The solidification of two-phase heterogeneous materials: Theory versus experiment

The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ɛ), ɛ=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium. Supported by the National Basic Research Program of China (“973” Project) (Grant Nos. 2006CB601202, 2006CB601203), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519).     

Development of Hydro-Informatic Modelling System and its application

The understanding of hydrological cycle is the core of hydrology and the scientific base of water resources management. Meanwhile, simulation of hydrological cycle has long been regarded as an important tool for the assessment, utilization and protection of water resources. In this paper, a new tool named Hydro-Informatic Modelling System (HIMS) has been developed and introduced with case studies in the Yellow River Basin in China and 331 catchments in Australia. The case studies showed that HIMS can be employed as an integrated platform for hydrological simulation in different regions. HIMS is a modular based framework of hydrological model designed for different utilization such as flood forecasting, water resources planning and evaluating hydrological impacts of climate change and human activities. The unique of HIMS is its flexibility in providing alternative modules in the simulation of hydrological cycle, which successfully overcome the difficulties in the availability of input data, the uncertainty of parameters, and the difference of rainfall-runoff processes. The modular based structure of HIMS makes it possible for developing new hydrological models by the users. Supported by the National Natural Science Foundation of China (Grant No. 40671031), National Key Basic Research Development Program of China (Grant Nos. G1999043601 and 2006CB403407) and National Key Technology R&D Program (Grant No. 2006BAB06N07)     

Composite modeling method in dynamics of planar mechanical system

This paper presents a composite modeling method of the forward dynamics in general planar mechanical system. In the modeling process, the system dynamic model is generated by assembling the model units which are kinematical determinate in planar mechanisms rather than the body/joint units in multi-body system. A state space formulation is employed to model both the unit and system models. The validation and feasibility of the method are illustrated by a case study of a four-bar mechanism. The advantage of this method is that the models are easier to reuse and the system is easier to reconfigure. The formulation reveals the relationship between the topology and dynamics of the planar mechanism to some extent. Supported by the National Natural Science Foundation of China (Grant No. 50605042) and the National Basic Research Program of China (973 Program) (Grant No. 2006CB705400)     

Ultralight X-type lattice sandwich structure (II): Micromechanics modeling and finite element analysis

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure, the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060, 10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Optimization model and algorithm for mixed traffic of urban road network with flow interference

In this paper, the problem of interferences between motors and non-motors in urban road mixed traffic network is considered and the corresponding link impedance function is presented based on travel demand. On the base of this, the main factors that influence travelers’ traffic choices are all considered and a combined model including flow-split and assignment problem is proposed. Then a bi-level model with its algorithm for system optimization of urban road mixed traffic network is proposed. Finally the application of the model and its algorithm is illustrated with a numerical example. Supported by the National Natural Science Foundation of China (Grant No. 70631001) and the National Basic Research Program of China (“973”) (Grant No. 2006CB705500)     

The friction and wear characteristics and lubrication mechanism of imidazole phosphate ionic liquid

Several imidazole phosphate ionic liquids with varying carbon chain length have been synthesized at room temperature. Corrosion characteristics and tribological properties of these synthesized ionic liquids were studied using four-ball friction and wear testing machine. Its lubrication mechanism was also investigated by means of electron microscopy and X-ray photoelectron spectroscopy. The experimental results showed that no corrosion was generated when the imidazole phosphate ionic liquid was applied to steel-steel pair. Meanwhile, the imidazole phosphate showed excellent anti-wear and lubricating performances, its frictional performance was related to the polarity of ionic liquids. It is suggested that the ionic liquids react with friction surface to form a protective film of iron phosphate and result in reduction in friction and wear. Supported by the National Natural Science Foundation of China (Grant Nos. 50721062 and 20533080) and the National Basic Research Program of China (973 Program) (Grant No. 2007CB607606)     

Analyzing and evaluating the three-line rail traffic

In this paper, we propose a method to simulate the three-line rail traffic. The aim is to evaluate the carrying capacity of the three-line rail traffic by studying the rail traffic flow when the passenger flow is unsymmetrical. The simulation results demonstrate that under the unsymmetrical condition, the three-line rail traffic system has almost the same carrying capacity as that of a four-line rail traffic system. Compared with the four-line rail traffic system, the three-line rail traffic system has better utilization of rail line. As a result, building the three-line rail traffic system is a more economical and rational selection. Supported by the National Basic Research Program of China (Grant No. 2006CB705500), the Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0605), the National Natural Science Foundation of China (Grant No. 60634010), New Century Excellent Talents in University (Grant No. NCET-06-0074), and the Key Project of Chinese Ministry of Education (Grant No. 107007)     

Optimal design of a new spatial 3-DOF parallel robot with respect to a frame-free index

Optimal design is one of the most important issues in robots. Since the very beginning, the concepts of the Jacobian matrix, manipulability and condition number, which are used successfully in the field of serial robots, have been applied to parallel robots. Unlike serial robots, parallel robots are good for motion/force transmission. Their performance evaluation and design should be correspondingly different. This paper is an attempt to optimally design a novel spatial three-degree-of-freedom (3-DOF) parallel robot by using the concept of motion/force transmission. Accordingly, three indices are defined. The suggested indices are independent of any coordinate frame and could be applied to the analysis and design of a parallel robot whose singularities can be identified wholly by using the relative angle between the output and adjacent links, and by using the relative angle between the input and adjacent links. Supported by the National Natural Science Foundation of China (Grant No. 50775118), High Technology Research and Development Program of China (863 Program) (Grant No. 2006AA04Z227), and National Basic Research Program of China (973 Program) (Grant No. 2007CB714000)     

Filterbank implementation for multi-channel sampling in fractional Fourier domain

Reconstruction of a continuous time signal from its periodic nonuniform samples and multi-channel samples is fundamental for multi-channel parallel A/D and MIMO systems. In this paper, with a filterbank interpretation of sampling schemes, the efficient interpolation and reconstruction methods for periodic nonuniform sampling and multi-channel sampling in the fractional Fourier domain are presented. Firstly, the interpolation and sampling identities in the fractional Fourier domain are derived by the properties of the fractional Fourier transform. Then, the particularly efficient filterbank implementations for the periodic nonuniform sampling and the multi-channel sampling in the fractional Fourier domain are introduced. At last, the relationship between the multi-channel sampling and the filterbank in the fractional Fourier domain is investigated, which shows that any perfect reconstruction filterbank can lead to new sampling and reconstruction strategies. Supported by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104), the National Natural Science Foundation of China (Grant Nos. 60890072, 60572094) and the National Key Basic Research Program Founded by MOST (Grant No. 2009CB724003)     

Adaptive integration of local region information to detect fine-scale brain activity patterns

With the rapid development of functional magnetic resonance imaging (fMRI) technology, the spatial resolution of fMRI data is continuously growing. This provides us the possibility to detect the fine-scale patterns of brain activities. The established univariate and multivariate methods to analyze fMRI data mostly focus on detecting the activation blobs without considering the distributed fine-scale patterns within the blobs. To improve the sensitivity of the activation detection, in this paper, multivariate statistical method and univariate statistical method are combined to discover the fine-grained activity patterns. For one voxel in the brain, a local homogenous region is constructed. Then, time courses from the local homogenous region are integrated with multivariate statistical method. Univariate statistical method is finally used to construct the interests of statistic for that voxel. The approach has explicitly taken into account the structures of both activity patterns and existing noise of local brain regions. Therefore, it could highlight the fine-scale activity patterns of the local regions. Experiments with simulated and real fMRI data demonstrate that the proposed method dramatically increases the sensitivity of detection of fine-scale brain activity patterns which contain the subtle information about experimental conditions. Supported by Chair Professors of Changjiang Scholars Program and CAS Hundred Talents Program, National Program on Key Basic Research Projects (Grant No. 2006CB705700), National High-Tech R&D Program of China (Grant No.2006AA04Z216), National Key Technology R&D Program (Grant No. 2006BAH02A25), Joint Research Fund for Overseas Chinese Young Scholars (Grant No.30528027), National Natural Science Foundation of China (Grant Nos.30600151, 30500131 and 60532050), and Natural Science Foundation of Beijing (Grant Nos. 4051002 and 4071003)     

Acoustic properties of sintered FeCrAlY foams with open cells (I): Static flow resistance

Open celled metal foams fabricated through the route of metal sintering are a new class of material that offers novel mechanical and acoustic properties. The metal sintering approach offers a cost-effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. The mechanical properties of open-celled steel alloy (FeCrAlY) foams have been characterized in previous studies, with focus placed on the influence of processing defects on stiffness and strength. In this work, the low-Reynolds number fluid properties of FeCrAlY foams were investigated both theoretically and experimentally. Specifically, the static flow resistance of the sintered foams important for heat transfer, filtration and sound absorption was modeled based on a cylinder and a sphere arranged in a periodic lattice at general incidence to the flow. Experimental measurements were subsequently carried out to validate theoretical predictions, with good agreement achieved. Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), and the National Hi-Tech Research Development Program (Grant No. 2006AA03Z519)     

Constitutive model for overconsolidated clays

Based on the relationships between the Hvorslev envelope, the current yield surface and the reference yield surface, a new constitutive model for overconsolidated clays is proposed. It adopts the unified hardening parameter, to which the potential failure stress ratio and the characteristic state stress ratio are introduced. The model can describe many characteristics of overconsolidated clays, including stress-strain relationships, strain hardening and softening, stress dilatancy, and stress path dependency. Compared with the Cam-clay model, the model only requires one additional soil parameter which is the slope of the Hvorslev envelope. Comparisons with data from triaxial drained compression tests for Fujinomori clay show that the proposed model can rationally describe overconsolidated properties. In addition, the model is also used to predict the stress-strain relationship in the isotropic consolidation condition and the stress paths in the undrained triaxial compression tests. Supported by the National Natural Science Foundation of China (Grant Nos. 50479001 and 10672010), the National Science and Technology Supporting Item (Grant No. 2006BAK12B12), and the National Basic Research Program of China (Grant No. 2007CB714203)     

A new transient stability margin based on dynamic security region and its applications

A new transient stability margin is proposed based on a new expression of dynamic security region (DSR) which is developed from the existing expression of DSR. Applications of the DSR based transient stability margin to contingency ranking and screening are discussed. Simulations in the 10-machine 39-bus New England system are performed to show the effectiveness of the proposed DSR based transient stability margin. Supported by Chinese National Basic Research Program (Grant No. 2004CB217900), the National Natural Science Foundation of China (Grant Nos. 50525721, 50595411, 50707035) and China Postdoctoral Science Foundation (Grant No. 20060400518)     

Acoustic properties of sintered FeCrAlY foams with open cells (II): Sound attenuation

Open-celled metal foams fabricated through metal sintering offers novel mechanical, thermal and acoustic properties. Previously, polymer foams were used as a means of absorbing acoustic energy. However, the structural applications of these foams are inherently limited. The metal sintering approach provides a cost-effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. The low Reynolds number fluid properties of sintered steel alloy (FeCrAlY) foams were investigated in a previous study. The static flow resistance of the foams was modeled based on a cylinder and a sphere arranged in a periodic lattice at general incidence to the flow, with the resulting predictions correlating well to measurements. The application of the flow resistance in an acoustic model is the primary focus of the present study. The predictions for the static flow resistance of the sintered foams are first used in a theoretical model to determine the characteristic impedances, as well as the propagation constants of the foams. Subsequently, the predicted acoustic performance of the foams is compared to experimental results. Finally, the design space for a simple acoustic absorber incorporating sintered foams is examined, with the effects of absorber size, foam selection, and foam spacing explored. Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), and the National H-Tech Research and Development Program of China (Grant No. 2006AA03Z519)     

Numerical modeling of concrete hydraulic fracturing with extended finite element method

The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advan- tages of ...     

Micro powder injection molding—large scale production technology for micro-sized components

Micro powder injection molding (μPIM), a miniaturized variant of powder injection molding, has advantages of shape complexity, applicability to many materials and good mechanical properties. Co-injection molding has been realized between metals and ceramics on micro components, which become the first breakthrough within the PIM field. Combined with the prominent characteristics of high features/cost ratio, micro powder injection molding becomes a potential technique for large scale production of intricate and three-dimensional micro components or microstructured components in microsystems technology (MST) field. Supported by National Basic Research Program of China (Grant No. 2004CB719802) and Hi-Tech Research and Development Program of China (Grant No. 2006AA03Z113)     

Synthesis and characterization of phase change memory cells

Phase change memory (PCM) cells based on Ge₂Sb₂Te₅ were synthesized and investigated. Current-voltage measurements demonstrated different final resistances. Transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and the energy dispersive X-ray spectroscopy (EDS) analyses were used to characterize the microstructures of the PCM cells. The architectures, structures and defects in the cells including the deposited elemental distributions and the interfacial structures between electrodes and barrier layers were studied in detail. Supported by the National Basic Research Program of China (Grant No. 2007CB935400), Key Project of Beijing Education Committee Program (Grant No. JB102001200801) and Program for New Century Excellent Talents in University (Grant No. 05009015200701)     

Development of ecohydrological assessment tool and its application

The development of Hydro-Informatic Modelling System (HIMS) provides an integrated platform for hydrological simulation. To extend the application of HIMS, an ecohydrological modeling system named ecohydrological assessment tool (EcoHAT) has been developed. Integrating parameter-management tools, RS (remote sensing) inversion tools, module-design tools and GIS analysis tools, the EcoHAT provides an integrated tool to simulate ecohydrological processes on regional scale, which develops a new method on sustainable use of water. EcoHAT has been applied to several case studies, such as, the Yellow River Basin, the acid deposition area in Guizhou province and the riparian catchment of Guanting reservoir in Beijing. Results prove that EcoHAT can efficiently simulate and analysis the ecohydrological processes on regional scale and provide technical support to integrated water resources management on basin scale. Supported by the National Key Technology R&D Program in the 11th Five-year Plan of China (Grant No. 2006BAB06B07), the National Natural Science Foundation of China (Grant No. 40671123), the National Basic Research Program of China (“973” Project) (Grant Nos. 2005CB422207, G19990436), and the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA12Z145)     

Theoretical calculation and experimental study of influence of oxygen vacancy on the electronic structure and hemocompatibility of rutile TiO2

In this work, the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO_2−x was studied by both theoretical calculation and experimental study. Based on the local density functional theory, first-principals method was performed to calculate the electronic structure of rutile TiO₂ with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration, the band gap of rutile TiO₂ increases with increasing O vacancy concentration, leading the TiO₂ changes from a p-type to an n-type semiconductor. The valance band of TiO₂ is predominated by O 2p orbital, while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO₂, and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood, the n-type semiconductor feature of oxygen deficient TiO_2−x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials, thus inhibiting the aggregation and activation of platelets, therefore improving the hemocompatibility of rutile TiO_2-x . Supported by the National Basic Research Program of China (Grant No. 2005CB623904), National High-Tech Research Program of China (Grant No. 2006AA02A139) and National Natural Science Foundation of China (Grant No. 20603027)