Application of High T/High P Rock Mechanics to the Problem of Extraction of Granitic Magma from its Protolith

The mechanical deformation behaviour of a partially molten granitic protolith is investigated, implications towards a mechanism for extraction of low melt percentages («30 %) are mathematically explored. For this purpose a series of experiments on Westerly granite (with no added water) are presented in which samples were heated to temperatures between 800 and 1200 °C, at a confining pressure of 250 MPa. Samples were uniaxially deformed to study the effects of constant strain-rate (4 * 10-4 to 2 * 10-7 s-1), creep and stress relaxation tests on the mechanical behaviour. The volumetric percentage of melt (Φ) in samples ranged from 3 % at 800 °C to 77 % a t 1200 °C at heating times between 2.5 and 170 hours. However, none of the samples attained chemical equilibrium, due to the short duration of tests. An equilibrium melt percentage was also not reached. Over this temperature interval the supported strength decreased from 500 MPa to less than 1 MPa (at a constant strain rate of 8 * 10-5 s-1) monotonically. No step-like drop in strength, corresponding to a rheological critical melt percentage (van der Molen & Paterson 1979) was observed. A preliminary flow law for the partially molten rock was obtained to allow extrapolation to lower strain-rates. The viscosity of the melt was estimated at 950 and 1000 °C from distances it could be made to permeate into porous sand under a known pressure gradient. Melt distribution in static tests indicated a very low wetting angle (< 5°) which results in high melt contiguity even at low melt percentages along grain boundaries. Under all conditions, the solid phases deformed by brittle fracture only. Samples with 3 shear enhanced compaction of melt filled voids by analogy with uniaxial compaction of porous sands. In samples with Φ > 45 % grains were carried about passively in the flowing liquid. A simple mathematical model is erected to describe a two stage process of extracting low volume percentage, granitic melt from its partially molten protolith with the aid of non-hydrostatic stress. Shear-enhanced compaction drives melt from the protolith into a series of interconnected melt-filled veins, whereupon porous flow through the high-permeability vein network allows rapid drainage of melt to higher crustal levels. Modeling suggests that melt extraction, with Φ11 Pas, is possible within geologically realistic time periods (10 Ma)

TOX defines the degree of CD8+ T cell dysfunction in distinct phases of chronic HBV infection

Objective Chronic hepatitis B virus (HBV) infection is characterised by HBV-specific CD8+ T cell dysfunction that has been linked to Tcell exhaustion, a distinct differentiation programme associated with persisting antigen recognition. Recently, Thymocyte Selection-Associated High Mobility Group Box (TOX) was identified as master regulator of CD8+ T cell exhaustion. Here, we addressed the role of TOX in HBV-specific CD8+ T cell dysfunction associated with different clinical phases of infection. Design We investigated TOX expression in HBV-specific CD8+ T cells from 53 HLA-A*01:01, HLA-A*11:01 and HLA-A*02:01 positive patients from different HBV infection phases and compared it to hepatitis C virus (HCV)-specific, cytomegalovirus (CMV)-specific, Epstein-Barr virus (EBV)-specific and influenza virus (FLU)-specific CD8+ T cells. Phenotypic and functional analyses of virus-specific CD8+ T cells were performed after peptide-loaded tetramer-enrichment and peptide-specific expansion. Results Our results show that TOX expression in HBV-specific CD8+ T cells is linked to chronic antigen stimulation, correlates with viral load and is associated with phenotypic and functional characteristics of T-cell exhaustion. In contrast, similar TOX expression in EBV-specific and CMV-specific CD8+ T cells is not linked to T-cell dysfunction suggesting different underlying programmes. TOX expression in HBV-specific CD8+ T cells is also affected by targeted antigens, for example, core versus polymerase. In HBV-specific CD8+ T cells, TOX expression is maintained after spontaneous or therapy-mediated viral control in chronic but not self-limiting acute HBV infection indicating a permanent molecular imprint after chronic but not temporary stimulation. Conclusion Our data highlight TOX as biomarker specific for dysfunctional virus-specific CD8+ T cells in the context of an actively persisting infection

Rapid bioerosion in a tropical upwelling coral reef

Coral reefs persist in an accretion-erosion balance, which is critical for understanding the natural variability of sediment production, reef accretion, and their effects on the carbonate budget. Bioerosion (i.e. biodegradation of substrate) and encrustation (i.e. calcified overgrowth on substrate) influence the carbonate budget and the ecological functions of coral reefs, by substrate formation/consolidation/erosion, food availability and nutrient cycling. This study investigates settlement succession and carbonate budget change by bioeroding and encrusting calcifying organisms on experimentally deployed coral substrates (skeletal fragments of Stylophora pistillata branches). The substrates were deployed in a marginal coral reef located in the Gulf of Papagayo (Costa Rica, Eastern Tropical Pacific) for four months during the northern winter upwelling period (December 2013 to March 2014), and consecutively sampled after each month. Due to the upwelling environmental conditions within the Eastern Tropical Pacific, this region serves as a natural laboratory to study ecological processes such as bioerosion, which may reflect climate change scenarios. Time-series analyses showed a rapid settlement of bioeroders, particularly of lithophagine bivalves of the genus Lithophaga/ Leiosolenus (Dillwyn, 1817), within the first two months of exposure. The observed enhanced calcium carbonate loss of coral substrate (>30%) may influence seawater carbon chemistry. This is evident by measurements of an elevated seawater pH (>8.2) and aragonite saturation state (Ωarag >3) at Matapalo Reef during the upwelling period, when compared to a previous upwelling event observed at a nearby site in distance to a coral reef (Marina Papagayo). Due to the resulting local carbonate buffer effect of the seawater, an influx of atmospheric CO2 into reef waters was observed. Substrates showed no secondary cements in thin-section analyses, despite constant seawater carbonate oversaturation (Ωarag >2.8) during the field experiment. Micro Computerized Tomography (μCT) scans and microcast-embeddings of the substrates revealed that the carbonate loss was primarily due to internal macrobioerosion and an increase in microbioerosion. This study emphasizes the interconnected effects of upwelling and carbonate bioerosion on the reef carbonate budget and the ecological turnovers of carbonate producers in tropical coral reefs under environmental change.Sistema Nacional de Áreas de Conservación/[028-2013-SINAC]/SINAC/Costa RicaSistema Nacional de Áreas de Conservación/[72-2013-SINAC]/SINAC/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Analysis of the Secondary Phases Formed by Corrosion of U3Si2-Al Research Reactor Fuel Elements in the Presence of Chloride Rich Brines

Corrosion experiments with non-irradiated U3Si2-Al research reactor fuel samples were carried out in synthetic MgCl2-rich brine to identify and quantify the secondary phases because depending on their composition and on their amount, such compounds can act as a sink for the radionuclide release in final repositories. Within the experimental period of 100 days at 90 °C and anoxic conditions the U3Si2-Al fuel sample was completely disintegrated. The obtained solids were subdivided into different grain size fractions and non-ambient X-ray diffraction (XRD) was applied for their qualitative and quantitative phase analysis. The secondary phases consist of lesukite (aluminum chloro hydrate) and layered double hydroxides (LDH) with varying chemical compositions. Furthermore, iron, residues of non-corroded nuclear fuel (U3Si2), iron oxy hydroxides and chlorides were also observed. In addition to high amorphous contents (>45 wt %) hosting the uranium, the quantitative phase analysis showed, that LDH compounds and lesukite were the major crystalline phases. Scanning electron microscopy (SEM) and energy dispersive -Xray spectroscopy (EDS) confirmed the results of the XRD analysis. Elemental analysis revealed that U and Al were concentrated in the solids. However, most of the iron, added as Fe(II) aqueous species, remained in solution

Corrosion of non-irradiated UAlx-Al fuel in the presence of clay pore solution: a quantitative XRD secondary phase analysis applying the DDM method

Corrosion experiments with non-irradiated metallic UAlx–Al research reactor fuel elements were carried out in autoclaves to identify and quantify the corrosion products. Such compounds, considering the long-term safety assessment of final repositories, can interact with the released inventory and this constitutes a sink for radionuclide migration in formation waters. Therefore, the metallic fuel sample was subjected to clay pore solution to investigate its process of disintegration by analyzing the resulting products and the remnants, i.e. the secondary phases. Due to the fast corrosion rate a full sample disintegration was observed within the experimental period of 1 year at 90°C. The obtained solids were subdivided into different grain size fractions and prepared for analysis. The elemental analysis of the suspension showed that, uranium and aluminum are concentrated in the solids, whereas iron was mainly dissolved. Non-ambient X-ray diffraction (XRD) combined with the derivative difference minimization (DDM) method was applied for the qualitative and quantitative phase analysis (QPA) of the secondary phases. Gypsum and hemihydrate (bassanite), residues of non-corroded nuclear fuel, hematite, and goethite were identified. The quantitative phase analysis showed that goethite is the major crystalline phase. The amorphous content exceeded 80 wt% and hosted the uranium. All other compounds were present to a minor content. The obtained results by XRD were well supported by complementary scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis

Synthesis, characterization and stability properties of Cl-bearing hydrotalcite-pyroaurite solids

Abstract A layered double hydroxides (LDH) hydrotalcite-pyroaurite solid solution series (Mg1−x Fe(II) x )3Al1Cl1·nH2O with variable xFesolid = Fe2+/(Fe2++Mg2+) iron mole fractions were studied in co-precipitation experiments at T = 25, 40, 45, 50, 55 and 60 ºC and pH = 10.00 ± 0.05. The compositions of the solids and reaction solutions were determined using ICP-OES, EDX (Mg, Al, Fe) and TGA techniques (Cl−, OH−, H2O). Powder X-ray diffraction was applied for phase identification and determination of unit-cell parameters a o = b o and c o from Bragg evaluation. Syntheses products containing xFesolid &gt; 0.13 display additional X-ray patterns attributed to the mixture of iron oxides and hydroxides. On the other side, precipitates with 0 ≤ xFesolid ≤ 0.13 show only X-ray reflexes typical for pure LDH compositions. Moreover, in this case unit-cell parameters a o = b o as a function of xFesolid follow Vegard's law corroborating the existence of a continuous solid solution series. TGA data demonstrated the temperatures at which interlayer H2O molecules and Cl−-anions are lost, and at which temperatures dehydroxylation of brucite-like layer occurs. Based on detailed analyses of TGA curves it was established that the increase of xFesolid does not result in a visible change of the thermal stability of hydrotalcite-pyroaurite solids. From the chemical analyses of both the solids and the reaction solutions after syntheses, preliminary Gibbs free energies of formation were estimated by using GEMS-PSI code package. Values of Gºf (Hydrotalcite) = −3619.04 ± 15.27 kJ/mol and Gºf(Pyroaurite) = −2703.61 ± 191.93 kJ/mol were found at 298.15 K. A comparison of our estimate with Gºf value −3746.90 ± 11.00 kJ/mol for CO3 2−-bearing hydrotalcite presented in our previous studies, denotes the effect of intercalated anion on the aqueous solubilities of LDH when Cl-containing solids have to be more soluble than CO3 2−-bearing substances. Estimation of the standard molar entropy of the hydrotalcite end-member by applying Helgeson's methods and using results of co-precipitation experiments at variable temperatures let us to conclude that derivation of more precise Sºf values would require calorimetric measurements.</jats:p