The Application of Alkenone-Based pCO2 Reconstructions

The changing of atmospheric carbon dioxide concentration is closely related with the changing of global ice sheet,temperature and sea level. Knowledge of the past atmospheric carbon dioxide concentration and its relationship with climate is an important method of predicting the future climate change. Coccolith derived long-chain alkenone carbon isotope is one of the important proxies to reconstruct past carbon dioxide, which is wildly applied in the reconstruction of the Cenozoic atmospheric carbon dioxide. In this paper, we focused on the method of alkenone-based atmospheric carbon dioxide concentration, including the geochemical properties of long-chain alkenone, carbon diffusive model and the carbon isotope fraction. Then, we introduced the development of alkenone-based carbon dioxide proxy and its uncertainty. Coccolith cell geometry and growth rate have great influence on carbon dioxide fraction. Besides, there are some uncertainties about carbon concentration mechanisms in coccolithes, which may have some influence on alkenone-based carbon dioxide method to reconstruct ancient carbon dioxide more accurately. At the end, we summarized the Cenozoic carbon dioxide record with various proxies including alkenone carbon dioxide, boron isotope, palaeosol carbonate nodules and stomatal indices of fossil leaves.     

Gibbs sampler for computing and propagating large covariance matrices

The use of sampling-based Monte Carlo methods for the computation and propagation of large covariance matrices in geodetic applications is investigated. In particular, the so-called Gibbs sampler, and its use in deriving covariance matrices by Monte Carlo integration, and in linear and nonlinear error propagation studies, is discussed. Modifications of this technique are given which improve in efficiency in situations where estimated parameters are highly correlated and normal matrices appear as ill-conditioned. This is a situation frequently encountered in satellite gravity field modelling. A synthetic experiment, where covariance matrices for spherical harmonic coefficients are estimated and propagated to geoid height covariance matrices, is described. In this case, the generated samples correspond to random realizations of errors of a gravity field model. AcknowledgementsThe authors are indebted to Pieter Visser and Pavel Ditmar for providing simulation output that was used in the GOCE error generation experiments. Furthermore, the NASA/NIMA/OSU team is acknowledged for providing public ftp access to the EGM96 error covariance matrix. The two anonymous reviewers are thanked for their valuable comments.     

浮球式海底取样器的结构及工作原理——海底取样技术介绍之四

介绍了浮球式海底取样器的结构、性能特点、典型应用及性能参数；论述了振动式及振动冲击式贯入理论的原理；并分析了海流及船体飘移对海上取样作业的影响及解决办法。     

顶空气相色谱法测定北京市地下水中的氯代烃

以国家标准方法和美国环保局（EPA）方法为基础，建立用自动顶空进样器对饮用水中的氯代烃进行测定的方法，探讨了影响实验空白的因素，所拟方法的检出限为：三氯甲烷0.096μg/L、四氯化碳0.034μg/L，三氯乙烯0.049μg/L，四氯乙烯0.033μg/L。方法回收率控制在82％－106％，其相对标准偏差（RSD，n=7)小于23％，符合国际有机污染物分析的标准，并用此方法对北京市地表水、地下水进行了测定。     

Estimation of the rate constant for the reaction of acid sulphate aerosol with NH3 gas from atmospheric measurements

Horizontal gradients in atmospheric aerosol strong acidity have been interpreted in terms of the rate of neutralisation of aerosol H⁺ by gaseous ammonia. The results indicate a pseudo-first-order rate constant for this reaction within the range 4×10^-6 s^-1 to 4.1×10^-4 s^-1 consistent with model results and experimental data derived by other methods. The rate constant is reduced as the aerosol becomes less acidic, which is reflected in a positive correlation between rate constant and aerosol H⁺/NH₄ ⁺ ratio.     

观测井水质垂向差异及对取样质量的影响

观测井水质垂向差异由三因素引起:抽、灌水过程中含水层水质改变、近井口表层水体氧化、含水层本身存在水质垂向分带。由此易造成不同浓度间水质弥散,从而对使用定深取样器取样带来影响。减缓取样器下放速度,适当加密取样频率有助于克服其影响。在观测井滤水管中部取样具有代表性,可用于定量研究。     

振动沉管灌注桩施工工艺

介绍了振动沉管灌注桩施工复杂地层的工艺，提高单桩承动力和成孔成桩效率的措施。讨论了取土器取土（砂）问题。评价了振动沉管灌注桩的应用前景。     

High spatial resolution monitoring of benzene and toluene in the Urban Area of Taranto (Italy)

Atmospheric concentrations of benzene and toluene were assessed during three different seasons in the city of Taranto, using Radiello® diffusive samplers, in order to detect the most critical areas and to point out the sources contributing to pollution (vehicular traffic or industrial activities). High spatial resolution maps were built using a grid of 30 meshes drawn on the urban area of the city. For each mesh a monitoring site as representative as possible was chosen. Besides, in order to describe the highest levels of pollutants to which people is exposed, other 10 sampling sites were detected near high vehicular traffic crossroads or in particular critical zones of the city. The measurements of the concentration of these pollutants were carried out with Radiello® diffusive samplers for thermal desorption. The analysis of the results and the comparison between the map of vehicular traffic flows and the map of the concentrations of benzene suggested that in urban area the main benzene source is the traffic and the most significant pollution phenomena happens in zones characterized by narrow roads. Moreover it was possible to observe that high concentrations of benzene found in the NE zone of Taranto could be assigned to the industrial activities. This hypothesis was confirmed considering the diagnostic ratio between the toluene and benzene concentrations.     

Using unsteady-state water level data to estimate channel roughness and discharge hydrograph

A novel methodology for simultaneous discharge and channel roughness estimation is developed and applied to data sets available at three experimental sites. The methodology is based on the synchronous measurement of water level data in two river sections far some kilometers from each other, as well as on the use of a diffusive flow routing solver and does not require any direct velocity measurement. The methodology is first analyzed for the simplest case of a channel with a large slope, where the kinematic assumption holds. A sensitivity and a model error analysis are carried out in this hypothesis in order to show the stability of the results with respect to the error in the input parameters in the case of homogeneous roughness and to analyze the effect of unknown roughness heterogeneity on the estimated discharges. The methodology is then extended to the more general case of channels with mild slope and validated using field data previously collected in three Italian rivers: the Arno (in Tuscany), the Tiber (in Latium) and the Vallo di Diana, a small tributary of the Tanagro river (in Southern Italy). The performance of the proposed algorithm has been investigated according to three performance criteria estimating the quality of the match between the measured and the computed stage and discharge hydrographs. Results of the field tests can be considered good, despite the uncertainties of the field data and of the measured values.     

Novel mass-aggregation-based calibration of an acoustic method of monitoring bedload flux by infrequent desert flash floods

The monitoring of bedload flux under flash flood conditions has been successfully achieved since 1992 using slot samplers in the semiarid Nahal Eshtemoa. In the present study, a surrogate bedload monitoring technique - the Japanese plate microphone - has been deployed and calibrated against data from the slot samplers. Since a slot sampler has a sensitivity threshold that becomes especially important when transport rates are low, different averaging periods should be considered for high and low fluxes. In order to overcome the deficiencies of time-based aggregation used hitherto, we have developed a new method involving mass aggregation and commensurably variable intervals, thereby enabling a more accurate analysis and optimizing the bedload sampler's capabilities. The data derived with this new method has then been utilized to calibrate the Japanese plate microphone. The Eshtemoa is an ephemeral gravel bed channel with a high proportion of fine gravel (< 0.02 m); for these conditions, acoustic sensors have not been calibrated as yet. Two multiple linear regression models incorporating the effect of median bedload grain size on pulse rate have been established to predict bedload flux and cumulative transported bedload mass. The coefficients in these models are statistically significant. Good predictions are obtained for bedload flux (adj. r² = 0.83) and for cumulative bedload mass (adj. r² = 0.98) during flood recession. Overall, the multiple linear regression models, used in conjunction with the mass aggregation method of estimating bedload flux, suggest that field calibration of acoustic devices is feasible under these conditions for ca. 90% of the duration of bedload transport. © 2020 John Wiley & Sons, Ltd.