Engineering Papers⌕ Search

Engineering topics

Dolginov, A. Z.

Publications and source records attributed to Dolginov, A. Z..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Magnetic moments and angular momenta of stars and planets

Using published data on magnetic fields, radii, masses, and rotation, we have compiled a data set of magnetic moments mu and angular momenta L for stars and planets. In our subsample of hotter stars (classes A, B, and O), there are 171 objects. In the subsample of cooler stars (classes F, G, K, and M), there are 54 objects. We include 33 white dwarfs, of which 19 are in cataclysmic variables. The pulsar subsample contains 32 pulsars in binaries and 429 isolated pulsars. Som subsamples exhibit significant empirical correlations between log mu and log L. For the hot and cool stars, the correlations are positive. However, the hot-star correlation is significantly shallower than for the cool stars. In the solar system subsample, the correlation has essentially the same slope as for the cool stars, although the magnetic moments are two to three orders of magnitude smaller for the solar system objects at a given L value. For isolated white dwarfs, the correlations are weak or absent. Pulsars and white dwarfs in close binaries show strong negative correlations: the results are quantitatively consistent with magnetically enforced synchronism with the orbital period. When we consider the centers of gravity of the different subsamples of objects, a significant positive correlation appears between log mu and log L.

Arge, C. N.↗
NASA NTRS1993

On quasiperiodic variations of pulsars' periods - An alternative to the planetary interpretation of PSR1257+12

The quasi-periodic timing residuals of PSR1257+12 are considered to be a result of two large-scale internal motions of the neutron star: core-crust relative motion and precession. The model requires that the superfluid core of a neutron star is not pinned to the solid crust. A very good fit to the observations is obtained for the set of parameters that corresponds to a nearly orthogonal rotator, and the period of the core-crust relative rotation that is nearly twice the period of precession.

Dolginov, A. Z.↗
NASA NTRS1993

Does the thermal wind exist near the Earth's core boundary?

Temperature distribution in the Earth core determines many important processes such as the following: convective motion, magnetic field generation, matter exchange between the core and the mantle, and the thermal flux. This distribution depends on conditions in the core-mantle boundary and on the distribution of the thermal conductivity in the mantle. Seismic tomography shows that large horizontal temperature and compositional gradients exists at the core-mantle boundary. The simple assumption that these inhomogeneities are extended into the top of the core contradicts the common opinion that the horizontal temperature gradient (the thermal wind) wipes them out in a short time. However, this conclusion has been obtained without taking into account that the core volume is closed and the motion, if it is started, can lead to a small redistribution of composition that stops this motion.

Dolginov, A. Z.↗
NASA NTRS1993

Magnetic fields and nonuniform structures of the Moon

Direct magnetic measurements performed by space probes demonstrated the existence of small-scale, stationary surface magnetic fields on the Moon. The magnetic field averaged over a region of approximately 600 km was found to be no larger than approximately 10(exp -5) G, that of the regions approximately 100-200 km is approximately 10(exp -5) to 10(exp -4) G, and that of approximately 10-100 km reaches approximately 10(exp -3) G. Investigations of certain lunar rocks reveal stable residual magnetization, which could have been acquired during the crystallization of the rocks in the presence of the outer magnetic field, provided such a field existed at the initial stage of lunar evolution. Estimates show that 4 x 10(exp 9) yr ago the field was small, then it rose to approximately 1.3 G at the beginning of 3.9 x 10(exp 9) yr with a subsequent exponential decrease during the period of 3.9 x 10(exp 9) yr to 3.2 x 10(exp 9) yr ago. Small-scale fields have been explained by some authors as due to mechanical impacts produced by meteors. The theory of this effect is not elaborated in detail. This can in no way explain the paleomagnetic data. These data are commonly explained as a result of the dynamo action in the liquid lunar core.

Dolginov, A. Z.↗
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.↗
NASA NTRS1993

Are cosmic rays effective for ionization of the solar nebula?

In this paper, we argue that the effectiveness of cosmic rays to ionize the bulk of the nebular gas may be further impaired by the influence of the magnetic field on the propagation of cosmic rays. When cosmic rays enter the nebular disk they ionize the gas and make the dynamo generation of magnetic fields possible. However, once magnetic fields are embedded in the nebular gas, the upcoming cosmic rays can no longer penetrate directly into the nebular disk because they start to interact with the magnetic field and lose their energy before propagating significantly toward the midplane. That, in turn, undercuts the ionization source within the bulk of the gas stopping the dynamo action. Nebular dynamo models ignored this back reaction of magnetic fields on cosmic rays. We calculate this back reaction effect, but for the sake of mathematical simplicity, we ignore the effect of magnetic field weakening due to diminishing ionization by cosmic rays.

Dolginov, A. Z.↗
NASA NTRS1993

Morphotectonics of Venus

Venus topography can be mapped morphostructurally to reveal nested hierarchical patterns of quasi-circular upland/lowland complexes. These patterns are interpreted as surficial effects of hierarchically structured, long-acting mantle convection. Beta Regio, Alpha Regio, and Artemis illustrate this process of dynamical interaction between the deforming lithosphere and the convecting mantle.

Finn, V. J.↗
NASA NTRS1993

Transmantle flux tectonics

Venus, Earth, and Mars have surfaces that display topographic domes and depressions with quasi-circular planimetric shapes, relief of 0 to several km, and large spatial scales (10(exp 2) to 10(exp 4) km). Our morphostructural mapping reveals hierarchical arrangements of these features. They are explained by a model of long-acting mantle convection, as a particular case of convection in a stratified and random inhomogeneous medium, which develops the form of a hierarchy of different convective pattern scales, each arising from different levels in the mantle. The hypothesis of transmantle flux tectonics parsimoniously explains a diversity of seemingly unrelated terrestrial planetary phenomena, including Earth megaplumes, global resurfacing epochs on Venus, and cyclic ocean formation and global climate change for Mars. All these phenomenon are hypothesized to be parsimoniously explained by a process of transmantle flux tectonics in which long-acting mantle convection generates stresses in blocks of planetary lithosphere to produce distinctive quasi-circular global-hierarchical morphostructure (QGM) patterns. Transmantle flux tectonics differs from plume tectonics in that individual plumes are not considered in isolation. Rather, a wholly interactive process is envisioned in which various spatial and temporal scales of convection operate contemporaneously and hierarchically within other scales. This process of continual change by hierarchical convective cells affects the surface at varying temporal and spatial scales, and its effects are discernable through their relic geological manifestations, the QGM patterns.

Finn, V. J.↗
NASA NTRS1992

Distribution of particles and fields in turbulent media

It is shown that fluctuations of kinetic coefficients can lead to the development of an instability that tends to increase the gradients of the distribution of particles and fields in turbulent media. It is found that high rank correlation functions of the cosmic medium turbulent velocity must be taken into account in most real cases. Turbulence in compressible media can lead to a decrease of the CR diffusion coefficient. In some cases the diffusion coefficient may become negative, which implies the development of an instability with respect to the formation of clusters of particles. A similar instability may exist for fields in turbulent media and in media with fluctuation parameters. It may lead to the bunching of magnetic field lines and to the fractal structure of waves propagating in the media.

Dolginov, A. Z.↗