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Nonsensitive Nonlinear Homotopy Approach
GAO Yuan, TANG Xiao-Yan, LOU Sen-Yue,
Chin. Phys. Lett. 2009, 26 (11):
110201
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DOI: 10.1088/0256-307X/26/11/110201
Generally, natural scientific problems are so complicated that one has to establish some effective perturbation or nonperturbation theories with respect to some associated ideal models. We construct a new theory that combines perturbation and nonperturbation. An artificial nonlinear homotopy parameter plays the role of a perturbation parameter, while other artificial nonlinear parameters, which are independent of the original problems, introduced in the nonlinear homotopy models are nonperturbatively determined by means of the principle of minimal sensitivity. The method is demonstrated through several quantum anharmonic oscillators and a non-hermitian parity-time symmetric Hamiltonian system. In fact, the framework of the theory is rather general and can be applied to a broad range of natural phenomena. Possible applications to condensed matter physics, matter wave systems, and nonlinear optics are briefly discussed.
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Regular Small-World Network
ZOU Zhi-Yun, MAO Bao-Hua, HAO Hai-Ming, GAO Jian-Zhi, YANG Jie-Jiao
Chin. Phys. Lett. 2009, 26 (11):
110502
.
DOI: 10.1088/0256-307X/26/11/110502
According to the deficiencies in Watts and Strogatz's small-world network model, we present a new regular model to establish the small-world network. Besides the property of the small-world, this model has other properties such as accuracy in controlling the average shortest path length L, and the average clustering coefficient C, also regular network topology as well as enhanced network robustness. This method improves the construction of the small-world network essentially, so that the regular small-world network closely resembles the actual network. We also present studies on the relationships among the quantities of a variety of edges, L and C in regular small-world network in detail. This research lays the foundation for the establishment of the regular small-world network and acts as a good guidanc
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Isospin Effects on Anisotropic Flows in Intermediate Energy Heavy Ion Collisions
YAN Ting-Zhi, HU Si-Ke, GUO Wen-Xue, WANG Sheng-Long, XU Jin-Ping
Chin. Phys. Lett. 2009, 26 (11):
112501
.
DOI: 10.1088/0256-307X/26/11/112501
Anisotropic flows per nucleon (v1/A, v2/A, v3/A and v4/A) of light fragments up to the mass number 4 as a function of transverse momentum per nucleon are studied for 55MeV/nucleon 58Fe+58Fe and 58Ni+58Ni at large impact parameters by the isospin-dependent quantum molecular dynamics model. The effects of symmetry energy and nucleon-nucleon cross sections, which are both isospin-dependent on anisotropic flows, are studied in detail. In comparison of the two systems with or without symmetry potential term, the results show that the strength of flows is sensitive to symmetry potential and nucleon-nucleon cross sections, which mainly cause a repulsion effect in this energy region.
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Generation of Continuum Extreme-Ultraviolet Radiation by Carrier-Envelope-Phase-Stabilized 5-fs Laser Pulses
TENG Hao, YUN Chen-Xia, ZHU Jiang-Feng, HAN Hai-Nian, ZHONG Xin, ZHANG Wei, HOU Xun, WEI Zhi-Yi
Chin. Phys. Lett. 2009, 26 (11):
113201
.
DOI: 10.1088/0256-307X/26/11/113201
Coherent extreme-ultraviolet (XUV) radiation is studied by interaction of carrier-envelope (CE) phase stabilized high energy 5-fs infrared (800\,nm) laser pulses with neon gas at a repetition rate of 1kHz. A broadband continuum XUV spectrum in the cut-off region is demonstrated when the CE phase is shifted to about zero, rather than modulated spectral harmonics when setting of CE phase is nonzero. The results show the generation of isolated attosecond XUV pulses.
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Planar Metamaterial Microwave Absorber for all Wave Polarizations
ZHU Bo, WANG Zheng-Bin, YU Zhen-Zhong, ZHANG Qi, ZHAO Jun-Ming, FENG Yi-Jun, JIANG Tian,
Chin. Phys. Lett. 2009, 26 (11):
114102
.
DOI: 10.1088/0256-307X/26/11/114102
We present a design for a polarization insensitive metamaterial absorber at 9.5GHz by utilizing properly arranged resonant unit cells with orthogonal polarization sensitivity. Full-wave electromagnetic simulation demonstrates nearly perfect microwave absorption, which has been verified by experimental measurement with a maximum absorption of about 92% for incident wave with different polarizations. Furthermore, we find such a metamaterial thin absorber could work for a wide incident angle ranging from 0°to 50° with absorption no less than 80% for both the transverse electric mode and transverse magnetic mode.
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Influence of Post-Annealing Temperature on Properties of Ta-Doped ZnO Transparent Conductive Films
CAO Feng, WANG Yi-Ding, YIN Jing-Zhi, CONG Meng-Long, HAN Liang-Yu
Chin. Phys. Lett. 2009, 26 (11):
114203
.
DOI: 10.1088/0256-307X/26/11/114203
Ta-doped ZnO transparent conductive films are deposited on glass substrates by rf sputtering at 300°C. The influence of the post-annealing temperature on the structural, morphologic, electrical, and optical properties of the films is investigated by x-ray diffraction, Hall measurement, and optical transmission spectroscopy. The lowest resistivity of 3.5×10-4Ω12539;cm is obtained from the film annealed at 400°C in N2. The average optical transmittance of the films is over 90%. The optical bandgap is found to decrease with the increase of the annealing temperature.
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High-Efficiency High-Power Nd:YAG Laser under 885nm Laser Diode Pumping
LI Fang-Qin, ZHANG Xiao-Fu, ZONG Nan, YANG Jing, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan,
Chin. Phys. Lett. 2009, 26 (11):
114206
.
DOI: 10.1088/0256-307X/26/11/114206
A high-efficiency high-power Nd:YAG laser under 885nm laser diode (LD) pumping is demonstrated. The laser crystal is carefully designed, and the overlapping between the pump modes and the laser modes is optimized. The maximum output power at 1064nm is 87W under the absorbed pump power 127.7W, corresponding to a slope efficiency of 72.4% and an optical-optical efficiency of 68.1%. The optical-optical efficiency is 58.4% for the pump power emitted directly from the LD. To our best knowledge, this is the maximal optical-optical conversion efficiency obtained for the LD end-pumped Nd:YAG lasers so far.
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A Sensitive Scheme to Observe Weak Photo-Refraction Effects in Some Nonlinear Optical Crystals Pumped by Ultrashort Optical Pulses
XU Shi-Xiang, GAO Yan-Xia, CAI Hua, LI Jing-Zhen
Chin. Phys. Lett. 2009, 26 (11):
114209
.
DOI: 10.1088/0256-307X/26/11/114209
We present a sensitive scheme, for the first time to our knowledge, to observe photo-refraction (PR) effects in some nonlinear optical crystals, e.g. β-BBO, LBO and BIBO, pumped by an intense ultrashort laser pulse chain. These quite weak effects are "amplified' by sensitive cw intracavity loss modulation. Our results show that they are repeatable and are dependent on pumping power and wavelength, and their response time ranges from tens of seconds to several minutes. The recorded dynamical transitions between the self-focusing to the self-defocusing (or vice versa) induced by the PR effect may be critically important for us to give more insight into the stability of some cascade nonlinear frequency conversions, e.g. multi-stage optical parametric amplifiers. See Also: XU Shi-Xiang, Withdrawal of Chinese Physics Letters 26 (2009) 114209
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Structural and Electrical Properties of Single Crystalline a-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy
LU Zhong-Lin, , ZOU Wen-Qin, XU Ming-Xiang, ZHANG Feng-Ming, DU You-Wei
Chin. Phys. Lett. 2009, 26 (11):
116102
.
DOI: 10.1088/0256-307X/26/11/116102
High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2at.% and the lowest resistivity can reach 1.92×10-4Ω12539;cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.
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Electro-oxidation of Formic Acid on Carbon Supported Edge-Truncated Cubic Platinum Nanoparticles Catalysts
LI She-Qiang, FU Xing-Qiu, HU Bing, DENG Jia-Jun, CHEN Lei
Chin. Phys. Lett. 2009, 26 (11):
116104
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DOI: 10.1088/0256-307X/26/11/116104
The oxidation of formic acid on edge-truncated cubic platinum nanoparticles/C catalysts is investigated. X-ray photoelectron spectroscopy analysis indicates that the surface of edge-truncated cubic platinum nanoparticles is composed of two types of coordination sites. The oxidation behavior of formic acid on edge-truncated cubic platinum nanoparticles/C is investigated using cyclic voltammetry. The apparent activation energies are found to be 54.2, 55.0, 61.8, 69.5, 71.9, 69.26, 65.28kJ/mol at 0.15, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7V, respectively. A specific surface area activity of 1.76mA12539;cm-2 at 0.4V indicates that the edge-truncated cubic Platinum nanoparticles are a promising anode catalyst for direct formic acid fuel cells.
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Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate
LIU Xu-Yan, LIU Wei-Li, MA Xiao-Bo, CHEN Chao, SONG Zhi-Tang, LIN Cheng-Lu
Chin. Phys. Lett. 2009, 26 (11):
116802
.
DOI: 10.1088/0256-307X/26/11/116802
Ultra-thin and near-fully relaxed SiGe substrate is fabricated using a modified Ge condensation technique, and then a 25-nm-thick biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGe-on-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiGe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000°C. According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.
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Various Recipes of SiNx Passivated AlGaN/GaN High Electron Mobility Transistors in Correlation with Current Slump
YANG Ling, HAO Yue, MA Xiao-Hua, QUAN Si, HU Gui-Zhou, JIANG Shou-Gao, YANG Li-Yuan
Chin. Phys. Lett. 2009, 26 (11):
117104
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DOI: 10.1088/0256-307X/26/11/117104
The current slump of different recipes of SiNx passivated AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. The dc and pulsed current-voltage curves of AlGaN/GaN HEMTs using different recipes are analyzed. It is found that passivation leakage has a strong relationship with NH3 flow in the plasma-enhanced chemical vapor phase deposition process, which has impacted on the current collapse of SiNx passivated devices. We analyze the pulsed IDS-VDS characteristics of different recipes of SiNx passivation devices for different combinations of gate and drain quiescent biases (VGS0, VDS0) of (0, 0), (-6, 0), (-6, 15) and (0, 15)V. The possible mechanisms are the traps in SiNx passivation capturing the electrons and the surface states at the SiNx/AlGaN interface, which can affect the channel of two-dimensional electron gas and cause the current collapse.
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Synthesis and Multiferroic Properties of BiFeO3 Nanotubes
WANG Jing, LI Mei-Ya, LIU Xiao-Lian, PEI Ling, LIU Jun, YU Ben-Fang, ZHAO Xing-Zhong,
Chin. Phys. Lett. 2009, 26 (11):
117301
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DOI: 10.1088/0256-307X/26/11/117301
Highly ordered BiFeO3(BFO) nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission electron microscopy and selected area electron diffraction analysis. The coexistence of ferroelectric and ferromagnetic ordering of these BFO nanotubes at room temperature is demonstrated, giving a remnant polarization of 26μC/cm2, a low coercive electric field of 60kV/cm, and a magnetization of 0.18emu/g. In addition, it is found that the leakage behavior of these nanotubes is dominated by the ohmic contact mechanism.
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Microstructure and Magnetic Domains of Iron Films on Liquid Surfaces
XIE Jian-Ping, XIA A-Gen, ZHANG Chu-Hang, YANG Bo, FANG Zheng-Nong, YE Gao-Xiang
Chin. Phys. Lett. 2009, 26 (11):
117501
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DOI: 10.1088/0256-307X/26/11/117501
Iron (Fe) films with a thickness ranging from 1.0nm to 80.0nm are deposited on silicone oil surfaces by a vapor phase deposition method. The films with a thickness of d<2.0nm do not exhibit planar morphology but ramified aggregates instead. Magnetic force microscopy studies for the Fe films (10.0nm≤d ≤80.0nm) show that the domain wall structure is widespread and irregularly shaped and the oscillation phase shift 8710; θ, which records as the magnetic force image, changes from 0.29° to 0.81°. Correspondingly, the magnetic force gradient varies from 1.4×10-3 to 4.0×10-3 N/m, respectively. In our measurement, the characteristic domain walls, such as Bloch walls, Néel walls and cross-tie walls, are not observed in the film system clearly.
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Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films
XING Peng-Fei, CHEN Yan-Xue, TANG Min-Jian, YAN Shi-Shen, LIU Guo-Lei, MEI Liang-Mo, JIAO Jun,
Chin. Phys. Lett. 2009, 26 (11):
117503
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DOI: 10.1088/0256-307X/26/11/117503
Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.
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AlGaN-Based Deep-Ultraviolet Light Emitting Diodes Fabricated on AlN/sapphire Template
SANG Li-Wen, QIN Zhi-Xin, FANG Hao, ZHANG Yan-Zhao, LI Tao, XU Zheng-Yu, YANG Zhi-Jian, SHEN Bo, ZHANG Guo-Yi, LI Shu-Ping, YANG Wei-Huang, CHEN Hang-Yang, LIU Da-Yi, KANG Jun-Yong
Chin. Phys. Lett. 2009, 26 (11):
117801
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DOI: 10.1088/0256-307X/26/11/117801
We report on the growth and fabrication of deep ultraviolet (DUV) light emitting diodes (LEDs) on an AlN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.
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Energy Transfer from Ce3+ to Eu2+ in LiSrBO3 and Its Potential Application in UV-LED-Based White LEDs
WANG Zhi-Jun, LI Pan-Lai, YANG Zhi-Ping, GUO Qing-Lin, FU Guang-Sheng
Chin. Phys. Lett. 2009, 26 (11):
117802
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DOI: 10.1088/0256-307X/26/11/117802
Ce3+/Eu2+ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3:Ce3+,Eu2+ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-type energy transfer from Ce3+ ion to Eu2+ ion and tuning the relative proportion of Ce3+/Eu2+ properly. Energy transfer mechanism in LiSrBO3:Ce3+, Eu2+ phosphor is dominated by the dipole-dipole interaction, and the critical distance of the energy transfer is estimated to be about 2nm by both spectral overlap and concentration quenching methods. Under UV radiation, white light is generated by coupling 436 and 565nm emission bands attributed to Ce3+ and Eu2+ radiations, respectively.
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Environmental Impacts on Spiking Properties in Hodgkin-Huxley Neuron with Direct Current Stimulus
YUAN Chang-Qing, ZHAO Tong-Jun, ZHAN Yong, ZHANG Su-Hua, LIU Hui, ZHANG Yu-Hong
Chin. Phys. Lett. 2009, 26 (11):
118701
.
DOI: 10.1088/0256-307X/26/11/118701
Based on the well accepted Hodgkin-Huxley neuron model, the neuronal intrinsic excitability is studied when the neuron is subject to varying environmental temperatures, the typical impact for its regulating ways. With computer simulation, it is found that altering environmental temperature can improve or inhibit the neuronal intrinsic excitability so as to influence the neuronal spiking properties. The impacts from environmental factors can be understood that the neuronal spiking threshold is essentially influenced by the fluctuations in the environment. With the environmental temperature varying, burst spiking is realized for the neuronal membrane voltage because of the environment-dependent spiking threshold. This burst induced by changes in spiking threshold is different from that excited by input currents or other stimulus.
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Worldwide Marine Transportation Network: Efficiency and Container Throughput
DENG Wei-Bing, GUO Long, LI Wei, CAI Xu
Chin. Phys. Lett. 2009, 26 (11):
118901
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DOI: 10.1088/0256-307X/26/11/118901
Through empirical analysis of the global structure of the Worldwide Marine Transportation Network (WMTN), we find that the WMTN, a small-world network, exhibits an exponential-like degree distribution. We hereby investigate the efficiency of the WMTN by employing a simple definition. Compared with many other transportation networks, the WMTN possesses relatively low efficiency. Furthermore, by exploring the relationship between the topological structure and the container throughput, we find that strong correlations exist among the container throughout the degree and the clustering coefficient. Also, considering the navigational process that a ship travels in a real shipping line, we obtain that the weight of a seaport is proportional to the total probability contributed by all the passing shipping lines.
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Evolution of Ring Current Protons Induced by Electromagnetic Ion Cyclotron Waves
XIAO Fu-Liang, TIAN Tian, CHEN Liang-Xu, SU Zhen-Peng, ZHENG Hui-Nan
Chin. Phys. Lett. 2009, 26 (11):
119401
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DOI: 10.1088/0256-307X/26/11/119401
We investigate the evolution of the phase space density (PSD) of ring current protons induced by electromagnetic ion cyclotron (EMIC) waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 103 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic (~100keV) protons, yielding a rapid decrement in PSD, typically by a factor of ~10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.
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ULF Waves Associated with Solar Wind Deceleration in the Earth's Foreshock
FU Hui-Shan, CAO Jin-Bin, YANG Biao, Lucek E, Rème H, Dandouras I
Chin. Phys. Lett. 2009, 26 (11):
119402
.
DOI: 10.1088/0256-307X/26/11/119402
Characteristics of ULF waves associated with the solar wind deceleration in the Earth's foreshock on 6-7 April 2003 is studied using the wave telescope technique. In the satellite frame, the ULF waves are the left-handed polarized and quasi anti-parallel propagating mode, with a power peak at about 18.63mHz. The wave vector in the GSE coordinates is estimated to be k = (-4.29, 2.28, 1.21)×10-4km-1. In the solar wind frame, the frequency of waves becomes -9.39mHz after the Doppler shift correction. The propagation direction of the waves is thus reversed and correspondingly the polarization of the waves becomes right-handed. The above-mentioned characteristics of the ULF waves in the solar wind frame indicate that the ULF waves associated with the solar wind deceleration are the Alfven-whistler waves, which have been frequently reported in both the observations and computer simulations.
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71 articles
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