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Efficiency-Controllable Random Walks on a Class of Recursive Scale-Free Trees with a Deep Trap
LI Ling, GUAN Ji-Hong, ZHOU Shui-Geng
Chin. Phys. Lett. 2015, 32 (03):
030501
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DOI: 10.1088/0256-307X/32/3/030501
Controls, especially efficiency controls on dynamical processes, have become major challenges in many complex systems. We study an important dynamical process, random walk, due to its wide range of applications for modeling the transporting or searching process. For lack of control methods for random walks in various structures, a control technique is presented for a class of weighted treelike scale-free networks with a deep trap at a hub node. The weighted networks are obtained from original models by introducing a weight parameter. We compute analytically the mean first passage time (MFPT) as an indicator for quantitatively measuring the efficiency of the random walk process. The results show that the MFPT increases exponentially with the network size, and the exponent varies with the weight parameter. The MFPT, therefore, can be controlled by the weight parameter to behave superlinearly, linearly, or sublinearly with the system size. This work provides further useful insights into controlling efficiency in scale-free complex networks.
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Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector
WANG Xiao-Dong, ZHANG Jun-Wei, HU Bi-Tao, YANG He-Run, DUAN Li-Min, LU Chen-Gui, HU Rong-Jiang, ZHANG Chun-Hui, ZHOU Jian-Rong, YANG Lei, AN Lv-Xing, LUO Wen
Chin. Phys. Lett. 2015, 32 (03):
032901
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DOI: 10.1088/0256-307X/32/3/032901
neutrons based on a 10×10 cm2 triple gas electron multiplier (GEM) device is developed and tested. A neutron converter, which is a high density polyethylene (HDPE) layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics (IMP) at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium (DT, 14 MeV), deuterium-deuterium (DD, 2.45 MeV), and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton (GEM material), and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.
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Liquid Concentration Sensing Properties of Microfibers with a Nanoscale-Structured Film
ZHOU Guo-Rui, LV Hai-Bing, YUAN Xiao-Dong, ZHOU Hai, LIU Hao, LI Ke-Xin, CHENG Xiao-Feng, MIAO Xin-Xiang
Chin. Phys. Lett. 2015, 32 (03):
034202
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DOI: 10.1088/0256-307X/32/3/034202
A type of compact solution concentration sensor based on a microfiber with a nanoscale-structured film is proposed and demonstrated experimentally. Additional loss at different solution concentrations is calculated by means of the three-dimensional finite-difference time-domain (3D-FDTD) method. The microfiber is fabricated by using the flame-heated scanning technique. Nanoscale-structured film is coated on the microfiber surface, which is assembled as a sensing unit. The sensitivity of this kind of sensor increases with the decreasing diameters of the microfiber. When the diameter of the microfiber is 2 μm, a minimum concentration sensitivity of 1% (under 450 s measuring time) is demonstrated in the experiment. Higher sensitivity can be attained when the solution concentration is higher. The sensing properties of this microfiber with the nanoscale-structured film may provide opportunities for new applications in optical sensing devices.
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Harmonic Dark Pulse Emission in Erbium-Doped Fiber Laser
Zian Cheak Tiu, Arman Zarei, Sin Jin Tan, Harith Ahmad, Sulaiman Wadi Harun
Chin. Phys. Lett. 2015, 32 (03):
034203
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DOI: 10.1088/0256-307X/32/3/034203
A harmonic dark pulse generation in an erbium-doped fiber laser is demonstrated based on a figure-of-eight configuration. It is found that the harmonic dark pulse can be shifted from the fundamental to the 5th order harmonic by increasing the pump power with an appropriate polarization controller orientation. The fundamental repetition rate of 20 kHz is obtained at the pump power of 29 mW. The highest pulse energy of 42.6 nJ is obtained at the fundamental repetition rate. The operating frequency of the dark pulse trains shifts to 2nd, 3rd, 4th and 5th harmonic as the pump powers are increased to 34 mW, 50 mW, 59 mW and 137 mW, respectively.
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Fabrication of Tm-Doped Fibers for High Power and 121 W Output All-Fiber Tm-Doped Fiber Laser
XING Ying-Bin, LIAO Lei, BU Fan, WANG Yi-Bo, PENG Jing-Gang, DAI Neng-Li, LI Jin-Yan
Chin. Phys. Lett. 2015, 32 (03):
034204
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DOI: 10.1088/0256-307X/32/3/034204
We fabricate the Tm-doped double cladding silica fiber by using the vapor-solution hybrid-doping method, then build up an all-fiber Tm-doped fiber laser which can provide the output power of up to 121 W, corresponding to a slope efficiency of 51% and an optical-optical efficiency of 48%. By using the domestic Tm-doped fiber, it is the first time a hundred-watt level output at 1915 nm has been achieved, to the best of our knowledge. The thermal effect of Tm-doped fiber laser is also analyzed.
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Numerical Simulation of Shock Bubble Interaction with Different Mach Numbers
YANG Jie, WAN Zhen-Hua, WANG Bo-Fu, SUN De-Jun
Chin. Phys. Lett. 2015, 32 (03):
034701
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DOI: 10.1088/0256-307X/32/3/034701
The interaction of a shock wave with a spherical helium bubble is investigated numerically by using the high-resolution piecewise parabolic method (PPM), in which the viscous and turbulence effects are both considered. The bubble is of the same size and is accelerated by a planar shock of different Mach numbers ( Ma). The results of low Ma cases agree quantitatively with those of experiments [G. Layes, O. Le Métayer, Phys. Fluids 19 (2007) 042105]. With the increase of Ma, the final geometry of the bubble becomes quite different, the compression ratio is highly raised, and the time-dependent mean bubble velocity is also influenced. The compression ratios measured can be well normalized when Ma is low, while less agreement has been achieved for high Ma cases. In addition, the mixedness between two fluids is enhanced greatly as Ma increases. Some existed scaling laws of these quantities for the shock wave strength cannot be directly applied to high Ma cases.
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Anomalous Convection Reversal due to Turbulence Transition in Tokamak Plasmas
SUN Tian-Tian, CHEN Shao-Yong, WANG Zhan-Hui, PENG Xiao-Dong, HUANG Jie, MOU Mao-Lin, TANG Chang-Jian
Chin. Phys. Lett. 2015, 32 (03):
035201
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DOI: 10.1088/0256-307X/32/3/035201
A critical physical model, based on the ion temperature gradient (ITG) mode and the trapped electron mode (TEM), trying to explain the spatio-temporal dynamics of anomalous particle convection reversal (i.e., the particle convective flux reverses from inward to outward), is developed numerically. The dependence of density peaking and profile shape on the particle convection is studied. Only the inward pinch could lead to the increase of the density peaking. The validation of the critical model is also analyzed. A comparison of the estimates calculated by the model and the experimental results from the Tore Supra tokamak shows that they are qualitatively both consistent.
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Effect of Wave Accessibility on Lower Hybrid Wave Current Drive in Experimental Advanced Superconductor Tokamak with H-Mode Operation
LI Xin-Xia, XIANG Nong, GAN Chun-Yun
Chin. Phys. Lett. 2015, 32 (03):
035202
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DOI: 10.1088/0256-307X/32/3/035202
The effect of the wave accessibility condition on the lower hybrid current drive in the experimental advanced superconductor Tokamak (EAST) plasma with H-mode operation is studied. Based on a simplified model, a mode conversion layer of the lower hybrid wave between the fast wave branch and the slow wave branch is proved to exist in the plasma periphery for typical EAST H-mode parameters. Under the framework of the lower hybrid wave simulation code (LSC), the wave ray trajectory and the associated current drive are calculated numerically. The results show that the wave accessibility condition plays an important role on the lower hybrid current drive in EAST plasma. For wave rays with parallel refractive index n||=2.1 or n||=2.5 launched from the outside midplane, the wave rays may penetrate the core plasma due to the toroidal geometry effect, while numerous reflections of the wave ray trajectories in the plasma periphery occur. However, low current drive efficiency is obtained. Meanwhile, the wave accessibility condition is improved if a higher confined magnetic field is applied. The simulation results show that for plasma parameters under present EAST H-mode operation, a significant lower hybrid wave current drive could be obtained for the wave spectrum with peak value n||=2.1 if a toroidal magnetic field BT=2.5 T is applied.
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Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon
CAO Yu, LIU Xiao-Liang, XIAN Wen-Duo, SUN Shao-Hua, SUN Ming-Ze, DING Peng-Ji, SHI Yan-Chao, LIU Zuo-Ye, HU Bi-Tao
Chin. Phys. Lett. 2015, 32 (03):
035203
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DOI: 10.1088/0256-307X/32/3/035203
An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium (LTE), the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.
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The Structural, Dielectric, Lattice Dynamical and Thermodynamic Properties of Zinc-Blende CdX (X= S, Se, Te) from First-Principles Analysis
FENG Shi-Quan, LI Jun-Yu, CHENG Xin-Lu
Chin. Phys. Lett. 2015, 32 (03):
036301
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DOI: 10.1088/0256-307X/32/3/036301
The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX (X=S, Se, Te) are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the published experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal optical-transverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX (X= S, Se, Te) are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX (X= S, Se, Te) and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.
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Ideal Strengths and Bonding Properties of UO2 under Tension
LI Li, WANG Bao-Tian, ZHANG Ping
Chin. Phys. Lett. 2015, 32 (03):
037102
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DOI: 10.1088/0256-307X/32/3/037102
By performing density functional theory plus U calculations, we systematically study the structural, electronic, and magnetic properties of UO2 under uniaxial tensile strain. The results show that the ideal tensile strengths along the [100], [110], and [111] directions are 93.6, 27.7, and 16.4 GPa at strains of 0.44, 0.24, and 0.16, respectively. After electronic-structure investigation for tensile stain along the [001] direction, we find that the strong mixed ionic/covalent character of U–O bond is weakened by the tensile strain and there will occur an insulator to metal transition at strain over 0.30.
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Enhancement of Thermoelectric Performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 Ceramics by A-Site Cation Nonstoichiometry
ZHANG Xin, LIU Jian, LI Yi, SU Wen-Bin, LI Ji-Chao, ZHU Yuan-Hu, LI Mao-Kui, WANG Chun-Ming, WANG Chun-Lei
Chin. Phys. Lett. 2015, 32 (03):
037201
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DOI: 10.1088/0256-307X/32/3/037201
Sr0.9Ba0.1?xTi0.8Nb0.2O3 ceramics (x=0, 0.01, 0.02 and 0.05) are prepared by solid state reaction, whose thermoelectric properties are investigated from 323 K to 1073 K. By introducing A-site nonstoichiometry, the absolute Seebeck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoichiometry.
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High-Temperature Performance Analysis of AlGaN/GaN Polarization Doped Field Effect Transistors Based on the Quasi-Multi-Channel Model
FANG Yu-Long, FENG Zhi-Hong, LI Cheng-Ming, SONG Xu-Bo, YIN Jia-Yun, ZHOU Xing-Ye, WANG Yuan-Gang, LV Yuan-Jie, CAI Shu-Jun
Chin. Phys. Lett. 2015, 32 (03):
037202
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DOI: 10.1088/0256-307X/32/3/037202
We report on the temperature-dependent dc performance of AlGaN/GaN polarization doped field effect transistors (PolFETs). The rough decrements of drain current and transconductance with the operation temperature are observed. Compared with the conventional HFETs, the drain current drop of the PolFET is smaller. The transconductance drop of PolFETs at different gate biases shows different temperature dependences. From the aspect of the unique carrier behaviors of graded AlGaN/GaN heterostructure, we propose a quasi-multi-channel model to investigate the physics behind the temperature-dependent performance of AlGaN/GaN PolFETs.
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Fabrication and Characterization of Fe-Doped In2O3 Dilute Magnetic Semiconducting Nanowires
ZHANG Jun-Ran, WU Zhen-Yao, LIU Yu-Jie, LV Zhan-Peng, NIU Wei, WANG Xue-Feng, DU Jun, LIU Wen-Qing, ZHANG Rong, XU Yong-Bing
Chin. Phys. Lett. 2015, 32 (03):
037501
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DOI: 10.1088/0256-307X/32/3/037501
Fe-doped In2O3 dilute magnetic semiconducting nanowires are fabricated on Au-deposited Si substrates by the chemical vapor deposition technique. It is confirmed by energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy that Fe has been successfully doped into lattices of In2O3 nanowires. The EDS measurements reveal a large amount of oxygen vacancies existing in the Fe-doped In2O3 nanowires. The Fe dopant exists as a mixture of Fe2+ and Fe3+, as revealed by the XPS. The origin of room-temperature ferromagnetism in Fe-doped In2O3 nanowires is explained by the bound magnetic polaron model.
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Magnetostriction Increase of Tb0.3Dy0.7Fe1.95 Alloy Prepared by Solidification in High Magnetic Fields
WANG Kai, LIU Tie, GAO Peng-Fei, WANG Qiang, LIU Yin, HE Ji-Cheng
Chin. Phys. Lett. 2015, 32 (03):
037502
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DOI: 10.1088/0256-307X/32/3/037502
Tb0.3Dy0.7Fe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe2 phase changed from <113> to <111> direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe2 phase.
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A High-Efficiency Broadband Superconducting Nanowire Single-Photon Detector with a Composite Optical Structure
GU Min, KANG Lin, ZHANG La-Bao, ZHAO Qing-Yuan, JIA Tao, WAN Chao, XU Rui-Ying, YANG Xiao-Zhong, WU Pei-Heng
Chin. Phys. Lett. 2015, 32 (03):
038501
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DOI: 10.1088/0256-307X/32/3/038501
Superconducting nanowire single-photon detectors (SNSPDs) with a composite optical structure composed of phase-grating and optical cavity structures are designed to enhance both the system detection efficiency and the response bandwidth. Numerical simulation by the finite-difference time-domain method shows that the photon absorption capacity of SNSPDs with a composite optical structure can be enhanced significantly by adjusting the parameters of the phase-grating and optical cavity structures at multiple frequency bands. The absorption capacity of the superconducting nanowires reaches 70%, 72%, 60.73%, 61.7%, 41.2%, and 46.5% at wavelengths of 684, 850, 732, 924, 1256, and 1426 nm, respectively. The use of a composite optical structure reduces the total filling factor of superconducting nanowires to only 0.25, decreases the kinetic inductance of SNSPDs, and improves the count rates.
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38 articles
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