Effects of the Influence of a Wave on an Underwater Obstacle by a Stratified Flow of Finite Depth

Equations are obtained for a hydrodynamic load on an obstacle, which is modeled by a point dipole during its circulated flow of a two-layered liquid of finite depth. The correlations between the wave resistance and rising force and the rate of the flow and circulation are studied. Examples of numerical calculations for real marine conditions are given. It is shown that the account of circulation can significantly change the value of the hydrodynamic reaction, which impacts the dipole.

     

Okenone in Bottom Sediments as a Proxy for Changes in the Water Level of a Saline Stratified Lake

Doklady Earth Sciences - Long-term measurements show that the sedimentation dynamics of okenone (a carotenoid of purple sulfur bacteria) reflects the abundance of purple sulfur bacteria, the...     

冷冻条件下天然包裹体中流体水分子氢键的拉曼光谱特征

水的拉曼图谱实际就是带氢键作用的OH伸缩振动峰(包括对称伸缩振动峰和反对称伸缩振动峰)和不带氢键作用的OH对称伸缩振动峰(包括对称伸缩振动峰和反对称伸缩振动峰)的叠加包络线,通过对流体中水的拉曼图谱的分析可以反映流体中氢键作用的强弱.因此,用Renishaw MK1-1000型显微激光拉曼探针原位分析了冷冻条件下天然的流体包裹体腔内流体水分子的氢键作用.研究表明,在冷冻条件下,水分子运动以带氢键作用的伸缩振动为主,同时还有微弱的非氢键作用的伸缩振动;随着温度的降低,流体中水分子的氢键作用不断地增强;在-130~-180 ℃区间氢键作用增强的趋势明显加大,暗示流体性质在此温度区间可能发生了突变.      

Propagation and coalescence of quasi-static cracks in Brazilian disks: an insight from a phase field model

The phase field model represents sharp cracks by diffusive mushy-zone and can simulate crack propagation automatically. Propagation and coalescence of quasi-static cracks in Brazilian disks are investigated by a phase field model. The phase field modeling is implemented in Comsol Multiphysics and initially verified by a benchmark of three-point bending test. The Brazilian disk specimens containing no initial crack, a single and two pre-existing cracks subjected to compression are then tested by the phase field model. Crack propagation patterns along with the load–displacement curves are fully discussed. Meanwhile, the effects of length scale parameter and critical energy release rate on crack propagation are evaluated. In addition, the effect of crack inclination angle on the pre-cracked Brazilian disk specimens is also investigated. The numerical results obtained by the phase field model are in good agreement with previous experimental and numerical results.

     

Propagation of a fast magnetoacoustic shock wave in the magnetosphere of an active region

The propagation of a fast magnetoacoustic shock wave the magnetosphere of a solar active region is considered the nonlinear geometrical acoustics approximation. The magnetic field is modeled as a subphotospheric magnetic dipole embedded in the radial field of the quiet corona. The initial parameters of the wave are specified at a spherical surface in the depths of the active region. The wave propagates asymmetrically and is reflected from regions of the strong magnetic field, which results in the radiation of the wave energy predominantly upwards. Substantial gradients in the Alfvén speed facilitate appreciable growth in the wave intensity. Non-linear damping of the wave and divergence of the wave front lead to the opposite effect. Analysis of the joint action of these factors shows that a fast magnetoacoustic perturbation outgoing from an active region can correspond to a shock wave of moderate intensity. This supports the scenario in which the primary source of the coronal wave is an eruptive filament that impulsively expands in the magnetosphere of an active region.     

Analysis of the Influence of a Natural Fracture Network on Hydraulic Fracture Propagation in Carbonate Formations

A new experimental model has been designed to simulate the influence of a natural fracture network on the propagation geometry of hydraulic fractures in naturally fractured formations using a tri-axial fracturing system. In this model, a parallel and symmetrical pre-fracture network was created by placing cement plates in a cubic mold and filling the mold with additional cement to create the final testing block. The surface of the plates will thus be weakly cemented and form pre-fractures. The dimension and direction of the pre-fractures can be controlled using the plates. The experiments showed that the horizontal differential stress $\Updelta \sigma$ and the angle $\Updelta \theta$ between the maximum horizontal principal in situ stress and the pre-fracture are the dominating factors for the initiation and propagation of hydraulic fractures. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma \ge 2{\text{ MPa}}$ or $\Updelta \theta = 60^\circ$ and $\Updelta \sigma \ge 4{\text{ MPa}}$ , the direction of the initiation and propagation of the hydraulic fractures are consistent with or deviate from the normal direction of the pre-fracture. When the hydraulic fractures approach the pre-fractures, the direction of the hydraulic fracture propagation will be consistent with the normal direction of the pre-fracture. Otherwise, the hydraulic fracture will deflect and perpendicularly cross the parallel and symmetric pre-fracture network. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma < 2{\text{ MPa}},\,\Updelta \theta = 60^\circ$ , and $\Updelta \sigma < 4{\text{ MPa}}$ or $\Updelta \theta = 45^\circ$ and $\Updelta \sigma = 4 - 8{\text{ MPa}}$ , before the hydraulic fracture and the pre-fractures intersect, the direction of the hydraulic fracture propagation remains unchanged, and the pre-fractures open or dilate when the hydraulic fracture propagates to the intersection point, forming a complicated hydraulic fracture network with the propagation region of the overall hydraulic fracture network taking the shape of an ellipse. In this condition, the complexity level of the hydraulic fracture is controlled by the net pressure, the compressive normal stress acting on the pre-fractures, the shearing strength and the cohesion strength of the planes of weakness. The conclusions of this research are inconsistent with the formulation of the approach angle that has been widely accepted by previous studies. The principle of hydraulic fracture propagation is that it follows the least resistance, the most preferential propagation, and the shortest propagation path.     

北调江水调蓄对石家庄地下水环境的影响

石家庄是我国北方利用地下水程度较高的城市,也是水资源危机较严重的城市之一.利用北调江水对其地下水进行补充调蓄,将极大缓解这种水危机压力.本文根据北调江水水源地丹江口水库的多年水质变化情况,结合受水区石家庄市的水文地质条件和地下水质特点,对其利用北调江水实施调蓄地下水后的水环境变化作了相关探讨.认为若以石家庄地下水降落漏斗为库容进行补充调蓄,将有效增加石家庄市的地下水资源量,提升其城市供水与储水能力.同时,还可明显改善其地下水质,提高地下水的自净化能力,恢复地下水的原始自然流向.为石家庄市的水资源调控提供科学依据.     

引江济太对锡澄片水环境的影响分析

通过对引江济太调水试验工程水质、水量的实测，以同步监测所得数据为基础，分析了其对水境的影响程度，阐述了引江济太对锡澄东部地区的利与弊，提出了引江济太应注意的一些问题。     

Magmatic Gradients in the Cretaceous Caleu Pluton (Central Chile): Injections of Pulses from a Stratified Magma Reservoir

The Caleu pluton (Central Chile) extending over 338 km² and with more than 1, 400 m of vertical relief intrudes the N-S trending Lower Cretaceous volcano-sedimentary and volcanic successions at a depth equivalent to a pressure of 2 kb. The host, stratified volcanic successions, are tilted about 30°–40° E, whereas the pluton shows paleomagnetic evidence of either tilting of <15° E or clockwise rotation by few degrees.A gradient of westward increasing SiO₂ content is recognized across the pluton, giving rise to three N-S elongated zones: Gabbro/Diorite Zone (GDZ), Tonalite Zone (TZ) and Granodiorite Zone (GZ). Biotite and hornblende compositions also exhibit a westward decreasing gradient in Mg/(Mg+Fe), indicating that the more mafic the zone is, the more oxidizing is its crystallization condition. Horizontal inward gradients of progressively less evolved rocks are recognized across GDZ and TZ, whereas no horizontal gradients were found in the GZ. Vertical compositional gradients are recognized in the GDZ and TZ, which consist of an upward increase in SiO₂ and decrease in MgO, FeO, Fe₂O₃, and compatible trace elements. A vertical compositional boundary was recognized along a traverse across the TZ separating two magma pulses with similar trends of compositional variations.The three zones of the Caleu pluton were derived from a common isotopically (Sr-Nd) depleted source. Each zone probably evolved independently, as their compositional characteristics would have not been acquired in situ. The resulting compositional characteristics of the zones would have been developed prior to the intrusion, in a subjacent stratified reservoir placed at about seven kilometers below the pluton.     

Comparative Study of Hydrogen and Carbon Isotopic Composition of Gases Generated from the Pyrolysis of a Peat under Saltwater and Freshwater Conditions

To understand the influence of the diagenetic water medium on the isotopic compositions of thermogenic coalbed gas, both hydrous and anhydrous closed-system pyrolyses were performed at temperatures of 250°C to 650°C on an herbaceous marsh peat. Compared to the results of anhydrous pyrolysis, the hydrocarbon gases generated from hydrous pyrolyses have very different hydrogen isotopic compositions. However, the carbon isotopic compositions of the hydrocarbon gases became only slightly heavier in hydrous pyrolysis, compared to that from anhydrous pyrolysis. With the progress of thermal evolution from peat to a more advanced thermal maturity of vitrinite reflectance values (Ro) of 5.5% during the pyrolysis, the difference in the average δD value increased from 52‰ to 64‰ between the hydrous pyrolysis with saltwater and anhydrous pyrolysis and increased from 18‰ to 29‰ between the hydrous pyrolysis with freshwater and anhydrous pyrolysis, respectively. The difference in the average δ13C value was only 1‰–2‰ between the hydrous and anhydrous pyrolysis. The relationships between the δD values of the generated hydrocarbon gases and Ro values as well as among δD values of the hydrocarbon gas species are established. The close relationships among these parameters suggest that the water medium had a significant effect on the hydrogen isotopic composition and a minimal effect on the carbon isotopic composition of the hydrocarbon gases. The results of these pyrolyses may provide information for the understanding of the genesis of coalbed gas from herbaceous marsh material with the participation of different diagenetic water media.     

异养细菌作用下岩溶水体惰性有机碳变化及其环境影响因素分析

惰性有机碳(RDOC, Recalcitrant Dissolved Organic Carbon)作为难以被生物降解的有机碳, 可以在水体中保存数千年, 构成长期碳储。岩溶区浮游植物利用岩溶水中丰富的HCO– 3进行光合作用, 为异养细菌生长提供充足的有机质底物, 促进异养细菌代谢, 形成RDOC。本文以广西柳江为例, 通过δ14C示踪法、荧光实时定量PCR法、原位微生物法对流域内细菌基因丰度、RDOC浓度等进行培养和测试, 结合环境因子对流域内RDOC的变化趋势进行分析讨论。研究区RDOC浓度介于1.46~2.66 mg·L–1之间, 平均1.85 mg·L–1, 占DOC的48.16%~92.61%, 平均占65.83%, 表现出明显的时空变化特征: 平水期水温升高、水体浊度降低, 浮游生物初级生产力增加, 产生较多内源有机碳, 为异养细菌提供充足的有机质底物, 细菌丰度和初级生产力增加, RDOC浓度明显高于丰水期, 主要受流域内异养细菌生物效应影响; RDOC浓度在水库坝后明显减小, 该采样点较缓的流速使有机质和生物聚合物更易沉降, 进而留存在水体中的DOC及RDOC减少, 主要受水动力条件控制。研究结果表明流域内RDOC受生物效应和水体理化性质共同影响, 异养细菌是流域内RDOC的主要贡献者, 同时浮游生物产生的内源有机碳对RDOC形成有促进作用。     

Pelagic Ecosystem of the Nansen Basin under the Influence of Variable Atlantic Water Inflow: The Mechanism Forming Diatom Bloom in the Marginal Ice Zone

Doklady Earth Sciences - Unique data were obtained on the abnormally high level of phytoplankton biomass (30 g m–3) in the marginal ice zone of the deep-water High Arctic (the Nansen Basin,...     

某水库库区侏罗系钙质砾岩对水库渗漏的影响

某拟建水库地层中存在溶孔和溶洞等溶蚀现象,可构成潜在渗漏通道。在对水库库区地质、水文地质条件调查、分析基础上,重点研究了库区钙质砾岩溶蚀的发育机理、特点和空间发育规律。由此,初步认为：库区钙质砾岩条带溶蚀不甚发育,不存在贯通性的渗漏通道,不会引起水库严重渗漏。     

中国西南河流碳、氮运移机制及其对水文条件变化的响应:以西江为例

流域碳、氮的生物地球化学循环过程关联着区域/全球尺度的气候变化,同时受到气候条件变化的影响。本次研究以我国西南喀斯特地区的西江为例,通过时间序列的高频次样品采集和分析,揭示水文条件变化对河流碳、氮动态变化的影响及其控制机制。结果表明,在高流量条件下,化学风化的加速、土壤CO2的汇入及流域内有机质的降解导致了水体δ13CDIC偏负,碳酸盐矿物的快速风化致使河水HCO3-浓度表现出强烈的"化学稳定性";对DIC、δ13CDIC、流量、温度的联合分析表明,矿物溶解、土壤CO2的汇入与河流中有机质降解的共同作用导致了西江河水碳动态的季节变化;河水NO3-浓度在高流量条件下并未表现出明显的稀释效应,反应了人为输入和化学转化过程对NO3-浓度的影响;硝酸盐氮、氧同位素的分析结果表明,西江NO3-来源受人为活动影响较大,主要转化过程为硝化作用;同位素和水化学证据表明碳酸、硫酸、硝酸共同参与流域岩石化学风化,雨季外源酸参与风化的减弱是河流中HCO3-稀释的重要原因。     

Partial melting during tectonic exhumation of a granulite terrane: an example from the Larsemann Hills, East Antarctica

Anatectic migmatites in medium- to low-pressure granulite facies metasediments exposed in the Larsemann Hills, East Antarctica, contain leucosomes with abundant quartz and plagioclase and minor interstitial K-feldspar, and assemblages of garnet–cordierite–spinel–ilmenite–sillimanite. Qualitative modelling in the system K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O₂, in conjunction with various P–T calculations indicate that the high-grade retrograde evolution of the terrane was dominated by decompression from peak conditions of c. 7 kbar at c. 800 °C to 4–5 kbar at c. 750 °C. Extensive partial melting during decompression involved the replacement of biotite by the assemblage cordierite–garnet–spinel within the leucosomes. These leucosomes represent the site of partial melt generation, the cordierite–garnet–spinel–ilmenite assemblage representing the solid products and excess reactants from the melting reaction. The extraction and accumulation of this decompression-generated melt led to the formation of syntectonic pegmatites and extensive granitic plutons. Leucosome development and terrane decompression proceeded during crustal transpression, synchronous with upper crustal extension, during a progressive Early Palaeozoic collisional event. Subsequent retrograde evolution was characterized by cooling, as indicated by the growth of biotite replacing spinel and garnet, thin mantles of cordierite replacing spinel and quartz within metapelites, and garnet replacing orthopyroxene and hornblende within metabasites. P–T calculations on late mylonites indicate lower grade conditions of formation of c. 3.5 kbar at c. 650 °C, consistent with the development of late cooling textures.     

The behaviour of uranium, thorium and tin during leaching from a coarse-grained porphyritic granite in an arid environment

During the routine analysis of chip samples from water boreholes it was noted that the DeBakken granite south of Kenhardt has high uranium and tin contents. Rock samples collected on surface, however, revealed low concentrations of both these elements indicating that they have been leached from the surface samples. The distribution of thorium in the borehole profiles showed that while both tin and uranium have been removed above the water table, other “immobile” elements and thorium remained unaffected.The geological data showed that the leaching took place since the start of the Tertiary. Initially, the movement of uranium was vertical and accumulated in pedogenic calcrete above the granite. This vertical leaching was controlled by fluctuations in the water table and took place from the Pliocene to Pleistocene. Later, in the Holocene, the pedogenic calcrete was removed and deposited as non-pedogenic calcrete along the rivers. These nodular calcrete deposits, which are abundant in Namaqualand, are mineralized only along those rivers which drain the DeBakken granite, indicating that this granite was the source of the uranium.When the water table reached depths of ten metres or more the vertical migration of uranium ceased and horizontal leaching caused by the movement of ground water became active. Where the water table cuts the surface, such as in the pans, uranium deposition due to evaporation of groundwater is still active.Leaching of uranium from this granite, together with the formation of the secondary deposits is mineralogically controlled, and is ascribed to the fact that uranium is not hosted in zircon. Granites such as the DeBakken granite, in which the uranium is hosted in biotite, monazite and apatite, cannot be recognized by surface sampling and hence a lithogeochemical approach, using sub-surface samples has to be adopted. Calculations showed that approximately 1400 tons of uranium metal has been leached from this granite since the start of the Tertiary and that the maximum reserve of the province as a whole is relatively small.The distribution of tin is erratic, and although it has been leached from the surface samples, it has not been transported for any significant distance. Thus the tin distribution in the profiles does not show the same degree of leaching as does uranium. This is ascribed to the fact that samples from a percussion drill would include both the rock fragments from which tin has been leached and the clay-rich alteration products in which it has been trapped. Tin is generally immobile when present as cassiterite, but when enclosed in biotite, and when the groundwater is enriched in chlorine and fluorine, it leaches readily from the biotite.     

High-resolution evidence from southern China of an early Holocene optimum and a mid-Holocene dry event during the past 18,000 years

Computer models suggest that the Holocene Optimum for East Asian summer monsoon precipitation occurred at different times in different regions of China. Previous studies indicate that this time-transgressive Holocene Optimum should have been experienced about 3000 yr ago in southern China. In this study we describe a section which allows us to test this timing directly. We have closely examined high-resolution eutrophic peat/mud sequences covering the past 18,000 cal yr at Dahu, Jiangxi, on the southern boundary of the mid subtropical zone in China. Late Pleistocene successions in the Dahu record indicate cooler and much wetter conditions relative to synchronous events in north-central China. Our results indicate that the Holocene Optimum occurred between ca. 10,000 and 6000 cal yr ago in southern China, consistent with the global pattern. Conditions were relatively dry and cold from 6000 to 4000 cal yr ago. Our data also support the conclusion that the last deglaciation to early Holocene in the south was much wetter, resulting in the formation of dense broad-leaved forests, which could have acted to moderate land temperature ∼10,000 to 6000 cal yr ago, yielding a stable early-Holocene climate. After 6000 cal yr, forest reduction led to unstable land temperatures, and possibly to a northerly shift of the subtropical high-pressure system. Whatever the mechanism, these changes resulted in decreased precipitation between 6000 and 4000 cal yr B.P. in southern China.     

Application of an Improved Flow-Stress-Damage Model to the Criticality Assessment of Water Inrush in a Mine: a Case Study

This paper presents a case study of water inrush on a mine working face from roof strata. The flow-rock failure process analysis (F-RFPA^2D) code with an improved flow-stress-damage (FSD) model was adopted to perform the failure and coupling analysis. The improved FSD model was used to represent the permeability variation at the four stages (elastic, damaged, cracked, and crack closure) of the rock failure process. The fracture initiation, propagation, and coalescence in the stressed strata and the seepage field evolution in the stress field are represented visually during the whole process of water inrush. The failure zone with high permeability induced by mining disturbance becomes the water-conducting zone after full excavation of the coal seam. The height of the water-conducting zone obtained in this study is in reasonable accordance with that predicted by an empirical formula. It is definitely clarified that the water inrush from the roof strata is induced by the failure zone full of vertical coalesced mine fractures. It is unlikely that roof accidents resulting in water inrush would occur if the water-conducting zone does not grow upwards into the aquifer. The main task for mine extraction under a confined aquifer is to locate the aquifer and find the maximum height of the water-conducting zone, which is very important for mine construction and support design.     

大王北洼陷浅水漫湖砂质滩坝沉积微相特征

通过岩心精细的观察,结合测井、三维地震以及岩石鉴定分析等资料的综合研究发现,大王北洼陷沙二段盆地断坳期为浅水漫湖砂质滩坝沉积,可分为:滩、坝主体、坝侧缘、坝间4种沉积微相,其中坝主体的成分成熟度和结构成熟度较高,且坝主体砂层最厚,滩、坝侧缘和坝间砂体次之.另外,沙二段时期盆地内河流三角洲不发育,大量坝砂呈条带状沿岸或斜交岸线发育,滩砂呈席状大面积覆盖于盆内与坝砂和其他沉积砂体相连,构成了洼陷"满盆砂"的浅水漫湖沉积的特征.这些砂体规律性地分布于洼陷内,并且与油源邻近(沙三段中部油页岩),是有利的油气储集体,与油气富集密切相关.     

Influence of a permanent low-friction boundary on rotation and flow in rigid inclusion/viscous matrix systems from an analogue perspective

Natural occurrences and recent experimental work show that a low-friction inclusion/matrix boundary can be responsible for antithetical rotation and development of stable shape preferred orientations in simple shear. The flow of a viscous matrix around a rigid inclusion to which it may or may not be adherent is still not well studied, but it is relevant to the understanding of the behaviour of structural elements in mylonite zones. We used two-dimensional (2-D) analogue experiments to address these issues. The experimental results with a permanent low-friction inclusion/matrix boundary (nonadherent mode) show the following. (1) The rotation behaviour of inclusions in this mode is markedly different from the theoretical predictions and experimental results for the adherent mode. (2) Inclusions with aspect ratio equal to 1 rotate synthetically at a rate that depends upon inclusion shape and orientation. (3) Ellipse-, rectangle- and lozenge-shaped inclusions rotate antithetically when starting with their greatest axis parallel to the shear direction. (4) Back rotation is limited in all cases studied, and the angle between the inclusion greatest axis and the shear direction represents a stable orientation, which depends on inclusion aspect ratio and shape. (5) A metastable orientation exists, which is strongly dependent upon inclusion shape and aspect ratio, and separates fields of antithetic and synthetic rotation.Our experimental results show that the overall flow pattern is bow tie-shaped in adherent and nonadherent modes. However, there are major differences in the way the matrix flows near the inclusion. (i) In the nonadherent mode, the nearby matrix flows past the inclusion, whereas in the adherent mode, the nearby matrix flows with and follows the inclusion. Therefore, in the adherent mode, passive marker lines parallel to the shear direction and streamlines show considerable deflections at the inclusion crests, in marked contrast with their straight character in the nonadherent mode. (ii) Stagnation points or closed flow lines near the inclusion were not observed in the nonadherent mode, which means that there is no closed separatrix around the inclusion in this mode, despite the fact that the overall flow shape is bow tie. (iii) In the adherent mode, the line of flow reversal is stable throughout deformation, but in the nonadherent mode, it changes position and orientation with progressive shearing. This shifting of the line of flow reversal can be an important factor controlling rotation behaviour in the nonadherent mode. (iv) In the nonadherent mode, the inclusion behaviour is similar to that observed in confined flow. (v) The flow pattern in the nonadherent mode provides an explanation for the observed lack of drag folds associated with small-scale rigid inclusions in mylonites.