Lepidocrocite to maghemite to hematite: A pathway to magnetic and hematitic Martian soil

Abstract— We examined decomposition products of lepidocrocite, which were produced by heating the phase in air at temperatures up to 525 °C for 3 and 300 h, by x-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic methods, and reflectance spectroscopy (visible and near-infrared (IR)). Single-crystal lepidocrocite particles dehydroxylated to polycrystalline particles of disordered maghemite that subsequently transformed to polycrystalline particles of hematite. Essentially pure maghemite was obtained at 265 and 223 °C for the 3 and 300 h heating experiments, respectively. Its saturation magnetization (J_s) and mass specific susceptibility are ～50 Am²/kg and ～400 × 10^?6 m³/kg, respectively. Because hematite is spectrally dominant, spectrally hematitic samples (i.e., a minimum near 860 nm and a maximum near 750 nm) also could be strongly magnetic (J_s up to ～30 Am²/kg) from the masked maghemite component. Analyses by TEM showed that individual particles are polycrystalline with respect to both maghemite and hematite. The spectrally hematitic and magnetic Mh + Hm particles can satisfy the spectral and magnetic constraints for Martian surface materials over a wide range of values of Mh/(Mh + Hm) either as pure oxide powders or (within limits) as components of multiphase particles. These experiments are consistent with lepidocrocite as the precursor of Mh + Hm assemblages on Mars, but other phases (e.g., magnetite) that decompose to Mh and Hm are also possible precursors. Simulations done with a copy of the Mars Pathfinder magnet array showed that spectrally hematitic Mh + Hm powders having J_s equal to 20.6 Am²/kg adhered to all five magnets.     

How to compare the surface of Io to laboratory samples

Since one does not know the photometric functions of various parts of Io, one cannot convert the observed geometric albedo of the satellite to a parameter more directly measurable in the laboratory. One must therefore convert laboratory reflectances to geometric albedos before quantitative comparisons between Io's surface and a laboratory sample are made. This procedure involves determining the wavelength dependence of the sample's photometric function. For substances such as sulfur, whose reflectance varies strongly with wavelength, it is incorrect to assume that the photometric function, and hence the ratio (laboratory reflectance/geometric albedo) is independent of wavelength. To illustrate this point, measurements of the color dependence of this ratio for sulfur are presented for the specific case in which the measured laboratory reflectance is the sample's normal reflectance. In general, unless the laboratory reflectance is precisely the geometric albedo, a wavelength-dependent correction factor must be determined before the laboratory sample can be compared quantitatively with Io's surface.     

Report to cross sections related to plasma-planetary atmosphere interaction processes

As a recent trend, the continuous increase of new technologies for space observations of new missions to Mars, Venus, and Titan, has stimulated vigorous experimental and theoretical studies on the collision process induced by interactions between plasma and planetary atmosphere. In order to facilitate the comprehension of these processes, this brief paper chose a collection of cross section data not always easily accessible. With the purpose of making a useful collection of such data we have collected both experimental and theoretical estimate for most of the expected collisions processes.     

An Introduction to Observations Relevant to Astrophysical Jets and Nebulae

This article reviews the basic physics and jargon associated with astronomical observations of nebulae, with an emphasis on processes relevant to shock waves in astrophysical jets.     

走向Internet网际

从１９９５年３月１３日开始，我们开始与中国科学院网络中心和昆明电信局通信处联系，准备建立云南天文台Ｅｍａｉｌ系统。到３月２１日本系统技术上已基本调试完成。本文介绍了这一系统的建立过程和通过这一系统可以得到的网络资源。     

Proposal to Use MAGDAS/CPMN to Study the Equatorial Electrojet: A Philippine Contribution to the International Heliophysical Year

As a Philippine contribution to the International Heliophysical Year, we propose to use the MAGnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network (MAGDAS/CPMN), installed by the Space Environment Research Center (SERC), Kyushu University along the 210° magnetic meridian and the magnetic equator, to study the equatorial electrojet (EEJ) and counter electrojet (CEJ). Through this installation, it is made possible to observe geomagnetic field variations in real time. By utilizing this network of ground-based instruments, we hope to elucidate their regular day-to-day and seasonal variabilities and variations during magnetic storms and substorms. We also want to study the behavior of this ionospheric current system before, during, and after the occurrence of an earthquake.     

Stabilization due to gyroscopic coupling in dual-spin satellites subject to gravitational torques

The stability of attitude equilibria relative to gravitational torques for a rigid satellite in a circular orbit has been divided into three inertia regions, the Lagrange region of assured Liapunov stability, the Beletskii-Delp region which is often described as stabilized due to gyroscopic coupling, and an assured instability region. The generalization of these regions to the case of dual-spin or gyrostat satellites whose internal spin momentum is along a principal axis is treated here. The stability boundaries are obtained for all possible equilibrium orientations for such vehicles, and the variations of these boundaries corresponding to changes in the internal momentum magnitude, or to aligning the momentum with a different principal axis, are determined.Alexander von Humboldt Research Fellow at the Institut für Mechanik; on sabbatical leave from Columbia University, New York, U.S.A.     

Using 2MASS to detect main sequence companions to subdwarf B stars

We explore the binary fraction of subdwarf B (sdB) stars by using the Two Micron All Sky Survey to search for main sequence companions. We have convolved Kurucz models with appropriate filter bandpasses to examine how various combinations separate single sdB stars from sdB+MS binaries. We notice that the 2MASS magnitude limits greatly increase the fraction of inferred sdB+MS binaries and examine a magnitude-limited sample appropriate for single sdB stars.