Far Field Deposition Of Scoured Regolith Resulting From Lunar Landings

As a lunar lander approaches a dusty surface, the plume from the descent engine impinges on the ground, entraining loose regolith into a high velocity dust spray. Without the inhibition of a background atmosphere, the entrained regolith can travel many kilometers from the landing site. In this work, we simulate the flow field from the throat of the descent engine nozzle to where the dust grains impact the surface many kilometers away. The near field is either continuum or marginally rarefied and is simulated via a loosely coupled hybrid DSMC - Navier Stokes (DPLR) solver. Regions of two-phase and polydisperse granular flows are solved via DSMC. The far field deposition is obtained by using a staged calculation, where the first stages are in the near field where the flow is quasi-steady and the outer stages are unsteady. A realistic landing trajectory is approximated by a set of discrete hovering altitudes which range from 20m to 3m. The dust and gas motions are fully coupled using an interaction model that conserves mass, momentum, and energy statistically and inelastic collisions between dust particles are also accounted for. Simulations of a 4 engine configuration are also examined, and the erosion rates as well as near field particle fluxes are discussed.Astronom

DSMC Modeling Of Gasdynamics, Radiation And Fine Particulates In Ionian Volcanic Jets

Aerospace Engineerin

One visual search, many memory searches: An eye-tracking investigation of hybrid search

Suppose you go to the supermarket with a shopping list of 10 items held in memory. Your shopping expedition can be seen as a combination of visual search and memory search. This is known as “hybrid search.” There is a growing interest in understanding how hybrid search tasks are accomplished. We used eye tracking to examine how manipulating the number of possible targets (the memory set size [MSS]) changes how observers (Os) search. We found that dwell time on each distractor increased with MSS, suggesting a memory search was being executed each time a new distractor was fixated. Meanwhile, although the rate of refixation increased with MSS, it was not nearly enough to suggest a strategy that involves repeatedly searching visual space for subgroups of the target set. These data provide a clear demonstration that hybrid search tasks are carried out via a “one visual search, many memory searches” heuristic in which Os examine items in the visual array once with a very low rate of refixations. For each item selected, Os activate a memory search that produces logarithmic response time increases with increased MSS. Furthermore, the percentage of distractors fixated was strongly modulated by the MSS: More items in the MSS led to a higher percentage of fixated distractors. Searching for more potential targets appears to significantly alter how Os approach the task, ultimately resulting in more eye movements and longer response times

Effects of valent image-based secondary tasks on verbal working memory

Two experiments examined if exposure to emotionally valent image-based secondary tasks introduced at different points of a free recall working memory (WM) task impair memory performance. Images from the International Affective Picture System (IAPS) varied in the degree of negative or positive valance (mild, moderate, strong) and were positioned at low, moderate and high WM load points with participants rating them based upon perceived valence. As predicted, and based on previous research and theory, the higher the degree of negative (Experiment 1) and positive (Experiment 2) valence and the higher the WM load when a secondary task was introduced, the greater the impairment to recall. Secondary task images with strong negative valance were more disruptive than negative images with lower valence at moderate and high WM load task points involving encoding and/or rehearsal of primary task words (Experiment 1). This was not the case for secondary tasks involving positive images (Experiment 2), although participant valence ratings for positive IAPS images classified as moderate and strong were in fact very similar. Implications are discussed in relation to research and theory on task interruption and attentional narrowing and literature concerning the effects of emotive stimuli on cognition

Applying a User-centred Approach to Interactive Visualization Design

Analysing users in their context of work and finding out how and why they use different information resources is essential to provide interactive visualisation systems that match their goals and needs. Designers should actively involve the intended users throughout the whole process. This chapter presents a user-centered approach for the design of interactive visualisation systems. We describe three phases of the iterative visualisation design process: the early envisioning phase, the global specification hase, and the detailed specification phase. The whole design cycle is repeated until some criterion of success is reached. We discuss different techniques for the analysis of users, their tasks and domain. Subsequently, the design of prototypes and evaluation methods in visualisation practice are presented. Finally, we discuss the practical challenges in design and evaluation of collaborative visualisation environments. Our own case studies and those of others are used throughout the whole chapter to illustrate various approaches

Modeling The Vapor And Dust Dynamics Due To The Impact Of The Lcross Spacecraft On The Moon

The implications of possibly large volatile reservoirs on the Moon are significant for the future of manned activity there and for space science and exploration in general. In autumn of 2008 NASA will launch the LCROSS mission to impact two spacecraft into a permanently shadowed crater-a cold trap - at the south pole of the Moon. The lead spacecraft will excavate its own several meter crater. The process will be observed by the following smaller vehicle and by orbiting and Earth-based instruments in hopes of observing the release of volatiles-predominantly water -- from the lunar soil. The following vehicle will then impact as well. We examine the plausible vapor dynamics following the impacts and concentrate on the observability of the gas from Earth or lunar orbit. In the free-molecular computational model of the vapor motion, water and OH molecules move ballistically, have a temperature-dependent surface residence time, and are subject to photo-dissociation and ionization losses. Sunlight shadowing, separation of the vapor from the dust grains, dust thermodynamics and different impact plume models are considered.Aerospace Engineerin

The Kuiper Belt and Other Debris Disks

We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book "Astrophysics in the Next Decade

Simulation Of Plasma Interaction With Io's Atmosphere

One dimensional Direct Simulation Monte Carlo (DSMC) simulations are used to examine the interaction of the jovian plasma torus with Io's sublimation atmosphere. The hot plasma sweeps past Io at 57 km/s due to the external Jovian magnetic and corotational electric fields and the resultant energetic collisions both heat and dissociate the neutral gas creating an inflated, mixed atmosphere of SO(2) and its daughter products. The vertical structure and composition of the atmosphere is important for understanding Io's mass loading of the plasma torus, electron excited aurora, and Io's global gas dynamics. Our 1D simulations above a fixed location on the surface of Io allows the O(+) and S(+) ions to drift down into the domain where they then undergo elastic and charge exchange collisions with the neutral gas. Each electron's position is determined by the motion of a corresponding ion; however, the electrons retain their own velocity components which are then used during elastic, ionization, and excitation collisions with the neutral gas. Charge exchange creates fast neutral O and S atoms. Molecular Dynamic/Quasi-Classical Trajectory (MD/QCT) calculations are used to generate total and reaction cross sections for energetic O+SO(2) collisions [1] as well as for O+O(2) collisions. In addition, the model accounts for photo-dissociation assuming the atmosphere is optically thin. Our previous plasma heating model (without chemistry) agrees well with the vertical structure of the current model at lower altitudes where the gas is collisional; however, at high altitudes (>100 km) significant differences among the models appear. The current model's constant E and B fields results in reacceleration of the ions and electrons to a constant ExB drift velocity towards the surface after collisions with the neutral gas and, while the results are an upper limit on the plasma interaction strength, the results indicate that joule heating is significant, causing large changes in the vertical structure of the atmosphere. Plasma heating of, not momentum transfer to, the atmosphere dominates even for radially inward plasma flows resulting in a hot, inflated atmosphere. The scale heights for the various species were found to be a competition between the hydrodynamic scale height based on the gas constant (for the mixture if collisional) and the production rate from dissociation of SO(2) which depends on the local SO(2) density and available plasma energy at that altitude.Center for Aeromechanics Researc