Box fractal dimension as a measure of statistical homogeneity of jointed rock masses

A written computer programme to estimate the box fractal dimension (D_B) is verified by estimating D_B of the triadic Koch curve for which the theoretical D is known. The influence of a number of input parameters of the box-counting method on the accuracy of estimated D_B is evaluated using the same Koch curve. The employed size range of the applied box networks was found to be the parameter which has the strongest influence on the accuracy of estimated D_B. This indicated the importance of finding the range of self-similarity or self-affinity for the object considered to select the proper range for the box sizes and, in turn, to obtain accurate estimates of D_B. By calculating D_B for different block sizes sampled from three generated two-dimensional joint patterns, it is shown that D_B can capture the combined effect of joint-size distribution and joint density on the statistical homogeneity of rock masses. The spatial variation of D_B along a 350 m stretch of a tunnel in the shiplock area of the Three Gorges dam site is computed using the joint data mapped on the walls and the roof of the tunnel. This spatial variation of D_B is used, along with the visual geological evaluation of the joint trace maps of the tunnel, in making decisions about statistical homogeneity of the rock mass around the tunnel. The results obtained on statistically homogeneous regions were found to be quite similar to the results obtained from a previous statistical homogeneity investigation which incorporated the effect of number of joint sets and their orientation distributions, but not the spatial variation of D_B. It is recommended that the spatial variation of D_B is used, along with the results of other methods such as contingency table analysis and equal area plots, which incorporate the effect of joint orientation distribution, in addition to the geology of the site, in determining the statistically homogeneous regions of jointed rock masses.     

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Effects of fixation and storage on flow cytometric analysis of marine bacteria

Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria. Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered.     

Effects of long-term sample preservation on flow cytometric analysis of natural populations of pico-and nanophytoplankton

The effects of long-term preservation on flow cytometric parameters of natural oceanic populations of pico-and nanophytoplankton have been examined. Populations collected at oligotrophic subtropical and subarctic locations in the North Pacific were fixed with glutaraldehyde and frozen in liquid nitrogen, according to Vaulot et al. (1989). During six months’ storage, chlorophyll red fluorescence declined in all the groups examined, while forward light scatter was enhanced in Synechococcus and Prochlorococcus, and weakened in nanoeucaryotes. Cell loss was not significant except for Synechococcus. Caution is required when analyzing flow cytometric data of samples stored for more than a month.     

温宿北—野云沟断裂的构造几何学与运动学特征及塔北隆起的成因机制

克拉通内古隆起的构造变形是探究板块内部变形行为与大陆流变构造学的理想场所,断裂研究则是其主要突破口。本文基于新的地球物理与钻探资料,对塔里木盆地北部隆起的断裂系统尤其是其北部边界断裂的几何学与运动学开展研究。分析表明,温宿北—野云沟断裂系在重磁场与反射地震剖面上具有清楚的反映,为塔北隆起的北部边界断裂,长达600 km,自西向东由温宿北断裂、温巴什断裂和野云沟断裂三段构成。该断裂系是在早奥陶世末沿基底软弱带自南向北逆冲形成的大型断层相关褶皱带基础上在前翼发生突破而形成的,加里东末期形成雏形,二叠纪末期,受南天山洋关闭的影响由北向南的强烈挤压形成自北而南的逆冲构造系统。该逆冲系统迁就原加里东期的滑脱面发育,并对原来的逆冲系统进行叠加、改造,形成一系列小断块叠加的大型背冲断裂系统,使得该断裂带基本定型。喜马拉雅期塔北隆起轴部发育张扭性断裂构造系统,该断裂系遭受左旋压扭,断裂的活动时序自东向西趋晚,具有长期演化、多期发育、继承、叠加与复合的特征。活动强度呈古生代强烈、中生代—新生代早期弱化、新生代晚期趋强的"强-弱-强"的演化趋势,在横向上呈西段强烈、东段略弱的特征。其成因主要与早奥陶世末期北昆仑洋关闭、二叠纪末期南天山洋关闭、古近纪新特提斯洋关闭引起的周缘地体与塔里木地块的碰撞拼合相关,表现出周缘板块构造事件对板内变形的强烈影响。该断裂系是重要的油气富集带。研究其成因与演化有助于该带油气勘探的拓展,例如西秋断裂带的油气发现。     

Joint probability analysis of water and sediment and predicting sediment load based on copula function

The Jinsha River comprises the upper reaches of the Yangtze River, which is the river section with the highest sediment content. Monitoring of sediment transport in the Jinsha River is done to the guarantee for the normal operation of the Three Gorges Reservoir. In the current study, a copula function was used to do a joint probability analysis of the water and sediment in the Jinsha River Basin (JRB), further a sediment load prediction model based on the copula function also was constructed. The results show that the average annual flow from 2001 to 2018 at the outlet of the Jinsha River (Yibin station) is about 60.43 billion m³, and the average annual sediment load is about 58.82 million t. The linear correlation coefficient between annual flow and annual sediment load is 0.28. The best marginal distribution for annual flow and sediment load is Pearson Type Three (PE3) and Generalized Normal (GNO), respectively, and the best fit for the combined distribution of the two variables is the Frank copula function. The synchronous probability of water and sediment occurrence is 0.459, and the asynchronous probability is 0.541. Based on the copula prediction model, the sediment load can be effectively simulated, and the correlation coefficient between the simulated sequence and the measured sequence reached 0.93. The current study provides important significance for the analysis of water and sediment in the JRB, which is beneficial to the management of Three Gorges Reservoir sediment discharge in the upstream and downstream.     

Geomorphometric pattern recognition of SRTM data applied to the tectonic interpretation of the Amazonian landscape

The Amazon landscape spatial variability and anisotropic trends in the Uatumã and Urubu River regions are evaluated using geomorphometric techniques such as fractal dimension, drainage network density and semivariogram. These procedures were applied to the digital elevation model (DEM) of the Shuttle Radar Topography Mission (SRTM). This evaluation facilitated the definition of geomorphometric domains with different degrees of roughness (fractal dimension) and elevation (semivariogram). These areas are consistent with known qualitative relief types. Furthermore, known geological structures in the subsurface and surface apparently influence the spatial variability of these geomorphometric variables. This is the Silves area case, where the hilly topography exhibits several annular and radial rivers, denoting subsurface control due to faults and folds that were mapped by seismic surveys. Another possible influence example is the spatial coincidence between structures mapped by magnetic data with low dissection zones delineated as a result of drainage network density analysis. In addition to the spatial distribution, the anisotropic trends of these geomorphometric variables were analyzed and compared with geological and geophysical information. Results indicate that the predominant directions for topographic semivariance anisotropy are NNE–SSW and NE–SW for the interfluvial regions, as well as NW–SE for the alluvial plains. The highest agglomeration direction in the drainage network, as shown by its anisotropy, coincides with the studied region’s current maximum horizontal stress direction, except in the floodplains. The direction with the most pronounced roughness, NNE–SSW, coincides with the direction of waterfalls and rapids. This study demonstrates that spatial variability knowledge and anisotropic trends of geomorphometric parameters is useful to understand the geology and geomorphology of the Central Amazon region.     

Computer simulation of flow through a lattice flow-cell model

For single-phase flow through a network model of a porous medium, we report (1) solutions of the Navier–Stokes equation for the flow, (2) micro-particle imaging velocimetry (PIV) measurements of local flow velocity vectors in the “pores throats” and “pore bodies,” and (3) comparisons of the computed and measured velocity vectors. A “two-dimensional” network of cylindrical pores and parallelepiped connecting throats was constructed and used for the measurements. All pore bodies had the same dimensions, but three-different (square cross-section) pore-throat sizes were randomly distributed throughout the network. An unstructured computational grid for flow through an identical network was developed and used to compute the local pressure gradients and flow vectors for several different (macroscopic) flow rates. Numerical solution results were compared with the experimental data, and good agreement was found. Cross-over from Darcy flow to inertial flow was observed in the computational results, and the permeability and inertia coefficients of the network were estimated. The development of inertial flow was seen as a “two-step” process: (1) recirculation zones appeared in more and more pore bodies as the flow rate was increased, and (2) the strengths of individual recirculation zones increased with flow rate. Because each pore-throat and pore-body dimension is known, in this approach an experimental (and/or computed) local Reynolds number is known for every location in the porous medium at which the velocity has been measured (and/or computed).     

地理学的模型建设及其选择标准——简析非欧几何学对地理学研究方法的影响

非欧几何学产生以后,科学研究的主要任务由寻求真理转变为建设模型,地理科学的任务也理当发生相应的转向．像其他科学分支一样,地理学的研究目标不再是发现真理,而是提出假设、建立模型．判断一个地理理论模型好坏的标准不是模型的假设是否符合实际,而是该模型对现实世界的解释和预言能力．在模型的解释和预言能力一定的情况下,模型越是简单,就越是可取;在模型的复杂程度一定的情况下,模型的解释和预言能力越强,就越是优越．当一个地理模型不仅仅对地理现象具有刻画能力,而且对其他相关领域具有某种启示作用的时候．该模犁就具有超学科的理论意义或者研究价值．