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1.
Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated
systematically by using a first-principles calculations method based on the density functional theory. The calculation results
of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean
Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated
as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen
diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface
to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively,
Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits
H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom
is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of
states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (E
F)) at Fermi level and more bonding electrons at the energy range blow the Fermi level of H/Mg (0001) system as compared with
that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should
be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding
electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving
the surface activity of Mg (0001) surface.
Supported by the PhD Programs Foundation of Ministry of Education of China (Grant No. 200805321032), the Science and Technology
Program Project of Hunan Province (Grant No. 2008GK3083) and the Program for Changjiang Scholars and the Innovative Research
Team in university (Grant No. 531105050037) 相似文献
2.
The mechanical oscillatory behaviors of multiwall carbon nanotube oscillators in gaseous environment are investigated using
the molecular dynamics method. The effects of ambient gas and temperature on intertube frictional force and oscillation frequency
are analyzed. It is found that the intertube frictional force increases with the ambient gas density and temperature. Higher
gas density and higher temperature cause a more rapid decay in the oscillation amplitude and an increase of the oscillation
frequency. Compared to the vacuum environmental condition, the collision between gas atoms and the nanotube walls is a main
ingredient leading to the increase of the energy dissipation. Gas damping may be the main reason for the failure of carbon
nanotube oscillators working in gas environment. The ambient temperature also has an important effect on oscillations and
low temperature is advantageous to sustain oscillations.
Supported by the National Basic Research Program of China (“973”) (Grant No. 2006CB300404), the National Natural Science Foundation
of China (Grant Nos. 50676019, 50775017), the Jiangsu Province Natural Science Foundation (Grant Nos. BK2006510, BK2007113),
and the Research Funding for the Doctor Program from Chinese Educational Ministry (Grant No. 20050286019) 相似文献
3.
Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior. 相似文献
4.
Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanometer magnetic material was fabricated through rapid solidification, crystallization and nitridation of Sm-Fe (Ti) alloy. The effect of combination of rapid solidification and Ti alloy addition on the phase formation and microstructure of the Sm-Fe alloy is investigated in this paper. The microstructure of amorphous phase and dual-phase nano-grain crystals before and after crystallization annealing were observed using a high-resolution transmission electron microscope (HREM). The dual-phase nano-grains after annealing were compacted together with a clear interface with the direct exchange-coupling mechanism. Different annealing processes were used to examine the melt-spun alloy. Comparison of the images of SEM showed that annealing at 750℃ for 10 min was most suitable to get homogeneous and nano-grains. No obvious kink was detected in the second quadrant of the hysteresis loop like a single hard magnet, and strong exchange coupling was found between hard magnets and soft magnets. 相似文献
5.
Alpha-calcium sulfate hemihydrate (α-HH) has been prepared from flue gas desulfurization (FGD) gypsum with salt solution method
under atmospheric pressure. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), optical
micrograph, X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), and scanning electron microscopy
(SEM) have been employed to characterize the α-HH crystals, based on which the formation and growth mechanisms of the α-HH
crystals have been discussed. The results show that FGD gypsum can be successfully transformed into high purity α-HH in salt
solution under mild conditions, and that a dissolution-recrystallization route is most probably adopted by this transition.
The growth of α-HH crystals in salt solution demonstrates a preferred direction along [001] and results in a bundle-of-sheets
or bundle-of-raphide texture. The characteristics revealed in this study can help to understand and control the growth of
the α-HH crystal from solution.
Supported by the National High-Tech Research & Development Program of China (Grant No. 2006AA06Z385), New Century Excellent
Talents in University (Grant No. NCET-04-0549), and the Project of Science and Technology Plan of Zhejiang Province (Grant
No. 2007C23055) 相似文献
6.
Calculations have been made for single-walled zigzag(n,0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory.It is found that the formation energies of these nanotubes depend on the tube diameter,as do the electronic properties,and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes.When more boron atoms are incorporated into a single-walled zigzag carbon nanotube,the substit... 相似文献
7.
HuiMin Xie ZhenXing Hu FuLong Dai YanJie Li PengWan Chen QingMing Zhang FengLei Huang 《中国科学E辑(英文版)》2009,52(7):2048-2053
This paper proposes a new method that reconstructs the information of specimen by using random phase shift step in digital
holographic microscopy (DHM). The principles of the method are described and discussed in detail. In practical experiment,
because the phase shifter is neither perfectly linear nor calibrated, digital holograms with inaccurate phase shift step are
recorded by the charge-coupled device (CCD). The phase could be accurately reconstructed from the recorded digital holograms
by using the random phase-shifting algorithm, which makes up for reconstructed phase error caused by ordinary phase-shifting
algorithm. The phase aberration compensation is also discussed. In order to verify the flexibility of the proposed method,
numerical simulation of random phase-shifting DHM was carried out. The simulation results illustrated that the presented method
is effective when the phase shift step is unknown or random in DHM.
Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2004CB619304), the National Natural Science
Foundation of China (Grant Nos. 10625209, 10472050, 10732080), the Project of Beijing Natural Sciences Foundation (Grant No.
3072007), the Program for New Century Excellent Talents (NCET) in Chinese University Ministry of Education (Grant No. NCET-05-0059),
and the Opening Funds from the State Key Laboratory of Explosion Science and Technology 相似文献
8.
TheFIMmicrographsofbinaryorderedintermetalliccompoundsarecomparablewiththoseofpuremetals,whichhaveperfectringstructure.Andinterestingenough,generallyonlyoneatomspeciescontributestotheimages[1,2].However,itisnotclearwhichatomspeciesimagesinmostsystems,andd… 相似文献
9.
BingQing Zhou MeiFang Zhu FengZhen Liu JinLong Liu YuQin Zhou GuoHua Li Kun Ding 《中国科学E辑(英文版)》2008,51(4):371-377
Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by high-pressure radio-frequency (13.56 MHz) plasma
enhanced chemical vapor deposition (rf-PECVD) with a screened plasma. The deposition rate and crystallinity varying with the
deposition pressure, rf power, hydrogen dilution ratio and electrodes distance were systematically studied. By optimizing
the deposition parameters the device quality μc-Si:H films have been achieved with a high deposition rate of 7.8 ?/s at a
high pressure. The V
oc of 560 mV and the FF of 0.70 have been achieved for a single-junction μc-Si:H p-i-n solar cell at a deposition rate of 7.8
?/s.
Supported by the National Natural Science Foundation of China (Grant No. 50662003) and the State Development Program for Basic
Research of China (Grant No. G2000028208) 相似文献
10.
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
11.
In order to detect the damage locations of complex spatial structures, a sensor region-based damage detection approach was
developed based on the damage locating vectors method. A normalized damage locating index was introduced to identify the damage
regions. An experiment on damage detection of a substructure model of the National Swimming Center ‘Water Cube’ was carried
out. Two damage patterns were involved in the experiment. The test model was excited by using hammer impacts. Acceleration
responses of the undamaged and damaged structure model were measured. Modal parameters were identified from the acceleration
responses by utilizing the eigensystem realization algorithm (ERA). By using the developed sensor region-based method, the
damage regions of the substructure model were located. The results show that the proposed method is able to effectively locate
the damage regions.
Supported by Beijing Natural Science Foundation (Grant No. 8041002), the National Natural Science Foundation of China (Grant
No. 8041002), the National Science and Technology Committee of China (Grant No. 2004BA904B02), and Beijing Science and Technology
Committee (Grant No. Z0004028040221) 相似文献
12.
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
13.
Based on experimental results that VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at.%V nanocomposite, H atoms diffusion and adsorption properties of MgH2-V systems have been investigated by using a first-principles plane-wave pseudopotential method based on the density functional
theory. The results are as follows. When VH/MgH2 interface is formed due to V alloying MgH2 phase, the vacancy formed by H atoms near VH phase region is more stable than that without V alloying, while vacancy near
MgH2 phase region is less stable than that without V alloying. During the process of H atoms diffusion after V alloying, the max
migration barrier energy of H atoms in MgH2-V systems is reduced compared with that of MgH2 phase, which means that H atoms diffuse easily. When H diffuses into VH from MgH2 across VH/MgH2 interface, among three substitutions such as the replacement of H for V vacancy, or interstitial site or V atoms, the replacement
of H for V vacancy has the strongest diffusion ability, next interstitial site, and finally V atoms site. As far as H adsorbed
on different surfaces of VH phase is concerned, physical adsorption is carried out more easily than chemical adsorption, and
the behavior of H atoms adsorbed on the surface near VH phase region can be found more easily than that near MgH2 phase region.
Supported by the Ministry of Science and Technology of China (Grant No. 2006CB605104) and the National Natural Science Foundation
of China (Grant No. 50771044) 相似文献
14.
To track and control the changes of process quality attributes in multistage machining processes (MMPs), an e-quality control
(e-QC) model is proposed. The e-QC model is defined as a quality information service node with e-formalizing technology, whose
input/output and intermediate process (that is IPO) are known to other nodes, and its implemention in MMPs is provided. In
order to establish the e-QC model, a measuring network is constructed to acquire the original quality data, and the changes
of process quality attributes are monitored and diagnosed by the integrated quality analysis tools attached to the e-QC, which
can be tracked by information template network in real time. Furthermore, a hierarchical control method is adopted to coordinate
e-QCs, in which the quality loss and adjusting cost are used to quantify the opportunities for e-QCs to improve process quality.
At last, a prototype is developed to verify the proposed methods.
Supported by the National Basic Research Program of China (“973”) (Grant No. 2005CB724106) and the National High-Tech Research
and Development Program of China (“863”) (Grant No. 2007AA00Z108) 相似文献
15.
HUANGYun-ping Yun-ping 《武汉理工大学学报(材料科学英文版)》2002,17(1):58-61
The topological index F^* is defined and obtained by the method of a non-dimensional unit calculation in which three matrices multiply with each other.These matrices represent the connectine cases of atoms in a molecule,the structural features of atoms on top and the bonded cases of the adjacent atoms respectively.The standard formation enthalpies of ABn(g) molecules were correlated with F^*(A=C,Al,Si,Ti,Zr,B=F,Cl,Br,I,H,n=1-4)and these correlation coefficients are all more than 0.96 .Some molecules(e.g CH4,SiH4,etc)can be preferably handled by F^* but can not be dealt with by other topological indices.By contrast to traditional hydrogen suppressed graph,the contribution of hydrogen atoms to structures and properties of molecules is considered. 相似文献
16.
By a novel controlled combustion synthesis method, a large amount of ZnO nano-whiskers with different morphologies like nanotetrapods,
long-leg nanotetrapod and multipods, were prepared without any catalysts and additives in open air at high temperature. Their
morphologies, structures and optical properties were investigated by using SEM, XRD and PL spectrum. The possible growth mechanisms
on the ZnO nano-whiskers were proposed in this paper.
Supported by the National Natural Science Foundation of China (Grant Nos. 50572010, 50742007 and 10672020), National Defense
Founds of China (Grant Nos. 51420205BQ0154 and A2220061080), “863” Project of China (Grant No. 2007AA03Z103), and the Scientific
Research Foundation of Graduate School of BIT (Grant No. AA200802) 相似文献
17.
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
18.
AfterthedevelopmentofnanocrystallinesoftmagneticalloysFeSiBNbCu[1,2],Suzukietal.[3]successfullydevelopednanocrystallinealloysFeZrBin1990,inwhichαFeparticlesofnanometerscalewererandomlyembeddedontheamorphousmatrix.BecauseoftheirlowsolutecontentinαFephase,thes… 相似文献
19.
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) 相似文献
20.
According to differential geometry and gear geometry, the equation of meshing for small teeth difference planetary gearing
and a universal equation of conjugated profile are established based on cylindrical pin tooth and given motion. The correct
meshing condition, contact line, contact ratio, calculating method for pin tooth’s maximum contact point are developed. Investigation
on the theory of conjugated meshing is carried out when the tooth difference numbers between pin wheel and cycloidal gear
are 1, 2, 3 and −1, respectively. A general method called enveloping method to generate hypocycloid and epicycloid is put
forward. The correct meshing condition for cycloid pin wheel gearing is provided, and the contact line and the contact ratio
are also discussed.
Supported by the National Science and Technology Supporting Program (Grant No. No. 2006BAF01B08) and Chongqing Science and
Technology Key Task (Grant No. CSCT2006AA3010-6) 相似文献