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Coherence of Disordered Bosonic Gas with Two- and Three-Body Interactions
Xin Zhang, Zi-Fa Yu, Ju-Kui Xue
Chin. Phys. Lett. 2016, 33 (04):
040302
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DOI: 10.1088/0256-307X/33/4/040302
We theoretically and numerically investigate the coherence of disordered bosonic gas with effective two- and three-body interactions within a two-site Bose–Hubbard model. By properly adjusting the two- and three-body interactions and the disorder, the coherence of the system exhibits new and interesting phenomena, including the resonance character of coherence against the disorder in the purely two- or three-body interactions system. More interestingly, the disorder and three-body interactions together can suppress the coherence of the purely three-body interactions system, which is different from the case in which the disorder and two-body interactions together can enhance the coherence in certain values of two-body interaction. Furthermore, when two- or three-body interactions are attractive or repulsive, the phase coherence exhibits completely different phenomena. In particular, if two- or three-body interactions are attractive, the coherence of the system can be significantly enhanced in certain regions. Correspondingly, the phase coherence of the system is strongly related to the effective interaction energy. The results provide a possible way for studying the coherence of bosonic gas with multi-atoms' interactions in the presence of the disorder.
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An Accurate Frequency Control Method and Atomic Clock Based on Coherent Population Beating Phenomenon
Yu-Xin Zhuang, Dai-Ting Shi, Da-Wei Li, Yi-Gen Wang, Xiao-Na Zhao, Jian-Ye Zhao, Zhong Wang
Chin. Phys. Lett. 2016, 33 (04):
040601
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DOI: 10.1088/0256-307X/33/4/040601
An accurate frequency control method and atomic clock based on the coherent population beating (CPB) phenomenon is implemented. In this scheme, the frequency difference of an rf and an atomic transition frequency can be digitally obtained by measuring the CPB oscillation frequency. The frequency measurement resolution of several milli-hertz can be achieved by using a 10 MHz oven controlled crystal oscillator as the reference. The expression of the Allan deviation of the CPB clock is theoretically deduced and it is revealed that the Allan deviation is inversely proportional to the signal-to-noise ratio and proportional to the line-width of coherent population trapping spectrum. We also approve that the CPB atomic clock has a large toleration of the drift of the local oscillator. In our CPB experimental system, a frequency instability of $3.0\times10^{-12}$ at 1000 s is observed. The important feature of high frequency measurement resolution of the CPB method may also be used in magnetometers, atomic spectroscopy, and other related research.
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Interesting Features of Ionization Potentials for Elements ($Z\le 119$) along the Periodic Table
Chun Gu, Rui Jin, De-Ling Zeng, Xian-Fang Yue, Xiang Gao, Jia-Ming Li
Chin. Phys. Lett. 2016, 33 (04):
043201
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DOI: 10.1088/0256-307X/33/4/043201
The ionization potential (IP) is a basic property of an atom, which has many applications such as in element analysis. With the Dirac–Slater methods (i.e., mean field theory), IPs of all occupied orbitals for elements with atomic number ($Z\le 119$) are calculated conveniently and systematically. Compared with available experimental measurements, the theoretical accuracies of IPs for various occupied orbitals are ascertained. The map of the inner orbital IPs with good accuracies should be useful to select x-ray energies for element analysis. Based on systematic variations of the first IPs for the outermost orbitals in good agreement with experimental values as well as other IPs, mechanisms of electronic configurations of all atomic elements ($Z\le 119$) along the periodic table are elucidated. It is interesting to note that there exist some deficiencies of the intermediate orbital IPs, which are due to electron correlations and should be treated beyond the mean field theory.
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Double Ionization Dynamics of Molecular Hydrogen in Ultrashort Intense Laser Fields
Yong-Ju Chen, Shao-Gang Yu, Ren-Ping Sun, Cheng Gong, Lin-Qiang Hua, Xuan-Yang Lai, Wei Quan, Xiao-Jun Liu
Chin. Phys. Lett. 2016, 33 (04):
043301
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DOI: 10.1088/0256-307X/33/4/043301
We experimentally investigate the double ionization of molecular hydrogen subjected to ultrashort intense laser pulses. The total kinetic energy release of the two coincident H$^{+}$ ions, which provides a diagnosis of different processes to double ionization of H$_{2}$, is measured for two different pulse durations, i.e., 25 and 5 fs, and various laser intensities. It is found that, for the long pulse duration (i.e., 25 fs), the double ionization occurs mainly via two processes, i.e., the charge resonance enhanced ionization and recollision-induced double ionization. Moreover, the contributions from these two processes can be significantly modulated by changing the laser intensity. In contrast, for a few-cycle pulse of 5 fs, only the recollsion-induced double ionization survives, and in particular, this process could be solely induced by the first-return recollision at appropriate laser intensities, providing an efficient way to probe the sub-laser-cycle molecular dynamics.
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Design of a Novel Folded Waveguide for 60-GHz Traveling-Wave Tubes
Ming-Liang Liao, Yan-Yu Wei, Hai-Long Wang, Jin Xu, Yang Liu, Guo Guo, Xin-Jian Niu, Yu-Bin Gong, Gun-Sik Park
Chin. Phys. Lett. 2016, 33 (04):
044201
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DOI: 10.1088/0256-307X/33/4/044201
The 60-GHz traveling-wave tube (TWT) prevails nowadays as the amplifier for the satellite communication and electronic countermeasures. The folded waveguide (FW) is a promising all-metal slow-wave structure (SWS) for the 60-GHz TWT with advantages of robust performance, fine heat dissipation, considerable power and bandwidth. A novel FW periodically loaded with rectangular grooves is analyzed for the purpose of gaining higher power and gain. The rf characteristics are investigated by numerical simulation, and the nonlinear large-signal performance of such a TWT is analyzed by a 3D particle-in-cell code MAGIC. Compared with normal circuits, relatively higher continuous-wave power (40–56 W) and similar bandwidth (5 GHz) are predicted by simulation. Meanwhile, the designed operation voltage is 10.5 kV, which keeps the low-voltage advantage of the popular helix TWT competitor. The novel FW will favor the design of a broadband and high-power 60-GHz TWT.
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Simulation of Far-Field Properties of Coherent Vertical Cavity Surface Emitting Laser Array
Meng Xun, Chen Xu, Yi-Yang Xie, Jun Deng, Guo-Qing Jiang, Guan-Zhong Pan, Yi-Bo Dong, Hong-Da Chen
Chin. Phys. Lett. 2016, 33 (04):
044204
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DOI: 10.1088/0256-307X/33/4/044204
Far-field properties dependent on array scale, separation, element width and emitted wavelength are systematically analyzed theoretically and experimentally. An array model based on the finite-difference method is established to simulate the far-field profile of the coherent arrays. Some important conclusions are obtained. To achieve a higher quality beam, it is necessary to decrease separation between elements, or to increase the element width. Higher brightness can be achieved in the array with larger scale. Emitted wavelength also has an influence on the far-field profile. These analyses can be extended to the future design of coherent vertical cavity surface emitting laser arrays.
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An Actively Mode-Locked Ho:YAG Solid-Laser Pumped by a Tm-Doped Fiber Laser
Bao-Quan Yao, He Li, Xiao-Lei Li, Yi Chen, Xiao-Ming Duan, Shuang Bai, Hong-Yu Yang, Zheng Cui, Ying-Jie Shen, Tong-Yu Dai
Chin. Phys. Lett. 2016, 33 (04):
044205
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DOI: 10.1088/0256-307X/33/4/044205
An actively mode-locked Ho:YAG laser pumped by a diode-pumped Tm-doped fiber laser is reported. For the cw operation, we obtain the maximum output power of 3.43 W with a central wavelength 2022.2 nm at the maximum incident pump power of 11.4 W, corresponding to a slope efficiency of 34.5%. The beam quality factor $M^{2}$ is 1.16, and the output beam is close to fundamental TEM$_{00}$. In the case of the CWML operation, a stable pulse train is generated with an average output power up to 3.41 W with a slope efficiency of 34.3% at the incident pump power of 11.4 W and a pulse duration of 294 ps at a repetition rate of 81.92 MHz. In addition, the maximum single pulse energy is 41.6 nJ.
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Raman Suppression in a Kilowatt Narrow-Band Fiber Amplifier
Man Hu, Yi-Feng Yang, Ye Zheng, Guang-Bo Liu, Jian-Hua Wang, Kai Liu, Xiao-Long Chen, Chun Zhao, Bing He, Jun Zhou
Chin. Phys. Lett. 2016, 33 (04):
044208
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DOI: 10.1088/0256-307X/33/4/044208
A novel technique to suppress stimulated Raman scattering in a high power narrow-band fiber amplifier is reported. By seeding with a combination of a broadband amplified spontaneous emission seed and a narrowband master oscillator seed, the Raman Stokes components can be reduced about 16 dB at a total output power of 1 kW. Raman suppression results are depicted in a different wavelengths seeding case and the same wavelength seeding case, respectively, with different seed power ratios.
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Extraordinary Acoustic Transmission in a Helmholtz Resonance Cavity-Constructed Acoustic Grating
Si-Yuan Yu, Xu Ni, Ye-Long Xu, Cheng He, Priyanka Nayar, Ming-Hui Lu, Yan-Feng Chen
Chin. Phys. Lett. 2016, 33 (04):
044302
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DOI: 10.1088/0256-307X/33/4/044302
We investigate both experimentally and numerically a complex structure, where 'face-to-face' Helmholtz resonance cavities (HRCs) are introduced to construct a one-dimensional acoustic grating. In this system, pairs of HRCs can intensely couple with each other in two forms: a bonding state and an anti-bonding state, analogous to the character of hydrogen molecule with two atoms due to the interference of wave functions of sound among the acoustic local-resonating structures. The bonding state is a 'bright' state that interferes with the Fabry–Pèrot resonance mode, thereby causing this state to break up into two modes as the splitting of the extraordinary acoustic transmission peak. On the contrary, the anti-bonding state is a 'dark' state in which the resonance mode remains entirely localized within the HRCs, and has no contribution to the acoustic transmission.
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Examination of the Thermal Cloaking Effectiveness with Layered Engineering Materials
Run Hu, Jin-Yan Hu, Rui-Kang Wu, Bin Xie, Xing-Jian Yu, Xiao-Bing Luo
Chin. Phys. Lett. 2016, 33 (04):
044401
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DOI: 10.1088/0256-307X/33/4/044401
The concentrically layered thermal cloaks with isotropic materials could realize the equivalent thermal cloaking effect with Pendry's cloak, while the effectiveness is scarcely investigated quantitatively. Here we examine the cloaking effectiveness quantitatively by evaluating the standard deviation of the temperature difference between the simulated plane with the layered thermal cloak and Pendry's thermal cloak. The design rules for the isotropic materials in terms of thermal conductivity and layer thickness are presented. The present method could quantitatively evaluate the cloaking effectiveness, and could open avenues for analyzing the cloaking effect, detecting the (anti-) cloaks, etc.
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Formation Process of Magnetized Fusion Target on the YingGuang 1 Device
Lu-Lu Li, Yue-Song Jia, Qi-Zhi Sun, Wei Liu, Zheng-Fen Liu, Wei-Dong Qin, Jun Li, Yuan Chi, Xian-Jun Yang
Chin. Phys. Lett. 2016, 33 (04):
045202
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DOI: 10.1088/0256-307X/33/4/045202
Magnetized target fusion is an alternative method to fulfill the goal of controlled fusion, which combines advantages of both magnetic confinement fusion and inertial confinement fusion since its parameter space lies between the two traditional ways. Field reversed configuration (FRC) is a good candidate of magnetized targets due to its translatable, compressible, high $\beta$ and high energy density properties. Dynamic formation process of high density FRC is observed on the YingGuang 1 device for the first time in China. The evolution of a magnetic field is detected with magnetic probes, and the compression process can be clearly seen from images taken with a high-speed multi-frame CCD camera. The process is also studied with two-dimensional magneto hydrodynamic code MPF-2D theoretically, and the results agree well with the experiment. Combining the experimental data and the theoretical analysis, the length of the formed FRC is about 39 cm, the diameter is about 2–2.7 cm, the average density is $1.3 \times 10^{16}$ cm$^{-3}$, and the average temperature is 137 eV.
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An Attempt to Prepare Metallic Glasses from Quasicrystals
Zi-Jing Li, Lin-Ran Zhao, Yu-Ting Wang, Ze-Ming Chen, Wen-Kang Tu, Ya-Qi Zhang, Hong Bo, Ying-Dan Liu, Li-Min Wang
Chin. Phys. Lett. 2016, 33 (04):
046401
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DOI: 10.1088/0256-307X/33/4/046401
Icosahedrons in supercooled liquids and glasses are considered to be of significance for the glass formation in alloy systems. Starting from the similarity of the local structure of quasicrystals to the icosahedrons in metallic glasses, a scheme is put forward to prepare metallic glasses based on a well-known quasicrystal Zr$_{40}$Ti$_{40}$Ni$_{20}$. A series of (Zr$_{40}$Ti$_{40}$Ni$_{20}$)$_{100-x}$Co$_{x}$ metallic glasses are fabricated, and the optimized glass forming composition is determined at (Zr$_{40}$Ti$_{40}$Ni$_{20}$)$_{92}$Co$_{8}$. The results show that the glass-forming ability of the alloys is closely related to the quasicrystalline phases. The mechanism of the enhanced glass-forming ability is discussed.
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Thermal Expansion and Deformation of Graphene
Zheng-Fu Cheng, Rui-Lun Zheng
Chin. Phys. Lett. 2016, 33 (04):
046501
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DOI: 10.1088/0256-307X/33/4/046501
Taking into consideration short-atomic-range interactions and anharmonic effects, we calculate the thermal expansion coefficients, Gruneisen parameters, the elastic modulus of graphene varying with temperature and the phonon frequency. The anharmonic effects associated with the graphene deformation are also discussed. The results show that the value of thermal expansion coefficient is negative in the moderate temperature range, and it becomes positive when the temperature grows to be higher than a certain value. The change rate of elastic modulus with respect to temperature and pressure are calculated, and phonon frequencies are estimated. In the process of graphene thermal expansion, it is accompanied with the change of bond length and the rotation around the axis normal to the plane. Our results indicate that the effects due to the bond change are more significant than that of the rotation. We also show that if anharmonic effects are ignored, the thermal expansion coefficient and the Gruneisen parameters are zero, and the elastic modulus and the phonon frequency are constant. If anharmonic effects are considered up to the second term, these values will vary with temperature, and become closer to the experimental value. The higher the temperature is, the more significant the anharmonic effects become.
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Effect of Chirality on the Electronic Transport Properties of the Thioxanthene-Based Molecular Switch
Cai-Juan Xia, Bo-Qun Zhang, Mao Yang, Chun-Lan Wang, Ai-Yun Yang
Chin. Phys. Lett. 2016, 33 (04):
047101
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DOI: 10.1088/0256-307X/33/4/047101
Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch. The molecule comprises the switch which can exhibit different chiralities, that is, cis-form and trans-form by ultraviolet or visible irradiation. The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form. Furthermore, the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes. The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction, suggesting potential applications of this type of junctions in future design of functional molecular devices.
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Broad-Band FMR Linewidth of Co2MnSi Thin Films with Low Damping Factor: The Role of Two-Magnon Scattering
Shi-Zhu Qiao, Quan-Nian Ren, Run-Run Hao, Hai Zhong, Yun Kang, Shi-Shou Kang, Yu-Feng Qin, Shu-Yun Yu, Guang-Bing Han, Shi-Shen Yan, Liang-Mo Mei
Chin. Phys. Lett. 2016, 33 (04):
047601
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DOI: 10.1088/0256-307X/33/4/047601
The low Gilbert damping factor, which is usually measured by ferromagnetic resonance, is crucial in spintronic applications. Two-magnon scattering occurs when the orthogonality of the ferromagnetic resonance mode and other degenerate spin wave modes was broken by magnetic anisotropy, voids, second phase, surface defects, etc., which is important in analysis of ferromagnetic resonance linewidth. Direct fitting to linewidth with Gilbert damping is advisable only when the measured linewidth is a linear function of measuring frequency in a broad band measurement. We observe the nonlinear ferromagnetic resonance linewidth of Co2MnSi thin films with respect to measuring frequency in broad band measurement. Experimental data could be well fitted with the model including two-magnon scattering with no fixed parameters. The fitting results show that two-magnon scattering results in the nonlinear linewidth behavior, and the Gilbert damping factor is much smaller than reported ones, indicating that our Co2MnSi films are more suitable for the applications of spin transfer torque.
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First-Principles Investigations of Pb$_{0.5}$Ba$_{0.5}$TiO$_3$ Alloys Based on Structure Predictions
Hong-Bo Wu, Yi-Feng Duan, Chang-Ming Zhao, Kun Liu, Li-Xia Qin
Chin. Phys. Lett. 2016, 33 (04):
047701
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DOI: 10.1088/0256-307X/33/4/047701
Crystal structure predictions of Pb$_{0.5}$Ba$_{0.5}$TiO$_3$ alloys under different pressures are performed based on the particle swarming optimization algorithm. The predicted stable ground-state and high-pressure phases are tetragonal ferroelectric ($I4mm$) and cubic para-electric ($Fm\bar{3}m$), respectively, whose structural details have not been reported. The pressure-induced colossal enhancements in piezoelectric response are associated with the mechanical and dynamical instabilities instead of polarization rotation. The band gap of the tetragonal phase is indirect and that of the cubic phase is always direct. As pressure increases, the alloy displays the similar band-gap behaviors to PbTiO$_3$, while different from BaTiO$_3$, which is attributed to the different orbital contributions to the valence bands. Our calculated results are in good agreement with the available data.
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Growth of InAlGaN Quaternary Alloys by Pulsed Metalorganic Chemical Vapor Deposition
Ru-Dai Quan, Jin-Cheng Zhang, Sheng-Rui Xu, Jun-Shuai Xue, Yi Zhao, Jing Ning, Zhi-Yu Lin, Ze-Yang Ren, Yue Hao
Chin. Phys. Lett. 2016, 33 (04):
048101
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DOI: 10.1088/0256-307X/33/4/048101
Epitaxial growth of InAlGaN/GaN structures are performed on the $c$-plane sapphire by pulsed metal organic chemical vapor deposition with different triethylgallium (TEGa) flows in the growth process of InAlGaN quaternary alloys. X-ray photoelectron spectroscopy results show that the Al/In ratio of the samples increases as the TEGa flows increase in the InAlGaN quaternary growth process. High-resolution x-ray diffraction results show that the crystal quality is improved with increasing TEGa flows. Morphology of the InAlGaN/GaN heterostructures is characterized by an atomic force microscopy, and the growth mode of the InAlGaN quaternary shows a 2D island growth mode. The minimum surface roughness is 0.20 nm with the TEGa flows equaling to 3.6 $\mu$mol/min in rms. Hall effect measurement results show that the highest electron mobility $\mu$ is 1005.49 cm$^{2}$/Vs and the maximal two-dimensional electron gas is $1.63\times10^{13}$ cm$^{-2}$.
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A Mixed Host Emitting Interlayer Based on CBP:TPBi in Green Phosphorescent Organic Light-Emitting Diodes
Yao Xu, Yu-Ting Zhang, Zhi-Qi Kou, Shuang Cheng, Sheng-Li Bu
Chin. Phys. Lett. 2016, 33 (04):
048501
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DOI: 10.1088/0256-307X/33/4/048501
A series of green phosphorescent organic light-emitting diodes based on bipolar-transporting material 4,4'-bis-(carbazol-9-yl) biphenyl (CBP) are prepared. We insert a mixed host emitting interlayer (CBP$_{x}$: electron-transporting material 1,3,5-tris (N-phenylbenzimidazole-2yl) (TPBi)$_{1-x}$) in the middle of the emitting layer, and the best performance appears when $x$ is 2/3. The position of this interlayer can also affect the performance of phosphorescent organic light-emitting diodes. When this interlayer is close to the side of the electron transporting layer, the maximum value of luminance, the current efficiency and the power efficiency are 34090 cd/m$^{2}$ at 12 V, 60.6 cd/A and 56.6 lm/W, respectively.
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Low Crosstalk Three-Color Infrared Detector by Controlling the Minority Carriers Type of InAs/GaSb Superlattices for Middle-Long and Very-Long Wavelength
Dong-Wei Jiang, Wei Xiang, Feng-Yun Guo, Hong-Yue Hao, Xi Han, Xiao-Chao Li, Guo-Wei Wang, Ying-Qiang Xu, Qing-Jiang Yu, Zhi-Chuan Niu
Chin. Phys. Lett. 2016, 33 (04):
048502
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DOI: 10.1088/0256-307X/33/4/048502
We report a type-II InAs/GaSb superlattice three-color infrared detector for mid-wave (MW), long-wave (LW), and very long-wave (VLW) detections. The detector structure consists of three contacts of NIPIN architecture for MW and LW detections, and hetero-junction NIP architecture for VLW detection. It is found that the spectral crosstalks can be significantly reduced by controlling the minority carriers transport via doping beryllium in the two active regions of NIPIN section. The crosstalk detection at MW, LW, and VLW signals are achieved by selecting the bias voltages on the device. At 77 K, the cutoff wavelengths of the three-color detection are 5.3 μm (at 0 mV), 14 μm (at 300 mV) and 19 μm (at $-$20 mV) with the detectivities of 4.6$\times$10$^{11}$ cm$\cdot$Hz$^{1/2}$W$^{-1}$, 2.3$\times$10$^{10}$ cm$\cdot$Hz$^{1/2}$W$^{-1}$, and 1.0$\times$10$^{10}$ cm$\cdot$Hz$^{1/2}$W$^{-1}$ for MW, LW and VLW. The crosstalks of the MW channel, LW channel, and VLW channel are almost 0, 0.25, and 0.6, respectively.
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Off-Axis Imaging in Keel-Edge Pinhole Single Photon Emission Computed Tomography System Based on Monte Carlo Simulation
Su-Ying Li, Zhao-Heng Xie, Zhi-Yu Huang, Kun Yang, Bai-Xuan Xu, Qiu-Shi Ren
Chin. Phys. Lett. 2016, 33 (04):
048701
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DOI: 10.1088/0256-307X/33/4/048701
Monte Carlo simulation is applied to investigate the off-axis effect in keel-edge pinhole single photon emission computed tomography imaging. Aiming at finding the effective field of view (FOV) for imaging, we simulate point source in off-axis imaging (0, 4, 8 and 12 mm from the central rotation axis) of different collimator designs (channel height with 1.38, 1 and 0.5 mm) with a fixed aperture diameter. Tradeoff curves of rms resolution and sensitivity are plotted to determine the effective FOV for different channel height pinhole collimators. The parameterized model can be further incorporated into image reconstruction algorithms, which compensates for the off-axis effect and is used as a reference for multi-pinhole design.
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A Collaboration Network Model with Multiple Evolving Factors
Xiu-Lian Xu, Chun-Ping Liu, Da-Ren He
Chin. Phys. Lett. 2016, 33 (04):
048901
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DOI: 10.1088/0256-307X/33/4/048901
To describe the empirical data of collaboration networks, several evolving mechanisms have been proposed, which usually introduce different dynamics factors controlling the network growth. These models can reasonably reproduce the empirical degree distributions for a number of well-studied real-world collaboration networks. On the basis of the previous studies, in this work we propose a collaboration network model in which the network growth is simultaneously controlled by three factors, including partial preferential attachment, partial random attachment and network growth speed. By using a rate equation method, we obtain an analytical formula for the act degree distribution. We discuss the dependence of the act degree distribution on these different dynamics factors. By fitting to the empirical data of two typical collaboration networks, we can extract the respective contributions of these dynamics factors to the evolution of each networks.
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39 articles
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