Predicting Flows of Rarefied Gases

DSMC Analysis Code (DAC) is a flexible, highly automated, easy-to-use computer program for predicting flows of rarefied gases -- especially flows of upper-atmospheric, propulsion, and vented gases impinging on spacecraft surfaces. DAC implements the direct simulation Monte Carlo (DSMC) method, which is widely recognized as standard for simulating flows at densities so low that the continuum-based equations of computational fluid dynamics are invalid. DAC enables users to model complex surface shapes and boundary conditions quickly and easily. The discretization of a flow field into computational grids is automated, thereby relieving the user of a traditionally time-consuming task while ensuring (1) appropriate refinement of grids throughout the computational domain, (2) determination of optimal settings for temporal discretization and other simulation parameters, and (3) satisfaction of the fundamental constraints of the method. In so doing, DAC ensures an accurate and efficient simulation. In addition, DAC can utilize parallel processing to reduce computation time. The domain decomposition needed for parallel processing is completely automated, and the software employs a dynamic load-balancing mechanism to ensure optimal parallel efficiency throughout the simulation

Analysis of Plume Impingement Effects from Orion Crew Service Module Dual Reaction Control System Engine Firings

Plume impingement effects on the Orion Crew Service Module (CSM) were analyzed for various dual Reaction Control System (RCS) engine firings and various configurations of the solar arrays. The study was performed using a decoupled computational fluid dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) approach. This approach included a single jet plume solution for the R1E RCS engine computed with the General Aerodynamic Simulation Program (GASP) CFD code. The CFD solution was used to create an inflow surface for the DSMC solution based on the Bird continuum breakdown parameter. The DSMC solution was then used to model the dual RCS plume impingement effects on the entire CSM geometry with deployed solar arrays. However, because the continuum breakdown parameter of 0.5 could not be achieved due to geometrical constraints and because high resolution in the plume shock interaction region is desired, a focused DSMC simulation modeling only the plumes and the shock interaction region was performed. This high resolution intermediate solution was then used as the inflow to the larger DSMC solution to obtain plume impingement heating, forces, and moments on the CSM and the solar arrays for a total of 21 cases that were analyzed. The results of these simulations were used to populate the Orion CSM Aerothermal Database

Radiation osteitis of the clavicle

The bone alterations in the region of the clavicle (3 cases) are similar to those we have observed and described elsewhere in the skeleton i.e., the mandible, maxillary and ethmoid bones. Rarefaction is the result of three different types of bone destruction: osteoclasia, a kind of osteocytic osteolysis only observed after irradiation and obviously related with infection, and a pure demineralization of the osseous tissue by contact with pus. Reconstruction processes, although unable to prevent spontaneous fracture, are also present and correspond to islets of chondroid tissue surrounded by lamellar bone. However, these recently deposited calcified tissues are already necrotic since most of their lacunae are empty.Les modifications osseuses dans la région de la clavicule (3 observations) sont semblables à celles observées ailleurs dans le squelette, par exemple la mandibule, le maxillaire et l’os ethmoïde. La raréfaction osseuse est le résultat de trois types différents de destruction: l’ostéoclasie, une espèce d’ostéolyse ostéocytaire observée après irradiation, en rapport certain avec une infection et une déminéralisation pure du tissu osseux en contact avec du pus. Les phénomènes de reconstruction, bien qu’incapables d’éviter une fracture spontanée, sont également présents et ils correspondent à des îlots de tissu chondroïde au sein de travées d’os lamellaire. Cependant ces tissus calcifiés récemment déposés sont déjà nécrosés puisque les ostéoplastes sont vides

Direct synthesis of mesoporous silica containing cobalt: A new strategy using a cobalt soap as a co-template

A novel approach to incorporate transition metals into porous structures is presented, which makes use of a cobalt soap in combination with the templating agent C16TMABr. An ordered mesoporous silica MCM-41 type material doped with Co is obtained after removal of the organic part by calcination. The a unit cell parameter of the cobalt containing mesoporous matrices is larger than that of pure MCM-41 and increases with the amount of cobalt present in the sample as well as the diameter of the pores. This is not observed when e.g. cobalt acetate is employed instead of the metal soap. The procedure presented establishes a new route for the incorporation of a transition metal into MCM-41 together with a tuning of the porous structure

NASA Aerosciences Activities to Support Human Space Flight

The Lyndon B. Johnson Space Center (JSC) has been a critical element of the United State's human space flight program for over 50 years. It is the home to NASA s Mission Control Center, the astronaut corps, and many major programs and projects including the Space Shuttle Program, International Space Station Program, and the Orion Project. As part of JSC's Engineering Directorate, the Applied Aeroscience and Computational Fluid Dynamics Branch is charted to provide aerosciences support to all human spacecraft designs and missions for all phases of flight, including ascent, exo-atmospheric, and entry. The presentation will review past and current aeroscience applications and how NASA works to apply a balanced philosophy that leverages ground testing, computational modeling and simulation, and flight testing, to develop and validate related products. The speaker will address associated aspects of aerodynamics, aerothermodynamics, rarefied gas dynamics, and decelerator systems, involving both spacecraft vehicle design and analysis, and operational mission support. From these examples some of NASA leading aerosciences challenges will be identified. These challenges will be used to provide foundational motivation for the development of specific advanced modeling and simulation capabilities, and will also be used to highlight how development activities are increasing becoming more aligned with flight projects. NASA s efforts to apply principles of innovation and inclusion towards improving its ability to support the myriad of vehicle design and operational challenges will also be briefly reviewed

Sollicitations sismiques dues aux exploitations minières : amplification des ondes en surface (et vibrations des structures)

National audienceL'objectif de ce travail est d'analyser l'impact des secousses induites par les exploitations minières sur les structures situées en surface. Du fait des conditions géologiques locales, le mouvement créé par les secousses peut parfois être amplifié de façon importante en surface (effet de site). A partir d'une modélisation numérique du problème, l'amplification du mouvement est analysée pour différentes formes de remplissages sédimentaires et des contrastes de propriétés entre couches variables. Les valeurs de fréquences fondamentales (i.e amplification maximale) sont comparées à des résultats antérieurs

Analog of Magnetoelectric Effect in High-Tc Granular Superconductors

We propose the existence of an electric-field induced nonlinear magnetization in a weakly coupled granular superconductor due to time-parity violation. As the field increases the induced magnetization passes from para- to dia-magnetic behavior. We discuss conditions under which this effect could be experimentally measured in high-temperature superconductors.Comment: REVTEX (epsf style), 1 PS figure; to appear in Europhysics Letter