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Physical Sciences and Mathematics Commons™

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Iowa State University

Selected Works

1995

Articles 1 - 10 of 10

Full-Text Articles in Physical Sciences and Mathematics

Variation In Lightness Of White Oak Dimension Stock, Douglas D. Stokke, Anton D. Pugel, John E. Phelps Oct 1995

Variation In Lightness Of White Oak Dimension Stock, Douglas D. Stokke, Anton D. Pugel, John E. Phelps

Douglas D. Stokke

The objectives of this research were to generate a set of sample parameters for the lightness of planed white oak dimension stock, to investigate the effect of grain angle on lightness values, and to determine the level of sampling needed to color match white oak dimension stock on the basis of lightness or darkness as quantified by the parameter L* (psychometric lightness). This information is important when used to determine the feasibility of low-cost portable instruments for evaluating color in an edge-glued hardwood panel production setting. Color measurements were obtained with a portable spectrophotometer interfaced with a notebook computer. The …

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Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski Aug 1995

Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

We have calculated the atomic short-range order (ASRO) and paramagnetic susceptibility in high-temperature, chemically disordered Au75Fe25 and Au90Fe10, using a density-functional-based, electronic-structure method. For both alloys, we obtain 〈11/20〉-type ASRO, in excellent agreement with experiments performed on samples that have been fast quenched from high temperature. We also identify the underlying electronic mechanism responsible for this unusual ordering behavior. During annealing at high temperatures, we suggest that aligning local moments via an external magnetic field will produce interesting AuFe alloys with 〈100〉-type ASRO.

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Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo Apr 1995

Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo

Duane D. Johnson

We describe an ordering mechanism that arises due to coupling between electronic states at van Hove singularities. This novel mechanism, which naturally leads to ordered structures with small unit cells, couples states near the Fermi energy which are localized at high-symmetry points in k space, in contrast to the conventional mechanism which relies on large parallel sheets of Fermi surface. Using first-principles calculations of the electronic structure of ordered and disordered alloys, we show that this mechanism drives the unusual short- and long-range order found in fcc CuPt.

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Ecological Risk Assessment For Chemical Stressors: Challenges In Predictive Ecotoxicology Research, Steven P. Bradbury Jan 1995

Ecological Risk Assessment For Chemical Stressors: Challenges In Predictive Ecotoxicology Research, Steven P. Bradbury

Steven P. Bradbury

Environmental management decisions are increasingly based on the results of ecological risk assessments that require data and models to establish the likelihood of adverse ecological effects that may occur or are occurring as a result of exposure to one or more stressors .. Research to support ecological risk assessments for chemical stressors must include a predictive capability.. The great number of chemicals, species and habitats (exposure conditions) associated with prospective and retrospective management decisions precludes the use of empirical testing as the sole means to fill data gaps .. Therefore, strategic laboratory and field testing must be undertaken in the …

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Sar Models For Futile Metabolism: One-Electron Reduction Of Quinones, Phenols And Nitrobenzenes, Steven P. Bradbury, Ovanes Mekenyan, G. D. Veith, N. Zaharieva Jan 1995

Sar Models For Futile Metabolism: One-Electron Reduction Of Quinones, Phenols And Nitrobenzenes, Steven P. Bradbury, Ovanes Mekenyan, G. D. Veith, N. Zaharieva

Steven P. Bradbury

Benzoquinones, naphthoquinones and aziridinylbenzoquinones, can be reduced by flavoproteins to semiquinones that react with molecular oxygen to form superoxide anion with the subsequent regeneration of the parent compounds. This redox cycling, a form of futile metabolism, produces reactive oxygen species and depletes the reducing equivalents of cells without concomitant energy production. The ability of a toxicant to redox cycle is related to its one-electron reduction potential, and this study attempted to estimate reduction potential from structure using semi-empirical quantum chemical models for a diverse set of chemicals. The results of this study suggest that one-electron reduction potentials, within structural classes …

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Quantitative Structure-Activity Relationships And Ecological Risk Assessment: An Overview Of Predictive Aquatic Toxicology Research, Steven P. Bradbury Jan 1995

Quantitative Structure-Activity Relationships And Ecological Risk Assessment: An Overview Of Predictive Aquatic Toxicology Research, Steven P. Bradbury

Steven P. Bradbury

In the field of aquatic toxicology, quantitative structure-activity relationships (QSARs) have developed as scientifically credible tools for predicting the toxicity of chemicals when little or no empirical data are available. A fundamental understanding of toxicological principles has been considered an important component to the acceptance and application of QSAR approaches as biologically relevant in ecological risk assessments. As a consequence, there has been an evolution of QSAR development and application from that of a chemical-class perspective to one that is more consistent with assumptions regarding modes of toxic action. In this review, techniques to assess modes of toxic action from …

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Use Of Knowledge Bases And Qsars To Estimate The Relative Ecological Risk Of Agrichemicals: A Problem Formulation Exercise, Steven P. Bradbury, C. L. Russom, A. R. Carlson Jan 1995

Use Of Knowledge Bases And Qsars To Estimate The Relative Ecological Risk Of Agrichemicals: A Problem Formulation Exercise, Steven P. Bradbury, C. L. Russom, A. R. Carlson

Steven P. Bradbury

Ecological risk assessments can be used to establish the likelihood that an adverse effect will result from exposure to one or more chemicals. When evaluating contaminated sites with many chemicals present, risk assessors must grapple with the problem of quickly identifying the chemicals that are most likely to be of concern, based on effect and exposure assessment information. Many times data gaps exist and the risk assessor is left with decisions on which models to use to estimate the parameter of concern. In the present paper, a procedure is presented for ranking agrichemicals, utilizing the ASTER (ASsessment Tools for the …

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Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski Jan 1995

Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

We show that Fermi-surface (FS) nesting drives both the incommensurate and commensurate ordering tendencies of the fcc ternary Cu-Ni-Zn system. Surprisingly, commensurate order persists over a wide range of composition, despite its origins. For Cu2NiZn, we discuss how FS nesting and the other effects of alloying lead to ordering tendencies consistent with the experimentally observed order-disorder transformations. All calculations are based on a first-principles theory of the atomic short-range order in alloys with an arbitrary number of components.

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Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker Jan 1995

Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker

Edward Yu

A frequency doubled tunable dye laser system with ∼0.4 cm−1 resolution was used to measure the integrated absorption cross sections of more than 20 rotational transitions in the O2 Herzberg I (A  3Σ+ u ←X  3Σ− g ) 8‐0 and 9‐0 vibrational bands near 248 nm and 249 nm. Oxygen pressures from 200 to 800 Torr and path lengths from 5 to 25 m were employed. The measured absorbances were fitted using a nonlinear least squares analysis and Beer’s Law to obtain absolute values for the individual transition integrated cross sections in good agreement with a recent spectral simulation and …

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Comparison Of Variable Rate To Single Rate Nitrogen Fertilizer Application: Corn Production And Residual Soil No3-N, N. R. Kitchen, D. F. Hughes, K. A. Sudduth, Stuart J. Birrell Jan 1995

Comparison Of Variable Rate To Single Rate Nitrogen Fertilizer Application: Corn Production And Residual Soil No3-N, N. R. Kitchen, D. F. Hughes, K. A. Sudduth, Stuart J. Birrell

Stuart J. Birrell

The questions most often asked by farmers when discussing variable rate (VR) fertilizer inputs are "How much will it cost?" and "How will it affect my yields?" Many farmers and custom application services share a reluctance to invest in the time and technology required for variable fertilizer application since studies to answer these questions are few and results have been inconsistent.

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