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1999

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Articles 1 - 30 of 2534

Full-Text Articles in Physical Sciences and Mathematics

Probing The Mechanisms Of Enantioselective Hydrogenation Of Simple Olefins With Chiral Rhodium Catalysts In The Presence Of Anions, Jillian M. Buriak, Jason C. Klein, Deborah Herrington, John A. Osborn Dec 1999

Probing The Mechanisms Of Enantioselective Hydrogenation Of Simple Olefins With Chiral Rhodium Catalysts In The Presence Of Anions, Jillian M. Buriak, Jason C. Klein, Deborah Herrington, John A. Osborn

Peer Reviewed Articles

The strong influence of various anions upon the hydrogenation of 2-phenyl-1-butene, catalyzed by chiral rhodium catalysts was investigated. Both sulfonates and halides exert large increases in the enantioselectivity when [Rh{(−)-bdpp}(NBD)]ClO4 (bdpp=2,4-bis(diphenylphosphino)pentane, NBD=2,5-norbornadiene) is used as the catalyst precursor at high pressures (70 atm) of dihydrogen in nonpolar solvents. A dihydride mechanism similar to that for Wilkinson's catalyst [RhCl(PPh3)3] was shown to be operating at both high- and low-pressure conditions through a combination of catalytic studies, 31P, 1H and parahydrogen-induced polarization (PHIP) NMR experiments. With sulfonate and in neat methanol, however, a mechanistic switch takes place from a dihydride route (dihydrogen …

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Dynamics Of The Dbi Spike Soliton, David Kastor, Jennie Traschen Dec 1999

Dynamics Of The Dbi Spike Soliton, David Kastor, Jennie Traschen

David Kastor

We compare oscillations of a fundamental string ending on a D3-brane in two different settings: (1) a test-string radially threading the horizon of an extremal black D3-brane and (2) the spike soliton of the DBI effective action for a D3-brane. Previous work has shown that overall transverse modes of the test-string appear as l=0 modes of the transverse scalar fields of the DBI system. We identify DBI world-volume degrees of freedom that have dynamics matching those of the test-string relative transverse modes. We show that there is a map, resembling T-duality, between relative and overall transverse modes for the test-string …

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Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg Dec 1999

Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg

Physics - All Scholarship

We have investigated the mean field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model introduced incorporates coexistence of pinned and sliding degrees of freedom and can exhibit continuous elastic depinning or first order hysteretic depinning. Numerical simulations indicate mean field instabilities that correspond to macroscopic stick-slip events and lead to premature switching. The model is relevant for the dynamics of driven vortex arrays in superconductors and other extended disordered systems.

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Nanocomposite Copt:C Films For Extremely High-Density Recording, M. Yu, Yi Liu, A. Moser, D. Weller, David J. Sellmyer Dec 1999

Nanocomposite Copt:C Films For Extremely High-Density Recording, M. Yu, Yi Liu, A. Moser, D. Weller, David J. Sellmyer

David Sellmyer Publications

Nanocomposite CoPt:C films were investigated as potential media for extremely high-density recording. An annealing temperature of over 600 °C is necessary to form nanocomposite CoPt:C films consisting of C matrix and fct CoPt nanocrystallites with grain sizes of 8–20 nm and coercivities of 3–12 kOe. Coercivity and grain size increase with increasing annealing temperature and decreasing C concentration and they are insensitive to film thickness. The average activation volumes are about 0.9×10-18 cm3. The properties of these nanocomposite CoPt:C films can be tailored to satisfy the thermal stability, coercivity, and media noise requirements for extremely high-density recording.

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Emissions Of Formaldehyde, Acetic Acid, Methanol, And Other Trace Gases From Biomass Fires In North Carolina Measured By Airborne Fourier Transform Infrared Spectroscopy, Robert J. Yokelson, Jon G. Goode, Darold E. Ward, Ronald A. Susott, Ronald E. Babbitt, D. D. Wade, Issac T. Bertschi, David W. T. Griffith, Wei Min Hao Dec 1999

Emissions Of Formaldehyde, Acetic Acid, Methanol, And Other Trace Gases From Biomass Fires In North Carolina Measured By Airborne Fourier Transform Infrared Spectroscopy, Robert J. Yokelson, Jon G. Goode, Darold E. Ward, Ronald A. Susott, Ronald E. Babbitt, D. D. Wade, Issac T. Bertschi, David W. T. Griffith, Wei Min Hao

Chemistry and Biochemistry Faculty Publications

Biomass burning is an important source of many trace gases in the global troposphere. We have constructed an airborne trace gas measurement system consisting of a Fourier transform infrared spectrometer (FTIR) coupled to a “flow-through” multipass cell (AFTIR) and installed it on a U.S. Department of Agriculture Forest Service King Air B-90. The first measurements with the new system were conducted in North Carolina during April 1997 on large, isolated biomass fire plumes. Simultaneous measurements included Global Positioning System (GPS); airborne sonde; particle light scattering, CO, and CO2; and integrated filter and canister samples. AFTIR spectra acquired within …

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(Teff,Log G,[Fe/H]) Classification Of Low-Resolution Stellar Spectra Using Artificial Neural Networks, Shawn Snider, Yuan Qu, Carlos Allende Prieto, Ted Von Hippel, Timothy C. Beers, Christopher Sneden, David L. Lambert, Silvia Rossi Dec 1999

(Teff,Log G,[Fe/H]) Classification Of Low-Resolution Stellar Spectra Using Artificial Neural Networks, Shawn Snider, Yuan Qu, Carlos Allende Prieto, Ted Von Hippel, Timothy C. Beers, Christopher Sneden, David L. Lambert, Silvia Rossi

Publications

New generation large-aperture telescopes, multi-object spectrographs, and large format detectors are making it possible to acquire very large samples of stellar spectra rapidly. In this context, traditional star-by-star spectroscopic analysis are no longer practical. New tools are required that are capable of extracting quickly and with reasonable accuracy important basic stellar parameters coded in the spectra. Recent analyses of Artificial Neural Networks (ANNs) applied to the classification of astronomical spectra have demonstrated the ability of this concept to derive estimates of temperature and luminosity. We have adapted the back-propagation ANN technique developed by von Hippel et al. (1994) to predict …

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Wavelength-Specific Fluorescence Coefficients For Simulating Hyperspectral Reflectance Signatures Of Water, Charles R. Bostater, Jan Rebman Dec 1999

Wavelength-Specific Fluorescence Coefficients For Simulating Hyperspectral Reflectance Signatures Of Water, Charles R. Bostater, Jan Rebman

Ocean Engineering and Marine Sciences Faculty Publications

A model1'2 which describes the transfer of irradiant light in water is used to predict the fluorescence response ofthe water surface reflectance under solar induced or an artificial light source such as a laser. Formulations for the estimation of wavelength dependent fluorescent coefficients. The techniques allows the description ofa fluorescence reflectance response in deep and shallow waters with various bottom reflectance signatures such as submerged vegetation, corals and sand. Recent advances in the model are presented for obtaining wavelength dependent fluorescence spectrum responses from the solutions of the two flow equations following the procedures developed by Bostater1'2'3. Synthetic or modeled …

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High-Order Derivative Spectroscopy For Selecting Spectral Regions And Channels For Remote Sensing Algorithm Development, Charles R. Bostater Dec 1999

High-Order Derivative Spectroscopy For Selecting Spectral Regions And Channels For Remote Sensing Algorithm Development, Charles R. Bostater

Ocean Engineering and Marine Sciences Faculty Publications

A remote sensing reflectance model, which describes the transfer of irradiant light within a plant canopy or water column has previously been used to simulate the nadir viewing reflectance of vegetation canopies and leaves under solar induced or an artificial light ur'2 and the water surface reflectance3' Wavelength dependent features such as canopy reflectance leafabsorption and canopy bottom reflectance as well as water absorption and water bottom reflectance have been used to simulate or generate synthetic canopy and water surface reflectance signatures3' ' This paper describes how derivative spectroscopy can be utilized to invert the synthetic or modeled as well …

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A Transiting "51 Peg-Like" Planet, Gregory W. Henry, Geoffrey W. Marcy, R. Paul Butler, Steve Vogt Dec 1999

A Transiting "51 Peg-Like" Planet, Gregory W. Henry, Geoffrey W. Marcy, R. Paul Butler, Steve Vogt

Information Systems and Engineering Management Research Publications

Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s-1 and a period of 3.5239 days, which is indicative of a "51 Peg-like" planet with a minimum mass (M sin i) of 0.62 MJup and a semimajor axis of 0.046 AU. Follow-up photometry reveals a drop of 0.017 mag at the predicted time (within the errors) of transit by the companion based on the velocities. This is the first extrasolar planet observed to transit its star. The radius of the planet derived …

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Electrical Resistivity Of A Thin Metallic Film, Horacio E. Camblong Dec 1999

Electrical Resistivity Of A Thin Metallic Film, Horacio E. Camblong

Physics and Astronomy

The electrical resistivity of a pure sample of a thin metallic film is found to depend on the boundary conditions. This conclusion is supported by a free-electron model calculation and confirmed by an ab initio relativistic Korringa-Kohn-Rostoker computation. The low-temperature resistivity is found to be zero for a free-standing film (reflecting boundary conditions) but nonzero when the film is sandwiched between two semi-infinite samples of the same material (outgoing boundary conditions). In the latter case, this resistivity scales inversely with the number of monolayers and is due to the background diffusive scattering by a finite lattice.

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A Patching Model For Surface Tension Of Spherical Droplet And Tolman Length. Ii, T.V. Bykov, Xiao Cheng Zeng Dec 1999

A Patching Model For Surface Tension Of Spherical Droplet And Tolman Length. Ii, T.V. Bykov, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

In the framework of density functional theory (DFT), two patching models for the density profile of spherical liquid droplet are developed. The patching is based on analytical expressions of the asymptote of the density profiles. The first model leads to analytic expressions of the Tolman length and the effective rigidity constant, from which the temperature dependence of the Tolman length and effective rigidity constant can be determined. The second model is developed particularly for small spherical droplets, from which the dependence of chemical potential and the surface tension of the droplet on the radius are obtained. The results are compared …

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Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William Donaldson Dec 1999

Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William Donaldson

Chemistry Faculty Research and Publications

The dicarbonyl(1,2-dimethylpentadienyl)triphenylphosphineiron(1+) cation (11) has been prepared from methyl 4-methyl-2E,4E-hexadienoate in four steps. The cation (11) reacts with hydride and carbon nucleophiles in a regiospecific fashion to afford (3-methyl-2E,4Z-diene)iron complexes. Dicarbonyl(3-methyl-7-nitro-2E,4Z-heptadiene)triphenylphosphineiron (15), the product from the reaction of 11 with nitromethane anion, has been utilized as a precursor for nitrile oxide–olefin cyclocondensations.

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Breeding Bird Census On Four Shelterwood-Cut Stands In Buckingham County, Virginia, Sally Ann Statham Dec 1999

Breeding Bird Census On Four Shelterwood-Cut Stands In Buckingham County, Virginia, Sally Ann Statham

Theses & Honors Papers

The Breeding Bird Census (BBC) technique was used to study breeding bird populations on two paired shelter wood-cut oak stands in Buckingham County, Virginia. The four plots are part of a study to determine oak regeneration following controlled burns in the Virginia piedmont. There is an interest in determining how shelter wood-cut plots affect the breeding birds of Virginia. A total of twenty-seven bird species established and defended territories among the four plots. Ten bird species defended territories on all four plots. All of these species were birds characteristic of forest habitats.

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Linear Optics Simulations Of The Quantum Baker’S Map, John C. Howell, John A. Yeazell Dec 1999

Linear Optics Simulations Of The Quantum Baker’S Map, John C. Howell, John A. Yeazell

Mathematics, Physics, and Computer Science Faculty Articles and Research

The unitary evolution of linear optics can be used to model quantum computational networks. In this paper, a quantum simulation of a classically chaotic map (the baker’s map) is developed using linear optics. Two different models are presented. The first model employs only 50-50 beam splitters and phase shifters to simulate universal 2-qubit gates of a quantum computer. The second model uses the discrete Fourier transform generated by symmetric N×N fiber couplers. If single photons are used as inputs for these linear optics models, the result is a physical realization of the quantum baker’s map.

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Fundamental Plane Distances To Early-Type Field Galaxies In The South Equatorial Strip. I. The Spectroscopic Data, K. R. Müller, G. Wegner, S. Raychaudhury, W. Freudling Dec 1999

Fundamental Plane Distances To Early-Type Field Galaxies In The South Equatorial Strip. I. The Spectroscopic Data, K. R. Müller, G. Wegner, S. Raychaudhury, W. Freudling

Dartmouth Scholarship

Radial velocities and central velocity dispersions are derived for 238 E/S0 galaxies from medium-resolution spectroscopy. New spectroscopic data have been obtained as part of a study of the Fundamental Plane distances and peculiar motions of early-type galaxies in three selected directions of the South Equatorial Strip, undertaken in order to investigate the reality of large-scale streaming motion; results of this study have been reported in M\"uller $et$ $al.$ (1998). The new APM South Equatorial Strip Catalog (−17.5 < δ < +2.5) was used to select the sample of field galaxies in three directions: (1) 15h10 – 16h10; (2) 20h30 – 21h50; (3) 00h10 – 01h30. The spectra obtained have a median S/N per ̊A of 23, an in- strumental resolution (FWHM) of ∼ 4 ̊A, and the spectro- graph resolution (dispersion) is ∼ 100 km s−1. The Fourier cross-correlation method was used to derive the radial ve- locities and velocity dispersions. The velocity dispersions have been corrected for the size of the aperture and for the galaxy effective radius. Comparisons of the derived radial velocities with data from the literature show that our values are accurate to 40 km s−1. A comparison with results from Jørgensen et al. (1995) shows that the derived central velocity dispersion have an rms scatter of 0.036 in log σ. There is no offset relative to the velocity dispersions of Davies et al. (1987).

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Interaction Second Virial Coefficients From A Recent H2-Co Potential Energy Surface, J. Gottfried, George C. Mcbane Dec 1999

Interaction Second Virial Coefficients From A Recent H2-Co Potential Energy Surface, J. Gottfried, George C. Mcbane

Peer Reviewed Articles

No abstract provided.

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Langmuir Monolayers As Disordered Solids: Disorder And Elastic Fluctuations In Mesophases , Tadeusz Luty, Craig J. Eckhardt, Jacques Lefebvre Dec 1999

Langmuir Monolayers As Disordered Solids: Disorder And Elastic Fluctuations In Mesophases , Tadeusz Luty, Craig J. Eckhardt, Jacques Lefebvre

Craig J. Eckhardt Publications

Ordering in Langmuir monolayer mesophases is examined using an approach based on the elastic theory of crystals. Molecular tails are modeled as ‘‘defects’’ grafted onto a two-dimensional elastic medium and are characterized by elastic dipoles. It is assumed that disorder in the parent, LS, phase is due to competition between local (within a domain) and global (hexagonal arrangement of domains) structure. By treating the LS phase as a mixture of rectangular and/or oblique domains (rectangular and/or oblique defects within the two-dimensional elastic medium), density fluctuations due to elastic interactions between domains are analyzed. The correlation function for the elastic dipoles …

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Noncommutative Computer Algebra In The Control Of Singularly Perturbed Dynamical Systems, J. W. Helton, F. Dell Kronewitter, Mark Stankus Dec 1999

Noncommutative Computer Algebra In The Control Of Singularly Perturbed Dynamical Systems, J. W. Helton, F. Dell Kronewitter, Mark Stankus

Mathematics

Most algebraic calculations which one sees in linear systems theory, for example in IEEE TAC, involve block matrices and so are highly noncommutative. Thus conventional commutative computer algebra packages, as in Mathematica and Maple, do not address them. Here we investigate the usefulness of noncommutative computer algebra in a particular area of control theory-singularly perturbed dynamic systems-where working with the noncommutative polynomials involved is especially tedious. Our conclusion is that they have considerable potential for helping practitioners with such computations. For example, the methods introduced here take the most standard textbook singular perturbation calculation, [KK086], one step further than had …

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Peculiar Velocities Of Nonlinear Structure: Voids In Mcvittie Spacetime, Sakai, Nobuyuki, Haines, Paul Dec 1999

Peculiar Velocities Of Nonlinear Structure: Voids In Mcvittie Spacetime, Sakai, Nobuyuki, Haines, Paul

Dartmouth Scholarship

As a study of peculiar velocities of nonlinear structure, we analyze the model of a relativistic thin-shell void in the expanding universe. (1) Adopting McVittie (MV) spacetime as a background universe, we investigate the dynamics of an uncompensated void with negative MV mass. Although the motion itself is quite different from that of a compensated void, as shown by Haines & Harris (1993), the present peculiar velocities are not affected by MV mass. (2) We discuss how precisely the formula in the linear perturbation theory applies to nonlinear relativistic voids, using the results in (1) as well as the previous …

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Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston Dec 1999

Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston

Faculty Publications

We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2×10^9 cm^-3, and the temperatures of electrons and ions are as low as 100 mK and 10 uK, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.

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17th International Herman F. Mark Symposium: Polypropylene - A Material Of The Future, Otto Vogl, Helga Roder Dec 1999

17th International Herman F. Mark Symposium: Polypropylene - A Material Of The Future, Otto Vogl, Helga Roder

Emeritus Faculty Author Gallery

No abstract provided.

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12. Pierre Sigwalt, Otto Vogl Dec 1999

12. Pierre Sigwalt, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.

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Local And Landscape Factors Affecting Nest Site Selection And Nest Success Of Burrowing Owls In Western Nebraska, Rebecca T. Ekstein Dec 1999

Local And Landscape Factors Affecting Nest Site Selection And Nest Success Of Burrowing Owls In Western Nebraska, Rebecca T. Ekstein

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Ecology Of Elk In Northwestern Nebraska: Demographics, Effects Of Human Disturbance, And Characteristics Of Calving Habitat, Bruce A. Stillings Dec 1999

Ecology Of Elk In Northwestern Nebraska: Demographics, Effects Of Human Disturbance, And Characteristics Of Calving Habitat, Bruce A. Stillings

School of Natural Resources: Dissertations, Theses, and Student Research

No abstract provided.

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Water Current, Volume 31, No. 6, December 1999 Dec 1999

Water Current, Volume 31, No. 6, December 1999

Water Current Newsletter

Conference to Develop a Management Agenda for Nebraska's Water Future
From the Director: We Have a Long Way, But We Need to Go Further; Water Center Recognized as "Groundwater Guardian" Partner
NU Research Faculty Voice Desires for Strong Water Center Leadership
Citizen Stewards of the Pines and Plains
Fourth Water Tabloid Now Available from NU
Water News Briefs
Sixth Annual Undergrad Research Conference
Publications
National Geographic Society Awarding Science Grants
Call for Papers: Spatial Symposium in Reno, Nevada
Call for Papers: 11th Platte River Basin Symposium
Cooperation and Tension: The History, Reality and Future of Nebraska's Interstate Agreements

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Experiments To Assess The Cost-Benefits Of Test-Suite Reduction, Gregg Rothermel, Mary Jean Harrold, Jeffery Von Ronne, Christie Hang, Jeffery Ostrin Dec 1999

Experiments To Assess The Cost-Benefits Of Test-Suite Reduction, Gregg Rothermel, Mary Jean Harrold, Jeffery Von Ronne, Christie Hang, Jeffery Ostrin

CSE Technical Reports

Test-suite reduction techniques attempt to reduce the cost of saving and reusing test cases during software maintenance by eliminating redundant test cases from test suites. A potential drawback of these techniques is that in reducing a test suite they might reduce the ability of that test suite to reveal faults in the software. Previous studies suggested that test-suite reduction techniques can reduce test suite size without significantly reducing the fault-detection capabilities of test suites. To further investigate this issue we performed experiments in which we examined the costs and benefits of reducing test suites of various sizes for several programs …

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Calibration, Installation Techniques, And Initial Measurements For Vertical Resistivity Probes Used In Hydrogeologic Investigations, Jeffrey Mark Groncki Dec 1999

Calibration, Installation Techniques, And Initial Measurements For Vertical Resistivity Probes Used In Hydrogeologic Investigations, Jeffrey Mark Groncki

Masters Theses

Vertical Resistivity Probes (VRPs) are being increasingly used in a variety of applications where detailed vertical resistivity information in both the vadose and saturated zones is needed. All the different possible array types and spacings must be calibrated for the effect of the 2" (outer diameter) insulating PVC cylinder on which the electrodes are mounted. Apparent resistivities must be corrected by calibration factors. Varying the installation parameters greatly influences the measured apparent resistivity because of the disturbed annulus and the composition of the backfill materials. Bentonite slurry is necessary for the installations to keep the electrodes in good contact with …

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Salinity History Of Coastal Marshes Reconstructed From Diatom Remains, Michael L. Parsons, Quay Dortch, R. Eugene Turner, Nancy N. Rabalais Dec 1999

Salinity History Of Coastal Marshes Reconstructed From Diatom Remains, Michael L. Parsons, Quay Dortch, R. Eugene Turner, Nancy N. Rabalais

Faculty Publications

Sediment cores were collected from three Louisiana coastal marsh ponds, dated with radioisotopes, and analyzed for diatom remains to determine if long-term salinity changes were evident in the sediment record. A diatom-based salinity index formulated from a statistical comparison of available salinity data and changing diatom assemblages demonstrated that diatom remains appear to preserve salinity signals in coastal brackish and salt marsh environments. The salinity index was applied to sediment cores spanning the late 1600s to the 1990s and provided a more complete record of salinity than field data, which were temporally and spatially incomplete. The salinity reconstructions indicated that …

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Grundlagenreflexionen Zur Thematik Anthropomorpher Schnittstellen, Rudolf Kaehr Dec 1999

Grundlagenreflexionen Zur Thematik Anthropomorpher Schnittstellen, Rudolf Kaehr

Rudolf Kaehr

Report for the EMBASSI Project

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12. Pierre Sigwalt, Otto Vogl Dec 1999

12. Pierre Sigwalt, Otto Vogl

Otto Vogl

No abstract provided.

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