2,681 research outputs found
The impact of vegetation on fractionation of rare earth elements(REE) during water–rock interaction
Previous studies on waters of a streamlet in the Vosges mountains (eastern France) have shown that Sr and rare earth elements (REE) principally originate from apatite dissolution during weathering. However, stream water REE patterns normalized to apatite are still depleted in light REE (LREE, La–Sm) pointing to the presence of an additional LREE depleting process. Speciation calculations indicate that complexation cannot explain this additional LREE depletion. In contrast, vegetation samples are strongly enriched in LREE compared to water and their Sr and Nd isotopic compositions are comparable with those of apatite and waters. Thus, the preferential LREE uptake by the plants at the root–water–soil (apatite) interface might lead to an additional LREE depletion of the waters in the forested catchment. Mass balance calculations indicate that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling the LREE depletion in river waters
Economic Geology Vo|
Abstract The lower Proterozoic uranium ore deposits in the Franceville basin (Gabon) are the oldest high-grade uranium accumulations known. They are unique in that they contain evidence for natural nuclear fission reactors. Sedimentologic, tectonic, petrographic, and geochemical studies have been performed in order to reconstruct the geologic conditions in which uranium mineralization took place. Uranium deposits are located in deltaic sediments overlying fiuviatile deposits of coarse sandstone and conglomerates which are the source rocks for uranium. Deltaic sediments are overlain by marine black shales (the FB formation). Petrographic observations, electron microscope studies, and geochemical and carbon isotope data indicate that these FB black shales are source rocks for petroleum trapped in the uranium deposits. Tectonic studies show that all the uranium deposits are in tectonic structures that served as traps for both petroleum and uranium. Uranium mineralization occurs in this setting when an oxidized uranium-bearing fluid has mixed with a reduced petroleum-bearing fluid. The uranium ores are affected by hydrofracturing which forms a good pathway for the oxidized uranium-bearing fluids and the reduced fluids. Hydrofracturing may be initiated by overpressured fluids coming from undercompacted zones in the FB black shales
A threshold-improved narrow-width approximation for BSM physics
A modified narrow-width approximation that allows for O(Gamma/M)-accurate
predictions for resonant particle decay with similar intermediate masses is
proposed and applied to MSSM processes to demonstrate its importance for
searches for particle physics beyond the Standard Model.Comment: 10 pages, 5 figures, version to appear in JHE
Disentangling Dimension Six Operators through Di-Higgs Boson Production
New physics near the TeV scale can generate dimension-six operators that
modify the production rate and branching ratios of the Higgs boson. Here, we
show how Higgs boson pair production can yield complementary information on
dimension-six operators involving the gluon field strength. For example, the
invariant mass distribution of the Higgs boson pair can show the extent to
which the masses of exotic TeV-scale quarks come from electroweak symmetry
breaking. We discuss both the current Tevatron bounds on these operators and
the most promising LHC measurement channels for two different Higgs masses: 120
GeV and 180 GeV. We argue that the operators considered in this paper are the
ones most likely to yield interesting Higgs pair physics at the LHC.Comment: 20 pages, 7 figures; v2: to match JHEP versio
2004 ATLAS Combined Testbeam : Computation and Validation of the Electronic Calibration Constants for the Electromagnetic Calorimeter
From July to November 2004, a full slice of the ATLAS barrel detector was studied in testbeam. A complete electromagnetic barrel module was used, read by the final electronics and operated by ATLAS TDAQ software. This note describes in details the electronic calibration procedure and the cell energy reconstruction: each step of the procedure and its associated software is explicitly described. The general calibration procedure is very similar to the one applied in previous barrel and endcap standalone testbeams. Emphasis is put on tools developed in the context of the combined testbeam which can be used for commissioning and operation of the calorimeters in ATLAS. Many validation studies were performed on each calibration constant. Previously unobserved effects such as the FEB temperature dependence of some constants were observed. Overall, the calibration performances are at the expected level
Determining R-parity violating parameters from neutrino and LHC data
In supersymmetric models neutrino data can be explained by R-parity violating
operators which violate lepton number by one unit. The so called bilinear model
can account for the observed neutrino data and predicts at the same time
several decay properties of the lightest supersymmetric particle. In this paper
we discuss the expected precision to determine these parameters by combining
neutrino and LHC data and discuss the most important observables. We show that
one can expect a rather accurate determination of the underlying R-parity
parameters assuming mSUGRA relations between the R-parity conserving ones and
discuss briefly also the general MSSM as well as the expected accuracies in
case of a prospective e+ e- linear collider. An important observation is that
several parameters can only be determined up to relative signs or more
generally relative phases.Comment: 13 pages, 13 figure
Measuring the Higgs Sector
If we find a light Higgs boson at the LHC, there should be many observable
channels which we can exploit to measure the relevant parameters in the Higgs
sector. We use the SFitter framework to map these measurements on the parameter
space of a general weak-scale effective theory with a light Higgs state of mass
120 GeV. Our analysis benefits from the parameter determination tools and the
error treatment used in new--physics searches, to study individual parameters
and their error bars as well as parameter correlations.Comment: 45 pages, Journal version with comments from refere
Porosity microstructures of a sandstone affected by a normal fault
Dans un système de failles normales de la bordure du fossé rhénan, les interactions eaux-roches de part et
d’autre de ces failles peuvent contrôler les conditions des circulations fluides. L’objectif de ce travail est de caractériser
les structures du réseau poreux dans la zone endommagée autour d’une de ces failles. Il est intéressant d’étudier la relation
entre porosité et perméabilité dans cette zone. Des études pétrographiques et pétrophysiques, des mesures microthermométriques
sur des inclusions fluides et la composition isotopique de l’oxygène ont permis de caractériser les
structures de porosité des roches et notamment des ciments primaires et secondaires.
Le couplage de ces approches montre qu’une faille normale peut à la fois jouer le rôle de drain et de barrière à la
circulation des fluides. En fonction de la direction de circulation, la faille joue le rôle de drain en laissant remonter les
fluides parallèlement au plan de faille et le rôle de barrière, en focalisant les circulations dans le toit. L’anisotropie, notamment
des propriétés de transfert héritées des conditions de dépôts fluviatiles, est profondément modifiée par les
transferts subits dans le matériau. Ainsi les modifications des transferts dépendent des modifications du réseau poreux :
l’hétérogénéité de la structure du réseau et l’anisotropie d’orientation ou de connectivité. Ce modèle de circulation est
contrôlé par une interaction entre les modifications des structures du réseau poreux et les circulations fluides, entraînant
des modifications de l’anisotropie de certaines propriétés du matériau autour de la faille
Full order alpha electroweak corrections to double Higgs-strahlung at the linear collider
We present the full order alpha electroweak radiative corrections to the
double Higgs-strahlung process e+e- --> ZHH. The computation is performed with
the help of GRACE-loop. After subtraction of the initial state QED radiative
corrections, we find that the genuine weak corrections in the -scheme
are small for Higgs masses and energies where this cross section is largest and
is most likely to be studied. These corrections decrease with increasing
energies attaining about at TeV. The full order alpha
correction on the other hand is quite large at threshold but small at energies
around the peak. We also study changes in the shape of the invariant mass of
the Higgs pair which has been shown to be a good discriminating variable for
the measurement of the triple Higgs vertex in this reaction.Comment: 18 pages, 5 figures and 3 table
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