The distribution of particulate material on Mars

The surface materials on Mars were extensively studied using a variety of spacecraft and Earth-based remote sensing observations. These measurements include: (1) diurnal thermal measurements, used to determine average particle size, rock abundance, and the presence of crusts; (2) radar observations, used to estimate the surface slope distributions, wavelength scale roughness, and density; (3) radio emission observations, used to estimate subsurface density; (4) broadband albedo measurements, used to study the time variation of surface brightness and dust deposition and removal; and (5) color observations, used to infer composition, mixing, and the presence of crusts. Remote sensing observations generally require some degree of modeling to interpret, making them more difficult to interpret than direct observations from the surface. They do, however, provide a means for examining the surface properties over the entire planet and a means of sampling varying depths within the regolith. Albedo and color observations only indicate the properties of the upper-most few microns, but are very sensitive to thin, sometimes emphemeral dust coatings. Thermal observations sample the upper skin depth, generally 2 to 10 cm. Rock abundance measurements give an indirect indication of surface mantling, where the absence of rocks suggests mantles of several meters. Finally, radar and radio emission data can penetrate several meters into the surface, providing an estimate of subsurface density and roughness

Variations of Martian surface albedo: Evidence for yearly dust deposition and removal

The purpose is to determine the degree, spatial distribution and timing of the deposition and removal of dust storm fallout, and to relate the current patterns of dust deposition and removal to the long-term evolution of the Martian surface. Southern Hemisphere dark areas are found to quickly return to close to their pre-storm albedos, suggesting rapid removal of any dust that was deposited. Northern Hemisphere dark regions are brighter post-storm, but gradually darken to pre-storm levels over the Mars year. In doing so they act as local sources of dust during otherwise clear periods. Dust does not appear to be removed from bright regions, resulting in the 1 to 2 m thick deposits observed today

On R-duals and the duality principle in Gabor analysis

The concept of R-duals of a frame was introduced by Casazza, Kutyniok and Lammers in 2004, with the motivation to obtain a general version of the duality principle in Gabor analysis. For tight Gabor frames and Gabor Riesz bases the three authors were actually able to show that the duality principle is a special case of general results for R-duals. In this paper we introduce various alternative R-duals, with focus on what we call R-duals of type II and III. We show how they are related and provide characterizations of the R-duals of type II and III. In particular, we prove that for tight frames these classes coincide with the R-duals by Casazza et el., which is desirable in the sense that the motivating case of tight Gabor frames already is well covered by these R-duals. On the other hand, all the introduced types of R-duals generalize the duality principle for larger classes of Gabor frames than just the tight frames and the Riesz bases; in particular, the R-duals of type III cover the duality principle for all Gabor frames

Some considerations in the fatigue design of launch and spacecraft structures

Metal fatigue, structural fatigue, and strength for launch vehicle and spacecraft structure

Correcting stellar oscillation frequencies for near-surface effects

In helioseismology, there is a well-known offset between observed and computed oscillation frequencies. This offset is known to arise from improper modeling of the near-surface layers of the Sun, and a similar effect must occur for models of other stars. Such an effect impedes progress in asteroseismology, which involves comparing observed oscillation frequencies with those calculated from theoretical models. Here, we use data for the Sun to derive an empirical correction for the near-surface offset, which we then apply three other stars (alpha Cen A, alpha Cen B and beta Hyi). The method appears to give good results, in particular providing an accurate estimate of the mean density of each star.Comment: accepted for publication in ApJ Letter

Hire Education: Mastery, Modularization and the Workforce Revolution

This new research identifies online competency-based learning as the solution to shifting demands for specialized workforce skills and the front runner for disrupting higher education

Measurements of Stellar Properties through Asteroseismology: A Tool for Planet Transit Studies

Oscillations occur in stars of most masses and essentially all stages of evolution. Asteroseismology is the study of the frequencies and other properties of stellar oscillations, from which we can extract fundamental parameters such as density, mass, radius, age and rotation period. We present an overview of asteroseismic analysis methods, focusing on how this technique may be used as a tool to measure stellar properties relevant to planet transit studies. We also discuss details of the Kepler Asteroseismic Investigation -- the use of asteroseismology on the Kepler mission in order to measure basic stellar parameters. We estimate that applying asteroseismology to stars observed by Kepler will allow the determination of stellar mean densities to an accuracy of 1%, radii to 2-3%, masses to 5%, and ages to 5-10% of the main-sequence lifetime. For rotating stars, the angle of inclination can also be determined.Comment: To appear in the Proceedings of the 253rd IAU Symposium: "Transiting Planets", May 2008, Cambridge, M