Strain partitioning across a subduction thrust fault near the deformation front of the Hikurangi subduction margin, New Zealand: A magnetic fabric study on IODP Expedition 375 Site U1518

Understanding the distribution of strain along thrust and splay faults in active accretionary systems is crucial to understand the mechanical properties of the sediments and the strength of the fault zone and its slip behavior. This paper investigates the distribution of strain through sediment compaction and texture development across the Pāpaku fault, a major splay fault near the deformation front of the Hikurangi subduction margin, New Zealand using the anisotropy of magnetic susceptibility technique (AMS). International Ocean Discovery Program Site U1518 penetrated hanging wall, fault zone and footwall sequences to a maximum depth of 484.9 meters below seafloor. A total of 330 discrete samples was subjected to AMS measurements and magnetic remanence data used to reconstruct the axial orientation of each sample in a geographic reference frame. The AMS display distinct fabric differences between hanging wall, through the fault zone and footwall domains, demonstrating that strain is partitioned across the fault zone. Hanging wall sequences show a strike-parallel northeasterly lineation of K$_{max}$ and weakly prolate shapes, typical for a component of northeast-southwest lateral shortening. In contrast, footwall sequences are more oblate and show a clustering of K$_{max}$ in northerly direction. This demonstrates that strain in the footwall is dominated by gravitational loading, however a component of sub-horizontal east-westerly strain, parallel to the convergence direction of the Pacific Plate exists. Strain decoupling between hanging- and footwall sequences occurs near the top of the Pāpaku fault zone. Differences in the degree of magnetic susceptibility between footwall sediments incorporated into the fault zone, and the underlying undeformed footwall sequences are indicative for the progressive dewatering of the underconsolidated footwall sequences

Patterns of entropy production in dissolving natural porous media with flowing fluid

The tendency for irreversible processes to generate entropy is the ultimate driving force for structure evolution in nature. In engineering, entropy production is often used as an indicator for loss of usable energy. In this study, we show that the analysis of entropy production patterns can provide insight into the diverse observations from experiments that investigate porous medium dissolution in imposed flow field. We first present a numerical scheme for the analysis of entropy production in dissolving porous media. Our scheme uses a greyscale digital model for chalk (an extremely fine grained rock), that was obtained using X-ray nanotomography. Greyscale models preserve structural heterogeneities with very high fidelity. We focussed on the coupling between two types of entropy production: the percolative entropy, generated by dissipating the kinetic energy of fluid flow, and the reactive entropy, originating from the consumption of chemical free energy. Their temporal patterns pinpoint three stages of microstructural evolution. We then showed that local mixing deteriorates fluid channelisation by reducing local variations of reactant concentration. We also showed that microstructural evolution can be sensitive to the initial transport heterogeneities, when the macroscopic flowrate is low. This dependence on flowrate indicates the need to resolve the structural features of a porous system when fluid residence time is long

Competition policy newsletter Volume 1, No 2, Summer 1994

When reactive fluids flow through a dissolving porous medium, conductive channels form, leading to fluid breakthrough. This phenomenon is caused by the reactive infiltration instability and is important in geologic carbon storage where the dissolution of CO₂ in flowing water increases fluid acidity. Using numerical simulations with high resolution digital models of North Sea chalk, we show that the breakthrough porosity is an important indicator of dissolution pattern. Dissolution patterns reflect the balance between the demand and supply of cumulative surface. The demand is determined by the reactive fluid composition while the supply relies on the flow field and the rock’s microstructure. We tested three model scenarios and found that aqueous CO₂ dissolves porous media homogeneously, leading to large breakthrough porosity. In contrast, solutions without CO₂ develop elongated convective channels known as wormholes, with low breakthrough porosity. These different patterns are explained by the different apparent solubility of calcite in free drift systems. Our results indicate that CO₂ increases the reactive subvolume of porous media and reduces the amount of solid residual before reactive fluid can be fully channelized. Consequently, dissolved CO₂ may enhance contaminant mobilization near injection wellbores, undermine the mechanical sustainability of formation rocks and increase the likelihood of buoyance driven leakage through carbonate rich caprocks

Structure of nanoparticles embedded in micellar polycrystals

We investigate by scattering techniques the structure of water-based soft composite materials comprising a crystal made of Pluronic block-copolymer micelles arranged in a face-centered cubic lattice and a small amount (at most 2% by volume) of silica nanoparticles, of size comparable to that of the micelles. The copolymer is thermosensitive: it is hydrophilic and fully dissolved in water at low temperature (T ~ 0{\deg}C), and self-assembles into micelles at room temperature, where the block-copolymer is amphiphilic. We use contrast matching small-angle neuron scattering experiments to probe independently the structure of the nanoparticles and that of the polymer. We find that the nanoparticles do not perturb the crystalline order. In addition, a structure peak is measured for the silica nanoparticles dispersed in the polycrystalline samples. This implies that the samples are spatially heterogeneous and comprise, without macroscopic phase separation, silica-poor and silica-rich regions. We show that the nanoparticle concentration in the silica-rich regions is about tenfold the average concentration. These regions are grain boundaries between crystallites, where nanoparticles concentrate, as shown by static light scattering and by light microscopy imaging of the samples. We show that the temperature rate at which the sample is prepared strongly influence the segregation of the nanoparticles in the grain-boundaries.Comment: accepted for publication in Langmui

The Tetraspanins CD9 and CD81 Regulate CD9P1-Induced Effects on Cell Migration

CD9P-1 is a cell surface protein with immunoglobulin domains and an unknown function that specifically associates with tetraspanins CD9 and CD81. Overexpression of CD9P-1 in HEK-293 cells induces dramatic changes in cell spreading and migration on various matrices. Experiments using time-lapse videomicroscopy revealed that CD9P-1 expression has led to higher cell motility on collagen I but lower motility on fibronectin through a β1-integrins dependent mechanism. On collagen I, the increase in cell motility induced by CD9P-1 expression was found to involve integrin α2β1 and CD9P-1 was observed to associate with this collagen receptor. The generation of CD9P-1 mutants demonstrated that the transmembrane and the cytoplasmic domains are necessary for inducing effects on cell motility. On the other hand, expression of tetraspanins CD9 or CD81 was shown to reverse the effects of CD9P-1 on cell motility on collagen I or fibronectin with a concomitant association with CD9P-1. Thus, the ratio of expression levels between CD9P-1 and its tetraspanin partners can regulate cell motility

How to drive phloem gene expression? A case study with preferentially expressed citrus gene promoters.

New approaches for developing disease-resistant genetically modified organisms have included specific targets for gene expression to enhance the chances for pathogen control. Gene expression driven by phloem-derived Citrus sinensis gene promoters could be evaluated and compared with the expression induced by a strong constitutive promoter in the same tissue, leading to the production of transgenic sweet oranges potentially more resistant to diseases caused by phloem-limited bacteria. ?Carrizo? citrange [Poncirus trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] was transformed, via Agrobacterium tumefaciens, with the binary vector pCAMBIA2301 bearing the uidA gene (?-glucuronidase) driven by the CaMV35S constitutive promoter (CaMV35S::uidA) or by the CsPP2.B1 (CsPP2.B1::uidA) or by the CsVTE2 (CsVTE2::uidA) citrus promoters. In vitro regenerated shoots were grafted onto ?Rangpur? lime (C. limonia Osbeck). The genetic transformation was confirmed by Southern blot analyses. uidA gene expression was evaluated by RT-qPCR, and gene histolocalization controlled by these three promoters was accessed by X-GLUC treated stem sections. uidA gene expression exhibited by tissue-specific promoters was overall lower than from the constitutive promoter CaMV35; however, constructs driven by tissuespecific promoters may lead to expression in restricted tissues. CsPP2.B1 and CsVTE2 promoters can be considered adequate for the utilization in gene constructs aiming disease resistance