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Using ARIMA Model to Fit and Predict Index of Stock Price Based on Wavelet De-Noising
Shihua Luo,Fang Yan,Dejian Lai,Wenyi Wu,Fucai Lu 보안공학연구지원센터 2016 International Journal of u- and e- Service, Scienc Vol.9 No.12
To accommodate non-stationarity and strong noise in the SPI data, the research used wavelet method for de-noising and autoregressive integrated moving average model(ARIMA) for prediction. Seven-day moving averages of closing time SPI data in four Asian stock marketswereanalyzed.Empiricalresults show that after de-noising more accurate forecasting results can be obtained in developed markets. More developed market indexes seem more significant improvement; while for less developed market indexes, the improvement of de-noising is less significant. This is in accordance with current situation of market.
Liu, Shihua,Liu, Simei,Wang, Jingjing,Sun, Pengfei,Zhong, Yifan,Jeong, Jung Hyun,Deng, Bin,Yu, Ruijin Elsevier 2018 Materials research bulletin Vol.108 No.-
<P><B>Abstract</B></P> <P>Novel single-phased white-light-emitting Ca<SUB>9</SUB>LiGd<SUB>2/3</SUB>(PO<SUB>4</SUB>)<SUB>7</SUB>:<I>x</I>Dy<SUP>3+</SUP> (<I>x</I> = 0.02, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) β-Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>-type phosphate phosphors were synthesized. The phase structure, luminescence, and thermal stability of the phosphors were characterized by X-ray powder diffraction analysis, photoluminescence excitation and emission spectra, thermal quenching, and decay curves. XRD analysis confirmed the phase formation of Ca<SUB>9</SUB>LiGd<SUB>2/3</SUB>(PO<SUB>4</SUB>)<SUB>7</SUB>:Dy<SUP>3+</SUP> materials. Under the excitation of 352 nm, the emission of the Ca<SUB>9</SUB>LiGd<SUB>2/3</SUB>(PO<SUB>4</SUB>)<SUB>7</SUB>:0.20Dy<SUP>3+</SUP> sample centered at blue (488 nm) and yellow (580 nm), which corresponded to <SUP>4</SUP>F<SUB>9/2</SUB>–<SUP>6</SUP>H<SUB>15/2</SUB> transition and <SUP>4</SUP>F<SUB>9/2</SUB>–<SUP>6</SUP>H<SUB>13/2</SUB> transition. The optimum dopant concentration of Dy<SUP>3+</SUP> ions was around 20 mol%, and the critical transfer distance of Dy<SUP>3+</SUP> was calculated as 18 Å. The thermal-quenching temperature was above 500 K for Ca<SUB>9</SUB>LiGd<SUB>2/3</SUB>(PO<SUB>4</SUB>)<SUB>7</SUB>:0.20Dy<SUP>3+</SUP>. The developed phosphor has a great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel single-phased Ca<SUB>9</SUB>LiGd<SUB>2/3</SUB>(PO<SUB>4</SUB>)<SUB>7</SUB>:<I>x</I>Dy<SUP>3+</SUP> phosphor was firstly synthesized. </LI> <LI> Its structure, luminescent properties are well studied and characterized. </LI> <LI> It was promising as a single-component white-light-emitting phosphor for w-LEDs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Liu, Shihua,He, Jianyue,Wu, Zhaoyi,Jeong, Jung Hyun,Deng, Bin,Yu, Ruijin Elsevier 2018 Journal of luminescence Vol.200 No.-
<P><B>Abstract</B></P> <P>Novel single-phased white-light-emitting Li<SUB>3</SUB>Gd<SUB>3</SUB>Te<SUB>2</SUB>O<SUB>12</SUB>:<I>x</I>Dy<SUP>3+</SUP> (<I>x</I> = 0.005, 0.01, 0.02, 0.05, 0.08, 0.10, and 0.15) garnet-type tellurate phosphors were firstly synthesized. The X-ray powder diffraction analysis, photoluminescence excitation and emission spectra, thermal quenching, and decay curves were applied to investigate the phase structure, luminescence, and thermal stability properties. Under the excitation of 351 nm, the emission of Li<SUB>3</SUB>Gd<SUB>3</SUB>Te<SUB>2</SUB>O<SUB>12</SUB>:0.02Dy<SUP>3+</SUP> sample centered at blue (488 nm) and yellow (580 nm), corresponding to <SUP>4</SUP>F<SUB>9/2</SUB>–<SUP>6</SUP>H<SUB>15/2</SUB> transition and <SUP>4</SUP>F<SUB>9/2</SUB>–<SUP>6</SUP>H<SUB>13/2</SUB> transition, respectively. The optimum dopant concentration of Dy<SUP>3+</SUP> ions in Li<SUB>3</SUB>Gd<SUB>3</SUB>Te<SUB>2</SUB>O<SUB>12</SUB>:<I>x</I>Dy<SUP>3+</SUP> was around 2 mol%. The thermal-quenching temperature was above 500 K for Li<SUB>3</SUB>Gd<SUB>3</SUB>Te<SUB>2</SUB>O<SUB>12</SUB>:0.02Dy<SUP>3+</SUP>. The tunable white light and correlated color temperature can be achieved in the present Li<SUB>3</SUB>Gd<SUB>3</SUB>Te<SUB>2</SUB>O<SUB>12</SUB>:<I>x</I>Dy<SUP>3+</SUP> phosphors by adjusting the yellow to blue intensity ratio based on the concentration of Dy<SUP>3+</SUP> ions. The fabricated warm white LED indicates the phosphor could be a single-component white light-emitting phosphor for UV light-emitting diodes.</P>
Analysis and Compensation Control of Dead-Time Effect on Space Vector PWM
Jie Shi,Shihua Li 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.2
Dead-time element must be set into space vector pulsed width modulation signals to avoid short circuits of the inverter. However, the dead-time element distorts the output voltage vector, which deteriorates the performance of electrical machine drive system. In this paper, dead-time effect and its compensation control strategy are analyzed. Based on the analysis, the voltage distortion caused by dead-time is regarded as two disturbances imposed on dq axes in the rotor reference frame, which degenerates the current tracking performance. To inhibit the adverse effect caused by the dead-time, a control scheme using two linear extended state observers is proposed. This method provides a strong ability to suppress dead-time effects. Simulations and experiments are conducted on a permanent magnet synchronous motor drive system to demonstrate the effectiveness of the proposed method.
Xiaodi Li,Shihua Li 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.3
In this paper, the speed regulation problem of permanent synchronous motor (PMSM) systems under the vector control framework is studied. A model reference adaptive controller (MRAC) based on the Lyapunov stability theory is first designed. Since the standard MRAC method provides poor disturbance rejection performance in the case of strong disturbances, a composite control method which combines the MRAC method and the disturbance estimation method, called the MRAC+ESO method, is proposed. An extended state observer (ESO) is introduced to estimate the lumped disturbances. The obtained estimated value acts as a feedforward compensation term to the MRAC controller. A stability analysis of the composite control method is given. Simulation and experimental results are presented and compared to show the effectiveness of the proposed control method.
Effect of silicon carbide on carbonization and morphology behavior of coal tar pitch
Wenjuan Zhang,Shihua Song,Xianren Zeng,Genhui Teng,Qi Wang 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.10
Coal tar pitch (CTP) is a quite promising candidate for the production of carbon materials. However, the application of CTP is restricted by its poor properties at elevated temperature. In this paper, silicon carbide was used to modify CTP and thecarbonization and morphology behavior of CTP and the CTP modified with silicon carbide were studied by thermogravimetry and differential scanning calorimetry (TG-DSC), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show silicon carbide and CTP can coalesce well when the ratio of silicon carbide to CTP is 12% and the carbonization yield of CTP at 900 o C increases from 35.86% to 40.56% after the modification of CTP. Further, the addition of silicon carbide to CTP can reduce the temperature at which the reaction of thermal polymerization happen during the carbonization process of CTP and can facilitate the carbonization of CTP. In addition, little pore distributes on the surface of the heat-treatment products after the modification of CTP with silicon carbide.
Wei He,Shihua Li,Jun Yang,Zuo Wang 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1
In this paper, the voltage tracking control of a conventional DC-DC boost converter affected by unknown, time-varying circuit parameter perturbations is investigated. Based on the fundamental property of incremental passivity, a passivity based control law is designed. Then, to obtain a better disturbance rejection property, two generalized proportional integral (GPI) observers are employed to estimate the time-varying uncertainties in the output voltage and inductor current channels, and the estimated values are applied as feedforward compensation. Moreover, the global trajectory tracking performance of a system with disturbances is ensured under the composite controller. Finally, simulation and experiment studies are provided to demonstrate the feasibility and effectiveness of the proposed method. The results show that the proposed controller delivers a promising disturbance rejection capability as well as a good nominal tracking performance.
Polymorphic Forms of Furosemide Characterized by THz Time Domain Spectroscopy
Min Ge,Shihua Ma,Guifeng Liu,Wenfeng Wang 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.10
Terahertz time domain spectroscopy (THz-TDS) is applied in transmission to identify the five forms of modifications of furosemide and one commercial product from 0.3 THz to 1.6 THz at room temperature. The different absorption spectra of the different forms are sensitive to crystal structures. Density function theory (DFT) calculation was used to understand the vibrational modes of furosemide in the THz region. X-ray powder diffractometry (XRPD) was applied to confirm the different forms of modifications. The results demonstrate that THz-TDS is a potential analytical technique in investigating polymorphic forms in the pharmaceutical fields.