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MICROSCOPE's final results report no violation of the Weak Equivalence Principle (Universality of Free Fall) for Pt and Ti test masses quantified by an E\"otv\"os parameter $\eta\simeq10^{-15}$, an improvement by about two orders of magnitude over the best ground tests. The measurement is limited by random noise with $1/\sqrt{\nu}$ frequency dependence attributed to thermal noise from internal damping occurring in the grounding wires. From information available and the physics of internal damping we calculate the differential acceleration noise spectral density at the signal frequency, and show it varies widely between experiment sessions. Such large variations are inexplicable if translated into physical quantities such as the quality factor. While calibrations interspersed with measurement sessions may cause some such changes, they cannot explain jumps between consecutive sessions without recalibration. A potential explanation is conjectured related to a fluctuating zero depending on measurement initialization errors. The experiment was severely affected by "glitches" -- anomalous acceleration spikes related to radiation from the Earth -- injecting significant power at the signal frequency and its harmonics. The procedure used to deal with the glitches depends on introducing artificial data and leaves spurious effects potentially mimicking a violation signal or canceling a real one. An alternative procedure, relying only on real measured data, is proposed, already used in ground tests of the Weak Equivalence Principle by the E\"ot-Wash group. Future experiments aiming to exploit the full potential of space must resolve these issues, rely solely on measured data, and, more generally, readdress the experiment design., Comment: 8 pages, 1 figure

Altres ajuts: Additionally, this work was funded by the CIBERNED program (Program 1, Alzheimer Disease), FondoEuropeo de Desarrollo Regional (FEDER), Unión Europea, "Una manera de hacer Europa" and a "Marató TV3" grant (grant number: 201412.10). The cerebrospinal fluid (CSF) biomarkers amyloid-β 1-42 (Aβ), total and phosphorylated tau (t-tau, p-tau) are increasingly used to assist in the clinical diagnosis of Alzheimer's disease (AD). However, CSF biomarker levels can be affected by confounding factors. To investigate the association of white matter hyperintensities (WMHs) present in the brain with AD CSF biomarker levels. We included CSF biomarker and magnetic resonance imaging (MRI) data of 172 subjects (52 controls, 72 mild cognitive impairment (MCI), and 48 AD patients) from 9 European Memory Clinics. A computer aided detection system for standardized automated segmentation of WMHs was used on MRI scans to determine WMH volumes. Association of WMH volume with AD CSF biomarkers was determined using linear regression analysis. A small, negative association of CSF Aβ, but not p -tau and t -tau, levels with WMH volume was observed in the AD (r 2 = 0.084, p = 0.046), but not the MCI and control groups, which was slightly increased when including the distance of WMHs to the ventricles in the analysis (r 2 = 0.105, p = 0.025). Three global patterns of WMH distribution, either with 1) a low, 2) a peak close to the ventricles, or 3) a high, broadly-distributed WMH volume could be observed in brains of subjects in each diagnostic group. Despite an association of WMH volume with CSF Aβ levels in AD patients, the occurrence of WMHs is not accompanied by excess release of cellular proteins in the CSF, suggesting that WMHs are no major confounder for AD CSF biomarker assessment.

Satellite Laser Ranging (SLR) represents a very important technique of the observational space geodesy. In fact, Lunar Laser Ranging, Very Long Baseline Interferometry, Global Navigation Satellite Systems, Doppler Orbitography and Radiopositioning Integrated by Satellite, together with SLR constitute the Global Geodetic Observing System (GGOS). In the context of the GGOS activities, improvements in technology and in modeling will produce advances in geodesy and geophysics as well as in General Relativity (GR) measurements. Therefore, these important research fields are not independent, but tightly related each other. The LARASE (LAser RAnged Satellites Experiment) research program has its main objectives in tests and measurements of Einstein's theory of GR via a Precise Orbit Determination (POD) from a set of geodetic satellites. In order to reach such goals by means of very precise measurements of a number of relativistic parameters (and, at the same time, to provide a robust and unassailable error budget of the main systematic effects), we are also reviewing previous models and we are developing new models of the main perturbations (both gravitational and non-gravitational) that act on the orbits of the two LAGEOS satellites and on that of LARES. Within this paper we focus on modeling the spin vector of these satellites. The spin knowledge, both in orientation and rate, is of fundamental importance in order to correctly model the thermal effects acting on the surface of these satellites. These are very important non-gravitational perturbations (NGP) that produce long-term effects on the orbit of the cited satellites, especially for the two LAGEOS, and improvements in their modeling will be very useful both in the field of GR measurements and in those of space geodesy and geophysical applications as said above. Indeed, the current RMS of the range residuals of the LAGEOS satellites, obtained by the Analysis Centers of the International Laser Ranging Service, is at the level of a few cm since 1992, down to a cm or less during last years. However, because of the incompleteness of the dynamical models of the orbit of the satellites, empirical accelerations have been strongly used to reach such results. In this context, a step forward in the models developed for the NGP will be very useful to avoid the need of empirical accelerations and it also represents an essential prerequisite to reach a sub-mm precision in the RMS of the SLR range residuals and the corresponding benefits in geophysics and geodesy, as for stations coordinates knowledge, Earth's geocenter and reference frame realization. The paper will focus upon the improvements we obtained with respect on previous models of the spin of the two LAGEOS satellites based on averaged equations for the external torques in the rapid-spin approximation, as well as in a new general model that we developed and based on the resolution of the full set of Euler equations.

The new laser-ranged satellite LARES (LAser RElativity Satellite) is expected to provide new refined measurements of relativistic physics as well as significant contributions to space geodesy and geophysics. The very low area-to-mass ratio of this passive and dense satellite was chosen to reduce as much as possible the disturbing effects due to the non-gravitational perturbations in order to compensate for its much lower altitude with respect to the two older LAGEOS (LAser GEOdynamic Satellite) satellites, currently the best tracked satellites of the International Laser Ranging Service network. Indeed, because of its height, about 1450 km with respect to the 5900 km of the two LAGEOS, LARES is subject to a much stronger perturbation provoked by the neutral drag than that on the two LAGEOS. From a Precise Orbit Determination (POD) of LARES over a time span of about 3.7 years we have been able to measure an orbital decay in the residuals of its semi-major axis of about 1 m/yr, that corresponds to a transversal mean acceleration of about -1.457 x 10-11 m/s^2. This POD has been obtained analyzing LARES normal points with the GEODYN II (NASA/GSFC) software. Neither the neutral drag nor the thermal effects have been included in the dynamical models of GEODYN II. By means of a modified version of the SATellite Reentry Analysis Program (SATRAP) of ISTI/CNR, the neutral drag perturbation has been computed over the same time span accounting for the measured decay and considering the real evolution of the solar and geomagnetic activities for several atmospheric models. In particular, assuming as reference for the unmodeled transversal acceleration due to the neutral atmosphere the above value, the drag coefficient estimated by SATRAP is comparable to the average value estimated by GEODYN II in a least square fit of the tracking data. This means that the current best models developed for the atmosphere behavior are able to account for the observed decay, within their errors and range of applicability. A further analysis is needed in order to extract from the observed decay a possible smaller contribution related with other unmodeled effects, as the thermal ones, acting on the satellite. In this context it will be necessary to fix the contribution of the signature of the drag and of the thermal effects in the residuals of the other orbital elements of LARES. This study falls within the activities of the LARASE (LAser RAnged Satellites Experiment) research program. LARASE main goal is to provide new and refined measurements of the relativistic effects acting on the orbit of the two LAGEOS and LARES satellites. In particular, a major point of these activities is to provide a final robust and reliable error budget for the main systematic effects of gravitational and non-gravitational origin. Therefore, a special attention is devoted to the modeling of the non-gravitational perturbations acting on these passive laser-ranged satellites. Improvements in their modeling will be useful both in the field of general relativity measurements and in those of space geodesy and geophysical applications.

The LAser RAnged Satellites Experiment (LARASE) research program aims to provide an original contribution in testing and verifying Einstein's theory of General Relativity (GR) in its Weak-Field and Slow-Motion (WFSM) limit by means of the powerful Satellite Laser Ranging (SLR) technique. Therefore, in this perspective, a Precise Orbit Determination (POD) of a dedicated set of passive laser-ranged satellites is required. In particular, the joint analysis of the orbit of the two LAGEOS (LAser GEOdynamic Satellite) satellites with that of the more recently launched LARES (LAser RElativity Satellite) satellite will be exploited in order to obtain precise measurements of the gravitational interaction in the field of the Earth. A major point to be reached within the activities of LARASE is to provide the relativistic measurements with an error budget of the various systematic effects (both gravitational and non-gravitational) that be robust and reliable. This requires a careful analysis of the various disturbing effects on the orbit of the considered satellites, especially for the new LARES. This activity has been planned both for the gravitational and the non-gravitational perturbations (NGP).Therefore, we started to re-visit, update and improve previous dynamical models, especially for the NGP, and we also developed new models in such a way to improve the current dynamical models used in space geodesy to account for the main perturbations acting on the orbit of LAGEOS and LARES. We focused especially on the spin dynamics, the drag effects (especially for LARES, because of its much lower height with respect to the two LAGEOS) and, at a preliminary level, the thermal ones that, as it is well known from the literature, are very important for the LAGEOS satellites. These studies are of fundamental importance not only for the objective of a reliable error budget, but also in order to improve the POD. In this context, because of the importance of the LAGEOS satellites in the fields of space geodesy and geophysics (and the foreseeable importance of LARES in the near future) we expect that all the geodetic products within those provided the International Laser Ranging Service (ILRS) will benefit of such improvements in order to contribute to the goal of a sub-mm precision in the RMS of the SLR residuals with respect to the current cm precision. In this paper we are going to focus upon the POD results we obtained for the considered satellites within the LARASE activities. The analysis strategy and models setup will be discussed, along with the POD quality in terms of fit statistics and residuals. The current level of accuracy will be briefly assessed, along with current work for its improvement. The use of empirical accelerations will be described, as well as their removal (or minor role) in the case of the implementation in the POD software of new improved dynamical models.