20,510 research outputs found
Detailed extensions of perturbation methods for nonlinear panel flutter Technical report, 11 Dec. 1969 - 15 Mar. 1971
Perturbation method extension for nonlinear panel flutter to include fifth-order nonlinear terms effect, flutter-buckling interaction, and small damping term
Steady subsonic flow around finite-thickness wings
The general method for analyzing steady subsonic potential aerodynamic flow around a lifting body having arbitrary shape is presented. By using the Green function method, an integral representation for the potential is obtained. Under small perturbation assumption, the potential at any point, P, in the field depends only upon the values of the potential and its normal derivative on the surface of the body. Hence if the point P approaches the surface of the body, the representation reduces to an integral equation relating the potential and its normal derivative (which is known from the boundary conditions) on the surface. The question of uniqueness is examined and it is shown that, for thin wings, the operator becomes singular as the thickness approaches zero. This fact may yield numerical problems for very thin wings. However, numerical results obtained for a rectangular wing in subsonic flow show that these problems do not appear even for thickness ratio tau = .001. Comparison with existing results shows that the proposed method is at least as fast and accurate as the lifting surface theories
Bifurcation in electrostatic resistive drift wave turbulence
The Hasegawa-Wakatani equations, coupling plasma density and electrostatic
potential through an approximation to the physics of parallel electron motions,
are a simple model that describes resistive drift wave turbulence. We present
numerical analyses of bifurcation phenomena in the model that provide new
insights into the interactions between turbulence and zonal flows in the
tokamak plasma edge region. The simulation results show a regime where, after
an initial transient, drift wave turbulence is suppressed through zonal flow
generation. As a parameter controlling the strength of the turbulence is tuned,
this zonal flow dominated state is rapidly destroyed and a turbulence-dominated
state re-emerges. The transition is explained in terms of the Kelvin-Helmholtz
stability of zonal flows. This is the first observation of an upshift of
turbulence onset in the resistive drift wave system, which is analogous to the
well-known Dimits shift in turbulence driven by ion temperature gradients.Comment: 21 pages, 11 figure
An econometric analysis of SARS and Avian flu on international tourist arrivals to Asia
This paper compares the impacts of SARS and human deaths arising from Avian Flu on international tourist arrivals to Asia. The effects of SARS and human deaths from Avian Flu will be compared directly according to human deaths. The nature of the short run and long run relationship is examined empirically by estimating a static line fixed effect model and a difference transformation dynamic model, respectively. Empirical results from the static fixed effect and difference transformation dynamic models are consistent, and indicate that both the short run and long run SARS effect have a more significant impact on international tourist arrivals than does Avian Flu. In addition, the effects of deaths arising from both SARS and Avian Flu suggest that SARS is more important to international tourist arrivals than is Avian Flu. Thus, while Avian Flu is here to stay, its effect is currently not as significant as that of SARS.Avian flu;international tourism;SARS;dynamic panel data model;static fixed effects model
Measurement of opaque film thickness
The theoretical and experimental framework for thickness measurements of thin metal films by low frequency thermal waves is described. Although it is assumed that the films are opaque and the substrates are comparatively poor thermal conductors, the theory is easily extended to other cases of technological interest. A brief description is given of the thermal waves and the experimental arrangement and parameters. The usefulness of the technique is illustrated for making absolute measurements of the thermal diffusivities of isotropic substrate materials. This measurement on pure elemental solids provides a check on the three dimensional theory in the limiting case of zero film thickness. The theoretical framework is then presented, along with numerical calculations and corresponding experimental results for the case of copper films on a glass substrate
Hermitian quark mass matrices with four texture zeros
We provide a complete and systematic analysis of hermitian, hierarchical
quark mass matrices with four texture zeros. Using triangular mass matrices,
each pattern of texture zeros is readily shown to lead to a definite relation
between the CKM parameters and the quark masses. Nineteen pairs are found to be
consistent with present data, and one other is marginally acceptable. In
particular, no parallel structure between the up and down mass matrices is
found to be favorable with data.Comment: 18 pages, no figure, references [8] and [10] adde
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