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Volume 26 Issue 9
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Multi-Soliton Solutions of the Levi Equations
YOU Fu-Cai, ZHANG Jiao, HAO Hong-Hai
Chin. Phys. Lett. 2009, 26 (9): 090201 .   DOI: 10.1088/0256-307X/26/9/090201
Abstract   PDF(pc) (211KB) ( 693 )
The multisoliton solutions of the Levi equations are derived with the Hirota method and Wronskian technique respectively.
Justification of a Monte Carlo Algorithm for the Diffusion-Growth Simulation of Helium Clusters in Materials
ZHOU Yu-Lu, HOU Qing, WANG Jun, DENG Ai-Hong
Chin. Phys. Lett. 2009, 26 (9): 090202 .   DOI: 10.1088/0256-307X/26/9/090202
Abstract   PDF(pc) (334KB) ( 687 )
A theoretical analysis of a Monte Carlo (MC) method for the simulation of the diffusion-growth of helium clusters in materials is presented. This analysis is based on an assumption that the diffusion-growth process consists of first stage, during which the clusters diffuse freely, and second stage in which the coalescence occurs with certain probability. Since the accuracy of MC simulation results is sensitive to the coalescence probability, the MC calculations in the second stage is studied in detail. Firstly, the coalescence probability is analytically formulated for the one-dimensional diffusion-growth case. Thereafter, the one-dimensional results are employed to justify the MC
simulation. The choice of time step and the random number generator used in the MC simulation are discussed.
Interactions between Components of Various Vector Solitons in Bose-Einstein Condensates
YAN Jia-Ren, PAN Liu-Xian, YU Hui-You, AO Sheng-Mei
Chin. Phys. Lett. 2009, 26 (9): 090301 .   DOI: 10.1088/0256-307X/26/9/090301
Abstract   PDF(pc) (263KB) ( 422 )
We investigate the interactions between components of various vector solitons in Bose-Einstein condensates by means of the least action principle, and derive the effective potentials for different vector solitons, which indicate that the interactions are of short range, and may be repulsive or attractive decided by the different intra- and inter-species interactions in such a system. In the case of attraction, the two solitons will oscillate about and pass through each other around the equilibrium state. The comparison of analytical results with mumertical simulation is presented.
Probabilistic Dense Coding Using Non-Maximally Entangled Three-Particle States
ZHANG Guo-Hua, YAN Feng-Li
Chin. Phys. Lett. 2009, 26 (9): 090302 .   DOI: 10.1088/0256-307X/26/9/090302
Abstract   PDF(pc) (200KB) ( 545 )
We present a scheme for probabilistic dense coding via quantum channels of non-maximally entangled three-particle states. Quantum dense coding will succeed with a certain probability if the sender introduces an auxiliary particle and performs a collective unitary transformation. The average information transmitted in this scheme is calculated.
Effects of Atom-Atom Interaction on Localization and Adiabaticity of BEC in One-Dimensional Disorder Optical Lattice
XU Zhen, DUAN Ya-Fan, ZHOU Shu-Yu, HONG Tao, WANG Yu-Zhu
Chin. Phys. Lett. 2009, 26 (9): 090303 .   DOI: 10.1088/0256-307X/26/9/090303
Abstract   PDF(pc) (634KB) ( 867 )
We numerically simulate the dynamical behavior of BEC in one-dimensional incommensurable optical lattice by split-step Fourier method in a time-dependent one-dimensional Gross-Pitaevskii equation. It is indicated that the atom-atom interaction will weaken the localization and broaden the wave function, and it will destroy the adiabaticity of the ramped loading process in both single lattice and incommensurate lattice due to the broadening effect. A band structure model can interpret the difference of the adiabatic condition with non-interacting BEC in these optical lattices.
Remote Information Concentration via a Four-Particle Cluster State
CHEN Yin-Hua, ZHANG Deng-Yu, GAO Feng, ZHAN Xiao-Gui
Chin. Phys. Lett. 2009, 26 (9): 090304 .   DOI: 10.1088/0256-307X/26/9/090304
Abstract   PDF(pc) (239KB) ( 483 )
We propose a protocol of remote information concentration achieved by a four-particle cluster state. To achieve the task, Bell state measurement and unitary operation are needed. The result shows a peculiar phenomenon that the remote information concentration is not always successful but with certain probability.
Exact Solutions of Effective Mass Dirac Equation with Non-PT-Symmetric and Non-Hermitian Exponential-type Potentials
Altug Arda, Ramazan Sever
Chin. Phys. Lett. 2009, 26 (9): 090305 .   DOI: 10.1088/0256-307X/26/9/090305
Abstract   PDF(pc) (173KB) ( 841 )
By using a two-component approach to the one-dimensional effective mass Dirac equation, bound states are investigated under the effect of two new non-PT-symmetric and non-Hermitian exponential type potentials. It is observed that the Dirac equation can be mapped into a Schrödinger-like equation by rescaling one of the two Dirac wave functions in the case of the position-dependent mass. The energy levels and the corresponding Dirac eigenfunctions are found analytically.
Quantum Locality for a Pair of Interacting Systems
M. Dugic, J. Jeknic-Dugic
Chin. Phys. Lett. 2009, 26 (9): 090306 .   DOI: 10.1088/0256-307X/26/9/090306
Abstract   PDF(pc) (149KB) ( 400 )
We discuss the quantum locality (non-transfer of information) for a pair of mutually interacting systems, and point out the relaxed locality. The models fulfilling the relaxed locality condition can serve as a guide for quantum engineers in designing quantum-information hardware.
Generalized Thermo Vacuum State Derived by the Partial Trace Method
HU Li-Yun, FAN Hong-Yi
Chin. Phys. Lett. 2009, 26 (9): 090307 .   DOI: 10.1088/0256-307X/26/9/090307
Abstract   PDF(pc) (225KB) ( 617 )
By virtue of the technique of integration within an ordered product of operators, we present a new approach for deriving the generalized thermo vacuum state which is simpler in form than that obtained from the Takahashi-Umezawa method. using this new approach, the thermo field dynamics can be developed. Applications of the new state are discussed.
Extra-Dimensional Cosmology with a Traversable Wormhole
Chin. Phys. Lett. 2009, 26 (9): 090401 .   DOI: 10.1088/0256-307X/26/9/090401
Abstract   PDF(pc) (176KB) ( 664 )
We discuss many interesting and attractive features of a higher-dimensional cosmology with a static traversable wormhole dominated by a variable effective cosmological constant depending on the scale factor a(t) as Λeffective =Ca-20, where C and Λ0 are positive constants.
Precision Measurement of Distribution of Film Thickness on Pendulum for Experiment of G
LIU Lin-Xia, GUAN Sheng-Guo, LIU Qi, ZHANG Ya-Ting, SHAO Cheng-Gang, LUO Jun
Chin. Phys. Lett. 2009, 26 (9): 090402 .   DOI: 10.1088/0256-307X/26/9/090402
Abstract   PDF(pc) (1594KB) ( 714 )
Distribution of film thickness coated on the pendulum of measuring the Newton gravitational constant G is determined with a weighing method by means of a precision mass comparator. The experimental result shows that the gold film on the pendulum will contribute a correction of -24.3ppm to our G measurement with an uncertainty of 4.3ppm, which is significant for improving the G value with high precision.
Synchronization of Chaos in Time-Delayed Systems under Parameter Mismatch
ZHANG Yan, LU Shuang, WANG Ying-Hai
Chin. Phys. Lett. 2009, 26 (9): 090501 .   DOI: 10.1088/0256-307X/26/9/090501
Abstract   PDF(pc) (433KB) ( 608 )
We report on synchronization between two identical time delay chaotic systems under parameter mismatch. It overcomes some limitations of the previous work where synchronization and antisynchronization has been investigated only in finite-dimensional chaotic systems under parameter mismatch, so we can achieve synchronization and antisynchronization in infinite-dimensional chaotic systems under parameter mismatch. For infinite-dimensional systems modelled by delay differential equations, we find stable synchronization and antisynchronization in long-, moderate- and short-time delay regions, in particular for the hyperchaotic case.
Functional Time Series Prediction Using Process Neural Network
DING Gang, LIN Lin, ZHONG Shi-Sheng
Chin. Phys. Lett. 2009, 26 (9): 090502 .   DOI: 10.1088/0256-307X/26/9/090502
Abstract   PDF(pc) (281KB) ( 555 )
Time series prediction methods based on conventional neural networks do not take into account the functional relations between the discrete observed values in the time series. This usually causes a low prediction accuracy. To solve this problem, a functional time series prediction model based on a process neural network is proposed in this paper. A Levenberg-Marquardt learning algorithm based on the expansion of the orthonormal basis functions is developed to train the proposed functional time series prediction model. The efficiency of the proposed functional time series prediction model and the corresponding learning algorithm is verified by the prediction of the monthly mean sunspot numbers. The comparative test results indicate that process neural network is a promising tool for functional time series prediction.
Stabilizing of Two-Dimensional Discrete Lorenz Chaotic System and Three-Dimensional Discrete Röossler Hyperchaotic System
LI Xin, CHEN Yong
Chin. Phys. Lett. 2009, 26 (9): 090503 .   DOI: 10.1088/0256-307X/26/9/090503
Abstract   PDF(pc) (504KB) ( 566 )
A method is used to stabilize the unstable discrete system: two-dimensional discrete Lorenz system and three-dimensional discrete Rössler system.
A New 3D Four-Wing Chaotic System with Cubic Nonlinearity and Its Circuit Implementation
LIU Xing-Yun
Chin. Phys. Lett. 2009, 26 (9): 090504 .   DOI: 10.1088/0256-307X/26/9/090504
Abstract   PDF(pc) (1461KB) ( 2558 )
A new 3D four-wing smooth autonomous chaotic system in which each equation contains a cubic product term is presented and physically implemented. Spectral analysis shows that the four-wing chaotic attractor has extremely wide frequency bandwidth compared with that of the Lorenz system and other four-wing chaotic systems, which is important in some relevant engineering applications such as secure communications.
Miscellaneous Rotating Solitary Waves to a Coupled Dispersionless System
Kuetche Kamgang Victor, Gambo Betchewe, , Bouetou Bouetou Thomas, , Timoleon Crepin Kofane,
Chin. Phys. Lett. 2009, 26 (9): 090505 .   DOI: 10.1088/0256-307X/26/9/090505
Abstract   PDF(pc) (452KB) ( 369 )
We investigate the soliton structure of a coupled dispersionless system describing a current-conducting string with infinite length within a magnetic field. Thus, following Hirota's method, we unwrap three typical localized waves with nonzero angular momentum depending strongly upon their angular velocities. Illustrating the soliton behavior of these waves, we focus our interests on breather-like waves and depict the elastic scattering amongst such waves.
Control of a Unified Chaotic System via Single Variable Feedback
GUO Rong-Wei, U. E. Vincent,
Chin. Phys. Lett. 2009, 26 (9): 090506 .   DOI: 10.1088/0256-307X/26/9/090506
Abstract   PDF(pc) (400KB) ( 727 )
Based on the LaSalle invariance principle, we propose a simple adaptive-feedback for controlling the unified chaotic system. We show explicitly with numerical proofs that our method can easily achieve the control of chaos in the unified chaotic system using only a single variable feedback. The present controller, to our knowledge, is the simplest control scheme for controlling a unified chaotic system.
Adaptive Functional Projective Lag Synchronization of a Hyperchaotic Rössler System
Tae H. Lee, Ju H. Park
Chin. Phys. Lett. 2009, 26 (9): 090507 .   DOI: 10.1088/0256-307X/26/9/090507
Abstract   PDF(pc) (273KB) ( 736 )
We explain the functional projective lag synchronization of a hyperchaotic Rössler system with four unknown parameters, where the output of the master system lags behind the output of the slave system proportionally. Based on Lyapunov stability theory, an active control method and adaptive control law are employed to make the states of two hyperchaotic Rössler systems asymptotically synchronized. Finally, some numerical examples are provided to show the effectiveness of our results.
Microwave Atomic Clock in the Optical Lattice with Specific Frequency
ZHOU Xiao-Ji, CHEN Xu-Zong, CHEN Jing-Biao, WANG Yi-Qiu, LI Jia-Ming
Chin. Phys. Lett. 2009, 26 (9): 090601 .   DOI: 10.1088/0256-307X/26/9/090601
Abstract   PDF(pc) (472KB) ( 606 )
A scheme for a microwave atomic clock is proposed for Cs or Rb atoms trapped in a blue detuned optical lattice. The ac Stark shift of the clock transition due to a trapping laser is calculated. We analyze it at some specific laser wavelength. Compared with the case of the fountain clock, the cavity related shifts, the collision shift and the Doppler effect are eliminated or suppressed dramatically in an atomic lattice clock. By analyzing various sources of clock uncertainty, a microwave atomic lattice clock with a high accuracy and small volume is feasible.
High Performance Micro-Structure Sensor Based on TiO2 Nanofibers for Ethanol Detection
LIU Li, ZHANG Tong, WANG Zhi-Jun, LI Shou-Chun, TIAN Yun-Xia, LI Wei,
Chin. Phys. Lett. 2009, 26 (9): 090701 .   DOI: 10.1088/0256-307X/26/9/090701
Abstract   PDF(pc) (1154KB) ( 801 )
TiO2 nanofibers are synthesized via a simple electrospinning method and coated on a silicon substrate with Pt electrodes to fabricate a micro-structure sensor. This sensor exhibits high ethanol sensing properties at 300°C. The sensitivity is up to 4 when the sensor is exposed to 1ppm ethanol, the response time is about 3s, and the recovery is about 5s.
Design, Fabrication and Test of a Soft X-Ray Even-Order Transmission Grating
MA Jie, XIE Chang-Qing, LIU Ming, CHEN Bao-Qin, YE Tian-Chun
Chin. Phys. Lett. 2009, 26 (9): 090702 .   DOI: 10.1088/0256-307X/26/9/090702
Abstract   PDF(pc) (661KB) ( 730 )
Most transmission gratings in the x-ray region work with their first orders and dispersion is limited by the line density achievable with current fabrication technology. We present a novel design of a two-dimensional x-ray
transmission grating. The grating works with higher dispersion using its second orders, and the influence from first and third orders can be suppressed. A grating according to the novel design is fabricated and its diffraction performance is tested in comparison with a traditional x-ray transmission grating with the same line density. The novel grating could be especially useful when high dispersion is desired while the fabrication of high-density gratings becomes more difficult.
S-Wave DK Interactions in the Chiral SU(3) Quark Model
ZHANG Dan, ZHAO Qiao-Yan, ZHANG Qiu-Yang
Chin. Phys. Lett. 2009, 26 (9): 091201 .   DOI: 10.1088/0256-307X/26/9/091201
Abstract   PDF(pc) (271KB) ( 611 )
The DK interaction is relevant to the interpretation of the DsJ(2317). We dynamically investigate S-wave DK interactions in the chiral SU(3) quark model by solving the resonating group method equation. The numerical results show an attraction between D and K, which is from boson exchanges between light quarks. However, such an attraction is not strong enough to form a DK molecule. Meanwhile, S partial wave phase shifts of DK elastic scattering are obtained. The case of S-wave D*K is rather similar to that of DK. To draw a definite conclusion of whether a molecular state exists in DK or the D*K system, more details of dynamics should be considered in a future study.
Band Structures of the Nucleus 129Cs
ZHAO Yan-Xin, MA Ying-Jun, ZHOU Wen-Ping, WANG Shou-Yu, LIU Gong-Ye, WU Xiao-Guang, ZHU Li-Hua, HAO Xin, LIU Ying, LI Xue-Qin, LI Ming-Fei
Chin. Phys. Lett. 2009, 26 (9): 092301 .   DOI: 10.1088/0256-307X/26/9/092301
Abstract   PDF(pc) (472KB) ( 545 )
High-spin states in 129Cs are populated via the 122Sn (11B, 4n) reaction at beam energies of 55 and 60MeV. Two additional bands are placed in the level scheme and the previously known bands are extended to higher spins. The results are compared to the cranked shell model calculations and to the systematics of the adjacent Cs isotpoes. One of the new bands is interpreted as the γ-vibrational band built on the π h11/2 orbital. The possible configuration for another new band is discussed. Upbend caused by (ν h11/2)2 alignment is observed both in the favored and unfavored sequences of the π h11/2 configuration. The band based on the π g7/2 configuration at low pins forks around spin 17/2, and the two different S-bands are attributed to (ν h11/2)2 and (π h11/2)2 rotational alignments, respectively.
Solving the Dirac Equation with Nonlocal Potential by Imaginary Time Step Method
ZHANG Ying, LIANG Hao-Zhao, MENG Jie,
Chin. Phys. Lett. 2009, 26 (9): 092401 .   DOI: 10.1088/0256-307X/26/9/092401
Abstract   PDF(pc) (577KB) ( 624 )
The imaginary time step (ITS) method is applied to solve the Dirac equation with the nonlocal potential in coordinate space by the ITS evolution for the corresponding Schrödinger-like equation for the upper component. It is demonstrated that the ITS evolution can be equivalently performed for the Schrödinger-like equation with or without localization. The latter algorithm is recommended in the application for the reason of simplicity and efficiency. The feasibility and reliability of this algorithm are also illustrated by taking the nucleus 16O as an example, where the same results as the shooting method for the Dirac equation with localized effective potentials are obtained.
Secondary Beam Fragments Produced by 200 and 400MeV/u 12C6+ Ions in Water
ZHAO Qiang, ZHANG Feng-Shou, , WANG Zhi-Ping, ZHOU Hong-Yu,
Chin. Phys. Lett. 2009, 26 (9): 092501 .   DOI: 10.1088/0256-307X/26/9/092501
Abstract   PDF(pc) (486KB) ( 513 )
Based on the GEANT4 toolkit, we study the transportation of nucleons and nuclei in tissue-like media. The fragmentation of projectile nuclei and secondary interactions of produced nuclear fragments are considered. Livermore data is used to calculate electromagnetic interaction of primary and secondary charged particles. We validate the models using experimental data of 200MeV/u and 400MeV/u carbon ions, interacting with tissue equivalent materials of water. The model can well describe the depth-dose distributions in water and the doses measured for secondary fragments of certain charge and certain mass number. The secondary beam fragments produced by 200MeV/u and 400MeV/u 12C6+ ions in water are investigated using the model. When the primary nuclei are in water, several neutron production mechanisms are involved. The light charged particles (p, d, t, 3He and 4He) and fast neutrons contribute to the dose tail behind the Bragg peak. The 11C fragments which may be the most suitable nuclei for monitoring the energy deposition in carbon-ion therapy are also discussed.
Reinvestigation of Collective Bands in 107Tc
GU Long, ZHU Sheng-Jiang, J. H. Hamilton, A. V. Ramayya, J. K. Hwang, S. H. Liu, WANG Jian-Guo, Y. X. Luo, J. O. Rasmussen, I. Y. Lee, DINGHuai-Bo, K. Li, XU Qiang, YANG Yun-Yi
Chin. Phys. Lett. 2009, 26 (9): 092502 .   DOI: 10.1088/0256-307X/26/9/092502
Abstract   PDF(pc) (390KB) ( 426 )
The high spin states of a neutron-rich 107Tc nucleus are reinvestigated by observing prompt γ-rays from the spontaneous fission of 252Cf. The previous level scheme is updated. A collective band based on the π5/2-[303] orbital is confirmed and extended. Inconsistencies in the configuration assignments for a type of positive parity bands of odd-A 105,107,109Tc in the previous reports are clarified according to the g factor calculations. A new band based on the 1499.5keV level in 107Tc is proposed as a two-phonon γ-vibrational band.
Etch Induction Time in CR-39 Detectors Etched in Na2CO3 Mixed NaOH Solution
N. Ali, E. U. Khan, K. Khan
Chin. Phys. Lett. 2009, 26 (9): 092901 .   DOI: 10.1088/0256-307X/26/9/092901
Abstract   PDF(pc) (228KB) ( 589 )
Six different solutions of 6M NaOH, containing different amounts of Na2CO3 at 70°C were used for the revelation of latent damage trails in CR-39 plastic track detectors. These detectors were earlier exposed to fission fragments from 252Cf source for 30min in vacuum and were then etched in the respective solutions for different etching time intervals of 5-20min starting from 5min up to 160min. The etch induction time in each detector was obtained by extrapolating the intersection of resulting curves of track lengths and track diameters with the time axis.
Development of Mini-LIA and Primary Experiments
CHENG Cheng, LIAO Shu-Qing, ZHENG Shu-Xin, LIN Yu-Zheng, TANG Chuan-Xiang, JING Xiao-Bing, MU Fan, PAN Hai-Feng, ZHANG Kai-Zhi, SHI Jin-Shui, DENG Jian-Jun
Chin. Phys. Lett. 2009, 26 (9): 092902 .   DOI: 10.1088/0256-307X/26/9/092902
Abstract   PDF(pc) (1316KB) ( 447 )
Mini-LIA is a miniature of a linear induction accelerator developed by China Academy of Engineering Physics and Tsinghua University in 2007. It has been constructed with a thermionic cathode in an electron injector and a metglas core in the induction accelerator cavities. A double-pulsed electron beam was produced for the first time in China on the Mini-LIA with a thermionic cathode in the electron gun and a metglas core in the induction accelerator cavities. A double-pulsed beam current of more than 1.1A was obtained on condition of 80kV double-pulsed high voltage produced by pulsed power system supplying to the injector and accelerating modules. Some primary experiments for measuring the parameters of Mini-LIA has been performed, and some beam characterizations of Mini-LIA are presented. Further improvement is underway.
Angular Distribution of Synchrotron Radiation in Low Frequency
WU Jian-Qing, YANG Zhi-Liang, NI Lei, ZHANG Tong-Jie
Chin. Phys. Lett. 2009, 26 (9): 092903 .   DOI: 10.1088/0256-307X/26/9/092903
Abstract   PDF(pc) (308KB) ( 511 )
The angular distribution of energy for synchrotron radiation in low frequency band (ω«ωc) is obtained by rigorously solving the Nicolo Tartaglia equation. The result shows that the critical angle increases with decreasing frequency, but it cannot exceed 90°. The relation between critical angle θc and frequency is common covering all wavelengths. For the small angle case, it is consistent with the result obtained by Jackson. With the increase of emanative angle, the radiant intensity increases first, then decays.
Coherent Control of Photodetachment of H- in Perpendicular Electric and Magnetic Fields
WANG De-Hua, HUANG Kai-Yun
Chin. Phys. Lett. 2009, 26 (9): 093201 .   DOI: 10.1088/0256-307X/26/9/093201
Abstract   PDF(pc) (344KB) ( 374 )
Using the semiclassical closed orbit theory, we study the coherent control of the photodetachment of H- by a single and double-pulse laser in perpendicular electric and magnetic fields. Theoretically, dependences of calculated cross section on laser pulse widths, time delays, relative phases and the classical detached electron's closed orbit period are presented and discussed in detail. The results suggest that for the single pulse laser, if the pulse width is shorter than the particular closed orbit period, then the contribution of that closed orbit to the photodetachment cross section is reduced. While for the double pulse laser, the cross section not only depends on the pulse width, but also depends on the time delay and the relative phase of the two pulses. If the pulse delay time equals to the period of one closed orbit, then the contribution of that orbit becomes significant. Therefore, we can use the pulse laser to control the photodetachment process of ion or atom in external fields.
Cooling and Trapping 88Sr Atoms with 461nm Laser
WANG Shao-Kai, WANG Qiang, LIN Yi-Ge, WANG Min-Ming, LIN Bai-Ke, ZANGEr-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2009, 26 (9): 093202 .   DOI: 10.1088/0256-307X/26/9/093202
Abstract   PDF(pc) (789KB) ( 867 )
We report the experimental realization of a 88Sr magneto-optical trap (MOT) operating at the wavelength of 461nm. The MOT is loaded via a 32cm long spin-flip type Zeeman slower which enhances the MOT population by a factor of 22. The total laser power available in our experiment is about 300mW. We have trapped 1.6×108 88Sr atoms with a 679nm and 707nm repumping laser. The two repumping lasers enhance the trap population and trap lifetime by factors of 11 and 7, respectively. The 88Sr cloud has a temperature of about 2.3mK, measured by recording the time evolution of the absorption signal.
Vibrational Spectroscopy of Stretching and Bending Modes of Nickel Tetraphenyl Porphyrin: an Algebraic Approach
Srinivasa Rao KARUMURI, Joydeep CHOUDHURY, Nirmal Kumar SARKAR, Ramendu BHATTACHARJEE
Chin. Phys. Lett. 2009, 26 (9): 093301 .   DOI: 10.1088/0256-307X/26/9/093301
Abstract   PDF(pc) (183KB) ( 859 )
We calculate the vibrational frequencies of nickel tetraphenyl porphyrin for 36 vibrational bands by using the U(2) algebraic approach. The algebraic parameters in the calculations are accurate with the experimental data.
Multiple Solutions of Laminar Flow in Channels with a Transverse Magnetic Field
LI Bo-Tong, ZHENG Lian-Cun, ZHANG Xin-Xin
Chin. Phys. Lett. 2009, 26 (9): 094101 .   DOI: 10.1088/0256-307X/26/9/094101
Abstract   PDF(pc) (319KB) ( 635 )
We present a numerical investigation for steady laminar flow of a viscous incompressible electrically conducting fluid through a channel of a rectangular cross-section with a transverse magnetic field and suction or injection walls. Multiple solutions are presented for values of suction Reynolds number R and velocity coefficients of accelerating walls. Additionally, the associated transfer characteristics are discussed in detail.
An Efficient Simulated Sea Slope Model for Backscattering from a Non-Gaussian Sea Surface
ZHANG Min, CHEN Hui, ZHOU Pin, ZHANG Xiang-Yang
Chin. Phys. Lett. 2009, 26 (9): 094102 .   DOI: 10.1088/0256-307X/26/9/094102
Abstract   PDF(pc) (572KB) ( 398 )
Based on the double superimposition model, a sea slope model is obtained on the basis of the generated oceanic surface instead of being assumed as a Gaussian distribution model. Then, a summation formula of the backscattering coefficient is derived from the Bass-Fuks two-scale model and its application is extended to the non-Gaussian oceanic surface with the help of simulated sea slopes, which can adequately reflect the non-Gaussian configuration of the sea surface. Finally, this scattering model is employed to describe the backscattering configuration of sea surfaces in different sea states and wind directions, and is confirmed by several numerical examples.
High-Q Microcavity in Two-Dimensional Diamond Photonic Crystal Thin Films Realized via a Mode Gap
ZHOU Chang-Zhu, XIONG Zhi-Gang, LI Zhi-Yuan
Chin. Phys. Lett. 2009, 26 (9): 094201 .   DOI: 10.1088/0256-307X/26/9/094201
Abstract   PDF(pc) (1035KB) ( 607 )
We design high quality factor (Q) photonic crystal microcavities in diamond films for applications in quantum information based on color centers. A photonic microcavity made from a waveguide heterostructure with a mode gap is demonstrated to have a high Q factor over 1051400 and a modal volume V of 2.24 cubic wavelengths by modifying the mode gap width and the tapered region geometry. Besides its ultrahigh Q factor, the waveguide-like geometry of the cavity allows for easy on-chip transportation of quantum information between different cavities.
Diode-Pumped Quasi-Three-Level Passively Q-Switched Nd:GGG Laser with a Codoped Nd,Cr:YAG Saturable Absorber
HE Kun-Na, GAO Chun-Qing, WEI Zhi-Yi, LI Qi-Nan, ZHANG Zhi-Guo, JIANG Hai-He, YIN Shao-Tang, ZHANG Qing-Li
Chin. Phys. Lett. 2009, 26 (9): 094202 .   DOI: 10.1088/0256-307X/26/9/094202
Abstract   PDF(pc) (528KB) ( 407 )
We demonstrate the first quasi-three-level passively Q-switched Nd:GGG laser at 937nm using a Nd,Cr:YAG crystal as the saturable absorber. The dependences of the average output power, the repetition rate and the pulse width on the incident pump power are obtained. A maximum average output power of 1.18W with repetition rate of 35kHz and pulse width of 45ns is achieved at an incident pump power of 18.3W. The corresponding optical-to-optical and slope efficiencies are 6% and 10%, respectively.
Fabrication of 3D Templates Using a Large Depth of Focus Femtosecond Laser
LI Xiao-Fan, WINFIELD Richard, O'BRIEN Shane, CHEN Liang-Yao
Chin. Phys. Lett. 2009, 26 (9): 094203 .   DOI: 10.1088/0256-307X/26/9/094203
Abstract   PDF(pc) (1003KB) ( 436 )
We report the use of a large depth of focus Bessel beam in the fabrication of cell structures. Two axicon lenses are investigated in the formation of high aspect ratio line structures. A sol-gel resin, with good mechanical strength, is polymerised in a modified two-photon polymerisation system. Examples of different two-dimensional grids are presented to show that the lateral resolution can be maintained even in the rapid fabrication of high-sided structures.
Tunable Direct Writing of FBGs into a Non-Photosensitive Tm-Doped Fiber Core with an fs Laser and Phase Mask
SONG Cheng-Wei, ZHANG Yun-Jun, WANG Yang, JU You-Lun
Chin. Phys. Lett. 2009, 26 (9): 094204 .   DOI: 10.1088/0256-307X/26/9/094204
Abstract   PDF(pc) (305KB) ( 582 )
Fiber Bragg gratings (FBGs) are successfully written in a non-photosensitive Tm-doped single-mode fiber by a 800nm fs laser and a 2.7μm period phase mask. The intra-core FBGs are written using the phase mask ±1 order interference, and have a period of 1.35μm, which responds to the second-order reflective central wavelength at 1946.4nm. Based on the magnification tuning writing technology, the tunable writing technology is also experimentally investigated. The distance between the phase mask and the fiber, between the phase mask and the tuning lens, and the focal length of the tuning lens all have an influence on the tunable characteristics. Four different FBGs tuning reflective central wavelengths located at 1958.7nm, 1970.8nm, 1882.5nm and 1899.7nm are obtained.
Entanglement Enhancement Via Collective CPT in Bichromatically Driven Three-Level Atoms
TAN Hua-Tang, DENG Wen-Wu
Chin. Phys. Lett. 2009, 26 (9): 094205 .   DOI: 10.1088/0256-307X/26/9/094205
Abstract   PDF(pc) (245KB) ( 389 )
We investigate the generation of two-mode entangled light from cooperative three-level cascade emitters driven by two lasers inside an optical cavity. It is found that through collective coherent population trapping (CPT) to prepare the atomic states close to the coherent superposition state |1>-|3>√2 of the top and ground levels, the entanglement and mean photon number of the entangled light can be significantly enhanced in comparison to the case of independent atoms.
Experimental Study on Dual Wavelength and Dual Pulse Q-Switched Frequency Doubling on a Tunable Cr: LiSAF Laser
CHEN Chang-Shui, ZHANG Yi-Shi, YU Jin-Wang, FANG Jian, LIU Song-Hao
Chin. Phys. Lett. 2009, 26 (9): 094206 .   DOI: 10.1088/0256-307X/26/9/094206
Abstract   PDF(pc) (309KB) ( 988 )
A flashlamp-pumped Cr:LiSAF laser system with a voltage controlled Q-switch structure in the cavity is designed. A dual-wavelength and dual-pulse tunable laser output is gained. The relation of laser output behavior with input energy is studied experimentally. The output is dual-pulsed with the energy of the 32mJ/pulse producing the total output energy of 64mJ and the pulse width is about 27ns at 850nm. Then, we use one LBO crystal as the frequency doubling crystal to obtain a dual wavelength (448.1nm and 449.15nm) and dual pulse laser. The output for one wavelength is about 10.3mJ and the line width is less than 0.02nm.
All-Solid-State Nd:YAG Laser Operating at 1064nm and 1319nm under 885nm Thermally Boosted Pumping
DING Xin, CHEN Na, SHENG Quan, YU Xuan-Yi, XU Xiao-Yan, WEN Wu-Qi, ZHOU Rui, WANG Peng, YAO Jian-Quan,
Chin. Phys. Lett. 2009, 26 (9): 094207 .   DOI: 10.1088/0256-307X/26/9/094207
Abstract   PDF(pc) (402KB) ( 695 )
We report a high-efficiency Nd:YAG laser operating at 1064nm and 1319nm, respectively, thermally boosted pumped by an all-solid-state Q-switched Ti:sapphire laser at 885nm. The maximum outputs of 825.4mW and 459.4mW, at 1064nm and 1319nm respectively, are obtained in a 8-mm-thick 1.1at.% Nd:YAG crystal with 2.1W of incident pump power at 885nm, leading to a high slope efficiency with respect to the absorbed pump power of 68.5% and 42.0%. Comparative results obtained by the traditional pumping at 808nm are presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power at 1064nm under the 885nm pumping are 12.2% higher and 7.3% lower than those of 808nm pumping. At 1319nm, the slope efficiency and the threshold with respect to the absorbed pump power under 885nm pumping are 9.9% higher and 3.5% lower than those of 808nm pumping. The heat generation operating at 1064nm and 1319nm is reduced by 19.8% and 11.1%, respectively.
Hybrid Active-Passive Microwave Photonic Filter with High Quality Factor
XU En-Ming, ZHANG Xin-Liang, ZHOU Li-Na, ZHANG Yu, HUANG De-Xiu
Chin. Phys. Lett. 2009, 26 (9): 094208 .   DOI: 10.1088/0256-307X/26/9/094208
Abstract   PDF(pc) (307KB) ( 579 )
A hybrid high quality factor (Q-factor) microwave photonic filter with a cascaded active filter and a passive filter is presented and experimentally demonstrated. The active infinite impulse response filter is realized by a recirculating delay line loop with a semiconductor optical amplifier, and a much narrower 3dB bandwidth of response peaks can be achieved. A passive finite impulse response filter is realized by an unbalance Mach-Zehnder interferometer, and it is cascaded to select the desired filter frequencies and to suppress the intermediate peaks. Compared with the purely active filter scheme, the free spectrum range and the Q-factor of the hybrid structure can be doubled. Stable operation and a high Q-factor of 362 are experimentally demonstrated.
Design and Fabrication of Chirped Mirror
WANG Yan-Zhi, SHAO Jian-Da, DONG Hong-Cheng, ZHANG Wei-Li, CUI Yun, HE Hong-Bo, FAN Zheng-Xiu
Chin. Phys. Lett. 2009, 26 (9): 094209 .   DOI: 10.1088/0256-307X/26/9/094209
Abstract   PDF(pc) (488KB) ( 409 )
Chirped mirrors (CMs) are designed and manufactured. The optimized CM provides a group delay dispersion (GDD) of around -60 fs2 and average reflectivity of 99.4% with bandwidth 200nm at a central wavelength of 800nm. The CM structure consists of 52 layers of alternating high refractive index Ta2O5 and low refractive index SiO2. Measurement results show that the control of CM manufacturing accuracy can meet our requirement through time control with ion beam sputtering. Because the GDD of CMs is highly sensitive to small discrepancies between the layer thickness of calculated design and those of the manufactured mirror, we analyze the error sources which result in thickness errors and refractive index inhomogeneities in film manufacture.
Properties of Fraunhofer Diffraction by an Annular Spiral Phase Plate for Sidelobe Suppression
CHEN Jun, KUANG Deng-Feng, FANG Zhi-Liang
Chin. Phys. Lett. 2009, 26 (9): 094210 .   DOI: 10.1088/0256-307X/26/9/094210
Abstract   PDF(pc) (574KB) ( 511 )
A simple and accurate method for calculating the optimal width of an annular spiral phase plate (SPP) to generate optical vortices with sidelobe suppression is proposed. The sidelobes can be sharply suppressed when the ratio of inner and outer radii of an annular SPP is equal to that of the principal ring and the first sidelobe diffracted by a circular SPP with the same topological charge n. Moreover, the ratio of the inner and outer radii of the optimal annular SPP depends only on the topological charge n and is not affected by the incident wavelength or the size of the SPP.
Interaction of a Two-Level Atom with the Morse Potential in the Framework of Jaynes-Cummings Model
M. R. Setare, Sh. Barzanjeh
Chin. Phys. Lett. 2009, 26 (9): 094211 .   DOI: 10.1088/0256-307X/26/9/094211
Abstract   PDF(pc) (1022KB) ( 594 )
A theoretical study of the dynamical behaviors of the interaction between a two-level atom with a Morse potential in the framework of the Jaynes-Cummings model (JCM) is discussed. We show that this system is equivalent to an intensity-dependent coupling between the two-level atom and the non-deformed single-mode radiation field in the presence of an additional nonlinear interaction. We study the dynamical properties of the system such as, atomic population inversion, the probability distribution of cavity-field, the Mandel parameter and atomic dipole squeezing. It is shown how the depth of the Morse potential can be affected by non-classical properties of the system. Moreover, the temporal evolution of the Husimi-distribution function is explored.
Coherence-Time of Matched-Field Processing in Shallow Water in the Presence of Linear Internal Waves
JI Gui-Hua, , LI Zheng-Lin, DAI Qiong-Xing
Chin. Phys. Lett. 2009, 26 (9): 094301 .   DOI: 10.1088/0256-307X/26/9/094301
Abstract   PDF(pc) (468KB) ( 435 )
Relationships among the signal coherence-time of matched-field processing (MFP), the acoustic frequency, the source-receiver range, and the sound speed standard deviation (STD) caused by internal waves in shallow water, are numerically investigated based on oceanographic data from two shallow water experiments. It is found that the coherence-time can be fitted with an inverse square-root power of range, a near inverse 1 power of frequency, and inverse 1.3 power of sound speed STD.
Thermoelastic Stress Field Investigation of GaN Material for Laser Lift-off Technique based on Finite Element Method
WANG Ting, CUI Zhan-Zhong, XU Li-Xin
Chin. Phys. Lett. 2009, 26 (9): 094601 .   DOI: 10.1088/0256-307X/26/9/094601
Abstract   PDF(pc) (326KB) ( 523 )
The transient thermoelastic stress fields of GaN films is analyzed by the finite element method for the laser lift-off (LLO) technique. Stress distributions in GaN films irradiated by pulse laser with different energy densities as functions of time and depth are simulated. The results show that the high thermoelastic stress distributions in GaN films localize within about 1μm below the GaN/Al2O3 interface using proper laser parameters. It is also found that GaN films can avoid the thermal deformation because the maximum thermoelastic stress 4.28GPa is much smaller than the yield strength of GaN 15GPa. The effects of laser beam dimension and the thickness of GaN films on stress distribution are also analyzed. The variation range of laser beam dimension as a function of the thickness of GaN films is simulated to keep the GaN films free of thermal deformation. LLO experiments are also carried out. GaN-based light-emitting diodes (LEDs) are separated from sapphire substrates using the parameters obtained from the simulation. Compared with devices before LLO, P-I-V measurements of GaN-based LEDs after LLO show that the electrical and optical characteristics improve greatly, indicating that no stress damage is brought to GaN films using proper parameters obtained by calculation during LLO.
Acoustic Calculation for Supersonic Turbulent Boundary Layer Flow
LI Xin-Liang, FU De-Xun, MA Yan-Wen, GAO Hui
Chin. Phys. Lett. 2009, 26 (9): 094701 .   DOI: 10.1088/0256-307X/26/9/094701
Abstract   PDF(pc) (1108KB) ( 484 )
An approach which combines direct numerical simulation (DNS) with the Lighthill acoustic analogy theory is used to study the potential noise sources during the transition process of a Mach 2.25 flat plate boundary layer. The quadrupole sound sources due to the flow fluctuations and the dipole sound sources due to the fluctuating surface stress are obtained. Numerical results suggest that formation of the high shear layers leads to a dramatic amplification of amplitude of the fluctuating quadrupole sound sources. Compared with the quadrupole sound source, the energy of dipole sound source is concentrated in the relatively low frequency range.
Ray-Tracing Simulation on Filamentation of Prefocused and Freely Propagated Laser Pulses in Air
MA Yuan-Yuan, LU Xin, XI Ting-Ting, GONG Qi-Huang, ZHANG Jie,
Chin. Phys. Lett. 2009, 26 (9): 095201 .   DOI: 10.1088/0256-307X/26/9/095201
Abstract   PDF(pc) (914KB) ( 454 )
The filamentation mechanisms of prefocused and freely propagated femtosecond laser pulses are compared using the ray-tracing method. The dynamic spatial replenishment mechanism takes place in the filaments with high electron density, which is generally formed by prefocused laser pulses. The mechanism of long-range filamentation over 100m distance is analyzed to be the spatiotemporal moving focus.
Microstructure and Properties of Cr3Si/γ-Fe Composite Coating Prepared by Plasma Transferred Arc Cladding Technique
LIU Yuan-Fu, CHEN De-Qiang, HAN Jian-Min, WU Hao, XU Xiang-Yang, YANG Si-Ze
Chin. Phys. Lett. 2009, 26 (9): 095202 .   DOI: 10.1088/0256-307X/26/9/095202
Abstract   PDF(pc) (1115KB) ( 642 )
Under optimized operating parameters, a wear and corrosion resistant Cr3Si/γ-Fe composite coating is fabricated on a normalized 0.45% carbon steel substrate by using the plasma transferred arc (PTA) cladding technique with Fe-Cr-Si elemental powder blend as the precursor material. Microstructure, microhardness, dry-sliding wear resistance and electrochemical corrosion characteristic of the coating are evaluated. Test results show that the composite coating is mainly composed of primary Cr3Si dendrites and the interdendritic supersaturated iron-base solid solution γ-Fe. Between the Cr3Si/γ-Fe composite coating and the normalized 0.45% carbon steel substrate, there is a narrow metallurgical bonding zone. The Cr3Si/γ-Fe composite coating exhibits high microhardness, excellent wear and corrosion resistance under test conditions.
Can the Fullerene C80 Encage the Tetrahedral Td-N4? A Density Functional Study
Can the Fullerene C0 Encage the Tetrahedral Td-N? A Density Functional Study
Chin. Phys. Lett. 2009, 26 (9): 096101 .   DOI: 10.1088/0256-307X/26/9/096101
Abstract   PDF(pc) (974KB) ( 515 )

The generalized gradient approximation based on density functional theory is used to study the structural, electronic and magnetic properties of the endohedral complex of C80 with tetrahedral Td-N4. The most unstable Ih-C80 can most effectively stabilize the N4 molecule, similar to the case of Ih-N4@C60 [Structural Chemistry 16(2005)567]. It is worth noting that the cage becomes nonmagnetic due to the encaging of N4.

Behavior of an Extended Dislocation near an Elliptical Blunt Crack
SONG Hao-Peng, FANG Qi-Hong, LIU You-Wen
Chin. Phys. Lett. 2009, 26 (9): 096102 .   DOI: 10.1088/0256-307X/26/9/096102
Abstract   PDF(pc) (332KB) ( 409 )
The behavior of an extended dislocation near an elliptical blunt crack is investigated. The equilibrium separation between Shockley partials and the critical value of stacking fault energy for the formation of extended dislocations by dissociation reaction as well as the extended dislocation emission criterion are developed. The results show that the equilibrium separation increases as the extended dislocation tends to the blunt crack. If the stacking fault energy is comparable to the critical energy for dissociation in a perfect medium, complete dislocations can dissociate to form extended dislocations near the blunt crack. The critical stress intensity factor (SIF) for extended dislocation emission increases with the stacking fault energy and the curvature radius of the blunt crack tip. Moreover, the critical SIF for extended dislocation emission is far lower than the critical SIF for edge dislocation emission.
Reshock Response of 2A12 Aluminum Alloy at High Pressures
HOU Ri-Li, , PENG Jian-Xiang, JING Fu-Qian, ZHANG Jian-Hua, ZHOU Ping
Chin. Phys. Lett. 2009, 26 (9): 096201 .   DOI: 10.1088/0256-307X/26/9/096201
Abstract   PDF(pc) (537KB) ( 421 )
By means of mounting the specimen on a low-impedance buffer, reshock experiments were carried out on a 2A12 aluminum alloy up to shock stresses of 67.6GPa. Reshock wave profiles from the initial shock stresses of 60.9-67.6GPa were measured with a velocity interferometer, and it shows that the 2A12 aluminum alloy characterizes as quasi-elastic response during recompression process. The Lagrange longitudinal velocities along the reloading path from initial shock state were obtained from two shots of experiments, while the bulk velocities at corresponding shock stresses were determined via extrapolating from the public reported unloading plastic sound velocities. Combining the reshock and the release experimental results, the yield strength of 2A12 aluminum alloy at shock stress of 60.9GPa was estimated to be about 1.7GPa.
Hydrostaticity of Pressure Media in Diamond Anvil Cells
YOU Shu-Jie, CHEN Liang-Chen, JIN Chang-Qing
Chin. Phys. Lett. 2009, 26 (9): 096202 .   DOI: 10.1088/0256-307X/26/9/096202
Abstract   PDF(pc) (358KB) ( 817 )
Hydrostaticity under high pressure of several materials from solid, fluid to gas, which are widely used as pressure media in modern high-pressure experiments, is investigated in diamond anvil cells. Judging from the R-line widths and R1-R2 peak separation of Ruby fluorescence, the inert argon gas is hydrostatic up to about 30GPa. The behavior of silicon oil is found to be similar to argon at pressures less than 10GPa, while the widening of R-lines and increase of R1-R2 peak separation at higher pressure loads indicate a significant degradation of hydrostaticity. Therefore silicon oil is considered as a good pressure medium at pressures less than 10GPa but poor at higher pressures.
Topological Structure of Vortices in Multicomponent Bose-Einstein Condensates
XU Tao
Chin. Phys. Lett. 2009, 26 (9): 096701 .   DOI: 10.1088/0256-307X/26/9/096701
Abstract   PDF(pc) (192KB) ( 389 )
The structure of the vortex in a two-component Bose-Einstein condensate is studied by the method of Dirac δ function. The vortex can be characterized by the Brouwer degree and Hopf index, i.e., β1η1, β2η2. The circulation of the vortex can be a fraction, which is different from the usual result for a one-component condensate. The kinetic helicity of vortices is calculated.
Characterization of Thick GaN Films Directly Grown on Wet-Etching Patterned Sapphire by HVPE
HU Qiang, WEI Tong-Bo, DUAN Rui-Fei, YANG Jian-Kun, HUO Zi-Qiang, LU Tie-Cheng, ZENG Yi-Ping
Chin. Phys. Lett. 2009, 26 (9): 096801 .   DOI: 10.1088/0256-307X/26/9/096801
Abstract   PDF(pc) (1215KB) ( 913 )
Thick GaN films of high quality are directly grown on wet-etching patterned sapphire in a vertical hydride vapour phase epitaxy reactor. The optical and structural properties of GaN films are studied using scanning electronic microscopy and cathodoluminescence. Test results show that initial growth of hydride vapour phase epitaxy GaN occurs not only on the mesas but also on the two asymmetric sidewalls of the V-shaped grooves without selectivity. After the two-step coalescence near the interface, the GaN films near the surface keep on growing along the direction perpendicular to the long sidewall. Based on Raman results, GaN of the coalescence region in the grooves has the maximum residual stress and poor crystalline quality over the whole GaN film, and the coalescence process can release the stress. Therefore, stress-free thick GaN films are prepared with smooth and crack-free surfaces by this particular growth mode on wet-etching patterned sapphire substrates.
Effect of the Pulse Duty Cycle on Characteristics of Plasma Electrolytic Oxidation Coatings Formed on AZ31 Magnesium Alloy
CHEN Huan, LV Guo-Hua, ZHANG Gu-Ling, PANG Hua, WANG Xing-Quan, ZHANG You-Wei, LEE Heon-Ju, YANG Si-Ze,
Chin. Phys. Lett. 2009, 26 (9): 096802 .   DOI: 10.1088/0256-307X/26/9/096802
Abstract   PDF(pc) (3027KB) ( 1165 )
Ceramic coatings are synthesized on AZ31 magnesium alloy in alkaline silicate solution by the method of plasma electrolytic oxidation. The effect of two different duty cycles (10% and 50%) on the structure and corrosive properties of the coatings is investigated. It is found that the coatings are mainly composed of MgO, Mg2SiO4 and MgF2 through XRD analysis. SEM images indicate that coatings formed at 50% duty cycle have a relatively coarse surface with larger pore size and fewer pores, and have a slower growth rate than those formed at 10% duty cycle with the same treatment time. However, the results of potentiodynamic polarization tests demonstrate that coatings formed at 50% duty cycle exhibit better corrosion resistance as a result of more compact microstructure.
Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations
LUO Fen, CHENG Yan, JI Guang-Fu, CHEN Xiang-Rong,
Chin. Phys. Lett. 2009, 26 (9): 097101 .   DOI: 10.1088/0256-307X/26/9/097101
Abstract   PDF(pc) (477KB) ( 418 )
The pressure induced phase transitions of RuB2 from the OsB2-type structure to the ReB2-type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6GPa. We predict the phase transition from the OsB2-type RuB2 to the ReB2-type RuB2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB2-type RuB2 and ReB2-type RuB2 are also investigated.
Conductance in an Aharonov-Bohm Interferometer with Parallel-Coupled Double Dots
AN Xing-Tao, ZHAO Jin-Rong, , LIU Jian-Jun,
Chin. Phys. Lett. 2009, 26 (9): 097201 .   DOI: 10.1088/0256-307X/26/9/097201
Abstract   PDF(pc) (318KB) ( 397 )
We present a theoretical study of the conductance in an Aharonov-Bohm interferometer containing two coupled quantum dots. The interdot tunneling divides the interferometer into two coupled subrings, where opposite magnetic fluxes are threaded separately while the net flux is kept zero. Using the Green function technique we derive the expression of the linear conductance. It is found that the Aharonov-Bohm effect still exists, and when the level of each dot is aligned, the exchange of the Fano and Breit-Wigner resonances in the conductance can be achieved by tuning the magnetic flux. When the two levels are mismatched the exchange may not happen. Further, for some specific asymmetric systems where the coupling strengths between the two dots and the leads are not equal, the flux can change the Fano resonance into an antiresonance, which is absent in symmetric systems.
Triple Quantum Dot Molecule as a Spin-Splitter
CHI Feng, YUAN Xi-Qiu
Chin. Phys. Lett. 2009, 26 (9): 097301 .   DOI: 10.1088/0256-307X/26/9/097301
Abstract   PDF(pc) (263KB) ( 445 )
We propose a spin-splitter composed of triple quantum dots that works due to the Coulomb blockade effect and the charge and spin biases applied on external electron source and drains. The spin biases are applied only on the two drains and give their spin-dependent chemical potentials, which act as the driving forces for electron spin-polarized transport. By tuning the biases and the dots' levels, spin-up and spin-down electrons can be simultaneously split or separated from the source into two different drains. We show that such a tunneling process is detectable in terms of the spin accumulations on the dots or the currents flowing through the external leads. The present device is quite simple and realizable within currently existing technologies.
Electron States in Parallel Double Quantum Dots with a Tunable Inter-Dot Coupling
CAO Gang, LI Hai-Ou, TU Tao, ZHOU Cheng, HAO Xiao-Jie, GUO Guang-Can, GUO Guo-Ping
Chin. Phys. Lett. 2009, 26 (9): 097302 .   DOI: 10.1088/0256-307X/26/9/097302
Abstract   PDF(pc) (1880KB) ( 580 )
We study the electron states on lateral double quantum dots coupled in parallel. The charge stability diagrams are given in terms of the gate voltages of both dots. We discover that the two electron states translate from separated states to coupled states continuously by increasing the inter-dot coupling strength. Our results demonstrate that the parallel-quantum-dot tunability bodes well for future quantum computing applications.
Upper Critical Fields and Anisotropy of BaFe1.9Ni0.1As2 Single Crystals
TAO Qian, SHEN Jing-Qin, LI Lin-Jun, LIN Xiao, LUO Yong-Kang, CAO Guang-Han, XU Zhu-An
Chin. Phys. Lett. 2009, 26 (9): 097401 .   DOI: 10.1088/0256-307X/26/9/097401
Abstract   PDF(pc) (350KB) ( 422 )
Temperature dependence of the upper critical magnetic field (Hc2) near Tc of 20K in a BaFe1.9Ni0.1As2 single crystal is determined via magneto-resistance measurements, for the out-plane (Hab) and in-plane (H || ab) directions in magnetic fields of up to 8T. The upper critical fields at zero temperature estimated by the Werthamer-Helfand-Hohenberg (WHH) formula are μ0 Hc2||(0)= 137T and μ0 Hc2(0) = 51T, both exceeding the weak-coupling Pauli paramagnetic limit (μ0Hp=1.84Tc). However, the WHH formula could overestimate the μ0Hc2|| (0) value. The anisotropy of upper critical fields is around 3 in the temperature range close to Tc. The result is very similar to the Co-doped 122 superconductor BaFe2-xCoxAs2, indicating that electron-doped 122 superconductors exhibit similar superconducting properties.
Mechanism of Pseudogap Detected by Electronic Raman Scattering: Phase Fluctuation or Hidden Order?
LU Hong-Yan, WAN Yuan, HE Xiang-Mei, WANG Qiang-Hua
Chin. Phys. Lett. 2009, 26 (9): 097402 .   DOI: 10.1088/0256-307X/26/9/097402
Abstract   PDF(pc) (275KB) ( 407 )
We study the electronic Raman scattering in the cuprates to distinguish the two possible scenarios of the pseudogap normal state. In one scenario, the pseudogap is assumed to be caused by phase fluctuations of the preformed Cooper pairs. We find that pair-breaking peaks appear in both the B1g and B2g Raman channels, and they are smeared and tend to shift to the same energy with the increasing strength of phase fluctuations. Thus both channels reflect the same pairing energy scale, irrespectively of the doping level. In another scenario, the pseudogap is assumed to be caused by a hidden order that competes with the superconducting order. As an example, we assume that the hidden order is the d-density-wave (DDW) order. We find analytically and numerically that in the DDW normal state there is no Raman peak in the B2g channel in a tight-binding model up to the second nearest-neighbor hopping, while the Raman peak in the B1g channel reflects the energy gap caused by the DDW order. This behavior is in agreement with experiments in the pseudogap normal state. To gain further insights, we also calculate the Raman spectra in the DDW+SC state. We study the doping and temperature dependence of the peak energy in both channels and find a two-gap behavior, which is in agreement with recent Raman experiments. Therefore, our results shed light on the hidden order scenario for the pseudogap.
Orbital Order and Orbital Excitations in Degenerate Itinerant Electron Systems
LU Feng, SONG Yun, CHEN Dong-Meng, ZOU Liang-Jian
Chin. Phys. Lett. 2009, 26 (9): 097501 .   DOI: 10.1088/0256-307X/26/9/097501
Abstract   PDF(pc) (282KB) ( 549 )
We present a theory of orbital ordering in orbital-degenerate itinerant electron systems. The orbital instability in a two-orbital degenerate Hubbard model is investigated in the random phase approximation (RPA). After demonstrating the criteria for the formation of orbital ordering or the orbital density wave ordering, we find that the orbital and the spin-orbital collective excitation spectra in the ferro-orbital ordered phase exhibit finite gaps. The possible application of the present theory in orbital-ordered 4d compounds is also discussed.
Structural and Magnetic Properties of Fe-Doped Anatase TiO2 Films Annealed in Vacuum
XU Jian-Ping, LI Lan, LV Li-Ya, ZHANG Xiao-Song, CHEN Xi-Ming, WANG Jian-Feng, ZHANG Feng-Ming, ZHONG Wei, DU You-Wei
Chin. Phys. Lett. 2009, 26 (9): 097502 .   DOI: 10.1088/0256-307X/26/9/097502
Abstract   PDF(pc) (516KB) ( 1256 )
Structural and magnetic properties of Fe-doped anatase TiO2 films fabricated by sol-gel spin coating are investigated. X-ray diffraction measurements reveal that Fe3+ ions are incorporated into the TiO2 lattice. No ferromagnetism-related secondary phases and magnetic nanoparticles are observed in the films. The presence of electron paramagnetic resonance signals at g ~ 2.0 supports oxygen vacancies and/or defects generated in the films after annealing in vacuum. Magnetic measurements indicate that Fe-doped anatase TiO2 films are ferromagnetic at room temperature. These observations suggest that oxygen vacancies and/or defects are energetically favorable for the long range Fe3+-Fe3+ ferromagnetic coupling in Fe-doped anatase TiO2 films.
Crystal Structure and Magnetic Properties of Sm2Fe17Nδ Thin Films Deposited on Si (100) Substrates
XUE Gang, PENG Long, ZHANG Huai-Wu
Chin. Phys. Lett. 2009, 26 (9): 097503 .   DOI: 10.1088/0256-307X/26/9/097503
Abstract   PDF(pc) (562KB) ( 558 )
This work focuses on the crystal structure and magnetic properties of the hard magnetic Sm2Fe17Nδ films prepared by dc magnetron sputtering and the subsequent nitriding process. The XRD, EDS, M-H and M-T data show that N enters the cell structure and the films with the single Th2Zn17 phase are obtained when the nitriding temperature varies from 300 to 400°C, thus the maximum value of the coercivity HC reaches 2561.7Oe. However, the Sm2Fe17 phase decomposes to the SmN nonmagnetic phase and the α-Fe soft magnetic phase with further increasing nitriding temperature, which corresponds to the decreasing HC. Furthermore, the easy magnetization direction (EMD) is found to locate randomly in the film plane. This texture can not give an excellent MR/MS higher than the Stoner-Wohlfarth limitation (MR/MS=0.5), which agrees well with the observed low MR/MS (0.58). It is suggested that the magnetization reversal process is dominated by the nucleation mechanism according to the initial magnetization curve and the dependence of HC on the field H.
Improved Performance of Polymer Light-Emitting Diodes with an Electron Transport Emitter by Post-Annealing
XIONG Yan, PENG Jun-Biao, WU Hong-Bin, WANG Jian
Chin. Phys. Lett. 2009, 26 (9): 097801 .   DOI: 10.1088/0256-307X/26/9/097801
Abstract   PDF(pc) (646KB) ( 1626 )
The enhancement of electroluminescent (EL) performance of polymer light emitting diodes (PLEDs) with electron transport emitter poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) through thermal annealing treatment is investigated. Post-annealing of the PLEDs at temperature 120°C over the glass transition temperature of F8BT (99°C) could bring about an improvement of EL efficiency to more than twice that of the untreated devices, up to 6.02cd/A. The improvement of the EL efficiency is due to the balance of electron and hole carriers in the exciton recombination zone, because the dominative electron current in the PLEDs could be reduced by post-annealing in terms of both issues of electron transport limited in the F8BT film and electron injection decreased by the interface between F8BT/cathode.
Characteristics of 355nm Laser Damage in KDP and DKDP Crystals
HU Guo-Hang, ZHAO Yuan-An, SUN Shao-Tao, LI Da-Wei, LIU Xiao-Feng, SUN Xun, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2009, 26 (9): 097802 .   DOI: 10.1088/0256-307X/26/9/097802
Abstract   PDF(pc) (547KB) ( 487 )
We present the characteristics of bulk damage induced by the third harmonic of Nd:YAG laser irradiation in KDP and DKDP crystals. Bulk damage occurs as a few or a series of pinpoints consisting of a core and the deforming zone. The results of a 1-on-1 test reveal that the pinpoint size increases with incvreasing fluence, and the pinpoint density increases exponentially with increasing fluence. The results of an s-on-1 test indicate that the pinpoint density increases gradually with laser pulse number, but the size does not grow. These results are consistent with a model in which nanoabsorbers are assumed to exist in the crystal and the initiation of damage is determined by heating them to the critical temperature.
A Thermal Approach to Model Laser Damage in KDP and DKDP Crystals
HU Guo-Hang, ZHAO Yuan-An, SUN Shao-Tao, LI Da-Wei, LIU Xiao-Feng, SUN Xun, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2009, 26 (9): 097803 .   DOI: 10.1088/0256-307X/26/9/097803
Abstract   PDF(pc) (507KB) ( 493 )
A thermal model is considered in order to better understand the mechanism of laser induced damage in KDP and DKDP crystals. We demonstrate that the expressions of pinpoint density and damage probability, predicted by the thermal model, are consistent with the experimental data. We also discuss the effect of particle interaction on the thermal model.
Large Third-Order Optical Nonlinearity of Cadmium Sulphide Nanoparticles Embedded in Polymer Thin Films
WANG Cun-Xiu, FU Shi-Shu, Gu Yu-Zong
Chin. Phys. Lett. 2009, 26 (9): 097804 .   DOI: 10.1088/0256-307X/26/9/097804
Abstract   PDF(pc) (1039KB) ( 902 )
A simple method for synthesis of well dispersed cadmium sulphide nanoparticles embedded in a polyethylene glycol matrix (PEG 400) in thin film form is presented. The large blue shift of the band gap energy of the CdS nanoparticles compared to the bulk semiconductors is observed via UV-vis absorption spectra. Photoluminescence spectra of CdS nanocomposite films show that the emission peaks shift towards the longer wavelength with the increase of annealing temperature. Transmission electron microscopic images as well as Raman scattering studies confirm the CdS nanometer size particle formation within the polymer matrix. The particle size is about 8 nm. Selected area electron diffraction (SAED) shows the cubic zinc blende polycrystalline rings. Third-order optical nonlinearity of the CdS nanoparticles embedded in polymer thin films is studied with the Z-scan technique under 1064 nm excitation. The results show that the CdS nanocomposite film exhibits negative nonlinear refraction index and positive absorption coefficient. The film shows large optical nonlinearity, and the magnitude of the third-order nonlinear susceptibility of the film is calculated to be 1.73×10-9 esu. The corresponding mechanism is discussed.
Explanation of Laser-Induced Damage Behavior of Fused Silica in a Large-Aperture Laser using a Small-Aperture Damage Test
HUANG Wan-Qing, HAN Wei, WANG Hai-Jun, MIAO Xin-Xiang, YE Ya-Yun, LIFu-Quan, FENG Bin, JING Feng, ZHENG Wan-Guo
Chin. Phys. Lett. 2009, 26 (9): 097901 .   DOI: 10.1088/0256-307X/26/9/097901
Abstract   PDF(pc) (573KB) ( 538 )
Laser-induced damage is a key lifetime limiter for optics in large laser facilities. Fused silica is tested to find the damage threshold on two different laser facilities of different apertures. The damage threshold shows that the corners of the component are less damage resistant. The acid etch on a corner does not effectively increase the damage threshold. A statistics-based model is presented to extrapolate the threshold data in a small-aperture test to predict the damage threshold under functional conditions.
Photoluminescence and X-Ray Photoelectron Spectroscopy of p-Type Phosphorus-Doped ZnO Films Prepared by MOCVD
LI Xiang-Ping, ZHANG Bao-Lin, GUAN He-Song, SHEN Ren-Sheng, PENG Xin-Cun, ZHENG Wei, XIA Xiao-Chuan, ZHAO Wang, DONG Xin, DUGuo-Tong,
Chin. Phys. Lett. 2009, 26 (9): 098101 .   DOI: 10.1088/0256-307X/26/9/098101
Abstract   PDF(pc) (483KB) ( 771 )
Reproducible p-type phosphorus-doped ZnO (p-ZnO:P) films are prepared on semi-insulating InP substrates by metal-organic chemical vapour deposition technology. The electrical properties of these films show a hole concentration of 9.02×1017cm-3, a mobility of 1.05cm2/V s, and a resistivity of 6.6 Ω・cm. Obvious acceptor-bound-exciton-related emission and P-induced zinc vacancy (VZn) emission are observed by low-temperature photoluminescence spectra of the films, and the acceptor binding energy is estimated to be about 125meV. The local chemical bonding environments of the phosphorus atoms in the ZnO are also identified by x-ray photoelectron spectra. Our results show direct experimental evidence that PZn-2VZn shallow acceptor complex most likely contributes to the p-type conductivity of ZnO:P films.
Au/Pt/InGaN/GaN Heterostructure Schottky Prototype Solar Cell
XUE Jun-Jun, CHEN Dun-Jun, LIU Bin, XIE Zi-Li, JIANG Ruo-Lian, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2009, 26 (9): 098102 .   DOI: 10.1088/0256-307X/26/9/098102
Abstract   PDF(pc) (354KB) ( 770 )
A patterned Au/Pt/In0.2Ga0.8N/GaN heterostructure Schottky prototype solar cell is fabricated. The forward current-voltage characteristics indicate that thermionic emission is a dominant current transport mechanism at the Pt/InGaN interface in our fabricated cell. The Schottky solar cell has an open-circuit voltage of 0.91V, short-circuit current density of 7mA/cm2, and fill factor of 0.45 when illuminated by a Xe lamp with a power density of 300mW/cm2. It exhibits a higher short-circuit current density of 30mA/cm2 and an external quantum efficiency of over 25% when illuminated by a 20-mW-power He-Cd laser.
Kinetic Model of the Lysogeny/Lysis Switch of Phage λ
DING Hui, LUO Liao-Fu
Chin. Phys. Lett. 2009, 26 (9): 098701 .   DOI: 10.1088/0256-307X/26/9/098701
Abstract   PDF(pc) (278KB) ( 420 )
A kinetic model of the interactions between operators and regulators is developed to study the stabilities of genetic states and lysogeny/lysis switch in Escherichia coli infected by bacteriophage lambda. Using adiabatic approximation, the kinetic evolutions of mRNA and regulator concentrations can be deduced from operators' equations. Furthermore, the stability of each state of the system is studied. The results show that the lysogenic state switches to the lytic state through two bifurcations: one from a single stable state to a three-point state, and the other from a three-point state to a single stable state. Then we indicate that the property of the lysogeny/lysis switch satisfies the topological characteristics theorem. Finally, the influence of the left operators on the lysogeny/lysis switch is briefly discussed. The results show that the cooperativity of the CI2 bound to left and right operators makes the lysogenic state more stable.
Competition of Multi-Agent Systems: Analysis of a Three-Company Econophysics Model
FU Xiu-Jun, Szeto K Y
Chin. Phys. Lett. 2009, 26 (9): 098901 .   DOI: 10.1088/0256-307X/26/9/098901
Abstract   PDF(pc) (262KB) ( 349 )
A three-company econophysics model for competing multi-agent systems in a triangular lattice is analyzed using mean field theory for its phase diagram. Interpretations for the temperature, spin density and lattice structures are presented. Suggestions for the use of this model for econophysics in the context of multi-agent systems are made.
Empirical Analysis and Modeling of the Global Economic System
DUAN Wen-Qi, SUN Bo-Liang
Chin. Phys. Lett. 2009, 26 (9): 098902 .   DOI: 10.1088/0256-307X/26/9/098902
Abstract   PDF(pc) (340KB) ( 463 )
In the global economic system, each economy stimulates the growth of its gross domestic products (GDP) by increasing its international trade. Using a fluctuation analysis of the flux data of GDP and foreign trade, we find that both GDP and foreign trade are dominated by external force and driven by each other. By excluding the impact of the associated trade dependency degree, GDP and the total volume of foreign trade collapse well into a power-law function. The economy's total trade volume scales with the number of trade partners, and it is distributed among its trade partners in an exponential form. The model which incorporated these empirical results can integrate the growth dynamics of GDP and the interplay dynamics between GDP and weighted international trade networks simultaneously.
A Law of Gravitation for Complex Networks
YANG Zong-Chang
Chin. Phys. Lett. 2009, 26 (9): 098903 .   DOI: 10.1088/0256-307X/26/9/098903
Abstract   PDF(pc) (209KB) ( 565 )
Inspiring Newton's law of universal gravitation and empirical studies, we propose a concept of virtual network mass and network gravitational force in complex networks. Then a network gravitational model for complex networks is presented. In the model, each node in the network is described with its position, edges (links) and virtual network mass. The proposed model is examined by experiments to show its potential applications.
77 articles