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Sample records for in-air spatial spread

  1. Modelling the spread of Wolbachia in spatially heterogeneous environments.

    PubMed

    Hancock, Penelope A; Godfray, H Charles J

    2012-11-07

    The endosymbiont Wolbachia infects a large number of insect species and is capable of rapid spread when introduced into a novel host population. The bacteria spread by manipulating their hosts' reproduction, and their dynamics are influenced by the demographic structure of the host population and patterns of contact between individuals. Reaction-diffusion models of the spatial spread of Wolbachia provide a simple analytical description of their spatial dynamics but do not account for significant details of host population dynamics. We develop a metapopulation model describing the spatial dynamics of Wolbachia in an age-structured host insect population regulated by juvenile density-dependent competition. The model produces similar dynamics to the reaction-diffusion model in the limiting case where the host's habitat quality is spatially homogeneous and Wolbachia has a small effect on host fitness. When habitat quality varies spatially, Wolbachia spread is usually much slower, and the conditions necessary for local invasion are strongly affected by immigration of insects from surrounding regions. Spread is most difficult when variation in habitat quality is spatially correlated. The results show that spatial variation in the density-dependent competition experienced by juvenile host insects can strongly affect the spread of Wolbachia infections, which is important to the use of Wolbachia to control insect vectors of human disease and other pests.

  2. Spread of pedigree versus genetic ancestry in spatially distributed populations.

    PubMed

    Kelleher, J; Etheridge, A M; Véber, A; Barton, N H

    2016-04-01

    Ancestral processes are fundamental to modern population genetics and spatial structure has been the subject of intense interest for many years. Despite this interest, almost nothing is known about the distribution of the locations of pedigree or genetic ancestors. Using both spatially continuous and stepping-stone models, we show that the distribution of pedigree ancestors approaches a travelling wave, for which we develop two alternative approximations. The speed and width of the wave are sensitive to the local details of the model. After a short time, genetic ancestors spread far more slowly than pedigree ancestors, ultimately diffusing out with radius ∼ t rather than spreading at constant speed. In contrast to the wave of pedigree ancestors, the spread of genetic ancestry is insensitive to the local details of the models. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

  3. Collective behavior in the spatial spreading of obesity

    NASA Astrophysics Data System (ADS)

    Gallos, Lazaros K.; Barttfeld, Pablo; Havlin, Shlomo; Sigman, Mariano; Makse, Hernán A.

    2012-06-01

    Obesity prevalence is increasing in many countries at alarming levels. A difficulty in the conception of policies to reverse these trends is the identification of the drivers behind the obesity epidemics. Here, we implement a spatial spreading analysis to investigate whether obesity shows spatial correlations, revealing the effect of collective and global factors acting above individual choices. We find a regularity in the spatial fluctuations of their prevalence revealed by a pattern of scale-free long-range correlations. The fluctuations are anomalous, deviating in a fundamental way from the weaker correlations found in the underlying population distribution indicating the presence of collective behavior, i.e., individual habits may have negligible influence in shaping the patterns of spreading. Interestingly, we find the same scale-free correlations in economic activities associated with food production. These results motivate future interventions to investigate the causality of this relation providing guidance for the implementation of preventive health policies.

  4. Collective behavior in the spatial spreading of obesity

    PubMed Central

    Gallos, Lazaros K.; Barttfeld, Pablo; Havlin, Shlomo; Sigman, Mariano; Makse, Hernán A.

    2012-01-01

    Obesity prevalence is increasing in many countries at alarming levels. A difficulty in the conception of policies to reverse these trends is the identification of the drivers behind the obesity epidemics. Here, we implement a spatial spreading analysis to investigate whether obesity shows spatial correlations, revealing the effect of collective and global factors acting above individual choices. We find a regularity in the spatial fluctuations of their prevalence revealed by a pattern of scale-free long-range correlations. The fluctuations are anomalous, deviating in a fundamental way from the weaker correlations found in the underlying population distribution indicating the presence of collective behavior, i.e., individual habits may have negligible influence in shaping the patterns of spreading. Interestingly, we find the same scale-free correlations in economic activities associated with food production. These results motivate future interventions to investigate the causality of this relation providing guidance for the implementation of preventive health policies. PMID:22822425

  5. Predicted Spatial Spread of Canine Rabies in Australia

    PubMed Central

    Fleming, Peter J. S.; Ward, Michael P.; Davis, Stephen A.

    2017-01-01

    Modelling disease dynamics is most useful when data are limited. We present a spatial transmission model for the spread of canine rabies in the currently rabies-free wild dog population of Australia. The introduction of a sub-clinically infected dog from Indonesia is a distinct possibility, as is the spillover infection of wild dogs. Ranges for parameters were estimated from the literature and expert opinion, or set to span an order of magnitude. Rabies was judged to have spread spatially if a new infectious case appeared 120 km from the index case. We found 21% of initial value settings resulted in canine rabies spreading 120km, and on doing so at a median speed of 67 km/year. Parameters governing dog movements and behaviour, around which there is a paucity of knowledge, explained most of the variance in model outcomes. Dog density, especially when interactions with other parameters were included, explained some of the variance in whether rabies spread 120km, but dog demography (mean lifespan and mean replacement period) had minimal impact. These results provide a clear research direction if Australia is to improve its preparedness for rabies. PMID:28114327

  6. Predicted Spatial Spread of Canine Rabies in Australia.

    PubMed

    Johnstone-Robertson, Simon P; Fleming, Peter J S; Ward, Michael P; Davis, Stephen A

    2017-01-01

    Modelling disease dynamics is most useful when data are limited. We present a spatial transmission model for the spread of canine rabies in the currently rabies-free wild dog population of Australia. The introduction of a sub-clinically infected dog from Indonesia is a distinct possibility, as is the spillover infection of wild dogs. Ranges for parameters were estimated from the literature and expert opinion, or set to span an order of magnitude. Rabies was judged to have spread spatially if a new infectious case appeared 120 km from the index case. We found 21% of initial value settings resulted in canine rabies spreading 120km, and on doing so at a median speed of 67 km/year. Parameters governing dog movements and behaviour, around which there is a paucity of knowledge, explained most of the variance in model outcomes. Dog density, especially when interactions with other parameters were included, explained some of the variance in whether rabies spread 120km, but dog demography (mean lifespan and mean replacement period) had minimal impact. These results provide a clear research direction if Australia is to improve its preparedness for rabies.

  7. Spreading of localized attacks in spatial multiplex networks

    NASA Astrophysics Data System (ADS)

    Vaknin, Dana; Danziger, Michael M.; Havlin, Shlomo

    2017-07-01

    Many real-world multilayer systems such as critical infrastructure are interdependent and embedded in space with links of a characteristic length. They are also vulnerable to localized attacks or failures, such as terrorist attacks or natural catastrophes, which affect all nodes within a given radius. Here we study the effects of localized attacks on spatial multiplex networks of two layers. We find a metastable region where a localized attack larger than a critical size induces a nucleation transition as a cascade of failures spreads throughout the system, leading to its collapse. We develop a theory to predict the critical attack size and find that it exhibits novel scaling behavior. We further find that localized attacks in these multiplex systems can induce a previously unobserved combination of random and spatial cascades. Our results demonstrate important vulnerabilities in real-world interdependent networks and show new theoretical features of spatial networks.

  8. Spatial spread of the West Africa Ebola epidemic

    PubMed Central

    Pulliam, J. Tomlin; Alexander, Laura W.; Rohani, Pejman; Drake, John M.

    2016-01-01

    Controlling Ebola outbreaks and planning an effective response to future emerging diseases are enhanced by understanding the role of geography in transmission. Here we show how epidemic expansion may be predicted by evaluating the relative probability of alternative epidemic paths. We compared multiple candidate models to characterize the spatial network over which the 2013–2015 West Africa epidemic of Ebola virus spread and estimate the effects of geographical covariates on transmission during peak spread. The best model was a generalized gravity model where the probability of transmission between locations depended on distance, population density and international border closures between Guinea, Liberia and Sierra Leone and neighbouring countries. This model out-performed alternative models based on diffusive spread, the force of infection, mobility estimated from cell phone records and other hypothesized patterns of spread. These findings highlight the importance of integrated geography to epidemic expansion and may contribute to identifying both the most vulnerable unaffected areas and locations of maximum intervention value. PMID:27853607

  9. On the Spatial Spread of Rabies among Foxes

    NASA Astrophysics Data System (ADS)

    Murray, J. D.; Stanley, E. A.; Brown, D. L.

    1986-11-01

    We present a simple model for the spatial spread of rabies among foxes and use it to quantify its progress in England if rabies were introduced. The model is based on the known ecology of fox behaviour and on the assumption that the main vector for the spread of the disease is the rabid fox. Known data and facts are used to determine real parameter values involved in the model. We calculate the speed of propagation of the epizootic front, the threshold for the existence of an epidemic, the period and distance apart of the subsequent cyclical epidemics which follow the main front, and finally we quantify a means for control of the spatial spread of the disease. By way of illustration we use the model to determine the progress of rabies up through the southern part of England if it were introduced near Southampton. Estimates for the current fox density in England were used in the simulations. These suggest that the disease would reach Manchester within about 3.5 years, moving at speeds as high as 100 km per year in the central region. The model further indicates that although it might seem that the disease had disappeared after the wave had passed it would reappear in the south of England after just over 6 years and at periodic times after that. We consider the possibility of stopping the spread of the disease by creating a rabies `break' ahead of the front through vaccination to reduce the population to a level below the threshold for an epidemic to exist. Based on parameter values relevant to England, we estimate its minimum width to be about 15 km. The model suggests that vaccination has considerable advantages over severe culling.

  10. PDMS spreading morphological patterns on substrates of different hydrophilicity in air vacuum and water.

    PubMed

    Zbik, Marek S; Frost, Ray L

    2010-04-15

    In paper has been to investigate the morphological patterns and kinetics of PDMS spreading on silicon wafer using combination of techniques like ellipsometry, atomic force microscope (AFM), scanning electron microscope (SEM) and optical microscopy. A macroscopic silicone oil drops as well as PDMS water based emulsions were studied after deposition on a flat surface of silicon wafer in air, water and vacuum. Our own measurements using an imaging ellipsometer, which also clearly shows the presence of a precursor film. The diffusion constant of this film, measured with a 60,000 cS PDMS sample spreading on a hydrophilic silicon wafer is D(f)=1.4x10(-11) m(2)/s. Regardless of their size, density and method of deposition, droplets on both types of wafer (hydrophilic and hydrophobic) flatten out over a period of many hours, up to 3 days. During this process neighbouring droplets may coalesce, but there is strong evidence that some of the PDMS from the droplets migrates into a thin, continuous film that covers the surface in between droplets. The thin film appears to be ubiquitous if there has been any deposition of PDMS. However, this statement needs further verification. One question is whether the film forms immediately after forced drying, or whether in some or all cases it only forms by spreading from isolated droplets as they slowly flatten out. 2010 Elsevier Inc. All rights reserved.

  11. Spatial sorting promotes the spread of maladaptive hybridization

    USGS Publications Warehouse

    Lowe, Winsor H.; Muhlfeld, Clint C.; Allendorf, Fred W.

    2015-01-01

    Invasive hybridization is causing loss of biodiversity worldwide. The spread of such introgression can occur even when hybrids have reduced Darwinian fitness, which decreases the frequency of hybrids due to low survival or reproduction through time. This paradox can be partially explained by spatial sorting, where genotypes associated with dispersal increase in frequency at the edge of expansion, fueling further expansion and allowing invasive hybrids to increase in frequency through space rather than time. Furthermore, because all progeny of a hybrid will be hybrids (i.e., will possess genes from both parental taxa), nonnative admixture in invaded populations can increase even when most hybrid progeny do not survive. Broader understanding of spatial sorting is needed to protect native biodiversity.

  12. Object size determines the spatial spread of visual time

    PubMed Central

    McGraw, Paul V.; Roach, Neil W.; Whitaker, David

    2016-01-01

    A key question for temporal processing research is how the nervous system extracts event duration, despite a notable lack of neural structures dedicated to duration encoding. This is in stark contrast with the orderly arrangement of neurons tasked with spatial processing. In this study, we examine the linkage between the spatial and temporal domains. We use sensory adaptation techniques to generate after-effects where perceived duration is either compressed or expanded in the opposite direction to the adapting stimulus' duration. Our results indicate that these after-effects are broadly tuned, extending over an area approximately five times the size of the stimulus. This region is directly related to the size of the adapting stimulus—the larger the adapting stimulus the greater the spatial spread of the after-effect. We construct a simple model to test predictions based on overlapping adapted versus non-adapted neuronal populations and show that our effects cannot be explained by any single, fixed-scale neural filtering. Rather, our effects are best explained by a self-scaled mechanism underpinned by duration selective neurons that also pool spatial information across earlier stages of visual processing. PMID:27466452

  13. Identification and influence of spatial outliers in air quality measurements

    NASA Astrophysics Data System (ADS)

    O'Leary, B. F.; Lemke, L. D.

    2015-12-01

    The heterogeneous nature of urban air complicates the analysis of spatial and temporal variability in air quality measurements. Evaluation of potentially inaccurate measurements (i.e., outliers) poses particularly difficult challenges in extensive air quality datasets with multiple measurements distributed in time and space. This study investigated the identification and impact of outliers in measurements of NO­2, BTEX, PM2.5, and PM10 in the contiguous Detroit, Michigan, USA and Windsor, Ontario, Canada international airshed. Measurements were taken at 100 locations during September 2008 and June 2009 and modeled at a 300m by 300m scale resolution. The objective was to determine if outliers were present and, if so, to quantify the magnitude of their impact on modeled spatial pollution distributions. The study built upon previous investigations by the Geospatial Determinants of Health Outcomes Consortium that examined relationships between air pollutant distributions and asthma exacerbations in the Detroit and Windsor airshed. Four independent approaches were initially employed to identify potential outliers: boxplots, variogram clouds, difference maps, and the Local Moran's I statistic. Potential outliers were subsequently reevaluated for consistency among methods and individually assessed to select a final set of outliers. The impact of excluding individual outliers was subsequently determined by revising the spatially variable air pollution models and recalculating associations between air contaminant concentrations and asthma exacerbations in Detroit and Windsor in 2008. For the pollutants examined, revised associations revealed weaker correlations with spatial outliers removed. Nevertheless, the approach employed improves the model integrity by increasing our understanding of the spatial variability of air pollution in the built environment and providing additional insights into the association between acute asthma exacerbations and air pollution.

  14. Increases in air temperature can promote wind-driven dispersal and spread of plants.

    PubMed

    Kuparinen, Anna; Katul, Gabriel; Nathan, Ran; Schurr, Frank M

    2009-09-07

    Long-distance dispersal (LDD) of seeds and pollen shapes the spatial dynamics of plant genotypes, populations and communities. Quantifying LDD is thus important for predicting the future dynamics of plants exposed to environmental changes. However, environmental changes can also alter the behaviour of LDD vectors: for instance, increasing air temperature may enhance atmospheric instability, thereby altering the turbulent airflow that transports seed and pollen. Here, we investigate temperature effects on wind dispersal in a boreal forest using a 10-year time series of micrometeorological measurements and a Lagrangian stochastic model for particle transport. For a wide range of dispersal and life history types, we found positive relations between air temperature and LDD. This translates into a largely consistent positive effect of +3 degrees C warming on predicted LDD frequencies and spread rates of plants. Relative increases in LDD frequency tend to be higher for heavy-seeded plants, whereas absolute increases in LDD and spread rates are higher for light-seeded plants for which wind is often an important dispersal vector. While these predicted increases are not sufficient to compensate forecasted range losses and environmental changes can alter plant spread in various ways, our results generally suggest that warming can promote wind-driven movements of plant genotypes and populations in boreal forests.

  15. Landscape modelling spatial bottlenecks: implications for raccoon rabies disease spread

    PubMed Central

    Rees, Erin E.; Pond, Bruce A.; Cullingham, Catherine I.; Tinline, Rowland R.; Ball, David; Kyle, Christopher J.; White, Bradley N.

    2009-01-01

    A landscape genetic simulation modelling approach is used to understand factors affecting raccoon rabies disease spread in southern Ontario, Canada. Using the Ontario Rabies Model, we test the hypothesis that landscape configuration (shape of available habitat) affects dispersal, as indicated by genetic structuring. We simulated range expansions of raccoons from New York into vacant landscapes in Ontario, in two areas that differed by the presence or absence of a landscape constriction. Our results provide theoretical evidence that landscape constriction acts as a vicariant bottleneck. We discuss implications for raccoon rabies spread. PMID:19324623

  16. Spreading speed and travelling waves for a spatially discrete SIS epidemic model

    NASA Astrophysics Data System (ADS)

    Zhang, Kate Fang; Zhao, Xiao-Qiang

    2008-01-01

    This paper is devoted to the study of the asymptotic speed of spread and travelling waves for a spatially discrete SIS epidemic model. By appealing to the theory of spreading speeds and travelling waves for monotonic semiflows, we establish the existence of asymptotic speed of spread and show that it coincides with the minimal wave speed for monotonic travelling waves. This also gives an affirmative answer to an open problem presented by Rass and Radcliffe (2003 Spatial Deterministic Epidemics (Mathematical Surveys and Monographs vol 102) (Providence, RI: American Mathematical Society)) in the case of discrete spatial habitat. Supported in part by the NSERC of Canada and the MITACS of Canada.

  17. Spreading and segregation of lipids in air-stable lipid microarrays.

    PubMed

    Fang, Ye

    2006-03-15

    As a result of heterogeneous spreading of distinct lipids within the same microspots of air-stable lipid microarrays, ganglioside GM1 tends to segregate and thus enrich within the center area of microspots where being predetermined by the quill pin used for array fabrication, as indicated by the binding pattern of fluorescein-cholera toxin subunit B.

  18. Implications of the spatial dynamics of fire spread for the bistability of savanna and forest.

    PubMed

    Schertzer, E; Staver, A C; Levin, S A

    2015-01-01

    The role of fire in expanding the global distribution of savanna is well recognized. Empirical observations and modeling suggest that fire spread has a threshold response to fuel-layer continuity, which sets up a positive feedback that maintains savanna-forest bistability. However, modeling has so far failed to examine fire spread as a spatial process that interacts with vegetation. Here, we use simple, well-supported assumptions about fire spread as an infection process and its effects on trees to ask whether spatial dynamics qualitatively change the potential for savanna-forest bistability. We show that the spatial effects of fire spread are the fundamental reason that bistability is possible: because fire spread is an infection process, it exhibits a threshold response to fuel continuity followed by a rapid increase in fire size. Other ecological processes affecting fire spread may also contribute including temporal variability in demography or fire spread. Finally, including the potential for spatial aggregation increases the potential both for savanna-forest bistability and for savanna and forest to coexist in a landscape mosaic.

  19. Spatial controls of occurrence and spread of wildfires in the Missouri Ozark Highlands

    Treesearch

    Jian Yang; Hong S. He; Stephen R. Shifley

    2008-01-01

    Understanding spatial controls on wildfires is important when designing adaptive fire management plans and optimizing fuel treatment locations on a forest landscape. Previous research about this topic focused primarily on spatial controls for fire origin locations alone. Fire spread and behavior were largely overlooked. This paper contrasts the relative importance of...

  20. Spatial assessment of animal manure spreading and groundwater nitrate pollution.

    PubMed

    Infascelli, Roberta; Pelorosso, Raffaele; Boccia, Lorenzo

    2009-11-01

    Nitrate concentration in groundwater has frequently been linked to non-point pollution. At the same time the existence of intensive agriculture and extremely intensive livestock activity increases the potential for nitrate pollution in shallow groundwater. Nitrate used in agriculture could cause adverse effects on human and animal health. In order to evaluate the groundwater nitrate pollution, and how it might evolve in time, it is essential to develop control systems and to improve policies and incentives aimed at controlling the amount of nitrate entering downstream water systems. The province of Caserta in southern Italy is characterized by high levels of animal manure loading. A comparison between manure nitrogen production and nitrate concentration in groundwater was carried out in this area, using geostatistical tools and spatial statistics. The results show a discrepancy between modelling of nitrate leaching and monitoring of the groundwater and, moreover, no spatial correlation between nitrogen production in livestock farms and nitrate concentration in groundwater, suggesting that producers are not following the regulatory procedures for the agronomic use of manure. The methodology developed in this paper could be applied also in other regions in which European Union fertilization plans are not adequately followed.

  1. Spatial Variations of Scintillation and TEC During Equatorial Spread F

    NASA Astrophysics Data System (ADS)

    Groves, K.; Basu, S.; Pedersen, T. R.; Beach, T. L.; Quinn, J. M.; Taliaferro, B.; de Paula, E. R.; Batista, I. S.; Abdu, M. A.; Livingston, R. C.; Ning, P.; Carrano, C.

    2004-05-01

    Numerous studies of geophysical observables associated with large-scale instabilities in the post-sunset equatorial ionosphere have been conducted for several decades; these observables include electric fields, electron density profiles, total electron content (TEC), plasma and neutral drift, scintillations and coherent radar backscatter. Despite a general understanding of the local correlations between these parameters during the on-set and evolution of equatorial bubbles, detailed knowledge of the variations of these parameters as a function of latitude on a given magnetic meridian is lacking. During the Oct-Nov 2002 Conjugate Points Equatorial Experiment (COPEX) campaign was conducted at three sites in western Brazil; one site was situated at the magnetic equator while the other two were selected at magnetic conjugate locations approximately ± 10° MLat. The campaign was organized and coordinated by the Aeronomy Group at the Brazilian National Institute for Space Research (Instituto Nacional de Pesquisas Espaciais- INPE). A number of diagnostic instruments, including digisondes, GPS scintillation and TEC diagnostics, VHF scintillations and plasma drifts, and all-sky imagers were operated routinely throughout the campaign period. The work presented here focuses on the meridional variations of GPS and VHF scintillations from the northern to the southern anomaly regions (~± 15° MLat) and their correlation with total electron content over the same spatial extent. The key issue for consideration is whether the scintillation intensity is directly proportional to electron density (i.e., TEC) across a flux tube implying constant Δ N/N within the instability region, or whether some other relative scaling between the density and scintillation exists. The results provide insight into the distribution of irregularities and, indirectly, the energetics of instabilities within a flux tube. The outcome of this investigation directly impacts techniques to extrapolate local

  2. Measurements of spatial and frequency coherence of an equatorial hf path during spread-F

    SciTech Connect

    Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

    1993-01-01

    In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four cw tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the cw broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the [open quotes]damage[close quotes] is done by the bottomside spread F.

  3. Measurements of spatial and frequency coherence of an equatorial hf path during spread-F

    SciTech Connect

    Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

    1993-07-01

    In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four cw tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the cw broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the {open_quotes}damage{close_quotes} is done by the bottomside spread F.

  4. Effects of various representations of temporally and spatially variable agricultural processes in air quality dispersion modeling

    USDA-ARS?s Scientific Manuscript database

    Agricultural activities that are both temporally and spatially variable, such as tillage and harvesting, can be challenging to represent as sources in air quality dispersion modeling. Existing models were mainly developed to predict concentrations resulting from a stationary and continuous source wi...

  5. Using the Gravity Model to Estimate the Spatial Spread of Vector-Borne Diseases

    PubMed Central

    Barrios, José Miguel; Verstraeten, Willem W.; Maes, Piet; Aerts, Jean-Marie; Farifteh, Jamshid; Coppin, Pol

    2012-01-01

    The gravity models are commonly used spatial interaction models. They have been widely applied in a large set of domains dealing with interactions amongst spatial entities. The spread of vector-borne diseases is also related to the intensity of interaction between spatial entities, namely, the physical habitat of pathogens’ vectors and/or hosts, and urban areas, thus humans. This study implements the concept behind gravity models in the spatial spread of two vector-borne diseases, nephropathia epidemica and Lyme borreliosis, based on current knowledge on the transmission mechanism of these diseases. Two sources of information on vegetated systems were tested: the CORINE land cover map and MODIS NDVI. The size of vegetated areas near urban centers and a local indicator of occupation-related exposure were found significant predictors of disease risk. Both the land cover map and the space-borne dataset were suited yet not equivalent input sources to locate and measure vegetated areas of importance for disease spread. The overall results point at the compatibility of the gravity model concept and the spatial spread of vector-borne diseases. PMID:23202882

  6. Using the gravity model to estimate the spatial spread of vector-borne diseases.

    PubMed

    Barrios, José Miguel; Verstraeten, Willem W; Maes, Piet; Aerts, Jean-Marie; Farifteh, Jamshid; Coppin, Pol

    2012-11-30

    The gravity models are commonly used spatial interaction models. They have been widely applied in a large set of domains dealing with interactions amongst spatial entities. The spread of vector-borne diseases is also related to the intensity of interaction between spatial entities, namely, the physical habitat of pathogens’ vectors and/or hosts, and urban areas, thus humans. This study implements the concept behind gravity models in the spatial spread of two vector-borne diseases, nephropathia epidemica and Lyme borreliosis, based on current knowledge on the transmission mechanism of these diseases. Two sources of information on vegetated systems were tested: the CORINE land cover map and MODIS NDVI. The size of vegetated areas near urban centers and a local indicator of occupation-related exposure were found significant predictors of disease risk. Both the land cover map and the space-borne dataset were suited yet not equivalent input sources to locate and measure vegetated areas of importance for disease spread. The overall results point at the compatibility of the gravity model concept and the spatial spread of vector-borne diseases.

  7. Effects of spatial heterogeneity in moisture content on the horizontal spread of peat fires.

    PubMed

    Prat-Guitart, Nuria; Rein, Guillermo; Hadden, Rory M; Belcher, Claire M; Yearsley, Jon M

    2016-12-01

    The gravimetric moisture content of peat is the main factor limiting the ignition and spread propagation of smouldering fires. Our aim is to use controlled laboratory experiments to better understand how the spread of smouldering fires is influenced in natural landscape conditions where the moisture content of the top peat layer is not homogeneous. In this paper, we study for the first time the spread of peat fires across a spatial matrix of two moisture contents (dry/wet) in the laboratory. The experiments were undertaken using an open-top insulated box (22×18×6cm) filled with milled peat. The peat was ignited at one side of the box initiating smouldering and horizontal spread. Measurements of the peak temperature inside the peat, fire duration and longwave thermal radiation from the burning samples revealed important local changes of the smouldering behaviour in response to sharp gradients in moisture content. Both, peak temperatures and radiation in wetter peat (after the moisture gradient) were sensitive to the drier moisture condition (preceding the moisture gradient). Drier peat conditions before the moisture gradient led to higher temperatures and higher radiation flux from the fire during the first 6cm of horizontal spread into a wet peat patch. The total spread distance into a wet peat patch was affected by the moisture content gradient. We predicted that in most peat moisture gradients of relevance to natural ecosystems the fire self-extinguishes within the first 10cm of horizontal spread into a wet peat patch. Spread distances of more than 10cm are limited to wet peat patches below 160% moisture content (mass of water per mass of dry peat). We found that spatial gradients of moisture content have important local effects on the horizontal spread and should be considered in field and modelling studies.

  8. Spatial spread of local field potential is band-pass in the primary visual cortex

    PubMed Central

    Dubey, Agrita

    2016-01-01

    Local field potential (LFP) is a valuable tool in understanding brain function and in brain machine-interfacing applications. However, there is no consensus on the spatial extent of the cortex that contributes to the LFP (its “spatial spread”), with different studies reporting values between a few hundred micrometers and several millimeters. Furthermore, the dependency of the spatial spread on frequency, which could reflect properties of the network architecture and extracellular medium, is not well studied, with theory and models predicting either “all-pass” (frequency-independent) or “low-pass” behavior. Surprisingly, we found the LFP spread to be “band-pass” in the primate primary visual cortex, with the greatest spread in the high-gamma range (60–150 Hz). This was accompanied by an increase in phase coherency across neighboring sites in the same frequency range, consistent with the findings of a recent model that reconciles previous studies by suggesting that spatial spread depends on neuronal correlations. PMID:27489369

  9. Satellite image restoration in the context of a spatially varying point spread function.

    PubMed

    Hajlaoui, Nasreddine; Chaux, Caroline; Perrin, Guillaume; Falzon, Frédéric; Benazza-Benyahia, Amel

    2010-06-01

    In this paper, we consider a deconvolution problem where the point spread function (PSF) of the optical imaging system varies between different spatial locations, thus leading to a spatially varying blur. This problem arises, for example, in synthetic aperture instruments and in wide-field optical systems. Unlike the classical deconvolution context where the PSF is assumed to be spatially invariant, the problem cannot be easily solved in the Fourier domain. We propose here an iterative algorithm based on convex optimization techniques and a wavelet frame regularization. This approach allows restoration of the image, taking into account the properties of the blur operator, the latter being known.

  10. STRONG GRAVITATIONAL LENS MODELING WITH SPATIALLY VARIANT POINT-SPREAD FUNCTIONS

    SciTech Connect

    Rogers, Adam; Fiege, Jason D.

    2011-12-10

    Astronomical instruments generally possess spatially variant point-spread functions, which determine the amount by which an image pixel is blurred as a function of position. Several techniques have been devised to handle this variability in the context of the standard image deconvolution problem. We have developed an iterative gravitational lens modeling code called Mirage that determines the parameters of pixelated source intensity distributions for a given lens model. We are able to include the effects of spatially variant point-spread functions using the iterative procedures in this lensing code. In this paper, we discuss the methods to include spatially variant blurring effects and test the results of the algorithm in the context of gravitational lens modeling problems.

  11. Spatial spreading model and dynamics of West Nile virus in birds and mosquitoes with free boundary.

    PubMed

    Lin, Zhigui; Zhu, Huaiping

    2017-04-04

    In this paper, a reaction-diffusion system is proposed to model the spatial spreading of West Nile virus in vector mosquitoes and host birds in North America. Transmission dynamics are based on a simplified model involving mosquitoes and birds, and the free boundary is introduced to model and explore the expanding front of the infected region. The spatial-temporal risk index [Formula: see text], which involves regional characteristic and time, is defined for the simplified reaction-diffusion model with the free boundary to compare with other related threshold values, including the usual basic reproduction number [Formula: see text]. Sufficient conditions for the virus to vanish or to spread are given. Our results suggest that the virus will be in a scenario of vanishing if [Formula: see text], and will spread to the whole region if [Formula: see text] for some [Formula: see text], while if [Formula: see text], the spreading or vanishing of the virus depends on the initial number of infected individuals, the area of the infected region, the diffusion rate and other factors. Moreover, some remarks on the basic reproduction numbers and the spreading speeds are presented and compared.

  12. Modeling the spatial spread of infectious diseases: the GLobal Epidemic and Mobility computational model

    PubMed Central

    Balcan, Duygu; Gonçalves, Bruno; Hu, Hao; Ramasco, José J.; Colizza, Vittoria

    2010-01-01

    Here we present the Global Epidemic and Mobility (GLEaM) model that integrates sociodemographic and population mobility data in a spatially structured stochastic disease approach to simulate the spread of epidemics at the worldwide scale. We discuss the flexible structure of the model that is open to the inclusion of different disease structures and local intervention policies. This makes GLEaM suitable for the computational modeling and anticipation of the spatio-temporal patterns of global epidemic spreading, the understanding of historical epidemics, the assessment of the role of human mobility in shaping global epidemics, and the analysis of mitigation and containment scenarios. PMID:21415939

  13. Heterogeneous length of stay of hosts’ movements and spatial epidemic spread

    PubMed Central

    Poletto, Chiara; Tizzoni, Michele; Colizza, Vittoria

    2012-01-01

    Infectious diseases outbreaks are often characterized by a spatial component induced by hosts’ distribution, mobility, and interactions. Spatial models that incorporate hosts’ movements are being used to describe these processes, to investigate the conditions for propagation, and to predict the spatial spread. Several assumptions are being considered to model hosts’ movements, ranging from permanent movements to daily commuting, where the time spent at destination is either infinite or assumes a homogeneous fixed value, respectively. Prompted by empirical evidence, here we introduce a general metapopulation approach to model the disease dynamics in a spatially structured population where the mobility process is characterized by a heterogeneous length of stay. We show that large fluctuations of the length of stay, as observed in reality, can have a significant impact on the threshold conditions for the global epidemic invasion, thus altering model predictions based on simple assumptions, and displaying important public health implications. PMID:22741060

  14. Heterogeneous length of stay of hosts’ movements and spatial epidemic spread

    NASA Astrophysics Data System (ADS)

    Poletto, Chiara; Tizzoni, Michele; Colizza, Vittoria

    2012-06-01

    Infectious diseases outbreaks are often characterized by a spatial component induced by hosts' distribution, mobility, and interactions. Spatial models that incorporate hosts' movements are being used to describe these processes, to investigate the conditions for propagation, and to predict the spatial spread. Several assumptions are being considered to model hosts' movements, ranging from permanent movements to daily commuting, where the time spent at destination is either infinite or assumes a homogeneous fixed value, respectively. Prompted by empirical evidence, here we introduce a general metapopulation approach to model the disease dynamics in a spatially structured population where the mobility process is characterized by a heterogeneous length of stay. We show that large fluctuations of the length of stay, as observed in reality, can have a significant impact on the threshold conditions for the global epidemic invasion, thus altering model predictions based on simple assumptions, and displaying important public health implications.

  15. Damage spreading in spatial and small-world random Boolean networks.

    PubMed

    Lu, Qiming; Teuscher, Christof

    2014-02-01

    The study of the response of complex dynamical social, biological, or technological networks to external perturbations has numerous applications. Random Boolean networks (RBNs) are commonly used as a simple generic model for certain dynamics of complex systems. Traditionally, RBNs are interconnected randomly and without considering any spatial extension and arrangement of the links and nodes. However, most real-world networks are spatially extended and arranged with regular, power-law, small-world, or other nonrandom connections. Here we explore the RBN network topology between extreme local connections, random small-world, and pure random networks, and study the damage spreading with small perturbations. We find that spatially local connections change the scaling of the Hamming distance at very low connectivities (K ≪ 1) and that the critical connectivity of stability K(s) changes compared to random networks. At higher K, this scaling remains unchanged. We also show that the Hamming distance of spatially local networks scales with a power law as the system size N increases, but with a different exponent for local and small-world networks. The scaling arguments for small-world networks are obtained with respect to the system sizes and strength of spatially local connections. We further investigate the wiring cost of the networks. From an engineering perspective, our new findings provide the key design trade-offs between damage spreading (robustness), the network's wiring cost, and the network's communication characteristics.

  16. Damage spreading in spatial and small-world random Boolean networks

    NASA Astrophysics Data System (ADS)

    Lu, Qiming; Teuscher, Christof

    2014-02-01

    The study of the response of complex dynamical social, biological, or technological networks to external perturbations has numerous applications. Random Boolean networks (RBNs) are commonly used as a simple generic model for certain dynamics of complex systems. Traditionally, RBNs are interconnected randomly and without considering any spatial extension and arrangement of the links and nodes. However, most real-world networks are spatially extended and arranged with regular, power-law, small-world, or other nonrandom connections. Here we explore the RBN network topology between extreme local connections, random small-world, and pure random networks, and study the damage spreading with small perturbations. We find that spatially local connections change the scaling of the Hamming distance at very low connectivities (K¯≪1) and that the critical connectivity of stability Ks changes compared to random networks. At higher K¯, this scaling remains unchanged. We also show that the Hamming distance of spatially local networks scales with a power law as the system size N increases, but with a different exponent for local and small-world networks. The scaling arguments for small-world networks are obtained with respect to the system sizes and strength of spatially local connections. We further investigate the wiring cost of the networks. From an engineering perspective, our new findings provide the key design trade-offs between damage spreading (robustness), the network's wiring cost, and the network's communication characteristics.

  17. Spatial spread of Eurasian beavers in river networks: a comparison of range expansion rates.

    PubMed

    Barták, Vojtěch; Vorel, Aleš; Símová, Petra; Puš, Vladimír

    2013-05-01

    1. Accurately measuring the rate of spread for expanding populations is important for reliably predicting their future spread, as well as for evaluating the effect of different conditions and management activities on that rate of spread. 2. Although a number of methods have been developed for such measurement, all these are designed only for one- or two-dimensional spread. Species dispersing along rivers, however, require specific methods due to the distinctly branching structure of river networks. 3. In this study, we analyse data regarding Eurasian beavers' modern recolonization of the Czech Republic. We developed a new methodology for quantifying spread of species dispersing along streams based on representation of the river network by means of a weighted graph. 4. We defined two different network-based spread rate measures, one estimating the rate of range expansion, with the range defined as the total length of occupied streams, and the second, named range diameter, quantifying the progress along one or several main streams. In addition, we estimated the population growth rates, and, dividing the population size by the range size, we measured the density of beaver records within their overall range. Using linear regression, we compared four beaver populations under different environmental conditions in terms of each of these measures. Finally, we discuss the differences between our method and the classical approaches. 5. Our method provided substantially higher spread rate values than did the classical methods. Both population growth and range expansion were found to follow logistic growth. In cases of there being no considerable barriers in dispersal routes, the rate of progress along main streams did not differ significantly among populations. In homogeneous environments, population densities remained relatively constant over time even though overall population sizes increased. This indicates that at large spatial scales, the population growth of beavers

  18. Damage Spreading in Spatial and Small-world Random Boolean Networks

    SciTech Connect

    Lu, Qiming; Teuscher, Christof

    2014-02-18

    The study of the response of complex dynamical social, biological, or technological networks to external perturbations has numerous applications. Random Boolean Networks (RBNs) are commonly used a simple generic model for certain dynamics of complex systems. Traditionally, RBNs are interconnected randomly and without considering any spatial extension and arrangement of the links and nodes. However, most real-world networks are spatially extended and arranged with regular, power-law, small-world, or other non-random connections. Here we explore the RBN network topology between extreme local connections, random small-world, and pure random networks, and study the damage spreading with small perturbations. We find that spatially local connections change the scaling of the relevant component at very low connectivities ($\\bar{K} \\ll 1$) and that the critical connectivity of stability $K_s$ changes compared to random networks. At higher $\\bar{K}$, this scaling remains unchanged. We also show that the relevant component of spatially local networks scales with a power-law as the system size N increases, but with a different exponent for local and small-world networks. The scaling behaviors are obtained by finite-size scaling. We further investigate the wiring cost of the networks. From an engineering perspective, our new findings provide the key design trade-offs between damage spreading (robustness), the network's wiring cost, and the network's communication characteristics.

  19. Damage spreading in spatial and small-world random boolean networks

    SciTech Connect

    Lu, Qiming; Teuscher, Christof

    2008-01-01

    Random Boolean Networks (RBNs) are often used as generic models for certain dynamics of complex systems, ranging from social networks, neural networks, to gene or protein interaction networks. Traditionally, RBNs are interconnected randomly and without considering any spatial arrangement of the links and nodes. However, most real-world networks are spatially extended and arranged with regular, small-world, or other non-random connections. Here we explore the RBN network topology between extreme local connections, random small-world, and random networks, and study the damage spreading with small perturbations. We find that spatially local connections change the scaling of the relevant component at very low connectivities ({bar K} << 1) and that the critical connectivity of stability K{sub s} changes compared to random networks. At higher {bar K}, this scaling remains unchanged. We also show that the relevant component of spatially local networks scales with a power-law as the system size N increases, but with a different exponent for local and small-world networks. The scaling behaviors are obtained by finite-size scaling. We further investigate the wiring cost of the networks. From an engineering perspective, our new findings provide the key trade-offs between damage spreading (robustness), the network wiring cost, and the network's communication characteristics.

  20. Temporal and spatial structure of a runaway electron beam in air at atmospheric pressure

    SciTech Connect

    Levko, D.; Krasik, Ya. E.; Tarasenko, V. F.; Rybka, D. V.; Burachenko, A. G.

    2013-05-21

    The time- and spatial structure of a runaway electron beam generated in air at atmospheric pressure by a high-voltage pulse with a rise time of {approx}300 ps is studied experimentally and numerically. It is obtained that the duration of the runaway electron current is a few tens of picoseconds, and it can consist of two or many peaks. It is shown that the many-peak temporal structure of the beam is caused by the non-simultaneous appearance of several emission centers on the cathode edge.

  1. Modeling the spatial dynamics of culture spreading in the presence of cultural strongholds

    NASA Astrophysics Data System (ADS)

    Lizana, Ludvig; Mitarai, Namiko; Sneppen, Kim; Nakanishi, Hiizu

    2011-06-01

    Cultural competition has throughout our history shaped and reshaped the geography of boundaries between humans. Language and culture are intimately connected and linguists often use distinctive keywords to quantify the dynamics of information spreading in societies harboring strong culture centers. One prominent example, which is addressed here, is Kyoto’s historical impact on Japanese culture. We construct a minimal model, based on shared properties of linguistic maps, to address the interplay between information flow and geography. We show that spreading of information over Japan in the premodern time can be described by an Eden growth process with noise levels corresponding to coherent spatial patches of sizes given by a single day’s walk (~15 km), and that new words appear in Kyoto at times comparable to the time between human generations (~30 yr).

  2. How is the effectiveness of immune surveillance impacted by the spatial distribution of spreading infections?

    PubMed Central

    Kadolsky, Ulrich D.; Yates, Andrew J.

    2015-01-01

    What effect does the spatial distribution of infected cells have on the efficiency of their removal by immune cells, such as cytotoxic T lymphocytes (CTL)? If infected cells spread in clusters, CTL may initially be slow to locate them but subsequently kill more rapidly than in diffuse infections. We address this question using stochastic, spatially explicit models of CTL interacting with different patterns of infection. Rather than the effector : target ratio, we show that the relevant quantity is the ratio of a CTL's expected time to locate its next target (search time) to the average time it spends conjugated with a target that it is killing (handling time). For inefficient (slow) CTL, when the search time is always limiting, the critical density of CTL (that required to control 50% of infections, C*) is independent of the spatial distribution and derives from simple mass-action kinetics. For more efficient CTL such that handling time becomes limiting, mass-action underestimates C*, and the more clustered an infection the greater is C*. If CTL migrate chemotactically towards targets the converse holds—C* falls, and clustered infections are controlled most efficiently. Real infections are likely to spread patchily; this combined with even weak chemotaxis means that sterilizing immunity may be achieved with substantially lower numbers of CTL than standard models predict. PMID:26150655

  3. Quantifying the Spatial Dimension of Dengue Virus Epidemic Spread within a Tropical Urban Environment

    PubMed Central

    Vazquez-Prokopec, Gonzalo M.; Kitron, Uriel; Montgomery, Brian; Horne, Peter; Ritchie, Scott A.

    2010-01-01

    Background Dengue infection spread in naive populations occurs in an explosive and widespread fashion primarily due to the absence of population herd immunity, the population dynamics and dispersal of Ae. aegypti, and the movement of individuals within the urban space. Knowledge on the relative contribution of such factors to the spatial dimension of dengue virus spread has been limited. In the present study we analyzed the spatio-temporal pattern of a large dengue virus-2 (DENV-2) outbreak that affected the Australian city of Cairns (north Queensland) in 2003, quantified the relationship between dengue transmission and distance to the epidemic's index case (IC), evaluated the effects of indoor residual spraying (IRS) on the odds of dengue infection, and generated recommendations for city-wide dengue surveillance and control. Methods and Findings We retrospectively analyzed data from 383 DENV-2 confirmed cases and 1,163 IRS applications performed during the 25-week epidemic period. Spatial (local k-function, angular wavelets) and space-time (Knox test) analyses quantified the intensity and directionality of clustering of dengue cases, whereas a semi-parametric Bayesian space-time regression assessed the impact of IRS and spatial autocorrelation in the odds of weekly dengue infection. About 63% of the cases clustered up to 800 m around the IC's house. Most cases were distributed in the NW-SE axis as a consequence of the spatial arrangement of blocks within the city and, possibly, the prevailing winds. Space-time analysis showed that DENV-2 infection spread rapidly, generating 18 clusters (comprising 65% of all cases), and that these clusters varied in extent as a function of their distance to the IC's residence. IRS applications had a significant protective effect in the further occurrence of dengue cases, but only when they reached coverage of 60% or more of the neighboring premises of a house. Conclusion By applying sound statistical analysis to a very detailed

  4. Lattice Three-Species Models of the Spatial Spread of Rabies among FOXES

    NASA Astrophysics Data System (ADS)

    Benyoussef, A.; Boccara, N.; Chakib, H.; Ez-Zahraouy, H.

    Lattice models describing the spatial spread of rabies among foxes are studied. In these models, the fox population is divided into three-species: susceptible (S), infected or incubating (I), and infectious or rabid (R). They are based on the fact that susceptible and incubating foxes are territorial while rabid foxes have lost their sense of direction and move erratically. Two different models are investigated: a one-dimensional coupled-map lattice model, and a two-dimensional automata network model. Both models take into account the short-range character of the infection process and the diffusive motion of rabid foxes. Numerical simulations show how the spatial distribution of rabies, and the speed of propagation of the epizootic front depend upon the carrying capacity of the environment and diffusion of rabid foxes out of their territory.

  5. Seasonal and spatial heterogeneities in host and vector abundances impact the spatiotemporal spread of bluetongue.

    PubMed

    Charron, Maud V P; Kluiters, Georgette; Langlais, Michel; Seegers, Henri; Baylis, Matthew; Ezanno, Pauline

    2013-06-19

    Bluetongue (BT) can cause severe livestock losses and large direct and indirect costs for farmers. To propose targeted control strategies as alternative to massive vaccination, there is a need to better understand how BT virus spread in space and time according to local characteristics of host and vector populations. Our objective was to assess, using a modelling approach, how spatiotemporal heterogeneities in abundance and distribution of hosts and vectors impact the occurrence and amplitude of local and regional BT epidemics. We built a reaction-diffusion model accounting for the seasonality in vector abundance and the active dispersal of vectors. Because of the scale chosen, and movement restrictions imposed during epidemics, host movements and wind-induced passive vector movements were neglected. Four levels of complexity were addressed using a theoretical approach, from a homogeneous to a heterogeneous environment in abundance and distribution of hosts and vectors. These scenarios were illustrated using data on abundance and distribution of hosts and vectors in a real geographical area. We have shown that local epidemics can occur earlier and be larger in scale far from the primary case rather than close to it. Moreover, spatial heterogeneities in hosts and vectors delay the epidemic peak and decrease the infection prevalence. The results obtained on a real area confirmed those obtained on a theoretical domain. Although developed to represent BTV spatiotemporal spread, our model can be used to study other vector-borne diseases of animals with a local to regional spread by vector diffusion.

  6. Punish, but not too hard: how costly punishment spreads in the spatial public goods game

    NASA Astrophysics Data System (ADS)

    Helbing, Dirk; Szolnoki, Attila; Perc, Matjaž; Szabó, György

    2010-08-01

    We study the evolution of cooperation in spatial public goods games where, besides the classical strategies of cooperation (C) and defection (D), we consider punishing cooperators (PC) or punishing defectors (PD) as an additional strategy. Using a minimalist modeling approach, our goal is to separately clarify and identify the consequences of the two punishing strategies. Since punishment is costly, punishing strategies lose the evolutionary competition in case of well-mixed interactions. When spatial interactions are taken into account, however, the outcome can be strikingly different, and cooperation may spread. The underlying mechanism depends on the character of the punishment strategy. In the case of cooperating punishers, increasing the fine results in a rising cooperation level. In contrast, in the presence of the PD strategy, the phase diagram exhibits a reentrant transition as the fine is increased. Accordingly, the level of cooperation shows a non-monotonous dependence on the fine. Remarkably, punishing strategies can spread in both cases, but based on largely different mechanisms, which depend on the cooperativeness (or not) of punishers.

  7. Spread of plague among black-tailed prairie dogs is associated with colony spatial characteristics

    USGS Publications Warehouse

    Johnson, T.L.; Cully, J.F.; Collinge, S.K.; Ray, C.; Frey, C.M.; Sandercock, B.K.

    2011-01-01

    Sylvatic plague (Yersinia pestis) is an exotic pathogen that is highly virulent in black-tailed prairie dogs (Cynomys ludovicianus) and causes widespread colony losses and individual mortality rates >95%. We investigated colony spatial characteristics that may influence inter-colony transmission of plague at 3 prairie dog colony complexes in the Great Plains. The 4 spatial characteristics we considered include: colony size, Euclidean distance to nearest neighboring colony, colony proximity index, and distance to nearest drainage (dispersal) corridor. We used multi-state mark-recapture models to determine the relationship between these colony characteristics and probability of plague transmission among prairie dog colonies. Annual mapping of colonies and mark-recapture analyses of disease dynamics in natural colonies led to 4 main results: 1) plague outbreaks exhibited high spatial and temporal variation, 2) the site of initiation of epizootic plague may have substantially influenced the subsequent inter-colony spread of plague, 3) the long-term effect of plague on individual colonies differed among sites because of how individuals and colonies were distributed, and 4) colony spatial characteristics were related to the probability of infection at all sites although the relative importance and direction of relationships varied among sites. Our findings suggest that conventional prairie dog conservation management strategies, including promoting large, highly connected colonies, may need to be altered in the presence of plague. ?? 2011 The Wildlife Society.

  8. Local introduction and heterogeneous spatial spread of dengue-suppressing Wolbachia through an urban population of Aedes aegypti.

    PubMed

    Schmidt, Tom L; Barton, Nicholas H; Rašić, Gordana; Turley, Andrew P; Montgomery, Brian L; Iturbe-Ormaetxe, Inaki; Cook, Peter E; Ryan, Peter A; Ritchie, Scott A; Hoffmann, Ary A; O'Neill, Scott L; Turelli, Michael

    2017-05-01

    Dengue-suppressing Wolbachia strains are promising tools for arbovirus control, particularly as they have the potential to self-spread following local introductions. To test this, we followed the frequency of the transinfected Wolbachia strain wMel through Ae. aegypti in Cairns, Australia, following releases at 3 nonisolated locations within the city in early 2013. Spatial spread was analysed graphically using interpolation and by fitting a statistical model describing the position and width of the wave. For the larger 2 of the 3 releases (covering 0.97 km2 and 0.52 km2), we observed slow but steady spatial spread, at about 100-200 m per year, roughly consistent with theoretical predictions. In contrast, the smallest release (0.11 km2) produced erratic temporal and spatial dynamics, with little evidence of spread after 2 years. This is consistent with the prediction concerning fitness-decreasing Wolbachia transinfections that a minimum release area is needed to achieve stable local establishment and spread in continuous habitats. Our graphical and likelihood analyses produced broadly consistent estimates of wave speed and wave width. Spread at all sites was spatially heterogeneous, suggesting that environmental heterogeneity will affect large-scale Wolbachia transformations of urban mosquito populations. The persistence and spread of Wolbachia in release areas meeting minimum area requirements indicates the promise of successful large-scale population transformation.

  9. Estimating wildland fire rate of spread in a spatially nonuniform environment

    Treesearch

    Francis M Fujioka

    1985-01-01

    Estimating rate of fire spread is a key element in planning for effective fire control. Land managers use the Rothermel spread model, but the model assumptions are violated when fuel, weather, and topography are nonuniform. This paper compares three averaging techniques--arithmetic mean of spread rates, spread based on mean fuel conditions, and harmonic mean of spread...

  10. A determination of character and frequency changes in air masses using a spatial synoptic classification

    NASA Astrophysics Data System (ADS)

    Kalkstein, Laurence S.; Sheridan, Scott C.; Graybeal, Daniel Y.

    1998-09-01

    Of the numerous climate change studies which have been performed, few of these have analyzed recent trends using an air mass-based approach. The air mass approach is superior to simple trend analysis, as it can identify patterns which may be too subtle to influence the entire climate record. The recently-developed spatial synoptic classification (SSC) is thus used to identify trends over the contiguous United States for summer and winter seasons from 1948 to 1993. Both trends in air mass frequency and character have been assessed.The most noteworthy trend in frequency is a decline in air mass transitional days (TR) during both seasons. In winter, decreases of up to 1% per decade are noted in parts of the central U.S. Other notable trends include a decrease in moist tropical (MT) air in winter, and an increase in MT in summer over the southeastern states.Numerous national and local air mass character changes have been uncovered. A large overall upward trend in cloudiness is noted in summer. All air masses feature an overnight increase, yet afternoon cloudiness increases are generally limited to the three dry air masses. Also in summer, a significant warming and increase in dew point of MT air has occurred at many locales. The most profound winter trend is a large decrease in dew point (up to 1.5°C per decade) in the dry polar (DP) air mass over much of the eastern states.

  11. Spatial spread of dengue in a non-endemic tropical city in northern Argentina.

    PubMed

    Gil, José F; Palacios, Maximiliano; Krolewiecki, Alejandro J; Cortada, Pedro; Flores, Rosana; Jaime, Cesar; Arias, Luis; Villalpando, Carlos; Alberti DÁmato, Anahí M; Nasser, Julio R; Aparicio, Juan P

    2016-06-01

    After more than eighty years dengue reemerged in Argentina in 1997. Since then, the largest epidemic in terms of geographical extent, magnitude and mortality, was recorded in 2009. In this report we analyzed the DEN-1 epidemic spread in Orán, a mid-size city in a non-endemic tropical area in Northern Argentina, and its correlation with demographic and socioeconomic factors. Cases were diagnosed by ELISA between January and June 2009. We applied a space-time and spatial scan statistic under a Poisson model. Possible association between dengue incidence and socio-economic variables was studied with the Spearman correlation test. The epidemic started from an imported case from Bolivia and space-time analysis detected two clusters: one on February and other in April (in the south and the northeast of the city respectively) with risk ratios of 25.24 and 4.07 (p<0.01). Subsequent cases spread widely around the city without significant space-temporal clustering. Maximum values of the entomological indices were observed in January, at the beginning of the epidemic (B=21.96; LH=8.39). No statistically significant association between socioeconomic variables and dengue incidence was found but positive correlation between population size and the number of cases (p<0.05) was detected. Two mechanisms may explain the observed pattern of epidemic spread in this non-endemic tropical city: a) Short range dispersal of mosquitoes and people generates clusters of cases and b) long-distance (within the city) human movement contributes to a quasi-random distribution of cases.

  12. Human mobility and time spent at destination: impact on spatial epidemic spreading.

    PubMed

    Poletto, Chiara; Tizzoni, Michele; Colizza, Vittoria

    2013-12-07

    Host mobility plays a fundamental role in the spatial spread of infectious diseases. Previous theoretical works based on the integration of network theory into the metapopulation framework have shown that the heterogeneities that characterize real mobility networks favor the propagation of epidemics. Nevertheless, the studies conducted so far assumed the mobility process to be either Markovian (in which the memory of the origin of each traveler is lost) or non-Markovian with a fixed traveling time scale (in which individuals travel to a destination and come back at a constant rate). Available statistics however show that the time spent by travelers at destination is characterized by wide fluctuations, ranging from a single day up to several months. Such varying length of stay crucially affects the chance and duration of mixing events among hosts and may therefore have a strong impact on the spread of an emerging disease. Here, we present an analytical and a computational study of epidemic processes on a complex subpopulation network where travelers have memory of their origin and spend a heterogeneously distributed time interval at their destination. Through analytical calculations and numerical simulations we show that the heterogeneity of the length of stay alters the expression of the threshold between local outbreak and global invasion, and, moreover, it changes the epidemic behavior of the system in case of a global outbreak. Additionally, our theoretical framework allows us to study the effect of changes in the traveling behavior in response to the infection, by considering a scenario in which sick individuals do not leave their home location. Finally, we compare the results of our non-Markovian framework with those obtained with a classic Markovian approach and find relevant differences between the two, in the estimate of the epidemic invasion potential, as well as of the timing and the pattern of its spatial spread. These results highlight the importance of

  13. Vertical Moist Thermodynamic Structure and Spatial-Temporal Evolution of the MJO in AIRS Observations

    NASA Technical Reports Server (NTRS)

    Tian, Baijun; Waliser, Duane E.; Fetzer, Eric J.; Lambrigtsen, Bjorn H.; Yung, Yuk L.; Wang, Bin

    2006-01-01

    The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit on the NASA Aqua mission, in combination with the precipitation from the Tropical Rainfall Measuring Mission (TRMM), are employed to study the vertical moist thermodynamic structure and spatial-temporal evolution of the Madden-Julian oscillation (MJO). The AIRS data indicate that, in the Indian Ocean and western Pacific, the temperature anomaly exhibits a trimodal vertical structure: a warm (cold) anomaly in the free troposphere (800-250 hPa) and a cold (warm) anomaly near the tropopause (above 250 hPa) and in the lower troposphere (below 800 hPa) associated with enhanced (suppressed) convection. The AIRS moisture anomaly also shows markedly different vertical structures as a function of longitude and the strength of convection anomaly. Most significantly, the AIRS data demonstrate that, over the Indian Ocean and western Pacific, the enhanced (suppressed) convection is generally preceded in both time and space by a low-level warm and moist (cold and dry) anomaly and followed by a low-level cold and dry (warm and moist) anomaly. The MJO vertical moist thermodynamic structure from the AIRS data is in general agreement, particularly in the free troposphere, with previous studies based on global reanalysis and limited radiosonde data. However, major differences in the lower-troposphere moisture and temperature structure between the AIRS observations and the NCEP reanalysis are found over the Indian and Pacific Oceans, where there are very few conventional data to constrain the reanalysis. Specifically, the anomalous lower-troposphere temperature structure is much less well defined in NCEP than in AIRS for the western Pacific, and even has the opposite sign anomalies compared to AIRS relative to the wet/dry phase of the MJO in the Indian Ocean. Moreover, there are well-defined eastward-tilting variations of moisture with height in AIRS over the

  14. Vertical Moist Thermodynamic Structure and Spatial-Temporal Evolution of the MJO in AIRS Observations

    NASA Technical Reports Server (NTRS)

    Tian, Baijun; Waliser, Duane E.; Fetzer, Eric J.; Lambrigtsen, Bjorn H.; Yung, Yuk L.; Wang, Bin

    2006-01-01

    The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit on the NASA Aqua mission, in combination with the precipitation from the Tropical Rainfall Measuring Mission (TRMM), are employed to study the vertical moist thermodynamic structure and spatial-temporal evolution of the Madden-Julian oscillation (MJO). The AIRS data indicate that, in the Indian Ocean and western Pacific, the temperature anomaly exhibits a trimodal vertical structure: a warm (cold) anomaly in the free troposphere (800-250 hPa) and a cold (warm) anomaly near the tropopause (above 250 hPa) and in the lower troposphere (below 800 hPa) associated with enhanced (suppressed) convection. The AIRS moisture anomaly also shows markedly different vertical structures as a function of longitude and the strength of convection anomaly. Most significantly, the AIRS data demonstrate that, over the Indian Ocean and western Pacific, the enhanced (suppressed) convection is generally preceded in both time and space by a low-level warm and moist (cold and dry) anomaly and followed by a low-level cold and dry (warm and moist) anomaly. The MJO vertical moist thermodynamic structure from the AIRS data is in general agreement, particularly in the free troposphere, with previous studies based on global reanalysis and limited radiosonde data. However, major differences in the lower-troposphere moisture and temperature structure between the AIRS observations and the NCEP reanalysis are found over the Indian and Pacific Oceans, where there are very few conventional data to constrain the reanalysis. Specifically, the anomalous lower-troposphere temperature structure is much less well defined in NCEP than in AIRS for the western Pacific, and even has the opposite sign anomalies compared to AIRS relative to the wet/dry phase of the MJO in the Indian Ocean. Moreover, there are well-defined eastward-tilting variations of moisture with height in AIRS over the

  15. Potential for preventing spread of fungi in air-conditioning systems constructed using copper instead of aluminium.

    PubMed

    Weaver, L; Michels, H T; Keevil, C W

    2010-01-01

    As copper has been previously suggested as an antimicrobial surface, we tested the effectiveness of copper as an antifungal surface which could be used in air-conditioning systems as an alternative to aluminium. Coupons of copper (C11000) and aluminium were inoculated with fungal isolates (Aspergillus spp., Fusarium spp., Penicillium chrysogenum and Candida albicans) for various time periods. Culture on potato dextrose agar and an in situ viability assay using the fluorochrome FUN-1 were used to determine whether spores had survived. The results showed increased die off of fungal isolates tested compared to aluminium. In addition, copper also prevented the germination of spores present, thereby reducing the risk of the release of spores. Copper offered an antifungal surface and prevented subsequent germination of spores present. FUN-1 demonstrated that fungal spores entered into a viable but not culturable (VBNC) state on copper indicating the importance of using such methods when assessing the effect of an antifungal as culture alone may give false results. Copper offers a valuable alternative to aluminium which could be used in air-conditioning systems in buildings, particularly in hospital environments where patients are more susceptible to fungal infections.

  16. Solute Spreading in Variably Saturated, Spatially Heterogeneous Formations: The Role of Water Saturation and Soil Texture

    NASA Astrophysics Data System (ADS)

    Russo, David

    2017-04-01

    Solute spreading provoked by the spatial heterogeneity in the soil hydraulic properties, and expressed in terms of the macrodispersion tensor, D, plays an important role in solute transport on the field scale. Under variably saturated flow conditions, quantification of D is rather complicated inasmuch as the relevant flow parameters, which depend on the formation properties, depend also on flow-controlled attributes in a highly nonlinear fashion, which, in turn, depends on the soil texture of the formation. The situation may be further complicated when the formation contains inclusions of different soil material and its hydraulic properties follow a bimodal distribution. The present talk focuses on the quantification of D in bimodal, heterogeneous, variably saturated formations, viewed as mixtures of two populations (background soil and embedded soil) of differing spatial structures. Two distinct cases are considered; in the first case, the texture of the embedded soil is finer than that of the background soil, while the second case conists of the reverse situation. First-order, Lagrangian stochastic analyses of vadose zone transport were used to invesigate the combined effect of the texture of the embedded soil and the mean pressure head on solute spreading in these formations. Results of the first-order analysis suggest that the embedded soil material may act as a capture zone for the solute particles, and, consequently, may enhance solute spreading in a manner which depends on both the texture of the embedded soil and the mean pressure head. In the first case, when the formation is relatively wet, the capture zone stems from the fine-textured embedded soil. In the second case, when the formation is relatively dry, the capture zone stems from coarse-textured embedded soil associated with very low unsaturated conductivity, which, in turn, may divert the flow into preferential flow paths around the coarse-texture, soil inclusions. Important finding of the first

  17. Retinal Image Denoising via Bilateral Filter with a Spatial Kernel of Optimally Oriented Line Spread Function

    PubMed Central

    He, Yunlong; Zhao, Yanna; Ren, Yanju; Gee, James

    2017-01-01

    Filtering belongs to the most fundamental operations of retinal image processing and for which the value of the filtered image at a given location is a function of the values in a local window centered at this location. However, preserving thin retinal vessels during the filtering process is challenging due to vessels' small area and weak contrast compared to background, caused by the limited resolution of imaging and less blood flow in the vessel. In this paper, we present a novel retinal image denoising approach which is able to preserve the details of retinal vessels while effectively eliminating image noise. Specifically, our approach is carried out by determining an optimal spatial kernel for the bilateral filter, which is represented by a line spread function with an orientation and scale adjusted adaptively to the local vessel structure. Moreover, this approach can also be served as a preprocessing tool for improving the accuracy of the vessel detection technique. Experimental results show the superiority of our approach over state-of-the-art image denoising techniques such as the bilateral filter. PMID:28261320

  18. Densely mapping the phase diagram of cuprate superconductors using a spatial composition spread approach

    NASA Astrophysics Data System (ADS)

    Saadat, Mehran; George, A. E.; Hewitt, Kevin C.

    2010-12-01

    A novel spatial composition spread approach was used successfully to deposit a 52-member library of La2-xSrxCuO4 (0 ⩽ x ⩽ 0.18) using magnetron sputtering combined with physical masking techniques. Two homemade targets of La2CuO4 and La1.82Sr0.18CuO4 were sputtered at a power of 41 W RF and 42 W DC, respectively, in a process gas of 15 mTorr argon. The libraries were sputtered onto LaSrAlO4 (0 0 1), SrTiO3 (1 0 0) and MgO (1 0 0) substrates through a 52-slot shadow mask for which a -20 V substrate bias was applied to prevent resputtering. The resulting amorphous films were post-annealed (800 °C for 1 h then at 950 °C for 2 h) in a tube sealed with oxygen gas. Wavelength Dispersive Spectroscopy (WDS) analysis revealed the expected linear variation of Sr content from 0 to 0.18 with an approximate change of 0.003 per library member. Transport measurements revealed superconducting transitions as well as changes in the quasiparticle scattering rate. These transitions and scattering rate changes were mapped to produce the T-hole concentration phase diagram.

  19. Retinal Image Denoising via Bilateral Filter with a Spatial Kernel of Optimally Oriented Line Spread Function.

    PubMed

    He, Yunlong; Zheng, Yuanjie; Zhao, Yanna; Ren, Yanju; Lian, Jian; Gee, James

    2017-01-01

    Filtering belongs to the most fundamental operations of retinal image processing and for which the value of the filtered image at a given location is a function of the values in a local window centered at this location. However, preserving thin retinal vessels during the filtering process is challenging due to vessels' small area and weak contrast compared to background, caused by the limited resolution of imaging and less blood flow in the vessel. In this paper, we present a novel retinal image denoising approach which is able to preserve the details of retinal vessels while effectively eliminating image noise. Specifically, our approach is carried out by determining an optimal spatial kernel for the bilateral filter, which is represented by a line spread function with an orientation and scale adjusted adaptively to the local vessel structure. Moreover, this approach can also be served as a preprocessing tool for improving the accuracy of the vessel detection technique. Experimental results show the superiority of our approach over state-of-the-art image denoising techniques such as the bilateral filter.

  20. Using mobile phone data to predict the spatial spread of cholera.

    PubMed

    Bengtsson, Linus; Gaudart, Jean; Lu, Xin; Moore, Sandra; Wetter, Erik; Sallah, Kankoe; Rebaudet, Stanislas; Piarroux, Renaud

    2015-03-09

    Effective response to infectious disease epidemics requires focused control measures in areas predicted to be at high risk of new outbreaks. We aimed to test whether mobile operator data could predict the early spatial evolution of the 2010 Haiti cholera epidemic. Daily case data were analysed for 78 study areas from October 16 to December 16, 2010. Movements of 2.9 million anonymous mobile phone SIM cards were used to create a national mobility network. Two gravity models of population mobility were implemented for comparison. Both were optimized based on the complete retrospective epidemic data, available only after the end of the epidemic spread. Risk of an area experiencing an outbreak within seven days showed strong dose-response relationship with the mobile phone-based infectious pressure estimates. The mobile phone-based model performed better (AUC 0.79) than the retrospectively optimized gravity models (AUC 0.66 and 0.74, respectively). Infectious pressure at outbreak onset was significantly correlated with reported cholera cases during the first ten days of the epidemic (p < 0.05). Mobile operator data is a highly promising data source for improving preparedness and response efforts during cholera outbreaks. Findings may be particularly important for containment efforts of emerging infectious diseases, including high-mortality influenza strains.

  1. Using Mobile Phone Data to Predict the Spatial Spread of Cholera

    PubMed Central

    Bengtsson, Linus; Gaudart, Jean; Lu, Xin; Moore, Sandra; Wetter, Erik; Sallah, Kankoe; Rebaudet, Stanislas; Piarroux, Renaud

    2015-01-01

    Effective response to infectious disease epidemics requires focused control measures in areas predicted to be at high risk of new outbreaks. We aimed to test whether mobile operator data could predict the early spatial evolution of the 2010 Haiti cholera epidemic. Daily case data were analysed for 78 study areas from October 16 to December 16, 2010. Movements of 2.9 million anonymous mobile phone SIM cards were used to create a national mobility network. Two gravity models of population mobility were implemented for comparison. Both were optimized based on the complete retrospective epidemic data, available only after the end of the epidemic spread. Risk of an area experiencing an outbreak within seven days showed strong dose-response relationship with the mobile phone-based infectious pressure estimates. The mobile phone-based model performed better (AUC 0.79) than the retrospectively optimized gravity models (AUC 0.66 and 0.74, respectively). Infectious pressure at outbreak onset was significantly correlated with reported cholera cases during the first ten days of the epidemic (p < 0.05). Mobile operator data is a highly promising data source for improving preparedness and response efforts during cholera outbreaks. Findings may be particularly important for containment efforts of emerging infectious diseases, including high-mortality influenza strains. PMID:25747871

  2. Definition of spatial patterns of bark beetle Ips typographus (L.) outbreak spreading in Tatra Mountains (Central Europe), using GIS

    Treesearch

    Rastislav Jakus; Wojciech Grodzki; Marek Jezik; Marcin Jachym

    2003-01-01

    The spread of bark beetle outbreaks in the Tatra Mountains was explored by using both terrestrial and remote sensing techniques. Both approaches have proven to be useful for studying spatial patterns of bark beetle population dynamics. The terrestrial methods were applied on existing forestry databases. Vegetation change analysis (image differentiation), digital...

  3. A spatial analysis of Phytophthora ramorum symptom spread using second-order point pattern and GIS-based analyses

    Treesearch

    Mark Spencer; Kevin O' Hara

    2006-01-01

    Phytophthora ramorum is a major source of tanoak (Lithocarpus densiflorus) mortality in the tanoak/redwood (Sequoia sempervirens) forests of central California. This study presents a spatial analysis of the spread of the disease using second-order point pattern and GIS analyses. Our data set includes four plots...

  4. Geostatistical analysis of spatial virus spread overtime provides new insights into the environmental safety of commercial virus-resistant squash

    USDA-ARS?s Scientific Manuscript database

    This is a review of a journal article published in 2006. The spatial and temporal patterns of aphid-vectored spread of Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV) were monitored over two consecutive years in plantings of nontransgenic and transgenic squash ZW-20H (commerci...

  5. Vector-borne pathogen spread through ticks on migratory birds: a probabilistic spatial risk model for South-Western europe.

    PubMed

    Bosch, J; Muñoz, M J; Martínez, M; de la Torre, A; Estrada-Peña, A

    2013-10-01

    Tick-borne pathogens can spread easily through the movements of infested birds. An important example is viruses that pose a threat to humans and that are carried in Hyalomma ticks that move from Africa into south-western Europe. This study evaluates the probability of arrival of migrating birds from Africa into Spain and the environmental suitability of different regions of Spain for the survival of tick stages introduced by these birds. This evaluation produced a spatial risk index measuring the probability that foreign tick populations will survive in the target area. Periods of highest risk were observed for large areas of Spain, from the second fortnight of April to the second fortnight of May. Although birds may arrive as early as January and massive migrations may take place in March, the environmental suitability for Hyalomma marginatum ticks is low in these periods and high mortality of the spread stages (nymphs) is expected. This study introduces new methods of objective analysis based on spatial and process-driven models for both ticks and hosts and critically evaluates the usefulness of spatial spreading methods for assessing the risk of tick-borne pathogens.

  6. The influence of photon depth of interaction and non-collinear spread of annihilation photons on PET image spatial resolution.

    PubMed

    Sánchez-Crespo, Alejandro; Larsson, Stig A

    2006-08-01

    The quality of PET imaging is impaired by parallax errors. These errors produce misalignment between the projected location of the true origin of the annihilation event and the line of response determined by the coincidence detection system. Parallax errors are due to the varying depths of photon interaction (DOI) within the scintillator and the non-collinear (NC) emission of the annihilation photons. The aim of this work was to address the problems associated with the DOI and the NC spread of annihilation photons and to develop a quantitative model to assess their impact on image spatial resolution losses for various commonly used scintillators and PET geometries. A theoretical model based on Monte Carlo simulations was developed to assess the relative influence of DOI and the NC spread of annihilation photons on PET spatial resolution for various scintillator materials (BGO, LSO, LuAP, GSO, NaI) and PET geometries. The results demonstrate good agreement between simulated, experimental and published overall spatial resolution for some commercial systems, with maximum differences around 1 mm in both 2D and 3D mode. The DOI introduces an impairment of non-stationary spatial resolution along the radial direction, which can be very severe at peripheral positions. As an example, the radial spatial resolution loss due to DOI increased from 1.3 mm at the centre to 6.7 mm at 20 cm from the centre of a BGO camera with a 412-mm radius in 2D mode. Including the NC, the corresponding losses were 3.0 mm at the centre and 7.3 mm 20 cm from the centre. Without a DOI detection technique, it seems difficult to improve PET spatial resolution and increase sensitivity by reducing the detector ring radius or by extending the detector in the axial direction. Much effort is expended on the design and configuration of smaller detector elements but more effort should be devoted to the DOI complexity.

  7. Spatial spread of an epidemic through public transportation systems with a hub.

    PubMed

    Xu, Fei; Connell McCluskey, C; Cressman, Ross

    2013-11-01

    This article investigates an epidemic spreading among several locations through a transportation system, with a hub connecting these locations. Public transportation is not only a bridge through which infections travel from one location to another but also a place where infections occur since individuals are typically in close proximity to each other due to the limited space in these systems. A mathematical model is constructed to study the spread of an infectious disease through such systems. A variant of the next generation method is proposed and used to provide upper and lower bounds of the basic reproduction number for the model. Our investigation indicates that increasing transportation efficiency, and improving sanitation and ventilation of the public transportation system decrease the chance of an outbreak occurring. Moreover, discouraging unnecessary travel during an epidemic also decreases the chance of an outbreak. However, reducing travel by infectives while allowing susceptibles to travel may not be enough to avoid an outbreak.

  8. Spatial localization of nonlinear waves spreading in materials in the presence of dislocations and point defects

    NASA Astrophysics Data System (ADS)

    Erofeev, V. I.; Leontieva, A. V.; Malkhanov, A. O.

    2017-06-01

    Within the framework of self consistent dynamic problems, the impact of dislocations and point defects on the spatial localization of nonlinear acoustic waves propagating in materials has been studied.

  9. Peculiarities of the spatial focusing of a high-power femtosecond laser pulse in air

    SciTech Connect

    Geints, Yu E; Zemlyanov, A A

    2008-12-31

    The propagation of focused high-power femtosecond laser pulses in air is numerically simulated. The dependences of the effective average size of a focal spot and the maximum achievable radiation intensity in the focal beam waist on the peak power of incident radiation are studied. It is shown that in the regime of nonstationary self-action of radiation, due to photoionisation of the medium and formation of plasma, it becomes impossible to focus radiation into a spot of diffraction-limited size predicted by a linear theory. (nonlinear optical phenomena)

  10. Nonlinear equatorial spread F: spatially large bubbles resulting from large horizontal scale initial perturbations. Memorandum report

    SciTech Connect

    Zalesak, S.T.; Ossakow, S.L.

    1980-02-06

    Motivated by the observations of large horizontal scale length equatorial spread F 'bubbles', we have performed numerical simulations of the nonlinear evolution of the collisional Rayleigh-Taylor instability in the nighttime equatorial ionosphere, using large horizontal scale length initial perturbations. The calculations were performed using a new, improved numerical code which utilizes the recently developed, fully multidimensional flux-corrected transport (FCT) techniques. We find that large horizontal scale initial perturbations evolve nonlinearly into equally large horizontal scale spread F bubbles, on a time scale as fast as that of the corresponding small horizontal scale length perturbations previously used. Further, we find the level of plasma depletion inside the large scale bubbles to be appreciably higher than that of the smaller scale bubbles, approaching 100%, in substantial agreement with the observations. This level of depletion is due to the fact that the plasma comprising the large scale bubbles has its origin at much lower altitudes than that comprising the smaller scale bubbles. Analysis of the polarization electric fields produced by the vertically aligned ionospheric irregularities show this effect to be due to fringe fields similar in structure to those produced at the edge of a parallel plate capacitor.

  11. Spatial diagnostics of the laser-produced tin plasma in air

    NASA Astrophysics Data System (ADS)

    Iqbal, Javed; Ahmed, R.; Rafique, M.; Anwar-ul-Haq, M.; Baig, M. A.

    2016-07-01

    We present here new experimental studies on the laser-produced tin plasma generated by focusing the beam of a Q-switched Nd:YAG laser (532 nm) on the sample in air at atmospheric pressure. The optical emission spectra were recorded with a set of five spectrometers covering the spectral range from 200-720 nm. The electron temperature has been calculated to be about (10 600  ±  600) K using three methods; the two-line ratio, Boltzmann plot and the Saha-Boltzmann plot method, whereas the electron number density of about (9.0  ±  0.8)  ×  1016 cm-3 has been calculated using the Stark broadened line profiles of tin lines and the hydrogen Hα-line. Furthermore, the branching fractions have been deduced for 15 spectral lines of the 5p5d  →  5p2 transition array in tin, whereas the absolute values of the transition probabilities have been calculated by combining the experimental branching fractions with the lifetimes of the excited levels. Our measured values are compared with those reported in the literature and NIST data base, showing good agreement.

  12. Quantification of spatial distribution and spread of bacteria in soil at microscale

    NASA Astrophysics Data System (ADS)

    Juyal, Archana; Eickhorst, Thilo; Falconer, Ruth; Baveye, Philippe; Otten, Wilfred

    2015-04-01

    Soil bacteria play an essential role in functioning of ecosystems and maintaining of biogeochemical cycles. Soil is a complex heterogeneous environment comprising of highly variable and dynamic micro-habitats that have significant impacts on the growth and activity of resident microbiota including bacteria and fungi. Bacteria occupy a very small portion of available pore space in soil which demonstrates that their spatial arrangement in soil has a huge impact on the contact to their target and on the way they interact to carry out their functions. Due to limitation of techniques, there is scant information on spatial distribution of indigenous or introduced bacteria at microhabitat scale. There is a need to understand the interaction between soil structure and microorganisms including fungi for ecosystem-level processes such as carbon sequestration and improving the predictive models for soil management. In this work, a combination of techniques was used including X-ray CT to characterize the soil structure and in-situ detection via fluorescence microscopy to visualize and quantify bacteria in soil thin sections. Pseudomonas fluorescens bacteria were introduced in sterilized soil of aggregate size 1-2 mm and packed at bulk-densities 1.3 g cm-3 and 1.5 g cm-3. A subset of samples was fixed with paraformaldehyde and subsequently impregnated with resin. DAPI and fluorescence in situ hybridization (FISH) were used to visualize bacteria in thin sections of soil cores by epifluorescence microscopy to enumerate spatial distribution of bacteria in soil. The pore geometry of soil was quantified after X-ray microtomography scanning. The distribution of bacteria introduced locally reduced significantly (P

  13. Spatial and temporal spread of Citrus tristeza virus and its aphid vectors in the North western area of Morocco.

    PubMed

    Elhaddad, Abdesslam; ElAmrani, Amal; Fereres, Alberto; Moreno, Aranzazu

    2016-12-01

    First report of Citrus tristeza virus (CTV,Closterovirus) in Morocco datesback to 1961 in collections of citrus varieties. An exhaustive survey of citrus in the north of the country in 2009 revealed that CTV was spread all over the citrus production area. We attempted to evaluate the relative contribution of different aphid species in the spread of CTV disease in a Citrus reticulata orchard at the Loukkous region during 2 years (2012 and 2013). The overall CTV incidence estimated in the experimental site increased from 17.8% in 2012 to 31.15% in 2013. The most abundant aphid species colonising clementine trees was Aphis spiraecola and A. gossypii. Both aphid species reached their maximum peaks during the spring season. The rate of viruliferous aphids, estimated by real-time RT-PCR of single aphid, revealed that 35.4% of winged A. gossypii and 28.8% of winged A. spiraecola were viruliferous, confirming a high inoculum pressure in the area surrounding the experimental site. The aphid species Toxoptera citricida, which is able to transmit the aggressive isolates of CTV, was not found in the Loukkous region. The study of the spatial distribution of the CTV showed that in general, the disease was randomly distributed in the field. Overall, the results seem to indicate that A. spiraecola may be considered as the major aphid species contributing to CTV spread in our experimental conditions. The prevalence of mild strains in the region and the high level of aphid flight activity could explain the rapid evolution of CTV incidence in the experimental area. © 2015 Institute of Zoology, Chinese Academy of Sciences.

  14. Anticipating knowledge to inform species management: predicting spatially explicit habitat suitability of a colonial vulture spreading its range.

    PubMed

    Mateo-Tomás, Patricia; Olea, Pedro P

    2010-08-25

    The knowledge of both potential distribution and habitat suitability is fundamental in spreading species to inform in advance management and conservation planning. After a severe decline in the past decades, the griffon vulture (Gyps fulvus) is now spreading its breeding range towards the northwest in Spain and Europe. Because of its key ecological function, anticipated spatial knowledge is required to inform appropriately both vulture and ecosystem management. Here we used maximum entropy (Maxent) models to determine the habitat suitability of potential and current breeding distribution of the griffon vulture using presence-only data (N = 124 colonies) in north-western Spain. The most relevant ecological factors shaping this habitat suitability were also identified. The resulting model had a high predictive performance and was able to predict species' historical distribution. 7.5% (approximately 1,850 km(2)) of the study area resulted to be suitable breeding habitat, most of which (approximately 70%) is already occupied by the species. Cliff availability and livestock density, especially of sheep and goats, around 10 km of the colonies were the fundamental factors determining breeding habitat suitability for this species. Griffon vultures could still spread 50-60 km towards the west, increasing their breeding range in 1,782 km(2). According to our results, 7.22% of the area suitable for griffon vulture will be affected by wind farms, so our results could help to better plan wind farm locations. The approach here developed could be useful to inform management of reintroductions and recovery programmes currently being implemented for both the griffon vulture and other threatened vulture species.

  15. Anticipating Knowledge to Inform Species Management: Predicting Spatially Explicit Habitat Suitability of a Colonial Vulture Spreading Its Range

    PubMed Central

    Mateo-Tomás, Patricia; Olea, Pedro P.

    2010-01-01

    Background The knowledge of both potential distribution and habitat suitability is fundamental in spreading species to inform in advance management and conservation planning. After a severe decline in the past decades, the griffon vulture (Gyps fulvus) is now spreading its breeding range towards the northwest in Spain and Europe. Because of its key ecological function, anticipated spatial knowledge is required to inform appropriately both vulture and ecosystem management. Methodology/Findings Here we used maximum entropy (Maxent) models to determine the habitat suitability of potential and current breeding distribution of the griffon vulture using presence-only data (N = 124 colonies) in north-western Spain. The most relevant ecological factors shaping this habitat suitability were also identified. The resulting model had a high predictive performance and was able to predict species' historical distribution. 7.5% (∼1,850 km2) of the study area resulted to be suitable breeding habitat, most of which (∼70%) is already occupied by the species. Cliff availability and livestock density, especially of sheep and goats, around 10 km of the colonies were the fundamental factors determining breeding habitat suitability for this species. Conclusions/Significance Griffon vultures could still spread 50–60 km towards the west, increasing their breeding range in 1,782 km2. According to our results, 7.22% of the area suitable for griffon vulture will be affected by wind farms, so our results could help to better plan wind farm locations. The approach here developed could be useful to inform management of reintroductions and recovery programmes currently being implemented for both the griffon vulture and other threatened vulture species. PMID:20811501

  16. [Spatial and temporal spread predictability of influenza A H1N1 epidemic in Argentina by the percolation method].

    PubMed

    Cuestas, Eduardo; Vilaró, Mario; Serra, Pablo

    2011-01-01

    The influenza A H1N1 epidemic has spread rapidly worldwide on account of the current conditions of high interconnectivity and transport speed both among people and countries. The spatial spread of the epidemics can be explained by the percolation theory which allows to estimate a threshold beyond which the transmission of the infection among different geographic regions occurs. The aim of this study was to test the predictive ability of the percolation model of influenza A H1N1 epidemic in Argentina according to data gathered by the National Department of Public Health. In the model, the country was considered as a set of irregular, contiguous and continuous geometric figures, which can be represented in two dimensions on a plane. We analyzed the proportion of infected provinces at the moment of percolation in relation to time in days and compared observed and expected values by curvilinear equations in a logistic model. Percolation occurred on day 45. The expected value generated by the model was 42.4 days, 95 % CI 28.5 to 56.3. The difference between observed and expected values was p = 0.997. We conclude that the model has good fit and predictive capacity.

  17. Polycyclic aromatic hydrocarbons in air on small spatial and temporal scales - I. Levels and variabilities

    NASA Astrophysics Data System (ADS)

    Lammel, Gerhard; Klánová, Jana; Ilić, Predrag; Kohoutek, Jiří; Gasić, Bojan; Kovacić, Igor; Lakić, Nataša; Radić, Ranka

    2010-12-01

    Polycyclic aromatic hydrocarbons (PAHs) were measured together with inorganic air pollutants at two urban sites and one rural background site in the Banja Luka area, Bosnia and Hercegovina, during 72 h in July 2008 using a high time resolution (5 samples per day) with the aim to study the spatial and temporal variabilities and to explore the significance of averaging effects inherent to 24 h-sampling. Measurement uncertainty was quantified on basis of three independent side-by-side samplers, deployed at one of the sites. PAH abundances in the urban and rural environments differed largely. Levels at the urban sites exceeded the levels at the rural site by >100%. The discrepancy was largely dominated by emission of 3-4 ring PAHs in the city, while 5-6 ring PAHs were more evenly distributed between city sites and the hill site. During the night a higher fraction of the semivolatile PAHs might have been stored in the soil or sorbed to surfaces. PAH patterns were undistinguishable across the three sites. However, concentrations of more particle-associated substances differed significantly between the urban sites than between one of the urban sites and the rural site (3 σ uncertainty). Time-averaging (on a 24 h-basis) would have masked the significant inter-site differences of half of the substances which were found at different levels (on a 4 h-basis).

  18. Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations.

    PubMed

    James, P J; Moon, R D

    1999-03-15

    The spatial distribution of chewing lice (Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.

  19. Mechanistic models for the spatial spread of species under climate change.

    PubMed

    Leroux, Shawn J; Larrivée, Maxim; Boucher-Lalonde, Véronique; Hurford, Amy; Zuloaga, Juan; Kerr, Jeremy T; Lutscher, Frithjof

    2013-06-01

    Global climate change is a major threat to biodiversity. The most common methods for predicting the response of biodiversity to changing climate do not explicitly incorporate fundamental evolutionary and ecological processes that determine species responses to changing climate, such as reproduction, dispersal, and adaptation. We provide an overview of an emerging mechanistic spatial theory of species range shifts under climate change. This theoretical framework explicitly defines the ecological processes that contribute to species range shifts via biologically meaningful dispersal, reproductive, and climate envelope parameters. We present methods for estimating the parameters of the model with widely available species occurrence and abundance data and then apply these methods to empirical data for 12 North American butterfly species to illustrate the potential use of the theory for global change biology. The model predicts species persistence in light of current climate change and habitat loss. On average, we estimate that the climate envelopes of our study species are shifting north at a rate of 3.25 +/- 1.36 km/yr (mean +/- SD) and that our study species produce 3.46 +/- 1.39 (mean +/- SD) viable offspring per individual per year. Based on our parameter estimates, we are able to predict the relative risk of our 12 study species for lagging behind changing climate. This theoretical framework improves predictions of global change outcomes by facilitating the development and testing of hypotheses, providing mechanistic predictions of current and future range dynamics, and encouraging the adaptive integration of theory and data. The theory is ripe for future developments such as the incorporation of biotic interactions and evolution of adaptations to novel climatic conditions, and it has the potential to be a catalyst for the development of more effective conservation strategies to mitigate losses of biodiversity from global climate change.

  20. Galapagos hotspot-spreading center system: 1. Spatial petrological and geochemical variations (83/sup 0/W-101/sup 0/W)

    SciTech Connect

    Schilling, J.; Kingsley, R.H.; Devine, J.D.

    1982-07-10

    We report on the petrology and geochemistry of basalts dredged at 40--50 km intervals along the Galapagos Spreading Center, between 83/sup 0/W and 101/sup 0/W (40 stations). Emphasis is on spatial variations of 'whole rock' major elements, rare earths, trace metals of the first transition series, and the nature of phenocryst assemblages and their abundances. These results provide new constraints on the nature and scale of mantle source heterogeneities, melting conditions, thermal field, and dynamics of crustal formation of the region. We suggest that ridge segments outside the high magnetic amplitude zone are at a steady state as a result of passive seafloor spreading. Basalts from these segments are apparently derived from an asthenosphere relatively uniformally depleted in incompatible elements, which appears of worldwide extent. We reject Vogt and DeBoer's (1976) model invoking damming at fracture zones of subaxial asthenosphere flow of crystal slushes and increasing fractional crystallization down the flow line, because this model would not explain the gradients in REE observed about the Galapagos Platform. Our preferred model combines the mantle-plume binary mixing model of Schilling (1973) with the concept of recurring rift propagation proposed by Hey (1977a). We further propose that pulsating mantle plume flux, perhaps in the form of a chain of blobs, may initiate the development of new rifts and their propagation. The present position of the tips of such new propagating rifts locate the wave fronts of such pulsating mantle plume flow. A two million year period is suggested for the last 4 m.y. from Wilson and Hey's (1979) information Rigorous testing of our preferred model is possible.

  1. Spatial variability in hydrothermal systems in fast-spreading crust: evidence from tectonic windows exposed at Pito and Hess Deeps

    NASA Astrophysics Data System (ADS)

    Gillis, K. M.

    2008-12-01

    Tectonic windows of the oceanic crust provide views of the internal structure of mid-ocean ridge hydrothermal systems. Targeted exploration of escarpments that formed at the fast- to very fast-spreading East Pacific Rise exposed at Pito and Hess Deeps have allowed us to address questions that 1-D "pinpricks" afforded by ocean drilling cannot. Outcrop imaging along closely spaced submersible and ROV tracks document the geological context of hydrothermal alteration in 3-dimensions. These broad views reveal how and why the conditions and products of fluid-rock reaction were spatially and temporally variable. Alteration characteristics in the sheeted dike complexes at Pito and Hess Deeps are similar. The dikes are relatively fresh (average extent of alteration is 27%, ranging from 0 to >80%) and the background alteration is amphibole- dominated. At Hess Deep chlorite dominates within a few hundred metre wide zones, whereas at Pito Deep chlorite-rich dikes are sporadically distributed throughout. Mineral assemblages and compositions, and distributed Cu and Zn depletion, indicate that peak temperatures ranged from <300 to >400° C and did not vary systematically with depth. Vein systems are rare at Hess Deep, whereas amphibole and chlorite veins are ubiquitous and quartz-filled fractures are only locally present at Pito Deep. Regional variability in alteration characteristics is found on a scale of <1 to 2 km, illustrating the diversity of fluid-rock interaction that can be expected at fast-spreading ridges. Migration of circulating cells along ridges and local evolution of fluid compositions produce sections of the upper crust with a distinctive character of alteration, on time scales of <5-20 kyr. It is interesting to note that the time-integrated fluid fluxes, calculated from Sr-isotopic mass balance, are comparable between areas, despite the distinctive character of alteration.

  2. Partial volume correction of PET-imaged tumor heterogeneity using expectation maximization with a spatially varying point spread function

    PubMed Central

    Barbee, David L; Flynn, Ryan T; Holden, James E; Nickles, Robert J; Jeraj, Robert

    2010-01-01

    Tumor heterogeneities observed in positron emission tomography (PET) imaging are frequently compromised of partial volume effects which may affect treatment prognosis, assessment, or future implementations such as biologically optimized treatment planning (dose painting). This paper presents a method for partial volume correction of PET-imaged heterogeneous tumors. A point source was scanned on a GE Discover LS at positions of increasing radii from the scanner’s center to obtain the spatially varying point spread function (PSF). PSF images were fit in three dimensions to Gaussian distributions using least squares optimization. Continuous expressions were devised for each Gaussian width as a function of radial distance, allowing for generation of the system PSF at any position in space. A spatially varying partial volume correction (SV-PVC) technique was developed using expectation maximization (EM) and a stopping criterion based on the method’s correction matrix generated for each iteration. The SV-PVC was validated using a standard tumor phantom and a tumor heterogeneity phantom, and was applied to a heterogeneous patient tumor. SV-PVC results were compared to results obtained from spatially invariant partial volume correction (SINV-PVC), which used directionally uniform three dimensional kernels. SV-PVC of the standard tumor phantom increased the maximum observed sphere activity by 55 and 40% for 10 and 13 mm diameter spheres, respectively. Tumor heterogeneity phantom results demonstrated that as net changes in the EM correction matrix decreased below 35%, further iterations improved overall quantitative accuracy by less than 1%. SV-PVC of clinically observed tumors frequently exhibited changes of ±30% in regions of heterogeneity. The SV-PVC method implemented spatially varying kernel widths and automatically determined the number of iterations for optimal restoration, parameters which are arbitrarily chosen in SINV-PVC. Comparing SV-PVC to SINV

  3. When Viruses Don’t Go Viral: The Importance of Host Phylogeographic Structure in the Spatial Spread of Arenaviruses

    PubMed Central

    Baird, Stuart J. E.; Goüy de Bellocq, Joëlle

    2017-01-01

    Many emerging infections are RNA virus spillovers from animal reservoirs. Reservoir identification is necessary for predicting the geographic extent of infection risk, but rarely are taxonomic levels below the animal species considered as reservoir, and only key circumstances in nature and methodology allow intrinsic virus-host associations to be distinguished from simple geographic (co-)isolation. We sampled and genetically characterized in detail a contact zone of two subtaxa of the rodent Mastomys natalensis in Tanzania. We find two distinct arenaviruses, Gairo and Morogoro virus, each spatially confined to a single M. natalensis subtaxon, only co-occurring at the contact zone’s centre. Inter-subtaxon hybridization at this centre and a continuum of quality habitat for M. natalensis show that both viruses have the ecological opportunity to spread into the other substaxon’s range, but do not, strongly suggesting host-intrinsic barriers. Such barriers could explain why human cases of another M. natalensis-borne arenavirus, Lassa virus, are limited to West Africa. PMID:28076397

  4. Evaluation of the risk of classical swine fever (CSF) spread from backyard pigs to other domestic pigs by using the spatial stochastic disease spread model Be-FAST: the example of Bulgaria.

    PubMed

    Martínez-López, Beatriz; Ivorra, Benjamin; Ramos, Angel Manuel; Fernández-Carrión, Eduardo; Alexandrov, Tsviatko; Sánchez-Vizcaíno, José Manuel

    2013-07-26

    The study presented here is one of the very first aimed at exploring the potential spread of classical swine fever (CSF) from backyard pigs to other domestic pigs. Specifically, we used a spatial stochastic spread model, called Be-FAST, to evaluate the potential spread of CSF virus (CSFV) in Bulgaria, which holds a large number of backyards (96% of the total number of pig farms) and is one of the very few countries for which backyard pigs and farm counts are available. The model revealed that, despite backyard pigs being very likely to become infected, infections from backyard pigs to other domestic pigs were rare. In general, the magnitude and duration of the CSF simulated epidemics were small, with a median [95% PI] number of infected farms per epidemic of 1 [1,4] and a median [95% PI] duration of the epidemic of 44 [17,101] days. CSFV transmission occurs primarily (81.16%) due to indirect contacts (i.e. vehicles, people and local spread) whereas detection of infected premises was mainly (69%) associated with the observation of clinical signs on farm rather than with implementation of tracing or zoning. Methods and results of this study may support the implementation of risk-based strategies more cost-effectively to prevent, control and, ultimately, eradicate CSF from Bulgaria. The model may also be easily adapted to other countries in which the backyard system is predominant. It can also be used to simulate other similar diseases such as African swine fever.

  5. Decoupling Substrate Stiffness, Spread Area, and Micropost Density: A Close Spatial Relationship between Traction Forces and Focal Adhesions

    PubMed Central

    Han, Sangyoon J.; Bielawski, Kevin S.; Ting, Lucas H.; Rodriguez, Marita L.; Sniadecki, Nathan J.

    2012-01-01

    Mechanical cues can influence the manner in which cells generate traction forces and form focal adhesions. The stiffness of a cell’s substrate and the available area on which it can spread can influence its generation of traction forces, but to what extent these factors are intertwined is unclear. In this study, we used microcontact printing and micropost arrays to control cell spreading, substrate stiffness, and post density to assess their effect on traction forces and focal adhesions. We find that both the spread area and the substrate stiffness influence traction forces in an independent manner, but these factors have opposite effects: cells on stiffer substrates produce higher average forces, whereas cells with larger spread areas generate lower average forces. We show that post density influences the generation of traction forces in a manner that is more dominant than the effect of spread area. Additionally, we observe that focal adhesions respond to spread area, substrate stiffness, and post density in a manner that closely matches the trends seen for traction forces. This work supports the notion that traction forces and focal adhesions have a close relationship in their response to mechanical cues. PMID:22947925

  6. Two-photon excitation of surface plasmon and the period-increasing effect of low spatial frequency ripples on a GaP crystal in air/water

    NASA Astrophysics Data System (ADS)

    Liu, Jukun; Jia, Tianqing; Zhao, Hongwei; Huang, Yaoqing

    2016-11-01

    We report the period-increasing effect of low spatial frequency ripples on a GaP crystal irradiated by 1 kHz, 50 fs, 800 nm femtosecond laser pulses. Massive free electrons are excited by a two-photon absorption process and surface plasmon is excited. The Drude model is used to estimate the changing of the dielectric constant of the GaP crystal. The period-increasing effects of low spatial frequency laser-induced ripples are theoretically predicted in air/water, and the experimental results agree well. The experimental and theoretical results indicate that surface plasmon excited by two-photon absorption plays a key role in the formation of low spatial frequency ripples.

  7. Disruptive Dynamics: The Spatial Dimensions of the Spanish Networks in the Spread of Monitorial Schooling (1815-1825)

    ERIC Educational Resources Information Center

    Caruso, Marcelo

    2007-01-01

    The monitorial system of education was the most promising device in the field of primary education at the beginning of the nineteenth century. Its astonishing spread across the five continents represents one of the earliest processes of internationalization in the field of elementary schooling, which has rarely been analysed from the point of view…

  8. A Spatial Modeling Approach to Predicting the Secondary Spread of Invasive Species Due to Ballast Water Discharge

    PubMed Central

    Sieracki, Jennifer L.; Bossenbroek, Jonathan M.; Chadderton, W. Lindsay

    2014-01-01

    Ballast water in ships is an important contributor to the secondary spread of invasive species in the Laurentian Great Lakes. Here, we use a model previously created to determine the role ballast water management has played in the secondary spread of viral hemorrhagic septicemia virus (VHSV) to identify the future spread of one current and two potential invasive species in the Great Lakes, the Eurasian Ruffe (Gymnocephalus cernuus), killer shrimp (Dikerogammarus villosus), and golden mussel (Limnoperna fortunei), respectively. Model predictions for Eurasian Ruffe have been used to direct surveillance efforts within the Great Lakes and DNA evidence of ruffe presence was recently reported from one of three high risk port localities identified by our model. Predictions made for killer shrimp and golden mussel suggest that these two species have the potential to become rapidly widespread if introduced to the Great Lakes, reinforcing the need for proactive ballast water management. The model used here is flexible enough to be applied to any species capable of being spread by ballast water in marine or freshwater ecosystems. PMID:25470822

  9. A spatial modeling approach to predicting the secondary spread of invasive species due to ballast water discharge.

    PubMed

    Sieracki, Jennifer L; Bossenbroek, Jonathan M; Chadderton, W Lindsay

    2014-01-01

    Ballast water in ships is an important contributor to the secondary spread of invasive species in the Laurentian Great Lakes. Here, we use a model previously created to determine the role ballast water management has played in the secondary spread of viral hemorrhagic septicemia virus (VHSV) to identify the future spread of one current and two potential invasive species in the Great Lakes, the Eurasian Ruffe (Gymnocephalus cernuus), killer shrimp (Dikerogammarus villosus), and golden mussel (Limnoperna fortunei), respectively. Model predictions for Eurasian Ruffe have been used to direct surveillance efforts within the Great Lakes and DNA evidence of ruffe presence was recently reported from one of three high risk port localities identified by our model. Predictions made for killer shrimp and golden mussel suggest that these two species have the potential to become rapidly widespread if introduced to the Great Lakes, reinforcing the need for proactive ballast water management. The model used here is flexible enough to be applied to any species capable of being spread by ballast water in marine or freshwater ecosystems.

  10. Fluid Spatial Dynamics of West Nile Virus in the United States: Rapid Spread in a Permissive Host Environment

    PubMed Central

    Di Giallonardo, Francesca; Geoghegan, Jemma L.; Docherty, Douglas E.; McLean, Robert G.; Zody, Michael C.; Qu, James; Yang, Xiao; Birren, Bruce W.; Malboeuf, Christine M.; Newman, Ruchi M.

    2015-01-01

    ABSTRACT The introduction of West Nile virus (WNV) into North America in 1999 is a classic example of viral emergence in a new environment, with its subsequent dispersion across the continent having a major impact on local bird populations. Despite the importance of this epizootic, the pattern, dynamics, and determinants of WNV spread in its natural hosts remain uncertain. In particular, it is unclear whether the virus encountered major barriers to transmission, or spread in an unconstrained manner, and if specific viral lineages were favored over others indicative of intrinsic differences in fitness. To address these key questions in WNV evolution and ecology, we sequenced the complete genomes of approximately 300 avian isolates sampled across the United States between 2001 and 2012. Phylogenetic analysis revealed a relatively star-like tree structure, indicative of explosive viral spread in the United States, although with some replacement of viral genotypes through time. These data are striking in that viral sequences exhibit relatively limited clustering according to geographic region, particularly for those viruses sampled from birds, and no strong phylogenetic association with well-sampled avian species. The genome sequence data analyzed here also contain relatively little evidence for adaptive evolution, particularly of structural proteins, suggesting that most viral lineages are of similar fitness and that WNV is well adapted to the ecology of mosquito vectors and diverse avian hosts in the United States. In sum, the molecular evolution of WNV in North America depicts a largely unfettered expansion within a permissive host and geographic population with little evidence of major adaptive barriers. IMPORTANCE How viruses spread in new host and geographic environments is central to understanding the emergence and evolution of novel infectious diseases and for predicting their likely impact. The emergence of the vector-borne West Nile virus (WNV) in North

  11. Spatial and Temporal Spread of Acute Viral Respiratory Infections in Young Children Living in High-Altitude Rural Communities: A Prospective Household-Based Study

    PubMed Central

    Cherry, Charlotte Buehler; Griffin, Marie R.; Edwards, Kathryn M.; Williams, John V.; Gil, Ana I.; Verastegui, Hector; Lanata, Claudio F.; Grijalva, Carlos G

    2016-01-01

    Background Few studies have described patterns of transmission of viral acute respiratory infections (ARI) in children in developing countries. We examined the spatial and temporal spread of viral ARI among young children in rural Peruvian highland communities. Previous work has described intense social interactions in those communities, which could influence the transmission of viral infections. Methods We enrolled and followed children <3 years of age for detection of ARI during the 2009–2011 respiratory seasons in a rural setting with relatively wide geographic dispersion of households and communities. Viruses detected included influenza, respiratory syncytial virus (RSV), human metapneumovirus (MPV), and parainfluenza 2 and 3 viruses (PIV2; PIV3). We used geospatial analyses to identify specific viral infection hot spots with high ARI incidence. We also explored the local spread of ARI from index cases using standard deviational ellipses. Results Geospatial analyses revealed hot spots of high ARI incidence around the index cases of influenza outbreaks and RSV outbreak in 2010. Although PIV3 in 2009 and PIV2 in 2010 showed distinct spatial hot spots, clustering was not in proximity to their respective index cases. No significant aggregation around index cases was noted for other viruses. Standard deviational ellipse analyses suggested that influenza B and RSV in 2010, and MPV in 2011 spread temporally in alignment with the major road network. Conclusions Despite the geographic dispersion of communities in this rural setting, we observed a rapid spread of viral ARI among young children. Influenza strains and RSV in 2010 had distinctive outbreaks arising from their index cases. PMID:27404599

  12. Reconstructing a spatially heterogeneous epidemic: Characterising the geographic spread of 2009 A/H1N1pdm infection in England

    NASA Astrophysics Data System (ADS)

    Birrell, Paul J.; Zhang, Xu-Sheng; Pebody, Richard G.; Gay, Nigel J.; de Angelis, Daniela

    2016-07-01

    Understanding how the geographic distribution of and movements within a population influence the spatial spread of infections is crucial for the design of interventions to curb transmission. Existing knowledge is typically based on results from simulation studies whereas analyses of real data remain sparse. The main difficulty in quantifying the spatial pattern of disease spread is the paucity of available data together with the challenge of incorporating optimally the limited information into models of disease transmission. To address this challenge the role of routine migration on the spatial pattern of infection during the epidemic of 2009 pandemic influenza in England is investigated here through two modelling approaches: parallel-region models, where epidemics in different regions are assumed to occur in isolation with shared characteristics; and meta-region models where inter-region transmission is expressed as a function of the commuter flux between regions. Results highlight that the significantly less computationally demanding parallel-region approach is sufficiently flexible to capture the underlying dynamics. This suggests that inter-region movement is either inaccurately characterized by the available commuting data or insignificant once its initial impact on transmission has subsided.

  13. Reconstructing a spatially heterogeneous epidemic: Characterising the geographic spread of 2009 A/H1N1pdm infection in England

    PubMed Central

    Birrell, Paul J.; Zhang, Xu-Sheng; Pebody, Richard G.; Gay, Nigel J.; De Angelis, Daniela

    2016-01-01

    Understanding how the geographic distribution of and movements within a population influence the spatial spread of infections is crucial for the design of interventions to curb transmission. Existing knowledge is typically based on results from simulation studies whereas analyses of real data remain sparse. The main difficulty in quantifying the spatial pattern of disease spread is the paucity of available data together with the challenge of incorporating optimally the limited information into models of disease transmission. To address this challenge the role of routine migration on the spatial pattern of infection during the epidemic of 2009 pandemic influenza in England is investigated here through two modelling approaches: parallel-region models, where epidemics in different regions are assumed to occur in isolation with shared characteristics; and meta-region models where inter-region transmission is expressed as a function of the commuter flux between regions. Results highlight that the significantly less computationally demanding parallel-region approach is sufficiently flexible to capture the underlying dynamics. This suggests that inter-region movement is either inaccurately characterized by the available commuting data or insignificant once its initial impact on transmission has subsided. PMID:27404957

  14. Contribution of human, climate and biophysical drivers to the spatial distribution of wildfires in a French Mediterranean area: where do wildfires start and spread?

    NASA Astrophysics Data System (ADS)

    Ruffault, Julien; Mouillot, Florent; Moebius, Flavia

    2013-04-01

    Understanding the contribution of biophysical and human drivers to the spatial distribution of fires at regional scale has many ecological and economical implications in a context of on-going global changes. However these fire drivers often interact in complex ways, such that disentangling and assessing the relative contribution of human vs. biophysical factors remains a major challenge. Indeed, the identification of biophysical conditions that promote fires are confused by the inherent stochasticity in fire occurrences and fire spread on the one hand and, by the influence of human factors -through both fire ignition and suppression - on the other. Moreover, different factors may drive fire ignition and fire spread, in such a way that the areas with the highest density of ignitions may not coincide with those where large fires occur. In the present study, we investigated the drivers of fires ignition and spread in a Mediterranean area of southern France. We used a 17 years fire database (the PROMETHEE database from 1989-2006) combined with a set of 8 explanatory variables describing the spatial pattern in ignitions, vegetation and fire weather. We first isolated the weather conditions affecting the fire occurrence and their spread using a statistical model of the weather/fuel water status for each fire event.. The results of these statistical models were used to map the fire weather in terms of average number of days with suitable conditions for burning. Then, we used Boosted regression trees (BRT) models to assess the relative importance of the different variables on the distribution of wildfire with different sizes and to assess the relationship between each variables and fire occurrence and spread probabilities. We found that human activities explained up to 50 % of the spatial distribution of fire ignitions (SDI). The distribution of large fire was chiefly explained by fuel characteristics (about 40%). Surprisingly, the weather indices explained only 20 % of

  15. Fluid spatial dynamics of West Nile virus in the USA: Rapid spread in a permissive host environment

    USGS Publications Warehouse

    Di Giallonardo , Francesca; Geoghegan, Jemma L.; Docherty, Douglas E.; McLean, Robert G.; Zody, Michael C.; Qu, James; Yang, Xiao; Birren, Bruce W.; Malboeuf, Christine M.; Newman, R.; Ip, Hon S.; Holmes, Edward C.

    2016-01-01

    The introduction of West Nile virus (WNV) into North America in 1999 is a classical example of viral emergence in a new environment, with its subsequent dispersion across the continent having a major impact on local bird populations. Despite the importance of this epizootic, the pattern, dynamics and determinants of WNV spread in its natural hosts remain uncertain. In particular, it is unclear whether the virus encountered major barriers to transmission, or spread in an unconstrained manner, and if specific viral lineages were favored over others indicative of intrinsic differences in fitness. To address these key questions in WNV evolution and ecology we sequenced the complete genomes of approximately 300 avian isolates sampled across the USA between 2001-2012. Phylogenetic analysis revealed a relatively ‘star-like' tree structure, indicative of explosive viral spread in US, although with some replacement of viral genotypes through time. These data are striking in that viral sequences exhibit relatively limited clustering according to geographic region, particularly for those viruses sampled from birds, and no strong phylogenetic association with well sampled avian species. The genome sequence data analysed here also contain relatively little evidence for adaptive evolution, particularly on structural proteins, suggesting that most viral lineages are of similar fitness, and that WNV is well adapted to the ecology of mosquito vectors and diverse avian hosts in the USA. In sum, the molecular evolution of WNV in North America depicts a largely unfettered expansion within a permissive host and geographic population with little evidence of major adaptive barriers.

  16. Temporal and spatial cyclicity of accretion at slow-spreading ridges-evidence from the Reykjanes Ridge

    NASA Astrophysics Data System (ADS)

    Peirce, Christine; Gardiner, Alex; Sinha, Martin

    2005-10-01

    A unifying model of oceanic crustal development at slow spreading rates is presented in which accretion follows a cyclic pattern of magmatic construction and tectonic destruction, controlled by along-axis variation in melt supply and coupled to along-axis variation in spreading rate and across-axis asymmetry in spreading. This study focuses on the Reykjanes Ridge, Mid-Atlantic Ridge south of Iceland, which is divided along its entire length into numerous axial volcanic ridges (AVR). Five adjacent AVRs have been analysed, located between 57°30'N and 58°30'N and south of any strong Iceland hotspot influence. The seabed morphology of each AVR is investigated using sidescan sonar data to determine relative age and eruptive history. Along-axis gravity profiles for each AVR are modelled relative to a seismically derived crustal reference model, to reveal the underlying crustal thickness and density structure. Correlating these models with seabed features, crustal structure, ridge segment morphology and relative ages, a model of cyclic ridge segmentation is developed in which accretion results in adjacent AVRs with a range of crustal features which, when viewed collectively, reveal that second-order segments on the Reykjanes Ridge have an along-axis length of ~70 km and comprise several adjacent AVRs which, in turn, reflect the pattern of third-order segmentation. Tectono-magmatic accretion is shown to operate on the scale of individual AVRs, as well as on the scale of the second-order segment as a whole.

  17. Evaluating spatial outliers and integrating temporal data in air pollution models for the Detroit-Windsor airshed

    NASA Astrophysics Data System (ADS)

    O'Leary, Brendan F.

    The heterogeneous nature of urban air complicates human exposure estimates and creates a need for accurate, highly detailed spatiotemporal air contaminant models. The study expands on previous investigations by the Geospatial Determinants of Health Outcomes Consortium that examined relationships between air pollutant distributions and asthma exacerbations. Two approaches, the removal of spatial data outliers and the integration of spatial and temporal data, were used to refine air quality models in the Detroit and Windsor international airshed. The evaluation of associations between the resulting air quality models and asthma exacerbations in Detroit and Windsor revealed weaker correlations with spatial outliers removed but improved correlations with the addition of temporal data. Recommendations for future work include increasing the spatial and temporal resolution of the asthma datasets and incorporating Windsor NAPS data through temporal scaling to help confirm the findings of the Detroit temporal scaling.

  18. Spatial amplification of a laser wave and the transverse spread of electrons in an undulator with a noncollinear configuration

    NASA Astrophysics Data System (ADS)

    Artem'ev, A. I.; Klochkov, D. N.; Oganesyan, K.; Rostovtsev, Yu. V.; Fedorov, M. V.

    2007-09-01

    The spatial amplification of a wave in a magnetostatic undulator with noncollinear electron and laser beams is studied in the framework of the dispersion relation for single-frequency and collective regimes. The dependence of the gain on the electron beam width is estimated with regard to the spatial boundedness of the beams. The laser power threshold at which the selection with respect to the transverse velocity is possible is obtained for a free-electron laser without inversion.

  19. Remote sensing to detect the movement of wheat curl mites through the spatial spread of virus symptoms, and identification of thrips as predators of wheat curl mites

    NASA Astrophysics Data System (ADS)

    Stilwell, Abby R.

    The wheat curl mite (WCM), Aceria tosichella Keifer, transmits three viruses to winter wheat: wheat streak mosaic virus, High Plains virus, and Triticum mosaic virus. This virus complex causes yellowing of the foliage and stunting of plants. WCMs disperse by wind, and an increased understanding of mite movement and subsequent virus spread is necessary in determining the risk of serious virus infections in winter wheat. These risk parameters will help growers make better decisions regarding WCM management. The objectives of this study were to evaluate the capabilities of remote sensing to identify virus infected plants and to establish the potential of using remote sensing to track virus spread and consequently, mite movement. Although the WCM is small and very hard to track, the viruses it vectors produce symptoms that can be detected with remote sensing. Field plots of simulated volunteer wheat were established between 2006 and 2009, infested with WCMs, and spread mites and virus into adjacent winter wheat. The virus gradients created by WCM movement allowed for the measurement of mite movement potential with both proximal and aerial remote sensing instruments. The ability to detect WCM-vectored viruses with remote sensing was investigated by comparing vegetation indices calculated from proximal remote sensing data to ground truth data obtained in the field. Of the ten vegetation indices tested, the red edge position (REP) index had the best relationship with ground truth data. The spatial spread of virus from WCM source plots was modeled with cokriging. Virus symptoms predicted by cokriging occurred in an oval pattern displaced to the southeast. Data from the spatial spread in small plots of this study were used to estimate the potential sphere of influence for volunteer wheat fields. The impact of thrips on WCM populations was investigated by a series of greenhouse, field, and observational studies. WCM populations in winter wheat increased more slowly when

  20. Spatial and Temporal Variations of Surface Temperature Over Greenland As Observed In AIRS, MODIS and In-Situ Measurements

    NASA Astrophysics Data System (ADS)

    Lee, J. N.; Susskind, J.; Wu, D. L.; Nowicki, S.; Hall, D. K.; Iredell, L. F.

    2015-12-01

    This paper compares the temporal and spatial characteristics of the AIRS and MODIS surface temperatures over Greenland. To estimate uncertainties in space-based temperature measurements, we reprojected the MODIS Ice Surface Temperature (IST) into 0.5 by 0.5 degree spatial resolution. We also re-gridded AIRS Skin Temperature (Ts) with same spatial resolution but classified with different cloud conditions and surface types. These co-located data sets make intercomparison between the two instruments relatively straightforward. By this approach, the spatial comparison between AIRS Ts and MODIS IST monthly mean is in good agreement with RMS less than 2K during May 2012. This approach also allows the detection of any long-term calibration drift and the careful examination of calibration consistency in MODIS and AIRS temperature data record. The temporal correlations between temperature data are also compared with those from in-situ measurements from GC-Net and NOAA stations. The most significant diurnal difference is found during spring season (April and May) in high altitude regions, when interannual variability is relatively smaller than summer and winter.

  1. Predicting the spread of sudden oak death in California: spatial-temporal modeling of susceptible-infectious transitions

    Treesearch

    Richard D. Hunter; Ross K. Meentemeyer; David M. Rizzo; Christopher A. Gilligan

    2008-01-01

    The number of emerging infectious diseases is thought to be increasing worldwide - many of which are caused by non-native, invasive plant pathogens I n forest ecosystems. As new diseases continue to emerge, the ability to predict disease outbreaks is critical for effective management and prevention of epidemics, especially in complex spatially heterogeneous landscapes...

  2. Spatial Variation in the Population Structure and Reproductive Biology of Rimicaris hybisae (Caridea: Alvinocarididae) at Hydrothermal Vents on the Mid-Cayman Spreading Centre

    PubMed Central

    Nye, Verity; Copley, Jonathan T.; Tyler, Paul A.

    2013-01-01

    The dynamics and microdistribution of faunal assemblages at hydrothermal vents often reflect the fine-scale spatial and temporal heterogeneity of the vent environment. This study examined the reproductive development and population structure of the caridean shrimp Rimicaris hybisae at the Beebe and Von Damm Vent Fields (Mid-Cayman Spreading Centre, Caribbean) using spatially discrete samples collected in January 2012. Rimicaris hybisae is gonochoric and exhibits iteroparous reproduction. Oocyte size-frequency distributions (21-823 µm feret diameters) varied significantly among samples. Embryo development was asynchronous among females, which may result in asynchronous larval release for the populations. Specimens of R. hybisae from the Von Damm Vent Field (2294 m) were significantly larger than specimens from the Beebe Vent Field. Brooding females at Von Damm exhibited greater size-specific fecundity, possibly as a consequence of a non-linear relationship between fecundity and body size that was consistent across both vent fields. Samples collected from several locations at the Beebe Vent Field (4944–4972 m) revealed spatial variability in the sex ratios, population structure, size, and development of oocytes and embryos of this mobile species. Samples from the Von Damm Vent Field and sample J2-613-24 from Beebe Woods exhibited the highest frequencies of ovigerous females and significantly female-biased sex ratios. Environmental variables within shrimp aggregations may influence the distribution of ovigerous females, resulting in a spatially heterogeneous pattern of reproductive development in R. hybisae, as found in other vent taxa. PMID:23555955

  3. Spatial variation in the population structure and reproductive biology of Rimicaris hybisae (Caridea: Alvinocarididae) at hydrothermal vents on the Mid-Cayman Spreading Centre.

    PubMed

    Nye, Verity; Copley, Jonathan T; Tyler, Paul A

    2013-01-01

    The dynamics and microdistribution of faunal assemblages at hydrothermal vents often reflect the fine-scale spatial and temporal heterogeneity of the vent environment. This study examined the reproductive development and population structure of the caridean shrimp Rimicaris hybisae at the Beebe and Von Damm Vent Fields (Mid-Cayman Spreading Centre, Caribbean) using spatially discrete samples collected in January 2012. Rimicaris hybisae is gonochoric and exhibits iteroparous reproduction. Oocyte size-frequency distributions (21-823 µm feret diameters) varied significantly among samples. Embryo development was asynchronous among females, which may result in asynchronous larval release for the populations. Specimens of R. hybisae from the Von Damm Vent Field (2294 m) were significantly larger than specimens from the Beebe Vent Field. Brooding females at Von Damm exhibited greater size-specific fecundity, possibly as a consequence of a non-linear relationship between fecundity and body size that was consistent across both vent fields. Samples collected from several locations at the Beebe Vent Field (4944-4972 m) revealed spatial variability in the sex ratios, population structure, size, and development of oocytes and embryos of this mobile species. Samples from the Von Damm Vent Field and sample J2-613-24 from Beebe Woods exhibited the highest frequencies of ovigerous females and significantly female-biased sex ratios. Environmental variables within shrimp aggregations may influence the distribution of ovigerous females, resulting in a spatially heterogeneous pattern of reproductive development in R. hybisae, as found in other vent taxa.

  4. Analysis of the Spatial Organization of Pastures as a Contact Network, Implications for Potential Disease Spread and Biosecurity in Livestock, France, 2010

    PubMed Central

    Palisson, Aurore; Courcoul, Aurélie; Durand, Benoit

    2017-01-01

    The use of pastures is part of common herd management practices for livestock animals, but contagion between animals located on neighbouring pastures is one of the major modes of infectious disease transmission between herds. At the population level, this transmission is strongly constrained by the spatial organization of pastures. The aim of this study was to answer two questions: (i) is the spatial configuration of pastures favourable to the spread of infectious diseases in France? (ii) would biosecurity measures allow decreasing this vulnerability? Based on GIS data, the spatial organization of pastures was represented using networks. Nodes were the 3,159,787 pastures reported in 2010 by the French breeders to claim the Common Agricultural Policy subsidies. Links connected pastures when the distance between them was below a predefined threshold. Premises networks were obtained by aggregating into a single node all the pastures under the same ownership. Although the pastures network was very fragmented when the distance threshold was short (1.5 meters, relevant for a directly-transmitted disease), it was not the case when the distance threshold was larger (500 m, relevant for a vector-borne disease: 97% of the nodes in the largest connected component). The premises network was highly connected as the largest connected component always included more than 83% of the nodes, whatever the distance threshold. Percolation analyses were performed to model the population-level efficacy of biosecurity measures. Percolation thresholds varied according to the modelled biosecurity measures and to the distance threshold. They were globally high (e.g. >17% of nodes had to be removed, mimicking the confinement of animals inside farm buildings, to obtain the disappearance of the large connected component). The network of pastures thus appeared vulnerable to the spread of diseases in France. Only a large acceptance of biosecurity measures by breeders would allow reducing this

  5. Analysis of the Spatial Organization of Pastures as a Contact Network, Implications for Potential Disease Spread and Biosecurity in Livestock, France, 2010.

    PubMed

    Palisson, Aurore; Courcoul, Aurélie; Durand, Benoit

    2017-01-01

    The use of pastures is part of common herd management practices for livestock animals, but contagion between animals located on neighbouring pastures is one of the major modes of infectious disease transmission between herds. At the population level, this transmission is strongly constrained by the spatial organization of pastures. The aim of this study was to answer two questions: (i) is the spatial configuration of pastures favourable to the spread of infectious diseases in France? (ii) would biosecurity measures allow decreasing this vulnerability? Based on GIS data, the spatial organization of pastures was represented using networks. Nodes were the 3,159,787 pastures reported in 2010 by the French breeders to claim the Common Agricultural Policy subsidies. Links connected pastures when the distance between them was below a predefined threshold. Premises networks were obtained by aggregating into a single node all the pastures under the same ownership. Although the pastures network was very fragmented when the distance threshold was short (1.5 meters, relevant for a directly-transmitted disease), it was not the case when the distance threshold was larger (500 m, relevant for a vector-borne disease: 97% of the nodes in the largest connected component). The premises network was highly connected as the largest connected component always included more than 83% of the nodes, whatever the distance threshold. Percolation analyses were performed to model the population-level efficacy of biosecurity measures. Percolation thresholds varied according to the modelled biosecurity measures and to the distance threshold. They were globally high (e.g. >17% of nodes had to be removed, mimicking the confinement of animals inside farm buildings, to obtain the disappearance of the large connected component). The network of pastures thus appeared vulnerable to the spread of diseases in France. Only a large acceptance of biosecurity measures by breeders would allow reducing this

  6. Age-specific contacts and travel patterns in the spatial spread of 2009 H1N1 influenza pandemic

    PubMed Central

    2013-01-01

    Background Confirmed H1N1 cases during late spring and summer 2009 in various countries showed a substantial age shift between importations and local transmission cases, with adults mainly responsible for seeding unaffected regions and children most frequently driving community outbreaks. Methods We introduce a multi-host stochastic metapopulation model with two age classes to analytically investigate the role of a heterogeneously mixing population and its associated non-homogeneous travel behaviors on the risk of a major epidemic. We inform the model with demographic data, contact data and travel statistics of Europe and Mexico, and calibrate it to the 2009 H1N1 pandemic early outbreak. We allow for variations of the model parameters to explore the conditions of invasion under different scenarios. Results We derive the expression for the potential of global invasion of the epidemic that depends on the transmissibility of the pathogen, the transportation network and mobility features, the demographic profile and the mixing pattern. Higher assortativity in the contact pattern greatly increases the probability of spatial containment of the epidemic, this effect being contrasted by an increase in the social activity of adults vs. children. Heterogeneous features of the mobility network characterizing its topology and traffic flows strongly favor the invasion of the pathogen at the spatial level, as also a larger fraction of children traveling. Variations in the demographic profile and mixing habits across countries lead to heterogeneous outbreak situations. Model results are compatible with the H1N1 spatial transmission dynamics observed. Conclusions This work illustrates the importance of considering age-dependent mixing profiles and mobility features coupled together to study the conditions for the spatial invasion of an emerging influenza pandemic. Its results allow the immediate assessment of the risk of a major epidemic for a specific scenario upon availability

  7. Activation of the cGMP/PKG pathway inhibits electrical activity in rabbit urethral interstitial cells of Cajal by reducing the spatial spread of Ca2+ waves

    PubMed Central

    Sergeant, G P; Johnston, Louise; McHale, N G; Thornbury, K D; Hollywood, M A

    2006-01-01

    In the present study we used a combination of patch clamping and fast confocal Ca2+ imaging to examine the effects of activators of the nitric oxide (NO)/cGMP pathway on pacemaker activity in freshly dispersed ICC from the rabbit urethra, using the amphotericin B perforated patch configuration of the patch-clamp technique. The nitric oxide donor, DEA-NO, the soluble guanylyl cyclase activator YC-1 and the membrane-permeant analogue of cGMP, 8-Br-cGMP inhibited spontaneous transient depolarizations (STDs) and spontaneous transient inward currents (STICs) recorded under current-clamp and voltage-clamp conditions, respectively. Caffeine-evoked Cl− currents were unaltered in the presence of SP-8-Br-PET-cGMPs, suggesting that activation of the cGMP/PKG pathway does not block Cl− channels directly or interfere with Ca2+ release via ryanodine receptors (RyR). However, noradrenaline-evoked Cl− currents were attenuated by SP-8-Br-PET-cGMPs, suggesting that activation of cGMP-dependent protein kinase (PKG) may modulate release of Ca2+ via IP3 receptors (IP3R).When urethral interstitial cells (ICC) were loaded with Fluo4-AM (2 μm), and viewed with a confocal microscope, they fired regular propagating Ca2+ waves, which originated in one or more regions of the cell. Application of DEA-NO or other activators of the cGMP/PKG pathway did not significantly affect the oscillation frequency of these cells, but did significantly reduce their spatial spread. These effects were mimicked by the IP3R blocker, 2-APB (100 μm). These data suggest that NO donors and activators of the cGMP pathway inhibit electrical activity of urethral ICC by reducing the spatial spread of Ca2+ waves, rather than decreasing wave frequency. PMID:16644801

  8. Activation of the cGMP/PKG pathway inhibits electrical activity in rabbit urethral interstitial cells of Cajal by reducing the spatial spread of Ca2+ waves.

    PubMed

    Sergeant, G P; Johnston, Louise; McHale, N G; Thornbury, K D; Hollywood, M A

    2006-07-01

    In the present study we used a combination of patch clamping and fast confocal Ca2+ imaging to examine the effects of activators of the nitric oxide (NO)/cGMP pathway on pacemaker activity in freshly dispersed ICC from the rabbit urethra, using the amphotericin B perforated patch configuration of the patch-clamp technique. The nitric oxide donor, DEA-NO, the soluble guanylyl cyclase activator YC-1 and the membrane-permeant analogue of cGMP, 8-Br-cGMP inhibited spontaneous transient depolarizations (STDs) and spontaneous transient inward currents (STICs) recorded under current-clamp and voltage-clamp conditions, respectively. Caffeine-evoked Cl- currents were unaltered in the presence of SP-8-Br-PET-cGMPs, suggesting that activation of the cGMP/PKG pathway does not block Cl- channels directly or interfere with Ca2+ release via ryanodine receptors (RyR). However, noradrenaline-evoked Cl- currents were attenuated by SP-8-Br-PET-cGMPs, suggesting that activation of cGMP-dependent protein kinase (PKG) may modulate release of Ca2+ via IP3 receptors (IP3R). When urethral interstitial cells (ICC) were loaded with Fluo4-AM (2 microm), and viewed with a confocal microscope, they fired regular propagating Ca2+ waves, which originated in one or more regions of the cell. Application of DEA-NO or other activators of the cGMP/PKG pathway did not significantly affect the oscillation frequency of these cells, but did significantly reduce their spatial spread. These effects were mimicked by the IP3R blocker, 2-APB (100 microm). These data suggest that NO donors and activators of the cGMP pathway inhibit electrical activity of urethral ICC by reducing the spatial spread of Ca2+ waves, rather than decreasing wave frequency.

  9. Metofluthrin: investigations into the use of a volatile spatial pyrethroid in a global spread of dengue, chikungunya and Zika viruses.

    PubMed

    Buhagiar, Tamara S; Devine, Gregor J; Ritchie, Scott A

    2017-05-30

    Metofluthrin reduces biting activity in Aedes aegypti through the confusion, knockdown, and subsequent kill of a mosquito. A geographical spread in dengue, chikungunya, and Zika viruses, increases intervention demands. Response to a Zika outbreak may require a different strategy than dengue, as high-risk individuals, specifically pregnant women, need to be targeted. In semi-field conditions within a residential property in Cairns, Queensland, the impacts of metofluthrin on biting behaviour of free-flying Wolbachia-infected Ae. aegypti were evaluated. Mortality in Ae. aegypti exposed to metofluthrin over a 22 h period was 100% compared to 2.7% in an untreated room. No biting activity was observed in mosquitoes up to 5 m from the emanator after 10 min of metofluthrin exposure. Use of metofluthrin reduced biting activity up to 8 m, regardless of the host's proximity (near or far) to a dark harbourage area (HA) (P < 0.0001 and P = 0.006), respectively. In the presence or absence of the metofluthrin emanator, the host was most likely bitten when located immediately next to a HA (within 1 m) versus 8 m away from the HA (P = 0.006). The addition of a ceiling fan (0.8 m/s airflow) prevented all biting activity after 10 min of metofluthrin exposure. Previously unexposed Ae. aegypti were less likely to reach the host in a metofluthrin-treated room [Formula: see text]= 31%) compared to an untreated room ([Formula: see text]) (P < 0.0001). In a treated room, if the mosquito had not reached the host within 30 s, they never would. Upon activation, the time required for metofluthrin to infiltrate protected locations within a room causing knockdown in caged mosquitoes, required more time than exposed locations (P < 0.003); however exposed and protected locations do eventually reach equilibrium, affecting mosquitoes equally throughout the room. Metofluthrin is effective in interrupting indoor host-seeking in Ae. aegypti. Metofluthrin's efficacy is increased by

  10. Spatial characterization of red and white skin potatoes using nano-second laser induced breakdown in air

    NASA Astrophysics Data System (ADS)

    Rehan, Imran; Rehan, Kamran; Sultana, S.; Haq, M. Oun ul; Niazi, Muhammad Zubair Khan; Muhammad, Riaz

    2016-01-01

    We presents spectroscopic study of the plasma generated by a Q-switched Nd:YAG (1064 nm) laser irradiation of the flesh of red and white skin potatoes. From the spectra recorded with spectrometer (LIBS2500+, Ocean Optics, USA) 11 elements were identified in red skin potato, whereas, the white skin potato was found to have nine elements. Their relative concentrations were estimated using CF-LIBS method for the plasma in local thermodynamic equilibrium. The target was placed in ambient air at atmospheric pressure. The electron temperature and number density were calculated from Boltzmann plot and stark broadened line profile methods, respectively using Fe I spectral lines. The spatial distribution of plasma parameters were also studied which show a decreasing trend of 6770 K-4266 K and (3-2.0) × 1016 cm-3. Concentrations of the detected elements were monitored as a function of depth of the potatoes. Our study reveals a decreasing tendency in concentration of iron from top to the centre of potato's flesh, whereas, the concentrations of other elements vary randomly.

  11. Densely mapping the phase diagram of the cuprate superconductor La2-xSrxCuO4 (0 <=x <=0.18), using a spatial composition spread approach

    NASA Astrophysics Data System (ADS)

    Hewitt, Kevin; Saadat, Mehran; George, Andrew

    2010-03-01

    Densely mapping the phase diagram of cuprate superconductors is the key to deciphering the normal state properties of these materials. A spatial composition spread approach was used to successfully deposit a 52-member composition spread library of La2-xSrxCuO4 (0 <=x <=0.18). Two home made targets of La2CuO4 and La1.82Sr0.18CuO4 were sputtered using 41 W RF and 42 W DC bias,respectively, at process gas pressure of 15 mTorr argon. A linear composition variation was produced by using specially designed masks in front of the La2CuO4 and La1.82Sr0.18CuO4 targets. The libraries were sputtered onto LaSrAlO4(001), SrTiO3(100) and MgO(100)substrates through a 52-slot shadow mask, and post annealed in a two step sequence - 800^oC for 1 h then at 950^oC for 2 h - in a tube sealed with oxygen gas. XRD and WDS analysis revealed the expected doping variation. Resistivity measurements reveal expected features such as a suppression of superconductivity near 18 (x = 0.125) doping and a novel one - that superconductivity appears near 3% (x=0.03) doping. The work present a powerful approach to studying the phase diagram of existing superconductors as well as offering a method to search for new materials.

  12. Galapagos Hot Spot-Spreading Center System: 1. Spatial petrological and geochemical variations (83°W-101°W)

    NASA Astrophysics Data System (ADS)

    Schilling, J.-G.; Kingsley, R. H.; Devine, J. D.

    1982-07-01

    We report on the petrology and geochemistry of basalts dredged at 40-50 km intervals along the Galapagos Spreading Center, between 83°W and 101°W (40 stations). Emphasis is on spatial variations of `whole rock' major elements, rare earths, trace metals of the first transition series, and the nature of phenocryst assemblages and their abundances. These results provide new constraints on the nature and scale of mantle source heterogeneities, melting conditions, thermal field, and dynamics of crustal formation of the region. We suggest that ridge segments outside the high magnetic amplitude zone are at a steady state as a result of passive seafloor spreading. Basalts from these segments are apparently derived from an asthenosphere relatively uniformally depleted in incompatible elements, which appears of worldwide extent. We reject Vogt and DeBoer's [1976] model invoking damming at fracture zones of subaxial astenosphere flow of crystal slushes and increasing fractional crystallization down the flow line, because this model would not explain the gradients in REE observed about the Galapagos Platform. Our preferred model combines the mantle-plume binary mixing model of Schilling [1973] with the concept of recurring rift propagation proposed by Hey [1977a]. We further propose that pulsating mantle plume flux, perhaps in the form of a chain of blobs, may initiate the development of new rifts and their propagation. The present position of the tips of such new propagating rifts locate the wave fronts of such pulsating mantle plume flow. A two million year period is suggested for the last 4 m.y. from Wilson and Hey's [1979] information. Rigorous testing of our preferred model is possible.

  13. Temporal and Spatial Variations in Volcanic Accretion Over the Past Few 100 Years on the EPR Axis at Superfast Spreading rates at 17 to 18 deg S

    NASA Astrophysics Data System (ADS)

    Rubin, K. H.; Sinton, J. M.; Bergmanis, E. C.

    2008-12-01

    Ridges at fast to superfast spreading rates are excellent locations to study temporal and spatial variations in volcanic construction because magma supply and eruption rates are high, and because much of the volcanic accretion occurs within a narrow (≤1-2 km) zone at the rise axis. This presentation will summarize temporal and spatial variations in volcanic accretion over the past few hundred years at 17.5° to 18.5°S on the East Pacific Rise using geological observations made by submersible and other methods, as well shore-based petrological, geochemical and radiometric analyses of samples recovered from mapped lava flow fields along the ridge axis. Collectively they demonstrate that the styles and rates of volcanic accretion can vary substantially both within and between volcanic segments over relatively short timescales. Mapped lavas indicate that single eruptions can span small structural discontinuities (ridge axis offsets). Compositional shifts accompany these offsets, indicating segmentation or zonation of the magma chamber that fed them. Similar observations have been made in analogous eruption sequences at subaerial rift zone volcanoes. U-series disequilibria, radiogenic isotopes and major and trace element compositions within and between single mapped lava flows indicate that magma chambers are open and poorly mixed over the timescale of volcanic repose (decades to ~1 century). Within flow compositional variations along axis can be used to test for magma emplacement by lateral injection from a central reservoir near inflated segment centers versus near vertical emplacement from magma bodies distributed along the axis. The latter best describes observations of lava flows at both 17.5°S and 18.5°S. Volcanic accretion occurs along a volcanically robust, inflated ridge segment at 17.5°S, whereas at 18.5°S the most recent eruptions have formed small, discontinuous lava shields and pillow mounds on the floor of a deep, few hundred year old graben that

  14. Comparative spatial spread overtime of Zucchini Yellow Mosaic Virus (ZYMV) and Watermelon Mosaic Virus (WMV) in fields of transgenic squash expressing the coat protein genes of ZYMV and WMV, and in fields of nontransgenic squash.

    PubMed

    Klas, Ferdinand E; Fuchs, Marc; Gonsalves, Dennis

    2006-10-01

    The spatial and temporal patterns of aphid-vectored spread of Zucchini Yellow Mosaic Virus (ZYMV) and Watermelon Mosaic Virus (WMV) were monitored over two consecutive years in plantings of nontransgenic and transgenic squash ZW-20H (commercial cv. Freedom II) and ZW-20B, both expressing the coat protein genes of ZYMV and WMV. All test plants were surrounded by nontransgenic plants that were mechanically inoculated with ZYMV or WMV, and served as primary virus source. Across all trials, none of the transgenic plants exhibited systemic symptoms upon infection by ZYMV and WMV but a few of them developed localized chlorotic dots and/or blotches, and had low mixed infection rates [4% (6 of 139) of ZW-20H and 9% (13 of 139) of ZW-20B], as shown by ELISA. Geostatistical analysis of ELISA positive transgenic plants indicated, (i) a lack of spatial relationship on spread of ZYMV and WMV for ZW-20H with flat omnidirectional experimental semivariograms that fitted poorly theoretical models, and (ii) some extent of spatial dependence on ZYMV spread for ZW-20B with a well structured experimental semivariogram that fitted poorly theoretical models during the first but not the second growing season. In contrast, a strong spatial dependence on spread of ZYMV and WMV was found for nontransgenic plants, which developed severe systemic symptoms, had prevalent mixed infection rates (62%, 86 of 139), and well-defined omnidirectional experimental semivariograms that fitted a spherical model. Geostatistical data were sustained by virus transmission experiments with Myzus persicae in screenhouses, showing that commercial transgenic squash ZW-20H alter the dynamics of ZYMV and WMV epidemics by preventing secondary plant-to-plant spread.

  15. Temporal and spatial evolution of EHD particle flow onset in air in a needle-to-plate negative DC corona discharge

    NASA Astrophysics Data System (ADS)

    Mizeraczyk, J.; Berendt, A.; Podlinski, J.

    2016-05-01

    In this paper we present images showing the temporal and spatial evolution of the electrohydrodynamic (EHD) flow of dust particles (cigarette smoke) suspended in still air in a needle-to-plate negative DC corona discharge arrangement just after the corona onset, i.e. in the first stage of development of the EHD particle flow. The experimental apparatus for our study of the EHD flow onset consisted of a needle-to-plate electrode arrangement, high voltage power supply and time-resolved EHD imaging system based on 2D time-resolved particle image velocimetry equipment. The time-resolved flow images clearly show the formation of a ball-like flow structure at the needle tip just after the corona discharge onset, and its evolution into a mushroom-like object moving to the collecting electrode. After a certain time, when the mushroom-like object is still present in the interelectrode gap a second mushroom-like object forms near the needle electrode and starts to move towards the collecting electrode. Before the first mushroom-like object reaches the collecting electrode several similar mushroom-like objects can be formed and presented simultaneously in the interelectrode gap. They look like a series of mushroom-like minijets shot from the needle electrode vicinity towards the collecting electrode. The simultaneous presence of mushroom-like minijets in the interelectrode gap in the corona discharge in particle-seeded air resembles the negative-ion-charged ‘clouds’ (induced by the Trichel pulses) traversing simultaneously the interelectrode gap of the corona discharge in air, predicted a long time ago by Loeb, and Lama and Gallo and recently by Dordizadeh et al. Analysing the time behaviours of the mushroom-like minijets and current waveform in the corona discharge in particle-seeded air, we found that the Trichel pulse trains, formed just after the corona onset initiates the mushroom-like minijets. The first stage of development of the EHD particle flow, the area of

  16. Spatial and temporal distribution of the seismicity along two mid-oceanic ridges with contrasted spreading rates in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Tsang-Hin-Sun, E.; Perrot, J.; Royer, J. Y.

    2015-12-01

    The seismicity of the ultra-slow spreading Southwest (14 mm/y) and intermediate spreading Southeast (60 mm/y) Indian ridges was monitored from February 2012 to March 2013 by the OHASISBIO array of 7 autonomous hydrophones. A total of 1471 events were located with 4 instruments or more, inside the array, with a median location uncertainty < 5 km and a completeness magnitude of mb = 3. Both ridges display similar average rates of seismicity, suggesting that there is no systematic relationship between seismicity and spreading rates. Accretion modes do differ, however, by the along-axis distribution of the seismic events. Along the ultra-slow Southwest Indian Ridge, events are sparse but regularly spaced and scattered up to 50 km off-axis. Along the fast Southeast Indian Ridge, events are irregularly distributed, focusing in narrow regions near the ridge axis at segment ends and along transform faults, whereas ridge-segment centers generally appear as seismic gaps (at the level of completeness of the array). Only two clusters, 6 months apart, are identified in a segment-center at 29°S. From the temporal distribution of the clustered events and comparisons with observations in similar mid-oceanic ridge setting, both clusters seem to have a volcanic origin and to be related to a dike emplacement or a possible eruption on the seafloor. Their onset time and migration rate are comparable to volcanic swarms recorded along the Juan de Fuca Ridge. Overall, the rate of seismicity along the two Indian spreading ridges correlates with the large-scale variations in the bathymetry and shear-wave velocity anomaly in the upper mantle, suggesting that the distribution of the low-magnitude seismicity is mainly controlled by along-axis variations in the lithosphere rheology and temperature.

  17. Spread Supersymmetry

    NASA Astrophysics Data System (ADS)

    Hall, Lawrence J.; Nomura, Yasunori

    2012-01-01

    In the multiverse the scale of supersymmetry breaking, widetilde{m} = {F_X}/{M_{ * }} ∗, may scan and environmental constraints on the dark matter density may exclude a large range of m from the reheating temperature after inflation down to values that yield a lightest supersymmetric particle (LSP) mass of order a TeV. After selection effects, for example from the cosmological constant, the distribution for widetilde{m} in the region that gives a TeV LSP may prefer larger values. A single environmental constraint from dark matter can then lead to multi-component dark matter, including both axions and the LSP, giving a TeV-scale LSP somewhat lighter than the corresponding value for single-component LSP dark matter. If supersymmetry breaking is mediated to the Standard Model sector at order X † X and higher, only squarks, sleptons and one Higgs doublet acquire masses of order widetilde{m} . The gravitino mass is lighter by a factor of M ∗ /M Pl and the gaugino masses are suppressed by a further loop factor. This Spread Supersymmetry spectrum has two versions, one with Higgsino masses arising from supergravity effects of order the gravitino mass giving a wino LSP, and another with the Higgsino masses generated radiatively from gaugino masses giving a Higgsino LSP. The environmental restriction on dark matter fixes the LSP mass to the TeV domain, so that the squark and slepton masses are order 103 TeV and 106 TeV in these two schemes. We study the spectrum, dark matter and collider signals of these two versions of Spread Supersymmetry. The Higgs boson is Standard Model-like and predicted to lie in the range 110-145 GeV; monochromatic photons in cosmic rays arise from dark matter annihilations in the halo; exotic short charged tracks occur at the LHC, at least for the wino LSP; and there are the eventual possibilities of direct detection of dark matter and detailed exploration of the TeV-scale states at a future linear collider. Gauge coupling unification is at

  18. The role of transnational mobility in the local spread of mosquito-borne disease: Measuring the determinants of spatial-temporal lags of imported dengue cases initiating indigenous epidemics in Taiwan

    NASA Astrophysics Data System (ADS)

    Wen, Tzai-Hung

    2014-05-01

    Dengue fever is one of the world's most widely spread mosquito-borne diseases. International travelers who acquire dengue infection are important routes for virus transmission from one country to another one. Previous studies have shown that imported dengue cases are able to initiate indigenous epidemics when appropriate weather conditions are present. However, the spatial-temporal associations between imported cases and indigenous epidemics in areas with different social-economic conditions are still unclear. This study investigated determinants of spatial-temporal lags of imported dengue cases who initiated indigenous epidemics from 2003 to 2012 in Taiwan. The quantile regression is used to explore the associations between spatial-temporal lags of imported cases and social-economic indicators with geographic heterogeneity. Our results indicated that imported cases in April and May have statistically significant contribution to initiate indigenous epidemics. Areas with high population density and low average income have significant risk of being imported virus from other areas. However, the areas with imported cases are not significant transmission risk. The results imply that imported cases reported in early summer may be an early-warning indicator of indigenous epidemics. Local demographic and economic conditions, rather than imported cases, may determine the areas with the risk of indigenous epidemics.

  19. Transport of semivolatile organic compounds to the Tibetan plateau: spatial and temporal variation in air concentrations in mountainous Western Sichuan, China.

    PubMed

    Liu, Wenjie; Chen, Dazhou; Liu, Xiande; Zheng, Xiaoyan; Yang, Wen; Westgate, John N; Wania, Frank

    2010-03-01

    The distribution of organochlorine pesticides and polychlorinated biphenyls in air along an altitudinal transect on Balang Mountain in western China was measured by deploying XAD-2 resin based passive air samplers in duplicate at seven sites with elevations ranging from 1242 to 4485 m above sea level for five consecutive six-month periods between 2005 and 2008. Analyzed by gas chromatography-high resolution mass spectrometry, concentrations of hexachlorobenzene were highest, followed by hexachlorocyclohexanes, DDT-related compounds and PCB congeners 28 and 52. Except for hexachlorobenzene, which had largely uniform concentrations in space and time, there were clear seasonal variations with concentrations in summer being higher than in winter. With a few exceptions, concentrations that vary little with altitude suggest that the presence of these chemicals in the area is almost entirely due to atmospheric transport, most likely from the Chengdu plain. This is supported by similarities in the relative abundance of different compounds and in the differences between summer and winter concentrations measured in the city of Chengdu and in the mountains. Furthermore, air mass trajectories during the sampling period often originate to the East, passing over the Western part of the Sichuan basin, including the Chengdu plain, prior to arriving at the sampling sites. Higher summer time values in the mountains are due to more contaminated air being blown into the region, presumably due either to higher pesticide usage in summer or due to higher temperatures leading to higher evaporation in source regions. Air and soil from the region are in equilibrium with respect to alpha-HCH, gamma-HCH, and HCB, whereas a situation of net deposition prevails for p,p'-DDE and p,p'-DDT.

  20. Drop spreading with random viscosity

    NASA Astrophysics Data System (ADS)

    Xu, Feng; Jensen, Oliver E.

    2016-10-01

    We examine theoretically the spreading of a viscous liquid drop over a thin film of uniform thickness, assuming the liquid's viscosity is regulated by the concentration of a solute that is carried passively by the spreading flow. The solute is assumed to be initially heterogeneous, having a spatial distribution with prescribed statistical features. To examine how this variability influences the drop's motion, we investigate spreading in a planar geometry using lubrication theory, combining numerical simulations with asymptotic analysis. We assume diffusion is sufficient to suppress solute concentration gradients across but not along the film. The solute field beneath the bulk of the drop is stretched by the spreading flow, such that the initial solute concentration immediately behind the drop's effective contact lines has a long-lived influence on the spreading rate. Over long periods, solute swept up from the precursor film accumulates in a short region behind the contact line, allowing patches of elevated viscosity within the precursor film to hinder spreading. A low-order model provides explicit predictions of the variances in spreading rate and drop location, which are validated against simulations.

  1. Drop spreading with random viscosity

    PubMed Central

    2016-01-01

    We examine theoretically the spreading of a viscous liquid drop over a thin film of uniform thickness, assuming the liquid’s viscosity is regulated by the concentration of a solute that is carried passively by the spreading flow. The solute is assumed to be initially heterogeneous, having a spatial distribution with prescribed statistical features. To examine how this variability influences the drop’s motion, we investigate spreading in a planar geometry using lubrication theory, combining numerical simulations with asymptotic analysis. We assume diffusion is sufficient to suppress solute concentration gradients across but not along the film. The solute field beneath the bulk of the drop is stretched by the spreading flow, such that the initial solute concentration immediately behind the drop’s effective contact lines has a long-lived influence on the spreading rate. Over long periods, solute swept up from the precursor film accumulates in a short region behind the contact line, allowing patches of elevated viscosity within the precursor film to hinder spreading. A low-order model provides explicit predictions of the variances in spreading rate and drop location, which are validated against simulations. PMID:27843398

  2. Discovery and Distribution of Black Smokers on the Western Galapagos Spreading Center: Implications for Spatial and Temporal Controls on High Temperature Venting at Ridge/Hotspot Intersections

    NASA Astrophysics Data System (ADS)

    Haymon, R. M.; Anderson, P. G.; Baker, E. T.; Resing, J. A.; White, S. M.; MacDonald, K. C.

    2006-12-01

    Though nearly one-fifth of the mid-ocean ridge (MOR) lies on or near hotspots, it has been debated whether hotspots increase or decrease MOR hydrothermal flux, or affect vent biota. Despite hotspot enhancement of melt supply, high-temperature vent plumes are enigmatically sparse along two previously-surveyed ridge- hotspot intersections [Reykjanes Ridge (RR), Southeast Indian Ridge (SEIR)]. This has been attributed to crustal thickening by excess volcanism. During the 2005-06 GalAPAGoS expedition, we conducted nested sonar, plume, and camera surveys along a 540 km-long portion of the Galapagos Spreading Center (GSC) where the ridge intersects the Galapagos hotspot at lon. 94.5 -89.5 deg. W. Although MOR hydrothermal springs were first found along the eastern GSC crest in 1977 near lon. 86 deg. W, the GalAPAGoS smokers are the first active high-temperature vents to be found anywhere along the Cocos-Nazca plate boundary. Active and/or recently-inactive smokers were located beneath plumes at 5 sites on the seafloor between lon. 91 deg. W and 94.5 deg. W (see Anderson et al., this session) during near-bottom, real-time fiber-optic Medea camera surveys. Smokers occur along eruptive seafloor fissures atop axial volcanic ridges near the middles of ridge segments, mainly in areas underlain by relatively shallow, continuous axial magma chamber (AMC) seismic reflectors. These findings (1) support magmatic, rather than tectonic, control of GSC smoker distribution; (2) demonstrate that thick crust at MOR-hotspot intersections does not prevent high-temperature hydrothermal vents from forming; and, (3) appear to be inconsistent with models suggesting that enhanced hydrothermal cooling causes abrupt deepening of the AMC and transition from non-rifted to rifted GSC morphology near lon. 92.7 deg. W. The widely-spaced smoker sites located on different GSC segments exhibit remarkably similar characteristics and seafloor settings. Most sites are mature or extinct, and are on lava

  3. Elemental mercury (Hg(0)) in air and surface waters of the Yellow Sea during late spring and late fall 2012: concentration, spatial-temporal distribution and air/sea flux.

    PubMed

    Ci, Zhijia; Wang, Chunjie; Wang, Zhangwei; Zhang, Xiaoshan

    2015-01-01

    The Yellow Sea in East Asia receives great Hg input from regional emissions. However, Hg cycling in this marine system is poorly investigated. In late spring and late fall 2012, we determined gaseous elemental Hg (GEM or Hg(0)) in air and dissolved gaseous Hg (DGM, mainly Hg(0)) in surface waters to explore the spatial-temporal variations of Hg(0) and further to estimate the air/sea Hg(0) flux in the Yellow Sea. The results showed that the GEM concentrations in the two cruises were similar (spring: 1.86±0.40 ng m(-3); fall: 1.84±0.50 ng m(-3)) and presented similar spatial variation pattern with elevated concentrations along the coast of China and lower concentrations in the open ocean. The DGM concentrations of the two cruises were also similar with 27.0±6.8 pg L(-1) in the spring cruise and 28.2±9.0 pg L(-1) in the fall cruise and showed substantial spatial variation. The air/sea Hg(0) fluxes in the spring cruise and fall cruise were estimated to be 1.06±0.86 ng m(-2) h(-1) and 2.53±2.12 ng m(-2) h(-1), respectively. The combination of this study and our previous summer cruise showed that the summer cruise presented enhanced values of GEM, DGM and air/sea Hg(0) flux. The possible reason for this trend was that high solar radiation in summer promoted Hg(0) formation in seawater, and the high wind speed during the summer cruise significantly increased Hg(0) emission from sea surface to atmosphere and subsequently enhanced the GEM levels.

  4. Myosin is involved in postmitotic cell spreading

    PubMed Central

    1995-01-01

    We have investigated a role for myosin in postmitotic Potoroo tridactylis kidney (PtK2) cell spreading by inhibitor studies, time- lapse video microscopy, and immunofluorescence. We have also determined the spatial organization and polarity of actin filaments in postmitotic spreading cells. We show that butanedione monoxime (BDM), a known inhibitor of muscle myosin II, inhibits nonmuscle myosin II and myosin V adenosine triphosphatases. BDM reversibly inhibits PtK2 postmitotic cell spreading. Listeria motility is not affected by this drug. Electron microscopy studies show that some actin filaments in spreading edges are part of actin bundles that are also found in long, thin, structures that are connected to spreading edges and substrate (retraction fibers), and that 90% of this actin is oriented with barbed ends in the direction of spreading. The remaining actin in spreading edges has a more random orientation and spatial arrangement. Myosin II is associated with actin polymer in spreading cell edges, but not retraction fibers. Myosin II is excluded from lamellipodia that protrude from the cell edge at the end of spreading. We suggest that spreading involves myosin, possibly myosin II. PMID:7559774

  5. Projecting rates of spread for invasive species.

    PubMed

    Neubert, Michael G; Parker, Ingrid M

    2004-08-01

    All else being equal, the faster an invading species spreads, the more dangerous its invasion. The projection of spread rate therefore ought to be a central part of the determination of invasion risk. Originally formulated in the 1970s to describe the spatial spread of advantageous alleles, integrodifference equation (IDE) models have since been co-opted by population biologists to describe the spread of populations. More recently, they have been modified to include population structure and environmental variability. We review how IDE models are formulated, how they are parameterized, and how they can be analyzed to project spread rates and the sensitivity of those rates to changes in model parameters. For illustrative purposes, we apply these models to Cytisus scoparius, a large shrub in the legume family that is considered a noxious invasive species in eastern and western North America, Chile, Australia, and New Zealand.

  6. Spreading of Cholera through Surface Water

    NASA Astrophysics Data System (ADS)

    Bertuzzo, E.; Casagrandi, R.; Gatto, M.; Rodriguez-Iturbe, I.; Rinaldo, A.

    2009-12-01

    Cholera epidemics are still a major public health concern to date in many areas of the world. In order to understand and forecast cholera outbreaks, one of the most important factors is the role played by the environmental matrix in which the disease spreads. We study how river networks, acting as environmental corridors for pathogens, affect the spreading of cholera epidemics. The environmental matrix in which the disease spreads is constituted by different human communities and their hydrologic interconnections. Each community is characterized by its spatial position, population size, water resources availability and hygiene conditions. By implementing a spatially explicit cholera model we seek the effects on epidemic dynamics of: i) the topology and metrics of the pathogens pathways that connect different communities; ii) the spatial distribution of the population size; and iii) the spatial distributions and quality of surface water resources and public health conditions, and how they vary with population size. The model has been applied to study the space-time evolution of a well documented cholera epidemic occurred in the KwaZulu-Natal province of South Africa. The epidemic lasted for two years and involved about 140,000 confirmed cholera cases. The model does well in reproducing the distribution of the cholera cases during the two outbreaks as well as their spatial spreading. We further extend the model by deriving the speed of propagation of traveling fronts in the case of uniformly distributed systems for different topologies: one and two dimensional lattices and river networks. The derivation of the spreading celerity proves instrumental in establishing the overall conditions for the relevance of spatially explicit models. The conditions are sought by comparison between spreading and disease timescales. Consider a cholera epidemic that starts from a point and spreads throughout a finite size system, it is possible to identify two different timescales: i

  7. The spreading of disorder.

    PubMed

    Keizer, Kees; Lindenberg, Siegwart; Steg, Linda

    2008-12-12

    Imagine that the neighborhood you are living in is covered with graffiti, litter, and unreturned shopping carts. Would this reality cause you to litter more, trespass, or even steal? A thesis known as the broken windows theory suggests that signs of disorderly and petty criminal behavior trigger more disorderly and petty criminal behavior, thus causing the behavior to spread. This may cause neighborhoods to decay and the quality of life of its inhabitants to deteriorate. For a city government, this may be a vital policy issue. But does disorder really spread in neighborhoods? So far there has not been strong empirical support, and it is not clear what constitutes disorder and what may make it spread. We generated hypotheses about the spread of disorder and tested them in six field experiments. We found that, when people observe that others violated a certain social norm or legitimate rule, they are more likely to violate other norms or rules, which causes disorder to spread.

  8. Flame spread across liquids

    NASA Technical Reports Server (NTRS)

    Ross, Howard D.; Miller, Fletcher; Schiller, David; Sirignano, William

    1995-01-01

    Recent reviews of our understanding of flame spread across liquids show that there are many unresolved issues regarding the phenomenology and causal mechanisms affecting ignition susceptibility, flame spread characteristics, and flame spread rates. One area of discrepancy is the effect of buoyancy in both the uniform and pulsating spread regimes. The approach we have taken to resolving the importance of buoyancy for these flames is: (1) normal gravity (1g) and microgravity (micro g) experiments; and (2) numerical modeling at different gravitational levels. Of special interest to this work, as discussed at the previous workshop, is the determination of whether, and under what conditions, pulsating spread occurs in micro g. Microgravity offers a unique ability to modify and control the gas-phase flow pattern by utilizing a forced air flow over the pool surface.

  9. The temporal and spatial distribution of magmatism during lower crustal accretion at an ultraslow-spreading ridge: High-precision U-Pb zircon dating of ODP Holes 735B and 1105A, Atlantis Bank, Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Rioux, Matthew; Cheadle, Michael J.; John, Barbara E.; Bowring, Samuel A.

    2016-09-01

    Ocean Drilling Program Hole 735B at Atlantis Bank on the Southwest Indian Ridge sampled 1508 m of plutonic oceanic crust, hosted in the footwall of an oceanic detachment fault. We present new high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon dates from samples spanning the length of Hole 735B, and from the shallower adjacent Hole 1105A (158 m). The new dates provide the most complete and precise record of both the spatial and temporal distribution of magmatism during accretion of the lower oceanic crust to date. Whole rock and mineral geochemistry from Hole 735B define three main igneous series. Weighted mean 206Pb/238U dates suggest each igneous series intruded beneath the preceding series. Weighted mean 206Pb/238U dates range from 12.175 to 11.986 Ma in Series 1; 11.974 to 11.926 Ma in Series 2; and 11.936 to 11.902 Ma in Series 3 (±0.015 to 0.069 Ma). Weighted mean 206Pb/238U dates from Hole 1105A range from 11.9745 to 11.9573 Ma (±0.0082 to 0.0086 Ma). The Hole 1105A dates are coeval with Series 2 in Hole 735B, consistent with previous correlations of Fe-Ti oxide-rich layers between the two holes, suggesting individual magmatic series formed sheet-like bodies that were ≥250 m thick and extended ≥1.1 km parallel to the ridge axis (E-W) and ≥0.48 km in the spreading direction (N-S). The data suggest a total duration of magmatism in Hole 735B of ≥ 0.214 ± 0.032 Ma, corresponding to accretion over a horizontal distance of ≥ 2.6 ± 0.4 km. The crust at Atlantis Bank was formed during active detachment faulting, and the successive underplating of each magmatic unit may have been favored in this environment. The combined U-Pb dates, and reported Ti-in-zircon temperatures, are consistent with magmatic cooling rates of 103-104 °C/Ma over the temperature interval of 900-700 °C.

  10. Drop Spreading with Random Viscosity

    NASA Astrophysics Data System (ADS)

    Xu, Feng; Jensen, Oliver

    2016-11-01

    Airway mucus acts as a barrier to protect the lung. However as a biological material, its physical properties are known imperfectly and can be spatially heterogeneous. In this study we assess the impact of these uncertainties on the rate of spreading of a drop (representing an inhaled aerosol) over a mucus film. We model the film as Newtonian, having a viscosity that depends linearly on the concentration of a passive solute (a crude proxy for mucin proteins). Given an initial random solute (and hence viscosity) distribution, described as a Gaussian random field with a given correlation structure, we seek to quantify the uncertainties in outcomes as the drop spreads. Using lubrication theory, we describe the spreading of the drop in terms of a system of coupled nonlinear PDEs governing the evolution of film height and the vertically-averaged solute concentration. We perform Monte Carlo simulations to predict the variability in the drop centre location and width (1D) or area (2D). We show how simulation results are well described (at much lower computational cost) by a low-order model using a weak disorder expansion. Our results show for example how variability in the drop location is a non-monotonic function of the solute correlation length increases. Engineering and Physical Sciences Research Council.

  11. Flame Spread Across Liquids

    NASA Technical Reports Server (NTRS)

    Ross, Howard D.; Miller, Fletcher J.; Sirignano, William A.; Schiller, David

    1997-01-01

    The principal goal of our recent research on flame spread across liquid pools is the detailed identification of the mechanisms that control the rate and nature of flame spread when the liquid pool is initially at an isothermal bulk temperature that is below the fuel's flash point temperature. In our project, we specialize the subject to highlight the roles of buoyancy-related processes regarding the mechanisms of flame spread, an area of research cited recently by Linan and Williams as one that needs further attention and which microgravity (micro-g) experiments could help to resolve. Toward resolving the effects of buoyancy on this flame spread problem, comparisons - between 1-g and micro-g experimental observations, and between model predictions and experimental data at each of these gravitational levels - are extensively utilized. The present experimental and computational foundation is presented to support identification of the mechanisms that control flame spread in the pulsating flame spread regime for which long-duration, micro-g flame spread experiments have been conducted aboard a sounding rocket.

  12. Visual attention spreads broadly but selects information locally

    PubMed Central

    Shioiri, Satoshi; Honjyo, Hajime; Kashiwase, Yoshiyuki; Matsumiya, Kazumichi; Kuriki, Ichiro

    2016-01-01

    Visual attention spreads over a range around the focus as the spotlight metaphor describes. Spatial spread of attentional enhancement and local selection/inhibition are crucial factors determining the profile of the spatial attention. Enhancement and ignorance/suppression are opposite effects of attention, and appeared to be mutually exclusive. Yet, no unified view of the factors has been provided despite their necessity for understanding the functions of spatial attention. This report provides electroencephalographic and behavioral evidence for the attentional spread at an early stage and selection/inhibition at a later stage of visual processing. Steady state visual evoked potential showed broad spatial tuning whereas the P3 component of the event related potential showed local selection or inhibition of the adjacent areas. Based on these results, we propose a two-stage model of spatial attention with broad spread at an early stage and local selection at a later stage. PMID:27759056

  13. Spreading of triboelectrically charged granular matter

    PubMed Central

    Kumar, Deepak; Sane, A.; Gohil, Smita.; Bandaru, P. R.; Bhattacharya, S.; Ghosh, Shankar

    2014-01-01

    We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures. PMID:24919483

  14. Spreading of triboelectrically charged granular matter.

    PubMed

    Kumar, Deepak; Sane, A; Gohil, Smita; Bandaru, P R; Bhattacharya, S; Ghosh, Shankar

    2014-06-12

    We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures.

  15. Epidemic spreading in a hierarchical social network

    NASA Astrophysics Data System (ADS)

    Grabowski, A.; Kosiński, R. A.

    2004-09-01

    A model of epidemic spreading in a population with a hierarchical structure of interpersonal interactions is described and investigated numerically. The structure of interpersonal connections is based on a scale-free network. Spatial localization of individuals belonging to different social groups, and the mobility of a contemporary community, as well as the effectiveness of different interpersonal interactions, are taken into account. Typical relations characterizing the spreading process, like a range of epidemic and epidemic curves, are discussed. The influence of preventive vaccinations on the spreading process is investigated. The critical value of preventively vaccinated individuals that is sufficient for the suppression of an epidemic is calculated. Our results are compared with solutions of the master equation for the spreading process and good agreement of the character of this process is found.

  16. Quantum Spread Spectrum Communication

    SciTech Connect

    Humble, Travis S

    2010-01-01

    We demonstrate that spectral teleportation can coherently dilate the spectral probability amplitude of a single photon. In preserving the encoded quantum information, this variant of teleportation subsequently enables a form of quantum spread spectrum communication.

  17. Role of dispersal in resistance evolution and spread.

    PubMed

    Miller, Nicholas J; Sappington, Thomas W

    2017-06-01

    Gene flow via immigration affects rate of evolution of resistance to a pest management tactic, while emigration from a resistant population can spread resistance alleles spatially. Whether resistance detected across the landscape reflects ongoing de novo evolution in different hotspots or spread from a single focal population can determine the most effective mitigation strategy. Pest dispersal dynamics determine the spatio-temporal scale at which mitigation tactics must be applied to contain or reverse resistance in an area. Independent evolution of resistance in different populations appears common but not universal. Conversely, spatial spread appears to be almost inevitable. However, rate and scale of spread depends largely on dispersal dynamics and interplay with factors such as fitness costs, spatially variable selection pressure and whether resistance alleles are spreading through an established population or being carried by populations colonizing new territory. Published by Elsevier Inc.

  18. Filamentational instability of partially coherent femtosecond optical pulses in air.

    PubMed

    Marklund, M; Shukla, P K

    2006-06-15

    The filamentational instability of spatially broadband femtosecond optical pulses in air is investigated by means of a kinetic wave equation for spatially incoherent photons. An explicit expression for the spatial amplification rate is derived and analyzed. It is found that the spatial spectral broadening of the pulse can lead to stabilization of the filamentation instability. Thus optical smoothing techniques could optimize current applications of ultrashort laser pulses, such as atmospheric remote sensing.

  19. Liquid drop spreading on surfaces: Initial regimes revisited

    NASA Astrophysics Data System (ADS)

    Mitra, Surjyasish; Mitra, Sushanta

    2016-11-01

    Liquid drop spreading on a given surface is fundamental towards technological processes like coating and paints, inkjet printing, surface characterization, etc. Though, the underlying dynamics is well understood, we have revisited this problem through experiments conducted on surfaces kept in air as well as immersed in water. It was found that the two key parameters that dictated the spreading process were drop-surrounding medium viscosity ratio and the characteristic viscous length scale. It was observed that irrespective of the drop liquid and surrounding liquid medium (air and water in this case), spreading always began in a regime dominated by drop viscosity, where the spreading radius scales as r t . However, the prefactor of the scaling observed was different for air (of the order of unity) and under-water (much less than unity). Following this initial regime, a second intermediate regime dominated by drop inertia (typically found for water drops spreading in air) was observed only when the characteristic viscous length scale favored such a transition. In this regime as well, a non-universal prefactor was noted for the scaling law, i.e., r t1/2. In all cases considered, the spreading process terminated in the Tanner's regime where the spreading radius scaled as r t1/10.

  20. Role of dispersal in resistance evolution and spread

    USDA-ARS?s Scientific Manuscript database

    Insect dispersal plays a pivotal role in both the evolution of insecticide resistance at a location, and in the rate and pattern of its spatial spread. While intuitively obvious, the dynamics of evolution and spread are complex and often difficult to characterize for a given species. Dispersal by in...

  1. Modeling daily flow patterns individuals to characterize disease spread

    SciTech Connect

    Smallwood, J.; Hyman, J. M.; Mirchandani, Pitu B.

    2002-11-17

    The effect of an individual's travels throughout a day on the spread of disease is examined using a deterministic SIR model. We determine which spatial and demographic characteristics most contribute to the disease spread and whether the progression of the disease can be slowed by appropriate vaccination of people belonging to a specific location-type.

  2. Modeling Viral Spread

    PubMed Central

    Graw, Frederik; Perelson, Alan S.

    2016-01-01

    The way in which a viral infection spreads within a host is a complex process that is not well understood. Different viruses, such as human immunodeficiency virus type 1 and hepatitis C virus, have evolved different strategies, including direct cell-to-cell transmission and cell-free transmission, to spread within a host. To what extent these two modes of transmission are exploited in vivo is still unknown. Mathematical modeling has been an essential tool to get a better systematic and quantitative understanding of viral processes that are difficult to discern through strictly experimental approaches. In this review, we discuss recent attempts that combine experimental data and mathematical modeling in order to determine and quantify viral transmission modes. We also discuss the current challenges for a systems-level understanding of viral spread, and we highlight the promises and challenges that novel experimental techniques and data will bring to the field. PMID:27618637

  3. Cortical spreading depression: An enigma

    NASA Astrophysics Data System (ADS)

    Miura, R. M.; Huang, H.; Wylie, J. J.

    2007-08-01

    The brain is a complex organ with active components composed largely of neurons, glial cells, and blood vessels. There exists an enormous experimental and theoretical literature on the mechanisms involved in the functioning of the brain, but we still do not have a good understanding of how it works on a gross mechanistic level. In general, the brain maintains a homeostatic state with relatively small ion concentration changes, the major ions being sodium, potassium, and chloride. Calcium ions are present in smaller quantities but still play an important role in many phenomena. Cortical spreading depression (CSD for short) was discovered over 60 years ago by A.A.P. Leão, a Brazilian physiologist doing his doctoral research on epilepsy at Harvard University, “Spreading depression of activity in the cerebral cortex," J. Neurophysiol., 7 (1944), pp. 359-390. Cortical spreading depression is characterized by massive changes in ionic concentrations and slow nonlinear chemical waves, with speeds on the order of mm/min, in the cortex of different brain structures in various experimental animals. In humans, CSD is associated with migraine with aura, where a light scintillation in the visual field propagates, then disappears, and is followed by a sustained headache. To date, CSD remains an enigma, and further detailed experimental and theoretical investigations are needed to develop a comprehensive picture of the diverse mechanisms involved in producing CSD. A number of mechanisms have been hypothesized to be important for CSD wave propagation. In this paper, we briefly describe several characteristics of CSD wave propagation, and examine some of the mechanisms that are believed to be important, including ion diffusion, membrane ionic currents, osmotic effects, spatial buffering, neurotransmitter substances, gap junctions, metabolic pumps, and synaptic connections. Continuum models of CSD, consisting of coupled nonlinear diffusion equations for the ion concentrations, and

  4. Wave directional spreading from point field measurements.

    PubMed

    McAllister, M L; Venugopal, V; Borthwick, A G L

    2017-04-01

    Ocean waves have multidirectional components. Most wave measurements are taken at a single point, and so fail to capture information about the relative directions of the wave components directly. Conventional means of directional estimation require a minimum of three concurrent time series of measurements at different spatial locations in order to derive information on local directional wave spreading. Here, the relationship between wave nonlinearity and directionality is utilized to estimate local spreading without the need for multiple concurrent measurements, following Adcock & Taylor (Adcock & Taylor 2009 Proc. R. Soc. A465, 3361-3381. (doi:10.1098/rspa.2009.0031)), with the assumption that directional spreading is frequency independent. The method is applied to measurements recorded at the North Alwyn platform in the northern North Sea, and the results compared against estimates of wave spreading by conventional measurement methods and hindcast data. Records containing freak waves were excluded. It is found that the method provides accurate estimates of wave spreading over a range of conditions experienced at North Alwyn, despite the noisy chaotic signals that characterize such ocean wave data. The results provide further confirmation that Adcock and Taylor's method is applicable to metocean data and has considerable future promise as a technique to recover estimates of wave spreading from single point wave measurement devices.

  5. Wave directional spreading from point field measurements

    PubMed Central

    Venugopal, V.; Borthwick, A. G. L.

    2017-01-01

    Ocean waves have multidirectional components. Most wave measurements are taken at a single point, and so fail to capture information about the relative directions of the wave components directly. Conventional means of directional estimation require a minimum of three concurrent time series of measurements at different spatial locations in order to derive information on local directional wave spreading. Here, the relationship between wave nonlinearity and directionality is utilized to estimate local spreading without the need for multiple concurrent measurements, following Adcock & Taylor (Adcock & Taylor 2009 Proc. R. Soc. A 465, 3361–3381. (doi:10.1098/rspa.2009.0031)), with the assumption that directional spreading is frequency independent. The method is applied to measurements recorded at the North Alwyn platform in the northern North Sea, and the results compared against estimates of wave spreading by conventional measurement methods and hindcast data. Records containing freak waves were excluded. It is found that the method provides accurate estimates of wave spreading over a range of conditions experienced at North Alwyn, despite the noisy chaotic signals that characterize such ocean wave data. The results provide further confirmation that Adcock and Taylor's method is applicable to metocean data and has considerable future promise as a technique to recover estimates of wave spreading from single point wave measurement devices. PMID:28484326

  6. Wave directional spreading from point field measurements

    NASA Astrophysics Data System (ADS)

    McAllister, M. L.; Venugopal, V.; Borthwick, A. G. L.

    2017-04-01

    Ocean waves have multidirectional components. Most wave measurements are taken at a single point, and so fail to capture information about the relative directions of the wave components directly. Conventional means of directional estimation require a minimum of three concurrent time series of measurements at different spatial locations in order to derive information on local directional wave spreading. Here, the relationship between wave nonlinearity and directionality is utilized to estimate local spreading without the need for multiple concurrent measurements, following Adcock & Taylor (Adcock & Taylor 2009 Proc. R. Soc. A 465, 3361-3381. (doi:10.1098/rspa.2009.0031)), with the assumption that directional spreading is frequency independent. The method is applied to measurements recorded at the North Alwyn platform in the northern North Sea, and the results compared against estimates of wave spreading by conventional measurement methods and hindcast data. Records containing freak waves were excluded. It is found that the method provides accurate estimates of wave spreading over a range of conditions experienced at North Alwyn, despite the noisy chaotic signals that characterize such ocean wave data. The results provide further confirmation that Adcock and Taylor's method is applicable to metocean data and has considerable future promise as a technique to recover estimates of wave spreading from single point wave measurement devices.

  7. Topography driven spreading.

    PubMed

    McHale, G; Shirtcliffe, N J; Aqil, S; Perry, C C; Newton, M I

    2004-07-16

    Roughening a hydrophobic surface enhances its nonwetting properties into superhydrophobicity. For liquids other than water, roughness can induce a complete rollup of a droplet. However, topographic effects can also enhance partial wetting by a given liquid into complete wetting to create superwetting. In this work, a model system of spreading droplets of a nonvolatile liquid on surfaces having lithographically produced pillars is used to show that superwetting also modifies the dynamics of spreading. The edge speed-dynamic contact angle relation is shown to obey a simple power law, and such power laws are shown to apply to naturally occurring surfaces.

  8. Applying fire spread simulators in New Zealand and Australia: Results from an international seminar

    Treesearch

    Tonja Opperman; Jim Gould; Mark Finney; Cordy Tymstra

    2006-01-01

    There is currently no spatial wildfire spread and growth simulation model used commonly across New Zealand or Australia. Fire management decision-making would be enhanced through the use of spatial fire simulators. Various groups from around the world met in January 2006 to evaluate the applicability of different spatial fire spread applications for common use in both...

  9. Spreading of miscible liquids

    NASA Astrophysics Data System (ADS)

    Walls, Daniel J.; Haward, Simon J.; Shen, Amy Q.; Fuller, Gerald G.

    2016-05-01

    Miscible liquids commonly contact one another in natural and technological situations, often in the proximity of a solid substrate. In the scenario where a drop of one liquid finds itself on a solid surface and immersed within a second, miscible liquid, it will spread spontaneously across the surface. We show experimental findings of the spreading of sessile drops in miscible environments that have distinctly different shape evolution and power-law dynamics from sessile drops that spread in immiscible environments, which have been reported previously. We develop a characteristic time to scale radial data of the spreading sessile drops based on a drainage flow due to gravity. This time scale is effective for a homologous subset of the liquids studied. However, it has limitations when applied to significantly chemically different, yet miscible, liquid pairings; we postulate that the surface energies between each liquid and the solid surface becomes important for this other subset of the liquids studied. Initial experiments performed with pendant drops in miscible environments support the drainage flow observed in the sessile drop systems.

  10. Spread spectrum image steganography.

    PubMed

    Marvel, L M; Boncelet, C R; Retter, C T

    1999-01-01

    In this paper, we present a new method of digital steganography, entitled spread spectrum image steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a discussion of steganographic communication theory and review of existing techniques, the new method, SSIS, is introduced. This system hides and recovers a message of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden message can be recovered using appropriate keys without any knowledge of the original image. Image restoration, error-control coding, and techniques similar to spread spectrum are described, and the performance of the system is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such a data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking.

  11. Reaction spreading on graphs.

    PubMed

    Burioni, Raffaella; Chibbaro, Sergio; Vergni, Davide; Vulpiani, Angelo

    2012-11-01

    We study reaction-diffusion processes on graphs through an extension of the standard reaction-diffusion equation starting from first principles. We focus on reaction spreading, i.e., on the time evolution of the reaction product M(t). At variance with pure diffusive processes, characterized by the spectral dimension d{s}, the important quantity for reaction spreading is found to be the connectivity dimension d{l}. Numerical data, in agreement with analytical estimates based on the features of n independent random walkers on the graph, show that M(t)∼t{d{l}}. In the case of Erdös-Renyi random graphs, the reaction product is characterized by an exponential growth M(t)e{αt} with α proportional to ln(k), where (k) is the average degree of the graph.

  12. Spread-Spectrum Communications.

    DTIC Science & Technology

    1984-08-07

    Articles M. B. Parsley and H. F. A. Roefs, "Numerical evaluation of correlation parameters for optimal phases of binary shift-register sequences," IEEE...Transactions on Communications, Vol. COM-27, pp. 1597-1604, October 1979. D. V. Sarwate and M. B. Parsley , "Crcuecorrehation proets Of psuoadmand related...Signal Processing, Vol. 128, pp. 104-109, April 1981. * M. B. Parsley , D. V. Sarwate, and W. E. Stark, ’Error probability for direct-sequence spread

  13. Effect of Longitudinal Oscillations on Downward Flame Spread over Thin Solid Fuels

    NASA Technical Reports Server (NTRS)

    Nayagam, Vedha; Sacksteder, Kurt

    2013-01-01

    Downward flame spread rates over vertically vibrated thin fuel samples are measured in air at one atmospheric pressure under normal gravity. Unlike flame spread against forced-convective flows, the present results show that with increasing vibration acceleration the flame spread rate increases before being blown off at high acceleration levels causing flame extinction. A simple scaling analysis seems to explain this phenomenon, which may have important implications to flammability studies including in microgravity environments.

  14. Hybrid spread spectrum radio system

    DOEpatents

    Smith, Stephen F [London, TN; Dress, William B [Camas, WA

    2010-02-09

    Systems and methods are described for hybrid spread spectrum radio systems. A method, includes receiving a hybrid spread spectrum signal including: fast frequency hopping demodulating and direct sequence demodulating a direct sequence spread spectrum signal, wherein multiple frequency hops occur within a single data-bit time and each bit is represented by chip transmissions at multiple frequencies.

  15. The Spread of Inequality

    PubMed Central

    Rogers, Deborah S.; Deshpande, Omkar; Feldman, Marcus W.

    2011-01-01

    The causes of socioeconomic inequality have been debated since the time of Plato. Many reasons for the development of stratification have been proposed, from the need for hierarchical control over large-scale irrigation systems to the accumulation of small differences in wealth over time via inheritance processes. However, none of these explains how unequal societies came to completely displace egalitarian cultural norms over time. Our study models demographic consequences associated with the unequal distribution of resources in stratified societies. Agent-based simulation results show that in constant environments, unequal access to resources can be demographically destabilizing, resulting in the outward migration and spread of such societies even when population size is relatively small. In variable environments, stratified societies spread more and are also better able to survive resource shortages by sequestering mortality in the lower classes. The predictions of our simulation are provided modest support by a range of existing empirical studies. In short, the fact that stratified societies today vastly outnumber egalitarian societies may not be due to the transformation of egalitarian norms and structures, but may instead reflect the more rapid migration of stratified societies and consequent conquest or displacement of egalitarian societies over time. PMID:21957457

  16. Illusory spreading of watercolor

    PubMed Central

    Devinck, Frédéric; Hardy, Joseph L.; Delahunt, Peter B.; Spillmann, Lothar; Werner, John S.

    2008-01-01

    The watercolor effect (WCE) is a phenomenon of long-range color assimilation occurring when a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour; the brighter color spreads into the entire enclosed area. Here, we determined the optimal chromatic parameters and the cone signals supporting the WCE. To that end, we quantified the effect of color assimilation using hue cancellation as a function of hue, colorimetric purity, and cone modulation of inducing contours. When the inner and outer contours had chromaticities that were in opposite directions in color space, a stronger WCE was obtained as compared with other color directions. Additionally, equal colorimetric purity between the outer and inner contours was necessary to obtain a large effect compared with conditions in which the contours differed in colorimetric purity. However, there was no further increase in the magnitude of the effect when the colorimetric purity increased beyond a value corresponding to an equal vector length between the inner and outer contours. Finally, L–M-cone-modulated WCE was perceptually stronger than S-cone-modulated WCE for our conditions. This last result demonstrates that both L–M-cone and S-cone pathways are important for watercolor spreading. Our data suggest that the WCE depends critically upon the particular spatiochromatic arrangement in the display, with the relative chromatic contrast between the inducing contours being particularly important. PMID:16881793

  17. Temporal solitons in air

    NASA Astrophysics Data System (ADS)

    Voronin, A. A.; Zheltikov, A. M.

    2017-02-01

    Analysis of the group-velocity dispersion (GVD) of atmospheric air with a model that includes the entire manifold of infrared transitions in air reveals a remarkably broad and continuous anomalous-GVD region in the high-frequency wing of the carbon dioxide rovibrational band from approximately 3.5 to 4.2 μm where atmospheric air is still highly transparent and where high-peak-power sources of ultrashort midinfrared pulses are available. Within this range, anomalous dispersion acting jointly with optical nonlinearity of atmospheric air is shown to give rise to a unique three-dimensional dynamics with well-resolved soliton features in the time domain, enabling a highly efficient whole-beam soliton self-compression of such pulses to few-cycle pulse widths.

  18. Synchrotron emission in air

    NASA Astrophysics Data System (ADS)

    Rafat, M. Z.; Melrose, D. B.

    2015-05-01

    A conventional astrophysical treatment of synchrotron emission is modified to include the refractive index of air, written as n = 1 + 1/(2γ 02), with γ0 ≫ 1. The angular distribution of emission by an electron with Lorentz factor γ is broadened, from a range of |θ - α| ≈ 1/γ in vacuo (θ = emission angle, α = pitch angle) to |θ - α| ≈ max{1/γ, 1/γ0} in air. The emission spectrum in air is almost unchanged from that in vacuo at sufficiently low frequencies and it is modified by extending to higher frequencies with increasing γ/γ0 < 1, and to arbitrarily high frequencies for γ/γ0 ≥ 1. We estimate the frequency at which this enhancement starts, and show that it decreases with increasing γ/γ0 > 1. We interpret the enhanced high-frequency emission as Cerenkov-like, and attribute it to the formation of caustic surfaces that sweep across the observer; we use a geometric model based on Huygens construction to support this interpretation. The geometric model predicts that the so-called Cerenkov ring present at high frequencies may be circular, elliptical, or crescent shaped. In the astrophysical treatment of synchrotron emission, the dependence on azimuthal angle is lost in the expression for emissivity. A motivation for this investigation is the application to extensive air showers, and for this purpose the loss of azimuthal dependence is a limitation. We comment on methods to overcome this limitation. We show that when an observer can see emission from inside the Cerenkov cone, emission from outside the Cerenkov cone, on either side of it, arrives simultaneously; there are three emission times for a given observation time.

  19. Spatial and seasonal variations, sources, air-soil exchange, and carcinogenic risk assessment for PAHs and PCBs in air and soil of Kutahya, Turkey, the province of thermal power plants.

    PubMed

    Dumanoglu, Yetkin; Gaga, Eftade O; Gungormus, Elif; Sofuoglu, Sait C; Odabasi, Mustafa

    2017-02-15

    Atmospheric and concurrent soil samples were collected during winter and summer of 2014 at 41 sites in Kutahya, Turkey to investigate spatial and seasonal variations, sources, air-soil exchange, and associated carcinogenic risks of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The highest atmospheric and soil concentrations were observed near power plants and residential areas, and the wintertime concentrations were generally higher than ones measured in summer. Spatial distribution of measured ambient concentrations and results of the factor analysis showed that the major contributing PAH sources in Kutahya region were the coal combustion for power generation and residential heating (48.9%), and diesel and gasoline exhaust emissions (47.3%) while the major PCB sources were the coal (thermal power plants and residential heating) and wood combustion (residential heating) (45.4%), and evaporative emissions from previously used technical PCB mixtures (34.7%). Results of fugacity fraction calculations indicated that the soil and atmosphere were not in equilibrium for most of the PAHs (88.0% in winter, 87.4% in summer) and PCBs (76.8% in winter, 83.8% in summer). For PAHs, deposition to the soil was the dominant mechanism in winter while in summer volatilization was equally important. For PCBs, volatilization dominated in summer while deposition was higher in winter. Cancer risks associated with inhalation and accidental soil ingestion of soil were also estimated. Generally, the estimated carcinogenic risks were below the acceptable risk level of 10(-6). The percentage of the population exceeding the acceptable risk level ranged from <1% to 16%, except, 32% of the inhalation risk levels due to PAH exposure in winter at urban/industrial sites were >10(-6).

  20. Hydrothermal mineralization at seafloor spreading centers

    NASA Astrophysics Data System (ADS)

    Rona, Peter A.

    1984-01-01

    The recent recognition that metallic mineral deposits are concentrated by hydrothermal processes at seafloor spreading centers constitutes a scientific breakthrough that opens active sites at seafloor spreading centers as natural laboratories to investigate ore-forming processes of such economically useful deposits as massive sulfides in volcanogenic rocks on land, and that enhances the metallic mineral potential of oceanic crust covering two-thirds of the Earth both beneath ocean basins and exposed on land in ophiolite belts. This paper reviews our knowledge of processes of hydrothermal mineralization and the occurrence and distribution of hydrothermal mineral deposits at the global oceanic ridge-rift system. Sub-seafloor hydrothermal convection involving circulation of seawater through fractured rocks of oceanic crust driven by heat supplied by generation of new lithosphere is nearly ubiquitous at seafloor spreading centers. However, ore-forming hydrothermal systems are extremely localized where conditions of anomalously high thermal gradients and permeability increase hydrothermal activity from the ubiquitous low-intensity background level (⩽ 200°C) to high-intensity characterized by high temperatures ( > 200-c.400°C), and a rate and volume of flow sufficient to sustain chemical reactions that produce acid, reducing, metal-rich primary hydrothermal solutions. A series of mineral phases with sulfides and oxides as high- and low-temperature end members, respectively, are precipitated along the upwelling limb and in the discharge zone of single-phase systems as a function of increasing admixture of normal seawater. The occurrence of hydrothermal mineral deposits is considered in terms of spatial and temporal frames of reference. Spatial frames of reference comprise structural features along-axis (linear sections that are the loci of seafloor spreading alternating with transform faults) and perpendicular to axis (axial zone of volcanic extrusion and marginal

  1. Spreading convulsions, spreading depolarization and epileptogenesis in human cerebral cortex

    PubMed Central

    Major, Sebastian; Pannek, Heinz-Wolfgang; Woitzik, Johannes; Scheel, Michael; Wiesenthal, Dirk; Martus, Peter; Winkler, Maren K.L.; Hartings, Jed A.; Fabricius, Martin; Speckmann, Erwin-Josef; Gorji, Ali

    2012-01-01

    Spreading depolarization of cells in cerebral grey matter is characterized by massive ion translocation, neuronal swelling and large changes in direct current-coupled voltage recording. The near-complete sustained depolarization above the inactivation threshold for action potential generating channels initiates spreading depression of brain activity. In contrast, epileptic seizures show modest ion translocation and sustained depolarization below the inactivation threshold for action potential generating channels. Such modest sustained depolarization allows synchronous, highly frequent neuronal firing; ictal epileptic field potentials being its electrocorticographic and epileptic seizure its clinical correlate. Nevertheless, Leão in 1944 and Van Harreveld and Stamm in 1953 described in animals that silencing of brain activity induced by spreading depolarization changed during minimal electrical stimulations. Eventually, epileptic field potentials were recorded during the period that had originally seen spreading depression of activity. Such spreading convulsions are characterized by epileptic field potentials on the final shoulder of the large slow potential change of spreading depolarization. We here report on such spreading convulsions in monopolar subdural recordings in 2 of 25 consecutive aneurismal subarachnoid haemorrhage patients in vivo and neocortical slices from 12 patients with intractable temporal lobe epilepsy in vitro. The in vitro results suggest that γ-aminobutyric acid-mediated inhibition protects from spreading convulsions. Moreover, we describe arterial pulse artefacts mimicking epileptic field potentials in three patients with subarachnoid haemorrhage that ride on the slow potential peak. Twenty-one of the 25 subarachnoid haemorrhage patients (84%) had 656 spreading depolarizations in contrast to only three patients (12%) with 55 ictal epileptic events isolated from spreading depolarizations. Spreading depolarization frequency and depression

  2. Plume Flux, Spreading Rate, and Obliquity of Seafloor Spreading

    NASA Astrophysics Data System (ADS)

    Zhang, T.; Gordon, R. G.

    2016-12-01

    Most of Earth's surface is created by seafloor spreading, a fundamental global tectonic process. While most seafloor spreading is orthogonal, i.e., the strike of mid-ocean ridge (MOR) segments is perpendicular to transform faults, obliquity of up to 45° occurs. Here, building on the work of DeMets et al. [2010] we investigate the global relationship between obliquity of seafloor spreading, spreading rates, and the flux of nearby plumes. While we confirm the well-known tendency for obliquity to decrease with increasing spreading rate [Atwater and Macdonald, 1977], we find exceptions at both intermediate (up to 18°) and ultra-fast (up to 12°) rates of spreading. Thus, factors other than the minimization of power dissipation across mid-ocean ridges and transform faults [Stein, 1978] may influence the amount of obliquity. Abelson & Agnon [1997] modeled spreading centers as fluid-filled cracks and found that the variation of segment orientation depends on the ratio of the magma overpressure to the remote tectonic tension that drives plate separation. A high ratio promotes oblique spreading and a low ratio promotes segmentation that results in orthogonal spreading. They further argued that if a hotspot lies near a MOR segment, the hotspot contributes to magma overpressure along the segment. We quantify their argument as follows: (1) that magma overpressure increases with increasing flux of a plume. (2) that effective magma overpressure decreases with increasing distance between a MOR segment and a plume. From this we estimate the effective plume flux delivered to each mid-ocean ridge using published plume flux estimates. Not only does obliquity tend to decrease with increasing spreading rate, but also it tends to increase with increasing effective plume flux delivered to a MOR segment. Many exceptions occur, however. Along slow spreading centers, many segments are less oblique than along the Reykjanes Ridge and western Gulf of Aden despite having higher effective

  3. Spatial and temporal variability in air concentrations of short-chain (C10-C13) and medium-chain (C14-C17) chlorinated n-alkanes measured in the U.K. atmosphere.

    PubMed

    Barber, Jonathan L; Sweetman, Andy J; Thomas, Gareth O; Braekevelt, Eric; Stern, Gary A; Jones, Kevin C

    2005-06-15

    Two studies were carried out on short-chain (C10-C13) and medium-chain (C14-C17) polychlorinated n-alkanes (sPCAs and mPCAs) in U.K. air samples. The first study entailed taking 20 24-h air samples with a pair of Hi-Vol air samplers at the Hazelrigg field station, near Lancaster University. These samples were carefully selected to coincide with times when air masses were predicted to have a fairly constant back trajectory for 24 h and to give a broad spectrum of different origins. The second study was a spatial survey of PCAs in the air at 20 outdoor sites in northern England and four indoor locations in Lancaster, using polyurethane foam (PUF) disk passive air samplers. Levels of the sPCAs in the Hi-Vol samples ranged from <185 to 3430 pg m(-3) (average 1130 pg m(-3)) and were higher than those previously measured at this site in 1997. Levels of the mPCAs ranged from <811 to 14500 pg m(-3) (average 3040 pg m(-3)); that is, they were higher than sPCAs. Both sPCA and mPCA air concentrations are of the same order of magnitude as PAH at this site. Back trajectory analysis showed that the history of the air mass in the 48 h prior to sampling had an important effect on the concentrations observed, with overland samples having higher levels than oceanic, implying that the U.K. is probably responsible for most of the PCAs measured in the U.K. atmosphere. Amounts of both sPCAs and mPCAs in the passive air samples followed a rural-urban gradient. PCAs appear to be released from multiple sources around the country, as a result of the diffusive, open industrial and construction use of the technical mixtures.

  4. Islamic Universities Spread through Africa

    ERIC Educational Resources Information Center

    Lindow, Megan

    2007-01-01

    This article reports on new universities for Muslims, many supported by groups in the Middle East, which are spreading through the sub-Saharan region. The Islamic University in Uganda is a prime example of a new kind of institution that has slowly been spreading its way across the continent. Embracing both conservative Muslim values and modern…

  5. Islamic Universities Spread through Africa

    ERIC Educational Resources Information Center

    Lindow, Megan

    2007-01-01

    This article reports on new universities for Muslims, many supported by groups in the Middle East, which are spreading through the sub-Saharan region. The Islamic University in Uganda is a prime example of a new kind of institution that has slowly been spreading its way across the continent. Embracing both conservative Muslim values and modern…

  6. Increased Spreading Activation in Depression

    ERIC Educational Resources Information Center

    Foster, Paul S.; Yung, Raegan C.; Branch, Kaylei K.; Stringer, Kristi; Ferguson, Brad J.; Sullivan, William; Drago, Valeria

    2011-01-01

    The dopaminergic system is implicated in depressive disorders and research has also shown that dopamine constricts lexical/semantic networks by reducing spreading activation. Hence, depression, which is linked to reductions of dopamine, may be associated with increased spreading activation. However, research has generally found no effects of…

  7. Increased Spreading Activation in Depression

    ERIC Educational Resources Information Center

    Foster, Paul S.; Yung, Raegan C.; Branch, Kaylei K.; Stringer, Kristi; Ferguson, Brad J.; Sullivan, William; Drago, Valeria

    2011-01-01

    The dopaminergic system is implicated in depressive disorders and research has also shown that dopamine constricts lexical/semantic networks by reducing spreading activation. Hence, depression, which is linked to reductions of dopamine, may be associated with increased spreading activation. However, research has generally found no effects of…

  8. Heat transfer and fire spread

    Treesearch

    Hal E. Anderson

    1969-01-01

    Experimental testing of a mathematical model showed that radiant heat transfer accounted for no more than 40% of total heat flux required to maintain rate of spread. A reasonable prediction of spread was possible by assuming a horizontal convective heat transfer coefficient when certain fuel and flame characteristics were known. Fuel particle size had a linear relation...

  9. Sinking, wedging, spreading - viscous spreading on a layer of fluid

    NASA Astrophysics Data System (ADS)

    Bergemann, Nico; Juel, Anne; Heil, Matthias

    2016-11-01

    We study the axisymmetric spreading of a sessile drop on a pre-existing layer of the same fluid in a regime where the drop is sufficiently large so that the spreading is driven by gravity while capillary and inertial effects are negligible. Experiments performed with 5 ml drops and layer thicknesses in the range 0.1 mm <= h <= 1 mm show that at long times the radius of the drop evolves as R tn , where the spreading exponent n increases with the layer thickness h. Numerical simulations, based on the axisymmetric free-surface Navier-Stokes equations, reveal three distinct spreading regimes depending on the layer thickness. For thick layers the drop sinks into the layer, accompanied by significant flow in the layer. By contrast, for thin layers the layer ahead of the propagating front is at rest and the spreading behaviour resembles that of a gravity-driven drop spreading on a dry substrate. In the intermediate regime the spreading is characterised by an advancing wedge, which is sustained by fluid flow from the drop into the layer.

  10. Connectivity disruption sparks explosive epidemic spreading

    NASA Astrophysics Data System (ADS)

    Böttcher, L.; Woolley-Meza, O.; Goles, E.; Helbing, D.; Herrmann, H. J.

    2016-04-01

    We investigate the spread of an infection or other malfunction of cascading nature when a system component can recover only if it remains reachable from a functioning central component. We consider the susceptible-infected-susceptible model, typical of mathematical epidemiology, on a network. Infection spreads from infected to healthy nodes, with the addition that infected nodes can only recover when they remain connected to a predefined central node, through a path that contains only healthy nodes. In this system, clusters of infected nodes will absorb their noninfected interior because no path exists between the central node and encapsulated nodes. This gives rise to the simultaneous infection of multiple nodes. Interestingly, the system converges to only one of two stationary states: either the whole population is healthy or it becomes completely infected. This simultaneous cluster infection can give rise to discontinuous jumps of different sizes in the number of failed nodes. Larger jumps emerge at lower infection rates. The network topology has an important effect on the nature of the transition: we observed hysteresis for networks with dominating local interactions. Our model shows how local spread can abruptly turn uncontrollable when it disrupts connectivity at a larger spatial scale.

  11. Lean in Air Permitting Guide

    EPA Pesticide Factsheets

    The Lean in Air Permitting Guide is designed to help air program managers at public agencies better understand the potential value and results that can be achieved by applying Lean improvement methods to air permitting processes.

  12. Chromatic assimilation: spread light or neural mechanism?

    PubMed

    Cao, Dingcai; Shevell, Steven K

    2005-04-01

    Chromatic assimilation is the shift in color appearance of a test field toward the appearance of nearby light. Possible explanations of chromatic assimilation include wavelength independent spread light, wavelength-dependent chromatic aberration and neural summation. This study evaluated these explanations by measuring chromatic assimilation from a concentric-ring pattern into an equal-energy-white background, as a function of the inducing rings' width, separation, chromaticity and luminance. The measurements showed, in the s direction, that assimilation was observed with different inducing-ring widths and separations when the inducing luminance was lower or higher than the test luminance. In general, the thinner the inducing rings and the smaller their separation, the stronger the assimilation in s. In the l direction, either assimilation or contrast was observed, depending on the ring width, separation and luminance. Overall, the measured assimilation could not be accounted for by the joint contributions from wavelength-independent spread light and wavelength-dependent chromatic aberration. Spatial averaging of neural signals explained the assimilation in s reasonably well, but there were clear deviations from neural spatial averaging for the l direction.

  13. Presunrise spread F at Fortaleza

    NASA Astrophysics Data System (ADS)

    MacDougall, J. W.; Abdu, M. A.; Jayachandran, P. T.; Cecile, J.-F.; Batista, I. S.

    1998-10-01

    At Fortaleza, Brazil, in the equatorial zone about 400 km south of the magnetic equator a presunrise (secondary) maximum of spread F occurrence is observed during sunspot minimum and, in particular, during December solstice. The spread F takes the form of patches of irregularities that are convecting eastwards at ~50 ms-1. Most of the patches are collocated with bottomside bulges of the ionosphere. Our measurements indicate that these bottomside bulges are unstable due to a gradient-drift instability that is slowly growing and produces the spread F. The bulges themselves seem to be evidence of a Rayleigh-Taylor instability proces.

  14. Spreading of Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Poulard, Christophe

    2004-11-01

    A cyanobiphenyl liquid crystal drop in the nematic phase should spread on a silicon wafer. In fact, the drop hardly spreads due to the strong antagonist anchoring on the substrate and at the free surface. In a humidity controlled box at high RH and on a hydrophilic substrate, the friction is considerably reduced and the drop spreads easily. A well defined instability develops at the contact line, with two characteristic wavelengths, associated with a modulation of the drop thickness. A theoretical analysis, made by M. Ben Amar and L. Cummings, allows to understand one of the wavelength by an elastic approach and gives a wavelength proportionnal to the local drop's thickness.

  15. Laser optoacoustic tomography for the study of femtosecond laser filaments in air

    NASA Astrophysics Data System (ADS)

    Bychkov, A. S.; Cherepetskaya, E. B.; Karabutov, A. A.; Makarov, V. A.

    2016-08-01

    We propose to use optoacoustic tomography to study the characteristics of femtosecond laser filamentation in air and condensed matter. The high spatial resolution of the proposed system, which consists of an array of broadband megahertz piezoelectric elements, ensures its effectiveness, despite the attenuation of ultrasonic waves in air.

  16. Point spread function of the optical needle super-oscillatory lens

    SciTech Connect

    Roy, Tapashree; Rogers, Edward T. F.; Yuan, Guanghui; Zheludev, Nikolay I.

    2014-06-09

    Super-oscillatory optical lenses are known to achieve sub-wavelength focusing. In this paper, we analyse the imaging capabilities of a super-oscillatory lens by studying its point spread function. We experimentally demonstrate that a super-oscillatory lens can generate a point spread function 24% smaller than that dictated by the diffraction limit and has an effective numerical aperture of 1.31 in air. The object-image linear displacement property of these lenses is also investigated.

  17. Modeling emerald ash borer spread in Ohio and Michigan

    Treesearch

    Anantha Prasad; Louis Iverson; Matthew Peters; Jonathan Bossenbroek; Davis Sydnor; Mark Schwartz

    2008-01-01

    Our group has been modelling the spread of emerald ash borer (EAB) in Ohio using a spatially explicit cell-based model that takes into account the insect's flight characteristics (Insect Flight Model) as well as external factors that enable the insects to travel passively (Insect Ride Model).

  18. Upward Flame Spread Over Thin Solids in Partial Gravity

    NASA Technical Reports Server (NTRS)

    Feier, I. I.; Shih, H. Y.; Sacksteder, K. R.; Tien, J. S.

    2001-01-01

    The effects of partial-gravity, reduced pressure, and sample width on upward flame spread over a thin cellulose fuel were studied experimentally and the results were compared to a numerical flame spread simulation. Fuel samples 1-cm, 2-cm, and 4-cm wide were burned in air at reduced pressures of 0.2 to 0.4 atmospheres in simulated gravity environments of 0.1-G, 0.16-G (Lunar), and 0.38-G (Martian) onboard the NASA KC-135 aircraft and in normal-gravity tests. Observed steady flame propagation speeds and pyrolysis lengths were approximately proportional to the gravity level. Flames spread more quickly and were longer with the wider samples and the variations with gravity and pressure increased with sample width. A numerical simulation of upward flame spread was developed including three-dimensional Navier-Stokes equations, one-step Arrhenius kinetics for the gas phase flame and for the solid surface decomposition, and a fuel-surface radiative loss. The model provides detailed structure of flame temperatures, the flow field interactions with the flame, and the solid fuel mass disappearance. The simulation agrees with experimental flame spread rates and their dependence on gravity level but predicts a wider flammable region than found by experiment. Some unique three-dimensional flame features are demonstrated in the model results.

  19. Spreading dynamics of polymer nanodroplets

    NASA Astrophysics Data System (ADS)

    Heine, David R.; Grest, Gary S.; Webb, Edmund B.

    2003-12-01

    The spreading of polymer droplets is studied using molecular dynamics simulations. To study the dynamics of both the precursor foot and the bulk droplet, large hemispherical drops of 200 000 monomers are simulated using a bead-spring model for polymers of chain length 10, 20, and 40 monomers per chain. We compare spreading on flat and atomistic surfaces, chain length effects, and different applications of the Langevin and dissipative particle dynamics thermostats. We find diffusive behavior for the precursor foot and good agreement with the molecular kinetic model of droplet spreading using both flat and atomistic surfaces. Despite the large system size and long simulation time relative to previous simulations, we find that even larger systems are required to observe hydrodynamic behavior in the hemispherical spreading droplet.

  20. Flame spread across liquid pools

    NASA Technical Reports Server (NTRS)

    Ross, Howard; Miller, Fletcher; Schiller, David; Sirignano, William A.

    1993-01-01

    For flame spread over liquid fuel pools, the existing literature suggests three gravitational influences: (1) liquid phase buoyant convection, delaying ignition and assisting flame spread; (2) hydrostatic pressure variation, due to variation in the liquid pool height caused by thermocapillary-induced convection; and (3) gas-phase buoyant convection in the opposite direction to the liquid phase motion. No current model accounts for all three influences. In fact, prior to this work, there was no ability to determine whether ignition delay times and flame spread rates would be greater or lesser in low gravity. Flame spread over liquid fuel pools is most commonly characterized by the relationship of the initial pool temperature to the fuel's idealized flash point temperature, with four or five separate characteristic regimes having been identified. In the uniform spread regime, control has been attributed to: (1) gas-phase conduction and radiation; (2) gas-phase conduction only; (3) gas-phase convection and liquid conduction, and most recently (4) liquid convection ahead of the flame. Suggestions were made that the liquid convection was owed to both vuoyancy and thermocapillarity. Of special interest to this work is the determination of whether, and under what conditions, pulsating spread can and will occur in microgravity in the absence of buoyant flows in both phases. The approach we have taken to resolving the importance of buoyancy for these flames is: (1) normal gravity experiments and advanced diagnostics; (2) microgravity experiments; and (3) numerical modelling at arbitrary gravitational level.

  1. Scaled experiments of volcanic spreading

    NASA Astrophysics Data System (ADS)

    Merle, Olivier; Borgia, Andrea

    1996-06-01

    Experiments were conducted to study the spreading of volcanic constructs. Volcanoes are simulated by a sand cone, and the volcanic substratum is simulated by a sand layer (brittle substratum) overlying a silicone layer (ductile substratum). Similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless π numbers. Experiments determine π values which predict whether or not spreading takes place. Of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano (π2) and the brittle/ductile ratio of the substratum (π3). π2 indicates that the volcano must be large enough to "break" the substratum before spreading occurs, whereas π3 controls the style of deformation. During spreading, these dimensionless numbers change with time, reaching values that tend toward those observed for stable configurations. Experimental values are compared with those from well-constrained natural examples. It is found that an essential requirement for volcanic spreading is the presence of a low-viscosity layer within the substratum. Flow of the weak layer away from the excess load is responsible for the spreading. The overlying edifice displays radial intersecting grabens, due to concentric stretching, dissected summit areas; concentric zones of thrusts and folds form in the substratum around the edifice, and diapirs of the ductile substratum rise within the fault zones.

  2. Spread dynamics of invasive species.

    PubMed

    Arim, Matías; Abades, Sebastián R; Neill, Paula E; Lima, Mauricio; Marquet, Pablo A

    2006-01-10

    Species invasions are a principal component of global change, causing large losses in biodiversity as well as economic damage. Invasion theory attempts to understand and predict invasion success and patterns of spread. However, there is no consensus regarding which species or community attributes enhance invader success or explain spread dynamics. Experimental and theoretical studies suggest that regulation of spread dynamics is possible; however, the conditions for its existence have not yet been empirically demonstrated. If invasion spread is a regulated process, the structure that accounts for this regulation will be a main determinant of invasion dynamics. Here we explore the existence of regulation underlying changes in the rate of new site colonization. We employ concepts and analytical tools from the study of abundance dynamics and show that spread dynamics are, in fact, regulated processes and that the regulation structure is notably consistent among invasions occurring in widely different contexts. We base our conclusions on the analysis of the spread dynamics of 30 species invasions, including birds, amphibians, fish, invertebrates, plants, and a virus, all of which exhibited similar regulation structures. In contrast to current beliefs that species invasions are idiosyncratic phenomena, here we provide evidence that general patterns do indeed exist.

  3. Spread dynamics of invasive species

    PubMed Central

    Arim, Matías; Abades, Sebastián R.; Neill, Paula E.; Lima, Mauricio; Marquet, Pablo A.

    2006-01-01

    Species invasions are a principal component of global change, causing large losses in biodiversity as well as economic damage. Invasion theory attempts to understand and predict invasion success and patterns of spread. However, there is no consensus regarding which species or community attributes enhance invader success or explain spread dynamics. Experimental and theoretical studies suggest that regulation of spread dynamics is possible; however, the conditions for its existence have not yet been empirically demonstrated. If invasion spread is a regulated process, the structure that accounts for this regulation will be a main determinant of invasion dynamics. Here we explore the existence of regulation underlying changes in the rate of new site colonization. We employ concepts and analytical tools from the study of abundance dynamics and show that spread dynamics are, in fact, regulated processes and that the regulation structure is notably consistent among invasions occurring in widely different contexts. We base our conclusions on the analysis of the spread dynamics of 30 species invasions, including birds, amphibians, fish, invertebrates, plants, and a virus, all of which exhibited similar regulation structures. In contrast to current beliefs that species invasions are idiosyncratic phenomena, here we provide evidence that general patterns do indeed exist. PMID:16387862

  4. Crown fuel spatial variability and predictability of fire spread

    Treesearch

    Russell A. Parsons; Jeremy Sauer; Rodman R. Linn

    2010-01-01

    Fire behavior predictions, as well as measures of uncertainty in those predictions, are essential in operational and strategic fire management decisions. While it is becoming common practice to assess uncertainty in fire behavior predictions arising from variability in weather inputs, uncertainty arising from the fire models themselves is difficult to assess. This is...

  5. Multiscale mobility networks and the spatial spreading of infectious diseases

    PubMed Central

    Balcan, Duygu; Colizza, Vittoria; Gonçalves, Bruno; Hu, Hao; Ramasco, José J.; Vespignani, Alessandro

    2009-01-01

    Among the realistic ingredients to be considered in the computational modeling of infectious diseases, human mobility represents a crucial challenge both on the theoretical side and in view of the limited availability of empirical data. To study the interplay between short-scale commuting flows and long-range airline traffic in shaping the spatiotemporal pattern of a global epidemic we (i) analyze mobility data from 29 countries around the world and find a gravity model able to provide a global description of commuting patterns up to 300 kms and (ii) integrate in a worldwide-structured metapopulation epidemic model a timescale-separation technique for evaluating the force of infection due to multiscale mobility processes in the disease dynamics. Commuting flows are found, on average, to be one order of magnitude larger than airline flows. However, their introduction into the worldwide model shows that the large-scale pattern of the simulated epidemic exhibits only small variations with respect to the baseline case where only airline traffic is considered. The presence of short-range mobility increases, however, the synchronization of subpopulations in close proximity and affects the epidemic behavior at the periphery of the airline transportation infrastructure. The present approach outlines the possibility for the definition of layered computational approaches where different modeling assumptions and granularities can be used consistently in a unifying multiscale framework. PMID:20018697

  6. Worldwide spreading of economic crisis

    NASA Astrophysics Data System (ADS)

    Garas, Antonios; Argyrakis, Panos; Rozenblat, Céline; Tomassini, Marco; Havlin, Shlomo

    2010-11-01

    We model the spreading of a crisis by constructing a global economic network and applying the susceptible-infected-recovered (SIR) epidemic model with a variable probability of infection. The probability of infection depends on the strength of economic relations between a given pair of countries and the strength of the target country. It is expected that a crisis that originates in a large country, such as the USA, has the potential to spread globally, such as the recent crisis. Surprisingly, we also show that countries with a much lower GDP, such as Belgium, are able to initiate a global crisis. Using the k-shell decomposition method to quantify the spreading power (of a node), we obtain a measure of 'centrality' as a spreader of each country in the economic network. We thus rank the different countries according to the shell they belong to, and find the 12 most central ones. These countries are the most likely to spread a crisis globally. Of these 12, only six are large economies, while the other six are medium/small ones, a result that could not have been otherwise anticipated. Furthermore, we use our model to predict the crisis spreading potential of countries belonging to different shells according to the crisis magnitude.

  7. Nonlinear diffusion and viral spread through the leaf of a plant

    NASA Astrophysics Data System (ADS)

    Edwards, Maureen P.; Waterhouse, Peter M.; Munoz-Lopez, María Jesús; Anderssen, Robert S.

    2016-10-01

    The spread of a virus through the leaf of a plant is both spatially and temporally causal in that the present status depends on the past and the spatial spread is compactly supported and progresses outwards. Such spatial spread is known to occur for certain nonlinear diffusion processes. The first compactly supported solution for nonlinear diffusion equations appears to be that of Pattle published in 1959. In that paper, no explanation is given as to how the solution was derived. Here, we show how the solution can be derived using Lie symmetry analysis. This lays a foundation for exploring the behavior of other choices for nonlinear diffusion and exploring the addition of reaction terms which do not eliminate the compactly supported structure. The implications associated with using the reaction-diffusion equation to model the spatial-temporal spread of a virus through the leaf of a plant are discussed.

  8. Clonal Spread in Second Growth Stands of Coast Redwood, Sequoia sempervirens

    Treesearch

    Vladimir Douhovnikoff; Richard S. Dodd

    2007-01-01

    Coast redwood (Sequoia sempervirens) is one of the rare conifers to reproduce successfully through clonal spread. The importance of this mode of reproduction in stand development is largely unknown. Understanding the importance of clonal spread and the spatial structure of clones is crucial for stand management strategies that would aim to maximize...

  9. Estimating spread rates of non-native species: the gypsy moth as a case study

    Treesearch

    Patrick Tobin; Andrew M. Liebhold; E. Anderson Roberts; Laura M. Blackburn

    2015-01-01

    Estimating rates of spread and generating projections of future range expansion for invasive alien species is a key process in the development of management guidelines and policy. Critical needs to estimate spread rates include the availability of surveys to characterize the spatial distribution of an invading species and the application of analytical methods to...

  10. Strong interactions in air showers

    SciTech Connect

    Dietrich, Dennis D.

    2015-03-02

    We study the role new gauge interactions in extensions of the standard model play in air showers initiated by ultrahigh-energy cosmic rays. Hadron-hadron events remain dominated by quantum chromodynamics, while projectiles and/or targets from beyond the standard model permit us to see qualitative differences arising due to the new interactions.

  11. Colony spreading in Staphylococcus aureus.

    PubMed

    Kaito, Chikara; Sekimizu, Kazuhisa

    2007-03-01

    Wild-type Staphylococcus aureus rapidly expands on the surface of soft agar plates. The rates of expansion and the shapes of the resultant giant colonies were distinct for different strains of laboratory stocks and clinical isolates. The colony spreading abilities did not correlate with the biofilm-forming abilities in these strains. Insertional disruption of the dltABCD operon, which functions at the step of D-alanine addition to teichoic acids, and of the tagO gene, which is responsible for the synthesis of wall teichoic acids, decreased the colony spreading ability. The results indicate that wall teichoic acids and D-alanylation of teichoic acids are required for colony spreading.

  12. Controlling droplet spreading with topography

    NASA Astrophysics Data System (ADS)

    Kant, P.; Hazel, A. L.; Dowling, M.; Thompson, A. B.; Juel, A.

    2017-09-01

    We present an experimental system that can be used to study the dynamics of a picoliter droplet (in-flight radius of 12.2 μ m ) as it spreads over substrates with topographic variations. We concentrate on the spreading of a droplet within a recessed stadium-shaped pixel, with applications to the manufacture of polymer organic light-emitting-diode displays, and find that the sloping sidewall of the pixel can either locally enhance or hinder spreading depending on whether the topography gradient ahead of the contact line is positive or negative, respectively. Locally enhanced spreading occurs via the formation of thin pointed rivulets along the sidewalls of the pixel through a mechanism similar to capillary rise in sharp corners. We demonstrate that a simplified model involving quasistatic surface-tension effects within the framework of a thin-film approximation combined with an experimentally measured dynamic spreading law, relating the speed of the contact line to the contact angle, provides excellent predictions of the evolving liquid morphologies. A key feature of the liquid-substrate interaction studied here is the presence of significant contact angle hysteresis, which enables the persistence of noncircular fluid morphologies. We also show that the spreading law for an advancing contact line can be adequately approximated by a Cox-Voinov law for the majority of the evolution. The model does not include viscous effects in the bulk of the droplet and hence the time scales for the propagation of the thin pointed rivulets are not captured. Nonetheless, this simple model can be used very effectively to predict the areas covered by the liquid and may serve as a useful design tool for systems that require precise control of liquid on substrates.

  13. Zeno dynamics in wave-packet diffraction spreading

    SciTech Connect

    Porras, Miguel A.; Luis, Alfredo; Gonzalo, Isabel; Sanz, Angel S.

    2011-11-15

    We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno, and inverse-Zeno effects in the observation of wave-packet spreading caused by free evolution. The scheme is valid both in spatial diffraction of classical optical waves and in time diffraction of a quantum wave packet. In the optical realization, diffraction spreading is observed by placing slits between a light source and a light-power detector. We show that the occurrence of Zeno or anti-Zeno effects depends just on the frequency of observations between the source and detector. These effects are seen to be related to the diffraction mode theory in Fabry-Perot resonators.

  14. Spectral and Spread Spectral Teleportation

    SciTech Connect

    Humble, Travis S

    2010-01-01

    We report how quantum information encoded into the spectral degree of freedom of a single-photon state is teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of a teleported waveform can be controllably and coherently dilated using a spread spectral variant of teleportation. We present analytical fidelities for spectral and spread spectral teleportation when complex-valued Gaussian states are prepared using a proposed experimental approach, and we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.

  15. Detonation spreading in fine TATBs

    SciTech Connect

    Kennedy, J.E.; Lee, K.Y.; Spontarelli, T.; Stine, J.R.

    1998-12-31

    A test has been devised that permits rapid evaluation of the detonation-spreading (or corner-turning) properties of detonations in insensitive high explosives. The test utilizes a copper witness plate as the medium to capture performance data. Dent depth and shape in the copper are used as quantitative measures of the detonation output and spreading behavior. The merits of the test are that it is easy to perform with no dynamic instrumentation, and the test requires only a few grams of experimental explosive materials.

  16. Braze alloy spreading on steel

    NASA Technical Reports Server (NTRS)

    Siewert, T. A.; Heine, R. W.; Lagally, M. G.

    1978-01-01

    Scanning electron microscopy (SEM) and Auger electron microscopy (AEM) were employed to observe elemental surface decomposition resulting from the brazing of a copper-treated steel. Two types of steel were used for the study, stainless steel (treated with a eutectic silver-copper alloy), and low-carbon steel (treated with pure copper). Attention is given to oxygen partial pressure during the processes; a low enough pressure (8 x 10 to the -5th torr) was found to totally inhibit the spreading of the filler material at a fixed heating cycle. With both types of steel, copper treatment enhanced even spreading at a decreased temperature.

  17. Point spread function engineering with multiphoton SPIFI

    NASA Astrophysics Data System (ADS)

    Wernsing, Keith A.; Field, Jeffrey J.; Domingue, Scott R.; Allende-Motz, Alyssa M.; DeLuca, Keith F.; Levi, Dean H.; DeLuca, Jennifer G.; Young, Michael D.; Squier, Jeff A.; Bartels, Randy A.

    2016-03-01

    MultiPhoton SPatIal Frequency modulated Imaging (MP-SPIFI) has recently demonstrated the ability to simultaneously obtain super-resolved images in both coherent and incoherent scattering processes -- namely, second harmonic generation and two-photon fluorescence, respectively.1 In our previous analysis, we considered image formation produced by the zero and first diffracted orders from the SPIFI modulator. However, the modulator is a binary amplitude mask, and therefore produces multiple diffracted orders. In this work, we extend our analysis to image formation in the presence of higher diffracted orders. We find that tuning the mask duty cycle offers a measure of control over the shape of super-resolved point spread functions in an MP-SPIFI microscope.

  18. Dimensionality reduction in epidemic spreading models

    NASA Astrophysics Data System (ADS)

    Frasca, M.; Rizzo, A.; Gallo, L.; Fortuna, L.; Porfiri, M.

    2015-09-01

    Complex dynamical systems often exhibit collective dynamics that are well described by a reduced set of key variables in a low-dimensional space. Such a low-dimensional description offers a privileged perspective to understand the system behavior across temporal and spatial scales. In this work, we propose a data-driven approach to establish low-dimensional representations of large epidemic datasets by using a dimensionality reduction algorithm based on isometric features mapping (ISOMAP). We demonstrate our approach on synthetic data for epidemic spreading in a population of mobile individuals. We find that ISOMAP is successful in embedding high-dimensional data into a low-dimensional manifold, whose topological features are associated with the epidemic outbreak. Across a range of simulation parameters and model instances, we observe that epidemic outbreaks are embedded into a family of closed curves in a three-dimensional space, in which neighboring points pertain to instants that are close in time. The orientation of each curve is unique to a specific outbreak, and the coordinates correlate with the number of infected individuals. A low-dimensional description of epidemic spreading is expected to improve our understanding of the role of individual response on the outbreak dynamics, inform the selection of meaningful global observables, and, possibly, aid in the design of control and quarantine procedures.

  19. The STIS CCD Spectroscopic Line Spread Functions

    NASA Technical Reports Server (NTRS)

    Gull, T.; Lindler, D.; Tennant, D.; Bowers, C.; Grady, C.; Hill, R. S.; Malumuth, E.

    2002-01-01

    We characterize the spectroscopic line spread functions of the spectroscopic CCD modes for high contrast objects. Our long range goal is to develop tools that accurately extract spectroscopic information of faint, point or extended sources in the vicinity of bright, point sources at separations approaching the realizable angular limits of HST with STIS. Diffracted and scattered light due to the HST optics, and scattered light effects within the STIS are addressed. Filter fringing, CCD fringing, window reflections, and scattering within the detector and other effects are noted. We have obtained spectra of several reference stars, used for flux calibration or for coronagraphic standards, that have spectral distributions ranging from very red to very blue. Spectra of each star were recorded with the star in the aperture and with the star blocked by either the F1 or F2 fiducial. Plots of the detected starlight along the spatial axis of the aperture are provided for four stars. With the star in the aperture, the line spread function is quite noticeable. Placing the star behind one of the fiducials cuts the scattered light and the diffracted light, is detectable even out to 1OOOOA. When the star is placed behind either fiducial, the scattered and diffracted light components, at three arcseconds displacement from the star, are below lop6 the peak of the star at wavelengths below 6000A; at the same angular distance, scattered light does contaminate the background longward of 6000A up to a level of 10(exp -5).

  20. Ignition, Transition, Flame Spread in Multidimensional Configurations in Microgravity

    NASA Technical Reports Server (NTRS)

    Kashiwagi, Takashi; Mell, William E.; McGrattan, Kevin B.; Baum, Howard R.; Olson, Sandra L.; Fujita, Osamu; Kikuchi, Masao; Ito, Kenichi

    1997-01-01

    Ignition of solid fuels by external thermal radiation and subsequent transition to flame spread are processes that not only are of considerable scientific interest but which also have fire safety applications. A material which undergoes a momentary ignition might be tolerable but a material which permits a transition to subsequent flame spread would significantly increase the fire hazard in a spacecraft. Therefore, the limiting condition under which flame cannot spread should be calculated from a model of the transition from ignition instead of by the traditional approach based on limits to a steady flame spread model. However, although the fundamental processes involved in ignition have been suggested there have been no definitive experimental or modeling studies due to the flow motion generated by buoyancy near the heated sample surface. In this study, microgravity experiments which required longer test times such as in air and surface smoldering experiment were conducted in the space shuttle STS-75 flight; shorter experimental tests such as in 35% and 50% oxygen were conducted in the droptower in the Japan Microgravity Center, JAMIC. Their experimental data along with theoretically calculated results from solving numerically the time-dependent Navier-Stokes equations are summarized in this paper.

  1. Ignition, Transition, Flame Spread in Multidimensional Configurations in Microgravity

    NASA Technical Reports Server (NTRS)

    Kashiwagi, Takashi; Mell, William E.; McGrattan, Kevin B.; Baum, Howard R.; Olson, Sandra L.; Fujita, Osamu; Kikuchi, Masao; Ito, Kenichi

    1997-01-01

    Ignition of solid fuels by external thermal radiation and subsequent transition to flame spread are processes that not only are of considerable scientific interest but which also have fire safety applications. A material which undergoes a momentary ignition might be tolerable but a material which permits a transition to subsequent flame spread would significantly increase the fire hazard in a spacecraft. Therefore, the limiting condition under which flame cannot spread should be calculated from a model of the transition from ignition instead of by the traditional approach based on limits to a steady flame spread model. However, although the fundamental processes involved in ignition have been suggested there have been no definitive experimental or modeling studies due to the flow motion generated by buoyancy near the heated sample surface. In this study, microgravity experiments which required longer test times such as in air and surface smoldering experiment were conducted in the space shuttle STS-75 flight; shorter experimental tests such as in 35% and 50% oxygen were conducted in the droptower in the Japan Microgravity Center, JAMIC. Their experimental data along with theoretically calculated results from solving numerically the time-dependent Navier-Stokes equations are summarized in this paper.

  2. Tuning magnetofluidic spreading in microchannels

    NASA Astrophysics Data System (ADS)

    Wang, Zhaomeng; Varma, V. B.; Wang, Z. P.; Ramanujan, R. V.

    2015-12-01

    Magnetofluidic spreading (MFS) is a phenomenon in which a uniform magnetic field is used to induce spreading of a ferrofluid core cladded by diamagnetic fluidic streams in a three-stream channel. Applications of MFS include micromixing, cell sorting and novel microfluidic lab-on-a-chip design. However, the relative importance of the parameters which govern MFS is still unclear, leading to non-optimal control of MFS. Hence, in this work, the effect of various key parameters on MFS was experimentally and numerically studied. Our multi-physics model, which combines magnetic and fluidic analysis, showed excellent agreement between theory and experiment. It was found that spreading was mainly due to cross-sectional convection induced by magnetic forces, and can be enhanced by tuning various parameters. Smaller flow rate ratio, higher magnetic field, higher core stream or lower cladding stream dynamic viscosity, and larger magnetic particle size can increase MFS. These results can be used to tune magnetofluidic spreading in microchannels.

  3. Spreading dynamics in complex networks

    NASA Astrophysics Data System (ADS)

    Pei, Sen; Makse, Hernán A.

    2013-12-01

    Searching for influential spreaders in complex networks is an issue of great significance for applications across various domains, ranging from epidemic control, innovation diffusion, viral marketing, and social movement to idea propagation. In this paper, we first display some of the most important theoretical models that describe spreading processes, and then discuss the problem of locating both the individual and multiple influential spreaders respectively. Recent approaches in these two topics are presented. For the identification of privileged single spreaders, we summarize several widely used centralities, such as degree, betweenness centrality, PageRank, k-shell, etc. We investigate the empirical diffusion data in a large scale online social community—LiveJournal. With this extensive dataset, we find that various measures can convey very distinct information of nodes. Of all the users in the LiveJournal social network, only a small fraction of them are involved in spreading. For the spreading processes in LiveJournal, while degree can locate nodes participating in information diffusion with higher probability, k-shell is more effective in finding nodes with a large influence. Our results should provide useful information for designing efficient spreading strategies in reality.

  4. Lateral Spreading of Visual Adaptation,

    DTIC Science & Technology

    1982-03-02

    adapting field. 2.4X10- 3 footlamberts to simulate the luminance of In studying the spreading of adaptational ef- grass on a clear night with a full ... moon . fects (sensitivity changes) to areas outside of the adaptational field we are also interested in discovering the mechanisms which produce such a

  5. Dual polarized, heat spreading rectenna

    NASA Technical Reports Server (NTRS)

    Epp, Larry W. (Inventor); Khan, Abdur R. (Inventor); Smith, R. Peter (Inventor); Smith, Hugh K. (Inventor)

    1999-01-01

    An aperture coupled patch splits energy from two different polarization components to different locations to spread heat. In addition, there is no physical electrical connection between the slot, patch and circuitry. The circuitry is located under a ground plane which shields against harmonic radiation back to the RF source.

  6. Spreading and collapse of big basaltic volcanoes

    NASA Astrophysics Data System (ADS)

    Puglisi, Giuseppe; Bonforte, Alessandro; Guglielmino, Francesco; Peltier, Aline; Poland, Michael

    2016-04-01

    Among the different types of volcanoes, basaltic ones usually form the most voluminous edifices. Because volcanoes are growing on a pre-existing landscape, the geologic and structural framework of the basement (and earlier volcanic landforms) influences the stress regime, seismicity, and volcanic activity. Conversely, the masses of these volcanoes introduce a morphological anomaly that affects neighboring areas. Growth of a volcano disturbs the tectonic framework of the region, clamps and unclamps existing faults (some of which may be reactivated by the new stress field), and deforms the substratum. A volcano's weight on its basement can trigger edifice spreading and collapse that can affect populated areas even at significant distance. Volcano instability can also be driven by slow tectonic deformation and magmatic intrusion. The manifestations of instability span a range of temporal and spatial scales, ranging from slow creep on individual faults to large earthquakes affecting a broad area. In the frame of MED-SVU project, our work aims to investigate the relation between basement setting and volcanic activity and stability at three Supersite volcanoes: Etna (Sicily, Italy), Kilauea (Island of Hawaii, USA) and Piton de la Fournaise (La Reunion Island, France). These volcanoes host frequent eruptive activity (effusive and explosive) and share common features indicating lateral spreading and collapse, yet they are characterized by different morphologies, dimensions, and tectonic frameworks. For instance, the basaltic ocean island volcanoes of Kilauea and Piton de la Fournaise are near the active ends of long hotspot chains while Mt. Etna has developed at junction along a convergent margin between the African and Eurasian plates and a passive margin separating the oceanic Ionian crust from the African continental crust. Magma supply and plate velocity also differ in the three settings, as to the sizes of the edifices and the extents of their rift zones. These

  7. Spreading And Collapse Of Big Basaltic Volcanoes

    NASA Astrophysics Data System (ADS)

    Puglisi, G.; Bonforte, A.; Guglielmino, F.; Peltier, A.; Poland, M. P.

    2015-12-01

    Among the different types of volcanoes, basaltic ones usually form the most voluminous edifices. Because volcanoes are growing on a pre-existing landscape, the geologic and structural framework of the basement (and earlier volcanic landforms) influences the stress regime, seismicity, and volcanic activity. Conversely, the masses of these volcanoes introduce a morphological anomaly that affects neighboring areas. Growth of a volcano disturbs the tectonic framework of the region, clamps and unclamps existing faults (some of which may be reactivated by the new stress field), and deforms the substratum. A volcano's weight on its basement can trigger edifice spreading and collapse that can affect populated areas even at significant distance. Volcano instability can also be driven by slow tectonic deformation and magmatic intrusion. The manifestations of instability span a range of temporal and spatial scales, ranging from slow creep on individual faults to large earthquakes affecting a broad area. Our work aims to investigate the relation between basement setting and volcanic activity and stability at Etna (Sicily, Italy), Kilauea (Island of Hawaii, USA) and Piton de la Fournaise (La Reunion Island, France). These volcanoes host frequent eruptive activity (effusive and explosive) and share common features indicating lateral spreading and collapse, yet they are characterized by different morphologies, dimensions, and tectonic frameworks. For instance, the basaltic ocean island volcanoes of Kilauea and Piton de la Fournaise are near the active ends of long hotspot chains while Mt. Etna has developed at junction along a convergent margin between the African and Eurasian plates and a passive margin separating the oceanic Ionian crust from the African continental crust. Magma supply and plate velocity also differ in the three settings, as to the sizes of the edifices and the extents of their rift zones. These volcanoes, due to their similarities and differences, coupled with

  8. Analytical representations of the spread harmonic measure density

    NASA Astrophysics Data System (ADS)

    Grebenkov, Denis S.

    2015-05-01

    We study the spread harmonic measure that characterizes the spatial distribution of reaction events on a partially reactive surface. For Euclidean domains in which Brownian motion can be split into independent lateral and transverse displacements, we derive analytical formulas for the spread harmonic measure density and analyze its asymptotic behavior. This analysis is applicable to slab domains, general cylindrical domains, and a half-space. We investigate the spreading effect due to multiple reflections on the surface, and the underlying role of finite reactivity. We discuss further extensions and applications of analytical results to describe Laplacian transfer phenomena such as permeation through semipermeable membranes, secondary current distribution on partially blocking electrodes, and surface relaxation in nuclear magnetic resonance.

  9. Analytical representations of the spread harmonic measure density.

    PubMed

    Grebenkov, Denis S

    2015-05-01

    We study the spread harmonic measure that characterizes the spatial distribution of reaction events on a partially reactive surface. For Euclidean domains in which Brownian motion can be split into independent lateral and transverse displacements, we derive analytical formulas for the spread harmonic measure density and analyze its asymptotic behavior. This analysis is applicable to slab domains, general cylindrical domains, and a half-space. We investigate the spreading effect due to multiple reflections on the surface, and the underlying role of finite reactivity. We discuss further extensions and applications of analytical results to describe Laplacian transfer phenomena such as permeation through semipermeable membranes, secondary current distribution on partially blocking electrodes, and surface relaxation in nuclear magnetic resonance.

  10. Spreading disease: integro-differential equations old and new.

    PubMed

    Medlock, Jan; Kot, Mark

    2003-08-01

    We investigate an integro-differential equation for a disease spread by the dispersal of infectious individuals and compare this to Mollison's [Adv. Appl. Probab. 4 (1972) 233; D. Mollison, The rate of spatial propagation of simple epidemics, in: Proc. 6th Berkeley Symp. on Math. Statist. and Prob., vol. 3, University of California Press, Berkeley, 1972, p. 579; J. R. Statist. Soc. B 39 (3) (1977) 283] model of a disease spread by non-local contacts. For symmetric kernels with moment generating functions, spreading infectives leads to faster traveling waves for low rates of transmission, but to slower traveling waves for high rates of transmission. We approximate the shape of the traveling waves for the two models using both piecewise linearization and a regular-perturbation scheme.

  11. Epidemic spread in coupled populations with seasonally varying migration rates

    NASA Astrophysics Data System (ADS)

    Muzyczyn, Adam; Shaw, Leah B.

    2009-03-01

    The H5N1 strain of avian influenza has spread worldwide, and this spread may be due to seasonal migration of birds and mixing of birds from different regions in the wintering grounds. We studied a multipatch model for avian influenza with seasonally varying migration rates. The bird population was divided into two spatially distinct patches, or subpopulations. Within each patch, the disease followed the SIR (susceptible-infected-recovered) model for epidemic spread. Migration rates were varied periodically, with a net flux toward the breeding grounds during the spring and towards the wintering grounds during the fall. The case of two symmetric patches reduced to single-patch SIR dynamics. However, asymmetry in the birth and contact rates in the breeding grounds and wintering grounds led to bifurcations to longer period orbits and chaotic dynamics. We studied the bifurcation structure of the model and the phase relationships between outbreaks in the two patches.

  12. Evaluating spread of invaders from gravity scores--a way of using gravity models in ecology.

    PubMed

    Järemo, Johannes

    2009-11-01

    This study is a theoretical excursion into gravity models and their usability in evaluating importance of spatial structure and population development for the spread of colonizing organisms. A so called "gravity score" for sites is deduced, and such a score could be used for predicting risk of colonization once one site in an area has been subject to introduction of a new species. The analysis further suggests that factors deciding spread between sites differs from those that govern expected population sizes. Gravity models of the kind presented here includes both population dynamics and spatial structure and could be a complement to other models describing organism spread.

  13. Flux-assisted wetting and spreading of Al on TiC.

    PubMed

    López, V H; Kennedy, A R

    2006-06-01

    The effect of a K-Al-F-based flux on the spreading of Al on TiC, at temperatures up to 900 degrees C, in Ar and in air has been studied. Whilst obtuse contact angles were observed without flux, the flux facilitated rapid spreading to a perfect wetting condition, in both Ar and in air. The atmosphere was found to have a weak effect on the spreading kinetics as the liquid flux provides a locally protective atmosphere by spreading over the TiC surface and also on the solid surface of Al. The flux dissolves the aluminium oxide, covering Al, so that when Al melts, and the oxide layer has been removed or weakened, intimate contact occurs between liquid Al and the TiC substrate facilitating spontaneous spreading and instantaneous wetting of liquid Al on TiC. Since flux-assisted spreading is very rapid and occurs without the formation of a reaction layer at the Al/TiC interface, this process is very different to the reactive wetting behaviour previously reported in the Al-TiC system.

  14. Spreading of a granular droplet

    NASA Astrophysics Data System (ADS)

    Clement, Eric; Sanchez, Ivan; Raynaud, Franck; Lanuza, Jose; Andreotti, Bruno; Aranson, Igor

    2008-03-01

    The influence of controlled vibrations on the granular rheology is investigated in a specifically designed experiment in which a granular film spreads under the action of horizontal vibrations. A nonlinear diffusion equation is derived theoretically that describes the evolution of the deposit shape. A self-similar parabolic shape (the``granular droplet'') and a spreading dynamics are predicted that both agree quantitatively with the experimental results. The theoretical analysis is used to extract effective friction coefficients between the base and the granular layer under sustained and controlled vibrations. A shear thickening regime characteristic of dense granular flows is evidenced at low vibration energy, both for glass beads and natural sand. Conversely, shear thinning is observed at high agitation.

  15. Spreading of a granular droplet

    NASA Astrophysics Data System (ADS)

    Sánchez, Iván; Raynaud, Franck; Lanuza, José; Andreotti, Bruno; Clément, Eric; Aranson, Igor S.

    2007-12-01

    The influence of controlled vibrations on the granular rheology is investigated in a specifically designed experiment in which a granular film spreads under the action of horizontal vibrations. A nonlinear diffusion equation is derived theoretically that describes the evolution of the deposit shape. A self-similar parabolic shape (the“granular droplet”) and a spreading dynamics are predicted that both agree quantitatively with the experimental results. The theoretical analysis is used to extract effective friction coefficients between the base and the granular layer under sustained and controlled vibrations. A shear thickening regime characteristic of dense granular flows is evidenced at low vibration energy, both for glass beads and natural sand. Conversely, shear thinning is observed at high agitation.

  16. Equatorial Spread F Fossil Plumes

    DTIC Science & Technology

    2010-11-01

    2007, 2007. Steenburgh, R. A., Smithtro, C. G., and Groves, K. M.: Ionospheric scintillation effects on single frequency GPS , Space Weather, 6, S04D02...issues, J. Geophys. Res., 107, 1468, doi:10.1029/2002JA009430, 2002. Retterer, J. M.: Forecasting low-latitude radio scintillation with 3- D ionospheric ... Ionosphere (Equatorial ionosphere ; Ionosphere - atmosphere interactions; Ionospheric irregularities) 1 Introduction Equatorial spread F (ESF), the result of

  17. Spread Spectrum Mobile Radio Communications.

    DTIC Science & Technology

    1986-03-31

    for radio frequency spectrum has led to a wide variety of techniques for solving the problem of spectral conjestion. Spectrally efficient modulation ...Kenkichi Hirade, " GMSK Modulation for Digital Mobile Radio Telephcny", IEEE Trans. on Commun., Vol. COM-29, No. 7, July 1981, pp. 1044-1050. [20.] .C...necessary and Identify by block number) Spread Spectrum Mobile Packet Radio Network Carrier Sense Multiple Access Spectrally Efficient Modulation Speech

  18. Spread of entanglement and causality

    NASA Astrophysics Data System (ADS)

    Casini, Horacio; Liu, Hong; Mezei, Márk

    2016-07-01

    We investigate causality constraints on the time evolution of entanglement entropy after a global quench in relativistic theories. We first provide a general proof that the so-called tsunami velocity is bounded by the speed of light. We then generalize the free particle streaming model of [1] to general dimensions and to an arbitrary entanglement pattern of the initial state. In more than two spacetime dimensions the spread of entanglement in these models is highly sensitive to the initial entanglement pattern, but we are able to prove an upper bound on the normalized rate of growth of entanglement entropy, and hence the tsunami velocity. The bound is smaller than what one gets for quenches in holographic theories, which highlights the importance of interactions in the spread of entanglement in many-body systems. We propose an interacting model which we believe provides an upper bound on the spread of entanglement for interacting relativistic theories. In two spacetime dimensions with multiple intervals, this model and its variations are able to reproduce intricate results exhibited by holographic theories for a significant part of the parameter space. For higher dimensions, the model bounds the tsunami velocity at the speed of light. Finally, we construct a geometric model for entanglement propagation based on a tensor network construction for global quenches.

  19. Spreading of Magnetic Reconnection X-lines in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Cassak, Paul; Shepherd, Lucas

    2012-03-01

    Naturally occurring magnetic reconnection often begins in a spatially localized region and spreads in the out-of-plane direction in time. A number of authors have studied this problem for magnetotail applications such as substorms and bursty bulk flows, for which the out-of-plane (guide) field is typically small. However, spreading also occurs in laboratory experiments and two-ribbon solar flares (such as the Bastille Day flare), and is inferred to occur at the dayside magnetopause. The reconnection site in each of these settings is known or thought to have a significant guide field. With no guide field, it was shown that the reconnection spreading is controlled by the species that carries the current. However, laboratory experiments with a large guide field (Katz et al., Phys. Rev. Lett., 104, 255004, 2010) revealed that spreading takes place in both directions at the Alfven speed based on the guide field. This implies a qualitative change of behavior as the guide field varies. We present a scaling argument for the condition on the guide field at which the nature of the spreading switches from being caused by current carriers to Alfven waves. Further, we show results of three-dimensional two-fluid simulations that agree with the theory. We discuss applications to observations.

  20. Dynamics of virus spread in the presence of fluid flow.

    PubMed

    Anekal, Samartha G; Zhu, Ying; Graham, Michael D; Yin, John

    2009-12-01

    The dynamics of viral infection spread, whether in laboratory cultures or in naturally infected hosts, reflects a coupling of biological and physical processes that remain to be fully elucidated. Biological processes include the kinetics of virus growth in infected cells while physical processes include transport of virus progeny from infected cells, where they are produced, to susceptible cells, where they initiate new infections. Mechanistic models of infection spread have been widely developed for systems where virus growth is coupled with transport of virus particles by diffusion, but they have yet to be developed for systems where viruses move under the influence of fluid flows. Recent experimental observations of flow-enhanced infection spread in laboratory cultures motivate here the development of initial continuum and discrete virus-particle models of infection spread. The magnitude of a dimensionless group, the Damköhler number, shows how parameters that characterize particle adsorption to cells, strain rates that reflect flow profiles, and diffusivities of virus particles combine to influence the spatial pattern of infection spread.

  1. Acceleration of evolutionary spread by long-range dispersal

    PubMed Central

    Hallatschek, Oskar; Fisher, Daniel S.

    2014-01-01

    The spreading of evolutionary novelties across populations is the central element of adaptation. Unless populations are well mixed (like bacteria in a shaken test tube), the spreading dynamics depend not only on fitness differences but also on the dispersal behavior of the species. Spreading at a constant speed is generally predicted when dispersal is sufficiently short ranged, specifically when the dispersal kernel falls off exponentially or faster. However, the case of long-range dispersal is unresolved: Although it is clear that even rare long-range jumps can lead to a drastic speedup—as air-traffic–mediated epidemics show—it has been difficult to quantify the ensuing stochastic dynamical process. However, such knowledge is indispensable for a predictive understanding of many spreading processes in natural populations. We present a simple iterative scaling approximation supported by simulations and rigorous bounds that accurately predicts evolutionary spread, which is determined by a trade-off between frequency and potential effectiveness of long-distance jumps. In contrast to the exponential laws predicted by deterministic “mean-field” approximations, we show that the asymptotic spatial growth is according to either a power law or a stretched exponential, depending on the tails of the dispersal kernel. More importantly, we provide a full time-dependent description of the convergence to the asymptotic behavior, which can be anomalously slow and is relevant even for long times. Our results also apply to spreading dynamics on networks with a spectrum of long-range links under certain conditions on the probabilities of long-distance travel: These are relevant for the spread of epidemics. PMID:25368183

  2. Acceleration of evolutionary spread by long-range dispersal.

    PubMed

    Hallatschek, Oskar; Fisher, Daniel S

    2014-11-18

    The spreading of evolutionary novelties across populations is the central element of adaptation. Unless populations are well mixed (like bacteria in a shaken test tube), the spreading dynamics depend not only on fitness differences but also on the dispersal behavior of the species. Spreading at a constant speed is generally predicted when dispersal is sufficiently short ranged, specifically when the dispersal kernel falls off exponentially or faster. However, the case of long-range dispersal is unresolved: Although it is clear that even rare long-range jumps can lead to a drastic speedup--as air-traffic-mediated epidemics show--it has been difficult to quantify the ensuing stochastic dynamical process. However, such knowledge is indispensable for a predictive understanding of many spreading processes in natural populations. We present a simple iterative scaling approximation supported by simulations and rigorous bounds that accurately predicts evolutionary spread, which is determined by a trade-off between frequency and potential effectiveness of long-distance jumps. In contrast to the exponential laws predicted by deterministic "mean-field" approximations, we show that the asymptotic spatial growth is according to either a power law or a stretched exponential, depending on the tails of the dispersal kernel. More importantly, we provide a full time-dependent description of the convergence to the asymptotic behavior, which can be anomalously slow and is relevant even for long times. Our results also apply to spreading dynamics on networks with a spectrum of long-range links under certain conditions on the probabilities of long-distance travel: These are relevant for the spread of epidemics.

  3. Reverse preferential spread in complex networks

    NASA Astrophysics Data System (ADS)

    Toyoizumi, Hiroshi; Tani, Seiichi; Miyoshi, Naoto; Okamoto, Yoshio

    2012-08-01

    Large-degree nodes may have a larger influence on the network, but they can be bottlenecks for spreading information since spreading attempts tend to concentrate on these nodes and become redundant. We discuss that the reverse preferential spread (distributing information inversely proportional to the degree of the receiving node) has an advantage over other spread mechanisms. In large uncorrelated networks, we show that the mean number of nodes that receive information under the reverse preferential spread is an upper bound among any other weight-based spread mechanisms, and this upper bound is indeed a logistic growth independent of the degree distribution.

  4. Assimilative and non-assimilative color spreading in the watercolor configuration.

    PubMed

    Kimura, Eiji; Kuroki, Mikako

    2014-01-01

    A colored line flanking a darker contour will appear to spread its color onto an area enclosed by the line (watercolor effect). The watercolor effect has been characterized as an assimilative effect, but non-assimilative color spreading has also been demonstrated in the same spatial configuration; e.g., when a black inner contour (IC) is paired with a blue outer contour (OC), yellow color spreading can be observed. To elucidate visual mechanisms underlying these different color spreading effects, this study investigated the effects of luminance ratio between the double contours on the induced color by systematically manipulating the IC and the OC luminance (Experiment 1) as well as the background luminance (Experiment 2). The results showed that the luminance conditions suitable for assimilative and non-assimilative color spreading were nearly opposite. When the Weber contrast of the IC to the background luminance (IC contrast) was smaller in size than that of the OC (OC contrast), the induced color became similar to the IC color (assimilative spreading). In contrast, when the OC contrast was smaller than or equal to the IC contrast, the induced color became yellow (non-assimilative spreading). Extending these findings, Experiment 3 showed that bilateral color spreading, i.e., assimilative spreading on one side and non-assimilative spreading on the other side, can also be observed in the watercolor configuration. These results suggest that the assimilative and the non-assimilative spreading were mediated by different visual mechanisms. The properties of the assimilative spreading are consistent with the model proposed to account for neon color spreading (Grossberg and Mingolla, 1985) and extended for the watercolor effect (Pinna and Grossberg, 2005). However, the present results suggest that additional mechanisms are needed to account for the non-assimilative color spreading.

  5. Assimilative and non-assimilative color spreading in the watercolor configuration

    PubMed Central

    Kimura, Eiji; Kuroki, Mikako

    2014-01-01

    A colored line flanking a darker contour will appear to spread its color onto an area enclosed by the line (watercolor effect). The watercolor effect has been characterized as an assimilative effect, but non-assimilative color spreading has also been demonstrated in the same spatial configuration; e.g., when a black inner contour (IC) is paired with a blue outer contour (OC), yellow color spreading can be observed. To elucidate visual mechanisms underlying these different color spreading effects, this study investigated the effects of luminance ratio between the double contours on the induced color by systematically manipulating the IC and the OC luminance (Experiment 1) as well as the background luminance (Experiment 2). The results showed that the luminance conditions suitable for assimilative and non-assimilative color spreading were nearly opposite. When the Weber contrast of the IC to the background luminance (IC contrast) was smaller in size than that of the OC (OC contrast), the induced color became similar to the IC color (assimilative spreading). In contrast, when the OC contrast was smaller than or equal to the IC contrast, the induced color became yellow (non-assimilative spreading). Extending these findings, Experiment 3 showed that bilateral color spreading, i.e., assimilative spreading on one side and non-assimilative spreading on the other side, can also be observed in the watercolor configuration. These results suggest that the assimilative and the non-assimilative spreading were mediated by different visual mechanisms. The properties of the assimilative spreading are consistent with the model proposed to account for neon color spreading (Grossberg and Mingolla, 1985) and extended for the watercolor effect (Pinna and Grossberg, 2005). However, the present results suggest that additional mechanisms are needed to account for the non-assimilative color spreading. PMID:25285074

  6. Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

    PubMed Central

    Ayata, Cenk; Lauritzen, Martin

    2015-01-01

    Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases. PMID:26133935

  7. Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature.

    PubMed

    Ayata, Cenk; Lauritzen, Martin

    2015-07-01

    Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

  8. Geodynamic environments of ultra-slow spreading

    NASA Astrophysics Data System (ADS)

    Kokhan, Andrey; Dubinin, Evgeny

    2015-04-01

    Ultra-slow spreading is clearly distinguished as an outstanding type of crustal accretion by recent studies. Spreading ridges with ultra-slow velocities of extension are studied rather well. But ultra-slow spreading is characteristic feature of not only spreading ridges, it can be observed also on convergent and transform plate boundaries. Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on divergent plate boundaries: 1. On spreading ridges with ultra-slow spreading, both modern (f.e. Gakkel, South-West Indian, Aden spreading center) and ceased (Labrador spreading center, Aegir ridge); 2. During transition from continental rifting to early stages of oceanic spreading (all spreading ridges during incipient stages of their formation); 3. During incipient stages of formation of spreading ridges on oceanic crust as a result of ridge jumps and reorganization of plate boundaries (f.e. Mathematicians rise and East Pacific rise); 4. During propagation of spreading ridge into the continental crust under influence of hotspot (Aden spreading center and Afar triple junction), under presence of strike-slip faults preceding propagation (possibly, rift zone of California Bay). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on transform plate boundaries: 1. In transit zones between two "typical" spreading ridges (f.e. Knipovich ridge); 2. In semi strike-slip/extension zones on the oceanic crust (f.e. American-Antarctic ridge); 3. In the zones of local extension in regional strike-slip areas in pull-apart basins along transform boundaries (Cayman trough, pull-apart basins of the southern border of Scotia plate). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on convergent plate boundaries: 1. During back-arc rifting on the stage of transition into back-arc spreading (central

  9. Hydroclimatological And Anthropogenic Drivers For Cholera Spreading

    NASA Astrophysics Data System (ADS)

    Righetto, Lorenzo; Bertuzzo, Enrico; Mari, Lorenzo; Casagrandi, Renato; Gatto, Marino; Rinaldo, Andrea

    2010-05-01

    The nature of waterborne diseases, among which cholera has a prominent importance, calls for a better understanding of the link between epidemic spreading, water and climate. To this end, we have developed a framework which involves a network-based description of a river system, connected with local communities which act as nodes of the network. This has allowed us to produce consistent simulations of real case studies. More recent investigations comprise the evaluation of the spreading velocity of an epidemic wave by means of a reaction-diffusion modeling approach. In particular, we have found that both transport processes and epidemiological quantities, such as the basic reproduction number, have a crucial effect in controlling the spreading of the epidemics. We first developed a description of bacterial movement along the network driven by advection and diffusion; afterward, we have included the movement of human populations. This latter model allowed us to establish the conditions that can trigger epidemic waves that start from the coastal region, where bacteria are autochthonous, and travel inland. In particular, our findings suggest that even relatively low values of human diffusion can have the epidemic propagate upstream. The interaction between climate, hydrology and epidemic events is still much debated, since no clear correlation between climatologic and epidemiological phenomena has emerged so far. However, a spatial assessment of hydrological and epidemiological mechanisms could be crucial to understand the evolution of cholera outbreaks. In particular, a hotly debated topic is the understanding of the mechanisms that can generate patterns of cholera incidence that exhibit an intra-annual double peak, as frequently observed in endemic region such as Bangladesh. One of the possible explanations proposed in the literature is that spring droughts cause bacteria concentration in water to rise dramatically, triggering the first peak. On the other hand

  10. Memory in network flows and its effects on spreading dynamics and community detection.

    PubMed

    Rosvall, Martin; Esquivel, Alcides V; Lancichinetti, Andrea; West, Jevin D; Lambiotte, Renaud

    2014-08-11

    Random walks on networks is the standard tool for modelling spreading processes in social and biological systems. This first-order Markov approach is used in conventional community detection, ranking and spreading analysis, although it ignores a potentially important feature of the dynamics: where flow moves to may depend on where it comes from. Here we analyse pathways from different systems, and although we only observe marginal consequences for disease spreading, we show that ignoring the effects of second-order Markov dynamics has important consequences for community detection, ranking and information spreading. For example, capturing dynamics with a second-order Markov model allows us to reveal actual travel patterns in air traffic and to uncover multidisciplinary journals in scientific communication. These findings were achieved only by using more available data and making no additional assumptions, and therefore suggest that accounting for higher-order memory in network flows can help us better understand how real systems are organized and function.

  11. Modeling the Spread of Ebola

    PubMed Central

    Do, Tae Sug; Lee, Young S.

    2016-01-01

    Objectives This study aims to create a mathematical model to better understand the spread of Ebola, the mathematical dynamics of the disease, and preventative behaviors. Methods An epidemiological model is created with a system of nonlinear differential equations, and the model examines the disease transmission dynamics with isolation through stability analysis. All parameters are approximated, and results are also exploited by simulations. Sensitivity analysis is used to discuss the effect of intervention strategies. Results The system has only one equilibrium point, which is the disease-free state (S,L,I,R,D) = (N,0,0,0,0). If traditional burials of Ebola victims are allowed, the possible end state is never stable. Provided that safe burial practices with no traditional rituals are followed, the endemic-free state is stable if the basic reproductive number, R0, is less than 1. Model behaviors correspond to empirical facts. The model simulation agrees with the data of the Nigeria outbreak in 2004: 12 recoveries, eight deaths, Ebola free in about 3 months, and an R0 value of about 2.6 initially, which signifies swift spread of the infection. The best way to reduce R0 is achieving the speedy net effect of intervention strategies. One day's delay in full compliance with building rings around the virus with isolation, close observation, and clear education may double the number of infected cases. Conclusion The model can predict the total number of infected cases, number of deaths, and duration of outbreaks among others. The model can be used to better understand the spread of Ebola, educate about prophylactic behaviors, and develop strategies that alter environment to achieve a disease-free state. A future work is to incorporate vaccination in the model when the vaccines are developed and the effects of vaccines are known better. PMID:26981342

  12. Hybrid spread spectrum radio system

    DOEpatents

    Smith, Stephen F.; Dress, William B.

    2010-02-02

    Systems and methods are described for hybrid spread spectrum radio systems. A method includes modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control an amplification circuit that provides a gain to the signal. Another method includes: modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control a fast hopping frequency synthesizer; and fast frequency hopping the signal with the fast hopping frequency synthesizer, wherein multiple frequency hops occur within a single data-bit time.

  13. Sea-Floor Spreading and Transform Faults

    ERIC Educational Resources Information Center

    Armstrong, Ronald E.; And Others

    1978-01-01

    Presents the Crustal Evolution Education Project (CEEP) instructional module on Sea-Floor Spreading and Transform Faults. The module includes activities and materials required, procedures, summary questions, and extension ideas for teaching Sea-Floor Spreading. (SL)

  14. Lexical Ambiguity: Making a Case against Spread

    ERIC Educational Resources Information Center

    Kaplan, Jennifer J.; Rogness, Neal T.; Fisher, Diane G.

    2012-01-01

    We argue for decreasing the use of the word "spread" when describing the statistical idea of dispersion or variability in introductory statistics courses. In addition, we argue for increasing the use of the word "variability" as a replacement for "spread."

  15. Lexical Ambiguity: Making a Case against Spread

    ERIC Educational Resources Information Center

    Kaplan, Jennifer J.; Rogness, Neal T.; Fisher, Diane G.

    2012-01-01

    We argue for decreasing the use of the word "spread" when describing the statistical idea of dispersion or variability in introductory statistics courses. In addition, we argue for increasing the use of the word "variability" as a replacement for "spread."

  16. Influence of slope on fire spread rate

    Treesearch

    B.W. Butler; W.R. Anderson; E.A. Catchpole

    2007-01-01

    Data demonstrate the effect of slope on heading and backing fires burning through woody fuels. The data indicate that the upper limit of heading fire rate of spread is defined by the rate of spread up a vertical fuel array, and the lower limit is defined by the rate of spread of a backing fire burning downslope. The minimum spread rate is found to occur at nominally --...

  17. Spatial variability of fine particle concentrations in three European areas

    NASA Astrophysics Data System (ADS)

    Hoek, Gerard; Meliefste, Kees; Cyrys, Josef; Lewné, Marie; Bellander, Tom; Brauer, Mike; Fischer, Paul; Gehring, Ulrike; Heinrich, Joachim; van Vliet, Patricia; Brunekreef, Bert

    Epidemiological studies of long-term air pollution effects have been hampered by difficulties in characterizing the spatial variation in air pollution. We conducted a study to assess the risk of long-term exposure to traffic-related air pollution for the development of inhalant allergy and asthma in children in Stockholm county, Munich and the Netherlands. Exposure to traffic-related air pollution was assessed through a 1-year monitoring program and regression modeling using exposure indicators. This paper documents the performance of the exposure monitoring strategy and the spatial variation of ambient particle concentrations. We measured the ambient concentration of PM2.5 and the reflectance of PM2.5 filters ('soot') at 40-42 sites representative of different exposure conditions of the three study populations. Each site was measured during four 14-day average sampling periods spread over one year (spring 1999 to summer 2000). In each study area, a continuous measurement site was operated to remove potential bias due to temporal variation. The selected approach was an efficient method to characterize spatial differences in annual average concentration between a large number of sites in each study area. Adjustment with data from the continuous measurement site improved the precision of the calculated annual averages, especially for PM2.5. Annual average PM2.5 concentrations ranged from 11 to 20 μg/m 3 in Munich, from 8 to 16 μg/m 3 in Stockholm and from 14 to 26 μg/m 3 in the Netherlands. Larger spatial contrasts were found for the absorption coefficient of PM2.5. PM2.5 concentrations were on average 17-18% higher at traffic sites than at urban background sites, but PM2.5 absorption coefficients at traffic sites were between 31% and 55% increased above background. This suggests that spatial variation of traffic-related air pollution may be underestimated if PM2.5 only is measured.

  18. nem_spread Ver. 5.10

    SciTech Connect

    HENNIGAN, GARY; SHADID, JOHN; SJAARDEMA, GREGORY; HUTCHINSON, SCOTT

    2009-06-08

    Nem_spread reads it's input command file (default name nem_spread.inp), takes the named ExodusII geometry definition and spreads out the geometry (and optionally results) contained in that file out to a parallel disk system. The decomposition is taken from a scalar Nemesis load balance file generated by the companion utility nem_slice.

  19. The spreading of misinformation online.

    PubMed

    Del Vicario, Michela; Bessi, Alessandro; Zollo, Fabiana; Petroni, Fabio; Scala, Antonio; Caldarelli, Guido; Stanley, H Eugene; Quattrociocchi, Walter

    2016-01-19

    The wide availability of user-provided content in online social media facilitates the aggregation of people around common interests, worldviews, and narratives. However, the World Wide Web (WWW) also allows for the rapid dissemination of unsubstantiated rumors and conspiracy theories that often elicit rapid, large, but naive social responses such as the recent case of Jade Helm 15--where a simple military exercise turned out to be perceived as the beginning of a new civil war in the United States. In this work, we address the determinants governing misinformation spreading through a thorough quantitative analysis. In particular, we focus on how Facebook users consume information related to two distinct narratives: scientific and conspiracy news. We find that, although consumers of scientific and conspiracy stories present similar consumption patterns with respect to content, cascade dynamics differ. Selective exposure to content is the primary driver of content diffusion and generates the formation of homogeneous clusters, i.e., "echo chambers." Indeed, homogeneity appears to be the primary driver for the diffusion of contents and each echo chamber has its own cascade dynamics. Finally, we introduce a data-driven percolation model mimicking rumor spreading and we show that homogeneity and polarization are the main determinants for predicting cascades' size.

  20. Cross spread pupil tracking technique

    NASA Astrophysics Data System (ADS)

    Wolski, Krzysztof; Mantiuk, Radosław

    2016-11-01

    We present a fast and minimum delay algorithm for detecting the pupil center, called the "cross spread" tracking technique. This algorithm is meant for video eye trackers that estimate gaze direction from the position of the pupil center in the captured images. Contrary to other solutions, we do not try to make this technique robust to distractors such as reflections, distortions caused by glasses, or eyelids covering the pupil, but rather we assume eye tracking in stable light conditions. We argue that this approach is useful in many eye tracking applications, such as gaze tracking during psychophysical experiments in stable laboratory conditions, and that this approach can significantly reduce the eye tracker's complexity while maintaining its accuracy and performance. The proposed cross spread technique estimates pupil by tracing rays in horizontal and vertical directions in the image, starting from a point in the pupil region and continuing to the pupil boundary. The found boundary points determine the next starting point and the procedure is iteratively repeated. Parallel processing can be efficiently used enabling accurate pupil center detection in <2 ms on typical laptops. We compare the proposed algorithm to other pupil detection algorithms.

  1. Spreading Astronomy Education Through Africa

    NASA Astrophysics Data System (ADS)

    Baki, P.

    2006-08-01

    Although Astronomy has been an important vehicle for effectively passing a wide range of scientific knowledge, teaching the basic skills of scientific reasoning, and for communicating the excitement of science to the public, its inclusion in the teaching curricula of most institutions of higher learning in Africa is rare. This is partly due to the fact that astronomy appears to be only good at fascinating people but not providing paid jobs. It is also due to the lack of trained instructors, teaching materials, and a clear vision of the role of astronomy and basic space science within the broader context of education in the physical and applied sciences. In this paper we survey some of the problems bedeviling the spread of astronomy in Africa and discuss some interdisciplinary traditional weather indicators. These indicators have been used over the years to monitor the appearance of constellations. For example, orions are closely intertwined with cultures of some ethnic African societies and could be incorporated in the standard astronomy curriculum as away of making the subject more `home grown' and to be able to reach out to the wider populace in popularizing astronomy and basic sciences. We also discuss some of the other measures that ought to be taken to effectively create an enabling environment for sustainable teaching and spread of astronomy through Africa.

  2. The spreading of misinformation online

    PubMed Central

    Del Vicario, Michela; Bessi, Alessandro; Zollo, Fabiana; Petroni, Fabio; Caldarelli, Guido; Stanley, H. Eugene; Quattrociocchi, Walter

    2016-01-01

    The wide availability of user-provided content in online social media facilitates the aggregation of people around common interests, worldviews, and narratives. However, the World Wide Web (WWW) also allows for the rapid dissemination of unsubstantiated rumors and conspiracy theories that often elicit rapid, large, but naive social responses such as the recent case of Jade Helm 15––where a simple military exercise turned out to be perceived as the beginning of a new civil war in the United States. In this work, we address the determinants governing misinformation spreading through a thorough quantitative analysis. In particular, we focus on how Facebook users consume information related to two distinct narratives: scientific and conspiracy news. We find that, although consumers of scientific and conspiracy stories present similar consumption patterns with respect to content, cascade dynamics differ. Selective exposure to content is the primary driver of content diffusion and generates the formation of homogeneous clusters, i.e., “echo chambers.” Indeed, homogeneity appears to be the primary driver for the diffusion of contents and each echo chamber has its own cascade dynamics. Finally, we introduce a data-driven percolation model mimicking rumor spreading and we show that homogeneity and polarization are the main determinants for predicting cascades’ size. PMID:26729863

  3. Picosecond laser filamentation in air

    NASA Astrophysics Data System (ADS)

    Schmitt-Sody, Andreas; Kurz, Heiko G.; Bergé, Luc; Skupin, Stefan; Polynkin, Pavel

    2016-09-01

    The propagation of intense picosecond laser pulses in air in the presence of strong nonlinear self-action effects and air ionization is investigated experimentally and numerically. The model used for numerical analysis is based on the nonlinear propagator for the optical field coupled to the rate equations for the production of various ionic species and plasma temperature. Our results show that the phenomenon of plasma-driven intensity clamping, which has been paramount in femtosecond laser filamentation, holds for picosecond pulses. Furthermore, the temporal pulse distortions in the picosecond regime are limited and the pulse fluence is also clamped. In focused propagation geometry, a unique feature of picosecond filamentation is the production of a broad, fully ionized air channel, continuous both longitudinally and transversely, which may be instrumental for many applications including laser-guided electrical breakdown of air, channeling microwave beams and air lasing.

  4. Superballistic wavepacket spreading in double kicked rotors

    NASA Astrophysics Data System (ADS)

    Fang, Ping; Wang, Jiao

    2016-08-01

    We investigate possible ways in which a quantum wavepacket spreads. We show that in a general class of double kicked rotor system, a wavepacket may undergo superballistic spreading; i.e., its variance increases as the cubic of time. The conditions for the observed superballistic spreading and two related characteristic time scales are studied. Our results suggest that the symmetry of the studied model and whether it is a Kolmogorov-Arnold-Moser system are crucial to its wavepacket spreading behavior. Our study also sheds new light on the exponential wavepacket spreading phenomenon previously observed in the double kicked rotor system.

  5. Cooperative spreading processes in multiplex networks

    NASA Astrophysics Data System (ADS)

    Wei, Xiang; Chen, Shihua; Wu, Xiaoqun; Ning, Di; Lu, Jun-an

    2016-06-01

    This study is concerned with the dynamic behaviors of epidemic spreading in multiplex networks. A model composed of two interacting complex networks is proposed to describe cooperative spreading processes, wherein the virus spreading in one layer can penetrate into the other to promote the spreading process. The global epidemic threshold of the model is smaller than the epidemic thresholds of the corresponding isolated networks. Thus, global epidemic onset arises in the interacting networks even though an epidemic onset does not arise in each isolated network. Simulations verify the analysis results and indicate that cooperative spreading processes in multiplex networks enhance the final infection fraction.

  6. Potential corridors and barriers for plague spread in Central Asia.

    PubMed

    Wilschut, Liesbeth I; Addink, Elisabeth A; Heesterbeek, Hans; Heier, Lise; Laudisoit, Anne; Begon, Mike; Davis, Stephen; Dubyanskiy, Vladimir M; Burdelov, Leonid A; de Jong, Steven M

    2013-10-31

    Plague (Yersinia pestis infection) is a vector-borne disease which caused millions of human deaths in the Middle Ages. The hosts of plague are mostly rodents, and the disease is spread by the fleas that feed on them. Currently, the disease still circulates amongst sylvatic rodent populations all over the world, including great gerbil (Rhombomys opimus) populations in Central Asia. Great gerbils are social desert rodents that live in family groups in burrows, which are visible on satellite images. In great gerbil populations an abundance threshold exists, above which plague can spread causing epizootics. The spatial distribution of the host species is thought to influence the plague dynamics, such as the direction of plague spread, however no detailed analysis exists on the possible functional or structural corridors and barriers that are present in this population and landscape. This study aims to fill that gap. Three 20 by 20 km areas with known great gerbil burrow distributions were used to analyse the spatial distribution of the burrows. Object-based image analysis was used to map the landscape at several scales, and was linked to the burrow maps. A novel object-based method was developed - the mean neighbour absolute burrow density difference (MNABDD) - to identify the optimal scale and evaluate the efficacy of using landscape objects as opposed to square cells. Multiple regression using raster maps was used to identify the landscape-ecological variables that explain burrow density best. Functional corridors and barriers were mapped using burrow density thresholds. Cumulative resistance of the burrow distribution to potential disease spread was evaluated using cost distance analysis. A 46-year plague surveillance dataset was used to evaluate whether plague spread was radially symmetric. The burrow distribution was found to be non-random and negatively correlated with Greenness, especially in the floodplain areas. Corridors and barriers showed a mostly NWSE

  7. Potential corridors and barriers for plague spread in central Asia

    PubMed Central

    2013-01-01

    Background Plague (Yersinia pestis infection) is a vector-borne disease which caused millions of human deaths in the Middle Ages. The hosts of plague are mostly rodents, and the disease is spread by the fleas that feed on them. Currently, the disease still circulates amongst sylvatic rodent populations all over the world, including great gerbil (Rhombomys opimus) populations in Central Asia. Great gerbils are social desert rodents that live in family groups in burrows, which are visible on satellite images. In great gerbil populations an abundance threshold exists, above which plague can spread causing epizootics. The spatial distribution of the host species is thought to influence the plague dynamics, such as the direction of plague spread, however no detailed analysis exists on the possible functional or structural corridors and barriers that are present in this population and landscape. This study aims to fill that gap. Methods Three 20 by 20 km areas with known great gerbil burrow distributions were used to analyse the spatial distribution of the burrows. Object-based image analysis was used to map the landscape at several scales, and was linked to the burrow maps. A novel object-based method was developed – the mean neighbour absolute burrow density difference (MNABDD) – to identify the optimal scale and evaluate the efficacy of using landscape objects as opposed to square cells. Multiple regression using raster maps was used to identify the landscape-ecological variables that explain burrow density best. Functional corridors and barriers were mapped using burrow density thresholds. Cumulative resistance of the burrow distribution to potential disease spread was evaluated using cost distance analysis. A 46-year plague surveillance dataset was used to evaluate whether plague spread was radially symmetric. Results The burrow distribution was found to be non-random and negatively correlated with Greenness, especially in the floodplain areas. Corridors and

  8. Spreading granular material with a blade

    NASA Astrophysics Data System (ADS)

    Dressaire, Emilie; Singh, Vachitar; Grimaldi, Emma; Sauret, Alban

    2015-11-01

    The spreading of a complex fluid with a blade is encountered in applications that range from the bulldozing of granular material in construction projects to the coating of substrates with fluids in industrial applications. This spreading process is also present in everyday life, when we use a knife to turn a lump of peanut butter into a thin layer over our morning toast. In this study, we rely on granular media in a model experiment to describe the three-dimensional spreading of the material. Our experimental set-up allows tracking the spreading of a sandpile on a translating flat surface as the blade remains fixed. We characterize the spreading dynamics and the shape of the spread fluid layer when varying the tilt of the blade, its spacing with the surface and its speed. Our findings suggest that it is possible to tune the spreading parameters to optimize the coating.

  9. Structural processes at slow-spreading ridges.

    PubMed

    Mutter, J C; Karson, J A

    1992-07-31

    Slow-spreading (<35 millimeters per year) mid-ocean ridges are dominated by segmented, asymmetric, rifted depressions like continental rifts. Fast-spreading ridges display symmetric, elevated volcanic edifices that vary in shape and size along axis. Deep earthquakes, major normal faults, and exposures of lower crustal rocks are common only along slow-spreading ridges. These contrasting features suggest that mechanical deformation is far more important in crustal formation at slow-spreading ridges than at fast-spreading ridges. New seismic images suggest that the nature and scale of segmentation of slow-spreading ridges is integral to the deformational process and not to magmatic processes that may control segmentation on fast-spreading ridges.

  10. The landscape genetics of infectious disease emergence and spread

    PubMed Central

    Biek, Roman; Real, Leslie A.

    2011-01-01

    The spread of parasites is inherently a spatial process often embedded in physically complex landscapes. It is therefore not surprising that infectious disease researchers are increasingly taking a landscape genetics perspective to elucidate mechanisms underlying basic ecological processes driving infectious disease dynamics and to understand the linkage between spatially-dependent population processes and the geographic distribution of genetic variation within both hosts and parasites. The increasing availability of genetic information on hosts and parasites when coupled to their ecological interactions can lead to insights for predicting patterns of disease emergence, spread, and control. Here, we review research progress in this area based on four different motivations for the application of landscape genetics approaches: (1) assessing the spatial organization of genetic variation in parasites as a function of environmental variability, (2) using host population genetic structure as a means to parameterize ecological dynamics that indirectly influence parasite populations, e.g. gene flow and movement pathways across heterogeneous landscapes and the concurrent transport of infectious agents, (3) elucidating the temporal and spatial scales of disease processes, and (4) reconstructing and understanding infectious disease invasion. Throughout this review, we emphasise that landscape genetic principles are relevant to infection dynamics across a range of scales from within host dynamics to global geographic patterns and that they can also be applied to unconventional “landscapes” such as heterogeneous contact networks underlying the spread of human and livestock diseases. We conclude by discussing some general considerations and problems for inferring epidemiological processes from genetic data and try to identify possible future directions and applications for this rapidly expanding field. PMID:20618897

  11. Virulence evolution at the front line of spreading epidemics.

    PubMed

    Griette, Quentin; Raoul, Gaël; Gandon, Sylvain

    2015-11-01

    Understanding and predicting the spatial spread of emerging pathogens is a major challenge for the public health management of infectious diseases. Theoretical epidemiology shows that the speed of an epidemic is governed by the life-history characteristics of the pathogen and its ability to disperse. Rapid evolution of these traits during the invasion may thus affect the speed of epidemics. Here we study the influence of virulence evolution on the spatial spread of an epidemic. At the edge of the invasion front, we show that more virulent and transmissible genotypes are expected to win the competition with other pathogens. Behind the front line, however, more prudent exploitation strategies outcompete virulent pathogens. Crucially, even when the presence of the virulent mutant is limited to the edge of the front, the invasion speed can be dramatically altered by pathogen evolution. We support our analysis with individual-based simulations and we discuss the additional effects of demographic stochasticity taking place at the front line on virulence evolution. We confirm that an increase of virulence can occur at the front, but only if the carrying capacity of the invading pathogen is large enough. These results are discussed in the light of recent empirical studies examining virulence evolution at the edge of spreading epidemics.

  12. Spreading of Impacting Droplets on Wettability-Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Elsharkawy, Mohamed; Russo, Antonio; Asinari, Pietro; Megaridis, Constantine

    2016-11-01

    Droplet collision on solid surfaces is a long-studied field that has focused mostly on droplets striking uniform-wettability surfaces. As of now, very few studies exist that analyzed droplet impact on non-uniform (spatially) wettability surfaces. More importantly, no model exists for predicting droplet impact behavior on spatially non-uniform surfaces. Using photolithograhically-produced surfaces, we study droplet impact on axially-symmetric, non-uniform wettability surfaces. We expand upon previously presented models for uniform-wettability surfaces, and predict the maximum spreading diameter of droplets impacting on symmetric patterns on varying wettability surfaces. The present model is expanded to account for n annular regions of different wettabilities, and calculate the corresponding maximum spreading diameter. In addition, within the model we explore the concept of a wettability contrast barrier that must be overcome by the impacting droplets in order to continue their spreading phase. We show under which conditions a droplet can successfully overcome this barrier, and under which conditions it cannot. The model put forth makes strong use of the previously-reported droplet impact model of Passandideh-Fard et al. It draws upon geometric assumptions, such as cylindrical shape for the expanding liquid and spherical cap for the impacting droplet. The work is fundamental in nature, but offers valuable insight that helps understand droplet impact dynamics on non-uniform wettability surfaces.

  13. SAW correlator spread spectrum receiver

    DOEpatents

    Brocato, Robert W

    2014-04-01

    A surface acoustic wave (SAW) correlator spread-spectrum (SS) receiver is disclosed which utilizes a first demodulation stage with a chip length n and a second demodulation stage with a chip length m to decode a transmitted SS signal having a code length l=n.times.m which can be very long (e.g. up to 2000 chips or more). The first demodulation stage utilizes a pair of SAW correlators which demodulate the SS signal to generate an appropriate code sequence at an intermediate frequency which can then be fed into the second demodulation stage which can be formed from another SAW correlator, or by a digital correlator. A compound SAW correlator comprising two input transducers and a single output transducer is also disclosed which can be used to form the SAW correlator SS receiver, or for use in processing long code length signals.

  14. Epidemic spreading on hierarchical geographical networks with mobile agents

    NASA Astrophysics Data System (ADS)

    Han, Xiao-Pu; Zhao, Zhi-Dan; Hadzibeganovic, Tarik; Wang, Bing-Hong

    2014-05-01

    Hierarchical geographical traffic networks are critical for our understanding of scaling laws in human trajectories. Here, we investigate the susceptible-infected epidemic process evolving on hierarchical networks in which agents randomly walk along the edges and establish contacts in network nodes. We employ a metapopulation modeling framework that allows us to explore the contagion spread patterns in relation to multi-scale mobility behaviors. A series of computer simulations revealed that a shifted power-law-like negative relationship between the peak timing of epidemics τ0 and population density, and a logarithmic positive relationship between τ0 and the network size, can both be explained by the gradual enlargement of fluctuations in the spreading process. We employ a semi-analytical method to better understand the nature of these relationships and the role of pertinent demographic factors. Additionally, we provide a quantitative discussion of the efficiency of a border screening procedure in delaying epidemic outbreaks on hierarchical networks, yielding a rather limited feasibility of this mitigation strategy but also its non-trivial dependence on population density, infector detectability, and the diversity of the susceptible region. Our results suggest that the interplay between the human spatial dynamics, network topology, and demographic factors can have important consequences for the global spreading and control of infectious diseases. These findings provide novel insights into the combined effects of human mobility and the organization of geographical networks on spreading processes, with important implications for both epidemiological research and health policy.

  15. Short range spread-spectrum radiolocation system and method

    DOEpatents

    Smith, Stephen F.

    2003-04-29

    A short range radiolocation system and associated methods that allow the location of an item, such as equipment, containers, pallets, vehicles, or personnel, within a defined area. A small, battery powered, self-contained tag is provided to an item to be located. The tag includes a spread-spectrum transmitter that transmits a spread-spectrum code and identification information. A plurality of receivers positioned about the area receive signals from a transmitting tag. The position of the tag, and hence the item, is located by triangulation. The system employs three different ranging techniques for providing coarse, intermediate, and fine spatial position resolution. Coarse positioning information is provided by use of direct-sequence code phase transmitted as a spread-spectrum signal. Intermediate positioning information is provided by the use of a difference signal transmitted with the direct-sequence spread-spectrum code. Fine positioning information is provided by use of carrier phase measurements. An algorithm is employed to combine the three data sets to provide accurate location measurements.

  16. Optical Trapping of Gold Nanoparticles in Air.

    PubMed

    Jauffred, Liselotte; Taheri, S Mohammad-Reza; Schmitt, Regina; Linke, Heiner; Oddershede, Lene B

    2015-07-08

    Most progress on optical nanoparticle control has been in liquids, while optical control in air has proven more challenging. By utilizing an air chamber designed to have a minimum of turbulence and a single laser beam with a minimum of aberration, we trapped individual 200 to 80 nm gold nanoparticles in air and quantified the corresponding trapping strengths. These results pave the way for construction of metallic nanostructures in air away from surfaces.

  17. Hidden tectonics at slow-spreading ridges: distinguishing magmatic from tectonic spreading

    NASA Astrophysics Data System (ADS)

    MacLeod, C. J.; Searle, R. C.; Mallows, C.; Young, E. C.

    2011-12-01

    relatively ephemeral, spatially restricted features in which the relative contributions of tectonic versus magmatic spreading vary on a 10s of km length- and 10^5 to 10^6 year time-scale. Alternative models, however, (e.g. Reston and Ranero 2011 G3 Q0AG05) view detachments instead as much long-lived features far greater in extent than the exposed OCCs, which simply represent places where the supposed mega-detachment breaks surface. In this contribution we critically review evidence for the spatial extent and longevity of detachments, using sidescan imagery and near-bottom magnetic data from the 13°N region together with new observations from the Troodos ophiolite which call into question our ability to recognise and quantify tectonic stretching from seafloor data alone. We conclude by considering the implications for the nature of the interactions between melts and faults beneath the ridge axis.

  18. Spread and SpreadRecorder An Architecture for Data Distribution

    NASA Technical Reports Server (NTRS)

    Wright, Ted

    2006-01-01

    The Space Acceleration Measurement System (SAMS) project at the NASA Glenn Research Center (GRC) has been measuring the microgravity environment of the space shuttle, the International Space Station, MIR, sounding rockets, drop towers, and aircraft since 1991. The Principle Investigator Microgravity Services (PIMS) project at NASA GRC has been collecting, analyzing, reducing, and disseminating over 3 terabytes of collected SAMS and other microgravity sensor data to scientists so they can understand the disturbances that affect their microgravity science experiments. The years of experience with space flight data generation, telemetry, operations, analysis, and distribution give the SAMS/ PIMS team a unique perspective on space data systems. In 2005, the SAMS/PIMS team was asked to look into generalizing their data system and combining it with the nascent medical instrumentation data systems being proposed for ISS and beyond, specifically the Medical Computer Interface Adapter (MCIA) project. The SpreadRecorder software is a prototype system developed by SAMS/PIMS to explore ways of meeting the needs of both the medical and microgravity measurement communities. It is hoped that the system is general enough to be used for many other purposes.

  19. Microwave guiding in air by a cylindrical filament array waveguide

    SciTech Connect

    Chateauneuf, M.; Dubois, J.; Payeur, S.; Kieffer, J.-C.

    2008-03-03

    Microwave guiding was demonstrated over 16 cm in air using a large diameter hollow plasma waveguide. The waveguide was generated with the 100 TW femtosecond laser system at the Advanced Laser Light Source facility. A deformable mirror was used to spatially shape the intense laser pulses in order to generate hundreds of filaments judiciously distributed in a cylindrical shape, creating a cylindrical plasma wall that acts as a microwave waveguide. The microwaves were confined for about 10 ns, which corresponds to the free electron plasma wall recombination time. The characteristics of the plasma waveguide and the results of microwave guiding are presented.

  20. Theoretical and Experimental study on multiple filaments in air

    SciTech Connect

    Zhang Jie; Lu Xin; Hao Zuoqiang; Xi Tingting; Zhang Zhe; Jin Zhan

    2007-07-11

    The physics of filaments formed by femtosecond laser pulses propagating in air is revealed both in theory and in experiment. An analytical method is used to investigate the interaction of two filaments. The interaction Hamiltonian of two filaments with different phase shifts is obtained and used to judge the properly of filaments interaction. The analytical results are in good agreement with simulation results. The influence of energy background on propagation of filaments is investigated in experiment. It is found that the characteristics of filaments can be changed by spatial and temporal control of laser pulses.

  1. Commuter Mobility and the Spread of Infectious Diseases: Application to Influenza in France

    PubMed Central

    Charaudeau, Segolene; Pakdaman, Khashayar; Boëlle, Pierre-Yves

    2014-01-01

    Commuting data is increasingly used to describe population mobility in epidemic models. However, there is little evidence that the spatial spread of observed epidemics agrees with commuting. Here, using data from 25 epidemics for influenza-like illness in France (ILI) as seen by the Sentinelles network, we show that commuting volume is highly correlated with the spread of ILI. Next, we provide a systematic analysis of the spread of epidemics using commuting data in a mathematical model. We extract typical paths in the initial spread, related to the organization of the commuting network. These findings suggest that an alternative geographic distribution of GP accross France to the current one could be proposed. Finally, we show that change in commuting according to age (school or work commuting) impacts epidemic spread, and should be taken into account in realistic models. PMID:24416152

  2. Commuter mobility and the spread of infectious diseases: application to influenza in France.

    PubMed

    Charaudeau, Segolene; Pakdaman, Khashayar; Boëlle, Pierre-Yves

    2014-01-01

    Commuting data is increasingly used to describe population mobility in epidemic models. However, there is little evidence that the spatial spread of observed epidemics agrees with commuting. Here, using data from 25 epidemics for influenza-like illness in France (ILI) as seen by the Sentinelles network, we show that commuting volume is highly correlated with the spread of ILI. Next, we provide a systematic analysis of the spread of epidemics using commuting data in a mathematical model. We extract typical paths in the initial spread, related to the organization of the commuting network. These findings suggest that an alternative geographic distribution of GP accross France to the current one could be proposed. Finally, we show that change in commuting according to age (school or work commuting) impacts epidemic spread, and should be taken into account in realistic models.

  3. Spread spectrum time domain reflectometry

    NASA Astrophysics Data System (ADS)

    Smith, Paul Samuel

    For many years, wiring has been treated as a system that could be installed and expected to work for the life of the aircraft. As aircraft age far beyond their original expected life span, this attitude is rapidly changing. Wiring problems have recently been identified as the cause of several tragic mishaps and hundreds of thousands of lost mission hours. Intermittent wiring faults have been and continue to be difficult to resolve. Test methods that pinpoint faults on the ground can miss intermittent failures. New test methods involving spread spectrum signals are investigated that could be used in flight to locate intermittent failures, including open circuits, short circuits, and arcs. Spread spectrum time domain reflectometry (SSTDR) and sequence time domain reflectometry (STDR) are analyzed in light of the signals commonly present on aircraft wiring. Pseudo noise codes used for the generation of STDR and SSTDR signals are analyzed for application in a STDR/SSTDR test system in the presence of noise. The effects of Mil-Std 1553 and white noise on the STDR and SSTDR signals are discussed analytically, through simulations, and with the use of test hardware. A test system using STDR and SSTDR is designed, built, and used to collect STDR and SSTDR test data. The data collected with the STDR/SSTDR test hardware is analyzed and compared to the theoretical results. Experimental data for open and short circuits collected using SSTDR and a curve fitting algorithm shows a maximum range estimation error of +/-0.2 ft for 75O coaxial cable up to 100ft, and +/-0.6ft for a sample 32.5ft non-controlled impedance aircraft cable. Mil-Std 1553 is specified to operate reliably with a signal-to-noise ratio of 17.5dB, and the SSTDR test system was able to locate an open circuit on a cable also carrying simulated Mil-Std 1553 data where the SSTDR signal was 50dB below the Mil-Std 1553 signal. STDR and SSTDR are shown to be effective in detecting and locating dry and wet arcs on wires.

  4. An agent-based computational model of the spread of tuberculosis

    NASA Astrophysics Data System (ADS)

    de Espíndola, Aquino L.; Bauch, Chris T.; Troca Cabella, Brenno C.; Souto Martinez, Alexandre

    2011-05-01

    In this work we propose an alternative model of the spread of tuberculosis (TB) and the emergence of drug resistance due to the treatment with antibiotics. We implement the simulations by an agent-based model computational approach where the spatial structure is taken into account. The spread of tuberculosis occurs according to probabilities defined by the interactions among individuals. The model was validated by reproducing results already known from the literature in which different treatment regimes yield the emergence of drug resistance. The different patterns of TB spread can be visualized at any time of the system evolution. The implementation details as well as some results of this alternative approach are discussed.

  5. Impacts of suppressing guide on information spreading

    NASA Astrophysics Data System (ADS)

    Xu, Jinghong; Zhang, Lin; Ma, Baojun; Wu, Ye

    2016-02-01

    It is quite common that guides are introduced to suppress the information spreading in modern society for different purposes. In this paper, an agent-based model is established to quantitatively analyze the impacts of suppressing guides on information spreading. We find that the spreading threshold depends on the attractiveness of the information and the topology of the social network with no suppressing guides at all. Usually, one would expect that the existence of suppressing guides in the spreading procedure may result in less diffusion of information within the overall network. However, we find that sometimes the opposite is true: the manipulating nodes of suppressing guides may lead to more extensive information spreading when there are audiences with the reversal mind. These results can provide valuable theoretical references to public opinion guidance on various information, e.g., rumor or news spreading.

  6. Perineural spread in head and neck tumors.

    PubMed

    Brea Álvarez, B; Tuñón Gómez, M

    2014-01-01

    Perineural spread is the dissemination of some types of head and neck tumors along nervous structures. Perineural spread has negative repercussions on treatment because it requires more extensive resection and larger fields of irradiation. Moreover, perineural spread is associated with increased local recurrence, and it is considered an independent indicator of poor prognosis in the TNM classification for tumor staging. However, perineural spread often goes undetected on imaging studies. In this update, we review the concept of perineural spread, its pathogenesis, and the main pathways and connections among the facial nerves, which are essential to understand this process. Furthermore, we discuss the appropriate techniques for imaging studies, and we describe and illustrate the typical imaging signs that help identify perineural spread on CT and MRI. Finally, we discuss the differential diagnosis with other entities.

  7. Nosocomial Spread of Viral Disease

    PubMed Central

    Aitken, Celia; Jeffries, Donald J.

    2001-01-01

    Viruses are important causes of nosocomial infection, but the fact that hospital outbreaks often result from introduction(s) from community-based epidemics, together with the need to initiate specific laboratory testing, means that there are usually insufficient data to allow the monitoring of trends in incidences. The most important defenses against nosocomial transmission of viruses are detailed and continuing education of staff and strict adherence to infection control policies. Protocols must be available to assist in the management of patients with suspected or confirmed viral infection in the health care setting. In this review, we present details on general measures to prevent the spread of viral infection in hospitals and other health care environments. These include principles of accommodation of infected patients and approaches to good hygiene and patient management. They provide detail on individual viral diseases accompanied in each case with specific information on control of the infection and, where appropriate, details of preventive and therapeutic measures. The important areas of nosocomial infection due to blood-borne viruses have been extensively reviewed previously and are summarized here briefly, with citation of selected review articles. Human prion diseases, which present management problems very different from those of viral infection, are not included. PMID:11432812

  8. On entanglement spreading from holography

    DOE PAGES

    Mezei, Márk

    2017-05-11

    A global quench is an interesting setting where we can study thermalization of subsystems in a pure state. We investigate entanglement entropy (EE) growth in global quenches in holographic field theories and relate some of its aspects to quantities characterizing chaos. More specifically we obtain four key results: 1. We prove holographic bounds on the entanglement velocity vE and the butterfly effect speed vB that arises in the study of chaos. 2. We obtain the EE as a function of time for large spherical entangling surfaces analytically. We show that the EE is insensitive to the details of the initialmore » state or quench protocol. 3. In a thermofield double state we determine analytically the two-sided mutual information between two large concentric spheres separated in time. 4. We derive a bound on the rate of growth of EE for arbitrary shapes, and develop an expansion for EE at early times. In a companion paper, these results are put in the broader context of EE growth in chaotic systems: we relate EE growth to the chaotic spreading of operators, derive bounds on EE at a given time, and compare the holographic results to spin chain numerics and toy models. In this paper, we perform holographic calculations that provide the basis of arguments presented in that paper.« less

  9. Modeling spreading of nematic droplets

    NASA Astrophysics Data System (ADS)

    Lin, Te-Sheng; Cummings, Linda; Kondic, Lou

    2011-03-01

    Experiments by Poulard & Cazabat on spreading droplets of nematic liquid crystal reveal a surprisingly rich variety of behavior, including at least two different emerging lengthscales resulting from a contact line instability. In earlier work we modified a lubrication model for nematic liquid crystals due to Ben Amar and Cummings, and showed that, in a qualitative sense, it can account for much of the observed behavior. In the present work we propose a new approach, that allows us to explore the effect of anchoring variations on the substrate. This in turn gives a simple way to model the presence of defects, which are always present during such liquid crystal flows. The new model leads to additional terms in the governing equation. We first explore the influence of these additional terms for some simple flow scenarios, to gain a basic understanding of their influence, before extending our simulations to the experimental geometry and comparing our results to the experiments. This work was partially supported by NSF Grant No. DMS-0908158.

  10. Drops spreading on flexible fibers

    NASA Astrophysics Data System (ADS)

    Somszor, Katarzyna; Boulogne, François; Sauret, Alban; Dressaire, Emilie; Stone, Howard

    2015-11-01

    Fibrous media are encountered in many engineered systems such as textile, paper and insulating materials. In most of these materials, fibers are randomly oriented and form a complex network in which drops of wetting liquid tend to accumulate at the nodes of the network. Here we investigate the role of the fiber flexibility on the spreading of a small volume of liquid on a pair of crossed flexible fibers. A drop of silicone oil is dispensed at the point of contact of the fibers and we characterize the liquid morphologies as we vary the volume of liquid, the angle between the fibers, and the length and bending modulus of the fibers. Drop morphologies previously reported for rigid fibers, i.e. a drop, a column and a mixed morphology, are also observed on flexible fibers with modified domains of existence. Moreover, at small inclination angles of the fibers, a new behavior is observed: the fibers bend and collapse. Depending on the volume, the liquid can adopt a column or a mixed morphology on the collapsed fibers. We rationalize our observations with a model based on energetic considerations. Our study suggests that the fiber flexibility adds a rich variety of behaviors that can be crucial for industrial applications.

  11. An updated rate-of-spread clock

    USGS Publications Warehouse

    Kolaks, Jeremy; Grabner, Keith W.; Hartman, George; Cutter, Bruce E.; Loewenstein, Edward F.

    2005-01-01

    Several years ago, Blank and Simard (1983) described an electronic timer, frequently referred to as a rate-of-spread (ROS) clock—a relatively simple instrument used in measuring fire spread. Although other techniques for measuring rate of spread are available (such as data loggers), the basic ROS clock remains a valuable and relatively inexpensive tool. However, several items described in the original article have changed. Therefore, we are describing an updated version of the ROS clock.

  12. Wetting and spreading at the molecular scale

    NASA Technical Reports Server (NTRS)

    Koplik, Joel; Banavar, Jayanth R.

    1994-01-01

    We have studied the microscopic aspects of the spreading of liquid drops on a solid surface by molecular dynamics simulations of coexisting three-phase Lennard-Jones systems of liquid, vapor and solid. We consider both spherically symmetric atoms and chain-like molecules, and a range of interaction strengths. As the attraction between liquid and solid increases we observed a smooth transition in spreading regimes, from partial to complete to terraced wetting. In the terraced case, where distinct monomolecular layers spread with different velocities, the layers are ordered but not solid, with qualitative behavior resembling recent experimental findings, but with interesting differences in the spreading rate.

  13. Differential Dynamics of Platelet Contact and Spreading

    PubMed Central

    Lee, Dooyoung; Fong, Karen P.; King, Michael R.; Brass, Lawrence F.; Hammer, Daniel A.

    2012-01-01

    Platelet spreading is critical for hemostatic plug formation and thrombosis. However, the detailed dynamics of platelet spreading as a function of receptor-ligand adhesive interactions has not been thoroughly investigated. Using reflection interference contrast microscopy, we found that both adhesive interactions and PAR4 activation affect the dynamics of platelet membrane contact formation during spreading. The initial growth of close contact area during spreading was controlled by the combination of different immobilized ligands or PAR4 activation on fibrinogen, whereas the growth of the total area of spreading was independent of adhesion type and PAR4 signaling. We found that filopodia extend to their maximal length and then contract over time; and that filopodial protrusion and expansion were affected by PAR4 signaling. Upon PAR4 activation, the integrin αIIbβ3 mediated close contact to fibrinogen substrata and led to the formation of ringlike patterns in the platelet contact zone. A systematic study of platelet spreading of GPVI-, α2-, or β3-deficient platelets on collagen or fibrinogen suggests the integrin α2 is indispensable for spreading on collagen. The platelet collagen receptors GPVI and α2 regulate integrin αIIbβ3-mediated platelet spreading on fibrinogen. This work elucidates quantitatively how receptor-ligand adhesion and biochemical signals synergistically control platelet spreading. PMID:22325269

  14. Algebraic and geometric spread in finite frames

    NASA Astrophysics Data System (ADS)

    King, Emily J.

    2015-08-01

    When searching for finite unit norm tight frames (FUNTFs) of M vectors in FN which yield robust representations, one is concerned with finding frames consisting of frame vectors which are in some sense as spread apart as possible. Algebraic spread and geometric spread are the two most commonly used measures of spread. A frame with optimal algebraic spread is called full spark and is such that any subcollection of N frame vectors is a basis for FN. A Grassmannian frame is a FUNTF which satisfies the Grassmannian packing problem; that is, the frame vectors are optimally geometrically spread given fixed M and N. A particular example of a Grassmannian frame is an equiangular frame, which is such that the absolute value of all inner products of distinct vectors is equal. The relationship between these two types of optimal spread is complicated. The folk knowledge for many years was that equiangular frames were full spark; however, this is now known not to hold for an infinite class of equiangular frames. The exact relationship between these types of spread will be further explored in this talk, as well as Plücker coordinates and coherence, which are measures of how much a frame misses being optimally algebraically or geometrically spread.

  15. The transcellular spread of cytosolic amyloids, prions, and prionoids.

    PubMed

    Aguzzi, Adriano; Rajendran, Lawrence

    2009-12-24

    Recent reports indicate that a growing number of intracellular proteins are not only prone to pathological aggregation but can also be released and "infect" neighboring cells. Therefore, many complex diseases may obey a simple model of propagation where the penetration of seeds into hosts determines spatial spread and disease progression. We term these proteins prionoids, as they appear to infect their neighbors just like prions--but how can bulky protein aggregates be released from cells and how do they access other cells? The widespread existence of such prionoids raises unexpected issues that question our understanding of basic cell biology.

  16. Spot Radiative Ignition and Subsequent Three Dimensional Flame Spread Over Thin Cellulose Fuels

    NASA Technical Reports Server (NTRS)

    Olson, Sandra L.; Kashiwagi, T.; Kikuchi, M.; Fujita, O.; Ito, K.

    1999-01-01

    Spontaneous radiative ignition and transition to flame spread over thin cellulose fuel samples was studied aboard the USMP-3 STS-75 Space Shuttle mission, and in three test series in the 10 second Japan Microgravity Center (JAMIC). A focused beam from a tungsten/halogen lamp was used to ignite the center of the fuel sample while an external air flow was varied from 0 to 10 cm/s. Non-piloted radiative ignition of the paper was found to occur more easily in microgravity than in normal gravity. Ignition of the sample was achieved under all conditions studied (shuttle cabin air, 21%-50% O2 in JAMIC), with transition to flame spread occurring for all but the lowest oxygen and flow conditions. While radiative ignition in a quiescent atmosphere was achieved, the flame quickly extinguished in air. The ignition delay time was proportional to the gas-phase mixing time, which is estimated using the inverse flow rate. The ignition delay was a much stronger function of flow at lower oxygen concentrations. After ignition, the flame initially spread only upstream, in a fan-shaped pattern. The fan angle increased with increasing external flow and oxygen concentration from zero angle (tunneling flame spread) at the limiting 0.5 cm/s external air flow, to 90 degrees (semicircular flame spread) for external flows at and above 5 cm/s, and higher oxygen concentrations. The fan angle was shown to be directly related to the limiting air flow velocity. Despite the convective heating from the upstream flame, the downstream flame was inhibited due to the 'oxygen shadow' of the upstream flame for the air flow conditions studied. Downstream flame spread rates in air, measured after upstream flame spread was complete and extinguished, were slower than upstream flame spread rates at the same flow. The quench regime for the transition to flame spread was skewed toward the downstream, due to the augmenting role of diffusion for opposed flow flame spread, versus the canceling effect of diffusion

  17. Computational Study of Ventilation and Disease Spread in Poultry Houses

    NASA Astrophysics Data System (ADS)

    Cimbala, John; Pawar, Sourabh; Wheeler, Eileen; Lindberg, Darla

    2006-11-01

    The air flow in and around poultry houses has been studied numerically with the goal of determining disease spread characteristics and comparing ventilation schemes. A typical manure-belt layer egg production facility is considered. The continuity, momentum, and energy equations are solved for flow both inside and outside poultry houses using the commercial computational fluid dynamics (CFD) code FLUENT. Both simplified two-dimensional and fully three-dimensional geometries are modeled. The spread of virus particles is considered to be analogous to diffusion of a tracer contaminant gas, in this case ammonia. The effect of thermal plumes produced by the hens in the poultry house is also considered. Two ventilation schemes with opposite flow directions are compared. Contours of temperature and ammonia mass fraction for both cases are obtained and compared. The analysis shows that ventilation and air quality characteristics are much better for the case in which the air flow is from bottom to top (enhancing the thermal plume) instead of from top to bottom (fighting the thermal plume) as in most poultry houses. This has implications in air quality control in the event of epidemic outbreaks of avian flu or other infectious diseases.

  18. Cortical spreading depolarization increases adult neurogenesis, and alters behavior and hippocampus-dependent memory in mice.

    PubMed

    Urbach, Anja; Baum, Eileen; Braun, Falko; Witte, Otto W

    2017-05-01

    Cortical spreading depolarizations are an epiphenomenon of human brain pathologies and associated with extensive but transient changes in ion homeostasis, metabolism, and blood flow. Previously, we have shown that cortical spreading depolarization have long-lasting consequences on the brains transcriptome and structure. In particular, we found that cortical spreading depolarization stimulate hippocampal cell proliferation resulting in a sustained increase in adult neurogenesis. Since the hippocampus is responsible for explicit memory and adult-born dentate granule neurons contribute to this function, cortical spreading depolarization might influence hippocampus-dependent cognition. To address this question, we induced cortical spreading depolarization in C57Bl/6 J mice by epidural application of 1.5 mol/L KCl and evaluated neurogenesis and behavior at two, four, or six weeks thereafter. Congruent with our previous findings in rats, we found that cortical spreading depolarization increases numbers of newborn dentate granule neurons. Moreover, exploratory behavior and object location memory were consistently enhanced. Reference memory in the water maze was virtually unaffected, whereas memory formation in the Barnes maze was impaired with a delay of two weeks and facilitated after four weeks. These data show that cortical spreading depolarization produces lasting changes in psychomotor behavior and complex, delay- and task-dependent changes in spatial memory, and suggest that cortical spreading depolarization-like events affect the emotional and cognitive outcomes of associated brain pathologies.

  19. Applying spatial thinking in social science research

    PubMed Central

    Logan, John R.; Zhang, Weiwei; Xu, Hongwei

    2010-01-01

    Spatial methods that build upon Geographic Information Systems are spreading quickly across the social sciences. This essay points out that the appropriate use of spatial tools requires more careful thinking about spatial concepts. As easy as it is now to measure distance, it is increasingly important to understand what we think it represents. To interpret spatial patterns, we need spatial theories. We review here a number of key concepts as well as some of the methodological approaches that are now at the disposal of researchers, and illustrate them with studies that reflect the very wide range of problems that use these tools. PMID:20431703

  20. Nonparaxial fields with maximum joint spatial-directional localization. I. Scalar case.

    PubMed

    Alonso, Miguel A; Borghi, Riccardo; Santarsiero, Massimo

    2006-03-01

    In paraxial optics, the spatial and angular localization of a beam are usually characterized through second moments in intensity. For these measures, Gaussian beams have the property of achieving a minimum angular spread for a given spatial spread (or beam waist). For wide-angle fields, however, the standard measures of spatial and angular localization become inappropriate, and new definitions must be used. Previously proposed definitions [J. Opt. Soc. Am. A 17, 2391 (2000)] are adopted, and the scalar monochromatic wave fields that achieve a minimum angular spread for a given spatial spread are found.

  1. Epidemic spreading through direct and indirect interactions

    NASA Astrophysics Data System (ADS)

    Ganguly, Niloy; Krueger, Tyll; Mukherjee, Animesh; Saha, Sudipta

    2014-09-01

    In this paper we study the susceptible-infected-susceptible epidemic dynamics, considering a specialized setting where popular places (termed passive entities) are visited by agents (termed active entities). We consider two types of spreading dynamics: direct spreading, where the active entities infect each other while visiting the passive entities, and indirect spreading, where the passive entities act as carriers and the infection is spread via them. We investigate in particular the effect of selection strategy, i.e., the way passive entities are chosen, in the spread of epidemics. We introduce a mathematical framework to study the effect of an arbitrary selection strategy and derive formulas for prevalence, extinction probabilities, and epidemic thresholds for both indirect and direct spreading. We also obtain a very simple relationship between the extinction probability and the prevalence. We pay special attention to preferential selection and derive exact formulas. The analysis reveals that an increase in the diversity in the selection process lowers the epidemic thresholds. Comparing the direct and indirect spreading, we identify regions in the parameter space where the prevalence of the indirect spreading is higher than the direct one.

  2. Tectonics and magmatism of ultraslow spreading ridges

    NASA Astrophysics Data System (ADS)

    Dubinin, E. P.; Kokhan, A. V.; Sushchevskaya, N. M.

    2013-05-01

    The tectonics, structure-forming processes, and magmatism in rift zones of ultraslow spreading ridges are exemplified in the Reykjanes, Kolbeinsey, Mohns, Knipovich, Gakkel, and Southwest Indian ridges. The thermal state of the mantle, the thickness of the brittle lithospheric layer, and spreading obliquety are the most important factors that control the structural pattern of rift zones. For the Reykjanes and Kolbeinsey ridges, the following are crucial factors: variations in the crust thickness; relationships between the thicknesses of its brittle and ductile layers; width of the rift zone; increase in intensity of magma supply approaching the Iceland thermal anomaly; and spreading obliquety. For the Knipovich Ridge, these are its localization in the transitional zone between the Gakkel and Mohns ridges under conditions of shear and tensile stresses and multiple rearrangements of spreading; nonorthogonal spreading; and structural and compositional barrier of thick continental lithosphere at the Barents Sea shelf and Spitsbergen. The Mohns Ridge is characterized by oblique spreading under conditions of a thick cold lithosphere and narrow stable rift zone. The Gakkel and the Southwest Indian ridges are distinguished by the lowest spreading rate under the settings of the along-strike variations in heating of the mantle and of a variable spreading geometry. The intensity of endogenic structure-forming varies along the strike of the ridges. In addition to the prevalence of tectonic factors in the formation of the topography, magmatism and metamorphism locally play an important role.

  3. Spreading to localized targets in complex networks

    PubMed Central

    Sun, Ye; Ma, Long; Zeng, An; Wang, Wen-Xu

    2016-01-01

    As an important type of dynamics on complex networks, spreading is widely used to model many real processes such as the epidemic contagion and information propagation. One of the most significant research questions in spreading is to rank the spreading ability of nodes in the network. To this end, substantial effort has been made and a variety of effective methods have been proposed. These methods usually define the spreading ability of a node as the number of finally infected nodes given that the spreading is initialized from the node. However, in many real cases such as advertising and news propagation, the spreading only aims to cover a specific group of nodes. Therefore, it is necessary to study the spreading ability of nodes towards localized targets in complex networks. In this paper, we propose a reversed local path algorithm for this problem. Simulation results show that our method outperforms the existing methods in identifying the influential nodes with respect to these localized targets. Moreover, the influential spreaders identified by our method can effectively avoid infecting the non-target nodes in the spreading process. PMID:27966613

  4. Spreading to localized targets in complex networks

    NASA Astrophysics Data System (ADS)

    Sun, Ye; Ma, Long; Zeng, An; Wang, Wen-Xu

    2016-12-01

    As an important type of dynamics on complex networks, spreading is widely used to model many real processes such as the epidemic contagion and information propagation. One of the most significant research questions in spreading is to rank the spreading ability of nodes in the network. To this end, substantial effort has been made and a variety of effective methods have been proposed. These methods usually define the spreading ability of a node as the number of finally infected nodes given that the spreading is initialized from the node. However, in many real cases such as advertising and news propagation, the spreading only aims to cover a specific group of nodes. Therefore, it is necessary to study the spreading ability of nodes towards localized targets in complex networks. In this paper, we propose a reversed local path algorithm for this problem. Simulation results show that our method outperforms the existing methods in identifying the influential nodes with respect to these localized targets. Moreover, the influential spreaders identified by our method can effectively avoid infecting the non-target nodes in the spreading process.

  5. Fire spread characteristics determined in the laboratory

    Treesearch

    Richard C. Rothermel; Hal E. Anderson

    1966-01-01

    Fuel beds of ponderosa pine needles and white pine needles were burned under controlled environmental conditions to determine the effects of fuel moisture and windspeed upon the rate of fire spread. Empirical formulas are presented to show the effect of these parameters. A discussion of rate of spread and some simple experiments show how fuel may be preheated before...

  6. Rapid induction and persistence of paracrine-induced cellular antiviral states arrest viral infection spread in A549 cells

    PubMed Central

    Voigt, Emily A; Swick, Adam; Yin, John

    2016-01-01

    The virus/host interaction is a complex interplay between pro- and anti-viral factors that ultimately determines the spread or halt of virus infections in tissues. This interplay develops over multiple rounds of infection. The purpose of this study was to determine how cellular-level processes combine to impact the spatial spread of infection. We measured the kinetics of virus replication (VSV), antiviral paracrine signal upregulation and secretion, spatial spread of virus and paracrine antiviral signaling, and inhibition of virus production in antiviral-exposed A549 human lung epithelial cells. We found that initially infected cells released antiviral signals 4-to-7 hours following production of virus. However, the subsequent rapid dissemination of signal and fast induction of a robust and persistent antiviral state ultimately led to a suppression of infection spread. This work shows how cellular responses to infection and activation of antiviral responses can integrate to ultimately control infection spread across host cell populations. PMID:27254596

  7. Spatial Databases

    DTIC Science & Technology

    2007-09-19

    for a city . Spatial attributes are used to define the spatial location and extent of spatial objects [35]. The spatial attributes of a spatial object...regarding both geometry and thematic differentiation. It can be used to model 2.5D data (e.g., digital terrain model), as well as 3D data ( walkable ...within a city , if the coverage area of a wireless antenna is considered to be the visible area, then the union of coverage areas of all the antennas in

  8. Contact line arrest in solidifying spreading drops

    NASA Astrophysics Data System (ADS)

    de Ruiter, Riëlle; Colinet, Pierre; Brunet, Philippe; Snoeijer, Jacco H.; Gelderblom, Hanneke

    2017-04-01

    When does a drop, deposited on a cold substrate, stop spreading? Despite the practical relevance of this question, for example, in airplane icing and three-dimensional metal printing, the detailed mechanism of arrest in solidifying spreading drops has remained debated. Here we consider the spreading and arrest of hexadecane drops of constant volume on two smooth wettable substrates: copper with a high thermal conductivity and glass with a low thermal conductivity. We record the spreading radius and contact angle in time for a range of substrate temperatures. The experiments are complemented by a detailed analysis of the temperature field near the rapidly moving contact line, by means of similarity solutions of the thermohydrodynamic problem. Our combined experimental and theoretical results provide strong evidence that the spreading of solidifying drops is arrested when the liquid at the contact line reaches a critical temperature, which is determined by the effect of kinetic undercooling.

  9. Using a spatially explicit analysis model to evaluate spatial variation of corn yield

    USDA-ARS?s Scientific Manuscript database

    Spatial irrigation of agricultural crops using site-specific variable-rate irrigation (VRI) systems is beginning to have wide-spread acceptance. However, optimizing the management of these VRI systems to conserve natural resources and increase profitability requires an understanding of the spatial ...

  10. Warning signals for eruptive events in spreading fires.

    PubMed

    Fox, Jerome M; Whitesides, George M

    2015-02-24

    Spreading fires are noisy (and potentially chaotic) systems in which transitions in dynamics are notoriously difficult to predict. As flames move through spatially heterogeneous environments, sudden shifts in temperature, wind, or topography can generate combustion instabilities, or trigger self-stabilizing feedback loops, that dramatically amplify the intensities and rates with which fires propagate. Such transitions are rarely captured by predictive models of fire behavior and, thus, complicate efforts in fire suppression. This paper describes a simple, remarkably instructive physical model for examining the eruption of small flames into intense, rapidly moving flames stabilized by feedback between wind and fire (i.e., "wind-fire coupling"-a mechanism of feedback particularly relevant to forest fires), and it presents evidence that characteristic patterns in the dynamics of spreading flames indicate when such transitions are likely to occur. In this model system, flames propagate along strips of nitrocellulose with one of two possible modes of propagation: a slow, structured mode, and a fast, unstructured mode sustained by wind-fire coupling. Experimental examination of patterns in dynamics that emerge near bifurcation points suggests that symptoms of critical slowing down (i.e., the slowed recovery of the system from perturbations as it approaches tipping points) warn of impending transitions to the unstructured mode. Findings suggest that slowing responses of spreading flames to sudden changes in environment (e.g., wind, terrain, temperature) may anticipate the onset of intense, feedback-stabilized modes of propagation (e.g., "blowup fires" in forests).

  11. Modelling the spread of American foulbrood in honeybees

    PubMed Central

    Datta, Samik; Bull, James C.; Budge, Giles E.; Keeling, Matt J.

    2013-01-01

    We investigate the spread of American foulbrood (AFB), a disease caused by the bacterium Paenibacillus larvae, that affects bees and can be extremely damaging to beehives. Our dataset comes from an inspection period carried out during an AFB epidemic of honeybee colonies on the island of Jersey during the summer of 2010. The data include the number of hives of honeybees, location and owner of honeybee apiaries across the island. We use a spatial SIR model with an underlying owner network to simulate the epidemic and characterize the epidemic using a Markov chain Monte Carlo (MCMC) scheme to determine model parameters and infection times (including undetected ‘occult’ infections). Likely methods of infection spread can be inferred from the analysis, with both distance- and owner-based transmissions being found to contribute to the spread of AFB. The results of the MCMC are corroborated by simulating the epidemic using a stochastic SIR model, resulting in aggregate levels of infection that are comparable to the data. We use this stochastic SIR model to simulate the impact of different control strategies on controlling the epidemic. It is found that earlier inspections result in smaller epidemics and a higher likelihood of AFB extinction. PMID:24026473

  12. Modelling the spread of American foulbrood in honeybees.

    PubMed

    Datta, Samik; Bull, James C; Budge, Giles E; Keeling, Matt J

    2013-11-06

    We investigate the spread of American foulbrood (AFB), a disease caused by the bacterium Paenibacillus larvae, that affects bees and can be extremely damaging to beehives. Our dataset comes from an inspection period carried out during an AFB epidemic of honeybee colonies on the island of Jersey during the summer of 2010. The data include the number of hives of honeybees, location and owner of honeybee apiaries across the island. We use a spatial SIR model with an underlying owner network to simulate the epidemic and characterize the epidemic using a Markov chain Monte Carlo (MCMC) scheme to determine model parameters and infection times (including undetected 'occult' infections). Likely methods of infection spread can be inferred from the analysis, with both distance- and owner-based transmissions being found to contribute to the spread of AFB. The results of the MCMC are corroborated by simulating the epidemic using a stochastic SIR model, resulting in aggregate levels of infection that are comparable to the data. We use this stochastic SIR model to simulate the impact of different control strategies on controlling the epidemic. It is found that earlier inspections result in smaller epidemics and a higher likelihood of AFB extinction.

  13. Spread F modeling over Brazil

    NASA Astrophysics Data System (ADS)

    Carrasco, A. J.; Batista, I. S.; Sobral, J. H. A.; Abdu, M. A.

    2017-08-01

    Based on a numerical model developed by Carrasco et al. (2014), the dynamics and morphology of ionospheric plasma bubbles for both magnetic hemispheres over Brazil are examined. Observational results show that the post sunset maximum velocity of the pre-reversal vertical drift velocity, VP , has different values at the conjugate points. This information on the asymmetry of the vertical drift or zonal electric field is used in the simulation of bubbles over Brazilian sector. The simulations were conducted considering two different cases: (a) simulation of trans-equatorial bubble neglecting the meridional winds, and (b) considering the effect of meridional winds. In case (a) the bubble development is symmetric in relation to the magnetic equator, while in case (b) we raise the conjecture of a possible asymmetry. The simulation shows that the trans-equatorial bubbles may develop between ±30° of latitude and present internal structures of different sizes and shapes. In addition, three spatial perspectives of the bubbles are displayed, where each perspective reveals interesting aspects of the bubble development.

  14. Irresponsibility clause in air traffic contracts

    NASA Technical Reports Server (NTRS)

    PORQUET

    1922-01-01

    This report examines the question of the responsibility of the carrier in air traffic. The French were concerned about the competitive advantage the English companies enjoyed because of differences in their respective laws.

  15. Measuring landscape-scale spread and persistence of an invaded submerged plant community from airborne remote sensing.

    PubMed

    Santos, Maria J; Khanna, Shruti; Hestir, Erin L; Greenberg, Jonathan A; Ustin, Susan L

    2016-09-01

    Processes of spread and patterns of persistence of invasive species affect species and communities in the new environment. Predicting future rates of spread is of great interest for timely management decisions, but this depends on models that rely on understanding the processes of invasion and historic observations of spread and persistence. Unfortunately, the rates of spread and patterns of persistence are difficult to model or directly observe, especially when multiple rates of spread and diverse persistence patterns may be co-occurring over the geographic distribution of the invaded ecosystem. Remote sensing systematically acquires data over large areas at fine spatial and spectral resolutions over multiple time periods that can be used to quantify spread processes and persistence patterns. We used airborne imaging spectroscopy data acquired once a year for 5 years from 2004 to 2008 to map an invaded submerged aquatic vegetation (SAV) community across 2220 km(2) of waterways in the Sacramento-San Joaquin River Delta, California, USA, and measured its spread rate and its persistence. Submerged aquatic vegetation covered 13-23 km(2) of the waterways (6-11%) every year. Yearly new growth accounted for 40-60% of the SAV area, ~50% of which survived to following year. Spread rates were overall negative and persistence decreased with time. From this dataset, we were able to identify both radial and saltatorial spread of the invaded SAV in the entire extent of the Delta over time. With both decreasing spread rate and persistence, it is possible that over time the invasion of this SAV community could decrease its ecological impact. A landscape-scale approach allows measurements of all invasion fronts and the spatial anisotropies associated with spread processes and persistence patterns, without spatial interpolation, at locations both proximate and distant to the focus of invasion at multiple points in time. © 2016 by the Ecological Society of America.

  16. Local and regional spread of chikungunya fever in the Americas

    PubMed Central

    Cauchemez, S; Ledrans, M; Poletto, C; Quenel, P; De Valk, H; Colizza, V; Boelle, PY

    2015-01-01

    Chikungunya fever (CHIKV), a viral disease transmitted by mosquitoes, is currently affecting several areas in the Caribbean. The vector is found in the Americas from southern Florida to Brazil, and the Caribbean is a highly connected region in terms of population movements. There is therefore a significant risk for the epidemic to quickly expand to a wide area in the Americas. Here, we describe the spread of CHIKV in the first three areas to report cases and between areas in the region. Local transmission of CHIKV in the Caribbean is very effective, the mean number of cases generated by a human case ranging from two to four. There is a strong spatial signature in the regional epidemic, with the risk of transmission between areas estimated to be inversely proportional to the distance rather than driven by air transportation. So far, this simple distance-based model has successfully predicted observed patterns of spread. The spatial structure allows ranking areas according to their risk of invasion. This characterisation may help national and international agencies to optimise resource allocation for monitoring and control and encourage areas with elevated risks to act. PMID:25060573

  17. Turbulence Spreading into Linearly Stable Zone and Transport Scaling

    SciTech Connect

    T.S. Hahm; P.H. Diamond; Z. Lin; K. Itoh; S.-I. Itoh

    2003-10-20

    We study the simplest problem of turbulence spreading corresponding to the spatio-temporal propagation of a patch of turbulence from a region where it is locally excited to a region of weaker excitation, or even local damping. A single model equation for the local turbulence intensity I(x, t) includes the effects of local linear growth and damping, spatially local nonlinear coupling to dissipation and spatial scattering of turbulence energy induced by nonlinear coupling. In the absence of dissipation, the front propagation into the linearly stable zone occurs with the property of rapid progression at small t, followed by slower subdiffusive progression at late times. The turbulence radial spreading into the linearly stable zone reduces the turbulent intensity in the linearly unstable zone, and introduces an additional dependence on the rho* is always equal to rho i/a to the turbulent intensity and the transport scaling. These are in broad, semi-quantitative agreements with a number of global gyrokinetic simulation results with zonal flows and without zonal flows. The front propagation stops when the radial flux of fluctuation energy from the linearly unstable region is balanced by local dissipation in the linearly stable region.

  18. Local and regional spread of chikungunya fever in the Americas.

    PubMed

    Cauchemez, S; Ledrans, M; Poletto, C; Quenel, P; de Valk, H; Colizza, V; Boëlle, P Y

    2014-07-17

    Chikungunya fever (CHIKV), a viral disease transmitted by mosquitoes, is currently affecting several areas in the Caribbean. The vector is found in the Americas from southern Florida to Brazil, and the Caribbean is a highly connected region in terms of population movements. There is therefore a significant risk for the epidemic to quickly expand to a wide area in the Americas. Here, we describe the spread of CHIKV in the first three areas to report cases and between areas in the region. Local transmission of CHIKV in the Caribbean is very effective, the mean number of cases generated by a human case ranging from two to four. There is a strong spatial signature in the regional epidemic, with the risk of transmission between areas estimated to be inversely proportional to the distance rather than driven by air transportation. So far, this simple distance-based model has successfully predicted observed patterns of spread. The spatial structure allows ranking areas according to their risk of invasion. This characterisation may help national and international agencies to optimise resource allocation for monitoring and control and encourage areas with elevated risks to act.

  19. Promoting information spreading by using contact memory

    NASA Astrophysics Data System (ADS)

    Gao, Lei; Wang, Wei; Shu, Panpan; Gao, Hui; Braunstein, Lidia A.

    2017-04-01

    Promoting information spreading is a booming research topic in network science community. However, the existing studies about promoting information spreading seldom took into account the human memory, which plays an important role in the spreading dynamics. In this letter we propose a non-Markovian information spreading model on complex networks, in which every informed node contacts a neighbor by using the memory of neighbor's accumulated contact numbers in the past. We systematically study the information spreading dynamics on uncorrelated configuration networks and a group of 22 real-world networks, and find an effective contact strategy of promoting information spreading, i.e., the informed nodes preferentially contact neighbors with a small number of accumulated contacts. According to the effective contact strategy, the high-degree nodes are more likely to be chosen as the contacted neighbors in the early stage of the spreading, while in the late stage of the dynamics, the nodes with small degrees are preferentially contacted. We also propose a mean-field theory to describe our model, which qualitatively agrees well with the stochastic simulations on both artificial and real-world networks.

  20. Vagus nerve stimulation inhibits cortical spreading depression.

    PubMed

    Chen, Shih-Pin; Ay, Ilknur; de Morais, Andreia Lopes; Qin, Tao; Zheng, Yi; Sadeghian, Homa; Oka, Fumiaki; Simon, Bruce; Eikermann-Haerter, Katharina; Ayata, Cenk

    2016-04-01

    Vagus nerve stimulation has recently been reported to improve symptoms of migraine. Cortical spreading depression is the electrophysiological event underlying migraine aura and is a trigger for headache. We tested whether vagus nerve stimulation inhibits cortical spreading depression to explain its antimigraine effect. Unilateral vagus nerve stimulation was delivered either noninvasively through the skin or directly by electrodes placed around the nerve. Systemic physiology was monitored throughout the study. Both noninvasive transcutaneous and invasive direct vagus nerve stimulations significantly suppressed spreading depression susceptibility in the occipital cortex in rats. The electrical stimulation threshold to evoke a spreading depression was elevated by more than 2-fold, the frequency of spreading depressions during continuous topical 1 M KCl was reduced by ∼40%, and propagation speed of spreading depression was reduced by ∼15%. This effect developed within 30 minutes after vagus nerve stimulation and persisted for more than 3 hours. Noninvasive transcutaneous vagus nerve stimulation was as efficacious as direct invasive vagus nerve stimulation, and the efficacy did not differ between the ipsilateral and contralateral hemispheres. Our findings provide a potential mechanism by which vagus nerve stimulation may be efficacious in migraine and suggest that susceptibility to spreading depression is a suitable platform to optimize its efficacy.

  1. Development of Pistachio (Pistacia vera L.) spread.

    PubMed

    Shakerardekani, Ahmad; Karim, Roselina; Ghazali, Hasanah Mohd; Chin, Nyuk Ling

    2013-03-01

    Pistachio nut (Pistacia vera L.) is one of the most delicious and nutritious nuts in the world. Pistachio spreads were developed using pistachio paste as the main component, icing sugar, soy protein isolate (SPI), and red palm oil (RPO), at different ratios. The highest mean scores of all the sensory attributes were depicted by spreads that were made without addition of SPI. It was found that the work of shear was 0 to 11.0 kg s for an acceptable spread. Sensory spreadability, overall texture, spreadability, and overall acceptability were negatively correlated (R > 0.83) with the work of shear of spreads. The findings indicated that the presence of RPO had a direct effect on the viscoelastic behavior of the pistachio spreads. The a values, which are related to the green color of the pistachio product ranged from 1.7 to 3.9 for spread without addition of RPO, and 4.0 to 5.3 in the presence of RPO. The development of pistachio spread would potentially increase the food uses of pistachio and introduce consumers with a healthier snack food. © 2013 Institute of Food Technologists®

  2. Spatial cognition

    NASA Technical Reports Server (NTRS)

    Kaiser, Mary Kister; Remington, Roger

    1988-01-01

    Spatial cognition is the ability to reason about geometric relationships in the real (or a metaphorical) world based on one or more internal representations of those relationships. The study of spatial cognition is concerned with the representation of spatial knowledge, and our ability to manipulate these representations to solve spatial problems. Spatial cognition is utilized most critically when direct perceptual cues are absent or impoverished. Examples are provided of how human spatial cognitive abilities impact on three areas of space station operator performance: orientation, path planning, and data base management. A videotape provides demonstrations of relevant phenomena (e.g., the importance of orientation for recognition of complex, configural forms). The presentation is represented by abstract and overhead visuals only.

  3. Ionospheric frequency spread and its relationship with range spread in mid-latitude regions

    SciTech Connect

    Bowman, G.G. )

    1991-06-01

    The distinction between range spread and frequency spread as seen on mid-latitude ionograms is discussed. A classification of these two types of spread F is proposed in terms of different arrangements of the duplicate traces which provide the basic trace structures of mid-latitude spread F ionograms. Experimental results are presented to support the idea that frequency spread results from multiple ray paths (associated with a shallow ripple structure in the isoionic contours) close to the direction of the zenith position, so that each ray path has a range approximately equal to that of its neighbor. Furthermore, a horizontal gradient of maximum electron density is an additional requirement to create frequency spread. Atmospheric conditions (involving ionospheric F{sub 2} region heights and upper atmosphere neutral particle densities) which seem to favor the generation of frequency spread are discussed.

  4. Spreading coefficients of aliphatic hydrocarbons on water

    SciTech Connect

    Takii, Taichi; Mori, Y.H. . Dept. of Mechanical Engineering)

    1993-11-01

    Experiments have been performed to determine the equilibrium spreading coefficients of some aliphatic hydrocarbons (C[sub 6]C[sub 10]) on water. The thickness of a discrete lens of each hydrocarbon sample floating on a stagnant water pool was measured interferometrically and used to calculate the spreading coefficient of the hydrocarbon with the aid of Langmuir's capillarity theory. The dependences of the spreading coefficient, thus observed, on temperature (0--50 C) and on the number of carbon atoms in the hydrocarbon molecule are in qualitative agreement with the predictions based on the Lifshitz theory of van der Waals forces.

  5. More efficient swimming by spreading your fingers

    NASA Astrophysics Data System (ADS)

    van de Water, Willem; van Houwelingen, Josje; Willemsen, Dennis; Breugem, Wim Paul; Westerweel, Jerry; Delfos, Rene; Grift, Ernst Jan

    2016-11-01

    A tantalizing question in free-style swimming is whether the stroke efficiency during the pull phase depends on spreading the fingers. It is a subtle effect-not more than a few percent-but it could make a big difference in a race. We measure the drag of arm models with increasing finger spreading in a wind tunnel and compare forces and moments to the results of immersed boundary simulations. Virtual arms were used in the simulations and their 3D-printed real versions in the experiment. We find an optimal finger spreading, accompanied by a marked increase of coherent vortex shedding. A simple actuator disk model explains this optimum.

  6. Coding for spread spectrum packet radios

    NASA Technical Reports Server (NTRS)

    Omura, J. K.

    1980-01-01

    Packet radios are often expected to operate in a radio communication network environment where there tends to be man made interference signals. To combat such interference, spread spectrum waveforms are being considered for some applications. The use of convolutional coding with Viterbi decoding to further improve the performance of spread spectrum packet radios is examined. At 0.00001 bit error rates, improvements in performance of 4 db to 5 db can easily be achieved with such coding without any change in data rate nor spread spectrum bandwidth. This coding gain is more dramatic in an interference environment.

  7. Pulsations, interpulsations, and sea-floor spreading.

    NASA Technical Reports Server (NTRS)

    Pessagno, E. A., Jr.

    1973-01-01

    It is postulated that worldwide transgressions (pulsations) and regressions (interpulsations) through the course of geologic time are related to the elevation and subsidence of oceanic ridge systems and to sea-floor spreading. Two multiple working hypotheses are advanced to explain major transgressions and regressions and the elevation and subsidence of oceanic ridge systems. One hypothesis interrelates the sea-floor spreading hypothesis to the hypothesis of sub-Mohorovicic serpentinization. The second hypothesis relates the sea-floor spreading hypothesis to a hypothesis involving thermal expansion and contraction.

  8. Forced Flow Flame-Spreading Test (FFFT)

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Forced Flow Flame-Spreading Test was designed to study flame spreading over solid fuels when air is flowing at a low speed in the same direction as the flame spread. Previous research has shown that in low-speed concurrent airflows, some materials are more flammable in microgravity than earth. This image shows a 10-cm flame in microgravity that burns almost entirely blue on both sides of a thin sheet of paper. The glowing thermocouple in the lower half of the flame provides temperature measurements.

  9. Pulsations, interpulsations, and sea-floor spreading.

    NASA Technical Reports Server (NTRS)

    Pessagno, E. A., Jr.

    1973-01-01

    It is postulated that worldwide transgressions (pulsations) and regressions (interpulsations) through the course of geologic time are related to the elevation and subsidence of oceanic ridge systems and to sea-floor spreading. Two multiple working hypotheses are advanced to explain major transgressions and regressions and the elevation and subsidence of oceanic ridge systems. One hypothesis interrelates the sea-floor spreading hypothesis to the hypothesis of sub-Mohorovicic serpentinization. The second hypothesis relates the sea-floor spreading hypothesis to a hypothesis involving thermal expansion and contraction.

  10. Flame Spread Across Liquids: Experimental Results

    NASA Technical Reports Server (NTRS)

    Ross, H. D.; Miller, F. J.

    1999-01-01

    The goal of our research on flame spread across a pool of liquid fuel is the quantitative identification of the mechanisms that control the rate and nature of flame spread when the initial temperature of the liquid pool is below the fuel's flash point temperature. Besides numerous experiments in drop towers and 1 g laboratories, we have flown five microgravity (mu-g) experiments on sounding rockets. As described in earlier papers, the first three flights examined the effect of forced opposed airflow over a 2.5 cm deep x 2 cm wide x 30 cm long pool of 1-butanol in mu-g. It was found that the flame spread is much slower and steadier than in 1 g where flame spread has a pulsating character. It was speculated that the flame spread in mu-g resembled the character of pseudo-uniform spread in 1 g; Ito et al later confirmed this conclusively in 1 g experiments. Much of the mu-g flame is also farther from the surface, dimmer, and with less soot, when compared to the 1 g flame. Three-dimensional liquid-phase flow patterns that control the liquid preheating were discovered in both 1 g and mu-g. Our numerical model, restricted to two dimensions, had predicted faster, pulsating flame spread in mu-g for opposed airflow. In examining the differences in the dimensionality of the model and experiment, it was noted that the experiment allowed gas expansion in the lateral direction (across the width of the pool), for which the model could not account. Such lateral expansion could reduce the expansion in the forward and upward directions. Because only these latter directions could be modeled, it was decided to artificially reduce the gas thermal expansion in the predictions. When this was done, satisfactory agreement could be obtained between the predicted and observed spread rates and the steadiness of the spread in microgravity. In 1 g, however, the predicted flame spread character also changed to pseudo-uniform, which disagreed with our 1 g experiments where the spread is pulsating

  11. Pricing and hedging Asian basket spread options

    NASA Astrophysics Data System (ADS)

    Deelstra, Griselda; Petkovic, Alexandre; Vanmaele, Michèle

    2010-04-01

    Asian options, basket options and spread options have been extensively studied in the literature. However, few papers deal with the problem of pricing general Asian basket spread options. This paper aims to fill this gap. In order to obtain prices and Greeks in a short computation time, we develop approximation formulae based on comonotonicity theory and moment matching methods. We compare their relative performances and explain how to choose the best approximation technique as a function of the Asian basket spread characteristics. We also give explicitly the Greeks for our proposed methods. In the last section we extend our results to options denominated in foreign currency.

  12. Flame Spread Across Liquids: Experimental Results

    NASA Technical Reports Server (NTRS)

    Ross, H. D.; Miller, F. J.

    1999-01-01

    The goal of our research on flame spread across a pool of liquid fuel is the quantitative identification of the mechanisms that control the rate and nature of flame spread when the initial temperature of the liquid pool is below the fuel's flash point temperature. Besides numerous experiments in drop towers and 1 g laboratories, we have flown five microgravity (mu-g) experiments on sounding rockets. As described in earlier papers, the first three flights examined the effect of forced opposed airflow over a 2.5 cm deep x 2 cm wide x 30 cm long pool of 1-butanol in mu-g. It was found that the flame spread is much slower and steadier than in 1 g where flame spread has a pulsating character. It was speculated that the flame spread in mu-g resembled the character of pseudo-uniform spread in 1 g; Ito et al later confirmed this conclusively in 1 g experiments. Much of the mu-g flame is also farther from the surface, dimmer, and with less soot, when compared to the 1 g flame. Three-dimensional liquid-phase flow patterns that control the liquid preheating were discovered in both 1 g and mu-g. Our numerical model, restricted to two dimensions, had predicted faster, pulsating flame spread in mu-g for opposed airflow. In examining the differences in the dimensionality of the model and experiment, it was noted that the experiment allowed gas expansion in the lateral direction (across the width of the pool), for which the model could not account. Such lateral expansion could reduce the expansion in the forward and upward directions. Because only these latter directions could be modeled, it was decided to artificially reduce the gas thermal expansion in the predictions. When this was done, satisfactory agreement could be obtained between the predicted and observed spread rates and the steadiness of the spread in microgravity. In 1 g, however, the predicted flame spread character also changed to pseudo-uniform, which disagreed with our 1 g experiments where the spread is pulsating

  13. Hubble Space Telescope Faint Object Camera calculated point-spread functions.

    PubMed

    Lyon, R G; Dorband, J E; Hollis, J M

    1997-03-10

    A set of observed noisy Hubble Space Telescope Faint Object Camera point-spread functions is used to recover the combined Hubble and Faint Object Camera wave-front error. The low-spatial-frequency wave-front error is parameterized in terms of a set of 32 annular Zernike polynomials. The midlevel and higher spatial frequencies are parameterized in terms of set of 891 polar-Fourier polynomials. The parameterized wave-front error is used to generate accurate calculated point-spread functions, both pre- and post-COSTAR (corrective optics space telescope axial replacement), suitable for image restoration at arbitrary wavelengths. We describe the phase-retrieval-based recovery process and the phase parameterization. Resultant calculated precorrection and postcorrection point-spread functions are shown along with an estimate of both pre- and post-COSTAR spherical aberration.

  14. The spread of excitation in neocortical columns visualized with infrared-darkfield videomicroscopy.

    PubMed

    Dodt, H U; D'Arcangelo, G; Pestel, E; Zieglgänsberger, W

    1996-07-08

    A combination of darkfield techniques and infrared videomicroscopy was used to measure the intrinsic optical signal (IOS) in slices of adult rat neocortex. The IOS, which reflects changes in light transmittance and scattering, provides a means of studying the spread of neuronal excitation and its modulation with high sensitivity and spatial resolution. The column-like IOS elicited by orthodromic stimulation is in accordance with models of neocortical circuitry. Blockade of synaptic transmission by the glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D-2-amino-5-phosphovaleric acid (D-APV) reduced the IOS. The GABAA agonist muscimol and the neuroactive steroid 5 alpha-tetrahydrodeoxy-corticosterone (5 alpha-THDOC) decreased the spread of excitation, whereas the GABAA antagonist bicuculline increased it. The present data suggest that the spatial spread of excitation in different neocortical layers is delimited by GABAergic inhibition mediated by the activation of GABAA receptors.

  15. The surface tension effect on viscous liquid spreading along a superhydrophobic surface

    NASA Astrophysics Data System (ADS)

    Aksenov, A. V.; Sudarikova, A. D.; Chicherin, I. S.

    2017-01-01

    Within the Stokes film approximation, unsteady plane-parallel spreading of a thin layer of a heavy viscous fluid along a horizontal superhydrophobic surface is studied. The forced spreading regimes induced by the mass supply are considered. Plane-parallel flow along the principal direction of the slip tensor of the superhydrophobic surface is studied in case that the corresponding slip tensor component is a power function of the spatial coordinate. An evolution equation for the film thickness is derived taking into account surface tension that is dependent on the spatial coordinate. The group classification problem is solved. Self-similar and invariant solutions are constructed for power and exponent time dependences on mass supply respectively at a special form of the surface tension coefficient. Surface tension is shown to have a significant influence on the character of the liquid spreading.

  16. Mode analysis of spreading of partially coherent beams propagating through atmospheric turbulence.

    PubMed

    Shirai, Tomohiro; Dogariu, Aristide; Wolf, Emil

    2003-06-01

    The spreading of partially coherent beams propagating through atmospheric turbulence is studied by use of the coherent-mode representation of the beams. Specifically, we consider partially coherent Gaussian Schell-model beams entering the atmosphere, and we examine the spreading of each coherent mode, represented by a Hermite-Gaussian function, on propagation. We find that in atmospheric turbulence the relative spreading of higher-order modes is smaller than that of lower-order modes, whereas the relative spreading of all order modes is the same as in free space. This modal behavior successfully explains why under certain circumstances partially coherent beams are less affected by atmospheric turbulence than are fully spatially coherent laser beams.

  17. Comparison of methods for estimating the spread of a non-indigenous species

    Treesearch

    Patrick C. Tobin; Andrew M. Liebhold; E. Anderson Roberts

    2007-01-01

    Aim: To compare different quantitative approaches for estimating rates of spread in the exotic species gypsy moth, Lymantria dispar L., using county-level presence/absence data and spatially extensive trapping grids. Location: USA. Methods: We used county-level presence/absence records of the gypsy moth?s distribution in the USA, which are available beginning in 1900,...

  18. Social Capital and Geography of Learning: Roles in Accelerating the Spread of Integrated Pest Management

    ERIC Educational Resources Information Center

    Palis, Florencia G.; Morin, Stephen; Hossain, Mahabub

    2005-01-01

    This paper aims to show the relevance of spatial proximity and social capital in accelerating the spread of agricultural technologies such as integrated pest management (IPM). The research was done in response to the problem of slow diffusion of agricultural technologies. Both quantitative and qualitative methods were used in investigating the…

  19. Evaluating crown fire rate of spread predictions from physics-based models

    Treesearch

    C. M. Hoffman; J. Ziegler; J. Canfield; R. R. Linn; W. Mell; C. H. Sieg; F. Pimont

    2015-01-01

    Modeling the behavior of crown fires is challenging due to the complex set of coupled processes that drive the characteristics of a spreading wildfire and the large range of spatial and temporal scales over which these processes occur. Detailed physics-based modeling approaches such as FIRETEC and the Wildland Urban Interface Fire Dynamics Simulator (WFDS) simulate...

  20. Comparing fire spread algorithms using equivalence testing and neutral landscape models

    Treesearch

    Brian R. Miranda; Brian R. Sturtevant; Jian Yang; Eric J. Gustafson

    2009-01-01

    We demonstrate a method to evaluate the degree to which a meta-model approximates spatial disturbance processes represented by a more detailed model across a range of landscape conditions, using neutral landscapes and equivalence testing. We illustrate this approach by comparing burn patterns produced by a relatively simple fire spread algorithm with those generated by...

  1. Introduced pathogens follow the invasion front of a spreading alien host

    Treesearch

    Ann E. Hajek; Patrick C. Tobin

    2011-01-01

    When an invasive species first colonizes an area, there is an interval before any host-specific natural enemies arrive at the new location. Population densities of newly invading species are low, and the spatial and temporal interactions between spreading invasive species and specific natural enemies that follow are poorly understood. We measured infection rates of two...

  2. Social Capital and Geography of Learning: Roles in Accelerating the Spread of Integrated Pest Management

    ERIC Educational Resources Information Center

    Palis, Florencia G.; Morin, Stephen; Hossain, Mahabub

    2005-01-01

    This paper aims to show the relevance of spatial proximity and social capital in accelerating the spread of agricultural technologies such as integrated pest management (IPM). The research was done in response to the problem of slow diffusion of agricultural technologies. Both quantitative and qualitative methods were used in investigating the…

  3. ECAP spread of excitation with virtual channels and physical electrodes.

    PubMed

    Hughes, Michelle L; Stille, Lisa J; Baudhuin, Jacquelyn L; Goehring, Jenny L

    2013-12-01

    The primary goal of this study was to evaluate physiological spatial excitation patterns for stimulation of adjacent physical electrodes and intermediate virtual channels. Two experiments were conducted that utilized electrically evoked compound action potential (ECAP) spread-of-excitation (SOE) functions obtained with the traditional forward-masking subtraction method. These two experiments examined spatial excitation patterns for virtual-channel maskers and probes, respectively. In Experiment 1, ECAP SOE patterns were obtained for maskers applied to physical electrodes and virtual channels to determine whether virtual-channel maskers yield SOE patterns similar to those predicted from physical electrodes. In Experiment 2, spatial separation of SOE functions was compared for two adjacent physical probe electrodes and the intermediate virtual channel to determine the extent to which ECAP SOE patterns for virtual-channel probes are spatially separate from those obtained with physical electrodes. Data were obtained for three electrode regions (basal, middle, apical) for 35 ears implanted with Cochlear (N = 16) or Advanced Bionics (N = 19) devices. Results from Experiment 1 showed no significant difference between predicted and measured ECAP amplitudes for Advanced Bionics subjects. Measured ECAP amplitudes for virtual-channel maskers were significantly larger than the predicted amplitudes for Cochlear subjects; however, the difference was <2 μV and thus is likely not clinically significant. Results from Experiment 2 showed that the probe set in the apical region demonstrated the least amount of spatial separation amongst SOE functions, which may be attributed to more uniform nerve survival patterns, closer electrode spacing, and/or the tapered geometry of the cochlea. As expected, adjacent physical probes demonstrated greater spatial separation than for comparisons between each physical probe and the intermediate virtual channel. Finally, the virtual-channel SOE

  4. ECAP Spread of Excitation with Virtual Channels and Physical Electrodes

    PubMed Central

    Hughes, Michelle L.; Stille, Lisa J.; Baudhuin, Jacquelyn L.; Goehring, Jenny L.

    2013-01-01

    The primary goal of this study was to evaluate physiological spatial excitation patterns for stimulation of adjacent physical electrodes and intermediate virtual channels. Two experiments were conducted that utilized electrically evoked compound action potential (ECAP) spread-of-excitation (SOE) functions obtained with the traditional forward-masking subtraction method. These two experiments examined spatial excitation patterns for virtual-channel maskers and probes, respectively. In Experiment 1, ECAP SOE patterns were obtained for maskers applied to physical electrodes and virtual channels to determine whether virtual-channel maskers yield SOE patterns similar to those predicted from physical electrodes. In Experiment 2, spatial separation of SOE functions was compared for two adjacent physical probe electrodes and the intermediate virtual channel to determine the extent to which ECAP SOE patterns for virtual-channel probes are spatially separate from those obtained with physical electrodes. Data were obtained for three electrode regions (basal, middle, apical) for 35 ears implanted with Cochlear (N = 16) or Advanced Bionics (N = 19) devices. Results from Experiment 1 showed no significant difference between predicted and measured ECAP amplitudes for Advanced Bionics subjects. Measured ECAP amplitudes for virtual-channel maskers were significantly larger than the predicted amplitudes for Cochlear subjects; however, the difference was <2 μV and thus is likely not clinically significant. Results from Experiment 2 showed that the probe set in the apical region demonstrated the least amount of spatial separation amongst SOE functions, which may be attributed to more uniform nerve survival patterns, closer electrode spacing, and/or the tapered geometry of the cochlea. As expected, adjacent physical probes demonstrated greater spatial separation than for comparisons between each physical probe and the intermediate virtual channel. Finally, the virtual-channel SOE

  5. Assessing the potential for Bluetongue virus 8 to spread and vaccination strategies in Scotland

    PubMed Central

    Bessell, Paul R.; Searle, Kate R.; Auty, Harriet K.; Handel, Ian G.; Purse, Bethan V.; Bronsvoort, B. Mark de C.

    2016-01-01

    Europe has seen frequent outbreaks of Bluetongue (BT) disease since 2006, including an outbreak of BT virus serotype 8 in central France during 2015 that has continued to spread in Europe during 2016. Thus, assessing the potential for BTv-8 spread and determining the optimal deployment of vaccination is critical for contingency planning. We developed a spatially explicit mathematical model of BTv-8 spread in Scotland and explored the sensitivity of transmission to key disease spread parameters for which detailed empirical data is lacking. With parameters at mean values, there is little spread of BTv-8 in Scotland. However, under a “worst case” but still feasible scenario with parameters at the limits of their ranges and temperatures 1 °C warmer than the mean, we find extensive spread with 203,000 sheep infected given virus introduction to the south of Scotland between mid-May and mid-June. Strategically targeted vaccine interventions can greatly reduce BT spread. Specifically, despite BT having most clinical impact in sheep, we show that vaccination can have the greatest impact on reducing BTv infections in sheep when administered to cattle, which has implications for disease control policy. PMID:27958339

  6. Double random phase spread spectrum spread space technique for secure parallel optical multiplexing with individual encryption key

    NASA Astrophysics Data System (ADS)

    Hennelly, B. M.; Javidi, B.; Sheridan, J. T.

    2005-09-01

    A number of methods have been recently proposed in the literature for the encryption of 2-D information using linear optical systems. In particular the double random phase encoding system has received widespread attention. This system uses two Random Phase Keys (RPK) positioned in the input spatial domain and the spatial frequency domain and if these random phases are described by statistically independent white noises then the encrypted image can be shown to be a white noise. Decryption only requires knowledge of the RPK in the frequency domain. The RPK may be implemented using a Spatial Light Modulators (SLM). In this paper we propose and investigate the use of SLMs for secure optical multiplexing. We show that in this case it is possible to encrypt multiple images in parallel and multiplex them for transmission or storage. The signal energy is effectively spread in the spatial frequency domain. As expected the number of images that can be multiplexed together and recovered without loss is proportional to the ratio of the input image and the SLM resolution. Many more images may be multiplexed with some loss in recovery. Furthermore each individual encryption is more robust than traditional double random phase encoding since decryption requires knowledge of both RPK and a lowpass filter in order to despread the spectrum and decrypt the image. Numerical simulations are presented and discussed.

  7. Reactive spreading: Adsorption, ridging and compound formation

    SciTech Connect

    Saiz, E.; Cannon, R.M.; Tomsia, A.P.

    2000-09-11

    Reactive spreading, in which a chemically active element is added to promote wetting of noble metals on nonmetallic materials, is evaluated. Theories for the energetics and kinetics of the necessary steps involved in spreading are outlined and compared to the steps in compound formation that typically accompany reactive wetting. These include: fluid flow, active metal adsorption, including nonequilibrium effects, and triple line ridging. All of these can be faster than compound nucleation under certain conditions. Analysis and assessment of recently reported experiments on metal/ceramic systems lead to a focus on those conditions under which spreading proceeds ahead of the actual formation of a new phase at the interface. This scenario may be more typical than believed, and perhaps the most effective situation leading to enhanced spreading. A rationale for the pervasive variability and hysteresis observed during high temperature wetting also emerges.

  8. Flu Cases Starting to Spread: CDC

    MedlinePlus

    ... fullstory_163159.html Flu Cases Starting to Spread: CDC Illness now being reported in middle sections of ... potential benefit from the vaccine," Lynnette Brammer, a CDC epidemiologist, said Friday. She said flu activity is " ...

  9. Information spreading and development of cultural centers

    NASA Astrophysics Data System (ADS)

    Dybiec, Bartłomiej; Mitarai, Namiko; Sneppen, Kim

    2012-05-01

    The historical interplay between societies is governed by many factors, including in particular the spreading of languages, religion, and other symbolic traits. Cultural development, in turn, is coupled to the emergence and maintenance of information spreading. Strong centralized cultures exist due to attention from their members, whose faithfulness in turn relies on the supply of information. Here we discuss a culture evolution model on a planar geometry that takes into account aspects of the feedback between information spreading and its maintenance. Features of the model are highlighted by comparing it to cultural spreading in ancient and medieval Europe, where it suggests in particular that long-lived centers should be located in geographically remote regions.

  10. Contact line arrest in solidifying spreading drops

    NASA Astrophysics Data System (ADS)

    de Ruiter, Rielle; Colinet, Pierre; Snoeijer, Jacco; Gelderblom, Hanneke

    2016-11-01

    When does a drop, deposited on a cold substrate, stop spreading? Despite the practical relevance of this question, for example in airplane icing and 3D metal printing, the exact mechanism of arrest in solidifying spreading drops has not yet been unraveled. Here, we consider the spreading and arrest of hexadecane drops of constant volume on two smooth wettable substrates; copper with a high thermal conductivity and glass with a low thermal conductivity. We record the spreading radius and contact angle in time for a range of substrate temperatures. We show that our measurements on both copper and glass are well explained by a contact line arrest condition based on crystallization kinetics, which takes into account the effect of kinetic undercooling and the thermal conductivity of the substrate.

  11. Zika Probably Not Spread Through Saliva: Study

    MedlinePlus

    ... page: https://medlineplus.gov/news/fullstory_167531.html Zika Probably Not Spread Through Saliva: Study Research with ... HealthDay News) -- Scientists have some interesting news about Zika: You're unlikely to get the virus from ...

  12. Spreading of oil spilled under ice

    SciTech Connect

    Yapa, P.D.; Chowdhury, T. )

    1990-12-01

    A new set of equations is presented to describe the process of oil spreading under ice in clam waters. These equations consider the gravity (buoyancy)-inertia phase, the gravity (buoyancy)-viscous phase, and the termination of spreading during the buoyancy-surface-tension phase. The derivation considers both the constant discharge mode and the constant volume mode. Therefore, a complete description of the spreading phenomena from the time of initial spill to the termination of spreading is presented. Laboratory experiments were conducted using both real ice covers in a cold room and artificial ice covers. The experiments included different ice-cover roughnesses from smooth to rough, oils of different viscosities, and a variety of discharge conditions. The experimental data show close agreement with the theory. These equations can be used during cleanup or environmental impact assessment to estimate the area of an oil slick with respect to time.

  13. Compressible spreading rates of supersonic coaxial jets

    NASA Technical Reports Server (NTRS)

    Schadow, K. C.; Gutmark, E.; Wilson, K. J.

    1990-01-01

    The compressible spreading rates of two supersonic coaxial jets were studied experimentally. The center jet had a fully expanded Mach number of 3 and the outer jet of M = 1.8. The geometries of the center jet were circular and rectangular with two configurations, both with a 3:1 aspect ratio. The convective Mach numbers Mc were varied in the range between 0.25 and 2.25. The spreading rate of the center circular jet decreased with increasing Mc until it reached a constant value of 0.2 to 0.3 of the incompresible spreading rate for Mc larger than 1.4. The rectangular jets exhibited a similar drop at the same range of Mc, but their spreading rate was higher relative to the circular jet over the entire Mc range.

  14. Liquid spreading along a nanostructured superhydrophilic microlane

    NASA Astrophysics Data System (ADS)

    Kim, Seungho; Kim, Ho-Young

    2016-11-01

    Deposition of functional liquids on solid surfaces is an important step in electronic circuit printing and fabrication of some biochips. Here we show that a liquid drop that gently touches a nanostructured superhydrophilic microlane surrounded by hydrophobic background spreads along the pre-defined pattern, allowing for a facile venue to liquid patterning. We find that different regimes of spreading dynamics occur depending on the lane width and the driving force at the liquid source. For a hydrophilic lane narrower than a critical width, the hemiwicking flow driven by capillarity but resisted by viscosity follows the Washburn law. For relatively wider lanes, on the other hand, the spreading rate is a sensitive function of the hydrostatic pressure at the liquid source, so that different power laws for spreading distance with time are observed. We rationalize the observed power laws with scaling analysis considering the effects of liquid bulk invading the hydrophilic lane.

  15. Liquefaction-Induced Lateral Spread Displacement

    DTIC Science & Technology

    1993-06-01

    DISPLACEMENT Abstract Lateral ground displacements generated by liquefaction-induced lateral spread are a severe threat to the Navy’s shore facilities. During...past earthquakes, lateral spread displace - ments have pulled apart or sheared shallow and deep foundations of buildings, several pipelines and other...structures and utilities that transect the ground displacement zone. buckle bridges or other structures constructed across the toe, and toppled

  16. 21 CFR 102.23 - Peanut spreads.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 2 2014-04-01 2014-04-01 false Peanut spreads. 102.23 Section 102.23 Food and... § 102.23 Peanut spreads. (a) The common or usual name of a spreadable peanut product that does not..., shall consist of the term “peanut spread” and a statement of the percentage by weight of peanuts in...

  17. [Global warming and spread of infectious diseases].

    PubMed

    Ebert, B; Fleischer, B

    2005-01-01

    At the end of the twentieth century, tropical infectious diseases increased despite earlier successes of eradication campaigns. As a global warming of 1.4-5.8 degrees C is anticipated to occur by 2100, mainly the vector-borne tropical diseases that are particularly sensitive to climate are expected to spread. Although biological reasons seemingly support this hypothesis, ecological and socioeconomic factors have in the past proven to be stronger driving forces for the spread of infectious disease than climate.

  18. Frequency Spreading in Underwater Acoustic Signal Transmission.

    DTIC Science & Technology

    1980-04-15

    acoustic signal transmitted and received underwater J-2 J.2 Signal spectrum computing block diagram. J-3 Chapter I. Frequency spreading 1.0 Introduction... transmitted frequency can be expected in the received signal [1] - [18]. This frequency spreading behavior is the result of the amplitude and phase...result of phase modulation of the transmitted sinusoid by the moving surface, and the separation between the spectral lines at the receiving point is

  19. Spatial Displays and Spatial Instruments

    NASA Technical Reports Server (NTRS)

    Ellis, Stephen R. (Editor); Kaiser, Mary K. (Editor); Grunwald, Arthur J. (Editor)

    1989-01-01

    The conference proceedings topics are divided into two main areas: (1) issues of spatial and picture perception raised by graphical electronic displays of spatial information; and (2) design questions raised by the practical experience of designers actually defining new spatial instruments for use in new aircraft and spacecraft. Each topic is considered from both a theoretical and an applied direction. Emphasis is placed on discussion of phenomena and determination of design principles.

  20. Cytoskeleton mediated spreading dynamics of immune cells

    NASA Astrophysics Data System (ADS)

    Hui, King-Lam; Wayt, Jessica; Grooman, Brian; Upadhyaya, Arpita

    2009-03-01

    We have studied the spreading of Jurkat T-cells on anti-CD3 antibody-coated substrates as a model of immune synapse formation. Cell adhesion area versus time was measured via interference reflection contrast microscopy. We found that the spread area exhibited a sigmoidal growth as a function of time in contrast to the previously proposed universal power-law growth for spreading cells. We used high-resolution total internal reflection fluorescence microscopy of these cells transfected with GFP-actin to study cytoskeletal dynamics during the spreading process. Actin filaments spontaneously organized into a variety of structures including traveling waves, target patterns, and mobile clusters emanating from an organizing center. We quantify these dynamic structures and relate them to the spreading rates. We propose that the spreading kinetics are determined by active rearrangements of the cytoskeleton initiated by signaling events upon antibody binding by T-cell receptors. Membrane deformations induced by such wavelike organization of the cytoskeleton may be a general phenomenon that underlies cell movement and cell-substrate interactions.

  1. Time reversal communication over doubly spread channels.

    PubMed

    Zeng, Wen-Jun; Jiang, Xue

    2012-11-01

    Conventional time reversal can mitigate multipath delay dispersion by temporal focusing. But it is not applicable to time-varying channels with a Doppler spread. Although recently time reversal communication has been adapted to time-variant channels, the modified technique requires frequent channel updates to track channel variations and cannot handle large Doppler spread, which means that it cannot achieve frequency focusing. In this paper, two time reversal receivers for underwater acoustic communications over doubly spread channels are proposed. The proposed approach, which can be interpreted as time-frequency channel matching, is based on the channel spreading function rather than impulse response adopted by the existing techniques; this leads to much less frequent channel updates. Unlike existing methods that only correct a single Doppler shift, the proposed approach uses a rake-like structure to compensate for multiple Doppler shifts and hence can eliminate severe Doppler spread induced by temporal channel variations. Simulation results verify the effectiveness of the proposed approach, indicating that it can simultaneously counteract delay and Doppler spreads, achieving both temporal and frequency focusing.

  2. Gossip spread in social network Models

    NASA Astrophysics Data System (ADS)

    Johansson, Tobias

    2017-04-01

    Gossip almost inevitably arises in real social networks. In this article we investigate the relationship between the number of friends of a person and limits on how far gossip about that person can spread in the network. How far gossip travels in a network depends on two sets of factors: (a) factors determining gossip transmission from one person to the next and (b) factors determining network topology. For a simple model where gossip is spread among people who know the victim it is known that a standard scale-free network model produces a non-monotonic relationship between number of friends and expected relative spread of gossip, a pattern that is also observed in real networks (Lind et al., 2007). Here, we study gossip spread in two social network models (Toivonen et al., 2006; Vázquez, 2003) by exploring the parameter space of both models and fitting them to a real Facebook data set. Both models can produce the non-monotonic relationship of real networks more accurately than a standard scale-free model while also exhibiting more realistic variability in gossip spread. Of the two models, the one given in Vázquez (2003) best captures both the expected values and variability of gossip spread.

  3. Emergence of blind areas in information spreading.

    PubMed

    Zhang, Zi-Ke; Zhang, Chu-Xu; Han, Xiao-Pu; Liu, Chuang

    2014-01-01

    Recently, contagion-based (disease, information, etc.) spreading on social networks has been extensively studied. In this paper, other than traditional full interaction, we propose a partial interaction based spreading model, considering that the informed individuals would transmit information to only a certain fraction of their neighbors due to the transmission ability in real-world social networks. Simulation results on three representative networks (BA, ER, WS) indicate that the spreading efficiency is highly correlated with the network heterogeneity. In addition, a special phenomenon, namely Information Blind Areas where the network is separated by several information-unreachable clusters, will emerge from the spreading process. Furthermore, we also find that the size distribution of such information blind areas obeys power-law-like distribution, which has very similar exponent with that of site percolation. Detailed analyses show that the critical value is decreasing along with the network heterogeneity for the spreading process, which is complete the contrary to that of random selection. Moreover, the critical value in the latter process is also larger than that of the former for the same network. Those findings might shed some lights in in-depth understanding the effect of network properties on information spreading.

  4. Landscape Connectivity Shapes the Spread Pattern of the Rice Water Weevil: A Case Study from Zhejiang, China

    NASA Astrophysics Data System (ADS)

    Wang, Zhengjun; Wu, Jianguo; Shang, Hanwu; Cheng, Jiaan

    2011-02-01

    The spread of invasive species is a complex ecological process that is affected by both the biology of the species and the spatial structure of a landscape. The rice water weevil ( Lissorhoptrus oryzophilus Kuschel), a notorious crop pest found in many parts of the world, is one of the most devastating invasive species in China, and has caused enormous economic losses and ecological damage. Little is known, however, as to how habitat and landscape features affect the spatial spread of this pest. Thus, the main goal of this study was to investigate the relationship between the observed spread pattern of L. oryzophilus and landscape structural factors in Zhejiang Province, China between 1993 and 2001. We quantified the invasive spread of the weevil in terms of both the proportion of infected area and spread distance each year as well as landscape structure and connectivity of rice paddies with landscape metrics. Our results showed that the spread of L. oryzophilus took place primarily in the southwest-northeast direction along coastal areas at a speed of about 36 km per year. The composition and spatial arrangement of landscape elements were key determinants of this unique spread pattern. In particular, the connectivity of early rice paddies was crucial for the invasive spread while other factors such as meteorological and geographical conditions may also have been relevant. To control the spread of the pest, we propose four management measures: (1) to implement a landscape-level planning scheme of cropping systems to minimize habitat area and connectivity for the pest, (2) to reduce the source populations at a local scale using integrated control methods, (3) to monitor and report invasive spread in a timely manner, and (4) to strengthen the quarantine system. To be most effective, all four management measures need to be implemented together through an integrated, multi-scaled approach.

  5. Landscape connectivity shapes the spread pattern of the rice water weevil: a case study from Zhejiang, China.

    PubMed

    Wang, Zhengjun; Wu, Jianguo; Shang, Hanwu; Cheng, Jiaan

    2011-02-01

    The spread of invasive species is a complex ecological process that is affected by both the biology of the species and the spatial structure of a landscape. The rice water weevil (Lissorhoptrus oryzophilus Kuschel), a notorious crop pest found in many parts of the world, is one of the most devastating invasive species in China, and has caused enormous economic losses and ecological damage. Little is known, however, as to how habitat and landscape features affect the spatial spread of this pest. Thus, the main goal of this study was to investigate the relationship between the observed spread pattern of L. oryzophilus and landscape structural factors in Zhejiang Province, China between 1993 and 2001. We quantified the invasive spread of the weevil in terms of both the proportion of infected area and spread distance each year as well as landscape structure and connectivity of rice paddies with landscape metrics. Our results showed that the spread of L. oryzophilus took place primarily in the southwest-northeast direction along coastal areas at a speed of about 36 km per year. The composition and spatial arrangement of landscape elements were key determinants of this unique spread pattern. In particular, the connectivity of early rice paddies was crucial for the invasive spread while other factors such as meteorological and geographical conditions may also have been relevant. To control the spread of the pest, we propose four management measures: (1) to implement a landscape-level planning scheme of cropping systems to minimize habitat area and connectivity for the pest, (2) to reduce the source populations at a local scale using integrated control methods, (3) to monitor and report invasive spread in a timely manner, and (4) to strengthen the quarantine system. To be most effective, all four management measures need to be implemented together through an integrated, multi-scaled approach.

  6. Electric field induced reversible spreading of droplets into films on lubricant impregnated surfaces

    NASA Astrophysics Data System (ADS)

    Brabcova, Zuzana; McHale, Glen; Wells, Gary G.; Brown, Carl V.; Newton, Michael I.

    2017-03-01

    Electric fields can be used to force a droplet to wet a solid surface using an applied voltage. However, significant hysteresis usually occurs associated with pinning forces at the contact line. Here, we report the forced spreading and subsequent retraction of droplets into liquid films in air on lubricant impregnated surfaces (also known as slippery liquid infused porous surfaces) where the contact line is completely mobile. We first confirm that we achieve a complete removal of hysteresis for the electrowetting of droplets above the saturation voltage. We then show that contact angle hysteresis can be reduced to less than 4° whilst retaining the ability to fully spread a droplet into a liquid film using an interface localized from liquid dielectrophoresis (dielectrowetting). In both cases, we find that the cosine of the contact angle has a quadratic dependence on applied voltage, consistent with previous theoretical expectations. Thus, our work demonstrates that fully reversible spreading encompassing a wide range of partial wetting droplet states and a film state can be achieved in air in a controllable manner with very low levels of hysteresis.

  7. The Effect of Magnetic Field on Positron Range and Spatial Resolution in an Integrated Whole-Body Time-Of-Flight PET/MRI System

    PubMed Central

    Huang, Shih-ying; Savic, Dragana; Yang, Jaewon; Shrestha, Uttam; Seo, Youngho

    2014-01-01

    Simultaneous imaging systems combining positron emission tomography (PET) and magnetic resonance imaging (MRI) have been actively investigated. A PET/MR imaging system (GE Healthcare) comprised of a time-of-flight (TOF) PET system utilizing silicon photomultipliers (SiPMs) and 3-tesla (3T) MRI was recently installed at our institution. The small-ring (60 cm diameter) TOF PET subsystem of this PET/MRI system can generate images with higher spatial resolution compared with conventional PET systems. We have examined theoretically and experimentally the effect of uniform magnetic fields on the spatial resolution for high-energy positron emitters. Positron emitters including 18F, 124I, and 68Ga were simulated in water using the Geant4 Monte Carlo toolkit in the presence of a uniform magnetic field (0, 3, and 7 Tesla). The positron annihilation position was tracked to determine the 3D spatial distribution of the 511-keV gammy ray emission. The full-width at tenth maximum (FWTM) of the positron point spread function (PSF) was determined. Experimentally, 18F and 68Ga line source phantoms in air and water were imaged with an investigational PET/MRI system and a PET/CT system to investigate the effect of magnetic field on the spatial resolution of PET. The full-width half maximum (FWHM) of the line spread function (LSF) from the line source was determined as the system spatial resolution. Simulations and experimental results show that the in-plane spatial resolution was slightly improved at field strength as low as 3 Tesla, especially when resolving signal from high-energy positron emitters in the air-tissue boundary. PMID:27076778

  8. The Effect of Magnetic Field on Positron Range and Spatial Resolution in an Integrated Whole-Body Time-Of-Flight PET/MRI System.

    PubMed

    Huang, Shih-Ying; Savic, Dragana; Yang, Jaewon; Shrestha, Uttam; Seo, Youngho

    2014-11-01

    Simultaneous imaging systems combining positron emission tomography (PET) and magnetic resonance imaging (MRI) have been actively investigated. A PET/MR imaging system (GE Healthcare) comprised of a time-of-flight (TOF) PET system utilizing silicon photomultipliers (SiPMs) and 3-tesla (3T) MRI was recently installed at our institution. The small-ring (60 cm diameter) TOF PET subsystem of this PET/MRI system can generate images with higher spatial resolution compared with conventional PET systems. We have examined theoretically and experimentally the effect of uniform magnetic fields on the spatial resolution for high-energy positron emitters. Positron emitters including (18)F, (124)I, and (68)Ga were simulated in water using the Geant4 Monte Carlo toolkit in the presence of a uniform magnetic field (0, 3, and 7 Tesla). The positron annihilation position was tracked to determine the 3D spatial distribution of the 511-keV gammy ray emission. The full-width at tenth maximum (FWTM) of the positron point spread function (PSF) was determined. Experimentally, (18)F and (68)Ga line source phantoms in air and water were imaged with an investigational PET/MRI system and a PET/CT system to investigate the effect of magnetic field on the spatial resolution of PET. The full-width half maximum (FWHM) of the line spread function (LSF) from the line source was determined as the system spatial resolution. Simulations and experimental results show that the in-plane spatial resolution was slightly improved at field strength as low as 3 Tesla, especially when resolving signal from high-energy positron emitters in the air-tissue boundary.

  9. Spreading of liquid drops over porous substrates.

    PubMed

    Starov, V M; Zhdanov, S A; Kosvintsev, S R; Sobolev, V D; Velarde, M G

    2003-07-01

    The spreading of small liquid drops over thin and thick porous layers (dry or saturated with the same liquid) has been investigated in the case of both complete wetting (silicone oils of different viscosities) and partial wetting (aqueous SDS solutions of different concentrations). Nitrocellulose membranes of different porosity and different average pore size have been used as a model of thin porous layers, glass and metal filters have been used as a model of thick porous substrates. The first problem under investigation has been the spreading of small liquid drops over thin porous layers saturated with the same liquid. An evolution equation describing the drop spreading has been deduced, which showed that both an effective lubrication and the liquid exchange between the drop and the porous substrates are equally important. Spreading of silicone oils over different nitrocellulose microfiltration membranes was carried out. The experimental laws of the radius of spreading on time confirmed the theory predictions. The spreading of small liquid drops over thin dry porous layers has also been investigated from both theoretical and experimental points of view. The drop motion over a dry porous layer appears caused by the interplay of two processes: (a). the spreading of the drop over already saturated parts of the porous layer, which results in a growth of the drop base, and (b). the imbibition of the liquid from the drop into the porous substrate, which results in a shrinkage of the drop base and a growth of the wetted region inside the porous layer. As a result of these two competing processes the radius of the drop base goes through a maximum as time proceeds. A system of two differential equations has been derived to describe the time evolution of the radii of both the drop base and the wetted region inside the porous layer. This system includes two parameters, one accounts for the effective lubrication coefficient of the liquid over the wetted porous substrate, and

  10. Junge relationships in measurement data for cyclic siloxanes in air.

    PubMed

    MacLeod, Matthew; Kierkegaard, Amelie; Genualdi, Susie; Harner, Tom; Scheringer, Martin

    2013-10-01

    In 1974, Junge postulated a relationship between variability of concentrations of gases in air at remote locations and their atmospheric residence time, and this Junge relationship has subsequently been observed empirically for a range of trace gases. Here, we analyze two previously-published datasets of concentrations of cyclic volatile methyl siloxanes (cVMS) in air and find Junge relationships in both. The first dataset is a time series of concentrations of decamethylcyclopentasiloxane (D5) measured between January and June, 2009 at a rural site in southern Sweden that shows a Junge relationship in the temporal variability of the measurements. The second dataset consists of measurements of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and D5 made simultaneously at 12 sites in the Global Atmospheric Passive Sampling (GAPS) network that shows a Junge relationship in the spatial variability of the three cVMS congeners. We use the Junge relationship for the GAPS dataset to estimate atmospheric lifetimes of dodecamethylcyclohexasiloxane (D6), 8:2-fluorotelomer alcohol and trichlorinated biphenyls that are within a factor of 3 of estimates based on degradation rate constants for reaction with hydroxyl radical determined in laboratory studies.

  11. Confounding and exposure measurement error in air pollution epidemiology.

    PubMed

    Sheppard, Lianne; Burnett, Richard T; Szpiro, Adam A; Kim, Sun-Young; Jerrett, Michael; Pope, C Arden; Brunekreef, Bert

    2012-06-01

    Studies in air pollution epidemiology may suffer from some specific forms of confounding and exposure measurement error. This contribution discusses these, mostly in the framework of cohort studies. Evaluation of potential confounding is critical in studies of the health effects of air pollution. The association between long-term exposure to ambient air pollution and mortality has been investigated using cohort studies in which subjects are followed over time with respect to their vital status. In such studies, control for individual-level confounders such as smoking is important, as is control for area-level confounders such as neighborhood socio-economic status. In addition, there may be spatial dependencies in the survival data that need to be addressed. These issues are illustrated using the American Cancer Society Cancer Prevention II cohort. Exposure measurement error is a challenge in epidemiology because inference about health effects can be incorrect when the measured or predicted exposure used in the analysis is different from the underlying true exposure. Air pollution epidemiology rarely if ever uses personal measurements of exposure for reasons of cost and feasibility. Exposure measurement error in air pollution epidemiology comes in various dominant forms, which are different for time-series and cohort studies. The challenges are reviewed and a number of suggested solutions are discussed for both study domains.

  12. A network model for Ebola spreading.

    PubMed

    Rizzo, Alessandro; Pedalino, Biagio; Porfiri, Maurizio

    2016-04-07

    The availability of accurate models for the spreading of infectious diseases has opened a new era in management and containment of epidemics. Models are extensively used to plan for and execute vaccination campaigns, to evaluate the risk of international spreadings and the feasibility of travel bans, and to inform prophylaxis campaigns. Even when no specific therapeutical protocol is available, as for the Ebola Virus Disease (EVD), models of epidemic spreading can provide useful insight to steer interventions in the field and to forecast the trend of the epidemic. Here, we propose a novel mathematical model to describe EVD spreading based on activity driven networks (ADNs). Our approach overcomes the simplifying assumption of homogeneous mixing, which is central to most of the mathematically tractable models of EVD spreading. In our ADN-based model, each individual is not bound to contact every other, and its network of contacts varies in time as a function of an activity potential. Our model contemplates the possibility of non-ideal and time-varying intervention policies, which are critical to accurately describe EVD spreading in afflicted countries. The model is calibrated from field data of the 2014 April-to-December spreading in Liberia. We use the model as a predictive tool, to emulate the dynamics of EVD in Liberia and offer a one-year projection, until December 2015. Our predictions agree with the current vision expressed by professionals in the field, who consider EVD in Liberia at its final stage. The model is also used to perform a what-if analysis to assess the efficacy of timely intervention policies. In particular, we show that an earlier application of the same intervention policy would have greatly reduced the number of EVD cases, the duration of the outbreak, and the infrastructures needed for the implementation of the intervention.

  13. Parallel Impurity Spreading During Massive Gas Injection

    NASA Astrophysics Data System (ADS)

    Izzo, V. A.

    2016-10-01

    Extended-MHD simulations of disruption mitigation in DIII-D demonstrate that both pre-existing islands (locked-modes) and plasma rotation can significantly influence toroidal spreading of impurities following massive gas injection (MGI). Given the importance of successful disruption mitigation in ITER and the large disparity in device parameters, empirical demonstrations of disruption mitigation strategies in present tokamaks are insufficient to inspire unreserved confidence for ITER. Here, MHD simulations elucidate how impurities injected as a localized jet spread toroidally and poloidally. Simulations with large pre-existing islands at the q = 2 surface reveal that the magnetic topology strongly influences the rate of impurity spreading parallel to the field lines. Parallel spreading is largely driven by rapid parallel heat conduction, and is much faster at low order rational surfaces, where a short parallel connection length leads to faster thermal equilibration. Consequently, the presence of large islands, which alter the connection length, can slow impurity transport; but the simulations also show that the appearance of a 4/2 harmonic of the 2/1 mode, which breaks up the large islands, can increase the rate of spreading. This effect is seen both for simulations with spontaneously growing and directly imposed 4/2 modes. Given the prevalence of locked-modes as a cause of disruptions, understanding the effect of large islands is of particular importance. Simulations with and without islands also show that rotation can alter impurity spreading, even reversing the predominant direction of spreading, which is toward the high-field-side in the absence of rotation. Given expected differences in rotation for ITER vs. DIII-D, rotation effects are another important consideration when extrapolating experimental results. Work supported by US DOE under DE-FG02-95ER54309.

  14. Single-bubble sonoluminescence in air-saturated water.

    PubMed

    Krefting, Dagmar; Mettin, Robert; Lauterborn, Werner

    2003-10-24

    Single bubble sonoluminescence (SBSL) is realized in air-saturated water at ambient pressure and room temperature. The behavior is similar to SBSL in degassed water, but with a higher spatial variability of the bubble position. A detailed view on the dynamics of the bubbles shows agreement between calculated shape stability borders but differs slightly in the equilibrium radii predicted by a mass diffusion model. A comparison with results in degassed water is done as well as a time resolved characterization of bubble oscillation, translation, and light emission for synchronous and recycling SBSL. The formation of streamer structures is observed in the same parameter range, when bubble nuclei are present. This may lead to a unified interpretation of SBSL and multibubble sonoluminescence.

  15. Single-Bubble Sonoluminescence in Air-Saturated Water

    NASA Astrophysics Data System (ADS)

    Krefting, Dagmar; Mettin, Robert; Lauterborn, Werner

    2003-10-01

    Single bubble sonoluminescence (SBSL) is realized in air-saturated water at ambient pressure and room temperature. The behavior is similar to SBSL in degassed water, but with a higher spatial variability of the bubble position. A detailed view on the dynamics of the bubbles shows agreement between calculated shape stability borders but differs slightly in the equilibrium radii predicted by a mass diffusion model. A comparison with results in degassed water is done as well as a time resolved characterization of bubble oscillation, translation, and light emission for synchronous and recycling SBSL. The formation of streamer structures is observed in the same parameter range, when bubble nuclei are present. This may lead to a unified interpretation of SBSL and multibubble sonoluminescence.

  16. Beam wandering of femtosecond laser filament in air.

    PubMed

    Yang, Jing; Zeng, Tao; Lin, Lie; Liu, Weiwei

    2015-10-05

    The spatial wandering of a femtosecond laser filament caused by the filament heating effect in air has been studied. An empirical formula has also been derived from the classical Karman turbulence model, which determines quantitatively the displacement of the beam center as a function of the propagation distance and the effective turbulence structure constant. After fitting the experimental data with this formula, the effective turbulence structure constant has been estimated for a single filament generated in laboratory environment. With this result, one may be able to estimate quantitatively the displacement of a filament over long distance propagation and interpret the practical performance of the experiments assisted by femtosecond laser filamentation, such as remote air lasing, pulse compression, high order harmonic generation (HHG), etc.

  17. Meningococcal meningitis in Mali: a long-term study of persistence and spread.

    PubMed

    Philippon, Solenne; Broutin, Hélène; Constantin de Magny, Guillaume; Toure, Kandioura; Diakite, Cheick Hamala; Fourquet, Nicole; Courel, Marie-Françoise; Sultan, Benjamin; Guégan, Jean-François

    2009-01-01

    Meningococcal meningitis (MM) is still a huge threat in the African meningitis belt. To fight against epidemics, a strengthened health information system, based upon weekly collected data, was set up in Mali. We aimed to study the spatio-temporal dynamics of MM in this country between 1992 and 2003. We were first interested in the impact of population size on the disease persistence. We then used cross-correlation analysis to study the spread of the disease on three different spatial scales, i.e., inter-region (global) and inter-district and intra-district (local) levels. We found no persistence of MM at district level in Mali during the whole of the study period. However, we found persistence on a nationwide scale after the 1997 big epidemics, as opposed to the 1992-1996 time periods. In terms of spread, two main regions seem to lead MM dynamics in Mali, even if on a local scale the 'cities-villages' diffusion pattern was not systematically observed. This study improves knowledge on the spread and persistence of MM in Mali in recent years. It constitutes a first spatial study describing persistence and spread of MM in an African meningitis belt country. The next step should be the integration of vaccination and genetic variability data to clarify the route of spread of the disease in the human population.

  18. Free energy analysis of cell spreading.

    PubMed

    McEvoy, Eóin; Deshpande, Vikram S; McGarry, Patrick

    2017-10-01

    In this study we present a steady-state adaptation of the thermodynamically motivated stress fiber (SF) model of Vigliotti et al. (2015). We implement this steady-state formulation in a non-local finite element setting where we also consider global conservation of the total number of cytoskeletal proteins within the cell, global conservation of the number of binding integrins on the cell membrane, and adhesion limiting ligand density on the substrate surface. We present a number of simulations of cell spreading in which we consider a limited subset of the possible deformed spread-states assumed by the cell in order to examine the hypothesis that free energy minimization drives the process of cell spreading. Simulations suggest that cell spreading can be viewed as a competition between (i) decreasing cytoskeletal free energy due to strain induced assembly of cytoskeletal proteins into contractile SFs, and (ii) increasing elastic free energy due to stretching of the mechanically passive components of the cell. The computed minimum free energy spread area is shown to be lower for a cell on a compliant substrate than on a rigid substrate. Furthermore, a low substrate ligand density is found to limit cell spreading. The predicted dependence of cell spread area on substrate stiffness and ligand density is in agreement with the experiments of Engler et al. (2003). We also simulate the experiments of Théry et al. (2006), whereby initially circular cells deform and adhere to "V-shaped" and "Y-shaped" ligand patches. Analysis of a number of different spread states reveals that deformed configurations with the lowest free energy exhibit a SF distribution that corresponds to experimental observations, i.e. a high concentration of highly aligned SFs occurs along free edges, with lower SF concentrations in the interior of the cell. In summary, the results of this study suggest that cell spreading is driven by free energy minimization based on a competition between decreasing

  19. Spreading paths in partially observed social networks

    PubMed Central

    Onnela, Jukka-Pekka; Christakis, Nicholas A.

    2012-01-01

    Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using a static, structurally realistic social network as a platform for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is. PMID:22587148

  20. Spreading of Emulsions on Glass Substrates

    NASA Astrophysics Data System (ADS)

    Mohammad Karim, Alireza; Kavehpour, Pirouz

    2012-11-01

    The wettability of emulsions is an important factor with explicit influence in an extensive variety of industrial applications ranging from the petroleum to food industries. Surprisingly, there is no comprehensive study of emulsion spreading to date; this is due to the complexity of the structure of the emulsions and non-homogeneity of the dispersed phase bubbles in size as well as distribution through the emulsion. The spreading of water/silicone oil emulsions on glass substrates was investigated. The emulsions were prepared with varying volume fractions of water dispersed in silicone oil, with addition of small amounts of surfactant to stabilize the emulsion structure. The time dependent variation of dynamic contact angle, base diameter, and the spreading rate of the droplets of an emulsion are different from a pure substance. The effect of water/silicone oil weight percentage as well as the droplet size and dispersed phase bubble size were also investigated. The weight percentage of water/silicone oil emulsion and droplet size did not have significant influence on the spreading dynamics; however the dispersed phase drop size affected the spreading dynamics substantially.

  1. Rapid epigenetic adaptation to uncontrolled heterochromatin spreading

    PubMed Central

    Wang, Jiyong; Reddy, Bharat D; Jia, Songtao

    2015-01-01

    Heterochromatin, a highly compact chromatin state characterized by histone H3K9 methylation and HP1 protein binding, silences the underlying DNA and influences the expression of neighboring genes. However, the mechanisms that regulate heterochromatin spreading are not well understood. In this study, we show that the conserved Mst2 histone acetyltransferase complex in fission yeast regulates histone turnover at heterochromatin regions to control heterochromatin spreading and prevents ectopic heterochromatin assembly. The combined loss of Mst2 and the JmjC domain protein Epe1 results in uncontrolled heterochromatin spreading and massive ectopic heterochromatin, leading to severe growth defects due to the inactivation of essential genes. Interestingly, these cells quickly recover by accumulating heterochromatin at genes essential for heterochromatin assembly, leading to their reduced expression to restrain heterochromatin spreading. Our studies discover redundant pathways that control heterochromatin spreading and prevent ectopic heterochromatin assembly and reveal a fast epigenetic adaptation response to changes in heterochromatin landscape. DOI: http://dx.doi.org/10.7554/eLife.06179.001 PMID:25774602

  2. Spatiotemporal spread of cucurbit downy mildew in the eastern United States.

    PubMed

    Ojiambo, P S; Holmes, G J

    2011-04-01

    The dynamics of cucurbit downy mildew, caused by Pseudoperonospora cubensis, in the eastern United States in 2008 and 2009 were investigated based on disease records collected in 24 states as part of the Cucurbit downy mildew ipmPIPE monitoring program. The mean season-long rate of temporal disease progress across the 2 years was 1.4 new cases per day. Although cucurbit downy mildew was detected in mid-February and early March in southern Florida, the disease progressed slowly during the spring and early summer and did not enter its exponential phase until mid-June. The median nearest-neighbor distance of spread of new disease cases was ≈110 km in both years, with ≈15% of the distances being >240 km. Considering disease epidemics on all cucurbits, the epidemic expanded at a rate of 9.2 and 10.5 km per day in 2008 and 2009, respectively. These rates of spatial spread are at the lower range of those reported for the annual spread of tobacco blue mold in the southeastern United States, a disease that is also aerially dispersed over long distances. These results suggest that regional spread of cucurbit downy mildew may be limited by opportunities for establishment in the first half of the year, when fewer cucurbit hosts are available for infection. The O-ring statistic was used to determine the spatial pattern of cucurbit downy mildew outbreaks using complete spatial randomness as the null model for hypothesis testing. Disease outbreaks in both years were spatially aggregated and the extent of spatial dependence was up to 1,000 km. Results from the spatial analysis suggests that disease outbreaks in the Great Lakes and mid-Atlantic regions may be due to the spread of P. cubensis sporangia from outbreaks of the disease near the Georgia/South Carolina/North Carolina border rather than from overwintering sites in southern Florida. Space-time point pattern analysis indicated strong (P < 0.001) evidence for a space-time interaction and a space-time risk window of ≈3

  3. Spatial agraphia.

    PubMed

    Ardila, A; Rosselli, M

    1993-07-01

    Twenty-one patients with right hemisphere damage were studied (11 men, 10 women; average age = 41.33; age range 19-65). Subjects were divided into two groups: pre-Rolandic (6) and retro-Rolandic (15) right hemisphere damaged patients. A special writing test was given to each patient. The writing errors observed included literal substitutions, feature omissions and additions, letter omissions and additions, inability to maintain horizontal writing, inappropriate grouping and fragmentation of elements, and changes in handwriting style. Associated disorders included left-hemiparesis, visual field defects, spatial hemi-neglect, constructional apraxia, spatial alexia, and spatial acalculia. It is proposed that spatial agraphia is related to: (1) left hemi-neglect, (2) constructional deficits, (3) general spatial defects, and (4) some motor disautomatization and tendency to perseverate. In cases of right frontal damage, motor-associated deficits (iterations of features and letters) predominated, whereas in cases of posterior right hemisphere damage, spatial defects (inappropriate distribution of written material in the space, grouping of letters belonging to different words, and splitting of words) were more evident. Writing impairments are in general more noticeable in cases of retro-Rolandic damage.

  4. Spreading and vanishing in a West Nile virus model with expanding fronts

    NASA Astrophysics Data System (ADS)

    Tarboush, Abdelrazig K.; Lin, ZhiGui; Zhang, MengYun

    2017-05-01

    In this paper, we study a simplified version of a West Nile virus model discussed by Lewis et al. [28], which was considered as a first approximation for the spatial spread of WNv. The basic reproduction number $R_0$ for the non-spatial epidemic model is defined and a threshold parameter $R_0 ^D$ for the corresponding problem with null Dirichlet boundary condition is introduced. We consider a free boundary problem with coupled system, which describes the diffusion of birds by a PDE and the movement of mosquitoes by a ODE. The risk index $R_0^F (t)$ associated with the disease in spatial setting is represented. Sufficient conditions for the WNv to eradicate or to spread are given. The asymptotic behavior of the solution to system when the spreading occurs are considered. It is shown that the initial number of infected populations, the diffusion rate of birds and the length of initial habitat exhibit important impacts on the vanishing or spreading of the virus. Numerical simulations are presented to illustrate the analytical results.

  5. Degree of host susceptibility in the initial disease outbreak influences subsequent epidemic spread.

    PubMed

    Severns, Paul M; Estep, Laura K; Sackett, Kathryn E; Mundt, Christopher C

    2014-12-01

    Disease epidemics typically begin as an outbreak of a relatively small, spatially explicit population of infected individuals (focus), in which disease prevalence increases and rapidly spreads into the uninfected, at-risk population. Studies of epidemic spread typically address factors influencing disease spread through the at-risk population, but the initial outbreak may strongly influence spread of the subsequent epidemic.We initiated wheat stripe rust Puccinia striiformis f. sp. tritici epidemics to assess the influence of the focus on final disease prevalence when the degree of disease susceptibility differed between the at-risk and focus populations.When the focus/at-risk plantings consisted of partially genetic resistant and susceptible cultivars, final disease prevalence was statistically indistinguishable from epidemics produced by the focus cultivar in monoculture. In these experimental epidemics, disease prevalence was not influenced by the transition into an at-risk population that differed in disease susceptibility. Instead, the focus appeared to exert a dominant influence on the subsequent epidemic.Final disease prevalence was not consistently attributable to either the focus or the at-risk population when focus/at-risk populations were planted in a factorial set-up with a mixture (~28% susceptible and 72% resistant) and susceptible individuals. In these experimental epidemics, spatial heterogeneity in disease susceptibility within the at-risk population appeared to counter the dominant influence of the focus.Cessation of spore production from the focus (through fungicide/glyphosate application) after 1.3 generations of stripe rust spread did not reduce final disease prevalence, indicating that the focus influence on disease spread is established early in the epidemic.Synthesis and applications. Our experiments indicated that outbreak conditions can be highly influential on epidemic spread, even when disease resistance in the at-risk population is

  6. Genetic structure of winter populations of the endangered Indiana bat (Myotis sodalis) prior to the white nose syndrome epidemic: implications for the risk of disease spread

    Treesearch

    Maarten J. Vonhof; Sybill K. Amelon; Robert R. Currie; Gary F. McCracken

    2016-01-01

    The spread of white nose syndrome raises serious concerns about the long-term viability of affected bat species. Here we examine the geographic distribution of genetic variation, levels of population connectivity that may influence the spatial spread of WNS, and the likelihood that recent population declines in regions affected by WNS have led to the loss of unique...

  7. The Crisis in Air Pollution Manpower Development

    ERIC Educational Resources Information Center

    Moeller, Dade W.

    1974-01-01

    Three studies conducted by the National Air Pollution Manpower Development Advisory Committee concluded there is a crisis in air pollution manpower development within the United States today. The studies investigated the existing federal manpower program, air pollution educational requirements and the quality of graduate level university programs.…

  8. The Crisis in Air Pollution Manpower Development

    ERIC Educational Resources Information Center

    Moeller, Dade W.

    1974-01-01

    Three studies conducted by the National Air Pollution Manpower Development Advisory Committee concluded there is a crisis in air pollution manpower development within the United States today. The studies investigated the existing federal manpower program, air pollution educational requirements and the quality of graduate level university programs.…

  9. Diaphragms in air-operated valves

    SciTech Connect

    Groeger, J.E.

    1996-12-01

    The author will present current issues related to diaphgrams in air-operated valves. Altran Materials Engineering, Inc., often performs root-cause analyses for nuclear power plant owners. The author will discuss various analyses that have been performed or are currently underway.

  10. Substrate stress relaxation regulates cell spreading

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Ovijit; Gu, Luo; Darnell, Max; Klumpers, Darinka; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Mooney, David J.

    2015-02-01

    Studies of cellular mechanotransduction have converged upon the idea that cells sense extracellular matrix (ECM) elasticity by gauging resistance to the traction forces they exert on the ECM. However, these studies typically utilize purely elastic materials as substrates, whereas physiological ECMs are viscoelastic, and exhibit stress relaxation, so that cellular traction forces exerted by cells remodel the ECM. Here we investigate the influence of ECM stress relaxation on cell behaviour through computational modelling and cellular experiments. Surprisingly, both our computational model and experiments find that spreading for cells cultured on soft substrates that exhibit stress relaxation is greater than cells spreading on elastic substrates of the same modulus, but similar to that of cells spreading on stiffer elastic substrates. These findings challenge the current view of how cells sense and respond to the ECM.

  11. Spreading dynamics following bursty human activity patterns

    NASA Astrophysics Data System (ADS)

    Min, Byungjoon; Goh, K.-I.; Vazquez, Alexei

    2011-03-01

    We study the susceptible-infected model with power-law waiting time distributions P(τ)~τ-α, as a model of spreading dynamics under heterogeneous human activity patterns. We found that the average number of new infections n(t) at time t decays as a power law in the long-time limit, n(t)~t-β, leading to extremely slow prevalence decay. We also found that the exponent in the spreading dynamics β is related to that in the waiting time distribution α in a way depending on the interactions between agents but insensitive to the network topology. These observations are well supported by both the theoretical predictions and the long prevalence decay time in real social spreading phenomena. Our results unify individual activity patterns with macroscopic collective dynamics at the network level.

  12. Cylindrical spreading due to downwind refraction.

    PubMed

    Makarewicz, Rufin

    2016-04-01

    Downwind propagation is analyzed for a low level jet (LLJ). The LLJ is characterized by a wind speed maximum (at least 10-20 m/s with peak speeds up to 30 m/s) a few hundred meters above the ground. Close to an elevated point source, such as a wind turbine or an aircraft, spherical spreading results in a 6 dB decrease in sound level per doubling of the distance. Wind turbine noise measurements show that at a transition distance, the downwind propagation changes the spherical spreading into a cylindrical spreading with a 3 dB decrease. It is shown how the transition distance and sound intensity depend on the LLJ parameters. The pivotal phenomenon is the non-coherent superposition of ground reflected rays in the turbulent atmosphere.

  13. Relative Capacity and the Spread of Rebellion

    PubMed Central

    2014-01-01

    This article explores how insurgencies emerge and spread within a country over time through an analysis of the Maoist insurgency in Nepal. It argues that important processes underpinning the spread of insurgency are likely to change with shifts in the relative military capacity of belligerents. Importantly, insurgents can to a greater extent spread the insurgency by using coercion, material incentives, and movement of forces when they are militarily strong than when they are weak. This in turn leads to changes in the local conditions favorable to insurgency. I hypothesize that inaccessible terrains, preexisting rebel networks, and proximity to insurgent areas are likely to be important determinants of local insurgency onset during rebel weakness, but should decline in importance as the rebels gain strength. I find support for these arguments in a mixed-methods analysis of Nepal’s insurgency that combines a qualitative narrative and a quantitative event history analysis. PMID:27019519

  14. Instrumented Floret Tests of Detonation Spreading

    NASA Astrophysics Data System (ADS)

    Kennedy, James; Plaksin, Igor; Thomas, Keith; Martin, Eric; Lee, Kien-Yin; Akinci, Adrian; Asay, Blaine; Campos, Jose; Direito, Jose

    2004-07-01

    The floret test was originally devised to permit comparison of detonation-spreading performance of various insensitive explosive materials, using only the dent in a copper witness plate as a metric. Dent depth in the copper plate is directly related to the fraction of a thin acceptor pellet that was detonated by impact of a small explosive-driven flyer plate. We have now added instrumentation to quantitatively measure the detonation corner-turning behavior of IHEs. Results of multi-fiber optical probe measurements are shown for LLM-105 and UF-TATB explosive materials. Results are interpreted and compared with predictions from one reaction-rate model used to describe detonation spreading, and may be advantageous for comparison with other reactive-flow wave-code models. Detonation spreading in UF-TATB occurred with formation of a non-detonating region surrounding a detonating core, and re-establishment of detonation in a "lateral" direction beyond that region.

  15. Extended oil spill spreading with Langmuir circulation.

    PubMed

    Simecek-Beatty, Debra; Lehr, William J

    2017-09-15

    When spilled in the ocean, most crude oils quickly spread into a thin film that ruptures into smaller slicks distributed over a larger area. Observers have also reported the film tearing apart into streaks that eventually merge forming fewer but longer bands of floating oil. Understanding this process is important to model oil spill transport. First, slick area is calculated using a spreading model. Next, Langmuir circulation models are used to approximate the merging of oiled bands. Calculations are performed on Troll blended and Alaska North Slope crude oils and results compared with measurements from the 1990s North Sea field experiments. Langmuir circulation increases the oil area but decreases the surface coverage of oil. This work modifies existing oil spreading formulas by providing a surface area correction due to the effects of Langmuir circulation. The model's simplicity is advantageous in situations with limited data, such as emergency oil spill response. Published by Elsevier Ltd.

  16. Droplet Spreading with Sol-Gel Transition

    NASA Astrophysics Data System (ADS)

    Jalaal, Maziyar; Stoeber, Boris; Balmforth, Neil J.

    2014-11-01

    The impact and spreading of liquid droplets on a smooth solid substrate is a classical subject with several industrial applications such as ink-jet printing, spray cooling, coating, and many others. For many of these deposition processes, controlling the final shape of the drop is critical. In the current research, a new technique for controlling the spreading of droplets impacting a substrate is presented. This technique exploits the rheology of a thermo-responsive polymer solution that undergoes a reversible sol/gel transition above a critical temperature. Experiments are conducted using a combination of shadowgraphy and micro-PIV to observe spreading drops. It is shown that the final diameter of a droplet can be controlled through the temperature of the substrate and the tunable sol/gel transition temperature of the fluid.A mathematical model is provided to further elucidate the flow dynamics.

  17. Disordered contact process with asymmetric spreading.

    PubMed

    Juhász, Róbert

    2013-02-01

    An asymmetric variant of the contact process where the activity spreads with different and independent random rates to the left and to the right is introduced. A real space renormalization scheme is formulated for the model by means of which it is shown that the local asymmetry of spreading is irrelevant on large scales if the model is globally (statistically) symmetric. Otherwise, in the presence of a global bias in either direction, the renormalization method predicts two distinct phase transitions, which are related to the spreading of activity in and against the direction of the bias. The latter is found to be described by an infinite randomness fixed point while the former is not.

  18. The East Pacific Rise: An Active Not Passive Spreading System

    NASA Astrophysics Data System (ADS)

    Rowley, D. B.; Rowan, C. J.; Forte, A. M.; Moucha, R.; Grand, S. P.; Simmons, N. A.

    2011-12-01

    Traditional plate tectonic interpretations of mid-oceanic ridges regard spreading as an entirely passive phenomenon. From this one would assume that the oceanic ridges will move over the mantle in response to the geodynamics of the diverging plates, and do not remain fixed spatially over any protracted period of time. An analysis of the kinematics of ridge motions in the Indo-Atlantic hotspot frame of reference since 83 Ma generally supports this view, with the notable exception of the East Pacific Rise (EPR). The Pacific-Nazca/Farallon segment of the EPR north of Easter Island (27°S) is oriented essentially N-S, and has produced more than 9500km of E-W spreading in the past 80 Ma, making it the dominant ridge in the world's plate system over this interval of time. Yet despite the large amount of E-W divergence, the spreading center has maintained its longitudinal position to within <±250 km of the current ridge axis. Global mantle convective flow modeling indicates that the EPR, unlike any other extensive segment of the mid-oceanic ridge system, is underlain by an active upwelling system extending from the core-mantle boundary to the surface. We suggest that the lack of E-W motion of the EPR apparent from the kinematics is a consequence of these mantle dynamics; this ridge is thus not behaving as a passive plate boundary, but is actively and directly linked to, and controlled by, whole mantle upwelling. This observation overturns the notion that ridges are always entirely passive features of the plate system. Subduction of the northern EPR beneath western North America has thus resulted in the overriding of an active upwelling system that has contributed significantly to the evolution of Basin and Range kinematics and superimposed dynamics, including significant contributions from dynamic topography.

  19. Warning signals for eruptive events in spreading fires

    PubMed Central

    Fox, Jerome M.; Whitesides, George M.

    2015-01-01

    Spreading fires are noisy (and potentially chaotic) systems in which transitions in dynamics are notoriously difficult to predict. As flames move through spatially heterogeneous environments, sudden shifts in temperature, wind, or topography can generate combustion instabilities, or trigger self-stabilizing feedback loops, that dramatically amplify the intensities and rates with which fires propagate. Such transitions are rarely captured by predictive models of fire behavior and, thus, complicate efforts in fire suppression. This paper describes a simple, remarkably instructive physical model for examining the eruption of small flames into intense, rapidly moving flames stabilized by feedback between wind and fire (i.e., “wind–fire coupling”—a mechanism of feedback particularly relevant to forest fires), and it presents evidence that characteristic patterns in the dynamics of spreading flames indicate when such transitions are likely to occur. In this model system, flames propagate along strips of nitrocellulose with one of two possible modes of propagation: a slow, structured mode, and a fast, unstructured mode sustained by wind–fire coupling. Experimental examination of patterns in dynamics that emerge near bifurcation points suggests that symptoms of critical slowing down (i.e., the slowed recovery of the system from perturbations as it approaches tipping points) warn of impending transitions to the unstructured mode. Findings suggest that slowing responses of spreading flames to sudden changes in environment (e.g., wind, terrain, temperature) may anticipate the onset of intense, feedback-stabilized modes of propagation (e.g., “blowup fires” in forests). PMID:25675491

  20. Warning signals for eruptive events in spreading fires

    DOE PAGES

    Fox, Jerome M.; Whitesides, George M.

    2015-02-09

    Spreading fires are noisy (and potentially chaotic) systems in which transitions in dynamics are notoriously difficult to predict. As flames move through spatially heterogeneous environments, sudden shifts in temperature, wind, or topography can generate combustion instabilities, or trigger self-stabilizing feedback loops, that dramatically amplify the intensities and rates with which fires propagate. Such transitions are rarely captured by predictive models of fire behavior and, thus, complicate efforts in fire suppression. This study describes a simple, remarkably instructive physical model for examining the eruption of small flames into intense, rapidly moving flames stabilized by feedback between wind and fire (i.e., “wind–firemore » coupling”—a mechanism of feedback particularly relevant to forest fires), and it presents evidence that characteristic patterns in the dynamics of spreading flames indicate when such transitions are likely to occur. Here, in this model system, flames propagate along strips of nitrocellulose with one of two possible modes of propagation: a slow, structured mode, and a fast, unstructured mode sustained by wind–fire coupling. Experimental examination of patterns in dynamics that emerge near bifurcation points suggests that symptoms of critical slowing down (i.e., the slowed recovery of the system from perturbations as it approaches tipping points) warn of impending transitions to the unstructured mode. Lastly, findings suggest that slowing responses of spreading flames to sudden changes in environment (e.g., wind, terrain, temperature) may anticipate the onset of intense, feedback-stabilized modes of propagation (e.g., “blowup fires” in forests).« less

  1. On the discontinuous Galerkin method for numerical pricing of basket spread options with the average strike

    NASA Astrophysics Data System (ADS)

    Hozman, J.; Tichý, T.

    2017-07-01

    The paper is based on the results from our recent research on path-dependent multi-asset options. Here we focus on options, payoff of which depends on the difference of the spread of two underlying assets at expiry and their average spread during the life of the option. The main idea uses a concept of the dimensional reduction to the PDE model with only two spatial variables describing this option pricing problem. Then the numerical option pricing scheme arising from the discontinuous Galerkin method is developed. Finally, a simple numerical result is presented on real market data.

  2. Universal function for the brilliance of undulator radiation considering the energy spread effect.

    PubMed

    Tanaka, Takashi; Kitamura, Hideo

    2009-05-01

    Angular and spatial profiles of undulator radiation have been investigated to derive a universal function that evaluates the brilliance of undulator radiation and takes into account the effects of electron beam emittance and energy spread. It has been found that the effects of energy spread on the angular divergence and source size can be expressed by simple analytic expressions, and a universal brilliance function has been derived by convolution with the electron beam distribution functions. Comparisons with numerical results have been carried out to show the validity and applicability of the universal function.

  3. The Effect of Dissipation Mechanism on X-line Spreading in 3D Magnetic

    NASA Astrophysics Data System (ADS)

    Shepherd, L. S.; Cassak, P.; Phan, T.; Shay, M. A.; Gosling, J. T.

    2012-12-01

    Naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. Reconnection spreading is associated with dawn-dusk asymmetries during substorms in the magnetotail and has been observed in two-ribbon flares (such as the Bastille Day flare) and laboratory experiments at the Versatile Toroidal Facility (VTF) and the Magnetic Reconnection eXperiment (MRX). It was suggested that X-line spreading is necessary to explain the existence of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006). Previous numerical studies exploring the spreading of localized magnetic reconnection exclusively addressed collisionless (Hall) reconnection. Here, we address the effect of dissipation mechanism has on X-line spreading with and without a guide field. We compare previous results with simulations using three alternate phases of reconnection - Sweet-Parker reconnection, collisional reconnection with secondary islands, and reconnection with anomalous resistivity. We present results from three-dimensional resistive magnetohydrodynamic numerical simulations to address the nature of X-line spreading. Applications to reconnection in the solar wind and corona will be discussed.

  4. Development of a Stereovision-Based Technique to Measure the Spread Patterns of Granular Fertilizer Spreaders.

    PubMed

    Cool, Simon R; Pieters, Jan G; Seatovic, Dejan; Mertens, Koen C; Nuyttens, David; Van De Gucht, Tim C; Vangeyte, Jürgen

    2017-06-15

    Centrifugal fertilizer spreaders are by far the most commonly used granular fertilizer spreader type in Europe. Their spread pattern however is error-prone, potentially leading to an undesired distribution of particles in the field and losses out of the field, which is often caused by poor calibration of the spreader for the specific fertilizer used. Due to the large environmental impact of fertilizer use, it is important to optimize the spreading process and minimize these errors. Spreader calibrations can be performed by using collection trays to determine the (field) spread pattern, but this is very time-consuming and expensive for the farmer and hence not common practice. Therefore, we developed an innovative multi-camera system to predict the spread pattern in a fast and accurate way, independent of the spreader configuration. Using high-speed stereovision, ejection parameters of particles leaving the spreader vanes were determined relative to a coordinate system associated with the spreader. The landing positions and subsequent spread patterns were determined using a ballistic model incorporating the effect of tractor motion and wind. Experiments were conducted with a commercial spreader and showed a high repeatability. The results were transformed to one spatial dimension to enable comparison with transverse spread patterns determined in the field and showed similar results.

  5. Development of a Stereovision-Based Technique to Measure the Spread Patterns of Granular Fertilizer Spreaders

    PubMed Central

    Cool, Simon R.; Pieters, Jan G.; Seatovic, Dejan; Mertens, Koen C.; Nuyttens, David; Van De Gucht, Tim C.; Vangeyte, Jürgen

    2017-01-01

    Centrifugal fertilizer spreaders are by far the most commonly used granular fertilizer spreader type in Europe. Their spread pattern however is error-prone, potentially leading to an undesired distribution of particles in the field and losses out of the field, which is often caused by poor calibration of the spreader for the specific fertilizer used. Due to the large environmental impact of fertilizer use, it is important to optimize the spreading process and minimize these errors. Spreader calibrations can be performed by using collection trays to determine the (field) spread pattern, but this is very time-consuming and expensive for the farmer and hence not common practice. Therefore, we developed an innovative multi-camera system to predict the spread pattern in a fast and accurate way, independent of the spreader configuration. Using high-speed stereovision, ejection parameters of particles leaving the spreader vanes were determined relative to a coordinate system associated with the spreader. The landing positions and subsequent spread patterns were determined using a ballistic model incorporating the effect of tractor motion and wind. Experiments were conducted with a commercial spreader and showed a high repeatability. The results were transformed to one spatial dimension to enable comparison with transverse spread patterns determined in the field and showed similar results. PMID:28617339

  6. Spreading and mixing of drops on a miscible liquid of different surface tension

    NASA Astrophysics Data System (ADS)

    Afkhami, S.; Seric, I.; Kondic, L.; Kim, H.; Shardt, O.; Stone, H. A.

    2016-11-01

    We carry out Volume-of-Fluid based numerical simulations of a Marangoni-driven spreading of isopropyl alcohol (IPA) drops placed on water-air interface. The two fully miscible liquids create a spatially varying surface tension, leading to the spreading of the IPA drop on the water surface. We study the spreading of drops as IPA concentration is varied. In particular, we compute the spreading velocity and show that the scaling of the front position, L, with time, t, is given by L t 0 . 7 . We observe that while the surface tension difference between the two liquids controls the spreading velocity, it only slightly alters the power-law behavior for the range of considered IPA concentrations. We also provide detailed insight of the mixing of the IPA and water, and show the time evolution of liquid-air surface tension distribution. We show that the mixing results in a volume flux in a thin region on the surface, generating a vortical flow underneath the spreading front; we investigate the details of these flow patterns and show the time evolution of the circulation within the water. The numerical results are supported by new experimental observations reported separately.

  7. The electrophysiological time course of the interaction of stimulus conflict and the multisensory spread of attention.

    PubMed

    Zimmer, U; Itthipanyanan, S; Grent-'t-Jong, T; Woldorff, M G

    2010-05-01

    Previously, we have shown that spatial attention to a visual stimulus can spread across both space and modality to a synchronously presented but task-irrelevant sound arising from a different location, reflected by a late-onsetting, sustained, negative-polarity event-related potential (ERP) wave over frontal-central scalp sites, probably originating in part from the auditory cortices. Here we explore the influence of cross-modal conflict on the amplitude and temporal dynamics of this multisensory spreading-of-attention activity. Subjects attended selectively to one of two concurrently presented lateral visually-presented letter streams to perform a sequential comparison task, while ignoring task-irrelevant, centrally presented spoken letters that could occur synchronously with either the attended or unattended lateral visual letters and could be either congruent or incongruent with them. Extracted auditory ERPs revealed that, collapsed across congruency conditions, attentional spreading across modalities started at approximately 220 ms, replicating our earlier findings. The interaction between attentional spreading and conflict occurred beginning at approximately 300 ms, with attentional-spreading activity being larger for incongruent trials. Thus, the increased processing of an incongruent, task-irrelevant sound in a multisensory stimulation appeared to occur some time after attention has spread from the attended visual part to the ignored auditory part, presumably reflecting the conflict detection and associated attentional capture requiring accrual of some multisensory interaction processes at a higher-level semantic processing stage.

  8. Spread of white-nose syndrome on a network regulated by geography and climate.

    PubMed

    Maher, Sean P; Kramer, Andrew M; Pulliam, J Tomlin; Zokan, Marcus A; Bowden, Sarah E; Barton, Heather D; Magori, Krisztian; Drake, John M

    2012-01-01

    Wildlife and plant diseases can reduce biodiversity, disrupt ecosystem services and threaten human health. Emerging pathogens have displayed a variety of spatial spread patterns due to differences in host ecology, including diffusive spread from an epicentre (West Nile virus), jump dispersal on a network (foot-and-mouth disease), or a combination of these (Sudden oak death). White-nose syndrome is a highly pathogenic infectious disease of bats currently spreading across North America. Understanding how bat ecology influences this spread is crucial to management of infected and vulnerable populations. Here we show that white-nose syndrome spread is not diffusive but rather mediated by patchily distributed habitat and large-scale gradients in winter climate. Simulations predict rapid expansion and infection of most counties with caves in the contiguous United States by winter 2105-2106. Our findings show the unique pattern of white-nose syndrome spread corresponds to ecological traits of the host and suggest hypotheses for transmission mechanisms acting at the local scale.

  9. 9 CFR 319.762 - Ham spread, tongue spread, and similar products.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 9 Animals and Animal Products 2 2010-01-01 2010-01-01 false Ham spread, tongue spread, and similar products. 319.762 Section 319.762 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE... AND VOLUNTARY INSPECTION AND CERTIFICATION DEFINITIONS AND STANDARDS OF IDENTITY OR COMPOSITION Meat...

  10. Technique for controlling spread of limnotic oncomelania

    NASA Astrophysics Data System (ADS)

    Li, Damei; Wang, Xiangsan; Lai, Yonggen

    2003-09-01

    Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation.

  11. Spectral and spread-spectral teleportation

    SciTech Connect

    Humble, Travis S.

    2010-06-15

    We report how quantum information encoded into the spectral degree of freedom of a single-photon state may be teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of the teleported wave form can be controllably and coherently dilated using a spread-spectral variant of teleportation. We calculate analytical expressions for the fidelities of spectral and spread-spectral teleportation when complex-valued Gaussian states are transferred using a proposed experimental approach. Finally, we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.

  12. Turbulent forces within river plumes affect spread

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Atreyee

    2012-08-01

    When rivers drain into oceans through narrow mouths, hydraulic forces squeeze the river water into buoyant plumes that are clearly visible in satellite images. Worldwide, river plumes not only disperse freshwater, sediments, and nutrients but also spread pollutants and organisms from estuaries into the open ocean. In the United States, the Columbia River—the largest river by volume draining into the Pacific Ocean from North America—generates a plume at its mouth that transports juvenile salmon and other fish into the ocean. Clearly, the behavior and spread of river plumes, such as the Columbia River plume, affect the nation's fishing industry as well as the global economy.

  13. Can rewiring strategy control the epidemic spreading?

    NASA Astrophysics Data System (ADS)

    Dong, Chao; Yin, Qiuju; Liu, Wenyang; Yan, Zhijun; Shi, Tianyu

    2015-11-01

    Relation existed in the social contact network can affect individuals' behaviors greatly. Considering the diversity of relation intimacy among network nodes, an epidemic propagation model is proposed by incorporating the link-breaking threshold, which is normally neglected in the rewiring strategy. The impact of rewiring strategy on the epidemic spreading in the weighted adaptive network is explored. The results show that the rewiring strategy cannot always control the epidemic prevalence, especially when the link-breaking threshold is low. Meanwhile, as well as strong links, weak links also play a significant role on epidemic spreading.

  14. Origin and turbulence spreading of plasma blobs

    SciTech Connect

    Manz, P.; Birkenmeier, G.; Stroth, U.; Ribeiro, T. T.; Scott, B. D.; Carralero, D.; Müller, S. H.; Müller, H. W.; Wolfrum, E.; Fuchert, G.

    2015-02-15

    The formation of plasma blobs is studied by analyzing their trajectories in a gyrofluid simulation in the vicinity of the separatrix. Most blobs arise at the maximum radial electric field outside the separatrix. In general, blob generation is not bound to one particular radial position or instability. A simple model of turbulence spreading for the scrape-off layer is derived. The simulations show that the blob dynamics can be represented by turbulence spreading, which constitutes a substantial energy drive for far scrape-off layer turbulence and is a more suitable quantity to study blob generation compared to the skewness.

  15. Spatial Dynamics of Multilayer Cellular Neural Networks

    NASA Astrophysics Data System (ADS)

    Wu, Shi-Liang; Hsu, Cheng-Hsiung

    2017-06-01

    The purpose of this work is to study the spatial dynamics of one-dimensional multilayer cellular neural networks. We first establish the existence of rightward and leftward spreading speeds of the model. Then we show that the spreading speeds coincide with the minimum wave speeds of the traveling wave fronts in the right and left directions. Moreover, we obtain the asymptotic behavior of the traveling wave fronts when the wave speeds are positive and greater than the spreading speeds. According to the asymptotic behavior and using various kinds of comparison theorems, some front-like entire solutions are constructed by combining the rightward and leftward traveling wave fronts with different speeds and a spatially homogeneous solution of the model. Finally, various qualitative features of such entire solutions are investigated.

  16. Seeding and layering of equatorial spread F by gravity waves

    SciTech Connect

    Hysell, D.L.; Kelley, M.C.; Swartz, W.E. ); Woodman, R.F. )

    1990-10-01

    Studies dating back more than 15 years have presented evidence that atmospheric gravity waves play a role in initiating nighttime equatorial F region instabilities. This paper analyzes a spectabular spread F event that for the first time demonstrates a layering which, the authors argue, is controlled by a gravity wave effect. The 50-km vertical wavelength of a gravity wave which they have found is related theoretically to a plasma layering irregularity that originated at low altitudes and then was convected, intact, to higher altitudes. Gravity waves also seem to have determined bottomside intermediate scale undulations, although this fact is not as clear in the data. The neutral wind dynamo effect yields wave number conditions on the gravity wave's ability to modulate the Rayleigh-Taylor instaiblity process. Finally, after evaluating the gravity wave dispersion relation and spatial resonance conditions, we estimate the properties of the seeding wave.

  17. Laser confocal microscope with wavelet-profiled point spread function

    NASA Astrophysics Data System (ADS)

    Romero, Mary Jacquiline; Bautista, Godofredo; Daria, Vincent Ricardo; Saloma, Caesar

    2010-04-01

    We report a laser-scanning confocal reflectance microscope with a wavelet-profiled point spread function (PSF) for rapid multi-resolution extraction and analysis of microscopic object features. The PSF is generated via holography by encoding a π-phase shifting disk unto a collimated laser beam via a phase-only spatial light modulator (SLM) that is positioned at the pupil plane of the focusing objective lens. Scaling of the transverse PSF distribution is achieved by selecting a suitable ratio of the π-phase shifting disk radius and the pupil aperture radius. With one and the same objective lens and one SLM to control the phase profile of the pupil function, we produce amplitude PSF distributions that are accurate scaled representations of the circularly-symmetric Mexican hat mother wavelet.

  18. Accurate point spread function (PSF) estimation for coded aperture cameras

    NASA Astrophysics Data System (ADS)

    Yang, Jingyu; Jiang, Bin; Ma, Jinlong; Sun, Yi; Di, Ming

    2014-10-01

    Accurate Point Spread Function (PSF) estimation of coded aperture cameras is a key to deblur defocus images. There are mainly two kinds of approaches to estimate PSF: blind-deconvolution-based methods, and measurement-based methods with point light sources. Both these two kinds of methods cannot provide accurate and convenient PSFs due to the limit of blind deconvolution or imperfection of point light sources. Inaccurate PSF estimation introduces pseudo-ripple and ringing artifacts which influence the effects of image deconvolution. In addition, there are many inconvenient situation for the PSF estimation. This paper proposes a novel method of PSF estimation for coded aperture cameras. It is observed and verified that the spatially-varying point spread functions are well modeled by the convolution of the aperture pattern and Gaussian blurring with appropriate scales and bandwidths. We use the coded aperture camera to capture a point light source to get a rough estimate of the PSF. Then, the PSF estimation method is formulated as the optimization of scale and bandwidth of Gaussian blurring kernel to fit the coded pattern with the observed PSF. We also investigate the PSF estimation at arbitrary distance with a few observed PSF kernels, which allows us to fully characterize the response of coded imaging systems with limited measurements. Experimental results show that our method is able to accurately estimate PSF kernels, which significantly make the deblurring performance convenient.

  19. Role of astrocyte connexin hemichannels in cortical spreading depression.

    PubMed

    Rovegno, Maximiliano; Sáez, Juan C

    2017-08-29

    Cortical spreading depression (CSD) is an intriguing phenomenon consisting of massive slow brain depolarizations that affects neurons and glial cells. It has been recognized since 1944, but its pathogenesis has only been uncovered during the last decade. Acute brain injuries can be further complicated by CSD in more than 50% of severe cases. This phenomenon is repetitive and produces a metabolic overload that increments secondary damage. Propagation of CSD is known to be linked to excitotoxicity, but the mechanisms associated with its initiation remain less understood. It has been shown that CSD can be initiated by increases in extracellular [K(+)] ([K(+)]e), and animal models use high [K(+)]e to promote CSD. Connexin hemichannel activity increases due to high [K(+)]e and low extracellular [Ca(2+)], conditions that occur after brain injury. Moreover, glial cell gap junction channels are fundamental in controlling extracellular medium composition, particularly in maintaining normal glutamate and [K(+)]e levels through "spatial buffering". However, the role of astrocytic gap junctions under tissue stress can change to damage spread in the acute damage zone whereas the reduced communication in adjacent zone would reduce cell dead propagation. Here, we review the main findings associated with CSD, and discuss the possible involvement of astrocytic connexin-based channels in secondary damage propagation. Copyright © 2017. Published by Elsevier B.V.

  20. Morphology of oceanic ridges in spreading colloidal suspensions: Influence of spreading rate and lithospheric thickness

    NASA Astrophysics Data System (ADS)

    Sibrant, A.; Davaille, A.; Mittelstaedt, E. L.

    2016-12-01

    Oceanic ridges exhibit significant changes in their structural, morphological, and volcanic characteristics with changes in spreading velocity. However, separating the role of correlated affects such as spreading rate and lithospheric thickness on the segmentation of the ridge axis is difficult with only field data. The goal of this study is (a) to conduct properly scaled laboratory simulations of oceanic ridges, and (b) to investigate how the morphology and geometry of spreading-normal oceanic ridges vary separately with extension rate and lithospheric thickness. We present a series of analogue experiments using colloidal silica dispersions as an Earth analogue. Saline water solutions placed in contact with these fluids, cause formation of a skin through salt diffusion, whose rheology evolves from purely viscous to elastic and brittle with increasing salinity. Applying a fixed spreading rate to this pre-formed, brittle plate resulting in cracks, faults and axial ridge structures. Lithospheric (skin) thickness at a given extension rate is varied by changing salinity of the surface water layer. With increasing spreading rate, we observe several regimes: (1) at the slowest spreading rates, the spreading axis is composed of several segments separated by non-transform offsets and has a fault-bounded, deep, U-shaped axial valley. The axis has a large sinuosity, rough topography, and jumps repeatedly. (2) At intermediate spreading rates, the spreading axis shows low sinuosity, overlapping spreading centers (OSC) , a smooth axial morphology, and very few to no jumps. The axial valley is shallow and shows a V-shape morphology. The OSCs have a ratio of length to width of 3 to 1. (3) At faster spreading rates, the axis is continuous and presents an axial high topography. (4) At the fastest spreading rates tested, the spreading axis is again segmented. Each segment is offset by well developed transform faults and the axis has a sinuosity comparable to those of regimes 2 and 3

  1. Security of Classic PN-Spreading Codes for Hybrid DS/FH Spread-Spectrum Systems

    SciTech Connect

    Ma, Xiao; Olama, Mohammed M; Kuruganti, Phani Teja; Smith, Stephen Fulton; Djouadi, Seddik M

    2013-01-01

    Hybrid direct sequence/frequency hopping (DS/FH) spread-spectrum communication systems have recently received considerable interest in commercial applications in addition to their use in military communications because they accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. The security of hybrid DS/FH systems strongly depends on the choice of PN-spreading code employed. In this paper, we examine the security, in terms of unicity distance, of linear maximal-length, Gold, and Kasami PN-spreading codes for DS, FH, and hybrid DS/FH spread-spectrum systems without additional encryption methods. The unicity distance is a measure of the minimum amount of ciphertext required by an eavesdropper to uniquely determine the specific key used in a cryptosystem and hence break the cipher. Numerical results are presented to compare the security of the considered PN-spreading codes under known-ciphertext attacks.

  2. Spreading speeds for plant populations in landscapes with low environmental variation.

    PubMed

    Gilbert, Mark A; Gaffney, Eamonn A; Bullock, James M; White, Steven M

    2014-12-21

    Characterising the spread of biological populations is crucial in responding to both biological invasions and the shifting of habitat under climate change. Spreading speeds can be studied through mathematical models such as the discrete-time integro-difference equation (IDE) framework. The usual approach in implementing IDE models has been to ignore spatial variation in the demographic and dispersal parameters and to assume that these are spatially homogeneous. On the other hand, real landscapes are rarely spatially uniform with environmental variation being very important in determining biological spread. This raises the question of under what circumstances spatial structure need not be modelled explicitly. Recent work has shown that spatial variation can be ignored for the specific case where the scale of landscape variation is much smaller than the spreading population׳s dispersal scale. We consider more general types of landscape, where the spatial scales of environmental variation are arbitrarily large, but the maximum change in environmental parameters is relatively small. We find that the difference between the wave-speeds of populations spreading in a spatially structured periodic landscape and its homogenisation is, in general, proportional to ϵ(2), where ϵ governs the degree of environmental variation. For stochastically generated landscapes we numerically demonstrate that the error decays faster than ϵ. In both cases, this means that for sufficiently small ϵ, the homogeneous approximation is better than might be expected. Hence, in many situations, the precise details of the landscape can be ignored in favour of spatially homogeneous parameters. This means that field ecologists can use the homogeneous IDE as a relatively simple modelling tool--in terms of both measuring parameter values and doing the modelling itself. However, as ϵ increases, this homogeneous approximation loses its accuracy. The change in wave-speed due to the extrinsic (landscape

  3. Buoyant downward diffusion flame spread and extinction in partial-gravity accelerations

    SciTech Connect

    Sacksteder, K.R.; Tien, J.S.

    1994-12-31

    This paper describes experimental observations of downward, opposed-flow flame spreading made under partial-gravity conditions aboard NASA research aircraft. Special apparatus and techniques for these tests are described, including schlieren imaging of dim near-limit flames. Flame-spreading and flammability limit behaviors of a thin cellulosic fuel, 1 {times} 10{sup {minus}3} g/cm{sup 2} tested at 1 atm of pressure in oxygen/nitrogen mixtures of 13-21% oxygen by volume, are described for effective acceleration levels ranging from 0.05 to 0.6 times normal earth gravity (1 g). Downward-burning flammability increases in partial gravity, with the limiting oxygen fraction falling from 15.6% oxygen in 1 g to 13--14% oxygen in 0.05--0.1 g. Flamespread rates are shown to peak in partial gravity, increasing by 20% over the 1-g value in air (21% oxygen). Partial-gravity flame-spreading results, corrected for fuel density and thickness, are consistent with results obtained at acceleration levels above 1 g in a centrifuge. The results compare qualitatively with predictions of flame spreading in buoyant flow by models that include finite-rate chemical kinetics and surface and gas-phase radiative loss mechanisms. A correlation of experimental buoyant downward flame-spread results is introduced that accounts for radiative heat losses using a dimensionless spread rate, a radiation/conduction number, and the Damkohler number, as parameters. The correlation includes data from 0.05 g to 4.25 g and oxygen-nitrogen mixtures from 14% to 50% oxygen.

  4. The spread of attention across features of a surface

    PubMed Central

    Ernst, Zachary Raymond; Jazayeri, Mehrdad

    2013-01-01

    Contrasting theories of visual attention have emphasized selection by spatial location, individual features, and whole objects. We used functional magnetic resonance imaging to ask whether and how attention to one feature of an object spreads to other features of the same object. Subjects viewed two spatially superimposed surfaces of random dots that were segregated by distinct color-motion conjunctions. The color and direction of motion of each surface changed smoothly and in a cyclical fashion. Subjects were required to track one feature (e.g., color) of one of the two surfaces and detect brief moments when the attended feature diverged from its smooth trajectory. To tease apart the effect of attention to individual features on the hemodynamic response, we used a frequency-tagging scheme. In this scheme, the stimulus features (color and direction of motion) are modulated periodically at distinct frequencies so that the contribution of each feature to the hemodynamics can be inferred from the harmonic response at the corresponding frequency. We found that attention to one feature (e.g., color) of one surface increased the response modulation not only to the attended feature but also to the other feature (e.g., motion) of the same surface. This attentional modulation was evident in multiple visual areas and was present as early as V1. The spread of attention to the behaviorally irrelevant features of a surface suggests that attention may automatically select all features of a single object. Thus object-based attention may be supported by an enhancement of feature-specific sensory signals in the visual cortex. PMID:23883860

  5. Evaluating the links between climate, disease spread, and amphibian declines.

    PubMed

    Rohr, Jason R; Raffel, Thomas R; Romansic, John M; McCallum, Hamish; Hudson, Peter J

    2008-11-11

    Human alteration of the environment has arguably propelled the Earth into its sixth mass extinction event and amphibians, the most threatened of all vertebrate taxa, are at the forefront. Many of the worldwide amphibian declines have been caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd), and two contrasting hypotheses have been proposed to explain these declines. Positive correlations between global warming and Bd-related declines sparked the chytrid-thermal-optimum hypothesis, which proposes that global warming increased cloud cover in warm years that drove the convergence of daytime and nighttime temperatures toward the thermal optimum for Bd growth. In contrast, the spatiotemporal-spread hypothesis states that Bd-related declines are caused by the introduction and spread of Bd, independent of climate change. We provide a rigorous test of these hypotheses by evaluating (i) whether cloud cover, temperature convergence, and predicted temperature-dependent Bd growth are significant positive predictors of amphibian extinctions in the genus Atelopus and (ii) whether spatial structure in the timing of these extinctions can be detected without making assumptions about the location, timing, or number of Bd emergences. We show that there is spatial structure to the timing of Atelopus spp. extinctions but that the cause of this structure remains equivocal, emphasizing the need for further molecular characterization of Bd. We also show that the reported positive multi-decade correlation between Atelopus spp. extinctions and mean tropical air temperature in the previous year is indeed robust, but the evidence that it is causal is weak because numerous other variables, including regional banana and beer production, were better predictors of these extinctions. Finally, almost all of our findings were opposite to the predictions of the chytrid-thermal-optimum hypothesis. Although climate change is likely to play an important role in worldwide amphibian declines

  6. Forced Flow Flame Spreading Test: Preliminary Findings From the USMP-3 Shuttle Mission

    NASA Technical Reports Server (NTRS)

    Sacksteder, Kurt R.; Greenberg, Paul S.; Pettegrew, Richard D.; Tien, James S.; Ferkul, Paul V.; Shih, Hsin-Yi

    1998-01-01

    The Forced Flow Flame spreading Test (FFFT) is a study of flame spreading over solid fuels in very low-speed air flows. The FFFT experiment is part of research entitled Solid Inflammability Boundary at Low Speeds, (SIBAL) intended for operations on the Space Station. In the FFFT experiment, a series of 15 experiments conducted aboard the space shuttle during the United States Microgravity Payload (USMP-3) mission provided information about the structure and spreading characteristics of flames in low-speed, concurrent flows. The test samples included flat sheets of cellulose and cast cylinders of cellulose, burned in air at velocities of approximately 1 to 8 cm/sec. The test results have been successfully compared to theoretical predictions of the SIBAL program, a fundamentally based numerical simulation of concurrent flow flame spread. Additionally, some guidance for the design characteristics of the SIBAL flight experiment have been obtained including some verification of the theoretical predictions of flame size versus the required size of the SIBAL flow duct, and the effect of the presence of thermocouples in the vicinity of near-limit flames in microgravity.

  7. Forced Flow Flame Spreading Test: Preliminary Findings From the USMP-3 Shuttle Mission

    NASA Technical Reports Server (NTRS)

    Sacksteder, Kurt R.; Greenberg, Paul S.; Pettegrew, Richard D.; Tien, James S.; Ferkul, Paul V.; Shih, Hsin-Yi

    1998-01-01

    The Forced Flow Flame spreading Test (FFFT) is a study of flame spreading over solid fuels in very low-speed air flows. The FFFT experiment is part of research entitled Solid Inflammability Boundary at Low Speeds, (SIBAL) intended for operations on the Space Station. In the FFFT experiment, a series of 15 experiments conducted aboard the space shuttle during the United States Microgravity Payload (USMP-3) mission provided information about the structure and spreading characteristics of flames in low-speed, concurrent flows. The test samples included flat sheets of cellulose and cast cylinders of cellulose, burned in air at velocities of approximately 1 to 8 cm/sec. The test results have been successfully compared to theoretical predictions of the SIBAL program, a fundamentally based numerical simulation of concurrent flow flame spread. Additionally, some guidance for the design characteristics of the SIBAL flight experiment have been obtained including some verification of the theoretical predictions of flame size versus the required size of the SIBAL flow duct, and the effect of the presence of thermocouples in the vicinity of near-limit flames in microgravity.

  8. Experiments in water spreading at Newark, Delaware

    USGS Publications Warehouse

    Boggess, Durward Haye; Rima, Donald Robert

    1962-01-01

    Two experiments in water spreading were made at Newark, Del., to evaluate the prospects of using excess storm runoff to recharge the shallow water-table aquifer which serves the community. Water was diverted from 1 of the city's 3 production wells and released into an infiltration ditch near the municipal well field. Although slightly more than 65,000 cubic feet of water (nearly 500,000 gallons ) was spread in the infiltration ditch and allowed to seep into the subsurface, there was no indication that any appreciable amount of water reached the producing aquifer. Instead, a perched zone of saturation was created by the presence of an impermeable or slightly permeable bed above the water table. So effective is this barrier to the downward movement of water that within a period of less than 1 day, the apex of the perched zone rose about 10 feet to the level of the bottom of the infiltration ditch. As more water was added, the mound of saturation spread laterally. On the basis of these experiments, it appears that the principal aquifer at Newark, Del., would not be benefited by spreading water in shallow infiltration ditches or basins. However, the absorptive capacity of the unsaturated materials which occur at a shallow depth, is sufficient to permit the disposal of large volumes of storm runoff.

  9. An Advanced Sea-Floor Spreading Model.

    ERIC Educational Resources Information Center

    Dutch, Steven I.

    1986-01-01

    Describes models which (1) illustrate spreading that varies in rate from place to place; (2) clearly show transform faults as arcs of small circles; and (3) illustrate what happens near a pole of rotation. The models are easy to construct and have been well received by students. (JN)

  10. Irregularities and Forecast Studies of Equatorial Spread

    DTIC Science & Technology

    2016-07-13

    AFRL-AFOSR-VA-TR-2016-0262 Irregularties and Forecast Studies of Equatorial Spread David Hysell CORNELL UNIVERSITY 373 PINE TREE RD ITHACA, NY 14850...NAME(S) AND ADDRESS(ES) CORNELL UNIVERSITY 373 PINE TREE RD ITHACA, NY 14850-2820 US 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING

  11. Anthropogenic drivers of gypsy moth spread

    Treesearch

    Kevin M. Bigsby; Patrick C. Tobin; Erin O. Sills

    2011-01-01

    The gypsy moth, Lymantria dispar (L.), is a polyphagous defoliator introduced to Medford, Massachusetts in 1869. It has spread to over 860,000 km2 in North America, but this still only represents 1/4 of its susceptible host range in the United States. To delay defoliation in the remaining susceptible host range, the government...

  12. Centerfolds: Your Newspaper's Most Exciting Spreads

    ERIC Educational Resources Information Center

    Quevedo, Jose

    1977-01-01

    Gives guidelines for planning copy and design for the centerfold spread of a newspaper in order to use this natural display section to enhance the overall interest of the newspaper. Shows how college and professional papers have used centerfolds effectively. (GW)

  13. Spread of dwarfmistletoe into Jeffrey pine plantation..

    Treesearch

    Robert F. Scarpf; J.R. Parmeter

    1967-01-01

    A study at the Institute of Forest Genetics, Placerville. Calif . showed that dwarfmistletoe could spread from infected overstory ponderosa pine into planted Jeffrey pine--a maximum distance of about 145 feet. About one-third of the trees within this distance were infected after 22 years. The level of infection in the trees remained low. however and the parasite had...

  14. Spreading of water nanodroplets on graphene

    NASA Astrophysics Data System (ADS)

    Andrews, Joseph; Sinha, Shayandev; Chung, Peter; Das, Siddhartha

    Understanding the wetting of 2D materials is central to the successful application of these materials in a variety of disciplines that involve the interaction of a liquid with such layered substrates. Recent studies focusing on wetting statics and contact angle selection on graphene-coated solids indicate a wetting translucent behavior of graphene. However, little research has been done on the wetting dynamics of graphene-coated systems. Here, we simulate the wetting dynamics of water drops on free-standing graphene layers using a molecular dynamics framework. We employ the extended simple point charge (SPC/E) model to simulate the water drops. Our simulations are validated against the experimental results of water drop contact angles on graphite. Unlike many existing MD studies, we obtain the results starting from a physical consideration of spherical water drops. We observe the half power law for the spreading dynamics, i.e., r~t(1/2) (r is the spreading radius and t is the spreading time). Identical spreading laws have been identified for Lennard Jones (LJ) nanodroplets on non-layered surfaces; therefore, we establish that the change in the nature of the substrate (non-layered to 2D) and the liquid (LJ to water) does not alter the physics of wetting dynamics of nanodroplets.

  15. Methodology of Spread-Spectrum Image Steganography

    DTIC Science & Technology

    1998-06-01

    ARMY RESEARCH LABORATORY Methodology of Spread-Spectrum Image Steganography by Lisa M. Marvel, Charles G. Boncelet, Jr., and Charles T. Retter...Image Steganography Lisa M. Marvel, Charles T. Retter Information Science and Technology Directorate, ARL Charles G. Boncelet, Jr. University of...Delaware, Newark, DE Approved for public release; distribution is unlimited. Abstract This report presents a new method of digital steganography

  16. Glucose modulation of spreading depression susceptibility

    PubMed Central

    Hoffmann, Ulrike; Sukhotinsky, Inna; Eikermann-Haerter, Katharina; Ayata, Cenk

    2013-01-01

    Spreading depression of Leão is an intense spreading depolarization (SD) wave associated with massive transmembrane ionic, water, and neurotransmitter shifts. Spreading depolarization underlies migraine aura, and occurs in brain injury, making it a potential therapeutic target. While susceptibility to SD can be modulated pharmacologically, much less is known about modulation by systemic physiological factors, such as the glycemic state. In this study, we systematically examined modulation of SD susceptibility by blood glucose in anesthetized rats under full physiological monitoring. Hyperglycemia and hypoglycemia were induced by insulin or dextrose infusion (blood glucose ∼40 and 400 mg/dL, respectively). Spreading depolarizations were evoked by direct cortical electrical stimulation to determine the intensity threshold, or by continuous topical KCl application to determine SD frequency. Hyperglycemia elevated the electrical SD threshold and reduced the frequency of KCl-induced SDs, without significantly affecting other SD properties. In contrast, hypoglycemia significantly prolonged individual and cumulative SD durations, but did not alter the electrical SD threshold, or SD frequency, amplitude or propagation speed. These data show that increased cerebral glucose availability makes the tissue resistant to SD. PMID:22968322

  17. Attentional Spreading in Object-Based Attention

    ERIC Educational Resources Information Center

    Richard, Ashleigh M.; Lee, Hyunkyu; Vecera, Shaun P.

    2008-01-01

    The authors investigated 2 effects of object-based attention: the spread of attention within an attended object and the prioritization of search across possible target locations within an attended object. Participants performed a flanker task in which the location of the task-relevant target was fixed and known to participants. A spreading…

  18. Social distancing strategies against disease spreading

    NASA Astrophysics Data System (ADS)

    Valdez, L. D.; Buono, C.; Macri, P. A.; Braunstein, L. A.

    2014-03-01

    The recurrent infectious diseases and their increasing impact on the society has promoted the study of strategies to slow down the epidemic spreading. In this review we outline the applications of percolation theory to describe strategies against epidemic spreading on complex networks. We give a general outlook of the relation between link percolation and the susceptible-infected-recovered model, and introduce the node void percolation process to describe the dilution of the network composed by healthy individual, i.e, the network that sustain the functionality of a society. Then, we survey two strategies: the quenched disorder strategy where an heterogeneous distribution of contact intensities is induced in society, and the intermittent social distancing strategy where health individuals are persuaded to avoid contact with their neighbors for intermittent periods of time. Using percolation tools, we show that both strategies may halt the epidemic spreading. Finally, we discuss the role of the transmissibility, i.e, the effective probability to transmit a disease, on the performance of the strategies to slow down the epidemic spreading.

  19. Social Distancing Strategies against Disease Spreading

    NASA Astrophysics Data System (ADS)

    Valdez, L. D.; Buono, C.; Macri, P. A.; Braunstein, L. A.

    2013-12-01

    The recurrent infectious diseases and their increasing impact on the society has promoted the study of strategies to slow down the epidemic spreading. In this review we outline the applications of percolation theory to describe strategies against epidemic spreading on complex networks. We give a general outlook of the relation between link percolation and the susceptible-infected-recovered model, and introduce the node void percolation process to describe the dilution of the network composed by healthy individual, i.e., the network that sustain the functionality of a society. Then, we survey two strategies: the quenched disorder strategy where an heterogeneous distribution of contact intensities is induced in society, and the intermittent social distancing strategy where health individuals are persuaded to avoid contact with their neighbors for intermittent periods of time. Using percolation tools, we show that both strategies may halt the epidemic spreading. Finally, we discuss the role of the transmissibility, i.e., the effective probability to transmit a disease, on the performance of the strategies to slow down the epidemic spreading.

  20. The universal dynamics of cell spreading.

    PubMed

    Cuvelier, Damien; Théry, Manuel; Chu, Yeh-Shiu; Dufour, Sylvie; Thiéry, Jean-Paul; Bornens, Michel; Nassoy, Pierre; Mahadevan, L

    2007-04-17

    Cell adhesion and motility depend strongly on the interactions between cells and extracellular matrix (ECM) substrates. When plated onto artificial adhesive surfaces, cells first flatten and deform extensively as they spread. At the molecular level, the interaction of membrane-based integrins with the ECM has been shown to initiate a complex cascade of signaling events [1], which subsequently triggers cellular morphological changes and results in the generation of contractile forces [2]. Here, we focus on the early stages of cell spreading and probe their dynamics by quantitative visualization and biochemical manipulation with a variety of cell types and adhesive surfaces, adhesion receptors, and cytoskeleton-altering drugs. We find that the dynamics of adhesion follows a universal power-law behavior. This is in sharp contrast with the common belief that spreading is regulated by either the diffusion of adhesion receptors toward the growing adhesive patch [3-5] or by actin polymerization [6-8]. To explain this, we propose a simple quantitative and predictive theory that models cells as viscous adhesive cortical shells enclosing a less viscous interior. Thus, although cell spreading is driven by well-identified biomolecular interactions, it is dynamically limited by its mesoscopic structure and material properties.

  1. Spread of English across Greater China

    ERIC Educational Resources Information Center

    Feng, Anwei

    2012-01-01

    Greater China is used in this article to refer to mainland China, Hong Kong, Singapore, Taiwan and Macao. While a holistic approach is adopted to present and compare the rapid spread of English and development in English language education in these geographically close, and sociopolitically, culturally and economically interrelated but hugely…

  2. Robust Interference Mitigation and Spread Spectrum Signaling

    DTIC Science & Technology

    2006-01-01

    AFRL-IF-RS-TR-2005-414 Final Technical Report January 2006 ROBUST INTERFERENCE MITIGATION AND SPREAD SPECTRUM SIGNALING State...reviewed by the Air Force Research Laboratory, Information Directorate, Public Affairs Office (IFOIPA) and is releasable to the National Technical ...s/ WARREN H. DEBANY JR., Technical Advisor Information Grid Division Information Directorate REPORT DOCUMENTATION PAGE

  3. Predicting fire spread in Arizona's oak chaparral

    Treesearch

    A. W. Lindenmuth; James R. Davis

    1973-01-01

    Five existing fire models, both experimental and theoretical, did not adequately predict rate-of-spread (ROS) when tested on single- and multiclump fires in oak chaparral in Arizona. A statistical model developed using essentially the same input variables but weighted differently accounted for 81 percent ofthe variation in ROS. A chemical coefficient that accounts for...

  4. New Concerns Emerge as Zebra Mussel Spreads.

    ERIC Educational Resources Information Center

    Walter, Martha L., Ed.

    1992-01-01

    Reports on the Zebra Mussel invasion of North American inland waterways. Discusses United States Army Corps of Engineers operations that may facilitate or be affected by the spread of Zebra Mussels, the threat to native clams, chemical and mechanical control methods, natural solutions, and ongoing research. (MCO)

  5. 21 CFR 102.23 - Peanut spreads.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 2 2011-04-01 2011-04-01 false Peanut spreads. 102.23 Section 102.23 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION COMMON OR USUAL NAME FOR NONSTANDARDIZED FOODS Requirements for Specific Nonstandardized Foods...

  6. 21 CFR 102.23 - Peanut spreads.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Peanut spreads. 102.23 Section 102.23 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION COMMON OR USUAL NAME FOR NONSTANDARDIZED FOODS Requirements for Specific Nonstandardized Foods...

  7. 21 CFR 102.23 - Peanut spreads.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 2 2013-04-01 2013-04-01 false Peanut spreads. 102.23 Section 102.23 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION COMMON OR USUAL NAME FOR NONSTANDARDIZED FOODS Requirements for Specific Nonstandardized Foods...

  8. 21 CFR 102.23 - Peanut spreads.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 2 2012-04-01 2012-04-01 false Peanut spreads. 102.23 Section 102.23 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION COMMON OR USUAL NAME FOR NONSTANDARDIZED FOODS Requirements for Specific Nonstandardized Foods...

  9. DataSpread: Unifying Databases and Spreadsheets.

    PubMed

    Bendre, Mangesh; Sun, Bofan; Zhang, Ding; Zhou, Xinyan; Chang, Kevin ChenChuan; Parameswaran, Aditya

    2015-08-01

    Spreadsheet software is often the tool of choice for ad-hoc tabular data management, processing, and visualization, especially on tiny data sets. On the other hand, relational database systems offer significant power, expressivity, and efficiency over spreadsheet software for data management, while lacking in the ease of use and ad-hoc analysis capabilities. We demonstrate DataSpread, a data exploration tool that holistically unifies databases and spreadsheets. It continues to offer a Microsoft Excel-based spreadsheet front-end, while in parallel managing all the data in a back-end database, specifically, PostgreSQL. DataSpread retains all the advantages of spreadsheets, including ease of use, ad-hoc analysis and visualization capabilities, and a schema-free nature, while also adding the advantages of traditional relational databases, such as scalability and the ability to use arbitrary SQL to import, filter, or join external or internal tables and have the results appear in the spreadsheet. DataSpread needs to reason about and reconcile differences in the notions of schema, addressing of cells and tuples, and the current "pane" (which exists in spreadsheets but not in traditional databases), and support data modifications at both the front-end and the back-end. Our demonstration will center on our first and early prototype of the DataSpread, and will give the attendees a sense for the enormous data exploration capabilities offered by unifying spreadsheets and databases.

  10. DataSpread: Unifying Databases and Spreadsheets

    PubMed Central

    Bendre, Mangesh; Sun, Bofan; Zhang, Ding; Zhou, Xinyan; Chang, Kevin ChenChuan; Parameswaran, Aditya

    2015-01-01

    Spreadsheet software is often the tool of choice for ad-hoc tabular data management, processing, and visualization, especially on tiny data sets. On the other hand, relational database systems offer significant power, expressivity, and efficiency over spreadsheet software for data management, while lacking in the ease of use and ad-hoc analysis capabilities. We demonstrate DataSpread, a data exploration tool that holistically unifies databases and spreadsheets. It continues to offer a Microsoft Excel-based spreadsheet front-end, while in parallel managing all the data in a back-end database, specifically, PostgreSQL. DataSpread retains all the advantages of spreadsheets, including ease of use, ad-hoc analysis and visualization capabilities, and a schema-free nature, while also adding the advantages of traditional relational databases, such as scalability and the ability to use arbitrary SQL to import, filter, or join external or internal tables and have the results appear in the spreadsheet. DataSpread needs to reason about and reconcile differences in the notions of schema, addressing of cells and tuples, and the current “pane” (which exists in spreadsheets but not in traditional databases), and support data modifications at both the front-end and the back-end. Our demonstration will center on our first and early prototype of the DataSpread, and will give the attendees a sense for the enormous data exploration capabilities offered by unifying spreadsheets and databases. PMID:26900487

  11. New Concerns Emerge as Zebra Mussel Spreads.

    ERIC Educational Resources Information Center

    Walter, Martha L., Ed.

    1992-01-01

    Reports on the Zebra Mussel invasion of North American inland waterways. Discusses United States Army Corps of Engineers operations that may facilitate or be affected by the spread of Zebra Mussels, the threat to native clams, chemical and mechanical control methods, natural solutions, and ongoing research. (MCO)

  12. “Modeling Trends in Air Pollutant Concentrations over the ...

    EPA Pesticide Factsheets

    Regional model calculations over annual cycles have pointed to the need for accurately representing impacts of long-range transport. Linking regional and global scale models have met with mixed success as biases in the global model can propagate and influence regional calculations and often confound interpretation of model results. Since transport is efficient in the free-troposphere and since simulations over Continental scales and annual cycles provide sufficient opportunity for “atmospheric turn-over”, i.e., exchange between the free-troposphere and the boundary-layer, a conceptual framework is needed wherein interactions between processes occurring at various spatial and temporal scales can be consistently examined. The coupled WRF-CMAQ model is expanded to hemispheric scales and model simulations over period spanning 1990-current are analyzed to examine changes in hemispheric air pollution resulting from changes in emissions over this period. The National Exposure Research Laboratory (NERL) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA mission to protect human health and the environment. AMAD research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for pr

  13. Spreading of the ocean floor: new evidence.

    PubMed

    Vine, F J

    1966-12-16

    It is suggested that the entire history of the ocean basins, in terms of oceanfloor spreading,is contained frozen in the oceanic crust. Variations in the intensity and polarity of Earth's magnetic field are considered to be recorded in the remanent magnetism of the igneous rocks as they solidified and cooled through the Curie temperature at the crest of an oceanic ridge, and subsequently spread away from it at a steady rate. The hypothesis is supported by the extreme linearity and continuity of oceanic magnetic anomalies and their symmetry about the axes of ridges. If the proposed reversal time scale for the last 4 million years is combined with the model, computed anomaly profiles show remarkably good agreement with those observed, and one can deduce rates of spreading for all active parts of the midoceanic ridge system for which magnetic profilesor surveys are available. The rates obtained are in exact agreement with those needed to account for continental drift. An exceptionally high rate of spreading (approximately 4.5 cm/year) in the South Pacific enables one to deduce by extrapolation considerable details of the reversal time scale back to 11.5 million years ago. Again, this scale can be applied to other parts of the ridge system. Thus one isled to the suggestion that the crest of the East Pacific Rise in the northeast Pacific has been overridden and modified by the westward drift of North America, with the production of the anomalous width and unique features of the American cordillera in the western United States. The oceanicmagnetic anomalies also indicate that there was a change in derection of crustal spreading in this region during Pliocene time from eastwest to southeast-northwest. A profile from the crest to the boundary of the East Pacific Rise, and the difference between axial-zone and flank anomalies over ridges, suggest increase in the frequency of reversal of Earth's magnetic field, together, possibly, with decrease in its intensity

  14. Unstable Spreading of Ionic Liquids on an Aqueous Substrate.

    PubMed

    Tsuchitani, Shigeki; Fukutake, Taiga; Mukai, Daiki; Miki, Hirofumi; Kikuchi, Kunitomo

    2017-10-04

    The spontaneous spreading of thin liquid films over substrate surfaces is attracting much attention due to its broad applications. Under particular conditions, surfactants deposited on substrates exhibit unstable spreading. In spite of the large effects of the stability of the spreading on the accuracy and efficiency of industrial processes that use the spreading, understanding how the stability of the spreading process is governed by the physical and chemical properties of the system is still little known. Recently, ionic liquids have been characterized as a new kind of surfactant due to their special properties. Here, we investigate the stability of the spreading of deposited imidazolium-based ionic liquids on an aqueous substrate. We focus mainly on the effects that the water solubility of the ionic liquids has on the stability. Hydrophobic ionic liquids exhibit spreading that has a highly periodic and petal-like unstable spreading front, whereas hydrophilic ionic liquids spread without such a regular spreading front and their spreading area shrinks after reaching its maximum. We propose a model for the generation of unstable spreading of hydrophobic ionic liquids, i.e., the unstable spreading front is created by the penetration of oncoming water in front of the spreading tip into the more viscous spreading ionic liquid layer, like the viscous fingering that occurs in a Hele-Shaw cell. However, the direction of the penetration is the opposite of the direction that the interface moves (the spreading direction), which is contrary to that in viscous fingering.

  15. High resolution mechano-optical method for acoustic field measurements in air

    NASA Astrophysics Data System (ADS)

    Welter, J. T.; Sathish, S.; Cherry, M. R.; Brodrick, P. G.

    2013-01-01

    Acoustic fields are typically visualized by measuring spatial variation of pressure in a medium, using optical (ie: Schlieren, laser interferometry) and electro-mechanical (ie: transducers, micro-electro-mechanical sensors) methods. These methods have limited ability to visualize acoustic fields in air, especially at high spatial resolution (< 0.5 mm). This paper presents a method to detect and quantify the acoustic fields in air by measuring the displacements of a micro-reflector attached to fiber with a laser interferometer. The potential of the method is demonstrated by measuring acoustic pressure of an air coupled transducer, and the variation of acoustic pressure in the focal region of an air coupled acoustic lens. In the current experimental arrangement an approximate spatial resolution of 250 microns and an approximate acoustic pressure of 7 mPa have been demonstrated. A physics based mathematical model is presented that has been used to analyze the spatial resolution and acoustic pressure. Limitations of the method and possible improvements to achieve higher spatial and temporal resolution are discussed.

  16. Microscopic analysis of filament in air

    DTIC Science & Technology

    2016-09-13

    in a chamber. Recently there had been reports that ”air lasing” is due to electron recollision in neutral and ionized molecular nitrogen in air, this...reconstruct the scene of the interaction. After the laser pulse has been sapped by the interaction, it is often ignored. In filament studies however...assembly of oscillating dipoles that radiate back into the applied field, but, in addition to the index contribution of the neutral molecules, the fields

  17. Studies on UV filaments in air

    SciTech Connect

    Schwarz, J.; Rambo, P.; Diels, J.C.; Luk, T.S.; Bernstein, A.C.; Cameron, S.M.

    2000-01-05

    UV filaments in air have been examined on the basis of the diameter and length of the filament, the generation of new spectral components, and the ionization by multiphoton processes. There have been numerous observations of filaments at 800 nm. The general perception is that, above a critical power, the beam focuses because nonlinear self-lensing overcomes diffraction. The self-focusing proceeds until an opposing higher order nonlinearity forms a stable balance.

  18. Topological data analysis of contagion maps for examining spreading processes on networks

    PubMed Central

    Taylor, Dane; Klimm, Florian; Harrington, Heather A.; Kramár, Miroslav; Mischaikow, Konstantin; Porter, Mason A.; Mucha, Peter J.

    2015-01-01

    Social and biological contagions are influenced by the spatial embeddedness of networks. Historically, many epidemics spread as a wave across part of the Earth’s surface; however, in modern contagions long-range edges—for example, due to airline transportation or communication media—allow clusters of a contagion to appear in distant locations. Here we study the spread of contagions on networks through a methodology grounded in topological data analysis and nonlinear dimension reduction. We construct “contagion maps” that use multiple contagions on a network to map the nodes as a point cloud. By analyzing the topology, geometry, and dimensionality of manifold structure in such point clouds, we reveal insights to aid in the modeling, forecast, and control of spreading processes. Our approach highlights contagion maps also as a viable tool for inferring low-dimensional structure in networks. PMID:26194875

  19. Topological data analysis of contagion maps for examining spreading processes on networks

    NASA Astrophysics Data System (ADS)

    Taylor, Dane; Klimm, Florian; Harrington, Heather A.; Kramár, Miroslav; Mischaikow, Konstantin; Porter, Mason A.; Mucha, Peter J.

    2015-07-01

    Social and biological contagions are influenced by the spatial embeddedness of networks. Historically, many epidemics spread as a wave across part of the Earth's surface; however, in modern contagions long-range edges--for example, due to airline transportation or communication media--allow clusters of a contagion to appear in distant locations. Here we study the spread of contagions on networks through a methodology grounded in topological data analysis and nonlinear dimension reduction. We construct `contagion maps' that use multiple contagions on a network to map the nodes as a point cloud. By analysing the topology, geometry and dimensionality of manifold structure in such point clouds, we reveal insights to aid in the modelling, forecast and control of spreading processes. Our approach highlights contagion maps also as a viable tool for inferring low-dimensional structure in networks.

  20. Quantification of Cell Edge Velocities and Traction Forces Reveals Distinct Motility Modules during Cell Spreading

    PubMed Central

    Cai, Yunfei; Xenias, Harry; Spielman, Ingrid; Shneidman, Anna V.; David, Lawrence A.; Döbereiner, Hans-Günther; Wiggins, Chris H.; Sheetz, Michael P.

    2008-01-01

    Actin-based cell motility and force generation are central to immune response, tissue development, and cancer metastasis, and understanding actin cytoskeleton regulation is a major goal of cell biologists. Cell spreading is a commonly used model system for motility experiments – spreading fibroblasts exhibit stereotypic, spatially-isotropic edge dynamics during a reproducible sequence of functional phases: 1) During early spreading, cells form initial contacts with the surface. 2) The middle spreading phase exhibits rapidly increasing attachment area. 3) Late spreading is characterized by periodic contractions and stable adhesions formation. While differences in cytoskeletal regulation between phases are known, a global analysis of the spatial and temporal coordination of motility and force generation is missing. Implementing improved algorithms for analyzing edge dynamics over the entire cell periphery, we observed that a single domain of homogeneous cytoskeletal dynamics dominated each of the three phases of spreading. These domains exhibited a unique combination of biophysical and biochemical parameters – a motility module. Biophysical characterization of the motility modules revealed that the early phase was dominated by periodic, rapid membrane blebbing; the middle phase exhibited continuous protrusion with very low traction force generation; and the late phase was characterized by global periodic contractions and high force generation. Biochemically, each motility module exhibited a different distribution of the actin-related protein VASP, while inhibition of actin polymerization revealed different dependencies on barbed-end polymerization. In addition, our whole-cell analysis revealed that many cells exhibited heterogeneous combinations of motility modules in neighboring regions of the cell edge. Together, these observations support a model of motility in which regions of the cell edge exhibit one of a limited number of motility modules that, together

  1. Scale-free correlations in the geographical spreading of obesity

    NASA Astrophysics Data System (ADS)

    Gallos, Lazaros; Barttfeld, Pablo; Havlin, Shlomo; Sigman, Mariano; Makse, Hernan

    2012-02-01

    Obesity levels have been universally increasing. A crucial problem is to determine the influence of global and local drivers behind the obesity epidemic, to properly guide effective policies. Despite the numerous factors that affect the obesity evolution, we show a remarkable regularity expressed in a predictable pattern of spatial long-range correlations in the geographical spreading of obesity. We study the spatial clustering of obesity and a number of related health and economic indicators, and we use statistical physics methods to characterize the growth of the resulting clusters. The resulting scaling exponents allow us to broadly classify these indicators into two separate universality classes, weakly or strongly correlated. Weak correlations are found in generic human activity such as population distribution and the growth of the whole economy. Strong correlations are recovered, among others, for obesity, diabetes, and the food industry sectors associated with food consumption. Obesity turns out to be a global problem where local details are of little importance. The long-range correlations suggest influence that extends to large scales, hinting that the physical model of obesity clustering can be mapped to a long-range correlated percolation process.

  2. Long-range epidemic spreading in a random environment

    NASA Astrophysics Data System (ADS)

    Juhász, Róbert; Kovács, István A.; Iglói, Ferenc

    2015-03-01

    Modeling long-range epidemic spreading in a random environment, we consider a quenched, disordered, d -dimensional contact process with infection rates decaying with distance as 1 /rd +σ . We study the dynamical behavior of the model at and below the epidemic threshold by a variant of the strong-disorder renormalization-group method and by Monte Carlo simulations in one and two spatial dimensions. Starting from a single infected site, the average survival probability is found to decay as P (t ) ˜t-d /z up to multiplicative logarithmic corrections. Below the epidemic threshold, a Griffiths phase emerges, where the dynamical exponent z varies continuously with the control parameter and tends to zc=d +σ as the threshold is approached. At the threshold, the spatial extension of the infected cluster (in surviving trials) is found to grow as R (t ) ˜t1 /zc with a multiplicative logarithmic correction and the average number of infected sites in surviving trials is found to increase as Ns(t ) ˜(lnt) χ with χ =2 in one dimension.

  3. Long-range epidemic spreading in a random environment.

    PubMed

    Juhász, Róbert; Kovács, István A; Iglói, Ferenc

    2015-03-01

    Modeling long-range epidemic spreading in a random environment, we consider a quenched, disordered, d-dimensional contact process with infection rates decaying with distance as 1/rd+σ. We study the dynamical behavior of the model at and below the epidemic threshold by a variant of the strong-disorder renormalization-group method and by Monte Carlo simulations in one and two spatial dimensions. Starting from a single infected site, the average survival probability is found to decay as P(t)∼t-d/z up to multiplicative logarithmic corrections. Below the epidemic threshold, a Griffiths phase emerges, where the dynamical exponent z varies continuously with the control parameter and tends to zc=d+σ as the threshold is approached. At the threshold, the spatial extension of the infected cluster (in surviving trials) is found to grow as R(t)∼t1/zc with a multiplicative logarithmic correction and the average number of infected sites in surviving trials is found to increase as Ns(t)∼(lnt)χ with χ=2 in one dimension.

  4. Spatial Moran models, II: cancer initiation in spatially structured tissue

    PubMed Central

    Foo, J; Leder, K

    2016-01-01

    We study the accumulation and spread of advantageous mutations in a spatial stochastic model of cancer initiation on a lattice. The parameters of this general model can be tuned to study a variety of cancer types and genetic progression pathways. This investigation contributes to an understanding of how the selective advantage of cancer cells together with the rates of mutations driving cancer, impact the process and timing of carcinogenesis. These results can be used to give insights into tumor heterogeneity and the “cancer field effect,” the observation that a malignancy is often surrounded by cells that have undergone premalignant transformation. PMID:26126947

  5. 9 CFR 319.762 - Ham spread, tongue spread, and similar products.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... AND VOLUNTARY INSPECTION AND CERTIFICATION DEFINITIONS AND STANDARDS OF IDENTITY OR COMPOSITION Meat... Spread,” and similar products shall contain not less than 50 percent of the meat ingredient...

  6. 9 CFR 319.762 - Ham spread, tongue spread, and similar products.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... AND VOLUNTARY INSPECTION AND CERTIFICATION DEFINITIONS AND STANDARDS OF IDENTITY OR COMPOSITION Meat... Spread,” and similar products shall contain not less than 50 percent of the meat ingredient...

  7. 9 CFR 319.762 - Ham spread, tongue spread, and similar products.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... AND VOLUNTARY INSPECTION AND CERTIFICATION DEFINITIONS AND STANDARDS OF IDENTITY OR COMPOSITION Meat... Spread,” and similar products shall contain not less than 50 percent of the meat ingredient...

  8. Point spread functions in imaging a Lambert surface from zenith through a thin scattering layer

    NASA Technical Reports Server (NTRS)

    Otterman, J.; Rehavi, S.; Dishon, M.

    1983-01-01

    Analytical techniques for good spatial resolution in remotely sensed images of renewable resources, such as crops, are discussed for satellite multispectral radiometry. A model is developed for an optically and geometrically thin scattering layer to account for atmospheric scattering above the object pixel of fluxes reflected from adjacent areas. The cross radiance is explored as a spread function of a point source and as a spurious component of measured radiance, and an integration over large source areas is formulated. The Henyey-Greenstein (HG) phase function is defined for an integral over a sphere and point-spread functions are presented for HG scattering. Cross radiance limited spatial resolution is also determined for the HG phase function and boundaries between reflecting and black half-planes are considered in terms of the cross radiance.

  9. Microenvironmental cooperation promotes early spread and bistability of a Warburg-like phenotype.

    PubMed

    Fernandez-de-Cossio-Diaz, Jorge; De Martino, Andrea; Mulet, Roberto

    2017-06-08

    We introduce an in silico model for the initial spread of an aberrant phenotype with Warburg-like overflow metabolism within a healthy homeostatic tissue in contact with a nutrient reservoir (the blood), aimed at characterizing the role of the microenvironment for aberrant growth. Accounting for cellular metabolic activity, competition for nutrients, spatial diffusion and their feedbacks on aberrant replication and death rates, we obtain a phase portrait where distinct asymptotic whole-tissue states are found upon varying the tissue-blood turnover rate and the level of blood-borne primary nutrient. Over a broad range of parameters, the spreading dynamics is bistable as random fluctuations can impact the final state of the tissue. Such a behaviour turns out to be linked to the re-cycling of overflow products by non-aberrant cells. Quantitative insight on the overall emerging picture is provided by a spatially homogeneous version of the model.

  10. Acoustic tomographic imaging of temperature and flow fields in air

    NASA Astrophysics Data System (ADS)

    Barth, Manuela; Raabe, Armin

    2011-03-01

    Acoustic travel-time tomography is a remote sensing technique that uses the dependence of sound speed in air on temperature and wind speed along the sound propagation path. Travel-time measurements of acoustic signals between several sound sources and receivers travelling along different paths through a measuring area give information on the spatial distribution of temperature and flow fields within the area. After a separation of the two influences, distributions of temperature and flow can be reconstructed using inverse algorithms. As a remote sensing method, one advantage of acoustic travel-time tomography is its ability to measure temperature and flow field quantities without disturbing the area under investigation due to insertion of sensors. Furthermore, the two quantities—temperature and flow velocity—can be recorded simultaneously with this measurement method. In this paper, an acoustic tomographic measurement system is introduced which is capable of resolving three-dimensional distributions of temperature and flow fields in air within a certain volume (1.3 m × 1.0 m × 1.2 m) using 16 acoustic transmitter-receiver pairs. First, algorithms for the 3D reconstruction of distributions from line-integrated measurements are presented. Moreover, a measuring apparatus is introduced which is suited for educational purposes, for demonstration of the method as well as for indoor investigations. Example measurements within a low-speed wind tunnel with different incident flow situations (e.g. behind bluff bodies) using this system are shown. Visualizations of the flow illustrate the plausibility of the tomographically reconstructed flow structures. Furthermore, alternative individual measurement methods for temperature and flow speed provide comparable results.

  11. Bifurcations, crisis, unstable dimension variability and the spreading transition in the coupled sine circle map system

    NASA Astrophysics Data System (ADS)

    Das, A.; Jabeen, Z.; Gupte, N.

    2014-12-01

    The dynamical behavior of spatially extended dynamical systems can have interesting consequences for their statistics. We demonstrate this in a specific context, a system of coupled sine circle maps, and discuss the interconnection between the statistical and dynamical behaviors of the system. The system has an interesting phase diagram in parameter space wherein a spreading transition is seen across an infection line, with spatio-temporal and spatial intermittency of distinct universality classes (directed percolation and non-directed percolation) seen in the spreading/non-spreading regimes. The dynamical origins of the spreading transition, lie in a crisis arising from a tangent bifurcation in the system. In addition to changing the statistics, and therefore the universality class of the system, the crisis also has dynamical consequences. Unstable dimension variability is seen in the neighbourhood of this crisis, and multiple routes to crisis are seen due to the presence of multi-attractor solutions. We examine the system using a variety of characterizers such as finite time Lyapunov exponents and their distributions. We discuss the signatures of the phenomena seen in the quantifiers, and also whether similar techniques can be extended to other situations. Finally, we demonstrate the success of the quantifiers in another regime, spatio-temporal intermittency with travelling wave laminar solutions, and a solitonic regime.

  12. Oceanic core complex development at the ultraslow spreading Mid-Cayman Spreading Center

    NASA Astrophysics Data System (ADS)

    Hayman, N. W.; Grindlay, N.; Perfit, M. R.; Mann, P.; Leroy, S.; Mercier De Lepinay, B. F.

    2011-12-01

    The Mid-Cayman Spreading Center (MCSC) was one of the early localities for seafloor studies of upper mantle and lower crustal exhumation during seafloor spreading. It has since garnered new attention as an accessible locality in which to study an ultraslow spreading center (15-17 mm per year, full rate) that hosts both axial and axial-flank hydrothermal vent sites. Additionally, there is a longstanding suggestion that the end-member axial depth, crustal thickness, and basalt composition at the MCSC are due to the thermal structure of the underlying mantle, a relationship widely applied at other spreading centers. Through a compilation of both previously published and unpublished data, the MCSC is here shown to have intraridge rift walls defined by kilometer-scale steeply-dipping escarpments and curviplanar massifs. Dredging and near-bottom work has imaged and sampled predominantly basaltic lavas from the greatest axial depths and about 15 percent peridotite surrounded by gabbroic rocks from the prominent massifs. The gabbroic rocks exhibit wide compositional variation (troctolites to ferrogabbros) and in many places contain high-temperature (amphibolite to granulite facies) shear zones. Gabbroic compositions primarily reflect the accumulation of near-liquidus phases that crystallized from a range of basaltic melts, as well as from interactions with interstitial melts in a subaxial mush zone. Magnetization variations inverted from aeromagnetic data are consistent with a discontinuous distribution of basaltic lavas and asymmetric spreading since the end of the Eocene rift-to-drift transition. These observations support an Oceanic Core Complex model for MCSC seafloor spreading through mush zone and detachment fault crustal processes. Additional near-bottom work in the MCSC along with seismic data acquisition will be required to further evaluate the magmatic system, kinematics of seafloor spreading, and importance and dynamics of mantle exhumation, in this potential

  13. Disease Spreading Model with Partial Isolation

    NASA Astrophysics Data System (ADS)

    Chakraborty, Abhijit; Manna, S. S.

    2013-08-01

    The effect of partial isolation has been studied in disease spreading processes using the framework of susceptible-infected-susceptible (SIS) and susceptible-infected-recovered (SIR) models. The partial isolation is introduced by imposing a restriction: each infected individual can probabilistically infect up to a maximum number n of his susceptible neighbors, but not all. It has been observed that the critical values of the spreading rates for endemic states are non-zero in both models and decrease as 1/n with n, on all graphs including scale-free graphs. In particular, the SIR model with n = 2 turned out to be a special case, characterized by a new bond percolation threshold on square lattice.

  14. Spreading Dynamics Following Bursty Activity Patterns

    NASA Astrophysics Data System (ADS)

    Vazquez, Alexei

    The dynamics of many social, technological and economic phenomena are driven by individual human actions, turning the quantitative understanding of human behavior into a central question of modern science. Recent empirical evidence indicates that the timing of individual human actions follow non-Poisson statistics, characterized by bursts of rapidly occurring events separated by long periods of inactivity. In this work we analyze how this bursty dynamics impacts the dynamics of spreading processes in computer and social systems. We demonstrate that the non-Poisson nature of the contact dynamics results in prevalence decay times significantly larger than predicted by the standard Poisson process based models. Thanks to this slow dynamics the spreading entity, namely a virus, rumor, etc., can persist in the system for long times.

  15. Epidemic spreading on weighted complex networks

    NASA Astrophysics Data System (ADS)

    Sun, Ye; Liu, Chuang; Zhang, Chu-Xu; Zhang, Zi-Ke

    2014-01-01

    Nowadays, the emergence of online services provides various multi-relation information to support the comprehensive understanding of the epidemic spreading process. In this Letter, we consider the edge weights to represent such multi-role relations. In addition, we perform detailed analysis of two representative metrics, outbreak threshold and epidemic prevalence, on SIS and SIR models. Both theoretical and simulation results find good agreements with each other. Furthermore, experiments show that, on fully mixed networks, the weight distribution on edges would not affect the epidemic results once the average weight of whole network is fixed. This work may shed some light on the in-depth understanding of epidemic spreading on multi-relation and weighted networks.

  16. Spreading and fingering in spin coating

    NASA Astrophysics Data System (ADS)

    Holloway, Kristi E.; Habdas, Piotr; Semsarillar, Naeim; Burfitt, Kim; de Bruyn, John R.

    2007-04-01

    We study the spreading and fingering of drops of silicone oil on a rotating substrate for a range of rotation speeds and drop volumes. The spreading of the drop prior to the onset of fingering is found to follow the theoretically predicted time dependence, but with a large shift in time scale. For the full range of experimental parameters studied, the contact line becomes unstable and fingers develop when the radius of the drop becomes sufficiently large. We study the growth of perturbations around the perimeter of the drop and find the growth rate of the most unstable mode to agree well with the predictions of lubrication theory. The number of fingers which form around the perimeter of the drop is found to be a function of both rotation speed and drop volume, and is also in excellent agreement with theoretical predictions.

  17. Hydrothermal processes at seafloor spreading centers,

    SciTech Connect

    Rona, P.A.; Bostrom, K.; Laubier, L.; Smith, K.L.

    1983-01-01

    This book examines research on the description and interpretation of hydrothermal and associated phenomena at seafloor spreading centers. An interdisciplinary overview of the subject is presented, including geological, geophysical, geochemical, and biological discoveries. The implications of the discoveries for understanding the earth's heat transfer, geochemical mass balances and cycles, mineralization, and biological adaptation are discussed. Topics considered include geologic setting (e.g., the four dimensions of the spreading axis, geological processes of the mid-ocean ridge), hydrothermal convection (e.g., oxygen and hydrogen isotope studies, the basic physics of water penetration into hot rock), Iceland and oceanic ridges (e.g., chemical evidence from Icelandic geothermal systems, the physical environment of hydrothermal systems), mass balances and cycles (e.g., reduced gases and bacteria in hydrothermal fluids, the effects of hydrothermal activity on sedimentary organic matter), ferromanganese deposits, hydrothermal mineralization, and the biology of hydrothermal vents.

  18. Epidemic spreading driven by biased random walks

    NASA Astrophysics Data System (ADS)

    Pu, Cunlai; Li, Siyuan; Yang, Jian

    2015-08-01

    Random walk is one of the basic mechanisms of many network-related applications. In this paper, we study the dynamics of epidemic spreading driven by biased random walks in complex networks. In our epidemic model, infected nodes send out infection packets by biased random walks to their neighbor nodes, and this causes the infection of susceptible nodes that receive the packets. Infected nodes recover from the infection at a constant rate λ, and will not be infected again after recovery. We obtain the largest instantaneous number of infected nodes and the largest number of ever-infected nodes respectively, by tuning the parameter α of the biased random walks. Simulation results on model and real-world networks show that spread of the epidemic becomes intense and widespread with increase of either delivery capacity of infected nodes, average node degree, or homogeneity of node degree distribution.

  19. Update on college and university programs in air pollution control

    SciTech Connect

    Cota, H.M.

    1983-04-01

    A survey of academic programs in air pollution control was made. Results from the 127 schools reporting are tabulated by state. Faculty involved in air pollution instruction are identified. Some conclusions and recommendations are presented. 1 figure, 5 tables.

  20. Computational And Experimental Studies Of Three-Dimensional Flame Spread Over Liquid Fuel Pools

    NASA Technical Reports Server (NTRS)

    Ross, Howard D. (Technical Monitor); Cai, Jinsheng; Liu, Feng; Sirignano, William A.; Miller, Fletcher J.

    2003-01-01

    Schiller, Ross, and Sirignano (1996) studied ignition and flame spread above liquid fuels initially below the flashpoint temperature by using a two-dimensional computational fluid dynamics code that solves the coupled equations of both the gas and the liquid phases. Pulsating flame spread was attributed to the establishment of a gas-phase recirculation cell that forms just ahead of the flame leading edge because of the opposing effect of buoyancy-driven flow in the gas phase and the thermocapillary-driven flow in the liquid phase. Schiller and Sirignano (1996) extended the same study to include flame spread with forced opposed flow in the gas phase. A transitional flow velocity was found above which an originally uniform spreading flame pulsates. The same type of gas-phase recirculation cell caused by the combination of forced opposed flow, buoyancy-driven flow, and thermocapillary-driven concurrent flow was responsible for the pulsating flame spread. Ross and Miller (1998) and Miller and Ross (1998) performed experimental work that corroborates the computational findings of Schiller, Ross, and Sirignano (1996) and Schiller and Sirignano (1996). Cai, Liu, and Sirignano (2002) developed a more comprehensive three-dimensional model and computer code for the flame spread problem. Many improvements in modeling and numerical algorithms were incorporated in the three-dimensional model. Pools of finite width and length were studied in air channels of prescribed height and width. Significant three-dimensional effects around and along the pool edge were observed. The same three-dimensional code is used to study the detailed effects of pool depth, pool width, opposed air flow velocity, and different levels of air oxygen concentration (Cai, Liu, and Sirignano, 2003). Significant three-dimensional effects showing an unsteady wavy flame front for cases of wide pool width are found for the first time in computation, after being noted previously by experimental observers (Ross

  1. Direct-Sequence Spread Spectrum System

    DTIC Science & Technology

    1990-06-01

    by directly modulating a conventional narrowband frequency-modulated (FM) carrier by a high rate digital code. The direct modulation is binary phase ...specification of the DSSS system will not be developed. The results of the evaluation phase of this research will be compared against theoretical...spread spectrum is called binary phase -shift keying 19 (BPSK). BPSK is a modulation in which a binary Ŕ" represents a 0-degree relative phase

  2. Morphogenetic action through flux-limited spreading

    NASA Astrophysics Data System (ADS)

    Verbeni, M.; Sánchez, O.; Mollica, E.; Siegl-Cachedenier, I.; Carleton, A.; Guerrero, I.; Ruiz i Altaba, A.; Soler, J.

    2013-12-01

    A central question in biology is how secreted morphogens act to induce different cellular responses within a group of cells in a concentration-dependent manner. Modeling morphogenetic output in multicellular systems has so far employed linear diffusion, which is the normal type of diffusion associated with Brownian processes. However, there is evidence that at least some morphogens, such as Hedgehog (Hh) molecules, may not freely diffuse. Moreover, the mathematical analysis of such models necessarily implies unrealistic instantaneous spreading of morphogen molecules, which are derived from the assumptions of Brownian motion in its continuous formulation. A strict mathematical model considering Fick's diffusion law predicts morphogen exposure of the whole tissue at the same time. Such a strict model thus does not describe true biological patterns, even if similar and attractive patterns appear as results of applying such simple model. To eliminate non-biological behaviors from diffusion models we introduce flux-limited spreading (FLS), which implies a restricted velocity for morphogen propagation and a nonlinear mechanism of transport. Using FLS and focusing on intercellular Hh-Gli signaling, we model a morphogen gradient and highlight the propagation velocity of morphogen particles as a new key biological parameter. This model is then applied to the formation and action of the Sonic Hh (Shh) gradient in the vertebrate embryonic neural tube using our experimental data on Hh spreading in heterologous systems together with published data. Unlike linear diffusion models, FLS modeling predicts concentration fronts and the evolution of gradient dynamics and responses over time. In addition to spreading restrictions by extracellular binding partners, we suggest that the constraints imposed by direct bridges of information transfer such as nanotubes or cytonemes underlie FLS. Indeed, we detect and measure morphogen particle velocity in such cell extensions in different

  3. Prediction of fire spread following nuclear explosions

    Treesearch

    Craig C. Chandler; Theodore G. Storey; Charles D. Tangren

    1963-01-01

    Mass fires are likely to follow a nuclear attack. Since it is important to the civil defense program to be able to predict rate, duration, and extent of spread of such fires, the Office of Civil Defense, U.S. Department of Defense, issued a joint contract to the Forest Service and to United Research Services, Inc., to study this field. We surveyed the literature,...

  4. Spectrally Shaped Random-Phase Spreading Functions

    DTIC Science & Technology

    2003-10-24

    gain reduction due to reference function windowing. 18 3.3 Excision of narrow band interference. 19 4 4.1 Hardware based adaptive system with...frequency-spread CW interference falling within the data-rate bandwidth. Assuming that fref(t) is at base band, i.e. having a spectrum extending from zero...report describes the baseband hardware demonstrator based upon AT&T DSP32C digital signal processing cards in an IBM personal computer host platform, and

  5. Morphogenetic action through flux-limited spreading.

    PubMed

    Verbeni, M; Sánchez, O; Mollica, E; Siegl-Cachedenier, I; Carleton, A; Guerrero, I; Ruiz i Altaba, A; Soler, J

    2013-12-01

    A central question in biology is how secreted morphogens act to induce different cellular responses within a group of cells in a concentration-dependent manner. Modeling morphogenetic output in multicellular systems has so far employed linear diffusion, which is the normal type of diffusion associated with Brownian processes. However, there is evidence that at least some morphogens, such as Hedgehog (Hh) molecules, may not freely diffuse. Moreover, the mathematical analysis of such models necessarily implies unrealistic instantaneous spreading of morphogen molecules, which are derived from the assumptions of Brownian motion in its continuous formulation. A strict mathematical model considering Fick's diffusion law predicts morphogen exposure of the whole tissue at the same time. Such a strict model thus does not describe true biological patterns, even if similar and attractive patterns appear as results of applying such simple model. To eliminate non-biological behaviors from diffusion models we introduce flux-limited spreading (FLS), which implies a restricted velocity for morphogen propagation and a nonlinear mechanism of transport. Using FLS and focusing on intercellular Hh-Gli signaling, we model a morphogen gradient and highlight the propagation velocity of morphogen particles as a new key biological parameter. This model is then applied to the formation and action of the Sonic Hh (Shh) gradient in the vertebrate embryonic neural tube using our experimental data on Hh spreading in heterologous systems together with published data. Unlike linear diffusion models, FLS modeling predicts concentration fronts and the evolution of gradient dynamics and responses over time. In addition to spreading restrictions by extracellular binding partners, we suggest that the constraints imposed by direct bridges of information transfer such as nanotubes or cytonemes underlie FLS. Indeed, we detect and measure morphogen particle velocity in such cell extensions in different

  6. Large Scale Flame Spread Environmental Characterization Testing

    NASA Technical Reports Server (NTRS)

    Clayman, Lauren K.; Olson, Sandra L.; Gokoghi, Suleyman A.; Brooker, John E.; Ferkul, Paul V.; Kacher, Henry F.

    2013-01-01

    Under the Advanced Exploration Systems (AES) Spacecraft Fire Safety Demonstration Project (SFSDP), as a risk mitigation activity in support of the development of a large-scale fire demonstration experiment in microgravity, flame-spread tests were conducted in normal gravity on thin, cellulose-based fuels in a sealed chamber. The primary objective of the tests was to measure pressure rise in a chamber as sample material, burning direction (upward/downward), total heat release, heat release rate, and heat loss mechanisms were varied between tests. A Design of Experiments (DOE) method was imposed to produce an array of tests from a fixed set of constraints and a coupled response model was developed. Supplementary tests were run without experimental design to additionally vary select parameters such as initial chamber pressure. The starting chamber pressure for each test was set below atmospheric to prevent chamber overpressure. Bottom ignition, or upward propagating burns, produced rapid acceleratory turbulent flame spread. Pressure rise in the chamber increases as the amount of fuel burned increases mainly because of the larger amount of heat generation and, to a much smaller extent, due to the increase in gaseous number of moles. Top ignition, or downward propagating burns, produced a steady flame spread with a very small flat flame across the burning edge. Steady-state pressure is achieved during downward flame spread as the pressure rises and plateaus. This indicates that the heat generation by the flame matches the heat loss to surroundings during the longer, slower downward burns. One heat loss mechanism included mounting a heat exchanger directly above the burning sample in the path of the plume to act as a heat sink and more efficiently dissipate the heat due to the combustion event. This proved an effective means for chamber overpressure mitigation for those tests producing the most total heat release and thusly was determined to be a feasible mitigation

  7. A constrained Gauss-Seidel method for correction of point spread function effect in MR spectroscopic imaging.

    PubMed

    Angelie, E; Sappey-Marinier, D; Mallet, J; Bonmartin, A; Sau, J

    2000-06-01

    Magnetic resonance spectroscopic imaging is limited by a low signal-to-noise ratio, so a compromise between spatial resolution and examination time is needed in clinical application. The reconstruction of truncated signal introduces a Point Spread Function that considerably affects the spatial resolution. In order to reduce spatial contamination, three methods, applied after Fourier transform image reconstruction, based on deconvolution or iterative techniques are tested to decrease Point Spread Function contamination. A Gauss-Seidel (GS) algorithm is used for iterative techniques with and without a non-negative constraint (GS+). Convergence and noise dependence studies of the GS algorithm have been done. The linear property of contamination was validated on a point sample phantom. A significant decrease of contamination without broadening the spatial resolution was obtained with GS+ method compared to a conventional apodization. This post-processing method can provide a contrast enhancement of clinical spectroscopic images without changes in acquisition time.

  8. Image reconstruction with analytical point spread functions

    NASA Astrophysics Data System (ADS)

    Asensio Ramos, A.; López Ariste, A.

    2010-07-01

    Context. The image degradation produced by atmospheric turbulence and optical aberrations is usually alleviated using post-facto image reconstruction techniques, even when observing with adaptive optics systems. Aims: These techniques rely on the development of the wavefront using Zernike functions and the non-linear optimization of a certain metric. The resulting optimization procedure is computationally heavy. Our aim is to alleviate this computational burden. Methods: We generalize the extended Zernike-Nijboer theory to carry out the analytical integration of the Fresnel integral and present a natural basis set for the development of the point spread function when the wavefront is described using Zernike functions. Results: We present a linear expansion of the point spread function in terms of analytic functions, which, in addition, takes defocusing into account in a natural way. This expansion is used to develop a very fast phase-diversity reconstruction technique, which is demonstrated in terms of some applications. Conclusions: We propose that the linear expansion of the point spread function can be applied to accelerate other reconstruction techniques in use that are based on blind deconvolution.

  9. Physical model for membrane protrusions during spreading

    PubMed Central

    Chamaraux, François; Ali, Olivier; Keller, Sébastien; Bruckert, Franz; Fourcade, Bertrand

    2008-01-01

    During cell spreading onto a substrate, the kinetics of the contact area is an observable quantity. This paper is concerned with a physical approach to model this process in the case of ameboid motility where the membrane detaches itself from the underlying cytoskeleton at the leading edge. The physical model we propose is based on previous reports which point out that membrane tension regulates cell spreading. Using a phenomenological feedback loop to mimic stress dependent biochemistry, we show that the actin polymerisation rate can be coupled to the stress which builds up at the margin of the contact area between the cell and the substrate. In the limit of small variation of membrane tension, we show that the actin polymerisation rate can be written in closed form. Our analysis defines characteristic lengths which depend on elastic properties of the membrane-cytoskeleton complex, such as the membrane-cytoskeleton interaction, and on molecular parameters, such as the rate of actin polymerisation. We discuss our model in the case of axi-symmetric and non axi-symmetric spreading and we compute the characteristic time scales as a function of fundamental elastic constants such as the strength of membrane-cytoskeleton adherence. PMID:18824791

  10. Spreading the word ... hospice information systems.

    PubMed

    Jackson, Avril; Hodson, Melanie; Brady, Denise; Pahl, Nick

    The rapid spread of Saunders' thinking across the world has been facilitated by the Hospice Information service and library at St Christopher's Hospice which she helped to create and further enhanced by Help the Hospices. We have set this article in the context of the Web and other information systems as they are developing today. "Connecting people" and "collecting people's experiences" were terms often used by Cicely Saunders when she described the work of Hospice Information, a service that has in some measure contributed to the rapid spread of her thinking across the world and which is currently in close contact with palliative care workers in over 120 countries. Connecting--or networking--putting people and organizations in touch with each other for mutual benefit and collecting and disseminating people's experiences are central to our work as a U.K. and international resource on hospice and palliative care for professionals and the public. Add to these the crucial role of information provision and advocacy for patients, carers, and health professionals alike and we hope that you may begin to appreciate how our respective organizations have contributed to the spread of Cicely Saunders' vision.

  11. On pool spreading around tanks: geometrical considerations.

    PubMed

    Brambilla, Sara; Manca, Davide

    2008-10-01

    The paper discusses a straightforward approach for evaluating the distance covered by a spreading liquid pool, when the axisymmetric hypothesis is no longer valid. This distance is evaluated by a three-steps methodology: the pre-processing of input data (bund radius, if present, and radial velocity); the simulation of pool spreading by a model based on the axisymmetric hypothesis; and the post-processing of results. The paper reports some geometrical correlations to pre- and post-process the data, with regard to four case-studies. Some numerical examples are also presented to prove that the pre-processed input data and post-processed results differ from those based on the axisymmetric hypothesis. Finally, we validate our modeling approach with the experimental data of Cronin and Evans [P.S. Cronin, J.A. Evans, A series of experiments to study the spreading of liquid pools with different bund arrangements, HSE Contract Research Report 405/2002, Advantica Technologies Limited, 2002].

  12. Branching dynamics of viral information spreading

    NASA Astrophysics Data System (ADS)

    Iribarren, José Luis; Moro, Esteban

    2011-10-01

    Despite its importance for rumors or innovations propagation, peer-to-peer collaboration, social networking, or marketing, the dynamics of information spreading is not well understood. Since the diffusion depends on the heterogeneous patterns of human behavior and is driven by the participants’ decisions, its propagation dynamics shows surprising properties not explained by traditional epidemic or contagion models. Here we present a detailed analysis of our study of real viral marketing campaigns where tracking the propagation of a controlled message allowed us to analyze the structure and dynamics of a diffusion graph involving over 31 000 individuals. We found that information spreading displays a non-Markovian branching dynamics that can be modeled by a two-step Bellman-Harris branching process that generalizes the static models known in the literature and incorporates the high variability of human behavior. It explains accurately all the features of information propagation under the “tipping point” and can be used for prediction and management of viral information spreading processes.

  13. Epidemic spreading on evolving signed networks.

    PubMed

    Saeedian, M; Azimi-Tafreshi, N; Jafari, G R; Kertesz, J

    2017-02-01

    Most studies of disease spreading consider the underlying social network as obtained without the contagion, though epidemic influences people's willingness to contact others: A "friendly" contact may be turned to "unfriendly" to avoid infection. We study the susceptible-infected disease-spreading model on signed networks, in which each edge is associated with a positive or negative sign representing the friendly or unfriendly relation between its end nodes. In a signed network, according to Heider's theory, edge signs evolve such that finally a state of structural balance is achieved, corresponding to no frustration in physics terms. However, the danger of infection affects the evolution of its edge signs. To describe the coupled problem of the sign evolution and disease spreading, we generalize the notion of structural balance by taking into account the state of the nodes. We introduce an energy function and carry out Monte Carlo simulations on complete networks to test the energy landscape, where we find local minima corresponding to the so-called jammed states. We study the effect of the ratio of initial friendly to unfriendly connections on the propagation of disease. The steady state can be balanced or a jammed state such that a coexistence occurs between susceptible and infected nodes in the system.

  14. Spread of epileptic activity in human brain

    NASA Astrophysics Data System (ADS)

    Milton, John

    1997-03-01

    For many patients with medically refractory epilepsy surgical resection of the site of seizure onset (epileptic focus) offers the best hope for cure. Determination of the nature of seizure propagation should lead to improved methods for locating the epileptic focus (and hence reduce patient morbidity) and possibly to new treatment modalities directed at blocking seizure spread. Theoretical studies of neural networks emphasize the role of traveling waves for the propagation of activity. However, the nature of seizure propagation in human brain remains poorly characterized. The spread of epileptic activity in patients undergoing presurgical evaluation for epilepsy surgery was measured by placing subdural grids of electrodes (interelectrode spacings of 3-10 mm) over the frontal and temporal lobes. The exact location of each electrode relative to the surface of the brain was determined using 3--D MRI imaging techniques. Thus it is possible to monitor the spread of epileptic activity in both space and time. The observations are discussed in light of models for seizure propagation.

  15. Branching dynamics of viral information spreading.

    PubMed

    Iribarren, José Luis; Moro, Esteban

    2011-10-01

    Despite its importance for rumors or innovations propagation, peer-to-peer collaboration, social networking, or marketing, the dynamics of information spreading is not well understood. Since the diffusion depends on the heterogeneous patterns of human behavior and is driven by the participants' decisions, its propagation dynamics shows surprising properties not explained by traditional epidemic or contagion models. Here we present a detailed analysis of our study of real viral marketing campaigns where tracking the propagation of a controlled message allowed us to analyze the structure and dynamics of a diffusion graph involving over 31,000 individuals. We found that information spreading displays a non-Markovian branching dynamics that can be modeled by a two-step Bellman-Harris branching process that generalizes the static models known in the literature and incorporates the high variability of human behavior. It explains accurately all the features of information propagation under the "tipping point" and can be used for prediction and management of viral information spreading processes.

  16. Wetting and spreading of individual latex particles

    SciTech Connect

    Unertl, W.N.; Luo, Y.; Woodland, D.; Bediwi, A.B.E.; Kamal, M.; El Farrash, A.E.

    1996-12-31

    The wetting and spreading of individual latex particles is an important factor in controlling the mechanical properties of coatings such as those used on paper. The interactions between latex particles that lead to coalescence and film formation has been extensively studied and the basic mechanisms have been identified. Surface aspects of the coalescence and film formation for bulk films and dense monolayers have also been studied including the effects of surfactants. However, in many practical applications, including most paper coatings, latex is present in concentrations that are too small for latex-latex interactions to be important. In these applications, the wetting, spreading, and adhesion of individual latex particles on surfaces of the other constituents of the coating are most important. In spite of its importance, this topic has received little attention. This paper describes measurements of the contact angle {theta} and determination of the work of adhesion W of styrene-butadiene latex particles on calcite, mica, cellophane, and polystyrene surfaces. The effects of humidity and latex glass transition temperature on the wetting and spreading are also described. Some implications for the strength of coatings containing low levels of latex binders are also discussed.

  17. Spread Across Liquids Continues to Fly

    NASA Technical Reports Server (NTRS)

    Miller, Fletcher J.

    2001-01-01

    The physics and behavior of a flame spreading across a flammable liquid is an active area of research at the NASA Glenn Research Center. Spills of fuels and other liquids often result in considerable fire hazards, and much remains unknown about the details of how a flame, once ignited, moves across a pool. The depth of the liquid or size of the spill, the temperature, and wind, if any, can all complicate the combustion processes. In addition, with the advent of the International Space Station there may be fire hazards associated with cleaning, laboratory, or other fluids in space, and it is essential to understand the role that gravity plays in such situations. The Spread Across Liquids (SAL) experiment is an experimental and computational effort dedicated to understanding the detailed mechanisms of flame spread across a flammable liquid initially below its flashpoint temperature. The experimental research is being carried out in-house by a team of researchers from Glenn, the National Center for Microgravity Combustion, and Zin Technologies, with computer modeling being provided via a grant with the University of California, Irvine. Glenn's Zero Gravity Facility is used to achieve short microgravity periods, and normal gravity testing is done in the Space Experiments Laboratory. To achieve longer periods of microgravity, the showcase SAL hardware flies aboard a sounding rocket launched from White Sands Missile Range, New Mexico, approximately once per year. In addition to extended microgravity, this carrier allows the use of detailed diagnostics that cannot be employed in a drop tower.

  18. Network analysis of global influenza spread.

    PubMed

    Chan, Joseph; Holmes, Antony; Rabadan, Raul

    2010-11-18

    Although vaccines pose the best means of preventing influenza infection, strain selection and optimal implementation remain difficult due to antigenic drift and a lack of understanding global spread. Detecting viral movement by sequence analysis is complicated by skewed geographic and seasonal distributions in viral isolates. We propose a probabilistic method that accounts for sampling bias through spatiotemporal clustering and modeling regional and seasonal transmission as a binomial process. Analysis of H3N2 not only confirmed East-Southeast Asia as a source of new seasonal variants, but also increased the resolution of observed transmission to a country level. H1N1 data revealed similar viral spread from the tropics. Network analysis suggested China and Hong Kong as the origins of new seasonal H3N2 strains and the United States as a region where increased vaccination would maximally disrupt global spread of the virus. These techniques provide a promising methodology for the analysis of any seasonal virus, as well as for the continued surveillance of influenza.

  19. Did ice-age bovids spread tuberculosis?

    PubMed

    Rothschild, Bruce M; Martin, Larry D

    2006-11-01

    Pathognomonic metacarpal undermining is a skeletal pathology that has been associated with Mycobacterium tuberculosis in bovids. Postcranial artiodactyl, perissodactyl, and carnivore skeletons were examined in major university and museum collections of North America and Europe for evidence of this and other pathology potentially attributable to tuberculosis. Among nonproboscidean mammals from pre-Holocene North America, bone lesions indicative of tuberculosis were restricted to immigrant bovids from Eurasia. No bone lesions compatible with diagnosis of tuberculosis were found in large samples of other pre-Holocene (164 Oligocene, 397 Miocene, and 1,041 Plio-Pleistocene) North American mammals, including 114 antilocaprids. Given the unchanged frequency of bovid tubercular disease during the Pleistocene, it appears that most did not die from the disease but actually reached an accommodation with it (as did the mastodon) (Rothschild and Laub 2006). Thus, they were sufficiently long-lived to assure greater spread of the disease. The relationships of the proboscidean examples need further study, but present evidence suggests a Holarctic spread of tuberculosis during the Pleistocene, with bovids acting as vectors. While the role of other animals in the transmission of tuberculosis could be considered, the unique accommodation achieved by bovids and mastodons makes them the likely "culprits" in its spread.

  20. Epidemic spreading on evolving signed networks

    NASA Astrophysics Data System (ADS)

    Saeedian, M.; Azimi-Tafreshi, N.; Jafari, G. R.; Kertesz, J.

    2017-02-01

    Most studies of disease spreading consider the underlying social network as obtained without the contagion, though epidemic influences people's willingness to contact others: A "friendly" contact may be turned to "unfriendly" to avoid infection. We study the susceptible-infected disease-spreading model on signed networks, in which each edge is associated with a positive or negative sign representing the friendly or unfriendly relation between its end nodes. In a signed network, according to Heider's theory, edge signs evolve such that finally a state of structural balance is achieved, corresponding to no frustration in physics terms. However, the danger of infection affects the evolution of its edge signs. To describe the coupled problem of the sign evolution and disease spreading, we generalize the notion of structural balance by taking into account the state of the nodes. We introduce an energy function and carry out Monte Carlo simulations on complete networks to test the energy landscape, where we find local minima corresponding to the so-called jammed states. We study the effect of the ratio of initial friendly to unfriendly connections on the propagation of disease. The steady state can be balanced or a jammed state such that a coexistence occurs between susceptible and infected nodes in the system.

  1. Did ice-age bovids spread tuberculosis?

    NASA Astrophysics Data System (ADS)

    Rothschild, Bruce M.; Martin, Larry D.

    2006-11-01

    Pathognomonic metacarpal undermining is a skeletal pathology that has been associated with Mycobacterium tuberculosis in bovids. Postcranial artiodactyl, perissodactyl, and carnivore skeletons were examined in major university and museum collections of North America and Europe for evidence of this and other pathology potentially attributable to tuberculosis. Among nonproboscidean mammals from pre-Holocene North America, bone lesions indicative of tuberculosis were restricted to immigrant bovids from Eurasia. No bone lesions compatible with diagnosis of tuberculosis were found in large samples of other pre-Holocene (164 Oligocene, 397 Miocene, and 1,041 Plio Pleistocene) North American mammals, including 114 antilocaprids. Given the unchanged frequency of bovid tubercular disease during the Pleistocene, it appears that most did not die from the disease but actually reached an accommodation with it (as did the mastodon) (Rothschild and Laub 2006). Thus, they were sufficiently long-lived to assure greater spread of the disease. The relationships of the proboscidean examples need further study, but present evidence suggests a Holarctic spread of tuberculosis during the Pleistocene, with bovids acting as vectors. While the role of other animals in the transmission of tuberculosis could be considered, the unique accommodation achieved by bovids and mastodons makes them the likely “culprits” in its spread.

  2. Data driven computing by the morphing fast Fourier transform ensemble Kalman filter in epidemic spread simulations

    PubMed Central

    Mandel, Jan; Beezley, Jonathan D.; Cobb, Loren; Krishnamurthy, Ashok

    2010-01-01

    The FFT EnKF data assimilation method is proposed and applied to a stochastic cell simulation of an epidemic, based on the S-I-R spread model. The FFT EnKF combines spatial statistics and ensemble filtering methodologies into a localized and computationally inexpensive version of EnKF with a very small ensemble, and it is further combined with the morphing EnKF to assimilate changes in the position of the epidemic. PMID:21031155

  3. The Potential Role of Direct and Indirect Contacts on Infection Spread in Dairy Farm Networks

    PubMed Central

    Natalini, Silvano; Zarenghi, Luca; Ricchi, Matteo; Bolzoni, Luca

    2017-01-01

    Animals’ exchanges are considered the most effective route of between-farm infectious disease transmission. However, despite being often overlooked, the infection spread due to contaminated equipment, vehicles, or personnel proved to be important for several livestock epidemics. This study investigated the role of indirect contacts in a potential infection spread in the dairy farm network of the Province of Parma (Northern Italy). We built between-farm contact networks using data on cattle exchange (direct contacts), and on-farm visits by veterinarians (indirect contacts). We compared the features of the contact structures by using measures on static and temporal networks. We assessed the disease spreading potential of the direct and indirect network structures in the farm system by using data on the infection state of farms by paratuberculosis. Direct and indirect networks showed non-trivial differences with respect to connectivity, contact distribution, and super-spreaders identification. Furthermore, our analyses on paratuberculosis data suggested that the contributions of direct and indirect contacts on diseases spread are apparent at different spatial scales. Our results highlighted the potential role of indirect contacts in between-farm disease spread and underlined the need for a deeper understanding of these contacts to develop better strategies for prevention of livestock epidemics. PMID:28125610

  4. In Vivo Visualizations of Drought-Induced Embolism Spread in Vitis vinifera1[W][OA

    PubMed Central

    Brodersen, Craig Robert; McElrone, Andrew Joseph; Choat, Brendan; Lee, Eric Franklin; Shackel, Kenneth Andrew; Matthews, Mark Allen

    2013-01-01

    Long-distance water transport through plant xylem is vulnerable to hydraulic dysfunction during periods of increased tension on the xylem sap, often coinciding with drought. While the effects of local and systemic embolism on plant water transport and physiology are well documented, the spatial patterns of embolism formation and spread are not well understood. Using a recently developed nondestructive diagnostic imaging tool, high-resolution x-ray computed tomography, we documented the dynamics of drought-induced embolism in grapevine (Vitis vinifera) plants in vivo, producing the first three-dimensional, high-resolution, time-lapse observations of embolism spread. Embolisms formed first in the vessels surrounding the pith at stem water potentials of approximately –1.2 megapascals in drought experiments. As stem water potential decreased, embolisms spread radially toward the epidermis within sectored vessel groupings via intervessel connections and conductive xylem relays, and infrequently (16 of 629 total connections) through lateral connections into adjacent vessel sectors. Theoretical loss of conductivity calculated from the high-resolution x-ray computed tomography images showed good agreement with previously published nuclear magnetic resonance imaging and hydraulic conductivity experiments also using grapevine. Overall, these data support a growing body of evidence that xylem organization is critically important to the isolation of drought-induced embolism spread and confirm that air seeding through the pit membranes is the principle mechanism of embolism spread. PMID:23463781

  5. The spreading front of invasive species in favorable habitat or unfavorable habitat

    NASA Astrophysics Data System (ADS)

    Lei, Chengxia; Lin, Zhigui; Zhang, Qunying

    2014-07-01

    Spatial heterogeneity and habitat characteristic are shown to determine the asymptotic profile of the solution to a reaction-diffusion model with free boundary, which describes the moving front of the invasive species. A threshold value R0Fr(D,t) is introduced to determine the spreading and vanishing of the invasive species. We prove that if R0Fr(D,t0)⩾1 for some t0⩾0, the spreading must happen; while if R0Fr(D,0)<1, the spreading is also possible. Our results show that the species in the favorable habitat can establish itself if the diffusion is slow or the occupying habitat is large. In an unfavorable habitat, the species dies out if the initial value of the species is small. However, big initial number of the species is benefit for the species to survive. When the species spreads in the whole habitat, the asymptotic spreading speed is given. Some implications of these theoretical results are also discussed.

  6. The Potential Role of Direct and Indirect Contacts on Infection Spread in Dairy Farm Networks.

    PubMed

    Rossi, Gianluigi; De Leo, Giulio A; Pongolini, Stefano; Natalini, Silvano; Zarenghi, Luca; Ricchi, Matteo; Bolzoni, Luca

    2017-01-01

    Animals' exchanges are considered the most effective route of between-farm infectious disease transmission. However, despite being often overlooked, the infection spread due to contaminated equipment, vehicles, or personnel proved to be important for several livestock epidemics. This study investigated the role of indirect contacts in a potential infection spread in the dairy farm network of the Province of Parma (Northern Italy). We built between-farm contact networks using data on cattle exchange (direct contacts), and on-farm visits by veterinarians (indirect contacts). We compared the features of the contact structures by using measures on static and temporal networks. We assessed the disease spreading potential of the direct and indirect network structures in the farm system by using data on the infection state of farms by paratuberculosis. Direct and indirect networks showed non-trivial differences with respect to connectivity, contact distribution, and super-spreaders identification. Furthermore, our analyses on paratuberculosis data suggested that the contributions of direct and indirect contacts on diseases spread are apparent at different spatial scales. Our results highlighted the potential role of indirect contacts in between-farm disease spread and underlined the need for a deeper understanding of these contacts to develop better strategies for prevention of livestock epidemics.

  7. Deciphering the impact of uncertainty on the accuracy of large wildfire spread simulations.

    PubMed

    Benali, Akli; Ervilha, Ana R; Sá, Ana C L; Fernandes, Paulo M; Pinto, Renata M S; Trigo, Ricardo M; Pereira, José M C

    2016-11-01

    Predicting wildfire spread is a challenging task fraught with uncertainties. 'Perfect' predictions are unfeasible since uncertainties will always be present. Improving fire spread predictions is important to reduce its negative environmental impacts. Here, we propose to understand, characterize, and quantify the impact of uncertainty in the accuracy of fire spread predictions for very large wildfires. We frame this work from the perspective of the major problems commonly faced by fire model users, namely the necessity of accounting for uncertainty in input data to produce reliable and useful fire spread predictions. Uncertainty in input variables was propagated throughout the modeling framework and its impact was evaluated by estimating the spatial discrepancy between simulated and satellite-observed fire progression data, for eight very large wildfires in Portugal. Results showed that uncertainties in wind speed and direction, fuel model assignment and typology, location and timing of ignitions, had a major impact on prediction accuracy. We argue that uncertainties in these variables should be integrated in future fire spread simulation approaches, and provide the necessary data for any fire model user to do so.

  8. Topographic Cues Reveal Two Distinct Spreading Mechanisms in Blood Platelets

    NASA Astrophysics Data System (ADS)

    Sandmann, Rabea; Köster, Sarah

    2016-03-01

    Blood platelets are instrumental in blood clotting and are thus heavily involved in early wound closure. After adhering to a substrate they spread by forming protrusions like lamellipodia and filopodia. However, the interaction of these protrusions with the physical environment of platelets while spreading is not fully understood. Here we dynamically image platelets during this spreading process and compare their behavior on smooth and on structured substrates. In particular we analyze the temporal evolution of the spread area, the cell morphology and the dynamics of individual filopodia. Interestingly, the topographic cues enable us to distinguish two spreading mechanisms, one that is based on numerous persistent filopodia and one that rather involves lamellipodia. Filopodia-driven spreading coincides with a strong response of platelet morphology to the substrate topography during spreading, whereas lamellipodia-driven spreading does not. Thus, we quantify different degrees of filopodia formation in platelets and the influence of filopodia in spreading on structured substrates.

  9. Topographic Cues Reveal Two Distinct Spreading Mechanisms in Blood Platelets

    PubMed Central

    Sandmann, Rabea; Köster, Sarah

    2016-01-01

    Blood platelets are instrumental in blood clotting and are thus heavily involved in early wound closure. After adhering to a substrate they spread by forming protrusions like lamellipodia and filopodia. However, the interaction of these protrusions with the physical environment of platelets while spreading is not fully understood. Here we dynamically image platelets during this spreading process and compare their behavior on smooth and on structured substrates. In particular we analyze the temporal evolution of the spread area, the cell morphology and the dynamics of individual filopodia. Interestingly, the topographic cues enable us to distinguish two spreading mechanisms, one that is based on numerous persistent filopodia and one that rather involves lamellipodia. Filopodia-driven spreading coincides with a strong response of platelet morphology to the substrate topography during spreading, whereas lamellipodia-driven spreading does not. Thus, we quantify different degrees of filopodia formation in platelets and the influence of filopodia in spreading on structured substrates. PMID:26934830

  10. A Bayesian space-time model for discrete spread processes on a lattice.

    PubMed

    Long, Jed A; Robertson, Colin; Nathoo, Farouk S; Nelson, Trisalyn A

    2012-06-01

    In this article we present a Bayesian Markov model for investigating environmental spread processes. We formulate a model where the spread of a disease over a heterogeneous landscape through time is represented as a probabilistic function of two processes: local diffusion and random-jump dispersal. This formulation represents two mechanisms of spread which result in highly peaked and long-tailed distributions of dispersal distances (i.e., local and long-distance spread), commonly observed in the spread of infectious diseases and biological invasions. We demonstrate the properties of this model using a simulation experiment and an empirical case study - the spread of mountain pine beetle in western Canada. Posterior predictive checking was used to validate the number of newly inhabited regions in each time period. The model performed well in the simulation study in which a goodness-of-fit statistic measuring the number of newly inhabited regions in each time interval fell within the 95% posterior predictive credible interval in over 97% of simulations. The case study of a mountain pine beetle infestation in western Canada (1999-2009) extended the base model in two ways. First, spatial covariates thought to impact the local diffusion parameters, elevation and forest cover, were included in the model. Second, a refined definition for translocation or jump-dispersal based on mountain pine beetle ecology was incorporated improving the fit of the model. Posterior predictive checks on the mountain pine beetle model found that the observed goodness-of-fit test statistic fell within the 95% posterior predictive credible interval for 8 out of 10 years. The simulation study and case study provide evidence that the model presented here is both robust and flexible; and is therefore appropriate for a wide range of spread processes in epidemiology and ecology.

  11. Measurements of monopolar and bipolar current spreads using forward-masking with a fixed probe.

    PubMed

    Bingabr, Mohamed G; Espinoza-Varas, Blas; Sigdel, Saroj

    2014-05-01

    This research employed a forward-masking paradigm to estimate the current spread of monopolar (MP) and bipolar (BP) maskers, with current amplitudes adjusted to elicit the same loudness. Since the spatial separation between active and return electrodes is smaller in BP than in MP configurations, the BP current spread is more localized and presumably superior in terms of speech intelligibility. Because matching the loudness requires higher current in BP than in MP stimulation, previous forward-masking studies show that BP current spread is not consistently narrower across subjects or electrodes within a subject. The present forward-masking measures of current spread differ from those of previous studies by using the same BP probe electrode configuration for both MP and BP masker configurations, and adjusting the current levels of the MP and BP maskers so as to match them in loudness. With this method, the estimate of masker current spread would not be contaminated by differences in probe current spread. Forward masking was studied in four cochlear implant patients, two females and two males, with speech recognition scores higher than 50%; that is, their auditory-nerve survival status was more than adequate to carry out the experiments. The data showed that MP and BP masker configurations produce equivalent masking patterns (and current spreads) in three participants. A fourth participant displayed asymmetrical patterns with enhancement rather than masking in some cases, especially when the probe and masker were at the same location. This study showed equivalent masking patterns for MP and BP maskers when the BP masker current amplitude was increased to match the loudness of the MP masker, and the same BP probe configuration is used with both maskers. This finding could help to explain why cochlear implant users often fail to accrue higher speech intelligibility benefit from BP stimulation.

  12. [Regulation and control of hexane level in air of workplace].

    PubMed

    2012-01-01

    The article covers discussion on necessity of changing MAC for hexane in air of workplace. That is justified by health disorders in the workers, supported by the authors' experimental studies. The authors analyzed methods to control hexane levels in air of workplace, suggested specific standardized method assessing hexane in air of workplace and in ambient air.

  13. Disruptive Innovation in Air Measurement Technology: Reality ...

    EPA Pesticide Factsheets

    This presentation is a big picture overview on the changing state of air measurement technology in the world, with a focus on the introduction of low-cost sensors into the market place. The presentation discusses how these new technologies may be a case study in disruptive innovation for the air pollution measurement field. The intended audience is primarily those with experience in air pollution measurement methods, but much of the talk is accessible to the general public. This is a keynote presentation on emerging air monitoring technology, to be provided at the AWMA measurements conference in March, 2016.

  14. Nonspherical liquid droplet falling in air

    NASA Astrophysics Data System (ADS)

    Agrawal, Meenu; Premlata, A. R.; Tripathi, Manoj Kumar; Karri, Badarinath; Sahu, Kirti Chandra

    2017-03-01

    The dynamics of an initially nonspherical liquid droplet falling in air under the action of gravity is investigated via three-dimensional numerical simulations of the Navier-Stokes and continuity equations in the inertial regime. The surface tension is considered to be high enough so that a droplet does not undergo breakup. Vertically symmetric oscillations which decay with time are observed for low inertia. The amplitude of these oscillations increases for high Gallilei numbers and the shape asymmetry in the vertical direction becomes prominent. The reason for this asymmetry has been attributed to the higher aerodynamic inertia. Moreover, even for large inertia, no path deviations or oscillations are observed.

  15. Evolution of a plasma vortex in air.

    PubMed

    Tsai, Cheng-Mu; Chu, Hong-Yu

    2016-01-01

    We report the generation of a vortex-shaped plasma in air by using a capacitively coupled dielectric barrier discharge system. We show that a vortex-shaped plasma can be produced inside a helium gas vortex and is capable of propagating for 3 cm. The fluctuation of the plasma ring shows a scaling relation with the Reynolds number of the vortex. The transient discharge reveals the property of corona discharge, where the conducting channel within the gas vortex and the blur plasma emission are observed at each half voltage cycle.

  16. Stereo-photography of streamers in air

    SciTech Connect

    Nijdam, S.; Moerman, J. S.; Briels, T. M. P.; Veldhuizen, E. M. van; Ebert, U.

    2008-03-10

    Standard photographs of streamer discharges show a two-dimensional projection. Here, we present stereophotographic images that resolve their three-dimensional structure. We describe the stereoscopic setup and evaluation, and we present results for positive streamer discharges in air at 0.2-1 bar in a point-plane geometry with a gap distance of 14 cm and a voltage pulse of 47 kV. In this case, an approximately Gaussian distribution of branching angles of 43 deg. {+-}12 deg. is found; these angles do not significantly depend on the distance from the needle or on the gas pressure.

  17. Stereo-photography of streamers in air

    NASA Astrophysics Data System (ADS)

    Nijdam, S.; Moerman, J. S.; Briels, T. M. P.; van Veldhuizen, E. M.; Ebert, U.

    2008-03-01

    Standard photographs of streamer discharges show a two-dimensional projection. Here, we present stereophotographic images that resolve their three-dimensional structure. We describe the stereoscopic setup and evaluation, and we present results for positive streamer discharges in air at 0.2-1bar in a point-plane geometry with a gap distance of 14cm and a voltage pulse of 47kV. In this case, an approximately Gaussian distribution of branching angles of 43°±12° is found; these angles do not significantly depend on the distance from the needle or on the gas pressure.

  18. Determination of microquantities of hexabromocyclododecane in air

    SciTech Connect

    Paama, L.A.; Kheinaste, T.A.; Kokk, K.Y.; Solov'eva, E.V.; Vostrikav, V.I.

    1985-08-01

    The authors develop and present a simple and accessible method of determining microquantities of hexabromocyclododecane (HBCD) from the air to be analyzed, and they remove elementary bromine. The analytical procedure is described and tables present the results of the experiments. They found that acetone and ethanol did not interfere with the determination of HBCD in air. It was established that in the method of collection of air samples described, hydrogen bromide and elementary bromide are not retained by silica gel and also do not interfere with the determination of HBCD.

  19. Spatial Displays and Spatial Instruments

    DTIC Science & Technology

    1989-01-01

    Direction Judgements in Computer-Generated Displays and Actual Scenes 19-1 Stephen R. Ellis, Stephen Smith, Michael W. McGreevy, and Arthur...can be used to correct underlying natural biases in spatial judgements . For example, exocentric direction judgements (Howard, 1982) made of extended...Roscoe, S. N. (1984). Judgements of size and distance with imaging displays. Human Factors, 26, 617-629. Roscoe, S. N. (1987). The trouble with

  20. Improving ammonia emissions in air quality modelling for France

    NASA Astrophysics Data System (ADS)

    Hamaoui-Laguel, Lynda; Meleux, Frédérik; Beekmann, Matthias; Bessagnet, Bertrand; Génermont, Sophie; Cellier, Pierre; Létinois, Laurent

    2014-08-01

    We have implemented a new module to improve the representation of ammonia emissions from agricultural activities in France with the objective to evaluate the impact of such emissions on the formation of particulate matter modelled with the air quality model CHIMERE. A novel method has been set up for the part of ammonia emissions originating from mineral fertilizer spreading. They are calculated using the one dimensional 1D mechanistic model “VOLT'AIR” which has been coupled with data on agricultural practices, meteorology and soil properties obtained at high spatial resolution (cantonal level). These emissions display high spatiotemporal variations depending on soil pH, rates and dates of fertilization and meteorological variables, especially soil temperature. The emissions from other agricultural sources (animal housing, manure storage and organic manure spreading) are calculated using the national spatialised inventory (INS) recently developed in France. The comparison of the total ammonia emissions estimated with the new approach VOLT'AIR_INS with the standard emissions provided by EMEP (European Monitoring and Evaluation Programme) used currently in the CHIMERE model shows significant differences in the spatiotemporal distributions. The implementation of new ammonia emissions in the CHIMERE model has a limited impact on ammonium nitrate aerosol concentrations which only increase at most by 10% on the average for the considered spring period but this impact can be more significant for specific pollution episodes. The comparison of modelled PM10 (particulate matter with aerodynamic diameter smaller than 10 μm) and ammonium nitrate aerosol with observations shows that the use of the new ammonia emission method slightly improves the spatiotemporal correlation in certain regions and reduces the negative bias on average by 1 μg m-3. The formation of ammonium nitrate aerosol depends not only on ammonia concentrations but also on nitric acid availability, which