周期脉冲撞击的两分量Bose-Einstein凝聚系统的单粒子相干和对纠缠

在周期脉冲撞击的两分量Bose-Einstein凝聚系统中,研究了量子混沌对单粒子相干和对纠缠性质的影响.研究表明,混沌促使单粒子相干发生强烈衰减并保持着较低的相干度,同时对纠缠出现最大值并在较短时间后消失.利用单粒子相干的这种性质可以直接测量量子混沌存在的相空间结构,有利于预防Bose-Einstein凝聚的瓦解和控制凝聚体的混沌行为.     

ATON型Hall推力器缓冲区预电离问题研究

ATON是20世纪90年代新提出的一种Hall推力器设计方案,其中的缓冲区是ATON新采用的一种结构.本文对缓冲区的作用进行分析,在此基础上提出了采用附加电源提高缓冲区预电离率的方法.并采用PIC(Particle-in-cell)粒子模拟方法对这种设计方式的等离子体分布进行数值模拟.结果表明,通过增加缓冲区内的附加电压,能够有效地提高缓冲区预电离率.     

The complex variable reproducing kernel particle method for two-dimensional elastodynamics

On the basis of the reproducing kernel particle method (RKPM), a new meshless method, which is called the complex variable reproducing kernel particle method (CVRKPM), for two-dimensional elastodynamics is presented in this paper. The advantages of the CVRKPM are that the correction function of a two-dimensional problem is formed with one-dimensional basis function when the shape function is obtained. The Galerkin weak form is employed to obtain the discretised system equations, and implicit time integration method, which is the Newmark method, is used for time history analysis. And the penalty method is employed to apply the essential boundary conditions. Then the corresponding formulae of the CVRKPM for two-dimensional elastodynamics are obtained. Three numerical examples of two-dimensional elastodynamics are presented, and the CVRKPM results are compared with the ones of the RKPM and analytical solutions. It is evident that the numerical results of the CVRKPM are in excellent agreement with the analytical solution, and that the CVRKPM has greater precision than the RKPM.     

Cadmium and phosphorus cycling in the water column of the South China Sea: The roles of biotic and abiotic particles

The concentrations of cadmium, phosphorus, and aluminum in size-fractionated phytoplankton, zooplankton, and sinking particles are determined using ICPMS to evaluate the roles of biotic and abiotic particles on the cycling and ratios of Cd and P in the water column. Plankton were collected with a filtration apparatus equipped with 10-, 60-, and 150-μm aperture plankton nets on two occasions (2002 and 2006), and sinking particles were sampled by moored sediment traps deployed at depths of 120, 600, and 3500 m from 2004 to 2005. In contrast to what our previous study revealed, i.e., that most of the other bioactive trace metals in plankton were strongly correlated with abiotic Al and adsorbed on phytoplankton [Ho, T.Y., Wen, L.S., You, C.F., Lee, D.C., 2007. The trace metal composition of size-fractionated plankton in the South China Sea: biotic versus abiotic sources. Limnol Oceanogr 52, 1776–88.], Cd/P ratios, ranging from 0.12 to 0.34 mmol/mol P, did not vary with Al and exhibited fairly consistent values among different sizes of plankton, showing that Cd was mostly incorporated on an intracellular basis. In terms of the sinking particles, fluxes in Cd and P as well as in Cd/P ratios were strongly influenced by both biotic and abiotic particles. Overall, the Cd/P ratios in the sinking particles ranged from 0.03 to 1.2 mmol/mol, with the highest value observed in traps at 120 m during the productive season. The lowest value was observed in deep water during high flux periods for lithogenic particles. At surface depth, flux and Cd/P ratios were elevated during the most productive season in the region. The elevated ratios in the traps at 120 m were most likely related to preferential uptake of Cd for the dominant species (coccolithophores) during the productive period. Relatively, Cd/P ratios sharply decreased with increasing Al flux in deep water and ratios were much lower than the expected Cd/P ratios obtained from the relative portion of lithogenic and biogenic particles, indicating that the adsorption of soluble P into lithogenic particles was significant in the deep water during high lithogenic particle flux periods. Using averaged annual fluxes and standing stock in the water column, the residence time of biogenic Cd and P are 0.10 and 0.20, 250 and 100, and 9100 and 5000 years respectively in the top 120 m, 600 m, and water column as a whole, also showing preferential removal for Cd in the euphotic zone but relatively higher removal rates for P in the deep water. Our study suggests that the shift in microalgal community structure along with input of lithogenic minerals are both potentially important factors in influencing Cd/P ratios in oceanic water on a geological time scale.     

闽江口入海悬沙输运的数值模拟

闽江河口位于福建省东部,本文利用欧拉-拉格朗日差分方法模拟闽江口及附近海域在不同径流下的潮流场,并建立拉格朗日水质点跟踪方法近似模拟了悬沙在海域中的迁移过程．水质点运动轨迹计算结果表明,闽江口悬沙在外海主要向南方或东南方输运,其轨迹呈现螺旋线．在洪峰流量下,悬沙运移距离较远．     

椒江河口洪季最大浑浊带核部的悬沙分选机制

以实测悬沙粒径、流速、含沙量资料为基础,通过悬沙不同粒级组分、中值粒径以及粒度参数的统计,分析椒江河口最大浑浊带核部悬沙粒径分布变化特性。研究表明,悬沙粒径分选主要受物质来源、潮流动力作用下底部部分物质再悬浮和絮凝沉降3个因素的影响。其中第二个因素起主导作用,大潮期比小潮期显著,第三个因素的作用主要发生在涨落憩前后低流速期,并在表层较近底层的水体明显。     

烟台芝罘湾底质沉积物粒度特征和沉积动力环境研究

根据芝罘湾海域110个底质沉积物样品粒度分析结果,对沉积物类型和粒度参数分布进行了总结。在此基础上,利用粒径趋势分析模型(GSTA)和沉积动力判别图解,探讨了底质沉积物的运移趋势及沉积水动力规律。研究表明,芝罘湾海域底质沉积物类型共有8种,其中砂质泥、砂质粉砂、泥和粉砂分布最广泛;平均粒径值具有从岸向海逐渐增大的趋势,分选性、偏度和峰度分别为差、正偏—极正偏、平坦—中等的特征;粒度运移趋势分析反映出套子湾泥沙向西、西南运移,芝罘湾及以东海域泥沙呈顺时针方向运移;沉积动力判别图解揭示出芝罘湾海域沉积水动力具有整体较弱的特征。     

Cavity expansion analyses of crushable granular materials with state‐dependent dilatancy

Crushability is one of the important behaviors of granular materials particularly under high stress states, and affects both the deformability and strength of the materials that are in essence associated with state‐dependent dilatancy. In this presentation, first, a new critical state model is proposed to take into account the three different modes of compressive deformation of crushable granular materials, i.e. particle rearrangement, particle crushing and pseudo‐elastic deformation. Second, the governing equations for cavity expansion in crushable granulates are introduced, in which the state‐dependent dilatancy as well as the bounding surface plasticity model are used. Then, the procedure to obtain semi‐analytical solutions to cavity expansion in the material is described in detail, in which a commercial differential equation solver is employed. Finally, cavity expansion analyses are carried out on Toyoura sand, a well‐documented granular material, to demonstrate the effects of crushability and state‐dependent dilatancy. The study shows that particle crushing does occur at both high stress and critical states and affects the stress fields and the deformation behavior of the material surrounding the cavity in association with state‐dependent dilatancy. This leads to conclusion that particle crushing and state‐dependent dilatancy have to be taken into account when cavity expansion theory is used to interpret cone penetration tests and pressuremeter tests. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical analysis of the effect of natural microcracks on the supercritical CO2 fracturing crack network of shale rock based on bonded particle models

The problem of predicting the geometric structure of induced fractures is highly complex and significant in the fracturing stimulation of rock reservoirs. In the traditional continuous fracturing models, the mechanical properties of reservoir rock are input as macroscopic quantities. These models neglect the microcracks and discontinuous characteristics of rock, which are important factors influencing the geometric structure of the induced fractures. In this paper, we simulate supercritical CO₂ fracturing based on the bonded particle model to investigate the effect of original natural microcracks on the induced‐fracture network distribution. The microcracks are simulated explicitly as broken bonds that form and coalesce into macroscopic fractures in the supercritical CO₂ fracturing process. A calculation method for the distribution uniformity index (DUI) is proposed. The influence of the total number and DUI of initial microcracks on the mechanical properties of the rock sample is studied. The DUI of the induced fractures of supercritical CO₂ fracturing and hydraulic fracturing for different DUIs of initial microcracks are compared, holding other conditions constant. The sensitivity of the DUI of the induced fractures to that of initial natural microcracks under different horizontal stress ratios is also probed. The numerical results indicate that the distribution of induced fractures of supercritical CO₂ fracturing is more uniform than that of common hydraulic fracturing when the horizontal stress ratio is small.