Fault-tolerant system considerations for a redundant strapdown inertial measurement unit

The development and evaluation of a fault-tolerant system for the Redundant Strapdown Inertial Measurement Unit (RSDIMU) being developed and evaluated by the NASA Langley Research Center was continued. The RSDIMU consists of four two-degree-of-freedom gyros and accelerometers mounted on the faces of a semi-octahedron which can be separated into two halves for damage protection. Compensated and uncompensated fault-tolerant system failure decision algorithms were compared. An algorithm to compensate for sensor noise effects in the fault-tolerant system thresholds was evaluated via simulation. The effects of sensor location and magnitude of the vehicle structural modes on system performance were assessed. A threshold generation algorithm, which incorporates noise compensation and filtered parity equation residuals for structural mode compensation, was evaluated. The effects of the fault-tolerant system on navigational accuracy were also considered. A sensor error parametric study was performed in an attempt to improve the soft failure detection capability without obtaining false alarms. Also examined was an FDI system strategy based on the pairwise comparison of sensor measurements. This strategy has the specific advantage of, in many instances, successfully detecting and isolating up to two simultaneously occurring failures

Flight Gate Assignment with a Quantum Annealer

Optimal flight gate assignment is a highly relevant optimization problem from airport management. Among others, an important goal is the minimization of the total transit time of the passengers. The corresponding objective function is quadratic in the binary decision variables encoding the flight-to-gate assignment. Hence, it is a quadratic assignment problem being hard to solve in general. In this work we investigate the solvability of this problem with a D-Wave quantum annealer. These machines are optimizers for quadratic unconstrained optimization problems (QUBO). Therefore the flight gate assignment problem seems to be well suited for these machines. We use real world data from a mid-sized German airport as well as simulation based data to extract typical instances small enough to be amenable to the D-Wave machine. In order to mitigate precision problems, we employ bin packing on the passenger numbers to reduce the precision requirements of the extracted instances. We find that, for the instances we investigated, the bin packing has little effect on the solution quality. Hence, we were able to solve small problem instances extracted from real data with the D-Wave 2000Q quantum annealer.Comment: Updated figure

Lower bounds for nodal sets of eigenfunctions

We prove lower bounds for the Hausdorff measure of nodal sets of eigenfunctions.Comment: To appear in Communications in Mathematical Physics; revised to include two additional references and update bibliographic informatio

Lower bounds for nodal sets of Dirichlet and Neumann eigenfunctions

Let \phi\ be a Dirichlet or Neumann eigenfunction of the Laplace-Beltrami operator on a compact Riemannian manifold with boundary. We prove lower bounds for the size of the nodal set {\phi=0}.Comment: 7 page

Multi-Scale Imaging and Informatics Pipeline for In Situ Pluripotent Stem Cell Analysis

Human pluripotent stem (hPS) cells are a potential source of cells for medical therapy and an ideal system to study fate decisions in early development. However, hPS cells cultured in vitro exhibit a high degree of heterogeneity, presenting an obstacle to clinical translation. hPS cells grow in spatially patterned colony structures, necessitating quantitative single-cell image analysis. We offer a tool for analyzing the spatial population context of hPS cells that integrates automated fluorescent microscopy with an analysis pipeline. It enables high-throughput detection of colonies at low resolution, with single-cellular and sub-cellular analysis at high resolutions, generating seamless in situ maps of single-cellular data organized by colony. We demonstrate the tool's utility by analyzing inter- and intra-colony heterogeneity of hPS cell cycle regulation and pluripotency marker expression. We measured the heterogeneity within individual colonies by analyzing cell cycle as a function of distance. Cells loosely associated with the outside of the colony are more likely to be in G1, reflecting a less pluripotent state, while cells within the first pluripotent layer are more likely to be in G2, possibly reflecting a G2/M block. Our multi-scale analysis tool groups colony regions into density classes, and cells belonging to those classes have distinct distributions of pluripotency markers and respond differently to DNA damage induction. Lastly, we demonstrate that our pipeline can robustly handle high-content, high-resolution single molecular mRNA FISH data by using novel image processing techniques. Overall, the imaging informatics pipeline presented offers a novel approach to the analysis of hPS cells that includes not only single cell features but also colony wide, and more generally, multi-scale spatial configuration

Numerical stability of the method of Brownian configuration fields

We investigate numerical aspects of the Brownian configuration fields method, and in particular its numerical stability as the Weissenberg number increases. Our results show the method to be immune to the type of instability leading to numerical blowup in the simulation of macroscopic models. We discuss this finding in the light of the stability criterion proposed in Fattal et al. [R. Fattal, R. Kupferman, Time-dependent simulation of viscoelastic flows at high Weissenberg using the log-conformation representation, J. Non Newtonian Fluid Mech. 126 (2005) 23–37]

Small Satellite Design and Development for Precision Pointing Applications

The move towards miniaturizing satellites will not be based solely on scaling down with a commensurate reduction in capability. The real goal should be to maintain high functionality and ultimately to increase capability in a small, low cost package. Conventional remote imaging has been based on the design approach that to achieve high resolution images from space, the satellite designer is driven to large apertures, expensive and complex attitude and articulation control hardware, with large, heavy, and power intensive inertial sensors. Micro-class satellites when faced with precision pointing requirements have traditionally not used active control to improve pointing performance. This paper describes MicroSat, a three axis stabilized satellite design for precision pointing applications. The heart of the design is the optics and the pointing subsystems. MicroSat uses an integrated INS/GPS based attitude reference system with custom designed and fabricated reaction wheels for pointing control. Multiple units can be launched from a Pegasus class vehicle providing a once-per-day revisit of a designated area with one meter class resolution in the visible range. This paper describes the satellite concept design and the hardware ground test demonstration

I1. Inferring Species-­Richness and Species-turnover by Statistical Multiresolution Texture Analysis of Satellite Imagery

The quantification of species-richness and turnover is one of the most important tasks in monitoring ecosystems. This is both for guaranteeing ecosystem function, and to understand the linkages between natural and human stressors with species patterns. Wetland ecosystems, particularly water-controlled subtropical wetlands, are extremely sensitive to external changes, for example in rainfall and water management. The effect of these changes at the metacommunity level in space and time are still not well understood. We analyze interseasonal and interannual average species-richness and turnover of the Arthur R. Marshall Loxahatchee National Wildlife Refuge (\Water Conservation Area 1» in the Greater Everglades Ecosystem) in South Florida as a case-study for the application of a novel multispectral image analysis technique. We use a texture augmented procedure to analyze high resolution satellite images (Landsat) in order to detect texture changes of vegetation, soil, and water components. α- and β-diversity, which are observed to be independent, are estimated for the green-band by the Shannon entropy and by the Kullback-Leibler divergence respectively. Validation with observations about the evolution of vegetation patterns shows that the analysis predicts 73 % and 100 % of species-richness and turnover within the study-area from 1984 to 2011. The KL divergence is a better metric than the difference of Shannon entropy which captures 85 % of the species-turnover. This is because the KL divergence takes in account the pairwise interactions between vegetation communities in time. α- and β-diversity are positively correlated, and diversity is strongly correlated to the average annual rainfall. We found that changes in vegetation, soil and water are positively correlated and that the fluctuations of the Shannon entropy for each component in the wet-season are smaller than in the dry-season. However, the KL divergence better predicts the species-turnover in the wet-season. The Gaussian density function in texture characterization and the use of the KL divergence constitute a promising technique for monitoring spatiotemporal ecohydrological patterns with particular focus on species-richness and turnover. We envision relevant applications of the KL divergence to infer species-dissimilarity, which is the diversity in space. This is particularly important when historical data or continuous monitoring data are not available in order to detect and potentially anticipate the effects of natural and anthropic changes on ecosystem structure