On the effects of wave drift on the dispersion of floating pollutants

The movement of floating pollutants such as oil slicks on the surface of the sea is due to a number different factors, among which wave drift is certainly significant.In principle, it has been known since Stokes' time that a floating particle is subject to the movement caused by the orbital motion of water particles and that an average drift velocity results because the trajectories are not closed. In the past, however, this effect was often either disregarded or simply included with the surface wind induced current. In recent times the difference between the two effects has been conceptually clarified, so that the average wave drift in random one-dimensional seas has been the object of research and the results are now included in most handbooks and models for oil slick forecasting.Due to the chaotic nature of the wave field, however, the drift also causes floating substances to disperse, and this phenomenon is a much more neglected area of research. Recent work by Bovolin et al. [IAHR Congress, 1997] and Sobey and Barker [J. Coast. Res. 13 (1997)] has brought the subject to attention, and computational tools can now be made to quantify the effect and to verify when and how it should be taken into consideration in oil slick accident practise.The work presented in this paper is based on random simulation of the wave induced Eulerian velocity field in a directional sea, by making use of standard offshore wave directional models and on the ensemble averaging of floating particles trajectories in order to compute the spatial dispersion.     

厦门东海域流刺网渔获鱼类种类组成及其多样性分析

2005年7月至2006年6月对厦门东海域的流刺网渔获鱼类的种类组成及其多样性进行采样分析.总共获得鱼类67种,隶属于14目40科50属.以鲈形目种类最多,共计29种,占总数的43.3%.主要的优势种有：皮氏叫姑鱼、黄鳍鲷、杜氏棱鳀、棱鮻、中华海鲶、斑鰶、黄斑鲾和褐蓝子鱼等.渔获种类的季节变化比较明显,种类的月更替率比较高,与海洋表层水温变化有关.     

Predicting the capability-polar-plots for dynamic positioning systems for offshore platforms using artificial neural networks

As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible as the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for offshore platforms. The main objective of this work is to present a new method of predicting the Capability-Polar-Plots for offshore platforms using the combination of the artificial neural networks (NNs) and the capability polar plots program (CPPP). The estimated results from a case study for a scientific drilling vessel are presented. A trained artificial NN is designed in this work and is able to predict the maximum wind speed at which the DP thrusters are able to maintain the offshore platform in a station-keeping mode in the field site. This prediction for the maximum wind speed will be a helpful tool for DP operators in managing station-keeping for offshore platforms in an emergency situation where the automation of the DP systems is disabled. It is obvious from the obtained results that the developed technique has potential for the estimation of the capability-polar-plots for offshore platforms. This tool would be suitable for DP operators to predict the maximum wind speed and direction in a very short period of time.     

区域电离层建模的单频伪距定位验证

针对电离层单层模型无法满足单频用户定位精度要求的问题,该文建立了区域电离层斜路径模型和单星多项式函数模型。基于河北省区域CORS站的实验结果表明:该文建立的区域电离层模型的拟合精度比CODE中心的格网电离层模型提高了近80%。并将其应用于北斗、GPS单频伪距单点定位,得出北斗的单点定位高程和平面定位精度分别优于3和2m,GPS的单点定位高程和平面定位精度分别优于1.5和1m;相对于CODE,GPS和北斗在平面及高程方向的定位精度均提高了50%左右。结果证明,采用斜路径电离层模型和多项式函数模型,可以较好地反映区域电离层的精细结构。     

Dynamics of a wave-dominated tidal inlet and influence on adjacent beaches,Currumbin Creek,Gold Coast,Australia

Currumbin Creek on the Australian Gold Coast is a wave-dominated tidal inlet which exhibits a particularly active morphology. The recent history of Currumbin Creek entrance has seen rapid growth of the entrance for access to the ocean by fishermen, as a world class surfing site, and as a recreational area. Before the construction of two groynes in the 70's, Currumbin Creek entrance was highly variable in terms of inlet location and sand bar characteristics due to a cyclical behaviour of spit migration. Nowadays, the entrance is stabilised. However, natural processes continue with the entrance infilling causing flood and navigation issues, resulting in a regular dredging program to maintain an open entrance and for regular beach nourishment plans.     

海湾扇贝性腺发育的生物学零度

采用数理统计的方法，对１９９１～１９９２年海湾扇贝控温促熟实验的有关数据进行分析。得到海湾扇贝在青岛地区性腺发育的生物学零度为６．６℃，产卵的有效积温为１７８．９℃。     

Zero Growth of Chemical Fertilizer and Pesticide Use:China’s Objectives,Progress and Challenges

In 2015 China’s Ministry of Agriculture introduced two Actions that seek to achieve zero growth in the use of chemical fertilizer and pesticides by 2020. Success in reaching these targets will help control agricultural non-point source pollution, increase cost efficiency, energy conservation and emission reductions, help to ensure the safety and quality of the national grain supply and agricultural products and the safety of the ecological environment, and realize the sustainable development of agriculture. However, successful implementation will be crucial. This article considers the main contents of the Actions and analyzes their feasibility from the perspectives of policy formulation, local practices, technical support and achievements. We identify problems and challenges and suggest that zero growth of chemical fertilizer and pesticide use can be achieved by undertaking basic research on the factors that shape the use of farm chemicals, making improvements to the monitoring and statistical system for chemical fertilizer and pesticide use, setting up demonstration projects and enhancing policies formulated to reduce chemical fertilizer and pesticide use.     

中国土地流转的区域差异及其影响因素——基于2003-2013年农村固定观察点数据

土地流转是实现农业适度规模经营的必经之路,理解土地流转的空间差异及影响因素具有重要意义。基于2003-2013年农业部农村固定观察点系统的169511个住户样本,本文揭示了中国土地流转的区域差异,并采用Heckman两阶段模型识别土地流转区域差异的影响因素,旨在为促进土地流转提供科学参考。结果发现：① 2003-2013年间,土地流转率从17.09%上升到24.1%,年均增幅近0.7个百分点;南方土地流转较为活跃,比如福建等地流转率超过30%,而北方土地流转率较低;② 转入土地支付租金平均为283.74元/亩,55.05%的转入户并未支付租金;相反,转出土地获得租金为243.23元/亩,52.63%的农户转出土地未获得租金;目前中国土地的“零租金”流转率超过50%;③ 土地质量、地理区位、交易费用、家庭及村庄特征等对土地流转的区域差异具有显著影响;土地质量和地理区位在平原地区的边际效应较大,但在丘陵和山区,交易成本已成为影响土地流转的重要因素。土地“零租金”流转的实质是土地资源错配的一种表现,丘陵和山区边际化及交易费用偏高降低了土地资源的潜在价值。政府应努力降低土地流转中面临的各类交易费用,建立健全土地流转的补偿机制,同时关注丘陵和山区的土地资产贬值和撂荒现象。     

河北唐山丰南4.5级地震前重力变化

利用首都圈地区2017~2019年流动重力观测资料,分析2019-12-05河北唐山丰南4.5级地震前不同时间尺度的重力场变化。结果表明：1）0.5 a尺度重力场变化图像可较好地反映此次地震“震前1 a重力场持续出现上升（正）变化-震前局部反向（负）变化-在重力变化梯度带零等值线附近发震”的演化过程;2）震前0.5 a、1 a和2 a尺度重力场均显示,地震发生在重力变化零等值线附近;3）地震前观测到的重力变化可能由深部热物质上涌引起。