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Search Results: 1 - 10 of 127097 matches for " Yushan Li "
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Thermodynamic properties of rotating trapped ideal Bose gases
Yushan Li,Qiang Gu
Physics , 2014, DOI: 10.1016/j.physleta.2014.02.040
Abstract: Ultracold atomic gases can be spined up either by confining them in rotating frame, or by introducing ``synthetic" magnetic field. In this paper, thermodynamics of rotating ideal Bose gases are investigated within truncated-summation approach which keeps to take into account the discrete nature of energy levels, rather than to approximate the summation over single-particle energy levels by an integral as does in semi-classical approximation. Our results show that Bose gases in rotating frame exhibit much stronger dependence on rotation frequency than those in ``synthetic" magnetic field. Consequently, BEC can be more easily suppressed in rotating frame than in ``synthetic" magnetic field.
THE PROPERTIES OF WATER CYCLE IN SOIL AND THEIR EFFECT ON WATER CYCLE FOR LAND IN THE LOESS REGION
黄土区土壤水分循环特征及其对陆地水分循环的影响

LI YUSHAN,
李玉山

生态学报 , 1983,
Abstract: The loess region lies in the middle reaches of Huung He River. The water-holding capacity, evapotranspiration, water deficit in soil, infiltration of rainfill into soil and the dry layer for soils in the loess region are investigated in this paper and their effect on ecological environment is also discussed.The soils in most of the loess region have a waterholding capacity of 250mm per metre of soil layer. The annual evapotranspiration corresponds approximately to annual average precipitation for the fields...
Ann-Based Pad Modeling Technique for Mosfet Devices
Xiuping Li;Yushan Li;Junhui Zhao
PIER , 2011, DOI: 10.2528/PIER11042702
Abstract: In this paper, an approach for the pad modeling of the test structure for Metal Oxide Semiconductor Field Effect Transistor (MOSFET) up to 40\,GHz is presented. The approach is based on a combination of the conventional equivalent circuit model and artificial neural network (ANN). The pad capacitances and series resistors are directly obtained from EM (electromagnetic) simulation of the $S$ parameters with different size of pad and operating frequency. The parasitic elements in the test structure can be modeled by using a sub artificial neural network (SANN). So the pad capacitances and series resistors can be regarded as functions of the dimensions of the pad structure and operating frequencies by using SANN. Good agreement between the ANN-based modeling and EM simulation results has been demonstrated. In order to remove the impact of the parasitic elements, the de-embedding procedure for MOSFET device using ANN-based pad model is also demonstrated.
Theoretical Research on Thermal Shock Resistance of Ultra-High Temperature Ceramics Focusing on the Adjustment of Stress Reduction Factor
Dengjian Li,Weiguo Li,Dingyu Li,Yushan Shi,Daining Fang
Materials , 2013, DOI: 10.3390/ma6020551
Abstract: The thermal shock resistance of ceramics depends on not only the mechanical and thermal properties of materials, but also the external constraint and thermal condition. So, in order to study the actual situation in its service process, a temperature-dependent thermal shock resistance model for ultra-high temperature ceramics considering the effects of the thermal environment and external constraint was established based on the existing theory. The present work mainly focused on the adjustment of the stress reduction factor according to different thermal shock situations. The influences of external constraint on both critical rupture temperature difference and the second thermal shock resistance parameter in either case of rapid heating or cooling conditions had been studied based on this model. The results show the necessity of adjustment of the stress reduction factor in different thermal shock situations and the limitations of the applicable range of the second thermal shock resistance parameter. Furthermore, the model was validated by the finite element method.
Lie Symmetry Analysis, Optimal Systems and Explicit Solutions of the Dispersive Long Wave Equations  [PDF]
Xiaomei Xue, Yushan Bai
Journal of Applied Mathematics and Physics (JAMP) , 2018, DOI: 10.4236/jamp.2018.612222
Abstract: In this paper, the dispersive long wave equation is studied by Lie symmetry group theory. Firstly, the Lie symmetries of this system are calculated. Secondly, one dimensional optimal systems of Lie algebra and all the symmetry reductions are obtained. Finally, based on the power series method and the extended Tanh function method, some new explicit solutions of this system are constructed.
Multiscale Simulation of Indentation, Retraction and Fracture Processes of Nanocontact
Mei Jifa,Li Junwan,Ni Yushan,Wang Huatao
Nanoscale Research Letters , 2010,
Abstract: The process of nanocontact including indentation and retraction between a large Ni tip and a Cu substrate is investigated using quasicontinuum (QC) method. The multiscale model reveals that significant plastic deformation occurs during the process of nanocontact between Ni tip and Cu substrate. Plastic deformation is observed in an area as large as 20 nm wide and 10 nm thick beneath Ni tip during the indentation and retraction. Also, plastic deformation at a deep position in the Cu substrate does not disappear after the neck failure. The analysis of generalized planar fault energy curve shows that there is a strong tendency for deformation twinning in Cu substrate. However, deformation twinning will be retarded during indentation due to the high stress intensity caused by stepped surface of Ni tip. The abrupt drop of load curve during tip retraction is attributed to the two different fracture mechanisms. One is atomic rearrangement near the interface of Ni tip and Cu substrate at the initial stage of neck fracture, the other is shear behavior of adjacent {111} planes at the necking point. A comparison of the critical load and critical contact radius for neck fracture is also made between theoretical values and our numerical results.
Effects of Crystalline Anisotropy and Indenter Size on Nanoindentation by Multiscale Simulation
Li Junwan,Ni Yushan,Wang Hongsheng,Mei Jifa
Nanoscale Research Letters , 2009,
Abstract: Nanoindentation processes in single crystal Ag thin film under different crystallographic orientations and various indenter widths are simulated by the quasicontinuum method. The nanoindentation deformation processes under influences of crystalline anisotropy and indenter size are investigated about hardness, load distribution, critical load for first dislocation emission and strain energy under the indenter. The simulation results are compared with previous experimental results and Rice-Thomson (R-T) dislocation model solution. It is shown that entirely different dislocation activities are presented under the effect of crystalline anisotropy during nanoindentation. The sharp load drops in the load–displacement curves are caused by the different dislocation activities. Both crystalline anisotropy and indenter size are found to have distinct effect on hardness, contact stress distribution, critical load for first dislocation emission and strain energy under the indenter. The above quantities are decreased at the indenter into Ag thin film along the crystal orientation with more favorable slip directions that easy trigger slip systems; whereas those will increase at the indenter into Ag thin film along the crystal orientation with less or without favorable slip directions that hard trigger slip systems. The results are shown to be in good agreement with experimental results and R-T dislocation model solution.
Intelligent thermal cloak-concentrators
Xiangying Shen,Ying Li,Jiping Huang,Yushan Ni
Physics , 2015,
Abstract: How to macroscopically control the flow of heat at will is up to now a challenge, which, however, is very important for human life since heat flow is a ubiquitous phenomenon in nature. Inspired by intelligent electronic components or intelligent materials, here we demonstrate, analytically and numerically, a unique class of intelligent bifunctional thermal metamaterials called thermal cloak-concentrators, which can automatically change from a cloak (concentrator) to a concentrator (cloak) when the applied temperature field decreases (increases). For future experimental realization, the behavior is also confirmed by assembling homogeneous isotropic materials according to the effective medium theory. The underlying mechanism originates from the effect of nonlinearity in thermal conduction. This work not only makes it possible to achieve a switchable Seebeck effect, but also offers guidance both for macroscopic manipulation of heat flow at will and for the design of similar intelligent multifunctional metamaterials in optics, electromagnetics, acoustics, or elastodynamics.
To Give Control to Learners or Not? A Comparative Study of Two Ways of Teaching Listening
Yushan Wang
English Language Teaching , 2010, DOI: 10.5539/elt.v3n2p162
Abstract: This paper reports a quasi-experimental study that was carried out in listening classes to address the following questions: What control do students expect in the listening classroom? What are the effects of the “zero class hour” way of teaching listening when more control is given to the students? The study was conducted at Huaiyin Normal University, where two non-English major classes taught by one teacher were selected. A questionnaire survey was conducted to get students’ opinion about the traditional way of teaching listening and what control they wanted to have. The results of the pretest and posttest were analyzed with SPSS. Both the experiment group and the control group made similar progress in the test of their listening comprehension, which indicates that the new way of teaching listening is as effective as the traditional one. From the amount of time that the experimental-group students spent on improving their listening comprehension, we can see that they made more efforts and became more active and more autonomous than before. The findings may give some support for the web-based distance education.
Influence of Plastic Zone and Tensile Stress Field Ahead of The Notch on The Arrest Crack Length Under Cyclic Compressive Fatigue
缺口根部塑性区和拉应力场对循环压缩疲劳裂纹止裂长度的影响

Luo Jinghua Zhang Jianzhong Li Zhonghua Tan Yushan,
罗景华
,张建中

实验力学 , 1990,
Abstract: The shape and size of plastic zone ahead of double edge-notched specimens under different compressive load have been measured with micro-image-plane holography and speckle photography separating method(MIHSS). The plastic zone and the stress field ahead of the notch have also been calculated by finite element method. The results obtained show that the measurment is easy and accurate enough in engineering. Comparing the arresed crack length under cyclic compressive fatigue with the size of the compressive plastic zone shows that there is no simple correspondance between them and the arresed carck length is mainly controlled by the tensile stress field ahead of the notch produced during unloading in the compressive cycle.
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