Variation of the electron flux spectrum along a solar flare loop as inferred from STIX hard X-ray observations

Regularized imaging spectroscopy was introduced for the construction of electron flux images at different energies from count visibilities recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). In this work we seek to extend this approach to data from the Spectrometer/Telescope for Imaging X-rays (STIX) on-board the Solar Orbiter mission. Our aims are to demonstrate the feasibility of regularized imaging spectroscopy as a method for analysis of STIX data, and also to show how such analysis can lead to insights into the physical processes affecting the nonthermal electrons responsible for the hard X-ray emission observed by STIX. STIX records imaging data in an intrinsically different manner from RHESSI. Rather than sweeping the angular frequency plane in a set of concentric circles (one circle per detector), STIX uses $30$ collimators, each corresponding to a specific angular frequency. In this paper we derive an appropriate modification of the previous computational approach for the analysis of the visibilities observed by STIX. This approach also allows for the observed count data to be placed into non-uniformly-spaced energy bins. We show that the regularized imaging spectroscopy approach is not only feasible for analysis of the visibilities observed by STIX, but also more reliable. Application of the regularized imaging spectroscopy technique to several well-observed flares reveals details of the variation of the electron flux spectrum throughout the flare sources. We conclude that the visibility-based regularized imaging spectroscopy approach is well-suited to analysis of STIX data. We also use STIX electron flux spectral images to track, for the first time, the behavior of the accelerated electrons during their path from the acceleration site in the solar corona toward the chromospher

ALP enzymatic activity related to different implant surface microtopographies

The aim of this study was an in vitro investigation of the Alkaline Phosphatase (ALP) enzymatic activity related to different surface treatments applied to ten implant systems in order to assess if the interaction between cells and implant (osteoblastic proliferation and differentiation) was influenced by the surface structure and/or surface composition of the fixture. The originality of this study was that all implants were tested as manufactured for clinical use. The implant systems object of this study divided by the surface treatment were the following: Machined: Mk III Branemark; Sandblasted: Ankylos, Silhouette and Galant (experimental fixture); Etched: Osseotite, Mac System,MK 4 (experimental fixture), ITI; Oxided: Ti Unite, Pilot. We used Sa-OS2 cultured osteoblasts and we analyzed n14 fixtures for each implant system (n11 fixture for the cellular growth curve and n13 fixtures for the ALP activity). After 14 days the assay for the ALP activity was carried out according to Wataha et al. (JBMR, 1997) After the cellular growth evaluation in a Burker\u2019s hemocytometer chamber we quantify by a spectrophotometer at 405nm the absorbance value for each sample (the absorbance value indicate the amount of the conversion by ALP of the P-Nitro-Phenyl-Phosphate into P-Nitro-Phenol) and we corrected the mean value for cell number determined before. The data were statistically analyzed by ANOVA and Post hoc Scheffe` Test. Within the limits of the in vitro investigations we can conclude that: The etched surfaces shown more cellular growth than others. The sandblasted surfaces shown the smallest amount of cellular proliferation but a very high differentiation (according to Postiglione et al 2003 that found an inverse correlation between the two factors) We found a statistically significant difference in ALP activity only between oxided and etched surfaces (p < 0.05) The sandblasted and oxided surfaces shown more osteoblastic differentiation (more ALP enzymatic activity) Themachined surface is competitive, as regard the osteoblastic differentiation, with the rougher surfaces. Actually it\u2019s still difficult to recommend a particular rougher surface

Mapped Variably Scaled Kernels: Applications to Solar Imaging

Variably scaled kernels and mapped bases constructed via the so-called fake nodes approach are two different strategies to provide adaptive bases for function interpolation. In this paper, we focus on kernel-based interpolation and we present what we call mapped variably scaled kernels, which take advantage of both strategies. We present some theoretical analysis and then we show their efficacy via numerical experiments. Moreover, we test such a new basis for image reconstruction tasks in the framework of hard X-ray astronomical imaging

First hard X-ray imaging results by Solar Orbiter STIX

Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is one of 6 remote sensing instruments on-board Solar Orbiter. It provides hard X-ray imaging spectroscopy of solar flares by sampling the Fourier transform of the incoming flux. Aims. To show that the visibility amplitude and phase calibration of 24 out of 30 STIX sub-collimators is well advanced and that a set of imaging methods is able to provide the first hard X-ray images of the flaring Sun from Solar Orbiter. Methods. We applied four visibility-based image reconstruction methods and a count-based one to calibrated STIX observations. The resulting reconstructions are compared to those provided by an optimization algorithm used for fitting the amplitudes of STIX visibilities. Results. When applied to six flares with GOES class between C4 and M4 which occurred in May 2021, the five imaging methods produce results morphologically consistent with the ones provided by the Atmospheric Imaging Assembly on-board the Solar Dynamic Observatory (SDO/AIA) in UV wavelengths. The $\chi^2$ values and the parameters of the reconstructed sources are comparable between methods, thus confirming their robustness. Conclusions. This paper shows that the current calibration of the main part of STIX sub-collimators has reached a satisfactory level for scientific data exploitation, and that the imaging algorithms already available in the STIX data analysis software provide reliable and robust reconstructions of the morphology of solar flares