Error characterization of the Gaia astrometric solution II. Validating the covariance expansion model

Context. To use the data in the future Gaia catalogue it is important to have accurate estimates of the statistical uncertainties and correlations of the errors in the astrometric data given in the catalogue. Aims. In a previous paper we derived a mathematical model for computing the covariances of the astrometric data based on series expansions and a simplified attitude description. The aim of the present paper is to determine to what extent this model provides an accurate representation of the expected random errors in the astrometric solution for Gaia. Methods. We simulate the astrometric core solution by making least-squares solutions of the astrometric parameters for one million stars and the attitude parameters for a five-year mission, using nearly one billion simulated elementary observations for a total of 26 million unknowns. Two cases are considered: one in which all stars have the same magnitude, and another with 30% brighter and 70% fainter stars. The resulting astrometric errors are statistically compared with the model predictions. Results. In all cases considered, and within the statistical uncertainties of the numerical experiments (typically below 0.4%), the theoretically calculated variances and covariances are consistent with the simulations. To achieve this it is however necessary to expand the covariances to at least third or fourth order, and to apply a (theoretically motivated and derived) "fudge factor" in the kinematographic model. Conclusions. The model provides a feasible method to estimate the covariance of arbitrary astrometric data, accurate enough for most applications, and as such it should be available as part of the user's interface to the Gaia catalogue. A main assumption in the current model is that the observational errors are uncorrelated (e.g., photon noise), and further studies are needed on how correlated modelling errors, in particular in the attitude, can be taken into account

Briefing Paper: Open Access Mandate Support

This briefing paper describes the supporting mechanisms that institutions can put in place to enhance the effectiveness of an Open Access mandate. These supporting mechanisms include infrastructural and technological systems and institutional processes

Joint astrometric solution of Hipparcos and Gaia: A recipe for the Hundred Thousand Proper Motions project

The first release of astrometric data from Gaia is expected in 2016. It will contain the mean stellar positions and magnitudes from the first year of observations. For more than 100 000 stars in common with the Hipparcos Catalogue it will be possible to compute very accurate proper motions due to the time difference of about 24 years between the two missions. This Hundred Thousand Proper Motions (HTPM) project will be part of the first release. Our aim is to investigate how early Gaia data can be optimally combined with information from the Hipparcos Catalogue in order to provide the most accurate and reliable results for HTPM. The Astrometric Global Iterative Solution (AGIS) was developed to compute the astrometric core solution based on the Gaia observations and will be used for all releases of astrometric data from Gaia. We adapt AGIS to process Hipparcos data in addition to Gaia observations, and use simulations to verify and study the joint solution method. For the HTPM stars we predict proper motion accuracies between 14 and 134 muas/yr, depending on stellar magnitude and amount of Gaia data available. Perspective effects will be important for a significant number of HTPM stars, and in order to treat these effects accurately we introduce a scaled model of kinematics. We define a goodness-of-fit statistic which is sensitive to deviations from uniform space motion, caused for example by binaries with periods of 10-50 years. HTPM will significantly improve the proper motions of the Hipparcos Catalogue well before highly accurate Gaia- only results become available. Also, HTPM will allow us to detect long period binary and exoplanetary candidates which would be impossible to detect from Gaia data alone. The full sensitivity will not be reached with the first Gaia release but with subsequent data releases. Therefore HTPM should be repeated when more Gaia data become available.Comment: Revised manuscript following referee report. Accepted for publication in A&

Activity of Daily Living Trajectories Surrounding Acute Hospitalization of Long‐Stay Nursing Home Residents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101804/1/jgs12511.pd

Beamline Simulation for the NNBAR Experiment at the European Spallation Source

The HIBEAM and NNBAR experiments are a proposed fundamental science experiments at the European Spallation Source, performing high precision searches for neutron conversions in several baryon number violating (BNV) channels. For simulations of the NNBAR beamline, a new sampling method has been developed. The method is based on probability density evaluation and duct source biasing and enables the simulations of the entire NNBAR beamline with high statistics while also preserving correlations of the neutron tracks

Sensitivity of Arctic CH4_4 emissions to landscape wetness diminished by atmospheric feedbacks

Simulations using land surface models suggest future increases in Arctic methane emissions to be limited by the thaw-induced drying of permafrost landscapes. Here we use the Max Planck Institute Earth System Model to show that this constraint may be weaker than previously thought owing to compensatory atmospheric feedbacks. In two sets of extreme scenario simulations, a modification of the permafrost hydrology resulted in diverging hydroclimatic trajectories that, however, led to comparable methane fluxes. While a wet Arctic showed almost twice the wetland area compared with an increasingly dry Arctic, the latter featured greater substrate availability due to higher temperatures resulting from reduced evaporation, diminished cloudiness and more surface solar radiation. Given the limitations of present-day models and the potential model dependence of the atmospheric response, our results provide merely a qualitative estimation of these effects, but they suggest that atmospheric feedbacks play an important role in shaping future Arctic methane emissions

Structure and oxidation kinetics of the Si(100)-SiO2 interface

We present first-principles calculations of the structural and electronic properties of Si(001)-SiO2 interfaces. We first arrive at reasonable structures for the c-Si/a-SiO2 interface via a Monte-Carlo simulated annealing applied to an empirical interatomic potential, and then relax these structures using first-principles calculations within the framework of density-functional theory. We find a transition region at the interface, having a thickness on the order of 20\AA, in which there is some oxygen deficiency and a corresponding presence of sub-oxide Si species (mostly Si^+2 and Si^+3). Distributions of bond lengths and bond angles, and the nature of the electronic states at the interface, are investigated and discussed. The behavior of atomic oxygen in a-SiO2 is also investigated. The peroxyl linkage configuration is found to be lower in energy than interstitial or threefold configurations. Based on these results, we suggest a possible mechanism for oxygen diffusion in a-SiO2 that may be relevant to the oxidation process.Comment: 7 pages, two-column style with 6 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#ng_sio

New Results and Lessons Learned from the MOVE-II and MOVE-IIb CubeSats

This paper covers the operations and lessons learned for the MOVE-II and MOVE-IIb satellites. Both are 1U CubeSats, with their purpose being hands-on education for students of all technical fields related to aerospace. The hardware of the spacecraft consists of a commercial on-board computer and an electrical power system, while all other systems, including the software, were designed by the student team. The MOVE-II CubeSat was successfully launched on December 3rd, 2018 and remains active in orbit to this day with almost daily commanding. The operations were full of surprises that pre-launch simulations did not foresee. With on-orbit data, we were able to correlate thermal, electrical and attitude dynamics simulations, thus uncovering flaws in former assumptions. We present the evolution of key properties of the spacecraft over its lifetime, such as the internal battery resistance, temperature and hardware defects. Compared to the expected 23°C average temperature, the satellite is quite cold at 3°C average. Furthermore, it shows a tendency to spin up uncontrollably due to a current loop in the solar cell wiring. To replicate the real behavior with simulations, a thermal model and a solar cell wiring current loop were added to the model. We also corrected the internal resistance of the battery in the model from 0.42 Ω to 1.26 Ω and added a temperature dependency to the internal resistance. The tendency to spin up, combined with a tight power budget, has remained a problem since the beginning of on-orbit operations. Although the anomaly shows non-deterministic behavior, regular detumbling maneuvers keep the spacecraft at tumbling rates between 2.5°s−1 and 200°s−1. At low turn rates, we downloaded a significant amount of data from the attitude determination and control system, enabling us to calibrate the magnetometer on ground with data recorded and downlinked over a span of several months. Additionally, we were also able to conduct payload measurements. The MOVE-IIb CubeSat, which launched on July 5th 2019 from the Vostochny Cosmodrome, is a copy of MOVE-II with minor improvements to correct the flaws of its predecessor. Unfortunately, a signal strength of 15 dB less than MOVE-II hindered any practical operations but it has been confirmed as alive in space. As possible causes we analyzed our initial guesses of a faulty deployment of the solar panels and antennae but also a malfunction of the transmitter. With the lessons learned from the MOVE-II/IIb missions, critical mistakes can be avoided for future CubeSat missions. As part of these lessons learned, the most useful and most hindering features of the spacecraft and its ground infrastructure are discussed. Furthermore, the training routine for the Mission Control team and its changes over time are described. The impact of the COVID-19 pandemic on spacecraft operations is also discussed, including lessons learned for future missions. This paper takes a look at the evolution of this mission since 2018. It discusses new findings, degradation of the spacecraft, lessons-learned and operations of the CubeSats

Employing user-centered design and education sciences to inform training of diabetes survival skills

Background: Patients newly diagnosed with diabetes mellitus (diabetes), who require insulin must acquire diabetes “survival” skills prior to discharge home. COVID-19 revealed considerable limitations of traditional in-person, time-intensive delivery of diabetes education and survival skills training (diabetes survival skills training). Furthermore, diabetes survival skills training has not been designed to meet the specific learning needs of patients with diabetes and their caregivers, particularly if delivered by telehealth. The objective of the study was to identify and understand the needs of users (patients newly prescribed insulin and their caregivers) to inform the design of a diabetes survival skills training, specifically for telehealth delivery, through the application of user-centered design and adult learning and education principles. Methods: Users included patients newly prescribed insulin, their caregivers, and laypersons without diabetes. In semi-structured interviews, users were asked about experienced or perceived challenges in learning diabetes survival skills. Interviews were audio-recorded and transcribed. Investigators performed iterative rounds of coding of interview transcripts utilizing a constant comparative method to identify themes describing the dominant challenges users experienced. Themes were then mapped to adult learning and education principles to identify novel educational design solutions that can be applied to telehealth-based learning. Results: We interviewed 18 users: patients (N = 6, 33 %), caregivers (N = 4, 22 %), and laypersons (N = 8, 44 %). Users consistently described challenges in understanding diabetes survival skills while hospitalized; in preparing needed supplies to execute diabetes survival skills; and in executing diabetes survival skills at home. The challenges mapped to three educational strategies: (1) spiral learning; (2) repetitive goal directed practice and feedback, which have the potential to translate into design solutions supporting remote/virtual learning; and (3) form fits function organizer, which supports safe organization and use of supplies to execute diabetes survival skills independently. Conclusion: Learning complex tasks, such as diabetes survival skills, requires time, repetition, and continued support. The combination of a user-centered design approach to uncover learning needs as well as identification of relevant adult learning and education principles could inform the design of more user-centered, feasible, effective, and sustainable diabetes survival skills training for telehealth delivery.</p

Review and assessment of smartphone apps for forest restoration monitoring

With increased interest in forest restoration comes an urgent need to provide accurate, scalable, and cost‐effective monitoring tools. The ubiquity of smartphones has led to a surge in monitoring apps. We reviewed and assessed monitoring apps found through web searches and conversations with practitioners. We identified 42 apps that (1) automatically monitor indicators or (2) facilitate data entry. We selected the five most promising from the first category, based on their relevance, availability, stability, and user support. We compared them to traditional field techniques in a well‐studied restoration project in Costa Rica. We received further feedback from 15 collaborator organizations that evaluated these in their corresponding field restoration sites. Diameter measurements correlated well with traditional tape‐based measurements (R2 = 0.86–0.89). Canopy openness and ground cover showed weaker correlations to densiometer and quadrat cover measurements (R2 = 0.42–0.51). Apps did not improve labor efficiency but do preclude the purchase of specialized field equipment. The apps reviewed here need further development and validation to support monitoring adequately, especially in the tropics. Estimates of development and maintenance costs, as well as statistics on user uptake, are required for cost‐effective development. We recommend a coordinated effort to develop dedicated restoration monitoring apps that can speed up and standardize the collection of indicators and provide evidence on restoration outcomes alongside a centralized repository of this information