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Experimental and molecular dynamics study of gas flow characteristics in nanopores

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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

Modeling the blast load induced by a close-in explosion considering cylindrical charge parameters

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Defence Technology（防务技术） 2023年第6期24卷 83-108页

作者： Yi Fan Li Chen Zhan Li heng-bo xiang Qin Fang State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact Army Engineering University of the PLANanjingJiangsu210007China Engineering Research Center of Safety and Protection of Explosion&Impact of the Ministry of Education Southeast UniversityNanjingJiangsu211189China

Structural damage is significantly influenced by the various parameters of a close-in *** establish a close-in blast loading model for cylindrical charges according to these parameters,a series of field experiments and a systematic numerical analysis were conducted.A high-fidelity finite element model developed using AUTODYN was first validated using blast data collected from field tests conducted in this and previous studies.A quantitative analysis was then performed to determine the influence of the charge shape,aspect ratio(length to diameter),orientation,and detonation configuration on the characteristics and distributions of the blast loading(incident peak overpressure and impulse)according to scaled *** results revealed that the secondary peak overpressure generated by a cylindrical charge was mainly distributed along the axial direction and was smaller than the overpressure generated by an equivalent spherical *** effects of charge shape on the blast loading at 45°and 67.5°in the axial plane could be neglected at scaled distances greater than 2 m/kg^(1/3);the effect of aspect ratios greater than 2 on the peak overpressure in the 90°(radial)direction could be neglected at all scaled distances;and double-end detonation increased the radial blast loading by up to 60%compared to singleend ***,an empirical cylindrical charge blast loading model was developed considering the influences of charge aspect ratio,orientation,and detonation *** results obtained in this study can serve as a reference for the design of blast tests using cylindrical charges and aid engineers in the design of blast-resistant structures.

关键词： Cylindrical charge Secondary peak overpressure Aspect ratio Orientation Detonation initiation point Blast loading model

Mesoscopic modelling of UHPCC material under dynamic tensile loadings

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Defence Technology（防务技术） 2023年第5期23卷 75-91页

作者： xiang-zhen Kong Shang-bin Yang Tao Zhang Qin Fang heng-bo xiang Rui-wen Li Engineering Research Centre for Safety and Protection of Explosion&Impact of Ministry of Education Southeast UniversityJiangsu Nanjing211189China State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact Army Engineering University of PLAJiangsu Nanjing210007China Research Institute for National Defense Engineering of Academy of Military Science PLALuoyang471023China School of Civil Engineering and Architecture Xi'an University of TechnologyXi'an710048China

This paper presents a new 3D mesoscopic model of ultra-high performance cement-based composite(UHPCC)to investigate its dynamic tensile *** this model,the UHPCC is regarded as a two-phase material composed of cementitious matrix and randomly distributed *** model is established using the commercial software LS-DYNA and involves generating the randomly distributed fiber elements with considerations of diameter,length,orientation and volume fraction,and then fully constraining them with the *** particular,to capture the slipping effect between fibers and matrix that has a strong influence on the dynamic tensile behavior,the fibers are modelled by a fictitious material represented by the load-slip *** strain-rate effect of slipping force neglected in most of previous studies is considered by calibrating constitutive parameters of the fictitious material under different strain-rates based on the single fiber pullout ***,the 3D mesoscopic model is validated against three sets of tension-dominated experiments covered a wide range of loading *** predictions demonstrate that strain-rate effect of slipping force must be considered,and the neglect of it may lead to a great underestimation of the dynamic tensile strength of UHPCC material and would unavoidably underestimate the blast resistance of UHPCC components.

关键词： UHPCC Dynamic tensile behavior Mesoscopic model Strain-rate effect Impact and blast loadings

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

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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

The Crystallization,Melting Behaviors and Thermal Stability of Cross-linked Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Octavinyloctasilasesquioxane

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Chinese Journal of Polymer Science 2018年第12期36卷 1353-1360页

作者： heng-Xue xiang Fatemeh Zabihi Xu-Zhen Zhang Mei-Fang Zhu State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and Engineering Donghua University The Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education College of Materials and Textile Zhejiang SciTech University

A series of cross-linked poly（3-hydroxybutyrate-co-3-hydroxyvalerate）/octavinyloctasilasesquioxane （PHBWOVS） composites were obtained by a simple melt reactive processing technique. Dicumyl peroxide （DCP） and OVS were employed as a free radical initiator and a cross-linking agent, respectively. The chemical structure of these produced composites were identified by 1H/13C/29Si-nuclear magnetic resonance spectroscopy （1H/13C/29Si-NMR） and Fourier transform infrared spectroscopy （FTIR）. The melting behavior, non-isothermal crystallization, spherulite morphology and thermal stability property of PHBV/OVS composites were also investigated. The nucleation behaviors and crystallization rate of PHBV/OVS were significantly enhanced with the formation of cross-linked networks with different side-chains and cross-linking points. The red shift of crystalline peak temperature with addition of a small amount of OVS content evidenced the higher crystalline ability compared with the neat PHBV. However there was a threshold content, beyond which the crystallization rate weakened again. Additionally, the cross-linked structure of PHBV/OVS composites could be adjusted by changing the amount of OVS.

关键词： Biodegradable PHBV Reactive processing Crystallization behavior Composite

Lead spall velocity of fragments of ultra-high-performance concrete slabs under partially embedded cylindrical charge-induced explosion

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Defence Technology（防务技术） 2023年第5期23卷 50-59页

作者： Yi Fan Li Chen heng-bo xiang Qin Fang Fang-yu Han State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact Army Engineering University of PLANanjingJiangsu210007China Engineering Research Center of Safety and Protection of Explosion&Impact of Ministry of Education Southeast UniversityNanjingJiangsu211189China State Key Laboratory of High Performance Civil Engineering Materials NanjingJiangsu211103China

When an explosion occurs close to or partially within the face of a concrete structure, fragments are rapidly launched from the opposite face of the structure owing to concrete spalling, posing a significant risk to nearby personnel and equipment. To study the lead fragment velocity of ultra-high-performance concrete(UHPC), partially embedded explosion experiments were performed on UHPC slabs of limited thickness using a cylindrical trinitrotoluene charge. The launch angles and velocities of the resulting fragments were the determined using images collected by high-speed camera to document the concrete spalling and fragment launching process. The results showed that UHPC slabs without fiber reinforcement had a fragment velocity distribution of 0-118.3 m/s, which are largely identical to that for a normal-strength concrete(NSC) slab. In addition, the fragment velocity was negatively correlated to the angle between the velocity vector and vertical direction. An empirical Eq. for the lead spall velocity of UHPC and NSC slabs was then proposed based on a large volume of existing experimental data.

关键词： Ultra-high-performance concrete Reinforced concrete slabs Explosion Fragment velocity Blast resistance

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

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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

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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

Dynamic responses of reinforced concrete beams under double-endinitiated close-in explosion

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Defence Technology（防务技术） 2018年第5期14卷 527-539页

作者： Bin Rao Li Chen Qin Fang Jian Hong Zhong-xian Liu heng-bo xiang State Key Laboratory for Disaster Prevention and Mitigation of Explosion and Impact Army Engineering University School of Civil Engineering Southeast University Tianjin Key Laboratory of Civil Structure Protection and Reinforcing Tianjin Chengjian University

The reinforced concrete(RC) structural component might suffer a great damage under close-in *** from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on the structural component and may cause both local and structural failure. In this study,an experimental study was conducted to investigate the dynamic responses of RC beams under doubleend-initiated close-in explosions. The experimental results show that the distribution of blast loads generated by the double-end-initiated explosion is much more non-uniform than those generated by single-point detonation, which is caused by the self-Mach-reflection effects. A 3 D finite element model was developed and validated in LS-DYNA by employing the modified K&C model. Intensive numerical calculations were conducted to study the influences of the initiation way, scaled distance and longitudinal reinforcement ratio on the dynamic responses and failure modes of RC beams. Numerical results show that the RC beam suffers greater damage as the cylindrical explosive is detonated at its double ends than the scenario in which the cylindrical explosive is detonated at its central point. RC beams mainly suffer flexural failure and flexure-shear failure under the double-end close-in explosion, and the failure modes of RC beams change from the flexural damage to flexure-shear damage as the scaled distance or the longitudinal reinforcement ratio decreases. The direct shear failure mode is not usually observed in the double-end-initiated explosion, since the intense blast loads is basically concentrated in the midspan of RC beam, which is due to self-Mach-reflection enhancement.

关键词： Reinforced concrete(RC)beam Close-in explosion Failure mode Dynamic response Double-end-initiation