41 research outputs found
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Evaluation And Use Of Parsimonious Reactive Solute Transport Models For Prediction Of Contaminant Behavior At An Acid Mine Drainage Site
No full textAcid mine drainage (AMD) results from biogeochemical oxidation of iron and sulfur minerals in flooded mine shafts and waste rock piles. In the presence of water and oxygen, sulfur rich minerals are oxidized to produce sulfate ions and cations such as ferrous, copper and aluminum ions, which lower the pH. The low pH further dissolves and releases other metals in the ore resulting in a high concentration of metal ions in the water. The solute concentration in a stream is a result of dynamic coupling between a number of chemical processes and transport processes. Creating a model encompassing all the processes occurring at an AMD affected area increases the complexity of the model multifold times. Different approaches toward modeling highly contaminated systems such as AMD sites have been employed over the past few decades. Two distinct styles of coupled reactive transport modeling have developed over time to model the contaminated systems such as AMD affected streams. This research evaluates the use of parsimonious coupled models of both types - kinetic and equilibrium to predict the fate and transport of four major ions - iron, aluminum, zinc and sulfate in the Effluent Creek at the Davis Mine Site. Model performances are accessed in terms of the ability of the model to accurately match the observed concentration in the Creek, along with the stability of the model determined by Akaike and Bayesian information criteria. In addition to the fundamental question of comparing kinetic and equilibrium model, we model processes affecting the fate and transport and model complexity. The simple kinetic models-precipitation, sorption and precipitation-sorption; outperform the equilibrium models for the three cations - iron, aluminum and zinc. For sulfate, both the kinetic and equilibrium models give comparable predictions. The simple kinetic model is however unable to define exact processes that causes the chemical transformations. The equilibrium sorption model predicts the expected chemical reactions at the given pH conditions. The chemical rates in the hyporheic zone are a couple orders of magnitude higher than the stream, except for the anion, sulfate, which shows comparable reactivity in the hyporheic zone and the stream.Doctor of Philosophy (Ph.D.
Antisymmetric tensor fields in a generalized Randall–Sundrum scenario
No full textAbstractBulk antisymmetric tensor fields of different ranks have been studied in the context of a generalized Randall–Sundrum model with a non-vanishing induced cosmological constant on the visible brane. It is shown that instead of the usual exponential suppression of the couplings of the zero modes of these bulk fields with the brane fermions in the original Randall–Sundrum model, here the couplings are proportional to the brane cosmological constant. Thus in an era of large cosmological constant these fields have significant role in physical phenomena because of their enhanced couplings with the visible brane fermions
Lightest Kaluza–Klein graviton mode in a back-reacted Randall–Sundrum scenario
No full textIn search of the extra dimensions in the ongoing LHC experiments, the signatures of the Randall–Sundrum (RS) lightest KK graviton have been in the main focus in recent years. The recent data from the dilepton decay channel at the LHC has determined the experimental lower bound on the mass of the RS lightest Kaluza–Klein (KK) graviton for different choices of the underlying parameters of the theory. In this work we explore the effects of the back-reaction of the bulk scalar field, which is employed to stabilise the RS model, in modifying the couplings of the lightest KK graviton with the standard model matter fields located on the visible brane. In such a modified background geometry we show that the coupling of the lightest KK graviton with the SM matter fields gets a significant suppression due to the inclusion of the back-reaction of the bulk stabilising scalar field. This implies that the back-reaction parameter weakens the signals from the RS scenario in collider experiments, which in turn explains the non-visibility of KK graviton in colliders. Thus we show that the modulus stabilisation plays a crucial role in the search of warped extra dimensions in collider experiments
126 GeV Higgs and ATLAS bound on the lightest graviton mass in Randall-Sundrum model
No full textIn the search for extra dimension through dilepton events in 7-TeV proton-proton collision, the ATLAS detector at LHC has set stringent lower bound on the mass of the Randall-Sundrum (RS) lightest graviton Kaluza-Klein (KK) mode. Considering that the Randall-Sundrum model undertakes to resolve the well-known gauge hierarchy/fine tuning problem to restrict the Higgs mass within the estimated GeV against large radiative correction upto the cut-off of the model, we explore the allowed parameter space within which the RS model can be trusted. We show that the consistency of the model with ATLAS results constrains the cut-off of the theory which is atleast two order lower than the Planck/Quantum gravity scale implying the possible existence of a new Physics at this lower scale
Development of a Multi-Index Method Based on Landsat Reflectance Data to Map Open Water in a Complex Environment
No full textMapping surface water extent is important for managing water supply for agriculture and the environment. Remote sensing technologies, such as Landsat, provide an affordable means of capturing surface water extent with reasonable spatial and temporal coverage suited to this purpose. Many methods are available for mapping surface water including the modified Normalised Difference Water Index (mNDWI), Fisher’s water index (FWI), Water Observations from Space (WOfS), and the Tasseled Cap Wetness index (TCW). While these methods can discriminate water, they have their strengths and weaknesses, and perform at their best in different environments, and with different threshold values. This study combines the strengths of these indices by developing rules that applies an index to the environment where they perform best. It compares these indices across the Murray-Darling Basin (MDB) in southeast Australia, to assess performance and compile a heuristic rule set for accurate application across the MDB. The results found that all single indices perform well with the Kappa statistic showing strong agreement, ranging from 0.78 for WOfS to 0.84 for TCW (with threshold −0.035), with improvement in the overall output when the index best suited for an environment was selected. mNDWI (using a threshold of −0.3) works well within river channels, while TCW (with threshold −0.035) is best for wetlands and flooded vegetation. FWI and mNDWI (with threshold 0.63 and 0, respectively) work well for remaining areas. Selecting the appropriate index for an environment increases the overall Kappa statistic to 0.88 with a water pixel accuracy of 90.5% and a dry pixel accuracy of 94.8%. An independent assessment illustrates the benefit of using the multi-index approach, making it suitable for regional-scale multi-temporal analysis
Why has spacetime torsion such negligible effect on the Universe?
No full textWe attempt an answer to the question as to why the evolution of a four-dimensional universe is governed by spacetime curvature but not torsion. An answer is found if there is an additional compact spacelike dimension with a warped geometry, with torsion caused by a Kalb-Ramond (KR) antisymmetric tensor field in the bulk. Starting from a Randall-Sundrum type of warped extra dimension, and including the inevitable backreaction ensuing from the radius stabilization mechanism, we show that there is always an extra exponential suppression of the KR field on the four-dimensional projection that constitutes our visible Universe. The backreaction is found to facilitate the process of such suppression
General characteristics of the studies included in the review sorted by author name alphabetically.
No full textGeneral characteristics of the studies included in the review sorted by author name alphabetically.</p
Intervention characteristics of studies included in the review sorted alphabetically by author.
No full textIntervention characteristics of studies included in the review sorted alphabetically by author.</p
Graviton modes in multiply warped geometry
No full textAbstractThe negative results in the search for Kaluza–Klein graviton modes at the LHC, when confronted with the discovery of the Higgs, have been construed to have severely limited the efficacy of the Randall–Sundrum model as an explanation of the hierarchy problem. We show, though, that the presence of multiple warping offers a natural resolution of this conundrum through modifications in both the graviton spectrum and their couplings to the Standard Model fields
