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111.
Our present relativistic part of the geodetic VLBI model for Earthbound antennas is a consensus model which is considered as a standard for processing high-precision VLBI observations. It was created as a compromise between a variety of relativistic VLBI models proposed by different authors as documented in the IERS Conventions 2010. The accuracy of the consensus model is in the picosecond range for the group delay but this is not sufficient for current geodetic purposes. This paper provides a fully documented derivation of a new relativistic model having an accuracy substantially higher than one picosecond and based upon a well accepted formalism of relativistic celestial mechanics, astrometry and geodesy. Our new model fully confirms the consensus model at the picosecond level and in several respects goes to a great extent beyond it. More specifically, terms related to the acceleration of the geocenter are considered and kept in the model, the gravitational time-delay due to a massive body (planet, Sun, etc.) with arbitrary mass and spin-multipole moments is derived taking into account the motion of the body, and a new formalism for the time-delay problem of radio sources located at finite distance from VLBI stations is presented. Thus, the paper presents a substantially elaborated theoretical justification of the consensus model and its significant extension that allows researchers to make concrete estimates of the magnitude of residual terms of this model for any conceivable configuration of the source of light, massive bodies, and VLBI stations. The largest terms in the relativistic time delay which can affect the current VLBI observations are from the quadrupole and the angular momentum of the gravitating bodies that are known from the literature. These terms should be included in the new geodetic VLBI model for improving its consistency. 相似文献
112.
A list of 171 stars in the galaxy M33 is presented. The stars could be considered as candidates for unique objects, such as SS 433, S Dor, P Cyg stars and possibly new kinds of peculiar objects. All these stars have been selected on the basis of the similarity to SS 433, free from interstellar absorption: OB star with strongH emission or with HeII 4686 and CIII, NIII 4630 - 4660 emission lines; a hot star inside a supernovae remnant or radio nebula. The variability of these stars has been used as an additional criterion of the selection. It is important to carry out spectral observations of the presented stars, which will allow us to select stars with intrinsicH emission. 相似文献
113.
Relativity, or gravitational physics, has widely entered geodetic modelling and parameter determination. This concerns, first
of all, the fundamental reference systems used. The Barycentric Celestial Reference System (BCRS) has to be distinguished
carefully from the Geocentric Celestial Reference System (GCRS), which is the basic theoretical system for geodetic modelling
with a direct link to the International Terrestrial Reference System (ITRS), simply given by a rotation matrix. The relation
to the International Celestial Reference System (ICRS) is discussed, as well as various properties and relevance of these
systems. Then the representation of the gravitational field is discussed when relativity comes into play. Presently, the so-called
post-Newtonian approximation to GRT (general relativity theory) including relativistic effects to lowest order is sufficient
for practically all geodetic applications. At the present level of accuracy, space-geodetic techniques like VLBI (Very Long
Baseline Interferometry), GPS (Global Positioning System) and SLR/LLR (Satellite/Lunar Laser Ranging) have to be modelled
and analysed in the context of a post-Newtonian formalism. In fact, all reference and time frames involved, satellite and
planetary orbits, signal propagation and the various observables (frequencies, pulse travel times, phase and travel-time differences)
are treated within relativity. This paper reviews to what extent the space-geodetic techniques are affected by such a relativistic
treatment and where—vice versa—relativistic parameters can be determined by the analysis of geodetic measurements. At the
end, we give a brief outlook on how new or improved measurement techniques (e.g., optical clocks, Galileo) may further push
relativistic parameter determination and allow for refined geodetic measurements. 相似文献
114.
Granulite facies tonalitic gneiss, mafic granulite and late metadolerite dykes from Bremer Bay in the Mesoproterozoic Albany Mobile Belt yield palaeomagnetic remanence that were acquired between ca 1.2 Ga and 1.1 Ga. A well‐constrained pole (66.6°N, 303.7°E) fits the ca 1.2 Ga part of the Precambrian Australian apparent polar wander path. This pole is in agreement with the high‐latitude position of Australia at ca 1.2–1.1 Ga shown on some Rodinia reconstructions. More data are required before any significance can be attributed to a second, poorly defined pole (41.8°S, 243.7°E) that falls at some distance from the ca 0.8 Ga part of the Australian apparent polar wander path. Magnetic anisotropy measurements from all samples except late granite dykes indicate northeast‐southwest elongation (i.e. parallel to the local trend of the orogenic belt) and northwest‐southeast contraction. This is in agreement with the orientation of principal strain axes deduced from structures formed during late stages of ductile deformation. The mean magnetic fabric lineation (long axis of the strain ellipsoid) is subparallel to a mineral elongation lineation and the axes of late upright to inclined folds. Short axes of the strain ellipsoid determined from magnetic fabric measurements are in a similar orientation to poles to the axial surfaces of these folds and to the associated cleavage. This mean shortening axis bisects late conjugate ductile shear zones that overprint the folds. This study has shown that structurally complex high‐grade gneisses and intrusive rocks with variable timing relationships may yield meaningful palaeomagnetic results for late stages of metamorphism. Magnetic anisotropy analysis is also seen to be a valuable tool in providing principal strain directions for late ductile deformation. 相似文献
115.
Christoph Breitkreuz Hassan Eliwa Ibrahim Khalaf Khaled El Gameel Benjamin Bühler Sergei Sergeev Alexander Larionov Mamoru Murata 《Precambrian Research》2010
Chronology of Neoproterozoic volcanosedimentary successions remains controversial for many regions of the Arabian–Nubian Shield, including the Dokhan Volcanics of NE Egypt. New U–Pb zircon SHRIMP ages have been obtained for 10 silica-rich ignimbrites and two subvolcanic dacitic bodies, mapped as Dokhan Volcanics, from the North Eastern Desert of Egypt. Crystallization ages range between 592 ± 5 and 630 ± 6 Ma (Early Ediacaran). Apparently, the late consolidation of the Arabian–Nubian Shield was accompanied by the evolution of isolated volcanic centres and basin systems which developed during a period of approx. 40 Ma, independently in space and time and probably under changing tectonic regimes. The obtained age data together with other previously published reliable ages for Dokhan Volcanics suggest two main pulses of volcanic activity: 630–623 Ma and 618–592 Ma. Five samples contain inherited zircons, with ages of 669, 715–746, 847 and 1530 Ma, supporting models that North Eastern Desert crust is mainly juvenile Neoproterozoic crust. 相似文献
116.
Nurur Rahman †‡ Janusz Krywult Patrick M. Motl Piotr Flin Sergei F. Shandarin 《Monthly notices of the Royal Astronomical Society》2006,367(2):838-850
We have made a comparative study of morphological evolution in simulated dark matter (DM) haloes and X-ray brightness distribution, and in optical clusters. Samples of simulated clusters include star formation with supernovae feedback, radiative cooling and simulation in the adiabatic limit at three different redshifts, z = 0.0, 0.10 and 0.25. The optical sample contains 208 Abell, Corwin & Olowin (ACO) clusters within redshift, z ≤ 0.25 . Cluster morphology, within 0.5 and 1.0 h −1 Mpc from cluster centre, is quantified by multiplicity and ellipticity.
We find that the distribution of the DM haloes in the adiabatic simulation appears to be more elongated than the galaxy clusters. Radiative cooling brings halo shapes in excellent agreement with observed clusters; however, cooling along with feedback mechanism makes the haloes more flattened.
Our results indicate relatively stronger structural evolution and more clumpy distributions in observed clusters than in the structure of simulated clusters, and slower increase in simulated cluster shapes compared to those in the observed one.
Within z ≤ 0.1 , we note an interesting agreement in the shapes of clusters obtained from the cooling simulations and observation. We also note that the different samples of observed clusters differ significantly in morphological evolution with redshift. We highlight a few possibilities responsible for the discrepancy in morphological evolution of simulated and observed clusters. 相似文献
We find that the distribution of the DM haloes in the adiabatic simulation appears to be more elongated than the galaxy clusters. Radiative cooling brings halo shapes in excellent agreement with observed clusters; however, cooling along with feedback mechanism makes the haloes more flattened.
Our results indicate relatively stronger structural evolution and more clumpy distributions in observed clusters than in the structure of simulated clusters, and slower increase in simulated cluster shapes compared to those in the observed one.
Within z ≤ 0.1 , we note an interesting agreement in the shapes of clusters obtained from the cooling simulations and observation. We also note that the different samples of observed clusters differ significantly in morphological evolution with redshift. We highlight a few possibilities responsible for the discrepancy in morphological evolution of simulated and observed clusters. 相似文献
117.
118.
119.
Sergei Popov David Blaschke Hovik Grigorian Mikhail Prokhorov 《Astrophysics and Space Science》2007,308(1-4):381-385
We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass
(M≲1M
⊙) objects. In our opinion this and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such
low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario
is given. However, the mechanism has its own problems, and so formation of such objects is not very probable. Secondly, we
discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations
we derive the mass spectrum of massive (M>1.8M
⊙) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of
mass constraint which can be helpful, in our opinion, in discussing different competitive models of the thermal evolution of NSs.
S.B.P. wants to thank the Organizers for support and hospitality. The work of S.B.P. was supported by the RFBR grant 06-02-16025
and by the “Dynasty” Foundation (Russia). The work of M.E.P.—by the RFBR grant 04-02-16720 and that of H.G. by DFG grant 436
ARM 17/4/05. 相似文献
120.