Vol. 59, No. 11 (2010)
2010-06-05
GENERAL
2010, 59 (11): 7531-7534.
doi: 10.7498/aps.59.7531
Abstract +
Using a home-made cryotarget system and infrared spectroscopy system, we measure the infrared absorption spectra of liquid hydrogen at low temperaturs. It is found that the fundamental vibration frequency of hydrogen molecule is 4237.3 cm-1. As liquid hydrogen cools from 19.75 K down to 16.75 K, the infrared absorption is enhanced. The vibration frequency of hydrogen molecules is calculated on the basis of non-harmonic approximation in order to explain the experimental ones.
2010, 59 (11): 7535-7539.
doi: 10.7498/aps.59.7535
Abstract +
Conventional image interpolation algorithm always introduces the the blur and jagged edges. To solve this problem, an improved adaptive image interpolation algorithm with using membership function is proposed in this paper. Fuzzy logic is used to obtain the membership function with the local characteristics of the gradient and phase angle. The first step is to correct the special distance of interpolated pixels along one dimension in the basis of local asymmetry features and the membership function, and then to convert the corrected distance of one dimension into two dimensions, applying the corrected distance to conventional image interpolation algorithm. Experimental results demonstrate that the improved algorithm can produce better results in regard to the signal-to-nosie ratio and succeed in preserving interpolation image edges in various directions.
2010, 59 (11): 7540-7545.
doi: 10.7498/aps.59.7540
Abstract +
By the projective equation approach and the variable separation method, a series of excitations of the (2+1)-dimensional asymmetric Nizhnik-Novikov-Veselov system is derived. Based on the derived solitary wave excitation, we obtain multi solitons and fractal solitons of the system.
2010, 59 (11): 7546-7551.
doi: 10.7498/aps.59.7546
Abstract +
With considering different anti-attack abilities of nodes and nonuniform transmission of edges in real networks, an SIR model is proposed to investigate the threshold behaviors of epidemic in scale-free networks based on the mean-field theory. In the proposed model, a vulnerability function related to node degree is introduced to describe the diversity of nodes’ anti-attack abilities, and a transmission function related to node degree is also introduced to describe the nonlinear infectivity of nodes. Theoretical analyse and numerical simulations show that the diversity of node anti-attack ability and the nonuniform transmission of diseases on edges can yield a positive epidemic threshold,meaning that the risk of epidemic prevalence is reduced.
2010, 59 (11): 7552-7555.
doi: 10.7498/aps.59.7552
Abstract +
A New type of conserved quantity induced by Mei symmetry of Appell equations for a holonomic system is studied. The definition and the criterion of Mei symmetry of Appell equations for a holonomic system are given. A new type of conserved quantity induced by Mei symmetry of Appell equations expressed by Appell functions is obtained. And an example is given to illustrate the application of the results.
2010, 59 (11): 7556-7563.
doi: 10.7498/aps.59.7556
Abstract +
Dissipative particle dynamics (DPD) is a meso-scale, Lagrangian particle method, and has been successfully applied to different areas including micro- and nano-fluidics, bio- and chemical technologies. The treatment of solid matrix and the implementation of solid boundary conditions have been an important task for the development and application of the DPD method. This paper presents a new method of treating complex solid boundary. Solid grains in complex flow geometry can be represented by freezing randomly distributed DPD particles which have reached an equilibrium state. To increase computational efficiency, only the boundary DPD particles within one cut-off distance from the flow region are frozen. A thin layer in the flow region next to the solid boundary is used to bounce mobile DPD particles in this layer back to the flow region. The DPD method and this new boundary treatment algorithm are used to model the Poiseuille flow and a flow problem in a complex porous media. It is demonstrated that this new boundary treatment algorithm can effectively model complex solid matrix and correctly implement non-slip boundary condition.
2010, 59 (11): 7564-7569.
doi: 10.7498/aps.59.7564
Abstract +
Based on the idea of the hyperbola function expansion method, some analytical solutions of the modified Korteweg-de Vries (mKdV) equation are obtained by introducing new expansion functions. One of the single soliton solutions has a kink-antikink structure and it reduces to a kink-like solution and bell-like solution under different limitations. The stability of the single soliton solution with double kinks is investigated numerically. The results indicate that the soliton is stable under different disturbances.
2010, 59 (11): 7570-7574.
doi: 10.7498/aps.59.7570
Abstract +
The transient eddy current field is analytically modeled by applying inverse Laplace transform to pulsed eddy current testing. The closed-form solution to transient eddy current field in a complex domain is obtained by using the truncated region eigenfunction expansion (TREE) method and the theory of reflection and transmission of electromagnetic waves. After extensive algebraic transform, the poles of the developed model and corresponding residues are able to be calculated. As a result, partial fraction expansion can be used to split up the complicated complex-domain model into the forms that are listed in the Laplace Transform table. Therefore, it is easy to derive the time-domain solutions to transient eddy current field with step and exponential current excitations respectively. The derived time-domain model not only has some advantages in the sense of implementation and efficiency, but also removes the Gibbs phenomenon. Finally, the inverse Fourier transform of induced voltage in the probe is performed and the good agreement demonstrates the validity of the established model.
2010, 59 (11): 7575-7580.
doi: 10.7498/aps.59.7575
Abstract +
The right-hand inverse operator of the annihilation operators and the left-hand inverse operator of the creation operator are given by using the contour integration. Furthermore, the corresponding relation between the right-hand inverse or left-hand inverse operator derived and the column elementary transformation or row transformation of a matrix is investigated.
2010, 59 (11): 7581-7585.
doi: 10.7498/aps.59.7581
Abstract +
The ground state solutions of superfluid Fermi gas in optical lattices are studied by means of the balance condition between the lattices potential and inter-atomic interaction energy. We derive the atoms density distribution, the atoms number and the energy of the ground state along the entire BEC-BCS crossover. It is shown that, the properties of the ground state present very different characters as the system transits from the BEC side to the BCS side.
2010, 59 (11): 7586-7590.
doi: 10.7498/aps.59.7586
Abstract +
The bound energy spectrum of a position-dependent mass particle which is trapped in a null potential is obtained by combining the point canonical transformation (PCT) method and the analytical transfer matrix (ATM) method. With the calculation for the transmission of a position-dependent mass particle passing through the null potential, the one-to-one correspondence between transmission resonance peak and eigenenergy is found and explained.
2010, 59 (11): 7591-7595.
doi: 10.7498/aps.59.7591
Abstract +
Decoding sparse quantum codes can be accomplished by syndrome-based decoding through using the sum-product algorithm (SPA). We significantly improve this decoding scheme by developing a new feedback adjustment strategy for the standard SPA. In our feedback strategy, we exploit not only the syndrome but also the values of the frustrated checks on individual qubits of the code and the channel model. Consequently, our decoding algorithm, on the one hand, can break the symmetric degeneracy, and on the other hand, can feed back more useful information to the SPA decoder to help the decoder determine a valid output, thereby significantly improving the decoding ability of the decoder. Moreover, our algorithm does not increase the measurement complexity compared with the previous method, but takes full advantage of the measured information.
2010, 59 (11): 7596-7601.
doi: 10.7498/aps.59.7596
Abstract +
A new method is produced of directly measuring EPR beams. This measurement scheme can be used for measuring the correlation degree of EPR beams with correlated amplitude quadratures and anticorrelated phase quadratures without using local oscillators. Then a new scheme for quantum dense coding is proposed based on this measurement scheme.
2010, 59 (11): 7602-7606.
doi: 10.7498/aps.59.7602
Abstract +
In this paper, the propagator and the effective potential in quantum Thirring model are derived by using the functional integral method, and the energy density fluctuations for coupled Fermi matter are calculated in two-dimensional point matter black hole and dilaton black hole models separately. We find that energy density fluctuation outside dilaton black hole is stronger under the same physical conditions.
2010, 59 (11): 7607-7611.
doi: 10.7498/aps.59.7607
Abstract +
We study analytically and numerically the probability density function in the stationary state of non-linear oscillators which are subjected to Lévy white noise and confined by a steep symmetric potential. The probability density function transforms from unimodality to bimodality or from bimodality to trimodality when the potential transforms from single well to double well; especially, the probability density function shows a peak at the saddle point of the potential. This result is far from the Gibbs-Boltzmann statistics.
2010, 59 (11): 7612-7617.
doi: 10.7498/aps.59.7612
Abstract +
The dynamics of a nonlinear capacitor circuit is investigated in this paper. The symmetric periodic solution and the chaotic attractor can be observed in numerical simulations. Furthermore, the generalized Jacobian matrix at the non-smooth boundaries is introduced to explore the non-smooth bifurcation mechanism for the periodic solutions. Discontinuous bifurcation in the combination of the Hopf bifurcation and the turning point bifurcation occurs at the non-smooth boundaries. Here, the Hopf bifurcation may result in a new frequency, which leads to periodic oscillation. With the variation of the parameter, the periodic symmetric solution oscillates more quickly, which can also be explained through non-smooth bifurcation, and the conclusion accord well with the numerical results.
2010, 59 (11): 7618-7622.
doi: 10.7498/aps.59.7618
Abstract +
Generalized synchronization of chaos is studied for two-dimensional time-delayed chaotic systems with different structurs. The auxiliary system method and the stability theory of functional differential equations are used. Compared with the conventional generalized synchronization approaches, the proposed method is convenient to realize generalized synchronization of chaos. Simulation results illustrate the validity of the method.
2010, 59 (11): 7623-7629.
doi: 10.7498/aps.59.7623
Abstract +
This paper proposes a method of information entropy optimized parameters (IEOP) of pahse space recon struction. First, it establishes an information entropy optimum model in phase space for embedding dimension and delay time by using conditional entropy. It then solves these two parameters with genetic algorithm (GA) simultaneously. IEOP constructs an optimum phase space, which maintains independence of reconstruction coordinate and retains the dynamic characteristics of the original system. In the numerical simulations, results of the Lorenz system and Mackey-Glass system show that it not only determines two parameters at the same time, but also can obtains more information in the optimized phase space, there by improving the performance of chaotic time series prediction.
2010, 59 (11): 7630-7634.
doi: 10.7498/aps.59.7630
Abstract +
In this paper, a new algorithm for all Lyapunov Exponents precisely configuraling a discrete-time dynamical system is proposed. A given deterministic discrete-time dynamical system can be chaotified by the algorithm. A new feed-back controller is designed via moduling operation. All Lyapunov Exponents of the controlled system are equal to a given set of ones. The new controller is simple and can be used to control or anti-control a chaotic system . The corresponding proof as well as two illustrative examples are presented. The simulation results show the effectiveness of the algorithm.
2010, 59 (11): 7635-7643.
doi: 10.7498/aps.59.7635
Abstract +
In this paper, we suggest an anticipating projective response scheme in coupled dynamical systems, from which a large class of different drive-response systems can be constructed by choosing different functions and changing the scaling factor. A specific case of the scheme, which is named the accelerative anticipating projective response scheme, is studied in detail. In this specific scheme, the amplitudes of the drive and response systems synchronize up to a scaling factor and the response system evolves with a faster speed. Further, the robustness of this scheme is proved under the existence of the small disturbance of the driving term, interference of the driving signal and parameter mismatches.
2010, 59 (11): 7644-7649.
doi: 10.7498/aps.59.7644
Abstract +
Designing a suitable response system to a class of fractional order chaotic systems, we can realize the modification of projective synchronization for these systems by only transmitting a single variable. Since chaos synchronization can be achieved by transmitting the single variable from driving system to response system, this method is more practical. Numerical simulation of fractional order unified chaotic system demonstrates the effectiveness of the proposed method.
2010, 59 (11): 7650-7656.
doi: 10.7498/aps.59.7650
Abstract +
Combining the phase space reconstruction theory and the time series analysis theory, a prediction network applied to time series multi-step prediction is proposed. The network is constructed in the weight-sum form of some chaotic operators. Constant connections are adopted among the units. The control parameters of chaotic operators are adjusted by chaos optimization algorithm. The training samples, constructed by known time series data, are used in the training process only once, which makes the dynamic characteristics of the network change and tend to the predicted system with the lapse of time. The validity of the network can be proved by computing the Lyapunov exponent of prediction data. The multi-step predictions for engineering data are also realized by the method. Simulation results prove that the method could validly predict time series when the predictive step is not too long.
2010, 59 (11): 7657-7662.
doi: 10.7498/aps.59.7657
Abstract +
This paper focuses on a new type of dislocated projective synchronization, in which, the state variables of drive system and resporse system, at least one pair is required not to synchronize in proportion to the original corresponding state variable, but to realige the projective synchronization in proportion to dislocation relation of vectors. Here a new Qi hyper-chaotic system is taken for example, which has 23 synchronized schemes. Using the Lyapunov stability theory, a nonlinear controller is presented and a kind of disorder projective synchronization for Qi system is successfully completed. Then this method is applied to secure communication through improved chaotic masking. The information signal is mixed with the chaotic signal before being transmitted, and is recovered without distortion through the synchronized receiver. Simulation results show that the scheme has a good performance.
2010, 59 (11): 7663-7668.
doi: 10.7498/aps.59.7663
Abstract +
Based on piecewise monotone interval maps and linear coupling, we study order patterns of spatiotemporal chaos. The forbidden patterns are found to arise mainly from the reduction of curve intersections due to time invariance of chaotic maps. It is proved that linear couplings may destroy the time invariance, and create the conditions for increasing intersections. We analyze the effects of chaotic map, coupling strength and coupling number order patterns. Simulation results and illustrative examples all confirm the correctness of the theoretical results.
2010, 59 (11): 7669-7678.
doi: 10.7498/aps.59.7669
Abstract +
Upon the analysis of the equilibrium points as well as the stabilities in coupled Jerk systems, bifurcation sets in parameter space are derived, which divide the parameter space into several regions associated with different forms of dynamics. The dynamical evolution of the coupled system is investigated with the variation of different parameters and specially, the influence of the coupling strength on the dynamics of the system is explored in details. The mechanism of some nonlinear phenomena such as the coexistence of multiple behaviors as well as the sequence of period-doubling bifurcations are presented.
2010, 59 (11): 7679-7685.
doi: 10.7498/aps.59.7679
Abstract +
In this paper, we employ chaotic light as an entropy source, generated by semiconductor lasers with optical feedback induced by external cavity, to generate 500 Mbit/s random number sequence and then study specifically the influence of external cavity length on randomness. The results indicate that the generated random sequence has an weak periodicity caused by the external cavity feedback under a single-channel chaotic source, and can only pass two or three tests of the National Institure of Standards and Technology(NIST) when the external-cavity round trip delay time is an integral multiple of the sampling time. On the other hand, the weak periodicity can be eliminated by using two different chaotic sources when their external cavity lengths are unproportional to each other, and the obtained random sequence can pass all tests of the NIST after XOR processing.
Computation of invariant manifolds with self-adaptive parameter and trajectories continuation method
2010, 59 (11): 7686-7692.
doi: 10.7498/aps.59.7686
Abstract +
Most work on manifold study focuses on two-dimensional manifolds and there have been proposed some good computing methods. However, the computation of two-dimensional manifold is still a hot research field. In this paper the two-dimensional manifold of hyperbolic equilibria for vector fields is computed by combining self-adaptive parameter with trajectories continuation, approximating the local manifold with an ellipse around the equilibria, extending the trajectory with equal distance, and adjusting the trajectory with self-adaptive parameter. This method is more accurate than the "trajectories and arc-length method", and better shows the trend of the manifolds than the "box covering method".
2010, 59 (11): 7693-7700.
doi: 10.7498/aps.59.7693
Abstract +
Based on the Fukui-Ishibashi model (FI model), the energy consumption in the mixed traffic flow is investigated via considering three factors: maximum velocity, length of vehicle, and the ratio of the mixed traffic flow. Simulations and analyses indicate that the energy consumption of the mixed traffic flow with the same length and different maximum velocities is related to the slow maximum velocity and its ratio. The slower the maximum velocity and its ratiare, the more energy will be consumed. Moreover, for the mixed traffic flow with the same maximum velocity and different lengths of vehicle, the energy consumption is related to the ratio of mixed vehicles. Longer vehicles induce more energy consumption. For a mixed traffic flow with the different maximum velocities and lengths of vehicle, its energy consumption is determined by the ratio of the mixed vehicles and delay probability p. The energy consumption of FI model drops off suddenly and trends to zero at the maximum flow rate, where there exits a maximum peak, which is significantly different from the result from the NaSch model.
2010, 59 (11): 7701-7707.
doi: 10.7498/aps.59.7701
Abstract +
On the basis of the previous cellular automaton evacuation model, we modify the method of calculating the pedestrians transition probability with considering the effect of aisle region in the classroom-like buildings, and analyze the difference among evcuation efficiencies imduced by different exit positions and different layoutt inside classrooms. The results demonstrate that it is very beneficial when the exit faces the aisle, that it is useful to set up exit on the side of the classroom compared with exit which is on the edge of the facing classroom in order to reduce the change in direction of pedestrian movement,that the exit situated at the central position in the front of classroom is the most efficient, however, is unrealistic; in addition, when the classroom is designed to have a side exit, the aisle is necessarily close to the exit side of the wall; when the total capacity of the classroom is fixed, we should give a priority to the design of aisle distribution, rather than the design of the arrangement of chairs and tables; the number of aisles is more significant to affect the evacuation efficiency than the width of a single aisle, the larger the number arisles is, the higher the evacuation efficiency will be. This paper is expected to be able to make suggestions for the design of internal layout and exit position of the classroom, as well as the design of the distribution of grandstand seats and aisles in similar buildings, such as theaters, stadiums, etc.
2010, 59 (11): 7708-7712.
doi: 10.7498/aps.59.7708
Abstract +
The control of thermal diffusion fractal growth of thin plate in reality under the environmental disturbance is introduced. The quantitative relationship between growth probability and environmental disturbance is obtained. According to the relationship, we predict that the growth surface will aggregate in the region of the environmental disturbance and be controlled by restricting the disturbance. The simulations show that the environmental disturbance, which is composed of a trigonometric function as a nonlinear term and a source term having a round region, controls the growth variation effectively. In addition, the change in fractal dimension of surface growth illustrates that the complexity of the growth increases as the environmental disturbance increases.
2010, 59 (11): 7713-7718.
doi: 10.7498/aps.59.7713
Abstract +
The amplitude statistical distribution funetion p(l) of the aerosol scattering pulse signals is measured with high resolution through combining the high-speed data acquisition card PCI-9812 and the photoelectric sensor of laser airborne particle counter. The experimental results show that the distribution founction p(l) of the whole signal group and the different pulse width subsets all fit the lognormal distribution with very high precision in the range of amplitude definition (V0,VM) under the condition of big samples, which indicates that the random signal group has a statistical fractal (self-similarity) characteristic. According to the further theoretical results, it is analyzed that function p(l) has a nonlinear scale invariance. Besides, this function shows a geometrical similarity to the power law l-(1-ε) when statistical parameter , where ε<<1.
2010, 59 (11): 7719-7723.
doi: 10.7498/aps.59.7719
Abstract +
The synchronizability of mobile Ad Hoc networks is investigated in this paper. The synchronizability is measured by eigenratio R. A smaller value of eigenratio R leads to a better synchronizability. The results indicate that with the increase of clustering coefficient C, eigenratio R increases in interval, but with the process going on, eigenratio R decreases. The eigenratio varies with clustering coefficient reither in direct proportion nor in inverse proportion, but rises first and reduces later,so there aooears a clear maximum value in between.
2010, 59 (11): 7724-7728.
doi: 10.7498/aps.59.7724
Abstract +
We report one-dimensional small displacement measurement of TEM00 mode with balanced homodyne detection. The smallest measurable displacement in our experimental setup is 0.3 nm. The conjugate properties of displacement and tilt are tested. Finally we analyze the effect of the deviation of local oscillator beam from TEM10 mode on the displacement measurement result. Experimental results are consistent well with the theoretical analyses.
2010, 59 (11): 7729-7735.
doi: 10.7498/aps.59.7729
Abstract +
The basic principle and the experimental results of measuring energy spectra of high energy pulsed X-ray are reported. The Monte-Carlo code is developed to calculate the energy deposition of high energy photons in each sensitive cell of the energy spectrometer. The intensity of high energy pulsed X-ray created on the Qiangguang-Ⅰ accelerator is measured by using the energy spectrometer. According to the deposited energy and the integral data, the time-resolved high pulsed x-ray energy spectrum is obtained. By using the voltage waveform and the current waveform of the diode, the energy spectrum is calculated in details. The results are in agree with the measured values from the experimental energy spectrum.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (11): 7736-7742.
doi: 10.7498/aps.59.7736
Abstract +
The geometry structure optimization and frequency calculation of the title compound molecule have been studied using density functional theory B3LYP method, and infrared spectrum, Raman spectrum and thermodynamic properties at different temperatures have been obtained. The electronic absorption spectrum in gas and different solvent have been calculated and simulated. The results showed that the formation of intra-molecular hydrogen bond was helpful to stability of the title compound molecule, which was in good agreement with experimental crystal structure. The peak of maximal absorption located at 236 nm in gas, belonging to near UV, and solvent effect made the maximal absorption wavelength blue-shifted about 20 nm, and independent of solvent polarity.
2010, 59 (11): 7743-7748.
doi: 10.7498/aps.59.7743
Abstract +
Based on the density functional theory DFT/ B3LYP at 6-311g level, the ground states of BeO molecule are optimized. The effects of electric field on the bond length, the system energy, the charge distribution, the energy levels, the HOMO-LUMO gaps and the infrared spectrum of BeO molecule are studied. The results indicate that the bond length of BeO molecule increass,but the system energy decreases as the external electric field increases from 0.0 to 0.05 a.u. At the same time, the energy gaps between the HOMO and LUMO become separated with the increase of electric field. It shows that the structure of BeO molecule is steady under external electric field so that oxygen atom in BeO is difficult to combine with hydrogen atom escaping from the reactor.
2010, 59 (11): 7749-7755.
doi: 10.7498/aps.59.7749
Abstract +
The ground states parameters, dipole moment, charge distribution of chloroethylene under different intense electric fields ranging from 0 to 0.05 a. u. are optimized using density functional theory (DFT)B3P86 at 6-311G basis set level. Without external electric fields, the excitation energy, wavelength, oscillator strengths from ground state to the first nine different excited states are calculated by employing the revised hybrid CIS-DFT method (CIS-B3P86) and the excited states under different electric fields are also investigated. The results show that with increasing the electric field the molecular geometry is strongly dependent on the field strength. The whole energy are proved firstly increasing, then decreasing and the dipole moment firstly decreasing then increasing. The excitation energies of the first nine excited states of chloroethylene decrease with the increase of the applied electric field, indicating that the molecule is easy to be excited and dissociated under the electric field.
2010, 59 (11): 7756-7761.
doi: 10.7498/aps.59.7756
Abstract +
The present work is devoted to the study of the excitation of two kinds of Si2O isomers. The results show that the is excitation energies, oscillator strengths, transition electric dipole moments and absorption spectra are affected evidently by external electric field. The triangular Si2O(C2v,1A1) has no visible light absorption spectrum under no external electric field, however, it has faint absorption spectrum(407.18—526.93 nm) in the visible region under external electric field. The linear Si-Si-O(C∞v,3Σ-) has absorption spectra in blue light region and in purple light both in the presence and in the absence of external electric field. One of the important results is that the linear Si-Si-O has strong blue light absorption spectrum(478.88—488.59 nm).
2010, 59 (11): 7762-7768.
doi: 10.7498/aps.59.7762
Abstract +
The present paper is devoted to the calculating of transition wavelengths, oscillator strength, Einstein An0 and B0ncoefficients of titanium monoxide molecule from ground state to the first six different excited states by employing the density function theory BLYP and the single substitute configuration interaction approach with basis set 6-311 + + G **. The excited states of titanium monoxide molecule under different external electric fields are also investigated. It is shown that the α HOMO-LUMO gaps become smaller and the electrons of the occupied orbital tend to the virtual orbital as the external electric field intensity increases, and the β HOMO-LOMO gaps become bigger, while the variation in excitation wavelength of high-excited states turns more complicated than that of low-excited states, and the coupling strengths of excited states increase with external electric field increasing.
2010, 59 (11): 7769-7774.
doi: 10.7498/aps.59.7769
Abstract +
By using a detailed configuration accounting method in the collisional radiative equilibrium model, and Cowans relativistic atomic structure code with respect to ionic averaged configurations and Hartree-Fock-Slater potential, we solve the rate equations for populations of all ionic and level populations of all excited states, in which main consider main atomic dynamic processes in a non-local thermodynamic equilibrium plasma can be considered, thereby obtaining the ionic populations and energy level populations and the ionic charge stage distribution and the average charge for Au. We also simulate and calculate the X-ray emission spectra of Au 5f—3d transition arrays. The calculated results are in good agreement with the experimental data for a well-characterized highly ionized Au plasma.
2010, 59 (11): 7775-7781.
doi: 10.7498/aps.59.7775
Abstract +
A three-dimensional classical micro-canonical model is used to investigate the ion momentum distributions of Ar atom in nonsequential double ionization with a few-cycle laser pulse. It is found that the momentum distribution has a strong dependence on the carrier-envelope phase of the few-cycle pulse. The centre of gravity of the asymmetry distribution shifts from negative to positive ion momenta with carrier-envelope phase increasing and it is reversed when the carrier-envelope phase changes by π. The momentum distributions of the Ar2+ ion show excellent agreement with the experimental results when we take into account the change in Coulomb potential between the nucleus and electron in the recollision process.
2010, 59 (11): 7782-7787.
doi: 10.7498/aps.59.7782
Abstract +
Around the near-infrared wavelength at which optical fiber gyroscope works, the effects of 120 krad γ-irradiation on single-mode quartz fiber are studied experimentally from the following several aspects: return loss, polarization dependent loss, scattering loss, absorption loss, mode field distribution and guided-mode propagation constants. The gap defect energy level and its increment are estimated from near-infrared spectroscopy and stimulated raman scattering experiment. The medium density change is studied by x-ray diffraction. The photothermal effect of irradiated fiber with γ-ray is observed by a high sensitivity interference circuit. The test data show that the UV anneal has some repairing effect, revealing the possibility that UV annealing method can serve as a mannes of active reinforcement.
2010, 59 (11): 7788-7795.
doi: 10.7498/aps.59.7788
Abstract +
The semiclassical rescattering model and the quantum-mechanical S matrix model are used to study the non-sequential double ionization of atoms and molecules in strong laser fields.Based on these two models, we can calculate ionization rate with different laser intensities, recoil ions momentum distribution and two-electron energy distribution. The numerical simulation results show that the semiclassical rescattering model coincides with the quantum-mechanical S matrix model when non-sequential double ionization of atoms and molecules is researched in strong laser fields.
2010, 59 (11): 7796-7802.
doi: 10.7498/aps.59.7796
Abstract +
The stereodynamics in the chemical reaction O+ +H2and its isotopic variants at a collision energy of 20 kcal /mol are investigated by using the quasi-classical trajectory (QCT) method on RODRIGO surface. The correlated k- j', k-k'-j' angular distributions, polarization-dependent differential cross sections (PDDCSs) and the product rotational alignment are discussed in detail. The calculations indicate that the stereodynamic properties of the reactions of O+ +H2→OH+ +H、O+ +DH→OD+ +H and O+ +TH→OT++H are sensitive to the mass factor and the repulsive energy of diatomic molecule.
2010, 59 (11): 7803-7807.
doi: 10.7498/aps.59.7803
Abstract +
The electron emission yields from the interaction of slow highly charged ions (SHCI)He2+,O2+and Ne2+ with clean Si surface are measured separately. It is found that electron emission yield γ increases proportionally to projectile kinetic energy EP/MP ranging from 0.75 keV/u to 10.5 keV/u (i.e. 3.8×105 m/s≤vP≤ 1.42×106 m/s), and it is higher for heavy ions (O2+and Ne2+) than for light ion (He2+). For O2+and Ne2+, γ increases with ZP decreasing in our energy range, and it shows quite different from the result for higher projectile kinetic energy. After calculating the stopping power by using TRIM 2006, it is found that the fraction of secondary electrons induced by recoil atoms increases significantly at lower projectile energy, thereby leads to the differences in γ for heavy ions O2+and Ne2+between lower and higher projectile kinetic energy.
2010, 59 (11): 7808-7814.
doi: 10.7498/aps.59.7808
Abstract +
The stereodynamical properties of O+HCl→OH+Cl reaction are studied by using the quasi-classical trajectory (QCT) method on Peterson ab initio potential energy surface. The vibrational level and the rotational level of the reactant molecule are taken as v=0—4 and j=0 respectively. The calculation results show that the vibrational quantum number has a considerable influence on the distribution of the k-j'vector correlation. The effects of vibrational quantum number on k-k' -j' three-vector correlation and on generalized polarization dependent differential cross section are minor. The effect of initial vibrational excited state of reactant molecule on the rotational alignment of product molecule is stronger than that on the P(r) distribution of product molecule.
2010, 59 (11): 7815-7823.
doi: 10.7498/aps.59.7815
Abstract +
The method to calculate the rate coefficient of dielectronic recombination (DR) in dense plasma is discussed in this paper. The formula for calculating the DR rate coefficient as a function of electron density is derived under the effects of transition processes among doubly excited states, collisional ionization and autoionization corresponding to doubly excited states. And the calculation results for DR of Ne-like Ni based on the formula are given. The results show the trend of the change in DR rate coefficient as electron density increases. Additionally, the DR rate coefficients under the effects of different atomic processes are given and analyzed.
2010, 59 (11): 7824-7829.
doi: 10.7498/aps.59.7824
Abstract +
We develop a computer code to calculate ab-initio variational configuration interaction of electronic structure of atoms via generalised Lagurre type orbitals. Treating the orbital effective charges as variational parameters and computing the absolute minimum of energy, yield its optimal wave function.Then utilizing the one-electron density and the probability distribution of the angular two-electron density according to the optimal wave function, we investigate the geometrically active atomic states (GAASs) of Be, B, C, N, O and Ne atoms that are in the first excited states with configurations sαpβ. These results reveal that as an intrinsic property of the wave function of atoms, the angle of the most probabl angular distribution of two-electron density is approximately equal to the bond angle of the molecule, which usually can be explained by the hybridization theory.
2010, 59 (11): 7830-7837.
doi: 10.7498/aps.59.7830
Abstract +
Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Cu-adsorbed (SiO2)n (n=1—8) clusters are investigated by using the density functional theory in the generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. Therefore the ability for Si to lose electron is weaker, while the ability for Si to gain electron is stronger. In addition, the energy gaps between the highest occupied and the lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO2)n (n=1—8) clusters, eventually approaching the near infrared radiation region.
2010, 59 (11): 7838-7844.
doi: 10.7498/aps.59.7838
Abstract +
Comparing the results of AlC cluster, computed by 7 methods of density functional theory (DFT), with experimental data, we choose B3lyp/6-311G(d) to optimize the structures and analyse the frequencies of AlnC and AlnC+(n=1—8) clusters. All ground states and metastable states of AlnC and AlnC+ clusters are obtained. Our calculations reveal that there exists a transition from planar to spacial structures with the number of Al atoms increasing. Planar structures is mostly triangle and spacial structure is primarily triangular prism cage structure. Of the high symmetry clusters, only one of neutral and cation has a stable structure. Compared with various kinds of AlnC and AlAlnC+(n=1—8) clusters under study, Al2C and Al5C are stable.
2010, 59 (11): 7845-7849.
doi: 10.7498/aps.59.7845
Abstract +
The initial geometries of FenO+m(n+m=4) clusters are built by using the "binomial" scheme. And 12 stable isomers are obtained by optimization and frequency analysis based on the density-functional theory GGA (PW91) and the all-electron numerical basis set. The binding energies, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and the magnetic moments of all the stable isomers are determined and analyzed. It is found that Fe—O bonds are important for stabilizing the FenO+m clusters, and that the total magnetic moments of the isomers are mainly dependent on the magnetic moment of iron atoms and the arrangement of the magnetic moments of the atoms.
2010, 59 (11): 7850-7856.
doi: 10.7498/aps.59.7850
Abstract +
By use of three-dimensional particle dynamics simulations, the explosion dynamics of methane clusters driven by an ultrashort intense laser pulse has been analyzed. Especially the influences of some classical inner ionization mechanisms on the charged state and kinetic energy of the ions produced in the laser-cluster interaction process have been discussed in detail. It is presented that when the laser intensity is low, the atoms are ionized by the laser field mainly through the tunnel ionization while the barrier suppression ionization dominates for the inner ionization as the laser intensity increases. Under the irradiation of the same laser pulse with high intensity, the cluster can attain highly-ionized charged states by the barrier suppression ionization rather than by the tunnel ionization. After the cluster is ionized, the ignition ionization effect from the inner Coulomb field of the cluster and the electron impact ionization effect from the free electrons resided inside the cluster will facilitate the process that the cluster can be ionized further.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (11): 7857-7862.
doi: 10.7498/aps.59.7857
Abstract +
The photo-induced insulator-metal transition for silicon-based VO2 nanofilm is studied by THz time-domain spectroscopy (THz-TDS). Obvious variations of THz ray transmittance are observed before and after the CW laser beam exciting, and the conductivity of metallic-phased VO2 film in the THz region is calculated in the thin film approximation. According to the measured results, the metallic-phased VO2 film is characterized equivalently with Drude’s model, and complex conductivity, dielectric function and refractive index are acquired by the model. As an examination on the equivalent Drude model, numerical simulation based on the finite integral method in time domain is carried out. The results show that they are in good agreement with the experimental results. This work provides a reference for the study on phase transition of VO2 nanofilm and its application in the THz region.
2010, 59 (11): 7863-7868.
doi: 10.7498/aps.59.7863
Abstract +
The electromagnetic tunneling properties of the sandwich structure with single negative material/positive index material (single negative material)/ single negative material are experimentally investigated based on the theoretical analysis. The tunneling properties come from the resonance coupling between the incident plane wave and the surface and bulk polaritons. First, the surface or bulk polariton dispersion relations under zero incident condition are discussed and calculated. It is found that the positive index material sandwiched by single negative material possesses bulk polaritons, the resonance frequency of polariton decreases with the thickness of the central layer increasing. The sandwhic structures composed of different single negative materials possess double surface polaritons, and the two surface polaritons degenerate with the thickness of the central single negative material layer. Subsequently, the tunneling properties of the sandwich structures are measured, which are consistent well with the simulation and theoretical analyses. The two structures both possess tunable tunneling modes, their properties have potential applications in designing tunable single or multiple-channeled filters.
EDITOR'S SUGGESTION
2010, 59 (11): 7869-7874.
doi: 10.7498/aps.59.7869
Abstract +
Coherent beam combination of Yb-doped fiber laser array is studied theoretically and experimentally by spatial filtering to passive phase locking. The principle of optical feedback phase locking based on spatial filtering is analyzed, and the relations of Strehl ratio in far field to wavelength and spectrum bandwidth are studied. The coherent beam combination of four Yb-doped fiber amplifier array is achieved experimentally, and stable interference pattern is obtained. The Strehl ratio in far field is 0.77. In the output spectrum, the bandwidth of single longitudinal mode is about 9.1 GHz consistent with the theoretical calculation.
2010, 59 (11): 7875-7879.
doi: 10.7498/aps.59.7875
Abstract +
By studying the interaction of isolated two-level atom with two-mode entangled coherent state optical field, the time evolution of dipole squeezing quantum effect in the system is investigated in detail. The results show that the properties of interaction coherent mode determine the degree of atom dipole squeezing. Parameter ΔV of violation of Cauchy-Schwarz inequality of the interaction system is defined. Time evolution of parameter ΔVis studied, and it can be seen evidently from the results that the degree of violation of Cauchy-Schwarz inequality accords with the nonclassical property of interaction system. Through tuning the parameter of the coherent field, we can easily perform the remote control of the noncommercial properties.
2010, 59 (11): 7880-7884.
doi: 10.7498/aps.59.7880
Abstract +
Nitrogen and silicon atoms have the smallest mismatch of bonding in the Si surface (111), and different percentages of nitrogen atoms are adopted to passivate silicon surface dangling bonds in the Si (111) orientation. The first-principle calculations showed that the band gap is broadened and the localized trap states are generated when the nitrogen atom content is 75%—100% in the Si surface (111). Then the corresponding local electronic-state model is proposed, and the physical mechanism of the previous experimental results of the visible PL emission on SiN films is clarified.
2010, 59 (11): 7885-7891.
doi: 10.7498/aps.59.7885
Abstract +
By employing a full-order dispersion model, we numerically investigat the filamentation of few-cycle laser pulse focused in argon. The focusing effect caused by lens is simulated by quadratic phases e－ik(ω)r2/2f and －ik(0)r2/2f, separately. We find that it is inaccurate to simulate the focusing effect by employing e－ik(0)r2/2f, especially for the propagation of few-cycle. So quadratic phase e－ik(ω)r2/2f must be used in order to accurately simulate the effect induced by lens.
2010, 59 (11): 7892-7898.
doi: 10.7498/aps.59.7892
Abstract +
The quasi-phase-matched (QPM) wavelength acceptation bandwidth for a difference frequency generation (DFG)mid-IR laser source with fiber lasers as the fundamental sources is effectively broadened by using the dispersion relations and its temperature characteristic of periodically poled MgO-doped LiNbO3 (PPMgLN). Our simulation results show that, with an erbium-doped fiber laser (EDFL) and a ytterbium-doped fiber laser (YDFL) respectively operating near 1550 and 1060 nm wave-bands as the signal source and pump source, for the same mid-IR wavelength regions, the allowable wavelength range given by the QPM condition for the pump wave is much larger than that for the signal wave. When the wavelength of the signal wave is fixed at 1560 nm, for a given optimized crystal temperature, the acceptance bandwidth for the pump wave is over 17 nm, corresponding to the acceptance bandwidth for the idler wave of about 180 nm. Based on it, by using a multiwavelength YDFL and a single wavelength EDFL cascaded by an erbium-doped fiber amplifier (EDFA) respectively as the pump source and the signal source, 14-wavelength mid-IR laser lines, with a spacing of about 14 nm in between, are obtained simultaneously with our QPM-DFG laser system when both the temperature and the grating period of the PPMgLN used being kept unchanged at 73.5 ℃ and 30 μm respectively. Moreover, the mid-IR multiwavelength laser lines may be tuned synchronously by varying the signal wavelength.
2010, 59 (11): 7899-7905.
doi: 10.7498/aps.59.7899
Abstract +
In this paper, a theoretical model of Tm3+ doped silica fiber laser(TDSFL) for 3H6—3H4 pumping mechanism is established based on the rate-equation theory, and the numerical simulation is performed by using the Runge-Kutta algorithm. The introcavity power distributions of the TDSFL are obtained for both pump and laser, and the effects of Tm3+ doped fiber length and Tm3+ concentration on laser performance are analyzed.
2010, 59 (11): 7906-7910.
doi: 10.7498/aps.59.7906
Abstract +
A novel variable fiber optical attenuator (VFOA)using an electrowetting microprisms (EMPs) and and two self-focusing lenses is proposed . EMPs can change the wetting angle of solid-liquid interface technology by electronic control methods. The attenuation of the VFOA is analyzed by the theory and experimental measurements . Theoretical analysis and experimental results show that a good control effect of light attenuation in the small voltage range (such as 135—139 V),and the optical attenuation range can achieve in 2—60dB. With the merits of novel conception, easy production, low cost and simple structure, the device will be widely used in communications fields after the optimized design. Disadvantage of this device is high voltage, in order to reduce the operating voltage to achieve the purpose of actual use, screening of high dielectric constant material as the dielectric layer material is topic of future research.
2010, 59 (11): 7911-7916.
doi: 10.7498/aps.59.7911
Abstract +
The flexural vibration of thick disk is studied in this paper. The general solutions of radial displacement and transverse displacement for flexural vibration thick disk under the Mindlin theory are derived. The resonance frequency equations are derived when the boundary conditions are free, simply supported and clamped, and The results obtained from the analyticae method are in good agreement with those from the finite element method and also with the experimental results. These results can serve as reference for the design of flexural vibration thick disk radiator.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (11): 7917-7921.
doi: 10.7498/aps.59.7917
Abstract +
This letter reports on the experimental investigation of the influence of a quartz tube on the nanosecond pulsed discharge in a cone-to-plane air gap, with the quartz tube inserted between the electrodes in the direction parallel to the electric field. While the tube is moved along the axies of the electric field, four different phenomena appear, of which the possible mechanism is discussed. The characteristics of the discharges are diagnosed by optical methods. For five conditions, the rotational temperatures are all 295 K, and the vibration temperatures are all 2200 K, the results mentioned above demonstrate that the plasmas generated in different conditions are in a nonequilibrium state each. Furthermore, a way to produce raise to a uniform glow-like discharge mode is proposed.
2010, 59 (11): 7922-7929.
doi: 10.7498/aps.59.7922
Abstract +
In this paper, the principle of the collisional-radiative model for the estimation of plasma parameters from the ratios of K-shell spectral lines was introduced. The structure of a computer program, ZSPEC, developed for the analysis of K-shell line spectra emitted by Z-pinch plasma based on the collisioanl-radiative model was described in detail. The calculation for neon plasma were presented, including the number fractions of major ionization stages at different electron temperature and the contours of K-shell line ratios in the plane defined by electron density and electron temperature. ZSPEC had been used to analyze the measured results of neon gas-puff Z-pinch experiment performed on Yang accelerator. By comparing the K-shell line ratios of neon plasma obtained by an elliptical crystal spectrometer with the results calculated by ZSPEC, the time and space averaged electron temperature and electron density of the K-shell plasma for the shot with 540 kA peaking current were determined to be 240 eV and 1.0×1019 cm-3, respectively.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (11): 7930-7940.
doi: 10.7498/aps.59.7930
Abstract +
A simulation study has been performed for the rapid solidification process of liquid Mg7Zn3 alloy by using molecular dynamics method. The pair distribution function g(r) curves, the bond-type index method of Honeycutt-Andersen (H-A), the cluster-type index method and the genetic tracking method have been used to analyze the formation and evolution properties of cluster structures during the solidification process. The results show that the bonding probability between Zn-Zn atoms is increased obviously during the solidification process at cooling rate of 1×1012 K ·s-1. The amorphous structures are formed mainly with the 1551, 1541 and 1431 bond-types, and the turning point of the relation curve of the characteristic 1551 bond-type with temperature is corresponding to the glass transition temperature Tg, thus it maybe become a new method to determine Tg. The basic cluster (12 0 12 0) consisting of 1551 bond-type plays a key role in forming amorphous structure, and becomes the main body of the large clusters which are formed by the combination of some middle and small clusters with distinctly different sizes, through mutual competition by unceasing annex and evolution in a seesaw manner (in turn of obtaining and losing).
2010, 59 (11): 7941-7948.
doi: 10.7498/aps.59.7941
Abstract +
The geometrical model is used to investigae the orientation of dendrite growth in a laser weld single crystal and the variation of the distribution of orientation zones when angle ξ between the laser scanning direction and the [100] orientation in (001) surface changes. With the increase of ξ, the 0] zone increases whereas the [010] zone shrinks. Meanwhile, the growth velocities of dendrite are different in different orientation zones inside the weld pool. The undercooling region is then constructed on the basis of the calculation results. It is found that the undercoolings are larger at the boundaries than in the grains for all orientation zones, which makes the boundaries vulnerable to the CET transition and production of the new grains. Moreover, with the increase of ξ, the abilities to form the new grains are different on the two sides of the weld pool. For comparison, the DD3 single crystals are laser welded and the experimental results are in good agree meent with theoretical ones.
2010, 59 (11): 7949-7955.
doi: 10.7498/aps.59.7949
Abstract +
A series of (100-x)(GeTe4)-xGa (x=0, 5, 10 mol%) far infrared transmitting chalcogenide glasses is prepared by the traditional melt-quenching method. In this paper, the differential thermal analysis (DTA), visible/near-infrared absorption spectroscopy, infrared transmission spectra are adopted to analyze composition, structure and performance of the GeTe4 glass system with the addition of Ga. The results show that the Te-Ga bond is formed, which can reduce Te metallic character. When the content of Ga is 10 mol%, the glass is of the best thermal stability. With the addition of Ga, the transmission percentage is improved and infrared cut-off wavelength of the glasses extends beyond 20 μm. Based on the metallization criterion and average bond energy, the relationship between optical band gap and composition is investigated.
2010, 59 (11): 7956-7960.
doi: 10.7498/aps.59.7956
Abstract +
On the basis of the ligamental reticulated carbon foam by Klett in 2000 and hollow microsphere carbon foam by Bruneton in 2002, a hollow microsphere/ reticulated composite carbon foam is prepared by microstructural optimization, carbonization and graphitization sequentially. The scanning electron microscope (SEM) and stereo microsccope tests demonstrate that both reticulated ligament and globe cavity show obvious spacial periodicities. Diffraction peak of X-ray diffraction (XRD) at 26°indicates that the sample features graphitization. Besides, the forming mechanism is also analyzed.
2010, 59 (11): 7961-7965.
doi: 10.7498/aps.59.7961
Abstract +
Using the first-principles method, the electronic properties of the armchair and the zigzag C/SiC nanotube heterojunctions are investigated. Both heterjunctions exhibit semiconducting behaviors with a direct energy band. For the armchair heterojunction, type I heterojection is formed at the interface between the C and the SiC nanotubes, and the electrons and holes are confined in the C nanotube part. In the zigzag heterojunction, the electrons are localized in the C nanotube part, whereas the holes are distributd in the heterojunction uniformly. These heterojunctions can be good candidates for the future nano-devices.
2010, 59 (11): 7966-7973.
doi: 10.7498/aps.59.7966
Abstract +
The resonant Raman behavior of the radial breathing modes are very useful to analyze the electronic property of carbon nanotubes. We investigated the resonant behaviors of Stokes and anti-Stokes radial breathing mode and its overtone of a metallic nanotube, and show how to accurately determine the electronic transition energy of carbon nanotubes from radial breathing modes and their overtones. Based on the present results, the previously reported resonant Raman behavior of the radial breathing modes of SWNT bundles can be interpreted very well.
2010, 59 (11): 7974-7978.
doi: 10.7498/aps.59.7974
Abstract +
In this paper, a theoretical method based on the discrete electronic states is proposed to calculate the Fermi-level of metal nanoparticles embedded in an insulator. According to the calculations, the structures of metal nanoparticle energy level are acquired. Meanwhile, the new formula for evaluating the size of metal nanoparticle by using the information about the surface plasmon resonance peak is also provided. Many known phenomena related to the metal nanoparticles can be explained by this theory. The calculation results on size of nanoparticle are found to be in good agreement with the AFM measurements for high dose Cu implanted Si3N4/Si samples.
2010, 59 (11): 7979-7985.
doi: 10.7498/aps.59.7979
Abstract +
The low-frequency internal frictions of La2-xNdi>xCuO4+δ(0.1≤x≤1.2) compounds are measured. The results show that the relaxation internal friction peak related to the excess oxygen atoms appears around 250K with 0.1≤x≤1.0.And the peak becomes higher with the value of x increasing for 0.1≤x≤0.4 and all these compounds have orthorhombic structures. When 0.5≤x≤1.0, the compounds have all tetragonal structures on a macro scale and the peak reduces as the value of x increases. However, the sample with x=1.2 exhibits tetragonal structure but the relaxation internal friction peak is not found. Further more, when 0.1≤x≤0.8, there exists a phase transition internal friction peak around 550K. The transition temperature shifts toward high temperature zone as the value of x increases and relative shear modulus M is enlarged. But for x=1.0 and 1.2, there appears no phase transition internal friction peak in the measurement range. We find that all these phase transition internal friction peaks are related to the transition between the orthorhombic structure and the tetragonal structure.
2010, 59 (11): 7986-7990.
doi: 10.7498/aps.59.7986
Abstract +
The results are reported of the spatially indirect photoluminescence (PL) spectrum measurements performed on undoped ZnSe/BeTe type-Ⅱ quantum wells with special interface structures at low temperatures (5—10 K). The PL spectra have two main peaks that show a weak PL intensity and a low linear polarization degree and that their linear polarizations are contrary to each other, And the PL spectra are strikingly dependent on an applied external electric field perpendicular to the layers. The results show that the special interface structures reduce spatially indirect radiative recombination efficiency and linear polarization degree, and that a weak built-in electric field exists in the heterostructure. With the increase of excitation intensity, the PL peak on high energy side shows a rapid increase. This is explained by the formation of high charge density on both sides of the high energy side interface.
2010, 59 (11): 7991-7997.
doi: 10.7498/aps.59.7991
Abstract +
Simulation of frost formation process on cold surface is carried out based on fractal theory combined with phase change dynamics. Before frosting, the phenomena of vapor condensation, droplet growth and frozen on cold plate are successfully simulated based on phase change dynamics and then a fractal simulation of the frost formation and growth process over the frozen droplets is carried out based on diffusion limited aggregation (DLA) model. The simulation results accord well with the experimental results. The time when the condensation droplets are present and frozen on the surface during simulation process is nearly the same as the experimental result. Before the droplets are frozen, the trend that the surface contact radius of the droplet varies with condensation time is similar to actual one. The simulation results also show that the thickness of frost layer is nearly equal to the measured value. By that means, the feasibility of this method of simulating the frost formation is verified and the new attempt made to foster the combination between fractal theory and phase change dynamics is of great significance. This study also provids a foundational theory work for a more reasonable and accurate frosting process model.
EDITOR'S SUGGESTION
2010, 59 (11): 7998-8004.
doi: 10.7498/aps.59.7998
Abstract +
The influence of electric field on near-interface 4-pentyl-4'-cyanobiphenyl(5CB) liquid crystal (LC) is investigated with quartz crystal microbalance (QCM). The results of QCM show that the process of frequency shifting with electric field, which reflects the viscoelasticity change of 5CB, can be divided into two parts. Then the two-layer model of 5CB is proposed to illuminate the results of QCM, thereby indicating that the effect of electric field on near-interface layer is different from on bulk layer. Quantitative analysis is carried out with two-layer model of QCM, which indicates that there is a near-interface layer of about 100nm, adsorbed on the upper electrode of quartz crystal. The complex shear viscosity of the near-interface layer decreases with electric field strength increasing, which is opposite to the rule of bulk viscosity of 5CB.
2010, 59 (11): 8005-8009.
doi: 10.7498/aps.59.8005
Abstract +
Using trans-2-butene and hydrogen as the precursor, the glow discharge polymer (GDP) films are successfully coated on glass microspheres with diameters of 350—400 μm and thicknesses of 2.5—3 μm by the glow discharge polymerization technology. Glass/GDP microsphere is heated to test its thermal stability, whose process is the same as the D2 gas charge procedure. The chemical structures, the thermal stabilities of the GDP films, the morphologies of glass/GDP microspheres are characterized by the FT-IR, TG, stereoscopic microscope and X-radiography technology. The Results show that the C/H and C C in GDP films decrease as pressure increases. Their thermal stabilities are better, and the adhesion between GDP film and glass microsphere is enhanced when the GDP coatings are fabricated at lower pressures.
2010, 59 (11): 8010-8014.
doi: 10.7498/aps.59.8010
Abstract +
The Zisman equation, the Fowkes equation and the Owens-Wendt equation, which are derived based on the Berthelot geometric averaging rule for the adhesion work of solid-liquid interface, are theoretical foundations of experimental measurements of surface tensions of solid-liquid interfaces. We generalize the Berthelot geometric averaging rule and obtain a generalized expression of the parameters in Zisman equation. We also obtain a generalized Fowkes equation and a generalized Owens-Wendt equation.
2010, 59 (11): 8015-8020.
doi: 10.7498/aps.59.8015
Abstract +
First-principles calculation is used to study the hydrogen molecule adsorbed on Ti-doped Al(110) surface and pure Al(110) surface separately. We find an adsorption path of hydrogen molecule for decomposing hydrogen atoms and forming TiH2 with Ti atoms on top site. Afterwards, the TiH2 molecule moves to hollow site and approaches to the Al(110) surface. The analyses of density of state and Milliken overlap population show that there is covalence interaction between hydrogen atoms and Al atoms of surface, which gives rise to the formation of Al-H, Na3AlH6 and NaAlH4. Hydrogen molecule is unable to decompose hydrogen atoms on pure Al(110) surface.These results contribute further towards the understanding of the improved observation in recycling of hydrogen with Ti-doped NaAlH4.
EDITOR'S SUGGESTION
2010, 59 (11): 8021-8025.
doi: 10.7498/aps.59.8021
Abstract +
Properties of unintentionally-doped GaN re-grown on molecular beam epitaxy grown AlN/Sapphire templates by metal organic vapor phase epitaxy (MOVPE) are studied in this article. X-ray diffraction (XRD), transmission electron microscope (TEM), and atomic force microscope are used to investigate the influence of the crystal quality and surface morphology of AlN on the GaN. It is found that when surface roughness of AlN is small, the GaN has a full width at half maximum (FWHM) values of XRD rocking curves (200—300 and 400—500 arcsec for (002) and (102) plane ω-scan, respectively) and surface roughness (0.1—0.2 nm), which are comparable to those grown on sapphire substrates by using "two-step" method, although the FWHMs of (102) plane XRD ω-scan curves of AlN are 900—1500 arcsec. The reason for dislocation reduction in GaN shown by TEM image is that a part of dislocations in AlN are eliminated in the interface between AlN and GaN. This is probably due to the lattice restoration from Ga atoms for their large size. On the other hand, when surface roughness of AlN is large, the surface migration of Ga atoms is nestricted during the MOVPE growth, which results in a poor GaN quality. Moreover, the resistivity of GaN confirmed with Van der Pauw method is between 105 and 106 Ω ·cm, which is about six orders of magnitude higher than that in GaN grown on sapphire substrates. This is attributed to the replacement of low temperature GaN buffer layer by the AlN.
2010, 59 (11): 8026-8030.
doi: 10.7498/aps.59.8026
Abstract +
InNSb alloy films are prepared on GaAs (001) substrates by the N2 radio frequency plasma-assisted molecular beam epitaxy ( RF-MBE). The N composition and the micro-structure of the samples are characterized by atom force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The measurement results reveal that the films have smooth surfaces and good crystalline quality, the N composition can reach 0.84%(from XRD) and most of the N atoms in the samples are at the sites of Sb atoms. The transport properties of the samples are also characterized, and the results demonstrate that our samples have lower carrier concentrations and higher mobilities. Owing to the introduction of N, a condside rable reduction of room-temperature magnetoresistance is observed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (11): 8031-8036.
doi: 10.7498/aps.59.8031
Abstract +
In order to reveal the physical nature of high temperature oxidation of Nb alloy in electron level, the density of states, the atomic embedded energy, the atomic affinity energy and other electronic structure parameters of Nb alloy are calculated by using the recursive method. The high-temperature oxidation mechanism of Nb alloy is investigated. The results show that the diffusion rate and the solid solubility of oxygen are high in the Nb alloy, so oxygen can easily react with Nb to form oxides, which makes the oxidation resistance of Nb alloy poor at high temperatures. The calculated results of atomic embedded energy show that the stabilities of alloying elements (Ti, Si, Cr) are lower in the matrix than in the surface of Nb alloy, so they diffuse easily in to the surface of Nb alloy to form a surface layer enrichment with Ti, Si, Cr. Alloying elements Nb, Ti, Si, Cr have negative affinity energies to oxygen in alloy surface layer, thereby forming the corresponding oxide film, which has a protective effect for Nb alloy.
2010, 59 (11): 8037-8041.
doi: 10.7498/aps.59.8037
Abstract +
Tetragonal distortions,crystal structure,magnetism,electronic structure and pressure response of Hg2CuTi-type Mn2NiGe are calculated by the first-principles method based on the density functional theory. The calculations show that 1)in the process of transform from cubic to a tetragonal in structure,Mn2NiGe alloys exhibit a stable martensitic phase at c/ a≈1.34; 2)in austenite and martensite,Mn atoms are the main contributors to the magnetism in Mn2NiGe,and Mn2NiGe alloys show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn(A) atom and Mn(B) atom; 3)in austenite and martensite,the direct d-d exchange interaction between Mn(A) atom and Mn(B) atom is weak because of small overlap of d-projected DOS of Mn(A) atom and Mn(B) atom nearby the Fermi level. This is the reason why the Mn2NiGe alloys show ferrimagnetism. We can predict the magnetic shape memory effect (MSME) in Mn2NiGe alloys based on the the results of calculation above.
2010, 59 (11): 8042-8047.
doi: 10.7498/aps.59.8042
Abstract +
Degradation of Bi4Ti3O12 ferroelectricity during forming gas annealing is investigated by the first-principles method based on the density functional theory(DFT) the generalized gradient approximation(GGA). We calculate the variations of total energy with the displacement of Ti along the c axis, electron density and total density of states in hydrogen-free and hydrogenated models. The results show that the electron densities of Ti-O and Bi-O exhibit significant changes between the Bi4Ti3O12 ferroelectric phases for the hydrogenated and hydrogen-free cases, and the strong hybridization between H and O is favorable to the formation of a convalent bond. The total energy of ferroelectric phase for the hydrogenated case is bigger than that of paraelectric phase because hydrogen incorporation into the lattice has a direct effect on polarization pinning by possibly forming a hydroxyl bond. This demonstrates that hydrogen introduction during forming gas annealing hinders the phase transition of the Bi4Ti3O12 from tetragonal paraelectricity to orthogonal ferroelectricity, and electrical conductivity of Bi4Ti3O12 is increased. This may be an important factor causing severe degradation of Bi4Ti3O12 ferroelectricity.
2010, 59 (11): 8048-8051.
doi: 10.7498/aps.59.8048
Abstract +
Unintentionally doped GaN epilayers are grown by the metalorganic chemical vapor deposition (MOCVD). Photovoltaic (PV) spectroscopy shows that there appears an abnormal photoabsorption in some undoped GaN films with high resistance. The peak energy of the absorption spectrum is smaller than the intrinsic energy band gap of GaN. This phenomenon may be related to exciton absorption. Then metal-semiconductor-metal (MSM) Schottky photodetectors are fabricated on these high resistance epilayers. The photo spectrum responses are different when the light individually irradiates each of the two electrodes with the photodetector which are differently biased. When the excitation light irradiates around the reverse biased Schottky junction,the responsivity is almost one order of magnitude larger than that around the forward biased junction. Furthermore,when the excitation light irradiates the reverse biased Schottky junction,the peak energy of the spectrum has a prominent red-shift compared with the peak energy of the spectrum measured with the excitation light irradiating the forward biased Schottky junction. The shift value is about 28 meV, and it is found to be insensitive to temperature. According to the analyses of the distribution of the electric field within the MSM device and the different dependences of the response on the electric field intensity between the free carriers and excitons,a reliable explanation for the different response among various areas is proposed.
2010, 59 (11): 8052-8062.
doi: 10.7498/aps.59.8052
Abstract +
We generalize Yamadas perturbation theory and develop a renormalized perturbation method to study the asymmetric Anderson model. We obtain the occupancy of the local electrons,the renormalization factor,the renormalized energy level,and the renormalized parameters,which are expanded by the bare parameters. We also calculate the density of states of local electrons and the conductance of impurity scattering. The results coveres the range from weak to strong coupling. We find that the approach we adopted is more convenient than Hewsons renormalization method in studying the asymmetric Anderson model.
2010, 59 (11): 8063-8070.
doi: 10.7498/aps.59.8063
Abstract +
In this paper,based on the research of the features about high voltage and high current under electrostatic discharge(ESD),the new 3D model of 0.6 μm gate-grounded NMOS(ggNMOS) ESD protection circuit with CSMC 6S06DPDM-CT02 CMOS technology have been derived from the optimization of lattice self-heating drift/diffusion model and its thermal model; systematic study about the effect of drain contact to gate spacing(DCGS)and the source contact to gate spacing(SCGS)on the relative protection circuit robustness index(turn-on voltage,breakdown voltage,self-heating peak,etc)have been done based on this model. The simulation results show that turn-on voltage and thermal balance are not influenced by the change of DCGS and SCGS,and compared to SCGS,DCGS is more sensitive to the breakdown voltage and the self-heating peak value of protection circuit. To improve the robustness of ESD protection circuit,it is not appropriate to monotonic increase the DCGS and SCGS for the reason that the breakdown voltage cannot be increased and the self-heating peak value of devices cannot be reduced by increasing DCGS and SCGS continuously. Compared to the TLP test results of 0.5 μm and 0.6 μm CMOS,a better reflection about the trend of electrical and heating features is derived from the simulation results,and the conclusions and test results are fully consistent. The reference for sub-micrometer ggNMOS ESD protection circuit layout parameter can be provided by the study.
2010, 59 (11): 8071-8077.
doi: 10.7498/aps.59.8071
Abstract +
Structural stability,electronic and optical properties of Ni-doped silicon nanowires are investigated by first-principles calculations based on the density functional theory. The results show that Ni can preferentially occupy substitutional sites near the surface of silicon nanowire. The doping of Ni atom in silicon nanowire introduces the impurity levels. The impurity level is mainly contributed by Ni 3d orbital. The decrease of the band gap results from the coupling of Ni 3d and Si 3p states. A strong absorption peak occurs in the low energy region of Ni-doped silicon nanowire,accompanied by the widening of the absorption band.
2010, 59 (11): 8078-8082.
doi: 10.7498/aps.59.8078
Abstract +
We grow green light emitting diodes (LEDs) on Si(111) substrates with p-AlGaN electron blocking layers (EBLs) which have different Al frations. The results show that the variation of quantum efficiency with current density displays a diversity. At lower current densities,the quantum efficiency of LED increases with Al fraction decreasing, at higher current densities, however, the quantum efficiency of LED increases with Al fraction decreasing, which is attributed to the complicated mechnism when electron and hole are recombined in the quantum well.
2010, 59 (11): 8083-8087.
doi: 10.7498/aps.59.8083
Abstract +
Some progress in the research of GaN based LED with photonic crystal structure has been made recently. Based on the photonic crystals photonic band gap effect and photon grating diffraction principle,the extraction efficiency of LED with photonic crystal can be improved. In this paper,the restriction on AlGaInP LEDs extraction efficiency is analyzed,and the photonic crystal is introduced in to the AlGaInP LED to improve the extraction efficiency. The theoretical analyses and the experiment results show that the output luminous intensity of LED with photonic crystal is improved by 16%,which results from some effect of the GaN based LED with photonic crystal.
2010, 59 (11): 8088-8092.
doi: 10.7498/aps.59.8088
Abstract +
Polymer-based thin film transistors (PTFTs) with poly(3-hexylthiophene) (P3HT) as semiconducting active layers are successfully fabricated on silicon substrates in air which are used as gate electrods. HfTiO film deposited by RF sputtering method is used as gate insulators,and gold metal is used as source and drain electrodes. The HfTiO surface is modified by using octadecyltrichlorosilane solution in the fabrication process. Experimental results indicate that the PTFTs show good saturation behaviors at low drive voltages (-2 cm2/V ·s. The frequency-dependence and hysteresis effect are observed in the C-V measurements for the metal-polymer-oxide-silicon (MPOS) capacitors,and discussed in detail to understand their physical mechanism.
2010, 59 (11): 8093-8097.
doi: 10.7498/aps.59.8093
Abstract +
Five kinds of organic quantum well structured light-emitting devices are fabricated, and their electrical characteristics are studied. The effects of quantum well period number and barrier thickness on device performance are analyzed. Experimental results show that appropriate cycle quantum well structured devices have higher brightness and current efficiency than the traditional three-layer devices. That is because of the limitation effect of quantum well structure on electrons and holes,and the structure of this kind could improve the composite probability of excitons in the light-emitting layer,thereby increasing brightness and efficiency of OLED. There is also an effect on brightness and efficiency when the potential well layer thickness of quantum well structured device is changed. Consequently,the adoption of appropriate potential well layer thickness can also improve the brightness and the efficiency of the device.
2010, 59 (11): 8098-8103.
doi: 10.7498/aps.59.8098
Abstract +
In this paper,changing patterns of electronic velocity and effective mass of the lowest conduction band for various carbon nanotubes are calculated systematically. Based on these calculation results,low-bias transport properties of single-walled carbon nanotubes (SWCNTs) and deduced thoroughly. It is found that under a low bias,chiral metallic SWCNTs belonging to the same series ( i.e,having the same chiral angles) have the entirely identical transport properties and are independent of diameter of the SWCNT. But those that belong to different series have obviously distinguishable transport properties. While for chiral semi-conducting SWCNTs belonging to the same series,they have some different transport properties. But those that belong to different series have greatly different transport properties. Our findings suggest that low-bias transport properties of SWCNTs are intimately related to the series and the chiral angle is the most important geometry parameter for the determination of different low-bias transport properties of various SWCNTs.
2010, 59 (11): 8104-8112.
doi: 10.7498/aps.59.8104
Abstract +
The ambipolar transporting characteristic is one of the most important factors that prevent the performance of Carbon Nanotube Field Effect Transistors (CNFETs) from further being improved. In order to reduce the ambipolar conductance and increase the ON-OFF current ratio of the device,a stair-case doping strategy in drain lead,which is suitable for not only the Conventional MOS-like CNFETs (C-CNFETs) but also Tunneling CNFET (T-CNFETs),is proposed in this paper. The non-equilibrium Greens function based simulation results show that this strategy can reduce the ambipolar conductance and increase the ON-OFF current ratio of the device effectively. Further study shows that many differences exist with using this stair-case doping strategy applied in C-CNFETs and T-CNFETs. First,the potential band pinning in stair-case doped C-CNFETs would weaken the ON-state performance of the device,while no band pinning exists in stair-case doped T-CNFETs. Second,applying such a stair-case doping strategy to both source and drain leads can further increase the device performances in C-CNFETs but not T-CNFEts. Third,the transporte property of T-CNFETs is dependent more strongly on the width of lightly doped drain region than that of C-CNFETs. However,certain device area would be costly because of using this stair-case doping strategy. So,much attention should be paid to the choice of device structure,doping concentration and lightly doped drain region width,to obtain a best tradeoff among speed,power and device area,in application.
2010, 59 (11): 8113-8117.
doi: 10.7498/aps.59.8113
Abstract +
In this article,organic thin-film transistors (OTFTs) with top-gate and bottom contact geometry based on pentacene as active layer were fabricated. The experimental data of the I-V were obtained from the organic thin-film transistors. The field-effect mobility of the OTFT was calculated by fitting of theoretical calculation to the experimental data. We find that field-effect mobility values have great difference by different fitting methods. We calculate the field-effect mobility by least-squares fitting method to the experimental data of the I-V away from the center of the linear region of the transfer characteristics curves 1/2 range. The inherent inaccuracy of other fitting method can be reduced. The results is the nearest field-effect mobility obtained with other methods.
2010, 59 (11): 8118-8124.
doi: 10.7498/aps.59.8118
Abstract +
A study of the internal damage process and mechanism of the typical n+-p-n-n+ structure bipolar transistor induced by the intense electromagnetic pulse (EMP) is carried out in this paper from the variation analysis of the distribution of the electric field,the current density and the temperature. Research shows that the damage position of the bipolar transistor is different with the different magnitude of the injecting voltage,when the magnitude of the injecting voltage is low the damage will appear firstly near the collector region under the center of the emitter region,and when the magnitude of the injecting voltage is sufficiently high the damage will appear firstly at the edge of the base near the emitter due to the breakdown of the PIN structure composed of the base-epitaxial layer-collector. Adopting the data analysis software,the relation equation between the device damage power P and the pulse width T under different injecting voltage is obtained. Owing to the variety of the device damage energy,it is demonstrated that the empirical formulas of the intense electromagnetic pulse P=AT-1 (A is a constant) is modified to P=AT-1.4 for the bipolar transistor.
2010, 59 (11): 8125-8130.
doi: 10.7498/aps.59.8125
Abstract +
The contact effect on the performances of organic thin film transistors (OTFTs) is studied here. We fabricate Bottom-gated top-contact Pentacene-OTFTs on heavily doped n type Silicon wafers with using Al modified by MoO3 as source and drain electrodes. Field effect mobility μef of the OTFT reaches 0.42cm2/V ·s,the threshold voltage and the on/off current ratio arrive at -5.0 V and 4.7×103 respectively. The electric potential distribution in the channel is qualitively investigated by means of middle probe method (MPM) and the output curve is simulated by the charge drift method. Considering the contact effect,the μef is greatly improved to 1.1 cm2/V ·s,which indicates the importance of the contact engineering in OTFTs.
2010, 59 (11): 8131-8136.
doi: 10.7498/aps.59.8131
Abstract +
A strained Si fully depleted SOI MOSFET,which has the advantages of strained Si,high-k gate and SOI structure, is presented in this paper. A two-dimensional analytical model for the threshold voltage in strained Si fully depleted SOI MOSFET with high-k dielectric is proposed by solving Possions equation. Several important parameters are taken into account in the model. Relationships between threshold voltage,Ge Profile and thickness of strained silicon are investigated. The result shows that the threshold voltage decreases with Ge Profile and strained silicon thickness increasing. Relationships between threshold voltage,dielectric constant of high k gate and doping conceration of strained silicon are also investigated. The result shows that the threshold voltage increases with dielectric constant of high-k and doping conceration of strained silicon increasing. SCE and DIBL are analyzed finally,which also demonstrate that this novel device can suppress SCE and DIBL effect greatly.
2010, 59 (11): 8137-8141.
doi: 10.7498/aps.59.8137
Abstract +
Pr0.5Ca0.5MnO3(PCMO) is been prepared by a solid-state reaction technique, and the thin film of PCMO is deposited on an n-type silicon substrate by a pulsed laser deposition method. Experimental results indicate the transport character of the film may be consistent with the variable range hopping model in a temperature range of 80—300 K, but it changes from one-dimension to two-dimensional and then turns three-dimensional with temperature increasing. It may be attributed to the effect of orbit order on the transport characteristics. The PCMO/Si heterojunction possesses good rectifieation property under a magnetic field,and at a positive voltage the heterojunction shows its magnetoresistance to have a remarkable transition from positive to negative.
2010, 59 (11): 8142-8147.
doi: 10.7498/aps.59.8142
Abstract +
The YBCO films were prepared on LAO single crystal by TFA-MOD process. The structure and properties of YBCO films were investigated through changing the Y123 stoichiometry. It is found that higher JC values in self-filed of YBCO films are achieved by using the starting solution with the Ba ∶Y ratio of 1.5 ∶1. X- ray diffraction analysis revealed that Y2Cu2O5 phases are formed in the final YBCO films,which may lead to very effective vortex pinning and then enhance the JC of YBCO films.
2010, 59 (11): 8148-8154.
doi: 10.7498/aps.59.8148
Abstract +
Temperature dependence of initial permeability is investigated for nanocrystalline Fe38.4Co40Si9B9Nb2.6Cu alloy annealed at 500 and 600℃,and the initial permeability of 600℃-annealed sample is observed not to drop sharply at the Curie temperature of the residual amorphous phase,which is a new magnetic phenomenon in dual-phase nanocrystalline alloys. The origin of the above phenomenon is explored by estimating the Curie temperature of amorphous ribbons which have the same compositions with the residual amorphous phase in annealed nanocrystalline alloys. The results indicate that the Curie temperature of the intergranular amorphous region can be enhanced drastically up to the Curie temperature of the crystalline phase (TAC=TαC) when the exchange-field between adjacent nanograins penetrates through the amorphous interphase thoroughly. Furthermore, the effective exchange penetration length of FeCo-based nanocrystalline alloys (LFeCo) is evaluated to be 0.61 nm much larger than that of Fe-based nanocrystalline alloys, which may be the main reason of the higher permeability of FeCo-based alloys at elevated temperature.
2010, 59 (11): 8155-8159.
doi: 10.7498/aps.59.8155
Abstract +
We report on a kind of all-proton spin quantum gate realized by fabric silicon cantilever in a semiconductor spin magnetic resonance microscopy system. In the paper, the Rf pulse sequence control and the spin rotate frame system are adopted according to spin-lattice and spin-spin relaxation times,and the small resonance force, the sensitivity and the spin density matrix are studied. The results show that all-proton spin quantum gates have high Q controlling and detecting sensitivity, and gain the effective force oscillating through the resonance slice and fiber interferometer. The system has advantages of MRI and AFM characteristics. In addition, the calculation indicates that it is powerful tool of magnetic resonance force technology and useful way to achieve quantum computation and quantum information.
2010, 59 (11): 8160-8166.
doi: 10.7498/aps.59.8160
Abstract +
Multiferroic ceramics of Bi5Fe1-xCo x Ti3O15(x=0.0—0.6) are synthesized by the conventional solid state reaction, and their microstructure,magnetic and ferroelectric properties are investigated. X-ray diffraction patterns show that a four-layer Aurivillius phase is formed in each sample with a suggested structural transformation at heavy doping of Co ions. The Raman results demonstrate that Co ions enter into the lattice,occupy the B-sites in the BFCT-x and have an effect on the order occupancy of cations at B sites. It is found that the Co ion modification induces remarkable ferromagnetism (FM) at room temperature with a greatest remanent magnetization (2M r) of 2.3 memu/g at x=0.5,which is three orders of magnitude larger than that of Bi5Ti3FeO15(BFTO). All samples with Co doping have ferroelectricity (EM). The remanent polarization (2P r) reaches a value of 11 μC/cm2 at x=0.1,which is about 38.2% higher than that of BFTO,and then decreases when 0.2≤x≤0.4 and increases again at x=0.5 and 0.6. Of all materials,the sample of x=0.5 is best in both good FE and FM.
2010, 59 (11): 8167-8171.
doi: 10.7498/aps.59.8167
Abstract +
A nonlinear thermodynamic theory is used to investigate the effect of external electric field on the phase transitions of Pb(Zr0.3Ti0.7)O3(PZT) thin films epitaxially grown on dissimilar cubic substrates. The "misfit strain-external electric filed" phase diagram and the relationship between electirc filed and polarization are constructed for PZT thin films. The external electric field can transform the monoclinic r phase into the c phase,when its value reaches 186 kV/cm for PZT thin film grown on the SrTiO3 substrate. On the other hand,the domain switching of PZT thin film is investigated experimentally by scanning probe microscopy(SPM) via varying the applied polarizing electric field. The piezo-phase images reveal that most ferroelectric domains are clearly detectable. In the r phase,the domains can be reversed into the direction of polarization of the c phase,when the applied electric field increases to 200 kV/cm,which is close to the theoretical value (186 kV/cm).
2010, 59 (11): 8172-8177.
doi: 10.7498/aps.59.8172
Abstract +
By reactive evaporation method, the SnO2:(Cu,In) transparent conductive films are prepared on glass, Corning7059 glass and quartz glass substrates separately. The element contents are analyzed, the distributions of all elements in the films are given, and the transmittances of samples are also measured. The results show that the UV transmittance of individual sample is high, and the transmittance of the film depends on annealing process. The resistance-temperature characteristics are measured and explained. The relationship between optical band gap and absorption coefficient is discussed. The simple method in which the transmittance curve is used to determine the optical band gap is given. The relation between mobility of the extended state and mobility edge with Fermi level is discussed. The results show that the preparation of copper and indium co-doped tin oxide transparent conductive films has achieved the purpose of reducing the cost, and some particular samples have wide band gap.
2010, 59 (11): 8178-8183.
doi: 10.7498/aps.59.8178
Abstract +
In this paper, we carry out the numerical simulation of spherical superlens by the Dyadic Green’s function method, and we prove the sub-wave length imaging capability of spherical superlens. Dyadic Green’s function method is an effective method and a systematic theory of dealing with the problem of electromagnetic fields, which makes up the deficiencies in coordinate transformation method. Compared with the flat lens, the spherical superlens have several advantages, including the finiteness cross-section, and ability in lensing with magnification or demagnification, high resolution, two-dimensional imaging, etc.
2010, 59 (11): 8184-8190.
doi: 10.7498/aps.59.8184
Abstract +
Hydrogenated silicon films are prepared on Corning 7059 glass by the plasma enhanced chemical vapour deposition technique with radio frequency ( RF),power,(13.56 MHz) and DC bias. The microstructures of hydrogenated silicon films investigated by Raman spectra. The photo-absorption coefficient is calculated by utilizing an established photo-absorption model. The I-V characteristics of hydrogenated silicon film solar cells are simulated by using software AMPS. The results show that photo-absorption coefficient curves and I-V curves are both consistent well with experimental data. At the same time, the difference between experimental results are calculated results were analyzed.
2010, 59 (11): 8191-8199.
doi: 10.7498/aps.59.8191
Abstract +
Recently the infrared quantum cutting has achieved an exciting development in enhancing the efficiency of solar cell. The infrared quantum cutting of Er0.3Gd0.7VO4 crystalline is studied in the present paper. It is found that the approximate quantum cutting efficiencies of 1532.5 nm 4I13/2→4I15/2 fluorescence, when the 2H11/2 and 4G11/2 levels are excited, are about 178.55% and 177.61% respectively. Especially, effective three-photon and four-photon infrared quantum cuttings of Er0.3Gd0.7VO4 crystalline excited by visible and near-violet light are found for the first time in the present paper. An interesting "peak - valley" conversion phenomenon in the excitation spectrum is also observed. It is also the first time for us to find the first-order infrared quantum cutting based single species Er3+ ion for Er0.3Gd0.7VO4 crystalline.
2010, 59 (11): 8200-8204.
doi: 10.7498/aps.59.8200
Abstract +
Green-emitting Ca3Sc2Si3O12:Ce3+ phosphors for white LED are successfully synthesized by a gel-combustion method. The as-synthesized phosphors are investigated by XRD, SEM, and fluorescence spectrophotometer. The results indicate that the crystal structure of the phosphor is pure. The particle morphology of the sample is basically spherical in shape. The particle size is smaller than 1μm. The emission spectrum shows a broad band emission, and the main emission peak locates at 505 nm. Bright green-emission broadening is attributed to the characteristic emissions 5d-2F5/2 and 5d-2F7/2 transitions of Ce3+. The optimal doping concentration of Ce in Ca3-xSc2Si3O12:Ce is x=0.1. The thermal stability and the luminescence intensity of the Ca3Sc2Si3O12:Ce3+ are significantly improved compare with those of YAG:Ce.
2010, 59 (11): 8205-8211.
doi: 10.7498/aps.59.8205
Abstract +
To balance the requirements for lifetime, cross section and crystallization stability in rare-earth-doped fluorophosphate(FP) glass, we studied the influence of LiF and AlF3 on the properties of FP. Results indicate that LiF plays an important role in improving the radiative lifetime of Tm3+, and the glass performs good crystallization stability with LiF proportion as high as 30mol%. Crystallization stability in high AlF3 glass is excellent but the radiative lifetime of Tm3+decreases fast. Emission cross section changes mildly with the variation of LiF and AlF3 proportions, so lifetime, cross section and crystallization stability can achieve their batter values through the ajustment of LiF and AlF3 proportions.Comparations between J-O parameters and several properties of the Tm3+ doped FP glass show that with AlF3 increasing, the overlap integral of 4f and 5d orbitals of the rare earth ions increases. Raman spectra testify the great variation of glass structure when LiF and AlF3 contents change largely.
2010, 59 (11): 8212-8217.
doi: 10.7498/aps.59.8212
Abstract +
Efficiency and current measurements of ferromagnetic Co thin layer based organic light emitting diode, which has a structure of ITO/Co/NPB/Alq3/LiF/Al, are performed as a function of magnetic field at room temperature.The efficiency first increases by up to 18.8% as magnetic field increased to about 80 mT, and then appears to be almost saturated. The changes result from the spin-polaried injection of Co and the magnetic field effects(MFEs), both of which increase the fraction of siglets among the total excitons, and the former is primary. The changing rate of current through the device is found to increase by up to 6.9% at about 60 mT, and then decrease slowly with magnetic field increasing. These observations are explained in terms of the MFEs of polaron pairs dissociation and magnetic-field dependence of triplet-charge reaction in excited states.
2010, 59 (11): 8218-8225.
doi: 10.7498/aps.59.8218
Abstract +
The phase-field crystal (PFC) model is used to simulate crystal growth from undercooled liquid by the finite difference method. The effects of phase region and undercooling on crystal growth process are analyzed. The simulation results show that crystal growth is inhibited in the region of liquid-crystal coexistence where liquid-crystal boundary becomes thicker gradually. In the single crystal phase region, crystallization is enhanced with undercooling increasing,while liquid-crystal boundary becomes thinner. It is found that there is a linear relationship between crystal growth velocity and undercooling.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (11): 8226-8230.
doi: 10.7498/aps.59.8226
Abstract +
Nano-level Sn-Al alloy thin-film electrode materials prepared by magnetic sputtering technology are characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The charge/discharge and the cyclic voltammograms of the film electrodes are tested by the high precision battery testing system. The results indicate that the materials prepared by direct current and radiofrequency methods have a large difference in performance. The films prepared by DC method have small particles and excellent cycling stability. Its initial discharge capacity and efficiency are 1060 mAh/g and 71.7%, respectively, and the specific capacitance is over 700 mAh/g after 30 cycles. But the films prepared by RF method have the bigger particles and inferior cycle performance, and its specific capacitance initially increases but after 5 times cycle it declines.
2010, 59 (11): 8231-8236.
doi: 10.7498/aps.59.8231
Abstract +
Based on the previous research on the deposition of amorphous/microcrystalline (micromorph) silicon tandem solar cells, silane concentration for the deposition of microcrystalline bottom cell is selected to further optimize the performance for micromorph tandem solar cells by using very high frequency technique. Finally, micromorph silicon tandem solar cell with 11.02% (Area=1.0cm2) initial conversion efficiency is fabricated at a certain silane concentration, and it has a structure suitable for trapping light. Furthermore, 100cm2 micromorph module with 9.04% initial conversion efficiency is also successfully obtained.
2010, 59 (11): 8237-8243.
doi: 10.7498/aps.59.8237
Abstract +
Micro CT system is a recently developed imaging technique for small animal, which have very high spatial resolution and sensitivity, and is widely used in drug development, cancer detection et al. But in Micro CT, the artifact, specially the aliasing artifact, become serious as the extremely high spatial resolution, which is the major degeneration of image quality. In this paper, we studied the cause of artifact, and simulated it in computer. Finally, we proposed an algorithm to reduce the artifact in CT slice, with artifact elimination rate of 70% or more, and the improved image contrase
2010, 59 (11): 8244-8248.
doi: 10.7498/aps.59.8244
Abstract +
Magnetic-field-induced strain(MFISs) in polycrystalline Mn1-xCux(0.1≤x≤0.3, atomic fraction) alloys are studied by means of X-ray, photomicrograph, DSC, resistance strain gauge method at room temperature. The results show that Mn1-xCux alloys consist of fcc (γ) and fct (γ’) phases after a long period of homogenization because of fcc(γ)→fct(γ’) martensitic transformation in the cooling process. The volume proportion of γ’ phase increases with the increase of Mn content, so that the samples possess much better MFIS performance. At room temperature, the MFIS in Mn0.9Cu0.1 sample reaches 91 ppm in 0.9 T magnetic field.
2010, 59 (11): 8249-8254.
doi: 10.7498/aps.59.8249
Abstract +
Computer simulations are performed to investigate the effect of opening angle on dilute-dense flow transition in a two-dimensional granular flow. Two methods, i.e. the fixed inflow rate and the fixed particle number, are adopted. Both results show that larger opening angle results in an increase of maximum outflow rate in dilute-dense flow transition when the opening angle is larger than zero. When granular flow keeps a dilute flow, the outflow rate is irrelative with the opening angle. When the flow becomes a dense flow, the dense flow rate inereases with opening angle increasing. Further studies show that the granules flow out with a higher velocity when the opening angle increases. The linear relationship between maximum outflow rate and granule flow velocity is observed.
2010, 59 (11): 8255-8263.
doi: 10.7498/aps.59.8255
Abstract +
The minimum-energy (wavelet) frame has an extensive application prospect in the field of signal processing, but now it can be applied only to continuous signals. In order to solve the problem, we define a minimum-energy frame in the discrete signal space, and then prove that it has some good properties. In the actual application, we propose a new de-noising algorithm which is special for the binary rectangular pulse signal polluted by the additive gaussian noise and obtain better processing effect by using a minimum-energy frame in the discrete signal space to denoise the sampled sequence of receiving waveform. The simulation results show that if a pre-processing link is used to denoise the receiving waveform through using the algorithm, the receiver can reduce the bit error rate and achieve a 3.4 dB performance gain at 4 dB signal-to-noise ratio.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (11): 8264-8271.
doi: 10.7498/aps.59.8264
Abstract +
A new method is proposed in this paper—moving cut data-rescaled range analysis (MC-R/S). Tests on the correlated time series suggest that the MC-R/S can accurately detect the time-instants of abrupt change, and the MC-R/S results almost do not depend on the length of subseries and are less affected by noises. So, MC-R/S is suitable to detecting an abrupt dynamic change in those time series exhibiting correlations, and can very well make up the deficiency of moving detrended fluctuation analysis (MDFA).
2010, 59 (11): 8272-8279.
doi: 10.7498/aps.59.8272
Abstract +
Statistical characteristic of daily temperature series (1954—2004) of Xiamen station is analyzed by using Gaussian and skew distribution functions, and then the future probable trend of record temperature events (RBTE) is also simulated by using Monte-Carlo(MC) methods based on the Gaussian and skew distribution functions, respectively. Results show that the statistical property of nearly 50a daily observation temperature data in June of Xiamen station is more consistent with that obtained from the skew function. However, the theoretical study shows that the skew function and Gaussian function have the same limit of convergence, i.e. the Gumbel distribution function. The results also show that the MC simulation based on the skew distribution with global warming background can reveal the future probable extreme events well, and the Xiamen's daily temperature distribution of June in the next 10 a is predicted. The global warming background can lead the occurrence probabilities of high-temperature record-breaking event and the average daily temperature to increase. In addition, based on the observed date in China, the spatial temperature distribution of the occurrence with the max probability over China in coming 10 years is also presented.
2010, 59 (11): 8280-8286.
doi: 10.7498/aps.59.8280
Abstract +
When the self-referencing interferometer wavefront sensor (SRIWFS) is applied to the absolute measurement of wavefront phase, the pinhole diameter should be less than half the Airy-disk diameter (dA) produced by an unaberrated optic so as to obtain a good approximation to a reference plane wave. In this way, however, the intensity transmission is also greatly reduced. To increase the intensity transmission as much as possible and improve the fringe contrast especially in the beginning of closed-loop correction, the maximal pinhole diameter allowed in the closed-loop correction with using SRIWFS is studied. Computer simulation and experiment demonstrate that a pinhole with not greater than 1.5dA can obtain a satisfied correction result and the Strehl ratio after correction is greater than 80%. Additionally, for a plane wavefront the intensity transmission will be increased from 63% to 90% as the pinhole diameter increases from 0.5dA to 1.5dA.
2010, 59 (11): 8287-8392.
doi: 10.7498/aps.59.8287
Abstract +
Using the thunder signals of a C-G lightning process recorded in the Qinghai region and the theory of signal processing, the frequency spectrum of thunder at observation point is obtained; Based on the propagation theory of acoustic waves, the absorption coefficients in air are calculated and their variations with environmental factors are analyzed. The results show that under a certain profpagation distance and environmental condition, the absorption coefficient increases with frequency increasing. The attenuation of signal below 100Hz is negligible under a certain propagation distance and environmental factors. The attenuations for high-frequency signals of more than 500 Hz are large, their absorption coefficients increase rapidly with the relative humidity inereasing and vary nor-monotonical with temperature. It is deduced that high frequency components of more than 500Hz should be contained in the thunder source.
2010, 59 (11): 8293-8303.
doi: 10.7498/aps.59.8293
Abstract +
In this paper, a 3-D chemical release dynamics model including neutral gas diffusion, chemical reaction and ambipolar diffusion of plasma, is proposed first. And then the software frame is developed for the study of chemical releases in the ionosphere. The computer simulation on some representative chemical releases including H2O, CO2, H2 and SF6 is carried out finally. The temporal-spatial effects of the local turbulence introduced by these chemical releases are discussed.
2010, 59 (11): 8304-8310.
doi: 10.7498/aps.59.8304
Abstract +
The importance of period estimation for pulsars in pulsar searching was discussed. In the paper, the radiation signal from pulsars was modeled as second-order cyclostationary process,and corresponding simulation was done to verify its reasonableness. Based on the model, a novel method was proposed to estimate pulsars’ cyclo-period by the coherent statistic of bispectrum, and then one robust strategy for periodicity searches was provided in order to eliminate its sensitivity to data amount. Using the method, the period of PSR J0437-4715 with single pulse was estimated based on original signal, and the period of PSR B1821-24 with double pulses was also estimated based on simulated signal. Results show that, compared with the classical Fourier-transform method, the algorithm is intuitive, effective, of good performance even in case of lower SNR,and also appropriate for the noncontinuous observing data. The method, though with higher computation complexity, can provide a powerful reference for period estimation of weak pulsar signal.
