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Articles 1 - 14 of 14

Full-Text Articles in Physical Sciences and Mathematics

Quantitative Structure-Activity Relationships For Polychlorinated Hydroxybiphenyl Estrogen Receptor Binding Affinity: An Assessment Of Conformer Flexibility, Steven P. Bradbury, Ovanes G. Mekenyan, Gerald T. Ankley Nov 1996

Quantitative Structure-Activity Relationships For Polychlorinated Hydroxybiphenyl Estrogen Receptor Binding Affinity: An Assessment Of Conformer Flexibility, Steven P. Bradbury, Ovanes G. Mekenyan, Gerald T. Ankley

Steven P. Bradbury

A diverse group of xenobiotics has a high binding affinity to the estrogen receptor (ER), suggesting that it can accommodate large variability in ligand structure. Relationships between xenobiotic structure, binding affinity, and estrogenic response have been suggested to be dependent on the conformational structures of the ligands. To explore the influence of conformational flexibility on ER binding affinity, a quantitative structure—activity relationship (QSAR) study was undertaken with estradiol, diethylstilbestrol, and a set of polychlorinated hydroxybiphenyls (PCHBs) of environmental concern. Although the low-energy minima of the PCHB congeners suggested that interconversions among conformers were likely, the electronic parameters associated with the …


Degradation Studies Of The Non-Lethal Bird Repellent, Methyl Anthranilate, Eugeny Aronov, Larry Clark Jan 1996

Degradation Studies Of The Non-Lethal Bird Repellent, Methyl Anthranilate, Eugeny Aronov, Larry Clark

Larry Clark

Methyl anthranilate (MA), a food grade flavor and fragrance additive, has been reported to be an effective non-lethal bird repellent in a variety of situations. Despite the experimental success of MA, field studies have yielded widely differing levels of efficacy. Diminished efficacy in some field trials prob­ ably results from the failure of specific formulations to retain or protect the active ingredient under natural conditions. Therefore, a clearer understanding of the physical and chemical factors affecting the stability of MA is needed. We undertook a series of laboratory studies on hydrolysis, photolysis and microbial degradation of MA, the results of …


Variation In Cell Dimensions And Fibril Angle For Two Fertilized Even-Aged Loblolly Pine Plantations, Douglas D. Stokke, Todd F. Shupe, Elvin T. Choong, Mark D. Gibson Jan 1996

Variation In Cell Dimensions And Fibril Angle For Two Fertilized Even-Aged Loblolly Pine Plantations, Douglas D. Stokke, Todd F. Shupe, Elvin T. Choong, Mark D. Gibson

Douglas D. Stokke

Increment core samples were obtained from randomly selected, nine-year-old lohlolly pine (Pinus faeda L.) in two even-aged plantations in Louisiana in order to determine the variation in cell dimensions and fibril angle of the sites. The Homer site is representative of the growing conditions in north Louisiana, and the Bogalusa site is typical of the conditions in southeastern Louisiana. Both sites were subjected to similar site preparation and weed control and were fertilized in the juvenile period. The anatomical properties that were measured include: fiber length, cell-wall thickness, and microfibril angle (MFA). Observations were made in order to compare corewood …


Estimating One-Electron Reduction Potentials Of Quinones, Steven P. Bradbury, Ovanes G. Mekenyan, V. B. Kamenska Jan 1996

Estimating One-Electron Reduction Potentials Of Quinones, Steven P. Bradbury, Ovanes G. Mekenyan, V. B. Kamenska

Steven P. Bradbury

The one-electron reduction potential ∗ E1 7 of benzo-, naphtho-and anthracenequinones is related to their ability to undergo redox cycling and elicit cytotoxicity through oxidative stress. To evaluate a general approach to estimate the E1 7 of benzo-, naphtho-and anthracenequinones, QSAR approaches based on gas phase and solvation based methods were employed. Stereoelectronic descriptors of ground state quinones, respective intermediates of the redox cycle, and the di erences in parameters for the transition between intermediates were evaluated. The variation of E1 7 was correlated with descriptors of the parent quinones and speci c transition parameters. The energy of the highest …


Presettlement Vegetation Of The Lower Chippewa River Valley, Lisa A. Schulte-Moore, William J. Barnes Jan 1996

Presettlement Vegetation Of The Lower Chippewa River Valley, Lisa A. Schulte-Moore, William J. Barnes

Lisa A. Schulte Moore

The lower Chippewa River of west-central Wisconsin is the portion that flows southwest from the city of Eau Claire to the Mississippi River at Nelson. The river has a gentle gradient of about 0.8 m/km and highly erodible banks of sand and gravel. The river valley occurs between 35 m to 70 m below the surrounding upland, is between 1 and 5 km wide, and was formed primarily by glacial meltwaters. The floodplain is defined by annual high water levels and is generally below the 25 year flood recurrence interval, which on this part of the Chippewa River is >5m …


2,3, 7,8-Tetrachlorodibenzo-P-Dioxin, Steven P. Bradbury Jan 1996

2,3, 7,8-Tetrachlorodibenzo-P-Dioxin, Steven P. Bradbury

Steven P. Bradbury

Since 1985, the United States Environmental Protection Agency (USEPA) has classified 2,3,7,8-tetrachloro-p-dioxin (TCDD) as a probable human carcinogen; subsequently, sources of TCDD in the environment have been regulated on the basis of animal cancer rates extrapolated to doses associated with human exposures. Two major activities have prompted the decision to reassess this approach for evaluating TCDD toxicity and its associated risks. First, an epidemiological study of cancer mortality in U.S. chemical workers by the National Institute of Occupational Safety and Health provided evidence of TCDD-mediated human carcinogenicity (Fingerhut et al. 1991 ). Second, at a 1990 Banbury conference a consensus …


Nutrient Mapping Implications Of Short-Range Variability, Stuart J. Birrell Jan 1996

Nutrient Mapping Implications Of Short-Range Variability, Stuart J. Birrell

Stuart J. Birrell

Successful site specific nutrient application depends on accurate soil nutrient maps, which are generally developed from grid samples. The implication of short range variability for soil nutrient mapping is investigated. Interpretation of soil nutrient maps must consider the level of confidence associated with estimated values.


Analysis Of Spatial Factors Influencing Crop Yield, K. A. Sudduth, S. T. Drummond, Stuart J. Birrell, N. R. Kitchen Jan 1996

Analysis Of Spatial Factors Influencing Crop Yield, K. A. Sudduth, S. T. Drummond, Stuart J. Birrell, N. R. Kitchen

Stuart J. Birrell

The spatial relationship between crop yields and soil and site parameters was modeled using several methods. Yield maps estimated by projection pursuit regression and neural network analysis agreed well with measured yields. These methods also allowed generation of response curves for estimated yield as a function of each of the input parameters. These response curves were useful for investigating the relationship between yields and individual soil and site parameters.


The Shape Of Self-Motion Perception. Ii. Framework And Principles For Simple And Complex Motions, Jan E. Holly, Gin Mccollum Jan 1996

The Shape Of Self-Motion Perception. Ii. Framework And Principles For Simple And Complex Motions, Jan E. Holly, Gin Mccollum

Gin McCollum

There have been numerous experimental studies on human perception and misperception of self-motion and orientation relative to the earth, each focusing on one or a few types of motion. We present a formal framework encompassing many types of motion and including all angular and linear components of velocity and acceleration. Using a mathematically rigorous presentation, the framework defines the space of all possible motions, the map from motion to sensor status, the space containing each possible status of the sensors, and the map from sensor status to perceived motion. The shape of the full perceptual map from actual motion to …


The Stomatogastric Nervous System: A Formal Approach, Patrick D. Roberts, Gin Mccollum Jan 1996

The Stomatogastric Nervous System: A Formal Approach, Patrick D. Roberts, Gin Mccollum

Gin McCollum

A discrete mathematical formalism (d-space) which is specifically designed to investigate discrete aspects of behavior is applied to the foregut of decapod crustacea. This approach differs from continuous modeling techniques in that the analysis determines a structure in which the observed behavior of the foregut is constrained. A notation for the implementation of the formalism is developed as well as a coordinate system natural to the functioning of the gastric mill. The formalism is used to organize previous observations that suggest potential courses of further experimental investigation. A detailed analysis of observed chewing modes of the gastric mill is presented, …


Lion-Tailed Macaques (Macaca Silenus) In A Disturbed Forest Fragment: Activity Patterns And Time Budget, Shaily Menon, Frank Poirier Dec 1995

Lion-Tailed Macaques (Macaca Silenus) In A Disturbed Forest Fragment: Activity Patterns And Time Budget, Shaily Menon, Frank Poirier

Shaily Menon

We describe the activity patterns and time budget of a feral group of lion-tailed macaques that were confined to a disturbed forest fragment of 65 ha and compare the results with those obtained for groups in protected forests. The degraded nature of the study site was reflected in low tree densities, low specific diversity, gaps in the girth distribution of trees, and frequent disturbance by humans. The study group of 43 subjects was twice as large as lion-tailed macaque groups in protected habitats. They spent the most time ranging (34.0%), followed by foraging (23.7%), feeding (17.9%), resting (16.0%), and other …


In-Situ Imaging Of Ionic Crystal Dissolution Using An Integrated Electrochemical/Afm Probe, Julie V. Macpherson, Patrick R. Unwin, Andrew C. Hillier, Allen J. Bard Dec 1995

In-Situ Imaging Of Ionic Crystal Dissolution Using An Integrated Electrochemical/Afm Probe, Julie V. Macpherson, Patrick R. Unwin, Andrew C. Hillier, Allen J. Bard

Andrew C. Hillier

The kinetics and mechanism controlling dissolution from the (100) cleavage face of potassium bromide single crystals in acetonitrile solutions have been identified using a novel integrated electrochemical/AFM probe and a scanning electrochemical microscope (SECM). With both techniques, dissolution is induced by perturbing the dynamic dissolution/growth equilibrium at the crystal/solution interface through the electrochemical oxidation of bromide ions. SECM measurements demonstrate that the dissolution reaction is diffusion-limited under the experimental conditions, suggesting that the surface reaction is characterized by a rate constant in excess of 5 cm s-1 (assuming a first-order dissolution process). The topography of the dissolving surface has been …


Brain Activation Modulated By Sentence Comprehension, Marcel Adam Just, Patricia A. Carpenter, Timothy A. Keller, William F. Eddy, Keith R. Thulborn Dec 1995

Brain Activation Modulated By Sentence Comprehension, Marcel Adam Just, Patricia A. Carpenter, Timothy A. Keller, William F. Eddy, Keith R. Thulborn

Marcel Adam Just

No abstract provided.


Measurement Of Double-Layer Forces At The Electrode/Electrolyte Interface Using The Atomic Force Microscope: Potential And Anion Dependent Interactions, Andrew C. Hillier, Sunghyun Kim, Allen J. Bard Dec 1995

Measurement Of Double-Layer Forces At The Electrode/Electrolyte Interface Using The Atomic Force Microscope: Potential And Anion Dependent Interactions, Andrew C. Hillier, Sunghyun Kim, Allen J. Bard

Andrew C. Hillier

The forces between a silica probe and silica and gold substrates were measured with an atomic force microscope in the presence of a series of alkali-halide electrolyte solutions. The interaction between two silica surfaces was repulsive and could be accurately predicted by Derjaguin-Landau-Verwey-Overbeek theory. The silica surface was negatively charged at a pH of 5.5 and the effective surface potential increased in magnitude with decreasing electrolyte concentration. In contrast, the force between the silica probe and a gold substrate was attractive at open circuit. This interaction was a strong function of the potential applied to the gold and the nature …