检索结果-南通市图书馆

Experimental and molecular dynamics study of gas flow characteristics in nanopores

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2012年第13期57卷 1488-1493页

作者： LIU QiXin JIANG PeiXue xiang heng Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Beijing Key Laboratory of CO_(2)Utilization and Reduction TechnologyDepartment of Thermal EngineeringTsinghua UniversityBeijing 100084China

Gas flow characteristics in nanopores were investigated experimentally and numerically using molecular dynamics (MD) simulations with an emphasis on the friction factor and gas viscosity. The results show that the viscosity and the friction factor in nanopores are much lower than those in macroscale channels. The actual viscosities obtained from the MD studies showed that the gas viscosity in nanopores is less than the macroscale viscosity because collisions between gas molecules are less frequent in high Knudsen number flows and there are more collisions with the wall. The MD simulations show that the velocity profile is composed of two parts, with a much steeper velocity gradient near the wall.

关键词：气体流动特性分子动力学特性实验纳米孔 Knudsen数气体粘度数值模拟摩擦系数

Optimization Study on Expansion Energy Used Air-Powered Vehicle with Pneumatic-Hydraulic Transmission

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical Engineering 2018年第1期31卷 220-229页

作者： xiang-heng Fu Mao-Lin Cai Yi-Xuan Wang Yan Shi School of Automation Science and Electrical Engineering Beihang University The State Key Laboratory of Fluid Power & Mechatronic Systems Zhejiang University

Pneumatic-hydraulic transmission has been developed for years. However, its dynamic properties are not good enough for application. In this paper, in order to increase the output characteristics, a late-model air-powered vehicle using expansion energy is proposed which can boost energy through a pneumatic-hydraulic transmission. The dynamic characteristics of the air-powered vehicle is modeled and verified by conducting experiment. In addition,the influence of the key parameters of the air-powered vehicle is researched for the optimization of the system performance. Through the results, the author got the conclusion that, firstly, comparison of the results of model and experiment proves the built model to be effective; secondly, input air pressure should be set according to the request of the practical loads, and range of 0.65 to 0.75 MPa can be chosen; thirdly, as a key structure parameter of the airpowered vehicle, ratio of the areas is considered to be set to approximate 8; what’s more, a bigger orifice with a limit will promote the system dynamic characteristic property, and the limit is about 3.5 mm; last but not the least, not too farther position of the rings will increase the quality of output dynamic characteristics. This paper can be a reference for system design of air-powered vehicle and dynamic improvement.

关键词： Air-powered vehicle Expansion energy Pneumatic-hydraulic transmission Output dynamic characteristics

Colo-colonic intussusception as a rare complication of colonoscopy with polypectomy: Two case reports

在线全文

学校读者我要写书评

暂无评论

World Journal of Gastrointestinal Surgery 2024年第6期16卷 1939-1947页

作者： Sai-heng xiang Guo-Qiang Xu Department of Gastroenterology The First Affiliated HospitalZhejiang University School of MedicineHangzhou 310003Zhejiang ProvinceChina

BACKGROUND Colonoscopy is the most frequently used diagnostic and therapeutic tool for the treatment of colorectal *** the complication rate is low,it can be potentially *** is a rare and severe complication often associated with *** a handful of post-colonoscopy intussusception cases have been reported,making this study a valuable addition to the medical *** SUMMARY Case 1:A 61-year-old man underwent colonoscopy with polypectomy for chronic abdominal *** patient experienced abdominal pain 11 hours later but was still discharged after pain *** was readmitted due to recurring *** tomography(CT)showed colo-colonic *** conservative management and attempts at endoscopic reduction failed;therefore,laparoscopic right hemicolectomy was *** examination revealed tubular adenomas in the polyps and inflammation in the resected *** 2:A 59-year-old woman underwent colonoscopy with polypectomy for a polyp in the transverse *** experienced upper abdominal pain,fever,nausea,and vomiting 9 hours after the *** CT and blood tests revealed a colo-colonic intussusception near the hepatic flexure and an elevated white blood cell *** attempts at endoscopic reduction failed and conservative treatment showed no *** underwent successful laparoscopic reduction and recovered *** examination of the resected polyp revealed *** Post-colonoscopy intussusception in adults is rare,and polypectomy may contribute to its *** diagnosis is crucial,with prompt CT examination serving as *** excluding malignancies,conservative management and reduction of intussusception should be considered before surgical bowel resection.

关键词： Intussusception Colonoscopy Polypectomy Complication Case report

Natural selection maintains the transcribed LTR retrotransposons in Nosema bombycis

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Genetics and Genomics 2010年第5期37卷 305-314页

作者： heng xiang Guoqing Pan Ruizhi Zhang Jinshan Xu Tian Li Wenle Li Zeyang Zhou Zhonghuai xiang Institute of Sericulture and Systems Biology Southwest University Beibei Chongqing 400715 China College of Life Science Chongqing Normal University Chongqing 400047 China Biotechnology Research Center Southwest University Beibei Chongqing 400715 China

Eight intact LTR retrotransposons （Nbr1-Nbr8） have been previously characterized from the genome of Nosema bombycis, a eu- karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed Nbr elements （Nbr9-Nbr14） identified through either cDNA library or RT-PCR. Like previously determined ones, all of them belong to the Ty3/Gypsy superfamily. Retrotransposon diversity and incomplete domains with insertions （Nbr12）, deletions （Nbrll） and in-frame stop codons in coding regions （Nbr9） were detected, suggesting that both defective and loss events of LTR retrotransposon have happened in N. bornbycis genome. Analysis of selection showed that strong purifying selection acts on all elements except Nbr11. This implies that selective pressure keeps both these Nbrs and their functions in genome. Interestingly, Nbrll is under positive selection and some positively selected codons were identified, indicating that new functionality might have evolved in the Nbrll retrotransposon. Unlike other transposable elements, Nbrll has integrated into a conserved syntenic block and probably resulted in the inversion of both flanking regions. This demonstrates that transposable element is an important factor for the reshuffling and evolution of their host genomes, and may be maintained under natural selection.

关键词： microsporidia LTR retrotransposon transcribed purifying selection positive selection

Frequency-domain L2-stability conditions for time-varying linear and nonlinear MIMO systems

在线全文

学校读者我要写书评

暂无评论

Control Theory and Technology 2014年第1期12卷 13-34页

作者： Zhihong HUANG Y. V. VENKATESH Cheng xiang Tong heng LEE Department of Electrical & Computer Engineering National University of Singapore Singapore

The paper deals with the g2-stability analysis of multi-input-multi-output （MIMO） systems, governed by integral equations, with a matrix of periodic/aperiodic time-varying gains and a vector of monotone, non-monotone and quasi-monotone nonlin- earities. For nonlinear MIMO systems that are described by differential equations, most of the literature on stability is based on an application of quadratic forms as Lyapunov-function candidates. In contrast, a non-Lyapunov framework is employed here to derive new and more general g2-stability conditions in the frequency domain. These conditions have the following features： i） They are expressed in terms of the positive definiteness of the real part of matrices involving the transfer function of the linear time-invariant block and a matrix multiplier function that incorporates the minimax properties of the time-varying linear/nonlinear block, ii） For certain cases of the periodic time-varying gain, they contain, depending on the multiplier function chosen, no restrictions on the normalized rate of variation of the time-varying gain, but, for other periodic/aperiodic time-varying gains, they do. Overall, even when specialized to periodic-coefficient linear and nonlinear MIMO systems, the stability conditions are distinct from and less restrictive than recent results in the literature. No comparable results exist in the literature for aperiodic time-varying gains. Furthermore, some new stability results concerning the dwell-time problem and time-varying gain switching in linear and nonlinear MIMO systems with periodic/aperiodic matrix gains are also presented. Examples are given to illustrate a few of the stability theorems.

关键词： Circle criterion K-P-Y lemma L2-stability Lur'e problem Multiplier function Nyquist's criterion Switched systems Time-varying system

COMPUTATIONAL RESEARCH ON WAVE MAKING OF MOVING WIGLEY HULL IN TIME DOMAIN

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2008年第4期20卷 469-476页

作者： YANG xiang-hui YE heng-kui FENG Da-kui LIU Juan College of Traffic Science and Engineering Huazhong University of Science and Technology Wuhan 430074 China Ship Information Center Beijing 100085 China

Based on Green＇s theorem, a time domain numerical model was constructed to simulate wave making phenomenon caused by a moving ship. In this article, the Rankine sources and dipoles were placed on boundary surfaces （i.e., the ship surface and free surface）, and a time-stepping scheme was employed. Its unique characteristic is that steady state can be realized from initial value by employing the time-stepping scheme and unsteady free surface conditions. In time domain, if the results of unsteady flow problem tend to data stabilization after many time steps of computation, they could be regarded as the data of steady ones. This model could be employed to steady or unsteady problems. Theoretical reasoning and computational process of this method was described in detail The linear and nonlinear boundary conditions on body surface were studied, and the relative means to realize these boundary conditions in iterative computation were also discussed. Some proper parameters about the model of the Wigley hull were determined by many numerical tests, and their influences on wave making resistance and wave pattern were discussed. According to the comparison between numerical results and data available in relative references, the method used in this work is proven to be a reliable method in time domain. And the lattice reorganization in every time step computation is a feasible numerical approach.

关键词： Rankine source dipole time domain Wigley hull lattice reorganization time-stepping scheme Green's theorem

A New ID-Based Proxy Multi-Signature Scheme from Bilinear Pairings

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2006年第1期11卷 193-197页

作者： GU Chun-xiang PAN heng ZHU Yue-fei Network Engineering Department Information Engineering University Zhengzhou 450002 Henan China

ID-based public key cryptosystem can be a good alternative for certifieate-based public key setting. This paper provides an efficient ID-based proxy multi signature scheme from pairings. In the random oracle model, we prove that our new scheme is secure against existential delegation forgery with the assumption that Hess＇s scheme-1 is existential unforgeable, and that our new scheme is secure against existential proxy multi-signature forgery under the hardness assumption of the computational Diffie-Hellman problem.

关键词： ID-based signatures proxy multi-signature ID-based proxy multi signatures bilinear pairlngs provable security

Easily-handled method to isolate mesenchymal stem cells from coagulated human bone marrow samples

在线全文

学校读者我要写书评

暂无评论

World Journal of Stem Cells 2015年第8期7卷 1137-1144页

作者： heng-xiang Wang Zhi-Yong Li Zhi-Kun Guo Zi-Kuan Guo Department of Hematology General Hospital of Air Force Key and Open Lab for Tissue Regeneration Xinxiang Medical University Department of Experimental Hematology Beijing Radiation Medicine

AIM:To establish an easily-handled method to isolate mesenchymal stem cells(MSCs) from coagulated human bone marrow samples. METHODS: Thrombin was added to aliquots of seven heparinized human bone marrow samples to mimic marrow coagulation. The clots were untreated,treated with urokinase or mechanically cut into pieces before culture for MSCs. The un-coagulated samples and the clots were also stored at 4 ℃ for 8 or 16 h before the treatment. The numbers of colony-forming unit-fibroblast(CFU-F) in the different samples were determined. The adherent cells from different groups were passaged and their surface profile was analyzed with flow cytometry. Their capacities of in vitro osteogenesis and adipogenesis were observed after the cells were exposed to specific inductive ***: The average CFU-F number of urokinasetreated samples(16.85 ± 11.77/106) was comparable to that of un-coagulated control samples(20.22 ± 10.65/106,P = 0.293),which was significantly higher than those of mechanically-cut clots(6.5 ± 5.32/106,P < 0.01) and untreated clots(1.95 ± 1.86/106,P < 0.01). The CFU-F numbers decreased after samples were stored,but those of control and urokinase-treated clots remained higher than the other two groups. Consistently,the numbers of the attached cells at passage 0 were higher in control and urokinase-treated clots than those of mechanically-cut clots and untreated *** attached cells were fibroblast-like in morphology and homogenously positive for CD44,CD73 and CD90,and negative for CD31 and CD45. Also,they could be induced to differentiate into osteoblasts and adipocytes in vitro. CONCLUSION: Urokinase pretreatment is an optimal strategy to isolate MSCs from human bone marrow samples that are poorly aspirated and clotted.

关键词： Coagulated marrow sample Mesenchymal stem cells Is

Recent progress of radiation response in nanostructured tungsten for nuclear application

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Tungsten 2021年第1期3卷 20-37页

作者： Hang Xu Lan-Li He Yong-Feng Pei Chang-Zhong Jiang Wen-Qing Li xiang-heng Xiao Hubei Nuclear Solid Physics Key Laboratory Department of PhysicsWuhan UniversityWuhan 430072China

Engineering materials for nuclear reactors exposed to high-dose irradiation breed various radiation damage,leading to performance degradation of materials,which seriously limits the application of materials in the future advanced nuclear ***-based materials applied in future nuclear reactors have to withstand not only the attack of high-energy neutron and plasma,but also the repeated impact of steady-state or even transient thermal *** in the past decades have proved that tailored nanostructure have advantage in annihilating radiation *** the rapid development of nanostructured tungsten,probing radiation application of nanostructured tungsten is of great significance in promoting the development of novel radiation-resistant ***,the development status of three kinds of nanostructured tungsten namely nanocrystalline,nanofilm and nanoporous tungsten designed for radiation tolerance and the performance enhancement mechanism of diverse nanostructure in irradiation environment is ***,future perspectives and technical challenges are discussed,to inspire more creative designs of novel nanostructured tungsten for radiation tolerance.

关键词： Tungsten Nanostructure Radiation damage Radiation resistance