Vol. 58, No. 9 (2009)
2009-05-05
GENERAL
2009, 58 (9): 5887-5893.
doi: 10.7498/aps.58.5887
Abstract +
Based on the auxiliary equation method and the trial function method, a method for combining function transformation with auxiliary equation is proposed. And the method is applied to construct new exact solitary wave solutions and triangle function solutions of Volterra and KdV difference-differential equations with the help of symbolic computation system Mathematica. Our method can also be applied to other nonlinear difference-differential equations.
2009, 58 (9): 5894-5902.
doi: 10.7498/aps.58.5894
Abstract +
A method for combining Riccati equation with function transformation is applied to seek exact solutions to the nonlinear difference-differential equations. And new exact solitary wave solutions and triangular function solutions to modified Volterra equation and general lattice equations are obtained with the help of symbolic computation system Mathematica.
2009, 58 (9): 5903-5910.
doi: 10.7498/aps.58.5903
Abstract +
In this paper, we propose a new routing strategy to improve the transportation performance on scale-free networks, named optimal routing strategy. It can proportionally distribute the traffic load between central nodes and the noncentral nodes. Analytical results indicate that by using the optimal routing strategy, the network capability in processing traffic is proportional to the square of the network size and is independent of each node degree. Simulations show that compared with the classic shortest path routing strategy, the new strategy can enhance the network capability several times with the small-world character and its performance is gradually improved with the increasing of the average degree. Moreover, the comparison with the efficient routing strategy also reveals the prominent performance of the new strategy.
2009, 58 (9): 5911-5918.
doi: 10.7498/aps.58.5911
Abstract +
In this paper, based on 1-D cellular automata, the probabilistic behaviors of malware propagation in complex networks are investigated. Neighborhood and state transition functions with integrated expression are established and two models of malware propagation are proposed to evaluate the probabilistic behavior of malware propagation in various networks. We run the proposed models on nearest-neighbor coupled network （NC） and Erdos-Renyi （ER） random graph network and Watts-Strogatz（WS） small world network and Barabasi-Albert （BA） power law network respectively. Analysis and simulations show that, the proposed models describe perfectly the dynamic behaviors of propagation in the above networks. Furthermore, the proposed models describe not only the average tendency of malware propagation but also the rare events such as saturation and extinction of malware, and overcome the limitation occurring in a deterministic model based on mean-field method that describes only the average tendency of malware propagation and neglects the probabilistic event. Meanwhile, the result of simulations shows that the heterogeneity of degree distribution and local spatial interaction are key factors affecting the malware propagation and immunization.
2009, 58 (9): 5919-5922.
doi: 10.7498/aps.58.5919
Abstract +
This paper studies the Lagrange symmetry of a dynamical system of relative motion. The definition and the criterion of the symmetry of the system are established. The condition under which there exists a conserved quantity and the form of the conserved quantity are obtained.
2009, 58 (9): 5923-5929.
doi: 10.7498/aps.58.5923
Abstract +
Experiments have been performed to investigate the effect of subharmonic motion on size segregation in vertically vibrated granular beds. In our experimental systems, symmetric normal convection of granular particles is induced when vibration acceleration is sufficiently large, and subharmonic motion of the particles appears when vibration acceleration is above another larger critical value. Observations reveal that particle convection is the main mechanism leading to the segregation of larger intruder particles imbedded in smaller ones, the convection flux dominates the rising time of the intruder, and a distinct retardation of the segregation time is induced when the bed’s bulk motion undergoes period-doubling and period-quadrupling bifurcations. An analysis of the convection due to the effects of air is given. Then the mechanism leading to such retardation is discussed and simple expression for the segregation time is formulated. The obtained results agree well with experimental values.
2009, 58 (9): 5930-5935.
doi: 10.7498/aps.58.5930
Abstract +
There is a continuum contradiction between the Wigner-Seitz model and the volume infinitesimal. By analyzing the attractive force and the repulsive force of the bcc and fcc double Wigner-Seitz model with the classical Lennard-Jones potential, the conclusion that the relative error satisfies the engineering analysis is established even if double Wigner-Seitz models superpose. By comparing the single atom Al sphere-surface force of the Wigner-Seitz model with the discrete simulation, a satisfactory result is obtained. Based on the Wigner-Seitz model, the dynamic equation of the digital micro-mirror device （DMD）, including the sticking effect, is found. The DMD simulation result is compared with the measurement result. The conclusion that the Wigner-Seitz model satisfies the micro-continuum requirement of the micro- and nano-engineering is arrivedat.
2009, 58 (9): 5936-5941.
doi: 10.7498/aps.58.5936
Abstract +
The supercoiling configuration of a thin elastic rod is discussed on the basis of Kirchhoff’s model. The equivalent twisting stiffness and bending stiffness of a thin helical rod are derived. The stability and bifurcation of a thin elastic rod under tension and twist are analyzed, and the results can be applied to determine the stability of a thin helical rod by use of the equivalent stiffness. In the case when the rod is under constant twist and increasing tension force the straight equilibrium can be unstable and transfers to helical equilibrium. When the tension force increases further the straight thin helical rod can be unstable and twins to a supercoiling state. Therefore the forming process of supercoiling configuration of a rod under tension and twist observed in Thompson/Champney experiment can be explained qualitatively.
2009, 58 (9): 5942-5949.
doi: 10.7498/aps.58.5942
Abstract +
Based on the Lagrange function, a new nonlinear relative rotational equation with Davidenkov hysteresis is established. Firstly, the bifurcation characteristics of the hysteretic relative rotational autonomous function and non-antonomous function are discussed. Secondly, the approximate solution of the nonlinear function under periodic force excitation is obtained by KBM method. At last, by numerical simulation, several bifurcation structures are obtained, and the comparisons result indicate the approximate solution of KBM method has higher accuracy and better reflects the dynamic characteristic of equation effectively.
2009, 58 (9): 5950-5954.
doi: 10.7498/aps.58.5950
Abstract +
The analytical model of probe impedance due to multilayered conductive structures is established using the reflection and transmission theory of electromagnetic waves in eddy current testing. The electromagnetic field in the region under considecation consists of the excitation field of the coil and the eddy current field. The eddy current field is regarded as the combination of the reflection and transmission of the excitation field. Therefore, the probe impedance is analytically modeled by applying the series-form representation of the excitation field and the reflection and transmission theory of electromagnetic waves, thus resulting in a series-form expression. Finally, the calculated results from the typical integral-form and developed series-form expressions were compared, and experiments were carried out. The good agreement between the calculated and experimental results justifies the presented analytical model. In comparison with the infinite integral of probe impedance, the series-form expansion has advantages of not needing the determination of the integral upper limit, saving time and easy control of the error.
2009, 58 (9): 5955-5960.
doi: 10.7498/aps.58.5955
Abstract +
The Heisenberg spin cluster with two particles controlled by a time-dependent magnetic field is investigated. Since the system possesses an SU（2） algebraic structure, the exact analytical solution to time evolution operator can be obtained by using algebraic dynamical method. Based on the analytical solution, the time evolution of wave function of the two-particle system can be obtained, then the entanglement can be calculated easily. The time evolution of the entanglement for different initial states is studied, and the effect of external field on the entanglement is discussed as well.
2009, 58 (9): 5961-5964.
doi: 10.7498/aps.58.5961
Abstract +
The Klein-Gordon equation in the presence of a spatially one-dimensional Hulthén potential barrier is solved and the scattering state solutions are obtained in terms of the hypergeometric functions. Both the reflection coefficient and transmission coefficient are calculated from the boundary condition of Klein-Gordon equation and the conditions for transmission resonance are then derived.The result shows that when the reflection coefficient is zero the transmission resonance takes place.
2009, 58 (9): 5965-5969.
doi: 10.7498/aps.58.5965
Abstract +
We analyze the quantum spectra of the two-dimensional annular billiard system based on the open-orbit quantum spectrum function, and respectively calculate the Fourier-transformed quantum spectra for various values of a parameter （in the case f=Rin/Rout）. The results show that the peak positions of quantum spectrum match with the lengths of classical orbits of particle motion very well ，and the semiclassical closed-orbit theory affords a good explanation. While the inner circle radius becomes comparaber with the de Brogile wavelength of the particle, the character of quantum spectrum changes essentially, turning out to be similar with the pattern of optical diffraction, which is a purely wavelike phenomenon and accords with Fresnel-Kirchhoff diffraction theorem. Our treatment provides a basis theory for researching the property of billiard system and microjunction transport, and opens a new way to investigate the diffraction of crystal and spectral analysis.
2009, 58 (9): 5970-5977.
doi: 10.7498/aps.58.5970
Abstract +
We present a scheme for establishing a multi-user quantum channel of multi-atom entangled W states and GHZ states based on cavity QED. Each user has shared EPR pairs with quantum switch during the leisure time of quantum network. An entangled W state is prepared base on two EPR pairs in cavity field by quantum switch at first，and entanglement swapping and direct measurement is operated on the other EPR pairs to establish a quantum channel of W states between three users. In the same way, we can establish a quantum channel of four atoms entangled W state. Three atoms of quantum switch simultaneously interact with cavity field to establish a quantum channel of entangled GHZ states between three users after direct measurement, and we also establish an N users’ quantum channel of entangled GHZ states.
2009, 58 (9): 5978-5982.
doi: 10.7498/aps.58.5978
Abstract +
In this letter, we propose an experimental scheme of universal unambiguous discrimination with only linear optical elements and the coincidence measurements. In addition, a modified scheme is presented to increase the success probability with ancillary photons. This scheme is feasible by current experimental technology and may be used in quantum cryptography.
2009, 58 (9): 5983-5987.
doi: 10.7498/aps.58.5983
Abstract +
In this article, an experimental scheme of quantum Fredkin gate is proposed. This scheme is based on the cross-Kerr effect between the photons and the ancillary coherent state. Only one coherent state is required, while the single photon detector and the coincidence measurement are not required, so this Fredkin gate is scalable. In addition, this is a nearly deterministic gate with the success probability 1/133, and it is feasible with the current experimental technology in optics.
2009, 58 (9): 5988-5992.
doi: 10.7498/aps.58.5988
Abstract +
We calculate the orbital effect of photon in the axisymmetric field created by the spinning mass with electric charge and a large number of magnetic monopoles. By analyzing the result we found that the deflection effect caused by the electric charge and magnetic charge decreases the deflection effect caused by the mass of the field source, but the deflection effect caused by the spinning of the field source depends on the angle between the spinning direction of the field source mass and the direction of photon motion. We obtained interesting results in discussing the parameters of the celestial body.
2009, 58 (9): 5993-5996.
doi: 10.7498/aps.58.5993
Abstract +
We extended the pruned-enriched Rosenbluth method, which was proposed by Grassberger for simulating a single self-avoiding walk （called GR method for the sake of convenience）, to simulate multi-avoiding walks. For simplicity this method is called extended GR （E-GR） method and used to investigate the screening behavior of linear polymer solutions. The simulations show that the screening is a cooperative behavior of monomers on other chains, i.e. it is not only dependent on the concentration of solutions but also on the length of other chains. The simulated screening behavior agrees with the experiments and the prediction of the self-consistent field theory. These results also show the validity and potential applications of E-GR to study other physical properties of linear polymer solutions.
2009, 58 (9): 5997-6005.
doi: 10.7498/aps.58.5997
Abstract +
In general, the prediction modeling of chaotic time series is conducted by Volterra filters through constructing nonlinear fitting functions according to the methodology of pattern training. Since the proposed approach is consistent with the nonlinear characteristics of chaotic systems, the corresponding model turns to be more effective than conventional models. However, something abnormal is likely to occur, such as inadequate trainingor, over training, and the training data set size is not easy to choose, because the existing Volterra filters are trained point by point along the chaotic orbit. Based on the similarity of the evolving tendency of neighbor orbits in phase space, the chaotic time series multi-step-prediction model （MSP-HONFIR） employing the adaptive higher-order nonlinear Volterra filter （HONFIR） is constructed in this paper. A new method of choosing neighbor orbits in phase space is presented by considering the Euclidean distance and the evolving tendency. In addition, the criterion for the choice of the training data set size is discussed. Numerical experiments demonstrate that the performances of multi-step-prediction are improved compared to the original HONFIR method.
2009, 58 (9): 6006-6015.
doi: 10.7498/aps.58.6006
Abstract +
The stability of the origin of the hyperchaotic Lorenz system with two time scales is investigated. The characteristics of Hopf bifurcation from the origin, including the existence condition, the direction as well as the stability of bifurcating periodic solutions are discussed in detail, which can be demonstrated by the numerical simulations. With certain parameter, the fast-slow system can exhibit symmetric bursting and further lead to hyperchaotic movement. Based on the method of slow-fast analysis, different bifurcation forms between quiescent state and spiking has been revealed and the influence of coupling strength on slow passage effect is disscussed.
2009, 58 (9): 6016-6025.
doi: 10.7498/aps.58.6016
Abstract +
The generalized projective synchronization of improved invariable-Lyapunov-exponent-spectrum chaotic system is studied. The appropriate nonlinear feedback controllers are designed by an active control method for synchronization of two chaotic systems with the same or different structures. The effectiveness of scaling factor and global linear amplitude adjuster in the generalized projective synchronization system is analyzed. The driving, control and response subsystems of the synchronization system are analyzed in detail and constructed based on modularization and reusing. Numerical simulation and circuit experiment simulation all show that any scale signal of driving system state variable can be obtained by adjusting the scaling factor. When the global linear amplitude adjuster is changed, the state variables of driving system and response system are modulated synchronously in linearity while the generalized projective synchronization between the two systems is not influenced.
2009, 58 (9): 6026-6029.
doi: 10.7498/aps.58.6026
Abstract +
Recent investigation has shown that the permanent magnet synchronous motor （PMSM） goes chaos for certain parameter values or under certain working conditions, which threatens the secure and stable operation of the motor. Hence, it is significant to study the method of controlling or suppressing chaos in PMSM. Based on LaSalle invariant theory, an adaptive law of controlling chaos was presented in this paper, which enablcs avoiding the influence of undeterministic equilibrium of the system. Simulation results show that the designed control method is effective and its control property is better than that of others. Our research results may help to maintain the system’s secure operation.
2009, 58 (9): 6030-6038.
doi: 10.7498/aps.58.6030
Abstract +
The existence of three types of generalized synchronization of unidirectionally coupled non-autonomous systems is studied. When the modified response system collapses to an asymptotically stable equilibrium, asymptotically stable periodic or quasi-periodic orbits, under certain conditions, the existence of generalized synchronization can be turned to the problem of compression fixed point in the family of Lipschitz functions. Theoretical proofs are proposed to the exponential attractive property of generalized synchronization manifold. In addition, the Duffing system was taken for illustration and verification.
2009, 58 (9): 6039-6044.
doi: 10.7498/aps.58.6039
Abstract +
This article proposes an adaptive synchronization method with only one controller for the fractional-order unified chaotic system, and adaptive controller and updating law of parameter are obtained. The controller employs a single variable, and the presented control scheme is suitable for a class of fractional-order chaotic systems. In addition, the synchronization is effective in the presence of noise. Numerical simulations are used to validate and demonstrate the effectiveness of the proposed method.
2009, 58 (9): 6045-6049.
doi: 10.7498/aps.58.6045
Abstract +
Intensive statistical complexity can reflect the random nature of chaos-based pseudorandom sequence. Based on this property, the definition of k-error intensive statistical complexity is presented and two basic properties of it are proved in this paper, which can be used to measure the stability of complexity of chaos-based pseudorandom sequences. Based on chaos-based pseudorandom sequences produced via Logistic, Henon, Cubic, Chebyshev and Tent maps, an example is given to demonstrate how it works. Simulation results indicate that the approach is effective, it can distinguish the stability of diverse chaos-based pseudorandom sequences, and is an effective way for evaluating the stability of chaos-based sequences.
2009, 58 (9): 6050-6057.
doi: 10.7498/aps.58.6050
Abstract +
The Markov chain Monte Carlo （MCMC） method is used to estimate the unknown parameters of air-sea oscillator system, which is a model of Eastern Pacific sea surface temperature （SST）. Firstly，the posterior probability density function for unknown parameters of air-sea oscillator system is deduced with the Bayesian formula. Secondly， the Adaptive Metropolis algorithm is used to construct the Markov Chains of unknown parameters. And the converged samples are used to calculate the mathematic expectation. The results of numerical experiments show that parameters estimated by the new method have high precision and the noise is filtered effectively from the observations.
2009, 58 (9): 6058-6062.
doi: 10.7498/aps.58.6058
Abstract +
The chaos characteristics of a DFB semiconductor laser subjected to single and double external cavity optical feedback are analyzed experimentally. The results show that the correlation dimension, bandwidth of the chaos generated by one external cavity optical feedback can be expanded by using double external cavity optical feedback. When the laser is subjected to double external cavity optical feedback, the bandwidth with one external cavity feedback is increased from 5.5 GHz to 11 GHz. Correspondingly, the correlation dimension is increased from 2.8 to 3.6. The information of the external cavity length of the chaos generated by double external cavity optical feedback can be masked in the autocorrelation function.
2009, 58 (9): 6063-6067.
doi: 10.7498/aps.58.6063
Abstract +
This is a basic work on the inverse scattering transform that constructs the complete orthonormal system of the free Jost solution. In order to establish the system for the DNLS equation, we introduce a new transform for the spectral parameter and a gauge transform. The Marchenko's equation and the Zakharov-Shabat's equation of inverse scattering are derived based on the new spectral parameter.
2009, 58 (9): 6068-6073.
doi: 10.7498/aps.58.6068
Abstract +
The efficient functioning of complex networks rely on their traffic capacity, so it is significant to improve their throughput. We propose a new efficient routing strategy called weighted routing strategy to enhance the traffic capacity. Each edge is assigned a value that is related with its end degree. Then packets are transported across the shortest paths of the weighted network. This kind of paths can more evenly go through the vertices and utilize their transport ability. They avoid collectively passing certain vertices which makes them congested, thus the throughput of the network is improved. It is demonstrated by simulations that our strategy is more powerful than the traditional shortest-path strategy, and improves tens of times the throughput for many structures of networks.
2009, 58 (9): 6074-6079.
doi: 10.7498/aps.58.6074
Abstract +
Without considering that the component which alternates between operating and storage states periodically is likely new after each repair, the method of equivalent failure time of time-sharing redundant system is studied, and the cumulative damage model is put forward. Basing on Weibull distribution, the model is developed and its parameters are estimated, and a simulation method for evaluating system reliability is also given. Finally, an example about 1-out-of-3 mechanical system is given to demonstrate the affectiveness of the model.
2009, 58 (9): 6080-6085.
doi: 10.7498/aps.58.6080
Abstract +
A non-contact measuring device for electrical resistivity has been designed, which is based on electromagnetic induction principle. Using the device, the electrical resistivity of metals can be monitored during transition from liquid to solid state, which shows that the device is suitable for analysing the structure transition of metals and alloys during the cooling process.The design principle and construction of the device are detailedly described in this paper. The change of electrical resistivity of pure Zn and pure Sb, and hypereutectic Zn-70wt.%Sb alloy during cooling was measured by the device. The experiment results show that the device preforms well.
NUCLEAR PHYSICS
2009, 58 (9): 6086-6090.
doi: 10.7498/aps.58.6086
Abstract +
Nuclear pairing energy of dozens of atomic nuclei in nuclear period chart are calculated along the stable line by extracting the swatch at a proton or neutron number interval of 4. Especially, we have studied the rule of pairing energy of the even-even nuclei of O isotopes changing with nucleon number under the relativistic mean-field model, and found, when energy gap Δ is fixed, the magnitude of nuclear pairing energy is related to nuclear shell structure. Thereof we propose a simple method to test closed shell, and further, we conclude that the neutron number N=6 is a new magic number not only in neutron-rich region, but also in proton-rich region of light nuclei.
ATOMIC AND MOLECULAR PHYSICS
2009, 58 (9): 6091-6095.
doi: 10.7498/aps.58.6091
Abstract +
The equilibrium structure, harmonic frequency and potential energy curves for two of the excited states a1Δg and b1Σ+g of O2 molecule were calculated by using MRCI method with aug-cc-pVQZ, cc-pV5Z, 6-311++g（d,p）and 6-311++g（3df,3pd） basis sets. The analytical potential energy functions for a1Δg and b1Σ+g of O2 was fitted by Murrell-Sorbie theory . The force constants and spectrum data were obtained according to fitted parameters. Results show that our results are good agreed with the experimental value.
2009, 58 (9): 6096-6100.
doi: 10.7498/aps.58.6096
Abstract +
By assuming the ion sphere model, the self-consistent field method for the Poisson-Boltzmann equation and the Dirac equation is used to calculate the energy levels of He-like titanium immersed in hot and dense plasmas. Consequently, the spectral shifts of the intercombination line and the resonance line and the shifts of the exchange energy of He-like titanium in hot and dense plasmas are studied. The results show that the two electronic dipole transitions red shift nearly linearly with the increase of plasma electron density. The formula of the linear relationship is found. The results may be useful in developing the new method of dense plasma diagnosis.
2009, 58 (9): 6101-6107.
doi: 10.7498/aps.58.6101
Abstract +
Terahertz time-domain spectroscopy （THz-TDS） has been used to measure the vibrational spectra of polycrystalline D-, L- and DL-ornidazole over the temperature range 6—298 K. The large differences of the spectra are observed in the frequency range 0.3 THz—2.5 THz, which indicates that THz-TDS is an effective tool to distinguish between enantiomers （D-, L-ornidazole） and its racemic compound （DL-ornidazole）. A number of absorption peaks which could not be observed at room temperature are well resolved in the low temperature range. This provides more experimental details for mode assignment. The evolution of these absorption features between 6 K and 298 K was continuously mapped. The absorption frequencies shift to lower values as temperature increases. The measured temperature dependence can be well fitted if we consider the phonon modes follow a Bose-Einstein distribution. Finally, the quantum chemical calculations were carried out to simulate the experimental THz spectra of the three samples in the range of 0.2—2.5 THz. Compared with the calculated results, the observed characteristic absorptions are explained at molecular level.
2009, 58 (9): 6108-6112.
doi: 10.7498/aps.58.6108
Abstract +
The influence of phonon distribution on the frequency upconverted fluorescence emission is studied with laser spectroscopy in different matrices and at different ambient temperatures. The spectrum of phonon energy can be adjusted by varying the content of SiO2 in the oxyfluoride glass and glass ceramics, which affects the upconverted fluorescence emission of doped ions. Since the phonon energy depends on the sample temperature, the variation of the temperature can also influence the population rate of 3H4 level in Tm3+ doped low-phonon-energy LaF3 crystal, resulting in a change of the fluorescence upconversion.
2009, 58 (9): 6113-6116.
doi: 10.7498/aps.58.6113
Abstract +
The experiments were performed at HI-13 tandem accelerator at the Chinese Institute of Atomic Energy （CIAE）, in which the L-shell X-ray relative production cross section was measured for solid targets Au bombarded by 20—50 MeV O5+ions. The ratios of Au L-subshell production cross sections σ（Lβ）/σ（Lα），σ（Lγ）/σ（Lα），σ（Ll）/σ（Lα） have been calculated according to the experimental data. The results are compared with the predictions of the ECPSSR theory. Reasonable agreement between theory and experiment was obtained.
EDITOR'S SUGGESTION
2009, 58 (9): 6117-6121.
doi: 10.7498/aps.58.6117
Abstract +
A small sized and low power consumption physical package of CPT atomic frequency standard developed by us is introduced in the paper. The experiments of locking laser frequency and microwave frequency were carried out and realized with the physical package. By locking laser frequency to atomic absorption spectrum through current negative feedback and locking microwave frequency to electromagnetic induced transparency resonance peak through voltage negative feedback respectively, the locking of the clock frequency of this laboratorial desktop experimental CPT frequency standard is realized. The measurement of the frequency stability of this experimental system demonstrate a performance better than 5×10-11τ-1/2 （1—200 s）.
2009, 58 (9): 6122-6127.
doi: 10.7498/aps.58.6122
Abstract +
A microcantilever sensor platform is used for detecting the self-assembly of poly-（N-isopropylacrylamide） （HS-PNIPAM） on gold surface. The change of the interaction between molecules caused by conformation transition will change the surface stress of the microcantilever which causes its bending. The kinetic curves of self-assembly can be obtained by real-time monitoring the deflection of the microcantilever using the optical lever read-out technique. HS-PNIPAMs of different molecular weight were used to study the self-assembly process, and the results showed that the kinetic curves can be divided into three stages corresponding to different conformations, respectively. The first stage cor responds to physical adsorption of HS-PNIPAM on gold-coated side. The second and third stages correspond to chemical adsorption on gold-coated side with conformation transition. The kinetic curves fit Langmuir adsorption isotherm well. The results also show that the reaction rate κ of HS-PNIPAM is far less than that of small molecules and decreases exponentially with the molecular weight; while the time of HS-PNIPAM’s self-assembly is far greater than that of small molecules and proportional to the molecular weight. The change of the surface stress is linear to the molecular weight of HS-PNIPAM.
2009, 58 (9): 6128-6133.
doi: 10.7498/aps.58.6128
Abstract +
The adsorption of CO on the Nin cluster surfaces has been systematically investigated by density functional theory. The result indicates that the lowest energy structures of NinCO are generated with CO being adsorbed on Nin clusters, and the lowest energy structures of Nin clusters are not changed by adsorbing CO molecule， The chemisorption of CO on Nin cluster surfaces belongs to non-dissociative adsorption. The increased theoretical CO bond length of 0.1180-0.1214?nm （compared with 0.1138?nm） demonstrates the activation of the CO bond. Natural bond orbital analysis shows that the interaction between Ni atoms and CO molecule is primarily contributed by the hybridized molecular orbital within CO and 3d, 4s, 4p orbital of Ni atoms.
2009, 58 (9): 6134-6140.
doi: 10.7498/aps.58.6134
Abstract +
The geometric structures, relative stability, electronic structure and their size dependence of scandium monoxide（ScnO, n=1—9） clusters are investigated by using density functional theory （DFT） at the BP86/CEP-121G level （the O atom treated with 6-311G** basis sets）. With the cluster size increasing, the geometries of the lowest energy clusters show that the oxygen atom situated on the surface turn to be embed in the interior. The doped O atom enhances the stability, increases the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital and changes the trends of stability and electronic properties with the cluster size increasing. Results on even-odd oscillation in cluster stability and electronic properties predicted that the oxide clusters with even number of Sc atoms are more stable than the neighboring clusters with odd number of Sc atoms. The calculated vertical ionization energy values agreed especially well with the experimental values. The trend of electron affinities shows an obvious oscillatorg increasing behavior as the cluster size increasing. The stability and electronic structure of ScnO clusters are also characterized by the maximum hardness principle of chemical reactivity.
CLASSICAL AREA OF PHENOMENOLOGY
2009, 58 (9): 6141-6145.
doi: 10.7498/aps.58.6141
Abstract +
RF phase Jitter is a very important parameter for a relativistic klystron amplifier, and it is closely related with the physical processes in the klystron. In view of the physical process in the klystron, the RF phase jitter is theoretically studied together with particle in cell （PIC） simulation. The main factor which affects the RF phase jitter is deduced and verified in the PIC simulation. The RF phase jitter is significantly affected by the fluctuation of the beam voltage at the steady state when the cavity is in resonanec. The relation is linear in a certain range.
2009, 58 (9): 6146-6151.
doi: 10.7498/aps.58.6146
Abstract +
A novel finite difference time domain （FDTD） method has been introduced to analyze multi-conductor transmission lines terminated with frequency-dependent loads. The admittance of frequency-dependent loads can be modeled by rational functions by using vector-fitting, then converting these functions into time-domain by inverse Fourier transform （IFT）. Based on the piecewise linear recursive convolution （PLRC） method, the relation between voltage and current of admittance parameters are deduced. Incorporating the formula into multiconductor transmission lines （MTL） FDTD equations, we get the general formula of MTL FDTD dealing with frequency-dependent loads. In simulating a typical circuit, the results agreed well with the results obtained by using the state-variable transmission model. It shows the method is valid in dealing with frequency-dependent loads.
2009, 58 (9): 6152-6157.
doi: 10.7498/aps.58.6152
Abstract +
Based on electromagnetic characteristic of metallic dendritic cell, negative permeability metamaterial composed of periodic arry of metallic dendritic cells is fabricated. A 2.64GHz microstrip antenna with dendritic structure is proposed. The results show that compared with the conventional microstrip antenna, the performance of the novel microstrip antenna with dendritic-structured negative permeability metamaterial has been improved remarkably. The 3-dB beam width of E-and H-plane can be reduced by 18°and 13°, respectively. The directional property of the antenna is enhanced, the gain is improved by 2.19dB and the efficiency is increased by 65%. It proves that the performance of the microstrip antenna is improved by using negative permeability metamaterial as the substrate.
2009, 58 (9): 6158-6166.
doi: 10.7498/aps.58.6158
Abstract +
A volume-surface composite model of rough sea surfaces with water bubble layer driven by wind is presented in this paper. Based on the modified two-scale rough surface scattering theory, MIE theory and VRT （vector radiative transfer） theory, the difference of electromagnetic scattering properties of the water bubbles compared with those of water particles is investigated. The relations between the foam coverage of the sea surface and wind speed and air-sea temperature difference are analyzed. The dependence of back- and bistatic-scattering coefficient of Gaussian rough surface and empirical sea surface with/without foam layer on the incident and azimuthal angle, the wind speed, the wind direction, as well as the polarization are discussed in detail. The results of numerical simulations are analyzed and compared with the measured data from the relevant references.
2009, 58 (9): 6167-6173.
doi: 10.7498/aps.58.6167
Abstract +
Based on the theory of the scattering of an eccentric sphere arbitrarily illuminated by a shaped beam which is recently presented by us, and according to generalized Lorenz-Mie theory （GLMT）, we derived the series expressions of radiation forces exerted by the incident beam on an eccentric sphere by using the conservation law of electromagnetic momentum and the Mexwell-Tensor. As an example, numerical results of radiation force of absorbing eccentric spheres for off-axis incidence of Gaussian beam are given, along with a discussion about the influence of the beam-waist radius, relative complex refractive index, relative size and location of the inclusion on the forces.
2009, 58 (9): 6174-6178.
doi: 10.7498/aps.58.6174
Abstract +
The dispersion relations and the reflectionless conditions are obtained by the Maxwell’s curl equations in a uniaxial anisotropic medium and the phase-matching. Using the shift operator finite difference time domain （SO-FDTD） method and the transform relationship of frequency domain to time domain （jω replaced by /t）, an FDTD absorbing boundary condition for three kinds of general dispersive media model, i.e. the Debye model, Lorentz model and Drude model, is given. The characteristics of our absorbing boundary condition are tested. The computed results illustrated the generality and the feasibility of the scheme.
2009, 58 (9): 6179-6184.
doi: 10.7498/aps.58.6179
Abstract +
We studied the new left-handed material cousisting of triangular and three rectangular split resonant rings （SRRs） based on rectangular resonators and metal wires through simulation and experiment. Simulated negative permeability material based on periodic structures of triangular and three rectangular SRRs, we found that two kinds of SRRs can generate negative permeability. We designed new kinds of left-handed materials consisting of two kinds of resonators based on rectangular resonators and copper wires, simulation shows the structures have good left-handed property in some frequency bands. We also fabricated experimental samples in which waves under go negative refraction when the frequency bands are 9.5—13.3GHz and 9.8—12.5GHz respectively. This has important significance on design and study of new periodic structures of left-handed materials.
2009, 58 (9): 6185-6191.
doi: 10.7498/aps.58.6185
Abstract +
Based on the generalized integral formula and the complex Gaussian expansion of the aperture function, an approximate analytical propagation formula for a Lorentz beam passing through a circular-apertured misaligned paraxial optical system is derived. The analytical propagation formula of a Lorentz beam through a unapertured misaligned paraxial optical system is treated as the special case of the general formula. As a numerical example, the propagation properties of a Lorentz beam through an apertured misaligned thin lens are investigated numerically. The results show that diffraction of different intensity, in other words, the radius of the circular aperture apparently influences on the distribution of the normalized light intensity of the diffracted beam and its propagation law.
EDITOR'S SUGGESTION
2009, 58 (9): 6192-6201.
doi: 10.7498/aps.58.6192
Abstract +
Analytical expressions for the cross-spectral density and intensity of two-dimensional nonparaxial partially coherent Hermite-Gaussian （H-G） beams in coherent and incoherent additions are derived, and some special cases are analyzed. The intensity of the resulting beam depends not only on the f-parameter, fσ-parameter, off-axis distances, beam numbers and orders of combined beams and propagation distance, but also on the addition scheme. The meaning of the terminology of coherent and incoherent addition of partially coherent beams is interpreted physically and the validity is confirmed by numerical examples.
2009, 58 (9): 6202-6209.
doi: 10.7498/aps.58.6202
Abstract +
An analysis of the orbital angular momentum of an optical beam misaligned with respect to a receiver during propagation in the information transfer is investigated. The analytical expressions of Laguerre-Gaussian beams laterally displaced， angularly deflected and simultaneously misaligned in both ways are derived, and the features of the spiral spectrum in these cases are studied. It is shown that both parallel displacement and angular tilt will lead to the spread of the spiral spectrum, which is independent of the misalign direction. The larger the misalign, the more serious the spectrum spread. However, with the increasing of the propagation distance, the degree of the spread for the laterally displacement is decreasing gradually, while that for the angular tilt is increasing. In the angular tilt case, the spread of the spiral spectrum always keeps symmetric during propagation, while in the case of lateral displacement, the spiral spectrum is asymmetric, and goes to a stable state. The spiral spectrum is also investigated for the case with simulataneous lateral misalignment and angular tilt, and we conclude that the effects of both misaligns on the spectrum are related with one another.
2009, 58 (9): 6210-6215.
doi: 10.7498/aps.58.6210
Abstract +
The model of laser spectrum used in the method of smoothing by spectral dispersion （SSD） affecting the beam smoothing was theoretically discussed based on the analysis of spatial frequency spectrum, and the response function to the spatial frequency modulation was put forward to describe the effects. With theoretical derivation and numerical simulation, it is concluded that the spatial frequency response function by SSD has periodical property and is determined by dispersion angle and spectrum shape. More generally, spectrum shape was related with the shape of response function, the dispersion angle affects the lowest spatial frequency, and color cycle number can modify the distribution of low and high spatial frequency to change the smoothing effect. Applied to multidimensional SSD, the response function characters can give the guiding principle for optimization.
2009, 58 (9): 6216-6221.
doi: 10.7498/aps.58.6216
Abstract +
Using finite-difference time-domain （FDTD） method, we found the relationship between filling factor and band gap of square and hexagonal array of circular photonic crystal, and obtained the geometric parameters of the 2D photonic crystal, for which the number of bandgaps are the greater. Using FDTD method to calculate the extraction efficiency of the photonic crystals with the parameters, we verified the enhancement in extraction efficency of the GaN-based blue light-emitting diode based on the square and hexagonal array of circular photonic crystals with the the parameters, and the hexagonal arrangement is better than the square arrangement. By using the bang gap theory and equivalent medium theory was analyzed the mechanism of antireflection.
2009, 58 (9): 6222-6226.
doi: 10.7498/aps.58.6222
Abstract +
Light scattering by a particle containing inclusions is calculated by a combination of ray-tracing and Monte Carlo techniques. The distribution of the inclusions can be sparse or dense. While the individual reflection and refraction events at the outer boundary of a sphere particle are considered by a ray-tracing program, the Monte Carlo routine simulates the internal scattering processes. A dense-medium light-scattering theory based on the introduction of the static structure factor is used to calculate the single scattering characteristics for densely packed inclusions. Numerical results of the single scattering characteristics for a spheroid containing inclusions are discussed.
2009, 58 (9): 6227-6235.
doi: 10.7498/aps.58.6227
Abstract +
We propose a new analytical model of range-Doppler image of cylinders and cones rotating around their axes. This analytical model can manifest the contribution of geometric parameters, roughness of the surface, and attitude as well as pulse duration to range-Doppler image. This analytical model degenerates into the analytical model of Doppler spectra for plane waves. The influence of geometric parameters, roughness of the surface, and attitude as well as pulse duration are analyzed numerically by applying the analytical model. Combining the theory and measurements, the analytical model can be used for parameter identification of cylinders and cones. This analytical solution may contribute to laser Doppler velocimetry and ladar applications.
2009, 58 (9): 6236-6242.
doi: 10.7498/aps.58.6236
Abstract +
A novel approach to design the subwavelength metal gratings for the polarizing beam splitters is presented. The method is based on effective medium theory （EMT） and thin film optics. The polarizing diffraction performance of subwavelength grating was analyzed by the rigorous couple-wave analysis （RCWA） for the wavelength of 650nm. The numerical calculus is used to analyze the effects of the zeroth diffraction efficiency caused by the grating period, the groove depth, the incident angle and the incident wavelength. The results show that subwavelength metal grating have the characteristics of high reflectivity like metal films for TE polarization and high transmission like dielectric films for TM polarization. Both transmission waves and reflected waves have high polarization extinction ratio and low insertion loss over a wide incident angle range （-30°θλ<800nm）. The optimal design agrees excellently well with the results simulated by RCWA method.
2009, 58 (9): 6243-6247.
doi: 10.7498/aps.58.6243
Abstract +
Amplification and simultaneous phase regeneration of differential phase-shift keying （DPSK） signals is demonstrated using a phase regenerator. Phase regeneration is achieved in a Sagnac fiber interferometer comprised of photonic crystal fiber operating in an un-depleted pump regime. The formula of signal after phase regenerator is derived. For different incident power of signal, the relations between signal-pump phase difference and signal gain are discussed, as well as the influence of fiber length on signal output intensity. The optimum parameters of the phase regenerator are given. The distributions of phase and intensities for both the non-regenerated and regenerated signals are simulated. Simulations show that nearly ideal regeneration can be achieved for the DPSK signals.
2009, 58 (9): 6248-6257.
doi: 10.7498/aps.58.6248
Abstract +
After analyzing the principle of imaging of the objective, a method of depth measurement in the direction of optical axis in micro-manipulation system is put forward. To measure depth, the relationship between defocus and blur of microscopic images is established based on optical transfer function （OTF）. This method has high precision and good linearity, since lens parameters and diffraction effect have been taken into account. Meanwhile, the fast identification algorithm of bar objects is utilized to simplify the original method, then depth can be measured online. In addition, the method is applied to micro-manipulation system, and an experiment to insert one needle into another automatically in defocused status is designed and carried out to show the effectiveness of the method. Thus, the operation range of the micro-manipulation system has been extended.
2009, 58 (9): 6258-6263.
doi: 10.7498/aps.58.6258
Abstract +
We put forward a model of calculating the threshold gain of random laser, a method for obtaining the distribution function and the relevant random variables according to the mean free path and scattering intensity distribution. The distribution functions are derived for isotropic scattering of light, and then we get the random variables according with the distribution at every scattering. Simulating the random walk of photons in random media by using Monte Carlo method, the threshold of random laser is got. The relationship of the threshold gain to the photon mean free path, the radius of gain zone, the depth of gain zone and light absorption coefficient of non-gain zone is discussed. We make some suggestions to lower the threshold. The theoretical results agree with the experimental data.
2009, 58 (9): 6264-6268.
doi: 10.7498/aps.58.6264
Abstract +
Generally, it is more suitable for studies on Ne-like X-ray laser by using fundamental frequency laser as driving beam than by frequency doubling. However, many huge laser facilities built for ICF research are usually designed for doubling and trebling of laser frequency, and they are unfit for use as fundamental frequency laser. We simulated the Ne-like Ge X-ray laser making use of JB19 codes, respectively in the case of doubled and trebled frequency diving. The results indicated that the higher power output of Ne-like Ge X-ray laser is also obtained when driven by doubled frequency laser. However the required output of driving laser beam was 3.3 times that in the case of the fundamental. Any way it presents a direction of studying Ne-like X-ray laser with huge laser facilities in the future. A preliminary experimental study has proved this point.
2009, 58 (9): 6269-6272.
doi: 10.7498/aps.58.6269
Abstract +
A home-made semiconductor saturable absorber mirror （SESAM） with or without high reflectivity coating is incorporated in the cavity of a laser with an Nd∶Gd0.1Y0.9VO4 crystal as the laser material and a Z-type cavity. In this paper, we explore the effect of the SESAM on the mode-locking property of the laser. The threshold value of the mode locking was found to decreased from 1.69W to 1.45W and the mode locking was more stable with the high reflectivity coating SESAM. At a pump power of 2 W, stable continuous-wave mode locking was obtained with an average output power of 250mW at an optical conversion efficiency of 12.5% at the central wavelength of 1064nm and a repetition rate of 142.25MHz.
2009, 58 (9): 6273-6278.
doi: 10.7498/aps.58.6273
Abstract +
In optical remote sensing, the calibration of remote sensor plays a key role in the quantificational remote sensing. A state-of-the-art highest accuracy standard transfer method is developed, which can transfer the standard cryogenic radiometer to secondary standard trap-type detector, and the absolute spectral responsivity calibration system is set up in the band between the visible to near-infrared in our laboratory. It is required that the process of standard transfer should produce little measurement uncertainty. In this paper a Ti: sapphire tunable laser, doubler and single wavelength laser in 24 interval of wavelengths respectively are used, the spectral responsivity of three silicon trap detectors are calibrated absolutely. The key techniques involved are the accurate positioning and adjustment of the infrared laser and the simulation calibration of window transmittance etc., which have bean successfully resolved. The result shows, in the visible （412nm to 800nm） reqion, the total relative standard uncertainty of the spectral responsivity at the laser lines is less than 0.05%, while in the UV （350nm） and NIR regions above 800nm, the total relative standard uncertainty is less than 0.065%. So the trap detector can be used as a transfer standard detector for calibration of space sensors in the band of 350nm to 1064nm.
2009, 58 (9): 6279-6284.
doi: 10.7498/aps.58.6279
Abstract +
The method of power spectral density（PSD） to describe defects existing on optical elements was proposed for the first time. An equivalent PSD algorithm was composed for treating the presence of plenty of amplitude-modulating micrometer-siged defects using statistical theory, and the method was validated by simulation.
2009, 58 (9): 6285-6290.
doi: 10.7498/aps.58.6285
Abstract +
A method is introduced to tune and optimize the photonic band gaps （PBGs） of two-dimensional photonic crystals （PCs）. PBGs between the bands at low frequency can be tuned by an additional atom rod at arbitrary positions. Moreover, fixing up the two atom rods at optimal positions and tuning the lengths of the two cylinders, the normalized gap widths of PBGs could be enlarged with a suitable configuration. The results also show that the setting up of large PBGs depends on different degrees of symmetry of the system in the case of two atom rods in a unit cell, the larger PBGs at higher frequency require lower symmetry.
2009, 58 (9): 6291-6295.
doi: 10.7498/aps.58.6291
Abstract +
The coupled Helmhotz-type differential equations for a general cylindrical structure containing chiral material were transformed into a pair of decoupled equations, and this new set was solved to find expressions for Ez and Hz with the expansion of the complete eigen functions in elliptical chiralwaveguide. There are no pure TE （TM） or even-type （odd-type） modes existing individually in the elliptical structure if Ez and Hz are coupled with each other. The influences of eccentricity and chiral admittance on dispersion of modes are discussed in this paper.
2009, 58 (9): 6296-6299.
doi: 10.7498/aps.58.6296
Abstract +
A photosensitive polarization-maintaining erbium-doped fiber was fabricated experimentally and a high efficiency resonance cavity was set up by writing three fiber Bragg gratings on this fiber using UV laser. The mono-wavelength laser with mean output power of 9.20dBm and mean wavelength of 1554.554nm was produced by pumping at a power of 23.617dBm and wavelength of 976nm. The fluctuations of output power and wavelength were less then ±0.05dB and ±0.0015nm for a test time of 800min, respectively, at room temperature.
2009, 58 (9): 6300-6303.
doi: 10.7498/aps.58.6300
Abstract +
The silica based Tm3+ doped fiber preform with high Ge concentration in preform core area was manufactured by solution doping method. It was made into an optic fiber preform with cross section of a hexagon by side polishing process, and drawn in to cladding pumping Tm3+ doped fiber with inner coverage layer of lower refraction index polymer. The absorption spectrum was measured, and the technical parameters were optimized. The uniform fiber Bragg gratings with reflectivity of 90% and 40% were written in both ends of the fiber by UV light respectively, and the linear optic cavity was constructed. The laser with wavelength of 1947.1031nm and power of 2.05W was emitted by pump laser excited with wavelength of 793nm and power of 5.6W. It shows that the fiber have excellent optical characteristics.
2009, 58 (9): 6304-6307.
doi: 10.7498/aps.58.6304
Abstract +
A device structure of resonant cavity light emitting diodes （RCLED） at 650nm wavelength was proposed by using AlGaAs as the n-type bottom DBR, AlGaInP as the p-type top DBR, and GaInP/AlGaInP MQW as the active region. The device was designed according to the transfer matrix method, and both RCLED and normal LED were fabricated for comparison. Results showed that the efficiency of RCLED is 30% higher than the normal LED, and the peak wavelength of RCLED changed only 1nm when the driving current increased from 3mA to 30mA, compared with that of 7nm for the normal LED. Meanwhile, RCLED has a narrower spectrum and a smaller far field divergence angle.
2009, 58 (9): 6308-6315.
doi: 10.7498/aps.58.6308
Abstract +
The interplay between the fabrication parameters during the fabrication of photonic crystal fibers（PCF） are numerically analyzed. Relation between these parameters and the final fiber’s geometry is identified. With the cooperative control of drawing temperature and feed speed, the final hole structure can be effectively controlled by tuning the applied pressure. A single-mode PCF with its d/Λ approaching 0.45, and a PCF with high air-filling fraction, whose d/Λ equals 0.8, are successfully fabricated. For fabrication of PCFs with uneven-sized holes, parameter control alone is sometimes inadequate in achieving the desired geometry. Taking a single-polarization single-mode（SPSM） PCF structure as example, the preform’s geometry is redesigned for optimization by inverse calculation. And the required SPSM PCF can thus be fabricated.
2009, 58 (9): 6316-6322.
doi: 10.7498/aps.58.6316
Abstract +
The mechanism of refractive index change of long period fiber gratings （LPFGs） induced by high frequency CO2 laser pulses is investigated in theory and by experiment. It is found that the release of residual stress, rapid solidification, fiber densification and fusion distortion are discovered to be the main mechanisms of formation of this kind of gratings. The above four mechanisms play different roles when different fibers, different scanning methods and the different laser power were used in the process of LPFG fabrication. The average refractive index changes of the core and cladding were measured by using M-Z interferometer formed by LPFG pair in this paper, which provides the experimental basis for fabricating all-fiber devices.
2009, 58 (9): 6323-6329.
doi: 10.7498/aps.58.6323
Abstract +
The nonlinear coupled-mode equations are rewritten by even and odd modes. We study modulation instability of photonic crystal fiber couplers when either even or odd mode is launched alone. The result shows that there are new types of modulation instability in both the normal and the anomalous-dispersion regimes. Modulation instability is related with four phase dispersion and has no relation with three phase dispersion. The gain spectra have been given as function of input power in various dispersion regimes. Quasi-cw can be changed into pulse array under certain conditions, and we can extract super-short pulses from it.
2009, 58 (9): 6330-6334.
doi: 10.7498/aps.58.6330
Abstract +
The mode-controlled nonlinear process in a highly nonlinear photonic crystal fiber is studied experimentally. The central wavelength of frequency-upconverted dispersive wave and its transverse intensity profile are controlled through a selective coupling of the pump field to the higher order modes of the fiber and a polarization-sensitive phase matching process. However, due to their large effective index difference, the two orthogonal modes cant be excited simultaneously. The index difference is lowered by injecting wax into the air holes which effectively modifies the core structure. This modification degenerates the two orthogonal high-order modes. As a result, they are excited simultaneously and form a hollow beam output.
2009, 58 (9): 6335-6343.
doi: 10.7498/aps.58.6335
Abstract +
The cross-spectrum characteristics of sound pressure between two hydrophones deployed vertically are analyzed in low frequency acoustic field of shallow water, more attentions are paid to the cross-spectrum active component of sound pressure when only two normal modes are trapped in the waveguide. The numerical results show that （1） the sign of the sound pressure cross-spectrum active component is independent of range when receiving transducers placed in appropriate depths, so it can be used to tell whether the sound source is near the surface or underwater by selecting a pair of appropriate deploying depth of transducers; （2） acoustic velocity profiles have little effects on the application of this method, the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range. Approximate theoretic analysis of cross-spectrum active component characteristics is proposed in the paper combined with the concept of effective depth, and the prediction formula of appropriate deploying depth of transducers is presented. The theoretic analysis indicates that the sum of the bi-hydrophone depths should be equal to the waveguide effective depth and the sign distribution of the sound pressure cross-spectrum active component is divided into three level regions in an ideal pressure-release waveguide. The theoretic analysis provides deeper understanding of the low-frequency sound field characteristics in shallow water and also guidance to the application of the algorithm.
2009, 58 (9): 6344-6350.
doi: 10.7498/aps.58.6344
Abstract +
The propagation of laser-generated Rayleigh wave in the viscoelastic material are studied theoretically. Taking account of the viscosity characteristic of the viscoelastic material, a numerical model for simulating laser-generated Rayleigh wave in the viscoelastic material is developed in the frequency domain. Based on the correctness of the finite element numerical model in the frequency domain, the laser generation of Rayleigh wave in the viscoelastic material is simulated. And then, the propagation characteristics of laser-generated Rayleigh wave are discussed and the difference of Rayleigh waves in the viscoelastic material and the elastic material are compared. The effect of different viscosity modulus to the characteristic of Rayleigh wave is analyzed in detail.
2009, 58 (9): 6351-6355.
doi: 10.7498/aps.58.6351
Abstract +
We fabricated a kind of 1D metamaterial which consists of periodic array of Helmholtz resonators and tested its acoustic transmission at audible sound frequency in air. The experimental results show that a transmission dip appears at the frequency range of 2.1—3.5 kHz. The transmission ratio simulated by acoustic transmission line method （ATLM） is in accordance with the experimental results. From the effective impedance calculated by ATLM, the transmission dip is ascribed to the backward wave reflection of HRsresonance. Furthermore, the transmission pressure distribution measurement of the inner sample clearly demonstrates the resonance effect in the metamaterial, in which there is an out-of-phase response to the driving field. The value of effective modulus is calculated to be negative based on the resonant model mentioned before.
2009, 58 (9): 6356-6362.
doi: 10.7498/aps.58.6356
Abstract +
The shift operator （SO） method is extended to the case of magnetized ferrite subject to an external dc magnetic field of arbitrary direction. The FDTD with shift operator （SO-FDTD） formulations are derived based on the relative permeability tensor in magnetized ferrite and Maxwell curl equations of anisotropic media. The electromagnetic （EM） scattering by magnetized ferrite layer, sphere and Von Karman radome with magnetized ferrite coating is computed by the proposed method respectively. The computed results indicate the correctness and feasibility of our method.
2009, 58 (9): 6363-6368.
doi: 10.7498/aps.58.6363
Abstract +
The band structures of shallow water surface wave propagating over a periodically perforated bottom are calculated by the plane wave expansion method，and complete band gaps appear. Through considering three drilling patterns （square holes arrayed in square lattice，circular holes arrayed in square and hexagonal lattices），we find that the number，width，frequency and location of band gaps are related to the area，shape，orientation of drilled holes and the lattice. These rules are similar to those in photonic/ phononic crystals.
2009, 58 (9): 6369-6375.
doi: 10.7498/aps.58.6369
Abstract +
The influence on the motion of single solid particles in a Newtonian fluid by melting and convection was directly simulated. The fluid motion was computed from the conservation laws. Density and viscosity change with the fluid temperature, the particles move according to the equations of motion of a rigid body under the action of gravity and hydrodynamic forces arising from the motion of the fluid. In the process of melting, a distinctive morphology develops due to the different heat flux around the particles surface, and the thermal gradient determines the melting rate. The phases were coupled by the fluid-particle mutual force, force moment and the boundary conditions. In our study four different situations were considered, namely the sedimentation in isothermal fluid without thermal convection and melting, sedimentation in cool fluid and hot fluid without melting, and sedimentation with thermal convection and melting. The results showed that the vortex shedding arising from the natural convection changes the sedimentation velocity and induces horizontal oscillating.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2009, 58 (9): 6376-6380.
doi: 10.7498/aps.58.6376
Abstract +
CaCu3Ti4O12were prepared using conventional solid state reaction processing techniques of ceramic. The CaCu3Ti4O12crystalline phase was verified by XRD patterns. From SEM micrographs, obvious grain and grain boundary structures were observed, and the grain boundary region was comprised of small grains, which were found to be CuO, by EDS, the dielectric constant almost remains at a constant value of 105 in a wide temperature range, but drops dramatically at the frequency of 103 Hz when temperature is below 150 K. The relationship between conductance and temperature of CaCu3Ti4O12 was obtained through the I-V characteristics measured in the temperature range from 93 K to 373 K. It can be separated into three parts with the corresponding activation energies of 0.681, 0.155 and 0.009 eV, which are consistent with the activation energy of CuO ceramics. It was concluded that the small CuO grains in the grain boundary region dominated the DC conductance in CaCu3Ti4O12 ceramics. Thus a new approach for explaining the extraordinary dielectric properties was provided.
2009, 58 (9): 6381-6386.
doi: 10.7498/aps.58.6381
Abstract +
Kelvin-Helmholtz instability in two-dimensional compressible fluid is analyzed by the high precision numerical scheme. The linear growth rate of the Kelvin-Helmholtz instability is especially explored. The relations among the initial static pressure, conductive Mach number and linear growth rate of the Kelvin-Helmholtz instability are quantitatively achieved at the case of the low and high Mach numbers. The simulation results agree with the experiment results in free shear layers and mixing layers. Simulation results show that the conductive Mach number is the proper parameter in definition the compression effect. The smaller the conductive Mach number is, the less compressible the fluid is. The linear growth rate of the Kelvin-Helmholtz instability decreases with the increasing conductive Mach number.
2009, 58 (9): 6387-6391.
doi: 10.7498/aps.58.6387
Abstract +
The simple low-dimensional model proposed by Guzdar and co-workers has been extended and applied to study the nonlinear diamagnetic effect on zonal flow in interchange turbulence. Based on the numerical solution to the derived nonlinear equations, we can draw the conclusion: diamagnetic effect suppresses the enhancement of the normal polarized drift nonlinearity, which could lead to the damping of zonal flow.
2009, 58 (9): 6392-6396.
doi: 10.7498/aps.58.6392
Abstract +
A two-fluid model is proposed to describe the collisional radio-frequency plasma sheath in a magnetic field, and the ion energy distribution incident on the radio-frequency sheath biased electrode is numerically investigated. The simulation results reveal that the external magnetic field dominates the ion flux and energy distribution of the sheath. The ion energy can be transferred between the perpendicular direction and parallel direction under the action of magnetic field.
2009, 58 (9): 6397-6402.
doi: 10.7498/aps.58.6397
Abstract +
Development of an multiple monochromatic X-ray imager based on flat Bragg mirror has been reported, The instrument consists of a pinhole array,a Bragg mirror,and a X-ray CCD camera.An array of approximately 300 pinhole in front of a flat Bragg mirrors projects hundreds of images onto the CCD camera afer reflection off the Bragg mirror,which introduces spectral dispersion along the reflection axis. This spectrometer has a spectral resolution of 50—200 （λ/Δλ） according to the Bragg device and processing technique for systematic reconstruction of quasimonochromatic image.Spatial resolution of 10um is achieved by combining it with pinhole imaging system.Specialism software package have been developed for systematic reconstruction an post date processing,it could restructure an image with flexible spectral bandwidth selection.The article mainly emphasizes the characteristic, optimization design of the spectrometer and the specialized X-ray W/B4C multilayer mirror with depth-graded interplannar spacing centered at 2.5 nm.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2009, 58 (9): 6403-6407.
doi: 10.7498/aps.58.6403
Abstract +
In a stainless steel autoclave of 15 ml capacity, pure hexagonal aluminum nitride （h-AlN） foam has been synthesized by direct reaction of AlCl3 with NaN3 in non-solvent system at 650 ℃ for 3h. The scanning electron microscopy （SEM） shows that the obtained foam material has characteristic sponge-like morphology. The results of X-ray diffraction （XRD） indicate that the AlN foam has a pure hexagonal structure. The absorption spectra at various temperatures indicate that there is a relatively strong absorption peak at about 202 nm. The infrared absorption spectrum shows that the foam has two absorption peaks, centered at 1381 cm-1 and 730 cm-1 respectively. In addition, a possible synthesis mechanism for h-AlN foam is discussed.
2009, 58 (9): 6408-6412.
doi: 10.7498/aps.58.6408
Abstract +
The growth of helium cluster in titanium crystals at room temperature has been simulated detailedly by means of molecular dynamics. The mechanism of helium cluster growth in metal materials has been investigated from the viewpoint of energy. It is found that, as the helium cluster grows, dislocation loops are formed around the cluster and the binding energy of each additional helium atom to these clusters tends to decrease. However, at certain point in the growth process, the defects escape rapidly and the binding energy increases, helping the further growth of the helium cluster. As more helium atoms are introduced, the shape of the helium cluster is transformed gradually to a prismatic morphology from the irregular morphology and its thickness is always observed to be about 1.2 nm, without any obvious variation with degree of helium filling.
2009, 58 (9): 6413-6418.
doi: 10.7498/aps.58.6413
Abstract +
With a two-step approach，a pressure，P，and temperature，T，dependent constitutive model of shear modulus，G，applicable to metals was developed in this work. The goal of the first step is to find the relation of G with P along 0 K isotherm，i.e. the functional form of G1=G1（P，0 K），and the second one is to find the relation of G，starting from a given state of （P，0 K） with a value that was already determined in the first step，with T along the isobar of P，i.e. the functional form of G=G（P，T） or the constitutive model proposed by us. In both steps，results of supersonic measurement and first principles calculation were used. Aluminum，as a model material，was utilized to validate the rationality of this model. It is demonstrated that the predicted results of this model are in satisfactory agreement with the measured and numerically simulated G despite whether it evolves along shock compressed，isentropic，isothermal，or isobaric loci，thereby displaying the rationality and the universal nature of this constitutive model.
2009, 58 (9): 6419-6424.
doi: 10.7498/aps.58.6419
Abstract +
La1-xSrx FeO3-δ systems were investigated by low-frequency internal friction method. The results show that the curves of the internal friction and modulus versus temperature vary with the Sr-dopant content （x）. For the undoped sample，no obvious change on the internal friction and modulus curves was observed between -150—380℃，but the samples with x=0.25，1/3，0.5 and 0.6 show an intenal friction peak P1 with the feature of phase transitions，and the peak temperature moves toward lower temperature with incresing Sr content. This peak was suggested to be associated with a phase transition from rhombohedral to orthorhombic. The samples with x=0.25，1/3，0.5，0.6 and 2/3 show a relaxation type peak P2 accompanied by a decrease in modulus，which can be attributed to the motion of domain walls whose mobility was contolled by the diffusion of oxygen vacancies. The samples with x=0.5，0.6 and 2/3 show a rapid change in the curves of modulus versus temperature，which is related to a ferroelastic phase transition from rhombohedral to cubic.
2009, 58 (9): 6425-6429.
doi: 10.7498/aps.58.6425
Abstract +
The root mean square （RMS） roughness and surface scattering of Ag films，Y2O3-stabilized ZrO2 films，TiO2 films，and 1064 nm & 532 nm two-wavelength-reflection-reducing films are studied respectively by the total integrated scatter. Considering the preparation condition，growth process，material composition，and optical characteristics of the samples，the above measurement results are explained reasonably.
2009, 58 (9): 6430-6435.
doi: 10.7498/aps.58.6430
Abstract +
The fluorinated diamond-like carbon （F-DLC） films were prepared by reactive magnetron sputtering under different radio-frequency power with trifluoromethane （CHF3） and argon （Ar） as source gases and pure graphite as a target. The hydrophobic nature of F-DLC films was studied. The result of measuring contact angle between double-stilled water and film surface shows that the maximal contact angle of film surface is approximately 115°. Factors influencing the hydrophobic nature of films were discussed by film surface morphology measured by atomic force microscopy （AFM）, Raman spectra as well as FTIR spectra. The result demonstrates that the hydrophobic nature of films lies on roughness and bonding configuration of film surfaces. The more the roughness，the stroncer the hydrophobic nature is，but it doesnt show a simple decrease or increase with the content of F in films and the ratio of sp3/sp2. Radio-frequency power influences the deposition rate，which correlates with the roughness of the film，proportion of mononuclear aromatics and bonding configuration of films surface （ways of F combination）.
2009, 58 (9): 6436-6440.
doi: 10.7498/aps.58.6436
Abstract +
Using low-pressure plasma chemical vapor deposition （LPPCVD）, with trans-2-butene and hydrogen as the precursors, we have successfully deposited 30 μm CH coatings on microshells in intermittent bounce mode .The surface finish was measured by atomic force microscopy （AFM）, It was found that the surface finish was improved greatly with reduced duty ratio. When the duty ratio was 1/5, the surface roughness was less than 30 nm for the 30 μm thick a-C:H film. Uniformity of a-C: H films were measured by X-rayradiography. The results showed that the influence was little of duty ratio to the uniformity of a-C: H film. When the duty ratio was 1/7, microshells could not keep on bouncing.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2009, 58 (9): 6441-6445.
doi: 10.7498/aps.58.6441
Abstract +
The atomic structure models of the surface，the interface of oxide scale and bulk of Fe-Cr-Al alloy were set up by using corresponding computer programming, and the electronic structure parameters （environment-sensitive embedding energy，affinity energy，total energy and total density of states） of alloying elements on the surface，the interface of oxide scale and bulk of Fe-Cr-Al alloy, were calculated by the recursion method. The formation mechanism of the oxide film，the influences of sulfur and rare earth metals on the adhesion of oxide film of Fe-Cr-Al alloy and on the formation course of the oxide film were studied systematically on electronic level. The results show that the driving force of Al atom to segregate on to the surface was larger than that of Cr and Y atom. This leads to the inward diffusion of O atoms and the outward diffusion of Al atoms at the early stage of oxidation，resulting in a surface layer rich in Al and O atoms. The affinity force between oxygen and Al was larger （the affinity energy being lower），oxygen is easy to combine with Al atoms to form Al2O3 oxide scale. Yttrium is segregated to the surface，which inhibits the diffusion of Al to the surface of Fe-Cr-Al alloy. The lateral growth of oxide film is effectively controlled，the occurrence of the convoluted morphology of the scale is avoided，the adhesion of the oxide film to the Fe-Cr-Al matrix is increased by the addition of Y. The diffusion of impurity S to the interface of Fe-Cr-Al matrix and Al2O3 oxide scale increases the total energy of the interface，decreases the total density of states，which reduces the stability of the interface，weakens the cohesion of Fe-Cr-Al matrix and Al2O3 oxide scale.
2009, 58 (9): 6446-6452.
doi: 10.7498/aps.58.6446
Abstract +
In the paper，electronic structure and optical properties of Zn1-xBexO are calculated by CASTEP program based on density functional theory and plane-wave pseudopotential method. The band gap increases in the range from 0.963 eV to 7.293 eV when Be content changes from 0 to 1. The lattice strain and band repulsion affecting band gap is investigated. The variation of the band gap is dominated by a/b-axis strain for x=0.125，0.25，0.375，0.5，0.625 and 0.75. The variation of the band gap is dominated by c-axis strain for x=0.875 and 1. In the paper，p-d and Γ1v-Γ1c repulsion are used to investigate the top of valence band and the bottom of conduction band，respectively. In addition，we also investigate the imaginary part of the dielectric function，ε2 of Zn1-xBexO.
2009, 58 (9): 6453-6458.
doi: 10.7498/aps.58.6453
Abstract +
The transport property of graphene quantum dot devices of different length is investigated by first-principles calculation. The changes of transport property caused by roughing effect are sensitive to size of graphene. The results demonstrate that whether the electrode is connected with zigzag edge or armchair edge of graphene，both the transmission coefficient and current always change. But the changes have reversed effect for the two different connections when the length is increased.
2009, 58 (9): 6459-6464.
doi: 10.7498/aps.58.6459
Abstract +
In this paper，the recombination rate of charges in low density polyethylene （LDPE） film was obtained by measuring the number of photons released from the film when the film was short-circuit discharged after being set to high voltage of direct current （HVDC）. Under different designed conditions, including changing the polarity of HVDC and the value of applied field and the time duration of applied field，the amount of photons was measured to calculate the charges’ combination rate. The result showed that the measured number of photons （recombination rate） was sensitive to the applied field but insensitive to the applying duration. When the field was higher than 80 MV/m，the number of released photon increased slowly with increasing voltage. Using the date obtained in our experiment as well as those in other papers，the luminous efficiency of LDPE film was calculated to be 5.9×10-6，and the charges’ recombination rate during first 0.2 second at the beginning stage of short-circuit is around 2.8%.
2009, 58 (9): 6465-6470.
doi: 10.7498/aps.58.6465
Abstract +
In this paper，CdS polycrystalline thin films were prepared with the close-spaced sublimation （CSS） technology. In the deposition process，a controlled ambient of Ar and O2 mixture was used. The effect of oxygen on the microstructure，composition，morphology as well as optical and electrical properties of CdS thin films were studied systemically by XRD，XPS，AFM，UV-VIS and four-probe array method. The results showed that the CSS-grown CdS thin film has the hexagonal structure with crystallite size about 40 nm and the composition of them were rich in S. The impurity oxygen atoms mixed into CdS thin films and partly formed CdO，and with the increase of O2 concentration the chemical composition tinds more closely to the ideal stoichiometric proportion of CdO，the optical gap of thin films broadened and the ratio of photoconductivity to darkconductivity increased. Fortunately these effects are benefitial to CdS thin films for the photovoltaic application as a window layer.Additionally，it view of CdS/CdTe interface，we investigated the influence of oxygen on the cross-section morphology of CdS/CdTe thin films and the spectral response （SR） of the device. Then the results indicated that with the increase of O2 concentration in deposition ambient，the interdiffusion between CdS and CdTe decreased，and the SR of device in the range from 500 nm to 600 nm increased.We believe that the oxygen in CSS-grown CdS thin films plays a very important role in two aspects，firstly in improving the quality of CdS thin films for photovoltaic application，secondly in optimizing the CdS/CdTe interfacial properties in the CdTe solar cells.
2009, 58 (9): 6471-6476.
doi: 10.7498/aps.58.6471
Abstract +
Using far-infrared time-resolved spectroscopy，we have investigated the effect of quantum-well confinement on the lifetime of shallow acceptor states in GaAs/AlAs multiple quantum wells with Be δ-doping. Low-temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of Be acceptor states from the ground state to the first three odd-parity excited states，respectively. It is found that the lifetime of excited states is monotonically reduced with decreasing quantum-well width，from 350 ps in bulk to 55 ps in a 100 ? well. We suggest that the effect of quantum-well confinement on zone-fold acoustic-phonon modes increases the intra-acceptor scattering rate of acoustic-phonon-assisted relaxation.
2009, 58 (9): 6477-6481.
doi: 10.7498/aps.58.6477
Abstract +
The modified M-DNA molecular wires were prepared by adding nickel ions of low concentration to the calf thymus DNA in alkaline solution. And we investigated the conductivity of single DNA and M-DNA molecules. The results indicated that the M-DNA and the B-DNA show semiconductor properties. But the conductivity of M-DNA is higher than that of the B-DNA，and the voltage gap is smaller. When the concentration of nickel ions is more than 0.1 m mol/L，the conductance of DNA does not change with the nickel concentration. In addition，the right to left-handed DNA transition was realized by adding nickel ions of appropriate concentration to the calf thymus DNA in neutral solution and the structure of left handed Z-DNA was observed by STM. The result showed that the major and minor grooves are obvious，unwinding and disordering regions can be found in the Z-DNA. The conductivity of left-handed DNA was much lower than that of the B-DNA. The conductivity relationship of B-DNA，M-DNA and Z-DNA is GM-DNA>GB-DNA>GZ-DNA. The UV absorption spectra and the Raman spectra indicated that the transition of B-Z DNA appears when the concentration of nickel ions is about 1.7 mol/L.
2009, 58 (9): 6482-6486.
doi: 10.7498/aps.58.6482
Abstract +
A series of Bi0.2Ca0.8MnO3 samples with average grain size ranging from 38 to 1500 nm have been prepared by the sol-gel method and their structure，electrical transport，and magnetic properties were investigated. It is found that with the reduction of the grain size，the charge ordered phase gradually diminishes till it is completely suppressed，leading to appearance of the spin-glass state at low temperature. These behaviors are discussed in terms of the martensitic transformation and surface effect.
2009, 58 (9): 6487-6493.
doi: 10.7498/aps.58.6487
Abstract +
Using a method of free energy minimization，the spin wave of ferromagnetic （FM）/antiferromagnetic （AFM） bilayers was investigated，in which the net magnetization of AFM layer has been considered. In this model，the thin FM layer is taken to be a single crystal with cubic and uniaxial magnetocrystalline anisotropies，but AFM layer has only single uniaxial magnetocrystalline anisotropy and its thickness is finite. Numerical calculation shows that there are two modes of spin waves：namely the acoustic mode and the optical mode. Moreover, only when there is net magnetization of AFM layer can the optical mode be observed. There are two branches of FMR curves，i.e. the branches of weak and strong external field，which are distinguished by the critical field，while the critical field depends on the exchange bias field，the magnetization and thickness of AFM layer. The effect of the exchange bias field on the optical mode is more obvious than that on the acoustic mode，while the effects groduced by net magnetization and thickness of AFM layer cant be distinguished. However，when the net magnetization of AFM layer is neglected，only an acoustic mode is observed.
2009, 58 (9): 6494-6499.
doi: 10.7498/aps.58.6494
Abstract +
The structural and magnetic properties have been investigated by means of X-ray diffraction, magnetization measurements, and positron annihilation technique. The X-ray diffraction shows that the Tb2AlFe16-xMnx （x=1—8） compounds have a hexagonal Th2Ni17-type structure. The positron annihilation spectra show that Mn substitution for Fe has the ferromagnetic interaction decreased, and that there exists a strong magnetoelastic effect in Tb2AlFe16-xMnx compound. The magnetization measurement shows that the Curie temperature and the spontaneous magnetization of Tb2AlFe16-xMnx compounds decrease rapidly with increasing x.
2009, 58 (9): 6500-6505.
doi: 10.7498/aps.58.6500
Abstract +
The dielectric properties of 0.75Pb（Mg1/3Nb2/3）O3-0.25PbTiO3 （PMN-25PT） ceramic under hydrostatic pressure and pressure-induced phase transition were investigated. PMN-25PT ceramic is pure perovskite with weak relaxation at 1 bar. With increasing hydrostatic pressure，the temperature，Tm，of top dielectric constant decreases，/+{dTm}/-{dP}≈-4℃/kbar，frequency dispersion and phase transition diffuse increases，remnant polarization decreased continuously. The hydrostatic pressure dependence of dielectric constant （ε） is similar to the temperature dependence of dielectric constant. The relax ferroelectric-paraelectric （RFE-PE） phase transition was induced by hydrostatic pressure and the transition was gradual change process with stronger relaxor behavior than by temperature-induced.
2009, 58 (9): 6506-6511.
doi: 10.7498/aps.58.6506
Abstract +
Based on a three-dimensional modulated free carrier absorption （MFCA） model，simulation was performed to investigate the dependences of MFCA amplitude and phase on the electronic transport properties （the carrier lifetime，the carrier diffusivity，and the front surface recombination velocity） of semiconductor wafers at different pump-to-probe separations and different modulation frequencies. Experiments were performed with a silicon wafer，in which amplitude and phase were recorded as functions of modulation frequencies at several different two-beam separations. The electronic transport properties of semiconductor wafers were determined simultaneously via multi-parameter fitting procedure. These results showed that the method is capable of improving the measurement precision of the simultaneous multi-parameter determination of transport properties.
2009, 58 (9): 6512-6517.
doi: 10.7498/aps.58.6512
Abstract +
The Eu2+ activated blue emitting BaAl2Si2O8：Eu2+ phosphor was synthesized by one-step calcination process of precursor prepared with chemical coprecipitation. X-ray diffraction （XRD），fluorescence spectrophotometry and scanning electron microscopy were used to investigate the structure，luminescent property and morphology of the BaAl2Si2O8：Eu2+ blue phosphor. The results showed that BaAl2Si2O8：Eu2+ phosphor synthesized by the process was pure. The crystal structure of BaAl2Si2O8 transformed from hexagonal structure to monoclinic structure after precursor doping H3BO3，which changed the emission peak and luminescence intensity of BaAl2Si2O8：Eu2+ phosphor. The luminescence intensity firstly increased with H3BO3 doping concentration increasing，then decreased. The optimum mass fraction of H3BO3 is about 1.5%. The use of H3BO3 as flux could help the phosphor to crystallize，thus enhance the intensities of the excitation and emission spectra of BaAl2Si2O8：Eu2+ phosphor，improve the morphology of particles，and endow them with round edges，smooth surfaces and nearly spherical shapes.
2009, 58 (9): 6518-6522.
doi: 10.7498/aps.58.6518
Abstract +
LaPO4：Dy phosphors with different morphology were prepared by adjusting phosphorus sources and reagent in hydrothermal reaction and their vacuum ultraviolet excited luminescence were investigated. The results show that the luminescent intensity of LaPO4：Dy phosphor varies for different morphologies and different particle size. The site symmetry of Dy3+ ions in the LaPO4：Dy phosphor with three different morphologies was consistent and the ratio of yellow emission to blue emission of the three phosphors was kept in 1 to 1.5. From the comparison of the excitation spectra of LaPO4：Dy and GdPO4：Eu it could been seen that the energy transfer efficiency from phosphate host to Dy3+ ion is lower than that to Eu3+ ion. Meanwhile stronger f-d transition was observed in the excitation spectra.
2009, 58 (9): 6523-6529.
doi: 10.7498/aps.58.6523
Abstract +
The photoelectric composites of poly （2，5-dibutyloxy-1，4-phenylene vinylene）/ multi-walled carbon nanotubes （PDBOPV/MWCNTs） were prepared by in-situ polymerization. The results of Fourier transform infrared spectroscopy and Raman spectroscopy indicate that PDBOPV is coated on the surface of MWCNTs. The dimensions of the composite were observed by high resolution transmission electron microscopy，the diameter of PDBOPV/MWCNTs was measured to be about 35—45 nm，and the thickness of the coated PDBOPV is about 15 nm. The absorption of PDBOPV/MWCNTs is strengthened with the contents of MWCNTs increasing，and a red shift of the absorption peak can be clearly observed in the UV-Vis spectrum. Photoluminescence spectroscopy indicates that the maximum emission wavelength of the PDBOPV/MWCNTs is blue-shifted and intensity of photoluminescence decreases with increasing MWCNTs concentration. PDBOPV/MWCNTs show fluorescence quenching，which involves the inter-molecular photo-induced charge transfer process. The optical band gap of PDBOPV/MWCNTs decreases gradually with the contents of MWCNTs increasing. Third-order optical nonlinear susceptibility of PDBOPV/MWCNT composites were measured by degenerate four wave mixing. The results showed that the third-order nonlinear optical responses of PDBOPV/MWCNT composites were enhanced gradually when MWCNT content increased，which can be attributed to inter-molecular photo-induced electron transfer and π-π electron coupling between PDBOPV and MWCNTs.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2009, 58 (9): 6530-6533.
doi: 10.7498/aps.58.6530
Abstract +
In this paper, high quality orthorhombic boron nitride （o-BN） films were prepared on Si（100） substrate by plasma-enhanced pulsed laser deposition （PE-PLD） for the first time. The films were characterized by Fourier transform infrared （FTIR） spectroscopy，glancing-angle X-ray diffraction （XRD） and atomic force microscopic （AFM）. In the FTIR spectrum of the film, we can see three characteristic peaks around 1189cm-1, 1585cm-1 and 1450cm-1 of o-BN. The diffraction peaks ［111］, ［020］, ［021］, ［310］ and ［243］ all appeared in XRD, especially ［243］ and ［310］ crystal plane diffraction were very strong. The surface morphology was closely observed by AFM photograph.
2009, 58 (9): 6534-6541.
doi: 10.7498/aps.58.6534
Abstract +
Carbon nanotube-nanostructure Al2O3-TiO2 composite powders were prepared by mixing carbon nanotubes with nanostructure Al2O3-TiO2 ceramics in an ultrasonic bath. Electromagnetic parameters of the composite material were determined at 2—18GHz. The experimental results show that the complex permititivity and loss tangent of the dielectric increase as the weight content of carbon nanotubes increases. The minimum absorption value increases firstly and then dtcreases and the resonance frequency gradually moves to the low frequency and with increase of the weight content of carbon nanotubes and the thickness of composite coatings. Carbon nanotube 7wt%-nanostructure Al2O3-TiO2 composite coatings were deposited by micro-plasma spraying. The minimum absorption value for 1.5mm thick composite coatings was -26.3dB. The frequency range for absorption value less than -10dB of 2.0mm thick composite coatings was 3.60GHz. When the 1.0mm thick composite coating was heated to 500℃, the minimum high temperature absorption value was -12.2dB and the frequency range for absorption value less than -10dB was 2.00GHz. There is a linear relationship between experimental and theoretical thickness of composite coatings:d=0.898D+0.515, where D is the experimental thickness and d is the theoretical thickness.
2009, 58 (9): 6542-6548.
doi: 10.7498/aps.58.6542
Abstract +
Waveguided grating structures were fabricated using interference lithography. The angle resolved tuning properties of the resonant waveguide mode and its dependence on the grating parameters and on the polarization properties of the incident light were investigated. In particular, the influence of the grating period and waveguide thickness on the tuning rate of the resonance waveguide mode was charatcerized. Theoretical simulation showed good agreement with the experimental results, which is important for futher applications of the waveguided grating device in filters and sensors.
2009, 58 (9): 6549-6553.
doi: 10.7498/aps.58.6549
Abstract +
Organized semiflexible networks composed of a large number of cross-linked quasi-linear filaments, such as actin filament semiflexible networks which determines cell stiffness and transmits force during cellular shape changes. The mechanical property of semiflexible networks plays an essential role in numerous physiological processes, and is a major research topic in the domain of complex network dynamics as well. In this work, by using the ANSYS code, we studied the shear modulus of semiflexible networks with both fixed crosslinks and free crosslinks. The scale factor L/λ, where L is the length of filament and λ the non-affine length, is appropriate for characterizing the shear modulus. The ratio of the two cases was calculated and we found a minimal value at L/λ≈1.05.
2009, 58 (9): 6554-6559.
doi: 10.7498/aps.58.6554
Abstract +
Directional solidification of SCN-3wt% H2O was carried out under externally imposed parallel shear flow, and the growth characteristics of dendritic tips, primary arms and secondary arms were investigated. A bright band related to solute boundary layer along the dendritic tip is observed for the first time. It was confirmed that the left-right symmetry of the dendritic tip is broken up by the shear flow, with the dendritic tip tilting toward the upstream side. The tilting angle increases with the pulling rate. Compared with the case of static condition, the primary spacing becomes lager under shear flow, and this is due to the coupling effect of flow and solute fields. The growth of secondary arm is promoted at the upstream side whereas greatly restrained at the downstream side, which is caused by the circumfluence among dendrites produced by force flow.
2009, 58 (9): 6560-6565.
doi: 10.7498/aps.58.6560
Abstract +
A new method to prepare polycrystalline silicon thin film from a-Si thin films using aluminate solution as induced source was introduced in this article. According to the analysis using optical microscope and Raman spectrum, it was indicated that the a-Si thin film could successfully be crystallized in certain Al-salt solutions. Using the X-ray photoelectron spectroscopy explored by shelling the samples into several sub-layers, the possible chemical reaction between the surface of silicon and aluminate solution was found and the continuous layer exchange process was confirmed. In the end, the mechanism of solution-based aluminum-induced crystallization was discussed.
2009, 58 (9): 6566-6572.
doi: 10.7498/aps.58.6566
Abstract +
Movement of intruder in jammed granular medium may result in interior reorganization of force chain structure. The form of drag force experienced by the intruder reflects the macro effect of the reorganization. By measuring the slow-pushing force of spheres intruding vertically into a granular bed, depth dependence of vertical drag force in jammed granular medium is studied experimentally. It is found that the drag force curve has a concave-convex transition with increasing penetration depth and the drag force follows different depth dependence in different regimes. In shallow regime, there is an exponent 1.3 power-law depth dependence; while in deep regime, the drag force is not saturated but has a tendency of power-law dependence with exponent 0.3. By studying the properties of the inflection point of the concave-convex transition, we have shown that the slowdown of the increasing rate of drag force is not a result of sidewall support proposed by previous researchers, but a result of volume effect of the intruder in granular medium. Moreover, the hydrostatic model is not appropriate in the case of slow drag and static granular bed, for not only the depth dependence of the drag force is higher than linear, but also its coefficient is much greater than the hydrostatic estimate.
2009, 58 (9): 6573-6581.
doi: 10.7498/aps.58.6573
Abstract +
Structure transformation and microstructure of the electrode active materials in a graphite / Li （Ni1/3Co1/3Mn1/3）O2 lithium ion battery during charge-discharge process have been studied by XRD. It is found that the lattice parameter of Li （Ni1/3Co1/3Mn1/3）O2, a and c, decrease and increase respectively. Its micro-strain ε and diffraction intensity ratio, I104/I101 and I012/I101, increases and decrease respectively, because Li atoms de-intercalate out of the crystal lattice of LiMO2. Meanwhile, the lattice parameter, a and c, micro-strain ε and stacking disorder P of 2H-graphite all increase, becausing Li atoms to intercalate into 2H-graphite.During charge process, Li atoms occupying （000） sites may preferentially de-intercalate from LiMO2 crystal lattice, and subsequently the Li atoms occupying （2/3 1/3 1/3）and（1/3 2/3 2/3）sites de-intercalate from LiMO2. When intercalating into 2H-graphite, Li atoms preferentially occupy interstitial sites between C atom hexagonal net planes. When the stacking disorder degree reaches a given value, 3R-graphite phase may separate out gradually. When the battery has been fully charged or over charged, LiC12 and LiC6 phases can be formed. During discharge process, intercalation and de-intercalation behaviors of Li atoms are reversed. Li atoms may de-intercalate preferentially from interstitial sites of 2H-graphite and intercalate preferentially into （000） sites of LiMO2 crystal lattice. But these processes are not fully reversible.
2009, 58 (9): 6582-6589.
doi: 10.7498/aps.58.6582
Abstract +
Bilayer TiO2/polymer photovoltaic cells are prepared by using regioregular poly（3-hexylthiophene） （P3HT） and branched poly（ethyleneimine） （BPEI） as an additive to P3HT. Influences of BPEI, an amorphous polymer, on the performance of bilayer TiO2/P3HT cells are investigated by means of steady-state current-voltage measurements and dynamic intensity-modulated photovoltage spectroscopy, in combination with differential thermal analysis, UV-vis absorption and photoluminescence spectroscopy. Due to the high crystallinity of P3HT, bilayer TiO2/P3HT cell exhibits a poor performance. As P3HT is blended with BPEI in the weight ratio of WBPEI/P3HT=1％—5％, the performance of the devices is greatly improved; in particular, as WBPEI/P3HT= 1%, the cell exhibits an open-circuit voltage of 0.8V and a short-circuit current of 20μA/cm2. Results show that the influence of BPEI on the cell performance originates from the changed interfacial contact at TiO2/P3HT interface rather than the varied optical properties of P3HT in P3HT-BPEI blend. BPEI imposes two competitive effects on interfacial contact between TiO2 and P3HT, depending on the compositional structure of the blend. On one hand, BPEI improves the interfacial contact by reducing the crystallinity of P3HT and enhancing the interaction between P3HT and TiO2. On the other hand, the interfacial contact will become worse with more BPEI chains accumulating on TiO2 surface. A good contact at TiO2/P3HT interface facilitates the access to a high exciton dissociation efficiency, a long lifetime of photogenerated electrons and further a high device efficiency. The results presented in this paper are expected to provide new insights and a novel strategy for improving the performance of polymer-based photovoltaic cells.
2009, 58 (9): 6590-6595.
doi: 10.7498/aps.58.6590
Abstract +
This paper investigates the dynamic behavior of the two coupled FitzHugh-Nagumo neurons connected by coupling. The system exhibits p∶q phase-locked （i.e. a periodic oscillation defined as p action potentials generated by q cycle stimulations） depending on the value of stimulus frequency. Whether phase-locking occurs or not relies on the fire patterns of the system. Furthermore, the stimulus frequency and coupling intensity can stir up rich bifurcation respectively, and the stimulus frequency affects the system fire patterns more obviously. The study has also found that chaotic behavior is the transition state to other fire patterns.
2009, 58 (9): 6596-6603.
doi: 10.7498/aps.58.6596
Abstract +
This study investigates the vibro-acoustography of sector array transducers. Based on the vibro-acoustography and basic sector-array field theory, a modified and accurate velocity potential function is obtained. We further calculated and simulated the point spread function （PSF） of the system, designed the phantom of tissue, and simulated the phantom imaging. In the end, the influencing factors on spatial resolution with sector array transducers are analyzed on the basis of the simulation results. The results reveal that high resolution and contrast can be achieved, and this imaging method is of great value in detecting thermal lesion after high intensity ultrasound surgery and so on. The resolution will be improved by increasing central frequency, reducing geometric focal distance, and using transducers with larger aperture size.
2009, 58 (9): 6604-6608.
doi: 10.7498/aps.58.6604
Abstract +
Polyacrylic acid （PAA） lead was successfully prepared as radiation-protection materials via graft copolymerization route. The product was characterized and analyzed with Fourier transform infrared spectroscopy （FT-IR） and scanning electron microscopy （SEM）. Gamma energy-spectrum measurement was carried out to evaluate its radiation-shielding properties. EGSnrc user code was also employed to theoretically simulate its above properties based on Monte Carlo method and analyze the influences of this material on the fluence and dose in the detecting area. The results revealed that this composite material has excellent radiation-shielding ability and this ability decreased with the increase of γ-ray energy. According to our theoretical simulation, in pure air, the change of fluence is discontinnous and looks like a ladder whose step width beomes narrower grdually and the dose increased slowly whith depth. When the sample was put into the air, in the air medium area, the changes of fluence and dose were no longer related with ray energy but with the sample thickness, while in the sample medium area, the changes of fluence and dose were not rectilinear and the rate of changes makes an obviously turn at the boundary between the sample and air.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2009, 58 (9): 6609-6615.
doi: 10.7498/aps.58.6609
Abstract +
The response of the South China Sea （SCS） to Typhoon Imbudo was examined using POM model. The results indicated that SST decreased by 2—6℃with a rightward-biased response as Typhoon Imbudo passed across the SCS. Due to a strong mixing process, the mixed layer （ML） depth deepened as much as 10—60m and ML heat budget lost 824.78W/m2, which was dominated by the vertical mixing. By the response of upper ML heat transport, the temperature below the ML increased and oscillated near the inertial period. Furthermore, strong inertial currents were generated by the storm with the max currents up to 1.4m/s in the upper ML.
2009, 58 (9): 6616-6626.
doi: 10.7498/aps.58.6616
Abstract +
Artificially triggered lightning experiments were carried out at Binzhou, Shandong Province, China during summer form 2005 to 2008. The discharge current at the channel base of triggered lightning were measured. The geometric mean value of the peak current for 21 negative return strokes was 14.6kA, the geometric mean of the 10%—90% risetime was 2.3μs, the geometric mean of the half peak width was 17 μs and the geometric mean of the charge transfer within 1ms of return strokes was 1.2C. There was essentially no correlation between the return stroke peak current and 10％—90% risetime or between return stroke peak and the width of the current waveform at half of its peak value. No dependence of peak current on grounding resistance was found either. There is correlation between return stroke current peak and charge transfer within 1ms after return stroke initiation, and the correlation between return stroke peak and the stepness of the front waveform of return stroke was also found. Compare the parameters of the triggered lightning with natural cloud to ground lightning, it was found that the triggered lightning stroke is similar to subsequent stroke of natural lightning. So the results of triggered lightning can be used to the lighting protection.
2009, 58 (9): 6627-6632.
doi: 10.7498/aps.58.6627
Abstract +
Observation weight is generally not considered in the works on inversion ocean duct using radar echo. In order to solve the problem，an exponential expression similar to that of the electromagnetic wave propagation loss is used to describe change of observation weight with distance，and the standard statistics retrieval algorithm is used to test the effect of retrieval speed and precision caused by different observation weight. Experimental results show that the exponential expression can approprielly describe change of observation weight with distance，and the determination of loss index is of great importance. Reasonable observation weight can eviclently improve the retrieval speed and precision，and the optimal loss index is different for electromagnetic waves of different frequency.
2009, 58 (9): 6633-6639.
doi: 10.7498/aps.58.6633
Abstract +
With respect to the problem of light uplinks and downlinks in atmospheric turbulence, the strength of turbulence changes greatly along the path. The distribution of phase screens on the path is a vital problem to be solved in the numerical simulation of light propagation. Three different approaches: uniform distributed phase screen （UDPS）, equivalent Rytov index-interval phase screen （ERPS） and equivalent Fried parameter-interval phase screen （EFPS） are discussed. It is found that, by using ERPS method, the distance between phase screens changes automatically according to the strength of turbulence, and the fluctuation of turbulence can also be sampled sufficiently. Under the precondition that the critera for phase screen interval are satisfied, the Rytov index interval of ERPS could be any arbitrary constant value. Statistical results show that, even the Rytov index interval changes by one order of magnitude, both effective beam radius and Strehl ratio of energy change for only 2.1%. And simulated results agree well with theoretical ones. All this indicates the stability and reliability of the ERPS method.
2009, 58 (9): 6640-6650.
doi: 10.7498/aps.58.6640
Abstract +
The paper investigates the height and temperature fields reanalysis data of NCEP/NCAR by means of detrended fluctuation analysis method, and gives their scaling exponent distribution of East Asia region. The empirical investigation indicates that both of height field and temperature filed have the property of long range correlation, which matches with the features of space distribution as a whole. As for the grid data of the same layer, the long range correlation varies obviously when the latitude changes. The low-latitude areas near the equator have a bigger scaling exponent and a better long range correlation, whereas the mid-latitude and high latitude areas have a smaller scaling exponent and a worse long range correlation. The average scaling exponent increases with the layer growth of height field data, and the scaling exponent varies obviously when the latitude changes. The scaling exponent of Qinghai-Tibet Plateau is obviously greater than other areas at the same latitude. For the data of temperature, the average scaling exponent first decreases with the layer growth then increases, and the average scaling exponent has a definite latitude trait. All in all, the scaling exponent of height field’s long range correlation is greater than that of temperature field. The investigation for different seasons displays that the long range correlation exists in height field and temperature field as well. And we find that the scaling exponent of winter time is greater than that of other seasons. This may provide a theory for the summer flood season forecast which is based on the winter information.
2009, 58 (9): 6651-6658.
doi: 10.7498/aps.58.6651
Abstract +
The spatial and temporal stability of temperature correlation network is analyzed based on extreme temperature, El Niňo/La Niňa abnormal year, key areas of temperature change and high frequent year of extreme respectively. Results show that, the connectivity of network decreases by filtering out extreme temperature, property of the network at the inflexion P=0.1 or 0.9, might be defined as the of boundary of extreme temperature. La Niňa network possesses more significan links and higher clustering coefficient than the El Niňo network, which indicates that the former is more communicative and more stable than the latter. And based on these statistical properties, we verified that during La Niňa years predictability is higher compared to El Niňo years and normal years. Furthermore, we also verified that during high frequency years of extreme high temperature predictability is higher than high frequent years of extreme low temperature and normal years. We also come to the conclusion that middle and east tropical Pacific （180°E—80°E，15°N—15°S） are key areas of global temperature changes, and exlernal forces acting on these areas have great effect on global temperature change.
2009, 58 (9): 6659-6664.
doi: 10.7498/aps.58.6659
Abstract +
In this paper, a Monte Carlo simulation model based on atmosphere model, cosmic ray model and geomagnetic field model has been developed for the near space atmospheric neutron environment. The neutron distributions induced by cosmic rays and solar particles have been calculated separately. What is more, the influence of cutoff rigidity to neutron flux has been analyzed. By comparing with ARM model, we can draw the conclusion that our model is credible and excellence in calculating neutron flux induced by solar particles. The model could be applied in many fields, such as evaluating single event effects of microelectronics and analyzing radiation dose received by the air crew.
2009, 58 (9): 6665-6670.
doi: 10.7498/aps.58.6665
Abstract +
A three-dimensional multifrequency interaction model for helix traveling wave tubes is described. Spatial variation of the amplitude of the wave is found by field theory. With the help of paticle-in-cell （PIC） method and space harmonic current and charge expansion, the three-dimensional space charge field is found. using the code, 8—18GHz wide band TWT is simulated for different frequencies. Also, the nonlinear AM-AM and AM-PM distortion,third-order intermodulation products and fifth-order intermodulation are computed. The hot data of experiment is close to the code computation in saturation output power and output gains in the range of 8—18GHz.
2009, 58 (9): 6671-6676.
doi: 10.7498/aps.58.6671
Abstract +
A sample including 22 BL Lac objects was collected. The possible correlations between the γ-ray emission at 1 GeV and the radio emission at 8.4GHz or 5.0GHz were investigated. Main results are as follows: 1） for minimum γ-ray data, there is no correlation between γ-ray and radio flux density. For maximum and average data, there are good correlations between γ-ray and radio emissions, with the maximum correlation coefficient reaching 0.85, and the chance probability p-4; 2） there are weak correlations between γ-ray spectral index and the radio spectral index. Therefore, the γ-ray radiation was the SSC process.
