Physical Sciences and Mathematics Commons^™

A Study Of The Gam Approach To Solve Laminar Boundary Layer Equations In The Presence Of A Wedge, Rahmat Khan, Muhammad Usman

Muhammad Usman

We apply an easy and simple technique, the generalized ap- proximation method (GAM) to investigate the temperature field associated with the Falkner-Skan boundary-layer problem. The nonlinear partial differ- ential equations are transformed to nonlinear ordinary differential equations using the similarity transformations. An iterative scheme for the non-linear ordinary differential equations associated with the velocity and temperature profiles are developed via GAM. Numerical results for the dimensionless ve- locity and temperature profiles of the wedge flow are presented graphically for different values of the wedge angle and Prandtl number.

Forced Oscillations Of A Class Of Nonlinear Dispersive Wave Equations And Their Stability, Muhammad Usman, Bingyu Zhang

Muhammad Usman

It has been observed in laboratory experiments that when nonlinear dispersive waves are forced periodically from one end of undisturbed stretch of the medium of propagation, the signal eventually becomes temporally periodic at each spatial point. The observation has been confirmed mathematically in the context of the damped Korteweg-de Vries (KdV) equation and the damped Benjamin-Bona-Mahony (BBM) equation. In this paper we intend to show the same results hold for the pure KdV equation (without the damping terms) posed on a finite domain. Consideration is given to the initial-boundary-value problem * {ut+ux=uux+u(0,t)=h(t),uxxx=0,u(x,0)=ϕ(x),u(1,t)=0,ux(1,t)=0,00,t>0. It is shown that if the boundary …

Modified Homotopy Perturbation Transform Method: A Paradigm For Nonlinear Boundary Layer Problems, Yasir Khan, Muhammad Usman

Muhammad Usman

This paper suggests a novel modified homotopy perturbation transform method (MHPTM) for a nonlinear boundary layer problem by suitable choice of an initial solution. The steady Navier–Stokes equations are reduced to nonlinear ordinary differential equations by using similarity variables. The governing nonlinear differential equations are solved by means of MHPTM. The equations are Laplace transformed and the nonlinear terms represented by He's polynomials. The series solution of the nonlinear boundary layer problem is obtained. For such a boundary layer problem, the second derivative at zero is an important point of function, so we have computed f″(0) and compared it …

Bifurcations In Steady State Solutions Of A Class Of Nonlinear Dispersive Wave Equation, Paul Eloe, Muhammad Usman

Muhammad Usman

We consider the damped externally excited KdV and BBM equations and use an asymptotic perturbation method to analyze the stability of solutions. We consider the primary resonance by defining the detuning parameter. External-excitation and frequency-response curves are shown to exhibit jump and hysteresis phenomena (dis-continuous transitions between two stable solutions) for both KdV and BBM equations.

Surrogate Markers For Time-Varying Treatments And Outcomes, Jesse Hsu, Edward Kennedy, Jason Roy, Alisa Stephens-Shields, Dylan Small, Marshall Joffe

Edward H. Kennedy

A surrogate marker is a variable commonly used in clinical trials to guide treatment decisions when the outcome of ultimate interest is not available. A good surrogate marker is one where the treatment effect on the surrogate is a strong predictor of the effect of treatment on the outcome. We review the situation when there is one treatment delivered at baseline, one surrogate measured at one later time point, and one ultimate outcome of interest and discuss new issues arising when variables are time-varying. Most of the literature on surrogate markers has only considered simple settings with one treatment, one …

Co Oxidation Over Au/Tio2 Catalyst: Pretreatment Effects, Catalyst Deactivation, And Carbonates Production, Johnny Saavedra, Camilah Powell, Basu Panthi, Christopher Pursell, Bert Chandler

Bert D Chandler

A commercially available Au/TiO₂ catalyst was subjected to a variety of thermal treatments in order to understand how variations in catalyst pretreatment procedures might affect CO oxidation catalysis. Catalytic activity was found to be inversely correlated to the temperature of the pretreatment. Infrared spectroscopy of adsorbed CO experiments, followed by a Temkin analysis of the data, indicated that the thermal treatments caused essentially no changes to the electronics of the Au particles; this, and a series of catalysis control experiments, and previous transmission electron microscopy (TEM) studies ruled out particle growth as a contributing factor to the activity loss. …

Nabr Poisoning Of Au/Tio2 Catalysts: Effects On Kinetics, Poisoning Mechanism, And Estimation Of The Number Of Catalytic Active Sites, Bert Chandler, Shane Kendell, Hieu Doan, Rachel Korkosz, Lars Grabow, Christopher Pursell

Bert D Chandler

Sodium bromide was used to intentionally poison a commercial Au/TiO2 catalyst with the goals of understanding the nature of halide poisoning and evaluating the number and nature of the catalytic active sites. A series of eight poisoned catalysts were prepared by impregnating the parent catalyst with methanolic solutions of NaBr. Each catalyst was tested with CO oxidation catalysis under differential reactor conditions; O2 reaction orders and Arrhenius activation energies were determined for each material. All of the kinetic data, including a Michaelis−Menten analysis, indicated that the primary effect of adding NaBr was to reduce the number of catalytically active sites. …

Fermions In An Ads₃ Black Hole Background And The Gauge-Gravity Duality, C. Fosco, E. Moreno, F. Schaposnik

Enrique F. Moreno

We study a model whose dynamics is determined by a Maxwell Lagrangian coupled to a complex scalar and a Dirac fermion field, in an AdS3 black hole background. Our study is performed within the context of the Euclidean formalism, in terms of an effective action Seff that results from integrating out the fermion field. In particular, Seff includes an induced parity breaking part which reduces, in the weak coupling limit, to Chern-Simons terms for both the gauge and spin connections, with temperature dependent coefficients. We find numerically the effective action minimum and, applying the AdS/CFT correspondence, we discuss the properties …

Comparative Response Of Dms And Dmsp Concentrations In Symbiodinium Clades C1 And D1 Under Thermal Stress, Elisabeth Deschaseaux, V Beltran, Graham Jones, Myrna Deseo, H Swan, Peter Harrison, Bradley Eyre

Dr Myrna A Deseo

Coral-associated Symbiodinium are known to produce dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP), two biogenic sulphur compounds that potentially play a role in the algal antioxidant system and climate regulation. Coral resistance to bleaching and oxidative stress partly depends upon the capacity of their symbionts to respond to environmental stressors, with DMS and DMSP possibly contributing to this response. Under increasing sea surface temperatures, zooxanthellate corals might dominantly associate with more thermally tolerant clades of Symbiodinium, of which the nutritional and biochemical contribution to the holobiont remains unknown. Here, the production of DMS and DMSP under increasing temperature (from 26 °C …

Role Of Organic Amendments On Enhanced Bioremediation Of Heavy Metal(Loid) Contaminated Soils, Jin Hee Park, Dane Lamb, Periyasamy Paneerselvam, Girish Choppala, Nanthi Bolan, Jae Chung

Dr Girish Choppala

As land application becomes one of the important waste utilization and disposal practices, soil is increasingly being seen as a major source of metal(loid)s reaching food chain, mainly through plant uptake and animal transfer. With greater public awareness of the implications of contaminated soils on human and animal health there has been increasing interest in developing technologies to remediate contaminated sites. Bioremediation is a natural process which relies on soil microorganisms and higher plants to alter metal(loid) bioavailability and can be enhanced by addition of organic amendments to soils. Large quantities of organic amendments, such as manure compost, biosolid and …

Chapter Two: Chromium Contamination And Its Risk Assessment In Complex Environmental Settings, Girish Choppala, Nanthi Bolan, Jin Hee Park

Dr Girish Choppala

Chromium reaches the soil environment through waste disposal emanating from a number of industrial activities, including coal-fired power production, electroplating, leather tanning, timber treatment, pulp production, and mineral ore and petroleum refining. Of the heavy metals, chromium (Cr) is a major pollutant, poses a great threat to flora and fauna and persists for long time. The most abundant species of Cr—Cr(III) and Cr(VI)—have very different properties. The toxicity, mobility, and bioavailability of Cr mainly depend on its speciation. In the natural environment, Cr(III) is most immobile, less soluble and stable, whereas Cr(VI) is highly mobile, soluble and bioavailable. Redox reactions …

Differential Effect Of Coal Combustion Products On The Bioavailability Of Phosphorus Between Inorganic And Organic Nutrient Sources, Belaji Seshadri, Nanthi Bolan, Girish Choppala, Ravi Naidu

Dr Girish Choppala

In farming systems, all the applied phosphorus (P) is not available to plants because they are either adsorbed in soil or lost to the environment through leaching or runoff. The effect of coal combustion products (CCPs) for enhancing the bioavailability of applied phosphorus (P) in soil was examined separately for inorganic (KH₂PO₄ – PP) and organic (poultry manure – PM) P treatments, where fluidised bed combustion (FBC) ash emerged as the most effective amendment. Greenhouse study was conducted by growing mustard plants on FBC amended soils under leaching and non-leaching setups. The FBC increased the biomass yield …

Comparative Sorption Of Pb And Cd By Biochars And Its Implication For Metal Immobilization In Soils, Jin Hee Park, Girish Choppala, Seul Lee, Nanthi Bolan, Jae Chung, Mansour Edraki

Dr Girish Choppala

Biochar has great potential as a soil amendment to immobilize heavy metals, thereby reducing their bioavailability. In this study, biochars derived from chicken manure and green waste were compared with commercial activated carbon (AC) and laboratory produced black carbon (BC) for the sorption of Pb and Cd. Sorption kinetics and equilibrium sorption isotherms for Pb and Cd were obtained for the char materials and the data were fitted to kinetic and sorption isotherm models.. Chicken manure-derived biochar (CM) showed the highest sorption capacity for both Pb and Cd, and the Pb sorption by biochars was higher than the Cd sorption …

Phytocapping: An Alternative Technology For The Sustainable Management Of Landfill Sites, Dane Lamb, Kartik Venkatraman, Nanthi Bolan, Nanjappa Ashwath, Girish Choppala, Ravi Naidu

Dr Girish Choppala

Landfill remains the predominant means of waste disposal throughout the globe. Numerous landfills exist in developed and underdeveloped countries, engineered with contrasting degrees of effectiveness. Modern landfill closure in developed countries involves the conventional capping of waste with materials such as compacted clay or geosynthetic clay liners, typically overlain with other soil materials. Conventional capping technologies are now accepted to be increasingly ineffective in reducing percolation into waste. Cost-effective alternative systems are of increasing interest, including the use of plants to control and limit water entry into waste, otherwise known as “Phytocapping”. Phytocapping reduces percolation through three main mechanisms: (a) …

Comparative Sorption And Mobility Of Cr(Iii) And Cr(Vi) Species In A Range Of Soils: Implications To Bioavailability, Girish Choppala, Nanthi Bolan, Dane Lamb, Anitha Kunhikrishnan

Dr Girish Choppala

The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species [Cr(III) and Cr(VI)] was examined using batch sorption, and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH, CEC, organic matter (OM), clay, water-extractable SO4 2– and PO4 3–, surface charge, and different iron (Fe) fractions of 12 different Australian representative soils on the sorption, and mobility of Cr(III) and Cr(VI) were examined. The amount of …

Chemodynamics Of Chromium Reduction In Soils: Implications To Bioavailability, Girish Choppala, Nanthi Bolan, Belaji Seshadri

Dr Girish Choppala

Chromium toxicity in soils can be mitigated by reduction of Cr(VI) to Cr(III) which is influenced by the presence of free Cr(VI) species in soil solution, and the supply of protons and electrons. In this study, the effects of Cr(VI) adsorption (i.e. availability of free Cr(VI) species in soil solution), soil pH (i.e. supply of protons) and three electron donor carbon sources [black carbon (BC), chicken manure biochar (CMB) and cow manure (CM)] on the reduction of Cr(VI) to Cr(III) in soils were investigated. The results indicated that the rate of Cr(VI) reduction decreased with an increase in Cr(VI) adsorption …

Phosphorus–Arsenic Interactions In Variable-Charge Soils In Relation To Arsenic Mobility And Bioavailability, Nanthi Bolan, Santiago Mahimairaja, Anitha Kunhikrishnan, Girish Choppala

Dr Girish Choppala

Phosphorus (P) influences arsenic (As) mobility and bioavailability which depends on the charge components of soil. The objective of this study was to examine P–As interaction in variable-charge allophanic soils in relation to P-induced As mobilization and bioavailability. In this work, the effect of P on arsenate [As(V)] adsorption and desorption was examined using a number of allophanic and non-allophanic soils which vary in their anion adsorption capacity. The effect of P on As uptake by Indian mustard (Brassica juncea L.) plants was examined using a solution culture, and a soil plant growth experiment involving two As-spiked allophanic and non-allophanic …

Microbial Transformation Of Trace Elements In Soils In Relation To Bioavailability And Remediation, Nanthi Bolan, Girish Choppala, Anitha Kunhikrishnan, Jin Hee Park, Ravi Naidu

Dr Girish Choppala

The term “trace elements” generally includes elements (both metals and metalloids) that occur in natural and perturbed environments in small amounts and that, when present in sufficient bioavailable concentrations, are toxic to living organisms (Adriano 2001). This group includes both biologically essential [e.g., cobalt (Co), copper (Cu), chromium (Cr), manganese (Mn), and zinc (Zn)] and nonessential [e.g., cadmium (Cd), lead (Pb), and mercury (Hg)] elements. The essential elements (for plant, animal, or human nutrition) are required in low concentrations and hence are known as “micro nutrients.” The nonessential elements are phytotoxic and/or zootoxic and are widely known as “toxic elements” …

Cellular Mechanisms In Higher Plants Governing Tolerance To Cadmium Toxicity, Girish Choppala, Saifullah, Nanthi Bolan, Sadia Bibi, Muhammad Iqbal, Zed Rengel, Anitha Kunhikrishnan, Nanjappa Ashwath, Yong Ok

Dr Girish Choppala

Cadmium (Cd) is an inorganic mineral in the earth's crust. Cadmium entry into the environment occurs through geogenic and anthropogenic sources. Industrial activities including mining, electroplating, iron and steel plants, and battery production employ Cd during their processes and often release Cd into the environment. When disseminated into soil, Cd can be detrimental to agro-ecosystems because it is relatively mobile and phytotoxic even at low concentrations. Cadmium's phytotoxicity is due to reductions in the rate of transpiration and photosynthesis and chlorophyll concentration resulting in retardation of plant growth, and an alteration in the nutrient concentration in roots and leaves. In …

Concomitant Reduction And Immobilization Of Chromium In Relation To Its Bioavailability In Soils, Girish Choppala, Nanthi Bolan, Anitha Kunhikrishnan, William Skinner, Balaji Seshadri

Dr Girish Choppala

In this study, two carbon materials [chicken manure biochar (CMB) and black carbon (BC)] were investigated for their effects on the reduction of hexavalent chromium [Cr(VI)] in two spiked [600 mg Cr(VI) kg−1] and one tannery waste contaminated [454 mg Cr(VI) kg−1] soils. In spiked soils, both the rate and the maximum extent of reduction of Cr(VI) to trivalent Cr [Cr(III)] were higher in the sandy loam than clay soil, which is attributed to the difference in the extent of Cr(VI) adsorption between the soils. The highest rate of Cr(VI) reduction was observed in BC-amended sandy loam soil, where it …

Biochar Reduces The Bioavailability And Phytotoxicity Of Heavy Metals, Jin Hee Park, Girish Choppala, Nanthi Bolan, Jae Chung, Thammared Chuasavathi

Dr Girish Choppala

Background and aims

Biochar has attracted research interest due to its ability to increase the soil carbon pool and improve crop productivity. The objective of this study was to evaluate the metal immobilizing impact of chicken manure- and green waste-derived biochars, and their effectiveness in promoting plant growth.

Methods

The immobilization and phytoavailability of Cd, Cu and Pb was examined using naturally contaminated shooting range and spiked soils. Biochar samples prepared from chicken manure and green waste were used as soil amendments.

Results

Application of biochar significantly reduced NH₄NO₃ extractable Cd, Cu and Pb concentrations of soils, …

Stabilization Of Carbon In Composts And Biochars In Relation To Carbon Sequestration And Soil Fertility, Nanthi Bolan, Anitha Kunhikrishnan, Girish Choppala, R Thangarajan, J Chung

Dr Girish Choppala

There have been increasing interests in the conversion of organic residues into biochars in order to reduce the rate of decomposition, thereby enhancing carbon (C) sequestration in soils. However energy is required to initiate the pyrolysis process during biochar production which can also lead to the release of greenhouse gasses. Alternative methods can be used to stabilize C in composts and other organic residues without impacting their quality. The objectives of this study include: (i) to compare the rate of decomposition among various organic amendments and (ii) to examine the effect of clay materials on the stabilization of C in …

Effect Of Coal Combustion Products In Reducing Soluble Phosphorus In Soil Ii. Leaching Study, Balaji Seshadri, Nanthi Bolan, Anitha Kunhikrishnan, Girish Choppala, Ravi Naidu

Dr Girish Choppala

Phosphorus (P) management in agriculture is crucial for both environmental health and future availability of P resource. Application of P as fertilisers (organic or inorganic) often results in either P accumulation in soil or loss to water bodies, rendering them unavailable to crops. In this study, the mobility of inorganic (KH₂PO₄ (PP)) and organic (poultry manure (PM)) P sources, as affected by coal combustion products (CCPs: fly ash (FA) and fluidised bed combustion ash (FBC)) application to soils, was evaluated using column leaching experiments. The incubated samples were also characterised using X-ray diffraction (XRD) and scanning electron …

Potential Of Novel Bacterial Consortium For The Remediation Of Chromium Contamination, Periyasamy Panneerselvam, Girish Choppala, Anitha Kunhikrishnan, Nanthi Bolan

Dr Girish Choppala

This study was aimed to examine the efficiency of a novel bacterial consortium on the reduction of toxic hexavalent chromium [Cr(VI)] to non-toxic trivalent Cr [Cr(III)]. Six Cr(VI)-resistant bacteria (IS1-IS6) were isolated from a tannery waste disposal site at Mount Barker, South Australia, of which three viz., IS1, IS2 and IS3 were selected based on Cr(VI) reduction ability in minimal salt medium. The isolates were identified as Bacillus endophyticus (IS1), Microbacterium paraoxydans (IS2) and Bacillus simplex (IS3) by 16S rRNA gene sequencing. All three isolates were able to tolerate chromium (Cr(VI), 300–400 mg L−1), arsenic (As(V), 1,000 mg L−1), copper …

Arsenic(Iii) And Iron(Ii) Co-Oxidation By Oxygen And Hydrogen Peroxide: Divergent Reactions In The Presence Of Organic Ligands, Zhaohui Wang, Richard Bush, J Liu

Dr Zhaohui Wang

Iron-catalyzed oxidation of As(III) to As(V) can be highly effective for toxic arsenic removal via Fenton reaction and Fe(II) oxygenation. However, the contribution of ubiquitous organic ligands is poorly understood, despite its significant role in redox chemistry of arsenic in natural and engineered systems. In this work, selected naturally occurring organic ligands and synthetic ligands in co-oxidation of Fe(II) and As(III) were examined as a function of pH, Fe(II), H2O2, and radical scavengers (methanol and 2-propanol) concentration. As(III) was not measurably oxidised in the presence of excess ethylenediaminetetraacetic acid (EDTA) (i.e. Fe(II):EDTA

Evaluation Of Spatial Variability Of Soil Arsenic Adjacent To A Disused Cattle-Dip Site, Using Model-Based Geostatistics, Nabeel Niazi, Thomas Bishop, Balwant Singh

Dr Nabeel Khan Niazi

This study investigated the spatial variability of total and phosphate-extractable arsenic (As) concentrations in soil adjacent to a cattle-dip site, employing a linear mixed model-based geostatistical approach. The soil samples in the study area (n = 102 in 8.1 m²) were taken at the nodes of a 0.30 × 0.35 m grid. The results showed that total As concentration (0-0.2 m depth) and phosphate-extractable As concentration (at depths of 0-0.2, 0.2-0.4, and 0.4-0.6 m) in soil adjacent to the dip varied greatly. Both total and phosphate-extractable soil As concentrations significantly (p = 0.004-0.048) increased toward the cattle-dip. Using …

Soil Contaminants: Sources, Effects And Approaches For Remediation, Ghulam Murtaza, Behzad Murtaza, Nabeel Niazi, Muhammad Sabir

Dr Nabeel Khan Niazi

The contamination of soils with various inorganic and organic contaminants led to the degradation of large expenses of urban and arable lands throughout the world. The presence of toxic contaminants poses a significant health risk to humans and other ecological systems. Scattered literature is harnessed to critically review the various natural and anthropogenic sources and potential hazards and to identify the best possible remediation strategies for a number of contaminants, mainly those inorganic in nature such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn) commonly found in the contaminated soils. …

Letter To The Editor Regarding, “First Evidence On Different Transportation Modes Of Arsenic And Phosphorus In Arsenic Hyperaccumulator Pteris Vittata” By Lei Et Al. (2012), Nabeel Niazi, Anthony Kachenko

Dr Nabeel Khan Niazi

No abstract provided.

Mechanisms Of Metal-Phosphates Formation In The Rhizosphere Soils Of Pea And Tomato: Environmental And Sanitary Consequences, Annabelle Austruy, Muhammad Shahid, Tiantian Xiong, Maryse Castrec, Virginie Payre, Nabeel Niazi, Muhammad Sabir, Camille Dumat

Dr Nabeel Khan Niazi

Purpose: At the global scale, soil contamination with persistent metals such as lead (Pb), zinc (Zn), and copper (Cu) induces a serious threat of entering the human food chain. In the recent past, different natural and synthetic compounds have been used to immobilize metals in soil environments. However, the mechanisms involved in amendment-induced immobilization of metals in soil remained unclear. The objective of the present work was therefore to determine the mechanisms involved in metal-phosphates formation in the rhizospheric soils of pea and tomato currently cultivated in kitchen gardens. Materials and methods: Pea and tomato were cultivated on a soil …

Mid-Infrared Spectroscopy And Partial Least-Squares Regression To Estimate Soil Arsenic At A Highly Variable Arsenic-Contaminated Site, Nabeel Niazi, Balwant Singh, B Minasny

Dr Nabeel Khan Niazi

The potential of mid-infrared spectroscopy in combination with partial least-squares regression was investigated to estimate total and phosphate-extractable arsenic contents in soil samples collected from a highly variable arsenic-contaminated disused cattle-dip site. Principal component analysis was performed prior to mid-infrared partial least-squares analysis to identify spectral outliers in the absorbance spectra of soil samples. The mid-infrared partial least-squares calibration model (n = 149) excluding spectral outliers showed an acceptable reliability (coefficient of determination, R2c = 0.75 (P < 0.01); ratio of performance to interquartile distance, RPIQ_c = 2.20) to estimate total soil arsenic. For total soil arsenic, the validation of final calibration model using 149 unknown …