Spatial variability of climatic hazards in Bangladesh

Natural Hazards - Climate change is evident with the extreme climatic indices changing all over the world. Bangladesh is one of the most vulnerable countries to climate change. The patterns of...     

Intra‐ and interannual export of nitrogen and phosphorus in the subtropical Richmond River catchment,Australia

Nitrogen and phosphorus concentrations were measured and exports were calculated in the subtropical Richmond River catchment between July 1994 and June 1996. A stratified sampling approach was adopted owing to the extreme and rapid changes in riverine discharge, which varied by up to 10 000 times over the study period. Nutrient concentrations were lowest during baseflow. During storm discharge, dissolve inorganic and organic and particulate nitrogen and phosphorus concentrations increased two‐ to five fold, and followed hysteresis patterns that were attributed to the integration and/or depletion of catchment nutrient sources during an event. Dissolved organic nitrogen and particulate phosphorus were the dominant nutrient forms. Land use and antecedent conditions had a large influence on nutrient concentrations and exports. During the 1995–96 year (slightly above the mean annual discharge) 96% of nitrogen and 98% of phosphorus loads were transported in less than 6% of the time. When averaged across the catchment, monthly riverine nutrient loads varied by up to 1061‐fold during the study and exports were approximately four‐fold greater during the second year relative to the first. The subtropical Richmond River catchment has greater intra‐ and potential interannual variability in nutrient loads and exports when compared with temperate catchments from other parts of the world. It is suggested that in tropical and subtropical Australian catchments with large intra‐ and interannual variation in discharge, the need for parameterizing the antecedent conditions, such as the degree of nutrient storage, may make it difficult to model spatial and temporal (short time‐scale) nutrient exports. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical investigation of the impact of uncertainties in satellite rainfall estimation and land surface model parameters on simulation of soil moisture

This study aims at evaluating the uncertainty in the prediction of soil moisture (1D, vertical column) from an offline land surface model (LSM) forced by hydro-meteorological and radiation data. We focus on two types of uncertainty: an input error due to satellite rainfall retrieval uncertainty, and, LSM soil-parametric error. The study is facilitated by in situ and remotely sensed data-driven (precipitation, radiation, soil moisture) simulation experiments comprising a LSM and stochastic models for error characterization. The parametric uncertainty is represented by the generalized likelihood uncertainty estimation (GLUE) technique, which models the parameter non-uniqueness against direct observations. Half-hourly infra-red (IR) sensor retrievals were used as satellite rainfall estimates. The IR rain retrieval uncertainty is characterized on the basis of a satellite rainfall error model (SREM). The combined uncertainty (i.e., SREM + GLUE) is compared with the partial assessment of uncertainty. It is found that precipitation (IR) error alone may explain moderate to low proportion of the soil moisture simulation uncertainty, depending on the level of model accuracy—50–60% for high model accuracy, and 20–30% for low model accuracy. Comparisons on the basis of two different sites also yielded an increase (50–100%) in soil moisture prediction uncertainty for the more vegetated site. This study exemplified the need for detailed investigations of the rainfall retrieval-modeling parameter error interaction within a comprehensive space-time stochastic framework for achieving optimal integration of satellite rain retrievals in land data assimilation systems.     

A new insight into onset of inertial flow in porous media using network modeling with converging/diverging pores

The network modeling approach is applied to provide a new insight into the onset of non-Darcy flow through porous media. The analytical solutions of one-dimensional Navier-Stokes equation in sinusoidal and conical converging/diverging throats are used to calculate the pressure drop/flow rate responses in the capillaries of the network. The analysis of flow in a single pore revealed that there are two different regions for the flow coefficient ratio as a function of the aspect ratio. It is found that the critical Reynolds number strongly depends on the pore geometrical properties including throat length, average aspect ratio, and average coordination number of the porous media, and an estimation of such properties is required to achieve more reliable predictions. New criteria for the onset of non-Darcy flow are also proposed to overcome the lack of geometrical data. Although the average aspect ratio is the main parameter which controls the inertia effects, the effect of tortuosity on the onset of non-Darcy flow increases when the coordination number of media decreases. In addition, the higher non-Darcy coefficient does not essentially accelerate the onset of inertial flow. The results of this work can help to better understand how the onset of inertial flow may be controlled/changed by the pore architecture of porous media.     

Synthesis of nano-γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/chitosan beads (AlCBs) and continuous heavy metals removal from liquid solution

In this work, synthesis of chitosan beads impregnated with nano-γ-Al₂O₃ (AlCB) was carried out. The characteristics of the synthesized adsorbent were obtained by using Brunauer Emmett and Teller technique and Scanning Electron Microscopy method. The use of AlCB in continuous removal of chromium, lead, nickel and cadmium ions from liquid solution was studied using fixed-bed column system. Bed depths and flow rate effects on breakthrough and uptake capacity of the adsorbent in column were also examined. Dynamic parameters of the adsorption were calculated by using bed depth service time (BDST) and Thomas models. In both models, the data were analyzed by error analyzing and combining the values of determined coefficient (R ²) from regression analysis. The adsorption capacities of AlCB in breakthrough were 158.33, 183.33, 63.33 and 31.67 mg/g for chromium, lead, nickel and cadmium, respectively. In addition, BDST model was found to be an acceptable kinetic model to describe the experimental data.     

The cyclical reversible transitions of the universe’s evolution

In this work we propose cyclical reversible transitions as the scenario in which the universe evolves, through a series consisting of reversible expansion, temporary stability, and contraction. Our model is based on the comparison between local and global time-dependent densities {ρ ₀(τ ₀),ρ(τ)} instead of the critical density ρ _c, local and global time-dependent Hubble parameters {H ₀(τ ₀),H(τ)}, and the variations {Δρ(τ),ΔH(τ)} due to cosmological chaotic fluctuations, which are generally ignored in certain oscillating models. By taking into account all these factors, a rate equation in the form of (H ₀/H)² ∝(ρ ₀/ρ) has been established, and from it we derive some others, to provide a mechanism that is responsible for the cyclical reversible transitions. Also, the problems of singularities, black hole overproduction, and the second law of thermodynamics arising in oscillating universe models are conceptually resolved.     

Stability Analyses of Municipal Solid Waste Landfills with Decomposition

A bioreactor landfill is operated to enhance refuse decomposition, gas production, and waste stabilization. Some of the potential advantages of bioreactor include rapid stabilization of waste, increased landfill gas generation, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. Due to the accelerated decomposition and settlement of solid waste, bioreactor landfills are gaining popularity as an alternative to the conventional Subtitle D landfills. However, the addition of leachate to accelerate the decomposition changes the physical and engineering characteristic of waste and therefore affects the geotechnical characteristics of waste mass. The changes in the physical and mechanical characteristics of solid waste with time and decomposition are expected to affect the shear strength of waste mass. The objective of this paper is to analyze the stability of solid waste slopes within the bioreactor landfills, as a function of time and decomposition. The finite element program PLAXIS is used for numerical modeling of bioreactor landfills. Stability analysis of bioreactor landfills was also performed using limit equilibrium program STABL. Finally the results from finite element program PLAXIS and limit equilibrium program STABL are compared. GSTABL predicted a factor of safety of more than 1 in all the cases analyzed, whereas PLAXIS predicted a factor of safety of less than 1 at advanced stages for a slope of 2:1. However, the interface failures between solid waste and landfill liners have not been considered in this paper.     

New Observations on the Brittle Failure Process of Simulated Crystalline Rocks

A biaxial testing program has been performed to study the process of brittle failure in crystalline rocks. Dental plaster has been selected as a model material, and mixing with different ratios of distilled water, different types of common minerals of crystalline rocks have been simulated in the form of brick-like small elements. These elements have been interlocked together according to four systematic patterns and final specimens with 180 × 180 × 76 mm dimensions have been obtained. Details of different types of cracks observed during loading process, effects of mechanical, geometrical and confining pressure on the cracking intensity, the influence of different types of heterogeneity on the macroscopic properties of a system of interlocked elements, and the sequence of events during the failure process are presented in this paper. Based on these observations, a revised mechanism for brittle failure is proposed.