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Articles 3001 - 3030 of 3417

Full-Text Articles in Physical Sciences and Mathematics

Non-Linear Development Of The Secular Bar-Mode Instability In Rapidly Rotating Neutron Stars, Shangli Ou Jan 2004

Non-Linear Development Of The Secular Bar-Mode Instability In Rapidly Rotating Neutron Stars, Shangli Ou

LSU Doctoral Dissertations

We present results from investigations of the nonlinear development of the secular bar-mode instability that is driven by gravitational radiation-reaction (GRR) forces in rotating neutron stars. Our fully three-dimensional hydrodynamical simulations have shown that, in the absence of any competing viscous effects, initially uniformly rotating axisymmetric n=1/2 polytropic stars with a ratio of rotational to gravitational potential energy greater than the critical limit are driven by GRR forces to a bar-like structure, as predicted by linear theory. The pattern frequency of the bar slows to nearly zero, that is, the bar becomes almost stationary as viewed from an inertial frame …


Pattern-Based Model Transformation: A Metamodel-Based Approach To Model Evolution, Sheena Judson Miller Jan 2004

Pattern-Based Model Transformation: A Metamodel-Based Approach To Model Evolution, Sheena Judson Miller

LSU Doctoral Dissertations

Software systems continue to grow in complexity at a rapid pace, creating systems that are complex to build and evolve. The problems that accompany changes in requirements, system upgrades, and error correction produce a desire for software evolution methods that increase the efficiency and effectiveness of adapting complex software to changes. As software systems evolve, design models must be modified to accommodate the required changes. Techniques that control the changes to models in a systematic manner are a key to model evolution. A process that improves the ability to effectively modify a design, thereby enhancing design qualities, supports the need …


Stormwater Diversion As A Potential Coastal Wetland Restoration Method, Jennifer Howard Woods Jan 2004

Stormwater Diversion As A Potential Coastal Wetland Restoration Method, Jennifer Howard Woods

LSU Master's Theses

The Barataria-Terrebonne estuary has been eroding at a rate of up to 103.6 km2 yr-1 for several decades. If the current rate of loss is not reduced, an additional 2,550 km2 of coastal wetlands will be lost by the year 2050. Currently, stormwater in Terrebonne Parish is pumped into canals, ultimately discharging into the Gulf of Mexico. An opportunity exists to use this stormwater for wetland restoration; however, the ecological impacts of stormwater diversions on wetlands are unknown. The objectives of this project were to 1) to investigate the seed banks of a degraded marsh to determine if a viable …


Foreland Basins: Lithospheric Flexure, Plate Strength And Regional Stratigraphy, John Londono Jan 2004

Foreland Basins: Lithospheric Flexure, Plate Strength And Regional Stratigraphy, John Londono

LSU Doctoral Dissertations

Foreland basin subsidence through time is reproduced in this study, as the flexure of an elastic beam in an inviscid fluid under the vertical stress, caused by discrete-distributed loads. Thus, seismostratigraphic data from the Timor Sea peripheral foreland basin, in northwestern Australia, and the Putumayo retroarc foreland basin in the Colombian Andes, are forward modeled, at chronostratigraphic intervals, to assess the evolving geodynamic conditions of the basins. Results show that the accommodation in foreland basins varies as the depositional basement is vertically adjusted according to the regionally isostatic compensation of the lithosphere. Distributed tectonic (thrust belts) and sedimentary loads that …


The Radon-Gauss Transform, Vochita Mihai Jan 2004

The Radon-Gauss Transform, Vochita Mihai

LSU Doctoral Dissertations

Gaussian measure is constructed for any given hyperplane in an infinite dimensional Hilbert space, and this is used to define a generalization of the Radon transform to the infinite dimensional setting, using Gauss measure instead of Lebesgue measure. An inversion formula is obtained and a support theorem proved.


Attachment Of Oligonucleotide Probes To Polymer Biochips And Its Application For The Detection Of Point Mutations, Yun Wang Jan 2004

Attachment Of Oligonucleotide Probes To Polymer Biochips And Its Application For The Detection Of Point Mutations, Yun Wang

LSU Doctoral Dissertations

This dissertation is on the fabrication of polymer-based microfluidic arrays for the detection of genetic mutations. Poly(methyl methacrylate) was chosen as one of the polymer substrate materials due to its low background noise, low adsorption of biomolecules, and low assembly temperature. The surface modification of polymer substrates for covalent attachment of oligonucleotide probes, the construction of fluidic channels/arrays, and hybridization kinetics will be covered. As an example of the application, point mutation detection using immobilized arrays constructed in microfluidic devices will be demonstrated. The PMMA surface was derivatized with N-lithioethylenediamine solution to introduce amine groups, which were utilized for the …


Physical, Chemical, And Mechanical Properties Of Bamboo And Its Utilization Potential For Fiberboard Manufacturing, Xiaobo Li Jan 2004

Physical, Chemical, And Mechanical Properties Of Bamboo And Its Utilization Potential For Fiberboard Manufacturing, Xiaobo Li

LSU Master's Theses

This study investigated the chemical, physical, and mechanical properties of the bamboo species Phyllostachys pubescens and its utilization potential to manufacture medium density fiberboard (MDF). The result showed holocellulose and alpha-cellulose content increased from the base to the top portion. There was no significant variation in Klason lignin content or ash content from the base to the top portion of the bamboo. The outer layer had the highest holocellulose, alpha cellulose, and Klason lignin contents and the lowest extractive and ash contents. The epidermis had the highest extractive and ash contents and the lowest holocellulose and alpha-cellulose content. Specific gravity …


Magnetic Susceptibility For The Paleocene-Eocene Boundary: Correlation Among Three Egyptian Sections, Kelli Willson Jan 2004

Magnetic Susceptibility For The Paleocene-Eocene Boundary: Correlation Among Three Egyptian Sections, Kelli Willson

Honors Theses

No abstract provided.


Microsatellite Instability In Squamous Cell Carcinoma And Lichen Sclerosus Of The Vulva, Sidney Joseph Marlborough Jan 2004

Microsatellite Instability In Squamous Cell Carcinoma And Lichen Sclerosus Of The Vulva, Sidney Joseph Marlborough

LSU Master's Theses

The usefulness of detecting genomic instability in the form of microsatellite instability (MSI) has been examined in a number of cancers. Squamous cell carcinoma (SCC) and adjacent normal and lichen sclerosis (LS) samples were taken from patients with radical vulvectomies. Vulvar SCC samples were compared with adjacent normal samples using four oligonucleotide markers (BAT-25, BAT-26, D10S208 and D10S587) found to be informative with other carcinomas. Using polymerase chain reaction techniques, 30 vulvar SCC DNA samples were examined for MSI. BAT-26 displayed the highest level of MSI and was considered to be the most sensitive marker in studying vulvar SCC. There …


An Analysis Of Cardiovascular And Respiratory Mortality As A Function Of Ambient Ozone And Fine Particulate Matter In The Baton Rouge Air Quality Control Region, Thomas James Wiley Iv Jan 2004

An Analysis Of Cardiovascular And Respiratory Mortality As A Function Of Ambient Ozone And Fine Particulate Matter In The Baton Rouge Air Quality Control Region, Thomas James Wiley Iv

LSU Master's Theses

The Baton Rouge Air Quality Control Region has come under fire due to difficulties in reaching attainment of one-hour daily ozone limitations and its general perception as being a polluted place to live. Ozone is a reactive oxygen species which has been shown to result in damage to biological molecules and is detrimental to human physiology, especially in regards to cardio-respiratory structure and function. In the last decade, fine particulate matter less than 2.5 microns in mean aerodynamic diameter have been identified as a possible pollutant that is affecting public health at levels lower than the EPA’s established limits. PM2.5 …


Validation Of Pet/Ct Dataset For Radiation Treatment Planning, Rajesh Manoharan Jan 2004

Validation Of Pet/Ct Dataset For Radiation Treatment Planning, Rajesh Manoharan

LSU Master's Theses

PET/CT scans are frequently used for radiation treatment planning (RTP). Our work demonstrates a practical approach for validating the PET/CT dataset for RTP. We tested this QA process on a Reveal HD PET/CT scanner. The phantom used is a TGM2 ISIS QA phantom, a 14 cm acrylic cube with a central bore for object inserts. It has four different built-in inserts for electron density verification. 22Na seeds are inserted into the pinholes at the side of the cube. PET/CT images of the phantom with 22Na seeds are acquired and fused in the scanner Syngo fusion software. Registration of the PET/CT …


Seismic Stratigraphic Investigation Of The Ukpokiti Field Channel Complex, Oml 108, Offshore Nigeria, Northwestern Niger Delta, Toby Latwan Stewart Jan 2004

Seismic Stratigraphic Investigation Of The Ukpokiti Field Channel Complex, Oml 108, Offshore Nigeria, Northwestern Niger Delta, Toby Latwan Stewart

LSU Master's Theses

Detailed seismic stratigraphic analyses and mapping show that a well defined Ukpokiti Field Channel complex (late Miocene) found on the up-thrown side of a major back-to-back fault system in the West Niger delta inner-continental shelf probably formed during a single eustatic fall. The channel (>500 msec, 10 km wide) shows several tributaries entering the trunk axis from what was probably a surface of subaerial exposure. Slumping is prominent on the north flank of the trunk channel. No channel unconformity is evident in the down-thrown block. This investigation seeks to resolve the lack of down-dip correlative seismic expression across the …


Post Monitoring Of A Cyclodextrin Remediated Chlorinated Solvent Contaminated Aquifer, Rebecca Mary Hinrichs Jan 2004

Post Monitoring Of A Cyclodextrin Remediated Chlorinated Solvent Contaminated Aquifer, Rebecca Mary Hinrichs

LSU Master's Theses

Hydroxypropyl-β-cyclodextrin (HPβCD) has been tested successfully in the laboratory and in the field for enhanced flushing of low-polarity contaminants from aquifers. The cyclodextrin molecule forms a toroidal structure, which has a hydrophobic cavity. Within this cavity, organic compounds of appropriate shape and size can form inclusion complexes, which is the basis for the use of cyclodextrin in groundwater remediation. The hydrophilic exterior of the molecule makes cyclodextrin highly water-soluble. The solubility of cyclodextrins can be further enhanced by adding functional groups, such as hydroxypropyl groups, to the cyclodextrin core. The aqueous solubility of HPβCD exceeds 950 g/L. These high solubilities …


A Meta-Analysis Of Randomness In Human Behavioral Research, Summer Ann Armstrong Jan 2004

A Meta-Analysis Of Randomness In Human Behavioral Research, Summer Ann Armstrong

LSU Master's Theses

This work analyzes the concept of randomness in binary sequences from three different perspectives: mathematically, statistically, and psychologically and examines the research on human perception of randomness and the question of whether or not humans can simulate random behavior. Generally, research shows that human subjects have great difficulty producing random sequences, even when they are instructed and motivated. We survey some of the literature and present some leading theoretical proposals. Finally, we present some basic statistical tests that can be used to evaluate randomness in a given binary sequence.


Comparative Analysis Between Different Flood Assessment Technologies In Hazus-Mh, Jennifer Carol Meyer Jan 2004

Comparative Analysis Between Different Flood Assessment Technologies In Hazus-Mh, Jennifer Carol Meyer

LSU Master's Theses

Natural disasters devastate the United States through both economic loss and loss of life. The world wide economic damage that results from natural disasters has more than tripled in the last thirty years. Of these natural disasters, floods are the most chronic and costly disasters, comprising an average $5 billion dollars of damage each year. FEMA has released a new software program called HAZUS-MH, which attempts to capture economic losses caused by flooding before losses occur and predict losses from real-time events. This estimate is accomplished through the coupling of flood hazard modeling with local data. FEMA’s goal is that …


Feeding Ecology And Morphometric Analysis Of Paddlefish, Polyodon Spathula, In The Mermentau River, Louisiana, Nicole Adele Smith Jan 2004

Feeding Ecology And Morphometric Analysis Of Paddlefish, Polyodon Spathula, In The Mermentau River, Louisiana, Nicole Adele Smith

LSU Master's Theses

Little is known about the morphometrics and the feeding ecology of paddlefish in Louisiana. I examined the morphometrics and feeding ecology of paddlefish from the Mermentau River, Louisiana from March 2002 to February 2003. Paddlefish were examined morphometrically by taking measurements of eye-fork length (EFL), body cavity length (BCL), girth (G), vent girth (VG), mouth vertical (MTB), mouth horizontal (MSS), and mouth gullet bottom (MGB) to determine which parameters would give a better estimate of weight (W). Regression analysis resulted in a morphometric model of the form: logW = 10.10 + 1.52 (logEFL) + 1.21 (logG) + 0.24 (logVG) (r2 …


An Examination Of The Relationship Between Environmental Science And Law Due To Emerging Micro-Scale Gas Chromatography Technology, Alfred Ruks Politzer Jan 2004

An Examination Of The Relationship Between Environmental Science And Law Due To Emerging Micro-Scale Gas Chromatography Technology, Alfred Ruks Politzer

LSU Master's Theses

The intersection of science and law is very complex. The two disciplines frequently interact due to environmental issues. Expert testimony is most often the method used to introduce scientific data into the legal system. Advances in technology have allowed scientists to increase the preciseness and reliability of data produced. The development of the gas chromatograph and the recent microFAST gas chromatograph has greatly increased the amounts of data available to the legal system. The legal system has relatively recently developed a set of guidelines with which to evaluate scientific evidence and determine whether it should be admitted into trial. Previously …


Durability Of Pine Strandboard Modified With Low Molecular Weight Phenol Formaldehyde, Matthew Daniel Voitier Jan 2004

Durability Of Pine Strandboard Modified With Low Molecular Weight Phenol Formaldehyde, Matthew Daniel Voitier

LSU Master's Theses

A continuing challenge for wood and wood-based composite building materials has been durability--the power of resisting agents or influences which tend to cause changes, decay, or dissolution; lastingness. In the case of wood-based products, this often requires a resistance to biological degradation and moisture related dimensional instability (particularly in particle and flake or strand boards). Borden Chemical Company has developed a new low molecular weight phenol formaldehyde additive, PD-112, to improve durability in composite wood products. This study investigated PD-112’s contribution to durability in oriented strand board (OSB) through laboratory testing of treated southern pine strandboard panels versus untreated control …


Short-Term Evolution Of A Marsh Island System And The Importance Of Cold Front Forcing, Terrebonne Bay, Louisiana, Dana Ann Watzke Jan 2004

Short-Term Evolution Of A Marsh Island System And The Importance Of Cold Front Forcing, Terrebonne Bay, Louisiana, Dana Ann Watzke

LSU Master's Theses

Short-term, wave induced erosion along bay beaches in the northern Gulf of Mexico has been linked to the postfrontal phase of cold front passages. Not until recently has consideration been given to the importance of wave erosion on marshes fringing large bays during the entire cold front event. Two WAVCIS (Wave-Current-Surge-Information System) stations were established on the north and south flank of a small marsh island in Terrebonne Bay, Louisiana, to measure and elucidate the hydrodynamic response to these events. Data from WAVCIS stations, which includes wind speed and direction, air temperature, significant wave height and water level, were collected …


Tuning Polymeric Chiral Surfactants For Enhanced Enantiomeric Recognition In Micellar Electrokinetic Chromatography, Jepkoech Tarus Jan 2004

Tuning Polymeric Chiral Surfactants For Enhanced Enantiomeric Recognition In Micellar Electrokinetic Chromatography, Jepkoech Tarus

LSU Doctoral Dissertations

The research presented in this dissertation involves the synthesis, modification, characterization, and the application of polymeric surfactants in micellar electrokinetic chromatography (MEKC). Sodium undecenoyl-L-Leucinate (L-SUL) was synthesized and modified by use of alkali metal counterions, alcohols, and Triton X-102. Characterization of the modified poly-L-SUL was performed in order to elucidate the structural changes on the surfactants by use of four techniques. While surface tensiometry was used for the determination of the critical micelle concentration (cmc), fluorescence measurements were used for the determination of the polarity of the modified polymeric surfactants. The information about the size of the polymeric surfactants was …


Spectroscopic Investigation Of Nitrogenase: Epr And Mcd Studies Of The Femo Cofactor And The P-Cluster, Robyn B. Broach Jan 2004

Spectroscopic Investigation Of Nitrogenase: Epr And Mcd Studies Of The Femo Cofactor And The P-Cluster, Robyn B. Broach

LSU Doctoral Dissertations

Little is known about substrate binding and reduction of nitrogenase. EPR spectroscopy is used here to observe intermediate states generated by different substrates. Two different spin states (S=3/2 and S=1/2) were exhibited for each substrate, which may result from different binding of the substrate to the cofactor (side-on or terminal binding) or the difference of the substrate binding to either Fe or Mo of the cofactor. Parallel studies were performed on a variant MoFe protein, alpha-195Gln, which exhibited different signals from the wild-type suggesting that the substituted amino acid maybe necessary to reach some mechanistic states that the …


Protein Aggregation Studies: Inhibiting And Encouraging Β-Amyloid Aggregation, Jed Paul Aucoin Jan 2004

Protein Aggregation Studies: Inhibiting And Encouraging Β-Amyloid Aggregation, Jed Paul Aucoin

LSU Doctoral Dissertations

This work demonstrates peptide-based aggregation mediation of fibril forming peptides, notably β-amyloid (1-40), Aβ1-40. To achieve the goals of this work, Aβ1-40 aggregation was governed by ionic strength, temperature, and pH. After controlling and reproducing Aβ1-40 aggregate formation (fibrils), each peptide-based aggregation mediator was evaluated for its ability to self-aggregate and to possess surface-active properties. The incorporation of these mediators in Aβ1-40 solutions changed the surface tension and produced aggregate complexes of mediator and Aβ1-40. Evidence that Aβ1-40 fibril formation may be mediated by disorder-to-order transitions has been observed by layer formation …


On Qualitative Properties And Convergence Of Time-Discretization Methods For Semigroups, Mihaly Kovacs Jan 2004

On Qualitative Properties And Convergence Of Time-Discretization Methods For Semigroups, Mihaly Kovacs

LSU Doctoral Dissertations

In this dissertation we use functional calculus methods to investigate convergence and qualitative properties of time-discretization methods for strongly continuous semigroups. Stability, convergence, and preservation of contractivity (or norm-bound) of the semigroup under time-discretization is investigated in a Banach space setting. Preservation of positivity, concavity and other qualitative shape properties which can be described via positivity are treated in a Banach lattice framework. The use of the Hille-Phillips (H-P) functional calculus instead of the Dunford-Taylor functional calculus allows us to extend fundamental qualitative results concerning time-discretization methods and simplify their proofs, including results on multi-step schemes and variable step-sizes. We …


Modeling Longleaf Pine (Pinus Palustris Mill) Wood Properties Using Near Infrared Spectroscopy, Brian Kipling Via Jan 2004

Modeling Longleaf Pine (Pinus Palustris Mill) Wood Properties Using Near Infrared Spectroscopy, Brian Kipling Via

LSU Doctoral Dissertations

This research demonstrated model development for important wood properties using near infrared spectroscopy (NIR); it considered the effect of outside sources of error, and the ability of NIR to measure fiber morphology. Strength, stiffness, and density were successfully modeled from wood samples taken throughout 10 longleaf (Pinus palustris Mill) trees. Principal components and multiple linear regression were compared for performance in prediction of density, strength, and stiffness. I found both modeling techniques to yield similar prediction accuracies. However, I found that density could be estimated through Beer-Lambert’s law since the absorbance at all wavelengths increased with density. Also, 5 of …


Spatial Analyses And Growth Of Trees In Selected Bottomland Hardwood Stands, Luben D. Dimov Jan 2004

Spatial Analyses And Growth Of Trees In Selected Bottomland Hardwood Stands, Luben D. Dimov

LSU Doctoral Dissertations

Sustainable management and conservation of the extensive bottomland hardwood forest resource in the southeastern U.S. requires a good understanding of basic structural and competitive relationships within these forests. To gain an insight into these relationships, plot information from stands in Arkansas, Louisiana, and Mississippi were analyzed. The effects of individual tree attributes, distance-dependant, and distance-independent competition measures on 5-yr radial growth of red oak crop trees were examined. Selected species included cherrybark oak (Quercus pagoda Raf.), water oak (Q. nigra L.), and Nuttall oak (Q. nuttallii Palmer). Spatial continuity of tree variables was explored through geostatistical analysis. Finally, spatial distribution …


Microelectrophoresis System Utilizing Conductivity Detection Analyzing Biological Molecues, Michelle Galloway Jan 2004

Microelectrophoresis System Utilizing Conductivity Detection Analyzing Biological Molecues, Michelle Galloway

LSU Doctoral Dissertations

Microfabrication technology has proven to be a valuable tool for creating polymer-based devices utilized in chemical and biochemical assays. Although, reducing the size of the device allows for short analysis times and reduces the reagent demand to ultrasmall volumes (< 1 nanoliter), a resulting consequence is the constraint placed on the limits of detection associated with the detector hardware required for readout. To overcome such constraints, laser-induced fluorescence (LIF) is often employed as a detection method as it provides low detection limits, which approach the single molecule level. Unfortunately, most LIF systems do not offer the benefits of miniaturization, with the detector components (i.e. laser, optics, filters) often times requiring a much larger footprint compared to the device. Another readout strategy that has shown promise for these devices is conductivity detection. Detection can be accomplished using either conventional-size or microfabricated electrodes, which can be integrated on the device. Although conductivity has been commonly used to detect inorganic or small organic species, the potential for detection of biological species has received little attention. In this work, an integrated conductivity detector was developed for the analysis of amino acids, peptides, proteins, and oligonucleotides (double-stranded DNA). Using the detector, mass detection sensitivities in the range of 10-18 - 10-21 moles were achieved. To increase the throughput of the system a state-of-the-art, multichannel device with a conductivity array detector was devised. This device, which consists of a 16-channel fluidic network and a printed circuit board, is geared toward automating three-processing steps onto a single fluidic platform including purification, preconcentration and detection for downstream parallel processing.


Comparison Studies Of The Mechanistic Formation Of Polyhalogentaed Dibenzo-P-Dioxins And Furans From The Thermal Degradation Of 2-Bromophenol And 2-Chlorophenol, Catherine Spearing Evans Jan 2004

Comparison Studies Of The Mechanistic Formation Of Polyhalogentaed Dibenzo-P-Dioxins And Furans From The Thermal Degradation Of 2-Bromophenol And 2-Chlorophenol, Catherine Spearing Evans

LSU Doctoral Dissertations

Emissions of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) from hazardous waste incinerators, and many other sources for combustion have been considered environmentally hazardous and a major health threat. Recently, a growing number of materials containing brominated hydrocarbons, commonly used flame retardants, have been disposed in municipal and hazardous waste incinerators. This results in the increased potential for formation of PBDD/Fs and other hazardous combustion by-products. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. In fact, studies have shown that brominated phenols form higher yields of PBDD/Fs than the …


Class Groups And Norms Of Units, Costel Ionita Jan 2004

Class Groups And Norms Of Units, Costel Ionita

LSU Doctoral Dissertations

Our object of study is relative quadratic extensions of algebraic number fields. In 'Class Number Parity', the authors P.E. Conner and J. Hurrelbrink study in detail the cases of real and CM-extensions. In this paper we generalize some of the results without any assumption on the type of the relative quadratic extension.


Orbit Structure On The Silov Boundary Of A Tube Domain And The Plancherel Decomposition Of A Causally Compact Symmetric Space, With Emphasis On The Rank One Case, Troels Roussau Johansen Jan 2004

Orbit Structure On The Silov Boundary Of A Tube Domain And The Plancherel Decomposition Of A Causally Compact Symmetric Space, With Emphasis On The Rank One Case, Troels Roussau Johansen

LSU Doctoral Dissertations

We construct a G-equivariant causal embedding of a compactly causal symmetric space G/H as an open dense subset of the Silov boundary S of the unbounded realization of a certain Hermitian symmetric space G1/K1 of tube type. Then S is an Euclidean space that is open and dense in the flag manifold G1/P', where P' denotes a certain parabolic subgroup of G1. The regular representation of G on L2(G/H) is thus realized on L2(S), and we use abelian harmonic analysis in the study thereof. In particular, …


Global Patterns Of Dissolved N, P And Si In Large Rivers, R. Eugene Turner, Nancy N. Rabalais, D. Justic', Q. Dortch Jul 2003

Global Patterns Of Dissolved N, P And Si In Large Rivers, R. Eugene Turner, Nancy N. Rabalais, D. Justic', Q. Dortch

Faculty Publications

The concentration of dissolved inorganic nitrogen (DIN), dissolved nitrate-N, Total-N (TN), dissolved inorganic phosphate (DIP), total phosphorus (TP), dissolved silicate-Si (DSi) and their ratios in the world's largest rivers are examined using a global data base that includes 37% of the earth's watershed area and half its population. These data were compared to water quality in 42 subbasins of the relatively well-monitored Mississippi River basin (MRB) and of 82 small watersheds of the United States. The average total nitrogen concentration varies over three orders of magnitude among both world river watersheds and the MRB, and is primarily dependent on variations …