3,769 research outputs found
Muon-induced neutrons do not explain the DAMA data
We present an accurate model of the muon-induced background in the DAMA/LIBRA
experiment. Our work challenges proposed mechanisms which seek to explain the
observed DAMA signal modulation with muon-induced backgrounds. Muon generation
and transport are performed using the MUSIC/MUSUN code, and subsequent
interactions in the vicinity of the DAMA detector cavern are simulated with
Geant4. We estimate the total muon-induced neutron flux in the detector cavern
to be cm s. We predict
counts/day/kg/keV, which accounts for less than of
the DAMA signal modulation amplitude.Comment: 6 pages, 4 figures, accepted for publication in PR
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Inference of Multiple Earthquake-Cycle Relaxation Timescales from Irregular Geodetic Sampling of Interseismic Deformation
Characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of highâresolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals (250â10,000 years). Here we approach this problem by comparing longâterm geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction (0.001%â0.1%) of a complete earthquake cycle along 15 continental strikeâslip faults. Geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle. The timing of the last earthquake on many of these faults is poorly known, and may vary greatly from fault to fault. Assuming that the underlying mechanics of the seismic cycle are similar for all faults, geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone. As an ensemble, we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0.94±0.09. To simultaneously explain both the ensemble agreement between geologic and geodetic slipârate estimates with observations of rapid postseismic deformation, we consider the predictions from simple twoâlayer earthquakeâcycle models with both Maxwell and Burgers viscoelastic rheologies. We find that a twoâlayer Burgers model, with two relaxation timescales, is consistent with observations of deformation throughout the earthquake cycle, whereas the widely used twoâlayer Maxwell model with a single relaxation timescale, is not, suggesting that the earthquake cycle is effectively characterized by a largely stressârecoverable rapid postseismic stage and a much more slowly varying interseismic stage.Earth and Planetary Science
Curvature invariants in type N spacetimes
Scalar curvature invariants are studied in type N solutions of vacuum
Einstein's equations with in general non-vanishing cosmological constant
Lambda. Zero-order invariants which include only the metric and Weyl (Riemann)
tensor either vanish, or are constants depending on Lambda. Even all
higher-order invariants containing covariant derivatives of the Weyl (Riemann)
tensor are shown to be trivial if a type N spacetime admits a non-expanding and
non-twisting null geodesic congruence.
However, in the case of expanding type N spacetimes we discover a
non-vanishing scalar invariant which is quartic in the second derivatives of
the Riemann tensor.
We use this invariant to demonstrate that both linearized and the third order
type N twisting solutions recently discussed in literature contain
singularities at large distances and thus cannot describe radiation fields
outside bounded sources.Comment: 17 pages, to appear in Class. Quantum Gra
Precision measurements of Linear Scattering Density using Muon Tomography
We demonstrate that muon tomography can be used to precisely measure the
properties of various materials. The materials which have been considered have
been extracted from an experimental blast furnace, including carbon (coke) and
iron oxides, for which measurements of the linear scattering density relative
to the mass density have been performed with an absolute precision of 10%. We
report the procedures that are used in order to obtain such precision, and a
discussion is presented to address the expected performance of the technique
when applied to heavier materials. The results we obtain do not depend on the
specific type of material considered and therefore they can be extended to any
application.Comment: 16 pages, 4 figure
An immediate-late gene expression module decodes ERK signal duration
The RAF-MEK-ERK signalling pathway controls fundamental, often opposing cellular processes such as proliferation and apoptosis. Signal duration has been identified to play a decisive role in these cell fate decisions. However, it remains unclear how the different early and late responding gene expression modules can discriminate short and long signals. We obtained both protein phosphorylation and gene expression time course data from HEK293 cells carrying an inducible construct of the proto-oncogene RAF By mathematical modelling, we identified a new gene expression module of immediate-late genes (ILGs) distinct in gene expression dynamics and function. We find that mRNA longevity enables these ILGs to respond late and thus translate ERK signal duration into response amplitude. Despite their late response, their GC-rich promoter structure suggested and metabolic labelling with 4SU confirmed that transcription of ILGs is induced immediately. A comparative analysis shows that the principle of duration decoding is conserved in PC12 cells and MCF7 cells, two paradigm cell systems for ERK signal duration. Altogether, our findings suggest that ILGs function as a gene expression module to decode ERK signal duration
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