Underway observation of surface temperature and salinity in north South China Sea in September 2006

通过2006年9月南海北部开放航次的走航观测,得到了该海区多个断面的表层温度、盐度分布曲线。QuikScat海面风场资料显示观测期间处于西南季风向东北季风的转换阶段,走航观测所得的温、盐资料显示出在这一季风转换的特殊阶段该海区表层的水文特征。珠江口冲淡水的扩散范围在季风转向前后有显著的变化,低盐的冲淡水在西南季风阶段向珠江口外海区的东南方延伸较远,而在东北季风阶段则受珠江径流量、南海北部表层环流等因素的影响收缩至珠江口附近。闽南近岸和台湾浅滩南部表层具有低温高盐特征,但CTD资料表明台湾浅滩区域存在上升流,结合风场资料,可证实观测期间此处的上升流由海流-地形因素所造成。Based on the underway observation data of Joint Survey of Northern South China Sea in September 2006,the distributions of surface temperature and salinity along several sections were obtained.The sea surface wind field data from QuikScat indicated that September was the conversion period from southwest wind to northeast wind in 2006,and the temperature and salinity data obtained from the underway observation could give a clear demonstration of the hydrological character of the northern South China Sea during this special period.The extension of diluted water near the estuary of Zhujiang River had a major change after the monsoon conversion.During the phase of southwest monsoon,the diluted water could extend to the southeast to a larger distance;while the diluted water was confined to the nearby area of the estuary in the northeast monsoon.In the inshore area off south Fujian and southern part of Taiwan Bank there existed cold and high salinity waters.It was proved by the CTD data that an upwelling was active in the southern part of Taiwan Bank.Considering the northeast monsoon,it could be confirmed that this upwelling was driven by the current-topography effect.国家自然科学基金项目(40576015,40521003,40576013

Observation of upwelling and diluted water in southern Taiwan Strait during July,2005

根据2005年7月台湾海峡西南部海域CTD观测数据,绘制出相关温盐分布图,分析了调查期间该海域的温盐分布特征。结果表明,调查期间东山海域、南澳海域以及台湾浅滩东南侧海域存在明显的上升流现象;在近岸上层,一股较强的冲淡水从西南部进入该海域并影响至台湾浅滩。Based on the CTD data of the southern Taiwan Strait obtained during July 2005,the sectional distributions of temperature and salinity in the studied area were drawn and analyzed.The results showed that:(1) upwelling appeared near the coastal areas of Dongshan and Nan'ao and around the Taiwan Bank;and(2) in the upper layer,fresh water came from the southwest and tongued into the investigated area,affecting the Taiwan Bank.国家自然科学基金项目(40331004,40576015,40521003

大亚湾及周边海区潮流和余流的季节变化特征

通过对大亚湾及其周边海区冬、夏两季和大潮、小潮多站位的海流观测，分析了调查海区潮流、余流的分布特征和季节变化。结果显示：大亚湾及周边海区较小的潮差导致冬季和夏季整体实测海流较弱，夏季潮差和潮流略大于冬季。大潮期间部分站位表现出明显的潮流涨、落的特征，但小潮期间在余流和其他因素的掩盖下涨潮流和落潮流不明显。该海区潮流振幅最强的分潮为M2分潮，而K1、O1、S2分潮振幅较弱，所有站位的潮流性质基本上都表现为不正规半日潮流，大多数站位的潮流运动形式主要表现为往复流。冬季大亚湾湾内的余流虽然流速较弱，但余流的流向体现出的反气旋结构明显且稳定。大亚湾湾口和惠东以东沿岸海区的余流受季节和天气过程影响显著，夏季期间台风或其他因素造成的天气过程可以使余流整体转向。国家自然科学基金(41776027);;\n惠州市海洋渔业资源环境调查项目(F2017-01-1);;\n厦门大学校长基金(20720180103

Thermodynamic Analysis of the Efficiency Improvement of a Photovoltaic-thermoelectric Hybrid System

太阳能电池和热电模块组成的复合系统有望获得较高的太阳能到电能的转换效率。本文利用热力学方法分析了由商业化太阳能电池构成的复合系统,并根据一维模型下能流输运特性计算了系统内各模块温度及其对转换效率的影响,发现低温度系数和低效率的太阳能电池可以通过构建复合系统获得更大的性能提升。同时,由于太阳辐照的有限性导致流经热电模块的热流受到限制,因此热电模块效率无法达到理想条件下的最优值。这表明复合系统的优化并非各个模块优化后结果的简单线性叠加,而需要考虑构成复合系统的各个模块间的约束条件进行整体计算和优化,即复合系统效率不仅与材料本征特性(如电导率、热导率等)有关,也和其工作状态(如入射太阳辐照强度、热电模块构成及几何尺寸、模块之间热学特性等)有关。上述模型与结果对于类似复合系统的设计有着指导作用。A hybrid system formed by a photovoltaic module and a thermoelectric module has a great potential to enhance the solar-to-electricity efficiency.A mathematical model based on the first law of thermodynamics and the heat transfer analyses of the hybrid system is built, where the overall efficiency of the system is enhanced by optimizing the system as a whole.The model is used to study hybrid systems formed by commercially available photovoltaic modules and thermoelectric modules.It is found that, due to a limited incoming heat flux for the thermoelectric module, the overall performance of the hybrid system depends not only on the intrinsic properties of the materials forming such a hybrid system, but also on their working conditions, such as incoming solar radiation, geometry of each module, and interfacial properties.The results indicate that only photovoltaic modules with low temperature coefficient and low efficiency can truly benefit from forming such hybrid system, and the optimization of a hybrid system must be done as a whole.教育部高等学校博士学科点专项科研基金新教师项目(20090121120028);教育部高等学校博士学科点专项科研基金博导类项目(20120121110021); 国家自然科学基金项目(U1232110

Drag reduction using riblets downstream of a high Reynolds number inclined forward step flow

Micro-riblet is an efficient passive method for controlling turbulent boundary layers, with the potential to reduce frictional drag. In various applications within the transportation industry, flow separation is a prevalent flow phenomenon. However, the precise drag reduction performance of riblets in the presence of flow separation remains unclear. To address this, an inclined forward step model is proposed to investigate the interaction between riblet and upstream flow separation. The large eddy simulation (LES) method is applied to simulate the flow over geometries with different step angles and riblet positions. The results show riblets still reduce wall frictional resistance when subjected to the upstream flow separation. Remarkably, as the angle of the step increases from 0 degrees to 30 degrees, the drag reduction experiences an increment from 9.5% to 12.6%. From a turbulence statistics standpoint, riblets act to suppress the Reynold stress in the near-wall region and dampen ejection motions, thus weakening momentum exchange. Quadrant analysis reveals that with the augmentation of flow separation, the Q2 motion within the flow field intensifies, subsequently enhancing the riblet-induced drag reduction. Moreover, the position of the rib lets has a significant impact on the pressure drag. Riblets close to the point of separation enhance flow separation, altering the surface pressure distribution and thus increasing the resistance. The results reveal that when the riblets are positioned approximately 160 riblet heights away from the step, their effect on the upstream flow separation becomes negligible. The precise performance of riblets under complex flow conditions is important for their practical engineering application

珠江口滨海湿地景观格局变化分析

以专题地图和遥感影像为数据源,采集1986、1995和2005年珠江口滨海湿地数据,选取基于景观类型的景观聚集度指数、景观分维数和基于景观面积的景观多样性指数,从景观类型和景观水平研究珠江口滨海湿地景观格局变化。结果表明:(1)在各湿地景观类型中,面积占绝对优势的是浅海水域景观,面积增加最多的是养殖水面,减少最多的是水田。(2)受人为开发因素影响,湿地总面积持续减少,1986―1995年和1995―2005年湿地总面积相继减少20821hm2和55708hm2,分别相当于研究区总面积的5.3﹪和14.2﹪。(3)湿地景观变化具有显著时间异质性,类型分布具有显著的空间异质性。人为开发和分割湿地景观导致各景观类型聚集度指数不同程度降低,而景观分维数增加,景观多样性指数先小幅增加后大幅下降。(4)湿地景观格局的变化导致湿地整体质心坐标经历了先向北移动0.4km,后向东南迁移6.1km。前后两个时期相比,湿地面积减少速度和质心迁移速度在后期明显加快,由此反映出岸线以上陆域湿地正在加速退化。研究珠江口滨海湿地景观格局变化,可为保护和长期规划珠江口滨海湿地提供科学依据。

2015年7—8月珠江冲淡水扩展特征的观测与分析

以航次实测温、盐剖面数据为基础,对2015年7—8月珠江冲淡水扩展特征进行观测,并结合定点浮标风场以及漂流浮球的数据,对影响其扩展特征的主要因素进行分析,从而为研究珠江口碳、营养盐等物质的输移、分布等过程提供基础资料.研究发现珠江冲淡水调查期间存在两种扩展形态:离岸东向扩展和沿岸西向扩展.在西南季风稳定时,冲淡水主要以离岸东向扩展为主,水平扩展范围距珠江口超过350km且垂向覆盖厚度(即盐度小于32的水层厚度)约为5～20m,表层32等盐线与南海北部陆架内50m等深线一致.夏季稳定的西南季风有利于珠江冲淡水在Ekman输运下持续被带离河口,当珠江冲淡水跨越20m等深线后受到沿岸东北向流和离岸运动的共同作用,以东向扩展为主;但在西南季风减弱甚至发生风向的变化时,珠江冲淡水的离岸运动也随之减弱,从而在20m等深线以内的珠江口区域形成堆积,在地转偏向力的作用下,此时珠江冲淡水的扩展形态以沿岸西向为主.国家重点基础研究发展计划(973计划)(2015CB954004);;国家自然科学基金(U1405233,41776027

Improvement and Validation of a Statistical Modeling Approach to Ocean Front Detection

统计模型检测法为检测海表温度(SST)锋面和提取SST锋面的结构提供了有利的工具,但其在陆架区的检测成功率和检测精度仍有待提高.本研究对该算法进行如下改进:1)在数据预处理阶段,通过梯度场拟合计算不同水团之间过渡区的边界,并利用边界处的温度数据重构过渡区两侧的温度场;2)利用遗传算法为锋面参数的迭代求解提供初值.理想实验结果表明:上述改进能有效地改善统计模型检测法在陆架区的稳定性和检测精度.最后,利用实测SST数据和遥感SST数据检验了算法在实际应用中的改进效果,以及改进后算法在陆架区的有效性.The statistical modeling approach to ocean front detection provides an useful tool for detecting sea surface temperature(SST)fronts and extracting the structure of SST fronts.But the robustness and accuracy of the algorithm still need to be improved when it is applied to the continental shelf.In this paper,the authors propose two improvements to the algorithm.1)On the stage of data preparation,fitting of gradient field is used to calculate boundaries of the transition zone between different water masses.Then,the temperature fields on both sides of the transition zone are reconstructed through the data extracted from the boundaries.2)Genetic algorithm is used to provide initial values for iterations.The idealized experiments show that the improved algorithm is robust to highly dynamic fronts and more accurate at the continental shelf.At last,in situ and remote sensing SST data are used to verify the improvements of the algorithm in practical application and the validity of the fronts detected by the improved algorithm at the continental shelf.国家重点基础研究发展计划(973)项目(2009CB421208); 国家自然科学基金(41276006;41121091

Study on Seasonal Variations in the Tropical Indian Ocean Mixed Layer Depth Derived From Argo Float Data

根据2004-2005年热带印度洋(30°S以北)的Argo浮标(自持式海洋剖面观测浮标)温度-盐度剖面观测资料,采用位势密度判据(Δσθ=0.03 kg/m3),针对每个Argo浮标的温度-盐度观测剖面确定了海洋混合层的深度,然后采用Krig插值方法构建了3°×3°空间分辨率的月平均网格化混合层深度产品。通过与已有气候平均混合层深度资料的比较表明了该产品的合理性,在此基础上进一步对热带印度洋海盆尺度的混合层深度空间特征和季节变化规律进行了讨论。研究结果表明,Argo浮标资料可用于热带印度洋混合层变化的研究,为进一步研究热带印度洋海-气相互作用提供了基础资料。Based on the Argo float profile data observed in the tropical Indian Ocean(north of 30°S) in 2004 and 2005,the mixed layer depth(MLD) in the tropical Indian Ocean is determined according to the potential density criteria(Δσθ=0.03 kg/m3),and the the Krig interpolation method is then used to construct a monthly mean gridded MLD product with a spatial resolution of 3°×3°.It is shown from the comparison between our MLD product and the available climatological MLD data that our product is reasonable,and the spatial characteristics and seasonal variabilities of basin-scale MLD in the tropical Indian Ocean are discussed based on our MLD product.It is shown from the study results that the Argo float data can be used for studying the variations in MLD of the tropical Indian Ocean,which provides basic data for further studying the air-sea interaction in the tropical Indian Ocean.国家自然科学基金项目——印度洋偶极子事件和太平洋ElNio事件的比较研究(40506012);; 国家科技部国际合作重点项目——太平洋-印度洋暖池Argo浮标观测研究(2002CB714001

对称加密方案的密文验证安全性

文中研究由密文的完整性检查而导致的数据保密性问题,提出一个新的安全概念——加密方案在密文验证攻击下的不可区分性(IND-CVA:indistinguishability ofencryption scheme under ciphertext verification attacks)来刻画加密方案在这种情况下的保密安全性。IND-CVA允许敌手访问加密oracle和密文验证oracle。与IND-CPA和IND-CCA相比,IND-CVA比IND-CPA稍微强些,但要比IND-CCA弱得多。IND-CVA能使多数常用的加密方案(如:OTP,CBC,及CTR)得以满足。并且,这个IND-CVA可以恰当地刻画安全信道的保密安全性。将认证方案和加密方案结合起来是保证通信安全的一种常用方法。然而,在IND-CVA模型下,当利用认证方案来加强保密安全性的时候,却有可能反而破坏了原有的保密安全性。IND-CVA揭示了完整性对保密性的影响,准确刻画了安全信道的保密性要求,为协议设计提供了有益的参考