177 research outputs found
Australian quasigeoid modelling: Review, current status and future plans
We provide a historical review and critique of regional geoid and quasigeoid modelling over the Australian continent, covering the earliest models from the late 1960s through to the present day and beyond. The most recently released official model for GPS/GNSS surveyors, AUSGeoid2020, was specifically calculated to enable them to determine Australian Height Datum heights from Geocentric Datum of Australia 2020 ellipsoidal heights in a more direct manner without the need for post-surveying adjustments. We summarise the deficiencies in the Australian Height Datum and how they are now being addressed by a proposed new vertical height system that is underpinned by a gravimetric-only quasigeoid model. We also summarise the results of some experiments that we have conducted to explore potential refinements that could be made to our computational processes, and future plans to acquire gravity data in the problematic coastal zones using airborne methods
Exome sequencing helped the fine diagnosis of two siblings afflicted with atypical Timothy syndrome (TS2)
BACKGROUND: Long-QT syndrome (LQTS) causes a prolongation of the QT-interval in the ECG leading to life threatening tachyarrhythmia and ventricular fibrillation. One atypical form of LQTS, Timothy syndrome (TS), is associated with syndactyly, immune deficiency, cognitive and neurological abnormalities as well as distinct cranio-facial abnormalities. CASE PRESENTATION: On a family with both children diagnosed with clinical LQTS, we performed whole exome sequencing to comprehensively screen for causative mutations after a targeted candidate gene panel screen for Long-QT syndrome target genes failed to identify any underlying genetic defect. Using exome sequencing, we identified in both affected children, a p.402G > S mutation in exon 8 of the CACNA1C gene, a voltage-dependent Ca2+ channel. The mutation was inherited from their father, a mosaic mutation carrier. Based on this molecular finding and further more careful clinical examination, we refined the diagnosis to be Timothy syndrome (TS2) and thereby were able to present new therapeutic approaches. CONCLUSIONS: Our study highlights the difficulties in accurate diagnosis of patients with rare diseases, especially those with atypical clinical manifestation. Such challenge could be addressed with the help of comprehensive and unbiased mutation screening, such as exome sequencing
Modified gravity with negative and positive powers of the curvature: unification of the inflation and of the cosmic acceleration
The modified gravity, which eliminates the need for dark energy and which
seems to be stable, is considered. The terms with positive powers of the
curvature support the inflationary epoch while the terms with negative powers
of the curvature serve as effective dark energy, supporting current cosmic
acceleration. The equivalent scalar-tensor gravity may be compatible with the
simplest solar system experiments.Comment: 23 pages, 3 figures, discussion is extended, references added,
version to appear in PR
Pulsar motions from neutrino oscillations induced by a violation of the equivalence principle
We analize a possible explanation of the pulsar motions in terms of resonant
neutrino transitions induced by a violation of the equivalence principle (VEP).
Our approach, based on a parametrized post-Newtonian (PPN) expansion, shows
that VEP effects give rise to highly directional contributions to the neutrino
oscillation length. These terms induce anisotropies in the linear and angular
momentum of the emitted neutrinos, which can account for both the observed
translational and rotational pulsar motions. The violation needed to produce
the actual motions is completely compatible with the existing bounds.Comment: 6 pages, no figure
How to reach a few percent level in determining the Lense-Thirring effect?
In this paper we discuss and compare a node-only LAGEOS-LAGEOS II combination
and a node-only LAGEOS-LAGEOS II-Ajisai-Jason1 combination for the
determination of the Lense-Thirring effect. The new combined EIGEN-CG01C Earth
gravity model has been adopted. The second combination cancels the first three
even zonal harmonics along with their secular variations but introduces the
non-gravitational perturbations of Jason1. The first combination is less
sensitive to the non-conservative forces but is sensitive to the secular
variations of the uncancelled even zonal harmonics of low degree J4 and J6
whose impact grows linearly in time.Comment: Latex2e, 22 pag. 1 table, 2 figures, 45 references. Changes in the
Abstract, Introduction and Conclusions. Discussion on the non-gravitational
perturbations on Ajisai and on the impact of the secular rates of the even
zonal harmonics added. EIGEN-CG01C CHAMP+GRACE+terrestrial
gravimetry/altimetry Earth gravity model used. Reference adde
Lensing at cosmological scales: a test of higher dimensional gravity
Recent developments in gravitational lensing astronomy have paved the way to
genuine mappings of the gravitational potential at cosmological scales. We
stress that comparing these data with traditional large scale structure surveys
will provide us with a test of gravity at such scales. These constraints could
be of great importance in the framework of higher dimensional cosmological
models.Comment: 4 pages, latex, 3 figure
WMAP constraints on scalar-tensor cosmology and the variation of the gravitational constant
We present observational constraints on a scalar-tensor gravity theory by
test for CMB anisotropy spectrum. We compare the WMAP temperature
power spectrum with the harmonic attractor model, in which the scalar field has
its harmonic effective potential with curvature in the Einstein
conformal frame and the theory relaxes toward Einstein gravity with time. We
found that the present value of the scalar coupling, i.e. the present level of
deviation from Einstein gravity , is bounded to be smaller than
(), and () for . This constraint is much stronger than the bound from the solar
system experiments for large models, i.e., and 0.3 in
and limits, respectively. Furthermore, within the framework
of this model, the variation of the gravitational constant at the recombination
epoch is constrained as , and
.Comment: 7 page
Cosmological Effects of Radion Oscillations
We show that the redshift of pressureless matter density due to the expansion
of the universe generically induces small oscillations in the stabilized radius
of extra dimensions (the radion field). The frequency of these oscillations is
proportional to the mass of the radion and can have interesting cosmological
consequences. For very low radion masses () these low frequency oscillations lead to oscillations in
the expansion rate of the universe. The occurrence of acceleration periods
could naturally lead to a resolution of the coincidence problem, without need
of dark energy. Even though this scenario for low radion mass is consistent
with several observational tests it has difficulty to meet fifth force
constraints. If viewed as an effective Brans-Dicke theory it predicts
( is the number of extra dimensions), while
experiments on scales larger than imply . By deriving the
generalized Newtonian potential corresponding to a massive toroidally compact
radion we demonstrate that Newtonian gravity is modified only on scales smaller
than . Thus, these constraints do not apply for
(high frequency oscillations) corresponding to scales less than the current
experiments (). Even though these high frequency oscillations can not
resolve the coincidence problem they provide a natural mechanism for dark
matter generation. This type of dark matter has many similarities with the
axion.Comment: Accepted in Phys. Rev. D. Clarifying comments added in the text and
some additional references include
Gravitomagnetism and the Clock Effect
The main theoretical aspects of gravitomagnetism are reviewed. It is shown
that the gravitomagnetic precession of a gyroscope is intimately connected with
the special temporal structure around a rotating mass that is revealed by the
gravitomagnetic clock effect. This remarkable effect, which involves the
difference in the proper periods of a standard clock in prograde and retrograde
circular geodesic orbits around a rotating mass, is discussed in detail. The
implications of this effect for the notion of ``inertial dragging'' in the
general theory of relativity are presented. The theory of the clock effect is
developed within the PPN framework and the possibility of measuring it via
spaceborne clocks is examined.Comment: 27 pages, LaTeX, submitted to Proc. Bad Honnef Meeting on: GYROS,
CLOCKS, AND INTERFEROMETERS: TESTING GENERAL RELATIVITY IN SPACE (22 - 27
August 1999; Bad Honnef, Germany
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