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)     

Transient pressure analysis in porous and fractured fractal reservoirs

Fluid flow in porous and fractured fractal reservoirs is studied in the paper. The basic formulae of seepage velocity, permeability and porosity in both porous and fractured fractal media are developed. The pressure diffusion equation of slightly compressible fluid in fractal reservoirs is derived. The analytical solutions of the transient pressure are given for the line-source well and the well with well-bore storage and skin factor. The typical curves of pressure and the derivative of pressure are established, along with the interpretation of the well-testing method via type-curve matching. In addition, 3-D pressure diffusion equations for anisotropic fractal media are given in both Cartesian coordinates and Cylindrical coordinates. Supported by the National Natural Science Foundation of China (Grant No. 10672159, 10702069) and National Basic Research Program of China (“973”) (Grant No. 2006CB705805)     

Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density. 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)     

Multi-channel micro neural probe fabricated with SOI

Silicon-on-insulator(SOI) substrate is widely used in micro-electro-mechanical systems(MEMS).With the buried oxide layer of SOI acting as an etching stop,silicon based micro neural probe can be fabri-cated with improved uniformity and manufacturability.A seven-record-site neural probe was formed by inductive-coupled plasma(ICP) dry etching of an SOI substrate.The thickness of the probe is 15 μm.The shaft of the probe has dimensions of 3 mm×100 μm×15 μm with typical area of the record site of 78.5 μm2.The im...     

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)     

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).     

A luminescence enhancement approach through Si/O nanostructure

An Si/O patterned shell array was fabricated by a technique utilizing nanosphere self assembly and reactive pressure pulsed laser deposition. The nanostructure produced by this technique enhanced the luminescence intensity by a factor of three compared with that of a flat film. The amount of enhancement observed coincided well with the expected enhancement by simulation. The technique in this paper provided a flexible, designable and compatible approach to luminescence enhancement. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2002CB613505) and the National Nature Science Foundation of China (Grant No. 90206046)     

Gate oxide punching thru mechanism in plasma dry etching

The punching thru mechanism of gate oxide (thickness about 15A) was investigated. Because of the thin thickness of gate oxide, gate oxide punching thru may easily happen during the plasma process. It was found that what caused the punching thru was not only the selectivity of poly-silicon/oxide but also the pattern topography. We used the basic SRAM pattern to check this topography effect, and found that gate oxide located at the narrow spacing of two parallel serpentine lines was the most easily punched thru. What caused the topography effect was the starvation of oxygen in these places which were induced by the residue of poly-silicon and enhanced by electron shading effect. So, to solve the issue of gate oxide punching thru, firstly the selectivity should be enough, secondly we should pay attention to the etching pattern topography. Supported by the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA843134) and the National Basic Research Program of China ("973" Project) (Grant No. 2007CB935302)     

Application of time reversal mirror technique in microwave-induced thermo-acoustic tomography system

Microwave-induced thermo-acoustic tomography (MITAT) is a promising technique with great potential in biomedical imaging. It has both the high contrast of the microwave imaging and the high resolution of the ultrasound imaging. In this paper, the proportional relationship between the absorbed microwave energy distribution and the induced ultrasound source distribution is derived. Further, the time reversal mirror (TRM) technique based on the pseudo-spectral time domain (PSTD) method is applied to MITAT system. The simulation results show that high contrast and resolution can be achieved by the TRM technique based on PSTD method even for the received signals with very low signal-to-noise ratio (SNR) and the model parameter with random fluctuation. Supported by the National Natural Science Foundation of China (Grant No. 60771042), the National Hi-Tech Research and Development Program (“863” Project) (Grant No. 2007AA12Z159), 111 Project (Grant No. B07046), SiChuan Excellent Youth Foundation (Grant No. 08ZQ026-039), Program for New Century Excellent Talents in University of China and Program for Changjiang Scholars     

New explicit algebraic stress and flux model for active scalar and simulation of shear stratified cylinder wake flow

On the numerical simulation of active scalar, a new explicit algebraic expression on active scalar flux was derived based on Wikstr?m, Wallin and Johansson model (a ^WWJ model). Reynolds stress algebraic expressions were added by a term to account for the buoyancy effect. The new explicit Reynolds stress and active scalar flux model was then established. Governing equations of this model were solved by finite volume method with unstructured grids. The thermal shear stratified cylinder wake flow was computed by this new model. The computational results are in good agreement with laboratorial measurements. This work is the development on modeling of explicit algebraic Reynolds stress and scalar flux, and is also a further modification of the a ^WWJ model for complex situations such as a shear stratified flow. Supported by the National Nature Science Foundation of China (Grant Nos. 50679019, 50009001), the National Basic Research Program of China (“973” Project) (Grant No. 2008CB418202), the Project of “Six Talent Peak” of Jiangsu Province (08-C), Social Technology Development Foundation of Jiangsu Province (Grant No. BS2006095) and the “908” Special Foundation of Jiangsu Province (Grant No. JS-908-02-06)     

The event-driven constant volume method for particle coagulation dynamics

Monte Carlo (MC) method, which tracks small numbers of the dispersed simulation particles and then describes the dynamic evolution of large numbers of real particles, constitutes an important class of methods for the numerical solution of population balance modeling. Particle coagulation dynamics is a complex task for MC. Event-driven MC exhibits higher accuracy and efficiency than time-driven MC on the whole. However, these available event-driven MCs track the “equally weighted simulation particle population” and maintain the number of simulated particles within bounds at the cost of “regulating” computational domain, which results in some constraints and drawbacks. This study designed the procedure of “differently weighted fictitious particle population” and the corresponding coagulation rule for differently weighted fictitious particles. And then, a new event-driven MC method was promoted to describe the coagulation dynamics between differently weighted fictitious particles, where “constant number scheme” and “stepwise constant number scheme” were developed to maintain the number of fictitious particles within bounds as well as the constant computational domain. The MC is named event-driven constant volume (EDCV) method. The quantitative comparison among several popular MCs shows that the EDCV method has the advantages of computational precision and computational efficiency over other available MCs. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB705800), the National Natural Science Foundation of China (Grant No. 20606015) and the Fok Ying Tong Education Foundation (Grant No. 114017)     

Preparation of nanocrystalline BaTiO<Subscript>3</Subscript> ceramics

The high-dense nanocrystalline BaTiO₃ (BT) ceramics with grain size smaller than 100 nm have been successfully prepared by the two step sintering and the spark plasma sintering (SPS) process. The successive transitions in nanograin BT ceramics from rhombohedral to orthorhombic, tetragonal and cubic transitions, similar to those in coarse BT ceramics, were revealed by in-situ temperature dependent Raman spectrum. The multiphase coexistence and the diffused phase transition character were demonstrated in the 8 nm nanocrystalline BT ceramics. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2002CB613301) and the National Natural Science Foundation of China (Grant No. 50872093)     

In-flight observations of electromagnetic interferences emitted by satellite

Using the data from STAFF/TC-1, this paper for the first time analyzes the electromagnetic interferences of Chinese scientific satellite. The electromagnetic interference of satellite exists mainly below 30 Hz, but can extend to 190 Hz with an obviously decreasing power spectral density. The electromagnetic interferences at frequencies below 190 Hz have good correlation with the solar aspect angle. The electromagnetic interferences at frequencies between 190 and 830 Hz have also correlation with solar aspect angle. However, the electromagnetic interferences at frequencies above 830 Hz have no correlation with the solar aspect angle. The correlation coefficient between solar aspect angel and electromagnetic interferences is around 0.90. The larger the solar aspect angle, the stronger the satellite electromagnetic interference. When the solar aspect angle increases from 90.6° to 93.6°, the electromagnetic interferences at frequencies <10 Hz increase by 8 times and those at frequencies 190–830 Hz increase by 60%. This close association of electromagnetic interferences with the solar aspect angle indicates that the solar aspect angle is the main factor to determine the electromagnetic interferences. The electromagnetic interferences of satellite in sunlight are larger than those in eclipse. The electromagnetic interference produced by solar panel occupies about 87% in the low frequency band (<100 Hz) and 94% in the high frequency band (>100 Hz) of the total electromagnetic interference produced by satellite. These in flight observations of electromagnetic radiation of satellites will be very helpful to the designs of future satellites of space sciences or earthquake sciences. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2008AA12A216), the National Science & Technology Supporting Program during the Eleventh Five-Year Plan, the National Natural Science Foundation of China (Grant No. 40523006), the National Basic Research Program of China (“973” Project) (Grant No. 2006CB806305), and the Specialized Research Fund for State Key Laboratories     

Research and application of CO<Subscript>2</Subscript> refrigeration and heat pump cycle

The environmental problem caused by refrigerant has become the focus all over the world. As the most typical natural refrigerant, CO₂, of course, becomes the research focus. This paper introduces the development and application status of CO₂ refrigeration and heat pump technology. The researches on CO₂ refrigeration and heat pump, carried out by Thermal Energy Research Institute, Tianjin University, also are presented in this paper. Supported by the National Natural Science Foundation of China (Grant Nos. 50676064, 50506019) and the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2007AA05Z262)     

On time transfer in X-ray pulsar navigation

Abstrac  X-ray pulsar navigation (XPNAV) is a new approach for spacecraft autonomous navigation. The system gets position information utilizing accurate timing methods. Among the timing models, the high-order relativistic effects on the propagated signal must be incorporated to attain precise timing. The time transfer model is provided in detail here in two parts: the time frame transformation and the relativistic effects. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2008AA12Z304)     

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 ...     

Uncertainty in magnetic activity indices

Magnetic activity indices are widely used in theoretical studies of solar-terrestrial coupling and space weather prediction. However, the indices suffer from various uncertainties, which limit their application and even mislead to incorrect conclusion. In this paper we analyze three most popular indices, Kp, AE and Dst. Three categories of uncertainties in magnetic indices are discussed: “data uncertainty” originating from inadequate data processing, “station uncertainty” caused by incomplete station covering, and “physical uncertainty” stemming from unclear physical mechanism. A comparison between magnetic disturbances and related indices indicate that the residual Sq will cause an uncertainty of 1–2 in K measurement, the uncertainty in saturated AE is as much as 50%, and the uncertainty in Dst index caused by the partial ring currents is about a half of the partial ring current. Supported by the National Natural Science Foundation of China (Grant No. 40436016), the National Basic Research Program of China (“973”) (Grant No. 2006CB806305), and the KIP Pilot Project of the Chinese Academy of Sciences (Grant No. kzcx3-sw-144)     

Optimizing solution of fault location using single terminal quantities

This paper firstly evaluated the impedance method and traveling waves method for fault location, and studied the robustness of fault location method based on impedance. Then it proposed an assembled fault location method for a transmission line based on single-terminal electrical quantities, in which the fault zone was firstly determined by impedance method with robustness then the accurate fault position was pinpointed by traveling waves method. EMTP (Electromagnetic Transient Program) simulations showed that the proposed method can overcome the drawbacks of impedance method and traveling waves method when either one is used alone, and improve both the accuracy and the reliability of fault location. Supported by the National Natural Science Foundation of China (Grant Nos. 50077011 and 50377019) and the National Basic Research Program of China (“973” Project) (Grant No. 2004CB217906)     

Heat mass transfer model of fouling process of calcium carbonate on heat transfer surface

A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the supersaturated solution. Based on experimental results of the fouling process, the deposition and removal rates of the mixing fouling were expressed. Furthermore, the coupling effect of temperature with the fouling process was considered in the physics model. As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions. The results showed that the present model could give a good prediction of fouling process, and the deviation was less than 15% of the experimental data in most cases. The new model is credible to predict the fouling process. Supported by the National Basic Research Program of China (“973”Project) (Grant No. G2000026304) and the Beijing Municipal Elitist Cultivation Project (Grant No. 20061D0501500186)     

Experimental study on pressure and temperature distributions for low mass flux steam jet in subcooled water

A low mass flux steam jet in subcooled water was experimentally investigated. The transition of flow pattern from stable jet to condensation oscillation was observed at relatively high water temperature. The axial total pressures, the axial and radial temperature distributions were measured in the jet region. The results indicated that the pressure and temperature distributions were mainly influenced by the water temperature. The correlations corrected with water temperature were given to predict the dimensionless axial pressure peak distance and axial temperature distributions in the jet region, the results showed a good agreement between the predictions and experiments. Moreover, the self-similarity property of the radial temperature was obtained, which agreed well with Gauss distribution. In present work, all the dimensionless properties were mainly dependent on the water temperature but weakly on the nozzle size under a certain steam mass flux. Supported by the National Natural Science Foundation of China (Grant Nos. 50676078, 50821064) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA05Z230)