最新刊期
卷 43 ， 期 6 ， 2011
- 摘要：Abstract:Prestressed steel reinforced concrete structure（PSRC） is composite structure, which has advantage of both prestressed reinforced concrete structure and reinforced concrete structure. In order to investigate the mechanical behavior and the law of moment redistribution, two large scale prestressed steel reinforced concrete frame were tested and their performance such as failure pattern, crack development, rigidity change were studied. The results show that PSRC is ductile failure and basically meets the plane section assumption. Based on experiments, the bearing capacity formulas considered secondary axial force were put forward. Test moment modulation is 30%,which is higher compared with prestressed reinforced concrete frame.关键词：prestressed steel reinforced concrete frames;static test;plastic hinge;internal force redistribution;moment modulation
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发布时间：2023-11-28 - 摘要：Abstract:Taking Kuye River as an example, a storm flood related statistical model, the nearest neighbor bootstrapping regression model, was used to analyze the impacts of water conservation measures on flood. The results showed that influenced by water conservation measures, the flood peak reduces 53%, and the flood volume reduces 47.6%. The water conservation measures have the greatest influence on small flood, then on the big flood, with the smallest influence on the medium flood.关键词：water conservancy measures;flood;impacts;Kuye River
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发布时间：2023-11-28 - 摘要：Abstract:Usually the geological and the climate environmental conditions are considered in designing bridge, but the requirements according to antiknock design for bridge structures are neglected. In order to investigate the dynamic response and damage process of bridge under blast loading, the dynamic response of continuous rigid frame bridge suffering blast loading was simulated numerically by LS-DYNA software, and the characteristics of shock wave propagating in air were analyzed. Also, the response of displacement and the Von-Mises stress distribution around the middle of bridge were obtained, and then the failure state and collapse process of the bridge were showed. Based on the Tuler-Butcher damage rule, the damage accumulation curves of specified elements were obtained. The calculative method and results are referenced for the engineering practice.关键词：blasting;dynamic response;damage tolerance;numerical analysis
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发布时间：2023-11-28 - 摘要：Abstract:In order to ensure the progressive collapse resistance design of long span steel structures, several practical methods or measures were proposed for the structure design based on the different structure systems. The methods were the lateral beam method for plane truss structure systems, the circular reinforced beam method for radial layout truss structures, and the separated load path method for the suspend dome structures,respectively. In the aspect of calculating methods, the suitable scopes of the linear static method, the nonlinear static method, and the nonlinear dynamic method were concluded. The computation formulas for the structures with local member failure were derived. The variation coefficient of the stiffness matrix condition number before and after the member failure was proposed to judge the illness of the matrix. Three examples proved the design measures and the calculating methods.关键词：long span steel structure;progressive collapse;ill-condition matrix;Variation coefficient of condition number
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发布时间：2023-11-28 - 摘要：Abstract:After the installation of lateral bracing, the effective length of column could be reduced, the stability bearing capacity and steel saving are profitted by it. Existing research focused in this area is insufficient, and the current design methods used in engineering field are not precise enough. In order to treat this problem, calculation equations were established based on the three-moment equation, and the influence of lateral bracing stiffness and residual stress were involved. A full scale test was conducted for comparing with the calculation result, and the test covered parameters Q420, 2L160 mm×14 mm, and λ=30~50. The relationship between lateral bracing and stability bearing capacity of column was acquired. The test results showed that the developed calculation method matches with these results, and is slightly lower than them. Though lateral bracing could enhance stability bearing capacity evidently, the maximum discrepancy between current design method and test results is larger than 20% for the simple reason that the method does not take the slenderness ratio into account. Proposed formula is the low limit of test and calculation results, and it can be a reference for such column during designing.关键词：lateral bracing;influence of stiffness;axial compression column;stability bearing capacity;built-up section
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发布时间：2023-11-28 - 摘要：Abstract:In order to develop a generally applicable evaluation system for regional water environment carrying capacities, databases, geographic information systems and visual programming technology were employed and an intelligent evaluation system platform of water environment carrying capacity was developed. The overall designs and functions, as well as the structure of evaluation system for regional water environment carrying capacity were also introduced. This system is effective not only for the calculation of water environment carrying capacity in present conditions, but also for the capacity prediction in the future, including the spatial distributions. The application in the Guanzhong region of Weihe River basin showed that this evaluation system is a useful tool for evaluation and prediction of regional water and environmental carrying capacity.关键词：water environment;pollution;carrying capacity;evaluation system;Guanzhong region of Weihe River Basin
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发布时间：2023-11-28 - 摘要：Abstract:Hardfill is a new material with low strength in which the granular materials are solidified with some cementing material.Based on the analysis of data from uniaxial and triaxial tests,the stress-strain characteristics were concluded that Hardfill has typical features as elastic-plastic material in its stress-strain relations.It has linear elasticity in low stress, and gradually shows the plasticity when the stress exceeds 60%~80% peak strength. Surpassing the peak strength,it goes soften obviously as the stress decreases along with the strain increase,and finally reaches the residual strength.A constitutive model for Hardfill material was put forth in which nine parameters can be determined by material triaxial test.The stress-strain curve calculated by the constitutive model fitted closely with the data from Hardfill material test,which showed that the model can display the stress strain features of Hardfill material appropriately.This constitutive model can be used for the nonlinear analysis of Hardfill dam conveniently.关键词：Hardfill material;stress;strain;nonlinear;constitutive model;triaxial test
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发布时间：2023-11-28 - 摘要：Abstract:For choosing the value of deformation modulus reasonably during optimally designing an arch dam, several arch dams with different height which supported by rock bases with various deformation modulus were optimized, and the rough value which was required by arch dams with different height and it’s variation law were obtained. The law could be referenced by other engineers who want to optimal design an arch dam. At the same time, the stress of an arch dam which was hold by rock bases with different deformation modulus was analyzed. It was concluded that the arch dam will not be more safety when small value of deformation modulus is chosen, and the value of an arch dam’s body stress should less than the tolerable value in case that the deformation modulus of the rock will change.关键词：optimizing;deformation modulus;foundation plane;arch dam
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发布时间：2023-11-28 - 摘要：Abstract:In order to develop the drag-reducing technology in turbulent water-transporting flow by environmental friendly surfactant additives to water,experimental investigation was carried out on the drag-reducing behavior,shear viscosity, and relaxation characteristics of shear stres of nonionic surfactant alkyl polyglucoside solution in a pipe,by a flow-drag test device driven by compressed air and a cone plate rheometer.The results showed that alkyl polyglucoside presents excellent drag-reducing ability, and when temperature and concentration increase, the critical Reynolds number with maximal drag-reducing rate increases.The shear viscosities are Newtonian at smaller shear-rates,and suddenly jump up at some critical shear rate,which is called as SIS (Shear-Induced Structure). Development and relaxation behavior of Shear stress is the same with water,which showed that the immediate causal connections is absent between SIS and viscoelastic effects.关键词：alkyl polyglucoside;pressure loss;drag characteristic;drag reduction;shear viscosity;shear stress relaxation
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发布时间：2023-11-28 - 摘要：Abstract:When the parameter optimization of hydrological models is done under the framework of multiobjective, how to select or construct proper combination of objective functions is one of the most important issues.To solve this problem, one simple and convenient method for the comparison of the influence of different objective function combinations on the optimization results, which were obtained by multi-objective evolutionary algorithms,was proposed.A hydrological model for daily streamflow forecasting was taken as an example.Three objective function combinations were constructed,and the multiobjective algorithm NSGA-II was employed to optimize the hydrological model.Based on the optimization results,the proposed method was applied to analyze the performance of model calibration with different combinations of objective functions.It was also expected to find a combination of objective functions which can well balance different objective functions.The results showed that the proposed method is effective to analyze the performance of different combinations of objective functions,can provide more comprehensive evidence for decision making in hydrological forecasting, and has good prospects in practical engineering.关键词：hydrological model calibration;streamflow forecasting;multi-objective;combination of objective functions
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发布时间：2023-11-28 - 摘要：Abstract:A virtual crack closure technique based on EFG method for thread-shape crack was introduced. The cracked component was discretized and the displacement field was determined using a coupled FE/EFG method, by which EFG nodes were arranged in the vicinity of crack tip and FE elements in the remain part in order to improve computational efficiency. Two typical parameters, nodal force and crack opening displacement attached to crack tip were calculated by means of setting up an auxiliary FE zone around crack tip. Strain energy release rate(SERR), further stress intensity factor(SIF) were determined by the two parameters. The method to calculate SIF was named as virtual crack closure technique based on EFG method. Several numerical examples using the presented method showed that SIF on the crack tip can be obtained accurately.关键词：strain energy release rate;virtual crack closure technique;stress intensity factor;EFG;numerical solution
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发布时间：2023-11-28 - 摘要：Abstract:To protect Chinese ancient building,strengthening methods on Chinese ancient tenon-mortise joint were studied by shaking table tests. Based on actual sizes of an ancient wooden building, wooden frame models with a scale of 1∶8 of the prototype structure were built considering Yan-wei type of tenon-mortise connections.Iron hook,steel components and CFRP(Carbon Fibre Reinforced Plastic) sheets were considered to strengthen tenon-mortise joint of model to enhance its stability. By white noise excitation values of basic frequency as well as damping ratio of model in both strengthened and unstrengthened conditions were obtained.By inputing El-Centro earthquake waves of different peak acceleration values, responses of displacement and acceleration for typical nodes of model were obtained, and vibration absorption ratio values for both model and tenon-mortise joint were discussed.Results showed that for different strengthening method:J(steel components)>J(CFRP sheets)>J(iron hook)>J(no-strengthen) in basic frequency of model(J).D(no-strengthen)>D(iron hook)>D(steel components)>D(CFRP sheets) in damping ratio of model(D).umax(CFRP sheets) keywords: wooden buildings earthquake resistance dynamic response tenon-mortise joint 文章编号：201100106 中图分类号： 文献标志码： 基金项目:国家自然科学基金资助项目（50878010）；故宫博物院科研基金资助项目（KT2007-4）；文化部科技创新基金资助项目（17-2009） 作者单位周乾 北京工业大学 工程抗震与结构诊治北京市重点实验室；故宫博物院 闫维明 北京工业大学 工程抗震与结构诊治北京市重点实验室 李振宝 北京工业大学 工程抗震与结构诊治北京市重点实验室 张博 北京工业大学 工程抗震与结构诊治北京市重点实验室 Author NameAffiliationZhou Qian Beijing Key Lab. of Earthquake Eng. and Structural Retrofit,Beijing Univ. of Technol.Imperial Palace Museum Yan Weiming Beijing Key Lab. of Earthquake Eng. and Structural Retrofit,Beijing Univ. of Technol. Li Zhenbao Beijing Key Lab. of Earthquake Eng. and Structural Retrofit,Beijing Univ. of Technol. Zhang Bo Beijing Key Lab. of Earthquake Eng. and Structural Retrofit,Beijing Univ. of Technol. 作者简介: 引用文本： 周乾,闫维明,李振宝,张博.古建筑榫卯节点加固方法振动台试验研究[J].工程科学与技术,2011,43(6):70-78. Zhou Qian,Yan Weiming,Li Zhenbao,Zhang Bo.Aseismic Strengthening Methods on Chinese Ancient Tenon-mortise Joint by Shaking Table Tests[J].Advanced Engineering Sciences,2011,43(6):70-78.关键词：wooden buildings;earthquake resistance;dynamic response;tenon-mortise joint
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发布时间：2023-11-28 - 摘要：Abstract:Pre-reinforced pile in high cutting slope can reduce the displacement of the slope and ensure the stabilization of the slope. Because of the largely structural stiffness of concrete pre-reinforced pile, the earth pressure acting on pile increases. In order to settle this problem, a layer of EPS backs on to the pre-reinforced pile was set to decrease the interaction force of pre-reinforced piles. Finite element analysis software of ANSYS was used to analyze the value and distribution of displacement, shearing force and bending moment acted on the pre-embedded pile with different thickness and types of EPS backs on to the pre-reinforced pile. The results showed that the thickness and types of EPS have large influence on pre-reinforced piles. With the increase of the thickness of EPS, the earth pressure acting on pile decreases, the displacement of pre-reinforced pile decreases, and the inner force of pre-reinforced pile decreases. With the decrease of the density of EPS, the earth pressure acting on pile decreases, the displacement of pre-reinforced pile decreases, and the inner force of pre-reinforced pile decreases.关键词：pre-embedded piles;soil-pile interaction;expanded polystyrene;numerical analysis
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发布时间：2023-11-28 - 摘要：Abstract:In order to study the evolutionary process of brittle rock damage and fracture under low-velocity impact loading, the dynamic damage was studied by variable angle impact test using compressed gas of SHPB to launch the ball to impact the lateral margin of rock plate. When a source of impact loading was applied to a rock plate specimen, damage cracks were developed from the source to the boundaries, and the surface cracks effectively represened sample internal cracking condition and reflected the impact energy dissipation in these tests. Test results showed that the cracks propagation length and break area are not arbitrary, but are influenced by the angle of dynamic impact loading. The crack length and the break area increase with the increase of the impact loading. When the break area decreases abruptly, the crack length increases suddenly, which shows that there is an obvious incubation period of crack forming, and at first some pits appear on the verge of the rock plate and the propagation rate of crack length and break area decrease with the increase of the impact velocity. According to test results, the scope of impact resistance optimized angle is about 15°~30°.关键词：impact loading;rock plate;laboratory simulation;damage;fracture
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发布时间：2023-11-28 - 摘要：Abstract:The long-term shear rheology strength of rock mass is an important base to the analysis of long-term operation stability of the rock engineering. Based on field shear rheology test data of dam zone diabase of Dagangshan hydropower station, the long-term shear rheology strength was obtained by stress-strain isochronal curves method, steady-state creep rate method, and nonsteady-state creep method, respectively, and the results were compared and analyzed. The stress-strain isochronal curves method could provide a more scientific and reasonable way for the analysis of long-term shear rheology strength of diabase. Compared with the short-term shear strength, the long-term shear rheology strength by reason of crack damage propagation had some reduction, internal friction angle decreased by 30.7% and cohesion decreased by 22.6%.关键词：field shear creep test;stress-strain isochronal curves method;nonsteady-state creep method;long-term shear rheology strength;long-term rheology shear strength index
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发布时间：2023-11-28 - 摘要：Abstract:Considering the change of frozen soil phase, the finite element method of unsteady temperature field-seepage field coupled problem was improved. According to the soil freezing characteristic curve, the pore ice containing volume was calculated and fixed. At the same time, a correction method of temperature derivate unfrozen soil’s water volume, and a new method accelerating the convergence speed were put forward, to eliminate the numerical oscillation phenomena that appears in the frozen soil’s temperature field-seepage field coupling calculation, and accelerate the convergence speed. Finally，two numerical examples were compared with the experiments to verify the reliability and effectiveness of the method.关键词：frozen soil;phase change;pore ice containing volume;accelerating convergence
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发布时间：2023-11-28 - 摘要：Abstract:The influences of different simulations of soft tissues around disk on the movement and stress distribution of the temporomandibular joint(TMJ) were analyzed. A three-dimensional finite element model of the mandible, temporal bone and articular disk was developed according to the CT of a volunteer with asymptomatic joints. The soft tissues around disk were simulated as four types. Contact elements were used to simulate the interaction of the disk with the soft tissues and the articular surfaces. The muscle forces corresponding to centric occlusion were applied to the four models. The results showed that the disks rotated round the condyles in the model with the soft tissues around disk constructed as solid models. Moreover the stresses of the intermediate zones of disk and the anterior regions of condyle and temporal bone were so low. The disks were close to the normal position in the models with the bilaminar zones constructed as solid models, whereas the stress distributions in the TMJs were abnormal. The disks in the model with the attachments of the disks simulated as nonlinear cable elements were in the normal position. Moreover the maximum stress of the disks occurred in the intermediate zones, and the maximum stress of the condyles and temporal bones occurred in the anterior regions. The attachments of disk should be modeled as cable elements, and the interaction of the disk and the articular surfaces should be simulated as contact elements.关键词：temporomandibular joint(TMJ);articular disk;finite element method;cable element;stress analysis
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发布时间：2023-11-28 - 摘要：Abstract:By using alumina supported manganese oxide, the manganese-based sulfur acceptor had good performance of sulfidation-regeneration. Mn-Al-O spinel phase was believed to be the active sites of this acceptor. Under 850 ℃, the S/O exchange occurred inside the whole bulk phase of this acceptor, which results in high sulfur capacity. Experimental results showed that the good synergy of Mn/Al is important for the regenerativity of the acceptor. Both the impregnation and co-precipitation can obtain high manganese loading and high sulfur capacity. Co-precipitation method is a easy way to achieve high manganese loading. The sulfur capacity reached 30 g(S)/100g(acceptor) when the manganese loading reached 46.4%. The sulfidation test showed that the sulfidation is a quick reaction. Using SO2 as the regenerative gas, the elemental S is recovered by combining the regenerative reaction and Clause reaction. The granulated acceptor showed very good chemical stability and mechanical stability under 850 ℃.关键词：high temperature sulfur removal;manganese sulfur acceptor;coal gas
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发布时间：2023-11-28 - 摘要：Abstract:After extracted from Voacanga africana Staph., the crude sample was purified and recrystallized to get polycrystalline powder. The crystal structure of Hydrochloride Tabersonine was determined from its X-ray powder diffraction pattern through calculational crystallography methods.The results showed that the the caystal structure of hydrochloride tabersonine is monoclinic,space group P21 with unit cell dimensions a=1.253 9 nm，b=0.737 1 nm，c=1.229 6 nm，α=γ＝90°，β＝106.192°，Z=2，V=113.649 7 nm3.关键词：hydrochloride tabersonine;X ray powder diffraction;crystal structure
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发布时间：2023-11-28 - 摘要：Abstract:The explosion process of urea reactor was studied. In order to investigate the shock wave formation and the characteristics of its propagation, the explosion of gas phase in the top regime of urea reactor was simulated numerically. Based on the simulation of shock wave propagation in the liquid phase, the shock wave velocity was obtained. The superposition point and the superimposed pressure for the shock wave in the liquid phase were determined by considering the propagation velocity and time difference of entering the liquid for the shock wave. The results showed that the shock wave pressure increased significantly after superposition, and the pressure was high enough to break the reactor at that point. The super high temperature liquid gasified and released out quickly, resulting in more hazardous secondary explosion.关键词：urea reactor;explosion;shock wave;numerical simulation
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发布时间：2023-11-28 - 摘要：Abstract:The metal salt catalytic agent and hydrogen peroxide were chosen to oxidize the soluble starch, and the content of aldehyde group was determined by electrictitration, which was 41.3%. The result of FT-IR and thermogravimetry analysis of oxidized starch also showed the existence of aldehyde group and symmetrical degree of oxidation. At last, the glycyglycine and glutin were treated with the oxidated starch. By testing the carbon nuclear magnetic resonance (13CNMR) spectrograms of native and modified glycyglycine, the kinetic viscosity and denaturation temperature (Td) of the native and treated glutin, it was concluded that oxidated starch could cross link with amido link of protein, and the viscosity of native glutin was 19.07 and 4.13 mm2/s at 30 and 50 ℃ respectively, which was reduced to 6.40 and 3.69 mm2/s for the modified glutin at the same temperature.This also was proved by the fact that the Td of treated glutin was increased to 194.0 ℃ from 122.4 ℃.关键词：catalyzing oxidation;oxidated starch;glycyglycine;glutin;maillard reaction
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发布时间：2023-11-28 - 摘要：Abstract:In order to develop a novel coating for tissue engineering, strontium-doped calcium polyphosphate(SCPP) nano-powders were coated on titanium substrate using the plasma-spraying technique with a series of different conditions. Constitution, phase composition, microstructure and bonding strength of the powders were investigated by inductively coupled plasma mass spectrometer，X-ray diffraction analysis, scanning electron microscope and strength test machine. Results showed that the main phase of these coatings is remain β-crystal SCPP. The surface and cross-sectional morphology of coating showed SCPP coatings are dense. The bonding strength and between the coating and titanium is higher than others and the coating exhibit a good biocompatibility by plasma-spraying. The condition in which the obtained coatings exhibited appropriate roughness of the surface and higher bonding strength with the substrates will be the reference for the investigation of better SCPP coatings in next step of the study.关键词：Strontium-doped calcium polyphosphate;plasma spraying;coating;bonding strength
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发布时间：2023-11-28 - 摘要：Abstract:An algorithm used to determine the termination of some polynomial loops by finite difference was proposed. Based on the basic principle of finite difference, the relation between the value of loop condition and its finite difference was discovered and proved rigorously. On this basis, a method for determining the termination of this class of polynomial loops was obtained. Furthermore, the more complex polynomial loops was analyzed, which had complex loop conditions and multiple branches.关键词：finite difference;loop;termination
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发布时间：2023-11-28 - 摘要：Abstract:A method used to eliminate the crosstalk between the neighboring parallax images by correcting the intensity values of subpixels on synthetic images in the autostereoscopic displays was proposed based on lenticular sheet. The causes of the crosstalk was analyzed based on a synthetic image, and the equations of crosstalk elimination was deduced according to the relationship among the crosstalk coefficients of each parallax image observed through the lenticular sheet, the intensity values of subpixels displayed on the synthetic images, and the intensity values of subpixels observed through the lenticular sheet at the optimal viewing position. The experiment results verified the effectiveness of the proposed method.关键词：autostereoscopic display;lenticular sheet;crosstalk
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发布时间：2023-11-28 - 摘要：Abstract:In order to overcome the premature convergence and poor running efficiency of the attribute reduction algorithm based on particle swarm optimization, based on some special searching optimization advantages of the niche technology, a novel incomplete attribute reduction robust algorithm (named NCNPSO-IAR) of niche conic neighborhood particle swarm optimization was proposed. It could construct niche subvector of neighborhood radius by the layered conic space. The main advantages of the proposed algorithm involves to partition the adaptive niche radius by avoiding depending on the prior domain knowledge and to overcome the premature convergence.It could maintain the diversity of populations, and improve the running converge speed. Further, reduction set subvectors could share some cooperative social cognition in their conic subspaces, so as to get the optimization attribute reduction sets. Experimental results demonstrated that the proposed algorithm is efficient and robust, especially for the incomplete and noisy attribute reduction.关键词：niche particle swarm optimization;adaptive neighborhood vector;incomplete decision table;attribute reduction;robustness
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发布时间：2023-11-28 - 摘要：Abstract:In order to reduce the hyperplane matrix when detecting simultaneous integer relations for several real vectors, a generalized Hermite reduction was presented. Based on generalized Hermite reduction and patial sum lower trapezoidal orthogonal decomposition (PSLQ ) algorithm, the algorithm of simultaneous integer relations detection ( SIRD ) was proposed. SIRD was implemented in computer algebra system Maple in two different routes of software float-point data type “sfloat” and hardware float point data type “hfloat”. The SIRD was compared with HJLS, and the results showed that SIRD is better. Furthermore, SIRD was applied to get a complete method for finding the minimal polynomial of an unknown complex algebraic number from its approximation.关键词：integer relation;algebraic number;minimal polynomial;symbolic-numeric computation
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发布时间：2023-11-28 - 摘要：Abstract:In order to solve the problem of asymmetric key management in mobile ad hoc networks, a new distributed asymmetric key management scheme based on lite CA public key authentication framework and Shamir secret sharing scheme was presented. The public key could be certified locally by the mechanism of distributed lite CA certification authentication and so the certification management was not need in the scheme. It also avoided the inherent key escrow problem in identity-based cryptography to combine with the advantages of certificateless public key cryptography and provided the ability to resist the public key substitution attacks. Security analysis and experiment results showed that the scheme is secure and efficient in implementation.关键词：mobile ad hoc networks;security;key management;lite CA;Shamir secret sharing
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发布时间：2023-11-28 - 摘要：Abstract:An access control model based on the security evaluation of subject and object was proposed. At first, some important concepts and their relationships, such as user (subject) security degree, resource (object) security degree, user security level, resource security level, and operation level were defined. Then a formula to qualify the condition that the user must satisfy when he accessed a certain system resource by a certain operation was provided from the angle of security. The object security degree was decided by the security evaluation value of the device that the accessed resource lied in, which equaled the weighting sum of the evaluation values of the threat, the vulnerability and the environment security. The user security degree was decided by five factors, such as the security of physical device used by the user, compliance of the use of the resources, the history behavior of the user, the evaluation of the user by a third party, and the identity certificate class. The methods to compute the values of these five factors were discussed and the subject security degree was equal to the weighting sum. At last, the proposed access control model based on the security evaluation of subject and object was verified in practical application. The statistics of experiment showed that, compared with the access control system depended on firewall and IDS, the total number and severity of security events of the system based on the proposed access control model decrease obviously.关键词：access control;subject;object;security degree;security level
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发布时间：2023-11-28 - 摘要：Abstract:Distributed Hash Tables ( DHT ) is the key technology for structured P2P system to make resources organized and positioned efficiently. The security threats and the corresponding solving methods existing in the message forwarding process of DHT system were analyzed. Based on multi-path method, a defense mechanism with mixed routing was proposed to optimize the forwarding efficiency and safety. Firstly, a mixed routing combined the advantages of iterative and recursive routing was described in detail, which can efficiently forward the message with fewer messages overhead. Secondly, the message reliability and source authentication mechanism were improved to ensure message security in the forwarding process. In addition, the defense mechanism with mixed routing was tested in Sichuan University campus network. The simulation results showed that it has obvious effect on reducing the number of queries and increasing the success rate of forwarding message, which has a better defense effect against the attack in the forward phase.关键词：DHT;message forwarding;routing;defense mechanism
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发布时间：2023-11-28 - 摘要：Abstract:In software transactional memory, transactions are aborted forcefully because correctness, which must be retried as new transactions immediately. After aborted and retried, transactions may conflict again, leading to more aborts and degrading the overall throughput. An abort manage algorithm that control all aborted transactions was presented. The results showed that forcefully aborted transactions are not same as the new and normal aborted ones, which avoid conflict and give chance to the others. After a while, these transactions restart. So the forcefully aborted transactions avoid conflict and should be helped to access the share memory.关键词：concurrent;Software Transactional Memory (STM),;contention;abort
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发布时间：2023-11-28 - 摘要：Abstract:Based on spectral analysis, a synchronization algorithm modulated multiple pilot symbols using Constant Amplitude Zero Auto-Correlation (CAZAC) sequence was presented for HF OFDM signal acquisition under low signal to noise ration. The fast signal acquisition was realized by time-frequency domain two-dimension estimation, and synchronously the integer frequency shift was obtained by the maximal peak position of spectrum function. Then the phase difference of adjacent pilot symbols was used for precisely fractional frequency shift estimation. Finally, Matlab simulations and on-chip real-time analysis of the algorithm using FPGA were done. The results demonstrated that this algorithm achieves fine performance at low SNR and can work efficiently as a block of an OFDM baseband receiver processor.关键词：Orthogonal Fequency Division Multiplexing(OFDM);synchronization acquisition;Field Programmable Gate Array (FPGA);low SNR
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发布时间：2023-11-28 - 摘要：Abstract:Spectrum sensing has been identified as the fundamental issue in cognitive radio networks(CRNs). To improve the overall sensing performance, the mechanisms of cooperative spectrum sensing are investigated. Specifically, aiming at the sensing scenario of channel searching, a joint optimized channel-searching scheme is proposed. In this scheme, the base station chooses the optimal searching sequence according to the channels’ static probabilities of being idle, and meanwhile, sets the searching durations of each candidate with different weights. Utilizing this optimal mechanism, the channels with higher idle probabilities can be guaranteed to be searched with higher priorities and longer durations, and thus, the delay due to channel switching and the corresponding QoS loss are minimized. The simulation results show that the average time for finding a new available channel by the proposed searching scheme is always much shorter than that of two existing schemes, and thus, visible performance improvement can be obtained.关键词：cognitive radio;spectrum sensing;cooperative spectrum sensing;sensing mechanisms;channel searching
- 2271
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- 10
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- 0
发布时间：2023-11-28 - 摘要：Abstract:The influence of noise uncertainty to Energy Detection(ED) of Cognitive Radio(CR) was investigated. The stability of ED was analyzed in order to obtain the stability probability and minimal sampling number. The interruptive detection probability was proposed to reflect the continuance of ED under noise uncertainty. Both the interruptive detection probabilities of single detection and cooperative detection were obtained, and the detection time of ED was also achieved. The detection probability was analyzed in order to achieve its Distribution Function(DFC), and the maximal objective detection probability under the specific interruptive detection probability was estimated through DFC.Simulations showed that the stability of ED could be improved with the increase of sampling number, while the interruptive detection probability increass with the improvment of noise uncertainty or the degrading of the normal Signal-to-Noise Rate(SNR). It also denoted that through cooperative detection, the interruptive detection probability could be degraded.关键词：cognitive systems;signal detection;sampling;electromagnetic interference
- 2825
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- 14
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- 7
发布时间：2023-11-28 - 摘要：Abstract:In order to accurately describe the potential risk of catastrophic accidents in a power system, a new united uncertainty method to assess catastrophic accidents was proposed based on their inherent physical properties and the uncertainty theory. The catastrophic accidents were regarded as the uncertain events, and the concepts of credibility measure and global fuzzy security index were developed to describe the likelihood and severity of catastrophic accidents. The N-1 contingencies were taken as the initial accidents and the most possible catastrophic accident sequences were identified through the risk ranking of all N-k contingencies in each simulation layer. The WSCC nine buses system and a regional practical system were simulated. Compared with the traditional methods, the proposed method was more accordant to practical power system operating conditions and had better accuracy and validity.关键词：electric power system;catastrophic accident;cascading failure;risk assessment;uncertainty theory
- 2132
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- 2
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- 0
发布时间：2023-11-28 - 摘要：Abstract:To decrease the lightning trip-out rate of transmission line, a new method therefore was put forward to reduce the grounding resistance of transmission tower foundation based on the constant current field theory.This method combined special reinforcing cage with proportional effective anti-corrosion resistance reduction agent to make tower foundation ground tightly,and took up a little space and soil. And all the problems such as reducing grounding resistance by horizontal radial grounding method because of topography were solved.The characteristic of small impulse coefficient and impulse grounding resistance of this device increased the lightning withstand level and power supply reliability of transmission line greatly.Results of instances and practices showed that this method is feasible and validated.关键词：rocky region;transmission tower;grounding resistance;the constant current field theory
- 2056
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- 8
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- 0
发布时间：2023-11-28 - 摘要：Abstract:This paper considers the formation control and attitude control problems of networked spacecraft flying in deep space.The control objectives are to design a coupled controller under which each spacecraft can track its desired position and attitude and,simultaneously,the whole group move to the desired formation and achieve desired relative attitudes.The proposed controller obtained by graph approach,only requires information links with a spacecraft’s neighbors and therefore reduce the total communication costs of the whole formation compared to a previse study. In addition,the proposed controller requires no measurements of a spacecraft’s neighbor’s velocity and acceleration and therefore reduces the accumulative errors accompanying with measurements.Simulation results demonstrate the effectiveness of the proposed controller.关键词：information graph;networked spacecraft;formation control;attitude control
- 2706
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- 2
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- 0
发布时间：2023-11-28 - 摘要：Abstract:A multi-model non-fragile soft switching robust tracking control strategy was proposed in the presence of the controller gain perturbations for a near space vehicle with variable sweep wings, which had complicated dynamic characteristics such as strong nonlinearity and coupling. The work space of the system was divided into multiple regions. Then local models were built and local controllers were designed according to the performance index by descriptor system method in each region. The complexity and calculation were decreased. The feasible solution could be obtained more easily and the conservatism was reduced as the limitations on undetermined matrices were relaxed. The system stateswere smooth in the process of switching controllers on the blurred boundaries. At last, the attitude tracking of the near space vehicle during its wing morphing was controlled. Simulation results showed that the control system has good control performance.关键词：near space vehicle;fuzzy systems;robust control;soft switching;linear matrix inequalities
- 2420
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- 0
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- 0
发布时间：2023-11-28 - 摘要：Abstract:Flash temperature on the friction surface has serious impacts on the material properties. Thermal differential equation of asperities on the friction surface of tool was established. The factors influencing the temperature in the asperities were analyzed. Flash temperature analytical model was derived under the condition of dry friction and water jet assisted friction based on the concept of surface contact coefficient. Surface contact coefficient based on uniform distribution model and probability distribution model also were presented. Calculation method of friction coefficient under water jet assisted friction which meet dynamic lubrication condition was determined. Computation and infrared temperature measurement results showed that flash temperature on the tool-rock friction surface is heavily dependent on both the contact friction coefficient and the distribution of asperities their surface. The flash temperature calculations obtained by this model is closer to the experimental measurements than the traditional calculation method.关键词：tool;rock;friction;flash temperature
- 1979
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- 0
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- 2
发布时间：2023-11-28 - 摘要：Abstract:The sliding mode variable structure control for spherical 2-DOF robots was proposed on the basis of kinematical and dynamical models. The mechanism and dynamic model for spherical 2-DOF robot were described. The exponential reaching law for determining additional compensation torque was introduced, and then the control algorithm of spherical 2-DOF robots was established. The influence of applied force, mass, moment of inertia and control parameters on the control accuracy and stability of spherical 2-DOF robots was studied. The example of simulation control for spherical 2-DOF robots was undertaken and the result showed that the method is effective. The oscillation of system can be avoided, and then stability and good robustness of system can be kept and the high accuracy of system can be obtained by choosing appropriate parameters.关键词：spherical 2-DOF robots;sliding mode variable structure control;control simulation
- 2386
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- 36
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- 1
发布时间：2023-11-28 - 摘要：Abstract:In order to study the relationships between the grinding temperature and grinding parameters for constant pressure grinding process, a finite element thermal model was derived and expressed. So the grinding process and quality was improved. Based on the elastic contact analysis in the grinding contact area, the heat distribution of the grinding contact area was studied for the constant pressure belt grinding process.A finite element thermal model was implemented.Thermal phenomena were analyzed in the constant pressure belt grinding process.The experiments of grinding temperature were completed. The results showed that most of grinding heat concentrates in the middle of a wide contact area. Grinding temperature rises faster in the heating stage, and drops slow in the cooling stage. When the grinding area is large, the grinding heat distribution is more average. Experiments of the constant pressure grinding process used two temperature measurement methods of buried outcrop and shallow buried. The grinding temperature was measured on the surface and under the surface in grinding area. Experiment results and simulation results were probably consistent.关键词：belt grinding;constant pressure grinding;finite element analysis;thermal model;temperature field
- 2162
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- 2
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- 2
发布时间：2023-11-28 - 摘要：Abstract:Compressed Natural Gas（CNG）storage well is an important underground container for energy conservation. According to the characteristics of natural gas storage wells in service, a human-computer interaction system for corrosion detection of the CNG wells wall was presented，which consists of an underground test unit and a ground control unit. In the corrosion inspection, the ultrosonic probes and the camera of the system could rise and rotate along with the wall of the CNG well for the acquisition of corrosion information.At the same time，the users could observe，analyze，and record the wall thickness and corrosion images and online control the corrosion inspection of the ultrasonic system and imaging system by the computer on the ground. The detection scheme and working principle of the system were described in detail, especially acquisition and transmission of the ultrosonic data,as well as hardware and software design of both ultrasonic detection subsystem and underground imaging subsystem. The laboratory and field experiments indicated that the system speed and accuracy can meet the test requirements. The system provided a new technique for the corrosion inspection of CNG wells in China.关键词：CNG storage well;corrosion detection;ultrasonic inspection;imaging system;human-computer interaction system
- 2158
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- 26
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- 0
发布时间：2023-11-28 - 摘要：Abstract:In order to study the frequency capture characteristic of wind turbine blade, a wind blade fatigue loading system with an unbalanced rotating shaft was established. With the Lagrange principle, the kinetic model was deduced and the coupling mathematical model was given. The simulation models fully explained the frequency capture process, and revealed the vibration self-synchronous properties. A series of wind blade fatigue loading trials proved that when the drive frequency was 0.48～0.58 Hz ,frequency capture phenomenon would carry out, not only the pendulum would happen, but also the wind turbine blade. When the drive frequency was out of 0.43 ～ 0.65 Hz , frequency capture phenomenon would not carry out and it would fluctuate obviously, and the more far away of the frequency capture points, the more obviously the wind turbine blade frequency and amplitude fluctuated.关键词：fatigue loading system;couple model;frequency capture;self-synchronization
- 2516
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- 4
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- 1
发布时间：2023-11-28
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