模度量空间下的不动点定理

推广了模度量空间,针对一类被称之为Chatterjea映射,在适当的条件下,建立了映射T具有不动点的存在性和唯一性结果.

Structural,mechanical and electronic properties of precipitates in Mg−Zn alloys

To accelerate the development and design of magnesium(Mg)alloys,the structural and mechanical properties of important precipitates in Mg−Zn alloys were studied by experiments and density functional theory.The nano-indentation tests revealed that the hardness of the precipitates initially increased and then decreased with increasing Zn content,and was significantly higher than that of pure Mg and Zn.The calculation results revealed that the precipitates stability initially increased and then decreased with increasing Zn concentration.The bulk moduli of the precipitates increased,whereas their shear and Young’s moduli initially increased and then decreased with increasing Zn content.The decreasing order of ductility for these compounds is MgZn_(2)>Mg_(21)Zn_(25)>Mg_(2)Zn_(11)>Mg_(4)Zn_(7).The surface profiles of the compounds revealed that they are obvious anisotropy.Both the degree of covalency and bond length of covalent bonds initially increased and then decreased with increasing Zn content.

Effect of gas saturation on P-wave velocity in tight sandstone

By measuring the variation of the P-and S-wave velocities of tight sandstone samples under water saturation,it was confirmed that with the decrease in water saturation,the P-wave velocity first decreased and then increased.The variation in velocity was influenced by the sandstone’s porosity.The commonly used Gassmann equation based on fluid substitution theory was studied.Comparing the calculated results with the measured data,it was found that the Gassmann equation agreed well with the measured data at high water saturation,but it could not explain the bending phenomenon of P-wave velocity at low saturation.This indicated that these equations could not accurately describe the relationship between fluid content and rock acoustic velocity.The reasons for this phenomenon were discussed through Taylor’s expansion.The coefficients of the fitting formula were calculated and verified by fitting the measured acoustic velocity changes of the cores.The relationship between P-wave velocity and saturation was discussed,which provides experimental support for calculating saturation using seismic and acoustic logging data.

面向互联网电子政务的定制数据安全交换技术研究综述

为了解决互联网电子政务信息的安全共享与交换问题,提出一种交换策略可定制、交换数据可信、交换行为可控的定制数据安全交换模式。重点分析了定制数据安全交换模式下存在的安全威胁;针对安全威胁提出了相应的解决方法,并总结分析了所涉及关键技术的研究现状与不足之处;最后指出了定制数据安全交换未来的研究热点及发展前景。

Effects of freeze-thaw cycles on fracture behavior of epoxy asphalt concrete

According to the winter temperature of Peking,the freeze-thaw（FT） condition in laboratory was determined.Seven groups of epoxy asphalt concrete（EAC） specimen were exposed to different FT cycles.The flexural modulus and fracture energy（G_F） of EAC exposed to different FT cycles were obtained through the 3-point bending test.Meanwhile,the plane strain fracture toughness（K_（IC）） of EAC was obtained through numerical simulation.The results show that the flexural modulus of the FT conditioned EAC samples decreases with the increase of FT cycles.The FT damage of flexural modulus is 60%after 30 FT cycles.Nevertheless,with the increase of FT cycles,the G_F and K_（IC） of EAC decrease first and then increase after 15 FT cycles.

Design of new biomedical titanium alloy based on d-electron alloy design theory and JMatPro software

A new kind offl biomedical titanium alloy, Ti-35Nb-4Sn-6Mo-9Zr, composed of non-toxic elements Nb, Mo, Zr and Sn with lower elastic modulus and higher strength was designed based on d-electron alloy design theory and JMatPro software using orthogonal experiment. The microstructure and basic mechanical properties of designed alloy were investigated. The results show that the alloy is composed of single fl equiaxed grains after solution treatment at 800 ~C. Compared with Ti-6A1-4V, the mechanical properties of the designed alloy are more excellent： E=65 GPa, σb=834 MPa, σ0.2=802 MPa, and σ=11%, which is expected to become a promising new type implanted material. The research approach adopted can reduce the experimental time and cost effectively, and get the ideal experimental results.

Variable Precision Rough Set and a Fuzzy Measure of Knowledge Based on Variable Precision Rough Set

Variable precision rough set (VPRS) is an extension of rough set theory (RST). By setting threshold value β , VPRS looses the strict definition of approximate boundary in RST. Confident threshold value for β is discussed and the method for deriving decision making rules from an information system is given by an example. An approach to fuzzy measures of knowledge is proposed by applying VPRS to fuzzy sets. Some properties of this measure are studied and a pair of lower and upper approximation operato...

Effects of parameters of asphalt concrete surfacing on mechanical property of paving layer

The important parameters that influence the mechanical property of the pavinglayer on an orthotropic steel bridge deck are the paving layer thickness and modulus of the asphaltconcrete surfacing. Three important indices that control the typical failures of the paving layerare the maximum tensile stress of paving layer, the maximum shear stress between the steel deck andthe paving layer, and the maximum deflection on the paving surface. In this paper, the analyticalmodel of paving systems on orthotropic steel bridge deck is established, and the finite elementmethod is adopted to study the stress and strain of paving system. With the variation of asphaltconcrete modulus in high or low temperature season, the influences of paving layer thickness onthree control indices are researched. The results provide a theoretical basis for the determinationof thickness of the paving layer on the steel bridge deck.

Extracting and evaluating method of web dense cores

This paper focuses on some key problems in web community discovery and link analysis.Based on the topic-oriented technology,the characteristics of a bipartite graph are studied.An Х bipartite core set is introduced to more clearly define extracting ways.By scanning the topic subgraph to construct Х bipartite graph and then prune the graph with i and j ,an Х bipartite core set,which is also the minimum element of a community,can be found.Finally,a hierarchical clustering algorithm is applied to many Х bipartite core sets and the dendrogram of the community inner construction is obtained.The correctness of the constructing and pruning method is proved and the algorithm is designed.The typical datasets in the experiment are prepared according to the way in HITS（hyperlink-induced topic search）.Ten topics and four search engines are chosen and the returned results are integrated.The modularity,which is a measure of the strength of the community structure in the social network,is used to validate the efficiency of the proposed method.The experimental results show that the proposed algorithm is effective and efficient.

Sea Surface Temperature Simulation of Tropical and North Pacific Basins Using a Hybrid Coordinate Ocean Model (HYCOM)

A Hybrid Coordinate Ocean Model （HYCOM） is used to simulate the sea surface temperature of the Tropical and North Pacific. Based on the different combinations of two air-Sea flux data sets （COADS and ECMWF） and two bulk parameter formulas （non-constant and constant）, four numerical experiments are carried out. The following conclusions can be deduced from the numerical results. （1） The numerical results using non-constant bulk parameter formula are much better than those using constant one. In the Pacific area from 40°N to 20°S, the annual average SST obtained from the experiment using non-constant bulk parameter formula is 0.21 ℃ higher than that from the satellite-based SST climatology （the pathfinder data）. However, the difference is 0.63 ℃ for the experiment when the using constant one. （2） HYCOM successfully simulates the monthly variation of climatological SST in tropical and north Pacific basins and monthly spatial variation of Western Pacific Warm Pool. Especially in the Pacific area from 40°N to 20°S, the difference of the seasonal averaged SST between pathfinder data and the result of experiment 2 （using COADS data set and non-constant bulk parameter formula） is only about 0.02 ℃. （3）The simulation results using different Air-Sea flux data are different and the difference is very large in some regions. In the northwest of the model region, the annual average SST obtained from experiment 2 （using COADS data set） is 1℃ higher than that obtained from experiment 4 （using ECMWF data set）. Contrarily, the result of experiment 4 is 1 ℃ larger than that of experiment 2 in the southeast of the model region. The largest difference is about 4 ℃ occurred near the area of 58°N, 140°E and the Bohai sea.

Use of the pilodyn for assessing wood properties in standing trees of Eucalyptus clones

The effectiveness of pilodyn was tested in evaluating wood basic density, outer wood density, heartwood density, and modulus of elasticity （MoE） at 22 four-year-old eucalyptus clones in Guangxi, China. Results indicated that the mean value ranged from 9.44 to 15.41 mm for Pilodyn penetration, 0.3514 to 0.4913 g.cm^-3 for wood basic density, and 3.94 to 7.53 Giga Pascal （GPa） for MoE, respectively. There were significant differences （1% level） in pilodyn penetration between different treatments, different directions and among the clones. Generally strongly negative correlations were found between pilodyn penetration and wood properties, and the coefficients ranged from -0,433 to -0,755. Our results, together with other studies, suggest that the use of pilodyn for assessing wood density and MoE was confirmed as a possibility.

Three methods for generating monotonic OWA operator weights with given orness level

Based on the properties of ordered weighted averaging (OWA) operator and regular increasing monotone (RIM) quantifier, three methods for generating monotonic OWA operator weights are proposed. They are geometric OWA operator weights, equidifferent OWA operator weights and the modified RIM quantifier OWA weights. Compared with most of the common OWA methods for generating weights, the methods proposed in this paper are more intuitive and efficient in computation. And as there are more than one solution in most cases, the decision maker can set some initial condition and chooses the appropriate solution in the real decision process, which increases the flexibility of decision making to some extent. All these three OWA methods for generating weights are illustrated by numerical examples.

Rock critical porosity inversion and S-wave velocity prediction

A critical porosity model is often used to calculate the dry frame elastic modulus by the rock critical porosity value which is affected by many factors. In practice it is hard for us to obtain an accurate critical porosity value and we can generally take only an empirical critical porosity value which often causes errors. In this paper, we propose a method to obtain the rock critical porosity value by inverting P-wave velocity and applying it to predict S-wave velocity. The applications of experiment and log data both show that the critical porosity inversion method can reduce the uncertainty resulting from using an empirical value in the past and provide the accurate critical porosity value for predicting S-wave velocity which significantly improves the prediction accuracy.

Vertical human-induced vibration of pedestrian bridge

The double degrees-of-freedom（DOFs）parallel model is adopted to analyze static vertical human-induced vibration with the finite element analysis（FEA）method.In the first-order symmetric vibration mode,the periods of the spring-mass model gradually decrease with the increase in K1 and K2,but they are always greater than the period of the add-on mass model.Meanwhile,the periods of the spring-mass model decrease with the decrease in m1 and m2,but they are always greater than the period of the hollow bridge model.Since the human＇s two degrees-of-freedom vibrate in the same direction as that of the bridge mid-span,the existence of human＇s rigidity leads to the reduction in the rigidity of the spring-mass model.In the second-order symmetric vibration mode,the changes of rigidity K2 and mass m2 result in the disappearance or occurrence of some vibration modes.It can be concluded that compared with the spring-mass model,the results of the add-on mass model lean to lack of safety to the structure;besides,the DOF with a smaller ratio of mass to rigidity plays the chief role in the vibration of the structure.

Reconstruction of the linac photon spectrum based on prior knowledge and the genetic algorithm

In order to derive the linac photon spectrum accurately both the prior constrained model and the genetic algorithm GA are employed using the measured percentage depth dose PDD data and the Monte Carlo simulated monoenergetic PDDs where two steps are involved.First the spectrum is modeled as a prior analytical function with two parameters αand Ep optimized with the GA.Secondly the linac photon spectrum is modeled as a discretization constrained model optimized with the GA. The solved analytical function in the first step is used to generate initial solutions for the GA’s first run in this step.The method is applied to the Varian iX linear accelerator to derive the energy spectra of its 6 and 15 MV photon beams.The experimental results show that both the reconstructed spectrums and the derived PDDs with the proposed method are in good agreement with those calculated using the Monte Carlo simulation.

Meta-analysis of potentially confounding effect of class size on associations between object-oriented metrics and maintainability

This paper uses three size metrics,which are collectable during the design phase,to analyze the potentially confounding effect of class size on the associations between object-oriented（OO）metrics and maintainability.To draw as many general conclusions as possible,the confounding effect of class size is analyzed on 127 C＋＋ systems and 113 Java systems.For each OO metric,the indirect effect that represents the distortion of the association caused by class size and its variance for individual systems is first computed.Then,a statistical meta-analysis technique is used to compute the average indirect effect over all the systems and to determine if it is significantly different from zero.The experimental results show that the confounding effects of class size on the associations between OO metrics and maintainability generally exist,regardless of whatever size metric is used.Therefore,empirical studies validating OO metrics on maintainability should consider class size as a confounding variable.

Laser Measurement and Intensity Evaluation of Intake Swirl in Engine Using a Water Analog

The intake swirl in the cylinder was induced by a swirler which was fixed in one of two intake ports. In order to understand the characteristics of the intake swirl, a transparent water analog was designed which simulated 150 type single cylinder engine. At the same time, the particle image velocimetry was used to measure the flow fields induced by various swirlers in the analog. After measurement, a new method was presented to evaluate the intensity of the intake swirl. Then, when the measured sections, the lifts of valve and the swirlers were different, the calculated results of the flow field were compared.

Multiple attribute decision making method based on trapezoid fuzzy linguistic variables

The problem of multiple attribute decision making under fuzzy linguistic environments, in which decision makers can only provide their preferences （attribute values）in the form of trapezoid fuzzy linguistic variables（TFLV）, is studied. The formula of the degree of possibility between two TFLVs is defined, and some of its characteristics are studied. Based on the degree of possibility of fuzzy linguistic variables, an approach to ranking the decision alternatives in multiple attribute decision making with TFLV is developed. The trapezoid fuzzy linguistic weighted averaging （TFLWA） operator method is utilized to aggregate the decision information, and then all the alternatives are ranked by comparing the degree of possibility of TFLV. The method can carry out linguistic computation processes easily without loss of linguistic information, and thus makes the decision results reasonable and effective. Finally, the implementation process of the proposed method is illustrated and analyzed by a practical example.

Reducing semantic bias of annotations for semantic web service discovery

In order to improve the effectiveness of semantic web service discovery, the semantic bias between an interface parameter and an annotation is reduced by extracting semantic restrictions for the annotation from the description context and generating refined semantic annotations, and then the semantics of the web service is refined. These restrictions are dynamically extracted from the parsing tree of the description text, with the guide of the restriction template extracted from the ontology definition. New semantic annotations are then generated by combining the original concept with the restrictions and represented via refined concept expressions. In addition, a novel semantic similarity measure for refined concept expressions is proposed for semantic web service discovery. Experimental results show that the matchmaker based on this method can improve the average precision of discovery and exhibit low computational complexity. Reducing the semantic bias by utilizing restriction information of annotations can refine the semantics of the web service and improve the discovery effectiveness.

Model Recognition of Astronauts Blood Flow Change Under Sustained +Gz Acceleration

Aim Using animals as object of experiment to acquire various patterns of low cerebral blood pressure and reduced blood capacity in cerebral tissues of astronauts due to the load of acceleration. Methods The isotope tracking technique was applied to mark the blood and record the dynamic curves of cerebral blood flow changes under various accelerations, and the relevant mathematical model was set up using the method of system recognition. Also the method of factor analyzing was used to select two out of the data collected by eight sensors as two factors. Results One of the two factors reflects the various patterns in the astronaut's upper body, the other for the lower body. Parameters of rise time, delay time and steady value reflect the results under different acceleration. Conclusion Whether for the upper body or the lower body, blood flow changes can be considered as a second order system model. This method provides a new technique and method of doing research on astronaut's endurance of acceleration and selecting astronauts.