检索结果-南通市图书馆

高双折射低有效模场面积SF57软玻璃光子晶体光纤设计(英文)

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

红外与毫米波学报 2014年第3期33卷 222-226页

作者：姜凌红郑义侯蓝田彭继迎郑凯北京交通大学理学院激光所北京100044 燕山大学亚稳材料制备技术与科学重点实验室河北秦皇岛066004

设计了一种包层为椭圆孔排列的六边形结构SF57软玻璃光子晶体光纤,在其纤芯区域引入了菱形排列的四个小椭圆孔.利用有限元法模拟了该光子晶体光纤的双折射和有效模场面积,获得了波长1.55μm处双折射为1.01×10^(-1),x和y偏振的有效模场... 详细信息

设计了一种包层为椭圆孔排列的六边形结构SF57软玻璃光子晶体光纤,在其纤芯区域引入了菱形排列的四个小椭圆孔.利用有限元法模拟了该光子晶体光纤的双折射和有效模场面积,获得了波长1.55μm处双折射为1.01×10^(-1),x和y偏振的有效模场面积分别为1.52μm^2、1.55μm^2的高双折射低有效模场面积光子晶体光纤.且对该光纤的结构参数进行了实验制作的容差性分析,得到了较大的制作容差对其光纤的双折射影响很小,具有较好的偏振稳定性.

关键词：光子晶体光纤双折射有效模场面积软玻璃

在线全文

学校读者我要写书评

暂无评论

活性炭吸附用于城市污水地下回灌技术的研究

中国给水排水 1999年第10期15卷 5-8页

作者：皮运正吴天宝清华大学核能技术设计研究院北京100084

通过静态吸附试验比较与Ｃｒｉｔｔｅｎｄｅｎ计算模型分析，选择ＧＨ—１６型粒状活性炭对北京高碑店污水处理厂二级出水进行深度处理试验。结果表明：ＧＨ—１６型活性炭的净化效果存在阈值，约２５％的ＤＯＣ不能被吸附，不被... 详细信息

通过静态吸附试验比较与Ｃｒｉｔｔｅｎｄｅｎ计算模型分析，选择ＧＨ—１６型粒状活性炭对北京高碑店污水处理厂二级出水进行深度处理试验。结果表明：ＧＨ—１６型活性炭的净化效果存在阈值，约２５％的ＤＯＣ不能被吸附，不被吸附的主要是分子量＞３０００ｕ的有机物。对以ＵＶ２５４表征的有机物去除效果最好，分子量＜１０００ｕ的弱极性有机物易被微孔吸附且吸附容量大，对以ＡＯＸ表征的极性有机物去除效果较差。二级出水经活性炭深度处理，出水的可生化性提高。活性炭柱可运行４０００床体积，吸附容量为２５ｍｇＤＯＣ／ｇ活性炭。

关键词：粒状活性炭城市污水地下回灌 Crittenden模型

基于蚯蚓背孔射流的仿生射流表面减阻性能研究

在线全文

学校读者我要写书评

暂无评论

物理学报 2015年第2期64卷 306-315页

作者：谷云庆牟介刚代东顺郑水华蒋兰芳吴登昊任芸刘福庆浙江工业大学机械工程学院杭州310014 浙江工业大学之江学院杭州310024

为了减小流体对固体壁面的阻力,基于蚯蚓生物学特征,对蚯蚓背孔射流特性进行分析,建立仿蚯蚓背孔射流的仿生射流表面计算模型,采用SST k-ω湍流模型对仿生射流表面的减阻特性进行数值模拟,同时对数值模拟结果进行实验验证,并以此研究了... 详细信息

为了减小流体对固体壁面的阻力,基于蚯蚓生物学特征,对蚯蚓背孔射流特性进行分析,建立仿蚯蚓背孔射流的仿生射流表面计算模型,采用SST k-ω湍流模型对仿生射流表面的减阻特性进行数值模拟,同时对数值模拟结果进行实验验证,并以此研究了仿蚯蚓背孔射流表面的减阻机理.结果表明,在一定条件下,仿蚯蚓背孔射流的仿生射流表面具有较好的减阻效果;在同一射流方向角下,随着射流速度的增加,减阻率逐渐增大;在同一射流速度下,随着射流方向角的增加,减阻率呈先减小后增大的变化趋势;数值模拟与实验均在射流速度为1 m·s-1、射流方向角为-30?时达到最大,分别为8.69%,7.86%;射流表面改变了原有光滑壁面的边界层结构,对壁面边界层进行了有效的控制,减小了壁面的剪应力,降低了壁面边界层的速度.

关键词：射流减阻数值模拟边界层

100 km wear-free sliding achieved by microscale superlubric graphite/DLC heterojunctions under ambient conditions

在线全文

学校读者我要写书评

暂无评论

National Science Review 2022年第1期9卷 17-24页

作者： Deli Peng Jin Wang Haiyang jiang Shuji Zhao Zhanghui Wu Kaiwen Tian Ming Ma Quanshui zheng Department of Engineering Mechanics Tsinghua University Center for Nano and Micro Mechanics Tsinghua University Institute of Superlubricity Technology Research Institute of Tsinghua University in Shenzhen State Key Laboratory of Tribology Tsinghua University Department of Mechanical Engineering Tsinghua University

Wear-free sliding between two contacted solid surfaces is the ultimate goal in the effort to extend the lifetime of mechanical devices,especially when it comes to inventing new types of micro-ele ctromechanical systems where wear is often a major *** we report experimental observations of wear-free sliding for a micrometer-sized graphite flake on a diamond-like-carbon（DLC） surface under ambient conditions with speeds up to 2.5 m/s,and over a distance of 100 *** coefficient of friction（COF） between the microscale graphite flake,a van der Waals（vdW） layered material and DLC,a non-vdW-layered material,is measured to be of the order of 10-3,which belongs to the superlubric *** ultra-low COFs are also demonstrated for a microscale graphite flake sliding on six other kinds of non-vdW-layered materials with sub-nanometer *** a synergistic analysis approach,we reve al the underlying mechanism to be the combination of interfacial vdW interaction,atomic-smooth interfaces and the low normal stiffness of the graphite *** features guarantee a persistent full contact of the interface with weak interaction,which contributes to the ultra-low *** with the extremely high in-plane strength of graphene,wear-free sliding is achieve *** results broaden the scope of superlubricity and promote its wider application in the future.

关键词： structural superlubricity wear-free microscale graphite DLC

Transport phenomena and keyhole evolution process in laser welding of stainless steel

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Central South University 2019年第8期26卷 2088-2099页

作者： LIU jiang-wei ZENG Ping-wang RAO zheng-hua ZHANG Tian-li School of Energy Science and Engineering Central South University Changsha 410083 China School of Materials Engineering Shanghai University of Engineering Science Shanghai 201620 China

Knowledge of transport phenomena and keyhole evolution is important for controlling laser welding process. However, it is still not well understood by far due to the complex phenomena occurring in a wide temperature range. A transient 3D model including heat transfer, fluid flow and tracking of free surface is built in this study. The transport phenomena are investigated by calculating the temperature and velocity fields. The 3D dynamic keyhole evolution process is revealed through tracking free surface using volume-of-fluid method. The results show that the keyhole deepening speed decreases with laser welding process before the quasi-steady state is reached. The plasma can greatly affect the keyhole depth through absorbing a great amount of laser energy and thus lowering the recoil pressure. Moreover, the relationship between keyhole depth and weld penetration is also discussed. This paper can help to better understand the dynamics in molten pool and then improve laser welding process.

关键词： laser welding keyhole evolution weld pool dynamics free surface tracking weld penetration

High-resolution records of Holocene from the Shuangchi Maar Lake in Hainan Island

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2003年第5期48卷 497-502页

作者： zheng Zhuo, WANG jianghua, WANG Bing, LIU Chunlian, ZOU Heping, ZHANG Hua, DENG yun & BAI Yan Department of Earth Sciences, Zhongshan University, Guangzhou 510275, China (e-mail: ee29@***) Department of Earth Sciences Zhongshan University Guangzhou China

The results of sedimentary characteristics, grain-size, clay mineral, C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tropical areas. It is testified that the Maar sediment system was sensitive in recording the rapid climate changes in the Holocene. These multidisciplinary results demonstrate that the thermal maximum in the Holocene climate lasted from 7200 to 2700 aBP, with several abrupt ephemeral vibrations occurring between 7250-6120 aBP and at around 4460, 3850 and 2700 aBP. In the late Holocene, particularly at ~2700 aBP, a distinct environmental change indicating an important climate transition in the tropical eastern Asia was recorded, probably responding to the enhancement of ENSO phenomena in the Pacific Ocean. In addition, the high-resolution algae record clearly indicates periodical climate fluctuations at 500 a cyclicity during the last 2500 years.

关键词：海南岛火山口湖全新世气候变化沉积物古气候

一种基于Workflow的作业流管理系统研究

在线全文

学校读者我要写书评

暂无评论

计算机工程 2005年第10期31卷 51-53页

作者：刘扬何华灿蒋芸西北工业大学计算机科学与工程系西安710072

将工作流技术应用于作业管理系统,提出了基于Workflow 的作业流管理系统,首先给出了系统的体系结构,然后从作业流的定义与描述、作业流的调度与执行等方面具体分析了作业流管理模型,该系统是对现有作业管理系统和工作流管理系统的动态扩... 详细信息

将工作流技术应用于作业管理系统,提出了基于Workflow 的作业流管理系统,首先给出了系统的体系结构,然后从作业流的定义与描述、作业流的调度与执行等方面具体分析了作业流管理模型,该系统是对现有作业管理系统和工作流管理系统的动态扩充,有着非常广阔的应用前景。

关键词：工作流作业流作业管理系统作业流管理系统

Porous carbon matrix-encapsulated MnO in situ derived from metalorganic frameworks as advanced anode materials for Li-ion capacitors

在线全文

学校读者我要写书评

暂无评论

Science China Materials 2022年第1期65卷 59-68页

作者： Sipeng jiang Shilin yun Haijie Cao Zhiqiang Zhang Hongbin Feng Haichao Chen Institute of Materials for Energy and Environment School of Materials Science and EngineeringQingdao UniversityQingdao 266071China

Conversion-type anode materials hold great potential for Li+storage applications owing to their high specific capacity,while large volume expansion and poor electrical conductivity limit their rate and cycling ***,a bimetal ZnMn-based metal-organic framework(ZnMn-MOF)is engineered for in situ conversion of MnO-encapsulated porous carbon(MnO/PC)*** templating and activation effects of coordinated Zn endow the converted PC matrix with a highly porous *** enhances the compatibility of PC matrix with MnO particles,resulting in the full encapsulation of MnO particles in the PC *** significantly,the PC matrix provides enough void space to buffer the volume change,which fully wraps the MnO without crack or fracture during repeated *** a result,MnO/PC shows high charge storage capability,extraordinary rate performance,and long-term cycling stability at the same *** MnO/PC exhibits high delithiation capacities of 768mA h g^(-1)at 0.1Ag^(-1)and 487mA h g^(-1)at a high rate of 0.7Ag^(-1),combined with an unattenuated cycling performance after 500 cycles at 0.3Ag^(-1).More significantly,MnO/PC demonstrates a well-matched performance with the capacitive activated carbon electrode in a Li-ion capacitor(LIC)full *** demonstrates a high specific energy of 153.6W h kg^(-1)at 210W kg^(-1),combined with a specific energy of 71.8W h kg^(-1)at a high specific power of 63.0kW kg^(-1).

关键词： Li-ion capacitors MnO/porous carbon composites metal-organic frameworks derivant conversion-type anode materials

在线全文

学校读者我要写书评

暂无评论

氮添加抑制温带草甸草原凋落物的长期分解

Journal of Plant Ecology 2023年第3期16卷 191-202页

作者： Pei zheng Ruonan Zhao Liangchao jiang Guojiao Yang Yinliu Wang Ruzhen Wang Xingguo Han Qiushi Ning State Key Laboratory of Vegetation and Environmental Change Institute of BotanyChinese Academy of SciencesBeijing 100093China University of Chinese Academy of Sciences Beijing 100049China College of Ecology and Environment Hainan UniversityHaikou 570228China Erguna Forest-Steppe Ecotone Ecosystem Research Station Institute of Applied EcologyChinese Academy of SciencesShenyang 110016China School of Life Sciences Hebei UniversityBaoding 071002China State Key Laboratory of Urban and Regional Ecology Research Center for Eco-Environmental SciencesChinese Academy of SciencesBeijing 100085China

植物凋落物分解是陆地生态系统碳平衡和养分周转的关键,对持续的人为氮输入增加十分敏感。氮素增加影响凋落物分解的研究大多依赖于短期实验,这可能掩盖氮素增加对凋落物分解的真实影响。因此,长期实验对于全面评价凋落物分解对氮素增... 详细信息

植物凋落物分解是陆地生态系统碳平衡和养分周转的关键,对持续的人为氮输入增加十分敏感。氮素增加影响凋落物分解的研究大多依赖于短期实验,这可能掩盖氮素增加对凋落物分解的真实影响。因此,长期实验对于全面评价凋落物分解对氮素增加的响应是非常必要的。本研究基于氮添加实验(0-50 g N m^(-2) yr^(-1)),对羊草(Leymus chinensis)凋落物分解进行了长达4年的研究,探讨了影响凋落物分解的非生物和生物因子。研究结果表明,随着氮添加速率的增加,凋落物分解速率呈持续下降趋势,为氮添加抑制凋落物分解提供了可靠的证据。氮添加条件下土壤环境(酸化和养分化学计量学)、微生物活性(微生物生物量和酶活性)、凋落物质量(残余木质素和养分含量)和植物群落(地上生产力和物种丰富度)的变化共同导致了凋落物分解速率的降低。在分解过程中,凋落物质量的变化,包括木质素的积累和养分的残留,主要受土壤环境和微生物活性的影响。该研究有助于阐明不同氮添加速率对凋落物分解的长期影响,并有助于理解生态系统氮素增加与碳循环之间的关系及相关机理。

关键词：氮添加凋落物碳氮损失木质素物种丰富度酶活性