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Fermi-Decay Law of Bose–Einstein Condensate Trapped in an Anharmonic Potential
LIU Yuan,JIA Ya-Fei,LI Wei-Dong**
Chin. Phys. Lett. 2012, 29 (4):
040304
.
DOI: 10.1088/0256-307X/29/4/040304
The Fermi-decay law of Bose–Einstein condensate, which is trapped by a cigar-shaped anharmonic trap and subjected to a weak random perturbation, is investigated by numerically calculating quantum fidelity (Loschmidt echo), to reveal the coherence loss of the condensate. We find that there are three indispensable factors, anharmonic trap, weak random perturbation and nonlinear interaction, in charging of the Fermi-decay law. The anharmonic trap creates anharmonic oscillations, and the weak random perturbation causes coherence loss by disturbing their coherent oscillations, while the nonlinear interaction enhances the loss to the Fermi-decay law. Based on the Fermi-decay law, some suggestions are presented to prolong the coherent time during coherently manipulating condensates.
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Boundary Conditions for NHEK through Effective Action Approach
CHEN Bin,NING Bo**,ZHANG Jia-Ju
Chin. Phys. Lett. 2012, 29 (4):
041101
.
DOI: 10.1088/0256-307X/29/4/041101
We study the asymptotic symmetry group (ASG) of the near horizon geometry of extreme Kerr black hole through the effective action approach developed by Porfyriadis and Wilczek (arXiv:1007.1031v1[gr-qc]). By requiring a finite boundary effective action, we derive a new set of asymptotic Killing vectors and boundary conditions, which are much more relaxed than the ones proposed by Matsuo Y et al. [Nucl. Phys. B 825 (2010) 231], and still allow a copy of a conformal group as its ASG. In the covariant formalism, the asymptotic charges are finite, with the corresponding central charge vanishing. By using the quasi-local charge and introducing a plausible cut-off, we find that the higher order terms of the asymptotic Killing vectors, which could not be determined through the effective action approach, contribute to the central charge as well. We also show that the boundary conditions suggested by Guica et al. [Phys. Rev. D 80 (2009) 124008] lead to a divergent first-order boundary effective action.
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Odd Systems in Deformed Relativistic Hartree Bogoliubov Theory in Continuum
LI Lu-Lu,MENG Jie,P. Ring,ZHAO En-Guang,ZHOU Shan-Gui,**
Chin. Phys. Lett. 2012, 29 (4):
042101
.
DOI: 10.1088/0256-307X/29/4/042101
In order to describe the exotic nuclear structure in unstable odd-A or odd−odd nuclei, the deformed relativistic Hartree Bogoliubov theory in continuum is extended to incorporate the blocking effect due to the odd nucleon. For a microscopic and self-consistent description of pairing correlations, continuum, deformation, blocking effects, and the extended spatial density distribution in exotic nuclei, the deformed relativistic Hartree Bogoliubov equations are solved in a Woods–Saxon basis in which the radial wave functions have a proper asymptotic behavior at large r. The formalism and numerical details are provided. The code is checked by comparing the results with those of spherical relativistic continuum Hartree Bogoliubov theory in the nucleus 19O. The prolate deformed nucleus 15C is studied by examining the neutron levels and density distributions.
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Measured and Simulated Performance of a Four-Segmented Clover Detector
ZHANG Ning-Tao**,LEI Xiang-Guo,ZHANG Yu-Hu,ZHOU Xiao-Hong,LIU Min-Liang,GUO Ying-Xiang,FANG Yong-De,LI Shi-Cheng,ZHOU Hou-Bing,DING Bing,WANG Hai-Xia,WU Xiao-Guang,HE Chuang-Ye,ZHENG Yun
Chin. Phys. Lett. 2012, 29 (4):
042901
.
DOI: 10.1088/0256-307X/29/4/042901
Gamma rays with energies between 80 keV and 1500 keV produced by 133Ba and 152Eu standard sources are measured with the clover detector. Relative efficiencies and add-back factors are determined in both crystals and full clover modes. The add-back characteristics have been calculated using Monte-Carlo simulation code Geant4. The simulation and measurements agree very well.
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Effect of Rotational Excitation on Stereodynamics for the Reactive Collision Between N(2D) and H2
CHENG Jie,YUE Xian-Fang**,FENG Hai-Ran
Chin. Phys. Lett. 2012, 29 (4):
043101
.
DOI: 10.1088/0256-307X/29/4/043101
Effect of rotational excitation on stereodynamics for the N( 2D)+H2(v=0, j=0−5)→NH(v', j')+H collision reactions is investigated by employing the quasiclassical trajectory method. Based on an accurate 12A" potential energy surface, three angular distributions P(θr ), P(φr ), P(θr,φr ), and polarized−dependent differential cross section 2π/σ dσ00 /dωt are calculated at a collision energy of 5.1 kcal/mol. It is found that the P(θr ) distribution has a distinct peak at about θr=90°. The P(φr ) distribution has a small peak at about φr=270° and no peak at about φr=90°. This implies that the product angular momentum j' is not only aligned perpendicular to k, but also orientated to the negative direction of the y axis. The product rotational alignment and orientation become increasingly weaker with an increase of the rotational quantum number j of H2. Analysis of trajectory propagation demonstrates that the title collision reaction has a dominant indirect insertion mechanism and a minor direct H-abstraction mechanism.
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Valence-Shell Excitations of Nitrous Oxide Studied by Fast Electron Impact
LIU Ya-Wei,WANG You-Yan,ZHU Lin-Fan**
Chin. Phys. Lett. 2012, 29 (4):
043302
.
DOI: 10.1088/0256-307X/29/4/043302
The valence-shell excitations of nitrous oxide are studied by fast electron energy loss spectroscopy. From the spectra measured at 2.5 keV and scattering angles of 3.5°–8.5°, it is found that the asymmetric peak of the transition B1Δ can be well fitted by Haarhoff−Van der Linde function, while the symmetric peaks of the transitions of C1Π and D1Σ+ can be well fitted by the Voigt function. The parameters of the peak profiles of B1Δ, C1Π and D1Σ+, i.e., their energy level positions and linewidths, are determined. With the aid of these parameters, the overlapping spectra measured at the low−energy electron impact can be deconvolved, which provides the possibility to determine the quantitative differential cross sections. The present results also show that the peak profiles of the transitions of B1Δ, C1Π and D1Σ+ are independent of the momentum transfer.
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The Improved Power of the Central Lobe in the Beam Combination and High Power Output
LIU Hou-Kang,XUE Yu-Hao,LI Zhen,HE Bing**,ZHOU Jun**,DING Ya-Qian,JIAO Meng-Li,LIU Chi,QI Yun-Feng,WEI Yun-Rong,DONG Jing-Xing,LOU Qi-Hong
Chin. Phys. Lett. 2012, 29 (4):
044204
.
DOI: 10.1088/0256-307X/29/4/044204
In order to increase the power fraction of the central lobe in the coherent beam combination of lasers in an array, the effects of the distance factor of near-field distribution on far-field interference patterns are calculated and demonstrated experimentally. An improved beam array of interwoven distribution is demonstrated to enable the power in the central lobe to reach 41%. An optimized mirror array is carefully designed to obtain a high duty ratio, which is up to 53.3% at a high power level. By using these optimized methods and designs, the passive phase locking of eight Yb-doped fiber amplifiers with ring cavities are obtained, and a pleasing interference pattern with 87% visibility is observed. The maximum coherent output power of the system is up to 1066 W.
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A 171.4 W Diode-Side-Pumped Q-Switched 2 µm Tm:YAG Laser with a 10 kHz Repetition Rate
CAO Dong,DU Shi-Feng**,PENG Qin-Jun,BO Yong,XU Jia-Lin,GUO Ya-Ding,ZHANG Jing-Yuan,CUI Da-Fu,XU Zu-Yan
Chin. Phys. Lett. 2012, 29 (4):
044210
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DOI: 10.1088/0256-307X/29/4/044210
A 785 nm diode-side-pumped high-power high-pulse-repetition-frequency Q-switched 2 µm Tm:YAG laser system is reported. Under a pump power of 1300 W, a 171.4 W average output power is achieved at a pulse repetition frequency of 10 kHz. To our knowledge, this is the highest average output power for a diode−pumped all solid-state Q-switched 2 µm Tm:YAG laser. The laser output corresponds to an optical-to-optical conversion efficiency of 13.3% and a slope efficiency of 18.9%.
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The Structure Evolution of Fused Silica Induced by CO2 Laser Irradiation
LIU Chun-Ming,JIANG Yong,LUO Cheng-Si,SHI Xiao-Yan,REN Wei,XIANG Xia,WANG Hai-Jun,HE Shao-Bo,YUAN Xiao-Dong**,LV Hai-Bing,ZHENG Wan-Guo,ZU Xiao-Tao
Chin. Phys. Lett. 2012, 29 (4):
044211
.
DOI: 10.1088/0256-307X/29/4/044211
The structure evolution of fused silica induced by CO2 laser irradiation (with a wavelength of 10.6 µm ) is studied in detail. In the non-evaporation mitigation process, the irradiation time should be long enough to completely eliminate damage. However, there is a raised rim around the mitigated site. The rim height is enhanced when the irradiation time increases, and the mitigated site can lead to off-axis and on-axis downstream light intensification. Volume shrinkage occurs during the irradiation and rapid cooling processes, and this may be due to a decrease in the Si–O–Si bond angle. The distribution of debris overlaps with the maximum phase retardance induced by stress. The debris arouses an enhanced light absorption in the region from 220 nm to 800 nm.
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Effects of Input Spectra on the Threshold of Modulation Instability in a Single-Mode Fiber
CHEN Wei,MENG Zhou**,ZHOU Hui-Juan,LUO Hong
Chin. Phys. Lett. 2012, 29 (4):
044213
.
DOI: 10.1088/0256-307X/29/4/044213
We investigate modulation instability (MI) in the presence of a monochromatic spectrum and on the background of a broadband amplified spontaneous emission spectrum induced by an erbium-doped fiber amplifier, respectively. For the former case, the MI threshold is ∼110 mW, which agrees well with the theoretical value. However, for the latter case, the threshold is as high as ∼170 mW, which indicates that the MI threshold depends on the shape of the input spectrum and that the broadband spectrum has a higher threshold than the monochromatic one.
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A Novel Method for Measuring the Temperature in the Active Region of Semiconductor Modules
LIU Jing,FENG Shi-Wei**,ZHANG Guang-Chen,ZHU Hui,GUO Chun-Sheng,QIAO Yan-Bin,LI Jing-Wan
Chin. Phys. Lett. 2012, 29 (4):
044401
.
DOI: 10.1088/0256-307X/29/4/044401
The temperature in the active region of semiconductor modules can be measured by a vacuum system method. The test device is positioned on a vacuum test platform and heated in two ways, from the chip and from the case, to identify the required heat to establish stable temperature gradients for the two processes, respectively. A complementary relationship between the temperatures under the two heating methods is found. By injecting the total heat into the device, the resulting uniform temperature can be derived from the temperature curves of the chip and case. It is demonstrated that the temperature obtained from this vacuum system method is equivalent to the normal operating temperature of the device in the atmosphere. Further comparison of our result with that of the electrical method also shows good agreement.
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Solution Fabrication of a Superconducting MgB2 Coated Conductor on Stainless Steel
WANG Yin-Bo,CHEN Li-Ping,**,ZHANG Chen,WANG Yue,GUO Zheng-Shan,CHEN Yi-Ling,FENG Qing-Rong**,GAN Zi-Zhao
Chin. Phys. Lett. 2012, 29 (4):
047401
.
DOI: 10.1088/0256-307X/29/4/047401
We report the solution fabrication of a MgB2 coated conductor on a stainless steel substrate. The precursor solution of Mg(BH4)2 diethyl ether is initially synthesized by refluxing the milled mixture of NaBH4 and MgCl2 in diethyl ether. Then the Mg(BH4)2 diethyl ether is spin coated on a stainless steel substrate and annealed in Mg vapor, which yields a homogeneous MgB2 coated conductor. X−ray diffraction indicates that the grown MgB2 coated conductor is polycrystalline. It has a superconducting transition temperature of 34–37 K. The slope of the upper critical field HC increases with decreasing temperature, and the extrapolated value of HC(0) reaches ∼28 T. The critical current density estimated by the Bean model is JC (25 K, 0 T)∼106 A⋅cm−2. These parameters indicate that the solution method is potentially able to produce MgB2 coated conductors that can satisfy application purposes.
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First-Principles Study of Doped Half-Metallic Spinels: Cu0.5Zn0.5Cr2S4, Cu0.5Cd0.5Cr2S4, Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5Cr2S4
ZHOU Tie-Ge,LIU Zhi-Qiang**,ZUO Xu
Chin. Phys. Lett. 2012, 29 (4):
047503
.
DOI: 10.1088/0256-307X/29/4/047503
Electronic structure and magnetic properties of Cu0.5Zn0.5Cr2S4, Cu0.5Cd0.5Cr2S4, Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5 Cr2S4 are investigated using the first−principles calculation based on the density functional theory. GGA+U exchange correlation is used in the calculation to correct the effective Coulomb repulsion energy of Cr underestimated by LSDA or GGA. The calculation results reveal that half−metallic Cu0.5Zn0.5Cr2S4 and Cu0.5Cd0.5Cr2S4 can be achieved by doping CuCr2S4 with Zn or Cd, though CuCr2S4 is not half−metallic. Half-metallic LiCr2O4 is experimentally unstable, but half−metallic Li0.5Zn0.5Cr2O4 and Li0.5Zn0.5Cr2S4 can be achieved by doping Li into experimentally stable ZnCr2O4 and ZnCr2S4, though ZnCr2O4 and ZnCr2S4 are not half−metallic. The influence of +U on the electronic structure and half-metallicity of the doped systems is also presented.
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Helium-Related Defect Evolution in Titanium Films by Slow Positron Beam Analysis
LI Yue,DENG Ai-Hong,**,ZHOU Yu-Lu,ZHOU Bing,WANG Kang,HOU Qing,SHI Li-Qun,QIN Xiu-Bo,WANG Bao-Yi
Chin. Phys. Lett. 2012, 29 (4):
047801
.
DOI: 10.1088/0256-307X/29/4/047801
Various helium-containing titanium films were deposited on Si substrates by magnetron sputtering under different helium/argon (He/Ar) ambiances. Helium concentrations and corresponding depth profiles in the Ti films are obtained by elastic recoil detection analysis (ERDA). X-ray diffraction (XRD) measurements are carried out to evaluate the crystallization of the titanium films. Vacancy-type defects and their depth profiles were revealed by slow positron beam analysis (SPBA). It is found that the defect-characteristic parameter S rises with the increment of the He/Ar flow ratios. The variation of S indicates the formation and evolution of various He-related defects, with uniform distribution into the depth around 400 nm.
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Fine Structural and Carbon Source Analysis for Diamond Crystal Growth using an Fe-Ni-C System at High Pressure and High Temperature
FAN Xiao-Hong,XU Bin**,NIU Zhen,ZHAI Tong-Guang,TIAN Bin
Chin. Phys. Lett. 2012, 29 (4):
048102
.
DOI: 10.1088/0256-307X/29/4/048102
Diamond is synthesized in an Fe-Ni-C system at high pressure and high temperature, the C sp3 content profile through different thicknesses of interface between diamond and the catalyst film is measured by using electron energy loss spectroscopy. It is found that the C sp3 content varies from 87.33% to 78.15% when the measured position is located at the inner face near the diamond and then changes to 6 µm further away. Transmission electron microscope examinations show that there are different phases in the interface, such as Fe3C, γ−(Fe,Ni), and graphite, but the graphite phase diminishes gradually towards the inner face of the interface. These results profoundly indicate that the carbon atoms, required for diamond growth, could only come from the carbon-rich phase, Fe3C, but not directly from the graphite. It is possible that carbon atoms from the graphite in the interface first react with Fe atoms to produce carbide Fe3C during diamond synthesis at high pressure and high temperature. The Fe3C finally decomposes into carbon atoms with the sp3 electron state at the interface to form the diamond.
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The Efficiency of a Small-World Functional Brain Network
ZHAO Qing-Bai,ZHANG Xiao-Fei,SUI Dan-Ni,ZHOU Zhi-Jin,CHEN Qi-Cai,TANG Yi-Yuan,**
Chin. Phys. Lett. 2012, 29 (4):
048702
.
DOI: 10.1088/0256-307X/29/4/048702
We investigate whether the small-world topology of a functional brain network means high information processing efficiency by calculating the correlation between the small-world measures of a functional brain network and behavioral reaction during an imagery task. Functional brain networks are constructed by multichannel event-related potential data, in which the electrodes are the nodes and the functional connectivities between them are the edges. The results show that the correlation between small-world measures and reaction time is task-specific, such that in global imagery, there is a positive correlation between the clustering coefficient and reaction time, while in local imagery the average path length is positively correlated with the reaction time. This suggests that the efficiency of a functional brain network is task-dependent.
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Effect of Ultrastrong Magnetic Field on the Electron Capture in the Stellar Surroundings
WANG Kun,LUO Zhi-Quan**,LI Ying-Lin
Chin. Phys. Lett. 2012, 29 (4):
049701
.
DOI: 10.1088/0256-307X/29/4/049701
Using the nuclear shell model, we study the influence of ultra-strong magnetic field on the electron capture nuclei reactions 56,58Co→56,58Fe, 56,57Ni→56,57Co, 52,53Fe→52,53Mn and 57,60Cu→57,60Ni. The results show that the electron capture rates of most iron group nuclei are increased greatly in the ultrastrong magnetic field, and even exceed three orders of magnitude in the range from 5×1013 G to 2.5×1017 G.
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70 articles
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