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141.
Paulo E. M. Melo Milton J. Porsani Michelângelo G. Silva 《Geophysical Prospecting》2009,57(3):343-353
We present a new filtering method for the attenuation of ground-roll. The method is based on the application of a bi-dimensional filter for obtaining the time-derivative of the seismograms. Before convolving the filter with the input data matrix, the normal moveout correction is applied to the seismograms with the purpose of flattening the reflections. The method can locally attenuate the amplitude of data of low frequency (in the ground-roll and stretch normal moveout region) and enhance flat events (reflections). The filtered seismograms can reveal horizontal or sub-horizontal reflections while vertical or sub-vertical events, associated with ground-roll, are attenuated. A regular set of samples around each neighbourhood data sample of the seismogram is used to estimate the time-derivative. A numerical approximation of the derivative is computed by taking the difference between the interpolated values calculated in both the positive and the negative neighbourhood of the desired position. The coefficients of the 2D time-derivative filter are obtained by taking the difference between two filters that interpolate at positive and negative times. Numerical results that use real seismic data show that the proposed method is effective and can reveal reflections masked by the ground-roll. Another benefit of the method is that the stretch mute, normally applied after the normal moveout correction, is unnecessary. The new filtering approach provides results of outstanding quality when compared to results obtained from the conventional FK filtering method. 相似文献
142.
Increase of nitrous oxide flux to the atmosphere upon nitrogen addition to red mangroves sediments 总被引:6,自引:0,他引:6
Response of nitrous oxide N20 sediment/air flux to nitrogen addition was assessed in mangrove (Rhizophora mangle) sediments. Fluxes were enhanced with both ammonium and nitrate loading. Greatest fluxes (52 micromol m(-2) h(-1)) were obtained with ammonium addition and saturation was achieved with additions of 0.9 mol m(-2). Maximum flux following ammonium addition was 2785 times greater than control plots and 4.5 times greater during low tide than with equivalent ammonium addition at high tide. Nitrate enrichment resulted in exponential growth, with maximal mean flux of 36.7 micromolm(-2) h(-1) at 1.9 molm(-2); saturation was not achieved. Differential response to ammonium and nitrate, and to tide and elevation, indicate that microbial nitrification is responsible for most of the observed gas flux. Mangrove sediments constitute an important source of global atmospheric N20 and increases in nitrogen loading will lead to significant increases in the flux of this atmospherically active gas. 相似文献
143.
Various physical and biological properties affect solute transport patterns in streams. We measured hydraulic characteristics of Payne Creek, a low‐gradient upper Coastal Plain stream, using tracer experiments and parameter estimation with OTIS‐P (one‐dimensional transport with inflow and storage with parameter optimization). The primary objective of this study was to estimate the effects of varying discharge, season, and litter accumulation on hydraulic parameters. Channel area A ranged from 0·081 to 0·371 m2 and transient storage area As ranged from 0·027 to 0·111 m2. Dispersion D ranged from 1·5 to 11·1 m2 min−1 and exchange coefficient α ranged from 0·009 to 0·038 min−1. Channel area and dispersion were positively correlated to discharge Q, whereas storage area and exchange coefficient were not. Relative storage size As/A ranged from 0·17 to 0·59, and was higher during fall than other seasons under a similar Q. The fraction of median travel time due to transient storage ranged from 8·8 to 34·5% and was significantly correlated with Q through a negative power function. Both metrics indicated that transient storage was a significant component affecting solute transport in Payne Creek, especially during the fall. Comparison between the measured channel area Ac and A suggested that surface storage was dominant in Payne Creek. During fall, accumulation of leaf litter resulted in larger A and As and lower velocity and D than during other seasons with similar discharge. Seasonal changes in discharge and organic matter accumulation, and dynamic channel morphology affected the magnitude of transient storage and overall hydraulic characteristics of Payne Creek. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
144.
Summary and Tentative Conclusion The eradication campaign faltered, for historical reasons some of which are tentatively suggested above and which would be worthy of fuller study as an important part of recent medical history; it is one of those historical topics so intertwined with political and social history that an interdisciplinary approach would be fruitful — if the necessary documents could be made accessible, in India and perhaps in international organisations and subscribing government archives too.Once the campaign faltered malaria seems to have diffused from the four foci suggested, the Kutch saltmarsh area and the hill-forest tracts of Madhya, Orissa and Assam. The role of wet years in areas normally arid, semi-arid or only moderately humid seems crucial in the diffusion process, and if the gaps in the rainfall anomaly maps can be filled we shall try to provide a more rigorous analysis of this relationship. Some humid and perhumid areas of high agricultural development, and dense or very dense rural populations, and one or two areas of considerable industrial and urban development like Greater Calcutta and nearby towns, seem so far to be happily little affected by the diffusion of malaria, even though as late as 1948 some including much of West Bengal were hyperendemic areas. It remains to be established by detailed studies if these areas are better prepared in some way — natural immunity must have faded especially in the considerable proportion of young people who have been born since malaria eradication was almost within grasp; or are they so far comparatively fortunate through some chances of the diffusion pattern?Urban malaria, and one might sayAnopheles stephensi malaria, is probably more widespread and more significant as an important public health problem than in former times. Once more the need for detailed local studies is clear.It is important to re-read the introductory paragraph of this paper. The fiftyfold increase from 100000 to 5 million cases represents a sharp resurgence but the 5 million cases of 1975 and 1976, and few scores of recorded deaths, still represent a remarkable achievement as compared with the 75 million cases and 800,000 deaths a year at the time of Independence. From over 5 million in 1976 to 10 million in the first nine months of 1977, however, is a quite disquieting increase. If complacence did indeed play a part in the crucial years of resurgence in the late 1960s, it is unlikely to continue today in medical circles. One can only hope that politicians will take the issue seriously. Studies of the economic, educational and demographic impact of the resurgence may help them to do so. 相似文献
145.
Zones of mixing between shallow groundwaters of different composition were unravelled by “two-way regionalized classification,” a technique based on correspondence analysis (CA), cluster analysis (ClA) and discriminant analysis (DA), aided by gridding, map-overlay and contouring tools. The shallow groundwaters are from a granitoid plutonite in the Fundão region (central Portugal). Correspondence analysis detected three natural clusters in the working dataset: 1, weathering; 2, domestic effluents; 3, fertilizers. Cluster analysis set an alternative distribution of the samples by the three clusters. Group memberships obtained by correspondence analysis and by cluster analysis were optimized by discriminant analysis, gridded over the entire Fundão region, and converted into “two-way regionalized classification” memberships as follows: codes 1, 2 or 3 were used when classification by correspondence analysis and cluster analysis produced the same results; code 0 when the grid node was first assigned to cluster 1 and then to cluster 2 or vice versa (mixing between weathering and effluents); code 4 in the other cases (mixing between agriculture and the other influences). Code-3 areas were systematically surrounded by code-4 areas, an observation attributed to hydrodynamic dispersion. Accordingly, the extent of code-4 areas in two orthogonal directions was assumed proportional to the longitudinal and transverse dispersivities of local soils. The results (0.7–16.8 and 0.4–4.3 m, respectively) are acceptable at the macroscopic scale. The ratios between longitudinal and transverse dispersivities (1.2–11.1) are also in agreement with results obtained by other studies. 相似文献
146.
Milton J. Porsani Bjorn Ursin Michelângelo G. Silva Paulo E. M. Melo 《Geophysical Prospecting》2013,61(1):42-52
We present a singular value decomposition (SVD) filtering method for the enhancement of coherent reflections and for attenuation of noise. The method is applied in two steps. First normal move‐out (NMO) correction is applied to shot or CMP records, with the purpose of flattening the reflections. We use a spatial SVD filter with a short sliding window to enhance coherent horizontal events. Then the data are sorted in common‐offset panels and the local dip is estimated for each panel. The next SVD filtering is performed on a small number of traces and a small number of time samples centred around the output sample position. Data in a local window are corrected for linear moveout corresponding to the dips before SVD. At the central time sample position, we sum over the dominant eigenimages of a few traces, corresponding to SVD dip filtering. We illustrate the method using land seismic data from the Tacutu basin, located in the north‐east of Brazil. The results show that the proposed method is effective and is able to reveal reflections masked by ground‐roll and other types of noise. 相似文献
147.
148.
M. J. Le Bas Yang Xueming Rex N. Taylor B. Spiro J. A. Milton Zhang Peishan 《Mineralogy and Petrology》2007,90(3-4):223-248
Summary New data on Sr and Nd isotope composition and major and trace element distribution in dolomite-calcite carbonatite dykes at
Bayan Obo are provided, and a Mid-Proterozoic age is deduced. The dykes and the neighbouring massive dolomite (H8) body have
similar geochemical characteristics, interpreted to indicate a carbonatitic magmatic origin. The occurrence of riebeckite-bearing
fenitized quartzites marginal to both dykes and H8 dolomite body, and the presence of xenoliths in the latter, supports this
conclusion. Taken together with previously published stable isotope data, these data confirm a mantle-derived origin for the
H8 body.
The oxygen isotope composition of the dolomite and magnetite in the dykes is lower than that in the fine-grained dolomite.
Oxygen data from samples of the coarse-grained dolomite host are either similar to the dykes or to the fine-grained type in
agreement with their other geochemical characteristics. The carbonate-magnetite thermometric pairs of the fine-grained dolomite
indicate a range of 350–540 °C, which is probably lower than that of the original main magmatic emplacement. This supports
the distinction made between the original coarse-grained dolomite marble and dyke composition from the later fine-grained
dolomite.
Thus the large H8 dolomite is interpreted as a carbonatite intrusion that contains wall-rock xenoliths and caused fenitization
of the hanging wall, foot wall and the xenoliths, and that the coarse-grained portions of the H8 marble are those portions
that, in the Late Proterozoic to Palaeozoic, escaped recrystallization to fine-grained dolomite and subsequent REE-Fe mineralization.
Currently at National Oceanography Centre, University of Southampton, Southampton, UK
An erratum to this article is available at . 相似文献
149.
Deniz Bozkurt Maisa Rojas Juan Pablo Boisier Jonás Valdivieso 《Climatic change》2018,150(3-4):131-147
This study examines the projections of hydroclimatic regimes and extremes over Andean basins in central Chile (~ 30–40° S) under a low and high emission scenarios (RCP2.6 and RCP8.5, respectively). A gridded daily precipitation and temperature dataset based on observations is used to drive and validate the VIC macro-scale hydrological model in the region of interest. Historical and future simulations from 19 climate models participating in CMIP5 have been adjusted with the observational dataset and then used to make hydrological projections. By the end of the century, there is a large difference between the scenarios, with projected warming of ~ + 1.2 °C (RCP2.6), ~ +?3.5 °C (RCP8.5) and drying of ~ ? 3% (RCP2.6), ~ ? 30% (RCP8.5). Following the strong drying and warming projected in this region under the RCP8.5 scenario, the VIC model simulates decreases in annual runoff of about 40% by the end of the century. Such strong regional effect of climate change may have large implications for the water resources of this region. Even under the low emission scenario, the Andes snowpack is projected to decrease by 35–45% by mid-century. In more snowmelt-dominated areas, the projected hydrological changes under RCP8.5 go together with more loss in the snowpack (75–85%) and a temporal shift in the center timing of runoff to earlier dates (up to 5 weeks by the end of the century). The severity and frequency of extreme hydroclimatic events are also projected to increase in the future. The occurrence of extended droughts, such as the recently experienced mega-drought (2010–2015), increases from one to up to five events per 100 years under RCP8.5. Concurrently, probability density function of 3-day peak runoff indicates an increase in the frequency of flood events. The estimated return periods of 3-day peak runoff events depict more drastic changes and increase in the flood risk as higher recurrence intervals are considered by mid-century under RCP2.6 and RCP8.5, and by the end of the century under RCP8.5. 相似文献