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Studies of the unsteady supersonic base flows around three afterbodies

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Acta Mechanica Sinica 2009年第4期25卷 471-479页

作者： Zhixiang Xiao Song Fu school of Aerospace Engineering,tsinghua university, 100084 Beijing, {3. school of Aerospace Engineering Tsinghua University 100084 Beijing China

Unsteady supersonic base flows around three afterbodies, cylindrical （Cy）, boattailed （BT） and three-step （MS）, are investigated in this paper. Reynolds-averaged Navier-Stokes （RANS） and two RANS/LES （large-eddy simulation） hybrid methods, detached eddy simulation （DES） and delayed-DES （DDES）, are used to predict the base flow characteristics around the baseline Cy afterbody. All the RANS and hybrid methods are based on the two-equation SST （shear-stress transport） model with compressible corrections （CC）. According to the comparison of measurements, both DES and DDES can produce more satisfactory results than RANS. RANS can only present the ＂stable＂ flow pat- terns, while the hybrid methods can demonstrate unsteady flow structures. DDES and DES results are little different from one another although the latter exhibits better agreement with the experiment. DES is taken to investigate the 5° BT and three-step afterbodies. The mean flow data and the instantaneous turbulent coherent structures are compared against available measurements.

关键词： Cylindrical Boattailed and three-stepafterbodies DES and DDES Unsteady flow

Competent predicate abstraction in model checking

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Science china(Information Sciences) 2011年第2期54卷 258-267页

作者： LI Li1,2,3. SONG XiaoYu4, GU Ming2,3.& LUO XiangYu2,3.1Department of Computer Science & Technology, tsinghua university, Beijing 100084, china 2Key Laboratory for Information System Security, Ministry of Education of china, Beijing 100084, china 3.6} of software, tsinghua university, Beijing 100084, china 4Department of ECE, Portland State university, Portland, Oregon 97207, USA 1. Department of Computer Science & Technology Tsinghua University Beijing 100084 China2. Key Laboratory for Information System Security Ministry of Education of China Beijing 100084 China3. School of Software Tsinghua University Beijing 100084 China4. Department of ECE Portland State University Portland Oregon 97207 USA

The paper presents a new approach to computing the abstract state and a maximum weight heuristic method for finding the shortest counter-example in verification of imperative programs. The strategy is incorporated in a verification system based on the counterexample-guided abstraction refinement method. The proposed method slashes both the size of the abstract state space and the number of invokes of a decision procedure. A number of benchmarks are employed to evaluate the effectiveness of the approach.

关键词： program model checking predicate abstraction weight heuristic

Multi-swingby optimization of mission to Saturn using global optimization algorithms

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Acta Mechanica Sinica 2009年第6期25卷 839-845页

作者： Kaijian Zhu Junfeng Li Hexi Baoyin school of Aerospace, tsinghua university,100084 Beijing, {3. school of Aerospace Tsinghua University 100084 Beijing China

Based on the trajectory design of a mission to Saturn, this paper discusses four different trajectories in various swingby cases. We assume a single impulse to be applied in each case when the spacecraft approaches a celestial body. Some optimal trajectories ofEJS, EMS, EVEJS and EVVEJS flying sequences are obtained using five global optimization algorithms： DE, PSO, DP, the hybrid algorithm PSODE and another hybrid algorithm, DPDE. DE is proved to be supe- rior to other non-hybrid algorithms in the trajectory optimi- zation problem. The hybrid algorithm of PSO and DE can improve the optimization performance of DE, which is vali- dated by the mission to Saturn with given swingby sequences. Finally, the optimization results of four different swingby sequences are compared with those of the ACT of ESA.

关键词： Swingby trajectory . Global optimization .Hybrid algorithm . Mission design

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灵光独耀:沈宗灵与中国法理学

中国法律评论 2024年第4期 149-154页

作者： Peking university Law school 北京大学法学院

在其诸多弟子的追忆中,沈宗灵先生一生专心治学、淡泊名利,由此常常对世事保持一种有意的疏离。“灵光独耀,迥脱根尘”,或许便是这位法理学大家的灵魂写照。壹“经国济民”:沈宗灵的早年岁月1923.2月24日,沈宗灵出生于浙江杭州的一个... 详细信息

在其诸多弟子的追忆中,沈宗灵先生一生专心治学、淡泊名利,由此常常对世事保持一种有意的疏离。“灵光独耀,迥脱根尘”,或许便是这位法理学大家的灵魂写照。壹“经国济民”:沈宗灵的早年岁月1923.2月24日,沈宗灵出生于浙江杭州的一个商人家庭,后随家人迁居上海。

关键词：沈宗灵淡泊名利法理学浙江杭州灵光

Remarks on the bounds for cryptanalysis of low private key RSA

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Progress in Natural Science:Materials International 2009年第10期19卷 1327-1331页

作者： Haijian Zhou a,Ping Luo b,Daoshun Wang a,Yiqi Dai a a Department of Computer Science and Technology,tsinghua university,Beijing 100084,china b {3. of software,tsinghua university,Beijing 100084,china [a]Department of Computer Science and Technology Tsinghua University Beijing 100084 China [b]school of software Tsinghua University Beijing 100084 China

Boneh and Durfee have developed a cryptanalytic algorithm on low private key *** algorithm is based on lattice basis reduction and breaks RSA with private key d < N0:*** on,an improved version by Blmer and May enhan... 详细信息

Boneh and Durfee have developed a cryptanalytic algorithm on low private key *** algorithm is based on lattice basis reduction and breaks RSA with private key d 4-bit public key eN;eT.

关键词： RSA Cryptanalysis Low private key Lattice basis reduction

Effects of binders on the performance of electric double-layer capacitors of carbon nanotube electrodes

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Progress in Natural Science:Materials International 2005年第5期15卷 453-457页

作者： LI Chensha1*, WANG Dazhi1, ZHANG Baoyou2, WANG Xiaofeng1, CAO Maosheng3. and LIANG Ji1(1. Department of Mechanical Engineering, tsinghua university, Beijing 100084, china 2. Center for Analysis and Measurement, Harbin Institute of Technology, Harbin 150001, china 3. school of Material Science and Engineering, tsinghua university, Beijing 100084, china) Department of Mechanical Engineering Tsinghua University Beijing 100084 China Center for Analysis and Measurement Harbin Institute of Technology Harbin 150001 China school of Material Science and Engineering Tsinghua University Beijing 100084 China

Polarizable electrodes of electric double layer capacitor (EDLCs) were made from carbon nanotubes. Effects of different binders, which are phenolic resin (PF) and polytetrafluoroethylene (PTFE), on the properties of polarizable electrodes are studied. Results indicate that the microstructure, pore size distribution and specific capacitance of the electrodes with PTFE binder are superior to those electrodes with PF binder after carbonization. The suitable binder (PTFE) for carbon nanotubes electrodes is proposed.

关键词： carbon nanotubes electric double-layer capacitors phenolic resin polytetrafluoroethylene.

The apparent contact angle of water droplet on the micro-structured hydrophobic surface

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Science china Chemistry 2010年第4期53卷 912-916页

作者： YANG ChangWei, HE Feng & HAO PengFei school of Aerospace, tsinghua university, Beijing 100084, {3. 1. school of Aerospace Tsinghua University Beijing 100084 China

The apparent contact angle of Cassie-Baxter state water droplets can be calculated by the existing theoretical formula, but due to the defects of the micro-structured hydrophobic surface and some inevitable tiny disturbances in the experiment, Cassie-Baxter state water droplets will appear partly in Wenzel state, that is, the mixed state water droplets. In this paper, apparent contact angles of Cassie-Baxter state and mixed state water droplets on micro-structured hydrophobic surfaces are compared. The research shows that if the projected area fraction of water-solid F in the Cassie-Baxter formula is replaced by the local projected area fraction of water-solid F′, the apparent contact angles of water droplets in both Cassie-Baxter state and the mixed state can be calculated. Further experimental results indicate that the contact state of water droplets nearby the outermost three-phase contact line plays a more important role in determining the apparent contact angle. This conclusion is significant to the understanding of the apparent contact angle and wetting property.

关键词： apparent contact angle three-phase contact line mixed model Cassie-Baxter model Wenzel model

Analysis of finite-element-based methods for reducing the ill-posedness in the reconstruction of fluorescence molecular tomography

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Progress in Natural Science:Materials International 2009年第4期19卷 501-509页

作者： Zhun Xu, Jing Bai Department of Biomedical Engineering, school of Medicine, tsinghua university, Beijing 100084, {3. [a]Department of Biomedical Engineering School of Medicine Tsinghua University Beijing 100084 China

The major issue in reconstruction of optical imaging might be the ill-posedness of the problem. In this paper, four different algorithms, including singular value decomposition (SVD), the truncated SVD, Tikhonov regularization and adaptive regularization, are analyzed and applied for solving the matrix equation generated from diffuse equation based on finite-element method in fluorescence molecular tomography. Results illustrate the need for either imposition of regularization term or elimination of too small singular values in reducing the illposedness. The results also suggest that the adaptive-regularization method offers superior performance in the reconstruction among the four methods in most cases even if the initially selected regularization parameter is not optimal, thus providing the convenience for the reconstruction.

关键词： Fluorescence molecular tomography Reconstruction Ill-posedness The truncated SVD Adaptive regularization

|m| Partial wave treatment for two-dimensional Coulomb-scattering and Regge pole

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Science china(Physics,Mechanics & Astronomy) 2004年第6期47卷 676-684页

作者： WANG Jing & ZENG Jinyan Department of Physics,tsinghua university,Beijing 100084,china {3. of Physics,Peking university,Beijing 100871,china Department of Physics Tsinghua University Beijing 100084 China school of Physics Peking University Beijing 100871 China

The symmetry and |m| partial-wave analysis for two-dimensional (2D) Coulomb-scattering is investigated. As a function of energyE, the |m| partial-wave scattering amplitudef |m|(θ) is analytically continuated to the, negativeE (complexk) plane, and it is found that the bound state energy eigenvalues (E<0) are just located at the poles off |m|(θ) on the positive imaginaryk axis as is expected. In addition, as a function of |m|,f |m|(θ) is analytically continuated to the complex |m| plane, the bound state energy eigenvalues are just located at the poles off |m|(θ) on the positive real |m| axis.

关键词： two-dimensional Coulomb scattering, |m| partial-wave, Regge pole.