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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The role of three-dimensional shapes in the break-up of charged drops

The nonlinear dynamics of nonaxisymmetric inviscid charged conducting drops near the Rayleigh charge limit (R = 4) is investigated analytically. It is shown that only axisymmetric spheroid drops bifurcate from the sphere family when the charge is increased, that oblate spheroids at R greater than 4 are unstable to nonaxisymmetric disturbances governing drop breakup, and that prolate spheroids at R less than 4 are unstable only to axisymmetric disturbances tending to increase the length of the drop along its symmetry axis. The effects of external electric fields and rigid-body rotation are also analyzed, and the solutions for the amplitude equations at R just less than 4 (equivalent to the dynamical equations of the Henon-Heiles Hamiltonian) are explored.

Natarajan, R.↗
NASA NTRS1987

Computational vortex dynamics in two and three dimensions

A discussion of some solutions and outstanding problems of dissipationless and nearly dissipationless flows in two and three dimensions is presented. In particular, two-dimensional steady-state solutions, linear stability and nonlinear evolutions including axisymmetrization of isolated vortex regions and merger or condensation of like-signed vorticity regions, are reviewed. These results are obtained from pseudo-spectral codes, contour dynamical (CD) codes and a new Hamiltonian moment-model of the Euler equations

Melander, Mogens V.↗
NASA NTRS1987

Phase-space-Lagrangian action principle and the generalized K-X theorem

The covariant coupled equations for plasma dynamics and the Maxwell field are expressed as a phase-space-Lagrangian action principle. The linear interaction is transformed to the bilinear beat Hamiltonian by a gauge-invariant Lagrangian Lie transform. The result yields the generalized linear susceptibility directly.

Kaufman, Allan N.↗
NASA NTRS1987

A quantum theoretical study of polyimides

One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.

Burke, Luke A.↗
NASA NTRS1988

The gamma 1 and gamma 3 bands of (16)O3: Line positions and intensities

Using 0.005/cm-resolution Fourier transform spectra of samples of ozone, the gamma 1 and gamma 3 bands of (16)O3 have been reanalyzed to obtain accurate line positions and an extended set of upper state rotational levels (J up to 69, K sub a up to 20). Combined with the available microwave data, these upper state rotational levels were satisfactorily fitted using a Hamiltonian which takes explicitly into account the strong Coriolis interaction affecting the rotational levels of these two interacting states. In addition, 350 relative line intensities were measured from which the rotational expansions of the transition moment operators for the gamma 1 and gamma 3 states have been deduced. Finally, a complete listing of line positions, intensities, and lower state energies of the gamma 1 and gamma 3 bands of (16)O3 has been generated.

Flaud, J.-M.↗
NASA NTRS1988

Line positions and intensities for the gamma 1 + gamma 2 and gamma 2 + gamma 3 bands of (16)O3

Using 0.005 cm-resolution Fourier transform spectra of (16)O3, generated by electric discharge from a greater than 99.98 percent pure sample of (16)O3, an extensive analysis of the gamma 1 + gamma 2 and the gamma 2 + gamma 3 bands in the 5.7 micron region was performed. The rotational energy levels of the upper (110) and (011) vibrational states of (16)O3 were reproduced within their experimental uncertainties using a Hamiltonian which takes explicitly into account the Coriolis-type interaction occurring between the rotational energy levels of both states. Improved vibrational energies and rotational and coupling constants were also derived for the (110) and (011) states. Precise transition moment constants for these two bands were deduced from analysis of 220 measured line intensities. Finally, a complete list of line positions, intensities, and lower state energies for both bands has been generated.

Devi, V. Malathy↗
NASA NTRS1988

Limitations of the semirelativistic approach in sum rules and related calculations in atomic physics

The semirelativistic approach, as applied to sum-rule calculations, can yield very inaccurate results for high-Z systems; the apparently good agreement previously reported is fortuitous, due to the application of an approximate eigenstate of the semirelativistic Hamiltonian. Attention is given to one-electron atomic systems, and the results obtained are discussed with a view to their implications for many-electron systems. The many-electron problem is complicated by a lack of clarity as to the relative importance of contributions due to correlation effects among the electrons, their effect on the E2 oscillator strength, and the retardation correction to the E1 transition.

Rustgi, M. L.↗
NASA NTRS1988

The rotational spectrum of nitric acid - The first five vibrational states

The details of work on the nu(8) vibrational state, which arise from the NO2 out-of-plane vibration, are reported. For this state, over 210 transitions have been measured in the millimeter and submillimeter spectral region and analyzed with Watson's A-reduced centrifugal distortion Hamiltonian. Also included in this work is a comparison of all these spectra and an overview of the millimeter and submillimeter spectra associated with these states. Although at the high sensitivity available in laboratory experiments, many additional lines are observable, all arise from vibrational states whose populations are more than 100 times lower than the ground state. The most prominent of these are due to the states which give rise to the perturbed 2 nu(9) and nu(5) bands near 11 microns. These results provide a significant data base for both atmospheric remote sensing experiments and spectral analyses of data in other spectral regions, especially the IR.

Crownover, Richard L.↗
NASA NTRS1988

Theoretical comparison of maser materials for a 32-GHz maser amplifier

The computational results of a comparison of maser materials for a 32 GHz maser amplifier are presented. The search for a better maser material is prompted by the relatively large amount of pump power required to sustain a population inversion in ruby at frequencies on the order of 30 GHz and above. The general requirements of a maser material and the specific problems with ruby are outlined. The spin Hamiltonian is used to calculate energy levels and transition probabilities for ruby and twelve other materials. A table is compiled of several attractive operating points for each of the materials analyzed. All the materials analyzed possess operating points that could be superior to ruby. To complete the evaluation of the materials, measurements of inversion ratio and pump power requirements must be made in the future.

Lyons, James R.↗
NASA NTRS1988

Identification of interstellar methanol lines

The extended internal axis method Hamiltonian of Herbst et al. (1984) was used to study the rotational spectrum of methanol out to high values of the rotational quantum number J. Laboratory data for 783 lines of (C-12)H3OH from the lowest three torsional levels out to a rotational quantum number of J = 22 were fitted to an rms deviation of 4.40 MHz. For (C-13)H3OH, 455 lines out to J = 22 were fitted to an rms of 2.28 MHz.

Sutton, E. C.↗
NASA NTRS1988

Geometric angles in cyclic evolutions of a classical system

A perturbative method, using Lie transforms, is given for calculating the Hannay angle for slow, cyclic evolutions of a classical system, taking into account the finite rate of change of the Hamiltonian. The method is applied to the generalized harmonic oscillator. The classical Aharonov-Anandan angle is also calculated. The interpretational ambiguity in the definitions of geometrical angles is discussed.

Bhattacharjee, A.↗
NASA NTRS1989

Effective-field-theory model for the fractional quantum Hall effect

Starting directly from the microscopic Hamiltonian, a field-theory model is derived for the fractional quantum Hall effect. By considering an approximate coarse-grained version of the same model, a Landau-Ginzburg theory similar to that of Girvin (1986) is constructed. The partition function of the model exhibits cusps as a function of density. It is shown that the collective density fluctuations are massive.

Zhang, S. C.↗
NASA NTRS1989

Frequency and intensity analysis of the nu3, nu4, and nu6 bands of formaldehyde

The infrared spectra of the nu3, nu4, and nu6 bands of formaldehyde in the region from 890/cm to 1580/cm have been obtained at high resolution using tunable diode laser and Fourier transform-infrared spectroscopy. The transition frequencies have been analyzed using a Hamiltonian including terms through sextic in centrifugal distortion and including five interstate vibration-rotation coupling terms. Excited-state pure rotational transitions are also included in the data, and their frequencies are reproduced well. Individual measured line intensities are used to determine dipole derivatives and band strengths using the fully coupled, asymmetric top eigenvectors.

Reuter, D. C.↗
NASA NTRS1989

Tidal evolution in the Neptune-Triton system

Triton, which is currently spiralling toward Neptune due to tides raised on both bodies, possesses an obliquity which may lie close to either a zero-deg 'state 1' or a 100-deg 'state 2' which correspond to the two stable Cassini extrema of its rotational Hamiltonian. The Kaula (1966) tidal formalism is presently used to model the past and future evolution of the system in both states. For nominal parameters in state 1, Triton will reach Neptune's Roche limit in about 3.6 Gyr with a decrease in orbital inclination to 145 deg from the current 159 deg; in the case of state 2, Triton's inclination will increase to 180 deg in 10-100 million years and then transition to state 1, subsequently reaching the Neptune Roche limit in about 1.4 Gyr.

Chyba, C. F.↗
NASA NTRS1989

Motion and force control for multiple cooperative manipulators

The motion and force control of multiple robot arms manipulating a commonly held object is addressed. A general control paradigm that decouples the motion and force control problems is introduced. For motion control, there are three natural choices: (1) joint torques, (2) arm-tip force vectors, and (3) the acceleration of a generalized coordinate. Choice (1) allows a class of relatively model-independent control laws by exploiting the Hamiltonian structure of the open-loop system; (2) and (3) require the full model information but produce simpler problems. To resolve the nonuniqueness of the joint torques, two methods are introduced. If the arm and object models are available, the allocation of the desired end-effector control force to the joint actuators can be optimized; otherwise the internal force can be controlled about some set point. It is shown that effective force regulation can be achieved even if little model information is available.

Wen, John T.↗
NASA NTRS1989

Radiation pressure dynamics in planetary exospheres - A 'natural' framework

Exospheric theory is reformulated to provide for the analysis of dynamical underpinning of exospheric features. The formulation is based on the parabolic-cylindrical separability of the Hamiltonian that describes particle motions in the combined fields of planetary gravity and solar radiation pressure. An approximate solution for trajectory evolution in terms of orbital elements is derived and the role of the exopause in the tail phenomenon is discussed. Also, an expression is obtained for the bound constituent atom densities at outer planetocoronal positions along the planet-sun axis for the case of an evaporative, uniform exobase. This expression is used to estimate midnight density enhancements as a function of radial distance for the terrestrial planets.

Bishop, James↗
NASA NTRS1989

Distributed parameter actuators for structural control

Timoshenko beam theory is applied to beams with multiple layers of piezoelectric material attached. The model is developed using a Hamiltonian approach, and includes the external electrical circuit as well as a complete set of boundary conditions. Resistors are added to the sensor layers for passive damping. The resulting model is then formulated in state space.

Cudney, H. H.↗
NASA NTRS1989

The nonconvex multi-dimensional Riemann problem for Hamilton-Jacobi equations

Simple inequalities for the Riemann problem for a Hamilton-Jacobi equation in N space dimension when neither the initial data nor the Hamiltonian need be convex (or concave) are presented. The initial data is globally continuous, affine in each orthant, with a possible jump in normal derivative across each coordinate plane, x sub i = 0. The inequalities become equalities wherever a maxmin equals a minmax and thus an exact closed form solution to this problem is then obtained.

Osher, Stanley↗