Search NASA⌕ Search

SEARCH · Search NASA

Results for “DIPOLES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Radiative lifetimes and transition probabilities for electric-dipole delta n equals zero transitions in highly stripped sulfur ions

The beam-foil time-of-flight method has been used to investigate radiative lifetimes and transition rates involving allowed intrashell transitions within the L shell of highly ionized sulfur. The results for these transitions, which can be particularly correlation-sensitive, are compared with current calculations based upon multiconfigurational models.

Pegg, D. J.↗
NASA NTRS1983

Magnetic dipole moment estimates for an ancient lunar dynamo

The four measured planetary magnetic moments combined with a recent theoretical prediction for dynamo magnetic fields suggests that no dynamo exists in the moon's interior today. For the moon to have had a magnetic moment in the past of sufficient strength to account for at least some of the lunar rock magnetism, the rotation would have been about twenty times faster than it is today and the radius of the fluid, conducting core must have been about 750 km. The argument depends on the validity of the Busse solution to the validity of the MHD problem of planetary dynamos.

Anderson, K. A.↗
NASA NTRS1984

Helicopter noise as predicted by three-dimensional monopole and quasi-steady full-potential dipole sources

A three-dimensional quasi-steady full-potential rotor-flow-analysis program, called ROT22 developed at NASA Ames Research Center is run in conjunction with Farassat's (1981) helicopter-noise-prediction code to assess the thickness and loading noises made by a rotor blade. As a model example, the case of a 1/7th UH-1H NACA-0012-profile straight nonlifting rotor blade in hover is studied. Results for tip Mach numbers ranging from .4 to .962 are presented. Also presented is the effect of blade-tip loading on the overall noise and of profile curvature on the thickness noise. The study confirms that the blade volume displacement is a dominant source of helicopter noise and further concludes that the blade tip makes only a small noise contribution that steadily decreases with increasing tip Mach numbers, and that the inclusion of blade profile curvature tends to improve the negative peak amplitudes overpredicted by Schmitz and Yu (1983).

Aggarwal, H. R.↗
NASA NTRS1985

Diffraction of a baffled dipole - Frequency dependence

Experimental results are presented which confirm the diffraction effects predicted by the MacDonald (1915) form of the Green's function for the baffled field in the theory of trailing edge noise. Using this Green's function, the acoustic intensity of noise generated by flow over a trailing edge has been determined to be proportional to the 5th-power of the flow velocity.

Mcinerny, S. A.↗
NASA NTRS1986

The ortho-para H2 distribution on Uranus: Constraints from the collision-induced 3-0 dipole band and 4-0 S(0) and S(1) quadrupole line profiles

Recent high quality spectral observations have allowed the derivation of constraints on the atmospheric structure of Uranus. The present analysis, which is based on the detailed modeling of a broadband geometric albedo spectrum and high resolution observations of the H2 4-0 quadrupole and 6818.9-A CH4 features, yields (1) a family of models which parameterize an upper tropospheric haze layer, (2) a lower, optically infinite cloud at a given pressure level, (3) the cloud-level methane molar fraction, and (4) the mean ortho/para ratio in the visible atmosphere. The single scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A.

Baines, K. H.↗
NASA NTRS1990

Collision strengths for dipole-allowed transitions in S II

Calculations of collision strengths for electron-impact excitations of S II from the ground state 3p3 4S0 to excited states 3p4 4P, 3d 4F, 3d 4D, 4s 4P, and 3d 4P were carried out using the R-matrix code described by Berrington et al. (1978) and the NIEM code described by Henry et al. (1981). Results are presented for the thermally averaged collision strengths for the five-state and six-state calculations. Convergence behaviors were examined by comparison with the six-state calculations and the previously obtained two-state calculations. Uncertainties for these transitions were estimated to be within 20 percent, except for the 4S0 - 3p4 4P transition in which a 40 percent uncertainty was estimated.

Ho, Y. K.↗
NASA NTRS1990

Moments of dipole oscillator-strength distribution for the helium sequence

The moments S(mu) for mu at least -6 but no more than 2 and L(mu) for mu = 0, 1, and 2 are calculated for the helium sequence for atomic numbers (Z) up to 30 under a screened hydrogenic model. The model describes the atom by single-particle hydrogenic wave functions and treats the initial and the final state as characterized by two different effective charge parameters Zi and Zf, respectively. The differential oscillator strength of the screened hydrogenic model is asymptotically expanded. Assuming the value of 287.6 for the coefficient of the term epsilon to the -7/2 for helium atoms, the parameter Zf is determined for the helium sequence.

Khan, F.↗
NASA NTRS1991

Magnetic flux transport and the sun's dipole moment - New twists to the Babcock-Leighton model

The mechanisms that give rise to the sun's large-scale poloidal magnetic field are explored in the framework of the Babcock-Leighton (BL) model. It is shown that there are in general two quite distinct contributions to the generation of the 'alpha effect': the first is associated with the axial tilts of the bipolar magnetic regions as they erupt at the surface, while the second arises through the interaction between diffusion and flow as the magnetic flux is dispersed over the surface. The general relationship between flux transport and the BL dynamo is discussed.

Wang, Y.-M.↗
NASA NTRS1991

Transient particle acceleration in strongly magnetized neutron stars. II - Effects due to a dipole field geometry

Sheared Alfven waves generated by nonradial crustal disturbances above the polar cap of a strongly magnetized neutron star induce an electric field component parallel to B. An attempt is made to determine the manner in which the strong radial dependence of B affects the propagation of these sheared Alfven waves, and whether this MHD process is still an effective particle accelerator. It is found that although the general field equation is quite complicated, a simple wavelike solution can still be obtained under the conditions of interest for which the Alfven phase velocity decouples from the wave equation. The results may be applicable to gamma-ray burst sources.

Fatuzzo, Marco↗
NASA NTRS1993

Polarity reversals and tilt of the Earth's magnetic dipole

There is evidence that the terrestrial magnetic field is connected with the Earth's mantle: (1) there are magnetic anomalies that do not take part in the westward drift of the main field, but are fixed with respect to the mantle; (2) the geomagnetic pole position flips in a particular way by preferred meridional paths during a reversal; and (3) magnetic polarity reversals are correlated with the activations of geological processes. These facts may be explained if we take into account that a significant horizontal temperature gradient can exist in the top levels of the liquid core because of the different thermoconductivity of the different areas of the core-mantle boundary. These temperature inhomogeneities can penetrate the core because fluxes along the core boundary (the thermal wind) can be strongly suppressed by a small redistribution of the chemical composition in the top of the core. The nonparallel gradients of the temperature, density, and composition on the top of the core create a curled electric field that produces a current and a magnetic field. This seed-field can be amplified by motions in the core. The resulting field does not forget the seed-field distribution and in this way the field on the Earth surface (that can be created only in regions with high conductivity, i.e. in the core) is connected with the core-mantle boundary. Contrary to the usual approach to the dynamo problem, we will take into account that the seed field of thermoelectric origin is acting not only at some initial moment of time but permanently.

Dolginov, A. Z.↗