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When L-band radio waves of space-based radio navigation systems such as Global Positioning System (GPS) travel through the atmosphere and ionosphere, their ray paths are bent and their travel time are increased as a result of refractive-index gradients. As the ionosphere is a dispersive medium the two GPS frequencies are subject to different delays in time and modifications in amplitude, phase and polarisation which is an effect of free electrons. By using these two radio frequencies one can derive information about the Total Electron Content integrated along the ray path. After calibration, these data are included into the tomographic reconstruction. The tomographic methode presented in this paper works on algebraic iterative methodes like SART and MART. Calculations are based on International GPS Service (IGS) ground received data. Space-based GPS is provided by LEO (Low Earth Orbiter) satellites like CHAMP. By means of incorporating such occultation data into tomography an improvement of reconstruction of the vertical structure of the electron density is expected. First confirming interpretations of a selected occulation event are presented in this paper. It is shown, that space-based GPS data can improve tomographic results mainly in middle to lower altitudes of the ionosphere. / Wenn sich Radiowellen eines Navigationssystemes, wie das des Global Positioning Systems (GPS), in der Atmosphäre und Ionosphäre ausbreiten, erfahren sie eine Beugung des Strahlweges und eine Erhöhung der Laufzeit aufgrund der Gradienten des atmosphärischen Refraktionsindexes. Da die Ionosphäre ein dispersives Medium darstellt, unterliegen beide GPS-Frequenzen dort unterschiedlichen Störungen in Laufzeit und Veränderungen in Amplitude, Phase und Polarisation, was auf die Effekt der freien Elektronen zurückzuführen ist. Unter der Verwendung der beiden Radiofrequenzen kann man Informationen über die Anzahl der über den Strahlweg integrierten Elektronen erhalten. Nach der Kalibrierung dieser Daten, können sie zur tomographischen Rekonstruktion verwendet werden. Die hier vorgestellte Tomographie verwendet algebraisch iterative Methoden, wie SART und MART. Die tomographischen Berechnungen bauen auf bodengestützte GPS-Daten des International GPS Services (IGS) und satellitengestützten GPS-Daten von LEO (Low earth orbiter) Satelliten wie CHAMP auf. Durch die Intergration von Okkultationsdaten in die Tomographie wird eine Verbesserung der Rekonstruktion der vertikalen Struktur der Elektronendichte erwartet. Erste bestätigende Interpretationen eines ausgewählten Okkultationsereignisses werden in diesem Artikel vorgeführt. Es wird gezeigt, dass satellitengestützte GPS-Daten die tomographischen Ergebnisse vorallem in der mittleren und unteren Ionosphäre verbessern können.

Neurologically normal individuals show a leftward spatial bias and tend to collide with objects on the right side more frequently than on the left. The upper visual field is associated with extrapersonal space, and mediated by the ventral stream through parvocellular projections. The lower visual field is associated with peripersonal space, and mediated by the dorsal stream through magnocellular projections. Upper and lower visual field differences have been observed in perceptual asymmetries but results have been mixed. Object- and space-based coordinates also both influence the leftward bias; however their relative contributions are unknown as similar spatial conditions are often collapsed across. More left-side collisions emerged on a route following task in the lower visual field and more right-side collisions were seen in the upper visual field (Thomas, Stuckel, Gutwin, & Elias, 2009). Left-handers made more right-side collisions in the central condition, whereas right-handers showed no bias. Leftward biases on the greyscales task were stronger in the lower visual field; however no distance-based differences were observed (Thomas & Elias, 2010). A stronger spatial bias was found on the greyscales task, whereas a stronger object-based bias was found on the object luminosity task (Thomas & Elias, in press). When individual spatial conditions were examined, the image chosen most often was always located in the lower field. Stimulus type and spatial location interacted to determine which coordinate type contributes more strongly to leftward biases. We also found that the leftward bias on the greyscales task was stronger in the lower visual field during prolonged presentation and in the upper visual field during brief presentation. A global motion task was created to preferentially engage magnocellular projections to the dorsal stream. Isoluminant red/green and blue/yellow colour tasks, which preferentially engage parvocellular projections to the ventral stream, were also created. Leftward biases were seen on the greyscales and motion tasks. On an isoluminant colour task, biases were significantly weakened, suggesting leftward biases exhibited by neurologically normal people are mediated by magnocellular projections to the dorsal stream and this preferential processing leads to a lower visual field advantage on the greyscales task.

Neurologically normal individuals show a leftward spatial bias and tend to collide with objects on the right side more frequently than on the left. The upper visual field is associated with extrapersonal space, and mediated by the ventral stream through parvocellular projections. The lower visual field is associated with peripersonal space, and mediated by the dorsal stream through magnocellular projections. Upper and lower visual field differences have been observed in perceptual asymmetries but results have been mixed. Object- and space-based coordinates also both influence the leftward bias; however their relative contributions are unknown as similar spatial conditions are often collapsed across. More left-side collisions emerged on a route following task in the lower visual field and more right-side collisions were seen in the upper visual field (Thomas, Stuckel, Gutwin, & Elias, 2009). Left-handers made more right-side collisions in the central condition, whereas right-handers showed no bias. Leftward biases on the greyscales task were stronger in the lower visual field; however no distance-based differences were observed (Thomas & Elias, 2010). A stronger spatial bias was found on the greyscales task, whereas a stronger object-based bias was found on the object luminosity task (Thomas & Elias, in press). When individual spatial conditions were examined, the image chosen most often was always located in the lower field. Stimulus type and spatial location interacted to determine which coordinate type contributes more strongly to leftward biases. We also found that the leftward bias on the greyscales task was stronger in the lower visual field during prolonged presentation and in the upper visual field during brief presentation. A global motion task was created to preferentially engage magnocellular projections to the dorsal stream. Isoluminant red/green and blue/yellow colour tasks, which preferentially engage parvocellular projections to the ventral stream, were also created. Leftward biases were seen on the greyscales and motion tasks. On an isoluminant colour task, biases were significantly weakened, suggesting leftward biases exhibited by neurologically normal people are mediated by magnocellular projections to the dorsal stream and this preferential processing leads to a lower visual field advantage on the greyscales task.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 100-105).

Cette thèse traite des dégradations induites par la pompe (photo-noircissement) et les radiations ionisantes externes (radio-noircissement) dans les fibres optiques en silice dopées ytterbium (FDY) utilisées en environnement sévère. Au travers de caractérisations expérimentales et de modélisations inédites, elle analyse leur interaction et en tire les conséquences quant à la tenue des FDY aux radiations sous pompe. La première partie porte sur l’identification des défauts induits (centres colorés) et leurs mécanismes de formation/guérison. Elle s’appuie sur un ensemble de caractérisations post-irradiation (RPE, ARI, TL) réalisées sur des échantillons de préformes et sur leur corrélation originale (guérison thermique, couplage TL et ARI). L’étude systématique en fonction de la composition met en évidence l’influence des co-dopants (Al, Ce) sur la capture des charges libérées lors des processus d’ionisation. La seconde partie analyse le noircissement se développant sous l’effet simultané de la pompe et de l’irradiation ionisante. A partir d’un banc de mesures autorisant le suivi de la dégradation en temps réel, on montre que photo- et radio-noircissements résultent des mêmes centres colorés blanchis par la pompe. Ce résultat, ajouté aux mécanismes préalablement identifiés, permet de proposer un modèle physique local de la dégradation photo-radio-induite. La confrontation des simulations issues de ce modèle à une large variété d’observations originales faites « en ligne » conduit à sa validation. Il est ainsi démontré que, pour des débits de dose inférieurs à une valeur critique, la dégradation des FDY pompées et irradiées ne peut excéder leur niveau de photo-noircissement. / This thesis deals with the degradation induced by the pump (photodarkening, PN) and ionizing radiations (radiodarkening, RN) in ytterbium-doped optical fiber (YDF) used in harsh environments. Through original experimental characterizations and modeling, it analyses the interplay between PN and RN and reveals important and novel properties of the radiation resistance of pumped YDF. The first part investigates induced defects (color centers) together with their creation/recovery mechanisms. It used a set of post-irradiation characterizations (ESR, RIA, TSL) conducted on preform samples and benefited from their original correlation (thermal recovery protocols coupling TSL and RIA). A systematic study as a function of composition reveals the influence of co-dopants (Al, Ce) on the trapping of carrier freed during ionization processes. The second part examines the darkening build-up under the simultaneous action of the pump and an ionizing irradiation. By using a measurement bench that allowed us to follow the real-time “on line” degradation of fiber samples, we showed that photo- and radio-darkening both arise from the same color centers that can be bleached by the pump. On the basis of this finding and of the preceding identified mechanisms, we propose a local physical model of the photo-radio-induced darkening. The latter is thoroughly validated by further successful comparisons of simulated degradation with a wide variety of “on line” original observations. Then, we notably demonstrate that for dose rates lying below a critical value (explicited by our theory), the degradation of pumped and irradiated YDF never exceeds the photo-darkening level.

When L-band radio waves of space-based radio navigation systems such as Global Positioning System (GPS) travel through the atmosphere and ionosphere, their ray paths are bent and their travel time are increased as a result of refractive-index gradients. As the ionosphere is a dispersive medium the two GPS frequencies are subject to different delays in time and modifications in amplitude, phase and polarisation which is an effect of free electrons. By using these two radio frequencies one can derive information about the Total Electron Content integrated along the ray path. After calibration, these data are included into the tomographic reconstruction. The tomographic methode presented in this paper works on algebraic iterative methodes like SART and MART. Calculations are based on International GPS Service (IGS) ground received data. Space-based GPS is provided by LEO (Low Earth Orbiter) satellites like CHAMP. By means of incorporating such occultation data into tomography an improvement of reconstruction of the vertical structure of the electron density is expected. First confirming interpretations of a selected occulation event are presented in this paper. It is shown, that space-based GPS data can improve tomographic results mainly in middle to lower altitudes of the ionosphere. / Wenn sich Radiowellen eines Navigationssystemes, wie das des Global Positioning Systems (GPS), in der Atmosphäre und Ionosphäre ausbreiten, erfahren sie eine Beugung des Strahlweges und eine Erhöhung der Laufzeit aufgrund der Gradienten des atmosphärischen Refraktionsindexes. Da die Ionosphäre ein dispersives Medium darstellt, unterliegen beide GPS-Frequenzen dort unterschiedlichen Störungen in Laufzeit und Veränderungen in Amplitude, Phase und Polarisation, was auf die Effekt der freien Elektronen zurückzuführen ist. Unter der Verwendung der beiden Radiofrequenzen kann man Informationen über die Anzahl der über den Strahlweg integrierten Elektronen erhalten. Nach der Kalibrierung dieser Daten, können sie zur tomographischen Rekonstruktion verwendet werden. Die hier vorgestellte Tomographie verwendet algebraisch iterative Methoden, wie SART und MART. Die tomographischen Berechnungen bauen auf bodengestützte GPS-Daten des International GPS Services (IGS) und satellitengestützten GPS-Daten von LEO (Low earth orbiter) Satelliten wie CHAMP auf. Durch die Intergration von Okkultationsdaten in die Tomographie wird eine Verbesserung der Rekonstruktion der vertikalen Struktur der Elektronendichte erwartet. Erste bestätigende Interpretationen eines ausgewählten Okkultationsereignisses werden in diesem Artikel vorgeführt. Es wird gezeigt, dass satellitengestützte GPS-Daten die tomographischen Ergebnisse vorallem in der mittleren und unteren Ionosphäre verbessern können.

This work presents on-orbit experiments conducted to validate SEU mitigation and detection techniques on FPGA devices and to measure SEU rates in FPGAs and SDRAM. These experiments were designed for the Cibola Flight Experiment Satellite (CFESat), which is an operational technology pathfinder satellite built around 9 Xilinx Virtex FPGAs and developed at Los Alamos National Laboratory. The on-orbit validation experiments described in this work have operated for over four thousand FPGA device days and have validated a variety of SEU mitigation and detection techniques including triple modular redundancy, duplication with compare, reduced precision redundancy, and SDRAM and FPGA block memory scrubbing. Regional SEU rates and the change in CFE's SEU rate over time show the measurable, expected effects of the South Atlantic Anomaly and the cycle of solar activity on CFE's SEU rates. The results of the on-orbit experiments developed for this work demonstrate that FPGA devices can be used to provide reliable, high-performance processing to space applications when proper SEU mitigation strategies are applied to the designs implemented on the FPGAs.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The transmission of high-rate telemetry data for space-based relay systems yields unique system requirements. The NASA Space-based Telemetry and Range-Safety (STARS) study evaluated system design requirements during Phase-1 flight tests. STARS Phase-2 efforts include the development of a high-rate transmitter and antenna system to demonstrate prototype system performance capabilities and new technologies for future operational systems to be incorporated into the NASA Next Generation Launch Technology (NGLT) vehicles. Phase-2 Range User (telemetry) system performance requirements and a prototype implementation approach are presented.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The use of remote ground stations for telemetry data-relay in space launch applications is costly and limits the geographic locations for launches of future Reusable Launch Vehicle (RLV) systems. The National Aeronautics and Space Administration Space-based Telemetry and Range-Safety (STARS) Study is investigating the use of satellite data relay systems as a replacement or supplement for ground-based tracking and relay stations. Phase-1 of STARS includes flight testing that evaluates satellite data-relay feasibility, defines satellite system performance limitations, and generates requirements for the development of future satellite telemetry data relay systems. STARS Phase-1 ground-test results and goals for the Phase-2 system development and flight-testing are also presented.