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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.8
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GENERAL

A type of conserved quantity of Mei symmetry of Nielsen equations for a holonomic system

Cui Jin-Chao, Han Yue-Lin, Jia Li-Qun
Chin. Phys. B 2012, 21 (8): 080201;  doi: 10.1088/1674-1056/21/8/080201
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A type of structural equation and conserved quantity which are directly induced by Mei symmetry of Nielsen equations for a holonomic system are studied. Under the infinitesimal transformation of groups, from the definition and the criterion of Mei symmetry, a type of structural equation and conserved quantity for the system by proposition 2 are obtained, and the inferences in two special cases are given. Finally, an example is given to illustrate the application of the results.

Controls for the generations of high-order harmonics and attosecond pulses by infrared laser field combined with a low-frequency pulse

He Hai-Xiang, Guo Ya-Hui, He Guo-Zhong
Chin. Phys. B 2012, 21 (8): 080202;  doi: 10.1088/1674-1056/21/8/080202
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We investigate high-order harmonic generations by controlling various quantum paths of harmonics in an infrared laser field which combines a low-frequency pulse. Both classical theory and quantum wavelet transform method are used to understand the physics of harmonics. By adjusting the carrier envelope phase of the fundamental field, the intensities of harmonic spectra increase and the harmonics in the plateau become regular. Attosecond pulses each with a duration of 58 as are obtained directly by compressing the harmonics, and with phase compensation an isolated attosecond pulse less than 30 as can be generated.

Quantum election scheme based on anonymous quantum key distribution

Zhou Rui-Rui, Yang Li
Chin. Phys. B 2012, 21 (8): 080301;  doi: 10.1088/1674-1056/21/8/080301
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An unconditionally secure authority-certified anonymous quantum key distribution scheme using conjugate coding is presented, based on which we construct a quantum election scheme without the help of entanglement state. We show that this election scheme ensures the completeness, soundness, privacy, eligibility, unreusability, fairness, and verifiability of a large-scale election in which the administrator and counter are semi-honest. This election scheme can work even if there exist loss and errors in quantum channels. In addition, any irregularity in this scheme is sensible.

New approach for obtaining the time-evolution law of chaotic light field in damping–gaining process

Gong Li-Hua, Zhou Nan-Run, Hu Li-Yun, Fan Hong-Yi
Chin. Phys. B 2012, 21 (8): 080302;  doi: 10.1088/1674-1056/21/8/080302
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A new approach for studying the time-evolution law of chaotic light field in damping-gaining coexisting process is presented. The new differential equation for determining the parameter of the density operator ρ(t) is derived and the solution of f′ for damping and gaining processes are studied separately. Our approach is direct and the result is concise since it is not necessarily for us to know the Kraus operators in advance.

Quantum superdense coding based on hyperentanglement

Zhao Rui-Tong, Guo Qi, Chen Li, Wang Hong-Fu, Zhang Shou
Chin. Phys. B 2012, 21 (8): 080303;  doi: 10.1088/1674-1056/21/8/080303
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We present a scheme for quantum superdense coding with hyperentanglement, in which the sender can transfer four bits of classical information by sending only one photon. The important device in the scheme is hyperentangled Bell-state analyzer in both of polarization and frequency degrees of freedom, which is also constructed in the paper by using quantum nondemolition detector assisted by cross-Kerr nonlinearity. Our scheme can transfer more information with less resources than the existing schemes and is nearly deterministic and nondestructive.

Squeeze-swapping by Bell measurement studied in terms of the entangled state representation

Li Xue-Chao, Xie Chuan-Mei, Fan Hong-Yi
Chin. Phys. B 2012, 21 (8): 080304;  doi: 10.1088/1674-1056/21/8/080304
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By virtue of the entangled state representation (Hong-Yi Fan and J R Klauder 1994 Phys. Rev. A 49 704) and the two-mode squeezing operator's natural representation (Hong-Yi Fan and Yue Fan 1996 Phys. Rev. A 54 958) we propose the squeeze-swapping mechanism that can generate quantum entanglement and new squeezed states of continuum variables.

Entanglement evolution of three-qubit mixed states in multipartite cavity–reservoir systems

Xu Jing-Zhou, Guo Jin-Bao, Wen Wei, Bai Yan-Kui, Yan Feng-Li
Chin. Phys. B 2012, 21 (8): 080305;  doi: 10.1088/1674-1056/21/8/080305
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We analyze the multipartite entanglement evolution of three-qubit mixed states composed of a GHZ state and a W state. For a composite system consisting of three cavities interacting with independent reservoirs, it is shown that the entanglement evolution is restricted by a set of monogamy relations. Furthermore, as quantified by the negativity, the entanglement dynamical property of the mixed entangled state of cavity photons is investigated. It is found that the three cavity photons can exhibit the phenomenon of entanglement sudden death (ESD). However, compared with the evolution of a generalized three-qubit GHZ state which has the equal initial entanglement, the ESD time of mixed states is latter than that of the pure state. Finally, we discuss the entanglement distribution in the multipartite system, and point out the intrinsic relation between the ESD of cavity photons and the entanglement sudden birth of reservoirs.

Thermal properties of Lense–Thirring spacetime in tetrad theory of gravity

Gamal G. L. Nashed
Chin. Phys. B 2012, 21 (8): 080401;  doi: 10.1088/1674-1056/21/8/080401
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Using the divergence term appearing in the Lagrangian of the teleparallel equivalent of general relativity (TEGR), we calculate the thermodynamic quantities of four-tetrads spacetime reproducing Lense-Thirring (LT) metric. We also investigate the first law of thermodynamics and quantum statistical relation.

Absorption of massless scalar wave from Schwarzschild black hole surrounded by quintessence

Liao Hao, Chen Ju-Hua, Wang Yong-Jiu
Chin. Phys. B 2012, 21 (8): 080402;  doi: 10.1088/1674-1056/21/8/080402
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By using the partial wave method, we investigate the absorption of massless scalar wave from Schwarzschild black hole surrounded by the quintessence. We obtained the expression of absorption cross section
080402
Then we numerically carry out the absorption cross section and we find that the larger angular momentum quantum number l is, the smaller the corresponding maximum value of partial absorption cross section is, and that the total absorption cross section tends to geometric-optical limit σabshf≈ π bc2. We also find that higher value of ωq (state parameter of the quintessence) corresponds the higher value of absorption cross section σabs.

Feshbach resonance management of vector solitons in two-component Bose–Einstein condensates Hot!

Wang Qiang, Wen Lin, Li Zai-Dong
Chin. Phys. B 2012, 21 (8): 080501;  doi: 10.1088/1674-1056/21/8/080501
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We consider two coupled Gross-Pitaevskii equations describing a two-component Bose-Einstein condensates with time-dependent atomic interactions loaded in an external harmonic potential, and investigate the dynamics of vector solitons. By using a direct method, we construct a novel family of vector soliton solutions, which are the linear combination between dark and bright solitons in each component. Our results show that due to the superposition between dark and bright solitons, such vector solitons possess many novel and interesting properties. The dynamics of vector solitons can be controlled by Feshbach resonance technique, and the vector solitons can keep the dynamic stability against the variation of the scattering length.

Entropic stochastic resonance in a confined structure driven by dichotomous noise and white noises

Guo Feng, Cheng Xiao-Feng, Li Shao-Fu, Cao Wen, Li Heng
Chin. Phys. B 2012, 21 (8): 080502;  doi: 10.1088/1674-1056/21/8/080502
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The entropic stochastic resonance (ESR) in a confined system subjected to dichotomous noise and white noise and driven by a periodic sinusoidal force along the x axis of the structure and a time-dependent force in the declining direction, is investigated. Under the adiabatic approximation condition and based on two-state theory, the expression of the output signal-to-noise ratio (SNR) is obtained. The results show that the SNR is a non-monotonic function of the strengths of dichotomous noise, white noise, and correlated strength of correlated noise. In addition, the SNR varies non-monotonically with the increase of the shape parameters of the confined structure, and also with the increase of the constant force along the y axis of the structure. The influence of the correlation rate of the dichotomous noise, and that of the frequency of the periodic force on the SNR are discussed.

Modeling and dynamics analysis of the fractional-order Buck–Boost converter in continuous conduction mode

Yang Ning-Ning, Liu Chong-Xin, Wu Chao-Jun
Chin. Phys. B 2012, 21 (8): 080503;  doi: 10.1088/1674-1056/21/8/080503
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In this paper, the fractional-order mathematical model and the fractional-order state-space averaging model of the Buck-Boost converter in continuous conduction mode (CCM) are established based on the fractional calculus and the Adomian decomposition method. Some dynamical properties of the current-mode controlled fractional-order Buck-Boost converter are analysed. The simulation is accomplished by using SIMULINK. Numerical simulations are presented to verify the analytical results. And we find that bifurcation points will be moved backward as α and β vary. At the same time, the simulation results show that the converter goes through different routes to chaos.

Multifractal analysis of complex networks

Wang Dan-Ling, Yu Zu-Guo, Anh V
Chin. Phys. B 2012, 21 (8): 080504;  doi: 10.1088/1674-1056/21/8/080504
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Complex networks have recently attracted much attention in diverse areas of science and technology. Many networks such as the WWW and biological networks are known to display spatial heterogeneity which can be characterized by their fractal dimensions. Multifractal analysis is a useful way to systematically describe the spatial heterogeneity of both theoretical and experimental fractal patterns. In this paper, we introduce a new box covering algorithm for multifractal analysis of complex networks. This algorithm is used to calculate the generalized fractal dimensions Dq of some theoretical networks, namely scale-free networks, small world networks, and random networks, and one kind of real networks, namely protein-protein interaction networks of different species. Our numerical results indicate the existence of multifractality in scale-free networks and protein-protein interaction networks, while the multifractal behavior is not clear-cut for small world networks and random networks. The possible variation of Dq due to changes in the parameters of the theoretical network models is also discussed.

A single adaptive controller with one variable for synchronization of fractional-order chaotic systems

Zhang Ruo-Xun, Yang Shi-Ping
Chin. Phys. B 2012, 21 (8): 080505;  doi: 10.1088/1674-1056/21/8/080505
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In this paper we investigate the synchronization of a class of three-dimensional fractional-order chaotic systems. Based on Lyapunov stability theory and adaptive control technique, a single adaptive-feedback controller is developed to synchronize a class of fractional-order chaotic systems. The presented controller which only contains a single driving variable is simple both in design and in implementation. Numerical simulation and circuit experimental results for fractional-order chaotic system are provided to illustrate the effectiveness of the proposed scheme.

Does the eigenratio λ2N represent the synchronizability of a complex network?

Duan Zhi-Sheng, Chen Guan-Rong
Chin. Phys. B 2012, 21 (8): 080506;  doi: 10.1088/1674-1056/21/8/080506
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In the study of complex networks, it is commonly believed that the eigenratio λ2N of the Laplacian matrix of a network represents the network synchronizability, especially for symmetric networks. This paper gives two counterexamples to show that this is not true for the case where the network has a disconnected synchronized region. Consequently, a simple answer is presented to the question of when the eigenratio λ2N does represent the network synchronizability.

Ultrashort optical solitons in the dispersion-decreasing fibers

Dai Chao-Qing, Chen Jun-Lang
Chin. Phys. B 2012, 21 (8): 080507;  doi: 10.1088/1674-1056/21/8/080507
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We derive analytical bright and dark solitons of the modified nonlinear Schrödinger equations with variable coefficients. Under constraint condition between system parameters, the optical soliton transmission in the dispersion-decreasing fibers can be exactly controlled by proper dispersion management. The analytical description of the interactions between the bright and dark solitons are firstly obtained.

Equation of state for solids with considering cohesive energy and anharmonic effect and its application to MgO

Zhang Da, Sun Jiu-Xun
Chin. Phys. B 2012, 21 (8): 080508;  doi: 10.1088/1674-1056/21/8/080508
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A simple equation of state (EOS) in wide ranges of pressure and temperature is constructed within the Mie-Grüneisen-Debye framework. Instead of the popular Birch-Murnaghan and Vinet EOS, we employ a five-parameter cold energy expression to represent the static EOS term, which can correctly produce cohesive energy without any spurious oscillations in extreme compression and expansion region. We developed a Padé approximation-based analytic Debye quasiharmonic model with high accuracy which improves the performance of EOS in low temperature region. The anharmonic effect is taken into account by using a semi-empirical approach. Its reasonability is verified by the fact that the total thermal pressure tends to the lowest-order anharmonic expansion in the literature at low temperature, and tends to ideal-gas limitation at high temperature, which is physically correct. Besides, based on this approach, the anharmonic thermal pressure can be expressed in the Grüneisen form, which is convenient for applications. The proposed EOS is used to study the thermodynamic properties of MgO including static and shock compression conditions, and the results are very satisfactory as compared with the experimental data.

Increasing rewriting speed of optical rewritable e-paper by selecting proper liquid crystals

Geng Yu, Sun Jiatong, Anatoli Murauski, Vladimir Chigrinov, Kwok Hoi Sing
Chin. Phys. B 2012, 21 (8): 080701;  doi: 10.1088/1674-1056/21/8/080701
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Effect of interaction between liquid crystal (LC) and photoalignment material on speed of optical rewriting process is investigated. The theoretical analysis shows that smaller frank elastic constant K22 of liquid crystal corresponds to larger twist angle, which gives rise to larger rewriting speed. Six different LC cells with the same boundary conditions (one substrate is covered with rubbed polyimide (PI) and other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity (450 nm, 80 mW/cm2). The results demonstrate that with suitable liquid crystal, LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 (K22 is larger) and 5CB (K22 is smaller), they require 11 s and 6 s corresponding to change alignment direction for generating image information.

Crystal structure and thermochemical properties of phase change materials bis(1-octylammonium) tetrachlorochromate

Lu Dong-Fei, Di You-Ying, He Dong-Hua
Chin. Phys. B 2012, 21 (8): 080702;  doi: 10.1088/1674-1056/21/8/080702
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A new crystalline complex (C8H17NH3)2CdCl4(s) (abbreviated as C8Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be UPOT (C8Cd(s))=978.83 kJ·mol-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3± 0.15 K, 10.15± 0.23 kJ·mol-1, and 33.05± 0.78 J·K-1·mol-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.

Effect of bias condition on heavy ion radiation in bipolar junction transistor

Liu Chao-Ming, Li Xing-Ji, Geng Hong-Bin, Yang De-Zhuang, He Shi-Yu
Chin. Phys. B 2012, 21 (8): 080703;  doi: 10.1088/1674-1056/21/8/080703
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The characteristic degradations in silicon NPN bipolar junction transistor (BJT) of 3DG142 type are examined under the irradiation with 40-MeV chlorine (Cl) ions under forward, grounded, and reverse bias conditions, respectively. Different electrical parameters are in-situ measured during the exposure under each bias condition. From the experimental data, larger variation of base current (IB) is observed after irradiation at a given value of base-emitter voltage (VBE), while the collector current is slightly affected by irradiation at a given VBE. The gain degradation is affected mostly by the behaviour of the base current. From the experimental data, the variation of current gain in the case of forward bias is much smaller than that in the other conditions. Moreover, for 3DG142 BJT, the current gain degradation in the case of reverse bias is more severe than that in the grounded case at low fluence, while at high fluence, the gain degradation in the reverse bias case becomes smaller than that in the grounded case.
ATOMIC AND MOLECULAR PHYSICS

Investigation of activities of grain boundaries in nanocrystalline Al under an indenter by a multiscale method

Shao Yu-Fei, Yang Xin, Zhao Xing, Wang Shao-Qing
Chin. Phys. B 2012, 21 (8): 083101;  doi: 10.1088/1674-1056/21/8/083101
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Activities of grain boundaries in nanocrystalline Al under an indenter are studied by a multiscale method. It is found that grain boundaries and twin boundaries can be transformed into each other by emitting and absorbing dislocations. The transition processes might result in grain coarsening and refinement events. Dislocation reflection generated by a piece of stable grain boundary is also observed, because of the complex local atomic structure within the nanocrystalline Al. This implies that nanocrystalline metals might improve their internal structural stability with the help of some special local grain boundaries.

Size-dependent surface tension of cylindrical nano-bubble in liquid Ar

Yan Hong, Zhu Ru-Zeng, Wei Jiu-An
Chin. Phys. B 2012, 21 (8): 083102;  doi: 10.1088/1674-1056/21/8/083102
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In view of the continued disputes on the fundamental question whether the surface tension of vapour bubble in liquid argon increases, or decreases, or remains unchanged with the increase of curvature radius, the cylindrical vapour bubble of argon is studied by molecular dynamics simulation in this paper instead of spherical vapour bubble so as to reduce the statistical error. So far the surface tension of the cylindrical vapour bubble has not been studied by molecular dynamics simulation in the literature. Our results show that the surface tension decreases with radius increasing. By fitting Tolman equation with our data, the Tolman length δ =-0.6225 sigma is given under cut-off radius 2.5σ, where σ =0.3405 nm is the diameter of argon atom. The Tolman length of Ar being negative is affirmed and the Tolman length of Ar being approximately zero given in the literature is negated, and it is pointed that this error is attributed to the application of the inapplicable empirical equation of state and the neglect of the difference between surface of tension and equimolar surface.

Dynamic mechanism for encapsulating two HIV replication inhibitor peptides with carbon nanotubes

Chen Bao-Dong, Yang Chuan-Lu, Wang Mei-Shan, Ma Xiao-Guang
Chin. Phys. B 2012, 21 (8): 083103;  doi: 10.1088/1674-1056/21/8/083103
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Encapsulation of biomolecules inside carbon nanotube (CNT) has attracted great interest because it could provide possibility to delivery nanoscale pharmaceutical drug with CNT-based devices. Using molecular dynamics simulation, we investigate the dynamic process by which human immunodeficiency virus (HIV) replication inhibitor peptides (HRIPs) are encapsulated in a water solution contained inside CNT. The van der Waals attraction between HRIP and CNT and the root-mean-square deviation are used to analyse the evolution of the encapsulation. It is found that the interaction between the HRIP and the CNT is the main drive force for the encapsulation process and the encapsulation without causing obvious conformational change of the HRIPs.

An ab initio investigation of the low-lying electronic states of BeH

Dong Yan-Ran, Zhang Shu-Dong, Hou Sheng-Wei, Cheng Qi-Yuan
Chin. Phys. B 2012, 21 (8): 083104;  doi: 10.1088/1674-1056/21/8/083104
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Potential energy curves (PECs) for the ground state (X2Σ+) and the four excited electronic states (A2Π, B2Π, C2Σ+, 4Π) of BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction (MRCI) approach in combination with the aug-cc-pVTZ basis sets. The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm, and the equilibrium bond length Re and the vertical excited energy Te are determined directly. It is evident that the X2Σ+, A2Π, B2Π, C2Σ+ states are bound and 4Π is a repulsive excited state. With the potentials, all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero (J = 0) by numerically solving the radial Schrödinger equation of nuclear motion. Then the spectroscopic data are obtained including the rotation coupling constant ωe, the anharmonic constant ωexe, the equilibrium rotation constant Be and the vibration–rotation coupling constant αe. These values are compared with theoretical and experimental results currently available, showing that they are in agreement with each other.

On long-time limit behavior of the solution of atom's master equation

Chen Jun-Hua, Fan Hong-Yi, Jiang Nian-Quan
Chin. Phys. B 2012, 21 (8): 083201;  doi: 10.1088/1674-1056/21/8/083201
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We study long-time limit behavior of the solution of atom's master equation, for the first time we derive that the probability of the atom being in the α-th (α =j+1-jz, j is the angular momentum quantum number, jz is the z-component of angular momentum) state is {(1-K/G)/[1-(K/G)2j+1]}(K/G)α-1 as t→+∞, which coincides with the fact that when K/G > 1, the larger the α is, the larger probability of the atom being in the α-th state (the lower excited state). We also consider the case for some possible generalizations of the atomic master equation.

Laser induced collisional energy transfer in Sr–Li system

Chen De-Ying, Lu Zhen-Zhong, Fan Rong-Wei, Xia Yuan-Qin, Zhou Zhi-Gang, Ji Yi-Qin
Chin. Phys. B 2012, 21 (8): 083202;  doi: 10.1088/1674-1056/21/8/083202
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A four-state model with considering the relative velocity distribution function for calculating the cross section of laser-induced collisional energy transfer in Sr-Li system is presented and profiles of laser induced collision cross section are obtained. The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry. Both of the two intermediate states have contributions to the finial state, and none of the intermediate states should be neglected. The peak of the laser-induced collisional energy transfer (LICET) profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing. A cross section of 1.2× 10-12 cm2 at a laser field intensity of 2.17× 107 V/m is obtained, which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state. The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process which is not accounted for in a two-state treatment.

The effect of anti-hydrogen bond on Fermi resonance: A Raman spectroscopic study of the Fermi doublet ν1ν12 of liquid pyridine

Li Dong-Fei, Gao Shu-Qin, Sun Cheng-Lin, Li Zuo-Wei
Chin. Phys. B 2012, 21 (8): 083301;  doi: 10.1088/1674-1056/21/8/083301
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The effects of anti-hydrogen bond on the ν1ν12 Fermi resonance (FR) of pyridine are experimentally investigated by using Raman scattering spectroscopy. Three systems, pyridine/water, pyridine/formamide, pyridine/carbon tetrachloride, provide varying degrees of strength for the diluent-pyridine anti-hydrogen bond complex. Water forms a stronger anti-hydrogen bond with pyridine than with formamide, and in the case of adding non-polar solvent carbon tetrachloride, which is neither a hydrogen bond donor nor an acceptor and incapable of forming hydrogen bond with pyridine, the intermolecular distance of pyridine will increase and the interaction of pyridine molecules will reduce. The dilution studies are performed on the three systems. Comparing with the values of Fermi coupling coefficient W of the ring breathing mode ν 1 and triangle mode ν 12 of pyridine at different volume concentrations, which are calculated according to the Bertran equations, in three systems, we find that the solution with the strongest anti-hydrogen bond, water, shows the fastest change in the ν1ν12 Fermi coupling coefficient W with the volume concentration varying, followed by the formamide and carbon tetrachloride solutions. These results suggest that the stronger anti-hydrogen bond-forming effect will cause a greater reduction in the strength of the ν1ν12 FR of pyridine. According to the mechanism of the formation of anti-hydrogen bond in the complexes and the FR theory, a qualitative explanation for the anti-hydrogen bond effect in reducing the strength of the ν1ν12 FR of pyridine is given.

Flexural resonance vibrations of piezoelectric ceramic tubes in Besocke-style scanners

Zhang Hui, Zhang Shu-Yi, Fan Li
Chin. Phys. B 2012, 21 (8): 083302;  doi: 10.1088/1674-1056/21/8/083302
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Flexural resonance vibrations of piezoelectric ceramic tubes in Besocke-style scanners with the nanometer resolution are studied by an electro-mechanical coupling Timoshenko beam model. Meanwhile, the effects of frictions, the first moment and moment of inertia induced by mass loads are considered. The predicted resonance frequencies of the ceramic tubes are sensitive to not only the mechanical parameters of the scanners, but also the frictions acting on the attached shaking ball and corresponding bending moment on the tubes. The theoretical results are in excellent agreement with the related experimental measurements. This model and corresponding results are applicable for optimizing the structures and performances of the scanners.

Fine-tuning the thicknesses of organic layers to realize high-efficiency and long-lifetime blue organic light-emitting diodes

Yu Jian-Ning, Zhang Min-Yan, Li Chong, Shang Yu-Zhu, Lü Yan-Fang, Wei Bin, Huang Wei
Chin. Phys. B 2012, 21 (8): 083303;  doi: 10.1088/1674-1056/21/8/083303
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By using p-bis(p-N, N-diphenyl-aminostyryl)benzene doped 2-tert-butyl-9, 10-bis-β-naphthyl)-anthracene as an emitting layer, we fabricate a high-efficiency and long-lifetime blue organic light emitting diode with a maximum external quantum efficiency of 6.19% and a stable lifetime at a high initial current density of 0.0375 A/cm2. We demonstrate that the change in the thicknesses of organic layers affects the operating voltage and luminous efficiency more greatly than the lifetime. This lifetime independent of thickness is beneficial to achieving high-quality full-colour display devices and white lighting sources with multi-emitters.

The effect of electron initial longitudinal velocity on non-sequential double ionization process in elliptically polarized laser field

Hao Xiao-Lei, Li Wei-Dong, Liu Jie, Chen Jing
Chin. Phys. B 2012, 21 (8): 083304;  doi: 10.1088/1674-1056/21/8/083304
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The effect of initial longitudinal velocity of the tunnelled electron on the non-sequential double ionization (NSDI) process in elliptically polarized laser field is studied by a semiclassical model. We find that the non-zero initial longitudinal velocity has a suppressing effect on single-return collision (SRC) events in double ionization process, more specifically, it results in an obvious reduction in the center part of the correlation momentum distributions in the direction of the major polarization axis (z axis) and makes the distribution of single-return collision in the minor polarization axis (x axis) become narrow.

Study of (e, 2e) process on potassium at 6 eV–60 eV above threshold in second-order Born approximation

Wang Yang, Zhou Ya-Jun, Jiao Li-Guang
Chin. Phys. B 2012, 21 (8): 083401;  doi: 10.1088/1674-1056/21/8/083401
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The standard distorted wave Born approximation (DWBA) method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target. Second-order DWBA calculations have been preformed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for alkali target potassium at excess energies of 6 eV-60 eV. Comparing with the first-order DWBA calculations before, the present theoretical model improves the degree of agreement with experiments, especially for backward scattering angle region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems in low and intermediate energy range.

A density functional theory study on size-dependent structures, stabilities, and electronic properties of the bimetallic MnAgm (M=Na, Li; n+m ≤ 7) clusters

Sun Hao-Ran, Kuang Xiao-Yu, Li Yan-Fang, Shao Peng, Zhao Ya-Ru
Chin. Phys. B 2012, 21 (8): 083601;  doi: 10.1088/1674-1056/21/8/083601
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The equilibrium geometries, relative stabilities, and electronic properties of MnAgm (M=Na, Li; n+m≤ 7) as well as pure Agn, Nan, Lin (n≤ 7) clusters are systematically investigated by means of density functional theory. The optimized geometries reveal that for 2≤ n ≤ 7, there are significant similarities in geometry among pure Agn, Nan, and Lin clusters, and the transitions from planar to three-dimensional configurations occur at n=7, 7, and 6, respectively. In contrast, the first three-dimensional (3D) structures are observed at n+m=5 for both NanAgm and LinAgm cluters. When n+m ≥ 5, a striking feature is that the trigonal bipyramid becomes the main subunit of LinAgm. Furthermore, dramatic odd-even alternative behaviours are obtained in the fragmentation energies, second-order difference energies, highest occupied and lowest unoccupied molecular orbital energy gaps, and chemical hardness for both pure and doped clusters. The analytic results exhibit that clusters with even electronic configuration (2, 4, 6) possess weakest chemical reactivity and more enhanced stability.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

HEM11 mode magnetically insulated transmission[2mm] line oscillator: simulation and experiment

Wang Dong, Qin Fen, Wen Jie, Chen Dai-Bing, Jin Xiao, An Hai-Shi, Zhang Xin-Kai
Chin. Phys. B 2012, 21 (8): 084101;  doi: 10.1088/1674-1056/21/8/084101
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A novel magnetically insulated transmission line oscillator (MILO) in which a modified HEM11 mode is taken as its main interaction mode (HEM11 mode MILO) is simulated and experimented in this paper. The excitation of the oscillation mode is made possible by carefully adjusting the arrangement of each resonant cavity in a two-dimensional slow wave structure. The special feature of such a device is that in the slow-wave-structure region, the interaction mode is HEM11 mode which is a TM-like one that could interact with electron beams effectively; and in the coaxial output region, the microwave mode is TE11 mode which has a favourable field density pattern to be directly radiated. Employing an electron beam of about 441 kV and 39.7 kA, HEM11 mode MILO generates a high power microwave output of about 1.47 GW at 1.45 GHz in particle-in-cell simulation. The power conversion efficiency is about 8.4 % and the generated microwave is in a TE11-like circular polarization mode. In a preliminary experiment investigation, high power microwave is detected from the device with a frequency of 1.46 GHz, an output energy of 43 J-47 J, and a pulse duration of 44 ns-49 ns when the input voltage is 430 kV-450 kV, and the diode current is 37 kA-39 kA.

Optimum design of photoresist thickness for 90-nm critical dimension based on ArF laser lithography

Chen De-Liang, Cao Yi-Ping, Huang Zhen-Fen, Lu Xi, Zhai Ai-Ping
Chin. Phys. B 2012, 21 (8): 084201;  doi: 10.1088/1674-1056/21/8/084201
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In this work, a 90-nm critical dimension (CD) technological process in an ArF laser lithography system is simulated, and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating (BARC). By analysing the simulation result, it can be found that in the absence of BARC the CD swing curve effect is very bigger than that in the presence of BARC. So, the BARC should be needed for the 90-nm CD manufacture. The optimum resist thickness for 90-nm CD in the presence of BARC is obtained, and the optimizing process in this work can be used for reference in practice.

Plasmon resonance coupling in strongly coupled gold nanotube arrays with structural defects

Zhou Xin, Fang Jian-Shu, Yang Di-Wu, Liao Xiang-Ping
Chin. Phys. B 2012, 21 (8): 084202;  doi: 10.1088/1674-1056/21/8/084202
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We theoretically investigate the transmission spectra and the field distributions with different defects in the gold nanotube arrays by using the finite-difference time-domain method. It is found that the optical properties of the nanotube arrays are strongly influenced by different defects. When there are no defects in the central nanotube, the values of peaks located at both sides of photonic band gap have their maxima. Based on the distributions of electric field component Ex and the total energy distribution of the electric and the magnetic field, we show that there exhibits mainly a dipole field distribution for the plasmon mode at the long-wavelength edge of the band gap but higher order modes of the composite are excited at the short-wavelength edge of the band gap. The plasmon resonant modes can also be controlled by introducing defects.

Propagation properties of stochastic electromagnetic double-vortex beams in turbulent atmosphere

Fang Gui-Juan, Pu Ji-Xiong
Chin. Phys. B 2012, 21 (8): 084203;  doi: 10.1088/1674-1056/21/8/084203
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Based on the extended Huygens-Fresnel principle, we study the propagation properties of stochastic electromagnetic double-vortex beams in turbulent atmosphere. The result shows that the spreading of the partially coherent double-vortex beams can be smaller than that of the fully coherent ones. The degree of polarization of this kind of beam will experience change, which is dependent on the degree of polarization of the source plane, the atmospheric turbulence, topological charge, and the spatial coherence. The results may have applications in space optical communication.

Wigner function and the entanglement of quantized Bessel–Gaussian vortex state of quantized radiation field

Zhu Kai-Cheng, Li Shao-Xin, Tang Ying, Zheng Xiao-Juan, Tang Hui-Qin
Chin. Phys. B 2012, 21 (8): 084204;  doi: 10.1088/1674-1056/21/8/084204
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A new kind of quantum non-Gaussian state with vortex structure, termed Bessel-Gaussian vortex state, is constructed, which is an eigenstate of sum of squared annihilation operators a2 + b2. The Wigner function of the quantum vortex state is derived and exhibits negativity which is an indication of nonclassicality. It is also found that quantized vortex state is always in entanglement. And a scheme for generating such quantized vortex states is proposed.

Distillability sudden death in a two qutrit systems under a thermal reservoir

Huang Jiang, Fang Mao-Fa, Yang Bai-Yuan, Liu Xiang
Chin. Phys. B 2012, 21 (8): 084205;  doi: 10.1088/1674-1056/21/8/084205
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The dynamics of distillability entanglement between qutrit-qutrit systems interacted with a thermal reservoir is investigated in this paper. We discovered an interesting phenomenon that under a thermal reservoir certain initially prepared free-entangled states become bound-entangled states in a finite time which is called distillability sudden death (DSD). We use realignment criterion to measure the nine-dimensional density matrix of the entanglement. Moreover, we analyze some other parameters to investigate the effects to the systems, the explanations are given, too.

Preparation of steady-state entanglement via a laser-excited resonant interaction

Cheng Guang-Ling, Chen Ai-Xi, Geng Jun, Zhong Wen-Xue, Deng Li
Chin. Phys. B 2012, 21 (8): 084206;  doi: 10.1088/1674-1056/21/8/084206
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In this paper we propose a scheme, in which two-mode entanglement in a steady state is produced by using two lasers to resonantly drive a single four-level atom embedded inside a two-mode optical cavity. In this scheme, atomic coherence induced by a classical laser plays an important role in the process of preparing the entangled state. With the coupling of a strong control field, direct two-photon transition is generated and the relatively weak pump field induces the parametric interaction between two photons, which makes them entangled with each other. By numerical calculation, we find that the degree of entanglement depends strongly on the Rabi frequencies of the classical laser fields and the cavity losses.

Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

Cao Xiao-Long, Li Zhong-Yang, Yao Jian-Quan, Wang Yu-Ye, Zhu Neng-Nian, Zhong Kai, Xu De-Gang
Chin. Phys. B 2012, 21 (8): 084207;  doi: 10.1088/1674-1056/21/8/084207
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An asymmetric quantum well (AQW) is designed to emit terahertz (THz) waves by using difference frequency generation (DFG) with the structure of GaAs/Al0.2Ga0.8As/Al0.5Ga0.5As. The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail. We find that the absorption coefficients vary with the two pump optical intensities, and they reach the maxima when the pump wavelengths are given as λ p1=9.70 μm and λ p2=10.64 μm respectively. Compared with non-parabolic condition, the total absorption coefficient under parabolic condition shows a blue shift, which is due to the increase in the energy difference between the ground and excited states. By adjusting the two pump optical intensities, the wave vector phase-matching condition inside the AQW is satisfied.

Theoretical analyses on improved beam properties of GaSb-based 2.X-μm quantum-well diode lasers with no degradation in laser parameters

Wang Yong-Bin, Xu Yun, Song Guo-Feng, Chen Liang-Hui
Chin. Phys. B 2012, 21 (8): 084208;  doi: 10.1088/1674-1056/21/8/084208
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Asymmetric laser heterostructure is developed to improve beam properties of GaSb-based diode lasers with no degradation in laser parameters. Employing the semivectorial finite difference method, the dependences of beam divergence and optical confinement factor on waveguide width and refractive index step are investigated theoretically. After carefully designing, a particular asymmetric laser structure is proposed. Its beam divergence in the fast axis is reduced from 61° to 34°compared with that of the broad-waveguide structure. The optical confinement factor is approximately equal to 0.0362 and comparable to that of the conventional broad-waveguide structure.

Thermal analysis of GaN laser diodes in a package structure

Feng Mei-Xin, Zhang Shu-Ming, Jiang De-Sheng, Liu Jian-Ping, Wang Hui, Zeng Chang, Li Zeng-Cheng, Wang Huai-Bing, Wang Feng, Yang Hui
Chin. Phys. B 2012, 21 (8): 084209;  doi: 10.1088/1674-1056/21/8/084209
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Using the finite-element method, the thermal resistances of GaN laser diode devices in TO 56 package for both epi-up configuration and epi-down configuration are calculated. The effects of various parameters on the thermal characteristics are analysed, and the thicknesses of AlN submount for both epi-up configuration and epi-down configuration are optimized. The obtained result provides a reference for the parameter selection of the package materials.

Chip design of a 5.8-GHz fractional-N frequency synthesizer with a tunable GmC loop filter

Huang Jhin-Fang, Liu Ron-Yi, Lai Wen-Cheng, Shin Chun-Wei, Hsu Chien-Ming
Chin. Phys. B 2012, 21 (8): 084210;  doi: 10.1088/1674-1056/21/8/084210
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This paper proposes a novel Gm-C loop filter instead of a conventional passive loop filter used in phase-locked loop. The innovative advantage of the proposed architecture is tunable loop filter bandwidth and hence the process variations of passive elements of resistance R and capacitance C can be overcome and the chip area is greatly reduced. Furthermore the MASH 1-1-1 sigma-delta (Σ Δ) modulator is adopted for performing the fractional division number and hence improves the phase noise as well. Measured results show that the locked phase noise is -114.1 dBc/Hz with lower Gm-C bandwidth and -111.7 dBm/C with higher Gm-C bandwidth at 1 MHz offset from carrier of 5.68 GHz. Including pads and build-in Gm-C filter, the chip area of the proposed frequency synthesizer is 1.06 mm2. The output power is -8.69 dBm at 5.68 GHz and consumes 56 mW with off-chip buffer from 1.8-V supply voltage.

Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

Zhang Jing, Zhang Qiu-Lin, Jiang Man, Zhang Dong-Xiang, Feng Bao-Hua, Zhang Jing-Yuan
Chin. Phys. B 2012, 21 (8): 084211;  doi: 10.1088/1674-1056/21/8/084211
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We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification. The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol. With the saturated amplification, we can obtain high energy incoherent light pulses, whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy. Moreover, the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy. Selecting s-polarized fluorescence with a Glan-Taylor prism, the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed. The maximum output energy is 0.67 mJ for the optical parametric amplifier. By using optical filter and compressor, the generated high energy incoherent light has a great potential as the incoherent pump, signal or idler wave of parametric down-conversion process, so that a wave with a high degree of coherence can be generated from an incoherent pump light.

Effect of different metal-backed waveguides on amplified spontaneous emission

Zhang Bo, Hou Yan-Bing, Lou Zhi-Dong, Teng Feng, Liu Xiao-Jun, Hu Bing, Meng Ling-Chuan, Wu Wen-Bin
Chin. Phys. B 2012, 21 (8): 084212;  doi: 10.1088/1674-1056/21/8/084212
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We investigate the effect of metallic electrode on the ability for poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) film to undergo amplified spontaneous emission (ASE). The threshold of the device with Ag cladding is about 10 times greater than that of a metal-free device, but metal such as Al completely shuts off ASE. The ASE recurs when a thin spacer layer, such as a few nanometers of SiO2, is introduced between the MEH-PPV film and the Al cladding. Compared with the Cu or Al electrode, the Ag cladding is most suited to serve as an electrode with its low optical loss due to its high work-function and reflectivity.

Numerical investigation on properties of attack angle for opposing jet thermal protection system

Lu Hai-Bo, Liu Wei-Qiang
Chin. Phys. B 2012, 21 (8): 084401;  doi: 10.1088/1674-1056/21/8/084401
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The three-dimensional Navier-Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow condition. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection is failure.

Numerical simulation study about spin resonant depolarization due to spin–orbit coupling

Lan Jie-Qin, Xu Hong-Liang
Chin. Phys. B 2012, 21 (8): 084501;  doi: 10.1088/1674-1056/21/8/084501
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Spin polarization phenomenon in lepton circular accelerators had been known for many years. It gives new approach for physicists to study about spin feature of fundamental particles and dynamics of spin-orbit coupling, such as spin resonances. We use numerical simulation to study the feature of spin under the modulation of orbital motion in electron storage ring. The various cases of depolarization due to spin-orbit coupling through emitting photon and misalignment of magnets in the ring are discussed.

Fractional differential equations of motion in terms of combined Riemann–Liouville derivatives

Zhang Yi
Chin. Phys. B 2012, 21 (8): 084502;  doi: 10.1088/1674-1056/21/8/084502
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In this paper, we focus on studying the fractional variational principle and the differential equations of motion for a fractional mechanical system. A combined Riemann-Liouville fractional derivative operator is defined, and a fractional Hamilton principle under this definition is established. The fractional Lagrange equations and the fractional Hamilton canonical equations are derived from the fractional Hamilton principle. A number of special cases are given, showing the universality of our conclusions. At the end of the paper, an example is given to illustrate the application of the results.

Response of thermal source in a transversely isotropic thermoelastic half-space with mass diffusion by finite element method

Ibrahim A. Abbas, Rajneesh Kumar, Vijay Chawla
Chin. Phys. B 2012, 21 (8): 084601;  doi: 10.1088/1674-1056/21/8/084601
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The two-dimensional problem of generalized thermoelastic diffusion material with thermal and diffusion relaxation times is investigated in the context of Lord-Shulman theory. As an application of the problem, a particular type of thermal source is considered and the problem is solved numerically by using a finite element method. The components of displacement, stress, temperature distribution, chemical potential, and mass concentration are obtained. The resulting quantities are depicted graphically for a special model. Appreciable effect of relaxation times is observed on various resulting quantities.

The study of a two-phase wedge-sliding model on the ingredients drift of stable mixed fluid and its computing method

Han Zhi-Hong, Liu Zuo-Min
Chin. Phys. B 2012, 21 (8): 084701;  doi: 10.1088/1674-1056/21/8/084701
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A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of stable system, and it is used to describe the ingredient distribution of mixed fluid in non-uniform stress field and to analyse its phase drift phenomenon. In the model, the drift-inhibition angle and the expansion-inhibition angle are also deduced and used as evaluating indexes to describe the drifting trend of different ingredients among the mixed fluids. For solving above two indexes of the model, a new calculation method is developed and used to compute the phase distributions of multiphase fluid at peak stress and gradient area stress respectively. As an example, the flow process of grease in a pipe is analysed by simulation method and used to verify the validity of the model.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Effect of passive plates on vertical instability in the EAST tokamak

Liu Guang-Jun, Wan Bao-Nian, Qian Jin-Ping, Sun You-Wen, Xiao Bing-Jia, Shen Biao, Luo Zheng-Ping, Ji Xiang, Chen Shu-Liang
Chin. Phys. B 2012, 21 (8): 085201;  doi: 10.1088/1674-1056/21/8/085201
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The effect of passive plates on vertical displacement control in EAST tokamak is investigated by open loop experiments and numerical simulations based on a rigid displacement model. The experiments and simulations indicate that the vertical instability growth rate is reduced by a factor of about 2 in the presence of the passive plates, where the adjacent segments are not connected to each other. The simulations also show that the vertical instability growth rate is reduced by a factor of about 10 if all adjacent segments on each passive plate loop are connected to each other. The operational window is greatly enlarged with the passive plates.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Mechanical properties of silicon nanobeams with undercut evaluated by combining dynamic resonance test and finite element analysis

Zhang Jia-Hong, Mao Xiao-Li, Liu Qing-Quan, Gu Fang, Li Min, Liu Heng, Ge Yi-Xian
Chin. Phys. B 2012, 21 (8): 086101;  doi: 10.1088/1674-1056/21/8/086101
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Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young's modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by laser Doppler vibrometer is presented in this paper. Silicon nanobeams test structures are fabricated from silicon-on-insulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value Δ L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including Δ L, we finally extract Young's modulus from the measured resonance frequency versus effective length dependency and find that Young's modulus of silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to surface effect does not play a role in mechanical elastic behaviour of silicon nanobeams with the thickness larger than 200 nm.

Amorphous-crystalline dual-layer structures resulting from metastable liquid phase separation in (Fe50Co25B15Si10)80Cu20 melt-spun ribbons

Cao Chong-De, Gong Su-Lian, Guo Jin-Bo, Song Rui-Bo, Sun Zhan-Bo, Yang Sen, Wang Wei-Min
Chin. Phys. B 2012, 21 (8): 086102;  doi: 10.1088/1674-1056/21/8/086102
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(Fe50Co25B15Si10)80Cu20 ribbons are prepared by the single-roller melt-spinning method. A dual-layer structure consisting of a (Fe, Co)-rich amorphous phase and a Cu-rich crystalline phase forms due to metastable liquid phase separation before solidification. The magnetic hysteresis loops of the as-quenched and annealed samples are measured at room temperature. It is indicated that the coercivity of the ribbon is almost zero in as-quenched state. The crystallization leads to the increase of coercivity and decrease of saturation magnetization.

Pressure-induced structural transition and thermodynamic properties of RhN2 and effect of metallic bonding on its hardness

Liu Jun, Kuang Xiao-Yu, Wang Zhen-Hua, Huang Xiao-Fen
Chin. Phys. B 2012, 21 (8): 086103;  doi: 10.1088/1674-1056/21/8/086103
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The elastic constant, structural phase transition, and effect of metallic bonding on the hardness of RhN2 under high pressure are investigated through the first principles calculation by means of the pseudopotential plane-waves method. Three structures are chosen to investigate for RhN2, namely, simple hexagonal P6/mmm (denoted as SH), orthorhombic Pnnm (marcasite), and simple tetragonal P4/mbm (denoted as ST). Our calculations show that the SH phase is energetically more stable than the other two phases at zero pressure. On the basis of the third-order Birch-Murnaghan equation of states, we find that phase transition pressures from SH to marcasite structure and from marcasite to ST structure are 1.09 GPa and 354.57 GPa, respectively. Elastic constants, formation enthalpies, shear modulus, Young's modulus, and Debye temperature of RhN2 are derived. The calculated values are, generally speaking, in good agreement with the previous theoretical results. Meanwhile, it is found that the pressure has an important influence on physical properties. Moreover, the effect of metallic bonding on the hardness of RhN2 is investigated. This is a quantitative investigation on the structural properties of RhN2, and it still awaits experimental confirmation.

High volumetric hydrogen density phases of magnesium borohydride at high-pressure: A first-principles study

Fan Jing, Bao Kuo, Duan De-Fang, Wang Lian-Cheng, Liu Bing-Bing, Cui Tian
Chin. Phys. B 2012, 21 (8): 086104;  doi: 10.1088/1674-1056/21/8/086104
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The previously proposed theoretical and experimental structures, bond characterization, and compressibility of Mg(BH4)2 in a pressure range from 0 to 10 GPa are studied by ab initio density-functional calculations. It is found that the ambient pressure phases of meta-stable I41/amd and unstable P-3m1 proposed recently are extra stable and cannot decompose under high pressure. Enthalpy calculation indicates that the ground state of F222 structure proposed by Zhou et al. [2009 Phys. Rev. B 79 212102] will transfer to I41/amd at 0.7 GPa, and then to P-3m1 structure at 6.3 GPa. And the experimental P6122 structure (α-phase) transfers to I41/amd at 1.2 GPa. Furthermore, both I41/amd and P-3m1 can exist as high volumetric hydrogen density phases at low pressure. Their theoretical volumetric hydrogen densities reach 146.351 g H2/L and 134.028 g H2/L at ambient pressure respectively. The calculated phonon dispersion curve shows that the I41/amd phase is dynamically stable in a pressure range from 0 to 4 GPa and the P-3m1 phase is stable at pressures higher than 1 GPa. So the I41/amd phase may be synthesized under high pressure and retained to ambient pressure. Energy band structures show that both of them are always ionic crystalline and insulating with a band gap of about 5 eV in this pressure range. In addition, they each have an anisotropic compressibility. The c axis of these structures is easy to compress. Especially, the c axis and volume of P-3m1 phase are extraordinarily compressible, showing that compressing alone c axis can increase the volumetric hydrogen content for both I41/amd and P-3m1 structures.

An AlGaN/GaN HEMT with reduced surface electric field and an improved breakdown voltage

Xie Gang, Edward Xu, Niloufar Hashemi, Zhang Bo, Fred Y. Fu, Wai Tung Ng
Chin. Phys. B 2012, 21 (8): 086105;  doi: 10.1088/1674-1056/21/8/086105
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A reduced surface electric field in AlGaN/GaN high electron mobility transistor (HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas (2-DEG) channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional source-connected field plate and double field plate, the HEMT with Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, Lm, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with VGS=-5 V, Lm=1.5 μm, a peak Mg doping concentration of 8× 1017 cm-3 and a drift region length of 10 μm, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.

First-order character of the displacive structural transition in BaWO4

Tan Da-Yong, Xiao Wan-Sheng, Zhou Wei, Chen Ming, Xiong Xiao-Lin, Song Mao-Shuang
Chin. Phys. B 2012, 21 (8): 086201;  doi: 10.1088/1674-1056/21/8/086201
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Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode (RUM) provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in BaWO4: a 1.6% volume collapse, coexistence of phases and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaO8 polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.

The effect of two-dimensional shear flow on the stability of a crystal interface in the supercooled melt

Cao Bin, Lin Xin, Wang Meng, Huang Wei-Dong
Chin. Phys. B 2012, 21 (8): 086401;  doi: 10.1088/1674-1056/21/8/086401
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A model is developed based on the time-related thermal diffusion equations to investigate the effects of two-dimensional shear flow on the stability of a crystal interface in the supercooled melt of pure substance. Similar to the three-dimensional shear flow as described in our previous paper, the two-dimensional shear flow can also be found to reduce the growth rate of perturbation amplitude. However, compared with the case of Laplace equation for steady state thermal diffusion field, due to the existence of time partial derivatives of the temperature fields in diffusion equation the absolute value of the gradients of the temperature fields increases, therefore destabilizing the interface. The circular interface is more unstable than in the case of Laplace equation without time partial derivatives. The critical stability radius of the crystal interface increases with shearing rate increasing. The stability effect of shear flow decreases remarkably with the increase of melt undercooling.

Liquid to glass transition of tetrahydrofuran and 2-methyltetrahydrofuran

Tan Rong-Ri, Shen Xin, Hu Lin, Zhang Feng-Shou
Chin. Phys. B 2012, 21 (8): 086402;  doi: 10.1088/1674-1056/21/8/086402
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Both tetrahydrofuran (THF) and 2-methyltetrahydrofuran (MTHF) are studied systematically at desired temperatures using molecular dynamics simulations. The results show that the calculated densities are well consistent with experiment. Their glass transition temperatures are obtained: 115 K ~130 K for THF and 131 K ~142 K for MTHF. The calculated results from the dipolar orientational time correlation functions indicate that the “long time” behavior is often associated with a glass transition. From the radial and spatial distributions, we also find that the methyl has a direct impact on the structural symmetry of molecules, which leads to the differences of physical properties between THF and MTHF.

Simulations of the flipping images and microparameters of molecular orientations in liquids according to molecule string model

Wang Li-Na, Zhao Xing-Yu, Zhang Li-Li, Huang Yi-Neng
Chin. Phys. B 2012, 21 (8): 086403;  doi: 10.1088/1674-1056/21/8/086403
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The relaxation dynamics of liquids is one of the fundamental problems in liquid physics, and it is also one of the key issues to understand the glass transition mechanism. It will undoubtedly give enlightenments on understanding and calculating the relaxation dynamics if the molecular orientation flipping images and relevant microparameters of liquids are studied. In this paper, we first give five microparameters to describe the individual molecular string (MS) relaxation based on the dynamical Hamiltonian of the MS model, and then simulate the images of individual MS ensemble, at the same time calculate the parameters of the equilibrium state. The results show that the main molecular orientation flipping image in liquids (including supercooled liquid) is similar to the random walk. In addition, two pairs of the parameters are equal, and one can be ignored compared with the other. This conclusion will effectively reduce the difficulties in calculating the individual MS relaxation based on the single-molecule orientation flipping rate of general Glauber type, and the computer simulation time of interaction MS relaxation. Moreover, the conclusion has no doubt of the reference significance for solving and simulating the multi-state MS model.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Electronic and structural properties of N-vacancy in AlN nanowires: A first-principles study

Qiao Zhi-Juan, Chen Guang-De, Ye Hong-Gang, Wu Ye-Long, Niu Hai-Bo, Zhu You-Zhang
Chin. Phys. B 2012, 21 (8): 087101;  doi: 10.1088/1674-1056/21/8/087101
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The stability and electronic structures of AlN nanowires with and without N-vacancy are investigated by using the first-principles calculations. We find that there is an inverse correlation between formation energy and diameter in ideal AlN nanowires. After calculating the formation energies of N-vacancy at different sits in AlN nanowires with different diameters, we obtain that the N-vacancy prefers to stay at the surface of the nanowires and it is easier to fabricate under Al-rich condition. Through studying the electronic properties of the AlN nanowires with N-vacancies, we further find that there are two isolated bands in the deep part of the band gap, one of them is fully occupied and the other is half occupied. The charge density indicates that the half-fully occupied band arises from the Al at surface, and this atom becomes an active centre.

Energetics and electronic structure of refractory elements in the dislocation of NiAl

Chen Li-Qun, Peng Xiao-Fang, Yu Tao
Chin. Phys. B 2012, 21 (8): 087102;  doi: 10.1088/1674-1056/21/8/087102
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Using the DMol and the discrete variational method within the framework of density functional theory, we study the alloying effects of Nb, Ti, and V in the [100] (010) edge dislocation core of NiAl. We find that when Nb (Ti, V) is substituted for Al in the center-Al, the binding energy of the system reduces 3.00 eV (2.98 eV, 2.66 eV). When Nb (Ti, V) is substituted for Ni in the center-Ni, the binding energy of the system reduces only 0.47 eV (0.16 eV, 0.09 eV). This shows that Nb (Ti, V) exhibits a strong Al site preference, which is in agreement with experimental and other theoretical results. The analyses of the charge distribution, the interatomic energy and the partial density of states show that some charge accumulations appear between impurity atom and Ni atoms, and the strong bonding states are formed between impurity atom and neighbouring host atoms due mainly to the hybridization of 4d5s(3d4s) orbitals of impurity atom and 3d4s4p orbitals of host Ni atoms. The impurity induces a strong pinning effect on the [100] (010) edge dislocation motion in NiAl, which is related to the mechanical properties of NiAl alloy.

Magnetization reversal within Dzyaloshinskii–Moriya interaction under on-site Coulomb interaction in BiCrO3

Feng Hong-Jian
Chin. Phys. B 2012, 21 (8): 087103;  doi: 10.1088/1674-1056/21/8/087103
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First-principals calculations show that the magnetization reversal is accompanying with the opposite sense of rotation of neighboring oxygen octahedra along [111] direction which is called the antiferrodistortive displacement in BiCrO3. The coupling between magnetization and antiferrodistortive distortion is mainly caused by Dzyaloshinskii-Moriya interaction which is driven by the eg-eg states antiferromagnetic interaction in Cr-3d. A critical value of on-site Coulomb interaction prohibiting the Dzyaloshinskii-Moriya interaction and thus the magnetization reversal is found to be 1.3 eV.

High sensitivity refractive index gas sensing enhanced by surface plasmon resonance with nano-cavity antenna array

Zhao Hua-Jun
Chin. Phys. B 2012, 21 (8): 087104;  doi: 10.1088/1674-1056/21/8/087104
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The surface plasmon resonance gas sensor is presented for refractive index detection using nano-cavity antenna array. The gas sensor monitors the changes of the refractive index by measuring the spectral shift of the resonance dip, for modulating the wavelength of incident light. It is demonstrated that minute changes in the refractive index of a medium close to the surface of a metal film, owing to a shift in the resonance dip of the wavelength, can be detected. The average detection sensitivity is about 3200 nm/RIU (refractive index units), which is twice more than that of metal grating-based gas sensor. The reflectivity of the surface plasmon resonance dip is only ~ 0.03%, and the full widths at half maximum (FWHMs) of bandwidth of the angle and wavelength are ~ 0.20° and 4.71 nm, respectively.

Defect properties of CuCrO2: A density functional theory calculation

Fang Zhi-Jie, Zhu Ji-Zhen, Zhou Jiang, Mo Man
Chin. Phys. B 2012, 21 (8): 087105;  doi: 10.1088/1674-1056/21/8/087105
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Using the first-principles methods, we study the formation energetics properties of intrinsic defects, and the charge doping properties of extrinsic defects in transparent conducting oxides CuCrO2. Intrinsic defects, some typical acceptor-type, and donor-type extrinsic defects in their relevant charge state are considered. By systematically calculating the formation energies and transition energy, the results of calculation show that, Vm Cu, Oi, and Om Cu are the relevant intrinsic defects in CuCrO2; among these intrinsic defects, Vm Cu is the most efficient acceptor in CuCrO2. It finds that all the donor-type extrinsic defects are difficult to induce n-conductivity in CuCrO2 because of their deep transition energy level. For all the acceptor-type extrinsic defects, substituting Mg for Cr is the most prominent doping acceptor with relative shallow transition energy levels in CuCrO2. Our calculation results are expected to be a guide for preparing promising n-type and p-type materials in CuCrO2.

Effective response in nonlinear spherical coated composites under external AC and DC electric field

Bao Shu-Hong, Chen Xiao-Gang, Li Qian-Qian, Guo Jun-Ming, Zhai Li-Li
Chin. Phys. B 2012, 21 (8): 087201;  doi: 10.1088/1674-1056/21/8/087201
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By using the perturbation method, effective nonlinear direct current (DC) and alternating current (AC) responses of nonlinear composites with spherical coated inclusions randomly embedded in a host medium are studied under the action of external electric field Ea =E0 +E1 sin ωt+E3 sin 3ωt with different amplitudes and frequencies. The local potentials of composites at all harmonics are given in the inclusion particles and the host regions. All effective nonlinear responses to composites and the relationship between the effective nonlinear responses at all harmonics are also deduced for the spherical coated inclusions in a dilute limit.

Oxygen vacancy in N-doped Cu2O crystals: A density functional theory study

Li Min, Zhang Jun-Ying, Zhang Yue, Wang Tian-min
Chin. Phys. B 2012, 21 (8): 087301;  doi: 10.1088/1674-1056/21/8/087301
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The N-doping effects on the electronic properties of Cu2O crystals are investigated using density functional theory. The calculated results show that N-doped Cu2O with or without oxygen vacancy exhibits different modifications of electronic band structure. In N anion-doped Cu2O, some N 2p states overlap and mix with the O 2p valence band, leading to a slight narrowing of band gap compared with the undoped Cu2O. However, it is found that the coexistence of both N impurity and oxygen vacancy contributes to band gap widening which may account for the experimentally observed optical band gap widening by N doping.

Electronic and optical properties of CdS/CdZnS nanocrystals

A. John Peter, Chang Woo Lee
Chin. Phys. B 2012, 21 (8): 087302;  doi: 10.1088/1674-1056/21/8/087302
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Cd1-xZnxS nanocrystals are prepared by co-precipitation method with different atomic fractions of Zn and their textures, structural transformations, and optical properties with increasing x value in Cd1-xZnxS are studied from scanning electron micrograph, electron diffraction pattern, and absorption spectra respectively. Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically. Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed, considering the internal electric field induced by the spontaneous and piezoelectric polarizations and thereby interband emission energy is calculated as a function of dot radius. The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically. Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm. X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with the increase of Zn content. The lattice constant gradually decreases as Zn content increases. The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as Zn content increases. The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for CdS film and 3.5 eV for ZnS film. Our numerical results are in good agreement with the experimental results.

Second-harmonic generation in asymmetric quantum dots in the presence of a static magnetic field

Li Xue-Chao, Wang An-Min, Wang Zhao-Liang, Yang Yang
Chin. Phys. B 2012, 21 (8): 087303;  doi: 10.1088/1674-1056/21/8/087303
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The second-harmonic generation (SHG) coefficient in an asymmetric quantum dot (QD) with a static magnetic field is theoretically investigated. Within the framework of the effective-mass approximation, we obtain the confined wave functions and energies of electrons in QD. We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method. The numerical results for the typical GaAs/AlGaAs QD show that the SHG coefficient depends strongly on the magnitude of magnetic field, parameters of the asymmetric potential and the radius of the QD. The resonant peak shifts with the magnetic field or the radius of the QD changing.

Formations and morphological stabilities of ultrathin CoSi2 films

Zhu Zhi-Wei, Gao Xin-Dong, Zhang Zhi-Bin, Piao Ying-Hua, Hu Cheng, Zhang David-Wei, Wu Dong-Ping
Chin. Phys. B 2012, 21 (8): 087304;  doi: 10.1088/1674-1056/21/8/087304
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In this paper we investigate the formations and morphological stabilities of Co-silicide films using 1-8-nm thick Co layers sputter-deposited on silicon (100) substrates. These ultrathin Co-silicide films are formed via solid-state reaction of the deposited Co films with Si substrate at annealing temperatures from 450 ℃ to 850 ℃. For Co layer with a thickness no larger than 1 nm, epitaxially aligned CoSi2 films readily grow on silicon (100) substrate and exhibit good morphological stabilities up to 600 ℃. For Co layer thicker than 1 nm, polycrystalline CoSi and CoSi2 films are observed. The critical thickness below which epitaxially aligned CoSi2 film prevails is smaller than the reported critical thickness of Ni layer for epitaxial alignment of NiSi2 on silicon (100) substrate. The larger lattice mismatch between CoSi2 film and silicon substrate is the root cause for the smaller critical thickness of the Co layer.

Monolithic integration of AlGaN/GaN metal–insulator field-effect transistor with ultra-low voltage-drop diode for self-protection

Wang Zhi-Gang, Chen Wan-Jun, Zhang Jing, Zhang Bo, Li Zhao-Ji
Chin. Phys. B 2012, 21 (8): 087305;  doi: 10.1088/1674-1056/21/8/087305
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In this paper, we present a monolithic integration of self-protected AlGaN/GaN metal-insulator field-effect transistor (MISFET). An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features self-protected function at reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block reverse bias (>70 V/μm) and suppress the leakage current (<5×10-11 A/mm). Compared with conventional monolithic integration, the numerical results show that the MISFET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.

High temperature thermoelectric properties of highly c-axis oriented Bi2Sr2Co2Oy thin films fabricated by pulsed laser deposition

Chen Shan-Shan, Wang Shu-Fang, Liu Fu-Qiang, Yan Guo-Ying, Chen Jing-Chun, Wang Jiang-Long, Yu Wei, Fu Guang-Sheng
Chin. Phys. B 2012, 21 (8): 087306;  doi: 10.1088/1674-1056/21/8/087306
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High-temperature thermoelectric transport properties measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3 (001). Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m·Ω·cm and 202 μV/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices.

High-sensitive automatic transient laser-induced breakdown spectroscopy system with high temporal and spatial resolution

Liu Qiao-Jun, S. K. Fong, Andrew Y. S. Cheng, Luo Shi-Rong, K. S. Tam, Zhu Jian-Hua, A. Viseu
Chin. Phys. B 2012, 21 (8): 087402;  doi: 10.1088/1674-1056/21/8/087402
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A high-sensitive automatic transient laser-induced breakdown spectroscopy (LIBS) system is designed and integrated. It successfully avoids the delay time selecting problem in conventional LIBS system, and realizes the LIBS data acquisition with high spatiotemporal resolution automatically. Multiple transient spectra can be obtained in each measurement, which will provide more information for spectral research. The water-vapour and liquid-water Raman scattering spectra are captured by this system, and the comparison of experimental water-vapour Raman scattering spectrum with theoretical data verifies the reliability of the LIBS system. Based on this system, the air laser induced air breakdown spectra are captured and analysed. The system is also useful for the research on water-vapour Raman Lidar remote sensing.

Wiedemann effect of Fe–Ga based magnetostrictive wires

Li Ji-Heng, Gao Xue-Xu, Zhu Jie, Bao Xiao-Qian, Cheng Liang, Xie Jian-Xin
Chin. Phys. B 2012, 21 (8): 087501;  doi: 10.1088/1674-1056/21/8/087501
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(Fe83Ga17)98Cr2 wires each with a diameter of 0.7 mm are prepared by hot swaging and warm drawing from the casting rods directly, because the ductility of Fe83Ga17 alloy is improved by adding Cr element. The Wiedemann twists and dependences on magnetostrictions of Fe83Ga17 and (Fe83Ga17)98Cr2 wires are investigated. The largest observed Wiedemann twists of 245 s·cm-1 and 182 s·cm-1 are detected in the annealed Fe83Ga17 and (Fe83Ga17)98Cr2 wires, respectively. The magnetostrictions of the annealed Fe83Ga17 and (Fe83Ga17)98Cr2 wires are 160 ppm and 107 ppm, respectively. The maximum of Wiedemann twist increases with magnetostriction increasing. However the magnetostriction is just an important factor that affects the Wiedemann effect of alloy wire, and the relationship between magnetostriction and Wiedemann effect is a complex function rather than a simple function.

Charge ordering modulations in Bi0.4Ca0.6MnO3 film with a thickness of 110 nm

Ding Yan-Hua, Wang Yi-Qian, Cai Rong-Sheng, Chen Yun-Zhong, Sun Ji-Rong
Chin. Phys. B 2012, 21 (8): 087502;  doi: 10.1088/1674-1056/21/8/087502
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Low temperature sample stage in transmission electron microscope is used to investigate the charge ordering behaviours in Bi0.4Ca0.6MnO3 film with a thickness of 110 nm at 103 K. Six different types of superlattice structures are observed using selected-area electron diffraction (SAED) technique, while three of them match well with the modulation stripes in high-resolution transmission electron microscopy (HRTEM) images. It is found that the modulation periodicity and direction are completely different in the region close to the Bi0.4Ca0.6MnO3/SrTiO3 interface from those in the region a little far from the Bi0.4Ca0.6MnO3/SrTiO3 interface, and the possible reasons are discussed. Based on the experimental results, structural models are proposed for these localized modulated structures.

Mean-field and high temperature series expansion calculations of some magnetic properties of Ising and XY antiferromagnetic thin-films

R. Masrour, M. Hamedoun, A. Benyoussef
Chin. Phys. B 2012, 21 (8): 087503;  doi: 10.1088/1674-1056/21/8/087503
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In this work, the magnetic properties of Ising and XY antiferromagnetic thin-films are investigated each as a function of Néel temperature and thickness for layers (n=2, 3, 4, 5, 6, and bulk (∞)) by means of mean-field and high temperature series expansion (HTSE) combined with the Padé approximant calculations. The scaling law of magnetic susceptibility and magnetization is used to determine the critical exponent γ, ν eff (mean), ratio of the critical exponents γ/ν, and magnetic properties of Ising and XY antiferromagnetic thin-films for different thickness layers n=2, 3, 4, 5, 6, and bulk (∞).

Investigation of 4H–SiC metal–insulation–semiconductor structure with Al2O3/SiO2 stacked dielectric

Tang Xiao-Yan, Song Qing-Wen, Zhang Yu-Ming, Zhang Yi-Men, Jia Ren-Xu, Lü Hong-Liang, Wang Yue-Hu
Chin. Phys. B 2012, 21 (8): 087701;  doi: 10.1088/1674-1056/21/8/087701
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Atomic layer deposited (ALD) Al2O3/dry-oxidized ultrathin SiO2 films as high-k gate dielectric grown on the 8° off-axis 4H-SiC (0001) epitaxial wafers are investigated in this paper. The metal-insulation-semiconductor (MIS) capacitors, respectively with different gate dielectric stacks (Al2O3/SiO2, Al2O3, and SiO2) are fabricated and compared with each other. The I-V measurements show that the Al2O3/SiO2 stack has a high breakdown field ( ≥ 12 MV/cm) comparable to SiO2, and a relatively low gate leakage current of 1× 10-7 A/cm2 at electric field of 4 MV/cm comparable to Al2O3. The 1-MHz high frequency C-V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating less effective charge and slow-trap density near the interface.

Influence of different oxidants on band alignment of HfO2 films deposited by atomic layer deposition

Fan Ji-Bin, Liu Hong-Xia, Gao Bo, Ma Fei, Zhuo Qing-Qing, Hao Yue
Chin. Phys. B 2012, 21 (8): 087702;  doi: 10.1088/1674-1056/21/8/087702
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Based on X-ray photoelectron spectroscopy (XPS), influences of different oxidants on band alignment of HfO2 films deposited by atomic layer deposition (ALD) are investigated in this paper. The measured valence band offset (VBO) value for H2O-based HfO2 increases from 3.17 eV to 3.32 eV after annealing, whereas the VBO value for O3-based HfO2 decreases from 3.57 eV to 3.46 eV. The research results indicate that the silicate layer changes in different ways for H2O-based and O3-based HfO2 films after annealing process, which plays a key role in generating the internal electric field formed by the dipoles. The variations of the dipoles at the interface between the HfO2 and SiO2 after annealing may lead the VBO values of H2O-based and O3-based HfO2 to vary in different ways, which is in agreement with the varition of flat band (VFB) voltage.

First-principles study of the elastic constants and optical properties of uranium metal

Chen Qiu-Yun, Tan Shi-Yong, Lai Xin-Chun, Chen Jun
Chin. Phys. B 2012, 21 (8): 087801;  doi: 10.1088/1674-1056/21/8/087801
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We perform first-principles calculations of the lattice constants, elastic constants, and optical properties for alpha- and gamma-uranium based on the ultra-soft pseudopotential method. Lattice constants and equilibrium atomic volume are consistent pretty well with the experimental results. Some difference exists between our calculated elastic constants and the experimental data. Based on the satisfactory ground state electronic structure calculations, the optical conductivity, dielectric function, refractive index, and extinction coefficients are also obtained. These calculated optical properties are compared with our results and other published experimental data.

Strain relaxation and optical properties of etched In0.19Ga0.81N nanorod arrays on the GaN template

Zhang Dong-Yan, Zheng Xin-He, Li Xue-Fei, Wu Yuan-Yuan, Wang Hui, Wang Jian-Feng, Yang Hui
Chin. Phys. B 2012, 21 (8): 087802;  doi: 10.1088/1674-1056/21/8/087802
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InGaN/GaN epilayers, which are grown on sapphire substrates by metal-organic chemical-vapour deposition (MOCVD) method, are formed into nanorod arrays using inductively coupled plasma etching via self-assembled Ni nanomasks. The formation of nanorod arrays eliminates the tilt of the InGaN (0002) crystallographic plane with respect to its GaN bulk layer. Photoluminescence results show an apparent S-shaped dependence on temperature. The light extraction efficiency and intensity of photoluminescence emission at low temperature less than 30 K for the nanorod arrays are enhanced by the large surface area, which increases the quenching effect because of high density of surface states for the temperature above 30 K. Additionally, a red-shift for the InGaN/GaN nanorod arrays is observed due to the strain relaxation, which is confirmed by reciprocal space mapping measurements.

The optimal thickness of transmission-mode GaN photocathode

Wang Xiao-Hui, Shi Feng, Guo Hui, Hu Cang-Lu, Cheng Hong-Chang, Chang Ben-Kang, Ren Ling, Du Yu-Jie, Zhang Jun-Ju
Chin. Phys. B 2012, 21 (8): 087901;  doi: 10.1088/1674-1056/21/8/087901
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A 150-nm-thick GaN photocathode with an Mg doping concentration of 1.6× 1017cm-3 is activated by Cs/O in ultrahigh vacuum chamber, and quantum efficiency (QE) curve of negative electron affinity transmission-mode (t-mode) GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5× 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

Research on field emission mechanism of nano-structured carbon film

Wang Yan-Yan, Li Ying-Ai, Xu Ji-Song, Gu Guang-Rui
Chin. Phys. B 2012, 21 (8): 087902;  doi: 10.1088/1674-1056/21/8/087902
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The field emission (FE) characteristics of nano-structrued carbon films (NSCFs) are investigated. The saturation behaviour of the field emission current density found at high electric field E cannot be reasonably explained by the traditional Fowler-Nordheim (F-N) theory. A three-region E model and the curve-fitting method are utilized for discussing the FE characteristics of NSCFs. In the low, high, and middle E regions, the FE mechanism is reasonably explained by a modified F-N model, a corrected space-charge-limited-current (SCLC) model and the joint model of F-N and SCLC mechanism, respectively. Moreover, the measured FE data accord well with the results from our corrected theoretical model.
RAPID COMMUNICATION

Interstitial vortex in superconducting film with periodic hole arrays Hot!

He Shi-Kun, Zhang Wei-Jun, Wen Zhen-Chao, Xiao Hong, Han Xiu-Feng, Gu Chang-Zhi, Qiu Xiang-Gang
Chin. Phys. B 2012, 21 (8): 087401;  doi: 10.1088/1674-1056/21/8/087401
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The response of superconducting Nb films with diluted triangular and square array of holes to perpendicular magnetic field are investigated. Due to small edge-to-edge separation of the holes, the patterned films are similar to multi-connected superconducting islands. Two regions in magnetoresistance R(H) curves can be identified according to the field intervals of the resistance minima. Moreover, in between these two regions, variation of the minima spacing was observed. Our results provide strong evidence of the coexistence of interstitial vortices in the islands and fluxoids in the holes.

Vertical assembly of carbon nanotubes for via interconnects Hot!

Wei Qin-Qin, Wei Zi-Jun, Ren Li-Ming, Zhao Hua-Bo, Ye Tian-Yang, Shi Zu-Jin, Fu Yun-Yi, Zhang Xing, Huang Ru
Chin. Phys. B 2012, 21 (8): 088103;  doi: 10.1088/1674-1056/21/8/088103
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The via interconnects are key components in ultra-large scale integrated circuits (ULSI). This paper deals with a new method to create single-walled carbon nanotubes (SWNTs) via interconnects using alternating dielectrophoresis (DEP). Carbon nanotubes are vertically assembled in the microscale via-holes successfully at room temperature under ambient condition. The electrical evaluation of the SWNT vias reveals that our DEP assembly technique is highly reliable and the success rate of assembly can be as high as 90%. We also propose and test possible approaches to reducing the contact resistance between CNT vias and metal electrodes.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Tunable structural color of anodic tantalum oxide films

Sheng Cui-Cui, Cai Yun-Yu, Dai En-Mei, Liang Chang-Hao
Chin. Phys. B 2012, 21 (8): 088101;  doi: 10.1088/1674-1056/21/8/088101
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Tantalum (Ta) oxide films with tunable structural color were fabricated facilely using anodic oxidation. The structure, components, and surface valence states of the oxide films were investigated by using gazing incidence X-ray diffractometry, X-ray photoelectron microscopy, and surface analytical techniques. Their thickness and optical properties were studied by using spectroscopic ellipsometry and total reflectance spectrum. Color was accurately defined using L*a*b* scale. The thickness of compact Ta2O5 films was linearly dependent on anodizing voltage. The film color was tunable by adjusting the anodic voltage. The difference in color appearance is resulted from the interference behavior between the interfaces of air-oxide and oxide-metal.

The influence of annealing temperature on the morphology of graphene islands

Huang Li, Xu Wen-Yan, Que Yan-De, Pan Yi, Gao Min, Pan Li-Da, Guo Hai-Ming, Wang Ye-Liang, Du Shi-Xuan, Gao Hong-Jun
Chin. Phys. B 2012, 21 (8): 088102;  doi: 10.1088/1674-1056/21/8/088102
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We report on temperature-programmed growth of graphene islands on Ru (0001) at annealing temperatures of 700 ℃, 800 ℃, and 900 ℃. The sizes of the islands each show a nonlinear increase with the annealing temperature. In 700 ℃ and 800 ℃ annealings, the islands have nearly the same sizes and their ascending edges are embedded in the upper steps of the ruthenium substrate, which is in accordance with the etching growth mode. In 900 ℃ annealing, the islands are much larger and of lower quality, which represents the early stage of Smoluchowski ripening. A longer time annealing at 900 ℃ brings the islands to final equilibrium with an ordered moiré pattern. Our work provides new details about graphene early growth stages that could facilitate the better control of such a growth to obtain graphene with ideal size and high quality.

Low-voltage antimony-doped SnO2 nanowire transparent transistors gated by microporous SiO2-based proton conductors

Xuan Rui-Jie, Liu Hui-Xuan
Chin. Phys. B 2012, 21 (8): 088104;  doi: 10.1088/1674-1056/21/8/088104
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A battery drivable low-voltage transparent lightly antimony(Sb)-doped SnO2 nanowire electric-double-layer (EDL) field-effect transistor (FET) is fabricated on an ITO glass substrate at room temperature. An ultralow operation voltage of 1 V is obtained on account of untralarge specific gate capacitance (~ 2.14 μF/cm2) directly bound up with mobile ions-induced EDL (sandwiched between top electrode and bottom electrode) effect. The transparent FET shows excellent electric characteristics with a field-effect mobility of 54.43 cm2/V·s, current on/off ration of 2× 104, and subthreshold gate voltage swing (S=d Vgs/d(log Ids)) of 140 mV/decade. The threshold voltage Vth (0.1 V) is estimated which indicates that SnO2 namowire transistor operates in an n-type enhanced mode. Such a low-voltage transparent nanowire transistor gated by microporous SiO2-based solid electrolyte is very promising for battery-powered portable nanoscale sensor.

The influence of long-range links on spiral waves and its application for control

Qian Yu
Chin. Phys. B 2012, 21 (8): 088201;  doi: 10.1088/1674-1056/21/8/088201
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The influence of long-range links on spiral waves in excitable medium has been investigated. Spatiotemporal dynamics in excitable small-world network transforms remarkably when we increase the long-range connection probability P. Spiral waves with few perturbations, broken spiral waves, pseudo spiral turbulence, synchronous oscillations, and homogeneous rest state are discovered under different network structures. Tip number is selected to detect non-equilibrium phase transition between different spatiotemporal patterns. The Kuramoto order parameter is used to identify these patterns and explain the emergence of the rest state. Finally, we use long-range links to control spiral wave and spiral turbulence successfully.

Effect of shear on the symmetric diblock copolymer/nanorod mixture: A dissipative particle dynamics study

He Lin-Li, Zhang Rui-Fen, Ji Yong-Yun
Chin. Phys. B 2012, 21 (8): 088301;  doi: 10.1088/1674-1056/21/8/088301
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The phase behaviours of lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics. We consider a wide range of nanorod concentrations, where nanorods each have a preferential affinity to one of blocks. Our results suggest that shear not only aligns the orientations of diblock copolymer templates and nanorods towards flow direction, but also regulates the distribution of nanorods within polymer matrix. Meanwhile, the shear-induced reorientation and morphology transitions of systems also significantly depend on the nanorod concentration. At certain nanorod concentrations, the competitions between shear-induced polymer thinning and nanorods dispersion behaviours determine the phase behaviours of composites. For high nanorod concentrations, no morphology transition is observed, but reorientation is present, in which the sheared nanorods are arranged into hexagonal packing arrays. Additionally, the orientation behaviour of nanorods is determined directly by the applied shear, also interfered by the shear-stretched copolymer molecules.

Experimental investigation of a compact relativistic magnetron with axial TE11 mode radiation

Li Wei, Liu Yong-Gui, Shu Ting, Qian Bao-Liang
Chin. Phys. B 2012, 21 (8): 088401;  doi: 10.1088/1674-1056/21/8/088401
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As one of the relativistic electron tubes having compact configuration and high efficient output, the relativistic magnetron with directly axial radiation is very attractive in pulsed power and high power microwave fields for industrial and military applications. In this paper, the experimental investigation of a relativistic magnetron with axial TE11 mode radiation is reported. Under a total length of ~ 0.3 m and the volume of ~ 0.014 m3, working at an applied voltage of 508 kV and a magnetic field of ~ 0.31 T, the relativistic magnetron radiates a microwave of 540 MW with TE11 mode at 2.35 GHz in the axial direction. The power conversion efficiency is 15.0%. After a lot of shots, the detected amplitudes of microwaves are nearly the same. The fluctuations of wave amplitudes are less than 0.3 dB.

Degradation of the transconductance of gate-modulated generation current in nMOSFET

Chen Hai-Feng, Guo Li-Xin, Du Hui-Min
Chin. Phys. B 2012, 21 (8): 088501;  doi: 10.1088/1674-1056/21/8/088501
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The degradation of transconductance (G) of gate-modulated generation current IGD in LDD nMOSFET is investigated. The G curve shifts rightward under the single electron-injection-stress (EIS). The trapped electrons located in the gate oxide over the LDD region (QL) makes the effective drain voltage minish. Accordingly, the G peak in depletion (GMD) and that in weak inversion (GMW) decrease. It is found that Δ GMD and Δ GMW each have a linear relationship with the n-th power of stress time (tn) in dual-log coordinate: Δ GMD ∝ tn, Δ GMDtn (n=0.25). During the alternate stress, the injected holes neutralize QL induced by the previous EIS. This neutralization makes the effective VD restore to the initial value and then the IGD peak recovers completely. Yet the threshold voltage recovery is incomplete due to the trapped electron located over the channel (QC). As a result, GMW only recovers to the circa 50% of the initial value after the hole-injection-stress (HIS). Instead, GMD is almost recovered. The relevant mechanisms are given in detail.

Fabrication and characterization of 4H–SiC bipolar junction transistor with double base epilayer

Zhang Qian, Zhang Yu-Ming, Yuan Lei, Zhang Yi-Men, Tang Xiao-Yan, Song Qing-Wen
Chin. Phys. B 2012, 21 (8): 088502;  doi: 10.1088/1674-1056/21/8/088502
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In this paper we report on a novel structure of 4H-SiC bipolar junction transistor with a double base epilayer that is continuously grown. The measured dc common-emitter current gain is 16.8 at IC=28.6 mA (JC=183.4 A/cm2), and it increases with the collector current density increasing. The specific on-state resistance (Rsp-on) is 32.3 mΩ·cm2 and the open-base breakdown voltage reaches 410 V. The emitter N-type specific contact resistance and N + emitter layer sheet resistance are 1.7× 10-3 Ω·cm2 and 150 Ω /□, respectively.

High-photosensitivity polymer thin-film transistors based on poly(3-hexylthiophene)

Liu Yu-Rong, Lai Pei-Tao, Yao Ruo-He
Chin. Phys. B 2012, 21 (8): 088503;  doi: 10.1088/1674-1056/21/8/088503
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Polymer thin-film transistors (PTFTs) based on poly(3-hexylthiophene) are fabricated by spin-coating process, and their photo-sensing characteristics are investigated under steady-state visible-light illumination. The photosensitivity of the device is strongly modulated by gate voltage under various illuminations. When the device is in the subthreshold operating mode, a significant increase in its drain current is observed with a maximum photosensitivity of 1.7× 103 at an illumination intensity of 1200 lx, and even with a relatively high photosensitivity of 611 at a low illumination intensity of 100 lx. However, when the device is in the on-state operating mode, the photosensitivity is very low: only 1.88 at an illumination intensity of 1200 lx for a gate voltage of -20 V and a drain voltage of -20 V. The results indicate that the devices could be used as photo-detectors or sensors in the range of visible light. The modulation mechanism of the photosensitivity in the PTFT is discussed in detail.

White organic light-emitting diodes based on combined electromer and monomer emission in doubly-doped polymers

Meng Ling-Chuan, Lou Zhi-Dong, Yang Sheng-Yi, Hou Yan-Bing, Teng Feng, Liu Xiao-Jun, Li Yun-Bai
Chin. Phys. B 2012, 21 (8): 088504;  doi: 10.1088/1674-1056/21/8/088504
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We report on white organic light-emitting diodes (WOLEDs) based on polyvinylcarbazole (PVK) doped with 1,1-bis((di-4-tolylamino)phenyl)cyclohexane (TAPC) and perylene, and investigate the luminescence mechanism of the devices. The chromaticity of light emission can be tuned by adjusting the concentration of the dopants. White light with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.34) is achieved by mixing the yellow electromer emission of TAPC and the blue monomer emission of perylene from the device ITO/PVK: TAPC: perylene (100:9:1 in wt.) (100 nm)/tris-(8-hydroxyquinoline aluminum (Alq3) (10 nm)/Al. The device exhibits a maximal luminance of 3727 cd/m2 and a current efficiency of 2 cd/A.

Fluctuations in airport arrival and departure traffic: A network analysis

Li Shan-Mei, Xu Xiao-Hao, Meng Ling-Hang
Chin. Phys. B 2012, 21 (8): 088901;  doi: 10.1088/1674-1056/21/8/088901
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Air traffic is a typical complex system, in which movements of traffic components (pilots, controllers, equipments, and environments), especially airport arrival and departure traffic, form complicated spatial and temporal dynamics. The fluctuations of airport arrival and departure traffic are studied from the point of view of networks as the special correlation between different airports. Our collected flow volume data on the time-dependent activity of US airport arrival and departure traffic indicate that the coupling between the average flux and the fluctuation on individual airport obeys a certain scaling law with a wide variety of scaling exponents between 1/2 and 1. These scaling phenomena can explain the interaction between the airport internal dynamics (e.g. queuing at airports, ground delay program, traffic following in flying) and change in the external (network-wide) traffic demand (e.g. the every day increase of traffic amount during peak hours), allowing us to further understand the mechanisms governing the transportation system collective behaviour. We separate the internal dynamics from the external fluctuations using scaling law which is helpful for us to systematically determine the origin of fluctuations in airport arrival and departure traffic, uncovering their collective dynamics. Hot spot features are observed in airport traffic data as the dynamical inhomogeneity in the fluxes of individual airports. The intrinsic characteristics of airport arrival and departure traffic under severe weather are discussed as well.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Temperature and drain bias dependence of single event transient in 25-nm FinFET technology

Qin Jun-Rui, Chen Shu-Ming, Li Da-Wei, Liang Bin, Liu Bi-Wei
Chin. Phys. B 2012, 21 (8): 089401;  doi: 10.1088/1674-1056/21/8/089401
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In this paper, we investigate the temperature and drain bias dependency of single event transient (SET) in 25-nm fin field-effect-transistor (FinFET) technology in a temperature range of 0-135 ℃ and supply voltage range of 0.4 V-1.6 V. Technology computer-aided design (TCAD) three-dimensional simulation results show that the drain current pulse duration increases from 0.6 ns to 3.4 ns when the temperature increases from 0 to 135 ℃. The charge collected increases from 45.5 fC to 436.9 fC and the voltage pulse width decreases from 0.54 ns to 0.18 ns when supply voltage increases from 0.4 V to 1.6 V. Furthermore, simulation results and the mechanism of temperature and bias dependency are discussed.

A set of new nucleon coupling constants and the proto neutron star matter

Zhao Xian-Feng, Jia Huan-Yu
Chin. Phys. B 2012, 21 (8): 089701;  doi: 10.1088/1674-1056/21/8/089701
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Using a new set of nucleon coupling constants CZ11 the properties of a proto neutron star is examined within the framework of the relativistic mean-field theory for the baryon octet system. It is found that the relative number density of Λ, Ξ-, and Ξ0 for CZ11 are all smaller than those for GL97 and either for CZ11 or for GL97, Σ-, Σ0, and Σ+ all do not appear. It is also found that the pressure and the maximum mass for CZ11 are all smaller than those for GL97. The maximum mass for CZ11 decreases by approximate 9 percent compared with that for GL97.
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