The permeability of fractured rocks in pressurised volcanic and geothermal systems

AbstractThe connectivity of rocks’ porous structure and the presence of fractures influence the transfer of fluids in the Earth’s crust. Here, we employed laboratory experiments to measure the influence of macro-fractures and effective pressure on the permeability of volcanic rocks with a wide range of initial porosities (1–41 vol. %) comprised of both vesicles and micro-cracks. We used a hand-held permeameter and hydrostatic cell to measure the permeability of intact rock cores at effective pressures up to 30 MPa; we then induced a macro-fracture to each sample using Brazilian tensile tests and measured the permeability of these macro-fractured rocks again. We show that intact rock permeability increases non-linearly with increasing porosity and decreases with increasing effective pressure due to compactional closure of micro-fractures. Imparting a macro-fracture both increases the permeability of rocks and their sensitivity to effective pressure. The magnitude of permeability increase induced by the macro-fracture is more significant for dense rocks. We finally provide a general equation to estimate the permeability of intact and fractured rocks, forming a basis to constrain fluid flow in volcanic and geothermal systems.</jats:p

Reduction of myocardial infarction by postischemic administration of the calpain inhibitor A-705253 in comparison to the Na(+)/H(+) exchange inhibitor Cariporide (R) in isolated perfused rabbit hearts

The calpain inhibitor A-705253 and the Na(+)/H(+) exchange inhibitor Cariporide (R) were studied in isolated perfused rabbit hearts subjected to 60 min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid solely or in combination at the beginning of reperfusion. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were performed. Myocardial infarct size and area at risk (transiently not perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 72.7 +/- 4.0% of the area at risk in untreated controls, but was significantly smaller in the presence of the inhibitors. The largest effect was observed with 10(-6) M A-705253, which reduced the infarcted area to 49.2 +/- 4.1% of the area at risk, corresponding to a reduction of 33.6%. Cariporide (R) at 10(-6) M reduced the infarct size to the same extent. The combination of both inhibitors, however, did not further improve cardioprotection. No significant difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, heart rate, or in the release of lactate dehydrogenase and creatine kinase from heart muscle

Permeability of compacting porous lavas

The highly transient nature of outgassing commonly observed at volcanoes is in part controlled by the permeability of lava domes and shallow conduits. Lava domes generally consist of a porous outer carapace surrounding a denser lava core with internal shear zones of variable porosity. Here we examine densification using uniaxial compression experiments on variably crystalline and porous rhyolitic dome lavas from the Taupo Volcanic Zone. Experiments were conducted at 900°C and an applied stress of 3MPa to 60% strain, while monitoring acoustic emissions to track cracking. The evolution of the porous network was assessed via X-ray computed tomography, He-pycnometry, and relative gas permeability. High starting connected porosities led to low apparent viscosities and high strain rates, initially accompanied by abundant acoustic emissions. As compaction ensued, the lavas evolved; apparent viscosity increased and strain rate decreased due to strain hardening of the suspensions. Permeability fluctuations resulted from the interplay between viscous flow and brittle failure. Where phenocrysts were abundant, cracks had limited spatial extent, and pore closure decreased axial and radial permeability proportionally, maintaining the initial anisotropy. In crystal-poor lavas, axial cracks had a more profound effect, and permeability anisotropy switched to favor axial flow. Irrespective of porosity, both crystalline samples compacted to a threshold minimum porosity of 17–19%, whereas the crystal-poor sample did not achieve its compaction limit. This indicates that unconfined loading of porous dome lavas does not necessarily form an impermeable plug and may be hindered, in part by the presence of crystals

Krafla magma testbed: Understanding and using the magma-hydrothermal connection

The Krafla Magma Testbed (KMT), Krafla Caldera, Iceland, is proposed to be the first magma observatory, an international multi-borehole facility where teams will conduct scientific experiments and engineering tests focused on the magma-hydrothermal interface in a superhot geothermal systems (SHGS). Objectives are to: 1) Core and monitor from the roots of the hydrothermal system to the top of the magma body; 2) Provide ground-truth testing of surface-based techniques for locating magma; 3) Perturb the deep system to understand signals interpreted as volcano “unrest”; 4) Advance drilling and completion technology so that superhot and supercritical fluids can be produced from the magma roof zone; and 5) Advance sensor technology so that magma bodies can be monitored directly, vastly improving the eruption warnings important to 10% of Earth's population. KMT will provide a vanguard view of magma and hydrothermal circulation as the single system that it is. It will integrate the separate communities of practice of geothermal energy, which relies heavily on direct drilling observations; and volcanology, which relies on surface observations and theoretical models. The driving force is that geothermal drilling hit magma in Iceland, Kenya, and Hawaii, revealing how close to the surface magma exists and how closely connected magma is to the hydrothermal system. KMT is a 3 rd path in efforts to expand geothermal use. One path is to go deeper in cooler places, the Enhanced Geothermal System (EGS) concept, relying on advances in drilling and reservoir stimulation for economic viability, e.g. Frontier Observatory for Research in Geothermal Energy (FORGE) of the U.S. Department of Energy. Another, within SHGS, is to drill to conditions where fluids should be supercritical, e.g. IDDP-2 of Iceland Deep Drilling Program (IDDP) at Reykjanes. The 3 rd , also SHGS and pursued by KMT, is to access the vicinity of a magma body. This takes advantage of magma's high energy density due to latent heat of crystallization and delivered by convection to sustain high power output. Not only have SHGS wells proximal to magma at Krafla Caldera, Iceland, exhibited high flow rates equivalent to >100 MWt, but the expected efficiency of conversion to electricity is ~30% vs. ~10% for conventional geothermal. When combined with the new efficiencies of High Voltage Direct Current (HVDC) tranmission, the economic balance could shift from low-grade geothermal sources near the consumer to high-grade sources farther from the consumer

From Youth Team to First Team: An Investigation into the Transition Experiences of Young Professional Athletes in Football

Using Wylleman and Lavallee (2004) and Stambulova (2003) models of transition as conceptual frameworks for the current study, we aimed to explore United Kingdom (UK) professional soccer players’ (N = 5) experiences going through a youth-to-senior career transition to first team level, and assess the immediate changes that occur during the move. Few studies have assessed this process, and no studies have focused on assessing the changes that may occur between pre and post transition. Data collection lasted 1 month with players interviewed twice, 2 weeks before, and 2 weeks after their transition to the first team. Data were abductively thematically content analyzed. Prior to transition, players reported high motivation to be successful, but also feeling anxious about the transition to senior sport. Post-transition, players felt more confident about their ability to succeed in senior sport and maintained high levels of motivation to succeed. Family, friends, coaches, and teammates provided emotional, technical, and tangible support to the players throughout the transition, but were also sources of stress for athletes moving to senior sport. These findings suggest ways to assist transitioning athletes, such as the use of buddy systems with senior players

The retirement experiences of elite female gymnasts: Self identity and the physical self

This study explored experiences of retirement from elite sport among a sample of retired female gymnasts. Given the young age at which female gymnasts begin and end their sport careers, particular attention was afforded to the role of identity and the physical self in the process of adaptation. Retrospective, semi-structured interviews were conducted and interview transcripts analyzed using interpretative phenomenological analysis. Analysis indicated that retirement from gymnastics engendered adjustment difficulties for six of the seven participants. Identity loss was particularly salient, and for two gymnasts, physical changes associated with retirement were a further source of distress. The challenge of athletic retirement was intensified because the gymnasts had heavily invested in sport during adolescence, a period demarcated for the pursuit of an identity. Furthermore, their retirement coincided with a time when adolescents typically undergo profound changes physiologically. Practical suggestions to facilitate athletes' disengagement from sport are discussed

Statistical analysis plan for the ‘Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke’ (TARDIS) trial

Rationale: Antiplatelet agents such as aspirin, clopidogrel and dipyridamole are effective in reducing the risk of recurrence after a stroke. Importantly, the risk of recurrence is highest immediately after the index event while antiplatelets cause bleeding. Aims and/or hypothesis: The ‘Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke’ (TARDIS) trial is testing whether short-term intensive antiplatelet therapy is safe and effective in reducing the early risk of recurrence as compared with standard guideline-based therapy. Design: TARDIS is an international multi-center prospective randomized open-label blinded–end-point trial, with funding from the UK Health Technology Assessment program. Patients with acute ischemic stroke or transient ischemic attack are randomized within 48 h to intensive/triple antiplatelet therapy or guideline antiplatelets taken for one-month. Patients or relatives give written informed (proxy) consent and all sites have research ethics approval. Analyses will be done by intention-to-treat. Study Outcome: The primary outcome is shift in stroke recurrent events and their severity, assessed using the modified Rankin Scale, at three-months. Discussion: This paper and attachment describe the trial’s statistical analysis plan, as developed from the protocol during recruitment and prior to unblinding of data. The statistical analysis plan contains design and methods for analyses, and unpopulated tables and figures for the primary and baseline publications. The data from the trial will provide the first large-scale randomized evidence for the use of intensive antiplatelet therapy for preventing recurrence after acute stroke and transient ischemic attack