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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.9
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Perturbation method of studying the EI Niño oscillation with two parameters using delay sea–air oscillator model

Du Zeng-Ji, Lin Wan-Tao, Mo Jia-Qi
Chin. Phys. B 2012, 21 (9): 090201;  doi: 10.1088/1674-1056/21/9/090201
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The EI Niño-southern oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interactions. In this paper, we develop an asymptotic method of solving the nonlinear equation using the ENSO model. Based on a class of oscillator of the ENSO model, a approximate solution of the corresponding problem is studied employing the perturbation method.

Lattice soliton equation hierarchy and associated properties

Zheng Xin-Qing, Liu Jin-Yuan
Chin. Phys. B 2012, 21 (9): 090202;  doi: 10.1088/1674-1056/21/9/090202
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As a new subject, soliton theory is shown to be an effective tool for describing and explaining the nonlinear phenomena in nonlinear optics, super conductivity, plasma physics, magnetic fluid, etc. Thus, the study of soliton equations has always been one of the most prominent events in the field of nonlinear science during the past few years. Moreover, it is important to seek lattice soliton equation and study its properties. In this study, firstly, we derive a discrete integrable system by use of Tu model. Then, some properties of the obtained equation hierarchies are discussed.

A new complex variable element-free Galerkin method for two-dimensional potential problems

Cheng Yu-Min, Wang Jian-Fei, Bai Fu-Nong
Chin. Phys. B 2012, 21 (9): 090203;  doi: 10.1088/1674-1056/21/9/090203
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In this paper, based on the element-free Galerkin (EFG) method and the improved complex variable moving least-square (ICVMLS) approximation, a new meshless method, which is the improved complex variable element-free Galerkin (ICVEFG) method, for two-dimensional potential problems is presented. In the method, the integral weak form of control equations is employed, and the Lagrange multiplier is used to apply the essential boundary conditions. Then the corresponding formulas of the ICVEFG method for two-dimensional potential problems are obtained. Compared with the complex variable moving least-square (CVMLS) approximation proposed by Cheng, the functional in the ICVMLS approximation has an explicit physical meaning. Furthermore, the ICVEFG method has greater computational precision and efficiency. Three numerical examples are given to show the validity of the proposed method.

An improved interpolating element-free Galerkin method with nonsingular weight function for two-dimensional potential problems

Wang Ju-Feng, Sun Feng-Xin, Cheng Yu-Min
Chin. Phys. B 2012, 21 (9): 090204;  doi: 10.1088/1674-1056/21/9/090204
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In this paper, an improved interpolating moving least-square (IIMLS) method is presented. The shape function of the IIMLS method satisfies the property of Kronecker δ function. The weight function used in the IIMLS method is nonsingular. Then the IIMLS method can overcome the difficulties caused by the singularity of the weight function in the IMLS method. And the number of unknown coefficients in the trial function of the IIMLS method is less than that of the moving least-square (MLS) approximation. Then by combining the IIMLS method with the Galerkin weak form of the potential problem, the improved interpolating element-free Galerkin (IIEFG) method for two-dimensional potential problems is presented. Compared with the conventional element-free Galerkin (EFG) method, the IIEFG method can directly use the essential boundary conditions. Then the IIEFG method has a higher accuracy. For demonstration, three numerical examples are solved using the IIEFG method.

Complex variable element-free Galerkin method for viscoelasticity problems

Cheng Yu-Min, Li Rong-Xin, Peng Miao-Juan
Chin. Phys. B 2012, 21 (9): 090205;  doi: 10.1088/1674-1056/21/9/090205
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Based on the complex variable moving least-square (CVMLS) approximation, the complex variable element-free Galerkin (CVEFG) method for two-dimensional viscoelasticity problems under the creep condition is presented in this paper. The Galerkin weak form is employed to obtain the equation system, and the penalty method is used to apply the essential boundary conditions, then the corresponding formulae of the CVEFG method for two-dimensional viscoelasticity problems under the creep condition are obtained. Compared with the element-free Galerkin (EFG) method, with the same node distribution, the CVEFG method has a higher precision, and to obtain the similar precision, the CVEFG method has a greater computational efficiency. Some numerical examples are given to demonstrate the validity and the efficiency of the method in this paper.

Direct discontinuous Galerkin method for the generalized Burgers–Fisher equation

Zhang Rong-Pei, Zhang Li-Wei
Chin. Phys. B 2012, 21 (9): 090206;  doi: 10.1088/1674-1056/21/9/090206
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In this study, we use the direct discontinuous Galerkin method to solve the generalized Burgers-Fisher equation. The method is based on the direct weak formulation of the Burgers-Fisher equation. The two adjacent cells are jointed by a numerical flux that includes the convection numerical flux and the diffusion numerical flux. We solve the ordinary differential equations arising in the direct Galerkin method by using the strong stability preserving Runge-Kutta method. Numerical results are compared with the exact solution and the other results to show the accuracy and reliability of the method.

Semi-classical theory and experimental research for polarization flipping in a single frequency laser with feedback effect

Chen Wen-Xue, Zhang Shu-Lian, Zhang Peng, Zeng Zhao-Li
Chin. Phys. B 2012, 21 (9): 090301;  doi: 10.1088/1674-1056/21/9/090301
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In this paper, we propose a semi-classical theory to successfully explain the polarization flipping in a single frequency laser. An experimental setup is built to verify this theory. The observed experimental phenomena are consistent with the theoretical analysis. We perform phase retardation measurements of birefringent components using this experimental system. The results show that the measurement repeatability is 0.12° and the measurement accuracy is 0.22°.

Effects of photon addition on quantum nonlocality of squeezed entangled coherent states

Zhou Ben-Yuan, Deng Lei, Duan Yong-Fa, Yu Li, Li Gao-Xiang
Chin. Phys. B 2012, 21 (9): 090302;  doi: 10.1088/1674-1056/21/9/090302
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Effects of photon addition on quantum nonlocality of squeezed entangled coherent states for Bell-inequality tests are studied theoretically. By utilizing the method of photon-parity measurement, it is found that photon addition can always increase the degrees of Bell violations within a certain parameter range. A possible scheme for generating photon-added squeezed entangled coherent states is proposed.

Multipartite entanglement concentration of electron-spin states with CNOT gates Hot!

Ren Bao-Cang, Hua Ming, Li Tao, Du Fang-Fang, Deng Fu-Guo
Chin. Phys. B 2012, 21 (9): 090303;  doi: 10.1088/1674-1056/21/9/090303
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We propose a different entanglement concentration protocol (ECP) for nonlocal N-electron systems in a partially entangled Bell-type pure state using the CNOT gates and the projection measurements on an additional electron. For each nonlocal N-electron system, Alice first entangles it with the additional electron, and then she projects the additional electron onto an orthogonal basis for dividing the N-electron systems into two groups. In the first group, the N parties obtain a subset of N-electron systems in a maximally entangled state directly. In the second group, they obtain some less-entangled N-electron systems, which are the resource for the entanglement concentration in the next round. By iterating the entanglement concentration process several times, the present ECP has the maximal success probability, which is the theoretical limit of an ECP, equals to the entanglement of the partially entangled state, higher than the others. This ECP may be useful in quantum computers based on electron-spin systems in the future.

Topological aspect of vortex lines in two-dimensional Gross–Pitaevskii theory

Zhao Li, Yang Jie, Xie Qun-Ying, Tian Miao
Chin. Phys. B 2012, 21 (9): 090304;  doi: 10.1088/1674-1056/21/9/090304
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Using the φ-mapping topological theory, we study the topological structure of vortex lines in a two-dimensional generalized Gross-Pitaevskii theory in (3+1)-dimensional space-time. We obtain the reduced dynamic equation in the framework of two-dimensional Gross-Pitaevskii theory, from which a conserved dynamic quantity is derived on the stable vortex lines. Such equations can also be used to discuss Bose-Einstein condensates in heterogeneous and highly nonlinear systems. We obtain an exact dynamic equation with a topological term, which is ignored in traditional hydrodynamic equations. The explicit expression of vorticity as a function of the order parameter is derived, where the δ function indicates that the vortices can only be generated from the zero points of Φ and are quantized in terms of the Hopf indices and Brouwer degrees. The φ-mapping topological current theory also provides a reasonable way to study the bifurcation theory of vortex lines in the two-dimensional Gross-Pitaevskii theory.

New exact solutions of Einstein–Maxwell equations for magnetostatic fields

Nisha Goyal, R. K. Gupta
Chin. Phys. B 2012, 21 (9): 090401;  doi: 10.1088/1674-1056/21/9/090401
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The symmetry reduction method based on the Fréchet derivative of differential operators is applied to investigate symmetries of the Einstein-Maxwell field equations for magnetostatic fields, which is a coupled system of nonlinear partial differential equations of the second order. The technique yields invariant transformations that reduce the given system of partial differential equations to a system of nonlinear ordinary differential equations. Some of the reduced systems are further studied to obtain the exact solutions.

Non-equilibrium Landauer transport model for Hawking radiation from a Reissner–Nordstrom black hole

Zeng Xiao-Xiong, Zhou Shi-Wei, Liu Wen-Biao
Chin. Phys. B 2012, 21 (9): 090402;  doi: 10.1088/1674-1056/21/9/090402
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The recent work of Nation et al., in which the Hawking radiation energy and entropy flow from a black hole is considered to be produced in a one-dimensional Landauer transport process, is extended to the case of a Reissner-Nordstrom black hole. The energy flow contains not only the contribution of the thermal flux but also that of the particle flux. It is found that the charge can also be transported via the one-dimensional quantum tunnel. Because of the existence of the electrostatic potential, the entropy production rate is shown to be smaller than that of the Schwarzschild black hole.

Temperature dependence of the energy-level shift induced by the Bose–Einstein condensation of photons

Zhang Jian-Jun, Cheng Ze, Yuan Jian-Hui, Zhang Jun-Pei
Chin. Phys. B 2012, 21 (9): 090502;  doi: 10.1088/1674-1056/21/9/090502
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We investigate the energy-level shift of a hydrogen atom in a two-dimensional optical microcavity, where there exists a Bose-Einstein condensation of photons. It is found that below the critical temperature Tc, the energy-level shift of the bound electron is dependent on temperature, and it is a monotonically increasing function of the absolute temperature T. Especially, at the absolute zero temperature, the energy-level shift entirely comes from the Lamb shift, and the atom can be treated approximately, that is, in vacuum.

Stochastic properties of tumor growth with coupling between non-Gaussian and Gaussian noise terms

Jiang Li-Li, Luo Xiao-Qin, Wu Dan, Zhu Shi-Qun
Chin. Phys. B 2012, 21 (9): 090503;  doi: 10.1088/1674-1056/21/9/090503
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Dynamical behavior of tumor-growth model with coupling between non-Gaussian and Gaussian noise terms is investigated. The departure from the Gaussian noise can not only reduce the probability of tumor cells in the active state, induce the minimum of the average tumor-cell population to move toward a smaller non-Gaussian noise, but also decrease the mean first-passage time. The increase of white-noise intensity can increase the tumor-cell population and shorten the mean first-passage time, while the coupling strength between noise terms has opposite effects, and the noise correlation time has a very small effect.

Fluctuations and dissipations in stochastic energetic resonance

Xue Sheng-Hu, Lin Min, Meng Ying
Chin. Phys. B 2012, 21 (9): 090504;  doi: 10.1088/1674-1056/21/9/090504
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By analyzing the fluctuations and dissipations of a Brownian particle colliding with the molecules in a fluid, the work exchanged between the Brownian particle constrained in a bistable potential well and an external periodic force is investigated. Characters of the stochastic energetic resonance are found and studied at different intensities of fluctuations and dissipations. The microscopic mechanism of energy exchange between the Brownian particle and the external force is revealed. The method used in this study provides a novel way of controlling the stochastic energetic resonance.

Control of fractional chaotic system based on fractional-order resistor–capacitor filter

Zhang Lu, Deng Ke, Luo Mao-Kang
Chin. Phys. B 2012, 21 (9): 090505;  doi: 10.1088/1674-1056/21/9/090505
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We present a new fractional-order resistor-capacitor controller and a novel control method based on the fractional-order controller to control an arbitrary three-dimensional fractional chaotic system. The proposed control method is simple, robust, and theoretically rigorous, and its anti-noise performance is satisfactory. Numerical simulations are given for several fractional chaotic systems to verify the effectiveness and the universality of the proposed control method.

A new pseudorandom number generator based on complex number chaotic equation

Liu Yang, Tong Xiao-Jun
Chin. Phys. B 2012, 21 (9): 090506;  doi: 10.1088/1674-1056/21/9/090506
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In recent years, various chaotic equation based pseudorandom number generators have been proposed, however, the chaotic equations are all defined in the real number field. In this paper, an equation is proposed and proved to be chaotic in the imaginary axis. And a pseudorandom number generator is constructed based on the chaotic equation. The alteration of the definitional domain of the chaotic equation from the real number field to the complex one provides a new approach to the construction of chaotic equations, and a new method to generate pseudorandom number sequences accordingly. Both theoretical analysis and experimental results show that the sequences generated by the proposed pseudorandom number generator possess many good properties.

An effective fractal image compression algorithm based on plane fitting

Wang Xing-Yuan, Guo Xing, Zhang Dan-Dan
Chin. Phys. B 2012, 21 (9): 090507;  doi: 10.1088/1674-1056/21/9/090507
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A new method using plane fitting to decide whether a domain block is similar enough to a given range block is proposed in this paper. First, three coefficients are computed for describing each range and domain block. Then, the best-matched one for every range block is obtained by analysing the relation between their coefficients. Experimental results show that the proposed method can shorten encoding time markedly, while the retrieved image quality is still acceptable. In the decoding step, a kind of simple line fitting on block boundaries is used to reduce blocking effects. At the same time, the proposed method can also achieve high compression ratio.

Projective synchronization of hyperchaotic system via periodically intermittent control

Huang Jun-Jian, Li Chuan-Dong, Zhang Wei, Wei Peng-Cheng
Chin. Phys. B 2012, 21 (9): 090508;  doi: 10.1088/1674-1056/21/9/090508
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We further study the projective synchronization of a new hyperchaotic system. Different from the most existing methods, intermittent control is applied to chaotic synchronization in the present paper. We formulate the intermittent control system that governs the dynamics of the projective synchronization error, then derive the sufficient conditions for the exponential stability of intermittent control system by using Lyapunov stability theory, and finally establish the periodically intermittent controller according to the stability criterion by which the projective synchronization is expected to be achieved. The analytical results are also demonstrated by several numerical simulations.

Controlling and synchronization of a hyperchaotic system based on passive control

Zhu Da-Rui, Liu Chong-Xin, Yan Bing-Nan
Chin. Phys. B 2012, 21 (9): 090509;  doi: 10.1088/1674-1056/21/9/090509
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In this paper, a new hyperchaotic system is proposed, and the basic properties of this system are analyzed by means of equilibrium point, Poincaré map, bifurcation diagram, and Lyapunov exponents. Based on the passivity theory, the controllers are designed to achieve the new hyperchaotic system globally, asymptotically stabilized at the equilibrium point, and also realize the synchronization between the two hyperchaotic systems under different initial values respectively. Finally, the numerical simulation results show that the proposed control and synchronization schemes are effective.

Cross-interference correction and simultaneous multi-gas analysis based on infrared absorption

Sun You-Wen, Zeng Yi, Liu Wen-Qing, Xie Pin-Hua, Chan Ka-Lok, Li Xian-Xin, Wang Shi-Mei, Huang Shu-Hua
Chin. Phys. B 2012, 21 (9): 090701;  doi: 10.1088/1674-1056/21/9/090701
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In this paper, we present the simultaneous multiple pollutant gases (CO2, CO, and NO) measurements by using the non-dispersive infrared (NDIR) technique. A cross-correlation correction method is proposed and used to correct the cross-interferences among the target gases. The calculation of calibration curves is based on least-square fittings with third-order polynomials, and the interference functions are approximated by linear curves. The pure absorbance of each gas is obtained by solving three simultaneous equations using the fitted interference functions. Through the interference correction, the signal created at each filter channel only depends on the absorption of the intended gas. Gas mixture samples with different concentrations of CO2, CO, and NO are pumped into the sample cell for analysis. The results show that the measurement error of each gas is less than 4.5%.

Failure of free energy relation under non-Markovian heat bath temperature change

Cao Liang, Michael Cross, Zheng Zhi-Gang
Chin. Phys. B 2012, 21 (9): 090501;  doi: 10.1088/1674-1056/21/9/090501
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We investigate the free energy relation for a system contacting with a non-Markovian heat bath and find that the validity of the relation sensitively depends on the non-Markovian memory effect, which is especially related to the initial preparation effect. This memory effect drives the statistical distribution of the system out of the initial preparation, even if the system starts from an equilibrium state. This leads to the violation of the free energy relation. A possible way of eliminating this memory effect is proposed.

Finite size effect on Raman frequency of phonons in nano-semiconductors

Xia Lei, Zhong Kai, Song Yang, Lu Xin, Xu Lü-Shun, Yan Yan, Li Hong-Dong, Yuan Fang-Li, Jiang Jian-Zhong, Yu Da-Peng, Zhang Shu-Lin
Chin. Phys. B 2012, 21 (9): 097801;  doi: 10.1088/1674-1056/21/9/097801
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A comprehensive study on Raman spectroscopy with different excitation wavelengths, sample sizes, and sample shapes for optic phonons (OPs) and acoustic phonons (APs) in polar and non-polar nano-semiconductors has been performed. The study affirms that the finite size effect does not appear in the OPs of polar nano-semiconductors, while it exists in all other types of phonons. The absence of the FSE is confirmed to be originated from the long-range Fröhlich interaction and the breaking of translation symmetry. The result indicates that the Raman spectra of OPs cannot be used as a method to characterize the scale and crystalline property of polar nano-semiconductors.

Asymmetric simple exclusion processes with complex lattice geometries: A review of models and phenomena

Liu Ming-Zhe, Li Shao-Da, Wang Rui-Li
Chin. Phys. B 2012, 21 (9): 090510;  doi: 10.1088/1674-1056/21/9/090510
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We summarize the findings of a large number of researches concerning the totally asymmetric simple exclusion process (TASEP) with complex lattice geometries. The TASEP has been recognized as a paradigm in modeling and analyzing non-equilibrium traffic systems. The paper surveys both the observed physical phenomena and several popular mean-field approaches used to analyze the extended TASEP models. Several interesting physical phenomena, such as phase separation, spontaneous symmetry breaking, and finite-size effect, have been identified and explained. The future investigations of the extended TASEP with complex lattice geometries are also introduced. This paper may help to obtain a better understanding of non-equilibrium systems.

Recent developments in high power near-infrared super-continuum generation based on photonic crystal fiber

Song Rui, Hou Jing, Chen Sheng-Ping, Yang Wei-Qiang, Lu Qi-Sheng
Chin. Phys. B 2012, 21 (9): 094211;  doi: 10.1088/1674-1056/21/9/094211
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High power supercontinuum generation witnessed rapid developments in the past few years. The mechanism and the latest achievements in high power supercontinuum generation are reviewed both for the continuous wave pump regime and the pulsed pump regime. The challenges in scaling the average power of supercontinuum generation are analyzed. Some of our works on high power supercontinuum generation are summarized, and perspectives for the future development are discussed.

High power terahertz pulses generated in intense laser-plasma interactions Hot!

Li Yu-Tong, Wang Wei-Min, Li Chun, Sheng Zheng-Ming
Chin. Phys. B 2012, 21 (9): 095203;  doi: 10.1088/1674-1056/21/9/095203
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Terahertz (THz) radiation has attracted much attention due to its wide potential applications. Though radiation can be generated with various ways, it is still a big challenge to obtain strong tabletop sources. Plasma, with the advantage of no damage limit, is a promising medium to generate strong THz radiation. This review reports recent advances on strong THz radiation generation from low-density gases and high-density solid targets at different laser intensities.

Unified treatment of one-range addition theorems for integer and non-integer n-STO, -GTO and -generalized exponential type orbitals with hyperbolic cosine in position, momentum and four-dimensional spaces

I. I. Guseinov
Chin. Phys. B 2012, 21 (9): 093101;  doi: 10.1088/1674-1056/21/9/093101
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The simpler formulas are derived for one-range addition theorems for the integer and noninteger n generalized exponential type orbitals, momentum space orbitals, and hyperspherical harmonics with hyperbolic cosine (GETO HC, GMSO HC, and GHSH HC) in position, momentum and four-dimensional spaces, respectively. The final results are expressed in terms of one-range addition theorems of complete orthonormal sets of ψ α -exponential type orbitals, φ α -momentum space orbitals and zα -hyperspherical harmonics. We notice that the one-range addition theorems for integer and noninteger n-Slater type orbitals and Gaussian type orbitals in position, momentum and four dimensional spaces are the special cases of GETO HC, GMSO HC, and GHSH HC. The theorems presented can be useful in the accurate study of electronic structure of atomic and molecular systems.

Density functional study of uranyl (VI) amidoxime complexes

Chi Fang-Ting, Li Peng, Xiong Jie, Hu Sheng, Gao Tao, Xia Xiu-Long, Wang Xiao-Lin
Chin. Phys. B 2012, 21 (9): 093102;  doi: 10.1088/1674-1056/21/9/093102
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Uranyl (VI) amidoxime complexes are investigated using relativistic density functional theory. The equilibrium structures, bond orders, and Mulliken populations of the complexes have been systematically investigated under a generalized gradient approximation (GGA). Comparison of (acet) uranyl amidoxime complexes ([UO2(AO)n]2-n, 1 ≤ n ≤ 4) with available experimental data shows an excellent agreement. In addition, the U-O(1), U-O(3), C(1)-N(2), and C(3)-N(4) bond lengths of [UO2(CH3AO)4]2- are longer than experimental data by about 0.088, 0.05, 0.1, and 0.056 Å. The angles of N(3)-O(3)-U, O(2)-N(1)-C(1), N(3)-C(3)-N(4), N(4)-C(3)-C(4), and C(4)-C(3)-N(3) are different from each other, which are due to existing interaction between oxygen in uranyl and hydrogen in amino group. This interaction is found to be intra-molecular hydrogen bond. Studies on the bond orders, Mulliken charges, and Mulliken populations demonstrate that uranyl oxo group functions as hydrogen-bond acceptors and H atoms in ligands act as hydrogen-bond donors forming hydrogen bands within the complex.

Effects of reagent's rotational and vibrational excitations on reaction O(3P) + H2(ν = 0, 3, j = 0, 3, 5, 7, 9, 12, 15) → OH + H

Xu Zeng-Hui, Zong Fu-Jian, Han Bo-Ran, Dong Shao-Hua, Liu Jian-Qiang, Ji Feng
Chin. Phys. B 2012, 21 (9): 093103;  doi: 10.1088/1674-1056/21/9/093103
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To investigate the effect of reagent's rotational and vibrational excitations on the stereo-dynamics of reaction product, the title reaction is theoretically simulated using the quasi-classical trajectory (QCT) method on the 3A" and 3A′ potential energy surfaces (PESs). The reaction cross section is considered as the only scalar property in this work at four different collision energies. Furthermore the vector properties including two polarization-dependent differential cross sections (PDDCSs), the angular distributions of product' rotational momentum are discussed at one fixed collision energy. Effects of reagents' rotational excitation on the reaction do exist regularly.

Brittle-ductile behavior of a nanocrack in nanocrystalline Ni: A quasicontinuum study

Shao Yu-Fei, Yang Xin, Zhao Xing, Wang Shao-Qing
Chin. Phys. B 2012, 21 (9): 093104;  doi: 10.1088/1674-1056/21/9/093104
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The effects of stacking fault energy, unstable stacking fault energy and unstable twinning fault energy on the fracture behavior of nanocrystalline Ni are studied via the quasicontinuum simulations. Two semi-empirical potentials for Ni are used to vary the values of these generalized planar fault energies. When the above three energies are reduced, a brittle-to-ductile transition of the fracture behavior is observed. In the model with higher generalized planar fault energies, a nanocrack proceeds along a grain boundary, while in the model with lower energies, the tip of the nanocrack becomes blunt. A greater twinning tendency is also observed in the more ductile model. These results indicate that the fracture toughness of nanocrystalline face-centered-cubic metals and alloys might be efficiently improved by controlling the generalized planar fault energies.

(e, 2e) triple-differential cross sections for Ag+(4p, 4s) in coplanar symmetric geometry

Zhou Li-Xia, Yan You-Guo
Chin. Phys. B 2012, 21 (9): 093401;  doi: 10.1088/1674-1056/21/9/093401
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The (e, 2e) triple-differential cross sections of Ag+(4p, 4s) were calculated based on the three-body distorted-wave Born approximation considering post-collision interaction in coplanar symmetric geometry. The energy of outgoing electron was set to be 50, 70, 100, 200, 300, 500, 700, and 1000 eV, and the intensity and splitting of forward and backward peaks were discussed in detail. Some new structures were observed around 15° and 85° for 4p and 4s orbitals. Structures in triple-differential cross sections at 15° have been reported for the first time. A double-binary collision was proposed to explain the formation of such structures. The structures at 85° were also considered as the result of one kind of double-binary collision.

Electron inelastic mean free paths in solids: A theoretical approach

Siddharth H. Pandya, B. G. Vaishnav, K. N. Joshipura
Chin. Phys. B 2012, 21 (9): 093402;  doi: 10.1088/1674-1056/21/9/093402
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In the present paper, the inelastic mean free path (IMFP) of incident electrons is calculated as a function of energy for silicon (Si), oxides of silicon (SiO2), SiO, and Al2O3 in bulk form by employing atomic/molecular inelastic cross sections derived by semi-empirical quantum mechanical method developed earlier. A general agreement of the present results is found with the most of the available data. It is of great importance that we have been able to estimate the minimum IMFP which corresponds to the peak of inelastic interactions of incident electrons in each solid investigated. New results are presented for SiO for which no comparison is available. The present work is important in view of the lack of experimental data on IMFP in solids.

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

Zhang Xiu-Rong, Yang Xing, Ding Xun-Lei
Chin. Phys. B 2012, 21 (9): 093601;  doi: 10.1088/1674-1056/21/9/093601
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The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have the potential utility in designing new spintronic nanomaterials with tunable magnetic properties.

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by a frequency shifter

Wu Ji-Zhou, Ma Jie, Ji Zhong-Hua, Zhang Yi-Chi, Li Yu-Qing, Wang Li-Rong, Zhao Yan-Ting, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys. B 2012, 21 (9): 093701;  doi: 10.1088/1674-1056/21/9/093701
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We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation spectra are recorded with two laser beams induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the photoassociation (PA) spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.

Controllable optical bistability of Bose–Einstein condensate in an optical cavity with Kerr medium

Zheng Qiang, Li Sheng-Chang, Zhang Xiao-Ping, You Tai-Jie, Fu Li-Bin
Chin. Phys. B 2012, 21 (9): 093702;  doi: 10.1088/1674-1056/21/9/093702
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We study the optical bistability for a Bose-Einstein condensate of atoms in a driven optical cavity with Kerr medium. We find that both the threshold point of optical bistability transition and the width of optical bistability hysteresis can be controlled by appropriately adjusting the Kerr interaction between the photons. In particular, we show that the optical bistability will disappear when the Kerr interaction exceeds a critical value.

A novel structure for broadband left-handed metamaterial

Xiong Han, Hong Jing-Song, Jin Da-Lin, Zhang Zhi-Min
Chin. Phys. B 2012, 21 (9): 094101;  doi: 10.1088/1674-1056/21/9/094101
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A low absorptivity broadband negative refractive index metamaterial with multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. From the numerical and experimental results, the effective media parameters were retrieved, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.

Simplified nonlinear theory of the dielectric loaded rectangular Cerenkov maser

Zhao Ding, Ding Yao-Gen
Chin. Phys. B 2012, 21 (9): 094102;  doi: 10.1088/1674-1056/21/9/094102
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To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser, a simplified nonlinear theory is proposed, in which the variations of wave amplitude and wave phase are determined by two coupled first-order differential equations. Through combining with the relativistic equation of motion and adopting the forward wave assumption, the evolutions of the forward wave power, the power growth rate, the axial wave number, the accumulated phase offset, and the information of the particle movement can be obtained in a single-pass calculation. For an illustrative example, this method is used to study the influences of the beam current, the gap distance between the beam and the dielectric surface, and the momentum spread on the forward wave. The variations of the saturated power and the saturation length with the working frequency for the beams with different momentum spreads have also been studied. The result shows that the beam-wave interaction is very sensitive to the electron beam state. To further verify this simplified theory, a comparison with the result produced from a rigorous method is also provided, we find that the evolution curves of the forward wave power predicted by the two methods exhibit excellent agreement. In practical applications, the developed theory can be used for the design and analysis of the rectangular Cerenkov maser.

Gain enhancement in two-stream free electron laser with planar wiggler and axial guide magnetic field

S. Saviz, Z. Rezaei, Farzin M. Aghamir
Chin. Phys. B 2012, 21 (9): 094103;  doi: 10.1088/1674-1056/21/9/094103
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The theory for the two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.

A modified phase diversity wavefront sensor with a diffraction grating

Luo Qun, Huang Lin-Hai, Gu Nai-Ting, Rao Chang-Hui
Chin. Phys. B 2012, 21 (9): 094201;  doi: 10.1088/1674-1056/21/9/094201
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Phase diversity wavefront sensor is one of the useful tools to estimate the wavefront aberration, and it is often used as a wavefront sensor in adaptive optics system. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.

Long-distance propagation of pseudo-partially coherent Gaussian Schell-model beams in atmospheric turbulence

Qian Xian-Mei, Zhu Wen-Yue, Rao Rui-Zhong
Chin. Phys. B 2012, 21 (9): 094202;  doi: 10.1088/1674-1056/21/9/094202
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Propagation properties of spatially pseudo-partially coherent Gaussian Schell-model beams through the atmospheric turbulence over a long-distance uplink path are studied by numerical simulation. A linear coordination transformation is introduced to overcome the window effect and the loss-of-resolution problem. The beam spreading, beam wandering, and intensity scintillation as functions of turbulence strength, source correlation length, and change frequency of random phase that models the partial coherence of the source are analyzed. It is found that the beam spreading and the intensity scintillation of the partially coherent beam are less affected by the turbulence than those of the coherent one, but it suffers from severer diffractive effect, and the change frequency of random phase has no evident influence on it. The beam wandering is insensitive to the variation of source correlation length, and decreases firstly then goes to a fixed value as the change frequency increases.

A method for phase reconstruction in the optical three-dimensional shape measurement

Qiao Nao-Sheng, He Zhi
Chin. Phys. B 2012, 21 (9): 094203;  doi: 10.1088/1674-1056/21/9/094203
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In the optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that lie in the x-axis direction of the phase domain are given. Partial derivatives of the phase function in the x- and y-axis directions are obtained with a phase-shifting mechanism, the origin of which is analysed. Furthermore, to avoid the phase unwrapping in the phase reconstruction, we derive the gradient of the phase function and perform a two-dimensional integral along the x- and y-axis directions. The reconstructed phase can be obtained directly by performing the numerical integration, and thus it is of great convenience for phase reconstruction. Finally, the results of numerical simulations and practical experiments verify the correctness of the proposed method.

Properties of a dielectric plate using entangled two-photon states

Zhou Zhi-Yuan, Ding Dong-Sheng, Shi Bao-Sen, Zou Xu-Bo, Guo Guang-Can
Chin. Phys. B 2012, 21 (9): 094204;  doi: 10.1088/1674-1056/21/9/094204
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We theoretically study the properties of a dielectric plate with a modified Hong-Ou-Mandel interferometer. The fourth-order correlation functions are calculated in two regimes divided depending on the relative size between the thickness of dielectric plate and one-photon coherence length. When the thickness of dielectric plate is less than the one-photon coherence length, a novel modulation behavior of the coincidence rate is observed, which has not been discussed before. If the thickness of dielectric plate is larger than the one-photon coherence length, the coalescence and anti-coalescence are observed. The results obtained highlight the effects of linear optical element on the fourth-order interference.

Study of frequency-modulated excitation of Rydberg potassium atoms by using B-spline

Li Xiao-Yong, Wang Guo-Li, Zhou Xiao-Xin
Chin. Phys. B 2012, 21 (9): 094205;  doi: 10.1088/1674-1056/21/9/094205
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With the B-spline expansion technique and a model potential of the alkali atoms, the properties of frequency-modulated excitation of Rydberg potassium atoms in a static electric field and a microwave field are investigated by using the time-dependent two-level approach. We successfully reproduce the square wave oscillations in the low frequency, the stair step population oscillations in the intermediate frequency, and the multiphoton transitions in the high frequency with respect to the unmodulated Rabi frequency, which have been observed experimentally by Noel et al. [Phys. Rev. A 58 2265 (1998)]. Furthermore, we also numerically obtain the discretized Rabi oscillations predicted in the Landau-Zener accumulation model.

Comparative study on the power scaling performance of three different coherent polarization beam combination system structures

Ma Peng-Fei, Zhou Pu, Ma Yan-Xing, Su Rong-Tao, Liu Ze-Jin
Chin. Phys. B 2012, 21 (9): 094206;  doi: 10.1088/1674-1056/21/9/094206
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Coherent polarization beam combination (CPBC) is a new kind of coherent beam combination configuration with high combining efficiency and excellent beam quality. In order to extend the CPBC system to a large scale, we provide a comparative study on the power scaling performance of three different coherent polarization beam combination system structures. It is found that the pairwise structure has high tolerance to aberrations and has a potential to extend to a large scale with high combining efficiency. In consideration of all the aberrations, the combining efficiency of the pairwise structure can be reached as high as 90% when the combined beams are more than 200. Some instructive suggestions are given to extend the CPBC system to a large scale.

Activation of silicon quantum dots for emission

Huang Wei-Qi, Miao Xin-Jian, Huang Zhong-Mei, Liu Shi-Rong, Qin Chao-Jian
Chin. Phys. B 2012, 21 (9): 094207;  doi: 10.1088/1674-1056/21/9/094207
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Emission of silicon quantum dots is weak when their surface is passivated well. Oxygen or nitrogen on surface of silicon quantum dots can break the passivation to form localized electronic states in band gap to generate active centers where stronger emission occurs. From this point of view, we can build up radiative matters for emission. By controlling the surface bonds of silicon quantum dots, emissions of various wavelengths can be obtained. Our experimental results demonstrate that annealing is important in treatment of the activation, and stimulated emissions at about 600 and 700 nm take place on active silicon quantum dots.

Dual-wavelength distributed Bragg reflector semiconductor laser based on composite resonant cavity

Chen Cheng, Zhao Ling-Juan, Qiu Ji-Fang, Liu Yang, Wang Wei, Lou Cai-Yun
Chin. Phys. B 2012, 21 (9): 094208;  doi: 10.1088/1674-1056/21/9/094208
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We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.

Tunnel regenerated coupled multi-active-region large optical cavity laser with high quality beam

Cui Bi-Feng, Guo Wei-Ling, Du Xiao-Dong, Li Jian-Jun, Zou De-Shu, Shen Guang-Di
Chin. Phys. B 2012, 21 (9): 094209;  doi: 10.1088/1674-1056/21/9/094209
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A novel coupled multi-active-region large optical cavity structure cascaded by tunnel junction is proposed to solve the problems of catastrophic optical damage (COD) of facet and large vertical divergence caused by the thin emitting area in the conventional laser diode. For the laser with three active regions, a slope efficiency as high as 1.49 W/A, a vertical divergence angle of 17.4°, and a threshold current density of 271 A/cm2 are achieved. By optimizing the structure parameters, the beam quality is greatly improved, and the level of COD power increases more than two times compared with that of the conventional laser.

Artificial spectral filtering in dissipative soliton fiber lasers with invisible bandpass filters

Kong Ling-Jie, Xiao Xiao-Sheng, Yang Chang-Xi
Chin. Phys. B 2012, 21 (9): 094210;  doi: 10.1088/1674-1056/21/9/094210
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We numerically study the artificial spectral-filtering effect in dissipative soliton fiber lasers without intracavity spectral filter. It is found that in the dissipative soliton lasers with real saturable absorbers (SAs), the dynamic spectral filtering of the real SAs serves as an artificial spectral filter and contributes to the pulse shaping. While in the dissipative soliton lasers with artificial SAs, such as nonlinear polarization rotation, the spectral filtering introduced by the intracavity polarization-dependent components acts as an artificial spectral filter and shapes the pulses to get mode-locking. The investigation of the artificial spectral-filtering effect reveals the operating mechanisms of the dissipative soliton fiber lasers without visible bandpass filter.

High-power high-stability Q-switched green laser with intracavity frequency doubling of diode-pumped composite ceramic Nd:YAG laser

Wang Yu-Ye, Xu De-Gang, Liu Chang-Ming, Wang Wei-Peng, Yao Jian-Quan
Chin. Phys. B 2012, 21 (9): 094212;  doi: 10.1088/1674-1056/21/9/094212
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We successfully obtain high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight plano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By use of a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.

Rear-surface light intensification caused by Hertzian-conical crack in 355-nm silica optics

Zhang Chun-Lai, Yuan Xiao-Dong, Xiang Xia, Wang Zhi-Guo, Liu Chun-Ming, Li Li, He Shao-Bo, Zu Xiao-Tao
Chin. Phys. B 2012, 21 (9): 094213;  doi: 10.1088/1674-1056/21/9/094213
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Theoretical studies show that the Hertzian-conical crack can be considered to be composed of double cone faces for simplification. In the present study, the three-dimensional finite-difference time-domain method is employed to quantify the electric-field distribution within the subsurface in the presence of such a defect under the normal incidence irradiation. Both impurities (inside the crack) and the chemical etching have been investigated. The results show that the maximum electric field amplitude |E| max is 9.57374 V/m when the relative dielectric constant of transparent impurity equals 8.5. And the near-field modulation will be improved if the crack filled with remainder polishing powders or water vapor/drops. Meanwhile, the laser-induced initial damage is moving to the glass-air surface. In the etched section, the magnitude of intensification is strongly dependent on the inclination angle θ. There will be a highest modulation when θ is around π /6, and the maximum value of |E| max is 18.57314 V/m. When θ ranges from π /8 to π /4, the light intensity enhancement factor can easily be larger than 100, and the modulation follows a decreasing trend. On the other hand, the modulation curves become smooth when θ > π /4 or θ < π /8.

Effects of temperature and input energy on quasi-three-level emission cross section of Nd3+:YAG pumped by flashlamp

Seyed Ebrahim Pourmand, Noriah Bidin, Hazri Bakhtiar
Chin. Phys. B 2012, 21 (9): 094214;  doi: 10.1088/1674-1056/21/9/094214
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The influence of temperature and input energy on fluorescence emission cross section of Nd3+:YAG crystal is studied. The stimulated emission cross sections of quasi-three-level systems are determined in a temperature range from -30 to 60 ℃ and an input energy range from 18 to 75 J. The cross section is found to decrease with the temperature and the input energy is increased. This is attributed to the thermal broadening mechanism of the emission line. This study is relevant for the development of laser design.

Phase-matching analysis of four-wave mixing induced by modulation instability in a single-mode fiber

Chen Wei, Meng Zhou, Zhou Hui-Juan
Chin. Phys. B 2012, 21 (9): 094215;  doi: 10.1088/1674-1056/21/9/094215
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Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will be guidable for the fiber communication and sensing systems using the wavelength division multiplexing technology.

Reflecting single attosecond pulse by periodic Mo/Si multilayer mirrors with different layers

Lin Cheng-You, Liu Da-He
Chin. Phys. B 2012, 21 (9): 094216;  doi: 10.1088/1674-1056/21/9/094216
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The reflecting of single attosecond pulse from a periodic Mo/Si multilayer was investigated. With changing the number of bi-layers, the periodic multilayer showed greatly different spectral and temporal responses of the attosecond pulse reflection, which has been discussed in detail in this paper. The capability of attosecond pulse reflection of the periodic multilayers with different bi-layer numbers has been evaluated using suitable temporal parameters. In addition, the condition for obtaining high-efficiency reflected pulses has been analyzed by comparing the pulse responses of the periodic multilayer with different layers. The transfer-matrix method together with the fast Fourier transform has been used in our simulation.

Influences of finite gain bandwidth on pulse propagating in parabolic fiber amplifiers with distributed gain profiles

Zhao Jia-Sheng, Li Pan, Chen Xiao-Dong, Feng Su-Juan, Mao Qing-He
Chin. Phys. B 2012, 21 (9): 094217;  doi: 10.1088/1674-1056/21/9/094217
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The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulating with the nonlinear Schrödinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful to the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.

Broadband and high efficiency metal multi-layer dielectric grating based on non-quarter wave coatings as reflective mirror

Zhang Wen-Fei, Kong Wei-Jin, Yun Mao-Jin, Liu Jun-Hai, Sun Xin
Chin. Phys. B 2012, 21 (9): 094218;  doi: 10.1088/1674-1056/21/9/094218
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This article deals with designing broadband and high efficiency metal multi-layer dielectric grating (MMDG) used to compress and stretch ultra-short laser pulse. The diffraction characteristics of MMDG are analysed with the method of rigorous coupled-wave method. The multi-layer dielectric used as reflective mirror is made up of non-quarter wave coatings. Taking the diffraction efficiency of the -1 order as the value of merit function, the parameters such as groove depth, residual thickness, duty cycle, and reflective mirror are optimized to obtain broadband and high diffraction efficiency. The optimized MMDG shows an ultra-broadband working spectrum with the average efficiency exceeding 97% over 160 nm wavelength centred at 1053 nm and TE polarization. The optimized MMDG should be useful for chirped pulse amplification.

Wavelength-selective characteristics of high birefringence photonic crystal fiber with Au nanowires selectively filled in the cladding air holes

Du Ying, Li Shu-Guang, Liu Shuo
Chin. Phys. B 2012, 21 (9): 094219;  doi: 10.1088/1674-1056/21/9/094219
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Filter characteristics of a designed gold-filled high birefringence photonic crystal fiber are investigated based on the finite element method. The wavelength filter resonances in the high birefringence photonic crystal fiber occur at different points for different polarized directions, and the resonance strength in the x-polarized case is much weaker than that in the y-polarized case. The much more obvious splitting filter characteristics and different resonance strength imply the study and application values in splitting and single polarization fiber devices. The simulation results show that increasing the number of the gold wires only enhances the resonance strength when there is no surface plasmon supermode formed. With the diameters of the gold wires increasing, the response wavelength moves to a longer wavelength, and the strength becomes stronger. When the diameter is increased to 1.4 μm, the response wavelength in the x-polarized case can be tuned to 1.318 μm, which is the communication wavelength. The strongest resonance occurs at 1.2375 μm in the y-polarized case, and the peaking loss can reach 435.83 dB/cm.

Effect of radiation-induced mean wavelength shift in optical fibers on the scale factor of interferometric fiber optic gyroscope at a wavelength of 1300 nm

Jin Jing, Wang Xue-Qin, Lin Song, Song Ning-Fang
Chin. Phys. B 2012, 21 (9): 094220;  doi: 10.1088/1674-1056/21/9/094220
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In order to analyze the effect of wavelength-dependent radiation-induced attenuation (RIA) on the mean transmission wavelength in optical fiber and the scale factor of interferometric fiber optic gyroscopes (IFOGs), three types of polarization-maintaining (PM) fibers is tested by using a 60Co γ -radiation source. The observed different mean wavelength shift (MWS) behaviors for different fibers are interpreted by color-center theory involving dose rate-dependent absorption bands in ultraviolet and visible range and total dose-dependent near infrared absorption bands. To evaluate the mean wavelength variation in fiber coil and the induced scale factor change for space-borne IFOG under low radiation dose in space environment, the influence of dose rate on the mean wavelength is investigated by testing four germanium (Ge) doped fibers and two germanium-phosphorus (Ge-P) codoped fibers irradiated at different dose rates. Experimental results indicate that the Ge-doped fibers show the least mean wavelength shift during irradiation and their mean wavelength of optical signal transmitting in fibers will shift to shorter wavelength in low-dose-rate radiation environment. Finally, the change in the scale factor of IFOG resulting from the mean wavelength shift is estimated and tested, and it is found that the significant radiation-induced scale factor variation must be considered during the design of space-borne IFOG.

Conformal invariance, Noether symmetry, Lie symmetry and conserved quantities of Hamilton systems

Chen Rong, Xu Xue-Jun
Chin. Phys. B 2012, 21 (9): 094501;  doi: 10.1088/1674-1056/21/9/094501
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In this paper, the relation of the conformal invariance, the Noether symmetry, and the Lie symmetry for the Hamilton system is discussed in detail. The definition of the conformal invariance for Hamilton systems is given. The relation between the conformal invariance and the Noether symmetry is discussed, the conformal factors of the determining expressions are found by using the Noether symmetry, and the Noether conserved quantity resulted from the conformal invariance is obtained. The relation between the conformal invariance and the Lie symmetry is discussed, the conformal factors are found by using the Lie symmetry, and the Hojman conserved quantity resulted from the conformal invariance of the system is obtained. Two examples are given to illustrate the application of the results.

Modelling of spall damage in ductile materials and its application to the simulation of plate impact on copper

Zhang Feng-Guo, Zhou Hong-Qiang, Hu Jun, Shao Jian-Li, Zhang Guang-Ca, Hong Tao, He Bin
Chin. Phys. B 2012, 21 (9): 094601;  doi: 10.1088/1674-1056/21/9/094601
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A statistical model of dynamic spall damage due to void nucleation and growth is proposed for ductile materials under intense loading, which takes into account inertia, elastic-plastic effect, and initial void size. To some extent, void interaction could be accounted for in this approach. Based on this model, the simulation of spall experiments for copper is performed with the Lagrangian finite element method. The simulation results are in good agreement with experimental data for the free surface velocity profile, stress record behind copper target, final porosity, and void concentrations across the target. The influence of elastic-plastic effect upon the damage evolution is explored. The correlation between the damage evolution and the history of the stress near the spall plane is also analyzed.

Response of plasma turbulence against externally-controlled perturbations

S. I. Itoh, K. Itoh
Chin. Phys. B 2012, 21 (9): 095201;  doi: 10.1088/1674-1056/21/9/095201
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A theory of the dynamic response of the turbulent plasma against the externally-controlled perturbations is reported. Based on the Mori's method [Prog. Theor. Phys. 33 423 (1965)], the nonlinear force is assumed to be separated into the memory function and the nonlinear fluctuating force. The former corresponds to the damping term, and the latter is categorized into the noise term. The response of the turbulent plasma against the externally-controlled source is formulated. The response kernel, which connects the externally-controlled source and the response of the turbulent field, is shown to have both the nonlocal property (in space) and the non-Markovian response (in time). A discussion is made on the nonlocal and non-Markovian response, including the case of disparate-scale interactions. A new method is proposed to observe experimentally the nonlocal interaction in the drift wave turbulence via the zonal flows.

Directly driven Rayleigh–Taylor instability of modulated CH targets

Jia Guo, Xiong Jun, Dong Jia-Qin, Xie Zhi-Yong, Wu Jiang
Chin. Phys. B 2012, 21 (9): 095202;  doi: 10.1088/1674-1056/21/9/095202
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Directly driven ablative Rayleigh-Taylor (R-T) instability of modulated CH targets was studied using the face-on X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R-T instability perturbation. The R-T instability growth factor has been obtained by using the methods of fast Fourier transform and seeking difference of light intensity between the peak and the valley of the targets. Through comparing with the the theoretical simulation, we found that the experimental data had a good agreement with the theoretical simulation results before 1.8 ns, and was lower than the theoretical simulation results after that.

Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

Kong Xiao-Yan, Yue Lei-Lei, Chen Yu, Liu Ying-Kai
Chin. Phys. B 2012, 21 (9): 096101;  doi: 10.1088/1674-1056/21/9/096101
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The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section into epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F=0.1-0.85. In addition, the influence of filling fraction on the relative width of the minimum band gap is discussed.

Ab initio investigation on mechanical properties of copper

Liu Yue-Lin, Gui Li-Jiang, Jin Shuo
Chin. Phys. B 2012, 21 (9): 096102;  doi: 10.1088/1674-1056/21/9/096102
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Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have investigated the theoretical mechanical properties of copper (Cu) systematically. The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young's modulus Ep, and Poisson's ratio ν.

Fabrication of Ti ohmic contact to n-type 6H-SiC without high-temperature annealing

Chang Shao-Hui, Liu Xue-Chao, Huang Wei, Xiong Ze, Yang Jian-Hua, Shi Er-Wei
Chin. Phys. B 2012, 21 (9): 096801;  doi: 10.1088/1674-1056/21/9/096801
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The effect of surface morphology of 6H-SiC substrate on the ohmic contact properties of Ti/6H-SiC structure is studied. The H-terminated surface on Si-face 6H-SiC is obtained by both dipping SiC into HF acid solution for 15 s and thermal heating SiC in hydrogen atmosphere at 1100 ℃ for 10 min, while the H-terminated surface on C-face 6H-SiC could be obtained only by the latter method. Ti is deposited on Si-face and C-face SiC substrates with H-terminated surfaces and ohmic contact is obtained without high-temperature annealing.

Structural, electronic, and magnetic properties of Co-doped ZnO

Bakhtiar Ul Haq, A. Afaq, R. Ahmed, S. Naseem
Chin. Phys. B 2012, 21 (9): 097101;  doi: 10.1088/1674-1056/21/9/097101
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Density functional theory based calculations have been carried out to study structural, electronic, and magnetic properties of Zn1-xCoxO (x = 0, 0.25, 0.50, 0.75) in the zinc-blende phase, and the generalized gradient approximation proposed by Wu and Cohen has been used. Our calculated lattice constants decrease while the bulk moduli increase with the increase of Co2+ concentration. The calculated spin polarized band structures show the metallic behavior of Co-doped ZnO for both the up and the down spin cases with various doping concentrations. Moreover, the electron population is found to shift from the Zn-O bond to the Co-O bond with the increase of Co2+ concentration. The total magnetic moment, the interstitial magnetic moment, the valence and the conduction band edge spin splitting energies, and the exchange constants decrease, while the local magnetic moments of Zn, Co, O, the exchange spin splitting energies, and crystal field splitting energies increase with the increase of dopant concentration.

Ab initio calculations of the elastic, electronic, optical, and vibrational properties of PdGa compound under pressure

H. Koc, A. Yildirim, E. Deligoz
Chin. Phys. B 2012, 21 (9): 097102;  doi: 10.1088/1674-1056/21/9/097102
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The structural, elastic, electronic, optical, and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the frame of density functional theory. The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data. The obtained electronic band structures show that PdGa compound has no band gap. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. Our calculated results of elastic constants show that this compound is mechanically stable. Furthermore, the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function, the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study. The phonon dispersion curves are also derived using the direct method.

The electronic and magnetic properties of (Mn,C)-codoped ZnO diluted magnetic semiconductor

Zhao Long, Lu Peng-Fei, Yu Zhong-Yuan, Ma Shi-Jia, Ding Lu, Liu Jian-Tao
Chin. Phys. B 2012, 21 (9): 097103;  doi: 10.1088/1674-1056/21/9/097103
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The electronic and magnetic properties of (Mn,C)-codoped ZnO are studied in the Perdew-Burke-Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic (FM) interaction without acceptor co-doping. We observe that the FM interaction for (Mn,C)-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, We demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the (Mn,C)-codoped ZnO is FM semiconductor with super-high Curie temperature (TC=5475 K). These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.

A simple method of extracting the polarization charge density in the AlGaN/GaN heterostructure from current–voltage and capacitance–voltage characteristics

Lü Yuan-Jie, Lin Zhao-Jun, Yu Ying-Xia, Meng Ling-Guo, Cao Zhi-Fang, Luan Chong-Biao, Wang Zhan-Guo
Chin. Phys. B 2012, 21 (9): 097104;  doi: 10.1088/1674-1056/21/9/097104
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An Ni Schottky contact on the AlGaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN/GaN heterostructure is obtained from the forward current-voltage characteristics. With the measured capacitance-voltage curve and the flat-band voltage, the polarization charge density in the AlGaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodinger's and Poisson's equations.

Current transport in ZnO/Si heterostructure grown by laser molecular beam epitaxy

Teng Xiao-Yun, Wu Yan-Hua, Yu Wei, Gao Wei, Fu Guang-Sheng
Chin. Phys. B 2012, 21 (9): 097105;  doi: 10.1088/1674-1056/21/9/097105
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The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15 V < V < 0.6 V, the transport property is dominated by diffusion or recombination in the junction space charge region, while at higher voltages (V >0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm2, respectively.

Physical meaning of conductivity spectra for ZnO ceramics

Cheng Peng-Fei, Li Sheng-Tao, Li Jian-Ying, Ding Can, Yang Yan
Chin. Phys. B 2012, 21 (9): 097201;  doi: 10.1088/1674-1056/21/9/097201
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With the help of broadband dielectric spectroscopy in a wide temperature and frequency range, conductivity spectra of ZnO polycrystalline ceramics are measured and direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis. According to classical Debye theory and Cole-Cole equation, the physical meanings of the two conductivities are discussed. It is found that the DC-like conductivity corresponds to electron transportation over Schottky barrier at grainboundary. The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy). When it is in the high frequency region, relaxation conductivity obeys the universal law with the index n equal to the index α in Cole-Cole equation as an indictor of disorder degree.

Phonon-assisted intersubband transitions in wurtzite GaN/InxGa1-xN quantum wells

Zhu Jun, Ban Shi-Liang, Ha Si-Hua
Chin. Phys. B 2012, 21 (9): 097301;  doi: 10.1088/1674-1056/21/9/097301
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A detailed numerical calculation on the phonon-assisted intersubband transition rates of electrons in wurtzite GaN/InxGa1-xN quantum wells is presented. The quantum-confined Stark effect induced by the built-in electric field and the ternary mixed crystal effect are considered. The electron states are obtained by iteratively solving the coupled Schrödinger and Poisson equations and the dispersion property of each type of phonon modes is considered in the derivation of Fermi's golden rule to evaluate the transition rates. It is indicated that the interface and half-space phonon scattering play an important role in the process of 1-2 radiative transition. The transition rate is also greatly reduced by the built-in electric field. The present work can be helpful for the structural design and simulation of new semiconductor lasers.

Drain-induced barrier lowering effect for short channel dual material gate 4H silicon carbide metal–semiconductor field-effect transistor

Zhang Xian-Jun, Yang Yin-Tang, Duan Bao-Xing, Chai Chang-Chun, Song Kun, Chen Bin
Chin. Phys. B 2012, 21 (9): 097302;  doi: 10.1088/1674-1056/21/9/097302
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Sub-threshold characteristics of the dual material gate 4H-SiC MESFET (DMGFET) are investigated and the analytical models to describe the drain-induced barrier lowering (DIBL) effect are derived by solving one- and two-dimensional Poisson's equations. Using these models, we calculate the bottom potential of the channel and the threshold voltage shift, which characterize the DIBL effect. The calculated results reveal that the DMG structure alleviates the deterioration of the threshold voltage and thus suppresses the DIBL effect due to the introduced step function which originates from the work function difference of the two gate materials when compared with the conventional single material gate metal-semiconductor field-effect transistor (SMGFET).

Compatibility and optoelectronic of ZnSe nano crystalline thin film

Taj Muhammad Khan, Tayyaba BiBi
Chin. Phys. B 2012, 21 (9): 097303;  doi: 10.1088/1674-1056/21/9/097303
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We report the room temperature synthesis of zinc selenide (ZnSe) nano crystalline thin film on quartz by using a relatively simple and low cost closed space sublimation process (CSSP). The compatibility of the prepared thin films for optoelectronic applications was assessed by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), Raman spectroscopy, photoluminescence, and Fourier transform infrared spectroscopy (FT-IR). The XRD confirmed that the films were polycrystalline with the preferential orientation along the (111) plane corresponding to the cubic phase (2θ = 27.28°). The AFM indicated that the ZnSe film presented a smooth and compact morphology with RMS roughness 19.86 nm. The longitudinal optical phonon modes were observed at 247 cm-1 and 490 cm-1 attributed to the cubic structured ZnSe. The Zn-Se stretching band was confirmed by the FT-IR. The microstructure and compositional analysis was made with the SEM. The grain size, dislocation density, and strain calculated were co-related. All these properties manifested a good quality, high stability, finely adhesive, and closely packed structured ZnSe thin film for optoelectronic applications.

Effect of surface morphology on the electron mobility of epitaxial graphene grown on 0° and 8° Si-terminated 4H-SiC substrates

Li Jia, Wang Li, Feng Zhi-Hong, Yu Cui, Liu Qing-Bin, Dun Shao-Bo, Cai Shu-Jun
Chin. Phys. B 2012, 21 (9): 097304;  doi: 10.1088/1674-1056/21/9/097304
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Graphene with different surface morphologies were fabricated on 8°-off-axis and on-axis 4H-SiC(0001) substrates by high-temperature thermal decomposition. Graphene grown on Si-terminated 8°-off-axis 4H-SiC(0001) shows lower Hall mobility than the counterpart of on-axis SiC substrates. The terrace width is not responsible for different electron mobility of graphene grown on different substrates, as the terrace width is much larger than the mean free path of the electrons. The electron mobility of graphene remains unchanged with increasing terrace width on Si-terminated on-axis SiC. The interface scattering and short-range scattering are the main factors affecting the mobility of epitaxial graphene. After the optimization of the growth process, the Hall mobility of the graphene reaches 1770 cm2/V · s at a carrier density of 9.8.× 1012 cm-2. Wafer-size graphene was successfully achieved with an excellent double-layer thickness uniformity of 89.7% on a 3-inch SiC substrate.

Effect of C doping on the structural and electronic properties of LiFePO4: A first-principles investigation

Xu Gui-Gui, Wu Jing, Chen Zhi-Gao, Lin Ying-Bin, Huang Zhi-Gao
Chin. Phys. B 2012, 21 (9): 097401;  doi: 10.1088/1674-1056/21/9/097401
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Using first-principles calculations within the generalized gradient approximation (GGA) +U framework, we investigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favored, and C dopants prefer to occupy O3 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electronic conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3+, and it will be helpful to the hopping of electrons.

Hydrogen storage of Mg1-xMxH2 (M=Ti, V, Fe) studied using first-principles calculations

M. Bhihi, M. Lakhal, H. Labrim, A. Benyoussef, A. El Kenz, O. Mounkachi, E. K. Hlil
Chin. Phys. B 2012, 21 (9): 097501;  doi: 10.1088/1674-1056/21/9/097501
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In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg1-xMxH2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) approximation. In particular, the nature and the concentrations of the alloying elements and their effects are studied. Moreover, the material's stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.

Electron-mediated ferromagnetism in Fe-doped InP: Theory and experiment

Dong Shan, Zhu Feng
Chin. Phys. B 2012, 21 (9): 097502;  doi: 10.1088/1674-1056/21/9/097502
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We report on the electron-mediated ferromagnetism in Fe-doped InP from both first-principles calculations and experiments. Theoretically, based on spin-polarized density functional theory within Heyd-Scuseria-Ernzerhof (HSE03) approach, we systematically investigate the magnetic properties of Fe-doped InP and predict the existence of electron-mediated ferromagnetism. Experimentally, by diffusing Fe into the n-type InP wafer with thermal annealing at 800 ℃, we observe room-temperature ferromagnetism in InP:Fe, which is in agreement with the theoretical prediction.

Effect of misfit strain on the electrocaloric effect of polydomain epitaxial ferroelectric thin films

Qiu Jian-Hua, Ding Jian-Ning, Yuan Ning-Yi, Wang Xiu-Qin
Chin. Phys. B 2012, 21 (9): 097701;  doi: 10.1088/1674-1056/21/9/097701
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The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTiO3 thin films at room temperature is investigated using the Ginzburg-Landau-Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ca2 phase is much larger than that in the monodomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Improvement of dielectric tunability and loss tangent of (Ba,Sr)TiO3 thin films with K doping

Zhang Wei-Jie, Dai Jian-Ming, Zhu Xue-Bin, Chang Qing, Liu Qiang-Chun, Sun Yu-Ping
Chin. Phys. B 2012, 21 (9): 097702;  doi: 10.1088/1674-1056/21/9/097702
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Ba0.6Sr0.4TiO3 thin films doped with K were deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition method. The structure, surface morphology, and dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin films have been studied in detail. The K content in Ba0.6Sr0.4TiO3 thin films has a strong influence on the material's properties including surface morphology, dielectric and tunable properties. It is found that the Curie temperature of K-doped Ba0.6Sr0.4TiO3 films shifts to higher values compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.

Photoluminescence of silicone oil treated by fluorocarbon plasma

Chen Tian, Ye Chao, Yuan Ying, Deng Yan-Hong, Ge Shui-Bin, Xu Yi-Jun, Ning Zhao-Yuan, Pan Xiao-Pin, Wang Zhen-Ming
Chin. Phys. B 2012, 21 (9): 097802;  doi: 10.1088/1674-1056/21/9/097802
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We investigated the photoluminescence characteristics of the silicone oils treated by C2F6 and CHF3 plasma. The silicone oil treated by the C2F6 plasma emitted a white light mainly composed of 415 nm, 469 nm, and 554 nm emissions, while that treated by the CHF3 plasma emitted a pink light (415 nm). Fourier transformed infrared spectroscopy and Raman spectroscopy studies showed that the photoluminescence correlated with the Si-C bond, the carbon-related defects, and the oxygen vacancies. It was suggested that the light emitting at 554 nm was related to the Si-C bond and the carbon-related defects, while the pink emission at 415 nm was related to the oxygen vacancies.

Intense up-conversion emissions of Yb3+/Dy3+ co-doped Al2O3 nanopowders prepared by non-aqueous sol–gel method

Li Cheng-Ren, Li Shu-Feng, Dong Bin, Sun Jing-Chang, Bo Xiao-Feng, Fan Xu-Nan
Chin. Phys. B 2012, 21 (9): 097803;  doi: 10.1088/1674-1056/21/9/097803
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Yb3+/Dy3+ co-doped Al2O3 nanopowders have been prepared by the non-aqueous sol-gel method and their up- conversion photoluminescence spectra are measured under excitation by 980-nm semiconductor laser. The results show that there are comparatively abundant spectra of up-conversion emissions centered at 378, 408, 527 and 543, and 663 nm, corresponding to 4G9/26H13/2, 4G9/26H11/2, 4I15/26H13/2, and 4F9/26H11/2 transitions of Dy3+, respectively. Two-photon and three-photon processes are involved in ultraviolet, violet, green, and red up-conversion emissions. The energy transition between Yb3+ and Dy3+ is discussed.

Relative enhancement of photoluminescence intensity of passivated silicon nanocrystals in silicon dioxide matrix

Wu Zhi-Yong, Liu Ke-Xin, Ren Xiao-Tang
Chin. Phys. B 2012, 21 (9): 097804;  doi: 10.1088/1674-1056/21/9/097804
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Photoluminescence (PL) intensity of passivated silicon nanocrystals (Si NCs) embeded in an SiO2 matrix is compared with that of unpassivated ones. We investigate the relative enhancement of PL intensity (IR) as a function of annealing temperature and implanted Si ion dose. The IR increases simultaneously with the annealing temperature. This demonstrates an increase in the number of dangling bonds (DBs) with the degree of Si crystallization via varying the annealing temperature. The increase in IR with implanted Si ion dose is also observed. We believe that the near-field interaction between DBs and neighboring Si NCs is an additional factor that reduces the PL efficiency of unpassivated Si NCs.

Electrospun fluorescein/polymer composite nanofibers and their photoluminescent properties

Zhang Zhi-Hua, Long Yun-Ze, Yin Hong-Xin, Sun Bin,Zheng Jie, Zhang Hong-Di, Ji Xin-Ming, Gu Chang-Zhi
Chin. Phys. B 2012, 21 (9): 097805;  doi: 10.1088/1674-1056/21/9/097805
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Fluorescein/polyvinyl pyrrolidone (PVP) composite nanofibers with different fluorescein loadings (with weight concentration of 0-5.0%) are fabricated via electrospinning. Morphologies, structures and photoluminescent (PL) properties of these straight, helical or wavelike fibers are characterized by scanning electron microscope (SEM), fluorescence microscope and spectrophotometer. It is found that the maximum emission of the as-spun fluorescein/PVP fibers occurs at 510 nm. The PL intensity of the composite fiber increases with the increase of fluorescein concentration, then fluorescence quenching appears when the concentration reaches 1.67%. The mechanism of fluorescence quenching of fluorescein is discussed. In addition, the composite fibers exhibit much stronger PL intensity than fluorescein/PVP bulk film owing to larger specific surface area, which makes them promising materials for biomedical applications such as probes and sensors.

Effect of Sb-doping on the morphology and the dielectric properties of chrysanthemum-like ZnO nanowire clusters Hot!

Yan Jun-Feng, You Tian-Gui, Zhang Zhi-Yong, Tian Jiang-Xiao, Yun Jiang-Ni, Zhao Wu
Chin. Phys. B 2012, 21 (9): 098001;  doi: 10.1088/1674-1056/21/9/098001
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Chrysanthemum-like ZnO nanowire clusters with different Sb-doping concentrations were prepared by using the hydrothermal process. The microstructures, morphologies, and dielectric properties of the as-prepared products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission environment scanning electron microscope (FEESEM), and microwave vector network analyzer respectively. The results indicate that the as-prepared products are Sb-doped ZnO single crystallines with hexagonal wurtzite structure, the flower bud saturation degree Fd is obviously different from that of the pure ZnO nanowire clusters, the good dielectric loss property is found in Sb-doped ZnO products with low density, and the dielectric loss tangent tanδ e increases with the increase of the Sb-doping concentration in a certain concentration range.

Effects of carbon convection field on large diamond growth under high-pressure high-temperature conditions

Hu Mei-Hua, Li Shang-Sheng, Ma Hong-An, Su Tai-Chao, Li Xiao-Lei, Hu Qiang, Jia Xiao-Peng
Chin. Phys. B 2012, 21 (9): 098101;  doi: 10.1088/1674-1056/21/9/098101
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Large diamond crystals were successfully synthesized by FeNi-C system using temperature gradient method under high-pressure high-temperature conditions. The assembly of the growth cell was improved and the growth process of diamond was investigated. Effects of the symmetry of carbon convection field around the growing diamond crystal were investigated systematically by adjusting the position of seed crystal in the melted catalyst/solvent. The results indicate that morphologies and metal inclusion distributions of the synthetic diamond crystals vary obviously in both symmetric and non-symmetric carbon convection fields with temperature. Moreover, finite element method was applied to analyze carbon convection mode of the melted catalyst/solvent around the diamond crystal. This work is helpful for understanding the growth mechanism of diamond.

Microstructure and photocatalytic activity of titanium dioxide nanoparticles

Li Chun-Yan, Wang Jiang-Bin, Wang Yi-Qian
Chin. Phys. B 2012, 21 (9): 098102;  doi: 10.1088/1674-1056/21/9/098102
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Titanium dioxide nanoparticles with an average diameter of about 10 nm are fabricated using a sintering method. The degradation of methyl orange indicates that the photocatalytic efficiency is greatly enhanced, which is measured to be 62.81%. The transmission electron microscopy is used to investigate the microstructure of TiO2 nanoparticles in order to correlate with their photocatalytic properties. High-resolution transmission electron microscopy examinations show that all the nanoparticles belong to the anatase phase, and pure edge dislocations exist in some nanoparticles. The great enhancement of photocatalytic efficiency is attributed to two factors, the quantum size effect and the surface defects in the nanoparticles.

Carbon nanotube film synthesized from ethanol and its oxidation behavior in air

Ren Yan, Ma Wen-Jun, Zeng Qing-Sheng, Li Jin-Zhu, Dong Hai-Bo, Zhou Wei-Ya
Chin. Phys. B 2012, 21 (9): 098103;  doi: 10.1088/1674-1056/21/9/098103
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In this paper, we propose an efficient way to synthesize carbon nanotube films using ferrocene and ethanol. The as-grown film is free-standing, semi-transparent, and of macro scale size. The tubes in the film are mostly single- or double-walled. The oxidation behavior of the film is studied via Raman spectroscopy, and the result indicates that the inner wall of the double-walled tube is effectively protected from oxidation by the outer wall.

ZnO microbowls grown on ITO glass substrate through thermal evaporation

Zhang Zheng-Lin, Zheng Gang, Qu Feng-Yu, Wu Xiang
Chin. Phys. B 2012, 21 (9): 098104;  doi: 10.1088/1674-1056/21/9/098104
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Novel ZnO microbowls are successfully synthesized by thermal evaporating of a mixture of ZnS powder and Zn powder. The morphologies of the as-synthesized products can be adjusted by changing the temperature and the type of substrate. The morphologies, microstructures, and photoluminescence properties are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscope, and photoluminescence spectroscopy respectively. The growth mechanism of the as-synthesized ZnO microbowls is proposed based on the experimental results. ZnO microbowls presented here can be used as building blocks to fabricate optical and optoelectronic micro/nano devices.

Dynamics of reaction of O with H2 and its isotopic variants in different rotational excited states

Liu Yu-Fang, Liu Yan-Lei, Liang Bin
Chin. Phys. B 2012, 21 (9): 098201;  doi: 10.1088/1674-1056/21/9/098201
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Scalar properties and vector correlations of the reactions O+H2 →OH+H, O+HD→OH+D, O+DH→OD+H, and O+D2 →OD+D at collision energies of 25 and 34.6 kcal/mole have been studied via quasi-classical-trajectory (QCT) method based on a BMS1 potential energy surface (PES). Generalized polarization-dependent differential cross section and the distributions of the dihedral angle at the collision energy of 34.6 kacl/mole are presented. The calculated results indicate that both reagent rotational angular momentum and the mass factor have a significant influence on the scalar properties and vector correlations of the title reactions.

Scaling properties of phase-change line memory

Du Xiao-Feng, Song San-Nian, Song Zhi-Tang, Liu Wei-Li, Lü Shi-Long, Gu Yi-Feng, Xue Wei-Jia, Xi Wei
Chin. Phys. B 2012, 21 (9): 098401;  doi: 10.1088/1674-1056/21/9/098401
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Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current-voltage (I-V) and resistance-voltage (R-V) characteristics demonstrate that the power consumption decreases with the width of the phase-change line. A three-dimensional simulation is carried out to further study the scaling properties of phase-change line memory. The results show that the resistive amorphous (RESET) power consumption is proportional to the cross-sectional area of the phase-change line, but increases as the line length decreases.

Tuning rf-SQUID flux qubit system's potential with magnetic flux bias

Hua Tao, Xu Wei-Wei, Shi Jian-Xin, An De-Yue, Sun Guo-Zhu, Yu Yang, Wu Pei-Heng
Chin. Phys. B 2012, 21 (9): 098501;  doi: 10.1088/1674-1056/21/9/098501
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At an extremely low temperature of 20 mK, we measured loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φf) and the small dc-SQUID (Φfcjj), respectively, the potential shape of the system can be fully controlled in situ. Variations of transition step and overlap size in switching current with the barrier flux bias are analyzed, from which we can obtain some relevant device parameters and built up a model to explain the experimental phenomenon.

Microwave damage susceptibility trend of bipolar transistor as a function of frequency

Ma Zhen-Yang, Chai Chang-Chun, Ren Xing-Rong, Yang Yin-Tang, Chen Bin, Song Kun, Zhao Ying-Bo
Chin. Phys. B 2012, 21 (9): 098502;  doi: 10.1088/1674-1056/21/9/098502
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We conduct a theoretical study of the damage susceptibility trend of a typical bipolar transistor induced by high-power microwave (HPM) as a function of frequency. The dependences of the burnout time and the damage power on the signal frequency are obtained. Studies of the internal damage process and the mechanism of the device are carried out from the variation analysis of the distribution of the electric field, current density, and temperature. The investigation shows that the burnout time linearly depends on the signal frequency. The current density and the electric field at the damage position decrease with increasing frequency. Meanwhile, the temperature elevation occurs in the area between the p-n junction and the n-n+ interface due to the increase of the electric field. Adopting the data analysis software, the relationship between the damage power and the frequency is obtained. Moreover, the thickness of the substrate has a significant effect on the burnout time.

A novel sensitivity model for short nets

Liu Shi-Gang, Wang Jun-Ping, Su Yong-Bang, Wang Le
Chin. Phys. B 2012, 21 (9): 098503;  doi: 10.1088/1674-1056/21/9/098503
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For modern processes at deep sub-micron technology node, yield design, especially the yield design at the stage of layout design is an important way to deal with the problem about manufacturability and yield. In order to reduce the yield loss caused by redundancy material defect, choice of nets to be optimized at first is an important step in the process of layout optimization. This paper provides a new sensitivity model for short net, which is net-based and reflects the size of the critical area between a single net and the nets around it. Since this model is based on a single net and includes the information of surrounding nets,the critical area between the single net and surrounding nets can be reduced at the same time. In this way, the efficiency of layout optimization becomes higher. According to experimental observations, this sensitivity model can be used to choose the position for optimization. Compared with the chip-area-based and basic-layout-based sensitivity models, our sensitivity model not only has higher efficiency, but also hold true for choosing the net to be optimized at first.

Color-converted remote phosphor prototype of multiwavelength excitable borosilicate glass for white light-emitting diodes

Tian Hua, Liu Ji-Wen, Qiu Kun, Song Jun, Wang Da-Jian
Chin. Phys. B 2012, 21 (9): 098504;  doi: 10.1088/1674-1056/21/9/098504
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We report a unique red light-emitting Eu-doped borosilicate glass to convert color for warm white light-emitting diodes. This glass can be excited by from 394 nm-peaked near ultraviolet light, 466 nm-peaked blue light, to 534 nm-peaked green light to emit desired red light with an excellent transmission in the wavelength range of 400-700 nm which makes this glass suitable for the color conversion without great cost of luminous power loss. In particular, assembling this glass to commercial white light-emitting diodes, the tested results show that the color rendering index is improved to 84 with a loss of luminous power by 12 percent at average, making this variety of glass promising for inorganic "remote-phosphor" color conversion.

A population-level model from the microscopic dynamics in Escherichia coli chemotaxis via Langevin approximation

He Zhuo-Ran, Wu Tai-Lin, Ouyang Qi, Tu Yu-Hai
Chin. Phys. B 2012, 21 (9): 098701;  doi: 10.1088/1674-1056/21/9/098701
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Recent extensive studies of Escherichia coli (E. coli) chemotaxis have achieved a deep understanding of its microscopic control dynamics. As a result, various quantitatively predictive models have been developed to describe the chemotactic behavior of E. coli motion. However, a population-level partial differential equation (PDE) that rationally incorporates such microscopic dynamics is still insufficient. Apart from the traditional Keller-Segel (K-S) equation, many existing population-level models developed from the microscopic dynamics are integro-PDEs. The difficulty comes mainly from cell tumbles which yield a velocity jumping process. Here, we propose a Langevin approximation method that avoids such a difficulty without appreciable loss of precision. The resulting model not only quantitatively reproduces the results of pathway-based single-cell simulators, but also provides new inside information on the mechanism of E. coli chemotaxis. Our study demonstrates a possible alternative in establishing a simple population-level model that allows for the complex microscopic mechanisms in bacterial chemotaxis.

SPICE modeling of memristors with multilevel resistance states

Fang Xu-Dong, Tang Yu-Hua, Wu Jun-Jie
Chin. Phys. B 2012, 21 (9): 098901;  doi: 10.1088/1674-1056/21/9/098901
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With CMOS technologies approaching the scaling ceiling, novel memory technologies have thrived in recent years, among which the memristor is a rather promising candidate for future resistive memory (RRAM). Memristor's potential to store multiple bits of information as different resistance levels allows its application in multilevel cell (MCL) technology, which can significantly increase the memory capacity. However, most existing memristor models are built for binary or continuous memristance switching. In this paper, we propose the simulation program with integrated circuits emphasis (SPICE) modeling of charge-controlled and flux-controlled memristors with multilevel resistance states based on the memristance versus state map. In our model, the memristance switches abruptly between neighboring resistance states. The proposed model allows users to easily set the number of the resistance levels as parameters, and provides the predicability of resistance switching time if the input current/voltage waveform is given. The functionality of our models has been validated in HSPICE. The models can be used in multilevel RRAM modeling as well as in artificial neural network simulations.

Effects of node buffer and capacity on network traffic

Ling Xiang, Hu Mao-Bin, Ding Jian-Xun
Chin. Phys. B 2012, 21 (9): 098902;  doi: 10.1088/1674-1056/21/9/098902
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In this paper, we study the optimization of network traffic by considering the effects of the node's buffer ability and capacity. Two node buffer settings are considered. The node capacity is considered to be proportional to its buffer ability. The node effects on network traffic systems are studied with the shortest path protocol and an extension of the optimal routing [Phys. Rev. E 74 046106 (2006)]. In the diagrams of flux-density relation, it is shown that the node's buffer ability and capacity have profound effects on the network traffic.

Parasitic bipolar amplification in single event transient and its temperature dependence

Liu Zheng, Chen Shu-Ming, Chen Jian-Jun, Qin Jun-Rui, Liu Rong-Rong
Chin. Phys. B 2012, 21 (9): 099401;  doi: 10.1088/1674-1056/21/9/099401
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Using three-dimensional technology computer-aided design (TCAD) simulation, parasitic bipolar amplification in single event transient (SET) current of single transistor and its temperature dependence are studied. We quantify the contributions of different current components in SET current pulse, and it is found that the proportion of parasitic bipolar amplification in total collected charge is about 30% in both 130-nm and 90-nm technologies. The temperature dependence of parasitic bipolar amplification and the mechanism of SET pulse are also investigated and quantified. The results show that the proportion of charge induced by parasitic bipolar increases with rising temperature, which illustrates that the parasitic bipolar amplification plays an important role in the charge collection of single transistor.

Proton capture reaction of 33S in nova V1065 Centauri

Luo Zhi-Quan, Zhang Jie, Long Jian-Hong
Chin. Phys. B 2012, 21 (9): 099701;  doi: 10.1088/1674-1056/21/9/099701
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The previous studies have shown that 33S(p, γ)34Cl is the most important reaction that affects the abundance of 33S in the product of nova nucleosynthesis. In this paper, a more accurate thermonuclear reaction rate of 33S (p, γ) 34Cl in the nova is calculated based on the newly measured 34Cl nuclear resonance levels. The electron screening correction and the non-resonance and the narrow-resonance contributions are considered. The calculations are also combined with the recent observational data of nova V1065 Centauri and show that the thermonuclear reaction rates of 33S (p, γ) 34Cl are significantly different in the improved method. Because these results can affect the isotopic ratio of sulfur in the nova ejecta significantly, we make an estimate of the values of 32S/33S and 33S/33S, which can be used as a diagnostic tool for the novae.
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