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A new model for simulating the transport of healing agents in self-healing (SH) cementitious materials is presented. The model is applicable to autonomic SH material systems in which embedded channels, or vascular networks, are used to supply healing agents to damaged zones. The essential numerical components of the model are a crack flow model, based on the Navier-Stokes equations, which is coupled to the mass balance equation for simulating unsaturated matrix flow. The driving forces for the crack flow are the capillary meniscus force and the force derived from an external (or internal) pressure applied to the liquid healing agent. The crack flow model component applies to non-uniform cracks and allows for the dynamic variation of the meniscus contact angle, as well as accounting for inertial terms. Particular attention is paid to the effects of curing on the flow characteristics. In this regard, a kinetic reaction model is presented for simulating the curing of the healing agent and a set of relationships established for representing the variation of rheological properties with the degree of cure. Data obtained in a linked experimental programme of work are employed to justify the choice and form of the constitutive relationships, as well as to calibrate the model's evolution functions. Finally, a series of validation examples are presented that include the analysis of a series of concrete beam specimens with an embedded vascular network. These examples demonstrate the ability of the model to capture the transport behaviour of this type of SH cementitious material system. 相似文献
114.
Compressed History Matching: Exploiting Transform-Domain Sparsity for Regularization of Nonlinear Dynamic Data Integration Problems 总被引:1,自引:1,他引:0
Behnam?JafarpourEmail author Vivek?K.?Goyal Dennis?B.?McLaughlin William?T.?Freeman 《Mathematical Geosciences》2010,42(1):1-27
In this paper, we present a new approach for estimating spatially-distributed reservoir properties from scattered nonlinear
dynamic well measurements by promoting sparsity in an appropriate transform domain where the unknown properties are believed
to have a sparse approximation. The method is inspired by recent advances in sparse signal reconstruction that is formalized
under the celebrated compressed sensing paradigm. Here, we use a truncated low-frequency discrete cosine transform (DCT) is
redundant to approximate the spatial parameters with a sparse set of coefficients that are identified and estimated using
available observations while imposing sparsity on the solution. The intrinsic continuity in geological features lends itself
to sparse representations using selected low frequency DCT basis elements. By recasting the inversion in the DCT domain, the
problem is transformed into identification of significant basis elements and estimation of the values of their corresponding
coefficients. To find these significant DCT coefficients, a relatively large number of DCT basis vectors (without any preferred
orientation) are initially included in the approximation. Available measurements are combined with a sparsity-promoting penalty
on the DCT coefficients to identify coefficients with significant contribution and eliminate the insignificant ones. Specifically,
minimization of a least-squares objective function augmented by an l
1-norm of DCT coefficients is used to implement this scheme. The sparsity regularization approach using the l
1-norm minimization leads to a better-posed inverse problem that improves the non-uniqueness of the history matching solutions
and promotes solutions that are, according to the prior belief, sparse in the transform domain. The approach is related to
basis pursuit (BP) and least absolute selection and shrinkage operator (LASSO) methods, and it extends the application of
compressed sensing to inverse modeling with nonlinear dynamic observations. While the method appears to be generally applicable
for solving dynamic inverse problems involving spatially-distributed parameters with sparse representation in any linear complementary
basis, in this paper its suitability is demonstrated using low frequency DCT basis and synthetic waterflooding experiments. 相似文献
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116.
We analyzed the deuterium composition of individual plant-waxes in lake sediments from 28 watersheds that span a range of precipitation D/H, vegetation types and climates. The apparent isotopic fractionation (εa) between plant-wax n-alkanes and precipitation differs with watershed ecosystem type and structure, and decreases with increasing regional aridity as measured by enrichment of 2H and 18O associated with evaporation of lake waters. The most negative εa values represent signatures least affected by aridity; these values were −125 ± 5‰ for tropical evergreen and dry forests, −130‰ for a temperate broadleaf forest, −120 ± 9‰ for the high-altitude tropical páramo (herbs, shrubs and grasses), and −98 ± 6‰ for North American montane gymnosperm forests. Minimum εa values reflect ecosystem-dependent differences in leaf water enrichment and soil evaporation. Slopes of lipid/lake water isotopic enrichments differ slightly with ecosystem structure (i.e. open shrublands versus forests) and overall are quite small (slopes = 0-2), indicating low sensitivity of lipid δD variations to aridity compared with coexisting lake waters. This finding provides an approach for reconstructing ancient precipitation signatures based on plant-wax δD measurements and independent proxies for lake water changes with regional aridity. To illustrate this approach, we employ paired plant-wax δD and carbonate-δ18O measurements on lake sediments to estimate the isotopic composition of Miocene precipitation on the Tibetan plateau. 相似文献
117.
Eric F. Freeman 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):4-12
The wet-sieving of sediments on the tonne scale has been used, probably since the mid-1800s, to search for Mesozoic mammal teeth and other microvertebrate fossils. Unfortunately, more sediment can usually be washed than can be searched, because of the very laborious nature of hand-picking non-enriched sediment residues.Such residues can be enriched cheaply and effectively using Interfacial Methods, which exploit differential wetting phenomena. Placed in a suspension of kerosene in water, microvertebrate fossils become wetted preferentially with the kerosene, which then allows them to adhere to granules of paraffin wax; these are removed and melted to release the fossils.One experiment is described where 8.92 kg of a quartz-rich residue (from 13 tonnes of raw sediment) was processed using apparatus centred on a cement mixer.Smaller scale ‘low tech’ apparatus designed for use in the field and improvised from various items of household waste, etc., were used to enrich various sediment residues weighing between 500 g and 1582 g.Theoretical aspects of the process were investigated experimentally with an eye to their practical significance. 相似文献
118.
E. Noordermeer † M. R. Merrifield L. Coccato M. Arnaboldi M. Capaccioli N. G. Douglas K. C. Freeman O. Gerhard K. Kuijken F. De Lorenzi N. R. Napolitano A. J. Romanowsky 《Monthly notices of the Royal Astronomical Society》2008,384(3):943-952
We investigate the manner in which lenticular galaxies are formed by studying their stellar kinematics: an S0 formed from a fading spiral galaxy should display similar cold outer disc kinematics to its progenitor, while an S0 formed in a minor merger should be more dominated by random motions. In a pilot study, an attempt to distinguish between these scenarios, we have measured the planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the Planetary Nebula Spectrograph, we have detected and measured the line-of-sight velocities of 204 candidate planetary nebulae (PNe) in the field of this galaxy. Out to intermediate radii, the system displays the kinematics of a normal rotationally supported disc system. After correction of its rotational velocities for asymmetric drift, the galaxy lies just below the spiral galaxy Tully–Fisher relation, as one would expect for a fading system. However, at larger radii the kinematics undergo a gradual but major transition to random motion with little rotation. This transition does not seem to reflect a change in the viewing geometry or the presence of a distinct halo component, since the number counts of PNe follow the same simple exponential decline as the stellar continuum with the same projected disc ellipticity out to large radii. The galaxy's small companion, NGC 1023A, does not seem to be large enough to have caused the observed modification either. This combination of properties would seem to indicate a complex evolutionary history in either the transition to form an S0 or in the past life of the spiral galaxy from which the S0 formed. More data sets of this type from both spirals and S0s are needed in order to definitively determine the relationship between these types of system. 相似文献
119.
G. M. Seabroke G. Gilmore A. Siebert O. Bienaymé J. Binney J. Bland-Hawthorn R. Campbell K. C. Freeman B. Gibson E. K. Grebel A. Helmi U. Munari J. F. Navarro Q. A. Parker A. Siviero M. Steinmetz F. G. Watson R. F. G. Wyse T. Zwitter J. Peñarrubia M. C. Smith M. Williams 《Monthly notices of the Royal Astronomical Society》2008,384(1):11-32
120.
Archaeal lipids record paleosalinity in hypersaline systems 总被引:2,自引:0,他引:2
We present an ecologically based biomarker method for estimating past salinity, especially in hypersaline conditions. The relative amounts of acyclic diether and tetraether membrane lipids synthesized by Archaea correlate with salinity from 0–250 practical salinity units (psu) in modern settings. We examined the preservation of this lipid biomarker–salinity relationship in ancient sedimentary organic matter using samples from two sequences of marls and diatomites deposited just prior to the Messinian Salinity Crisis. Salinity estimates were consistent with expected absolute salinity, as well as the amplitude of variations leading up to the Messinian Salinity Crisis. This lipid biomarker approach to salinity reconstruction complements existing paleosalinity proxies because (i) Archaea survive and thrive over a broad salinity range, well beyond that of haptophyte algae and other plankton which form the microfossil record and (ii) it provides fine salinity resolution for the wide range broadly defined as hypersaline. With the proxy, there is the potential to provide novel insights into salinity variation within desiccating basins in climatically sensitive seas (e.g. Dead Sea, Permian Delaware Basin), evolution of brines, timing of onset of hypersaline conditions and evaporite deposition. 相似文献