The Global sphere reconstruction (GSR) - Demonstrating an independent implementation of the astrometric core solution for Gaia

Context. The Gaia ESA mission will estimate the astrometric and physical data of more than one billion objects, providing the largest and most precise catalog of absolute astrometry in the history of Astronomy. The core of this process, the so-called global sphere reconstruction, is represented by the reduction of a subset of these objects which will be used to define the celestial reference frame. As the Hipparcos mission showed, and as is inherent to all kinds of absolute measurements, possible errors in the data reduction can hardly be identified from the catalog, thus potentially introducing systematic errors in all derived work. Aims. Following up on the lessons learned from Hipparcos, our aim is thus to develop an independent sphere reconstruction method that contributes to guarantee the quality of the astrometric results without fully reproducing the main processing chain. Methods. Indeed, given the unfeasibility of a complete replica of the data reduction pipeline, an astrometric verification unit (AVU) was instituted by the Gaia Data Processing and Analysis Consortium (DPAC). One of its jobs is to implement and operate an independent global sphere reconstruction (GSR), parallel to the baseline one (AGIS, namely Astrometric Global Iterative Solution) but limited to the primary stars and for validation purposes, to compare the two results, and to report on any significant differences. Results. Tests performed on simulated data show that GSR is able to reproduce at the sub-$\mu$as level the results of the AGIS demonstration run presented in Lindegren et al. (2012). Conclusions. Further development is ongoing to improve on the treatment of real data and on the software modules that compare the AGIS and GSR solutions to identify possible discrepancies above the tolerance level set by the accuracy of the Gaia catalog.Comment: Accepted for publication on Astronomy & Astrophysic

Gaia Reference frame determination: the AVU/GSR pipeline

The main goal of the Gaia ESA mission is the production of a 5 parameters astrometric catalog - i.e. including positions, parallaxes and the two components of the proper motions - of about 1 billion stars of our Galaxy at an accuracy level going from the few micro-arcseconds of the brightest objects to some ~100 micro-arcseconds of the faintests. This goal will be reached by means of high-precision astrometric measurements conducted by a satellite sweeping continuously the celestial sphere during its 5-years mission.A fundamental step toward the realization of this catalog is the so-called ''Sphere Reconstruction'', which determines the celestial reference frame using the observations of a subset of up to 100 million ''primary stars'' among those observed by Gaia.From a mathematical point of view, these observations translate into a large number of equations, linearized with respect to the unknown parameters around known initial values, whose solution in the least-squares sense eventually provides the catalog with its errors, and determines the Gaia reference frame.This represents an extremely challenging problem because of the high accuracy of the observations and of the large number of unknowns involved. The former issue implies that an adequately accurate relativistic astrometric model has to be used, while the huge number of unknowns and observations puts this task at the forefront of the High-Performance Computing problems.These challenges, and the absolute character of the Gaia measurements and results, calls for a careful scientific validation of the sphere reconstruction, as it was done for the previous HIPPARCOS mission. For these reasons the Gaia Data Processing and Analysis Consortium (DPAC) decided to replicate the baseline process, named AGIS (Astrometric Global Iterative Solution) with another independent solution, named GSR (Global Sphere Reconstruction) which uses a different astrometric model and different algorithms for the system solution.This talk will show the goals of GSR, describing its implementation, its results for complete sphere reconstructions and its first tests with real data. <P /

Detecting the gravito-magnetic field of the dark halo of the Milky Way - the LaDaHaD mission concept

We propose to locate transponders and atomic clocks in at least three of the Lagrange points of the Sun-Earth pair, with the aim of exploiting the time of flight asymme- try between electromagnetic signals travelling in opposite directions along polygonal loops having the Lagrange points at their vertices. The asymmetry is due to the pres- ence of a gravito-magnetic field partly caused by the angular momentum of the Sun, partly originating from the angular momentum of the galactic dark halo in which the Milky Way is embedded. We list also various opportunities which could be associated with the main objective of this Lagrange Dark Halo Detector (LaDaHaD)

Interpretable surface-based detection of focal cortical dysplasias:a Multi-centre Epilepsy Lesion Detection study

One outstanding challenge for machine learning in diagnostic biomedical imaging is algorithm interpretability. A key application is the identification of subtle epileptogenic focal cortical dysplasias (FCDs) from structural MRI. FCDs are difficult to visualize on structural MRI but are often amenable to surgical resection. We aimed to develop an open-source, interpretable, surface-based machine-learning algorithm to automatically identify FCDs on heterogeneous structural MRI data from epilepsy surgery centres worldwide. The Multi-centre Epilepsy Lesion Detection (MELD) Project collated and harmonized a retrospective MRI cohort of 1015 participants, 618 patients with focal FCD-related epilepsy and 397 controls, from 22 epilepsy centres worldwide. We created a neural network for FCD detection based on 33 surface-based features. The network was trained and cross-validated on 50% of the total cohort and tested on the remaining 50% as well as on 2 independent test sites. Multidimensional feature analysis and integrated gradient saliencies were used to interrogate network performance. Our pipeline outputs individual patient reports, which identify the location of predicted lesions, alongside their imaging features and relative saliency to the classifier. On a restricted 'gold-standard' subcohort of seizure-free patients with FCD type IIB who had T1 and fluid-attenuated inversion recovery MRI data, the MELD FCD surface-based algorithm had a sensitivity of 85%. Across the entire withheld test cohort the sensitivity was 59% and specificity was 54%. After including a border zone around lesions, to account for uncertainty around the borders of manually delineated lesion masks, the sensitivity was 67%. This multicentre, multinational study with open access protocols and code has developed a robust and interpretable machine-learning algorithm for automated detection of focal cortical dysplasias, giving physicians greater confidence in the identification of subtle MRI lesions in individuals with epilepsy

PCDD/Fs in sediments of Central Vietnam coastal lagoons: In search of TCDD

Samples from nine Central Vietnam coastal lagoons, together with three soils and sediments collected in 24 two freshwater reservoirs of the Thua Thien-Hué province, were analysed for polychlorinated dibenzo-p- 25 dioxins and dibenzofurans (PCDD/Fs). Total concentrations are low, from 192 to 2912 pg g1 and depth 26 profiles in Tam Giang-Cau Hai (TG-CH) sediment cores show only minor changes over time in PCDD/F 27 input and composition. Octachloro dibenzo-p-dioxin (OCDD) is the prevailing congener (approximately 28 90%), indicating combustion as the main PCDD/F source to these coastal systems, whereas natural forma- 29 tion might be partly responsible for the presence at depth. 2,3,7,8-Tetrachloro dibenzo-p-dioxin (TCDD), 30 largely sprayed together with Agent Orange over the study areas during the war (1961–1971), is absent 31 or very low. This result supports the hypothesis of strong degradation soon after spraying. Multivariate 32 statistical analyses account for the presence of local, short-range sources as observed in the northern part 33 of the TG-CH lagoon

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P &lt; .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients

Theoretical development and experimental validation of the Peak Stress Method for the fatigue design of steel welded structures

In the context of fatigue design of welded structures by using local approaches, the Peak Stress Method (PSM) is a rapid technique to estimate the Notch Stress Intensity Factors (NSIFs) at the weld toe and weld root, which are idealised and modelled as sharp notches having null tip radius. Essentially, the PSM takes advantage of the singular, linear elastic, opening, sliding, and tearing peak stresses evaluated at the notch tip using coarse free mesh patterns to estimate the mode I, II, and III NSIF-terms, respectively. By adopting the averaged Strain Energy Density (SED) as a fatigue strength criterion, a PSM-based design stress, i.e. the so-called equivalent peak stress, can be defined as a function of the relevant peak stresses. In present manuscript the Peak Stress Method has been theoretically developed and the proposed modifications have been verified against experimental data. Chapter 1 introduce the problem and gives the theoretical background on the local approaches used in the rest of the manuscript. In particular, the concepts of Stress Intensity Factor (SIF), the Notch Stress Intensity Factor approach (NSIF), the averaged Strain Energy Density (SED) criterion and the Peak Stress Method (PSM) will be introduced along with their theoretical background, and their application to fatigue lifetime assessment of welded joints. The Chapter 2 deals with the first extension of the PSM which allows to account for variable amplitude (VA) uniaxial as well as in-phase and out-of-phase multiaxial fatigue loadings applied to steel arc-welded joints. The extension to VA loading situations has been based on Palmgren-Miner’s linear damage rule (LDR) to account for cumulative damage. The proposed method has been validated against a large bulk of VA fatigue data taken from the literature proving the PSM as an extremely valid technique to design welded joints against CA or VA uniaxial as well as multiaxial fatigue local stresses. The proposed method has also been checked against new experimental data generated by fatigue testing non-load-carrying (nlc) fillet-welded double transverse or inclined attachments made of S355 structural steel under pure axial loading. In Chapter 3, another extension of the PSM will be presented, to estimate the constant amplitude uniaxial fatigue limit of welded structures in the stress-relieved state. A fracture mechanics criterion based on the cyclic R-curve analysis has been considered. The application of the method required the definition of an initial crack size, which value has been accurately calibrated by means of dedicate experimental tests. After the calibration, the method based on the cyclic R-curve analysis has been combined with the PSM obtaining a new procedure that allows to a rapid and effective design of weld toe failures in the infinite life region, without the need of complex and time-consuming fracture mechanics-based calculations. Finally, in Chapter 4, the possibility of experimentally determining the cyclic R-curve on complex specimens’ geometries has been investigated. In particular, the real-time crack length measurement is the most critical aspect, therefore the Direct Current Potential Drop (DCPD) method has been applied to single-edge-crack round bars subject to axial fatigue. Firstly, 3D electrical FE analyses have been performed to investigate the effect of the current and the potential probes position on the performances of the DCPD method in terms of measurability, sensitivity and reproducibility. Secondly, the accuracy of the numerical analyses has been checked against experimental results.In the context of fatigue design of welded structures by using local approaches, the Peak Stress Method (PSM) is a rapid technique to estimate the Notch Stress Intensity Factors (NSIFs) at the weld toe and weld root, which are idealised and modelled as sharp notches having null tip radius. Essentially, the PSM takes advantage of the singular, linear elastic, opening, sliding, and tearing peak stresses evaluated at the notch tip using coarse free mesh patterns to estimate the mode I, II, and III NSIF-terms, respectively. By adopting the averaged Strain Energy Density (SED) as a fatigue strength criterion, a PSM-based design stress, i.e. the so-called equivalent peak stress, can be defined as a function of the relevant peak stresses. In present manuscript the Peak Stress Method has been theoretically developed and the proposed modifications have been verified against experimental data. Chapter 1 introduce the problem and gives the theoretical background on the local approaches used in the rest of the manuscript. In particular, the concepts of Stress Intensity Factor (SIF), the Notch Stress Intensity Factor approach (NSIF), the averaged Strain Energy Density (SED) criterion and the Peak Stress Method (PSM) will be introduced along with their theoretical background, and their application to fatigue lifetime assessment of welded joints. The Chapter 2 deals with the first extension of the PSM which allows to account for variable amplitude (VA) uniaxial as well as in-phase and out-of-phase multiaxial fatigue loadings applied to steel arc-welded joints. The extension to VA loading situations has been based on Palmgren-Miner’s linear damage rule (LDR) to account for cumulative damage. The proposed method has been validated against a large bulk of VA fatigue data taken from the literature proving the PSM as an extremely valid technique to design welded joints against CA or VA uniaxial as well as multiaxial fatigue local stresses. The proposed method has also been checked against new experimental data generated by fatigue testing non-load-carrying (nlc) fillet-welded double transverse or inclined attachments made of S355 structural steel under pure axial loading. In Chapter 3, another extension of the PSM will be presented, to estimate the constant amplitude uniaxial fatigue limit of welded structures in the stress-relieved state. A fracture mechanics criterion based on the cyclic R-curve analysis has been considered. The application of the method required the definition of an initial crack size, which value has been accurately calibrated by means of dedicate experimental tests. After the calibration, the method based on the cyclic R-curve analysis has been combined with the PSM obtaining a new procedure that allows to a rapid and effective design of weld toe failures in the infinite life region, without the need of complex and time-consuming fracture mechanics-based calculations. Finally, in Chapter 4, the possibility of experimentally determining the cyclic R-curve on complex specimens’ geometries has been investigated. In particular, the real-time crack length measurement is the most critical aspect, therefore the Direct Current Potential Drop (DCPD) method has been applied to single-edge-crack round bars subject to axial fatigue. Firstly, 3D electrical FE analyses have been performed to investigate the effect of the current and the potential probes position on the performances of the DCPD method in terms of measurability, sensitivity and reproducibility. Secondly, the accuracy of the numerical analyses has been checked against experimental results

Triggering cooperation among firms: an empirical assessment of the Italian Network Contract Law

In this paper, we empirically investigate if and how the Italian Law on Network Contracts was able to trigger the establishment of networks among the involved firms. This law defined network contracts as agreements among firms to cooperate in order to improve, both individually and collectively, their innovative capacity and competitiveness in the market. It promoted them in virtually all Italian regions. During the year 2012, 213 network contracts were signed involving a total of 1083 firms. The empirical analysis shows that network contracts provide an answer to the various needs that the firms involved, if acting as single entities, cannot tackle. Indeed, on the one side, when firms that signed a network contract were characterised by mixed types of ownerships regimes, this fact negatively affected the performance of the firms involved although they ranked in the top positions in terms of correspondence with the aims of the law. The opposite holds when we consider firms within network contracts characterised by the presence of joint shareholding: this shows that despite a positive impact on performance, these networks are not specifically targeted by the law