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Stability of the toroidicity-induced Alfven eigenmodes in JT-60U ICRF experiments

Description: It is shown that the stability of toroidicity-induced Alfven eigenmodes (TIE) in JT-60U ICRF experiments is strongly dependent on mode location. This dependence results in sequential excitation of high-n TIE modes as the central safety factor, q, drops in time.
Date: April 1, 1996
Creator: Fu, G.Y.; Cheng, C.Z.; Kimura, H.; Ozeki, T. & Saigusa, M.
Partner: UNT Libraries Government Documents Department

Eigenmodes in two simplified chamber structures studied for spurious microwaves in the APS storage ring beam chamber.

Description: The vertical readback errors are one order of magnitude greater than the horizontal ones in the APS storage ring beam chamber. To learn and solve this problem, we simulate the eigenmodes in two chamber structures, which are simplified from the APS storage ring beam chamber, and find their dependence on the variation of the chamber structures. These two structures are introduced as the solutions to separate and then restrain the spurious microwave modes by using a metal short block and a plate inside the chamber. The short block can shift and separate the frequencies of every mode evidently.
Date: July 9, 2003
Creator: Sun, X. & Decker, G.
Partner: UNT Libraries Government Documents Department

Waveguide and loop coupling to fast MHD toroidal eigenmodes

Description: Heating of plasmas by wave techniques requires an effective method of coupling rf energy to the plasma. In cavities the presence of weakly damped eigenmodes will enhance the loading of antennas when the wave frequency equals an eigenmode frequency. This report considers two methods of coupling to fast MHD eigenmodes in a toroidal cavity: one is by a waveguide mounted perpendicular to the vacuum vessel wall; and the other by a loop placed within the cavity. (auth)
Date: December 1, 1975
Creator: Paoloni, F.J.
Partner: UNT Libraries Government Documents Department

Global mirror modes in the magnetosheath

Description: A global stability analysis of mirror modes in the magnetosheath is presented. The analysis is based upon the kinetic-MHD formulation which includes relevant kinetic effects such as Landau resonance and gradient drift effects related to inhomogeneities in the background density, temperature, pressure and its anisotropy, magnetic field, and plasma flow velocity. Pressure anisotropy provides the free energy for the global mirror mode. The local theory of mirror modes predicts purely growing modes confined in the unstable magnetosheath region; however, the nonlocal theory that includes the effects of gradients and plasma flow predicts modes with real frequencies which propagate with the flow from the magnetosheath toward the magnetopause boundary. The real frequency is on the order of a combination of the diamagnetic drift frequency and the Doppler shift frequency associated with the plasma flow. The diamagnetic drift frequency provides a wave phase velocity in the direction of the magnetopause so that wave energy accumulates against the magnetopause boundary, and the amplitude is skewed in that direction. On the other hand, plasma flow also gives rise to a real phase velocity, but the phase velocity is smaller than the flow velocity. As a result, the wave amplitude is increased in the wake of the plasma flow and piles up against the bow shock boundary.
Date: May 1, 1996
Creator: Johnson, J.R. & Cheng, C.Z.
Partner: UNT Libraries Government Documents Department

Periodized Daubechies wavelets

Description: The properties of periodized Daubechies wavelets on [0,1] are detailed and counterparts which form a basis for L{sup 2}(R). Numerical examples illustrate the analytical estimates for convergence and demonstrated by comparison with Fourier spectral methods the superiority of wavelet projection methods for approximations. The analytical solution to inner products of periodized wavelets and their derivatives, which are known as connection coefficients, is presented, and their use ius illustrated in the approximation of two commonly used differential operators. The periodization of the connection coefficients in Galerkin schemes is presented in detail.
Date: March 1996
Creator: Restrepo, J. M.; Leaf, G. K. & Schlossnagle, G.
Partner: UNT Libraries Government Documents Department

Advanced system identification techniques for wind turbine structures

Description: The new approach to modal parameter identification, presented in this paper, uses an asymptotically stable observed to form a discrete state-space model for a wind turbine structure. The identification is performed using input-output time-series. A special software package developed in this research has been tested using the data generated by the ADAMS{trademark} model of the Micon 65/13 wind turbine structure. Numerical and graphical presentation of some of the results, generated by the programs developed, illustrates the range of their applicability.
Date: March 1, 1995
Creator: Bialasiewicz, J.T. & Osgood, R.M.
Partner: UNT Libraries Government Documents Department

Observed asymptotic properties of low-degree solar gravity-mode eigenfrequencies

Description: The asymptotic properties of the low-degree solar gravity modes classified by Hill and Gu are studied in the framework of first- and second-order asymptotic theory predictions. The results of this analysis demonstrate the necessity of retaining the second-order term in asymptotic theory to describe the eigenfrequency spectrum. In this theory, there are two first-order parameters, T/sub 0/ and delta, and two second-order parameters, V/sub 1/ and V/sub 2/. Values of the parameters obtained in this analysis are: T/sub 0/ = 36.31 +- 0.12 min, delta = /minus/0.43 +- 0.13, V/sub 1/ = 0.35, and V/sub 2/ = 4.76. There remain differences of approx.0.3 ..mu..Hz between the asymptotic theory eigenfrequencies and observed eigenfrequencies which are quasi-periodic functions of the radial order n for a given value of the degree /ell/. 26 refs., 1 fig., 1 tab.
Date: January 1, 1988
Creator: Gu, Ye-ming; Hill, H.A. & Rosenwald, R.D.
Partner: UNT Libraries Government Documents Department

Inversion of quasi-periodic deviations between low-degree solar gravity mode eigenfrequencies and asymptotic theory eigenfrequencies

Description: The fine structure found by Gu, Hill and Rosenwald between asymptotic theory eigenfrequencies and the observed eigenfrequencies reported by Hill and Gu is interpreted as the result of conditions not being met for the applicability of asymptotic theory at one or more radii in the solar interior. From an inversion of the observed fine structure, reasonably good agreement is obtained between observation and theory for either a localized perturbation in internal structure at r/R approx. 0.06 or at r/R approx. 0.23. The latter solution is, however, the better one. The amplitude of the perturbation in the mean molecular weight required to produce the fine structure is also inferred. 11 refs., 2 figs.
Date: January 1, 1988
Creator: Hill, H.A.; Gao, Qiang & Rosenwald, R.D.
Partner: UNT Libraries Government Documents Department

Properties of solar gravity mode signals in total irradiance observations

Description: Further evidence has been found that a significant fraction of the gravity mode power density in the total irradiance observations appears in sidebands of classified eigenfrequencies. These sidebands whose amplitudes vary from year to year are interpreted as harmonics of the rotational frequencies of the nonuniform solar surface. These findings are for non axisymmetric modes and corroborate the findings of Kroll, Hill and Chen for axisymmetric modes. It is demonstrated the the generation of the sidebands lifts the usual restriction on the parity of the eigenfunctions for modes detectable in total irradiance observations. 14 refs.
Date: January 1, 1988
Creator: Kroll, R.J.; Chen, J. & Hill, H.A.
Partner: UNT Libraries Government Documents Department

Small-amplitude periodic sloshing modes of a liquid in a vertical right circular cylinder with a concave spheroidal bottom

Description: The small-amplitude periodic sloshing modes of a liquid in a vertical right circular cylinder with a concave spheroidal bottom are calculated for the case in which there is not sufficient liquid to cover the bottom entirely. Equilibrium free surfaces of the liquid were calculated by the program CAPIL for the case in which the ratio of the minor and major semi-axes of the spheroidal bottom was 0.724. Perturbations about these surfaces were calculated by the program SLOSH. For the fill heights that were studied, and to the accuracy of these calculations the same critical Bond number, B/sub crit/, was found for instability of the free surface as was found in the static analysis of Concus and Karasalo for the same test problem. Furthermore, and in agreement with their calculation, no equilibrium surfaces were found for this problem for fill heights greater than 0.503 and for Bond numbers B < B/sub crit/ < 0. For fill heights ranging from 0.20 to 0.45, unstable equilibrium surfaces were found for a range of Bond numbers, B/sub conv/ < or = B < B/sub crit/. Frequencies or growth rates were calculated for numerous equilibrium surfaces. Growth rates of the maximally unstable modes were calculated for fill height 0.30 and various Bond numbers. 12 figures, 27 tables.
Date: November 1, 1977
Creator: Albright, N. & Concus, P.
Partner: UNT Libraries Government Documents Department

Modes of elliptical waveguides; A correction

Description: We show that the fields associated with the TM{sub 01} mode of an elliptical wave guide are qualitatively different from those which have appeared in the standard literature for the past fifty years, and that the original fields as plotted were also in qualitative disagreement with the analytic expressions which accompanied them. Nonetheless, the cutoff frequencies given for that mode, as well as for the five other modes described in those references, are exceedingly accurate (within roughly 1%) for elliptical eccentricities as large as 0.75; for eccentricities in excess of 0.9, the inaccuracy increases to from 5 to nearly 50%, depending on the mode in question.
Date: March 1, 1990
Creator: Goldberg, D.A.; Laslett, L.J. & Rimmer, R.A.
Partner: UNT Libraries Government Documents Department

Order reduction of large-scale linear oscillatory system models

Description: Eigenanalysis and signal analysis techniques of deriving representations of power system oscillatory dynamics result in very high-order linear models. In order to apply many modern control design methods, the models must be reduced to a more manageable order while preserving essential characteristics. Presented in this paper is a model reduction method well suited for large-scale systems. The method searches for the optimal subset of the high-order model that best represents the system. An Akaike information criterion is used to define the optimal reduced model. The method is first presented, and then examples of applying it to Prony analysis and eigenanalysis models of power systems are given.
Date: February 1, 1993
Creator: Trudnowski, D.J.
Partner: UNT Libraries Government Documents Department

Eigenmodes of classical fluids in thermal equilibrium

Description: The eigenmodes of a classical fluid in thermal equilibrium are discussed. For long wavelengths and times, they can be computed from linear hydrodynamic equations. They are then the hydrodynamic modes, in particular, the heat mode, which describes the diffusion of heat in the fluid and two sound modes. For short wavelengths and times they can be derived from linear kinetic operators. For low densities, the linear Boltzmann operator can be employed and the three most important eigenmodes are direct extensions of the kinetic analogues of the heat and sound modes. For high densities, a generalization of the Boltzmann operator is used. The most important eigenmode is the extended heat mode, while next in importance come two eigenmodes that are extensions of the sound modes. These three extended hydrodynamic modes can be used to obtain the light and neutron spectra of fluids and vice versa. 42 refs., 8 figs.
Date: January 1, 1985
Creator: Cohen, E.G.D.
Partner: UNT Libraries Government Documents Department

Solar oscillations, gravitational multipole field of the sun and the solar neutrino paradox

Description: The visual solar oblateness work and the solar seismological work on the internal rotation of the sun are reviewed and their implications concerning the static gravitational multipole moments of the sun are discussed. The results of this work are quite deviant which is indicative of the complexity encountered and of the necessity for continued studies based on a diverse set of observing techniques. The evidence for phase-locked internal gravity modes of the sun is reviewed and the implications for the solar neutrino paradox are discussed. The rather unique possibility for testing the relevance which the phase-locked gravity modes have to this paradox is also noted. The oscillating perturbations in the sun's gravitational field produced by the classified internal gravity modes and the phase-locked modes are inferred from the observed temperature eigenfunctions. Strains of the order of 10/sup -18/ in gravitational radiation detectors based on free masses are inferred for frequencies near 100 ..mu..Hz. The relevance of these findings is discussed in terms of a new technique for use in solar seismological studies and of producing background signals in studies of low-frequency gravitational radiation. 64 refs., 2 figs.
Date: November 4, 1986
Creator: Hill, H.A. & Rosenwald, R.D.
Partner: UNT Libraries Government Documents Department

Gyrokinetic analysis of ion temperature gradient modes in the presence of sheared flows

Description: The linearized gyrokinetic equation governing electrostatic microinstabilities in the presence of sheared equilibrium flow in both the {cflx z} and {cflx y} directions has been systematically derived for a sheared slab geometry, where in the large aspect ratio limit {cflx z} and {cflx y} directions correspond to the toroidal and poloidal directions respectively. In the familiar long perpendicular wavelength regime ({kappa}{perpendicular}{rho}i > 1), the analysis leads to a comprehensive kinetic differential eigenmode equation which is solved numerically. The numerical results have been successfully cross-checked against analytic estimates in the fluid limit. For typical conditions, the Ion Temperature Gradient ({eta}i) modes are found to be stabilized for {cflx y}-direction flows with a velocity shear scale comparable to that of the ion temperature gradient and velocities of a few percent of the sound speed. Sheared flows in the {cflx z}-direction taken along are usually destabilizing, with the effect being independent of the sign of the flow. However, when both types are simultaneously considered, it is found that in the presence of shared {cflx z}-direction flow, sheared {cflx y}-direction flow can be either stabilizing or destabilizing depending on the relative sign of these flows. However, for sufficiently large values of {upsilon}{prime}{sub y} the mode is completely stabilized regardless of the sign of {upsilon}{prime}{sub z} {upsilon}{prime}{sub y}. The importance of a proper kinetic treatment of this problem is supported by comparisons with fluid estimates. In particular, when such effects are favorable, significantly smaller values of sheared {cflx y}-direction flow are required for stability than fluid estimates would indicate.
Date: January 1, 1992
Creator: Artun, M. & Tang, W.M.
Partner: UNT Libraries Government Documents Department

Systematic studies of molecular vibrational anharmonicity and vibration-rotation interaction by self-consistent-field higher derivative methods: Applications to asymmetric and symmetric top and linear polyatomic molecules

Description: Inclusion of the anharmonicity normal mode vibrations (i.e., the third and fourth (and higher) derivatives of a molecular Born-Oppenheimer potential energy surface) is necessary in order to theoretically reproduce experimental fundamental vibrational frequencies of a molecule. Although ab initio determinations of harmonic vibrational frequencies may give errors of only a few percent by the inclusion of electron correlation within a large basis set for small molecules, in general, molecular fundamental vibrational frequencies are more often available from high resolution vibration-rotation spectra. Recently developed analytic third derivatives methods for self-consistent-field (SCF) wavefunctions have made it possible to examine with previously unavailable accuracy and computational efficiency the anharmonic force fields of small molecules.
Date: April 1, 1987
Creator: Clabo, D.A. Jr.
Partner: UNT Libraries Government Documents Department

Elastic-wave radiation from spherical sources

Description: The radiation of spherical compressional waves from a spherical cavity in an ideal elastic solid is treated. The equations for the radiation source and field are written in terms of the reduced-displacement potential. The source equation is studied in terms of characteristic frequencies, corresponding periods and wavelengths, and damping. The field equations for the stresses, strains, radial displacement, etc., are reviewed with regard to the transitions between the near and far fields. The natural parameters for defining the dynamic source and field characteristics are 2b/R and b/a in some cases and a/R in others, where a is the compressional-wave velocity, b the shear-wave velocity, and R the cavity radius. Transient solutions for stresses, strains, radial displacement, etc., include damped sinusoidal oscillations. The initial- and final-value theorems for the Laplace transform are used to obtain solutions for tau (reduced time) ..-->.. 0 + (high-frequency, farfield) and tau ..-->.. infinity (zero-frequency, near-field). 14 figures, 4 tables.
Date: December 7, 1979
Creator: Rodean, H.C.
Partner: UNT Libraries Government Documents Department