131,368 research outputs found
Generalized Stable Multivariate Distribution and Anisotropic Dilations
No full textSchertzer, D.; Larchevêque, M.; Duan, J.; Lovejoy, S.. (1999). Generalized Stable Multivariate Distribution and Anisotropic Dilations. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/3388
Fractional Fokker-Planck equation for nonlinear stochastic differential equations driven by non-Gaussian Levy stable noises
No full textSchertzer, D.; Larchevêque, M.; Duan, J.; Yanovsky, V.V.; Lovejoy, S.. (1999). Fractional Fokker-Planck equation for nonlinear stochastic differential equations driven by non-Gaussian Levy stable noises. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/3387
Symmetries and stochastic symmetry breaking in multifractal geophysics: analysis and simulation with the help of the Lévy-Clifford algebra of cascade generators
No full textInternational audienceMultifractal fields, whose definition is rather independent of their domain dimension, have opened a new approach of geophysics enabling to explore its spatial extension that is of prime importance as underlined by the expression “spatial chaos”. However multifractals have been until recently restricted to be scalar valued, i.e. to one-dimensional codomains. This has prevented to deal with the key question of complex component interactions and their non trivial symmetries.We first emphasize that the Lie algebra of stochastic generators of cascade processes enables us to generalize multifractals to arbitrarily large codomains, e.g. flows of vector fields on large dimensional manifolds. In particular, we have recently investigated the neat example of stable Levy generators on Clifford algebra that have a number of seductive properties, e.g. universal statistical and robust algebra properties, both defining the basic symmetries of the corresponding fields (Schertzer and Tchiguirinskaia, 2015). These properties provide a convenient multifractal framework to study both the symmetries of the fields and how they stochastically break the symmetries of the underlying equations due to boundary conditions, large scale rotations and forcings. These developments should help us to answer to challenging questions such as the climatology of (exo-) planets based on first principles (Pierrehumbert, 2013), to fully address the question of the limitations of quasi- geostrophic turbulence (Schertzer et al., 2012) and to explore the peculiar phenomenology of turbulent dynamics of the atmosphere or oceans that is neither two- or three-dimensional.Pierrehumbert, R.T., 2013. Strange news from other stars. Nature Geoscience, 6(2), pp.8183.Schertzer, D. et al., 2012. Quasi-geostrophic turbulence and generalized scale invariance, a theoretical reply. Atmos. Chem. Phys., 12, pp.327336.Schertzer, D. & Tchiguirinskaia, I., 2015. Multifractal vector fields and stochastic Clifford algebra. Chaos: An Interdisciplinary Journal of Nonlinear Science, 25(12), p.12312
Und Scheffler Verstummet/ und sprach. das ist L. Johann Adam Scherzers P.P. Kurtze Anmerckungen/ Uber den Abdruck eines Send-Schreibens/ Darinnen ihme D. Joh. Scheffler antwortet: Er wolle auff seine Deduction-Schrifft stillschweigen
No full textNicht identisch mit VD17 12:154460D (dort 1644 als Erscheinungsjahr auf dem Titelblatt) und VD17 23:237405M (dort z.B. "Schertzers" und "ihm" im Titel und "Abdruck eines Send-Schreibens ..." beim komm. Werk)Vorlageform des Erscheinungsvermerks: Gedruckt in Leipzig/ Anno 1664. - Kommentiertes Werk: Verfertiget zur Neiß/ im Jahr Christi M.DC.LXIV.Enth.: Abdruck eines Sendschreibens D. Johannis Schefflers der Heil. Röm. Kirchen-Priesters/ a Die b verläumbderische Schmäh-Karte bedreffende/ Welche Johann Adam Schertzer/ der Heil. Schrifft Licentiät c (wie er sich schreibt) Wieder dessen Türcken-Schrifft außgeworffen ha
Multifractal analysis and simulation of Chernobyl radioactive fall-out in Europe
No full textMultifractal application to the description of the geographic distribution of radioactive contamination over Europe, generated by the Chernobyl nuclear acciden
Single and multiscale remote sensing techniques, multifractals and MODIS derived vegetation and soil moisture
No full textScaling processes are increasingly understood to be the result of nonlinear dynamic mechanisms repeating scale after scale from large to small scales leading to nonclassical resolution dependencies. This means that the statistical properties systematically vary in strong, power-law ways with the resolution. When present in geophysical and remotely sensed fields, it implies that when classical (single-scale) remote sensing algorithms are used to determine surrogates of various geophysical fields, they can at most be correct at the unique (and subjective) calibration resolution. Scaling analysis and modeling techniques were applied to MODIS TERRA Bands 1 through 7 and to the standard derived vegetation and soil moisture indices in order to quantitatively characterize the wide range of scaling of these fields. The scaling exponents we found are not so large; however, they act across wide scale ranges and imply large effects. For example, for the statistics near the mean, the MODIS (500-m) resolution would be biased by a factor of ~1.52 when compared with similar results from an "ideal" sensor at 1-mm resolution. Applying the standard index algorithms on lower and lower resolution satellite data, we obtained indices with significantly different statistical properties than if the same algorithm was used at the finest resolution and then degraded to an intermediate value (a difference of a factor ~1.54). This shows that the algorithms can, at best, be accurate at the unique calibration scale and this points to the need to develop resolution-independent algorithms based on the scaling exponents
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
What is the place of communication impacts in climate resilience assessment practices?
No full textInternational audienceImpact assessment of communication on climate risks is quite a new practice. The emergent recognition of the importance of communication can also be observed in the literature on climate resilience indicators. This study analyses and compares different resilience assessment frameworks that consider communication processes and infrastructure, a feature that has recently gained importance among the available indicators for cities coping with climate risks. Following this review, we conceived a new approach to comprehend the impact of communication on urban resilience to extreme weather. We designed and tested novel "Resilience Communication Indicators" (RCIs), with the aim of detecting possible correlations between communication processes and environmental processes. At the same time, we adopted a dynamic perspective that goes beyond a description of the state of communication processes and infrastructure in an urban area exposed to climate risks. Indeed, the RCIs are tailored to appraise how specific communication activities contribute to achieving local resilience goals. These indicators require a rich and detailed selection of communication variables that are activity driven; i.e. of resilience changes that occur even in a brief time, and the causes related to a past or ongoing communication activity.The results of this study are presented in R. Vicari, I. Tchiguirinskaia, D. Schertzer, Assessing public outreach strategies in cities coping with climate risks, Geoscience Communication Discussion, doi.org/10.5194/gc-2018-4This research was supported by the Chair Hydrology for Resilient Cities (endowed by Veolia) and the Interreg NWE IVB RainGain project
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
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