Sparse inversion of Stokes profiles. I. Two-dimensional Milne-Eddington inversions

Inversion codes are numerical tools used for the inference of physical properties from the observations. Despite their success, the quality of current spectropolarimetric observations and those expected in the near future presents a challenge to current inversion codes. The pixel-by-pixel strategy of inverting spectropolarimetric data that we currently utilize needs to be surpassed and improved. The inverted physical parameters have to take into account the spatial correlation that is present in the data and that contains valuable physical information. We utilize the concept of sparsity or compressibility to develop an new generation of inversion codes for the Stokes parameters. The inversion code uses numerical optimization techniques based on the idea of proximal algorithms to impose sparsity. In so doing, we allow for the first time to exploit the presence of spatial correlation on the maps of physical parameters. Sparsity also regularizes the solution by reducing the number of unknowns. We compare the results of the new inversion code with pixel-by-pixel inversions, demonstrating the increase in robustness of the solution. We also show how the method can easily compensate for the effect of the telescope point spread function, producing solutions with an enhanced contrast.Comment: 13 pages, 8 figures, accepted for publication in A&

Connection between electrical conductivity and diffusion coefficient of a conductive porous material filled with electrolyte

The paper focuses on the cross-property connection between the effective electrical conductivity and the overall mass transfer coefficient of a two phase material. The two properties are expressed in terms of the tortuosity parameter which generalized to the case of a material with two conductive phases. Elimination of this parameter yields the cross-property connection. The theoretical derivation is verified by comparison with computer simulation

Real-time multiframe blind deconvolution of solar images

The quality of images of the Sun obtained from the ground are severely limited by the perturbing effect of the turbulent Earth's atmosphere. The post-facto correction of the images to compensate for the presence of the atmosphere require the combination of high-order adaptive optics techniques, fast measurements to freeze the turbulent atmosphere and very time consuming blind deconvolution algorithms. Under mild seeing conditions, blind deconvolution algorithms can produce images of astonishing quality. They can be very competitive with those obtained from space, with the huge advantage of the flexibility of the instrumentation thanks to the direct access to the telescope. In this contribution we leverage deep learning techniques to significantly accelerate the blind deconvolution process and produce corrected images at a peak rate of ~100 images per second. We present two different architectures that produce excellent image corrections with noise suppression while maintaining the photometric properties of the images. As a consequence, polarimetric signals can be obtained with standard polarimetric modulation without any significant artifact. With the expected improvements in computer hardware and algorithms, we anticipate that on-site real-time correction of solar images will be possible in the near future.Comment: 16 pages, 12 figures, accepted for publication in A&

Shape evolution and shape coexistence in Pt isotopes: comparing interacting boson model configuration mixing and Gogny mean-field energy surfaces

The evolution of the total energy surface and the nuclear shape in the isotopic chain $^{172-194}$Pt are studied in the framework of the interacting boson model, including configuration mixing. The results are compared with a self-consistent Hartree-Fock-Bogoliubov calculation using the Gogny-D1S interaction and a good agreement between both approaches shows up. The evolution of the deformation parameters points towards the presence of two different coexisting configurations in the region 176 $\leq$ A $\leq$ 186.Comment: Submitted to PR

Synthesis of noble metal-decorated NH2-MIL-125 titanium MOF for the photocatalytic degradation of acetaminophen under solar irradiation

This work reports the solvothermal synthesis of a titanium-based metal organic framework (NH2-MIL-125(Ti)) and the further deposition of palladium, platinum and silver nanoparticles on its framework, with the aim to obtain visible light-driven photocatalysts. The structure of the NH2-MIL-125 was not affected by the incorporation of the metal nanoparticles, while the textural properties changed depending on the metal used. All M/NH2-MIL-125 (M = Pd, Pt, Ag) synthesized materials showed enhanced light absorption in the visible region due to the effect of the metal nanoparticles, which were mainly in reduced state as confirmed by XPS analyses. The metal nanoparticles were between 1.8 and 3.8 nm in size depending of the metal. They were responsible for the reduction in the recombination process, as suggested by photoluminescence measurements. The photocatalytic performance of M/NH2-MIL-125 was tested for the degradation of acetaminophen (ACE) under simulated solar irradiation. Pt/NH2-MIL-125 achieved the highest conversion rate (rate constant of 0.0165 min−1), with complete conversion of the contaminant in less than three hours. Scavengers studies confirmed that O.-2[rad]− radicals play a main role in the degradation process, followed by .OH radicals. The catalytic stability of Pt/NH2-MIL-125 was confirmed upon three successive reaction cycles. Different water matrices were tested to understand the effect of common inorganic ions, being the presence of bicarbonates the most detrimental to the performance of the photocatalytic processThis research was funded by the State Research Agency (PID2019-106186RB-I00/AEI/10.13039/501100011033). V. Muelas-Ramos thanks to MCIU for BES-2017-082613 gran