Interpretation of mullite HREM images along [010] and [100]

200 kV and 300 kV HREM images of mullite with beam direction parallel to [010] and [100] have been compared with extensive multi-slice calculations of structure models with different oxygen vacancy arrangements. The simulations reveal that changes of the contrast pattern in HREM images are correlated with enhanced vacancy concentrations and coupled cation shifts (Al^*). Furthermore, the direct relationship between contrast variation and projected vacancy concentration permits the detection of 20% oxygen vacancies along [010] and [100]. An analysis of HREM images indicates preferred orientations of vacancies parallel to 〈102〉 in the (010) plane, whereas the (010) plane yields arrangements parallel to 〈012〉 and 〈001〉, resulting in an average direction of 〈013〉. Distances of 1.5a and 1.5b between these arrangements result from preferred inter-vacancy correlation vectors of 1/2 〈310〉 and 1/2 〈130〉 in the (001) plane. The investigated 2:1 and 3:2-mullites (x = 0.40 and x = 0.25) do not show long-range ordered arrangements of oxygen vacancies, but reveal the composition-dependent formation of short-range order regions of enhanced vacancy concentrations. These regions are distributed in a matrix with a minor degree of order.     

Metamorphic P–T evolution of the Gotsu blueschists from the Suo metamorphic belt in SW Japan: Implications for tectonic correlation with the Heilongjiang Complex,NE China

Mineralogy and Petrology - In the Gotsu area of the c. 200 Ma high-P/T Suo metamorphic belt in the Inner Zone of southwest Japan, blueschists occur as lenses or layers within pelitic...     

Summer monsoon rainfall scenario over Bangladesh using a high-resolution AGCM

Summer monsoon rainfall was simulated by a global 20 km-mesh atmospheric general circulation model (AGCM), focusing on the changes in the summer monsoon rainfall of Bangladesh. Calibration and validation of AGCM were performed over Bangladesh for generating summer monsoon rainfall scenarios. The model-produced summer monsoon rainfall was calibrated with a ground-based observational data in Bangladesh during the period 1979–2003. The TRMM 3B43 V6 data are also used for understanding the model performance. The AGCM output obtained through validation process made it confident to be used for near future and future summer monsoon rainfall projection in Bangladesh. In the present-day (1979–2003) climate simulations, the high-resolution AGCM produces the summer monsoon rainfall better as a spatial distribution over SAARC region in comparison with TRMM but magnitude may be different. Summer monsoon rainfall projection for Bangladesh was experimentally obtained for near future and future during the period 2015–2034 and 2075–2099, respectively. This work reveals that summer monsoon rainfall simulated by a high-resolution AGCM is not directly applicable to application purpose. However, acceptable performance was obtained in estimating summer monsoon rainfall over Bangladesh after calibration and validation. This study predicts that in near future, summer monsoon rainfall on an average may decrease about ?0.5 % during the period 2015–2034 and future summer monsoon rainfall may increase about 0.4 % during the period 2075–2099.     

Hydrochemistry in coastal aquifer of southwest Bangladesh: origin of salinity

In the coastal region of Bangladesh, groundwater is mainly used for domestic and agricultural purposes, but salinization of many groundwater resources limits its suitability for human consumption and practical application. This paper reports the results of a study that has mapped the salinity distribution in different aquifer layers up to a depth of 300 m in a region bordering the Bay of Bengal based on the main hydrochemistry and has investigated the origin of the salinity using Cl/Br ratios of the samples. The subsurface consists of a sequence of deltaic sediments with an alternation of more sandy and clayey sections in which several aquifer layers can be recognized. The main hydrochemistry shows different main water types in the different aquifers, indicating varying stages of freshening or salinization processes. The most freshwater, soft NaHCO₃-type water with Cl concentrations mostly below 100 mg/l, is found in the deepest aquifer at 200–300 m below ground level (b.g.l.), in which the fresh/saltwater interface is pushed far to the south. Salinity is a main problem in the shallow aquifer systems, where Cl concentrations rise to nearly 8000 mg/l and the groundwater is mostly brackish NaCl water. Investigation of the Cl/Br ratios has shown that the source of the salinity in the deep aquifer is mixing with old connate seawater and that the saline waters in the more shallow aquifers do not originate from old connate water or direct seawater intrusion, but are derived from the dissolution of evaporite salts. These must have been formed in a tidal flat under influence of a strong seasonal precipitation pattern. Long dry seasons with high evaporation rates have evaporated seawater from inundated gullies and depressions, leading to salt precipitation, while subsequent heavy monsoon rains have dissolved the formed salts, and the solution has infiltrated in the subsoil, recharging groundwater.     

A study on selection of probability distributions for at-site flood frequency analysis in Australia

The most direct method of design flood estimation is at-site flood frequency analysis, which relies on a relatively long period of recorded streamflow data at a given site. Selection of an appropriate probability distribution and associated parameter estimation procedure is of prime importance in at-site flood frequency analysis. The choice of the probability distribution for a given application is generally made arbitrarily as there is no sound physical basis to justify the selection. In this study, an attempt is made to investigate the suitability of as many as fifteen different probability distributions and three parameter estimation methods based on a large Australian annual maximum flood data set. A total of four goodness-of-fit tests are adopted, i.e., the Akaike information criterion, the Bayesian information criterion, Anderson–Darling test, and Kolmogorov–Smirnov test, to identify the best-fit probability distributions. Furthermore, the L-moments ratio diagram is used to make a visual assessment of the alternative distributions. It has been found that a single distribution cannot be specified as the best-fit distribution for all the Australian states as it was recommended in the Australian rainfall and runoff 1987. The log-Pearson 3, generalized extreme value, and generalized Pareto distributions have been identified as the top three best-fit distributions. It is thus recommended that these three distributions should be compared as a minimum in practical applications when making the final selection of the best-fit probability distribution in a given application in Australia.     

The relationship between the shear strength and water retention curve of unsaturated sand at different hydraulic phases

Acta Geotechnica - This technical paper focuses on evaluating the shear strength of unsaturated sand at drying, wetting and alternate drying–wetting cycles, as well as the correlation between...     

Simultaneous monitoring of soil 222Rn in the Eastern Himalayas and the geothermal region of eastern India: an earthquake precursor

Natural Hazards - Activity of 222Rn gas in soil has been recorded continuously at three monitoring centres, namely Ravangla and Diphu in the Eastern Himalayan region and Tantloi in the geothermal...     

Assessing income-wise household environmental conditions and disease profile in urban areas: Study of an Indian city

The main objectives of the present study are: (i) to assess the income-wise household environmental conditions of the sampled households in Aligarh city, (ii) to examine income-wise disease profile of the population, (iii) to assess the relationship between income and four most occurring diseases, (iv) draw out inter-relationship between income, non-ideal household environmental conditions and environment related diseases. The quality of life and diseases in any urban areas get reflected by the immediate neighborhood in different parts of the city which depends upon the income strata of the households, their way of living, and their understanding of their household environment. This is because it is the household environment, which exerts the most and immediate influence on the life of the people. This study was carried out in order to assess household environmental conditions (i.e. housing conditions, bathroom and sanitation conditions, water supply conditions, water logging conditions, household garbage and solid waste, household pests, indoor air and indoor noise pollution) and their effect on the health of the resident population of Aligarh city. The method includes household survey of Aligarh city using questionnaires. The sampled households were classified into five income groups from very low to very high. Relationship was tested between income and household environmental conditions and also between income and diseases using Chi-Square technique. About 55% of the total sampled households suffer from diarrhea/dysentery, 43% jaundice, 42% malaria and 41% respiratory diseases. About 40% suffer from skin diseases, small pox/chicken pox. All these diseases are a result of poor household environmental conditions. Whereas 35% people reported other diseases (i.e. heart disease, hypertension and diabetes), only 14.42% households reported of tuberculosis. The study concludes that there exists a significant positive relationship between income level and household environmental conditions, and also between income and various diseases among sampled households of Aligarh city.     

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet,north-eastern Bangladesh

Acta Geochimica - To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and...     

Numerical simulation of stress distributions and displacements around an entry roadway with igneous intrusion and potential sources of seam gas emission of the Barapukuria coal mine, NW Bangladesh

This paper uses two-dimensional boundary element method (BEM) numerical modeling to analyze the deformation and failure behavior of a coal seam and to understand the nature of gas flow into a roadway entering the Barapukuria coal mine in Bangladesh. The Barapukuria basin contains Permian-aged Gondwana coals with high volatile B bituminous rank. Three models (A, B, and C) are presented here. Model A assumes horseshoe-shaped geometry, model B assumes trapezoid-shaped geometry, and model C assumes horseshoe-shaped geometry coupled with a roof fall-induced cave generated by the break-up of rock materials along the vertical dimension of an igneous dyke. The simulation results show that there is little difference in strata deformation between models A and B. In model A, there is no horizontal tensional stress and the overall horizontal stress patterns are compressive, while the distribution and magnitude of vertical stress show higher tensional stresses on the immediate rib sides and floor. In model B, both horizontal and vertical stress distributions indicate low to medium tensional stresses on the immediate roof, floor, and rib sides, but compressive stresses are prominent toward the interior of the coal seam. Deformation vectors indicate that failure extends laterally to about 7.5 m around the excavation geometry.On the contrary, for model C, the distributions and magnitudes of horizontal and vertical stress show higher tensional stresses in both rib sides of the roof fall zone. The deformation around the dyke-induced perturbation zone affects a large volume of coal. The deformation vectors with high magnitudes are nearly horizontal and propagate laterally up to 30 m; whereas, low-magnitude deformation vectors extend about 25 m toward the roof and 20 m toward the floor. The vertical tensional displacement, which is concentrated in the floor and the left and right hand sides of the roof, propagates about 30 m on both sides and about 22 m in the floor. From these simulation results, it is thought that the extension of the dyke-induced perturbation zone toward the roof, floor, and rib sides of the entry roadway initially creates small tensional cracks that gradually grow into large-scale tensional features. These features could also be responsible for high concentrations of gas, which are emitted into the mine from fractured coals due to insufficient mine ventilation and low atmospheric pressure.