GOCE: assessment of GPS-only gravity field determination   总被引：2，自引：1，他引：1  

Adrian Jäggi  H. Bock  U. Meyer  G. Beutler  J. van den IJssel 《Journal of Geodesy》2015,89(1):33-48

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The Restricted Three-Body Problem: Comments on the Rotational Effect     

Rodica Roman  Sorin Adrian Roman 《Astrophysics and Space Science》2006,301(1-4):179-184

The synchronization between the orbital motion and axial rotation of the two component stars of a binary system is reviewed. Some previous published papers are mentioned and the general conclusion is outlined: If we shall use a rotating coordinate system synchronous with one of the two stellar axial rotations, it is not possible to obtain a Jacobi integral and the Roche geometry cannot be further analyzed. In addition, a theoretical approach is summarized in order to use the axial rotations of the two component stars, even if the constants of the stellar structure (k₂)₁, (k₂)₂must be taken into consideration. So it is found that if the stellar angular velocities are higher than the corresponding Keplerian angular velocity (ω_i≫ ω_k, i= ), the problem of the rotational effect could be of practical consideration. Finally, a theoretical relationship between the two constants (k₂)₁and (k₂)₂of the stellar structure is established.  相似文献   

Empirical models of pressure and density in Saturn's interior: Implications for the helium concentration, its depth dependence, and Saturn's precession rate     

Ravit Helled  Gerald Schubert 《Icarus》2009,199(2):368-377

We present ‘empirical’ models (pressure vs. density) of Saturn's interior constrained by the gravitational coefficients J₂, J₄, and J₆ for different assumed rotation rates of the planet. The empirical pressure-density profile is interpreted in terms of a hydrogen and helium physical equation of state to deduce the hydrogen to helium ratio in Saturn and to constrain the depth dependence of helium and heavy element abundances. The planet's internal structure (pressure vs. density) and composition are found to be insensitive to the assumed rotation rate for periods between 10h:32m:35s and 10h:41m:35s. We find that helium is depleted in the upper envelope, while in the high pressure region (P?1 Mbar) either the helium abundance or the concentration of heavier elements is significantly enhanced. Taking the ratio of hydrogen to helium in Saturn to be solar, we find that the maximum mass of heavy elements in Saturn's interior ranges from ∼6 to 20 M_⊕. The empirical models of Saturn's interior yield a moment of inertia factor varying from 0.22271 to 0.22599 for rotation periods between 10h:32m:35s and 10h:41m:35s, respectively. A long-term precession rate of about ^0.754″ yr⁻¹ is found to be consistent with the derived moment of inertia values and assumed rotation rates over the entire range of investigated rotation rates. This suggests that the long-term precession period of Saturn is somewhat shorter than the generally assumed value of 1.77×¹⁰⁶ years inferred from modeling and observations.  相似文献   

Will point sources spoil 21-cm tomography?     

Adrian Liu  Max Tegmark  Matias Zaldarriaga 《Monthly notices of the Royal Astronomical Society》2009,394(3):1575-1587

21-cm tomography is emerging as a promising probe of the cosmological dark ages and the epoch of reionization, as well as a tool for observational cosmology in general. However, serious sources of foreground contamination must be subtracted for experimental efforts to be viable. In this paper, we focus on the removal of unresolved extragalactic point sources with smooth spectra, and evaluate how the residual foreground contamination after cleaning depends on instrumental and algorithmic parameters. A crucial but often ignored complication is that the synthesized beam of an interferometer array shrinks towards higher frequency, causing complicated frequency structure in each sky pixel as 'frizz' far from the beam centre contracts across unresolved radio sources. We find that current-generation experiments should none the less be able to clean out this point source contamination adequately, and quantify the instrumental and algorithmic design specifications required to meet this foreground challenge.  相似文献   

Resolving cosmic structure formation with the Millennium-II Simulation     

Michael Boylan-Kolchin  Volker Springel  Simon D. M. White  Adrian Jenkins  Gerard Lemson 《Monthly notices of the Royal Astronomical Society》2009,398(3):1150-1164

We present the Millennium-II Simulation (MS-II), a very large N -body simulation of dark matter evolution in the concordance Λ cold dark matter (ΛCDM) cosmology. The MS-II assumes the same cosmological parameters and uses the same particle number and output data structure as the original Millennium Simulation (MS), but was carried out in a periodic cube one-fifth the size  (100  h ⁻¹ Mpc)  with five times better spatial resolution (a Plummer equivalent softening of  1.0  h ⁻¹ kpc  ) and with 125 times better mass resolution (a particle mass of  6.9 × 10⁶  h ⁻¹ M_⊙  ). By comparing results at MS and MS-II resolution, we demonstrate excellent convergence in dark matter statistics such as the halo mass function, the subhalo abundance distribution, the mass dependence of halo formation times, the linear and non-linear autocorrelations and power spectra, and halo assembly bias. Together, the two simulations provide precise results for such statistics over an unprecedented range of scales, from haloes similar to those hosting Local Group dwarf spheroidal galaxies to haloes corresponding to the richest galaxy clusters. The 'Milky Way' haloes of the Aquarius Project were selected from a lower resolution version of the MS-II and were then resimulated at much higher resolution. As a result, they are present in the MS-II along with thousands of other similar mass haloes. A comparison of their assembly histories in the MS-II and in resimulations of 1000 times better resolution shows detailed agreement over a factor of 100 in mass growth. We publicly release halo catalogues and assembly trees for the MS-II in the same format within the same archive as those already released for the MS.  相似文献   

Output and abatement effects of allocation readjustment in permit trade   总被引：2，自引：0，他引：2  

Thomas Sterner  Adrian Muller 《Climatic change》2008,86(1-2):33-49

In permit trading systems, free initial allocation is common practice. A recent example is the European Union Greenhouse Gas Emission Trading Scheme (EU-ETS). We investigate effects of different free allocation schemes on incentives and identify significant perverse effects on abatement and output employing a simple multi-period model. Firms have incentives for strategic action if allocation in one period depends on their actions in previous ones and thus can be influenced by them. These findings play a major role where trading schemes become increasingly popular as environmental or resource use policy instruments. This is of particular relevance in the EU-ETS where the current period is a trial-period before the first commitment period of the Kyoto protocol. Finally, this paper fills a gap in the literature by establishing a consistent terminology for initial allocation.  相似文献   

Polar night vortex breakdown and large-scale stirring in the southern stratosphere     

Alvaro de la Cámara  C. R. Mechoso  K. Ide  R. Walterscheid  G. Schubert 《Climate Dynamics》2010,35(6):965-975

The present paper examines the vortex breakdown and large-scale stirring during the final warming of the Southern Hemisphere stratosphere during the spring of 2005. A unique set of in situ observations collected by 27 superpressure balloons (SPBs) is used. The balloons, which were launched from McMurdo, Antarctica, by the Stratéole/VORCORE project, drifted for several weeks on two different isopycnic levels in the lower stratosphere. We describe balloon trajectories and compare them with simulations obtained on the basis of the velocity field from the GEOS-5 and NCEP/NCAR reanalyses performed with and without VORCORE data. To gain insight on the mechanisms responsible for the horizontal transport of air inside and outside the well-isolated vortex we examine the balloon trajectories in the framework of the Lagrangian properties of the stratospheric flow. Coherent structures of the flow are visualized by computing finite-time Lyapunov exponents (FTLE). A combination of isentropic analysis and FTLE distributions reveals that air is stripped away from the vortex’s interior as stable manifolds eventually cross the vortex’s edge. It is shown that two SPBs escaped from the vortex within high potential vorticity tongues that developed in association with wave breaking at locations along the vortex’s edge where forward and backward FTLE maxima approximately intersect. The trajectories of three SPBs flying as a group at the same isopycnic level are examined and their behavior is interpreted in reference to the FTLE field. These results support the concept of stable and unstable manifolds governing transport of air masses across the periphery of the stratospheric polar vortex.  相似文献   

Desiccation Induced Shrinkage of Compacted Lateritic Soil Treated with Blast Furnace Slag     

Kolawole J. Osinubi  Adrian O. Eberemu 《Geotechnical and Geological Engineering》2010,28(5):537-547

A reddish brown lateritic soil treated with up to 15% blast furnace slag was compacted with three compactive efforts, (standard Proctor, West African Standard and modified Proctor) with moulding water contents ranging between 10 and 20% of weight of dry mixture. Compacted samples were extruded and allowed to dry in the laboratory for 30 days with measurements taken every 5 days to monitor volumetric changes due to drying. Four specimens compacted on the wet side of optimum using standard proctor effort; at the various slag treatments after 10 days of drying were subjected to four cycles of drying and three cycles of wetting. The results obtained showed that the changes in mass and volumetric shrinkage were rapid within the first 5 days of drying. These changes were proportional to the moulding water contents and were unaffected by the compactive effort. The volumetric shrinkage strain increased with increasing moulding water content and compactive efforts. As the water content relative to the optimum increased towards the wet side, the volumetric shrinkage strain increased and it decreased towards the dry side. For all compaction energies, the initial degree of saturation increased and regardless of the slag content, the volumetric shrinkage strain increased. As the slag content increased, the initial degree of saturation at which the permissible 4% volumetric shrinkage occurred increased. Slag content had marginal effects on the volumetric shrinkage strain as no clear trend was established. For each slag treatment the volumetric shrinkage strain did not vary significantly with increasing number of drying cycles.  相似文献   

Photoluminescence of zircon (ZrSiO4) doped with REE3+ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er)     

Henrik Friis  Adrian A. Finch  C. Terry Williams  John M. Hanchar 《Physics and Chemistry of Minerals》2010,37(6):333-342

The photoluminescence properties of synthetic zircon, ZrSiO₄, doped with REE³⁺ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er) were investigated using combined excitation and emission spectroscopy. All samples showed luminescence characteristics of intra-ion energy transitions, similar to other lanthanide-doped materials. However, the relative intensities were dependent on the energy of excitation and the presence of charge-transfer bands were inferred from excitation spectra. From the data, we conclude that the lanthanides in zircon occur in more than one type of coordination. Energy transfer between different lanthanides was observed in some co-doped samples and emissions that were unassigned in previous studies have been assigned to specific lanthanides based on excitation spectroscopy.  相似文献   

δB, Sr, Mg and B in a modern Porites coral: the relationship between calcification site pH and skeletal chemistry     

Nicola Allison  Adrian A. Finch 《Geochimica et cosmochimica acta》2010,74(6):1790-6360

Sr/Ca, B/Ca, Mg/Ca and δ¹¹B were determined at high spatial resolution across ∼1 year of a modern Hawaiian Porites lobata coral by secondary ion mass spectrometry (SIMS). We observe significant variations in B/Ca, Mg/Ca, Sr/Ca and δ¹¹B over short skeletal distances (nominally equivalent to periods of <20 days). This heterogeneity probably reflects variations in the composition of the extracellular calcifying fluid (ECF) from which the skeleton precipitates. Calcification site pH (total scale) was estimated from skeletal δ¹¹B and ranged from 8.3 to 8.8 (± ∼0.1) with a mean of ∼8.6. Sr/Ca and B/Ca heterogeneity is not simply correlated with calcification site pH, as might be expected if Ca-ATPase activity increases the pH and decreases the Sr/Ca and B(OH)₄⁻/CO₃²⁻ ratios of the ECF. We produced a simple model of the ECF composition and the skeleton deposited from it, over a range of calcium transport and carbonate scenarios, which can account for these observed geochemical variations. The relationship between the pH and Sr/Ca of the ECF is dependent on the concentration of DIC at the calcification site. At higher DIC concentrations the ECF has a high capacity to buffer the [H⁺] changes induced by Ca-ATPase pumping. Conversely, at low DIC concentrations, this buffering capacity is reduced and ECF pH changes more rapidly in response to Ca-ATPase pumping. The absence of a simple correlation between ECF pH and skeletal Sr/Ca implies that calcification occurred under a range of DIC concentrations, reflecting variations in the respiration and photosynthesis of the coral and symbiotic zooxanthellate in the overlying coral tissues. Our observations have important implications for the use of coral skeletons as indicators of palaeo-ocean pH.  相似文献