Preliminary observations of solar radio sources with the Culgoora radioheliograph operating at four frequencies

The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona.     

Lithology and stratigraphy of the Ordovician facies complexes of Gornyi Altai

In the Ordovician time, the transform margin of the Gornyi Altai region consisted of two bathymetric stages: (1) shelf and upper parts of continental slope; (2) foothills and lower parts of continental slope. The first stage includes the shallow-water facies complexes (terrigenous and terrigenous-carbonate schlieren and variegated flyschoid), while the second stage is composed of deep-water (black shale terrigenous) and subflysch gray (carbonate terrigenous) complexes. Model series of the facies complexes established in our work should be taken into account during the geodynamic analysis of fold zones.     

The WRF model performance for the simulation of heavy precipitating events over Ahmedabad during August 2006

The summer monsoon season of the year 2006 was highlighted by an unprecedented number of monsoon lows over the central and the western parts of India, particularly giving widespread rainfall over Gujarat and Rajasthan. Ahmedabad had received 540.2mm of rainfall in the month of August 2006 against the climatological mean of 219.8mm. The two spells of very heavy rainfall of 108.4mm and 97.7mm were recorded on 8 and 12 August 2006 respectively. Due to meteorological complexities involved in replicating the rainfall occurrences over a region, the Weather Research and Forecast (WRF-ARW version) modeling system with two different cumulus schemes in a nested configuration is chosen for simulating these events. The spatial distributions of large-scale circulation and moisture fields have been simulated reasonably well in this model, though there are some spatial biases in the simulated rainfall pattern. The rainfall amount over Ahmedabad has been underestimated by both the cumulus parameterization schemes. The quantitative validation of the simulated rainfall is done by calculating the categorical skill scores like frequency bias, threat scores (TS) and equitable threat scores (ETS). In this case the KF scheme has outperformed the GD scheme for the low precipitation threshold.     

Quick-look assessments to identify optimal CO2 EOR storage sites

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.     

Controls on porphyroblast size along a regional metamorphic field gradient

Garnet-bearing schists from the Waterville Formation of south-central Maine provide an opportunity to examine the factors governing porphyroblast size over a range of metamorphic grade. Three-dimensional sizes and locations for all garnet porphyroblasts were determined for three samples along the metamorphic field gradient spanning lowest garnet through sillimanite grade, using high-resolution X-ray computed tomography. Comparison of crystal size distributions to previous data sets obtained by stereological methods for the same samples reveals significant differences in mode, mean, and shape of the distributions. Quantitative textural analysis shows that the garnets in each rock crystallized in a diffusion-controlled nucleation and growth regime. In contrast to the typical observation of a correlation between porphyroblast size and position along a metamorphic field gradient, porphyroblast size of the lowest-grade specimen is intermediate between the high- and middle-grade specimens’ sizes. Mean porphyroblast size does not correlate with peak temperatures from garnet-biotite Fe-Mg exchange thermometry, nor is post-crystallization annealing (Ostwald Ripening) required to produce the observed textures, as was previously proposed for these rocks. Robust pseudosection calculations fail to reproduce the observed garnet core compositions for two specimens, suggesting that these calc-pelites experienced metasomatism. For each of these two specimens, Monte Carlo calculations suggest potential pre-metasomatism bulk compositions that replicate garnet core compositions. Pseudosection analyses allow the estimation of the critical temperatures for garnet growth: ∼481, ∼477, and ∼485°C for the lowest-garnet-zone, middle-garnet-zone, and sillimanite-zone specimens, respectively. Porphyroblast size appears to be determined in this case by a combination of the heating rate during garnet crystallization, the critical temperature for the garnet-forming reaction and the kinetics of nucleation. Numerical simulations of thermally accelerated, diffusion-controlled nucleation, and growth for the three samples closely match measured crystal size distributions. These observations and simulations suggest that previous hypotheses linking the garnet size primarily to the temperature at the onset of porphyroblast nucleation can only partially explain the observed textures. Also important in determining porphyroblast size are the heating rate and the distribution of favorable nucleation sites.     

Thermodynamic model for arsenic speciation in sulfidic waters: A novel use of ab initio computations

Recent discoveries demonstrate that the chemistry of arsenic in sulfidic waters is much more complex that previously believed. One implication is that all earlier thermodynamic data on stabilities of As thioanions require revision. Previously used experimental approaches for determining As thioanion stabilities may be inadequate to deal with the full range of complexity. Here we use computational as well as empirical information to construct a provisional model for equilibrium As thioanion distributions in sulfidic waters. Whereas previous authors have argued for either As(III) or As(V) thioanions, the new model predicts that both are important and can occur simultaneously under commonly encountered pH and ΣS^−II conditions. At the order of magnitude level, the model reasonably predicts the solubility of As₂S₃ in sulfidic solutions, provides tentative peak assignments for published Raman spectroscopic data and plausibly accounts for how sulfide modifies the bacterial toxicity of As. The model yields a thermodynamic justification for how sulfide, which is usually regarded as a reducing agent, can counter-intuitively drive oxidation of As(III) to As(V), as has been observed both in the laboratory and in the field. Despite its uncertain accuracy, the model serves as a useful source of new, testable hypotheses about As geochemistry and highlights crucial experimental data needs.     

An Attempt to Predict the Failure Time of Abandoned Mine Pillars

Summary  Left in place pillars of abandoned mines are subject to weathering (e.g action of water, bacteria) that degrades their mechanical strength and eventually leads to collapse. A simple weathering model is proposed, that is governed by two parameters: the rate of progression of weathered front and the rate of degradation of the compressive strength with time. Both plane strain and axisymmetric analyses are performed and closed form solutions of the variation with time of the bearing capacity of the pillar are given. Experimental data of the tests conducted on gypsum and anhydrite specimens attacked by water are presented. It is shown that in order to fit the experimental data a third parameter must be introduced. New closed form solutions are given and the data are used for estimating the time to failure of abandoned gypsum mines in Northern Italy. Authors’ address: Dr. Riccardo Castellanza, Research Assistant, Department of Structural Engineering, Milan University of Technology (Politecnico), Piazza Leonardo da Vinci 32, 20133 Milan, Italy     

Methodology of hydrogeological characterization of deep carbonate aquifers as potential reservoirs of groundwater. Case of study: the Jurassic aquifer of <Emphasis Type="Italic">El Maestrazgo</Emphasis> (Castellón,Spain)

A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (¹⁸O, ²H and ³H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system. Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater uses in the area of study.