Dynamic Reconstruction and Multivariable Control for Force-Actuated, Thin Facesheet Adaptive Optics

The Multiple Mirror Telescope (MMT) under development at the University of Arizona takes a new approach in adaptive optics placing a large (0.65 m) force-actuated, thin facesheet deformable mirror at the secondary of an astronomical telescope, thus reducing the effects of emissivity which are important in IR astronomy. However, The large size of the mirror and low stiffness actuators used drive the natural frequencies of the mirror down into the bandwidth of the atmospheric distortion. Conventional adaptive optics takes a quasi-static approach to controlling the, deformable mirror. However, flexibility within the control bandwidth calls for a new approach to adaptive optics. Dynamic influence functions are used to characterize the influence of each actuator on the surface of the deformable mirror. A linearized model of atmospheric distortion is combined with dynamic influence functions to produce a dynamic reconstructor. This dynamic reconstructor is recognized as an optimal control problem. Solving the optimal control problem for a system with hundreds of actuators and sensors is formidable. Exploiting the circularly symmetric geometry of the mirror, and a suitable model of atmospheric distortion, the control problem is divided into a number of smaller decoupled control problems using circulant matrix theory. A hierarchic control scheme which seeks to emulate the quasi-static control approach that is generally used in adaptive optics is compared to the proposed dynamic reconstruction technique. Although dynamic reconstruction requires somewhat more computational power to implement, it achieves better performance with less power usage, and is less sensitive than the hierarchic technique

Information systems ethics – challenges and opportunities

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI linkThe purpose of this paper is to explore the ethical issues surrounding information systems (IS) practice with a view to encouraging greater involvement in this aspect of IS research. Information integrity relies upon the development and operation of computer-based information systems. Those who undertake the planning, development and operation of these information systems have obligations to assure information integrity and overall to contribute to the public good. This ethical dimension of information systems has attracted mixed attention in the IS academic discipline

SPHERES flight operations testing and execution

Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) is a formation flight testing facility consisting of three satellites operating inside the International Space Station (ISS). The goal is to use the long term microgravity environment of the ISS to mature formation flight and docking algorithms. The operations processes of SPHERES have also matured over the course of the first seven test sessions. This paper describes the evolution of the SPHERES program operations processes from conception to implementation to refinement through flight experience. Modifications to the operations processes were based on experience and feedback from Marshall Space Flight Center Payload Operations Center, USAF Space Test Program office at Johnson Space Center, and the crew of Expedition 13 (first to operate SPHERES on station). Important lessons learned were on aspects such as test session frequency, determination of session success, and contingency operations. This paper describes the tests sessions; then it details the lessons learned, the change in processes, and the impact on the outcome of later test sessions. SPHERES had very successful initial test sessions which allowed for modification and tailoring of the operations processes to streamline the code delivery and to tailor responses based on flight experiences.United States. Dept. of Defense. Space Technologies ProgramUnited States. National Aeronautics and Space Administration. Johnson Space Center ISS Operations TeamUnited States. National Aeronautics and Space Administration. Marshall Space Flight Center Astronaut OfficeUnited States. National Aeronautics and Space Administration. Johnson Space Center Reduced Gravity Offic

Sustained Magnetorotational Turbulence in Local Simulations of Stratified Disks with Zero Net Magnetic Flux

We examine the effects of density stratification on magnetohydrodynamic turbulence driven by the magnetorotational instability in local simulations that adopt the shearing box approximation. Our primary result is that, even in the absence of explicit dissipation, the addition of vertical gravity leads to convergence in the turbulent energy densities and stresses as the resolution increases, contrary to results for zero net flux, unstratified boxes. The ratio of total stress to midplane pressure has a mean of ~0.01, although there can be significant fluctuations on long (>~50 orbit) timescales. We find that the time averaged stresses are largely insensitive to both the radial or vertical aspect ratio of our simulation domain. For simulations with explicit dissipation, we find that stratification extends the range of Reynolds and magnetic Prandtl numbers for which turbulence is sustained. Confirming the results of previous studies, we find oscillations in the large scale toroidal field with periods of ~10 orbits and describe the dynamo process that underlies these cycles.Comment: 13 pages, 18 figures, submitted to Ap

SPHERES as Formation Flight Algorithm Development and Validation Testbed: Current Progress and Beyond

The MIT-SSL SPHERES testbed provides a facility for the development of algorithms necessary for the success of Distributed Satellite Systems (DSS). The initial development contemplated formation flight and docking control algorithms; SPHERES now supports the study of metrology, control, autonomy, artificial intelligence, and communications algorithms and their effects on DSS projects. To support this wide range of topics, the SPHERES design contemplated the need to support multiple researchers, as echoed from both the hardware and software designs. The SPHERES operational plan further facilitates the development of algorithms by multiple researchers, while the operational locations incrementally increase the ability of the tests to operate in a representative environment. In this paper, an overview of the SPHERES testbed is first presented. The SPHERES testbed serves as a model of the design philosophies that allow for the various researches being carried out on such a facility. The implementation of these philosophies are further highlighted in the three different programs that are currently scheduled for testing onboard the International Space Station (ISS) and three that are proposed for a re-flight mission: Mass Property Identification, Autonomous Rendezvous and Docking, TPF Multiple Spacecraft Formation Flight in the first flight and Precision Optical Pointing, Tethered Formation Flight and Mars Orbit Sample Retrieval for the re-flight mission

Improving the Mechanical Response of the IWP Exo-skeletal Lattice Through Shape Optimization

Triply Periodic Minimal Surfaces have been identified as good candidates for the generation of lattice structures produced with additive manufacturing. These TPMS-based lattice structures avoid sharp features that are characteristic of strut-based lattice structures because of their constant zero mean curvature. Although studies have explored part-scale optimization using TPMS-based lattice structures, they have only varied the volume fraction by changing the level set in the approximate surface equations. By defining new parameterizations in the approximate surface equation, we can redistribute volume within the lattice structure at any volume fraction. In this paper, we introduce an approach for optimization of this new parameterization of TPMS equations using the Borg multi-objective evolutionary algorithm. We demonstrate this framework on the IWP exo-skeletal lattice under uniaxial compression. A relationship between the new parameters and the level set is derived for designs on the Pareto frontier of the optimized IWP TPxS. The performance of the Pareto optimal designs and the efficacy of the optimization approach are shown by comparing to the standard IWP lattice and four other lattices that share the same topology. The optimized designs are implemented and shared in custom nTopology blocks.Mechanical Engineerin

Reducing in-stent restenosis therapeutic manipulation of miRNA in vascular remodeling and inflammation

Background: Drug-eluting stents reduce the incidence of in-stent restenosis, but they result in delayed arterial healing and are associated with a chronic inflammatory response and hypersensitivity reactions. Identifying novel interventions to enhance wound healing and reduce the inflammatory response may improve long-term clinical outcomes. Micro–ribonucleic acids (miRNAs) are noncoding small ribonucleic acids that play a prominent role in the initiation and resolution of inflammation after vascular injury.<p></p> Objectives: This study sought to identify miRNA regulation and function after implantation of bare-metal and drug-eluting stents.<p></p> Methods: Pig, mouse, and in vitro models were used to investigate the role of miRNA in in-stent restenosis.<p></p> Results: We documented a subset of inflammatory miRNAs activated after stenting in pigs, including the miR-21 stem loop miRNAs. Genetic ablation of the miR-21 stem loop attenuated neointimal formation in mice post-stenting. This occurred via enhanced levels of anti-inflammatory M2 macrophages coupled with an impaired sensitivity of smooth muscle cells to respond to vascular activation.<p></p> Conclusions: MiR-21 plays a prominent role in promoting vascular inflammation and remodeling after stent injury. MiRNA-mediated modulation of the inflammatory response post-stenting may have therapeutic potential to accelerate wound healing and enhance the clinical efficacy of stenting

Investigation of Energy Modelling Methods of Multiple Fidelities: A Case Study

Building energy modelling has become an integral part of building design due to energy consumption concerns in sustainable buildings. As such, energy modelling methods have evolved to the point of including higher-order physics, complex interconnected components and sub-systems. Despite advances in computer capacity, the cost of generating and running complex energy simulations makes it impractical to rely exclusively on such higher fidelity energy modelling for exploring a large set of design alternatives. This challenge of exploring a large set of alternatives efficiently might be overcome by using surrogate models to generalize across the large design space from an evaluation of a sparse subset of design alternatives by higher fidelity energy modelling or by using a set of multi-fidelity models in combination to efficiently evaluate the design space. Given there exists a variety of building energy modelling methods for energy estimation, multi-fidelity modelling could be a promising approach for broad exploration of design spaces to identify sustainable building designs. Hence, this study investigates energy estimates from three energy modelling methods (modified bin, degree day, EnergyPlus) over a range of design variables and climatic regions. The goal is to better understand how their outputs compare to each other and whether they might be suitable for a multi-fidelity modelling approach. The results show that modified bin and degree day methods yield energy use estimates of similar magnitude to each other but are typically higher than results from EnergyPlus. The differences in the results were traced, as expected, to the heating and cooling end-uses, and specifically to the heat gain and heat loss through opaque (i.e., walls, floors, roofs) and window surfaces. The observed trends show the potential for these methods to be used for multi-fidelity modelling, thereby allowing building designers to broadly consider and compare more design alternatives earlier in the design process

EFFECTIVENESS OF EX-SITU HEAT TREATMENT OF L-PBF AM 17-4PH STAINLESS STEEL SPECIMENS INTENTIONALLY EXPOSED TO DIFFERENT AS-BUILT THERMAL HISTORIES

The presented research demonstrates the effectiveness of H900 heat treatment in eliminating microstructural and mechanical property differences between additively manufactured 17-4PH stainless steel samples of varying thermal histories. For this effort, 17-4PH stainless steel was manufactured using laser-based powder bed fusion on an EOS M280 machine in two geometries: ASTM Standard E8 subsize rectangular tensile specimen geometry with thicknesses of 2mm and 6mm. Thermal histories were manipulated by adding secondary laser passes on each layer at varying levels of reduced power. All samples were heat treated after the build following H900 procedures. Mechanical performance was evaluated with uniaxial quasi-static tensile testing and Vickers microhardness measurements. Metallography was examined qualitatively with optical and electron microscopy as well as quantitatively through electron backscatter diffraction. No statistically significant mechanical property or microstructural differences were discovered, suggesting a successful ex-situ heat treatment.Mechanical Engineerin