
Percolation plays an important role in fields and phenomena as diverse as the study of social networks, the dynamics of epidemics, the robustness of electricity grids, conduction in disordered media, and geometric properties in statistical physics. We analyze a new percolation problem in which the first-order nature of an equilibrium percolation transition can be established analytically and verified numerically. The rules for this site percolation model are physical and very simple, requiring only the introduction of a weight W(n)=n+1 for a cluster of size n. This establishes that a discontinuous percolation transition can occur with qualitatively more local interactions than in all currently considered examples of explosive percolation; and that, unlike these, it can be reversible. This greatly extends both the applicability of such percolation models in principle and their reach in practice. PMID:26172657
Search for Extragalactic Point Sources in WMAP First Year Data
NASA Astrophysics Data System (ADS)
Chen, X.; Wright, E. L.
2005-12-01
In 2003, Bennett et al. made a search for point sources in the WMAP maps and provided a catalog of 208 detected sources (with 98% reliability). These sources tend to be radio galaxies and quasars, and most of them have strong radiation at the K, Ka and Q bands, but not necessarily at the V and W bands. Here we present a new search for extragalactic point sources in V- and W-band full sky WMAP maps, using a different approach that cancels the ``noise'' due to the CMB anisotropy signal. 29 point sources are found in our study including 16 WMAP point sources, which is a strong proof of the feasibility and reliability of our method. Also since in our method the major noise contribution is due to random errors in the observations which can be minimized by repeated observations, the sensitivity of our study is expected to be greatly enhanced when more years of WMAP data are available. A comparison to previous surveys shows that 5 of our point source candidates have nearby infrared sources which cannot be positively associated due to insufficient spectral data; and another 3 do not have any companions in a 4-arcmin radius vicinity, which are most likely sources undetected before. We have proposed VLA X-band observations for these unidentified sources. The observation results should be available at the time of this meeting and will be presented along with the WMAP analysis. We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science.
NASA Astrophysics Data System (ADS)
Liu, Jie; Regenauer-Lieb, Klaus
2011-01-01
Percolation theory provides a tool for linking microstructure and macroscopic material properties. In this paper, percolation theory is applied to the analysis of microtomographic images for the purpose of deriving scaling laws for upscaling of properties. We have tested the acquisition of quantities such as percolation threshold, crossover length, fractal dimension, and critical exponent of correlation length from microtomography. By inflating or deflating the target phase and percolation analysis, we can get a critical model and an estimation of the percolation threshold. The crossover length is determined from the critical model by numerical simulation. The fractal dimension can be obtained either from the critical model or from the relative size distribution of clusters. Local probabilities of percolation are used to extract the critical exponent of the correlation length. For near-isotropic samples such as sandstone and bread, the approach works very well. For strongly anisotropic samples, such as highly deformed rock (mylonite) and a tree branch, the percolation threshold and fractal dimension can be assessed with accuracy. However, the uncertainty of the correlation length makes it difficult to accurately extract its critical exponents. Therefore, this aspect of percolation theory cannot be reliably used for upscaling properties of strongly anisotropic media. Other methods of upscaling have to be used for such media.
NASA Astrophysics Data System (ADS)
Wehrer, Markus; Lissner, Heidi; Totsche, Kai
2013-04-01
A quantitative knowledge of the fate of deicing chemicals in the subsurface can be provided by analysis of laboratory and field experiments with numerical simulation models. In the present study, experimental data of microbial degradation of the deicing chemical propylene glycol (PG) under flow conditions in soil columns and field lysimeters were simulated to analyze the process conditions of degradation and to obtain the according parameters. Results from the column experiment were evaluated applying different scenarios of an advection-dispersion model using HYDRUS-1D. To reconstruct the data, different competing degradation models were included, i.e., zero order, first order and inclusion of a growing and decaying biomass. The general breakthrough behavior of propylene glycol in soil columns can be simulated well using a coupled model of solute transport and degradation with growth and decay of biomass. The susceptibility of the model to non-unique solutions was investigated using systematical forward and inverse simulations. We found that the model tends to equifinal solutions under certain conditions. Complex experimental boundary conditions can help to avoid this. Under field conditions, the situation is far more complex than in the laboratory. Studying the fate of PG with undisturbed lysimeters we found that aerobic and anaerobic degradation occurs simultaneously. We attribute this to the physical structure and the aggregated nature of the undisturbed soil material . This results in the presence of spatially disjoint oxidative and reductive regions of microbial activity and requires, but is not fully reflected by a dual porosity model. Currently, the numerical simulation of this system is in progress, considering several flow and transport models. A stochastic global search algorithm (DREAM-ZS) is used in conjuction with HYDRUS-1D to avoid local minima in the inverse simulations. The study shows the current limitations and potentials of modeling degradation
NASA Astrophysics Data System (ADS)
Faulkner, B. R.; Lyon, W. G.
2001-12-01
We present a probabilistic model for predicting virus attenuation. The solution employs the assumption of complete mixing. Monte Carlo methods are used to generate ensemble simulations of virus attenuation due to physical, biological, and chemical factors. The model generates a probability of failure to achieve 4-log attenuation. We tabulated data from related studies to develop probability density functions for input parameters, and utilized a database of soil hydraulic parameters based on the 12 USDA soil categories. Regulators can use the model based on limited information such as boring logs, climate data, and soil survey reports for a particular site of interest. Plackett-Burman sensitivity analysis indicated the most important main effects on probability of failure to achieve 4-log attenuation in our model were mean logarithm of saturated hydraulic conductivity (+0.396), mean water content (+0.203), mean solid-water mass transfer coefficient (-0.147), and the mean solid-water equilibrium partitioning coefficient (-0.144). Using the model, we predicted the probability of failure of a one-meter thick proposed hydrogeologic barrier and a water content of 0.3. With the currently available data and the associated uncertainty, we predicted soils classified as sand would fail (p=0.999), silt loams would also fail (p=0.292), but soils classified as clays would provide the required 4-log attenuation (p=0.001). The model is extendible in the sense that probability density functions of parameters can be modified as future studies refine the uncertainty, and the lightweight object-oriented design of the computer model (implemented in Java) will facilitate reuse with modified classes. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.
Bak–Tang–Wiesenfeld model on the square site-percolation lattice
NASA Astrophysics Data System (ADS)
Najafi, M. N.
2016-08-01
The Bak–Tang–Wiesenfeld (BTW) model is considered on the site-diluted square lattice, tuned by the occupancy probability p. Various statistical observables of the avalanches are analyzed in terms of p, e.g. the fractal dimension of their exterior frontiers, gyration radius, loop lengths and Green’s function. The model exhibits critical behavior for all amounts of p, and the exponents of the statistical observables are analyzed. We find a distinct universality class at p={p}c, which is unstable towards a p = 1 (BTW) fixed point. This universality class displays some common features such as a two-dimensional (2D) Ising universality class, e.g. the fractal dimension of loops in the thermodynamic limit is {D}Fp={pc}=1.38\\mp 0.01 which is compatible with the fractal dimension of geometrical spin clusters of the 2D critical Ising model (with {D}F{{Ising}}=\\tfrac{11}{8}).
Impact of point source clustering on cosmological parameters with CMB anisotropies
Serra, Paolo; Cooray, Asantha; Amblard, Alexandre; Pagano, Luca; Melchiorri, Alessandro
2008-08-15
The faint radio point sources that are unresolved in cosmic microwave background (CMB) anisotropy maps are likely to be a biased tracer of the large-scale structure dark matter distribution. While the shot-noise contribution to the angular power spectrum of unresolved radio point sources is included either when optimally constructing the CMB angular power spectrum, as with WMAP data, or when extracting cosmological parameters, we suggest that clustering part of the point source power spectrum should also be included. This is especially necessary at high frequencies above 150 GHz, where the clustering of far-IR sources is expected to dominate the shot-noise level of the angular power spectrum at tens of arcminute angular scales of both radio and sub-mm sources. We make an estimate of source clustering of unresolved radio sources in both WMAP and ACBAR, and marginalize over the amplitude of source clustering in each CMB data set when model fitting for cosmological parameters. For the combination of WMAP 5-year data and ACBAR, we find that the spectral index changes from the value of 0.963{+-}0.014 to 0.959{+-}0.014 (at 68% C.L.) when the clustering power spectrum of point sources is included in model fits. While we find that the differences are marginal with and without source clustering in current data, it may be necessary to account for source clustering with future data sets such as Planck, especially to properly model fit anisotropies at arcminute angular scales. If clustering is not accounted and point sources are modeled with a shot noise only out to l{approx}2000, the spectral index will be biased by about 1.5{sigma}.
First Passage Percolation on the Newman-Watts Small World Model
NASA Astrophysics Data System (ADS)
Komjáthy, Júlia; Vadon, Viktória
2016-02-01
The Newman-Watts model is given by taking a cycle graph of n vertices and then adding each possible edge (i,j), |i-j|≠ 1 mod n with probability ρ /n for some ρ >0 constant. In this paper we add i.i.d. exponential edge weights to this graph, and investigate typical distances in the corresponding random metric space given by the least weight paths between vertices. We show that typical distances grow as 1/λ log n for a λ >0 and determine the distribution of smaller order terms in terms of limits of branching process random variables. We prove that the number of edges along the shortest weight path follows a Central Limit Theorem, and show that in a corresponding epidemic spread model the fraction of infected vertices follows a deterministic curve with a random shift.
NASA Astrophysics Data System (ADS)
Seiffert, Franz; Bandow, Nicole; Kalbe, Ute; Milke, Ralf; Gorbushina, Anna
2016-04-01
Sub-aerial biofilms (SAB) are ubiquitous, self-sufficient microbial ecosystems found on mineral surfaces at all altitudes and latitudes. SABs, which are the principal causes of weathering on exposed terrestrial surfaces, are characterised by patchy growth dominated by associations of algae, cyanobacteria, fungi and heterotrophic bacteria. A recently developed in vitro system to study colonisation of rocks exposed to air included two key SAB participants - the rock-inhabiting ascomycete Knufia petricola (CBS 123872) and the phototrophic cyanobacterium Nostoc punctiforme ATCC29133. Both partners are genetically tractable and we used them here to study weathering of granite, K-feldspar and plagioclase. Small fragments of the various rocks or minerals (1 to 6 mm) were packed into flow-through columns and incubated with 0.1% glucose and 10 µM thiamine-hydrochloride (90 µL.min-1) to compare weathering with and without biofilms. Dissolution of the minerals was followed by: analysing (i) the degradation products in the effluent from the columns via Inductively Coupled Plasma Spectroscopy and (ii) by studying polished sections of the incubated mineral fragment/grains using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analyses. K. petricola/N. punctiforme stimulated release of Ca, Na, Mg and Mn. Analyses of the polished sections confirmed depletion of Ca, Na and K near the surface of the fragments. The abrupt decrease in Ca concentration observed in peripheral areas of plagioclase fragments favoured a dissolution-reprecipitation mechanism. Percolation columns in combination with a model biofilm can thus be used to study weathering in closed systems. Columns can easily be filled with different minerals and biofilms, the effluent as well as grains can be collected after long-term exposure under axenic conditions and easily analysed.
Lateral diffusion and percolation in membranes.
Sung, Bong June; Yethiraj, Arun
2006-06-01
An algorithm based on Voronoi tessellation and percolation theory is presented to study the diffusion of model membrane components (solutes) in the plasma membrane. The membrane is modeled as a two-dimensional space with integral membrane proteins as static obstacles. The Voronoi diagram consists of vertices, which are equidistant from three matrix obstacles, joined by edges. An edge between two vertices is said to be connected if solute particles can pass directly between the two regions. The percolation threshold, pc, determined using this passage criterion is pc approximately equal to 0.53. This is smaller than if the connectivity of edges were assigned randomly, in which case the percolation threshold pr=2/3, where p is the fraction of connected edges. Molecular dynamics simulations show that diffusion is determined by percolation of clusters of edges. PMID:16803348
Simulation of Urban Runoff Non-point Source Pollution Load and Analysis on Its Influencing Factors
NASA Astrophysics Data System (ADS)
Li, R.; Ruan, X.
2013-12-01
As the point source pollution control has advanced, the proportion of urban non-point pollution caused by rainfall in urban water pollution is increasing. For quantitative evaluation of non-point source pollution in urban rivers and to study their influencing factors, this study takes the inner Qinhuai River in Nanjing as the study area. The non-point source pollution load simulation model of the study area was built based on the Storm Water Management Model (SWMM), and was calibrated using the real-time monitoring data of rainfall and the outlet of the pipes during a short duration rainfall in 2011. TSS, CODMn, TN and TP were selected as the major pollution load indicators to quantitatively assess the rainfall runoff and non-point source pollution of 328.2ha confluence area of inner Qinhuai River, emphatically probe into the variation of the rainfall runoff and non-point source pollution in response to variability in underlying surface and drainage pipes. The results show that: (1) the pollution load concentration in the outlet of the popes increases initially and then decreases, the peak concentration appears at 5~15minutes after the effluent. The concentration of TN and TP appears apparent randomness and fluctuation due to the spatial-temporal uncertainty of the distribution of the non-point source pollution. The maximum flow into the river, the total runoff, the total output of TSS, CODMn, TN and TP during a typical year rainfall in two years return period are 19.67m3/s, 81.74×103m3, 2318.59kg, 1598.08kg, 476.09kg and 24.24kg, respectively. (2)The percentage of impervious underlying surface, the slope of the underlying surface, the percentage of no depression of the impervious underlying surface and the roughness of the pipes, which are the sensitive parameters of the model, have an significant impact on the runoff and pollution load in the outlet of the pipes. Urban rainfall runoff and non-point source pollution can be reduced by reducing the percentage of
SEARCH FOR ASTROPHYSICAL NEUTRINO POINT SOURCES AT SUPER-KAMIOKANDE
Thrane, E.; Abe, K.; Hayato, Y.; Iida, T.; Ikeda, M.; Kameda, J.; Kobayashi, K.; Koshio, Y.; Miura, M.; Moriyama, S.; Nakahata, M.; Nakayama, S.; Obayashi, Y.; Ogawa, H.; Sekiya, H.; Shiozawa, M.; Suzuki, Y.; Takeda, A.; Takenaga, Y.; Takeuchi, Y.
2009-10-10
It has been hypothesized that large fluxes of neutrinos may be created in astrophysical 'cosmic accelerators'. The primary background for a search for astrophysical neutrinos comes from atmospheric neutrinos, which do not exhibit the pointlike directional clustering that characterizes a distant astrophysical signal. We perform a search for neutrino point sources using the upward-going muon data from three phases of operation (SK-I, SK-II, and SK-III) spanning 2623 days of live time taken from 1996 April 1 to 2007 August 11. The search looks for signals from suspected galactic and extragalactic sources, transient sources, and uncataloged sources. While we find interesting signatures from two objects-RX J1713.7-3946 (97.5% CL) and GRB 991004D (95.3% CL)-these signatures lack compelling statistical significance given trial factors. We set limits on the flux and fluence of neutrino point sources above energies of 1.6 GeV.
Fluid flow into vertical fractures from a point source
Clark, P.E.; Zhu, Q.
1995-03-01
Flow into a fracture from a point source recently has been the focus of attention in the petroleum industry. The suggestion has been made that, in this flow configuration, convection (gravity-driven flow) would dominate Stokes`-type settling for determining final proppant distribution. The theory is that when a dense fluid flows into a fracture filled with a less dense fluid from a point source, the density of the fluid will force it to the bottom of the fracture. This clearly happens when the two fluids have low viscosity. However, viscosity of both the fluid in the fracture and the displacing fluid and nonuniformities in the fracture influence displacement process significantly. Results presented in this study clearly show the effects of viscosity and fracture nonuniformity on the convective settling mechanism.
2011 Radioactive Materials Usage Survey for Unmonitored Point Sources
Sturgeon, Richard W.
2012-06-27
This report provides the results of the 2011 Radioactive Materials Usage Survey for Unmonitored Point Sources (RMUS), which was updated by the Environmental Protection (ENV) Division's Environmental Stewardship (ES) at Los Alamos National Laboratory (LANL). ES classifies LANL emission sources into one of four Tiers, based on the potential effective dose equivalent (PEDE) calculated for each point source. Detailed descriptions of these tiers are provided in Section 3. The usage survey is conducted annually; in odd-numbered years the survey addresses all monitored and unmonitored point sources and in even-numbered years it addresses all Tier III and various selected other sources. This graded approach was designed to ensure that the appropriate emphasis is placed on point sources that have higher potential emissions to the environment. For calendar year (CY) 2011, ES has divided the usage survey into two distinct reports, one covering the monitored point sources (to be completed later this year) and this report covering all unmonitored point sources. This usage survey includes the following release points: (1) all unmonitored sources identified in the 2010 usage survey, (2) any new release points identified through the new project review (NPR) process, and (3) other release points as designated by the Rad-NESHAP Team Leader. Data for all unmonitored point sources at LANL is stored in the survey files at ES. LANL uses this survey data to help demonstrate compliance with Clean Air Act radioactive air emissions regulations (40 CFR 61, Subpart H). The remainder of this introduction provides a brief description of the information contained in each section. Section 2 of this report describes the methods that were employed for gathering usage survey data and for calculating usage, emissions, and dose for these point sources. It also references the appropriate ES procedures for further information. Section 3 describes the RMUS and explains how the survey results are
Percolation in a nanotube-polymer system and its lumped-circuit modeling
Tuncer, Enis; Vaia, Richard A; Arlen, Michael Jeffrey
2010-01-01
Electrical properties of composites composed of polyurethane polymer and multi-walled nanotubes are reported. Samples with different nanotube volume fractions are prepared, and an impedance spectroscopy technique in the frequency range from 10 mHz to 10 MHz is used to characterize the properties of the samples. It is observed that the resistivity of the mixture can be varied widely, from {approx}10 M{Omega}m to {approx}1 {Omega}m, just by slightly altering the volume fraction of nanotubes. A lumped-circuit model illustrated that the micro-scale morphology between nanotube-clusters influences the resistive relaxation in the composite system. The investigations show that the presented binary mixture has a potential to be utilized in conductive electrical components (flexible electrodes), electromagnetic shielding, and electrostatic and field grading materials for electronic and high voltage insulation technologies.
Percolation in a nanotube-polymer system and its lumped-circuit modeling
NASA Astrophysics Data System (ADS)
Tuncer, Enis; Vaia, Richard A.; Arlen, Michael
2010-09-01
Electrical properties of composites composed of polyurethane polymer and multi-walled nanotubes are reported. Samples with different nanotube volume fractions are prepared, and an impedance spectroscopy technique in the frequency range from 10 mHz to 10 MHz is used to characterize the properties of the samples. It is observed that the resistivity of the mixture can be varied widely, from ∼10 MΩm to ∼1 Ωm, just by slightly altering the volume fraction of nanotubes. A lumped-circuit model illustrated that the micro-scale morphology between nanotube-clusters influences the resistive relaxation in the composite system. The investigations show that the presented binary mixture has a potential to be utilized in conductive electrical components (flexible electrodes), electromagnetic shielding, and electrostatic and field grading materials for electronic and high voltage insulation technologies.
Lunar occultations of IRAS point sources, 1986-1990
NASA Technical Reports Server (NTRS)
Simon, M.; Chen, W. P.; Cassar, L.
1986-01-01
A complete listing is given for objects in the IRAS Point Source Catalog which will be occulted by the moon over the course of 1986-1990. A total of 14,148 ASCII card images is encompassed by the complete listing of objects having geocentric events during this period. The results contained in this complete listing are illustrated in two of the present tables for the brightest objects at 12 and 100 micron wavelengths.
Algorithm for astronomical, point source, signal to noise ratio calculations
NASA Technical Reports Server (NTRS)
Jayroe, R. R.; Schroeder, D. J.
1984-01-01
An algorithm was developed to simulate the expected signal to noise ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point source signal to noise ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.
Percolation on correlated random networks
NASA Astrophysics Data System (ADS)
Agliari, E.; Cioli, C.; Guadagnini, E.
2011-09-01
We consider a class of random, weighted networks, obtained through a redefinition of patterns in an Hopfield-like model, and, by performing percolation processes, we get information about topology and resilience properties of the networks themselves. Given the weighted nature of the graphs, different kinds of bond percolation can be studied: stochastic (deleting links randomly) and deterministic (deleting links based on rank weights), each mimicking a different physical process. The evolution of the network is accordingly different, as evidenced by the behavior of the largest component size and of the distribution of cluster sizes. In particular, we can derive that weak ties are crucial in order to maintain the graph connected and that, when they are the most prone to failure, the giant component typically shrinks without abruptly breaking apart; these results have been recently evidenced in several kinds of social networks.
The XXL Survey. VI. The 1000 brightest X-ray point sources
NASA Astrophysics Data System (ADS)
Fotopoulou, S.; Pacaud, F.; Paltani, S.; Ranalli, P.; Ramos-Ceja, M. E.; Faccioli, L.; Plionis, M.; Adami, C.; Bongiorno, A.; Brusa, M.; Chiappetti, L.; Desai, S.; Elyiv, A.; Lidman, C.; Melnyk, O.; Pierre, M.; Piconcelli, E.; Vignali, C.; Alis, S.; Ardila, F.; Arnouts, S.; Baldry, I.; Bremer, M.; Eckert, D.; Guennou, L.; Horellou, C.; Iovino, A.; Koulouridis, E.; Liske, J.; Maurogordato, S.; Menanteau, F.; Mohr, J. J.; Owers, M.; Poggianti, B.; Pompei, E.; Sadibekova, T.; Stanford, A.; Tuffs, R.; Willis, J.
2016-06-01
Context. X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). Usually, a combination of deep and wide surveys is necessary to create a complete picture of the population. Deep X-ray surveys provide the faint population at high redshift, while wide surveys provide the rare bright sources. Nevertheless, very wide area surveys often lack the ancillary information available for modern deep surveys. The XXL survey spans two fields of a combined 50 deg2 observed for more than 6Ms with XMM-Newton, occupying the parameter space that lies between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. Aims: This paper marks the first release of the XXL point source catalogue including four optical photometry bands and redshift estimates. Our sample is selected in the 2 - 10 keV energy band with the goal of providing a sizable sample useful for AGN studies. The limiting flux is F2 - 10 keV = 4.8 × 10-14 erg s-1 cm-2. Methods: We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources by means of a likelihood ratio test. We improve upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift category (passive, star forming, starburst, AGN, quasi-stellar objects (QSO)). Additionally, we assign a probability to each source that indicates whether it might be a star or an outlier. We apply Bayesian analysis to model the X-ray spectra assuming a power-law model with the presence of an absorbing medium. Results: We find that the average unabsorbed photon index is ⟨Γ⟩ = 1.85 ± 0.40 while the average hydrogen column density is log ⟨NH⟩ = 21.07 ± 1.2 cm-2. We find no trend of Γ or NH with redshift and a fraction of 26% absorbed sources (log NH> 22) consistent with the literature on bright sources (log
Crossover from percolation to self-organized criticality
NASA Astrophysics Data System (ADS)
Drossel, Barbara; Clar, Siegfried; Schwabl, Franz
1994-10-01
We include immunity against fire into the self-organized critical forest-fire model. When the immunity assumes a critical value, clusters of burnt trees are identical to percolation clusters of random bond percolation. As long as the immunity is below its critical value, the asymptotic critical exponents are those of the original self-organized critical model, i.e., the system performs a crossover from percolation to self-organized criticality. We present a scaling theory and computer simulation results.
Percolation under noise: Detecting explosive percolation using the second-largest component
NASA Astrophysics Data System (ADS)
Viles, Wes; Ginestet, Cedric E.; Tang, Ariana; Kramer, Mark A.; Kolaczyk, Eric D.
2016-05-01
We consider the problem of distinguishing between different rates of percolation under noise. A statistical model of percolation is constructed allowing for the birth and death of edges as well as the presence of noise in the observations. This graph-valued stochastic process is composed of a latent and an observed nonstationary process, where the observed graph process is corrupted by type-I and type-II errors. This produces a hidden Markov graph model. We show that for certain choices of parameters controlling the noise, the classical (Erdős-Rényi) percolation is visually indistinguishable from a more rapid form of percolation. In this setting, we compare two different criteria for discriminating between these two percolation models, based on the interquartile range (IQR) of the first component's size, and on the maximal size of the second-largest component. We show through data simulations that this second criterion outperforms the IQR of the first component's size, in terms of discriminatory power. The maximal size of the second component therefore provides a useful statistic for distinguishing between different rates of percolation, under physically motivated conditions for the birth and death of edges, and under noise. The potential application of the proposed criteria for the detection of clinically relevant percolation in the context of applied neuroscience is also discussed.
Breaking of the site-bond percolation universality in networks
Radicchi, Filippo; Castellano, Claudio
2015-01-01
The stochastic addition of either vertices or connections in a network leads to the observation of the percolation transition, a structural change with the appearance of a connected component encompassing a finite fraction of the system. Percolation has always been regarded as a substrate-dependent but model-independent process, in the sense that the critical exponents of the transition are determined by the geometry of the system, but they are identical for the bond and site percolation models. Here, we report a violation of such assumption. We provide analytical and numerical evidence of a difference in the values of the critical exponents between the bond and site percolation models in networks with null percolation thresholds, such as scale-free graphs with diverging second moment of the degree distribution. We discuss possible implications of our results in real networks, and provide additional insights on the anomalous nature of the percolation transition with null threshold. PMID:26667155
Roots at the percolation threshold.
Kroener, Eva; Ahmed, Mutez Ali; Carminati, Andrea
2015-04-01
The rhizosphere is the layer of soil around the roots where complex and dynamic interactions between plants and soil affect the capacity of plants to take up water. The physical properties of the rhizosphere are affected by mucilage, a gel exuded by roots. Mucilage can absorb large volumes of water, but it becomes hydrophobic after drying. We use a percolation model to describe the rewetting of dry rhizosphere. We find that at a critical mucilage concentration the rhizosphere becomes impermeable. The critical mucilage concentration depends on the radius of the soil particle size. Capillary rise experiments with neutron radiography prove that for concentrations below the critical mucilage concentration water could easily cross the rhizosphere, while above the critical concentration water could no longer percolate through it. Our studies, together with former observations of water dynamics in the rhizosphere, suggest that the rhizosphere is near the percolation threshold, where small variations in mucilage concentration sensitively alter the soil hydraulic conductivity. Is mucilage exudation a plant mechanism to efficiently control the rhizosphere conductivity and the access to water? PMID:25974526
Roots at the percolation threshold
NASA Astrophysics Data System (ADS)
Kroener, Eva; Ahmed, Mutez Ali; Carminati, Andrea
2015-04-01
The rhizosphere is the layer of soil around the roots where complex and dynamic interactions between plants and soil affect the capacity of plants to take up water. The physical properties of the rhizosphere are affected by mucilage, a gel exuded by roots. Mucilage can absorb large volumes of water, but it becomes hydrophobic after drying. We use a percolation model to describe the rewetting of dry rhizosphere. We find that at a critical mucilage concentration the rhizosphere becomes impermeable. The critical mucilage concentration depends on the radius of the soil particle size. Capillary rise experiments with neutron radiography prove that for concentrations below the critical mucilage concentration water could easily cross the rhizosphere, while above the critical concentration water could no longer percolate through it. Our studies, together with former observations of water dynamics in the rhizosphere, suggest that the rhizosphere is near the percolation threshold, where small variations in mucilage concentration sensitively alter the soil hydraulic conductivity. Is mucilage exudation a plant mechanism to efficiently control the rhizosphere conductivity and the access to water?
Percolation in real interdependent networks
NASA Astrophysics Data System (ADS)
Radicchi, Filippo
2015-07-01
The function of a real network depends not only on the reliability of its own components, but is affected also by the simultaneous operation of other real networks coupled with it. Whereas theoretical methods of direct applicability to real isolated networks exist, the frameworks developed so far in percolation theory for interdependent network layers are of little help in practical contexts, as they are suited only for special models in the limit of infinite size. Here, we introduce a set of heuristic equations that takes as inputs the adjacency matrices of the layers to draw the entire phase diagram for the interconnected network. We demonstrate that percolation transitions in interdependent networks can be understood by decomposing these systems into uncoupled graphs: the intersection among the layers, and the remainders of the layers. When the intersection dominates the remainders, an interconnected network undergoes a smooth percolation transition. Conversely, if the intersection is dominated by the contribution of the remainders, the transition becomes abrupt even in small networks. We provide examples of real systems that have developed interdependent networks sharing cores of `high quality’ edges to prevent catastrophic failures.
Low-energy point source searches with IceCube
NASA Astrophysics Data System (ADS)
Euler, Sebastian; Altmann, David; Ström, Rickard
2016-04-01
Due to the overwhelming background of atmospheric muons, the traditional IceCube point source search in the Southern Hemisphere is mainly sensitive to neutrinos with energies above 100TeV. A new approach focuses on events starting inside the instrumented volume. By utilizing different veto techniques we are able to significantly reduce the energy threshold and can now for the first time explore the entire Southern Hemisphere at neutrino energies as low as 100GeV. We present the results of two analyses targeting slightly different energy ranges. Both use one year of data taken with the completed IceCube detector in 2011/12.
NASA Astrophysics Data System (ADS)
Ganjeh-Ghazvini, Mostafa; Masihi, Mohsen; Ghaedi, Mojtaba
2014-07-01
Fluid flow modeling in porous media has many applications in waste treatment, hydrology and petroleum engineering. In any geological model, flow behavior is controlled by multiple properties. These properties must be known in advance of common flow simulations. When uncertainties are present, deterministic modeling often produces poor results. Percolation and Random Walk (RW) methods have recently been used in flow modeling. Their stochastic basis is useful in dealing with uncertainty problems. They are also useful in finding the relationship between porous media descriptions and flow behavior. This paper employs a simple methodology based on random walk and percolation techniques. The method is applied to a well-defined model reservoir in which the breakthrough time distributions are estimated. The results of this method and the conventional simulation are then compared. The effect of the net to gross ratio on the breakthrough time distribution is studied in terms of Shannon entropy. Use of the entropy plot allows one to assign the appropriate net to gross ratio to any porous medium.
A search for point sources of EeV photons
Aab, A.; Abreu, P.; Andringa, S.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Al Samarai, I.; Albuquerque, I. F. M.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Castillo, J. Alvarez; Alvarez-Muñiz, J.; Batista, R. Alves; Ambrosio, M.; Aramo, C.; Aminaei, A.; Anchordoqui, L.; Arqueros, F.; Collaboration: Pierre Auger Collaboration102; and others
2014-07-10
Measurements of air showers made using the hybrid technique developed with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for point sources of EeV photons anywhere in the exposed sky. A multivariate analysis reduces the background of hadronic cosmic rays. The search is sensitive to a declination band from –85° to +20°, in an energy range from 10{sup 17.3} eV to 10{sup 18.5} eV. No photon point source has been detected. An upper limit on the photon flux has been derived for every direction. The mean value of the energy flux limit that results from this, assuming a photon spectral index of –2, is 0.06 eV cm{sup –2} s{sup –1}, and no celestial direction exceeds 0.25 eV cm{sup –2} s{sup –1}. These upper limits constrain scenarios in which EeV cosmic ray protons are emitted by non-transient sources in the Galaxy.
Limitation of point source pesticide pollution: results of bioremediation system.
Spanoghe, P; Maes, A; Steurbaut, W
2004-01-01
Groundwater and surface water is at risk of contamination from the use of some agricultural pesticides. In many circumstances pesticide contamination of water resources is more likely to result from point sources than from diffuse sources following approved application to crops in the field. Such point sources include areas on farms where pesticides are handled, filled into sprayers or where sprayers are washed down. To overcome this way of contamination different kind of bio-remediation systems are nowadays in development. In Flanders, Belgium two pilot plants of bioremediation systems for the in situ retention and/or degradation of pesticides were installed. Both systems were based on the Phytobac concept, a watertight excavation filled with straw, peat, compost and soil. The channel was made in the bottom from plastic foil. All kinds of spray rests were captured by the phytobacs. This study focuses on what level pesticides leach, bio-degrade or are retained by the filling of the phytobac. The soil-properties of the filling were investigated. Pesticide tracers were added for monitoring to both phytobacs. Soil and water samples were taken during one year. Pesticides are retained at least for one month by the filling of the phytobac. Almost no pesticide leached out. In winter hardly any pesticide degradation was observed in the filling of the phytobac. In summer no detectable pesticides were still left in the phytobacs. PMID:15756863
Correcting STIS CCD Point-Source Spectra for CTE Loss
NASA Technical Reports Server (NTRS)
Goudfrooij, Paul; Bohlin, Ralph C.; Maiz-Apellaniz, Jesus
2006-01-01
We review the on-orbit spectroscopic observations that are being used to characterize the Charge Transfer Efficiency (CTE) of the STIS CCD in spectroscopic mode. We parameterize the CTE-related loss for spectrophotometry of point sources in terms of dependencies on the brightness of the source, the background level, the signal in the PSF outside the standard extraction box, and the time of observation. Primary constraints on our correction algorithm are provided by measurements of the CTE loss rates for simulated spectra (images of a tungsten lamp taken through slits oriented along the dispersion axis) combined with estimates of CTE losses for actual spectra of spectrophotometric standard stars in the first order CCD modes. For point-source spectra at the standard reference position at the CCD center, CTE losses as large as 30% are corrected to within approx.1% RMS after application of the algorithm presented here, rendering the Poisson noise associated with the source detection itself to be the dominant contributor to the total flux calibration uncertainty.
Recent advances in percolation theory and its applications
NASA Astrophysics Data System (ADS)
Saberi, Abbas Ali
2015-05-01
Percolation is the simplest fundamental model in statistical mechanics that exhibits phase transitions signaled by the emergence of a giant connected component. Despite its very simple rules, percolation theory has successfully been applied to describe a large variety of natural, technological and social systems. Percolation models serve as important universality classes in critical phenomena characterized by a set of critical exponents which correspond to a rich fractal and scaling structure of their geometric features. We will first outline the basic features of the ordinary model. Over the years a variety of percolation models has been introduced some of which with completely different scaling and universal properties from the original model with either continuous or discontinuous transitions depending on the control parameter, dimensionality and the type of the underlying rules and networks. We will try to take a glimpse at a number of selective variations including Achlioptas process, half-restricted process and spanning cluster-avoiding process as examples of the so-called explosive percolation. We will also introduce non-self-averaging percolation and discuss correlated percolation and bootstrap percolation with special emphasis on their recent progress. Directed percolation process will be also discussed as a prototype of systems displaying a nonequilibrium phase transition into an absorbing state. In the past decade, after the invention of stochastic Löwner evolution (SLE) by Oded Schramm, two-dimensional (2D) percolation has become a central problem in probability theory leading to the two recent Fields medals. After a short review on SLE, we will provide an overview on existence of the scaling limit and conformal invariance of the critical percolation. We will also establish a connection with the magnetic models based on the percolation properties of the Fortuin-Kasteleyn and geometric spin clusters. As an application we will discuss how percolation
Reprint of : Dynamics of a quantum wave emitted by a decaying and evanescent point source
NASA Astrophysics Data System (ADS)
Delgado, F.; Muga, J. G.
2016-08-01
We put forward a model that describes a decaying and evanescent point source of non-interacting quantum waves in 1D. This point-source assumption allows for a simple description that captures the essential aspects of the dynamics of a wave traveling through a classically forbidden region without the need to specify the details of the inner region. The dynamics of the resulting wave is examined and several characteristic times are identified. One of them generalizes the tunneling time-scale introduced by Büttiker and Landauer and it characterizes the arrival of the maximum of the wave function. Diffraction in time and deviations from exponential decay are also studied. Here we show that there exists an optimal injection frequency and detection point for the observation of these two quantum phenomena.
Exploring percolative landscapes: Infinite cascades of geometric phase transitions
NASA Astrophysics Data System (ADS)
Timonin, P. N.; Chitov, Gennady Y.
2016-01-01
The evolution of many kinetic processes in 1+1 (space-time) dimensions results in 2 D directed percolative landscapes. The active phases of these models possess numerous hidden geometric orders characterized by various types of large-scale and/or coarse-grained percolative backbones that we define. For the patterns originated in the classical directed percolation (DP) and contact process we show from the Monte Carlo simulation data that these percolative backbones emerge at specific critical points as a result of continuous phase transitions. These geometric transitions belong to the DP universality class and their nonlocal order parameters are the capacities of corresponding backbones. The multitude of conceivable percolative backbones implies the existence of infinite cascades of such geometric transitions in the kinetic processes considered. We present simple arguments to support the conjecture that such cascades of transitions are a generic feature of percolation as well as of many other transitions with nonlocal order parameters.