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Effects of built-in electric field and donor impurity on linear and nonlinear optical properties of wurtzite InxGa1-xN/GaN nanostructures

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Chinese Physics B 2020年第8期29卷 479-484页

作者： xiao-chen yang Yan Xing School of Physical Science and Technology Inner Mongolia UniversityHohhot 010021China

The linear and nonlinear optical absorption coefficients(ACs)and refraction index changes(RICs)of 1s-1p,1p-1d,and 1f-1d transitions are investigated in a wurtzite InxGa1-xN/GaN core-shell quantum dot(CSQD)with donor impurity by using density matrix *** effects of built-in electric field(BEF),ternary mixed crystal(TMC),impurity,and CSQD size are studied in *** finite element method is used to calculate the ground and excited energy state energy and wave *** results reveal that the BEF has a great influence on the linear,nonlinear,and total ACs and *** presence of impurity leads the resonant peaks of the ACs and RICs to be blue-shifted for all transitions,especially for 1s-1p *** is also found that the resonant peaks of the ACs and RICs present a red shift with In-composition decreasing or core radius ***,the amplitudes of the ACs and RICs are strongly affected by the incident optical *** absorption saturation is more sensitive without the impurity than with the impurity,and the appearance of absorption saturation requires a larger incident optical intensity when considering the BEF.

关键词： core-shell quantum dot linear and nonlinear optical properties impurity ternary mixed crystal

Joint probability distribution of winds and waves from wave simulation of 20 years (1989-2008) in Bohai Bay

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Water Science and Engineering 2013年第3期6卷 296-307页

作者： xiao-chen yang Qing-he ZHANG State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University

The joint probability distribution of wind speed and significant wave height in the Bohai Bay was investigated by comparing the Gurnbel logistic model, the Gumbel-Hougaard （GH） copula function, and the Clayton copula function. Twenty years of wind data from 1989 to 2008 were collected from the European Centre for Medium-Range Weather Forecasts （ECMWF） database and the blended wind data of the Quick Scatterometer （QSCAT） satellite data set and re-analysis data from the United States National Centers for Environmental Prediction （NCEP）. Several typhoons were taken into account and merged with the background wind fields from the ECMWF or QSCAT/NCEP database. The 20-year data of significant wave height were calculated with the unstructured-grid version of the third-generation wind wave model Simulating WAves Nearshore （SWAN） under extreme wind process conditions. The Gumbel distribution was used for univariate and marginal distributions. The distribution parameters were estimated with the method of L-moments. Based on the marginal distributions, the joint probability distributions, the associated return periods, and the conditional probability distributions were obtained. The GH copula function was found to be optimal according to the ordinary least squares （OLS） test. The results show that wind waves are the prevailing type of wave in the Bohai Bay.

关键词： wind speed wave simulation joint probability distribution copula function,conditional probability distribution

Microstructure and mechanical properties of AZ91-Ca magnesium alloy cast by different processes

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China Foundry 2018年第4期15卷 263-269页

作者： xiao-yang chen yang zhang ya-lin lu xiao-ping li Key lab of advanced Materials Design and Additive Manufacturing of Jiangsu Province Jiangsu University of TechnologyChangzhou 213001China

The microstructure and mechanical properties of magnesium （Mg） alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2wt.% Ca （AZX912） Mg alloy samples prepared by gravity casting （GC）, squeeze casting （SC） and rheo-squeeze casting （RSC）, respectively, was carried out. The results show that mMg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 ~C to 200 ~C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.

关键词： magnesium alloys casting process microstructure mechanical properties

Increasing Solidification Rate of M2 High-Speed Steel Ingot by Fusible Metal Mold

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Acta Metallurgica Sinica(English Letters) 2016年第4期29卷 382-387页

作者： Yan-Liang Ji Wei Zhang xiao-yang chen Jian-Guo Li School of Materials Science and Engineering Shanghai Jiao Tong University

As one of the most popular used high-speed steels, M2 possesses excellent hardness and toughness as cutting tools. Networks of eutectic carbides distributing in the inter-dendritic region are academically considered to be the typical microstructure of M2, which can be refined by increasing cooling rate. In this paper, a novel casting method named fusible metal mold （FMM） is employed to refine the microstructure of M2 high-speed steel. Results show that FMM casting method can improve cooling rate by 100% without any contamination of the melts＇ composition.

关键词： Carbide Cooling rate Solidification process Microstructure Dendritic spacing

A rotary ultrasonic motor using radial bending mode of ring with nested PZT excitation

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2012年第3期13卷 189-196页

作者： Ying-xiang LIU Jun-kao LIU Wei-shan chen xiao-hui yang State Key Laboratory of Robotics and System Harbin Institute of Technology Horbin 150001 China

This study presents and verifies a new idea for constructing a rotary traveling wave ultrasonic motor （USM） that uses the radial bending mode of a ring. In the new design, 20 trapezoid cross section slots are cut symmetrically in the outer surface of a thick duralumin alloy ring, where 20 PZT stacks are nested. In each slot, two wedging blocks are set between the PZT stack and the two sides of the slot respectively to apply preloading on the PZT ceramics. Two radial bending modes of the stator that have a phase difference of a quarter wavelength on space are generated by using the d33 operating mode of the PZT elements, and then a flexural traveling wave is formed by the superimposing of two standing waves whose amplitudes are equal and phases are different by 90~ temporally. Two conical rotors are pressed to each end of the ring type stator by a coiled spring. The finite element method （FEM） simulation is developed to validate the feasibility of the proposed motor. The maximal speed and torque of the prototype are tested to be 126 r/rain and 0.8 N＇m, respectively.

关键词： Rotary ultrasonic motor Radial bending mode Traveling wave Wedging block clamped structure

Phase Separation and Crystallization Induced by Electron Irradiation in Nanoscale Fe_(56.5)Mn_(11)Cr_(8.5)Ni_4Si_(10)C_(10) Metallic Glass

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Acta Metallurgica Sinica(English Letters) 2015年第11期28卷 1332-1335页

作者： xiao-yang chen Shu-Guang Zhang Ming-Xu Xia Jian-Guo Li School of Materials Science and Engineering Shanghai Jiao Tong University

A nanoscale Fe56.5Mn11Cr8.5Ni4Si10C10 metallic glass was irradiated by electron beam in a 200 kV trans- mission electron microscope. Structure evolution in the metallic glass was investigated in situ during continuous irradi- ation, where phase separation was observed after irradiation for 5 min and crystallization was observed after 33.5 min. Based on the analysis of irradiation effect, atomic displacement is believed to be the main reason for the structure rearrangement. Accumulation of atomic displacement increases the energy of the sample and promotes atomic diffusion during transformation. On the other hand, the large specific surface area of the sample also contributes to increasing free energy and atomic diffusion.

关键词： Metallic glass Electron irradiation Transmission electron microscopy Phase separation Crystallization

Construction of daily precipitation series and the observational characteristics of extreme precipitation in Tianjin,China during 1888-2022

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Advances in Climate Change Research 2024年第1期15卷 52-61页

作者： Peng SI Qing-Xiang LI xiao-yang chen Min WANG Chuan-Jun LUO Tianjin Meteorological Information Center Tianjin Meteorological BureauTianjin 300074China Research Centerfor Ecology and Environment of Central Asia Chinese Academy of SciencesWulumuqi 830011China School of Atmospheric Sciences Sun Yat-sen UniversityZhuhai 528478China Key Laboratory of Tropical Amosphere-Ocean System Ministry of EducationZhuhai 528478China Shaoguan Meteorological Service Shaoguan 512028China

Given the difficulties in rescuing and ensuring the quality of long-term climate data,current studies on century-scale climate change are usually limited to annual and monthly data,resulting in the poor detection of extreme climate events and their changes before *** this study,we reconstructed a daily precipitation series for Tianjin from 15 September 1887 to 31 December 2022 on the basis of the most comprehensive daily precipitation records collected from the Tianjin Meteorological Archive,China,and in reference to the precipitation analysis results based on the datasets developed by the Climatic Research Unit Time-Series version 4.06,Global Precipitation Climatology Centre and University of Delaware along with the application of various homogenisation methods for climate *** approach provides a complete and reliable century-long daily precipitation series for the study of regional or local extreme weather and climate *** reconstructed daily dataset reveals that the annual precipitation amount and R95 intensity in Tianjin during 1888-2022 lack significant trends and have values of 0.74±6.99 and-1.84±3.22 mm per decade,*** the annual and seasonal scales,the precipitation amount and R95 intensity,particularly those in autumn,have increased since the latter half of the 20th century relative to those in ***,the increase in precipitation amount and R95 intensity is relatively limited compared with that in atmospheric water vapour content due to surface warming,indicating the highly sensitive response of extreme precipitation events to *** addition,the estimates for the return periods of 5,10,20,50 and 100 years covering 1888-2022,1888-1950 and 1951-2022 depict that the intensity of heavy rain and above magnitude was highest in 1888-1950 and decreased in 1951-2022.

关键词： Over a century-long timescale Daily precipitation series Extreme precipitation Return period

Commissioning and operation of the cryostat for 3W1 SC wiggler

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Nuclear Science and Techniques 2023年第6期34卷 43-54页

作者： Miao-Fu Xu Xiang-Zhen Zhang Rui Ye Jin-Can Wang xiao-Juan Bian Yao Gao Min-Xian Li Fu-San chen xiao-chen yang Rui Ge Institute of High Energy Physics Chinese Academy of SciencesBeijing100049China Key Laboratory of Particle Acceleration Physics and Technology Chinese Academy of SciencesBeijing100049China Center for Superconducting RF and Cryogenics Institute of High Energy PhysicsBeijing100049China University of Chinese Academy of Sciences Beijing100049China

A 3W1 superconducting wiggler(SCW)with the pole gap of 68 mm was successfully tested and installed in a BEPC II storage ring in November,*** goal of zero liquid helium consumption was achieved,and the cryogenic system exhibited a 12%residual cooling capacity(approximately 0.69 W@4.2 K).The 3W1-SCW was set to operate at 2.49 T and has been operating for more than seven *** instances of magnet quenching occurred during the normal *** evaporated helium gas can be recycled to the helium gas recycling system when the pressure in the helium tank is higher than the parameter value(the setpoint of the pressure value is 1.2 bara).The cryogenic system can be recovered within 4 h if sufficient liquid helium is available to inject into the cryostat.

关键词： Cryostat Commissioning SC wiggler Synchrotron radiation

Spatial Interpolation of Soil Texture Using Compositional Kriging and Regression Kriging with Consideration of the Characteristics of Compositional Data and Environment Variables

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Journal of Integrative Agriculture 2013年第9期12卷 1673-1683页

作者： ZHANG Shi-wen SHEN Chong-yang chen xiao-yang YE Hui-chun HUANG Yuan-fang LAI Shuang China Agricultural University/Key Laboratory of Arable Land Conservation (North China) Minstry of Agriculture/Key Laboratory of Agricultural Land Quality MonitoringMinistry of Land and Resources School of Earth and Environment Anhui University of Science and Technology Afforestation Management Office Sichuan Forestry Department

The spatial interpolation for soil texture does not necessarily satisfy the constant sum and nonnegativity constraints. Meanwhile, although numeric and categorical variables have been used as auxiliary variables to improve prediction accuracy of soil attributes such as soil organic matter, they （especially the categorical variables） are rarely used in spatial prediction of soil texture. The objective of our study was to comparing the performance of the methods for spatial prediction of soil texture with consideration of the characteristics of compositional data and auxiliary variables. These methods include the ordinary kriging with the symmetry logratio transform, regression kriging with the symmetry logratio transform, and compositional kriging （CK） approaches. The root mean squared error （RMSE）, the relative improvement value of RMSE and Aitchison＇s distance （DA） were all utilized to assess the accuracy of prediction and the mean squared deviation ratio was used to evaluate the goodness of fit of the theoretical estimate of error. The results showed that the prediction methods utilized in this paper could enable interpolation results of soil texture to satisfy the constant sum and nonnegativity constraints. Prediction accuracy and model fitting effect of the CK approach were better, suggesting that the CK method was more appropriate for predicting soil texture. The CK method is directly interpolated on soil texture, which ensures that it is optimal unbiased estimator. If the environment variables are appropriately selected as auxiliary variables, spatial variability of soil texture can be predicted reasonably and accordingly the predicted results will be satisfied.

关键词： compositional kriging auxiliary variables regression kriging symmetry logratio transform