► We apply detrended fluctuation analysis to analyse karstic discharge variability. ► We analyse discharge time series at three sampling time from low to high resolution. ► We provide evidence for a ...scaling behavior in the response of karstic watersheds.
This contribution presents a study of discharge variability at two karst springs outlet in southwestern France and aims at presenting the Detrended Fluctuation Analysis (DFA), which method is not very usual in hydrology, to the community interested in investigating the scaling behavior of karst hydrological responses. Several studies have already highlighted the existence of a power law scaling behavior in the spectral variance distribution of hydrological signals such as rainfall rates, stream flow and groundwater levels. This power law behavior provides evidence for characteristic scales that correspond to different physical responses of the system depending on its complexity and occurring at distinct temporal scales. We derive in this contribution particular scaling behavior of karstic watersheds, in particular, the assessment of time interval of karstic watershed responses to rainfall. Based on DFA analysis and relying on a unique high resolution long-term discharge database, we provide evidence for a scaling behavior in the response of two French karstic watersheds. The DFA analysis of discharge time series fluctuations at daily, half hourly and 3-min sampling rate allows to detect scaling behavior in the fluctuation of karstic stream flow from 1
h up to 100-h, from 100-h up to 1-year time scales and for scales larger than 1
year. The DFA analysis can also be useful in investigating groundwater levels or chemical conductance time series scaling behavior and deserves to be more largely disseminated in hydrology as valuable complement to Fourier or wavelet analyses.
Copper export and mobility in acid mine drainage are difficult to understand with conventional approaches. Within this context, Cu isotopes could be a powerful tool and here we have examined the ...relative abundance of dissolved (<0.22 μm) Cu isotopes (δ65Cu) in the Meca River which is an outlet of the Tharsis mine, one of the largest abandoned mines of the Iberian Pyrite Belt, Spain. We followed the chemical and isotopic composition of the upstream and downstream points of the catchment during a 24-h diel cycle. Additional δ65Cu values were obtained from the tributary stream, suspended matter (>0.22 μm) and bed sediments samples. Our goals were to 1) assess Cu sources variability at the upstream point under contrasted hydrological conditions and 2) investigate the conservative vs. non conservative Cu behavior along a stream. Average δ65Cu values varied from −0.47 to −0.08‰ (n = 9) upstream and from −0.63 to −0.31‰ downstream (n = 7) demonstrating that Cu isotopes are heterogeneous over the diel cycle and along the Meca River. During dry conditions, at the upstream point of the Meca River the Cu isotopic composition was heavier which is in agreement with the preferential release of heavy isotopes during the oxidative dissolution of primary sulfides. The more negative values obtained during high water flow are explained by the contribution of soil and waste deposit weathering. Finally, a comparison of upstream vs. downstream Cu isotope composition is consistent with a conservative behavior of Cu, and isotope mass balance calculations estimate that 87% of dissolved Cu detected downstream originate from the Tharsis mine outlet. These interpretations were supported by thermodynamic modelling and sediment characterization data (X-ray diffraction, Raman Spectroscopy). Overall, based on contrasted hydrological conditions (dry vs flooded), and taking the advantage of isotope insensitivity to dilution, the present work demonstrates the efficiency of using the Cu isotopes approach for tracing sources and processes in the AMD regions.
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•We observe rapid change of both riverine Cu isotopic signature and water regime.•This change indicates the contribution of various sources within the mining area.•δ65Cu appears to be controlled by water regime rather than upstream processes.
We correct an overestimation of the production rate of
137
Xe in the DARWIN detector operated at LNGS. This formerly dominant intrinsic background source is now at a level similar to the irreducible ...background from solar
8
B neutrinos, thus unproblematic at the LNGS depth. The projected half-life sensitivity for the neutrinoless double beta decay (
0
ν
β
β
) of
136
Xe improves by
22
%
compared to the previously reported number and is now
T
1
/
2
0
ν
=
3.0
×
10
27
yr
(90% C.L.) after 10 years of DARWIN operation.
In this article, we propose a novel image reconstruction technique for three-gamma (3-<inline-formula> <tex-math notation="LaTeX"> {\gamma } </tex-math></inline-formula>) imaging systems that aims at ...reaching high image quality with a low statistics. The proposed approach is based on the utilization of a (<inline-formula> <tex-math notation="LaTeX"> {\beta +} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{\gamma } </tex-math></inline-formula>) emitter and a liquid xenon (LXe) camera, the Xenon Medical Imaging System 2 (XEMIS2), that is currently being manufactured. The third gamma emitted is more energetic than the two 511-keV photons and interacts mostly through Compton scattering in LXE; therefore, we utilize the interactions' position and the deposited energy to define a Compton cone that gives the direction from where the third gamma was emitted. The intersection point between the cone and the two coincidence photons' lines of response (LOR) is the center of the probability distribution function (PDF), a resolution model similar to that of time-of-flight (TOF)-positron emission tomography (PET). The third gamma's information is used to narrow the LOR portion employed during reconstruction. In this article, we show reconstruction results from simulation using highly realistic Geant4 Application for Emission Tomography (GATE) Monte Carlo simulation of the imaging device and a NEMA-like phantom.
Multivariate methods have been recently introduced and successfully applied for the discrimination of signal from background in the selection of genuine very-high energy γ-ray events with the ...H.E.S.S. Imaging Atmospheric Cerenkov Telescope. The complementary performance of three independent reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas, model and 3D-model suggests the optimization of their combination through the application of a resulting efficient multivariate estimator. In this work the boosted decision tree method is proposed leading to a significant increase in the signal over background ratio compared to the standard approaches. The improved sensitivity is also demonstrated through a comparative analysis of a set of benchmark astrophysical sources.
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