Percolation

Distribution by Scientific Domains

Kinds of Percolation

  • deep percolation

  • Terms modified by Percolation

  • percolation behavior
  • percolation model
  • percolation process
  • percolation theory
  • percolation threshold

  • Selected Abstracts


    Percolation phenomena in carbon black,filled polymeric concrete

    POLYMER ENGINEERING & SCIENCE, Issue 9 2000
    L. Rejón
    Percolation in carbon black-filled polymeric concrete, is discussed based on the measured changes in electrical conductivity and morphology of the composite at different concentrations of carbon black. The percolation threshold ranged between 6 and 7 wt% (based on resin weight) of carbon black. Above this concentration, the filler particles formed agglomerates in contact with each other, suggesting that the conduction process is nearly ohmic in nature. A power law predicted by percolation theory described the behavior of the conductivity as a function of carbon black content. Microscopic analysis showed the presence of a continuous structure formed by the polyester resin and carbon black, in which silica particles were embedded. [source]


    Percolation for the vacant set of random interlacements

    COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 6 2009
    Vladas Sidoravicius
    We investigate random interlacements on ,d, d , 3. This model, recently introduced in [8], corresponds to a Poisson cloud on the space of doubly infinite trajectories modulo time shift tending to infinity at positive and negative infinite times. A nonnegative parameter u measures how many trajectories enter the picture. Our main interest lies in the percolative properties of the vacant set left by random interlacements at level u. We show that for all d , 3 the vacant set at level u percolates when u is small. This solves an open problem of [8], where this fact has only been established when d , 7. It also completes the proof of the nondegeneracy in all dimensions d , 3 of the critical parameter u* of [8]. © 2008 Wiley Periodicals, Inc. [source]


    Estrogenic effect of leachates and soil extracts from lysimeters spiked with sewage sludge and reference endocrine disrupters

    ENVIRONMENTAL TOXICOLOGY, Issue 2 2002
    Halim Dizer
    Abstract Several experiments were conducted to evaluate the behavior and performance of some potential endocrine disrupters (ECDs). Two in vitro screening assays, one based on MCF7-cell proliferation (E-screen test) and the other on estrogenic receptor activity [enzyme-linked receptor assay (ELRA)], were used for the tests, which were done in lysimeters 80 cm in diameter with depths of 30 cm (shallow) or 90 cm (deep). A sandy soil was used to fill in all lysimeters, which were spiked on the surface with either: (a) a sewage sludge (SS) at a dose equivalent to 20 tons ha,1; (b) a mixture of reference ECDs, comprising 17,- and 17,-estradiol (E2), nonylphenol, octylphenol, and bisphenol A at doses 100 times higher than the maximum concentrations respectively found in the applied SS; or (c) a mixture of ECDs and SS. After percolation of the lysimeters with rain and/or artificial water, five leachates were sampled from each lysimeter during a period of 210 days. Immediately after the lysimeter percolation experiments, four and six soil fractions were dissected from, respectively, the 30-cm and 90-cm lysimeters and extracted by water. Both the leachate and soil extract samples were analyzed for their estrogenicity using the assays indicated above. The E-screen assay was highly sensitive only for some leachate and extract samples but gave no response for most leachates and soil extracts. The results of the ELRA assay suggests a significantly higher estrogenicity of leachate samples from shallow lysimeters compared with that of leachates from deep lysimeters. In contrast, the estrogenic effect measured for soil extracts of shallow lysimeters was lower than that measured for soil extracts of deep lysimeters. The results of the E-screen assay suggests the occurrence of a fast mobilization of applied ECDs and a moderate retardation effect of native ECDs contained in applied SS in the sandy soil used in the lysimeters. In lysimeters spiked with a mixture of SS and ECDs, the washing-out effect of ECDs in the first leachate fraction decreased, but the distribution of ECDs in the lysimeters increased. The relatively high estrogenic impact measured for soil water extracts suggests that the ECDs were mostly associated with water-soluble fractions of organic matter and/or water-suspended fractions of the mineral soil matrix. The application of SS to agricultural and forest fields may determine the immobilization of ECDs in soil or their movement to surface and/or groundwater. Therefore, an endocrine risk of exposure exists for the water and soil organisms. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 105,112, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10038 [source]


    Impact of stone content on water movement in water-repellent sand

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2009
    E. Urbanek
    Summary Soils are commonly stony, especially in steep upland or heavily degraded sites. The hydrological effect of large stone contents has been previously investigated in wettable but not in water-repellent soils. For the latter, the focus has instead been on the impact of other soil characteristics (e.g. cracks and macropores) likely to promote water percolation. This paper investigates stone effects on water flow in water-repellent sand under laboratory conditions. Seventy-five experiments were performed on a water-repellent sand mixed with a range of quantities of different-sized wettable and water-repellent stones. The time taken for water to pass through each sand,stone mix, the percolated water volumes and numbers of dry and wet stones following each 60-minute experiment were recorded. At large stone contents (> 55% or > 65% by weight, depending on stone wettability), percolation occurred relatively quickly and in comparatively large quantities. At intermediate stone contents (45,65%) percolation response was variable and at stone contents < 45% for wettable and < 55% for water-repellent soils no water percolation occurred. We argue that with large stone contents flow pathways develop along sand,stone interfaces and a continuous preferential flow path can form provided there are sufficient stone-to-stone connections. The distribution and alignment of the stones, especially at intermediate stone contents, are important for promoting water movement. Water repellency determinations based only on the fine sediment component in stony soils could therefore be misleading as regards determining their hydrological response: the influence of the clastic component must also be considered. [source]


    Percolation characteristics of a water-repellent sandy forest soil

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008
    G. Wessolek
    Summary In a tracer experiment TDR transect measurements were made to study percolation behaviour in a 120-year-old pine stand (Pinus sylvestris) on a water-repellent sandy soil (Haplic Arenosol). The experiment (with potassium iodide) showed an 80% labelling of the total flow in organic layers, whereas the area of transport in the mineral soil was sharply reduced to 12,30%. The average diameters of these preferential flow paths were about 8,15 cm. The TDR measurements indicate a homogeneous flow only for a short period from February until April. At this time of the year preferential flow is insignificant, because the soil is at approximately field capacity and not repellent to water. During summer (May to September) the soil dries out, and most precipitation results in preferential flow during this period. For any daily rainfall exceeding 10 mm, water infiltrates down to 1 m depth in the soil, which nevertheless, is still within the root zone. This kind of deep percolation results in the subsoil's wetting to field capacity (pF 1.8) earlier than the topsoil. A one-dimensional numerical model (SWAP) was used to simulate mean water balance with hydraulic functions with and without a water-repellency term. From the results of our tracer experiment we showed that the de-watering process in spring could be simulated well using the traditional piston flow concept, while the rewetting behaviour could be described more realistically using the mobile,immobile concept for water repellency. [source]


    Molecular Origins of the Mechanical Behavior of Hybrid Glasses

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Mark S. Oliver
    Abstract Hybrid organic-inorganic glasses exhibit unique electro-optical properties along with excellent thermal stability. Their inherently mechanically fragile nature, however, which derives from the oxide component of the hybrid glass network together with the presence of terminal groups that reduce network connectivity, remains a fundamental challenge for their integration in nanoscience and energy technologies. We report on a combined synthesis and computational strategy to elucidate the effect of molecular structure on mechanical properties of hybrid glass films. We first demonstrate the importance of rigidity percolation to elastic behavior. Secondly, using a novel application of graph theory, we reveal the complex 3-D fracture path at the molecular scale and show that fracture energy in brittle hybrid glasses is fundamentally governed by the bond percolation properties of the network. The computational tools and scaling laws presented provide a robust predictive capability for guiding precursor selection and molecular network design of advanced hybrid organic-inorganic materials. [source]


    Adhesion and Percolation Parameters in Two Dimensional Pd,LSCM Composites for SOFC Anode Current Collection

    ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
    Samir Boulfrad
    Abstract This paper is concerned with palladium,(La0.75Sr0.25)0.97Cr0.5Mn0.5O3 (LSCM) composite current collectors for solid oxide fuel cells (SOFCs); the composites, which are in a 2D configuration (thickness of about 8,10,µm), are deposited upon an LSCM electrode layer on top of an yttria zirconia electrolyte substrate. The influence of the LSCM particle size on the adhesion between palladium and LSCM are reported and discussed. Compositions using four different LSCM particle sizes (0.21, 0.49, 0.64, and 0.81,µm) with sintered Pd particle sizes approaching 10,µm are investigated. The best bonding is obtained when smaller particles are used. The electrical dc conductivity of the composite is reported as a function of the palladium volume fraction for all used LSCM particle sizes. The measured experimental values present typical insulating,conductive percolation. However, the transition occurs at ,33% of the conductive phase, that is, a lower percentage than for 2D ideal systems and a higher percentage than for 3D ideal systems. This is consistent with lower-dimension percolation for a system of large-grained conductors and small-grained insulators. The general effective media (GEM) equation is used to fit the experimental data, and the two main parameters (the threshold point ,c and the exponent t) are defined. [source]


    Ultralow Dielectric Constant Tetravinyltetramethylcyclotetrasiloxane Films Deposited by Initiated Chemical Vapor Deposition (iCVD)

    ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
    Nathan J. Trujillo
    Abstract Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140,cm,1) and Raman (1117,cm,1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma-enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as-deposited films. The high degree of structural retention in the as-deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ,Q' groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as-deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade-off between improved mechanical properties and higher dielectric constants. Films annealed at 410,°C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4,GPa, respectively. The solvent-less and low-energy nature of iCVD make it attractive from an environmental safety and health perspective. [source]


    How good are the Electrodes we use in PEFC?

    FUEL CELLS, Issue 3 2004
    M. Eikerling
    Abstract Basically, companies and laboratories implement production methods for their electrodes on the basis of experience, technical capabilities and commercial preferences. But how does one know whether they have ended up with the best possible electrode for the components used? What should be the (i) optimal thickness of the catalyst layer? (ii) relative amounts of electronically conducting component (catalyst, with support , if used), electrolyte and pores? (iii) "particle size distributions" in these mesophases? We may be pleased with our MEAs, but could we make them better? The details of excellently working MEA structures are typically not a subject of open discussion, also hardly anyone in the fuel cell business would like to admit that their electrodes could have been made much better. Therefore, we only rarely find (far from systematic) experimental reports on this most important issue. The message of this paper is to illustrate how strongly the MEA morphology could affect the performance and to pave the way for the development of the theory. Full analysis should address the performance at different current densities, which is possible and is partially shown in this paper, but vital trends can be demonstrated on the linear polarization resistance, the signature of electrode performance. The latter is expressed through the minimum number of key parameters characterizing the processes taking place in the MEA. Model expressions of the percolation theory can then be used to approximate the dependence on these parameters. The effects revealed are dramatic. Of course, the corresponding curves will not be reproduced literally in experiments, since these illustrations use crude expressions inspired by the theory of percolation on a regular lattice, whereas the actual mesoscopic architecture of MEA is much more complicated. However, they give us a flavour of reserves that might be released by smart MEA design. [source]


    Multilayer Hybrid Films Consisting of Alternating Graphene and Titania Nanosheets with Ultrafast Electron Transfer and Photoconversion Properties

    ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
    Kiran Kumar Manga
    Abstract Alternating graphene (G) and titania (Ti0.91O2) multilayered nanosheets are fabricated using layer-by-layer electrostatic deposition followed by UV irradiation. Successful assemblies of graphene oxide (GO) and titania nanosheets in sequence with polyethylenimine as a linker is confirmed by UV,vis absorption and X-ray diffraction. Photocatalytic reduction of GO into G can be achieved upon UV irradiation. Ultrafast photocatalytic electron transfer between the titania and graphene is demonstrated using femtosecond transient absorption spectroscopy. Efficient exciton dissociation at the interfaces coupled with cross-surface charge percolation allows efficient photocurrent conversion in the multilayered Ti0.91O2/G films. [source]


    The microstratigraphic record of abrupt climate changes in cave sediments of the Western Mediterranean

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2001
    Marie-Agnès Courty
    The purpose of this paper is to illustrate how calcareous sediments from Pleistocene and Holocene rockshelters and open caves of the Western Mediterranean can provide a stratigraphic record of abrupt climate change. The method proposed here is based on microstratigraphic examination of sedimentary sequences using microscopic techniques. The most important processes for characterizing the sensitivity of each cave to climate variables are: (1) the modes and rate of carbonate sediment production, (2) the nature and intensity of the pedogenic processes responsible for the synchronous alteration of carbonate materials (either those derived from the cave walls or those deposited on the ground surface), and (3) the supply of allogenic sediments, particularly by eolian activity. The cave sediment sequences presented record the marked coolings known as Dansgaard-Oeschger stadials and Heinrich events that occurred during the Pleistocene and the Holocene, as demonstrated by the high resolution records from ice and deep sea cores. At Abric Romanì in northeastern Spain, a series of sharp climatic deteriorations of increasing severity is shown to have occurred synchronously with the transition from the Middle to the Upper Paleolithic, with a period of seasonal frost and strong winds at ca. 37,000 yr B.P., tentatively correlated with Heinrich event 4. At Pigeon Cave, Taforalt (northern Morocco), the transition from the Aterian to Ibero-Maurusian/Epipalaeolithic cultures is dated to around 24,000,20,000 yr B.P. and is punctuated by a series of short cold pulses with evidence for seasonal freezing, soil erosion, and minimal evapotranspiration. In El Miron cave in north-central Spain, the exceptional nature of the Younger Dryas cooling produced a marked destabilization of the cave walls and roof. At El Miron, the stratigraphic evidence for sediment removal due to the rapid percolation of snow melt under a degraded soil cover allows us to reconstruct the nature of the negative excursion at ca. 8200 yr B.P. This example also illustrates how climate-controlled pedogenic processes can create a stratigraphic signature which has often been confused with a sedimentary hiatus. We conclude that cave sediments provide a valuable record of Pleistocene and Holocene climate changes. In appropriate contexts, these sequences allow us to examine the ecological stress generated by these unique global events at a local and regional level and improve our understanding of the complex anthropological processes that occurred at the same time. © 2001 John Wiley & Sons, Inc. [source]


    Distribution of Chemical Constituents in Superimposed Ice from Austre Brøggerbreen, Spitsbergen

    GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2000
    H. Motoyama
    10 m and 2.3 m ice cores were obtained on Austre Brøggerbreen, Spitsbergen in Svalbard (78°53,N, 11°56,E, 450 m a.s.l.) in September 1994 and in March 1995, respectively. Stratigraphy, bulk density, pH, electrical conductivity, and major ions were obtained from the core samples. The chemical effect of meltwater percolation through snow/ice is examined. Good correlation between Cl, and Na+ was obtained. The ratio of Cl, to Na+ was 1.14 which was nearly the same value as in bulk sea water. However, the variation of Cl,/Na+ shows that higher ratio occured in the bubble-free ice. Furthermore the Cl, ions remain in higher concentration than SO 4 2, or Na+ ions. [source]


    Origin of quartz geodes from Laño and Tubilla del Agua sections (middle,upper Campanian, Basque-Cantabrian Basin, northern Spain): isotopic differences during diagenetic processes

    GEOLOGICAL JOURNAL, Issue 2 2002
    Juan J. Gómez-Alday
    Abstract Quartz geodes and nodular chert have been found within middle,upper Campanian carbonate sediments from the Laño and Tubilla del Agua sections of the Basque-Cantabrian Basin, northern Spain. The morphology of geodes together with the presence of anhydrite laths included in megaquartz crystals and spherulitic fibrous quartz (quartzine-lutecite), suggest an origin from previous anhydrite nodules. The anhydrite nodules at Laño were produced by the percolation of marine brines, during a period corresponding to a sedimentary gap, with ,34S and ,18O mean values of 18.8, and 13.6, respectively, consistent with Upper Cretaceous seawater sulphate values. Higher ,34S and ,18O mean values of 21.2, and 21.8, recorded in the Tubilla del Agua section are interpreted as being due to a partial bacterial sulphate reduction process in a more restricted marine environment. The idea that sulphates may have originated from the leaching of previously deposited Keuper sulphate evaporites with subsequent precipitation as anhydrite, is rejected because the ,34S, ,18O and 87Sr/86Sr values of anhydrite laths observed at both the Tubilla del Agua and Laño sections suggest an origin from younger marine brines. Later calcite replacement and precipitation of geode-filling calcite is recorded in both sections, with ,13C and ,18O values indicating the participation of meteoric waters. Synsedimentary activity of the Peñacerrada diapir, which lies close to the Laño section, played a significant role in the local shallowing of the basin and the formation of quartz geodes. In contrast, eustatic shallowing of the inner marine series of the Tubilla del Agua section led to the generation of morphologically similar quartz geodes. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Seismic singularities at upper-mantle phase transitions: a site percolation model

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004
    Felix J. Herrmann
    SUMMARY Mineralogical phase transitions are usually invoked to account for the sharpness of globally observed upper-mantle seismic discontinuities. We propose a percolation-based model for the elastic properties of the phase mixture in the coexistence regions associated with these transitions. The major consequence of the model is that the elastic moduli (but not the density) display a singularity at the percolation threshold of the high-pressure phase. This model not only explains the sharp but continuous change in seismic velocities across the phase transition, but also predicts its abruptness and scale invariance, which are characterized by a non-integral scale exponent. Using the receiver-function approach and new, powerful signal-processing techniques, we quantitatively determine the singularity exponent from recordings of converted seismic waves at two Australian stations (CAN and WRAB). Using the estimated values, we construct velocity,depth profiles across the singularities and verify that the calculated converted waveforms match the observations under CAN. Finally, we point out a series of additional predictions that may provide new insights into the physics and fine structure of the upper-mantle transition zone. [source]


    Simple Patterning via Adhesion between a Buffered-Oxide Etchant-Treated PDMS Stamp and a SiO2 Substrate,

    ADVANCED FUNCTIONAL MATERIALS, Issue 13 2007
    Y.-K. Kim
    Abstract A very simple polydimethylsiloxane (PDMS) pattern-transfer method is devised, called buffered-oxide etchant (BOE) printing. The mechanism of pattern transfer is investigated, by considering the strong adhesion between the BOE-treated PDMS and the SiO2 substrate. PDMS patterns from a few micrometers to sub-micrometer size are transferred to the SiO2 substrate by just pressing a stamp that has been immersed in BOE solution for a few minutes. The patterned PDMS layers work as perfect physical and chemical passivation layers in the fabrication of metal electrodes and V2O5 nanowire channels, respectively. Interestingly, a second stamping of the BOE-treated PDMS on the SiO2 substrate pre-patterned with metal as well as PDMS results in a selective transfer of the PDMS patterns only to the bare SiO2. In this way, the fabrication of a device structure consisting of two Au electrodes and V2O5 nanowire network channels is possible; non-ohmic semiconducting I,V characteristics, which can be modeled by serially connected percolation, are observed. [source]


    Modelling investigation of water partitioning at a semiarid ponderosa pine hillslope

    HYDROLOGICAL PROCESSES, Issue 9 2010
    Huade Guan
    Abstract The effects of vegetation root distribution on near-surface water partitioning can be two-fold. On the one hand, the roots facilitate deep percolation by root-induced macropore flow; on the other hand, they reduce the potential for deep percolation by root-water-uptake processes. Whether the roots impede or facilitate deep percolation depends on various conditions, including climate, soil, and vegetation characteristics. This paper examines the effects of root distribution on deep percolation into the underlying permeable bedrock for a given soil profile and climate condition using HYDRUS modelling. The simulations were based on previously field experiments on a semiarid ponderosa pine (Pinus ponderosa) hillslope. An equivalent single continuum model for simulating root macropore flow on hillslopes is presented, with root macropore hydraulic parameterization estimated based on observed root distribution. The sensitivity analysis results indicate that the root macropore effect dominates saturated soil water flow in low conductivity soils (Kmatrix below 10,7 m/s), while it is insignificant in soils with a Kmatrix larger than 10,5 m/s, consistent with observations in this and other studies. At the ponderosa pine site, the model with simple root-macropore parameterization reasonably well reproduces soil moisture distribution and some major runoff events. The results indicate that the clay-rich soil layer without root-induced macropores acts as an impeding layer for potential groundwater recharge. This impeding layer results in a bedrock percolation of less than 1% of the annual precipitation. Without this impeding layer, percolation into the underlying permeable bedrock could be as much as 20% of the annual precipitation. This suggests that at a surface with low-permeability soil overlying permeable bedrock, the root penetration depth in the soil is critical condition for whether or not significant percolation occurs. Copyright © 2010 John Wiley & Sons, Ltd. [source]


    Water fluxes at a fluctuating water table and groundwater contributions to wheat water use in the lower Yellow River flood plain, China

    HYDROLOGICAL PROCESSES, Issue 6 2007
    Jianfeng Yang
    Abstract Capillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7,2·3 m during the maize growth period and 1·6,2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO-Penman,Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd. [source]


    Transformations of runoff chemistry in the Arctic tundra, Northwest Territories, Canada

    HYDROLOGICAL PROCESSES, Issue 14 2006
    W. L. Quinton
    Abstract The transformation of snowmelt water chemical composition during melt, elution and runoff in an Arctic tundra basin is investigated. The chemistry of the water flowing along pathways from the surface of melting snow to the 95·5 ha basin outlet is related to relevant hydrological processes. In so doing, this paper offers physically based explanations for the transformation of major ion concentrations and loads of runoff water associated with snowmelt and rainfall along hydrological pathways to the stream outlet. Late-lying snowdrifts were found to influence the ion chemistry in adjacent reaches of the stream channel greatly. As the initial pulse of ion-rich melt water drained from the snowdrift and was conveyed through hillslope flowpaths, the concentrations of most ions increased, and the duration of the peak ionic pulse lengthened. Over the first 3 m of overland flow, the concentrations of all ions except for NO increased by one to two orders of magnitude, with the largest increase for K+, Ca2+ and Mg2+. This was roughly equivalent to the concentration increase that resulted from percolation of relatively dilute water through 0·25 m of unsaturated soil. The Na+ and Cl, were the dominant ions in snowmelt water, whereas Ca2+ and Mg2+ dominated the hillslope runoff. On slopes below a large melting snowdrift, ion concentrations of melt water flowing in the saturated layer of the soil were very similar to the relatively dilute concentrations found in surface runoff. However, once the snowdrift ablated, ion concentrations of subsurface flow increased above parent melt-water concentrations. Three seasonally characteristic hydrochemical regimes were identified in a stream reach adjacent to late-lying snowdrifts. In the first two stages, the water chemistry in the stream channel strongly resembled the hillslope drainage water. In the third stage, in-stream geochemical processes, including the weathering/ion exchange of Ca2+ and Mg2+, were the main control of streamwater chemistry. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Hydrology and nitrogen balance of a seasonally inundated Danish floodplain wetland

    HYDROLOGICAL PROCESSES, Issue 3 2004
    Hans Estrup Andersen
    Abstract This paper characterizes a seasonally inundated Danish floodplain wetland in a state close to naturalness and includes an analysis of the major controls on the wetland water and nitrogen balances. The main inputs of water are precipitation and percolation during ponding and unsaturated conditions. Lateral saturated subsurface flow is low. The studied floodplain owes its wetland status to the hydraulic properties of its sediments: the low hydraulic conductivity of a silt,clay deposit on top of the floodplain maintains ponded water during winter, and parts of autumn and spring. A capillary fringe extends to the soil surface, and capillary rise from groundwater during summer maintains near-saturated conditions in the root zone, and allows a permanently very high evapotranspiration rate. The average for the growing season of 1999 is 3·6 mm day,1 and peak rate is 5·6 mm day,1. In summer, the evapotranspiration is to a large degree supplied by subsurface storage in a confined peat layer underlying the silt,clay. The floodplain sediments are in a very reduced state as indicated by low sulphate concentrations. All nitrate transported into the wetland is thus denitrified. However, owing to modest water exchange with surrounding groundwater and surface water, denitrification is low; 71 kg NO3,N ha,1 during the study period of 1999. Reduction of nitrate diffusing into the sediments during water ponding accounts for 75% of nitrate removal. Biomass production and nitrogen uptake in above-ground vegetation is high,8·56 t dry matter ha,1 year,1 and 103 kg N ha,1 year,1. Subsurface ammonium concentrations are high, and convective upward transport into the root zone driven by evapotranspiration amounted to 12·8 kg N ha,1year,1. The floodplain wetland sediments have a high nitrogen content, and conditions are very favourable for mineralization. Mineralization thus constitutes 72% of above-ground plant uptake. The study demonstrates the necessity of identifying controlling factors, and to combine surface flow with vadose and groundwater flow processes in order to fully comprehend the flow and nitrogen dynamics of this type of wetland. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    Characteristics of soil moisture in permafrost observed in East Siberian taiga with stable isotopes of water

    HYDROLOGICAL PROCESSES, Issue 6 2003
    A. Sugimoto
    Abstract Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998, 1999, and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its ,18O showed large interannual variation depending on the amount of summer rainfall. The soil water ,18O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the ,18O of soil water increased due to percolation of summer rain with high ,18O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the ,18O because of the low ,18O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra-annual variation of soil moisture. Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Drainage and salinity assessment in the Huinong Canal Irrigation District, Ningxia, China,

    IRRIGATION AND DRAINAGE, Issue 2 2005
    Peter Hollanders
    irrigation; drainage; salinisation; développement durable Abstract In the Huinong Canal Irrigation District, Ningxia, China, annually almost half of the amount of irrigation water, which is supplied from the Yellow River, is drained back to the river through an open drainage system. Waterlogging and salinization occur in parts of the irrigated area and part of the water drains to the surrounding desert. While 85,90% of inflow to the area is irrigation water there are good possibilities for water saving. To analyse water movement at field level and resulting drainage needs, from autumn 1998 until spring 2001 observations were made in two experimental areas: Pingluo and Huinong. The data were used for the calibration and validation of three computer models: SWAP, MODFLOW and DUFLOW. Different scenarios of water and salt behaviour in the unsaturated and saturated zone were simulated, as well as the flow through one of the main drains. The effects of various irrigation amounts and groundwater tables on crop growth, percolation and drainage needs were analysed. The present average irrigation water application during the growing season is 630,mm. On average 15% of the supplied water (665 million m3,yr,1) remains in the area. This is mainly irrigation water that was not used by the crops and did not reach the drainage system. It was found that an irrigation level of 75% of the present practice with a groundwater table of 1.0,m below the surface during the growing season gave the best results. Under such a practice the soil salinity will fluctuate around 3,3.5,dS,m,1, resulting in a good growth of wheat and a yield reduction for maize of about 20%. When adequate amounts of irrigation water are supplied in combination with local drainage improvements, the areas with middle and low-yielding crops can be reduced, as well as the area of wasteland. Copyright © 2005 John Wiley & Sons, Ltd. Annuellement presque la moitié de la quantité d'eau d'irrigation dans le district d'irrigation du canal Huinong, Ningxia, Chine, alimenté par la Rivière Jaune, est retournée à la rivière par un système de drainage à ciel ouvert. Des cas de saturation d'eau et de salinisation surgissent dans certaines parties de la zone irriguée et une partie de l'eau suinte vers le désert environnant. Comme 85,90% de l'entrée de l'eau dans la zone est de l'eau d'irrigation il y a de bonnes possibilités pour économiser de l'eau. Pour analyser la circulation de l'eau au niveau du champ et la nécessité de drainage des observations ont été effectuées pendant la période d'automne 1998 jusqu'au printemps 2001 dans deux zones expérimentales, Pingluo et Huinong. Les données rassemblées ont servi pour le calibrage et la validation de trois modèles informatiques: SWAP, MODFLOW et DUFLOW. Ces modèles ont été employés pour simuler plusieurs scénarios de comportement de l'eau et du sel dans la zone non saturée et dans la zone saturée tout comme l'écoulement par un des tuyaux d'écoulement principaux: le cinquième tuyau d'écoulement. L'effet de l'apport de différentes quantités d'eau d'irrigation, de différents niveaux de la nappe phréatique sur la croissance des cultures, la percolation et la nécessité de drainage a été analysé. L'actuel apport d'eau d'irrigation est de 630,mm en moyenne pendant la saison de croissance. Quinze pour cent en moyenne de l'eau fournie (665 millions m3/année) reste dans la zone, principalement de l'eau d'irrigation qui n'a pas servi aux cultures et qui n'a pas atteint le système de drainage. Un niveau d'irrigation représentant 75% des valeurs actuelles et une surface de la nappe phréatique de 1.0,m sous la surface donnent les meilleurs résultats pendant la saison de croissance. De tels apports entretiennent une salinisation du sol qui fluctuera entre environ 3 et 3.5,dS,m,1, donnant un bon résultat de la croissance du blé et une diminution du rendement pour le maïs d'environ 20%. Lorsque l'alimentation par des quantités adéquates d'eau d'irrigation sera assurée en combinaison avec des améliorations du drainage local, la zone donnant des récoltes moyennes et basses peut être réduite ainsi que les zones incultes. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Linear and non-linear optimization models for allocation of a limited water supply,

    IRRIGATION AND DRAINAGE, Issue 1 2004
    Bijan Ghahraman
    optimisation de l'irrigation; déficit d'irrigation; Iran Abstract One partial solution to the problem of ever-increasing demands on our water resources is optimal allocation of available water. A non-linear programming (NLP) optimization model with an integrated soil water balance was developed. This model is the advanced form of a previously developed one in which soil water balance was not included. The model also has the advantage of low computer run-time, as compared to commonly used dynamic programming (DP) models that suffer from dimensionality. The model can perform over different crop growth stages while taking into account an irrigation time interval in each stage. Therefore, the results are directly applicable to real-world conditions. However, the time trend of actual evapotranspiration (AET) for individual time intervals fluctuates more than that for growth-stage AETs. The proposed model was run for the Ardak area (45,km NW of the city of Mashhad, Iran) under a single cropping cultivation (corn) as well as a multiple cropping pattern (wheat, barley, corn, and sugar beet). The water balance equation was manipulated with net applied irrigation water to overcome the difficulty encountered with incorrect deep percolation. The outputs of the model, under the imposed seasonal irrigation water shortages, were compared with the results obtained from a simple NLP model. The differences between these two models (simple and integrated) became more significant as irrigation water shortage increased. Oversimplified assumptions in the previous simple model were the main causes of these differences. Copyright © 2004 John Wiley & Sons, Ltd. L'allocation optimale des ressources d'eau disponibles est une réponse partielle au problème de la demande sans cesse croissante de consommation d'eau. Un modèle d'optimisation à programmation non linéaire (NLP) qui intègre un bilan hydrique a été développé. Ce modèle est une version avancée d'un modéle précédent qui n'intégrait pas ce bilan hydrique. Il présente l'avantage de nécessiter moins de puissance informatique en comparaison des modèles à programmation dynamique (DP) généralement utilisés. Le modèle peut s'appliquer à différentes étapes de la croissance des cultures et prend en compte des fréquences d'irrigation variables. Ainsi, les résultats sont directement applicables aux conditions réelles. Le modèle proposé a été utilisé sur une seule culture (maïs) dans la région d'Ardak à 45,km nord-ouest de Mashad, Iran, et sur de multiples cultures (blé, orge, maïs, betterave sucrière). L'équation de bilan hydrique a été calibrée pour maîtriser les difficultés rencontrées avec des mesures d'infiltration incorrectes. Les résultats du modèle, dans le cadre de restrictions d'irrigation saisonnière imposées, ont été comparés avec ceux obtenus par un modèle simple NLP. Les différences entre ces deux modèles (simple et intégré) deviennent plus significatives à mesure que les restrictions d'irrigation augmentent. Les hypothèses trop simplistes du modèle simple sont la cause de ces différences. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    Sustainable use of groundwater for irrigation: a numerical analysis of the subsoil water fluxes,

    IRRIGATION AND DRAINAGE, Issue 3 2002
    Mobin-ud-Din Ahmad
    irrigation; eaux souterraines; surexploitation de l'aquifère; recharge des eaux souterraines; utilisation nette de l'eau souterraine; modélisation au niveau de la parcelle cultivée; le Pakistan Abstract The food-producing regions of the world increasingly rely on irrigation from groundwater resources. Further increases of groundwater use can adversely affect the sustainability of irrigated agriculture and put food security at risk. Sustainability of irrigation at field scale with groundwater is obtained if groundwater recharge is in equilibrium with tubewell extractions and capillary rise. Traditional information on phreatic surface behaviour does not explain the processes causing a phreatic surface to decline or incline. In this study, the physically based numerical model Soil,Water,Atmosphere,Plant (SWAP) was applied to compute soil moisture content and vertical soil water fluxes in the unsaturated zone for the cotton,wheat and rice,wheat cropping system of Punjab, Pakistan. SWAP has been calibrated and verified with in situ measurements of soil moisture content and evapotranspiration fluxes measured by means of the Bowen ratio surface energy balance technique. Accurate data of the soil hydraulic properties are critical for the calibration of the soil moisture distribution. With knowledge of the van Genuchten,Mualem parameters available, SWAP could be applied to assess recharge and capillary rise for most field conditions, including basin irrigation. The results under Pakistani conditions show that deep percolation cannot always be estimated from root zone water balances. An annual recharge of 23.3 cm was computed for the cotton,wheat area. Sustainability of irrigation with groundwater is obtained if a reduction in irrigation with groundwater by 36% is obtained. An annual recharge of 38.9 cm is estimated in rice,wheat systems, and a reduction of 62% in groundwater extraction is required to reach sustainability of groundwater use at field scale. Such information cannot be obtained from classical phreatic surface fluctuation data, and unsaturated zone modelling therefore provides additional insights for groundwater policy making. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Les régions de production alimentaire de la planète se servent de plus en plus de l'eau souterraine pour l'irrigation. Ultérieurs accroissements de l'utilisation des eaux souterraines peuvent avoir des répercussions négatives sur l'irrigation agricole soutenable et sur la sécurité alimentaire. Une irrigation soutenable au niveau de la parcelle cultivée en utilisant l'eau souterraine est obtenue si le taux de recharge de cette dernière est en équilibre avec le taux d'extraction des puits et la remontée capillaire. L'information traditionellement disponible concernant l'évolution du niveau phréatique ne permet pas d'expliquer les procès qui causeraient son abaissement ou son accroissement. Cette étude présente les resultats obtenus grâce à l'utilisation d'un modèle numérique appelé Soil,Water,Atmosphere,Plant (SWAP), qui se base sur des principes physiques, avec lequel ont été calculés les taux d'humidité du sol et les flux verticaux d'humidité dans la zone non-saturée du sol pour ce qui concèrne le système de cultivation coton,blé et riz,blé du Pounjab, au Pakistan. SWAP a été calibré et verifié grâce à des mesures in situ du taux d'humidité du sol et des flux d'évapotranspiration quantifiés en appliquant le rapport de Bowen, basé sur le concept du bilan énergétique au niveau du sol. Disposer de données prises concernant les propriétés hydrauliques du sol est essentiel pour calibrer la distribution de l'humidité du sol. Grâce à la connaissance des paramètres de van Genuchten,Mualem disponibles, SWAP a pu être utilisé pour évaluer le taux de recharge et la remontée capillaire en fonction de différentes conditions du terrain, irrigation de bassin incluse. Les résultats sous les conditions Pakistanes montrent que la percolation profonde ne peut pas toujours être estimée par les équilibres hydrologiques de la zone radicale. Une recharge annuelle de 23,3 cm a été estimée pour la zone coton,blé. L'utilisation soutenable de l'eau souterraine pour l'irrigation serait obtenue si on en réduisait l'extraction de 36%. Pour ce qui concerne la zone riz,blé, une recharge annuelle de 38,9 cm a été estimée, et une réduction de 62% de l'extraction de l'eau souterraine serait nécessaire pour une utilisation soutenable de l'eau souterraine à l'échelle de la parcelle cultivée. Ces informations ne peuvent pas être obtenues sur la base des données ordinaires concernant les fluctuations du niveau phréatique; la modélisation représente donc un appui essentiel en matière de prise de décision concernant la gestion de l'eau souterraine. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Expulsion of a geopressured hydrothermal system associated with destructive earthquakes and buried active faults in the Shinanogawa Seismic Belt, Japan

    ISLAND ARC, Issue 2 2004
    Huilong Xu
    Abstract The Shinanogawa Seismic Belt in the Northern Fossa Magna, Honshu Island, Japan, extends along the Shinano River, bounding the Eurasian Plate and the Okhotsk Plate. The geopressured hydrothermal system occurs widely in the Northern Fossa Magna region. Many destructive earthquakes are related to the activity of this system in the Shinanogawa Seismic Belt. Expulsion of a geopressured hydrothermal system and rising from depth along an active fault triggers the occurrence of an earthquake and opens the fault as a pathway. Anomalous areas in temperature, electrical conductivity and Cl, concentration of groundwater trend north,east in a linear distribution, and convincingly demonstrate the presence of a buried active fault at the epicentral area of the destructive earthquake in the Shinanogawa Seismic Belt. The distribution of the major axis of the anomalous area in groundwater temperature shows a strong positive relationship with earthquake magnitude, which means that the distribution of this area may indicate the scale of earthquake fault. The linearly anomalous areas in groundwater temperature, resulting from the percolation of a geopressured hydrothermal system, that have no record of previous destructive earthquake are predicted to be areas where destructive earthquakes could occur in the future. Four potential earthquake areas are proposed and discussed in this paper, based on re-examination of active faults and seismicity in the Shinanogawa Seismic Belt. [source]


    Dielectric studies of conductive carbon black reinforced microcellular ethylene,propylene,diene monomer vulcanizates

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
    S. P. Mahapatra
    Abstract The alternating-current and electrical conductivity of conductive, carbon black reinforced, microcellular ethylene,propylene,diene monomer vulcanizates was measured in the frequency range of 100 Hz to 1 MHz. The effects of variations in the filler and blowing-agent loadings on the dielectric constant and percolation behavior were studied. The phenomenon of percolation was examined on the basis of measured changes in the electrical conductivity and morphology of composites with different concentrations of the filler. Scanning electron microphotographs showed the agglomeration of the filler above these concentrations and the formation of a continuous network structure. The experimental results were not in agreement with the predictions of the statistical percolation theory; this deviation was explained in light of the formation of an interphase or mesostructure in the composites. The variation of the dielectric constant with the filler and blowing-agent loadings was explained on the basis of polarization of the filler in the polymer matrix. Additionally, the use of dielectric mixture laws in describing the dielectric constants of both solid and microcellular composites was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]


    Estimation of soil water content and evapotranspiration from irrigated cropland on the North China Plain

    JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2008
    Jie Jiang
    Abstract For nearly 30 y, cropland on the North China Plain (NCP) has been irrigated primarily by pumping groundwater with no sustainable management strategy. This has caused a continuous decline of the water table. A sustainable groundwater management and irrigation strategy must be established in order to prevent further decline of the water table; to do this, one must quantify soil water content and daily rates of deep percolation and locate evapotranspiration from irrigated cropland. For that purpose, we developed a three-layer soil,water balance (SWB) model based on an approach described by Kendy et al. (2003). In this model, the unsaturated soil zone is divided into three layers: a surface active layer, a middle active soil layer, and a lowest passive soil layer. The middle and the lowest layers dynamically change with the development of crop rooting depth. A simple "tipping bucket" routine and an exponential equation are used to redistribute soil water in the three soil layers. The actual evapotranspiration estimated is partitioned into soil evaporation and crop transpiration using a dual crop coefficient reference approach. At first, the model was calibrated using data obtained from five deficiently irrigated field plots located at an experimental site in the NCP between 1998 and 2003. Then, the model was validated by comparing estimated soil water contents with measured ones at three other plots with nondeficient irrigation. The estimates of actual evapotranspiration were compared with those measured with a large-scale weighing lysimeter (3 m2). The index of agreement (IA) for soil water contents varied between 0.62 and 0.80; the concordance correlation coefficient (CCC) and the root mean square error obtained from the same comparison were 0.34,0.65 and 0.043,0.074,cm3,cm,3, respectively. The rates of 10 d mean evapotranspiration estimated by the model show a good fit to those measured by the large-scale lysimeter; this is indicated by IA = 0.94 and CCC = 0.88. Our results indicate that at the irrigated cropland on the plain, deep soil water,percolation rates are usually <200,mm y,1 under nondeficient-irrigation conditions. [source]


    Is tile drainage water representative of root zone leaching of pesticides?

    PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 5 2007
    Ole H Jacobsen
    Abstract Given the methods presently available, determination of flux-averaged concentrations of pesticides in structured soils is always a compromise. Most of the available methods entail major uncertainties and limitations. Tile drainage monitoring has several advantages, but the extent to which it is representative of overall leaching has been questioned because it comprises a mixture of water of different origins. This literature review evaluates whether drainage water pesticide concentrations are representative of root zone leaching of pesticides. As there are no reports quantifying the extent to which the flux-averaged concentration of pesticides in drainage water differs from that found between the drains, evidence-based conclusions cannot be drawn. Nevertheless, the existing literature does suggest that the concentration in drainage water does not always correspond to the concentration at drain depth between the drains; depending on the conditions pertaining, the concentrations may be higher or lower. As to whether the flux-averaged concentration of pesticides in drainage water is representative of the interdrain concentration at drain depth it is concluded that (1) the representativeness of drainage water concentrations can be questioned on very well-drained soils and on poorly drained soils with little capacity for lateral transport beneath the plough layer, (2) the conditions provided by relatively porous soils and moderate climatic conditions are conducive to the drainage water concentration being representative and (3) drainage water will be more representative in the case of weakly sorbed pesticides than for strongly sorbed pesticides. Used critically, it is thus believed that drainage water concentrations can serve to characterize the flux-averaged concentration of pesticides at drain depth. However, the use of drainage water for determining average concentrations necessitates thorough investigation and interpretation of precipitation, percolation, drain outflow and concentration dynamics. Copyright © 2007 Society of Chemical Industry [source]


    Sensitivity analyses for four pesticide leaching models

    PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 9 2003
    Igor G Dubus
    Abstract Sensitivity analyses using a one-at-a-time approach were carried out for leaching models which have been widely used for pesticide registration in Europe (PELMO, PRZM, PESTLA and MACRO). Four scenarios were considered for simulation of the leaching of two theoretical pesticides in a sandy loam and a clay loam soil, each with a broad distribution across Europe. Input parameters were varied within bounds reflecting their uncertainty and the influence of these variations on model predictions was investigated for accumulated percolation at 1-m depth and pesticide loading in leachate. Predictions for the base-case scenarios differed between chromatographic models and the preferential flow model MACRO for which large but transient pesticide losses were predicted in the clay loam. Volumes of percolated water predicted by the four models were affected by a small number of input parameters and to a small extent only, suggesting that meteorological variables will be the main drivers of water balance predictions. In contrast to percolation, predictions for pesticide loss were found to be sensitive to a large number of input parameters and to a much greater extent. Parameters which had the largest influence on the prediction of pesticide loss were generally those related to chemical sorption (Freundlich exponent nf and distribution coefficient Kf) and degradation (either degradation rates or DT50, QTEN value). Nevertheless, a significant influence of soil properties (field capacity, bulk density or parameters defining the boundary between flow domains in MACRO) was also noted in at least one scenario for all models. Large sensitivities were reported for all models, especially PELMO and PRZM, and sensitivity was greater where only limited leaching was simulated. Uncertainty should be addressed in risk assessment procedures for crop-protection products. Copyright © 2003 Society of Chemical Industry [source]


    The effective-site percolation approach in two dimensions

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007
    G. Paw, owski
    Abstract A new Monte Carlo cluster approach to describe the order,order and order,disorder transitions in two-dimensional (2D) correlated systems is presented. It is shown that a phase transition of a physical system can be correctly described in terms of the percolation language of the effective-site approach. In contrast to the well-known bond approaches, the method proposed does not require additional assumptions as to the acceptance of the bonds. The new idea is based on the site approach to elementary ordered plaquettes, leading to the accurate coincidence of percolation and the phase transitions in 2D. Here I present the analysis of the spin-system in the Blume,Capel model and the charged-system in the atomic limit of the extended Hubbard model. In both cases the interpretation of the phase transition is made in terms of the percolation of different types of order. The new method allows precise identification of the pure and mixed phases. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Single-walled carbon nanotube/ultrahigh-molecular-weight polyethylene composites with percolation at low nanotube contents

    POLYMER ENGINEERING & SCIENCE, Issue 12 2009
    Brian P. Grady
    To mix single-walled carbon nanotubes (SWCNTs) with a polymer and to achieve low percolation thresholds, a low-viscosity liquid has been required in order to achieve sufficiently good dispersion. In this article, data are presented which show that percolation occurs at ,0.14 wt % carbon nanotubes and the dispersion procedure does not involve dispersing the SWCNTs in a low-viscosity liquid. Specifically, ultrahigh-molecular-weight polyethylene powder was mixed with a powder containing nanotubes and catalyst support, e.g., the powder contains 93% silica and 7% SWCNTs. The powder blend is compression molded into sheets using high pressure and temperature. Because of the very high viscosity of the resin, the nanotube/silica mixture largely stays segregated at the interface as shown by scanning electron microscopy. A significant drop in tensile properties (modulus, tensile strength, and elongation at break) occurs with filler incorporation. Non isothermal crystallization measurements indicate that this filler does not nucleate crystallinity when mixed in this manner; although there is a definite sharpening of the melt endotherm indicating that crystallites with smaller lamellar thicknesses are reduced significantly with filler addition. The addition of filler also slightly reduces the overall fractional crystallinity measured after a constant cooling rate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]