共查询到20条相似文献,搜索用时 15 毫秒
1.
The current paper focuses on the influence of the process parameters on the peak values of the inter-facial heat transfer coefficient (IHTC) at metal/die interface during high pressure die casting (HPDC) process. A "step shape" casting and AM50 alloy were used during the experiment. The IHTC was de-termined by solving the inverse thermal problem based on the measured temperature inside the die. Results show that the initial die surface temperature (IDST, TDI) has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values. By curve fitting, it was found that the IHTC peak value (hmax) changes as a function of the IDST in a manner of hmax =eαTγDI. Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12, indicating that this phenomenon is a common characteristic in the HPDC process. 相似文献
2.
Liang Wang XiaoShuang Chen Wei Lu Yan Huang XiaoFang Wang JiJun Zhao 《中国科学E辑(英文版)》2009,52(7):1928-1932
The structural and optical properties of amorphous semiconductor mercury cadmium telluride (a-MCT) are obtained by the first
principles calculations. The total pair distribution functions and the density of states show that the a-MCT has the semiconductor
characteristic. The calculated results of dielectric function show that E
2 peak of the imaginary of dielectric function for the crystal mercury cadmium telluride abruptly disappears in the amorphous
case due to the long-range disorders. And the imaginary of dielectric function of a-MCT shows a large broad peak, which is
in agreement with the available results of other amorphous semiconductors. From the linear extrapolation of the curve ħωɛ
2(ω)1/2 versus ħω, it can be obtained that the optical energy gap of amorphous semiconductor Hg0.5Cd0.5Te is 0.51±0.05 eV.
Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2007CB613205), the National Natural Science
Foundation of China (Grant Nos.10725418, 10734090, 60576068), the Key Fund of Shanghai Science and Technology Foundation (Grant
No. 08JC1421100) and the Knowledge Innovation Program of the Chinese Academy of Sciences 相似文献
3.
WenYao Xu 《中国科学E辑(英文版)》2008,51(10):1659-1664
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) 相似文献
4.
LI Kai XIE ErQing WANG Li LIU YanXia YANG Yang SUN YanZheng CUI XinYu & MAI ShengLi School of Physical Science Technology Lanzhou University Lanzhou China Lanzhou Institute of Physics Lanzhou China Tianjin Institute of Power Source Tianjin China 《中国科学E辑(英文版)》2007,50(2):213-220
It has been reported that sustained arc discharge induced by electrostatic discharge (ESD) could cause permanent damage to high-power and high-voltage solar array of spacecrafts. The paper focuses on ESD simulating experiments on Si and GaAs samples, and induces sustained arc discharge. The physical mechanism of sustained arc discharge is discussed by comparing the charging/discharging phenomena between Si and GaAs samples. The experiments show that sustained arc discharge can produce a permanent short-circuit channel between solar cell strings through which the solar array’s photovoltaic power may flow out sustainedly. The analyses show that sustained arc discharge strongly depends on solar array structure, solar array operating voltage, ESD characteristics and cell materials. 相似文献
5.
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
6.
(ZrO2)
x
(SiO2)1−x
(Zr-Si-O) films with different compositions were deposited on p-Si(100) substrates by using pulsed laser deposition technique.
X-ray photoelectron spectra (XPS) showed that these films remained amorphous after annealing at 800°C with RTA process in
N2 for 60 s. The XPS spectra indicated that Zr-Si-O films with x=0.5 suffered no obvious phase separation after annealing at 800°C, and no interface layer was formed between Zr-Si-O film
and Si substrate. While Zr-Si-O films with x >0.5 suffered phase separation to precipitate ZrO2 after annealing under the same condition, and SiO2 was formed at the interface. To get a good interface between Zr-Si-O films and Si substrate, Zr-Si-O films with bi-layer
structure (ZrO2)0.7(SiO2)0.3/(ZrO2)0.5(SiO2)0.5/Si was deposited. The electrical properties showed that the bi-layer Zr-Si-O film is of the lowest equivalent oxide thickness
and good interface with Si substrate.
Supported by the National Nature Science Foundation of China (Grant No. 60636010) and the National Basic Research Program
of China (“973” Program) (Grant No. 2004CB619004) 相似文献
7.
The Morris-Lecar (ML) neuronal model with current-feedback control is considered as a typical fast-slow dynamical system to
study the combined influences of the reversal potential V
Ca of Ca2+ and the feedback current I on the generation and transition of different bursting oscillations. Two-parameter bifurcation analysis of the fast subsystem
is performed in the parameter (I, V
Ca)-plane at first. Three important codimension-2 bifurcation points and some codimension-1 bifurcation curves are obtained
which enable one to determine the parameter regions for different types of bursting. Next, we further divide the control parameter
(V
0, V
Ca)-plane into five different bursting regions, namely, the “fold/fold” bursting region R1, the “fold/Hopf” bursting region
R2, the “fold/homoclinic” bursting region R3, the “subHopf/homoclinic” bursting region R4 and the “subHopf/subHopf” bursting
region R5, as well as a silence region R6. Codimension-1 and -2 bifurcations are responsible for explanation of transition
mechanisms between different types of bursting. The results are instructive for further understanding the dynamical behavior
and mechanisms of complex firing activities and information processing in biological nervous systems.
Supported by the National Natural Science Foundation of China (Grant Nos. 10872014 and 10702002) 相似文献
8.
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) 相似文献
9.
The microstructure of composite diffusion layer of the nitrided and chromized 0.2% carbon steel is investigated using TEM and EDS. It is found that laths of austenite with high nitrogen (λN) precipitate from α-ferrite matrix in the deeper zone of the diffusion layer. These λN laths are all twins, with their {111} twinning planes parallel to the lath axis, thus forming a characteristic "back-to-back" morphology. There are two types of λN lath. The first is a genuinely {111} twin, and λN and α keep the accurate K-S relationship, and each λN and α form a sharp and smooth λN/α interface of {335}λN//{341}a, namely habit plane {335}fcc. The second is a pseudo-twin, with micro-twins {111} or faults formed within the two twin components. Localized lattice deformation (relaxation) seems to have occurred at the interfaces of the second type of λN due to the formation of micro-twins or faults within the twin components. These micro-twins or faults make the orientation relationship (OR) between each of the λN and the (-matrix deviate from the accurate K-S OR, and the OR between two λN twin components deviate from the genuine {111} twin relationship. In addition, the λN/α interface of the second type of λN is not as sharp or smooth as that of the first one. 相似文献
10.
Based on the empirical electron theory of solids and molecules (EET), the statistical values of valence electron structure
parameters Sn
A and SE
A which can characterize the properties of alloy phases are calculated, and influences of alloying elements (e.g., V, Nb, Mo,
Hf, Zr, Fe, Mn, Co, Cr, Si, and so on) on the phase transition temperature and eutectoid reaction of titanium alloy are discussed
with the statistical values of valence electron structure parameters. The research results agree well with real situations.
Supported by the National Natural Science Foundation of China (Grant No. 50471022, 50741004) and National Key Basic Research
Program of China (“973”) (Grant No. 2007CB613807) 相似文献
11.
YuJie Yuan GuoFu Hou JianJun Zhang JunMing Xue LiRan Cao Ying Zhao XinHua Geng 《中国科学E辑(英文版)》2009,52(6):1756-1761
High pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to investigate the
effect of constant hydrogen dilution technique and gradient hydrogen dilution technique on the structural evolution of intrinsic
films and the performance of n-i-p microcrystalline silicon solar cells. The experiment results demonstrated that the grain size and crystalline volume fraction
along the growth direction of intrinsic films can be controlled and the performance of solar cells can be greatly improved
by gradient hydrogen dilution technique. An initial active-area efficiency of 5.7% (V
oc=0.47 V, J
sc=20.2 mA/cm2, FF=60%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.12% (V
oc=1.2 V, J
sc=12.05 mA/cm2, FF=70%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells has been achieved.
Supported by the National Basic Research Program of China (“973” Program) (Grant Nos. 2006CB202602, 2006CB202603) and the
Tianjin Assistant Foundation for the National Basic Research Program of China (Grant No. 07QTPTJC29500) 相似文献
12.
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
13.
Tao Zhang JunHong Jin DaYong Hu ShengLin Yang Guang Li JianMing Jiang 《中国科学E辑(英文版)》2009,52(4):906-909
The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation
bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical
properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results
indicated that in PPA/H2O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine
crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved.
Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project
(Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program)
(Grant No. 111-2-04) 相似文献
14.
研究自感应式和交流高压式静电消除器的消电性能,对影响其消电电流的条件进行了测试和分析,并且研究出一种消电性和安全性都较好的针——针型放电极的交流高压式消电器. 相似文献
15.
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) 相似文献
16.
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
17.
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) 相似文献
18.
LIU XiaoWei XU MingHou? YAO Hong YU DunXi ZHANG ZhongHua & Lü DangZhen State Key Laboratory of Coal Combustion Huazhong University of Science Technology Wuhan China 《中国科学E辑(英文版)》2009,52(6):1521-1526
Measurements of the characteristics of particulate matter(PM)were performed at the inlet and outlet of the electrostatic precipitators(ESP)of four boilers in two full-scale pulverized coal power plants.PM was collected with a 13-stages low-pressure-impactor(LPI)having aerodynamic cut-off diameter ranging from 10.0 to 0.03μm for a size-segregated collection.The properties of PM including its con-centration,mass size distribution,emission characteristics,percent penetration of PM through ESP and elemental com... 相似文献
19.
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
20.
A number of three-point bending and fracture tests of 200 MPa-level reactive powder concrete (RPC) with the various fiber
contents have been conducted to probe the nature and characteristics of toughness of RPC200. The contribution of the embedded
fibers to improving the crack-resistant capacity, energy absorption capacity and toughness with various deformation mechanisms
has been analyzed. Taking account of that the first-crack deformation, peak-load deformation and their improvement varied
with the fiber contents and that the deformation mechanism affected differently the performance at the first crack and the
peak load, we took the peak-load deformation of plain RPC200 as the reference deformation to measure the toughness of fibered
RPC200. Two toughness indices T
2(n−1)(n) and FT
2(n−1)(n) have been formulated based on P-δ responses and P-CMOD responses. The indices quantify the toughness of RPC200 with the various deformation mechanisms relative to perfectly
elastoplastic materials by setting the toughness level 2(n−1) as the initial reference. It is shown that the toughness index T
2(n−1)(n) reflects the function of fibers to improve the toughness of RPC with the deformation throughout specimens, but overestimates
the contribution to enhancing the toughness in post-peak periods. It underestimates, on other hands, the contribution to improving
the toughness in the period from the first crack to the peak load. In contrast, the toughness index FT
2(n−1)(n) properly presents the capability that fibers absorb energy and constrain crack propagation in the matrix when the deformation
is concentrated on the open crack. The proposed index unveils the contribution of fibers to toughening RPC200 both in the
period from the first-crack to the peak load and in the period of post peak. This characterization method not only reveals
the nature of toughness but also levels the toughness of RPC200. It could provide a way to establish an objective toughness
characterization for RPC200 and facilitate its applications.
Supported by the New Century Excellent Talents Program (Grant No. NCET-05-0215), the Natural Science and Engineering Research
Council of Canada (Grant No. PGS D2 2006), the Laboratory Innovation Plan of Beijing Science and Education Committee (Grant
No. JD102900671) and the National Basic Research Project of China (“973” Project) (Grant No. 2002CB412705) 相似文献