最新刊期
卷 50 ， 期 1 ， 2018
- 摘要：Nowadays,blood purification technology is required to improve the life qualities and work abilities of the patients.Herein,To meet the demands of clinic and industry,and the desires of the advanced blood purification materials and equipments,the close cooperations among industry,study,research and medicine,and the systematical connections among innovation,industry and clinical practise,four objectives will be achieved:1)localization of polyethersulfone raw material,spinning production line,dialysis membrane and blood dialyzer:research and development of miniature blood dialyzer and filter;2)research and development of efficient specific antibody,β2-microglobulin and endotoxin adsorbents,which can match with the individual treatment of the patients;3)research and development of wearable artificial kidney;4)establishment of evaluation standards and real-time communication system among industry,study,research and medicine.Correspondingly,the research contents of the project are as following:1)improve the property stability of polyethersulfone product via new purification technology;improve the biocompatibility of hollow fiber membrane;research and establish spinning production line;research and produce polyethersulfone raw material,anticoagulant high flux dialysis membrane and dialyzer;2)accurately compound efficient specific adsorbents and biomimetic molecular brush;produce specific antibody in quantity;research and develop efficient specific β2-microglobulin and endotoxin adsorbents;establish the adsorbent production line;3)overcome the technical difficulty of miniature pump and monitoring device fabrication and dialysate regeneration;research and develop wearable artificial kidney;4)build a bridge between clinical applications and scientific research of biomaterials and medical instruments;establish real-time communication system among industry,study,research and medicine;establish platform of clinical evaluation.We believe that by this project research,the domestic blood purification technology,including the material production and method improvement,will make significant advance and breakthrough;the suffering will be reduced and the harms of uremia to humanity and society will be prevented basically.关键词：Blood purification;anticoagulant high flux hemodialyzer;efficient and specific hemoditoxifier;wearable artificial kidney
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发布时间：2024-01-10 - 摘要：The vulnerability in software and system is an important resource for national cyberspace security.By now,some key techniques of Chinese critical infrastructures and significant information system are controlled by other countries.The ubiquity of vulnerabilities in software and system cannot be eliminated in a short while.Therefore,it is necessary to carry outin-depth,large-scale,intelligent vulnerability mining research.With the popularization of new technologies and applications in the fields of mobile Internet,industrial control network and Internet of Things,the existing technical architecture of vulnerability mining and analysis cannot meet the new requirements.Besides,China’s vulnerability research teams are relatively fragmented and collaboration mechanisms at the national level have not yet been established,which makes it difficult to support the country’s control of vulnerability resources.In view of the current situation of software and system vulnerability research,four major problems are urgently needed to be solvedin order to enhance the country’s ability to control the strategic resources of vulnerabilities:1)The weak intelligence of vulnerability mining;2)The low monitoring accuracy of large flow;3)The difficulty in verifying hazard assessment;4)The lacking in large-scale collaborative ability.Focusing on the four major problems above,this paper carries out the following five aspects of research.1)Intelligent vulnerability mining methods and key techniques in software and system,including the construction method of fuzzy inference experience base,the genetic map based method of vulnerability mining,optimization problem guided by intelligence,the strategy-based method of vulnerability identification.2)The techniques to parse vulnerabilities in software and system and judge whether they could be exploited,including techniques of analyzing the causes of vulnerabilities,construction techniques of the abnormal path,analytical techniques of homology vulnerabilities,techniques on the exploitability determination of vulnerabilities,the construction of multi-scene vulnerability analysis platform.3)The network flow-based analytical techniques to parse and detect vulnerabilities,including:The techniques to detect the vulnerability attack samples with dynamic and static methods,development of the prototype system to automatically detect vulnerabilities in software,the techniques to detect and identify the suspected network attacks,automatic analysis and precise verification of the network attacks samples,the attack-oriented platform to offer the vulnerability detection and comprehensive service.4)The techniques to evaluate and verify the vulnerability damages,including:The dynamic hardware virtualization-based techniques to parse stains,the techniques to automatically exploit vulnerabilities,development of the virtual environment-based system to automatically verify the vulnerabilities,the system and algorithm to evaluate the damages of vulnerabilities.5)The study and application of large-scale cooperative vulnerabilities mining techniques,including:The multi-tasking multi-engine adaptive large-scale vulnerability mining techniques;the multi-dimensional multi-tasking intelligent collaborative techniques;the open and collaborative techniques to reuse knowledge;the study of the multi-computing environments-oriented integration platform for large-scale collaborative vulnerability mining;vulnerability mining,analysis and availability evaluation techniques under large-scale collaborative conditions;the verification of the large-scale collaborative vulnerability mining integration platform application in typical industries.The project realized the innovation in the following five aspects with the research mentioned above:1)The fixed reconstruction of gene mapping,in detail,the gene mapping construction and knowledge reuse-based intelligent vulnerability mining techniques;2)Multi-source analysis and polymorphism utilization,in detail,the multi-source vulnerability analysis-based techniques to evaluate availability of polymorphism;3)Dynamic and static intention deduction,in detail,the data driven and behavior recognition-based techniques to detect attacks in the large-flow;4)Status slice overlay recurrence,in detail,the techniques to build the living vulnerability library;5) Iterative adaptation of intelligent connection,in detail,the multi-tasking multi-engine adaptive large-scale vulnerability mining techniques.Finally,a large-scale collaborative platform,that integrating vulnerability mining,analysis,monitoring,evaluation and verification,is build.It forms an ecosystem with knowledge reuse,intelligent connectivity and open collaboration,which provides technical support for our country to find out the security circumstances of cyberspace and reverse the passive situation of the game of attack-and-defense.关键词：vulnerabilities in software and system;intelligence mining;expolitable inference;safety monitoring of large flow;vulnerability assessment;large-scale collaboration
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发布时间：2024-01-10 - 摘要：The Guanzhou reach,located in the middle Yangtze River,is a typical anabranching channel with its mainstream alternating between the two branches within a year.After the impoundment of Three Gorges Reservoir (TGR),the channel of Guanzhou changed significantly.The influence of channel adjustment of Guanzhou on the flow diversion at Songzikou became obvious and has been paid more and more attention.Based on the topographical data in the period 2002—2013 and the hydrological data in 1984—2017,the channel evolution of the Guanzhou reach after the impoundment of TGR was analyzed.Then the impact of upstream channel adjustment on flow diversion at Songzikou was studied from the following three aspects: the channel erosion and deposition,the development of left branch,and the duration of the left branch staying as main channel.The results show that,after the impoundment of TGR,the Guanzhou Reach was eroded continuously,and about 90% of the total channel scouring occurred in the low-water channel.The scour pattern changed from purely downward erosion to left convex bank erosion along with left branch erosion due to finer river bed materials; now the thalweg elevation in left branch is lower than that in right branch which was opposite before.The status of the right branch being the main channel was weakened in dry season.The critical flow rate for the mainstream alternation was decreased.When the incoming flow was less than 20 000 m3/s,the flow diversion ratio at Songzikou was reduced,while the reducing trend was weakened gradually with the channel developing into an equilibrium state.The development of the left branch will increase the diversion ratio at Songzikou in larger discharge,and the longer the duration of the larger discharge,that is,the duration being the main channel for the left branch,the greater the annual averaged flow diversion ratio at Songzikou.It’s worth noting that,the over-development of the left branch may cause the mainstream of Guanzhou Reach to cease alternating between two branches within a year,and to stay in the left branch.The field monitoring should be strengthened in the future and proper engineering measures taken if needed.关键词：flow diversion at Songzikou;channel adjustments;Three Gorges Reservoir;alternation within a year;Guanzhou Reach
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发布时间：2024-01-10 - 摘要：In the process of upstream propagation,the tidal bore with strong aeration has a great impact on water circulation,sediment transportation,pollutant diffusion,and ecological balance in the estuary.Hence,the aeration characteristics of a tidal bore is a particularly important research subject.The tide bore was generated in a rectangle glass flume,and the status of aeration was recorded and observed by high-speed camera.Through observation and statistical analysis of the crushing process of aeration of tidal bore in the flume,the response relationship between the status of aeration and the tidal bore Froude number was found to be consistent with that of the tidal bore happened in the estuary.The crushing process of tidal bore aeration experienced four stages repeatedly,then a series of bubble clouds was formed at the front of tidal bore.The aeration form had a close relationship with the velocity of ebb flow and the height of tidal bore.For the further study of aeration characteristics of tidal bore,the aeration length of tidal bore was defined,and it was related to the height and the propagation velocity of tidal bore and the depth and velocity of the ebb flow.Using the dimensional analysis to determine the function relationship between the relative aeration length of the tidal bore and the Froude number & the intensity of tidal bore,an experimental formula was obtained to calculate the aeration length of tidal bore by nonlinear regression analysis.Eventually,the applicability of the empirical formula was verified by comparing several sets of observation values in Yanguan Station of the Qiantang River to the calculated values using the empirical formulas.关键词：tidal bore;aeration of tidal bore;aeration length of tidal bore;intensity of tidal bore;Froude number of tidal bore
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发布时间：2024-01-10 - 摘要：Stepped boulder arrays induced by flash flood are common riverbed forms in mountainous areas,and they can greatly affect the river flow structure and bed transformation.Although boulder arrays increase flow and river erosion resistance,they also stabilize river boundary and change the ability of the water to carry sediment,and therefore restrict the evolution of river bed.Based on the field investigation of typical riverbed and open channel experiments,the influence of stepped boulder array on flow structure with shallow depth conditions has been analyzed and discussed.All of the experiments were conducted on the fixed bed made of 4.0 cm plastic ball as model boulders.A side-view acoustic Doppler velocimeter (ADV) was equipped to record rapidly responding flow movement so as to analyze the flow turbulence.Our study showed that velocity and turbulence intensity were greatly affected by different spacing of stepped boulder arrays.Within the stepped boulder arrays,the turbulence intensities in u,v and w directions increased first and then decreased and their peak points of the turbulence intensities in v and w directions were located at boulder downstream 0<y/h≤0.2.The scale of far-wake region,which is mainly concentrated at x<2D area in the longitudinal and h=1D in the vertical impact range of boulder,was positively correlated with the boulder size.The boulders arrays had a "uniform" effect on turbulence near the bed,and the increase of the spacing of stepped boulder arrays significantly reduced the turbulence intensity near bed.关键词：mountain river;boulder array;velocity distribution;turbulent intensity
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发布时间：2024-01-10 - 摘要：The rock block can be fragmented readily during rock-fall or rock-avalanche.This process produces many highly energetic and randomly sized rock fragments which can be very hazardous to human lives and lifeline facilities nearby.However,the upon impact of rock fragmentation is usually not considered in the analysis of rockfall kinematics,because the trajectories and destructive power of rock fragments are very difficult to predict.Therefore,the investigation of the rock fragmentation mechanism plays a critical role in the analysis of rockfall kinematics.In this paper,the discrete element method was applied to establish a numerical model of rock block impacting on a rigid ground.The spherical rock block was represented as an assembly of densely packed particles.The rigid ground was represented by a layer of fixed particles.The relationship between the impact loading rate and the fragmentation characteristic were analyzed.The results indicated that the instantaneous impact can lead to a lot of fractures generated in the rock block.The nucleation of these fractures breaks the rock block into fragments.As the impact loading rate increases,the fragmentation intensity and number of fragments increase,while the fragment size decreases.The number of fragments and the maximum fragment size both exhibit a power law dependence on the impact loading rate.The fragments size distribution could be well fitted by the three parameters generalized extreme value distribution function.关键词：rockfall;discrete element method;loading rate;fragmentation;size distribution
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发布时间：2024-01-10 - 摘要：In order to effectively reduce the damage of transmission facilities such as substation and ensure the safety of transmission engineering,four representative rock slopes were selected as the research object.The propagation characteristics of ground motions with different lithology,topography and geology were studied.The amplification coefficients of slope under different terrain were preliminarily determined and compared with the seismic design codes (GB 50011—2010) (later referred to as the code) and the following understanding and conclusions were gotten.The sorting of the magnification coefficient calculated for the homogeneous and heterogeneous types is basically as upper soft lower hard rock > soft rock> medium hard rock > upper medium hard lower hard rock > hard rock.For covering soil layer rock slope,different thickness of the soil layer has a great impact on the magnification factor.The magnification coefficient of the weak intercalation rock slope is consistent with that of the homogeneous rock slope,but the former is basically larger than the latter,and is basically within 0.1,indicating that when the thickness of the weak interlayer is relatively small,the effect of weak interlayer on the magnification factor is independent of slope height,slope and lithology.The effect of different thickness of weak interlayer of the slope on the amplification factor is basically like a half sine form.By analyzing the Fourier spectrum of the top and the foot of the slope,it was found that the high slope has obvious amplification effect,while the low slope is not obvious.The Fourier amplitude of soft rock is obviously larger than that of medium hard rock and hard rock,and hard rock and medium hard rock are basically the same.Therefore,from the spectral characteristics,it can also explain the different lithology can lead to different site effects and the higher the slope,this difference is even more obvious.At medium and low height (below 80 m),the Fourier amplitude is almost constant with respect to the slope,and the maximum amplitude of the slow slope is substantially the same in this height range,and for high slope,it will be different.The steeper slope,the larger the amplitude,basically showing a linear increase trend.For the heterogeneous layers slope,the slope is different,the Fourier spectrum is not the same,and the main frequency band is not the same,which is different from the homogeneous slope; The Fourier spectra of the weak sandwich rock slope are basically the same as the Fourier spectra of the corresponding homogeneous slope.The Fourier spectrum of different interlayer thickness is basically the same,which indicates that the effect of interlayer thickness on Fourier spectrum is small and basically negligible.Compared with the specification,the magnification coefficient of homogeneous slope with the soft rock type is basically the same.For the medium hard rock,hard rock and upper medium hard lower hard rock types of slope,magnification coefficient is less than the standard value,indicating that the provision restrictions for the slope height and slope by specification are relatively small,and should increase the slope height and slope requirements.关键词：different topographic and geologic conditions;site effect;spectrum characteristics;seismic design code;rock slope
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发布时间：2024-01-10 -
Optimal Support in Soft Rock Tunnel Based on the Unified Strength Theory and Steady Creep Guideline AI导读
摘要：The optimal support of tunnel can achieve the best supporting state with both safety and economy as suggested by New Austrian Tunnelling Method (NATM).Theoretical solutions for the optimal support pressure of tunnel and the allowable maximum displacement of surrounding rock under two steady creep guidelines are presented on the basis of the controlling principle of soft rock rheology.The unified strength theory is adopted to reasonably consider the influences of both the intermediate principal stress and the chosen of strength criteria.Then,the applicable conditions and application steps about the proposed solutions are provided.Finally,these theoretical solutions are validated by two engineering cases,and the influences of a wide range of variation of parameters like intermediate principal stress,long-term strength of rock as well as shear strength of surrounding rock on the optimal support pressure of tunnel and the allowable maximum displacement of surrounding rock have been discussed.It is found that the obtained theoretical solutions in this study have good comparability and can degenerate into the available results from the literature,the expressions of the obtained theoretical solutions are concise,and the parameters involved are easy to been determined.Thus the proposed theoretical solutions have a good prospect of engineering applications.Generally speaking,the evolution of the optimal parameters of tunnel support under two steady creep guidelines is in good agreement with little differences,however the result according to the third invariant guideline of deviator stress tensor has broader applicable scope.The influences of intermediate principal stress and choosing strength criteria on the optimal parameters of tunnel support are significant,and the result of Mohr-Coulomb criterion is too conservative to make use of potential rock strength.Long-term strength of rock is a key parameter for the optimal design of tunnel support,and the cohesion of surrounding rock has a more noticeable influence than that of its internal friction angle.The variability of rock strength parameters shoud be taken into full account.The obtained results can provide a theoretical guidance to the design and construction of the optimal support in soft rock tunnel.关键词：soft rock tunnel;unified strength theory;steady creep guideline;optimal support- 2465
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发布时间：2024-01-10 - 摘要：The measurement of geostress of deep rock masses is of great significance to rock and soil mechanics and engineering geology.Traditional geostress testing process is complicated and more difficult to perform in downhole.Hence,a testing method,which can rapidly,effectively and accurately determine geostress direction was proposed based on panoramic stereo-borehole imaging technology and borehole morphological characteristics in stress state.The principle of this method is to obtain two stereopair images of the same position of borehole wall in different visual angles with the panoramic borehole imaging technology based on double-conic mirror image-forming principle,and construct the aperture variation values of the borehole wall based on the image pairs,to describe the geometric characteristics of the borehole wall.Under the action of geostress,a circular borehole will turn elliptic,thus the standard equation of ellipse is given out,and the correlation between the morphological parameter of ellipse and geostress is established.Besides,the geometric shape (ellipse) of the borehole wall is obtained in combination with the panoramic stereo borehole imaging technology,and the direction of geostress is solved on the intersection angle of the ellipse macroaxis and x axis.It is verified by a simulation model and the testing results show that the measured geometric shape of the model roughly agrees with the actual direction of borehole.In this method,the latest borehole imaging technology is applied,and the ground stress direction is obtained based on borehole morphology without consideration of the physical property parameters of rock mass,which provides a new approach and testing method for the measurement of deep rock mass geostress.关键词：geostress direction;stereopair imaging;elliptic equation;borehole shape;aperture variation
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发布时间：2024-01-10 - 摘要：Based on the investigation of the operation conditions for different wastewater treatment plants around the world,it is found that the distribution of the air bubbles in the aeration tank is not uniform in temporal and spatial scale,which in turn results in the difference of oxygen transfer.The effluent quality and the operation cost would be affected accordingly.The experiments were conducted in a plug-flow aeration tank model in which the oxygen transfer in clean water was measured.The high speed camera and digital image processing technique was employed to investigate the shape and variation characteristics of air bubble cloud.The air flow ratios of a single diffuser disc are 0.25 m3/h,0.5 m3/h,1.0 m3/h and 2.0 m3/h,respectively.The results showed that the ratio of axis length to water depth is around 1.03 to 1.30,with the identical shape of flow velocity distribution.The cloud axis length and bubble residence time increased first and then decreased as the air flow rate increased.The air bubble cloud shape became irregular and the shape variation frequency was high as the increasing of air flow ratios.For multiple aeration disc design,the bubble plume upstream had an effect on the shape of bubble plume downstream,and the width of bubble plume was almost the same in both air flow direction and lateral direction.The average width of bubble plume was greater at the position of 0.8h0 and 0.5h0 than that at 0.2h0.The width of bubble plume at different water depths varied with time,and the trend was more significant at 0.8h0.For air discharge rate 0.25 m3/h,1.0 m3/h and 2.0 m3/h,the average width of bubble plume was 1.0~1.5,1.6~2.5 and 1.75~3.5 times of the diameter of the aeration disc,respectively.There are mainly three regions of bubble plume in plug-flow aeration tank,namely,the adjustment region at the bottom area,the free surface region and the turbulent diffusion region at the middle,with different bubble mechanics and kinematics characteristics.With the increase of air flow discharge,the residence time of air bubble increased and then decreased with the diffusion width.These characteristics of bubble plume may provide theoretical support on the numerical simulation of bubble mechanics and kinematics in plug-flow aeration tank.关键词：aeration tank;air bubble cloud;axis length;diffusion characteristic
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发布时间：2024-01-10 - 摘要：The Xiaolangdi Reservoir is characterized by its many tributaries.The storage capacity of tributaries accounts for 41.3% of the total capacity of the reservoir,and the flow exchanges between the main channel and tributaries have a great impact on the flood routing and sedimentation distribution.Therefore,a one-dimensional model for open channel flows and turbidity currents with the effect of flow exchanges with tributaries was proposed in this study.A composite method to calculate the flow exchanges between the main channel and tributaries was presented.For flow exchange caused by the water level variation of the main channel,the storage cell algorithm was implemented in the numerical model based on the finite volume method.For turbidity current intrusion into tributaries,an improved formula to estimate the intrusion discharge was introduced,with the effect of bed slope of the tributary being considered.These two methods were integrated with an existing coupled model of open channel flow and turbidity current to simulate the whole process of flow-sediment regulation in the Xiaolangdi reservoir in 2006.Successful predictions were obtained,including the processes of water level falling,bed erosion in the upstream reach,and formation and development of the artificially created turbidity current.The simulations indicate that the flow exchange processes have great impacts on the amount of released sediment during an event of water-sediment regulation.As compared to the simulation methods neglecting or oversimplifying the flow exchanges,the proposed model produces a better prediction to the sediment delivery ratio,which demonstrates its potential to help design the scheduling scheme for water-sediment regulation.关键词：turbidity current;water-sediment regulation;flow exchange;Xiaolangdi Reservoir
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发布时间：2024-01-10 - 摘要：In order to determine the shear strength of rock joint,the triaxial tests for specimens with irregular and unfilled rock joints were conducted using the rock mechanics test system (MTS815).A series of maximum axial failure stresses under different confining pressures applied to the same specimen was continuously acquired on MTS and the normal and shear stresses of joint surface under different confining pressures were obtained through the theory of elastic mechanics combined with the maximum axial failure stresses.In addition to deriving the cohesive force and friction angle with the test results of each specimen by linear Mohr-Coulomb criterion fitting,the curve-fitting tool in MATLAB was employed to treat the linear Mohr-Coulomb criterion fitting,the power fitting,and the nonlinear Barton criterion fitting.The comparison of the three fitting methods showed that when it comes to determine the shear strength of rock joints,the fitting of linear Mohr-Coulomb criterion is obviously worse than the power function fitting and Barton formula fitting,especially under the low normal stress conditions.Linear Mohr-Coulomb criterion fitting will overestimate the shear strength of rock joints.The curves of Power function fitting and Barton formula fitting are nearly overlap,as well as both of them can reflect the nonlinear characteristics of shear strength of rock joints.Under the high normal stress,the fitting results of the shear strength of rock joints will higher when using Mohr-Coulomb criterion,power function and nonlinear Barton formula to fit.In addition,the reliable interval is estimated for the basic parameters of Barton formula fitting getting from the triaxial testing results.关键词：rock joint;triaxial testing;shear strength;nonlinear fitting;interval estimation of parameter;Barton formula
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发布时间：2024-01-10 - 摘要：With the increase in heat release rate of electronic devices such as large scale integrated chips,etc.,it has been very difficult for conventional microchannel heat sink (MHS) to meet the demand of heat dissipation of these devices.As a new design of heat sink,Self-Similarity microchannel Heat Sink (SSHS) has a better comprehensive performance and wider application prospect compared with a conventional MHS.In spite of this,it still has deficiencies of flow maldistribution and nonuniform heat transfer to a certain extent.In order to overcome the defect of its own and improve its performance,the manifold channel of the original SSHS is modified to a contracting one.At the same time,an optimization work was carried out with numerical method on the basis of the analysis of the influence of the structural parameters.In view of the same substructure of a SSHS,a single unit consisting of ten overflow channel,half of a manifold channel and outflow channel was chosen to be analyzed and optimized.Water was selected as working fluid with the mass flow rate covering the range of 0.27～0.90 kg/h.A uniform heat flux of 1 MW/m2 was imposed on the cover plate under the atmospheric pressure.The flow is assumed to be laminar due to Re in the range from 150 to 500.The numerical analysis results showed that there existed a strong flow stagnation in the end of the manifold channel,leading to flow maldistribution among the overflow channels.The difference in flow rates is up to 9.5~12.9 times with each other,and this directly results in uneven heat transfer process.The temperature difference across the outer surface of the cover plate reaches 10.8~12.1 ℃.Modifying the manifold channel to a contracting tapered one eliminated the stagnation effect to a certain extent.The optimization and comparison analysis showed that the uniformity in flow distribution and heat transfer could be further improved with increasing the slope angle,but with the cost of increasing the flow resistance to a certain extent.The best comprehensive performance can be obtained with the slope angle specified as 4.3° for current situation.Although the maximum pressure drop is increased by about 12%,the maximum relative difference in flow rates is reduced to 2.7 from 12.9,and the increase in heat transfer uniformity exceeds 50%.The improved and optimized design of SSHS offers a reference to the application of SSHS.关键词：micro channel;heat sink;heat dissipation;electrical device;self-similarity structure;optimization
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发布时间：2024-01-10 - 摘要：Focusing on dynamic power consumption of the chip,this paper proposed a new energy-saving strategy named BP-DVFS.Currently,DVFS (dynamic voltage and frequency scaling) technology failed to predict future behavior of CPU.In order to improve the performance of CPU utilization and predict more accurate CPU dynamic frequency,it is essential to reduce its operating power consumption.A CPU model named FPU-CPU (forward predict utilization) was built in strategy.A non-linear relationship between the CPU utilization in next period and the CPU running resource was assumed in the model.Five events related to CPU resources and extracted from run-time processor environment were measured as features.Afterwards,the training phase of was performed by the BP (back propagation) neural network.Various experiments were then carried out to predict different kinds of tasks including CPU utilization,processing and power consumption through BP neural network.To evaluate the performance of proposed method,the experimental results under same situation were compared with three traditional CPU frequency modulation strategies.The experimental results showed that the CPU power consumption of BP-DVFS based strategy is lower than that of other three strategies when CPU handles different kinds of program tasks.The experimental verification indicated that the proposed technique wasnot only accurate inpredicting performance of CPU utilization,but also helpful to reduce power consumption of CPU.关键词：energy saving;DVFS;BP neural network;dynamic voltage and frequency scaling
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发布时间：2024-01-10 - 摘要：In order to reveal the inherent laws of information diffusion in social network,the process of information diffusion in social network was studied in-depth.It was found that the process of information diffusion in social network was not only influenced by the attraction of information and social environment,but also influenced by the attitude of nodes to information.However,the existing information diffusion models rarely considered the attitude of the nodes,and thuscould not reflect the impact of different attitudes of the nodes on the process of information diffusion.Therefore,a node attitude-based information diffusion model was proposed in social network,which combined the node attitude and SIRS model to analyze the influence of node attitude on information diffusion.It also provided the theoretical basis for the study of information diffusion mechanism in social network.In particular,considering the differences in the attitude of different nodes and their change rules,the node attitudes of nodes and their updating principles were respectively defined based on the node behavior.Furthermore,combining the information diffusion and the SIRS model-based infection spread mechanism as well as the impact of node attitude on diffusion state transition,an information diffusion model in social network based on node attitude were obtained by exploiting the social learning theory.The model could describe the diffusion rules,reveal the evolution law of information diffusion and analyze the influence of node attitude on information diffusion.At last,datasets from Sina micro-blog were used as the experimental data in the simulation.The simulation results showed that the attitude of node affected the information diffusion.Meanwhile,it was also demonstrated that the proposed model was more accurate in revealing the information diffusion law and reflecting the process of information diffusion.关键词：social network;information diffusion model;SIRS;node attitude
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发布时间：2024-01-10 - 摘要：A main problem of cognitive radio (CR) is how to optimize the spectrum sensing and power allocation parameters.In the traditional CR,spectrum sensing is only performed in the sensing phase,however,information in the decision-making and transmission phases are also useful for spectrum sensing.In this paper,a decoding information-based spectrum sensing strategy for transmission phase was proposed for CR system and the transmission power for the next phase was optimized correspondingly.In the transmission phase,after receiving the signals from the secondary transmitter,decoding was performed and the secondary transmission signals were removed.Then,the state of the primary user (PU) were detected based on the remainder signals,and the transmission power were optimized correspondingly.The simulation results showed that,on the case of certain average interference power to the PU,the proposed model provided better system performance and made better use of the channel.By fully using the signals in the transmission phase,the transmission parameters of the SU can be optimized and more information for spectrum sensing can be collected,leading to higher detection accuracy of the state of PU.关键词：cognitive radio;transmission phases;spectrum sensing;power allocation
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发布时间：2024-01-10 - 摘要：In order to more effectively represent the higher-order sparse structure of images,a novel compressed sensing (CS) reconstruction algorithm based on the graph sparsity regularization was proposed in this paper.The graph theory method was introduced for describing the dependency of sparse coefficients.First,the nonlocal similarity of images was constrained to be graph-structured sparse.To achieve more efficient sparse representation,the structure of sparse coefficients was simplified from the complete graph structure to a star graph of which the coefficients are only connected with the mean node.Second,for obtaining the adaptive reconstruction,the weighted norm was utilized to reflect the different significances of sparsity coefficients.A numerical optimization algorithm was then proposed to solve the star graph structured reconstruction model by the approximate message passing (AMP) algorithm.Finally,the weight parameters and sparse coefficients were estimated easily by introducing auxiliary variables.Experiments results showed that,compared with several image reconstruction algorithms based on nonlocal sparse models,the proposed method presented competitive results in terms of both objective and subjective quality,which validated the effectiveness of the star graph structured model.关键词：Compressed sensing;nonlocal similarity;star graph structured sparsity;weighted norm;approximate message passing
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发布时间：2024-01-10 -
Research on Satellite Covert Communication Based on the Information Encryption of Physical Layer AI导读
摘要：In order to enhance the concealment and security of satellite communications,a weighted fractional Fourier transform (WFRFT) modulation scheme based on the information encryption of physical layer was proposed.The low probability interception features of WFRFT and the dynamic uniqueness of channel state information (CSI) were collaborated to guarantee the secrecy of wireless communications.In the proposed WFRFT system,a unitary matrix with the encryption properties was constructed,which overcomes the shortcoming of traditional WFRFT method and increases the diversity of signal processing.In addition,the physical properties of wireless channels were taken into account and the CSI matrix was converted into a phase rotation factor as a final key.Then,the encryption and demodulation between legitimate users were completed by certain means with this key.Simulation results showed that the encrypted satellite signal has more complex constellation distribution while maintaining the statistical characteristics of WFRFT signal,besides,the bit error rate for eavesdropper keeps 0.5,which could effectively guarantee the secure transmission.关键词：satellite communication;weighted fractional Fourier transform;physical layer;channel state information- 3241
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发布时间：2024-01-10 - 摘要：In gas metal arc welding,it is difficult to establish an accurate model of arc length nonlinear systems.Moreover,the system has various uncertainties and is vulnerable to the problem of internal and external disturbance.In this paper,an improved model-free adaptive control method was proposed to address the above issues.First of all,a dynamic linear generalized model with measurable and unmeasurable disturbances and uncertain factors was designed.A parameter estimation algorithm was used to estimate pseudo partial derivative online.Then,the disturbance observer was introduced to compensate the internal and external disturbances and uncertainties in real time. Furthermore,the control law of arc length system was designed by constructing a criterion function.On this basis,a model-free adaptive control scheme was developed.Finally,the robust stability of the method was validated.The simulation results showed that the method had better tracking performance and faster response speed than the existing model-free adaptive control schemes.It also had a stronger robustness when the unmeasured disturbances and uncertain factors are encountered in the welding process,which ensuring the stability of the arc length in welding process and the better control of quality.关键词：gas metal arc welding;model-free adaptive control;non parametric dynamic linearization;disturbance observer
- 2360
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- 2009
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- 0
发布时间：2024-01-10 - 摘要：Traditional cam mechanism with oscillating follower has the advantages of small size,low price,complex motion,and so on,which is widely used in printing machinery,agricultural machinery,textile machinery and automated office equipment,etc.As the automation machinery keeps moving towards high speed,high accuracy and lightweight,higher requirements are proposed for traditional cam mechanism with oscillating follower.When outputting a large angle,traditional cam mechanism with oscillating follower is required in great size structures.In addition,carrying capacity of traditional cam mechanism with oscillating follower is lower,because the contact between cam and follower is mostly high pair.So to some extent,applications of traditional cam mechanism with oscillating follower are limited.On the basie of movable teeth transmission and cam mechanism,a swing output movable teeth cam mechanism with advantages of both was proposed which has many superior attributes,such as flexible teeth number,full teeth mesh,wide range of swing angular and swing output regularly.The structure and transmission principle of the mechanism were introduced,besides,the angle relation of input and output cam were built by introducing cam curve and the equations of theoretical profile line and practical profile surface of input and output cam were deduced.The equations of curvature of cam theoretical profile line were given,and the change rules of the most values of theoretical profile line curvature and non-interference condition of cam practical profile surface were analyzed.From the graphical results,the most values of theoretical profile line curvature of input cam were on addendum and dedendum,and that of output cam appeared on start and end points,and the maximum curve with e/R ratio of cam theoretical profile line curvature had growth inflection point and peak,and the interference happened in the maximum offset profile surface cutting line of theoretical profile line.Therefore,when R,e and r parameters of cam practical profile surface are assigned,movable teeth radius r shouldn’t exceed the threshold,and trying to guarantee that e/R ratio is lesser than corresponding value of growth inflection point and far away from corresponding value of peak,and then,ensuring that cam profile surface has no interference and mechanism runs more calmly.关键词：movable teeth cam mechanism;swing output;profile surface equation;curvature analysis;profile surface interference
- 2595
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- 2417
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- 0
发布时间：2024-01-10 - 摘要：The use of axial fans for cooling is one of the common ways for cooling the power electronic components.Through the analysis of the air flow velocity at the outlet section of axial fan,it can be inferred that the air flows is in a similar thread shape in the chassis.When the circuit board position is different,the local surface heat transfer coefficient (
${h_x}$ ${h_x}$ ${h_x}$ 关键词：electronic chassis;heat dissipation;forced air-cooling;local heat transfer coefficient- 2603
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- 2303
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- 0
发布时间：2024-01-10 - 摘要：In order to overcome the disadvantage of conventional precise point methods,optimization approaches and numerical atlas,and further improve the accuracy and efficiency of rigid-body guidance synthesis of planar four-bar linkages with prescribes timing,a novel analytical approach with Fourier series was presented to solve the rigid-body guidance synthesis problem of planar four-bar linkages.Firstly,according to the periodicity of the linkage rotation angle function,the series mathematical formula of the linkage rotation angle function was established by using Fourier series theory.The harmonic parameters of the linkage rotation angle function were obtained by DFT.As a result,the linkage rotation angle function was expressed as the summation of a Fourier series with the input angle as the variable.The harmonic parameters relationship between the linkage rotation angle function and the rigid-body guidance rotation angle function was obtained by analysing the internal connection between them in the planar motion.Then,according to the theory of complex vector,the vector loop equation of planar four-bar linkages was established.The linkage rotation angle function was formulated according to the Fourier series,and was substituted into a vector loop equation.By using eliminated element method,the vector loop equation was changed into a complex number equation that contained only the fundamental dimensions of mechanism, the harmonic parameters of the linkage rotation angle function and the input angle.With regard to the properties of the complex exponent, the mathematic expression containing the fundamental dimensions of mechanism and the harmonic parameters of the linkage rotation angle function was obtained.Accordingly,the relationship between the fundamental dimensions of mechanism and the harmonic parameters of the rigid-body guidance rotation angle function was obtained by variable substitution in terms of the previous harmonic parameters relationship.Based on this relationship,the new design equations for rigid-body guidance synthesis of planar four-bar linkages were established.A cubic equation that contained only the fundamental dimensions of mechanism and the harmonic parameters of the rigid-body guidance rotation angle function was obtained by dialytic elimination.Through solving the cubic equation,a general formula was derived for the rigid-body guidance synthesis problem of planar four-bar linkages using the harmonic parameters of the rigid -body guidance rotation angle function.After the fundamental dimensions of mechanism are determined,the harmonic parameters of position of rigid-body guidance were obtained by DFT.According to the harmonic parameters relationship between the linkage rotation angle function and the position of rigid-body guidance,the formula,which can compute the real size and installing dimensions of the linkage mechanism,was obtained.Based on the aforementioned theory,the procedure of solving rigid-body guidance synthesis problem by the proposed method can be obtained.As a result,a new analytical method for rigid-body guidance synthesis of planar four-bar linkages with prescribes timing was established.Based on the synthesis procedure,the computer programs have been developed for the proposed method by MATLAB.An example was provided to verify the validity and feasibility of the proposed method.Verification results showed that the proposed approach can overcome the shortage of precise point method and directly to solve rigid-body guidance synthesis problems for planar four-bar linkages with no limitations on the number of precision points.Compared with numerical atlas and optimization approaches,the proposed method avoided the use of extensive numerical atlas databases and optimal initial solutions,and obtained the results by solving the equation.Therefore,this approach has the characteristics of high accuracy,fast solution velocity and high repeatability,and is suitable for computer programming.The research of this approach provided the theory basis for development of convenient synthesis software.关键词：linkage mechanism;rigid-body guidance synthesis;Fourier series;analytical approach
- 2411
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- 1926
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- 0
发布时间：2024-01-10 - 摘要：According to the processing principle of cylindrical gear with variable hyperbolic circular-arc-tooth-trace (VH-CATT) and the deduced tooth surface equation of the gear,the range of parameters was determined.Based on the obtained tooth surface equation and the differential geometry,the calculation method of the principal curvature of concave and convex gear of VH-CATT was obtained.Based on the principle of spatial meshing,the relative velocity of gear teeth on meshing point at an input angular velocity was calculated.According to the calculated method of the curvature of the tooth surface and the relative velocity,the formula for calculating the sliding ratio of VH-CATT pair was derived.Setting a certain VH-CATT design parameters for example,principal curvature,induced curvature and sliding ratio were calculated and their change trends were analyzed.Sliding ratios under different design parameters were obtained,as the reference of analysis and optimization for gear design.Analysis results showed that for the VH-CATT pair,the greater the modulus,tooth number ratio and tooth trace radius,the smaller the range of sliding ratio of gears is,and the abrasion in working process would be more uniform.Gear pair with larger modulus,smaller tooth number ratio,greater tooth trace radius has better performance in wear process.The quantitative relationship between sliding ratio and wear of VH-CATT was established,which provides reference for the calculation of gear wear.关键词：VH-CATT;geometric characteristics;principal curvature;relative velocity;sliding ratio;wear
- 2863
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- 2419
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- 1
发布时间：2024-01-10 - 摘要：In order to solve the problems,that force analysis is not comprehensive and the results cannot reflect the change of key parameters,such as particle acceleration,drag coefficient and Reynolds number,exist in the existing velocity models of pre-mixed abrasive water jet.Based on the theory of solid-liquid two-phase flow,the velocity model of particle in the high pressure pipeline and the nozzle was established.And the particle velocity model was solved by a numerical solution based on the bisection method and iterative algorithm.The developed models were finally verified by that the model calculations and the corresponding reference data are in good agreement with less than 5% average errors.At the same time,the variations rule of velocity,acceleration,drag coefficient and Reynolds number of the abrasive in the high-pressure pipeline and nozzle have been obtained by using the velocity model: In the high pressure pipeline,the particle velocity increases with the increase of the moving distance of particle,and finally it is infinitely close to the velocity of the water.The particle acceleration and the Reynolds number decrease with the increase of the moving distance of particle,and finally become zero.The drag coefficient increases with the increase of the moving distance of particle. In the convergent section of nozzle,the particle velocity increases with the increase of the moving distance of particle.The particle acceleration,drag coefficient and Reynolds number have a process of decreasing first and then increasing with the increase of the moving distance of particle. In the straight section of the nozzle,the particle velocity increases with the increase of the moving distance of particle.and the acceleration,the Reynolds number and the drag coefficient decrease with the increase of the moving distance of particle.关键词：abrasive water jet;velocity model;bisection method;iterative solution;particle acceleration;drag coefficient;Reynolds number
- 2293
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- 1771
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- 2
发布时间：2024-01-10 - 摘要：With the structural complexity of machine tool and the diversity and time-sequence characteristic of state data,in order to solve the problem that the future state of machine tool is difficult to accurately predict,a novel state prediction method based on multidimensional time series was proposed.Firstly,the ole for process control (OPC) technology was used to collect data of machine tool,and the Min-max normalization and autoregressive moving average model were adopted to data preprocessing.The state and evaluation models of multidimensional time series were established.Meanwhile,the feature vector and trend distance were also used to represent state model,and then the state match of multidimensional time series was completed by difference degree analysis.Secondly,through constructing the time sliding window technique,the historical state sets of machine tool were obtained by the length of time window length and sliding.On this basis,multiple matching technique based on window sliding was developed,and then the
$\beta $ 关键词：machine tools;multidimensional time series;multiple matching;state prediction- 2697
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- 2528
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- 3
发布时间：2024-01-10 - 摘要：Because the difference of elastic modulus between titanium alloy implants and human bones is large,prosthetic loosening and osseous change usually happen due to the stress shielding.Though bioactive films are coated onto the Ti-base implants for the clinical application,the thickness is limited several microns.Therefore it is necessary to search a method,which can improve the biocompatibilities and smooth the stress gradient.Ultrasonic surface impact (ultrasonic nanocrystal surface modification,UNSM) was carried out with the condition of a static load of 25 N,vibration amplitude of 30 μm and 36 000 strikes per unit on Ti6Al4V.The surface topography,severe plastic defornation layer,polarisation curve in simulated body fluid (SBF),corrosion feature,surface depositions,corrosion fatigue behavior of Ti6Al4V which was pre-soaked into SBF for two weeks,and the adhension of fibrochondrocyte were studied.A depth of 40 μm nanocrystal surface layer is achieved.UNSM improves the fatigue strengths of Ti6Al4V in SBF though the current density of corrosion is increased and the pitting corrosion is accelerated.Inner cracks usually appear at coarse grained deformation layer between the depth of 100~250 μm,because the residual compressive stress is reduced and the toughness is lower than the surface.Calcium and phosphorus nodules are significantly enhanced on UNSMed surface.The earlier adhension of fibrochondrocyte can be promoted at the same while.Coating a TiN film on the UNSMed surface helps to improve the whole biocompatibilities of Ti6Al4V further.The gradient of elastic modulus and grain size are helpful to resist stress shielding.Hybrid surface modification has positive significance for metal implants.关键词：UNSM;polarisation curve;SBF;corrosion fatigue;fibrochondrocyte
- 2592
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- 2367
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- 3
发布时间：2024-01-10 - 摘要：The flow field analysis of most dry gas seal end faces is carried out on the assumption of parallel gap for end faces.But because of the force deformation and thermal deformation working together,the gap between the end faces of two sealing rings is almost linearly convergent.The gas film flow fields for parallel gap and convergent wedge gaps with different angles were simulated and analyzed.ANSYS is used to pretreat the gas film flow field model.For the changes of gas density and viscosity in the flow field,the user-defined function (UDF) was used to define the density and viscosity of sealing medium as pressure functions.Fluent software was used for numerical simulation of the flow field of gas film.It was found that the variable density viscosity method used is feasible for the simulation of wedge flow field for a dry gas seal.The change of the convergent angle
$\beta $ $\beta $ $\beta $ $\beta $ $\beta $ $\beta $ $\beta $ 关键词：dry gas seal;wedge gap;spiral groove;gas film flow field;numerical simulation- 2325
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- 1932
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- 1
发布时间：2024-01-10
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