Actuators for a space manipulator

The robotic manipulator can be decomposed into distinct subsytems. One particular area of interest of mechanical subsystems is electromechanical actuators (or drives). A drive is defined as a motor with an appropriate transmission. An overview is given of existing, as well as state-of-the-art drive systems. The scope is limited to space applications. A design philosophy and adequate requirements are the initial steps in designing a space-qualified actuator. The focus is on the d-c motor in conjunction with several types of transmissions (harmonic, tendon, traction, and gear systems). The various transmissions will be evaluated and key performance parameters will be addressed in detail. Included in the assessment is a shuttle RMS joint and a MSFC drive of the Prototype Manipulator Arm. Compound joints are also investigated. Space imposes a set of requirements for designing a high-performance drive assembly. Its inaccessibility and cryogenic conditions warrant special considerations. Some guidelines concerning these conditions are present. The goal is to gain a better understanding in designing a space actuator

Sensitivity of comorbidity network analysis.

Objectives: Comorbidity network analysis (CNA) is a graph-theoretic approach to systems medicine based on associations revealed from disease co-occurrence data. Researchers have used CNA to explore epidemiological patterns, differentiate populations, characterize disorders, and more; but these techniques have not been comprehensively evaluated. Our objectives were to assess the stability of common CNA techniques. Materials and Methods: We obtained seven co-occurrence data sets, most from previous CNAs, coded using several ontologies. We constructed comorbidity networks under various modeling procedures and calculated summary statistics and centrality rankings. We used regression, ordination, and rank correlation to assess these properties\u27 sensitivity to the source of data and construction parameters. Results: Most summary statistics were robust to variation in link determination but somewhere sensitive to the association measure. Some more effectively than others discriminated among networks constructed from different data sets. Centrality rankings, especially among hubs, were somewhat sensitive to link determination and highly sensitive to ontology. As multivariate models incorporated additional effects, comorbid associations among low-prevalence disorders weakened while those between high-prevalence disorders shifted negative. Discussion: Pairwise CNA techniques are generally robust, but some analyses are highly sensitive to certain parameters. Multivariate approaches expose additional conceptual and technical limitations to the usual pairwise approach. Conclusion: We conclude with a set of recommendations we believe will help CNA researchers improve the robustness of results and the potential of follow-up research

Management Innovations for Resilient Public Rangelands: Adoption Constraints and Considerations for Interagency Diffusion

Maintaining healthy rangeland ecosystems requires adaptive co-management at the landscape scale. Because the majority of western rangelands are publicly owned, it is critical that federal land management agencies work together in generating and sharing information. Promotion and communication of rangeland management innovations among agencies is one means of sharing information. Two rangeland management innovations, the Weather-Centric Restoration Tool and Interpreting Indicators of Rangeland Health, were studied in order to better understand agency adoption decisions and barriers to diffusion of the innovations across agencies. Using a mixed qualitative methodology, we interviewed land managers across the floristic Great Basin and in southeastern Utah responsible for making or advising rangeland management decisions. Using thematic analysis of participant interviews and land managers’ social networks in southeastern Utah, we were able to identify variables at the innovation, individual, organization, and external system levels that affect innovation adoption and diffusion across agencies. In line with previous research, desirable innovation traits were related to five constructs: complexity, relative advantage, compatibility, trialability, and observability. Interagency siloing was found to be the biggest factor affecting individual and organization-level adoption decisions. External sociopolitical factors were also found to create organization-level barriers including funding streams, legal considerations, and differing institutional cultures between agencies. While management innovations are hindered by these hurdles, innovations also serve as promoters of institutional change that reshape these constraints. However, overcoming barriers to innovation requires the presence of innovation champions who can influence both incremental bottom-up and top-down processes

Reaction-controlled diffusion: Monte Carlo simulations

We study the coupled two-species non-equilibrium reaction-controlled diffusion model introduced by Trimper et al. [Phys. Rev. E 62, 6071 (2000)] by means of detailed Monte Carlo simulations in one and two dimensions. Particles of type A may independently hop to an adjacent lattice site provided it is occupied by at least one B particle. The B particle species undergoes diffusion-limited reactions. In an active state with nonzero, essentially homogeneous B particle saturation density, the A species displays normal diffusion. In an inactive, absorbing phase with exponentially decaying B density, the A particles become localized. In situations with algebraic decay rho_B(t) ~ t^{-alpha_B}, as occuring either at a non-equilibrium continuous phase transition separating active and absorbing states, or in a power-law inactive phase, the A particles propagate subdiffusively with mean-square displacement ~ t^{1-alpha_A}. We find that within the accuracy of our simulation data, \alpha_A = \alpha_B as predicted by a simple mean-field approach. This remains true even in the presence of strong spatio-temporal fluctuations of the B density. However, in contrast with the mean-field results, our data yield a distinctly non-Gaussian A particle displacement distribution n_A(x,t) that obeys dynamic scaling and looks remarkably similar for the different processes investigated here. Fluctuations of effective diffusion rates cause a marked enhancement of n_A(x,t) at low displacements |x|, indicating a considerable fraction of practically localized A particles, as well as at large traversed distances.Comment: Revtex, 19 pages, 27 eps figures include

Trusted CI Experiences in Cybersecurity and Service to Open Science

This article describes experiences and lessons learned from the Trusted CI project, funded by the US National Science Foundation to serve the community as the NSF Cybersecurity Center of Excellence. Trusted CI is an effort to address cybersecurity for the open science community through a single organization that provides leadership, training, consulting, and knowledge to that community. The article describes the experiences and lessons learned of Trusted CI regarding both cybersecurity for open science and managing the process of providing centralized services to a broad and diverse community.Comment: 8 pages, PEARC '19: Practice and Experience in Advanced Research Computing, July 28-August 1, 2019, Chicago, IL, US

Evolutionary Events in a Mathematical Sciences Research Collaboration Network

This study examines long-term trends and shifting behavior in the collaboration network of mathematics literature, using a subset of data from Mathematical Reviews spanning 1985-2009. Rather than modeling the network cumulatively, this study traces the evolution of the "here and now" using fixed-duration sliding windows. The analysis uses a suite of common network diagnostics, including the distributions of degrees, distances, and clustering, to track network structure. Several random models that call these diagnostics as parameters help tease them apart as factors from the values of others. Some behaviors are consistent over the entire interval, but most diagnostics indicate that the network's structural evolution is dominated by occasional dramatic shifts in otherwise steady trends. These behaviors are not distributed evenly across the network; stark differences in evolution can be observed between two major subnetworks, loosely thought of as "pure" and "applied", which approximately partition the aggregate. The paper characterizes two major events along the mathematics network trajectory and discusses possible explanatory factors.Comment: 30 pages, 14 figures, 1 table; supporting information: 5 pages, 5 figures; published in Scientometric

Brief of Tax Law Professors as \u3ci\u3eAmici Curiae\u3c/i\u3e in Support of Petitioner in \u3ci\u3eLoudoun County, Virginia v. Dulles Duty Free, LLC\u3c/i\u3e

Amici are professors of tax law at universities across the United States. As scholars and teachers, they have considered the doctrinal roots and practical consequences of judicial limits on state and local taxation. Amici join this brief solely on their own behalf and not as representatives of their universities. A full list of amici appears in the Appendix to this brief

Prenatal Stress and Risk of Febrile Seizures in Children: A Nationwide Longitudinal Study in Denmark

We aimed to examine whether exposure to prenatal stress following maternal bereavement is associated with an increased risk of febrile seizures. In a longitudinal population-based cohort study, we followed 1,431,175 children born in Denmark. A total of 34,777 children were born to women who lost a close relative during pregnancy or within 1 year before the pregnancy and they were included in the exposed group. The exposed children had a risk of febrile seizures similar to that of the unexposed children (hazard ratio (HR) 1.00, 95% CI 0.94–1.06). The HRs did not differ according to the nature or timing of bereavement. Our data do not suggest any causal link between exposure to prenatal stress and febrile seizures in childhood