共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
In order to establish an environmental-condition-normalized structural damage alarming method, the seasonal correlation analysis
of wavelet packet energy spectrum (WPES) and temperature of Runyang Suspension Bridge is performed by means of the 236-day
health monitoring data. The analysis results reveal that the measured WPES has remarkable seasonal correlation with the environmental
temperature. The seasonal change of environmental temperature accounts for the variation of the damage alarming parameter
I
p
of the dominant frequency bands with an averaged variance of 200%. The statistical modeling technique using a 6th-order polynomial
is adopted to formulate the correlation between the WPES and temperature, on the basis of which the abnormal changes of measured
damage alarming parameter I
p
are detected using the mean value control chart. It is found that the proposed method can effectively eliminate temperature
complications from the time series of WPES and exhibit good capability for detecting the damage-induced 10% variances of the
damage alarming parameter I
p
. And the proposed WPES-based method is superior the modal frequency and hence is more suitable for online real-time damage
alarming for long-span bridges.
Supported by the National Natural Science Foundation of China (Grant Nos. 50725828, 50808041) and the Natural Science Foundation
of Jiangsu Province (Grant No. BK2008312) 相似文献
4.
A novel asymmetrical twin-core photonic crystal fiber was proposed, whose effective overlap core area A
eff can be designed to synchronize the variation of Raman gain coefficient with respect to frequency. This fiber possesses a
higher and flatter Raman gain efficiency coefficient curve r
R=g
R/A
eff over a specified band of wavelength than a conventional fiber. Therefore, it is a good candidate of gain medium for a flat,
broad gain band fiber Raman amplifier. It was numerically demonstrated that for the Raman gain efficiency r
R, relative fluctuations of less than 2.2% and 5.7% are achievable in the C (1530−1565 nm) band and L (1565−1625 nm) band, respectively.
Supported by the National Natural Science Foundation of China (Grant Nos. 60588502, 60607005, 60877033), the Science and Technology
Bureau of Sichuan Province (Grant No. 2006z02-010-3) and the Youth Science and Technology Foundation of UESTC (Grant No. JX0628) 相似文献
5.
KIM Tongbeum 《中国科学E辑(英文版)》2009,52(6):1688-1697
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). 相似文献
6.
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
7.
The humanoid robot SJTU-HR1’s concept is introduced and its characteristics tree is given. The basic states for SJTU-HR1 are
proposed, including lying, sitting, standing and handstanding, abstracted from the daily exercises of human beings. The G
F
(generalized function) set theory is exploited to achieve the kinematic characteristics of the interested EEs (end-effectors)
of SJTU-HR1 for the lying states. Finally, the results show that the large amounts of states can be described using the abbreviations
in a systematic manner. Although we have focused on the application of the G
F
set theory to humanoid robots, particularly the SJTU-HR1, this methodology can also be applied to quadruped robots and hexapedal
robots, especially when the desired tasks are complex.
Supported by the Natural Basic Research Program of China (“973”) (Grant No. 2006CB705400), the National Natural Science Foundation
of China (Grant Nos. 60534020, 30770538), Joint Research Fund for Young Scholars in China and Abroad (Grant No. 50728503),
and the Graduate Innovation Foundation of Shanghai Jiao Tong University 相似文献
8.
Pin-reinforced foam is a novel type of sandwich core materials formed by inserting pins (trusses) into a foam matrix to create
a truss-like network reinforced foam core. Upon loading, the pins deform predominantly by local stretching whilst the deformation
of foam is governed by local bending. This paper presents a theoretical study on the thermoelasticity of pin-reinforced foam
sandwich cores. To calculate the effective thermoelastic properties of pin-reinforced foam cores, the energy-based homogenization
approach is employed to develop a micromechanicsbased model, calibrated by the existing experimental data. It is found that
the stiffness of the sandwich core is mainly governed by pin reinforcements: the foam matrix contributes little to sandwich
stiffness. Compared with traditional foam cores without pin reinforcements, the changes in in-plane thermal expansion coefficients
are not vigorous as a result of pin reinforcements, while the throughthickness thermal expansion coefficient changes significantly.
It is also demonstrated that it is possible to design materials with zero or negative thermal expansion coefficients under
such a context.
Supported by the National Basic Research Program of China (Grant No. 2006CB601202), the National Natural Science Foundation
of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024), the National High Technology
Research Development Program (Grant No. 2006AA03Z519), the NPU Foundation for Fundamental Research, the Open Foundation of
State Key Laboratory of Structural Analysis of Industrial Equipment (Grant No. GZ0701), and the NPU Foundation for Scientific
Innovation 相似文献
9.
Stable superhydrophobic n-tetradecanoic acid (CH3(CH2)14COOH) film was prepared by means of sol-gel and self-assembly techniques, with a very high seawater contact angle (158°) and
a small sliding angle (<5°). There are many microconvexities with binary structure uniformly distributed on the surface atop
the film with an average diameter of about 80 nm by observation of scanning electron microscope (SEM), and the film surface
structure is similar to that of lotus surface. The corrosion resistance behavior of intermetallic Fe3Al with the biomimetic superhydrophobic film surface is improved obviously when compared with pure Fe3Al sample by measurement of electrochemical impedance spectroscopy (EIS).
Supported by the Excellent Mid-youthful Scientist Encouraging Foundation of Shandong Province (Grant No. 2006BS04021) and
the National Natural Science Foundation of China (Grant Nos. 50672090 and 50702053) 相似文献
10.
ZiLi Xie Rong Zhang RuoLian Jiang Bin Liu HaiMei Gong XiangQian Xiu Peng Chen Hai Lu Ping Han Yi Shi YouDou Zheng 《中国科学E辑(英文版)》2009,52(2):332-335
AlN/Al0.3Ga0.7N superlattices were grown on (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The superlattice
period varies from 6 to 30. The layer thickness of different period stack was designed. GaN or AlGaN template was employed
for growing AlN/AlGaN superlattices. Reflectivity, SEM, AFM and XRD data of the Al
x
Ga1-x
N/AlN superlattices are presented. It is found that the templates used have an intensive impact on surface roughness and interfacial
properties of following AlN/AlGaN superlattices. The result of atomic force microscopy indicates that AlN/AlGaN superlattices
grown on GaN template exhibit quasi-two-dimensional growth mode. The resulting superlattice has a smooth surface morphology
and distinct interface. No crack is observed in the area of a 2-inch wafer.
Supported by the Special Funds for Major State Basic Research Project (973 Project) (Grant No. 2006CB6049), the Hi-tech Research
Project (Grant Nos. 2006AA03A103, 2006AA03A118, and 2006AA03A142), the National Natural Science Foundation of China (Grant
No. 60676057), and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004) 相似文献
11.
In order to endow titanium metals with bioactivity and antimicrobial properties, titanium plates were subjected to anodic
oxidation treatment in NaCl solutions in this study. The treated titanium metals could induce apatite formation in the fast
calcification solution, and osteoblasts on the treated titanium surfaces proliferated well as those on the untreated titanium
metal surfaces. The treated metals could inhibit S. aureus growth in the microbial culture experiments. It was assumed that Ti-OH groups and Ti-Cl groups formed on the treated titanium
surface were responsible for the bioactivity and antimicrobial properties of the metals. The anodic oxidation treatment was
an effective way to prepare bioactive titanium surfaces with antimicrobial properties.
Supported by the National Natural Science Foundation of China (Grant Nos. 50672062 and 30870615), Key Programs for Science
and Technology Development of Sichuan Province, China (Grant No. 2008SZ0104) and Sichuan Youth Science & Technology Foundation,
China (Grant No. 09ZQ026-033) 相似文献
12.
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
13.
A molecular dynamics (MD) model of the fluidic electrokinetic transport in a nano-scale channel with two bulk sinks was presented,
and the process of ion transport in the nanochannel was simulated in this paper. The model consists of two water sinks at
the two ends and a pump in the middle, which is different from a single pump model in previous MD simulations. Simulation
results show that the charged surfaces of the nanochannel result in the depletion of co-ions and the enrichment of counterions
in the nanochannel. A stable current is induced because of the motion of ions when an external electric field is applied across
the nanochannel, and the current in the pump region is mainly induced by the motion of counterions. In addition, the ion number
in the pump region rapidly decreases as the external electric field is applied. In the equilibrated system, the electrically
neutral character in the pump region is destroyed and this region displays a certain electrical character, which depends on
the surface charge. The ion distribution is greatly different from the results predicted by the continuum theory, e.g. a smaller
peak value of Na+ concentration appears near the wall. The transport efficiency of counterions (coions) can be effectively increased (decreased)
by increasing the surface charge density. The simulation results demonstrate that the ion distribution in the electric double
layer (EDL) of a nanochannel cannot be exactly described by the classical Gouy-Chapman-Stern (GCS) theory model. The mechanism
of some special experimental phenomena in a nanochannel and the effect of the surface charge density on the ion-transport
efficiency were also explored to provide some theoretical insights for the design and application of nano-scale fluidic pumps.
Supported by the National Basic Research Program of China (Grant No. 2006CB300404), the National Natural Science Foundation
of China (Grant Nos. 50475077, 50676019, 50506008), the Natural Science Foundation of Jiangsu Province (Grant No. BK2006510),
and the Foundation of Education Ministry of China (Grant No. 20050286019). The author Y. Chen also acknowledges the financial
support from the Program for New Century Excellent Talents in University (NCET-04-0470). 相似文献
14.
Risk assessment method of major unsafe hydroelectric project 总被引:4,自引:3,他引:1
Based on the characteristics of major unsafe hydroelectric projects and the data from field detection, in situ monitoring,
and regular safety inspection, the fundamental principles of operation risk assessment are proposed in this paper. Meanwhile,
a three layer hierarchical system is constructed, and an improved analytical hierarchical process combining genetic algorithm
and analytical hierarchical process is established, with corresponding program. The operation risk of some unsafe dam was
assessed with the principles, method and program presented in this paper and the major factors which would affect the operation
of the dam were pointed out.
Supported by Key Project of NNSF and Yalongjiang Hydroelectric Development Joint Research Fund (Grant No. 50539110), Science
and Technology Support Plan (Grant No. 20006BAC14B03), National Natural Science Foundation Major Project (Grant Nos. 50539010,
50539030) and National Natural Science Foundation of China (Grant No. 50579010) 相似文献
15.
In order to improve the corrosion resistance of AZ31 magnesium alloy, the amorphous/nanocrystal Al-Cr-Fe film has been successfully
prepared on AZ31 magnesium alloy by double glow plasma technology. The amorphous/nanocrystalline consists of two different
regions, i.e., an amorphous layer on outmost surface and an underlying lamellar nanocrystalline layer with a grain size of
less than 10 nm. The corrosion behavior of amorphous/nanocrystalline Al-Cr-Fe film in 3.5% NaCl solution is investigated using
an electrochemical polarization measurement. Compared with the AZ31 magnesium alloy, the amorphous/nanocrystalline Al-Cr-Fe
film exhibits more positive corrosion potentials and lower corrosion current densities than that of AZ31 magnesium alloy.
XPS measurement reveals that the passive film formed on the Al-Cr-Fe film after the anodic polarization tests is strongly
enriched in Cr2O3, Fe2O3 and Al2O3 at outer surface of the film and in the inner layer consists of Cr2O3, FeO and Al2O3.
Supported by the National Natural Science Foundation of China (Grant Nos. 50571045 and 50704022) and the Natural Science Foundation
of Jiangsu Province, China (Grant No. BK2007591) 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.
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
18.
Multi-channel micro neural probe fabricated with SOI 总被引:1,自引:0,他引:1
WeiHua Pei Lin Zhu ShuJing Wang Kai Guo Jun Tang Xu Zhang Lin Lu ShangKai Gao HongDa Chen 《中国科学E辑(英文版)》2009,52(5):1187-1190
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... 相似文献
19.
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) 相似文献
20.
Nanoparticle (NP) is the matter between molecule and bulk material. It has attracted much attention in catalysis, optoelectronics
and biology due to its unique physical and chemical properties. Incorporation of these NPs into the polymer matrix is one
of the best methods to display their special functions, which not only stabilize the NPs but also realize the functional assembly
of NPs and polymers. However, realization of this idea depends largely on the compatibility of NPs and polymers as well as
the interaction between them. Therefore, many methods have been developed to prepare the composites of NPs and polymers in
order to obtain the function expected. In this review, we mainly focus on the combination of in situ method with other methods to synthesize different functional one-dimension, two-dimension as well as bulk composites, which
has been recently developed by our group. The most striking character of our method is the excellent compatibility between
NPs and polymers which ensures a homogeneous distribution of NPs in the polymer matrix. The existence of the polymer network
makes the NPs more stable, and is significant for displaying their functions.
Supported by the National Natural Science Foundation of China (Grant Nos. 2007CB936402, 20534040) and Science Foundation for
Young Teachers of Northeast Normal University (Grant No. 20070306) 相似文献