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.
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.
Modeling the contribution of point sources and non-point sources to Thachin River water pollution.
Schaffner, Monika; Bader, Hans-Peter; Scheidegger, Ruth
2009-08-15
Major rivers in developing and emerging countries suffer increasingly of severe degradation of water quality. The current study uses a mathematical Material Flow Analysis (MMFA) as a complementary approach to address the degradation of river water quality due to nutrient pollution in the Thachin River Basin in Central Thailand. This paper gives an overview of the origins and flow paths of the various point- and non-point pollution sources in the Thachin River Basin (in terms of nitrogen and phosphorus) and quantifies their relative importance within the system. The key parameters influencing the main nutrient flows are determined and possible mitigation measures discussed. The results show that aquaculture (as a point source) and rice farming (as a non-point source) are the key nutrient sources in the Thachin River Basin. Other point sources such as pig farms, households and industries, which were previously cited as the most relevant pollution sources in terms of organic pollution, play less significant roles in comparison. This order of importance shifts when considering the model results for the provincial level. Crosschecks with secondary data and field studies confirm the plausibility of our simulations. Specific nutrient loads for the pollution sources are derived; these can be used for a first broad quantification of nutrient pollution in comparable river basins. Based on an identification of the sensitive model parameters, possible mitigation scenarios are determined and their potential to reduce the nutrient load evaluated. A comparison of simulated nutrient loads with measured nutrient concentrations shows that nutrient retention in the river system may be significant. Sedimentation in the slow flowing surface water network as well as nitrogen emission to the air from the warm oxygen deficient waters are certainly partly responsible, but also wetlands along the river banks could play an important role as nutrient sinks. PMID:19501876
An optoacoustic point source for acoustic scale model measurements.
Bolaños, Javier Gómez; Pulkki, Ville; Karppinen, Pasi; Hæggström, Edward
2013-04-01
A massless acoustic source is proposed for scale model work. This source is generated by focusing a pulsed laser beam to rapidly heat the air at the focal point. This produces an expanding small plasma ball which generates a sonic impulse that may be used as an acoustic point source. Repeatability, frequency response, and directivity of the source were measured to show that it can serve as a massless point source. The impulse response of a rectangular space was determined using this type of source. A good match was found between the predicted and the measured impulse responses of the space.
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.
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.
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.
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
Pollutant runoff from non-point sources and its estimation by runoff models.
Noguchi, M; Hiwatashi, T; Mizuno, Y; Minematsu, M
2002-01-01
In order to attain a sound and sustainable water environment, it is important to carry out the environmental management of the watershed. For this purpose, knowledge on the pollutant runoff mechanism from non-point sources becomes very important especially under rainy conditions. At Isahaya, Nagasaki, Japan, a big project of construction of sea-dyke and reclamation is now going on, so reducing the pollutant runoff, especially from non-point sources, becomes more important. Some runoff models of rainwater are developed to predict the rate of pollutant loads from the non-point sources, and their results are compared with each other to investigate the accuracy of prediction. In this paper, runoff analysis of both rainwater and pollutants has been carried out using three models: the tank model, the kinematic wave (K-W) model, and a model using the digital elevation model (DEM). For precise estimation, it becomes necessary to identify the parameters included in these models. Here, total nitrogen has been considered as pollutants, and detachment rates are evaluated, correlated with a class of land use, soil type, and moisture content. Finally, it has been shown that pollutant runoff from non-point sources can be predicted fairly well, identifying the model parameter appropriately.
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.
Point source modeling of matched case–control data with multiple disease subtypes
Li, Shi; Mukherjee, Bhramar; Batterman, Stuart
2015-01-01
In this paper, we propose nonlinear distance-odds models investigating elevated odds around point sources of exposure, under a matched case-control design where there are subtypes within cases. We consider models analogous to the polychotomous logit models and adjacent-category logit models for categorical outcomes and extend them to the nonlinear distance-odds context. We consider multiple point sources as well as covariate adjustments. We evaluate maximum likelihood, profile likelihood, iteratively reweighted least squares, and a hierarchical Bayesian approach using Markov chain Monte Carlo techniques under these distance-odds models. We compare these methods using an extensive simulation study and show that with multiple parameters and a nonlinear model, Bayesian methods have advantages in terms of estimation stability, precision, and interpretation. We illustrate the methods by analyzing Medicaid claims data corresponding to the pediatric asthma population in Detroit, Michigan, from 2004 to 2006. PMID:22826092
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.
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.
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.
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.
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
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...
Equivalence of several generalized percolation models on networks
NASA Astrophysics Data System (ADS)
Miller, Joel C.
2016-09-01
In recent years, many variants of percolation have been used to study network structure and the behavior of processes spreading on networks. These include bond percolation, site percolation, k -core percolation, bootstrap percolation, the generalized epidemic process, and the Watts threshold model (WTM). We show that—except for bond percolation—each of these processes arises as a special case of the WTM, and bond percolation arises from a small modification. In fact "heterogeneous k -core percolation," a corresponding "heterogeneous bootstrap percolation" model, and the generalized epidemic process are completely equivalent to one another and the WTM. We further show that a natural generalization of the WTM in which individuals "transmit" or "send a message" to their neighbors with some probability less than 1 can be reformulated in terms of the WTM, and so this apparent generalization is in fact not more general. Finally, we show that in bond percolation, finding the set of nodes in the component containing a given node is equivalent to finding the set of nodes activated if that node is initially activated and the node thresholds are chosen from the appropriate distribution. A consequence of these results is that mathematical techniques developed for the WTM apply to these other models as well, and techniques that were developed for some particular case may in fact apply much more generally.
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.
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
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.
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
Exact Solution of a Drop-Push Model for Percolation
NASA Astrophysics Data System (ADS)
Majumdar, Satya N.; Dean, David S.
2002-08-01
Motivated by a computer science algorithm known as ``linear probing with hashing,'' we study a new type of percolation model whose basic features include a sequential ``dropping'' of particles on a substrate followed by their transport via a ``pushing'' mechanism. Our exact solution in one dimension shows that, unlike the ordinary random percolation model, the drop-push model has nontrivial spatial correlations generated by the dynamics itself. The critical exponents in the drop-push model are also different from those of the ordinary percolation. The relevance of our results to computer science is pointed out.
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.
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.
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.
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.
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.
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
Gaussian model of explosive percolation in three and higher dimensions
NASA Astrophysics Data System (ADS)
Schrenk, K. J.; Araújo, N. A. M.; Herrmann, H. J.
2011-10-01
The Gaussian model of discontinuous percolation, recently introduced by Araújo and Herrmann [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.035701 105, 035701 (2010)], is numerically investigated in three dimensions, disclosing a discontinuous transition. For the simple cubic lattice, in the thermodynamic limit we report a finite jump of the order parameter J=0.415±0.005. The largest cluster at the threshold is compact, but its external perimeter is fractal with fractal dimension dA=2.5±0.2. The study is extended to hypercubic lattices up to six dimensions and to the mean-field limit (infinite dimension). We find that, in all considered dimensions, the percolation transition is discontinuous. The value of the jump in the order parameter, the maximum of the second moment, and the percolation threshold are analyzed, revealing interesting features of the transition and corroborating its discontinuous nature in all considered dimensions. We also show that the fractal dimension of the external perimeter, for any dimension, is consistent with the one from bridge percolation and establish a lower bound for the percolation threshold of discontinuous models with a finite number of clusters at the threshold.
Bourque, C P; Arp, P A
1996-01-01
Dispersion and subsequent deposition of SO(2) downwind from a stationary point source are affected by several transport processes: buoyancy at the source, advection, and air turbulence en route from the source to the area of impact. In this paper, SO(2) transport processes are simulated by way of Lagrangian air parcel trajectory simulations. In these simulations, the source releases air parcels in puffs. The calculations cover both daytime and night-time conditions and take into account: (i) solar geometry, (ii) diurnal variations of wind speed and air turbulence, (iii) resistance to the transfer of SO(2) from the air to the land, and (iv) flat terrain. Deposition to the forest is determined by calculating the rate of SO(2) flux from individual air parcels to the land according to the parcel's velocity and an assumed air-to-surface SO(2) transfer coefficient. Daily cumulative SO(2) deposition rates are calculated by summing the simulated diffusional fluxes of SO(2) from air to land over each simulated time step. Daily cumulative SO(2) amounts are calculated for downwind distances from 0 to 42 km, for smokestack heights from 30 to 200 m, and for each day of the year according to historical year-round and local weather patterns representative of days with neutral conditions and days with transitions from stable to unstable conditions. Annual per hectare rates of SO(2) deposition are calculated by way of Monte Carlo simulations, according to historical patterns for daily wind, atmospheric stability, and precipitation. These simulations are calibrated for the area surrounding a coal-burning power generator at Grand Lake in south-central New Brunswick, Canada. Calculated concentrations for SO(2) were similar to those obtained with a mobile SO(2) detection unit and a SO(2)-monitoring unit 42 km NE from the emission source. Cumulative SO(2) deposition rates were reasonably similar to those obtained with PbO(2) sulfation plates. A detailed comparison revealed topography
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
Yao, Hong; Qian, Xin; Yin, Hong; Gao, Hailong; Wang, Yulei
2015-02-01
Point source pollution is one of the main threats to regional environmental health. Based on a water quality model, a methodology to assess the regional risk of point source pollution is proposed. The assessment procedure includes five parts: (1) identifying risk source units and estimating source emissions using Monte Carlo algorithms; (2) observing hydrological and water quality data of the assessed area, and evaluating the selected water quality model; (3) screening out the assessment endpoints and analyzing receptor vulnerability with the Choquet fuzzy integral algorithm; (4) using the water quality model introduced in the second step to predict pollutant concentrations for various source emission scenarios and analyzing hazards of risk sources; and finally, (5) using the source hazard values and receptor vulnerability scores to estimate overall regional risk. The proposed method, based on the Water Quality Analysis Simulation Program (WASP), was applied in the region of the Taipu River, which is in the Taihu Basin, China. Results of source hazard and receptor vulnerability analysis allowed us to describe aquatic ecological, human health, and socioeconomic risks individually, and also integrated risks in the Taipu region, from a series of risk curves. Risk contributions of sources to receptors were ranked, and the spatial distribution of risk levels was presented. By changing the input conditions, we were able to estimate risks for a range of scenarios. Thus, the proposed procedure may also be used by decisionmakers for long-term dynamic risk prediction.
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.)
Modeling approach to assess the impact of point source air pollutant emission on vegetation
Dauzvardis, P.A.; Veselka, T.; Ballou, S.W.
1980-09-01
Dose-response effects of gases emitted from industrial sources on vegetation were investigated. Some of the techniques available for vegetation damage assessments are outlined in this report. A new method of assessing potential chronic and visible damage has been developed and is described. Predictive models that will estimate plant damage in terms of decreased yields and the geographic area exposed are developed. An example is presented in which the modeling technique is used to determine the possible occurrence of yield reductions in crops grown near coal-fired power plants. (RJC)
NASA Astrophysics Data System (ADS)
Hansen, Scott K.; Vesselinov, Velimir V.
2016-10-01
We develop empirically-grounded error envelopes for localization of a point contamination release event in the saturated zone of a previously uncharacterized heterogeneous aquifer into which a number of plume-intercepting wells have been drilled. We assume that flow direction in the aquifer is known exactly and velocity is known to within a factor of two of our best guess from well observations prior to source identification. Other aquifer and source parameters must be estimated by interpretation of well breakthrough data via the advection-dispersion equation. We employ high performance computing to generate numerous random realizations of aquifer parameters and well locations, simulate well breakthrough data, and then employ unsupervised machine optimization techniques to estimate the most likely spatial (or space-time) location of the source. Tabulating the accuracy of these estimates from the multiple realizations, we relate the size of 90% and 95% confidence envelopes to the data quantity (number of wells) and model quality (fidelity of ADE interpretation model to actual concentrations in a heterogeneous aquifer with channelized flow). We find that for purely spatial localization of the contaminant source, increased data quantities can make up for reduced model quality. For space-time localization, we find similar qualitative behavior, but significantly degraded spatial localization reliability and less improvement from extra data collection. Since the space-time source localization problem is much more challenging, we also tried a multiple-initial-guess optimization strategy. This greatly enhanced performance, but gains from additional data collection remained limited.
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.
Hansen, Scott K.; Vesselinov, Velimir Valentinov
2016-09-09
We develop empirically-grounded error envelopes for localization of a point contamination release event in the saturated zone of a previously uncharacterized heterogeneous aquifer into which a number of plume-intercepting wells have been drilled. We assume that flow direction in the aquifer is known exactly and velocity is known to within a factor of two of our best guess from well observations prior to source identification. Other aquifer and source parameters must be estimated by interpretation of well breakthrough data via the advection-dispersion equation. We employ high performance computing to generate numerous random realizations of aquifer parameters and well locations, simulatemore » well breakthrough data, and then employ unsupervised machine optimization techniques to estimate the most likely spatial (or space-time) location of the source. Tabulating the accuracy of these estimates from the multiple realizations, we relate the size of 90% and 95% confidence envelopes to the data quantity (number of wells) and model quality (fidelity of ADE interpretation model to actual concentrations in a heterogeneous aquifer with channelized flow). We find that for purely spatial localization of the contaminant source, increased data quantities can make up for reduced model quality. For space-time localization, we find similar qualitative behavior, but significantly degraded spatial localization reliability and less improvement from extra data collection. Since the space-time source localization problem is much more challenging, we also tried a multiple-initial-guess optimization strategy. Furthermore, this greatly enhanced performance, but gains from additional data collection remained limited.« less
Correlation function of four spins in the percolation model
NASA Astrophysics Data System (ADS)
Dotsenko, Vladimir S.
2016-10-01
By using the Coulomb gas technics we calculate the four-spin correlation function in the percolation q → 1 limit of the Potts model. It is known that the four-point functions define the actual fusion rules of a particular model. In this respect, we find that fusion of two spins, of dimension Δσ =5/96, produce a new channel, in the 4-point function, which is due to the operator with dimension Δ = 5 / 8.
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Nikkhoo, M.; Walter, T. R.; Lundgren, P.; Prats-Iraola, P.
2015-12-01
Ground deformation at active volcanoes is one of the key precursors of volcanic unrest, monitored by InSAR and GPS techniques at high spatial and temporal resolution, respectively. Modelling of the observed displacements establishes the link between them and the underlying subsurface processes and volume change. The so-called Mogi model and the rectangular dislocation are two commonly applied analytical solutions that allow for quick interpretations based on the location, depth and volume change of pressurized spherical cavities and planar intrusions, respectively. Geological observations worldwide, however, suggest elongated, tabular or other non-equidimensional geometries for the magma chambers. How can these be modelled? Generalized models such as the Davis's point ellipsoidal cavity or the rectangular dislocation solutions, are geometrically limited and could barely improve the interpretation of data. We develop a new analytical artefact-free solution for a rectangular dislocation, which also possesses full rotational degrees of freedom. We construct a kinematic model in terms of three pairwise-perpendicular rectangular dislocations with a prescribed opening only. This model represents a generalized point source in the far field, and also performs as a finite dislocation model for planar intrusions in the near field. We show that through calculating the Eshelby's shape tensor the far-field displacements and stresses of any arbitrary triaxial ellipsoidal cavity can be reproduced by using this model. Regardless of its aspect ratios, the volume change of this model is simply the sum of the volume change of the individual dislocations. Our model can be integrated in any inversion scheme as simply as the Mogi model, profiting at the same time from the advantages of a generalized point source. After evaluating our model by using a boundary element method code, we apply it to ground displacements of the 2015 Calbuco eruption, Chile, observed by the Sentinel-1
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.
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
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
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.
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)
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.
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
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.
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.
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...
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
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.
Lattice percolation approach to 3D modeling of tissue aging
NASA Astrophysics Data System (ADS)
Gorshkov, Vyacheslav; Privman, Vladimir; Libert, Sergiy
2016-11-01
We describe a 3D percolation-type approach to modeling of the processes of aging and certain other properties of tissues analyzed as systems consisting of interacting cells. Lattice sites are designated as regular (healthy) cells, senescent cells, or vacancies left by dead (apoptotic) cells. The system is then studied dynamically with the ongoing processes including regular cell dividing to fill vacant sites, healthy cells becoming senescent or dying, and senescent cells dying. Statistical-mechanics description can provide patterns of time dependence and snapshots of morphological system properties. The developed theoretical modeling approach is found not only to corroborate recent experimental findings that inhibition of senescence can lead to extended lifespan, but also to confirm that, unlike 2D, in 3D senescent cells can contribute to tissue's connectivity/mechanical stability. The latter effect occurs by senescent cells forming the second infinite cluster in the regime when the regular (healthy) cell's infinite cluster still exists.
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.
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
Effect of root distribution on modelling percolation and groundwater evapotranspiration
NASA Astrophysics Data System (ADS)
Orellana, F. A.; Daly, E.
2011-12-01
In groundwater-dependent ecosystems, vegetation is able to extend its root system deep in the soil to wet zones strongly influenced by the water table. As a result, either part or all transpired water is supplied by groundwater. In many models, roots are assumed to be submerged in groundwater; however, this is not the case for many species. We analised the effect of using different root systems in estimating evapotranspiration and recharge in groundwater-dependent ecosystems. A 2D finite-elements model was developed using the program SEEPW to simulate the interaction between saturated and unsaturated soil in a riparian area. The domain of the model consists in a soil layer 8 meters deep and 100 meters long, with a constant water table outside of the vegetated area and a variable water table in the opposite side, controlled by the stage level of a river. Five root distributions were simulated: homogeneous in the saturated zone, homogeneous in the unsaturated zone, concentrated in the top layer of the soil, concentrated in the capillary fringe and a dimorphic distribution. The water-table level in the vegetated zone is always close to three meter depth; therefore, the direct evaporation from groundwater is neglected. Preliminary results show a significant impact of differing root distributions on the modelled water-table levels. The daily pattern of transpiration produces daily fluctuations in the water-table level, whose amplitude is higher when the total transpiration is uptaken from groundwater, and is considerably smaller when the root system is only in the unsaturated zone. These differences are also reflected in the net recharge and groundwater evapotranspiration. When transpiration comes directly from groundwater, most of the infiltrated water reaches the water table. However, when roots are distributed in the unsaturated zone, they are able to intercep part of the infiltration, with a decrease in percolation. Likewise, groundwater evapotranspiration reduces
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.
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...
Gao, X P; Li, G N; Li, G R; Zhang, C
2015-01-01
The Dragon lake diversion channel (DLDC) is the only river that recharges Dragon Lake, an artificial lake in China. This paper examines the main factors influencing water quality by investigating point source and non-point source pollutants along the main route. Based on the complicated system of rivers and desilting basins, a three-dimensional water quality model using environmental fluid dynamics code (EFDC) was developed. The model of DLDC was calibrated and verified using observed data. The error ranges of river water level, total phosphorus, total nitrogen and chemical oxygen demand were within 5%, 10%, 16% and 20%, respectively, all of which meet the precision requirement. The model was employed to predict the concentrations of pollutants in the main stream under current pollution loads within a year and a flood lasting for 24 hours. The results revealed that the main pollution sources that influence the water quality of waterways were the point sources followed by the non-point pollution sources. Water quality improved when large water quantities were delivered and this trend can be described as dilution. The water quality of the Dongfeng main channel meets the requirement; however, the water quality of the Dongfeng River is somewhat poor, and the water quality of the Wei River is seriously contaminated. To address these problems, we suggest that the Dongfeng River and Wei River adopt a culvert under its riverbeds.
Grain Boundary Percolation Modeling of Fission Gas Release in Oxide Fuels
Paul C. Millett; Michael R. Tonks; S. B. Biner
2012-05-01
We present a new approach to fission gas release modeling in oxide fuels based on grain boundary network percolation. The method accounts for variability in the bubble growth and coalescence rates on individual grain boundaries, and the resulting effect on macroscopic fission gas release. Two-dimensional representa- tions of fuel pellet microstructures are considered, and the resulting gas release rates are compared with traditional two-stage Booth models, which do not account for long-range percolation on grain boundary net- works. The results show that the requirement of percolation of saturated grain boundaries can considerably reduce the total gas release rates, particularly when gas resolution is considered.
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.
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...
Percolation of the site random-cluster model by Monte Carlo method
NASA Astrophysics Data System (ADS)
Wang, Songsong; Zhang, Wanzhou; Ding, Chengxiang
2015-08-01
We propose a site random-cluster model by introducing an additional cluster weight in the partition function of the traditional site percolation. To simulate the model on a square lattice, we combine the color-assignation and the Swendsen-Wang methods to design a highly efficient cluster algorithm with a small critical slowing-down phenomenon. To verify whether or not it is consistent with the bond random-cluster model, we measure several quantities, such as the wrapping probability Re, the percolating cluster density P∞, and the magnetic susceptibility per site χp, as well as two exponents, such as the thermal exponent yt and the fractal dimension yh of the percolating cluster. We find that for different exponents of cluster weight q =1.5 , 2, 2.5 , 3, 3.5 , and 4, the numerical estimation of the exponents yt and yh are consistent with the theoretical values. The universalities of the site random-cluster model and the bond random-cluster model are completely identical. For larger values of q , we find obvious signatures of the first-order percolation transition by the histograms and the hysteresis loops of percolating cluster density and the energy per site. Our results are helpful for the understanding of the percolation of traditional statistical models.
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.
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.
NASA Astrophysics Data System (ADS)
Korneta, W.; Pytel, Z.
1988-04-01
Bond percolation in films with simple cubic structure is considered. It is assumed that the probability of a bond being present between nearest-neighbor sites depends on the distances to surfaces. Based on the relation between the Potts model and the bond percolation model, and using the mean-field approximation, the phase diagram and profiles of the percolation probability have been obtained.
Mesoscale modeling of intergranular bubble percolation in nuclear fuels
Millett, Paul C.; Tonks, Michael; Biner, S. B.
2012-04-15
Phase-field simulations are used to examine the variability of intergranular fission gas bubble growth and percolation on uranium dioxide grain boundaries on a mesoscopic length scale. Three key parameters are systematically varied in this study: the contact angle (or dihedral angle) defining the bubble shape, the initial bubble density on the grain boundary plane, and the ratio of the gas diffusivity on the grain boundary versus the grain interiors. The simulation results agree well with previous experimental data obtained for bubble densities and average bubble areas during coalescence events. Interestingly, the rate of percolation is found to be highly variable, with a large dependency on the contact angle and the initial bubble density and little-to-no dependency on the grain boundary gas diffusivity.
MESOSCALE MODELING OF INTERGRANULAR BUBBLE PERCOLATION IN NUCLEAR FUELS
Paul C. Millett; Michael Tonks; S. B. Biner
2012-04-01
Phase-field simulations are used to examine the variability of intergranular fission gas bubble growth and percolation on uranium dioxide grain boundaries on a mesoscopic length scale. Three key parameters are systematically varied in this study: the contact angle (or dihedral angle) defining the bubble shape, the initial bubble density on the grain boundary plane, and the ratio of the gas diffusivity on the grain boundary versus the grain interiors. The simulation results agree well with previous experimental data obtained for bubble densities and average bubble areas during coalescence events. Interestingly, the rate of percolation is found to be highly variable, with a large dependency on the contact angle and the initial bubble density, and little-to-no dependency on the grain boundary gas diffusivity.
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
NASA Astrophysics Data System (ADS)
Kourakos, G.; Harter, T.
2013-12-01
Non-point source pollution on groundwater of agricultural regions is an alarming issue of global importance. The very large response times of contaminants which may vary from decades to centuries, require mitigation measures to be based on reliable modeling. Here we present a novel computational framework to assess and evaluate the dynamic, spatio-temporally distributed linkages between non-point sources above a groundwater basin and groundwater discharges to wells, streams, or other compliance discharge surfaces (CDSs) within a groundwater basin. The modeling framework allows for efficient evaluation of NPS pollution scenarios and of their short- and long-term effects on pollutant exceedance probabilities in CDSs. We apply the model to simulate 100 years of nitrate pollution at high resolution in a 2 million hectare semi-arid, irrigated agricultural region with a large diversity of crops, but also natural lands and urban areas, and highly heterogeneous, temporally variable loading landscape in the Southern California Central Valley. Results show that the timing of nitrate breakthrough in wells is significantly controlled by aquifer recharge and pumping rates in NPS areas and by the effective porosity of the aquifer system. MLast the model predictions are compared against a highly heterogeneous, spatio-temporally varying in space and time database of historic nitrate records and an attempt is made to compute the spatial distribution of nitrate half-life due to denitrification.
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.
Economopoulos, A P
1991-01-01
A pollutant dispersion model is developed, allowing fast evaluation of the maximum credible 1-h average concentration on any given ground-level receptor, along with the corresponding critical meteorological conditions (wind speed and stability class) for stacks with buoyant plumes in urban or rural areas. Site-specific meteorological data are not required, as the computed concentrations are maximized against all credible combinations of wind speed, stability class, and mixing height. The analysis is based on the dispersion relations of Pasquill-Gifford and Briggs for rural and urban settings, respectively, the buoyancy induced dispersion correlation of Pasquill, the wind profile exponent values suggested by Irwin, the buoyant plume rise relations of Briggs, as well as the Benkley and Schulman's model for the minimum mixing heights. The model is particularly suited for air pollution management studies, as it allows fast screening of the maximum impact on any selected receptor and evaluation of the ways to have this impact reduced. It is also suited for regulatory purposes, as it can be used to define the minimum stack size requirements for a given source as a function of the exit gas volume and temperature, the pollutant emission rates and their hourly concentration standards, as well as the source location relative to sensitive receptors.
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.
NASA Astrophysics Data System (ADS)
Coletti, Cristian F.; Miranda, Daniel; Mussini, Filipe
2016-02-01
In this work we study the Poisson Boolean model of percolation in locally compact Polish metric spaces and we prove the invariance of subcritical and supercritical phases under mm-quasi-isometries. More precisely, we prove that if a metric space M is mm-quasi-isometric to another metric space N and the Poisson Boolean model in M exhibits any of the following: (a) a subcritical phase; (b) a supercritical phase; or (c) a phase transition, then respectively so does the Poisson Boolean model of percolation in N. Then we use these results in order to understand the phase transition phenomenon in a large family of metric spaces. Indeed, we study the Poisson Boolean model of percolation in the context of Riemannian manifolds, in a large family of nilpotent Lie groups and in Cayley graphs. Also, we prove the existence of a subcritical phase in Gromov spaces with bounded growth at some scale.
Lee, MiSeon; Park, GeunAe; Park, MinJi; Park, JongYoon; Lee, JiWan; Kim, SeongJoon
2010-01-01
This study evaluated the reduction effect of non-point source pollution by applying best management practices (BMPs) to a 1.21 km2 small agricultural watershed using a SWAT (Soil and Water Assessment Tool) model. Two meter QuickBird land use data were prepared for the watershed. The SWAT was calibrated and validated using daily streamflow and monthly water quality (total phosphorus (TP), total nitrogen (TN), and suspended solids (SS)) records from 1999 to 2000 and from 2001 to 2002. The average Nash and Sutcliffe model efficiency was 0.63 for the streamflow and the coefficients of determination were 0.88, 0.72, and 0.68 for SS, TN, and TP, respectively. Four BMP scenarios viz. the application of vegetation filter strip and riparian buffer system, the regulation of Universal Soil Loss Equation P factor, and the fertilizing control amount for crops were applied and analyzed.
NASA Astrophysics Data System (ADS)
Nozu, A.; Wakai, A.
2015-12-01
In a previous study (Nozu, 2012, Zisin; Nozu, 2013, AGU), we developed a new simplified source model (the pseudo point-source model) to explain strong ground motions from a mega-thrust earthquake. In the model, the source spectrum associated with the rupture of a subevent is modeled and it is assumed to follow the omega-square model. By multiplying the source spectrum with the path effect and the site amplification factor, the Fourier amplitude at a target site can be obtained. Then, combining it with the Fourier phase characteristics of a smaller event, the time history of strong ground motions from the subevent can be calculated. Finally, by summing up contributions from the subevents, strong ground motions from the entire rupture can be obtained. The pseudo point-source model developed for the Tohoku earthquake consisted of nine subevents. The model could reproduce the velocity waveforms and the Fourier spectra quite accurately at sites close to the source region along the east coast of Japan from Iwate to Ibaraki. In this study, we investigated the applicability of the model to larger distances. In particular, we simulated strong ground motions in the Kanto Region including Tokyo. In the application of our model to larger distances, careful consideration of the path effect was required. The original path model used in our previous study can be expressed as P(f)=(1/r)*exp(-πfr/Qβ) and Q=114f0.92(Satoh and Tatsumi, 2002). However, there are two factors not included in the original path model that could potentially lead to underestimation at larger distances: (1) the geometrical spreading term inversely proportional to the square root of distance at larger distances, and (2) the lower bound of the Q value at lower frequencies (e.g., Aki, 1980). The simulation based on the original path model resulted in underestimation of Fourier spectra at larger distances as shown in Figure (a). In this case the error was an increasing function with the distance. Then we
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.
Li, Kai; Zeng, Fan-Tang; Fang, Huai-Yang; Lin, Shu
2013-11-01
Based on the Long-term Hydrological Impact Assessment (L-THIA) model, the effect of land use and rainfall change on nitrogen and phosphorus loading of non-point sources in Shiqiao river watershed was analyzed. The parameters in L-THIA model were revised according to the data recorded in the scene of runoff plots, which were set up in the watershed. The results showed that the distribution of areas with high pollution load was mainly concentrated in agricultural land and urban land. Agricultural land was the biggest contributor to nitrogen and phosphorus load. From 1995 to 2010, the load of major pollutants, namely TN and TP, showed an obviously increasing trend with increase rates of 17.91% and 25.30%, respectively. With the urbanization in the watershed, urban land increased rapidly and its area proportion reached 43.94%. The contribution of urban land to nitrogen and phosphorus load was over 40% in 2010. This was the main reason why pollution load still increased obviously while the agricultural land decreased greatly in the past 15 years. The rainfall occurred in the watershed was mainly concentrated in the flood season, so the nitrogen and phosphorus load of the flood season was far higher than that of the non-flood season and the proportion accounting for the whole year was over 85%. Pearson regression analysis between pollution load and the frequency of different patterns of rainfall demonstrated that rainfall exceeding 20 mm in a day was the main rainfall type causing non-point source pollution.
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.
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.
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.
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).
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.
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.
Faro, J; Velasco, S
1993-11-22
In immune network models it is assumed that membrane immunoglobulin (mIg) crosslinking leads to B-cell activation. To analyse further the implications of this idea, a model of B-cell activation by ligand-induced mIg crosslinking in the absence of cell-to-cell interactions is proposed. The present model, based on a simple crosslinking mechanism previously proposed by other authors, assumes that activation of B-cells is possible once crosslinks of mIgs percolate and that percolation of crosslinks can only happen within a relatively short time tau. Given a lattice (regular or not), a molecular cluster is said to percolate or to become a percolating cluster if it spans the whole lattice (this is the case, for instance, of a polymer in a gel phase). From this model of B-cell activation we define the activation function fa (LK) as the fraction of B-cells activated after tau minutes of interaction with a ligand at concentration L and with affinity K. Numerical calculations show that, for current estimates of kinetic constants involved in the interaction of a given ligand with a B-cell clone, the activation function fa shifts when k-, the dissociation rate constant, is varied below 10(-3) s-1, this shift being linearly proportional to the variation of k-. This result contradicts and, therefore, challenges the assumption in immune network models that the activation function is identical for all ligands. This is important because the behaviour of at least some of those immune network models is quite sensitive to the relative values of the activation function thresholds.
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
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.
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.
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.
Monte Carlo modeling of the fiber curliness effect on percolation of conductive composites
NASA Astrophysics Data System (ADS)
Ma, H. M.; Gao, X.-L.; Tolle, T. Benson
2010-02-01
A three-dimensional (3D) Monte Carlo model is developed to study the fiber curliness effect on the percolation threshold of a composite filled with electrically conductive curved fibers. These fibers are simulated as zigzag-shaped fibers that are randomly positioned in the composite, forming a 3D random network. The simulation results show that the fiber curliness can significantly affect the percolation threshold: the more curved the fibers, the higher the threshold. The results also reveal an exponential relationship between the threshold and the fiber aspect ratio: the higher the aspect ratio, the lower the threshold. These predicted trends agree well with existing experimental and simulation results based on straight fibers or curved fibers with simpler shapes.
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.
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.
Cont-Bouchaud Percolation Model Including Tobin Tax
NASA Astrophysics Data System (ADS)
Ehrenstein, Gudrun
The Tobin tax is an often discussed method to tame speculation and get a source of income. The discussion is especially heated when the financial markets are in crisis. In this article we refer to the foreign exchange markets. The Tobin tax should be a small international tax affecting all currency transactions and thus consequently reducing destabilizing speculations. In this way this tax should take over a control function. By including the Tobin tax in the microscopic model of Cont and Bouchaud one finds that this tax could be the right method to control foreign exchange operations and to get a good source of income.
Can the glass transition in bulk polymers be modeled by percolation picture?
Yilmaz, Yaşar; Kaya, Demet; Pekcan, Onder
2004-09-01
Recent observations (Eur. Phys. J. E 9, 135 (2002)) showed that the vitrification process, which sets in during the linear bulk methyl methacrylate (MMA) polymerization carried out below glass transition temperatures, can be modelled by static percolation picture. To generalize this observation for different kind of bulk linear or crosslinked polymers not enough data are present in the literature. To cover partly this deficit we studied the glass transition of MMA and styrene (Sty) crosslinking copolymerization in varying ratios of MMA and Sty. Both the fluorescence intensity I and the lifetime tau of pyrene (Py) used as a nanosecond in situ fluoroprobe were monitored during the gelation time. Both I and tau increase dramatically as a result of the reduced mobility of the probes trapped in the "glassy" regions, appearing near the glass transition point. The average size of the glassy regions just below, and the strength of the infinite network formed upon the connection of the glassy regions above the glass transition point tg obey power law relations. The data around tg were interpreted on the basis of the percolation theory and we observed that the corresponding exponents gamma and beta give static percolation values independent of the polymer composition.
NASA Astrophysics Data System (ADS)
Lorenz, Christian D.; Ziff, Robert M.
2001-02-01
Precise values for the critical threshold for the three-dimensional "Swiss cheese" continuum percolation model have been calculated using extensive Monte Carlo simulations. These simulations used a growth algorithm and memory blocking scheme similar to what we used previously in three-dimensional lattice percolation. The simulations yield a value for the critical number density nc=0.652 960±0.000 005, which confirms recent work but extends the precision by two significant figures.
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.
Pore Level Modeling of Immiscible Drainage: Validation in the Invasion Percolation and DLA Limits
Ferer, M.V.; Bromhal, G.S.; Smith, D.H.
2003-03-01
Motivated by a wide-range of applications from ground water remediation to carbon dioxide sequestration and by difficulties in reconciling experiments with previous modeling, we have developed a pore-level model of two-phase flow in porous media. We have attempted to make our model as physical and as reliable as possible, incorporating both capillary effects and viscous effects. After a detailed discussion of the model, we validate it in the very different limits of zero capillary number and zero-viscosity ratio. Invasion percolation (IP) models the flow in the limit of zero capillary number; results from our model show detailed agreement with results from IP, for small capillary numbers. Diffusion limited aggregation (DLA) models the flow in the limit of zero-viscosity ratio; flow patterns from our model have the same fractal dimension as patterns from DLA for small viscosity ratios.
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.
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
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)
NASA Astrophysics Data System (ADS)
Ghanbarian, Behzad; Sahimi, Muhammad; Daigle, Hugh
2016-07-01
Accurate prediction of the relative permeability to water under partially saturated condition has broad applications and has been studied intensively since the 1940s by petroleum, chemical, and civil engineers, as well as hydrologists and soil scientists. Many models have been developed for this purpose, ranging from those that represent the pore space as a bundle of capillary tubes, to those that utilize complex networks of interconnected pore bodies and pore throats with various cross-section shapes. In this paper, we propose an approach based on the effective-medium approximation (EMA) and percolation theory in order to predict the water relative permeability. The approach is general and applicable to any type of porous media. We use the method to compute the water relative permeability in porous media whose pore-size distribution follows a power law. The EMA is invoked to predict the relative permeability from the fully saturated pore space to some intermediate water saturation that represents a crossover from the EMA to what we refer to as the "critical region." In the critical region below the crossover water saturation Swx, but still above the critical water saturation Swc (the residual saturation or the percolation threshold of the water phase), the universal power law predicted by percolation theory is used to compute the relative permeability. To evaluate the accuracy of the approach, data for 21 sets of undisturbed laboratory samples were selected from the UNSODA database. For 14 cases, the predicted relative permeabilities are in good agreement with the data. For the remaining seven samples, however, the theory underestimates the relative permeabilities. Some plausible sources of the discrepancy are discussed.
Some Properties of Weight Factors arising in Low-Density Series Expansion for Percolation Models
NASA Astrophysics Data System (ADS)
Bhatti, Faqir M; Abu, Nur Azman
2002-01-01
Let F(G) be any additive property of a simple graph such that F(G)=F(G1)+F(G2), where G is the series combination of graphs G1 and G2. The weight factor W(G) which is based on F(G) arises in the low-density series expansion techniques for percolation models as W(G)=\\sumG\\prime\\subseteq G(-1)e-e^{\\prime}F(G\\prime)η(G\\prime), where η(G\\prime) is the indicator that G\\prime cover-able sub-graph or without dangling ends. The purpose of this paper is to prove the weight factor formula for additive property of F as W(G)=d(G2)W(G1)+d(G1)W(G2), where d(G1) are d(G2) the d-weight for graphs G1 and G2 respectively. This result will be more simplified in the case of Directed Percolation Models using Mobius function property. A new few formulas for the resistive weight factors are also derived for a graph, which is parallel combination of n edges.
Directed percolation in a two-dimensional stochastic fire-diffuse-fire model.
Timofeeva, Y; Coombes, S
2004-12-01
We establish, from extensive numerical experiments, that the two dimensional stochastic fire-diffuse-fire model belongs to the directed percolation universality class. This model is an idealized model of intracellular calcium release that retains both the discrete nature of calcium stores and the stochastic nature of release. It is formed from an array of noisy threshold elements that are coupled only by a diffusing signal. The model supports spontaneous release events that can merge to form spreading circular and spiral waves of activity. The critical level of noise required for the system to exhibit a nonequilibrium phase transition between propagating and nonpropagating waves is obtained by an examination of the local slope delta (t) of the survival probability Pi(t) proportional exp [-delta(t)] for a wave to propagate for a time t .
Pore-level modeling of drainage: crossover from invasion percolation fingering to compact flow.
Ferer, M; Bromhal, Grant S; Smith, Duane H
2003-05-01
A pore-level model of drainage, which has been quantitatively validated, is used to study the effect of increased injection rate (i.e., increased capillary number) upon the flow, with matched-viscosity fluids. For small enough capillary number, the flows from the model correctly reproduce the flows from the invasion percolation with trapping (IPWT) model. As the capillary number is increased, the early-time flows mimic those of the IPWT-model, but then deviate towards compact flow at a characteristic time that decreases as the capillary number increases. That is, the larger the capillary number, the sooner the flow crosses over from IPWT flows towards compact (linear) flows. PMID:12786157
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 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
2015-09-01
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 Magnetoelectric Effects in Ferrite/Piezoelectric Bulk Composite
NASA Astrophysics Data System (ADS)
Petrov, V. M.; Bichurin, M. I.; Tuskov, D. S.; Srinivasan, G.
2006-03-01
A bulk composite consisting of ferrite-ferroelectric phases shows magnetoelectric (ME) effects that are product properties of the magnetostrictive deformation and piezoelectric charge generation. Bulk composites with strong ME effects are desirable over layered samples due to superior mechanical strength. Here we discuss a percolation approach for modeling the ME effect in bulk composite [1]. We calculated percolation threshold corresponding to structural phase transition of bulk composites from the state with ME interactions to a state with no ME interactions.Expressions for longitudinal and transverse low-frequency ME voltage coefficients have been obtained. Volume fractions corresponding to peak ME voltage coefficients are given. We obtained a piezoelectric volume fraction of 0.45 for maximum ME effect in bulk samples of lead zirconate titanate and nickel-cobalt ferrite. These estimates are in excellent agreement with data. supported by a grant from the NSF. [1] V. M. Petrov, M. I. Bichurin, V. M. Laletin, N. Paddubnaya, and G. Srinivasan, Magnetoelectric Interaction Phenomena in Crystals-NATO Science Series II. Vol. 164, Eds. M. Fiebig, V. V. Eremenko, and I. E. Chupis (Kluwer Academic Publishers, London, 2004), p.65-70.
Self-organization with equilibration: A model for the intermediate phase in rigidity percolation
NASA Astrophysics Data System (ADS)
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 [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.
Aging and percolation dynamics in a Non-Poissonian temporal network model
NASA Astrophysics Data System (ADS)
Moinet, Antoine; Starnini, Michele; Pastor-Satorras, Romualdo
2016-08-01
We present an exhaustive mathematical analysis of the recently proposed Non-Poissonian Activity Driven (NoPAD) model [Moinet et al., Phys. Rev. Lett. 114, 108701 (2015), 10.1103/PhysRevLett.114.108701], a temporal network model incorporating the empirically observed bursty nature of social interactions. We focus on the aging effects emerging from the non-Poissonian dynamics of link activation, and on their effects on the topological properties of time-integrated networks, such as the degree distribution. Analytic expressions for the degree distribution of integrated networks as a function of time are derived, exploring both limits of vanishing and strong aging. We also address the percolation process occurring on these temporal networks, by computing the threshold for the emergence of a giant connected component, highlighting the aging dependence. Our analytic predictions are checked by means of extensive numerical simulations of the NoPAD model.
Aging and percolation dynamics in a Non-Poissonian temporal network model.
Moinet, Antoine; Starnini, Michele; Pastor-Satorras, Romualdo
2016-08-01
We present an exhaustive mathematical analysis of the recently proposed Non-Poissonian Activity Driven (NoPAD) model [Moinet et al., Phys. Rev. Lett. 114, 108701 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.108701], a temporal network model incorporating the empirically observed bursty nature of social interactions. We focus on the aging effects emerging from the non-Poissonian dynamics of link activation, and on their effects on the topological properties of time-integrated networks, such as the degree distribution. Analytic expressions for the degree distribution of integrated networks as a function of time are derived, exploring both limits of vanishing and strong aging. We also address the percolation process occurring on these temporal networks, by computing the threshold for the emergence of a giant connected component, highlighting the aging dependence. Our analytic predictions are checked by means of extensive numerical simulations of the NoPAD model. PMID:27627326
Variational Formulas and Cocycle solutions for Directed Polymer and Percolation Models
NASA Astrophysics Data System (ADS)
Georgiou, Nicos; Rassoul-Agha, Firas; Seppäläinen, Timo
2016-09-01
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.
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...
NASA Astrophysics Data System (ADS)
Li, Tianhong; Bai, Fengjiao; Han, Peng; Zhang, Yuanyan
2016-11-01
Urban sprawl is a major driving force that alters local and regional hydrology and increases non-point source pollution. Using the Bao'an District in Shenzhen, China, a typical rapid urbanization area, as the study area and land-use change maps from 1988 to 2014 that were obtained by remote sensing, the contributions of different land-use types to NPS pollutant production were assessed with a localized long-term hydrologic impact assessment (L-THIA) model. The results show that the non-point source pollution load changed significantly both in terms of magnitude and spatial distribution. The loads of chemical oxygen demand, total suspended substances, total nitrogen and total phosphorus were affected by the interactions between event mean concentration and the magnitude of changes in land-use acreages and the spatial distribution. From 1988 to 2014, the loads of chemical oxygen demand, suspended substances and total phosphorus showed clearly increasing trends with rates of 132.48 %, 32.52 % and 38.76 %, respectively, while the load of total nitrogen decreased by 71.52 %. The immigrant population ratio was selected as an indicator to represent the level of rapid urbanization and industrialization in the study area, and a comparison analysis of the indicator with the four non-point source loads demonstrated that the chemical oxygen demand, total phosphorus and total nitrogen loads are linearly related to the immigrant population ratio. The results provide useful information for environmental improvement and city management in the study area.
Message passing theory for percolation models on multiplex networks with link overlap
NASA Astrophysics Data System (ADS)
Cellai, Davide; Dorogovtsev, Sergey N.; Bianconi, Ginestra
2016-09-01
Multiplex networks describe a large variety of complex systems, including infrastructures, transportation networks, and biological systems. Most of these networks feature a significant link overlap. It is therefore of particular importance to characterize the mutually connected giant component in these networks. Here we provide a message passing theory for characterizing the percolation transition in multiplex networks with link overlap and an arbitrary number of layers M . Specifically we propose and compare two message passing algorithms that generalize the algorithm widely used to study the percolation transition in multiplex networks without link overlap. The first algorithm describes a directed percolation transition and admits an epidemic spreading interpretation. The second algorithm describes the emergence of the mutually connected giant component, that is the percolation transition, but does not preserve the epidemic spreading interpretation. We obtain the phase diagrams for the percolation and directed percolation transition in simple representative cases. We demonstrate that for the same multiplex network structure, in which the directed percolation transition has nontrivial tricritical points, the percolation transition has a discontinuous phase transition, with the exception of the trivial case in which all the layers completely overlap.
NASA Astrophysics Data System (ADS)
Moradi Kurdestany, Jamshid; Satpathy, Sashi
Motivated by the recent progress in understanding of Mott insulators away from half filling, observed in many perovskite oxides, we study the metal-insulator transition in the Hubbard-Holstein model, which contains both the Coulomb and the electron-lattice (Jahn Teller) interactions by using the Gutzwiller variational method. We find that strong electron-lattice Interaction leads to phase separation, which however can be frustrated due to the long-range Coulomb interaction, resulting in a mixed phase consisting of puddles of metallic phases embedded in an insulating matrix. When the dopant concentration exceeds a threshold value xc , the metallic part forms a percolating network leading to metallic conduction. Depending on the strength of the electron-lattice interaction, xc can be of the order of 0.05 - 0.20 or so, which is the typical value observed in the perovskites.
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.
Pore Size Distributions Inferred from Modified Inversion Percolation Modeling of Drainage Curves
NASA Astrophysics Data System (ADS)
Dralus, D. E.; Wang, H. F.; Strand, T. E.; Glass, R. J.; Detwiler, R. L.
2005-12-01
Experiments have been conducted of drainage in sand packs. At equilibrium, the interface between the fluids forms a saturation transition fringe where the saturation decreases monotonically with height. This behavior was observed in a 1-inch thick pack of 20-30 sand contained front and back within two thin, 12-inch-by-24-inch glass plates. The translucent chamber was illuminated from behind by a bank of fluorescent bulbs. Acquired data were in the form of images captured by a CCD camera with resolution on the grain scale. The measured intensity of the transmitted light was used to calculate the average saturation at each point in the chamber. This study used a modified invasion percolation (MIP) model to simulate the drainage experiments to evaluate the relationship between the saturation-versus-height curve at equilibrium and the pore size distribution associated with the granular medium. The simplest interpretation of a drainage curve is in terms of a distribution of capillary tubes whose radii reproduce the the observed distribution of rise heights. However, this apparent radius distribution obtained from direct inversion of the saturation profile did not yield the assumed radius distribution. Further investigation demonstrated that the equilibrium height distribution is controlled primarily by the Bond number (ratio of gravity to capillary forces) with some influence from the width of the pore radius distribution. The width of the equilibrium fringe is quantified in terms of the ratio of Bond number to the standard deviation of the pore throat distribution. The normalized saturation-vs-height curves exhibit a power-law scaling behavior consistent with both Brooks-Corey and Van Genuchten type curves. Fundamental tenets of percolation theory were used to quantify the relationship between the apparent and actual radius distributions as a function of the mean coordination number and of the ratio of Bond number to standard deviation, which was supported by both MIP
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)
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.
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/
Critical behavior of a tumor growth model: Directed percolation with a mean-field flavor
NASA Astrophysics Data System (ADS)
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 , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.85.010901 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⊥, 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.
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
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.
Bohman-Frieze-Wormald model on the lattice, yielding a discontinuous percolation transition
NASA Astrophysics Data System (ADS)
Schrenk, K. J.; Felder, A.; Deflorin, S.; Araújo, N. A. M.; D'Souza, R. M.; Herrmann, H. J.
2012-03-01
The BFW model introduced by Bohman, Frieze, and Wormald [Random Struct. Algorithms1042-983210.1002/rsa.20038, 25, 432 (2004)], and recently investigated in the framework of discontinuous percolation by Chen and D'Souza [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.115701 106, 115701 (2011)], is studied on the square and simple-cubic lattices. In two and three dimensions, we find numerical evidence for a strongly discontinuous transition. In two dimensions, the clusters at the threshold are compact with a fractal surface of fractal dimension df=1.49±0.02. On the simple-cubic lattice, distinct jumps in the size of the largest cluster are observed. We proceed to analyze the tree-like version of the model, where only merging bonds are sampled, for dimension two to seven. The transition is again discontinuous in any considered dimension. Finally, the dependence of the cluster-size distribution at the threshold on the spatial dimension is also investigated.
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)
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).
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.
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.
Chesapeake Bay Program: Point-Source Atlas
Macknis, J.
1988-08-01
The atlas contains pollutant loadings from Chesapeake Bay watershed municipal and industrial point sources drawn from the Chesapeake Bay Program computerized data base. Nutrient and toxic discharges are included. Effluent data are averaged for the calendar year 1985. Detailed information is presented in 23 tables and 14 figures.
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.
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
Percolation technique for galaxy clustering
NASA Technical Reports Server (NTRS)
Klypin, Anatoly; Shandarin, Sergei F.
1993-01-01
We study percolation in mass and galaxy distributions obtained in 3D simulations of the CDM, C + HDM, and the power law (n = -1) models in the Omega = 1 universe. Percolation statistics is used here as a quantitative measure of the degree to which a mass or galaxy distribution is of a filamentary or cellular type. The very fast code used calculates the statistics of clusters along with the direct detection of percolation. We found that the two parameters mu(infinity), characterizing the size of the largest cluster, and mu-squared, characterizing the weighted mean size of all clusters excluding the largest one, are extremely useful for evaluating the percolation threshold. An advantage of using these parameters is their low sensitivity to boundary effects. We show that both the CDM and the C + HDM models are extremely filamentary both in mass and galaxy distribution. The percolation thresholds for the mass distributions are determined.
Flow rates of ions in waters percolating through a model ecosystem with forest trees.
Seufert, G
1990-01-01
From 1983-88 the long-term effects of low level exposure with O(3), SO(2) and simulated acid rain on mineral cycling in model ecosystems with spruce, fir and beech seedlings were investigated. Systems consisting of open-top chambers built above lysimeters were protected against the intrusion of ambient rain and dust. As part of the investigations on mineral cycling the fluxes of elements with water input and output of the canopy and soil compartments are presented. During the 5 year duration of the experiment, pronounced effects on canopy deposition and cation leaching were observed. Most noticeable were throughfall enrichment with sulfate through dry deposition of SO(2) as influenced by duration of needlewetting and factors promoting SO(2) oxidation. Depending on sulfur deposition, leaching of calcium, magnesium, manganese, zinc and ammonium from canopies was elevated, in total leading to enhanced soil input of acid. After 15 months, the water percolating the soils in the lysimeters of these treatments was acidified, with elevated flowrates of sulfate, manganese, calcium and magnesium. The results on canopy/soil leaching are compared to those from old conifer stands in the field.
A stratified percolation model for saturated and unsaturated flow through natural fractures
Pyrak-Nolte, L.J.; Cook, N.G.W.; Myer, L.R.
1990-01-01
The geometry of the asperities of contact between the two surfaces of a fracture and of the adjacent void spaces determines fluid flow through a fracture and the mechanical deformation across a fracture. Heuristically we have developed a stratified continuum percolation model to describe this geometry based on a fractal construction that includes scale invariance and correlation of void apertures. Deformation under stress is analyzed using conservation of rock volume to correct for asperity interpenetration. Single phase flow is analyzed using a critical path along which the principal resistance is a result of laminar flow across the critical neck in this path. Results show that flow decreases with apparent aperture raised to a variable power greater than cubic, as is observed in flow experiments on natural fractures. For two phases, flow of the non-wetting phase is likewise governed by the critical neck along the critical path of largest aperture but flow of the wetting phase is governed by tortuosity. 17 refs., 10 figs.
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.
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
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
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.
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
Percolation in sign-symmetric random fields: topological aspects and numerical modeling
Milovanov; Zimbardo
2000-07-01
The topology of percolation in random scalar fields psi(x) with sign symmetry [i.e., that the statistical properties of the functions psi(x) and -psi(x) are identical] is analyzed. Based on methods of general topology, we show that the zero set psi(x)=0 of the n-dimensional (n>/=2) sign-symmetric random field psi(x) contains a (connected) percolating subset under the condition |nablapsi(x)| not equal0 everywhere except in domains of negligible measure. The fractal geometry of percolation is analyzed in more detail in the particular case of the two-dimensional (n=2) fields psi(x). The improved Alexander-Orbach conjecture [Phys. Rev. E 56, 2437 (1997)] is applied analytically to obtain estimates of the main fractal characteristics of the percolating fractal sets generated by the horizontal "cuts," psi(x)=h, of the field psi(x). These characteristics are the Hausdorff fractal dimension of the set, D, and the index of connectivity, straight theta. We advocate an unconventional approach to studying the geometric properties of fractals, which involves methods of homotopic topology. It is shown that the index of connectivity, straight theta, of a fractal set is the topological invariant of this set, i.e., it remains unchanged under the homeomorphic deformations of the fractal. This issue is explicitly used in our study to find the Hausdorff fractal dimension of the single isolevels of the field psi(x), as well as the related geometric quantities. The results obtained are analyzed numerically in the particular case when the random field psi(x) is given by a fractional Brownian surface whose topological properties recover well the main assumptions of our consideration.
NASA Astrophysics Data System (ADS)
Xu, C. Q.; Yan, S. L.
2016-10-01
Within the effective field theory, we investigate critical behaviors of transverse crystal field and bimodal magnetic field mixed spin-1/2 and spin-1 Ising model with bond dilution or percolation threshold on a simple cubic lattice. A-type double tricritical points and zigzag reentrant phenomenon can be found at pure bond and large bimodal magnetic field status. The ordered phase is impaired sharply due to bond dilution. The positive transverse crystal field can induce ordered phase at ordinary bond percolation threshold. The bimodal magnetic field can suppress the induced ordered phase and form a series of closed ordered regions. An extraordinary bond percolation threshold is determined, at which the induced ordered phase vanishes completely. The different effects of bimodal magnetic field and bond percolation threshold on induced ordered phase are discussed.
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 .
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.
Entanglement Theories: Packing vs. Percolation
NASA Astrophysics Data System (ADS)
Wool, Richard
2007-03-01
There are two emergent theories of polymer entanglements, the Packing Model (Fetters, Lohse, Graessley, Milner, Whitten, ˜'98) and the Percolation Model (Wool ˜'93). The Packing model suggests that the entanglement molecular weight Me is determined by Me = K p^3, where the packing length parameter p = V/R^2 in which V is the volume of the chain (V=M/ρNa), R is the end-to end vector of the chain, and K 357 ρNa, is an empirical constant. The Percolation model states that an entanglement network develops when the number of chains per unit area σ, intersecting any load bearing plane, is equal to 3 times the number of chain segments (1/a cross-section), such that when 3aσ =1 at the percolation threshold, Me 31 MjC∞, in which Mj is the step molecular weight and C∞ is the characteristic ratio. There are no fitting parameters in the Percolation model. The Packing model predicts that Me decreases rapidly with chain stiffness, as Me˜1/C∞^3, while the Percolation model predicts that Me increases with C∞, as Me˜C∞. The Percolation model was found to be the correct model based on computer simulations (M. Bulacu et al) and a re-analysis of the Packing model experimental data. The Packing model can be derived from the Percolation model, but not visa versa, and reveals a surprising accidental relation between C∞ and Mj in the front factor K. This result significantly impacts the interpretation of the dynamics of rheology and fracture of entangled polymers.
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.
Systematic identification of IRAS point sources
NASA Technical Reports Server (NTRS)
Savage, A.; Clowes, R. G.; Macgillivray, H. T.; Wolstencroft, R. D.; Leggett, S. K.; Puxley, P. J.
1987-01-01
A large scale program was initiated to identify IRAS point sources. At ROE the ideal facilities are at hand to undertake such a large program, viz. the rapid scanning capabilities of the COSMOS measuring machine to exploit the depth and resolution of the U.K. Schmidt Telescope J survey plates. Sources in 44 Schmidt plate areas were identified including 1300 sources and covering 1100 square degrees. The identification comprise 700 galaxy identifications and 600 stellar identifications. There are also about 40 sources with no obvious identification but which can be most easily explained by cirrus, confusion between two sources or sources just outside the 2 sigma error box. A major aim with the galaxy identification is to provide a data base from which sound statistical analyses can be made. Accurate blue magnitudes and morphological classifications for each identification were produced.
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
NASA Astrophysics Data System (ADS)
Zhang, Renquan; Wei, Wei; Guo, Binghui; Zhang, Yang; Zheng, Zhiming
2013-03-01
Recently, the modified BFW model on random graphs [W. Chen, R.M. D’Souza, Phys. Rev. Lett. 106 (2011) 115701], which shows a discontinuous percolation transition with multiple giant components, has attracted much attention from physicists and statisticians. In this paper, by establishing the evolution equations on the modified BFW model, the evolution process and steady-states on both random graphs and finite-dimensional lattices are analyzed. On a random graph, by varying the edge accepted rate α, the system stabilizes in a steady-state with different numbers of giant components. Moreover, a close correspondence is built between the values of α and the number of giant components in steady-states, the efficiency of which is verified by the numerical simulations. Then, the sizes of giant components for different evolution strategies can be obtained by solving some constraints derived from the evolution equations. Meanwhile, a similar analysis is expanded to finite-dimensional lattices, and we find the BFW (α) model on a finite-dimensional lattice has different steady-states from those on a random graph, but they have the same evolution mechanism. The analysis of the evolution process and steady-state is of great help to explain the properties of discontinuous percolation and the role of nonlocality.
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)
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.
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.
Explosive Percolation Transition is Actually Continuous
NASA Astrophysics Data System (ADS)
da Costa, R. A.; Dorogovtsev, S. N.; Goltsev, A. V.; Mendes, J. F. F.
2010-12-01
Recently a discontinuous percolation transition was reported in a new “explosive percolation” problem for irreversible systems [D. Achlioptas, R. M. D’Souza, and J. Spencer, Science 323, 1453 (2009)SCIEAS0036-807510.1126/science.1167782] in striking contrast to ordinary percolation. We consider a representative model which shows that the explosive percolation transition is actually a continuous, second order phase transition though with a uniquely small critical exponent of the percolation cluster size. We describe the unusual scaling properties of this transition and find its critical exponents and dimensions.
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.
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)
Pfeffer, Michael; Kumar, Praveen; Eibl, Oliver
2016-11-01
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)
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.
Distinguishing dark matter from unresolved point sources in the Inner Galaxy with photon statistics
Lee, Samuel K.; Lisanti, Mariangela; Safdi, Benjamin R. E-mail: mlisanti@princeton.edu
2015-05-01
Data from the Fermi Large Area Telescope suggests that there is an extended excess of GeV gamma-ray photons in the Inner Galaxy. Identifying potential astrophysical sources that contribute to this excess is an important step in verifying whether the signal originates from annihilating dark matter. In this paper, we focus on the potential contribution of unresolved point sources, such as millisecond pulsars (MSPs). We propose that the statistics of the photons—in particular, the flux probability density function (PDF) of the photon counts below the point-source detection threshold—can potentially distinguish between the dark-matter and point-source interpretations. We calculate the flux PDF via the method of generating functions for these two models of the excess. Working in the framework of Bayesian model comparison, we then demonstrate that the flux PDF can potentially provide evidence for an unresolved MSP-like point-source population.
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.
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
Watersheds and Explosive percolation
NASA Astrophysics Data System (ADS)
Herrmann, Hans J.; Araujo, Nuno A. M.
The recent work by Achlioptas, D'Souza, and Spencer opened up the possibility of obtaining a discontinuous (explosive) percolation transition by changing the stochastic rule of bond occupation. Despite the active research on this subject, several questions still remain open about the leading mechanism and the properties of the system. We review the largest cluster and the Gaussian models recently introduced. We show that, to obtain a discontinuous transition it is solely necessary to control the size of the largest cluster, suppressing the growth of a cluster di_ering significantly, in size, from the average one. As expected for a discontinuous transition, a Gaussian cluster-size distribution and compact clusters are obtained. The surface of the clusters is fractal, with the same fractal dimension of the watershed line.
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.
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.
NASA Astrophysics Data System (ADS)
Tang, Y. B.; Li, M.; Bernabe, Y.
2014-12-01
We modeled the electrical transport behavior of dual-pore carbonate rocks in this paper. Based on experimental data of a carbonate reservoir in China, we simply considered the low porosity samples equivalent to the matrix (micro-pore system) of the high porosity samples. For modeling the bimodal porous media, we considered that the matrix is homogeneous and interconnected. The connectivity and the pore size distribution of macro-pore system are varied randomly. Both pore systems are supposed to act electrically in parallel, connected at the nodes, where the fluid exchange takes place, an approach previously used by Bauer et al. (2012). Then, the effect of the properties of matrix, the pore size distribution and connectivity of macro-pore system on petrophysical properties of carbonates can be investigated. We simulated electrical current through networks in three-dimensional simple cubic (SC) and body-center cubic (BCC) with different coordination numbers and different pipe radius distributions of macro-pore system. Based on the simulation results, we found that the formation factor obeys a "universal" scaling relationship (i.e. independent of lattice type), 1/F∝eγz, where γ is a function of the normalized standard deviation of the pore radius distribution of macro-pore system and z is the coordination number of macro-pore system. This relationship is different from the classic "universal power law" in percolation theory. A formation factor model was inferred on the basis of the scaling relationship mentioned above and several scale-invariant quantities (such as hydraulic radius rH and throat length l of macro-pore). Several methods were developed to estimate corresponding parameters of the new model with conventional core analyses. It was satisfactorily tested against experimental data, including some published experimental data. Furthermore, the relationship between water saturation and resistivity in dual-pore carbonates was discussed based on the new 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.
NASA Astrophysics Data System (ADS)
Zadneprovski, B. I.; Klyuev, I. Yu.; Turkov, V. E.
2016-08-01
We have studied the electric conductivity of composites with various carbonaceous fillers (multiwalled carbon nanotubes, colloidal graphite, and amorphous carbon) as a function of the filler content. The widths of critical regions of the percolation transition to the conducting state are determined and the percolation critical exponents are estimated. It is established that there is a tendency to increase in the width of transition region and values of critical exponents when the filler is varied in the following order: carbon nanotubes-colloidal graphite-amorphous carbon.
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.
NASA Astrophysics Data System (ADS)
Hair, Thomas W.; Hedman, Andrew D.
2013-01-01
A model of the spatial emergence of an interstellar civilization into a uniform distribution of habitable systems is presented. The process of emigration is modelled as a three-dimensional probabilistic cellular automaton. An algorithm is presented which defines both the daughter colonies of the original seed vertex and all subsequent connected vertices, and the probability of a connection between any two vertices. The automaton is analysed over a wide set of parameters for iterations that represent up to 250 000 years within the model's assumptions. Emigration patterns are characterized and used to evaluate two hypotheses that aim to explain the Fermi Paradox. The first hypothesis states that interstellar emigration takes too long for any civilization to have yet come within a detectable distance, and the second states that large volumes of habitable space may be left uninhabited by an interstellar civilization and Earth is located in one of these voids.
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}).
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}).
Quantum entanglement percolation
NASA Astrophysics Data System (ADS)
Siomau, Michael
2016-09-01
Quantum communication demands efficient distribution of quantum entanglement across a network of connected partners. The search for efficient strategies for the entanglement distribution may be based on percolation theory, which describes evolution of network connectivity with respect to some network parameters. In this framework, the probability to establish perfect entanglement between two remote partners decays exponentially with the distance between them before the percolation transition point, which unambiguously defines percolation properties of any classical network or lattice. Here we introduce quantum networks created with local operations and classical communication, which exhibit non-classical percolation transition points leading to striking communication advantages over those offered by the corresponding classical networks. We show, in particular, how to establish perfect entanglement between any two nodes in the simplest possible network—the 1D chain—using imperfectly entangled pairs of qubits.
Multipartite entanglement percolation
Perseguers, S.; Cavalcanti, D.; Lapeyre, G. J. Jr.; Lewenstein, M.; Acin, A.
2010-03-15
We present a percolation strategy based on multipartite measurements to propagate entanglement in quantum networks. We consider networks spanned on regular lattices whose bonds correspond to pure but nonmaximally entangled pairs of qubits, with any quantum operation allowed at the nodes. Despite significant effort in the past, improvements over standard (classical) percolation have been found for only a few lattices, often with restrictions on the initial amount of entanglement in the bonds. In contrast, multipartite entanglement percolation outperform the classical percolation protocols, as well as all previously known quantum ones, over the entire range of initial entanglement and for every lattice that we considered. Finally, we briefly show that our ideas also find application in noisy networks.
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.
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
Connecting the vulcanization transition to percolation.
Peng, W; Goldbart, P M; McKane, A J
2001-09-01
The vulcanization transition is addressed via a minimal replica-field-theoretic model. The appropriate long-wavelength behavior of the two- and three-point vertex functions is considered diagrammatically, to all orders in perturbation theory, and identified with the corresponding quantities in the Houghton-Reeve-Wallace field-theoretic approach to the percolation critical phenomenon. Hence, it is shown that percolation theory correctly captures the critical phenomenology of the vulcanization transition associated with the liquid and critical states.
Long-wave phonons in ZnSe-BeSe mixed crystals: Raman scattering and percolation model
NASA Astrophysics Data System (ADS)
Pagès, O.; Ajjoun, M.; Tite, T.; Bormann, D.; Tournié, E.; Rustagi, K. C.
2004-10-01
We extend to longitudinal-optical (LO) phonons the percolation model set for the basic understanding of the atypical transverse-optical (TO) one-bond→two-mode behavior observed by Raman scattering in the Be-Se spectral range of the random Zn1-xBexSe alloy (0⩽x⩽1) , which opens the class of mixed crystals with contrast in the bond stiffness. The study is supported by contour modeling of the TO and LO Raman line shapes. This is achieved via application of the Hon and Faust treatment to a version of the modified-random-element-isodisplacement model generalized to multioscillators. While the TO signal clearly discriminates between Be-Se vibrations within the hard Be -rich region and the soft Zn -rich one, complexity arises in the LO symmetry due to vibration coupling via the 1ong-range longitudinal polarization field. In particular this generates a massive transfer of oscillator strength from the low-frequency (LO-) (hard, soft)-mixed mode to the high-frequency (LO+) one, which results in an apparent LO+ single-mode behavior. Moreover the contrasts between the Zn-Se and Be-Se bond lengths and bond stiffness are proposed to force a Verleur and Barker-like (VB) discrete multimode Raman response from each region. Accordingly LO- and LO+ intramode transfers of oscillator strength superimpose to the LO-→LO+ intermode one. This accounts for the spectacular distortions of the LO+ line shape. On the whole, the puzzling LO behavior can be regarded as the result of a cooperative phenomenon between two discrete assemblies of polar LO phonons, driven by the long-range longitudinal polarization field. Also, the Verleur and Barker description accounts for subtle unexplained behaviors in the TO symmetry. More generally it appears to provide a much attractive area for the discussion of the asymmetries of the TO and LO Raman line shapes in random alloys, as a possible alternative to the much debated spatial correlation model or to internal/external strain effects.
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
[Mathematical simulation of point source average infiltration depth under film hole irrigation].
Sun, Xiu-Juan; Ma, Xiao-Yi; Liu, Ji-Long; Zhan, Guo-Long
2010-03-01
By using RETC and SWMS-3D software, the point source infiltration characteristics of several typical soils under film hole irrigation were simulated, with the infiltration characteristics and related affecting factors analyzed. One simplified point source infiltration model with the parameters opening film hole rate, film hole diameter, soil clay particle content, and soil bulk density was established, and tested by infiltration experiments with the typical soils from Loess Plateau. It was shown that the infiltration coefficient under film hole irrigation increased with increasing opening film hole rate and decreased with increasing film hole diameter and soil clay particle content, while the infiltration index decreased with increasing opening film hole rate and soil clay particle content. This model could simply and accurately reflect the point source infiltration characteristics under film hole irrigation, and credibly determine the infiltration coefficient and index.
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.
Critical exponents of the explosive percolation transition
NASA Astrophysics Data System (ADS)
da Costa, R. A.; Dorogovtsev, S. N.; Goltsev, A. V.; Mendes, J. F. F.
2014-04-01
In a new type of percolation phase transition, which was observed in a set of nonequilibrium models, each new connection between vertices is chosen from a number of possibilities by an Achlioptas-like algorithm. This causes preferential merging of small components and delays the emergence of the percolation cluster. First simulations led to a conclusion that a percolation cluster in this irreversible process is born discontinuously, by a discontinuous phase transition, which results in the term "explosive percolation transition." We have shown that this transition is actually continuous (second order) though with an anomalously small critical exponent of the percolation cluster. Here we propose an efficient numerical method enabling us to find the critical exponents and other characteristics of this second-order transition for a representative set of explosive percolation models with different number of choices. The method is based on gluing together the numerical solutions of evolution equations for the cluster size distribution and power-law asymptotics. For each of the models, with high precision, we obtain critical exponents and the critical point.
Short-time dynamics of percolation observables
Wanzeller, Wanderson G.; Mendes, Tereza; Krein, Gastao
2006-11-15
We consider the critical short-time evolution of magnetic and droplet-percolation order parameters for the Ising model in two and three dimensions, through Monte Carlo simulations with the (local) heat-bath method. We find qualitatively different dynamic behaviors for the two types of order parameters. More precisely, we find that the percolation order parameter does not have a power-law behavior as encountered for the magnetization, but develops a scale (related to the relaxation time to equilibrium) in the Monte Carlo time. We argue that this difference is due to the difficulty in forming large clusters at the early stages of the evolution. Our results show that, although the descriptions in terms of magnetic and percolation order parameters may be equivalent in the equilibrium regime, greater care must be taken to interpret percolation observables at short times. In particular, this concerns the attempts to describe the dynamics of the deconfinement phase transition in QCD using cluster observables.
Atmospheric measurement of point source fossil CO2 emissions
NASA Astrophysics Data System (ADS)
Turnbull, J. C.; Keller, E. D.; Baisden, T.; Brailsford, G.; Bromley, T.; Norris, M.; Zondervan, A.
2014-05-01
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 above ground level. We also determined the surface CO2ff content averaged over several weeks from the 14C 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 ~ one 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 14C sampling strategies.
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?
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
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.
Percolation under noise: Detecting explosive percolation using the second-largest component.
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. PMID:27300904
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.
Percolation and Physical Properties of Rock Salt
NASA Astrophysics Data System (ADS)
Ghanbarzadeh, S.; Hesse, M. A.; Prodanovic, M.
2015-12-01
Textural equilibrium controls the distribution of the liquid phase in many naturally occurring porous materials such as partially molten rocks and alloys, salt-brine and ice-water systems. In these materials, pore geometry evolves to minimize the solid-liquid interfacial energy while maintaining a constant dihedral angle, θ, at solid-liquid contact lines. A characteristic of texturally equilibrated porous media, in the absence of deformation, is that the pore network percolates at any porosity for θ<60° while a percolation threshold exists for θ>60°. However, in ductile polycrystalline materials including rock salt, the balance between surface tension and ductile deformation controls the percolation of fluid pockets along grain corners and edges. Here we show sufficiently rapid deformation can overcome this threshold by elongating and connecting isolated pores by examining a large number of accessible salt samples from deep water Gulf of Mexico. We first confirm the percolation threshold in static laboratory experiments on synthetic salt samples with X-ray microtomography. We then provide field evidence on existence of interconnected pore space in rock salt in extremely low porosities, significantly below the static percolation threshold. Scaling arguments suggest that strain rates in salt are sufficient to overcome surface tension and may allow percolation. We also present the first level-set computations of three-dimensional texturally equilibrated melt networks in realistic rock fabrics. The resulting pore space is used to obtain the effective physical properties of rock, effective electrical conductivity and mechanical properties, with a novel numerical model.
Point source reconstruction principle of linear inverse problems
NASA Astrophysics Data System (ADS)
Terazono, Yasushi; Fujimaki, Norio; Murata, Tsutomu; Matani, Ayumu
2010-11-01
Exact point source reconstruction for underdetermined linear inverse problems with a block-wise structure was studied. In a block-wise problem, elements of a source vector are partitioned into blocks. Accordingly, a leadfield matrix, which represents the forward observation process, is also partitioned into blocks. A point source is a source having only one nonzero block. An example of such a problem is current distribution estimation in electroencephalography and magnetoencephalography, where a source vector represents a vector field and a point source represents a single current dipole. In this study, the block-wise norm, a block-wise extension of the ellp-norm, was defined as the family of cost functions of the inverse method. The main result is that a set of three conditions was found to be necessary and sufficient for block-wise norm minimization to ensure exact point source reconstruction for any leadfield matrix that admit such reconstruction. The block-wise norm that satisfies the conditions is the sum of the cost of all the observations of source blocks, or in other words, the block-wisely extended leadfield-weighted ell1-norm. Additional results are that minimization of such a norm always provides block-wisely sparse solutions and that its solutions form cones in source space.
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 ...
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.
Understanding and predicting deep percolation under surface irrigation
NASA Astrophysics Data System (ADS)
Bethune, M. G.; Selle, B.; Wang, Q. J.
2008-12-01
A lysimeter experiment was conducted in southeastern Australia to quantify the deep percolation response under irrigated pasture to different soil types, water table depths, and ponding times during surface irrigation. Deep percolation was governed by the final infiltration rate of the subsoil, the ponding time, the water table depth, and the amount of water stored in the rootzone between saturation and field capacity. These key variables were used to characterize both steady- and nonsteady-state percolation in a conceptual model of deep percolation. The conceptual model was found to provide an effective representation of deep percolation for both the lysimeter and field-scale water balance data. Steady-state percolation during irrigation was the dominant process contributing to deep percolation on most of the studied soils. Nonsteady-state percolation (redistribution) was very important for the sandiest soil type. The conceptual model provided better prediction of deep percolation than both data-based model (artificial neural network) and process-based modeling approach (1-D Richards' equation model).
Percolation with long-range correlations for epidemic spreading
NASA Astrophysics Data System (ADS)
Tan, Zhi-Jie; Zou, Xian-Wu; Jin, Zhun-Zhi
2000-12-01
A percolation model with long-range correlations was introduced to investigate the phenomena of epidemic spreading by Monte Carlo simulations. The correlation exponent α and pathogenic ratio s correspond to different spreading methods and pathogenicity of variant epidemics. As the correlation changes from a weak one to a strong one, the patterns change from site percolation to Eden cluster when pathogenic ratio s=1, or Leath percolation cluster when s<1. Corresponding to change of patterns, the fractal dimension increases up to space dimension. The critical behavior in epidemic spreading has been examined based on the model. It is found that correlation has a great influence on the threshold of spreading percolation.
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
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.
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
Optical Identifications of IRAS Point Sources. Galaxies. VII
NASA Astrophysics Data System (ADS)
Mickaelian, A. M.
2001-04-01
A seventh list of objects from the BIG (Byurakan-IRAS galaxies) sample is given: 95 galaxies identified with 63 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Observatory Sky Survey, and infrared fluxes at 12, 25, 60, and 100 m in the region of +65° 69° and 14h00m 18h05m with an area of 96 deg2. For the identified galaxies the optical coordinates, their departures from the IR coordinates, the stellar V magnitudes, morphological types, angular sizes, and position angles were determined. The objects have optical magnitudes in the range of 13 m .8-21 m .5 and angular sizes in the range of 4″-38″. Finder charts from the DSS are given for these objects.
Optical Identifications of IRAS Point Sources. Galaxies. VIII
NASA Astrophysics Data System (ADS)
Mickaelian, A. M.
2002-07-01
A list of objects of the BIG (Byurakan-IRAS galaxies) sample is given: 89 galaxies identified with 55 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps of the Palomar Observatory Sky Survey, and infrared fluxes at wavelengths of 12, 25, 60, and 100 mm in the region of +61° +65° and 05h30m 18h 00m with an area of 340 deg2 (additional IR sources were identified). The optical coordinates of the identified galaxies, their departure from the IR coordinates, the V stellar magnitude, morphological type, angular size, and position angle were determined. The objects have optical magnitudes in the range of 12 m .5 - 21 m .5 and angular sizes in the range of 3″ - 43″. Finder charts for these objects from the DSS are given.
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.
The Extraction of the NIRS Point Source Catalogs
NASA Technical Reports Server (NTRS)
Freund, Minoru M.
1999-01-01
The Near Infrared Spectrometer (NIRS) on the Infrared Telescope in Space, IRTS (a Japanese-US collaboration project), surveyed about 7% of the sky during its one month mission. In this work we extracted spectro-photometric point source (PS) data between 1.4 and 4 micron of high quality absolutely calibrated (2% flux uncertainties) and unbiased PS spectra in the near-IR. This database facilitates the study and understanding of a variety of science objectives, including stellar evolution of late type stars, determination of the Cosmic Infrared Background (CIB), and provides unprecedented faint stellar spectral calibrators. The objective of this work was to provide the community with a series of absolutely calibrated NIRS point source catalogs (PSC), with classification and association files. The catalogs will be archived at IRSA/IPAC.
Guo, En-Yu; Chawla, Nikhilesh; Jing, Tao; Torquato, Salvatore; Jiao, Yang
2014-03-01
Heterogeneous materials are ubiquitous in nature and synthetic situations and have a wide range of important engineering applications. Accurate modeling and reconstructing three-dimensional (3D) microstructure of topologically complex materials from limited morphological information such as a two-dimensional (2D) micrograph is crucial to the assessment and prediction of effective material properties and performance under extreme conditions. Here, we extend a recently developed dilation–erosion method and employ the Yeong–Torquato stochastic reconstruction procedure to model and generate 3D austenitic–ferritic cast duplex stainless steel microstructure containing percolating filamentary ferrite phase from 2D optical micrographs of the material sample. Specifically, the ferrite phase is dilated to produce a modified target 2D microstructure and the resulting 3D reconstruction is eroded to recover the percolating ferrite filaments. The dilation–erosion reconstruction is compared with the actual 3D microstructure, obtained from serial sectioning (polishing), as well as the standard stochastic reconstructions incorporating topological connectedness information. The fact that the former can achieve the same level of accuracy as the latter suggests that the dilation–erosion procedure is tantamount to incorporating appreciably more topological and geometrical information into the reconstruction while being much more computationally efficient. - Highlights: • Spatial correlation functions used to characterize filamentary ferrite phase • Clustering information assessed from 3D experimental structure via serial sectioning • Stochastic reconstruction used to generate 3D virtual structure 2D micrograph • Dilation–erosion method to improve accuracy of 3D reconstruction.
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.
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.
Incremental theory of diffraction for complex point source illumination
NASA Astrophysics Data System (ADS)
Polemi, A.; Carluccio, G.; Albani, M.; Toccafondi, A.; Maci, S.
2007-12-01
The complex point source (CPS) is a solution of the Helmholtz equation obtained by analytical continuation of the free-space Green's function for complex position of the point source. The CPS representation of radiated fields can be used within a ray code to predict the interaction between an antenna and its actual environment, when standard diffraction formulations are extended to the CPS illumination. In the past, ray-based diffraction theories such as the geometrical theory of diffraction and its uniform version (UTD) were extended to complex point source fields, leaving, however, open some problematic issues concerning the "complex ray tracing". In this paper, the generalization of the incremental theory of diffraction (ITD) to CPS is formulated. The total field scattered by the object is given in terms of line integration along edge discontinuities of ITD diffraction coefficients plus the discontinuous geometrical optics (GO). An incremental form of the discontinuous GO is also proposed to overcome GO "complex ray tracing" difficulties. The final formulation is very simple and leads to accurate results that are successfully validated by comparison against a method of moment solution.
Percolation conductivity in hafnium sub-oxides
Islamov, D. R. Gritsenko, V. A.; Cheng, C. H.; Chin, A.
2014-12-29
In this study, we demonstrated experimentally that formation of chains and islands of oxygen vacancies in hafnium sub-oxides (HfO{sub x}, x < 2) leads to percolation charge transport in such dielectrics. Basing on the model of Éfros-Shklovskii percolation theory, good quantitative agreement between the experimental and theoretical data of current-voltage characteristics was achieved. Based on the percolation theory suggested model shows that hafnium sub-oxides consist of mixtures of metallic Hf nanoscale clusters of 1–2 nm distributed onto non-stoichiometric HfO{sub x}. It was shown that reported approach might describe low resistance state current-voltage characteristics of resistive memory elements based on HfO{sub x}.
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
NASA Astrophysics Data System (ADS)
Nakayama, Masanobu; Kimura, Mayumi; Jalem, Randy; Kasuga, Toshihiro
2016-01-01
Fast ion conductive solid oxide electrolytes are urgently needed because of the development of batteries, fuel cells, and sensors. Ab initio density functional theory can predict ionic conductivities with high accuracy, although it often requires large computational resources and time. In this paper, we use empirical bond valence relations [Adams et al., Phys. Status Solidi A 208, 1746 (2011)] and a percolation algorithm for fast, efficient, fully automated evaluation of migration energies for Li ion conduction in 14 olivine-type LiMXO4 compounds. The results showed a high correlation coefficient with the ab initio density functional theory (DFT) approach, indicating that our method could be attractive for identifying fast ion conductors in databases of numerous candidates.
Resnicoff, M.; Medrano, E.E.; Podhajcer, O.L.; Bravo, A.I.; Bover, L.; Mordoh, J.
1987-10-01
Exponentially growing MCF7 human breast cancer cells were separated in Percoll gradients into six different fractions of increasing density (A to F). These fractions could be subcultured and were found to contain different cellular subpopulations as defined by the following criteria: ability to generate other cellular subpopulations; growth rate; DNA synthesis; and expression of estrogen receptors, ras oncogene-encoded protein p21, and carcinoembryonic antigen. One of the minor fractions (E), which contained about 5% of the total cell number, appeared to contain the stem cells, on the basis of the following criteria: (i) its ability to reproduce the other cellular subpopulations, (ii) its high rate of growth and DNA synthesis, and (iii) the inability of the other subpopulations to generate it. The most differentiated subpopulation appeared to be the densest one (F), since it was the slowest growing and appeared to be the end point of the other subpopulations.
Deep Chandra Observations of NGC 3115: Properties of Point Sources
NASA Astrophysics Data System (ADS)
Lin, Dacheng; Irwin, J.; Wong, K.; Romanowsky, A. J.; Strader, J.; Sivakoff, G. R.
2013-01-01
Our recent Chandra X-ray Visionary Project to observe the nearby S0 galaxy NGC3115 for 1 Msec has provided the deepest look to date of the low-mass X-ray binary (LMXB) population of a normal early-type galaxy. Here we report our study of the 450 point sources detected in these long observations, including many supersoft and highly variable sources. We compare the luminosity distribution of the LMXBs with those obtained from other galaxies. We also investigate their possible nature based on the spectral evolution and multiwavelength cross-correlation and matching with globular clusters.
Supervised and unsupervised classification - The case of IRAS point sources
NASA Astrophysics Data System (ADS)
Adorf, Hans-Martin; Meurs, E. J. A.
Progress is reported on a project which aims at mapping the extragalactic sky in order to derive the large scale distribution of luminous matter. The approach consists in selecting from the IRAS Point Source Catalog a set of galaxies which is as clean and as complete as possible. The decision and discrimination problems involved lend themselves to a treatment using methods from multivariate statistics, in particular statistical pattern recognition. Two different approaches, one based on supervised Bayesian classification, the other on unsupervised data-driven classification, are presented and some preliminary results are reported.
Bond Percolation on Multiplex Networks
NASA Astrophysics Data System (ADS)
Hackett, A.; Cellai, D.; Gómez, S.; Arenas, A.; Gleeson, J. P.
2016-04-01
We present an analytical approach for bond percolation on multiplex networks and use it to determine the expected size of the giant connected component and the value of the critical bond occupation probability in these networks. We advocate the relevance of these tools to the modeling of multilayer robustness and contribute to the debate on whether any benefit is to be yielded from studying a full multiplex structure as opposed to its monoplex projection, especially in the seemingly irrelevant case of a bond occupation probability that does not depend on the layer. Although we find that in many cases the predictions of our theory for multiplex networks coincide with previously derived results for monoplex networks, we also uncover the remarkable result that for a certain class of multiplex networks, well described by our theory, new critical phenomena occur as multiple percolation phase transitions are present. We provide an instance of this phenomenon in a multiplex network constructed from London rail and European air transportation data sets.
A Search for Point Sources of EeV Photons
NASA Astrophysics Data System (ADS)
Aab, A.; Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Samarai, I. Al; Albuquerque, I. F. M.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Aramo, C.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Badescu, A. M.; Barber, K. B.; Bäuml, J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellido, J. A.; Berat, C.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brancus, I.; Brogueira, P.; Brown, W. C.; Buchholz, P.; Bueno, A.; Buscemi, M.; Caballero-Mora, K. S.; Caccianiga, B.; Caccianiga, L.; Candusso, M.; Caramete, L.; Caruso, R.; Castellina, A.; Cataldi, G.; Cazon, L.; Cester, R.; Chavez, A. G.; Cheng, S. H.; Chiavassa, A.; Chinellato, J. A.; Chudoba, J.; Cilmo, M.; Clay, R. W.; Cocciolo, G.; Colalillo, R.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cooper, M. J.; Coutu, S.; Covault, C. E.; Criss, A.; Cronin, J.; Curutiu, A.; Dallier, R.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; de Jong, S. J.; de Mello Neto, J. R. T.; De Mitri, I.; de Oliveira, J.; de Souza, V.; del Peral, L.; Deligny, O.; Dembinski, H.; Dhital, N.; Di Giulio, C.; Di Matteo, A.; Diaz, J. C.; Díaz Castro, M. L.; Diep, P. N.; Diogo, F.; Dobrigkeit, C.; Docters, W.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; Dorosti Hasankiadeh, Q.; Dova, M. T.; Ebr, J.; Engel, R.; Erdmann, M.; Erfani, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Fang, K.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Fernandes, M.; Fick, B.; Figueira, J. M.; Filevich, A.; Filipčič, A.; Fox, B. D.; Fratu, O.; Fröhlich, U.; Fuchs, B.; Fuji, T.; Gaior, R.; García, B.; Garcia Roca, S. T.; Garcia-Gamez, D.; Garcia-Pinto, D.; Garilli, G.; Gascon Bravo, A.; Gate, F.; Gemmeke, H.; Ghia, P. L.; Giaccari, U.; Giammarchi, M.; Giller, M.; Glaser, C.; Glass, H.; Gomez Albarracin, F.; Gómez Berisso, M.; Gómez Vitale, P. F.; Gonçalves, P.; Gonzalez, J. G.; Gookin, B.; Gorgi, A.; Gorham, P.; Gouffon, P.; Grebe, S.; Griffith, N.; Grillo, A. F.; Grubb, T. D.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Heimann, P.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Hollon, N.; Holt, E.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huber, D.; Huege, T.; Insolia, A.; Isar, P. G.; Islo, K.; Jandt, I.; Jansen, S.; Jarne, C.; Josebachuili, M.; Kääpä, A.; Kambeitz, O.; Kampert, K. H.; Kasper, P.; Katkov, I.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Krause, R.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuempel, D.; Kunka, N.; La Rosa, G.; LaHurd, D.; Latronico, L.; Lauer, R.; Lauscher, M.; Lautridou, P.; Le Coz, S.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lu, L.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Malacari, M.; Maldera, S.; Maller, J.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, V.; Mariş, I. C.; Marsella, G.; Martello, D.; Martin, L.; Martinez, H.; Martínez Bravo, O.; Martraire, D.; Masías Meza, J. J.; Mathes, H. J.; Mathys, S.; Matthews, A. J.; Matthews, J.; Matthiae, G.; Maurel, D.; Maurizio, D.; Mayotte, E.; Mazur, P. O.; Medina, C.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Messina, S.; Meyhandan, R.; Mićanović, S.; Micheletti, M. I.; Middendorf, L.; Minaya, I. A.; Miramonti, L.; Mitrica, B.; Molina-Bueno, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morello, C.; Moreno, J. C.; Mostafá, M.; Moura, C. A.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navas, S.; Necesal, P.; Nellen, L.; Nelles, A.; Neuser, J.; Niechciol, M.; Niemietz, L.; Niggemann, T.; Nitz, D.; Nosek, D.; Novotny, V.; Nožka, L.; Ochilo, L.; Olinto, A.; Oliveira, M.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Papenbreer, P.; Parente, G.; Parra, A.; Pastor, S.; Paul, T.; Pech, M.; Peķala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Peters, C.; Petrera, S.; Petrolini, A.; Petrov, Y.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Porcelli, A.; Porowski, C.; Privitera, P.; Prouza, M.; Purrello, V.; Quel, E. J.; Querchfeld, S.; Quinn, S.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rizi, V.; Roberts, J.; Rodrigues de Carvalho, W.; Rodriguez Cabo, I.; Rodriguez Fernandez, G.; Rodriguez Rojo, J.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Roulet, E.; Rovero, A. C.; Rühle, C.; Saffi, S. J.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Sanchez-Lucas, P.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, B.; Sarmento, R.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Scholten, O.; Schoorlemmer, H.; Schovánek, P.; Schulz, A.; Schulz, J.; Sciutto, S. J.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Sima, O.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Squartini, R.; Srivastava, Y. N.; Stanič, S.; Stapleton, J.; Stasielak, J.; Stephan, M.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Szuba, M.; Taborda, O. A.; Tapia, A.; Tartare, M.; Thao, N. T.; Theodoro, V. M.; Tiffenberg, J.; Timmermans, C.; Todero Peixoto, C. J.; Toma, G.; Tomankova, L.; Tomé, B.; Tonachini, A.; Torralba Elipe, G.; Torres Machado, D.; Travnicek, P.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Urban, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van den Berg, A. M.; van Velzen, S.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Varner, G.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Verzi, V.; Vicha, J.; Videla, M.; Villaseñor, L.; Vlcek, B.; Vorobiov, S.; Wahlberg, H.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Werner, F.; Whelan, B. J.; Widom, A.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Wittkowski, D.; Wundheiler, B.; Wykes, S.; Yamamoto, T.; Yapici, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Zhou, J.; Zhu, Y.; Zimbres Silva, M.; Ziolkowski, M.; Auger Collaboration102, The Pierre
2014-07-01
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 1017.3 eV to 1018.5 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-2 s-1, and no celestial direction exceeds 0.25 eV cm-2 s-1. These upper limits constrain scenarios in which EeV cosmic ray protons are emitted by non-transient sources in the Galaxy.
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.
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.
Electrical Percolation Based Biosensors
Bruck, Hugh Alan; Yang, Minghui; Kostov, Yordan; Rasooly, Avraham
2013-01-01
A new approach to label free biosensing has been developed based on the principle of “electrical percolation”. In electrical percolation, long-range electrical connectivity is formed in randomly oriented and distributed systems of discrete elements. By applying this principle to biological interactions, it is possible to measure biological components both directly and electronically. The main element for electrical percolation biosensor is the biological semiconductor (BSC) which is a multi-layer 3-D carbon nanotube-antibody network. In the BSC, molecular interactions, such as binding of antigens to the antibodies, disrupt the network continuity causing increased resistance of the network. BSCs can be fabricated by immobilizing conducting elements, such as pre-functionalized single-walled carbon nanotubes (SWNTs)-antibody complex, directly onto a substrate, such as a Poly(methyl methacrylate) (PMMA) surface (also known as plexi-glass or Acrylic). BSCs have been demonstrated for direct (label-free) electronic measurements of antibody-antigen binding using SWNTs. If the concentration of the SWNT network is slightly above the electrical percolation threshold, then binding of a specific antigen to the pre-functionalized SWNT dramatically increases the electrical resistance due to changes in the tunneling between the SWNTs. Using anti-Staphylococcal enterotoxin B (SEB) IgG as a “gate” and SEB as an “actuator”, it was demonstrated that the BSC was able to detect SEB at concentrations of 1 ng/ml. Based on this concept, an automated configuration for BSCs is described here that enables real time continuous detection. The new BSC configuration may permit assembly of multiple sensors on the same chip to create “Biological Central Processing Units (CPUs)” with multiple biological elements, capable of processing and sorting out information on multiple analytes simultaneously. PMID:24041756
Moulton, C R; Fleming, A J; Ebert, M A
2011-04-01
Despite ongoing active research, the role of the radiation bystander effect in modifying local tissue response to an ionising radiation dose remains unclear. The present study aims to provide new insight by simulating the diffusion-mediated inter-cellular communication processes in 2D and 3D cell-like structures to calculate likely signal ranges in the diffusion limited case. Random walks of individual signalling molecules were tracked between cells with inclusion of molecule-receptor interactions. The resulting diffusion anomaly is a function of cell density, signal uptake probability and the spatial arrangement of cells local to the signal origin. Uptake probability effects dominate percolation effects in disordered media. Diffusion through 2D structures is more conducive to anomalous diffusion than diffusion through 3D structures. Values for time-dependent diffusion constants and permeability are derived for typical simulation parameters. Even at low signal uptake probabilities the communication range is restricted to a mean value of less than 100 μm owing to complete signal uptake by 600 s. This should be considered in light of the potential influence of signal relaying, flow-dynamics or vasculature-mediated signalling.
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.
Gamma-ray observations of Ophiuchus with EGRET: The diffuse emission and point sources
NASA Technical Reports Server (NTRS)
Hunter, S. D.; Digel, S. W.; De Geus, E. J.; Kanbach, G.
1994-01-01
Observations of the Ophiuchus region made with the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) during the first 2 1/2 years of operation show the diffuse emission from the interstellar gas in Ophiuchus as well as variable emission from two point sources. The gamma-ray emission is modeled in terms of cosmic-ray interactions with atomic and molecular hydrogen in Ophiuchus and with low-energy photons along the line of sight. The model also includes the flux from the two point sources and an isotropic diffuse contribution. The cosmic-ray density is assumed to be uniform. The derived ratio of molecular hydrogen column density to integrated CO intensity is (1.1 +/- 0.2) x 10(exp 20) H-mols/sq cm (K km/s)(exp -1). At the sensitivity and resolution of the gamma-ray data, no variation of this ratio over the modeled region is discernible, nor are any regions of enhanced cosmic-ray density apparent. The model was fitted to seven narrow energy bands to obtain the energy depedence of the gamma-ray production function and the spectra of the point sources. The derived production function is in good agreement with theoretical calculations and the local cosmic-ray electron and proton spectra. The positions of the point sources were determined from maximum likelihood analysis of the gamma-ray emission observed in excess of the diffuse model. We identify one point source with the quasar PKS 1622-253, which has an average flux, E greater than 100 MeV, of (2.5 +/- 0.5) x 10(exp -7) photons/sq cm/s and photon spectral index -1.9 +/- 0.3. The other source, denoted GRO J1631-27, has not yet been identified at other wavelengths. Its average flux, E greater than 100 MeV, is (1.1 +/- 0.4) x 10(exp -7) photons/sq cm/s; however, its spectral index is poorly determined. The spectral index and intensity of the isotropic contribution to the model agree well with the extragalactic diffuse emission derived from the SAS 2 data.
Temporal percolation in activity-driven networks
NASA Astrophysics Data System (ADS)
Starnini, Michele; Pastor-Satorras, Romualdo
2014-03-01
We study the temporal percolation properties of temporal networks by taking as a representative example the recently proposed activity-driven-network model [N. Perra et al., Sci. Rep. 2, 469 (2012), 10.1038/srep00469]. Building upon an analytical framework based on a mapping to hidden variables networks, we provide expressions for the percolation time Tp marking the onset of a giant connected component in the integrated network. In particular, we consider both the generating function formalism, valid for degree-uncorrelated networks, and the general case of networks with degree correlations. We discuss the different limits of the two approaches, indicating the parameter regions where the correlated threshold collapses onto the uncorrelated case. Our analytical predictions are confirmed by numerical simulations of the model. The temporal percolation concept can be fruitfully applied to study epidemic spreading on temporal networks. We show in particular how the susceptible-infected-removed model on an activity-driven network can be mapped to the percolation problem up to a time given by the spreading rate of the epidemic process. This mapping allows us to obtain additional information on this process, not available for previous approaches.
Microstructures, percolation thresholds, and rock physical properties
NASA Astrophysics Data System (ADS)
Guéguen, Y.; Chelidze, T.; Le Ravalec, M.
1997-09-01
The physical properties (transport properties and mechanical properties) of porous/cracked rocks are mainly functions of their microstructure. In this connection the problem of critical (threshold) porosity for transport, elasticity and mechanical strength is especially important. Two dominant mathematical formalisms — effective medium theory (EMT) and percolation theory — pretend to give answers to this problem. Some of the EMT models do not predict any threshold (differential effective medium). Other EMT models (self-consistent models) do predict thresholds, but it is shown that these thresholds are fictitious and result from an extension of a theory beyond its limit of validity. The failure of EMT methods at high pores/crack concentrations is the result of clustering effects. The appropriate formalism to correctly describe the phenomenon of clustering of pores and cracks and the behaviour of a system close to its critical porosity is percolation theory. Percolation thresholds can be predicted in that case from classical site or bond percolation on regular or random lattices. The threshold values depend on the density and average size of pores/cracks so that porosity is not sufficient in general to characterize the threshold for a specific physical property. The general term 'critical porosity' should thus be used with caution and it is preferable to specify which property is concerned and what kind of microstructure is present. This term can be more safely used for a population of rocks which have an identical average shape of pores/cracks and for a given physical property.
Detecting Long-term Changes in Point Source Fossil CO2 Emissions with Tree Ring Archives
NASA Astrophysics Data System (ADS)
Keller, E. D.; Turnbull, J. C.; Norris, M. W.
2015-12-01
We examine the utility of tree ring 14C archives for detecting long term changes in fossil CO2 emissions from a point source. Trees assimilate carbon from the atmosphere during photosynthesis, in the process faithfully recording the average atmospheric 14C content over the growing season in each annual tree ring. Using 14C as a proxy for fossil CO2, we examine interannual variability over six years of fossil CO2 observations between 2004 and 2012 from two trees growing near the Kapuni Natural Gas Plant in rural Taranaki, New Zealand. We quantify the amount of variability that can be attributed to transport and meteorology by simulating constant point source fossil CO2 emissions over the observation period with the atmospheric transport model WindTrax. We then calculate the amount of change in emissions that we can detect with new observations over annual or multi-year time periods given both measurement uncertainty of 1ppm and the modelled variation in transport. In particular, we ask, what is the minimum amount of change in emissions that we can detect using this method, given a reference period of six years? We find that changes of 42% or more could be detected in a new sample from one year at the pine tree, or 22% in the case of four years of new samples. This threshold lowers and the method becomes more practical with a larger signal; for point sources 10 times the magnitude of the Kapuni plant (a typical size for large electricity generation point sources worldwide), it would be possible to detect sustained emissions changes on the order of 10% given suitable meteorology and observations.
A Photometric Classification of the SAGE LMC Point Source Catalog
NASA Astrophysics Data System (ADS)
Marengo, Massimo; Antoniou, V.; SAGE Collaboration
2014-01-01
The Spitzer SAGE Large Magellanic Cloud (LMC) photometric catalog lists over 7.2 million sources detected with the Spitzer space telescope. This catalog has been cross-correlated with the near-IR 2MASS and IRSF surveys, as well as with optical photometry from the MCPS database. This combined catalog is an invaluable tool for the study of LMC stellar populations, and to understand the life cycle of gas and dust in the LMC. To fully leverage the broad wavelength coverage of this database, we have developed a novel technique for the photometric classification of the SAGE LMC point source catalog, based on a weighted k-Nearest Neighbor method. This technique allows the classification of most LMC sources based on templates that have been identified spectroscopically, without a-priori assumptions about their spectral characteristics. We present here the details of our classification method, and the main results of our work.
Discretized energy minimization in a wave guide with point sources
NASA Technical Reports Server (NTRS)
Propst, G.
1994-01-01
An anti-noise problem on a finite time interval is solved by minimization of a quadratic functional on the Hilbert space of square integrable controls. To this end, the one-dimensional wave equation with point sources and pointwise reflecting boundary conditions is decomposed into a system for the two propagating components of waves. Wellposedness of this system is proved for a class of data that includes piecewise linear initial conditions and piecewise constant forcing functions. It is shown that for such data the optimal piecewise constant control is the solution of a sparse linear system. Methods for its computational treatment are presented as well as examples of their applicability. The convergence of discrete approximations to the general optimization problem is demonstrated by finite element methods.
Positive deconvolution for superimposed extended source and point sources
NASA Astrophysics Data System (ADS)
Giovannelli, J.-F.; Coulais, A.
2005-08-01
The paper deals with the construction of images from visibilities acquired using aperture synthesis instruments: Fourier synthesis, deconvolution, and spectral interpolation/extrapolation. Its intended application is to specific situations in which the imaged object possesses two superimposed components: (i) an extended component together with (ii) a set of point sources. It is also specifically designed to the case of positive maps, and accounts for a known support. Its originality lies within joint estimation of the two components, coherently with data, properties of each component, positivity and possible support. We approach the subject as an inverse problem within a regularization framework: a regularized least-squares criterion is specifically proposed and the estimated maps are defined as its minimizer. We have investigated several options for the numerical minimization and we propose a new efficient algorithm based on augmented Lagrangian. Evaluation is carried out using simulated and real data (from radio interferometry) demonstrating the capability to accurately separate the two components.
Optical Identification of IRAS Point Sources. Galaxies. IX
NASA Astrophysics Data System (ADS)
Mickaelian, A. M.; Sargsyan, L. A.
2004-01-01
The ninth list of objects from the BIG (Byurakan-IRAS Galaxies) sample is presented; 87 galaxies are identified with 60 point sources from the IRAS PSC catalog in the region +69° +73° and 03h50m 09h50m with an area of 117 deg2. Most of the identified galaxies are compact with bright bulges and faint peripheries. The identified objects include 7 Sy candidates, 8 interacting pairs (of which one is a merger” candidate), and 6 LSB galaxies. The optical coordinates and their deviations from the IR coordinates, the V magnitudes, morphological types, angular dimensions, and position angles are given. The identified galaxies are of morphological types Sa-Sc and have optical stellar magnitudes in the range 15.5m-21.5m with angular sizes in the range 3″-26″. Finding charts from DSS2 are provided for these objects.
Quantum Theory of Superresolution for Two Incoherent Optical Point Sources
NASA Astrophysics Data System (ADS)
Tsang, Mankei; Nair, Ranjith; Lu, Xiao-Ming
2016-07-01
Rayleigh's criterion for resolving two incoherent point sources has been the most influential measure of optical imaging resolution for over a century. In the context of statistical image processing, violation of the criterion is especially detrimental to the estimation of the separation between the sources, and modern far-field superresolution techniques rely on suppressing the emission of close sources to enhance the localization precision. Using quantum optics, quantum metrology, and statistical analysis, here we show that, even if two close incoherent sources emit simultaneously, measurements with linear optics and photon counting can estimate their separation from the far field almost as precisely as conventional methods do for isolated sources, rendering Rayleigh's criterion irrelevant to the problem. Our results demonstrate that superresolution can be achieved not only for fluorophores but also for stars.
The Chandra Cosmos Legacy Survey: Overview and Point Source Catalog
NASA Astrophysics Data System (ADS)
Civano, F.; Marchesi, S.; Comastri, A.; Urry, M. C.; Elvis, M.; Cappelluti, N.; Puccetti, S.; Brusa, M.; Zamorani, G.; Hasinger, G.; Aldcroft, T.; Alexander, D. M.; Allevato, V.; Brunner, H.; Capak, P.; Finoguenov, A.; Fiore, F.; Fruscione, A.; Gilli, R.; Glotfelty, K.; Griffiths, R. E.; Hao, H.; Harrison, F. A.; Jahnke, K.; Kartaltepe, J.; Karim, A.; LaMassa, S. M.; Lanzuisi, G.; Miyaji, T.; Ranalli, P.; Salvato, M.; Sargent, M.; Scoville, N. J.; Schawinski, K.; Schinnerer, E.; Silverman, J.; Smolcic, V.; Stern, D.; Toft, S.; Trakhtenbrot, B.; Treister, E.; Vignali, C.
2016-03-01
The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg2 of the COSMOS field with an effective exposure of ≃ 160 ks over the central 1.5 deg2 and of ≃ 80 ks in the remaining area. The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2 × 10-5. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft, and hard band). The limiting depths are 2.2 × 10-16, 1.5 × 10-15, and 8.9 × 10-16 {\\text{erg cm}}-2 {{{s}}}-1 in the 0.5-2, 2-10, and 0.5-10 keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density >1022 cm-2 from the hardness ratio (HR) is ˜50{}-16+17%. Given the large sample we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5%-10%. For the first time we compute number counts for obscured (HR > -0.2) and unobscured (HR < -0.2) sources and find significant differences between the two populations in the soft band. Due to the unprecedent large exposure, COSMOS-Legacy area is three times larger than surveys at similar depths and its depth is three times fainter than surveys covering similar areas. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.
Search for point sources of high energy neutrinos with Amanda
Ahrens, J.
2002-08-01
Report of search for likely point sources for neutrinos observed by the Amanda detector. Places intensity limits on observable point sources. This paper describes the search for astronomical sources of high-energy neutrinos using the AMANDA-B10 detector, an array of 302 photomultiplier tubes, used for the detection of Cherenkov light from upward traveling neutrino-induced muons, buried deep in ice at the South Pole. The absolute pointing accuracy and angular resolution were studied by using coincident events between the AMANDA detector and two independent telescopes on the surface, the GASP air Cherenkov telescope and the SPASE extensive air shower array. Using data collected from April to October of 1997 (130.1 days of livetime), a general survey of the northern hemisphere revealed no statistically significant excess of events from any direction. The sensitivity for a flux of muon neutrinos is based on the effective detection area for through-going muons. Averaged over the Northern sky, the effective detection area exceeds 10,000 m{sup 2} for E{sub {mu}} {approx} 10 TeV. Neutrinos generated in the atmosphere by cosmic ray interactions were used to verify the predicted performance of the detector. For a source with a differential energy spectrum proportional to E{sub {nu}}{sup -2} and declination larger than +40{sup o}, we obtain E{sup 2} (dN{sub {nu}}/dE) {le} 10{sup -6} GeV cm{sup -2} s{sup -1} for an energy threshold of 10 GeV.
Roots at the Percolation Threshold
NASA Astrophysics Data System (ADS)
Kroener, E.; Ahmed, M. A.; Kaestner, A.; Vontobel, P.; Zarebanadkouki, M.; Carminati, A.
2014-12-01
Much of the carbon assimilated by plants during photosynthesis is lost to the soil via rhizodepositions. One component of rhizopdeposition is mucilage, a hydrogel that dramatically alters the soil physical properties. Mucilage was assumed to explain unexpectedly low rhizosphere rewetting rates during irrigation (Carminati et al. 2010) and temporarily water repellency in the rhizosphere after severe drying (Moradi et al. 2012).Here, we present an experimental and theoretical study for the rewetting behaviour of a soil mixed with mucilage, which was used as an analogue of the rhizosphere. Our samples were made of two layers of untreated soils separated by a thin layer (ca. 1 mm) of soil treated with mucilage. We prepared soil columns of varying particle size, mucilage concentration and height of the middle layer above the water table. The dry soil columns were re-wetted by capillary rise from the bottom.The rewetting of the middle layer showed a distinct dual behavior. For mucilage concentrations lower than a certain threshold, water could cross the thin layer almost immediately after rewetting of bulk soil. At slightly higher mucilage concentrations, the thin layer was almost impermeable. The mucilage concentration at the threshold strongly depended on particle size: the smaller the particle size the larger the soil specific surface and the more mucilage was needed to cover the entire particle surface and to induce water repellency.We applied a classic pore network model to simulate the experimental observations. In the model a certain fraction of nodes were randomly disconnected to reproduce the effect of mucilage in temporarily blocking the flow. The percolation model could qualitatively reproduce well the threshold characteristics of the experiments. Our experiments, 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
[Characteristics of non-point source pollution in Tiaoxi watershed and related affecting factors].
Jin, Jing-liang; Wang, Fei-er; Dai, Lu-ying; Tian, Ping; Zhang, Zhi-jian
2011-08-01
By using soil and water assessment tool (SWAT) model, this paper simulated the surface runoff intensity and the export loadings of sediment particulates and nutrients via non-point source hydrological pathway in Tiaoxi watershed, and integrated with the simulation results, analyzed the temporal and spatial distribution characteristics of non-point source pollution in the watershed in 2008. In the study area, the per unit area non-point source pollution was stronger in northern region than in southern region and in eastern region than in western region, and the weakest in central region. Among the land utilization types, farmland had the biggest contribution to the sediment loading. There were significantly positive correlations between the loadings of surface runoff and associated sediment particulates and the rainfall intensity. The export loadings of nutrients through surface runoff were higher in rainy season (from June to September) than in dry season (from December to next March), and there existed significant correlations between the surface runoff loadings of sediment particulates, organic nitrogen, and nitrate and the average gradient of lands.
Schulman, L S; Seiden, P E
1986-07-25
A theory is presented in which much of the structure of spiral galaxies arises from a percolation phase transition that underlies the phenomenon of propagating star formation. According to this view, the appearance of spiral arms is a consequence of the differential rotation of the galaxy and the characteristic divergence of correlation lengths for continuous phase transitions. Other structural properties of spiral galaxies, such as the distribution of the gaseous components and the luminosity, arise directly from a feedback mechanism that pins the star formation rate close to the critical point of the phase transition. The approach taken in this article differs from traditional dynamical views. The argument is presented that, at least for some galaxies, morphological and other features are already fixed by general properties of phase transitions, irrespective of detailed dynamic or other considerations. PMID:17794566
Phase transitions in supercritical explosive percolation
NASA Astrophysics Data System (ADS)
Chen, Wei; Nagler, Jan; Cheng, Xueqi; Jin, Xiaolong; Shen, Huawei; Zheng, Zhiming; D'Souza, Raissa M.
2013-05-01
Percolation describes the sudden emergence of large-scale connectivity as edges are added to a lattice or random network. In the Bohman-Frieze-Wormald model (BFW) of percolation, edges sampled from a random graph are considered individually and either added to the graph or rejected provided that the fraction of accepted edges is never smaller than a decreasing function with asymptotic value of α, a constant. The BFW process has been studied as a model system for investigating the underlying mechanisms leading to discontinuous phase transitions in percolation. Here we focus on the regime α∈[0.6,0.95] where it is known that only one giant component, denoted C1, initially appears at the discontinuous phase transition. We show that at some point in the supercritical regime C1 stops growing and eventually a second giant component, denoted C2, emerges in a continuous percolation transition. The delay between the emergence of C1 and C2 and their asymptotic sizes both depend on the value of α and we establish by several techniques that there exists a bifurcation point αc=0.763±0.002. For α∈[0.6,αc), C1 stops growing the instant it emerges and the delay between the emergence of C1 and C2 decreases with increasing α. For α∈(αc,0.95], in contrast, C1 continues growing into the supercritical regime and the delay between the emergence of C1 and C2 increases with increasing α. As we show, αc marks the minimal delay possible between the emergence of C1 and C2 (i.e., the smallest edge density for which C2 can exist). We also establish many features of the continuous percolation of C2 including scaling exponents and relations.
Multi-point sources and imaging compound infrared target simulator
NASA Astrophysics Data System (ADS)
Shi, Rui; Xu, Rui; Wang, Hongjie; Wang, Xin; Wu, Di; Li, Zhuo
2014-11-01
Infrared target simulator is an important unit in guidance hardware-in-the-loop simulation systems. It is used to simulate the radiation and motion characteristics of target, decoy and background. This paper proposed a multi-channel IR target simulator. It could generate one IR point target, two pairs of IR decoys and background respectively in the same field of view of the seeker's optical system simultaneously. An IR imaging fiber bundle as the focal plane of the projection optical system was used to compound the target, decoys and background. The compound scene was projected to the seeker by the projection optical system. In IR imaging channel, IR scene was generated by an optical film chip as a visible to thermal transducer which was placed in a vacuum cell. The simulated temperature range of IR scene could be from room temperature to 430K.The thin film transducer had 512×512 pixels. Its frame rate could reach to 100Hz. Light sources with high equivalent black body temperature were adopted in IR target and decoy channels. The size and the radiation intensity of the IR point target and decoys could be controlled by pin holes and attenuators. The point target and decoys driven by high precise motors could travel through the whole instantaneous field of view of the seeker's optical system. Two pairs of decoys could move away from the center to the edge of the instantaneous field of view. The highest simulated black body temperature of the point source was 1200K.
Super-resolution for a point source using positive refraction
NASA Astrophysics Data System (ADS)
Miñano, Juan C.; Benítez, Pablo; González, Juan C.; Grabovičkić, Dejan; Ahmadpanahi, Hamed
Leonhardt demonstrated (2009) that the 2D Maxwell Fish Eye lens (MFE) can focus perfectly 2D Helmholtz waves of arbitrary frequency, i.e., it can transport perfectly an outward (monopole) 2D Helmholtz wave field, generated by a point source, towards a receptor called "perfect drain" (PD) located at the corresponding MFE image point. The PD has the property of absorbing the complete radiation without radiation or scattering and it has been claimed as necessary to obtain super-resolution (SR) in the MFE. However, a prototype using a "drain" different from the PD has shown λ/5 resolution for microwave frequencies (Ma et al, 2010). Recently, the SR properties of a device equivalent to the MFE, called the Spherical Geodesic Waveguide (SGW) (Miñano et al, 2012) have been analyzed. The reported results show resolution up to λ /3000, for the SGW loaded with the perfect drain, and up to λ /500 for the SGW without perfect drain. The perfect drain was realized as a coaxial probe loaded with properly calculated impedance. The SGW provides SR only in a narrow band of frequencies close to the resonance Schumann frequencies. Here we analyze the SGW loaded with a small "perfect drain region" (González et al, 2011). This drain is designed as a region made of a material with complex permittivity. The comparative results show that there is no significant difference in the SR properties for both perfect drain designs.
Optimizing Photon Collection from Point Sources with Adaptive Optics
NASA Astrophysics Data System (ADS)
Hill, Alexander; Hervas, David; Nash, Joseph; Graham, Martin; Burgers, Alexander; Paudel, Uttam; Steel, Duncan; Kwiat, Paul
2015-05-01
Collection of light from point-like sources is typically poor due to the optical aberrations present with very high numerical-aperture optics. In the case of quantum dots, the emitted mode is nonisotropic and may be quite difficult to couple into single- or even few-mode fiber. Wavefront aberrations can be corrected using adaptive optics at the classical level by analyzing the wavefront directly (e.g., with a Shack-Hartmann sensor); however, these techniques are not feasible at the single-photon level. We present a new technique for adaptive optics with single photons using a genetic algorithm to optimize collection from point emitters with a deformable mirror. We first demonstrate our technique for improving coupling from a subwavelength pinhole, which simulates isotropic emission from a point source. We then apply our technique in situto InAs/GaAs quantum dots, obtaining coupling increases of up to 50% even in the presence of an artificial source of drift.
Optical Identification of IRAS Point Sources. Galaxies. X
NASA Astrophysics Data System (ADS)
Mickaelian, A. M.; Sargsyan, L. A.
2004-04-01
The tenth list of objects from the BIG (Byurakan-IRAS Galaxies) sample, containing 104 galaxies identified with 60 point sources from the IRAS PSC catalog, is introduced. The identifications have been made in the region +69°+73° and 09h50m15h20m with an area of 107 sq.deg. The identified objects include 13 Sy candidates, 5 compact star-formation galaxies, 11 interacting pairs (including 5 merger candidates) and 1 interacting triple system, 5 LSB galaxies, and 5 groups. 21 objects are also identified with radio sources. The optical coordinates, their deviations from the IR coordinates, V stellar magnitudes, morphological types, angular sizes of the central regions, and position angles have been determined. The identified galaxies are of Sa-Sc, SB, and Irr morphological types, the optical stellar magnitudes lie in the range 15m.0-21m.5, and the angular sizes of the central regions lie in the range 3″-32″. Finding charts from the DSS2 are included for these objects.
Rounds, Stewart A.
2007-01-01
Water temperature is an important factor influencing the migration, rearing, and spawning of several important fish species in rivers of the Pacific Northwest. To protect these fish populations and to fulfill its responsibilities under the Federal Clean Water Act, the Oregon Department of Environmental Quality set a water temperature Total Maximum Daily Load (TMDL) in 2006 for the Willamette River and the lower reaches of its largest tributaries in northwestern Oregon. As a result, the thermal discharges of the largest point sources of heat to the Willamette River now are limited at certain times of the year, riparian vegetation has been targeted for restoration, and upstream dams are recognized as important influences on downstream temperatures. Many of the prescribed point-source heat-load allocations are sufficiently restrictive that management agencies may need to expend considerable resources to meet those allocations. Trading heat allocations among point-source dischargers may be a more economical and efficient means of meeting the cumulative point-source temperature limits set by the TMDL. The cumulative nature of these limits, however, precludes simple one-to-one trades of heat from one point source to another; a more detailed spatial analysis is needed. In this investigation, the flow and temperature models that formed the basis of the Willamette temperature TMDL were used to determine a spatially indexed 'heating signature' for each of the modeled point sources, and those signatures then were combined into a user-friendly, spreadsheet-based screening tool. The Willamette River Point-Source Heat-Trading Tool allows the user to increase or decrease the heating signature of each source and thereby evaluate the effects of a wide range of potential point-source heat trades. The predictions of the Trading Tool were verified by running the Willamette flow and temperature models under four different trading scenarios, and the predictions typically were accurate
NASA Astrophysics Data System (ADS)
Kawanishi, T.; Ninagawa, K.; Hayashi, Y.
2006-12-01
Power law tailings are often seen in removal of pollutants from soil or ground water. We have found that the power law tailing can also be seen in laboratory scale column air-sparging experiments. Researchers so far have found that power law tailings can occur due to the distribution of the micro-pore diffusion rates, or Freundlich type adsorption equilibrium. In addition to that we propose the following hypothesis. Introducing gas to the water saturated glass bead column causes some fractal-like gas flow path, which causes the power law distribution of distance that solute has to travel until it reaches the gas-water interface, this causes the power law tailing. In order to prove this, we constructed a model for removal of solute by diffusion to gas/water interface based on the invasion percolation. In a simple cubic bond lattice, invasion percolation is performed, assuming that the invading phase is gas and remaining phase is water. Then, set the initial concentration in water uniformly unity, set the boundary conditions as the concentration of the solute at the gas/water interfacial nodes is zero. Then diffusion calculation is performed by assuming that in the local scale (in a bond) the diffusion is Fickian. The model successfully reproduced the power law tailings. In the 80x80x80 and 100x100x100 node-lattice, the estimated slope in double-log plots raged from -1.08 to -0.72. The values are different from the normal diffusion in infinite media, -0.50, suggesting that the non-uniform shape of gas/water interface caused this kind of power law tailing. In the column experiments, we found the slope in double-log plots ranging from -0.77 to - 0.54, these values lie mostly between the calculated results and Fickian diffusion, 0.5. This, we consider, is reasonable that the real flow paths should be somewhere between the invading cluster and the straight line.
Social percolation and the influence of mass media
NASA Astrophysics Data System (ADS)
Proykova, Ana; Stauffer, Dietrich
2002-09-01
In the marketing model of Solomon and Weisbuch, people buy a product only if their neighbours tell them of its quality, and if this quality is higher than their own quality expectations. Now we introduce additional information from the mass media, which is analogous to the ghost field in percolation theory. The mass media shift the percolative phase transition observed in the model, and decrease the time after which the stationary state is reached.
NASA Astrophysics Data System (ADS)
Fang, Huaiyang; Lu, Qingshui; Gao, Zhiqiang; Shi, Runhe; Gao, Wei
2013-09-01
China economy has been rapidly increased since 1978. Rapid economic growth led to fast growth of fertilizer and pesticide consumption. A significant portion of fertilizers and pesticides entered the water and caused water quality degradation. At the same time, rapid economic growth also caused more and more point source pollution discharge into the water. Eutrophication has become a major threat to the water bodies. Worsening environment problems forced governments to take measures to control water pollution. We extracted land cover from Landsat TM images; calculated point source pollution with export coefficient method; then SWAT model was run to simulate non-point source pollution. We found that the annual TP loads from industry pollution into rivers are 115.0 t in the entire watershed. Average annual TP loads from each sub-basin ranged from 0 to 189.4 ton. Higher TP loads of each basin from livestock and human living mainly occurs in the areas where they are far from large towns or cities and the TP loads from industry are relatively low. Mean annual TP loads that delivered to the streams was 246.4 tons and the highest TP loads occurred in north part of this area, and the lowest TP loads is mainly distributed in middle part. Therefore, point source pollution has much high proportion in this area and governments should take measures to control point source pollution.
NASA Astrophysics Data System (ADS)
Mogus, Mamaru; Schmitter, Petra; Tilahun, Seifu; Steenhuise, Tammo
2016-04-01
Intensification of agriculture will bring along non-point source pollution in the Ethiopian highlands resulting in eutrophication of lakes. The first signs of eutrophication have been observed already in Lake Tana. The lake it supports the lives of millions in the surrounding through fishing, tourism, transportation and hydropower.Presently, information on non-point source pollution is lacking in the Ethiopian highlands. There are few studies carried out in the highlands on the extent and the source areas of pollution, and models are not available for predicting sediment and phosphorus loading other than those developed for temperate climates. The objective of this chapter is to review existing non-point source studies, report on our findings of sediment and phosphorus sources that are related the non-point source pollution of Lake Tana and to present a non-point source model for the Ethiopian highland based on the Parameter Efficient Semi-distributed Watershed Hydrology Model (PED-WHM).In our research we have found that the saturation excess runoff from valley bottoms and from degraded lands are prevalent in the Ethiopia highlands. The periodically runoff source areas are also the sources for the non-point source pollution and by concentrating best management practices in these source areas we expect that we can reduce pollution without affecting the profitability of the existing farms. The water balance component of the non-point source model has been performing well in predicting both the discharge and the location of the runoff source areas. Sediment and phosphorus prediction models have been developed and are currently being tested for the 7km2Awramba watershed and the 1350 km2Gumara basin. Initial results indicate that 11.2 ton/ha/year sediment load and an accumulation rate of 17.3 mg/kg/year of dissolved phosphorus from Gumara watershed joining the lake. By developing best management practices at this time before non-point source pollution is rampant and
NASA Astrophysics Data System (ADS)
Zhang, W. S.; Swaney, D. P.; Li, X. Y.; Hong, B.; Howarth, R. W.; Ding, S. H.
2015-07-01
This study provides a new approach to estimate both anthropogenic non-point-source and point-source nitrogen (N) inputs to the landscape, and determines their impacts on riverine ammonia-nitrogen (AN) flux, providing a foundation for further exploration of anthropogenic effects on N pollution. Our study site is Huai River basin of China, a water-shed with one of the highest levels of N input in the world. Multi-year average (2003-2010) inputs of N to the watershed are 27 200 ± 1100 kg N km-2 yr-1. Non-point sources comprised about 98 % of total N input, and only 2 % of inputs are directly added to the aquatic ecosystem as point sources. Fertilizer application was the largest non-point source of new N to the Huai River basin (69 % of net anthropogenic N inputs), followed by atmospheric deposition (20 %), N fixation in croplands (7 %), and N content of imported food and feed (2 %). High N inputs showed impacts on riverine AN flux: fertilizer application, point-source N input, and atmospheric N deposition were proved as more direct sources to riverine AN flux. Modes of N delivery and losses associated with biological denitrification in rivers, water consumption, interception by dams may influence the extent of export of riverine AN flux from N sources. Our findings highlight the importance of anthropogenic N inputs from both point sources and non-point sources in heavily polluted watersheds, and provide some implications for AN prediction and management.
Radio-Quiet Pulsars and Point Sources in Supernova Remnants
NASA Astrophysics Data System (ADS)
Helfand, David
2002-04-01
Since Baade and Zwicky made their prescient remark identifying the central blue star in the Crab Nebula as a neutron star, this pulsar's period has increased by 0.9 msec, turning 10^48 ergs of rotational kinetic energy into a relativistic wind that has been deposited in its surroundings. This makes the compact remnant of the supernova of 1054 AD highly conspicuous. It also makes this remnant highly anomalous. Nowhere else in the Galaxy does such a luminous young pulsar exists, despite the fact that at least half a dozen core-collapse supernovae have occurred since the Crab's birth. Indeed, the newly discovered central object in Cas A is four orders of magnitude less luminous in the X-ray band. While the Chandra and XMM-Newton Observatories are discovering an increasing number of Crab-like synchrotron nebulae (albeit, far less luminous than the prototype), they are also revealing X-ray point sources inside supernova remnants that lack detectable radio pulses and show no evidence of a relativistic outflow to power a surrounding nebula. I will provide an inventory of these objects, discuss whether or not truly radio-silent young neutron stars exist, and speculate on the emission mechanisms and power sources which make such objects shine. I will conclude with a commentary on the implications of this population for the distributions of pulsar birth parameters such as spin period, magnetic field strength, and space velocity, as well as offer a glimpse of what future observations might reveal about the demographics of core-collapse remnants.
Field-scale operation of methane biofiltration systems to mitigate point source methane emissions.
Hettiarachchi, Vijayamala C; Hettiaratchi, Patrick J; Mehrotra, Anil K; Kumar, Sunil
2011-06-01
Methane biofiltration (MBF) is a novel low-cost technique for reducing low volume point source emissions of methane (CH₄). MBF uses a granular medium, such as soil or compost, to support the growth of methanotrophic bacteria responsible for converting CH₄ to carbon dioxide (CO₂) and water (H₂O). A field research program was undertaken to evaluate the potential to treat low volume point source engineered CH₄ emissions using an MBF at a natural gas monitoring station. A new comprehensive three-dimensional numerical model was developed incorporating advection-diffusive flow of gas, biological reactions and heat and moisture flow. The one-dimensional version of this model was used as a guiding tool for designing and operating the MBF. The long-term monitoring results of the field MBF are also presented. The field MBF operated with no control of precipitation, evaporation, and temperature, provided more than 80% of CH₄ oxidation throughout spring, summer, and fall seasons. The numerical model was able to predict the CH₄ oxidation behavior of the field MBF with high accuracy. The numerical model simulations are presented for estimating CH₄ oxidation efficiencies under various operating conditions, including different filter bed depths and CH₄ flux rates. The field observations as well as numerical model simulations indicated that the long-term performance of MBFs is strongly dependent on environmental factors, such as ambient temperature and precipitation. PMID:21414700
Search for Cosmic Neutrino Point Sources with Four Years of Data from the ANTARES Telescope
NASA Astrophysics Data System (ADS)
Adrián-Martínez, S.; Samarai, I. Al; Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Anvar, S.; Ardid, M.; Astraatmadja, T.; Aubert, J.-J.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bigongiari, C.; Bogazzi, C.; Bou-Cabo, M.; Bouhou, B.; Bouwhuis, M. C.; Brunner, J.; Busto, J.; Capone, A.; Cârloganu, C.; Carr, J.; Cecchini, S.; Charif, Z.; Charvis, Ph.; Chiarusi, T.; Circella, M.; Coniglione, R.; Core, L.; Costantini, H.; Coyle, P.; Creusot, A.; Curtil, C.; De Bonis, G.; Decowski, M. P.; Dekeyser, I.; Deschamps, A.; Distefano, C.; Donzaud, C.; Dornic, D.; Dorosti, Q.; Drouhin, D.; Eberl, T.; Emanuele, U.; Enzenhöfer, A.; Ernenwein, J.-P.; Escoffier, S.; Fehn, K.; Fermani, P.; Ferri, M.; Ferry, S.; Flaminio, V.; Folger, F.; Fritsch, U.; Fuda, J.-L.; Galatà, S.; Gay, P.; Geyer, K.; Giacomelli, G.; Giordano, V.; Gleixner, A.; Gómez-González, J. P.; Graf, K.; Guillard, G.; Hallewell, G.; Hamal, M.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Herold, B.; Hößl, J.; Hsu, C. C.; de Jong, M.; Kadler, M.; Kalekin, O.; Kappes, A.; Katz, U.; Kavatsyuk, O.; Kooijman, P.; Kopper, C.; Kouchner, A.; Kreykenbohm, I.; Kulikovskiy, V.; Lahmann, R.; Lambard, G.; Larosa, G.; Lattuada, D.; Leonora, E.; Lefèvre, D.; Lim, G.; Lo Presti, D.; Loehner, H.; Loucatos, S.; Louis, F.; Mangano, S.; Marcelin, M.; Margiotta, A.; Martínez-Mora, J. A.; Meli, A.; Montaruli, T.; Morganti, M.; Motz, H.; Neff, M.; Nezri, E.; Palioselitis, D.; Păvălaş, G. E.; Payet, K.; Petrovic, J.; Piattelli, P.; Popa, V.; Pradier, T.; Presani, E.; Racca, C.; Reed, C.; Riccobene, G.; Richter, R.; Rivière, C.; Robert, A.; Roensch, K.; Rostovtsev, A.; Ruiz-Rivas, J.; Rujoiu, M.; Samtleben, D. F. E.; Sapienza, P.; Schmid, J.; Schnabel, J.; Schuller, J.-P.; Schüssler, F.; Seitz, T.; Shanidze, R.; Simeone, F.; Spies, A.; Spurio, M.; Steijger, J. J. M.; Stolarczyk, Th.; Sánchez-Losa, A.; Taiuti, M.; Tamburini, C.; Trovato, A.; Vallage, B.; Vallée, C.; Van Elewyck, V.; Vecchi, M.; Vernin, P.; Visser, E.; Wagner, S.; Wijnker, G.; Wilms, J.; de Wolf, E.; Yepes, H.; Zaborov, D.; Zornoza, J. D.; Zúñiga, J.
2012-11-01
In this paper, a time-integrated search for point sources of cosmic neutrinos is presented using the data collected from 2007 to 2010 by the ANTARES neutrino telescope. No statistically significant signal has been found and upper limits on the neutrino flux have been obtained. Assuming an E -2 ν spectrum, these flux limits are at 1-10 ×10-8 GeV cm-2 s-1 for declinations ranging from -90° to 40°. Limits for specific models of RX J1713.7-3946 and Vela X, which include information on the source morphology and spectrum, are also given.
On percolation as a cosmological test
NASA Technical Reports Server (NTRS)
Dekel, A.; West, M. J.
1985-01-01
Difficulties in the use of percolation as a complementary statistic for the galaxy clustering pattern are pointed out by studying simple toy models and dynamical N-body models that represent the competing clustering scenarios. The percolation properties are found not to be very sensitive to the presence of pancakes and strings once they are clumpy, and hence they do not distinguish properly between models that are very different. In the case of very smooth pancakes, the ability to percolate depends on sampling parameters, such as the mean number density and the volume, in a way which is unknown a priori because it depends on the same properties that the test ought to measure. This problem could, in principle, be eased by using volume-limited samples of high mean number density (an order of magnitude denser than the CfA redshift survey volume limited at 4000 km/s) and by comparing to models of identical number density and volume. An alternative approach, based on the sampling effects themselves, may provide a qualitative test for pancakes in samples of lower densities.
Percolation transition in networks with degree-degree correlation
NASA Astrophysics Data System (ADS)
Noh, Jae Dong
2007-08-01
We introduce an exponential random graph model for networks with a fixed degree distribution and a tunable degree-degree correlation. We then investigate the nature of the percolation transition in a correlated network with a Poisson degree distribution. It is found that negative correlation is irrelevant in that the percolation transition in the disassortative network belongs to the same universality class as in the uncorrelated network. Positive correlation turns out to be relevant. The percolation transition in the assortative network is characterized by the nondiverging mean size of finite clusters and power-law scalings of the density of the largest cluster and the cluster size distribution in the nonpercolating phase as well as at the critical point. Our results suggest that the unusual type of percolation transition in the growing network models reported recently may be inherited from the assortative degree-degree correlation.
THE CHANDRA COSMOS SURVEY. I. OVERVIEW AND POINT SOURCE CATALOG
Elvis, Martin; Civano, Francesca; Aldcroft, T. L.; Fruscione, Antonella; Vignali, Cristian; Puccetti, Simonetta; Fiore, Fabrizio; Cappelluti, Nico; Brusa, Marcella; Finoguenov, Alexis; Brunner, Hermann; Zamorani, G.; Comastri, Andrea; Gilli, Roberto; Miyaji, Takamitsu; Damiani, Francesco; Koekemoer, Anton M.; Urry, C.M.; Silverman, John; Mainieri, Vincenzo
2009-09-01
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg{sup 2} of the COSMOS field (centered at 10 {sup h}, +02 deg.) with an effective exposure of {approx}160 ks, and an outer 0.4 deg{sup 2} area with an effective exposure of {approx}80 ks. The limiting source detection depths are 1.9 x 10{sup -16} erg cm{sup -2} s{sup -1} in the soft (0.5-2 keV) band, 7.3 x 10{sup -16} erg cm{sup -2} s{sup -1} in the hard (2-10 keV) band, and 5.7 x 10{sup -16} erg cm{sup -2} s{sup -1} in the full (0.5-10 keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2 x 10{sup -5} (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily ({approx}50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform ({+-}12%) exposure across the inner 0.5 deg{sup 2} field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper. The full catalog is described here in detail and is available online.
Estimating dispersed and point source emissions of methane in East Anglia: results and implications
NASA Astrophysics Data System (ADS)
Harris, Neil; Connors, Sarah; Hancock, Ben; Jones, Pip; Murphy, Jonathan; Riddick, Stuart; Robinson, Andrew; Skelton, Robert; Manning, Alistair; Forster, Grant; Oram, David; O'Doherty, Simon; Young, Dickon; Stavert, Ann; Fisher, Rebecca; Lowry, David; Nisbet, Euan; Zazzeri, Guilia; Allen, Grant; Pitt, Joseph
2016-04-01
We have been investigating ways to estimate dispersed and point source emissions of methane. To do so we have used continuous measurements from a small network of instruments at 4 sites across East Anglia since 2012. These long-term series have been supplemented by measurements taken in focussed studies at landfills, which are important point sources of methane, and by measurements of the 13C:12C ratio in methane to provide additional information about its sources. These measurements have been analysed using the NAME InTEM inversion model to provide county-level emissions (~30 km x ~30 km) in East Anglia. A case study near a landfill just north of Cambridge was also analysed using a Gaussian plume model and the Windtrax dispersion model. The resulting emission estimates from the three techniques are consistent within the uncertainties, despite the different spatial scales being considered. A seasonal cycle in emissions from the landfill (identified by the isotopic measurements) is observed with higher emissions in winter than summer. This would be expected from consideration of the likely activity of methanogenic bacteria in the landfill, but is not currently represented in emission inventories such as the UK National Atmospheric Emissions Inventory. The possibility of assessing North Sea gas field emissions using ground-based measurements will also be discussed.
Percolation thresholds for rod-like particles: polydispersity effects
NASA Astrophysics Data System (ADS)
Chatterjee, Avik P.
2008-06-01
A model based upon excluded volume considerations is presented for the connectedness percolation thresholds in polydisperse systems of cylindrical rod-like nanoparticles. The dependence of the percolation threshold upon polydispersity index and number-averaged aspect ratio is examined for two different distribution functions for the rod radii and lengths. The importance of accounting for polydispersity is explored in the context of measurements of the elastic moduli and electrical conductance in fibre-filled nanocomposites.
Color and Variability Characteristics of Point Sources in the Faint Sky Variability Survey
Huber, M E; Everett, M E; Howell, S B
2005-03-07
The authors present an analysis of the color and variability characteristics for point sources in the Faint Sky Variability Survey (FSVS). The FSVS cataloged {approx} 23 square degrees in BVI filters from {approx} 16-24 mag to investigate variability in faint sources at moderate to high Galactic latitudes. Point source completeness is found to be >83% for a selected representative sample (V - 17.5-22.0 mag, B-V = 0.0-1.5) containing both photometric B, V detections and 80% of the time-sampled V data available compared to a basic internal source completeness of 99%. Multi-epoch (10-30) observations in V spanning minutes to years modeled by light curve simulations reveal amplitude sensitivities to {approx} 0.015-0.075 mag over a representative V = 18-22 mag range. Periodicity determinations appear viable to time-scales of an order 1 day or less using the most sampled fields ({approx} 30 epochs). The fraction of point sources is found to be generally variable at 5-8% over V = 17.5-22.0 mag. For V brighter than 19 mag, the variable population is dominated by low amplitude (< 0.05 mag) and blue (B-V < 0.35) sources, possibly representing a population of {gamma} Doradus stars. Overall, the dominant population of variable sources are bluer than B-V = 0.65 and have Main Sequence colors, likely reflecting larger populations of RR Lyrae, SX Phe, {gamma} Doradus, and W UMa variables.
Independent evaluation of point source fossil fuel CO2 emissions to better than 10.
Turnbull, Jocelyn Christine; Keller, Elizabeth D; Norris, Margaret W; Wiltshire, Rachael M
2016-09-13
Independent estimates of fossil fuel CO2 (CO2ff) emissions are key to ensuring that emission reductions and regulations are effective and provide needed transparency and trust. Point source emissions are a key target because a small number of power plants represent a large portion of total global emissions. Currently, emission rates are known only from self-reported data. Atmospheric observations have the potential to meet the need for independent evaluation, but useful results from this method have been elusive, due to challenges in distinguishing CO2ff emissions from the large and varying CO2 background and in relating atmospheric observations to emission flux rates with high accuracy. Here we use time-integrated observations of the radiocarbon content of CO2 ((14)CO2) to quantify the recently added CO2ff mole fraction at surface sites surrounding a point source. We demonstrate that both fast-growing plant material (grass) and CO2 collected by absorption into sodium hydroxide solution provide excellent time-integrated records of atmospheric (14)CO2 These time-integrated samples allow us to evaluate emissions over a period of days to weeks with only a modest number of measurements. Applying the same time integration in an atmospheric transport model eliminates the need to resolve highly variable short-term turbulence. Together these techniques allow us to independently evaluate point source CO2ff emission rates from atmospheric observations with uncertainties of better than 10%. This uncertainty represents an improvement by a factor of 2 over current bottom-up inventory estimates and previous atmospheric observation estimates and allows reliable independent evaluation of emissions. PMID:27573818
Multiple-well invasion percolation.
Araújo, A D; Romeu, M C; Moreira, A A; Andrade, R F S; Andrade, J S
2008-04-01
When the invasion percolation model is applied as a simplified model for the displacement of a viscous fluid by a less viscous one, the distribution of displaced mass follows two distinct universality classes, depending on the criteria used to stop the displacement. Here we study the distribution of mass for this process, in the case where four extraction wells are placed around a single injection well in the middle of a square lattice. Our analysis considers the limit where the pressure of the extraction well Pe is zero; in other words, an extraction well is capped as soon as less viscous fluid reaches that extraction well. Our results show that, as expected, the probability of stopping the production with small amounts of displaced mass is greatly reduced. We also investigate whether or not creating extra extraction wells is an efficient strategy. We show that the probability of increasing the amount of displaced fluid by adding an extra extraction well depends on the total recovered mass obtained before adding this well. The results presented here could be relevant to determine efficient strategies in oil exploration. PMID:18517620
Discontinuous percolation transitions in real physical systems
NASA Astrophysics Data System (ADS)
Cho, Y. S.; Kahng, B.
2011-11-01
We study discontinuous percolation transitions (PTs) in the diffusion-limited cluster aggregation model of the sol-gel transition as an example of real physical systems, in which the number of aggregation events is regarded as the number of bonds occupied in the system. When particles are Brownian, in which cluster velocity depends on cluster size as vs˜sη with η=-0.5, a larger cluster has less probability to collide with other clusters because of its smaller mobility. Thus, the cluster is effectively more suppressed in growth of its size. Then the giant cluster size increases drastically by merging those suppressed clusters near the percolation threshold, exhibiting a discontinuous PT. We also study the tricritical behavior by controlling the parameter η, and the tricritical point is determined by introducing an asymmetric Smoluchowski equation.
Fission gas bubble percolation on crystallographically consistent grain boundary networks
NASA Astrophysics Data System (ADS)
Sabogal-Suárez, Daniel; David Alzate-Cardona, Juan; Restrepo-Parra, Elisabeth
2016-07-01
Fission gas release in nuclear fuels can be modeled in the framework of percolation theory, where each grain boundary is classified as open or closed to the release of the fission gas. In the present work, two-dimensional grain boundary networks were assembled both at random and in a crystallographically consistent manner resembling a general textured microstructure. In the crystallographically consistent networks, grain boundaries were classified according to its misorientation. The percolation behavior of the grain boundary networks was evaluated as a function of radial cracks and radial thermal gradients in the fuel pellet. Percolation thresholds tend to shift to the left with increasing length and number of cracks, especially in the presence of thermal gradients. In general, the topology and percolation behavior of the crystallographically consistent networks differs from those of the random network.
NASA Astrophysics Data System (ADS)
Tang, Y. B.; Li, M.; Bernabé, Y.; Tang, H. M.; Li, X. F.; Bai, X. Y.; Tao, Z. W.
2015-06-01
In this paper, we modelled the electrical transport behaviour of bimodal carbonate rocks from a reservoir in China using dual-pore networks. One basic assumption, generally supported by experimental data and microstructure observations in the reservoir samples, was that the low porosity, monomodal rocks had the same properties and structure as the microporous matrix of the high porosity, bimodal samples. We assumed that the matrix was homogeneous and always interconnected but that the connectivity and the pore size distribution of macropore system was randomly variable. Both pore systems were supposed to act locally as `in parallel' electrical conductors, an approach previously used by Bauer et al. Hence, the effect of matrix properties, macropore size distribution and connectivity on electrical properties of bimodal rocks could be modelled and investigated. We simulated electrical current through 3-D, simple cubic and body-centred cubic networks with different coordination numbers, different pipe radius distributions of macropore system and different matrix properties. The main result was that the formation factor of dual-pore network obeyed a `universal' scaling relationship (i.e. independent of lattice type). Based on this result, we extended the power-law model derived by Bernabé et al. for monomodal porous media. We developed methods for evaluating the scale-invariant pore structure parameters in the model using conventional core analysis and satisfactorily tested the proposed model against experimental data from the Chinese reservoir as well as some other previously published data sets.
Percolation Theory and Modern Hydraulic Fracturing
NASA Astrophysics Data System (ADS)
Norris, J. Q.; Turcotte, D. L.; Rundle, J. B.
2015-12-01
During the past few years, we have been developing a percolation model for fracking. This model provides a powerful tool for understanding the growth and properties of the complex fracture networks generated during a modern high volume hydraulic fracture stimulations of tight shale reservoirs. The model can also be used to understand the interaction between the growing fracture network and natural reservoir features such as joint sets and faults. Additionally, the model produces a power-law distribution of bursts which can easily be compared to observed microseismicity.
Clique percolation in random graphs
NASA Astrophysics Data System (ADS)
Li, Ming; Deng, Youjin; Wang, Bing-Hong
2015-10-01
As a generation of the classical percolation, clique percolation focuses on the connection of cliques in a graph, where the connection of two k cliques means that they share at least l
NASA Astrophysics Data System (ADS)
Cheng, Wei Ping; Jia, Yafei
2010-04-01
A backward location probability density function (BL-PDF) method capable of identifying location of point sources in surface waters is presented in this paper. The relation of forward location probability density function (FL-PDF) and backward location probability density, based on adjoint analysis, is validated using depth-averaged free-surface flow and mass transport models and several surface water test cases. The solutions of the backward location PDF transport equation agreed well to the forward location PDF computed using the pollutant concentration at the monitoring points. Using this relation and the distribution of the concentration detected at the monitoring points, an effective point source identification method is established. The numerical error of the backward location PDF simulation is found to be sensitive to the irregularity of the computational meshes, diffusivity, and velocity gradients. The performance of identification method is evaluated regarding the random error and number of observed values. In addition to hypothetical cases, a real case was studied to identify the source location where a dye tracer was instantaneously injected into a stream. The study indicated the proposed source identification method is effective, robust, and quite efficient in surface waters; the number of advection-diffusion equations needed to solve is equal to the number of observations.
Evaluation of the Legibility for Characters Composed of Multiple Point Sources in Fog
NASA Astrophysics Data System (ADS)
Tsukada, Yuki; Toyofuku, Yoshinori; Aoki, Yoshiro
The luminance conditions were investigated, at that the characters composed of multiple point sources were as legible as a character having a uniformly luminous surface in fog, in order to make the use of variable-message signs practical at airports. As the results, it was found that the thicker the fog or the higher the illuminance, the better the legibility of the point source characters become compared with the uniformly luminous surface characters. It is supposed that the ease of extracting each individual point source makes the characters composed of multiple point sources more legible even if their luminance is low. So the results show that if the conventional luminance standard is applied to the average luminance of a character composed of multiple point sources, a character composed of multiple point sources could be recognized without any degradation in legibility.
Fiber Optic Distributed Temperature Sensing of Recharge Basin Percolation Dynamics
NASA Astrophysics Data System (ADS)
Becker, M.; Allen, E. M.; Hutchinson, A.
2014-12-01
into question the relevance of simple wetting models for predicting percolation behavior in infiltration basins.
Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics.
Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang
2016-08-01
Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics.
Percolation velocity dependence on local concentration in bidisperse granular flows
NASA Astrophysics Data System (ADS)
Jones, Ryan P.; Xiao, Hongyi; Deng, Zhekai; Umbanhowar, Paul B.; Lueptow, Richard M.
The percolation velocity, up, of granular material in size or density bidisperse mixtures depends on the local concentration, particle size ratio, particle density ratio, and shear rate, γ ˙. Discrete element method computational results were obtained for bounded heap flows with size ratios between 1 and 3 and for density ratios between 1 and 4. The results indicate that small particles percolate downward faster when surrounded by large particles than large particles percolate upward when surrounded by small particles, as was recently observed in shear-box experiments. Likewise, heavy particles percolate downward faster when surrounded by light particles than light particles percolate upward when surrounded by heavy particles. The dependence of up / γ ˙ on local concentration results in larger percolation flux magnitudes at high concentrations of large (or light) particles compared to high concentrations of small (or heavy) particles, while local volumetric flux is conserved. The dependence of up / γ ˙ on local concentration can be incorporated into a continuum model, but the impact on global segregation patterns is usually minimal. Partially funded by Dow Chemical Company and NSF Grant No. CBET-1511450.
Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics.
Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang
2016-01-01
Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics. PMID:27476998
Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics
NASA Astrophysics Data System (ADS)
Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang
2016-08-01
Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics.
Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics
Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang
2016-01-01
Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics. PMID:27476998
Quantification and index of non-point source pollution in Taihu Lake region with GIS.
Guo, H Y; Wang, X R; Zhu, J G
2004-01-01
The contribution of phosphorus and nitrogen from non-point source pollution (NPS) in the Taihu Lake region was investigated through case study and surveying in the town of Xueyan, From experimental results coupled with survey and statistics in the studied area, the distribution of nitrogen and phosphorus input to the water body is achieved from four main sources: agricultural land, village, the town center and the poultry factory. The results showed that about 38% of total phosphorus (TP) and 48% of total nitrogen (TN) discharged is from agricultural land, 33% of TP and 40% TN from village residents, 25% of TP and 10% of TN from the town center and 4% of TP and 2% of TN from the poultry factory. The Agricultural Non-point Pollution Potential Index (APPI) system for identifying and ranking critical areas of NPS was established with a Geographic Information Systems (GIS)-based technology. Quantification of the key factors in non-point sources pollution was carried out utilizing the following: Sediment Production Index (SPI), Runoff Index (RI), People and Animal Loading Index (PALI) and Chemical Use Index (CUI). These are the core parts of the model, and the weighting factor of each index was evaluated according the results of quantification. The model was successfully applied for evaluating APPI in Xueyan. Results from the model showed that the critical area identified for NPS control in Xueyan. The model has several advantages including: requiring fewer parameters, easy acquirement of these parameters, friendly interface, and convenience of operation. In addition it is especially useful for identifying critical areas of NPS when the basic data are not fully accessible, which is the present situation in China. PMID:15499770
Percolation transition in thermal conductivity of β-Si3N4 filledepoxy
NASA Astrophysics Data System (ADS)
Zhu, Yuan; Chen, Kexin; Kang, Feiyu
2013-03-01
Homemade β-Si3N4 particles of different aspect ratio and commercial epoxy resin were used to form heterogeneous composites and a percolation transition was observed. The pre-percolation phase, near percolation phase and post-percolation phase were discussed with different models. In the near percolation phase, multicrystal model was taken to modify the percolation scaling law and provide physical images to the dumb proportional coefficient. X-ray holograph was used to compare the 3D morphology of the composites, and surface modification was found capable of enhancing the particle dispersion. The aspect ratio dependence was also discussed and the competition between the bridging effect and the interface thermal resistance was considered as the cause of the turning point in the thermal conductivity.
Epidemic Percolation Networks, Epidemic Outcomes, and Interventions
Kenah, Eben; Miller, Joel C.
2011-01-01
Epidemic percolation networks (EPNs) are directed random networks that can be used to analyze stochastic “Susceptible-Infectious-Removed” (SIR) and “Susceptible-Exposed-Infectious-Removed” (SEIR) epidemic models, unifying and generalizing previous uses of networks and branching processes to analyze mass-action and network-based S(E)IR models. This paper explains the fundamental concepts underlying the definition and use of EPNs, using them to build intuition about the final outcomes of epidemics. We then show how EPNs provide a novel and useful perspective on the design of vaccination strategies.
Percolation analysis of force networks in anisotropic granular matter
NASA Astrophysics Data System (ADS)
Pastor-Satorras, Romualdo; Miguel, M.-Carmen
2012-02-01
We study the percolation properties of force networks in an anisotropic model for granular packings, the so-called q-model. Following the original recipe of Ostojic et al (2006 Nature 439 828), we consider a percolation process in which forces smaller than a given threshold f are deleted in the network. For a critical threshold fc, the system experiences a transition akin to percolation. We determine the point of this transition and its characteristic critical exponents applying a finite-size scaling analysis that takes explicitly into account the directed nature of the q-model. By means of extensive numerical simulations, we show that this percolation transition is strongly affected by the anisotropic nature of the model, yielding characteristic exponents which are neither those found in isotropic granular systems nor those in the directed version of standard percolation. The differences shown by the computed exponents can be related to the presence of strong directed correlations and mass conservation laws in the model under scrutiny.
Percolation of interaction diffusing particles
NASA Technical Reports Server (NTRS)
Selinger, Robin Blumberg; Stanley, H. Eugene
1990-01-01
The connectivity properties of systems of diffusing interacting particles with the blind and myopic diffusion rules are studied. It is found that the blind rule case is equivalent to the lattice gas with J = 0 in all dimensions. The connectivity properties of blind rule diffusion are described by random site percolation due to the fact that the density on neighboring sites is uncorrelated.
Krings, Thomas; Mauerhofer, Eric
2011-06-01
This work improves the reliability and accuracy in the reconstruction of the total isotope activity content in heterogeneous nuclear waste drums containing point sources. The method is based on χ(2)-fits of the angular dependent count rate distribution measured during a drum rotation in segmented gamma scanning. A new description of the analytical calculation of the angular count rate distribution is introduced based on a more precise model of the collimated detector. The new description is validated and compared to the old description using MCNP5 simulations of angular dependent count rate distributions of Co-60 and Cs-137 point sources. It is shown that the new model describes the angular dependent count rate distribution significantly more accurate compared to the old model. Hence, the reconstruction of the activity is more accurate and the errors are considerably reduced that lead to more reliable results. Furthermore, the results are compared to the conventional reconstruction method assuming a homogeneous matrix and activity distribution.
SEARCH FOR COSMIC NEUTRINO POINT SOURCES WITH FOUR YEARS OF DATA FROM THE ANTARES TELESCOPE
Adrian-Martinez, S.; Ardid, M.; Bou-Cabo, M.; Andre, M.; Anghinolfi, M.; Anton, G.; Anvar, S.; Astraatmadja, T.; Bogazzi, C.; Bouwhuis, M. C.; Baret, B.; Bouhou, B.; Basa, S.; Biagi, S.; and others
2012-11-20
In this paper, a time-integrated search for point sources of cosmic neutrinos is presented using the data collected from 2007 to 2010 by the ANTARES neutrino telescope. No statistically significant signal has been found and upper limits on the neutrino flux have been obtained. Assuming an E {sup -2} {sub {nu}} spectrum, these flux limits are at 1-10 Multiplication-Sign 10{sup -8} GeV cm{sup -2} s{sup -1} for declinations ranging from -90 Degree-Sign to 40 Degree-Sign . Limits for specific models of RX J1713.7-3946 and Vela X, which include information on the source morphology and spectrum, are also given.
Mixing of a point-source indoor pollutant: Numerical predictions and comparison with experiments
Lobscheid, C.; Gadgil, A.J.
2002-01-01
In most practical estimates of indoor pollutant exposures, it is common to assume that the pollutant is uniformly and instantaneously mixed in the indoor space. It is also commonly known that this assumption is simplistic, particularly for point sources, and for short-term or localized indoor exposures. We report computational fluid dynamics (CFD) predictions of mixing time of a point-pulse release of a pollutant in an unventilated mechanically mixed isothermal room. We aimed to determine the adequacy of the standard RANS two-equation ({kappa}-{var_epsilon}) turbulence model to predict the mixing times under these conditions. The predictions were made for the twelve mixing time experiments performed by Drescher et al. (1995). We paid attention to adequate grid resolution, suppression of numerical diffusion, and careful simulation of the mechanical blowers used in the experiments. We found that the predictions are in good agreement with experimental measurements.
Resolving the Location of Acoustic Point Sources Scattered Due to the Presence of a Skull Phantom
NASA Astrophysics Data System (ADS)
Sadler, J.; Shapoori, K.; Malyarenko, E.; DiCarlo, A.; Dech, J.; Severin, F.; Maev, R. Gr.
This paper considers resolving the location of a foreign object in the brain without the removal of the skull bone by detecting and processing the acoustic waves emitted from the foreign object modeled as point source. The variable thickness of the skull bone causes propagation acoustic waves to be scattered in such a manner that the acoustic wave undergoes a variable time delay relative to its entry point on the skull. Matched filtering can be used to detect the acoustic wave front, the time delay variations of the skull can be corrected for, and matched filtering time reversal algorithms can then detect the location of the acoustic source. This process is examined experimentally in a water tank system containing an acoustic source, custom-made skull phantom, and receiver. The apparatus is arranged in transmission mode so that the acoustic waves are emitted from the source, scattered by the phantom, and then received by a second transducer. The skull phantom has been designed so that the acoustic properties (velocity, density, and attenuation correspond approximately to those of a typical human skull. In addition, the phantom has been molded so that the surface closest to the acoustic source has smoothly oscillating ridges and valleys and a flat outer surface, approximately modeling a real-world skull bone. The data obtained from the experiment is processed to detect and extract the scattered acoustic wave front and correct for the time of flight variations in the skull. This re-creates the approximate wave front of a point source, whose location can be resolved via a matched filtering time reversal algorithm. The results of this process are examined for cases where there is no phantom present (no scattering), and with the phantom present. Comparison of these results shows a correlation between the calculated locations of the acoustic source and the expected location.
Radio Astronomical Polarimetry and Point-Source Calibration
NASA Astrophysics Data System (ADS)
van Straten, W.
2004-05-01
A mathematical framework is presented for use in the experimental determination of the polarimetric response of observatory instrumentation. Elementary principles of linear algebra are applied to model the full matrix description of the polarization measurement equation by least-squares estimation of nonlinear, scalar parameters. The formalism is applied to calibrate the center element of the Parkes Multibeam receiver using observations of the millisecond pulsar PSR J0437-4715 and the radio galaxy 3C 218 (Hydra A).
A CMB foreground study in WMAP data: Extragalactic point sources and zodiacal light emission
NASA Astrophysics Data System (ADS)
Chen, Xi
The Cosmic Microwave Background (CMB) radiation is the remnant heat from the Big Bang. It serves as a primary tool to understand the global properties, content and evolution of the universe. Since 2001, NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite has been napping the full sky anisotropy with unprecedented accuracy, precision and reliability. The CMB angular power spectrum calculated from the WMAP full sky maps not only enables accurate testing of cosmological models, but also places significant constraints on model parameters. The CMB signal in the WMAP sky maps is contaminated by microwave emission from the Milky Way and from extragalactic sources. Therefore, in order to use the maps reliably for cosmological studies, the foreground signals must be well understood and removed from the maps. This thesis focuses on the separation of two foreground contaminants from the WMAP maps: extragalactic point sources and zodiacal light emission. Extragalactic point sources constitute the most important foreground on small angular scales. Various methods have been applied to the WMAP single frequency maps to extract sources. However, due to the limited angular resolution of WMAP, it is possible to confuse positive CMB excursions with point sources or miss sources that are embedded in negative CMB fluctuations. We present a novel CMB-free source finding technique that utilizes the spectrum difference of point sources and CMB to form internal linear combinations of multifrequency maps to suppress the CMB and better reveal sources. When applied to the WMAP 41, 64 and 94 GHz maps, this technique has not only enabled detection of sources that are previously cataloged by independent methods, but also allowed disclosure of new sources. Without the noise contribution from the CMB, this method responds rapidly with the integration time. The number of detections varies as 0( t 0.72 in the two-band search and 0( t 0.70 in the three-band search from one year to five years
NASA Astrophysics Data System (ADS)
Zhang, S.; Tang, L.
2007-05-01
Panjiakou Reservoir is an important drinking water resource in Haihe River Basin, Hebei Province, People's Republic of China. The upstream watershed area is about 35,000 square kilometers. Recently, the water pollution in the reservoir is becoming more serious owing to the non-point pollution as well as point source pollution on the upstream watershed. To effectively manage the reservoir and watershed and develop a plan to reduce pollutant loads, the loading of non-point and point pollution and their distribution on the upstream watershed must be understood fully. The SWAT model is used to simulate the production and transportation of the non-point source pollutants in the upstream watershed of the Panjiakou Reservoir. The loadings of non-point source pollutants are calculated for different hydrologic years and the spatial and temporal characteristics of non-point source pollution are studied. The stream network and topographic characteristics of the stream network and sub-basins are all derived from the DEM by ArcGIS software. The soil and land use data are reclassified and the soil physical properties database file is created for the model. The SWAT model was calibrated with observed data of several hydrologic monitoring stations in the study area. The results of the calibration show that the model performs fairly well. Then the calibrated model was used to calculate the loadings of non-point source pollutants for a wet year, a normal year and a dry year respectively. The time and space distribution of flow, sediment and non-point source pollution were analyzed depending on the simulated results. The comparison of different hydrologic years on calculation results is dramatic. The loading of non-point source pollution in the wet year is relatively larger but smaller in the dry year since the non-point source pollutants are mainly transported through the runoff. The pollution loading within a year is mainly produced in the flood season. Because SWAT is a
X-Ray Analysis of Point Sources and Diffuse Gas in Hickson Compact Groups
NASA Astrophysics Data System (ADS)
Broming, Emma J.; Fuse, C.
2010-01-01
In an effort to determine the evolutionary state of Hickson Compact Groups (HCGs), we have performed an analysis of the sixteen HCGs in the Chandra X-Ray Observatory archives. HCGs are dense galactic systems, interacting on short time scales, which are ideal for studying galaxy mergers and interactions. We have analyzed both the diffuse gas emission of the compact groups as well as their associated individual point source populations. The total X-ray gas and total point source luminosities were used to determine the group's state of evolution. It was expected that the point source activity would allow for a clear-cut separation between compact groups in different evolutionary states. The sample groups were sorted into three evolutionary categories. Type-A groups are young systems, displaying a group dominated by spiral galaxies, active star formation, and little intragroup X-ray gas. Type-B groups are characterized by an intermediate X-ray point source population, an increased activity and interaction between group members, and intermediate diffuse gas component. HCG 97 is an example of a type-B system. It contains an intragroup gas medium, and eleven associated point sources. As the system further evolves, we expect to find a greater number of point sources. Type-C systems display an advanced stage of interaction between members, an extensive luminous point source population and a large diffuse gas reservoir. HCG 92, Stephan's Quintet, is the archetypical type-C system; it contains a large intragroup gas halo and twenty-six associated point sources. The archival HCGs investigated display a positive correlation between total point source luminosity and total diffuse gas luminosity. The results suggest X-ray point sources can be used to evaluate the evolutionary state of a group. Further research will probe the connection between fully coalesced compact groups and isolated elliptical galaxies.
Explosive percolation transitions in growing networks
NASA Astrophysics Data System (ADS)
Oh, S. M.; Son, S.-W.; Kahng, B.
2016-03-01
Recent extensive studies of the explosive percolation (EP) model revealed that the EP transition is second order with an extremely small value of the critical exponent β associated with the order parameter. This result was obtained from static networks, in which the number of nodes in the system remains constant during the evolution of the network. However, explosive percolating behavior of the order parameter can be observed in social networks, which are often growing networks, where the number of nodes in the system increases as dynamics proceeds. However, extensive studies of the EP transition in such growing networks are still missing. Here we study the nature of the EP transition in growing networks by extending an existing growing network model to a general case in which m node candidates are picked up in the Achiloptas process. When m =2 , this model reduces to the existing model, which undergoes an infinite-order transition. We show that when m ≥3 , the transition becomes second order due to the suppression effect against the growth of large clusters. Using the rate-equation approach and performing numerical simulations, we also show that the exponent β decreases algebraically with increasing m , whereas it does exponentially in a corresponding static random network model. Finally, we find that the hyperscaling relations hold but in different forms.
Explosive percolation transitions in growing networks.
Oh, S M; Son, S-W; Kahng, B
2016-03-01
Recent extensive studies of the explosive percolation (EP) model revealed that the EP transition is second order with an extremely small value of the critical exponent β associated with the order parameter. This result was obtained from static networks, in which the number of nodes in the system remains constant during the evolution of the network. However, explosive percolating behavior of the order parameter can be observed in social networks, which are often growing networks, where the number of nodes in the system increases as dynamics proceeds. However, extensive studies of the EP transition in such growing networks are still missing. Here we study the nature of the EP transition in growing networks by extending an existing growing network model to a general case in which m node candidates are picked up in the Achiloptas process. When m = 2, this model reduces to the existing model, which undergoes an infinite-order transition. We show that when m ≥ 3, the transition becomes second order due to the suppression effect against the growth of large clusters. Using the rate-equation approach and performing numerical simulations, we also show that the exponent β decreases algebraically with increasing m, whereas it does exponentially in a corresponding static random network model. Finally, we find that the hyperscaling relations hold but in different forms. PMID:27078375
Point source atom interferometry with a cloud of finite size
NASA Astrophysics Data System (ADS)
Hoth, Gregory W.; Pelle, Bruno; Riedl, Stefan; Kitching, John; Donley, Elizabeth A.
2016-08-01
We demonstrate a two axis gyroscope by the use of light pulse atom interferometry with an expanding cloud of atoms in the regime where the cloud has expanded by 1.1-5 times its initial size during the interrogation. Rotations are measured by analyzing spatial fringe patterns in the atom population obtained by imaging the final cloud. The fringes arise from a correlation between an atom's initial velocity and its final position. This correlation is naturally created by the expansion of the cloud, but it also depends on the initial atomic distribution. We show that the frequency and contrast of these spatial fringes depend on the details of the initial distribution and develop an analytical model to explain this dependence. We also discuss several challenges that must be overcome to realize a high-performance gyroscope with this technique.
Uncertainty Analysis of non-point source pollution control facilities design techniques in Korea
NASA Astrophysics Data System (ADS)
Lee, J.; Okjeong, L.; Gyeong, C. B.; Park, M. W.; Kim, S.
2015-12-01
The design of non-point sources control facilities in Korea is divided largely by the stormwater capture ratio, the stormwater load capture ratio, and the pollutant reduction efficiency of the facility. The stormwater capture ratio is given by a design formula as a function of the water quality treatment capacity, the greater the capacity, the more the amount of stormwater intercepted by the facility. The stormwater load capture ratio is defined as the ratio of the load entering the facility of the total pollutant load generated in the target catchment, and is given as a design formula represented by a function of the stormwater capture ratio. In order to estimate the stormwater capture ratio and load capture ratio, a lot of quantitative analysis of hydrologic processes acted in pollutant emission is required, but these formulas have been applied without any verification. Since systematic monitoring programs were insufficient, verification of these formulas was fundamentally impossible. However, recently the Korean ministry of Environment has conducted an long-term systematic monitoring project, and thus the verification of the formulas became possible. In this presentation, the stormwater capture ratio and load capture ratio are re-estimated using actual TP data obtained from long-term monitoring program at Noksan industrial complex located in Busan, Korea. Through the re-estimated process, the uncertainty included in the design process that has been applied until now will be shown in a quantitative extent. In addition, each uncertainty included in the stormwater capture ratio estimation and in the stormwater load capture ratio estimation will be expressed to quantify the relative impact on the overall non-point pollutant control facilities design process. Finally, the SWMM-Matlab interlocking module for model parameters estimation will be introduced. Acknowledgement This subject is supported by Korea Ministry of Environment as "The Eco Innovation Project : Non-point
Percolation on bipartite scale-free networks
NASA Astrophysics Data System (ADS)
Hooyberghs, H.; Van Schaeybroeck, B.; Indekeu, J. O.
2010-08-01
Recent studies introduced biased (degree-dependent) edge percolation as a model for failures in real-life systems. In this work, such process is applied to networks consisting of two types of nodes with edges running only between nodes of unlike type. Such bipartite graphs appear in many social networks, for instance in affiliation networks and in sexual-contact networks in which both types of nodes show the scale-free characteristic for the degree distribution. During the depreciation process, an edge between nodes with degrees k and q is retained with a probability proportional to (, where α is positive so that links between hubs are more prone to failure. The removal process is studied analytically by introducing a generating functions theory. We deduce exact self-consistent equations describing the system at a macroscopic level and discuss the percolation transition. Critical exponents are obtained by exploiting the Fortuin-Kasteleyn construction which provides a link between our model and a limit of the Potts model.
Guided wave radiation from a point source in the proximity of a pipe bend
Brath, A. J.; Nagy, P. B.; Simonetti, F.; Instanes, G.
2014-02-18
Throughout the oil and gas industry corrosion and erosion damage monitoring play a central role in managing asset integrity. Recently, the use of guided wave technology in conjunction with tomography techniques has provided the possibility of obtaining point-by-point maps of wall thickness loss over the entire volume of a pipeline section between two ring arrays of ultrasonic transducers. However, current research has focused on straight pipes while little work has been done on pipe bends which are also the most susceptible to developing damage. Tomography of the bend is challenging due to the complexity and computational cost of the 3-D elastic model required to accurately describe guided wave propagation. To overcome this limitation, we introduce a 2-D anisotropic inhomogeneous acoustic model which represents a generalization of the conventional unwrapping used for straight pipes. The shortest-path ray-tracing method is then applied to the 2-D model to compute ray paths and predict the arrival times of the fundamental flexural mode, A0, excited by a point source on the straight section of pipe entering the bend and detected on the opposite side. Good agreement is found between predictions and experiments performed on an 8” diameter (D) pipe with 1.5 D bend radius. The 2-D model also reveals the existence of an acoustic lensing effect which leads to a focusing phenomenon also confirmed by the experiments. The computational efficiency of the 2-D model makes it ideally suited for tomography algorithms.
Guided wave radiation from a point source in the proximity of a pipe bend
NASA Astrophysics Data System (ADS)
Brath, A. J.; Simonetti, F.; Nagy, P. B.; Instanes, G.
2014-02-01
Throughout the oil and gas industry corrosion and erosion damage monitoring play a central role in managing asset integrity. Recently, the use of guided wave technology in conjunction with tomography techniques has provided the possibility of obtaining point-by-point maps of wall thickness loss over the entire volume of a pipeline section between two ring arrays of ultrasonic transducers. However, current research has focused on straight pipes while little work has been done on pipe bends which are also the most susceptible to developing damage. Tomography of the bend is challenging due to the complexity and computational cost of the 3-D elastic model required to accurately describe guided wave propagation. To overcome this limitation, we introduce a 2-D anisotropic inhomogeneous acoustic model which represents a generalization of the conventional unwrapping used for straight pipes. The shortest-path ray-tracing method is then applied to the 2-D model to compute ray paths and predict the arrival times of the fundamental flexural mode, A0, excited by a point source on the straight section of pipe entering the bend and detected on the opposite side. Good agreement is found between predictions and experiments performed on an 8" diameter (D) pipe with 1.5 D bend radius. The 2-D model also reveals the existence of an acoustic lensing effect which leads to a focusing phenomenon also confirmed by the experiments. The computational efficiency of the 2-D model makes it ideally suited for tomography algorithms.
Point source influence on observed extreme pollution levels in a monitoring network
NASA Astrophysics Data System (ADS)
Ensor, Katherine B.; Ray, Bonnie K.; Charlton, Sarah J.
2014-08-01
This paper presents a strategy to quantify the influence major point sources in a region have on extreme pollution values observed at each of the monitors in the network. We focus on the number of hours in a day the levels at a monitor exceed a specified health threshold. The number of daily exceedances are modeled using observation-driven negative binomial time series regression models, allowing for a zero-inflation component to characterize the probability of no exceedances in a particular day. The spatial nature of the problem is addressed through the use of a Gaussian plume model for atmospheric dispersion computed at locations of known emissions, creating covariates that impact exceedances. In order to isolate the influence of emitters at individual monitors, we fit separate regression models to the series of counts from each monitor. We apply a final model clustering step to group monitor series that exhibit similar behavior with respect to mean, variability, and common contributors to support policy decision making. The methodology is applied to eight benzene pollution series measured at air quality monitors around the Houston ship channel, a major industrial port.
Numerical simulation of electromagnetic acoustic transducers using distributed point source method.
Eskandarzade, M; Kundu, T; Liebeaux, N; Placko, D; Mobadersani, F
2010-05-01
In spite of many advances in analytical and numerical modeling techniques for solving different engineering problems, an efficient solution technique for wave propagation modeling of an electromagnetic acoustic transducer (EMAT) system is still missing. Distributed point source method (DPSM) is a newly developed semi-analytical technique developed since 2000 by Placko and Kundu (2007) [12] that is very powerful and straightforward for solving various engineering problems, including acoustic and electromagnetic modeling problems. In this study DPSM has been employed to model the Lorentz type EMAT with a meander line and flat spiral type coil. The problem of wave propagation has been solved and eddy currents and Lorentz forces have been calculated. The displacement field has been obtained as well. While modeling the Lorentz force the effect of dynamic magnetic field has been considered that most current analyses ignore. Results from this analysis have been compared with the finite element method (FEM) based predictions. It should be noted that with the current state of knowledge this problem can be solved only by FEM.
Bond percolation in higher dimensions
NASA Astrophysics Data System (ADS)
Corwin, Eric I.; Stinchcombe, Robin; Thorpe, M. F.
2013-07-01
We collect results for bond percolation on various lattices from two to fourteen dimensions that, in the limit of large dimension d or number of neighbors z, smoothly approach a randomly diluted Erdős-Rényi graph. We include results on bond-diluted hypersphere packs in up to nine dimensions, which show the mean coordination, excess kurtosis, and skewness evolving smoothly with dimension towards the Erdős-Rényi limit.
Percolation in dense storage arrays
NASA Astrophysics Data System (ADS)
Kirkpatrick, Scott; Wilcke, Winfried W.; Garner, Robert B.; Huels, Harald
2002-11-01
As computers and their accessories become smaller, cheaper, and faster the providers of news, retail sales, and other services we now take for granted on the Internet have met their increasing computing needs by putting more and more computers, hard disks, power supplies, and the data communications linking them to each other and to the rest of the wired world into ever smaller spaces. This has created a new and quite interesting percolation problem. It is no longer desirable to fix computers, storage or switchgear which fail in such a dense array. Attempts to repair things are all too likely to make problems worse. The alternative approach, letting units “fail in place”, be removed from service and routed around, means that a data communications environment will evolve with an underlying regular structure but a very high density of missing pieces. Some of the properties of this kind of network can be described within the existing paradigm of site or bond percolation on lattices, but other important questions have not been explored. I will discuss 3D arrays of hundreds to thousands of storage servers (something which it is quite feasible to build in the next few years), and show that bandwidth, but not percolation fraction or shortest path lengths, is the critical factor affected by the “fail in place” disorder. Redundancy strategies traditionally employed in storage systems may have to be revised. Novel approaches to routing information among the servers have been developed to minimize the impact.
Bounds for percolation thresholds on directed and undirected graphs
NASA Astrophysics Data System (ADS)
Hamilton, Kathleen; Pryadko, Leonid
2015-03-01
Percolation theory is an efficient approach to problems with strong disorder, e.g., in quantum or classical transport, composite materials, and diluted magnets. Recently, the growing role of big data in scientific and industrial applications has led to a renewed interest in graph theory as a tool for describing complex connections in various kinds of networks: social, biological, technological, etc. In particular, percolation on graphs has been used to describe internet stability, spread of contagious diseases and computer viruses; related models describe market crashes and viral spread in social networks. We consider site-dependent percolation on directed and undirected graphs, and present several exact bounds for location of the percolation transition in terms of the eigenvalues of matrices associated with graphs, including the adjacency matrix and the Hashimoto matrix used to enumerate non-backtracking walks. These bounds correspond t0 a mean field approximation and become asymptotically exact for graphs with no short cycles. We illustrate this convergence numerically by simulating percolation on several families of graphs with different cycle lengths. This research was supported in part by the NSF Grant PHY-1416578 and by the ARO Grant W911NF-11-1-0027.
NASA Astrophysics Data System (ADS)
Foster-Wittig, Tierney A.; Thoma, Eben D.; Albertson, John D.
2015-08-01
Emerging mobile fugitive emissions detection and measurement approaches require robust inverse source algorithms to be effective. Two Gaussian plume inverse approaches are described for estimating emission rates from ground-level point sources observed from remote vantage points. The techniques were tested using data from 41 controlled methane release experiments (14 studies) and further investigated using 7 field studies executed downwind of oil and gas well pads in Wyoming. Analyzed measurements were acquired from stationary observation locations 18-106 m downwind of the emission sources. From the fluctuating wind direction, the lateral plume geometry is reconstructed using a derived relationship between the wind direction and crosswind plume position. The crosswind plume spread is determined with both modeled and reconstructed Gaussian plume approaches and estimates of source emission rates are found through inversion. The source emission rates were compared to a simple point source Gaussian emission estimation approach that is part of Draft EPA Method OTM 33A. Compared to the known release rates, the modeled, reconstructed, and point source Gaussian controlled release results yield average percent errors of -5%, -2%, and 6% with standard deviations of 29%, 25%, and 37%, respectively. Compared to each other, the three methods agree within 30% for 78% of all 48 observations (41 CR and 7 Wyoming).
Novel percolation transitions and coupled catastrophes
NASA Astrophysics Data System (ADS)
D'Souza, Raissa
Collections of interdependent networks are at the core of modern society, spanning physical, biological and social systems. Simple mathematical models of the structure and function of networks can provide important insights into real-world systems, enhancing our ability to steer and control them. Here our focus is on abrupt changes in networks, due both to phase transitions and to jumping between bi-stable equilibria. We begin with an overview of novel classes of percolation phase transitions that result from repeated, small interventions intended to delay the transition. These new phenomena allow us to extend percolation approaches to modular networks, Brownian motion, and cluster growth dynamics. We then focus on abrupt transitions due to a system jumping between bi-stable equilibria, modeled as a cusp catastrophe in nonlinear dynamics. We show that when systems that each undergo a cusp catastrophe interact, we can observe a new phenomena of catastrophe-hopping leading to non-local cascading failures. Here an intermediate system facilitates the propagation of a sudden change or collapse, and we show that catastrophe hopping is consistent with the outbreak of protests observed during the Arab Spring of 2011.
Federal Register 2010, 2011, 2012, 2013, 2014
2010-03-08
... From the Federal Register Online via the Government Publishing Office ENVIRONMENTAL PROTECTION... and Development Point Source Category; Correction AGENCY: Environmental Protection Agency. ACTION: Correcting amendments. SUMMARY: The Environmental Protection Agency (EPA) is correcting a date in a...
Percolation-based precursors of transitions in extended systems
NASA Astrophysics Data System (ADS)
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.
2016-07-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon.
Variable percolation threshold of composites with fiber fillers under compression
NASA Astrophysics Data System (ADS)
Lin, Chuan; Wang, Hongtao; Yang, Wei
2010-07-01
The piezoresistant effect in conducting fiber-filled composites has been studied by a continuum percolation model. Simulation was performed by a Monte Carlo method that took into account both the deformation-induced fiber bending and rotation. The percolation threshold was found to rise with the compression strain, which explains the observed positive piezoresistive coefficients in such composites. The simulations unveiled the effect of the microstructure evolution during deformation. The fibers are found to align perpendicularly to the compression direction. As the fiber is bended, the effective length in making a conductive network is shortened. Both effects contribute to a larger percolation threshold and imply a positive piezoresistive coefficient according the universal power law.
Percolation-based precursors of transitions in extended systems
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.
2016-01-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon. PMID:27412567
Scaling behavior of explosive percolation on the square lattice
NASA Astrophysics Data System (ADS)
Ziff, Robert M.
2010-11-01
Clusters generated by the product-rule growth model of Achlioptas, D’Souza, and Spencer on a two-dimensional square lattice are shown to obey qualitatively different scaling behavior than standard (random growth) percolation. The threshold with unrestricted bond placement (allowing loops) is found precisely using several different criteria based on both moments and wrapping probabilities, yielding pc=0.526565±0.000005 , consistent with the recent result of Radicchi and Fortunato. The correlation-length exponent ν is found to be close to 1. The qualitative difference from regular percolation is shown dramatically in the behavior of the percolation probability P∞ (size of largest cluster), of the susceptibility, and of the second moment of finite clusters, where discontinuities appear at the threshold. The critical cluster-size distribution does not follow a consistent power law for the range of system sizes we study (L≤8192) but may approach a power law with τ>2 for larger L .
Percolation-based precursors of transitions in extended systems.
Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M; Hernández-García, Emilio; Ramasco, José J
2016-01-01
Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system's time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system's tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon. PMID:27412567
The central point source in G76.9+1.0
NASA Astrophysics Data System (ADS)
Marthi, V. R.; Chengalur, J. N.; Gupta, Y.; Dewangan, G. C.; Bhattacharya, D.
2011-10-01
We describe the serendipitous discovery of a radio point source in a 618-MHz image of the supernova remnant(SNR) G76.9+1.0. The SNR has a bipolar structure and the point source is located near a faint bridge of emission joining the two lobes of emission. The point source was also detected in follow-up higher frequency (1170 MHz) observations. The spectral index for the point source obtained from the Giant Metrewave Radio Telescope (GMRT) observations is α=-2.1-0.45+ 0.36. The steep spectrum as well as the location of the point source near the centre of the SNR establishes the fact that it is indeed the pulsar J2022+3842 associated with this SNR. The weighted-mean radio position of this point source is ?, J2000. Consistent with this, subsequent analysis of archival Chandra X-ray data shows a point source coincident with the radio point source, as well as diffuse extended X-ray emission surrounding the unresolved source. However, no pulsed emission was detected despite deep searches at both 610 and 1160 MHz, although pulsed emission has been seen at 2 GHz. It appears that the most likely reason for not detecting the pulsed signal at the GMRT is temporal broadening: for the estimated Dispersion Measure (DM) towards this SNR, the pulse broadening time could be as large as tens of milliseconds. The diffuse X-ray emission is elongated along the same direction as the bipolar structure seen in the radio. We interpret the radio lobes as having been formed from an equatorial wind. Although direct detection of pulsed signal has not been possible, we show convincingly that sensitive, high-resolution radio imaging at multiple frequencies is a useful method to search for pulsar candidates.
NASA Astrophysics Data System (ADS)
Mauzerall, D. L.; Sultan, B.; Kim, N.; Bradford, D.
2004-12-01
We present a proof-of-concept analysis of the measurement of the health damage of ozone (O3) produced from nitrogen oxides (NOx = NO + NO2) emitted by individual large point sources in the eastern United States. We use a regional atmospheric model of the eastern United States, the Comprehensive Air Quality Model with Extensions (CAMx), to quantify the variable impact that a fixed quantity of NOx emitted from individual sources can have on the downwind concentration of surface O3, depending on temperature and local biogenic hydrocarbon emissions. We also examine the dependence of resulting ozone-related health damages on the size of the exposed population. The investigation is relevant to the increasingly widely used "cap and trade" approach to NOx regulation, which presumes that shifts of emissions over time and space, holding the total fixed over the course of the summer O3 season, will have minimal effect on the environmental outcome. By contrast, we show that a shift of a unit of NOx emissions from one place or time to another could result in large changes in the health effects due to ozone formation and exposure. We indicate how the type of modeling carried out here might be used to attach externality-correcting prices to emissions. Charging emitters fees that are commensurate with the damage caused by their NOx emissions would create an incentive for emitters to reduce emissions at times and in locations where they cause the largest damage.
Percolation transition in active neural networks with adaptive geometry
NASA Astrophysics Data System (ADS)
Iudin, F. D.; Iudin, D. I.; Kazantsev, V. B.
2015-02-01
A mathematical model has been proposed for a neural network whose morphological structure varies dynamically depending on activity. This is the property of the so-called structural plasticity typical of developed neural systems of a brain. It has been shown that the spontaneous generation and propagation of a signal in such networks correspond to a percolation transition and the appearance of the connectivity component covering the entire system. Furthermore, adaptive change in the geometric structure of a network results in the clustering of cells and in the reduction of the effective percolation threshold, which corresponds to experimental neurobiological observations.
Jamming versus caging in three dimensional jamming percolation
NASA Astrophysics Data System (ADS)
Segall, Nimrod; Teomy, Eial; Shokef, Yair
2016-05-01
We investigate a three-dimensional kinetically-constrained model that exhibits two types of phase transitions at different densities. At the jamming density $ \\rho_J $ there is a mixed-order phase transition in which a finite fraction of the particles become frozen, but the other particles may still diffuse throughout the system. At the caging density $ \\rho_C > \\rho_J $, the mobile particles are trapped in finite cages and no longer diffuse. The caging transition occurs due to a percolation transition of the unfrozen sites, and we numerically find that it is a continuous transition with the same critical exponents as random percolation.
NASA Astrophysics Data System (ADS)
Wilkins, J. L.; de Foy, B.
2012-12-01
Power plant emissions play a key role in anthropogenic sulfur dioxide (SO2) generated pollution. The emissions of regulated point sources in many cases is well understood and can be monitored in real time. Although, remaining problems include emissions estimations of poorly characterized sources, SO2 mean lifetime and transport of the emissions. With the development of satellite remote sensing, a top-down estimate approach to SO2 emissions can be made world-wide using oversampled SO2 measurements from NASA's Aura Ozone Monitoring Instrument (OMI). Initially this study will focus on large point sources in the United States. OMI retrievals are oversampled to fine rectangular or polar grids with grid spacing between 1 to 5 km. Constrained nonlinear optimization is used to determine the parameters of the scalar decay function of SO2 from a point source. Applying this technique on OMI SO2 measurements over a period of several years coupled with observational and/or modeled wind data improves the estimations of pollution transport, dispersion, decay, and the mean lifetime of SO2 emissions.
Gibson, Alexander
2015-08-23
In my research, I analyzed how two gamma-ray source models interact with one another when optimizing to fit data. This is important because it becomes hard to distinguish between the two point sources when they are close together or looking at low energy photons. The reason for the first is obvious, the reason why they become harder to distinguish at lower photon energies is the resolving power of the Fermi Gamma-Ray Space Telescope gets worse at lower energies. When the two point sources are highly correlated (hard to distinguish between), we need to change our method of statistical analysis. What I did was show that highly correlated sources have larger uncertainties associated with them, caused by an optimizer not knowing which point source’s parameters to optimize. I also mapped out where their is high correlation for 2 different theoretical mass dark matter point sources so that people analyzing them in the future knew where they had to use more sophisticated statistical analysis.
Liu, Mei-bing; Chen, Xing-wei; Chen, Ying
2015-07-01
Identification of the critical source areas of non-point source pollution is an important means to control the non-point source pollution within the watershed. In order to further reveal the impact of multiple time scales on the spatial differentiation characteristics of non-point source nitrogen loss, a SWAT model of Shanmei Reservoir watershed was developed. Based on the simulation of total nitrogen (TN) loss intensity of all 38 subbasins, spatial distribution characteristics of nitrogen loss and critical source areas were analyzed at three time scales of yearly average, monthly average and rainstorms flood process, respectively. Furthermore, multiple linear correlation analysis was conducted to analyze the contribution of natural environment and anthropogenic disturbance on nitrogen loss. The results showed that there were significant spatial differences of TN loss in Shanmei Reservoir watershed at different time scales, and the spatial differentiation degree of nitrogen loss was in the order of monthly average > yearly average > rainstorms flood process. TN loss load mainly came from upland Taoxi subbasin, which was identified as the critical source area. At different time scales, land use types (such as farmland and forest) were always the dominant factor affecting the spatial distribution of nitrogen loss, while the effect of precipitation and runoff on the nitrogen loss was only taken in no fertilization month and several processes of storm flood at no fertilization date. This was mainly due to the significant spatial variation of land use and fertilization, as well as the low spatial variability of precipitation and runoff. PMID:26710649
Liu, Mei-bing; Chen, Xing-wei; Chen, Ying
2015-07-01
Identification of the critical source areas of non-point source pollution is an important means to control the non-point source pollution within the watershed. In order to further reveal the impact of multiple time scales on the spatial differentiation characteristics of non-point source nitrogen loss, a SWAT model of Shanmei Reservoir watershed was developed. Based on the simulation of total nitrogen (TN) loss intensity of all 38 subbasins, spatial distribution characteristics of nitrogen loss and critical source areas were analyzed at three time scales of yearly average, monthly average and rainstorms flood process, respectively. Furthermore, multiple linear correlation analysis was conducted to analyze the contribution of natural environment and anthropogenic disturbance on nitrogen loss. The results showed that there were significant spatial differences of TN loss in Shanmei Reservoir watershed at different time scales, and the spatial differentiation degree of nitrogen loss was in the order of monthly average > yearly average > rainstorms flood process. TN loss load mainly came from upland Taoxi subbasin, which was identified as the critical source area. At different time scales, land use types (such as farmland and forest) were always the dominant factor affecting the spatial distribution of nitrogen loss, while the effect of precipitation and runoff on the nitrogen loss was only taken in no fertilization month and several processes of storm flood at no fertilization date. This was mainly due to the significant spatial variation of land use and fertilization, as well as the low spatial variability of precipitation and runoff.
Lowering IceCube's Energy Threshold for Point Source Searches in the Southern Sky
NASA Astrophysics Data System (ADS)
Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Andeen, K.; Anderson, T.; Ansseau, I.; Anton, G.; Archinger, M.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blot, S.; Boersma, D. J.; Bohm, C.; Börner, M.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brayeur, L.; Bretz, H.-P.; Burgman, A.; Buzinsky, N.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Coenders, S.; Collin, G. H.; Conrad, J. M.; Cowen, D. F.; Cruz Silva, A. H.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; del Pino Rosendo, E.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; di Lorenzo, V.; Dujmovic, H.; Dumm, J. P.; Dunkman, M.; Eberhardt, B.; Ehrhardt, T.; Eichmann, B.; Euler, S.; Evenson, P. A.; Fahey, S.; Fazely, A. R.; Feintzeig, J.; Felde, J.; Filimonov, K.; Finley, C.; Flis, S.; Fösig, C.-C.; Fuchs, T.; Gaisser, T. K.; Gaior, R.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Gladstone, L.; Glagla, M.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Góra, D.; Grant, D.; Griffith, Z.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hansen, E.; Hansmann, B.; Hansmann, T.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Holzapfel, K.; Homeier, A.; Hoshina, K.; Huang, F.; Huber, M.; Huelsnitz, W.; Hultqvist, K.; In, S.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jeong, M.; Jero, K.; Jones, B. J. P.; Jurkovic, M.; Kappes, A.; Karg, T.; Karle, A.; Katz, U.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kemp, J.; Kheirandish, A.; Kim, M.; Kintscher, T.; Kiryluk, J.; Klein, S. R.; Kohnen, G.; Koirala, R.; Kolanoski, H.; Konietz, R.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, M.; Krückl, G.; Krüger, C.; Kunnen, J.; Kunwar, S.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lennarz, D.; Lesiak-Bzdak, M.; Leuermann, M.; Leuner, J.; Lu, L.; Lünemann, J.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Mancina, S.; Mandelartz, M.; Maruyama, R.; Mase, K.; Matis, H. S.; Maunu, R.; McNally, F.; Meagher, K.; Medici, M.; Meier, M.; Meli, A.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Middell, E.; Mohrmann, L.; Montaruli, T.; Nahnhauer, R.; Naumann, U.; Neer, G.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke Pollmann, A.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Pandya, H.; Pankova, D. V.; Penek, Ö.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Quinnan, M.; Raab, C.; Rädel, L.; Rameez, M.; Rawlins, K.; Reimann, R.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Riedel, B.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ryckbosch, D.; Sabbatini, L.; Sandrock, A.; Sandroos, J.; Sarkar, S.; Satalecka, K.; Schimp, M.; Schlunder, P.; Schmidt, T.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schumacher, L.; Seckel, D.; Seunarine, S.; Soldin, D.; Song, M.; Spiczak, G. M.; Spiering, C.; Stahlberg, M.; Stamatikos, M.; Stanev, T.; Stasik, A.; Steuer, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Sutherland, M.; Taavola, H.; Taboada, I.; Tatar, J.; Ter-Antonyan, S.; Terliuk, A.; Tešić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Toscano, S.; Tosi, D.; Tselengidou, M.; Turcati, A.; Unger, E.; Usner, M.; Vallecorsa, S.; Vandenbroucke, J.; van Eijndhoven, N.; Vanheule, S.; van Rossem, M.; van Santen, J.; Veenkamp, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallace, A.; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Whitehorn, N.; Wickmann, S.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wills, L.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zoll, M.; IceCube Collaboration
2016-06-01
Observation of a point source of astrophysical neutrinos would be a “smoking gun” signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current ν μ interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (˜100 TeV) starting event in the sample found that this event alone represents a 2.8σ deviation from the hypothesis that the data consists only of atmospheric background.
Gas transport through magma near the percolation threshold (Invited)
NASA Astrophysics Data System (ADS)
Llewellin, E. W.; Blower, J.; Leslie, D.
2009-12-01
Explosive silicic eruptions may simultaneously produce both tube pumice - containing highly-elongate vesicles - and pumice containing sub-spherical vesicles. This has been cited as evidence for strain localization within the volcanic conduit: in a relatively-undeformed axial ‘plug’ bubbles are spherical (regime 1) whilst near the conduit margin rapidly-shearing magma bears elongate bubbles (regime 2). Published numerical studies support this model and indicate that bubbly-magma rheology or viscous heating may be responsible for strain localization. The difference in bubble morphology in these two regimes has important consequences for magma permeability. We present the results of fluid dynamic simulations which quantify the anisotropy of permeability in regime 2 as a function of gas volume fraction and bubble aspect ratio. In this regime, we find that vertical permeability may be many times greater than radial permeability, and that permeability anisotropy is most pronounced near the percolation threshold. We further use a network model to quantify the development of permeability in regime 1. In the case where the predominantly vertical expansion of the magma is slow compared with bubble relaxation time, we find that permeability is, again, anisotropic, but that radial permeability dominates. This effect is also most pronounced near the percolation threshold, and percolation is expected to occur radially before vertical percolation occurs. Our findings imply that gas transport in regime 1 is predominantly radial, whilst vertical gas transport is favoured in regime 2. Consequently, near the percolation threshold, conditions are appropriate for effective degassing of the central magma plug as gas permeates radially to the conduit margin and then vertically upwards. Repeated cycles of percolation, radial gas loss and densification may degas the central magma plug without the development of large gas volume fractions.
Spectral Dimension of a Percolation Network
NASA Astrophysics Data System (ADS)
Rudra, Jayanta
2005-03-01
While the fractal dimension df describes the self-similar static nature of the lattice, the spectral dimension ds dictates the dynamic properties on it. Alexander and Orbach^1 conjectured that the spectral dimension might be exactly 4/3 for percolation networks with embedding euclidian dimension de >= 2. Recent numerical simulations^2, however, could not decisively prove or disprove this conjecture, although there are other indirect evidences that it is true. We believe that the failure of the simulations to decisively check the validity of the conjecture is due to the non-stochastic nature of the methods. Most of these simulations are Monte Carlo Methods based on a random-walk model and, in spite of very large number of walks on huge lattices, the results do not reach the satisfactory level. In this work we apply a stochastic approach^3 to determine the spectral dimension of percolation network for de >= 2 and check the validity of the Alexander-Orbach-conjecture. Due to its stochastic nature this method is numerically superior and more accurate than the conventional Monte Carlo simulations. References: 1. S. Alexander and R. Orbach, J. Phys. Lett. (Paris) 43 (1982) L625. 2. N. Pitsianis, G. Bleris and P. Argyrakis, Phys. Rev. B 39 (1989) 7097. 3. J. Rudra and J. Kozak, Phys. Lett A 151 (1990) 429.
Percolation effect in thick film superconductors
Sali, R.; Harsanyi, G.
1994-12-31
A thick film superconductor paste has been developed to study the properties of granulated superconductor materials, to observe the percolation effect and to confirm the theory of the conducting mechanism in the superconducting thick films. This paste was also applied to make a superconducting planar transformer. Due to high T{sub c} and advantageous current density properties the base of the paste was chosen to be of Bi(Pb)SrCaCuO system. For contacts a conventional Ag/Pt paste was used. The critical temperature of the samples were between 110 K and 115 K depending on the printed layer thickness. The critical current density at the boiling temperature of the liquid He- was between 200-300 A/cm{sup 2}. The R(T) and V(I) functions were measured with different parameters. The results of the measurements have confirmed the theory of conducting mechanism in the material. The percolation structure model has been built and described. As an application, a superconducting planar thick film transformer was planned and produced. Ten windings of the transformer were printed on one side of the alumina substrate and one winding was printed on the other side. The coupling between the two sides was possible through the substrate. The samples did not need special drying and firing parameters. After the preparation, the properties of the transformer were measured. The efficiency and the losses were determined. Finally, some fundamental advantages and problems of the process were discussed.
Outdoor air pollution in close proximity to a continuous point source
NASA Astrophysics Data System (ADS)
Klepeis, Neil E.; Gabel, Etienne B.; Ott, Wayne R.; Switzer, Paul
Data are lacking on human exposure to air pollutants occurring in ground-level outdoor environments within a few meters of point sources. To better understand outdoor exposure to tobacco smoke from cigarettes or cigars, and exposure to other types of outdoor point sources, we performed more than 100 controlled outdoor monitoring experiments on a backyard residential patio in which we released pure carbon monoxide (CO) as a tracer gas for continuous time periods lasting 0.5-2 h. The CO was emitted from a single outlet at a fixed per-experiment rate of 120-400 cc min -1 (˜140-450 mg min -1). We measured CO concentrations every 15 s at up to 36 points around the source along orthogonal axes. The CO sensors were positioned at standing or sitting breathing heights of 2-5 ft (up to 1.5 ft above and below the source) and at horizontal distances of 0.25-2 m. We simultaneously measured real-time air speed, wind direction, relative humidity, and temperature at single points on the patio. The ground-level air speeds on the patio were similar to those we measured during a survey of 26 outdoor patio locations in 5 nearby towns. The CO data exhibited a well-defined proximity effect similar to the indoor proximity effect reported in the literature. Average concentrations were approximately inversely proportional to distance. Average CO levels were approximately proportional to source strength, supporting generalization of our results to different source strengths. For example, we predict a cigarette smoker would cause average fine particle levels of approximately 70-110 μg m -3 at horizontal distances of 0.25-0.5 m. We also found that average CO concentrations rose significantly as average air speed decreased. We fit a multiplicative regression model to the empirical data that predicts outdoor concentrations as a function of source emission rate, source-receptor distance, air speed and wind direction. The model described the data reasonably well, accounting for ˜50% of the log
Distribution of pollutant concentrations downwind of a point source in the near wake of a building
Huber, A.H.
1988-01-01
The purpose of this study was to examine the primary spatial and temporal scales of pollutant diffusion and transport in the wake of a building. A series of wind-tunnel experiments was conducted to study the influence of the highly turbulent air flow adjacent to a model building upon point-source emissions through smoke flow visualization and inert tracer gas concentration mapping. The experiments were designed to evaluate the influences of source height, building width, building orientation into the wind, and overall building scale. Dispersion data correspond to time-averaged concentrations for periods of constant wind direction. The digitization of video recorded images of smoke provided a practical method for estimating the primary spatial and temporal scales of dispersion in the wake of a building. A method was developed for estimating enhanced dispersion parameters resulting from the overall effect of the building. A Gaussian plume equation, modified to incorporate the building-wake-enhanced dispersion parameters beyond the wake cavity region, provided estimates of concentrations at ground level. The model was evaluated against field measurements from previous studies.
NASA Astrophysics Data System (ADS)
Felber, R.; Münger, A.; Neftel, A.; Ammann, C.
2015-02-01
Methane (CH4) from ruminants contributes one third to global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analysers the instrumentation at many flux sites have been amended for these gases. However the application of EC over pastures is challenging due to the spatial and temporal uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d-1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to two orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head-1 d-1 (best guess of this study) correspond well to animal respiration chamber measurements reported in the literature. However a systematic effect of the distance between source and EC tower on cow emissions was found which is attributed to the analytical footprint model used. We show that the EC method allows to determine CH4 emissions of grazing cows if the data evaluation is adjusted for this purpose and if some cow distribution information is available.
NASA Astrophysics Data System (ADS)
Felber, R.; Münger, A.; Neftel, A.; Ammann, C.
2015-06-01
Methane (CH4) from ruminants contributes one-third of global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analyzers, the instrumentation at many flux sites has been amended for these gases. However, the application of EC over pastures is challenging due to the spatially and temporally uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d-1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to 2 orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head-1 d-1 (best estimate from this study) correspond well to animal respiration chamber measurements reported in the literature. However, a systematic effect of the distance between source and EC tower on cow emissions was found, which is attributed to the analytical footprint model used. We show that the EC method allows one to determine CH4 emissions of cows on a pasture if the data evaluation is adjusted for this purpose and if some cow distribution information is available.
Crossover phenomena of percolation transition in evolution networks with hybrid attachment
NASA Astrophysics Data System (ADS)
Chen, Xiaolong; Yang, Chun; Zhong, Linfeng; Tang, Ming
2016-08-01
A first-order percolation transition, called explosive percolation, was recently discovered in evolution networks with random edge selection under a certain restriction. For many real world networks, the mechanism of preferential attachment plays a significant role in the formation of heterogeneous structures, but the network percolation in evolution process with preferential attachment has not yet been concerned. We propose a tunable network percolation model by introducing a hybrid mechanism of edge selection into the Bohman-Frieze-Wormald model, in which a parameter adjusts the relative weights between random and preferential selections. A large number of simulations indicate that there exist crossover phenomena of percolation transition by adjusting the parameter in the evolution processes. When the strategy of selecting a candidate edge is dominated by random selection, a single discontinuous percolation transition occurs. When a candidate edge is selected more preferentially based on nodes degree, the size of the largest component undergoes multiple discontinuous jumps, which exhibits a peculiar difference from the network percolation of random selection with a certain restriction. Besides, the percolation transition becomes continuous when the candidate edge is selected completely preferentially.
Crossover phenomena of percolation transition in evolution networks with hybrid attachment.
Chen, Xiaolong; Yang, Chun; Zhong, Linfeng; Tang, Ming
2016-08-01
A first-order percolation transition, called explosive percolation, was recently discovered in evolution networks with random edge selection under a certain restriction. For many real world networks, the mechanism of preferential attachment plays a significant role in the formation of heterogeneous structures, but the network percolation in evolution process with preferential attachment has not yet been concerned. We propose a tunable network percolation model by introducing a hybrid mechanism of edge selection into the Bohman-Frieze-Wormald model, in which a parameter adjusts the relative weights between random and preferential selections. A large number of simulations indicate that there exist crossover phenomena of percolation transition by adjusting the parameter in the evolution processes. When the strategy of selecting a candidate edge is dominated by random selection, a single discontinuous percolation transition occurs. When a candidate edge is selected more preferentially based on nodes degree, the size of the largest component undergoes multiple discontinuous jumps, which exhibits a peculiar difference from the network percolation of random selection with a certain restriction. Besides, the percolation transition becomes continuous when the candidate edge is selected completely preferentially. PMID:27586610
Crossover phenomena of percolation transition in evolution networks with hybrid attachment.
Chen, Xiaolong; Yang, Chun; Zhong, Linfeng; Tang, Ming
2016-08-01
A first-order percolation transition, called explosive percolation, was recently discovered in evolution networks with random edge selection under a certain restriction. For many real world networks, the mechanism of preferential attachment plays a significant role in the formation of heterogeneous structures, but the network percolation in evolution process with preferential attachment has not yet been concerned. We propose a tunable network percolation model by introducing a hybrid mechanism of edge selection into the Bohman-Frieze-Wormald model, in which a parameter adjusts the relative weights between random and preferential selections. A large number of simulations indicate that there exist crossover phenomena of percolation transition by adjusting the parameter in the evolution processes. When the strategy of selecting a candidate edge is dominated by random selection, a single discontinuous percolation transition occurs. When a candidate edge is selected more preferentially based on nodes degree, the size of the largest component undergoes multiple discontinuous jumps, which exhibits a peculiar difference from the network percolation of random selection with a certain restriction. Besides, the percolation transition becomes continuous when the candidate edge is selected completely preferentially.
Spin dynamics on percolating networks
Aeppli, G.; Guggenheim, H.; Uemura, Y.J.
1985-01-01
We have used inelastic neutron scattering to measure the order parameter relaxation rate GAMMA in the dilute, two-dimensional Ising antiferromagnet Rb/sub 2/CoMg/sub 1-c/F/sub 4/ with c very close to the magnetic percolation threshold. Where kappa is the inverse magnetic correlation length, GAMMA approx. kappa/sup z/ with z = 2.4/sub -0.1//sup +0.2/. Our results are discussed in terms of current ideas about spin relaxation on fractals. 13 refs., 1 fig.
[Nitrogen non-point source pollution identification based on ArcSWAT in Changle River].
Deng, Ou-Ping; Sun, Si-Yang; Lü, Jun
2013-04-01
The ArcSWAT (Soil and Water Assessment Tool) model was adopted for Non-point source (NPS) nitrogen pollution modeling and nitrogen source apportionment for the Changle River watershed, a typical agricultural watershed in Southeast China. Water quality and hydrological parameters were monitored, and the watershed natural conditions (including soil, climate, land use, etc) and pollution sources information were also investigated and collected for SWAT database. The ArcSWAT model was established in the Changle River after the calibrating and validating procedures of the model parameters. Based on the validated SWAT model, the contributions of different nitrogen sources to river TN loading were quantified, and spatial-temporal distributions of NPS nitrogen export to rivers were addressed. The results showed that in the Changle River watershed, Nitrogen fertilizer, nitrogen air deposition and nitrogen soil pool were the prominent pollution sources, which contributed 35%, 32% and 25% to the river TN loading, respectively. There were spatial-temporal variations in the critical sources for NPS TN export to the river. Natural sources, such as soil nitrogen pool and atmospheric nitrogen deposition, should be targeted as the critical sources for river TN pollution during the rainy seasons. Chemical nitrogen fertilizer application should be targeted as the critical sources for river TN pollution during the crop growing season. Chemical nitrogen fertilizer application, soil nitrogen pool and atmospheric nitrogen deposition were the main sources for TN exported from the garden plot, forest and residential land, respectively. However, they were the main sources for TN exported both from the upland and paddy field. These results revealed that NPS pollution controlling rules should focus on the spatio-temporal distribution of NPS pollution sources. PMID:23798104
Ding, Xiao-Wen; Shen, Zhen-Yao
2012-11-01
In order to provide regulatory support for management and control of non-point source (NPS) pollution in Fujiang watershed, agricultural NPS pollution is simulated, spatial distribution characteristics of NPS pollution are analyzed, and the primary pollution sources are also identified, by export coefficient model (ECM) and geographic information system (GIS). Agricultural NPS total nitrogen (TN) loading was of research area was 9.11 x 10(4) t in 2010, and the average loading was intensity was 3.10 t x km(-2). Agricultural NPS TN loading mainly distributed over dry lands, Mianyang city and gentle slope areas; high loading intensity areas were dry lands, Deyang city and gentle slope areas. Agricultural land use, of which contribution rate was 62. 12%, was the most important pollution source; fertilizer loss in dry lands, of which contribution rate was 50.49%, was the prominent. Improving methods of agricultural cultivation, implementing "farm land returning to woodland" policy, and enhancing treatment efficiency of domestic sewage and livestock waster wate are effective measures.
Discriminating between point and non-point sources of atrazine contamination of a sandy aquifer.
Leterme, Bertrand; Vanclooster, Marnik; Rounsevell, Mark D A; Bogaert, Patrick
2006-06-01
This study analyses the sources of atrazine contamination in the Brusselian sandy aquifer of central Belgium. Atrazine has in the past been used for both agricultural and non-agricultural applications, but it is difficult to distinguish the contamination originating from these two sources. The spatial and temporal covariance of atrazine concentrations was studied by fitting semi-variogram models to monitoring data. Correlation ranges were found to be 600 m and 600-700 days, respectively. The results were used to apply a declustering algorithm before examining the distribution of atrazine concentrations measured in groundwater. Monitoring data appeared to follow a pseudo-lognormal distribution, as a lognormality test was negative. An inflexion point on the cumulative density function was thought to indicate the two different pollution processes, i.e., agricultural and non-agricultural contamination sources. A non-parametric one-way analysis of variance suggested that the vast majority of atrazine in groundwater was from non-agricultural, point sources. This was supported by the strong relationship between mean concentrations and land use, whilst other environmental variables, such as soil organic matter or groundwater depth, produced less meaningful results.
NASA Astrophysics Data System (ADS)
Corwin, Dennis L.; Loague, Keith; Ellsworth, Timothy R.
The information age has ushered in a global awareness of complex environmental problems that do not respect political or physical boundaries: climatic change, ozone layer depletion, deforestation, desertification, and non-point source (NPS) pollution. Among these global environmental problems, NPS pollutants represent a perfect example of a complex multidisciplinary problem that exists over multiple scales with tremendous spatial and temporal complexity. To address the NPS problem, specific to the vadose zone, advanced information technologies must be applied in a spatial context. An integrated system of advanced information technologies (i.e., global positioning, geographic information system, geostatistics, remote sensing, solute transport modeling, neural networks, transfer functions, fuzzy logic, hierarchical theory, and uncertainty analysis) provides a framework from which real-time and/or simulated assessments of NPS pollution can be made. The ability to accurately assess present and future NPS-pollution impacts on ecosystems ranging from local to global scales provides a powerful tool for environmental stewardship and guiding future human activities.
Bootstrap percolation on spatial networks
NASA Astrophysics Data System (ADS)
Gao, Jian; Zhou, Tao; Hu, Yanqing
2015-10-01
Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around -1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value -1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading.
Bootstrap percolation on spatial networks
Gao, Jian; Zhou, Tao; Hu, Yanqing
2015-01-01
Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around −1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value −1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading. PMID:26423347
Bootstrap percolation on spatial networks.
Gao, Jian; Zhou, Tao; Hu, Yanqing
2015-10-01
Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links' lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around -1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value -1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading.
Estimation of the skull insertion loss using an optoacoustic point source
NASA Astrophysics Data System (ADS)
Estrada, Héctor; Rebling, Johannes; Turner, Jake; Kneipp, Moritz; Shoham, Shy; Razansky, Daniel
2016-03-01
The acoustically-mismatched skull bone poses significant challenges for the application of ultrasonic and optical techniques in neuroimaging, still typically requiring invasive approaches using craniotomy or skull thinning. Optoacoustic imaging partially circumvents the acoustic distortions due to the skull because the induced wave is transmitted only once as opposed to the round trip in pulse-echo ultrasonography. To this end, the mouse brain has been successfully imaged transcranially by optoacoustic scanning microscopy. Yet, the skull may adversely affect the lateral and axial resolution of transcranial brain images. In order to accurately characterize the complex behavior of the optoacoustic signal as it traverses through the skull, one needs to consider the ultrawideband nature of the optoacoustic signals. Here the insertion loss of murine skull has been measured by means of a hybrid optoacoustic-ultrasound scanning microscope having a spherically focused PVDF transducer and pulsed laser excitation at 532 nm of a 20 μm diameter absorbing microsphere acting as an optoacoustic point source. Accurate modeling of the acoustic transmission through the skull is further performed using a Fourier-domain expansion of a solid-plate model, based on the simultaneously acquired pulse-echo ultrasound image providing precise information about the skull's position and its orientation relative to the optoacoustic source. Good qualitative agreement has been found between the a solid-plate model and experimental measurements. The presented strategy might pave the way for modeling skull effects and deriving efficient correction schemes to account for acoustic distortions introduced by an adult murine skull, thus improving the spatial resolution, effective penetration depth and overall image quality of transcranial optoacoustic brain microscopy.
NASA Astrophysics Data System (ADS)
Tohme, Michel S.; Qi, Jinyi
2009-06-01
The accuracy of the system model in an iterative reconstruction algorithm greatly affects the quality of reconstructed positron emission tomography (PET) images. For efficient computation in reconstruction, the system model in PET can be factored into a product of a geometric projection matrix and sinogram blurring matrix, where the former is often computed based on analytical calculation, and the latter is estimated using Monte Carlo simulations. Direct measurement of a sinogram blurring matrix is difficult in practice because of the requirement of a collimated source. In this work, we propose a method to estimate the 2D blurring kernels from uncollimated point source measurements. Since the resulting sinogram blurring matrix stems from actual measurements, it can take into account the physical effects in the photon detection process that are difficult or impossible to model in a Monte Carlo (MC) simulation, and hence provide a more accurate system model. Another advantage of the proposed method over MC simulation is that it can easily be applied to data that have undergone a transformation to reduce the data size (e.g., Fourier rebinning). Point source measurements were acquired with high count statistics in a relatively fine grid inside the microPET II scanner using a high-precision 2D motion stage. A monotonically convergent iterative algorithm has been derived to estimate the detector blurring matrix from the point source measurements. The algorithm takes advantage of the rotational symmetry of the PET scanner and explicitly models the detector block structure. The resulting sinogram blurring matrix is incorporated into a maximum a posteriori (MAP) image reconstruction algorithm. The proposed method has been validated using a 3 × 3 line phantom, an ultra-micro resolution phantom and a 22Na point source superimposed on a warm background. The results of the proposed method show improvements in both resolution and contrast ratio when compared with the MAP
Tohme, Michel S.; Qi, Jinyi
2009-01-01
The accuracy of the system model in an iterative reconstruction algorithm greatly affects the quality of reconstructed positron emission tomography (PET) images. For efficient computation in reconstruction, the system model in PET can be factored into a product of a geometric projection matrix and sinogram blurring matrix, where the former is often computed based on analytical calculation, and the latter is estimated using Monte Carlo simulations. Direct measurement of sinogram blurring matrix is difficult in practice because of the requirement of a collimated source. In this work, we propose a method to estimate the 2D blurring kernels from uncollimated point source measurements. Since the resulting sinogram blurring matrix stems from actual measurements, it can take into account the physical effects in the photon detection process that are difficult or impossible to model in a Monte Carlo (MC) simulation, and hence provide a more accurate system model. Another advantage of the proposed method over MC simulation is that it can be easily applied to data that have undergone a transformation to reduce the data size (e.g., Fourier rebinning). Point source measurements were acquired with high count statistics in a relatively fine grid inside the microPET II scanner using a high-precision 2-D motion stage. A monotonically convergent iterative algorithm has been derived to estimate the detector blurring matrix from the point source measurements. The algorithm takes advantage of the rotational symmetry of the PET scanner and explicitly models the detector block structure. The resulting sinogram blurring matrix is incorporated into a maximum a posteriori (MAP) image reconstruction algorithm. The proposed method has been validated using a 3-by-3 line phantom, an ultra-micro resolution phantom, and a 22Na point source superimposed on a warm background. The results of the proposed method show improvements in both resolution and contrast ratio when compared with the MAP
Percolation induced heat transfer in deep unsaturated zones
Lu, N.; LeCain, G.D.
2003-01-01
Subsurface temperature data from a borehole located in a desert wash were measured and used to delineate the conductive and advective heat transfer regimes, and to estimate the percolation quantity associated with the 1997-1998 El Ni??no precipitation. In an arid environment, conductive heat transfer dominates the variation of shallow subsurface temperature most of the time, except during sporadic precipitation periods. The subsurface time-varying temperature due to conductive heat transfer is highly correlated with the surface atmospheric temperature variation, whereas temperature variation due to advective heat transfer is strongly correlated with precipitation events. The advective heat transfer associated with precipitation and infiltration is the focus of this paper. Disruptions of the subsurface conductive temperature regime, associated with the 1997-1998 El Ni??no precipitation, were detected and used to quantify the percolation quantity. Modeling synthesis using a one-dimensional coupled heat and unsaturated flow model indicated that a percolation per unit area of 0.7 to 1.3 m height of water in two weeks during February 1998 was responsible for the observed temperature deviations down to a depth of 35.2 m. The reported study demonstrated quantitatively, for the first time, that the near surface temperature variation due to advective heat transfer can be significant at a depth greater than 10 m in unsaturated soils and can be used to infer the percolation amount in thick unsaturated soils.
Extending the search for neutrino point sources with IceCube above the horizon.
Abbasi, R; Abdou, Y; Abu-Zayyad, T; Adams, J; Aguilar, J A; Ahlers, M; Andeen, K; Auffenberg, J; Bai, X; Baker, M; Barwick, S W; Bay, R; Bazo Alba, J L; Beattie, K; Beatty, J J; Bechet, S; Becker, J K; Becker, K-H; Benabderrahmane, M L; Berdermann, J; Berghaus, P; Berley, D; Bernardini, E; Bertrand, D; Besson, D Z; Bissok, M; Blaufuss, E; Boersma, D J; Bohm, C; Botner, O; Bradley, L; Braun, J; Breder, D; Carson, M; Castermans, T; Chirkin, D; Christy, B; Clem, J; Cohen, S; Cowen, D F; D'Agostino, M V; Danninger, M; Day, C T; De Clercq, C; Demirörs, L; Depaepe, O; Descamps, F; Desiati, P; de Vries-Uiterweerd, G; DeYoung, T; Díaz-Vélez, J C; Dreyer, J; Dumm, J P; Duvoort, M R; Edwards, W R; Ehrlich, R; Eisch, J; Ellsworth, R W; Engdegård, O; Euler, S; Evenson, P A; Fadiran, O; Fazely, A R; Feusels, T; Filimonov, K; Finley, C; Foerster, M M; Fox, B D; Franckowiak, A; Franke, R; Gaisser, T K; Gallagher, J; Ganugapati, R; Gerhardt, L; Gladstone, L; Goldschmidt, A; Goodman, J A; Gozzini, R; Grant, D; Griesel, T; Gross, A; Grullon, S; Gunasingha, R M; Gurtner, M; Ha, C; Hallgren, A; Halzen, F; Han, K; Hanson, K; Hasegawa, Y; Helbing, K; Herquet, P; Hickford, S; Hill, G C; Hoffman, K D; Homeier, A; Hoshina, K; Hubert, D; Huelsnitz, W; Hülss, J-P; Hulth, P O; Hultqvist, K; Hussain, S; Imlay, R L; Inaba, M; Ishihara, A; Jacobsen, J; Japaridze, G S; Johansson, H; Joseph, J M; Kampert, K-H; Kappes, A; Karg, T; Karle, A; Kelley, J L; Kemming, N; Kenny, P; Kiryluk, J; Kislat, F; Klein, S R; Knops, S; Kohnen, G; Kolanoski, H; Köpke, L; Koskinen, D J; Kowalski, M; Kowarik, T; Krasberg, M; Krings, T; Kroll, G; Kuehn, K; Kuwabara, T; Labare, M; Lafebre, S; Laihem, K; Landsman, H; Lauer, R; Lehmann, R; Lennarz, D; Lundberg, J; Lünemann, J; Madsen, J; Majumdar, P; Maruyama, R; Mase, K; Matis, H S; McParland, C P; Meagher, K; Merck, M; Mészáros, P; Meures, T; Middell, E; Milke, N; Miyamoto, H; Montaruli, T; Morse, R; Movit, S M; Nahnhauer, R; Nam, J W; Niessen, P; Nygren, D R; Odrowski, S; Olivas, A; Olivo, M; Ono, M; Panknin, S; Patton, S; Paul, L; Pérez de los Heros, C; Petrovic, J; Piegsa, A; Pieloth, D; Pohl, A C; Porrata, R; Potthoff, N; Price, P B; Prikockis, M; Przybylski, G T; Rawlins, K; Redl, P; Resconi, E; Rhode, W; Ribordy, M; Rizzo, A; Rodrigues, J P; Roth, P; Rothmaier, F; Rott, C; Roucelle, C; Rutledge, D; Ruzybayev, B; Ryckbosch, D; Sander, H-G; Sarkar, S; Schatto, K; Schlenstedt, S; Schmidt, T; Schneider, D; Schukraft, A; Schulz, O; Schunck, M; Seckel, D; Semburg, B; Seo, S H; Sestayo, Y; Seunarine, S; Silvestri, A; Slipak, A; Spiczak, G M; Spiering, C; Stamatikos, M; Stanev, T; Stephens, G; Stezelberger, T; Stokstad, R G; Stoufer, M C; Stoyanov, S; Strahler, E A; Straszheim, T; Sullivan, G W; Swillens, Q; Taboada, I; Tamburro, A; Tarasova, O; Tepe, A; Ter-Antonyan, S; Terranova, C; Tilav, S; Toale, P A; Tooker, J; Tosi, D; Turcan, D; van Eijndhoven, N; Vandenbroucke, J; Van Overloop, A; van Santen, J; Voigt, B; Walck, C; Waldenmaier, T; Wallraff, M; Walter, M; Wendt, C; Westerhoff, S; Whitehorn, N; Wiebe, K; Wiebusch, C H; Wiedemann, A; Wikström, G; Williams, D R; Wischnewski, R; Wissing, H; Woschnagg, K; Xu, C; Xu, X W; Yodh, G; Yoshida, S
2009-11-27
Point source searches with the IceCube neutrino telescope have been restricted to one hemisphere, due to the exclusive selection of upward going events as a way of rejecting the atmospheric muon background. We show that the region above the horizon can be included by suppressing the background through energy-sensitive cuts. This improves the sensitivity above PeV energies, previously not accessible for declinations of more than a few degrees below the horizon due to the absorption of neutrinos in Earth. We present results based on data collected with 22 strings of IceCube, extending its field of view and energy reach for point source searches. No significant excess above the atmospheric background is observed in a sky scan and in tests of source candidates. Upper limits are reported, which for the first time cover point sources in the southern sky up to EeV energies. PMID:20366087
Long Term Temporal and Spectral Evolution of Point Sources in Nearby Elliptical Galaxies
NASA Astrophysics Data System (ADS)
Durmus, D.; Guver, T.; Hudaverdi, M.; Sert, H.; Balman, Solen
2016-06-01
We present the results of an archival study of all the point sources detected in the lines of sight of the elliptical galaxies NGC 4472, NGC 4552, NGC 4649, M32, Maffei 1, NGC 3379, IC 1101, M87, NGC 4477, NGC 4621, and NGC 5128, with both the Chandra and XMM-Newton observatories. Specifically, we studied the temporal and spectral evolution of these point sources over the course of the observations of the galaxies, mostly covering the 2000 - 2015 period. In this poster we present the first results of this study, which allows us to further constrain the X-ray source population in nearby elliptical galaxies and also better understand the nature of individual point sources.
Extending the search for neutrino point sources with IceCube above the horizon
IceCube Collaboration; Abbasi, R.
2009-11-20
Point source searches with the IceCube neutrino telescope have been restricted to one hemisphere, due to the exclusive selection of upward going events as a way of rejecting the atmospheric muon background. We show that the region above the horizon can be included by suppressing the background through energy-sensitive cuts. This approach improves the sensitivity above PeV energies, previously not accessible for declinations of more than a few degrees below the horizon due to the absorption of neutrinos in Earth. We present results based on data collected with 22 strings of IceCube, extending its field of view and energy reach for point source searches. No significant excess above the atmospheric background is observed in a sky scan and in tests of source candidates. Upper limits are reported, which for the first time cover point sources in the southern sky up to EeV energies.
Baseline point source load inventory, 1985. 1991 reevaluation report No. 2
Not Available
1993-02-04
The report finalizes and documents the Chesapeake Bay Agreement states' 1985 point source nutrient load estimates initially presented in the Baywide Nutrient Reduction Strategy (BNRS). The Bay Agreement states include Maryland, Virginia, Pennsylvania, and the District of Columbia. Each of the states final, annual, discharged, 1985 point source total phosphorus and total nitrogen nutrient load estimates are presented. These estimates are to serve as the point source baseline for the year 2000 40% nutrient reduction goal. Facility by facility flows, nutrient concentrations and nutrient loads for 1985 from above the fall line (AFL) and from below the fall line (BFL) are presented. The report presents the percent change in the 1985 baseline loads for each of the Bay agreement states relative to 1991. Estimates of 1991 nutrient loads are not available for non-agreement states at this time.
Detecting long-term changes in point-source fossil CO2 emissions with tree ring archives
NASA Astrophysics Data System (ADS)
Keller, Elizabeth D.; Turnbull, Jocelyn C.; Norris, Margaret W.
2016-05-01
We examine the utility of tree ring 14C archives for detecting long-term changes in fossil CO2 emissions from a point source. Trees assimilate carbon from the atmosphere during photosynthesis, in the process faithfully recording the average atmospheric 14C content in each new annual tree ring. Using 14C as a proxy for fossil CO2, we examine interannual variability over six years of fossil CO2 observations between 2004-2005 and 2011-2012 from two trees growing near the Kapuni Gas Treatment Plant in rural Taranaki, New Zealand. We quantify the amount of variability that can be attributed to transport and meteorology by simulating constant point-source fossil CO2 emissions over the observation period with the atmospheric transport model WindTrax. We compare model simulation results to observations and calculate the amount of change in emissions that we can detect with new observations over annual or multi-year time periods, given both the measurement uncertainty of 1ppm and the modelled variation in transport. In particular, we ask, what is the minimum amount of change in emissions that we can detect using this method, given a reference period of six years? We find that changes of 42 % or more could be detected in a new sample from one year at the same observation location or 22 % in the case of four years of new samples. This threshold is reduced and the method becomes more practical the more the size of the signal increases. For point sources 10 times larger than the Kapuni plant (a more typical size for power plants worldwide), it would be possible to detect sustained emissions changes on the order of 10 %, given suitable meteorology and observations.
NASA Astrophysics Data System (ADS)
Lai, Xiaoming; Liao, Kaihua; Feng, Huihui; Zhu, Qing
2016-09-01
Knowledge of soil water percolation below the rooting zone and its responses to the dynamic interactions of different factors are important for the control of non-point source pollution. Based on 3600 scenarios in Hydrus-1D simulation, this study revealed the integrated effects of rainfall characteristics (rainfall amount, maximum rainfall intensity or MRI, time distribution characteristics of rainfall or TDC), antecedent moisture and the season on deep percolation (DP) at a forest site in Taihu Lake Basin, China. Results showed that Hydrus-1D model can well simulate the soil water dynamics at this site. Antecedent moisture had the greatest relative contribution to DP (85.7%), followed by rainfall amount (10.9%) and MRI (3.4%). As the antecedent moisture increased, the relative contribution of the season on DP increased from 0.0% to 16.4%. In comparison, that of MRI decreased from 58.7% to 38.5% and that of rainfall amount followed a bell shape pattern (greatest when the antecedent moisture was 0.26 m3 m-3). The relative contribution of antecedent moisture to DP in summer was the greatest (87.8%), while that of the rainfall was the least. The TDC influenced DP by affecting the responses of DP to other factors. When the rainfall amount was ⩾80 mm and the antecedent moisture content was ⩾0.34 m3 m-3, effect of TDC on DP could be observed. The DP of TDC_B (rainfall intensity linearly increased with time) was the lowest, while that of TDC_E (rainfall intensity kept constant with time) was the greatest. Findings of this study have practical significance for investigating the water and pollutant transport in vadose zone.
Analysis of SO II point source emissions using NASA atmospheric infrared sounder data
NASA Astrophysics Data System (ADS)
Shen, Sylvia S.; Miller, David P.; Lewis, Paul E.
2007-04-01
Determining the extent to which large power plant emission sources interacting with atmospheric constituents affect the environment could play a significant role in future U.S. energy production policy. The effects on the environment caused by the interaction between power plant emissions and atmospheric constituents has not been investigated in depth due to the lack of calibrated spectral data on a suitable temporal and spatial scale. The availability of NASA's space-based Atmospheric Infrared Sounder (AIRS) data makes it possible to explore, and begin the first steps toward establishing, a correlation between known emission sources and environmental indicators. An exploratory study was conducted in which a time series of 26 cloud-free AIRS data containing two coal-fired power plants in northern New Mexico were selected, acquired, and analyzed for SO II emissions. A generic forward modeling process was also developed to derive an estimate of the expected AIRS pixel radiance containing the SO II emissions from the two power plants based on published combustion analysis data for coal and available power plant documentation. Analysis of the AIRS NEΔR calculated in this study and subsequent comparison with the radiance values for SO II calculated from the forward model provided essential information regarding the suitability and risk in the use of a modified AIRS configuration for monitoring anthropogenic point source emissions. The results of this study along with its conclusions and recommendations in conjunction with additional research collaboration in several specific topics will provide guidance for the development of the next generation infrared spectrometer system that NASA is considering building for environmental monitoring.
Chandra Observations of the X-Ray Point Source Population in NGC 4636
NASA Astrophysics Data System (ADS)
Posson-Brown, Jennifer; Raychaudhury, Somak; Forman, William; Donnelly, R. Hank; Jones, Christine
2009-04-01
We present the X-ray point-source population in the nearby Virgo elliptical galaxy NGC 4636 from three Chandra X-ray observations. These observations, totaling ~193 ks after time filtering, were taken with the Advanced CCD Imaging Camera (ACIS) over a three-year period. Using a wavelet decomposition detection algorithm, we detect 318 individual point sources. For our analysis, we use a subset of 277 detections with >= net 10 counts (a limiting luminosity of approximately 1.2 × 1037 erg s-1 in the 0.5-2 keV band, outside the central 1farcm5 bright galaxy core). We present a radial distribution of the point sources. Between 1farcm5 and 6' from the center, 25% of our sources are likely to be background sources (active galactic nuclei (AGNs)) and 75% are low-mass X-ray binaries (LMXBs) within the galaxy, while at radial distances greater than 6', background sources (AGN) will dominate the point sources. We explore short and long-term variability (over timescales of 1 day to three years) for X-ray point sources in this elliptical galaxy. 54 sources (24%) in the common ACIS fields of view show significant variability between observations. Of these, 37 are detected with at least 10 net counts in only one observation and thus may be "transient." In addition, ~10% of the sources in each observation show significant short-term variability; we present an example light curve for a variable bright source. The cumulative luminosity function (LF) for the point sources in NGC 4636 can be represented as a power law of slope α = 1.14 ± 0.03. We do not detect, but estimate an upper limit of ~4.5 × 1037 erg s-1 to the current X-ray luminosity of the historical supernova SN1939A. We find 77 matches between X-ray point sources and globular cluster (GC) candidates found in deep optical images of NGC 4636. In the annulus from 1farcm5 to 6' of the galaxy center, 48 of the 129 X-ray point sources (37%) with >=10 net counts are matched with GC candidates. Since we expect 25% of these
Continuous time random walk approach to dynamic percolation
NASA Astrophysics Data System (ADS)
Hilfer, R.; Orbach, R.
1988-12-01
We present an approximate solution for time (frequency) dependent response under conditions of dynamic percolation which may be related to excitation transfer in some random structures. In particular, we investigate the dynamics of structures where one random component blocks a second (carrier) component. Finite concentrations of the former create a percolation network for the latter. When the blockers are allowed to move in time, the network seen by the carriers changes with time, allowing for long-range transport even if the instantaneous carrier site availability is less than pc, the critical percolation concentration. A specific example of this situation is electrical transport in sodium β″-alumina. The carriers are Na + ions which can hop on a two-dimensional honeycomb lattice. The blockers are ions of much higher activation energy, such as Ba 2+. We study the frequency dependence of the conductivity for such a system. Given a fixed Ba 2+ hopping rate, 1/τ, the Na + ions experience a frozen site percolation environment for frequencies ω > 1/τ. At frequencies ω < 1/τ, the Na + ions experience a dynamic environment which allows long-range transport, even below pc. A continuous time random walk model combined with an effective medium approximation allows us to arrive at a numerical solution for the frequency-dependent Na+ conductivity σ(ω) which clearly exhibits the crossover from frozen to dynamic environment.
Tunable Percolation in Semiconducting Binary Polymer Nanoparticle Glasses.
Renna, Lawrence A; Bag, Monojit; Gehan, Timothy S; Han, Xu; Lahti, Paul M; Maroudas, Dimitrios; Venkataraman, D
2016-03-10
Binary polymer nanoparticle glasses provide opportunities to realize the facile assembly of disparate components, with control over nanoscale and mesoscale domains, for the development of functional materials. This work demonstrates that tunable electrical percolation can be achieved through semiconducting/insulating polymer nanoparticle glasses by varying the relative percentages of equal-sized nanoparticle constituents of the binary assembly. Using time-of-flight charge carrier mobility measurements and conducting atomic force microscopy, we show that these systems exhibit power law scaling percolation behavior with percolation thresholds of ∼24-30%. We develop a simple resistor network model, which can reproduce the experimental data, and can be used to predict percolation trends in binary polymer nanoparticle glasses. Finally, we analyze the cluster statistics of simulated binary nanoparticle glasses, and characterize them according to their predominant local motifs as (p(i), p(1-i))-connected networks that can be used as a supramolecular toolbox for rational material design based on polymer nanoparticles. PMID:26854924
NASA Astrophysics Data System (ADS)
David, Laurence P.; Jones, Christine; Forman, William; Murray, Steven S.
2005-12-01
A Chandra observation of the intermediate-luminosity (MB=-20) elliptical galaxy NGC 3379 resolves 75% of the X-ray emission within the central 5 kpc into point sources. Spectral analysis of the remaining unresolved emission within the central 770 pc indicates that 90% of the emission probably arises from undetected point sources, while 10% arises from thermal emission from kT=0.6 keV gas. Assuming a uniform density distribution in the central region of the galaxy gives a gas mass of 5×105 Msolar. Such a small amount of gas can be supplied by stellar mass loss in only 107 yr. Thus, the gas must be accreting into the central supermassive black hole at a very low radiative efficiency as in the ADAF or RIAF models, or it is being expelled in a galactic wind driven by the same AGN feedback mechanism as that observed in cluster cooling flows. If the gas is being expelled in an AGN-driven wind, then the ratio of mechanical to radio power of the AGN must be 104, which is comparable to that measured in cluster cooling flows that have recently been perturbed by radio outbursts. Only 8% of the detected point sources are coincident with globular cluster positions, which is significantly less than that found among other elliptical galaxies observed by Chandra. The low specific frequency of globular clusters and the small fraction of X-ray point sources associated with globular clusters in NGC 3379 is more similar to the properties of lenticular galaxies rather than elliptical galaxies. The brightest point source in NGC 3379 is located 360 pc from the central AGN with a peak luminosity of 3.5×1039 ergs s-1, which places it in the class of ultraluminous X-ray point sources (ULXs). Analysis of an archival ROSAT HRI observation of NGC 3379 shows that this source was at a comparable luminosity 5 yr prior to the Chandra observation. The spectrum of the ULX is well described by a power-law model with Γ=1.6+/-0.1 and galactic absorption, similar to other ULXs observed by Chandra and
A New Method for Finding Point Sources in High-energy Neutrino Data
NASA Astrophysics Data System (ADS)
Fang, Ke; Miller, M. Coleman
2016-08-01
The IceCube collaboration has reported the first detection of high-energy astrophysical neutrinos, including ˜50 high-energy starting events, but no individual sources have been identified. It is therefore important to develop the most sensitive and efficient possible algorithms to identify the point sources of these neutrinos. The most popular current method works by exploring a dense grid of possible directions to individual sources, and identifying the single direction with the maximum probability of having produced multiple detected neutrinos. This method has numerous strengths, but it is computationally intensive and because it focuses on the single best location for a point source, additional point sources are not included in the evidence. We propose a new maximum likelihood method that uses the angular separations between all pairs of neutrinos in the data. Unlike existing autocorrelation methods for this type of analysis, which also use angular separations between neutrino pairs, our method incorporates information about the point-spread function and can identify individual point sources. We find that if the angular resolution is a few degrees or better, then this approach reduces both false positive and false negative errors compared to the current method, and is also more computationally efficient up to, potentially, hundreds of thousands of detected neutrinos.
Federal Register 2010, 2011, 2012, 2013, 2014
2010-11-05
... From the Federal Register Online via the Government Publishing Office ENVIRONMENTAL PROTECTION... Point Source Category AGENCY: Environmental Protection Agency (EPA). ACTION: Direct final rule. SUMMARY... instructions for submitting comments. E-mail: OW-Docket@epa.gov . Mail: USEPA Docket Center,...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-01-03
... Section 450.10 of the December 1, 2009 final rule (74 FR 62995) and the definition of ``storm water... Development Point Source Category (hereafter referred to as the ``C&D rule'') on December 1, 2009 (74 FR 62995... Elimination System (NPDES) stormwater regulations (55 FR 47990) on November 16, 1990. The Phase I...
Mestdagh, Inge; Bonicelli, Bernard; Laplana, Ramon; Roettele, Manfred
2009-01-01
Based on the results and lessons learned from the TOPPS project (Training the Operators to prevent Pollution from Point Sources), a proposal on a sustainable strategy to avoid point source pollution from Plant Protection Products (PPPs) was made. Within this TOPPS project (2005-2008), stakeholders were interviewed and research and analysis were done in 6 pilot catchment areas (BE, FR, DE, DK, IT, PL). Next, there was a repeated survey on operators' perception and opinion to measure changes resulting from TOPPS activities and good and bad practices were defined based on the Best Management Practices (risk analysis). Aim of the proposal is to suggest a strategy considering the differences between countries which can be implemented on Member State level in order to avoid PPP pollution of water through point sources. The methodology used for the up-scaLing proposal consists of the analysis of the current situation, a gap analysis, a consistency analysis and organisational structures for implementation. The up-scaling proposal focuses on the behaviour of the operators, on the equipment and infrastructure available with the operators. The proposal defines implementation structures to support correct behaviour through the development and updating of Best Management Practices (BMPs) and through the transfer and the implementation of these BMPs. Next, the proposal also defines requirements for the improvement of equipment and infrastructure based on the defined key factors related to point source pollution. It also contains cost estimates for technical and infrastructure upgrades to comply with BMPs.
40 CFR 1066.930 - Equipment for point-source measurement of running losses.
Code of Federal Regulations, 2014 CFR
2014-07-01
...-source measurement of running losses. For point-source measurement of running loss emissions, use equipment meeting the specifications in 40 CFR 86.107-96(i) Evaporative and Refueling Emission Test... of running losses. 1066.930 Section 1066.930 Protection of Environment ENVIRONMENTAL...
Effect of tissue inhomogeneity on dose distribution of point sources of low-energy electrons.
Kwok, C S; Bialobzyski, P J; Yu, S K; Prestwich, W V
1990-01-01
Perturbation in dose distributions of point sources of low-energy electrons at planar interfaces of cortical bone (CB) and red marrow (RM) was investigated experimentally and by Monte Carlo codes EGS and the TIGER series. Ultrathin LiF thermoluminescent dosimeters were used to measure the dose distributions of point sources of 204Tl and 147Pm in RM. When the point sources were at 12 mg/cm2 from a planar interface of CB and RM equivalent plastics, dose enhancement ratios in RM averaged over the region 0-12 mg/cm2 from the interface were measured to be 1.08 +/- 0.03 (SE) and 1.03 +/- 0.03 (SE) for 204Tl and 147Pm, respectively. The Monte Carlo codes predicted 1.05 +/- 0.02 and 1.01 +/- 0.02 for the two nuclides, respectively. However, EGS gave consistently 3% higher dose in the dose scoring region than the TIGER series when point sources of monoenergetic electrons up to 0.75 MeV energy were considered in the homogeneous RM situation or in the CB and RM heterogeneous situation. By means of the TIGER series, it was demonstrated that aluminum, which is normally assumed to be equivalent to CB in radiation dosimetry, leads to an overestimation of backscattering of low-energy electrons in soft tissue at a CB-soft-tissue interface by as much as a factor of 2.
Status of the BATSE Enhanced Earth Occultation Analysis Package for Studying Point Sources
NASA Technical Reports Server (NTRS)
Skelton, R. T.; Ling, J. C.; Radocinski, R.; Wheaton, Wm. A.
1993-01-01
The compton Gama-Ray Observatory's Burst and Transient Source Experiment (BATSE) has a powerful capability to provide nearly uninterrupted monitoring in the 25keV--2MeV range of cosmic point sources using occultation by the Earth.
40 CFR 414.110 - Applicability; description of the subcategory of indirect discharge point sources.
Code of Federal Regulations, 2010 CFR
2010-07-01
... 40 Protection of Environment 28 2010-07-01 2010-07-01 true Applicability; description of the subcategory of indirect discharge point sources. 414.110 Section 414.110 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS ORGANIC CHEMICALS, PLASTICS,...
NASA Astrophysics Data System (ADS)
Pepin, Matthew; Hayat, Majeed M.
2013-05-01
The almost unique ability of azimuth deramping to preserve a smooth phase function in azimuth is exploited here to link two disparate spatial processing methods, Direction of Arrival (DOA) localization and Interferometric Synthetic Aperture Radar (IFSAR) and explore the achievable accuracy inherent in their common measurement scenario. Deramping in range quickly provides a first component for point source localization. Deramping in azimuth is phase preserving and provides an approximate localization in azimuth that is more accurate over narrower apertures and can be corrected in scenarios involving range migration and for its point source, azimuth location dependence. In cross-track IFSAR two antenna measurements azimuth/elevation DOAs can be calculated from their smooth azimuth functions at each range with a 1 D parametric estimate (exponential model) of point sources. Joint frequency estimates (both antennae) provide the azimuth DOA while the phase di¤erence between antenna amplitude estimates provides the elevation DOA. The cross track antenna measurements can also be processed via the IFSAR methodology producing two SAR images and the phase di¤erence between the two (an interferogram). This provides two images coordinates and a height for each pixel. The connection between the phase history DOA localization and the IFSAR is used to attain accuracy bounds for IFSAR. Extrapolation of the bounds is provided from two spatially un-aliased antennas to IFSAR scenarios with large baseline separations of the antennas. In addition imaging from the azimuth-elevation-range localization data and its ability to minimize layover (building tops imaged closer than their bases) is explored.
Watershed-based point sources permitting strategy and dynamic permit-trading analysis.
Ning, Shu-Kuang; Chang, Ni-Bin
2007-09-01
Permit-trading policy in a total maximum daily load (TMDL) program may provide an additional avenue to produce environmental benefit, which closely approximates what would be achieved through a command and control approach, with relatively lower costs. One of the important considerations that might affect the effective trading mechanism is to determine the dynamic transaction prices and trading ratios in response to seasonal changes of assimilative capacity in the river. Advanced studies associated with multi-temporal spatially varied trading ratios among point sources to manage water pollution hold considerable potential for industries and policy makers alike. This paper aims to present an integrated simulation and optimization analysis for generating spatially varied trading ratios and evaluating seasonal transaction prices accordingly. It is designed to configure a permit-trading structure basin-wide and provide decision makers with a wealth of cost-effective, technology-oriented, risk-informed, and community-based management strategies. The case study, seamlessly integrating a QUAL2E simulation model with an optimal waste load allocation (WLA) scheme in a designated TMDL study area, helps understand the complexity of varying environmental resources values over space and time. The pollutants of concern in this region, which are eligible for trading, mainly include both biochemical oxygen demand (BOD) and ammonia-nitrogen (NH3-N). The problem solution, as a consequence, suggests an array of waste load reduction targets in a well-defined WLA scheme and exhibits a dynamic permit-trading framework among different sub-watersheds in the study area. Research findings gained in this paper may extend to any transferable dynamic-discharge permit (TDDP) program worldwide.
Evidence of Universal Temperature Scaling in Self-Heated Percolating Networks.
Das, Suprem R; Mohammed, Amr M S; Maize, Kerry; Sadeque, Sajia; Shakouri, Ali; Janes, David B; Alam, Muhammad A
2016-05-11
During routine operation, electrically percolating nanocomposites are subjected to high voltages, leading to spatially heterogeneous current distribution. The heterogeneity implies localized self-heating that may (self-consistently) reroute the percolation pathways and even irreversibly damage the material. In the absence of experiments that can spatially resolve the current distribution and a nonlinear percolation model suitable to interpret them, one relies on empirical rules and safety factors to engineer these materials. In this paper, we use ultrahigh resolution thermo-reflectance imaging, coupled with a new imaging processing technique, to map the spatial distribution ΔT(x, y; I) and histogram f(ΔT) of temperature rise due to self-heating in two types of 2D networks (percolating and copercolating). Remarkably, we find that the self-heating can be described by a simple two-parameter Weibull distribution, even under voltages high enough to reconfigure the percolation pathways. Given the generality of the phenomenological argument supporting the distribution, other percolating networks are likely to show similar stress distribution in response to sufficiently large stimuli. Furthermore, the spatial evolution of the self-heating of network was investigated by analyzing the spatial distribution and spatial correlation, respectively. An estimation of degree of hotspot clustering reveals a mechanism analogous to crystallization physics. The results should encourage nonlinear generalization of percolation models necessary for predictive engineering of nanocomposite materials.
Discrimination between diffuse and point sources of arsenic at Zimapán, Hidalgo state, Mexico.
Sracek, Ondra; Armienta, María Aurora; Rodríguez, Ramiro; Villaseñor, Guadalupe
2010-01-01
There are two principal sources of arsenic in Zimapán. Point sources are linked to mining and smelting activities and especially to mine tailings. Diffuse sources are not well defined and are linked to regional flow systems in carbonate rocks. Both sources are caused by the oxidation of arsenic-rich sulfidic mineralization. Point sources are characterized by Ca-SO(4)-HCO(3) ground water type and relatively enriched values of deltaD, delta(18)O, and delta(34)S(SO(4)). Diffuse sources are characterized by Ca-Na-HCO(3) type of ground water and more depleted values of deltaD, delta(18)O, and delta(34)S(SO(4)). Values of deltaD and delta(18)O indicate similar altitude of recharge for both arsenic sources and stronger impact of evaporation for point sources in mine tailings. There are also different values of delta(34)S(SO(4)) for both sources, presumably due to different types of mineralization or isotopic zonality in deposits. In Principal Component Analysis (PCA), the principal component 1 (PC1), which describes the impact of sulfide oxidation and neutralization by the dissolution of carbonates, has higher values in samples from point sources. In spite of similar concentrations of As in ground water affected by diffuse sources and point sources (mean values 0.21 mg L(-1) and 0.31 mg L(-1), respectively, in the years from 2003 to 2008), the diffuse sources have more impact on the health of population in Zimapán. This is caused by the extraction of ground water from wells tapping regional flow system. In contrast, wells located in the proximity of mine tailings are not generally used for water supply.
Tritium percolation, convection, and permeation in fusion solid breeder blankets
Billone, M.C.; Liu, Y.Y.
1985-01-01
Models are developed to describe the percolation of released tritium through the breeder interconnected porosity to the purge stream, convection of tritium by the helium purge stream, and leakage or permeation of tritium through the structural material to the primary coolant system. Important parameters in the models are tritium generation rate, breeder microstructure, tritium species in the gas phase, temperatures, tritium diffusivities and permeabilities, and effectiveness of oxide barriers.
Damage percolation during stretch flange forming of aluminum alloy sheet
NASA Astrophysics Data System (ADS)
Chen, Zengtao; Worswick, Michael J.; Keith Pilkey, A.; Lloyd, David J.
2005-12-01
A multi-scale finite element (FE)-damage percolation model was employed to simulate stretch flange forming of aluminum alloys AA5182 and AA5754. Material softening and strain gradients were captured using a Gurson-based FE model. FE results were then fed into the so-called damage percolation code, from which the damage development was modelled within measured microstructures. The formability of the stretch flange samples was predicted based upon the onset of catastrophic failure triggered by profuse void coalescence within the measured second-phase particle field. Damage development is quantified in terms of crack and void areal fractions, and compared to metallographic results obtained from interrupted stretch flange specimens. Parametric study is conducted on the effect of void nucleation strain in the prediction of formability of stretch flanges to "calibrate" proper nucleation strains for both alloys.
Near-field transport of {sup 129}I from a point source in an in-room disposal vault
Kolar, M.; Leneveu, D.M.; Johnson, L.H.
1995-12-31
A very small number of disposal containers of heat generating nuclear waste may have initial manufacturing defects that would lead to pin-hole type failures at the time of or shortly after emplacement. For sufficiently long-lived containers, only the initial defects need to be considered in modeling of release rates from the disposal vault. Two approaches to modeling of near-field mass transport from a single point source within a disposal room have been compared: the finite-element code MOTIF (A Model Of Transport In Fractured/porous media) and a boundary integral method (BIM). These two approaches were found to give identical results for a simplified model of the disposal room without groundwater flow. MOTIF has then been used to study the effects of groundwater flow on the mass transport out of the emplacement room.
Saremi, Saeed; Sejnowski, Terrence J.
2016-01-01
Natural images are scale invariant with structures at all length scales. We formulated a geometric view of scale invariance in natural images using percolation theory, which describes the behavior of connected clusters on graphs. We map images to the percolation model by defining clusters on a binary representation for images. We show that critical percolating structures emerge in natural images and study their scaling properties by identifying fractal dimensions and exponents for the scale-invariant distributions of clusters. This formulation leads to a method for identifying clusters in images from underlying structures as a starting point for image segmentation. PMID:26415153
Adjustment of the osmolality of Percoll for the isopycnic separation of cells and cell organelles.
Vincent, R; Nadeau, D
1984-09-01
The addition of 1 part of 1.5 M NaCl or 2.5 M sucrose (10 X concentrate) to 9 parts of Percoll produces a stock solution that is hypertonic (350-360 mOsm/kg H2O). Because the osmolality is a critical variable in the isopycnic separation of cells and cell organelles, the factors accountable for this hypertonicity were investigated. Percoll, a colloidal suspension of silica particles coated with polyvinylpyrrolidone, can be described as a medium composed of two distinct compartments, an aqueous phase and a solid phase. According to this model, solutes (e.g., NaCl, sucrose) should have access to the aqueous phase and add to the intrinsic osmolality of Percoll, but should be excluded from the solid phase. In order to verify this hypothesis, mathematical equations were derived and tested. It was found that the ratio of the aqueous volume to the total volume of Percoll (R value) was dependent on the ionic strength of the stock solution. With this parameter, the osmolality of Percoll stock solutions could be predicted (+/-2%) and, consequently, one could calculate the proper dilution to be used with saline, culture medium, or sucrose concentrates to obtain a truly isotonic Percoll stock solution (congruent to 290 mOsm/kg H2O). The relative importance of an accurate control of the osmolality in the preparation of density gradients made up of Percoll is also discussed.
Factors affecting water balance and percolate production for a landfill in operation.
Poulsen, Tjalfe G; Møoldrup, Per
2005-02-01
Percolate production and precipitation data for a full-scale landfill in operation measured over a 13-year period were used to evaluate the impact and importance of the hydrological conditions of landfill sections on the percolate production rates. Both active (open) and closed landfill sections were included in the evaluation. A simple top cover model requiring a minimum of input data was used to simulate the percolate production as a function of precipitation and landfill section hydrology. The results showed that changes over time in the hydrology of individual landfill sections (such as section closure or plantation of trees on top of closed sections) can change total landfill percolate production by more than 100%; thus, percolate production at an active landfill can be very different from percolate production at the same landfill after closure. Furthermore, plantation of willow on top of closed sections can increase the evapotranspiration rate thereby reducing percolate production rates by up to 47% compared to a grass cover. This process, however, depends upon the availability of water in the top layer, and so the evaporation rate will be less than optimal during the summer where soil-water contents in the top cover are low.
Biosolid stockpiles are a significant point source for greenhouse gas emissions.
Majumder, Ramaprasad; Livesley, Stephen J; Gregory, David; Arndt, Stefan K
2014-10-01
The wastewater treatment process generates large amounts of sewage sludge that are dried and then often stored in biosolid stockpiles in treatment plants. Because the biosolids are rich in decomposable organic matter they could be a significant source for greenhouse gas (GHG) emissions, yet there are no direct measurements of GHG from stockpiles. We therefore measured the direct emissions of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) on a monthly basis from three different age classes of biosolid stockpiles at the Western Treatment Plant (WTP), Melbourne, Australia, from December 2009 to November 2011 using manual static chambers. All biosolid stockpiles were a significant point source for CH4 and N2O emissions. The youngest biosolids (<1 year old) had the greatest CH4 and N2O emissions of 60.2 kg of CO2-e per Mg of biosolid per year. Stockpiles that were between 1 and 3 years old emitted less overall GHG (∼29 kg CO2-e Mg(-1) yr(-1)) and the oldest stockpiles emitted the least GHG (∼10 kg CO2-e Mg(-1) yr(-1)). Methane emissions were negligible in all stockpiles but the relative contribution of N2O and CO2 changed with stockpile age. The youngest stockpile emitted two thirds of the GHG emission as N2O, while the 1-3 year old stockpile emitted an equal amount of N2O and CO2 and in the oldest stockpile CO2 emissions dominated. We did not detect any seasonal variability of GHG emissions and did not observe a correlation between GHG flux and environmental variables such as biosolid temperature, moisture content or nitrate and ammonium concentration. We also modeled CH4 emissions based on a first order decay model and the model based estimated annual CH4 emissions were higher as compared to the direct field based estimated annual CH4 emissions. Our results indicate that labile organic material in stockpiles is decomposed over time and that nitrogen decomposition processes lead to significant N2O emissions. Carbon decomposition favors CO2 over
Biosolid stockpiles are a significant point source for greenhouse gas emissions.
Majumder, Ramaprasad; Livesley, Stephen J; Gregory, David; Arndt, Stefan K
2014-10-01
The wastewater treatment process generates large amounts of sewage sludge that are dried and then often stored in biosolid stockpiles in treatment plants. Because the biosolids are rich in decomposable organic matter they could be a significant source for greenhouse gas (GHG) emissions, yet there are no direct measurements of GHG from stockpiles. We therefore measured the direct emissions of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) on a monthly basis from three different age classes of biosolid stockpiles at the Western Treatment Plant (WTP), Melbourne, Australia, from December 2009 to November 2011 using manual static chambers. All biosolid stockpiles were a significant point source for CH4 and N2O emissions. The youngest biosolids (<1 year old) had the greatest CH4 and N2O emissions of 60.2 kg of CO2-e per Mg of biosolid per year. Stockpiles that were between 1 and 3 years old emitted less overall GHG (∼29 kg CO2-e Mg(-1) yr(-1)) and the oldest stockpiles emitted the least GHG (∼10 kg CO2-e Mg(-1) yr(-1)). Methane emissions were negligible in all stockpiles but the relative contribution of N2O and CO2 changed with stockpile age. The youngest stockpile emitted two thirds of the GHG emission as N2O, while the 1-3 year old stockpile emitted an equal amount of N2O and CO2 and in the oldest stockpile CO2 emissions dominated. We did not detect any seasonal variability of GHG emissions and did not observe a correlation between GHG flux and environmental variables such as biosolid temperature, moisture content or nitrate and ammonium concentration. We also modeled CH4 emissions based on a first order decay model and the model based estimated annual CH4 emissions were higher as compared to the direct field based estimated annual CH4 emissions. Our results indicate that labile organic material in stockpiles is decomposed over time and that nitrogen decomposition processes lead to significant N2O emissions. Carbon decomposition favors CO2 over
NASA Astrophysics Data System (ADS)
Borrello, M. C.; Scribner, M.; Chessin, K.
2013-12-01
A growing body of research draws attention to the negative environmental impacts on surface water from large livestock facilities. These impacts are mostly in the form of excessive nutrient loading resulting in significantly decreased oxygen levels. Over-application of animal waste on fields as well as direct discharge into surface water from facilities themselves has been identified as the main contributor to the development of hypoxic zones in Lake Erie, Chesapeake Bay and the Gulf of Mexico. Some regulators claim enforcement of water quality laws is problematic because of the nature and pervasiveness of non-point source impacts. Any direct discharge by a facility is a violation of permits governed by the Clean Water Act, unless the facility has special dispensation for discharge. Previous research by the principal author and others has shown runoff and underdrain transport are the main mechanisms by which nutrients enter surface water. This study utilized previous work to determine if the effects of non-point source discharge can be distinguished from direct (point-source) discharge using simple nutrient analysis and dissolved oxygen (DO) parameters. Nutrient and DO parameters were measured from three sites: 1. A stream adjacent to a field receiving manure, upstream of a large livestock facility with a history of direct discharge, 2. The same stream downstream of the facility and 3. A stream in an area relatively unimpacted by large-scale agriculture (control site). Results show that calculating a simple Pearson correlation coefficient (r) of soluble reactive phosphorus (SRP) and ammonia over time as well as temperature and DO, distinguishes non-point source from point source discharge into surface water. The r value for SRP and ammonia for the upstream site was 0.01 while the r value for the downstream site was 0.92. The control site had an r value of 0.20. Likewise, r values were calculated on temperature and DO for each site. High negative correlations
Shen, Zhenyao; Hong, Qian; Yu, Hong; Liu, Ruimin
2008-11-01
The generation and formation of non-point source pollution involves great uncertainty, and this uncertainty makes monitoring and controlling pollution very difficult. Understanding the main parameters that affect non-point source pollution uncertainty is necessary to provide the basis for the planning and design of control measures. In this study, three methods were adopted to do the parameter uncertainty analysis with the Soil and Water Assessment Tool (SWAT). Based on the results of parameter sensitivity analysis by the Morris screening method, the ten parameters that most affect runoff, sediment, organic N, nitrate, and total phosphorous (TP) were chosen for further uncertainty analysis. First-order error analysis (FOEA) and the Monte Carlo method (MC) were used to analyze the effect of parameter uncertainty on model outputs. FOEA results showed that only a few parameters had significantly affected the uncertainty of the final simulation results, and many parameters had little or no effect. The SCS curve number was the parameter with significant uncertainty impact on runoff, sediment, organic N, nitrate and TP, and it showed that the runoff process was mainly responsible for the uncertainty of non-point source pollution load. The uncertainty of sediment was the biggest among the five model output results described above. MC results indicated that neglecting the parameter uncertainty of the model would underestimate the non-point source pollution load, and that the relationship between model input and output was non-linear. The uncertainty of non-point source pollution exhibited a temporal pattern: It was greater in summer than in winter. The uncertainty of runoff was smaller compared to that of sediment, organic N, nitrate, and TP, and the source of uncertainty was mainly affected by parameters associated with runoff. PMID:18639918
NASA Technical Reports Server (NTRS)
Weistrop, D.; Shaffer, D. B.; Mushotzky, R. F.; Reitsma, H. J.; Smith, B. A.
1981-01-01
Visual and far red surface photometry were obtained of two X-ray emitting BL Lacertae objects, 1218+304 (2A1219+305) and 1727+50 (Izw 187), as well as the highly variable object 1219+28 (ON 231, W Com). The intensity distribution for 1727+50 can be modeled using a central point source plus a de Vaucouleurs intensity law for an underlying galaxy. The broad band spectral energy distribution so derived is consistent with what is expected for an elliptical galaxy. The spectral index of the point source is alpha = 0.97. Additional VLBI and X-ray data are also reported for 1727+50. There is nebulosity associated with the recently discovered object 1218+304. No nebulosity is found associated with 1219+28. A comparison of the results with observations at X-ray and radio frequencies suggests that all the emission from 1727+50 and 1218+304 can be interpreted as due solely to direct synchrotron emission. If this is the case, the data further imply the existence of relativistic motion effects and continuous particle injection.
XMM-Newton observation of the X-ray point source population of the starburst galaxy IC 342
NASA Astrophysics Data System (ADS)
Kong, Albert K. H.
2003-11-01
We present the results of an XMM-Newton observation of the starburst galaxy IC 342. Thirty-seven X-ray point sources were detected down to a luminosity limit of ~1037 erg s-1. Most of the sources are located near the spiral arms. The X-ray point source luminosity function is consistent with a power-law shape with a slope of 0.55, typical of starburst galaxies. We also present the energy spectra of several ultraluminous X-ray sources (ULXs), including the luminous X-ray source in the galactic nucleus. Except for the nucleus and a luminous supersoft X-ray source, other ULXs can generally be fitted with a simple power-law spectral model. The nucleus is very luminous (~1040 erg s-1 in 0.2-12 keV) and requires disc blackbody and power-law components to describe the X-ray emission. The spectral fit reveals a cool accretion disc (kT= 0.11 keV) and suggests that the source harbours either an intermediate-mass black hole or a stellar-mass black hole with outflow.
Tohme, Michel S.; Qi, Jinyi
2010-01-01
Purpose: The accuracy of the system model that governs the transformation from the image space to the projection space in positron emission tomography (PET) greatly affects the quality of reconstructed images. For efficient computation in iterative reconstructions, the system model in PET can be factored into a product of geometric projection and sinogram blurring function. To further speed up reconstruction, fully 3D PET data can be rebinned into a stack of 2D sinograms and then be reconstructed using 2D iterative algorithms. The purpose of this work is to develop a method to estimate the sinogram blurring function to be used in reconstruction of Fourier-rebinned data. Methods: In a previous work, the authors developed an approach to estimating the sinogram blurring function of nonrebinned PET data from experimental scans of point sources. In this study, the authors extend this method to the estimation of sinogram blurring function for Fourier-rebinned PET data. A point source was scanned at a set of sampled positions in the microPET II scanner. The sinogram blurring function is considered to be separable between the transaxial and axial directions. A radially and angularly variant 2D blurring function is estimated from Fourier-rebinned point source scans to model the transaxial blurring with consideration of the detector block structure of the scanner; a space-variant 1D blurring kernel along the axial direction is estimated separately to model the correlation between neighboring planes due to detector intrinsic blurring and Fourier rebinning. The estimated sinogram blurring function is incorporated in a 2D maximum a posteriori (MAP) reconstruction algorithm for image reconstruction. Results: Physical phantom experiments were performed on the microPET II scanner to validate the proposed method. The authors compared the proposed method to 2D MAP reconstruction without sinogram blurring model and 2D MAP reconstruction with a Monte Carlo based blurring model. The
Quantum percolation in cuprate high-temperature superconductors
Phillips, J. C.
2008-01-01
Although it is now generally acknowledged that electron–phonon interactions cause cuprate superconductivity with Tc values ≈100 K, the complexities of atomic arrangements in these marginally stable multilayer materials have frustrated both experimental analysis and theoretical modeling of the remarkably rich data obtained both by angle-resolved photoemission (ARPES) and high-resolution, large-area scanning tunneling microscopy (STM). Here, we analyze the theoretical background in terms of our original (1989) model of dopant-assisted quantum percolation (DAQP), as developed further in some two dozen articles, and apply these ideas to recent STM data. We conclude that despite all of the many difficulties, with improved data analysis it may yet be possible to identify quantum percolative paths. PMID:18626024
Influence of non-point source pollution on riverine fish assemblages in South West France.
Ibarra, Alonso Aguilar; Dauba, Francis; Lim, Puy
2005-07-01
The relationship between non-point source pollution (NSP) and fish assemblages in the Garonne basin, SW France was studied. Two independent data sets were coupled, one containing 20 physico-chemical variables and another containing 40 fish species in 84 study sites. Species were classified in guilds according to their feeding habitat and their diet composition. The physico-chemical variables were log-transformed and standardized for a factor analysis in which they were grouped into four factors which accounted for 80% of the total variability. These were named according to factor loadings (i.e. a measure of the variance of a given variable) whose absolute values were larger than 0.5. Hence, the first factor (F1) was formed by variables linked to NSP, most notably by sodium, chloride, potassium, orthophosphates, nitrites and chemical oxygen demand. The second factor (F2) was related to alkalinity (i.e. bicarbonates, calcium, conductivity and pH). The third factor (F3) included oxygen saturation rate and dissolved oxygen, and F4 combined both temperature and flow. Factor scores (i.e. weighted sums of the original variables) were then introduced in stepwise multiple regression models as explanatory variables of log-transformed fish species richness of trophic guilds. The NSP factor was significant (p < 0.05) for the following models: benthic omnivores (r2 = 0.66), all species (r2 = 0.65), total benthic species (r2 = 0.63), total water-column species (r2 = 0.57), benthic invertivores (r2 = 0.32) and water-column invertivores (r2 = 0.16). The guilds for which NSP was not significant were water-column omnivores, water-column piscivores and benthic detritivores. Thus, there was evidence of an inversely proportional association, though not causation, of NSP with species richness of riverine fish trophic guilds on a large spatio-temporal scale. Fish assemblages may respond in different ways to NSP depending on their species composition, on the region and on the scale, and
Percolation of secret correlations in a network
Leverrier, Anthony; Garcia-Patron, Raul
2011-09-15
In this work, we explore the analogy between entanglement and secret classical correlations in the context of large networks--more precisely, the question of percolation of secret correlations in a network. It is known that entanglement percolation in quantum networks can display a highly nontrivial behavior depending on the topology of the network and on the presence of entanglement between the nodes. Here we show that this behavior, thought to be of a genuine quantum nature, also occurs in a classical context.
The resolution of point sources of light as analyzed by quantum detection theory
NASA Technical Reports Server (NTRS)
Helstrom, C. W.
1972-01-01
The resolvability of point sources of incoherent light is analyzed by quantum detection theory in terms of two hypothesis-testing problems. In the first, the observer must decide whether there are two sources of equal radiant power at given locations, or whether there is only one source of twice the power located midway between them. In the second problem, either one, but not both, of two point sources is radiating, and the observer must decide which it is. The decisions are based on optimum processing of the electromagnetic field at the aperture of an optical instrument. In both problems the density operators of the field under the two hypotheses do not commute. The error probabilities, determined as functions of the separation of the points and the mean number of received photons, characterize the ultimate resolvability of the sources.
Resolution of point sources of light as analyzed by quantum detection theory.
NASA Technical Reports Server (NTRS)
Helstrom, C. W.
1973-01-01
The resolvability of point sources of incoherent thermal light is analyzed by quantum detection theory in terms of two hypothesis-testing problems. In the first, the observer must decide whether there are two sources of equal radiant power at given locations, or whether there is only one source of twice the power located midway between them. In the second problem, either one, but not both, of two point sources is radiating, and the observer must decide which it is. The decisions are based on optimum processing of the electromagnetic field at the aperture of an optical instrument. In both problems the density operators of the field under the two hypotheses do not commute. The error probabilities, determined as functions of the separation of the points and the mean number of received photons, characterize the ultimate resolvability of the sources.
Tackling non-point source water pollution in British Columbia: An action plan
1998-12-31
Efforts to protect British Columbia water quality by regulating point discharges from municipal and industrial sources have generally been successful, and it is recognized that the major remaining cause of water pollution in the province is from non-point sources. These sources are largely unregulated and associated with urbanization, agriculture, and other forms of land development. The first part of this report reviews the provincial commitment to clean water, the effects of non-point-source (NPS) pollution, and the management of NPS in the province. Part 2 describes the main causes of NPS in British Columbia: Land development, agriculture, stormwater runoff, on-site sewage systems, forestry and range activities, atmospheric deposition, and boating/marine activities. Finally, it presents key components of the province`s NPS action plan: Education and training, prevention at site, land use planning and co-ordination, assessment and reporting, economic incentives, legislation and regulation, and implementation.
Tackling non-point source water pollution in British Columbia: An action plan
Not Available
1998-01-01
Efforts to protect British Columbia water quality by regulating point discharges from municipal and industrial sources have generally been successful, and it is recognized that the major remaining cause of water pollution in the province is from non-point sources. These sources are largely unregulated and associated with urbanization, agriculture, and other forms of land development. The first part of this report reviews the provincial commitment to clean water, the effects of non-point-source (NPS) pollution, and the management of NPS in the province. Part 2 describes the main causes of NPS in British Columbia: Land development, agriculture, stormwater runoff, on-site sewage systems, forestry and range activities, atmospheric deposition, and boating/marine activities. Finally, it presents key components of the province's NPS action plan: Education and training, prevention at site, land use planning and co-ordination, assessment and reporting, economic incentives, legislation and regulation, and implementation.
Quantitative point source photoacoustic inversion formulas for scattering and absorbing media
NASA Astrophysics Data System (ADS)
Ripoll, Jorge; Ntziachristos, Vasilis
2005-03-01
We present here an expression for the photoacoustic contribution of an optical point source in a diffusive and absorbing medium. By using this measurement as a reference, we present a direct inversion formula that recovers the absorption map quantitatively, at the same time accounting for instrumental factors such as the source strength, the shape of the optical pulse, and the impulse response and finite size of the transducers. We further validate this expression through accurate numerical simulations showing that the absorption map is recovered quantitatively in the presence of a rotating geometry. We finally discuss how the presented solutions for point sources within the photoacoustic problem enable the use of concurrent fluorescence and ultrasound measurements as appropriate for a hybrid tomographic system. The proposed system could retrieve absorption information using photoacoustic measurements, and use these data to more accurately describe the fluorescence problem and improve reconstruction fidelity.
VizieR Online Data Catalog: LMC point source classification in SAGE-Spec (Woods+, 2011)
NASA Astrophysics Data System (ADS)
Woods, P. M.; Oliveira, J. M.; Kemper, F.; van Loon, J. T.; Sargent, B. A.; Matsuura, M.; Szczerba, R.; Volk, K.; Zijlstra, A. A.; Sloan, G. C.; Lagadec, E.; McDonald, I.; Jones, O.; Gorjian, V.; Kraemer, K. E.; Gielen, C.; Meixner, M.; Blum, R. D.; Sewilo, M.; Riebel, D.; Shiao, B.; Chen, C.-H. R.; Boyer, M. L.; Indebetouw, R.; Antoniou, V.; Bernard, J.-P.; Cohen, M.; Dijkstra, C.; Galametz, M.; Galliano, F.; Gordon, K. D.; Harris, J.; Hony, S.; Hora, J. L.; Kawamura, A.; Lawton, B.; Leisenring, J. M.; Madden, S.; Marengo, M.; McGuire, C.; Mulia, A. J.; O'Halloran, B.; Olsen, K.; Paladini, R.; Paradis, D.; Reach, W. T.; Rubin, D.; Sandstrom, K.; Soszynski, I.; Speck, A. K.; Srinivasan, S.; Tielens, A. G. G. M.; van Aarle, E.; van Dyk, S. D.; van Winckel, H.; Vijh, U. P.; Whitney, B.; Wilkins, A. N.
2011-09-01
We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy programme on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two HII regions and 12 other objects, seven of which remain unclassified. (1 data file).
Mapping Correlation of Two Point Sources in the Gamma-Ray Sky
Gibson, Alexander
2015-08-20
The Fermi Gamma-Ray Space Telescope has been taking data on high energy photons or γ rays since June 11th, 2008, and people have been cataloging and profiling point sources of these γ rays ever since. After roughly one year of being in operation over 1400 sources were cataloged. Now, in 2015 we have 3033 sources cataloged. With the increasing amount of sources it’s important to think about the limitations of likelihood analysis for highly correlated sources. In this paper I will present the problems of using likelihood analysis for sources that are highly correlated as well as show under what circumstances sources can be considered highly correlated. Dark matter over densities may show up as a point source, so it is a necessary step to learn how the two signals will interact to allow for a proper search for dark matter.
Generalized epidemic process and tricritical dynamic percolation
NASA Astrophysics Data System (ADS)
Janssen, Hans-Karl; Müller, Martin; Stenull, Olaf
2004-08-01
The renowned general epidemic process describes the stochastic evolution of a population of individuals which are either susceptible, infected, or dead. A second order phase transition belonging to the universality class of dynamic isotropic percolation lies between the endemic and pandemic behavior of the process. We generalize the general epidemic process by introducing a fourth kind of individuals, viz., individuals which are weakened by the process but not yet infected. This weakening gives rise to a mechanism that introduces a global instability in the spreading of the process and therefore opens the possibility of a discontinuous transition in addition to the usual continuous percolation transition. The tricritical point separating the lines of first and second order transitions constitutes an independent universality class, namely, the universality class of tricritical dynamic isotropic percolation. Using renormalized field theory we work out a detailed scaling description of this universality class. We calculate the scaling exponents in an ɛ expansion below the upper critical dimension dc=5 for various observables describing tricritical percolation clusters and their spreading properties. In a remarkable contrast to the usual percolation transition, the exponents β and β' governing the two order parameters, viz., the mean density and the percolation probability, turn out to be different at the tricritical point. In addition to the scaling exponents we calculate for all our static and dynamic observables logarithmic corrections to the mean-field scaling behavior at dc=5 .
NASA Astrophysics Data System (ADS)
Génois, Mathieu; Hersen, Pascal; Bertin, Eric; Courrech du Pont, Sylvain; Grégoire, Guillaume
2016-10-01
The exploration of the phase diagram of a minimal model for barchan fields leads to the description of three distinct phases for the system: stationary, percolable, and unstable. In the stationary phase the system always reaches an out-of-equilibrium, fluctuating, stationary state, independent of its initial conditions. This state has a large and continuous range of dynamics, from dilute—where dunes do not interact—to dense, where the system exhibits both spatial structuring and collective behavior leading to the selection of a particular size for the dunes. In the percolable phase, the system presents a percolation threshold when the initial density increases. This percolation is unusual, as it happens on a continuous space for moving, interacting, finite lifetime dunes. For extreme parameters, the system exhibits a subcritical instability, where some of the dunes in the field grow without bound. We discuss the nature of the asymptotic states and their relations to well-known models of statistical physics.
Percolation analysis of nonlinear structures in scale-free two-dimensional simulations
NASA Technical Reports Server (NTRS)
Dominik, Kurt G.; Shandarin, Sergei F.
1992-01-01
Results are presented of applying percolation analysis to several two-dimensional N-body models which simulate the formation of large-scale structure. Three parameters are estimated: total area (a(c)), total mass (M(C)), and percolation density (rho(c)) of the percolating structure at the percolation threshold for both unsmoothed and smoothed (with different scales L(s)) nonlinear with filamentary structures, confirming early speculations that this type of model has several features of filamentary-type distributions. Also, it is shown that, by properly applying smoothing techniques, many problems previously considered detrimental can be dealt with and overcome. Possible difficulties and prospects with the use of this method are discussed, specifically relating to techniques and methods already applied to CfA deep sky surveys. The success of this test in two dimensions and the potential for extrapolation to three dimensions is also discussed.
NASA Astrophysics Data System (ADS)
Minato, Shohei; Ghose, Ranajit
2014-05-01
The inverse scattering of seismic waves can reveal the spatial distribution of the elastic compliances along a non-welded interface, such as a fracture surface. The spatial heterogeneity along the surface of a fracture is a key determinant for fracture-associated hydraulic properties. In this paper, we demonstrate that the inverse scattering solution can be successfully applied to the point source response of a subhorizontal fracture. In the scale of seismic exploration, it is more appropriate to consider spherical waves from a point source than plane waves. Further, from only the P-wave point source response it is possible to estimate both normal and tangential fracture compliances. The synthetic seismic wavefield due to a P-wave point source in a 2-D elastic medium was computed using a time-domain finite difference approach. On this spherical wave data set, the correct estimation of the position and dip of the non-welded interface was possible through reverse-time migration followed by least-square fitting of the maximum amplitude of the P-P reflection. In order to estimate the heterogeneity along the non-welded interface, we first extract the elastic wavefield at the interface position. The extrapolated wavefield is then rotated such that the horizontal axis aligns along the fracture plane. Next, using this extrapolated and rotated wavefield, we solve the linear-slip boundary condition to obtain the distribution of normal and tangential compliances. Our result shows that the estimates of normal compliance are very accurate around the dominant frequency of the incident seismic wavefield. At lower frequencies, the estimated compliance distribution is less accurate and rather smooth due to the presence of evanescent waves. Extracting the distribution of the tangential compliance requires a larger stabilization factor. For a correct estimation of the tangential compliance, one needs S-wave sources or multiple sources providing more grazing angles to avoid the shadow
Zhou, Liang; Xu, Jian-Gang; Sun, Dong-Qi; Ni, Tian-Hua
2013-02-01
Agricultural non-point source pollution is of importance in river deterioration. Thus identifying and concentrated controlling the key source-areas are the most effective approaches for non-point source pollution control. This study adopts inventory method to analysis four kinds of pollution sources and their emissions intensity of the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in 173 counties (cities, districts) in Huaihe River Basin. The four pollution sources include livestock breeding, rural life, farmland cultivation, aquacultures. The paper mainly addresses identification of non-point polluted sensitivity areas, key pollution sources and its spatial distribution characteristics through cluster, sensitivity evaluation and spatial analysis. A geographic information system (GIS) and SPSS were used to carry out this study. The results show that: the COD, TN and TP emissions of agricultural non-point sources were 206.74 x 10(4) t, 66.49 x 10(4) t, 8.74 x 10(4) t separately in Huaihe River Basin in 2009; the emission intensity were 7.69, 2.47, 0.32 t.hm-2; the proportions of COD, TN, TP emissions were 73%, 24%, 3%. The paper achieves that: the major pollution source of COD, TN and TP was livestock breeding and rural life; the sensitivity areas and priority pollution control areas among the river basin of non-point source pollution are some sub-basins of the upper branches in Huaihe River, such as Shahe River, Yinghe River, Beiru River, Jialu River and Qingyi River; livestock breeding is the key pollution source in the priority pollution control areas. Finally, the paper concludes that pollution type of rural life has the highest pollution contribution rate, while comprehensive pollution is one type which is hard to control.
HerMES: point source catalogues from Herschel-SPIRE observations II
NASA Astrophysics Data System (ADS)
Wang, L.; Viero, M.; Clarke, C.; Bock, J.; Buat, V.; Conley, A.; Farrah, D.; Guo, K.; Heinis, S.; Magdis, G.; Marchetti, L.; Marsden, G.; Norberg, P.; Oliver, S. J.; Page, M. J.; Roehlly, Y.; Roseboom, I. G.; Schulz, B.; Smith, A. J.; Vaccari, M.; Zemcov, M.
2014-11-01
The Herschel Multi-tiered Extragalactic Survey (HerMES) is the largest Guaranteed Time Key Programme on the Herschel Space Observatory. With a wedding cake survey strategy, it consists of nested fields with varying depth and area totalling ˜380 deg2. In this paper, we present deep point source catalogues extracted from Herschel-Spectral and Photometric Imaging Receiver (SPIRE) observations of all HerMES fields, except for the later addition of the 270 deg2 HerMES Large-Mode Survey (HeLMS) field. These catalogues constitute the second Data Release (DR2) made in 2013 October. A sub-set of these catalogues, which consists of bright sources extracted from Herschel-SPIRE observations completed by 2010 May 1 (covering ˜74 deg2) were released earlier in the first extensive data release in 2012 March. Two different methods are used to generate the point source catalogues, the SUSSEXTRACTOR point source extractor used in two earlier data releases (EDR and EDR2) and a new source detection and photometry method. The latter combines an iterative source detection algorithm, STARFINDER, and a De-blended SPIRE Photometry algorithm. We use end-to-end Herschel-SPIRE simulations with realistic number counts and clustering properties to characterize basic properties of the point source catalogues, such as the completeness, reliability, photometric and positional accuracy. Over 500 000 catalogue entries in HerMES fields (except HeLMS) are released to the public through the HeDAM (Herschel Database in Marseille) website (http://hedam.lam.fr/HerMES).
ETNA software used for efficiency transfer from a point source to other geometries.
Radu, Daniela; Stanga, Doru; Sima, Octavian
2009-09-01
The quality of the results of gamma spectrometry measurement depends directly on the accuracy of the detection efficiency in the specific measurement conditions. The purpose of this work is to examine the applicability of the efficiency transfer method using ETNA software for the computation of the efficiency in various measurement geometries on the basis of the measured efficiency for reference point source geometry located at 100 mm distance from the high purity germanium (HPGe) detector.
[Transformation of Non-point Source Soluble Nitrogen in Simulated Drainage Ditch].
Li, Qiang-kun; Song, Chang-ji; Hu, Ya-wei; Peng, Cong; Ma, Qiang; Jiang, Zheng-xi; Ju, Yi-rheng
2016-02-15
The drainage ditch has a compound ecosystem structure consisting of water, sediment and plants. Migration and transformation of the non-point source solute is important to study interception, control and management of agricultural non-point source pollution in the drainage ditch. Based on the experiment on static simulation of drainage ditches, the article used typical non-point source soluble nitrogen as an example to analyze the changing process of nitrogen content in water, sediment and reeds, and to study the effects of the sediment adsorption and desorption, reeds growth and death in different periods on nitrogen concentration in water. The article discussed nitrogen migration in water-sediment-reeds compound ecosystem and its influence on nitrogen concentration in water. The results showed that both adsorption and desorption in sediment and absorption and assimilation of reeds growth had effect on nitrogen concentration in water. The effect before October was reducing the nitrogen concentration in water, which was the process of nitrogen purification in water. After October, the nitrogen concentration in water increased and made it easy to form secondary nitrogen pollution. Meanwhile, the migration in the water-sediment-seeds ecosystem in simulated drainage ditch had close ties, any migration and transformation of nitrogen in a single medium or between different mediums would cause adjustment of nitrogen concentration in water.
[Transformation of Non-point Source Soluble Nitrogen in Simulated Drainage Ditch].
Li, Qiang-kun; Song, Chang-ji; Hu, Ya-wei; Peng, Cong; Ma, Qiang; Jiang, Zheng-xi; Ju, Yi-rheng
2016-02-15
The drainage ditch has a compound ecosystem structure consisting of water, sediment and plants. Migration and transformation of the non-point source solute is important to study interception, control and management of agricultural non-point source pollution in the drainage ditch. Based on the experiment on static simulation of drainage ditches, the article used typical non-point source soluble nitrogen as an example to analyze the changing process of nitrogen content in water, sediment and reeds, and to study the effects of the sediment adsorption and desorption, reeds growth and death in different periods on nitrogen concentration in water. The article discussed nitrogen migration in water-sediment-reeds compound ecosystem and its influence on nitrogen concentration in water. The results showed that both adsorption and desorption in sediment and absorption and assimilation of reeds growth had effect on nitrogen concentration in water. The effect before October was reducing the nitrogen concentration in water, which was the process of nitrogen purification in water. After October, the nitrogen concentration in water increased and made it easy to form secondary nitrogen pollution. Meanwhile, the migration in the water-sediment-seeds ecosystem in simulated drainage ditch had close ties, any migration and transformation of nitrogen in a single medium or between different mediums would cause adjustment of nitrogen concentration in water. PMID:27363139
Nonpoint and Point Sources of Nitrogen in Major Watersheds of the United States
Puckett, Larry J.
1994-01-01
Estimates of nonpoint and point sources of nitrogen were made for 107 watersheds located in the U.S. Geological Survey's National Water-Quality Assessment Program study units throughout the conterminous United States. The proportions of nitrogen originating from fertilizer, manure, atmospheric deposition, sewage, and industrial sources were found to vary with climate, hydrologic conditions, land use, population, and physiography. Fertilizer sources of nitrogen are proportionally greater in agricultural areas of the West and the Midwest than in other parts of the Nation. Animal manure contributes large proportions of nitrogen in the South and parts of the Northeast. Atmospheric deposition of nitrogen is generally greatest in areas of greatest precipitation, such as the Northeast. Point sources (sewage and industrial) generally are predominant in watersheds near cities, where they may account for large proportions of the nitrogen in streams. The transport of nitrogen in streams increases as amounts of precipitation and runoff increase and is greatest in the Northeastern United States. Because no single nonpoint nitrogen source is dominant everywhere, approaches to control nitrogen must vary throughout the Nation. Watershed-based approaches to understanding nonpoint and point sources of contamination, as used by the National Water-Quality Assessment Program, will aid water-quality and environmental managers to devise methods to reduce nitrogen pollution.
FIRST NEUTRINO POINT-SOURCE RESULTS FROM THE 22-STRING ICECUBE DETECTOR
IceCube Collaboration; Klein, Spencer
2009-05-14
We present new results of searches for neutrino point sources in the northern sky, using data recorded in 2007-08 with 22 strings of the IceCube detector (approximately one-fourth of the planned total) and 275.7 days of livetime. The final sample of 5114 neutrino candidate events agrees well with the expected background of atmospheric muon neutrinos and a small component of atmospheric muons. No evidence of a point source is found, with the most significant excess of events in the sky at 2.2 {sigma} after accounting for all trials. The average upper limit over the northern sky for point sources of muon-neutrinos with E{sup -2} spectrum is E{sup 2} {Phi}{sub {nu}{sub {mu}}} < 1.4 x 10{sup -1} TeV cm{sup -2}s{sup -1}, in the energy range from 3 TeV to 3 PeV, improving the previous best average upper limit by the AMANDA-II detector by a factor of two.
General and exact approach to percolation on random graphs
NASA Astrophysics Data System (ADS)
Allard, Antoine; Hébert-Dufresne, Laurent; Young, Jean-Gabriel; Dubé, Louis J.
2015-12-01
We present a comprehensive and versatile theoretical framework to study site and bond percolation on clustered and correlated random graphs. Our contribution can be summarized in three main points. (i) We introduce a set of iterative equations that solve the exact distribution of the size and composition of components in finite-size quenched or random multitype graphs. (ii) We define a very general random graph ensemble that encompasses most of the models published to this day and also makes it possible to model structural properties not yet included in a theoretical framework. Site and bond percolation on this ensemble is solved exactly in the infinite-size limit using probability generating functions [i.e., the percolation threshold, the size, and the composition of the giant (extensive) and small components]. Several examples and applications are also provided. (iii) Our approach can be adapted to model interdependent graphs—whose most striking feature is the emergence of an extensive component via a discontinuous phase transition—in an equally general fashion. We show how a graph can successively undergo a continuous then a discontinuous phase transition, and preliminary results suggest that clustering increases the amplitude of the discontinuity at the transition.
Percolation and cooperation with mobile agents: Geometric and strategy clusters
NASA Astrophysics Data System (ADS)
Vainstein, Mendeli H.; Brito, Carolina; Arenzon, Jeferson J.
2014-08-01
We study the conditions for persistent cooperation in an off-lattice model of mobile agents playing the Prisoner's Dilemma game with pure, unconditional strategies. Each agent has an exclusion radius rP, which accounts for the population viscosity, and an interaction radius rint, which defines the instantaneous contact network for the game dynamics. We show that, differently from the rP=0 case, the model with finite-sized agents presents a coexistence phase with both cooperators and defectors, besides the two absorbing phases, in which either cooperators or defectors dominate. We provide, in addition, a geometric interpretation of the transitions between phases. In analogy with lattice models, the geometric percolation of the contact network (i.e., irrespective of the strategy) enhances cooperation. More importantly, we show that the percolation of defectors is an essential condition for their survival. Differently from compact clusters of cooperators, isolated groups of defectors will eventually become extinct if not percolating, independently of their size.
Analytic results for the percolation transitions of the enhanced binary tree.
Minnhagen, Petter; Baek, Seung Ki
2010-07-01
Percolation for a planar lattice has a single percolation threshold, whereas percolation for a negatively curved lattice displays two separate thresholds. The enhanced binary tree (EBT) can be viewed as a prototype model displaying two separate percolation thresholds. We present an analytic result for the EBT model which gives two critical percolation threshold probabilities, p(c1) = 1/2 square root(13) - 3/2 and p(c2) = 1/2, and yields a size-scaling exponent Φ = ln[(p(1+p))/(1-p(1-p))]/ln 2. It is inferred that the two threshold values give exact upper limits and that pc1 is furthermore exact. In addition, we argue that p(c2) is also exact. The physics of the model and the results are described within the midpoint-percolation concept: Monte Carlo simulations are presented for the number of boundary points which are reached from the midpoint, and the results are compared to the number of routes from the midpoint to the boundary given by the analytic solution. These comparisons provide a more precise physical picture of what happens at the transitions. Finally, the results are compared to related works, in particular, the Cayley tree and Monte Carlo results for hyperbolic lattices as well as earlier results for the EBT model. It disproves a conjecture that the EBT has an exact relation to the thresholds of its dual lattice.
NASA Astrophysics Data System (ADS)
Fessel, Adrian; Oettmeier, Christina; Bernitt, Erik; Gauthier, Nils C.; Döbereiner, Hans-Günther
2012-08-01
We study the formation of transportation networks of the true slime mold Physarum polycephalum after fragmentation by shear. Small fragments, called microplasmodia, fuse to form macroplasmodia in a percolation transition. At this topological phase transition, one single giant component forms, connecting most of the previously isolated microplasmodia. Employing the configuration model of graph theory for small link degree, we have found analytically an exact solution for the phase transition. It is generally applicable to percolation as seen, e.g., in vascular networks.
NASA Astrophysics Data System (ADS)
Arnold, Tim; Manning, Alistair J.; Li, Shanlan; Kim, Jooil; Park, Sunyoung; Fraser, Paul J.; Mitrevski, Blagoj; Steele, L. Paul; Krummel, Paul B.; Mühle, Jens; Weiss, Ray F.
2016-04-01
The fluorinated species carbon tetrafluoride (CF4; PFC-14), nitrogen trifluoride (NF3) and trifluoromethane (CHF3; HFC-23) are potent greenhouse gases with 100-year global warming potentials of 6,630, 16,100 and 12,400, respectively. Unlike the majority of CFC-replacement compounds that are emitted from fugitive and mobile emission sources, these gases are largely emitted from large single point sources - semiconductor manufacturing facilities (all three), aluminium smelting plants (CF4) and chlorodifluoromethane factories (HFC-23). In this work we show the potential for atmospheric measurements to understand regional sources of these gases and to highlight emission 'hotspots'. We target our analysis on measurements from two Advanced Global Atmospheric Gases Experiment (AGAGE) long term monitoring sites that are particularly sensitive to regional emissions of these gases: Gosan on Jeju Island in the Republic of Korea and Cape Grim on Tasmania in Australia. These sites measure CF4, NF3 and HFC-23 alongside a suite of greenhouse and stratospheric ozone depleting gases every two hours using automated in situ gas-chromatography mass-spectrometry instrumentation. We couple each measurement to an analysis of air history using the regional atmospheric transport model NAME (Numerical Atmospheric dispersion Modelling Environment) driven by 3D meteorology from the Met Office's Unified Model, and use a Bayesian inverse method (InTEM - Inversion Technique for Emission Modelling) to calculate yearly emission changes over a decade (2005-2015) at high spatial resolution. At present these gases make a small contribution to global radiative forcing, however, given that their impact could rise significantly and that point sources of such gases can be mitigated, atmospheric monitoring could be an important tool for aiding emissions reduction policy.
Percolation mechanism drives actin gels to the critically connected state
NASA Astrophysics Data System (ADS)
Lee, Chiu Fan; Pruessner, Gunnar
2016-05-01
Cell motility and tissue morphogenesis depend crucially on the dynamic remodeling of actomyosin networks. An actomyosin network consists of an actin polymer network connected by cross-linker proteins and motor protein myosins that generate internal stresses on the network. A recent discovery shows that for a range of experimental parameters, actomyosin networks contract to clusters with a power-law size distribution [J. Alvarado, Nat. Phys. 9, 591 (2013), 10.1038/nphys2715]. Here, we argue that actomyosin networks can exhibit a robust critical signature without fine-tuning because the dynamics of the system can be mapped onto a modified version of percolation with trapping (PT), which is known to show critical behavior belonging to the static percolation universality class without the need for fine-tuning of a control parameter. We further employ our PT model to generate experimentally testable predictions.
Percolation mechanism drives actin gels to the critically connected state.
Lee, Chiu Fan; Pruessner, Gunnar
2016-05-01
Cell motility and tissue morphogenesis depend crucially on the dynamic remodeling of actomyosin networks. An actomyosin network consists of an actin polymer network connected by cross-linker proteins and motor protein myosins that generate internal stresses on the network. A recent discovery shows that for a range of experimental parameters, actomyosin networks contract to clusters with a power-law size distribution [J. Alvarado, Nat. Phys. 9, 591 (2013)1745-247310.1038/nphys2715]. Here, we argue that actomyosin networks can exhibit a robust critical signature without fine-tuning because the dynamics of the system can be mapped onto a modified version of percolation with trapping (PT), which is known to show critical behavior belonging to the static percolation universality class without the need for fine-tuning of a control parameter. We further employ our PT model to generate experimentally testable predictions. PMID:27300931
Price of anarchy is maximized at the percolation threshold.
Skinner, Brian
2015-05-01
When many independent users try to route traffic through a network, the flow can easily become suboptimal as a consequence of congestion of the most efficient paths. The degree of this suboptimality is quantified by the so-called price of anarchy (POA), but so far there are no general rules for when to expect a large POA in a random network. Here I address this question by introducing a simple model of flow through a network with randomly placed congestible and incongestible links. I show that the POA is maximized precisely when the fraction of congestible links matches the percolation threshold of the lattice. Both the POA and the total cost demonstrate critical scaling near the percolation threshold.
Vulnerability of networks: Fractional percolation on random graphs
NASA Astrophysics Data System (ADS)
Shang, Yilun
2014-01-01
We present a theoretical framework for understanding nonbinary, nonindependent percolation on networks with general degree distributions. The model incorporates a partially functional (PF) state of nodes so that both intensity and extensity of error are characterized. Two connected nodes in a PF state cannot sustain the load and therefore break their link. We give exact solutions for the percolation threshold, the fraction of giant cluster, and the mean size of small clusters. The robustness-fragility transition point for scale-free networks with a degree distribution pk∝k-α is identified to be α =3. The analysis reveals that scale-free networks are vulnerable to targeted attack at hubs: a more complete picture of their Achilles' heel turns out to be not only the hubs themselves but also the edges linking them together.
The September 11 attack: A percolation of individual passive support
NASA Astrophysics Data System (ADS)
Galam, S.
2002-04-01
A model to terrorism is presented using the theory of percolation. Terrorism power is related to the spontaneous formation of random backbones of people who are sympathetic to terrorism but without being directly involved in it. They just don't oppose in case they could. In the past such friendly-to-terrorism backbones have been always existing but were of finite size and localized to a given geographical area. The September 11 terrorist attack on the US has revealed for the first time the existence of a world wide spread extension. It is argued to have result from a sudden world percolation of otherwise unconnected and dormant world spread backbones of passive supporters. The associated strategic question is then to determine if collecting ground information could have predict and thus avoid such a transition. Our results show the answer is no, voiding the major criticism against intelligence services. To conclude the impact of military action is discussed.
Finite-size effects and percolation properties of Poisson geometries
NASA Astrophysics Data System (ADS)
Larmier, C.; Dumonteil, E.; Malvagi, F.; Mazzolo, A.; Zoia, A.
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d -dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d =3 . We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size.
The price of anarchy is maximized at the percolation threshold
NASA Astrophysics Data System (ADS)
Skinner, Brian
2015-03-01
When many independent users try to route traffic through a network, the flow can easily become suboptimal as a consequence of congestion of the most efficient paths. The degree of this suboptimality is quantified by the so-called ``price of anarchy'' (POA), but so far there are no general rules for when to expect a large POA in a random network. Here I address this question by introducing a simple model of flow through a network with randomly-placed ``congestible'' and ``incongestible'' links. I show that the POA is maximized precisely when the fraction of congestible links matches the percolation threshold of the lattice. Both the POA and the total cost demonstrate critical scaling near the percolation threshold.
Price of anarchy is maximized at the percolation threshold.
Skinner, Brian
2015-05-01
When many independent users try to route traffic through a network, the flow can easily become suboptimal as a consequence of congestion of the most efficient paths. The degree of this suboptimality is quantified by the so-called price of anarchy (POA), but so far there are no general rules for when to expect a large POA in a random network. Here I address this question by introducing a simple model of flow through a network with randomly placed congestible and incongestible links. I show that the POA is maximized precisely when the fraction of congestible links matches the percolation threshold of the lattice. Both the POA and the total cost demonstrate critical scaling near the percolation threshold. PMID:26066138
Price of anarchy is maximized at the percolation threshold
NASA Astrophysics Data System (ADS)
Skinner, Brian
2015-05-01
When many independent users try to route traffic through a network, the flow can easily become suboptimal as a consequence of congestion of the most efficient paths. The degree of this suboptimality is quantified by the so-called price of anarchy (POA), but so far there are no general rules for when to expect a large POA in a random network. Here I address this question by introducing a simple model of flow through a network with randomly placed congestible and incongestible links. I show that the POA is maximized precisely when the fraction of congestible links matches the percolation threshold of the lattice. Both the POA and the total cost demonstrate critical scaling near the percolation threshold.
Finite-size effects and percolation properties of Poisson geometries.
Larmier, C; Dumonteil, E; Malvagi, F; Mazzolo, A; Zoia, A
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d-dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d=3. We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size. PMID:27575099
Quantum walk coherences on a dynamical percolation graph
NASA Astrophysics Data System (ADS)
Elster, Fabian; Barkhofen, Sonja; Nitsche, Thomas; Novotný, Jaroslav; Gábris, Aurél; Jex, Igor; Silberhorn, Christine
2015-08-01
Coherent evolution governs the behaviour of all quantum systems, but in nature it is often subjected to influence of a classical environment. For analysing quantum transport phenomena quantum walks emerge as suitable model systems. In particular, quantum walks on percolation structures constitute an attractive platform for studying open system dynamics of random media. Here, we present an implementation of quantum walks differing from the previous experiments by achieving dynamical control of the underlying graph structure. We demonstrate the evolution of an optical time-multiplexed quantum walk over six double steps, revealing the intricate interplay between the internal and external degrees of freedom. The observation of clear non-Markovian signatures in the coin space testifies the high coherence of the implementation and the extraordinary degree of control of all system parameters. Our work is the proof-of-principle experiment of a quantum walk on a dynamical percolation graph, paving the way towards complex simulation of quantum transport in random media.
Can percolation theory be applied to the stock market?
NASA Astrophysics Data System (ADS)
Stauffer, Dietrich
1998-11-01
The fluctuations of the stock market - the price changes per unit time - seem to deviate from Gaussians for short time steps. Power laws, exponentials, and multifractal descriptions have been offered to explain this short-time behavior. Microscopic models dealing with the decisions of single traders on the market have tried to reproduce this behavior. Possibly the simplest of these models is the herding approach of Cont and Bouchaud. Here a total of Nt traders cluster together randomly as in percolation theory. Each cluster randomly decides by buy or sell an amount proportional to its size, or not to trade. Monte Carlo simulations in two to seven dimensions at the percolation threshold depend on the number N of clusters trading within one time step. For N 1, the changes follow a power law; for 1 N Nt they are bell-shaped with power-law tails; for N Nt they crossover to a Gaussian. The correlations in the absolute value of the change decay slowly with time. Thus percolation not only describes the origin of life or the boiling of your breakfast egg, but also explains why we are not rich.
Percolative theories of strongly disordered ceramic high-temperature superconductors
Phillips, J. C.
2010-01-01
Optimally doped ceramic superconductors (cuprates, pnictides, etc.) exhibit transition temperatures T c much larger than strongly coupled metallic superconductors like Pb (T c = 7.2 K, E g/kT c = 4.5) and exhibit many universal features that appear to contradict the Bardeen, Cooper, and Schrieffer theory of superconductivity based on attractive electron-phonon pairing interactions. These complex materials are strongly disordered and contain several competing nanophases that cannot be described effectively by parameterized Hamiltonian models, yet their phase diagrams also exhibit many universal features in both the normal and superconductive states. Here we review the rapidly growing body of experimental results that suggest that these anomalously universal features are the result of marginal stabilities of the ceramic electronic and lattice structures. These dual marginal stabilities favor both electronic percolation of a dopant network and rigidity percolation of the deformed lattice network. This “double percolation” model has previously explained many features of the normal-state transport properties of these materials and is the only theory that has successfully predicted strict lowest upper bounds for T c in the cuprate and pnictide families. Here it is extended to include Coulomb correlations and percolative band narrowing, as well as an angular energy gap equation, which rationalizes angularly averaged gap/T c ratios, and shows that these are similar to those of conventional strongly coupled superconductors. PMID:20080578
NASA Astrophysics Data System (ADS)
Yu, Li; Zhang, Yi-He; Shang, Jiwu; Ke, Shan-Ming; Tong, Wang-shu; Shen, Bo; Huang, Hai-Tao
2012-09-01
Exfoliated graphite/polyimide composite films were synthesized by in situ polymerization. The electrical and dielectric properties of composite films with different volume fraction of exfoliated graphite were investigated over the frequency range from 103 Hz to 3 × 106 Hz. The dielectric behavior of the composite films was investigated by percolation theory and a microcapacitor model. A low percolation threshold f c ≈ 3.1 vol.% was obtained due to the high aspect ratio of the exfoliated graphite. Both the dielectric constant and alternating-current (AC) conductivity showed an abrupt increase in the vicinity of the percolation threshold. The ultralarge enhancement of the dielectric constant near and beyond the percolation threshold was due to Maxwell-Wagner-Sillars (MWS) interfacial polarization between the exfoliated graphite and polyimide and interface polarization between the composite film and electrode.
Managed aquifer recharge in South India: What to expect from small percolation tanks in hard rock?
NASA Astrophysics Data System (ADS)
Massuel, S.; Perrin, J.; Mascre, C.; Mohamed, W.; Boisson, A.; Ahmed, S.
2014-05-01
Many states in India are currently facing general overuse of their groundwater resources mainly due to growing demand for irrigated agriculture. Groundwater levels are declining despite water harvesting measures to enhance aquifer recharge which are supported on a massive scale by watershed development programmes. New programmes are being implemented to improve artificial percolation (i.e., managed aquifer recharge, MAR) although the impact of former measures on aquifer recharge has not yet been assessed. It is therefore crucial to increase our understanding of MAR to successfully overcome the threat of groundwater scarcity in the near future. This paper scrutinizes the ability of a typical percolation tank to recharge the aquifer using a comprehensive approach combining water accounting, geochemistry and hydrodynamic modelling. Over 2 years of observation, the percolation efficiency (percolated fraction of stored water) of the tank ranged from 57% to 63%, the rest being evaporated. Modelling showed that the percolated water was mostly (80%) pumped straight back by the neighbouring boreholes, limiting the area of MAR influence but increasing percolation efficiency.
Code of Federal Regulations, 2011 CFR
2011-07-01
... subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. 414.100... Not Use End-of-Pipe Biological Treatment § 414.100 Applicability; description of the subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. The provisions of...
Code of Federal Regulations, 2011 CFR
2011-07-01
... subcategory of direct discharge point sources that use end-of-pipe biological treatment. 414.90 Section 414.90... Biological Treatment § 414.90 Applicability; description of the subcategory of direct discharge point sources that use end-of-pipe biological treatment. The provisions of this subpart are applicable to the...
Code of Federal Regulations, 2014 CFR
2014-07-01
... subcategory of direct discharge point sources that use end-of-pipe biological treatment. 414.90 Section 414.90... Biological Treatment § 414.90 Applicability; description of the subcategory of direct discharge point sources that use end-of-pipe biological treatment. The provisions of this subpart are applicable to the...
Code of Federal Regulations, 2013 CFR
2013-07-01
... subcategory of direct discharge point sources that use end-of-pipe biological treatment. 414.90 Section 414.90... Biological Treatment § 414.90 Applicability; description of the subcategory of direct discharge point sources that use end-of-pipe biological treatment. The provisions of this subpart are applicable to the...
Code of Federal Regulations, 2012 CFR
2012-07-01
... subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. 414.100... Not Use End-of-Pipe Biological Treatment § 414.100 Applicability; description of the subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. The provisions of...
Code of Federal Regulations, 2013 CFR
2013-07-01
... subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. 414.100... Not Use End-of-Pipe Biological Treatment § 414.100 Applicability; description of the subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. The provisions of...
Code of Federal Regulations, 2012 CFR
2012-07-01
... subcategory of direct discharge point sources that use end-of-pipe biological treatment. 414.90 Section 414.90... Biological Treatment § 414.90 Applicability; description of the subcategory of direct discharge point sources that use end-of-pipe biological treatment. The provisions of this subpart are applicable to the...
Code of Federal Regulations, 2010 CFR
2010-07-01
... subcategory of direct discharge point sources that use end-of-pipe biological treatment. 414.90 Section 414.90... Biological Treatment § 414.90 Applicability; description of the subcategory of direct discharge point sources that use end-of-pipe biological treatment. The provisions of this subpart are applicable to the...
Code of Federal Regulations, 2010 CFR
2010-07-01
... subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. 414.100... Not Use End-of-Pipe Biological Treatment § 414.100 Applicability; description of the subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. The provisions of...
Code of Federal Regulations, 2014 CFR
2014-07-01
... subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. 414.100... Not Use End-of-Pipe Biological Treatment § 414.100 Applicability; description of the subcategory of direct discharge point sources that do not use end-of-pipe biological treatment. The provisions of...
Percolation on hypergraphs with four-edges
NASA Astrophysics Data System (ADS)
Khatib Damavandi, Ojan; Ziff, Robert M.
2015-10-01
We study percolation on self-dual hypergraphs that contain hyperedges with four bounding vertices, or ‘four-edges’, using three different generators, each containing bonds or sites with three distinct probabilities p, r, and t connecting the four vertices. We find explicit values of these probabilities that satisfy the self-duality conditions discussed by Bollobás and Riordan. This demonstrates that explicit solutions of the self-duality conditions can be found using generators containing bonds and sites with independent probabilities. These solutions also provide new examples of lattices where exact percolation critical points are known. One of the generators exhibits three distinct criticality solutions (p, r, t). We carry out Monte-Carlo simulations of two of the generators on two different hypergraphs to confirm the critical values. For the case of the hypergraph and uniform generator studied by Wierman et al, we also determine the threshold p = 0.441 374 ± 0.000 001, which falls within the tight bounds that they derived. Furthermore, we consider a generator in which all or none of the vertices can connect, and find a soluble inhomogeneous percolation system that interpolates between site percolation on the union-jack lattice and bond percolation on the square lattice.
Continuum percolation of congruent overlapping spherocylinders
NASA Astrophysics Data System (ADS)
Xu, Wenxiang; Su, Xianglong; Jiao, Yang
2016-09-01
Continuum percolation of randomly orientated congruent overlapping spherocylinders (composed of cylinder of height H with semispheres of diameter D at the ends) with aspect ratio α =H /D in [0 ,∞ ) is studied. The percolation threshold ϕc, percolation transition width Δ, and correlation-length critical exponent ν for spherocylinders with α in [0, 200] are determined with a high degree of accuracy via extensive finite-size scaling analysis. A generalized excluded-volume approximation for percolation threshold with an exponent explicitly depending on both aspect ratio and excluded volume for arbitrary α values in [0 ,∞ ) is proposed and shown to yield accurate predictions of ϕc for an extremely wide range of α in [0, 2000] based on available numerical and experimental data. We find ϕc is a universal monotonic decreasing function of α and is independent of the effective particle size. Our study has implications in percolation theory for nonspherical particles and composite material design.
NuSTAR Hard X-Ray Survey of the Galactic Center Region. II. X-Ray Point Sources
NASA Astrophysics Data System (ADS)
Hong, JaeSub; Mori, Kaya; Hailey, Charles J.; Nynka, Melania; Zhang, Shuo; Gotthelf, Eric; Fornasini, Francesca M.; Krivonos, Roman; Bauer, Franz; Perez, Kerstin; Tomsick, John A.; Bodaghee, Arash; Chiu, Jeng-Lun; Clavel, Maïca; Stern, Daniel; Grindlay, Jonathan E.; Alexander, David M.; Aramaki, Tsuguo; Baganoff, Frederick K.; Barret, Didier; Barrière, Nicolas; Boggs, Steven E.; Canipe, Alicia M.; Christensen, Finn E.; Craig, William W.; Desai, Meera A.; Forster, Karl; Giommi, Paolo; Grefenstette, Brian W.; Harrison, Fiona A.; Hong, Dooran; Hornstrup, Allan; Kitaguchi, Takao; Koglin, Jason E.; Madsen, Kristen K.; Mao, Peter H.; Miyasaka, Hiromasa; Perri, Matteo; Pivovaroff, Michael J.; Puccetti, Simonetta; Rana, Vikram; Westergaard, Niels J.; Zhang, William W.; Zoglauer, Andreas
2016-07-01
We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3–79 keV) X-ray point sources in a 0.6 deg{}2 region around Sgr A* with a total exposure of 1.7 Ms, and 7 sources in the Sgr B2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ˜4× and ˜8 × 10{}32 erg s{}-1 at the GC (8 kpc) in the 3–10 and 10–40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the Sgr A diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%–60%). Both spectral analysis and logN–logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT > 20 keV on average for a single temperature thermal plasma model or an average photon index of Γ = 1.5–2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.
Habasaki, Junko; Ngai, K. L.
2015-04-28
The typical ionic liquid, 1-ethyl-3-methyl imidazolium nitrate (EMIM-NO{sub 3}), was examined by molecular dynamics simulations of an all-atomistic model to show the characteristics of networks of cages and/or bonds in the course of vitrification of this fragile glass-former. The system shows changes of dynamics at two characteristic temperatures, T{sub B} (or T{sub c}) and the glass transition temperature T{sub g}, found in other fragile glass forming liquids [K. L. Ngai and J. Habasaki, J. Chem. Phys. 141, 114502 (2014)]. On decreasing temperature, the number of neighboring cation-anion pairs, N{sub B}, within the first minimum of the pair correlation function, g(r){sub min}, increases. On crossing T{sub B} (>T{sub g}), the system volume and diffusion coefficient both show changes in temperature dependence, and as usual at T{sub g}. The glass transition temperature, T{sub g}, is characterized by the saturation of the total number of “bonds,” N{sub B} and the corresponding decrease in degree of freedom, F = [(3N − 6) − N{sub B}], of the system consisting of N particles. Similar behavior holds for the other ion-ion pairs. Therefore, as an alternative, the dynamics of glass transition can be interpreted conceptually by rigidity percolation. Before saturation occurring at T{sub g}, the number of bonds shows a remarkable change at around T{sub B}. This temperature is associated with the disappearance of the loosely packed coordination polyhedra of anions around cation (or vice versa), related to the loss of geometrical freedom of the polyhedra, f{sub g}, of each coordination polyhedron, which can be defined by f{sub g} = [(3N{sub V} − 6) − N{sub b}]. Here, 3N{sub v} is the degree of freedom of N{sub V} vertices of the polyhedron, and N{sub b} is number of fictive bonds. The packing of polyhedra is characterized by the soft percolation of cages, which allows further changes with decreasing temperature. The power spectrum of displacement of the central ion
Habasaki, Junko; Ngai, K L
2015-04-28
The typical ionic liquid, 1-ethyl-3-methyl imidazolium nitrate (EMIM-NO3), was examined by molecular dynamics simulations of an all-atomistic model to show the characteristics of networks of cages and/or bonds in the course of vitrification of this fragile glass-former. The system shows changes of dynamics at two characteristic temperatures, TB (or Tc) and the glass transition temperature Tg, found in other fragile glass forming liquids [K. L. Ngai and J. Habasaki, J. Chem. Phys. 141, 114502 (2014)]. On decreasing temperature, the number of neighboring cation-anion pairs, NB, within the first minimum of the pair correlation function, g(r)min, increases. On crossing TB (>Tg), the system volume and diffusion coefficient both show changes in temperature dependence, and as usual at Tg. The glass transition temperature, Tg, is characterized by the saturation of the total number of "bonds," NB and the corresponding decrease in degree of freedom, F = [(3N - 6) - NB], of the system consisting of N particles. Similar behavior holds for the other ion-ion pairs. Therefore, as an alternative, the dynamics of glass transition can be interpreted conceptually by rigidity percolation. Before saturation occurring at Tg, the number of bonds shows a remarkable change at around TB. This temperature is associated with the disappearance of the loosely packed coordination polyhedra of anions around cation (or vice versa), related to the loss of geometrical freedom of the polyhedra, fg, of each coordination polyhedron, which can be defined by fg = [(3NV - 6) - Nb]. Here, 3Nv is the degree of freedom of NV vertices of the polyhedron, and Nb is number of fictive bonds. The packing of polyhedra is characterized by the soft percolation of cages, which allows further changes with decreasing temperature. The power spectrum of displacement of the central ion in the cage is found to be correlated with the fluctuation of Nb of cation-cation (or anion-anion) pairs in the polyhedron, although the
Point source pollution and variability of nitrate concentrations in water from shallow aquifers
NASA Astrophysics Data System (ADS)
Nemčić-Jurec, Jasna; Jazbec, Anamarija
2016-01-01
Agriculture is one of the several major sources of nitrate pollution, and therefore the EU Nitrate Directive, designed to decrease pollution, has been implemented. Point sources like septic systems and broken sewage systems also contribute to water pollution. Pollution of groundwater by nitrate from 19 shallow wells was studied in a typical agricultural region, middle Podravina, in northwest Croatia. The concentration of nitrate ranged from <0.1 to 367 mg/l in water from wells, and 29.8 % of 253 total samples were above maximum acceptable value of 50 mg/l (MAV). Among regions R1-R6, there was no statistically significant difference in nitrate concentrations (F = 1.98; p = 0.15) during the years 2002-2007. Average concentrations of nitrate in all 19 wells for all the analyzed years were between recommended limit value of 25 mg/l (RLV) and MAV except in 2002 (concentration was under RLV). The results of the repeated measures ANOVA showed statistically significant differences between the wells at the point source distance (proximity) of <10 m, compared to the wells at the point source distance of >20 m (F = 10.6; p < 0.001). Average annual concentrations of nitrate during the years studied are not statistically different, but interaction between proximity and years is statistically significant (F = 2.07; p = 0.04). Results of k-means clustering confirmed division into four clusters according to the pollution. Principal component analysis showed that there is only one significant factor, proximity, which explains 91.6 % of the total variability of nitrate. Differences in water quality were found as a result of different environmental factors. These results will contribute to the implementation of the Nitrate Directive in Croatia and the EU.
Percolation of heteronuclear dimers irreversibly deposited on square lattices
NASA Astrophysics Data System (ADS)
Gimenez, M. C.; Ramirez-Pastor, A. J.
2016-09-01
The percolation problem of irreversibly deposited heteronuclear dimers on square lattices is studied. A dimer is composed of two segments, and it occupies two adjacent adsorption sites. Each segment can be either a conductive segment (segment type A ) or a nonconductive segment (segment type B ). Three types of dimers are considered: A A , B B , and A B . The connectivity analysis is carried out by accounting only for the conductive segments (segments type A ). The model offers a simplified representation of the problem of percolation of defective (nonideal) particles, where the presence of defects in the system is simulated by introducing a mixture of conductive and nonconductive segments. Different cases were investigated, according to the sequence of deposition of the particles, the types of dimers involved in the process, and the degree of alignment of the deposited objects. By means of numerical simulations and finite-size scaling analysis, the complete phase diagram separating a percolating from a nonpercolating region was determined for each case. Finally, the consistency of our results was examined by comparing with previous data in the literature for linear k -mers (particles occupying k adjacent sites) with defects.
Covering by random intervals and one-dimensional continuum percolation
Domb, C. )
1989-04-01
A brief historical introduction is given to the problem of covering a line by random overlapping intervals. The problem for equal intervals was first solved by Whitworth in the 1890s. A brief resume is given of his solution. The advantages of the present author's approach, which uses a Poisson process, are outlined, and a solution is derived by Laplace transforms. The asymptotic behavior as the line becomes long is calculated and is related to the one-dimensional continuum percolation problem. It is shown that as long as the mean interval size is finite, the probability of complete coverage decays exponentially, so that the critical percolation probability p{sub c} = 1. However, as soon as the mean interval size becomes infinite, the critical percolation probability p{sub c} switches to 0. This is in accord with previous results for a lattice model by Chinese workers, but differs from those of Schulman. A possible reason for the discrepancy is a difference in boundary conditions.
Transport pathways within percolating pore space networks of granular materials
NASA Astrophysics Data System (ADS)
Vo, Kevin; Walker, David M.; Tordesillas, Antoinette
2013-06-01
Granular media can be regarded as a mixture of two components: grains and the material filling the voids or pores between the grains. Pore properties give rise to a range of applications such as modelling ground water flow, carbon capture and sequestration. The grains within a dense granular material respond to deformation (e.g., shearing or compression) by rearranging to create local zones of compression and zones of dilatation (i.e., regions of high pore space). Descriptions of the deformation are typically focused on analysis of the solid skeleton via topology of physical contact networks of grains but an alternative perspective is to consider network representations of the evolving anisotropic pore space. We demonstrate how to construct pore space networks that express the local size of voids about a grain through network edge weights. We investigate sectors of the loading history when a percolating giant component of the pore space network exists. At these states the grains are in a configuration more prone to the efficient transport of material (e.g., fluid flow, mineral/gas deposits). These pathways can be found through examination of the weighted shortest paths percolating the boundaries of the material. In particular, network weights biased towards large void space results in efficient percolating pathways traversing the shear band in the direction of principal stress within a 2D granular assembly subject to high strains.
The Fermi paradox: An approach based on percolation theory
NASA Technical Reports Server (NTRS)
Landis, Geoffrey A.
1993-01-01
If even a very small fraction of the hundred billion stars in the galaxy are home to technological civilizations which colonize over interstellar distances, the entire galaxy could be completely colonized in a few million years. The absence of such extraterrestrial civilizations visiting Earth is the Fermi paradox. A model for interstellar colonization is proposed using the assumption that there is a maximum distance over which direct interstellar colonization is feasible. Due to the time lag involved in interstellar communications, it is assumed that an interstellar colony will rapidly develop a culture independent of the civilization that originally settled it. Any given colony will have a probability P of developing a colonizing civilization, and a probability (1-P) that it will develop a non-colonizing civilization. These assumptions lead to the colonization of the galaxy occuring as a percolation problem. In a percolation problem, there will be a critical value of percolation probability, P(sub c). For P less than P(sub c), colonization will always terminate after a finite number of colonies. Growth will occur in 'clusters', with the outside of each cluster consisting of non-colonizing civilizations. For P greater than P(sub c), small uncolonized voids will exist, bounded by non-colonizing civilizations. For P approximately = to P(sub c), arbitrarily large filled regions exist, and also arbitrarily large empty regions.
The Unicellular State as a Point Source in a Quantum Biological System
Torday, John S.; Miller, William B.
2016-01-01
A point source is the central and most important point or place for any group of cohering phenomena. Evolutionary development presumes that biological processes are sequentially linked, but neither directed from, nor centralized within, any specific biologic structure or stage. However, such an epigenomic entity exists and its transforming effects can be understood through the obligatory recapitulation of all eukaryotic lifeforms through a zygotic unicellular phase. This requisite biological conjunction can now be properly assessed as the focal point of reconciliation between biology and quantum phenomena, illustrated by deconvoluting complex physiologic traits back to their unicellular origins. PMID:27240413
An analysis of the facsimile-camera response to radiant point sources. [visual and red stars
NASA Technical Reports Server (NTRS)
Huck, F. O.; Katzberg, S. J.; Jobson, D. J.; Fales, C. L., Jr.
1973-01-01
In addition to imaging the surrounding terrain, planetary lander cameras may also be used to survey the stars to aid in locating the lander site. The response of the facsimile camera, which was selected for the Viking lander missions to Mars, to a radiant point source is formulated and shown to result in a statistical rather than deterministic signal. The signal statistics are derived and magnitudes are evaluated for the brighter visual and red stars. The probability of detecting the resultant statistical signals in photosensor and preamplifier noise and the associated probability of false alarms are also determined.
Point source moving above a finite impedance reflecting plane - Experiment and theory
NASA Technical Reports Server (NTRS)
Norum, T. D.; Liu, C. H.
1978-01-01
A widely used experimental version of the acoustic monopole consists of an acoustic driver of restricted opening forced by a discrete frequency oscillator. To investigate the effects of forward motion on this source, it was mounted above an automobile and driven over an asphalt surface at constant speed past a microphone array. The shapes of the received signal were compared to results computed from an analysis of a fluctuating-mass-type point source moving above a finite impedance reflecting plane. Good agreement was found between experiment and theory when a complex normal impedance representative of a fairly hard acoustic surface was used in the analysis.
A point-source norovirus outbreak caused by exposure to fomites.
Repp, Kimberly K; Keene, William E
2012-06-01
We investigated a norovirus outbreak (genotype GII.2) affecting 9 members of a soccer team. Illness was associated with touching a reusable grocery bag or consuming its packaged food contents (risk difference, 0.636; P < .01). By polymerase chain reaction, GII norovirus was recovered from the bag, which had been stored in a bathroom used before the outbreak by a person with norovirus-like illness. Airborne contamination of fomites can lead to subsequent point-source outbreaks. When feasible, we recommend dedicated bathrooms for sick persons and informing cleaning staff (professional or otherwise) about the need for adequate environmental sanitation of surfaces and fomites to prevent spread.
An international point source outbreak of typhoid fever: a European collaborative investigation*
Stanwell-Smith, R. E.; Ward, L. R.
1986-01-01
A point source outbreak of Salmonella typhi, degraded Vi-strain 22, affecting 32 British visitors to Kos, Greece, in 1983 was attributed by a case—control study to the consumption of a salad at one hotel. This represents the first major outbreak of typhoid fever in which a salad has been identified as the vehicle. The source of the infection was probably a carrier in the hotel staff. The investigation demonstrates the importance of national surveillance, international cooperation, and epidemiological methods in the investigation and control of major outbreaks of infection. PMID:3488842
Electromagnetic field generated by a modulated moving point source in a planarly layered waveguide
NASA Astrophysics Data System (ADS)
Barrera-Figueroa, V.; Rabinovich, V. S.
2016-04-01
In the present work, we consider a modulated point source in an arbitrary motion in an isotropic planarly layered waveguide. The radiation field generated by this source is represented in the form of double oscillatory integrals in terms of the time and the frequency, depending on the large parameter λ. By means of the stationary phase method, we analyze, in the waveguide, the Doppler effect, the retarded time, and the Vavilov-Cherenkov radiation. Numerically, the problem of the moving source is approached by the method of spectral parameter power series.
Jericho, M H; Kreuzer, H J; Kanka, M; Riesenberg, R
2012-04-01
Point-source digital in-line holographic microscopy with numerical reconstruction is ideally suited for quantitative phase measurements to determine optical path lengths and to extract changes in refractive index within accuracy close to 0.001 on the submicrometer length scale. This is demonstrated with simulated holograms and with detailed measurements on a number of different micrometer-sized samples such as suspended drops, optical fibers, as well as organisms of biological interest such as E. coli bacteria, HeLa cells, and fibroblast cells.
A search for gamma-ray point sources with the Carpet shower array
NASA Technical Reports Server (NTRS)
Alexeenko, V. V.; Chudakov, A. E.; Khaerdinov, N. S.; Lidvansky, A. S.; Navarra, G.; Ozrokov, S. S.; Sklyarov, V. V.; Tizengauzen, V. A.
1985-01-01
A search for super-high energy gamma-ray point sources has been carried out. The well known source Cyg X-3 was observed first and preliminary results of data analysis are presented. There is not positive excess of showers from the source region, but phase analysis discovers a small pulse at phase 0.6 which corresponds to the integral flux (6 + or - 3) X 10 to the minus 14th power cm-2 sec-1 at E sub gamma 3x10 to the 14th power eV.
Search for UHE point-source emission over various time scales
Not Available
1993-01-01
A method has been developed to search for pulsed and/or unpulsed ultra high energy (UHE) emission from point sources over a range of time scales. This method has been applied to data accumulated with the CYGNUS extensive air-shower array for events associated with the directions of Cyg X-3, Her X-1, the Crab nebula, and a collection of 48 secondary source candidates. An examination of time scales ranging from minutes to years has yielded results consistent with background fluctuations.
Search for UHE point-source emission over various time scales
The CYGNUS Collaboration
1993-05-01
A method has been developed to search for pulsed and/or unpulsed ultra high energy (UHE) emission from point sources over a range of time scales. This method has been applied to data accumulated with the CYGNUS extensive air-shower array for events associated with the directions of Cyg X-3, Her X-1, the Crab nebula, and a collection of 48 secondary source candidates. An examination of time scales ranging from minutes to years has yielded results consistent with background fluctuations.
Preliminary data summary for the pulp, paper and paperboard point source category
Not Available
1989-08-01
The Preliminary Data Summary for the Pulp, Paper and Paperboard Point Source category is a collection of four documents: (1) Overview of the United States Pulp, Paper and Paperboard Industry and Production Processes (October 1987); (2) U.S. EPA/Paper Industry Cooperative Dioxin Screening Study (March 1988); (3) Statement of Martha G. Prothro, Director, Office of Water Regulations and Standards, before the Subcommittee on Water Resources of the Committee on Public Works and Transportation, U.S. House of Representatives (July 13, 1988); (4) U.S. EPA/Paper Industry Cooperative Dioxin Study, Analytical Results (June 16, 1989).
[Quantification of non-point sources phosphorus pollution in key protection area of Taihu Lake].
Guo, Hongyan; Wang, Xiaorong; Zhu, Jianguo
2004-01-01
The distribution of various kinds of non-point sources phosphorus pollution in Xueyan Town, Wujin city, Taihu area was researched through field experiments and local investigation during rice growth season. The results showed that of all kinds of phosphorus pollution, about 56.2% (1313 kg P) was from farmland, 22.2% (518 kg P) was from town residents, 18.9% (442 kg P) was from village residents, and 2.7% (62 kg P) was from livestock. Besides the strict control of the phosphorus pollution from farmland, attention should also be paid on the control of domestic water pollution from towns and villages. PMID:15139206
Spitzer mid-infrared point sources in the fields of nearby galaxies
NASA Astrophysics Data System (ADS)
Williams, S. J.; Bonanos, A. Z.
2016-03-01
Aims: To complement the study of transient phenomena and to assist subsequent observations in the mid-infrared, we extract point source photometry from archival mosaics of nearby galaxies with high star formation rates within 4 Mpc. Methods: Point spread function photometry was performed on sources detected in both Spitzer IRAC 3.6 μm and 4.5 μm bands at greater than 3σ above background. These data were then supplemented by aperture photometry in the IRAC 5.8 μm and 8.0 μm bands conducted at the positions of the shorter wavelength sources. For sources with no detected object in the longer wavelengths, we estimated magnitude limits based on the local sky background. Results: We present Spitzer IRAC mid-infrared point source catalogs for mosaics covering the fields of the nearby (≲4 Mpc) galaxies NGC 55, NGC 253, NGC 2366, NGC 4214, and NGC 5253. We detect a total of 20159 sources in these five fields. The individual galaxy point source breakdown is the following: NGC 55, 8746 sources; NGC 253, 9001 sources; NGC 2366, 505 sources; NGC 4214, 1185 sources; NGC 5253, 722 sources. The completeness limits of the full catalog vary with bandpass and were found to be m3.6 = 18.0, m4.5 = 17.5, m5.8 = 17.0, and m8.0 = 16.5 mag. For all galaxies, this corresponds to detection of point sources brighter than M3.6 = -10. These catalogs can be used as a reference for stellar population investigations, individual stellar object studies, and in planning future mid-infrared observations with the James Webb Space Telescope. Based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.Full Tables 2-6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A121
NASA Astrophysics Data System (ADS)
Chen, Daifen; Zhang, Qiang; Lu, Liu; Periasamy, Vijay; Tade, Moses O.; Shao, Zongping
2016-01-01
H+ based solid oxide fuel cell (SOFC) composite cathodes are generally agreed to be of quite different relationships among the microstructure parameters, electrode properties and detailed working processes from the conventional O2--SOFC composite cathodes. In this paper, the percolation theory is significantly generalized and developed to suit most of the typical H+-SOFC composite cathodes with e-/H+, e-/O2- or e-/H+/O2- mixed conducting characteristics; not just limited to the BCZY, SDC and LSCF materials. It provides an easy way to investigate the effect of microstructure parameters on the H+-SOFC electrode characteristics in quantity. The studied electrode properties include: i) the potential coexisting sites of O2, e-, and O2- transport paths for the oxygen reduction; ii) the potential coexisting sites of O2-, H+ and H2O transport paths for the vapor formation; iii) the effective e-, O2-, and H+ conducting and gas diffusing capabilities of the composite cathodes, and so on. It will be helpful for the H+-SOFC composite cathode manufacture to achieve the expected properties. Furthermore, it is also an important step for the developing of the multiphysics-model in manuscript part B to study the effect of the microstructure parameters on the H+-SOFC working details.
Fluid leakage near the percolation threshold
NASA Astrophysics Data System (ADS)
Dapp, Wolf B.; Müser, Martin H.
2016-02-01
Percolation is a concept widely used in many fields of research and refers to the propagation of substances through porous media (e.g., coffee filtering), or the behaviour of complex networks (e.g., spreading of diseases). Percolation theory asserts that most percolative processes are universal, that is, the emergent powerlaws only depend on the general, statistical features of the macroscopic system, but not on specific details of the random realisation. In contrast, our computer simulations of the leakage through a seal—applying common assumptions of elasticity, contact mechanics, and fluid dynamics—show that the critical behaviour (how the flow ceases near the sealing point) solely depends on the microscopic details of the last constriction. It appears fundamentally impossible to accurately predict from statistical properties of the surfaces alone how strongly we have to tighten a water tap to make it stop dripping and also how it starts dripping once we loosen it again.
Quantum percolation by Arnoldi-Saad diagonalization
NASA Astrophysics Data System (ADS)
Nakanishi, Hisao
1998-03-01
A quantum percolation problem is studied in two and three dimensions numerically by approximately diagonalizing the corresponding Hamiltonian using the Arnoldi-Saad method. In this problem, the randomness is implemented as random site percolation with probability p for site occupation but is reflected as a random hopping term v_ij in the tight-binding Hamiltonian: H = sumi ɛi |i>v_ij|i>
Fluid leakage near the percolation threshold.
Dapp, Wolf B; Müser, Martin H
2016-01-01
Percolation is a concept widely used in many fields of research and refers to the propagation of substances through porous media (e.g., coffee filtering), or the behaviour of complex networks (e.g., spreading of diseases). Percolation theory asserts that most percolative processes are universal, that is, the emergent powerlaws only depend on the general, statistical features of the macroscopic system, but not on specific details of the random realisation. In contrast, our computer simulations of the leakage through a seal--applying common assumptions of elasticity, contact mechanics, and fluid dynamics--show that the critical behaviour (how the flow ceases near the sealing point) solely depends on the microscopic details of the last constriction. It appears fundamentally impossible to accurately predict from statistical properties of the surfaces alone how strongly we have to tighten a water tap to make it stop dripping and also how it starts dripping once we loosen it again. PMID:26839261
Fluid leakage near the percolation threshold
Dapp, Wolf B.; Müser, Martin H.
2016-01-01
Percolation is a concept widely used in many fields of research and refers to the propagation of substances through porous media (e.g., coffee filtering), or the behaviour of complex networks (e.g., spreading of diseases). Percolation theory asserts that most percolative processes are universal, that is, the emergent powerlaws only depend on the general, statistical features of the macroscopic system, but not on specific details of the random realisation. In contrast, our computer simulations of the leakage through a seal—applying common assumptions of elasticity, contact mechanics, and fluid dynamics—show that the critical behaviour (how the flow ceases near the sealing point) solely depends on the microscopic details of the last constriction. It appears fundamentally impossible to accurately predict from statistical properties of the surfaces alone how strongly we have to tighten a water tap to make it stop dripping and also how it starts dripping once we loosen it again. PMID:26839261
Spitzer infrared spectrograph point source classification in the Small Magellanic Cloud
NASA Astrophysics Data System (ADS)
Ruffle, Paul M. E.; Kemper, F.; Jones, O. C.; Sloan, G. C.; Kraemer, K. E.; Woods, Paul M.; Boyer, M. L.; Srinivasan, S.; Antoniou, V.; Lagadec, E.; Matsuura, M.; McDonald, I.; Oliveira, J. M.; Sargent, B. A.; Sewiło, M.; Szczerba, R.; van Loon, J. Th.; Volk, K.; Zijlstra, A. A.
2015-08-01
The Magellanic Clouds are uniquely placed to study the stellar contribution to dust emission. Individual stars can be resolved in these systems even in the mid-infrared, and they are close enough to allow detection of infrared excess caused by dust. We have searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS) staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209 Infrared Array Camera (IRAC) point sources within the footprint of the Surveying the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer Legacy programme were targeted, within a total of 311 staring-mode observations. We classify these point sources using a decision tree method of object classification, based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information. We find 58 asymptotic giant branch (AGB) stars, 51 young stellar objects, 4 post-AGB objects, 22 red supergiants, 27 stars (of which 23 are dusty OB stars), 24 planetary nebulae (PNe), 10 Wolf-Rayet stars, 3 H II regions, 3 R Coronae Borealis stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB stars. We use these classifications to evaluate the success of photometric classification methods reported in the literature.
Eckley, Chris S; Parsons, Matthew T; Mintz, Rachel; Lapalme, Monique; Mazur, Maxwell; Tordon, Robert; Elleman, Robert; Graydon, Jennifer A; Blanchard, Pierrette; St Louis, Vincent
2013-09-17
The Flin Flon, Manitoba copper smelter was Canada's largest point source of mercury emissions until its closure in 2010 after ~80 years of operation. The objective of this study was to understand the variables controlling the local ground-level air mercury concentrations before and after this major point source reduction. Total gaseous mercury (TGM) in air, mercury in precipitation, and other ancillary meteorological and air quality parameters were measured pre- and postsmelter closure, and mercury speciation measurements in air were collected postclosure. The results showed that TGM was significantly elevated during the time period when the smelter operated (4.1 ± 3.7 ng m(-3)), decreased only 20% during the year following its closure, and remained ~2-fold above background levels. Similar trends were observed for mercury concentrations in precipitation. Several lines of evidence indicated that while smelter stack emissions would occasionally mix down to the surface resulting in large spikes in TGM concentrations (up to 61 ng m(-3)), the largest contributor to elevated TGM concentrations before and after smelter closure was from surface-air fluxes from mercury-enriched soils and/or tailings. These findings highlight the ability of legacy mercury, deposited to local landscapes over decades from industrial activities, to significantly affect local air concentrations via emissions/re-emissions. PMID:23978035
Natural Wetlands Mediate Non-point Source Water Pollution From Irrigated Pastures
NASA Astrophysics Data System (ADS)
Knox, K.; Dahlgren, R. A.; Tate, K. W.
2005-12-01
Non-point source discharge from grazed pastures may be high in nutrients, sediment, and pathogens, three major contributors to water quality impairment in California. Intercepting pollution at its source and managing water quality within the landscape are essential to maintaining healthy downstream waters. We investigated the efficacy of flow-through wetlands interspersed throughout the agricultural landscape to reduce non-point source pollution of tailwater from cattle-grazed, irrigated pastures in the Sierra Nevada Foothills of California. Wetlands are known to positively impact water quality through ecological processes such as filtration, sedimentation, microbial transformations and plant uptake of nutrients. Influent and effluent water of small (0.25 ha), natural wetlands located downstream from flood irrigated pastures was analyzed for Escherichia coli, NO3-N, total N, total suspended solids (TSS), total P, and dissolved organic carbon (DOC) throughout two summer irrigation seasons (June to October). We compared reductions of sediment, nutrients and E. coli provided by a healthy, non-degraded wetland with reductions from flow through a channelized, degraded wetland. Large reductions in E. coli (>75%) and TSS (>50%) were observed in water exiting the healthy wetland while nutrient and DOC (~ 20%) concentrations were less affected by flow through the wetland. The channelized wetland provided smaller reductions in all constituents than did the non-degraded wetland. Results from this study demonstrate that small flow-through wetlands can improve water quality through the attenuation of E. coli and suspended sediments, and to a lesser degree DOC and nutrients.
The removal of nutrients from non-point source wastewater by a hybrid bioreactor.
Wu, Yonghong; Hu, Zhengyi; Yang, Linzhang; Graham, Bruce; Kerr, Philip G
2011-02-01
The aim of this project was to establish an economical and environmentally benign biotechnology for removing nutrients from non-point source wastewater. The proposal involves a hybrid bioreactor comprised of sequential anaerobic, anoxic and aerobic (A(2)/O) processes and an eco-ditch being constructed and applied in a suburban area, Kunming, south-western China, where wastewater was discharged from an industrial park and suburban communities. The results show that the hybrid bioreactor fosters heterotrophic and autotrophic microorganisms. When the hydraulic load is 200 m(3) per day with the running mode in 12h cycles, the removal efficiencies of the nutrients were 81% for TP, 74% for TDP, 82% for TN, 79% for NO(3)-N and 86% for NH(4)-N. The improved bacterial community structure and bacterial habitats further implied enhanced water quality and indicates that the easily-deployed, affordable and environmentally-friendly hybrid bioreactor is a promising bio-measure for removing high loadings of nutrients from non-point source wastewater. PMID:21093255
Percolation threshold on planar Euclidean Gabriel graphs
NASA Astrophysics Data System (ADS)
Norrenbrock, Christoph
2016-04-01
In the present article, numerical simulations have been performed to find the bond and site percolation thresholds on two-dimensional Gabriel graphs (GG) for Poisson point processes. GGs belong to the family of "proximity graphs" and are discussed, e.g., in context of the construction of backbones for wireless ad-hoc networks. Finite-size scaling analyses have been performed to find the critical points and critical exponents ν, β and γ. The critical exponents obtained this way verify that the associated universality class is that of standard 2D percolation.
Wu, Lei; Long, Tian-Yu; Li, Chong-Ming
2010-01-01
Xiao-jiang, with a basin area of almost 5,276 km(2) and a length of 182.4 km, is located in the center of the Three Gorges Reservoir Area, and is the largest tributary of the central section in Three Gorges Reservoir Area, farmland accounts for a large proportion of Xiao-jiang watershed, and the hilly cropland of purple soil is much of the farmland of the watershed. After the second phase of water storage in the Three Gorges Reservoir, the majority of sub-rivers in the reservoir area experienced eutrophication phenomenon frequently, and non-point source (NPS) pollution has become an important source of pollution in Xiao-jiang Watershed. Because dissolved nitrogen and phosphorus non-point source pollution are related to surface runoff and interflow, using climatic, topographic and land cover data from the internet and research institutes, the Semi-Distributed Land-use Runoff Process (SLURP) hydrological model was introduced to simulate the complete hydrological cycle of the Xiao-jiang Watershed. Based on the SLURP distributed hydrological model, non-point source pollution annual output load models of land use and rural residents were respectively established. Therefore, using GIS technology, considering the losses of dissolved nitrogen and phosphorus in the course of transport, a dissolved non-point source pollution load dynamic model was established by the organic coupling of the SLURP hydrological model and land-use output model. Through the above dynamic model, the annual dissolved non-point source nitrogen and phosphorus pollution output as well as the load in different types were simulated and quantitatively estimated from 2001 to 2008, furthermore, the loads of Xiao-jiang Watershed were calculated and expressed by temporal and spatial distribution in the Three Gorges Reservoir Area. The simulation results show that: the temporal changes of dissolved nitrogen and phosphorus load in the watershed are close to the inter-annual changes of rainfall runoff, and the
Identifying non-point source critical source areas based on multi-factors at a basin scale with SWAT
NASA Astrophysics Data System (ADS)
Liu, Ruimin; Xu, Fei; Zhang, Peipei; Yu, Wenwen; Men, Cong
2016-02-01
The identification of critical source areas (CSAs) is a precondition for non-point source (NPS) pollution control at a basin scale, especially in areas with limited resources. Based on the Soil and Water Assessment Tool (SWAT), nutrient loads coupled with population density and water quality requirements are regarded as multi-factors for CSAs identification in Xiangxi river watershed, the first tributary of the Yangtze River. The results based on the calibrated model found that the subbasins heavily and seriously polluted by nutrient loads were different from the subbasins identified as CSAs, demonstrating integrating socio-economic factors like population density and water quality requirements to identify CSAs is of much necessity. The CSAs occupied 19.7% of the total subbasins, and accounted for 53% total nitrogen loads, 54% total phosphorus loads and 36% of the total population. Considering the model calibration and validation will take a long time as well as data deficiency in some subbasins, the influence of uncalibrated SWAT on CSAs identifications was discussed. The comparative results between CSAs identification with calibrated and uncalibrated SWAT model revealed that model calibration had little effect on nutrients distribution and CSAs locations in the study area. Uncalibrated SWAT model may be applied when the research objective is less related to model calibration. The results will be greatly effective for CSAs identification and NPS pollution control at a basin scale.
Percolation Theory for the Distribution and Abundance of Species
NASA Astrophysics Data System (ADS)
He, Fangliang; Hubbell, Stephen P.
2003-11-01
We develop and test new models that unify the mathematical relationships among the abundance of a species, the spatial dispersion of the species, the number of patches occupied by the species, the edge length of the occupied patches, and the scale on which the distribution of species is mapped. The models predict that species distributions will exhibit percolation critical thresholds, i.e., critical population abundances at which the fragmented patches (as measured by the number of patches and edge length) start to coalesce to form large patches.
NASA Technical Reports Server (NTRS)
Weistrop, D.; Mushotzky, R. F.; Shaffer, D. B.; Reitsema, H. J.; Smith, B. A.
1981-01-01
Visual and far-red surface photometry has been obtained for the X-ray emitting BL Lacertae objects 1218+304 and 1727+50, and the highly variable object 1219+28. The intensity distribution for 1727+50 can be modeled by means of a central point source and a de Vaucouleurs intensity law for an underlying galaxy. The spectral index of the point source of 1727+50 is found to be 0.97, while the indices for 1218+304 and 1219+28 are 0.91 and 1.7, respectively. Comparison of the results presented with X-ray and radio-frequency observations suggests that all emission from 1727+50 and 1218+304 is due to direct synchrotron emission. If this is the case, the relativistic motion effects and continuous particle injection are also implied by the data.
AKARI Infrared Camera Survey of the Large Magellanic Cloud. I. Point-source Catalog
NASA Astrophysics Data System (ADS)
Kato, Daisuke; Ita, Yoshifusa; Onaka, Takashi; Tanabé, Toshihiko; Shimonishi, Takashi; Sakon, Itsuki; Kaneda, Hidehiro; Kawamura, Akiko; Wada, Takehiko; Usui, Fumihiko; Koo, Bon-Chul; Matsuura, Mikako; Takahashi, Hidenori
2012-12-01
We present a near- to mid-infrared point-source catalog of five photometric bands at 3.2, 7, 11, 15, and 24 μm for a 10 deg2 area of the Large Magellanic Cloud (LMC) obtained with the Infrared Camera on board the AKARI satellite. To cover the survey area the observations were carried out at three separate seasons from 2006 May to June, 2006 October to December, and 2007 March to July. The 10σ limiting magnitudes of the present survey are 17.9, 13.8, 12.4, 9.9, and 8.6 mag at 3.2, 7, 11, 15, and 24 μm, respectively. The photometric accuracy is estimated to be about 0.1 mag at 3.2 μm and 0.06-0.07 mag in the other bands. The position accuracy is 0farcs3 at 3.2, 7, and 11 μm and 1farcs0 at 15 and 24 μm. The sensitivities at 3.2, 7, and 24 μm are roughly comparable to those of the Spitzer SAGE LMC point-source catalog, while the AKARI catalog provides the data at 11 and 15 μm, covering the mid-infrared spectral range contiguously. Two types of catalog are provided: a Catalog and an Archive. The Archive contains all the detected sources, while the Catalog only includes the sources that have a counterpart in the Spitzer SAGE point-source catalog. The Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at 3.2, 7, 11, 15, and 24 μm, respectively. Based on the catalog, we discuss the luminosity functions at each band, the color-color diagram, and the color-magnitude diagram using the 3.2, 7, and 11 μm band data. Stars without circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects, and background galaxies are located at distinct regions in the diagrams, suggesting that the present catalog is useful for the classification of objects toward the LMC.
AKARI INFRARED CAMERA SURVEY OF THE LARGE MAGELLANIC CLOUD. I. POINT-SOURCE CATALOG
Kato, Daisuke; Onaka, Takashi; Shimonishi, Takashi; Sakon, Itsuki; Ita, Yoshifusa; Tanabe, Toshihiko; Takahashi, Hidenori; Kaneda, Hidehiro; Kawamura, Akiko; Wada, Takehiko; Usui, Fumihiko; Koo, Bon-Chul; Matsuura, Mikako E-mail: onaka@astron.s.u-tokyo.ac.jp
2012-12-01
We present a near- to mid-infrared point-source catalog of five photometric bands at 3.2, 7, 11, 15, and 24 {mu}m for a 10 deg{sup 2} area of the Large Magellanic Cloud (LMC) obtained with the Infrared Camera on board the AKARI satellite. To cover the survey area the observations were carried out at three separate seasons from 2006 May to June, 2006 October to December, and 2007 March to July. The 10{sigma} limiting magnitudes of the present survey are 17.9, 13.8, 12.4, 9.9, and 8.6 mag at 3.2, 7, 11, 15, and 24 {mu}m, respectively. The photometric accuracy is estimated to be about 0.1 mag at 3.2 {mu}m and 0.06-0.07 mag in the other bands. The position accuracy is 0.''3 at 3.2, 7, and 11 {mu}m and 1.''0 at 15 and 24 {mu}m. The sensitivities at 3.2, 7, and 24 {mu}m are roughly comparable to those of the Spitzer SAGE LMC point-source catalog, while the AKARI catalog provides the data at 11 and 15 {mu}m, covering the mid-infrared spectral range contiguously. Two types of catalog are provided: a Catalog and an Archive. The Archive contains all the detected sources, while the Catalog only includes the sources that have a counterpart in the Spitzer SAGE point-source catalog. The Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at 3.2, 7, 11, 15, and 24 {mu}m, respectively. Based on the catalog, we discuss the luminosity functions at each band, the color-color diagram, and the color-magnitude diagram using the 3.2, 7, and 11 {mu}m band data. Stars without circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects, and background galaxies are located at distinct regions in the diagrams, suggesting that the present catalog is useful for the classification of objects toward the LMC.
X-RAY POINT-SOURCE POPULATIONS CONSTITUTING THE GALACTIC RIDGE X-RAY EMISSION
Morihana, Kumiko; Tsujimoto, Masahiro; Ebisawa, Ken; Yoshida, Tessei
2013-03-20
Apparently diffuse X-ray emission has been known to exist along the central quarter of the Galactic Plane since the beginning of X-ray astronomy; this is referred to as the Galactic Ridge X-ray emission (GRXE). Recent deep X-ray observations have shown that numerous X-ray point sources account for a large fraction of the GRXE in the hard band (2-8 keV). However, the nature of these sources is poorly understood. Using the deepest X-ray observations made in the Chandra bulge field, we present the result of a coherent photometric and spectroscopic analysis of individual X-ray point sources for the purpose of constraining their nature and deriving their fractional contributions to the hard-band continuum and Fe K line emission of the GRXE. Based on the X-ray color-color diagram, we divided the point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). The group A sources are further decomposed spectrally into thermal and non-thermal sources with different fractions in different flux ranges. From their X-ray properties, we speculate that the group A non-thermal sources are mostly active galactic nuclei and the thermal sources are mostly white dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and C sources are X-ray active stars in flares and quiescence, respectively. In the log N-log S curve of the 2-8 keV band, the group A non-thermal sources are dominant above Almost-Equal-To 10{sup -14} erg cm{sup -2} s{sup -1}, which is gradually taken over by Galactic sources in the fainter flux ranges. The Fe K{alpha} emission is mostly from the group A thermal (WD binaries) and the group B (X-ray active stars) sources.
Search for neutrino point sources with ANTARES 2007-2012 data
Zornoza, J. D.
2014-11-18
Neutrinos are unique probes to study the high energy Universe, since they are neutral, only interact weakly and are stable. Furthermore, they can provide key information about several fundamental questions in Physics like the origin of cosmic rays and the nature of dark matter. The ANTARES neutrino telescope, installed in the Mediterranean Sea, has been taking data since 2007. In this paper we review the results concerning the search for point sources of cosmic neutrinos, using data of 2007–2012. Two main strategies have been followed: to look towards the direction of sources candidate to emmit neutrinos and to make an all-sky scan. Although no significant cluster has been found above the background, flux limits have been set at the level of E{sup 2}φν{sup 90CL}∼1–2×10{sup −8} GeV cm{sup −}2s{sup −1}.
Spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion
NASA Technical Reports Server (NTRS)
Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.
1981-01-01
To facilitate geologic interpretation of satellite elevation potential field data, analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation. A powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion. Linear transformations of the equivalent source field lead to corresponding geoidal anomalies, pseudo-anomalies, vector anomaly components, spatial derivatives, continuations, and differential magnetic pole reductions. A number of examples using 1 deg-averaged surface free-air gravity anomalies of POGO satellite magnetometer data for the United States, Mexico, and Central America illustrate the capabilities of the method.
NASA Astrophysics Data System (ADS)
Perera, T. A.; Wilson, G. W.; Scott, K. S.; Austermann, J. E.; Schaar, J. R.; Mancera, A.
2013-07-01
A new technique for reliably identifying point sources in millimeter/submillimeter wavelength maps is presented. This method accounts for the frequency dependence of noise in the Fourier domain as well as nonuniformities in the coverage of a field. This optimal filter is an improvement over commonly-used matched filters that ignore coverage gradients. Treating noise variations in the Fourier domain as well as map space is traditionally viewed as a computationally intensive problem. We show that the penalty incurred in terms of computing time is quite small due to casting many of the calculations in terms of FFTs and exploiting the absence of sharp features in the noise spectra of observations. Practical aspects of implementing the optimal filter are presented in the context of data from the AzTEC bolometer camera. The advantages of using the new filter over the standard matched filter are also addressed in terms of a typical AzTEC map.
Kido, K; Magara, Y; Furuichi, T; Ikeda, M
1989-03-01
Tetrachloroethylene contamination of well water occurred in a primarily residential area. To search for point source(s) of tetrachloroethylene contamination, 91 water samples were collected on three separate occasions from 41 shallow wells scattered in the areas. Three methods of groundwater level analysis (limited to 30 wells), cluster analysis of water quality indicators and contour drawing of tetrachloroethylene concentrations were applied. The former two analyses showed that the pollution took place in aquifers of two terraces out of the three in the polluted area. The contour mapping demonstrated the presence of three spots of suspected pollution sources as the estimated points of highest tetrachloroethylene concentrations. The available information suggested the existence of a facility with possible use of tetrachloroethylene in the past.
An efficient method to compute microlensed light curves for point sources
NASA Technical Reports Server (NTRS)
Witt, Hans J.
1993-01-01
We present a method to compute microlensed light curves for point sources. This method has the general advantage that all microimages contributing to the light curve are found. While a source moves along a straight line, all micro images are located either on the primary image track or on the secondary image tracks (loops). The primary image track extends from - infinity to + infinity and is made of many sequents which are continuously connected. All the secondary image tracks (loops) begin and end on the lensing point masses. The method can be applied to any microlensing situation with point masses in the deflector plane, even for the overcritical case and surface densities close to the critical. Furthermore, we present general rules to evaluate the light curve for a straight track arbitrary placed in the caustic network of a sample of many point masses.
A search for T Tauri stars based on the IRAS point source catalog.
NASA Astrophysics Data System (ADS)
Gregorio-Hetem, J.; Lepine, J. R. D.; Quast, G. R.; Torres, C. A. O.; de La Reza, R.
1992-02-01
The results of the first part of a survey for new T Tauri stars, with spectroscopic and photometric observations of about 100 stars, are presented. A list of candidates has been selected by means of the IRAS Point Source Catalog, based on appropriate far-infrared colors. Coude spectra of the selected objects in the 655-673 nm wavelength range, which includes H-alpha and the resonance Li I line, have been obtained. Thirty-three new T Tauri stars, and a number of other interesting objects, like early type premain-sequence stars and Li-rich K giants, have been detected. Several new isolated T Tauri were found, including Hen 1, which may be the T Tauri star with the highest galactic latitude known, if its nature is confirmed.
Personnel exposure from flood phantoms and point sources during quality assurance procedures.
La Fontaine, R; Graham, L S; Behrendt, D; Greenwell, K
1983-07-01
Nuclear medicine technologists routinely use flood phantoms containing 5 to 10 mCi (185-370 MBq) of Tc-99m to perform quality assurance tests on scintillation cameras. This paper presents the results of a study that measured the radiation exposure received by three individuals from a Tc-99m flood phantom during the daily performance of flood-field uniformity tests on three scintillation cameras. The extrapolated annual personnel exposure to the anterior trunk and the back of the hand were 172 mR and 220 mR, respectively. Additional measurements indicate that personnel performing these tests with a 10-mCi Co-57 flood disk source or a 200-muCi point source would receive approximately 25% and 1%, respectively, of the exposure from a 10-mCi Tc-99m flood phantom. These exposure levels should be considered when evaluating personnel radiation exposure in a nuclear medicine clinic.
NASA Technical Reports Server (NTRS)
Seo, Byoung-Joon; Nissly, Carl; Troy, Mitchell; Angeli, George
2010-01-01
The Normalized Point Source Sensitivity (PSSN) has previously been defined and analyzed as an On-Axis seeing-limited telescope performance metric. In this paper, we expand the scope of the PSSN definition to include Off-Axis field of view (FoV) points and apply this generalized metric for performance evaluation of the Thirty Meter Telescope (TMT). We first propose various possible choices for the PSSN definition and select one as our baseline. We show that our baseline metric has useful properties including the multiplicative feature even when considering Off-Axis FoV points, which has proven to be useful for optimizing the telescope error budget. Various TMT optical errors are considered for the performance evaluation including segment alignment and phasing, segment surface figures, temperature, and gravity, whose On-Axis PSSN values have previously been published by our group.
Isotopic Tracers for Delineating Non-Point Source Pollutants in Surface Water
Davisson, M L
2001-03-01
This study tested whether isotope measurements of surface water and dissolved constituents in surface water could be used as tracers of non-point source pollution. Oxygen-18 was used as a water tracer, while carbon-14, carbon-13, and deuterium were tested as tracers of DOC. Carbon-14 and carbon-13 were also used as tracers of dissolved inorganic carbon, and chlorine-36 and uranium isotopes were tested as tracers of other dissolved salts. In addition, large databases of water quality measurements were assembled for the Missouri River at St. Louis and the Sacramento-San Joaquin Delta in California to enhance interpretive results of the isotope measurements. Much of the water quality data has been under-interpreted and provides a valuable resource to investigative research, for which this report exploits and integrates with the isotope measurements.
Relevance of percolation theory to the vulcanization transition.
Janssen, H K; Stenull, O
2001-08-01
The relationship between vulcanization and percolation is explored from the perspective of renormalized local field theory. We show to arbitrary order in perturbation theory that the vulcanization and percolation correlation functions are governed by the same Gell-Mann-Low renormalization-group equation. Hence, all scaling aspects of the vulcanization transition are reigned by the critical exponents of the percolation universality class.
Disinfection of secondary effluents by infiltration percolation.
Makni, H
2001-01-01
Among the most attractive applications of reclaimed wastewater are: irrigation of public parks, sports fields, golf courses and market gardening. These uses require advanced wastewater treatment including disinfection. According to WHO guidelines (1989) and current rules and regulations in Tunisia, faecal coliform levels have to be reduced to < 10(3) or 10(2) CFU/100 mL. In Tunisia, most wastewater plants are only secondary treatment and, in order to meet health related regulations, the effluents need to be disinfected. However, it is usual for secondary effluents to need filtration prior to disinfection. Effectiveness of conventional disinfection processes, such as chlorination and UV radiation, are dependent upon the oxidation level and the levels of suspended solids of the treated water. Ozonation is relatively expensive and energy consuming. The consideration of the advantages and disadvantages of conventional techniques, their reliability, investment needs and operational costs will lead to the use of less sophisticated alternative techniques for certain facilities. Among alternative techniques, soil aquifer treatment and infiltration percolation through sand beds have been studied in Arizona, Israel, France, Spain and Morocco. Infiltration percolation plants have been intermittently fed with secondary or high quality primary effluents which percolated through 1.5-2 m unsaturated coarse sand and were recovered by under-drains. In such infiltration percolation facilities, microorganisms were eliminated through numerous physical, physicochemical and biological inter-related processes (mechanical filtration, adsorption and microbial degradation respectively). Efficiency of faecal coliform removal was dependent upon the water detention times in the filtering medium and on the oxidation of the filtered water. Effluents of Sfax town aerated ponds were infiltrated through 1.5 m deep sand columns in order to determine the performance of infiltration percolation in the
Pennline, H.W.; Luebke, D.R.; Jones, K.L.; Morsi, B.I.; Heintz, Y.J.; Ilconich, J.B.
2007-06-01
The capture/separation step for carbon dioxide (CO2) from large-point sources is a critical one with respect to the technical feasibility and cost of the overall carbon sequestration scenario. For large-point sources, such as those found in power generation, the carbon dioxide capture techniques being investigated by the in-house research area of the National Energy Technology Laboratory possess the potential for improved efficiency and reduced costs as compared to more conventional technologies. The investigated techniques can have wide applications, but the research has focused on capture/separation of carbon dioxide from flue gas (post-combustion from fossil fuel-fired combustors) and from fuel gas (precombustion, such as integrated gasification combined cycle or IGCC). With respect to fuel gas applications, novel concepts are being developed in wet scrubbing with physical absorption; chemical absorption with solid sorbents; and separation by membranes. In one concept, a wet scrubbing technique is being investigated that uses a physical solvent process to remove CO2 from fuel gas of an IGCC system at elevated temperature and pressure. The need to define an ideal solvent has led to the study of the solubility and mass transfer properties of various solvents. Pertaining to another separation technology, fabrication techniques and mechanistic studies for membranes separating CO2 from the fuel gas produced by coal gasification are also being performed. Membranes that consist of CO2-philic ionic liquids encapsulated into a polymeric substrate have been investigated for permeability and selectivity. Finally, dry, regenerable processes based on sorbents are additional techniques for CO2 capture from fuel gas. An overview of these novel techniques is presented along with a research progress status of technologies related to membranes and physical solvents.
THE CHANDRA LOCAL VOLUME SURVEY: THE X-RAY POINT-SOURCE CATALOG OF NGC 300
Binder, B.; Williams, B. F.; Dalcanton, J. J.; Anderson, S. F.; Weisz, D. R.; Eracleous, M.; Gaetz, T. J.; Plucinsky, P. P.; Skillman, E. D.; Kong, A. K. H.
2012-10-10
We present the source catalog of a new Chandra ACIS-I observation of NGC 300 obtained as part of the Chandra Local Volume Survey. Our 63 ks exposure covers {approx}88% of the D{sub 25} isophote (R Almost-Equal-To 6.3 kpc) and yields a catalog of 95 X-ray point sources detected at high significance to a limiting unabsorbed 0.35-8 keV luminosity of {approx}10{sup 36} erg s{sup -1}. Sources were cross-correlated with a previous XMM-Newton catalog, and we find 75 'X-ray transient candidate' sources that were detected by one observatory, but not the other. We derive an X-ray scale length of 1.7 {+-} 0.2 kpc and a recent star formation rate of 0.12 M{sub Sun} yr{sup -1} in excellent agreement with optical observations. Deep, multi-color imaging from the Hubble Space Telescope, covering {approx}32% of our Chandra field, was used to search for optical counterparts to the X-ray sources, and we have developed a new source classification scheme to determine which sources are likely X-ray binaries, supernova remnants, and background active galactic nucleus candidates. Finally, we present the X-ray luminosity functions (XLFs) at different X-ray energies, and we find the total NGC 300 X-ray point-source population to be consistent with other late-type galaxies hosting young stellar populations ({approx}< 50 Myr). We find that XLF of sources associated with older stellar populations has a steeper slope than the XLF of X-ray sources coinciding with young stellar populations, consistent with theoretical predictions.
Variability of Point Sources of Gamma Rays Detected by the Fermi Large-Area Telescope
NASA Astrophysics Data System (ADS)
Wallace, Eric
The Large Area Telescope (LAT) aboard the Fermi Gamma-Ray Space Telescope has revolutionized gamma-ray astronomy, allowing the detection of thousands of point sources of gamma rays. Variability studies are of significant interest as a potential source of information about the emission mechanisms, and as a means to identify gamma-ray sources with known sources in other wavelengths and to improve detection sensitivity in searches for new sources. The inclusion of temporal resolution, however, adds to the already considerable complexity of the required analysis, and as a result, variability studies have generally been limited either in scope or in detail, or both, compared to time-integrated spectral analyses. pointlike is a software package designed for fast maximum likelihood analysis of LAT data, allowing for interactive and large-scale analyses. Here, we present an application of pointlike to the characterization of the variability of the full sample of known gamma-ray point sources. We describe the construction of light curves in one-month time bins, spanning the first 42 months of the Fermi mission, for a sample of 2652 sources. We discuss the use of the detection significance in individual months to improve the significance of detection of marginal sources, and show that including that measure of significance increases the set of significantly detected sources by nearly 20% compared to using only the average significance. We describe a statistical measure of the significance of variability in a light curve, and examine the variability of thesample as whole, and of subsets associated with particular source types, especially pulsars. We discuss the use of pulsars, which are generally non-variable on long timescales, to calibrate variability statistics, and to assess the importance of systematic errors in estimates of variability. Finally, we discuss the potential to extend the method to produce light curves of longer duration and finer time binning, and to search
OBJECT X: THE BRIGHTEST MID-INFRARED POINT SOURCE IN M33
Khan, Rubab; Stanek, K. Z.; Kochanek, C. S.; Bonanos, A. Z. E-mail: kstanek@astronomy.ohio-state.edu E-mail: bonanos@astro.noa.gr
2011-05-01
We discuss the nature of the brightest mid-IR point source (which we dub Object X) in the nearby galaxy M33. Although multi-wavelength data on this object have existed in the literature for some time, it had not previously been recognized as the most luminous mid-IR object in M33 because it is entirely unremarkable in both optical and near-IR light. In the Local Group Galaxies Survey, Object X is a faint red source visible in VRI and H{alpha} but not U or B. It was easily seen at JHK{sub s} in the Two Micron All Sky Survey. It is the brightest point source in all four Spitzer IRAC bands and is also visible in the MIPS 24 {mu}m band. Its bolometric luminosity is {approx}5 x 10{sup 5} L{sub sun}. The source is optically variable on short timescales (tens of days) and is also slightly variable in the mid-IR, indicating that it is a star. Archival photographic plates (from 1949 and 1991) show no optical source, so the star has been obscured for at least half a century. Its properties are similar to those of the Galactic OH/IR star IRC+10420, which has a complex dusty circumstellar structure resulting from episodic low-velocity mass ejections. We propose that Object X is an M {approx}> 30 M{sub sun} evolved star obscured in its own dust ejected during episodic mass-loss events over at least {approx}half a century. It may emerge from its current ultra-short evolutionary phase as a hotter post-red-supergiant star analogous to M33 Var A. The existence and rarity of such objects can be an important probe of a very brief yet eventful stellar evolutionary phase.
Lessons Learned from OMI Observations of Point Source SO2 Pollution
NASA Technical Reports Server (NTRS)
Krotkov, N.; Fioletov, V.; McLinden, Chris
2011-01-01
The Ozone Monitoring Instrument (OMI) on NASA Aura satellite makes global daily measurements of the total column of sulfur dioxide (SO2), a short-lived trace gas produced by fossil fuel combustion, smelting, and volcanoes. Although anthropogenic SO2 signals may not be detectable in a single OMI pixel, it is possible to see the source and determine its exact location by averaging a large number of individual measurements. We describe new techniques for spatial and temporal averaging that have been applied to the OMI SO2 data to determine the spatial distributions or "fingerprints" of SO2 burdens from top 100 pollution sources in North America. The technique requires averaging of several years of OMI daily measurements to observe SO2 pollution from typical anthropogenic sources. We found that the largest point sources of SO2 in the U.S. produce elevated SO2 values over a relatively small area - within 20-30 km radius. Therefore, one needs higher than OMI spatial resolution to monitor typical SO2 sources. TROPOMI instrument on the ESA Sentinel 5 precursor mission will have improved ground resolution (approximately 7 km at nadir), but is limited to once a day measurement. A pointable geostationary UVB spectrometer with variable spatial resolution and flexible sampling frequency could potentially achieve the goal of daily monitoring of SO2 point sources and resolve downwind plumes. This concept of taking the measurements at high frequency to enhance weak signals needs to be demonstrated with a GEOCAPE precursor mission before 2020, which will help formulating GEOCAPE measurement requirements.
Strategies for satellite-based monitoring of CO2 from distributed area and point sources
NASA Astrophysics Data System (ADS)
Schwandner, Florian M.; Miller, Charles E.; Duren, Riley M.; Natraj, Vijay; Eldering, Annmarie; Gunson, Michael R.; Crisp, David
2014-05-01
Atmospheric CO2 budgets are controlled by the strengths, as well as the spatial and temporal variabilities of CO2 sources and sinks. Natural CO2 sources and sinks are dominated by the vast areas of the oceans and the terrestrial biosphere. In contrast, anthropogenic and geogenic CO2 sources are dominated by distributed area and point sources, which may constitute as much as 70% of anthropogenic (e.g., Duren & Miller, 2012), and over 80% of geogenic emissions (Burton et al., 2013). Comprehensive assessments of CO2 budgets necessitate robust and highly accurate satellite remote sensing strategies that address the competing and often conflicting requirements for sampling over disparate space and time scales. Spatial variability: The spatial distribution of anthropogenic sources is dominated by patterns of production, storage, transport and use. In contrast, geogenic variability is almost entirely controlled by endogenic geological processes, except where surface gas permeability is modulated by soil moisture. Satellite remote sensing solutions will thus have to vary greatly in spatial coverage and resolution to address distributed area sources and point sources alike. Temporal variability: While biogenic sources are dominated by diurnal and seasonal patterns, anthropogenic sources fluctuate over a greater variety of time scales from diurnal, weekly and seasonal cycles, driven by both economic and climatic factors. Geogenic sources typically vary in time scales of days to months (geogenic sources sensu stricto are not fossil fuels but volcanoes, hydrothermal and metamorphic sources). Current ground-based monitoring networks for anthropogenic and geogenic sources record data on minute- to weekly temporal scales. Satellite remote sensing solutions would have to capture temporal variability through revisit frequency or point-and-stare strategies. Space-based remote sensing offers the potential of global coverage by a single sensor. However, no single combination of orbit
NASA Astrophysics Data System (ADS)
Mauzerall, Denise L.; Sultan, Babar; Kim, Namsoug; Bradford, David F.
We present a proof-of-concept analysis of the measurement of the health damage of ozone (O 3) produced from nitrogen oxides (NO=NO+NO) emitted by individual large point sources in the eastern United States. We use a regional atmospheric model of the eastern United States, the Comprehensive Air quality Model with Extensions (CAMx), to quantify the variable impact that a fixed quantity of NO x emitted from individual sources can have on the downwind concentration of surface O 3, depending on temperature and local biogenic hydrocarbon emissions. We also examine the dependence of resulting O 3-related health damages on the size of the exposed population. The investigation is relevant to the increasingly widely used "cap and trade" approach to NO x regulation, which presumes that shifts of emissions over time and space, holding the total fixed over the course of the summer O 3 season, will have minimal effect on the environmental outcome. By contrast, we show that a shift of a unit of NO x emissions from one place or time to another could result in large changes in resulting health effects due to O 3 formation and exposure. We indicate how the type of modeling carried out here might be used to attach externality-correcting prices to emissions. Charging emitters fees that are commensurate with the damage caused by their NO x emissions would create an incentive for emitters to reduce emissions at times and in locations where they cause the largest damage.
da Costa, R A; Dorogovtsev, S N; Goltsev, A V; Mendes, J F F
2015-03-01
We describe the effect of power-law initial distributions of clusters on ordinary percolation and its generalizations, specifically, models of explosive percolation processes based on local optimization. These aggregation processes were shown to exhibit continuous phase transitions if the evolution starts from a set of disconnected nodes. Since the critical exponents of the order parameter in explosive percolation transitions turned out to be very small, these transitions were first believed to be discontinuous. In this article we analyze the evolution starting from clusters of nodes whose sizes are distributed according to a power law. We show that these initial distributions change dramatically the position and order of the phase transitions in these problems. We find a particular initial power-law distribution producing a peculiar effect on explosive percolation, namely, before the emergence of the percolation cluster, the system is in a "critical phase" with an infinite generalized susceptibility. This critical phase is absent in ordinary percolation models with any power-law initial conditions. The transition from the critical phase is an infinite-order phase transition, which resembles the scenario of the Berezinskii-Kosterlitz-Thouless phase transition. We obtain the critical singularity of susceptibility at this peculiar infinite-order transition in explosive percolation. It turns out that susceptibility in this situation does not obey the Curie-Weiss law.
Dewji, Shaheen Azim; Bellamy, Michael B.; Hertel, Nolan E.; Leggett, Richard Wayne; Sherbini, Sami; Saba, Mohammad S.; Eckerman, Keith F.
2015-09-01
The U.S. Nuclear Regulatory Commission (USNRC) initiated a contract with Oak Ridge National Laboratory (ORNL) to calculate radiation dose rates to members of the public that may result from exposure to patients recently administered iodine-131 (^{131}I) as part of medical therapy. The main purpose was to compare dose rate estimates based on a point source and target with values derived from more realistic simulations that considered the time-dependent distribution of ^{131}I in the patient and attenuation of emitted photons by the patient’s tissues. The external dose rate estimates were derived using Monte Carlo methods and two representations of the Phantom with Movable Arms and Legs, previously developed by ORNL and the USNRC, to model the patient and a nearby member of the public. Dose rates to tissues and effective dose rates were calculated for distances ranging from 10 to 300 cm between the phantoms and compared to estimates based on the point-source method, as well as to results of previous studies that estimated exposure from ^{131}I patients. The point-source method overestimates dose rates to members of the public in very close proximity to an ^{131}I patient but is a broadly accurate method of dose rate estimation at separation distances of 300 cm or more at times closer to administration.