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1999

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Articles 1 - 30 of 2358

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 ...


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 ...


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

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.


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 ...


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 ...


The Reflectance Spectrum Of Human Skin, Elli Angelopoulou Dec 1999

The Reflectance Spectrum Of Human Skin, Elli Angelopoulou

Technical Reports (CIS)

The automated detection of human skin has become an important task for machine vision systems. Prior vision and graphics research on this topic has primarily focused on images acquired with conventional color cameras. Formal spectrographic analyses have largely been undertaken in the medical domain and focus on the detection of pathology. We have constructed a facility capable of producing accurate, dense and repeatable reflectance measurements. The light reflected from the skin is measured using a high resolution, high accuracy spectrograph under precisely calibrated lighting conditions. This paper presents observations from the first body of data gathered at this facility. From ...


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 ...


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.


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 ...


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.


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.


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).


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.


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 ...


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 ...


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 results ...


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.


12. Pierre Sigwalt, Otto Vogl Dec 1999

12. Pierre Sigwalt, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.


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.


Grundlagenreflexionen Zur Thematik Anthropomorpher Schnittstellen, Rudolf Kaehr Dec 1999

Grundlagenreflexionen Zur Thematik Anthropomorpher Schnittstellen, Rudolf Kaehr

Rudolf Kaehr

Report for the EMBASSI Project


Synthesis And Characterization Of Metal Ion Sensing High Performance Polymers And Directional Metallopolymers, Odessa N. Petzold Dec 1999

Synthesis And Characterization Of Metal Ion Sensing High Performance Polymers And Directional Metallopolymers, Odessa N. Petzold

ETD Collection for AUC Robert W. Woodruff Library

High performance polyamides containing the 4,4’-disubstituted-2,2’-bipyridyl moiety were synthesized by phosphorylation polycondensation from 2,2’-bipyridyl-4,4’-dicarboxylic acid and a series of primary aromatic diamines with triphenylphosphite and pyridine as the agents to facilitate condensation. Polyamides exhibiting improved solubility in organic solvents and strong acids, melting transitions at low temperatures and good thermal properties were prepared by introducing bulky methyl and fluoro groups, flexible ether and propyl linkages, and by using monomers with reduced symmetry. Solutions of the polyamides with rigid mainchains (II, III, IV, V, VI, and VIII) showed birefringence (colorful spherulites) at concentrations ...


La Gestion De La Faune Aux Aeroports, Edward C. Cleary , Richard A. Dolbeer Dec 1999

La Gestion De La Faune Aux Aeroports, Edward C. Cleary , Richard A. Dolbeer

Other Bird Strike and Aviation Materials

L’homme a toujours ete intrigue et inspire par la beaute des oiseaux et leur capacite de voler. Mais si les oiseaux ont colonise le ciel il y a quelque 150 millions d’annees, nous ne partageons leur espace aerien que depuis cent ans. Helas, ce partage forcement simultane est source de collisions. Certes, les oiseaux ne sont pas les seuls problemes des pilotes.


The Probe, Issue 207 – December 1999 Dec 1999

The Probe, Issue 207 – December 1999

The Probe: Newsletter of the National Animal Damage Control Association

NADCA: A Proud History, A New Future -- Robert H. Schmidt, President, NADCA
Position Announcement: WILDLIFE ECOLOGIST - Urban Wildlife & Urban-Human Conflict Management Illinois Natural History Survey, Urbana-Champaign, IL
In Memoriam: Guy R. Hodge
Personnel Changes in USDA Wildlife Services: Two new State Directors
Book review: "Wildlife of the New Millennium: A Field Guide" by Buck Peterson. Published by Longstreet Press, Marietta, Georgia 1999. (152 pages, illustrated. $11.95) ISBN 1-56352-546-1
Euthanasia Chamber Available from Pioneer Wildlife Control of Westwood, MA

Abstracts from the 6th Annual Conference of The Wildlife Society - September 1999, Austin, TX
Public health significance of bat rabies in ...


Disclosure Detection In Multivariate Categorical Databases: Auditing Confidentiality Protection Through Two New Matrix Operators, Sumit Dutta Chowdhury, George T. Duncan, Ramayya Krishnan, Stephen F. Roehrig, Sumitra Mukherjee Dec 1999

Disclosure Detection In Multivariate Categorical Databases: Auditing Confidentiality Protection Through Two New Matrix Operators, Sumit Dutta Chowdhury, George T. Duncan, Ramayya Krishnan, Stephen F. Roehrig, Sumitra Mukherjee

CCE Faculty Articles

As databases grow more prevalent and comprehensive, database administrators seek to limit disclosure of confidential information while still providing access to data. Practical databases accommodate users with heterogeneous needs for access. Each class of data user is accorded access to only certain views. Other views are considered confidential, and hence to be protected. Using illustrations from health care and education, this article addresses inferential disclosure of confidential views in multidimensional categorical databases. It demonstrates that any structural, so data-value-independent method for detecting disclosure can fail. Consistent with previous work for two-way tables, it presents a data-value-dependent method to obtain tight ...


Applications And Algorithms For Least Trimmed Sum Of Absolute Deviations Regression, Douglas M. Hawkins, David Olive Dec 1999

Applications And Algorithms For Least Trimmed Sum Of Absolute Deviations Regression, Douglas M. Hawkins, David Olive

Articles and Preprints

High breakdown estimation (HBE) addresses the problem of getting reliable parameter estimates in the face of outliers that may be numerous and badly placed. In multiple regression, the standard HBE's have been those defined by the least median of squares (LMS) and the least trimmed squares (LTS) criteria. Both criteria lead to a partitioning of the data set's n cases into two “halves” – the covered “half” of cases are accommodated by the fit, while the uncovered “half”, which is intended to include any outliers, are ignored. In LMS, the criterion is the Chebyshev norm of the residuals of ...


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 ...


12. Pierre Sigwalt, Otto Vogl Dec 1999

12. Pierre Sigwalt, Otto Vogl

Otto Vogl

No abstract provided.


Measurement Of TC Suppression In Tungsten Using Magnetic Impurities, Betty A. Young, T. Saab, Blas Cabrera, J. J. Cross, R. M. Clarke, R. A. Abusaidi Dec 1999

Measurement Of TC Suppression In Tungsten Using Magnetic Impurities, Betty A. Young, T. Saab, Blas Cabrera, J. J. Cross, R. M. Clarke, R. A. Abusaidi

Physics

We have measured the effects of dilute magnetic-atom doping on the superconducting transition temperature of tungsten thin films. Our “Tc tuning” technique is accurate, precise, and simple. Experiments were performed using dc-magnetron-sputtered tungsten films with undoped values of Tc in the range of 70–150 mK. The magnetic-atom doping was achieved using ion implantation. Specific Tc suppressions of between 5% and 65% were targeted and observed in this study. The transition width of each undoped sample was ≈1 mK and the transition widths remained sharp after implantation with 56Fe+ ions. Our data are in good agreement ...


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

Otto Vogl

No abstract provided.


Year In Review - 1999, Annis Water Resources Institute Dec 1999

Year In Review - 1999, Annis Water Resources Institute

AWRI Reviews

No abstract provided.