Design evolution of the orbiter reaction control subsystem

The challenges of space shuttle orbiter reaction control subsystem development began with selection of the propellant for the subsystem. Various concepts were evaluated before the current Earth storable, bipropellant combination was selected. Once that task was accomplished, additional challenges of designing the system to satisfy the wide range of requirements dictated by operating environments, reusability, and long life were met. Verification of system adequacy was achieved by means of a combination of analysis and test. The studies, the design efforts, and the test and analysis techniques employed in meeting the challenges are described

No-go theorem for bimetric gravity with positive and negative mass

We argue that the most conservative geometric extension of Einstein gravity describing both positive and negative mass sources and observers is bimetric gravity and contains two copies of standard model matter which interact only gravitationally. Matter fields related to one of the metrics then appear dark from the point of view of an observer defined by the other metric, and so may provide a potential explanation for the dark universe. In this framework we consider the most general form of linearized field equations compatible with physically and mathematically well-motivated assumptions. Using gauge-invariant linear perturbation theory, we prove a no-go theorem ruling out all bimetric gravity theories that, in the Newtonian limit, lead to precisely opposite forces on positive and negative test masses.Comment: 19 pages, no figures, journal versio

Multimetric extension of the PPN formalism: experimental consistency of repulsive gravity

Recently we discussed a multimetric gravity theory containing several copies of standard model matter each of which couples to its own metric tensor. This construction contained dark matter sectors interacting repulsively with the visible matter sector, and was shown to lead to cosmological late-time acceleration. In order to test the theory with high-precision experiments within the solar system we here construct a simple extension of the parametrized post-Newtonian (PPN) formalism for multimetric gravitational backgrounds. We show that a simplified version of this extended formalism allows the computation of a subset of the PPN parameters from the linearized field equations. Applying the simplified formalism we find that the PPN parameters of our theory do not agree with the observed values, but we are able to improve the theory so that it becomes consistent with experiments of post-Newtonian gravity and still features its promising cosmological properties.Comment: 19 pages, no figures, journal versio

Non-linear MPC for winding loss optimised torque control of anisotropic PMSM

For a non-linear anisotropic permanent magnet synchronous machine (PMSM), a prediction model for model predictive control (MPC) considering effects like cross-coupling and saturation is developed in a straight forward procedure. The objective of the designed MPC is either tracking of reference currents or torque tracking. Both approaches use the projected fast gradient method (PFGM) as optimisation algorithm. The latter approach makes look-up-tables for current references obsolete and additionally minimises winding losses. This two approaches are compared in a simulation study with a state of the art PI controller

Propagation of gravitational waves in multimetric gravity

We discuss the propagation of gravitational waves in a recently discussed class of theories containing N >= 2 metric tensors and a corresponding number of standard model copies. Using the formalism of gauge-invariant linear perturbation theory we show that all gravitational waves propagate at the speed of light. We then employ the Newman-Penrose formalism to show that two to six polarizations of gravitational waves may exist, depending on the parameters entering the equations of motion. This corresponds to E(2) representations N_2, N_3, III_5 and II_6. We finally apply our general discussion to a recently presented concrete multimetric gravity model and show that it is of class N_2, i.e., it allows only two tensor polarizations, as it is the case for general relativity. Our results provide the theoretical background for tests of multimetric gravity theories using the upcoming gravitational wave experiments.Comment: 21 pages, no figures, journal versio

Auditory reafferences: The influence of real-time feedback on movement control

© 2015 Kennel, Streese, Pizzera, Justen, Hohmann and Raab. Auditory reafferences are real-time auditory products created by a person's own movements. Whereas the interdependency of action and perception is generally well studied, the auditory feedback channel and the influence of perceptual processes during movement execution remain largely unconsidered. We argue that movements have a rhythmic character that is closely connected to sound, making it possible to manipulate auditory reafferences online to understand their role in motor control. We examined if step sounds, occurring as a by-product of running, have an influence on the performance of a complex movement task. Twenty participants completed a hurdling task in three auditory feedback conditions: a control condition with normal auditory feedback, a white noise condition in which sound was masked, and a delayed auditory feedback condition. Overall time and kinematic data were collected. Results show that delayed auditory feedback led to a significantly slower overall time and changed kinematic parameters. Our findings complement previous investigations in a natural movement situation with non-artificial auditory cues. Our results support the existing theoretical understanding of action-perception coupling and hold potential for applied work, where naturally occurring movement sounds can be implemented in the motor learning processes

Health-related motor testing of children in primary school: A systematic review of criterion-referenced standards

Being physically fit in younger years prevents several diseases in the presence as well as in the life course. Therefore, monitoring physical fitness and motor competence through motor testing is essential for determining developmental status and identifying health-related risks. The main objectives of this systematic review were (1) to identify currently available health-related criterion-referenced standards and cut-off points for physical fitness and motor competence test items, (2) to frame the methodological background on setting health-related criterion-referenced standards and (3) to give implications for a health-related evaluation system for physical fitness and motor competence tests. The electronic data base search (PubMed, Web of Science and SURF) yielded 2062 records in total and identified six empirical studies reporting cut-off points of motor test items for children (7–10 years), as well as 30 methodological papers discussing determination approaches to health-related criterion-referenced standards. Data collection, selection and analyses followed the PRISMA guidelines. Health-related motor test standards need to be gender- and age-specific but should refer to an absolute cut-off point rather than to relative performance in the reference group. Due to the lack of data on health-related criterion referenced standards, receiver-operating-characteristic (ROC) curves provide a tool for the determination of cut-off points and criterion referenced standards for physical fitness and motor competence tests. A standardized approach forms the fundamental base for a globally applicable evaluation of health-related fitness tests

Non-invasive genetic approaches for estimation of ungulate population size: a study on roe deer (Capreolus capreolus) based on faeces

Estudios genéticos no invasivos, para la estimación del tamaño de una población de ungulados: estudio sobre el corzo (Capreolus capreolus) basado en sus heces La estimación de los tamaños de población es particularmente difícil en las especies de animales que viven en hábitats de vegetación densa, en la que se pueden mimetizar. Este es el caso del corzo, al igual que el de muchos otros ungulados. Nuestro objetivo fue desarrollar una aproximación genética no invasiva de captura–marcado–recaptura basada en las heces de corzo recogidas a lo largo de transectos. En un estudio piloto, recogimos 1.790 heces de corzo durante cinco días de muestreo en un área de estudio boscosa en el sudoeste de Alemania. Extrajimos el ADN de 410 de dichas muestras y llevamos a cabo un análisis de microsatélites utilizando siete marcadores de dinucleótidos. Los análisis tuvieron como resultado 328 genotipos consenso, que se asignaron a 174 individuos. La población estimada usando el enfoque bayesiano fue de 94 (82–111) machos y 136 (121–156) hembras. Nuestro estudio demuestra que los métodos genéticos no invasivos constituyen una herramienta de gestión muy valiosa para el corzo.Estudios genéticos no invasivos, para la estimación del tamaño de una población de ungulados: estudio sobre el corzo (Capreolus capreolus) basado en sus heces La estimación de los tamaños de población es particularmente difícil en las especies de animales que viven en hábitats de vegetación densa, en la que se pueden mimetizar. Este es el caso del corzo, al igual que el de muchos otros ungulados. Nuestro objetivo fue desarrollar una aproximación genética no invasiva de captura–marcado–recaptura basada en las heces de corzo recogidas a lo largo de transectos. En un estudio piloto, recogimos 1.790 heces de corzo durante cinco días de muestreo en un área de estudio boscosa en el sudoeste de Alemania. Extrajimos el ADN de 410 de dichas muestras y llevamos a cabo un análisis de microsatélites utilizando siete marcadores de dinucleótidos. Los análisis tuvieron como resultado 328 genotipos consenso, que se asignaron a 174 individuos. La población estimada usando el enfoque bayesiano fue de 94 (82–111) machos y 136 (121–156) hembras. Nuestro estudio demuestra que los métodos genéticos no invasivos constituyen una herramienta de gestión muy valiosa para el corzo.Estimating population size is particularly difficult for animal species living in concealing habitats with dense vegetation. This is the case for roe deer as for many other ungulates. Our objective was to develop a non–invasive genetic capture–mark–recapture approach based on roe deer faeces collected along transects. In a pilot study, we collected 1,790 roe deer faeces during five sampling days in a forested study area in south western Germany. We extracted DNA from 410 of these samples and carried out microsatellite analysis using seven dinucleotide markers. The analyses resulted in 328 useable consensus genotypes which were assigned to 174 individuals. The population size estimated using a Bayesian approach was 94 (82–111) male and 136 (121–156) female roe deer. Our study shows that non–invasive genetic methods are a valuable management tool for roe deer