Ekman Convective Layer Flow of a Viscous Incompressible Fluid

Analytical solutions for generalizing the Ekman stationary flow of a viscous incompressible fluid in an infinite layer are obtained. The solution of an overdetermined system of the Oberbeck–Boussinesq equations is considered. It is suggested to use a class of exact solutions for this problem. It is shown that the structure of the solutions allows one to preserve the advective derivative in the heat-conductivity equation; this makes it possible to model the stratification of the temperature and pressure fields and describe the oceanic countercurrents.     

Surface Oscillations of a Free-Falling Droplet of an Ideal Fluid

According to observations, drops freely falling in the air under the action of gravity are deformed and oscillate in a wide range of frequencies and scales. A technique for calculating surface axisymmetric oscillations of a deformed droplet in the linear approximation under the assumption that the amplitude and wavelength are small when compared to the droplet diameter is proposed. The basic form of an axisymmetric droplet is chosen from observations. The calculation results for surface oscillations agree with recorded data on the varying shape of water droplets falling in the air.     

Seasonal Dynamics of Microbial Processes in Bottom Sediments of the Sevastopol Coastal Area

Oceanology - A seasonal study of microbial methane oxidation (MO) and sulfate reduction (SR) processes in bottom sediments was carried out at five stations in the estuarian Sevastopol coastal area,...     

Subphotospheric Resonator and Local Oscillations in Sunspots

The conditions under which the subphotospheric slow-wave resonator can be responsible for the local oscillations in a sunspot have been determined. A rich spectrum of local 3-min oscillations can be produced by the subphotospheric resonator only if the magnetic field in the resonator magnetic flux tube is much weaker than the surrounding sunspot magnetic field. Convective upflows of hot plasma in the sunspot magnetic field satisfy this condition. Consequently, there must be a correlation between the local oscillations and umbral dots, because the latter are produced by convective flows. Various modes of operation of the subphotospheric resonator give rise to wave packets of 3-min oscillations and umbral flashes. It is shown that giant local umbral flashes can emerge under certain conditions for the excitation of oscillations in the subphotospheric resonator.     

基于纹理和空间特征的中分辨率影像滨海水产养殖用地提取研究

近年来,水产养殖用地分布广泛,但由于其在影像上所表现的复杂性和不均匀性,造成该用地类型提取中的困难,尤其针对中分辨率遥感影像。对此,本文提出了一种基于纹理和空间特征的养殖用地提取方法,该方法主要包括3个步骤：首先,利用纹理熵和归一化差异水体指数NDWI实现水产养殖用地的粗提取;然后,依据相邻地物间的关系实现同类型地物合并;最后,本文构建一种相对宽度作为地物的近似宽度,再次利用NDWI实现水产养殖用地的准确识别。本文以越南万丰湾为研究区域,以Landat-8融合影像（融合后的像元大小为15 m）的目视解译结果为标准,对本文方法与最小距离法分类结果进行比较。实验结果表明,该方法的精度可达91.13%,远高于传统的面向对象方法,并且所提方法的错误率和虚假率分别为0.09%和8.87％,表明了该方法可靠性,因而该方法可为基于中分辨率影像的地物类型提取提供一种有效手段。     

Leak-off mechanism and pressure prediction for shallow sediments in deepwater drilling

Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS (minimum horizontal principle stress) model and the FIF (fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC (permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling.     

三亚海域浮游病毒与细菌丰度的时空变化规律以及相关环境因子*

在三亚海域设置3个站位, 分别于各站位连续采集12个月表层水样。利用流式细胞仪进行浮游病毒及浮游细菌丰度的测定, 并对两者及其与环境因子之间的相关性进行研究, 同时对不同站位之间进行差异性分析。结果表明, 调查海域浮游病毒丰度(平均7.63×10⁶viruses·mL^-1)高于浮游细菌丰度(平均1.52×10⁶cells·mL^-1)。浮游病毒及浮游细菌丰度在三亚河口最高, 且有明显的季节变化, 冬春季高于夏秋季, 并且其与鹿回头半岛西侧、小东海之间均有极显著差异(P<0.01), 不同类群病毒代表的宿主类群也有所不同。调查海域总体水平浮游病毒丰度与浮游细菌丰度显著正相关(r=0.800, P<0.01); 叶绿素(Chl a)和氮盐(NO- 2、NO- 2+NO- 3、NH+ 4)是影响两者的关键因子。     

基于SODA资料的南海表层风能输入的空间分布与长期趋势研究

海面风不仅是驱动上层海洋运动的主要动力, 其能量也是维持海洋表层流动的主要机械能来源。为了分析南海表层流风能输入的变化, 用SODA(Simple Ocean Data Assimilation)(1901—2010)资料估算了风向南海表层流(表层地转流+表层非地转流)的能量输入。结果表明, 风向南海表层流、表层地转流和表层非地转流输入的能量总体均呈减少趋势, 110年间分别减小了约56%、65%和49%。导致风能输入减小的最主要因素是风应力的减弱(减小了35%)。由于南海受季风系统的控制, 风向表层流及其各成分输入的能量呈现出显著的季节性变化。冬季风能输入最强, 高值区位于南海西部及北部区域, 呈一个显著的“回力镖”状结构。这些结果对深入认识南海环流具有理论意义。     

Dynamical model of binary asteroid systems using binary octahedrons

We used binary octahedrons to investigate the dynamical behaviors of binary asteroid systems. The mutual potential of the binary polyhedron method is derived from the fourth order to the sixth order. The irregular shapes, relative orbits, attitude angles, as well as the angular velocities of the binary asteroid system are included in the model. We investigated the relative trajectory of the secondary relative to the primary, the total angular momentum and total energy of the system, the three-axis attitude angular velocity of the binary system, as well as the angular momentum of the two components. The relative errors of the total angular momentum and the total energy indicate that the calculation has a high precision. It is found that the influence of the orbital and attitude motion of the primary from the gravitational force of the secondary is obvious. This study is useful in understanding the complicated dynamical behaviors of the binary asteroid systems discovered in our Solar system.