Data-driven estimation of change-points with mean shift

Yang Wenzhi,Liu Huanshuo,Wang Yiwei,Wang Xuejun 한국통계학회 2023 Journal of the Korean Statistical Society Vol.52 No.1

Asymptotically linear negative quadrant dependent (ALNQD) sequence is more general than negatively associated (NA) sequence and \rho∗-mixing sequence. Based on ALNQD errors, the CUSUM estimator of mean change-point is studied with common conditions. We obtain a limiting distribution of CUSUM estimator, which can be used to judge the existence of mean change-point. Meanwhile, some weak and strong convergence rates are established for the CUSUM estimator of change-point. In addition, a data-driven algorithm of multiple change-point detection is given, which performs better than Lasso algorithm. Last, multiple change-point detection simulations and real data analysis illustrate the accuracy of our results.

Research for the bearing fit effect on the vibration characteristics of spindle rotor-bearing system

Zhan Wang,Siyang Chen,Wenzhi He,Zinan Wang,Zhongxian Xia 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12

Spindle bearing fits mainly include interference fit of inner ring and clearance fit of outer ring, which directly affect the vibration characteristics of spindle rotor-bearing system. In this paper, the influence of spindle bearing inner and outer ring fits on bearing support stiffness is firstly studied. Considering the spindle bearing inner and outer ring fits, a dynamic model of spindle rotor-bearing system is established. Then, the analysis methods of bifurcation and time domain are used to perform simulation analysis. The influence of bearing fit on the vibration characteristics of rotor system is researched. Lastly, at different rotating speeds, bearing fits experiments are conducted on built motorized spindle test platform, which verifies the correctness of the dynamic model. The results show that the influence of bearing fit on vibration is nonlinear. The influence of clearance fit on vibration is smaller, when the clearance fit value of bearing outer ring is about 4-6 μm. The vibration characteristics of rotor are more sensitive to the clearance fit of bearing outer ring than the interference fit of bearing inner ring. The research work provides an important theoretical basis for the optimal of spindle bearing assembly.

Fluorination of dichlorodifluoromethane to synthesize tetrafluoromethane over Cr_2O_3–AlF_3 catalyst

Wenzhi Jia,Mengfei Luo,Lingyun Jin,Yuejuan Wang,Jiqing Lu 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.3

A series of Cr_2O_3–AlF_3 catalysts with different Cr_2O_3 contents were prepared by a deposition–precipitation method for the fluorination of dichlorodifluoromethane (CCl_2F_2) to synthesize tetrafluoromethane (CF4). The highest activity was obtained on the Cr_2O_3–AlF_3 catalyst containing 61.2 wt.% of Cr_2O_3, with the CF_4 yield of 94% at 400℃. X-ray diffraction (XRD) and Raman spectroscopy results indicated the presence of bulk Cr_2O_3 and a-AlF_3 phases in the catalysts. Ammonia temperature programmed desorption (NH3-TPD) and Fourier transformation infrared spectroscopy (FTIR) of pyridine chemisorption revealed strong Lewis acidity of the catalysts. The Cr species and Lewis acid in the Cr_2O_3–AlF_3 catalysts were the active sites of fluorination and dismutation reaction of CCl_2F_2, respectively. This indicated bi-function catalytic performance of Cr_2O_3–AlF_3 catalysts for fluorination and dismutation reaction.

Exponential inequalities and complete convergence for a LNQD sequence

Wang Xuejun,Hu Shuhe,Yang Wenzhi,Li Xiaoqin 한국통계학회 2010 Journal of the Korean Statistical Society Vol.39 No.4

Some exponential inequalities for a linearly negative quadrant dependent sequence are obtained. By using the exponential inequalities, we give the complete convergence and almost sure convergence for a linearly negative quadrant dependent sequence. In addition,the asymptotic behavior of the probabilities for the partial sums of a linearly negative quadrant dependent sequence is studied.

A new cable force identification method considering cable flexural rigidity

Wang, Long,Wu, Bo,Gao, Junyue,Shi, Kairong,Pan, Wenzhi,He, Zhuoyi,Ruan, Zhijian,Lin, Quanpan 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.2

Cables are the main load-bearing members of prestressed structure and other tensegrity structures. Based on the static equilibrium principle, a new cable force identification method considering cable flexural rigidity is proposed. Its computational formula is derived and the strategy to solve its implicit formula is introduced as well. In order to improve the reliability and practicality of this method, the influence of the cable flexural rigidity on cable force identification accuracy is also investigated. Through cable force identification experiments, the relationships among certain parameters including jacking force, jacking displacement, initial cable force, and sectional area (flexural rigidity) are studied. The results show that the cable force calculated by the proposed method considering flexural rigidity is in good agreement with the finite element results and experimental results. The proposed method with high computational accuracy and resolution efficiency can avoid the influences of the boundary condition and the length of the cable on calculation accuracy and is proven to be conveniently applied to cable force identification in practice.

A new strategy for protein crystallization : Effect of ionic liquids on lysozyme crystallization and morphology

Zhanzhong Wang,Qing Gu,Wenzhi Fang,Yan Li,Jingshu Zhang 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.6

Protein crystallization is a complex physical and chemical process. The high-quality protein crystal is still apersistent bottleneck to the application of X-ray crystallography in structural biology. The additives may promote formationof crystal nucleus and subsequent growth in protein crystallization. As a distinct material, ionic liquids (ILs)have aroused great attention and interest for protein crystallization due to their unique properties. We reviewed the progressof protein crystallization and reported research about protein crystal morphology control by ILs, as crystal growthtemplate, in aqueous solutions. ILs encourage changes in some cases in terms of growth morphology and crystal size. The effect of ILs on lysozyme growth morphology can be attributed to changing interaction among lysozyme moleculesin aqueous solutions. This work can provide some initial insight into the preparation of high quality crystal and thedevelopment of new crystal form.

Simultaneous Improvement of Thermal Conductivity and Strength for Commercial A356 Alloy Using Strontium Modification Process

Kang Wang,Wenfang Li,Wenzhi Xu,Shengyu Hou,Shaodong Hu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11

The Aluminum–Silicon (Al–Si) die-casting alloys, such as the commercial A356 alloy, are expected to be used in heat-sinkand the device with high thermal conductivity due to their high production efficiency of casting process. These fields alsorequired them to possess sound mechanical properties. To meet these demands, the Strontium (Sr) was often utilized tomodify the silicon phase. According to our current work, the secondary dendrite arm spacing of the α-Al grains prominentlywas decreased when 0.05%–0.25% strontium was added. The decrease of the secondary dendrite arm spacing (SDAS) lead tothe enhancement of the mechanical strength as well as the improvement of the thermal and electrical conductivity. When theSr dosage was 0.15% in the commercial A356 alloy, the strength and the thermal conductivity of the A356 alloy simultaneouslyreached the maximum value. The improvement of the electrical and thermal conductivity might by contributed by theformation of a good conductor, Al2Si2Srphase, on the Si surface. Further investigations suggested that the improvement ofthermal conductivity was mainly due to the modification effect of Sr on the eutectic Si phase, which enlarged the specificarea between the α-Al/eutectic Si interface. The WDS analysis indicated that the solubility of Si decreased in aluminummatrix by increasing in the Sr dosage. However, the excessive dosage of strontium would result in the coarsening of themodified silicon phase, deteriorating the strength and the thermal and electrical conductivity of the modified A356 alloys.

MAXIMAL INEQUALITIES AND STRONG LAW OF LARGE NUMBERS FOR AANA SEQUENCES

Xuejun, Wang,Shuhe, Hu,Xiaoqin, Li,Wenzhi, Yang Korean Mathematical Society 2011 대한수학회논문집 Vol.26 No.1

Let {$X_n$, $n{\geq}1$} be a sequence of asymptotically almost negatively associated random variables and $S_n=\sum^n_{i=1}X_i$. In the paper, we get the precise results of H$\acute{a}$jek-R$\acute{e}$nyi type inequalities for the partial sums of asymptotically almost negatively associated sequence, which generalize and improve the results of Theorem 2.4-Theorem 2.6 in Ko et al. ([4]). In addition, the large deviation of $S_n$ for sequence of asymptotically almost negatively associated random variables is studied. At last, the Marcinkiewicz type strong law of large numbers is given.

A new cable force identification method considering cable flexural rigidity

Long Wang,Bo Wu,Junyue Gao,Kairong Shi,Wenzhi Pan,Zhuoyi He,Zhijian Ruan,Quanpan Lin 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.2

Cables are the main load-bearing members of prestressed structure and other tensegrity structures. Based on the static equilibrium principle, a new cable force identification method considering cable flexural rigidity is proposed. Its computational formula is derived and the strategy to solve its implicit formula is introduced as well. In order to improve the reliability and practicality of this method, the influence of the cable flexural rigidity on cable force identification accuracy is also investigated. Through cable force identification experiments, the relationships among certain parameters including jacking force, jacking displacement, initial cable force, and sectional area (flexural rigidity) are studied. The results show that the cable force calculated by the proposed method considering flexural rigidity is in good agreement with the finite element results and experimental results. The proposed method with high computational accuracy and resolution efficiency can avoid the influences of the boundary condition and the length of the cable on calculation accuracy and is proven to be conveniently applied to cable force identification in practice.

Solvated behavior and crystal growth mechanism of erythromycin in aqueous acetone solution

Zhanzhong Wang,Wenzhi Fang,Yan Li 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.1

The solubility of erythromycin acetone solvate and dihydrate was experimentally determined in aqueous acetone mixtures at different temperature. It has been demonstrated that solubility curves of the two solvates intersected at given solvent composition at various temperature, suggesting a transition behavior between two solvates. The induction period of acetone solvate at different supersaturation was measured by the laser monitoring observation technique. Based on classical homogeneous nucleation theory, the solid-liquid interfacial tension and surface entropy factor were calculated from the induction period data. From the surface entropy factor values calculated, together with surface morphology observation by the atomic force microscopy (AFM), the growth mechanism of erythromycin acetone solvate is consistent with continuous growth mode.