Preparation and performance of fine-diameter SiC-based ceramic fiber

连续细直径的碳化硅（SiC）纤维由于其高强度、耐高温、抗氧化等性能被用来做陶瓷基复合材料增强纤维。为了提高先驱体转化法制备的碳化硅纤维的性能，本文采用硼改性的聚钛碳硅烷，经过熔融纺丝，氧化交联，热解与烧结，制备含钛硼的碳化硅纤维。系统地研究了硼改性的聚钛碳硅烷高分子先驱体的结构及其纺丝性能，高分子纤维的氧化交联以及碳化硅纤维力学性能与吸波性能。 首先，采用液态聚硅烷、钛酸丁酯、硼酸丁酯反应合成含钛硼的高分子，然后将其与聚碳硅烷（PCS）混合制备了不同钛硼含量的硼改性聚钛碳硅烷。以纯聚碳硅烷作对比进行熔融纺丝，并探索碳化硅纤维的制备工艺。结果表明，所制备的硼改性聚钛碳硅烷与聚钛碳硅烷具有相似的...Fine-diameter silicon carbide (SiC) fiber is promising reinforcing fiber for ceramic matrix composites at high temperature applications, because of its high tensile strength and high temperature oxidation resistance. The titanium and boron-containing SiC fiber was prepared from the boron-modified polytitanocarbosilane to improve the performance of SiC fiber prepared by polymer precursor method. Th...学位：工学硕士院系专业：材料学院_工程硕士(材料工程)学号：2072014115012

CEPA框架下的服务贸易开放评析

自从2003年10月17日《内地与香港关于建立更紧密经贸关系的安排》(简称CFPA)诞生之后,很多学者围绕其主要内容和政策效应做了大量论述和分析,那么CEPA中有关服务业开放都做了哪些规定,这些条款会给香港与内地服务业及服务贸易发展带来怎样的影响?本文将结合目前香港与内地服务业发展现状及CEPA中服务业的具体规定,对这些问题做一初步回答

数据挖掘中基于密度的聚类分析算法

聚类在数据挖掘、模式识别等许多领域有着重要的应用。本文介绍了聚类算法的几种分类,并例举了几种基于密度的聚类算法。最后以一种新颖的基于最大不相含核心点集的聚类算法LSNCCP为例,详细介绍整个聚类算法的工作过程

Method of incrementing updating FreeCube

数据立方体是联机分析处理的一个重要应用。如何对数据立方体(CUBE)进行更新目前研究相对较少。给出了CUBE的一种新颖的存储结构——FreeCube的定义,该结构大大降低了CUBE存储的空间,分析了它的相关性质,提出了增量更新FreeCube的理论,并给出了具体的算法,以实例说明了该算法的正确性,总结了下一步的工作方向。Data cube is an important application in OLAP system. The study on how to update data cube lags behind at present. A kind of the novel structure of CUBE— — Free is described that can reduce the size of CUBE quickly. And then the characteristics of the con- strictive freecube is analyzed. The theory of incrementing updating freecube is proposed, and algorithm for it and then a instance to indicate the correctness of the algorithm is provided. At last, the directions in the future is summarized.福建省自然科学基金项目(A0310008);; 福建省高新技术研究开放计划重点基金项目(2003H043

SPT—Method of Fast Calculation FreeCube

文章首先分析了目前国内外数据立方体计算的研究现状,指出其优缺点。接着在free-set的概念上,给出了一系列相关定义,挖掘了free-set的性质,建立了FreeCube的概念结构。就FreeCube的计算而言,充分考虑到free-set的性质,结合BUC算法的特点,提出了高效的算法SPT(Selecting-PartitionandTrimmingComputationofFreeCube),并从多个角度进行了实验,与相关工作做了对比,说明该算法的优越性。First of all,the current domestic and international research situation of Data Cube calculation is analyzed.Then the thesis points out its merits and demerits.And it gives out a series of related definitions on the free-set conception,excavates the free-set property and establishes the concept construction of FreeCube.With regard to FreeCube calculation,fully considering the free-set characteristics while combining the characteristics of BUC’s calculation,the thesis puts forward an efficient calculation way SPT(Selecting-Partition and Trimming Computation of FreeCube),and while comparing with related work,it engages in experiments from many aspects,which illustrates the superiority of the algorithm.FreeCube maintenance problem is also discussed theoretically.福建省自然基金资助项目(编号:A0310008);; 福建省高新技术研究开放计划重点资助项目(编号:2003H043

LSNCCP:A Clustering Algorithm Based on the Largest Set of Not-Covered Core Points

聚类在数据挖掘、模式识别等许多领域有着重要的应用 提出了一种新颖的聚类算法 :一种基于最大不相含核心点集的聚类算法LSNCCP(aclusteringalgorithmbasedonthelargestsetofnot coveredcorepoints) 在密度定义的基础上 ,考察核心点之间的距离关系 ,定义相含、相交、相离这 3种核心点之间的关系 ,最后找出一个最大不相含核心点集 ,在此基础上进行聚类 ,并且找到解决丢失点问题的快速方法 该最大不相含核心点集只是全部核心点集合的一个很小的子集 ,因此有效地缩减了同类算法中搜寻核心点的时间 理论和实验上证明了这种算法的可行性和优越性Clustering is an important application area for many fields including data mining, pattern recognition, etc. In this paper, a novel clustering algorithm LSNCCP(a clustering algorithm based on the largest set of not-covered core points) is proposed. On the basis of the definition of density, the distance between the core points is discussed. And then, the three essential distance relation: covered core points, intersectant core points, and separate core points. Finally, the largest set of not-covered core points is found and based on the set the data can cluster very well. Because the largest set of not-covered core points is a lesser subset of the all core points, the new algorithm cuts short the time of searching all core points in the similar algorithms. The feasibility and the advantage or the new algorithm are proved in theory and experiment.福建省自然科学基金项目 (A0 3 10 0 0 8) ;; 福建省高新技术研究开放计划重点项目 (2 0 0 3H0 43

定量磁化率成像重建方法及其应用

磁共振成像(MRI)中,相位图像包含丰富的组织磁化率变化信息,获取相位图像不需要额外的扫描时间.组织中的顺磁性物质会影响组织磁化率差异,从而导致局部磁场不均匀.对组织内顺磁性物质的定量有利于许多脑血管疾病和神经系统疾病的诊断,但利用局部相位信息重建组织磁化率分布是一个不适定逆问题,目前仍然有许多问题亟待解决.该文着重介绍定量磁化率成像(QSM)的原理、重建方法及其在MRI中的应用.国家自然科学基金资助项目(81171331,11174239);中央高校基本业务费资助项目(2010121101

塔里木沙漠公路防护林生态工程的综合生态环境效应

为了探讨重大工程的生态环境效应,从风沙环境、土壤环境、小气候、生物多样性和地下水环境5个方面对塔里木沙漠公路防护林工程的综合生态环境效应进行了研究.结果表明:(1)防护林改变了近地表风沙运动过程,防沙体系内风速、输沙率降低幅度分别达64%~80%和87.45%~99.02%,风沙流结构、沙物质粒度、地表蚀积状况也发生了明显变化;(2)与自然流沙地相比,防护林土壤容重减小,全盐含量、总孔隙度和含水量增大,土壤肥力质量明显提高,其变化基本呈现"先快后慢"的规律;(3)防护林对于小环境改善作用明显,距地面6m范围内,林地不同高度的空气温度普遍低于自然流沙地,而空气湿度则高于自然流沙地,林地土壤温度也低于自然流沙地;(4)随着防护林内生境的变化,土壤微生物种类显著增加,但不同种类微生物的种群分布并不均匀;(5)目前防护林灌溉抽水对地下水位、地下水矿化度的影响不大,水位在厘米级范围波动,矿化度的变化幅度在±1g·L-1左右,且没有明显的变化趋势

Critical tidal level for Kandelia candel forestation in strong tidal range area

以国内最大潮差值的乐清湾西门岛海域为研究地点,选定黄零为1.96、1.66、1.35和1.03M4个高程断面,对各高程上1年生和3年生秋茄(kAndElIA CAndEl)幼苗的成活率、生长指标以及污损生物(藤壶)等因子进行了统计分析.结果表明:不同高程内,1年生和3年生秋茄幼苗的生长存在显著性差异;秋茄幼林植株上附生有白脊藤壶(bAlAnuS AlbICOSTATuS)和纹藤壶(bAlAnuS AMPHITrITE AMPHITrITE)2种藤壶,其中优势种白脊藤壶在黄零1.35M的高程对秋茄的污损最为严重.西门岛秋茄的宜林线为黄零1.66M,即不低于当地平均海平面以上1.29M、每个潮水周期平均淹水时间小于3.65H的潮滩.藤壶、强潮和极端天气是该地区秋茄宜林线明显高于当地平均海平面的主要原因.Taking Ximen island of Yueqing bay,the biggest tidal range area among the coasts of China,as study site,an investigation was made on the survival rate,growth characteristics,and attached barnacles of 1-and 3-year old Kandelia candel seedlings at the elevations 1.96,1.66,1.35,and 1.03 m above the zero tidal level of Yellow Sea.Significant differences were observed in the survival rate and growth situation of the seedlings among the elevations.There were two barnacle species,Balanus albicostatus and Balanus amphitrite amphitrite,and B.albicostatus was the major species which attached K.candel most seriously at elevation 1.35 m.The critical tidal level for K.candel in the site was 1.66 m above the zero tidal level,i.e.,at least 1.29 m higher than the local mean sea level,and the flooding time per tide cycle being less than 3.65 h.Barnacle,strong tide,and extreme weather event were the main reasons for the higher critical tidal level.海洋公益性行业科研专项(200805072);浙江省科技计划项目(2008F1009);温州市科技计划项目(S20060037);浙江省科技厅创新团队建设与人才培养项目(2009F20009)资

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