Volcanic rocks, preserving paleorecords of Earth's magnetic field, are essential to constrain the working of the geodynamo, provided their primary signal was not biased. Using a thermomagnetometer, ...we simulate a situation where a sample's primary record, carried by a thermoremanence (TRM, acquired by cooling in air from 600°C to room temperature), is partly overprinted by a chemical remanence (CRM, acquired by 200 hr of isothermal exposure at 400°C). This situation leads to two directional and intensity components (in the form of linear segments) in the Zijderveld and Arai‐Nagata diagrams. In the case of unstable titanomagnetite grains prior to CRM acquisition, we show that both components can be strongly biased by up to ∼50° for paleodirections and ∼50% for paleointensities. In such a worst‐case scenario, the secondary CRM strongly overprints the primary TRM, rendering the common interpretation of Zijderveld and Arai‐Nagata diagrams in terms of characteristic components invalid.
Plain Language Summary
Volcanic rocks, the magnetic minerals of which can acquire a thermoremanent magnetization (TRM) from Earth's magnetic field during their initial cooling, are essential to constrain the working of the geodynamo through Earth's history. However, if the rock is subsequently reheated at moderate temperature in another ambient field, the initial record can be partly overprinted by a chemical remanence (CRM). Starting from a TRM applied on materials of various thermostability, we reproduced in laboratory conditions the acquisition of a CRM by annealing the rock in a controlled ambient field for 200 hr at 400°C. Rock‐magnetic and structural analyses at regular intervals, supplemented by continuous measurements of the remanent magnetization, indicate the creation of new phases as a result of oxidation processes. The paleomagnetic analysis of the final products reveals the existence of two distinct components that can be associated with the initial TRM and the secondary CRM. Whereas the paleomagnetic record of the initial TRM is trustworthy for the most stabilized initial products, directional (up to 50°) and intensity (up to 50%) biases are observed for the least stabilized initial products, illustrating a critical example where the interpretation of characteristic components (linear segments in the interpretation diagrams) is invalid.
Key Points
We overprint a thermoremanent magnetization (TRM) by cooling from 600°C with a chemical remanent magnetization by 200 hr exposure at 400°C
Chemical remanent magnetization was produced by the creation of cation‐deficient titanomagnetite phases, then stabilized by oxyexsolution
Paleodirections and intensities are strongly biased in the worst scenario, making the interpretation of characteristic components invalid
The reactor antineutrino anomaly might be explained by the oscillation of reactor antineutrinos toward a sterile neutrino of eV mass. In order to explore this hypothesis, the STEREO experiment ...measures the antineutrino energy spectrum in six different detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this Letter, results from 66 days of reactor turned on and 138 days of reactor turned off are reported. A novel method to extract the antineutrino rates has been developed based on the distribution of the pulse shape discrimination parameter. The test of a new oscillation toward a sterile neutrino is performed by comparing ratios of cells, independent of absolute normalization and of the prediction of the reactor spectrum. The results are found to be compatible with the null oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5% C.L.
We conducted an absolute palaeointensity (API) survey on Ethiopian volcanics from Early Oligocene (Belessa section) and Middle Miocene (Debre Sina section). After a careful selection based on the ...reversibility of high-field thermomagnetic curves from samples yielding unambiguous palaeodirections, we restricted our analysis to five (resp. six) cooling units from Belessa (resp. Debre Sina), submitted to both Thellier and Wilson-style experiments. X-ray diffraction measurements and microscopical observations under reflected light gave us good confidence in the reliability of the remanence carriers of the Belessa basalts, with pseudo-brookite exsolutions in titanomagnetite (TM) grains, synonymous of an advanced stage of high-temperature (i.e. deuteric) oxidation. In contrast, the Debre Sina trachybasalts may have been submitted to low-temperature (i.e. post-consolidation) alteration featured by granulation of TM grains and leading to a higher dispersion of API estimates. Compared to the world palaeointensity database', the lower dipole moment found in Ethiopia for the Early Oligocene (30 +/- 8ZAm(2)) than the Middle Miocene (65 +/- 20ZAm(2)) is compatible with a global increase of dipole strength from 30 Ma to present, and also suggestive of a dipole low during the Oligocene. This observation must however be treated with caution because of the over-representation of Plio-Pleistocene determinations in the global database and the partial correlation between dipole strength and number of palaeointensity determinations.
We investigate the possible origins of the reactor antineutrino anomalies in norm and shape within the framework of a summation model where β^{-} transitions are simulated by a phenomenological model ...of Gamow-Teller decay strength. The general trends of divergence from the Huber-Mueller model on the antineutrino side can be reproduced in both norm and shape. From the exact electron-antineutrino correspondence of the summation model, we predict similar distortions in the electron spectra, suggesting that biases on the reference spectra of fission electrons could be the cause of the anomalies.
New U–Pb and
40
Ar/
39
Ar isotopic dates on volcanic rocks of the East Chukotka segment of the Okhotsk–Chukotka Belt correspond to 76–71 Ma span, which is partially beyond the conventional lifetime ...of this volcanic province. This could result from the migration of magmatic loci along the strike of the volcanic belt, and/or from the overprint by a younger magmatic event.
The NUCLEUS experiment aims at measuring the coherent elastic scattering of nuclear reactor antineutrinos off nuclei using cryogenic calorimeters. Operating at an overburden of 3 m.w.e., muon-induced ...backgrounds are expected to be dominant. It is therefore essential to develop an efficient muon veto, with a detection efficiency of more than 99 %. This will be realized in NUCLEUS through a compact cube assembly of plastic scintillator panels. In order to prevent a large unshielded area where the cryostat intersects the shielding arrangement without unnecessarily increasing the induced detector dead time, a novel concept has been investigated, featuring a plastic scintillator-based active muon veto operating inside the NUCLEUS cryostat at sub-Kelvin temperatures. The verification of the key physical aspects of this cryogenic muon veto detector led to the first reported measurements of organic plastic scintillators at sub-Kelvin temperatures. The functionality of the principal scintillation process of organic plastic scintillators at these temperatures has been confirmed. On the basis of these findings, a disk-shape plastic scintillator equipped with wavelength shifting fibers and a silicon photomultiplier to guide and detect the scintillation light has been developed. The NUCLEUS cryogenic muon veto will be the first of its kind to be operated at sub-Kelvin temperatures.
Genome-wide analysis of 67 ancient Near Eastern cattle,
remains reveals regional variation that has since been obscured by admixture in modern populations. Comparisons of genomes of early domestic ...cattle to their aurochs progenitors identify diverse origins with separate introgressions of wild stock. A later region-wide Bronze Age shift indicates rapid and widespread introgression of zebu,
from the Indus Valley. This process was likely stimulated at the onset of the current geological age, ~4.2 thousand years ago, by a widespread multicentury drought. In contrast to genome-wide admixture, mitochondrial DNA stasis supports that this introgression was male-driven, suggesting that selection of arid-adapted zebu bulls enhanced herd survival. This human-mediated migration of zebu-derived genetics has continued through millennia, altering tropical herding on each continent.
The magnetic record, preserved by igneous rocks in the form of thermoremanent magnetization (TRM) or thermo‐chemical remanent magnetization (TCRM), is essential to reconstruct Earth's absolute ...paleointensity (API) but strongly depends on the kinetic conditions in which the remanence was acquired. In this paper, we present exact analytical solutions describing the time‐dependent processes of acquisition and thermal demagnetization of various kinds of thermally activated remanences for non‐interacting single‐domain grains with uniaxial shape anisotropy. Our solutions, derived in less‐restrictive conditions than previous studies, are also valid for TCRMs acquired either by growth of grain volume or by increase of the Curie point Tc. We first show that TCRMs by Tc increase and TRMs are of comparable intensity whereas TCRMs by volume growth are significantly less intense. We then model Arai‐Nagata diagrams for assemblies of coercivity‐variable grains and find that all Thellier‐type protocols yield reliable API determinations for TRMs and TCRMs by Tc increase, with the peculiarity of the IZZI protocol to produce small zigzags in the Arai‐Nagata diagram. In contrast, TCRMs by volume growth yield convex Arai‐Nagata diagrams. The most conspicuous kinetic effect is the influence of cooling rate on API determinations due to a ∼5% increase of the remanent magnetization for a 10‐fold increase in cooling time. We show that the situation is problematic when the cooling time of natural samples coincides with the geomagnetic secular‐variation time scales. Natural samples with cooling times sufficient to average out secular variation conversely yield reliable API determinations provided a cooling‐rate correction is applied.
Plain Language Summary
When a lava or a magma cools down, iron‐rich minerals acquire magnetic properties while crossing their Curie point Tc and then fossilize the properties of the ambient magnetic field while passing through their blocking temperature. While rapidly cooled objects produce instantaneous records of Earth's magnetic field, called thermoremanences (TRMs), slowly cooled objects may be blurred by geomagnetic secular variation (SV) and additionally experience mineralogical transformations either due to the growth of grains or the increase of Tc, leading to more complex thermochemical remanent magnetizations (TCRMs). A big challenge of modern paleomagnetism is thus to identify the most appropriate remanences that yield robust paleointensity estimates. To address this issue, we derived analytical solutions that describe the acquisition and demagnetization processes of such remanences for assemblies of uniformly magnetized particles. We first show that TRMs and TCRMs by Tc increase yield equally robust paleointensities, whereas the magnetic signal is harder to deconvolve for TCRMs by grain growth. We then confirm that uncorrected contrasts in cooling rate between natural and laboratory conditions can strongly overestimate paleointensities. If the cooling rate exceeds the typical SV time scales, we demonstrate that average paleointensities, representative of geodynamo activity, can be robustly determined provided that a cooling‐rate correction is applied.
Key Points
Analytical solutions for the kinetics of thermoremanent magnetization (TRM) and thermo‐chemical remanent magnetization (TCRM) acquisition for single‐domain grains are derived and used to construct Arai diagrams
At fast cooling rate, TCRM acquired by Curie point increase yield reliable paleointensity estimates but not TCRM acquired by volume growth
Slowly cooled TRMs yield reliable paleointensities provided geomagnetic secular variation is averaged and cooling‐rate effect is corrected
.
The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The ...detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes,
155
Gd and
157
Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8MeV. The complex level schemes of
156
Gd and
158
Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd (n,
γ
) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user.
While the role of landmarks is well documented, little research has focused on the characteristics that allow landmarks to benefit the construction of spatial representations. Although their visual ...saliency has already been explored, cognitive saliency deserves attention. It could benefit to older people who experience decline in their spatial abilities. To explore this issue, young and older participants watched virtual itineraries including landmarks varying in their visual and cognitive saliency. They then performed various landmark and direction-related tasks. The combination of visual and cognitive saliency improved performance in both age groups, without canceling age-related differences but reducing them in some cases. Our results provide evidence that visually and cognitively salient landmarks facilitate the construction of mental representations of environments.
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