最新刊期
卷 46 ， 期 1 ， 2014
- 摘要：Abstract:According to the revelation of American cyberspace security strategy, the main task and challenges of information security in China were described. In terms of strengthening the construction of information security system, trusted computing system framework, the innovation and development of trusted computing and so on, how to use trusted computing for actively build a deep defense system and the innovation of the construction process of this system were elaborated. Finally, some suggestions in defence of sovereignty for cyberspace, independent research and development, network security frame, personnel training and development treads were put forward.关键词：information security;trusted computing;systematic frame;cryptosystem;trusted software base
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发布时间：2023-11-14 - 摘要：Abstract:In order to protect the integrity of operating system kernel files,a method of active protection of kernel data was proposed based on hardware-assisted virtualization.The method recognizes the key points of some registers,code pointers, and function codes,which are often attacked by malicious codes,and maps these points into a protection table,and then it can avoid kernel modification through R/W bit of PTE.At the same time,single step execution is used to legally write data in protected points,and events injection keeps the compatibility of operation system.In addition,continuous pages in the protection table are merged to reduce the size of the protection table and improve the efficiency.Finally,based on this method,a prototype system,called HV_KDAP,was designed and implemented.HV_KDAP can detect 9 kinds of Rootkits,which contain popular techniques in Rootkit,and its overhead is about 12.7%.Moreover,HV_KDAP can also detect the attacking of local privilege escalation exploiting,and be applied to the kernel forensics.关键词：hardwarevirtualization;kerneldataintegrity;Rootkitdetection
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发布时间：2023-11-14 - 摘要：Abstract:A binary code protection system, named MEPE, was developed. In MEPE, some functions were designed to substitute an original instruction with a functional equivalent sequence of instructions. Theoretical analysis showed that the binary code protected with this method would have diverse appearances. After deformation, the protected codes were fragmented into small snippets which were connected through jump instructions. The destination addresses of these jump instructions were managed by an address table, and the table itself was protected by the technique of dynamic encryption and decryption. Based on the analysis of the impact of instructions in loops on execution time , a tuning method was proposed to balance the effect of protection and time overhead. The experimental results and the analyses showed that the tuning method is effective and the protected codes are much more resistant to static and dynamic analysis.关键词：binarycodeobfuscation;iterativetransform;metamorphicengine;diversity
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发布时间：2023-11-14 - 摘要：Abstract:Trusted computing technology has been introduced to build a secure cloud infrastructure, which can improve the dilemma of software security. However, traditional trusted hardware technology does not provide sufficient protection for runtime security for cloud. To solve this problem, a UEFI based dynamic security framework for virtual machine, named VirtinSpector, was proposed. The VirtinSpector treated UEFI firmware as a trusted computing base to acquire a run-time and dynamic security measurement for cloud, providing a dynamic protection out of traditional solution. And a prototype of VirtinSpector for the Xen hypervisor was implemented. The experiments showed that the framework can measure and explore some mainstream attacks of cloud, and its performance payload is restricted whining an acceptable range, without affecting the user’s daily use.关键词：cloudsecurity;trustedcomputing;dynamicmeasurement;virtualization
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发布时间：2023-11-14 - 摘要：Abstract:The difference in structure between virtual desktop system and traditional PC desktop system causes “semantic differences” and efficiency issues, when improving the trust level of the security mechanisms of virtual desktop system.A security virtual machine integrity monitor (SVMIM) was build based on network bootstrap mechanism. SVMIM adopted a hybrid security structure, monitored and controlled the loading process of executable files in virtual desktop systems, which could effectively overcome the shortcomings of “semantic gap” and ensure the trustworthiness of security mechanism. In addition, SVMIM used storage clone technology on network storage to reduce the impact of security mechanism to the system performance. The performance testing on SVMIM prototype and the performance analysis showed its flexibility and advantage.关键词：virtualdesktop;trustedplatform;integritymeasurement;storageclone
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发布时间：2023-11-14 - 摘要：Abstract:By introducing process algebra to analyze system call sequences, a model of description and detection concurrent behavior was presented. Firstly, control flow graphs of system (CFGs) were generated by static binary code analysis. Secondly, by analyzing CFGs, process expressions were generated. Then according to synchronization and mutex of concurrent behaviors, process expressions were rewritten by adding concurrent operation. By extending algebraic properties and algorithms, three basic elements (action, operator and process) were constructed. Finally, the CBDPA model was constructed and concurrent behavior detection methods were given. Experiments demonstrated that this method has linear space-time complexity.关键词：intrusiondetection;concurrentbehavior;staticanalysis;processalgebra;systemcall
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发布时间：2023-11-14 - 摘要：Abstract:JEPG format of images is the most widely used image format in people’s daily life, so the tamper detection on this kind of image has a more important significance.Under the theoretical basis that the tampered area in the compressed JPEG image is equivalent to one compression, the basic principles of one and double compressed JEPG image were researched. The influence of the size of relationship between quality factors Q1and Q2on the histogram of DCT coefficients of the double compressed image was analyzed, and two cases were carried out to find its histogram by the image block DCT coefficients. Then different methods were used to determine whether the image block was compressed once or twice. Finally, image tamper detection algorithm for JPEG image based on DCT coefficients histogram was proposed. Experiments showed that the algorithm is not only low computational complexity, but also has a good detection and location results.关键词：imageforensics;JPEGcompressed;histogram
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发布时间：2023-11-14 - 摘要：Abstract:The influences of inlet concentration,inlet discharge,and bottom outlet aperture on the percentage of clear water in large scale turbid water hydraulic power separation device were investigated based on the experimental study.The results showed that the overflow turbidity influenced by different inlet discharge and bottom outlet aperture is not obviously different when overflow discharge is small. The overflow turbidity will increase with the increase of overflow discharge, and the overflow discharge almost varies directly with inlet discharge. The percentage of clearwater decreases with increase of bottom outlet aperture and inlet concentration, but increases with increase of of device increased under the same inlet concentration. The formula among inlet concentration, diameter and overflow discharge under the same overflow turbidity was proposed.关键词：turbid water hydraulic power separation device;water-sediment separation;experimental study
- 1964
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发布时间：2023-11-14 - 摘要：Abstract:Based on the Shiono and Knight method(SKM) and the secondary flow motion characteristics,the determination of the lateral distribution of depth-averaged velocity in compound channels with one-line vegetation along the edge of the floodplain was proposed.The results showed that there is large disagreement between the computed results and the experiment data,especially in the main channel,when the secondary flow is ignored.When using the traditional divisions of sub-region, the prediction doesn’t largely agree with the experiment data. However,the results showed that by considering the effect of secondary flow,increasing the division of sub-regions and adjusting the available parameters for each region,the proposed method can be capable of predicting the lateral distributions of depth-averaged velocity in this type of channel.关键词：one-line vegetation;compound channels;secondary flow;region division;velocity distribution
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发布时间：2023-11-14 - 摘要：Abstract:Standard turbulence model,combined with Reynolds-averaged Navier-Stokes(RANS) equations,was used to study the turbulence structure of open channel flow through double layer rigid submerged vegetation.The calculated velocity distributions are in good agreement with test data,which proves the validity of the computational method.The velocity distribution,Reynolds stress,and turbulent energy distribution were derived by using the double-averaged(in space and in time) hydrodynamic equations.The vertical velocity distribution was divided into four regions by three turning points.The results showed that Reynolds stress and turbulent energy distribution dramatic increases at each top of the vegetation layer,and maximum value can be found near the taller vegetation.Turbulent dissipation and pressure dissipation play a leading role in the balance of turbulent energy equation.The vortex that generated at the top of vegetation results in a massive mass and momentum transfer through ejection and sweeps.关键词：open channel flow;vegetation;turbulence models;turbulent kinetic energy;double-averaging concept;turbulent energy budget
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发布时间：2023-11-14 - 摘要：Abstract:Scheme decision-making on the construction diversion based on discharge control of the upstream hydropower station is characterized by multi-objective and bilateral conflictive. The combination of the upstream reservoir limited water level and the downstream hydropower station construction diversion standard were used as diversion scheme set. Based on the establishment of comprehensive evaluation index system and with the consideration of the randomness of the hydrological and hydraulic, Monte Carlo method was used to estimate every risk-performance evaluation index. Based on bargaining weight theory, the weight distribution was regarded as focus of conflict and dispute between upstream and downstream hydropower station in the decision process, a bargaining weigh situation was set up, and the improved entropy weight was introduced to establish loss function calculating model. Engineering case analysis showed that this model and method are practical and effective, the weight distribution after negotiation is more balanced and overall, reflects the coordination and solving of conflict, and decision results are reliable.关键词：construction diversion scheme;bargaining weight;discharge control;limited water level;conflict;entropy weight
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发布时间：2023-11-14 - 摘要：Abstract:The temporal distribution of the flood of the hydropower station can be altered when the upstream hydropower station is constructed synchronously, which may lead to the inapplicability of current diversion risk estimation method.Considering the hydrologic uncertainty of diversion system, a system risk analysis model was established based on risk analysis theory. In view of the correlation between the sectional flood of upper hydropower station and interval-basin flood, the Copula function was used to establish the joint probability distribution, and each flood process was simulated in following by using Monte Carlo method. On this basis, the construction flood of hydropower station was calculated by coupling the simulation of the cofferdam-break flood, routing of river flood and composition of regional flood. Subsequently the system risk was obtained. An engineering case was presented to validate the applicability of the proposed model. And the sensitivity analysis of other risk factors was performed. Additionally, the effect of upper hydropower station on diversion risk was investigated.The study could offer a referential basis for establishment of the diversion standard under the construction of cascade power stations.关键词：construction diversion;risk analysis;Copula function;Monte Carlo;cofferdam break;joint probability distribution
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发布时间：2023-11-14 - 摘要：Abstract:In order to find out the influence of embedded walls to aseismic performances of timber structure,Taihe Palace in the Forbidden City was taken as example for analysis by simulation methods. Based on mechanical characteristics of tenon-mortise joint as well as bracket sets, 2 finite element models of Taihe Palace were built with and without embedded walls. By modal analysis, spectrum response and time history analysis, the influence of embedded walls to main modes as well as seismic responses of timber structure under different intensity of earthquakes were studied. Results showed that with the consideration of embedded walls, the basic frequency of Taihe Palace increases. Its vibration at wall locations is inconspicuous. Under 8 degree intensity of earthquakes, its internal forces generally increase, however peak distortion value of its timber structure decreases to avoid overturn, especially under rarely occurred earthquakes.关键词：embedded walls;timber structure;aseismic performances;ancient buildings;Taihe Palace
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发布时间：2023-11-14 - 摘要：Abstract:In order to solve the problem that the cable sag of rigid bracing dome can not be ignored, cables were simulated by catenary cable element.According to Hooke’s law,small strain assuming and deformation compatibility equation,the calculation formula of cable original length was deduced. With any known positive value,the able original length was calculated by dichotomy.For orthogonal cable net,the initial length of cable was compared with known cable original length.The errors are less than 0.16%.And the difference of the calculated cable original lengths is very small for different initial values.According to the form-finding analysis of rigid bracing dome,FEDR method was given to improve the accuracy and reliability of DR method.Solving strategies of form-finding analysis were given.Form-finding analysis program was programmed by FORTRAN language and ANSYS APDL language.Form-finding analysis was done for cable net and the span 71.2 m of rigid bracing dome.Internal forces of rods that were calculated by form finding program were compared with internal forces of rods of finite element analysis software,and the errors are less than 0.42%.关键词：rigid bracing dome;form-finding;FEDR(finite element dynamic relaxation) method;catenary cable element;cables;dichotomy
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发布时间：2023-11-14 - 摘要：Abstract:Cryptography algorithm can be reduced to solve difficult mathematical problems in the standard model (without random oracle assumption). In order to overcome the problem that in the standard model, an existed identity-based partially blind signature (IBPBS) scheme does not prevent a tampering, an enhanced IBPBS scheme was put forward. The original algorithm was improved by the enhanced scheme in two ways. One was to adopt an implicit signature which effectively prevented the entities who were involved in the signature tampering the public information. The other was to avoid using additional supplementary protocols. Based on the standard model of signature mentioned by Paterson et al, a standard model of IBPBS was defined. The enhanced IBPBS scheme was reduced to resolve the CDH problem on an elliptic curve in the standard model, and was proved to achieve the unforgeability and the unlinkability. Comparative analysis showed that the new IBPBS scheme wins enhanced security, lower computational overhead and lower algorithm overhead, and can be used to build secure protocols on electronic cash or electronic voting as well.关键词：identity-based cryptography;partially blind signature;bilinear pairing;standard model
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发布时间：2023-11-14 - 摘要：Abstract:The provably secure public-key cryptosystems in the standard model are more practical, but the provably secure lattice-based proxy signature schemes in the standard model have not been constructed up to now. A new lattice-based proxy signature scheme was constructed by using the Boyen’s preimage sampling algorithm.The proposed proxy signature scheme was proved to satisfy the existential unforgeability against adaptive chosen-message attacks based on the hardness of the small integer solution (SIS) problem in the standard model.Finally,the computational performance of the proposed proxy signature scheme was compared with that of the existing lattice-based proxy signature schemes.The comparative results showed that the proposed proxy signature scheme has higher efficiency.关键词：proxy signature;unforgeability;standard model;lattices
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发布时间：2023-11-14 - 摘要：Abstract:In order to effectively restrain the strong nonlinearity of Doherty power amplifiers (DPA), an augmented general fractional order memory polynomial model (AGFMP) was proposed,and used to design a digital predistortion linearizer. AGFMP model was on the basis of general memory polynomial (GMP), removing a lag and replace even order items by fractional order items to reduce the number of parameters and improve the lianearization ability. The dual-band dual-mode signal （bandwidth up to 25 MHz） and 1000001 CDMA2000 signal were used as test signal, and DPA which designed with the peak power of 51 dBm was utilized as test power amplifier to do the linearize experiment. The experimental results showed that the numbers of the parameters of AGFMP are 30% less than GMP in terms of the strong memory effect and static nonlinear. Moreover, linearization ability of the AGFMP is very close to that of GMP. In addition, it is better than the fractional order memory polynomial for the suppression IMD out of band and in-band.关键词：linearization;digital predistorter(DPD);Doherty power amplifiers;memory polynomial
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发布时间：2023-11-14 - 摘要：Abstract:The performance of modulation classification in single radio is sensitive to signal-to-noise ratio(SNR).A hybrid maximum likelihood(ML) modulation classification algorithm using multiple radios was proposed.All received baseband signals from different radios working on synchronous mode were fused at a fusion center to make the global classification decision by using the hybrid ML.Due to the spatial diversity,the performance of modulation classification in low SNR regimes was improved.The joint likelihood function contained multiple dimensional unknown parameters.In order to alleviate the computational complexity associated with the ML estimates of the unknown parameters,the expectation-maximization(EM) algorithm was adopted, in which the constellation symbols were represented unobserved data.The proposed algorithm completed the classification of BPSK,QPSK,8PSK and 16QAM,as well as the unknown parameters estimation. Compared to the algorithm based on moments, the unknown parameters estimate based on EM estimation provided superior performance in precision.The simulation results showed that when the number of radios is four and SNR of signal is more than -2 dB, the average probability of correct classification is more than 95%.关键词：modulation classification;hybrid maximum likelihood;maximum likelihood estimation;expectation maximization algorithm
- 2002
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发布时间：2023-11-14 - 摘要：Abstract:A joint sparsity and sparse channel estimation algorithm based on CoSaMP was proposed.A new kind of sparsity vector substitute was proposed in the new algorithm,which can remarkably reduce the overhead of training sequence and increase the channel capacity.Besides,a new sparsity estimation method was provided for the improved algorithm. Simulation results showed that the new proxy of sparse signal has obvious advantages in both sparsity and channel estimation.The performance of joint sparsity and sparse channel estimation algorithm is better than mCoSaMP algorithm.关键词：Compressed sensing;CoSaMP;sparse channel estimation;sparsity estimation;multipath
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发布时间：2023-11-14 - 摘要：Abstract:To study the Internet public opinion evolution, an analysis method taking the parameters’ increment of the network and the Agent as the study object， which was based on social network analysis (SNA), was proposed. By the quantitative analyses of SNA properties, the general evolution rules of the incident in the Internet public opinion were revealed. The information for decision of guiding the public opinion was provided according to the rule. The method was verified with the records of an incident in Tianya BBS forum and the result showed that the study is practically useful.关键词：Internet public opinion;SNA;public opinion evolution;evolution characteristics
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发布时间：2023-11-14 - 摘要：Abstract:In order to treat the problem that the effect of traditional speech enhancement methods is not satisfactory under the condition of non-stationary noise environment and low SNR(signal to noise ratio), an algorithm of speech enhancement based on probabilistic latent component analysis was proposed. By analyzing and introducing probabilistic latent component analysis, phonic spectrogram was explicitly modeled as a mixture of marginal distribution products and noise was described by a dictionary of marginals. The estimation of the most appropriate marginal distributions was performed using expectation-maximization algorithm, which is used selectively to reconstruct the signal, separating it from noise, and the goal of speech enhancement was achieved. Simulation results demonstrated that the proposed algorithm is more effective in terms of reducing background noise, improving SNR and decreasing speech distortion than traditional speech enhancement algorithms.关键词：latent variable;PLCA(probabilistic latent component analysis);EM（expectation-maximization） algorithm;speech enhancement
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发布时间：2023-11-14 - 摘要：Abstract:To investigate the dynamics of memory chaotic systems, a simple three-dimensional autonomous chaotic system containing a generalized memory element was proposed. The memory effects and chaotic characteristics of the memory chaotic system were analyzed, and circuit design and corresponding experimental verifications were performed. Based on the analysis of the equilibrium point and stability, the dynamical behaviors of the memory chaotic system with the variations of the parameter were discussed. The results indicated that, different from memristor based chaotic circuits, the new proposed system has unique equilibrium point, its dynamical behaviors only depend on the system control parameter and have complex nonlinear phenomena, such as bifurcation, chaos, and intermittency chaos.关键词：memory element;memory chaotic system;dynamics;circuit realization
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发布时间：2023-11-14 - 摘要：Abstract:Based on the effects of magnetization of permanent magnet(PM) on the magnetic field distribution, an analytical method was presented to solve the slotted air-gap of a surface PM contra-rotating motor(CRM) with three common types of magnetization field patterns, Radial, Parallel and Halbach magnetization. This analytical method is very effective for forecasting the magnetic field distribution and in agreement with the results of finite-element simulations. According to the analysis of the differences between the fields of the machine with different magnetizations, the accurate 2D finite-element analysis model was established in both internal and external rotor CRM. The testing and simulation results showed that the external rotor CRM with radial magnetization has a greater flux density and trapezoidal wave which is suitable for brushless DC motor, and the internal rotor CRM with parallel magnetization can improve the sinusoidal waveform distribution and has a greater flux density. The air-gap flux density of Halbach magnet motor has the most sinusoidal waveform distribution which demonstrates that Halbach magnet is suitable for multi-polar PM motor.关键词：radial magnetization;parallel magnetization;halbach magnetization;contra-rotating PM motor;air-gap flux density
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发布时间：2023-11-14 - 摘要：Abstract:In order to separate PM2.5 from air efficiently, PM2.5 separating by the surface of falling liquid cylinders from the aerosol contaminated fluid was studied experimentally and numerically.Titanium dioxide whose particle size was 0.3 μm was used as the experimental particles.An Euler-Lagrange model was employed to describe the gas-liquid cross flow and the trap of particles.The influencing factors of purifying process, such as thermophoresis force caused by temperature difference between gas and liquid, gas and liquid flow rate were investigated.The results showed that when liquid temperature kept 20 ℃, the PM2.5trap efficiencies were 6.8%~20% in a four-row liquid columns array with a temperature difference of 0~30 ℃ in the experiments.The experimental data showed a similar trend with the numerical simulation results.关键词：PM2.5;gas-liquid cross flow;numerical simulation;thermophoresis force
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发布时间：2023-11-14 - 摘要：Abstract:The kinetics of Ni (Ⅱ) extraction by dinonylnaphthalene sulfonic acid (DNNSA) in kerosene from wastewater was investigated using a Lewis Cell. The different parameters affecting the extraction rate such as stirring speed, interfacial area，DNNSA concentration, Ni (Ⅱ) concentration and temperature were separately studied. When stirring speed was more than 200 r/min, there was a chemical reaction kinetic region where the extraction rate of Ni (Ⅱ) was independent of the stirring speed. The experimental results demonstrated that the rate of Ni (Ⅱ) extraction was apparently proportional to the interfacial area between the aqueous phase and the organic phase,indicated that the rate of Ni (Ⅱ) extraction was controlled by a chemical reaction at the interface rather than in the bulk phase. In the kinetic region, the rate of Ni (Ⅱ) extraction was first order for DNNSA, while it zero order with respect to the Ni (Ⅱ). The extraction rate also increased with the increase of extraction temperature. The activation energy of extraction was calculated to be 31.56 kJ/mol and the kinetic equation of Ni (Ⅱ) extraction from wastewater was put forward. The mechanism of Ni (Ⅱ) extraction was proposed.关键词：kinetics;extraction;reverse micelles;Nickel;wastewater;dinonylnaphthalene sulfonic acid（DNNSA）
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发布时间：2023-11-14 - 摘要：Abstract:Sulfur could be removed effectively in the process of copper slags smelting chlorination,which is beneficial to the recovery of iron from copper slags. With the help of the thermodynamic calculation,X-ray diffraction analysis and inductively coupled plasma analysis, the sulfur behavior characteristic in the process of copper slags smelting chlorination was studied.In a certain range, the sulfur removal rate from copper slags was improved with the increase of the holding temperature,residence time and O2 velocity. However,SO2 was oxidized by the pumped O2and then reacted with CaO forming CaSO4when the holding temperature was 1 723 K,which caused the sulfur content increase. When O2 velocity was increased to 0.5 L/min,the reaction interface of SO2 and O2 nearly coincided with the molten slag surface,and then the CaSO4mode was formed through the reaction of SO2,O2and CaO.It caused the sulfur removal rate being decreased.The sulfur content of the copper slag was decreased from 0.52% to 0.005 11% treated in the condition of holding temperature of 1 573 K,residence time of 25 minutes,O2 velocity of 0.4 L/min,and CaCl2 addition amounts of 0.1(the mass ratio of CaCl2 and copper slags). Sulfur can be removed in the chlorination of copper slags.关键词：copper slags;smelting chlorination;desulfurization;waste utilization
- 1901
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发布时间：2023-11-14 - 摘要：Abstract:Using the steel as electrode, nine cement mortar specimens with or without crack were designed to be tested for the peak-to-peak values of voltage signal, as well as phase difference, based on AC impedance spectroscopy testing technology. Sine wave pulses with different frequency were used as excitation signal during testing. The dimension of crack designed in the cement mortar varied to investigate crack dimension effect on electrochemical impedance properties of the specimens. The impedance amplitude for each sample was figured out, and the fitted curve equation for the relationship between impedance modulus and frequency of each group was built with the least square method. Results showed that the impedance spectrums of specimens with the same crack configuration are similar to each other, so impedance spectrum is the intrinsic property of cement mortar.The impedance amplitude for the specimens with or without crack is quite different from one to another.A mathematics model was proposed to present the relationship between impedance characteristics and crack geometry scale.关键词：cement mortar;AC impedance spectroscopy;impedance amplitude;crack;detection
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发布时间：2023-11-14 - 摘要：Abstract:Since the dispersed phase uniformity of polymer modified asphalt plays a great role in the evaluation of modified asphalt compatibility,fluorescence microscopic images of styrene-butadiene-styrene block copolymer (SBS) modified asphalt were preprocessed in digitization.Then characteristic parameters of the dispersed phase in microscopic images were extracted through professional image processing and analysis software.Morishita index method,Poisson comparison method,Gini coefficient method and Christiansen coefficient method were adopted to estimate the dispersible uniformity of polymer modified particles.The comparison of the accuracy and rationality of several evaluation methods showed that Morishita index deviation and Christiansen coefficient are effective for the quantitative evaluation of polymer modified asphalt phase distribution uniformity.关键词：SBS modified asphalt;digital images;preprocess;phase uniformity;evaluation
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发布时间：2023-11-14 - 摘要：Abstract:The effects of l/d and Vcof polypropylene fiber on the working performance,mechanical behavior and water absorption of model-gypsum were presented.The result showed that when the l/d≤600 and Vc≤0.88 kg/m3,fiber had little influence on the fluidity of gypsum slurry,and the setting time was slightly shortened by the increasing of Vc and l/dof fiber.The mechanical properties of fiber-gypsum composite were significantly influenced by the change of l/dand Vc.Coefficient of softness and flexural toughness grew stronger with the increase of l/d and Vc.Flexural strength decreased as parabola with the increase of l/d.The best parameter of polypropylene fiber was l/d=400 and Vc=0.88 kg/m3.SEM indicated that polypropylene takes advantages on the improvement of model-gypsum properties.The most influence factors to composite are interface bounding of fiber-gypsum and the degree of scatter of fiber in the compound.关键词：model-gypsum;polypropylene fiber;working ability;mechanical action;water absorption;action mechanism
- 1870
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发布时间：2023-11-14 - 摘要：Abstract:Water is one of the main factors that influence asphalt aging on long-term use of the process of asphalt pavement.In order to study the impacts of the water work phase and the amount of water on performances of the rubber asphalt aging,taking rubber asphalt and TOR rubber asphalt for example,the influence of different water aging methods on softening point,viscosity,fatigue factor,creep stiffness and creep rate was studied through changing the water work phase and the amount of water.The test results showed that the way of the pressure aging with water for the beginning one third of standard time (400 min) and the pressure aging without water for the remaining two thirds of the time was selected for the most feasible.Comparison of pressure aging test and water pressure aging test,the existence of water can promote the thermal oxygen aging of rubber asphalt.With the increase of water,high temperature stability of TOR rubber asphalt is declined,anti-fatigue cracking performance and low temperature performance of TOR rubber asphalt is declined and asphalt aging intensifies.关键词：rubber asphalt;water aging;the amount of water;high temperature stability;fatigue cracking;low temperature performance
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发布时间：2023-11-14 - 摘要：Abstract:An automatic definition method was proposed for adding the datum to assemble similar components’models,to solve the automatic assembly of models from different sources and with different processes of modeling under the distributed resources environment.The core of this method was achieved the geometries involved in assembly shared by the similar components’models and set criteria by them.The assembling geometries were found by traversing the models,and then the datums were added by them automatically.After that,the added datum was unified naming by traversing the feature tree of the model.Then,the automatic assembly of models was realized using the added datums.Meanwhile,took two gears with different processes of modeling and different structures as an example,the definition principle and process of assembly datum were studied.The features of six similar components in the single-stage cylindrical gear reducer were analyzed,and the corresponding programs were developed to accomplish the automatic definition of datum of the components in the single-stage cylindrical gear reducer and then they were assembled automatically.The result showed that the automatic definition of the datum could be completed effectively,without the limited of the modeling process and non-main structures.This method was feasible and efficient,which can provide support for knowledge fusion of the mechanical system under distributed resources environment.关键词：distributed resources environment;similar components;assembly datum;automatic definition;automatic assembly
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发布时间：2023-11-14 - 摘要：Abstract:In order to investigate the effects of multiple coupling parameters on multi-cylinder hydraulic parallel drive system,a dynamic mathematic model of drive system for hydraulic press was established based on analytic methodology.The influences of system parameters of viscous damping coefficient,elastic modulus,mass of moving beam,and load stiffness on dynamic behaviors of hydraulic drive system were studied using variable step length Runge-Kutta method.Results showed that the magnitude of transient oscillation is diminished by increasing viscous damping coefficient or decreasing mass of moving beam.System dynamic response can be accelerated provided that the elastic modulus is increased or the pipe diameter is decreased.The pressure of major cylinder and system steady-state error rise with the increase of load stiffness. Furthermore,active synchronization control is not recommended when the machine is in fast approaching period.The stability of the system must be emphasized if the hydraulic press is driven under on-load or the forged piece is in plastic deformation stage,while tracking accuracy is a key issue when the workpiece is under elastic stage.The research results could provide theoretical basis for the design of system and parameter selection.关键词：dynamic response;simulation;mathematical model;hydraulic press;drive system
- 2008
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发布时间：2023-11-14 - 摘要：Abstract:Micro laval nozzle has been widely used in such areas as micro propulsion system, supersonic air-jet pulverization,laser cutting,etc.The gas flow characteristics for micro nozzles with different section shapes and different divergent section lengths were analyzed with the aid of computational fluid dynamics(CFD) simulation technology, which helped to determine the rules of nozzle type selection and the optimum divergent section length. The simulation results indicated that the exit velocity of two-dimensional axisymmetric nozzle is larger than that of rectangular section one, which shows that the two-dimensional axisymmetric type is recommended when the nozzle is in millimeter level. The flow fields of the two-dimensional axisymmetric nozzles with different divergent section lengths were investigated through the comparison of their exit velocities, thrust forces and efficiencies, which presents that the optimal divergent length is 3 mm in this research. The proposed simulation method can be applied to the selection of other nozzle parameters and the optimization of length determination, which can help to reduce the difficulty of manufacturability of micro-nozzle with excellent performance.关键词：micro nozzle;computational fluid dynamics(CFD);propulsive performance;manufacturability
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发布时间：2023-11-14
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