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901.
Susanne I. Schmidt Hans J. Hahn Gerald D. Watson Robert J. Woodbury Thomas J. Hatton 《洁净——土壤、空气、水》2004,32(2):131-137
Groundwater bores act as traps. Net samplers are regularly used for sampling this type of trap for fauna. To enable direct comparisons of faunal communities in groundwater bores and stream sediments, stream sediment tubes were built similar to groundwater bores and were sampled with net samplers for fauna. These stream sediment tubes consisted of a tube anchored in the stream sediment, also called interstitial space. To test the efficacy of this trap method in stream sediments, it was compared to another type of trap, Hahn's trap. Faunal communities sampled by a net in the stream sediment tubes did not differ hugely from fauna in Hahn's trap samples. Physical and chemical factors of sampled water in both the stream sediment tubes, the surrounding interstitial sediments and the second type of traps, Hahn's traps, showed that water in both the tubes and Hahn's traps was closely related to interstitial water. The net sampler is inexpensive and easy to handle. It is suggested that sampling stream tubes with nets may be an appropriate method for long‐term monitoring studies. 相似文献
902.
D. A. Yuen G. Erlebacher O. V. Vasilyev D. E. Goldstein M. Fuentes 《Pure and Applied Geophysics》2004,161(11-12):2231-2244
— Today, wavelets are recognized to have a wide range of useful properties that allow them to treat effectively multifacet problems, such as data compression, scale-localization analysis, feature extraction, statistics, numerical simulation, visualization, and communication. Second-generation wavelets represent a recent improvement of the wavelet algorithm, allowing for greater flexibility in the spatial domain and other computational advantages. We will show how these wavelets can be employed to extract large-scale coherent structures from (1) three-dimensional turbulent flows and (2) high Rayleigh number thermal convection. We will discuss the concept of modelling via decomposition into coherent and incoherent fields, taking into account the effect of the incoherent field via statistical modelling. We will discuss wavelet properties and how they can be utilized and integrated in handling large-scale problems in earthquake physics and other nonlinear phenomena in the geosciences. 相似文献
903.
A portable narrowband spectroradiometer was used to detect sclerotinia stem rot infection, caused by the fungus Sclerotinia sclerotiorum in soybeans. Increasing levels of fungal inoculum were used to cause a gradient of disease infection in the field. Canopy reflectance measured in narrowband R/sub 675/-R/sub 685/ and broadband R/sub 635/-R/sub 685/ could estimate 86% of the variation in soybean plants damage measured by a count of early dead plants. Plant damage was also associated with the chlorophyll absorption in reflectance and the normalized pigment chlorophyll vegetation indexes, showing a loss of chlorophyll pigment compared to healthy plants. A new field approach is suggested for the investigation of plant damage with narrowband spectroradiometry. 相似文献
904.
905.
In this study, a capillary barrier system was designed and tested for an arid land environment. To simulate arid land conditions
of high temperature and sub-irrigation systems, the barrier was subjected to thermal and hydraulic gradients in opposite directions;
to test the barrier system under these severe conditions, an experimental apparatus was designed and fabricated. The multilayer
capillary barrier consisted of three layers made of silica sand, a mixture of sand and bentonite in equal portions, and a
mixture of clay (25%) and aggregate (75%). Several one dimensional coupled heat and moisture tests were performed. Temperature
variations along the thickness of the barrier were recorded as a function of time, and at the end of each test, the barrier
was sliced into small sections, for the determination of volumetric water content as a function of distance from the heat
source. The experimental results were discussed in view of the barrier's intended purpose of its ability to store moisture
for long time durations.
Coupled heat and moisture flow equations were developed and solved numerically via a finite difference method. Diffusivity
parameters were calculated by using experimental results, a numerical model, and Powell's conjugate directions method of nonlinear
optimization. The model was calibrated and the results were discussed. Good agreement between calculated and experimental
results was obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
906.
Isotope provinces, mechanisms of generation and sources of the continental crust in the Central Asian mobile belt: geological and isotopic evidence 总被引:17,自引:0,他引:17
V. I. Kovalenko V. V. Yarmolyuk V. P. Kovach A. B. Kotov I. K. Kozakov E. B. Salnikova A. M. Larin 《Journal of Asian Earth Sciences》2004,23(5):605-627
The available geological, geochronological and isotopic data on the felsic magmatic and related rocks from South Siberia, Transbaikalia and Mongolia are summarized to improve our understanding of the mechanisms and processes of the Phanerozoic crustal growth in the Central Asian mobile belt (CAMB). The following isotope provinces have been recognised: ‘Precambrian’ (TDM=3.3–2.9 and 2.5–0.9 Ga) at the microcontinental blocks, ‘Caledonian’ (TDM=1.1–0.55 Ga), ‘Hercynian’ (TDM=0.8–0.5 Ma) and ‘Indosinian’ (TDM=0.3 Ga) that coincide with coeval tectonic zones and formed at 570–475, 420–320 and 310–220 Ma. Continental crust of the microcontinents is underlain by, or intermixed with, ‘juvenile’ crust as evidenced by its isotopic heterogeneity. The continental crust of the Caledonian, Hercynian and Indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments. The crustal growth in the CAMB had episodic character and important crust-forming events took place in the Phanerozoic. Formation of the CAMB was connected with break up of the Rodinia supercontinent in consequence of creation of the South-Pacific hot superplume. Intraplate magmatism preceding and accompanying permanently other magmatic activity in the CAMB was caused by influence of the long-term South-Pacific plume or the Asian plume damping since the Devonian. 相似文献
907.
The behavior of chalcophile metals in volcanic environments is important for a variety of economic and environmental applications, and for understanding large-scale processes such as crustal recycling into the mantle. In order to better define the behavior of chalcophile metals in ocean island volcanoes, we measured the concentrations of Re, Cd, Bi, Cu, Pb, Zn, Pt, S, and a suite of major elements and lithophile trace elements in moderately evolved (6-7% MgO) tholeiitic glasses from Ko’olau and Moloka’i volcanoes. Correlated variations in the Re, Cd, and S contents of these glasses are consistent with loss of these elements as volatile species during magmatic outgassing. Bismuth also shows a good correlation with S in the Ko’olau glasses, but undegassed glasses from Moloka’i have unexpectedly low Bi contents. Rhenium appears to have been more volatile than either Cd or Bi in these magmas.Undegassed glasses with 880-1400 ppm S have 1.2-1.5 ppb Re and 130-145 ppb Cd. In contrast, outgassed melts with low S (<200 ppm) are depleted in these elements by factors of 2-5. Key ratios such as Re/Yb and Cu/Re are fractionated significantly from mantle values. Copper, Pb, and Pt contents of these glasses show no correlation with S, ruling out segregation of an immiscible magmatic sulfide phase as the cause of these variations. Undegassed Hawaiian tholeiites have Re/Yb ratios significantly higher than those of MORB, and extend to values greater than that of the primitive mantle. Loss of Re during outgassing of ocean island volcanoes, may help resolve the apparent paradox of low Re/Os ratios in ocean island basalts with radiogenic Os isotopic compositions. Plume source regions with Re/Yb ratios greater than that of the primitive mantle may provide at least a partial solution to the “missing Re” problem in which one or more reservoirs with high Re/Yb are required to balance the low Re/Yb of MORB.Lithophile trace element compositions of most Ko’olau and Moloka’i tholeiites are consistent with variable degrees of melting of fertile mantle peridotite. However, light rare earth element (LREE)-enriched glasses have trace element compositions more consistent with a garnet-rich source having a distinctive trace element composition. This provides additional evidence for a unique source component possibly related to recycled oceanic crust contributing to Ko’olau tholeiites. 相似文献
908.
A. B. Pushkarev Yu. Yu. Kovalev I. E. Molotov M. B. Nechaeva Yu. N. Gorshenkov G. Tuccari C. Stanghellini X. Hong J. Quick S. Dougherty X. Liu 《Astronomy Reports》2004,48(11):900-908
VLBI observations of several quasars and BL Lacertae objects were carried out at 1.66 GHz in November–December 1999 using six antennas (Medvezh'i Ozera, Svetloe, Pushchino, Noto, HartRAO, and Shanghai). Maps of six sources (0420+022, 0420-014, 1308+326, 1345+125, 1803+784, and DA 193) obtained with milliarcsecond resolution are presented and discussed, together with their broad-band (1–22 GHz) spectra obtained on the RATAN-600 radio telescope at epochs close to those of the VLBI observations. Comparison of the VLBI maps with maps of these sources obtained on standard VLBI networks and with the RATAN-600 quasisimultaneous total-flux measurements indicates the reliability of the results obtained on this Low Frequency VLBI Network and the good efficiency of this network. 相似文献
909.
Phase equilibria in the ternary systems H2O–CO2–NaCl and H2O–CO2–CaCl2 have been determined from the study of synthetic fluid inclusions in quartz at 500 and 800 °C, 0.5 and 0.9 GPa. The crystallographic control on rates of quartz overgrowth on synthetic quartz crystals was exploited to prevent trapping of fluid inclusions prior to attainment of run conditions. Two types of fluid inclusion were found with different density or CO2 homogenisation temperature (Th(CO2)): a CO2-rich phase with low Th(CO2), and a brine with relatively high Th(CO2). The density of CO2 was calibrated using inclusions in the binary system H2O–CO2. Mass balance calculations constrain tie lines and the miscibility gap between brines and CO2-rich fluids in the H2O–CO2–NaCl and H2O–CO2–CaCl2 systems at 500 and 800 °C, and 0.5 and 0.9 GPa. The miscibility gap in the CaCl2 system is larger than in the NaCl system, and solubilities of CO2 are smaller. CaCl2 demonstrates a larger salting-out effect than NaCl at the same P–T conditions. In ternary systems, homogeneous fluids are H2O-rich and of extremely low salinity, but at medium to high concentrations of salts and non-polar gases fluids are unlikely to be homogeneous. The two-phase state of crustal fluids should be common. For low fluid-rock ratios the cation compositions of crustal fluids are buffered by major crustal minerals: feldspars and micas in pelites and granitic rocks, calcite (dolomite) in carbonates, and pyroxenes and amphiboles in metabasites. Fluids in pelitic and granitic rocks are Na-K rich, while for carbonate and metabasic rocks fluids are Ca-Mg-Fe rich. On lithological boundaries between silicate and carbonate rocks, or between pelites and metabasites, diffusive cation exchange of the salt components of the fluid will cause the surfaces of immiscibility to intersect, leading to unmixing in the fluid phase. Dispersion of acoustic energy at critical conditions of the fluid may amplify seismic reflections that result from different fluid densities on lithological boundaries.Editorial responsibility: I. Parsons 相似文献
910.
A comparative analysis of oscillatory spectra based on 66 time series for 14 active regions observed in 2001 shows that, although the chromospheric and photospheric oscillations in the Evershed flow zone possess many common features, there is no firm evidence that the direct and inverse flows have the same physical origin. The interactions between the various oscillation modes and stationary flows results in a complex pattern of wave motions in a sunspot. We studied the Doppler-velocity variations in the sunspot NOAA 0051 during its motion over the disk. The spatial-temporal distribution of the line-of-sight velocity in the chromospheric umbra displays a chevron structure, clearly indicating the presence of propagating waves. These waves move from the center of the umbra to outer regions with a phase speed of 45–60 km/s, a period of 2.8 min, and a measured Doppler speed of 2 km/s. The amplitude of these oscillations decreases abruptly at the boundary between the umbra and penumbra, and the observed waves are not directly related to propagating penumbral waves. Furthermore, the observed pattern of the photospheric velocities shows periodic motions (with a period of 5 min) directed from the inner boundary of the penumbra and superpenumbra toward the line of maximum Evershed velocity. 相似文献