Dust Formation and Mass Loss in Evolved Stars     

Jan Martin Winters 《Astrophysics and Space Science》1997,255(1-2):257-266

The problem of dust formation in the circumstellar envelopes of Asymptotic Giant Branch stars is addressed. We summarize the basic thermodynamic prerequisites necessary to enable the formation and growth of solid particles from the gas phase and draw some conclusions on the evolution of the emergent dust component. In a circumstellar environment the dust grains interact with the stellar radiation field, which leads to a strong coupling among the local thermodynamic conditions and the dust formation process itself. By a consistent treatment of the physics describing the dust forming circumstellar shells of evolved stars we demonstrate, that the non-linear interaction among the dust formation process and the hydrodynamic and thermodynamic conditions of the dust forming system leads to a complex dynamical structure of these shells. Some observable consequences resulting from corresponding model calculations are given. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

First-order effects of the Earth's oblateness upon coasting bodies     

Jan F. Andrus 《Celestial Mechanics and Dynamical Astronomy》1977,15(2):217-224

The Kustaanheimo-Stiefel transformation and perturbation techniques are employed in deriving approximate closed-form expressions for the trajectories of bodies coasting about an oblate Earth. The solutions are used to obtain Lambert type solutions which include oblateness effects.Research primarily supported by a NASA-ASEE Fellowship, supporting work with the Mission Planning and Analysis Division, Johnson Space Center.  相似文献   

Use of non-tidal effects from records of tidal observations in studying recent crustal movements     

Jan Pícha 《Studia Geophysica et Geodaetica》1966,10(1):101-105

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Tropospheric ozone chemistry. The impact of cloud chemistry     

Jan E. Jonson  Ivar S. A. Isaksen 《Journal of Atmospheric Chemistry》1993,16(2):99-122

The effect of clouds and cloud chemistry on tropospheric ozone chemistry is tested out in a two-dimensional channel model covering a latitudinal band from 30 to 60° N. Three different methods describing how clouds affect gaseous species are applied, and the results are compared. The three methods are:

?A first order parameterization scheme for the removal of sulphur and other soluble gases by liquid droplets.

?A parameterization scheme for SO₂, O₃, and H₂O₂ removal is constructed. The scheme is based on the solubility of gases in liquid droplets, cycling times of air masses between clouds and cloud free areas and on the chemical interaction of SO₂ with H₂O₂ and O₃ in the liquid phase.

?Gas-aqueous-phase interactions and aqueous-phase chemical reactions are included in the reaction scheme for a number of components in areas where clouds are present.

In all three methods, a full gas-phase chemistry scheme is used. Particular emphasis is given to the study of how the ozone and hydrogen peroxide levels are affected. Significant changes in the distributions are found when aqueous-phase chemical reactions are included. The result is loss of ozone in the aqueous phase, with pronounced reductions in ozone levels in the middle and lower troposphere. Ozone levels are reduced by 10 to 30% with the largest reductions in the remote middle troposphere, bringing the values in better agreement with observations. Changes in H₂O₂ are harder to predict. Although, in one case study, hydrogen peroxide is produced within the aqueous phase, concentrations are mostly comparable or even lower than in the other cases. Hydrogen peroxide levels are, however, shown to be very pH sensitive. pH values around 5 seem to favour high H₂O₂ levels. High H₂O₂ concentrations may be found particularly in the upper part of the clouds under favourable conditions.  相似文献   

ITERATIVE SOLUTION TO PERTURBED KEPLER PROBLEM VIA KUSTAANHEIMO–STIEFEL EQUATION     

Jan Vrbik 《Celestial Mechanics and Dynamical Astronomy》1998,71(4):273-287

The main purpose of this paper is to supply a proof of formulas for constructing a perturbative solution to the perturbed Kepler problem by utilizing quaternion algebra of the Kustaanheimo–Stiefel formulation. The main advantage of this approach is a removal, from the corresponding solution, of fast oscillations (in the case of conservative forces) and small divisors (in the case of time-dependent forces). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Stratigraphic inversion of siliciclastic basin fills: a note on the distinction between supply signals resulting from tectonic and climatic forcing   总被引：2，自引：0，他引：2  

Gert Jan Weltje  Xander D. Meijer  & Poppe L. de Boer 《Basin Research》1998,10(1):129-153

Rates of accommodation and sediment supply are the principal controls on stacking patterns in siliciclastic basin fills. Stratigraphic inversion is aimed at reconstruction of these controls from the detrital record. Efforts to ‘explain’ siliciclastic basin fills have been focused on analysis and numerical modelling of sequence geometry in response to changes in accommodation, whereas comparatively few studies have attempted to address the role of sediment supply. The compositional and textural properties of siliciclastic basin fills are linked with the evolution of drainage basins through the principle of climatic–physiographic control of sediment production and supply. Application of this principle leads to a method of compositional analysis for distinguishing sequences controlled by high-frequency changes in the rate of accommodation from sequences controlled by high-frequency variations in the rate of sediment supply (order of 10 kyr). This method does not require detailed time control. Changes in rate and type of sediment supplied to depositional systems in response to environmental perturbations in drainage basins are explored in greater detail by means of a numerical model of sediment production under various scenarios of climatic and tectonic forcing. Simulation experiments suggest that drainage basins respond differently to high-frequency tectonic and climatic perturbations. Synthetic time series of cyclically forced sediment production display different types of asymmetric variations in grain size, accumulation rate and residence time of sediments in response to tectonic and climatic forcing. The results also highlight the role of vegetation as the principal modulator of climate forcing, and show that the nonlinear response to climate change may frustrate any attempts at providing broad generalizations of the system's responses. The modelling results confirm the usefulness of a combined analysis of sediment composition and sequence geometry, and the mathematically rich behaviour of the system suggests that further development of this approach is likely to increase our ability to reconstruct forcing mechanisms and initial boundary conditions from the detrital record.  相似文献   

Determination of the geopotential scale factor from satellite altimetry     

Milan Burša  Zdislav Šíma  Jan Kostelecký 《Studia Geophysica et Geodaetica》1992,36(2):101-108

Summary The geopotential scale factor R ₀ =GM/W ₀ has been determined on the basis of satellite altimetry as R _{0=(6 363 672·5±0·3) m} and/or the geopotential value on the geoid W ₀ =(62 636 256·5±3) m ² s ^–2 . It has been stated that R ₀ and/or W ₀ is independent of the tidal distortion of surface W=W ₀ due to the zero frequency tide.

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¶rt;a nmu amumuu u ama amnmuaa R ₀ =GM/W ₀ =(6 363 672,5±0,3) m u/uu aunmuaa a nmuu¶rt;a W ₀ =(62 636 256,5±3) m² s^–2. m, m R ₀ u/uu W ₀ auum m nm amu a a nuu ¶rt;au nmu W=W ₀ .

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Tidal friction — on the phase lag of body tides     

Jan Kostelecký 《Studia Geophysica et Geodaetica》1992,36(4):302-306

Summary Oceanography, seismology, gravimetry, lunar laser ranging (LLR) and satellite observations yield various values of the amplitude of the phase lag of body (solid) tides. These results are discussed, the probable value of is lower than 0.3 deg, but a sufficiently accurate value is not yet known.Dedicated to the 75th Birthday of Professor Academician Tibor Kolbenheyer  相似文献   

Shear stress results from a mixed spectral finite-difference model: Application to the Askervein Hill project data     

John L. Walmsley  Jacob Padro 《Boundary-Layer Meteorology》1990,51(1-2):169-177

Beljaars et al. (1987) developed a model for neutrally stratified boundary-layer flow over roughness changes and topography. It has been discovered that a constant parameter, , was missing in the algebraic-stress closure equations of their paper. This omission also occurred in the MSFD model code but only affects the Askervein Hill shear-stress results for the E-- turbulence closure in Beljaars et al. It also changes the stress results of Karpik (1988), but not his conclusions regarding the robustness of his improved numerical scheme. The present paper demonstrates the effect of the omission of the parameter, , and tests the sensitivity of the model to variations in its value. The new results are compared with the data and model results of Zeman and Jensen (1987).  相似文献   

The moon: Composition determined by nebular processes     

John W. Morgan  Jan Hertogen  Edward Anders 《Earth, Moon, and Planets》1978,18(4):465-478

The bulk composition of the Moon was determined by the conditions in the solar nebula during its formation, and may be quantitatively estimated from the premise that the terrestrial planets were formed by cosmochemical processes similar to those recorded in the chondrites. The calculations are based on the Ganapathy-Anders 7-component model using trace element indicators, but incorportate improved geophysical data and petrological constraints.A model Moon with 40 ppb U, a core 2% by weight (1.8% metal with 35% Ni and 0.2% FeS) and Mg/(Fe²⁺+Mg)0.75 meets the trace element restrictions, and has acceptable density, heat flow and moment of inertia ratio. The high Ni content of the core permits low-Ti mare basalts to equilibrate with metal, yet still retain substantial Ni. The silicate resembles the Taylor-Jake composition (and in some respects the waif Ganapathy-Anders Model 2a), but has lower SiO₂.Minor modifications of the model composition (U=30–35 ppb) yield a 50% melt approximating Apollo 15 green glass and a residuum of olivine plus 3 to 4% spinel; the low SiO₂, favors spinel formation, and, contrary to expectation, Cr is not depleted in the liquid. There may no longer be any inconsistency between the cosmochemical approach and arguments based on experimental petrology.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978.Unless otherwise stated, this ratio refers to themolar ratio throughout this paper.  相似文献