Mass Density Variations Research Articles

Transient attitude dynamics of satellites with deploying flexible appendages

The paper presents a general formulation for librational dynamics of satellites with an arbitrary number, types, and orientation of deploying flexible appendages. The generalized force term is incorporated making the formulation applicable to a wide variety of situations where aerodynamic forces, solar radiation, earth's magnetic field, etc. become significant. In particular, the case of a beam-type flexible appendage deploying from a satellite in an arbitrary orbit is considered. The corresponding nonlinear, non-autonomous equations for in-plane and out-of-plane vibrations are derived, allowing for the variation of mass density and flexural rigidity along the length with time dependent deployment velocity and spin rate. Next, the attention is focused on the linearized analysis of the in-plane vibrational equation using the assumed-mode method and its substantiation through numerical integration. Finally, the paper presents results for both steady-state and transient attitude behaviour for a representative gravity gradient configuration for a range of initial conditions and system parameters. Results show the combined effect of flexibility and deployment on the dynamics of the system to be substantial. Disturbance of the appendage can excite large amplitude librations. On the other hand, the converse situation is not necessarily true. Furthermore, Coriolis loading, induced by the extending appendages, can become a limiting factor in arriving at a deployment strategy; an effect not pointed out in the literature.

Photometric studies of spiral structure. I - The disks and arms of six SB I and SC I galaxies

view Abstract Citations (322) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric studies of spiral structure. I. The disks and arms of six Sb I and Sc I galaxies. Schweizer, F. Abstract This paper presents detailed surface photometry of the galaxies NGC 3031, 4254, 4321, 5194, 5364, and 5457. Profiles showing the variation of surface brightness with azimuthal angle in each galaxy are given and used to separate the light into disk and arm components. The disk level at each radius is defined by the two main minima of the azimuthal light distribution, and the light above this level is assigned to the arms. The disks are e2xp9nential with an extrapolated central surface brightness of (Bo)D = 21.67 + 0.35 mag arcsec , in excellent agreement with Freeman. The disk colors are very uniform, with radial gradients mostly below the detection limit (10.010 mag kpc-1 in B - V), and lie in the narrow range of colors between old galactic clusters (B - V +0.7) and giant elliptical galaxies (B- V +0.9). The arms are significantly bluer than the disks and have a highly composite spectrum, as judged from the color indices. The ratio of arm intensity to disk intensity increases with radius, which explains the well-known outward bluing of spiral galaxies. There are indications that the ratio of total arm intensity to total disk intensity, which is a coarse measure of the strength of star formation, correlates with van der Kruit's compression strength of the gas. The most interesting result is the detection of broad spiral patterns in the underlying disks of the galaxies. We present evidence that these patterns represent variations in the surface mass density of the old disk population. The fractional amplitudes of the patterns increase with radius, reaching about + 20 percent to 130 percent of the mean surface mass density near the ii regions. The intriguing "red arms" discovered by Zwicky (1955) on composite photographs of NOC 5194 are a good example of such a disk pattern. By reanalyzing the photographic composition process, we show that these arms are regions of enhanced surface brightness in the old disk, rather than regions of enhanced color; this agrees with their interpretation as "massive" arms. Subject headings: galaxies: photometry - galaxies: stellar content - galaxies: structure Publication: The Astrophysical Journal Supplement Series Pub Date: July 1976 DOI: 10.1086/190384 Bibcode: 1976ApJS...31..313S Keywords: Astronomical Photometry; Galactic Structure; Spiral Galaxies; Ubv Spectra; Astronomical Maps; Galactic Clusters; Star Distribution; Astrophysics full text sources ADS | data products NED (7)

On the diurnal variations of total mass density, number density and temperature in the upper thermosphere

Theoretical work on the time of occurrence of the diurnal maxima of total mass density (ϱ), number densities ( n) and temperature ( T) in the upper thermospheric region is discussed. It is suggested that the observed ρ- T phase difference is due to the neutral air wind acting as a heating or cooling agent and to variations in n and T at the lower boundary of the region. The observed n(O)- n(N 2)- T phase differences may be caused by vertical diffusion of atomic oxygen through molecular nitrogen and by variations in n and T at the lower boundary.

Geophysical data and long-wave heterogeneities of the Earth's mantle

To investigate the presence and nature of the lateral heterogeneities in the earth's mantle, geophysical data with global distribution are analyzed and correlated. Surface heat flow, seismic travel-time residuals, and crustal thickness data are expanded in spherical harmonics. Using these, and the coefficients of similar expansions of surface topography of the earth, and the gravitational potential variations as revealed by satellite data, both total and degree correlation coefficients are obtained. From the interpretation of these results, jointly with available laboratory data on velocity-density relationships and the temperature coefficient of velocity, the following are concluded: (1) Lateral mass anomalies and/or density variations in the earth's mantle are larger by at least an order of magnitude from what is required to explain the satellite data. Earth's surface topography and crustal structure introduce loads which are compensated in the upper, and perhaps lower, mantle giving rise to lateral density anomalies in the mantle. (2) Surface heat flow variations are controlled primarily by the shallow structure and tectonic features of the earth. (3) At long wavelengths (n ≤ 6), gravitational, heat flow, and seismic travel-time variations are not correlated with topographic elevations.

Finite-Difference Methods for Plate Vibration Problems

A finite-difference method is developed to determine the transverse deflections of a vibrating plate. Explicit and implicit difference formulas are considered. The implicit formulation, which has been programmed for a digital computer, is derived to permit variations in bending stiffness, support stiffness, mass density, and loading. Numerical results demonstrate that the method is applicable to a wide range of problems involving both transient and steady-state response of plates.

Quantum variation of the carrier mass density of Bi at high magnetic fields

It was observed by means of Alfvèn wave propagation that the two band model of magnetic quantum levels in Bi due to Smith et al. fails for high magnetic fields parallel to the trigonal direction.

Dynamic Behavior of Imploding Magnetically Driven Axisymmetric Slug-Type Plasma Sheets

The dynamic behavior of magnetically driven axisymmetric plasma sheets of negligible thickness is examined by postulating a simplified two-dimensional plasma sheet model. The equations of motion in the axial and radial directions are derived in Lagrangian form for the general case of time-varying current. For the case of constant current, the general solution of the equations of motion is obtained. These equations of motion are solved for three different types of small sinusoidal perturbations of a cylindrical implosion. The plasma sheet configurations, particle trajectories, and surface mass density variations are presented for representative examples.

Nonthermal Ionization Caused by Aerodynamic Discontinuities in Charged Aerosol Jets

Significant space-charge accumulations caused by thermodynamic changes are produced whenever an electrical corona discharge of the streamer type is maintained in a region of rapid and sustained mass density variation. The experimential investigation uses a highly charged supersonic aerosol jet (0.03 C/m3) at temperatures below 300°K and pressures below 3 atm. The aerosol emerges from an underexpanded nozzle producing a characteristic series of expansion and compression regions. The charge density of the aerosol is sufficiently high so that electrical breakdown is induced at a grounded needle placed near or within the jet. It is shown that the ionization produced within the supersonic region, where rapid mass density changes occur, liberates charge in excess of the charge carried by the aerosol and that the current to the induced corona needle reproduces density variations in the underexpanded jet. A model is presented whereby changes in electrical conductivity, produced by the streamers propagating through the jet, result in space charge accumulations. Computation shows that the charge accumulation on shocks and compression and expansion waves is of sufficient magnitude to be responsible for the excess ionization and the visual appearance of the corona discharge.