1,720,994 research outputs found
Strategies to remove hydrological effects in continuous gravity time series
Full text linkMulti-annual gravity time series offer a unique, noninvasive way to monitor mass redistributions within the Earth. However, for non-hydrological purposes, gravity time series must be corrected from hydrological effects to properly quantify mass redistribution involved in other geodynamic processes, such as volcanic activities or sedimentation processes. Such a hydrological correction remains challenging. The objective of this work is to investigate various ways to remove hydrological effects from a 11-years long gravity time series acquired by a superconducting gravimeter (SG) located at the Onsala Space Observatory (Sweden). For that we use hydrological loading corrections distributed by the EOST loading service, and local in situ groundwater level measurements. The most efficient approaches correct up to 89% of the seasonal component of the hydrological signal in the gravity series. On the other hand, for that specific site, we observe local water redistributions at shorter time scales, hours to few days, have a negligible influence on the gravity time series
Arduino-based device for sensing urban air quality at high spatial resolution.
No full textInternational audienceUrban areas are severely exposed to man-made air pollution (motor vehicles, industry, heating. . . ), which threatensthe health of inhabitants of major cities. Quantifying precisely this pollution is therefore becoming an imperativeand air quality sensor networks are being installed in more and more agglomerations. However, most of thesenetworks monitor pollutants at a fixed location and data are interpolated to produce maps of air pollution. Giventhe extreme compartmentation of urban environments, essentially due to buildings, such interpolation may missthe fine scale heterogeneity of the pollutant distribution. Here I present a prototype of a portable Arduino-based airquality sensor coupled to a GNSS antenna that aims at being carried by pedestrians or bicyclists, hence acquiringair quality data all along their paths through the city. The sensor communicates data to the user’s phone for areal-time inspection of his own exposure to air pollution. Assuming several people use this device at the same timeacross the same city, all data could be quickly reanalyzed to provide high resolution spatio-temporal maps of airquality. The two main perspectives would then to 1) build a phone application that helps users to find the healthiestitinerary from one place to another and 2) developing data analysis schemes able to provide local and short-termprediction of the air quality
Contribution of gravimetry to the Taiwanese orogeny study
No full textL’étude des variations temporelles de pesanteur suscite un intérêt croissant en raison de l’amélioration de la précision des gravimètres et des ses nombreuses applications en géosciences. L’exploitation de cette méthode dans le domaine des études tectoniques, en particulier des processus d’orogenèse, trouve sa justification dans les transferts de masses et les déformations qui caractérisent la formation des chaînes de montagnes. Nous nous sommes intéressés aux variations temporelles de pesanteur qui existent à Taïwan, à partir de mesures de gravimétrie absolue et relative dans le sud de cette île. L’orogenèse taïwanaise, entretenue par la convergence rapide de la plaque de la mer des Philippines vers la plaque Eurasie, est en effet le siège de nombreux transferts de masses et de déformations importantes. Après avoir détaillé l’acquisition et le traitement des mesures gravimétriques que nous utilisons, nous constatons l’existence de variations temporelles significatives de la pesanteur à Taïwan, atteignant parfois plusieurs dizaines de microgals (un microgal vaut un cent-millionième de mètre par seconde carré). Nous considérons que trois phénomènes sont responsables de l’essentiel des variations de pesanteur mesurées : les mouvements verticaux du sol, l’hydrologie locale et les forts taux de sédimentation et d’érosion qui surviennent `a la suite de typhons. Leur séparation se fait à l’aide de données complémentaires issues d’autres méthodes (GPS, pluviométrie, observations de terrain). Nous montrons l’influence des mouvements verticaux du sol sur nos mesures, dans l’est et l’ouest de l’île, mais sans pouvoir conclure sur les redistributions de masses profondes qui les accompagnent, du fait de séries temporelles encore trop courtes. Nous relevons également l’utilité des mesures de pluviométrie pour expliquer les variations de pesanteur observées. Cependant leur valorisation rigoureuse dans l’étude du signal gravimétrique nécessite plus d’une campagne par an. Enfin nous identifions les transferts de masses, par érosion ou sédimentation, qui surviennent dans la chaîne centrale de Taïwan lors du passage de typhons. Nous estimons les auteurs de matériaux déposés ou érodés et proposons des améliorations d’acquisition pour mieux quantifier les volumes mobilisés.The rising interest in the study of temporal gravity changes is due to the improvements of gravimeters and to its usefulness in Earth sciences. Tectonic processes, especially mountain building, imply deformations and mass transfers. Consequently, this should lead to temporal gravity changes. Here we study the case of Taiwan mountain building, using both absolute and relative gravity data acquired in the south of this island. This study is motivated by the vigorous mass transfers and deformations which take place in Taiwan, as a result of the fast convergence of the Philippine sea plate toward the Eurasian plate. Once the acquisition and the processing of our gravity data has been performed, we observe significant gravity changes between surveys, up to tens of microgals (one microgal is one hundred-millionth of meter per second square). We suggest that three main processes are responsible for these gravity changes: vertical movements of the ground, local hydrology and the high erosion and sedimentation rates induced by typhoons. The separation of these effects is done jointly with the use of complementary data (GPS time series, rainfall measures, field observation). We especially show the influence of ground vertical movements on gravity changes in the east and in the west of Taiwan. Yet we do not get the mass transfer information, theoretically associated to this signal, because of the youth of our gravity time series. We also note how useful are the rainfall data to explain gravity changes at the first order. More frequent gravity measures are however needed to clearly demonstrate their benefits. To finish, we observe and quantify surface mass transfers which occur with landslides and debris flows, both triggered by typhoons. This is mainly observed in the central range of Taiwan and we suggest improvements to better quantify volumes of moved rocks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Loading-induced stress variation on active faults and seismicity modulation in the Kuril Islands-Japan region [Elektronisk resurs]
No full textThe Earth's crust experiences continual stress variations due to the loads of the ocean, atmosphere, and continental water. We investigate if these stress variations can influence the seismicity of the Kuril megathrust, a part of the subduction zone positioned between the Pacific and Okhotsk plates, in the Kuril Islands-Japan region. Using established fault geometries and loading-induced stress variations, we calculate monthly Coulomb stress change resulting from hydrological, atmospheric, and non-tidal ocean loads, as well as their combined effects, from 2005 to 2016. We subsequently compare these stress variations with the observed monthly seismic rate along the Kuril megathrust during the same period. Our analysis reveals a weak but statistically significant positive correlation between the multi-loading-induced Coulomb stress changes and seismic activity, particularly in the shallow segment of the southern Kuril trench near Hokkaido island. This finding suggests that relatively small Coulomb stress changes, on the order of a few kPa, induced by surface loads, have the potential to locally trigger earthquakes within stressed fault systems. We also show that the summed contribution of atmospheric, non-tidal oceanic, and hydrological loads to this seismic triggering differs from the results obtained when taking each load separately. In addition, the relative contribution of each load to the Coulomb stress change varies as a function of time and space. Anticipating future studies, we emphasize the importance of extending the research throughout the entire study period and the interest in considering the cumulative impact of multiple loading sources when investigating their role in seismic activity
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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