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71.
Joaquín Delgado Fernández 《Celestial Mechanics and Dynamical Astronomy》1988,44(3):299-307
In a recent paper [3], Lacomba and Llibre showed numerically the existence of two transversal ejection-collision orbits in Hill's problem for a valueC=5 of the Jacobian constant. This result can be used to prove the non-existence ofC
1-extendable regular integrals for Hill's problem. Here we give an analytic proof of the existence of four ejection-collision orbits which are transversal for large enough values ofC. 相似文献
72.
María Lina Berríos-Salas Margarita Guzmán-Vega José Fernández-Labra Manlio Maldini-Sánchez 《Astrophysics and Space Science》1989,162(2):205-209
This work presents the light curves for rotating spotted stars generated by a computational code developed by us. This code is based in a model of the system and its analytical solution. The work also present an analysis of the photometric curve variations with the changes in the model's parameters.As a first result we have simulated a temporal evolution of the light curve when the photospheric spot varies its size and position and we reproduced some observational light curves of the II Peg star.Work supported by Dirección de Investigación, Universidad de La Serena, Chile. 相似文献
73.
Summary Metamorphosed carbonatites and related skarn deposits, located in Fuerteventura Basal Complex, contain unusual Sr-rich minerals. Maximum SrO concentration in the following minerals are: calcite, 7.23wt%; apatite, 5.22wt%; epidote, 11.64wt%; clinozoisite, 1.25wt%; allanite, 5.63wt%; britholite, 4.11wt% and a Sr–Na aluminosilicate (probably stronalsite), 16.44wt% SrO. Calcite and apatite are chemically similar to those found in carbonatites and are therefore considered to be of igneous origin. Textural evidence indicates that the first skarn stage garnet+diopside+Sr–Na aluminosilicate formed as the result of chemical interaction between carbonatites and adjacent silicate rocks. The formation of Sr-bearing epidote/clinozoisite, allanite and britholite appears to be related to the release of Sr into the fluid phase from the breakdown of high temperature assemblages during the retrograde skarn stage. During the final evolution stages, further alteration of britholite by bastnäsite and törnebohmite took place. The occurrence of REE minerals shows that the fluids responsible for this metasomatism must also have transported significant quantities of REE. 相似文献
74.
On 25 April 1998 the tailings dam of the Aznalcóllar mine burst, a great quantity of pyrite waste sludge and acid water was spilled reaching the vicinity of the Doñana National Park. In surface and ground water samples taken a week after dam breaking, metals, trace elements and Pb isotopic ratios (206Pb/207Pb and 208Pb/206Pb) were analysed. In September 1998 a second sampling survey was carried out. The surface waters have a similar isotopic composition as the lead contained in the pyrite from the Aznalcóllar mine. The polluted groundwater of the Guadiamar aquifer also shows the influence of the mining origin of the lead. Lead isotope ratios (206Pb/207Pb and 208Pb/206Pb) in the groundwater of the Almonte-Marismas are very low and they differ clearly from the rest of groundwater samples. A further group of wells has a lead isotope composition intermediate between the Aznalcóllar mine and the atmospheric aerosols of the Iberian Peninsula. 相似文献
75.
76.
Vicente Marcano Javier Campins Cesyen Cedeño Ernesto Palacios-Prü 《Planetary and Space Science》2004,52(7):613-621
There is evidence that space energy sources could give place to the appearance of phosphorylated nucleosides outside of Earth. These compounds may have been delivered mainly by interplanetary dust particles due to the lower temperatures experienced during atmospheric deceleration and impacts to the terrestrial surface. In this report, we communicate the results of pyrolytic studies to simulate atmospheric survivability of adenosine-5′-diphosphates (ADP) (and adenosine-5′-monophosphate, adenosine and adenine as degradation products) at temperatures <500°C and at various time intervals. Our results revealed that phosphorylated and non-phosphorylated nucleosides transported by IDPs having sizes of 10−6- could resist temperatures up to 500°C generated during atmospheric entry. However, atmospheric passage should not exceed a time due to the thermal lability of these molecules. Because of the high half-life showed by ADP in the presence of meteoritic powder, it is thought that extraterrestrial delivery of very complex biomolecules is more suitable under such protected conditions. These data indicate that the formation of a Fe2+- and/or Ca2+-complex could increase the stability of the molecules in the presence of meteoritic matter. Therefore, if the synthesis of nucleosides, nucleotides or oligonucleotides could take place in icy bodies, then micron-sized dust could have contributed significantly to the availability of phosphorylated nucleosides in the early Earth or in extrasolar early Earth-like planets, and thereby could have allowed the arising of an early biological activity. 相似文献
77.
78.
A sample of 21 light duty vehicles powered by Otto cycle engines were tested on a chassis dynamometer to measure the exhaust emissions of nitrous oxide (N2O). The tests were performed at the Vehicle Emission Laboratory of CETESB (Environmental Company of the State of Sao Paulo) using the US-FTP-75 (Federal Test Procedure) driving cycle. The sample tested included passenger cars running on three types of fuels used in Brazil: gasohol, ethanol and CNG. The measurement of N2O was made using two methods: Non Dispersive InfraRed (NDIR) analyzer and Fourier Transform InfraRed spectroscopy (FTIR). Measurements of regulated pollutants were also made in order to establish correlations between N2O and NOx. The average N2O emission factors obtained by the NDIR method was 78?±?41?mg.km?1 for vehicles running with gasohol, 73?±?45?mg.km?1 for ethanol vehicles and 171?±?69?mg.km?1 for CNG vehicles. Seventeen results using the FTIR method were also obtained. For gasohol vehicles the results showed a good agreement between the two methods, with an average emission factor of 68?±?41?mg.km?1. The FTIR measurement results of N2O for ethanol and CNG vehicles were much lower than those obtained by the NDIR method. The emission factors were 17?±?10?mg.km?1 and 33?±?17?mg.km?1, respectively, possibly because of the interference of water vapor (present at a higher concentration in the exhaust gases of these vehicles) on measurements by the NDIR method. 相似文献
79.
J. Angel Fernández Angela Ares Ana Rey-Asensio Alejo Carballeira Jesus R. Aboal 《Journal of Atmospheric Chemistry》2009,63(1):1-11
The effects of growth of autoirrigated, shaded transplants of Pseudoscleropodium purum on the quantification of tissue concentrations of Cd, Cu, Hg, V and Zn, were investigated in 4 exposure periods, each of
56 days, at 7 sampling sites (contaminated and uncontaminated). Concentrations of the elements in the basal portions of the
moss shoots were compared with the concentrations in the portions of the shoots that grew during the exposure period. Mercury
and V were present at lower concentrations in the new portions of the shoots than in the basal portions, whereas the opposite
was true for Cd, Cu and Zn. The magnitude of error introduced by growth was not negligible, and in some cases was higher than
40%, relative to the results obtained by analysis of the whole shoot. Devitalization of moss prior to its use as transplant
material is recommended to avoid growth of the plant during the exposure period. 相似文献
80.
Extreme rainfalls in SE South America 总被引:1,自引:0,他引:1
Heavy rainfall trends in a region of south-eastern South America during 1959–2002 were discussed using daily data of 52 meteorological stations of Argentina, Brazil and Uruguay. Changes in intensity and frequency were both studied with different statistical tests and approaches to check the significance of trends of single and regional aggregated rainfall series. There were predominant positive trends in the annual maximum rainfalls, as well as a remarkable increment in the frequency of heavy rainfalls over thresholds ranging from 50 to 150 mm. However, significant positive trends were not shown in the series of annual maximums and shown only in 15% to 30% of the series of frequencies over thresholds. This lack of significance is due to the high variability of heavy rainfalls in space and time, which makes difficult their capture by single rain gauges. Thus, when the assessment of the heavy rainfall indicators of intensity and frequency were conducted at the regional and sub-regional level, it showed significant trends, both in intensity and frequency over thresholds, with a clearer signal in central and eastern Argentina between 30° and 40° S. 相似文献