131 research outputs found
Detection of Phase Jumps of Free Core Nutation of the Earth and their Concurrence with Geomagnetic Jerks
We detected phase jumps of the Free Core Nutation (FCN) of the Earth directly
from the analysis of the Very Long Baseline Interferometer (VLBI) observation
of the Earth rotation for the period 1984-2003 by applying the Weighted Wavelet
Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function
(SPG) method. During the period, the FCN had two significant phase jumps in
1992 and 1998. These epochs coincide with the reported occurrence of
geomagnetic jerks.Comment: 8 pages, 4 figure
Constraining Ceres' interior from its Rotational Motion
Context. Ceres is the most massive body of the asteroid belt and contains
about 25 wt.% (weight percent) of water. Understanding its thermal evolution
and assessing its current state are major goals of the Dawn Mission.
Constraints on internal structure can be inferred from various observations.
Especially, detailed knowledge of the rotational motion can help constrain the
mass distribution inside the body, which in turn can lead to information on its
geophysical history. Aims. We investigate the signature of the interior on the
rotational motion of Ceres and discuss possible future measurements performed
by the spacecraft Dawn that will help to constrain Ceres' internal structure.
Methods. We compute the polar motion, precession-nutation, and length-of-day
variations. We estimate the amplitudes of the rigid and non-rigid response for
these various motions for models of Ceres interior constrained by recent shape
data and surface properties. Results. As a general result, the amplitudes of
oscillations in the rotation appear to be small, and their determination from
spaceborne techniques will be challenging. For example, the amplitudes of the
semi-annual and annual nutations are around ~364 and ~140 milli-arcseconds, and
they show little variation within the parametric space of interior models
envisioned for Ceres. This, combined with the very long-period of the
precession motion, requires very precise measurements. We also estimate the
timescale for Ceres' orientation to relax to a generalized Cassini State, and
we find that the tidal dissipation within that object was probably too small to
drive any significant damping of its obliquity since formation. However,
combining the shape and gravity observations by Dawn offers the prospect to
identify departures of non-hydrostaticity at the global and regional scale,
which will be instrumental in constraining Ceres' past and current thermal
state. We also discuss the existence of a possible Chandler mode in the
rotational motion of Ceres, whose potential excitation by endogenic and/or
exogenic processes may help detect the presence of liquid reservoirs within the
asteroid.Comment: submitted to Astronomy and Astrophysic
Submillimetric GPS distance measurement over short baselines: case study in inner consistency
Distance determination in the open air with submillimetric accuracy is a challenging task
usually carried out with the use of submillimetric distancemeters and costly observation
campaigns. The present paper represents a first step in the research of the potential use of GPS
for submillimetric distance determination for distances up to a few hundred metres consisting
in the evaluation of GPS distance determination reproducibility. As will be concluded, reliable
submillimetric precision is attainable after some hours of observation if the same equipment in
both baseline ends is used, even considering that there still remain some long-term systematic
effects of a few tenths of a millimetre. The need for precise absolute antenna calibration values
is also shown to be critical for submillimetric distance reproducibility.This research is funded by the Spanish Ministry of Science and Innovation (AYA2011-23232). The authors are grateful to the editor and the anonymous reviewers for their valuable suggestions, corrections and comments that helped improve the original manuscript.Baselga Moreno, S.; GarcĂa-Asenjo Villamayor, L.; Garrigues Talens, P. (2013). Submillimetric GPS distance measurement over short baselines: case study in inner consistency. Measurement Science and Technology. 24(7):750011-750018. https://doi.org/10.1088/0957-0233/24/7/075001S750011750018247Amiri-Simkooei, A. R., & Tiberius, C. C. J. M. (2006). Assessing receiver noise using GPS short baseline time series. GPS Solutions, 11(1), 21-35. doi:10.1007/s10291-006-0026-8Bruyninx, C., Altamimi, Z., Boucher, C., Brockmann, E., Caporali, A., Gurtner, W., … Weber, G. (2009). The European Reference Frame: Maintenance and Products. International Association of Geodesy Symposia, 131-136. doi:10.1007/978-3-642-00860-3_20Doloca, N. R., Meiners-Hagen, K., Wedde, M., Pollinger, F., & Abou-Zeid, A. (2010). Absolute distance measurement system using a femtosecond laser as a modulator. Measurement Science and Technology, 21(11), 115302. doi:10.1088/0957-0233/21/11/115302Dow, J. M., Neilan, R. E., & Rizos, C. (2009). The International GNSS Service in a changing landscape of Global Navigation Satellite Systems. Journal of Geodesy, 83(3-4), 191-198. doi:10.1007/s00190-008-0300-3Firuzabadì, D., & King, R. W. (2011). GPS precision as a function of session duration and reference frame using multi-point software. GPS Solutions, 16(2), 191-196. doi:10.1007/s10291-011-0218-8Hyun, S., Kim, Y.-J., Kim, Y., Jin, J., & Kim, S.-W. (2009). Absolute length measurement with the frequency comb of a femtosecond laser. Measurement Science and Technology, 20(9), 095302. doi:10.1088/0957-0233/20/9/095302Koivula, H., Häkli, P., Jokela, J., Buga, A., & Putrimas, R. (2011). GPS Metrology: Bringing Traceable Scale to a Local Crustal Deformation GPS Network. International Association of Geodesy Symposia, 105-112. doi:10.1007/978-3-642-20338-1_13Ray, J., Altamimi, Z., Collilieux, X., & van Dam, T. (2007). Anomalous harmonics in the spectra of GPS position estimates. GPS Solutions, 12(1), 55-64. doi:10.1007/s10291-007-0067-7Schuhler, N., SalvadĂ©, Y., LĂ©vĂŞque, S., Dändliker, R., & Holzwarth, R. (2006). Frequency-comb-referenced two-wavelength source for absolute distance measurement. Optics Letters, 31(21), 3101. doi:10.1364/ol.31.003101Snay, R. A., & Soler, T. (2008). Continuously Operating Reference Station (CORS): History, Applications, and Future Enhancements. Journal of Surveying Engineering, 134(4), 95-104. doi:10.1061/(asce)0733-9453(2008)134:4(95
ABC transporter architecture and regulatory roles of accessory domains
AbstractWe present an overview of the architecture of ATP-binding cassette (ABC) transporters and dissect the systems in core and accessory domains. The ABC transporter core is formed by the transmembrane domains (TMDs) and the nucleotide binding domains (NBDs) that constitute the actual translocator. The accessory domains include the substrate-binding proteins, that function as high affinity receptors in ABC type uptake systems, and regulatory or catalytic domains that can be fused to either the TMDs or NBDs. The regulatory domains add unique functions to the transporters allowing the systems to act as channel conductance regulators, osmosensors/regulators, and assemble into macromolecular complexes with specific properties
Estimation of the Free Core Nutation parameters from SG data: Sensitivity study and comparative analysis using linearized least-squares and Bayesian methods
Potentiel de marées, nutations et précession d'une terre rigide
Doctorat en sciences physiques -- UCL, 199
De rol van apolipoproteine ai(apo ai) en de atp bindende cassette transporter a1 (abca1) bij het cholesterol metabolisme / Stein Roosbeek.
La période de la nutation libre du noyau est de 432 + ou - 2 jours
Doctorat en sciences physiques -- UCL, 199
Les missions diplomatiques permanentes auprès des organisations internationales
Master [120] en droit, Université catholique de Louvain, 201
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