Chemical composition of the Orion nebula derived from echelle spectrophotometry     

C.Esteban  M.Peimbert  S.Torres-Peimbert  V.Escalante 《Monthly notices of the Royal Astronomical Society》1998,295(2):401-422

We present echelle spectroscopy in the 3500- to 7060-... range for two positions of the Orion nebula. The data were obtained using the 2.1-m telescope at Observatorio Astronómico Nacional in San Pedro Mártir, Baja California. We have measured the intensities of about 220 emission lines, in particular 81 permitted lines of C⁺, N⁺, N⁺⁺, O⁰, O⁺, Ne⁰, Si⁺, Si⁺⁺ and S⁺, some of them produced by recombination only and others mainly by fluorescence. We have determined electron temperatures, electron densities and ionic abundances using different continuum and line intensity ratios. We derived the He, C and O abundances from recombination lines and find that the C/H and O/H values are very similar to those derived from B stars of the Orion association, and that these nebular values are independent of the temperature structure. We have also derived abundances from collisionally excited lines. These abundances depend on the temperature structure; accurate t ² values have been derived comparing the O II recombination lines with the [O III ] collisionally excited lines. The gaseous abundances of Mg, Si and Fe show significant depletions, implying that a substantial fraction of these atoms is tied up in dust grains. The derived depletions are similar to those found in warm clouds of the Galactic disc, but are not as large as those found in cold clouds. A comparison of the solar and Orion chemical abundances is made.  相似文献   

Compositional dependence of REE partitioning between diopside and melt at 1 atmosphere   总被引：1，自引：1，他引：0  

Michael Schosnig  Edgar Hoffer 《Contributions to Mineralogy and Petrology》1998,133(3):205-216

The effects of composition on pyroxene-melt partitioning of several REE (rare earth elements), Y, and Sr were experimentally evaluated. Using the synthetic model systems anorthite–diopside, diopside–titanite and anorthite–diopside–titanite different diopsides were grown at atmospheric conditions in a double-ellipsoid mirror furnace. The single samples were melted and crystallised in a Pt/Au crucible with compositions corresponding to the invariant points of these systems. Rotational motion with approximately 25 rpm around the longitudinal axis of the crucible increases the prevailing convection flows. By this means, the exclusively diffusional transport of assembly groups onto the growing crystals is avoided. Quenching is achieved by dropping the crucible into water. Crystals up to 2 mm were obtained and analysed by electron microprobe. No inhomogeneities or compositional zonation, either in the diopsides or in the coexisting melts, were observed within the analytical uncertainty of the electron microprobe. The crystallised diopsides occur as both euhedral single crystals and large symplectitic lamellar intergrowths with anorthite or titanite. The chemical homogeneity and the texture indicate near-equilibrium conditions. The analyses show strong positive correlations between D_REE and tetrahedrally coordinated Al in diopside but are not affected by octahedral Al or Ti-concentration. By means of correlations and mass balances the incorporation of REE can be described by 2 different coupled substitutions: The Al-coupled incorporation of REE³⁺ (1) dominates the D-values. The Na-coupled substitution (2) is of minor importance. Depending on the compositions investigated the D-values vary by up to a factor of 10. This range overlaps most of the published pyroxene-melt partition coefficients. Because we conducted isothermal and isobaric experiments, this overlap indicates that a wide range of D-values is a function of composition. For the coupled substitutions (1) and (2) this indicates that the D_REE strongly depends on the amount of tetrahedrally coordinated Al³⁺ in clinopyroxenes. Received: 5 January 1998 / Accepted: 11 June 1998  相似文献   

The geology of the lower valley of the Gade,and its bearing upon problems connected with the erosion of the chalk and the deposition of superficial gravels,etc.     

Edgar A. Merrett 《Proceedings of the Geologists' Association. Geologists' Association》1927,38(2):217-236

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Juvenile capelin (Mallotus villosus) off Newfoundland and Labrador in the 1990s     

Anderson  John T.; Dalley  Edgar L.; O'Driscoll  Richard L. 《ICES Journal of Marine Science》2002,59(5):917-928

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Reproduction and seasonal occurrence of the copper shark, Carcharhinus brachyurus, from north Patagonia, Argentina     

Lucifora  Luis O.; Menni  Roberto C.; Escalante  Alicia H. 《ICES Journal of Marine Science》2005,62(1):107-115

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Removal of antimony and arsenic from circum-neutral mine drainage in Poproč, Slovakia: a field treatment system using low-cost iron-based material     

Peter Sekula  Edgar Hiller  Peter Šottník  Ľubomír Jurkovič  Tomáš Klimko  Jaroslav Vozár 《Environmental Earth Sciences》2018,77(13):518

The main aim of this paper was to investigate the removal efficiency of antimony (Sb) and arsenic (As) from circum-neutral mine drainage in the former Sb mine in Popro? (Slovakia) using a simple field treatment system based on the adsorption onto iron fillings. The treatment system consisted of two batch reactors with a volume of 1 m³: the first was used for settling of spontaneously precipitated ochreous sediments and the second, filled with reactive iron material, was designed to remove Sb and As from mine water. This passively operated treatment system contained 150 kg of low-cost iron fillings and was able to treat approximately 360 l of mine drainage per hour. The average removal efficiency of Sb and As reached 84 and 89% during a period of 2.3 years of the system operation, respectively. On average, dissolved Sb and As concentrations in mine drainage decreased from 175 to 24.3 µg/l and from 452 to 50.6 µg/l, respectively. Based on the electron microprobe (EMP) analyses of corrosion products developed on the surfaces of iron fillings, average Sb and As contents were 0.28 and 0.73 wt%, respectively. The chemical analyses of precipitated HFOs in the settling reactor showed that these ochreous precipitates contained up to 19.3 g/kg Sb and 65.8 g/kg As, indicating their natural role in the removal of the two metalloids from circum-neutral mine drainage. The results of transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses confirmed the presence of ferrihydrite and goethite in ochreous sediments.  相似文献   

Characterization of Risks in Coastal Zones: A Review     

Mireille Escudero Castillo  Edgar Mendoza Baldwin  Rodolfo Silva Casarin  Gregorio Posada Vanegas  Maritza Arganis Juaréz 《洁净——土壤、空气、水》2012,40(9):894-905

Interest in sustainable development for the natural, socio‐economic, and cultural resources of coastal zones is growing worldwide. On the other hand, the range of threats to coastal zones increasingly posed by hydro‐meteorological natural phenomena has led to a trend in the analysis and assessment of risks to these areas. The available literature dealing with coastal risk assessment is quite wide, focusing mainly on the risk evaluation of coastal flooding and erosion resulting directly from the occurrence of extreme natural events. The risk assessment methodologies are usually specific to the conditions and available data of each country, society or location, though most have evolved to assess the risk concept more precisely and rigorously. However, there are still very few studies that present feasible and effective methodologies, which lead to the effective integration of risk analysis at all levels. In Mexico coastal risk analysis has barely begun despite our extensive coastline, which is highly vulnerable to the threat of tropical cyclones. This paper aims to give a broad view of the risk assessment methodologies which already exist, in order to provide a starting point for future efforts in Mexico and elsewhere.  相似文献   

Hydro‐morphologic Revision of the Cuautla Channel at Nayarit,Mexico     

Cuauhtemoc Franco Ochoa  Edgar Mendoza Baldwin  Rodolfo Silva Casarín  Gabriel Ruiz Martínez 《洁净——土壤、空气、水》2012,40(9):920-925

Pollution, habitat modification, and species migration are some of the results of human activities on natural environments which can be mitigated or compensated with proper planning. Irresponsibility or ignorance in planning coastal projects too often produces damage to natural systems which can be unpredictable and sometimes irrevocable. The specific site analyzed in this paper is the Cuautla littoral sub‐system which was originally a lagoon that diverted river water to other lagoons and estuaries, thus irrigating the Mexican Marismas Nacionales system, in the states of Nayarit and Sinaloa, Mexico. In the 1970s social and economic considerations motivated the construction of a small breaching canal from the sea to the lagoon. The subsequent growth of this channel was unforeseen and has produced an irreversible impact not only in the sub‐system but probably in the entire area of Marismas Nacionales. A lack of understanding of the present balances in the damaged system and of the impacts the changing morphology has on future change has created the need to study this area using numerical hydrodynamic simulation. The present distribution of water in the sub‐system was established and the governing processes were detected. By means of an analytical estimation of equilibrium conditions it was found that if nothing is done, the channel will continue eroding and the ecosystem will continue to degrade. Only by understanding the dramatic perturbations caused by the construction of the channel to the hydrologic and morphologic equilibriums can there be any hope of rescuing the ecosystem, including its human activities.  相似文献   

Land cover change and carbon stores in a tropical montane cloud forest in the Sierra Madre Oriental,Mexico   总被引：1，自引：0，他引：1  

Edgar G.LEIJA-LOREDO  Numa P.PAVóN  Arturo SáNCHEZ-GONZáLEZ  Rodrigo RODRIGUEZ-LAGUNA  Gregorio áNGELES-PéREZ 《山地科学学报》2018,15(10):2136-2147

Tropical montane cloud forest is one of the ecosystems with the highest biomass worldwide, representing an important carbon store. Globally its deforestation index is –1.1%, but in Mexico it is higher than –3%. Carbon estimates are scarce globally, particularly in Mexico. The objective of this study was to simulate future land-cover scenarios for the Sierra Madre Oriental in Mexico, by analyzing past forest cover changes. Another objective was to estimate stored carbon in the two study areas. These objectives involve the generation of information that could be useful inputs to anti-deforestation public policy such as the REDD+ strategy. Remote sensing was used to measure land cover change and estimate carbon stocks. Satellite images from 2015, 2000 and 1986 were used, and Dinamica EGO freeware generatedmodels of future projections. Between 1986 and 2015, 5171 ha of forest were converted to pasture. The annual deforestation rates were –1.5% for Tlanchinol and –1.3% for the San Bartolo Tutotepec sites. Distance to roads and marginalization were highly correlated with deforestation. By 2030, an estimated 3608 ha of forest in these sites will have been converted to pasture. Stored carbon was estimated at 16.35 Mg C ha-1 for the Tlanchinol site and 12.7 Mg C ha-1 for the San Bartolo site. In the Sierra Madre Oriental deforestation due to land cover change(–1.4%) is higher than levels reported worldwide. Besides having high values of stored carbon(14.5 Mg C ha-1), these forests have high biodiversity. The models' outputs show that the deforestation process will continue if action is not taken to avoid the expansion of livestock pasturing. This can be done by paying incentives for forest conservation to the owners of the land. The results suggest that REDD+ is currently the most viable strategy for reducing deforestation rates in tropical montane cloud forests in Sierra Madre Oriental.  相似文献   

Petrogenesis of the gabbros from Mt. St. Hilaire,Quebec, Canada     

R. C. Greenwood  A. D. Edgar 《Geological Journal》1984,19(4):353-376

Mt. St. Hilaire occurs as a small funnel-shaped intrusion in the Monteregian petrographic province of Quebec and consists of alkali gabbros and later nepheline syenites. Based on field relations, petrography, and geochemistry, five types of gabbro are recognized. In order of intrusion these are: leucogabbro, foliated gabbro, kaersutite-biotite gabbro, kaersutite gabbro, and a gabbro-melagabbro series. Based on analyses of the early-forming ilmenite-titanomagnetite, the gabbros crystallized under high fO₂ conditions which lead to subsequent crystallization of olivines with high MnO contents. Fractionation of ilmenite and titanomagnetite was a major control on the Ti and A[TV]concentrations in the clinopyroxenes. Plagioclase compositions in the gabbros became richer in Ab contents in the sequence gabbro-melagabbro to leucogabbro. Whole-rock analyses suggest that the parental magma of alkali basaltic composition was fairly evolved prior to emplacement. Lack of olivine in the cumulate gabbro-melagabbros and low Ni and Cr in all gabbros may reflect either extreme olivine fractionation and/or a very low olivine content in the source material for these basalts. Differentiation of the gabbros occurred both pre- and post-emplacement, probably by a process of crystal-liquid fractionation at depths between 3-5 and 8 km. This is in accordance with geophysical measurements for other Monteregian intrusions. A model is presented for the mechanism of emplacement.  相似文献