Potentials for stationary point-axial stellar system models

Some potentials for a stationary stellar system model with point-axial symmetry and equatorial plane of symmetry that verifies Chandrasekhar's postulates have been obtained.Paper presented at the 12th European Astronomical Meetings of the IAU on European Astronomers Look to the Future, held 8–11 October, 1990, Davos, Switzerland.     

A new Bolivia-USSR astronomical observatory and its astrometric activities

In 1982 a Bolivia-USSR astronomical observatory began its activities near Tarija, Bolivia. Observations of 200 000 faint stars, 2822 bright stars (m6) and Halley's comet have been made with the expedition's astrograph.     

Phase transition in K2Cd2(SO4)3: Order parameter and microscopic distortions

The transition from P2₁3(T ⁴) to P2₁2₁2₁(D ₂ ⁴ ) in the langbeinite K₂Cd₂(SO₄)₃ has been analyzed using group theoretical methods and previously published structural data above and below the transition. We find that because the transition is strongly first-order, the primary-order parameter has relatively large values at the transition temperature, and higher order terms which involve the order parameter, the strain, and the coupling of the two must be included in the Landau expansion for the free energy. Complex displacements occur at the transition for all atoms of the unit cell, but these displacements can be resolved into contributions which can be shown from symmetry considerations to transform as the _{2 3} irrep of P2 ₁ 3(T ⁴) as well as contributions from symmetry-preserving displacements which transform under the irrep ₁. Therefore, the transition is not a simple one and involves sulfate rotations and cadmium and potassium ion displacements.     

Footprint prediction of scalar fluxes from analytical solutions of the diffusion equation

The use of analytical solutions of the diffusion equation for footprint prediction is explored. Quantitative information about the footprint, i.e., the upwind area most likely to affect a downwind flux measurement at a given height z, is essential when flux measurements from different platforms, particularly airborne ones, are compared. Analytical predictions are evaluated against numerical Lagrangian trajectory simulations which are detailed in a companion paper (Leclerc and Thurtell, 1990). For neutral stability, the structurally simple solutions proposed by Gash (1986) are shown to be capable of satisfactory approximation to numerical simulations over a wide range of heights, zero displacements and roughness lengths. Until more sophisticated practical solutions become available, it is suggested that apparent limitations in the validity of some assumptions underlying the Gash solutions for the case of very large surface roughness (forests) and tentative application of the solutions to cases of small thermal instability be dealt with by semi-empirical adjustment of the ratio of horizontal wind to friction velocity. An upper limit of validity of these solutions for z has yet to be established.     

Cooling rates of seven hexahedrites

Cooling rates for seven hexahedrites, (Uwet, Coahuila, Walker County, Lombard, Quillagua, Hex River Mountains and Tocopilla) have been determined using a ternary diffusion controlled phase growth analysis developed by the authors. The model is applied to the exsolution and growth of plate phosphides in the kamacite phase of hexahedrites during cooling of the meteorite in its parent body. The effects of cooling rate, bulk composition, nucleation temperature and diffusion field length are considered. A unique cooling rate was determined by comparing the Ni content and width of several phosphides in a given hexahedrite to computer-generated curves of Ni content vs phosphide width. Six hexahedrites have cooling rates of approximately 2°C/10⁶yr. One hexahedrite, Coahuila, has a somewhat higher cooling rate of 10°C/10⁶ yr. These cooling rates fall within the range calculated by an independent method for octahedrites. The cooling rate analysis indicates that the hexahedrites, except for one possible exception, were formed in or close to the core of a parent body ~ 150 km in radius.     

The formation and clay mineral reactions of melanoidins

Sugars and amino acids condense readily to form polymers known as melanoidins that closely resemble natural humic substances. In this study melanoidins are formed by reacting glucose with each of three amino acids: glutamic acid, valine and lysine. The basic amino acid, lysine, reacts with glucose at a much greater rate than either of the other two compounds. The chemical properties of the melanoidins are strongly influenced by the amino acid from which they are formed. The nitrogen contents, acidities and electrophoretic behavior of the polymers all reflect functional group distributions inherited from the amino acids. These chemical differences strongly influence the extent of association of the melanoidins with kaolinite and montmorillonite clay minerals. Laboratory simulations suggest that melanoidin formation may be favored in marine environments where basic amino acids should preferentially condense with sugars to form nitrogen-rich polymers that have a great affinity for clay mineral surfaces.     

The polarization of X-ray emission of some solar flares in July 1974

Preliminary results of polarization measurements at three solar flares of July 5 and 6, 1974, are given. The measurements were performed at h 15 keV with Thomson-scattering polarimeter on the Intercosmos 11 satellite.At the decay phase of the flare on July 5 we obtained P = 3.4–5.0%, which did not exclude some contribution from non-thermal processes. At the flares of July 6 we found P =1.0–1.9% and P = 0.1–2.0%, respectively: neither value exceeds the level of statistical fluctuations.Presented at XVIII COSPAR Meeting (VARNA, May–June 1975), contribution III.B.2.9.     

Some simple limits on size and rotation speed of astrophysical objects emitting by accretion

We demonstrate that the so-called force balance point, due to either magnetic fields (then known more specifically as the Alfvén point) or to co-rotation (Roche point), together with the concepts of flux and mass conservation, allows one to place interesting limits on both the size and angular velocity of astrophysical objects emitting by mass accretion. We give three numerical examples, which would seem to be of some astrophysical interest.     

The atmosphere of Io from Pioneer 10 radio occultation measurements

The occultation of the Pioneer 10 spacecraft by Io (JI) provided an opportunity to obtain two S-band radio occultation measurements of its atmosphere. The dayside entry measurements revealed an ionosphere having a peak density of about 6 × 10⁴ elcm^?3 at an altitude of about 100 km. The topside scale height indicates a plasma temperature of about 406 K if it is composed of Na⁺ and 495 K if N₂⁺ is principal ion. A thinner and less dense ionosphere was observed on the exit (night side), having a peak density of 9 × 10³ elcm^?3 at an altitude of 50 km. The topside plasma temperature is 160 K for N₂^? and 131 K for Na⁺. If the ionosphere is produced by photoionization in a manner analogous to the ionospheres of the terrestrial planets, the density of neutral particles at the surface of Io is less than 10¹¹?10¹² cm³, corresponding to a surface pressure of less than 10^?8 to 10^?9 bars. Two measurements of its radius were also obtained yielding a value of 1830 km for the entry and 192 km for the exit. The discrepancy between these values may indicate an ephemeris uncertainty of about 45 km. The two measurements yield an average radius of 1875 km, which is not in agreement with the results of the Beta Scorpii stellar occultation.