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Gravitational wave research using pulsar timing arrays

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National Science Review 2017年第5期4卷 707-717页

作者： George Hobbs shi dai Australia Telescope National Facility CSIRO

A pulsar timing array(PTA) refers to a program of regular, high-precision timing observations of a widely distributed array of millisecond pulsars. Here we review the status of the three primary PTA projects and the joint International Pulsar Timing Array project. We discuss current results related to ultra-low-frequency gravitational wave searches and highlight opportunities for the near future.

关键词： pulsars gravitational waves radio astronomy

RESEARCH ON STABILITY OF LIQUID FILM ON HOT SOLID SURFACE IMPINGED BY SMALL DROPLETS

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Journal of Hydrodynamics 2007年第3期19卷 264-271页

作者： GUO Jia-hong dai shi-qiang Shanghai Institute of Applied-Mathematics and Mechanics Shanghai University Shanghai 200072 China

A heat and mass transfer model was proposed for the thin liquid film on the hot solid surface cooled by the impinging small droplets, with consideration of the effect of the droplet impact, surface tension, thermocapillary, evaporation/condensation, and van der Waals attraction. The nondimensional equation for predicting the evolution of the interface of the thin liquid film was derived in the presented model with the relevant boundary conditions. The stability of the thin liquid film impacted by cool small droplets is discussed.

关键词： stability liquid film hot surface droplet

The plateau of gamma-ray burst:hint for the solidification of quark matter?

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Science China(Physics,Mechanics & Astronomy) 2011年第8期54卷 1541-1545页

作者： dai shi LI LiXin XU RenXin School of Physics and State Key Laboratory of Nuclear Physics and Technology Peking University Beijing 100871 China Kavli Institute for Astronomy and Astrophysics Peking University Beijing 100871 China

The origin of the shallow decay segment in γ-ray bursts' (GRB) early light curves remains a mystery, especially those cases with a long-lived plateau followed by an abrupt falloff. In this paper, we propose to understand the origins of the long-lived plateau by considering the solidification of newborn quark stars with latent heat released as energy injection to the GRB afterglow, and we suggest that an abrupt falloff would naturally appear after the plateau due to the energy injection cutoff. We estimated the total latent heat released during the phase transition of quark stars from liquid to solid states to be on the order of ～ 1051 ergs, which is comparable to the emission energy in the shallow decay segment. We also estimated the time scale of radiating the latent heat through thermal photon emission, and found that the time scale agrees with the observations. Based on our estimation, we analyzed the process of energy injection to GRB afterglow. We will show that the steady latent heat of quark star phase transition will continuously inject into the GRB afterglow in a form similar to that of a Poynting-flux-dominated outflow and naturally produce the shallow decay phase and the abrupt falloff after the plateau. We conclude that the latent heat of quark star phase transition is an important contribution to the shallow decay radiation in some GRB afterglows, and explains the long-lived plateau followed by an abrupt falloff, if pulsar-like stars are really (solid) quark stars.

关键词： γ-rays: bursts X-rays neutronstars elementaryparticles

NUMERICAL SIMULATION FOR 2D SHALLOW WATER EQUATIONS BY USING GODUNOV-TYPE SCHEME WITH UNSTRUCTURED MESH

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Journal of Hydrodynamics 2006年第4期18卷 475-480页

作者： PAN Cun-hong dai shi-qiang CHEN Sen-mei Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200436 China Zhejiang Institute of Hydraulics and Estuary Hangzhou 310020 China Shanghai Institute of Applied Mathematics and Mechanics Shanghai University. Shanghai 200436 China Zhejiang Institute of Hydraulics and Estuary Hangzhou 310020. China

In order to establish a well-balanced scheme, 2D shallow water equations were transformed and solved by using the Finite Volume Method （FVM） with unstructured mesh. The numerical flux from the interface between cells was computed with an exact Riemann solver, and the improved dry Riemann solver was applied to deal with the wet/dry problems. The model was verified through computing some typical examples and the tidal bore on the Qiantang River. The results show that the scheme is robust and accurate, and could be applied extensively to engineering problems.

关键词： 2D shallow water equations Finite Volume Method (FVM) unstructured mesh Godunov-type scheme Riemann solver

A high strength pH responsive supramolecular copolymer hydrogel

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Science China(Technological Sciences) 2017年第1期60卷 78-83页

作者： WANG Qing ZHANG YinYu dai XiYang shi XiaoHuan LIU WenGuang School of Materials Science and Engineering Tianjin Key Laboratory of Composite and Functional Materials Tianjin University Tianjin 300354 China

Constructing high strength pH sensitive supramolecular polymer hydrogel remains very challenging due to the unavoidable network swelling caused by ionization of acid or basic groups at a specified *** this work,we proposed a simple and very convenient approach to fabricate high strength pH responsive supramolecular polymer(SP) hydrogels by one-pot copolymerization of N-acryloyl glycinamide(NAGA) and 2-vinyl-4,6-diamino-1,3,5-triazine(VDT),two feature hydrogen bonding *** these PNAGA-PVDT SP hydrogels obtained,the hydrogen bonding of NAGA was shown to play a dominant role in reinforcing strength,while the hydrogen bonding of diaminotriazine served as a pH sensitive *** pH 3,the mechanical properties of PNAGA-PVDT hydrogels decreased to a different extent due to the breakup of hydrogen bonding;in contrast,the hydrogel resumed the original strength while pH was raised to 7.4 because of reconstruction of hydrogen *** the selected pH range,the PNAGA-PVDT hydrogels exhibited up to 1.25 MPa tensile strength,845% breaking strain,69 kPa Young's modulus and 21 MPa compressive *** novel high strength pH-responsive SP hydrogels may find applications in biomedical and industrial fields.

关键词： high strength pH responsive supramolecular polymer hydrogel

CONJUGATE FLOWS OVER A STEP IN A THREE-LAYER FLUID

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Journal of Hydrodynamics 2002年第4期14卷 15-23页

作者： Wei, Gang Le, Ja-Chun dai, shi-Qiang Inst. of Appl. Math. and Mech. Shanghai Univ. Shanghai 200072 China Sch. of Sci. P.L.A Univ. of Sci. and Eng. Nanjing 211101 China

The conjugate flows over a step with the height h_0, which might be positive or negative, was studied in a three-layer fluid and the coupled nonlinear equations were derived, with which the effects of varying height h_0 on the existence and evolution of conjugate flows were examined. It is concluded that the conjugate flow is sharply sensitive to the thickness of fluid layers and its characteristics alters remarkably due to the existence of the step. As the flow climbs up a step (h_0>0), the conjugate flow with a convex lower interface and a concave upper interface is allowed to appear, while the flow with the concave lower interface or the simultaneous concave interfaces will be depressed. As the flow goes down a step (i.e., h_0<0), on most occasions only one kind of conjugate flow could exist, which prossesses the form with the simultaneous convex interfaces and will disappear rapidly with the increase of the step depth.

关键词： conjugate flow flat solitary wave stratified flow step topography three-layer fluid

Design and verification of a lightweight reliable virtual machine monitor for a many-core architecture

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Frontiers of Computer Science 2013年第1期7卷 34-43页

作者： Yuehua dai Yi shi Yong QI Jianbao REN Peijian WANG School of Electronic and Information Engineering Xi'an Jiaotong University Xi' an 710049 China

Virtual machine monitors （VMMs） play a central role in cloud computing. Their reliability and availability are critical for cloud computing. Virtualization and device emu- lation make the VMM code base large and the interface be- tween OS and VMM complex. This results in a code base that is very hard to verify the security of the VMM. For exam- ple, a misuse of a VMM hyper-call by a malicious guest OS can corrupt the whole VMM. The complexity of the VMM also makes it hard to formally verify the correctness of the system＇s behavior. In this paper a new VMM, operating sys- tem virtualization （OSV）, is proposed. The multiprocessor boot interface and memory configuration interface are virtu- alized in OSV at boot time in the Linux kernel. After booting, only inter-processor interrupt operations are intercepted by OSV, which makes the interface between OSV and OS sim- ple. The interface is verified using formal model checking, which ensures a malicious OS cannot attack OSV through the interface. Currently, OSV is implemented based on the AMD Opteron multi-core server architecture. Evaluation re- sults show that Linux running on OSV has a similar perfor- mance to native Linux. OSV has a performance improvement of 4%-13% over Xen.

关键词： virtual machine monitor model operating sys tem many core formal verification

Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment

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Chinese Journal of Chemical Physics 2008年第1期21卷 21-26页

作者： dai-shi Guo Zi-feng Ma Chun-sheng Yin Qi-zhong Jiang Department of Chemical Engineering Shanghai Jiao Tong University Shanghai 200240 China School of Environmental Science and Engineering Shanghai Jiao Tong University Shanghai 200240China

TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Brφnsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.

关键词： TiO2 grafting Sulfate treatment Silica MCM-41 Acid catalytic activity Cyclization of pseudoionone

Coupling simulation of fluid structure interaction in the stirred vessel with a pitched blade turbine

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Chinese Journal of Chemical Engineering 2018年第5期26卷 922-929页

作者： Yangyang Liang Zhengming Gao dai'en shi Wanli Zhao Ziqi Cai State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical Technology Beijing 100029 China Mechanical Engineering School Yancheng Institute of Technology Yancheng 224051 China

The interaction between fluid and a down-pumping pitched blade turbine fixed with a flexible shaft in the stirred vessel, as a typical fluid structure interaction phenomenon, was simulated by coupling the Computational Fluid Dynamics and Computational Structural Dynamics. Based on the verification of the simulated impeller torque and dimensionless shaft bending moment with experimental result, the dimensionless shaft bending moment and various loads acting on impeller(including lateral force, axial force and bending moment) were discussed in detail. By separating and extracting the fluid and structural components from those loads, the results show that the shaft bending moment mainly results from the lateral force on impeller although the axial force on impeller is much larger. The impeller mass imbalance increases the shaft bending moment and the lateral force on impeller, but has little influence on the axial force and bending moment acting on impeller. The dominant frequencies of impeller forces are macro-frequency, speed frequency and blade passing frequency, and are associated with the impeller mass imbalance.

关键词： Fluid structure interaction Shaft bending moment Impeller lateral force Impeller axial force Bending moment on impeller