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Assessment of Time Series Complexity Using Improved Approximate Entropy
KONG De-Ren, XIE Hong-Bo**
Chin. Phys. Lett. 2011, 28 (9):
090502
.
DOI: 10.1088/0256-307X/28/9/090502
Approximate entropy (ApEn), a measure quantifying complexity and/or regularity, is believed to be an effective method of analyzing diverse settings. However, the similarity definition of vectors based on Heaviside function may cause some problems in the validity and accuracy of ApEn. To overcome the problems, an improved approximate entropy (iApEn) based on the sigmoid function is proposed. The performance of iApEn is tested on the independent identically distributed (IID) Gaussian noise, the MIX stochastic model, the Rossler map, the logistic map, and the high-dimensional Mackey–Glass oscillator. The results show that iApEn is superior to ApEn in several aspects, including better relative consistency, freedom of parameter selection, robust to noise, and more independence on record length when characterizing time series with different complexities.
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High-Performance Humidity Sensors Based on Double-Layer ZnO-TiO2 Nanofibers via Electrospinning
YUE Xue-Jun, HONG Tian-Sheng**, XU Xing, LI Zhen
Chin. Phys. Lett. 2011, 28 (9):
090701
.
DOI: 10.1088/0256-307X/28/9/090701
ZnO and TiO2 nanofibers are synthesized via electrospinning methods and characterized by x−ray diffraction, scanning electron microscopy, and transmission electron microscopy. Humidity sensors with double-layer sensing films are fabricated by spinning the ZnO and TiO2 nanofibers on ceramic substrates sequentially. Compared with sensors loading only one type of nanofiber, the double-layer sensors exhibit much better sensing properties. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 11% to 95% relative humidity, and the response and recovery times are about 11 and 7 s, respectively. Maximum hysteresis is around 1.5% RH, and excellent stability is also observed after 180 days. The humidity sensing mechanism is discussed in terms of the sensor structure. The experimental results provide a possible route for the design and fabrication of high performance humidity sensors based on one-dimensional nanomaterials.
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Experiments on Broadband EMP Radiation with an Axial Mode Helix Antenna
SUN Qi-Zhi, FANG Dong-Fan**, LIU Wei, LIU Zheng-Fen, CHI Yuan, DAI Wen-Feng, HAN Wen-Hui
Chin. Phys. Lett. 2011, 28 (9):
090702
.
DOI: 10.1088/0256-307X/28/9/090702
To produce broadband electromagnetic pulse (EMP) radiation, we design and test a sub-ns pulse system which is utilized to drive an axial mode helix antenna. This sub-ns pulse system consists of a 10-stage Marx generator, an intermediate storage capacitor, an impedance transforming line, and can generate a high voltage of 570 kV with a rise time of 1–1.5 ns on a 300-Ω-resistance load. The diameter, pitch and turns of the helix antenna are 29 cm, 19.5 cm and 5, respectively, with a design frequency of 300 MHz. When the charging voltage of the Marx generator is 30 kV, the electric field of radiated EMP measured 3m from the source is 35 kV/m with a central frequency of 250 MHz. The relatively spectral bandwidth is 25%. The radiated EMP results are reproducible and the system will work in repetition mode if the available dc power is utilized.
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Effect of Collision Energy on the Reactivity O++T2→OT++T by the Quasiclassical Trajectory Method
CHEN Jia-Wu, LIU Xin-Guo**, SUN Hai-Zhu, ZHANG Qing-Gang
Chin. Phys. Lett. 2011, 28 (9):
093101
.
DOI: 10.1088/0256-307X/28/9/093101
The reactivity O++T2→OT++T is studied by the quasiclassical trajectory method on the RODRIGO potential energy surface at the collision energies of 1.0, 1.3, 1.6 and 1.9 eV, respectively. The four polarization−dependent generalized differential cross sections (PDDCSs) (2π/σ)(dσ00 /dωt ), (2π/σ)(dσ20 /dωt ), (2π/σ)(dσ22+/dωt ) and (2π/σ)(dσ21− /dωt ) are calculated in the center-of-mass frame. Furthermore, the P(θr ) distribution describing the k–j′ correlation, the distribution of dihedral angle P(φr ) and the distribution of P(θr ,φr ), which describes the angular distribution of product rotational vectors in the form of polar plots in θr and φr are also investigated. The results demonstrate that the stereo-dynamical properties of the title reactivity are sensitive to collision energies.
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Collisional Energy Transfer between Highly Vibrationally Excited CsH(X1Σ+, v=15–22) and H2
ZHU Dong-Hui, ZHANG Bin, SHEN Yi-Fan**, DAI Kang
Chin. Phys. Lett. 2011, 28 (9):
093401
.
DOI: 10.1088/0256-307X/28/9/093401
The Cs atoms are prepared in the 6D state by two−photon absorption. CsH(X1 Σ+,v"=0) is generated from the Cs(6D)+H2 reaction. By overtone excitation with a pulsed dye laser, highly vibrational states v"≥15 of CsH in its ground electronic state are obtained. A diode laser is used to probe either the prepared vibrational state or the collisionally populated states. The decay signal of the time−resolved fluorescence from the A1 Σ+(v')→X1 Σ+(v") transition is monitored. Based on the Stern–Volmer equation, the total rate coefficients for v"=15–22 are yielded. The time evolution and relative intensities of three related states, v", v"−1 and v"−2, made by the initially prepared v" state of CsH are measured. Rate coefficients of single− and double-quantum relaxation are obtained. These results show that single-quantum relaxation accounts for ≥50% of the total relaxation out of states v"=17–20. Multiquantum relaxation (Δv≥2) makes major contribution (≥62%) to the vibrational relaxation at v"=21 and 22. A simple explanation is given.
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High Power Widely Tunable Narrow Linewidth All-Solid-State Pulsed Titanium-Doped Sapphire Laser
DING Xin, LI Xue, SHENG Quan, **, SHI Chun-Peng, YIN Su-Jia, LI Bin, YU Xuan-Yi, WEN Wu-Qi, YAO Jian-Quan,
Chin. Phys. Lett. 2011, 28 (9):
094205
.
DOI: 10.1088/0256-307X/28/9/094205
We report a widely tunable, narrow linewidth, pulsed Ti:sapphire laser pumped by an all-solid-state Q-switched intra-cavity frequency-doubled Nd:YAG laser. By using four dense flint glass prisms as intra-cavity dispersive elements, the output wavelength can be continuously tuned over 675–970 nm and the spectral linewidth is shortened to 0.5 nm. The maximum output power of 6.65 W at 780 nm is obtained under 23.4 W pump power with repetition rate of 5.5 kHz; corresponding to an conversion efficiency of 28.4%. Due to the gain-switching characteristics of the Ti:sapphire laser, the output pulse duration is as short as 17.6 ns.
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Improvement of Response Performance of Liquid Crystal Optical Devices by using a Low Viscosity Component
PENG Zeng-Hui, LIU Yong-Gang, YAO Li-Shuang, CAO Zhao-Liang, MU Quan-Quan, HU Li-Fa, LU Xing-Hai, XUAN Li**, ZHANG Zhi-Yong
Chin. Phys. Lett. 2011, 28 (9):
094207
.
DOI: 10.1088/0256-307X/28/9/094207
Difluorooxymethylene-bridged (CF2O) liquid crystal (LC) with low viscosity is prepared and used as a fast response LC material. When the material is mixed with isothiocyanato LCs with high birefringence, the visco−elastic coefficient of the mixture decreases evidently and, accordingly, the response performance increases. While the concentration of CF2O LCs is about 7%, the LC mixture approximately maintains high birefringence and exhibits a fastest response performance that is 14% higher than that of pure isothiocyanato LCs. Therefore, the LC material and mixing method could find useful applications in optical devices.
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A 526 W Diode-Pumped Nd:YAG Ceramic Slab Laser
CHEN Yan-Zhong, LIU Wen-Bin, BO Yong**, JIANG Ben-Xue, XU Jian, KOU Hua-Min, XU Yi-Ting, PAN Yu-Bai, XU Jia-Lin, GUO Ya-Ding, YANG Feng-Tu, PENG Qin-Jun, CUI Da-Fu, JIANG Dong-Liang, XU Zu-Yan
Chin. Phys. Lett. 2011, 28 (9):
094208
.
DOI: 10.1088/0256-307X/28/9/094208
A diode-side-pumped Nd:YAG ceramic slab laser with a high power output is presented. An average power of 526 W is achieved at 1064 nm with a repetition rate of 120 Hz and a pulse width of 180 µs from a 93mm×52mm×8mm ceramic slab at a pump power of 1928 W, corresponding to an optical-to-optical efficiency of 27.3%.
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Dust Particle Density and Charges in Radio-Frequency Mixture Discharge Plasma
WU Jing, **, ZHANG Peng-Yun, SUN Ji-Zhong, YAO Lie-Ming, DUAN Xu-Ru
Chin. Phys. Lett. 2011, 28 (9):
095201
.
DOI: 10.1088/0256-307X/28/9/095201
We develop a method for measuring the density and charges of dust particles in a capacitive coupled cylinder discharge chamber in mixtures of gases SiH4/C2H4/Ar. Dust particles are created in situ using these reactive mixtures in rf discharge. A Langmuir probe is employed for the measurement of important plasma parameters, such as electron density, electron temperature and ion density. The density and charges of dust particles is then calculated based on the data of the measurement of these parameters and a known dust plasma sheath model. The curves of dust particle density versus rf power and gas pressure are presented, respectively, under various experimental conditions. The dust charges versus different experimental conditions are also evaluated and presented.
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Development of a Real-Time Ion Spectrometer with a Scintillator for Laser-Driven Ion Acceleration Experiments
XU Miao-Hua**, LI Hong-Wei, LIU Bi-Cheng, LIU Feng, SU Lu-Ning, DU Fei, ZHANG Lu, ZHENG Yi, MA Jing-Long, David Neely, Paul McKenna, WANG Zhao-Hua, WEI Zhi-Yi, YAN Xue-Qing, LI Yu-Tong**, LI Ying-Jun, ZHANG Jie,
Chin. Phys. Lett. 2011, 28 (9):
095203
.
DOI: 10.1088/0256-307X/28/9/095203
A real-time ion spectrometer mainly based on a high-resolution Thomson parabola and a plastic scintillator is designed and developed. The spectrometer is calibrated by protons from an electrostatic accelerator. The feasibility and reliability of the diagnostics are demonstrated in laser-driven ion acceleration experiments performed on the XL-II laser facility. The proton spectrum extrapolated from the scintillator data is in excellent agreement with the CR39 spectrum in terms of beam temperature and the cutoff energy. This real-time spectrometer allows an online measurement of the ion spectra in single shot, which enables efficient and statistical studies and applications in high-repetition-rate laser acceleration experiments.
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Photorefractive Effect of a Liquid Crystal Cell with a ZnO Nanorod Doped in Only One PVA Layer
GUO Yu-Bing, CHEN Yong-Hai**, XIANG Ying, QU Sheng-Chun, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (9):
096101
.
DOI: 10.1088/0256-307X/28/9/096101
We observe obviously different diffraction efficiencies with forward and reverse dc voltages in a forced-light-scattering (FLS) experiment for a cell with ZnO nanorod doped in only one poly (vinyl alcohol) (PVA) layer. When a dc voltage with a positive pole on the ZnO nanorod doped side is applied, the excited charge carriers primarily move along the transverse direction, which results in a higher diffraction efficiency. Conversely, when the dc voltage with a negative pole on the ZnO nanorod doped side is applied, the excited charge carriers primarily move along the longitudinal direction, which leads to a lower diffraction efficiency. A largest diffraction efficiency of about 9% is achieved in the ZnO nanorod doped liquid crystal cell.
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Accurately Predicting the Density and Hydrostatic Compression of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine from First Principles
SONG Hua-Jie, HUANG Feng-Lei**
Chin. Phys. Lett. 2011, 28 (9):
096103
.
DOI: 10.1088/0256-307X/28/9/096103
We predict the densities of crystalline hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by introducing a factor of (1+1.5 × 10−4 T) into the wavefunction-based potential of RDX constructed from first principles using the symmetry-adapted perturbation theory and the Williams–Stone–Misquitta method. The predicted values are within an accuracy of 1% of the density from 0 to 430 K and closely reproduced the RDX densities under hydrostatic compression. This work heralds a promising approach to predicting accurately the densities of high explosives at temperatures and pressures to which they are often subjected, which is a long-standing issue in the field of energetic materials.
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Magnetic Resonance Imaging Study on the Miscibility of a CO2/n-Decane System
SONG Yong-Chen, ZHU Ning-Jun, LIU Yu**, ZHAO Jia-Fei, LIU Wei-Guo, ZHANG Yi, ZHAO Yue-Chao, JIANG Lan-Lan
Chin. Phys. Lett. 2011, 28 (9):
096401
.
DOI: 10.1088/0256-307X/28/9/096401
We provide a feasible method to estimate the minimum miscibility pressure (MMP) of a CO2/n−decane system by using high spatial resolution magnetic resonance imaging (MRI). During the measurement, the signal intensity of n-decane with CO2 dissolved is measured. The MRI images show that the signal intensity of n−decane decreases to zero and the interface disappears at the MMP. A good exponential growth relation is found between the signal intensity and the pressure of the CO2/n−decane system. The relationship between the MMP and the temperature is established quantitatively, which is in close agreement with previous studies. Moreover it could be used to predict the MMP of the CO2/n-decane system.
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Preparation and Properties of Diluted Magnetic Semiconductors GaMnAs by Low-Temperature Molecular Epitaxy
JI Chang-Jian**, ZHANG Cheng-Qiang, ZHAO Gang, WANG Wen-Jing, SUN Gang, YUAN Hui-Min, HAN Qi-Feng
Chin. Phys. Lett. 2011, 28 (9):
097101
.
DOI: 10.1088/0256-307X/28/9/097101
GaMnAs films are prepared by low-temperature molecular beam epitaxy. Based on the experimental results, the influence of growth and annealing conditions on the physical properties and defect configurations is discussed. In particular, the major compensating defects, such as As antisite (AsGa) and Mn interstitials (MnI), are studied in detail. Thereby, the relationship between structure and magnetic properties is given. It is indicated that a higher annealing temperature can remove MnI out of the GaMnAs lattices so as to raise the Curie temperature TC. Meticulous optimization of growth techniques (TS=230°C, As2:Ga=5:1 and Ta=250°C) leads to reproducible physical properties and ferromagnetic transition temperatures well above 148 K.
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Mechanism of the Pyroelectric Response under Direct-Current Bias in La-Modified Lead Zirconate Titanate Stannate Ceramics
ZHANG Hong-Ling, WANG Gen-Shui, CHEN Xue-Feng, CAO Fei, DONG Xian-Lin**, GU Yan, HE Hong-Liang, LIU Yu-Sheng
Chin. Phys. Lett. 2011, 28 (9):
097701
.
DOI: 10.1088/0256-307X/28/9/097701
Dielectric and pyroelectric properties of Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 ceramics are investigated as functions of temperature and dc bias field. Induced and intrinsic pyroelectric coefficients pind and p0 are calculated and analyzed. It is found that the sign, value and variation of the net pyroelectric coefficient p with increasing dc bias all are dominated by p0 under applied biases. Polarization and depolarization processes under dc biases are analyzed. Besides the contribution of pind, the diffuse and decreased pyroelectric response under dc bias compared with that of an identical field poled sample without dc bias is mainly attributed to the depolarization process under dc bias.
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A Universal Formula for the Secondary Electron Yield of Metals at an Incident Angle of θ
XIE Ai-Gen**, ZHANG Jian, WANG Tie-Bang
Chin. Phys. Lett. 2011, 28 (9):
097901
.
DOI: 10.1088/0256-307X/28/9/097901
Based on the main physical processes, we deduce the relationships among the incident energy Wp0 of the primary electron, the number of released secondary electrons (i.e. δPEθ) per primary electron entering the metal at incident angle θ and the angle θ itself. In addition, the relationship of δ PEθ at θ = 0°, i.e. δPE0, with Wp0 is determined. From the experimental results, the relationship of the ratio at θ = 0°, i.e. β0 which is the ratio of the average number of released secondary electrons generated by a single primary electron backscattered at the metal surface to that generated by a single primary electron entering the metal, with Wp0 is determined. Moreover, the relationships among the ratio βθ , Wp0 and θ are obtained. Based on the relationships among the secondary electron yield at θ (i.e. δθ), the yield at θ = 0° (i.e. δ0), the backscattering coefficient at θ (i.e. ηθ), the coefficient at θ = 0° (i.e. η0), δPEθ and δPE0, we deduce the universal formula for δθ,δ0, ηθ, η0, and Wp0 for the primary electrons at an incident energy of 2–10 keV. The secondary electron yields calculated from the universal formula and the experimental yields of some metals are compared, and the results suggest that the proposed formula is universal for estimation of secondary electron yields at θ=0°−80°.
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Influence of Size of ZnO Nanorods on Light Extraction Enhancement of GaN-Based Light-Emitting Diodes
DAI Ke-Hui, **, WANG Lian-Shan**, HUANG De-Xiu, SOH Chew-Beng, CHUA Soo-Jin,
Chin. Phys. Lett. 2011, 28 (9):
098501
.
DOI: 10.1088/0256-307X/28/9/098501
We investigate the influence of size of ZnO nanorods on the light extraction efficiency (LEE) enhancement of GaN-based light-emitting diodes (GaN-LEDs). ZnO nanorods with different sizes are hydrothermally grown on patterned indium-doped tin oxide (ITO) electrodes of the GaN-LEDs in zinc acetate aqueous solutions of different concentrations. Measurements are conducted for the LEE enhancement of the LEDs with ZnO nanorods, compared to these without ZnO nanorods. The results suggest that the LEE of the LEDs with ZnO nanorods increases with the increasing size of ZnO nanorods. However, a saturation trend for the LEE improvement is also observed, which is attributed to the maximum limitation of light coupled into ZnO nanorods from GaN-based LEDs, and the reflection is increased by the increasing top surface of the ZnO nanorods.
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73 articles
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