最新刊期
卷 39 ， 期 3 ， 2007
- 摘要：Abstract:Three-point bending beam is widely used in test of fracture properties for materials.However, a sharp crack can hardly be prepared for the specimen of quasi-brittle materials, alternatively it is reasonable to consider a U-shaped notch, then use stress concentration factor (SCF) to characterize the peak stress at the notch bottom. We studied the SCFs of the three-point bending beams with a U-shaped notch using finite element method, and the results show the variation of the SCF with changing notch depth and notch width, filling the existing vacancy in SCF handbooks. The SCF at the bottom of U-shaped notch of three-point bending beam is smaller than that of the counterpart pure bending beam, and the largest relative difference is -7.3%. We applied the results to determine the dimensionless maximum load bearing capacity and the corresponding deflection of the three-point bending beams, the effect of notch depth and notch width can be considered in a comprehensive way关键词：stress concentration factor (SCF);three-point bending beam;U-shaped notch;notch depth;notch width
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发布时间：2023-11-28 - 摘要：Abstract:Dehiscence on arch dam is very common and worried by the engineers, so it is very important to find the essential cause of dehiscence and provide some useful countermeasures. The essential causes of asymmetric cracks in Si’de arch dam， analyzed by using structural mechanics method and 3D finite element method，is the asymmetric topography and the inadequate design of spillway and dam. The rational measures to deal with the cracks and to strengthen the dam have been provided, namely making upstream rock symmetric, mending the cracks under adequate temperature and pouring reinforced concrete slab on the upstream dam till grouting flat.关键词：arch dam;asymmetric cracks;structure mechanics method;finite element method
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发布时间：2023-11-28 - 摘要：Abstract:As for the coal mining roadway with bolt support, it’s the most dangerous that the roof usually falls because roof bedding separation value is too large. In order to calculate the critical value of roof bedding separation, the mechanism of roof bedding separation was analyzed, moreover, the mechanical models of solid-coal roadway and gob-side roadway were built. Based on analyzing the mechanical property of the two different roadways supported with bolts, the mathematical representations of roof bedding separation critical value were got. Finally, a calculation example was showed, and the results indicated that the roof separation critical value of gob-side roadway is more than that of solid-coal roadway. Furthermore, the representation of gob side roadway coincided with the monitoring value, and the representation of solid-coal roadway can be used to predict the critical value in the period of driving.关键词：bolt support;solid coal roadway;gob-side roadway;roof bedding separation
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发布时间：2023-11-28 - 摘要：Abstract:A step spillway placed behind X-shaped flaring gate pier was proposed and applied in practical engineering. If the first step is higher than the others, cavity will exist between the nappe and the step spillway.The flow with air entrainment will occur on the flow surface of steps. Under this condition, the step can be protected from damage at the discharge over 30 m3/(ｓ·m). The relation of the cavity size, the weir head, the difference between the weir crest and the exit of the flaring gate pier, the drop height, the weir end slope and the step slope were studied in this paper. The formula was deduced to calculate the length of cavity. Calculating results were identical with that of numerical stimulations and experiments. It is shown that the cavity is mainly affected by the drop height, the weir end slope and the step slope.关键词：X-shaped of flaring gate pier;stepped spillway;aerated cavity;numerical simulation
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发布时间：2023-11-28 - 摘要：Abstract:The principle of set pair analysis (SPA) has been attempted to apply to the relation of flood peak and volume. According to the data from Zipingpu station in the Min River, analysis of the relation for flood peak and volume studied with the SPA has been compared with the traditional methods. The results showed that their solutions were consistent, but the presented method of set pair analysis is simpler and easier. The method can display the form of relation visually, and so be potential superior in practice.关键词：set pair analysis;related coefficients;membership grade;grey correlation
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发布时间：2023-11-28 - 摘要：Abstract:Fuzzy C Means(FCM) clustering method and Self-Organizing Feature Map(SOM) clustering method were both employed to decomposed the flow hydrograph to several segments, and the situation of rain and runoff was analyzed in each segment, then two hybrid artificial neural networks (FCMMFN & SOMMFN), based on Fuzzy C Means clustering method and Self-Organizing Feature Map clustering method separately, were applied to simulate the rainfall runoff relationship. The case study in Wangjiachang Reservoir indicated that two clustering methods have the ability to decomposed the flow hydrograph to several segments in which the under-lying mechanisms of streamflow generation appear different. Besides, the two classification based artificial neural networks are both superior to the single multi-layer feedforward network, furthermore, the performance of FCMMFN is better than the one of SOMMFN.关键词：Fuzzy C Means(FCM);Self-Organizing Feature Map(SOM);flood forecasting;clustering analysis;artificial neural networks
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发布时间：2023-11-28 - 摘要：Abstract:In order to study the effect of tunnel to nearby structure on layered soft soil with different foundations,non linear interaction finite element model was set up, which is composed of structure, foundation, soil and tunnel. On the premise of considering gravity, this interaction model was analyzed with time domain numerical method. The results showed when the structure on raft foundation was close to the tunnel, the total displacement at the top of superstructure took place irreclaimable excursions to another direction, the foundation swung, too. But that of the structure on pile raft foundation was not. When tunnel was under structure, the peak shearing force of frame columns was the biggest; then, the structure closing to tunnel, the structure away from tunnel to ten meter; the structure without tunnel was the smallest. When tunnel was away from structure to ten meter, the influence structure was little. The superstructure on the pile raft foundation turning into plasticity more was than that on the raft foundation, and soils around pile-raft foundation turning into plasticity was less than that around the raft foundation.
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发布时间：2023-11-28 - 摘要：Abstract:A combined optimization method is proposed to detect the plate structure with multiple damages. Firstly the variety of the first mode can be superposed under the multiple damages. Then the variety rate of the first mode is introduced as the damage signature, and the feature of the superposition is certificated. Finally a combined optimization method is advanced to resolve the detection of the multiple damages of the plate structure. The example of the damage detection to the plate fixed at four sides reveals that the new method is feasible and effective, it not only can finish the damage detection with high precision, but also can simplify the process of the damage detection of the plate structure.关键词：combined optimization method;variety rate of mode;multiple damages;damage detection;signature for damage detection
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发布时间：2023-11-28 - 摘要：Abstract:To clarify the drag-reducing behaviors of a surfactant solution in turbulent boundary layers, the turbulence structures of cetyltrimethylammonium bromide(CTAB) surfactant solution mixed with NaSal which provide counter ions in a zero pressure gradient boundary layer on flat plates were investigated by a two dimensional laser doppler velocimetry(LDV). The results were found as follows: The peak of the streamwise velocity turbulence intensity for surfactant solution appeared away farther from the wall than that for water, and the second peak occured near the center of the boundary layer where the flow was not in SIS. The drag-reducing surfactant solution depressed the motions associated with ejections of low momentum fluid away from the wall and sweeps of high momentum fluid toward the wall so that Reynolds shear stress was almost zero throughout the thickness of the boundary layer. In the power spectrum of the streamwise velocity fluctuation, the power intensity at low frequencies was larger and the power intensity at high frequencies was smaller than that for water. These showed that the surfactant additives can weaken the correlation between the two components of velocity fluctuation, and enlarge the turbulent structure scales in the boundary layers.关键词：reducing-drag surfactant solution;turbulent boundary layer;reynolds shear stress;turbulent density;quadrant analysis
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发布时间：2023-11-28 - 摘要：Abstract:Under the day-ahead electricity market, it is an important strategy to improve the profit of an electricity producer by reasonably bidding the block electric quantity and price. In order to present the strategy that satisfy risk requirement, this paper presents a new method to bid block electric quantity and price. The method analyses MCP forecasted error at first, and then calculate its probability distribution. At last, the VaRs of error under different confidence are obtained, which could guide IPP to submit block electric quantity and price. The results declare that the method is not only satisfies the request of simple and practicality, but it also meets all the conditions of day-ahead power market.关键词：electric power market;bidding;Market Clearing Price (MCP);Value at Risk (VaR);block price
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发布时间：2023-11-28 - 摘要：Abstract:In order to solve the optimal problems of complex and gigantic hydro power system, a new global optimization method, named Triangle Gyration Algorithm (TGA) was proposed. It embodies the characteristics of simple structure, good robust and fast convergence. The individual of algorithm in every generation is guided by the best objective function value and transformed by the trigonometric function, which ensure the whole progress converge quickly at the global optimal points. Compared to the usual optimization methods with a numerical example and short term scheduling of a hydro plant, TGA manifests the better performance in running time and optimal results and it provides a profit 8.58% more than DP does. The algorithm has the catastrophe mechanism capable of preventing algorithm being trapped in local optimization, simple structure, and overcomes the blindness of random searching. Iteration mechanism and value selection of TGA manifests essential difference from other traditional optimal methods.
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发布时间：2023-11-28 - 摘要：Abstract:The single crystal of 1,1-diamino-2,2-dinitroethylene was measured by the tetracyclic diffractometer. The crystal has monoclinic P21/n symmetry with a=0.69283 nm，b=0.66201 nm，c=1.13230 nm，α＝89.948°，β＝90.533°，γ＝89.894°，V＝0.5193 nm3，Dx=1.893 g·cm-3，Z＝4，F(000)=304. The results indicated that the molecular arrangement inside the crystal is two dimensional wave shaped layers, with extensive intermolecular hydrogen bonding within the layers and with simple van der Waals interaction between the layers. The phase transitions of FOX-7 was tested by temperature controlled X-ray power diffraction (XRD) when FOX-7 had been heated. It was found that there are two temperature dependent phase transitions, and the XRD patterns of α-phase,β-phase,γ-phase were obtained. When the temperature decreases, α-phase can directly change to β-phase.关键词：1,1-diamino-2,2-dinitroethylene;crystal structure;phase transition
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发布时间：2023-11-28 - 摘要：Abstract:The acid relaxed collagen fiber was prepared from pigskin, which was unhaired, pretreated with A.S.1398 protease and sodium borohydride. The pretreated pigskin was relaxed in the dilute acetic acid system, and the relaxed mass was dispersed, neutralized and ice dried to prepare acid relaxed collagen fiber. The purity and properties of the fiber were determined. The results showed that the yield could reach 47.8% on the basis of dry weight. According to the electrophoresis and amino acid analysis results, except a little amount cystine existed, the fibers have good purity. The thermal denaturation temperature of the fiber was 58.2 ℃, and its isoelectric point was 7.44, which determined by Zeta potential determination method, and its natural triple helix conformation was maintained according to the circular dichroism and FT-IR results.关键词：acid relaxed collagen;collagen fiber;native characteristic;pigskin
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发布时间：2023-11-28 - 摘要：Abstract:The growth and response of Gracilaria lemaneiformis to Cadmium stress in different cultivation conditions were studied, the effects of physiological and biochemical characteristics of G. lemaneiformis were explored while appending phosphate or ethylenediaminetetra-acetic acid (EDTA) into the cultured medium. The results showed that the growth of G. lemaneiformis was inhabited gradually with the increase of the content of Cadmium, the contents of phycoerythrin, Chlorophyll and soluble protein decreased, the activity of peroxidase increased at first reached the maximum value at 4.5 mg/L of Cadmium, and then dropped. While appending phosphate or EDTA into different cultured medium, the growth of G. lemaneiformis, the contents of Chlorophyll and soluble protein increased and dropped gradually with the increase of the content of Cadmium, the activity of peroxidase increased during the initial days and decreased with the prolong of time (>6 days). All results indicated that the resistance of G. lemaneiformis to Cadmium stress in low content environment was strong, the poisons of Cadmium was restricted to the factors of time and its concentration; meanwhile, phosphate and EDTA could benefit G. lemaneiformis to resist Cadmium stress to some degree.关键词：Cadmium stress;Gracilaria lemaneiformis;ethylenediaminetetra-acetic acid (EDTA);soluble protein;peroxidase
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发布时间：2023-11-28 - 摘要：Abstract:Using the thermal simulation instrument Gleeble-1500D, the effect of electric current magnitude (1.0×104~2.3×104 A) on the combustion synthesis of Fe-V-C system was studied. It was shown that with the action of electric field, VC/Fe composite with hardness about 60~67 HRC can be obtained at rather low temperature (632~740 ℃). With the increasing of electric current, the ignition temperature becomes lower, the ignition delay time becomes shorter, the densification and the hardness of samples increase, the particle size in the sample does not change considerably in the range of 1.0×104~1.6×104 A but increases in the range of 1.6×104~2.3×104 A.关键词：Fe-V-C system;combustion synthesis;electric field;composite
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发布时间：2023-11-28 - 摘要：Abstract:Relaxor ferroelectric 0.68 Pb(Mg1/3Nb2/3)O3-0.32 PbTiO3 ceramics with fluoride (LiF、MgF2、CaF2) sintering aids were prepared by the columbite precursor method. The phase composition and microstructure of ceramic samples was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the dielectric and piezoelectric properties were measured. The results showed that pure perovskite phase was obtained for all the specimens and no other phase was detected. The grain size is larger (about 3~4 μm) for the PMN-PT ceramics with LiF and MgF2 sintering aids, but smaller (approximately 0.5~1 μm) for the pure PMN-PT ceramics and that with CaF2 sintering aids. For the PMN-PT ceramics with LiF and MgF2 sintering aids, the maximum dielectric constants increase, the piezoelectric properties are improved and the diffusion phase transition become weak. But for the PMN-PT ceramics with CaF2 sintering aids, the maximum dielectric constants decrease, the piezoelectric properties deteriorate and the diffusion phase transition become strong.关键词：PMN-PT ceramics;columbite precursor method;fluoride;dielectric and piezoelectric properties
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发布时间：2023-11-28 - 摘要：Abstract:The reinforced HDPE/PA66 in situ fiberized composites were prepared by extrusion-drawing injection method. The influence of PA66 mass content(cm) on the PA66 fiberization, tensile strength(σt) and Young’s modulus(E) of the composites, together with their functional mechanisms were studied in contrast to the normal blended materials without drawing. The results showed that as cm rises from 0 to 25%, the number of PA66 fibers in-situ formed increases whereas their cross size and dispercity decrease till cm =15% and then increase. The σt and E of in-situ composites increase 45% and 60%,respectively,relative to neat HDPE at cm=15%. The fiberization of PA66 droplets through coalescence-deformation during melt-drawing plays a key role in the above variation of PA66 phase morphology with cm. The counterbalanced function between the reinforcing effect of dispersed phase on matrix and the interfacial flaw effect of the two phase and the rigidizing effect of fiber on matrix controlled by morphology of dispersed phase, are dominant factors of deciding the above σt ~ cm and E ~ cm relations, respectively.关键词：polyamide 66;high-density polyethylene;in-situ composites;composition;fiberization;reinforcing effect
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发布时间：2023-11-28 - 摘要：Abstract:Two kinds of light-shield agents of ZnO and carbon black were used to improve the ageing resistance of polyacetal (POM). Changes in exterior and interior characteristics, such as melting point, crystallinity, carbonyl and molecular weight of POM under UV-irradiated or thermal-oxidative ageing were investigated via DSC, FTIR and Ubblohde type viscosity in relation to molecular weight. The results showed that UV radiation mainly led to crystal destruction and molecular degradation on the surface and recrystallization on the interior part of the sample. The restructuring and crystallizing of the amorphous phase occurred during thermal-oxidative ageing. Both changes induced crystallinity and tensile yield strength increase but toughness and elongation at break decrease，for example, after UV irradiation for 1000 h, the crystallinity of polyacetal exterior part increased from 42.06% to 76.27%,while the charpy impact strength declined quickly from 6.74 kJ/m2 to 1.85 kJ/m2. Adding 1.5%~3% carbon black or ZnO could maintain the properties of POM by means of restraining the molecular degradation and recrystallization attributed to UV-irradiation. However, the adsorption to antioxidant of carbon black might accelerate thermal-oxidative degradation of POM.关键词：light shield agent;POM;crystallization;ageing-resistance
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发布时间：2023-11-28 - 摘要：Abstract:The capabilities of the fractional differential approach for enhancing textural features of two-dimensional digital images, involved Lateral Inhibition Principle, the multiform covering templates and algorithms of digital image’s fractional differentiation were discussed. Firstly, the kinetic physical meaning of fractional differential and the relationship between fractional calculus and classical time-frequency analysis were deduced,and used to handle x-y separability of two-dimensional fractional calculus in undemanding conditions. Secondly, the difference of two Gaussians receptive field between fractional and integral differential of digital image was discussed in view of signal processing and biologic vision nerve model respectively. An analysis of its Mach band was also included. Finally, multiform covering templates and a numerical algorithm for computing fractional differential for digital image were discussed. Numerical experiments showed that the textural detail enhancing capabilities of fractional differential-based texture operator are better than that of integral differential-based one for rich-grained digital images.关键词：fractional order stable coefficient;partial fractional calculus;antagonism;fractional differential covering template;motion blur;multi-scale fractional differential
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发布时间：2023-11-28 - 摘要：Abstract:To efficiently solve the private key leak and management problems in broadcast encryption systems, a new efficient practical ID-based broadcast encryption scheme was presented. The bilinear paring on a super-elliptic curve was used to construct the broadcast encryption and decryption algorithms, which greatly saves the broadcasting communication transmission bandwidth. In the key distribution process, self-enforcing protection strategy was introduced by computing one user’s decryption key through his secret information, which reduces the risk for one user of leaking his private keys. Security proof against k collusion attack under the difficulty of extended k-BDHI assumption was given.关键词：broadcast encryption;key management;bilinear map;Public Key Infrastructure (PKI)
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发布时间：2023-11-28 - 摘要：Abstract:It is a critical problem to detect distributed denial service (DDoS) attack with low false positive and negative in Internet. However, precisely detecting DDoS attack is very difficult, because there isn’t an essential difference between attack flow and normal flow. Attack packets with spoofing source IP address, consuming out bandwidth and system resources of destination hosts, can’t build a two way connection with destination. From this view,a new conception to reflect the exception of network flow, One-Way Connection Density (OWCD), which can detect DDoS attack,was proposed. In order to understand the characters of OWCD series, the time series analysis of OWCD series was studied and the OWCD was used to detect DDoS. Experiments showed that OWCD series is a white noise series. It can not only detect DDoS attack, but also indicate attack intensity.关键词：distributed denial of service attack;One-Way Connection Density(OWCD);time series analysis
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发布时间：2023-11-28 - 摘要：Abstract:The realization of analog circuit of fractance is most important for the fractional calculus application. An approach to design alterable order fractance using Operational Transconductance Amplifiers (OTA) by cascading finite two-port circuit network was presented. The fractance order can be changed by adjusting the controlling current of OTA without changing the circuit structure. The simulations are in agreement with the theoretical values.关键词：fractional calculus;fractance;fractional operator;Operational Transconductance Amplifier (OTA);function approximation
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发布时间：2023-11-28 - 摘要：Abstract:In order to save the communication channel resource, the synchronization of two 5-scroll hyperchaotic attractors was realized using wavelet transform to remove the detailed information of the feedback variable so as to compress its frequency spectrum width. In the transmitter, the high frequency parts of variable z were filtered out through a wavelet filter, then the low frequency parts were reconstructed and sent to the receiver. In the receiver, this reconstructed signal was used as feedback signal and the synchronization was realized. Using this synchronous method, the system resource was saved, and because the transported signal was not a whole chaotic signal, the security performance of the system was improved.关键词：5-scroll hyperchaotic attractor;wavelet transform;synchronization
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发布时间：2023-11-28 - 摘要：Abstract:Weak signal detection of strong fractional noise was proposed using Duffing oscillator and fuzzy adaptive Kalman filter. A dynamic system was formulated based on the orthonormal wavelet decomposition coefficients of fractional noise. The noisy error signal was added into Duffing chaotic oscillator, and based on the motion transition of a chaotic system, new schemes of detecting weak sinusoidal signal berried in strong fractional noise were put forward. A new statistical understanding of immunity to noise of Duffing systems was also presented. Simulation results demonstrated the effectiveness of the proposed algorithm.关键词：fractional noise;Duffing oscillator;weak signal detection;Kalman filter
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发布时间：2023-11-28 - 摘要：Abstract:In view of the high demand on the coaxial tolerance of linear induction accelerator in centering assembling and considering the interaction among flange, bolts and gasket, finite element analysis was adopted and a 3-D finite element model of accelerator in centering assembling with bolted flange connection was built. The influence of the bolt forces on coaxial tolerance in the accelerator centering assembling was analyzed. The difference of the bolt forces in the horizontal position has more contribution to coaxial tolerance while the difference of the bolt forces in the vertical position has less so that the control of the bolt forces in the horizontal position should be imposed. The result can be used to instruct the centering assembling process to improve the coaxial tolerance of accelerator.关键词：bolted-flange connection;accelerator;centered assembling;coaxial tolerance;finite element analysis
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发布时间：2023-11-28 - 摘要：Abstract:Based on the information prediction characteristics of the grey system theory and bootstrapt statistics, a grey bootstrap model (GBM) of dynamic prediction for manufacturing errors was proposed to resolve problems about information prediction. Bootstrap resampling is used in the process of modeling the grey differential coefficient function to mine more information about systems, and the grey bootstrap model can predict transient state of the true value and its distributing interval exactly. Computer simulation was applied to deals with the prediction of many kinds of random errors such as normal distribution, Rayleigh distribution, triangular distribution, uniform distribution and mixed distribution etc, and prediction of some systematic errors such as increasing tendency errors, decreasing tendency errors and periodic change tendency errors were involved in it as well. Experiment was carried out to predict the roundness errors of grinding rolling bearing rings. Computer simulation and experiment showed that the grey bootstrap model allows small sample, different type of random errors and systematic errors, and the percentage of accuracy can be up to above 95%.关键词：manufacture;errors;prediction;grey system theory;bootstrap
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发布时间：2023-11-28 - 摘要：Abstract:The dynamic performance of engine can be improved by supplying gas intake in the course of intake. Dynamic performances in inlet pipe were analyzed theoretically in engine. Structural parameters of inlet pipes and resonator were calculated and validated in single-cylinder motorcycle engine. Results showed that, in a certain velocity interval, resonance of gas intake can improve the maximum power and torque of motorcycle engine about 6 to 8 percent, and with the changes of resonator’s cubage, the power and torque of engine are changed regularly. It can be concluded that in a certain velocity interval, resonance of gas intake can improve the dynamic performance of single-cylinder engine.关键词：single-cylinder engine;resonance;dynamic performances
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发布时间：2023-11-28 - 摘要：Abstract:The regeneration purging and filter is one of the prevent pollution methods efficiently for diesel engine. The structures of the regeneration purging and filter system in diesel engine,the transition device, and the regeneration chamber were studied.The method of estimating the efficiency of the purging and filter was proposed.关键词：diesel engine;exhaust PM;regeneration;purging and filter
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发布时间：2023-11-28
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