Abstract: The core-shell CdTe/ZnS quantum dots were prepared with an improved process in aqueous phase. CdTe QDs were synthesized under conditions of pH 9.1, 96 °C, refluxing for 5h, and which was used as core material; ZnS was formed as shell material to enhance the optical properties. Optical properties were characterized with fluorescence spectrum (FS), and morphology of QDs was investigated via transmission electron microscopy (TEM) method. Moreover, composition and formation of CdTe/ZnS core-shell QDs was characterized via x-ray diffraction (XRD) method. Optimum conditions were investigated to obtain the qualified CdTe/ZnS core-shell QDs, the results indicated QDs with high quantum yields and fluorescence intensity were achieved under conditions of pH 9.0, 45 °C, refluxing for 1h, and v/v/v ratio of CdTe/Na2S/ZnSO4 is 4/1/1. The TEM data indicated that average size of 5 nm CdTe core was prepared, and CdTe/ZnS core-shell QDs with average size of 11 nm were achieved under the optimum conditions. ca 30nm of red shift of a maximum emission wavelength from ca 530 nm (CdTe) to 560 nm (CdTe/ZnS) was observed via FS under the optimum conditions, which inferred the growth of QDs and formation of ZnS shells. Furthermore, the enhanced fluorescence intensity of CdTe/ZnS core-shell QDs was detected and over two times of fluorescence intensity was increased after formation of ZnS shell. The obtained QDs will have great potential application in biological researches and biosensing system based on fluorescence resonance energy transition (FRET).
Abstract: The niclel nanoparticles were prepared via polyol process with hydrazine hydrate as reductant, the optimum conditions were investigated and proposed to be the molar ratio of NiCl2: NaOH: Hydrazine hydrate =1: 2: 11, 60 °C, pH5.5. The qualified fluorescent-magnetic dual functional CdTe/Ni nanoparticles were synthesized via layer-by-layer (LBL) technique, Ni was designed to be magnetic core and CdTe was used as fluorescent shell material, the molar ratio of CdTe:Ni is 4.5:1. The morphology of the Ni nano particles and CdTe/Ni core shell dual functional nano particles were characterized by transmission electron microscopy (TEM), and optical properties were investigated with fluorescence spectrum (FS) and ultra violet spectrum (UV). The synthesized CdTe/Ni nanoparticles showed yellow fluorescence when excited at 365nm, CdTe/Ni magnetic core shell QDs can be simply precipitated with a common magnet. TEM data indicated that ~15nm of Ni nanoparticles were obtained and ~25nm of CdTe/Ni core shell dual functional nanoparticles were prepared. Red shift of maximum absorbance peak was detected via UV, and these results inferred the QDs growth, moreover, 40nm red shift of maximum emission wavelength from 530nm to 570nm was observed, and which showed the growth QDs and formation of CdTe shell. The prepared magnetic core shell CdTe/Ni nanoparticles showed excellent optical properties, and it is expected to be useful and helpful in DNA sensing based on fluorescence resonance energy transfer, biological separating, and DNA labeling process.
Abstract: Statistics models are effective to describe the relation of strain-stress of rock. But the constitutive relations in the statistical models are too simple for rock. Using the Eshelby equivalent inclusion method, a Helmholtz free energy for e damage rock is set up in the present paper. A constitutive model for damage rock is set up . The presented model is verified as reasonable and practical with comparion to the experiment data.
Abstract: The laconic calculating formulae of arbitrary multiple-layer model’s acoustic characteristics are introduced with sound transmission theoretics in multilayer mediums. Taking properties of viscoelastic material in account, the sound absorption characteristics of multiple-layer model covered with viscoelastic material underwater are calculated using formulae deduced. By numerical analysis, the relation between absorption model and material parameters is simulated and the effect of proportion among layers’ natural impedance on acoustic characteristics of sound absorption model is analyzed. Then the method of designing sound absorption model by multiple-layer structures each layer natural impedance is studied. The result is of significance to devising sound absorption material and model.
Abstract: The inverse kinematics of serial robots is a central problem in the automatic control of robot manipulators. The aim of this paper is to obtain a computational algorithm to compute the inverse kinematics problem of a spatial serial robot. We use a series of algebraic and numeric transformations to reduce the problem to a univariate polynomial equation. The results can be directly applied to symbolic calculations and decreased considerably the calculation time.
Abstract: By using the universal mechanical testing machine and SEM, the influence of quenching parameters on the mechanical properties of 7075 aluminum alloy has been studied, and the optimal quenching parameters have been got. The experimental results show that the temperature range of the quenching treatment is too wide. However, the over-burning will occur when the temperature is above 490°C. So the optimal quenching temperature is from 465°C to 475°C. The water temperature and the transfer time are below 40°C and 30s, respectively. The time interval between the quenching and aging treatment is found to have little influence on the mechanical properties of 7075 aluminum alloys.
Abstract: The sintering of M42 P/M high speed steel followed by jointing to 45 steel had been accomplished at one step by using spark plasma sintering (SPS) technique. Based on the traditional diffusion theory and the designed structure of M42/45 steel joint, the bonding mechanism and models with the interface forming process of the bimetal have been proposed systematcally. The jointing and valuation of M42/45 steel interface are a comprehensive synergy process between fusion and diffusion mechanism. The former one takes priority at the early sintering process, while the later one becomes dominant over the followed sintering process.
Abstract: Taken the nanoparticles Fe3O4 as the magnetic carrier, and styrene ( St ) and Methyl Acrylate (MA) as the monomers, the magnetic polystyrene-methyl acrylate (P(St-MA)) microspheres were prepared by microsuspension copolymerization. The effect of various parameters(e.g. reaction temperature, initiator, Fe3O4/styrene ratio and disperser) on the properties of the P(St-MA) microspheres were studied.The microspheres were characterized by different techniques (e.g. SEM, VSM, TG-DSC, FTIR, ). The interaction of magnetic microspheres and BSA were studied by microcalorimetry. The results showed the P(St-MA) microspheres, with abundant –COOH, superparamagnetic and high magnetic content, were possessed much higher protein adsorbance compared to those of magnetic polystyrene(PS) microspheres.
Abstract: As the uncertainty of the influencing factors including the vehicle load and road environment and the complexity of road structure design parameters making the structural design of concrete pavement does not match with the actual existing situation, therefore, how to further improve the existing pavement design methods and how to scientifically and reasonably evaluate the reliability of the existing pavement performance have been a hot issue among academics and engineers at home and abroad. This paper analyzes and summarizes results of recent studies on the basis, combining with the actual situation of concrete pavement project, and carries out a more in-depth systematic study on the reliability analysis of concrete pavement. By studying the basic theory of engineering structure reliability, this paper proposes analysis methods of pavement reliability which are appropriate for the characteristics of pavement structure.
Abstract: Management and auditing of construction project, which is a certain trend of management development of modern construction project, is a new theory in audit practicing of construction project and an effective way to work out at the highest degree the returns on construction project investment, improve construction project management performance levels, avoid at the highest degree redundancy of construction projects and eliminate waste of resources. This essay points out the importance of the use of management auditing in construction projects based on the analysis of disadvantages in conventional construction projects management. And it builds up frame for management auditing of construction projects, puts forward performance evaluation methods of management control auditing.