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Performance of miniaturized atomic clocks in static laboratory and dynamic flight environments / Ankit Jain in GPS solutions, vol 25 n° 1 (January 2021)
Titre : Performance of miniaturized atomic clocks in static laboratory and dynamic flight environments Type de document : Article/Communication Auteurs : Ankit Jain, Auteur ; Thomas Krawinkel, Auteur ; Steffen Schön, Auteur ; Andreas Bauch, Auteur Année de publication : 2021 Article en page(s) : 16 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] décalage d'horloge
[Termes IGN] fréquence
[Termes IGN] horloge atomique
[Termes IGN] horloge du récepteur
[Termes IGN] oscillateur
[Termes IGN] récepteur GNSS
[Termes IGN] stabilité
[Termes IGN] variance d'AllanRésumé : (auteur) Miniaturized atomic clocks with high frequency stability as local oscillators in global navigation satellite system (GNSS) receivers promise to improve real-time kinematic applications. For a number of years, such oscillators are being investigated regarding their overall technical applicability, i.e., transportability, and performance in dynamic environments. The short-term frequency stability of these clocks is usually specified by the manufacturer, being valid for stationary applications. Since the performance of most oscillators is likely degraded in dynamic conditions, various oscillators are tested to find the limits of receiver clock modeling in dynamic cases and consequently derive adequate stochastic models to be used in navigation. We present the performance of three different oscillators (Microsemi MAC SA.35m, Spectratime LCR-900 and Stanford Research Systems SC10) for static and dynamic applications. For the static case, all three oscillators are characterized in terms of their frequency stability at Physikalisch-Technische Bundesanstalt, Germany's national metrology institute. The resulting Allan deviations agree well with the manufacturer's data. Furthermore, a flight experiment was conducted in order to evaluate the performance of the oscillators under dynamic conditions. Here, each oscillator is replacing the internal oscillator of a geodetic-grade GNSS receiver and the stability of the receiver clock biases is determined. The time and frequency offsets of the oscillators are characterized with regard to the flight dynamics recorded by a navigation-grade inertial measurement unit. The results of the experiment show that the frequency stability of each oscillator is degraded by about at least one order of magnitude compared to the static case. Also, the two quartz oscillators show a significant g-sensitivity resulting in frequency shifts of − 1.2 × 10−9 and + 1.5 × 10−9, respectively, while the rubidium clocks are less sensitive, thus enabling receiver clock modeling and strengthening of the navigation performance even in high dynamics. Numéro de notice : A2021-003 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-020-01036-4 Date de publication en ligne : 13/10/2020 En ligne : https://doi.org/10.1007/s10291-020-01036-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96081
in GPS solutions > vol 25 n° 1 (January 2021) . - 16 p.[article]
Titre : Slope engineering Type de document : Monographie Auteurs : Ali Ismet Kanlı, Éditeur scientifique Editeur : London [UK] : IntechOpen Année de publication : 2021 Importance : 206 p. ISBN/ISSN/EAN : 978-1-83962-924-2 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image mixte
[Termes IGN] analyse diachronique
[Termes IGN] bande L
[Termes IGN] cartographie des risques
[Termes IGN] compréhension de l'image
[Termes IGN] effondrement de terrain
[Termes IGN] image Landsat
[Termes IGN] interféromètrie par radar à antenne synthétique
[Termes IGN] Normalized Difference Vegetation Index
[Termes IGN] pente
[Termes IGN] Pol-INSAR
[Termes IGN] prospection minérale
[Termes IGN] risque naturel
[Termes IGN] stabilité
[Termes IGN] télédétection en hyperfréquence
[Termes IGN] tunnelRésumé : (Editeur) The field of slope engineering encompasses slope stability analysis and design, movement monitoring, and slope safety management and maintenance. Engineers in this field are concerned with landslides and other gravity-stimulated mass movements. Their job is to frequently evaluate existing and proposed slopes to assess their stability. As such, this book provides information on remote sensing in landslide detection, tunnel face stability, stability analysis and maintenance of cut slopes, design techniques in rock and soil engineering, statistical models for landslide risk mapping, slope stability analysis in open-pit mines, ecological engineering for slope stabilization, and asphalt-stabilized strengthening in open-pit coal mining. Note de contenu : 1. Design and Construction for Tunnel Face Stability: Theoretical and Modeling Approach / Adel Aissi, Abdelghani Brikat, Ali Ismet Kanlı, Aissa Benselhoub and Oussama Kessal
2. Geoysynthetic Reinforced Embankment Slopes / Akshay Kumar Jha and Madhav Madhira
3. Design Techniques in Rock and Soil Engineering / Zahid Ur Rehman, Sajjad Hussain, Noor Mohammad, Akhtar Gul and Bushra Nawaz
4. Three Dimensional Slope Stability Analysis of Open Pit Mine / Masagus Ahmad Azizi, Irfan Marwanza, Muhammad Kemal Ghifari and Afiat Anugrahadi
5. Asphalt Fill Strengthening of Free Slip Surfaces of Shale Slopes in Asphaltite Open Quarry: Stability Analysis of Free Sliding Surface for Wet Shale Slopes in Avgamasya Asphaltite Open Quarry No 2. Site / Yildırım İsmail Tosun
6. The Potential of Remote Sensing to Assess Conditioning Factors for Landslide Detection at a Regional Scale: The Case in Southeastern Colombia / Nixon Alexander Correa-Muñoz and Carol Andrea Murillo-Feo
7. Comparative Evaluation of Various Statistical Models and Its Accuracy for Landslide Risk Mapping: A Case Study on Part of Himalayan Region, India / C. Prakasam, Aravinth R., Varinder S. Kanwar and B. Nagarajan
8. Integrated Analysis Method for Stability Analysis and Maintenance of Cut-Slope in Urban / Mincheol Park, Heuisoo Han and Yoonhwa Jin
9. Ecological Engineering Measures for Ravine Slope Stabilization and Its Sustainable Productive Utilization / Gaurav Singh, Raj Kumar, Dinesh Jinger and Dinesh DhakshanamoorthyNuméro de notice : 26761 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Recueil / ouvrage collectif DOI : 10.5772/intechopen.82508 Date de publication en ligne : 17/03/2021 En ligne : https://doi.org/10.5772/intechopen.82508 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=99819
Titre : Positioning stability improvement with inter-system biases on multi-GNSS PPP Type de document : Article/Communication Auteurs : Byung-Kyu Choi, Auteur ; Hasu Yoon, Auteur Année de publication : 2018 Article en page(s) : pp. 239 - 248 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement
[Termes IGN] affaiblissement géométrique de la précision
[Termes IGN] erreur systématique inter-systèmes
[Termes IGN] positionnement par GNSS
[Termes IGN] positionnement ponctuel précis
[Termes IGN] précision du positionnement
[Termes IGN] stabilitéRésumé : (auteur) The availability of multiple signals from different Global Navigation Satellite System (GNSS) constellations provides opportunities for improving positioning accuracy and initial convergence time. With dual-frequency observations from the four constellations (GPS, GLONASS, Galileo, and BeiDou), it is possible to investigate combined GNSS precise point positioning (PPP) accuracy and stability. The differences between GNSS systems result in inter-system biases (ISBs). We consider several ISB values such as GPS-GLONASS, GPS-Galileo, and GPS-BeiDou. These biases are compliant with key parameters defined in the multi-GNSS PPP processing. In this study, we present a unified PPP method that sets ISB values as fixed or constant. A comprehensive analysis that includes satellite visibility, position dilution of precision, position accuracy is performed to evaluate a unified PPP method with constrained cut-off elevation angles. Compared to the conventional PPP solutions, our approach shows more stable positioning at a constrained cut-off elevation angle of 50 degrees. Numéro de notice : A2018-432 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2018-0005 Date de publication en ligne : 05/04/2018 En ligne : https://doi.org/10.1515/jag-2018-0005 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90999
in Journal of applied geodesy > vol 12 n° 3 (July 2018) . - pp. 239 - 248[article]Optimisation discrète et indices de stabilité appliqués à la stéréoscopie en contexte routier / Mathias Paget (2018)
Titre : Optimisation discrète et indices de stabilité appliqués à la stéréoscopie en contexte routier Type de document : Thèse/HDR Auteurs : Mathias Paget Editeur : Champs/Marne : Université Paris-Est Année de publication : 2018 Note générale : bibliographie Langues : Français (fre) Descripteur : [Termes IGN] optimisation (mathématiques)
[Termes IGN] programmation dynamique
[Termes IGN] reconstruction 3D
[Termes IGN] stabilité
[Termes IGN] stéréoscopieIndex. décimale : THESE Thèses et HDR Résumé : (auteur) Les tâches réalisées en traitement d'image tendent à devenir de plus en plus complexes. Par exemple, dans le contexte routier, les systèmes d'aide à la conduite, (Advanced driver-assistance systems), visent à une automatisation complète de la tâche de conduite. L’évaluation de la fiabilité représente un enjeu important pour ce type d’application. Face à la difficulté des tâches à réaliser, les chaînes de traitements sont souvent divisées en de nombreuses étapes de calculs de sorte qu'il est difficile de caractériser les sorties de la chaîne en fonction des perturbations des entrées. Les étapes du traitement consistent le plus souvent en des problèmes formulés comme la minimisation d'une énergie. Cette énergie est généralement difficile à optimiser, ce qui nécessite la mise en œuvre de méthodes d’optimisation adaptées. Dans cette thèse, nous cherchons à caractériser la solution d’un traitement à partir des calculs réalisés au cours de l’étape d'optimisation. Cette approche nous a permis de proposer des indices de stabilité de la solution dans le cadre de deux méthodes d’optimisation discrètes : la coupure de graphe et la programmation dynamique. Tout d’abord, nous nous sommes intéressés au problème de la reconstruction stéréoscopique en contexte routier et au dé-bruitage, dans le cadre de l’optimisation par coupure de graphe. Les modèles issus de l’interprétation bayésienne amènent à optimiser des énergies qui ne peuvent pas être traitées avec les schémas d’optimisation classiques par fusion binaire. Nous avons proposé un schéma adapté qui met en jeu des fusions binaires par expansion et par saut. L’application de ce schéma aux problèmes de la reconstruction stéréoscopique et au dé-bruitage, nous a permis d’obtenir des solutions possédant les caractéristiques que nous recherchions : des contours d’objets nets et des dégradés progressifs dans les zones homogènes. Ensuite, dans le contexte de la programmation dynamique, nous avons réinterprété l’a priori mis en jeu dans la méthode de reconstruction Semi-Global Matching ainsi que certaines de ses variantes. Nous avons proposé d’ajouter un paramètre à ces méthodes afin de modifier les directions privilégiées par l’a priori. Enfin, nous avons proposé des indices de stabilité de la solution dans le cadre de la coupure de graphe et de la programmation dynamique. La prise en compte de ces indices, dans une étape de raffinement des solutions, permet une amélioration des résultats. Numéro de notice : 17677 Affiliation des auteurs : non IGN Thématique : IMAGERIE/MATHEMATIQUE Nature : Thèse française Organisme de stage : LEPSIS - Laboratoire Exploitation, Perception, Simulateurs et Simulations En ligne : https://tel.archives-ouvertes.fr/tel-01800049/document Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=98015
Titre : Biodiversity effects on ecosystem functioning in a 15-year grassland experiment: patterns, mechanisms, and open questions Type de document : Article/Communication Auteurs : Wolfgang W. Weisser, Auteur ; Christiane Roscher, Auteur ; Sebastian Meyer, Auteur ; et al., Auteur Année de publication : 2017 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Ecologie
[Termes IGN] azote
[Termes IGN] biomasse
[Termes IGN] carbone
[Termes IGN] écosystème
[Termes IGN] gaz à effet de serre
[Termes IGN] nutriment végétal
[Termes IGN] placette d'échantillonnage
[Termes IGN] potassium
[Termes IGN] puits de carbone
[Termes IGN] richesse floristique
[Termes IGN] sol
[Termes IGN] stabilitéRésumé : (auteur) In the past two decades, a large number of studies have investigated the relationship between biodiversity and ecosystem functioning, most of which focussed on a limited set of ecosystem variables. The Jena Experiment was set up in 2002 to investigate the effects of plant diversity on element cycling and trophic interactions, using a multi-disciplinary approach. Here, we review the results of 15 years of research in the Jena Experiment, focussing on the effects of manipulating plant species richness and plant functional richness. With more than 85,000 measures taken from the plant diversity plots, the Jena Experiment has allowed answering fundamental questions important for functional biodiversity research.
First, the question was how general the effect of plant species richness is, regarding the many different processes that take place in an ecosystem. About 45% of different types of ecosystem processes measured in the ‘main experiment’, where plant species richness ranged from 1 to 60 species, were significantly affected by plant species richness, providing strong support for the view that biodiversity is a significant driver of ecosystem functioning. Many measures were not saturating at the 60-species level, but increased linearly with the logarithm of species richness. There was, however, great variability in the strength of response among different processes. One striking pattern was that many processes, in particular belowground processes, took several years to respond to the manipulation of plant species richness, showing that biodiversity experiments have to be long-term, to distinguish trends from transitory patterns. In addition, the results from the Jena Experiment provide further evidence that diversity begets stability, for example stability against invasion of plant species, but unexpectedly some results also suggested the opposite, e.g. when plant communities experience severe perturbations or elevated resource availability. This highlights the need to revisit diversity-stability theory.
Second, we explored whether individual plant species or individual plant functional groups, or biodiversity itself is more important for ecosystem functioning, in particular biomass production. We found strong effects of individual species and plant functional groups on biomass production, yet these effects often occurred mostly in addition to, but not instead of, effects of plant species richness.
Third, the Jena Experiment assessed the effect of diversity on multitrophic interactions. The diversity of most organisms responded positively to increases in plant species richness, and the effect was stronger for above- than for belowground organisms, and stronger for herbivores than for carnivores or detritivores. Thus, diversity begets diversity. In addition, the effect on organismic diversity was stronger than the effect on species abundances.
Fourth, the Jena Experiment aimed to assess the effect of diversity on N, P and C cycling and the water balance of the plots, separating between element input into the ecosystem, element turnover, element stocks, and output from the ecosystem. While inputs were generally less affected by plant species richness, measures of element stocks, turnover and output were often positively affected by plant diversity, e.g. carbon storage strongly increased with increasing plant species richness. Variables of the N cycle responded less strongly to plant species richness than variables of the C cycle.
Fifth, plant traits are often used to unravel mechanisms underlying the biodiversity-ecosystem functioning relationship. In the Jena Experiment, most investigated plant traits, both above- and belowground, were plastic and trait expression depended on plant diversity in a complex way, suggesting limitation to using database traits for linking plant traits to particular functions.
Sixth, plant diversity effects on ecosystem processes are often caused by plant diversity effects on species interactions. Analyses in the Jena Experiment including structural equation modelling suggest complex interactions that changed with diversity, e.g. soil carbon storage and greenhouse gas emission were affected by changes in the composition and activity of the belowground microbial community. Manipulation experiments where particular organisms, e.g. belowground invertebrates, were excluded from plots in split-plot experiments, supported the important role of the biotic component for element and water fluxes.
Seventh, the Jena Experiment aimed to put the results into the context of agricultural practices in managed grasslands. The effect of increasing plant species richness from 1 to 16 species on plant biomass was, in absolute terms, as strong as the effect of a more intensive grassland management, using fertiliser and increasing mowing frequency. Potential bioenergy production from high-diversity plots was similar to that of conventionally used energy crops. These results suggest that diverse ‘High Nature Value Grasslands’ are multifunctional and can deliver a range of ecosystem services including production-related services.
A final task was to assess the importance of potential artefacts in biodiversity–ecosystem functioning relationships, caused by the weeding of the plant community to maintain plant species composition. While the effort (in hours) needed to weed a plot was often negatively related to plant species richness, species richness still affected the majority of ecosystem variables. Weeding also did not negatively affect monoculture performance; rather, monocultures deteriorated over time for a number of biological reasons, as shown in plant-soil feedback experiments.
To summarize, the Jena Experiment has allowed for a comprehensive analysis of the functional role of biodiversity in an ecosystem. A main challenge for future biodiversity research is to increase our mechanistic understanding of why the magnitude of biodiversity effects differs among processes and contexts. It is likely that there will be no simple answer. For example, among the multitude of mechanisms suggested to underlie the positive plant species richness effect on biomass, some have received limited support in the Jena Experiment, such as vertical root niche partitioning. However, others could not be rejected in targeted analyses. Thus, from the current results in the Jena Experiment it seems likely that the positive biodiversity effect results from several mechanisms acting simultaneously in more diverse communities, such as reduced pathogen attack, the presence of more plant growth promoting organisms, less seed limitation, and increased trait differences leading to complementarity in resource uptake. Distinguishing between different mechanisms requires careful testing of competing hypotheses. Biodiversity research has matured such that predictive approaches testing particular mechanisms are now possible.Numéro de notice : A2017-352 Affiliation des auteurs : non IGN Thématique : BIODIVERSITE/FORET Nature : Article DOI : 10.1016/j.baae.2017.06.002 Date de publication en ligne : 26/06/2017 En ligne : https://doi.org/10.1016/j.baae.2017.06.002 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85690
in Basic and Applied Ecology > vol 23 (September 2017)[article]
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