A tomographic test of cosmic anisotropy with the recently-released quasar sample

We test the cosmic anisotropy in the dipole-modulated $$\Lambda $$ Λ CDM model and Finslerian cosmological model with the recently-released quasar sample. Based on the redshift tomographic method, the quasar sample is divided into two subsets $$z \le z_{cut}$$ z ≤ z cut and $$z > z_{cut}$$ z > z cut by different cutting redshifts. The dipole amplitudes of the two cosmological models from the subsets $$z \le z_{cut}$$ z ≤ z cut are very weak. We find that quasars at a higher redshift range may provide more detailed information about the dipole amplitude $$A_D$$ A D . The dipole directions of each cosmological model from the subsets $$z \le 1.1$$ z ≤ 1.1 and $$z > 1.1$$ z > 1.1 are deviated by $$1\sigma $$ 1 σ level. The Pantheon sample is combined with the two subsets. The dipole amplitude from the two combined datasets is also very weak. In the dipole-modulated $$\Lambda $$ Λ CDM model, the dipole direction from the combined dataset quasar at $$z \le 1.1$$ z ≤ 1.1 and Pantheon sample is far away from the one given by the Pantheon sample. In the Finslerian cosmological model, the dipole directions from the two combined datasets are close to the one in the Pantheon sample.

A spectroscopical study of H$$_{2}$$ emission in a simply magnetized toroidal plasma

A noninvasive diagnostic technique relying on optical emission spectroscopy is used for studying plasma confined in a purely toroidal magnetic field. Visible emission lines of molecular hydrogen were specifically targeted. Bi-dimensional structures and poloidal plasma profiles were reconstructed from the emissivity distribution of hydrogen Fulcher system using a tomographic method. A few details concerning the methods employed to capture different emission viewlines, data reduction and tomographic reconstruction techniques are also addressed. We report also the first measurement of the excitation temperature of the $$\text {H}_2$$ H 2 [3c] level in the center of the plasma column, $$T_{\mathrm{exc}}=0.67 \pm 0.11$$ T exc = 0.67 ± 0.11 eV. Graphic Abstract

3D anisotropic structure of the Japan subduction zone

How mantle materials flow and how intraslab fabrics align in subduction zones are two essential issues for clarifying material recycling between Earth’s interior and surface. Investigating seismic anisotropy is one of a few viable technologies that can directly answer these questions. However, the detailed anisotropic structure of subduction zones is still unclear. Under a general hexagonal symmetry anisotropy assumption, we develop a tomographic method to determine a high-resolution three-dimensional (3D) P wave anisotropic model of the Japan subduction zone by inverting 1,184,018 travel time data of local and teleseismic events. As a result, the 3D anisotropic structure in and around the dipping Pacific slab is firstly revealed. Our results show that slab deformation plays an important role in both mantle flow and intraslab fabric, and the widely observed trench-parallel anisotropy in the forearc is related to the intraslab deformation during the outer-rise yielding of the subducting plate.

Small Scale Rain Field Sensing and Tomographic Reconstruction with Passive Geostationary Satellite Receivers

Sensing of the rain rate and the movement of the rain field over a relatively small geographical area may often be necessary for agricultural purposes, water management objectives or transport management in airports or harbors. In this paper, an entirely passive method is suggested to sense rainfall rate and extension of a rain field, with reconstruction in two dimensions using a tomographic method. In order to achieve this goal, multiple colocated satellite receivers are proposed to measure the beacon signal levels of geostationary satellites received at different azimuth angles. The tomographic reconstruction of the rain field takes the advantage of the dis-placement of the rain field due to the movement of air masses, while the rain intensity along the receiving path is estimated by the attenuation of the radio signal between the satellite and the ground receiver. To realize the proposed system, a complete receiver setup and an existing, operational group of satellites are selected. A widely known rain field modeling method is applied to generate test data and evaluate the system. The feasibility of a technically realizable system is provided, and its capabilities are compared with a hypothetical, ideal system. The methods and algorithms are tested on an existing geographical location, simulating a real operating environment.

Combining asynchronous data sets in regional body-wave tomography

SUMMARY Regional body-wave tomography is a very popular tomographic method consisting in inverting relative traveltime residuals of teleseismic body waves measured at regional networks. It is well known that the resulting inverse seismic model is relative to an unknown vertically varying reference model. If jointly inverting data obtained with networks in the vicinity of each other but operating at different times, the relative velocity anomalies in different areas of the model may have different reference levels, possibly introducing large-scale biases in the model that may compromise the interpretation. This is very unfortunate as we have numerous examples of asynchronous network deployments which would benefit from a joint analysis. We show here how a simple improvement in the formulation of the sensitivity kernels allows us to mitigate this problem. Using sensitivity kernels that take into account that data processing implies a zero mean residual for each event, the large-scale biases that otherwise arise in the inverse model using data from asynchronous station deployment are largely removed. We illustrate this first with a very simple 3-station example, and then compare the results obtained using the usual and the relative kernels in synthetic tests with more realistic station coverage, simulating data acquisition at two neighbouring asynchronous networks.

Tomography of cool giant and supergiant star atmospheres

Context. Asymptotic giant branch (AGB) stars are characterized by substantial mass loss, however the mechanism behind it not yet fully understood. The knowledge of the structure and dynamics of AGB-star atmospheres is crucial to better understanding the mass loss. The recently established tomographic method, which relies on the design of spectral masks containing lines that form in given ranges of optical depths in the stellar atmosphere, is an ideal technique for this purpose. Aims. We aim to validate the capability of the tomographic method in probing different geometrical depths in the stellar atmosphere and recovering the relation between optical and geometrical depth scales. Methods. We applied the tomographic method to high-resolution spectro-interferometric VLTI/AMBER observations of the Mira-type AGB star S Ori. The interferometric visibilities were extracted at wavelengths contributing to the tomographic masks and fitted to those computed from a uniform disk model. This allows us to measure the geometrical extent of the atmospheric layer probed by the corresponding mask. We then compared the observed atmospheric extension with others measured from available 1D pulsation CODEX models and 3D radiative-hydrodynamics CO5BOLD simulations. Results. While the average optical depths probed by the tomographic masks in S Ori decrease (with ⟨log τ0⟩ = −0.45, − 1.45, and − 2.45 from the innermost to the central and outermost layers), the angular diameters of these layers increase, from 10.59 ± 0.09 mas through 11.84 ± 0.17 mas, up to 14.08 ± 0.15 mas. A similar behavior is observed when the tomographic method is applied to 1D and 3D dynamical models. Conclusions. This study derives, for the first time, a quantitative relation between optical and geometrical depth scales when applied to the Mira star S Ori, or to 1D and 3D dynamical models. In the context of Mira-type stars, knowledge of the link between the optical and geometrical depths opens the way to deriving the shock-wave propagation velocity, which cannot be directly observed in these stars.