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排序方式: 共有213条查询结果,搜索用时 15 毫秒
61.
A series of experiments was performed using artificial seawater samples of increasing complexity, in order to identify, qualitatively and quantitatively, the contribution of main seawater components on the buffer capacity for CO2.The results show that magnesium plays the most important role in the uptake, enhancing the capacity of the carbonate system alone by more than 100%. 相似文献
62.
Use of radon isotopes,gamma radiation and dye tracers to study water interactions in a small stream in Brazil 总被引:1,自引:0,他引:1
Vinícius V. M. Ferreira Rubens M. Moreira Zildete Rocha Cláudio J. Chagas Raquel L. M. Fonseca Talita O. Santos Paulo C. H. Rodrigues Maria Angela B. C. Menezes 《Environmental Earth Sciences》2018,77(19):699
In this study, natural (222Rn) and fluorescent (uranin) tracers were used to investigate the interactions between surface and subsurface waters in a small hydrographical basin located in the southeast region of Brazil. Levels of 222Rn were measured in 117 water samples with the use of an alpha solid-state detector. After the identification of the probable discharge sections along the stream, a measurement of the natural flows, upstream and downstream of these sections, was done with the use of a fluorimeter and fluorescent tracers. Also, scanning was done to verify a correlation between the natural gamma radiation and the 222Rn in the areas where its activity was higher. The results showed some sections where the 222Rn activity is more significant and contributed to the growth of the flows along the stream. It was possible to confirm a correlation between the discharge sections and the natural gamma radiation, what can be used as a preliminary approach to finding these sections in scenarios similar to the one studied here. 相似文献
63.
In order to perform a good pulse compression, the conventional spike deconvolution method requires that the wavelet is stationary. However, this requirement is never reached since the seismic wave always suffers high‐frequency attenuation and dispersion as it propagates in real materials. Due to this issue, the data need to pass through some kind of inverse‐Q filter. Most methods attempt to correct the attenuation effect by applying greater gains for high‐frequency components of the signal. The problem with this procedure is that it generally boosts high‐frequency noise. In order to deal with this problem, we present a new inversion method designed to estimate the reflectivity function in attenuating media. The key feature of the proposed method is the use of the least absolute error (L1 norm) to define both the data and model error in the objective functional. The L1 norm is more immune to noise when compared to the usual L2 one, especially when the data are contaminated by discrepant sample values. It also favours sparse reflectivity when used to define the model error in regularization of the inverse problem and also increases the resolution, since an efficient pulse compression is attained. Tests on synthetic and real data demonstrate the efficacy of the method in raising the resolution of the seismic signal without boosting its noise component. 相似文献
64.
Seeking a possible explanation for recent data indicating a space-time variation of the electron-to-proton mass ratio within the Milky Way, we consider a phenomenological model where the effective fermion masses depend on the local value of the Weyl tensor. We contrast the required values of the model’s free parameters with bounds obtained from modern tests on the violation of the weak equivalence principle and we find that these quantities are incompatible. This result indicates that the variation of nucleon and electron masses through a coupling with the Weyl tensor is not a viable model. 相似文献
65.
Kamil Teke Tobias Nilsson Johannes Böhm Thomas Hobiger Peter Steigenberger Susana García-Espada Rüdiger Haas Pascal Willis 《Journal of Geodesy》2013,87(10-12):981-1001
Continuous, very long baseline interferometry (VLBI) campaigns over 2 weeks have been carried out repeatedly, i.e., CONT02 in October 2002, CONT05 in September 2005, CONT08 in August 2008, and CONT11 in September 2011, to demonstrate the highest accuracy the current VLBI was capable at that time. In this study, we have compared zenith total delays (ZTD) and troposphere gradients as consistently estimated from the observations of VLBI, Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) at VLBI sites participating in the CONT campaigns. We analyzed the CONT campaigns using the state-of-the-art software following common processing strategies as closely as possible. In parallel, ZTD and gradients were derived from numerical weather models, i.e., from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields, the High Resolution Limited Area Model (European sites), the Japan Meteorological Agency-Operational Meso-Analysis Field (MANAL, over Japan), and the Cloud Resolving Storm Simulator (Tsukuba, Japan). Finally, zenith wet delays were estimated from the observations of water vapor radiometers (WVR) at sites where the WVR observables are available during the CONT sessions. The best ZTD agreement, interpreted as the smallest standard deviation, was found between GNSS and VLBI techniques to be about 5–6 mm at most of the co-located sites and CONT campaigns. We did not detect any significant improvement in the ZTD agreement between various techniques over time, except for DORIS and MANAL. On the other hand, the agreement and thus the accuracy of the troposphere parameters mainly depend on the amount of humidity in the atmosphere. 相似文献
66.
Michael James Friedel Oderson Ant?nio de Souza Filho Fabio Iwashita Adalene Moreira Silva Sueli Yoshinaga 《Hydrogeology Journal》2012,20(6):1061-1080
It is not possible, using numerical methods, to model groundwater flow and transport in the fractured crystalline rock of northeastern Brazil. As an alternative, the usefulness of self-organizing map (SOM), k-means clustering, and Davies-Bouldin techniques to conceptualize the hydrogeology was evaluated. Also estimated was the well yield and groundwater quality across the Juá region. This process relies on relations in the underlying multivariate density function associated with a sparse local set of hydrogeologic (electrical conductivity, geology, temperature, and well yield) and a complete regional set of airborne geophysical (electromagnetic, magnetic, and radiometric) and satellite spectrometric measurements. Resampling of the regional well yield and electrical conductivity estimates provides sufficient resolution to construct variograms for stochastic modeling of the hydrogeologic variables. The combination of these stochastic maps provides a way to identify potential drilling targets for future groundwater development. The data-driven estimation approach, when applied to available airborne electromagnetic and water-well hydrogeologic measurements, provides a low-cost alternative to numerical groundwater flow modeling. In addition to fractured rock environments, the alternative modeling framework can provide spatial parameter estimates and associated variograms for constraints to improve the traditional calibration of equivalent groundwater-porous-media models. 相似文献
67.
Wang Qiuxuan Song Li Agusti Susana Duarte Carlos Christakos George Wu Jiaping 《Ocean Science Journal》2021,56(4):395-405
Ocean Science Journal - Macrobenthos organisms are vital ecological components of intertidal wetlands. This work studied effects of non-native mangrove rehabilitation (Kandelia obovata) and salt... 相似文献
68.
69.
The European Atlantic area has been the scene of a number of extensive shipping incidents with immediate and potential long-term impacts to marine ecosystems. The occurrence of accidental spills at sea requires an effective response that must include a well executed monitoring programme to assess the environmental contamination and damage of the affected marine habitats. Despite a number of conventions and protocols developed by international and national authorities that focused on the preparedness and response to oil and HNS spills, much remains to be done, particularly in relation to the effectiveness of the environmental monitoring programmes implemented after oil and HNS spills. Hence, the present study reviews the status of the environmental monitoring programmes established following the major spill incidents over the last years in European waters, aiming at identifying the key monitoring gaps and drawing priorities for an effective environmental monitoring of accidental spills. 相似文献
70.
Mariano Bonomo Alejandro Fabián Zucol Beatriz Gutiérrez Téllez Andrea Coradeghini María Susana Vigna 《Journal of Paleolimnology》2009,41(2):273-296
This paper presents results of interdisciplinary palaeoenvironmental research carried out on a sediment sequence from the
Nutria Mansa 1 archaeological site. This late Holocene site is located in the Pampean plains, Argentina. Siliceous microfossils
were recorded (i.e. phytoliths, diatoms, chrysophytes, sponges) and micro-charcoal was analyzed. In addition, fauna identified
at the site were correlated with regional palaeoclimatic evidence. Based on the microfossil associations, we concluded that
the human occupations occurred beside a fluvial and brackish-freshwater lacustrine setting. Grass communities were located
on its margins that developed under a warm temperate climate with evidence for dryness and marked seasonality in part of the
record. Although some stratigraphic and faunal evidence indicates a possible temperature increase, these fluctuations were
not sufficient to extirpate mammals of arid and cold environments. 相似文献