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 Waves and tides (7)
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 Meteorology and Atmospheric Dynamics: Theoretical modeling (3)
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Articles 1  16 of 16
FullText Articles in Physical Sciences and Mathematics
OneGas Models With HeightDependent Mean Molecular Weight: Effects On Gravity Wave Propagation, R. L. Walterscheid, Michael P. Hickey Ph.D.
OneGas Models With HeightDependent Mean Molecular Weight: Effects On Gravity Wave Propagation, R. L. Walterscheid, Michael P. Hickey Ph.D.
Publications
Many models of the thermosphere employ the onegas approximation where the governing equations apply only to the total gas and the physical properties of the gas that depend on composition (mean molecular weight and specific heats) are heightdependent. It is further assumed that the physical properties of the gas are locally constant; thus motioninduced perturbations are nil. However, motion in a diffusively separated atmosphere perturbs local values of mean molecular weight and specific heats. These motioninduced changes are opposed by mutual diffusion of the constituent gases, which attempts to restore diffusive equilibrium. Assuming that composition is locally constant is equivalent ...
Reflection Of A LongPeriod Gravity Wave Observed In The Nightglow Over Arecibo On May 8–9, 1989?, Michael P. Hickey Ph.D.
Reflection Of A LongPeriod Gravity Wave Observed In The Nightglow Over Arecibo On May 8–9, 1989?, Michael P. Hickey Ph.D.
Publications
During the Arecibo Initiative for Dynamics of the Atmosphere (AIDA) campaign in 1989 a characteristic of gravity wave perturbations observed in mesopause region airglow emissions was that airglow brightness fluctuations and airglowderived temperature fluctuations often occurred either in phase or in antiphase. This stimulated the development of a theory suggesting that such inphase fluctuations were most probably the result of strong reflections occurring in the mesosphere and lower thermosphere region. Recent examination of a particular wave event and application of simple WKBtype theory has appeared to support this hypothesis. Here we use a fullwave model and a WKBtype model, each ...
ThreeDimensional Spectral Classification Of LowMetallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.
ThreeDimensional Spectral Classification Of LowMetallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.
Publications
We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (T_{eff}, log g, and [Fe/H]) for Galactic F and Gtype stars. The ANNs are fed with mediumresolution (Δλ ~ 12 Å) nonfluxcalibrated spectroscopic observations. From a sample of 279 stars with previous highresolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict T_{eff} with an accuracy of σ(T_{eff}) = 135150 K over the range 4250 ≤ T_{eff} ≤ 6500 K, log g with an accuracy of σ(log g) = 0.250.30 ...
Acoustic Wave Heating Of The Thermosphere, Michael P. Hickey Ph.D., G. Schubert, R. L. Walterscheid
Acoustic Wave Heating Of The Thermosphere, Michael P. Hickey Ph.D., G. Schubert, R. L. Walterscheid
Publications
A numerical model is used to study the dissipation in the thermosphere of upward propagating acoustic waves. Whereas dissipating gravity waves can cool the upper atmosphere through the effects of sensible heat flux divergence, it is found that acoustic waves mainly heat the thermosphere by viscous dissipation. Though the amplitudes of acoustic waves in the atmosphere are poorly constrained, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at rates of tens of kelvins per day and thereby contribute to the thermospheric energy balance. It is shown that viscous heating cannot be calculated from the divergence of ...
Plasma Transport At The Magnetospheric Boundary Due To Reconnection In KelvinHelmholtz Vortices, K. Nykyri, A. Otto
Plasma Transport At The Magnetospheric Boundary Due To Reconnection In KelvinHelmholtz Vortices, K. Nykyri, A. Otto
Publications
The KelvinHelmholtz( KH) mode has long been considered for viscous interaction at the magnetospheric boundary but it is not expected to produce significant mass transport. The presented results indicate that the Kelvin Helmholtz instability can indeed cause a transfer of mass into the magnetotail during times of northward IMF. The vortex motion of KH waves can generate a strongly twisted magnetic field with multiple current layers. Magnetic reconnection in the strong current layers inside the vortices can detach high density plasma filaments from the magnetosheath. This may explain observed high density and low temperature filaments in the magnetosphere and the ...
Airglow Variations Associated With Nonideal Ducting Of Gravity Waves In The Lower Thermosphere Region, Michael P. Hickey Ph.D.
Airglow Variations Associated With Nonideal Ducting Of Gravity Waves In The Lower Thermosphere Region, Michael P. Hickey Ph.D.
Publications
A numerical fullwave model is used to study the response of the O2 atmospheric airglow to ducted gravity waves in the mesopause region. For an isothermal, quasiadiabatic, and motionless background atmosphere the calculated phase differences between airglow brightness fluctuations and fluctuations of temperatures derived from the airglow, as given by Krassovsky's ratio, are in good agreement with the predictions of published theory. Significant departures from the predictions of the basic theory are obtained when we consider ducting in the presence of the eddy and molecular diffusion of heat and momentum in a nonisothermal background atmosphere. Wind shears also affect ...
Simulation Of Engineering Systems Described By HighIndex Dae And Discontinuous Ode Using Single Step Methods, Marc Compere
Simulation Of Engineering Systems Described By HighIndex Dae And Discontinuous Ode Using Single Step Methods, Marc Compere
Publications
This dissertation presents numerical methods for solving two classes of ordinary diferential equations (ODE) based on singlestep integration methods. The ﬁrst class of equations addressed describes the mechanical dynamics of constrained multibody systems. These equations are ordinary diﬀerential equations (ODE) subject to algebraic constraints. Accordinly they are called diﬀerentialalgebraic equations (DAE).
Speciﬁc contributions made in this area include an explicit transformation between the Hessenberg index3 form for constrained mechanical systems to a canonical statespace form used in the nonlinear control communities. A hybrid solution method was developed that incorporates both slidingmode control (SMC) from the controls literature and poststabilization from ...
ThreeDimensional Spectral Classification Of LowMetallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.
ThreeDimensional Spectral Classification Of LowMetallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.
Publications
We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F and Gtype stars. The ANNs are fed with mediumresolution (Δλ ~ 12 Å) nonfluxcalibrated spectroscopic observations. From a sample of 279 stars with previous highresolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy of σ(log g) = 0.250.30 ...
Interfering Solutions Of A Nonhomogeneous Hamiltonian System, Gregory S. Spradlin
Interfering Solutions Of A Nonhomogeneous Hamiltonian System, Gregory S. Spradlin
Publications
A Hamiltonian system is studied which has a term approaching a constant at an exponential rate at infinity. A minimax argument is used to show that the equation has a positive homoclinic solution. The proof employs the interaction between translated solutions of the corresponding homogeneous equation. What distinguishes this result from its few predecessors is that the equation has a nonhomogeneous nonlinearity.
Cluster Computing In The Classroom: Topics, Guidelines, And Experiences, Amy Apon, Rajkumar Buyya, Hai Jin, Jens Mache
Cluster Computing In The Classroom: Topics, Guidelines, And Experiences, Amy Apon, Rajkumar Buyya, Hai Jin, Jens Mache
Publications
With the progress of research on cluster computing, more and more universities have begun to offer various courses covering cluster computing. A wide variety of content can be taught in these courses. Because of this, a difficulty that arises is the selection of appropriate course material. The selection is complicated by the fact that some content in cluster computing is also covered by other courses such as operating systems, networking, or computer architecture. In addition, the background of students enrolled in cluster computing courses varies. These aspects of cluster computing make the development of good course material difficult. Combining our ...
Climatology And Modeling Of QuasiMonochromatic Atmospheric Gravity Waves Observed Over Urbana Illinois, J. H. Hecht, R. L. Walterscheid, Michael P. Hickey Ph.D., S. J. Franke
Climatology And Modeling Of QuasiMonochromatic Atmospheric Gravity Waves Observed Over Urbana Illinois, J. H. Hecht, R. L. Walterscheid, Michael P. Hickey Ph.D., S. J. Franke
Publications
From analyzing nine months of airglow imaging observations of atmospheric gravity waves (AGWs) over Adelaide, Australia (35°S) [Walterscheid et al., 1999] have proposed that many of the quasimonochromatic waves seen in the images were primarily thermally ducted. Here are presented 15 months of observations, from February 1996 to May 1997, for AGW frequency and propagation direction from a northern latitude site, Urbana Illinois (40°N). As Adelaide, Urbana is geographically distant from large orographic features. Similar to what was found in Adelaide, the AGWs seem to originate from a preferred location during the time period around summer solstice. In ...
Gravity Wave Propagation Directions Inferred From Satellite Observations Including Smearing Effects, Jason S. Brown, Michael P. Hickey Ph.D.
Gravity Wave Propagation Directions Inferred From Satellite Observations Including Smearing Effects, Jason S. Brown, Michael P. Hickey Ph.D.
Publications
We simulate spacebased, sublimb viewing observations of airglow brightness fluctuations caused by atmospheric gravity wave interactions with the O2 atmospheric airglow, and we demonstrate that because of the geometry associated with such observations, the brightness fluctuations observed for the optically thick 0–0 band emission will always appear stronger for waves traveling toward the observer (the satellite). The effect should be most noticeable for waves having relatively small vertical wavelengths (∼10 km) and horizontal wavelengths of 50 km or greater. For waves of short (∼100 km) horizontal wavelength, the brightness fluctuation anisotropy with respect to viewing direction may also be ...
Secular Variations Of Oi 5577 Å Airglow In The Mesopause Region Induced By Transient Gravity Wave Packets, Michael P. Hickey Ph.D., R. L. Walterscheid
Secular Variations Of Oi 5577 Å Airglow In The Mesopause Region Induced By Transient Gravity Wave Packets, Michael P. Hickey Ph.D., R. L. Walterscheid
Publications
We employ a 2dimensional, timedependent, fully nonlinear model of minor species in the mesopause region and our Spectral FullWave Model to simulate the response of minor species and the OI 5577 Å airglow to a gravity wave packet in the mesopause region. Gravity waves affect the timeaveraged distribution of minor species in the mesosphere and lower thermosphere (MLT) region through constituent fluxes induced by violation of the nonacceleration conditions due to wave transience and dissipation. In addition, wave perturbed chemistry can induce a flux of chemically active species. Simulations are performed with nominal values of eddy diffusion coefficients in the ...
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
Publications
The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or colorbased distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such wellknown systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is ...
Two Photon Absorption In Chromophore Doped Solid Matrices, Stefan Mancas, Michael Canva, Yves Levy, Kathleen A. Richardson, Giselle Roger
Two Photon Absorption In Chromophore Doped Solid Matrices, Stefan Mancas, Michael Canva, Yves Levy, Kathleen A. Richardson, Giselle Roger
Publications
Over the past decades organic materials have shown an important potential for applications in the field of nonlinear optics. Twophoton absorbing materials can be optically addressed in three dimensions of space, which make them unique for many new applications, including 3D displays, optical memories, biosensors, etc. Fluorescent organic chromophores can be synthesized with structures especially optimized for this nonlinear optical property. Yet, for some applications, they have to be incorporated in solid state matrices. We especially investigate hybrid organic/inorganic doped matrices synthesized by solgel process. However , the linear transmission for such molecules is often significantly less than unity. Twophoton ...
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion
Publications
We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 M_{Ꙩ.} This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average T_{eff }̴ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf ...