Decrease In Fluid Pressure Research Articles

The precipitation mechanisms of scheelite from CO2-rich hydrothermal fluids: Insight from thermodynamic modeling

Scheelite and wolframite are two main tungsten-bearing ore minerals in tungsten deposits. Compared to wolframite formed mostly by NaCl–H2O fluids, scheelite in many but not all tungsten deposits is associated with CO2–bearing hydrothermal fluids, but its precipitation mechanisms from these fluids are poorly understood. The replacement of wolframite by scheelite is common among tungsten deposits where these two tungstates coexist, but how CO2, as the pH-buffering agent, affects their replacement remains unclear. To answer these questions, we first tested the pH-buffering effect of CO2 by comparing available experimental pH values of H2O–CO2±NaCl solutions at 200–280 °C and the corresponding thermodynamic modeling results. The mean absolute errors between the calculated and experimental pH values are 0.14 log units in H2O–CO2 solutions and 0.13 log units in H2O–CO2–NaCl solutions, indicating that the calculated acitivities of H+ in CO2-bearing solutions are reliable. Then, the solubilities of scheelite, scheelite-ferberite, and scheelite-hübnerite in NaCl–H2O–CO2 systems were modeled in this study. Our modeling results suggest that scheelite solubility in CO2-rich fluids is highly dependent on fluid pressure but is insensitive to fluid temperature. A decrease in fluid pressure from lithostatic to hydrostatic levels at a depth of 3–8 km causes CO2 escape and pH rise and precipitates over 70 % of tungsten contents in fluids on average. Therefore, CO2 escape is an efficient mechanism for precipitating scheelite from CO2–rich hydrothermal fluids. The independence of scheelite solubility on temperature at high pressures and the slightly retrograde solubility at low pressures allows CO2–rich hydrothermal fluids to carry a great amount of tungsten far away from its sources. This may be one of reasons why some scheelite deposits occur at greater distances (>500 m) from the granite or extend along its strike for several kilometers. Similar to the cases in NaCl–H2O systems, two mechanisms for scheelite replacing wolframite in CO2–rich fluids are identified, a single decrease in fluid pressure or simple cooling plus an increase in the ratios of total Ca contents to total Fe (or Mn) contents in fluids.

A 3D Non-Linear FE Model and Optimization of Cavity Die Sheet Hydroforming Process

Cryo-rolled aluminum alloys have a much higher strength-to-weight ratio than cold-rolled alloys, which makes them invaluable in the aerospace and automotive industries. However, this strength gain is frequently accompanied by a formability loss. When uniformly applied to the blank surface, hydroforming provides a solution by generating geometries with constant thickness, making it possible to produce complex structures with “near-net dimensions”, which are difficult to achieve with conventional approaches. This study delves into the cavity die sheet hydroforming (CDSHF) process for high-strength cryo-rolled AA5083 aluminum alloy, focusing on two primary research questions. Firstly, we explored the utilization of a nonlinear 3D finite-element (FE) model to understand its impact on the dimensional accuracy of hydroformed components within the CDSHF process. Specifically, we investigated how decreasing fluid pressure and increasing the holding time of peak fluid pressure can be quantitatively assessed. Secondly, we delved into the optimization of process parameters—fluid pressure (FP), blank holding force (BHF), coefficient of friction (CoF), and flange radius (FR)—to achieve dimensional accuracy in hydroformed square cups through the CDSHF process. Our findings reveal that our efforts, such as reducing peak fluid pressure to 22 MPa, implementing a 30 s holding period, and utilizing an unloading path, enhanced component quality. We demonstrated this with a 35 mm deep square cup exhibiting a 16.1 mm corner radius and reduced material thinning to 5.5%. Leveraging a sophisticated nonlinear 3D FE model coupled with response surface methodology (RSM) and multi-objective optimization techniques, we systematically identified the optimal process configurations, accounting for parameter interactions. Our results underscore the quantitative efficacy of these optimization strategies, as the optimized RSM model closely aligns with finite-element (FE) simulation results, predicting a thinning percentage of 5.27 and a corner radius of 18.64 mm. Overall, our study provides valuable insights into enhancing dimensional accuracy and process optimization in CDSHF, with far-reaching implications for advancing metal-forming technologies.

Monitoring induced microseismicity in an urban context using very small seismic arrays: The case study of the Vendenheim EGS project

Monitoring the seismicity induced by fluid injections in deep geothermal reservoirs is often limited by the significant anthropogenic ambient noise level inherent to most enhanced geothermal system (EGS) projects in urban contexts. We report on the performance of a monitoring network made of three small aperture (72 m) seismic arrays composed of 21 3D nodes. We test the setup for four months (from 12 December 2020 to 8 April 2021) of the Strasbourg sequence of induced earthquakes (2019–2022) related to the EGS Georhin project (Vendenheim, France). The deployment starts a few days after the MLv = 3.6 induced earthquake of 4 December 2020 and covers the early shut-in period of the wells. We use a beamforming technique to characterize the main noise sources, which consist of slow apparent velocities of surface waves emitted from mobile anthropogenic sources (motorway and railway traffic). We detect events with a phase-weighted stacking method, which is efficient when wavefronts illuminate the arrays with a high apparent velocity. Earthquakes associated with these detections are located using a matched field processing technique. The obtained catalog includes 216 seismic events, which represent four times more events than the reference catalog from Le Bureau Central Sismologique Français–Renass (the national academic agency in charge of seismicity monitoring in France), and a reduction of the completeness magnitude from 0.3 to −0.5. The clustering of the seismicity is analyzed using waveform correlation. The enriched catalog reveals intermittent seismic activity during the slow and continuous decrease in fluid pressure after shut-in.

Factors Regulating Fluid Restitution and Plasma Volume Reduction over the Course of Hemodialysis.

Over the course of hemodialysis, fluid and protein are restituted from the tissue compartment to the circulation compartment through the endothelia. Our previous model analysis on fluid and protein transport during hemodialysis is expanded to account for changes occurring in the tissue. The measured initial and end plasma protein concentration (PPC, Cp and Cp') for six hemodialysis studies are analyzed by this expanded model. The computation results indicate that the total driving pressure to restitute fluid from the tissue to the circulation ranges from 5.4 to 20.3 mmHg. The analysis identifies that the increase in plasma colloidal osmotic pressure (COP) contributes 78 ± 6% of the total driving pressure, the decrease in microvascular blood pressure 32 ± 4%, the increase in the COP of interstitial fluid -6 ± 3%, and the decrease in interstitial fluid pressure -5 ± 2%. Let this ratio (Cp' - Cp)/Cp' be termed the PPC increment. The six HDs can be divided into three groups which are to have these PPC increments 25.7%, 14.5 ± 2.6(SD)% and 8.3%. It is calculated that their correspondent filtration coefficients are 0.43, 1.29 ± 0.28 and 5.93 mL/min/mmHg and the relative reductions in plasma volume (RRPV) -22.1%, -13.1 ± 6% and -9.4%. The large variations in PPC increments and RRPV show the filtration coefficient is a key factor to regulate the hemodialysis process.

Numerical simulation of flow and heat transfer performance during supercritical water injection in vertical wellbore: A parameter sensitivity analysis

Supercritical water injection is a promising technology for heavy oil thermal recovery. Predicting and regulating the thermophysical parameters of supercritical water at bottomhole are the prerequisite for achieving high recovery efficiency. In this paper, a novel numerical model was proposed to simulate wellbore flow and heat transfer of supercritical water injection. A modified correlation of frictional coefficient was developed to calculate water flow resistance near its critical point, where its properties change abruptly. The unsteady heat loss to the formation was calculated directly by solving two-dimensional unsteady heat conduction equations. They were respectively coupled in momentum and energy balance equations using an iterative scheme. This model was proved to be accurate by two oilfield cases in which the relative errors of wellbore fluid pressure and temperature are less than 1%. Then parameters sensitivity analysis of the injection pressure, temperature, mass flux and the apparent heat conductivity of insulating tube was conducted. The results indicated that the temperature variation of wellbore fluid depended on both enthalpy drop (or heat loss) and Joule-Thomson effect. An abnormal phenomenon that the fluid temperature increased with wellbore depth near the critical and pseudo-critical points was found because of the sudden increase in high heat capacity and Joule-Thomson coefficient of water. Raising the bottomhole fluid temperature was the key to enhanced oil recovery by supercritical water injection. Low apparent heat conductivity of insulating tube contributed richly to raise bottomhole fluid temperature by enlarging thermal resistance and reducing wellbore heat loss. There existed an optimal mass flux for maximizing bottomhole temperature, because when the mass flux increased, the shortened resident time within wellbore and the decreased fluid pressure favored temperature increase and decrease respectively. Selecting an injection pressure near the critical or pseudo-critical point and raising the injection temperature would increase the bottomhole temperature and reduce relative fluid heat loss.

Failure modes in fluid saturated rocks: deformation processes and mode-switching

AbstractWe consider the implications of adding a cap to the yield surface for elastic–plastic and elastic–visco-plastic solids with coupling between deformation, fluid flow and mineral reactions. For a suitable combination of (low) permeability and strain rate, opening-mode veins can form in compression. Such behaviour is enhanced by dissolution and by simultaneous mineral reactions with negative ΔV. These are the opening-mode equivalents of compaction bands in rocks with high permeability. Stylolite parallel veins are considered as forming in this way; such veins are commonly the laminated or ribbon-quartz veins associated with intense gold mineralization. Axial plane veins and melt segregations are in this class also. The addition of a yield surface cap limits the permissible stress states portrayed by a failure-mode diagram and has implications for breccia formation. Failure discontinuities that form at the cap require adecreasein fluid pressure to form as opposed to extension joints and veins that require anincreasein fluid pressure; discontinuities that form at the cap are in orientations that are commonly interpreted as reactivated early discontinuities. The switching between high fluid pressure and low fluid pressure, which we callmode-switching, arises from competition between mineral dissolution and deposition. This is an alternative to the fault-valve mechanism and does not require fault reactivation or failure at a ‘seal’ linked to seismicity or fault reactivation. The capped yield surface concept provides a unifying self-consistent approach for vein/breccia formation and for the kinematics of brittle and visco-plastic rocks.

The Utilization of Bevacizumab in Patients with Advanced Ovarian Cancer: A Systematic Review of the Mechanisms and Effects.

Most ovarian cancer cases are diagnosed at an advanced stage (III or IV), in which a primary debulking surgery combined with adjuvant systemic chemotherapy is the standard management. Since targeted therapy is less toxic to human cells than systemic chemotherapy, it has drawn much attention and become more popular. Angiogenesis is a critical process during the proliferation of ovarian cancer cells. Currently, many studies have put emphases on anti-angiogenetic medication, such as bevacizumab, the first and most investigated angiogenesis inhibitor that can exert anti-neoplastic effects. Bevacizumab is a recombinant humanized monoclonal antibody that has been approved for first-line maintenance treatment of advanced ovarian cancer. This review is a summary of current literature about the molecular mechanisms of actions, safety, and effects of bevacizumab for use in advanced epithelial ovarian cancer. Some common side effects of bevacizumab will be also discussed. As an inhibitor of angiogenesis, bevacizumab binds to circulating vascular endothelial growth factor (VEGF) and thereby inhibits the binding of VEGF to its receptors on the surface of endothelial cells. Neutralization of VEGF prevents neovascularization and leads to apoptosis of tumor endothelial cells and a decrease in interstitial fluid pressure within the tumors, which allows greater capacity for chemotherapeutic drugs to reach specific targeted sites. Grossly, bevacizumab has demonstrated some significant therapeutic benefits in many randomized trials in combination with the standard chemotherapy for advanced epithelial ovarian cancer. Based on the available evidence, a higher dosage and a longer duration of bevacizumab appear to achieve better therapeutic effects and progression-free survival. On the other hand, patients with more severe diseases or at a higher risk of progression seem to benefit more from bevacizumab use. However, many unknown aspects of bevacizumab, including detailed mechanisms of actions, effectiveness, and safety for the treatment of ovarian cancer, warrant further investigation.

Numerical Analysis of Thermal, Fluid, and Electrical Performance of a Photovoltaic Thermal Collector at New Micro-Channels Geometry

Abstract In this article, different paths (direct, spiral, and curved) for water flow in a photovoltaic/thermal (PV/T) system are studied, and they are compared together. The intensity of radiation to the cell surface is taken 800 W/m2, and the fluid flow is considered to be laminar in the micro-channels. The PV cell absorbing radiation is of an aluminum type. The numerical solution of the three geometries is carried out using the finite volume method using ansys-fluent software. The pressure decomposition, momentum and energy discretization, and the solution of the pressure–velocity coupling are performed based on the standard method, the second-order upwind method, and the semi-implicit method for pressure-linked equations (SIMPLE) method, respectively. The convergence factor is considered to be respected and for continuity and energy equations. The results indicate that the cell surface temperature and the outlet fluid temperature decrease by increasing the Reynolds (Re) number. Moreover, electricity efficiency increases with the increased Reynolds number. The curved path has the highest electrical efficiency in comparison to other two paths. The decrease in fluid pressure of the curved path in Re = 600 is 4% and 1.3% higher than the direct and spiral paths, respectively.

Hydrothermal activity along a strike-slip fault zone and host units in the São Francisco Craton, Brazil – Implications for fluid flow in sedimentary basins

This study combines multiscale analyses of geological, fault, fracture, and stable isotope data to investigate strike-slip deformation and channeling of hydrothermal fluids along the Cafarnaum fault and calcite veins at different distances from the fault, which is a structure in the São Francisco Craton, northeastern Brazil. Meteoric fluids with δD values near −45‰ and δ18O values near −6.5‰ and temperatures at 40–70 °C precipitated as calcite veins in the host carbonate units. The Cafarnaum fault, a N-S-striking vertical, ~170 km long fault zone, juxtaposes Neoproterozoic carbonate rocks in the western block and Mesoproterozoic siliciclastic rocks in the eastern block. A zone of restraining bends occurs at the central part of the fault, whereas termination zones of horsetail geometry occur at both ends of the Cafarnaum fault. These zones are marked by NW-SE-striking extensional faults that are oblique to the main N-S-striking fault zone, where hydrothermal deposits occur. The zone of influence of the Cafarnaum fault is ~ 20 km wide around the main fault. The fault formed during the Brasiliano orogeny (740–560 Ma) after Neoproterozoic carbonate platform deposition. In contrast with the host units, fluids along the fault zone originated in deeper levels of the crust and show much lower δ18O values, indicating higher crystallization temperatures. These fluids caused brecciation in the Neoproterozoic carbonate host rocks, whereas a subsequent decrease in fluid pressure and cooling near the surface resulted in the precipitation of a hydrothermal paragenesis in veins, also affecting the host rock.

The relative solubilities of wolframite and scheelite in hydrothermal fluids: Insights from thermodynamic modeling

The occurrence of either scheelite (CaWO4) or wolframite ([Fe,Mn]WO4) in tungsten deposits is generally explained by the Ca content of the host rocks, but scheelite/wolframite ratios in granitoids-hosted tungsten deposits are highly variable, ranging from scheelite-dominated to wolframite-dominated. Wolframite is also commonly replaced by scheelite or vice versa- among many granitoids-hosted tungsten deposits. To fill this gap in understanding the stabilities of wolframite and scheelite under hydrothermal conditions, the relative solubilities of scheelite and wolframite in hydrothermal fluids were constrained using two modeled chemical systems: W-Ca-Mn-Cl-Na-O-H and W-Ca-Fe-Cl-Na-O-H. The two modeled chemical systems can well reproduce the available experimental data for scheelite, ferberite, and hübnerite solubilities under hydrothermal conditions. The modeling results indicate that scheelite is more soluble than hübnerite and ferberite under most W-mineralizing conditions (300–400 °C, 500–1500 bars, and 1–3 mol/kg NaCl). Scheelite can replace ferberite (hübnerite) over a wide range of temperatures and pressures; therefore, the replacement of ferberite (hübnerite) by scheelite does not necessarily represent late stages of mineralization. Two mechanisms can cause scheelite to replace ferberite (hübnerite). The first mechanism is cooling with an increase in the ∑Ca∑Fe (∑Ca∑Mn) molality ratio in fluids, and the second mechanism is a decrease in fluid pressure with constant ∑Ca∑Fe (∑Ca∑Mn). Neither leaching Ca from Ca-rich wallrocks nor removing Fe (Mn) from hydrothermal fluids is required for the second mechanism. The second mechanism may account for vein-type or disseminated scheelite mineralization in host rocks whose Ca is low compared to carbonates.

Mechanical Impact Effects of Fluid Hammer Effects on Drag Reduction of Coiled Tubing

Abstract Aiming at the oscillation drag reduction tool that improves the extension limit of coiled tubing downhole operations, the fluid hammer equation of the oscillation drag reducer is established based on the fluid hammer effect. The fluid hammer equation is solved by the asymptotic method, and the distribution of fluid pressure and flow velocity in coiled tubing with oscillation drag reducers is obtained. At the same time, the axial force and radial force of the coiled tubing caused by the fluid hammer oscillator are calculated according to the momentum theorem. The radial force will change the normal contact force of the coiled tubing, which has a great influence on frictional drag. The results show that the fluid flowrate and pressure decrease stepwise from the oscillator position to the wellhead position, and the fluid flowrate and pressure will change abruptly during each valve opening and closing time. When the fluid passes through the oscillator, the unit mass fluid will generate an instantaneous axial tension due to the change in the fluid velocity, thereby converting the static friction into dynamic friction, which is conducive to the extend limit of coiled tubing.

Effect of Nano-CaCO3 on the Sealing Efficiency of Grouts in Flowing Water Grouting

Flowing water grouting is a big challenge in the tunneling and underground engineering. To enhance the early strength and grouting effectiveness of slurry for flowing water grouting, nano-CaCO3 and fly ash were mixed with cement based grout. A series of physical simulation tests were conducted to simulate the flowing water grouting process in rough rock fracture, and investigate the effect of nano-CaCO3 content on the fluid pressure and sealing efficiency of grouts. Results of viscosity tests show that the viscosity of grouts decreased with an increase of nano-CaCO3 content. Scanning electron microscope (SEM) tests indicate that nano-CaCO3 can promote the formation of fibrous hydrates and enhance the flowing water resistance of grouts. Increasing nano-CaCO3 content resulted in the first increase while later decrease of maximal fluid pressure (MFP) and sealing efficiency (SE) of grouts. Reducing water cement ratio of grouts and incorporating fly ash can effectively improve the SE of flowing water grouting.

Localized fluid discharge by tensile cracking during the post-seismic period in subduction zones

It is thought that extensional structures (extensional cracks and normal faults) generated during the post-seismic period create fluid pathways that enhance the drainage of the subducting plate interface, thus reducing the pore pressure and increasing fault strength. However, it remains to be elucidated how much pore fluid pressure decreases by the extension crack formation. Here we examined (i) the pore fluid pressure decrease, and (ii) the degree fault strength recovery by the extension crack formation during the post-seismic period by analyzing extension quartz veins exposed around the Nobeoka Thrust, southwestern Japan. The Nobeoka Trust is an on-land analog of the modern splay fault at shallow depths (~ 8 km) in the Nankai Trough. The poro-elastic model of extensional quartz vein formation indicates that the formation of extensional cracks only releases up to ~ 7–8% of the total pore fluid pressure at ~ 8 km depth. The pore pressure around the Nobeoka Thrust was close to lithostatic pressure during the entire seismic cycle. The estimated effective frictional coefficient along the Nobeoka Thrust after this small fluid-loss by the extensional crack formation does not exceed 0.15. Hence, the pore fluid pressure reduction due to the post-seismic extensional cracks contributes little to increase the fault strength of the megasplay fault.

Experimental investigation on hydraulic fracturing of granite specimens with double flaws based on DIC

Hydraulic fracturing is a crucial technology for shale gas exploitation and enhanced geothermal systems. However, the fundamental mechanisms of hydraulic fracturing, such as the mechanism (tensile or shear) of cracks, physical process of crack initiation, propagation, and coalescence, are not comprehensively understood. Therefore, further direct observations and quantitative investigations are required. Accordingly, an experiment of hydraulic fracturing on double-flaw granite specimens was performed. The fracturing processes were captured using a high-speed camera, and a quantitatively study based on digital image correlation (DIC) was achieved. DIC was proved to be a powerful analysis tool, especially for visualising the crack evolution process. Results show that the crack types in the hydraulic fracturing tests were primarily Type I or Type Ib tensile cracks. The process of strain localisation zones (SLZs) revealed the physical process of the hydraulic fracturing: SLZs initiated at or near pre-existing flaw tips before fracturing, and then cracks initiated and propagated along the SLZs. Some cracks initiated previously may close with the decrease in fluid pressure after fracturing and evolved into closure cracks. The bridging angle was the main factor determining the coalescence patterns, and the specimens exhibited direct coalescence (Category 6 or 7) when β ≥ 90°. SLZs were initiated at both inner tips in Category 6, while SLZs could only be observed at one inner tip in Category 7. The ultimate fracturing pressure first decreased then increased as the bridging angle increased.

Decompression boiling and natural steam cap formation in high-enthalpy geothermal systems

Many high-enthalpy geothermal systems exhibit vapor-rich boiling zones at shallow depths (<1 km), commonly known as steam caps. While the spatial extent and vapor content of steam caps often increases in response to fluid extraction and subsequent pressure decline, the geologic factors controlling steam cap formation and development are poorly understood. Numerical simulations of groundwater convection driven by a transiently cooling intrusion elucidate a natural mechanism by which steam caps can develop from initially liquid-dominated boiling zones. In the simulations, intensive decompression boiling and steam cap development occurs after the heat of a subsurface magmatic intrusion is exhausted by prolonged hydrothermal convection. A reduction in the strength of the upflow leads to a fluid pressure decrease of 2–4 MPa in boiling zones beneath an impermeable cap rock. As the vertical pressure gradient decreases, approaching vapor-static, zones of liquid-vapor counterflow (i.e., heat pipes) develop at the base of steam caps, efficiently isolating overlying vapor-rich zones from underlying liquid. The reservoir rock permeability and the cap rock thickness are main controls on the enthalpy and spatial extent of steam caps, with thicker and higher enthalpy (potentially superheated) steam caps developing in intermediate permeability reservoir rocks (∼ 10−15 m2). Due to the importance of transient changes in geothermal system structure to steam cap development, the dynamics of natural steam cap formation may not be captured in standard approaches to natural state reservoir modeling, which express the role of the heat source in terms of fixed boundary conditions.

The superlarge Malmyzh porphyry Cu-Au deposit, Sikhote-Alin, eastern Russia: Igneous geochemistry, hydrothermal alteration, mineralization, and fluid inclusion characteristics

The Malmyzh porphyry Cu-Au deposit cluster (>10 Mt Cu-eq.) is the largest in eastern Russia. It is located in the turbidite terrane and was formed in a transform continental margin setting. The deposit is related to a magnetite-series, dominantly low-K calc-alkaline diorite-tonalite igneous suite, with a higher potassium content in the younger (quartz monzonite to granodiorite) intrusive phases. These metaluminous to peraluminous I-type igneous rocks exhibit slightly elevated Sr/Y and have combined subduction-related to post-subduction geochemical signatures. The magma was emplaced in a series of separated local magmatic “porphyry centres” that vary in petrologic features and relative abundance of different igneous rocks as well as in the dominant development of different hydrothermal alteration and mineralization types. The deposit comprises quartz-K-feldspar ± biotite ± chalcopyrite stockworks in zones of potassic alteration, followed by quartz-magnetite ± chlorite and then by quartz-sulfide-magnetite (with chalcopyrite and bornite) stockworks in zones of propylitic alteration. The latter is partially overprinted by quartz-sericite-chalcopyrite and quartz-sericite-pyrite stockworks formed during phyllic alteration stage. The most productive Cu mineralization is related to a later (quartz-sulfide-magnetite) hydrothermal event during the propylitic alteration stage, and to an early (quartz-sericite-chalcopyrite) event during the phyllic alteration stage. Further development of phyllic alteration caused a dilution of Cu grades. Minor Au, Bi and Te mineralization accompanied Cu mineralization.Potassic alteration assemblages formed from a homogenous high-salinity (57–78 wt% NaCl and 13–12 wt% KCl), high-temperature (>525–535 °C), sodic-potassic aqueous-chloride fluid, under a pressure of 500 ± 100 bars. At the propylitic stage, the early quartz-magnetite-chlorite assemblage was formed from a lower temperature (480 ± 5 °C), sodic-dominant aqueous-chloride fluid, under near-critical conditions, and at a similar pressure (~500 bars). This was followed by two episodes of the most intense Cu and Au deposition that occurred under overlapping temperatures (~380 to 250 °C) but from compositionally distinct (sodic-potassic- to sodic-calcic-dominant) boiling to homogenous fluids during the end of the propylitic alteration stage and the beginning of the phyllic alteration stages, respectively. The different cycles of fluid exsolution likely corresponded to degassing of different magmatic intrusions during a multistage magmatic evolution. Corresponding fluid pressure decrease (to ~250 bars and lower) indicates a transition from lithostatic to hydrostatic conditions.

Effects of macro-cracks on the load bearing capacity of articular cartilage.

Macro-cracks on the surface of articular cartilage are one of the hallmarks of early osteoarthritis and joint damage initiation. Macro-cracks negatively affect cartilage mechanobiology and load bearing capacity. The aim of this study was to quantify the changes in transient and steady-state force response of healthy cartilage in the presence of macro-cracks when compressed. Ten macro-cracks were created on the surface of intact articular cartilage. The force-time responses of intact cartilage and cartilage with macro-cracks (n = 22) were compared for multiple nominal axial compressive strain levels and strain rates. Experiments were simulated using a fiber-reinforced biphasic finite element model to gain insight into the possible mechanisms contributing to changes in the mechanical response of articular cartilage when introducing macro-cracks. We found a significant reduction in the transient and steady-state load bearing capacity of cartilage samples following the introduction of macro-cracks. Two mechanisms were identified as potential causes of this reduction: (1) an increase in permeability and associated decrease in fluid pressure, and (2) damage of the structural integrity of the solid matrix. The first cause was predicted by the finite element model, while the second cause was not.

Geochemistry and mineral chemical behavior of hydrothermal alteration of the Tuwu porphyry copper deposit, Eastern Tianshan, Northwest China

The Tuwu deposit is one of the largest porphyry copper deposits in the Eastern Tianshan, Northwest China. Ore bodies of the deposit are associated with the tonalite porphyry, which intruded the Early Carboniferous Qi´eshan Group. The hydrothermal ore‐forming processes include the porphyry mineralization episode with potassic, chlorite‐sericite/albite, phyllic, and propylitic alteration and the overprinting mineralization episode. These hydrothermal alteration episodes were studied on the basis of mass transfer and element mobility. The mass balance data and isocon diagrams reveal that Cu is highly associated with the chlorite‐sericite (albite) stage and followed by phyllic and potassic stages. On the basis of electron probe analysis, the SO3 contents of the igneous apatite from the tonalite porphyries range from 0.016 to 0.288 wt.%, which are higher than those from the diorite porphyries (SO3 = 0.088–0.179 wt.%). Similarly, the apatite saturation temperature (861–926°C) and magmatic S content (mean = 52.16 ppm) from the tonalite porphyries are also higher that from the diorite porphyries (T = 813–877°C; S = 28.25 ppm). These results suggest that the S content of the apatite is related to the temperature and S content of the melt. In the hydrothermal alteration zones, the F favours partitioning into apatite under lower temperature, the F contents of hydrothermal apatite increase from the potassic zones to the propylitic zones accompanying with the decrease of temperature. Cl element is much more sensitive to the pH, pressure, and fluid composition than F element. The Cl contents of the apatite increase from the potassic zones (0.18–0.46 wt.%) to the chorite‐sericite (albite) zones (0.28–0.58 wt.%), resulting from the decrease of fluid pH and pressure. The lower Cl contents of apatite (0.07–0.48 wt.%) in the phyllic zones were due to the lower Cl content of hydrothermal fluids. The highest Cl contents (0.09–0.69 wt.%) of apatite in the propylitic zones were caused by the decrease of pressure. The δ18Owater values of quartz in chlorite‐sericite (albite) zones and phyllic zones range from −0.8‰ to −0.4‰ and from −5.3‰ to 4.8‰, and the δD values vary from −57‰ to −47‰ and from −52‰ to −44‰, respectively. Gaseous compositions of the fluid inclusions in quartz are dominated by H2O with minor CO2, and the liquid compositions mainly consist of Na+ and Cl−. These data imply that the ore‐forming fluids belong to the H2O‐NaCl system and evolved from magmatic water to meteoric water in origin.

Geodynamic simulation of the WenChuan Ms8.0 and Lushan Ms7.0 earthquakes

The Lushan Ms7.0 earthquake, occurred on April 20th, 2013, is another strong earthquake that occurred on Longmen Mountain Faults after the Wenchuan Ms8.0 earthquake. In this paper we construct a finite element model depicting fault frictional mechanism to study the geodynamics of these two strong earthquakes. The locations of the initial rupture points and the dislocation forms of the Wenchuan earthquake and Lushan earthquake are simulated to find out the potential relationship between the two earthquakes. Simulative results show that the elevation, fault geometry, and the different rheological strengths between the Sichuan basin and Tibetan plateau play an important role in the earthquake dynamics. The dynamic simulation shows the initial rupture points are located at Yingxiu county and the rupture process is mainly along the northeast direction for the Wenchuan earthquake. In particular, the different frictional strengths caused by the fluid pressure decrease between the southern and northern segments of Longmenshan faults after the Wenchuan earthquake have affected the initial rupture point and the fault dislocation form of the Lushan earthquake, when considering the thrust of Tibetan plateau to Sichuan basin as the major dynamic source.

New Insight into the Mechanism of Mannitol Effects on Cerebrospinal Fluid Pressure Decrease and Craniospinal Fluid Redistribution

Intracranial hypertension, which often follows a severe brain injury, is usually treated with intravenous (i.v.) application of hyperosmolar solutions. The mechanism of intracranial cerebrospinal fluid (CSF) pressure decrease after such a treatment is still unclear. The aim of this article was to try to explain the mechanism of CSF pressure reduction after i.v. hyperosmolar mannitol bolus in regard to the changes in CSF volume. Two types of experiments were done on anesthetized cats before and after hyperosmolar mannitol application: ventriculo-cisternal perfusion at different perfusion rates, simultaneously measuring the perfusate outflow volume, and CSF pressure recording in the lateral ventricle before and during artificial CSF infusion. Mannitol application in the first group of cats significantly reduced collected prefusate volume during ventriculo-cisternal perfusion, and in the second group it prevented CSF pressure increase caused by artificial CSF infusion. Our results strongly suggest that the mechanism of hyperosmolar mannitol action after its i.v. application is based on osmotic fluid retrieval from interstitial and cerebrospinal compartments into the microvessels. This shift, without significant volume change inside the cranium, causes a predominant decrease of CSF volume in the spinal part of the system, which in turn leads to lowering of the CSF pressure. Spinal CSF volume decrease is enabled by the extensibility of the spinal dura, this way providing the possibility for CSF volume redistribution inside the CSF system, together with CSF pressure decrease. This mechanism of mannitol action is in accordance with the new hypothesis of CSF physiology.