Search results for " Tim"
showing 10 items of 3152 documents
Analysis of psychoactive substances in water by information dependent acquisition on a hybrid quadrupole time-of-flight mass spectrometer.
2016
Emerging drugs of abuse, belonging to many different chemical classes, are attracting users with promises of “legal” highs and easy access via internet. Prevalence of their consumption and abuse through wastewater-based epidemiology can only be realized if a suitable analytical screening procedure exists to detect and quantify them in water. Solid-phase extraction and ultra-high performance liquid chromatography quadrupole time-of-flight-mass spectrometry (UHPLC–QqTOF–MS/MS) was applied for rapid suspect screening as well as for the quantitative determination of 42 illicit drugs and metabolites in water. Using this platform, we were able to identify amphetamines, tryptamines, piperazines, p…
Controlled time integration for the numerical simulation of meteor radar reflections
2016
We model meteoroids entering the Earth[U+05F3]s atmosphere as objects surrounded by non-magnetized plasma, and consider efficient numerical simulation of radar reflections from meteors in the time domain. Instead of the widely used finite difference time domain method (FDTD), we use more generalized finite differences by applying the discrete exterior calculus (DEC) and non-uniform leapfrog-style time discretization. The computational domain is presented by convex polyhedral elements. The convergence of the time integration is accelerated by the exact controllability method. The numerical experiments show that our code is efficiently parallelized. The DEC approach is compared to the volume …
Stochastic Galerkin method for cloud simulation
2018
AbstractWe develop a stochastic Galerkin method for a coupled Navier-Stokes-cloud system that models dynamics of warm clouds. Our goal is to explicitly describe the evolution of uncertainties that arise due to unknown input data, such as model parameters and initial or boundary conditions. The developed stochastic Galerkin method combines the space-time approximation obtained by a suitable finite volume method with a spectral-type approximation based on the generalized polynomial chaos expansion in the stochastic space. The resulting numerical scheme yields a second-order accurate approximation in both space and time and exponential convergence in the stochastic space. Our numerical results…
Interpretation of the nitrogen isotopic composition of Precambrian sedimentary rocks: Assumptions and perspectives
2016
International audience; Nitrogen isotope compositions in sedimentary rocks (d(15)N(sed)) are routinely used for reconstructing Cenozoic N-biogeochemical cycling and are also being increasingly applied to understanding the evolution of ancient environments. Here we review the existing knowledge and rationale behind the use of d(15)N(sed) as a proxy for the Precambrian N-biogeochemical cycle with the aims of (i) identifying the major uncertainties that affect analyses and interpretation of nitrogen isotopes in ancient sedimentary rocks, (ii) developing a framework for interpreting the Precambrian d(15)N(sed) record, (iii) testing this framework against a database of Precambrian d(15)N(sed) va…
Enhanced detection of terrestrial gamma-ray flashes by AGILE
2015
At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma-Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with lightning sfer…
Optimizing Gaussian Process Regression for Image Time Series Gap-Filling and Crop Monitoring
2020
Image processing entered the era of artificial intelligence, and machine learning algorithms emerged as attractive alternatives for time series data processing. Satellite image time series processing enables crop phenology monitoring, such as the calculation of start and end of season. Among the promising algorithms, Gaussian process regression (GPR) proved to be a competitive time series gap-filling algorithm with the advantage of, as developed within a Bayesian framework, providing associated uncertainty estimates. Nevertheless, the processing of time series images becomes computationally inefficient in its standard per-pixel usage, mainly for GPR training rather than the fitting step. To…
A space-time rainfall generator for highly convective Mediterranean rainstorms
2003
Distributed hydrological models require fine resolution rainfall inputs, enhancing the practical interest of space-time rainfall models, capable of generating through numerical simulation realistic space-time rainfall intensity fields. Among different mathematical approaches, those based on point processes and built upon a convenient analytical description of the raincell as the fundamental unit, have shown to be particularly suitable and well adapted when extreme rainfall events of convective nature are considered. Starting from previous formulations, some analytical refinements have been considered, allowing practical generation of space-time rainfall intensity fields for that type of rai…
Landsat and Local Land Surface Temperatures in a Heterogeneous Terrain Compared to MODIS Values
2016
Land Surface Temperature (LST) as provided by remote sensing onboard satellites is a key parameter for a number of applications in Earth System studies, such as numerical modelling or regional estimation of surface energy and water fluxes. In the case of Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra or Aqua, pixels have resolutions near 1 km 2 , LST values being an average of the real subpixel variability of LST, which can be significant for heterogeneous terrain. Here, we use Landsat 7 LST decametre-scale fields to evaluate the temporal and spatial variability at the kilometre scale and compare the resulting average values to those provided by MODIS for the same obser…
A multisensor fusion approach to improve LAI time series
2011
International audience; High-quality and gap-free satellite time series are required for reliable terrestrial monitoring. Moderate resolution sensors provide continuous observations at global scale for monitoring spatial and temporal variations of land surface characteristics. However, the full potential of remote sensing systems is often hampered by poor quality or missing data caused by clouds, aerosols, snow cover, algorithms and instrumentation problems. A multisensor fusion approach is here proposed to improve the spatio-temporal continuity, consistency and accuracy of current satellite products. It is based on the use of neural networks, gap filling and temporal smoothing techniques. …
The first 40Ar-39Ar date from Oxfordian ammonite-calibrated volcanic layers (bentonites) as a tie-point for the Late Jurassic.
2013
AbstractEight volcanic ash layers, linked to large explosive events caused by subduction-related volcanism from the Vardar Ocean back-arc, interbedded with marine limestones and cherts, have been identified in the Rosso Ammonitico Veronese Formation (northeastern Italy). The thickest ash layer, attributed to the Gregoryceras transversarium ammonite Biozone (Oxfordian Stage), yields a precise and reliable 40Ar–39Ar date of 156.1 ± 0.89 Ma, which is in better agreement with GTS2004 boundaries than with the current GTS2012. This first biostratigraphically well-constrained Oxfordian date is proposed as a new radiometric tie-point to improve the Geologic Time Scale for the Late Jurassic, where a…