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Coevolution of Structure and Strategy Promoting Fairness in the Ultimatum Game
DENG Li-Li, TANG Wan-Sheng**, ZHANG Jian-Xiong
Chin. Phys. Lett. 2011, 28 (7):
070204
.
DOI: 10.1088/0256-307X/28/7/070204
We try to figure out how the structure evolution and strategy evolution commonly affect the emergence of fair behaviors in the ultimatum game under a complex network framework. By allowing the players to change their neighbors in the network as well as their strategies, several experiments have been conducted. Results of the simulations show that the coevolution has substantial impacts on the resulting outcomes for the strategy adopted as well as the ultimate structure. With increasing structure updating rate, players offer more in the ultimatum game, but players will offer less with increasing strategy updating rate. In particular, the ratio of structure updating to strategy updating also affects the emergence of fairness substantially because the larger the ratio, the more the players offer. In addition, the mutation in strategies plays a promoting role in the emergence of fairness. Moreover, the initial random network is evolved into the structure with small-world effects. By comparison with the traditional models of static structures, we show that allowing the network structure and strategy to coevolve generally promotes the emergence of fairness.
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Enhanced Total Ionizing Dose Susceptibility in Narrow Channel Devices
LIU Zhang-Li, **, HU Zhi-Yuan, ZHANG Zheng-Xuan, SHAO Hua, NING Bing-Xu, BI Da-Wei, CHEN Ming, ZOU Shi-Chang
Chin. Phys. Lett. 2011, 28 (7):
070701
.
DOI: 10.1088/0256-307X/28/7/070701
Total ionizing dose effects of different transistor sizes in a 0.18 µm technology are studied by 60Co γ-ray irradiation. Significant threshold voltage shift is observed for the narrow channel devices, which is called the radiation induced narrow channel effect (RINCE). A charge sharing model is introduced to understand the phenomenon. The devices' characteristic degradations after irradiation, such as threshold voltage shift, increase in on-state current under different drain biases and substrate biases, are discussed in detail. Radiation induced oxide trapped charge at the edges of shallow trench isolation plays an important role in the RINCE. Narrow channel devices are susceptible to the total ionizing dose effect.
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AMS Measurement of 53Mn at CIAE
DONG Ke-Jun, HE Ming, LI Chao-Li, HU Hao, LIU Guang-Shan, CHEN Zhi-Gang, LI Zhen-Yu, WU Shao-Yong, LIU Jian-Cheng, YOU Qu-Bo, JIN Chun-Sheng, WANG Xiang-Gao, SHEN Hong-Tao, GUAN Yong-Jing, YUAN Jian, JIANG Shan**
Chin. Phys. Lett. 2011, 28 (7):
070703
.
DOI: 10.1088/0256-307X/28/7/070703
The long-lived isotope 53Mn cosmogenically produced in situ is a very useful indicator for geochronological dating. A new 53Mn accelerator−mass-spectrometry (AMS) measurement method is developed based on the HI-13 Tandem Accelerator and ΔE−Q3D detection system at China Institute of Atomic Energy. The performance of 53Cr isobar separation and suppression is tested by a series of 53Mn standards and commercial MnO samples. The results show that the ΔE−Q3D detection system brought about an overall suppression factor of more than 107 for the interfering isobar 53Cr.
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Hamiltonian of Green–Schwarz IIB Superstring Theory in AdS3×S3 Background
KE San-Min, **, WANG Chun, WANG Zhan-Yun, JIANG Ke-Xia, SHI Kang-Jie
Chin. Phys. Lett. 2011, 28 (7):
071101
.
DOI: 10.1088/0256-307X/28/7/071101
We parameterize the Green–Schwarz IIB superstring in the AdS3×S3 background under the light cone gauge by the method of Metsaev and Tseytlin in AdS3 and by the method of Rahmfeld and Rajaraman in S3. After some calculation, we obtain the corresponding Maurer–Cartan 1−forms and the action. Then we fix two bosonic variables x+=τ and y5=σ, perform the partial Legendre transformation of the remaining bosonic variables, and find a Lagrangian that is linear in velocity after eliminating the metric of the world sheet. We also give the Hamiltonian and prove that the system is local and the Poisson bracket of the theory can be well defined. Using these results, one can further study the properties of solution space, solution transformation and the structure of the flat current algebra of the superstring in the AdS3×S3 background.
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A Primary Study of Heavy Baryons ΛQ, ΣQ, ΞQ and ΩQ
ZHAO Qiao-Yan, ZHANG Dan**, ZHANG Qiu-Yang
Chin. Phys. Lett. 2011, 28 (7):
071201
.
DOI: 10.1088/0256-307X/28/7/071201
We perform a preliminary study of the 1/2+ and 3/2+ ground−state baryons containing a heavy quark in the framework of the chiral SU(3) quark model. By using the calculus of variations, masses of ΛQ, ΣQ, ΞQ, ΩQ, ΣQ*, ΞQ* and ΩQ*, where Q means c or b quark, are calculated. By taking reasonable model parameters, the numerical results of established heavy baryons are generally in agreement with the experimental data available, except that those of ΞQ are somewhat heavier. For Ωb with undetermined experimental mass and unobserved Ξb*, Ωb*, reasonable theoretical predictions are obtained. Interactions inside baryons are also discussed.
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Power Test of the Ladder IH-RFQ Accelerator at Peking University
LU Yuan-Rong, CHEN Wei, NIE Yuan-Cun**, LIU Ge, GAO Shu-Li, ZENG Hong-Jin, YAN Xue-Qing, CHEN Jia-Er
Chin. Phys. Lett. 2011, 28 (7):
072901
.
DOI: 10.1088/0256-307X/28/7/072901
A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator (T-IH-RFQ) is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heavy Ion Physics, Peking University. It could accelerate ions with a mass-to-charge ratio of less than 14, from 2.9 keV/u to 35.7 keV/u within a length of 1.1 m. The T-IH-RFQ cavity operating at H21(0) mode was constructed successfully. Based on a well designed rf power feeding system, the cavity was cold measured and tested with high rf power. In the case of cold measurement, the rf properties were obtained using a vector network analyzer with the help of a perturbation capacitor. During a high power test, the inter−electrode voltage was derived from the energy spectrum of x-rays measured by a high purity Ge detector. The results show that the specific shunt impedance of the T-IH-RFQ cavity reaches 178 kΩm, which could meet the requirements of beam dynamics design.
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Magic Wavelength of an Optical Clock Transition of Barium
YU Geng-Hua, , ZHONG Jia-Qi, , LI Run-Bing, WANG Jin, ZHAN Ming-Sheng, **
Chin. Phys. Lett. 2011, 28 (7):
073201
.
DOI: 10.1088/0256-307X/28/7/073201
Similar to most of the other alkaline earth elements, barium atoms can be candidates for optical clocks, thus the magic wavelength for an optical lattice is important for the clock transition. We calculate the magic wavelength of a possible clock transition between 6s2 1S0 and 6s5d3D2 states of barium atoms. Our theoretical result shows that there are three magic wavelengths 615.9 nm, 641.2 nm and 678.8 nm for a linearly polarized optical lattice laser for barium.
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An All-Fiber Gas Raman Light Source Based on a Hydrogen-Filled Hollow-Core Photonic Crystal Fiber Pumped with a Q-Switched Fiber Laser
CHEN Xiao-Dong, , MAO Qing-He**, SUN Qing, ZHAO Jia-Sheng, LI Pan, FENG Su-Juan
Chin. Phys. Lett. 2011, 28 (7):
074201
.
DOI: 10.1088/0256-307X/28/7/074201
A gas Raman light source based on a H2−filled hollow-core photonic-crystal-fiber cell with a Q-switched fiber laser followed by a fiber amplifier as the Raman pump source is demonstrated. The Stokes frequency-shift lasing line is observed at 1135.7 nm with the Q-switched pump pulses at 1064.7 nm. Our experimental results show that the generated Stokes pulse is much narrower than the pump pulse, and the generated Stokes pulse duration is increased with the single pulse energy for the same duration pump pulses. For the 125 ns pump pulses with a repetition rate of 5 kHz, the Raman threshold pump energy and the conversion efficiency at the Raman threshold are 2.13 µJ and 9.82%. Moreover, by choosing narrower pump pulses, the Raman threshold pump energy may be reduced and the conversion efficiency may be improved.
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A Compact and Highly Efficient Silicon-Based Asymmetric Mach–Zehnder Modulator with Broadband Spectral Operation
ZHOU Liang, LI Zhi-Yong**, XIAO Xi, XU Hai-Hua, FAN Zhong-Chao, HAN Wei-Hua, YU Yu-De, YU Jin-Zhong
Chin. Phys. Lett. 2011, 28 (7):
074202
.
DOI: 10.1088/0256-307X/28/7/074202
An asymmetric Mach–Zehnder electro-optic modulator is demonstrated by using a silicon-based p-i-n diode embedded in compact 200 µm long phase shifters. The measured figure of merit VπL=0.23 V⋅mm shows highly efficient modulation by the device, and an open eye−diagram at 3.2 Gbit/s confirmed its fast electro-optic response. Integrated with the grating coupler, the device exhibits a broad operational wavelength range of 70 nm with a uniform 18 dB extinction ratio covering the C−band and part L-band of optical communication.
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Room-Temperature Continuous-Wave Operation of a Tunable External Cavity Quantum Cascade Laser
ZHANG Jin-Chuan, , WANG Li-Jun**, LIU Wan-Feng, LIU Feng-Qi, YIN Wen, LIU Jun-Qi, LI Lu, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (7):
074203
.
DOI: 10.1088/0256-307X/28/7/074203
A room-temperature cw operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of 4.6 µm is presented. Strain−compensation combined with two-phonon resonance in an active region design promises low threshold current density. A very low threshold current density of 1.47 kA/cm2 for an EC−QCL operated in cw mode is realized. Single-mode cw operation with a side-mode suppression ratio of 20 dB and a wide tuning range of over 110 cm-1 are achieved. Moreover, an even wider tuning range of over 135 cm−1 is obtained in pulsed mode at room temperature.
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Laser Cleaning Techniques for Removing Surface Particulate Contaminants on Sol-Gel SiO2 Films
ZHANG Chun-Lai, LI Xi-Bin, WANG Zhi-Guo**, LIU Chun-Ming, XIANG Xia, LV Hai-Bing, YUAN Xiao-Dong, ZU Xiao-Tao
Chin. Phys. Lett. 2011, 28 (7):
074205
.
DOI: 10.1088/0256-307X/28/7/074205
Dry laser cleaning (DLC) and laser shockwave cleaning (LSC) are used to remove the particulate contamination from SiO2 sol−gel optical films. The results show that the LSC with a shockwave initiated by plasma formation under a focused laser beam pulse offers much better efficiency than DLC. Silica particles up to 10 µm on SiO2 films can be removed without substrate damage at a gap distance of 0.5 mm, and a more uniform surface microstructure can be obtained after LSC. Furthermore, it is demonstrated that the transmittance of contaminated SiO2 films can be restored to the as-deposited value after the LSC on dispersed-particle zones. LSC has potential applications in engineering-oriented large components.
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High-Efficiency Supercontinuum Generation at 12.8W in an All-Fiber Device
WANG Yan-Bin**, HOU Jing**, CHEN Zi-Lun, CHEN Sheng-Ping, SONG Rui, LI Ying, YANG Wei-Qiang, LU Qi-Sheng
Chin. Phys. Lett. 2011, 28 (7):
074208
.
DOI: 10.1088/0256-307X/28/7/074208
We report 12.8 W supercontinuum generation with a high optical-to-optical conversion efficiency of up to 85% in an all-fiber device. This is achieved by using an all-fiber picosecond master oscillator power amplifier laser, which has an output pigtail double clad fiber, to pump a 3-m photonic crystal fiber with the core at one end enlarged by adiabatically collapsing two inner layers of air holes while keeping other holes open. Our experimental results show that the short-wavelength generation is due to dispersive wave trapping by redshifted solitons.
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Acousto-Optic Q-Switched Operation Ho:YAP Laser Pumped by a Tm-Doped Fiber Laser
ZHOU Ren-Lai**, JU You-Lun, WANG Wei, ZHU Guo-Li, WANG Yue-Zhu
Chin. Phys. Lett. 2011, 28 (7):
074210
.
DOI: 10.1088/0256-307X/28/7/074210
We report on the acousto-optic Q-switched operation of a Ho:YAP laser double-passed pumped by an all-fiber Tm-doped fiber laser. The output characteristics of the Ho:YAP laser are studied at pulse repetition frequencies of 1, 2, 5 and 10 kHz. The shortest pulse width, the maximum pulse energy and the highest peak power are measured to be 17 ns, 1.71 mJ and 71.25 kW, respectively. The output wavelength is centered at 2115.96 nm with a bandwidth of about 1.5 nm. The beam quality factor M2=2.41±0.03 at the output power of 3.54 W was measured by using the traveling knife-edge method.
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Photocurrent Effect in Reverse-Biased p-n Silicon Waveguides in Communication Bands
ZHAO Yong, XU Chao, WANG Wan-Jun, ZHOU Qiang, HAO Yin-Lei, YANG Jian-Yi, WANG Ming-Hua, JIANG Xiao-Qing**
Chin. Phys. Lett. 2011, 28 (7):
074216
.
DOI: 10.1088/0256-307X/28/7/074216
The photocurrent effect in reverse biased p-n silicon waveguides at wavelength 1550 nm is experimentally investigated. The photocurrent, which is mainly related to surface-state absorption, defect-state absorption and/or two-photon absorption, is more than 0.08 µA/mm under 8 V reverse biasing and 0.75 mW irradiation. The responsivity of a silicon waveguide with length of 4500 µm achieves 0.5 mA/W. Moreover, the enhancement of the photocurrent effect under the electric field is discussed.
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Kerr-Lens Self-Mode-Locked Laser Characteristics of Yb:Lu2SiO5 Crystal
LIU Jie**, YANG Ji-Min, WANG Wei-Wei, ZHENG Li-He, SU Liang-Bi, XU Jun
Chin. Phys. Lett. 2011, 28 (7):
074220
.
DOI: 10.1088/0256-307X/28/7/074220
A diode-pumped Kerr-lens self-mode-locked laser is achieved by using Yb: Lu2SiO5 (Yb:LSO) crystal without additional components. Under the incident pump power of 14.44 W, a self-mode-locked output power of 2.98 W is obtained in the five-mirror cavity, corresponding to an optical-optical efficiency of 20.6%. Pulses as short as 8.2 ps are realized at 1059 nm, with the corresponding pulse energy and peak power of 28.9 nJ and 3.5 kW, respectively. A pair of SF10 prisms are inserted into the laser cavity to compensate for the group velocity dispersion. The pulse width is compressed to 2.2 ps with an average output power of 1.25 W.
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Emission Lines of Boron, Carbon, Oxygen and Iron in Tokamak Plasma
DI Long, SHI Jian-Rong, WANG Shou-Jun, DONG Quan-Li, ZHAO Jing, LI Yu-Tong, FU Jia, WANG Fu-Di, SHI Yue-Jiang, WAN Bao-Nian, ZHAO Gang**, ZHANG Jie,
Chin. Phys. Lett. 2011, 28 (7):
075201
.
DOI: 10.1088/0256-307X/28/7/075201
The emission lines of B, C, O and Fe in tokamak plasma are reported. The spectra are compared with those calculated by the CHIANTI code, which is based on the collisional-radiative models with a large amount of accurate atomic data. General agreement is obtained between the results of experiment and computation. Most of the lines in the spectra are identified, and the relative number density ratios of B, C, O and Fe are determined. It is found that the processes of line formation in our experiment are similar to those in the stellar coronae. The line-averaged electron density of the tokamak plasma is measured by the HCN laser, indicating a good agreement with the theoretical prediction by the density-dependent line ratio of Fe XXI.
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High Pressure X-Ray Diffraction Study of a Grossular–Andradite Solid Solution and the Bulk Modulus Variation along this Solid Solution
FAN Da-Wei**, WEI Shu-Yi, LIU Jing, LI Yan-Chun, XIE Hong-Sen
Chin. Phys. Lett. 2011, 28 (7):
076101
.
DOI: 10.1088/0256-307X/28/7/076101
In-situ angle-dispersive x-ray diffraction measurements on three samples of Gr14An84, Gr34An64 and Gr63An34 were performed by using a diamond anvil cell instrument with synchrotron radiation at the Beijing Synchrotron Radiation Facility at up to 13.7 GPa. A least−square fit of the pressure-volume to the Birch–Murnaghan equation of state, when fixed K'0=4.0 yields bulk modulus values of K0=166±2, 168±3, 173±2 GPa for Gr14An84, Gr34An64 and Gr63An34, respectively. The bulk modulus increases from 166±2 GPa for Gr14An84 and to 173±2 GPa for Gr63An34 with the increasing An content. Furthermore, by linear interpolation, the bulk modulus of the Gr−An binary system as a function of An content can be expressed as K0(GPa) =176.9(9)−0.12(1)XAn (R2=0.987).
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Electronic Structure and Optical Properties of SrBi2A2O9(A=Nb,Ta)
ZHAO Na, WANG Yue-Hua**, ZHAO Xin-Yin, ZHANG Min, GONG Sai
Chin. Phys. Lett. 2011, 28 (7):
077101
.
DOI: 10.1088/0256-307X/28/7/077101
The first-principles calculation is performed to investigate the energy band structures, density of states (DOS) and optical properties of SrBi2A2O9 (A=Nb,Ta), by using density functional theory (DFT) with the generalized gradient approximation (GGA). The results show that the band−gap of SrBi2Nb2O9 is smaller than that of SrBi2Ta2O9, and that there are strong hybridizations of A−O bands, which play very important roles in the electronic properties and optical responses of SrBi2A2O9. SrBi2Ta2O9 stimulates much higher photocatalytic activity than SrBi2Nb2O9, which is due to its suitable crystal structure.
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Effects of an Intense Laser Field and Hydrostatic Pressure on the Intersubband Transitions and Binding Energy of Shallow Donor Impurities in a Quantum Well
U. Yesilgul**, F. Ungan, E. Kasapoglu, H. Sari, I. Sö, kmen
Chin. Phys. Lett. 2011, 28 (7):
077102
.
DOI: 10.1088/0256-307X/28/7/077102
We have calculated the intersubband transitions and the ground-state binding energies of a hydrogenic donor impurity in a quantum well in the presence of a high-frequency laser field and hydrostatic pressure. The calculations are performed within the effective mass approximation, using a variational method. We conclude that the laser field amplitude and the hydrostatic pressure provide an important effect on the electronic and optical properties of the quantum wells. According to the results obtained from the present work, it is deduced that (i) the binding energies of donor impurity decrease as the laser field increase, (ii) the binding energies of donor impurity increase as the hydrostatic pressure increase, (iii) the intersubband absorption coefficients shift toward lower energies as the hydrostatic pressure increases, (iv) the magnitude of absorption coefficients decrease and also shift toward higher energies as the laser field increase. It is hopeful that the obtained results will provide important improvements in device applications.
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CMOS Compatible Nonvolatile Memory Devices Based on SiO2/Cu/SiO2 Multilayer Films
WANG Yan, LIU Qi, LV Hang-Bing, LONG Shi-Bing, ZHANG Sen, LI Ying-Tao, LIAN Wen-Tai, YANG Jian-Hong**, LIU Ming
Chin. Phys. Lett. 2011, 28 (7):
077201
.
DOI: 10.1088/0256-307X/28/7/077201
We systematically investigate the resistive switching characteristics of SiO2 films with a Cu/SiO2/Cu/SiO2/Pt multilayer structure. The device exhibits good resistive switching performances, including a high ON/OFF resistance ratio (>103), good retention characteristic (>104s), satisfactory switching endurance (>200 cycles), a fast programming speed (<100 ns) and a high device yield (∼100%). Considering these results, SiO2-based memories have highly promising applications for nonvolatile memory devices.
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Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors Using a Nano-Channel Array Structure
LIU Sheng-Hou, CAI Yong**, GONG Ru-Min, WANG Jin-Yan, ZENG Chun-Hong, SHI Wen-Hua, FENG Zhi-Hong, WANG Jing-Jing, YIN Jia-Yun, Cheng P. Wen, QIN Hua, ZHANG Bao-Shun
Chin. Phys. Lett. 2011, 28 (7):
077202
.
DOI: 10.1088/0256-307X/28/7/077202
A nano-channel array (NCA) structure is applied to realize enhancement-mode (E-mode) AlGaN/GaN high-electron mobility transistors (HEMTs). The fabricated NCA-HEMT, consisting of 1000 channels connected in parallel with a channel width of 64 nm, shows a threshold voltage of 0.15 V and a subthreshold slope of 78 mV/dec, compared to −3.92 V and 99 mV/dec for a conventional HEMT (C-HEMT), respectively. Both the NCA-HEMT and C-HEMT show similar gate leakage current, indicating no significant degradation in gate leakage characteristics for the NCA-HEMT. The surrounding-field effect and relieved polarization contribute to the very large positive threshold voltage shift, while the work function difference makes it positive.
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Crystalline, Optical and Electrical Properties of NiZnO Thin Films Fabricated by MOCVD
WANG Jin, WANG Hui, ZHAO Wang, MA Yan, LI Wan-Cheng, XIA Xiao-Chuan, SHI Zhi-Feng, ZHAO Long, ZHANG Bao-Lin, DONG Xin**, DU Guo-Tong
Chin. Phys. Lett. 2011, 28 (7):
077301
.
DOI: 10.1088/0256-307X/28/7/077301
NiZnO thin films are grown on c-plane sapphire substrates by using a photo-assisted metal organic chemical vapor deposition (MOCVD) system. The effect of the Ni content on the crystalline, optical and electrical properties of the films are researched in detail. The NiZnO films could retain a basic wurtzite structure when the Ni content is less than 0.18. As Ni content increases, crystal quality degradation could be observed in the x-ray diffraction patterns and a clear red shift of the absorption edge can be observed in the transmittance spectrum. Furthermore, the donor defects in the NiZnO film can be compensated for effectively by increasing the Ni content. The change of Ni content has an important effect on the properties of NiZnO films.
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Magnetostrictions and Magnetic Properties of Nd-Fe-B and SrFe12O19
CHEN Hai-Ying, ZHANG Yan, YANG Yun-Bo, CHEN Xue-Gang, LIU Shun-Quan, WANG Chang-Sheng, YANG Ying-Chang, YANG Jin-Bo, **
Chin. Phys. Lett. 2011, 28 (7):
077501
.
DOI: 10.1088/0256-307X/28/7/077501
The magnetostrictions of polycrystalline Nd-Fe-B and Sr-ferrite at different temperatures are reinvestigated using a strain gauge rotating-sample method. It is found that the magnetostriction λs of Nd−Fe-B is +52×10−6, and that of Sr-ferrite is −25×10-6 under a magnetic field of 8 T at room temperature. The maximum energy product (BH)max of the Nd-Fe-B magnet is improved when the powders are magnetically aligned perpendicular to the pressing direction, whereas that of the Sr-ferrite magnet is better when the powders are aligned parallel to the pressing direction. These experimental results suggest that the magnetostriction can generate compressive strain anisotropy resulting from the inverse effect of the magnetostriction. Thus, the magnetization of materials with a negative coefficient of magnetostriction are easier to be aligned normal to the stress direction, while for the materials with a positive coefficient of magnetostriction, the magnetization is easier to be aligned along the stress direction. Therefore, the magnetostriction anisotropy can be used to improve the alignment of the magnetic powders as well as the performance of the magnets.
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Sol-Gel Template Synthesis and Photoluminescence Properties of (Pb0.5Sr0.5)TiO3 Nanotube Arrays
JIANG Yan-Ping, **, WANG Yu, CHAN Lai Wa Helen, TANG Xin-Gui, ZHOU Yi-Chun**
Chin. Phys. Lett. 2011, 28 (7):
077702
.
DOI: 10.1088/0256-307X/28/7/077702
Lead strontium titanate (Pb0.5Sr0.5)TiO3 (PST) nanotube arrays are prepared by a sol-gel and spin-coating process using an anodic aluminium oxide template. The structure and morphology of the as-prepared sample are characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as-prepared PST sample possesses a perovskite structure with a relatively uniform diameter of about 200 nm. Photoluminescence (PL) spectrum of the sample shows emission bands centered at about 2.87 eV at room temperature, which consists of three intense emission sub-bands at 3.02, 2.87 and 2.76 eV, respectively. The energy corresponding to the central PL peak is lower than the band-gap energy (3.2 eV) of PST bulk materials, which may originate from the size effect of the PST nanotube arrays. The multi-peaks in the PL spectrum may be attributed to the radiative recombination of trapped electrons and holes in tail and gap states induced by local defect and oxygen vacancies. The Raman scattering spectrum of the PST nanotube arrays, which are obviously broadened in comparison with the bulk materials, show that their phonon modes are in agreement with those allowed in the tetragonal phase.
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Bias Effects on the Growth of Helium-Containing Titanium Films
ZHANG Li-Ran, DENG Ai-Hong, **, YANG Dong-Xu, ZHOU Yu-Lu, HOU Qing, SHI Li-Qun, ZHONG Yu-Rong, WANG Bao-Yi
Chin. Phys. Lett. 2011, 28 (7):
077802
.
DOI: 10.1088/0256-307X/28/7/077802
Helium-containing titanium films were prepared on Si substrates with various biases applied by magnetron sputtering under stable He/Ar ambiance. Rutherford backscattering and elastic recoil detection analyses are used to measure the thickness of the He-Ti films and the helium depth profile, respectively. Experiments of x-ray diffraction and variable energy positron annihilation spectroscopy are carried out to investigate the microstructures of titanium films and the corresponding helium-related defects developed. The behavior of the implanted He, the microstructure of the He-Ti film and the formation of He-related defects all are affected by the substrate biases applied.
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Infrared Luminescent Properties of a Pr-Doped KBr Submicron Rod
WEI Feng-Wei, ZHANG Xiao-Song**, LI Lan, XU Jian-Ping, ZHOU Yong-Liang, LIU Pei
Chin. Phys. Lett. 2011, 28 (7):
077803
.
DOI: 10.1088/0256-307X/28/7/077803
KBr:Pr with a submicron rod structure is successfully synthesized by a solid-state reaction using absolute alcohol as the abrasive. X-ray diffraction, scanning electron microscopy, photoluminescence spectra and fluorescence decay curves are used to characterize the resulting materials. The influences of Pr3+ dopant concentration on the luminescence and lifetime are discussed. Furthermore, luminescent measurements show that KBr:Pr has a high emission intensity compared with other Pr-doped matrixes, which is related to the low phonon energy of KBr. The results suggest that the phonon energy of the host is important in determining the luminescent efficiency.
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Structural Analysis of In xGa1−xN/GaN MQWs by Different Experimental Methods
DING Bin-Beng, PAN Feng, FENG Zhe-Chuan, FA Tao, CHENG Feng-Feng, YAO Shu-De**
Chin. Phys. Lett. 2011, 28 (7):
078201
.
DOI: 10.1088/0256-307X/28/7/078201
Structural properties of InxGa1−xN/GaN multi-quantum wells (MQWs) grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction (SRXRD), Rutherford backscattering/channelling (RBS/C) and high-resolution transmission electron microscopy. The sample consists of eight periods of InxGa1−xN/GaN wells of 2.1 nm thickness and 8.5 nm thickness of GaN barrier, and the results are very close, which verifies the accuracy of the three methods. The indium content in InxGa1−xN/GaN MQWs by SRXRD and RBS/C is estimated, and results are in general the same. By RBS/C random spectra, the indium atomic lattice substitution rate is 94.0%, indicating that almost all indium atoms in InxGa1−xN/GaN MQWs are at substitution, that the indium distribution of each layer in InxGa1−xN/GaN MQWs is very homogeneous and that the InxGa1−xN/GaN MQWs have a very good crystalline quality. It is not accurate to estimate indium content in InxGa1−xN/GaN MQWs by photoluminescence (PL) spectra, because the result from the PL experimental method is very different from the results by the SRXRD and RBS/C experimental methods.
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Restabilizing Mechanisms after the Onset of Thermal Instability in Bipolar Transistors
CHEN Liang**, ZHANG Wan-Rong, XIE Hong-Yun, JIN Dong-Yue, DING Chun-Bao, FU Qiang, WANG Ren-Qing, XIAO Ying, ZHAO Xin
Chin. Phys. Lett. 2011, 28 (7):
078501
.
DOI: 10.1088/0256-307X/28/7/078501
The restabilizing mechanisms after the onset of thermal instability in bipolar transistors are studied by theoretical analyses, computer simulations and experimental measurements. Restability conditions are described by novel analytical formulae. Furthermore, the expression of collect current in the second fly-back point is given for the first time. The effects of emitter ballast resistance, collector-emitter voltage and thermal resistance on restabilization mechanisms are expressed and investigated.
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Significant Improvement of Organic Thin-Film Transistor Mobility Utilizing an Organic Heterojunction Buffer Layer
PAN Feng, QIAN Xian-Rui, HUANG Li-Zhen, WANG Hai-Bo, YAN Dong-Hang**
Chin. Phys. Lett. 2011, 28 (7):
078504
.
DOI: 10.1088/0256-307X/28/7/078504
High-mobility vanadyl phthalocyanine (VOPc)/5,5"'−bis(4-fluorophenyl)-2,2':5',2":5",2"'−quaterthiophene (F2-P4T) thin-film transistors are demonstrated by employing a copper hexadecafluorophthalocyanine (F16CuPc)/copper phthalocyanine (CuPc) heterojunction unit, which are fabricated at different substrate temperatures, as a buffer layer. The highest mobility of 4.08 cm2/Vs is achieved using a F16CuPc/CuPc organic heterojunction buffer layer fabricated at high substrate temperature. Compared with the random small grain-like morphology of the room-temperature buffer layer, the high-temperature organic heterojunction presents a large-sized fiber-like film morphology, resulting in an enhanced conductivity. Thus the contact resistance of the transistor is significantly reduced and an obvious improvement in device mobility is obtained.
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Direct Urca Processes with Hyperons in Cooling Neutron Stars
XU Yan, LIU Guang-Zhou**, WU Yao-Rui, ZHU Ming-Feng, YU Zi, WANG Hong-Yan, ZHAO En-Guang
Chin. Phys. Lett. 2011, 28 (7):
079701
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DOI: 10.1088/0256-307X/28/7/079701
In the relativistic mean field approximation, the relativistic energy losses of the direct Urca processes with nucleons (N-DURCA) and hyperons (Y-DURCA) are studied in the degenerate baryon matter of neutron stars. We investigate the effects of hyperon degrees of freedom and the Y-DURCA processes on the N-DURCA processes, and the total neutrino emissivity of neutron star matter. The results show that the existence of hyperons decreases the abundance of protons and leptons, and can sharply suppress the neutrino emissivity of the N-DURCA processes.
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90 articles
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