最新刊期
卷 38 ， 期 3 ， 2006
- 摘要：Abstract:The non-linear dynamic stability and chaotic motion of viscoelastic transmission belt with time-dependent velocities and subjected to a transverse distributed varying external excitation is investigated. Based on the constitutive description of Kelvin viscoelastic material and the motion equation of the axially moving belt, the nonlinear dynamic model that dominates the transverse vibration of the viscoelastic transmission belt is established. And then one mode approximation of the governing equation is obtained by the Galerkin's method. This approximation leads to a parametrically excited Duffing's oscillator which exhibits a symmetric pitchfork bifurcation as the axial velocity of the belt is varied beyond a critical value. Finally, Melnikov's criterion is employed to find out the parameter regime（such as steady velocity, fluctuation velocity, external force and material property etc） in which chaos occurs. It is found that:1) Chaos region is above a line in the first quadrant if both velocity and external fluctuation coexist. And chaos region become large with the increasing of frequency of external excitation, but chaos region become small with the increasing of frequency of velocity fluctuation. Meanwhile the line always passes a fixed point if the frequency of external excitation or velocity fluctuation is not change. At this time chaos can not be controlled by the adjustment of external force or speed magnitude. 2) For lower speed fluctuation frequencies, one can employ higher steady speeds and maintain the amplitude of speed fluctuations to avoid chaos, however, for higher speed fluctuation frequencies, one can only avoid chaos by decreasing the steady velocity of the belt. 3) Chaos region become small with the increasing of material viscosity, but chaos regions become large with the increasing of material stiffness.关键词：transmission belt;viscoelasticity;non-linear dynamic stability;bifurcation;chaos
- 1920
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发布时间：2023-11-28 - 摘要：Abstract:The process of clear-water scour is very usual phenomena in natural river. So far, most of the previous studies mainly aim at the calculation of bed armoring layer and process of sediment transport with the action of the flow scour. However, there has been very little attention paid to the flow structure, in particular, the changes of flow structure among different armoring levels for the limitation of monitoring setups. The stable bedform and flow structure on the clear-water scour in gravel-bed flume have been measured by means of acoustic doppler velocimeter (Sontec ADV) and Nikon DTM. The results show there is a close relationship among flow, bedload transport, bed material and bedform. The distribution of coarse surface on the armoring layer was affected by the initial bed and its armoring degree with the closely experimental condition. The mean velocity profile may be changed from the logarithmic velocity distribution to the S-shaped curve along relative water depth direction because of the changes of impacted factors, in addition, there is a very good interrelationship between the maximum of turbulence kinetic energy (TKE) and the minimum of mean velocity, but the transitional region and detail location were strongly related to the experimental conditions of flow, sediment and bedform.关键词：clear-water scour;stable bedform;flow structure;gravel-bed
- 2097
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发布时间：2023-11-28 - 摘要：Abstract:Large historical flood discharges can play an important role in hydrologic frequency analysis.However their magnitude and recurrence interval must be estimated and they suffer from a serious uncertainty. Such uncertainties ought to be taken into account in frequency analysis.The study on influence of uncertainty upon frequency analysis has been conducted by using a statistical experimental method. The results indicate that although estimated magnitude and recurrence interval of large historical flood discharges are involved in uncertainties, their positive role may be significant in most cases. Moreover, under the situation of uncertainties in large historical flood, the quantities estimated by probability weighted moments may be more robust than those by a optimal curve fitting method.关键词：extraordinary flood (large historical flood);frequency analysis;statistical experiment
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发布时间：2023-11-28 - 摘要：Abstract:The conventional design approach of soil nails often results in an underestimation of bond stress, which in turn gives an uneconomical design. Therefore this paper aims to propose a methodology to account for the effect of pullout tests on the bond stress. This procedure is formalized in the Bayesian framework. The prior distribution of bond stress is formulated on the basis of the available pullout test data. Three cases of Bayesian updating of bond stress based on pullout tests are studied; namely, all pullout tests not conducted to failure, a part of pullout tests conducted to failure, and all pullout tests conducted to failure. The results indicate that the updated coefficient of variation of bond stress can be significantly smaller than that before the pullout tests. The updated mean bond stress is higher than the prior value when all pullout tests do not conduct to failure. The updated mean bond stress is smaller than the prior value when all pullout tests conduct to failure. With the increase of test loads, the updated mean bond stress increases, but the updated coefficient of variation decreases.关键词：soil nails;bond stress;pullout tests;Bayesian analysis;failure
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发布时间：2023-11-28 - 摘要：Abstract:A 3-D viscous combined model adopting the large eddy simulation technology was developed, and employed in simulating the 3-D flow through a high head and high-rotation hydraulic turbine with the runner calculated in relative coordinate system and the draft tube computed in absolute coordinate system. The finite volume approach in space and the predictor-corrector method in time for the weakly compressible flow governing equations and a “tinny-slip" boundary condition for the solid wall were adopted, and the connected condition at the interface between the absolute coordinate system and the relative coordinate system was established. The pressure and velocity fields in the hydraulic turbine are simulated, which are consistent with the experimental results. Under partial load operating condition, especially, the separated flow and the negative pressure at the exit surface of the blade of the runner and a strong vortex in the cone and elbow section in the draft tube appear, even the back-flow near center line at entrance of the draft tube is in existence. The demonstration of the vortical band in the draft tube under partial load operating condition is successfully simulated, and its frequency is about one third of the rotating frequency of the runner, this vortical band is one of the main reasons for the vibration of the turbine generator unit.关键词：hydraulic turbine;vortical band;large eddy simulation;finite volume approach
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发布时间：2023-11-28 - 摘要：Abstract:In order to study evolution of natural runoff, this paper introduces fuzzy pattern recognition theory and method to research runoff series, presents the method of analyzing runoff characteristic with clustering of high, middle and low levels of runoff.This paper also gives the method of analyzing multidimensional high and low states periodicity of natural runoff based on fuzzy recognition arithmetic.The runoff characteristic, its periodicity and subjective of high and low levels of annul runoff from monthly average runoff of Sanleiba hydrology station in lower Bailongjiang River, a branch of Jialingjiang River are giver as example. The results of multidimensional runoff characteristic analysis are related to analysis scale and data dimension.关键词：runoff characteristic;analysis of low and high runoff;fuzzy cluster analysis;fuzzy pattern recognition
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发布时间：2023-11-28 - 摘要：Abstract:Unloading confining pressure tests of rock specimens with fixed displacement after conventional triaxial compression are conducted. Based on the complete procedure of unloading confining pressure, the failure features and strength of specimens are analyzed. The test results show that unloading fracture type is shear failure at the pre-peak and tensile-shear failure at the post peak. Failure phenomenon is easier to happen suddenly in the process of unloading confining pressure at the pre-peak than at the post-peak. In addition, the axial supporting capacity is very sensitive to the change of confining pressure. This is the result of the mosaic community between fractured rock blocks and reflects the structure effect along friction-sliding surface.关键词：unloading confining pressure;deformation;supporting capacity
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发布时间：2023-11-28 - 摘要：Abstract:The Elman network has a context layer which feeds the hidden-layer output at previous moment back to the hidden layer current input. This article improves the Elman network. The monthly runoff of the upper reach of the Min-jiang River is examined by improved Elman Network. The result of prediction shows the model is feasible and reasonable.关键词：upper reach of the Min-jiang River;Zi Ping-pu;improve Elman network;monthly runoff prediction
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发布时间：2023-11-28 - 摘要：Abstract:In order to evaluate the dam safety of Tanzikou reservoir, the arch dam and its gravity abutments on the left and right sides of the reservoir have been studied to ascertain the defects and the main reasons causing the defects. Results indicate that defects do exist due to irreasonable designs and poor construction quality of the arch dam. On the basis of the reasons causing the defects of the arch dam, treatment measures and design proposal have been put forward in this study. Results of the observation and inspection after the treatment of the dam have justified the feasibility of the treatment measures. Furthermore, a satisfactory operation of the dam has been obtained.关键词：arch dam;gravity abutment;stability;stress;defects
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发布时间：2023-11-28 - 摘要：Abstract:Based on an on-line mini-column continuous determination system (MCCD), the exchange performances of macroporous strong base anion exchange resins (MSBAR) were determined. Various effect factors to the performance of MSBAR were examined under the dynamic exchange condition, and optimizing parameters for determining the exchange capacities of MSBAR were obtained. Length of the minicolumn is 60 mm, its inner diameter is 3.0 mm; the exchange layer height of the resins is 40 mm, the added resin amount is 0.1720 g， the concentration and flow rate of sodium hydroxide used as regenerant is 3% and 0.6 ml/min, respectively; the consumption of the regenerant is 433 ml/g (resin), 20 mg/L hydrogen chloride solution is used as the sample water, its flow rate is 1.3 ml/min; the experimental temperature is （23±5） ℃. The exchange performances of various MSBAR, gel type resin, uniform and non uniform size resin were determined and compared. The correlation of MCCD and GB methods are very good (r=0.990). The MCCD method possesses some merits: a little of reagent consume, simply to operation, easy to automatization and so on. Five parameters of the breakthrough exchange capacity, equilibrium exchange capacity, total exchange capacity, exchange rate and utilizing ratio can be obtained simultaneously by using once MCCD.关键词：dynamic determination;macroporous strong-basic resin;mini column;chloride;exchange capacity
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发布时间：2023-11-28 - 摘要：Abstract:With the p-DCB, o-DCB simple eutectic system, the purification process of organic materials in an inclined column crystallizer at total reflux and steady state was investigated and an axial dispersion model for purification section of the inclined column crystallizer was developed on the basis of sweating mechanism. The results indicated that inclined column crystallizer has strong adaptability for purifying organic materials, the product purity can easily exceed 99.9% at the range of feed composition among 62.0%～85.0% and internal stirring speed among 5～10 r/min.The axial dispersion model can be used to explain the concentration distribution profile in inclined column crystallizer.关键词：column crystallizer;axial dispersion model;sweating;melt crystallization;purification
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发布时间：2023-11-28 - 摘要：Abstract:The separation performance of the hydrocyclone is affected by its flow field characteristic, based on this reason, the study of flow field is very important. But because of various restrictive conditions, application of the experiment method to detect the flow field of all hydrocyclones is not possible, 3D computational fluid dynamics algorithms is an efficient method, the flow field and the turbulent flow characteristics are predicted here by a Reynolds stress model and SIMPLEC calculation method, the results give some new understanding on three-dimensional velocity distribution. Furthermore, the calculation results indicated that the main separation area existed asymmetry and unsteady flow field which was produced by inlet velocity and inlet arrangement structure, as well as the cone angle of hydrocyclones. Besides, the simulation results showed that the pressure gradient was existed within air core from the underflow orifice to vortex finder, this is a reason of the gas flow inside air core. Depending on the aforementioned flow field characteristics, the factors of forming high concentration area were analyzed. Those above provided the evidence for new understanding of a hydrocycloe flow field and separation mechanism.关键词：hydrocyclone;Reynolds stress model;numerical simulation;flow field character
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发布时间：2023-11-28 - 摘要：Abstract:Poly(ethylene oxide) alkyl ether C18E20 was in combination with each of three n-fatty alcohols (1-octanol, n-dodecanol and n-octadecanol) respectively as a model of non-ionic surfactant and polar organic substance composites, which was spreaded onto air-water interface and formed a mixed monolayer on a Langmuir trough. The stability of each mixed monolayer was analyzed by use of π-A isotherms at various mole fractions of the C18E20-fatty alcohol pair. It was found that the stability of the C18E20 monolayer could be enhanced by combining with fatty alcohols, based two points. The one is the expanding degree of the monolayer decreases as the surface pressure of the mixed monolayer is under the inflexion of the π-A curve, and the other is that the plateau length of the curve decreases after the surface pressure is above the inflexion of the π-A curve. The condensability of the mixed monolayer increases with the mole ratio of fatty alcohol, or with the hydrophobic chain length of the alcohol more close to that of C18E20. For almost all of the π-A isotherms of the mixed monolayers, the inflexion and the plateau always appeared near the surface pressure 30 mN/m, which showed that a phase separating occurs at a higher surface pressure. It was also observed that the mixed monolayer is in a favorable condition to the compatibility of the multiple surfactants, as the mole ratio of C18E20 and octadecanoic alcohol is equal to 3 ∶1.关键词：poly(ethylene oxide) alkyl ether;fatty alcohol;mixed monolayer;stability;air-water interface
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发布时间：2023-11-28 - 摘要：Abstract:A new type of adsorbents was prepared by loading Zr(Ⅳ), Al(Ⅲ) and Fe(Ⅲ) onto collagen fiber through coordinating reaction and the adsorption performances of the absorbents to F- in aqueous solution were investigated. The results showed that all the three adsorbents exhibited good ability of removing F- in the pH range of 4～9. The sequence of their adsorption capacity for F- is ZrCF >AlCF > FeCF, and their adsorption isotherms can be well fitted by the Langmuir equation. Furthermore, it was shown that the adsorption kinetics of F- on the ZrCF can be well fitted by the pseudo-second-order rate model, and the adsorption capacities caculated by this model were consistent with measurements. The F- adsorbed on ZrCF can be easily desorbed by using 0.05 mol/L sodium hydroxide solution with the extent of desorption > 97%.关键词：collagen fiber;loaded metal ions;fluoride ion;adsorption
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发布时间：2023-11-28 - 摘要：Abstract:The systematic experimental investigations were carried out using TCF-360 centrifugal air classifier with the vane rotor. The relationship among the operating parameters and cut size and sharpness index of the air classifier was established. The results showed that the classifier rotating speed, the volumetric flow rate, the secondary air flow rate, the solids loading in the classification zone, and the particle size distribution of raw material have strong influence on the performance of an air classifier. If the air flow and the rotating speed of the classifier are altered to the same extent between the air drag force and the centrifugal force, the cut size will change a little, but the sharpness index and the wear rate will increases as the air flow rate and rotating speed are raised. The investigations can help to improve the operation conditions and also to optimize the geometry of an air classifier.关键词：air classifier;solids loading;cut size
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发布时间：2023-11-28 - 摘要：Abstract:The kinetics and thermodynamics of Pb2+、Cd2+、Ni2+、Ag+ adsorption on a low-cost adsorbent, natural vermiculite, were studied under the condition of pH=4～5, t=(20±1) ℃. Pseudo second order model was used to describe the reaction rate,and the adsorption capacity calculated by the model was consistent measurement, with the correlation coefficient（r） more than 0.9. The kinetic rate constants for metal ions are in the order of Ag+＞Pb2+＞Cd2+＞Ni2+.The adsorption isotherms for metal ion follow both Langmiur and Freundlich isotherm model, with r is more than 0.99. The adsorption capacities for metal ions are in the order of Pb2+＞Cd2+＞Ag+＞Ni2+. Also, the competitive adsorption of four metals adsorbed on vermiculite was studied. The Pb2+ is most effectively adsorbed on vermiculite and the selectivity of metal ions adsorbed on vermiculite is in the order of Pb2+＞Cd2+＞Ni2+＞Ag+.关键词：vermiculite;metal ions;kinetics;thermodynamics
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发布时间：2023-11-28 - 摘要：Abstract:Hydroxypropyl chitosan (HPCTS) with good water-soluble was synthesized through modified chitosan, which is pre-basified with propylene epoxide in the isopropanol solvent. The properties of HPCTS were studied. The results showed that HPCTS with degree of substitution(DS)≥0.40, is dissolved completely in water over pH＝1~13, and has higher moisture absorption; and moisture retention than CTS in the same condition, and has good antibacterial effect as CTS.
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发布时间：2023-11-28 - 摘要：Abstract:Ultrasonic irradiation was employed to prepare polyaniline (PANI)/carbon nanotubes (CNTs) nanocomposite by chemical oxidative polymerization of aniline on the surface of CNTs. The dispersion of CNTs in HCl solution with the aid of aniline by ultrasonic irradiation was better than that by conventional stirring. CNTs were shortened by ultrasonic irradiation and well encapsulated by PANI. The thickness of PANI coating can be adjusted by changing the ratio of aniline to CNTs. CNTs didn’t affect the doping degree of PANI, however stabilized the quinoid structure of PANI. The conductivity of PANI/CNTs composite with the CNTs content of 12.82% was 9.5 times of pure PANI.关键词：ultrasonic irradiation;carbon nanotube;polyaniline;chemical oxidative polymerization
- 1930
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发布时间：2023-11-28 - 摘要：Abstract:For utilizing phosphogypsum effectively in cement, by measurement techniques such as infrared spectrum and color mass spectrum et al, organic matters in phosphogypsum were analyzed qualitatively and quantitatively. Their influence on the properties of cement was also investigated. The results showed that organic matters in phosphogypsum were mainly C5H10O3, C2H3O5, C6H14O, C5H10O2. They were physically adsorbed on the surface of phosphogypsum crystals and their content fell within the range of about 0.1%～0.2%. The presence of organic matters increased the setting time of cement and reduced the strength, particularly remarkablely in the 28 days compressive strength. Their influence could be cleaned out by floating pretreatment.关键词：phosphogypsum;organic matter;cement
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发布时间：2023-11-28 - 摘要：Abstract:Using a new lubricant with superfine WS2 powder (grain size ＜ 500 nm), as additive, a new type of WS2 high temperature lithium complex grease was studied. This grease has fine fiction and wear characteristics such as high drop point, high oil film strength, low friction factor. It provided a new method for taking full advantage of rich tungsten resource in China. In addition, the mechanism of resistance to wear and anti-attrition of superfine WS2 powder was analyzed. The results showed that superfine WS2 powder has the lamellar structure, which can takes shearing effect along weak-bonded bedding-plane and oil micro-pool effect. Under high temperature, solid transferred films are created on worn surface, and WS2 is transformed to WO3 which can prevent being further oxidized.关键词：WS2;superfine powder;lithium complex grease;high temperature friction and wear
- 1882
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发布时间：2023-11-28 - 摘要：Abstract:The aim of route optimization in Mobile IPv6 is to shorten the end-to-end delay between the mobile node and the correspondent node, but the impact of route optimization on the network performance is still unclear. The NS-2, a network simulation software,was used to create a fairly complicated Mobile IPv6 network environment for observing the impact of the route optimization on some typical Mobile IPv6 network performance parameters, such as handoff latency, packet loss and end-to-end delay. By analyzing the simulation results, an advanced formulas of handoff latency and packet loss was put forward,and the results showed that the route optimization may increase the handoff latency and packet loss.关键词：Mobile IPv6;route optimization;network performance;NS-2
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发布时间：2023-11-28 - 摘要：Abstract:For optimizing the Grid resource management and task scheduling effectively, a Grid Resource's Domain Split Management Method (GR-DSMM) was presented, which was based on association rules to group the sub-tasks. Firstly, in order to enhance the association between the sub-tasks in one sub-task-group and strengthen the independency between the groups, the method grouped all sub tasks, which was syncopated in users' tasks according to the association between the sub-tasks. Next, the GR-DSMM took the sub-task-group as one execution unit, which could reduce the frequent communication between the sub-task-groups, and could improve the system's efficiency. At the same time, the method divided the grid resources into domain split according to the sub-task group's resource demands. The method managed the Grid resources taking a domain split as one basic unit. Finally, the performance of GR DSMM was compared with that of multiple queue Backfilling scheduling algorithm and FCFS scheduling policy by emluator, and the superiority and practicability of this method was proved.关键词：Grid;association rules;resource management;task scheduling
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发布时间：2023-11-28 - 摘要：Abstract:The automated geometry reasoning system based-on forward chaining is used as the reasoning engine in the intelligent geometry teaching system. The reasoning engine spends much time match geometry information to rules in the reasoning process and then decreases the reasoning efficiency of the system seriously. In order to improve the efficiency of the reasoning engine, a new geometry theorem proving method, named automated geometry reasoning network was put forward,in which the Rete pattern matching algorithm is integrated into the reasoning engine. The reasoning efficiency can be improved by eliminating redundancy computation on matching geometry information to rules in the reasoning process. The reasoning program based on the automated geometry reasoning network method, named iGeo, was implemented in Lisp. The iGeo was tested with more than 50 nontrivial geometry theorems. The experimental results demonstrated that the iGeo is very efficient.关键词：redundant match;Rete algorithm;reasoning fixed-point;forward chaining;Lisp
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发布时间：2023-11-28 - 摘要：Abstract:A nonuniform quantization index modulation watermarking algorithm based on image wavelet transform was presented to improve the robustness and invisibility of digital watermark. By taking discrete wavelet transform of original image, the middle-frequency wavelet coefficients, which were divided into small blocks, were selected as carrier of watermark information. A two-value watermark sequence was embedded into the mean values of block coefficients by applying non-uniform quantization index modulation. According to human vision system, different blocks used different quantization steps and were adaptive to the difference of adjacent coefficients. Experimental results showed that this algorithm can get a watermarked image with perceptual invisibility, high security and strong robustness against common image attacks.关键词：digital watermarking;discrete wavelet transform;nonuniform quantization index modulation
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发布时间：2023-11-28 - 摘要：Abstract:An all-digital carrier phase acquisition scheme was presented to solve the problem of carrier phase recovery, which is specially critical and hard in the demodulation of trellis coded quadrature amplitude modulation (TC-QAM). Algorithms,such as automatic frequency control (AFC), automatic gain control (AGC), phase amplitude tracking (PAT), and phase ambiguity detecting (PAD), were jointly used in this scheme. Simulations indicated that, in the condition of without any preambles, carrier phase could be acquired fast and tracked steadily, and this scheme still worked well even in low SNR level condition.关键词：carrier phase acquisition;quadrature amplitude modulation;phase ambiguity
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发布时间：2023-11-28 - 摘要：Abstract:To improve the efficiency and performance of signal recognitions, based on the analysis of the short-time signal's ambiguity function in the time-lag domain, the kernel function of Choi-Williams Distribution(CWD) was improved for short-time signals. After several short-time sections of the signal to be recognized, a new recognition approach was realized by comparing them in the time frequency domain using the improved CWD.The experimental results showed that the approach not only reduces the calculation and improves the agility of the recognition but also maintains the high performance of CWD under noise environments.关键词：short-time signal;Choi-Williams distribution;time-frequency domain;recognition
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发布时间：2023-11-28
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