9,075 research outputs found
Spin precession in the Dvali-Gabadadze-Porrati braneworld scenario
In this letter we work out the secular precession of the spin of a gyroscope
in geodesic motion around a central mass in the framework of the
Dvali-Gabadadze-Porrati multidimensional gravity model. Such an effect, which
depends on the mass of the central body and on the orbit radius of the
gyroscope, contrary to the precessions of the orbital elements of the orbit of
a test body, is far too small to be detected.Comment: Latex, 5 pages, no figures, no tables, 10 reference
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
The dynamical nature of time
It is usually assumed that the "" parameter in the equations of dynamics
can be identified with the indication of the pointer of a clock. Things are not
so easy, however. In fact, since the equations of motion can be written in
terms of but also of , being any well behaved function, each
one of those infinite parametric times is as good as the Newtonian one to
study classical dynamics. Here we show that the relation between the
mathematical parametric time in the equations of dynamics and the physical
dynamical time that is measured with clocks is more complex and subtle
than usually assumed. These two times, therefore, must be carefully
distinguished since their difference may have significant consequences.
Furthermore, we show that not all the dynamical clock-times are necessarily
equivalent and that the observational fingerprint of this non-equivalence has
the same form as that of the Pioneer anomaly.Comment: 13 pages, no figure
The impact of tidal errors on the determination of the Lense-Thirring effect from satellite laser ranging
The general relativistic Lense-Thirring effect can be detected by means of a
suitable combination of orbital residuals of the laser-ranged LAGEOS and LAGEOS
II satellites. While this observable is not affected by the orbital
perturbation induced by the zonal Earth solid and ocean tides, it is sensitive
to those generated by the tesseral and sectorial tides. The assessment of their
influence on the measurement of the parameter mu, with which the
gravitomagnetic effect is accounted for, is the goal of this paper. After
simulating the combined residual curve by calculating accurately the
mismodeling of the more effective tidal perturbations, it has been found that,
while the solid tides affect the recovery of mu at a level always well below
1%, for the ocean tides and the other long-period signals Delta mu depends
strongly on the observational period and the noise level: Delta mu(tides)
amounts to almost 2% after 7 years. The aliasing effect of K1 l=3 p=1 tide and
SRP(4241) solar radiation pressure harmonic, with periods longer than 4 years,
on the perigee of LAGEOS II yield to a maximum systematic uncertainty on
\m_{LT} of less than 4% over different observational periods. The zonal
18.6-year tide does not affect the combined residuals.Comment: 24 pages, 4 tables, 6 figures, submitted to Int. Journal of Mod.
Phys. D. Changes in auctorship, references and conten
On the possibility of measuring the Earth's gravitomagnetic force in a new laboratory experiment
In this paper we propose, in a preliminary way, a new Earth-based laboratory
experiment aimed to the detection of the gravitomagnetic field of the Earth. It
consists of the measurement of the difference of the circular frequencies of
two rotators moving along identical circular paths, but in opposite directions,
on a horizontal friction-free plane in a vacuum chamber placed at South Pole.
The accuracy of our knowledge of the Earth's rotation from VLBI and the
possibility of measuring the rotators'periods over many revolutions should
allow for the feasibility of the proposed experiment.Comment: Latex2e, 8 pages, no figures, no tables, accepted for publication by
Classical and Quantum Gravity. Typo corrected in the formula of the error in
the difference of the orbital period
The relativistic precession of the orbits
The relativistic precession can be quickly inferred from the nonlinear polar
orbit equation without actually solving it.Comment: Accepted for publication in Astrophysics & Space Scienc
The stellar mass-halo mass relation of isolated field dwarfs: a critical test of CDM at the edge of galaxy formation
We fit the rotation curves of isolated dwarf galaxies to directly measure the
stellar mass-halo mass relation () over the mass range . By accounting for cusp-core
transformations due to stellar feedback, we find a monotonic relation with
little scatter. Such monotonicity implies that abundance matching should yield
a similar if the cosmological model is correct. Using the 'field
galaxy' stellar mass function from the Sloan Digital Sky Survey (SDSS) and the
halo mass function from the Cold Dark Matter Bolshoi simulation, we
find remarkable agreement between the two. This holds down to M, and to M if we
assume a power law extrapolation of the SDSS stellar mass function below M.
However, if instead of SDSS we use the stellar mass function of nearby galaxy
groups, then the agreement is poor. This occurs because the group stellar mass
function is shallower than that of the field below M,
recovering the familiar 'missing satellites' and 'too big to fail' problems.
Our result demonstrates that both problems are confined to group environments
and must, therefore, owe to 'galaxy formation physics' rather than exotic
cosmology.
Finally, we repeat our analysis for a Warm Dark Matter cosmology,
finding that it fails at 68% confidence for a thermal relic mass of keV, and keV if we use the power law extrapolation
of SDSS. We conclude by making a number of predictions for future surveys based
on these results.Comment: 22 pages; 2 Tables; 10 Figures. This is the version accepted for
publication in MNRAS. Key changes: (i) added substantially more information
on the surveys used to measure the stellar mass functions; (ii) added tests
of the robustness of our results. Results and conclusions unchanged from
previously. Minor typos corrected from previous versio
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
Locally vascularized pelvic accessory spleen
Il polisplenismo e la milza accessoria sono anomalie congenite generalmente asintomatiche. Riportiamo un raro caso di polisplenismo con milza pelvica ectopica in una donna bianca di 67 anni. Nella pelvi di sinistra all’ecografia transvaginale è stata ritrovata una massa soffice, ben definita, omogenea e vascolarizzata. La paziente è stata quindi sottoposta a valutazione con RM e TC addominale con contrasto: sono state ottenute immagini con aspetto parenchimale simile alla milza. E’ stata eseguita una scintigrafia addominale con albumina umana colloidale radiomarcata con tecnezio sulla regione pelvica con scansioni planari e SPECT. I risultati hanno mostrato la presenza di un’area di captazione del radiofarmaco nella pelvi, mentre la milza è stata normalmente visualizzata. Questi ritrovamenti hanno confermato la presenza di una milza accessoria con una arteria originante dall’aorta ed una vena che si anastomizzava con la vena mesenterica superiore. Alla nostra conoscenza, nella letteratura, esiste solo un caso di vera milza ectopica localmente vascolarizzata nella pelvi.Polysplenism and accessory spleen are congenital, usually asymptomatic anomalies. A rare case of polysplenism with ectopic spleen in pelvis of a 67-year-old, Caucasian female is reported here. A transvaginal ultrasound found a soft well-defined homogeneous and vascularized mass in the left pelvis. Patient underwent MRI evaluation and contrast-CT abdominal scan: images with parenchymal aspect, similar to spleen were obtained. Abdominal scintigraphy with 99mTc-albumin nanocolloid was performed and pelvic region was studied with planar scans and SPECT. The results showed the presence of an uptake area of the radiopharmaceutical in the pelvis, while the spleen was normally visualized. These findings confirmed the presence of an accessory spleen with an artery originated from the aorta and a vein that joined with the superior mesenteric vein. To our knowledge, in the literature, there is just only one case of a true ectopic, locally vascularized spleen in the pelvis
Will the recently approved LARES mission be able to measure the Lense-Thirring effect at 1%?
After the approval by the Italian Space Agency of the LARES satellite, which
should be launched at the end of 2009 with a VEGA rocket and whose claimed goal
is a about 1% measurement of the general relativistic gravitomagnetic
Lense-Thirring effect in the gravitational field of the spinning Earth, it is
of the utmost importance to reliably assess the total realistic accuracy that
can be reached by such a mission. The observable is a linear combination of the
nodes of the existing LAGEOS and LAGEOS II satellites and of LARES able to
cancel out the impact of the first two even zonal harmonic coefficients of the
multipolar expansion of the classical part of the terrestrial gravitational
potential representing a major source of systematic error. While LAGEOS and
LAGEOS II fly at altitudes of about 6000 km, LARES will be placed at an
altitude of 1450 km. Thus, it will be sensitive to much more even zonals than
LAGEOS and LAGEOS II. Their corrupting impact \delta\mu has been evaluated by
using the standard Kaula's approach up to degree L=70 along with the sigmas of
the covariance matrices of eight different global gravity solutions
(EIGEN-GRACE02S, EIGEN-CG03C, GGM02S, GGM03S, JEM01-RL03B, ITG-Grace02s,
ITG-Grace03, EGM2008) obtained by five institutions (GFZ, CSR, JPL, IGG, NGA)
with different techniques from long data sets of the dedicated GRACE mission.
It turns out \delta\mu about 100-1000% of the Lense-Thirring effect. An
improvement of 2-3 orders of magnitude in the determination of the high degree
even zonals would be required to constrain the bias to about 1-10%.Comment: Latex, 15 pages, 1 table, no figures. Final version matching the
published one in General Relativity and Gravitation (GRG
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