共查询到20条相似文献,搜索用时 15 毫秒
1.
Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite
as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed
by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress
relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction
and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer.
The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The
results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural
bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link
and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress
relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of
the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient
reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular
cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite
hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing
cycles and the HA content.
Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century
Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403) 相似文献
2.
王馨 《武汉理工大学学报(材料科学英文版)》2009,24(2):273-277
The friction and wear properties of silicon surface covered with octadecyltrichlorosilane (OTS) self-assembled monolayers
(SAMs) were investigated by a UMT-2 microtribometer with and without water as lubricant, and then compared with that of bare
silicon surface. Dry friction measurement results show that OTS SAMs have a very low friction coefficient compared to bare
silicon surface under lower sliding velocity and normal contact load. However, heavy wear occurs on OTS SAMs under higher
contact stress and sliding velocity. Under water lubrication, OTS SAMs can prevent wear obviously and meanwhile present low
coefficient of friction even under high velocities. The improved frictional and anti-wear property on OTS SAMs surface is
attributed to the hydrophobic property of OTS and hydrodynamic effect of water. Furthermore, a wear critical phase diagram
for OTS SAMs with and without water was proposed, which indicates that OTS SAMs working under water lubrication owns a wider
range of available load and velocity to reduce friction and prevent wear.
Funded by the National Natural Science Foundation of China (Nos. 50575123, 50275071, 50545035) and National Basic Research
Program of China (“973” Program) (No. 2003CB716205) 相似文献
3.
WenMing Jiang ZhongLiang Liu HengWei Liu HuiZhong Pang LingLing Bao 《中国科学E辑(英文版)》2009,52(9):2653-2659
A mathematical model was developed to investigate the water vapor spontaneous condensation under supersonic flow conditions.
A numerical simulation was performed for the water vapor condensable supersonic flows through Laval nozzles under different
flow friction conditions. The comparison between numerical and experimental results shows that the model is accurate enough
to investigate the supersonic spontaneous condensation flow of water vapor inside Laval nozzles. The influences of flow friction
drag on supersonic spontaneous condensation flow of water vapor inside Laval nozzles were investigated. It was found that
the flow friction has a direct effect on the spontaneous condensation process and therefore it is important for an accurate
friction prediction in designing this kind of Laval nozzles.
Supported by the National Natural Science Foundation of China (Grant No. 50676002), the Specialized Research Fund for the
Doctoral Program of Higher Education (Grant No. 20040005008) and the Beijing Best Innovation Person Selecting Project (2006) 相似文献
4.
An automatic brush-plating system was developed for component remanufacturing. With this system, Ni/nano-alumina composite
coatings from an electrolyte containing 20 g/L nano-alumina particles were prepared. Microstructure, surface morphology, microhardness
and wear resistance of automatically plated coating and manually plated coatings were investigated comparatively. The results
show that the automatically plated coatings are relatively dense and uniform and have lower friction coefficient of 0.089
under lubricant condition, when compared with manually plated coatings with friction coefficient of 0.14.
Foundation item: Project(50235030) supported by the National Natural Science Foundation of China; Project(G1999065009) supported by the National
Basic Research Program of China 相似文献
5.
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) 相似文献
6.
Ke Wang XiaoDong Han Ze Zhang LiangCai Wu Bo Liu ZhiTang Song SongLin Feng 《中国科学E辑(英文版)》2009,52(9):2724-2726
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) 相似文献
7.
A macro-micro dual-drive positioning system showing good potential for high acceleration and high precision positioning required
in IC packaging applications is devised in this paper. The dual-drive positioning stage uses a VCM (voice coil motor) driven
macro positioning stage and a PZT piezo-electric driven micro positioning stage. The coupling characteristics of the system
are analyzed to produce a control structure with a micro positioning stage that can dynamically compensate for the positioning
error produced by the macro positioning stage. Models of the two positioning stages are described. The models cover both the
mechanism and the actuator. For the macro positioning stage, friction characteristics are taken into account, and a controller
with an LQG (linear-quadratic-Gaussian) control algorithm combining a feed-forward compensation algorithm is derived. A PID
controller is used to control the micro positioning stage. Detailed designs are derived for the proposed approach, and the
performance is validated by simulation.
Supported by the National Natural Science Foundation of China (Grant No. 50705027), the National High Technology Research
and Development Program of China (“863” Program) (Grant No. 2007AA04Z315) and Self-Planned Task of State Key Laboratory of
Robotics and System (HIT) (Grant No. SKLRS200804B) 相似文献
8.
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) 相似文献
9.
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) 相似文献
10.
To solve the engineering and scientific problems in construction diversion and its simulation analysis, a complete scheme
is presented. Firstly, the complex constraint relationship was analyzed among main buildings, diversion buildings and flow
control. Secondly, the time-space relationship model of construction diversion system and the general block diagram-oriented
simulation model of diversion process were set up. Then, the corresponding numerical simulation method and 3D dynamic visual
simulation method were put forward. Further, the simulation and optimization platform of construction diversion control process
was developed, integrated with simulation modeling, computation and visualization. Finally, these methods were applied to
a practical project successfully, showing that the modeling process is convenient, the computation and the visual analysis
can be coupled effectively, and the results conform to practical state. They provide new theoretical principles and technical
measures for analyzing the control problems encountered in construction diversion of hydraulic and hydroelectric engineering
under complex conditions.
Supported by the National Basic Research Program of China (“973” Program) (Grant No. 2007CB714101), the National Key Technology
R&D Program in the 11th Five year Plan of China (Grant No. 2006BAB04A13) and the National Science Fund for Distinguished Young
Scholars of China (Grant No. 50525927) 相似文献
11.
Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization 总被引:1,自引:1,他引:0
ZHANG QianCheng HAN YunJie CHEN ChangQing & LU TianJian State Key Laboratory for Mechanical Behavior of Materials School of Material Science Engineering Xi’an Jiaotong University Xi’an China MOE Key Laboratory for Strength Vibration School of Aerospace Department of Engineering Mechanics AML Tsinghua University Beijing 《中国科学E辑(英文版)》2009,52(8):2147-2154
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) 相似文献
12.
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) 相似文献
13.
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) 相似文献
14.
The microstructure and mechanical properties of Cu-12wt%Al alloy wires which are composed of continuous columnar crystals after dieless drawing forming at drawing speed of 1.0―1.4 mm/s and deformation temperature of 600―900℃ were analyzed, and deformation behavior of the alloy during dieless drawing forming was experimentally investigated. The results showed that in the abovemen-tioned conditions, recrystallization phenomenon was not found during dieless drawing forming. When a drawing speed of 1.0 mm/s was... 相似文献
15.
Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation 总被引:1,自引:0,他引:1
The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing
a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis
(DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids
to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids
and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric
field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But
when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong
friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on
the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be
weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive
potential energy, which accorded with the DLVO theory.
Supported by the National Hi-Tech Research and Derelopment Program of China (“863” Project) (Grant No. 2006AA04Z351) and the
National Natural Science Foundation of China (Grant Nos. 50675033, 30770553) 相似文献
16.
In the study of finite element model updating or damage detection, most papers are devoted to undamped systems. Thus, their
objective has been exclusively restricted to the correction of the mass and stiffness matrices. In contrast, this paper performs
the model updating and damage detection for damped structures. A theoretical contribution of this paper is to extend the cross-model
cross-mode (CMCM) method to simultaneously update the mass, damping and stiffness matrices of a finite element model when
only few spatially incomplete, complex-valued modes are available. Numerical studies are conducted for a 30-DOF (degree-of-freedom)
cantilever beam with multiple damaged elements, as the measured modes are synthesized from finite element models. The numerical
results reveal that applying the CMCM method, together with an iterative Guyan reduction scheme, can yield good damage detection
in general. When the measured modes utilized in the CMCM method are corrupted with irregular errors, assessing damage at the
location that possesses larger modal strain energy is less sensitive to the corrupted modes.
Supported by the National High-Tech Research and Development Program of China (“863”) (Grant No. 2006AA09Z331), the China
National Science Fund for Distinguished Young Scholars (Grant No. 50325927), and the National Natural Science Foundation of
China (Grant No. 50739004) 相似文献
17.
JunHu Ma HeQing Yang YuZhe Song Li Li XiaoLi Xie RuiNi Liu LinFang Wang 《中国科学E辑(英文版)》2009,52(5):1264-1272
Large-scale oriented ZnO nanocone arrays were directly grown on zinc substrate through a hydro-thermal reaction of Zn foil with aqueous butylamine solution(3 mol/L) at 100—180 ℃ for 12 h.The syn-thesized products were characterized with X-ray diffraction,Raman spectrum,scanning electron mi-croscopy and transmission electron microscopy.The results showed that the ZnO nanocones were single crystalline with the wurtzite structure and grown along the [0001] direction.The diameter of nanocones is decreased with ... 相似文献
18.
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 相似文献
19.
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) 相似文献
20.
The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors
of the ceramic nozzles and the outstanding properties of FGM. The purpose is to reduce the tensile stress at the entry region
of the nozzle during sand blasting processes. The design theory and methods of gradient ceramic nozzle were proposed. The
physical, micromechanical, and composition distribution models of gradient ceramic nozzle were established. The optimum composition
distribution of the gradient ceramic nozzle material was determined from the solution of the multi-objective optimization
calculation by constructing the models of the composition distribution versus the structural integrity of the compact in fabricating
process. Results showed that compressive residual stresses appeared at the entry area of the gradient ceramic nozzle. The
optimized component distribution exponent p is 0.5. An SiC/(W,Ti)C gradient ceramic nozzle material was synthesized by hot-pressing according to the design result. Results
showed that the surface Vickers hardness of the FGM-1 gradient ceramic nozzle materials was greatly improved in comparison
with that of the other layers.
Supported by the Specialized Research Fund for Doctoral Program of Higher Education (Grant No. 20030422105), the Natural Science
Foundation of Shandong Province (Grant Nos. Y2004F08, Z2003F01) and the Program for New Century Excellent Talents in University
(Grant No. NCET-04-0622) 相似文献