191 research outputs found
The Combined Solution C04 for Earth Orientation Parameters Consistent with International Terrestrial Reference Frame 2005
The Earth Orientation Center of the IERS, located at Paris Observatory, SYRTE, has the task to provide to the scientific community the international reference time series for the Earth Orientation Parameters (EOP), referred as âIERS C04 â (Combined 04), resulting from a combination of operational EOP series, each of them associated with a given geodetic technique. The procedure developed to derive the C04 solution was recently upgraded back to 1993. The main objective is to insurre its consistency with respect to the newly release ITRF 2008. Due to the separate determination of both terrestrial reference frames and EOP, there has been a slow degradation of the overall consistency since the least ITRF release in 2005, and discrepancies at the level of 50 micoarseconds for x pole coordinate exists between the current IERS C04 and the ITRF realization. We have taken this opportunity to upgrade the numerical combination procedure. Now there are better estimates of the errors of combined values. Individual EOP series have been reprocessed since 1993. Pole coordinates are now fully consistent with ITRF. The new C04 solution, referred as 08 C04, updated two times per week became the official C04 solution since february 2010
Measurement of CNGS muon neutrino speed with Borexino
We have measured the speed of muon neutrinos with the Borexino detector using
short-bunch CNGS beams. The final result for the difference in time-of-flight
between a =17 GeV muon neutrino and a particle moving at the speed of light
in vacuum is {\delta}t = 0.8 \pm 0.7stat \pm 2.9sys ns, well consistent with
zero.Comment: 6 pages, 5 figure
Estimation and analysis of multi-GNSS differential code biases using a hardware signal simulator
In ionospheric modeling, the differential code biases (DCBs) are a non-negligible error source, which are routinely estimated by the different analysis centers of the International GNSS Service (IGS) as a by-product of their global ionospheric analysis. These are, however, estimated only for the IGS station receivers and for all the satellites of the different GNSS constellations. A technique is proposed for estimating the receiver and satellites DCBs in a global or regional network by first estimating the DCB of one receiver set as reference. This receiver DCB is then used as a âknownâ parameter to constrain the global ionospheric solution, where the receiver and satellite DCBs are estimated for the entire network. This is in contrast to the constraint used by the IGS, which assumes that the involved satellites DCBs have a zero mean. The âknownâ receiver DCB is obtained by simulating signals that are free of the ionospheric, tropospheric and other group delays using a hardware signal simulator. When applying the proposed technique for Global Positioning System legacy signals, mean offsets in the order of 3 ns for satellites and receivers were found to exist between the estimated DCBs and the IGS published DCBs. It was shown that these estimated DCBs are fairly stable in time, especially for the legacy signals. When the proposed technique is applied for the DCBs estimation using the newer Galileo signals, an agreement at the level of 1â2 ns was found between the estimated DCBs and the manufacturerâs measured DCBs, as published by the European Space Agency, for the three still operational Galileo in-orbit validation satellites
Long-term evolution of orbits about a precessing oblate planet: 1. The case of uniform precession
It was believed until very recently that a near-equatorial satellite would
always keep up with the planet's equator (with oscillations in inclination, but
without a secular drift). As explained in Efroimsky and Goldreich (2004), this
opinion originated from a wrong interpretation of a (mathematically correct)
result obtained in terms of non-osculating orbital elements. A similar analysis
carried out in the language of osculating elements will endow the planetary
equations with some extra terms caused by the planet's obliquity change. Some
of these terms will be nontrivial, in that they will not be amendments to the
disturbing function. Due to the extra terms, the variations of a planet's
obliquity may cause a secular drift of its satellite orbit inclination. In this
article we set out the analytical formalism for our study of this drift. We
demonstrate that, in the case of uniform precession, the drift will be
extremely slow, because the first-order terms responsible for the drift will be
short-period and, thus, will have vanishing orbital averages (as anticipated 40
years ago by Peter Goldreich), while the secular terms will be of the second
order only. However, it turns out that variations of the planetary precession
make the first-order terms secular. For example, the planetary nutations will
resonate with the satellite's orbital frequency and, thereby, may instigate a
secular drift. A detailed study of this process will be offered in the
subsequent publication, while here we work out the required mathematical
formalism and point out the key aspects of the dynamics
Demonstrator of Time Services based on European GNSS signals: the H2020 DEMETRA Project
During 2015-2016, a European Consortium of 15 partners from 8 different
countries, developed the DEMETRA (DEMonstrator of EGNSS services based
on Time Reference Architecture), a project funded by the European Union
in the frame of the Horizon 2020 program. This project aims at
developing and experimenting time dissemination services dedicated to
specific users like traffic control, energy distribution, finance,
telecommunication, and scientific institutions. Nine services have been
developed. These services provide time dissemination with accuracy
levels from millisecond to the sub-ns, and also additional services like
certification, calibration, or integrity. Five of these services are
based on the European GNSS.
After a development phase (see PTTI 2016 presentation) the full DEMETRA
system has been working during six months for demonstration. The paper
will report about the experimentation results, showing performances and
limits of the proposed time dissemination services, aiming to foster the
exploitation of the European GNSS for timing applications
Bodily tides near spin-orbit resonances
Spin-orbit coupling can be described in two approaches. The method known as
"the MacDonald torque" is often combined with an assumption that the quality
factor Q is frequency-independent. This makes the method inconsistent, because
the MacDonald theory tacitly fixes the rheology by making Q scale as the
inverse tidal frequency.
Spin-orbit coupling can be treated also in an approach called "the Darwin
torque". While this theory is general enough to accommodate an arbitrary
frequency-dependence of Q, this advantage has not yet been exploited in the
literature, where Q is assumed constant or is set to scale as inverse tidal
frequency, the latter assertion making the Darwin torque equivalent to a
corrected version of the MacDonald torque.
However neither a constant nor an inverse-frequency Q reflect the properties
of realistic mantles and crusts, because the actual frequency-dependence is
more complex. Hence the necessity to enrich the theory of spin-orbit
interaction with the right frequency-dependence. We accomplish this programme
for the Darwin-torque-based model near resonances. We derive the
frequency-dependence of the tidal torque from the first principles, i.e., from
the expression for the mantle's compliance in the time domain. We also explain
that the tidal torque includes not only the secular part, but also an
oscillating part.
We demonstrate that the lmpq term of the Darwin-Kaula expansion for the tidal
torque smoothly goes through zero, when the secondary traverses the lmpq
resonance (e.g., the principal tidal torque smoothly goes through nil as the
secondary crosses the synchronous orbit).
We also offer a possible explanation for the unexpected frequency-dependence
of the tidal dissipation rate in the Moon, discovered by LLR
Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line
Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskersâ size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability
Tachyonic Field Theory and Neutrino Mass Running
In this paper three things are done. (i) We investigate the analogues of
Cerenkov radiation for the decay of a superluminal neutrino and calculate the
Cerenkov angles for the emission of a photon through a W loop, and for a
collinear electron-positron pair, assuming the tachyonic dispersion relation
for the superluminal neutrino. The decay rate of a freely propagating neutrino
is found to depend on the shape of the assumed dispersion relation, and is
found to decrease with decreasing tachyonic mass of the neutrino. (ii) We
discuss a few properties of the tachyonic Dirac equation (symmetries and
plane-wave solutions), which may be relevant for the description of
superluminal neutrinos seen by the OPERA experiment, and discuss the
calculation of the tachyonic propagator. (iii) In the absence of a commonly
accepted tachyonic field theory, and in view of an apparent "running" of the
observed neutrino mass with the energy, we write down a model Lagrangian, which
describes a Yukawa-type interaction of a neutrino coupling to a scalar
background field via a scalar-minus-pseudoscalar interaction. This constitutes
an extension of the standard model. If the interaction is strong, then it leads
to a substantial renormalization-group "running" of the neutrino mass and could
potentially explain the experimental observations.Comment: 13 pages; RevTeX; to appear in Cent. Eur. J. Phy
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