The Ray Tracing Analytical Solution within the RAMOD framework. The case of a Gaia-like observer

This paper presents the analytical solution of the inverse ray tracing problem for photons emitted by a star and collected by an observer located in the gravitational field of the Solar System. This solution has been conceived to suit the accuracy achievable by the ESA Gaia satellite (launched on December 19, 2013) consistently with the measurement protocol in General relativity adopted within the RAMOD framework. Aim of this study is to provide a general relativistic tool for the science exploitation of such a revolutionary mission, whose main goal is to trace back star directions from within our local curved space-time, therefore providing a three-dimensional map of our Galaxy. The results are useful for a thorough comparison and cross-checking validation of what already exists in the field of Relativistic Astrometry. Moreover, the analytical solutions presented here can be extended to model other measurements that require the same order of accuracy expected for Gaia.Comment: 29 pages, 1 figur

Effects of membrane and biological target on the structural and allosteric properties of recoverin: a computational approach

Recoverin (Rec) is a prototypical calcium sensor protein primarily expressed in the vertebrate retina. The binding of two Ca2+ ions to the functional EF-hand motifs induces the extrusion of a myristoyl group that increases the affinity of Rec for the membrane and leads to the formation of a complex with rhodopsin kinase (GRK1). Here, unbiased all-atom molecular dynamics simulations were performed to monitor the spontaneous insertion of the myristoyl group into a model multicomponent biological membrane for both isolated Rec and for its complex with a peptide from the GRK1 target. It was found that the functional membrane anchoring of the myristoyl group is triggered by persistent electrostatic protein-membrane interactions. In particular, salt bridges between Arg43, Arg46 and polar heads of phosphatidylserine lipids are necessary to enhance the myristoyl hydrophobic packing in the Rec-GRK1 assembly. The long-distance communication between Ca2+-binding EF-hands and residues at the interface with GRK1 is significantly influenced by the presence of the membrane, which leads to dramatic changes in the connectivity of amino acids mediating the highest number of persistent interactions (hubs). In conclusion, specific membrane composition and allosteric interactions are both necessary for the correct assembly and dynamics of functional Rec-GRK1 complex

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

Some aspects of Relativistic Astrometry from within the Solar System

In this article we outline the structure of a general relativistic astrometric model which has been developed to deduce the position and proper motion of stars from 1-microarcsecond optical observations made by an astrometric satellite orbiting around the Sun. The basic assumption of our model is that the Solar System is the only source of gravity, hence we show how we modeled the satellite observations in a many-body perturbative approach limiting ourselves to the order of accuracy of $(v/c)^2$. The microarcsecond observing scenario outlined is that for the GAIA astrometric mission.Comment: 11 pages, 2 figures, accepted by Cel. Me

Antagonism of the prokineticin system prevents and reverses allodynia and inflammation in a mouse model of diabetes

Neuropathic pain is a severe diabetes complication and its treatment is not satisfactory. It is associated with neuroinflammation-related events that participate in pain generation and chronicization. Prokineticins are a new family of chemokines that has emerged as critical players in immune system, inflammation and pain. We investigated the role of prokineticins and their receptors as modulators of neuropathic pain and inflammatory responses in experimental diabetes. In streptozotocin-induced-diabetes in mice, the time course expression of prokineticin and its receptors was evaluated in spinal cord and sciatic nerves, and correlated with mechanical allodynia. Spinal cord and sciatic nerve pro- and anti-inflammatory cytokines were measured as protein and mRNA, and spinal cord GluR subunits expression studied. The effect of preventive and therapeutic treatment with the prokineticin receptor antagonist PC1 on behavioural and biochemical parameters was evaluated. Peripheral immune activation was assessed measuring macrophage and T-helper cytokine production. An up-regulation of the Prokineticin system was present in spinal cord and nerves of diabetic mice, and correlated with allodynia. Therapeutic PC1 reversed allodynia while preventive treatment blocked its development. PC1 normalized prokineticin levels and prevented the up-regulation of GluN2B subunits in the spinal cord. The antagonist restored the pro-/anti-inflammatory cytokine balance altered in spinal cord and nerves and also reduced peripheral immune system activation in diabetic mice, decreasing macrophage proinflammatory cytokines and the T-helper 1 phenotype. The prokineticin system contributes to altered sensitivity in diabetic neuropathy and its inhibition blocked both allodynia and inflammatory events underlying disease

Effects of limited irrigation water volumes on near-isohydric ‘Montepulciano’ vines trained to overhead trellis system

The thermal increase, due to the changed climatic context, is leading to marked variations in the yield and quality of the grapes and causing an increase in the use of water resources in several viticultural areas. Nevertheless, in some environments, rainfalls are scarce and there is no water availability. In this study, we compared the impact of low water irrigation volumes (DI, replacement of 70% of crop evapotranspiration) with respect to non-irrigated vines (NI), on the physiological, yield and qualitative performances of near-isohydric variety ‘Montepulciano’, trained to overhead trellis system, which requires a high-water supply. The stomatal conductance and photosynthesis values, in basal and median leaves, were higher in DI vines. All NI leaves sufered water stress, showing in the youngest leaves (position 20 and 25 along the main shoot) higher carbon isotope discrimination (δ13C) (− 25.38‰ and 25–25.77‰, respectively). At harvest, DI vines showed yield higher of 30% and 33% than NI vines in 2005 and 2006, respectively, and 18% in 2007. In environments with prolonged water shortage and low water resource, near-isohydric ‘Montepulciano’ vines, trained to overhead trellis system and irrigated with limited volumes, determined a signifcant improvement of ‘vineyard efciency’ with a yield of 19.2 t/ha with respect to 13.4 t/ha of NI vines, ensuring also more sugar content (+31%), anthocyanin concentration (+13%) and polyphenolic substances (+8%) than NI vines

The MPI + CUDA Gaia AVU-GSR Parallel Solver Toward Next-generation Exascale Infrastructures

We ported to the GPU with CUDA the Astrometric Verification Unit-Global Sphere Reconstruction (AVU-GSR) Parallel Solver developed for the ESA Gaia mission, by optimizing a previous OpenACC porting of this application. The code aims to find, with a [10,100]$\mu$as precision, the astrometric parameters of $\sim$$10^8$ stars, the attitude and instrumental settings of the Gaia satellite, and the global parameter $\gamma$ of the parametrized Post-Newtonian formalism, by solving a system of linear equations, $A\times x=b$, with the LSQR iterative algorithm. The coefficient matrix $A$ of the final Gaia dataset is large, with $\sim$$10^{11} \times 10^8$ elements, and sparse, reaching a size of $\sim$10-100 TB, typical for the Big Data analysis, which requires an efficient parallelization to obtain scientific results in reasonable timescales. The speedup of the CUDA code over the original AVU-GSR solver, parallelized on the CPU with MPI+OpenMP, increases with the system size and the number of resources, reaching a maximum of $\sim$14x, >9x over the OpenACC application. This result is obtained by comparing the two codes on the CINECA cluster Marconi100, with 4 V100 GPUs per node. After verifying the agreement between the solutions of a set of systems with different sizes computed with the CUDA and the OpenMP codes and that the solutions showed the required precision, the CUDA code was put in production on Marconi100, essential for an optimal AVU-GSR pipeline and the successive Gaia Data Releases. This analysis represents a first step to understand the (pre-)Exascale behavior of a class of applications that follow the same structure of this code. In the next months, we plan to run this code on the pre-Exascale platform Leonardo of CINECA, with 4 next-generation A200 GPUs per node, toward a porting on this infrastructure, where we expect to obtain even higher performances.Comment: 17 pages, 4 figures, 1 table, published on 1st August 2023 in Publications of the Astronomical Society of the Pacific, 135, 07450

General relativistic observable for gravitational astrometry in the context of the Gaia mission and beyond

With the launch of the Gaia mission, general relativity (GR) is now at the very core of astrometry. Given the high level of accuracy of the measurements, the development of a suitable relativistic model for carrying out the correct data processing and analysis has become a critical necessity; its primary goal is to have a consistent set of stellar astrometric parameters by which to map a relativistic kinematic of a large portion of the Milky Way and, therefore, taking the first step of the cosmic distance ladder to higher accuracy. To trace light trajectories back to the emitting stars requires an appropriate treatment of local gravity and a relativistic definition of the observable, according to the measurement protocol of GR, so that astrometry cannot be set apart from fundamental physics. Consequently, the final Gaia outputs, following completion of its operational life, will have important new implications and an overwhelming potential for astrophysical phenomena requiring the highest precision. In this regard, the present work establishes the background GR procedure to treat such relativistic measurements from within the weak gravitational field of the Solar System. In particular, we make the method explicit in the framework of the RAMOD relativistic models, consistent with the IAU (standard) resolutions and, therefore, suitable for validating the GREM approach baselined for Gaia