5,676 research outputs found
Conservative evaluation of the uncertainty in the LAGEOS-LAGEOS II Lense-Thirring test
We deal with the test of the general relativistic gravitomagnetic
Lense-Thirring effect currently ongoing in the Earth's gravitational field with
the combined nodes \Omega of the laser-ranged geodetic satellites LAGEOS and
LAGEOS II.
One of the most important source of systematic uncertainty on the orbits of
the LAGEOS satellites, with respect to the Lense-Thirring signature, is the
bias due to the even zonal harmonic coefficients J_L of the multipolar
expansion of the Earth's geopotential which account for the departures from
sphericity of the terrestrial gravitational potential induced by the
centrifugal effects of its diurnal rotation. The issue addressed here is: are
the so far published evaluations of such a systematic error reliable and
realistic? The answer is negative. Indeed, if the difference \Delta J_L among
the even zonals estimated in different global solutions (EIGEN-GRACE02S,
EIGEN-CG03C, GGM02S, GGM03S, ITG-Grace02, ITG-Grace03s, JEM01-RL03B, EGM2008,
AIUB-GRACE01S) is assumed for the uncertainties \delta J_L instead of using
their more or less calibrated covariance sigmas \sigma_{J_L}, it turns out that
the systematic error \delta\mu in the Lense-Thirring measurement is about 3 to
4 times larger than in the evaluations so far published based on the use of the
sigmas of one model at a time separately, amounting up to 37% for the pair
EIGEN-GRACE02S/ITG-Grace03s. The comparison among the other recent GRACE-based
models yields bias as large as about 25-30%. The major discrepancies still
occur for J_4, J_6 and J_8, which are just the zonals the combined
LAGEOS/LAGOES II nodes are most sensitive to.Comment: LaTex, 12 pages, 12 tables, no figures, 64 references. To appear in
Central European Journal of Physics (CEJP
LAGEOS-type Satellites in Critical Supplementary Orbit Configuration and the Lense-Thirring Effect Detection
In this paper we analyze quantitatively the concept of LAGEOS--type
satellites in critical supplementary orbit configuration (CSOC) which has
proven capable of yielding various observables for many tests of General
Relativity in the terrestrial gravitational field, with particular emphasis on
the measurement of the Lense--Thirring effect.Comment: LaTex2e, 20 pages, 7 Tables, 6 Figures. Changes in Introduction,
Conclusions, reference added, accepted for publication in Classical and
Quantum Gravit
Min-Max Theorems for Packing and Covering Odd -trails
We investigate the problem of packing and covering odd -trails in a
graph. A -trail is a -walk that is allowed to have repeated
vertices but no repeated edges. We call a trail odd if the number of edges in
the trail is odd. Let denote the maximum number of edge-disjoint odd
-trails, and denote the minimum size of an edge-set that
intersects every odd -trail.
We prove that . Our result is tight---there are
examples showing that ---and substantially improves upon
the bound of obtained in [Churchley et al 2016] for .
Our proof also yields a polynomial-time algorithm for finding a cover and a
collection of trails satisfying the above bounds.
Our proof is simple and has two main ingredients. We show that (loosely
speaking) the problem can be reduced to the problem of packing and covering odd
-trails losing a factor of 2 (either in the number of trails found, or
the size of the cover). Complementing this, we show that the
odd--trail packing and covering problems can be tackled by exploiting
a powerful min-max result of [Chudnovsky et al 2006] for packing
vertex-disjoint nonzero -paths in group-labeled graphs
A critical approach to the concept of a polar, low-altitude LARES satellite
According to very recent developments of the LARES mission, which would be
devoted to the measurement of the general relativistic Lense--Thirring effect
in the gravitational field of the Earth with Satellite Laser Ranging, it seems
that the LARES satellite might be finally launched in a polar, low--altitude
orbit by means of a relatively low--cost rocket. The observable would be the
node only. In this letter we critically analyze this scenario.Comment: LaTex2e, 11 pages, 4 figures, 1 table. Accepted for publication in
Classical and Quantum Gravit
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Towards a Multimodal Time-Based Empathy Prediction System
We describe our system for empathic emotion recognition. It is based on deep learning on multiple modalities in a late fusion architecture. We describe the modules of our system and discuss the evaluation results. Our code is also available for the research community
The LArase Satellites Spin mOdel Solutions (LASSOS): a comprehensive model for the spin evolution of the LAGEOS and LARES satellites
The two LAGEOS and LARES are laser-ranged satellites tracked with the best
accuracy ever achieved. Using their range measurements many geophysical
parameters were calculated and some General Relativity effects were directly
observed. To obtain precise and refined measurements of the effects due to the
predictions of General Relativity on the orbit of these satellites, it is
mandatory to model with high precision and accuracy all other forces, reducing
the free parameters introduced in the orbit determination. A main category of
non-gravitational forces to be considered are those of thermal origin, whose
fine modeling strongly depends on the knowledge of the evolution of the spin
vector. We present a complete model, named LASSOS, to describe the evolution of
the spin of the LAGEOS and LARES satellites. In particular, we solved Euler
equations of motion considering not-averaged torques. This is the most general
case, and the predictions of the model well fit the available observations of
the satellites spin. We also present the predictions of our model in the
fast-spin limit, based on the application of averaged equations. The results
are in good agreement with those already published, but with our approach we
have been able to highlight small errors within these previous works. LASSOS
was developed within the LARASE research program. LARASE aims to improve the
dynamical model of the two LAGEOS and LARES satellites to provide very precise
and accurate measurements of relativistic effects on their orbit, and also to
bring benefits to geophysics and space geodesy
On a new observable for measuring the Lense-Thirring effect with Satellite Laser Ranging
In this paper we present a rather extensive error budget for the difference
of the perigees of a pair of supplementary SLR satellites aimed to the
detection of the Lense-Thirring effect.Comment: LaTex2e, 14 pages, 1 table, no figures. Some changes and additions to
the abstract, Introduction and Conclusions. References updated, typos
corrected. Equation corrected. To appear in General Relativity and
Gravitatio
Perspectives in measuring the PPN parameters beta and gamma in the Earth's gravitational fields with the CHAMP/GRACE models
The current bounds on the PPN parameters gamma and beta are of the order of
10^-4-10^-5. Various missions aimed at improving such limits by several orders
of magnitude have more or less recently been proposed like LATOR, ASTROD,
BepiColombo and GAIA. They involve the use of various spacecraft, to be
launched along interplanetary trajectories, for measuring the effects of the
solar gravity on the propagation of electromagnetic waves. In this paper we
investigate what is needed to measure the combination nu=(2+2gamma-beta)/3 of
the post-Newtonian gravitoelectric Einstein perigee precession of a test
particle to an accuracy of about 10^-5 with a pair of drag-free spacecraft in
the Earth's gravitational field. It turns out that the latest gravity models
from the dedicated CHAMP and GRACE missions would allow to reduce the
systematic error of gravitational origin just to this demanding level of
accuracy. In regard to the non-gravitational errors, the spectral noise density
of the drag-free sensors required to reach such level of accuracy would amounts
to 10^-8-10^-9 cm s^-2 Hz^-1/2 over very low frequencies. Although not yet
obtainable with the present technologies, such level of compensation is much
less demanding than those required for, e.g., LISA. As a by-product, an
independent measurement of the post-Newtonian gravitomagnetic Lense-Thirring
effect with a 0.9% accuracy would be possible as well. The forthcoming Earth
gravity models from CHAMP and GRACE will further reduce the systematic
gravitational errors in both of such tests.Comment: LaTex2e, 14 pages, 3 tables, no figures, 75 references. To appear in
Int. J. Mod. Phys.
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