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排序方式: 共有45条查询结果,搜索用时 15 毫秒
1.
S. Torres V. Cañon R. Casas A. Umaña C. Tello T. Villela M. Bersanelli M. Bensadoun G. De Amici M. Limon G. Smoot C. Witebsky 《Astrophysics and Space Science》1996,240(2):225-234
The GEM (Galactic Emission Mapping) project is an international collaboration established with the aim of surveying the full sky at long wavelengths with a multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz were completed from an Equatorial site in Colombia. The observations cover the celestial band 0
h
<<24
h
, and –24° 22<<+35° 37. Preliminary results of this partial survey will be discussed. A review of the instrumental setup and a 10° resolution sky map at 408 MHz is presented.Presented by S. Torres at the UN/ESA Workshop on Basic Space Sciences: From Small Telescopes to Space Missions, Colombo, Sri Lanka 11–14 January 1996 相似文献
2.
The anisotropy of magnetic susceptibility (AMS) of lava flows is an innovative method which has been proved to be directly related to the shear history of lava. One of the advantages of this method is that it can be used in the absence of other morphological features commonly employed to study the mechanism of emplacement of lava flows. This feature of the AMS method makes it very attractive to gain insight into the mechanism of emplacement of massive, relatively featureless, long lava flows such as those forming flood basalt provinces. In this work, we report the results of the measurement of AMS as a function of vertical position within the Birkett lava flow, one of the Columbia River Basalt Group flows. The observed variation of AMS allows us to identify at least 16 discrete events of lava injection and to estimate the thickness of individual injection events. The AMS-estimated thickness of each injection event (in the range of 0.5-4.0 m) coincides with the range inferred for injected lava pulses in modern Hawaiian lava flows. Thus, the evidence provided by the AMS method supports the notion that at least some flood basalt lava flows were emplaced by the same mechanism as many present-day inflated pahoehoe flows. Regarding the orientation of the principal susceptibilities, in the central part of the flow they define a preferred orientation along an E-W trend, whereas in the outer parts of the flow they have a NNE-SSW trend. This difference in the orientation of the principal susceptibilities is interpreted as the result of a change of flow direction of the lava as emplacement progressed. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00445-002-0203-8. 相似文献
3.
Enzymatic activity in the rhizosphere of Spartina maritima: potential contribution for phytoremediation of metals 总被引:2,自引:0,他引:2
Extracellular enzymatic activity (EEA) of five enzymes (peroxidase, phenol oxidase, beta-glucosidase, beta-N-acetylglucosaminidase and acid phosphatase) was analysed in sediments colonised by Spartina maritima in two salt marshes (Rosário and Pancas) of the Tagus estuary (Portugal) with different characteristics such as sediment parameters and metal contaminant levels. Our aim was a better understanding of the influence of the halophyte on microbial activity in the rhizosphere under different site conditions, and its potential consequences for metal cycling and phytoremediation in salt marshes. Acid phosphatase and beta-N-acetylglucosaminidase presented significantly higher EEA in Rosário than in Pancas, whereas the opposite occurred for peroxidase. This was mainly attributed to differences in organic matter between the two sites. A positive correlation between root biomass and EEA of hydrolases (beta-glucosidase, beta-N-acetylglucosaminidase and acid phosphatase) was found, indicating a possible influence of the halophyte in sediment microbial function. This would potentially affect metal cycling in the rhizosphere through microbial reactions. 相似文献
4.
Edgardo Cañón-Tapia 《Pure and Applied Geophysics》1994,142(2):365-382
Twenty-eight parameters used to characterize measurements of the anisotropy of magnetic susceptibility are compared theoretically in this work by introducing the concept of the field of susceptibility tensors, which allows the representation of parameters as families of lines in a plane. It is demonstrated that the foliation and lineation parameters are but a special case of the shape parameters, implying that the resolution of these two rock fabric elements using AMS measurements alone is more an artifact of the numerical range of definition of some parameters than a quantification of two physically independent features. Also, it is shown that parameters presumably of the same type do not necessarily yield equivalent interpretation of results in a qualitative sense, and therefore, caution should be strongly exercised when parameters are to be selected. Paramters quantifying the degree of anisotropy are, in general, equivalent to each other because of the very small departure observed in natural rocks from the isotropic case. However, a final consideration of the possible ability to differentiate rock types and a convenient range of values allowing expression of the degree of anisotropy in a well-defined percentage are pointed out as the main factors to be considered before selecting one parameter within this class. 相似文献
5.
M. Hoyos V. Soler J. C. Cañaveras S. Sánchez-Moral E. Sanz-Rubio 《Environmental Geology》1998,33(4):231-242
The Candamo Cave contains an important group of paleolithic paintings which have been seriously deteriorated due to mass tourism.
In this work, an analysis was carried out of different climatic parameters (CO2, temperature, humidity, 222Rn) during annual cycles with the cave closed to the public and during an experimental period of controlled visits. The effect
of visits on the geochemical characteristics of karstic water was also analyzed together with the cave ventilation.
The natural variations in the cave air CO2 were above 3000 ppm, the increase produced through visits was only 100–110 ppm and since the humidity is almost permanently
at saturation point, the critical parameter which limits the visitor capacity becomes air temperature. The temperature changes
during the annual cycle are of the order of 1 °C in the external part and less than 0.5 °C in the internal part of the cave
and a maximum increase of 0.13 °C was observed during the period of the visits. The 222Rn and CO2 concentration minimums in the summer period (July–October) show that this is the most propitious time for visits, since the
greatest ventilation is produced in the cave at this time and, therefore, the greatest capacity for recovery. The geochemistry
of the water, on the other hand, indicated that this is the period of the year in which processes of wall corrosion can be
most easily introduced, although this would be of limited magnitude. The visitor capacity calculated was 29 visitors/day.
Received: 29 August 1996 · Accepted: 23 June 1997 相似文献
6.
Devonian sediments of the Malaguide Complex potentially could include the Frasnian–Famennian boundary, one of the five greatest Phanerozoic biotic crises. Conodont biofacies and microfacies of carbonate clasts from a pebbly mudstone underlying Tournaisian radiolarites allows identification, for the first time in the Malaguide Complex, of Devonian shallow marine environments laterally grading to deeper realms. The clasts yielded Frasnian conodont associations of the falsiovalis to rhenana biozones, with six biofacies that reveal different environmental conditions in their source areas. Source sediments were dismantled and redeposited within the pebbly mudstone, whose origin is tentatively related to one of the events that are associated worldwide with the Frasnian–Famennian crisis. The latter is recorded, in two equivalent Malaguide pelagic successions, by stratigraphic discontinuities, and it was, probably, tectonically and/or eustatically controlled, as in other Alpine‐Mediterranean Paleotethyan margins. 相似文献
7.
V. Rull M. C. Trapote E. Safont N. Cañellas-Boltà N. Pérez-Zanón J. Sigró T. Buchaca T. Vegas-Vilarrúbia 《Journal of Paleolimnology》2017,57(1):95-108
Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcortès, Central Pyrenees (Spain), as a modern analog for high-resolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a 2-year period (fall 2013 to fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer, coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed for most pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall/winter. This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcortès exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen assembalges, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns. 相似文献
8.
AbstractThe Hilhorst model was used to convert bulk electrical conductivity (σb) to pore water electrical conductivity (σp) under laboratory conditions by using the linear relationship between the soil dielectric constant (εb) and σb. In the present study, applying the linear relationship εb–σb to data obtained from field capacitance sensors resulted in strong positive autocorrelations between the residuals of that regression. We were able to derive an accurate offset of the relationship εb–σb and to estimate the evolution of σp over time by including a stochastic component to the linear model, rearranging it to a time-varying dynamic linear model (DLM), and using Kalman filtering and smoothing. The offset proved to vary for each depth in the same soil profile. A reason for this might be the changes in soil temperature along the soil profile.
Editor D. Koutsoyiannis; Associate editor M.D. Fidelibus 相似文献
9.
D. Benavente S. Sanchez-Moral A. Fernandez-Cortes J. C. Cañaveras J. Elez C. Saiz-Jimenez 《Environmental Earth Sciences》2011,63(7-8):1529-1543
The necropolis of Carmona (Seville, Spain) is one of the most significant Roman burial sites in southern Spain used during the first and second centuries ad. Of its more than 600 tombs, the Postumius Tomb is one of the best examples of a tomb affected by severe salt damage. To define safe microclimatic conditions for its conservation, environmental parameters were recorded from June 2007 to April 2009, both inside and outside the tomb, and mineralogical, textural, petrophysical, and durability characterization studies of the host-rock were made. Experimental tests revealed a high susceptibility to salt deterioration of a host-rock (calcarenite) with low mechanical properties and a complex porous medium that favors salt weathering, water condensation, and capillary rise. The analysis of the weathered material showed the presence chiefly of gypsum (CaSO4·2H2O), thenardite (Na2SO4) and halite (NaCl) in the tomb of Postumius, with alteration that was more intensive in spring and autumn, and less so during summer months. Salt damage activity was calculated by quantifying the number of transitions of crystallization–dissolution of saline phases. The calculated seasonality for water condensation and salt damage is coeval. The host-rock alteration is in accord with the estimated salt decay, and was more intensive in spring and autumn and less so during summer. The seasonality of halite transitions is similar to that of the sodium sulfate system, which suggests that salt weathering is produced by the two types of salts. By combining different methodological approaches (pore structure, water condensation, salt and environmental conditions), it is possible to explain why salt crystallization occurs in a tomb with hygrometric conditions that are not suitable for this process to occur. These methodological approaches are also used to other rock-decaying processes, such as the development of microorganisms, clay swelling and calcite dissolution by NaCl- and CO2-rich pore waters, and can be used to predict safe threshold microclimatic conditions that minimize all rock-decaying processes. 相似文献
10.
A Dinis F Alves C Nicolau C Ribeiro M Kaufmann A Cañadas 《African Journal of Marine Science》2016,38(2):151-160
The bottlenose dolphin Tursiops truncatus is one of the most frequently sighted cetacean species in the Madeira Archipelago (North-East Atlantic); however, little is known about its population ecology in these waters. Photo-identification undertaken during systematic, non-systematic and opportunistic surveys conducted between 2001 and 2012 was used to assess group dynamics, site fidelity, residency and movement patterns of bottlenose dolphins in the archipelago. Three different patterns of residency were assigned, based on individual sighting histories. Group size ranged between 2 and 90 individuals (median 12), with no significant monthly difference in group size. All resident dolphins formed a core, complex network with migrant and transient dolphins. In contrast, satellite clusters were formed exclusively by transient individuals. The lagged identification rate (LIR) model indicated that a dolphin remained in the area for an average of 90 days, whereas the average time an individual spent outside the study area was approximately 313 days. The Madeira Archipelago appears to be only a section of a much larger home range for this population, with the dolphins exhibiting three different patterns of occurrence that associate with each other. The information gained about this poorly studied population contributes to the overall knowledge of bottlenose dolphins in insular oceanic habitats. 相似文献