Review of the Study of Nonlinear Atmospheric Dynamics in China （1999-2002）

Researches on nonlinear atmospheric dynamics in China (1999-2002) are briefly surveyed. This review includes the major achievements in the following branches of nonlinear dynamics: nonlinear stability theory,nonlinear blocking dynamics, 3D spiral structure in the atmosphere, traveling wave solution of the nonlinear evolution equation, numerical predictability in a chaotic system, and global analysis of climate dynamics.Some applications of nonlinear methods such as hierarchy structure of climate and scaling invariance, the spatial-temporal series predictive method, the nonlinear inverse problem, and a new difference scheme with multi-time levels are also introduced.     

Morphology, photometry and kinematics of N-body bars – I. Three models with different halo central concentrations

We discuss the morphology, photometry and kinematics of the bars which have formed in three N -body simulations. These have initially the same disc and the same halo-to-disc mass ratio, but their haloes have very different central concentrations. The third model includes a bulge. The bar in the model with the centrally concentrated halo (model MH) is much stronger, longer and thinner than the bar in the model with the less centrally concentrated halo (model MD). Its shape, when viewed side-on, evolves from boxy to peanut and then to 'X'-shaped, as opposed to that of model MD, which stays boxy. The projected density profiles obtained from cuts along the bar major axis, for both the face-on and the edge-on views, show a flat part, as opposed to those of model MD which are falling rapidly. A Fourier analysis of the face-on density distribution of model MH shows very large  m=2  , 4, 6 and 8 components. Contrary to this, for model MD the components  m=6  and 8 are negligible. The velocity field of model MH shows strong deviations from axial symmetry, and in particular has wavy isovelocities near the end of the bar when viewed along the bar minor axis. When viewed edge-on, it shows cylindrical rotation, which the MD model does not. The properties of the bar of the model with a bulge and a non-centrally concentrated halo (MDB) are intermediate between those of the bars of the other two models. All three models exhibit a lot of inflow of the disc material during their evolution, so that by the end of the simulations the disc dominates over the halo in the inner parts, even for model MH, for which the halo and disc contributions were initially comparable in that region.     

Functional responses for zooplankton feeding on multiple resources: a review of assumptions and biological dynamics

Modelers often need to quantify the rates at which zooplankton consume a variety of species, size classes and trophic types. Implicit in the equations used to describe the multiple resource functional response (i.e. how nutritional intake varies with resource densities) are assumptions that are not often stated, let alone tested. This is problematic because models are sensitive to the details of these formulations. Here, we enable modelers to make more informed decisions by providing them with a new framework for considering zooplankton feeding on multiple resources. We define a new classification of multiple resource responses that is based on preference, selection and switching, and we develop a set of mathematical diagnostics that elucidate model assumptions. We use these tools to evaluate the assumptions and biological dynamics inherent in published multiple resource responses. These models are shown to simulate different resource preferences, implied single resource responses, changes in intake with changing resource densities, nutritional benefits of generalism, and nutritional costs of selection. Certain formulations are further shown to exhibit anomalous dynamics such as negative switching and sub-optimal feeding. Such varied responses can have vastly different ecological consequences for both zooplankton and their resources; inappropriate choices may incorrectly quantify biologically-mediated fluxes and predict spurious dynamics. We discuss how our classes and diagnostics can help constrain parameters, interpret behaviors, and identify limitations to a formulation's applicability for both regional (e.g. High-Nitrate-Low-Chlorophyll regions comprising large areas of the Pacific) and large-scale applications (e.g. global biogeochemical or climate change models). Strategies for assessing uncertainty and for using the mathematics to guide future experimental investigations are also discussed.     

水下砂土层非线性动力反应的直接差分法

应用多孔介质动力学进行了水下的砂土地层的动力反应分析,水下砂层可以看作是多相介质,孔隙水是可压缩的,土壤采用了非线性本构,考虑了砂土的刚度退化和剪胀性及土水相对运动等因素,并研究了多孔介质波动模拟的边界条件,建立了水体下地层平面动力非线性动力反应的直接差分法,直接求解水体的压力和饱和土层的动孔隙压力,可以进一步分析水下砂土地震液化问题。     

沙坡头地区固沙植被土壤水分动态研究

沙坡头地区始建于1956年的无灌溉人工固沙植被,是我国交通干线防沙体系的成功模式。利用40余年的土壤水分定位观测数据,分析了不同期间建立的固沙植被土壤水分的时空变化特征及对植被的影响。结果表明,固沙植被发展至9~10a后土壤含水量开始明显下降,特别是较深层(>100cm)的含水量下降明显;0~40cm层土壤水分含量与降水相关显著,而降水对40~300cm层土壤水分的含量影响不显著;深根系固沙植物对根际区域水分的利用,进一步恶化了固沙区土壤深层的水分状况,进而抑制了这些植物的生长和生存,间接地影响了原有固沙植被组成和稳定性;经过40多年的演变,固沙植被中优势灌木种的盖度从最大盖度47.6%降至6%~9%,群落中草本和微生物结皮层得到发育。当深根系灌木的盖度降低至6%~9%时,深层土壤可维持一个相对稳定的低含水量。     

Turbulence fields in the lee of two‐dimensional transverse dunes simulated in a wind tunnel

The turbulence field of airflow in the lee of a dune has significant impacts on dune dynamics and related processes. We used particle image velocimetry in a wind tunnel simulation to obtain detailed velocity measurements in the lee of two‐dimensional transverse dune models, then used the results to analyse their turbulence fields. The dune models used in this study had a single lee angle of 30°, and a total of six stoss angles: 3°, 5°, 10°, 15°, 20° and 25°. We used vorticity, turbulence intensity, Reynolds stress and turbulent kinetic energy to characterize the turbulence fields. These parameters were functions of stoss angle, wind velocity, distance from the dune crest and height above the ground surface. The stoss angles could generally be divided into two groups based on the profiles of mean velocity, turbulence and Reynolds stress. Stoss angles of 3° and 5° usually had similar profiles, and angles of 15°, 20° and 25° formed a second group with similar profiles. The profiles for the stoss angle of 10° were usually transitional and were intermediate between the two groups. Vorticity, Reynolds stress and turbulent kinetic energy increased monotonically with increasing free‐stream wind velocity, but their variations with respect to the stoss angle were complex. The stoss angles of 15° and 20° had the maximum values of these three parameters, thus these angles may have special significance in dune development given the characteristics of the mean velocity fields and turbulence fields they produce within the lee airflow. It is the streamwise velocity component and its turbulence that determine the surface shear stress. Copyright © 2008 John Wiley and Sons, Ltd.     

Metallicity and kinematical clues to the formation of the Local Group

The kinematics and elemental abundances of resolved stars in the nearby Universe can be used to infer conditions at high redshift, trace how galaxies evolve and constrain the nature of dark matter. This approach is complementary to direct study of systems at high redshift, but I will show that analysis of individual stars allows one to break degeneracies, such as between star formation rate and stellar Initial Mass Function, that complicate the analysis of unresolved, distant galaxies (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coastal erosion in response to wave dynamics operative in Sagar Island, Sundarban delta, India

Coastal erosion at Sagar Island of Sunderban delta, India, has been critically studied. The area is in the subtropical humid region. There are mainly three seasons viz: winter, summer and the monsoon. Different wave dynamic parameters were measured from theodolite observations with leveling staff and measuring gauges during lunar days at two sections of the western and eastern parts of the coastal zone during post-and pre-monsoons. A comparative study was made on the erosion/depositional pattern between the two sections in relation to different hydrodynamic parameters prevailing in these two sections. Plane table mapping was carried out to demarcate the different geomorphic units. The marine coastal landforms show dune ridges with intervening flats bordered by gently sloping beach on one side and a flat beach on the other side. The western part of the beach is mainly sandy; whereas the eastern part is silty and clayey with mud bank remnants. Actual field measurements indicate that the coastal dune belt has retreated to the order by about 20 m since 1985. The eastern part of the beach has lowered by about 2 m since 1985 and the western part was raised almost to the same tune. It is observed that accretion in the western and central parts of the beach took place; whereas severe erosion in the eastern part made the beach very narrow with remnants of mud banks and tree roots. Frequent embankment failures, submergence and flooding, beach erosion and siltation at jetties and navigational channels, cyclones and storm surges made this area increasingly vulnerable.     

中国稀土对外贸易格局演化及影响因素

从中美贸易摩擦到“科技冷战”以来,被誉为“高科技命脉”的稀土,日益成为国际博弈的前沿领域。在此背景下,厘清中国稀土进出口贸易流动态势、把握中国在国际稀土市场中的地位变动,对中国资源安全格局的整体优化和科技自立自强的长久维持具有一定意义。本文基于2008—2018年中国稀土进出口贸易数据、相关国家社会经济政治指标及联合国投票数据,借助相互依存指数、地缘亲和度模型、GIS空间技术以及负二项面板回归等手段,探讨了中国稀土产品对外贸易格局的演化及影响因素。研究发现：① 中国稀土贸易存在较大波动,出口额远大于进口额,整体呈现“升—降—升”发展态势。② 中国稀土进口市场高度集中且路径依赖增强,出口市场逐步多元且路径依赖减弱。中国主要出口具有较高附加值的中、下游产品,进口具有较低附加值的上游矿物类产品。③ 中国在全球稀土贸易相互依存格局中的优势地位整体强化。中国与多数友好型国家间的相互依存关系呈现优化态势,但与美国、加拿大、澳大利亚等分歧型国家之间的相互依存关系呈现恶化态势。④ 国家主体属性、国家间邻近性以及中国的贸易政策、贸易环境等对中国稀土对外贸易产生重要影响。