366 research outputs found
Variation in syn-subduction sedimentation patterns from inner to outer portions of deep-water fold and thrust belts: examples from the Hikurangi subduction margin of New Zealand
The structure and distribution of accommodation in fold and thrust belts vary both laterally and longitudinally. Here we integrate gravity, bathymetry and 2D seismic datasets to investigate the structural and stratigraphic variation in the southern part of the Hikurangi subduction wedge, onshore and offshore North Island, New Zealand. Three morphostructural portions are recognized:
The inner portion demonstrates reactivation of inherited structures, producing thick-skinned deformation. Pre-subduction rocks are represented by kilometres of acoustically chaotic seismofacies. Thick-skinned deformation and readily deformable substrate lead to the development of wide trench-slope sub-basins, infilled with >5 km of syn-subduction sediments.
The mid portion typically demonstrates thrust faults with connections to deeper structures, leading to the development of an imbricate system with asymmetrical sub-basins typically <5 km thick developed on the back-limb of thrust related folds.
An antiformal stack marks the transition from the thick-skinned interior of the basin to the thin-skinned accretionary prism. Beyond this, the relatively non-deformed outer portion demonstrates frontal folds, propagating thrusts and up to 3 km thickness of syn-subduction strata.
Structural variation across the subduction wedge controls the generation of accommodation with implications for sediment distribution within fold and thrust belts and for petroleum system development
Distinct magnetic regimes through site-selective atom substitution in the frustrated quantum antiferromagnet CsCuClBr
We report on a systematic study of the magnetic properties on single crystals
of the solid solution CsCuClBr (0 x 4), which
include the two known end-member compounds CsCuCl and CsCuBr,
classified as quasi-two-dimensional quantum antiferromagnets with different
degrees of magnetic frustration. By comparative measurements of the magnetic
susceptibility () on as many as eighteen different Br concentrations,
we found that the inplane and out-of-plane magnetic correlations, probed by the
position and height of a maximum in the magnetic susceptibility, respectively,
do not show a smooth variation with x. Instead three distinct concentration
regimes can be identified, which are separated by critical concentrations
x = 1 and x = 2. This unusual magnetic behavior can be explained
by considering the structural peculiarities of the materials, especially the
distorted Cu-halide tetrahedra, which support a site-selective replacement of
Cl- by Br- ions. Consequently, the critical concentrations x (x)
mark particularly interesting systems, where one (two) halidesublattice
positions are fully occupied.Comment: 15 pages, 4 figure
Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand
Concepts of the interaction between autogenic (e.g., flow process) and allogenic (e.g., tectonics) controls on sedimentation have advanced to a state that allows the controlling forces to be distinguished. Here we examine outcropping and subsurface Neogene deep-marine clastic systems that traversed the Hikurangi subduction margin via thrust-bounded trench-slope basins, providing an opportunity to examine the interplay of structural deformation and deep-marine sedimentation. Sedimentary logging and mapping of Miocene outcrops from the exhumed portion of the subduction wedge record heavily amalgamated, sand-rich lobe complexes, up to 200 m thick, which accumulated behind NE–SW-oriented growth structures. There was no significant deposition from low-density parts of the gravity flows in the basin center, although lateral fringes demonstrate fining and thinning indicative of deposits from low-density flows. Seismic data from the offshore portion of the margin show analogous lobate reflector geometries. These deposits accumulate into complexes up to 5 km wide, 8 km long, and 300 m thick, comparable in scale with the outcropping lobes on this margin. Mapping reveals lobe complexes that are vertically stacked behind thrusts. These results illustrate repeated trapping of the sandier parts of turbidity currents to form aggradational lobe complexes, with the finer-grained suspended load bypassing to areas downstream. However, the repeated development of lobes characterized by partial bypass implies that a feedback mechanism operates to perpetuate a partial confinement condition, via rejuvenation of accommodation. The mechanism proposed is a coupling of sediment loading and deformation rate, such that load-driven subsidence focuses stress on basin-bounding faults and perpetuates generation of accommodation in the basin, hence modulating tectonic forcing. Recognition of such a mechanism has implications for understanding the tectono-stratigraphic evolution of deep-marine fold and thrust belts and the distribution of resources within them
Relativistic diffusion with friction on a pseudoriemannian manifold
We study a relativistic diffusion equation on the Riemannian phase space
defined by Franchi and Le Jan. We discuss stochastic Ito (Langevin)
differential equations (defining the diffusion) as a perturbation by noise of
the geodesic equation. We show that the expectation value of the angular
momentum and the energy grow exponentially fast. We discuss drifts leading to
an equilibrium. It is shown that the diffusion process corresponding to the
Juettner or quantum equilibrium distributions has a bounded expectation value
of angular momentum and energy. The energy and the angular momentum tend
exponentially fast to their equilibrium values. As examples we discuss a
particle in a plane fronted gravitational wave and a particle in de Sitter
universe. It is shown that the relativistic diffusion of momentum in de Sitter
space is the same as the relativistic diffusion on the Minkowski mass-shell
with the temperature proportional to the de Sitter radius.Comment: the version published in CQ
The orbital parameters of the del Cep inner binary system determined using 2019 HARPS-N spectroscopic data
An inner companion has recently been discovered orbiting the prototype of
classical Cepheids, delta Cep, whose orbital parameters are still not fully
constrained. We collected new precise radial velocity measurements of delta Cep
in 2019 using the HARPS-N spectrograph mounted at the Telescopio Nazionale
Galileo. Using these radial velocity measurements, we aimed to improve the
orbital parameters of the system. We considered a template available in the
literature as a reference for the radial velocity curve of the pulsation of the
star. We then calculated the residuals between our global dataset (composed of
the new 2019 observations plus data from the literature) and the template as a
function of the pulsation phase and the barycentric Julian date. This provides
the orbital velocity of the Cepheid component. Using a Bayesian tool, we
derived the orbital parameters of the system. Considering priors based on
already published Gaia constraints, we find for the orbital period a maximum a
posteriori probability of Porb=9.32+/-0.03 years (uncertainties correspond to
the 95% highest density probability interval), and we obtain an eccentricity
e=0.71+/-0.02, a semimajor axis a=0.029 +/-0.003 arcsecond, and a
center-of-mass velocity V0=-17.28+/-0.08 km/s, among other parameters. In this
short analysis we derive the orbital parameters of the delta Cep inner binary
system and provide a cleaned radial velocity curve of the pulsation of the
star, which will be used to study its Baade-Wesselink projection factor in a
future publication.Comment: accepted for publication in A&A Letter
Impaired photoprotection in Phaeodactylum tricornutum KEA3 mutants reveals the proton regulatory circuit of diatoms light acclimation
International audienceDiatoms are successful phytoplankton clades able to acclimate to changing environmental conditions, including e.g. variable light intensity. Diatoms are outstanding at dissipating light energy exceeding the maximum photosynthetic electron transfer (PET) capacity via the nonphotochemical quenching (NPQ) process. While the molecular effectors of NPQ as well as the involvement of the proton motive force (PMF) in its regulation are known, the regulators of the PET/PMF relationship remain unidentified in diatoms. We generated mutants of the H /K antiporter KEA3 in the model diatom . Loss of KEA3 activity affects the PET/PMF coupling and NPQ responses at the onset of illumination, during transients and in steady-state conditions. Thus, this antiporter is a main regulator of the PET/PMF coupling. Consistent with this conclusion, a parsimonious model including only two free components, KEA3 and the diadinoxanthin de-epoxidase, describes most of the feedback loops between PET and NPQ. This simple regulatory system allows for efficient responses to fast (minutes) or slow (e.g. diel) changes in light environment, thanks to the presence of a regulatory calcium ion (Ca )-binding domain in KEA3 modulating its activity. This circuit is likely tuned by the NPQ-effector proteins, LHCXs, providing diatoms with the required flexibility to thrive in different ocean provinces
Tomographic diffractive microscopy: towards highresolution 3-D real-time data acquisition, image reconstruction and display of unlabeled samples
Tomographic diffractive microscopy allows for imaging unlabeled specimens, with a better resolution than conventional microscopes, giving access to the index of refraction distribution within the specimen, and possibly at high speed. Principles of image formation and reconstruction are presented, and progresses towards realtime, three-dimensional acquisition, image reconstruction and final display, are discussed
Finite-temperature dynamical magnetic susceptibility of quasi-one-dimensional frustrated spin-1/2 Heisenberg antiferromagnets
We study the dynamical response of frustrated, quasi-one-dimensional spin-1/2
Heisenberg antiferromagnets at finite temperatures. We allow for the presence
of a Dzyaloshinskii-Moriya interaction. We concentrate on a model of weakly
coupled planes of anisotropic triangular lattices. Combining exact results for
the dynamical response of one dimensional Heisenberg chains with a Random Phase
Approximation (RPA) in the frustrated interchain couplings, we calculate the
dynamical susceptibility in the disordered phase. We investigate the
instability of the disordered phase to the formation of collective modes. We
find a very weak instability to the formation of incommensurate magnetic order
and determine the ordering temperature and wave vector. We also determine the
effects of uniform magnetic fields on the ordering transition.Comment: 17 pages, 17 Postscript figure
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