Mechanisms of time-dependent deformation in porous limestone

We performed triaxial deformation experiments on a water-saturated porous limestone under constant strain rate and constant stress (creep) conditions. The tests were conducted at room temperature and at low effective pressures Peff=10 and Peff=20 MPa, in a regime where the rock is nominally brittle when tested at a constant strain rate of 10−5 s−1. Under these conditions and at constant stress, the phenomenon of brittle creep occurs. At Peff=10 MPa, brittle creep follows similar trends as those observed in other rock types (e.g., sandstones and granites): only small strains are accumulated before failure, and damage accumulation with increasing strain (as monitored by P wave speeds measurements during the tests) is not strongly dependent on the applied stresses. At Peff=20 MPa, brittle creep is also macroscopically observed, but when the creep strain rate is lower than ≈10−7 s−1, we observe that (1) much larger strains are accumulated, (2) less damage is accumulated with increasing strain, and (3) the deformation tends to be more compactant. These observations can be understood by considering that another deformation mechanism, different from crack growth, is active at low strain rates. We explore this possibility by constructing a deformation mechanism map that includes both subcritical crack growth and pressure solution creep processes; the increasing contribution of pressure solution creep at low strain rates is consistent with our observations

Impact of Normothermic Preservation with Extracellular Type Solution Containing Trehalose on Rat Kidney Grafting from a Cardiac Death Donor

BACKGROUND: The aim of this study was to investigate factors that may improve the condition of a marginal kidney preserved with a normothermic solution following cardiac death (CD) in a model of rat kidney transplantation (RTx). METHODS: Post-euthanasia, Lewis (LEW) donor rats were left for 1 h in a 23°C room. These critical kidney grafts were preserved in University of Wisconsin (UW), lactate Ringer's (LR), or extracellular-trehalose-Kyoto (ETK) solution, followed by intracellular-trehalose-Kyoto (ITK) solution at 4, 23, or 37°C for another 1 h, and finally transplanted into bilaterally nephrectomized LEW recipient rats (n = 4-6). Grafts of rats surviving to day 14 after RTx were evaluated by histopathological examination. The energy activity of these marginal rat kidneys was measured by high-performance liquid chromatography (HPLC; n = 4 per group) and fluorescence intensity assay (n = 6 per group) after preservation with UW or ETK solutions at each temperature. Finally, the transplanted kidney was assessed by an in vivo luciferase imaging system (n = 2). RESULTS: Using the 1-h normothermic preservation of post-CD kidneys, five out of six recipients in the ETK group survived until 14 days, in contrast to zero out of six in the UW group (p<0.01). Preservation with ITK rather than ETK at 23°C tended to have an inferior effect on recipient survival (p = 0.12). Energy activities of the fresh donor kidneys decreased in a temperature-dependent manner, while those of post-CD kidneys remained at the lower level. ETK was superior to UW in protecting against edema of the post-CD kidneys at the higher temperature. Luminescence intensity of successful grafts recovered within 1 h, while the intensity of grafts of deceased recipients did not change at 1 h post-reperfusion. CONCLUSIONS: Normothermic storage with extracellular-type solution containing trehalose might prevent reperfusion injury due to temperature-dependent tissue edema

Role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium deposits: insights from reactive-flow modeling

The role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium (URU) deposits in sedimentary basins during tectonically quiet periods is investigated. A number of reactive-flow modeling experiments at the deposit scale were carried out by assigning different dip angles and directions to a fault and various permeabilities to hydrostratigraphic units). The results show that the fault dip angle and direction, and permeability of the hydrostratigraphic units govern the convection pattern, temperature distribution, and uranium mineralization. Avertical fault results in uranium mineralization at the bottom of the fault within the basement, while a dipping fault leads to precipitation of uraninite below the unconformity either away from or along the plane of the fault, depending on the fault permeability. A more permeable fault causes uraninite precipitates along the fault plane,whereas a less permeable one gives rise to the precipitation of uraninite away from it. No economic ore mineralization can form when either very low or very high permeabilities are assigned to the sandstone or basement suggesting that these units seem to have an optimal window of permeability for the formation of uranium deposits. Physicochemical parameters also exert an additional control in both the location and grade of URU deposits. These results indicate that the difference in size and grade of different URU deposits may result from variation in fluid flow pattern and physicochemical conditions, caused by the change in structural features and hydraulic properties of the stratigraphic units involved

Absence of Stress-Induced Anisotropy During Brittle Deformation in Antigorite Serpentinite

Knowledge of the seismological signature of serpentinites during deformation is fundamental for interpreting seismic observations in subduction zones, but this has yet to be experimentally constrained. We measured compressional and shear wave velocities during brittle deformation in polycrystalline antigorite, at room temperature and varying confining pressures up to 150 MPa. Ultrasonic velocity measurements, at varying directions to the compression axis, were combined with mechanical measurements of axial and volumetric strain, during direct loading and cyclic loading triaxial deformation tests. An additional deformation experiment was conducted on a specimen of Westerly granite for comparison. At all confining pressures, brittle deformation in antigorite is associated with a spectacular absence of stress‐induced anisotropy and with no noticeable dependence of wave velocities on axial compressive stress, prior to rock failure. The strength of antigorite samples is comparable to that of granite, but the mechanical behavior is elastic up to high stress ( urn:x-wiley:jgrb:media:jgrb53171:jgrb53171-math-0001 of rock strength) and nondilatant. Microcracking is only observed in antigorite specimens taken to failure and not in those loaded even at 90–95% of their compressive strength. Microcrack damage is extremely localized near the fault and consists of shear microcracks that form exclusively along the cleavage plane of antigorite crystals. Our observations demonstrate that brittle deformation in antigorite occurs entirely by “mode II” shear microcracking. This is all the more remarkable than the preexisting microcrack population in antigorite, is comparable to that in granite. The mechanical behavior and seismic signature of antigorite brittle deformation thus appears to be unique within crystalline rocks

Characterization of Pore Geometry of Indiana Limestone in Relation to Mechanical Compaction Caractérisation de la géométrie des pores dans le calcaire de l’Indiana (États-Unis) en relation avec la compaction mécanique

We studied the pore structure in intact and inelastically compacted Indiana limestone using X-ray microtomography imaging. Guided by detailed microstructural observations and using Otsu’s global thresholding method, the 3D images acquired at voxel side length of 4 μm were segmented into three domains: solid grains, macropores and an intermediate zone dominated by microporosity. The macropores were individually identified by morphological processing and their shape quantified by their sphericity and equivalent diameter. Our new data revealed a significant reduction of the number of macropores in hydrostatically and triaxially compressed samples with respect to the intact material, in agreement with previous microstructural analysis. The intermediate (microporosity) domains remained interconnected in compacted samples. Our data suggest that the inelastic compaction in Indiana limestone is manifested as not only a decrease in the volume fraction of the microporosity backbone but also a corresponding decrease in its thickness. La structure des pores dans des echantillons de calcaire de l’Indiana intact et deforme a ete etudiee par microtomographie a rayons X. En se basant sur une etude detaillee de la microstructure et en utilisant la methode de seuillage global d’Otsu, les images 3D acquises avec un voxel de 4 μm ont ete segmentees en trois domaines : les grains, les macropores et une zone intermediaire dominee par la microporosite. Les macropores ont ete individualises grace a une analyse morphologique qui a egalement permis de quantifier leurs formes (sphericite et diametre equivalent). Nos nouvelles donnees 3D montrent une reduction significative du nombre de macropores dans les echantillons deformes sous chargements hydrostatique et triaxial par rapport a la roche intacte, en accord avec les etudes anterieures sur la microstructure du calcaire de l’Indiana. Le domaine intermediaire (microporosite) reste interconnecte dans les echantillons deformes. Notre analyse suggere que la deformation irreversible dans le calcaire de l’Indiana se manifeste par une diminution a la fois du volume et de la surface de cette zone microporeuse

Micromechanics of inelastic compaction in two allochemical limestones

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Algorithmic optimization of the calculation with the consideration of the interconnection of the basic economic parameters of the flight route of the model air carrier

The load factor is the determining factor for airlines in economic terms and the prediction of the future development of the flight route. The combination of load factor and break-even point provides the airline with a comprehensive picture of the business of the flight route and the optimization of pricing for the flight route. The purpose of the article is to propose and adapt the development of air transport prices on a given line using maximally recalculated values and maximize profit. The optimized calculation algorithm then facilitates the understanding of the individual steps of the load factor calculation and the monitoring of price development by means of the chi-square mathematical method by which we observed the interconnection of the ticket price and the load factor. To describe the problem, we chose the Bratislava – Larnaca route