Characterization and mapping of surface physical properties of Mars from CRISM multi-angular data: application to Gusev Crater and Meridiani Planum

The analysis of the surface texture from the particle (grain size, shape and internal structure) to its organization (surface roughness) provides information on the geological processes. CRISM multi-angular observations (varied emission angles) allow to characterize the surface scattering behavior which depends on the composition but also the material physical properties (e.g., grain size, shape, internal structure, the surface roughness). After an atmospheric correction by the Multi-angle Approach for Retrieval of the Surface Reflectance from CRISM Observations, the surface reflectances at different geometries are analyzed by inverting the Hapke photometric model depending on the single scattering albedo, the 2-term phase function, the macroscopic roughness and the 2-term opposition effects. Surface photometric maps are created to observe the spatial variations of surface scattering properties as a function of geological units at the CRISM spatial resolution (200m/pixel). An application at the Mars Exploration Rover (MER) landing sites located at Gusev Crater and Meridiani Planum where orbital and in situ observations are available, is presented. Complementary orbital observations (e.g. CRISM spectra, THermal EMission Imaging System, High Resolution Imaging Science Experiment images) are used for interpreting the estimated Hapke photometric parameters in terms of physical properties. The in situ observations are used as ground truth to validate the interpretations. Varied scattering properties are observed inside a CRISM observation (5x10km) suggesting that the surfaces are controlled by local geological processes (e.g. volcanic resurfacing, aeolian and impact processes) rather than regional or global. Consistent results with the in situ observations are observed thus validating the approach and the use of photometry for the characterization of Martian surface physical properties

The Sun's Supergranulation

Supergranulation is a fluid-dynamical phenomenon taking place in the solar photosphere, primarily detected in the form of a vigorous cellular flow pattern with a typical horizontal scale of approximately 30--35~megameters, a dynamical evolution time of 24--48~h, a strong 300--400~m/s (rms) horizontal flow component and a much weaker 20--30~m/s vertical component. Supergranulation was discovered more than sixty years ago, however, explaining its physical origin and most important observational characteristics has proven extremely challenging ever since, as a result of the intrinsic multiscale, nonlinear dynamical complexity of the problem concurring with strong observational and computational limitations. Key progress on this problem is now taking place with the advent of 21st-century supercomputing resources and the availability of global observations of the dynamics of the solar surface with high spatial and temporal resolutions. This article provides an exhaustive review of observational, numerical and theoretical research on supergranulation, and discusses the current status of our understanding of its origin and dynamics, most importantly in terms of large-scale nonlinear thermal convection, in the light of a selection of recent findings.Comment: Major update of 2010 Liv. Rev. Sol. Phys. review. Addresses many new theoretical, numerical and observational developments. All sections, including discussion, revised extensively. Also includes previously unpublished results on nonlinear dynamics of convection in large domains, and lagrangian transport at the solar surfac

Stochastic analysis of different rough surfaces

This paper shows in detail the application of a new stochastic approach for the characterization of surface height profiles, which is based on the theory of Markov processes. With this analysis we achieve a characterization of the scale dependent complexity of surface roughness by means of a Fokker-Planck or Langevin equation, providing the complete stochastic information of multiscale joint probabilities. The method is applied to several surfaces with different properties, for the purpose of showing the utility of this method in more details. In particular we show the evidence of Markov properties, and we estimate the parameters of the Fokker-Planck equation by pure, parameter-free data analysis. The resulting Fokker-Planck equations are verified by numerical reconstruction of conditional probability density functions. The results are compared with those from the analysis of multi-affine and extended multi-affine scaling properties which is often used for surface topographies. The different surface structures analysed here show in details advantages and disadvantages of these methods.Comment: Minor text changes to be identical with the published versio

Nucleoporin mRNA localization and Annulate Lamellae biosynthesis during Drosophila melanogaster oogenesis

Nuclear pore complexes (NPCs) are large protein assemblies that connect the eukaryotic nucleus with the cytoplasm, thus facilitating all transport between them. Besides the nuclear envelope (NE), NPCs also occur in parallel stacks of cytoplasmic membranes called Annulate Lamellae (AL) that can serve as storage, facilitating rapid nuclear growth via NE insertion during fruit fly embryogenesis. How and when AL are assembled is largely unknown. In this work, I established that AL are already abundant in late stage oocytes, and progressively accumulate throughout oogenesis specifically in the oocyte. By screening the localization of 39 nucleoporin and related mRNAs, I detected the specific enrichment of two nucleoporin and three importin encoding transcripts to AL, the NE, and previously unidentified nucleoporin granules throughout the egg chamber. Perturbation experiments revealed a dependence on active translation, but independence of an intact microtubule network on mRNA localization. Generation of GFP::Nup358 transgenic flies revealed granules with distinct partial nucleoporin contents, that are subject to microtubule-dependent transport and interactions among them. Their spatiotemporal abundance distribution is indicative of NPC precursors, and they contain partial accumulations of pore complexes within internal membranes. These granules further displayed characteristics of biomolecular condensates, including fast intra-granule dynamics, exclusion of cytoplasmic constituents, and sensitivity to 1,6-hexanediol. Both condensation state and AL assembly were dependent on Ran, a protein also fundamental for NPC assembly at the NE. Its nucleotide status throughout this is likely controlled by differential localization of its modulators RanGAP and Rcc1 to granules and cytoplasm respectively. This work thus established a molecular framework and basic sequence of events that leads to the assembly of AL, which are crucial during early development, and might have broader implications for NPC assembly also at the NE

Simulation model of erosion and deposition on a barchan dune

Erosion and deposition over a barchan dune near the Salton Sea, California, are modeled by bookkeeping the quantity of sand in saltation following streamlines of transport. Field observations of near surface wind velocity and direction plus supplemental measurements of the velocity distribution over a scale model of the dune are combined as input to Bagnold type sand transport formulas corrected for slope effects. A unidirectional wind is assumed. The resulting patterns of erosion and deposition compare closely with those observed in the field and those predicted by the assumption of equilibrium (downwind translation of the dune without change in size or geometry). Discrepancies between the simulated results and the observed or predicted erosional patterns appear to be largely due to natural fluctuations in the wind direction. The shape of barchan dunes is a function of grain size, velocity, degree of saturation of the oncoming flow, and the variability in the direction of the oncoming wind. The size of the barchans may be controlled by natural atmospheric scales, by the age of the dunes, or by the upwind roughness. The upwind roughness can be controlled by fixed elements or by sand in the saltation. In the latter case, dune scale is determined by grain size and wind velocity

GRANULATION OF ULTRA-FINE POWDERS: EXAMINATION OF GRANULE MICROSTRUCTURE, CONSOLIDATION BEHAVIOR, AND POWDER FEEDING

Davis, Nathan B. Ph.D., Purdue University, December 2015. Granulation Behavior of Ultra-Fine Powders: Examination of Granule Microstructure, Consolidation Behavior, and Powder Feeding. Major Professor: James Litste

Modeling of particle segregation in a rotating drum

Mixing of granular solids is a processing step in a wide range of industries. The fundamental phenomena in granule mixing are still poorly understood, making it difficult to a priori predict the effectiveness of mixing processes. While mixing of granules is easy when the particles are homogeneous in size, shape and density and other properties, in practice they are not. With such a mixture, homogenizing is far more complex, since the heterogeneous particles tend to segregate, and special care has to be taken in the design of the mixing process to avoid this. In view of the practical need for better understanding and control of solids mixing, the work in this thesis has two closely coupled objectives. The first objective is to obtain a better understanding of segregation mechanisms. This insight should enable the enhancement of mixing and at the same time suppress segregation, or vice versa, namely the deliberate and controlled segregation of a mixture. The second objective is to provide guidelines for mixing operations that can be derived from insights extracted from the data on mixing behaviour at different rotational velocities and fill levels. From this perspective, we here report an extensive numerical study of mixing and segregation in a bed of bidisperse granules in a rotating horizontal drum, which is the simplest relevant geometry in industrial practice. Two types of segregation can occur: fast radial segregation during which smaller or denser particles accumulate along the axis of rotation; and slow axial segregation with fully segregated bands of small and large particles perpendicular to the rotating axis, with in general particle bands of large particles adjacent to the end walls. This thesis reports on both radial and axial segregation phenomena in a horizontally rotating drum. While visual observation of the particle bed was used as a qualitative observation technique to determine the degree of mixing/segregation, in parallel a more quantitative method was developed as well, which was based on calculating the entropy over the systems. By subdividing the system with a lattice, calculating the entropy of mixing in each cell of the lattice, and summarizing them over the system, a measure for the degree of overall segregation was obtained. By using different grids (a 3D mesh, a 2D set of slices perpendicular to the axis, or 2D bars parallel to the axis), different types of segregation could be distinguished. The radial segregation dynamics were investigated in semi-2D (very short) drums, which inhibits axial segregation. Diagrams were prepared that visualise the mixing behaviour as function of the Froude number (rotational speed) for systems with different bidisperse systems. It was found that while almost all systems showed radial segregation at low Fr (rolling regime), and most showed inverted radial segregation at high Fr (cataracting or centrifuging regime), at Fr ≈ 0.56 all systems became radially mixed. This could be understood by assuming a percolation mechanism. In the moving layer on top of the load, smaller particles percolate in between the moving larger particles, down to the centre of the load, as long as the motion is not too fast. The same phenomenon is inverted at high speeds. In between, the flowing layer is expanded in such a way that many large voids are present, which makes the percolation mechanism less selective on the particle size. The little segregation that occurs is negligible, since the two phenomena described above work in different directions. Surprisingly this transitional Fr number is the same for all investigated systems. Since axial segregation is always preceded by radial segregation, it is logical to also study axial segregation. This was done by studying longer drums, which allows axial segregation to develop along the axis. Axial segregation was found for most systems; its occurrence is mostly dictated by differences in size. It was found that for drums that have intermediate length, surprising dynamic behaviour results. The axial segregation developed with low and high frequency oscillations. While the low frequency oscillations could be understood as the development and migration of segregated areas in the system, the higher frequency oscillations, with a period of 10 to 20 revolutions, were not identified before. This oscillatory behaviour is probably coupled to the use of intermediately sized drums, as this behaviour has not been seen with very long drums. We ascribe the oscillations to the influence of the (vertical) end walls, which expose the adjacent particles to different forces than those particles inside the drum load. These differences induce an axial flow in the system. The particles adjacent to the vertical walls tend to be lifted higher than the particles far away from the vertical walls. This creates a concave profile of the load surface throughout the drum, inducing the particles (in the rolling regime) to follow a path away from the vertical walls towards the centre of the drum. Once past the centre, the particles flow back to the vertical walls in response to the locally convex bed profile. Even in this particular flow profile the percolation mechanism is of importance: smaller particles percolate through the flowing layer and end up deeper inside the bed, while the larger particles accumulate on top of the flowing layer and are conveyed back to the vertical walls. Due to the percolation of the small particles the final end configuration must clearly be a banding configuration of large-small-large particle bands. Prolonged rotation of the bed increases the concave form of the flowing layer. This induces fast oscillations and a sudden mixing of a part of the large particle band with the small particle band, giving fast mixing and leading to a configuration, in which a small-particle band is formed below the large-particles bands. Subsequently segregation into three bands (large-small-large) slowly occurs again, after which the asymmetry in the angel of repose further increases. The configuration, in which larger particles accumulate on top of the bed adjacent to the end walls, coincides with a minimum in energy dissipation, which is not present when the systems segregates radially or axially into three pure bands. The effect found implies that the end walls are important in the dynamics of axial segregation. This effect is studied further by varying the end wall properties. The above mentioned fast and slow oscillations vanish in systems that have smoother end walls, while also the rate of segregation decreases; nevertheless the same axially segregated three band (large-small-large) state of mixing resulted finally. Reducing the friction further to completely smooth end walls however changed the final configuration into a two-banded system. Systems with no end wall at all, simulated through periodic end walls, only gave radial segregation over the (considerable) simulated time span. We expect here that as long as there is still a driving force for axial segregation, the absence of the induction of axial flow by the end walls make the transition very slow or impossible. The formation of two axial bands lowers the energy dissipation by the bed, whereas neither radial segregation nor axial segregation into three bands reduced the power absorption at constant angular velocity. While the oscillatory behaviour is relevant in its own right, their study also allows shedding some light on the fundamental mechanisms underlying the segregation mechanisms, and especially the transition from radial to axial segregation. The fact that this is dependent on not only the properties of the granular materials, but also on the geometry and design of the drum, implies that these findings have relevance to the design and operation of processes. <br/