Compression of ephemerides     

Deprit  André  Poplarchek  Walter  Deprit-Bartholomé  Andrée 《Celestial Mechanics and Dynamical Astronomy》1975,11(1):53-58

Approximations in the normL ₁ by Chebyshev polynomials are generated to represent astronomical ephemerides over large intervals of time.  相似文献   

Spin-forbidden resonance multiplets in light elements     

B. Edlén  H. P. Palenius  K. Bockasten  R. Hallin  J. Bromander 《Solar physics》1969,9(2):432-438

We present new laboratory data on the multiplets 2s ^{2 1} S -2s2p ³ P, 2s ²2p ² P - 2s2p ^{2 4} P, and 2s ²2p ^{2 3} P - 2s2p ^{3 5} S in nitrogen, oxygen and fluorine, and discuss theZ-dependence of their wave-numbers. These multiplets are very faint in laboratory light sources, but can become prominent in astrophysical sources of low density. Our results confirm the solar identifications of the nitrogen and oxygen multiplets made by Burtonet al. Predicted positions of the corresponding multiplets in neon are given.  相似文献   

Origin and evolution of the earth-moon system     

Hannes Alfvén  Gustaf Arrhenius 《Earth, Moon, and Planets》1972,5(1-2):210-230

The origin and evolution of the Earth-Moon system is studied by comparing it to the satellite systems of other planets. The normal structure of a system of secondary bodies orbiting around a central body depends essentially on the mass of the central body. The Earth with a mass intermediate between Uranus and Mars should have a normal satellite system that consists of about half a dozen satellites each with a mass of a fraction of a percent of the lunar mass. Hence, the Moon is not likely to have been generated in the environment of the Earth by a normal accretion process as is claimed by some authors.Capture of satellites is quite a common process as shown by the fact that there are six satellites in the solar system which, because they are retrograde, must have been captured. There is little doubt that the Moon is also a captured satellite, but its capture orbit and tidal evolution are still incompletely understood.The Earth and the Moon are likely to have been formed from planetesimals accreting in particle swarms in Kepler orbits (jet streams). This process leads to the formation of a cool lunar interior with an outer layer accreted at increasingly higher temperatures. The primeval Earth should similarly have formed with a cool inner core surrounded in this case by a very strongly heated outer core and with a mantle accreted slowly and with a low average temperature but with intense transient heating at each individual impact site.  相似文献   

Collective resonant phenomena on small bodies in the solar system     

Ch. Froeschlé  C. Froeschlé 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):71-89

For both asteroids and meteor streams, and also for comets, resonances play a major role for their orbital evolutions but on different time scales. For asteroids both mean motion resonances and secular resonances not only structure the phase space of regular orbits but are mainly at the origin for the inherent chaos of planet crosser objects.For comets and their chaotic routes temporary trapping into orbital resonances is a well known phenomenon. In addition for slow diffusion through the Kuiper belt resonances are the only candidates for originating a slow chaos.Like for asteroids, resonances with Jupiter play a major role for the orbital evolution of meteor streams. Crossing of separatrix like zones appears to be crucial for the formation of arcs and for the dissolution of streams. In particular the orbital inclination of a meteor stream appears to be a critical parameter for arc formation. Numerical results obtained in an other context show that the competition between the Poynting-Robertson drag and the gravitational interaction of grains near the 2/1 resonance might be very important in the long run for the structure of meteor streams.  相似文献   

Chlorinated hydrocarbons in the seawater and surface sediments of Blanca Bay,Argentina     

JoséLuis Sericano  Adan E. Pucci 《Estuarine, Coastal and Shelf Science》1984,19(1):27-51

In order to characterize our study area and to provide reference values to be used in the future to measure the changes produced by an increase in contamination, the concentrations of chlorinated hydrocarbons have been investigated in fifty-one samples of seawater, taken at four different depths: air-sea interface, surface, one metre and bottom waters, and in twenty-three samples of surface sediments from Blanca Bay, Argentina. Of eleven organochlorine compounds we were looking for (α BHC, lindane, heptachlor, δ BHC. aldrin, heptachlor epoxide, dieldrin, o-p′DDD, p-p′DDD, o-p′DDT and p-p′DDT), seven could be detected in seawater and three in surface sediments with the following mean concentrations: α-BHC=48·2 ng l^?1; lindane=54·2 ng l^?1; heptachlor=45·0 ng l^?1; δ BHC=12·5 ng l^?1; aldrin=61·8 ng l^?1 and ΣDDT=67·0 ng l^?1; and δ BHC=3·2 ng g^?1; lindane=4·2 ng g^?1 and heptachlor=1·0 ng g^?1 for seawater, regarding the surface waters, and sediment samples, respectively.Concentration factors among the different water layers were also studied to see if there was any correlation between chlorinated hydrocarbon contents and the water depths from which the samples were taken. As a mean value, the air-sea interface water contains 18 times more of these compounds than that of the water near the bottom. A comparison of the values corresponding to seawater and surface sediments from our study area with those levels measured in samples from other geographic locations is also presented.With the purpose to detect a relationship between chlorinated hydrocarbon concentrations and the contents of particulate matter (PM) on the one hand, and particulate organic material (POM) on the other hand, four groups of samples containing different amounts of PM and POM, respectively were formed. From a comparison of the results obtained, lindane, heptachlor and δ BHC showed a tendency to lower concentrations in those samples containing little PM whereas α BHC and aldrin remained without important changes. No significant correlation was found between organochlorine levels and contents of POM.  相似文献   

Far-infrared properties of metallic dust grains     

Toshihiko Tanabé  Takashi Onaka  Fumio Kamijo 《Astrophysics and Space Science》1984,98(2):323-342

Far-infrared properties of metallic particle are reinvestigated in detail. In the far-infrared region, absorption due to the eddy current generally dominates over that obtained by using the Rayleigh approximation erroneusly. The wavelength dependence of the eddy current term is examined carefully and shown to be less steep than that predicted by the Rayleigh approximation for dust grains larger than 100 nm in radius. It also depends more sensitively on the grain size. A wider temperature distribution is expected corresponding to a given size distribution and hence the emission spectrum becomes less steep than the preductions by the Rayleigh approximation. Iron and graphite particles are investigated as typical interstellar metallic grains. Effects of coating of dielectric materials are also examined. Comparisons with experimental results and with observations are discussed.  相似文献   

Position and velocity reliability testing in degraded GPS signal environments   总被引：3，自引：2，他引：1  

Heidi?Kuusniemi  Gérard?LachapelleEmail author  Jarmo?H.?Takala 《GPS Solutions》2004,8(4):226-237

Reliability testing, namely receiver autonomous integrity monitoring (RAIM), consists of statistical testing of least-squares residuals of observations, e.g., on an epoch-by-epoch basis aiming towards reliable navigation fault detection and exclusion (FDE). In this paper, classic RAIM and FDE methods are extended with testing of range-rate residuals to find inconsistent velocity solutions in order to contribute to the reliability of the system with special focus on degraded signal environments. Reliability enhancement efforts discussed include a Backward-FDE scheme based on statistical outlier detection and an iteratively reweighted robust estimation technique, a modified Danish method. In addition, measurement weighting assigned to code and Doppler observations is assessed in the paper in order to allow fitting a priori variance models to the estimation processes. The schemes discussed are also suitable in terms of computational convenience for a combined GPS/Galileo system. The objective of this paper is to assess position and velocity reliability testing and enhancement in urban and indoor conditions and to analyze the navigation accuracy conditions with high sensitivity GPS (HSGPS) tests. The results show the necessity of weighted estimation and FDE for reliability enhancement in degraded signal-environment navigation.  相似文献   

Zinc, Lead and Cadmium Content in Meadow Plants and Mosses Along the M3 Motorway (Hungary)     

T. Naszradi  A. Badacsonyi  N. Németh  Z. Tuba  F. Batiĉ 《Journal of Atmospheric Chemistry》2004,49(1-3):593-603

The heavy metal content was investigated in meadow plants located in a cultivated area and situated along the M3 motorway (Hungary). In addition to the meadow plants used as passive bioindicators, active bioindicators were also exposed to examine the accumulation rate of air pollutants. Tortula ruralis (Hedw.) Geartn. ssp. ruralis was applied to monitor the status of the environment. Meadow plant samples were collected at distances of 5, 10, 25, 50 and 100 m from the motorway and moss samples were exposed at the same distances. The zinc, lead and cadmium content of meadow plants and moss samples were analysed by ICP spectrophotometry. It was found that the zinc, lead and cadmium contents of the meadow plants decreased as the distance increased from the motorway. There was a significant difference even between values measured at the distances of 5 m and 10 m. The heavy metal contents in the moss samples exceeded those of the meadow plants. The heavy metal content in moss samples decreased with distance from the motorway. On comparing the data with Hungarian standards, it was found that measured values did not exceed the maximum allowed concentration levels.  相似文献   

Polycyclic aromatic hydrocarbons in coastal sediments from the subtropical Mexican Pacific     

García-Ruelas C  Botello AV  Ponce-Vélez G  Díaz-González G 《Marine pollution bulletin》2004,49(5-6):514-519

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Water quality and presence of pesticides in a tropical coastal wetland in southern Mexico   总被引：6，自引：0，他引：6  

Hernández-Romero AH  Tovilla-Hernández C  Malo EA  Bello-Mendoza R 《Marine pollution bulletin》2004,48(11-12):1130-1141

The water quality of the Pozuelos-Murillo lagoon system in southern Mexico was evaluated during three periods between March and October 2002, with particular emphasis on the detection of organochlorine and organophosphorous pesticide residues in water and sediments. Physicochemical and microbiological parameters of water were also measured and integrated in a water quality index (WQI). Multivariate analysis was used to regionalise the lagoon system as a function of the behaviour of all measured parameters. Solid phase micro-extraction followed by gas chromatography (SPME-GC) was used for pesticide analysis. The concentration of phosphorous was found to be higher than that of nitrogenous compounds. This, besides a deficiency in dissolved oxygen and a high organic matter concentration (as COD), reflects eutrophication processes in some areas of the system. Measured levels of faecal coliforms and oils and greases were above the limits established by Mexican law and comparable to the concentrations reported for other highly polluted systems in Mexico. Residues of DDD (2.0 microg L(-1)) in water and DDE (247 ng g(-1)) and endosulfan I (814 ng g(-1)) sediments were detected by SPME-GC. The spatial distribution of these contaminants implies major potential risks because the most polluted sites were found to be those with the highest fishing activity. Although in general the WQI is on acceptable levels (65-80%), some contamination problems are evident.  相似文献