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Study on Congestion and Bursting in Small-World Networks with Time Delay from the Viewpoint of Nonlinear Dynamics
LIU Yan, LIU Li-Guang, WANG Hang
Chin. Phys. Lett. 2012, 29 (6):
060504
.
DOI: 10.1088/0256-307X/29/6/060504
The small-world network model represented by a set of evolution equations with time delay is used to investigate the nonlinear dynamics of networks, and the nature of instability phenomena in traffic, namely, congestion and bursting in the networks, are studied and explained from bifurcation analysis. Then, the governing equation in the vector field is further reduced into a map, and the ensuing period-doubling bifurcation, sequence of period-doubling bifurcation and period-3 are studied intuitively. The existence of chaos is verified numerically. In particular, the influences of time delay on the nonlinear dynamics are presented. The results show that there are a rich variety of nonlinear dynamics related to the intermittency of the traffic flows in the system, and the results can gain a fundamental understanding of the instability in the networks, and the time delay can be used as a key parameter in the control of the systems.
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Influence of Passivation Layers for Metal Grating-Based Quantum Well Infrared Photodetectors
LIU Dong, FU Yong-Qi, YANG Le-Chen, ZHANG Bao-Shun, LI Hai-Jun, FU Kai, XIONG Min
Chin. Phys. Lett. 2012, 29 (6):
060701
.
DOI: 10.1088/0256-307X/29/6/060701
To improve absorption of quantum well infrared photodetectors (QWIPs), a coupling layer with metallic grating is designed and fabricated above the quantum well. The metal grating is composed of 100 nm Au film on top, and a 20-nm Ti thin layer between the Au film and the sapphire substrate is coated as an adhesion/buffer layer. To protect the photodetector from oxidation and to decrease leakage, a SiO2 film is deposited by means of plasma-enhanced chemical vapor deposition. A value of about 800 nm is an optimized thickness for the SiO2 applied in the metallic grating?based mid-infrared QWIP. In addition, a QWIP passivation layer is studied experimentally. The results demonstrate that the contribution from the layer is positive for metal grating coupling with the quantum well. The closer the permittivity of the two dielectric layers (SiO2 and the passivation layers), and the closer the two transmission peaks, the greater the QWIP enhancement will be.
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The Symmetry Energy from the Neutron-Rich Nucleus Produced in the Intermediate-Energy 40,48Ca and 58,64Ni Projectile Fragmentation
MA Chun-Wang, PU Jie, WANG Shan-Shan, WEI Hui-Ling
Chin. Phys. Lett. 2012, 29 (6):
062101
.
DOI: 10.1088/0256-307X/29/6/062101
In the framework of a modified Fisher model, using the isobaric yield ratio method, we investigate the fragments produced in the 140 A MeV 40,48Ca+9Be and 58,64Ni+9Be projectile fragmentation reactions. Using different approximation methods, asym/T (the ratio of symmetry?energy coefficient to temperature) of symmetric and neutron-rich fragments are extracted. It is found that asym/T of fragments depend on the reference nucleus and the neutron excess of fragments. The asym/T of the isobar decreases when the neutron?excess of the isobar increases, while for a fragment with the same neutron-excess, asym/T increases as the mass of the fragment increases but saturate when the mass of the fragment becomes larger.
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High Spin States of 113In
MA Ke-Yan, LU Jing-Bin, YANG Dong, LI Jian, WANG Hui-Dong, LIU Yun-Zuo, WU Xiao-Guang, ZHU Li-Hua, ZHENG Yun, HE Chuang-Ye
Chin. Phys. Lett. 2012, 29 (6):
062102
.
DOI: 10.1088/0256-307X/29/6/062102
Level structures of 113In are studied through the fusion-evaporation reaction 110Pd(7Li,4n)113In at a beam energy of 50 MeV. Two new bands are established for the first time. Here the ΔI = 2 band based on proton excitation is assigned to the πg9/2-2⊗νh11/22d5/2 configuration. In addition, the backbending associated with the additional aligned h11/2 neutron pair is found in the negative parity yrast band. The experimental results are compared with self-consistent tilted axis cranking relativistic mean field calculations. Several decay paths of the πh11/2 intruder band are established, by which the level energies and spins of the πh11/2 intruder band are determined. The bandcrossing delay of the πh11/2 intruder bands around the Z=50 shell and the dynamic moment of inertia of the πg9/2-1⊗νh11/22 bands in 113,115,117,119In are studied systematically.
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High-Spin Structure in Odd-Odd 160Lu Nucleus
WANG Lie-Lin, LU Jing-Bin, YANG Dong, MA Ke-Yan, ZHOU Yin-Hang, YIN Li-Chang, WU Xiao-Guang, WEN Shu-Xian, LI Guang-Sheng, YANG Chun-Xiang
Chin. Phys. Lett. 2012, 29 (6):
062103
.
DOI: 10.1088/0256-307X/29/6/062103
The high-spin states of 160Lu are populated by the fusion-evaporation reaction 144Sm(19F,3n)160Lu at beam energies of 90 and 106 MeV. A new level scheme of 160Lu is established. A possible isomeric state based on the πh11/2⊗νh9/2 configuration is observed. The new decoupled band with the configuration of πd3/2[411]1/2+⊗νi13/2[660]1/2+ is established, and the configurations of these similar decoupled bands in the neighboring odd-odd 162-166Lu nuclei are suggested. A positive parity coupled band is assigned as the πd5/2 [402]5/2+⊗νi13/2[660]1/2+ configuration.
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Radio-Frequency Power Test of a Four-Rod RFQ Accelerator for PKUNIFTY
ZENG Hong-Jin, LIU Ge, LU Yuan-Rong, CHEN Wei, ZHOU Quan-Feng, ZHU Kun, XIA Wen-Long, SHI Ben-Liang, GAO Shu-Li, YAN Xue-Qing, GUO Zhi-Yu, CHEN Jia-Er
Chin. Phys. Lett. 2012, 29 (6):
062901
.
DOI: 10.1088/0256-307X/29/6/062901
A four-rod radio frequency quadruple (RFQ) accelerator is designed, manufactured, installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY). This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88 mm is operating at 201.5 MHz in pulse mode. An inter-electrode voltage of 70 kV is needed to accelerate the injected 50 keV 40 mA D+ ions up to 2 MeV. We present the rf system, high rf power feeder design, lower rf measurements and higher rf power test. Especially, the rf commissioning was carried out with rf power up to ~280 kW and duty factor of 4%. The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV. It is found that the specific shunt impedance of the RFQ cavity reaches 52.7 kΩ⋅m.
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All-Fiber Gain-Switched Thulium-Doped Fiber Laser Pumped by 1.558μm Laser
ZHOU Ren-Lai, ZHAO Jie, YUANG-Chi, CHEN Zhao-Yu, JU You-Lun, WANG Yue-Zhu
Chin. Phys. Lett. 2012, 29 (6):
064201
.
DOI: 10.1088/0256-307X/29/6/064201
We present an all-fiber gain-switched thulium (Tm) doped fiber laser operating in the eye-safe region at 1940 nm. The fibre Bragg gratings (FBGs) inscribed by phase mask technology are used as cavity mirrors, and the transmission spectra of FBGs are also measured. The output characteristics are studied at pulse repetition frequencies of 10, 20 and 30 kHz, and the maximum output powers of 28.9, 67.0 and 71.0 mW are achieved under incident pump powers of 122, 247 and 250 mW. The narrowest pulse width of 29 ns and shortest pulse built-time of 140 ns are obtained at 10 kHz. The relation between pulse built-time and cavity length are discussed.
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Characteristic Optimization of 1.3 μm High-Speed MQW InGaAsP-AlGaInAs Lasers
MAO Yi-Wei, WANG Yao, CHEN Yang-Hua, XUE Zheng-Qun, LIN Qi, DUAN Yan-Min, SU Hui
Chin. Phys. Lett. 2012, 29 (6):
064204
.
DOI: 10.1088/0256-307X/29/6/064204
We investigate 1.3 μm multi quantum-well (MQW) lasers with InGaAsP (well) and InGaAlAs (barrier) on InP for high speed application, compared to the typical structures of InGaAsP (well)-InGaAsP (barrier)/InP and InGaAlAs (well)-InGaAlAs (barrier)/InP with the same quaternary in the well and barrier. We calculate the characteristics of band offset and gain of InGaAsP-AlGaInAs quantum wells (QWs). The advances of the new QW design are mainly rooted in the large ratio between conduction-band and valence-band offsets (ΔEc:ΔEv=7:1), higher than the typical value of 4:6 in InGaAsP-InGaAsP and 7:3 in InGaAlAs-InGaAlAs for 1.3 μm lasers. Due to the low confinement energy of holes, non-uniformity of carrier distribution over multi-InGaAsP-AlGaInAs QWs is significantly reduced. The enhancement of high-speed performance of InGaAsP-AlGaInAs MQW lasers is investigated in terms of turn-on oscillation.
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A Polarization-Adjustable Picosecond Deep-Ultraviolet Laser for Spin- and Angle-Resolved Photoemission Spectroscopy
ZHANG Feng-Feng, YANG Feng, ZHANG Shen-Jin, WANG Zhi-Min, XU Feng-Liang, PENG Qin-Jun, ZHANG Jing-Yuan, WANG Xiao-Yang, CHEN Chuang-Tian, XU Zu-Yan
Chin. Phys. Lett. 2012, 29 (6):
064206
.
DOI: 10.1088/0256-307X/29/6/064206
We report on a polarization-adjustable picosecond deep-ultraviolet (DUV) laser at 177.3 nm. The DUV laser was produced by second harmonic generation from a mode-locked laser at 355 nm in nonlinear optical crystal KBBF. The laser delivered a maximum average output power of 1.1 mW at 177.3 nm. The polarization of the 177.3 nm beam was adjusted with linear and circular polarization by means of λ/4 and λ/2 wave plates. To the best of our knowledge, the laser has been employed as the circularly polarized and linearly polarized DUV light source for a spin- and angle-resolved photoemission spectroscopy with high resolution for the first time.
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Self-Trapping of Three-Dimensional Spatiotemporal Solitary Waves in Self-Focusing Kerr Media
YANG Zheng-Ping, ZHONG Wei-Ping
Chin. Phys. Lett. 2012, 29 (6):
064211
.
DOI: 10.1088/0256-307X/29/6/064211
We theoretically demonstrate that Kerr media under self-focusing nonlinearity support three-dimensional spatiotemporal solitary waves in various patterns, such as necklace-, disk-, and vortex-ring shapes. The structures of these solitons are defined by the set of radial, orbital, and azimuthal quantum numbers, (n,l,m), respectively.
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The Laser Action of a Yb:CLNGG Crystal with an Efficiency Approaching Its Quantum Defect Imposed Limit
ZHOU Zhi-Chao, TIAN Xue-Ping, DAI Qi-Biao, HAN Wen-Juan, HUANG Jia-Yin, LIU Jun-Hai, ZHANG Huai-Jin
Chin. Phys. Lett. 2012, 29 (6):
064212
.
DOI: 10.1088/0256-307X/29/6/064212
Continuous-wave laser operation is demonstrated at room temperature with a new disordered Yb:CLNGG crystal. A maximum output power of 5.05 W is generated with 7.8 W of pump power absorbed in the crystal, resulting in an optical-to-optical efficiency of 65%, whereas the slope efficiency is determined to be 92%, approaching the limit imposed by the quantum defect in the laser emission process.
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Large-Eddy Simulation of Underexpanded Supersonic Swirling Jets
WANG Guo-Lei, LU Xi-Yun
Chin. Phys. Lett. 2012, 29 (6):
064704
.
DOI: 10.1088/0256-307X/29/6/064704
A large-eddy simulation of underexpanded supersonic swirling jets issuing into a quiescent environment was carried out for two typical swirl numbers. The corresponding nonswirling jet was also calculated for comparison and validation against the experimental data. The swirling effect on the various fundamental mechanisms that dictate the intricate flow phenomena, including flow features, shock cell structures, jet spreading characteristics and turbulence behaviors, was carefully analyzed, and it is found that the first shock cell length is reduced in the swirling jet in comparison with the nonswirling jet. A recirculation zone is formed in the high swirl number case, and the jet spreads quickly in the radial direction due to the swirling effect. Moreover, intensive turbulent fluctuations are generated along the jet shear layer and at the end of the jet potential core, which will be helpful in the mixing process. The obtained results provide a physical insight into understanding the mechanisms relevant to underexpanded supersonic swirling jets.
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Cross-over of the Plasticity Mechanism in Nanocrystalline Cu
YUE Yong-Hai, WANG Li-Hua, ZHANG Ze, HAN Xiao-Dong
Chin. Phys. Lett. 2012, 29 (6):
066201
.
DOI: 10.1088/0256-307X/29/6/066201
Via in situ uniaxial tensile tests in a high-resolution transmission electron microscope, we directly observed a cross-over of plastic deformation mechanisms in a nanocrystalline (nc) Cu thin film containing nano-twin lamellae. For a certain twin lamellae length, the twin lamellae with a larger thickness emit dislocations inclined (Schmidt-factor dislocations, i.e., S-dislocations) toward the twin boundaries. Upon decreasing the twin lamellae thickness to a critical value, such as approximately 15 nm, the plasticity switches toward emission of twinning partial dislocations (T-dislocations) parallel to the twin planes that cause migration of the twin boundaries. The critical twin thickness value also depends on the length of the twin. These results provide direct evidence for the strengthening and softening mechanisms in nano-twinning structured metals.
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Nano-Metal Film Thermal Conductivity Measurement by using the Femtosecond Laser Pump and Probe Method
ZHU Li-Dan, SUN Fang-Yuan, ZHU Jie, TANG Da-Wei, LI Yu-Hua, GUO Chao-Hong
Chin. Phys. Lett. 2012, 29 (6):
066301
.
DOI: 10.1088/0256-307X/29/6/066301
Heat management at nanoscale is a critical issue across many areas of science and engineering, where the size effect of thermal properties plays an important role. We measure the transient thermoreflectance signals of thin metal films with thicknesses from 50 to 200 nm by using the femtosecond laser pump and probe method, and the experimental data are combined with the parabolic two-step model to enable us to measure thermal conductivity of the thin metal films. The measurement results of Ni and Al films show that, in the thickness range from tens to hundreds of nanometer, the thermal conductivity increases with the increasing thicknesses of the films, which agrees well with the previous conclusions.
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The Structural Modification of LiTaO3 Crystal Induced by 100-keV H-ion Implantation
PANG Li-Long, WANG Zhi-Guang, YAO Cun-Feng, ZANG Hang, LI Yuan-Fei, SUN Jian-Rong, SHEN Tie-Long, WEI Kong-Fang, ZHU Ya-Bin, SHENG Yan-Bin, CUI Ming-Huan, JIN Yun-Fan
Chin. Phys. Lett. 2012, 29 (6):
066801
.
DOI: 10.1088/0256-307X/29/6/066801
The effects of 100 keV H-ion implantation on the structure of LiTaO3 crystal are investigated by Raman and UV/VIS/NIR spectroscopies. The implantation fluence is in the range from 1.0×1013 to 1.0×1017 H+/cm2. The experimental results show the dependence of the crystal structure on ion fluence. It is found that the structural modification of the LiTaO3 crystal is due to two processes. One is H?ions occupying lithium vacancies (VLi), which is predominant at a fluence less than 1.0×1014 H+/cm2. This process causes the reduction of negative charge centers in the crystal and relaxation of distortion in the local lattice structure. The other is the influence of defects created during implantation, which plays a dominant role gradually in the structural modification at a fluence larger than 1.0×1015 H+/cm2.
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Modulation of Step Heights of Thin Pb Films by the Quantum Size Effect Observed by Non-Contact Atomic Force Microscopy
MAO Han-Qing, LI Na, CHEN Xi, XUE Qi-Kun
Chin. Phys. Lett. 2012, 29 (6):
066802
.
DOI: 10.1088/0256-307X/29/6/066802
Using a home-made Q-plus sensor, simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) measurements were performed on the wedge-shaped Pb islands grown on Si(111)-7-7. Atomic resolved AFM images were observed. The contrast of AFM topography shows no dependence on the sample bias (tip is grounded), while the simultaneously obtained tunneling current image exhibits strong bias dependence due to quantum well states (QWS). Furthermore, In the AFM mode, neighboring Pb films with one monolayer (ML) thickness difference within the same Pb island show the same apparent height, which means that the apparent step heights of Pb films oscillate with a bilayer periodicity, being consistent with previous observations by helium atom scattering, x-ray diffraction, and STM. The possible reasons underlying the oscillation of apparent step heights in AFM topography are discussed.
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Effect of Cleaving Temperature on the Surface and Bulk Fermi Surface of Sr2RuO4 Investigated by High Resolution Angle-Resolved Photoemission
LIU Shan-Yu, ZHANG Wen-Tao, WENG Hong-Ming, ZHAO Lin, LIU Hai-Yun, JIA Xiao-Wen, LIU Guo-Dong, DONG Xiao-Li, ZHANG Jun, MAO Zhi-Qiang, CHEN Chuang-Tian, XU Zu-Yan, DAI Xi, FANG Zhong, ZHOU Xing-Jiang
Chin. Phys. Lett. 2012, 29 (6):
067401
.
DOI: 10.1088/0256-307X/29/6/067401
High resolution angle-resolved photoemission measurements are carried out to systematically investigate the effect of cleaving temperature on the electronic structures and Fermi surfaces of Sr2RuO4. Unlike previous reports, which found that a high cleaving temperature can suppress the surface Fermi surface, we find that the surface Fermi surface remains obvious and strong in Sr2RuO4 cleaved at high temperature, even at room temperature. This indicates that cleaving temperature is not a key effective factor in suppressing surface bands. On the other hand, the bulk bands can be enhanced in an aged surface of Sr2RuO4 that has been cleaved and held for a long time. We have also carried out laser ARPES measurements on Sr2RuO4 by using a vacuum ultra-violet laser (photon energy at 6.994 eV) and found an obvious enhancement of bulk bands even for samples cleaved at low temperature. This information is important for realizing an effective approach to manipulating and detecting the surface and bulk electronic structure of Sr2RuO4. In particular, the enhancement of bulk sensitivity, along with the super-high instrumental resolution of VUV laser ARPES, will be advantageous in investigating fine electronic structure and superconducting properties of Sr2RuO4 in the future.
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NMR Study of Superconductivity and Spin Fluctuations in Hole-Doped Superconductor Ca1-xNaxFe2As2 (Tc=32 K)
MA Long, ZHANG Jin-Shan, WANG Du-Ming, HE Jun-Bao, XIA Tian-Long, CHEN Gen-Fu, YU Wei-Qiang
Chin. Phys. Lett. 2012, 29 (6):
067402
.
DOI: 10.1088/0256-307X/29/6/067402
We report both 23Na and 75As nuclear magnetic resonance (NMR) studies on hole?doped Ca1-xNaxFe2As2 superconducting single crystals (x≈0.67) with the superconducting temperature Tc=32 K. Singlet superconductivity is suggested by a sharp drop of the Knight shift 75K below Tc. The spin-lattice relaxation rate 1/T1 does not show the Slichter–Hebel coherence peak, which suggests an unconventional pairing. The penetration depth is estimated to be 0.24 μm at temperature T=2 K. Here 1/75T1T shows an anisotropic behavior and a prominent low-temperature upturn , with 75T1 denoting the 75As spin-lattice relaxation time and T the temperature, which indicates strong low-energy antiferromagnetic spin fluctuations and supports a magnetic origin of superconductivity.
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The Influences of Temperature, Concentration and Pressure Uncertainties on the Measurement Results of Wavelength Modulation Spectroscopy
CHE Lu, DING Yan-Jun, PENG Zhi-Min
Chin. Phys. Lett. 2012, 29 (6):
067801
.
DOI: 10.1088/0256-307X/29/6/067801
Gas temperature, species concentration, and pressure uncertainties inevitably affect the measurement results of wavelength modulation spectroscopy. We analyze and calculate the influences of these uncertainties on CO2 concentration and temperature measurement results. Calculation results show that uncertainties in the pressure and CO2 concentration have little influence on temperature measurement results. On the contrary, CO2 concentration measurement results are notably influenced by pressure uncertainty, and greatly influenced by temperature uncertainty. To solve these problems in the temperature, species concentration, and pressure uncertainties, we take the experimental data from the previous study and analyze them using the iteration method with the purpose of obtaining the optimal values of gas temperature and CO2 concentration.
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Green Emission from a Strain-Modulated InGaN Active Layer
WANG Guo-Biao, XIONG Huan, LIN You-Xi, FANG Zhi-Lai, KANG Jun-Yong, DUAN Yu, SHEN Wen-Zhong
Chin. Phys. Lett. 2012, 29 (6):
068101
.
DOI: 10.1088/0256-307X/29/6/068101
Strain-induced quantum dots (QDs) like island formations are demonstrated to effectively suppress pits/dislocation generation in high indium content (26.8%) InGaN active layers. In addition to the strain redistribution in the QD-like islands, strain modulation on the InGaN active layers by using the GaN island capping is employed to form an increased surface potential barrier around the dislocation cores, which inhibits the carrier transport to the surrounding dislocations. Cathodoluminescence shows distinct double-peak emissions at 503 nm and 444 nm, corresponding to the In-rich QD-like emission and the normal quantum well emission, respectively. The QD-like emission becomes dominated in photoluminescence due to the carrier localization effect of In-rich InGaN QDs at relatively low "carrier injection current". Accordingly, green emission may be enhanced by the following origins: (1) reduction in pits/dislocations density, (2) carrier localization and strain reduction in QDs, (3) strain modulation by GaN island capping, (4) enhanced light extraction with faceted GaN islands on the surface.
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82 articles
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