The Spectrometer/Telescope for Imaging X-rays (STIX) will study solar flares across the hard X-ray window provided by the Solar Orbiter cluster. Similarly to the Reuven Ramaty High Energy Solar ...Spectroscopic Imager (RHESSI), STIX is a visibility-based imaging instrument that will require Fourier-based image reconstruction methods. However, in this paper we show that as for RHESSI, count-based imaging is also possible for STIX. Specifically, we introduce and illustrate a mathematical model that mimics the STIX data formation process as a projection from the incoming photon flux into a vector consisting of 120 count components. Then we test the reliability of expectation maximization for image reconstruction in the case of several simulated configurations that are typical of flare morphology.
Unbiased CLEAN for STIX in Solar Orbiter Perracchione, Emma; Camattari, Fabiana; Volpara, Anna ...
The Astrophysical journal. Supplement series,
10/2023, Letnik:
268, Številka:
2
Journal Article
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Abstract
CLEAN is an iterative deconvolution method for radio and hard-X-ray solar imaging. In a specific step of its pipeline, CLEAN requires the convolution between an idealized version of the ...instrumental point-spread function (PSF), and a map collecting point sources located at positions from where most of the flaring radiation is emitted. This step has highly heuristic motivations and the shape of the idealized PSF, which depends on the user’s choice, impacts the shape of the reconstruction. This study introduces a user-independent release of CLEAN for image reconstruction from observations recorded by the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter. Specifically, we show here that this unbiased release of CLEAN outperforms the standard version of the algorithm, with reconstructions in line with the ones offered by other imaging methods developed in the STIX framework.
In this “Methods” paper, we investigate how to compress SDO/AIA data by transforming the AIA source maps into the Fourier domain at a limited set of spatial frequency points. Specifically, we show ...that compression factors of one order of magnitude or more can be achieved without significant loss of information. The exploration of data compression techniques is motivated by our plan to train Neural Networks on AIA data to identify features that lead to a solar flare. Because the data is spatially resolved and polychromatic (as opposed to spatially-integrated, such as GOES, or monochromatic, such as magnetograms), the network can be trained to recognize features representing changes in plasma properties (e.g., temperature, density), in addition to temporal changes revealed by Sun-integrated data or physical restructuring revealed by monochromatic spatially-resolved data. However, given the immense size of a suitable training set of SDO/AIA data (more than 10
11
pixels, requiring more than one TB of memory), some form of data compression scheme is highly desirable and, in this paper, we propose a Fourier based one. Numerical experiments show that, not only Fourier maps retain more information on the original AIA images compared to straightforward binning of spatial pixels, but also that certain types of changes in source structure (e.g., thinning or thickening of an elongated filamentary structure) may be equally, if not more, recognizable in the spatial frequency domain. We conclude by describing a program of work designed to exploit the use of spatial Fourier transform maps to identify features in four-dimensional data hypercubes containing spatial, spectral, and temporal information of the state of the solar plasma prior to possible flaring activity.
Collective memory processes have been studied from many different perspectives. For example, while psychology has investigated collaborative recall in small groups, other research traditions have ...focused on flashbulb memories or on the cultural processes involved in the formation of collective memories of entire nations. In this article, considering the online encyclopedia Wikipedia as a global memory place, we analyze online commemoration patterns of traumatic events. We extracted 88 articles and talk pages related to traumatic events, and using logistic regression, we analyzed their edit activity comparing it with more than 370,000 other Wikipedia pages. Results show that the relative amount of edits during anniversaries can significantly distinguish between pages related to traumatic events and other pages. The logistic regression results, together with the transcription of a group of messages exchanged by the users during the anniversaries of the September 11 attacks and the Virginia Tech massacre, suggest that commemoration activities take place in Wikipedia, opening the way to the quantitative study of online collective memory building processes on a large scale.
Background
Patients who undergo polypectomy are at increased risk of adenoma recurrence. The preventive potential of vitamins (A, C and E) and selenium supplementation represent an interesting ...opportunity for colorectal cancer prevention.
Methods
To assess the efficacy of a combination of these micronutrients in reducing the incidence of recurrent adenomas in subjects on post-polypectomy endoscopic follow-up, a double-blind placebo-controlled randomized trial was started in Italy in 1988. A total of 411 patients were randomized to receive either an active compound (200 μg selenium, 30 mg zinc, 2 mg vitamin A, 180 mg vitamin C, 30 mg vitamin E) or a placebo daily for 5 years. Of them, 330 had follow-up colonoscopy (164 in the intervention and 166 in the placebo group).
Results
After a median follow-up of 4 years (range 1–15 years), 100 patients had recurrence: 38 in the intervention and 62 in the placebo arm. The 15-year cumulative incidence of recurrence was 48.3 % in the intervention and 64.5 % in the placebo arm (HR = 0.59; log-rank
P
= 0.009). A 39 % reduction of the risk of recurrence was observed in the intervention compared to the placebo group (adjusted HR = 0.61; 95 % CI 0.41–0.92): the risk reduction was similar for small tubular (adjusted HR = 0.61; 95 % CI 0.37–0.99) and advanced adenomas (adjusted HR = 0.50; 95 % CI 0.24–1.01).
Conclusions
Our study showed a statistically significant effect of antioxidant supplementation on adenoma recurrence. Further clinical trials are needed to address the role of antioxidants in subgroups of subjects at increased risk for colorectal cancer.
Designing more sustainable cities is increasingly pressing, and mobility behaviour plays an important role in how much cities are socially, economically and environmentally sustainable. We report our ...experience in deploying the third edition of an urban game that exploits gamification for promoting a positive behavioural change of mobility habits. This edition of Play&Go ran for 6 months and involved 635 active players who tracked their trips on sustainable transportation means such as by bike, bus, train and walking trips. Players tracked 54293 trips in total, corresponding to 244.394 sustainable kilometres. We evaluated the user experience of Play&Go and its impact through questionnaires, interviews and game log analysis, and we report on players’ participation and engagement, reported behaviour change and impact of different gamification motivational elements.
Abstract
In this work, we introduce a novel estimator of the predictive risk with Poisson data, when the loss function is the Kullback–Leibler divergence, in order to define a regularization ...parameter’s choice rule for the expectation maximization (EM) algorithm. To this aim, we prove a Poisson counterpart of the Stein’s Lemma for Gaussian variables, and from this result we derive the proposed estimator showing its analogies with the well-known Stein’s unbiased risk estimator valid for a quadratic loss. We prove that the proposed estimator is asymptotically unbiased with increasing number of measured counts, under certain mild conditions on the regularization method. We show that these conditions are satisfied by the EM algorithm under the hypothesis that the underlying matrix has positive entries and then we apply this estimator to select the EM optimal reconstruction. We present some numerical tests in the case of image deconvolution, comparing the performances of the proposed estimator with other methods available in the literature, both in the inverse crime and non-inverse crime setting.
Cardiac amyloidosis is a serious and progressive infiltrative disease caused by the deposition of amyloid fibrils in the heart. In the last years, a significant increase in the diagnosis rate has ...been observed owing to a greater awareness of its broad clinical presentation. Cardiac amyloidosis is frequently associated to specific clinical and instrumental features, so called "red flags", and it appears to occur more commonly in particular clinical settings such as multidistrict orthopedic conditions, aortic valve stenosis, heart failure with preserved or mildly reduced ejection fraction, arrhythmias, plasma cell disorders. Multimodality approach and new developed techniques such PET fluorine tracers or artificial intelligence may contribute to strike up extensive screening programs for an early recognition of the disease.
Models of particle acceleration in solar eruptive events suggest that roughly equal energy may go into accelerating electrons and ions. However, while previous solar X-ray spectroscopic imagers have ...transformed our understanding of electron acceleration, only one resolved image of γ-ray emission from solar accelerated ions has ever been produced. This paper outlines a new satellite instrument concept—the large imaging spectrometer for solar accelerated nuclei (LISSAN)—with the capability not only to observe hundreds of events over its lifetime, but also to capture multiple images per event, thereby imaging the dynamics of solar accelerated ions for the first time. LISSAN provides spectroscopic imaging at photon energies of 40 keV–100 MeV on timescales of ≲10 s with greater sensitivity and imaging capability than its predecessors. This is achieved by deploying high-resolution scintillator detectors and indirect Fourier imaging techniques. LISSAN is suitable for inclusion in a multi-instrument platform such as an ESA M-class mission or as a smaller standalone mission. Without the observations that LISSAN can provide, our understanding of solar particle acceleration, and hence the space weather events with which it is often associated, cannot be complete.
Abstract
In this work we deal with parametric inverse problems, which consist in recovering a finite number of parameters describing the structure of an unknown object, from indirect measurements. ...State-of-the-art methods for approximating a regularizing inverse operator by using a dataset of input–output pairs of the forward model rely on deep learning techniques. In these approaches, a neural network (NN) is trained to predict the value of the sought parameters directly from the data. In this paper, we show that these methods provide suboptimal results when a regularizing inverse operator is discontinuous with respect to the Euclidean topology. Hence, we propose a two-step strategy for approximating it by means of a NN, which works under general topological conditions. First, we embed the parameters into a subspace of a low-dimensional Euclidean space; second, we use a NN to approximate a homeomorphism between the subspace and the image of the parameter space through the forward operator. The parameters are then retrieved by applying the inverse of the embedding to the network predictions. The results are shown for the problem of x-ray imaging of solar flares with data from the
Spectrometer/Telescope for Imaging X-rays
. In this case, the parameter space is homeomorphic to a Moebius strip. Our simulation studies show that the use of a NN for predicting the parameters directly from the data yields systematic errors due to the non-Euclidean topology of the parameter space. The proposed strategy overcomes the discontinuity issues and furnishes stable and accurate reconstructions.
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