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An Open Rectangular Waveguide Grating for Millimeter-Wave Traveling-Wave Tubes
Ming-Liang Liao, Yan-Yu Wei, Hai-Long Wang, Yu Huang, Jin Xu, Yang Liu, Guo Guo, Xin-Jian Niu, Yu-Bin Gong, Gun-Sik Park
Chin. Phys. Lett. 2016, 33 (09):
090701
.
DOI: 10.1088/0256-307X/33/9/090701
Millimeter-wave traveling-wave tube (TWT) prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimensions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating (ORWG) has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simulation results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.
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Investigation of Compton Profile of Molecular Propane
Xiao-Xun Mei, Xiao-Li Zhao, Long-Quan Xu, Ya-Wei Liu, Xu Kang, Shuai Yan, Dong-Dong Ni, Ke Yang, Lin-Fan Zhu
Chin. Phys. Lett. 2016, 33 (09):
093301
.
DOI: 10.1088/0256-307X/33/9/093301
The experimental Compton profile of the propane molecule is measured at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved near $p_{z}=0$. The calculated Compton profile by the density functional theory with aug-cc-pVTZ basis set reproduces the experimental observation very well. The joint experimental and theoretical investigation provides the benchmark data of the electronic structure of propane.
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Creation of Multiple Subwavelength Focal Spot Segments Using Phase Modulated Radially Polarized Multi Gaussian Beam
K. Prabakaran, K. B. Rajesh, S. Sumathira, M. D. Bharathi, R. Hemamalini, A. M. Musthafa, V. Aroulmoji
Chin. Phys. Lett. 2016, 33 (09):
094203
.
DOI: 10.1088/0256-307X/33/9/094203
Based on the vector diffraction theory, the effect of complex phase filters on intensity distribution of a radially polarized multi Gaussian beam in the focal region of high NA lens is theoretically investigated. It is observed that a properly designed multi belt complex phase filter can generate subwavelength novel focal patterns including splitting of focal spots and generation of multiple focal spot segments such as eight, six and four focal spots along the optical axis are obtained. We expect that such an investigation is useful for optical manipulation and material processing, multiple high refractive index particle trapping technologies.
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Passively Mode-Locked Femtosecond Laser with Disordered Crystal Nd:CGA as Gain Medium
Kun-Na He, Jia-Xing Liu, Wen-Long Tian, Zhong-Wei Shen, Xiao-Dong Xu, Zhao-Hua Wang, De-Hua Li, Jun Xu, Ju-Qing Di, Chang-Tai Xia, Zhi-Yi Wei
Chin. Phys. Lett. 2016, 33 (09):
094204
.
DOI: 10.1088/0256-307X/33/9/094204
We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd:CaGdAlO$_{4}$ (Nd:CGA) as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850 fs at 1079 nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122 mW is obtained under the pump power of 5.9 W. These results show that Nd:CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.
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Spectrum-Splitting Diffractive Optical Element of High Concentration Factor and High Optical Efficiency for Three-Junction Photovoltaics
Dong-Feng Lin, Bao-Gang Quan, Qiu-Lin Zhang, Dong-Xiang Zhang, Xin Xu, Jia-Sheng Ye, Yan Zhang, Dong-Mei Li, Qing-Bo Meng, Li Pan, Guo-Zhen Yang
Chin. Phys. Lett. 2016, 33 (09):
094207
.
DOI: 10.1088/0256-307X/33/9/094207
A spectrum-splitting and beam-concentrating (SSBC) diffractive optical element (DOE) for three-junction photovoltaics (PV) system is designed and fabricated by five-circle micro-fabrication. The incident solar light is efficiently split into three sub-spectrum ranges and strongly concentrated on the focal plane, which can be directly utilized by suitable spectrum-matching solar cells. The system concentration factor reaches 12$\times$. Moreover, the designed wavelengths (450 nm, 550 nm and 650 nm) are spatially distributed on the focal plane, in good agreement with the theoretical results. The average optical efficiency of all the cells over the three designed wavelengths is 60.07%. The SSBC DOE with a high concentration factor and a high optical efficiency provides a cost-effective approach to achieve higher PV conversion efficiencies.
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Laser Wakefield Acceleration Using Mid-Infrared Laser Pulses
Guo-Bo Zhang, N. A. M. Hafz, Yan-Yun Ma, Lie-Jia Qian, Fu-Qiu Shao, Zheng-Ming Sheng
Chin. Phys. Lett. 2016, 33 (09):
095202
.
DOI: 10.1088/0256-307X/33/9/095202
We study a laser wakefield acceleration driven by mid-infrared (mid-IR) laser pulses through two-dimensional particle-in-cell simulations. Since a mid-IR laser pulse can deliver a larger ponderomotive force as compared with the usual 0.8 μm wavelength laser pulse, it is found that electron self-injection into the wake wave occurs at an earlier time, the plasma density threshold for injection becomes lower, and the electron beam charge is substantially enhanced. Meanwhile, our study also shows that quasimonoenergetic electron beams with a narrow energy-spread can be generated by using mid-IR laser pulses. Such a mid-IR laser pulse can provide a feasible method for obtaining a high quality and high charge electron beam. Therefore, the current efforts on constructing mid-IR terawatt laser systems can greatly benefit the laser wakefield acceleration research.
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Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores
Yun Ling, Dong-Xiao Yan, Peng-Fei Wang, Mao Wang, Qi Wen, Feng Liu, Yu-Gang Wang
Chin. Phys. Lett. 2016, 33 (09):
096103
.
DOI: 10.1088/0256-307X/33/9/096103
A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide (PI) membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130 mW/m$^{2}$ with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.
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Structural Phase Transitions of ZnTe under High Pressure Using Experiments and Calculations
Hu Cheng, Yan-Chun Li, Gong Li, Xiao-Dong Li
Chin. Phys. Lett. 2016, 33 (09):
096104
.
DOI: 10.1088/0256-307X/33/9/096104
The pressure-induced structural transitions of ZnTe are investigated at pressures up to 59.2 GPa in a diamond anvil cell by using synchrotron powder x-ray diffraction method. A phase transition from the initial zinc blende (ZB, ZnTe-I) structure to a cinnabar phase (ZnTe-II) is observed at 9.6 GPa, followed by a high pressure orthorhombic phase (ZnTe-III) with $Cmcm$ symmetry at 12.1 GPa. The ZB, cinnabar (space group $P3_{1}21$), $Cmcm$, $P3_{1}$ and rock salt structures of ZnTe are investigated by using density functional theory calculations. Based on the experiments and calculations, the ZnTe-II phase is determined to have a cinnabar structure rather than a $P3_{1}$ symmetry.
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Synthesis of Ordered Ultra-long Manganite Nanowires via Electrospinning Method
Jun Zheng, Kai Du, Di Xiao, Zheng-Yang Zhou, Wen-Gang Wei, Jin-Jie Chen, Li-Feng Yin, Jian Shen
Chin. Phys. Lett. 2016, 33 (09):
097501
.
DOI: 10.1088/0256-307X/33/9/097501
We develop a new electrospinning method to prepare ultra-long ordered La$_{1-x}$Sr$_{x}$MnO$_{3}$ (LSMO) nanowires. The length is up to several centimeters and is only limited by the size of the collector. The well-ordered straight-line structure ensures the transport measurement, which is impossible to be carried out for the random nanowires fabricated by the traditional electrospinning method. Magnetic and transport measurements indicate that the physical properties of the LSMO nanowires depend sensitively on the doping concentration. At the optimum doping, the LSMO wires are ferromagnetic at room temperature with a metal-insulator transition temperature close to room temperature. Magnetic force microscopy studies are also performed to provide a microscopic view of these ultra-long nanowires.
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Effect of In$_{x}$Ga$_{1-x}$As Interlayer on Surface Morphology and Optical Properties of GaSb/InGaAs Type-II Quantum Dots Grown on InP (100) Substrates
Yu-Long Chen, You Gao, Hong Chen, Hui Zhang, Miao He, Shu-Ti Li, Shu-Wen Zheng
Chin. Phys. Lett. 2016, 33 (09):
098101
.
DOI: 10.1088/0256-307X/33/9/098101
The effects of indium composition in InGaAs interlayer on morphology of GaSb/InGaAs quantum dots (QDs) and on optical properties of GaSb/InGaAs QD material system are studied. AFM images show that the change of the indium composition in InGaAs interlayer can alter the GaSb QD morphology. It is found that low indium composition in InGaAs interlayer can promote the formation of QDs, while high indium composition can inhibit the formation of QDs. The photoluminescence (PL) spectra of GaSb/InGaAs QDs at 8 K under low excitation power indicate that the third root of the excitation power is linear with the peak position, which provides a direct evidence for their luminescence belonging to type-II material optical transition. The PL spectra at 8 K under an excitation power of 90 mW show that the optical properties of GaSb/InGaAs QD material system can be affected by the indium composition in the InGaAs interlayer, and the PL peak position is linear with the indium composition. The optical properties of GaSb/InGaAs QDs can be improved by adjusting the indium composition in the InGaAs interlayer.
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Excellent-Performance AlGaN/GaN Fin-MOSHEMTs with Self-Aligned Al$_{2}$O$_{3}$ Gate Dielectric
Xin Tan, Xing-Ye Zhou, Hong-Yu Guo, Guo-Dong Gu, Yuan-Gang Wang, Xu-Bo Song, Jia-Yun Yin, Yuan-Jie Lv, Zhi-Hong Feng
Chin. Phys. Lett. 2016, 33 (09):
098501
.
DOI: 10.1088/0256-307X/33/9/098501
AlGaN/GaN fin-shaped metal-oxide-semiconductor high-electron-mobility transistors (fin-MOSHEMTs) with different fin widths (300 nm and 100 nm) on sapphire substrates are fabricated and characterized. High-quality self-aligned Al$_{2}$O$_{3}$ gate dielectric underneath an 80-nm T-shaped gate is employed by aluminum self-oxidation, which induces 4 orders of magnitude reduction in the gate leakage current. Compared with conventional planar MOSHEMTs, short channel effects of the fabricated fin-MOSHEMTs are significantly suppressed due to the tri-gate structure, and excellent dc characteristics are obtained, such as extremely flat output curves, smaller drain induced barrier lower, smaller subthreshold swing, more positive threshold voltage, higher transconductance and higher breakdown voltage.
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Three-Dimensional Simulations of RESET Operation in Phase-Change Random Access Memory with Blade-Type Like Phase Change Layer by Finite Element Modeling
Qiu-Xue Jin, Bo Liu, Yan Liu, Wei-Wei Wang, Heng Wang, Zhen Xu, Dan Gao, Qing Wang, Yang-Yang Xia, Zhi-Tang Song, Song-Lin Feng
Chin. Phys. Lett. 2016, 33 (09):
098502
.
DOI: 10.1088/0256-307X/33/9/098502
An optimized device structure for reducing the RESET current of phase-change random access memory (PCRAM) with blade-type like (BTL) phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67 mA to 0.32 mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.
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Effects of Tensor Couplings on Nucleonic Direct URCA Processes in Neutron Star Matter
Yan Xu, Xiu-Lin Huang, Cheng-Zhi Liu, Tmurbagan Bao, Guang-Zhou Liu
Chin. Phys. Lett. 2016, 33 (09):
099701
.
DOI: 10.1088/0256-307X/33/9/099701
The relativistic neutrino emissivity of the nucleonic direct URCA processes in neutron star matter is investigated within the relativistic Hartree–Fock approximation. We particularly study the influences of the tensor couplings of vector mesons $\omega$ and $\rho$ on the nucleonic direct URCA processes. It is found that the inclusion of the tensor couplings of vector mesons $\omega$ and $\rho$ can slightly increase the maximum mass of neutron stars. In addition, the results indicate that the tensor couplings of vector mesons $\omega$ and $\rho$ lead to obvious enhancement of the total neutrino emissivity for the nucleonic direct URCA processes, which must accelerate the cooling rate of the non-superfluid neutron star matter. However, when considering only the tensor coupling of vector meson $\rho$, the neutrino emissivity for the nucleonic direct URCA processes slightly declines at low densities and significantly increases at high densities. That is, the tensor coupling of vector meson $\rho$ leads to the slow cooling rate of a low-mass neutron star and rapid cooling rate of a massive neutron star.
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34 articles
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