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Light Hadron Production in Proton–Proton Collisions at Different LHC Energies: Measured Data versus a Model
P. Guptaroy, S. Guptaroy
Chin. Phys. Lett. 2014, 31 (08):
082501
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DOI: 10.1088/0256-307X/31/8/082501
Experiments involving proton–proton collisions at energies √sNN=0.9, 2.76 and 7 TeV in the large hadron collider produce a vast amount of high-precision data. In this work, we analyze two aspects of the measured data, viz., (i) the pT-spectra of pions, kaons, proton-antiproton at the above-mentioned energies, and (ii) some of their very important ratio behaviors, in the light of a version of the sequential chain model. The agreements between the measured data and the model-based results are generally found to be modestly satisfactory.
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A Module Test of CCDA: an Array to Select the Centrality of Collisions in Heavy Ion Collisions
FU Fen, LIN Wei-Ping, LIU Xing-Quan, HUANG Mei-Rong, WADA Roy, ZHANG Su-Ya-La-Tu, SHI Fu-Dong, HAN Rui, JIN Zeng-Xue, LIU Jian-Li, REN Pei-Pei, ZHAO Ming-Hui, CHEN Zhi-Qiang, WANG Jian-Song
Chin. Phys. Lett. 2014, 31 (08):
082502
.
DOI: 10.1088/0256-307X/31/8/082502
A test result of a module for the collision centrality detector array (CCDA), a simple detector array for the event classification of the centrality, is presented. The CsI(Tl) module has PMTs on both ends to read out signals. The beam test results indicate that it provides a good light charged particles (LCP) identification and a reasonable energy resolution. The energy spectra of LCPs are compared with the GEANT simulation.
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Velocity Transfer Spectroscopy of Rb 420 nm Transition
ZHANG Li-Guo, LIU Zhong-Zheng, TAO Zhi-Ming, LING Li, CHEN Jing-Biao
Chin. Phys. Lett. 2014, 31 (08):
083101
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DOI: 10.1088/0256-307X/31/8/083101
We propose and demonstrate the velocity transfer spectroscopy of a V-type energy structure with Rb atoms at 420 nm transition. The weak oscillator strength of a lower excited state for V-type energy structure atoms limits the high signal-to-noise ratio of atomic laser spectroscopy, which can be usually realized by optical-optical double-resonance or double-resonance optical pumping for cascade-type energy structure atoms. For 87Rb atoms, the weak 420 nm transition spectrum between the energy level of 52S1/2 and 62P3/2 is transferred to the spectrum on lower excited states at 780 nm with strong oscillator strength, which is recorded by a 780 nm probe laser. This method, which is similar to the electron-shelving detection method, at a certain degree can indirectly measure a higher excited state transition with weak oscillator strength for any V-type energy structure of atoms by transferring the transition spectrum information of the very weak oscillator strength to the strong oscillator strength in an optical-optical double-resonance configuration.
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Absolute Cross Sections for Near-Threshold Electron-Impact Excitation of the 2s 2S→2p 2P Transition of Li-Like C3+, N4+, and O5+ Ions
YANG Ning-Xuan, ZHANG Jian-Jun, DONG Chen-Zhong
Chin. Phys. Lett. 2014, 31 (08):
083401
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DOI: 10.1088/0256-307X/31/8/083401
Excitation cross sections of 1s22s 2S1/2→1s22p 2P1/2, 3/2 transition among the fine-structure levels in Li-like C3+, N4+, and O5+ ions are calculated for energies of the near-threshold by using the relativistic distorted-wave program REIE06. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are studied in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. The results of the Li-like C3+ ion settle the discrepancy between several previous experiments by using the crossed-beams fluorescence method, in good agreement with the measurements of Savin et al. Moreover, the results in Li-like N4+, and O5+ ions are compared with the previous experiments, and a good agreement is obtained.
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Long-Term Stabilization of Carrier-Envelope Phase for Few Cycles Ti:Sapphire Laser Amplifier
ZHANG Wei, TENG Hao, YUN Chen-Xia, YE Peng, ZHAN Min-Jie, ZHONG Shi-Yang, HE Xin-Kui, WANG Li-Feng, WEI Zhi-Yi
Chin. Phys. Lett. 2014, 31 (08):
084204
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DOI: 10.1088/0256-307X/31/8/084204
We realize a long-term carrier-envelope phase (CEP) stabilization for a chirped pulse amplified Ti:sapphire laser by locking the oscillator and amplifier independently. Based on the measurement of CEP by employing f-to-2f interference technique between the octave-spanning spectrum which is generated from a rare gas filled hollow fiber, continuous locking time up to 7.2 h with 85 mrad fluctuation is demonstrated. Finely compensating the dispersion by a set of chirped mirrors, quasi-mono cycle pulses as shorter as 3.8 fs are obtained. Further experimental research on high harmonic generation dependence on CEP shown the waveform of laser pulses has been successfully controlled.
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Passive Phase Locking of Three Nanosecond Fiber Amplifiers Using a Dammann Grating Spatial Filter
YANG Yi-Feng, ZHENG Ye, HE Bing, ZHOU Jun, LIU Hou-Kang, HU Man, WEI Yun-Rong, LOU Qi-Hong
Chin. Phys. Lett. 2014, 31 (08):
084206
.
DOI: 10.1088/0256-307X/31/8/084206
A passive coherent beam combination of three nanosecond Yb-doped fiber amplifiers by an all-optical feedback loop is realized by a Dammann grating intracavity spatial filter. By using this diffractive-optics-based spatial filtering technique, three tile-aperture laser beams are phase-locked with a peak power of 1.02 kW. The width of the combined pulses is 9.6 ns, and the repetition frequency is 2.208 MHz. The visibility of the far-field interference pattern is up to 82.9%. The results show that this approach can scale to larger arrays and higher powers.
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Anode and Cathode Spots in High-Voltage Nanosecond-Pulse Discharge Initiated by Runaway Electrons in Air
SHAO Tao, Victor F. Tarasenko, YANG Wen-jin, Dmitry V. Beloplotov, ZHANG Cheng, Mikhail I. Lomaev, YAN Ping, Dmitry A. Sorokin
Chin. Phys. Lett. 2014, 31 (08):
085201
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DOI: 10.1088/0256-307X/31/8/085201
We report the experimental results with nanosecond-pulse discharges formed in the air gap between a flat electrode and a sharp electrode. The appearance of anode and cathode spots on the electrodes is studied experimentally. It is considered that bright spots on the flat cathode with positive polarity of the sharp electrode are formed due to the explosive electron emission on the cathode and the dynamic displacement current in the gap. It is also shown that with negative polarity of the sharp electrode, bright spots on the flat anode are formed after changing the polarity of the flat electrode due to the discharge oscillatory mode. Under these conditions, the explosive electron emission firstly forms on the sharp cathode. With negative polarity of the sharp electrode of the subnanosecond-pulse pulser, the runaway electron beam current is measured behind the anode foil with a time resolution of no more than 100 ps.
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Radiation Induced Optical Absorption of Cubic Lead Fluoride Crystals and the Effect of Annealing
REN Guo-Hao, CHEN Xiao-Feng, LI Huan-Ying, WU Yun-Tao, SHI Hong-Sheng, QIN Lai-Shun
Chin. Phys. Lett. 2014, 31 (08):
086102
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DOI: 10.1088/0256-307X/31/8/086102
Transparent and colorless lead fluoride crystals with sizes of 20×20×20 (mm3) are irradiated with several doses of γ-rays from a 60Co source. Their transmittance spectra before and after irradiation are measured, and a new parameter ΔT=Tb?Ta is defined to evaluate the irradiation damage. Three optical absorption bands peaking at 270 nm, 370 nm and 500 nm are found in the plots of ΔT versus wavelength, and their intensities increase with the irradiation dose. These optical absorption bands, except the one at 270 nm, can recover spontaneously with time. Thermal annealing treatment can enhance this recovery of the transmittance, while the optimum annealing temperature for different samples depends on the irradiation dose.
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Effects of 1.0–11.5 MeV Electron Irradiation on GaInP/GaAs/Ge Triple-junction Solar Cells for Space Applications
WANG Rong, LU Ming, YI Tian-Cheng, YANG Kui, JI Xiao-Xia
Chin. Phys. Lett. 2014, 31 (08):
086103
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DOI: 10.1088/0256-307X/31/8/086103
GaInP/GaAs/Ge triple-junction solar cells are irradiated with 1.0, 1.8, and 11.5 MeV electrons with fluence ranging up to 3×1015, 3×1015, and 3×1014 cm?2, respectively. Their performance degradation effects are analyzed by using current-voltage characteristics, spectral response measurements, and electron irradiation-induced displacements. The degradation rates of the maximum power and the spectral response of the solar cells increase with the electron fluence, and also increase with the increasing electron energy. It is observed that the spectral response of the GaAs middle cell degrades more significantly than that of the GaInP top cell.
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Cavitation Simulation with Consideration of the Viscous Effect at Large Liquid Temperature Variation
YU An, LUO Xian-Wu, JI Bin, HUANG Ren-Fang, HIDALGO Victor, KIM Song Hak
Chin. Phys. Lett. 2014, 31 (08):
086401
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DOI: 10.1088/0256-307X/31/8/086401
The phase change due to cavitation is not only driven by the pressure difference between the local pressure and vapor saturated pressure, but also affected by the physical property changes in the case of large liquid temperature variation. The present work simulates cavitation with consideration of the viscous effect as well as the local variation of vapor saturated pressure, density, etc. A new cavitation model is developed based on the bubble dynamics, and is applied to analyze the cavitating flow around an NACA0015 hydrofoil at different liquid temperatures from 25°C to 150°C. The results by the proposed model, such as the pressure distribution along the hydrofoil wall surface, vapor volume fraction, and source term of the mass transfer rate due to cavitation, are compared with the available experimental data and the numerical results by an existing thermodynamic model. It is noted that the numerical results by the proposed cavitation model have a slight discrepancy from the experimental results at room temperature, and the accuracy is better than the existing thermodynamic cavitation model. Thus the proposed cavitation model is acceptable for the simulation of cavitating flows at different liquid temperatures.
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Pairing Symmetry of Heavy Fermion Superconductivity in the Two-Dimensional Kondo–Heisenberg Lattice Model
LIU Yu, ZHANG Guang-Ming, YU Lu
Chin. Phys. Lett. 2014, 31 (08):
087102
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DOI: 10.1088/0256-307X/31/8/087102
In the two-dimensional Kondo–Heisenberg lattice model away from half-filled, the local antiferromagnetic exchange coupling can provide the pairing mechanism of quasiparticles via the Kondo screening effect, leading to the heavy fermion superconductivity. We find that the pairing symmetry strongly depends on the Fermi surface (FS) structure in the normal metallic state. When JH/JK is very small, the FS is a small hole-like circle around the corner of the Brillouin zone, and the s-wave pairing symmetry has a lower ground state energy. For the intermediate coupling values of JH/JK, the extended s-wave pairing symmetry gives the favored ground state. However, when JH/JK is larger than a critical value, the FS transforms into four small hole pockets crossing the boundary of the magnetic Brillouin zone, and the d-wave pairing symmetry becomes more favorable. In that regime, the resulting superconducting state is characterized by either a nodal d-wave or nodeless d-wave state, depending on the conduction electron filling factor as well. A continuous phase transition exists between these two states. This result may be related to the phase transition of the nodal d-wave state to a fully gapped state, which has recently been observed in Yb-doped CeCoIn5.
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Thermodynamics of the CaLi2 Superconductor in the Vicinity of Structural Phase Transition
D. Szczęśniak, R. Szczęśniak
Chin. Phys. Lett. 2014, 31 (08):
087401
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DOI: 10.1088/0256-307X/31/8/087401
Eliashberg formalism is used to investigate the thermodynamic properties of the high-pressure superconducting phase of the CaLi2 compound. In particular, our calculations are conducted in the vicinity of the C2/c →P21/c pressure-induced structural phase transition. We show that, in the considered case, the value of the Coulomb pseudopotential is high and equals 0.26. Moreover, we give the analysis of the thermodynamic parameters such as the superconducting transition temperature (TC), the energy gap at the Fermi level (2Δ(0)), the thermodynamic critical field (HC), and the specific heat of superconducting (CS) and normal (CN) states. We emphasize that the characteristic dimensionless ratios RΔ ≡2Δ(0)/kBTC, RH≡TCCN(TC)/HC2(0), and RC≡ΔC(TC)/CN(TC), have values that are beyond the predictions of the BCS theory in the case of the considered material. In particular, RΔ=3.85, RH=0.161, and RC=1.86. Furthermore, it is proved that the effective electron mass is high and equals 2.02me, where me denotes the bare electron mass.
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The Phase Stability, Thermodynamics Properties and Electronic Structures of L12-Type Al3Sc and Al3Y under High Pressures
DUAN Yong-Hua, HUANG Bo, SUN Yong, PENG Ming-Jun, ZHOU Sheng-Gang
Chin. Phys. Lett. 2014, 31 (08):
088101
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DOI: 10.1088/0256-307X/31/8/088101
The phase stability, thermodynamics properties and electronic structures of L12-Al3Sc and Al3Y compounds under pressure up to 40 GPa are investigated by using first-principles within a local density approximation. The results of formation energies show that Al3Sc is more stable than Al3Y and the stability of Al3Sc will be better with the increasing pressure. The Gibbs free energy, heat capacity, Debye temperature and thermal expansion coefficient are also investigated. The decreasing density of states at the Fermi level and the strengthening Sc/Y-d orbital hybridization with Al (s, p) under high pressure lead to the observed increase of the structural stability for L12-Al3Sc and Al3Y under pressures.
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Enhanced Depth of Lift-off Pattern Defined with Soft Mold Ultraviolet Nanoimprint by Multi-Layer Masks
WANG Zhi-Hao, LIU Wen, ZUO Qiang, WANG Lei, ZHAO Yan-Li, XU Zhi-Mou
Chin. Phys. Lett. 2014, 31 (08):
088102
.
DOI: 10.1088/0256-307X/31/8/088102
The traditional lift-off process can hardly be carried out in ultraviolet nanoimprint defined patterns due to the poor solubility of the ultraviolet resist. Moreover, the depth of lift-off pattern defined by an ultraviolet nanoimprint is limited by that of the soft mold. In this work, a modified nanoimprint process by a multi-layer mask method is introduced to enhance the depth of the final lift-off pattern. Pillar photonic crystal is fabricated from the hole pattern defined by NIL to prove the pattern-reversal capability. On its basis, combining the features of overetching technology and the lateral diffusion phenomenon in the metal depositing process, pillar-shaped photonic crystal stamps with different duty cycles have been fabricated by adjusting the etching time of the lift-off layer. Based on this process, a 50-nm line width metal grating is fabricated from a soft stamp with an aspect ratio as low as 1.
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Photoluminescence of Nanoporous GaN Films Prepared by Electrochemical Etching
WANG Qiang, JI Zi-Wu, XIAO Hong-Di, LV Hai-Yan, LI Jian-Fei, XU Xian-Gang, LV Yuan-Jie, FENG Zhi-Hong
Chin. Phys. Lett. 2014, 31 (08):
088103
.
DOI: 10.1088/0256-307X/31/8/088103
Nanoporous (NP) GaN is prepared by electrochemical etching on a GaN epilayer grown on a sapphire substrate by metal-organic chemical vapor deposition. Scanning electron microscopy reveals that the average pore diameter and inter-pore spacing are approximately 25 and 45 nm, respectively. The photoluminescence (PL) spectra show that in contrast to the initial as-grown GaN epilayer, the NP GaN exhibits a high near-band-edge UV intensity, significant relaxation of compressive strain, and a lower yellow luminescence intensity. Both the line shape and line width of the PL spectra are almost the same for these two samples. The high quality of the NP GaN can be explained by the enhancement of the PL extraction efficiency and the decrease of impurity and defect density after etching.
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Nano-Crystalline Diamond Films with Pineapple-Like Morphology Grown by the DC Arcjet vapor Deposition Method
LI Bin, ZHANG Qin-Jian, SHI Yan-Chao, LI Jia-Jun, LI Hong, LU Fan-Xiu, CHEN Guang-Chao
Chin. Phys. Lett. 2014, 31 (08):
088104
.
DOI: 10.1088/0256-307X/31/8/088104
A nano-crystlline diamond film is grown by the dc arcjet chemical vapor deposition method. The film is characterized by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and Raman spectra, respectively. The nanocrystalline grains are averagely with 80 nm in the size measured by XRD, and further proven by Raman and HRTEM. The observed novel morphology of the growth surface, pineapple-like morphology, is constructed by cubo-octahedral growth zones with a smooth faceted top surface and coarse side surfaces. The as-grown film possesses (100) dominant surface containing a little amorphous sp2 component, which is far different from the nano-crystalline film with the usual cauliflower-like morphology.
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46 articles
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