最新刊期
卷 50 ， 期 2 ， 2018
- 摘要：This paper systematically analyzes the present situation and technological difficulties of middle-low temperature geothermal power generation in China.The concept of thermovoltaic materials is proposed.The key technologies such as large scale single crystals of thermovoltaic materials and thermovoltaic devices are utilized as the starting point.We systematically proposed the high efficient and stable middle-low temperature geothermal thermovoltaic power generation system,and proposed the technological principle and conception of engineering implementation and precise transfer based on cold,hot,and electrical consolidated integration.The technological conception breaks through the traditional restriction of middle-low temperature geothermal thermovoltaic power generation from mechanical energy to electricity,and directly converts heat energy into electricityeffectively by utilizing large-scale single crystalsof thermovoltaic materials.The research and development of such subversive technology is of great strategic guiding significance,especially in the middle-low temperature region,to maintain our country’s international core competitiveness in geothermal power,to acquire independent intellectual property,and to realize the efficient utilization of geothermal energy and scale development.Meanwhile,this strategic technology concept is expected to lead a new technological revolution of geothermal power generation in the world,to establish our country in the field of middle-low temperature geothermal power generation for global leader,and to achieve the clean and green sustainable utilization of geothermal resources.关键词：middle-low temperature geothermal power generation;thermovoltaic materials;large-scale single crystals;electric generation by temperature difference;engineering technology transfer
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发布时间：2024-01-10 - 摘要：Nowadays,a large number of chemical products are manufactured by oxidation reaction in chemical industry,such as the important organic chemical materials of propylene oxide (PO),epichlorohydrin (ECH) and hydroxylamine hydrochloride.The current manufacturing technology exists serious problems of high pollution,high energy consumption and high emissions,hence it is necessary to comprehensively upgrade technology considering environment,economy and safety issues.The independently- and domestically-developed H2O2 oxidation technology is a catalytic oxidation process with H2O2 as an oxidant and Ti-Si molecular sieve as catalysts,which has advantages of atomeconomy,environment-friendly and so on.However,since this process is a strong exothermic multiphase reaction,it is urgent to solve the problems of highly-efficient mixture,rapid heat exchange and safety in the design and engineering scale-up of reactors.Another common problem is the highly efficient separation of the oxidation by-products.In order to overcome these above problems,a research was carried out integratedly by whole-chain design from basic research to industrial application,and three common scientific problems of molecular mixing and interfacial transmission mechanism of H2O2 oxidation system,cross-scale transfer and reaction coupling mechanism,and reactor scale-up law and new approach for process enhancement were mainly studied.Upon the project completion,manysets of independently-developed industrialization technologies will be formed,and two industrial demonstration units of H2O2 green oxidation system,including a PO industrial demonstration unit and a hydroxylamine hydrochloride industrial demonstration unit,as well as a complete set of new technical packages for ECH,will be constructed.The project offers an opportunity to break the blockade and monopoly of foreign technologies and to subvert and eliminate the existing and highly-polluted technology for energy-saving,environmentally-benign and green manufacturing.关键词：H2O2 oxidation;reactor;epichlorohydrin;epoxide propane;hydroxylamine hydrochloride
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发布时间：2024-01-10 - 摘要：Embankment piping erosion is a common infiltration deformation in flood embankment projects.Its occurrence is completely inside the embankment or dam body.It is usually not easy to find and it is difficult to take timely measures to control it.At the same time,with the development of the eroded pipe,the embankment will further produce uneven settlement and finally threaten the safety of the dam.Therefore,the research on its development and failure characteristics has been a hot and difficult topic.In order to explore the occurrence and development of eroded pipe pits and the failure rules,the multi-color sand-filling tracer method was used to distinguish the order and direction of the fine particles migration in the soil samples so as to reveal the development of piping in a more direct way.Three types of intermittent gradation soil samples are selected,according to different discriminant method of soil piping,and a model test of double-layer dike foundation in a flume is used to conduct the test.The effectiveness of the existing methods for determining soil piping were compared to each other.In the same time,considering the influence of water head and material gradation on the results of piping erosion,the relationship between" disturbance”and piping development was analyzed.It is shown that the piping erosion begins with the loss of fine particles around the piping outlet.With the further development of erosion,the starting point and the loss of fine material are gradually moved to the upstream.The study also shows that the loss of fine particles in the process of erosion is progressive obviously and the starting of loss can occur outside of erosion range.The external factors or seepage stability factors that lead to" disturbance”have the effect of enhancing the process of piping erosion.关键词：double-layer dike foundation;piping erosion;color sand tracer;model test
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发布时间：2024-01-10 - 摘要：Since the cushion generally exists on the top and a substratum below the bottom of sand-drained ground,impeded boundaries were used to describe its effect on consolidation process of sand-drained ground.Assuming that ground deformation satisfies the condition of equal vertical strain and considering the radial variation of horizontal permeability coefficient,consolidation theory was established for sand-drained ground with top and bottom impeded boundaries under vacuum preloading.The series analytical solutions of consolidation degree and settlement were achieved by the separated variable method.The effect of the pervious coefficient of top boundary,the pervious coefficient of bottom boundary,the well resistance and the radial distribution feature of permeability coefficient on the consolidation degree and settlement of sand-drained ground were analyzed.The researches show that the final negative pore pressure and the effective stress exhibit a decrease with increasing depth of ground.When the other conditions are same,the ground with big bottom pervious coefficient has big consolidation degree,while it has small final settlement and the consolidation settlement at same radial consolidation time factor.When the bottom boundary of ground is impervious,the final settlement of ground hardlychange with the top pervious coefficient,but when the bottom boundary of ground is impeded or completely permeable,the final settlement increases with top pervious coefficient.The ground with big top pervious coefficient has big consolidation degree and consolidation settlement at the same radial consolidation time factor.Resistance of sand drain neither affect the final vertical distribution features of negative pressure,nor change the magnitude of the final settlement,while the resistance of sand drain can significantly decreases the consolidation degree of sand-drained ground and extends the finish time of consolidation.The radial distribution mode of permeability coefficient affects the consolidation degree of sand-drained ground.The consolidation degree of mode 1 is the biggest,mode 2 is the smallest,and mode 3 falls between mode 1 and mode 2.The effect laws of impeded boundary on the consolidation process of sand-drained ground under vacuum preloading are obviously different from those under surcharged preloading.关键词：sand-drained ground;vacuum preloading;impeded boundary;consolidation settlement;analytical theory of consolidation
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发布时间：2024-01-10 - 摘要：Welded flange-bolted web connection is one of the common joints in the steel structure,and the mechanical performance and failure mode of the joint is related to the collapse resistance of steel frame closely.To compare and analyze the failure mode,mechanical property and resistance mechanism under the condition of progressive collapse,the beam-column substructures of three different span ratios(1∶0.6,1∶1.0,1∶1.4)with welded flange-bolted web connection in minor-axis direction were selected,which included three columns and two beams,to conduct monotonic static loading test by alternate load path method.The test results indicated that the fracture of specimens begins with the beam tension flange,and then part of the main internal force is transferred by the bolts on web,followed by buckling of the compression flange of the beam end.Finally,specimens are deactivated because of the shear failure on bolt holes or fracture of web and junction plate.The process of anti-collapse mechanism appears the flexure phase,flexure-catenary mixed phase and catenary phase.It could be found that joint with welded flange-bolted web connection possesses high redundancy,which has enough rotational capacity after the fracture of tension flange.The catenary could be developed and take the lead in the following great deformation in two factors,which are the magnitude of the axial tension generated in the beam-column members,and the sufficient rotation angle of the beam end.The deformation of the beam-column joint is beneficial for the beam-column substructure to bear the load by collaboration between the beam and the column.For the unequal span specimens,the initial fracture of substructure is always at the short-span beam with small span-depth ratio and the short beam has better catenary mechanism than the long one.关键词：connection in minor-axis direction;welded flange-bolted web connection;beam-column substructure;anti-collapse performance;catenary action
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- 1968
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发布时间：2024-01-10 - 摘要：In the construction of deep buried underground cavern,the surrounding rock masses of underground caverns are prone to appear splitting failure due to the high in-situ stress and the brittleness of rock mass.In this study,based on the energy dissipation principle and a transversely isotropic model,a kind of new custom transverse isotropic calculation model is estabilished which is judged by the splitting failure criterion of model element stress state,and the stability of excavation of large underground caverns in Dagangshan hydropower station is evaluated based on this new custom model.Besides,the displacement and the entire process of rock splitting failure of each excavation steps of the main house have been achieved through field monitoring on side walls of the construction site of large-scale caverns in Dagangshan.Then,the results of field monitoring are compared with the calculated results of the stability analysis of different constitutive models,and the following conclusions are obtained: during the excavation of the Dagangshan Hydropower Station underground caverns,the average depth of splitting zone of the sidewall in the main power house calculatedby the new model is quite consistent with the field monitoring result; compared with other models ,the new model is better to reflect the change trend of surrounding rock displacement between the main power house and the main transformer chamber.According to the results of the stability analysis,the key point displacement of the downstream side wall and the position near the crane beam of the main power house is larger,the maximum horizontal displacement of the sidewall is 29.46 mm.The vault displacement of the main powerhouse is larger in the initial stage of excavation,and the maximum vertical displacement of the vault is 10.58 mm.The results show that,compared with other existing FDTD model,calculation results by the new custom model is closer to the actual monitoring value,which reflects the displacement of the surrounding rock mass in different excavation steps and the change trend of the surrounding rock displacements of the key points.This new model is reasonable to calculate and predict the splitting zone of the surrounding rock when the underground cavity in high geostrese areas during excavation and is also appropriate to the stability analysis on the surrounding rock after excavation.or Referring to the strengthen the monitoring and management of key areas,our proposed model is beneficial for reducing the splitting failure effect on tunnel stability.关键词：high geostress;underground cavern;energy dissipation;transverse isotropy;field monitoring;splitting failure;stability analysis
- 2892
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- 1968
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- 1
发布时间：2024-01-10 - 摘要：After collecting and analyzing the data of existing dam failure cases summarized in foreign references,as well as extra cases in China,a basic database containing 154 dam breaching cases with detailed information is constructed.Taking dam type,reservoir shape coefficient, ratio of water level to breach depth and dam height,which are all expressed in dimensionless forms,as independent variables into account,the regression analysis is adopted to establish dimensionless formulas for calculating peak outflow discharge,final average breach width and failure time.The new empirical model considers the influences of dam type,failure type,storage capacity,water level,dam height and breach depth.Comparing to the existing models for dam breaching parameters,the present model has the advantage of using larger database,easier acquisition of input variables,and including more influence factors of dam breaching parameters,in particular,the dam characteristics and current hydraulic conditions.Then,for all the dam breach cases collected in the database,the calculation using different models is carried out.The result shows that the present model has better adaptability and prediction accuracy based on the statistics of overall computing error,the value of root-mean-squared error and coefficient of determination,by comparing to the previous models.Furthermore,four typical breach cases of different dam types and failure types are selected to verify the rationality and superiority of the present model,and the calculation results of present model are more accurate in most of the cases than those of the other models.关键词：earth-rock dam;database of dam breach;parametric model for dam breaching;model comparison
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发布时间：2024-01-10 - 摘要：The fault-fracture zone is an important tectonic factor for geological hazards such as cave-in and mud bursting.However,the research on grouting theory and technology of fault treatment develops slowly.Based on the treatment project of water-and-mud inrush hazard at F2 fault in yonglian tunnel,the property of rock mass medium in fault-fracture zone is analyzed,and a grouting conceptual model is established.The grouting control equations of three kinds of medium are built up,to analyze the influence of the rock mass property on the grouting process.Through the grouting test,the grouting process in heterogeneous fault-fracture zone is modeled,during which the diffusion process is analyzed,based on the distribution of slurry veins,variations of grouting pressure and the stress of media.The results show that the rock mass in heterogeneous fault-fracture zone can be classified into three kinds of medium,i.e.,incompact,compressible and compact media; while the slurry diffuses in different forms,i.e.,penetration in incompact media,consolidation in compressible media and split in compact media.In compact media,the grouting diffusion distance is positively related to the number of structural planes of rock mass,and negatively related to the compression modulus of rock mass as well as the grouting rate.According to the results of grouting test,the grouting diffusion process in heterogeneous fault-fracture zone can be divided into two stages,advantage filling and split grouting,and the transition point corresponds to the curve break of grouting pressure from creeping up to sharp down.The advantage filling stage,in which the slurry intensively diffuses and the grouting pressure increasing slowly,occurs mainly in compressible and compact media,while the split grouting stage,in which the grouting pressure rises faster,occurs mainly in incompact media.In order to effectively implement the advantage diffusion of slurry in the treatment process of unfavorable geologic bodies filled with incompact or compressible media,a grouting control technique is proposed,and applied to the treatment project of water-and-mud inrush hazard at F2 fault in yonglian tunnel.The technique was proved to have good grouting treatment effects.关键词：fault-fracture zone;grouting conceptual model;grouting diffusion
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- 2030
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- 8
发布时间：2024-01-10 - 摘要：The soil swelling deformation will happen when swelling soils absorb water.Swelling soils are widely distributed in the world,which have complex hydrological characteristics and mechanical properties,and have significant influence on the national economy.As the current research on soil water movement is mostly aimed at non-swelling soil,the related research results are not suitable for describing the process of swelling soil water movement.Consequently,it is of great practical and theoretical significance to carry out the study of swelling soil moisture movement.The soil swelling deformation is mainly the result of the combined effect of the soil swelling pressure and self-weigh stress,and the stress and deformation characteristics of swelling soils vary with the soil depth.To quantify the effect of the soil swelling deformation on water movement parameters,the calculating models of parameters including saturated water content,saturated water conductivity and saturated ratio of volume were established by using soil swelling characteristic curve and soil stress-strain relationship curve.Then,Loessial soil and Lou soil were selected as typical swelling soils,and their saturated water movement parameters in different soil thickness were measured based on the indoor experiment,and the applicability and reliability of the parameters were verified.The results show that the relative error are less than 10%,RSME are less than 0.07,and Nash efficiency coefficient are larger than 0.85 between the observed and predicted values of the three parameters,which indicates that the calculating models can be applied to simulate swelling soil saturated water movement parameters.The results enrich the theoretical research of soil water movement,and provide reference for swelling soil water utilization and management.In future,to improve the performance of the model,the effect of the soil swelling pressure and self-weigh stress on saturated water movement parameters under different initial water content and different initial bulk density needs to be explored.关键词：swelling soils;soil water movement;soil saturated water content;soil saturated hydraulic conductivity;soil saturated ratio of volume
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发布时间：2024-01-10 - 摘要：The mid-long term economic scheduling of cascade hydropower stations is a typical nonlinear optimization problem. It is usually required to maximize the total power generation giving consideration to efficiency of solution while simultaneously meeting complicated hydraulic and electrical constraints. To solve this problem effectively, an improved bat algorithm (IBA) was proposed by improving the updating strategies in Bat Algorithm and introducing the mutation and selection operation in Differential Evolution algorithm. The following improvements were made to the updating strategies in BA: 1) The pulse frequency of each bat was not updated with the population iteration. 2) The impulse emission rate and the pulse volume of each bat were updated with the population iteration. 3) New individuals generated by global search were accepted unconditionally in IBA, but individuals generated by local search were accepted conditionally. 4) The flight velocity formula was improved to reduce the deviation between the new individual and the optimal individual of the current population. In order to increase the diversity of the population and to avoid local optimum, the mutation and selection operation in DE was introduced, and the mutation probability was thus dynamic. A model was established to maximize the annual energy output and maximize the minimal output of cascaded hydropower stations. Based on the economic dispatch problem of cascade hydropower stations of Dadu River, the main control parameters (zoom factor and maximum iterations) of IBA were tested and analyzed. IBA, BA and POA were used to simulate the scheduling at the same year. Taking account to the characteristics of output in the dry season, the total power generation and the running time, we can conclude that compared with the other two algorithms, the simulation results obtained by using IBA verified its superiority in both efficiency and precision.关键词：optimal scheduling;improved bat algorithm;differential mutation;cascade hydropower stations
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发布时间：2024-01-10 - 摘要：Aiming at the problem that the flow determined by the traditional ecological basic flow method is difficult to consider both the ecological and economic benefits,in this paper we propose an optimization model suitable for the ecological flow process of the dam-diversion type hydroelectric station.This model adjusts the diversion radio by optimizing the vulnerable areas of hydraulic factors in natural river channels to make the ecological and economic benefits reach the joint optimum,in which the WUA is adopted as the decision index and a hypothesis is assumed that the fish habitat does not change greatly if the WUA of improved ecological base flow keeps in line with that before improvement.Taking the Changbo Hydropower Station for example,this paper emphasized on the changes of hydrological regime in the vulnerable areas of hydraulic factors and the improved ecological flow process of the river channel was determined after considering the fish of Schizothorax dolichonema’s requirement for the hydraulic factors in its spawning period when the vulnerable areas were optimized through using the spur dike.The results showed that when selected 3 vulnerable areas to optimize,the river ecological base flow is 10% of the average annual flow while the calculation results of traditional methods is 20%,the two corresponding effective area is 87 782.02 m2 and 87 726.2 m2 respectively.The former flow rate was decreased by 10% compared with the latter under the condition that the habitat’s hydraulic condition remained unchanged.The ecological flow process of Changbo Hydropower Station which could preserve the basis of the optimized ecological fluctuation of runoff and process of flow pulse while satisfying the water demand of target fish is obtained on the basis of the optimized ecologicalbase flow and the study results of rise rate and fall rate.This process provides a demonstration for the establishment of appropriate hydraulics habitat for protected fish and the optimization of the ecological flow regime of mixed type hydropower stations.Meanwhile,it also provides a basis for the ecological dispatching management of power station.关键词：dam-diversion type hydroelectric station;Schizothorax dolichonema;ecological flow optimization;diversion radio;ecological flow regime
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- 1993
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- 0
发布时间：2024-01-10 - 摘要：In order to address the problem of visible image degradation caused by the hazy weather conditions,a dehazing algorithm was proposed,in which the color information of the visible image and details information of the near-infrared image were fully taken advantage of.Firstly,the haze density of visible image was estimated according to the information of dark channel,based on which the visible image was partitioned.Then the visible image and near-infrared image were decomposed by stationary wavelet transform.By using haze density partitioning and pulse coupled neural network,the high-frequency component and low-frequency component in visible and near-infrared images werefused,and a clear and high-fidelity image was obtained.Afterwards,the composited image was filtered by a guidance filter to smooth the boundaries of partitioned areas and preserve the edge information of source image.To validate the effectiveness of the proposed algorithm,groups of experiments were conducted to compare it and other state-of-the-art dehazing algorithms.The comparison indexes include information entropy,mean value and standard deviation of dehazed image as well as computation time of algorithms.The results showed that the proposed algorithm achieved a better visual effect,and the color information in haze-free areas was retained.Besides,all the comparison indexes related to image detail and image clarity were superior to that of other algorithms.Meanwhile,the computation time cost of the proposed algorithmwas significantly decreased.关键词：haze removal;near-infrared image;image fusion;dark channel
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发布时间：2024-01-10 - 摘要：In order to suppress the pilot contamination in Massive MIMO system,a pilot scheduling scheme based on path loss to perform user grouping (PLUG) was proposed.The proposed PLUG scheme divided the users into the center user group and the edge user group according to different levels of pilot contamination.The proposed PLUG scheme assigned the same pilot sequences to the center users who suffering from slight pilot contamination and assigns orthogonal pilot sequences to the edge users who suffering from severe pilot contamination,thus inhibiting the impact of pilot contamination.The PLUG scheme assumed that the number of edge users in each cell is the same.To improve flexibility of PLUG,an improved pilot scheduling scheme based on path loss to perform user grouping (IPLUG) was proposed.By introducing the decision parameters,the strategy dynamically grouped and selected the number of edge users per cell.It avoided users in good channel conditions being wrongly divided into edge user group which would increase the pilot overhead,or users in bad channel conditions being wrongly divided into center user group whichwould decrease the quality of communication.In this way,the accuracy and rationality of user grouping were improved. Theory analysis and simulation results showed that the proposed scheduling can improve the channel estimation normalized MSE,uplink SINR and achievable rate of edge users with little performance loss of center users.In conclusion,the proposed schemes can effectively suppress the pilot pollution of Massive MIMO system and reduce the probability of communication interruption.关键词：Massive MIMO;pilot contamination;pilot scheduling;user grouping
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发布时间：2024-01-10 - 摘要：In order to improve the performance of block diagonalization precoding algorithm,an improved algorithm was proposed for multiuser multiple-input multiple-output (MIMO) downlink systems,which employs QR decomposition based on Givens transformation.In the block diagonalization precoding algorithm,the first half of the precoding matrix is required to solve the problem of multi-user interference,and the latter one to reduce the interference between the antennas of each user.The core algorithm of the first half matrix is orthogonalization algorithm,which will directly affect the bit error rate (BER) performance of the block diagonalization precoding algorithm.Therefore,the original orthogonalization algorithm was replaced by QR decomposition algorithm based on Givens transformation.Using this algorithm to solve the first half of the precoding matrix,the orthogonal basis of the interference matrix’s zero space can be obtained.By using the Givens transformation,the matrix with better orthogonality can be obtained,so as to further reduce the BER of the system.The simulation results showed that compared with the traditional block diagonalization algorithms,the complexity of the system was decreased and the BER performance can be improvedgreatly.Compared with the block diagonalization algorithms based on Gram-Schmidt orthogonalization,the BER performance can be improved by 3~5 dB,with a slight increase in the algorithm complexity.关键词：multiple-input multiple-output (MIMO);precoding;block diagonalization;computational complexity;bit error rate (BER)
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发布时间：2024-01-10 - 摘要：Virtual network embedding algorithm mainly focus on the problem of how to carry more virtual networks on the substrate network by reasonably allocating resources.Inter-domain embedding is able to offer more substrate resources for virtual networks.On the one hand,the inter-domain embedding policy needs to consider how to reduce the inter-domain embedding overhead.On the other hand,it also needs to consider how to satisfy the selfishness of network providers.Therefore,an inter-domain virtual network embedding policy for revenue maximization was presented in this paper.In order to establish a synchronization solution model of virtual network topology partition and local embedding scheme,the policy firstly transformed the domain view of the local infrastructure provider to introduce the concept of domain nodes into the model.Then an auction-based local infrastructure provider selection strategy was designed.Finally,a local embedding algorithm based on genetic evolution was designed to solve the model.The algorithm modified the steps of initialization and chromosome crossover according to the constraints of virtual network embedding.The embedding scheme generated by the algorithm preferentially embedded the virtual nodes and the links on the local domain,while reducing the virtual link occupancy of inter-domain link bandwidth resources as much as possible.The policy supported the tuning of parameters based on the actual overhead of inter-domain embedding,resulting in a partition scheme that maximizes the local infrastructure provider’s revenue.Simulation results showed that the more overhead the inter-domain embedding expends,the more the policy will tend to reduce the number of inter-domain virtual links.In terms of embedding effect,the embedding cost of the policy was lower than that of the same type of policy,so it had obvious improvement in indicators such as actual profit and acceptance rate.关键词：virtual network;inter-domain embedding;revenue;embedding cost
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发布时间：2024-01-10 - 摘要：In order to solve the problems that traditional virtual network embedding algorithms were inefficient,and the reliability evaluation of physical nodes in substrate network was one-sided which will lead poor reliability of virtual network,a node reliability-aware efficient virtual network embedding algorithm was proposed.Firstly,in order to improve the embedding efficiency of virtual network embedding algorithm,the global network topology and local network topology were considered synthetically.The node centrality and physical node nearest hops were introduced into virtual network node embedding phase separately to reduce the resource consumption of link embedding.A node importance index was proposed and used as a sort index for virtual network embedding.Secondly,in order to reduce the harm of physical node failure,the physical node reliability was proposed by exploiting physical node usage,recent failure time and node failure times as the measurements of physical node reliability.Then the node importance and physical node reliability were used to determine the physical node reliable importance,which is the ranking index of physical node.Finally,virtual nodes and physical nodes were sorted separately and then virtual network were embedded.Simulation results showed that compared with other algorithms,the algorithm proposed in this paper not only improved the acceptance ratio of virtual network,long-term average revenue and long-term average revenue-to-cost ratio,reduced the reduced the vulnerable rate of virtual network greatly.At the same time,compared with other node reliability method based on single metric,the proposed node reliability method had a lower vulnerability rate of virtual network.It was verified that the node reliability-aware virtual network embedding algorithm took into account the high efficiency of virtual network embedding and the reliability of virtual network.关键词：virtual network;node reliability;high efficiency;embedding algorithm
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发布时间：2024-01-10 - 摘要：Description of data distribution has been commonly used in databases to support query optimization,among which histograms are of particular interest.The existing conventional histogram construction methods have the problem of low efficiency of parallel resource utilization and high data transmission.To address these issues,a distributed and parallel constructing method was proposed for equi-width histogram in relational cloud database.Since the data ranges of different storage nodes are not the same,firstly,the local maximum and minimum values of working nodes were transferred to the application request node using the RPC protocol.These values were compared with each other to get the global maximum and minimum values based on master-slave model before the start of the histogram construction.Secondly,considering the optimization of data transmission during the histogram estimation,each working node scanned,sorted and partitioned the data into buckets according to the global maximum and minimum values which were transmitted from the application request node.Sub-histograms that were constructed in parallel improved the efficiency of resource utilization in the cluster.Finally,sub-histograms were aggregated to obtain the global histogram in the application request node.The algorithm divided the histogram task into multiple small tasks that could be simultaneously executed in a distributed cluster.During the histogram estimation,only a small portion of information about buckets and a few necessary data need to be transmitted over the network.The algorithm has been applied to the relational cloud database to optimize the initial scanning cost of the SQL statement,the data selection rate and other key parameters.The experimental results of the synthetic data and the real data demonstratedthat the amount of the data transmission was unrelated with the table size and the proposed algorithm achievedgood scalability.关键词：velation cloud databased;equi-width histogram;data distribution;parallel computing;data transmission
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发布时间：2024-01-10 - 摘要：At present,ccLDA (cross collection LDA) model has been found only applicable to data sources that topic similarity is very high,and its global topics and local topics of each data source will be forced alignment,hence causing words sparse.In order to solve the problem of ccLDA model,an improved ccLDA topic model (IccLDA) was proposed.When sampling,this model firstly decides whether words are global topics or local topics,and then takes samples respectively.In this way,it can avoid the problem that the global topics and local topics in ccLDA model must be aligned,and also can reduce the dispersion degree of the words in the global topics and local topics,making the model suitable for multiple data source scenarios.The topic discovery experiments of multiple data source were conducted on public data sets,and a comparative analysis of topics was conducted.The experimental results showed that the confusion degree of IccLDA model is lower than LDA model and ccLDA model,indicating that IccLDA model has better modeling ability.Finally,further experimental verification was performed with the data sets of real-world scenarios.The result showed that the improved model not only has better modeling ability than the traditional models,but also can effectively discover public topics discussed by various data sources and local topics discussed by each data source,and is more suitable for topic discovery in multiple data source scenarios.关键词：topic detection;topic model;LDA;multi-source;IccLDA
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发布时间：2024-01-10 - 摘要：The strong mobility of wireless mesh clients incurs the frequent handover among multiple wireless mesh routers.In order to overcome the problem that current handover authentication schemes cannot achieve high efficiency and privacy protection simultaneously,an efficient anonymous handover authentication scheme with privacy protection was proposed.The proposed scheme was based on the idea of identity-based blind signature in cryptography.Firstly,the wireless mesh router sends its identity to the authentication server to get a key pair that is used to generate the pseudo identities for the wireless mesh client.Secondly,the wireless mesh client sends blind messages to the wireless mesh router to request the pseudo identities that is used in the handover authentication phase.Finally,the wireless mesh client sends a pre-acquired pseudo identity to the target router to complete the handover authentication.The proposed scheme adopted identity-based cryptographic technology,which effectively reduces the whole network consumption caused by the generation,management and revocation of the traditional public key certificate.On the other hand,through the blind signature technique,the client only needs to use thepre-acquired pseudo identity for handover authentication.Using the pseudo identity could protect the confidentiality of the user’s true identity information and the moving path,as well as the data privacy of the client.Security analysis showed that the proposed scheme can satisfied the security requirements of mutual authentication,anonymity,revocation and resistance to attacks.Performance analysis showed that the handover authentication process is achieved after two handshakes without pairing operations.Comparing with other schemes,the proposed scheme effectively reduces the communication cost and the number of calculation times,lightens the load of authentication server,and improves the authentication efficiency as well.关键词：wireless Mesh networks;authentication;data privacy;cryptography
- 3297
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- 2016
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发布时间：2024-01-10 - 摘要：In order to explore the solution of the problems of the short of knowledge and immature theoretical research about large scale,specifically wide-area,quantum key distribution network research,the structure model,the secret key model and the active model of the trusted relaying quantum key distribution network were proposed from the viewpoints of structure,inner secret key relationship and working principle respectively for the trusted relaying quantum key distribution network which is the only real practical one so far.Firstly,from the viewpoint of system theory,the quantum key distribution network was divided into five layers according to the basic principle of key relaying based on the existing structure model.The constitution of each layer and the relationship between them were explained in detail.Secondly,from the viewpoint of information theory,the quantum key distribution network was abstracted as a key information graph according to the key sharing relationship among all nodes and the node and edge were formally defined.Therefore,the secret key information in the five layers quantum key distribution network could be explained by the graph theory in details.Lastly,from the viewpoint of the cybernetics, the key distribution process was resolved into two basic parts of key relationship establishment and secrete key generation,then the works of the quantum key distribution network could be explained by the development of key information graphs.The analysis showed that the proposed quantum key distribution network model can achieve the goal of hierarchical,parallel and pipelining key distribution,and can ensure the security of key distribution,which establishes the foundation for the future theoretical and technology research.关键词：QKD network;quantum key distribution;secret key network model;trusted relaying
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发布时间：2024-01-10 - 摘要：The emergence of some quantum algorithms has brought a serious threat to modern cryptography,among which Shor’s algorithm is the most important threatening algorithm for cryptanalysis currently.Shor’s algorithm can solve the integer factorization problem (IFP) and discrete logarithm problem (DLP) in polynomial-time,which makes the current widely used RSA,ElGamal and ECC public key cryptosystem unsafe any more under the quantum computing environment.Therefore,it is necessary to research the cryptanalysis in the quantum computing environment.Solving the IFP is the core idea of Shor’s algorithm for attacking RSA,but breaking RSA does not have to be solved by solving the IFP.A quantum algorithm is designed to attack the RSA cryptosystem starting from the angle of non-factorization.Focusing on the characteristics of RSA public key cryptosystem,using the quantum Fourier transform,the RSA plaintext
$M$ ${e^{{th}}}$ $n$ $M$ $n$ $C$ $n$ 关键词：information security;cryptology;RSA cryptography;quantum computing- 2970
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发布时间：2024-01-10 -
Design of a Device for Ultrasonic Elliptical Vibration Cutting Based on the Finite Element Method AI导读
摘要：Ultrasonic elliptical vibration cutting (UEVC) is a processing technology developed for ultra-precision in recent years.Its structure design is one of difficulties in current research.Based on the analysis of the current UEVC devices,a different UEVC that uses the circular flexure hinge was designed in this paper.Modal analysis of the device was carried out using finite element method (FEM) to identify the key structural parameters that affect the resonant frequencies.Its structure was optimized by the global optimization module to ensure that the resonant frequencies of the longitudinal and flexural vibration modal are the same.In addition,multi-field coupled analysis was performed to predict the motion trajectory of the tool tip in different phase shift.FEM results indicated that length of the back cylinder greatly affects the resonant frequency of longitudinal and flexural vibration modal,while the thickness of the base had almost no effect on the resonant frequency,and length of the tip slightly affects the resonant frequency.Based on the FEM analysis and optimization,a prototype of UEVC device was fabricated.Its resonant frequency and vibration characteristics were measured by an impedance analyzer.Experimental results showed that the measured resonant frequency correlates well with the simulated one.Therefore,the designed UEVC device can generate elliptical trajectory at the resonant frequency.In addition,the vibration trajectory can be tuned by adjusting the phase shift and the amplitude of the applied voltage,which enables the machining of micro-structured surface on the brittle material.Besides,when alternating current is applied to the UEVC device, and the frequency of the current equals to the resonant frequency of the device.The amplitude of the longitudinal and flexural vibration linearly increases with the amplitude of the voltage.Nevertheless,the flexural vibration is more sensitive to the change of the voltage than the longitudinal vibration.关键词：ultrasonic elliptical vibration cutting;finite element method;flexure hinge;resonant frequency- 2929
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- 2361
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发布时间：2024-01-10 - 摘要：With the continuous innovation of cross wedge rolling technology,its product range is also expanding.When the stepped shaft is formed to equal diameter shaft by the cross wedge rolling,the quality of the shaft end is directly affected by its length due to the inhomogeneous flow of metal.Besides,the material utilization ratio is reduced.To obtain the better end-face quality and higher material utilization rate,it is necessary to study the influence rule in the cross wedge rolling process.The rolling-forming process was studied with numerical simulations on the DEFORM-3D finite element software and rolling experiments.Based on analysis of the distributions of the stress field,the strain field and the feature points,initially,the law of metal flow was revealed and the deformation mechanism of rolling process was clarified.Taking into account the complexity of influencing factors, the mutual orthogonal experiment was adopted to design the four process parameters of shaft-end length,step angle,step length and cross-section shrinkage ratio.The influence of these parameters on the end concave was verified,and the results showed that the concave value gradually increases as the step length and cross-section shrinkage ratio increase,while with the decrease of shaft length and step angle.Therefore,a smaller concave can be attained by reducing the shaft end length.The software SPSS 22.0 was used to analyze statistical data,and the relationship equation between the process parameters and the quality of the shaft end-face was ascertained.With the concave heart value of zero as the goal,it also determined the influence equation of the optimum shaft-end length on end-face quality.By comparative analyses of the rolling test and the simulation,shapes of the rolled piece and concave values of the end-face were basically same,so the reliability of the simulation analysis was further verified.Theoretically,these influence rules and formulas can effectively improve the end-face quality of rolled piece,and determine the optimum length of the shaft end,achieving near net forming without material head in cross wedge rolling.关键词：shaft-end length;process parameters;end-face quality;cross wedge rolling;concave
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发布时间：2024-01-10 - 摘要：In order to study the mechanical properties of the composite insulator mandrel under corrosion conditions,using the self-developed insulator torsional vibration simulator,the fatigue test of composite insulators was carried out under different corrosion conditions.The FXBW4-110/100 insulator was selected as the research object.The macro-morphology and optical-microscope of the surface morphology of specimen fracture was analyzed by three-dimensional profiler and scanning electron microscope.Combined with surface analysis techniques,the relationship between the fracture of insulator core and its swing force,torsion force and tensile force under different corrosion test conditions was studied.The results showed that the corrosive liquid has little influence on the mechanical properties of the composite insulator under the neutral and alkaline corrosion solution conditions.However,when the corrosive liquid is acidic solution,the composite insulator core rod would be obviously corroded.When the resin glass fiber inside the rod is corroded by strong acid,the sample is flat and bright.When the surface cracks in mechanical properties,the crack will gradually expand.And the section of the insulator core rod is prone to fatigue fracture.After the insulator is eroded by acidic salt spray,the acid will infiltrate the surface of the core rod and the sheath.The surface of the mandrel or the interface of the plexiglass will be corroded.When the fatigue fracture appears,the fracture surface changes from bright flat to gray uneven,the crack changes from the river pattern to the shell line like shape changes to the fiber bulk,and the root mean square height and the maximum sag height of the surface topography decrease.The anti-pendulum power of the mandrel is decreased with the increase of corrosion test time.Furthermore,the mechanical properties of the insulator are reduced,which will result in the shorter fracture time,larger fractal dimension of fracture,and more complex fracture surface topography of the core rod.关键词：composite insulator mandrel;surface topography;corrosion;torsional vibration fatigue;fractal dimension
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- 1882
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发布时间：2024-01-10 - 摘要：The traditional single-drum optimization model,which only contains the haulage speed and the rotational speed,has been widely used in motion parameter optimization of shearer in academic area.However,the single-drum optimization model cannot totally suits the stress difference between the left drum and the right drum,which leads to the optimized results are not completely applicable to the double-drum shearer.For this sake,a double-drum shearer was taken as the research subject.The double-drum optimization model was proposed whose design variables were the rotational speed of left drum,the rotational speed of right drum and the haulage speed.The motion parameters of the double-drum shearer were optimized by genetic algorithm (GA).The comparison results showed the double-drum shearer with the optimal motion parameters has better cutting performance than that of the industrial application parameters.Further comparison between the optimization results of the double-drum optimization model and that of the single-drum optimization model showed an enhancement of 16.42% in the cutting performance.Thus,the double-drum optimization model is more effective than the traditional single-drum optimization model.关键词：shearer;double-drum model;parameter optimization;cutting performance
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- 2020
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发布时间：2024-01-10 - 摘要：The lubrication state of the working interface of the filtering reducer turning arm bearing is affected by load,contact geometry,rough surface thermal effect and other factors.It is difficult to figure out the lubrication condition of the working interface with different working conditions.In order to study the lubrication performance of the filtering reducer turning arm bearing,the mixed thermal elastohydrodynamic lubrication (TEHL) model was established.Based on the statics and kinematics,the filtering reducer turning arm bearing (ball rolling element-rolling bearing) mechanics was analyzed.Also,the numerical model of TEHL performance of the bearing was established.The discrete convolution fast Fourier transform method was used to solve elastic deformation and surface temperature rise.And the Reynolds equation and energy equation were solved by using the finite difference method.The physical properties,load,velocity, rough surface topography on the bearing lubrication characteristics,and the influence of three-dimensional subsurface stress were investigated.Results indicated that the big radius of roller element of bearing would help to form oil film,and improve the bearing capacity.The average film thickness and temperature has the same change rule with speed and slide-to-roll ratio under different machining surface.When the TEHL of turning arm bearing is gradually getting into the full-film lubrication from mixed lubrication,the max temperature rise will increase at first and then decrease.Decreasing surface roughness would help to improve the lubrication condition of turning arm bearing,decrease the max stress of subsurface,and improve surface contact strength.The established mixed TEHL model of the turning arm bearing can simulate the mixed lubrication state,in which,the contact and fluid lubrication exist simultaneously.The model can reflect all kinds of work conditions turning arm bearing lubrication performance.and judge its working efficiency and service life.关键词：rolling bearing;mixed TEHL;rough surface;subsurface stress
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发布时间：2024-01-10 - 摘要：With the continuous integration of manufacturing and service industries,service plays an increasingly important role in the manufacturing industry.In order to assist designers to achieve product serviceability in the product design process,an information integration method of product design for service-embedded manufacturing was proposed.In order to realize the integration of product design information in the whole life cycle of product,the relationship between manufacturing and service was analyzed firstly,and the integration model for manufacturing and service was proposed.Then the service check list was used to guide designers to focus on the innovation design for product serviceability.The flow and mapping model of information in each stage of service-embedded manufacturing was analyzed,a strategy of information integration was put forward,which consists of five modules of decision-making module,design module,manufacturing module,operation and maintenance module,and recovery module,and the information framework structure of service-embedded manufacturing was constructed.On this basis,an information integration model based on module-driven for service-embedded manufacturing was proposed to organize information resources of design,manufacture,service etc.and support services and manufacturing effectively.Due to the information resources required in each stage of product design need to be collected,organized and matched so as to be used by designers,the ontology semantic extension could be used to standardize the service strategy and service knowledge to realize the information service.In the whole life cycle of product design,the driving module could link up the required information with business process to help enterprises to track and apply the required information resources for service-embedded manufacturing.Finally,a prototype system of product design information integration was developed,and the recycling of waste printed circuit boards was used to illustrate the practicability and validity of the proposed method.关键词：service-embedded manufacturing;product design;serviceability;module-driven;information integration
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- 2000
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发布时间：2024-01-10 - 摘要：Time varying mesh stiffness is one of the main reasons leading to the vibration in a gear transmission system.In order to obtain more accurate dynamic characteristics of gear systems,it is important to investigate the influence of sliding friction and tooth deviation of a gear pair on mesh stiffness.A complete mesh stiffness model was proposed base on the improved energy method with consideration of sliding friction.According to parameter equations of cutting tool tooth flank,the parameter equations of both involute tooth profile and transition curve of gears can be obtained.The presented model considered the influence of wear and profile modification on mesh stiffness by utilizing parameter equations of gear tooth flank and the total mesh stiffness of two meshing gear pairs was obtained by the relationship of tooth clearances derived from tooth deviations and deformation under loading.The influence of tool fillet radius and sliding friction on gear meshing stiffness was analyzed.The total mesh stiffness,load sharing ratio between two meshing tooth pairs and loaded static transmission errors of wear gears and profile modification gears under different loading conditions were investigated.Numerical simulations showed that mesh stiffness decreases with the decrease of tool tip fillet radius.Sliding friction between meshing gear teeth increases the meshing stiffness during the access process but decreases it during the recess process,and the greater the friction,the greater the amount of change in stiffness.Especially under light loading condition,nonuniform wear of tooth profile induces remarkable mesh stiffness reduction and contact ratio decrement.When the load is greater than the profile modification design load,the benefits of modification are not obvious.If the load is lighter than the profile modification design load,the following problems may arise,such as a lack of mesh stiffness,a decrease in contact ratio and a significant increment of loaded static transmission.关键词：mesh stiffness;friction;tooth wear;tooth profile modification;transmission error
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发布时间：2024-01-10 - 摘要：In order to solve the problem of porcelain cracking and peeling of dental Co-Cr-Mo alloys fabricated by traditional cast (CAST) in the clinical application,the metal-ceramic bond properties of Co-Cr-Mo alloys fabricated by selective laser melting (SLM)was studied to explore the feasibility of SLM technology for dental application.Metal-ceramic specimens and thermal expansion coefficient specimens were prepared by SLM machine.Compared with the Co-Cr-Mo alloys made by CAST,the metal-ceramic bond properties of Co-Cr-Mo alloy prepared by SLM were evaluated comprehensively by analyzing the microstructures,phase compositions,thermal expansion coefficient,bonding strength and interface between metal and ceramic,which were obtained with the aid of metallographic microscope,scanning electron microscope,X-ray diffractometer,thermal expansion instrument,and other analytical methods.Experimental results showed that the phase composition of Co-Cr-Mo alloy produced by SLM mainly contains the α phase (84%) with FCC structure,and the ε phase (16%) with HCP structure,and no harmful σ phase.The average linear thermal expansion coefficient in the range of 25～500 ℃ of Co-Cr-Mo alloy by SLM is 13.874
$ \times $ 关键词：selective laser melting;Co-Cr-Mo alloy;bond strength;dental restoration- 2731
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- 2635
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发布时间：2024-01-10 - 摘要：7–ethyl–14–Aminocamptothecin (EAC) is a novel derivate of camptothecin which exhibits favorable antitumor activity.To determine the concentrations of the parent drug and lactam form metabolite (EAC-M) in vivo after intravenous administration of EAC,an UPLC-MS/MS method was established to simultaneously quantify EAC and EAC-M in SD rat plasma.7–ethyl–14–Nitrocamptothecin (ENC) and Chimmitecan (CMT) were used as internal standards.After protein precipitation by adding solution of internal standards and acetonitrile,plasma samples were separated on a Phenyl-Hexyl colum (2.1mm
$ \times $ 关键词：7–ethyl–14–Aminocamptothecin;lactam metabolite;rat plasma;UPLC-MS/MS;simultaneous quantitative analysis- 2343
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- 1932
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发布时间：2024-01-10
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