Geothermal systems simulation: A case study

Geothermal reservoir simulation is a key step for developing sustainable and efficient strategies for the exploitation of geothermal resources. It is applied in the assessment of several areas of reservoir engineering, such as reservoir performance and re-injection programs, pressure decline in depletion, phase transition conditions, and natural evolution of hydrothermal convection systems. Fluid flow and heat transfer in rock masses, fluid-rock chemical interaction and rock mass deformation are some of the processes addressed in reservoir modelling. The case study of the Las Tres Virgenes (LTV) geothermal field (10 MWe), Baja California Sur, Mexico is presented. Three dimensional (3D) natural state simulations were carried out from emplacement and cooling of two spherical magma chambers using a conductive approach. A conceptual model of the volcanic system was developed on a lithostratigraphic and geochronological basis. Magma chamber volumes were established from eruptive volumes estimations. The thermophysical properties of the medium were assumed to correspond to the dominant rock in each lithological unit as an initial value, and further calibration was made considering histograms of experimentally obtained thermophysical properties of rocks. As the boundaries of the model lie far from the thermal anomaly, we assumed specified temperature boundaries. A Finite Volume (FV) numerical scheme was implemented in a Fortran 90 code to solve the heat equation. Static formation temperatures from well logs were used for validation of the numerical results. Good agreement was observed in those geothermal wells dominated by conductive heat transfer. For other wells, however, it is clear that conduction alone cannot explain observed behaviour, three-dimensional convective models are being implemented for future multiphysics simulations

Investigation of a mesospheric bore event over northern China

A mesospheric bore event was observed using an OH all-sky airglow imager (ASAI) at Xinglong (40.2° N, 117.4° E), in northern China, on the night of 8–9 January 2011. Simultaneous observations by a Doppler meteor radar, a broadband sodium lidar, and TIMED/SABER OH intensity and temperature measurements are used to investigate the characteristics and environment of the bore propagation and the possible relations with the Na density perturbations. The bore propagated from northeast to southwest and divided the sky into bright and dark halves. The calculations show that the bore has an average phase velocity of 68 m s−1. The crests following the bore have a horizontal wavelength of ~ 22 km. These parameters are consistent with the hydraulic jump theory proposed by Dewan and Picard, as well as the previous bore reports. Simultaneous wind measurements from the Doppler meteor radar at Shisanling (40.3° N, 116.2° E) and temperature data from SABER on board the TIMED satellite are used to characterize the propagating environment of the bore. The result shows that a thermal-Doppler duct exists near the OH layer that supports the horizontal propagation of the bore. Simultaneous Na lidar observations at Yanqing (40.4° N, 116.0° E) suggest that there is a downward displacement of Na density during the passage of the mesospheric bore event.Q. Li, J. Xu, J. Yue, X. Liu, W. Yuan, B. Ning, S. Guan, and J. P. Younge

Mergers, Active Galactic Nuclei and Normal Galaxies: Contributions to the Distribution of Star Formation Rates and Infrared Luminosity Functions

We use a novel method to predict the contribution of normal star-forming galaxies, merger-induced bursts and obscured active galactic nuclei (AGN), to infrared luminosity functions (LFs) and global star formation rate (SFR) densities. We use empirical halo occupation constraints to populate haloes with galaxies and determine the distribution of normal and merging galaxies. Each system can then be associated with high-resolution hydrodynamic simulations. We predict the distribution of observed luminosities and SFRs, from different galaxy classes, as a function of redshift from z= 0 to 6. We provide fitting functions for the predicted LFs, quantify the uncertainties, and compare with observations. At all redshifts, ‘normal’ galaxies dominate the LF at moderate luminosities ∼L* (the ‘knee’). Merger-induced bursts increasingly dominate at L≫L*; at the most extreme luminosities, AGN are important. However, all populations increase in luminosity at higher redshifts, owing to increasing gas fractions. Thus, the ‘transition luminosity’ between normal and merger-dominated sources increases from the luminous infrared galaxy (LIRG)–ultraluminous infrared galaxy threshold at z∼ 0 to bright Hyper-LIRG thresholds at z∼ 2. The transition to dominance by obscured AGN evolves similarly, at factor of several higher LIR. At all redshifts, non-merging systems dominate the total luminosity/SFR density, with merger-induced bursts constituting ∼5–10 per cent and AGN ∼1–5 per cent. Bursts contribute little to scatter in the SFR–stellar mass relation. In fact, many systems identified as ‘ongoing’ mergers will be forming stars in their ‘normal’ (non-burst) mode. Counting this as ‘merger-induced’ star formation leads to a stronger apparent redshift evolution in the contribution of mergers to the SFR density. We quantify how the evolution in LFs depends on evolution in galaxy gas fractions, merger rates, and possible evolution in the Schmidt–Kennicutt relation. We discuss areas where more detailed study, with full radiative transfer treatment of complex three-dimensional clumpy geometries in mixed AGN–star-forming systems, is necessary

Cosmological Simulations of the Preheating Scenario for Galaxy Cluster Formation: Comparison to Analytic Models and Observations

We perform a set of non--radiative cosmological simulations of a preheated intracluster medium in which the entropy of the gas was uniformly boosted at high redshift. The results of these simulations are used first to test the current analytic techniques of preheating via entropy input in the smooth accretion limit. When the unmodified profile is taken directly from simulations, we find that this model is in excellent agreement with the results of our simulations. This suggests that preheated efficiently smoothes the accreted gas, and therefore a shift in the unmodified profile is a good approximation even with a realistic accretion history. When we examine the simulation results in detail, we do not find strong evidence for entropy amplification, at least for the high-redshift preheating model adopted here. In the second section of the paper, we compare the results of the preheating simulations to recent observations. We show -- in agreement with previous work -- that for a reasonable amount of preheating, a satisfactory match can be found to the mass-temperature and luminosity-temperature relations. However -- as noted by previous authors -- we find that the entropy profiles of the simulated groups are much too flat compared to observations. In particular, while rich clusters converge on the adiabatic self--similar scaling at large radius, no single value of the entropy input during preheating can simultaneously reproduce both the core and outer entropy levels. As a result, we confirm that the simple preheating scenario for galaxy cluster formation, in which entropy is injected universally at high redshift, is inconsistent with observations.Comment: 11 pages, 13 figures, accepted for publication in Ap

What are the key issues regarding the role of geothermal energy in meeting energy needs in the global south?

Globally, the potential of geothermal far exceeds that of all other renewable sources together, although investment in the other sources to date has far exceeded investment in geothermal. World Energy Assessment estimates in 2000 for the global potential of all renewables (EJ/yr) were Geothermal 5000, Solar 1575, Wind 640, Biomass 276, Hydro 50, giving a total of 7541 (UNDP, 2000). When installed, geothermal plants have a far higher capacity factor than other sources (solar depends on the level of direct insolation, wind power on wind, etc.); estimates (REN21, 2009) give wind-power 21%, solar PV 14% but geothermal is at least as high as 75% and often more than 95%, given that once a plant is established it operates continuously except for routine down-time for maintenance and rare break-downs

Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum

The plant cytotoxin ricin enters target mammalian cells by receptor-mediated endocytosis and undergoes retrograde transport to the endoplasmic reticulum (ER). Here, its catalytic A chain (RTA) is reductively separated from the cell-binding B chain, and free RTA enters the cytosol where it inactivates ribosomes. Cytosolic entry requires unfolding of RTA and dislocation across the ER membrane such that it arrives in the cytosol in a vulnerable, nonnative conformation. Clearly, for such a dislocated toxin to become active, it must avoid degradation and fold to a catalytic conformation. Here, we show that, in vitro, Hsc70 prevents aggregation of heat-treated RTA, and that RTA catalytic activity is recovered after chaperone treatment. A combination of pharmacological inhibition and cochaperone expression reveals that, in vivo, cytosolic RTA is scrutinized sequentially by the Hsc70 and Hsp90 cytosolic chaperone machineries, and that its eventual fate is determined by the balance of activities of cochaperones that regulate Hsc70 and Hsp90 functions. Cytotoxic activity follows Hsc70-mediated escape of RTA from an otherwise destructive pathway facilitated by Hsp90. We demonstrate a role for cytosolic chaperones, proteins typically associated with folding nascent proteins, assembling multimolecular protein complexes and degrading cytosolic and stalled, cotranslocational clients, in a toxin triage, in which both toxin folding and degradation are initiated from chaperone-bound states